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How to Clean Parts Without Moving to Mexico - P2 InfoHouse

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"How to Clean Parts Without"'
Moving to Mexico"
THE COMPLETE GUIDE
TO REDUCING THE USE OF
HAZARDOUS SOLVENTS
IN THE WORKPLACE
by
Michael S. Callahan, P.E.
and
Bill Green
0 Ecolink 1994
pdF
DISCLAIMER
The mention of commercial products, their source, or their use in connection with material reported
.herein is not to be construed as either an actual or implied endorsement of such products. Neither
the authors or publishers of this guide, nor any persons acting on their behalf a) makes any
warranty or representation, expressed or implied, with respect to the accuracy, completeness or
usefulness of the information contained in this report, or that the use of any information, cost
estimate, apparatus, method, or process disclosed in this report may not infringe privately owned
rights; or b) assumes any liabilities with respect to the use of, or damage resulting from the use of,
any information, cost estimate, apparatus, method, or process disclosed in this report, including
consequential or other indirect or contingent liabilities whether due to the negligence of the authors
or publishers or otherwise. Any person, entity or third party using this report or its contents or
relying thereon does so at hisher own risk.
FIRST EDITION (1 .O)
Copyright 0 1994 by Ecolink (Environmentally Preferred Solutions for Industry), a Division of
Sentry Chemical Company. 1481 Rock Mountain Blvd. / Stone Mountain Georgia 30086
(404) 62 1-8240 (404) 62 1-8245 (FAX)
All rights reserved. No part of this publication may be reproduced, stored, transmitted, or copied
in any form or by any means be it electronic, mechanical, photocopying, audio recording, or
otherwise without the written permission of the authors. Quotation of short passages for the
purposes of criticism and review is permissible.
11
~~
-
Table of Contents
1.0
2.0
3.0
4.0
5.0
INTRODUCTION
1.1
Objectives
1.2
How Are Solvents Used?
1.2.1 Maintenance and Production Activities
1.2.2 Precision Cleaning
1.2.3 Semiconductor Production
1.2.4 Printed Circuit Board Fabrication
1.2.5 Paint Stripping
How Much Solvent Is Used?
1.3
WHY CHANGE ?
2.1
Regulatory Constraints
2.2
Solvent Supply and Demand
2.3
Corporate Image and Liability
2.4
Worker Health and Safety
WHERE DO I START ?
3.1
Defining the Problem
3.2
Creating the Plan
3.2.1 Set Goals
3.2.2 Get Management Commitment
3.2.3 Organize a Team
3.3
Working the Plan
3.3.1 Gather Process Information
3.3.2 Formulate Options
3.3.3 Screen Options for Testing
3.3.4 Conduct Tests
3.3.5 Make Recommendations
Where
to From Here ?
3.4
THE SCIENCE OF CLEANING
4.1
How Cleaners Work
4.1.1 Mechanical Abrasion
4.1.2 Solvency
4.1.3 Detergency
4.1.4 Chemical Reaction
4.2
Predicting Cleaner Effectiveness
4.3
Testing Cleaner Performance
4.3.1 Cleaning Effectiveness
4.3.2 Material Compatibility
4.3.3 Other Performance Characteristics
WHAT ARE MY OPTIONS ?
Avoid The Need To Clean
5.1
1
1
3
3
6
7
7
10
12
15
16
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21
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24
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25
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35
37
37
38
39
40
41
43
46
46
49
49
53
53
...
111
Modify the Part or Contaminant
Use Non-Solvent Based Cleaning Technologies
5.3.1 Water
5.3.2 Abrasives
5.3.3 Cryogenic Techniques
5.3.4 Thermal Technologies
5.3.5 Aqueous Cleaners
Use Non-Halogenated Solvent Cleaning Technologies
5.4
5.4.1 Petroleum Distillates
5.4.2 Aliphatic Hydrocarbons
5.4.3 Alcohols
5.4.4 Terpenes
5.4.5 N-Methyl-2-Pyrollidone
5.4.6 Dibasic Esters
5.4.7 Glycol Ethers
5.4.8 Semi-Aqueous Cleaners
5.5
Use of Interim Technologies
5.6
Emerging and Experimental Technologies
5.6.1 Supercritical Carbon Dioxide
5.6.2 Carbon Dioxide Pellets and Snow Blasting
5.6.3 Ultraviolet Light and Ozone
5.6.4 Laser Cleaning and Stripping
5.6.5 High Intensity Light
IMPROVING PROCESS EFFICIENCY
6.1
Good Operating Practices
6.1.1 Part Drainage and Improved Racking
6.1.2 Monitor Cleaning Bath Quality
6.1.3 Rigid Inventory Control
6.2
Process Improvements
6.2.1 Use Demineralized Water
6.2.2 Increase Tank Agitation
6.2.3 Employ Two Stage Cleaning
6.2.4 Provide Mechanically Assisted Parts Handling
6.2.5 Install and Use Tank Covers
6.2.6 Improve Vapor Degreaser Operation
6.2.7 Enclosed Paint Gun Cleaning Stations
RECYCLING SPENT CLEANING BATHS
7.1
General Issues
7.1.1 On Site Recycling
7.1.2 Off Site Recycling
7.1.3 Other Options
7.2
Recycling Technologies
5.2
5.3
6.0
7.0
iv
57
61
61
63
68
69
70
75
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77
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84
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86
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101
102
104
104
104
106
109
109
109
110
111
112
8.0
9.0
10.0
7.2.1 Gravity Separation
7.2.2 Filtration
7.2.3 Distillation
7.3
Distillation System Design
CONTROLLING SOLVENT EMISSIONS TO AIR
8.1
General Design Criteria
8.2
Fume Incineration
8.2.1 Direct Thermal
8.2.2 Catalytic Oxidation
8.3
Carboflolymer Adsorption
8.4
Liquid Absorption
8.5
Condensation
8.6
Membrane Separation
IMPLEMENTING A NEW PROCESS
9.1
Establish a Baseline
9.2
Select a Replacement System
9.3
Perform an Economic Evaluation
9.4
Prepare the Final Report
9.5
Example Economic Analysis
9.5.1 The Existing Facility
9.5.2 Installation of Emission Controls
9.5.3 Switch to Aqueous Cleaning
9.6
Conversion of Existing Equipment
SOURCES OF INFORMATION
112
113
114
116
119
119
121
12 1
122
122
126
127
128
13 1
131
133
134
137
138
138
140
144
149
151
APPENDICES
-
A BLANK USEPA WASTE MINIMIZATION ASSESSMENT WORKSHEETS
B - GOVERNMENT AGENCIES OFFERING P2 ASSISTANCE
LIST OF FIGURES
Figure 1-1
Figure 1-2
Figure 3-1
Figure 3-2
Figure 5-1
Figure 6-1
Figure 6-2
Figure 6-3
Figure 6-4
A Typical Cold Cleaning Tank and Sources of Emissions
A Typical Open Top Vapor Degreaser
Method to Assign Weighing Factors to Screening Criteria
Weighted Sum Option Screening
A Typical Aqueous Cleaning System
Adding a Drainage Bar to a Process Tank
Stoddard Solvent Usage Versus Light Transmittance
Cold Cleaner Modified for Two-Stage Cleaning
Zero Emission Vapor Degreasing Process
4
5
33
34
71
97
98
103
107
V
LIST OF TABLES
Table 1-1
Table 1-2
Table 1-3
Table 2-1
Table 2-2
Table 2-3
Table 3-1
Table 3-2
Table 3-3
Table 4-1
Table 4-2
Table 4-3
Table 4-4
Table 5-1
Table 6-1
Table 6-2
Table 6-3
Table 9- 1
Table 9-2
Table 9-3
Table 9-4
Table 9-5
Table 9-6
Table 9-7
Table 9-8
vi
Organic Solvents Commonly Used in Cleaning
Characteristics of Commonly Used Soldering Flux
Estimate of Halogenated Solvent Use by Select Operations
Pressures Impacting Continued Use of Halogenated Solvents
U.S. Production, Export, Import, and Demand Data for
Halogenated Solvents
Solvents Listed in the 33/50 Program
Facility Information Usefbl for Conducting an Assessment
Guidelines for Site and Process Inspection
Information Sources for Waste Minimization Options
Contaminant Sources and Forms
Comparison of Cleaning Method Effectiveness for Soil Removal
Kauri-Butanol Values for Various Solvents
Cleaning Effectiveness Versus Surface Condition
Listing of Viable Alternative Cleaning Techniques
Effect of Liquid Viscosity on Drag-out
Effect of Part Configuration and Drainage on Drag-out
General Guidelines to Minimize Drag-out
Capital Investments for a Large Scale Project
Summary of Operational Parameters for the Base Case
Summary of Operating Costs for the Base Case
Summary of Operational Parameters for the Carbon Bed
Comparison of Existing to Carbon Bed System Emissions
Summary of Costs for the Carbon System
Summary of Operational Parameters for Aqueous Cleaning
Summary of Costs for Aqueous Cleaning System
1
8
13
15
18
20
28
29
31
37
44
45
46
55
94
95
96
135
138
139
140
141
143
145
149
1.0 INTRODUCTION
'
Welcome. Because you are reading this guide, we assume that you are faced with the
difficult challenge of reducing or eliminating the use of hazardous solvents in your workplace. We
have constructed this guide to be flexible, so that you can obtain comprehensive information
quickly and easily. Please use the table of contents to source the information you need most, while
using other parts of the guide for reference and backup. The authors welcome your comments,
questions, and suggestions for improving this guide.
1.1
OBJECTIVES
Cleaning is a common practice in many diverse sectors of industry. Cleaning may range
from simple maintenance activities such as wiping grease off a part with a solvent soaked rag to
critical cleaning requiring the removal of microscopic particulates and oxides. Commonly used
halogenated solvents include perchloroethylene (PERC), trichloroethylene (TCE), methylene
chloride (METH), 1,1,1 trichloroethane (TCA), and trichlorotrifluoroethane (CFC-113). Many
non-halogenated solvents are in use. Table 1-1 provides a listing of commonly used solvents.
Many commercial cleaners are blends of one or more solvents. Additives to the formulation may
include alkaline cleaners, detergents, surfactants, diluents, or stabilizers. The specific formulation
is heavily dependent on the cleaning application and target effectiveness of the cleaner.
TABLE 1-1
ORGANIC SOLVENTS COMMONLY USED IN CLEANING
Alcohols
Butanol
Isopropanol (IPA)
Methanol
Aromatics
Benzene*
Toluene*
Xylene*
Gasoline*
Esters & Ethers
Acetates
Di-Ethylene Glycol Ethers (Carbitols)
Ethylene Glycol Ethers (Cellosolves)
Ketones
Acetone
Methyl Ethyl Ketone (MEK)
Methyl Isobutyl Ketone (MIBK)
Aliphatics
Kerosene
Mineral Spirits
Naphtha
Refined Distillate
Stoddard
Solvent
~.
Chlorinated Hydrocarbons
Carbon Tetrachloride*
Chlorobenzene*
1, 1,l Trichloroethane (Methyl Chloroform)
Methylene Chloride
Perchloroethylene
Trichloroethvlene
Fluorinated Hvdrocarbons
Trichloro Monofluoromethane (CFC-11)
Trichloro Trifluoroethane (CFC- 1 13)
Notes:
Asterisk indicates solvents no longer
widely used due to adverse health impacts
or other safety issues.
1
CHAPTER 1.0
Given the large volume of solvents currently in use, and the regulatory pressures forcing
some solvents out of the marketplace, industry is faced with a difficulttask. Industrial sectors
dependent on these materials must seek out replacements while maintaining productivity. Many
companies presently using hazardous solvents are quickly moving to find viable alternatives. Most
of the large companies making these moves have the capital and resources to assess and evaluate
their ongoing needs. For larger solvent consumers, the stakes in finding and implementing viable
substitutes are high.
For many small and medium sized companies, the stakes are even higher. This is
especially true for those unaware of current regulatory events andor those who believe that they
will be exempted. Without an active program to seek-out, identifl, test, and implement acceptable
alternatives, these companies will be left high and dry. The availability of CFC-113 and TCA is
actively declining and purchase costs are skyrocketing. Lead times to procure replacement
equipment are increasing. At the same time, more and more manufacturing business will be given
to competitors able to promote their changeover to llcleanll process technology.
If this sounds scary, it is meant to. While other materials have been regulated out of use in
the past (e.g., asbestos insulation, carbon tetrachloride and benzene for parts cleaning, CFC-113 as
an aerosol propellant), there were always special exemptions granted and near drop-in
replacements available. This will not be the case with halogenated solvents. Each use and
application will require careful consideration and investigation to find a viable alternative. If you
haven't taken a hard look at your operation, you are already late.
To get back into the race, you need to take action now. When you have finished reading
this guide, you will be able to prepare a comprehensive program for eliminating hazardous and
ozone depleting solvents in your workplace. Whenever possible, we have provided actual
information and reports on the activities of real companies. While this anecdotal data may not be
fully applicable to your specific activity, it is provided to enhance your feel for the type of action
that has been successful (or unsuccessful), in various fields. We have collected the most current
information on what others are doing in the fields of parts cleaning, electronics production and
fabrication, and paint stripping.
In the following chapters, key concepts on locating and testing environmentally preferred
cleaning agents are presented. In addition, information is presented on cleaning solution testing
and monitoring, waste recycling, air emission controls, and replacement system economics. The
data in this guide has been collected from hundreds of sources, encompassing literally thousands of
hours of lab and shop-floor research. We trust this information will help you establish a good
point of departure in your search for viable, environmentally preferred cleaning technologies.
The balance of this chapter deals with general use of solvents in industry. Various
cleaning techniques are discussed and estimates of solvent usage are given. Chapter 2 continues
with a discussion of the reasons we are now faced with change. The primary reasons include
2
~
~
INTRODUCTION
regulatory, public perception, and economic trends. This material is intended to provide a broad
overview and foundation for the interested reader. The details for your "action plan" begin with
Chapter 3, entitled, Where Do I Start.
1.2
HOW ARE SOLVENTS USED?
Solvents are widely used to remove contaminants from a variety of substrate materials.
Common contaminants include solid particulates, waxes, greases, cutting and lubrication fluids,
b u f i g compounds, slushing oils, quenching oils, heat treating salts, rosin fluxes, protective
coatings, and finishes. Selection of a particular solvent and cleaning process is based on the type
of substrate@)to be cleaned, the type of soil(s) to be removed, the degree of cleanliness required,
the desired method of application, and many other operating conditions and constraints. Solvent
usage in maintenance and general production activities, precision cleaning, semiconductor
production, printed circuit board fabrication, and paint stripping is discussed below.
1.2.1
Maintenance and Production Activities
Parts cleaning is a common component of maintenance and production activities. These
activities often involve the removal of bulk or gross contamination. In the past, maintenance
activities were mainly conducted with petroleum solvents such as mineral spirits while production
activities employed the use of alkaline cleaners. The use of halogenated solvents became popular
because they exhibited good solvency for organic contaminants, evaporated readily leaving the
cleaned part dry, were less toxic than the solvents commonly in use, were non-flammable, and were
less costly to operate and maintain than alkaline cleaners.
The most common method of using a solvent for cleaning is referred to as cold cleaning.
Cold cleaning techniques include wiping or swabbing surfaces with a solvent soaked rag or shop
towel, dipping and immersing the part into a small tank or container of solvent, and spraying with
an aerosol product. Most methods involve relatively simple and inexpensive equipment. The small
amount of emissions per source and the diverse nature of these operations makes emission control
hard to apply. The large number of cold cleaners in use, however, makes cold cleaning a major
source of emissions; over 55 percent of all halogenated solvent emissions from degreasing
operations nationwide can be attributed to cold cleaning (USEPA, 1977; S W , 1992a).
Cold cleaners require the simplest equipment; typically a small rectangular tank with lid
and a pump to recirculate the solvent (see Figure 1-1). Maintenance cleaning often employs
nothing more than a metal pail or bucket. Dirty parts are placed in the solvent bath and allowed to
soak until the soil softens and dissolves. To speed cleaning, the parts may be manually wire
brushed or sprayed with solvent prior to immersion. Other methods to speed cleaning include
mechanical agitation by means of vertical conveyors (the parts are raised and lowered in the
solvent bath) and ultrasonic agitation, Automatic pump-around and particulate filtration systems
may also be employed.
3
CHAPTER 1.0
FIGURE 1-1
A TYPICAL COLD CLEANING TANK AND SOURCES OF EMISSIONS
Hinged
Lid
Source: USEPA, 1977
Following cleaning, the parts are withdrawn from the bath. Prudent operators rotate the
parts during withdrawal and allow solvent drag-out to drain back into the bath. Rapid withdrawal
without drainage can result in extensive loss of solvent, increased air emissions, increased waste
generation in subsequent operations, and contamination of the workplace.
Spray cleaning of parts with solvent, using an airless gun similar to a paint sprayer, is also
practiced. Spray cleaning is typically performed in a ventilated fume hood so as to protect the
worker from solvent fumes. In addition to the b e hood, an emissions control system is often
required. Many local air quality agencies prohibit the spray cleaning of parts with solvent or
require an appropriate emission control system to be in place. Fire department regulations and
insurance requirements often require the inclusion of fire suppression systems when spraying
flammable or combustible solvents.
Vapor degreasing differs from cold cleaning in that cleaning is performed by condensation
of hot solvent vapor onto the part as opposed to immersion of the part into cold solvent. Vapor
degreasing offers a faster rate of cleaning because dissolution of dirt takes place at elevated
temperatures and because the wetted part surface is always contacted with clean solvent. In
4
INTRODUCTION
addition to metals, vapor degreasing has been used for cleaning other materials such as glass,
ceramics, plastics, elastomers, coated items, or combinations thereof.
Vapor degreasers are usually classified as either being open-top or conveyorized. They
can have a number of basic cleaning cycles, such as vapor only, vaporkprayhapor, or
vapor/soak/vapor. In general, a vapor degreaser is a steel tank with a steam or electrical heating
coil below the liquid level to effect vapor generation. A water jacketed vapor cooling and
condensing zone above the vapor level is used to re-condense solvent and control vapor loss. An
additional level of emissions control may be achieved through the use of refrigerated freeboard
condensers andor carbon units. A typical vapor degreaser is presented in Figure 1-2 below.
To effect cleaning, dirty parts are typically placed into a metal mesh basket and lowered
into the vapor degreaser. As the hot solvent vapors condense on the cool workload, the solvent
dissolves and flushes away the contaminants. Condensed solvent, dissolved contaminants, and
removed particulates fall into the boiling sump where they remain until the degreaser is cleanedout. Compared to cold cleaning, vapor degreasing equipment requires more energy and is more
expensive to purchase and operate, but provides a greater degree of cleanliness.
FIGURE 1-2
A TYPICAL OPEN TOP VAPOR DEGREASER
Condensing
COllS
\
/
Water
Jacket
5
CHAPTER 1.0
The effectiveness of cleaning is highly dependent on the volume of solvent vapor that
condenses on the part. This volume is a function of the weight of the part, the specific heat of the
part, the difference in temperature between the cold part and the solvent vapor, and the latent heat
of solvent condensation. Where as heavy metal parts may be effectively cleaned in a vapor
degreaser, thin or light weight parts may be difficult to clean due to inadequate vapor condensation.
Cleaning may be improved by spraying the parts with cool solvent, which drops their temperature
and allows more solvent vapor to condense on the surface.
Unlike cold cleaners, vapor degreasers lose relatively small amounts of solvent as solid
waste or liquid drag-out. Most emissions are due to vapor loss and the loss level is highly
dependent on operator and operating conditions. Solvent losses for a poorly operated open-top
vapor degreaser may be eight or more times greater than for a well operated unit. Conveyorized
degreasers are less prone to changes in emission levels due to inconsistent operator practices.
Conveyorized in-line degreasers are usually enclosed boxes with openings only at the
entrance and exit ports. The work piece is continually conveyed in either a straight-through or a
return-circuit route. -This type of degreaser is often selected for large-volume continuous
production. The entrance and exit ports are typically sealed by flexible flaps and solvent emissions
are well controlled. Recently, conveyorized degreasers designed to emit virtually "zero emissions''
have been introduced to the market. The objective, of course, is to control and virtually eliminate
METH, TCE, or PERC emissions now that CFC-113 and TCA are no longer viable choices.
1.2.2
Precision Cleaning
Precision cleaning involves both cold cleaning and vapor degreasing processes. The
halogenated solvent CFC-113 has traditionally been the cleaning solvent of choice because of its
chemical inertness and ability to penetrate extremely small gaps and spaces. Major applications
include gyroscope, hydraulic, and liquid oxygen system flushing, cleaning medical components,
and nuclear equipment decontamination.
Gyroscope flushing rigs are dedicated systems designed specifically for a particular
gyroscope. Coupling fixtures attach to the gyroscope instrument casing and CFC-113 is forced
through the gyroscope at high pressure. The CFC-113 is used to remove particulate contamination
from inside the gyroscope before filling it with flotation fluid or to flush out the fluid during
rework. Ultrafiltration of the CFC-113 before use is performed by the flushing rig.
Hydraulic system flushing rigs and spray booths are similar to gyroscope flushing rigs but
are larger. The flushing rig pumps filtered CFC-113 through the hydraulic system and is used to
remove hydraulic fluid. Hand held spray cleaners are often used for manual cleaning of valve
seats. Most flushing operations are "dead loss" in which none of the CFC-113 used for cleaning is
recovered or reused. Most CFC-113 is vented to the atmosphere while a small amount is disposed
of with the removed fluid.
6
~
-
INTRODUCTION
Medical and surgical equipment, orthopedic prostheses such as hip and knee joints, as well
as many other biomedical products are cleaned with CFC- 113. In the production of plastic
moldings such as syringes, spoons, bottles, and sample phials, CFC-113 may be used as a release
agent. CFC-113 is also used as a carrier for ethylene oxide (ETO)in the sterilization of
biologically contaminated equipment and supplies.
In the nuclear power industry, pieces of ancillary equipment that become contaminated
with radioactive dusts are often cleaned in glove boxes using remote handling systems. With
continued use, the glove boxes also become contaminated. Glove boxes are decontaminated by
spraying and washing down with CFC-113. The radioactive dusts can then be recovered from the
CFC-113 by filtration. CFC-113 is also used for the dry cleaning of protective clothing.
1.2.3
Semiconductor Production
Integrated circuits (ICs) are the major product of the semiconductor industry and their
production involves the use of hundreds of materials, products, and processes. Many different
machines are used in the wafer fabrication step and these machines need to be cleaned periodically.
Most machine cleaning is performed with CFC- 113.
During the component fabrication process, CFC-113 and TCA are widely used for
cleaning surfaces and for stripping negative photoresist. Non-halogenated solvents are often used
for stripping positive resist. Following fabrication, the chips are tested for defects and the wafers
cut into individual chips. Leads are soldered to the chip and the device encapsulated. Both CFC113 and TCA may be used to remove flux residues that remain after soldering though it is more
common to use isopropyl alcohol (IPA). Mixtures of CFC-113 and IPA are also used.
M e r encapsulation, the devices are stamped with part numbers and other identification
markings. It is following this operation that CFC-113 combined with METH is used to test the
permanency or cure of the ink. The military specification for mark permanency testing requires the
use of either a 50/50 percent azeotropic mixture or'a 35/65 percent blend. A properly cured ink
will resist the stripping action of these mixtures.
1.2.4
Printed Circuit Board Fabrication
There are three main methods for producing PC boards: additive, subtractive, and semiadditive. The subtractive technique accounts for nearly 80 percent of the board market and is
discussed below. Fabrication begins by cutting the copper clad boards from sheet material and
then drilling component holes. Mechanical cleaning is used to remove cuttings and burrs, followed
by chemical cleaning with acids to remove metal oxides. Alkaline cleaners, electrolytic cleaners,
abrasive cleaners, or halogenated solvents are then used to remove oils and greases. Once clean,
the boards are electroless plated with copper to obtain a continuous metallic surface from one side
of the board to the other (through-hole plating).
7
CHAPTER 1.0
Silk screening, offset printing, or photolithography is used to transfer the circuit pattern
from a master to the drilled and cleaned board. The circuit pattern may be positive or negative
depending on the type of photoresist employed. In addition to being positive or negative, the
photoresist may be solvent-based, aqueous-based, or semi-aqueous. Solvent-based resist is
developed with TCA and stripped off with METH. Aqueous-based resist may be developed with
carbonate solutions while semi-aqueous resists may be developed with glycol ethers and alcohols.
Both aqueous and semi-aqueous resists are stripped off with water-based formulations.
In the past, military specifications required the use of solvent-based resists only. This has
since changed and most new systems being installed employ the use of semi-aqueous resists.
Conversion has been rapid since the overall costs of developing and stripping semi-aqueous resist
are lower. The semi-aqueous process is now the most widely used method.
In the assembly process, the circuit boards are populated with the desired components and
then soldered either by hand or by passing through a wave, dip, or drag soldering machine. Flux is
used to remove oxides from the metal surface being soldered and reduce the surface tension of the
solder. This improves wetability so that the solder flows more evenly and provides a good
electrical bond. Three major types of flux are employed; rosin flux, organic acid flux, and
synthetically activated flux. Characteristics of commonly used fluxes are presented in Table 1-2.
TABLE 1-2
CHARACTERISTICS OF COMMONLY USED SOLDERING FLUX
Flux Type
Rosin
Common
Reference
R
Mildly
Activated
Activated
RMA
Super
Activated
Organic
Acid
Synthetic
Activated
Resin
RSA
Resin
Low Solids
Low Solids
RA
OA
SA
Note: Data from Markenste
Composition
Cleaner
Employed
Abietic acid and other isomeric acids; solid content
ranges from 15 to 35 percent.
Abietic acid and other isomeric acids; low conc. of
amine hydrochloride activators.
Abietic acid and other isomeric acids; medium conc.
of amine hydrochloride activators.
Abietic acid and other isomeric acids; high conc. of
amine hydrochloride activators.
Abietic acid and other isomeric acids; halide or
non-halide activators.
Alkyl acid phosphates with halide activators.
cs, ws
cs, ws
cs, ws
cs, ws
W
cs
Chemically synthesized rosin.
W
Rosin flux with 2 to 5 percent solids content.
NR
(1983); Morrison and Wolf (1985). Flux removal can : achieved by
use of chlorinated solvent (CS), water with saponifier (WS),
water only (W), or not required (NR).
8
INTRODUCTION
Rosin flux accounts for about 55 percent of the soldering flux market. Rosin flux is a
mixture of isomeric acids including abietic acid. Activators, which have traditionally consisted of
halide compounds, may be used to increase the wetability of the flux during soldering. Compared
to the other two flux types, rosin flux is the least corrosive. Removal can be performed with
CFC-113, TCA, or water containing a suitable saponifier (a mildly alkaline compound that
converts the organic acids into soaps). Until recently, only rosin and mildly activated rosin fluxes
were approved for use by the military.
Organic acid flux, representing 40 percent of the market, is more aggressive than rosin
flux and allows for faster soldering rates. Being water soluble, organic acid flux can be removed
with aqueous cleaners. The remaining 5 percent of the market consists of synthetically activated
flux. This flux is similar to organic acid flux in terms of effectiveness but must be removed with
halogenated solvents. Usage of no clean / low solid fluxes is making rapid ingress into this market.
After soldering, flux residue is not the only contaminant that needs to be removed.
Nonpolar or semipolar contaminants may include greases, oils, and waxes which are generally
composed of long-chain hydrocarbons. Polar contaminants may consist of flux activators and their
residues, sodium chloride, and soldering, plating, and etching salts. Particulate contaminants such
as dust and machining, drilling, and punching fiagments may also be present. Failure to remove
these contaminants may lead to early failure of the board.
Depending on the type of flux to be removed and the defluxing agent selected, board
cleaning may be performed by cold cleaning or vapor defluxing. In cold cleaning, equipment can
range from shallow trays into which boards are placed by hand up to hlly automated in-line
defluxing systems. These automated systems often employ the use of rotating brushes, spray
nozzles, andor ultrasonic agitation to enhance cleaning. In vapor defluxing, the equipment used is
identical to batch or conveyorized in-line vapor degreasers. The most common solvents used are
azeotropic blends of CFC- 113 or TCA with alcohol.
Because of the upcoming phase-out of CFC- 113 and TCA, an Industry/DOD/EPA
working group was convened in 1988 to investigate the use of alternative defluxing agents. While
the military and government sectors account for a small percentage of the total PC board market,
their standards have a large impact on the industry. One source suggests that as much as 40 to 50
percent of the CFC-113 used in electronics is driven by military specifications and that these
specifications have become a de facto world standard (Naegele, 1989).
The alternative defluxing agent program was divided into three phases. The first phase
involved benchmark testing to verify protocols and to establish a performance baseline. The
baseline was established by defluxing standardize PC board assemblies with a blend of CFC- 113,
methanol, and nitromethane, (the industry standard). In Phase 2, alternative cleaning media were
tested at a number of facilities. In Phase 3, more extensive testing is being conducted, along with
testing of alternative fluxes and cleaning processes.
9
CHAPTER 1.0
The specific project requirements and testing protocols have been published by the
Institute for Interconnecting and Packaging Circuitry (IPC, 1988; IPC, 1991). Results of the
Phase 2 work have also been released, The military has reviewed its specifications and will, under
Mil-2000A and proposed Mil-2000B, allow a manufacturer to use a non-CFC based defluxing
process as long as proper verification of cleanliness is provided. Current information on the status
of this issue is available through the IPC at (708) 677-2850.
-
1.2.5
Paint Stripping
Paint stripping is commonly performed by one of three methods: physical removal,
chemical reaction and degradation, or thermal destruction. Physical methods such as wire brushing
or abrasive blasting rely on abrasion to remove the coating. Chemical paint stripping, which may
involve the use of solvents, acids, andor caustics, involves physical and chemical reactions.
Solvents may be used to either dissolve or swell the coating so that it detaches from the substrate
while acids and caustics may be used to react with and break down the coating. Thermal methods
rely on heat to burn away the organic components of the coating. The inorganic components (Le.,
pigments and ash) may then be removed by rinsing or abrasive blasting.
In the formulation of cold (i.e., no heat required) chemical-based paint strippers, METH is
the primary halogenated solvent used. METH based strippers offer a major advantage over many
other chemical-based strippers in that it is effective on a wide variety of coating materials. Many
of the alternative strippers are effective on a more narrow range of coating types. To its
disadvantage, M E W based strippers are highly toxic and inappropriate usage at many sites has
resulted in problems involving worker exposure and environmental damage. The major markets for
METH based paint strippers include equipment maintenance, Original Equipment Manufacturing
(OEM), and home improvementhepair.
In maintenance stripping, parts may be stripped either in the field or in the shop. Stripping
is performed to remove old coatings so that the parts can be inspected for damage, cracks, or
corrosion. Following repair (if required), the parts are reprimed, repainted, and reassembled. In
the OEM sector, paint stripper is used to remove defective coatings from rejected parts so that the
parts can be repainted. Stripper is also used for cleanup of the paint booths and paint application
equipment. In the home market, stripping is mainly done on wooden building exteriors and on
wooden goods such as chairs, tables, and cabinets.
Except for the direct use of METH in equipment cleanup, most paint strippers sold are
formulated products. Solvent-based strippers commonly employ a number of components that
each accomplish a given task or finction. The first component (usually METH), is a primary
solvent that serves to penetrate the paint film and promote swelling. Cosolvents may also be used
to increase the rate of penetration and to keep the various components from separating. Water
soluble solvents such as methanol and isopropyl alcohol are commonly used to promote mixing of
METH with other water soluble components.
10
INTRODUCTION
Other paint stripper ingredients include surface active agents, emulsifiers, thickeners,
sealants, and corrosion inhibitors. Thickeners such as methyl cellulose derivatives are used to
thicken the stripper so that it can be brushed onto vertical surfaces. Sealants such as crude or
refined paraffin wax act to retard evaporation of the METH so that the stripper remains effective
over a long period of time.
For many years, the Department of Defense (DOD) has employed METH based strippers
for field stripping a variety of vehicles. Stripper is sprayed onto the vehicle and allowed to stand
until the paint blisters. The stripped paint is then removed manually with a squeegee, a rubber
edged scraping tool. Most of the stripped paint and stripper is generally collected and put in drums
for disposal as hazardous waste while the remainder is flushed from the vehicle during wash-down.
Similar operations are conducted in the airline transportation industry.
Handling and disposal of the rinse water generated can be a major problem for many
facilities. In the past, rinse water may have been sent to unlined aeration and settling basins to
remove METH and paint solids before discharge. With the concern for soil and groundwater
contamination coupled with tougher air emission standards, operation of these basins may no
longer be viable. In addition to the METH, the presence of phenolic compounds in the stripper has
prevented some facilities from discharging their rinse water to a Publicly Owned Treatment Works
(POTW). For facilities denied this option, all rinse water must be treated and handled as
hazardous waste.
Immersion stripping is often employed to remove paint from disassembled parts or
components. Tanks used for immersion stripping are similar to cold cleaning tanks used for
cleaning. Most tanks are equipped with manual or automatic parts handling systems so that the
parts do not have to be touched during stripping. Unlike cold cleaning tanks, most immersion
stripper tanks are followed by a rinse water tank for rinsing. In some older facilities with limited
tank space, stripped parts may be manually rinsed on the shop floor using a water hose. This is a
highly questionable activity since it can result in undue worker exposure, contamination of the
work area, and contamination of the ground beneath the work area.
To control emissions from an immersion stripper, a water blanket is used. This is a layer
of water that floats on top of the METH formulation and suppresses evaporative losses. While
effective at reducing emissions, the water blanket can become acidic due to decomposition of the
METH and cause etching of metal parts (both METH and TCA in the presence of water can form
hydrochloric acid unless proper stabilizers are present). Problems associated with the handling and
disposal of this water, along with rinse water from the rinsing tank,are the same as mentioned
above for fieldstripping.
In the OEM sector, paint stripper is commonly used for the cleaning and maintenance of
paint application equipment. Air-driven spray guns as well as the paint circulation lines that
supply the guns with paint must be cleaned whenever a production run is completed or when the
11
CHAPTER 1.0
paint color is changed. Failure to properly clean this equipment can lead to increased reject rates
and hence the increased need for parts stripping. To clean the guns, lines, and hoses, paint stripper
is circulated through the system. Since the paint being removed is uncured, the use of pure METH
is typically adequate. Use of a formulated product is seldom required and if used, must be purged
from the system with a compatible solvent so as not to contaminate the next batch of paint.
To clean paint booths, workers may spray the stripper or apply it with wax applicators to
the inside walls and surfaces of the booth. The stripper is allowed to stand for 10 to 15 minutes
and is then removed. Stripped paint may be scraped from the walls and placed in drums for
disposal (in dry filter booths) or flushed from the walls using high pressure hoses (in water wash
booths). Immersion cleaning of hooks, racks, and painting masks is also a common maintenance
activity. Facilities that require the cleaning of a large number of hooks and racks on a constant
basis seldom use METH based strippers. Instead, they often employ high temperature burn-off
ovens or high pressure water blasting systems.
In commercial furniture stripping, a modified form of immersion stripping known as "flow
over" stripping is practiced. Furniture is placed inside an empty tank and the operator hoses it
down with stripper. The tank is designed to collect the stripper and pump it back through the hose.
The operator directs the flow over the furniture, hence the term "flow over." After draining, the
piece is transferred to a separate area where the loosened paint is removed by hand scraping and
water spraying. Additional brush-on stripper may be used. When finished, the furniture is given a
final rinse and allowed to dry. This is followed by sanding to smooth out the raised grain.
On an average day, a commercial shop might use 50 to 300 gallons of water in the rinse
area. Small amounts of METH will contaminate this water. Some local sanitation districts may
set limits on sewer releases as a matter of course. Often, the rinse water contains unacceptably
high levels of METH and other contaminants and must be disposed of as hazardous waste. Paint
stripped from the furniture must also be disposed of as hazardous waste. Stripped paint is
typically removed from the tank when it reaches a level of 4 to 6 inches in the tank bottom.
Home consumers generate a significant portion of paint stripping waste. Stripped items
include doors, door frames, porches and decks, as well as pieces of furniture. Most of the paint
stripper employed by home consumers is for the refinishing of furniture. Stripper is generally
applied with a brush and removed with a scraper. The furniture may then be rinsed off with water
or cleaned with a solvent soaked rag. Use of water on wood would be followed by drying and
sanding since the use of water on wood often results in the raising of the grain. Most consumers
dispose of the stripped paint in the trash.
1.3
HOW MUCH SOLVENT IS USED ?
In a word, lots. A recent study by the Source Reduction Research Partnership placed the
total amount of halogenated solvent used for parts cleaning, electronics, and paint stripping in 1988
12
INTRODUCTION
at 484 thousand metric tons (MT). This is equivalent to 534 thousand short tons, 1.8 million
drums, or 97 million gallons. Solvent use and loss estimates for each type of halogenated solvent
and each industrial use sector are presented in Table 1-3.
Of the 34 1 thousand MT of halogenated solvent consumed in parts cleaning operations,
280 thousand MT was virgin solvent, and the remainder was recycled solvent, recovered by offsite services. Waste sent off site for recovery or for fuel use in cement kilns represented one-third
of total solvent loss. The remaining two-thirds loss was due to uncontrolled air emissions. Most of
the solvent waste generated contained 75 to 99 percent solvent and it was typically sent to off-site
recyclers for processing.
In line with the significant growth in the electronics industry over the last few decades,
usage of halogenated solvents was high in 1988. The total amount of halogenated solvent used was
estimated to be 76,700 MT. More than half of this was CFC-113.Unlike the parts cleaning
sector, usage of recycled solvent was relatively minor. This is believed due to the strict solvent
purity standards established in the industry.
TABLE 1-3
ESTIMATE OF HALOGENATED SOLVENT USE BY SELECT OPERATIONS
~~
Industrial
Omration
Parts Cleaning
Cold Cleaning
Vapor Open Top
Vapor In Line
Total Use / Loss
Electronics
Semi. Wafer Fabrication
Semi. Wafer Assembly
PCB Resist Developing
PCB Resist Stripping
PCB Degreasing & Dry
PCB Assembly Deflux
Critical Cleaning
Total Use / Loss
Paint Stripping
OEM Equip. Clean-up
OEM Parts Stripping
Maintenance, Field
Maintenance, Shop
Consumer, Home
Consumer, Shop
Total Use / Loss
Solvent Use (Thousand Metric Tons)
PERC
METH
TCA
54.5
2.2
0.3
I
3.0
1:;
32.4
I ?!I I
1
I
I CFC-113
I
I
I
18.3
117.9
66.7
22.2
206.8
1:
29.3
2.7
1.7
----4.8
25.7
4.8
39.7
-------
---
---
---
0.0
13
CHAPTER 1.0
Unlike parts cleaning and electronics which use a variety of halogenated solvents, paint
stripping primarily employs the use of METH. Estimated METH use in 1988 was reported to be
66,000 MT with 60,000 MT being virgin solvent and 6,000 MT being recycled solvent. Much of
the recycled solvent used would be from waste generated by the parts cleaning and electronics
industry. Spent METH from paint stripping can be recovered, but the formulated nature of the
stripper and low volume of METH in the final waste makes this a difficult practice to implement.
14
2.0 WHY CHANGE ?
It is now painfully clear to users of hazardous and ozone depleting solvents that they must
find alternative ways to clean their parts. During the later part of 1992, some thought the pressure
on ozone depleting solvents might ease, due to new data which indicated that chlorofluorocarbons
might not be the sole contributor or even the major component of the ozone depletion equation.
This concept was quickly challenged by new atmospheric models that indicate the destructive
powers of CFC-113 and TCA are perhaps even greater than previously thought. Even if all
releases of ODS (Ozone Depleting Substances) stopped today, ongoing ozone layer destruction will
continue for decades due to the long atmospheric life of these chemicals. The legislative fate of the
ozone depleters has been sealed for good.
As for other hazardous cleaning solvents and processes, a flurry of new regulations from
the Clean Air Act to local VOC ordinances are impacting their continued use in dramatic fashion.
In order for you to make informed decisions, it will be helpful to have an understanding of the
forces driving this change. After you have assessed this information, you can plan your actions
around the forces at work in the marketplace. The key pressure points are reviewed in the
following section and summarized below in Table 2- 1.
TABLE 2-1
PRESSURES IMPACTING CONTINUED USE OF HALOGENATED SOLVENTS
CFC-113
Legislative
Activity
Available
Supplies
Complete
phase-out
no later than
1995.
Short,
becoming
shorter.
Extreme,
high
awareness.
No major
issues.
TCA
TCE
METH
Complete
Production
Production
Production
phase-out
continues.
continues.
continues.
no later than
1995.
Still available, Still available. Still available. Still available.
I
becoming
shorter.
Moderate,
Moderate,
growing
some
awareness.
awareness.
OSHA
Regulated, Significant
controls are hazard,
in place.
suspected
carcinogen.
Solid Waste Regulated as Regulated as Regulated as
Disposal
hazardous
hazardous
hazardous
waste.
waste.
waste.
Regulatory
SARA 31 3
SARA 31 3
SARA 31 3
Compliance reportable.
reportable.
reportable &
air Dermits.
Public
Pressure
PERC
I
Moderate,
some
awareness.
Significant
hazard,
suspected
carcinogen.
Regulated as
hazardous
waste.
SARA 31 3
reportable &
air Dermits.
I
Moderate,
some
awareness.
~-~
Significant
hazard,
suspected
carcinogen.
Regulated as
hazardous
waste.
SARA 31 3
reportable.
~
15
~
~
CHAPTER 2.0
2.1
Regulatory Constraints
Several of the halogenated, non-ozone depleting solvents have been associated with human
carcinogenesis. These include TCE, METH, and PERC. As ozone depleters, CFC-113 and TCA
contribute to enhanced ultraviolet radiation at the earthls surface, with resulting increases in skin
cancers. While a number of specific points of disagreement remain in regard to the health and
environmental impacts of halogenated hydrocarbons, a regulatory consensus has emerged that these
substances pose major problems when released into the environment. Significantly reducing their
use can consequently reduce the health and environmental threats associated with them.
One of the most internationally significant actions taken on this issue was the creation and
ratification of the Montreal Protocol. The Protocol is an international treaty, signed and ratified
by the 43 nations producing and using the bulk of ozonedepleting chlorofluorocarbons (CFCs), as
well as TCA. Non-solvent ozone depleters (Le., halons used in fire extinguishers and CFC-based
refrigerants and foam blowing agents) are also covered. Under the Protocol, which the United
States has signed, both CFC-113 and TCA production will be phased out on a short timeline. The
current deadline, moved up at the November 1992 session in Copenhagen, will end production of
CFC-113 and TCA no later than December 3 1, 1995. Since new supplies of these two popular
chlorinated solvents will soon be unavailable, this is a major driving force when considering the
need to change processes.
The 1990 amendments to the Federal Clean Air Act point toward strict regulations of
METH, PERC, TCE, TCA, and other halogenated solvents identified as toxic air pollutants. In
California, METH and PERC were recently identified as toxic air contaminants. As a result of
this new determination, their use will be strictly controlled throughout the state. The Air Resources
Board (ARB) is in the process of developing regulations that are likely to severely curtail METH
use in California. Similar regulations for PERC are likely to follow.
M E W , PERC, and TCE are listed by the State of California as known carcinogens.
Under the state's landmark toxic control law, passed by the voters in 1986 and commonly known as
Proposition 65, any business that exposes people to a listed chemical must give clear and
reasonable warning to the individuals exposed. In addition, businesses may not discharge a listed
chemical into any source or potential source of drinking water. Exceptions to both requirements
exist if the business can show that the amount in question was within 'In0 significant risk" levels
(currently defined as 50 micrograms per day for METH, 14 micrograms per day for PERC, and 60
micrograms per day for TCE).
The South Coast Air Quality Management District (SCAQMD), has promulgated Rule
1122 which regulates solvent cleaners that use solvent containing VOCs to degrease or clean
surfaces. The rule requires that open top vapor degreasers be equipped with a cover, a drainage
facility for the solvent, a freeboard ratio equal to or greater than 0.75, and a below freezing
refrigerated freeboard chiller, a carbon adsorption system, or an equivalent control system if the
16
~~
~
~
WHY CHANGE ?
degreaser has more than one square meter open area. Rules regulating the vapor pressure and
VOC content of solvents used for cold cleaning are also in effect.
VOC regulations, often modeled after the strict Southern California code (administered by
the SCAQMD), are springing up around the nation. Tough VOC regulations are enforced in New
Jersey, Pennsylvania and North Carolina. Many other states are presently promulgating new rules,
as part of their Clean Air Act programs. While these regulations have historically exempted
halogenated solvents such as CFC-113, TCA, and M E W , they place severe limits on allowable
emissions of photochemically reactive halogenated solvents such as TCE and PERC. After the
phase out of the ozone depleters, it seems tough VOC regulations will become the next major
regulatory hurdle for industrial solvent users to face.
2.2
Solvent Supply and Demand
It is now clear that December 3 1, 1995 will be the last day of production for all ozone
depleting chlorinated solvents in the U.S. If the corporations who manufacture these solvents
follow the lead of the DuPont Corporation (the Nation's largest producer of CFC-113 under the
Freon trademark announced that it will discontinue production in 1994, one year ahead of the
Montreal Protocol deadline), it is conceivable that they will voluntarily move the phase-out date up,
possibly to December 3 1, 1994. This will result in severely limited availability of supplies.
If your cleaning operation is still set up to use TCA or CFC-113, you may be faced with a
severe supply shortage at anytime. This shortage will not be predictable, since solvent distributors
have no way of knowing who will be needing material on an ongoing basis. In other words, if 1/3
of the present users of TCA in your area switch to an alternative method tomorrow, this may ease
the supply crunch slightly, for those users who have yet to switch. If on the other hand, you are in
an area where few of the present users of TCA or CFC-113 make the switch, you are sure to be
heavily impacted.
We expect non-ozone depleting halogenated solvents such as TCE and PERC to remain
readily available. Supplies of these halogenated solvents may be impacted if they are adopted as
wide-spread replacements for CFC-113 and TCA. However, due to the problems outlined in other
parts of this section, TCE or PERC may not be the best alternatives to ozone-depleters, even if
they remain available.
Given the extent of ongoing activity in identifying and implementing environmentally
preferred alternatives, one may ask how this use reduction is impacting solvent supply and demand.
While more recent process by process usage data is not available, one can compare virgin solvent
demand by several industrial sectors in the available 1988 to 1991 data, and view the overall trend.
Table 2-2 presents U.S. production, export, import, and demand data for TCE, PERC, M E W ,
and TCA in the years 1988 and 1991. Limited data regarding changes in the demand for CFC-113
is also presented.
17
CHAPTER 2.0
TABLE2-2
U.S. PRODUCTION, EXPORT, IMPORT, AND DEMAND DATA FOR
HALOGENATED SOLVENTS
Solvent Profile
(1988)
U.S. Production
Exports
Imports
U.S. Demand
Electronics
Paint Stripping
Parts Cleaning
Other
I
I
Solvent Profile
(1991)
U.S. Production
Exports
Imports
U.S. Demand
Electronics
Paint Stripping
Parts Cleaning
Other
Solvent Profile
(1988 to 1991)
U.S. Production
Exports
Imports
U.S.Demand
Electronics
Paint Stripping
Parts Cleaning
Other
Solvent Us (Thousand Metric Tons)
PERC
226.8
299.3
224.5
27.9
54.9
251.4
269.8
203.2 I
0.0
16.7
12.7
0.0
66.9
0.0
146.0
19.1
25.1
100.4
226.3
111.1
TCE
86.2
18.4
5.7
73.5
0.0
0.0
64.3
9.2
I
I
CFC-113
77.4
39.9
0.0
29.3
8.2
Solvent Us (Thousand Metric Tons)
TCE
72.6
27.2
1.4
46.7
0.0
0.0
42.0
4.7
TCE
(15.8)
48.1
(76.0)
(36.4)
----(34.6)
(49.1)
I
PERC
111.1
20.4
31.7
122.4
0.0
0.0
15.9
106.5
CFC- 113
181.4
290.2
125.6
238.1
32.4
38.9
13.8
67.8
116.7
114.3
NA
NA
Change in Profile (percent)
PERC
METH
TCA
CFC-113
(50.5)
(20.0)
(3.0)
(57.9)
--64.5
38.1
(26.9)
(42.1)
(74.1)
(25.0)
--(51.3)
(38.2)
(11.8)
(58.1)
--(70.0)
(43.7)
--------(41.8)
(36.7)
(27.7)
(20.1)
----(52.9)
(32.4)
2.9
As shown, U.S.demand for TCE declined by 36 percent, demand for PERC declined by
5 1 percent, demand for METH declined by 38 percent, and TCA demand decreased by 12 percent.
While it is not known how much of this reduction was due to changes in cleaning methods
employed or shutdowns and declines in business activity, it does imply that major changes have
occurred. Additional changes must occur as the chemical industry phases out the production of
CFC- 113 and TCA and existing supplies become depleted.
18
-
I
WHY CHANGE ?
By the end of 1991, production of CFC-113 had declined 58 percent. Many major users
of CFC-113 had already implemented alternative cleaning technologies or were close to
implementation. The chemical industry was conducting major research and development programs
in the field of HCFCs. This is all for a chemical that was targeted for complete phase-out by the
year 2000, ten years hence. With the new phasesut set for 1995, much of industry is well on its
way to meeting this date.
The situation for TCA is much more drastic. From 1988 to 1991, production declined 3
percent. During this time, the expected phase-out date was 2005. This gave a lesser sense of
urgency to the issue of TCA substitution. Now the date has been pushed up to 1995 and the
industry must make drastic cuts. With a rapid drop in production and large segments of industry
caught off guard and scrambling to find alternatives, high cost speculation is sure to follow.
In addition to the availability issue, short term price pressure on CFC-113 and TCA is
being felt in the form of the "ozone depletion excise tax", imposed by congress on ozone depleting
substances in January 1990. This is a stepped tax, written with incremental increases over the next
few years. As a historic guide, when the CFC-113 tax went into effect in January 1990, the street
price almost doubled. Prices will continue to rise with regularity as the tax increases steadily until
1995. The present average single 55 gallon drum price of CFC-113, as of this writing, is
approximately $4,400. The excise tax schedule for CFC-113 is $2.68 per pound in 1993, $3.48
per pound in 1994, and $4.28 per pound in 1995.
2.3
Corporate Image and Liability
The 90's are being billed as "The Decade of the Environment". All sorts of groups have
formed, on national, state and local levels, to address a myriad of environmental concerns. Some
groups promote the purchase and use of "Green Products". Other groups act as watchdogs, calling
public attention to manufacturers and corporations they perceive to be lagging in environmental
responsibility. Obviously this doesnlt make things easy on anyone using hazardous solvents,
especially if they are released into the atmosphere and can be linked to holes in the ozone layer.
Provisions of Title I11 of the Superfbnd Amendments and Reauthorization Act (SARA)
have resulted in public pressure on users of hazardous materials, including halogenated solvents.
By mandating a national toxic chemical emissions inventory and delineating mechanisms for public
disclosure of all toxic and hazardous chemicals in use by industry, SARA Title I11 is providing
both a database on which to build source reduction programs and effective stimuli for generators to
minimize their inclusion in this publicly scrutinized database.
Now that we report our environmental releases of hazardous by-products and waste,
everyone knows just how much methyl ethyl bad-stuff we release into the air over our communities
in a given year. Since release figures are quoted in pounds, the numbers lend themselves to adverse
publicity, as facility releases are quoted in the thousands, and hundreds of thousands of pounds.
19
~
CHAPTER 2.0
Quantification and estimation of health risks from air toxics is also being required by some states.
Instead of pounds emitted, emissions impacts are being reported as "number of cancers per
population exposed." Any effort that a facility can make to curb their use of hazardous solvents
will certainly accrue to the positive side of the public relations balance sheet.
The Federal Pollution Prevention Act of 1990 increases USEPA visibility in source
reduction activities and provides increased resources to state programs aimed at source reduction.
USEPA's so-called 33-50 cooperative government-industryprogram calls for voluntary emission
reductions of 33 percent in 17 toxic and hazardous chemicals by the end of 1992 and 50 percent by
1995. CEO's of over 600 US corporations have personally signed onto the 33/50 plan, obligating
their companies to comply with program goals. Four of the five major halogenated solvents are
targeted in the 33-50 effort. Solvents included in the 33/50 program are listed in the table below.
TABLE 2-3
SOLVENTS LISTED IN THE 33/50 PROGRAM
Benzene
Carbon Tetrachloride
Chloroform (Trichloromethane)
Methylene Chloride
Methyl Ethyl Ketone
Methyl Isobutyl Ketone
Tetrachloroethylene
Toluene
1,1,l - Trichloroethane
Trichloroethylene
Xylenes
On May 15,1993 another regulatory hammer fell. This new law, commonly known as the
Label Law, requires manufacturers who use ozone depleting substances in their manufacturing
process to label those parts as follows:
-
W m I N G : This product was manufactured with finsert solvent name CFC-113or
1,1,I trichloroethane), a substance which harms public health and the environment by
destroying ozone in the upper atmosphere.
Manufacturers may use alternatives to labels, such as hang tangs, tape cards, or
supplemental printed material, but the method employed must be something the buyer is likely to
read, at the point of purchase. Warnings may not be in fine print, hidden inside the box, or buried
inside the instruction manual. When the law was originally crafted, it required manufacturers who
use 'labeled" parts to label their finished products as well. This would have meant that the
computer manufacturer who purchased a disk drive cleaned in CFC-113 would have to label the
box that the finished computer was shipped in, because it contained a part that was labeled! The
final law only requires manufacturers to label their parts, and eliminates the pass-through
requirement. Nevertheless, the burden of labeling, and the stigma attached to it, is one more
reason to move away from CFCs and TCA as fast as possible.
20
WHY CHANGE ?
In the late 1970's incidents at Love Canal in New York and at Stringfellow Acid Pits in
Califomia focused national attention on the failure of prevalent hazardous waste management
practices to keep substances out of our land and water. Environmental cleanup of formerly
permitted disposal sites under RCRA and the Supefind Program established that parties disposing
of hazardous waste were responsible for clean-up costs, regardless of the amount of waste disposed
of at a given site. The specter of endless liability continues to plague industry today, causing some
companies to incinerate all suspect waste as hazardous, regardless of the extra cost involved.
Since the generator of the waste remains responsible for his waste until it is ultimately
made 'Inon-hazardous", (cradle to grave liability), the generator has every incentive to eliminate the
waste stream, thereby eliminating the associated liabilities. Everyone associated with your
business from your insurance company to your banker has an interest in the way you handle your
hazardous waste. After all, companies have been forced out of business simply by being named
"PRP" or Potentially Responsible Party to a hazardous waste incident. The best way to insure that
your company will never have to deal with the ongoing liability associated with hazardous solvent
waste disposal is to eliminate the waste stream.
2.4
Worker Health and Safety
The Right-to-Know/Right-to-Actlegislation cleared the way for expanded employee
participation in the chemical use process. Now we are required to make sure that our employees
know all about the chemicals they use, before they use them. Exposure to TCA, PERC, TCE and
METH all have been shown to cause acute and chronic health problems.
The Food and Drug Administration (FDA) and EPA consider METH to be a suspected
carcinogen based on the results of animal studies. The International Agency for Research on
Cancer (IARC) classifies METH as "possibly carcinogenic to humans'' and the NTP or National
Toxicology Program lists it as one of the substances that "may reasonably be anticipated to be
carcinogens." A new workplace exposure level for METH has been set by the Occupational Safety
and Health Administration (OSHA) at 25 parts per million (ppm), revised downward from the
original 500 ppm level. Exposure limits for TCA are 350 ppm, 25 ppm for PERC, 500 ppm for
TCE, and 1,000 ppm for CFC-113. All of these limits are subject to revision.
While Right-to-Know laws do not prohibit the use of various solvents in the workplace, the
burden of action falls heavily on the employer to educate and inform employees as to the materials
being used. The time and manpower spent in Right-to-Know related activities can be significant.
The courts have yet to rule on employer liability regarding adverse health impacts to employees
due to hazardous material exposure. Should proposed sister legislation become law, employees
will be able to refuse to perform jobs involving use of hazardous materials if they feel they may be
in danger. This legislation is often referred to as the Right-to-Act law.
21
CHAPTER 2.0
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22
3.0 WHERE DO I START ?
Reducing the use of hazardous solvents in the workplace can be a daunting task, made no
easier by the fact that the present solvent ''does the job'' and presumably has done so for a long
time. The use of a carefblly crafted action plan will insure that the time you and your co-workers
spend on this project will produce tangible results. The following sections will help you begin the
journey to solvent substitution, replacement, and elimination.
3.1.
Defining the Problem
In an effort to more clearly define our problem (and by extension, our objective), we can
state our two major goals as follows: 1) To replace the use of hazardous solvents with a process,
technology, or product that is environmentally preferred when compared to the original product or
process, and 2) To identi@ ways to reduce the volume of hazardous materials used in a specific
process. By using the safest viable products and by minimizing their use to the fbllest extent, the
potential for your operation resulting in adverse environmental impact will be minimized.
To replace the use of a hazardous solvent with something safer, you must first establish
why that particular solvent is being used. When you go out to the shop floor and ask around, be it
CFC-113 in a printed circuit board facility or TCA in a manufacturing facility, you may find that
its use predates all of the employees presently using it! When you ask, "Why do we use this
solvent?" (the first and foremost question in any process change), the answers may not be readily
available or make your task any easier. "Why do we use TCA in this application, Joe?" "Well,
we've always used it for cleaning and the products always work. We've been using it as long as
I've been around this place."
The absence of historical selection data is by no means our only obstacle at this stage.
Natural resistance to change and the absence of a clearly superior drop-in alternative are perhaps
the two biggest roadblocks to smooth introduction of environmentally preferred cleaning
alternatives. But since we have come to the undeniable conclusion that we must do something, let's
begin by developing an understanding of what we wish to accomplish, of why we need a plan.
Since we will deal with many variables before we complete our process and achieve our
goal, we need to structure a clear plan for action. Your plan will be a written guide which you and
your co-workers will use to study, test, and implement a series of solvent substitutions and waste
minimization actions. One of the biggest pitfalls in this process is to assume that the plan does not
need to be written out in advance and followed closely. With the proliferation of alternatives being
offered these days, there is some temptation to "just try a few of these "green" products and see
which ones the guys on the shop floor like"...DON'T DO IT! Most program failures can be traced
back to lack of planning and inability to stick to the plan once it is created.
Two problems emerge when the plan is not committed to writing and clearly understood by
all. First, it is easy for the plan to loose momentum. As soon as the next project hits, or labor
23
CHAPTER 3.0
resources are reallocated, you may find that your project is all but forgotten. Second, once you
have made progress, there is always the possibility that someone will come into your office and
raise what they believe is a new objection or problem ("That stuff doesn't dry as fast as TCA 'I,
"That new cleaner is giving the guys headaches", etc.).
The reality is that you dealt with those issues four meetings ago, but without careful
documentation, you may have to respond to the same issues again and again. Further, without
careful documentation, you will have no record of group agreements and consensus. Without
consensus, assignment of blame and finger-pointing will occur when a group decision fails.
Using the forms found in Appendix A, and the guidelines presented in the following
section, you can set out to create a written plan of attack. Much of the following information is
based on the USEPA's Waste Minimization Opportunity Assessment Manual, a manual designed
to assist facilities in reducing their generation of hazardous waste in a logical and practical manner.
The manual has been proven in use at numerous facilities throughout the world and is an
invaluable tool for anyone undertaking a waste minimization project for the very first time.
Another manual, USEPA's Facility Pollution Prevention Guide, discusses these same topics from
the broader view of minimizing both hazardous and nonhazardous wastes.
3.2
Creating the Plan
A plan can be organized in one of a number of ways. The only absolute requirement is
that it be in writing and be understood by all. As you look through the forms in Appendix A, you
will see that it is possible to create a very detailed and technical plan. You may not need to use all
of the forms. In fact, the simpler your plan, the easier it will be to follow. View the forms as a
guide. The importance of a written plan is to help you identify, test, and implement a solution to
your problem. It is not to create a mountain of paper. As with all industrial activity, the K.I.S.S.
(Keep It Simple, Sailor), principle applies here!
Some of the key elements the plan should include are: project goals, a demonstration of
management commitment, the organization of the team, project protocols for identieing and
screening options, project deliverables, a budget estimate of project costs, and a timetable or
project schedule. The importance of each of these plan elements is discussed below.
3.2.1
Set Goals
To facilitate the program, clearly defined goals and objectives must be established. Goals
may be qualitative or quantitative. For example, a qualitative goal might be ''a significant
reduction of toxic substance emissions into the workplace environment." Other goals might be to
eliminate all nonessential uses of ozone depleting substances and to research alternatives for
critical applications, to save money by cutting down on the amount of hazardous waste shipped
24
WHERE DO I START ?
offsite for disposal, or to reduce emissions of TRI (Toxic Release Inventory) reportable pollutants
so as not to be listed as a top ten or hundred polluter in the state or local county.
While qualitative goals are workable, it is better to establish measurable, quantifiable
goals, since qualitative goals can be interpreted ambiguously. Quantifiable goals establish a clear
guide as to the degree of success expected of the program. A major chemical company has adopted
a corporate-wide goal of 5 percent waste reduction per year. In addition, each facility within the
company is setting its own waste reduction goal. Many of the plants have already reported
significant reductions in waste. Any and all of these goals are commendable and all should
probably be entertained, if they apply to your situation. Write them down, review them with the
people you report to, and get them into an order that accurately reflects your priorities.
3.2.2
Get Management Commitment
A project of this type requires complete support from management, on all levels. For
every successhl case study you read, there were fifty false starts. This process is fraught with
trial and error. Some of the alternatives you test may remove the soil but prove to be incompatible
with the materials used to fabricate the part. Other alternatives may require a water rinse, which
will then require the installation of dryers and rinse water treatment systems. If management
doesn't understand that this is a process that will take time (and cost money), they may not be
offering you a fair challenge.
Management must also empower the team to act. Team members given all the
responsibility (and even a budget), but none of the authority, will not succeed. If management does
not actively demonstrate that they expect all employees to support your efforts, they are not
empowering your team. They are not giving you the commitment you will need to succeed.
What sort of resources will you require to work this plan? Certainly time is going to be
required. Will you have access to people on the production line? Test equipment may need to be
purchased or leased. Outside assistance may be required in the form of consultants (i.e., to review
your work and to design a system or to evaluate the effect of alternatives on your regulatory
status). To avoid upsets in the future, find out up front what your management is prepared to do to
support this effort.
3.2.3
Organize a Team
Following management commitment, the selection and organization of the project team is
the second most important hnction for success. The team should be represented by members of
the various groups that will be affected by the process change. For a manufacturing company,
include representatives from the following departments/fhctions:
0
0
Process Engineering
Quality Control
25
CHAPTER 3.0
e
e
e
Production
Facilities Engineering/Maintenance
Environmental Staff
Depending on the nature of the program and the facility, also include representatives from
the following departments, as appropriate: Health and Safety; Purchasing; Material Inventory and
Control; Management Information Systems; Legal; Finance and Accounting; Product Inventory
and Distribution. You must have participation on all levels to insure a successfbl program.
Remenber, it isn't just management that must be part of the team. The focus of the team is
specific, concentrating on a particular waste stream or a particular area of the facility. As such,
the team should include people with direct responsibility and knowledge of the process. Also look
for people w i h the organization that will need to play a role in helping implement any changes
the team suggests. The most often overlooked department, in this context, is the purchasing
department. After all, isn't it the purchasing people who will have the ongoing responsibility of
procuring the environmentally preferred alternatives that are eventually specified? Bring them into
the loop early, to insure hture cooperation.
Next, consider the facilities people. Will you need new plumbing, vents, electrical
connections, etc.? Another often overlooked area is the financial department. They can provide
insight as to how best to present the request for capital finds to management. Ready formed teams
may exist if your company promotes the concept of quality circles. Several large manufacturing
companies have reported successfid suggestions for waste minimization originating from such
teams. In summary, bring aboard all the people you may need to interface with along the way.
In addition to the internal staff, consider using outside people, especially in the audit and
implementation phases. They may be independent consultants or experts from a different facility
of your company. In large multidivision companies, a centralized staff of corporate experts may
be available. One or more "outsiders" can bring in new ideas and provide an objective view. An
outsider also provides you with a safety net. If the outsider agrees with the teams suggestion and it
works, everyone gets the credit. If it fails, then the team is protected because they sought-out
advice before acting. Facility staff often have great ideas for solving problems but are inhibited
from acting for a number of reasons. The outsider provides your staff with the assurance to act.
As for the level of participation required by the team members, that will depend on their
roles. During the testing of alternative cleaners, the largest burden will be placed on the members
doing the hands-on testing. This will most likely involve your R&D and production departments.
Health and Safety may also have heavy involvement with the review of material and safety data
sheets. For other team members, you can ask them to participate in a review capacity only if they
have limited time available for the project. Your goal is to insure that no employee or department
can torpedo your work in the fbture by claiming they were not kept informed throughout the
process. One more reason to communicate with as many people as possible: you never know who
will contribute the one good idea that is finally adopted.
26
~
WHERE DO I START ?
Finally, any successful waste minimization program and/or team needs one or more people
to champion the cause. The "cause champions'' overcome the inertia present when changes to an
existing operation are proposed. They also lead the team, either formally or informally. Some
desirable attributes of an effective team leader include:
e
Familiarity with the company's production departments including:
Facilities / Processes / People
Familiarity with the company's waste management operations.
Familiarity with new production and waste treatment technologies.
Familiarity with waste minimization principles and techniques.
Aggressive managerial style.
Understanding of environmental regulations.
Understanding of product quality control requirements.
Ability to communicate and interact will with people.
Good rapport with top management.
Although an environmental engineer, production manager, or plant process engineer may
be good candidates, the interplay of personalities between the team members will usually determine
who takes on this role. If the champion is lacking in certain traits, then he or she must rely more
heavily on the other team members.
3.3
Working the Plan
Once you have created your written plan, secured management support, and organized a
committed team, you can start the actual process of working the plan. Working the plan consists
of gathering process information, formulating options, screening or selecting options for testing,
conducting the tests, and making recommendations to management. The complexity of your
challenge will dictate the detail that will be required. As such, the team may be required to draw
on expertise either within the company or outside of the company as required.
3.3.1
Gather Process Information
With a specific area or solvent waste stream selected, and with the assessment team in
place, you can begin to gather information about the target process. This can be done through site
visits and observation of the processes, interviews with users, and review of historical data. A
listing of facility information useful for conducting an assessment is presented in Table 3-1.
In reviewing this information, you should be looking for answers to a number of questions.
How are the parts cleaned now? Why? What step precedes cleaning, and why are the parts dirty
as a result? What step follows cleaning, and why do the parts have to be clean when they get
there? Are the parts compatible with water? Do they have to be dry? The answers to these
questions should help you to develop a list of solutions and to guide you towards a successfid one.
As you can see, the questions that you can ask are limitless, and often followed by "why?"
27
CHAPTER 3.0
TABLE 3-1
FACILITY INFORMATION USEFUL FOR CONDUCTING AN ASSESSMENT
DESIGN INFORMATION
Process flow diagrams
Material and heat balances (both design balances and actual balances) for
production processes and pollution control processes
Operating manuals and process descriptions
Equipment lists
Equipment specifications and data sheets
Piping and instrument diagrams
Plot and elevation plans
General arrangement diagrams and work flow diagrams
ENVIRONMENTAL INFORMATION
Hazardous waste manifests
Emission inventories
Biennial hazardous waste reports
Waste assays
Environmental audit reports
Permits and/or permit applications
RAW MATERIAL / PRODUCTION INFORMATION
Product composition and batch sheets
Material application diagrams
Material safety data sheets
Product and raw material inventory records
Operator data logs
Production schedules
OTHER INFORMATION
Company environmental policy statements
Organization charts
Perhaps the most important distinction to make during the information gathering stage is to
determine if a process is done a certain way for a reason, or simply out of habit. This knowledge
will be critical when you begin to formulate and screen options. Table 3-2 offers some guidelines
for your inspection process. While it is written from the viewpoint of an outsider conducting the
inspection, as opposed to someone intimately familiar with the operation, it has proven effective for
uncovering waste minimization opportunities in numerous facilities.
In addition to the guidelines offered in Table 3-2, the worksheets presented in Appendix A
can be used to document your assessment. These worksheets were developed by the USEPA for
28
WHERE DO I START ?
TABLE3-2
GUIDELINES FOR SITE AND PROCESS INSPECTION
0
Prepare an agenda in advance that covers all points that still require clarification. Provide
staff contacts at the facility with the agenda several days before the inspection. Schedule the
inspection to coincide with the particular operation that is of interest (Le.; make-up chemical
addition, bath sampling, bath replacement, etc.).
Monitor the operation at different times during the shift, and if needed, during all 3 shifts,
especially when waste generation is highly dependent on human involvement (for example, in
painting or parts cleaning operations).
0
Interview operators, shift supervisors, and foremen directly. Do not hesitate to question more
than one person if an answer is not forthcoming. Assess the operators' and their supervisors'
awareness of waste generation aspects of the operation. Note their familiarity (or the lack
thereof) with the impacts their operation may have on other operations.
0
Photograph the operation:" Photographs are especially valuable in the absence of plan layout
drawings. Many details can be captured in photographs that otherwise could be forgotten or
inaccurately recalled at a later date.
0
Observe the "housekeeping" aspect of the operation. Check for signs of spills or leaks. Ask to
visit the maintenance shop and inquire about their problems in maintaining the equipment leakfree. Assess the overall cleanliness and order of the site.
0
Assess the organizational structure and level of coordination of environmental activities
between various departments.
0
Assess administrative controls, such as cost accounting procedures, material purchasing
procedures, and waste collection procedures.
conducting waste minimization opportunity assessments at waste generating facilities. Many
facilities have used them as is and many more have modified them as part of their program. If you
decide to use them, please note that not all of the data requested is mandatory or necessary. These
forms were developed to serve as a guide, a means to an end. Gather only what you need to
document the existing process, understand how the process works and why, then move on to the
formulation of options stage. The biggest mistake you can make at this point is to spend a large
amount of time and effort obtaining detailed and accurate estimates of variable and hzzy data.
3.3.2
Formulate Options
Once you have a clear picture of what you are cleaning and why, the process enters the
creative stage. The objective of this step is to develop a list of options that have a reasonably good
29
CHAPTER 3.0
chance of success and meet the guidelines established earlier. The activity of formulating options
should occur in an environment that encourages creativity and independent thinking by the
members of the assessment team. Individual team members may suggest options, and the group
can develop concepts as a whole.
Two methods that are particularly effective for generating options are "brainstorming" and
"nominal group". In brainstorming, the participants review the background information and the
requirements of the project before the meeting. One participant serves as the leader. Another
serves as the recorder. The meeting starts with a description of the project as a problem in need of
a solution. The participants propose solutions to the problem. The participants are not allowed to
critique the proposed solutions, but are encouraged to build and expand on earlier responses. All
responses are recorded for later review and evaluation. Review and evaluation methods are
discussed in the following section.
In the nominal group technique, the participants are brought together for the meeting
without reviewing the problem beforehand. The coordinator describes the problem and asks each
participant to review it. The participants individually write down as many possible solutions as
they can think of. The participants then, one by one, read one of their responses, going around the
table as often as necessary to read all of the responses. After all of the ideas have been read, the
ideas are discussed individually. Duplicate responses are eliminated. Finally, the participants
individually prioritize the ideas. The results are totaled (based on "one participant, one vote") to
arrive at the group consensus. Each method has its advantages and disadvantages and many other
techniques are viable.
One of the best sources for generating a list of specific options is this guide. Both chapters
4 and 5 will help you understand the environmentally preferred cleaning options available for use.
Other chapters discuss ways to improve process efficiency and how to capture and recycle any
resulting wastes. Add to this the proliferation of other commercially available information, and
you will have a basis from which to formulate and screen options. Table 3-3 provides information
on where to look for additional alternative technology options.
3.3.3
Screen Options For Testing
The final product of the option formulation phase should be a list of options for the
process being addressed. Depending on the option formulation technique employed, some
impractical or unattractive options may have already been eliminated from consideration. It is also
possible that one option stands out from the rest and the screening choice is obvious. Typically,
such options involve application of good operating practices (e.g., closer supervision, keeping
covers on degreasers, or training of operators) which require little or no capital expenditure.
Sometimes however, the team will be faced with competing options that all appear to be
technically and economically viable on the surface. Since you cannot afford to test or develop a
30
--
-
WHERE DO I START ?
TABLE3-3
INFORMATION SOURCES FOR WASTE MINIMIZATION OPTIONS
Published Literature
Technical magazines, particularly industry trade journals, often
describe specific techniques. These articles tend to be quite
practical. Use annual index issues (Dec.) to speed your search.
State Environmental
The following states have, or are developing, programs that
include technical assistance, information on industry-specific
waste minimization techniques, and compiled bibliographies:
California
Connecticut
Georgia
Illinois
Kentucky
Maryland
Massachusetts
Minnesota
New Jersey
New York
North Carolina
Pennsylvania
Tennessee
Many of these states maintain lists of consultants knowledgeable
in waste minimization and able to assist you for a small fee.
Equipment Vendors
Meetings with equipment vendors, as well as vendor literature, is
particularly useful in identifying potential equipmentsriented
options. Vendors are eager to assist companies in implementing
projects. Remember, though, that the vendor's job is to sell his
company's equipment, product, or service.
Plant Engineers and
Operators
The employees that are intimately familiar with a facility's
operations can often make significant practical suggestions.
detailed implementation plan for all of the options, you need some way to narrow your choices.
This is where option screening comes in to play and a variety of methodologies exist. Two such
methods, informal evaluation and weighted sum method are commonly employed. These methods
are, in essence, activity management tools for evaluation. Their main advantages are that they 1)
compel the team members to consider a wide range of criteria before making a decision; and 2)
provide a framework for resolving differences concerning specific options. Such screening should
not be confked with the more detailed feasibility analysis required for implementing an option,
which is discussed in the next section.
An informal screening of options is useful in small facilities, with small management
groups, or in situations in which only a few options have been generated. The method consists of
31
CHAPTER 3.0
informal discussion and examination of each option among team members. At the extreme, the
team leader may decide unilaterally which options to pursue. Useful questions to consider for
discussion include:
0
0
0
0
0
Does the necessary technology exist to develop the option?
How much does it cost? Is it cost effective?
Can the option be implemented within a reasonable amount of time?
Does the option have a good ''track record"? If not, is there convincing evidence
that the option will work as required?
What other benefits will occur?
A formal screening process actually consists of a two step task. The first part of the
screening process is to nail down your specific screening criteria. Again, this must be in the form
of a list, which can be agreed on by a majority of the team members. Some of the criteria you may
want to consider are:
Is the option safe for the workers?
Will product quality be maintained?
How quickly can the option be implemented?
Is the new procedure compatible with current production rates and procedures?
Is additional labor required?
Can we afford the additional equipmentkapital expense?
Will the workers accept the new product/procedure?
Does the vendor provide adequate service?
After developing the list of criteria, each option may be assessed qualitatively. Each
option will most likely have pros and cons. Some will require equipment purchases, others will be
expensive to use, others will require more process time. It is rare that a single option will present
itself as a clear winner. In reviewing each option, some may demonstrate an unwanted attribute
such as flammability. After reviewing each option in terms of the agreed upon criteria, the team
may vote and the top candidate carried forward for testing. This is an informal screening process.
For conducting a more formal and quantitative screening of the options, the weighted sum
method may be used. To each of criteria, weighmg factors are applied. This allows you to weigh
the relative importance of each criteria to your particular facility or operation. For facilities keen
on reducing waste generation regardless of cost, a much higher weighing factor would be applied to
the percent reduction in waste generation each option provides compared to the implementation or
operating cost of the option. Commonly used weighing scales are 1 for low to 10 for high or 1 for
low, 2 for medium, and 3 for high in terms of relative importance. Commonly used criteria for
conducting a weighted sum evaluation include:
0
0
0
0
32
Reduction in waste quantity
Reduction in waste hazard (e.g., toxicity, flammability, reactivity, corrosivity)
Reduction in waste treatment/disposal costs
Reduction in raw material costs
WHERE DO I START ?
Reduction in liability and insurance costs
Previous successfbl use within the company
Previous successhl use in industry
Not detrimental to product quality
Low capital cost
Low operating and maintenance costs
Short implementation period (and minimal disruption of plant operations)
Ease of implementation
Since it is often difficult for people to directly assign relative weights to a long list of
criteria, a simple two criteria ranking method may be employed to generate weighing factors and to
maintain group focus. Starting with criteria 1, the group is asked if it is more important or less
important than criteria 2. If it is more important, then it is given a point. Criteria 1 is then
compared to criteria 3 and a point given to the one of higher importance. After criteria 1 has been
compared to all other criteria, the process is repeated with criteria 2 being compared with criteria 3
and so on. When finished, the points won by each criteria are added up and the total scores
represent the weighing factors. The use of this method to develop weighing factors is presented in
Figure 3-1 below.
FIGURE 3-1
METHOD TO ASSIGN WEIGHING FACTORS TO SCREENING CRITERIA
Weighing Criteria
Installed Cost
Operating Cost
Waste Volume
Waste Toxicity
Permitting Ease
1
2
3
4
5
1
2
3
4
5
Weight
--
1
1
0
--
0
0
0
--
1
2
1
3
2
1
0
0
1
1
1
1
0
0
0
-0
1
1
1
--
The second part of the task is rating each proposed option against the selected criteria.
Again, a I to 10 scale may be employed. To produce meaningfbl results, it is important that the
screening criteria are stated and rated in a consistent fashion. High scores should be assigned to
good or better performance while low scores should be assigned to poor or worse performance.
Also note that the phrasing of a given criteria may taint or bias the rating for a particular option.
To guard against this, the assigned ratings should be reviewed for consistency after all options
have been rated. Once this step has been completed, the ratings are multiplied by the weighing
factors and then summed to provide an overall option score.
An example of weighted sum screening is presented in Figure 3-2 and a screening form
may be found in Appendix A (Worksheet 13). The example is for the screening of a high installed
33
CHAPTER 3.0
cost option (option l), a medium cost option (option 2), and a low cost option (option 3) all of
which have been found to be technically viable for implementation. An assigned score of IO
represents low cost, little or no waste generation, low waste toxicity, and virtually no additional
permitting or regulatory requirements. A score of zero represents high cost, little or no reduction in
the volume or toxicity of waste produced, and a low potential for being permitted or gaining
regulatory acceptance.
-~
~
FIGURE 3-2
WEIGHTED SUM OPTION SCREENING
Weighmg Criteria
Weight
Option 1
Option 2
Option 3
As shown in the example, the high cost option demonstrates the best overall performance
followed by the lowest cost option. The installed cost savings of the second option compared to the
first option does not make up for its poorer performance with regards to the other criteria. The
second option also lacks in providing a distinct advantage over the lowest cost option. For a
facility with limited capital, option 3 should be considered as an immediate or short-term solution
with option 1 being viewed as the long-term solution. Option 2 might be reconsidered in the future
if some unforeseen problem with implementing options 1 or 3 arises.
3.3.4
Conduct Tests
After selecting an option or set of options to pursue, some form of performance testing
may be required. How you test various options will depend on what you are trying to clean and the
flexibility you have within your organization. Is there a laboratory, or do you work in the back of
a garage? Regardless of your level of sophistication, there are always ways to run useful tests.
The key to a successful test program is standardization. If you test cleaner A in a heated ultrasonic
tank,test cleaner B the same way. Make sure you know what the suggested dilution ratio is for
aqueous cleaners, and dilute all samples to the same ratio.
In designing the test, get all the information you can from the various technology vendors.
They should be intimately familiar with their products or processes and be able to provide much
guidance. Since the assumption is that you are not the very first person to request test data or to
34
WHERE W I START ?
conduct testing of their technology, ask for case studies and references from other users. Ask how
the manufacturer or product formulator suggests you conduct the testing. More often than not,
such inquiry can lead to the offer of loaned demonstration equipment, laboratory support services,
and on-site technical assistance. Two useful sources for identifying equipment vendors and
material suppliers is the Thomas Register and the Metal Finishing Guidebook Directory.
If you are not able to set-up and conduct a test program at your facility, there are
equipment suppliers and chemical formulators who will accept your parts for testing. This is a
good way to get a detailed test report without having to actually do the testing yourself. You also
avoid the burden and liability of having to handle and dispose of spent cleaning solutions. If
possible, you should be present during the test so that you gain first-hand experience with the
equipment or cleaner. Many who offer this service prefer that you attend the test since it is
difficult to return the parts to you and maintain their cleanliness during transit.
3.3.5
Make Recommendations
After screening and testing, you may or may not be ready to recommend a specific solution
for your problem. Being able to recommend a specific product or technology means that you have
decided on the type, make, model, and brand of equipment andor cleaner you will adopt. It is
often more common that you will only decide on a generic solution (e.g., ultrasonic cleaning with a
pH neutral detergent) and that the final choice will be determined by competitive bidding.
Generic technology recommendations are usually made in larger corporations or
government facilities. The purchasing department will not want to be obligated (or may not be
allowed) to buy from a single provider. Unless you can demonstrate that no other provider can
supply the equipment, materials, and services required for the job, it is most likely that the contract
will be competitively bid.
The burden of writing a bid specification tight enough so that you get what you want is
squarely on your shoulders. Failure to adequately state the mandatory minimum requirements of a
given product or service has often resulted in shop personnel testing a product that works well and
then being given a cheaper copy that doesn't. If the cheaper copy doesn't meet spec, then it is a
simple matter to throw the problem back upon the supplier. More often however, is that the
cheaper copy does meet spec and that some important performance criteria has been overlook or
omitted from the specification.
3.4
Where to From Here?
Implementing your newly selected option will require the same persistence and dedication
required to select it. You may need to design, specify, and procure new equipment (information on
system design and equipment costs are found elsewhere in this guide). This phase of the process is
not dissimilar from other capital expenditure projects. Construction budgets must be set and
35
CHAPTER 3.0
funding obtained. In some cases, implementation of the selected alternative may not require capital
expenditures and the implementation process can proceed rapidly.
You will also need to persevere through the initial objections of those who may feel
threatened by anything new. There will be inevitable problems, and adjustments to make. This is
when you will find out how valuable the records you have been keeping really are. You should be
prepared to look back through the process notes, to answer questions about how you arrived at this
particular endpoint, at anytime.
Now that you have an overview of how the process works, we'll take a step back, to build
some necessary fundamentals. In order to make informed decisions about which cleaning options
to try, you will need to understand the science of cleaning. In the next chapter, we will provide a
basis for understanding how cleaners work and the differences among the various options.
36
__
.
-
4.0 THE SCIENCE OF CLEANING
While the aim of cleaning is simple - to avoid the generation of rejects due to soil
contamination during subsequent use or processing steps, the science of cleaning is very complex.
Much research work has been conducted in this field and it continues to be an active area of
investigation. The following sections are intended to provide you with a basic knowledge of the
science. A detailed discussion is beyond the scope of this guide and the reader would best be
served by consulting the various references listed in the bibliography.
4.1
HOW CLEANERS WORK
To understand how cleaners work, one needs to be aware of the various types of dirt or
contamination commonly encountered. Dirt is nothing more than material out of place. Parts
become dirty just lying around because of airborne contaminants. Parts react with moisture in the
air and corrode. The aim of effective cleaning is to control part contamination to a level that will
not create problems in the future. A listing of contaminant sources typically encountered in
industrial operations is presented in Table 4-1 below.
TABLE 4-1
CONTAMINANT SOURCES AND FORMS
I
Sources and
Related Contaminants
Outside Environment
Condensates
Dust, Soil, & Plants
Exhaust Fumes
Salt Spray
Industrial Processes
Chemical Film/Vapors
Chips and Burrs
Coolants, Oils, & Solve
Flux Particles/Vapors
Oxides
Plating Baths
Sand and Abrasives
Smoke Fumes
Solder & Weld Splatter
Workers
Bacteria and Virus
Body Vapors
Clothing Lint & Fiber
Cosmetics
Epidermal Scale
Hair
Skin Oils
Tobacco Smoke
Product
Corrosion
Material Shedding
Outgassing
Wear Particles
Source: Adapted from N
I
Contaminant Form
State
-TzTpzm
37
CHAPTER 4.0
The removal of contamination from a surface can be achieved in a number of ways.
Common methods rely on one or more actions of mechanical abrasion, solvency, detergency, or
chemical reaction. Selection of a method is dependent on the type of soil being remove, the type of
substrate being cleaned, and the degree of cleanliness required. Depending on the subsequent
processing steps employed, the degree of cleanliness may range from surfaces being visually clean
to those that are metallurgically or microscopically clean.
The various cleaning methods employed all seek to overcome the forces that bind and hold
the soil to the part. Retention mechanisms include gravity, electrostatic charges, molecular
attraction, presence of viscous surface coatings, and physical entrapment in surface pores and
crevices. The magnitude of these retention forces is highly dependent on the type of soil being
removed and the condition of the substrate being cleaned.
4.1.1
Mechanical Abrasion
Mechanical removal methods typically rely on the use of an abrasive or coarse material to
dislodge and knock-offcontamination from the part. Abrasive cleaning and stripping is highly
effective for removing rust, heat scale, paint, and mixes of organic and inorganic contaminants.
The chief disadvantages of abrasives is that their use may cause part damage, the method is limited
to line of sight cleaning, and the method may generate dust that needs to be controlled.
The cleaning effectiveness of abrasive methods is a direct hnction of the properties of
abrasive used. Such properties include particle abrasiveness, hardness, size, and impact energy.
Materials commonly used include silica sand, steel grit or shot, aluminum oxide, copper slag,
garnet, walnut shells, rice hulls, glass beads, plastic beads, and high pressure water. Some, such
as silica sand and copper slag are seeing lesser and lesser use due to their hazards to health and
impact on waste generation. Newer materials actively being investigated for use include wheat
starch, sodium carbonate sluny, ice, and carbon dioxide pellets. Traditional sanding, wire
brushing, and power tool cleaning are also practiced.
Selection of a particular material depends on the type of contamination to be removed, the
size and shape of the work piece, the finish desired, and rate of production. The hard media are
often used to produce a rough, textured surface or for removing corrosion from steel. In paint
stripping, this rough textured surface provides "tooth1'for the paint to adhere too. The use of sand
or steel shot can lead to silica or iron contamination when cleaning soft metals such as aluminum.
Removal of these contaminants may require subsequent processing in an acid bath followed by
rinsing and drying.
In addition to abrasives, thermal techniques are often employed. Cryogenic freezing may
be used to make a coating more brittle so that it will crack and debond when struck by an abrasive.
Direct flame and fluidized hot sand baths may be used to blister and burn-off the paint from a part.
In most applications, the use of heat for cleaning results in a part covered with ash and heat scale.
38
THE SCIENCE OF CLEANING
These contaminants are removed by the use of abrasives. New thermal burn off systems
employing the use of lasers and high intensity flash lamps are being developed. These systems
generate ash but do not heat or warp the substrate and heat scale formation is avoided.
4.1.2
Solvency
The solvency of a given cleaning medium is mainly a function of the contaminants
molecular structure. Contaminants with a non polar molecular structure such as aliphatic
hydrocarbons are often referred to as being hydrophobic or water fearing. Polar molecules are
referred to as being hydrophilic or water loving, Water is a polar molecule and is effective at
dissolving or removing many salts, acids, alcohols, and sugars. Water may also serve as the
solvent medium for various compounds used to remove oils and greases by means of detergency
and saponification. Water alone is not suitable for the removal of most oils and greases commonly
encountered in industry.
Solvents have little trouble dissolving most oils and greases as well as resins, rubber,
bitumens, waxes, and plastics. Solvents are also effective at removing hard carbon deposits from
engines and stripping off old paints and coatings. While both carbon and pigment are insoluble,
suitable solvents may be employed to soften, swell, and dissolve the resinous materials that bind
them to the part. Strong alkaline cleaners may also be effective at removing resinous materials but
their use may damage reactive metals such as aluminum, magnesium, copper, and zinc.
Common solvents used for cleaning include aliphatic, aromatic, halogenated, and polar
organic hydrocarbons. Solvents are good for rapid removal of bulk soils, particularly hydrocarbon
soils. Their use in cold tanks often results in the coating of the cleaned parts with an oily residue.
The amount of residue is a function of tank use (i.e., soil loading) and drag-out. While this residue
of oil and grease does provide a short-term degree of rust and corrosion protection, it may not be
acceptable if subsequent processes such as electroplating or painting require a hydrophilic surface.
High levels of surface cleanliness can be achieved in cold cleaning by the use of
emulsifiable solvents or emulsion cleaners, commonly referred to as semi-aqueous cleaners.
Emulsifiable solvents are used at full strength in a cold tank and the parts are then rinsed after
cleaning. It is during this rinse step that the solvent in water emulsion is formed. With emulsion
cleaners, the parts are first cleaned in a solvent water emulsion and are then rinsed. Both
emulsifiable solvents and emulsion cleaners are formulated with non-water soluble solvents and
suitable surfactants.
The use of halogenated solvents in vapor degreasers generally does not leave an oily
residue on the part because the part is continuously flushed with clean solvent. A residue may be
left on the part if the boiling sump is heavily contaminated with oil and grease. Other advantages
of vapor degreasing over cold cleaning is that the high temperature softens solid fats and reduces
the viscosity of grease. This allows for rapid penetration and removal of the contaminant from
39
CHAPTER 4.0
holes and crevices. Vapor degreasing of parts leaves a dry and water-free surface that may be an
advantage in many operations.
4.1.3
Detergency
The action of detergency is based on the ability of some compounds to form oil and water
emulsions. Basic materials include soaps, surfactants, and detergents (a blended formulation of
soaps, surfactants, and other compounds such as corrosion inhibitors, water softeners, solubilizers,
foam stabilizers, and chelators). Soaps are produced by reacting naturally derived organics such
as fatty acids, rosins, or oils with strong alkali. Surfactants are made by a number of different
processes depending on the type of surfactant produced.
The ability of a given cleaner to penetrate and remove soil is based on its ability to wet a
given surface. The ability to wet is a function of several factors or measures such as surface
tension, interfacial tension, and adhesion. Surface tension represents the molecular attraction at the
surface of a liquid that causes the exposed area to contract to the smallest possible area.
Interfacial tension represents the molecular attraction that exists between two immisible fluids or a
fluid and a solid. Both surface and interfacial tension may be related by the work of adhesion.
As a simple example, pure water has a much higher surface tension than most oils (water
has a surface tension of 72.8 dynes per centimeter while a typical value for oil would be 35
dyneskm). If carefully poured on an oil covered surface, the water will not spread out in a thin
layer. It will instead assume the shape of a round droplet, the droplet representing the least surface
area for a given volume of liquid. The water is not able to penetrate the oil film and cannot wet the
surface below. Therefore, pure water is an ineffective cleaner for removing oils.
If however a soap or surfactant is added to the water, a marked decrease in surface tension
and interfacial tension occurs. The water can now penetrate the oil film and wet the substrate
below. As the oil is displaced by the water, the oil gathers and assumes a spherical shape. The
rate of gathering is dictated by the speed at which the oil can move (Le., its viscosity). Since
viscosity is a function of temperature, one can see the importance of heating the solution. For soils
such as wax, removal can only be achieved when the wax is heated to a fluid state. As this
gathering process continues, a point is reached where the oil detaches from the substrate.
Depending on the type of soap, surfactant, or detergent blend employed, further emulsification of
the oil may take place. Once detached and dispersed, the oil cannot be redeposited as a film.
Both soap and surfactant molecules consist of two major parts. One is a chain of
hydrocarbons that is hydrophobic (oil soluble) and a terminal group that is hydrophilic or water
soluble. The soap molecule consists of a long chain hydrocarbon that makes it very oil soluble and
therefore a good emulsifier. Surfactant molecules can be tailored to be either good emulsifiers
(very oil soluble), good wetting agents (very water soluble), or both. This is achieved by varying
40
THE SCIENCE OF CLEANING
the length of the hydrocarbon chain and size of the terminal group. Some surfactants allow for
good emulsification of oil while agitated, but will release the oil when agitation is stopped.
Critical properties in the selection of soaps include solubility, cleaning temperature, foam
formation and stability, rinsability, and cost. A major disadvantage of soaps is that the water
soluble group readily reacts with calcium and magnesium ions present in hard water. Once
reacted, the soap becomes insoluble and forms a sticky precipitate known as soap scum. To
overcome this problem, many cleaning formulations include chelating and sequestering agents to
combine with and tie-up the calcium and magnesium ions so that they cannot react with the soap.
The most common chelating agent in widespread use is ethylene diamine tetracetic acid (EDTA).
Common sequestering agents include phosphates, orthophosphates, and orthosilicates.
Surfactants, depending on the type employed, may or may not require the use of chelating
and sequestering agents to prevent reaction with hard water ions. Surfactants can be designed or
selected to provide differing functions such as wetting agent, cleaner, or emulsifier. Function is
determined by the length of oil-soluble and water-soluble segments attached to the base molecule.
The four major classifications of surfactants include anionic, non-ionic, cationic, and amphoteric.
The non-ionic surfactants are not prone to reaction with hard water ions and are widely used in
many different types of cleaning formulations.
4.1.4
Chemical Reaction
Cleaners employing the method of chemical reaction include alkaline degreasers, hot
caustic strippers, molten salt baths, and acidic deoxidizers. Some confkion always occurs when
discussing alkaline degreasers since a major part of the cleaning process involves detergency.
However, detergents tend to alter only the physical nature or behavior of the contaminant while
alkaline degreasing may cause a change in its chemical composition (i.e., conversion of fatty acids
and oils to soap). For this reason, alkaline degreasers are discussed in this section.
Alkaline degreasers are widely used for industrial metal cleaning. A good alkaline
degreaser typically consists of several different alkaline salts and organic surfactants. Operating
concentrations of formulated degreaser may range from 10 weight percent for a soak cleaner down
to 0.5 percent for an electrocleaner, operating temperatures may range from 120 to 160 OF. Many
low temperature formulations have entered the market in recent years and they offer significant
savings in avoided energy costs.
Three basic components of an alkaline degreaser include a source of available alkali, a
buffer to control alkalinity or pH, and a soap or surfactant. Common sources of alkali include
sodium hydroxide (caustic soda or lye) and sodium carbonate (soda ash). Other commonly used
compounds include sodium metasilicate, sodium orthosilicate, trisodium phosphate (TSP),
tetrasodium pyrophosphate (TSPP), borax, and sodium metaborate. Some alkali sources may also
act as sequestering and buffering agents. High pH degreasers may include inhibitors.
41
CHAPTER 4.0
Except for sodium hydroxide, all of the other alkalis react with water to form hydroxyl
ions (the source of alkalinity). This reaction proceeds until an equilibrium is established. When an
acidic soil is introduced, it reacts with the hydroxyl ions and upsets the equilibrium. As the
hydroxyl ions are consumed, more of the alkali reacts with water and maintains the hydroxyl
balance. The ability of an alkali to generate more hydroxyl ions is known as alkaline reserve.
With sodium hydroxide, all of the material ionizes to form sodium and hydroxyl ions upon contact
with water. As hydroxyl ions are consumed, no material is available to replace them.
The importance of alkaline reserve is that a large amount of alkali may be present without
having a high concentration of alkalinity. This is very important when cleaning materials that are
sensitive to alkaline attack. This reserve also provides some buffering capacity and serves to
maintain the concentration of alkalinity (measured in terms of pH) at an optimum level. When
introduced into the alkaline degreaser, fatty oils and acids react with the hydroxyl ions and form
water soluble soaps. This process is called saponification. The hydroxyl ions have little or no
effect on alkali resistant soils such as mineral oils. To remove these, the degreaser relys on the
effect of detergency due to the soaps formed and surfactants added. It has often been noted that
alkaline degreasers tend to operate better with age due to this build-up of soap.
In addition to hydroxyl ions, the other products of hydrolysis may assist in cleaning.
Silicates yield silicic acid which is insoluble and serves to disperse removed solids. Silicates may
prevent the etching and tarnishing of aluminum, zinc, brass, or steel. They may also interfere with
rinsing which can lead to problems in subsequent processing steps. Phosphates aid in the break-up
of large particles into smaller ones (peptization) and are effective at controlling the detrimental
effects of hard water salts. Phosphates have seen decreased use due to the problems they cause
with waste water discharges to rivers and streams.
To speed cleaning in an alkaline degreaser, the system may be operated as an electrolytic
cell. Iron or nickel electrodes may be used with the part acting as the second electrode. The
passage of electric current through the cleaner causes the formation of hydrogen gas at the cathode
and oxygen at the anode. The generation of gas results in a high level of localized agitation which
assists in cleaning. This process, commonly referred to as electrocleaning, is often used as a
cleaning process before electroplating.
Connection of the part as cathode or anode depends on the composition of the part. Metals
prone to oxidation such as nickel, stainless steel, or aluminum, are typically cleaned cathodically.
Brass is cleaned cathodically to avoid loss of zinc. Steel may be cleaned either way though the
tendency is to favor anodic cleaning. Anodic cleaning avoids the potential for hydrogen
embrittlement which can be a serious concern in parts subject to high stress loads.
Very strong caustic baths are often used for paint stripping. The strong caustic saponifis
or breaks the ester bonds in the coating and decomposes the paint. The addition of surfactants aids
in lifting the paint from the substrate and hence speeds stripping. Strong alkali strippers are
42
THE SCIENCE OF CLEANING
effective at removing paints based on varnishes or drying oils, but have difficulty removing
phenolics, epoxies, polyurethanes, and acrylics. The removal of these paints, as well as the
removal of heat scale, is sometimes performed in molten baths of alkaline salts.
After alkaline degreasing, electrocleaning, and molten salt baths, the final method relying
on chemical reaction is acid cleaning or pickling. Acidic cleaners are commonly used for the
removal of mill scale (hot rolled scale), scale developed during welding or heat treating, superficial
oxide which interferes with subsequent painting or electroplating, rust and corrosion products, and
hard water scale. Acids commonly used in include mineral acids such as sulfuric, nitric,
hydrochloric, phosphoric, chromic, or hydrofluoric and organic acids such as acetic, oxalic, or
cresylic acid. Other ingredients include detergents, chelating agents, and small amounts of water
miscible solvents.
Nitric and hydrofluoric acids are commonly used for brightening aluminum and stainless
steel. When acids such as phosphoric are used on steel, or chromic on aluminum, a protective
coating is formed which provides an excellent base for paint adhesion. A disadvantage of acid
cleaning is that it may corrode or cause hydrogen embrittlement of steel and iron. Contact between
stainless steel and hydrochloric or heated sulfuric acid should be minimized. Prolonged contact of
stainless steel with acidic solutions containing chlorides can lead to severe pitting. Slightly acidic
cleaners containing chlorides will attack magnesium.
4.2
Predicting Cleaner Effectiveness
Traditionally, the prediction of cleaning effectiveness has been based on past experience
with a given cleaner. Knowing the type of parts to be cleaned and the types of soil to be removed,
an experienced or knowledgeable investigator can make a fairly good educated guess. This would
then be followed up by laboratory testing, final cleaner selection, and design of the cleaning
system. Optimization of the cleaning system during start-up could usually be relied upon to correct
any minor deficiencies in cleaning performance (e.g., increasing bath temperature or providing
additional agitation).
Listings of parts cleaned, soils removed, and cleaner employed can be found in numerous
references and are available from many equipment and material suppliers. As an example, a
cleaning comparison chart (Table 4-2) is presented. The chart covers five major types of soil
removed and six major ways of cleaning. By comparing the performance of vapor degreasing to
the other cleaning methods, one can see that many of the altemative cleaners perform better at
removing a given soil.
While the use of charts and past experience is the most straight forward and practical
method for quickly narrowing the field of investigation, it does little to place the art of predicting
cleaner effectiveness on a scientific basis. By creating a scientific basis, predictions can be
quantified and evaluated on an absolute numeric scale. The major measure of predicting the
43
TABLE 4-2
P
P
COMPARISON OF CLEANING METHOD EFFECTIVENESS FOR SOIL REMOVAL
Unpigmented
Pigmented
Cutting and
Oil and Grease
Cooling Fluids
Drawing Compounds
Effective, removes dried Good, often used with
Effective when used with
power spray.
compounds when used
spray. May etch
non-ferrous metals.
with spray.
Marginal. More effectivc Effective on most soils. Effective and economical.
Aqueous,
Must have a good rinse Must be inhibited to use
if sprayed, agitated, or
Alkaline
and be inhibited for use on non-ferrous metals.
if parts are first spot
on non-ferrous metals.
I
cleaned.
Not recommended. May Produces a high level of Produces a high level of
Aqueous,
Electrolytic be used as final cleaner cleanliness. Often used cleanliness. Often used
as a final cleaner prior
after other methods are as a final cleaner prior
to electroplating.
to electroplating.
Often used as precleaner Effective with immersion
Aqueous,
and sprays. Used after
to remove bulk soil.
oil film on part if not
Semi
rinsed off. Often used
Has found increased
alkaline bath to provide
protective oil film.
usage.
I as s w t cleaner.
Immersion, spraying, & Immersion, agitation, &
Usually not suitable.
Solvent,
spraying are effective on
brushing are effective
Cold (2)
May be used as a
precleaning operations. solvent soluble soils.
spot or precleaner.
Very effective & widely Good for solvent soluble
Solvent,
Limited value. Spray,
used. Very repeatable
soils only. Use spray &
results.
immersion dip.
1) Acid cleaning is effective with many
when cleaning high strength steels.
2) Cold cleaning and vapor degreasing i
3) In removing rust and scale, other me
Note: Adapted from NASA SP-5076
Cleaner
or Methd
Aqueous,
Acidic (1)
1
I
I
I
I
I
Polishing and
Buffing Compounds
Not recommended. May
be effective if soil has
not burned or aged.
Widely used, least costly
method. Agitation or
spray with surfactant
is recommended.
Use after precleaning.
Solids can readily
contaminate bath and
reduce effectiveness.
Used on steel, some
non-ferrous. More
effective when sprayed,
should be rinsed off.
Immersion, spraying, &
brushing are effective
precleaning operations.
Limited. Soil may bake
on part unless spray
is used for cooling.
Rust
and Scale (3)
Removes rust on ferrous
metals. Acid pickling
can remove mill scale.
Removes rust and light
scale. No hydrogen
embrittlement or metal
loss.
Faster than alkaline bath
alone. Can be used to
remove other soils in
one operation.
Not recommended.
I
Not recommended.
Not recommended.
THE SCIENCE OF CLEANING
effectiveness of a hydrocarbon solvent is solvent power or solvency. Many measures of solvency
have been proposed and two are discussed below. The reader is cautioned to note that direct
testing is still the only way to be sure that a given cleaner will effectively remove a given soil.
The most common measure of solvency is known as the Kauri-Butanol method. The
method was developed by the paint and varnish industry as a way to measure the solvent power of
an aromatic hydrocarbon used as thinner. The more solvent that could be added to a given coating
without causing separation or breaksut of the resin, the stronger the solvency of the thinner. The
method employs 20 milliliters of standard kauri gum in butanol solution to which measured
amounts of solvent are added. Solvent is added until enough kauri gum precipitates so that a
printed sheet of 10 point century type will appear blurred and illegible when viewed through the
flask. This same procedure is then performed with benzene and the ratio of solvent to benzene
times 100 is reported as the Kb value for the solvent. In most cases, 100 milliliters of benzene will
cause sufficient turbidity and it has been assigned the standard reference value of 100. Listed in
Table 4-3 are Kb values for some typical cleaning solvents.
TABLE 4-3
KAURI-BUTANOL VALUES FOR VARIOUS SOLVENTS
Solvent
Kerosene
CFC- 113
Stoddard
Mineral spirits
Dipentene
PERC
Xylene
TCA
TCE
METH
Kb
- Value
30
31
34
39
62
90
94
124
130
136
On a more theoretical level, investigators have developed solvent solubility prediction
methods based on thermodynamics. When a material dissolves, it is accompanied by a change in
its free energy. Methods for predicting this change in energy have been developed, ranging from
the very simple to the very complex. The major limitation with the simple model is that its
application is too limited while the use of the complex models require an extensive amount of
mathematical manipulation. Most of these models have been used to predict solvent solubility for
use in formulating paints and coatings. In this application, the composition of all components is
known. In parts cleaning, the composition of the various contaminants present on the parts may
not be constant or known.
45
CHAPTER 4.0
4.3
Testing Cleaner Performance
As previously noted, the prediction of solubility does not necessarily mean that one can
accurately predict the cleaning ability or effectiveness of a given cleaner. The effectiveness of
cleaning is a complex function of soil composition, surface condition, cleaner formulation, and
operating conditions. For aqueous or alkaline cleaners which effect cleaning by their ability to wet
the surface and emulsifj, oils, surface finish can play a role in determining the level of cleanliness
achieved. As shown in Table 4-4, a rough surface can prevent surfactants from penetrating
beneath the oil and lifting it from the surface. For solvents which solubilize the oil, surface
roughness is not a major factor. Given the myriad of factors that can affect cleaning efficiency, the
development of a robust prediction methodology that would be reliable enough to eliminate the
need for testing is doubtful.
TABLE 4-4
CLEANING EFFECTIVENESS VERSUS SURFACE CONDITION
Tvpe of Oil
Light Mineral Oil
Heavy Mineral Oil in Toluol
Lard Oil (Prime No. 1)
Sulfurized Mineral Oil
Sulfurized Fatty Mineral Oil
Sulfurized Fatty Base in Mineral Oil
Cleaning Index (% Clean)
Mirror Finish
Roughened
99
97
94
95
88
84
89
11
17
23
2
11
Note: Data presented by Spring (1963) for an alkaline cleaner used to remove oils from
aluminum panels.
The testing of cleaner performance can be divided into two major activities: testing to see if
a new cleaner will remove a given soil in a reasonable time and without damaging the part and the
testing of a cleaner in an existing operation to determine the cause of poor performance. This
second activity is associated with maintenance of an existing cleaner and the discussion of these
techniques is deferred to Section 6, Improving Process Efficiency. The following discussion
focuses on the testing of cleaners as part of a selection process.
4.3.1
Cleaning Effectiveness
Given the diverse nature of cleaning activities, it is not surprising to find that dozens of test
methods have been developed to test cleaning performance. Most methods routinely employed test
the effectiveness of soil removal and not the actual level of surface cleanliness. Effectiveness is
46
-
~
~~
THE SCIENCE OF CLEANING
often reported as "pass/fail" though some methods do provide quantitative results. Major criteria
for the selection of an appropriate method includes:
e
0
0
e
e
Direct versus indirect measurement.
Qualitative versus quantitative measurement.
Laboratory'versus production testing.
Hydrophobic versus hydrophilic sensitivity.
Sensitivity versus ease of use.
Test methods commonly employed include visual inspection and paper tissue wiping, water
break and spray atomizer testing, copper dipping, paint adhesion, gravimetric measurement, and
solvent monitoring. The first three methods only provide a qualitative indication of cleaning
effectiveness while the last two provide a quantitative measure. Each of these methods is discussed
briefly below. For additional test methods, and for detailed information on each of the methods
below, the reader should contact the American Society of Testing Materials (ASTM) in
Philadelphia at (215) 299-2632.
Visual inspection and paper tissue wiping are two highly subjective but widely used
methods to denote cleaning effectiveness. The tests are limited to visible soils, mainly grease, soot,
and particulate matter. For visual inspection, the use of a microscope by a trained individual
increases the validity of test results. Determination of particulates by the paper wipe method is
sensitive to the pressure applied while wiping. The method is most sensitive when performed on a
wet surface rather than dry.
Water break and water spray atomization are quick and effective ways to determine the
cleanliness of a cleaned part. The method is based on the observation that water will not bead on a
clean surface, it will form a continuous film. Cleaned parts may be dipped into water and the flow
behavior of the water as it drains from the part noted. In the spray method, the formation of
beaded areas denotes the presence of hydrophobic soils. Both of these methods are best performed
on flat parts and they are often used as pasdfail tests in programs comparing the cleaning
effectiveness of various cleaners on standard soiled panels. Trained observers can produce reliable
results though their are several limitations with the methods. The major limitation is that they can
only detect the presence of hydrophobic soils.
In performing these tests, one should always use clean, cool water. Warm water may
evaporate readily and promote the formation of rust on ferrous surfaces. These methods may also
produce false positives when testing parts cleaned in an aqueous or semi-aqueous cleaner unless
they are properly rinsed. Alkali or surfactant residues will cause the water to wet out and form a
continuous film yielding a false indication of cleanliness. Depending on the nature of subsequent
processes, the presence of these residues may or may not be a problem. Likewise, failure of the
water break test may not indicate a problem if the remaining soil does not cause downstream
problems. Such may be the case where a slight oil film left on the parts after cleaning is desirable
for subsequent rust protection.
47
CHAPTER 4.0
Copper dipping is often used to test the effectiveness of a cleaning operation that will
precede an electroplating step. The method utilizes an acid copper sulfate solution (often referred
to as copper flash) to lay down a layer of copper on the clean part. Improperly cleaned areas are
revealed by either poor adhesion of the copper plating or discoloration of the copper. The method
is very sensitive but is limited to ferrous metals and requires an experienced operator to produce
consistent and reliable results.
The paint adhesion method can be applied to more substrate materials than the copper
dipping method but due to the nature of painting, the control of more variables is required. The
method is based on the assumption that an improperly cleaned part will not provide a good surface
for paint adhesion. Clean, dry parts are painted and allowed to cure for a specified length of time.
A baking cycle may be employed to speed curing. The paint is then cross-cut with a razor blade
and a piece of adhesive tape placed over the area. The cuts should be of equal width, forming a
checkerboard pattern. The depth of cut should be down to the substrate. The tape is lifted off at a
steady rate of pull and the number of squares remaining serves as an indication of part cleanliness.
Gravimetric measurement involves the weighing and soiling of a test piece with a known
contaminant and then weighing the piece both before and after cleaning. Cleaning effectiveness
may be reported as the weight or percentage of contaminant removed. The direct measurement of
removal has good sensitivity but does not truly indicate surface cleanliness. Residual films of
cleaning solution, metal and cleaner reaction products, or metal removal and etching by the cleaner
can affect weighing measurements.
An indirect method of measuring cleaning effectiveness is solvent monitoring. Clean parts
are soiled with a known amount of grease or oil, are cleaned in a known amount of solvent, and
afterwards, the solvent is evaporated and the residue weighed. The ratio of soil removed to soil
originally added is the fraction of removal achieved for a given volume of solvent. When testing
dirty parts on which the amount of starting soil is not known, a multi-step cleaning is employed.
The first cleaning and evaporation run determines the amount of soil initially removed. Solvent
cleaning, evaporation, and soil weighing is then repeatedly performed until all soil has been
removed. The ratio of soil removed in the first cleaning to the total amount of soil removed overall
is the fraction of soil removed per initial volume of solvent. The method assumes that a part is
clean if solvent no longer removes any contamination from the part.
To monitor the effectiveness of particulate contamination removal, the solvent used for
cleaning may be passed through a membrane filter and a particulate count performed. This method
can also be used for testing the particulate removal efficiency of aqueous cleaners (the testing of oil
and grease removal requires the cleaner to be evaporated which would result in erroneous weighing
due to mineral salts). For testing the removal efficiency of ionic contaminants, deionized water
rinses may be monitored for resistivity. This method is commonly used to test for the removal of
ionic fluxes from soldered printed circuit boards. Resistivity measurements may also be used to
check for ionic surfactant contamination following the water break test.
48
THE SCIENCE OF CLEANING
4.3.2
Material Compatibility
When dealing with the cleaning of metals, the subject of corrosion and hydrogen
embrittlement always comes up. Corrosion may be due to adverse chemical reactions between a
given metal and some component of a cleaning formulation. Extensive metal corrosion may result
in etching of the parts. Less severe corrosion may be indicated by metallic tamishing or
discoloration. Typically, highly alkaline cleaners result in the most severe problems and may
require the use of high levels of corrosion inhibitor such as sodium silicate. While effective, high
levels of inhibitor can result in rinsing problems. Solvents do not typically produce corrosion
problems unless an halogenated solvent such as 1,1,l TCA has been allowed to decompose and
form acids or if one is using a semi-aqueous solvent that is formulated with an alkaline cleaner.
Strongly alkaline cleaners can tarnish aluminum, copper, tin, and brass. They can also
leach zinc out of brass and other metals. On the other hand, strong alkaline cleaners are not a
problem when cleaning steel, titanium, nickel alloys, or magnesium (a metal highly sensitive to
attack from acidic or mildly alkaline cleaners). To test for corrosion, metallic coupons are allowed
to soak in the cleaner for a specified length of time.- The cleaner is tested at the concentration and
operating temperature at which it will be used in the shop. At the end of the test, the coupon is
rinsed, dried, and weighed to determine metal loss.
Hydrogen embritlement is often a concem when acid cleaning high carbon, heat treated
steels. The reaction of metal and acid results in the generation of hydrogen which can cause an
embrittlement of the metal. Hydrogen embrittlement of high strength steels may also occur when
cleaned cathodically in an alkaline bath. Testing for hydrogen embrittlement is an expensive and
time consuming effort. Fortunately, it is seldom an issue in most cleaning activities unless the
proposed cleaner is acidic.
While most solvents do not exhibit material compatibility problems when cleaning metals,
they can exhibit problems when used to clean elastomers, rubber, plastics, and other organic based
materials. Attack is typically reported as a softening of the material or a swelling and increase in
material volume. Cleaning of assembled parts can present a very difficult challenge when the
metals are sensitive to alkaline attack and the elastomers are sensitive to solvent attack. Solvent
swelling and attack is typically not a problem when dealing with relatively inert materials such as
Teflon. Many material compatibility guides are available for determining the potential of solvent
attack on a given polymeric material.
4.3.3
Other Performance Characteristics
Other measures of cleaner performance include impurity loading limits and material
stability. While these two measures may not play a role in determining how clean the parts will be,
they do impact the overall economics and design of the given system. Both of these measures
apply to the design of a solvent or aqueous-based cleaning system. The issue of foam generation
49
CHAPTER 4.0
does not apply to solvents but it is a critical performance characteristic of most aqueous cleaners.
As such, this issue is also discussed below.
The impurity loading limit is the maximum amount of solute that can be dissolved into the
solvent at a given temperature. Typically, this value sets the maximum upper limit of solvent life.
In maintenance cleaning, practical loading levels may be fixed by the time allowed for cleaning.
Since the rate of dissolution (i.e., cleaning) slows down with increased loading, most solvent is
replaced long before the maximum loading limit is reached. A solvent capable of holding 10
percent grease by weight may be replaced at 2 to 3 percent loading due to slow cleaning action.
The decision to change-out baths is often left to the operator.
Loading limits in a vapor degreasing operation are set by the allowable rise in solvent
boiling temperature. As grease loading increases, vapor generation in the sump decreases for a
given temperature. This is offset by increasing the sump temperature to maintain vapor production.
Allowable grease loading in the sump may sometimes run as high as 20 to 25 percent although 5
percent loading is more common for precision cleaning applications. Maintaining a low level of
grease in the sump reduces the amount of grease volatilized and present in the vapor.
The issue of contaminant loading in an aqueous or alkaline immersion cleaning operation
is much more complex. Some cleaners will effectively emulsify oil and grease under conditions of
agitation but release them when agitation is stopped. Competing reactions may occur that either
reduce or improve the cleaning performance of the bath over time. Alkaline cleaners will react
with oils and greases to form soaps which provide their own cleaning characteristics. Many soils
tend to be acidic in nature which neutralizes alkalinity. With subsequent addition of cleaner to
maintain alkalinity, the cleaning bath becomes richer in surfactant. Use of air agitation and hard
water make-up can result in reactions which shorten cleaner life and reduce the capacity for soil
loading. Typically, the determination of contaminant loading for an aqueous or alkaline cleaner is
best based on operating experience in similar facilities and operations.
The stability of a solvent or cleaner determines its ability to retain its chemistry under
various operating conditions such as temperature, concentration, and contaminant loading. With
the halogenated solvents used in vapor degreasing, exposure to water and reactive metals such as
magnesium and aluminum can lead to solvent decomposition. When decomposition occurs, the
chlorine is released to form hydrochloric acid. This acid can etch parts, and worse, lead to
destructive attack on the degreasing equipment. Stabilizers are included in solvent formulations to
control acid formation and the level of these stabilizers can be determined by performing an acid
acceptance test.
With naturally derived solvents such as terpenes, exposure to air, light, and heat can lead
to formation of oxidation products. The citrus solvent d-limonene exhibits an orange or lemony
odor that mat turn terpeny due to oxidation product formation. Extreme oxidation can render the
solvent acidic and result in the formation of a viscous sludge or residue which may leave a varnish
50
~
~
THE SCIENCE OF CLEANING
Id& film on cleaned parts. To retard solvent oxidation and promote storage stability, many
formulations include an anti-oxidant. These anti-oxidants were developed in the citrus industry for
the preservation of processed orange oils.
One performance test for aqueous cleaners that can be performed readily and is useful for
selecting spray cleaners is foaming tendency. Aqueous or alkaline cleaners that perform well as
immersion cleaners do not always perform satisfactorily as spray cleaners. Many facilities have
installed spray cleaners only to find that none of the immersion cleaners selected for testing will
behave in a spray application. Excessive foam generation leads to use of foam suppressants or
major modifications of the spray equipment. Unless these facilities have great patience to make the
system work, many will give up the fight.
To conduct a foam test, a given cleaner is diluted to its normal operating concentration.
Spray cleaners typically operate at 0.5 to 2 ounces per gallon compared to 6 to 14 ounces per
gallon for an immersion cleaner. A given volume of heated solution is then poured from a fixed
height into the center of a graduated cylinder. The liquid stream should not touch the sides of the
cylinder. The test is similar to pouring a bottle of beer into a tall glass so as to maximize the
volume of foam produced.
After pouring, the height of foam and free liquid are recorded as a function of time. The
test should be repeated with different cleaners and at different solution temperatures. The least
troublesome cleaner will be the one that produces the least amount of foam andor the one that
produces a fast breaking brittle foam. The amount of foam produced by fatty acid soaps tends to
vary with the titer (i.e., level of unsaturation) of the fatty acid stock. Tallow soaps may generate
tolerable amounts of foam at low temperatures and excessive amounts at temperatures greater than
160 OF. Rosin soaps may form large amounts of foam at low temperatures but relatively little at
temperatures above 170 OF. Most nonionic surfactants are modest foam generators.
Consideration should also be given to the potential for foam generation due to soil loading.
Soils rich in fatty acids will react with alkali to form soaps which may foam when sprayed. The
potential for soil foaming may be determined by conducting the foam test with fresh cleaners and
then loading the cleaners with soil and allowing them to age. By repeating the test with the aged
cleaners and comparing the results, an indication of foaming tendency over time can be obtained.
A similar test can be performed to determine the potential recyclability (Le., rate of phase
separation) of semi-aqueous cleaners from an emulsion rinse. The rate of separation is important
in sizing equipment since the faster the rate, the smaller the holding tank required. A mixture of
semi-aqueous cleaner and water is placed in a graduated cylinder and well shaken to insure
complete mixing. The shaking is then stopped and the heights of the three phases (ie., cleaner,
cleaner / water emulsion, and water) recorded as a function of time. Depending on the composition
of the semi-aqueous cleaner and the amount of time allowed for separation, the cleaner / water
emulsion phase (the middle layer) may or may not separate completely. Soil loading may also
51
CHAPTER 4.0
afkct the stability of this middle emulsion phase since soaps, surfactants, and small particles tend
to stabilize emulsions. Phase separation may occur more rapidly if the agitated mixture is heated
and maintained hot during the separation process. If so, this may indicate the need to insulate all
phase separation equipment, especially in cold weather environments.
52
5.0 WHAT ARE M Y OPTIONS ?
c
Having gathered information regarding the nature of the contaminant to be removed, the
type of substrate to be cleaned, and the operational constraints present in your facility, the search
for environmentally preferred replacement technologies can begin. This search should follow a
proscribed sequence or hierarchy of investigation. The hierarchy is:
4
0
First, attempt to eliminate the need to clean by eliminating upstream contamination or by
changing cleanliness requirements.
0
If that isn't possible, modi@ the part or contaminant to enable the use of a less hazardous
cleaning material or method.
0
And finally, select the least hazardous cleaning material or method that achieves the
desired level of cleaning.
Eliminating the need to clean by a change in operating practice and the modification of the
part or contaminant so as to alter the requirements for cleaning are two often overlooked ways to
eliminate solvent use. Selecting the least hazardous cleaning material is the next best choice. A
listing of various cleaning options, in descending order of environmental preference, as well as their
advantages and disadvantages is presented in Table 5-1 on the following page.
The information contained in this table is a highly condensed version of the information
that follows in this section. Please note that while the order in which the options are listed is based
on relative perceived benefits and impacts, the actual order is highly dependent on many site
specific and regulatory specific circumstances. A more accurate weighing of environmental
benefits and impacts, and their importance in each individuals selection process, can best be
performed by using the option screening methodology discussed in Chapter 3 and the forms
presented in Appendix A.
5.1
Avoid The Need To Clean
While engineering out the cleaning step may not be a viable solution for everyone seeking
to eliminate their use of hazardous solvents, it has long been overlooked as a potential solution.
An investigation of ways to avoid the need to clean should begin with the questions 'Why do we
clean ?'I and "What can we do to keep our parts from getting dirty ?'I Certainly, both of these
questions are worthy of a few moments of creative consideration. By raising this question at the
outset of your search, you may discover the most direct and preferred option of all: avoiding the
need to clean. By avoiding the need to clean, solvent usage, solvent waste generation, and worker
exposure can be entirely eliminated or highly reduced. While this approach may appear to be too
simplistic for your operation, there are many examples of where it has been successfully adopted.
In the metal fabrication industry, one of the most common cleaning requirements is the
removal of metal chips and cutting fluids from the metal work piece. Oil-based cutting fluids are
53
CHAPTER 5.0
of& used to cool the part and prevent heat build-up during machining. Machined parts may be
cleaned with solvents several times during production so that operators may check their progress
along the way and take accurate measurements. In situations where the cooling fluid is only being
used for its cooling effect and not for lubrication, use of cold air to cool the part is a viable option.
Cold air cooling may be used to replace fluid cooling in such operations as tool sharpening, surface
grinding, drilling, milling, and band sawing. Eliminating the use of the cutting oil eliminates the
subsequent need to clean.
-~
~
Clean metal parts are often deliberately soiled with a rust inhibitor oil before being placed
in storage. The parts may require storage because they are produced in lot sizes that exceed the
capacity of the downstream operation. When the downstream operations are ready, the parts are
recleaned and processed. Ways to eliminate this cleaning step include production of the parts in
smaller lots to match downstream capacity (e.g. using "just-in-time" scheduling principles),
removal of bottle-necks in downstream operations so as to increase capacity and eliminate the need
for intermediate storage, or storage of parts in a humidity controlled environment so as to reduce
the potential for rusting and avoid the need for inhibitor.
Automation and the removal of contaminant sources is another way to avoid the need for
cleaning. Injection molded parts used in biomedical devices are often cleaned with CFC-113 after
molding. One major source of surface contamination is the mold release agent used in the injection
process. Other major contaminants include fingerprints, skin oils, and particulates resulting from
manual parts handling. By using a different mold release agent, placing the injection molding
machines in a clean room environment, and automating the part removal and handling operation,
one facility found that these ''clean-molded" parts passed all of their required tests for cleanliness.
This eliminated the need for the final cleaning in their CFC- 1 13 vapor degreaser.
Similar work in the microelectronics industry points to the complete automation of the
fabrication and assembly operation as a viable way to reduce product cleaning requirements. Even
with the proper protective gear, workers are responsible for generating the bulk of contaminants
inside the cleanroom environment. After the workers, the second major source of contamination is
the ventilation air supplied to the room. By removing workers from the cleanroom environment, a
higher level of cleanliness can be achieved and maintained. Many of the cleaning steps typically
required to control particulate contamination can be eliminated. In addition to reducing the need
for cleaning, overall product quality and reliability is improved.
Another benefit of process automation is the ability to precisely control and optimize the
production environment. This ability to control and optimize the environment can be employed to
avoid product contamination either from existing contaminants or from new contaminants created
during the production process. By conducting soldering operations under an inert gas environment,
many microelectronics and printed circuit board fabricators have been able to eliminate their use of
solvents for defluxing.
54
-
WHAT ARE M Y OPTIONS ?
TABLE 5-1
f.
LISTING OF VIABLE ALTERNATIVE CLEANING TECHNIQUES
?
Option
Advantages & Disadvantages
Avoid or reduce the need
to clean.
Modify the part or
contaminant
Use of Water
Use of Abrasives
Use of Cryogenic Methods
Use of Thermal Stripping
Use of Aqueous Cleaners
Use of Non-Halogenated
Solvents
Use of Semi-Aqueous
Cleaners
Use of HCFCs
Use of Supercritical C02
Use of UV light and ozone
Use of Laser Stripping
I
Reduces the use of solvents, reduces worker exposure, and
reduces solvent waste generation. Option is highly plant and
process specific. Concerns over product quality and reliability
Reduces the use of solvents, reduces worker exposure, and
reduces solvent waste generation. Option is highly plant and
process specific. Concerns over product quality and reliability
Good for the removal of ionic soils. If soil is non-hazardous,
water can be discharged to POTW without pretreatment. May
need water demineralization system. Increased water usage
and energy demand. Potential rust problem.
Wide range of abrasives available. Starch and C02 pellets are
promising methods. Need for dust control depending on type
of abrasive. Potential damage to part. Line of sight method.
Only waste generated is removed paint and a small amount of
abrasive. Cold can damage parts. Not effective on thin
coatings. Limited to small and medium sued parts.
Burn-off ovens and molten salt baths widely used to remove
paint from hooks and racks. Can remove heavy deposits.
Leaves ash and heat scale on parts which then require further
cleaning. Heat can ruin part. Need for air emission controls.
Provides higher level of cleaning than solvents. Good for
organic soil and particulate removal. Long established method
Need for wash tank, rinse tanks, dryer, and wastewater
treatment system. Steel parts may rust. Worker exposure to
acids and caustics.
Stoddard solvent widely used in cold cleaning for maintenance.
Alcohols common in electronics for water displacement. Manj
are flammable and photochemically reactive. Toxicity varies.
Similar to aqueous cleaning. Oil film provides short-term
rust protection. Waste water contains solvents, emissions
of VOCs. Low dirt holding capacity.
Reduces use of CFC-113. Not widely available, not a drop-in
replacement, and very expensive.
Highly effective at removing oil from porous parts. Oil is
recovered in a concentrated form. Technology is expensive
and not suited for high volume production. High pressures
may result in part damage.
Used to remove organic contaminants and sterilize equipment.
Experimental technology. Requires worker protection from
UV light and ozone exposure.
System can be tuned to remove specific contaminant. Method
is experimental. Stripping rate is slow.
Page
53
57
61
63
89
68
69
70
75
86
87
88
90
91
-
55
CHAPTER 5.0
*
During the soldering of printed circuit boards, the metal component leads and conductive
pads must be heated to the melting temperature of the solder. As these metal surfaces are heated,
they react with oxygen in the air to form metal oxides. These oxides interfere with the ability of
the solder to wet the metal surfaces and form a reliable bond. To clean the metal surfaces and
remove the oxides that form, a rosin flux is used. Rosin flux consists of several organic acids
(mainly abietic) and activators which are capable of removing metal oxides and tarnishes. After
soldering, a solvent may be used to remove flux residues from the board.
By performing the soldering operation under an inert gas, reaction of the hot metal
surfaces with oxygen in the air cannot occur. It is the formation of oxides during soldering that
necessitates the need for flux (assuming that the boards have been properly cleaned before they
enter the soldering process). Since complete oxide removal and prevention of metal oxidation
before soldering is seldom possible, some form of oxide control is incorporated into the inert gas
process. Surface activators such as formic or abietic acid may be ultrasonically injected into the
inert atmosphere to improve solderability and control oxides. By dispersing the surface activators
into the gas phase, as opposed to applying them directly to the board, activator use can be precisely
controlled. The amount of activator left on the board after soldering is virtually insignificant.
Hence, the final cleaning and defluxing step can be eliminated.
In painting operations, use of solvents to clean-up the application equipment is a common
daily routine. Solvent use may be reduced by the use of easy to clean equipment such as Teflonlined metal spray cups or disposable polyethylene spray cups. Teflon-lined spray cups promote
drainage and hence reduce the amount of paint remaining inside. After draining, the inside of the
cup can be wiped clean rather than being washed out with solvent. Another option might be the
use of disposable cups. These relatively inexpensive spray cups are made of translucent, 100-mil
polyethylene. When new, very little paint sticks to the cup and cleaning can be performed by
draining and wiping. Excessively dirty cups can be disposed of instead of being cleaned. For paint
pressure pots, use of disposable polyethylene bags or liners is an option. Savings in solvent
purchase and waste disposal costs can more than off-set the cost of these items.
Avoiding the need to clean can also be applied to the practice of paint stripping associated
with field equipment maintenance activities. Many maintenance facilities in the defense sector are
questioning the routine practice of stripping everything down to bare metal and then repainting.
Several facilities have adopted "Inspect and Repair Only as Needed'' (IROAN) policies to cut down
on waste generation. In the past, vehicles would be routinely disassembled, stripped of paint,
inspected, and repaired (if necessary). This would be followed by complete repainting and
reassembly. The routine removal of top-coat, base-coat, and primer with solvent and caustic-based
paint strippers generated a large volume of hazardous waste.
The new IROAN policies now call for vehicle disassembly and inspection followed by
paint stripping only if the part shows signs of damage or corrosion. Staff at one military facility
reported that 90 percent of the parts they were formerly stripping did not actually require stripping.
56
WHAT ARE MY OPTIONS ?
W h the reduced workload, a higher percentage of the parts that require stripping are now stripped
with abrasives such as steel shot, glass beads, and plastic media. Use of abrasives also allows for
the selective stripping of old coatings which may be preferable when the reason for repainting is
only cosmetic (i.e., the top-coat has faded but the base-coat and primer still provide adequate
corrosion protection). Selective stripping may also be the best way to avoid generating a large
volume of lead-based stripping waste when removing coatings from old equipment and building
structures (many primers formerly used for corrosion protection contained a very high percentage
of lead-based compounds such as lead oxides and chromates).
This same philosophy is being applied in the field of parts cleaning where many are asking
the question "How clean is clean ?'I Given that the role of cleaning is to control the level of
contamination present on a part to some minimally acceptable level that will not interfere with
subsequent processes or operations, one should seek to determine just how clean a given part needs
to be. Adoption of inflexible cleaning standards or the use of the same cleaning sequence without
regard to the subsequent use or processing of the part can lead to excessive waste generation.
As an example, many shops clean and then oil ferrous-based parts before final shipment.
The cleaning is viewed as being necessary since many customers will complain if they receive dirty
parts. The parts must be oiled since they may form rust during shipment and subsequent storage at
the customers facility. Because the received parts are "dirty" with oil, they must often be cleaned
by the customer before they can be used. Many customers routinely clean the parts they receive
because they do not trust the ability of their suppliers to provide adequately clean parts and they
are unable to maintain the cleanliness of the received parts during storage. Hence, the final
cleaning performed by the supplier may only serve to improve the parts cosmetic appearance and
may not serve any other use&! purpose (note: final cleaning to remove harmkl residues that could
damage the part or result in the shipment of a hazardous product should always be performed).
Some shops have been able to eliminate the need for final cleaning by offering their clients a price
break or credit for acceptance of uncleaned parts.
5.2
Modify the Part or Contaminant
.
In the previous section, ways to eliminate or reduce the need for cleaning by avoiding the
contamination of clean parts or by reducing the requirements for part cleanliness were discussed.
This section continues with a discussion of part modification or contaminant modification so as to
ease the burden of cleaning. While adoption of these methods may be outside the control of the
facility performing the cleaning operation, they are worthy of discussion. While modification of
the part or contaminant is listed as a second option, it is actually a continuation of avoiding the
need to clean. These two options are often inter-related and the line between them is often blurred.
In addition to automation and improved handling techniques so as to avoid contamination,
the need to clean can be avoided by a change in process materials that do not leave excessive or
harmful residues on the processed parts. The use of heavy oils for lubrication during machining
57
CHAPTER 5.0
a d fabrication operations often creates an excessively soiled part. Removal of the heavy oil with
solvent is often necessary so that the part can be tested and gauged. At one facility using a heavy
dil in a tube bending operation, the subsequent need for degreasing with TCA was eliminated by
switching to a light "vanishing" oil. The light oil has a higher vapor pressure than the heavy oil
and hence evaporates after use. To speed evaporation, hot air knives were installed at the end of
the tube bending system. This change traded high emission loses from TCA degreasing for much
lower loses of a light oil.
Conversion from oil-based to water-based cutting and cooling fluids is an effective way to
ease the task of cleaning. In addition to offering better performance, subsequent removal of the
water-based fluids can be achieved by the use of water or a slight amount of detergent dissolved in
water. Water-based fluids are primarily oil in water emulsions which lend themselves readily to
removal by water. Removal of the traditional oil-based fluids often requires the use of solvent.
In situations where a slight protective oil film is desired for rust protection, the waterbased fluids can be used to provide this film. When used as a protectant, care should be taken that
the fluid is not allowed to dry on the part. When it does, the oil in water emulsion can invert to a
water in oil emulsion which is much more difficult to remove.
The emergence of "no-clean" flux in the electronics industry is yet another example of an
industry attempt to modifL the contaminant and engineer out the cleaning step. Both CFC-I 13 and
TCA are used for removing solder flux from printed circuit boards after soldering. Conventional
solder flux contains rosin which leaves a residue on the boards. This residue may be sticky or hard
depending on soldering conditions. It may contain ionic compounds and be conductive (which can
cause electrical reliability problems) or it may act as an insulator and interfere with bed-of-nails
test methods. Soldering flux is generally composed of 15 to 35 percent rosin dissolved in isopropyl
alcohol. The "no clean" fluxes contain 2 to 5 percent solids and therefore leave less residue.
Because of the lesser amount of flux residue left on the board, cleaning or defluxing may
not be required. Another advantage of these fluxes is that they offer finer control of the soldering
process so that solder does not bridge over densely packed surface mounted components. Many
suppliers of "no clean'' fluxes claim that board reliability is equal to boards soldered with the
conventional flux and defluxed with solvent. Some have reported that the use of llno clean" or low
solids solder flux is suitable for use on high reliability electronics but they do not satisfL current
Military specifications. This is changing, however, and the Department of Defense has reportedly
allowed several manufacturers to use it.
To leave no residue, the flux must be very dilute and relatively inactive (an active flux
would leave an ionic residue that would lower the electrical resistance of the board and create
reliability problems). All metal surfaces must be clean and in a very solderable condition. With
"no-clean" flux, there is virtually no tolerance for solderability or process control problems
(Bemier, 1988). While the use of no-clean flux requires much more attention to process control,
58
WHAT ARE M Y OPTIONS ?
th& increased attention may reveal potential problems that otherwise would not be detected. One
manufacturer of flux indicates that the high solid content of conventional flux sometimes masks a
sblderability problem that only becomes apparent when a "no-clean" flux is used.
In one study, AT&T Bell Laboratories in Princeton, NJ reported on their use of low solid
fluxes which showed that careful process control and monitoring was essential to avoid overapplication (Guth, 1989). Use of too much flux can result in excessive residue which can impact
the reliability of the board. Low solid flux must be applied uniformly with precise control and
must be performed in a closed system to maintain flux composition. In an open system, the solvent
component of the flux will evaporate and alter the composition over time. To properly use this
flux, AT&T developed a low solids fluxer that employs an ultrasonic spray unit for precise
application of flux to the board. Both air and nitrogen blanketed models are offered for sale and a
prototype fluxer is available for testing.
At Hewlett Packard in Loveland Colorado, Freon TMS is no longer used for cleaning and
defluxing of soldered wiring boards due to a number of changes. These include improved handling
methods to reduce board contamination from skin oils and fingerprints and conversion to a noclean solder paste. Following the soldering operation, general purpose boards do not require
cleaning. Boards requiring a high level of cleanliness use the no-clean flux followed by aqueous
cleaning. No terpenes or saponifiers are used in the process. Stand-off heights for the boards
range from 30 mils down to zero depending on the program.
The use of saponifiers for defluxing the boards was ruled-out due to the problems they
may create. Saponifier residue left on the boards results in ionic contamination which reduces
surface resistance. Saponifier use also increases the potential for lead leaching from the solder and
may make waste water treatment more difficult. Most of the contamination previously found on
the soldered boards was the result of improper handling and not flux residue. By improving board
handling methods and avoiding unnecessary contamination, the use of no clean flux with aqueous
cleaning has been very successful.
While some may argue that the use of k o clean" fluxes may lower the reliability of the
board due to trace residue, a fair question to ask is, "Just how reliable does the board need to be ?'I
Boards used in toys or short-lived equipment may not need the same level of reliability as would
military or avionic equipment. While it is clear that a ''no clean" option does not fit every process,
there are many cases where it could be employed. While the use of aqueous and semi-aqueous
cleaners to replace ozone depleting solvents is being rapidly adopted through-out the printed circuit
board industry, many companies view their use as an interim solution. Development and
refinement of "no-clean" fluxes being the long-term solution.
Another major development in the electronics industry is the development of water-soluble
fluxes. Hughes Aircraft Company in El Segundo, California developed a product named HF-1189
that is effective at replacing conventional RMA (rosin, mildly activated) fluxes. The flux is based
59
CHAPTER 5.0
o m extract of lemon juice, most notably citric acid, and a foaming agent. The inventor of this
flux, Ray Turner, reportedly came across this discovery while conducting some experiments in his
kitchen. A similar water-soluble flux is offered by Alpha Metals under the name Alpha 6030. A
major advantage of water-soluble fluxes over RMA flux is that residue removal after soldering
may be performed with water as opposed to halogenated solvents.
An electronics facility in the Southern California area has been using HF-1189 for more
than a year and their s t a f f has been helping the military to develop and approve a specification for
its use. Previously, the facility was using 25 gallons per week of RMA flux. Operating costs for
the TCA vapor degreaser used to deflux the boards was averaging $250,000 per year. With
conversion to the water-soluble flux, usage has decreased to 5 gallons per week. Boards are
defluxed with deionized water in a Westek in-line system, no saponifier is added. Carbon filters
are used to treat the water for reuse. Total water consumption is 6 to 8 gallons per day. The
system is highly automated with a computer screen providing system status such as solution levels,
operating temperatures, and spraying rates. The operating cost for the Westek defluxer, including
the operation of the wave soldering system, is estimated to be $25,000. Payback for this
conversion was approximately 6 months.
While the facility has had problems converting to the use of water soluble flux, they feel its
benefits are worth the effort. One major problem they encountered was the tendency of the flux to
form white residue on the boards. To avoid this, the temperature of the prewash stage must be held
below 90 O F . An alternative solution is to maintain a pH range of 8 to 8.5 for the rinse water. Lab
analysis of the residue was inconclusive and its exact composition is still unknown. Similar work
conducted by Texas Instruments has found that residue formation may be prevented by rinsing the
boards with an ammonia solution before defluxing.
In the airline industry, several companies have reduced their need for paint stripping by
adopting minimal paint designs on their aircraft (i.e., they have modified their parts to minimize the
need for cleaning). Commercial aircraft are painted every 4 years on the average and often require
complete stripping before repainting. While some believe that paint protects the aircraft surfaces
from oxidation and corrosion due to exposure to salt water spray and jet he1 spills, the largest
producer of fhelage skin material in the US. (Alcoa) recommends against painting for safety,
cost, and environmental reasons (AWST, 1989). For airlines that do not paint, there are savings in
he1 due to lower weight, reduced aircraft downtime, savings in labor, savings in waste disposal
costs, and in stripper and paint purchases. To prevent corrosion of the unpainted surfaces, the
aircraft must be washed and buffed more frequently. US Air, for example, washes their aircraft
every 90 to 120 days and buffs the exterior skin panels two to three times a year (AWST, 1989).
Paint stripping is also performed on buildings and other structures that must be stripped in
place. One way to avoid the need for stripping is to design the structure so that it does not require
painting. Examples would be the use of vinyl siding in home construction and the use of colored
concrete in building construction. Use of corrosion resistant metal trim materials such as stainless
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WHAT ARE M Y OPTIONS 7
stdel, copper, bronze, and aluminum are known. To promote the development and use of surfacecoating-free materials, the USEPA has conducted several workshops to address the issue of
material selection and its subsequent impact on production and maintenance waste generation.
5.3
Use Non-Solvent Based Cleaning Technologies
The following sections discuss cleaning media selection in their order of relative
environmental hazard. As mentioned earlier, it is difficult, if not impossible, to assign absolute
values to the hazard of any given cleaning media or method. In order to provide you with some
perspective, we have ranked various cleaning technologies in relative terms. The first level of
materials and methods to be discussed are non-solvent based. This includes the use of water,
abrasives, cryogenic methods, thermal methods, and aqueous cleaners.
i
While these methods may or may not be judged as being "environmentally preferred''
compared to your current solvent-based cleaning operation, they do tend to be recognized as being
preferred on a generic level. Each of these methods eliminates the creation of spent solvent wastes,
eliminates atmospheric emissions of VOCs, and eliminates worker exposure to solvents. For
facilities not able to adopt the use of non-solvent based cleaning technologies, selection of a less
hazardous solvent or adoption of an emerging technology may be viable. Subsequent sections in
the Chapter discuss the use of non-halogenated solvents followed by interim technologies (e.g., the
HCFCs and PFAs) and emerging or experimental technologies (e.g., supercritical CO,, CO, pellet
blasting, laser stripping, and others).
5.3.1
Water
Ultra-pure water can be an effective cleaning medium for removing water-based cutting
and cooling fluids, ionic salt contaminants, and water-based fluxes. The use of a hot deionized
water rinse to remove trace contaminants from steel and prevent pin-point rusting has been known
for many years. Few organic fluids are completely immissible in water and will dissolve over time
if the water is pure enough. Unfortunately, the loading capacity of ultra-pure water is very low
and its cost of production is high. Therefore, usage of ultra-pure water is mainly limited to the
cleaning of high value added items or to the final &sing of parts after cleaning in a solvent or
aqueous cleaner.
Halogenated solvents are often used to dry and displace water from wet parts. This
practice may be performed to prevent ferrous parts from rusting or if subsequent process steps
cannot tolerate the presence of water. In this situation, the water is an unwanted contaminant. At
Intemational Business Machines disk drive production facility in San Jose California, they were
able to replace their CFC-113 drying system by converting to hot deionized water. The processed
parts are aluminum disks used in the production of rigid magnetic media disks for direct access
storage devices. The manufacturing process involves flattening, smoothing, and rounding a
61
CHAPTER 5.0
&ped aluminum blank. The next step is to clean and dry the disk so that a magnetic coating can
be applied. The disk must be absolutely dry to insure adhesion of the coating.
i!
The new drying system that replaced the CFC- I 13 displacement system relies on a hot
deionized water spray to rinse off and heat the disks. When the spraying is stopped, heat from the
now hot metal causes the remaining water to evaporate. An air tunnel supplied with HEPA filtered
air effects "finish" drying and cooling of the disks. To ensure spot-free drying, the quality of the
water must be very high. A typical specification would be ohmic resistance greater than 16
megohms, ionic contamination less than 1 parts per billion, and total organic carbon less than 25
ppb. IBM has also evaluated the use of deionized water for cleaning other diskdrive components
(KO,1989).
To remove bulk or gross contamination such as dirt, grit, and grease, the use of high
pressure water or steam, with no chemical additives, can be effective. Rather than dissolution, the
main removal action is mechanical force. The dirt, grit, and grease is knocked off the part. High
pressure water blasting has been used to remove mill scale from steel, barnacles from ship hulls,
paint from aircraft, and to clear clogged he1 oil pipelines. The main disadvantage of water
blasting, as with any aqueous cleaning method, is that some means of drying ferrous parts is
necessary to prevent rusting. While corrosion inhibitors such as nitrates or chromates may be
added to the water to prevent rusting, these chemicals create their own environmental hazards.
Handling of waste water may be a problem for facilities not equipped with appropriate systems.
The Swedish automobile manufacturer SAAB, uses a high pressure cold water spray to
remove metal fines and clean aluminum engine cylinder heads after machining (Anonymous, 1989).
The water is pressurized to 4,000 pounds per square inch and exits the nozzles at a velocity of 500
miles per hour. While water blast systems tend to be line of sight, the high pressures involved are
effective at removing metal fines and trapped fluids from recessed areas. No detergent additives
are used to aid cleaning although a small amount of corrosion inhibitor is employed. Waste water
generation is minimal since the cold water is continuously filtered and reused. The overall
processing time for producing one clean cylinder head is 48 seconds.
According to a case study prepared by the North Carolina Office of Waste Reduction, a
manufacturer of brass keys successhlly replaced their use of a TCA vapor degreaser with a
system using hot water high pressure sprays. The new system is used to remove a ''medium grade"
cutting oil from more than 1.5 million brass keys per day. After washing, the keys are blow dried
using high pressure air. No surfactants or other additives are used, an oil skimmer is used to
remove recovered oil and the water is recirculated. System costs were approximately $1 19,000
with overall annual savings amounting to $1 10,000. The annual usage of TCA before the switch
was 200,000 pounds.
The Air Force Wright Laboratory and the Oklahoma City Air Logistics Center are
investigating the use of an automated high pressure water system for stripping B-IB, B-52,C-135,
62
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WHAT ARE MY OPTIONS ?
a d E-3 aircraft. If successful, the system will reduce the need for MEW-based strippers by 90
percent, reduce labor costs by 53 percent, reduce material costs by 50 percent, and reduce waste
treatment and disposal costs by 75 percent. The process has been in use since 1986 on NASA's
Space Shuttle Program and has been demonstrated at several naval facilities for stripping paint
from ships. Process validation work and refinement of the nozzle design is currently underway.
Water blasting by means of high pressure hoses can be employed to remove uncured paint
from the walls and grates of paint booths. While this method eliminates all use of chemicals for
stripping and reduces worker exposure to METH,it does introduce a new hazard into the paint
booth. High pressure water sprays can seriously injure a worker if all of the proper precautions
are not taken. A safer, highly automated blasting system can be used to strip paint from paint
hooks and removable floor grates.
5.3.2
Abrasives
Abrasive blasting can be used in place of cold cleaning for the preparation of parts before
rebuilding, soldering, printing, plating, or finishing. Self-contained compartmentalized blasting
systems are capable of cleaning various sized parts and workloads. Portable equipment is also
available and offers advantages for certain applications. Abrasive blasting can be used to remove
contaminants other than oil and grease such as products of corrosion, heat scale, and carbon
deposits. Since the main advantage of solvents and chemical-based paint strippers is that they do
not damage the substrate, abrasive methods must also maintain this feature. Therefore, abrasives
considered to be potentially viable substitutes for solvents must be relatively soft.
Cleaning applications which potentially lend themselves to abrasive blasting include:
cleaning of internal combustion engine parts such as engine heads, pistons, rods, and valves,
cleaning of transmission parts and related items, and cleaning of storage tanks, piping, bridge
structures, and construction equipment. Blast cleaning with abrasives is not appropriate for
critical cleaning of precision electronic components, with the possible exception of carbon dioxide
pellet blasting. The abrasive action of this technique can be finely controlled and it does not
generate an abrasive dust that might contaminate the cleaned surface.
With most abrasives, the blasting systems employed are either direct pressure or suction
induction design. The direct pressure method employs a pressurized hopper that contains the
blasting material, which is fed and mixed with air at the bottom of the hopper. Air pressure
propels the abrasive through a nozzle which is directed at the surface to be cleaned. This type of
blasting provides a higher impact pressure and requires more operator attention to prevent
overblasting. This system is particularly usefil when cleaning hard metal surfaces.
In the suction induction method, the abrasive is mixed with air in the blasting gun instead
of the hopper. The air and abrasive are supplied to the gun, where the abrasive to air ratio is
determined by the air jet and nozzle geometry. This system provides more control over the extent
63
CHAPTER 5.0
ofseverity of blasting and is appropriate where a higher level of selective cleaning is required. As
with the direct pressure system, both methods are linesf-sight.
!
Work conducted by the Boeing Defense and Space Group in Seattle Washington, indicates
that wheat starch blasting is effective for removing most organic coatings, produces no
macroscopic damage to metal, and is more effective and forgiving than plastic media, sodium
bicarbonate slurry, carbon dioxide pellets, or ice crystal blasting. The media (Envirostrip from
Ogilvie Mills) consists of crystallized wheat starch and has a hardness value of 3.0 moh. Blasting
pressures employed in the test were 25 to 45 pounds per square inch and flow rates varied from 6
to 10 pounds per minute through a 3/8 inch nozzle.
- - -
___
One interesting finding of the test work was that the Envirostrip did not remove the alodine
layer from treated aluminum. Even after depainting, the stripped parts were able to pass a 7 day
salt spray exposure test (Larson, 1993). Cleaning of the stripped aluminum prior to repainting can
be performed with warm water plus surfactant. Reactivation of the alodine prior to repainting is
recommended to improve paint adhesion. This can be performed by a short dip in a tank of fresh
alodine solution or by spray application of the alodine. Boeing is currently working with United
Airlines to determine the effect of the process on composite materials.
Boeing has also developed a way to use the Envirostrip product in a manual cleaning
application. Nylon bristle foam-backed painting pads are dipped in the starch and rubbed against
the oil and grease stained metal. The electrostatic charge of the nylon holds the starch to the pad
and the starch provides an oil absorbing and mild scouring action. Laboratory tests indicate that
the level of cleaning achieved with this method is greater than that achieved with solvent (in this
case, MEK). No scratching of the metal surface was noted.
Many military facilities have reduced their reliance on paint strippers employing methylene
chloride by using plastic media blasting (PMB) systems. Blast cabinets and glove boxes can be
used to remove paint from small parts. Larger components may be stripped inside an automated
blasting chamber. In both systems, personnel protective gear is not required because the operator
remains outside the cabinet. The media is fed into the cabinet or chamber and directed against the
part being stripped. Used media and paint waste are pneumatically conveyed from the blast area to
the reclaimer. Reusable media is separated from the waste and returned to the cabinet. Media
fines and paint waste are removed by a dust collector and discharged to a drum for disposal. Other
abrasive materials commonly in use include glass beads, sand, slag, and steel shot.
Field use of PMB may be performed in an open area or in an enclosed blast room or booth.
To protect the operators from dust, self-contained or air supplied breathing apparatus must be
worn. The high risk of physical injury from exposure to the abrasive spray requires the wearing of
heavy protective garments. PMB systems, regardless of their size, always consist of certain
fUndamenta1components that include the blasting machine, a source of clean, dry, and oil-free
64
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WHAT ARE M Y OPTIONS 7
cdhpressed air, a system for recovering and recycling the plastic media, and some means of dust
suppression or control.
?
U.S. Technology Corporation was the first firm to introduce plastic media into the market.
Three grades are available: Polyextra (a thermoset polyester resin) with a moh hardness of 3 .O,
Polyplus (a urea formaldehyde resin) with a hardness of 3.5, and Type I11 (melamine formaldehyde
resin) with a hardness of 4.0. DuPont manufactures two types of plastic media used for abrasive
stripping, Type L with a hardness greater than 3.5 and Type C with a hardness greater than 4.0.
Other suppliers include MCP Industries, Aerolyte, and Tierco. These latter two also manufacturer
plastic media blasting equipment.
In the media recycling system, the spent media and stripped paint must be collected and
separated. Additions of fresh media must be made and the recovered media returned to the blasting
equipment for reuse. In blast rooms and booths, pneumatic floor recovery systems collect the spent
media. In the field, plastic media may be collected manually with shovels or vacuum hoses. Some
blasting systems are equipped with a collection pick-up hose that is mounted near the discharge
nozzle. With these systems, blasting and media recovery occur simultaneously. Manufacturers
claim that 90 to 95 percent of the media can be reclaimed after each blast cycle.
Plastic media blasting has been used with success at a number of military facilities. The
Corpus Christi Army Depot (CCAD) in Corpus Christi Texas has been examining the use of PMB
since the early 1980's. CCAD is responsible for overhauling various types of helicopters, which
are stripped every 5 to 8 years on average. One reason CCAD began investigating the use of PMB
was the then new military requirement to switch to chemical agent resistant coating (CARC). This
change was projected to increase stripper requirements to three times the previous level. Since the
facility was having a difficult time meeting its USEPA NPDES permit limitations, increased use of
MEW-based strippers was not viable. The depot's investigation of PMB showed that the
technique would be more cost-effective than the continued use of MEW-based strippers.
Projected savings associated with annual labor, materials, and waste disposal costs were estimated
to be $1 million.
Hill Air Force Base in Ogden California was another military facility that first pioneered
the use of PMB. Several F-4 aircraft were found to be coated with multiple layers of epoxy,
enamel, lacquer, and polyurethane, which had been applied on top of one another. Because the
weight of the coatings were impacting aircraft performance, it was decided to strip the F-45 down
to bare metal and repaint with a standard polyurethane. PMB was investigated and projections
were that the technique would save $2.8 million annually and reduce stripping time by 50 percent.
One F-4 aircraft requires 364 hours to prepare and strip with MEW-based strippers. Hill AFB
has since installed a stripping hanger for depainting aircraft.
The first commercial airline to use PMB was Republic Airlines, now part of Northwest
Airlines. It began the operation in May of 1985. Between May 1985 and March 1986, the process
65
CHAPTER 5.0
w16 used to strip more than 50 aircraft. Savings were estimated at $60,000 to $70,000 for each
aircraft stripped. These savings m a d y resulted from reduced tum-around time. Chemical-based
stripping required 7 days to complete where as 5 days were required with PMB (AWST, 1986).
At an estimated down-time cost of $30,000 per day, the two day reduction in down-time equates to
a savings of $60,000 per plane stripped. These savings are augmented by an average savings of
$4,000 per plane in labor and other expenses for PMB (AWST, 1987).
At the Republic Airlines facility, plastic media collects on the hanger flooras aircraft are
stripped. Each aircraft generates about 30,000 pounds of used media and it is cleaned up using a
motorized floor sweeper. The floor sweeper then retums the used media to the classifier for
removal of paint chips and dust from the reusable media. The classifier is able to recover 90 to 95
percent of the media for reuse and the waste passes the USEPA EP toxicity test for metal leaching.
The waste is disposed of in a sanitary landfill.
While many facilities have had success with PMB, there are several disadvantages which
must be considered. First, there is a concem that the dust generated during the blasting operation
creates an unsafe working environment. The dust load due to breakdown of the plastic media and
stripped paint in a blasting operation can be significant. This dust may be explosive and the
probability that the dust will ignite depends on a variety of factors including the concentration of
dust, particle size, and presence of ignition source. Workers must wear protective equipment
inside blast rooms and booths and when working with abrasives in the field. Equipment for
working inside a booth includes a helmet air filter, a climate control tube to allow the operator to
heat or air condition the air, hearing protection, leather gloves, and a leather faced cotton-backed
blast suit (NCEL, 1986).
Additional concem arises over the issue of substrate damage. There is considerable
controversy over this issue and it is an extremely important one because of safety, reliability, and
liability concems. Major issue areas include the potential for removal of protective cladding,
reduction in the fatigue life of the vehicle, covering of fatigue cracks that would prevent their
detection, and the promotion of stress cracks by the PMB itself.
Most military aircraft have aluminum cladding over metal to protect it from oxidation,
which would lead to corrosion. If this protective coating were removed, the aircraft could be
subject to increased corrosion. Tests conducted at Corpus Christi Army Depot indicated that
walnut shells, which require three times the blast pressure of plastic media, removed more of the
aluminum clad (NCEL, 1986). Other studies suggest that PMB does remove some clad but that
even after numerous cycles, the clad is degraded by only 25 to 50 percent. Hand sanding, which is
sometimes done after chemical stripping, may actually remove more (ADL, 1987).
Tests sponsored by the Corrosion Program Office at Wamer Robins Air Force Base in
Georgia were designed to determine whether PMB shortened the fatigue life of aircraft. The tests
showed that fatigue life was reduced by less than 25 percent when blasting aluminum sheet of
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WHAT ARE M Y OPTIONS ?
0.665 inch thickness. With aluminum sheet of 0.030 inch thickness or less, significant fatigue life
reductions of 90 percent can occur (ADL, 1987). Other tests showed fatigue life loss in thin
aluminum sheets of 0.016 to 0.032 inch thickness. As can be expected, less damage was observed
with increasing sheet thickness (Battelle, 1987). Tests conducted at the Naval Air Station North
Island Materials Engineering Lab in San Diego California concluded that PMB did not damage
low-alloy steels, corrosion resistant steels, or titanium (NCEL, 1986).
Tests conducted at Hill AFB indicated that covering over of existing stress or fatigue
cracks is not a problem except at very high blast pressures. However, tests conducted by the
Materials Engineering Division at the Naval Air Repair Facilities in Pensacola and Jacksonville
Florida did lead to some crack closure on certain aluminum alloys (NCEL, 1986).
As to the generation of stress cracks, tests performed at Warner Robins AFB found that
surface pits containing foreign metals or silica were produced after blasting with plastic media.
The pits containing foreign matter can act as stress risers, which can initiate cracks. Even when
using virgin media, foreign contamination was found. Results of testing suggested that fatigue
cracks were initiated at small surface craters, which were believed to be produced by contaminants
in the media. The findings also indicated that PMB created stress that caused crack growth
(Battelle, 1987). Proponents of PMB indicate that more serious stress risers are created by hand
sanding (ADL, 1987).
Another major problem with PMB is dust intrusion into the aircraft interior. In particular,
intrusion into surface panel overlapping areas can cause stress, especially around rivets where
fatigue cracks can propagate (Parrish, 1987). Severe intrusion may also result in contamination of
hydraulic systems. In the small aircraft commercial sector, several refinishers have reported
serious dust intrusion into engine compartments and landing gear. To some extent, these problems
can be solved by better masking of potential entry points.
The level of waste that is generated in the PMB process depends on several factors
including the number of stripping operations, the amount of media used, the degree of recycling
that is possible, the number of paint coats requiring removal, and the composition of the paint. At
Hill AFB, PMB stripping of each F-4 aircraft yielded 1,500 pounds of waste. On an annual basis,
the stripping of 205 aircraft resulted in 307,500 pounds or about 140 metric tons of waste.
Although much of the media is recycled, this still represents a large amount of waste requiring
disposal. This waste may be classified as hazardous if the stripped paint contains lead, chromium,
or cadmium, which is often the case with paints used by the military and in transportation services.
Sodium bicarbonate slurry blasting, or the bicarbonate of soda stripping (BOSS) process,
is similar to the PMB process except that it uses an abrasive media that is semi-soluble in water.
The major advantage of this process is that spent abrasive can be dissolved in water after use and
be discharged for treatment. The only solid waste that remains behind is the stripped paint. The
San Antonio Air Logistics Center at Kelly Air Force Base in Texas has been investigating this
67
CHAPTER 5.0
p&cess. Kelly AFB has installed a new PMB operation, but wanted to have an alternative process
available for use. According to the base, the operating costs (excluding waste disposal) for PMB
and the bicarbonate process are about the same. The PMB process requires 800 pounds per hour
of abrasive where as the bicarbonate process requires 150 to 200 pounds per hour. The total cost
of the bicarbonate process tends to be lower because the process does not generate a large volume
of hazardous waste. Stripped paint can be filtered from the slurry and the slurry can then be used
to neutralize any acid waste generated elsewhere at the facility.
Although carbonate blasting is not as likely as PMB to mechanically damage the substrate,
it does introduce the potential for long-term corrosion damage. Alkaline compounds left on the
metal can cause corrosion or lead to failure of the adhesive bond between the metal and the paint.
Proper rinsing of the stripped surfaces is difficult. To overcome these potential problems, some
firms are investigating the use of corrosion inhibitors added to the bicarbonate slurry. Depending
on the corrosion inhibitors employed, the resulting slurry waste may be classified as hazardous.
Leaching of lead or chromium from the paint may also render the sludge hazardous. If so, this
would negate a major advantage of this process over PMB. To reduce or avoid potential problems
associated with corrosion, the use of magnesium carbonate is also being investigated.
5.3.3
Cryogenic Techniques
Cryogenic techniques have been used to remove paint from body carriers, hooks, fixtures,
and racks. Such items are placed in a specially designed cryogenic chamber and either sprayed
with liquid nitrogen or immersed in a nitrogen bath for several minutes. The cryogenic
temperatures create large stresses between the substrate and the coating due to differences in the
degree of contraction. Steel will contract about 1 percent when its temperature is reduced from
293 OK to 173 OK while a powder coating will contract by 6 percent (IF, 1986). The difference in
contraction between the substrate and coating causes hairline fractures in the coating.
To subsequently remove the brittle and highly stressed coating, it may be bombarded with
high-velocity plastic media which causes hrther cracking and debonding. In other systems, the
parts are placed in a vibratory trough after immersion in the nitrogen. The parts knock into each
other and the coating flakes off. The plastic media method is best suited for large parts where as
smaller parts can be effectively stripped in the vibratory trough.
Cryogenic stripping of paint hangers and racks coated with baked on acrylic is performed
at a Whirlpool plant in Ohio. This plant produces 1,200 ranges and 2,000 dishwashers a day and
has an inventory of 13,000 racks and hangers. Based on this workload, 375 racks and hangers
require stripping each day. The chamber is operated at -130 O F . The media used for abrasion is
recycled and the paint chips are drummed and disposed of (presumably as hazardous waste). The
nitrogen gas is exhausted to the atmosphere. The cost of the stripping operation is reported to be
$0.54 per hanger stripped (IF, 1985).
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WHAT ARE MY OPTIONS 7
*
While the cryogenic process appears to be viable for a wide range of parts, there are some
limitations to its widespread use. Alkyd, acrylic, polyester, vinyl, and lacquer coatings have been
removed successfblly, but epoxy and urethane coats are difficult to remove. For these coatings,
lower nitrogen temperatures in the -250 O F range are required. Furthermore, coatings thicker than
0.01 inches are effectively removed where as thicknesses less than 0.01 inches are not (IF, 1984).
This means that the method is best suited for stripping heavy accumulations of paint from items
such as hooks and racks as opposed to thin coatings on finished goods.
In addition to limitations based on paint type and coating thickness, large bulky parts
cannot be stripped. The weight of parts in the chamber is limited to 400 pounds per cycle. There
are also two safety concerns with this process: the inert character of the nitrogen and the extremely
low temperatures. To prevent oxygen depletion, the spent nitrogen must be exhausted from the
chamber and be safely vented outside. Workers must wear protective gloves when unloading the
parts though the parts can be safely handled several minutes after removal from the chamber.
5.3.4
Thermal Technologies
Thermal methods such as flame bum-off are sometimes used to strip paint and remove
other contaminants from large metal structures such as bridges before repainting. The method is
highly labor intensive, results in emissions of bumed paint that cannot be easily controlled, and
typically results in a metal surface fouled by heat scale. The burn-off of paint containing high
levels of lead, zinc, and chromium is extremely hazardous and should not be performed. Heat scale
must subsequently be removed by abrasive methods such as scraping, sanding, wire brushing, or
power brushing.
Bum-off ovens and molten salt baths are often used to remove paint overspray from hooks,
racks, grates, and body carriers used in automotive plants. Stripped parts are left with a residue of
ash, which can be removed by rinsing with water or high pressure water sprays. Use of thermal
technologies has been limited in the area of parts cleaning due to the high temperatures involved,
which often lead to distortion of the part and formation of heat scale. Thermal technologies are
widely used in some paint stripping applications.
One highly efficient method for stripping paint covered parts is the use of a fluidized bed
system. These systems consist of a large tank containing quartz sand or aluminum oxide. An air
stream is blown into the bottom of the tank and fluidizes the bed. Natural gas is mixed with the air
and ignited above the surface of the bed. The operating temperature is adjustable but typically
operates around 800 OF.
The plastic or paint coated parts are lowered into the bed where the organic materials are
pyrolized and abraded in the fluidized sand. To control the resulting off-gases, the system may be
vented to an after-burner or post-combustion chamber. The exhaust from the after-burner may
pass through a wet scrubber to remove solids prior to discharge to atmosphere depending on
69
CHAPTER 5.0
s a e m design. The Red River Army facility in Texas is currently testing a fluidized bed stripping
system. This method has proved successhl for cleaning and stripping steel parts, but cannot be
&ed on aluminum due to the high temperatures involved.
In addition to fluidized sand, molten salt baths operating at 900 O F have been used for
many years to strip heavy accumulations of paint from metal parts not subject to heat warpage and
distortion. Many new salt baths with lower melting points, lower viscosity, and lower operating
temperatures have been developed. With these baths, problems associated with heat warpage and
distortion have been significantly reduced. These new baths operate in a temperature range of 500
OF to 700 OF and they are capable of stripping organic coatings from aluminum without damage.
Typical process equipment for molten salt stripping consists of a salt bath &mace, a water
rinse tank,an acid tank, a second water rinse tank,and a sludge receiving station. All of these
tanks may be contained with-in a protective steel enclosure. There are entry and exit doors at each
end and operator viewing windows at each station. A slot down the center of the enclosure allows
for overhead hoist access. The work load is engaged by an overhead hoist, moved through the
entrance door of the unit, and lowered into the salt bath where the stripping process begins.
On the completion of stripping, the parts are raised from the bath, allowed to drain, and
then rinsed and cooled in the first rinse tank. The procedure for stripping aluminum parts will
usually include immersion in a dilute organic acid to neutralize any caustic residue remaining after
the first rinse. Reaction between organic coatings and molten salts creates a residue or sludge
consisting of paint pigments and fillers along with used or reacted salt. This residue has a higher
density than the salt, and settles to the bottom of the bath where it is periodically removed at the
sludge receiving station.
There are two potential disadvantages in using molten salt baths for stripping aluminum
components. First, when aluminum stampings are run through a salt bath at 600 OF, a degree of
metallurgical change takes place. This is primarily in the form of relieving stresses created in
forming the part. If the stripping time exceeds 60 seconds, parts may be softened or distorted
sufficiently to affect end use. Second, a potential problem may arise if salt becomes trapped or has
solidified in an area that allows only limited or no entry of rinse water. This salt can result in later
"bleed-out" and corrosion.
5.3.5 Aqueous Cleaners
Aqueous cleaners have received a great deal of attention since the demise of chlorinated
solvent cleaning. On first glance, water with some additives appears to be a benign solution which
does not move us too far from our comfort zones. After all we bathe in soapy water, so it is not
difficult to envision washing our parts in a similar solution. Aqueous or water-based cleaning
methods usually employ a simple hot water bath with some additives in combination with
mechanical or ultrasonic agitation. Aqueous cleaning is popular for removing oils and greases
70
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WHAT ARE M Y OPTIONS ?
frh metal furniture, fabricated products, and transportation equipment. Hot water washers (with
or without surfactants), can also be used in some heavy duty cleaning applications such as removal
t$ oil and grease from engine components.
Various studies have concluded that the cleaning capability of an aqueous system is
comparable to, or better than,an halogenated solvent system. Aqueous cleaning can remove
potentially damaging chloride residues in industrial soils that cannot be removed by vapor
degreasing. Aqueous cleaning is highly effective for removing particulate contamination. Many
users are switching to aqueous cleaners as a way of producing cleaner parts, not just to get out of
the use of solvents. In the automotive industry, testing of automotive transmissions in 100,000
mile tests showed that over 60 percent of the particulate contamination leading to breakdown was
introduced during the manufacturing process (Sprow, 1993). Production of cleaner parts should
translate into higher quality and more trouble-free products.
Due to the variety of cleaning operations that can be performed using aqueous cleaners,
equipment size, type, and configuration can vary widely. Typically, aqueous cleaning equipment
can be divided into three general categories: immersion cleaners including ultrasonic tanks, spray
washers that may include batch, conveyorized, and rotary designs, and steam cleaners with high
pressure spray lances. Conversion from solvents to aqueous cleaners will not in all cases require
total replacement of existing equipment. With cold cleaning tanks, a change in cleaning medium
and the addition of a tank heater may be adequate. Conversion of vapor degreasing units designed
for immersion service may be possible. Figure 5-1 presents a typical aqueous cleaning system.
FIGURE 5-1
A TYPICAL AQUEOUS CLEANING SYSTEM
Water
Make-up
Make-up
71
CHAPTER 5.0
*
Alkaline cleaning solutions are the most common form of aqueous chemistry. These
solutions may range in pH value from 8 to 14. Alkaline cleaning solutions are typically used at a
concentration of 2 to 4 ounces per gallon for spray cleaning and 6 to 12 ounces per gallon for soak
tanks. The operating temperature for a typical alkaline bath may range from 130 O F to 190 OF.
Some room temperature cleaning formulations are offered as a means to reduce the energy demand
associated with heating. These low temperature formulations also reduce evaporative water loss.
Alkaline chemistries commonly consist of various additives to improve performance. Such
additives commonly include sequestering agents, emulsifiers, surfactants, and corrosion inhibitors.
Because of their high pH, alkaline solutions may attack aluminum or other reactive metals. To
prevent attack, inhibitors such as silicates are added to the formulation. While reducing the
potential for metal etching or attack, the use of inhibitors can lead to difficulties in rinsing the
cleaner from the parts. Failure to rinse off all of the alkaline cleaner may lead to problems in the
painting or plating operations which follow. Depending on the extent of residue left on the parts,
these problems may show up immediately as rejects in the plant or may result in short-term part
failure when placed in the field.
Those that have experimented with aqueous cleaners have leamed that, while apparently
benign, this technology must be approached thoughtfblly . Water evaporates slowly, thereby
leaving cleaned metal parts wet and subject to rusting or staining. Some manufacturers of aqueous
cleaning systems recommend the use of a final rinse with a rust inhibitor to resolve the rusting
problem. As previously mentioned, these inhibitors may create a waste water treatment problem.
The use of a final hot rinse in ultra-pure water can also minimize the potential for rusting and
staining. This solution however, requires the inclusion of a demineralizer or deionization system
that also generates it own types of waste.
.
When aqueous cleaners become loaded with grease, the resulting mixture may be difficult
to dispose of. Due to high organic soil content (and who knows what else), spent aqueous cleaner
cannot be put into the drain unless it discharges to a waste water treatment facility that will accept
that particular type of waste. Some vendors claim that their cleaners will readily separate from the
soil and that the decanted cleaner can be dumped down the drain. The truth is that an acceptable
level of separation is highly dependent on a number of factors. Such factors include the type of
surfactants and additives used in the cleaning formulation, the way in which the cleaner is used and
handled, and the type of soils and contaminants being removed. Before discharging anything fiom
your facility, KNOW where it is going and SECURE approval for its discharge. When converting
from a solvent-based cleaning system, remember that the disposal of spent aqueous cleaner is a
new issue you must deal with and carefully exam to avoid getting yourself in trouble.
When aqueous cleaning can be accomplished without the use of surfactants, subsequent
separation of the oil and water becomes easier. A simple oil / water separator or coalescing filter
may be used to treat the resulting waste water since the oil and grease will not be emulsified.
Skimmer booms may also be installed inside the cleaning tank to remove free oil that separates and
72
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WHAT ARE MY OPTIONS ?
flbats on the surface of the bath.
Formation of free oil often occurs after periods of inactivity and
the bath has been allowed to cool. Recovered oils and greases may be disposed of in a waste he1
Mending program while the waste water may require pH adjustment and treatment. This treatment
may be performed on site or at a Publicly Owned Treatment Works ( P O W ) .
As might be expected, the overall energy consumption of aqueous cleaning is generally
higher than that of solvent cleaning. Various sources report that the relative levels of energy
consumption can range from 2 to 5 times higher for an aqueous cleaning system processing the
same workload as a vapor degreaser. While the relative use of energy weighs in favor of vapor
degreasing, this may only be true at the local or shop level. The inclusion of the energy used to
produce halogenated solvents and aqueous cleaners narrows the difference significantly. What you
pay for in energy costs, you save in raw material costs.
In addition to energy costs, labor costs are typically greater for aqueous cleaning than for
solvent cleaning. Aqueous solutions should be routinely tested and the tanks maintained at their
proper level. Since the build-up of alkaline salts on the equipment can lead to failure of automatic
flow control valves, many facilities elect to make manual additions to the tanks. Capital costs for
aqueous systems are typically higher since in addition to the cleaning tank,a well designed system
may require the purchase of two similarly sized rinse tanks, a drying oven, and a waste water
neutralization system. Of course, the inclusion of costs for purchasing and installing an air
emission control system for the continued use of a vapor degreaser would offset any major cost
disadvantage for the aqueous system.
Aqueous cleaning technology has become an accepted method for defluxing printed circuit
boards in the electronics industry. Water alone can be employed to remove water-soluble organic
acid flux and flux residue. Removal of conventional rosin-based flux and flux residue often
requires the addition of a saponifier or detergent to the bath. In many military applications, the use
of water with saponifier requires the permission of the Government Contracting Officer in charge.
Deionized and filtered water may be effectively used to remove water-soluble organic acid
flux. A three stage process is generally required: washing, rinsing, and drying. A small amount of
saponifier (typically monoethanolamine) is added to the water in the wash stage to improve
defluxing. The saponifier reacts with the removed oil, grease, and rosin to form a water-soluble
soap. The pH of the solution is generally in the range of 10.5 to 12. In the rinse stage, the most
effective method is to use a high pressure spray to ensure removal of the cleaner and any remaining
flux. Drying may be accomplished with a hot air knife.
A potential disadvantage of the water / water-soluble organic acid flux combination is that
a highly acidic wash may be required to avoid tin and lead hydroxide deposition on the boards. Tin
and lead hydroxide residues left on the boards can lead to insulation failure. When impurities are
not completely cleaned from the boards, they can lead to corrosion or allow electromigrationto
occur (Momson and Wolf, 1985).
73
CHAPTER 5.0
When using saponifiers or detergents to remove rosin flux, the same sequence of wash,
rinse, and dry is employed. In this case, the cleaning solution emulsifies the nonpolar soils and
saponifies the organic components (primarily abietic acid) of rosin flux. The soap produced in the
saponifLingreaction can carry over to the water rinse and create foaming problems. Antifoaming
agents may be employed in the rinse stage to prevent foaming. A hot air knife is used to remove
rinse water and dry the boards.
*.
As in the first method, the use of water can lead to leaching of tin and lead from the solder
which eventually may lead to the formation of deposition of insoluble tin and lead hydroxides on
the boards. The rosin flux may not be completely saponified and residues may be left on the board.
This residue may lead to subsequent insulation failure. A third difficulty is that alkaline soaps tend
to be difficult to rinse. Rinsing is not as much of a problem with the first option since organic acid
flux is water-soluble.
As mentioned earlier, disposal of effluent may be a barrier to the use of either water-based
system for board cleaning. The effluents released from the process may exceed local or federal
regulations for copper, lead, pH, or Biological Oxygen Demand. Another barrier to the use of
aqueous defluxing arises with the movement toward surface mount technology. Some users claim
that problems with water cleaning arise when the spacing between components and the board is
less than 10 mils. Recent inquiry among users by the authors indicates that some users are able to
achieve effective cleaning at stand-off heights as low as 1 to 2 mils. By specifying a minimum
stand-off height in their specifications, cleaning problems are avoided.
High pressure sprays can, to some extent, improve the ability of water to clean under
surface mounted devices. The high pressure jets of water must be used at low spray impingement
angles. The impingement angle for surface mounted assemblies can vary from 10 degrees to 40
degrees with an average of about 25. The water jets must impinge at a very low angle to the board
so that the water can penetrate under the components (Ellis, 1987). High pressure air knives
installed between the wash and rinse steps can also facilitate water cleaning (Keeler, 1987).
The Hughes Aircraft Electro-Optical Division in El Segundo California has been
instrumental in the development of the Hughes RADS technology. RADS stands for Reactive
Aqueous Defluxing System, an aqueous cleaning system capable of removing conventional RMA
flux and its residues. Installation and commissioning of the RADS system occurred during 1992
and it has been in production use since January 1993. The system was built by Westek and
consists of a spray cleaning section, a water spray rinsing section, and a hot air blowoff and drying
section. The system can clean down to a 2 mil stand-off height as confirmed by visual inspection.
Two 10 HP pumps were included in the packaged system so that the effect of operating
parameters such as spray pressure and spray head configuration could be studied and optimized.
Operator experience has shown that the pressure of the top sprays must be 5 to 10 pounds per
square inch higher than the bottom sprays so as to hold the boards down on the conveyor and
74
WHAT ARE M Y OPTIONS ?
pdvent bouncing. The use of wire baskets for holding the boards to the conveyor was considered
but rejected due to concern over shadow effects. The use of baskets might also retain water and
prevent adequate drying.
The cleaning solution used in the system was formulated by Hughes and is produced and
marketed by London Chemical under the tradename Ecosolve. The Ecosolve material is highly
alkaline and reportedly contains no volatile organic compounds. With normal usage, the dirty
Ecosolve defluxing solution is dumped from the system one a week, no attempt is made to recycle
it. Approximately 3 gallons per minute of rinse water is continuously discharged to the industrial
sewer. The spray rinse consists of three spray sections arranged in a counter-current flow
configuration to conserve water. An add-on unit which would allow for the reuse of the rinse water
is available from Westek.
In the field of paint stripping, alkaline-based strippers have been used for many years and
are common in industry. They typically consist of a I to 3 pounds per gallon hot caustic solution
held in an immersion dip tank. Generally, the alkaline strippers cannot remove all of the paint
pigments and a residue is left on the parts. Removal of this residue may be performed by
immersion rinsing followed by spraying the parts with high pressure water hoses on the shop floor.
Alkaline strippers can attack reactive metals such as aluminum but are safely used on steel.
In the case of oil-based paints or alkyds, stripping is effected by the saponification of the
fatty acid components in the paint. With cellulosics, stripping is due to the breakage of the ester
linkages. Alkaline strippers are also effective on gum vamishes and phenolics, but they are seldom
effective on epoxies. Additives such as sequestering agents, surfactants, and activators are
included in most stripper formulations to improve their effectiveness. The wastes resulting from
the use of alkaline strippers are often hazardous due to their high pH value. Paint sludges may also
be hazardous due to the presence of lead and chromium compounds in the paint.
Acidic strippers are less commonly used and they tend to attack more types of metal. They
should not be allowed to contact high-strength steel (Hans, 1980). These strippers work by
oxidizing or dehydrating the paint. Inhibitors must be used to prevent metal attack. Solvents such
as alcohols and glycol ethers are sometimes added to the formulation to make the strippers easier to
work with and more easily inhibited against metal attack (Sizelove, 1972). Nitric acid can be used
to strip off tough, hard coatings and it can effectively remove epoxy coatings. Heated phosphoric
acid can be used to strip aluminum and zinc-based parts. As with alkaline strippers, the wastes
generated by acidic strippers must be handled as hazardous.
5.4
Use Non-Halogenated Solvent Cleaning Technologies
As we move to the next class or type of cleaning technology, we re-emphasize that this
listing does not imply a strict hierarchy of environmental benefit. It does seem appropriate, as we
near the phase-out date for 1,l ,1 trichloroethane and CFC- 113 (the two most popular cleaning
75
CHAPTER 5.0
s&ents ever developed) to look at solvents which are not halogenated. While there are several
halogenated solvents in widespread use which do not contribute to global ozone depletion and are
ribt subject to the immediate phase-out (e.g, trichloroethylene, perchloroethylene, and methylene
chloride), these solvents carry their own negative attributes such as human toxicity, resistance to
biological degradation, and photochemical reactivity. Many users are seeking substitutes in
response to these problems and in response to voluntary phase-out programs by the USEPA.
While the technologies discussed in this section (Le., petroleum distillates, aliphatic
hydrocarbons, alcohols, terpenes, n-methyl-2-pyrollidone, and dibasic esters) may exhibit some of
the same problems as the halogenated solvents mentioned above ,they tend to be viewed by many
as being slightly higher on the ladder of environmental desirability. Some of these solvents have
been used for many years by industry and many of their potential short comings are known. Some
of these solvents have been used for years but only to a limited extent. For these, wide spread
usage has demanded the need for additional performance testing and determination of impacts to
the user and the environment. While our extent of knowledge increases ever year, it is doubtful we
will soon know, or ever know, all we need to make a completely safe decision. As such, one can
only make an informed decision and rely on common sense measures to protect his workers and the
environment. This applies equally for the use of highly toxic solvents on down to the use of water.
5.4.1
Petroleum Distillates
Before the introduction of non-flammable chlorinated solvents, petroleum distillates were
widely used to clean metal after machining or during the manufacturing process. With the advent
of non-flammable "safety" solvents, widespread production cleaning with flammable spirits began
to decline. Today, mineral spirits are mainly used in the transportation, printing, equipment
reconditioning, and metal working industries for maintenance cleaning activities.
The major use of petroleum distillates is in remote reservoir cold cleaning applications
employing mechanically agitated cleaning equipment. This equipment can be as simple as a 30 or
55 gallon drum-mounted parts washer with a recirculating pump. Equipment can be more complex
and consist of an immersion tank into which a platform raises and lowers the parts. This raising
and lowering action may be performed 130 times per minute or more and is an effective way of
pumping solvent through the parts (provided the parts break through the surface of the bath). To
control emissions, this mechanical agitation may be performed with the lid closed.
Petroleum distillates are often flammable, and often have flash points of less than 140 O F
as determined by the closed-cup test method. Therefore, upon disposal, spent distillates may be
listed as a RCRA hazardous waste due to ignitability. Petroleum distillates are classified as
volatile organic compounds or VOC's and may be defined as being photochemically reactive
depending on their olefinic (i.e., unsaturated or double bond) content. In areas where
photochemical smog is a problem and local air regulations are particularly stringent, such as
76
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WHAT ARE M Y OPTIONS 7
SdClthern California, the uncontrolled use of organic solvents may not be practical due to the
imposed emission caps. Regulations may also prohibit the use of specific solvent substitutes.
Companies offering rental of parts washers still rely on mineral spirits as an inexpensive,
effective, recyclable solvent medium. The Safety-Kleen Corporation (and similar, smaller sized
services), continues to supply spirits along with a parts washer and service contract on a monthly
rental basis. Customers include industries as diverse as automotive and vehicle repair, machine
shop operations, screw machine parts manufacturing, and tool and die production. An advantage
of the leasing arrangement is that the cost and bother of arranging for solvent waste pick-up and
recycling is included in the fee.
5.4.2
Aliphatic Hydrocarbons
Well known petroleum distillates such as mineral spirits, stoddard solvent, and kerosines
have been used as cleaners for many years. These solvents represent a given "cut" of the distilled
petroleum and do not represent any specific formulation. Due to the low flash point of these
materials, as well as their low and uncontrolled purity level, they do not lend themselves to
replacing CFC-113 and 1,1,1 trichloroethane used in critical cleaning applications. Distillates may
also contain fractions of listed solvents such as benzene, toluene, and other poly-aromatic
hydrocarbons which are very toxic. To prevent worker exposure and release to the environment of
these toxic compounds, extensive controls may be required. An alternative solution is to specifir
the use of a higher purity distillate product.
New, high purity, aliphatic (i.e., saturated or single bond) hydrocarbons are being offered
to take the place of lower quality distillates. These materials, with flash points ranging from 100 O
F to 300 O F or more, can be used for critical cleaning and degreasing applications. Long chain
aliphatic hydrocarbons tend to be highly immisible in water, making them attractive for cleaning
water-sensitive parts. They are effective in solubilizing a range of hydrocarbon-based soils, and
they have relatively low environmental impact because they are biodegradable. While all
hydrocarbon cleaners are classified as VOCs, saturated hydrocarbons are not defined as being
photochemically reactive.
The low vapor pressure and high boiling point of these solvents indicates that they are not
highly volatile. When used in a cold tank,they tend to evaporate slowly, there by minimizing VOC
emissions. This same quality means that these solvents do not exhibit very rapid dry-time
characteristics. If parts with blind holes and complex configurations are cleaned by immersion,
liquid drag-out can be significant.
Because of VOC and flammability concerns, pressure spraying of aliphatic hydrocarbons
without effective controls in place is not a recommended procedure. If spray impingement is the
desired application method, and the solvent will be used in quantity (e.g., more than 1 to 2 gallons
per day), some type of vapor recovery system must be implemented. Depending on the flash point
77
CHAPTER 5.0
oPEhe aliphatic hydrocarbon selected for spraying, inclusion of inert gas suppression and explosion
protection may be required as part of the enclosed vapor-capture system.
I
Perhaps the area of greatest use for these materials is as a hand wipe solvent. The hand
wipe application generally does not call for large volumes of material, so VOC emissions will be
limited and the potential for creating a flammable or explosive vapor minimized (this problem may
carry-over into the safe and proper handling of solvent contaminated wiping cloths). The
mechanical action of the wiping facilitates cleaning and spreading of the solvent so that it dries
rapidly. The absence of water in the cleaner means that parts of various substrates can be cleaned
without fear of water entrapment or metal oxidation and rusting.
When selecting an aliphatic hydrocarbon to test, pay careful attention to its flash point.
The selection of a 100 percent aliphatic with a flash point above 140 O F will insure that waste
solvent can be manifested as a non-hazardous waste oil (provided that the solvent does not pick-up
other hazardous components during cleaning such as PCBs or heavy metal fines). Hydrocarbons
with a flash point in the 140 O F to 165 O F range may exhibit moderately fast dry-times but they do
not dry as quickly as CFC-113or 1,1,1 trichloroethane.
To insure the fastest dry-time, the aliphatic hydrocarbon selected for use should exhibit a
narrow boiling range. The boiling range is dictated by the mix or blend of aliphatic hydrocarbons
present in the solvent. Recent studies indicate that the wider the boiling range, the slower the
solvent will dry. Actually, the slower dry time is the effect of different hydrocarbons contained in
the solvent evaporating at different rates. As the more volatile and low boiling components
evaporate, they leave behind the slower and higher boiling components. Specification of a narrow
boiling solvent insures that all of the hydrocarbons present are of similar behavior. The difference
in boiling ranges can also explain why solvents with the same flash point may dry at different rates.
Flash point is a hnction of volatility and composition. With the range of hydrocarbons on the
market today, this additional consideration may help with selection of a potential candidate.
5.4.3
Alcohols
Alcohols, such as methyl alcohol, ethyl alcohol, and isopropyl alcohol are very effective
for the removal of water-soluble, polar compounds and ionic residues. Alcohol offers the solvent
user two important characteristics, rapid dry time and the ability to absorb water and serve as an
effective d y n g method. Both of these characteristics could be attractive to CFC-113users
searching for viable substitutes. Indeed, use of pure alcohol is an acceptable alternative to CFC113 for the cleaning of critical components, especially if they contain ferrous metals.
The user must be prepared to negotiate the difficulties that accompany the use of most
alcohols. Not the least of these problems is flammability. Another disadvantage is their short
atmospheric lifetimes; they are classified as VOCs and are photochemically reactive. Flammable
solvents cannot be easily or safely used in heated and enclosed systems because of solvent vapor
78
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WHAT ARE M Y OPTIONS ?
bdfld-up and the risk of fire and explosion. In an effort to safely adopt alcohol cleaning, some
closed-loop systems are appearing on the market. This equipment is completely enclosed, is
ekplosion proof, and is fitted with fire protection devices. Some equipment uses nitrogen gas
purging for fire protection. Printed circuit board defluxing equipment for use with alcohols or
other non-halogenated flammable solvents is available in Europe. Two other approaches taken to
improve the safety of cleaning in heated alcohol include the use of highly-branched long-chain
alcohols with high flash points and the use of perfluorinated compounds to suppress flammability.
The use of perfluorinated compounds to suppress the flammability of alcohol vapors is
being adopted by some users, primarily in the aerospace industry for the cleaning of precision
components. Perfluorocarbons (PFCs) are nonflammable and two phase mixtures of PFC and
alcohol can be heated with minimized potential for flash fire danger. This allows one to degrease
parts in an alcohol vapor degreaser without the threat of fire or explosion (provided the proper
mixture of PFC and alcohol is monitored and maintained in the system). PFCs are very expensive
and possess very high global warming potentials. To control PFC loss, expensive control or
containment systems will be required.
The Kyzen Corporation in Nashville Tennessee has recently introduced a series of aqueous
cleaning formulations employing the use of a proprietary non-linear alcohol derived from biomass
material. The Kyzen alcohol has a very low vapor pressure and a flash point in excess of 180 OF.
The alcohol is biodegradable and completely water soluble. This eases the rinsing of parts such as
printed circuit boards following cleaning and defluxing. When formulated with the appropriate
activators and surfactants, the alcohol-based cleaning solution exhibits no flash point and can be
safely used in hot immersion and spray cleaning systems.
In the field of paint stripping, another non-linear alcohol (i.e., furfuryl alcohol) is
sometimes employed. Furfuryl alcohol-based formulations are blended by CLM Company, Nalco,
and Charles J. Haas. One source estimates that it is used to perform 20 to 30 percent of all booth
stripping in the automotive industry. Fu&ryl alcohol formulations have relatively low flash points
ranging from 105 to 150 OF, making them a potential fire hazard. Furfuryl alcohol-based
formulations generally contain 20 to 30 percent alcohol along with naphtha or petroleum solvents
and various other ingredients (ICF, 1988). The cost of these formulations ranges from $7.50 to
$10 per gallon. Compared to traditional methylene chloride-based strippers, the hrfuryl alcohol
formulation is slightly less effective and more stripper may be required in use. Care must be taken
with its use since it is a photochemically reactive solvent and the allowable worker exposure limit
(i.e., its Time Weighted Average (TWA) value) is 10 parts per million.
5.4.3
Terpenes
Terpenes have long been used on a limited scale as industrial solvents. In recent years,
they have been actively investigated as viable substitutes for CFC-113 and TCA. Terpenes are
naturally occurring hydrocarbons found in most essential oils and oleoresins of plants. Depending
79
CHAPTER 5.0
otftheir specific molecular structure, they may be classified as being monocyclic (d-limonene),
dicyclic (pinene), or acyclic (myrcene). Perhaps the most popular terpene used in industrial
applications is d-limonene, a biodegradable solvent derived from orange peels. Another commonly
used terpene is pinene, found in many household cleaners and derived from pine trees.
The terpene solvents may be formulated into three basic types of cleaner. The first type
uses the terpene in its pure form, with only a small amount of surfactant added to make the mixture
miscible in water. By adding a small amount of surfactant, the resulting solvent blend is more
effective at removing ionic contaminants and can be rinsed from the surface after use. The second
type of cleaner which has become popular uses only a small amount of terpene (usually less than
10 percent), in a water suspension. This type of cleaner contains any one of a number of
surfactants to enhance its cleaning ability and hold the terpene in suspension. In this application,
the terpene is little more than an enhancer to the standard aqueous cleaning formulation. The third
cleaner is a non-aqueous formulation employing terpene blended with an aliphatic hydrocarbon to
create a non-rinsable solvent cleaner.
A terpene / surfactant mixture (Bioact EC-7) was the first CFC-113 alternative to receive
a great deal of attention when it was introduced in 1987. This cleaner consists of 95 percent
d-limonene by weight and is specifically formulated to remove rosin flux from soldered printed
wiring assemblies. Rosin flux is composed primarily of abietic acid and other related substances
which are similar in structure to d-limonene. Test data indicates that d-limonene is one of the best
solvents for dissolving and removing abietic acid (Cabelka and Archer, 1987). Effective removal
of the ionic contaminants is achieved by the surfactant during subsequent rinsing of the boards.
The cleaner was shown to achieve lower ionic contaminant levels than the CFC-113 / methanol
control in subsequent performance testing (Hayes, 1990).
Equipment designed to safely deflux printed circuit boards with terpene formulations was
developed in the late 1980s and is commercially available (Attalla, 1990). Equipment typically
consists of either a small dishwasher unit that spins the boards while spraying the terpene cleaner
or an enclosed series of small dip tanks or spray stations. After cleaning and defluxing, the boards
are rinsed with deionized water and sent through a hot air drying system. To prevent fire, the
system may be blanketed with inert nitrogen or carbon dioxide gas.
To treat the terpene contaminated rinse water resulting from these processes, phase
separation followed by carbon adsorption or membrane filtration may be practiced. Depending on
the extent of terpene removal, the rinse water may be reused or be discharged to sewer. Any user
of a terpene-based product should note that terpenes exhibit very high levels of aquatic toxicity.
Great care must be taken to prevent their release to a stream, lake, or body of water. Luckily,
terpenes volatilize rapidly and are biodegradable which minimizes their impact in the event of
release. Discharges to an activated sludge treatment system or P O W is not a problem since the
biological systems can adapt to terpenes following a brief acclimation period.
80
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In the area of precision mechanical equipment rework and repair, the replacement of TCA
and CFC solvents with terpenes must be approached with care. Terpenes have found increased
usage in this application, but not without carefbl investigation and concern over the issue of
material compatibility. Rework and repair operations typically involve the cleaning of assembled
parts that consist of a wide variety of metals and elastomers. Terpenes are known to react with
some elastomeric materials and cause swelling. CFC-113 was a good solvent because it was
compatible with so many materials of construction. Some military branches have begun to place
restrictions on the use of terpenes and terpene-based cleaning formulations. Depending on the
outcome of ongoing tests, the Navy may opt for continued use of CFC-113 in certain applications.
C
Development of effective CFC-113 and TCA substitute solvents using blends of various
terpenes and aliphatic hydrocarbons has been very active and rapid in recent years. These solvents
are non-aqueous-based and as such, do not cause rusting or corrosion of ferrous metals. Solvent
blends typically contain 70 to 80 percent aliphatic hydrocarbon and 20 to 30 percent terpene.
Many blends possess flash points greater than 140 OF and depending on their purity, leave little or
no residue upon evaporation. Usage of high purity hydrocarbons and terpenes may result in a
blended product with high dielectric strength (greater than 30,000 volts or more). These dielectric
solvents have become very popular for cleaning electrical equipment, where the presence of any
water or surfactant in the cleaner would be unacceptable and unsafe.
Many major utilities have substituted, or are in the process of substituting, these blends for
TCA used in general cleaning applications. The Department of Defense has also shown interest in
these products and they are now available in the national stock system. The major drawback or
limitation keeping products of this type from completely replacing all chlorinated solvents used in
electrical maintenance applications is dry-time. The evaporation rate of terpene / hydrocarbon
blends is slower than chlorinated or low flash point petroleum solvents. By way of rough
comparison, if 1,1,1 trichloroethane evaporates in 1 minute, the same amount of a terpene blend
will evaporate in 10 minutes. The dry-time issue can be overcome by the use of drying cloths (for
accessible surfaces) or compressed air blow-off.
In order to meet the rigorous standards for use in electrical equipment maintenance and
perform as stated above, the terpene component of the solvent blend must be purified to remove the
contaminants normally present in the commercial grade product. Commercial grade terpenes may
contain fibers, sugars, and other naturally occurring contaminants that will vary by source. Much
of the citrus and pine terpenes used in janitorial-type water rinsable formulations is commercial
grade. While the presence of these contaminants in janitorial cleaners is not serious or harmfbl (the
cleaned surfaces will be subsequently rinsed off with water), they are unacceptable in precision
cleaning and electrical cleaning formulations. Terpene purification requires specialized equipment
since the terpenes are temperature sensitive and prone to auto-oxidation.
Similar terpene blends are also playing a new role in the field of non-destructive testing
(NDT), specifically dye penetrant testing and magnetic particle testing. A variety of chlorinated
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CHAPTER 5.0
sdvents are present in the products traditionally used in these tests. Such products include
precleaners, postcleaners, solvent removers, penetrants, and developers. Some of the chlorinated
solvents used in these formulated products are not global ozone depleters, but they are being
severely regulated due to their toxicity and other undesirable characteristics. Such solvents include
methylene chloride and perchloroethylene. While some manufacturers are promoting the use of
low flash point (Le., flammable) hydrocarbons such as mineral spirits, alcohols, hexane, and other
aromatics as alternatives, substitution with the terpene / hydrocarbon blends may be a safer and
equally effective choice.
The blend used in this application has a flash point near 150 OF, offering a good degree of
user safety. It evaporates completely and leaves no residue to interfere with penetrant application
and inspection. The terpene component provides exceptional solvency, enabling the user to quickly
and easily remove all types of penetrant, insuring low background readings after penetrant
removal. Several terpene / hydrocarbon blends have been extensively tested for NDT work by both
the private sector and the military. A group of these blends were recently added to the Qualified
Product List of Air Force MIL Spec 1-25135-D.
While the terpene / hydrocarbon blends are combustible, their average closed cup flash
point of 145 OF to 150 O F makes them considerably less dangerous to use than the flammable
solvents discussed earlier. Formulation of these blends to possess a flash point greater than 140 OF
also means that the waste solvent can be managed as a waste oil instead of a RCRA ignitable
waste. This assumes, of course, that the spent solvent has not been contaminated with a more
flammable material or solvent. Care should always be taken when handling solvent soaked rags
since the wicking action of the cloth may make them more susceptible to ignition. As with any
combustible material, proper storage and handling practices are essential.
Terpene / hydrocarbon blends are classified as being volatile organic compounds and their
use may be regulated by your local air quality authority. Terpene blends containing more than 5
percent terpene are also defined as being photochemically reactive. Terpenes are highly reactive
and as such, are considered by many to contribute to local smog formation. Some have countered
however that basing the potential for smog formation on reaction rate alone is not always correct.
Terpenes react rapidly in the atmosphere and there is some evidence that this reaction results in a
net consumption of ozone. The USEPA is reportedly aware of this issue but it is likely that many
years will pass before enough evidence is available and a decision can be made.
Straight terpene is a very effective cleaning agent, exhibiting excellent solvency
comparable to some halogenated solvents. In many applications, straight terpene might be
preferable over a blended product if it were not for two major limitations. The first is the very
pronounced odor of most terpenes, either citrus or pine depending on type. The odor is very strong
and some find it irritating and objectable. People who are sensitive to citrus-based products may
develop severe headaches when exposed to these odors. Contact dermititus has also been reported.
The second problem is flammability. Pure terpenes are rated as combustible liquids by the NFPA
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WHAT ARE MY OPTIONS ?
o#Wational Fire Protection Association since their flash points are much lower than 140 OF (the
flash point for d-limonene is 115 to 120 OF). Both problems are mitigated by blending with an
udorless and less flammable hydrocarbon.
Another limitation to the use of terpenes is that permissible exposure levels (PELS) in the
workplace have not been set by the U.S. Occupational Safety and Health Adrmnistration (OSHA).
Terpenes are known to be skin and eye irritants and must be handled properly. To prevent contact
dermatitis, proper protective gear such as gloves, safety glasses, and aprons should be wom as a
mini". By following some common sense measures, many users have been able to successfully
adopt terpene-based cleaners in their operations without incident.
5.4.5
N-Methyl-2-Pyrollidone
The solvent n-methyl-2-pyrollidone (NMP) is produced by two companies, the GAF
Chemicals Corporation (now called Intemational Specialty Products or ISP) and the BASF
Chemicals Corporation. NMP is a colorless liquid with a mild amine odor and slightly alkaline
pH. It is completely miscible in water and in most organic solvents including alcohols, ethers,
ketones, aromatics, and chlorinated hydrocarbons. It is commonly used in the pure state but can
also be blended with various surfactants and thickeners for special applications. NMP may be
used in both immersion and ultrasonic equipment.
In 1992, ISP qualified a NMP-based defluxer called MICROPURE CDF to the MIL-2000
specification, thereby opening the door to the micro-electronics field. NMP is widely used in the
industry for removal of photoresist. While NMP very effectively solubilizes flux and flux residues
at room temperature, it is quite aggressive on plastic. It must be used with care, lest it damage
components on the populated circuit boards. Many plastics, including polystyrene, ABS, polyvinyl
chloride, and polyesters are soluble in NMP. Assemblies containing these materials should be
tested for material compatibility. Because it is so aggressive, the solvent is proving effective as a
conformal coating remover for the re-work of coated boards.
The application of NMP in the field of parts cleaning and degreasing is comparatively new
and little data has been accumulated. It has been used to remove oil and carbon deposits from
engine parts and ink from printing equipment. Many industrial oils only become miscible in NMP
at temperatures above 63 to 68 "C. This means that if oil-loaded NMP is allowed to cool in a
settling tank,the oils will separate and the NMP can be recycled for additional use.
Previously, the largest use of NMP was in paint strippers intended to replace conventional
methylene chloride-based strippers. These relatively new products have found use in the areas of
paint application equipment clean-up and the consumer paint stripping market. They have not
found wide-spread use in the area of industrial immersion stripping because they are less effective
at removing fully cured, high performance paints.
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CHAPTER 5.0
*
Compared to methylene chloride, NMP is slower acting but is also less volatile. The low
volatility results in lower levels of air emissions and allows more of the stripper to remain on the
sbbstrate and work for a longer period of time. Industry sources claim that 1 gallon of stripper
containing 70 to 90 percent methylene chloride can be replaced with half a gallon of stripper
containing 25 to 40 percent NMP. Therefore, four to six times as much methylene chloride-based
stripper must be used to strip the same amount of surface area as an NMP-based stripper.
On the down side, NMP-based formulations take much longer to work when stripping
cured paint. In tests conducted by one manufacturer, it took 24 minutes and three applications of a
methylene chloride-based stripper to remove four coats of alkyd paint. It took 66 minutes and two
applications of NMP-based stripper to remove the same four coats of paint. Stripping times are
equivalent for removal of uncured paint.
Another disadvantage is cost. NMP-based formulations are about five times the cost of a
conventional methylene chloride-based formulation, about $30 per gallon. Even when the
differences in the volume of paint stripper required to strip a given area are taken into account, the
NMP formula is more expensive. While NMP can be recycled, very few recyclers presently have
this capability. Vacuum distillation equipment is required and the recovered NMP would still need
to be formulated back into a viable product.
Pure NMP has a closed cup flash point of 190 O F and is considered to be combustible.
Aqueous-based formulations, depending on NMP content, may not be combustible. NMP is
biodegradable and photochemically reactive but its low vapor pressure minimizes atmospheric
emissions. The most serious drawback to widespread usage of NMP is its linkage to harmhl
reproductive effects to workers and consumers using paint strippers and similar products. Animal
testing has shown NMP to demonstrate reproductive toxicity effects at high exposure levels. Given
the low volatility of NMP, the most likely route of exposure is through the skin. The risk to users
of NMP may be greatly reduced by wearing gloves, but data is insufficient as yet. According to
ISP, NMP is not carcinogenic, mutagenic, or teratogenic. Both manufacturers have set the TLV
for worker exposure at 100 ppm.
5.4.6
Dibasic Esters
The dibasic esters (DBE) are a mixture of methyl esters of adipic, glutaric, and succinic
acid produced by DuPont. DBE is typically composed of 17 percent dimethyl adipate, 66 percent
dimethyl glutarate, and 17 percent dimethyl succinate. It is readily soluble in alcohol, ketone,
ether, and most other hydrocarbons, but only slightly soluble in water and higher paraffinic
hydrocarbons. DBE has a flash point of 212 O F and is photochemically reactive. The major use of
DBE today is in paint stripping formulations, often blended with NMP to improve effectiveness.
Unlike methylene chloride which swells the paint and lifts it from the surface by bubbling,
DBE strippers only soften the paint and do not cause it to lift or bubble. For spray booth cleaning,
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WHAT ARE M Y OPTIONS ?
or& recommended formulation consists of 40 percent by weight DBE, 15 percent NMP, 35 to 38
percent aromatic 150 solvent, 2 percent monoethanolamine, 4 percent potassium oleate, and 1 to 4
@rcent thickener (Lucas, 1988). The mixture of DBE and NMP allows the stripper to remove a
wider variety of paints than either solvent could alone. Typical immersion stripper formulations
include 100 percent DBE; 60 percent DBE and 40 percent NMP; and 60 percent DBE and 40
percent ethyl 3ethoxypropionate or EEP. As with most paint strippers, these formulations give
better results with increased temperature; 95 O F to 100 O F appears to be optimum. Line purging
and gun cleaning can best be accomplished with 100 percent DBE. Compared to methylene
chloride-based formulations, DBE formulations take two to three times longer to perform an
equivalent amount of stripping (ICF, 1988).
Like NMP, DBE is not exempt from air emission regulations regarding VOCs. Because it
is not especially volatile, however, air emissions are likely to be low and its low volatility allows
more of it to remain on the surface rather than evaporate. This results in less stripper being
required for a particular operation. DBE is also biodegradable and like NMP, can be recycled in a
vacuum distillation system. DBE has not been tested for chronic toxicity.
A product containing DBE, called Safest Stripper from 3M Corporation, has recently been
put on the market for home and consumer use on wood. It is a water-based material with the
consistency of a paste. Because Safest Stripper is water-based, some raising of the wood grain
may occur during stripping. To restore a smooth surface, the wood must be sanded. Clean-up of
the work area and stripping tools can be accomplished by water rinsing.
As mentioned, an advantage of DBE-based strippers over conventional strippers is that
DBE is less volatile. Therefore, the stripper retains its effectiveness for a longer period of time.
Safest Stripper maintains its paste form for at least 10 hours. The major disadvantage to DBEbased strippers is that they work more slowly. Depending on the thickness of paint being removed,
several applications of stripper may be required. This would increase the amount of stripper used
and increase stripping costs. The price for DBE-based strippers and methylene chloride-based
strippers are roughly equivalent on a per gallon basis.
5.4.7
Glycol Ethers
Many different types of glycol ethers and acetates are in use. Commonly encountered
types include ethylene glycol ethers (i.e., Cellosolves), diethylene glycol ethers (Le., Carbitols),
ethylene glycol ether acetates, diethylene glycol ether acetates, propylene glycol ethers, and
dipropylene glycol ethers. The two most widely used E-series (ethyl) glycol ethers in cleaning
formulations are ethylene glycol butyl ether (EB) and diethylene glycol butyl ether (DB). Glycol
ethers are also used in the semi-conductor industry for the stripping of photoresist materials and
are found in many water-based paints. While long considered to be relatively safe, the toxicity of
glycol ethers and acetates has recently been called in to question.
85
CHAPTER 5.0
*
Recent toxicity testing indicates that exposure to several of the glycol ethers can result in
red blood cell damage. A study sponsored by the Semiconductor Industry Association (SIA)also
W e d female assembly line worker exposure to diethylene glycol dimethyl ether and ethylene
glycol monethyl ether acetate to an increased rate of miscamages. Miscamage rates were found to
be 20 to 40 percent higher for chip fabrication workers using glycol ethers than for other workers
in the same companies.
___
As such, the E-series of glycol ethers are subject to heavy regulation. New permissible
exposure levels (PELS)are being proposed that would reduce the level for many of the E-series
glycol ethers to less than 0.5 parts per million. Five E-series glycol ethers (Le., diethylene glycol
monobutyl ether, diethylene glycol monobutyl ether acetate, triethylene glycol monomethyl ether,
triethylene glycol monoethyl ether, and triethylene glycol monobutyl ether) have been listed as
hazardous air pollutants (HAPS)under the 1990 Clean Air Act (CAA) Amendments.
Toxicity testing has also shown that the degree of toxicity for most glycol ethers can be
related to the size of the molecule. As the series progresses from ethylene to propylene, the toxicity
decreases markedly. P-series (propyl) glycol ethers reportedly offer performance that is
comparable to E-series products with lower toxicity and less odor. Propylene glycol ethers (PGE)
have been tested on removing fluxes from wave and reflow soldering operations. Propylene glycol
methyl ether (PM) and propylene glycol methyl ether acetate (PMA) have been shown to be
effective substitutes for methylene chloride used in paint stripping applications. The P-series
glycol ethers are also being promoted as a safer solvent for use in water-based paints.
Another substitute for E-series glycol ethers being investigated by industry is the use of
ethyl lactate, a lactate ester. Ethyl lactate is currently being tested as a possible substitute for the
glycol ethers used in the semiconductor industry. Testing has shown that ethyl lactate is an
excellent solvent for removing silicone oils and greases, lithium grease, finger prints, layout inks,
tapping oils, and machining coolants. Ethyl lactate will affect some polymers but most metals are
unaffected by short-term exposure.
5.4.8
Semi-Aqueous Cleaners
Semi-aqueous cleaners are viable substitutes for halogenated solvent in many maintenance
type operations. Approximately 15 percent by volume of all cleaning being performed in the early
1980s was done so by semi-aqueous cleaners (USEPA, 1983). With the phase-out of CFC-113
and TCA, and the increased restrictions placed on the use of TCE and PERC, these cleaners have
seen increased usage in recent years.
Semi-aqueous cleaning is commonly employed for the cleaning and rust protecting of
welded auto wheels prior to shipment, of engine blocks prior to assembly, of steel sheet metal, and
of bearings in process and before assembly. Semi-aqueous cleaners consist of an organic solvent
dispersed as fine droplets with the aid of emulsifying agents in an aqueous cleaner. Typical
86
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WHAT ARE M Y OPTIONS ?
s&ents include mineral spirits or a similar petroleum fraction sometimes blended with an aromatic
or naphthenic solvent to improve solvency. Terpenes such as d-limonene are often employed.
Semi-aqueous cleaners possess neutral to slightly alkaline pH values so that they are less
corrosive to metals than straight alkaline cleaners. They are primarily used for the removal of
pigmented drawing compounds, lubricants, cutting fluids, heavy oily soils, and metal chips.
Because these cleaners tend to leave a slight oil film on the cleaned parts, they are useful for
providing a limited degree of short-term rust protection to ferrous metals. To provide a highly
clean part, semi-aqueous cleaners are often used as a pre-cleaner followed by alkaline cleaning.
The most common methods of semi-aqueous cleaning are immersion and spray. Cold
cleaning equipment designed for halogenated solvents can be modified for use with semi-aqueous
cleaners with-out too much difficulty. Vapor degreasing equipment can seldom be modified and
the results are often sub-optimal. Disposal of spent semi-aqueous cleaners can be a problem.
Methods to break the semi-aqueous emulsion include heating, distillation, aeration, chemical
coagulation, and chlorination (Mauzerall, 1987). Aeration may result in undue VOC emissions
which could violate local air quality regulation. Chlorination is a process not many facilities would
want to undertake due to worker safety concems over the handling of chlorine. The use of ceramic
membrane filtration units to remove emulsified solvents from water and to break oil-in-water
emulsions holds much promise.
5.5
Use of Interim Technologies
The three hydrochlorofluorocarbonsHCFC-123, HCFC-14 1b, and HCFC-225 have ozone
depletion potentials of 0.02,O. 11, and 0.03 respectively and were at one time viewed as likely
replacement candidates for CFC-113 and TCA. Given the amended phase-out schedules imposed
by the Fourth Montreal Protocol meeting held in Copenhagen, usage of HCFCs is likely to be
limited. Production levels will be frozen in 1996 based on 3.1 percent of CFC consumption plus
HCFC consumption that occurred in 1989. This level will be reduced by 35 percent by the year
2004,65 percent by 2010,90 percent by 2020, and complete phase-out by 2030.
In addition to the phase-out, the HCFCs have several drawbacks for use in parts cleaning
applications. HCFC-123 has been found to cause tumors in male rats and DuPont plans to sell the
solvent only to pre-approved users. Users must demonstrate that they are capable of containing the
solvent and not allow a concentration greater than 10 ppm to exist in the work place. While these
conditions can be readily met when the material is used in a closed system as a refrigerant, it is
doubtful that many will be able to use it as a parts cleaning solvent. Its use will require the
purchase of emission tight equipment.
Usage of HCFC- 141byanother proposed candidate, will also require the use of emission
tight equipment. DuPont has developed a new open-top vapor degreaser employing their Triple
Guard condenser system to control vapor emissions. The degreaser has a freeboard ratio of 2.0
87
CHAPTER 5.0
a d a dual set of refrigerated cooling coils located above the primary condenser. The dual coils
create a very cold and dry blanket of air that effectively minimizes diffusional losses. While the
level of control is high compared to conventional open-top systems, the control efficiency is most
likely less than that obtainable by hlly enclosed "zero emission" style degreasers.
In addition to its usage in vapor degreasing, some HCFC-14lb is being sold in aerosol
spray form for use as an electrical contact cleaner. When used as a substitute for CFC-113 based
aerosol products, it use represents a reduction in ozone depletion impacts (HCFC-14lb has an
ODP of 0.1 versus 1.1 for CFC-113). However, many of the electrical contact cleaners currently
in use are based on TCA. Since TCA has an ozone depletion potential value of 0.1, substitution
with HCFC-14lb is of questionable benefit. It is also more toxic.
Development of new halogenated solvents, some with no ozone depletion potential, is
continuing at a rapid pace. Several hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) have
seen increased production and use in recent years. While PFCs are relatively poor solvents when it
comes to removing common oils, they are effective at removing perfluorinated greases and heavy
flotation oils from precision equipment. PFCs tend to be very chemically stable and inert. They
are non-flammable and are used in alcohol vapor degreasers to suppress alcohol ignition.
Because PFCs are stable and inert, they are slow to decompose and possess very long
atmospheric lifetimes. They are strong absorbers of infrared (IR) radiation and hence have a very
high global warming potential. While PFCs tend to be low in toxicity and are not ozone depleters,
their high global warming potential, their relative ineffectivenessat removing most common soils,
and their very high cost will serve to limit their use.
5.6
Emerging and Experimental Technologies
The following sections discuss emerging or experimental cleaning technologies. Several
are at an advanced state of development and they have been readied for introduction into the
marketplace. These technologies present exciting opportunities for providing highly clean parts
while eliminating the generation of hazardous waste. Unfortunately, their initially high purchase
costs as compared to conventional cleaning technologies may limit their rapid acceptance and widespread use.
5.6.1
Supercritical Carbon Dioxide
Supercritical carbon dioxide cleaning is a new technology which was primarily developed
in the food extraction industry. The technology utilizes carbon dioxide gas in its liquid or
supercritical state (depending on system pressure) to perform cleaning. The solvency power of
supercritical and liquid carbon dioxide, as well as its low surface tension and low viscosity suggest
that it can perform as a highly effective solvent and provide a high level of cleaning. Supercritical
carbon dioxide is especially attractive for critical cleaning and precision cleaning applications.
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WHAT ARE MY OPTIONS 7
Two companies, Hughes Aircraft Company and the Phasex Corporation, have been
instrumental in developing competing systems for the commercial market. The Hughes system,
known as Superscrub and marketed by EnviroPro Technologies in Erie Pennsylvania, is a one-step
cleaning process that allows for continuous on-line monitoring of contaminant removal. The
technology allows for a consistent level of cleaning and employs no cleaning chemicals that can
attack and corrode metal parts. The volume of waste produced is minimal since only the removed
contaminants require disposal.
k
The cleaning process begins by placing parts inside a pressure vessel which is then sealed
automatically. Next, the C02 gas is introduced into the vessel and its temperature and pressure
raised until it enters the supercritical state. The supercritical gas is then circulated through an
extraction vessel for the recovery of removed contaminants and returned to the pressure vessel for
additional use. A basic system consists of a compressor for moving the gas through the system, a
heat exchanger for heating the gas, an extraction (i.e., pressure) vessel for holding the parts and
containing the supercritical gas, a pressure control valve, a heat exchanger for cooling the gas, and
a separation vessel for recovering the removed contaminants from the gas. Process temperatures
may range from 35 to 65 "C and pressures may vary from 2,000 to 4000 pounds per square inch.
On the down-side, the technology is expensive due to the need for special high-strength
steels used to construct the high pressure chamber. The high process pressures involved have also
been known to cause crushing of hermetically sealed devices. Hence, supercritical cleaning is not
suitable for defluxing assembled printed wiring boards or other devices incapable of withstanding
high external pressures.
5.6.2
Carbon Dioxide Pellets and Snow Blasting
Several firms such as Dell Crane Cryogenics, Alpheus Cleaning Technologies, and
Cold-Jet are currently marketing carbon dioxide pellet blasting systems for paint stripping and
cleaning applications. This technique uses a high-velocity stream of carbon dioxide pellets (Le.,
dry ice) to clean or strip a surface. Upon impact, the abrasive pellets remove the coating or
contaminant and then sublime, returning to their gaseous state. By adjusting the pellet parameters
such as size, hardness, velocity, and quantity, it is possible to strip and clean a wide variety of
materials. Carbon dioxide pellet blasting is particularly usefbl for the cleaning of sensitive
equipment that may require masking, covering, or disassembly to prevent damage from the use of
conventional abrasives.
The use of carbon dioxide pellets to remove paint has several environmental advantages in
that the stripping media is relatively safe, the only waste produced is the stripped paint, and the
carbon dioxide used is mainly recovered from waste gas. Hence, the emissions of carbon dioxide
gas that occur do not result in a net increase of global warming gases. The pellets are also
relatively soft and do not scratch the metals being stripped. This may be an advantage or
disadvantage depending on the given application.
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CHAPTER 5.0
*
On the negative side however, system costs are very high with pelletizer systems typically
costing more than $100,000. This does not include the cost for a liquid carbon dioxide storage
tM< and a compressor capable of delivering oil-free dry air (-40 O F dew point minimum). The use
of dry air is important so as to prevent ice formation or moisture condensation which can lead to
flash rusting of steel surfaces.
Test work conducted by the McDonnell Douglas Corporation in St. Louis has shown that
the process also suffers from slow stripping rates and that it can cause damage to aircraft skins and
composite structures. Development and optimization work conducted by the military has shown
that stripping rates can be increased substantially by using liquid nitrogen to cool the air used for
conveying the pellets through the nozzle. Their findings were that slow stripping rates were the
effect of pellets subliming before they exited the nozzle. Maintaining a colder air temperature
insures a higher rate of pellet delivery to the surface. McDonnell Douglas is no longer considering
the technology for paint removal but is investigating its use as a cleaning method.
Alpheus Cleaning Technologies has also investigated the use of low pressure carbon
dioxide pellets for stripping photoresist from printed circuit boards. Test work indicated that the
use of high pressures resulted in some damage to the board. In addition, static charge build-up was
observed which could lead to damage of static-sensitive parts. By reducing the blast pressure and
using a snow rather than pellets, defluxing of the boards was achieved, but with mixed results.
A number of other firms have investigated the use of carbon dioxide snow to remove
particulate contaminants from silicon wafer surfaces (Hoenig, 1985). In this process, liquid carbon
dioxide from a cylinder is fed into a siphon tube and flashed to form 'how." The snow knocks the
particulate contamination free from the surface of the wafer and then sublimes. The cost for a
siphon tube ''snow gun" was reported to be approximately $400 (Hoenig, undated). Several
aerospace and electronics firms have also experimented with this method.
5.6.3
Ultraviolet Light and Ozone
Researchers have been examining the use of ultraviolet (UV) light and ozone for removing
organic contaminates from hard surfaces for many years. The method relies on the combination of
UV light from a low pressure mercury lamp and ozone to oxidize hydrocarbons to carbon dioxide
and water. Two wavelengths of W energy, 185 nanometers (nm) and 254 nm, are used in the
process. Oxygen absorbs the 185 nm energy and is converted to ozone. The 254 nm energy is
absorbed by the organic contaminants which increases their molecular activity and makes them
more reactive with the ozone.
The process usually takes place in a sealed chamber which shields the operator from W
light and ozone exposure. The cleaning process is line of sight and is best suited for simple, flat
surfaces such as semiconductor wafers. Exposure times are usually 5 to 10 minutes, depending on
90
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WHAT ARE M Y OPTIONS ?
chtamination thickness. The cleaning rate is about 5 to 10 Angstroms per minute. One source
recommends that contaminant film thickness should not exceed 100 Angstroms.
'.
I
The process is intended for removing trace amounts of organic contaminants, it is not
applicable to particle removal. Inorganic materials such as oxides and salts are not removed.
Another disadvantage of the method is that it may be corrosive to some metals and may attack
some plastic materials. Copper is readily oxidized when exposed to UV / ozone. Exposed alumina
will turn yellow although the discoloration can be removed by heating the part to 150 to 170 "C. If
not conducted in a sealed chamber, then workers would be required to wear goggles to protect their
eyes from U V exposure. The issue of ozone exposure would also need to be addressed. Given
these limitations and disadvantages, it is unlikely that this option will see wide-spread use.
5.6.4
Laser Cleaning and Stripping
Laser cleaning has been practiced for some years in the restoration and preservation of
historical artifacts. The advantage of the laser technique is that by tuning the frequency of the
laser, specific organic contaminants can be effectively removed or bumedsff while minimizing
damage to the substrate. A disadvantage of this technique is that the characteristics of both the
contaminant and substrate must be known so that the optimal absorption frequency can be chosen.
This technique is still in the early research stage.
The use of lasers for ablative material removal and paint stripping has been under
investigation by the military for several years. Paint stripping and removal is believed to be due to
the breaking of the chemical bonds in the paint resin. This causes an instantaneous increase in the
volume of the resin, which then causes the inorganic solids to be blown away from the surface
(Allison and Rudness, 1987). An advantage of the laser system is that a specific adsorption
frequency can be selected to maximize paint removal and minimize substrate damage.
Research into this process by the U.S. Air Force has involved the use of a pulsed carbon
dioxide laser for paint removal from aircraft (Lovoi, 1989). Laser pulsing is controlled by a
computerized system that monitors color variation of the stripped surface. The technique has been
successfully applied to a variety of coatings (polyurethane, epoxy primer, chemical agent
resistance coatings, and polysulfide sealant) on a range of substrates (anodized aluminum, graphite
epoxy composite, and glass reinforced plastic). As the coating material is removed, it is vacuumed
up in a collection system and sent to a two stage waste processor. The waste processor separates
the waste into particulate material and vapors. The particulates are filtered-out and placed in a
waste receptacle for disposal. The vapors are controlled by a thermal oxidizer.
The U.S. Navy has also conducted pilot-scale testing of a pulsed carbon dioxide system.
Test data indicates that a single pulse can remove 1 cubic centimeter of paint at a thickness of 1
mil, that the system can be adjusted to remove one coat at a time, that the typical rise in substrate
temperature is no greater than 3 OF, and that the removed paint particles average 3 microns in size.
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CHAPTER 5.0
Tlk pilot apparatus used a system of optical mirrors to automatically reposition the laser after each
pulse. The hll-size prototype uses a prism system to guide the 30-foot long robotic arm over the
surface of the aircraft (Los, 1991).
In the electronics industry, IBM has been investigating the use of the laser ablation process
for removal of particles from semiconductorwafers. The wafers are sprayed with a thin film of
liquid and a laser is used to rapidly heat and volatilize the liquid. The rapid conversion of the
liquid film into a vapor lifts the particles off of the wafer where they can be vacuumed away.
Tested liquids included water, methanol, ethanol, and 2-propanol with the best results derived from
the use of a 10 percent alcohol in water solution. The water provides a high transient pressure
wave due to superheating while the alcohol aids in wetting. Photographic records of the process
can best be described as a miniature steam explosion occurring on the surface of the wafer.
5.6.5
High Intensity Light
High intensity light stripping (sometimes referred to as flash lamp stripping) is similar to
laser stripping and is also being investigated by the military. This system utilizes a tubular quartz
flash lamp filled with xenon gas at low pressure. A pulse of light is absorbed by the surface
material, which may then sublime, pyrolyze, or chemically dissociate. A shock wave is caused by
the reaction at the surface and a loud report occurs with each pulse of the flash lamp (Surfprep,
undated). The residue left on the stripped surface is a fine, black dust that can be easily wiped
away. Because of the presence of heavy metals in the paint, this dust may be listed as hazardous.
Laboratory investigation of the technique was performed at McClellan Air Force Base
using a 9-inch xenon arc flash lamp. Tests were conducted on an F-111 aircraft wing with an
epoxy primer and an acrylic top-coat and on composites of graphite epoxy with a fiberglass outer
layer coated with an epoxy primer and a polyurethane top-coat. The flash lamp was able to
selectively strip 1 mil of paint at a time without damaging the substrate.
The group concluded that the flash lamp has potential for field use. One problem that
remains to be investigated is how the system can be used to strip coating from comers and other
complex geometry. One solution would involve the use of a mobile arm fitted with quick
disconnect adapters that could handle flash lamps of various shapes. The Base anticipates a 5-year
savings of $1,660,000 from use of the flash lamp compared to use of chemical-based strippers.
Current research involves the use of flash lamps to strip paint combined with carbon dioxide pellet
blasting to remove the fine dust created.
92
-
(r
6.0 IMPROVING PROCESS EFFICIENCY
Maximum process efficiency is defined as achieving the required degree of cleanliness
while consuming the least amount of cleaning media. This section investigates ways to minimize
the use of cleaning materials for a given level of cleaning performance. The methods discussed
either involve modification and improvement of the equipment being used or changes in material
handling and equipment operating procedures.
?
6.1
Good Operating Practices
While much has been said and written about good operating practices, they are still the
most cost-effective but under used methods for improving efficiency. The enforcement of good
operating practices can result in reduced solvent use, reduced emissions, improved cleaning
efficiency, and a safer working environment. Implementation can often be achieved at little or no
cost. Various methods include defining worker responsibilities and providing training, following
proper start-up, shut down, maintenance, and repair procedures, locating equipment away from
areas where it will be prone to upsets, and segregation of the wastes produced so as to promote the
potential for recycling. Detailed information regarding these methods as they apply to vapor
degreasing can be obtained from most halogenated solvent suppliers and from many local air
quality or pollution control agencies. Many of these methods must be practiced by law.
6.1.1
Part Drainage and Improved Racking
Drag-out, the cleaning solution that remains on parts as they are pulled out of the bath, is
one of the major reasons for material loss. High levels of drag-out represent an expensive loss of
cleaner. Solvent drag-out represents a potential air emission source that may require control.
Since the presence of cleaning chemicals on the part may interfere with subsequent processing
operations, removal of drag-out by rinsing is often required. When all is said and done, the best
place for the cleaner to be is in its own tank where it belongs.
Unfortunately, the complete elimination of drag-out is not possible. The physical shape of
some parts will catch and trap fluids that can only be removed by rinsing with another fluid,
typically water. This is common when attempting to clean bent tubing or components with narrow
passages. Specific cures may be possible, but what works for one part may not work on others.
Facilities engaged in maintenance cleaning, where a wide variety of parts must be handled, are
faced with an ever changing challenge. Hence, the search for ways to reduce drag-out should be
viewed as an attempt to achieve the optimum answer as opposed to the absolute best answer.
To find ways to reduce drag-out, it is often helpfid to understand how drag-out occurs.
Drag-out may be viewed as two sequential processes involving liquid removal and drainage. The
thickness of a liquid film that clings to a flat vertical surface as it is removed from a bath is mainly
a knction of the liquids inertia or resistance to flow (i.e., viscosity) and the speed of removal. The
greater its viscosity andor the more rapid the speed of withdrawal, the greater the amount of liquid
93
CHAPTER 6.0
m e d - o u t on the part will be. To illustrate the effect of liquid viscosity on drag-out, data for
several liquids are presented below (Betz, 1963).
5
TABLE 6-1
EFFECT OF LIQUID VISCOSITY ON DRAG-OUT
Liquid
Water
Kerosene
Dye Penetrant
Ethylene Glycol
Neutral Oil
SAE 10-W Oil
SAE 40-W Oil
Viscosity
Drag-out
(Centistokes @ 100 OF)
(Gallons/1000 ft2)
0.50
1.45
5 .oo
9.38
22.82
50.3
171.2
0.266
0.186
0.295
0.630
0.478
0.827
1S O 5
As shown, it is obvious that the relationship between viscosity and drag-out is not exact.
The amount of water lost by drag-out is much greater than one would expect based on viscosity
alone. However, for a given fluid or family of fluids, reduced viscosity should lead to reduced
drag-out losses. Common ways of reducing the viscosity of a cleaning solution are by using a less
concentrated solution or by operating the solution bath at a higher temperature. By increasing the
temperature of a water bath from 100 to 120 OF, an 18 percent reduction in viscosity and a 9
percent reduction in drag-out can be achieved. With another 20 O F increase, viscosity will decrease
an additional 16 percent and drag-out will decrease an additional 8 percent. Roughly speaking,
increasing solution temperature by 2 O F will result in a 1 percent reduction in drag-out.
In addition to viscosity, another major influence is withdrawal speed. Parts removed
quickly from a process bath will have much more liquid clingage than parts removed slowly.
Equations have been proposed for the modeling of withdrawal losses (e.g., Tallmadge and
Gutfinger, 1967), and the one developed by Kushner (1 95 1) is presented below. While it may not
be as accurate or robust as others, it can be used to explain many observations made in the field.
The equation relates the volume of liquid removed to three part parameters (area, vertical length,
and speed of withdrawal) and two liquid parameters (viscosity and density). The equation is:
V = 0.02 x A x (1 x p / t x P ) ” ~
where:
94
V = Volume of liquid, cm3
A = Areaofpiece, cm2
1 = Vertical length, cm
p = Viscosity of liquid, poise
t = Time of withdrawal, sec
p = Density of liquid
IMPROVING PROCESS EFFICIENCY
The major points to note are that for a given fluid and work piece, withdrawal losses are
mainly a function of fluid viscosity (which is a function of concentration and temperature) and
withdrawal speed. By decreasing withdrawal speed from 1 second to 10 seconds, a 68 percent
decrease in withdrawal losses can be achieved. Increased withdrawal time may be accomplished
by reprogramming conveyorized systems or by regearing hoists.
f
Manual operations are most difficult to control. The last thing an operator wants to do is
to remove a 20 pound part slowly from a bath of liquid. Not only is this uncomfortable, it places a
tremendous strain on the operator. This is where the use of an overhead hoist is essential. In
facilities handling small parts, slowing down the manual speed of removal may not be a problem
for the operators. However, the success of this method is dependent on repeated training of
operators and approval by managers. Contrary to common belief, training of operators to slow
down does no good if managers want to maintain a "cheaper, faster" mode of operation.
Liquid drainage is the next part of the process that determines overall loses due to dragout. All of the previously mentioned factors apply including the surface tension of the liquid.
Surface tension may cause liquids to be retained within crevices and small openings, hence
increasing drag-out. To overcome the effect of surface tension, wetting agents may be added to the
cleaner and rinse water. Part configuration is also important in determining the extent of liquid
withdrawal and subsequent drainage. The effect of part configuration and drainage is illustrated in
the table below (Pinkerton and Graham,1984).
TABLE 6-2
EFFECT OF PART CONFIGURATION AND DRAINAGE ON DRAG-OUT
Parts
Vertical, Well Drained
Vertical, Poorly Drained
Vertical, Very Poorly Drained
Horizontal, Well Drained
Horizontal, Very Poorly Drained
Cup-Shaped7Very Poorly Drained
Drag-out Loss
(Gallons/IO00 ft2)
0.4
2.0
4.0
0.8
10.0
8 to 24+
By following proper racking practices, drag-out can be reduced by 50 percent or more.
Proper racking may involve the proper orientation of parts inside a basket so as not to collect and
retain liquid. Drinking glasses placed inside a dish washer should always be placed up-side-down
so as to promote drainage. Dishes are best cleaned by stacking them vertically. Why should the
cleaning of industrial parts be different ? For complex shapes, the determination of the most
optimum racking position will likely require experimentation. Modification of the part to promote
drainage (e.g., by adding several drainage holes) may be a possibility but is a very limited solution
95
CHAPTER 6.0
inqractice. While each part may represent a unique challenge, the guidelines presented in the table
below have been found to be effective at many facilities.
TABLE 6-3
GENERAL GUIDELINES TO MINIMIZE DRAG-OUT
Favor slower withdrawal speed over longer drainage time. For a fixed time cycle, spend two-
thirds of the time withdrawing the part from the bath and one-third of the time draining over
the bath.
Drain parts over the tank or use drainage boards to extend the effective length of the tank.
Drainage boards may be installed inside manual tanks to serve as a scrubbing table. Make
sure drainage boards slope back towards the tank so that drained liquid is returned.
Do not rack parts directly over one another. Drippage from the top parts may dirty the parts
below and cause spotting or staining.
Orient part surfaces as close to vertical as possible. Rack parts with their lower edge tilted
from the horizontal. Run-off should be from a comer rather than an entire edge. Burp bars
may help to knock solution off the part after removal from the tank.
Ensure that all cavities and recessed pockets are oriented downward. Rotation of parts during
withdrawal and drainage may help.
Use the correct size and type of basket so as to minimize the wetted surface area of the basket.
A wire mesh basket can retain much liquid if the mesh is too tight. Never use porous materials
such as ropes or cloth bags to hold parts.
In a manual operation handling small racks or baskets of parts, installation and usage of
drainage bars may help promote liquid drainage and reduce drag-out. Such bars run the length of
the tank and are used to hold the parts while they drain. This eliminates much of the physical
strain placed on the operator. To remove and recover more of the drag-out and to minimize the
potential for aqueous or semi-aqueous solutions to dry on hot parts, the parts may be rinsed off and
cooled down by spraying with demineralized water. For parts cleaned in solvent, a quick blast of
compressed air may be helpful for removing entrapped liquid. Figure 6-1 illustrates a simple way
drainage bars may be added to an existing tank. In situations where the integrity of the tank wall is
questionable, use of free standing scaffolding would be recommended.
6.1.2
Monitor Cleaning Bath Quality
Halogenated solvents used in vapor degreasers should be routinely checked for acid
acceptance. Both TCA and METH are highly susceptible to break-down in the presence of
catalytic contaminants such as aluminum or zinc metal fines. Other causes of acid formation
96
L I Z a g 4
IMPROVING PROCESS EFFICIENCY
f
FIGURE 6-1
ADDING A DRAINAGE BAR TO A PROCESS TANK
Re-movable
Drip Bar
1" SchlOS 304L
1.5" Sch40 CS
Pipe Welded to
Tank
include degreasing of parts wet with water or water-based fluids and failure to routinely remove
lost metal parts, oils, fines, and sludges from the boiling sump. When solvent breakdown occurs,
hydrochloric acid is formed which may etch parts and cause extensive equipment damage. To
prevent breakdown, stabilizers are added to the virgin solvent by the producer. A number of
causes may result in stabilizer loss and the most direct way to determine solvent stability is to
perform an acid acceptance test. This test should be performed monthly or quarterly as facility
conditions warrant. Users of PERC and TCE should also perform acid acceptance tests if their
solvent is reclaimed or used for extensive lengths of time.
While much less of a problem in terms of causing damage to parts or cleaning equipment,
acid formation may also occur in non-halogenated solvents. Exposure to air and failure to remove
sludge from cleaning baths may lead to the formation of organic acids. Many of the soils typically
encountered in an industrial setting are acidic and these too can lead to acid build-up. Monitoring
of the acid acceptance value of a given organic solvent may be used to monitor the quality of the
solvent during use. Acid acceptance is typically reported as the milligrams of potassium hydroxide
needed to neutralize the acid in one gram of solvent. The titration is often performed on a water
extract of the solvent (Le., the solvent is mixed with an equal volume of water and the separated
water phase is then titrated to determine acidity). A water extraction can only be performed when
testing water immisible solvents.
97
PJf
CHAPTER 6.0
*
Another monitoring test that may be useful in establishing the quality of a given solvent is
soil loading. Field test kits used to determine when a given level of contamination has been reached
h v e been developed by the military (Joshi et al, 1988). The military found that leaving the
decision to replace solvent up to the operator produced arbitrary results. Some operators would
tolerate very high levels of contamination while others would change-out solvent as soon as the rate
of cleaning slowed down slightly. Such practice could result in parts not being properly cleaned
due to the use of heavily contaminated solvent or large volumes of relatively clean solvent being
prematurely disposed. The intent of developing the test kits was to place the decision for
replacement on a more quantifiable and reliable basis.
The most reliable tests found for checking halogenated solvents such as TCA were acid
acceptance, light transmittance, and electrical conductivity. Reliable tests for Stoddard solvent
(PD-680) included light transmittance, electrical conductivity, and specific gravity. The results of
the light transmittance test on Stoddard solvent are shown in the figure below. This test was
conducted at the Anniston Army Depot in Alabama using a Milton-Roy Mini 20 spectrophotometer
operating at 500 nm wavelength.
FIGURE 6-2
STODDARD SOLVENT USAGE VERSUS LIGHT TRANSMITTANCE
P
e
r
C
e
n
t
L
i
g
h
t
T
r
a
n
S
m
1
t
t
a
n
C
e
98
~
~
IMPROVING PROCESS EFFICIENCY
*
The monitoring of aqueous cleaners is typically limited to the determination of alkalinity or
acidity by titration. Recalling that many alkaline cleaners have a reserve capacity for producing
Bydroxide ions, titrations often involve determining the free and total alkalinity of a cleaner.
Titrations are performed by adding a few drops of indicator to a fixed volume of cleaner and then
adding a standard acid solution until a color change takes place. For example, phenolphthalein
solution will change from clear to pink over a pH range of 8 to 10. The pH of most alkaline
cleaners is in the range of 9 to 13 and will turn a phenolphthalein solution bright pink.
By comparing the level of free alkalinity to total alkalinity, changes in the quality of an
alkaline cleaner can be monitored. Such changes can be due to loading of the cleaner with acidic
soil, excessive drag-out, use of hard water, and failure to make proper additions of replacement
cleaner. Monitoring of cleaner strength can also be used to determine if undue dilution of the
cleaner is occurring. This is a common problem with poorly maintained automatic make-up water
supply systems. Monitoring solution strength during periods of unuse such as over a weekend or
holiday can point out if water supply valve or tank leakage is occurring.
6.1.3
Rigid Inventory Control
Studies in the automotive refinishing industry have shown that the amount of solvent used
for wipe cleaning and paint application equipment clean-up is directly related to the degree of
inventory control practiced (CDHS, 1987). Interviews by the authors with paint spray booth
operators in other industries indicate that many are not watchfbl of the amount of solvent used for
cleaning. According to the automotive study, rigid inventory control can reduce solvent waste
generation rates by 50 to 75 percent. Control measures included sign-out for supplies, use of low
volume cleaning techniques and equipment such as enclosed cleaning stations, and reuse of
decanted thinner.
Making employees sign out for cleaning supplies often results in the reduction of material
use. Operators are less likely to flush out equipment with large volumes of solvent when they must
go through some time delaying procedure to obtain the solvent. If the carehl cleaning of
equipment with a minimal volume of solvent takes less time than obtaining a large volume of
solvent for a quick flush, then low volume cleaning techniques will be promoted. In order to track
solvent usage, several large aerospace companies have experimented with issuing solvent users
with procurement debit cards. Reductions in solvent usage were similar to those reported above
for the automotive refinishing industry.
A common example of the way in which operators can reduce their use of clean-up solvent
in response to restricted supplies is to eliminate the "fill and dump" method of cleaning spray cups
and pressure pots. The "fill and dump" method involves filling the spray cup or pot with solvent,
stirring until the paint dissolves, and then dumping the waste into a dirty thinner storage container.
Depending on the care taken to stir and mix the contents of the spray cup or pressure pot, repeated
cleanings are often necessary.
99
CHAPTER 6.0
dr
Instead of practicing the "fill and dump" method, the paint inside the spray cups and
pressure pots should be drained into a waste paint container. The sides and bottom of the cups and
pots may be wiped or scraped free of residual paint by using a soft wood or plastic spatula. They
may then be rinsed with a small amount of solvent and wiped clean with a lint-free rag. To
promote the reuse of the rinse solvent, it should be stored in a container separate fiom the initially
removed paint sludge. By not loading the rinse solvent with paint solids, it can be decanted and
reused for cleaning several times.
6.2
Process Improvements
Process improvements often involve physical modification of the existing equipment or
installation of additional equipment. Many of these methods can provide substantial increases in
process efficiency but the ability to implement them is not always present. Improvements requiring
substantial physical modification to the equipment may not be possible due to the questionable
integrity of the existing system. In these cases, replacement of the system with a new one that
incorporates some of the following features may be a more viable and cost effective solution.
6.2.1
Use Demineralized Water
With the use of aqueous and semi-aqueous cleaners, make-up water is required to
compensate for losses due to evaporation and drag-out. Use of demineralized water is preferred
over use of tap water since tap water may have a very high mineral or dissolved solids content. As
the water evaporates fiom the tank,these minerals are left behind. To prevent their precipitation,
many cleaning formulations employ additives such as chelators that tie-up and maintain these
minerals in solution. This is fine so long as the additives are active and if their use does not create
problems elsewhere. For example, chelators may complex with heavy metals and make their
treatment and removal from rinse water much more difficult.
In addition to these additives, sodium hydroxide (caustic) will react with the minerals and
serve to soften the water as it is added to the tank. It has been reported that as much as 10 to 25
percent of the cleaner may be consumed by this effect (Spring, 1963). This leads to more frequent
bath replacement and higher operating costs. Use of soften (or preferably demineralized) water
avoids this problem and makes monitoring of bath quality easier since its use eliminates a potential
source of bath contamination.
Rinsing operations can also benefit from the use of demineralized water. Use of
demineralized water for rinsing is often considered to be costly and impractical due to the large
quantities of water involved. However, use of demineralized water may allow for counter-current
and closed-loop rinsing techniques which can substantially reduce the need for water. In the
electroplatingindustry, some shops have been able to eliminate all rinse water discharges by use of
demineralized water and closed-loop rinsing techniques.
100
~~
-
IMPROVING PROCESS EFFICIENCY
*
An important point to note is that much of the hazardous sludge produced by a wastewater
treatment system is due to nonhazardous minerals. These minerals enter the system by way of the
raw water supply used for rinsing, Chemical analysis of wastewater treatment sludges from shops
using tap water for rinsing often shows the sludge to consist of 80 percent or more non-hazardous
calcium and magnesium minerals. By removing these minerals from the water before it is used, the
generation of hazardous wastewater treatment sludge is minimized.
6.2.2
Increase Tank Agitation
Mechanical agitation, either in the form of a liquid jet pump, spraying, basket rotation,
basket raising and lowering, ultrasonic cavitation, or manual brushing is an effective way to
increase cleaning efficiency. Many solvents used in cold cleaning applications are replaced when
the speed at which they clean is no longer acceptable to the operator. This may correspond to a
contaminant level of 2 to 3 percent. By providing mechanical agitation, soil loading levels as high
as 10 percent can be achieved (USEPA, 1989~).Disadvantages of mechanical agitation include
higher electrical costs, more equipment to maintain, and increased worker exposure depending on
the method employed.
One recent development in the field of tank agitation is the use of small, sealless, in-tank
agitation pumps. By placing the pump inside the tank, energy losses due to piping pressure drops
and the potential for solution spillage due to pipe or seal leakage is eliminated. Reusable filter
units may be attached to the pump inlet so as to provide filtration and agitation at the same time.
As reported by Horvath (1990), outsf-tank filtration systems typically consume 1 to 6 square feet
of floor space compared to 0.12 square feet of tank space for an in-tank portable system. A 1/15
horsepower model weights under 10 pounds and can provide 1,200 gallons per hour of solution
flow. At 4 tum-overs per hour, this would be suitable for a 300 gallon tank. These pumps are
available from Flo King Filter Systems, Serfilco, and others.
To achieve even greater levels of agitation, ultrasonic agitation may be considered. This
technique uses high frequency sound waves to create a cavitation effect in the liquid. Small vapor
bubbles are formed in the liquid by the rarefaction (low pressure) sound waves. The subsequent
pressure waves then result in bubble collapse. Very high pressures and temperatures are created
within the bubbles as they collaspe and implode. This cavitation effect blasts the soil away from
all surfaces of the part in contact with the liquid.
Ultrasonic agitation is more difficult to implement on an existing tank than in-tank
agitation. Ultrasonic transducers must be tightly coupled to the tank to minimize mechanical stress
and tank wall erosion. Holding fixtures are often prone to attack due to repeated exposure. For a
new system, erosion and deterioration due to ultrasonic agitation is directly dependent on weld and
fabrication quality. System life should be at least 5 years for properly built equipment. The cost
for an ultrasonic system varies widely depending on tank size and level of control. Small table-top
or desk sized systems may be purchased for less than $1,000 (no pumps, filters, etc.).
101
CHAPTER 6.0
*
The ability to ultrasonically agitate a solution is a function of the solutions viscosity, vapor
pressure, surface tension, and density. Generally speaking, the most suitable solutions have low
viscosity, medium vapor pressure and surface tension, and high density. Most aqueous and diluted
semi-aqueous cleaners are suitable candidates. Since the limiting properties are a function of
temperature, operation at a lower temperature setting may be necessary to maintain agitation.
In operating an ultrasonic cleaning system, several factors of operation take on more
importance than in general cleaning systems. Two such factors are solution degassing and parts
loading. Solutions should always be degassed before use. This may be accomplished by heating
the solution to within 3 to 5 O F of its boiling point or by operating the unit with a pulsed wave.
Degassing may be noted by a hissing sound and may take 30 minutes or more to complete. Parts
loading should not exceed 0.35 pounds per kilowatt of generator power (NASA, 1969). Parts and
baskets should never be allowed to contact the bottom or side walls of the tank.
Parts fabricated from materials that are poor conductors of sound may not be effectively
cleaned in an ultrasonically agitated system. Instead, they may absorb the sonic energy and deaden
the effect. The same is true for the materials used to fabricate baskets and part holders. Parts held
in a glass beaker are effectively cleaned since the glass walls of the beaker will transmit the sonic
waves. With a polyethylene beaker, the intensity of the sound waves will be attenuated or reduced
by 25 to 50 percent. Similar effects may be noted with metal mesh baskets. Fine mesh (300 mesh)
and coarse mesh baskets will allow the sound to pass while medium mesh (40 to 60 mesh) baskets
tend to absorb the most energy.
When erosion and part damage due to ultrasonic agitation is a problem, higher frequency
acoustic waves may be used. This process is sometimes called acoustic streaming or megasonic
agitation. The difference between ultrasonic and megasonic agitation is the range of frequencies
used. Ultrasonic systems typically operate in the 20 to 40 kHz range while megasonic agitation
operates in the range of 700 to 1,000 kHz. The higher frequencies do not cause cavitation of the
fluid and hence eliminates the potential for erosion. Megasonic agitation is primarily used for
particle removal and its effect is line of sight. Only the side of the part that is facing the
transducer(s) will be cleaned. Typical exposure times are 10 to 30 minutes.
6.2.3
Employ Two Stage Cleaning
Two stage counter-current cleaning can effectively reduce the amount of solvent used in
cold cleaning. The process involves soaking the part in a tank of dirty solvent followed by rinsing
and final cleaning in a tank of clean solvent. The dirty solvent is used to remove the bulk or gross
contamination while the clean solvent is used to ensure that the part is clean. When the clean
solvent finally becomes too loaded with dirt and grease, the dirty solvent is disposed of and the
clean solvent is transferred into the dirty tank. Fresh solvent is then added to the empty clean tank.
102
IMPROVING PROCESS EFFICIENCY
As an example of the type of reduction possible by converting a cold cleaning tank into a
two stage cleaner, assume that a 100 gallon tank of solvent is disposed of weekly when the level of
C
ail contamination reaches 2 percent. When the contamination level exceeds 2 percent, the parts
will drag-out enough oil to be considered not clean enough for subsequent use. The parts being
cleaned are small; consequently, the existing 100 gallon tank can be converted into two 50 gallon
tanks by welding a divider inside (see Figure 6-3). The parts are first soaked in the dirty solvent
where 80 percent of the oil is removed followed by a rinse and spray flush in the clean solvent.
Given that the loading rate of oil into the cleaner is 2 gallons per week and that the first
stage removes 80 percent of the oil, it will take 2.5 weeks for the first stage to reach 8 percent
contamination and the second stage 2 percent. Disposing of the dirty solvent and transferring the
clean solvent into the dirty stage, the clean stage will then be filled with fresh solvent. To provide a
margin of safety, the facility elects to change-out the dirty stage every 2 weeks. Therefore, 50
gallons will be disposed of every 2 weeks with a two-stage cleaner as compared to 100 gallons per
week from a single stage cleaner. This represents a 75 percent reduction in solvent use provided
air emissions remain the same in both cases.
FIGURE 6-3
COLD CLEANER MODIFIED FOR TWO-STAGE CLEANING
Hinged
Cover
103
CHAPTER 6.0
6.2.4
Provide Mechanically Assisted Parts Handling
When parts are rapidly lowered into or raised out of a vapor degreaser, the parts can push
or drag out vapors from the degreaser. Many air quality regulations and operational guidelines
specifL an entrance and exit speed of no more than 1I feet per minute (fpm). Human operators are
seldom able to maintain this speed and if parts weigh more than 10 pounds, then fatigue occurs.
Typical speeds with human operators may be greater than 60 fpm. Tests have shown that reducing
speed from 20 to 10 fpm reduces working loss by 28 percent (USEPA, 1989b). This same study
reported that one test showed a reduction of 8 1 percent when reducing the speed from 11 to 3 fpm.
3
As previously discussed, rapid withdrawal of a part from a cleaning bath is also a prime
cause of solution loss. Automation of the part handling operation can result in substantial
reductions of lost cleaning solution. The cost of purchasing, installing, and operating a
mechanically assisted parts handling system varies widely. For example, a simple push button
operated mechanical hoist can be purchased for less than $1,000 while a filly automated robot
elevator may cost $10,000 or more (USEPA, 1989b). A less tangible benefit is the reduction in
worker exposure that may be achieved by installing a mechanical parts handling system.
6.2.5
Install and Use Tank Covers
Equipping solvent cold cleaners and vapor degreasers with covers can effectively reduce
solvent emissions. Covers may be manual or mechanically-assisted (e.g., spring loaded, counterweighted, or power/pedal operated). In the past, units were often supplied with a single piece,
removable metal cover. The covers were heavy and awkward to use and because they were
removable, they were often damaged or misplaced. Integral hinged covers cannot be misplaced but
their single piece design creates a piston effect when opened and closed. This effect pushes vapor
out of the tank and increases emissions. Most modern units are equipped with roll-type covers.
Regardless of design, manual covers should fit well and should be operated carehlly to
ensure that they do not become bent or otherwise damaged. In cases where lip exhaust is used to
prevent vapors from reaching the worker, the cover should be located above the vapor zone and
below the exhaust inlet. Automated biparting covers are often an effective way to keep the tank
closed while cleaning parts. Biparting covers can be closed around the cable or rig holding the
parts and provide closure during the cleaning phase. The most advanced biparting covers are
electrically powered and automated to coordinate cover movement with the movement of an
automated parts handling system. Biparting covers may reduce emissions from vapor degreasers
by 38 percent in calm air conditions and by 53 percent in drafty locations (USEPA, 1989b).
6.2.6
Improve Vapor Degreaser Operation
The freeboard height is the distance from the top of the solvent vapor/air interface to the
lip of the tank. This zone serves to reduce air/solvent interface disturbances caused by room
104
~
~
IMPROVING PROCESS EFFICIENCY
d&s.
The ratio of freeboard height to tank width is referred to as freeboard ratio. In newer
equipment, this ratio ranges from 0.75 to 1 or more. For a given width, increasing the freeboard
tatio reduces the disturbance of the vapor zone and slows solvent diffusion out of the machine. On
the downside, an elevated work platform and hoist system may be required to move parts in and
out of the higher tank. Depending on height restrictions inside the facility, increased freeboard may
not be feasible.
Increasing freeboard height can often be achieved by welding extensions to the vapor
degreaser. The cost for such an undertaking has been estimated to be $500 to $1200 depending on
the size of degreaser (USEPA, 1988a). By increasing the freeboard ratio from 0.75 to 1, tests have
shown emission reductions of 20 percent (USEPA, 1989b). Increases from 1 to 1.25 reduced
emissions by an additional 6 to 10 percent.
Idling and working losses can be reduced from a vapor degreaser by conversion to an
enclosed design. By creating an enclosed environment, solvent diffusion is controlled and reduced.
The enclosed design consists of mounting a shroud or hood over the top of the degreaser and
installing a conveyorized parts handling system that allows the parts to be raised and lowered into
the degreaser. Sliding doors in the hood allow access to the conveyor. Tests have shown that such
systems can reduce emissions by 42 to 67 percent (USEPA, 1989b).
Although primary condensing coils are standard equipment on all vapor degreasers, the
temperature of these coils and the design of the coils and coolant flow have a direct effect on
emission losses. A refrigerated primary condenser, as opposed to a water cooled one, lowers
diffusional losses because it not only condenses more solvent vapor, but also acts to cool the air
above the airholvent vapor interface. While the magnitude of this effect varies depending on the
design of the coils and the type of solvent controlled, reported tests show that working emissions
from a TCA degreaser can be reduced 41 percent by reducing the water temperature from 85 O F to
50 O F (USEPA, 1989b). In reducing the water temperature from 70 OF to 50 O F , a reduction of 29
percent can be achieved. An additional 18 percent reduction is possible by going to 40 OF.
Refrigerated freeboard chillers, also known as "cold traps", consist of a second set of
condensing coils located above the primary condensing coils inside the vapor degreaser. While the
primary condensing coils define the vapor zone, the freeboard chiller coils chill the air above the
vapor zone, creating a second cold air blanket. Freeboard chillers are effective in combination with
a condensation trough to collect condensed moisture and to help control the introduction of water
into the degreaser. Since water contamination of the vapor degreasing solvent can cause excessive
vapor loss and depiete the water soluble stabilizers used in TCA thereby leading to acid formation,
these chillers must be used judiciously with TCA degreasers.
There are two types of refrigerated freeboard chiller, above freezing and below freezing.
Above freezing devices operate at temperature ranges around 5 "C (4 1 OF). Below freezing devices
operate at temperatures usually in the range of -20 "C to -30 "C (-4 OF to -22 O F ) . Due to the low
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CHAPTER 6.0
ofirating temperature of the below freezing units, provision must be made for a timed defrost cycle
to melt the solventlwater ice that forms on the coils. This ice layer can reduce heat transfer and
hence control efficiency. When melting, the water/solvent mixture drains to a trough located below
the coils and is directed to a water separator.
Despite the common belief that below freezing chillers are more efficient than above
freezing chillers, the need to periodically defrost a below freezing freeboard device can offset the
performance advantage (USEPA, 1989b). For example, working loss emissions were reduced by
36 percent with an above freezing chiller. Under the same conditions with a below freezing chiller,
the average emission reduction was 32 percent. Freeboard refrigeration devices primarily reduce
difisional losses, and during working conditions losses are mostly due to drag-out on parts. These
drag-out emissions are usually greater than diffusional losses, except for when the degreaser is
located in a drafty location. Control efficiency is also dependent on the temperature of the primary
coils. As the temperature of the primary coils goes down, so does the control efficiency of the
refrigerated coils.
A recent twist on the below freezing freeboard chiller has been developed by DuPont and is
referred to as the Triple Guard system. The Triple Guard system consists of three independent
condensing coils; the main coil operating at 45 O F a second coil operating at -20 O F and
overlapping the top of the main coil, and a third coil operating at -20 O F located around the top of
the degreaser. This third coil dehumidifies the vapor zone and maintains the efficiency of the
second coil. This system was designed to control emissions from vapor degreasers using the new
HCFC solvents. A similar arrangement is incorporated into the AVD (Advanced Vapor
Degreasing) system developed by Petroferm Inc. This system uses an unidentified solvating agent
supplied by Petroferm and a perfluorocarbon rinsing agent supplied by 3M. The system is
manufactured by Detrex.
For facilities desiring to minimize emissions to the fullest extent while still using a vapor
degreaser, zero emission or filly enclosed vapor degreaser designs are now available. These units
allow parts to be cleaned only when the parts have been placed inside and the lid fully closed. A
small carbon bed filter is included in some units so that emissions are also controlled when the unit
is purged of solvent vapor before opening. Captured vapors are returned to the unit during the next
cleaning cycle. Zero emission vapor degreasers are available from Durr Industries, Pero Systems,
and others. The Pero Systems model 2500 1N can handled 20" by 12" by 7" baskets, emits no
more than 10 ppm or 1 gram of solvent per cleaning cycle, and costs $145,000 (Sprow, 1993). A
simplified diagram of the "zero emission'' concept is presented in Figure 6-4 on the following page.
6.2.7
Enclosed Paint Gun Cleaning Stations
To cut down on air emissions and promote recycling, the use of an enclosed cleaning
station is often required by local regulations. Some of these units are designed to mount on top of
a 55-gallon drum and they contain an air-driven, solvent condensing unit. To use the unit, the
106
IMPROVING PROCESS EFFICIENCY
oderator pours some clean solvent into the spray cup or pressure pot, locks the spray gun into the
receiving hole of the unit, and then triggers the gun on. Solvent vapors enter the condensing unit
where they are condensed and retumed to the drum. Provided that operators are carehl not to
introduce too much paint sludge into the drum (sludge should be stored in another drum), relatively
clean solvent can be decanted from the drum for reuse. Several waste solvent recycling companies
and coating suppliers offer dirty thinner recycling equipment for lease or sale.
FIGURE 6-4
ZERO EMISSION VAPOR DEGREASING PROCESS
1. Parts Enter Cleaning
Chamber, System Sealed
-
2. Parts are Degreased
in Clean Solvent Vapor
3. Solvent Vapors Recovered 4. Parts Leave System Clean,
Dry, and Solvent Free
Before System Can Be Opened
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CHAPTER 6.0
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1
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7.0 RECYCLING SPENT CLEANING BATHS
In this age of pollution prevention, the ability to recycle waste materials, be it halogenated
solvents, nonhalogenated solvents, or aqueous cleaners, is a concept worthy of examination.
Shrinking supplies of CFC-I I3 and TCA will make emission reduction and solid waste recovery of
these materials much more important during the impending phase-out. Recovery and reuse of the
nonhalogenated solvents and aqueous cleaners may be just as important with sewerage and waste
disposal costs ever rising. While the world is currently focused on eliminating ozone depleting
chemicals, it is certain that critical attention will be placed on the handling and disposal of their
replacements in the years to come.
The following sections present a general overview of recycling issues as well as discussion
of the many technologies available for use. In alternative solvent and aqueous cleaning
applications, many of these technologies represent a key component to the economic viability of a
given cleaner. An example would be membrane recovery of a water-soluble terpene cleaner in a
printed circuit board defluxer.
Excluded from the following discussion is the combustion of waste solvents for thermal
energy recovery. While often listed as a viable waste recycling technique and viewed as an
effective means of managing waste solvents, it does not reduce the amount of virgin chemical
consumed and waste produced by a given operation. Hence, it is not pollution prevention. Also
excluded from this discussion are experimental recycling technologies such as microwave heating
of solvent-bearing sludge or regeneration of spent aqueous cleaning baths by means of ozonation.
7.1
General Issues
The goal of recycling is to recover the cleaning medium in a form suitable for reuse. This
may involve filtration, decantation, distillation, concentration, or a combination of methods. In
many applications, continuous recycling is used to maintain an acceptable level of contamination in
the cleaner. This may range from low or none in the case of maintaining a near virgin grade of
solvent to just maintaining an acceptable level so that parts are not over or under cleaned.
The recovery of spent solvents may be performed either on or off site. The recovery of
emulsion cleaners (Le., semi-aqueous or water soluble solvents) and aqueous cleaners is
exclusively performed on site. The decision to recycle on or off site generally depends on the
volume of waste to be processed, the capital and operating costs of the system, as well as the
availability of in-house expertise. If the volume of waste to be recycled is small or if the level of
in-house expertise is low, companies are more likely to recycle the waste off site.
7.1.1
On Site Recycling
The decision to recycle wastes on site is typically based on the economics of cleaner
reuse. Recycling may be incorporated into the process design as an integral part of the initial
109
CHAPTER 7.0
inhallation or as an separate endsf-pipe system. For most companies installing new cleaning
lines, initial inclusion of the recycling system is the norm. In fact, cleaner selection is often
dictated on the cleaners ability to achieve an acceptable level of cleaning efficiency and its ability
to be effectively recycled. Major advantages and disadvantages of on site recycling include:
e
e
0
e
0
e
e
Less waste leaves the facility.
Tighter control of recovered cleaner purity.
Reduced cost and liability associated with waste transport.
Possible lower unit cost for reclaimed cleaner.
Capital outlay for recycling system.
Additional operating costs and need for operator training.
Increased liability associated with worker health, fires, leaks, and spills.
In designing an on-site recycling system a number of key items must be addressed. These
include chemical volatility, solubility, thermal stability, potential corrosion or reaction with
materials of construction, purity requirements for the recovered cleaner, system capacity, steam
and cooling water availability, worker exposure, regulatory permitting, and overall economics.
These issue areas are fiirther discussed in Section 7.3, Distillation Svstem Desim.
7.1.2
Off Site Recycling
For facilities deciding not to recycle on site, off site recycling or toll arrangements are
possible. Most commercial recyclers readily accept halogenated or nonhalogenated solvents and
recycle them by means of distillation. Generators should be careful to maintain spent solvents in as
pure a form as possible (i.e., keep all solvents segregated) so as to maximize their recyclability. In
a survey of commercial recycling facilities (CDHS, 1986), the following waste handling guidelines
were recommended:
Segregate solvent wastes. Specifically, segregate chlorinated from nonchlorinated
solvents; aliphatic from aromatic solvents; CFC- 1 13 from methylene chloride; and water
fiom flammable solvents.
Keep water out of solvent waste. Storage drums should be covered to prevent rain water
infiltration.
Maintain as high a solvent content in the waste as practical, 40 percent or more. Try to
minimize the contamination of solvent with solids.
Label each waste container with an identification label that includes the exact composition
and the method in which the waste was generated.
Failure to keep solvents segregated may lead to rejection of the solvent by the recycler.
Depending on the waste volumes handled, off site recycling may be economically favorable over on
site recycling. Off site commercial recycling services are well suited to small quantity generators.
The recycler may charge the generator by volume of waste accepted and later credit the generator
110
RECYCLING SPENT CLEANING BATHS
f d t h e value of recoverable solvent received. Other recyclers charge a straight fee or accept waste
at no charge depending on its market value. With the rapidly increasing price for CFC-113 and
TCA, it is likely that recyclers will be offering attractive prices for these solvents unless the market
demand drops off faster than the supply.
In selecting an off site recycler, one should remember that the waste generator can be held
liable for the mishandling of waste by the hauler or recycler. In choosing a commercia! recycling
service, one should investigate and verify the following:
e
e
e
e
e
e
e
e
e
e
e
e
7.1.3
Types of wastes typically managed.
Permits held by the facility.
State compliance records and site inspection reports.
Type and extent of insurance held.
Type of record keeping and reporting practices followed.
Availability of registered trucks and licensed haulers to transport the waste solvents.
Distance to the recycling facility and associated transportation costs.
Expertise of in-plant waste management personnel and process controls (how well do the
recyclers know their own facility).
Disposal procedures for still bottoms and solvents that cannot be recycled.
Laboratory facilities and analytical procedures employed to ensure solvent purity.
Availability of custom recycling services (e.g. vendor-owned recycling units that are
operated at the generators property).
Customer comments.
Other Options
For facilities choosing not to recycle either on or off site, a few alternatives are available.
The first is to list your waste either on an information exchange or material exchange. Information
exchanges act as clearinghouses for information on waste availability and demand. You will be
required to provide such information as type of waste, composition, quantity, method of delivery
(Le., drums or bulk), frequency of generation (i.e., one time or continuous), and regional location.
Once listed, the clearinghouse will provide you with the names of facilities that inquire about your
waste. All arrangements for transferring and delivering the waste is between you and them.
A material exchange differs from an information exchange in that it takes temporary
physical possession of the waste and may initiate or actively participate in the transfer of the waste
to the user. Advantages of this arrangement include less involvement of the generator and
receiving facility in deciding on equitable terms and conditions (these may already be dictated by
the material exchange) and the ability to participate in an exchange with-out the facilities having to
identity themselves with one another. A disadvantage of a material exchange is that you will pay
more for this service, many information exchanges are free. Information regarding available
exchanges in your area can be obtained from state and local regulatory agencies involved in
pollution prevention or recycling activities.
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CHAPTER 7.0
*
For facilities generating small quantities of waste and not wishing to go on their own,
cooperative recycling arrangements may be an option. The arrangement here is that solvent
mllection is performed on a milk-run basis with the waste solvent from many small generators
being collected and recycled together. This arrangement typically involves a high level of
coordination and involvement of a trade or industry association. Most arrangements are also for
facilities engaged in the same line of business so that the wastes collected by the milk-run do not
differ widely from shop to shop. This arrangement is most viable for shops located in close
proximity to one another.
7.2
.
Recycling Technologies
Dilute aqueous streams which may contain small amounts of solvent (e.g., rinse water
from a semi-aqueous cleaning operation) are usually treated before disposal to Publicly Owned
Treatment Works ( P O W via sewer. Depending on the treatment process employed, recovery of
the removed solvents may be feasible. Hence, there is a fine line between calling a given
technology treatment or recycling. The regulatory distinction is often based on with what is done
with the recovered material. Many new technologies are being developed to recycle all of the
solvents, cleaners, and rinse waters back to the process so as to achieve near zero discharge.
The following sections discuss the techniques of gravity settling, size separation by
filtration, and vapor liquid separation by distillation. Gravity settling is a very old technique used
for separating coarse particles from liquids. Distillation is also a time honored technique used for
separating volatile solvent from less volatile oils and greases. Filtration, which dates back to the
use of sand filters for removing turbidity from water, has progressed into the realm of micro and
ultra filtration. Rapid advances in membrane technology as resulted in the ability to remove
smaller and smaller particles fiom very aggressive solutions. Some filtration devices can remove
particles so small that they can effectively be used to break an oil in water emulsion. Since many
detergents rely on emulsification of oils to effect cleaning, these filtration devices are capable of
regenerating spent aqueous cleaners. Similar advances in recovering semi-aqueous cleaners fiom
rinse waters are occurring.
7.2.1
Gravity Separation
Gravity separation involving the removal of particles suspended in a liquid is often referred
to as sedimentation. The contaminated liquid is introduced into a settling tank and after a sufficient
settling time, the clarified liquid is drawn off from the solids resting on the bottom of the vessel.
The solids are removed and usually treated before disposal. This process is widely employed as a
preliminary purification or prefiltration step. Capital, operating, and maintenance costs for a
sedimentation system are low . Disadvantages of the method include poor removal of fine colloidal
particles and potential for excessive air emissions if conducted in a large open holding tank or
basin. Sedimentation is typically employed in the recycling of dirty clean-up solvents and thinners
from painting operations.
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RECYCLING SPENT CLEANING BATHS
*
Decantation is a gravity separation technique used to separate immiscible liquids of
different densities. The mixture is slowly introduced into a decant tank where continuous phase
*paration occurs. Dust and dirt particles can interfere with the separation so they are often
removed by filtration beforehand. Decantation is often used to remove insoluble oils from spent
solvents in the dry cleaning industry and to recover semi-aqueous solvents that enter the emulsion
rinse stage. The main factors in designing a decant tank are the droplet size of the discontinuous
phase and its volume fraction.
To achieve a greater degree of solid or immiscible liquid separation, the acting forces may
be increased by pumping the contaminated liquid through a hydrocyclone or centrifuge. These
devices spin the liquid and create a very large centrifugal force that acts on the suspended matter in
a way similar to gravity, except much greater. Solids are removed in the underflow of the device
while clean liquid is discharged in the overflow. As expected, capital and operating costs for these
devices is greater but so is the effectiveness of separation. Use of a hydrocyclone to remove
suspended dirt and oil from an aqueous cleaning bath can sometime double solution life.
Centrifuges are sometimes used to remove water from oils but they are not commonly encountered
in parts cleaning operations.
7.2.2
Filtration
The process of filtration removes insoluble particulate matter from a fluid by means of
entrapment in a porous medium. It is often used to extend the life of a cold cleaning bath or to
continuously remove metal fines and sludge from a vapor degreaser sump. Some of the process
related factors important in the selection of a filter system include particle size distributions,
solution viscosity, production through-put, process conditions, performance requirements, and
permissible materials of construction. Common styles include bag and disposable cartridge,
though a wide array of equipment is available.
While standard filtration does not remove soluble contaminants such as dissolved oils from
a solvent, it can be used to remove solid dirt and grease particles. Passing the dirty solvent through
a fine metal screen may remove these contaminants before they have a chance to dissolve and load
the solvent bath. Routine screening and removal of undissolved contaminants can be an effective
way to extend the life of a cold cleaning bath.
Microfiltration systems are filtration technologies that can remove soils to a much finer
degree than standard filtration. In the field of precision cleaning, their use is essential. Typically,
vapor degreasers are equipped with a 5 or 10 micron filter for removal of particulates. The smaller
particles that are not removed accumulate in the sump and eventually contaminate the solvent
vapor and hence the assemblies being cleaned. The use of a microfiltration system can remove
particulates down to less than 0.1 microns in size. This minimizes the potential for particulate
contamination of the solvent vapor. Because of the fine filtration capability of the filter, removal
of water, organic acids, and other soils from the solvent is feasible.
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CHAPTER 7.0
*
Moving beyond microfiltration, membrane filtration (which includes ultrafiltration) is
capable of removing emulsified oil and grease from aqueous cleaning solutions. Membrane
filtration is sometimes so effective that it will also remove surfactants and other special additives
from the cleaner. Removal of particles as fine as 0.01 to 0.003 microns and organic molecules
with molecular weights exceeding 500 can be removed by ultrafiltration. Therefore, selection of a
suitable aqueous cleaner and the ability to recycle that cleaner often involves optimizing ingredients
used in the formulation to removal efficiency of the system. In terms of cost, Marshall and Daily
(1989) reported the installed capital cost for a system capable of handling a 4,000 gallon bath
operated at 6 ounces of cleaner per gallon to be $59,000. The payback period was 2.4 years.
7.2.3
~
Distillation
On-site recycling is becoming more and more popular as a way of reducing virgin solvent
use and reducing the disposal of halogenated solvent. According to Dow Chemical Co. (undated),
64 percent of their large-scale vapor degreaser customers were performing on-site solvent recycling
in 1987. This was up from 52 percent in 1984. The performance of on-site recycling can reduce a
facilities purchase of virgin solvent by 20 percent. Still bottoms from the recycling operation are
often sent off site for additional solvent recovery or are sent to a cement kiln for use as fuel. Since
off-site recyclers pay for recovered solvent value and charge for sludge disposal, many on-site
recyclers have found that the most economical level of on-site recovery is to recover solvent to the
point where the solvent value in the waste equals the disposal charge for the sludge. This way, onsite recyclers achieve maximum value for the solvent they recover while maintaining a zero cost
way of managing their wastes off-site. Details of these arrangements are highly site specific.
On-site recycling equipment for halogenated solvents falls into one of three categories: 1)
process stills, 2) batch stills, and 3) semiportable mini-stills. Process stills are used in conjunction
with vapor degreasers to provide continuous cleaning of the solvent. Dirty solvent from the sump
of the degreaser is pumped to the still for processing and then returned to the degreaser's clean
solvent storage tank. Solvent recovery with a process still typically ranges from 60 to 80 percent.
Dow reports that 62 percent of those facilities that recycle on-site do so with process stills. An
advantage to process stills over batch stills is that the degreaser does not have to be shut down
while the solvent is being processed. Another advantage is that the level of contamination in the
degreaser stays at a steady low level. Process stills may also be used for recycling solvent from
cold cleaning operations through this practice is not very common.
Batch distillation is performed whenever the degreaser requires cleaning; anywhere from
once per week to once per month or longer. Batch distillation is also commonly used to recycle
solvent fromcold cleaning operations. To be recycled, dirty solvent is pumped into the still, heated
and condensed, and then put back into drums or storage tanks for return to its point of use. Batch
stills are typically capable of much higher solvent recovery rates than process stills, usually around
70 to 95 percent. The reason for this is that waste from a process still must often be pumped out
into drums while batch stills are often equipped with lining bags that are then used to lift the waste
114
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RECYCLING SPENT CLEANING BATHS
odc of the unit. Since the waste does not have to be pumped out, the viscosity of the waste is less
of an issue and higher solvent recovery can be practiced. According to Dow, 36 percent of the
fiicilities that recycle their vapor degreaser waste do so with batch stills. The use of batch ministills is not common with vapor degreasing but they are widely used in maintenance parts cleaning.
If the boiling point of the solvent is high (greater than 200 OF as with PERC), distillation
can be performed under vacuum to minimize thermal decomposition of the solvent or impurities.
Vacuum distillation can also be used to recover d-limonene at low temperatures so as to avoid
auto-oxidation and polymerization. Another technique is to inject live steam into the solvent which
allows the solvent to boil at a lower temperature. The condensate of water and solvent is then
phase separated by gravity in a decanter. Steam injection should not be used when the solvent
contains water soluble inhibitors. The use of steam sparging can also result in increased air
emissions if the sparging and condensing equipment is not designed and operated properly.
For facilities that do not want to invest capital in on-site recycling equipment and do not
want their solvent recycled at an off-site facility, a viable option is to contract with a mobile on-site
solvent reclamation service. One such service is offered by Solvent Processors and Reclaimers
Corporation (SPaR) of Fairfield, Ohio. SPaR operates a mobile recycling system that pays regular
visits to the shop. Dirty solvent is pumped into the mobile recycling unit, is distilled, and the
cleaned solvent retumed to the degreaser or storage tank. Arrangements are then made to dispose
of the still bottoms. SPaR charges a single fixed price for their service which depends on the type
and quantity of the solvent to be processed. Similar services are offered by Cleanland Corporation
and First Source Company in the Atlantic seaboard states.
For generators who are not able to either economically or technically install and operate
on-site recycling equipment, off-site reclamation may be a viable option. The off-site recycler,
under a contractual agreement, picks up the generator's contaminated solvent, recycles it, and
delivers the purified solvent back to the generator. If the generator does not want the recycled
solvent back, then he receives a lesser credit for the solvent and the recycler sells the solvent to
another user. The sludges that result from the off-site reclamation operation contain halogenated
solvent and are usually blended with non-halogenated solvent waste and sent as fuel supplement to
cement kilns. The production of cement requires a source of chlorine and the use of halogenated
solvent suits this need well.
Since the 1986 land disposal ban on halogenated solvents was enacted, off-site reclamation
has gained widespread use because of the high cost of other available options such as thermal
destruction. While the economics of solvent reclamation are favorable, some users question the
quality of recycled solvent and hence are reluctant to use it. Many users are prevented from using
recycled solvents because of imposed product specifications based on high purity virgin solvents.
Work is currently underway to revise the military specification procedures which may allow the
use of recycled solvent in many applications.
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CHAPTER 7.0
*
The military specification for TCA (Mil-T-81533A) requires a maximum water content of
100 parts per million (ppm). While some recyclers can meet this specification by passing the
recycled solvent through a staged molecular sieve dryer, many others cannot. Recyclers operating
molecular sieves can typically produce a solvent with a moisture content of 25 to 50 ppm. High
moisture levels in TCA can be dangerous because the solvent tends to be unstable and is subject to
hydrolysis or acid formation. The maximum allowable moisture content specified by the military
for CFC-113 (Mil-C-81302D) is 10 ppm.
~
~
The other military specification requirement that some recycled solvents may not meet is
the "other halogenated constituent" limit. The limit for TCA is 0.5 percent by volume. In some
cases, recycled TCA may contain one to two percent METH and CFC- 1 13. These contaminants
may be present in the original solvent waste or may be due to improper cleaning of the distillation
equipment between batches. Today, many recyclers will perform a detailed analysis on each batch
of solvent so that they know exactly what is being introduced into their system. This allows them
to adjust their distillation process accordingly and produce a high purity reclaimed solvent.
7.3
Distillation System Design
Most batch distillation systems encountered in parts cleaning applications are of single
stage design and range in sizes of 1 to 5 gallon desk-top units, 15 to 100 gallon desk-sized units,
and 100 to 1,000 gallon custom designed systems. Distillation systems that operate continuously
are not common although the large size systems are often configured to operate in semicontinuous
mode. Semicontinuous operation involves continuous feeding of dirty solvent and recovery of
clean solvent from the system without removing the still bottoms. When the system becomes
loaded with solids, it is shutdown and the still bottoms removed. Several key features to be
considered when specifying an on-site solvent recovery system are discussed below.
The first is stream characteristics. This includes the quantities, compositions, and physical
properties of the waste solvent to be processed and the required purity of the recovered solvent.
Flow rates should be based on the maximum throughput desired and not some average value. Use
of an average value may be acceptable if the system is to include a sizable waste storage tank for
smoothing out any fluctuations. Inclusion of a holding tank may also allow for the specifjwg of a
smaller system that will operate overnight during facility shut-down. The more information you
can provide the supplier, the better able he or she will be to match your needs.
Another key parameter is choice of internal operating pressure (Le., atmospheric or
vacuum). This choice depends on the vapor pressure of the solvent, its thermal stability, and the
vapor pressure and stability of the contaminants present. To provide the largest driving force for
separation, the operating pressure should be kept as low as practical. For most solvents,
specifirlng atmospheric pressure is sufficient. For high boiling liquids, distillation under vacuum is
often required. When a system operates under vacuum, air may leak into the system due to poor
fitting seals and gaskets. Air leakage may increase the risk of fire or explosion if the solvent is
I16
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RECYCLING SPENT CLEANING BATHS
f l h a b l e . Such risk may be minimized by specifying explosion proof equipment and controlling
the level of vacuum by means of a nitrogen bleed.
Operating temperature is determined by the operating pressure and the relative volatility of
solvent and contaminant. The choice of heating mode @e., steam or electricity) is determined by
available utilities, preference of the operator, and the characteristicsof the bottom stream. Viscous
bottoms may best be heated by means of direct steam injection unless the recovered solvent cannot
tolerate water contamination. To overcome the problem of poor heat transfer into a viscous
material, some manufacturers have experimented with microwave heating.
The extent of process automation must also be considered. Automatic control of flow,
level, temperature, and pressure is common. The rate of heat input may be fixed or it can be
modulated or ramped up and down in some prescribed manner. Microprocessor control of heat
input may allow for the separation of various components over time. An example would be to first
operate at 2 12 O F to remove water from a less volatile solvent and to then increase the temperature
setting to recover clean solvent from grease. Heat input can be independently interrupted by a low
level condition, by a high temperature condition, and by loss of cooling water to the condenser.
Such controls increase the safety of the system and can minimize damage in the event of failure.
Low liquid level shutdown can prevent severe fouling and damage to the heating coils should they
be accidentally exposed (heating coils should always operate in a submerged mode).
In closing, this discussion is far from complete. Other important decisions include location
of system, adherence to building, fire, and safety codes, required safety features such as pressure
rupture disks and fire suppression, feed conditioning requirements, means of removing still
bottoms, and suitable materials of construction. Rather than going it alone, you should view the
equipment supplier as a partner tasked with providing you the answers needed to make a decision.
Many of the above items are commonly incorporated into the standard systems offered.
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8.0 CONTROLLING SOLVENT EMISSIONS TO AIR
Recovery and reuse technologies for halogenated solvent vapors and volatile organic
1
compound (VOC)emissions have been available and practiced for many years. The most common
method is carbon adsorption with steam regeneration. Newer methods include polymeric
adsorption, Brayton cycle heat pump regeneration, membrane separation, and direct condensation.
For the control of VOCs without recovery, both thermal and catalytic fume incineration has been
practiced. With aqueous cleaning systems, sufficient ventilation is required to maintain an
acceptable level of humidity in the work place but emission "controls" are not typically required.
The following sections discuss general design criteria followed by fume incineration, carbon and
polymer adsorption, liquid absorption, condensation, and membrane separation.
8.1
General Design Criteria
The technical evaluation of any control measure must address its suitability to the given
application. Selection of an appropriate control system is very dependent on the concentration and
composition of the emissions being controlled. Insurance that selected control technologies will be
suitable for a given application is achieved two ways. The first way consists of defining all of the
parameters which will affect control system design. The second way consists of developing an
equipment design specification so that the control system meets certain physical / structural
requirements and constraints. Select items of concern include:
0
What is the collection and control efficiency of the system ? Overall efficiency is
dependent on the ability to capture emissions and remove them from the air stream. With
open-top cleaning tanks, the ability to capture emissions is often more difficult than actual
control. Venting large volumes of air to insure capture is seldom viable since this reduces
efficiency and increases control costs.
What is the system's tolerance to particulate matter (if any) entrained in the air stream ?
Some technologies, such as thermal incineration, can handle particulate matter. Other
systems, such as catalytic incineration or carbon adsorption, cannot and thus require
prefiltration equipment. Particulate matter may be a problem when solvent tanks are
located near abrasive blasting equipment.
0
Is space available ? Are utilities available ? Retrofit systems often require more ducting
and piping than new systems because they must be located further away due to existing
space constraints. For utilities, electrical power, natural gas, and cooling water
connections are typically available although they may require upgrading. Control options
that require large volumes of compressed air, instrument air, refrigeration, or steam must
include utility equipment as part of the basic system.
0
Is the new equipment compatible with existing production operating procedures, work
flow, and production rates ? Retrofit systems often impact existing production schedules
during installation.
119
CHAPTER 8.0
t0
Is special expertise required to operate or maintain the new system ? Does the vendor
provide acceptable service ? Most systems tend to be highly instrumented and automated,
Cost cutting measures that reduce the degree of automation and place more responsibility
on the operators are often regretted.
%
0
Does the control system create other environmental problems ? Solvent recovery systems
create hazardous liquid waste if the solvent cannot be reused. Steam stripping of carbon
produces a solvent contaminated wastewater stream. Spent catalysts and carbon are
typically not difficult to dispose of but do require special handling (catalysts may have
salvage value for their metal content and carbon can be thermally regenerated or
incinerated off-site).
With most control systems, the major factor that influences the size of the system is the
volume of exhaust handled. High exhaust rates may be required to maintain the level of worker
exposure to acceptable levels or to ensure that the concentration of combustible organic vapor
stays below its explosive limit. Ventilation rates for worker protection are typically established as
a minimum velocity (i.e., feet per minute) into a collection hood or as a minimum ventilation rate
(Le., cubic feet per minute) per square foot of open surface area. Typical minimum velocities
range from 50 to 100 feet per minute for enclosing hoods and from 75 to 150 for canopy hoods.
Lateral hoods, which consist of collection slots located around the perimeter of the tank,are
typically designed to operate at 75 to 250 cubic feet per minute per square foot of open surface
area. The actual rate required is a function of tank size and shape, tank location in relation to
drafts, rate of liquid evaporation, and toxicity of materials held in the tank.
In addition to maintaining a low concentration of solvent vapors in the work place, the
degree of ventilation must insure that vapor concentration does not exceed the ''lower explosive
limit" for the solvent in question. Many combustible solvents form explosive mixtures with air at
concentrations of 1to 3 percent by volume. To provide a safe operation, minimum ventilation
rates are typically maintained at 20 percent of the solvents lower explosive limit. Depending on the
solvent, rates of 1,000 to 2,000 cubic feet of air per pound of solvent emitted are specified. The
amount of solvent emitted is highly dependent on the operating temperature of the solvent, the open
area of the tank,the degree of agitation, and the amount of drag-out on the parts.
Once ventilation rates for worker protection and explosion prevention have been
determined, the ventilation system for the cleaning tanks may be sized. This is the same rate to
which the emission control system should be sized. Since the cost of most emission control
systems is a direct function of ventilation rate, care should be taken to not over-design or over
specify ventilation requirements. At existing facilities contemplating the installation of an emission
control system, re-evaluation of ventilation requirements can often result in sizable emission
reductions and reduced control costs. At one facility that the authors are aware of, redesign of a
tank lid to provide a better seal eliminated the need to ventilate the tank when it was closed. This
reduced solvent emissions substantially and eliminated the justification for installing a vapor
recovery system.
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CONTROLLING SOLVENT EMISSIONS TO AIR
8.2
Fume Incineration
Incineration of nonhalogenated solvent-laden air streams is an established conventional
technology. With the incineration of halogenated solvents, hydrochloric acid hmes are generated
which must then be controlled. Acidic fume control is typically performed by passing the gas
through a packed bed scrubber and contacting it with a caustic solution. The caustic reacts with
the acid forming a salt and is eventually discharged as a spent brine solution. For most small to
medium size emitters, fume incineration of halogenated solvents is seldom employed. Both direct
thermal and catalytic incineration of VOCs is discussed in the following sections.
8.2.1
Direct Thermal
Direct thermal incineration, also called thermal or direct flame oxidation, involves
oxidation of organics at temperatures ranging from 850 to 1,800 OF with 1,400 O F being fairly
typical. Destruction efficiencies ranging from 85 to nearly 100 percent (with a typical range of 90
to 95 percent), are achieved when residence times are kept within 0.3 to 1.O seconds and gas
velocities in the oxidation chamber range between 15 and 25 feet per second.
An advantage of thermal incineration over other control technologies is that VOC
destruction efficiency does not degrade over time. Catalytic incineration experiences a gradual
decrease in performance due to particulate fouling and other deactivation mechanisms. Thermal
incinerators can maintain 90 to 95 percent (or greater) destruction efficiency for the life of the
system. With catalytic systems, replacement of the catalyst may be required every few years.
A disadvantage of thermal incineration is that all of the exhaust must be heated to a high
temperatureto insure VOC destruction. This can result in high annual fuel costs unless there is
enough VOC present to support combustion. With low VOC concentrations ,the amount of NOx
produced from fuel gas combustion can sometimes equal or exceed the amount of VOC controlled.
To save fiel, many systems incorporate a heat recovery unit. Emissions of NOx may be
minimized by incorporating a Lo-NOx burner in the design.
To reduce fuel requirements, the incoming air stream may be preheated against the hot flue
gas using a heat exchanger or recuperator. Heat recovery systems offering 50 to 95 percent
thermal efficiency are commercially available. As expected, the higher the thermal efficiency, the
greater the equipment cost. Heat recovery employing a waste heat boiler or secondary exchanger is
achievable in situations where low temperature heat can be used for process or space heating.
Various manufacturers of these systems include Anderson, CE-Raymond, Catalytic Products
International, Conversion Technology, John Zink, Hirt Combustion, Kennedy Van Saun, McGill
Environmental Systems, Precision Quincy, Process Combustion, Reeco, Salem Industries, Smith
Engineering, and Sur Lite, among others. Many highly efficient units designed for low volume air
streams have recently entered the market. One such system is discussed below.
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CHAPTER 8.0
*
The Reeco Re-Therm VF system is an example of a highly modular thermal oxidizer and
recuperator unit designed to handle low volume air streams. The contaminated air stream enters
d e Re-Therm system through an inlet manifold. Flow control valves direct the air from this
manifold into energy recovery chambers (packed beds of ceramic material) that are in "inlet" mode.
The air stream is progressively heated as it passes through the ceramic bed. The air stream leaves
at a temperature very close to the incineration temperature. Oxidation is completed in the central
chamber where a gas burner maintains a preset incineration temperature.
The purified hot air exhaust is pulled from the central chamber through cold ceramic beds
which are in "outlet" mode. The air heats the bed and then exits to the atmosphere via exhaust fan
and stack. When the outlet bed reaches a pre-set temperature, the direction of air flow is reversed.
Energy which was stored in the outlet bed is now used to heat the air and the depleted inlet bed is
used to cool the exhaust. A thermal energy recovery factor of 95 percent is claimed by the Reeco.
8.2.2
Catalytic Oxidation
Catalytic incineration or oxidation of solvent-laden air streams takes place at temperatures
ranging from 500 to 900 OF, considerably lower than thermal incineration. The lower combustion
temperatures result in considerably lower fuel consumption rates. The catalysts usually involve
various noble metals, such as palladium, platinum, ruthenium, or rhodium deposited on an alumina
support. Systems may be of fixed bed design employing catalyst beads, rings, or monolithic
"honeycomb" blocks. Fluidized bed systems are also on the market. Commercial systems are
available from ARI Technologies, CE-Air Preheater, Catalytic Products International, Conversion
Technologies, Dedert, Enders Engineer, McGill Environmental System, Met Pro, Smith
Environmental, and John Zink.
Many catalytic systems suffer from fouling when treating air streams that contain resinous
particulates. Liquid or solid particles that deposit on the catalyst form a coating that reduces
activity by preventing contact of the VOC with the active catalyst sites. Catalyst fouling can be
reduced or prevented by means of adequate filtering. Catalyst life is also limited by thermal aging
and by loss of active sites. Active sites may be lost due to erosion, attrition, and vaporization.
With proper control of operating temperatures, the rate of site loss can be minimized and
performance is usually maintained for a period of three to five years. After that, the catalyst bed or
catalyst material must be replaced. Depending on the concentration of rare metals contained in the
spent catalyst, recovery by an off-site recycler may be a viable alternative to disposal.
8.3
Carbon/Polymer Adsorption
Removal of contaminants using activated carbon is a well established technology.
Recently, new polymeric materials that overcome the limitations of carbon have also entered the
marketplace. The process consists of three discrete sequential steps: adsorption, desorption, and
desorbed gas processing. Adsorption is the accumulation of molecules (adsorbate) at the interface
122
~
___
CONTROLLING SOLVENT EMISSIONS TO AIR
bdween the fluid and solid phases, where the molecules are selectively attached to the surface of
the solid. Activated carbon is used extensively because of its low polarity. This results in high
selectivity for organic vapors and low selectivity for water vapor. This is in contrast to other
adsorbents such as alumina, zeolite, or molecular sieves. Other advantages of activated carbon
include large intemal surface area and relatively low cost.
The conventional adsorption step relies on passing solvent-laden air through a fixed bed of
granular activated carbon. Adsorption of organics takes place with an associated release of heat
(heat of adsorption) until the saturation capacity of carbon is reached or approached. Typical
loading for virgin carbon may range from 5 to 20 weight percent or more depending on the VOC
controlled. At this point, the carbon inventory must either be replaced or regenerated. Other
systems include granular carbon maintained in a fluidized bed or carbon fiber spun into a mesh.
Once saturated, the carbon must be regenerated or replaced. Replacement eliminates the
need for regeneration equipment and insures maximum loading capacity. With carbon regenerated
on site, the loading capacity seldom exceeds 25 percent of the loading capacity for virgin carbon.
Off-site high temperature regeneration can restore the spent carbon to its maximum capacity.
4
Two major vendors of off-site regenerable systems are Calgon and Westates Carbon. The
Westates system consists of a number of carbon panels in series through which the solvent-laden
air stream must pass. Flow rates of 1,000 standard cubic feet per minute or less and VOC
concentrations below 300 parts per million can be controlled. The typical adsorption system is
designed with two carbon panels in series, each 3 to 12 inches thick depending on VOC loading
the potential for VOC breakthrough, a sensor is
and desired change-out schedule. To " i z e
placed between the two panels and wams when breakthrough of the first panel has occurred. In
response, an operator removes the spent panel, slides the second panel back and places a new panel
into the available space. The VOC removal efficiency typically ranges from 97 to 99 percent.
Operating costs include power for running ventilation blowers and carbon regeneration fees (about
$2 per pound of carbon). Pick-up, regeneration, and delivery of carbon for the system is provided
by the vendor.
When the amount of VOC to be controlled is high, off-site carbon regeneration becomes
impractical and some means of on-site regeneration is required. Regeneration (or desorption) relies
on heating the adsorbing medium to release captured solvents. A carrier gas is provided as a heat
transfer medium and as a diluent to lower the partial pressure of solvents in the gas phase. This
increases the driving force and rate of desorption from the solid. The desorption modes used in
commercial applications include steam regeneration, hot nitrogen regeneration, hot air regeneration,
vacuum regeneration, and UV/ozone regeneration.
Steam regeneration is practiced most frequently - over 90 percent of all carbon beds in the
United States are steam regenerated. Steam has the advantage of providing more than 40 times the
available heat per unit weight compared to hot air or nitrogen. This is due to its release of heat
123
CHAPTER 8.0
u p n condensation to water. Additionally, the formation of low boiling point azeotropes between
certain high boiling organic solvents and water facilitates their desorption. With hot air or
njtrogen, very high desorption temperatures would be required to effect their removal. The amount
of steam required for desorbing a bed is commonly set at 4 to 6 pounds per pound of solvent to be
desorbed. From the bed, steam and desorbed solvent are routed to a water cooled or refrigerated
condenser and then to a decanter for phase separation (if immiscible).
Proper design, operation, and maintenance of the equipment is critical to the successfir1
operation of a carbon bed system. Examples of common design errors and operational problems
include: selection and use of carbon that does not meet design specifications, use of poorly
designed andor maintained dampers which do not open and close properly and allow solvent
vapors to bypass the bed, improper timing of the desorption cycle so that beds are either oversteamed and energy is wasted or under-steamed and subsequent solvent breakthrough of the bed
occurs, and installation of faulty and unreliable emission monitoring controls and sensors.
Principal disadvantages of steam regeneration include the creation of a potentially
troublesome regenerant stream (discussed below) and the enhancement of equipment corrosion.
Certain halogenated solvents such as TCA or METH are prone to reaction with water and may
form hydrochloric acid. While most halogenated solvents contain stabilizers to prevent this
occurrence during use, the carbon system may selectively remove them. Esters of acetic acid may
also decompose to form acetic acid. Metallic impurities present in some grades of granular carbon
may catalyze decomposition. The potential for corrosion may necessitate the use of expensive
construction materials such as Hasteloy C or titanium.
When steam is used for regeneration, water pollution problems may result from the
chemicals contained in the recovered water stream. Water-soluble stabilizers removed during
steam desorption will be present in the condensed water and may enter the sewer unless handled as
a hazardous waste or treated. Some halogenated solvent will also remain dissolved in the steam
condensate. For example, the solubility of PERC in water is 0.015grams per 100 grams of water.
While the amount of PERC is small, the water may require treatment before discharge. Removal
of contaminants from the water can be performed by steam stripping or by water phase carbon
adsorption. Both of these activities generate their own wastes which must be dealt with and
handled properly.
A relatively new system that avoids the need for regenerant vapor processing is the W
Oxidation (WOx) System manufactured by Traiger Energy Systems. The system is essentially a
conventional dual fixed-bed carbon adsorption system that employs an ozone-rich air stream to
effect regeneration. Rather than heating the bed and desorbing the organics, the ozone-rich air
oxidizes the organics directly on the carbon. To prevent blockage of the carbon pores, the inlet
stream is filtered with a chemically inert polypropylene fiber filter. The General Dynamics facility
in San Diego California is known to be operating two of these systems for the control of VOC
emissions from their paint booths.
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CONTROLLING SOLVENT EMISSIONS TO AIR
*
For on-site systems requiring regenerant vapor processing, such processing may be
accomplished by means of condensation followed by phase separation or by direct vapor
ihcineration. Direct incineration usually employs a catalytic oxidizer so as to minimize fuel costs.
Condensation should be considered when the recovered solvent is highly immiscible with water and
has a high market value. Condensation is, by far, the most conventional method of handling the
solvent-rich regenerant vapors.
Condensation is commonly applied with steam, hot nitrogen, or vacuum regeneration. The
hot vapor is passed through a water-cooled condenser and the condensate flows into a vented
receiver / separator vessel. If steam is used as a regenerant, a mixture of solvent and water is
obtained. Those solvents which are insoluble or only slightly soluble in water will separate from
the water phase. In many cases, however, the solvents stripped from the carbon bed are watersoluble to an appreciable extent (e.g., ethyl acetate, some ketones, and alcohols). This significantly
decreases their recyclability. Frequently, a complex azeotropic distillation process using solvent
entrainers is required to perform the separation. Potential alternatives include solvent extraction,
membrane separation, or molecular sieves. In most cases, the additional processing steps
necessary to recover the solvent for reuse make the economics of recovery unattractive. The net
result is the generation of a solvent-laden wastestream that may pose a costly or difficult treatment
and disposal problem.
The above problems can be significantly reduced if nitrogen or, in some cases, a vacuum is
used to regenerate the bed. Condensed solvent quality is high, since any water present is limited to
the ambient moisture adsorbed on the carbon. This is usually a very small amount relative to the
solvent. In such cases, dewatering can be accomplished relatively inexpensively through the use of
desiccants. Depending on how the recovered solvent will be used, dewatering may not be required.
Incineration of regenerant vapor offers an attractive alternative to condensation in cases
where the economics do not justifjr solvent recovery. Thermal oxidation is practiced with steam
regenerated beds in the so-called "hybrid system." Regenerant vapor from desorption is thermally
oxidized in a direct fbme or catalytic incinerator. To reduce operating costs, the incinerator is
coupled with a waste heat boiler which generates the steam used for desorption. Such systems are
marketed by Amcec Corporation, Combustion Engineering, and by Pullman Industries in
.cooperation w
ith VIC Manufacturing. Incineration is also practiced with systems that are
regenerated with hot air. In this application, the carbon bed acts as a concentrator, increasing the
VOC concentration and reducing the volume of gas the incinerator must handle. Depending on the
original VOC content of the air stream, concentration ratios as high as 20 to 1 are typical.
The Cadre VOC control process by Calgon Carbon Corporation is a concentration system
using granular activated carbon adsorption with hot flue gas desorption. The hot gas is supplied
from the afterburner used to combust the desorbed solvents. The system can typically handle inlet
VOC concentrations ranging from 10 to 300 parts per million and volumes ranging from 10,000 to
125
CHAPTER 8.0
3d0,OOO standard cubic feet per minute. The VOC destruction efficiency of the system is typically
greater than 95 percent.
!
Other concentrating systems but of different design are the KPR Solvent Concentrating
System from Met Pro Corporation and the Rotosorbon system from Dedert Corporation, Both
systems utilize an activated carbon fiber contained in a rotating cylinder. The cylinder, made of
carbon fiber spun into a honey comb structure, is rotated through the incoming solvent-laden air
stream. Following an extremely rapid adsorption process, the solvent-rich segment of the cylinder
rotates into the desorption zone where hot air at 250 O F regenerates the carbon. Since the quantity
of hot air used for regeneration is considerably smaller in volume than the solvent-laden air stream,
a large degree of concentration is achieved. Stripped solvents are then sent to a catalytic unit for
incineration. The systems are typically designed to concentrate inlet streams containing less than
500 parts per million VOC. Capture and combustion efficiencies of these systems typically range
from 95 to 98 percent.
Polymeric adsorption is a new process for solvent recovery and purification, developed by
Nobel Industries in Sweden. The process is based on adsorption of solvent on specially developed
macro-porous polymer particles, using fluidized bed technology. The polymers have been
optimized for use as adsorbents; they consist of small 0.5 millimeter diameter cross-linked styrene
divinyl benzene pellets. According to the manufacturer, advantages of polymer adsorption over
carbon includes ability to handle humid air streams, ease of polymer regeneration, long lifetime,
and absence of catalytic effects on halogenated solvents. Control of flows as small as 300 cubic
feet per minute at efficienciesof 90 to 95 percent is possible.
In the process, solvent is adsorbed by the polymer particles as the solvent laden air passes
through the adsorption bed. The flow of air causes the polymer bed to fluidize and behave like a
liquid. Heavy,solvent laden polymer particles drop to the bottom of the bed while the lighter
unladen particles remain at the top. The solvent laden particles are continuously removed from the
bottom of the bed, regenerated, and fed back to the top of the adsorption bed. In the desorber or
regenerator, the solvent laden polymer is heated with a hot inert gas such as nitrogen which causes
the solvent to desorb. The solvent and hot gas are then routed to a condenser where the solvent is
condensed and collected while the inert gas is reheated and retumed to the desorber. The desorbed
polymer is retumed to the adsorption bed. The process is attractive because it has few moving
parts and energy consumption is low. Several installations have been built in Europe.
8.4
Liquid Absorption
In addition to adsorption onto a solid substance, removal and recovery of solvent vapors
from air streams can be accomplished by means of liquid absorption. In such a system, the air
stream is contacted with a scrubbing solution into which the solvent is soluble. The contacting
takes place in a packed bed or trayed column through which the gas and liquid flow in a countercurrent contiguration. The choice of scrubbing solution is central to the success of the process.
126
CONTROLLING SOLVENT EMISSIONS T O AIR
W%er is a good scrubbing medium for acetone, alcohols, and other water-soluble solvents.
However, water scrubbing will result in the necessity for extensive wastewater treatment
auipment. Most municipalities impose severe restrictions on the concentrations and quantities of
solvents discharged to sewer. Viable wastewater treatment technologies may include steam
stripping and disposal of the condensate or biological oxidation of the scrubber water. Care must
be taken that the biological oxidation system is not excessively aerated and that an air emission
problem is not transferred from one system to another.
Organic vapors can be scrubbed and subsequently recovered using high-boiling oils as a
scrubbing medium. The Ceilcote Corporation manufacturers a VOC absorption system which
utilizes a proprietary low vapor pressure organic liquid (Solvolex). The system consists of a sieve
tray scrubber column, a ceramic packed stripping column, a heat exchanger, a series of
condensers, a steam reboiler, a demister, and an accumulator. Solvolex is continuously
recirculated in a closed-loop and is preheated by waste heat from the absorbent regenerator or
stripper. The Ceilcote system can handle VOC feed concentrations as low as 50 to 100 parts per
million. Given the amount of equipment required, the system is most cost effective when treating
large volume air streams. The VOC removal efficiency typically ranges from 90 to 99 percent
depending upon the type of solvent recovered.
8.5
Condensation
Direct condensation of vapors from an air stream is technically the most straight forward
and simple recovery method. If vapor concentrations are high enough (typically greater than 5,000
parts per million), good recovery efficiencies can be achieved by passing the solvent-laden air
stream over a refrigerated cooling coil. In cases where the solvent concentration is low,
compressing the air stream to a higher pressure and raising the dew point of the solvent vapor can
improve recovery. At very high pressures, the use of a refrigerant can be avoided altogether.
Because the cost of cooling andor compressing a large volume of air is prohibitively high,
condensation sees limited application for solvent recovery in most cleaning operations.
To improve the economic viability of condensation processes, solvent concentrations must
be raised. This can sometimes be accomplished by enclosing the solvent emitting process and
reducing air flow from the unit. Since high levels of ventilation are often required for worker
protection, automation may be necessary to limit worker exposure. In the case of flammable
solvents, vapor concentrations above 20 percent of the lower explosive limit should be avoided.
Concentration of vapors above this level may necessitate the need for inert gas blanketing of the
emission source. Automatic fire suppression, explosion suppression, and oxygen gas monitoring
may also be required.
High recovery efficiencies can be achieved with condensation by means of direct
refrigerant injection. This approach injects a liquid gas such as nitrogen or carbon dioxide directly
into the air stream. This method is very effective and does not suffer from many of the mechanical
127
CHAPTER 8.0
prClblems (such as ice fouling of condenser surfaces) that plague other condensation methods. The
Cryosolv Process developed by Meisser Griesheim, a German company, uses liquid nitrogen as a
cboling agent in direct or indirect contact with the solvent laden air stream. Condensation
temperatures range from -150 to -220 OF. Liquid Carbonic also offers a similar process for sale in
the United States (Liquid Carbonic, 1989).
To promote development of high pressure condensation technology, the U.S. Department
of Energy (DOE) in conjunction with 3M and Garrett Air Research has been supporting research
and development of the Brayton Cycle Heat Pump. The technique uses a reverse Brayton
refrigeration cycle to condense solvent vapor to liquid. The process cools the incoming gas stream
to a very low temperature, as low as -298 O F , and condenses the solvent for collection. Because
the heat pump is a precision built turbine unit, capital equipment costs are high. The system also
performs best on clean, steady flows which are seldom encountered in most facilities. Therefore,
direct application of this process to a solvent emitting source has been viewed as having very
limited application potential.
Most of the current research work underway focuses on the use of carbon adsorption with
coupled or decoupled Brayton cycle regeneration (Scheiling, 1991; and Marr, 1991). The systems
being investigated are identical to conventional carbon bed adsorption systems during the
adsorption cycle. Once saturated, the beds are then regenerated using the Brayton process. Hot,
inert gas (typically nitrogen) passes through the adsorbent bed and desorbs the solvent. The
solvent laden gas is then cooled, compressed, cooled again, and then sent through the compressor
side of the heat pump (a free-spindle turbo unit). The gas stream is further cooled in an interchanger and enters the expander side of the heat pump where it is cooled to -80 O F . The solvent
condenses and is recovered for reuse while the inert gas is reheated and used for regeneration.
To prevent ice formation, water must be eliminated from the regeneration gas. Use of
either drymg steps or appropriate water rejecting adsorbents can eliminate this problem. The
Brayton process avoids the use of steam for regeneration and thereby does not produce a
wastewater stream. The process also eliminates the problem of water-soluble stabilizer depletion
from halogenated solvents. This method has been demonstrated at 3M for solvent recovery from a
commercial size magnetic tape manufacturing facility (Nucon, 1989). A demonstration program
using a decoupled Brayton system (the carbon beds remain on-site and a transportable Brayton
system is routinely brought on-site to regenerate the beds) is currently being set-up in the Southem
California area by the Southem Califomia Edison Company (Marr, 1991).
8.6
Membrane Separation
Synthetic membranes have been used to separate aqueous and gaseous mixtures and to
recover hydrogen from petrochemical and chemical production purge gas streams. Since
membranes can be tailor fitted to a given mass separation task, they tend to be suitable for
separations that are difficult to achieve by other methods. Semi-permeable composite membranes
128
CONTROLLING SOLVENT EMISSIONS TO AIR
M e been used to separate organic solvents from air. The membrane modules, which are made by
coating a tough, relatively open, microporous support membrane with a very thin dense film,
allows a large membrane surface area to be packed into a small volume. The support membrane
provides mechanical strength and the thin dense coating performs the separation. Organic solvents
are preferentially drawn through the membrane by a vacuum pump and the solvent is condensed
and removed as a liquid.
The manufacturer of these systems claims that comparison to carbon adsorption shows
that the membrane process is more cost-effective if the solvent concentration is relatively high (0.5
percent or higher) and the air stream volume low, less than 1,000 standard cubic feet per minute
(Wijmans et al., undated). Given the high concentration required for this process to be cost
effective, membrane systems have limited application potential for direct use. Where they do show
promise is for controlling emissions from inert blanketed systems and in recovering solvents from
carbon bed regenerant vapors. Both of these applications involve high solvent concentrations and
low flow rates. The use of membrane separation technology for VOC emission control and
recovery is a very new field and may offer some potential in the future.
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CHAPTER 8.0
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7
130
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*
9.0 IMPLEMENTING A NEW PROCESS
Implementing a new process, or making major modificationsand improvements to an
existing process can be a considerable undertaking. This is especially true when a major project is
undertaken in an operating facility. Quite often, demolition and removal of existing equipment may
be required before the new system can be installed. Delays in construction schedules, even minor
ones, can have major impacts on facility productivity during the transition period.
While it would be nice to say that these impacts can be avoided quite easily, such is not the
case. Minimizing impacts during the transition phase requires planning, more planning, and a fair
amount of luck. As with any change to the status quo, the assumption of risk is inevitable. The
amount of risk one assumes however is a direct h c t i o n of preparation and planning. The
following sections discuss various aspects of modifjmg an existing system or implementing a new
one. The chapter ends with several examples of preparing a capital and operating cost analysis.
9.1
Establish a Baseline
Before undertaking the modification of an existing system or design of a new system, one
should take a step back and look at the operation. One should try to establish a baseline in terms
of cleaning requirements, work loads, part configuration, processing times, and operating costs.
Other data should include items such as utility availability and costs, space availability, regulatory
constraints, and others. Collection of baseline data should be an ongoing task so as to avoid the
mad scramble that occurs when someone finally decides that something must be done.
Another good reason for establishing a baseline is to educate the various decision makers
at the facility as to the true cost of cleaning. Quite often, the "sticker shock" syndrome that occurs
when one is faced with spending a considerable amount of capital for the replacement of a paid for
and hnctional system is as much due to the size of the price tag as it is due to ignorance of current
operating costs. The danger of "sticker shock" is that decision makers may respond by delaying
projects until the last possible moment (which thereby impacts the ability to plan) or by slashing
the size and scope of the replacement system which may place a greater burden on the operating
personnel. By developing a baseline cost, one should be better prepared and more able to obtain
funding for the system they want.
The first step in determining costs is to construct a material balance. In its simplest form,
the material balance is represented by the mass conservation principle:
Material In = Material Out + Material Accumulated
The quantities are best expressed on a mass basis. The material balance should be made
individually for all of the components that enter and leave the process. When chemical reactions
take place in a system, there is often an advantage to doing "elemental balances" for specific
chemical elements. Fortunately, the effect of chemical reactions can be ignored in most cleaning
13 1
CHAPTER 9.0
ofirations. Of greater importance is the accumulation of material such as grease and sludge inside
the equipment.
To construct a mass balance, start by listing the types and quantities of all materials
entering a given tank or process unit. In the case of cold cleaning with solvents, the number of
drums emptied into the tank each year would be appropriate. Next estimate the amount of waste
removed from the tank each year in the form of spent solvent or sludge. Since this waste consists
of both solvent and dirt, you will need to estimate the percentage of solvent and dirt. This
percentage can be determined by direct analysis or it can be estimated based on the number of parts
cleaned per year and the average amount of dirt per part. Estimation of dirt loading is not as
accurate as direct measurement since it assumes that all dirt is removed by the solvent and that
none remains on the parts.
By taking the amount of solvent removed from the tank as waste and subtracting this from
the amount of solvent added to the tank as make-up, one now knows how much solvent was lost by
way of drag-out and evaporation. Using the drag-out factors presented in Chapter 6 and the total
square footage of parts cleaned in the year, drag-out losses, and hence evaporative losses can be
estimated. Likewise, emission testing of the tank may provide a reliable estimate of evaporative
losses and drag-out can be back calculated by difference.
In performing a material balance, one should remember to always look for closure (i.e., in
= out + accumulation). Just because the data used appears to be reliable, does not mean that
closure is assured. Data reported in literature, and this guide is no exception, more often than not
represents averages or typical values and not absolutes. The same applies to many of the
assumptions one must make to construct a mass balance. Quite often, it is beneficial to construct
several mass balances for the same system using data from different sources. This can help one
develop a feel for what is reasonable and what is not. An example would be an operator reporting
that vapor loss from a degreaser was negligible while solvent make-up and disposal records
indicate a significant vapor loss. A listing of sources of information that can be used to construct a
mass balance is presented below:
e
e
e
e
e
e
e
e
e
e
Stream analyses and flow measurements
Raw material purchase records
Emission Inventories
Equipment cleaning and validation procedures
Product specifications
Design material balances
Production records
Operating logs
Standard operating procedures/manuals
Waste manifests
There are several factors that must be considered when preparing material balances in
order to avoid errors that could significantly overstate or understate stream flows. The precision of
132
IMPLEMENTING A NEW PROCESS
analytical data and flow measurements may not allow an accurate measure of the stream. In
particular, in processes with very large inlet and outlet streams, the absolute error associated with
measurement of these quantities may be greater in magnitude than the size of secondary streams
leading into or out of the process. In this case, a reliable estimate of secondary streams cannot be
obtained by difference. Generally, subtraction of two large numbers to obtain a small number
yields erroneous results.
In calculating material balances, it is necessary to know how much material enters the
process. Raw material purchase records can be used to provide this data if more direct measures
are not available. However, using purchasing data for feed streams entails the same problems as
using manifest data for waste streams. The main problem is that quantities and ordering
frequencies may not directly relate to production rate. Large volumes of materials may be ordered
quarterly or when prices are low. This can lead to errors in the calculation if not accounted for.
After performing a material balance, the next step is to perform an economic evaluation.
This establishes the baseline for operational cost comparisons. Major items to account for include
raw material procurement costs, hazardous waste handling and disposal fees, operating and
maintenance labor, utilities, permitting fees, and others. Some costs, such as potential liability, are
intangible and cannot be readily quantified. The issue of operating cost is explored further in
subsequent sections of this chapter.
9.2
Select a Replacement System
In most small to medium size operations, selection of a replacement system will involve
submission of baseline process data to several equipment manufacturers for recommendations and
bids. General design criteria may involve the specification of immersion, immersion and spray, or
spray only for cleaning; use of steam, gas, or electricity for heating; number of rinse stages; need
for drying; method of parts handling; and extent of automation. For large installations, alternative
cleaning systems may be designed by in-house s t a f f fiom the ground up or may be contracted-out
to a consulting firm for design.
In addition to equipment selection, one must select the type of cleaner that will be used in
the system. The issue of cleaner selection has been discussed in several of the previous chapters
and will not be repeated here. To insure a happy marriage between cleaner and equipment, close
coordination among the cleaner formulator, equipment manufacturer, and system user is essential.
Before selecting a formulator or equipment manufacturer, one should contact or visit one or more
facilities where the products are in use. First-hand user experience is a good way to weigh various
claims made. User comments can also help in refining "wish lists" and in establishing a level of
confidence in the replacement technology.
In addition to site visits and user comments, bench-scale or pilot-scale demonstrations are
useful for establishing the performance characteristics of a proposed system. Some equipment
133
CHAPTER 9.0
suppliers offer rental test units while others will install systems on a trial basis. Most cleaning
solution suppliers will readily supply samples of their products for testing. By setting-up a small
scale test system at the facility, operators can see how well the system will or will not clean the
various parts to be handled.
Perform an Economic Evaluation
9.3
The economic evaluation is carried out using standard measures of profitability such as
payback period, return on investment, and net present value. Each company tends to have its own
set of economic criteria for selecting projects for implementation. In performing the evaluation,
various costs and savings must be considered. The two major components to be determined are
capital and operating costs.
Table 9-1lists capital cost items typically associated with a major engineering project.
These costs include not only the fixed capital costs for designing, purchasing, and installing
equipment, but also costs for working capital, permitting, training, start-up, and finance charges.
Many items are included in the table that are not normally required for projects going into an
existing facility. For example, new utility systems are usually not required although connections or
improvements to existing utility systems may be necessary.
As imagined, developing a detailed capital cost estimate can be quite an undertaking. The
price one pays for developing such an estimate is that a carefilly prepared estimate can often be
with-in plus or minus 5 to 10 percent of the final actual cost. Less precise, and hence less accurate
methods include order of magnitude estimates (plus or minus 50 percent), factored or budget grade
estimates (plus or minus 30 percent), and study grade estimates (plus or minus 15 to 20 percent).
Order of magnitude estimates are typically reported in terms of total dollars per ton of parts
cleaned or volume of cleaner required. A factored estimate is based on summing the cost for all
major equipment items such as tanks, filters, and pumps and then applying factors to account for
other costs such as piping, installation, etc.
Once the capital costs have been derived, the next step is to determine the operating costs
for the new system. In making the economic evaluation, it is sometimes more convenient to use
incremental operating costs than absolute costs. Incremental operating costs represent the
difference between the estimated operating costs associated with the new cleaning technique and
the actual operating costs of the existing system. Listed below are several incremental operating
costs and savings that should be considered in the analysis:
0
Raw Materials - Prices for CFC-113and TCA are rising rapidly. Prices for abrasives,
aqueous cleaners, and many alternative solvents are much lower and are more stable.
Hazardous Wastes - Cost and/or potential savings are highly dependent on alternative
selected. Items to consider include off-site treatment, storage, and disposal fees; state fees
and taxes on hazardous waste generators; transportation costs; on-site treatment, storage,
and handling costs; permitting, reporting, and record keeping.
134
IMPLEMENTING A NEW PROCESS
TABLE 9-1
CAPITAL INVESTMENTS FOR A LARGE SCALE PROJECT
Direct Capital Costs
Site Demolition
Demolition and alteration work
Site clearing and grading
Walkways and fencing
Process Equipment
All equipment listed on flow sheets
Spare parts
Taxes, freight, insurance, and duties
Materials
Piping and ducting (includes valves, fittings, and hangers)
Insulation and painting
Electrical (including wiring, conduits, panels, switches, and motors)
Building and structures (including foundations, supports, cranes, ladders,
platforms, concrete, and structural steel)
Connections to existing building
Process water, cooling water, and wastewater connections
Heating, ventilation, air conditioning, and dust collection
Electric power, steam, refrigeration, fuels, plant air, and inert gas
Lighting and fire control
New utility and service facilities
Storage and handling equipment
Laboratory equipment
Other non-process equipment
Construction and installation
Labor salaries and burden
Safety, medical, and fringe
Supervision, accounting, time keeping, purchasing, and expediting
Temporary facilities
Construction tools and equipment
Taxes and insurance
Building permits, field tests, and licenses
Indirect Capital Costs
In-house engineering, procurement, and other home office costs
Outside engineering, design, and consulting services including contractors' fee
Permitting and source testing costs
Training and start-up costs
Initial charge of chemicals
Contingency
Interest accrued during construction
Working Capital
Raw material inventory
Finished product inventory
Materials and supplies
135
CHAPTER 9.0
Product Quality - Reduction in product quality may result in increased costs for rework,
scrap, or quality control inspections. Some alternative technologies may provide a more
consistent and higher level of cleanliness hence improving quality.
Operating and Maintenance Labor - Labor requirements may increase or decrease. This
may be reflected in changes in overtime charges or in changes in the number of employees
required. In addition to direct labor, burden and benefit costs will change accordingly.
~~
Utilities - As with labor, the cost for utilities such as steam, electricity, process and cooling
water, plant air, refrigeration, or inert gas may increase or decrease. Required utilities
associated with emission controls such as VOC recovery systems, solvent stills, or
wastewater treatment units must be included.
-
Other Operating costs / savings that should be considered when performing an economic
comparison include required operating and maintenance supplies, insurance and liability,
overhead costs, changes in revenue from increased or decreased production, and generation
of a marketable by-product.
For facilities currently using halogenated solvents, operating costs for procuring these
solvents have been rising dramatically and will continue to do so. In addition to recently imposed
federal taxes, the rapidly declining supply of these chemicals will make them much more expensive
to procure. Use of an inflated procurement cost or use of a higher rate of escalation for these
materials is often appropriate. For facilities using TCE, PERC, or M E W , inclusion of future
costs for increased monitoring of worker exposure and increased requirements for control may be
considered for inclusion. Alternative cleaning technologies that were economically unattractive in
the past are quickly showing economic advantages over the continued use of halogenated solvents.
A projects profitability is measured using the estimated net cash flows (cash income minus
cash outlay) for each year of the project life. Normally, internal company projects are evaluated on
a pretax basis. The revenue and costs used to calculate net cash flows for a typical project are:
Increased Revenues + Operating Cost Savings
= Net Operating Savings
Net Operating Savings - Interest of Loans
= Pretax Profits
Pretax Profits - Loan Principal Repayment - Capital Investment + Salvage Value
= Net Cash Flow
It should be noted that net cash flows should be calculated for each year of the project life
beginning with the construction period. The outlay for capital investment takes place at the start of
the project and the salvage value is recovered at the end. Once the annual cash flows have been
determined, the projects profitability can be determined. The three standard measures of
profitability most commonly used in business include calculation of the payback period, internal
rate of return (IRR), or net present value (NPV).
136
-
IMPLEMENTING A N E W PROCESS
The payback period for a project is the amount of time it takes to recover the initial cash
outlay for the project. Payback period is determined by dividing the total capital investment by
annual operating costs savings. For example, a $150,000 project that will save $50,000 per year
in operating costs has a payback period of 3 years. Typically, a payback period of 3 years or less
is economically favorable.
For projects with longer payback periods, consideration of intangible savings have been
practiced by some companies to improve the outlook for the option. In the case of CFC or TCA
replacement, some projection of fbture costs and eventual unavailability must be made. In this
situation, it may be possible that no alternative will yield a cost saving and hence the goal is to find
the least expensive option to install.
The IRR and NPV are both discounted cash flow (DCF) techniques for determining
profitability. Many companies use these two methods as the means of ranking competing capital
projects. Capital funding for a project may well hinge on the ability of a project to generate
positive cash flow beyond the payback period to realize an acceptable retum on investment. Both
the IRR and NPV recognize the time value of money by discounting the projected fbture net cash
flows to the present. For investments with a low level of risk, an after-tax IRR of 12 to 15 percent
is typically acceptable. Many popular computer spreadsheet programs can calculate IRR and
NPV for a series of cash flows. Detailed information about these methods can be found in most
cost accounting and financial management textbooks.
Prepare The Final Report
9.4
Once completed, a final report should be prepared. A well prepared final report can be an
important tool for obtaining h d i n g , either from your upper management or local bank. In
presenting the feasibility analysis, it is often useful to evaluate the project under different scenarios.
This may involve different product rates, material costs, or competitive technologies. The report
should include not only how much the project will cost to implement but also how the project will
be implemented. It is important to discuss:
0
Whether the technology is established, with mention of successful applications elsewhere.
0
The required resources (for example, technical expertise and labor available in-house
versus those that must be brought in from outside).
0
Estimated time to complete construction and start-up, including production downtime.
Contingency plans in case the equipment does not perform as expected (this may include
phased installation or keeping the existing system on-line until the new system is proven).
After completing the report, it is time to get financing. Private sector financing includes
bank loans and other conventional sources of funds. Government financing may also be available
137
CHAPTER 9.0
in some cases. Contact the Small Business Administration for information regarding loans for
implementing P2 projects. Some states can also provide technical as well as financial assistance.
Once funding is obtained, the installation of the project proceeds in much the same way as
with any capital improvement project. Major phases include project planning, design (both
preliminary and detailed), procurement, and construction (or installation). The installation of the
equipment should be scheduled during long holiday weekends so that the impact on production is
lessened. Many facilities prefer the time period between Christmas and New Years Day.
9.5
Example Economic Analysis
An example economic analysis is presented in the following sections for a facility faced
with updating or replacing their PERC vapor degreaser. Updating involves retrofitting the unit
with an automated roll top lid and installing a carbon bed system to control vapor loss.
Replacement would involve removal of the unit and installation of an aqueous cleaning system in
its place. Since each facility and operation represents a unique set of operating conditions and
constraints, the analysis presented is based on emission factors and operating conditions that mimic
a Yypicall' operation. Given that no such "typical" facility exists and that every operation is
unique, the results presented may not be representative over a fill application range. To this end,
all of the assumptions used are so stated. The interested reader should not have a difficult time
adopting the analysis to his or her own use.
9.5.1
The Existing Facility
A hypothetical facility currently operates a 10 year old medium-sized vapor degreaser that
contains 80 gallons of PERC. The vapor zone is 3 foot wide by 5 foot long by 3 foot deep and the
baskets used are 2 foot by 4 foot by 2 foot. The maximum loading capacity of the degreaser is
3,000 pounds per hour. The maximum heat input rate is 90,000 British Thermal Units (Btu) per
hour and the cooling water flow is 160 gallons per hour. These values are based on data presented
in ASM (1982) for a medium-sized degreaser. Existing case operating data is shown in Table 9-2.
The facility operates 8 hours per day, 5 days per week, and 50 weeks per year. The hourly
workload is 4 baskets of (8) 2 foot by 3 foot by one-eighth inch steel plates. The weight of steel
cleaned is 250 pounds per basket or 1,000 pounds per hour. Including the weight of the basket, a
total of 1,200 pounds per hour is run through the degreaser. The amount of oil removed is taken to
be 0.2 gallons per hour or 0.5 gallons per 1,000 square feet of surface cleaned. The average heat
input for processing parts is taken to be 50,000 Btu per hour.
Energy use for the basket conveyor system is 5 horsepower or 4 kilowatt hours.
Ventilation requirements are 2 horsepower or 1.5 kilowatt hours and the lip exhaust is operated
continuously to remove vapors from the work area. The amount of exhaust removed from the area
is 100 cubic feet per minute per square foot of degreaser open-top area or 1,500 actual cubic feet
138
IMPLEMENTING A NEW PROCESS
TABLE 9-2
SUMMARY OF OPERATIONAL PARAMETERS FOR THE BASE CASE
Operating Conditions
Operation
Parts + Baskets
Heating (Start-up)
Heating (Operation)
Conveying Baskets
Ventilation
Cooling Water
Solvent Purchases
Waste. Disposal
Air Emissions
Maint. Materials
Maint. Labor (Testing)
Maint. Labor (Cleansut)
8 hrs/day, 250 days/yr
1,200 Ibs/hr, 500 ft2/hr
90,000 Btu/hr, 1 hr/day
50,000 Btu/hr, 7 hrs/day
4 kw-hr, 8 hrs/day
1.5 kw-hr, 8760 hrdyear
160 g a m , 8 hrs/day
1290 gallons per year
800 gallons per year
6 tons per year
2 percent of capital
1 hour per week
4 hours every 2 weeks
Utility Costs and Fees
Ste.alll
Electricity
Water Purchase
Sewer Fees
Solvent Cost
SCAQMD Emission Fees
SCAQMD Permit Fees
Waste Disposal
Maint. Labor
$5 per 1,000,000 Btu
$0.09 per kw-hr
$0.15 per 1,000 gallons
$1.15 per 1,000 gallons
$4 per gallon delivered
$289 per ton of PERC
$570 per year per unit
Negligible
$25 per hour, burdened
per minute overall. The degreaser has a manual lid but it is difficult to use and does not provide a
good seal. Therefore, the degreaser is left open when not in use. The facility pays 9 cents per
kilowatt hour for electricity and $5 per million Btu for steam heat. Adequate utility capacity is
available for expansion.
Air emissions from the working vapor degreaser are taken to be 0.3 pounds per hour per
square foot of open top area. This value is an average and applies to both working losses and idle
losses that occur during the eight hour shift. Idle emission losses of 0.1 pounds per hour per
square foot and working losses of 0.1 to 0.8 pounds per hour per square foot are typical. During
the remaining 16 hours each working day and over the weekends and holidays, the degreaser is
tumed off. To account for solvent losses during downtime, it is assumed that the downtime
emission rate is 10 percent of the operating loss rate. Overall air emissions of PERC are
approximately 12,000 pounds or 890 gallons per year.
Solvent waste must be removed from the degreaser when the level of contamination
reaches 25 percent by volume. Since it takes 12.5 days to reach this level of contamination, the
139
CHAPTER 9.0
cleansut schedule is once every two weeks (1 0 working days). At the end of 10 days, the
concentration of oil will be 20 percent. Assuming that the facility practices solvent boil-back to
recover PERC, and that the final concentration of oil in the sump after boil-back is 50 percent, the
annual amount of waste generated will be 400 gallons of oil and 400 gallons of PERC.
The mount of fresh solvent required for the degreaser each year amounts to 1,290gallons
at a delivered cost of $4 per gallon. Waste disposal costs are assumed to be negligible since an offsite reclamation service will take the waste for its solvent value. Being located in the South Coast
Air Quality Management District, the plant is charged an emission fee of $289 per ton of PERC
emitted annually to atmosphere. This is in addition to paying $570 per year for the permit to
operate. For the supply of water, the facility is charged approximately $0.15per 1,000gallons.
Sewer fees cost $1.15 per 1,000 gallons.
The cost for maintenance supplies is difficult to determine but assuming that the capital
cost for a similar sized degreaser is $50,000 and that annual maintenance materials represent 2
percent of capital, then $1,000 should be a reasonable estimate. Maintenance for the system
consists of 4 hours every two weeks for boil-back, clean-out, solvent replacement, and waste
handling for reclamation. Additional labor consists of 1 hour per week for solvent testing. The
filly burden labor rate for all workers involved is $25 per hour. Direct operating labor costs have
not been accounted for since it is assumed that they will remain the same for each option. A
summary of the costs associated with the existing vapor degreaser is presented in Table 9-3.
TABLE9-3
SUMMARY OF OPERATING COSTS FOR THE BASE CASE
Heating
Conveying
Ventilation
Cooling Water
Sewer Fees
Solvent Purchases
Waste Disposal
SCAQMD Emission Fees
SCAQMD Permit Fees
Maint. Materials
Maint. Labor
Total
$550
$720
$1,180
$50
$370
$5,160
---
$1,730
$570
$1,000
$3,750
$15,080
As shown, the cost of operating the vapor degreaser is $15,080per year. This cost does
not include the labor directly involved in the cleaning operation since it is assumed that these costs
will be the same for each option. Additional operating and maintenance labor costs, as needed, are
accounted for under each option. Annualized equipment costs are also excluded due to the age of
140
IMPLEMENTING A NEW PROCESS
the equipment. Assuming the degreaser cost $85,000 hlly installed, the annualized cost would be
$13,860. This is based on a capital recovery factor (CRF) of 0.163 for equipment with a 10 year
life and 10 percent interest rate.
9.5.2
Installation of Emission Controls
To control PERC emissions, the facility considers installing a carbon bed adsorption
system with steam regeneration. During operation, a maximum of 4.5 pounds per hour of PERC
will be vented to the unit (this assumes 100 percent capture efficiency). With an air flow rate of
1,500 actual cubic feet per minute, the concentration of PERC will be 114 parts per million by
volume. During downtime, the concentration will drop to 11 parts per million. When running at
this low of a concentration, there is the potential for the airflow to desorb the carbon. To prevent
this from occurring, the system will only be operated during the 8 hour working shift. To control
emissions during down-time, the ventilation fan will be turned off and the degreaser covered by
means of an automated roll type cover. A summary of the operational parameters used in
analyzing this option are presented in Table 9-4.
TABLE 9-4
SUMMARY OF OPERATIONAL PARAMETERS FOR THE CARBON BED
Operating Conditions, Degreaser
Ventilation
Solvent Purchases
Air Emissions
Other
1.5 kw-hr, 8 hrslday
645 gallons per year
1.5 tons per year
See Table 9-2
Operating Conditions, Carbon Bed System
Operation
2 hours per day
100,000 Btu/hr, 1 hr/day
Heating (Regeneration)
Ventilation
2.25 kw-hr, 9 hrslday
72 g a m , 2 hrslday
Cooling Water
100 pounds per day
Steam Condensate
Included in maint. materials
Waste Disposal
0.2 tons per year
Air Emissions
5 percent of capital
Maint. Materials
0.5 hours per day
Maint. Labor
1 hour per day
Operating Labor
A major factor in determining the efficiency of any air emission control system is its ability
to capture emissions. The capture efficiency of the lip exhaust is taken to be 70 percent, the
control efficiency of the carbon bed system is 95 percent, and the control efficiency of the lid is 90
percent. While the efficiency of the roll top lid is high compared to values reported in the
literature, reported values are for the control of working and idle losses, not down-time losses.
141
CHAPTER 9.0
Since the system is not heated during down-time, the ability of the lid to suppress evaporative
losses will be greater. The overall control efficiency for this system is 72 percent. A comparison
of PERC emissions for both the before and after cases is presented in Table 9-5.
TABLE 9-5
COMPARISON OF EXISTING TO CARBON BED SYSTEM EMISSIONS
Stream
Solvent Feed
Idle Emissions
Working Emissions
Carbon Bed Emissions
Solid Waste
Existing;
(lbs/yr)
17,440
3,040
9,000
0
5,400
-Carbon Bed
(lbs/yr)
8,720
3 04
2,700
315
5,400
The size of the carbon bed system is mainly dictated by the amount of PERC vented to the
unit. Based on a capture efficiency of 70 percent, an adsorption value of 0.2 pounds of PERC per
pound of carbon, and a safety factor of 4,the system will require 63 pounds of carbon per hour of
operation. Assuming an eight hour operating cycle before regeneration, the total amount of carbon
in the system will be 500 pounds. A safety factor of 2 is more commonly assumed when designing
a dual bed system with hourly cycling, but given the small amount of PERC that must be recovered
each day, the installation of an oversized single bed unit is more appropriate. With its simpler
control scheme, a single bed system should be easier to maintain and be more reliable than a dual
bed system. The extra system capacity also allows the facility to run two 8 hour shifts with-out
stopping if so required. The basic cycle for this system would be 8 hours on-line, 1 hour desorb,
and 1 hour cooldown.
Steam requirements for the system are based on 4 pounds of steam for regeneration per
pound of PERC adsorbed. Approximately 100 pounds of steam per eight hour shift will be
required to desorb the bed. Steam will be provided from the plants boiler and a separate steam
generation unit will not be required. Cooling water requirements are based on 6 pounds of water
per pound of steam used. This equates to a flow of 1.2gallons per minute or 72 gallons for 1 hour
of steaming. To provide for emission control during the cool-down cycle, the cooling water
remains on during this period. The installation of the carbon bed system will require the inclusion
of a 3 horsepower (2.25 kilowatt hour) ventilation blower in addition to the 2 horsepower blower
already present at the lip exhaust of the degreaser.
As a result of the regeneration process, 25,000 pounds of steam and 6,000 pounds of
PERC each year will be condensed and phase separated in the decanter vessel. The solubility of
142
IMPLEMENTING A NEW PROCESS
PERC in water is 0.015 pounds per 100 pounds of water and the amount of PERC discharged in
the water amounts to 4 pounds per year. While the water could be steam stripped to remove
PERC, steam stripping would consume additional energy and result in air emissions of PERC. To
control this stream, the water will be passed through a small water phase carbon canister before
discharge to sewer. The recovered PERC will be passed though a small desiccant dryer cartridge
to remove moisture followed by a fine micron cartridge filter to remove particulates.
To determine the cost of the control system, a correlation presented by Vatavuk and
Neveril(l983) for a fully packaged, carbon steel, dual bed absorber system including blower,
instrumentation, and steam generator is used. While dated, the correlation is fairly accurate and
serves to illustrate the estimating process. The cost for a dual bed system was reported to be
$10,000 plus $721 times the weight of carbon raised to the 0.48 1 power. This places the capital
cost for a 500 pound system at $24,300 in 1977 dollars. To account for inflation and cost
escalation, the Marshall & Swift equipment price indexes for 1977 and 1992 were applied. The
M&S index was 505 for 1977 and 945 for 1991. This increases the price by 87 percent (100 x
945 / 505) to $45,000.
Next, the facility decides that the use of carbon steel may not be appropriate. Steam
stripping of halogenated solvents from carbon can result in solvent degradation and formation of
hydrochloric acid. This acid will react with carbon steel, corrode the equipment, and contaminate
the recovered solvent. Carbon recovery of TCA or M E W often requires the use of highly
corrosion resistant materials of construction due to their tendency to form acid. PERC may also
form acid, but it is much more stable. It is decided that the equipment will be fabricated from 304
stainless steel, increasing the equipment cost by 70 percent to $77,350.
As previously stated, this price is for a dual bed system with steam generator. To account
for the lesser cost of a single bed design and the elimination of the steam generator (i.e., steam will
be provided to the system by the shop), a markdown of 20 percent is taken. This places the
Uninstalled equipment cost (excluding tax and freight) at $62,000. A call to several system
manufacturers indicates that this estimate is reasonable, with most single bed systems quoted in the
$55,000 to $75,000 price range. Adding a 10 percent mark-up to cover the cost of tax and freight,
the total purchase price for the system is $68,200.
Installation costs are highly variable and are very dependent on existing site conditions.
To determine the fully installed cost of this system, a factor of 30 percent for direct costs such as
site preparation, electrical and plumbing hook-ups, insulation work, etc., and 40 percent for
indirect costs such as permitting, start-up assistance, engineering fees, etc. is assumed. Actual
costs can be much greater. Air quality permitting, which involves modification of the existing
vapor degreaser permit and filing for a permit to construct the carbon bed system, is expected to be
$5,000 for the filing fees alone. This does not include staff time for the preparation of the forms
and assembly of the necessary supporting documents. Applying the 1.7 factor for installation, the
143
CHAPTER 9.0
installed system cost is estimated to be $1 15,900. To account for the installation of the automated
roll lid, a total installed cost of $120,000 is assumed.
Material supply costs for the carbon bed system are taken to be 5 percent of the uninstalled
equipment cost or $3,100 per year. This would include the cost for change-out and disposal of the
water-phase carbon canister, change-out and replacement of the PERC desiccant dryer and
particulate filter, and one-time change-out of the carbon bed after five years. Operator
requirements are taken to be one hour per day during steam regeneration and 0.5 hours per day for
maintenance activities. A summary of the costs for this option are presented in Table 9-6 below.
TABLE 9-6
SUMMARY OF COSTS FOR THE CARBON SYSTEM
Equipment and Installation
Carbon Bed System
Taxes and Freight
Installation
Lid Installation
Total
Annualized Cost
Operating Expenses, Degreaser
Heating
Conveying
Ventilation
Cooling Water
Sewer Fees
Solvent Purchases
Waste Disposal
SCAQMD Emission Fees
SCAQMD Permit Fees
Maint. Materials
Maint. Labor
Total
Operating Expenses, Carbon System
Regeneration
Ventilation
Cooling Water
Sewer Fees
Emission Fees
SCAQMD Permit Fees
Maint. Materials
Maint. Labor
Operating Labor
Total
144
$62,000
$6,200
$47,700
$4,100
$120,000
$19,560
$550
$720
$270
$50
$370
$2,580
---
$430
$570
$1,000
$3,750
$10,290
$130
$460
---
$40
$60
$5 70
$3,100
$3,130
$6,250
$13,740
IMPLEMENTING A NEW PROCESS
As shown in Table 9-3 previously, annual operating costs for the existing degreaser are
$15,080. Installation of a roll top lid and carbon bed system reduces the operating cost of the
degreaser to $10,290 but adds its own operating cost of $13,740. Combined with the annualized
capital and installation costs, overall costs increase to $43,590 per year. This represents an
incremental increase of $283 10 to reduce 4.4 tons of PERC emissions. The cost effectiveness of
this option is therefore $6,480 per ton of solvent saved.
9.5.3
Switch to Aqueous Cleaning
Rather than investing capital to install a control system on a piece of equipment that is 10
years old, the facility decides to investigate the cost effectiveness of converting to an aqueous
cleaning system. The proposed aqueous cleaning system consists of a conveyorized tunnel and
three 250 gallon tanks located below the tunnel. A summary of operational parameters used in this
analysis of aqueous cleaning is presented in Table 9-7 on the following page.
In the proposed system, the first tank serves as the hot alkaline cleaner while the second
and third tanks serve as warm water rinse and hot water rinse, respectively. The hot rinse is
performed after the warm rinse so as to aid in parts drying. Spray washers are installed throughout
the tunnel to enhance cleaning and rinsing. Drainage from the sprayed parts is designed to run
back into the respective wash or rinse tank.
The cleaning solution used in the cleaner stage is maintained at 4 ounces per gallon and
140 O F . The two rinse tanks are operated in a counter-current sequence so as to conserve rinse
water. That is, hot rinse water from the second rinse stage is used as make-up to the first warm
rinse stage. Fresh water is added to the hot stage and all water discharged from the system occurs
from the first stage. Both the cleaning and hot rinse stages are heated and maintained at 140 OF.
The first rinse stage is not heated but is warmed by heat removed from the parts and by hot rinse
water used as make-up.
To determine energy requirements for the system, it is assumed that each stage will spray
100 gallons per minute for two minutes per load and that the heated solution or rinse water sprayed
will decrease in temperature by 7 O F . This is an empirical observation that has been noted in
several references dealing with the sizing of aqueous spray systems. To provide this heat, two
350,000 Btu per hour heaters will be required. Operation of these two heaters at hll load can
ready the system for cleaning in one hour from a cold start.
Since the heaters will not be operated continuously at full load once the system is ready, a
heat and material balance was performed on the system to determine the average load during
cleaning. The results of that exercise were that 14,600 Btu per hour are used to overcome wall
losses, 160,000 Btu per hour are used to heat parts, 16,800 Btu per hour are lost due to water
evaporation from the surfhce of the tanks,455,200 Btu per hour go into heating and humidifying
the ventilation air during spraying, and 53,400 Btu per hour are required to heat make-up water.
145
CHAPTER 9.0
TABLE 9-7
SUMMARY OF OPERATIONAL PARAMETERS FOR AQUEOUS CLEANING
Operating Conditions, Aqueous Cleaner
Operation
Parts + Baskets
Heating (Start-up)
Heating (Operation)
Conveying Baskets
Pumping
Ventilation
Water (Make-up/Rinsing)
Water (Clean-out)
Cleaner Purchase
Waste Disposal (Oil)
Maint. Materials
Maint. Labor (Testing)
Maint. Labor (Clean-out)
8 hrdday, 250 dayslyr
1,200 Ibshr, 500 ft2/hr
700,000Btuhr, 1 hr/day
210,000 Btu/hr, 7 hrslday
5 kw-hr, 8 hr~/day
6 kw-hr, 8 hrslday
4 kw-hr, 8 hrs/day
44 g a m , 8 hrslday
750 gals, 12 times/yr
1,250 pounds per year
500 gallons per year
4 percent of capital
1 hour per day
4 hours per month
Operating Conditions, Drying Oven
Heating
Ventilation
Maint. Materials
25,300Btu/hr, 8 hrlday
1.5 kw-hr, 8 hrslday
2 percent of capital
Operating Conditions, Neutralization
Pumping
Treatment (Rinsing)
Treatment (Clean-out)
Waste Disposal (Sludge)
Maint. Materials
Maint. Labor
Operating Labor
4.5 kw-hr, 2 hrslday
30 g a m , 8 hrslday
750 gallons, 12 times/yr
2 drums per year
2 percent of capital
0.5 hours per day
0.5 hours per day
Utility Costs and Fees
Cleaner
Treatment Cost
Waste Disposal (Oil)
Waste Disposal (Sludge)
$1 per pound
$2.75per 1,000 gallons
$0.60 per gallon
$110 per drum
Given that spraying of parts occurs for 16 minutes per hour (4batches per hour, 2 gallons per
minute, and 2 hot sprays per batch), the average hourly heat load is estimated to be 210,000 Btu.
To operate the pumps, filters, and conveyor, a total electrical demand of 15 kilowatt hours is
assumed (5 kw for conveying, 6 kw for pumping and spraying, and 4 kw for ventilation).
To determine the rate of rinse water discharge, it is assumed that the maximum level of
cleaner build-up allowed in the rinse tank is 3 percent. Based on cleaning 4 loads of plates per
hour, the total surface area cleaned is 384 square feet per hour (both the front and back sides of the
146
IMPLEMENTING A NEW PROCESS
plates must be included). To account for drag-out of solution by the basket, a total area of 500
square feet per hour is assumed. Based on a typical drag-out rate of 2 gallons per 1,000 square
feet, the amount of drag-out equals 1 gallon per hour. The drag-out rate used in this analysis is for
vertical parts, poorly drained. The actual rate could be one-tenth to ten times this amount
depending on the physical shape of the parts and how they are racked inside the basket. At a rate
of 1 gallon per hour, the concentration inside the warm rinse tank will reach 3 percent at the end of
the 8 hour shift. Rather than dumping the tank once per day, a continuous purge of 30 gallons per
hour is set. Make-up to the system is estimated to be 44 gallons per hour.
Since there is the potential for the steel plates to rust if they are not properly cleaned and
dried, the facility is faced with two choices. Demineralized water can be used for the final hot rinse
and the parts allowed to flash dry,or plant water can be used and the parts force dried to minimize
rusting. For this analysis, it is assumed that the facility elects to attach a drying tunnel after the
hot rinse stage and that the use of demineralized water will be a fiture consideration. The energy
consumption for the drymg tunnel is based on the operating assumptions that drying is 85 percent
efficient, that the 1,200 pounds per hour of parts plus baskets will be heated from 140 to 250 OF,
and that 1 gallon per hour of drag-out must be evaporated. The total heat load for drying is
therefore 25,350 Btu per hour. Since 250 OF parts will be too hot to handle, the tunnel dryer
includes a 2 horsepower blower to cool down parts after drying.
The capital cost for a 30 inch wide, 3 stage cleaner constructed of 304 stainless steel is
taken to be $60,000. This cost includes all pumps, filters, heaters, spray headers, the conveyor,
and an oil skimmer mounted in the cleaning tank. An additional $18,000 will be required for the
tunnel dryer. Also required will be a neutralization system to adjust the pH of the rinse water
before discharge to the Publicly Owned Treatment Works (POTW). Since the alkaline cleaner
specified does not contain any hazardous materials and the oils removed are not considered to be
hazardous, spent cleaning baths can also be discharged to the P O W after neutralization. The cost
for the neutralization and pH adjustment system is taken to be $15,000. Total equipment cost,
including 10 percent mark-up for tax and freight, is therefore $102,300.
For this analysis, a 50 percent mark-up for direct costs and a 30 percent mark-up for
indirect costs is assumed. The use of 50 percent for direct costs instead of 30 percent used for the
carbon bed system seems appropriate since the carbon bed system would be a skid-mounted system
installed outdoors. Installation of the aqueous cleaning system would require major renovation to a
large area inside the facility. The demolition of the existing vapor degreaser may also be required.
Indirect costs have been reduced slightly since the facility will not have to procure permits from the
local air agency. Wastewater treatment permits may not be required if the rinse water can be
determined to be non-hazardous. Based on an installation factor of 1.8, the total installed cost for
this system will be $184,140.
Given the complexity of this system, there are a number of annual operating costs that
must be accounted for in addition to electrical, water, and sewer fees. While the warm water rinse
147
CHAPTER 9.0
will discharge continuously, all three stages will have to be dumped monthly and cleaned out. This
will require 4 hours of maintenance stafftime and the replenishment of the system with cleaner.
Daily maintenance for the cleaning system (and dryer) is taken to be 1 hour per day and includes
change-out of filters, testing of the solution for proper strength, cleaner addition, etc.
The oil skimmer mounted inside the cleaning stage will recover most of the oil removed by
the cleaner. Assuming that the recovered waste is 80 percent oil and 20 percent water, a total of
500 gallons per year of waste will be generated. This waste will be handled be a waste oil hauler
to which the facility pays $0.60 per gallon. Maintenance materials (excluding cleaner) are taken to
be 4 percent of capital or $2,400 per year. Oven maintenance is taken to be 2 percent of capital or
$360. The system requires 1,250 pounds per year of dry cleaner at a cost of $1 per pound.
The final operating expenses involve the operation of the neutralization system. According
to Mauzerall(1987), the cost for neutralizing cleaner and rinsewater from an aqueous cleaner is
$2.75 per 1,000 gallons treated. Maintenance materials for the neutralization system are taken to
be 2 percent of capital or $300 per year. Operator requirements for an automated neutralization
system should be low, 0.5 hours per day is assumed. Maintenance labor is also taken to be 0.5
hours per day. No treatment permit fees will be required since no heavy metals are present in the
waste and the amount of precipitate formed is minimal (note: some states may require a treatment
permit for pH adjustment of a hazardous liquid even if no precipitates are formed). Since some
precipitation of hardness salts present in the water will occur during neutralization, it is assumed
that 2 drums per year of water scale sludge will be generated at a disposal cost of $1 10 per drum.
As shown in Table 9-8 on the following page, the general view that aqueous systems are
more expensive to operate and maintain than vapor degreasers is supported. The total annual
operating cost for the aqueous cleaning system is $24,950 compared to $15,080 for the existing
vapor degreaser and $24,030 for the controlled degreaser. Including the annualized capital and
installation costs, the aqueous cleaning system costs $54,960 per year while the controlled
degreaser costs $43,590. While the cost effectiveness of the controlled degreaser is $6,480 per ton
of PERC recovered, the cost effectiveness of the aqueous cleaning system is $4,570 per ton of
PERC. Therefore, in terms of overall emission control, the conversion to an aqueous cleaner is
more cost effective than installing an emission control system. The aqueous cleaner is also favored
if one factors in the potential liabilities of worker exposure and accidental release.
Another item worth mentioning is the general view that aqueous cleaners consume more water than
vapor degreasers. Many facilities use water as an inexpensive means of cooling their vapor
degreasers and the cost for water does not justi% conversion to closed loop cooling. Maximizing
the use of cooling water conserves solvent. In aqueous cleaning, when any of the rinse stages are
heated, water conservation is essential for conserving energy. Hot water discharge represents a
sizable expense to the operation. Minimizing the use of hot water conserves energy. In the
examples presented in this section, the aqueous cleaning system uses 97,000 gallons per year for
rinsing and make-up compared to 320,000 gallons per year used for cooling the degreaser.
148
IMPLEMENTING A NEW PROCESS
TABLE 9-8
SUMMARY OF COSTS FOR AQUEOUS CLEANING SYSTEM
Equipment and Installation
Aqueous System
Tunnel Dryer
Neutralization System
Taxes and Freight
Installation
Total
Annualized Cost
$60,000
$18,000
$15,000
$9,300
$8 1,840
$184,140
$30,010
Operating Expenses, Aqueous Cleaner
Heating
Conveying
Pumping
Ventilation
Water
Cleaner Purchases
Waste Disposal (Oil)
Maint. Materials
Maint. Labor
Total
$2,710
$900
$1,080
$720
$10
$1,250
$300
$2,400
$7,450
$16,820
Operating Expenses, Drying Oven
Heating
Ventilation
Maint. Materials
Total
Operating Expenses, Neutralization System
Pumping
Treatment
Waste Disposal (Sludge)
Sewer Fees
Maint. Materials
Maint. Labor
Operating Labor
Total
9.6
$250
$270
$360
$880
$200
$190
$220
$80
$300
$3,130
$3,130
$7,250
Conversion of Existing Equipment
Some vapor degreasing equipment may be suitable for conversion to an aqueous cleaning
system. While conversion may not represent the most effective cleaning system in terms of
performance, conversion can save you a sizable investment in new equipment. In addition to
aqueous or alkaline chemistries, conversion to semi-aqueous service may be possible although the
conversion will be more extensive. Such conversion may require the inclusion of decantation or
149
CHAPTER 9.0
recycling equipment. All systems may require the inclusion of a rinsing and drying stage. The
conversion of an existing vapor degreaser for use with flammable solvents is not recommended.
Vapor only degreasers may be readily converted to an aqueous spray cleaning station by
installing a small pump spray unit. Installation of the spray unit may not be required if the
degreaser is already so equipped. The boiling sump may be used to heat the solution. Conversion
of a vapor only degreaser to aqueous immersion service may not be practical since the side walls of
the degreaser may not withstand the weight of the liquid. The ability to support the weight of the
liquid is less of an issue with a vapor/immersion style degreaser.
Conversion of an existing degreaser will also require the disconnection of the cooling water
from the water jacket and disconnection of electrical power to any freeboard chillers or condensers.
Operation of these systems with aqueous cleaners is not necessary and they will only serve to rob
heat from the unit. To reduce the heating load and protect workers from thermal exposure, it may
also be advantageous to insulate the unit. Agitation of the immersion bath may be accomplished
through the addition of an in-tank filtration pump or immersible ultrasonic generators. Air
agitation should not be used since it is not very effective and is a major source of heat loss.
Another item to check is the compatibility of the selected cleaner with the materials of
construction. Stainless steel degreasers should be compatible with most aqueous cleaners but it is
still best to check all liquid service components. Be aware that pumps, valves, and fittings may
contain brass components. Brass may be attacked by the new solution and lose structural integrity.
Leached copper and lead may contaminate the solution and render it a hazardous waste. To help
identi% the original materials of construction, contact the manufacturer for assistance. Some
manufacturers also offer retrofit kits. These kits provide the proper replacement parts based on the
original equipment list. If you have made modifications or repairs to the degreaser, you will still
need to veri@ the compatibility of the replaced parts.
150
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157
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-
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166
Appendix A
Waste Minimization Assessment Worksheets
The worksheets that follow are designed to facilitate the WM assessment procedure. Table A-1 lists the worksheets.
according to the particular phase of the'program, and a brief description of the purpose of the worksheets.
Table A-1.
Phase
List of Waste Minimization Assessment Worksheets
Number and Title
Purpose/Remarks
~
1. Assessment Overview
Planning and Organization
(Section 2)
2. Program Organization
3. Assessment Team Make-up
Summarizes the overall assessment procedure.
Records key members in the WMA program task force and the WM
assessment teams. Also records the relevant organization.
Lists names of assessment team members as well as duties. Includes
a list of potential departments to consider when selecting the teams.
Assessment Phase
(Section 3)
4. Site Description
Lists background information about the facility, including location,
products, and operations.
5. Personnel
Records information about the personnel who work in the area to be
assessed.
6. Process Information
This is a checklist of useful process information to look for before
starting the assessment.
7. Input Materials Summary
Records input material information for a specific production or process
area. This includes name, supplier, hazardous component or
properties, cost, delivery and shelf-life information, and possible
substitutes.
8. Products Summary
Identifies hazardous components, production rate, revenues, and
other information about products.
9. IndividualWaste Stream
Characterization
Records source, hazard, generation rate, disposal cost, and method
of treatment or disposal for each waste stream.
10. Waste Stream Summary
Summarizes all of the information collected for each waste stream.
This sheet is also used to prioritize waste streams to assess.
(continued)
A- 1
Table A-1 . List of Waste Minimization Assessment Worksheets (continued)
Phase
Number and Title
Purpose/Remarks
Assessment Phase (continued)
(Section 3)
11. Option Generation
Records options proposed during brainstorming or nominal group
technique sessions. Includes the rationale for proposing each option.
12. Option Description
Describes and summarizes information about a proposed option. Also
notes approval of promising options.
13. Options Evaluation by
Weighted Sum Method
Used for screening options using the weighted sum method.
Feasibility Analysis Phase
(Section 4)
~
14. Technical Feasibility
Detailed checklist for performing a technical evaluation of a WM optior
This worksheet is divided into sections for equipment-related options,
personneVprocedural-related options, and materials-related options.
15. Cost Information
Detailed list of capital and operating cost information for use in the
economic evaluation of an option.
16. Profitability Worksheet #1
Payback Period
Based on the capital and operating cost information developed from
Worksheet 15, this worksheet is used to calculate the payback period.
This worksheet is used to develop cash flows for calculating NPV or IRf
Cash Flow for NPV and IRR
17. Profitability Worksheet #2
Implementation
(Section 5)
18. Project Summary
Summarizes important tasks to be performed during the
implementation 'of an option. This includes deliverable, responsible
person, budget, and schedule.
19. Option Performance
Records material balance information for evaluating the
performance of an implemented option.
A-2
1
IFirm
Waste Minimization Assessment
Proc. UniVOper.
Proj. No.
Site
FFl
I
I
4
I
Prepared BY
Checked By
S h e e t 1 of J-
Page
ASSESSMENT OVERVIEW
I
I
Begin the Waste Minimization
Assessment Program
c
Worksheets used
PLANNING AND ORGANIZATION
Get management commitment
Set overall assessment program goals
Organize assessment program task force
b
-
Select new assessment targets
and reevaluate
previous options
ASSESSMENT PHASE
Compile process and facility data
Prioritize and select assessment targets
Select people for assessment teams
Review data and inspect site
Generate options
Screen and select options for further study
2
4,6,7,8,9,10
10
3
11,12
13
FEASIBILITY ANALYSIS PHASE
Technical evaluation
Economic evaluation
Select options for implementation
14
1 5 16,17
IMPLEMENTATION
Repeat the Process
Justify projects and obtain funding
Installation (equipment)
Implementation (procedure)
Evaluate performance
c
Successfully operating
waste minimization projects
A-3
18
18
19
of
Waste Minimization Assessment
Firm
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Date
Sheet 1of
Proj. No.
I
WORKSHEET
I
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of
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PROGRAM ORGANIZATION
121
FUNCTION
NAME
LOCATION
arogram Manager
4ssessment Team Leader
1 Page
I
Oraanization Chart
(sketch)
A-4
TELEPHONE #
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Proj. No.
ASSESSMENT
TEAM MAKE-UP
Page
of
?
Duties
Lead
R&D
Legal
Management
Contractor/Consultant
Safety
-
-
A-5
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Waste Minimization Assessment
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WORKSHEET
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1 4 1
I
Firm:
Plant:
Department:
Area:
-Street Address:
,
Prepared By
city:
Statealp Code:
Telephone: (
1
Major Products:
Major Unit or:
Product or:
Operations:
Facilities/Equipment Age:
I
SITE DESCRIPTION
Sheetl-
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of
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Sheet _L_ of
1- Page
-
PERSONNEL
DepartmentlArea
Attribute
Overall
Total Staff
_ _
-
Direct Supv. Staff
Management
-_
Average Age, yrs.
--
__
Annual Turnover Rate %
~
Seniority, yrs.
Yrs. of Formal Education
-
Training, hrs./yr.
_ _
Additional Remarks
A-7
of
I PROCESS INFORMATION I
161
WORKSHEET
I
Operation Type:
U Continuous
L.+
0Batch or Semi-Batch
0Other
Discrete
-
Status
Document
Complete? Current?
(Y/N)
(Y/N)
-Process Flow Diagram
Last
Revision
Used in this
Document
Report (y/N) Number
__
-
_____
MateriaVEnergy Balance
_____
Design
___-_____
Operating
_______________
‘Flow/Amount
~ - _Measurements
_ _ .
-
____
_
tS’”””--_____
L ____
-_--
~
~
_
_
-
____.
c--.
Analy ses/Assays
i
-
- - Stream
~____-__
Location
-__
A-a
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Page
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WORKSHEET
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INPUT MATERIALS SUMMARY
I
==:Description’
Attribute
Stream No.-
Name/lD
Source/Supplier
Stream No.-
Stream No.-
-
Combonent/Attribute of Concern
-
I
.
Annual Consumption Rate
Overall
Component(s) of Concern
Purchase Price, $ per
______
I
_
_
Overall Annual Cost
____
IDelivery Mode2
-
-__
Shipping
Container Size & Type3
___
Storaae Mode4
ITransfer Mode5
Disposal/Management6 Sumlier Would
- accept expired material (Y/N)
~.
accept shipping
.-. containers
-_ _ (YIN)
- -.
I - revise exDiration date W I N )
-_-.
.
Substitute@),if any
Alternate Supplier(s)
I
3
4
5
6
I
I
stream numbers, if applicable, should correspond to those used on process flow diagrams.
e.g., pipeline, tank car, 100 bbl. tank truck, truck, etc.
e.g., 55 gal. drum, 100 Ib. paper bag, tank, etc.
e.g., outdoor, warehouse, underground, aboveground, etc.
e.g., pump, forklift, pneumatic transport, conveyor, etc.
e.g., crush and landfill, clean and recycle, return to supplier, etc.
A-9
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WORKSHEET
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PRODUCTS SUMMARY
1Page
-
1
Description'
Attribute
Stream No.-
Stream No.-
Stream No.I
Component/Attribute of Concern
I
__
Annual Production Rate
Overall
Component(s) of Concern
_________
Annual Revenues, $
-
Shipping Mode
Shipping Container Size 81Type
Onsite Storage Mode
Containers Returnable (Y/N)
I
I
I
Shelf Life
I
I
I
I
I
Rework Possible (Y/N)
.____
Customer Would
- relax specification (Y/N)
- accept larger containers (Y/N)
1
stream numbers, if applicable, should correspond to those used on process flow diagrams.
A-1 0
~~~
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S h e e t L of 4 Page
Proj. No.
Date
l
a
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WORKSHEET
1.
~
INDIVIDUAL WASTE STREAM
CHARACTERIZATION
Waste Stream Name/lD:
I
-
Stream Number
Process Unit/Operation
2.
0 liquid
High Heating Value, Btu/lb
Viscosity/Consistency
,Flash Point
PH
-~
__
-
waste water Osolid waste
hazardous waste
Occurrence
0 continuous
0 discrete
discharge triggered by
u
-
chemical analysis
other (describe)
length of period:
0 periodic
0 sporadic (irregular occurrence)
0 non-recurrent
Type:
Generation Rate
Annual
Ibs per year
Maximum
Average
Ibs per
tbs per
Frequency
batches per
Batch Size
average
A-11
_ _ ~
___-
; o/o Water
Waste Leaves Process as:
air emission
5.
-
0 mixed phase
0solid
Density, Ib/cuft
4.
~-
Waste Characteristics (attach additional sheets with composition data, as necessary.)
0 gas
3.
of
~
range
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Waste Minimization Assessment
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Proc. UniVOper.
.___
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ISheet 2 of 4 Page
Proj. NO.
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I INDIVIDUAL WASTE STREAM 1
I
6.
Prepared By
CHARACTERIZATION
(continued)
1
Waste Origins/Sources
Fill out this worksheet to identify the origin of the waste. If the waste is a mixture of waste
streams, fill out a sheet for each of the individual waste streams.
Is the waste mixed with other wastes?
Yes
0 No
Describe how the waste is generated.
Example:
Formation and removal of an undesirable compound, removal of an unconverted input material, depletion of a key component (e.g., drag-out), equipment cleaning waste, obsolete input material, spoiled batch and roduction
run, spill or leak cleanup, evaporative loss, breathing or venting osses, etc.
P
A-12
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Sheet 3 of 4
Page
of
<
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WORKSHEET
I
I
INDIVIDUAL WASTE STREAM
CHARACTERIZATION
I
(continued)
Waste Stream
7.
Management Method
Leaves site in
0
bulk
17]
roll off bins
u
55galdrums
0
other (describe)
Disposal Frequency
Applicable Regulations1
Regulatory Classification2
0
onsite
Managed
0
offsite
commercial TSDF
ownTsDF
other (describe)
Recycling
0
0
direct usehe-use
combusted for energy content
redistilled
0
other (describe)
~~~
reclaimed material returned to site?
0
Yes
0
NO
0 used by others
residue yield
residue disposal/repository
Note’
Note2
list federal, state & local regulations, (e.g., RCRA, TSCA, etc.)
list pertinent regulatory classification (e.g., RCRA - Listed KO1 1 waste, etc.)
A-1 3
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_________ Sheet
4 of 4 Page
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INDIVIDUAL WASTE STREAM
CHARACTERIZATION
(continued)
Waste Stream
7.
-
Checked By
_____
Management Method (continued)
Treatment
I
biological
-
oxidation/reduction _______
incineration
pH adjustment
-~
precipitation
-
solidification
other (describe)
residue disposal/repository
-
Final Disposition
landfill
pond
lagoon
deep well
ocean
other (describe)
Costs as of
(quarter and year)
Cost Element:
Unit Price
$ per
ReferenceBource:
~
Onsite Storage & Handling
-
Pretreatment
Container
TransDortation Fee
Disposal Fee
Local Taxes
State Tax
Federal Tax
Total DisDosal Cost
I
A-1 4
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Sheet 1of 1 -
Page
of
WASTE STREAM SUMMARY
I
Description’
Attribute
Stream No. -
Stream No. -
Stream No. -
I
Waste ID/Name:
~
_
_
_
_
_
_
_
_
Source/Origin
_
_
-~
ComponenVor Property of Concern
Annual Generation Rate (units
)
Overall
Component@)of Concern
Cost of Disposal
Unit Cost ($ per:
1
Overall (per year)
I
I
Method of Management*
-
I
Priority Rating Criteria3
I
Wt. (W
Rating (R)
I
Rxw
Rating (R)
RxW
1
I
Regulatory Compliance
%%-p
t
Treatment/DisDosal Cost
~
Potential Liability
Waste Quantity Generated
Waste Hazard
Safety Hazard
Minimization Potential
~
Potential to Remove Bottleneck
Potential By-product Recovery
Sum of Priority Rating Scores
U R x W)
I
X(R x W)
I
Priority Rank
Notes: 1.
Stream numbers, if applicable, should correspond to those used on process flow diagrams.
2.
For example, sanitary landfill, hazardous waste landfill, onsite recycle, incineration, combustion
with heat recovery, distillation, dewatering, etc.
3.
Rate each stream in each category on a scale from 0 (none) to 10 (high).
A-1 5
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I 11 I
I OPTION GENERATION I
Meeting format (e.g., brainstorming, nominal group technique)
Meeting Coordinator
__---____-___~_~__~_~__
---
Meeting Participants
____ __
A-1 6
________~_____
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Sheet 1of
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-____
Page
of
I
OPTION DESCRIPTION
Option Name:
A-
-
Briefly describe the option
- .-
.-
~~
Waste Stream(s) Affected:
__
Input Material@)Affected:
______
__
_-__ -_
Product(s) Affected:
Indicate Type:
~~.~
~
-
-~ -~
0Source Reduction
-
-
Equipment-RelatedChange
PersonneVProcedure-Related Change
Materials-Related Change
Recycling/Reuse
- Onsite
-
Offsite
-
Material used for a lower-quality purpose
-
Material burned for heat recovery
Material reused for original purpose
Material sold
Originally proposed by:
Date:
-
Reviewed by:
Date:
_ _ _ ___
Approved for study?
Yes
no,
Reason for Acceptance or Rejection
A-1 7
by:
-
______
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WORKSHEET
I
Weight
(W)
Reduction in waste's hazard
Reduction of treatmentldisposal costs
__.
Reduction of safety hazards
- __
Effect on product quality (no effect = 10)
Low capital cost
Low 0 8t M cost
Short implementation period
Ease of implementation
-
I Sum of Weighted Ratings
Option Ranking
Feasibility Analysis Scheduled for (Date)
of
1
I
1
Criteria
Final
-.
Evaluation
1
OPTIONS EVALUATION BY
WEIGHTED SUM METHOD
ODtions Ratina
D Reduction of input material costs
4
a Extent of current use in industry
Page 1
Z
W x R)
#1 Option
#2 Option
R
R
RxW
3)
#3 Option
#4 Option
#5 Option
R
R
R
RxW
RxW
RxW
9
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Waste Minimization Assessment
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Sheet 1of
6 Page
of
TECHNICAL FEASlBILlTY
WM Option Description
_______-___
1. Nature of WM Option
~_
__
~
__
Equipment-Related
Personnel/Procedure-Related
Materials-Related
2. Ifthe option appears technically feasible, state your rationale for this.
Is further analysis required? - Yes - No.
worksheet. If not, skip to worksheet 15.
If yes, continue with this
-
3. Equipment Related Option
YES
Equipment available commercially?
Demonstrated commercially?
In similar application?
Successfully?
Describe closest industrial analog
-
____
-
._
Describe status of development
___.-
__
~~
Prospective Vendor
t______
1.
-
~
Working Installation(s)
I
Contact Person@)
Also attach filled out phone conversation notes, installation visit report, etc.
A-19
~
~
IDate Contacted 1.
Firm
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Waste Minimization Assessment
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Proc. UniVOper.
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Proj. No.
Date
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WORKSHEET
14b
I
I
I TECHNICAL FEASIBILITY I
(continued)
WM Option Description
.
_.
3. Equipment-RelatedOption (continued)
Performance information required (describe parameters):
Scaleup information required (describe):
Testing Required:
Scale:
yes
0bench 0 pilot
Test unit available?
____
no
c]
yes
no
Test Parameters (list)
Number of test runs:
Amount of material(s) required:
Testing to be conducted:
U
._____
in-plant
Facility/ProductConstraints:
Space Requirements
Possible locations within facility
A-20
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Page
of
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WORKSHEET
WM Option Description
___
--
2. Equipment-RelatedOption (continued)
Utility Requirements:
Electric Power
Volts(ACor DC) ----
Process Water
Flow
Cooling Water
Quality (tap, demin, etc.) _ _
Flow
Pressure ---
kW
Pressure ----___
~~
Temp. In
Temp. Out
Coolant/Heat Transfer Fluid
Temp. In
Temp. Out
Duty
Pressure
Temp.
Steam
-
_____
Plant Air
Flow
Estimated production downtime __ __-
__
.
_
__
-
-
Flow
_.
Estimated delivery time (after award of contract).-Installation dates-
--
Flow _ _ _ _ _
- ~
Duty -
Estimated installation time
~
__
Flow
Type __
Inert Gas
-
-
---
Duty
Fuel
_-
~
-
______
-
-
___-
__-
Will production be otherwise affected? Explain the effect and impact on production.
Will product quality be affected? Explain the effect on quality.
__
---__
- -~
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S h e e t 4 of
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WORKSHEET
6 Page
__
of
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TECHNICAL FEASIBILITY
I
WM Option Description
3. Equipment-RelatedOption (continued)
Will modifications to work flow or production procedures be required? Explain.
Operator and maintenance training requirements
n
U Onsite
Number of people to be trained
0 Offsite
Duration of training
Describe catalyst, chemicals, replacement parts, or other supplies required.
Rate or Frequency
of Replacement
Item
Supplier, Address
A
Does the option meet government and company safety and health requirements?
0Yes
No
Explain
How is service handled (maintenance and technical assistance)? Explain
~
What warranties are offered?
A-22
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Sheet 5 - of 6
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WORKSHEET
WM Option Description
-~
~
-~
_ _ _
~
~
3. Equipment-RelatedOption (continued)
Describe any additional storage or material handling requirements.
-
-
-
Describe any additional laboratory or analytical requirements.
~-
_ _ _ _ ~-
_____-
__
___
_
4.
Personnel/Procedure-Related Changes
Affected DepartmentsIAreas
_ _ _ ~
-________---
Training Requirements
-
Operating Instruction Changes. Describe responsible departments.
___
--___
5.
Materials-RelatedChanges (Note: If substantial changes in equipment are required, then handle the
option as an equipment-related one.)
Yes
m
Has the new material been demonstrated commercially?
U
n
n
In a similar application?
0
0
0
0
SuccessfuIly?
~
-~
~~
U
-
Describe closest application.
-~
A-23
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Waste Minimization Assessment
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WORKSHEET
Prepared By
_
_
_
~
Checked By
__ __
~-
-
Sheet 6- of -6-
Page
of
-
-~
TECHNICAL FEASlBILlTY
(continued)
WM Option Description
4.
__ __
__--
-
-_
-
._
~-
Materials-RelatedChanges (continued)
Will production be affected? Explain the effect and impact on production.
-
Will product quality be affected? Explain the effect and the impact on product quality.
~______
Will additional storage, handling or other ancillary equipment be required? Explain.
Describe any training or procedure changes that are required.
Decribe any material testing program that will be required.
- .
__-.
A-24
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Firm
____
_
_
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Waste Minimization Assessment
.
Unit/Oper. -
Site
Proc.
Date
Pro!. No. ____
WORKSHEET
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Prepared
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By
Checked By
of 6
Sheet 1
__
Page
of
m
COST INFORMATION
. .
WM Option Descriptton _____
- --
-
TOTALS
CAPITAL COSTS Include all costs as appropriate.
Purchased Process Equipment
Price (fob factory)
____
-
__
-
-
_ ~ _
Taxes, freight, insurance
Delivered equipment cost
___p_____-p_p.
Price for Initial Spare Parts Inventory
~
0Estimated Materials Cost
Piping
_ _ ~
Electrical
Instruments
~-~
______
___ ____
_ _-
-
______-p.
Structural
Insulation/Piping
Estimated Costs for Utility Connections and New Utility Systems
Electricity
Steam
Cooling Water
Process Water
Refrigeration
Fuel (Gas or Oil)
Plant Air
Inert Gas
-__-_p-__-___-.
0Estimated Costs for Additional Equipment
Storage & Material Handling
Laboratory/Analytical
__.
____
_-
-
Other
0Site Preparation
(Demolition, site clearing, etc.)
0Estimated Installation Costs
Vendor
Contractor
In-house Staff
________
~
_______
I______
_____-
_
I
_
_
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Waste Minimization Assessment
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Proc. UniUOper.
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Proj. No.
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Prepared B~
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Sheet& of
-
6
Page
-
of
__
COST INFORMATION
I
c
I
(continued)
TOTALS
CAPITAL COSTS (Cont.)
u Engineering and Procurement Costs (In-house
Planning
& outside)
-
Engineering
Procurement
Consultants
-
0Start-up Costs
Vendor
Contractor
In-house
0Training Costs
U Permitting Costs
Fees
In-house Staff Costs
0Initial Charge of Catalysts and Chemicals
Item #1
Item #2
a
Working Capital [Raw Materials, Product, Inventory, Materials and Supplies (not elsewhere specified)].
item #1
item #2
Item #3
Item #4
c
Estimated Salvage Value (if any)
A-26
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Sheet 3 - of 6 . Page
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WORKSHEET
1
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COSTINFORMATION
L
I
(continued)
Cost Item
of
I
I
cost
~~
Purchased Process Equipment
-
Materials
-
Utility Connections
-
Additional Equipment
_ _
Site Preparation
I_
_
___
-
Installation
_ - ~
~
Engineering and Procurement
___
Start-up Cost
__-
Training Costs
_-_
Permitting Costs
-
Initial Charge of Catalysts and Chemicals
-
~
--
.-
Fixed Capital Investment
~
Working Capital
Total .Capital Investment
~~~
Salvage Value
I
A-27
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Firm
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WasteMinimization Assessment
COST INFORMATION
u Estimated Decrease (or Increase) in Utilities
I
I
I
Utility
I
Unit Cost
$ per unit
INCREMENTAL OPERATING COSTS
-
I
I
Decrease (or Increase) in Quantity
Unit per time
I
Total Decrease (or Increase)
$ per time
Include all relevant operating savings. Estimate these costs on an incremental basis (Le., as decreases or increases over existing costs).
0
BASIS FOR COSTS
u
Estimated Disposal Cost Saving
Annual ___ Quarterly
___
Monthly
___
Daily
___
Other-
Decrease in TSDF Fees
Decrease in State Fees and Taxes
Decrease in Transportation Costs
Decrease in Onsite Treatment and Handling
Decrease in Permitting, Reporting and Recordkeeping
Total Decrease in Disposal Costs
Materials
-- --__
~~
~
Unit Cost
$ per unit
~
-
~
___
-_
A-28
Reduction in Quantity
Units per time
Decrease in Cost
$ per time
-
Waste Minimization Assessment
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Sheet 5 of 6-
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WORKSHEET
15e
I
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CatalystlChemical
~
~
Page
of
1
COST INFORMATION
(continued)
Unit Cost
$ per unit
Decrease (or Increase) in Quantity
Unit per time
Total Decrease (or Increase)
$ per time
-~
__-
.
_-__-
_-
_
0 Estimated
Decrease (or Increase) in Operating Costs and Maintenance Labor Costs
(include cost of supervision, benefits and burden).
-
._
_
-_--___
_
D Estimated Decrease (or Increase) in Operating and Maintenance Supplies and Costs.
___ -
-___---_
~ _ -
--__
Estimated Decrease (or Increase) in Insurance and Liability Costs (explain).
-
-.__-
___
____
--
_____
--
p__--_
_-
E! Estimated Decrease (or Increase) in Other Operating Costs (explain).
____
.-
____
~
INCREMENTAL REVENUES
Estimated Incremental Revenues from an Increase (or Decrease) in Production or Marketable
u
By-products (explain).
r-!
.__
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Prepared B~ Sheet 6 of
-___
6
-_
Page
__
of __
COST INFORMATION
(continued)
INCREMENTAL OPERATING COST AND REVENUE SUMMARY (ANNUAL BASIS)
Decreases in Operating Cost or Increases in Revenue are Positive.
increases in Operating Cost or Decrease in Revenue are Negative.
$ per year
Operating Cost/Revenue Item
Decrease in Disposal Cost
Decrease in Raw Materials Cost
-~
Decrease (or Increase) in Utilities Cost
-.
Decrease (or Increase) in Catalysts and Chemicals
~
Decrease
(or increase) in 0 & M Labor Costs
Decrease (or Increase) in 0 & M Supplies Costs
~~
Decrease (or Increase) in Insurance/Liabilities Costs
Decrease (or Increase) in Other Operating Costs
Incremental Revenues from Increased (Decreased) Production
Incremental Revenues from Marketable By-products
~
Net Operating Cost Savings
A-30
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WORKSHEET
PROFITABILITY WORKSHEET # 1
PAYBACK PERIOD
-
Total Capital Investment ($) (from Worksheet 15c)
._
Annual Net Operating Cost Savings ($ per year) (from Worksheet 15f)
Payback Period (in years) =
Total Capital Investment
Annual Net Operating Cost Savings
A-3 1
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WORKSHEET
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Sheet
PROFlTABlLlTY WORKSHEET #2
CASH FLOW FOR NPV. IRR
.~
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of
I
Cash incomes (such as net operating cost savings and salvage value) are shown as positive.
Cash outlays (such as capital investments and increased operating costs) are shown as negative.
Operating’ Year
Constr.
Line
0
0
2
1
3
4
5
1
6
7
B-(
CashFlow
-
-
_-_
Q Net Present Value (NPV)S
Present Worth6
(5% discount)
0.9070
0.8264 0.751 3 0.6830
-_
.-
_______
(25% discount)
1
2
3.
4
5
6
0.7462 0.7107
0.6768
0.6209 0.5645 0.51 32 0.4665
0.7561 0.6575 0.571 8 0.4972 0.4323 0.3759 0.3269
(15% discount)
. .
It
0.8638 0.8227 0.7835
10.6944 0.5787 0.4823
0.401 9 0.3349
0.2791 0.2326
10.6400 0.51 20 0.4096 0.3277 0.2621 0.2097 0.1678
Adjust table as necessary if the anticipated project life is less than or more than 8 years.
Salvage value includes scrap value of equipment plus sale of working capital minus demolition costs.
The worksheet is used for calculating an aftertax cash flow. For pretax cash flow, use an income tax rate of 0%.
The present value of the cash flow is equal to the cash flow multiplied by the present worth factor.
The net present value is the sum of the present value of the cash flow for that year and all of the preceeding years.
where n is years and r is the discount rate.
The formula for the present worth factor is
1
(l+r)”
A-32
.
Waste Minimization Assessment
Firm
Site
Date
Proc. Unitloper.
Proj. No.
WORKSHEET
Approval By
Date
.
Authorization By
PROJECT SUMMARY
.
Date
Project Started (Date)
A-33
Prepared By
Checked By
-~
Sheet 1of
1
Page
of
Waste Minimization Assessment
Firm
Site
Proc. Unitloper.
Date
Proj. No.
m
Prepared By
Checked By
___
Sheet 1of
1 Page
-
of
-
I
WORKSHEET
OPTION PERFORMANCE
WM Option Description
0Actual
c]Projected
Baseline
(without option)
(a)
Period Duration
From
(b)
Production per Period
Units (
(c)
Input Materials Consumption per Period
Material
~-
To
___
Pounds
)
-
Pounds/Unit Product
-
(d)
Waste Generation per Period
Waste Stream
(e)
Waste Stream
Pounds/Unit Produd
-
Substance(s) of Concern Generation Rate per Period
Substance
Pound3
A-34
Pounds/Unit Product
Appendix B
Government Agencies Offering P2 Assistance
The following contact list was extracted from the Solvent Alternatives Guide (SAGE),
Version 1.1 software program distributed by the U.S. Environmental Protection Agency Control
Technology Center in Research Triangle Park, North Carolina. Errors, omissions, and corrections
should be directed to the Center at 919-541-0800 (voice hotline) or 919-541-5742 (BBS). Copies
of the SAGE program may be obtained by contacting the Center.
ALABAMA
Daniel E. Cooper, Chief of Special Projects
Department of Environmental Management, Waste Reduction and Technology Transfer
(WR4TT) Program
205-260-2779
ALASKA
David Wigglesworth, Chief
Department of Environmental Conservation, Pollution Prevention Office
907-465-5275
Kristine Benson
Waste Reduction Assistance Program (WRAP)
Small Business Hazardous Material Management Project (HMMP)
907-276-2864
ARIZONA
Sandra Eberhardt, Manager
Department of Environmental Quality, Pollution Prevention Unit
602-207-42 10
ARKANSAS
RobertJ. Finn
Department of Pollution Prevention and Ecology, Hazardous Waste Division
50 1-570-286 1
Ed Davis
Arkansas Energy Office, Biomass Resource Recovery Program
50 1-682-7322 50 1-682-734 1 (FAX)
CALIFORNIA
Mr. Kim Wilhelm
Department of Toxic Substances Control, Pollution Prevention, Public and Regulatory
Assistance Division
916-322-3670
B- 1
Tony Eulo
Local Government Commission
916-448-1 198
California Integrated Waste Management Board
800-553-2962 (Recycling Hotline) 9 16-255-2289 (General Information)
COLORADO
Kate Kramer, Program Manager
Department of Health, Pollution Prevention and Waste Reduction Program
303-692-3003 303-782-4969 (FAX)
Michael Nemecek
Colorado Public Interest Research Group (COPIRG)
303-355-1 86 1
CONNECTICUT
Andrew Vecchio
Hazardous Waste Management Service, Connecticut Technical Assistance Program (ConnTAP)
203-241-0777
Liz Napier
Department of Environmental Protection, Bureau of Waste Management
203-566-5217
DELAWARE
Philip J. Cherry & Andrea K. Farrell
Department of Natural Resources and Environmental Control, Pollution Prevention Program
302-739-507 113822
Herb Allen
University of Delaware, Department of Civil Engineering
302-45 1452218449
DISTRICT OF COLUMBIA
Evelyn Shields, Recycling Coordinator
Department of Public Works
202-727-5887 202-727-5872 (FAX)
George Nichols
Department of Environmental Programs, Council of Governments
202-962-3355 202-962-3201 (FAX)
Kenneth Laden
Department of Public Works, Environmental Policy Division
202-939-8 115 202-939-7185 (FAX)
Ms. Ferial Bishop, Administrator
Department of Consumer and Regulatory Mairs, Environmental Regulation Administration
202-404-1 136 202-404-1 150 (FAX)
B-2
FLORIDA
Janeth A. Campbell
'
Department of Environmental Regulation, Waste Reduction Assistance Program (WRAP)
904-488-0300
GEORGIA
Susan Hendricks, Program Coordinator
Department of Natural Resources, Multimedia Source Reduction and Recycling Program
404-362-2537
HAWAII
Jane Dewell, Waste Minimization Coordinator
Department of Health, Hazardous Waste Minimization Program
808-586-4226
IDAHO
Joy Palmer & Katie Sewell
Department of Health and Welfare, Division of Environmental Quality
208-334-5860
ILLINOIS
Dr. David Thomas, Director
Illinois Hazardous Waste Research and Information Center (HWRIC)
2 1 7-333-8940
Mike Hayes
Illinois Environmental Protection Agency, Office of Pollution Prevention
2 17-785-0533
Michael Nechvatal, Manager
Illinois Environmental Protection Agency, Solid Waste Division
2 17-785-8604
INDIANA
Joanne Joice, Director
Charles Sullivan, Environmental Manager
Department of Environmental Management, Office of Pollution Prevention and Technical
Assistance
3 17-232-8172
Rick Bossingham, Coordinator
Jeff Burbrink, Agricultural Pollution Prevention Coordinator
Purdue University Environmental Management and Education Program
3 17-494-5038
IOWA
John Konefes, Director
Kim Gunderson, Environmental Specialist
University of Northern Iowa, Iowa Waste Reduction Center (IWRC)
3 19-273-2079
B-3
Tom Blewett, Bureau Chief
Scott Cahail, Environmental Specialist
Department of Natural Resources, Waste Management Authority Division
5 15-28 1-894 1
KANSAS
Tom Gross, Bureau Chief
Department of Health and Environment, State Technical Action Plan (STAP)
9 13-296-1603
Lani Himegamer, Program Manager
Kansas State University Engineering Extension RITTA Program
913-532-6026
800-332-0036 (Kansas Residents)
KENTUCKY
Joyce St. Clair, Executive Director
University of Louisville, Kentucky Partners State Waste Reduction Center
-
502-5 88-7260
LOUISIANA
Gary Johnson, Waste Minimization Coordinator
Department of Environmental Quality
504-765-0720
MAINE
Ron Dyer
Department of Environmental Protection
207-287-28 11
Gayle Briggs
Maine Waste Management Agency
207-287-5300
MARYLAND
James Francis
Department of the Environment, Hazardous Waste Program
410-631-3344
George G. Perdikakis, Director
Maryland Environmental Services
4 10-974-728 1
Travis Walton, Director
University of Maryland Engineering Research Center, Technical Extension Service
301-454-194 1
MASSACHUSETTS
Suzi Peck
Department of Environmental Protection
617-292-5870
B-4
Barbara Kelley, Director
Richard Reibstein, Outreach Director
Department of Environment, Office of Technical Assistance for Toxics Use
Reduction
6 17-727-3260
Jack Luskin, Director of Education and Outreach
University of Lowell Toxics Use Reduction Institute
508-934-3262
MICHIGAN
Nan Merrill, Manager
Departments of Commerce and Natural Resources, Office of Waste Reduction Services
5 17-335-1 178
MINNESOTA
Kevin McDonald, Sr., Pollution Prevention Planner
Office of Waste Management
612-649-575015744
Eric Kilberg, Pollution Prevention Coordinator
Minnesota Pollution Control Agency (MPCA), Environmental Assessment Office
6 12-296-8643
Cindy McComas, Director
University of Minnesota, Environmental Health School of Public Health, Minnesota Technical
Assistance Program (MnTAP)
6 12-627-455514646
MISSISSIPPI
Dr. Caroline Hill
Mississippi Technical Assistance Program (MissTAP)
Mississippi Solid Waste Reduction Assistance Program (MissWRAP)
60 1-325-8454
Thomas E. Whitten, Director
Department of Environmental Quality, Waste Reductioflaste Minimization Program
601-961-5 171
MISSOURI
Becky Shannon, Pollution Prevention Coordinator
Department of Natural Resources, Hazardous Waste Management Program (WMP)
314-751-3176
Steve Mahfood, Director
Tom Welch, Deputy Director
Environmental Improvement and Energy Resources Authority (EIERA)
3 14-75 1-4919
MONTANA
Dan Fraser, Water Quality Bureau Chief
Department of Health and Environmental Sciences, Solid and Hazardous Waste Bureau
406-444-2406
B-5
Jeff Jacobsen
Montana State University Extension Service
406-994-5683
406-994-3933 (FAX)
NEBRASKA
Teri Swam, Waste Minimization Coordinator
Department of Environmental Control, Hazardous Waste Section
402-47 1-4217
NEVADA
Kevin Dick, Manager
University of Nevada Reno, Nevada Small Business Development Center, Business
Environmental Program
.702-784-17 17 800-882-3233 (Nevada Residents)
-
Doug Martin
Bureau of Waste Management, Division of Environmental Protection
702-687-5 872
Curtis Framel, Manager
Office of Community Services, Nevada Energy Conservation Program
702-885-4420
NEW HAMPSHIRE
Emily Hess
New Hampshire Waste Cap, New Hampshire Business and Industry Association
603-224-53 88
Vincent R. Perelli and Paul Lockwood
Department of Environmental Services, New Hampshire Pollution Prevention Program
603-27 1-2902
NEW JERSEY
Jean Herb, Director
Department of Environmental Protection CN-402, Office of Pollution Prevention
609-777-05 18
Kevin Gashlin, Director
New Jersey Institute of Technology, Hazardous Substance Management Research Center, New
Jersey Technical Assistance Program (NJTAP)
201-596-5864
NEW MEXICO
Alex Puglisi, Program Manager
New Mexico Environment Department, Municipal Water Pollution Prevention Program
505-827-2804
NEW YORK
John Ianotti, Director
State Department of Environmental Conservation, Bureau of Pollution Prevention
5 18-457-7267
B-6
Harold Snow, Program Manager
New York State Environmental Facilities Corporation
518-457-4138
Thomas Hersey, Pollution Prevention Coordinator
Erie County Office of Pollution Prevention (ECOPP)
7 16-858-623 1
NORTH CAROLINA
Gary Hunt, Director
Stephanie Richardson, Manager
Department of Environment, Health, and Natural Resources, North Carolina Pollution
Prevention Program
9 19-571-4100
NORTH DAKOTA
Jeffrey L. Burgess
Department of Health & Consolidated Laboratories, Environmental Health Section
703-221-5 150 701-221-5200 (FAX)
OHIO
Jeff Shick, State Coordinator
Jackie Rudolf
Ohio Technology Transfer Organization (OTTO)
6 14-644-4286
Dan Berglund
Ohio's Thomas Edison Program
6 14-466-3887
Roger Hannahs, Michael W. Kelley, & Anthony Sasson
Ohio Environmental Protection Agency, Pollution Prevention Section
6 14-644-3969
Helen L. Hurlburt
Department of Natural Resources, Division of Litter Prevention and Recycling
614-265-6333
OKLAHOMA
Ellen Bussert & Mary Jane Calvey
State Department of Health, Environmental Quality Council
405-271-7353
Chris Varga
State Department of Health, Pollution Prevention Technical Assistance Program
405-271-7047
OREGON
Roy W. Brower, Manager
David Rozell, Pollution Prevention Specialist
Phil Berry, Pollution Prevention Specialist
B-7
Department of Environmental Quality, Hazardous Waste Reduction and Technical Assistance
Program (WRAP)
503-229-6585
Dr. Ken Williamson
Oregon State University, Environmental Engineering Office
503-754-275 1
PENNSYLVANIA
Meredith Hill, Assistant to Deputy Secretary
Department of Environmental Resources, Office of Air & Waste Management
717-772-2724 7 17-783-8965 (FAX)
David Piposzar, Assistant Director
Allegheny Health Department
412-578-8030 412-578-8325 (FAX)
Jack Gido, Director
Perm State University, Pennsylvania Technical Assistance Program (PennTAP)
814-865-0427 8 14-865-5909 (FAX)
Roger Price
University of Pittsburgh, Applied Research Center, Center for Hazardous Materials Research
4 12-826-53 20 8 00-334-CHMR
Devon Streit
University of Pittsburgh, Applied Research Center, National Technology Applications
Corporation (NaTAC)
412-826-55 1 1
RHODE ISLAND
Richard Enander, Chief
Janet Keller
Eugene Pepper, Senior Environmental Planner
Department of Environmental Management, Hazardous Waste Reduction Program
40 1-277-3434
SOUTH CAROLINA
Eric Snider, Ph.D., P.E., Director
Clemson University, Continuing Engineering Education, Hazardous Waste Management
Research Fund
803-656-3308
Ray Guerrein
Department of Health and Environmental Control, Center for Waste
802-734-4715
Minimization
SOUTH DAKOTA
Wayne Houtcooper
Department of Environment and Natural Resources, Waste Management Program
605-773-4216 605-773-6035 (FAX)
B-8
TENNESSEE
Paul Evan Davis
Tennessee Department of Health and Environment, Bureau of Environment
6 15-74 1-3 657
George Smelcer, Director
University of Tennessee, Center for Industrial Services, Waste Reduction Assessment and
Technology Transfer Program (WRATT)
6 15-242-2456
Carroll Duggan, Section Manager
Tennessee Valley Authority, Waste Reduction and Management Section
615-751-4574
Steve Hillenbrand
Tennessee Valley Authority
615-632-8489
TEXAS
Nancy R. Worst, Director
Texas Water Commission, Office of Pollution Prevention and Conservation
5 12-463-7869
John R. Bradford, Director
Texas Tech University, Center for Hazardous and Toxic Waste Studies
806-742-1413
UTAH
Sonja F. Wallace, Pollution Prevention Co-Coordinator
Stephanie K. Bernkopf, Pollution Prevention Co-Coordinator
Department of Environmental Quality, Office of Executive Director
80 1-536-4480 80 1-538-6016 (FAX)
VERMONT
Gary Gulka
Department of Environmental Conservation, Pollution Prevention Program
802-244-8702
VIRGINIA
Sharon Kenneally-Baxter, Director
Department of Waste Management, Waste Minimization Program
804-37 1-8716
Virginia Polytechnic Institute and State University, University Center for Environmental and
Hazardous Materials Studies
703-23 1-7508
WASHINGTON
Stan Springer, Joy St. Germain, & Peggy Morgan
Department of Ecology, Waste Reduction, Recycling, and Litter Control Program
206-438-7541
B-9
WEST VIRGINIA
Richard Ferrell, Environmental Analyst
Division of Natural Resources, Pollution Prevention and Open Dump Program (PPOD)
304-5 5 8-4000
Randy Huf€man
Division of Natural Resources, Generator Assistance Program
304-558-6350
WISCONSIN
Phil Albert
Department of Development, Hazardous Pollution Prevention Audit Grant Program
608-266-3075
Lynn Persson, Hazardous Waste Reduction and Recycling Coordinator
Kate Cooper, Assistant Recycling Coordinator
Department of Natural Resources, Bureau of Solid & Hazardous Waste Management
608-267-3 763
WYOMING
David Finley, Manager
Pat Gallagher, Senior Environmental Analyst
Department of Environmental Quality, Solid Waste Management Program
307-777-7752 307-634-0799 (FAX)
B-10
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