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Material Transformation and Recycling of Automotive Shredder Residues An Industrial Case Study.

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Dev. Chem. Eng. Mineral Process. 14(1/2), pp. 183-192, 2006.
Material Transformation and Recycling of
Automotive Shredder Residues: An
Industrial Case Study
V.G. Gomes
Department of Chemical Engineering, The University of Sydney,
Sydney, New South Wales 2006, Australia
Environmental pressures have pushed automotive shredder residues (ASR) into the
hazardous waste category, and hence special disposal measures need to be
investigated urgently f o r its sustainability. The possible impacts of ASR on the
environment were assessed by using the Toxicity Characteristic Leaching Procedure
(TCLP. US EPA 1311) and the Specific Contaminant Concentration (SCC, US-EPA
3050). these were performed with the aid of an ICP-AES (Inductively Coupled Plasma
with Atomic Emission Spectroscopy) instrument. A suite of options were analyzed f o r
wuste ryres and the ASR generated by companies in the Greater Sydney region. Four
classes of recycling options were considered, namely primary, secondary, tertiary,
and quaternary recycling, in order to determine the extent to which they can help
improve the overall optimisation of materials and energyflows f o r the ASR.
Introduction
Plastics currently account for more than 20% of the locally generated automotive
shredder residues (ASR), including waste tyres. Market forecasts indicate that the
amount of plastics used in automobiles will continue to increase and could rise to
40% within a decade. Furthermore, about 60,000 tonnes of discarded tyres are
generated each year in New South Wales alone (170,000 tonnes Australia-wide), of
which about 90% is disposed to landfill. Deterrents for such practices include possible
long-term impacts and the escalating land costs, which in turn cause elevated landfill
prices. The NSW EPA (Environmental Protections Agency) has identified ASR and
waste tyres as products subject to Extended Producer Responsibility Schemes.
Each year an estimated fifty million vehicles reach the end of (useful) life (ELV)
worldwide and produce about thirty million of tonnes of ASR. In Australia, the
average life of a motor vehicle is about ten years and the current average weight of a
vehicle is about 1000-1200 kg. Approx. 600,000 vehicles are registered and due for
scrap, consequently, the amount of plastics to be disposed from scrapped vehicles is
significant. ASR generated by one company alone in Sydney is about 25,000 tonnes
per year resulting in an annual landfill cost in excess of US$l million to the company.
~~
~
~~~
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* Author for correJpoiztlence (vgorneJ@chemeng uJyd edu au)
I83
V.G.Gomes
According to the Plastics and Chemicals Industries Association (PACIA), about
2200 plastics manufacturers operate in Australia and account for two-thirds of the
total 1.5 million tomes of plastics material consumed, with imports making up the
deficit [PACIA, 19981. About 500,000 tomes of plastic materials are disposed of
annually, and 85% of the plastic waste goes to landfill each year. Of the disposed
plastics, only 2000 tonnes are reprocessed, that is a low 0.4% of the total. Thus
substantial potential exists for cost reduction and reclamation through recycling. This
case study focuses on finding recycling options to minimise ASR sent to landfill
through evaluation of available realistic recycling options.
Vehicle Composition
An important change in car composition is the amount of plastics used. In 1960, only
2% of a car was polymer based. Today, a typical vehicle contains more than 10%
plastics, which is projected to increase in the future. For the plastics recycler, a
challenging aspect is that a typical vehcle can contain up to 100 different polymers.
Table 1 shows the main plastics consumed by the transport industry in Australia.
Table 1. Polymers consumed by the transport industry in Australia (1995-1997).
Process Description and Impact Assessment
A typical flow diagram for shredder operation is shown in Figure 1. Often two basic
forms of separation are carried out in industry: (a) cyclone separation to separate the
light and heavy residues; and (b) magnetic separation to mainly recover the ferrous
components of the waste material.
I84
Material Transformationand Recycling of Automotive Shredder Residues
Figure 1. Schematic processjlow diagram of EL V shredding.
Significant proportion of research studies is often devoted to identifying suitable
separation methods. The separation technology adopted depends on the technoeconomic feasibility of the selected process and relies on one or more characteristic
properties of the materials, usually related to the following: (a) density; (b)
wettability; (c) electrical properties; and (d) chemical activity. For the industries
surveyed, typically density-based separation is carried out using large-scale screening
followed by air cyclone units. The ferrous and non-ferrous components are separated
using electromagnetic methods. First, the magnetised rotating drums help carry
forward mainly ferrous material. The non-ferrous materials, which include ASR and
V.G. Comes
other metals, are further separated within a rotating tunnel where the induced current
causes the metallic particles to magnetise in a direction opposite to the spin. Thus the
ASR are finally separated from the metallic components. The metallic components
are readily recycled while the ASR is yet to be effectively recycled. Industries
engaged in the further separation of plastics, to enable blending of polymers with
different grades, often utilise density difference. A comparison of densities of a
sample of representative polymers is shown in Table 2. As considerable overlap
exists among polymer densities, and separation processes based on density suffer
from lack of precision. However, hydrocyclone-based separation processes are
relatively simple and inexpensive to operate in terms of energy requirements. In any
case, it is important to take density differential into account for any subsequent
processing of ASR. The main question to address is whether appropriate downstream
markets exist for the variety of polymers obtained.
As the majority of ASR currently goes to landfill, it is essential to carry out
toxicity and contamination tests to determine its viability. To assess the impact of
ASR on the environment, the Toxicity Characteristic Leaching Procedure (TCLP, US
EPA 1311) and the Specific Contaminant Concentration (SCC, US EPA 3050) tests
were performed with the help of ICP-AES (Inductively Coupled Plasma with Atomic
Emission Spectroscopy), atomic absorption spectroscopy and UV spectrophotometer
as analytical instruments [Paniker, 19991.
The TCLP helps determine the amount of material that leaches out from the ASR,
and the SCC helps determine the amount of metals in waste soil. The representative
TCLP (sample results are given in Table 3) and SCC data collected shows that in the
short term, ASR poses no significant leaching problems. The measured values
(C, mg/L) are within the EPA (mg/L) requirements [EPA, 19991 shown in Table 3.
EPA (NSW) do not recommend the testing for copper, iron, manganese and zinc and
these are not listed in the table. However, the deterrents to landfill are possible longterm impacts due to contamination and escalating land prices. The leachates from
metals such as arsenic, cadrmum and chromium could accumulate, 1e:ak into the
groundwater and exacerbate water pollution problems. Land prices in metropolitan
cities have increased significantly and are already affecting landfill costs and balance
sheets for shredder companies.
Table 2. Comparison of typical ASR polymer densities.
Polymer type
186
Density range (g/cm3)
Material Transformation and Recycling of Automotive Shredder Residues
Table 3. Sample TCLP test results.
I Species
c(mg4
EPA (mg/L}
1
A1
0.5
1
As
0.2
-
1
Ba
0.94
1
Zn
Fe
c (mgW
465
135
EPA (mg/L)
Cr
<0.05
<0.05
1.o
5.0
5.0
Species
I
Cd
Pb
1.o
5.0
Mn
5.9
I
cu
<0.05
I
CN 1
~0.1
16
F
2.1
150
Hg
C0.2
Se
c0.2
Ag
<0.2
0.2
1.o
5 .O
Recycling or Reuse
The following four categories of recycling options were considered:
-
Primary Recycling mechanical recycling transforms a waste stream into a
product of characteristics equal to that of the original material.
0
-
Secondary Recycling mechanical recycling transforms a waste stream into
products with quality characteristics which are secondary to that of the original
material, or utilised in a completely new application.
Tertiary Recycling - waste streams are used as a feedstock in processes designed
to recover fuels and chemicals.
0
-
Quaternary Recycling waste streams are used as feed for energy recovery.
Primary and Secondary Recycling
Although, primary recycling is desirable, existing significant constraints for primary
recycling act as deterrents. For example, the recovered components must be pure, and
the recyclate must be single streamed, have minimum contaminants, and must have
sustained minimal deterioration. Predominantly plastic wastes generated during the
manufacturing step can achieve a degree of primary recycling, since these streams
mainly consist of off-cuts, mould scraps, rejects, and newly extruded parts. However,
ASR and mixed plastics waste have limited prospects for undergoing primary
recycling due to contamination and substantial wear, although separation technologies
applied prior to shredding can recover the waste plastics for reuse.
Secondary recycling involves mechanical recovery for a different application. The
material, although not as high in quality as the original, can be reused where the
stringency of primary recyclate characteristics do not apply. For example, recovered
PET is ground and re-extruded to make flowerpots, crates, etc. Polymers such as PE,
PP and PS can be recovered, preferably in single streams, granulated, and sold as
beads which can then be re-extruded into a large variety of products. Constraints
include the product quality dependent upon recyclate purity, contaminant separation
]
V.G. Gomes
from recyclate, compatibility considerations, and development of appropriate target
applications. The key to primary and secondary recycling is disassembly, polymer
separation and part identification.
Disassembly and Separation
With respect to the plant we studied, first the batteries are removed (implemented
based on recommendations from our study) and gasoline is drained prior to shredding.
Tyres are then shredded (our recommendation on tyre removal is yet to be
implemented) with the rest of the material. After inspection, the car body with all
contents is transported to a conveyor belt feeding to the shredding unit housed in a
large concrete room. The mill is doused with steam to contain explosions from fuel,
puncturing cylinders, etc.
A surrounding grid allows particles of size 11.4 cm (4.5 in.) or less to be carried
away by a conveyor belt. The light stream is carried through to a cyclone unit. The
particles are thrown to the sides and circulate to the bottom while the clean air is
recycled back to the Z-box. Once the metal is removed, a light waste stream is
produced which consists of everything remaining from the shredding plant. Apart
from the main components of a car, contaminants include debris, soil, dirt, rust, oils,
fabric, glass, sand, wood and paper. This combined residue is collectively called ASR
or flocs. The light waste material is dumped from the shredding facility, shovelled by
cranes into trucks, and transported to landfills.
Shredding limits the recyclability of materials because of difficulties with
identification, separation and cleaning. Thus to maximize primary and. secondary
recycling, dismantling as far as is feasible is recommended prior to shredding. A
typical recommended dismantling schedule is shown in Table 4.
PUR foam accounts for more than 5 wt% of ASR, and up to 30%. Removal of
foam will enable savings on transport costs to landfill. A PUR-foam dismantling
feasibility experiment involving removal of front seats was carried out. It took a total
of two minutes to recover 2 kg of foam from a Datsun car. The price range offered by
a receiving company ranged from $0.30-$0.70 per kg based on foam grade and
condition.
For the plants studied, two persons hired to dismantle 50 cars per day could
generate enough revenue to pay their wages, and help reduce landfill and
transportation costs. Procedures being implemented by car manufacturers for ease of
vehicle disassembly include the labelling of parts with internationally recognised
identification, limiting the types of polymers used, and unifying fixtures, joints and
adhesives to limit contamination of plastics with other materials and parts.
Nevertheless not all parts can be successfully dismantled from vehicles, thus
shredding will be necessary followed by separation and/or post-processing.
Separation technologies take advantage of differences in the materials characteristic
properties. For plastics, properties often exploited are density, wettabilit.y, electrical
and chemical characteristics.
When ASR separation is not feasible, then integration with another product or
tertiary/quaternary recycling needs to be considered. Our initial study showed that the
addition of ASR to concrete was safe and provided improved strength and structural
properties required in cement, as also indicated by others [Soroushian et al., 19961.
188
Material Transformation and Recycling of Automotive Shredder Residues
Table 4. Estimated dismantling schedule for plastic parts
Parts
Polymer
Battery tray
Battery holder clip
Fender liner
Fuel tank shield
Engine splash shield
Fan shroud
Garnish moulding
Door trim panel
Console
Luggage compartment
Windshield wash
reservoir
Radiator end tank
Grille opening panel
Bodyside moulding
Armrest
Wiring harness
PP
PP
PP or PE
PP or PE
PP or PE
PP
PP or ABS
P P or A B S
PP or ABS
PP or ABS
PE or PP
PA
SMC
PVC
PVC
PVC
Mass
(kgl
0.45
0.05
1.04
2.22
Dismantle
time (s)
30
25
105
Cleaning
time (s)
15
NR
30
100
NR
0.91
I35
132
15
1.72
0.14
1.36
1.63
0.54
0.54
220
24
28
NR
82.5
7.5
25
30
10
20
0.36
4.08
1.59
0.14
4.54
105
280
30
30
48
18
ND
ND
ND
ND
200
(NR =not required; ND =n ot done)
Tertiary Recycling
This is also known as feedstock recycling, the concept of tertiary recycling is to use
waste streams to recover fuels or chemicals which can be used again. Mixed streams
of ASR are often too contaminated for mechanical recycling. The difficulties of
separation and decontamination impose large costs for potential mechanical recycling
processes. Hence, feedstock recycling may have advantages via pyrolysis, hydrolysis
or depolymerisation. Pyrolysis process requirements are lugh temperature (-900OC)
depending on the reactor chosen, long residence times, and downstream treatment. To
assess feasible applications, the relevant data [Brandrup, 19961 on the feedstock and
on corresponding product distributions (see Table 5) of pyrolysis, were examined. It
is noted that from light ASR, approximately 52% solid residue is produced with about
27% gas and 22% oil. The implications for the various streams are:
s Gas products - efficient scrubbing is needed to remove contaminants.
0
Solid residues - disposal of significant ASR residue (class: hazardous) is
required.
Oils - separation and post-processing is needed prior to marketing.
The estimated cost for implementing this technology at present exceeds the
current landfill disposal costs, and the product processing is complex. Thus the cost
effectiveness of such a process, in the absence of an available unit, was questionable
for the plant studied.
I89
V.G. Gomes
Table 5. Pyrolysis products from variousfeedstocks
I
Feedstock
I
Reaction
temp. (Y)
787
700
733
700
Mixed plastics
ASR (light)
ASR (heavy)
Scrap ryres
I
Gas
(w%)
I
44
27
30
22
I
(W%)
Residue
(wt%)
26
21
27
22
25
52
28
39
Oil
I
Orher
(wt%)
I
5
0
16
17
Quaternary Recycling
Quaternary recycling of waste streams takes advantage of stored energy in waste
materials for energy production. Although this form of recycling is often perceived as
a waste of resources and an environmental hazard, there are benefits of using this
technology, such as the ASR utilization in the absence of other feasible technologies
and a reduction in waste volume. Difficulties with current incineration methods
include ineecient energy production, inadequate volume reduction, and pollution
from halogens, furans and dioxins. To minimise the environmental impact, expensive
scrubbing and emission monitoring is required. The incineration alternative requires
an estimated US$200 million to process 300,000 tonnes per year, giving an
incineration cost of about US$50 per car.
However, kilns for cement production may be able to accommodate ASR as an
inexpensive fuel source. Some of the requirements for cement kilns are particle size
(-15-20 mm), energy needs (-20,000 tonnes of ASWyear required), toxic emission
clean-up, and cost issues (material and transport costs). Figure 2 shows the particle
size distribution. For this case study, particle size limitations could be easily
overcome by using a rotary cutting unit, however a major concern was that the ASR
contains PVC which is difficult to separate and remove.
0
50
100
150
Partidesize (mm)
Figure 2. ASR particle size distribution.
I90
200
250
Material Transformationand Recycling of Automotive Shredder Residues
In terms of its calorific value, ASR was found to be suitable as a fuel, and
compares with wood as an energy source. A comparison of different fuels with ASR
in Figure 3 (PP - polypropylene; PE polyethylene, PUR polyurethane) shows that
cleaning ASR and recovering mixed polymers would enhance the heating value of
ASR significantly to that of a suitable fuel. This can partly be facilitated through scrap
metal detection and recovery, and fines sieving to remove inert dust and dirt, which
do not contribute to combustion. Therefore, refined ASR was recommended as a fuel
source for cement companies.
-
-
Figure 3. Comparison of calor$c values of various fuels with ASR.
Conclusions
Currently ASR is sent to landfill in Australia. Options for diverting ASR (or part
thereof) are limited. This is because of a lack of feasible technology, expensive
treatment, high risk in recycling, and limited market opportunities. A range of options
were analyzed for those ASR generation companies in Sydney engaged entirely in
ASR landfilling. Mechanical recycling was considered first, followed by feedstock
and then energy recovery. For the plants studied, battery removal was recommended
and implemented. Further recommendations included recovery of PUR foam, tyres
and other readily accessible parts. Parts not amenable to mechanical recovery are to
be processed for generating ASR, and this was found to be suitable as an additive to
cement and as a supplementary fuel for cement kilns. The presence of PVC was a
deterrent to incineration. Shredding companies were advised to minimise variations in
waste composition, reduce landfill, maximize dismantling, and develop mutually
beneficial relations with downstream processing industries in order to use ASR as a
construction material and as a fuel.
191
V.G. Gomes
References
Brandrup, J. (ed). 1996. Recycling and Recovery of Plastics, Hanser, Germany.
EPA (NSW). 1999. Environmental Guidelines: Assessment, Classification and Management of Liquid and
Non-liquid Wastes, New South Wales, Australia.
PACIA. 1998: http://www.pacia.orgl
Paniker, S . 1999. Recycling ASR. Honours Thesis, Dept. of Chemical Engineering, University of Sydney,
New South Wales, Australia.
Soroushian, P. et al. 1996. Recycling of automobile plastics in concrete construction. Report MSU-ENGR001-96. Michigan State University, Michigan, USA.
I92
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