close

Вход

Забыли?

вход по аккаунту

?

184893-MS

код для вставкиСкачать
SPE-184893-MS
The Use of WalnutShell Filtration with Enhanced Media for Reduction and/or
Elimination of Upstream Produced Water Treatment Equipment
Shane Wiercinski, Siemens Water Solutions
Copyright 2017, Society of Petroleum Engineers
This paper was prepared for presentation at the SPE Latin America and Caribbean Mature Fields Symposium held in Salvador, Bahia, Brazil, 15–16 March 2017.
This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents
of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect
any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written
consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may
not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.
Abstract
Walnut shell media filtration has traditionally been used in upstream and downstream produced water
treatment applications onshore. This has been largely driven by the footprint required for the flux rates
traditionally applied to walnut shell filtration. At the traditional flux rates, walnut shell filters typically
require a larger footprint atop a platform or FPSO than equipment such as hydrocyclones and gas flotation
units. Recent developments including the incorporation of internalized backwash systems as well as
increased processing capacity using reduced footprint has made media filtration using walnut shells more
appealing to both onshore and offshore users and operators. In addition, there has been a trend to use tertiary
treatment technologies downstream of secondary equipment such as flotation cells, due to the need to reduce
hydrocarbon discharge to the environment.
One limitation in using walnut shell media is that walnut, as well as other nut shell media, are produced
by, and are subject to, an agricultural season. Due to the fact that nut shell media are subject to uncontrollable
environmental factors, crop yields can be sparse resulting in reduced availability. More recently, a synthetic
alternative has been developed to replace nut shell media. The synthetic media is manufactured from
materials that are not subject to yearly agricultural limitations. Through experimental and field testing, the
following benefits have been observed in using this synthetic media:
•
•
•
Ability to handle greater than four to five times the amount of oil before requiring a backwash as
compared to standard nut shell media
Ability to maintain feed concentrations of greater than 500 mg/L while producing effluent well
under 29 ppm
Applicability to a wide range of oil API from 10-35+ and elevated temperatures greater than 90°C
This paper will highlight the performance data and results, backwash frequency, ability to remove and/
or eliminate treatment equipment upstream of media filtration such as gas flotation and its combination
with standard nut shell filtration. It will also highlight the potential reduction of treatment chemicals needed
to enhance gas flotation and reduction or elimination of waste sludge into recoverable crude. It will also
capture comparison of reduced footprint and weight as compared to full produced water treatment systems.
Keywords: walnut shell, filtration, enhanced media, equipment elimination, produced water
2
SPE-184893-MS
Introduction
Walnut shell media filtration has traditionally been used in upstream and downstream produced water
treatment applications onshore; walnut shell filtration has rarely been used offshore. This difference in use
has been driven by two factors: the need for better treatment for onshore disposal; and the footprint required
for the walnut shell filters using traditional design flux. On an offshore platform or Floating Production
Storage and Offloading Vessel (FPSO), any additional footprint required for treatment is very expensive.
Traditional hydrocyclones and flotation equipment have been refined to minimize the area required. At
traditional design flux, walnut shell filters typically require a larger footprint atop a platform or FPSO than
is readily available, especially for equipment that is not needed to reach the less-stringent discharge limits
that have been used offshore in the past. Recent developments, including the incorporation of internalized
backwash systems as well as increased processing capacity using reduced footprint, has made media
filtration using walnut shells more appealing to both onshore and offshore users and operators. In addition,
there has been a trend to use tertiary treatment technologies downstream of secondary equipment such as
flotation cells, due to the need to reduce hydrocarbon discharge to the environment for both regulatory and
public relations reasons.
One limitation in using walnut shell media, however, is that walnut shells, as well as other nut shell
media, are produced by, and are subject to, an agricultural season. Due to the fact that nut shell media is
subject to growing seasons and uncontrollable environmental factors, crop yields can be sparse, resulting
in dramatic market fluctuations. A new synthetic media has been developed – PerforMedia™ oil removal
media – as a direct replacement of nut shells. This media is manufactured from materials that are not subject
to annual agricultural limitations.
Through experimental and field testing, the following benefits have been observed in using this synthetic
media:
•
•
•
Ability to handle greater than four to five times the amount of oil before requiring a backwash,
compared to standard nut shell media
Ability to maintain feed concentrations of greater than 500 mg/L while producing an effluent well
under 10 ppm
Applicability to a wide range of oil API from 10 – 35+ and elevated temperatures as high as 90 °C.
With these realized benefits, this paper will highlight the performance and ability to remove and/or
eliminate treatment equipment upstream of media filtration, such as gas flotation and its combination with
standard nut shell filtration. It will also highlight the potential reduction of treatment chemicals used to
enhance gas flotation and the reduction or elimination of waste sludge into recoverable crude.
Tests and Pilots
Lab Testing
Laboratory testing was performed using synthetic produced water. The produced water was made by
injecting crude oil into a pressurized water stream. A globe valve and static mixer were used to shear the oil
into droplets to simulate produced water. The produced water was then routed to the top of a packed column,
and treated water exited the bottom. After the bed had been exhausted, found by monitoring effluent oil
concentrations, the media was backwashed using up-flow water and an internal gas lift pump.
The same produced water that the unit was treating was used for backwash. Following backwash, the
produced water was routed to the top of the bed for filtration. The lab test configuration is presented in
Figure 1.
SPE-184893-MS
3
Figure 1—Laboratory testing process flow diagram
Results and Discussion
Laboratory testing was conducted to compare the oil loading of PerforMedia™ media to walnut shells,
presented in Figure 2. At the same flux (13.5 gpm/ft2 or 22 m3/h/m2), the synthetic media was able
to load approximately four times more oil before break through than walnut shells. This increased oil
loading capacity will decrease the required backwash frequency, allowing for either longer loading between
backwashing or the ability to withstand higher oil concentrations.
Figure 2—Media comparison of laboratory results
Testing was performed using different oils, a range of 13 to 32 API, at different fluxes. Figure 3 presents
the results of the testing.
4
SPE-184893-MS
Figure 3—Oil loading based on API of oil and flux
The testing indicates that as the flux is increased, the oil loading decreases. The decrease in loading
capacity is likely due to the increase in velocity as the flux is increased. As the velocity through the interstitial
space increases, larger droplets can be carried through the media bed. Also, as the API of oil decreases,
so does the oil loading. This is likely due to higher density particles requiring less velocity to be carried
through the bed.
Walnut shells are effective at removing small free oil droplets. For an effective alternative, the new media
must be able to remove small free oil droplets too. A particle analyzer was used to compare the influent
and effluent particle distribution.
Figure 4 presents oil droplet analysis data from laboratory testing. The influent contained about 75% of
the oil particles greater than 15 microns. The effluent contained nearly zero oil droplets remaining larger
than 10 microns, showing that PerforMedia™ oil removal media is effective at removing oil droplets greater
than 15 microns.
SPE-184893-MS
5
Figure 4—Oil droplet size distribution
In order to reduce capital cost, the tertiary treatment system must be made smaller, or other equipment
must be removed from the treatment system. Since PerforMedia™ media operates at fluxes similar to
walnut shells, the tertiary system has a similar footprint to walnut shells. A test was performed to see if
PerforMedia™ media could produce effluent quality equal to tertiary systems with primary effluent as feed.
The test unit was operated with heavy oil, API 13, at 500 mg/L feed oil concentration. The synthetic media
was able to produce effluent less than 10 mg/L for three consecutive runs, presented in Figure 5.
Figure 5—Laboratory testing of high influent concentrations
Based on all laboratory testing results, this alternative media appears to be effective at handling oil inlet
loading typical of both secondary and tertiary treatment applications.
6
SPE-184893-MS
South America Pilot Testing
Upon completion of laboratory testing, the pilot unit was taken to the field to validate the effectiveness on
real world produced water. Pilot testing was performed in South America on heavy crude oil, API 11.
The pilot unit contained two media vessels that could be used either in stand-alone or parallel mode,
allowing for the ability to perform side by comparisons between media or manage larger feed flows. The
unit was tested using PerforMedia™ oil removal media in one of the vessels. The principal of operation
and more detailed description are discussed below:
Principal of Operation. The pilot unit was a continuous flow system. A single feed source was the inlet to
two vessels that could be operated in parallel or stand-alone. The untreated feed flowed from the top down in
order to maintain a packed bed. The free oil droplets and suspended solids in the water were captured by the
media. Once the media bed was saturated, a breakthrough (oil/solids concentration increase in the effluent)
occured. At the breakthrough point, a backwash was performed to regenerate the media. The backwash was
accomplished by using a gas lift pump to agitate and turn over the media bed. A backwash was initiated
by a pressure differential across the bed, breakthrough, or on timed intervals. The backwash used the same
internal distribution system as the outlet for forward flow.
Pilot Vessel Description. The pilot consisted of two vessels that could be operated in parallel, each 24
inches (0.6096 m) in diameter, with one vessel containing PerforMedia™ media. Each vessel contained a
header at the bottom, a gas lift pump located at the center of vessel, a gas distribution nozzle that drove the
gas lift pump and a top screen to retain media inside the vessel.
The pilot unit was used upstream of the flotation units and prior to chemical addition, as noted in Figure 6.
Figure 6—Site process flow diagram
The unit was operated 24 hours per day for approximately 17 days, and encountered temperatures ranging
from 50-70 °C and oil feed concentrations greater than 1200 mg/L.
Results and Discussion
Over the course of this pilot test, three fluxes were tested. The unit was run at a flux of 10, 8, and 5 gpm/
ft2 (24.5, 20, 12.2 m3/h/m2). The initial test was performed at a flux of 10 gpm/ft2 (24.5 m3/h/m2) since a
majority of laboratory testing with lower API was done around this flux. Figures 7 and 8 below show the
oil and total suspended solids removal during a test.
SPE-184893-MS
7
2
3
2
Figure 7—Oil removal at 10gpm/ft (24.5 m /h/m )
2
3
2
Figure 8—Solids removal at 10gpm/ft (24.5 m /h/m )
As noted in the above figures, the removal efficiencies were not as high as expected and this API of oil
was not included in the laboratory testing. It was decided to further reduce the flux to determine the effect.
Figures 9 and 10 below show the oil and total suspended solids removal while running at a flux of 5 gpm/
ft2 (12.2 m3/h/m2).
8
SPE-184893-MS
2
3
2
Figure 9—Oil removal at 5 gpm/ft (12.2 m /h/m )
2
3
2
Figure 10—Solids removal at 5 gpm/ft (12.2 m /h/m )
The reduction in the flux from 10 gpm/ft2 (24.5 m3/h/m2) to 5 gpm/ft2 (12.2 m3/h/m2) made a noticeable
difference in the removal efficiencies. It appeared that at this oil API, solids loading, and temperature, the
media required a lower flux. It was decided to increase the flux to 8 gpm/ft2 (20 m3/h/m2) and note the
effects. Figures 11 and 12 below show the oil and total suspended solids removal while running at a flux
of 8 gpm/ft2 (20 m3/h/m2).
SPE-184893-MS
9
2
3
2
Figure 11—Oil removal at 8 gpm/ft (20 m /h/m )
2
3
2
Figure 12—Solids removal at 8 gpm/ft (20 m /h/m )
As noted in the above figures, the increase in flux caused the removal efficiency to deteriorate. Figure
13 shows the comparison between the three different fluxes and percent removals.
10
SPE-184893-MS
Figure 13—South American pilot study flux comparison
As noted in the above figure, the optimal flux for this API oil is between 5 gpm/ft2 (12.2 m3/h/m2) and
8 gpm/ft2 (20 m3/h/m2).
Since PerforMedia™ media was found to be effective for secondary treatment without the use of flotation
and flotation chemicals, the oil can be recovered from the backwash. In addition, the chemical costs will be
reduced, as well as flotation waste disposal or flotation waste handling costs.
North America Pilot Testing
A second pilot test was conducted at a Western USA refinery in a downstream application where the oil
API was around 35. The testing was conducted as secondary treatment prior to chemicals and flotation, as
seen in the process flow diagram in Figure 14.
Figure 14—Site process flow diagram
SPE-184893-MS
11
Principal of Operation. A smaller pilot unit with a single, 6″-diameter vessel was used for this pilot
study. It operated in the same fashion as the larger pilot that was used in the South America pilot study
referenced above. A backwash was initiated by a pressure differential across the bed, breakthrough, or on
timed intervals. The backwash used the same internal distribution system as the outlet for forward flow.
Pilot Vessel Description. The pilot consisted of a single, 6″ (0.15 m)-diameter vessel that contained
PerforMedia™ oil removal media. The vessel contained a header at the bottom, a gas lift pump located at
the center of vessel, a gas distribution nozzle that drove the gas lift pump and a top screen to retain media
inside the vessel. The pilot unit was used upstream of the flotation units and prior to chemical addition as
noted in Figure 14.
Results and Discussion
The feed oil concentration in this application was very low, averaging only 37.3 mg/L during the entire pilot
study. The oil removal efficiency of PerforMedia™ media increased as the feed oil increased.
The PerforMedia™ media pilot was tested at a flux of 10 gpm/ft2 for 45 days and at a flux of 15 gpm/ft2
for 11 days. The pilot was operated in parallel with two IGF units to directly compare their performance.
The results from a portion of the 10 gpm/ft2 flux testing are shown below in Table 1.
2
Table 1—PerforMedia™ Media vs IGF - 10 gpm/ft
Feed
Total O&G (mg/L)
IGF Effluent
Range
1.0 – 142.0
2.0 – 10.0
4.1 – 27.3
Average
31.0
5.6
12.7
82%
59%
% Removal
TSS (mg/L)
PerforMedia™ Effluent
Range
18.8 – 163.0
8.4 – 23.0
n/a
Average
46.6
14.7
n/a
70%
n/a
% Removal
During the 10 gpm/ft2 flux testing, PerforMedia™ media had an average oil removal efficiency of
82%. The IGF's were only able to remove 59% of oil, even when assisted by chemical addition. The
PerforMedia™ media pilot was also able to remove 70% of all TSS.
Toward the end of the study, the flux of the pilot unit was increased to 15 gpm/ft2. Results from a portion
of this test condition are shown below in Table 2.
Table 2—PerforMedia™ Media vs IGF - 15 gpm/ft
Total O&G (mg/L)
Feed
PerforMedia™ Effluent
IGF Effluent
Range
12.6 – 61.4
3.8 – 9.8
9.9 – 31.1
Average
32.6
6.2
20.1
81%
38%
% Removal
TSS (mg/L)
2
Range
25.2 – 94.0
8.0 – 15.0
n/a
Average
60.0
12.2
n/a
80%
n/a
% Removal
12
SPE-184893-MS
During the 15 gpm/ft2 flux testing, PerforMedia™ media had an average oil removal efficiency of 81%
(only 1% lower than the 10 gpm/ft2 test) and the IGF's were only able to remove 38% of the oil, even when
assisted by chemical addition. The PerforMedia™ media pilot also was able to remove 80% of all TSS.
The PerforMedia™ oil removal media pilot was able to remove over 80% of the influent feed oil during
both the 10 gpm/ft2 and 15 gpm/ft2 flux test conditions. There was very low oil in the API effluent and
it is likely that a filter system using PerforMedia™ oil removal media could displace both primary and
secondary treatment in this application since the synthetic media can handle feed oil concentrations greater
than of 500 mg/L. It is also likely that as the feed oil concentration is increased the oil removal efficiency
will also increase.
Conclusions
•
•
•
•
•
•
•
•
PerforMedia™ media can tolerate higher influent oil concentrations and produce equivalent
effluent concentrations as nut shells.
PerforMedia™ media has a higher specific load as compared to nut shells, thus reducing backwash
frequency.
PerforMedia™ media used in a secondary treatment application produces equivalent effluent
quality to traditional secondary and tertiary treatment processes within a single step. When used
in a secondary treatment application, chemical costs can be reduced and oil can be recovered
from backwash. Chemical contamination of the remaining crude within the produced water can
be reduced or eliminated.
PerforMedia™ media is manufactured from materials that are not subject to agricultural
limitations.
Data is consistent with a trend observed in previous testing in which lower API oil required a lower
flux. With higher API oil, higher flux may be used.
Particle analysis has shown that PerforMedia™ media is effective at removing oil droplets larger
than 15 microns.
Depending upon variables such as temperature and flux, removal efficiencies can be increased or
decreased.
In applications governed by stringent discharge limits, further downstream treatment may still be
required based upon feed concentrations.
Future Outlook
•
•
•
Further studies/pilot unit usage to collect operational experience and close knowledge gaps.
Gather more details about cleaned water quality and flow rates
Check performance in the presence of Enhanced Oil Recovery polymers
Документ
Категория
Без категории
Просмотров
2
Размер файла
1 455 Кб
Теги
184893
1/--страниц
Пожаловаться на содержимое документа