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Evaluation of Membrane desalination schemes in desert oil field
with emphasis on membrane separation technologies
Mohamed H. Sorour,* Heba A. Hani, Ghada A. Al-Bazedi and Hayam F.
Shaalan
Chemical engineering and pilot plant department, National research center
Address: El-Bohouth Street, Dokki-Giza- Egypt; P.O. Box 12622
Tel.: (+2) 02 33389935, Fax: (+2) 02 33370931
* Corresponding author e-mail: [email protected] ; Tel:01005276183
Abstract
Most large-scale petroleum production sites are located in remote and
coastal locations. Securing availability, accessibility, reliability, and affordability
are key issues for sustainable water production in oil fields locations. In this
paper, comparative assessment of reverse osmosis (RO), electro-dialysis (ED)
and electro-dialysis reversal (EDR) has been conducted from the technical,
financial and environmental standpoints. The special features of brine
management in remote desert locations have been addressed through possible
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cost effective salt recovery interventions. Thus, a comparative evaluation of deep
well injection versus salt recovery based on solar ponds has been addressed. The
paper is concluded with addressing the economic criteria for implementation of
integrated membrane schemes in remote desert locations. The attractive features
of electro-dialysis have been emphasized taking into consideration the latest
development in ion exchange membrane and EDR electrode assembly.
Key words: Brackish water, desalination, reverse osmosis, electrodialysis
reversal, cost, salt recovery
1. Introduction
The global water demand is continuously increasing due to population growth
and economic development. The decreasing per capita water share in the middle
east and north Africa, especially, Egypt is below the scarcity limit (<1000
m3/capita) [1-3]. Desalination and water reuse are key parameters in water
shortage issue and future needs in Egypt since the current freshwater resources
will not be able to meet all requirements [4,5]. ADW in Egypt amounts to 9
billion m3/ year (with high salinity 1500- 3000 ppm and more) could be
considered as an important water supply if desalting is considered [5]. Thermal,
ion exchange, reverse osmosis (RO), electro dialysis reversal (EDR) are the
most prevailing options for desalination of seawater, brackish groundwater as
well as agriculture drainage water (ADW) to cope with the population growth,
development, and industrial applications [5-10]. RO is considered to have an
economic advantage for the desalination of saline water with total dissolved salts
(TDS) in excess of 10,000 mg/l where, EDR is generally the most economic
process in comparison to RO when the salinity of the feed water is not more than
about 6 g/l of dissolved solids [11-13]. Rapid advance in desalination using ERD
technique is due to improvement in ion exchange membrane properties, better
materials of construction and advances in technology. However, there are
concerns of creating point of pollution, causing contamination of groundwater
supplies, while brine discharge downstream with agricultural drainages affecting
aquatic life [14]. Some other applications of EDR were its use to reduce
inorganics like radium, perchlorate, bromide, floride and nitrate [15-19]. In
addition, EDR can be used to recycle municipal and industrial waste water [20],
recovering RO reject [21]. In water desalination, EDR is mainly used in small
to medium size plants with capacities of less than a few 100 m3/d to more than
20,000 m3/d. One of the biggest EDR system (220,000 m
3/d; 576 stacks in two
stages, provided by GE Water & Process) for desalting brackish water to
improve the quality of the produced drinking water is located near to Barcelona
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(Spain) [2,22,23]. Energy consumption and the required membrane area are
strongly increasing with increasing feed water TDS in EDR. The EDR system
has a nominal initial brackish water recovery in the range of 80%-90% while,
RO system normally has a water recovery in a much lower range, 65%-75%. In
this paper, three schemes have been investigated for developing brackish water
(BW) desalination unit (20,000 m3/d) namely, RO, EDR and EDR/RO dual
system. Possibility of salt recovery has been examined.
2. Approach and Methodology
The adopted approach enables the development of a technical and economic
feasibility investigation for brackish water desalination using RO and /or EDR
technologies.
Relevant worldwide reported RO and EDR cost data in addition to
experimental results presented in different contributions [11,17,24] have been
collected, screened and analyzed for the development of financial indicators. The
selection of the capacity (20,000 m3/d) and adopted technologies features state of
the art brackish desalination facility is recommended for future implementation.
It is worth mentioning that the environmental benefits associated with salt
recovery have not been addressed in the current analysis. Typical brackish water
analysis comprising Ca, Mg, Na, Cl, SO4 and TDS are 110, 80, 815, 811, 1100,
and 3081 mg/l, respectively. Possibility of salt recovery has been examined.
2.1 Basis of cost estimation
The preliminary design cost estimate determines the financial indicators
including capital, annual O&M, and unit costs of brackish water desalination
using a visual basic software (WT Cost II ©) software developed by the Bureau
of Reclamation and Moch Associates dealing with water treatment costs[25].
Basis of capital and operating costs for BW desalting facility are as follows [26-
29]:
Direct capital cost includes the cost of land, major and auxiliary process
equipment and construction costs. Freight and insurance, construction
overheads and contingency costs are part of the indirect capital costs.
Annual operating costs are after plant commissioning and during plant
operation including chemicals, energy, wages, plant maintenance,
expenditures … etc.
Plant life is based on 30 years.
All capital costs have been updated to 2013 using ENR-CCI cost index.
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0.5 %of direct capital cost and 2% of O&M costs are accounted for
auxiliary items.
Financial analysis does not account for the capital and operating costs of
the marine intake & outfall.
Electricity cost was considered 0.045 $/m3
3. Results and Discussion
3.1 Process description
3.1.1 Configuration
Three brackish water desalination schemes for 20,000 m3/d water
production have been developed. Schemes (1) and (2) represent single process
comprising EDR or RO desalination systems, respectively. The cost estimation
has been conducted for these two schemes based on the international reported
performance range of recovery and rejection for EDR and RO. Scheme (3)
comprising EDR followed by RO and solar pond then developed in view of the
later results as shown in figure (1) to produce almost the same water quality as
presented in the aforementioned schemes.
3.1.2 Performance
The performance indicators and main technical specifications of the
selected membrane units were screened. Selected recovery and rejection values
for EDR are (75-95%) and (60-90%), respectively. While, the corresponding
values for RO are (75-85%) and (65-95%), respectively [11,17,22,28,30,31]. The
developed integrated brackish water desalination/salt recovery zero discharge
desalination (ZDD) facility for water production capacity 20,000 m3/d is shown
in figure (1). The figure presents the flow and TDS of each stream, as well as,
salt recovery from different units based on material balance.
The selected values for membrane rejection and recovery for scheme (1)
were to be 90% and 75%, respectively to obtain product water of TDS 411 mg/l,
which is acceptable as a drinking water TDS range according to WHO guidelines
[32] and brine TDS approaching 11100 mg/l. The corresponding values for
scheme (2) were 85% and 85%, respectively to obtain product water of TDS 544
mg/l and brine TDS approaching 17500 ppm.
As for scheme (3), EDR and RO rejection and recovery values have been
studied in the pre-mentioned ranges and in view of the above results to obtain the
desired water TDS. The values for membrane rejection and recovery for EDR
were 85% and 85%, respectively. The corresponding values for RO were 85%
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and 99.8%, respectively to obtain product water of TDS 499 ppm and very high
brine TDS approaching 58100 ppm.
In summary, EDR can offer the benefit of higher recovery relative to
reverse osmosis systems. RO and EDR are well suited to different site
applications requiring high recovery ratios. There are several advantages for
using membrane desalination; firstly, EDR can be used for a majority of feed
water and easily recovered as a product. This is in contrast to RO, where high
recovery ratios require multiple stages in a continuous process as well as the
need for a proper pretreatment stage. EDR can treat feed water with high
suspended solids feed, while bacteria and other ionic substances and turbidity are
not affected by the desalination step and remain in the product if not well
pretreated. RO has low energy consumption comparing to EDR, as energy
required in EDR is proportional to the amount of salts to be removed. EDR and
RO have a high recovery ratio, as well as high space/production capacity ratio.
3.1.3 Brine management
The environmental effect of waste disposal problem in rural and arid
areas, as disposal of inland desalination concentrate, is governed by several
factors, starting from environmental impact criteria of the disposal method to
socio-economic parameters. Table (4) shows the criteria of selection for
concentrate disposal methods [33-36]. Land application, deep well injection and
solar evaporation ponds may require permits on a site specific basis.
3.2 Financial indicators
The costs of producing desalinated brackish water have been investigated
for the three developed schemes. Tables(1, 2) present the total capital, annual
O&M, total annual, unit costs and the product water TDS for schemes 1 and 2,
respectively. The financial indicators for scheme (1) revealed that the total
capital cost value for the studied recovery and rejection values was 4.89 M$
while, total annual cost range was 1.4 to 1.43 M$/year and unit costs lies in the
range: from 0.212 to 0.216 $/m3 with product water TDS range of 324-1640
mg/l.
The financial indicators for scheme (2) show higher total capital cost (4.95 - 5
M$) and lower total annual cost (0.71 - 0.75 M$/year) and unit cost (0.108 -
0.114 $/m3 with product water TDS range of 181-1440 mg/l.
The financial indicators for scheme (3) without salt recovery revealed that the
total capital cost was 6.3 M$ while, total annual cost was 1.5 M$/year and unit
cost of 0.226 $/m3with product water TDS was 490 mg/l. The selected technical
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specifications, as well as, the financial indicators for the three schemes are
presented in table (3).
3.2.1 Impact of salt recovery
Scheme (3) is most likely adopted as the brine water generated is of higher
TDS than the other schemes, which can be disposed to a solar pond. The effect
of salt recovery on total system revenues is illustrated in scheme (3).
For scheme (3), the expected daily produced raw sodium chloride was 14 ton/d
as shown in figure (1) with total annual revenues approaching 4.9 M$/year and
estimated net annual profit of 3.07 M$/year. The possible excess in revenues for
salt recovery approached 0.28 M$/year. In addition, the unit cost was reduced
upon salt recovery from 0.277 to 0.235 $/m3 (15% reduction). It should be
emphasized that salt recovery reduces the possible ground water contamination
and problems of increasing feed salinity.
3.3 Environmental benefits and constrains
Concentrate management and reuse is being a considerable option for some
inland desalination applications, where there is no obvious possibility of utilizing
conventional disposal options (deep well injection, surface water disposal and
land applications). The impacts of brine characteristics on the marine
environment can be avoided. Development of beneficial salt reuse options and
specific salt separation methods are important to cost reduction of the overall
process. Final brine can be processed all the way to mixed solids, by discharging
to evaporation ponds. Possible commercial salt exploitation can be achieved with
low technological and managing efforts. Environmental concerns associated with
evaporation ponds, higher salinity can result in greater impacts on groundwater
from pond leakage, consideration in pond design and lining material are
subjected to local conditions.
3.4 Uncertainty
In view of the current findings, its perceived that the cost of brackish water
desalination is subjected to numerous uncertainties including but not limited to
design and characteristics of feed water pretreatment, design and characteristics
of brine outfall/salt recovery, opportunities, energy optimization pertinent to the
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entire desalination package, operational and maintenance costs variations in
target sites in addition to water recovery of the specified membrane set. Thus
accurate cost calculations and energy optimization should be undertaken for
target sites under appropriate operating procedures.
4. Conclusion
Brackish water desalination using RO or EDR are the most widely adopted
technologies. A techno-economic study for (20,000 m3/d) desalination facility
has been undertaken incorporating two membrane processes namely RO and
EDR. Preliminary technical indicators revealed that the product water TDS for
schemes 1, 2 and 3 were 411, 544 and 499 mg/l for the selected membrane
recovery and rejection values. Preliminary financial indicators were estimated
and revealed that the unit cost of produced water using RO, EDR and the dual
system with salt recovery was $0.114/m3, $ 0.216/m
3 and $0.235/m
3,
respectively. The possible excess in revenues for salt recovery approached 0.28
M$/year.
It should be emphasized that salt recovery reduces the possible ground water
contamination and problems of increasing feed salinity.
Acknowledgements:
“This work was financially supported by the Science and Technology Development
Fund (STDF) of Egypt, under grant number STDF/3991”.
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Figure 1.Brackish water desalination scheme (3)
Table (1) Capital, O&M and unit costs for developed scheme (1) (EDR)
Sodium Chloride14 ton/day
RO Reject945 m3/d58090 mg/l
Combined
Permeate20000 m3/d
490 mg/l
RO Permeate
EDR Reject3120 m3/d17460 mg/l
EDR Permeate17850 m3/d544 mg/l
EDR
Brackish water
21000 m3/d3080 mg/l
RO
Solar Pond
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Rejection
%
Recovery
% Total
capital
1000$
Annual
O&M
1000$
Total
annual
cost
1000$
Unit
cost
$/m3
Product
TDS
mg/l
60
75 4888 1265 1428 0.216 1640
85 4888 1244 1407 0.213 1450
95 4888 1234 1397 0.212 1300
70
75 4888 1265 1428 0.216 1230
85 4888 1244 1407 0.213 1090
95 4888 1234 1397 0.212 973
80
75 4888 1265 1428 0.216 822
85 4888 1244 1407 0.213 725
95 4888 1234 1397 0.212 649
90
75 4888 1265 1428 0.216 411
85 4888 1244 1407 0.213 363
95 4888 1234 1397 0.212 324
Table (2) Capital, O&M and unit costs for developed scheme (2) (RO)
Rejection
%
Recovery
% Total
capital
1000$
Annual
O&M
cost
1000$
Total
annual
cost
1000$
Unit
cost
$/m3
Product
TDS
mg/l
65
75 4945 548 713 0.108 1440
80 4931 556 720 0.109 1360
85 5003 582 749 0.114 1270
75
75 4945 548 713 0.108 1030
80 4931 556 720 0.109 963
85 5003 582 749 0.114 906
85
75 4945 548 713 0.108 616
80 4931 556 720 0.109 578
85 5003 582 749 0.114 544
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95
75 4945 548 713 0.108 205
80 4931 556 720 0.109 193
85 5003 582 749 0.114 181
Table (3) Selected technical specifications and financial indicators for the
three schemes
Item Scheme (1) Scheme (2) Scheme (3)
Arrangement EDR RO EDR/RO EDR/RO/Solar
Pond
Recovery % 90 85 85/70 85/70
Rejection % 75 85 85/99.8 85/99.8
Product water
TDS, mg/l
411 544 499 499
Concentrate
TDS, mg/l
11100 17500 58100 58100
Capital Cost,
M $
4.89 5 6.3 14
Annual O&M
cost, M$/year
1.27 0.58 1.28 1.36
Total annual
cost, M$/year
1.43 0.75 1.5 1.83
Revenues
M$/year
4.62 4.62 4.62 4.9
Unit cost,$/m3 0.216 0.114 0.226 0.235
Table (4) Criteria of selection for concentrate disposal method
Parameter Requirements
Technical feasibility Availability to submit the technology without
any complications
Environmental Impact Impact on the surrounded environment and
effect on life
Public Acceptance Desirable technology and public acceptance
Land Availability Availability of land for the project and for
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expected future expansion
Economic and Financial Issues Cost of the process, product market cost
Regulations and legislation Following the local regulations and legislations
Future expansion Availability to future expansion and in what
direction
Risks and Hazard Hazard effect on the surrounding ecosystem
Footprint Land required
Power Access to power needed as well as amount of
energy required
Technological Availability Available technology for establishment