evaluation of membrane desalination schemes in desert oil

January 2015 TESCE, Vol. 41, No.1

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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

http://cdn.intechopen.com/pdfs-wm/33989.pdf

http://www.fwrj.com/articles3/0005.pdf


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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

evaluation of membrane desalination schemes in desert oil

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