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The case for seawater desalination to solve the water shortage in the Gaza Strip
Desalination, 99 (1994) 447-458 Elsevier Science B.V. Amsterdam -
447 Printed in The Netherlands
The case for seawater desalination to solve the. water shortage in the Gaza Strip T. Loewy IDE Technologies, Ltd., POB 591, Ra ‘anana 43104, Israel Tel +972 (9) 909777; Fax +972 (9) 909715
SUMMARY
The Gaza Strip very urgently needs additional fresh water. The only practical source is the Mediterranean Sea. This water can be produced economically by combining a power plant with a water plant and by properly employing the hybrid process. Water at costs of $.50-.65/m3 can be produced.
INTRODUCTION
The Gaza Strip is a densely populated area, situated along the Mediterranean coast bordering with Egypt in the south and with Israel in the east and north. Over the last 100 years it has been under the rule of the Ottoman Empire, the British Empire, Egypt, and finally Israel. According to the recently signed peace accords, the Gaza Strip shall obtain self-rule for the next several years. It is assumed that the local authorities would be interested in maintaining control on the vital resources of water and power rather than being dependent on supply from across the borders. Presently the population of the area is dependent upon Israel for the supply of power and the major part of its required water. An acute OOll-9164/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDZOOll-9164(94)00194-4
Fig. 1. Map of the Gaza strip.
imbalance exists between the demand for water and the available resources. This situation naturally leads to over-pumping of the underground aquifer and consequently to an increase in the salinity of the water. As the soil is mostly sandy or alluvial clay mixed with sand, seepage of raw sewage into the dwindling aquifer is a constant danger which has to be resolved on a very urgent basis. It is obvious that the only solution to the present situation is to desalinate seawater. Production of high purity distilled water will serve the following purposes: l l l
introduce “new” water from an exogenous source improve the hygienic and sanitary living conditions enable to blend part of this high purity water with brackish water from the aquifer and permit the revitalization of a doomed agriculture if not provided with additional water sources
449
This paper deals with the facts and figures to determine the size of the proposed desalination plant and outlines the possible processes and configuration for such a plant. It shall not deal with any of the political aspects of the present situation, nor will it attempt to evaluate the feasibility or probability for success of “political” solutions such as piping Nile water to the area or redistribution of the water resources between Israel and the autonomous Palestinian state.
BASIC DATA
The following basic data served as the information for deciding the size of the recommended plant. The figures in Table I assume that the standard of living and sophistication of agriculture in the Gaza Strip should be upgraded at least to the one presently prevailing in Israel. TABLE I
Gaza Strip Basic figures Data
Gaza Strip
Israel
1. Total area, km2 2. Total population (1991) Forecast (2000) 3. Annual water consumption overall (1990), M m3 Forecast for 2000, M m3 Per capita consumption (1990) m3/d
360 676,000 850-950,000
21,000 4,820,OOO 5,200,OOO
90 90-150 0.37
170 1,950 0.96
It is now a world-wide accepted fact that the per capita consumption of water can serve as an index for the welfare of a particular society. While Israel is within the range of the developed countries, we can see that the population of the Gaza Strip is well behind. Actually the figure given for Israel is a bit misleading, as treated sewage used for agriculture is not included. The overall balance as shown in Table II indicates a shortcome of 40 M m3/y for the year 1990. The present forecast for the year 2000 indicates a shortfall of an additional 13-15 M m3/y.
450
TABLE II Overall water balance for the Gaza Strip (correct for 1990) Out (M m3/y)
In (M m3/y) Replenishment of aquifer due to rainfall
34
Pumping
Subsoil flow from Judean mountains
26
Overflow into the sea
Total
60
Net shortcome
38 (say 40)
90 8 98
Based upon the figures presented in Tables I and II, it has been decided to review the alternatives for the implementation of a 40 M m3/y desalination plant using seawater as feed water.
CONSIDERATIONS FOR SELECTION OF THE OPTIMAL CONFIGURATIONS OF THE DESALINATION PLANT
Forty mcb/y equal 120,000 m3/d. Today it is generally accepted that the optimal way for building a water plant of this size is in combination with a power plant. One can assume that both Egypt and Israel would be ready to sell power from their national grid to the Gaza Strip. Therefore, whether the water plant should be self-sufficient in power. but refrain from selling power to the grid or whether the water plant should produce power in excess of its own demand is a question which should be left for political and commercial considerations outside the scope of this paper. Preliminary discussions took place between Egypt and Israel regarding the supply of natural gas by pipeline from Egypt to Israel. In case such a pipeline is indeed laid, it is safe to assume that it shall be routed via the Gaza Strip into Israel. Therefore, four different cases reviewed: Case A - The water plant shall not sell power to the grid Case B - The water plant shall sell power to the grid Subcase 1 - Natural gas will be available in the Gaza Strip Subcase 2 - Natural gas will not be available in the Gaza Strip
451
It is further assumed that water with a TDS of 400-500 ppm is considered of adequate quality. Based on detailed calculations already previously reported, it can be shown that the hybrid process, when properly employed, yields water at the lowest production cost. In the hybrid process warm seawater (“coolant out”) from the condenser of an MED plant serves as the feed water to the RO plant. Using warm seawater as feed leads to high fluxes through the membranes. Furthermore, by correctly proportioning between the distillation plants and the RO plant, one can accept a permeate with a TDS of +700 ppm. By blending the streams of distillate and permeate, an overall water quality of 400-500 TDS is obtained. In order to properly balance between the two water qualities, MVC plants are added to increase the portion of distilled water in the blend. In any case the MED plant is sized to use the majority of the waste heat available. The principle of the hybrid process is outlined in Fig. 2. The configuration chosen for the water plan is therefore: l 1 X MED plant of 10,000 m3/d l 8 X VC plants of 5000 m3/d l 1 x RO plant of 70,000 m3/d This configuration
is not rigid and can still be optimized.
As to the power plants, various configurations
were reviewed:
l Configuration Al - Gas turbine 29-32 MW, combined steam turbine. See Fig. 3 for basic diagram.
cycle with
l Configuration Bl - Gas turbine 80 MW, combined cycle with steam turbine (to enable sale of 50 MW into the grid of the Gaza Strip). See Fig. 4 for basic diagram.
l Configuration A2 - 2 x 15 MW diesel gensets with waste heat boilers and usage of heat from jacket cooling system as energy source for the MED plant. See Fig. 5 for basic diagram.
Configuration B2 - 3 ~28 MW diesel gensets with a common waste heat boiler and usage of heat from jacket cooling system as energy source for the MED plant (to enable sale of 50 MW into the grid of the Gaza Strip. See Fig. 6 for basic diagram. l
Fig. 3. Diagram of Configuration
Al y
454
Fig. 5. Diagram of Configuration
A2.
456
457
ECONOMIC EVALUATION OF CONFIGURATIONS AND CALCULATION OF COST OF WATER
The investment for each of the configurations is summarized in Table III. The figures are based on actual preliminary quotations for equipment as offered by suppliers in the first half of 1993. The basic parameters for the calculation of the price of water were: Return on investment:
7.5%
BOO duration:
20 Y
Availability of plants:
92%
Implementation
36 months
time:
Location:
along the seashore
Sale price of power:
US$O.OS/kWh (average)
The cost of water for the various alternatives is summarized
in Table IV.
TABLE III
Capital investment of the various alternatives (millions US dollars) Configuration
Al
A2
Bl
B2
Water plant
81
81
81
81
Power plant
15
26
39
69
Site development
24
28
30
40
Total investment
120
135
150
190
458
TABLE IV Cost
of water for the various configurations (US$ 000/y)
Configuration
Al
A2
Yearly desalination output (OOO/m3) Yearly power output for sale (MW) costs: Fuel Oil Membranes Chemicals Maintenance Operation
40,296
40,296
2,557 1,760 1,680 1,125
5,171 703 2,557 1,760 2,090 1,125
Total operation costs Income from sale of electric power Depreciation costs (20 y @7.5%)
13,278 -
Bl
B2
40,296
40,296
402,960
402,960
16,734 2,557 1,760 3,470 1,125
14,056 1,912 2,557 1,760 2,350 1,125
13,406 -
25,646 26,192
23,760 26,192
11,771
13,242
14,714
18,637
Overall yearly costs
25,059
26,648
14,168
16,205
Price of m’ water (US$)
0.62
0.66
0.35
0.40
-
6,156 -
-
447 Printed in The Netherlands
The case for seawater desalination to solve the. water shortage in the Gaza Strip T. Loewy IDE Technologies, Ltd., POB 591, Ra ‘anana 43104, Israel Tel +972 (9) 909777; Fax +972 (9) 909715
SUMMARY
The Gaza Strip very urgently needs additional fresh water. The only practical source is the Mediterranean Sea. This water can be produced economically by combining a power plant with a water plant and by properly employing the hybrid process. Water at costs of $.50-.65/m3 can be produced.
INTRODUCTION
The Gaza Strip is a densely populated area, situated along the Mediterranean coast bordering with Egypt in the south and with Israel in the east and north. Over the last 100 years it has been under the rule of the Ottoman Empire, the British Empire, Egypt, and finally Israel. According to the recently signed peace accords, the Gaza Strip shall obtain self-rule for the next several years. It is assumed that the local authorities would be interested in maintaining control on the vital resources of water and power rather than being dependent on supply from across the borders. Presently the population of the area is dependent upon Israel for the supply of power and the major part of its required water. An acute OOll-9164/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDZOOll-9164(94)00194-4
Fig. 1. Map of the Gaza strip.
imbalance exists between the demand for water and the available resources. This situation naturally leads to over-pumping of the underground aquifer and consequently to an increase in the salinity of the water. As the soil is mostly sandy or alluvial clay mixed with sand, seepage of raw sewage into the dwindling aquifer is a constant danger which has to be resolved on a very urgent basis. It is obvious that the only solution to the present situation is to desalinate seawater. Production of high purity distilled water will serve the following purposes: l l l
introduce “new” water from an exogenous source improve the hygienic and sanitary living conditions enable to blend part of this high purity water with brackish water from the aquifer and permit the revitalization of a doomed agriculture if not provided with additional water sources
449
This paper deals with the facts and figures to determine the size of the proposed desalination plant and outlines the possible processes and configuration for such a plant. It shall not deal with any of the political aspects of the present situation, nor will it attempt to evaluate the feasibility or probability for success of “political” solutions such as piping Nile water to the area or redistribution of the water resources between Israel and the autonomous Palestinian state.
BASIC DATA
The following basic data served as the information for deciding the size of the recommended plant. The figures in Table I assume that the standard of living and sophistication of agriculture in the Gaza Strip should be upgraded at least to the one presently prevailing in Israel. TABLE I
Gaza Strip Basic figures Data
Gaza Strip
Israel
1. Total area, km2 2. Total population (1991) Forecast (2000) 3. Annual water consumption overall (1990), M m3 Forecast for 2000, M m3 Per capita consumption (1990) m3/d
360 676,000 850-950,000
21,000 4,820,OOO 5,200,OOO
90 90-150 0.37
170 1,950 0.96
It is now a world-wide accepted fact that the per capita consumption of water can serve as an index for the welfare of a particular society. While Israel is within the range of the developed countries, we can see that the population of the Gaza Strip is well behind. Actually the figure given for Israel is a bit misleading, as treated sewage used for agriculture is not included. The overall balance as shown in Table II indicates a shortcome of 40 M m3/y for the year 1990. The present forecast for the year 2000 indicates a shortfall of an additional 13-15 M m3/y.
450
TABLE II Overall water balance for the Gaza Strip (correct for 1990) Out (M m3/y)
In (M m3/y) Replenishment of aquifer due to rainfall
34
Pumping
Subsoil flow from Judean mountains
26
Overflow into the sea
Total
60
Net shortcome
38 (say 40)
90 8 98
Based upon the figures presented in Tables I and II, it has been decided to review the alternatives for the implementation of a 40 M m3/y desalination plant using seawater as feed water.
CONSIDERATIONS FOR SELECTION OF THE OPTIMAL CONFIGURATIONS OF THE DESALINATION PLANT
Forty mcb/y equal 120,000 m3/d. Today it is generally accepted that the optimal way for building a water plant of this size is in combination with a power plant. One can assume that both Egypt and Israel would be ready to sell power from their national grid to the Gaza Strip. Therefore, whether the water plant should be self-sufficient in power. but refrain from selling power to the grid or whether the water plant should produce power in excess of its own demand is a question which should be left for political and commercial considerations outside the scope of this paper. Preliminary discussions took place between Egypt and Israel regarding the supply of natural gas by pipeline from Egypt to Israel. In case such a pipeline is indeed laid, it is safe to assume that it shall be routed via the Gaza Strip into Israel. Therefore, four different cases reviewed: Case A - The water plant shall not sell power to the grid Case B - The water plant shall sell power to the grid Subcase 1 - Natural gas will be available in the Gaza Strip Subcase 2 - Natural gas will not be available in the Gaza Strip
451
It is further assumed that water with a TDS of 400-500 ppm is considered of adequate quality. Based on detailed calculations already previously reported, it can be shown that the hybrid process, when properly employed, yields water at the lowest production cost. In the hybrid process warm seawater (“coolant out”) from the condenser of an MED plant serves as the feed water to the RO plant. Using warm seawater as feed leads to high fluxes through the membranes. Furthermore, by correctly proportioning between the distillation plants and the RO plant, one can accept a permeate with a TDS of +700 ppm. By blending the streams of distillate and permeate, an overall water quality of 400-500 TDS is obtained. In order to properly balance between the two water qualities, MVC plants are added to increase the portion of distilled water in the blend. In any case the MED plant is sized to use the majority of the waste heat available. The principle of the hybrid process is outlined in Fig. 2. The configuration chosen for the water plan is therefore: l 1 X MED plant of 10,000 m3/d l 8 X VC plants of 5000 m3/d l 1 x RO plant of 70,000 m3/d This configuration
is not rigid and can still be optimized.
As to the power plants, various configurations
were reviewed:
l Configuration Al - Gas turbine 29-32 MW, combined steam turbine. See Fig. 3 for basic diagram.
cycle with
l Configuration Bl - Gas turbine 80 MW, combined cycle with steam turbine (to enable sale of 50 MW into the grid of the Gaza Strip). See Fig. 4 for basic diagram.
l Configuration A2 - 2 x 15 MW diesel gensets with waste heat boilers and usage of heat from jacket cooling system as energy source for the MED plant. See Fig. 5 for basic diagram.
Configuration B2 - 3 ~28 MW diesel gensets with a common waste heat boiler and usage of heat from jacket cooling system as energy source for the MED plant (to enable sale of 50 MW into the grid of the Gaza Strip. See Fig. 6 for basic diagram. l
Fig. 3. Diagram of Configuration
Al y
454
Fig. 5. Diagram of Configuration
A2.
456
457
ECONOMIC EVALUATION OF CONFIGURATIONS AND CALCULATION OF COST OF WATER
The investment for each of the configurations is summarized in Table III. The figures are based on actual preliminary quotations for equipment as offered by suppliers in the first half of 1993. The basic parameters for the calculation of the price of water were: Return on investment:
7.5%
BOO duration:
20 Y
Availability of plants:
92%
Implementation
36 months
time:
Location:
along the seashore
Sale price of power:
US$O.OS/kWh (average)
The cost of water for the various alternatives is summarized
in Table IV.
TABLE III
Capital investment of the various alternatives (millions US dollars) Configuration
Al
A2
Bl
B2
Water plant
81
81
81
81
Power plant
15
26
39
69
Site development
24
28
30
40
Total investment
120
135
150
190
458
TABLE IV Cost
of water for the various configurations (US$ 000/y)
Configuration
Al
A2
Yearly desalination output (OOO/m3) Yearly power output for sale (MW) costs: Fuel Oil Membranes Chemicals Maintenance Operation
40,296
40,296
2,557 1,760 1,680 1,125
5,171 703 2,557 1,760 2,090 1,125
Total operation costs Income from sale of electric power Depreciation costs (20 y @7.5%)
13,278 -
Bl
B2
40,296
40,296
402,960
402,960
16,734 2,557 1,760 3,470 1,125
14,056 1,912 2,557 1,760 2,350 1,125
13,406 -
25,646 26,192
23,760 26,192
11,771
13,242
14,714
18,637
Overall yearly costs
25,059
26,648
14,168
16,205
Price of m’ water (US$)
0.62
0.66
0.35
0.40
-
6,156 -
-