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Prospects of the exploitation of advanced energy resources in water production in the middle east
DesaMaation,20(1977)27S-287 0 ELwvierScientificPublishing Company, Amsterdam-Printedin The Netherlands PROSPECTS
OF THE EXPLOITATION IN WATER PRODUCTION
OF ADVANCED ENERGY IN THE MIDDLE EAST
279
RESOURCES
Z. A. SABRI and A. A. HUSSEINY, Department of Chemical Engineering and Nuclear Engineering, Engineering Research Institute, Iowa State University, Ames, Iowa, United States of America 50011 Development Consultants Association, Cairo, Egypt A. VALFELLS, Department of Chemical Engineering and Nuclear Engineering, Engineering Research Institute, Iowa State University, Ames, Iowa, United States of America 50011. Science Institute, University of Iceland A. F. ABDUL-FATTAH, Department of Chemical Engineering and Nuclear Engineering, Iowa State University, Ames, Iowa, United States of America 50011, University of Riyadh. Saudi Arabia and SALAH GALAL Scientific Department of Alahram, Alahram, Cairo, Egypt.
SlJRJY\RY--Theutilization of oil and natural gas in water production and in supplying steam for desalination plants is progressing with a remarkable rate in the Middle East and especially in the oil producing countries. Nevertheless, some of the available economically feasible energy sources are yet to be exploited. Available hot brine and steam fields in the Red Sea Deeps and in other locations in the Middle East are a valuable source The rapidly growing geothermal techof useful energy for desalination. nology can be utilized in supplying fresh water to the Red Sea coasts for both of the western cities of Saudi Arabia and the new settlements on the eastern Egyptian coast. An assessment is made of the geothermal fields in the area and their characteristics with special consideration of their utility in water desalination projects. Other energy sources are also considered; such as the future exploitation of heavy water and heavy hydrogen isotopes obtained from the Red Sea in energy sources for desalination. In addition, the Potential use of natural depressions in the production of power and water is discussed. A comparison is made between these advanced systems and contemporary alternates in a longterm plan for agricultureal and industrial expansion. .'
280
Z.A.
SABRI
AND
A.A.
HUSSEINY
INTRODUCTION
The abundance of oil fields in the Arab countries and in the Middle East has introduced the unwarrantable conclusion that the use of oil and/ or natural gas in desalination and power generation is the optimum eco-
choice even in the long-term planning. Concern for the future of these localities and consideration of expansion in water supply and demand calls for large size plants and for the search for other energy options. This will be the case especially as the global energy picture gets dimmer, oil fields start to dry up, and alternate strategies of harnessing natural energy resources becomes inevitably limited. Also, until another form of mobile energy is proven feasible, oil is the only fuel for strategic machinery and transportation systems. The use of oil as a feedstock for basic industries and the fact that the depletion rate of this valuable energy source is rather fast will eventually force people to curb its usage for steam generation and power production. This is actually the present situation in most of the energy consuming nations. Viewing on the near and far future of desalination in the Middle East energy resources other than oil are likely to be more competitive. Those include solar and Aeolian or wind energy for small scaleapplicationsand geothermal energy as well as contemporary and advanced nuclear systems for massive agricultural and industrial expansion. Figure 1 shows an example of a complex for water, food, power, metals, and chemicals production which would be suitable for development of arid areas. The energy sources shown are heavy water and gas-cooled reactors; however, the concept is not limited to this option. Other fissile fueled plants and fusion reactors can be used as well as geothermal fields and heliohydroelectric systems. nomic
GEOTHERMAL FIELDS The Red Sea and the Mediterranean regions are of intense geothermal manifestations. The hot-water of the Red Sea brine pools contain very high salinity brines.[l.Z] The salinity is about 260,000 ppm [3] or approximately 10 times saltier than the average sea water-[41 The temperature reaches 13j°F (56OC). A measurable increase in temperature over short periods o time has been reported. About 12.219 billion cubic foot (3.46 million m 5. ) of water of minimum temperature of 219.2OF (104OC) have been added to the hot brine of the Atlantis Deep facing the port of Jeddah by a natural physical process over a period of 52 months; from 1967 to 1971. This corresponds to an average monthly increase of 0.052°C to 0.12 OC.[2] This indicates the existence of an ongoing dynamic process leading to the formation of the underlying deposits which are rich in heavy metals. The main areas are in the central rift portion of the sea between Jeddah and Abu Shagara. The major hot-water fields are those of Discovery,[S] Atlantis II, [6] and Chain Deeps [7] which are called after the
ships
in which
the
initial
discoveries
were
made.
Recently,
thirteen
ENERGY RESOURCES IN M.D-EAST WATER PRODUCTION
281
hot brine pools have been discovered between Subair Islands and Abu-elKizaan. The new deeps are covered by sediments ofhydrotiermal origin and have a considerable variety of physical and chemical parameters.[S] A map giving the geographical location of some of the important deeps is shown in Fig. 2. The axial brine temperature distribution of the Atlantis II Deep shows the existence of two layers. The maximum temperatures range between 121.44OF (49.69OC) to 121.86OF (49.92°Cf for the upper layer and 138.6'F (59.22'C) to 139.6OF (59.78OC) for the brine at the lower layer. [?I The brine in the Atlantis II Deep contains concentration of various trace metals that are roughly 1000 times greater than the concentrations found in normal seawater. For example, lead is 30,000 and zinc is about 1,500 times that found in seawater.141 This brine is rich in manganese but relatively low in iron.[lCl] However, a smectite rich in ferrous iron and low in aluminum is found to abundantly occur in the Red Sea geothermal deposits and continues its formation at present.[ll] Hydrogen sulphite is present in remarkable quantities in the Kebrit (which means sulpher in Arabic) Deep north of Jeddah,fS] This is aside from general excess of uranium and deuterium in most of the hot brines especially in the northern part of the sea. The in situ gross value of the Atlantis II Deep heavy metal deposits is about 2.335 billion $ based on 1973 prices. The value of the zinc is about 1.16 billion $.[12] UTILIZATION OF RED SE4 GEOTHERMAL SYSTEMS Although present emphasis in developed geothermal systems is on electric power generation the thermal-to-electricalenergy conversion efficiency is very low in geothermal power stations compared to other conventional systems. Actual conversion efficiencies is about 15% for steam-producingor vapor-dominated fields and is approximately 7.5% for hot-water or liquid-dominatedsystems.[13] The discovered Red Sea heat mines are of the liquid-dominated type and hence the indirect utilization of the heat content in electric power generation seems to be wasteful unless a great need has developed. The need for water and other commodities in the area greatly exceeds the demand for power. However, stimulation of the discovered fields to release vapor-dominated brines from existing geothermal reservoirs would have a great potential for power generation and other applications. The produced steam can be used efficiently with a great deal of flexibility whether directly or indirectly. The most efficient method of exploitation of geothermal sources is in direct utilization in multipurpose plants of the type illustrated in Fig. 1 including desalination capabilities. Actually, direct utilization of geothermal energy is growing at a fast rate especially in eastern Europe.[14] Among the suggested general industrial applications of geothermal fields are salt recovery, mining. animal husbandry. horticulture and fisheries.[lS] Nining heavy metals from the deposits in the Red Sea deeps fan be of great value for developing industries in the region_ This is in addition to the high return on the overall investment in terms of net cash flow.
282
2-A.
SABRI
ANU
A.A.
HUSSEINY
GEOTHERMAL DESALINATION In the U.S. a demonstration dual-purpose plant for electric power generation and water conversion is planned to operate by 1980 in the Imperial Valley. The electric power output is expected to be between Liquid-dominated geothermal systems with 10 and 20 EllJelectric.[14] low enthalpy water; that is less than 179.99 Btu/lbm (100 Cal/g); can only be employed in power generation at very low efficiencies and hence Direct utilization membrane desalting processes will not be economical. in distillation processes is preferred except in situation wherein the product has to be transmitted for long distance to centers of consumption. Since the liquid water produced from the geothermal wells is saline and hot.,distillation processes can be economically exploited to make fresh water. If the geothermal reservoirs contain mostly steam, this can be Steam-water sysrecovered directly as purified water by condensation. tems can be employed in the production of flash steam. The risidual hotwater water under
which is contaminated with dissolved saits is then used as raw wa Additional raw water is available in the region for distillation. study since the reservoirs are located in the sea proper. On the
other hand, liquid-dominated reservoirs can be exploited in the same manner or through a multiple effect (ME) distillation process depending on the water enthalpy. Several desalination systems have been suggested for water producing geothermal plants.[l6,17] The main processes considered by far are the PIE. the vertical-tube evaporator (VTE) and the MF. A possible system for water conversion using low enthalpy water is shown in Fig. 3. This system is suitable for Red Sea hot brines if no stimulation is used. For high enthalpy waters the system shown in Fig. 4 is more appropriate due to the availability of raw water in the region. The feed hot produces
brine flash
enters steam.
a flash vessel wherein surplus heat of the feed The flash steam is directed to an MSF process fed water is by cold (heated) seawater. The inherent heat of the geothermal Other configurations also allowed to self-distillate in a ME evaporator. are possible and a careful assessment of alternate routes is necessary
to design the system which is compatible with the local geothermal field. The choice of the desalting technique depends on the physical and chemical parameters of the hot stuff ejected from the geothermal well, on the location of the plant. on the capacity of the water conversion unit and on the degree of stimulation of the field. Using the WSF process in conjunction with geothermal water has some merits aside from being the most developed and exploited process in the industry. Obstruction-free hot-brine channels can be constructed thus eliminating one of the most strenuous problems associated with the precipitation of solid materials such as silica which is apt to be present Piling up of low to very low solubility in geothermal distillation. SiOz, CaCOS, CaS04 and similar constituants represents a potential of trouble since this effect can result in reduction in the plant effectiveness. In contrast scrapping off of deposits which may adhere to channel surfaces can be done without great economical penalities.[l6] A second advantage of MSF geothermal distillation systems is that no additional heating is required for the feedwater while in the case of sea wafer
ENERGY RESOURCES IN MID-EAST WATER PRODUCTION
283
distillation the feed must be heated. Nevertheless, in sea water MSF units the feed is heated while passing inside the condenser tubes for cooling. This cooling method can not be employed in geothermal desalination unless cool raw seawater is also used. This drawback may result in a low fresh water output. The ME process can convert as much as desired of the geothermal brine and hence is compatible with the Red Sea brine conditions if no stimulation is used. Among the disadvantages of geothermal desalination in the Red Sea environment is the fact that the fields are far from the land. In this case the cost of water transportation to the main land would offset the expected low cost of produced fresh water. One solution to this problem would be the use of the hot-brines in electric power generation on a floating station. Electricity can then be transmitted to the shores and employed in membrane desalting units. However, the existence of the numerous Red Sea deeps may be an evidence of the presence of near-shore geothermal reservoirs. Thus, an effort may be spent in exploration of such reservoirs. OTHER ENERGY SOURCES FOR DESALINATION The temperature difference between the hot-brine layers and the surface temperature which is about 36OC can be utilized in power generation for desalination. Several conceptual designs have been developed for temperature differentials much less than those avialable in the Red Sea.[lS] Efficiency is expected to be much higher for Red Sea applications than those calculated for such designs and hence may become more economical. The Red Sea location would be ideal for a prototype plant of this sort especially if a desalination facility is connected to the original concept. The use of fission energy through the employment of gas-cooled and heavy water reactors either as single purpose desalination plants or dualpurpose plants has an edge over the use of fossil-fueled plants cost-wise and for the inherent flexibility of nuclear systems. These can be used adequately in remote isolated areas as is the case in the Middle East. Gas-cooled reactors are suitable for desert dry environment and heavywater reactors can utilize heavy water produced by the geothermal energy. Deuterium can also be obtained from the Red Sea water and hot-brine and then utilized in fusion dual-purpose plants in the future. Immediate plans can include utilization of natural depressions such as that at Qattara in Egypt. The scheme involves admitting sea water from the Mediterranean to the depression through hydraulic turbines thus producing electric energy and creating an artificial lake which acts as a sink for evaporation. Electric power can be used in desalination projects. In addition, the availability of a vast evaporation surface area would enhance rainfall in the desert. The equival nt surface area of the Qattara depression at sea level is about 19,500 kmt with an effective area of 13,500 km* of 50 m depth and 12,000 km2 at 60 m below sea level. The lowest point is at 134 m. The eastern edge of the depression is 56
2-A. SABRI AND A.A. HUSSEINY
284
km from the northwestern seashore.[19] A system based on the same principle is being suggested in the Arabian Gulf-Dawhat Sawah area which separates the Qatar Peninsula fron the Saudi Arabian mainland.[20J The entire Dawhat can be transformed in a large open sea sink reservoir and hence heliohydroelectric energy conversion schemes can be used to
produce electricity and water. These systems although feasible if a huge complex of agriculture and industrial projects are included, are still limited to specific sites and hence can not substitute for other systems. In addition, environmental effects and weather modification impact on neighboring areas are het to be studied. References: 1. H. Craig, Science 154. 1544 (1966). 2. D. A. Ross, Science 175, 1455 (1972). 3. D.E. White, in Geothermal Energy, P. Kruger and C. Otte cd. (Stanford University Press, Stanford, California, 1973),p.78. E.T. Degens and D.A. Ross, Scientific American, April, 86 (1970). 4. J.C. Swallow and J. Crease, Nature 205, 165 (1965). 5. A. R. Miller, et al., Geochtinochim. 6. Acta 30. 341 (1966). D.A. Ross and J-M. Hunt, Nature 213, 687 (1967)T 7. H. Backer and Cl.Schoell,wePhysical Science 240, 1% (1972). 8. El.Schoell and &l.Hartmann, Marine Geology 14, 1 (1973). 9. 10. P.G. Brewer and D.W. Spencer, in Hot Brines and Recent Heavy bletal Deposits in the Red Sea, E.T. Degens and D.A. Ross, ed. (SpringerVerlag, New York, 1959), p. 174. il. J.L. Bischoff. Clays and Clay Minerals 20. 217 (1972). 12. J.P. Hackett and J. Bischoff, Economic Geology 68, 553 (1973). 13. 14.
A.J. Ellis, Am. Scientist 63, 510 (1975). J.B. Koenig, in GeothermalEnergy.op tit, p- 15.
IS.
B. Lindal, in Geothermal Energy, H.C.H. Armstead. ed. (UNEsCD Earth Sciences Series No. 12, Paris, 1973) p. 135. 16. A.D.K. Laird, in Geothermal Energy, op tit Ref. 5, p. 177. 17. H.C.H. Armstead, Int. Conf. Water for Peace, Washington D-C.. 1967, Vol. 3, P. 106.
18. C. Zeneri Phys. Today z, 48 (1973). 19. J. Ball, Geographic J. 82, 4 (1933). 20.
M.A. Kettani and L.M. Gonslaves, Prog. Rep. HHE 1, The College of Petroleum and Minerals. Dhahran. Saudi Arabia, May 1970.
Water,
PO TABLE WATER
1.
Power,
-
ALGAE
PLANKTON
4
1
- BRINE
I
HYDROGEN
c COA!grR-
I\
Food Production Plant,
_+kJEp
Fig.
7
1
1 J
Fl
FOOD
1
CLOSED SYSTEM
4% 1 AGRICULTURE” 1
1
BASIC ELEMENTS
FooD
HORTICULTURAL FOOD
--f-r--L
-lI
TREATMENT
MIXING 8
+-
h
MSf PLANT A
I
--
2-A.
286
Atlant
i
z- .
SABRI
AND
A.A.
See;,
rintense geothemal activities)
Fqyue
2
Location
o= Geothemal
Activitres
in the
Red
Sea.
HUSSEINY
ENERGY RESOURCES IN MID-EAST WATER PRODUCTION
F1dS.h
.287
Condenser
vessel
f@ i!ot Water
Figure 7
Cieothernal Desalination of Lo-r Enthalpy Water
feed
Fresh ,.ater
Fig. 1
Geothermal Desalination of High Enthalpy Water.(17)
OF THE EXPLOITATION IN WATER PRODUCTION
OF ADVANCED ENERGY IN THE MIDDLE EAST
279
RESOURCES
Z. A. SABRI and A. A. HUSSEINY, Department of Chemical Engineering and Nuclear Engineering, Engineering Research Institute, Iowa State University, Ames, Iowa, United States of America 50011 Development Consultants Association, Cairo, Egypt A. VALFELLS, Department of Chemical Engineering and Nuclear Engineering, Engineering Research Institute, Iowa State University, Ames, Iowa, United States of America 50011. Science Institute, University of Iceland A. F. ABDUL-FATTAH, Department of Chemical Engineering and Nuclear Engineering, Iowa State University, Ames, Iowa, United States of America 50011, University of Riyadh. Saudi Arabia and SALAH GALAL Scientific Department of Alahram, Alahram, Cairo, Egypt.
SlJRJY\RY--Theutilization of oil and natural gas in water production and in supplying steam for desalination plants is progressing with a remarkable rate in the Middle East and especially in the oil producing countries. Nevertheless, some of the available economically feasible energy sources are yet to be exploited. Available hot brine and steam fields in the Red Sea Deeps and in other locations in the Middle East are a valuable source The rapidly growing geothermal techof useful energy for desalination. nology can be utilized in supplying fresh water to the Red Sea coasts for both of the western cities of Saudi Arabia and the new settlements on the eastern Egyptian coast. An assessment is made of the geothermal fields in the area and their characteristics with special consideration of their utility in water desalination projects. Other energy sources are also considered; such as the future exploitation of heavy water and heavy hydrogen isotopes obtained from the Red Sea in energy sources for desalination. In addition, the Potential use of natural depressions in the production of power and water is discussed. A comparison is made between these advanced systems and contemporary alternates in a longterm plan for agricultureal and industrial expansion. .'
280
Z.A.
SABRI
AND
A.A.
HUSSEINY
INTRODUCTION
The abundance of oil fields in the Arab countries and in the Middle East has introduced the unwarrantable conclusion that the use of oil and/ or natural gas in desalination and power generation is the optimum eco-
choice even in the long-term planning. Concern for the future of these localities and consideration of expansion in water supply and demand calls for large size plants and for the search for other energy options. This will be the case especially as the global energy picture gets dimmer, oil fields start to dry up, and alternate strategies of harnessing natural energy resources becomes inevitably limited. Also, until another form of mobile energy is proven feasible, oil is the only fuel for strategic machinery and transportation systems. The use of oil as a feedstock for basic industries and the fact that the depletion rate of this valuable energy source is rather fast will eventually force people to curb its usage for steam generation and power production. This is actually the present situation in most of the energy consuming nations. Viewing on the near and far future of desalination in the Middle East energy resources other than oil are likely to be more competitive. Those include solar and Aeolian or wind energy for small scaleapplicationsand geothermal energy as well as contemporary and advanced nuclear systems for massive agricultural and industrial expansion. Figure 1 shows an example of a complex for water, food, power, metals, and chemicals production which would be suitable for development of arid areas. The energy sources shown are heavy water and gas-cooled reactors; however, the concept is not limited to this option. Other fissile fueled plants and fusion reactors can be used as well as geothermal fields and heliohydroelectric systems. nomic
GEOTHERMAL FIELDS The Red Sea and the Mediterranean regions are of intense geothermal manifestations. The hot-water of the Red Sea brine pools contain very high salinity brines.[l.Z] The salinity is about 260,000 ppm [3] or approximately 10 times saltier than the average sea water-[41 The temperature reaches 13j°F (56OC). A measurable increase in temperature over short periods o time has been reported. About 12.219 billion cubic foot (3.46 million m 5. ) of water of minimum temperature of 219.2OF (104OC) have been added to the hot brine of the Atlantis Deep facing the port of Jeddah by a natural physical process over a period of 52 months; from 1967 to 1971. This corresponds to an average monthly increase of 0.052°C to 0.12 OC.[2] This indicates the existence of an ongoing dynamic process leading to the formation of the underlying deposits which are rich in heavy metals. The main areas are in the central rift portion of the sea between Jeddah and Abu Shagara. The major hot-water fields are those of Discovery,[S] Atlantis II, [6] and Chain Deeps [7] which are called after the
ships
in which
the
initial
discoveries
were
made.
Recently,
thirteen
ENERGY RESOURCES IN M.D-EAST WATER PRODUCTION
281
hot brine pools have been discovered between Subair Islands and Abu-elKizaan. The new deeps are covered by sediments ofhydrotiermal origin and have a considerable variety of physical and chemical parameters.[S] A map giving the geographical location of some of the important deeps is shown in Fig. 2. The axial brine temperature distribution of the Atlantis II Deep shows the existence of two layers. The maximum temperatures range between 121.44OF (49.69OC) to 121.86OF (49.92°Cf for the upper layer and 138.6'F (59.22'C) to 139.6OF (59.78OC) for the brine at the lower layer. [?I The brine in the Atlantis II Deep contains concentration of various trace metals that are roughly 1000 times greater than the concentrations found in normal seawater. For example, lead is 30,000 and zinc is about 1,500 times that found in seawater.141 This brine is rich in manganese but relatively low in iron.[lCl] However, a smectite rich in ferrous iron and low in aluminum is found to abundantly occur in the Red Sea geothermal deposits and continues its formation at present.[ll] Hydrogen sulphite is present in remarkable quantities in the Kebrit (which means sulpher in Arabic) Deep north of Jeddah,fS] This is aside from general excess of uranium and deuterium in most of the hot brines especially in the northern part of the sea. The in situ gross value of the Atlantis II Deep heavy metal deposits is about 2.335 billion $ based on 1973 prices. The value of the zinc is about 1.16 billion $.[12] UTILIZATION OF RED SE4 GEOTHERMAL SYSTEMS Although present emphasis in developed geothermal systems is on electric power generation the thermal-to-electricalenergy conversion efficiency is very low in geothermal power stations compared to other conventional systems. Actual conversion efficiencies is about 15% for steam-producingor vapor-dominated fields and is approximately 7.5% for hot-water or liquid-dominatedsystems.[13] The discovered Red Sea heat mines are of the liquid-dominated type and hence the indirect utilization of the heat content in electric power generation seems to be wasteful unless a great need has developed. The need for water and other commodities in the area greatly exceeds the demand for power. However, stimulation of the discovered fields to release vapor-dominated brines from existing geothermal reservoirs would have a great potential for power generation and other applications. The produced steam can be used efficiently with a great deal of flexibility whether directly or indirectly. The most efficient method of exploitation of geothermal sources is in direct utilization in multipurpose plants of the type illustrated in Fig. 1 including desalination capabilities. Actually, direct utilization of geothermal energy is growing at a fast rate especially in eastern Europe.[14] Among the suggested general industrial applications of geothermal fields are salt recovery, mining. animal husbandry. horticulture and fisheries.[lS] Nining heavy metals from the deposits in the Red Sea deeps fan be of great value for developing industries in the region_ This is in addition to the high return on the overall investment in terms of net cash flow.
282
2-A.
SABRI
ANU
A.A.
HUSSEINY
GEOTHERMAL DESALINATION In the U.S. a demonstration dual-purpose plant for electric power generation and water conversion is planned to operate by 1980 in the Imperial Valley. The electric power output is expected to be between Liquid-dominated geothermal systems with 10 and 20 EllJelectric.[14] low enthalpy water; that is less than 179.99 Btu/lbm (100 Cal/g); can only be employed in power generation at very low efficiencies and hence Direct utilization membrane desalting processes will not be economical. in distillation processes is preferred except in situation wherein the product has to be transmitted for long distance to centers of consumption. Since the liquid water produced from the geothermal wells is saline and hot.,distillation processes can be economically exploited to make fresh water. If the geothermal reservoirs contain mostly steam, this can be Steam-water sysrecovered directly as purified water by condensation. tems can be employed in the production of flash steam. The risidual hotwater water under
which is contaminated with dissolved saits is then used as raw wa Additional raw water is available in the region for distillation. study since the reservoirs are located in the sea proper. On the
other hand, liquid-dominated reservoirs can be exploited in the same manner or through a multiple effect (ME) distillation process depending on the water enthalpy. Several desalination systems have been suggested for water producing geothermal plants.[l6,17] The main processes considered by far are the PIE. the vertical-tube evaporator (VTE) and the MF. A possible system for water conversion using low enthalpy water is shown in Fig. 3. This system is suitable for Red Sea hot brines if no stimulation is used. For high enthalpy waters the system shown in Fig. 4 is more appropriate due to the availability of raw water in the region. The feed hot produces
brine flash
enters steam.
a flash vessel wherein surplus heat of the feed The flash steam is directed to an MSF process fed water is by cold (heated) seawater. The inherent heat of the geothermal Other configurations also allowed to self-distillate in a ME evaporator. are possible and a careful assessment of alternate routes is necessary
to design the system which is compatible with the local geothermal field. The choice of the desalting technique depends on the physical and chemical parameters of the hot stuff ejected from the geothermal well, on the location of the plant. on the capacity of the water conversion unit and on the degree of stimulation of the field. Using the WSF process in conjunction with geothermal water has some merits aside from being the most developed and exploited process in the industry. Obstruction-free hot-brine channels can be constructed thus eliminating one of the most strenuous problems associated with the precipitation of solid materials such as silica which is apt to be present Piling up of low to very low solubility in geothermal distillation. SiOz, CaCOS, CaS04 and similar constituants represents a potential of trouble since this effect can result in reduction in the plant effectiveness. In contrast scrapping off of deposits which may adhere to channel surfaces can be done without great economical penalities.[l6] A second advantage of MSF geothermal distillation systems is that no additional heating is required for the feedwater while in the case of sea wafer
ENERGY RESOURCES IN MID-EAST WATER PRODUCTION
283
distillation the feed must be heated. Nevertheless, in sea water MSF units the feed is heated while passing inside the condenser tubes for cooling. This cooling method can not be employed in geothermal desalination unless cool raw seawater is also used. This drawback may result in a low fresh water output. The ME process can convert as much as desired of the geothermal brine and hence is compatible with the Red Sea brine conditions if no stimulation is used. Among the disadvantages of geothermal desalination in the Red Sea environment is the fact that the fields are far from the land. In this case the cost of water transportation to the main land would offset the expected low cost of produced fresh water. One solution to this problem would be the use of the hot-brines in electric power generation on a floating station. Electricity can then be transmitted to the shores and employed in membrane desalting units. However, the existence of the numerous Red Sea deeps may be an evidence of the presence of near-shore geothermal reservoirs. Thus, an effort may be spent in exploration of such reservoirs. OTHER ENERGY SOURCES FOR DESALINATION The temperature difference between the hot-brine layers and the surface temperature which is about 36OC can be utilized in power generation for desalination. Several conceptual designs have been developed for temperature differentials much less than those avialable in the Red Sea.[lS] Efficiency is expected to be much higher for Red Sea applications than those calculated for such designs and hence may become more economical. The Red Sea location would be ideal for a prototype plant of this sort especially if a desalination facility is connected to the original concept. The use of fission energy through the employment of gas-cooled and heavy water reactors either as single purpose desalination plants or dualpurpose plants has an edge over the use of fossil-fueled plants cost-wise and for the inherent flexibility of nuclear systems. These can be used adequately in remote isolated areas as is the case in the Middle East. Gas-cooled reactors are suitable for desert dry environment and heavywater reactors can utilize heavy water produced by the geothermal energy. Deuterium can also be obtained from the Red Sea water and hot-brine and then utilized in fusion dual-purpose plants in the future. Immediate plans can include utilization of natural depressions such as that at Qattara in Egypt. The scheme involves admitting sea water from the Mediterranean to the depression through hydraulic turbines thus producing electric energy and creating an artificial lake which acts as a sink for evaporation. Electric power can be used in desalination projects. In addition, the availability of a vast evaporation surface area would enhance rainfall in the desert. The equival nt surface area of the Qattara depression at sea level is about 19,500 kmt with an effective area of 13,500 km* of 50 m depth and 12,000 km2 at 60 m below sea level. The lowest point is at 134 m. The eastern edge of the depression is 56
2-A. SABRI AND A.A. HUSSEINY
284
km from the northwestern seashore.[19] A system based on the same principle is being suggested in the Arabian Gulf-Dawhat Sawah area which separates the Qatar Peninsula fron the Saudi Arabian mainland.[20J The entire Dawhat can be transformed in a large open sea sink reservoir and hence heliohydroelectric energy conversion schemes can be used to
produce electricity and water. These systems although feasible if a huge complex of agriculture and industrial projects are included, are still limited to specific sites and hence can not substitute for other systems. In addition, environmental effects and weather modification impact on neighboring areas are het to be studied. References: 1. H. Craig, Science 154. 1544 (1966). 2. D. A. Ross, Science 175, 1455 (1972). 3. D.E. White, in Geothermal Energy, P. Kruger and C. Otte cd. (Stanford University Press, Stanford, California, 1973),p.78. E.T. Degens and D.A. Ross, Scientific American, April, 86 (1970). 4. J.C. Swallow and J. Crease, Nature 205, 165 (1965). 5. A. R. Miller, et al., Geochtinochim. 6. Acta 30. 341 (1966). D.A. Ross and J-M. Hunt, Nature 213, 687 (1967)T 7. H. Backer and Cl.Schoell,wePhysical Science 240, 1% (1972). 8. El.Schoell and &l.Hartmann, Marine Geology 14, 1 (1973). 9. 10. P.G. Brewer and D.W. Spencer, in Hot Brines and Recent Heavy bletal Deposits in the Red Sea, E.T. Degens and D.A. Ross, ed. (SpringerVerlag, New York, 1959), p. 174. il. J.L. Bischoff. Clays and Clay Minerals 20. 217 (1972). 12. J.P. Hackett and J. Bischoff, Economic Geology 68, 553 (1973). 13. 14.
A.J. Ellis, Am. Scientist 63, 510 (1975). J.B. Koenig, in GeothermalEnergy.op tit, p- 15.
IS.
B. Lindal, in Geothermal Energy, H.C.H. Armstead. ed. (UNEsCD Earth Sciences Series No. 12, Paris, 1973) p. 135. 16. A.D.K. Laird, in Geothermal Energy, op tit Ref. 5, p. 177. 17. H.C.H. Armstead, Int. Conf. Water for Peace, Washington D-C.. 1967, Vol. 3, P. 106.
18. C. Zeneri Phys. Today z, 48 (1973). 19. J. Ball, Geographic J. 82, 4 (1933). 20.
M.A. Kettani and L.M. Gonslaves, Prog. Rep. HHE 1, The College of Petroleum and Minerals. Dhahran. Saudi Arabia, May 1970.
Water,
PO TABLE WATER
1.
Power,
-
ALGAE
PLANKTON
4
1
- BRINE
I
HYDROGEN
c COA!grR-
I\
Food Production Plant,
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Fig.
7
1
1 J
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FOOD
1
CLOSED SYSTEM
4% 1 AGRICULTURE” 1
1
BASIC ELEMENTS
FooD
HORTICULTURAL FOOD
--f-r--L
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TREATMENT
MIXING 8
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h
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286
Atlant
i
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See;,
rintense geothemal activities)
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Location
o= Geothemal
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HUSSEINY
ENERGY RESOURCES IN MID-EAST WATER PRODUCTION
F1dS.h
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Figure 7
Cieothernal Desalination of Lo-r Enthalpy Water
feed
Fresh ,.ater
Fig. 1
Geothermal Desalination of High Enthalpy Water.(17)