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This paper demonstrates a new co-generation application of hydropower development with reverse osmosis (RO) desalination, in which the technical feasibility of the hydropowered reverse osmosis desalination system is examined in the Aqaba-Disi water pipeline project in Jordan and the Mediterranean-Dead Sea (MDS) Conduit scheme in Israel/Jordan. Substantial reduction in operating cost and energy could improve the cost constraints of the desalination technology. The unit cost of hydropowered reverse osmosis desalination is preliminarily estimated to be US $0.4/m3 for brackish groundwater and US $0.68/m3 for seawater.
Most countries in the Middle East already have a water deficit. They consume every drop of the rechargeable (annually renewed) water available to them in the rivers and subsurface aquifers and are rapidly mining underground fossil water that can be used once and then is gone for good. Israel has just been overcommitted and depleteting virtually all of their renewable sources of fresh water in the 1980s. The neighbor state of Jordan and many other Arab states will also soon be depleted their own renewable sources if current patterns of water consumption are not quickly and radically altered.
Nonconventional water resources and energy development, including desalination of seawater and brackish water by the co-generation method, will be a key issue of the water resources planning in arid to semiarid countries in the 21st century, The applications of groundwater-hydro and solar-hydro with reverse osmosis (RO) desalination, which is a new type of co-generation system proposed herewith, is likely to be a key technological development in this region for the strategic objectives of saving fossil energy and the global environment. Two case studies of “hydropowered brackish groundwater reverse osmosis (RO) desalination in the Aqaba-Disi water pipeline project in Jordan” and “hydropowered seawater reverse osmosis (RO) desalination in the Mediterranean-Dead Sea (MDS) conduit scheme in Israel” are examined in this study.
Aqaba is situated at the head of the Gulf of Aqaba on the Red Sea and at the southern end of the Wadi Araba (Fig. 1) Aqaba is an important commercial center in Jordan with expansion being accompanied by a rapid growth of industrial development along Jordan’s limited coastline. Owing to a hyperarid climate in southern Jordan’s, water supply has been a major constraint for Aqaba’s regional development. The Disi wellfield, which is located 50 km northeast for Aqaba with an elevation of 840 m, was selected as the source for the water supply. The Disi is a nonrenewable (fossil) aquifer, but with low salinity in the range between 300 ppm and 400 ppm of total dissolved solids. From the model simulation study, the aquifer has been estimated to support a maximum abstraction in the range between 17x106 m3 and 19x106 m3 per annum for at least 50 years (NRA, 1986). A ductile iron trunk main 800-450 mm in diameter and 92 km long, carries the water from Disi to Aqaba and southwards to the fertilizer factory near the Saudi border. Pressure is broken at three locations along the pipeline to limit the pressure to a maximum of 25 kg/cm2, as shown in the profile of the trunk main in Fig. 1.
The proposed hydropowered reverse osmosis (RO) desalination is a nonconventional application of the co-generating system by annexing the groundwater-hydro system with the reverse osmosis (RO) desalination unit. The pioneer research on the brackish groundwater reverse osmosis (RO) desalination system in Jordan includes the following objectives:
- Development of the potential energy in a water pipeline (trunk main) which comprises 5.2 MW of theoretical hydropotential for a total head of 840 m, not only for hydropower, but also for the reverse osmosis (RO) desalination.
- Conservation of nonrenewable fresh groundwater in the Disi aquifer, by replacing it with developed brackish groundwater in the Khreim and/or Kurnub sandstones.
- Hydroelectric development, using 400 m of water head difference in the existing trunk main.
- Brackish groundwater reverse osmosis (RO) desalination with direct use of hydropotential energy at 200 m of water head difference in the existing trunk main.
The brackish groundwater, with salinity of about 4,000 ppm/TDS, would be exploited from the potential wellfields in the Khreim and/or Kurnub formations near the Disi, of which the potential is preliminarily estimated to be 1 m3/sec, and replaced with the fossil groundwater in the Disi aquifer. The average discharge of the trunk main is assumed to be 17.5x106/year (0.555 m3/sec), which is equivalent to a design capacity of 0.663 m3/sec with a unit operating time of 21 hours per day. The brackish water flows down from the collecting reservoir (E.L=840 m) to the desalination plant as terminal reservoir (E.L=220 m), through the existing pipeline system passing two hydropower stations by steps; the 1st hydropower station at E.L=630 m and the 2nd hydropower station at E.L=410 m. The installed capacity and annual power output of the two stations are estimated to be 2,078 KW and 15,900 MWh per annum in total, respectively. The following equations are used by assuming a friction head loss of 5%, a synthesized efficiency of 0.8 and a generating efficiency of 0.873;
P = Pth*Ef (2)
Wp = 365*24*Gf*P (3)
where
Pth : Theoretical hydropotential (KW)
Q : Flow discharge (m3/sec)
He : Effective difference head of water (m)
P : Installed capacity (KW)
Ef : Synthesized efficiency (-)
Wp : Potential power generation per annum (KWh)
Gf : Generating efficiency
The hydropowered reverse osmosis (RO) system is composed of three parts: (1) the pre-treatment unit, (2) the pressure pipeline unit, and (3) the RO unit. The pre-treatment unit is to be sited just beside the outlet of the 2nd mini-hydropower station (E.L=410 m), including dual-media filters (hydroanthracite & fine sands) and cartridge filter. After passing through the cartridge filter, the flow water is connected with a pressure pipeline (trunk main between 410 m and 220 m) to obtain hydraulic pressure of 18 kg/cm2, which is directly used to transfer the osmosis pressure to permeate the RO membrane. The main heart of the RO unit is a membrane, which is a low-pressure type, spiral-wounded compost type with 8-inch diameter, including the following specifications: i) salt rejection rate of 99.4%, ii) design operating pressure of 18 kg/cm2, iii) design amount of permeate of 12 m3 per day, and iv) maximum operating water temperature of 40oC, and pH of feedwater between 6.0 and 6.5.
A unit line of the RO vessel consists of a series circuit with six modules. Recovery is estimated at 60% of the feedwater, including 28,800 m3/day of permeate with salinity at 100 ppm of the total dissolved solids and 19,200 m3/day of brine reject of at 10,000 ppm. The effective pressure of the brine reject is estimated to be 15 kg/cm2 by assuming the friction loss of 3 kg/cm2 in the RO circuit. The potential energy recovery from the RO brine reject is preliminarily estimated to be 460 KW (=9.8*0.4*15*9.8*0.8), which is equivalent to an electricity generation of 2,740 MWh per annum by assuming a generating efficiency of 68%. The unit cost of the permeate is preliminarily estimated to be US$0.4/ m3.
The Mediterranean-Dead Sea (MDS) Canal Scheme, also known as a hydrosolar power development, is made possible by the existence of a vast depression (sea surface area of 1,000 km2 with elevation at -400m) at a distance not too far from the sea (:72 km), and the region’s characteristically arid climate (with evaporation rate of 1600 mm per annum from the sea surface). The Mediterranean-Dead Sea (MDS) Canal hydropower project, as it was named in 1980, was designed to exploit the 400m elevation difference between the Mediterranean Sea (zero meters) and the Dead Sea (-402 meters) by linking the two seas (Fig. 2).
Israel’s Mediterranean-Dead Sea (MDS) Canal plan was conceived to provide hydroelectric power (WPDC, 1980), but it did not offer any concept of shared resources and solution to the urgent need for fresh water supply. The joint Israel/Jordan Mediterranean-Dead Sea conduit scheme is a co-generation application which would combine hydrosolar power development with hydropowered seawater reverse osmosis (RO) desalination (Fig. 2). The scheme, which would be maintained at a steady-state level with some seasonal fluctuations of about 2 meters to sustain the seawater level between -402 m and -390 m below the mean seawater level, includes following major components:
1) An upstream reservoir (the Mediterranean) at zero sea level, essentially an unlimited amount of water.
2) A water carrier, assuming several alternative schemes, depending on the route considered, including a gravitational canal, a tunnel with booster pumping, or an open gravitational canal.
3) An upper reservoir and surge shaft at the outlet of the water carrier for regulation the water flow.
4) A storage-type hydroelectric unit capable of reverse operation to allow the system to also work as a pumped-storage unit, if required.
5) A downstream reservoir of the Dead Sea, at a present surface elevation of approximately 402 m below sea level.
6) A hydropowered reverse osmosis (RO) desalination plant, including pre-treatment unit, pressure converter unit, RO unit, energy recovery unit, post-treatment unit, and regulation reservoirs for distribution.
The theoretical hydropotential, installed capacity for peak power, and potential power generation (annual output) were preliminarily estimated to be 194 MW, 480 MW and 1.26x109 KWh per annum, respectively, by assuming 8 hours a day of the peak power operation, 1.03 of specific weight of the intake water, 50.7-152.1 m3/sec of flow discharge, 5% of friction loss of the total water head, 0.85 of the synthesized efficiency.
The marginal operation of the RO system is designed to use the hydropotential energy in the pipeline-tunnel system (400 m of differential water head) for 16 hours a day of the off-peak time. The feedwater requirements to produce 86,400-259,000 m3 per day of permeate with 1,000 ppm of the total dissolved solids are estimated to be 288,000-864,000 m3 per day, assuming a 30% recovery ratio (70% for brine reject). The energy recovery from the brine reject is estimated at 9,460-28,390 KW by assuming that 70% of the feedwater is rejected. The recovered energy (electricity) is estimated to produce 12 kg/cm2 of pressure, which will be returned to the pressure control unit to generate 50 Kg/cm2 of pressure required to permeate seawater through RO membrane. The unit cost of the permeate is preliminarily estimated to be US $0.68/m3.
Application studies on the hydropowered reverse osmosis (RO) desalination, including two case studies in Jordan (brackish groundwater) and Israel (seawater), suggest a substantial reduction in operating costs and energy which have long been a major constraints in desalination practice. The desalination of saline water by the membrane process with low energy requirements, will play an increasingly important role in water resources planning of the next decade. Joint Israel/Jordan development of the Mediterranean-Dead Sea Conduit scheme is based on the concept of shared resources and benefit between the two riparian states in the Jordan river system. This study attempts to evaluate some new nonconventional approaches to water resources which need to be taken into account in building the new peace of the Middle East. These new approaches offer the opportunity to introduce new applications of well-tried technology to solve long-standing water problems which are at the center of many of the potential sources of conflict.
NRA - Howard Humphereys Ltd., “Groundwater Resources Study in the Shidiya Area”, Main Report, 1986, pp. 49-112.
WPDC, INTERNATIONAL NEWS, “Israel Decides on Canal Route”, Water Power & Dam Construction, October 1980, p.4.
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