The Al Taweelah water desalination plant was situated in Taweelah complex, Abu Dhabi in the United Arab Emirates. The plant was roughly eighty kilometres on the North-Eastern side of the city of Abu Dhabi. It was an Abu Dhabi Water Electricity and Authority (ADWEA) program and part of the three power and water generation firms that ran on the Taweelah location. The plant was one of the world’s leading desalination plants with a capacity to produce 3,000 megawatts of electric power and 1.3 million m3/d of water (IDA, 2006-2007).
The three firms on the site were the Al Taweelah Power Company (ATPC) that ran the B and B2 plants, the Gulf Total Tractebel Power Company (GTTPC) that ran A1’s phase 1 and phase 2 plants and the Emirates CMS Power Company (ECPC), which ran the Taweelah A2 plant. All three companies sold their yield and capacity to Abu Dhabi water and Electricity Company (ADWEC) (United Arab Emirates, n.d.).
Taweelah B and B2 plants yielded a total capacity of 1,075 megawatts of power and 431,492 m3/d of water and were build and authorized to operate in two stages. Plant B, which was the initial phase, utilized the cogeneration model and was allowed to operate between the years 1995 and 1997 (IDA, 2006-2007). It comprised six duplicate sections. Each section had a boiler that used steam, a steam turbine that was energized by natural gas with steam removal to a desalination element of the multi-flash variety (Silbermann & Koerdt, 2009). The instrumentation and monitoring system used a single button to manage the entire system and permitted the automated activation of the turbines, boilers, desalination system as well as the supporting systems (Al Taweelah –B Steam Power Plant – UAE, n.d.). Plant B2, on the other hand, used the combined cycle model and was commissioned between the years 1999 and 2001. The plant had a pair of gas turbines that had the capacity to function in the simple or combined cycle modes. Each of the turbines drained into a heat recovery steam generator, which produced steam that propelled another ‘back pressure turbine generator’ that also used steam. The second generator delivered steam to “three multi-stage-flash seawater desalination distillers” (IDA, 2006-2007, p. 19).
The Taweelah A2 plant had a space of 710 megawatts of power and 227,100 m3/d for water and utilized the combined cycle model (Abu Dhabi Water and Electricity Company, 2012). The cost of producing water at the plant was estimated at around $0.84 per cubic meter.
The Taweelah A1 plant, on the other hand, had a capacity of 1,350 megawatts for electricity and 381,530 m3/d for water after being upgraded from a previous capacity of 255 megawatts of power and 132,626 m3/d of water in the year 2000. The plant consisted of four (MSF) multi-stage flash desalination elements as well as fourteen multi-effect distillation (MED) units with potential of 17,138 m3 daily (Abu Dhabi Water and Electricity Company, 2012). These MED components were made of stainless steel and functioned at a maximum temperature of 63 oC and yielded a gain output ratio of 8.0. In addition, it was estimated that they were 7.5 percent cheaper to maintain than equivalent MSF plants. The documented cost of producing water at the plant in its first year of operation was found to be approximately $0.7 per cubic meter.
Materials Used in the Construction of Condensers and Brine Heaters
Condensers and brine heaters were essential components of any desalination plant. Consequently, the efficiency of those components was vital in the overall efficacy of the entire desalination plant. Therefore, it was important to establish the materials that made up these essential components. The condenser consisted of a shell, 16 tube stages, 16 tube sheet stages, a tube support plate, a distillate tray and trough, a demister, and a water box. It was also made up of weir and orifice plates as well as a cascade vent pipe. The shell of the condenser (evaporator) was made of carbon steel (stainless steel) 316L. Tube stages 1 to 3 consisted of titanium (ASTM B338-Gr-2-W), whereas tube stages 4 to 13 were made of 90/10 CuNi (BS2871, Part 3 CN -102). Tube stages 13 to 16 were made of titanium (ASTM B338-Gr-2-W). The tube sheet stage 1 to 3 consisted of 70/30 CuNi (ASTM B171-C71500), whereas tube sheet stages 4 to 13 were made of 70/30 CuNi (ASTM B171-C70600). Tube sheet stages 13 to 16, on the other hand, were made of Al-bronze (ASTM B171-C61400). The tube support plate, the weir and orifice plates, the demister, and the distillate tray and trough, were made from stainless steel 316L. Carbon steel with CuNi clad was used in making the water box, whereas the cascade vent pipe was made of stainless steel 316L.
The brine heater, on the other hand, comprised of a shell, a hot well, water box, tubes, tube sheet, tube plate, and a tube support plate. The shell and the hot well were made of carbon steel, whereas the water box was made of carbon steel with CuNi clad. The tubes’ body comprised an alloy of several metals such as copper (Cu), nickel (Ni), iron (Fe), and manganese (Mn). These metals were mixed in the proportion of 66Cu30Ni2Fe2Mn (BS2871, Part3 CN108). The tube sheet was made of copper and nickel blended in the ratio of 70 to 30 (ASTM B171-C1500). The tube support plate was made of carbon steel.
Technology Employed
The technologies used at the three plants were the multi-stage flash (MSF) and the multi-effect distillation (MED), which were both part of thermal technologies of water desalination. Taweelah B1, B2, A1-phase 1, and A2 employed the MSF technique, whereas Taweelah A1-phase 1 used the MED technique.
The Plant’s Output
The plant was capable of yielding a capacity of 1458 m3 of water per hour, which translated to 35,000m3 per day. That output was realized at seawater temperatures of 35oC. The efficiency of the plant was also investigated, and it was realized that the plant realized a gain output ratio/ performance ratio of 6.5 kg/ 2326 KJ. The recovery ratio was given by 13500 divided by 1458, which was equivalent to 9.25.
Technical Specifications in the Plant’s Operations
The recovery ratio for the plant was calculated by obtaining the quotient of 13500 divided by1458, which was equivalent to 9.25. The entire desalination process consisted of 16 stages. The salinity of the sea water that was fed into the plant was estimated at 44 grams of salt per kilogram of seawater. That water also had temperatures that ranged between 18 oC and 35 oC. The heating steam that was utilized in the plant was LP & MP steam from IBE power plant. In the scaling process, the acid/anti scalant used was Belgard EV2030S. The other scaling system that was employed was the ball cleaning system. The maximum limit of top brine temperature was found to be 105 oC, whereas the TDS or salinity of brine blow down was allowed to reach a maximum of 66 g/Kg. The specific heat transfer area for water production was approximately 56,251 m2 for the heat recovery section and around 13551 m2 for the heat rejection section. The average overall heat transfer coefficient for the brine heater was 2200 W/m3K. The plant’s lifetime was categorized as longterm life.
Power Consumption
It was estimated that the specific power consumption of the plant in terms of consumption in kilojoules (KJ) per kilogram of distillate produced was between 4.2 and 4.5 KW per m3 of distillate.
Challenges Faced by the Plant
Al Taweelah desalination plant was currently facing a number of challenges in its operations. Such challenges included the leaking of the condenser bundle tubes and cracking of the brine casing. In addition, the ball cleaning system had a problem with the ball collection process.
Environmental Impact of the Plant
One of the key environmental concerns of the plant is pollution of the environment with brine, which was produced as the key waste product from the desalination process. A common discharge culvert was employed in the disposal of the resultant brine. The brine was discharged into a culvert channel that was located approximately 3 to 4 kilometres away from the seawater inlet. Apart from brine, the other environmental concern was the emission of greenhouse gases to the environment. The plant took care of that problem by undertaking a 24-hour monitoring of the quantities of gas emitted to ensure that they did not surpass the PWPA (Power and Water Purchase Agreement) limits.
Future Plans for the Plant
It was expected that reverse osmosis would be incorporated into the company by the year 2010. However, the status of that scheme still remained uncertain. The plant had future plans of meeting the rising demand for desalinated water by the rising population as well as plant retrofitting. It aimed to achieve those plans by carrying out weekly internal and external monitoring of the seawater inlet and outlet parameters so that they did not exceed the maximum levels established by the PWPA. The plant currently used energy released from the power plant in its desalination processes (cogeneration process), which was a process that was self-sustaining in terms of energy use. However, future plans for use of sustainable energy involved the establishment of reverse osmosis systems in water desalination that would minimize the use of energy (Barriers to thermal desalination in the United States, 2008).
References
Abu Dhabi Water and Electricity Company. (2012). Web.
Al Taweelah –B Steam Power Plant – UAE. (n.d.). Web.
Barriers to thermal desalination in the United States. (2008). Web.
IDA. (2006-2007). International Desalination Association Yearbook. Web.
Silbermann, G. & Koerdt, R. (2009). Al Taweelah B power station – electricity and water for Abu Dhabi. (1999). Web.
United Arab Emirates. (n.d.). Web.