Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/459793
PROJECTS | 16 | Desalination & Water Reuse | February-March 2015 Under pressure: the Hadera plant produces top-quality permeate under severe regulatory and cost constraints • Total Dissolved Solids: 270 mg/l max • Sodium: 30 mg/l max • Dissolved oxygen: 3 mg/l min • Langelier Saturation Index (a measure of capacity to dissolve or deposit calcium): 0 – 0.5 The end result of the operation of the Hadera SWRO desalination plant is finished water produced for US$ 0.58 a cubic metre at the time of its bid submission in July 2006. The challenges of minimizing total water cost and complying with chemical limitations were both met through the unique design of the plant. UniqUE dESign IDE holds patents for its design of certain parts of the desalination process used at Hadera as well as at the Ashkelon and Sorek plants. There are two chief, unique design features which are: three independent RO process centers and a single-pass SWRO treatment step followed by a patented cascade brackish water RO (BWRO) treatment step. Commonly, SWRO systems have a dedicated high-pressure pump and energy recovery device (ERD) for each RO membrane rack. When a high-pressure pump is shut down, the membrane rack and associated ERD are shut down. Each time an RO unit is taken down, flushing must occur which costs energy and product water. IDE's way to be able to run from 38% to 100% capacity at any time, with 15 minutes required for changing the capacity, is to have three centers: a pressure centre, a membrane centre and an energy recovery centre as shown in Figure 1. The recovery rate can be reduced or raised on all racks and the high-pressure pump and ERD configurations independently changed. Note that figure 1 shows only two of the installed racks in the Hadera plant. The plant is divided into two independent sub-plants - east and west. Each sub-plant has four high-pressure pumps in operation for night-time, high-flow operation (figure 1) and one lower pressure pump for daily operation. The most common way to control boron concentration is a double pass configuration in which a single stage SWRO treatment step is followed by a two-stage BWRO treatment step. Caustic is injected ahead of the BWRO units to ionize boron so that it is well rejected by the BWRO membrane (figure 2). A measure common to Hadera and other IDE SWRO desalination plants is to take permeate off the front and tail ends of the SWRO racks which makes economic sense. The permeate produced in the first membrane elements is higher quality than the permeate produced in the last membrane elements. The front-end permeate can go directly to Figure 1. Figure 2.