With TARGA UF membrane cartridges used as pretreatmentto an SWRO system, the Zhuanghe plant is able to cost-effectively tap limitless seawater and avoid draining the region’s scarce surface water resources.
Click here to enlarge image Construction of the Zhuanghe plant was divided into two phases. The first phase, completed in October 2006, provides 1,200 megawatts. When the second phase was to be complete at the end of 2007, the total capacity would expand to 3,200 mW. During the first phase, the plant drew surface water from a reservoir located 19 kilometers away. With completion of the second phase, the plant was to switch over to seawater for all cooling water and boiler makeup needs.
UF makes RO economical
“The Zhuanghe plant has been designed as a model facility to showcase the best available technology,” according to plant manager Mr. Zhang. “The first large saltwater desalination plant in China was commissioned in 1999, and it has since been well-established that reverse osmosis is an incredibly economical process, with lower operating costs and a smaller footprint than thermal distillation.”
Optimizing SWRO/BWRO processes
The reverse osmosis system at the Zhuanghe plant also has an advantage of being a twostage process that can be tailored to meet different requirements for particular applications. Only the first stage, seawater reverse osmosis (SWRO), is required for the cooling water used by accessory equipment. Boiler makeup requires higher quality water that must also pass through the second stage, a brackish water reverse osmosis (BWRO) system.
To optimize RO systems performance, and protect them from fouling, an effective pretreatment system is required. Zhuanghe plant officials chose ultrafiltration (UF) as the pretreatment solution because UF occupies a small footprint and provides higher permeate quality as compared to conventional pretreatment systems. Fully automatic control and relatively low investment costs were also important factors in the selection of UF technology. UF pretreatment for RO systems is an increasingly common combination in desalinations plants and other large-scale RO systems in China and around the world.
Hollow fiber UF solution
Beijing Lucency Enviro-Tech Co., Ltd., one the largest providers of industrial and municipal water filtration systems in China, was responsible for designing and installing the UF pretreatment system. TARGA®-10 UF cartridges from Koch Membrane Systems Inc. (KMS) were chosen for the project after plant officials visited two power plants that employ TARGA cartridges for very similar RO pretreatment applications.
The cartridges employ a proprietary semi-permeable polysulfone hollow fiber membrane successfully deployed in municipal and industrial water treatment plants in China and many other countries for more than a decade. In China alone, TARGA cartridges treat over 500,000 m3/d (132 MGD) of water from a variety of sources.
The hollow fibers are true ultrafiltration membranes, with a nominal molecular weight cut-off of 100,000 Daltons, resulting in removal of particulates and larger molecular weight components. These KMS fibers have demonstrated the ability to reduce turbidity to less than 0.1 NTU and SDI to between 1.0 and 3.0, making these UF units an ideal pretreatment step for spiral-wound RO membranes.
Two trains of UF cartridges were commissioned in October 2006, and three additional trains were commissioned in the second half of 2007 for the second phase of the plant’s construction. The trains operate in parallel, and are each equipped with 44 TARGA cartridges having a total capacity of 232 m3/h per train.
