The Asian power industry is currently experiencing a significant increase in power plant construction. India, for example, has planned to add more than 100,000 megawatts of capacity in the next five years. The single largest industrial use of water in India is for power plants, as these plants consume around 90% of the water used by all industries combined. A reliable water supply, therefore, is vital for the region’s power generation. Among the critical areas for water treatment and use in power plants are intake screening, the steam turbines cycle (boiler feed and condensate treatment) and the cooling water system. Providing these and other solutions, Evoqua recently secured several power projects in Asia.
Water treatment systems for the power generation market have to fulfill specific requirements depending on their application within the power plant. Intake systems help protect the power plant’s condenser cooling system from damage, by removing debris from the incoming cooling water. Bar racks first capture rough and larger debris to prevent it from reaching the finer mesh of the traveling water screen. The bar racks are cleaned by trash rakes. Evoqua's dual-flow traveling water screens are positioned parallel to the direction of the flow, and present nearly twice the screening area and debris carrying capacity of other designs. These screens help to eliminate debris carryover downstream of the system, making them ideal for intakes that require high volumes of water or heavy duty debris handling. Evoqua is supplying a comprehensive intake system for a Vietnamese power plant. The system will include dual-flow traveling water screens, bar racks, grab-style trash rake, interconnecting piping and associated controls for the plant’s once-through condenser cooling system.
Water treatment solutions for the steam turbines cycle
Evoqua's triple membrane (3Mi) integrated solution is an innovative membrane treatment approach to achieving consistent, cost-effective boiler feed water. It consists of a Memcor ultrafiltration system, a Vantage reverse osmosis system and an Ionpure continuous electrodeionization system, for removing suspended solids, dissolved inorganic impurities and dissolved and suspended organics. Historically, boiler feed water treatment systems have been based on chemically regenerated ion exchange resins. In the 3Mi process, the bulk consumption of chemicals, such as acid and caustic, is eliminated, together with the hazards associated with chemical handling. It also reduces the production of solid wastes that typically require dewatering and disposal.
Condensate is formed when the steam from the boiler cools. It can be collected and reused as boiler feed. Prior to reuse, impurities, such as metal oxides, trace ionic impurities and silica from the power plant’s condensate, have to be removed. Evoqua's spherical condensate polishers help to improve and maintain the boiler feed water chemistry and increase the likelihood that the power plant will stay online during small to moderate condenser leaks. To remove impurities from the condensate, exchange resins can be used. The exhausted resins can be transferred and regenerated in a Fullsep external regeneration system that allows separation of the resins with minimum cross-contamination, thus assisting the customer in maintaining consistent high-quality water.
In India, Larsen & Toubro Limited selected Evoqua to provide a condensate polisher package with external regeneration facility to treat condensate for two 660-megawatt super-critical boilers for a new power plant. The project involves design, engineering, fabrication, installation, testing and commissioning of the condensate polisher system, scheduled for start-up in April 2013. Evoqua India and Evoqua Singapore will work together to execute the project, including design and project management.
Chlorination and clarification systems support power plants in India
In the cooling water circuit, micro and macro fouling can occur, which in turn affects the heat transfer efficiency in the power plant condenser tubes; this can affect the overall power plant efficiency. This fouling can be controlled by chlorinating the cooling water. The Chloropac seawater electrochlorination system from Evoqua is designed for this purpose. During electrochlorination, special transformer rectifiers provide DC power with high amperage for electrolysis of the seawater. The electrolysis produces sodium hypochlorite, which acts as an effective disinfectant to control biofouling.
One of the largest Greenfield ultra mega power plants in India selected the Chloropac system to control biofouling in the cooling water. The power plant owner evaluated possible options for biofouling control including gas chlorination, chlorine dioxide treatment, non-oxidizing biocide treatment and electrochlorination. Gas chlorination would have required a large number of chlorine gas storage containers. Safety requirements during handling, storage and use at the site, and during transport to the site, as well as space requirements, were major considerations. The Chloropac system not only provided a safer alternative to gas chlorination, but also provided the lowest lifecycle cost for the application.
Power plants need a consistent, reliable source of water for cooling tower make-up that is also cost effective and sustainable. In many cases, cooling tower make-up water must be treated for suspended solids reduction and/or hardness reduction. With properly treated water, the potential for scaling in the cooling tower is significantly reduced. This reduces cooling circuit cleaning requirements, extends the life of the cooling equipment, and reduces the cooling tower blowdown flow to the environment. The Evoqua Contrafast Concentric system is a high-rate clarification and thickening process that consists of a solids contact reaction chamber, clarifier with tube settler and gravity thickener in a single tank. The entire process is contained in a single, unitized steel basin, and is designed to simplify installation time and reduce cost. The design allows up to an 80% reduction in footprint compared to conventional clarification systems, and the process enhances suspended solids’ removal, lime softening and heavy metals removal.
Evoqua received a recent order from Torrent Power Limited for two Contrafast Concentric systems, which will treat water for the 382.5 megawatt UNOSUGEN gas-based combined cycle power plant in Surat, district Gujarat, India. The Contrafast Concentric systems will treat water from the Tapi River and are designed to produce up to 4 million gallons per day (15,142 m3/day) of cooling tower make-up water.
Chloropac, Contrafast, Fullsep, Memcor, Vantage and Ionpure are trademarks of Evoqua and/or its affiliates in some countries.
SOURCE: Evoqua Water Technologies