A circulating water plant or circulating water system is an arrangement of flow of water in fossil-fuel power stations, chemical plants, and oil refineries. Such a system is required because various industrial process plants uses heat exchangers, and also for active fire protection measures. In chemical plants, for example in caustic soda production, water is needed in bulk for the preparation of brine. The circulating water system in any plant consists of a circulator pump, which develops an appropriate hydraulic head, and pipelines to circulate the water in the entire plant.
Circulating water systems are normally of the wet-pit type, but for sea-water circulation, both the wet-pit type and the concrete-volute type are employed. In some industries, one or two standby pumps are also connected parallel to CW pumps. It is recommended that these pumps must be constantly driven by constant-speed squirrel-cage induction motors. CW pumps are designed as per IS:9137, standards of the Hydraulic Institute, USA, or equivalent.
In the present era, mechanical induced draftâÂÂtype cooling towers are employed in cooling of water. Performance testing of cooling towers (both IDCT and NDCT) shall be carried out as per ATC-105 at a time when the atmospheric conditions are within the permissible limits of deviation from the design conditions. As guidelines of Central Electricity Authority, two mechanical-draft cooling towers or one natural-draft cooling tower must be established for each 500 MW unit in power plants. The cooling towers are designed as per Cooling Tower Institute codes.
Some coastal power stations or chemical plants intake water from sea for condenser cooling. They use either closed-cycle cooling by using cooling towers or once-through cooling. The selection of the type of system is based on the thermal pollution effect on seawater and techno-economics based on the distance of the power station from the coast and the cost of pumping seawater.
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