Challenges of Recycling Power Plant Cooling Tower Blowdown
By Joseph Lander and Michael T. Chan, P.E.
Recycling water from a cooling tower in a power plant requires a complete understanding of the cooling tower chemistry and operation. Large volumes of water are supplied to the power plant from various sources such as, lakes or reservoirs, rivers, subsurface aquifers, or municipal suppliers. The composition of the feedwater from these sources can vary from season to season, based upon source availability and composition. The components of the water that are of importance to the cooling tower operation are pH, total suspended solids (TSS), total dissolved solids (TDS), alkalinity (alk), total hardness (TH), heavy metals (HM), chemical oxygen demand (COD), phosphate (PO4), and silica (SiO2). Incoming water is normally pH adjusted, and TSS is coagulated and separated in a high-rate clarifier and sand-filter combination. This water is used for non-contact cooling in the power generation process and the hot water is sent to the cooling tower. Feedwater flowrates to the tower can vary from 1,000 gallons per minute (gpm) to several thousand gpm. The water is cooled by evaporation and the components in the incoming water are concentrated by a factor of 5 times or more, depending on the water chemical composition and the operating conditions, and material of construction of the towers.
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