Cooling Tower Blowdown

Description: Power plant cooling-tower blowdown data are estimated from the Union of Concerned Scientists 2012 EW3 Energy-Water Database V.1.3. This database is free and its use is unrestricted. www.ucsusa.org/ew3database

The database was filtered to examine thermo-electric power plants in the western United States that utilize recirculating cooling towers. A preliminary estimate of blowdown flow volumes was made by calculating the difference between the “calculated withdrawal” and “calculated consumption,” as reported within the database. This resulted in an estimated 60 billion gallons per year (616,000 m3/day), but yielded zero blowdown for many of these power plants, which is an unrealistic result. It was assumed that sites whose results were zero flow were not discharging any water from the site either via use of evaporation ponds, reinjection, or other means.

Blowdown flow volumes were subsequently estimated by assigning conversion efficiencies to each technology and assuming a representative blowdown fraction and cycles of concentration in the cooling tower. The following assumptions were made as part of the calculation of blowdown water flows: (1) Power plant thermo-electric efficiencies were biomass = 30%, coal = 35%, geothermal = 15%, natural gas combined cycle = 55%, nuclear = 30%, oil = 35%, CSP = 35% (2) Blowdown = Evaporation ÷ (Cycles of Concentration – 1), and (3) Cooling systems operating at four cycles of concentration. This method led to a total blowdown estimate of 69 billion gallons per year (720,000 m3/day). The blowdown estimates are sensitive to the assumed cycles of concentration.

References: U.S. Department of Energy, “Cooling Towers: Understanding Key Components of Cooling Towers and How to Improve Water Efficiency,” DOE/PNNL-SA-75820, 2011.

Union of Concerned Scientists, “Freshwater Use by U.S. Power Plants: Electricity’s Thirst for a Precious Resource,” 2011. [Online]. Available: http://www.ucsusa.org/clean_energy/our-energy-choices/energy-and-water-use/freshwater-use-by-us-power-plants.html#.VfGyBkZa3K0. (Accessed August 2015)