Special Report. Water Managment: Power plants and water must mix

Power, Mar 2007

The U.S. Department of Energy's National Energy Technology Laboratory (NETL) is actively developing technologies for reducing water consumption by the next generation of power plants. The U.S. Geological Survey reports that 345 billion gallons of fresh water were withdrawn from American public supply and other sources daily in 2000. According to NETL, it takes an average of 25 gallons of water to produce 1 kilowatt-hour of electricity, or almost 100 billion gallons of fresh water a day to cool the entire U.S. thermal power plant fleet (Figure 3) The only sector that uses more water is agriculture (for irrigation). But plentiful supplies in the past are not a valid indicator of future availability in many regions.

NETL, in its latest research report, "Freshwater Needs Project for Future Fleet" (available online at www.netl.doe.gov/technologies/coalpower/ewr/water/index.html), notes the distinction between water use and water consumption. Water use is a temporary "borrowing" of the water, as in a once-through cooling system. Consumption, by contrast, represents actual water loss to a process or evaporation.

The report notes that in 1995 (the last year for which NETL says data are available), fossil-fueled power plants "were second only to agriculture in total freshwater withdrawals . . . [with] more than 34 trillion gallons from fresh surface and ground waters." The report then notes that "more than 97% of all withdrawals were returned to the source. Of the 36.5 trillion gallons of U.S. fresh water consumed in 1995, thermoelectric generators were responsible for less than 3.5% of the total, making it the smallest consumer category of U.S. fresh water resources. In comparison, 81% of the water used in irrigation is consumed [Figure 4]."

The challenge for the industry is to reduce withdrawal and consumption of fresh water at the same time that Clean Water Act Section 316(b) regulations and a concerted push to reduce river and ocean once-through cooling will inevitably require more makeup water for closed-loop cooling water systems.