The energy industry has known for decades that federal regulators eventually would set rules under the Clean Air Act to govern emissions of mercury and other air toxics from coal-fired power...
Power-Plant Cooling: How Many Fish Per kWh?
EPA flounders on the Clean Water rule, while producers tackle the real enemy—shortage.
- direct dry cooling adapted for new power plants is a recirculated cooling system with mechanical draft towers. Natural draft towers are used infrequently for power-plant installations in the United States.
- Indirect Dry Cooling . Uses a closed-cycle water system to condense steam; the heated water is then air cooled. Indirect dry-cooling systems are used generally in retrofit situations at existing power plants, because a water-cooled condenser would be in place already for a once-through or recirculated cooling system.
Water Consumption. As explained by Joe O’Hagan, specialist with the California Energy Commission, the cooling water demand for a 500-MW, combined-cycle power plant using once-through cooling is about 15,000 gallons per megawatt-hour, whereas closed loop (re-circulating) cooling requires about 200 to 250 gallons per MWh. The same type of plant using dry cooling will use no water for cooling, while a hybrid system’s water use will be somewhere between a wet and dry system.
Electric Output and Cost . Dry cooling offers certain environmental advantages, but also has serious economic drawbacks. According to statistics from the Electric Power Research Institute of Palo Alto, electric output from gen plants using dry cooling output runs about 2 percent less than with wet energy cooling systems. EPA estimates that the penalty in electric output for dry cooling on average over the year can run as high as 8.6 percent versus once-through wet cooling, and as much as 10 percent during peak periods. Yet the costs of dry cooling run anywhere from 3.5 to 4.5 times more for dry cooling than for wet cooling.
Aesthetics. “Dry Cooling involves a bigger facility and may be noisier,” says John Howard, an energy environmental and public policy attorney and former deputy director for the White House Council on Environmental Quality. “You’re relying on ambient air, which is harder to cool off,” and it requires special fans, he says. Estimates vary greatly, but a standard fan and its gear box can run about $30,000 or more.
A special low-noise fan can cost one to two times that amount.
(See Technical Development Document for the Final Regulations (EPA-821-R-01-036) November 2001, Chapter 4—Dry Cooling, at http://www.epa.gov/waterscience/316b/technical/ch4.pdf)—CB