August 15, 2006

Currant Creek Power Plant, Mona, Utah

Odis F. Hill, Jr., PE, The Shaw Group, and Robert Van Engelenhoven, PacifiCorp

All power plants are local

Currant Creek's design incorporates an air-cooled condenser that uses only 10% of the amount of water that a similarly sized plant with wet cooling towers would require. Supplied by GEA Power Cooling Inc. (Lakewood, Colo.), the condenser uses thirty 250-hp variable-speed fans (controlled by a computer) to maintain optimum vacuum conditions and maximize steam turbine performance over the wide range of ambient conditions at the plant site. In winter, the fans' motors are reversed to pull warmer air across the finned-tube surfaces, ensuring that no part of the condenser could possibly freeze. The condenser is sized to maintain a vacuum of 6.7 inches (Hg) at 87F and to operate effectively during the summer, when the temperature may reach more than 100F (Figure 6).

6. Blowing hot and cold. Thirty 250-hp variable-speed fans maintain optimum vacuum conditions in the air-cooled condenser year-round (top). Air flow is reversed during the freezing winter months to prevent subcooling of the condensate (bottom). Courtesy: PacifiCorp

What little water the plant needs (for feedwater and auxiliaries) comes from two deep-bore wells on the outskirts of Mona, near the I-15 freeway, 3 miles from the project site. A wet cooling system would have been much cheaper to build but more costly (in a different sense) in the long run. Locally, water is scarcer than hens' teeth, and multi-year droughts have occurred twice in the past 20 years. PacifiCorp realized that buying up agricultural land to secure the necessary water rights wouldn't have been neighborly. Investing in the air-cooled condenser was a no-brainer.

PacifiCorp paid just as much attention to effluent as influent. All wastewater streams from drains, boiler and evaporative cooler blowdown, and the water treatment plant are directed to a 20-acre evaporative pond nearby. Sewerage goes to an on-site septic tank. An all-volatile chemistry regime enables the plant to maintain satisfactory water chemistry without the use of hydrazine. The mixed beds of the water treatment plant are designed to be regenerated off-site, eliminating the need to bring in bulk acid and caustic and store them on-site.