August 15, 2006

Currant Creek Power Plant, Mona, Utah

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

The same, but different

At first glance, Currant Creek is similar to many 2 x 1 combined-cycle plants based on the ubiquitous General Electric 7FA gas turbine (see the profiles of PSEG Power's Linden Generating Plant and Bethlehem Energy Center). It has a nominal generating capacity of 145 MW at its elevation of 5,051 feet. The two triple-pressure, horizontal gas-flow heat-recovery steam generators (HRSGs)—manufactured by Louisville-based Vogt Power International Inc., a subsidiary of Babcock Power Inc. (Danvers, Mass.)—generate low-pressure (LP) steam at 78 psig and 565F, intermediate-pressure (IP) steam at 462 psig and 1,048F, and high-pressure (HP) steam at 1,950 psig and 1,050F from turbine exhaust gas at 1,125F (Figure 4). Currant Creek is supplied by a 1,075-psig dedicated pipeline that brings gas to the plant from a trunk line 13 miles away.

Each HRSG is fitted with natural gas–fired duct burners from Forney Corp. (Carrollton, Texas) that boost the unit's output by 52 MW when they kick in. NOx emissions are kept under control by a selective catalytic reduction (SCR) system; its reagent of choice is aqueous ammonia. CO emissions are likewise reduced by a catalyst incorporated into each HRSG (see the table). Currant Creek's steam turbine, from Toshiba, is rated at a nominal 250 MW. Its combined HP/IP cylinder is connected to a separate, double-flow LP cylinder (Figure 5).

5. Made in Japan. Toshiba supplied the single 250-MW steam turbine. Courtesy: PacifiCorp