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The 550-MW, oil- and gas-fueled Emery Generating Station is a significant addition to Interstate Power & Light's fleet because its black-start capability can trigger the restoration of system service in the event of a regional blackout. Emery's two GE 7FA combustion turbines are the first in the U.S. with a static starting system that enables them to be started up in island mode.
Owner/operator: Interstate Power & Light Co.
Over the past decade, electricity demand in northern Iowa has increased by 20%. That's a modest rate, but significant enough that the incumbent utility--Interstate Power & Light Co. (IPL), based in Cedar Rapids--realized a few years ago that it would need to expand its capacity. Consequently, system planners at IPL, which is a subsidiary of Alliant Energy (Madison, Wis.), launched the "Power Iowa" initiative. The $400 million Emery Generating Station (EGS) is the first project completed as part of it.
According to Lee Hanson, Alliant's project manager for EGS (Figure 1), more raw generating capacity wasn't the only reason the plant was built. Another was Alliant's need to increase the dispatching flexibility of its fleet. Hence, EGS was designed for intermediate-load service, and its commissioning enables Alliant's baseload and peaking plants to be ramped up and down as needed. A third reason for building EGS was a new Iowa law that allows utilities to secure funding for a new plant before it breaks ground, reducing their capital risks.
Plant layout
IPL retained Kansas City-based Burns & McDonnell to assist in the design and construction of EGS. The combined-cycle plant has two General Electric 7FA combustion turbine-generators (Figure 2), two heat-recovery steam generators (HRSGs) from ABB Alstom Power Inc., and one GE D11 steam turbine-generator (Figure 3). Both combustion turbines, which can burn oil or natural gas, employ evaporative cooling, power augmentation, and fuel gas efficiency heating. The steam turbine operates at a pressure of 1,900 psi at a main/reheat temperature of 1,050F/1,050F. Hanson explains that "the 7FAs were designed to be able to burn oil should there be a problem with the plant's natural gas supply."
The HRSGs are equipped with simple-cycle bypass stacks, duct firing, and fuel gas efficiency heating. Each is followed by a Hitachi selective catalytic reduction (SCR) system for NOx control...