At Morgantown Generating Station, plant personnel used innovative methods to combine model predictive control with distributed control system–based process control algorithms to improve waterwall temperature control and main steam temperature control and to enhance unit ramp rate capability. The previous heat rate and NOx optimization performance gains were retained. Focusing beyond basic loops of feedwater, air, and O2, the project considered issues such as PID controller override configuration and limitations. The techniques used to overcome these challenges improved unit ramp rate capability beyond any previous unit performance.
The typical coal-fired power plant has been updated with digital controls and other performance and environmental improvements by the time it reaches middle age. Units 1 and 2 of GenOn Energy’s Morgantown Generating Station—which is situated on the Potomac River near Newburg, in Charles County, Md.—represent that class of plants with a twist. Over the years, a widening of the coal specifications and modifications to coal mill equipment adversely affected waterwall outlet steam temperature control and thereby unit ramp rate. With a recent emphasis on economic dispatch of the two units, those ramp rates had to increase in order to remain competitive.
Morgantown’s two units are are split- furnace 630-MW coal-fired once-through units constructed in the 1970s. The plants were retrofitted in the mid-1990s with low-NOx burners. A modern distributed control system (DCS) also was installed at that time, enabling significant control and ramp rate improvement. Furthermore, a dynamic NOx/heat rate optimization system (based on model predictive control and neural nets) combined with an intelligent sootblower optimization system were integrated with the DCS in 2006 to meet near-term NOx objectives.
Plant Profile
Each unit consists of a single tandem-compound turbine generator and a single pulverized coal-fired once-through controlled circulation supercritical boiler utilizing a single reheat-regenerative cycle. The steam generators are, in essence, twins; the turbine generators are of like capability but were designed and built by two manufacturers.
Unit 1 (Westinghouse) has a nameplate rating of 572.5 MW; the Unit 2 (General Electric) rating is 575.2 MW. Both units have throttle steam conditions of 3,500 psig, 1,000F, reheat steam temperature of 1,000F, and seven stages of feedwater heating.
Both 625-MW steam generating units were designed and manufactured by Combustion Engineering Inc. and are designed to deliver maximum continuous steam at a rate of 4,250,000 pounds of steam per hour with steam pressure of 3,810 psig, and steam temperature of 1,005F at the superheater outlet. The units were placed into service in 1970 and 1971.
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