The enhanced plant performance achieved at the 1,477-MW Morgantown Generating Station shows the value of model predictive control in conjunction with intelligent distributed control algorithms. This project update looks at how the project team moved from ramp rate improvements to reducing tube metal temperatures to improved component life.
Morgantown Generating Station is on the Potomac River in Charles County, Maryland. Each unit consists of a single tandem-compound turbine generator (one Westinghouse and the other General Electric) and a single pulverized coal–fired once-through controlled circulation supercritical boiler utilizing a single reheat-regenerative cycle. Each has a nameplate rating of 572.5 MW with throttle steam conditions of 3,500 psig, 1,000F and reheat steam temperature of 1,000F and seven stages of feedwater heating. The units are capable of generating 625 MW each and were placed into service in 1970 and 1971.
The Combustion Engineering steam generators are a balance draft divided furnace type, consisting of a tangentially fired, center wall furnace with economizer, and superheater and reheater surfaces.
The split furnace design with dual selective catalytic reduction (SCR) systems poses unique challenges to balancing steam temperatures and limiting peak metal temperatures in the various boiler circuits. Because high peak metal temperatures are often a precursor to premature tube failure, control enhancements that decrease peak temperatures offer substantial payback to GenOn, the plant’s owner.
Through the expansion of the model predictive control within the dynamic nitrogen oxide/heat rate optimization system and additional distributed control system (DCS)–based process control algorithms, the objectives of improved steam temperature balance in the boiler circuits and lower peak metal temperatures were achieved.
These control improvements widened the load range of fast dispatch operation while protecting boiler tubes from excessive thermal-induced stress, promoting long boiler tube life. After instrumentation failures, boiler tube leaks cause more unit forced outages than any other component failure in the typical steam plant.
The experiences on Unit 2 are described in this article. The methodologies were then applied to Unit 1, and results were essentially similar, if not better. Earlier Morgantown control upgrades were described in “Increasing Generation Ramp Rate at Morgantown Generating Station’s Coal-Fired Units” in the February 2011 issue, also found in the POWER archives at http://www.powermag.com.
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