A RealTime Output–Loss Method for Monitoring Heat Rate for CoalFired Power Plants

Abstract

This paper describes a realtime performance monitoring method based on PTC 42013 for determining instantaneous heat rates for coalfired power plants. The calculation protocol uses a modified output–loss approach applied to a control volume that closely conforms to the boiler. The largest energy balance term is the heat transfer rate to the steam, which is known accurately in realtime when the plant employs properly calibrated instrumentation. The firstlaw energy balance also requires a balanced combustion equation which depends on coal composition, which is not known in realtime. A periodic or alertdriven calibration utilizes an ultimate analysis of a carefully collected coal sample and historic plant data obtained during the collection time of the coal sample. This is used to calculate correction factors for the coal mass flowrate, air preheater leakage, and CO2 and SO2 concentrations at the economizer exit derived from continuous emissions monitoring systems (CEMS) measurements performed at that location. The iterative calculations required to determine the coal composition in realtime are presented. The realtime performance algorithm exhibited significant sensitivity associated with measurements of the steam heat transfer rate, which was the dominant term in the overall boiler energy balance. Other input parameters generally yielded a much lower influence on calculated heat rate. It was concluded that for optimal accuracy of the output–loss method the steam and coal mass flowrates must be measured as accurately as possible.