Derating of 75 MWe Pulverised Coal Fired Power Plant without HP Heaters in Service – A Case Study

Chittatosh Bhattacharya , Anuj Pathak

The case study is related to an assessment of derating of power generation capacity of 75 MWe nameplate capacity units due to unavailability of high pressure (HP) heaters of a pulverized coalfired power generating station in India. The generation capacity of the said Power Plant units, which were commissioned since the 1960s onward, was deteriorated due to trouble in the regenerative feed water heating system. The power generating station was consisting of three 75 MWe BTG units and the generated steam from any of the three similar 320 TPH boilers may be fed to any one of 75 MWe turbo generators through available crossover connections. The study summarizes the results of the series of calculation on collected in-situ data to evaluate the performance and efficiency deterioration due to fall in final feed water (FW) temperature at boiler inlet, as per the provisions of standard thermodynamic 1st law based cycle efficiency evaluation practices. The erosion in IP turbine blades degrades the back pressure on the high-pressure turbine with aging and thereby degrades last HP Heater shell pressure resulting degradation in FW temperature. Bypassing HP heaters affects the same way along increasing condenser losses. Cycle heat rate loss is also inevitable due to emergency drip operation, turbine gland steam leakage, makeup water flow in the condenser. These findings discuss the impact on unit heat rate with reference to design and operating data of 75 MWe generating units while HP Heaters were available and the same were partly or fully unavailable causing performance deterioration.