Steam turbine bottoming cycle deterioration under different load conditions

Abstract

This paper investigates the performance diagnostics and the deterioration analysis of the steam cycle, which is the bottoming cycle of a combined cycle power plant. A proposed model has been created to simulate the steam turbine (ST) performance at various loads and working conditions in order to estimate the deterioration percentages of the steam cycle components. Performance modeling and degradation analysis have been performed on 2650 reading points over five operational years (2013–2017). The deterioration percentage was studied for different load conditions including full load (100%) and part loads (75% and 50%). The degradation of the steam cycle components has been investigated namely: the high-pressure steam turbine, the low-pressure steam turbine, and the condensate extraction pump. Besides, the effects of the degradation of the components on the ST generated power, and the overall steam cycle thermal efficiency have been studied. This analysis has been performed according to the actual logged data obtained from the power plant; this gives a realistic value to this study. The results indicate that the deterioration percentage increase with time and operational load, whereas the degradation rate decreased with time. Moreover, ambient air conditions affected the low-pressure steam turbine (LPST) performance and degradation by increasing the air-cooled condenser backpressure. Furthermore, the maximum degradation of the steam turbine components reached −2.1% in the LPST and the maximum overall deterioration of the steam turbine reached −2.97% at the full operational load.