Dynamic Simulation Analysis of the Bottoming Cycle of a 400-MW Combined Cycle Power Plant with Proportional-Derivative Control of the Drum Water Level

Abstract

This study presents a dynamic simulation analysis of the bottoming cycle in a 400 MW combined cycle power plant (CCPP) featuring a heat recovery steam generator (HRSG) and triple-pressure reheat steam cycle. Traditional simulation tools have limitations in controlling specific design parameters, such as the heat transfer coefficient and equipment geometry, which affect the accuracy of transient response simulations. Therefore, a MATLAB-based simulation program was developed to more precisely model the transient behavior of the CCPP, including the pressure, flow rate, and temperature variations across the heat exchangers and the steam turbine power outputs under partial load conditions. This study focuses on the effect of proportional-derivative (PD) control on the stability of HRSG drum water levels. Transient conditions were simulated by reducing the load, which resulted in significant changes in the steam cycle parameters. The results demonstrate that the PD controller effectively stabilizes the drum water levels during load changes, which prevents issues, such as overheating or turbine blade damage, caused by excessive water levels. Moreover, the findings reveal that the choice of PD controller parameters directly influences water level fluctuations and recovery time, with higher gains improving stability. In addition, the simulation results confirm that even at a partial load, the steam turbine inlet temperature stabilizes, and the steam cycle operates efficiently, producing approximately 93.4% of the net power generated under full-load conditions. Hence, this study highlights the importance of accurate simulations and effective control mechanisms to ensure the safe and reliable operation of large CCPPs under transient conditions.