Simulating combined cycle gas turbine power plants in Aspen HYSYS

Combined cycle gas turbine (CCGT) power plants are becoming increasingly important for electricity generation. Enhancing their thermal performance is essential for mitigating carbon emissions. This paper aims to present a methodology for simulating the off-design operation of a triple-pressure reheat CCGT plant in Aspen HYSYS. The modeling equations that rigorously capture the full off-design characteristics of various plant components (i.e. compressor, combustor, turbine, heat recovery steam generator, and steam turbines) are implemented in Aspen HYSYS, and a specially tailored procedure is proposed for solving them. The modeling strategy and solution procedure can be extended to simulate the off-design operation of any CCGT plants and are generically applicable to other process simulators (e.g. Aspen Plus, Unisim, and Pro II). To evaluate the model's performance, its predictions are compared with those of an equivalent model from GateCycle. The results show the predictions of the two models (Aspen HYSYS and GateCycle) agree well. The average differences for the power outputs and thermal efficiencies of the gas turbine, steam cycle, and CCGT plant are less than 2.0%, 1.5%, and 0.6%, respectively. Besides, the differences arise primarily from the different gas enthalpy calculations. Since the model enables easy integration with various energy systems and can be made dynamic for predicting real-time behavior in Aspen HYSYS, it is very useful with wide applications.