Optimal selection of supercritical CO2 Brayton cycle layouts based on part-load performance

Abstract

The supercritical CO2 (S–CO2) Brayton cycle is considered a promising power generation system owing to its high efficiency and compactness. This cycle has numerous layouts which have been extensively investigated for design condition performance, whereas it often operates under part-load conditions, Therefore, it is vital to compare layouts based on part-load performance. Because part-load performance is influenced by control strategies and layout elements such as recompression, reheating, and intercooling processes, the part-load performance of four typical S–CO2 Brayton cycles including simple recuperated cycle, recompression cycle, reheating cycle, and intercooling cycle with different control strategies are explored using dynamic models. The results indicated that the thermal efficiency of the four layouts was simultaneously influenced by the layouts and control strategies. Safety performance is mainly determined by the control strategies. Moreover, when the turbine bypass valve and inventory are adopted to follow the load, the intercooling cycle overtakes the reheating cycle to attain the maximum thermal efficiency at low and medium loads. There was no overpressure or surge for the four layouts with the necessary controllers. However, when using bypass valves following the load, the four layouts are at risk of operating with overloaded drive motors at low loads. This is beneficial for guiding the selection of layouts and corresponding control strategies in different operation scenarios.