A thermodynamic system of coal-fired power unit coupled S–CO2 energy-storage cycle

Abstract

An S–CO2 energy-storage cycle system is added to a 660 MW coal-fired power unit to increase operational flexibility. With a round-trip efficiency (RTE) of 56.14%, a thermodynamic system for coal-fired units (with an additional S–CO2 energy-storage cycle) is built. Turbine extraction steam was used as energy source for the energy-storage system. An analysis of the impact of different factors on the thermodynamic system-performance reveals that both the S–CO2 flow rate and the compressor/turbine pressure ratio have a significant impact. For example, a 5 kg/s increase in S–CO2 mass flow rate improves the RTE by roughly 5%. Furthermore, the system RTE increases by about 10% when the S–CO2 turbine pressure ratio was increased by 1.0. The higher the steam temperature of the energy-storage source, the lower the RTE. Moreover, the effect of both S–CO2 flow rate and turbine pressure ratio on the system investment cost and payback period is determined based on a technical and economic analysis. This study provides a reference that can be used to improve the operational flexibility of coal-fired power units.