Multi-objective optimization and off-design performance evaluation of coaxial turbomachines for a novel energy storage-based recuperated S–CO₂ Brayton cycle driven by nuclear energy

The frequent fluctuation of power load in the isolated grid requires the quick response of the power system and the conventional bypass regulation for the Brayton cycle leads to energy waste. To explore the high efficiency and quick response system configuration, this paper proposes an energy storage-based recuperated S–CO₂ Brayton cycle to achieve energy storage and release by the tank and the ejector. Furthermore, the multi-objective optimization strategy is established considering the condensation margin of the compressor, the compactness and thermal efficiency of the system. The system performance in energy storage and energy release conditions are examined based on the thermodynamic analysis. The 1-D design and 3-D simulation of the compressor and turbine are completed to obtain the off-design performance. The results show that energy storage and energy release realize a decrease in power load by 38.8% and an increase in power load by 27.4%, respectively. The power load in energy release conditions is significantly affected by the pressure of the high-pressure tank. Moreover, the coupled performance of coaxial turbomachines leads to the deviation of design mass flow rate and compressor outlet pressure in rated condition but also results in a higher system thermal efficiency of 36.93%.