Conceptual design of novel He-SCO2 Brayton cycles for ultra-high-temperature concentrating solar power

Abstract

In this study, to improve the power cycle performance of the ultra-high-temperature (1300 °C) concentrating solar power, four novel He-SCO2 combined Brayton cycles are conceptually designed. After the design, firstly, parameter analysis of the cycles is conducted by developing a thermodynamic model. It is found that two key performance criteria, including the thermal efficiency of the cycle and the temperature difference of the heat transfer fluid, are affected by many parameters, where the temperature difference represents the capability to couple with the thermal energy storage. Moreover, it is found that the two criteria cannot be maximized concurrently by an identical group of operating parameters. Then, multi-objective optimizations are employed to optimize the cycles, where the thermal efficiency and the temperature difference are regarded as the objective functions. The results suggest that the He-SCO2 cycles can achieve better performance than a typical He cycle. Moreover, comparisons of the Pareto optimal fronts of the four He-SCO2 cycles show that the combined cycle with more components can achieve superior performance than those with fewer components. The cycle 4 can yield the highest optimized thermal efficiency of 64.72%, and the cycle 3 can yield the highest temperature difference of 1014.7 °C. Moreover, it is found different cycles can be recommended under different requirements. If the thermal efficiency is required to be as high as possible, the cycles 3 and 4 should be suggested. If the temperature difference is required to be as large as possible, the cycle 1 that needs the fewest components should be recommended. Comparisons among the optimal solutions of the four He-SCO2 cycles show that the cycles 3 and 4 should be recommended when the thermal efficiency and temperature difference are required to be balanced. The optimal cycles 3 and 4 can provide quite high thermal efficiencies of 60.49% and 60.74%, respectively. And their corresponding temperature differences reach 906.1 °C and 899.7 °C, respectively. The above results suggest the designed He-SCO2 cycles are promising for improving the power cycle performance under ultra-high-temperature.