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• Effects of key parameters on performance of CO 2 -based mixture cycles are revealed. • Comprehensive performance evaluation method is proposed based on η exe, SPT - w -Δ T MH. • Trade-off relations for 3 performance metrics are found based on Pareto fronts. • Optimal cycle configuration, operating parameters and additive are recommended. This study provides an exploration on improving the performance of solar power tower (SPT) plant via integrating with the CO 2 -based mixture Brayton cycle, and proposes a comprehensive comparison method. The effects of the crucial parameters on the SPT system are firstly revealed. Then, a comprehensive evaluation method is proposed based on 3 performance metrics including exergy efficiency, specific work and temperature difference of the main-heater, which are used to assess the thermodynamic performance and the compatibility between the thermal storage system and power cycle. Finally, the trade-off relationships of these metrics are found. The optimal layout, additive and operating parameters are also pointed out based on the comparative results to meet different design requirements. The findings show that the effects of crucial parameters on the performance of SPT system are not monotonous and individual criterion cannot comprehensively evaluate the system performance. Using xenon as an additive can yield excellent performance with higher exergy efficiency and better compatibility between cycle and thermal storage system than the CO 2 alone. While the ability to generate specific work is decreased to 105–112 kW·kg−1 with xenon-added that compares to the inter-cooling S-CO 2 cycle (121–130 kW·kg−1). When the exergy efficiency is required higher than 33%, the inter-cooling CO 2 /xenon cycle is the primarily recommended layout for its large specific work and good compatibility between the thermal storage system and cycle. The findings provide a novel way to improve the efficiency of SPT system as well as the compatibility between the cycle and thermal storage system. [ABSTRACT FROM AUTHOR]

Supercritical CO 2 (S-CO 2 ) Brayton cycles are recently proposed to be integrated into the solar power tower (SPT) due to their high efficiency and compactness. Comparison of different S-CO 2 Brayton cycle layouts is of great significance for selecting a suitable one in the SPT plant. Both of the efficiency and specific work are important performance criteria for the SPT plant. However, previous studies compared only one individual criterion, or both of them just separately. This paper puts forward a systematic comparison of different S-CO 2 Brayton cycle layouts based on multi-objective optimizations. The two performance criteria are compared simultaneously between different S-CO 2 cycle layouts by comparing the Pareto optimal fronts obtained from multi-objective optimizations. The results suggest that the inter-cooling cycle layout and the partial-cooling cycle layout can generally yield the most excellent performances, and followed by the recompression cycle layout and the pre-compression cycle layout, while the simple recuperation cycle layout has the worst performances. The advantages of the partial-cooling cycle layout and the inter-cooling cycle layout are more prominent compared with the other cycle layouts in the case of high compressor inlet temperature. The provided systematic comparison can be helpful in selecting the most suitable cycle layout for the application in SPT when there are specified requirements for the efficiency and the specific work. In addition, novel salts with high upper limit temperature (higher than 650 °C) are recommended to be developed as the heat transfer fluid for improving system performances. [ABSTRACT FROM AUTHOR]