Thermodynamic analysis and comparison for different direct-heated supercritical CO2 Brayton cycles integrated into a solar thermal power tower system

In this paper, a complete mathematical model is developed to carry out the thermodynamic analysis and comparison for different direct-heated S-CO2 Brayton cycles (simple, pre-compression, recompression, partial-cooling, and intercooling) integrated into a solar power tower (SPT) system. Based on the model, the effect of turbine inlet temperature (TIT) on the thermodynamic performances of the receiver, the thermal energy storage unit, the S-CO2 power cycle blocks and the integrated SPT systems is investigated respectively for these cycles. Additionally, a comparison of cycle efficiencies and overall integrated SPT system efficiencies is performed for five S-CO2 cycles at a series of total recuperator conductance (UA(totat)) values. The results reveal that the TIT exhibits a parabolic effect on the overall efficiencies for each S-CO2 cycle, and the intercooling S-CO2 cycle achieves the highest overall efficiencies followed by the recompression, the partial-cooling, the pre-compression, and the simple cycles at different TIT values. Furthermore, the partial-cooling cycle possesses the highest overall specific work at each TIT and offers higher overall efficiencies than the recompression cycle at a constant TIT (650 degrees C) as the UA(total) is rather low, having the potential to reduce the costs of integrated SPT systems with limited UA(total) values. (C) 2017 Elsevier Ltd. All rights reserved.