Design Comparison for the Supercritical CO2 Brayton Cycle with Recompression and Thermal Regeneration: Numerical Results

The supercritical carbon dioxide (sCO2) Brayton cycle shows obvious advantages (e.g., higher efficiency, compact system design, etc.) compared with the traditional Rankine cycle for high temperature thermal sources due to the special physical properties of CO2 near the critical points. Though it is generally considered suitable for a wide range of applications, including power generation systems, and has become a very hot topic, real system efficiency is still a problem, for the system efficiency design and optimization analysis. This study proposed a recompression sCO2 Brayton cycle with the heat regeneration process and thermodynamic optimization of the sCO2 Brayton cycle was tested. For the sCO2 Brayton cycle, the parameters, especially for the main compressor inlet temperature, have significant effect on the system performance, and it was investigated in detail. The influence of the adiabatic efficiency of the compressors and turbines and the heat transfer temperature difference of the recuperators on the cycle efficiency were analyzed to evaluate the system performance under actual equipment parameters and the feasibility of practical applications. The main compressor inlet temperature has a significant effect on performance, and the system show high efficiency only when the main compressor inlet temperature is close to the critical point. When the isentropic efficiency of the compressors or the turbines decreases to 0.7 or the minimum heat transfer temperature difference of the recuperators increases to 50.0 °C, the cycle efficiency drops close to 30.0%, which has few advantages compared with the traditional Rankine cycles. Still, the real application parameter of compressor inlet is considered one critical reason for the efficiency analysis.