An optimal split ratio in design and control of a recompression supercritical CO2 Brayton system

Abstract

The sCO2 Brayton cycle is considered an alternative to the conventional Brayton and Rankine cycles. The recompression Brayton cycle is advantageous because of its simple cycle layout and high cycle efficiency. The split ratio (SR) is defined as the recompression fraction of the working fluid that significantly affects the corresponding parameters of the system, particularly the cycle efficiency. However, studies focusing on the influence of SR on the design and off-design performance remain limited. The factors influencing the optimal SR and regulation mechanism under the design and off-design conditions of recompression cycle are considered in this study. The results demonstrate that the optimal SR under the design conditions is primarily affected by the high pressure, low pressure and efficiency of the recuperators. The optimal SR decreases with a reduction in the load demand, and the recompression loop can be cut off under a low load to improve the cycle efficiency. A simplified control can be achieved by controlling the temperature difference at the flow merge point to achieve a higher system efficiency. Moreover, the SR regulation mechanism is unaffected by the load control method. These findings are of significance to recompression configuration with different design parameters.