Optimal design of heat exchange configuration for the supercritical CO2 Brayton cycle applied to gas turbine waste heat recovery

The thermodynamic performance of improved supercritical CO2 closed Brayton cycles applied to gas turbine waste heat recovery is achieved at the expense of greater system complexity. This study investigates the improvement pathways of the supercritical CO2 Brayton cycle by analyzing the internal heat exchange configuration and summarizes five single flow split cycles that are most frequently investigated in existing literature. Three novel cycles are proposed by relocating the mixer position and increasing the heating stages. Based on the arrangement of recuperators, the eight cycles comprising both single heating and dual heating configurations with comparable complexity are categorized into two types: parallel recuperative cycles and series recuperative cycles. Under key assumptions including steady-state operation, the isentropic model for turbomachinery (constant isentropic efficiencies), and the specified pressure drop model for heat exchangers (constant pressure drop percentages), comprehensive optimization and analysis are carried out using thermodynamic performance and economic cost as evaluation criteria. Results indicate that among the single flow split with dual recuperative cycles, the parallel cross recuperative with single heating cycle Ι (mixer located after the hot-side outlet of the recuperator) and the series recuperative with dual heating cycle achieve the highest net power output under different operating conditions, respectively. The former reduces unit power generation cost by 8.96% compared to the simple recuperative cycle at high heat source temperatures (600 °C). The latter achieves near-maximum waste heat recovery efficiency across all heat source conditions due to the absence of temperature interference between CO2's heat absorption and flue gas's heat release.