Deconstruction and modular optimization of the S-CO2 Brayton bottom cycle for waste heat recovery

Following the pursuit of improved thermodynamic performance and increasing system complexity, this study summarizes the evolutionary pathway of the supercritical CO2 (S-CO2) Brayton cycle configuration. Novel improved cycle configurations are proposed by adjusting the mixer position. To address the lack of comparative studies on single flow split S-CO2 Brayton cycle configurations with comparable system complexity, a deconstruction method is proposed. By separating the internal heat exchange components, the S-CO2 cycle configuration is decomposed into two independent modules: the non-heat exchange module (power-generating configuration) and the heat exchange module (heat exchange configuration). The results indicate that the optimal power-generation configuration after deconstruction is the parallel cross recuperative with single heating cycle I. Under various heat source conditions and maximum cycle pressures, net power output increases by 2.47–24.29% compared with that before deconstruction and even exceeds that of the typical dual flow split cycle configuration. By reconfiguring the heat exchange process during optimization, the deconstruction method effectively mitigates temperature interference caused by preheating, thereby significantly enhancing the waste heat recovery (WHR) performance of the cycle. Although the upstream mixer can reduce heat exchange exergy destruction (by up to 27.41%), its power-generation performance is limited by the high exergy destruction occurring within the mixer. Through deconstruction, this adverse effect is significantly mitigated, increasing the net power output of the corresponding cycle by 15.21%–48.64%. Multi-objective optimization results indicate that the parallel cross recuperative with single heating cycle Ⅰ represents a trade-off between power generation and heat transfer matching.