Evolution of supercritical CO2 Rankine cycle configuration for composite waste heat recovery based on ideal cycle with case implementation

The optimization design of supercritical CO₂ (S-CO₂) Rankine cycle configuration is crucial for enhancing the efficiency of energy utilization. This paper proposes a framework for cycle configuration evolution based on construction of ideal cycle. An improved sequential Carnot cycle method is proposed and employed to establish ideal Rankine cycle under composite heat sources for the first time. Cycle matching degree, which is defined as the net power output ratio of the actual S-CO₂ Rankine cycle to the ideal Rankine cycle, is used as criterion to evaluate various modified cycle configurations. Then, a specific S-CO₂ Rankine cycle evolution case for composite waste heat recovery from liquid natural gas engine is presented. With the maximum power output of 135.3 kW achieved by the ideal Rankine cycle, analysis results indicate that prioritizing the utilization of the high-temperature heat source is beneficial to approach the superior power output. The basic cycle can only achieve a matching degree of 26.8 %. After cycle evolution, the novel configurations of dual split dual regenerative and triple split dual expansion are obtained. The triple split dual expansion configuration obtains the highest matching degree of 55.6 %, which is significantly close to the ideal cycle. While the dual split dual regenerative cycle achieves the lowest specific investment cost of 5075 $/kW. This framework delineates a clear path for the evolution of cycle configurations, offering invaluable guidance to engineering and technical professionals.