Thermodynamic, economic analysis and multi-objective optimization of an improved self-condensing transcritical CO 2 Rankine cycle with two-stage ejector for low grade heat utilization

An improved self-condensing transcritical CO2 Rankine cycle (TCRC) with two-stage ejector on the basis of the preliminarily designed one with an ejector is proposed in this study, aiming to enable the condensation of CO2 using conventional cooling source and achieve desirable performance. Thermodynamic and economic mathematical models of the improved self-condensing TCRC are developed, and detailed parametric analysis is carried out to investigate the effect of main parameters on both thermodynamic and economic performances of the system. Then the multi-objective optimization is conducted to examine the potential for performance enhancement. Thereafter, a comparative analysis of the performances between the improved self-condensing TCRC and preliminary self-condensing TCRC is performed. Results show that the improved self-condensing TCRC with two-stage ejector outperforms the preliminary one with an ejector in both thermodynamic and economic aspects, achieving a 3.93% increase in maximum exergy efficiency and a 13.84% reduction in minimum unit net power cost through multi-objective optimization. Under optimal conditions, the exergy efficiency for the improved self-condensing TCRC is 45.48% with a unit net power cost of 0.1241$/kWh.