Thermo-economic analysis and optimization of a novel self-condensing transcritical CO₂ power cycle with ejector refrigeration

The transcritical CO₂ power cycle stands out as a promising approach for the utilization of waste heat and renewable energy, but its practical application is restricted by the condensation challenges of working fluid. To tackle this issue, a novel self-condensing transcritical CO₂ power cycle (SC-TCO₂PC), which integrates the transcritical CO₂ power cycle with an ejector refrigeration cycle, is proposed. Detailed mathematical models are formulated, and parametric study is carried out to illustrate the correlations between the crucial parameters and system performance from both thermodynamic and economic viewpoints. Then a multi-objective optimization is applied to explore the potential for performance enhancement. Furthermore, the comparative analysis of the SC-TCO₂PC and the recuperative supercritical CO₂ Brayton cycle (SCO₂BC) are conducted under optimized conditions. The results demonstrated that the enhanced turbine inlet pressure and temperature positively influence the thermal-economic performance of the SC-TCO₂PC. Furthermore, the maximum thermal efficiency of 43.90 %, exergy efficiency of 72.97 % and minimum cost per unit of electricity of 0.0372$/kWh are attainable for the SC-TCO₂PC, reflecting the improvements of 4.88 %pt for maximum thermal efficiency, 6.60 %pt for maximum exergy efficiency and a 8.87 % reduction for minimum unit power cost in comparison to the recuperative SCO₂BC. In optimum conditions, the SC-TCO₂PC is capable of achieving a thermal efficiency of 42.11 % and an exergy efficiency of 70.54 % with the cost per unit of electricity of 0.0440$/kWh.