Thermodynamic and economic analysis and multi-objective optimization of a novel transcritical CO2 Rankine cycle with an ejector driven by low grade heat source

Transcritical CO2 Rankine cycle (T-CO2) is a promising technology for the utilization of low temperature heat source. The low critical temperature of CO2 (about 31 °C) leads to a restriction in the practical application of the cycle, since CO2 could hardly be condensed into liquid using higher temperature heat sink under the environment conditions. In this paper, a novel transcritical CO2 Rankine cycle with an ejector is proposed to solve the condensation problem of CO2 under the higher temperature heat sink. By establishing the mathematical model, a parametric analysis is carried out to examine the effects of five key parameters on thermodynamic and economic performances of the system. A multi-objective optimization is also conducted to obtain the optimum performance of cycle. The results indicate that increasing turbine inlet temperature and ejector back pressure could increase the exergy efficiency. In addition, lower investment cost of the system could be achieved by increasing the turbine back pressure and the valve expansion pressure. Furthermore, according to the Pareto frontier solution of multi-objective optimization, the exergy efficiency could reach a maximum of 19.33% and the investment cost of the system could reach a minimum of 657.9 × 103 USD.