Performance optimization of combined supercritical CO2 recompression cycle and regenerative organic Rankine cycle using zeotropic mixture fluid

Thermodynamic and exergoeconomic analysis are performed for a novel combined supercritical CO2 (S-CO2) recompression cycle and regenerative organic Rankine cycle (ORC) using zeotropic mixture. Comprehensive parametric studies are carried out to investigate the effect of significant system parameters as pressure ratio, split ratio, evaporation temperature, pinch point temperature difference in the evaporator and the mass fraction of zeotropic mixture on the exergy efficiency and total product unit cost. Employing the multi-objective optimization method based on genetic algorithm and the TOPSIS (Technique for Order Preference by Similarity to Ideal Situation) decision making, the Pareto front solutions and optimum system parameters are obtained. In particular, several zeotropic mixtures are parameterized and used as a decision variable to participate in the multi-objective optimization process to obtain the optimal zeotropic mixture. The result shows that the optimal zeotropic mixture is R236fa/R227ea (0.46/0.54). The optimum values of exergy efficiency and total product unit cost are found to be 73.65% and 10.93 $/GJ, respectively. Furthermore, comparison analysis reveals the superiority of the proposed combined cycle to the single S-CO2 cycle and the combined S-CO2 cycle and basic ORC.