Energy, exergy, exergoeconomic, economic, and environmental analyses and multiobjective optimization of a SCMR–ORC system with zeotropic mixtures

Abstract

This paper proposes a SCMR–ORC system with zeotropic mixtures. Zeotropic mixtures are separated into two pure fluids in a partial condenser, the pure fluids recover condensation heat in a gas–liquid heat exchanger, and are then compressed, mixed, and recycled. Energy, exergy, exergoeconomic, economic, and environmental (5E) models based on the residual Helmholtz free energy are established to analyze the SCMR–ORC system performance, which is then compared with that of a SCR–ORC system with pure fluids. Multiobjective optimization is performed to obtain 3D Pareto frontiers, and TOPSIS is used to reveal the best performance. The results indicate that when the mass fraction of the low-boiling-point fluid (θ) is low, the SCMR–ORC system can reduce the condensation heat released and increase the condensation heat recovery, and its 5E performances are better than those of the SCR–ORC system. The exergy destruction sum of the partial condenser and gas–liquid heat exchanger can be reduced by 101.03 kW, and their capital cost rate can be saved by 34.89 $/h. The optimal bubble point evaporation temperature of three zeotropic mixtures is approximately 80 °C, their optimal outlet temperature at expander 1 is in the range of 42–45 °C, and their optimal θ is small.