Economical evaluation and optimization of organic Rankine cycle with mixture working fluids using R245fa as flame retardant

A detailed economic model of organic Rankine cycle (ORC) system using mixtures as working fluid has been built. By using R245fa as the flame retardant, R245fa/Isopentane, R245fa/Pentane, R245fa/Cisbutene and R245fa/Butene were considered as the potential working fluids. The heat source temperatures investigated were 373.15–453.15 K. The optimization of 4 mixture and 5 pure working fluids were carried out with the objective function of minimizing the Electricity Production Cost (EPC). Genetic Algorithm (GA) was employed as the optimized method. Different from the most of the optimization researches about ORC with mixture working fluid, the mixture composition was set as one of the variables in the present work. The results show that the mixture working fluid is more economic-efficient than pure working fluid. The lower EPC value obtained by mixture working fluid was mainly due to the decrease of capital cost, which is essentially caused by the decrease of capital cost of the evaporator. R245fa/Isopentane and R245fa/Pentane were recommended as the optimal working fluids for their minimum EPC values. In addition, the correlations between the optimized mixture composition and heat source temperature were obtained.