Thermodynamic Analysis and Improvement of a Flash/ORC Geothermal Plant Using ZeotropicMixtures as Working Fluids in ORC

A thermodynamic analysis of a flash/ORC geothermal plant using zeotropic mixtures as working fluid is carried out to investigate and improve the performance of the system from the viewpoint of first and second laws of thermodynamic. The mixtures of three hydrocarbons (Hexane, Cyclohexane and Isohexane) with two refrigerants (R245fa and R236ea) are investigated as the working fluid of organic Rankine cycle (ORC). Variation of first and second laws efficiencies, net output power and exergy destruction as a function of the mass fraction of refrigerants from 0 to 1 is reported. The results showed that the first and second laws efficiencies maximized at a specific value of refrigerant mass fraction. Also, the net power output of ORC shows an optimum amount by changing the refrigerant’s mass fraction. Furthermore, exergy destruction in evaporator which is the main source of exergy destruction in ORC has its lowest value in the average amounts of refrigerant mass fraction. According to the results, Cyclohexane/R236ea mixture with a ratio of 0.6/0.4 represents the best performance from the viewpoint of energy and exergy which leads the system net output power production of 7.31 MW.