Optimal selection of working fluid for the organic rankine cycle driven by low-temperature geothermal heat

Abstract

To select the optimal organic working fluid for organic Rankine cycles driven by low-temperature geothermal heat, the exergetic analysis method and PR equation of state are utilized to calculate the exergy efficiency and other main thermal performances of low-temperature geothermal heat powered organic Rankine cycles using 10 kinds of dry fluids as working fluids. The results show that: As the critical temperature of working fluid increases, the evaporation pressure, condensing pressure, output power and exergy efficiency show a decreasing trend, but the cycle thermal efficiency and the final discharge (or rejection) temperature of the geothermal fluid show an increasing trend as a whole. Moreover, the organic Rankine cycle charged with R227ea (heptafluoropropane) gets the highest power output and exergy efficiency, and the evaporation and condensation pressures are in the appropriate range, therefore, R227ea appears to be the optimal working fluid for organic Rankine cycles used in low-temperature geothermal power plant. © 2012 Springer-Verlag.