Waste heat recovery through organic flash cycle (OFC) using R245fa-R600 mixture as the working fluid

R245fa and R600 are two working fluids with which organic flash cycle (OFC) yields acceptable thermodynamic and economic performance to recover waste heat from low-temperature flue gas free from SO2. However, very high flammability of R600 and higher global warming potential (GWP) of R245fa are two issues of serious concern. Mixture with suitable mole fraction of these two fluids as the optimum working fluid for OFC is explored in this study. A mixture of R245fa and R600 with a mole fraction ratio (0.6/0.4) is selected conservatively as the working fluid of the OFC to suppress the flammability of R600. The corresponding value of GWP of the mixture comes below 800 kg of CO2 per kg of working fluid. It is observed that OFC using this mixture may yield higher work output per kg of flue gas flow and lower bare module cost/kW compared to that of OFC using either of the pure working fluid. OFC yields the highest work output per kg of flue gas for an R245fa/R600 mixture with (0.4/0.6) mole fraction ratio. Bare module cost per unit power output becomes a minimum when R245fa mole fraction is 0.37 in the mixture.