Comparative thermo-economic analysis of low-GWP refrigerants and zeotropic blends for organic Rankine cycles under variable ambient conditions

This study presents a comprehensive energy-exergy-economic assessment of a recuperated organic Rankine cycle employing bio-alcohol-based binary mixtures 2-propanol/1-butanol, 2-propanol/water, and ethanol/water as environmentally benign alternatives to conventional fluorocarbon refrigerants. The organic Rankine cycle model was developed in Aspen Plus and validated against published experimental literature with deviations below 2%, ensuring model reliability. An integrated framework was applied to evaluate system performance under varying operating conditions. At sub-atmospheric condenser pressure (0.1 bar), ethanol/water (0.5/0.5) achieved the highest turbine power output of 480.9 kW, representing nearly a fourfold increase compared to the conventional R245fa/isopentane blend (127.1 kW). The 2-propanol/water mixture exhibited superior second-law performance, attaining the highest exergetic efficiency (82.65%) and the lowest exergy destruction ratio (1.26), indicating minimal irreversibility. Thermal efficiency for bio-alcohol mixtures increased from approximately 22% at 1 bar to 27–28% at 0.1 bar, demonstrating strong sensitivity to condenser pressure, and the optimal performance is consistently observed near a 0.5 mole fraction of alcohol. Economic analysis reveals that ethanol/water and 2-propanol/water mixtures offer the lowest levelized cost of electricity (0.067 to 0.073 USD/kWh), substantially outperforming conventional R245fa/isopentane blends (0.245 to 0.444 USD/kWh). The findings demonstrate that bio-alcohol-based mixtures, being low-GWP and ODP-free, provide a technically robust and economically competitive solution for sustainable organic Rankine cycle power generation. Future work will focus on supercritical operation, transient performance, and experimental validation.