Investigation of Hydrochlorofluoroolefins as Potential Working Fluids in the Closed-Cycle OTEC Process

Abstract

Ocean Thermal Energy Conversion (OTEC) is a promising marine renewable energy technology, but its commercial viability depends heavily on maximizing cycle efficiency and using safe and environmentally sustainable working fluids. This paper analyzes the feasibility of using two newly developed hydrochlorofluoroolefins (HCFOs), specifically R1224yd(Z) and R1233zd(E), as working fluids to replace R-717 in the Ocean Thermal Energy Conversion (OTEC) cycle. The study investigates the effects of evaporation and condensation temperatures on the performance of the OTEC plant. The results indicate that optimal temperatures are 22.0 °C for evaporation and 12.11 °C for condensation. The system parameters, including cycle efficiency, objective parameter, volumetric flow ratio, turbine size parameter, and net power output of the OTEC cycle, are quantified for four working fluids: R717, R134a, R1224yd(Z), and R1233zd(E), in a 2 MW gross power capacity plant. The findings reveal that the net power output is highest when R717 is used as the working fluid, with net power available being 12.3%, 24.6%, and 26.8% lower for the OTEC plants using R134a, R1224yd(Z), and R1233zd(E), respectively. Furthermore, as compared to R1233zd(E), the plant using R1224yd(Z) as the working fluid delivers 27 kW more net power at the targeted gross power output of 2 MW. A transient analysis is performed in this study using real-time seawater temperature data collected at Kavaratti Island, which indicates that seasonal variation reduces net power by more than 25% in all four investigated working fluids.

Keywords

Ocean thermal energy conversion / Hydrochlorofluoroolefin / Working fluid / Ocean thermal energy / Fourth generation refrigerants

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