Organic Rankine cycle environmental impact investigation under various working fluids and heat domains concerning refrigerant leakage rates

More recently, exploration and utilization of the renewable or waste fuel sources are increasingly attracting people's attention toward the power generation in organic Rankine cycle (ORC) system, while the sustainability is usually neglected, only few simple and fragmented studies there. In this study, the ORC environmental impacts (EIs) have been revealed comprehensively from working fluid and heat domain aspects for the functional description of impact categories. The effect of ORC refrigerant leakage aspects, which is mostly neglected in previous ORC studies, is involved in the environmental performance assessment and of high importance for high-global warming potential (GWP) working fluids. GWP, as the most serious EI, is revealed with a constant turbine output power (30kW). A similar to 30% total emission is produced for R227ea (GWP(100) 3220) from leakage aspects,similar to 24% for R236ea (GWP(100) 1200),similar to 28% for R245fa (GWP(100) 950), and similar to 60% for SES36 (GWP(100) 3710), respectively. In general, the emission due to the energy consumption by the pump power dominates the largest, followed by the refrigerant annual leakage, refrigerant end of life, etc. A working fluid with a higher critical temperature and a higher heat domain, and a lower condensing temperature and a lower evaporating pressure can favor a lower emission. Utilizing the fluids with a lower GWP can produce 50-84% emission reduction compared with high-GWP ones, and adding the annual leakage rate from 2 to 8% for high-GWP fluids produces 60-124% total emission rise. Increasing the pump or turbine efficiency from 75 to 90% can give a 10-16% emission reduction. Other EIs of the inventory have also been briefly studied.