Comparative life-cycle assessment of a novel osmotic heat engine and an organic Rankine cycle for energy production from low-grade heat

A comparative life-cycle assessment (LCA) was performed to evaluate the environmental impacts of an osmotic heat engine (OHE) and an organic Rankine cycle (ORC) for electrical energy generation from low-grade heat. The OHE is a novel membrane-based process that couples pressure retarded osmosis (an energy generating process) and membrane distillation (a working fluid regeneration process), whereas the ORC is an established power cycle. The LCA considered the material use for system construction and operation, and found that the environmental impacts for both the construction and operation stages of the OHE were higher than the ORC. The sensitivity analysis concluded that OHE environmental impacts could be reduced by 80% with future improvements to PRO membranes and membrane module performance. Additionally, with further improvements the OHE could be a viable energy production process that can increase energy efficiency and reduce CO₂ emissions from coal and natural gas power plants by 20.5 and 11.9 million kg of CO₂ per year, respectively.