LIS-PRO: A new concept of power generation from low temperature heat using liquid-phase ion-stripping-induced salinity gradient

In this work, a new concept to convert low temperature heat (<100 °C) into electrical power is proposed and theoretically studied. This concept integrates a unique Liquid-phase Ion-Stripping (LIS) process, which uses low temperature heat to generate a salinity gradient, and a pressure retarded osmosis (PRO) process, which converts the salinity gradient into power. The LIS process utilizes a kind of organic solvent to reject ions from a saline source when going through a thermal cycle, thus producing a concentrated brine stream and a fresh water stream. The PRO process then harvests the osmotic pressure from the two streams to produce power. The whole system is a closed loop with no working medium loss. The thermal and electrical energy consumption of the system is analyzed. The overall energy efficiency of the system can reach ∼3.1% when it operates between 40 and 80 °C, and this corresponds to an exergy efficiency of ∼27%. The energy and exergy efficiencies are found to increase with higher solvent extraction efficiency and heat recovery system efficiency. Engineering better solvents can potentially achieve energy and exergy efficiency respectively to 5.6% and 90%.