Integration of desalination and energy conversion in a thermo-osmotic system using low-grade heat: Performance analysis and techno-economic evaluation

Abstract

Freshwater and electricity cogeneration systems, using renewable energy sources, can play a crucial role at the water-energy nexus. By placing a hydrophobic, porous membrane between a hot saline water flow and a pressurized cold freshwater flow, thermal-osmotic energy conversion and thermal-osmotic desalination can be implemented simultaneously. A novel open-loop freshwater and electricity cogeneration system is proposed and evaluated, which consists of a hydrophobic membrane module, a seawater pump, two heat exchangers, and a hydraulic turbine. In the base case designed for a daily freshwater production of 3.9 × 104 m3/day, the net power output is estimated to be 2.15 MWe and the energy efficiency of power generation is 0.24%. Considering the economic benefits brought by the electricity production, the water production cost is 0.36 $/m3 with a global average industrial electricity price of 0.11 $/kWh. Compared with the commercial reverse osmosis desalination technology, the desalination cost of the hybrid system is reduced by over 28%. The parameter analysis is carried out and reveals that optimizing membrane properties and operating conditions can greatly improve the energy efficiency and reduce the water production cost. Improving the liquid entry pressure and permeability coefficient and reducing the thermal conductivity of the membrane are the key to improving the application prospect of the system.