Thermodynamic analysis of a solar thermal facilitated membrane seawater desalination process

Abstract

Seawater reverse osmosis (RO) desalination is an attractive but energy-intensive process used to produce freshwater. A reduction in high-grade energy (electricity) consumption during the seawater RO desalination process can be achieved by utilizing renewable energy sources and harvesting osmotic energy during the desalination process. This study proposes a novel method to reduce the energy consumption of RO desalination by incorporating solar thermal energy into the reverse osmosis-pressure retarded osmosis (RO-PRO) hybrid system (medium capacity of 5000 m3/day). Osmotic energy is harvested by mixing seawater and tertiary wastewater in PRO at an elevated temperature before the RO desalination step. Solar thermal energy is used to heat the solutions to enhance the energy production of the PRO. The hybrid system can achieve wastewater reclamation and RO brine management simultaneously. Energy analysis shows that the net specific energy (electricity) consumption of the hybrid system is as low as 0.39 kWh/m3, which is much lower than that of conventional RO desalination systems (∼1.1 kWh/m3). Exergy analysis is conducted on the system to determine the second law efficiency of the system. In addition, the analytic hierarchy process shows that the overall system operation benefits from a high PRO operating temperature.