Design of Forward Osmosis Desalination Configurations: Exergy and Energy Perspectives

This study presents a detailed energy and exergy analysis of two forward osmosis (FO) desalination systems: single-pass and regenerative configurations. Both utilize osmotic pressure from a concentrated draw solution to drive water transport through a semi-permeable membrane. The regenerative system includes extra components for draw solute recovery, which increases electrical energy consumption to 188.9 kW and slightly lowers water recovery to 54%, compared to 98 kW and 60% for the single-pass FO system. Equivalent work for desalination is 1.4 kWh/m3 for single-pass and 1.8 kWh/m3 for regenerative FO systems. Exergy analysis shows the distillation column as the largest contributor to exergy destruction in both systems, responsible for over 44% of losses. The regenerative system adds 57.9 MW of chemical exergy destruction in the regenerator. Physical exergy destruction mainly occurs in the reboiler and condenser, while chemical exergy destruction is dominant in the FO membrane unit and regenerator. These findings provide valuable insights for improving the efficiency and sustainability of FO desalination technologies.