Development, 4E-analysis, and optimization of a seawater thermal energy-driven desalination system based on seawater source heat pump, multi-effect desalination, and pressure retarded osmosis with reduced effluent concentration

There is an urgent call for more sustainable water desalination technologies to secure the supply of the everincreasing freshwater demand while lowering the dependence on fossil resources, mitigating GHGs and pollutant emissions, and hindering aquatic ecosystem degradation. In this regard, this research proposes a novel integrated system composed of a seawater source heat pump, multi-effect desalination, and pressure retarded osmosis, which utilizes seawater thermal energy as a renewable heat source to drive the system. Energy, exergy, exergoeconomic, and environmental (4E) analyses are performed. Sensitivity analyses are conducted to determine the effective parameters of the system's performance. Besides, single objective optimization is applied for different modes to ascertain the most optimal operating condition of the system. According to the results, the heat pump condenser has the largest share in exergy destruction with 29 %. After that, the expansion valve with 12 %, the compressor with 11 %, and the seawater heat exchanger with 8 % are in the next rank. PRO membrane modules and heat pump compressor with 100 % and 60.3 % present the highest exergoeconomic factors, respectively, while heat pump condenser and seawater heat exchanger yield the lowest values with 0.33 % and 2.48 %, respectively. Comparing the proposed system results in its optimum state with conventional MED plants reveals that the system is capable of producing freshwater at an 80 % lower price and a 15 % decrease in carbon dioxide emissions. Integration of the PRO unit downstream of the MED process has led to a reduction of brine salinity and temperature from 51.89 to 39.4 g/kg and 38 to 32 celcius, respectively.

Automated summary

There is a pressing need for sustainable water desalination technologies to meet the growing demand for freshwater. This study proposes an integrated system that utilizes seawater thermal energy to drive the system and evaluates its performance through energy, exergy, exergoeconomic, and environmental analyses.