RETRACTED: Limitations of osmotic gradient resource and hydraulic pressure on the efficiency of dual stage PRO process
Dual stage PRO process has been proposed for power generation from a salinity gradient across a semi-permeable membrane. Closed-loop and open-loop dual stage PRO system were evaluated using 2 M NaCl and Dead Sea as draw solutions whereas the feed solution was either fresh water or seawater. The impact of feed salinity gradient resource and feed pressure on the net power generation and water flux was evaluated. The results showed that power density in stage one reached a maximum amount atΔP = π/2 but the maximum net power generation occurred atΔP < π/2. This was mainly attributed to the variation of net driving pressure in stage one and two of the PRO process. The dual stage PRO process was found to perform better at high osmotic pressure gradient across the PRO membrane, for example when Dead Sea brine or highly concentrated NaCl is the draw solution. Total power generation in the dual stage PRO process is up to 40% higher than that in the conventional PRO process. This was achieved through harvesting the rest of energy remaining in the diluted draw solution. Therefore, dual stage PRO process has the potential of maximizing power generation from a salinity gradient resource.