Pressure retarded osmosis for power generation and seawater desalination: Performance analysis

The present study evaluated the performance of pressure retarded osmosis–reverse osmosis (PRO–RO) process for power generation and seawater desalination. Two pre-developed software were used separately to estimate the performance of forward osmosis (FO) and RO process. The draw and feed solutions in the FO process were seawater and low-quality water; i.e. wastewater effluent and brackish water. The simulation results showed that the FO performance increased with increasing seawater salinity and decreased with increasing feed water TDS. Increasing the feed and draw solution flow rate resulted in an increase in the FO performance especially when brackish water was used as a feed solution in the FO process. Power generation from the PRO process was found to increase with increasing the TDS of seawater and the flow rate of feed and draw solutions. The simulation results, however, showed that the PRO process was more sensitive to the increase in the seawater TDS than the flow rate of feed and draw solutions. For fresh water supply, the diluted seawater from the FO process was treated by RO membrane system. Up to 31% decrease in the desalination power consumption can be achieved by the PRO–RO process. It was also found that the increase in the draw solution flow rate resulted in an increase of the permeate concentration and power consumption. This issue should be considered in the operation of the PRO–RO system in order to reduce the overall treatment cost. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.

The PRO–RO system was evaluated for combined power generation and seawater desalination. The FO process showed higher performance at higher seawater salinities and that was attributed to the higher driving force across the FO membrane. The performance of FO was further improved by increasing the flow rate of the draw solutions due to reducing the effect of concentration polarization. Draw solution flow rate, however, can't be increased indefinitely since the effect of concentration polarization cannot be completely eliminated and the higher draw solution flow rate will negatively effect the permeate TDS and power consumption in the RO process. Power generation in the turbine system was found to be also affected by the FO feed and draw solution flow rates, although the impact of changing the draw solution flow rate was higher than that of the feed solution. Therefore, it is recommended to increase the draw solution flow rate in order to generate more power from the PRO process. Furthermore, the simulation results showed that the cost of FO membrane was at least 4.5 times higher than that of the RO but it decreases with the increasing seawater salinity. However, the cost of FO membrane should be decreased in the future to encourage more investment in the process technology.