Design optimization of high performance dual stage pressure retarded osmosis

•Two dual stage PRO designs were evaluated.•The second PRO stage was modified in the new PRO process.•The modified design showed higher power density than old dual stage PRO design.•The modified design requires less membrane area than old dual stage PRO design.•PRO power consumption was less in the modified design.

Dual stage PRO process was proposed for power generation. The present study evaluated two design configurations of the dual stage PRO process. The old dual stage PRO design was modified to enhance the process performance. In the new design, the entire seawater flow from the first stage goes to the second stage to increase the second stage membrane flux. Seawater salinities between 32 g/L and 45 g/L were tested to investigate the effect of draw solution TDS on the process performance. The results showed that PRO process performed better at higher seawater salinity. Furthermore, the performance of the new dual stage PRO design was higher than that of the old dual stage PRO process. Power density in the new dual stage PRO design was 17.4% higher than that in the old dual stage PRO design. Mainly, this was attributed to the higher membrane flux in the modified PRO design. It was also found that the specific power consumption of the new PRO design was about 8% less than that of the old PRO design. Finally, the results also showed that for a given plant capacity, the membrane elements required in the new PRO design were less than that in the old PRO design. As such, the proposed new design would be suggested for power generation for being more efficient and at cheaper cost.