Enhanced Dual Stage PRO Process for Power Generation
Dual stage PRO process was evaluated for power generation using colossal salinity gradient resource. 2 M and Dead Sea brine were considered as the draw solution while fresh water and seawater of different salinities were the feed solutions of the PRO process. Closed-loop and open-loop PRO systems were investigated and power density was calculated in stage one and two of each PRO system. The impact of internal and external concentration polarization on the water flux was evaluated. As expected, the theoretical water flux was much lower than the actual water flux due to the effect of concentration polarization. Reverse salt diffusion was also calculated in open-loop PRO process which results in draw agent loss and lower process performance. The results show that dual stage PRO process is more efficient than conventional PRO process especially when the draw solution is concentrated brine. High efficiency Dual Stage PRO (DSPRO) process may replace the conventional PRO process in future because of its higher performance especially at high salinity gradient.
The present study investigates the application of dual stage PRO process for power generation using colossal salinity gradient resource. Impact of feed and draw solutions and operating parameters on the performance of dual stage PRO process was evaluated. Closed-loop and opened-loop dual stage PRO system were evaluated using 2 M NaCl and Dead Sea draw solutions respectively. The feed solution was either fresh water or seawater. The impact of concentration polarization and salt back diffusion was taken into account in the membrane flux calculation. The results showed that increasing feed salinity flow rates resulted in a trivial increase in the first stage permeate flow rate but there was a slight decrease of the second stage permeate flow rate. Whereas increasing the draw solution flow rate caused a tangible increase in the first and second stage permeate flow rates. Depending on the feed salinity and operating pressure, net power generation increased between 65% and 80% when the second stage was introduced. Increasing feed salinity from 32 g/L to 50 g/L didn't significantly affect the performance of dual stage PRO process because underperformance of the first stage was compensated in the stage of the PRO process. The net power generation was more than 90% of the gross power generation whereas power consumption was less than 10% of the gross power generation. Dual stage PRO process demonstrated high efficiency of power generation without compromising the net power consumption due to introducing the second PRO membrane process.
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