Experimental study on progressive freeze-concentration based desalination employing a rectangular channel crystallizer

This paper reports an experimental study on progressive freeze-concentration based desalination of saltwater to produce drinking water, irrigation water, and concentration-reduced brine waste. A vertically-aligned rectangular channel crystallizer was utilized for the study. In the crystallizer, the saltwater flows upward over the vertically aligned cooling surface kept at a temperature adequately below the liquidus temperature and produces ice. The thawing of ice provides diluted saltwater. A parametric analysis was conducted to explore the influence of saltwater flow rate (4400-5600 ml min(-1)) and initial saltwater concentration (1.5-15 wt%) on thawed ice and liquid concentration. The freezing-thawing stages required to produce drinking/irrigation water from seawater and concentration-reduced brine waste from brine without ice seeding were determined experimentally. It was found that three and four freezing-thawing stages are required to obtain irrigation and drinking water from seawater, respectively. The three-stage and four-stage freezing-thawing of seawater achieved salt separation efficiencies of 96% and 99%, respectively, at a seawater circulation flow rate equal to 5200 ml min(-1) and a coolant inlet temperature equal to -9 degrees C. The multi-stage freezing-thawing process was adequate to separate the salt even from the brine (concentration of 5 wt% and above). After three stages, brine with an initial concentration of 10 wt% was desalinated to concentration-reduced brine waste of 2.2 wt% concentration. The three-stage freezing-thawing of brine achieved a salt separation efficiency of 78%.