Vacuum Freezing

Vacuum Freezing or Freeze desalination is a process in which the temperature and pressure of the seawater is lowered in order to produce ice crystals. The ice so produced is washed and melted in order to obtain pure water. Freeze process technology is still informative stage and is being developed for use in

The process work on the principle that on freezing the salts dissolved in the saline water are excluded from the ice. The saline water is cooled and then sprayed in a vacuum chamber at a low pressure. This results in the vapor to be released from the water thereby removing more heat and causing the formation of ice. Since the density of ice is less it flows on the brine and is later washed with fresh water and melted. The fresh water produced is flush out of the washer melter.

Ice can be separated from the brine through number of process but the popular techniques adopted is flowing the slush upward in the column. Using peripheral discharge screens, the brine is then drawn off. For the remaining brine in the ice counter current flow of freshwater is fed into the top of the column. During washing only fraction of freshwater is lost. Melter is used to melt the ice and to recover fresh product water. The energy is recovered from the fresh water using heat exchanger that also precol the feed and reject the brine.

With respect to other thermal processes, this method require less energy. Susceptibility to the scaling problem is also very less in this system. Though the technology has potential it is still not used for the commercial process.