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.
