The production of fresh water from sea water is produced from an evaporation of the water from the salt water and then condensing the purified water vapor. Another commercial method is the use of reverse osmosis. Fresh water also, can be produced by using a freezing process that separates the water as it freezes from the salt water.
Desalination of water by freezing has been studied, but not commercialized. One such desalination process using the cold temperatures of liquefied natural gas (LNG) is shown in U.S. Pat. No. 3,675,436, issued on Jul. 11, 1972. This process uses LNG to cool butane to a liquid and sprays the liquid butane into a crystallizer with seawater to form a butane-ice-brine mixture. The drawback of this process is the use of an intermediate heat exchange material, and the direct mixing of the butane with the seawater to form the butane-ice-brine mixture. This requires further processing to remove and recover the butane from the desalinated water and from the brine.
Even when there is no direct contacting of a cold hydrocarbon stream with seawater, the use of LNG for freezing seawater involves the liquefaction of a higher hydrocarbon stream for subsequent use in freezing seawater, as shown in U.S. Pat. No. 3,892,103, issued on Jul. 1, 1975. The use of an intermediate heat transfer medium requires more equipment, and entails greater losses, or lower efficiency in the process of freeze desalination.
A more common method of freeze desalination involves the use of vacuum freezing of water by spraying cooled seawater into an evacuated chamber creating small ice crystals that are subsequently separated from the brine and then melted. An example of this process is shown in U.S. Pat. No. 3,724,229, issued on Apr. 3, 1973. This process has the significant drawback of working with systems under vacuum.
Improvements in the process of freeze desalination can improve access to fresh water, while saving costs.