to the availability of fresh water produced by desalting brackish water and seawater.About half of the world s desalted water is produced with heat to distill fresh water from seawater. The distillation process mimics the natural water cycle in that saltwater is heated, producing water vapor that is in turn condensed to form fresh water. In a laboratory or industrial plant, water is heated to the boiling point to produce the maximum amount of water vapor. The process that accounts for the most desalting capacity for seawater is multi-stage flash distillation, commonly referred to as the Multi-Stage Flash process or MSF.In the MSF process, seawater is heated in a vessel called the brine heater. This is generally done by condensing steam on a bank of tubes that carry seawater, which passes through the vessel or brine-heater. This heated seawater then flows into another vessel, called a stage; where the ambient pressure is lower, causing the water to immediately boil. The sudden introduction of the heated water into the chamber causes it to boil rapidly, almost exploding or flashing into steam. Generally, only a small percentage of this water is converted to steam (water vapor), depending on the pressure maintained in this stage, since boiling will continue only until the water cools (furnishing the heat of vaporization) to the boiling point. This process of lowering ambient pressure continues for many stages depending on the size of the plant. Distillation is not the only means of saltwater purification. Another process includes membranes.In nature, membranes play an important role in the separation of salts, including both the process of dialysis and osmosis, which occur in the body. Membranes are used in two commercially important desalting processes: Electrodialysis and reverse osmosis. Each process uses the ability of the membranes to differentiate and selectively separate salts and water. However, membranes are used differently in...
