What is the working principle of seawater desalination equipment?

Seawater desalination equipment is often used to obtain fresh water from various ships, offshore platforms, islands and other fields, mainly using distillation and Anti-Infiltration Act. What principle does it use to turn seawater into fresh water.

Principle of distillation method:

Distillation method is a method of simulating the natural water cycle. Seawater evaporates from the heat of the sun to form clouds, which condense into rain when cooled in the high air. The falling rain is freshwater. Using this main principle, various distillation desalination technologies have been developed, but they all involve converting electrical energy into thermal energy or using waste heat to evaporate water molecules from seawater into water vapor, achieving saltwater separation and then cooling to produce fresh water. This method is a traditional dilution method, but after continuous improvement, it still holds an important position to this day.

Principle of Anti-Infiltration Act method:

Reverse osmosis membrane is a kind of Semipermeable membrane with selective permeability, which allows water molecules to pass through. When the same volume of fresh water and seawater are placed on both sides of the membrane, the water molecules in the fresh water will naturally pass through the Semipermeable membrane and flow to the seawater side spontaneously, a natural phenomenon called osmosis.

When the flow stops, the water level on the seawater side will be higher than the fresh water level by a certain height, which forms a pressure difference, which is called Osmotic pressure.

If a pressure greater than Osmotic pressure is applied to the seawater side, the flow direction of water molecules will be opposite to the original seepage direction, and start to flow from the seawater side to the fresh water side. This process is called reverse osmosis.

By utilizing this principle, a high-pressure pump is used to pressurize seawater, allowing water molecules in the seawater to pass through a reverse osmosis membrane, thereby achieving the separation of water and salt.

The above are the desalination principles of two commonly used seawater desalination devices. With the advancement of technology and the continuous reduction of desalination costs, seawater desalination devices will be more widely used.