Seawater desalination technology

Seawater desalination technology, seawater due to its very high salt content, and can not be used directly, mainly using two methods to desalinate seawater, namely distillation and reverse osmosis method. The distillation process is mainly used in the super large seawater desalination treatment and the place where the heat energy is abundant. Reverse osmosis membrane method is widely applied, and the desalination rate is very high, so it is widely used. Reverse osmosis membrane method is first to extract seawater for preliminary treatment, reduce turbidity of seawater, prevent the growth of bacteria, algae and other microorganisms, and then pressurized by special high-pressure pump, so that seawater into reverse osmosis membrane, because of the high salt content of seawater, so seawater reverse osmosis membrane must have a high desalination rate, corrosion resistance, high pressure resistance, anti-pollution and other characteristics, after reverse osmosis membrane treatment of seawater, The salt content is much lower, dropping from 36,000 mg/l to around 200 mg/l. The water quality after desalination is even better than tap water, so that it can be used by industry, commerce, residents and ships and naval vessels.

There are more than 20 kinds of desalination technologies in the world, including reverse osmosis, low multi-effect, multi-stage flash evaporation, electrodialysis, pressure steam distillation, dewpoint evaporation, water and electricity co-generation, hot film co-generation and the use of nuclear energy, solar energy, wind energy, tidal energy desalination technology, as well as micro-filtration, ultrafiltration, nanofiltration and many other pretreatment and post-treatment processes.

From the perspective of broad classification, it is mainly divided into two categories: distillation (thermal method) and membrane method, among which low multi-effect distillation, multi-stage flash distillation and reverse osmosis membrane method are the mainstream technologies in the world. Generally speaking, low multi effect has the advantages of energy saving, low requirement of seawater pretreatment and high quality of desalinated water. Reverse osmosis membrane method has the advantages of low investment and low energy consumption, but it requires high pretreatment of seawater. Multistage flash evaporation method has the advantages of mature technology, reliable operation and large output, but high energy consumption. It is generally believed that low multiple effect distillation and reverse osmosis membrane method are the future directions. It is expected that during the 12th Five-Year Plan period, China's seawater desalination will reach 1.5 million to 2 million tons per day, three or four times the current capacity, and the investment scale will reach about 20 billion yuan.