What Is Water Desalination?

Desalination is the use of seawater desalination to produce fresh water. ^[1] is an open source incremental technology to realize water resource utilization, which can increase the total amount of fresh water without being affected by time, space and climate, and can ensure stable water supply for coastal residents' drinking water and industrial boiler make-up water.

Desalination is the use of seawater desalination to produce fresh water. ^[3]

Sea water desalination

There are more than 20 kinds of desalination technologies in the world, including reverse osmosis, low multi-effect, multi-stage flash, electrodialysis, steam distillation, dew point evaporation, combined hydropower, hot film cogeneration, and the use of nuclear, solar and wind , Tidal energy seawater desalination technology, etc., as well as microfiltration, ultrafiltration, nanofiltration and other pre-treatment and post-treatment processes.

From the big classification, it can be divided into two categories: distillation method (thermal method) and membrane method. Among them, low-efficiency distillation method, multi-stage flash evaporation method and reverse osmosis membrane method are the mainstream technologies in the world. Generally speaking, low multi-effect has the advantages of energy saving, low requirements for seawater pretreatment, and high quality of desalinated water; reverse osmosis membrane method has advantages such as low investment and low energy consumption, but high requirements for seawater pretreatment; multistage flash method has technology The advantages are mature, reliable operation and large output, but the energy consumption is high. It is generally believed that low-efficiency distillation and reverse osmosis membrane methods are the future direction. During the "Twelfth Five-Year Plan" period, China's desalination will reach 1.5 million to 2 million tons per day, which is three to four times the existing capacity, and the investment scale will reach about 20 billion yuan.

Principle of frozen seawater desalination method: The three-phase point of seawater is a special point where the three phases of seawater vapor, liquid, and solid coexist and reach equilibrium. If the pressure or temperature deviates from the three-phase point, the balance is broken, and the three phases will automatically approach one or two phases. Vacuum freezing seawater desalination is a low-cost desalination method that uses the three-phase point principle of seawater and uses water itself as a refrigerant to simultaneously evaporate and freeze seawater. The ice crystals are then separated and washed to obtain desalinated water. Compared with distillation method and membrane desalination method, frozen seawater desalination method has low energy consumption, light corrosion and scaling, simple pretreatment, small equipment investment, and can handle seawater with high salt content. It is an ideal seawater desalination method. law.

Global desalination daily output is about 35 million cubic meters, 80% of which is used for drinking water, which solves the problem of water supply for more than 100 million people, that is, 1/50 of the world's population provides drinking water by desalination. There are more than 13,000 seawater desalination plants in the world. As a substitute and incremental technology for freshwater resources, seawater desalination is more and more valued by many coastal countries in the world. The total global direct use of seawater as industrial cooling water is about 600 billion cubic meters per year. A large number of valuable freshwater resources are replaced by the left and right; the world extracts 50 million tons of salt, more than 2.6 million tons of magnesium and magnesium oxide, and 200,000 tons of bromine every year. Desalination requires a lot of energy, so the economic benefits are not high in non-rich countries.

The lack of fresh water resources in the world has become a growing concern. Some people predict that in the 19th century, there will be competition for coal, in the 20th century for oil, and in the 21st century, for water.

As an open source incremental technology for water resources, desalination has become an important way to resolve the global water crisis. By 2006, more than 120 countries and regions in the world were applying desalination technology, and the global daily output of desalination was about 37.75 million tons, of which 80% was used for drinking water, which solved the problem of water supply for more than 100 million people.

"Ask for fresh water from the ocean" has formed an emerging industry. As of the end of 2006, China's daily desalination capacity was close to 150,000 tons, doubling the previous year. China has made major breakthroughs in the key technologies of mainstream desalination, such as reverse osmosis and distillation, and has completed the 3000 m3 / day low-temperature multi-effect seawater desalination project with independent intellectual property rights and the 5000 m3 / day reverse osmosis desalination project; The seawater DC cooling technology has entered the 10,000 cubic meters / hour industrial demonstration stage. The cost of desalination in China is gradually decreasing, and it is close to 5 yuan / m3.

Although China's seawater desalination basically has the conditions for industrialized development, its research level and innovation ability, equipment development and manufacturing ability, system design and integration are still far from foreign countries. It is imperative to form a complete industrial chain of China's desalination equipment market as soon as possible. Focusing on the key issues restricting the cost reduction of seawater desalination, develop core technologies such as membranes and membrane materials, and key equipment, and develop new technologies, processes, equipment and products for seawater desalination with independent intellectual property rights.

United States

The Ministry of Water Resources is considering whether to include desalination in the overall planning of the Ministry of Water Resources and related plans such as local water resources allocation. For this reason, a major issue of the Ministry of Water Resources in 2014 is "Current Situation, Problems and Development Countermeasures of Seawater Utilization in China".

Since July 25, 2011, the Ministry of Water Resources has organized related research groups to conduct six-month investigations in Tianjin, Dalian, Qingdao, Zhejiang, Xiamen and Tangshan. This survey is the largest survey on the status and problems of seawater utilization in China's history. In addition to domestic research, the research team will also specially engage in desalination experts to conduct surveys in countries with more developed seawater desalination, such as Israel, the United States, Japan, and Spain. Industry insiders have analyzed that relevant research reports will provide decision support for the integration of seawater desalination into national planning and local water resources allocation.

The Chinese government attaches great importance to seawater desalination and has adopted a series of measures to promote the development of the seawater desalination industry. During the "Eleventh Five-Year Plan" period, China's seawater desalination has developed rapidly. As of the end of 2010, more than 70 seawater desalination units have been built, with a designed production capacity of 600,000 cubic meters per day, with an average annual growth rate of more than 60%; breakthroughs have been made in technologies with independent intellectual property rights, reverse osmosis seawater membranes, high-pressure pumps, energy Significant progress has been made in recovery equipment, and the desalination rate has increased from 99.2% to more than 99.7%. The industry has developed conditions and the seawater desalination market has basically formed. Governments at all levels attach great importance to seawater desalination, and all sectors of society are generally concerned about the development of the seawater desalination industry. At the same time, in China, there are still problems such as insufficient understanding of the significance of seawater desalination strategies, weak independent innovation capabilities, low levels of industrial development, and insufficient supporting policies. Therefore, it is a very necessary and urgent task to make overall plans and accelerate the development of the desalination industry. According to the spirit of the "Opinions", based on the full investigation and extensive listening to the opinions of all parties, the National Development and Reform Commission organized the "Twelfth Five-Year Plan" for the development of the desalination industry (Development and Reform Environmental Capital [2012] No. 3867).

In addition, the Opinions on Accelerating the Development of the Seawater Desalination Industry, which was formulated by 11 ministries and commissions and led by the National Development and Reform Commission, has completed several rounds of soliciting opinions and reported them to relevant departments. It is expected to be introduced in the name of the State Council this year. The National Development and Reform Commission will also issue the Twelfth Five-Year Plan for desalination industry development. Analysts point out that in this context, the desalination industry will usher in a golden period of development, and support policies are expected to be intensive.

due to"

In today's mature seawater desalination technology, economics is an important factor that determines its widespread application. In China, "costs and investment costs are too high" has always been regarded as the main problem of desalination difficult to use, but in fact it is a "recognition" problem.

There are three types of freshwater withdrawal methods commonly used in the world: underground water withdrawal, remote water diversion, and desalination of seawater (brass and salt water). Mining groundwater is an important open source measure, with a small amount of engineering and low cost. This is an attractive advantage, but underground water extraction is greatly restricted by resource conditions. In many areas, over-exploitation of groundwater has formed over the years.

The relationship between the desalination efficiency of the key water for desalination, the environment, and energy, no matter which method is used to evaluate the indicators, it is impossible to leave the environmental impact and energy consumption. The recovery rate of water is 35-55%, and the desalination process is also a process of seawater concentration. Therefore, if the yield of freshwater is increased, the enrichment of valuable elements in concentrated seawater will increase, providing good conditions for chemical resource recovery.