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Desalination is the dream that mankind has pursued for hundreds of years. The reporter learned from the New Energy Research and Development Institute of Hohai University yesterday that the solar heating device jointly developed by Zhang Yaoming, an academician of the Chinese Academy of Sciences, and Zou Ningyu, a senior engineer of the institute, can serve as a clean and pollution-free energy source for seawater desalination plants. Change" to drinking water.
According to reports, the total length of China's coastline is 32,647 kilometers. The coastal and central and western regions also have extremely rich underground brackish water resources. Achieving desalination of seawater and brackish water is undoubtedly an important strategic way to solve the shortage of fresh water in China. At present, among the more than 20 kinds of seawater desalination technologies that have been developed, the distillation method, electrodialysis method and reverse osmosis method have reached a certain level. Unfortunately, these technologies are difficult to promote because these desalination equipments use electricity, coal and other energy sources. The technology to exchange water for the cost.
Zou Ningyu introduced that after the efforts and research of the scientific and technical personnel of Hohai University and Nanjing Fiberglass Institute, the institute has developed high-efficiency and high-temperature collectors, providing key technologies for the desalination industry. It is understood that solar desalination water is similar in process to the process of making distilled water. The difference is that it uses a "heliostat" that can fix sunlight and a "collector" that converts electric energy to make the sea water boiling. The fresh water is distilled off, and the water thus produced can be directly consumed. Zou Ningyu emphasized that in this desalination process, no energy is consumed, but the salt produced after the process of desalination through the solar heat storage is discharged to the sea, and can also be processed into edible salt and industrial salt. Therefore, this technology It is an economic and environmentally friendly new eco-friendly technology.
At present, the international application techniques for seawater desalination are mainly thermal and membrane methods, which are also called distillation and reverse osmosis.
Distillation is the process of turning seawater into steam and cooling it to obtain high purity fresh water. According to the way of evaporative cooling, the distillation method is divided into two types of multi-stage flashing and multi-effect distillation. Among them, the multi-stage flashing is to suddenly decompress the hot sea water to generate steam to obtain fresh water. At present, the world's large-scale multi-stage flashing project in Saudi Arabia has a daily output of 450,000 tons. The multi-effect distillation is to continuously evaporate and obtain fresh water while steam cooling. The representative project is in Spain, with a daily output of 35,000 tons.
The reverse osmosis method is to press seawater into a reverse osmosis membrane under a certain pressure (60 kg/cm 2 ). This membrane only allows the water molecules in the seawater to pass through, and intercepts most of the salt molecules to obtain fresh water. . At present, the world's largest construction projects are in Israel, with a daily output of 330,000 tons.