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Development background and introduction of membrane distillation technology

来源: 作者: 阅读:108668 网友评论0 Updated: 2011-02-15 16:04 Source: Author: reading: 108 668 2010 0 comments

In recent years, with the rapid development of membrane separation technology, reverse osmosis membrane technology (RO) has gradually become the preferred technology for deep reuse treatment of industrial wastewater and circulating water in the power and metallurgical sectors. However, the water production rate of reverse osmosis membrane technology is generally only 75%, and the problems of treatment and discharge of concentrated water are becoming increasingly prominent.

At present, there are three main solutions used to solve the reverse osmosis discharge of concentrated water: (1) the concentrated water is discharged after washing the multi-media filter; (2) the concentrated recovery and treatment of the discharged water, using the lime softening method to remove the hardness of calcium and magnesium Reuse or meet discharge standards; (3) Comprehensive utilization directly in combination with production process conditions. However, these methods have not completely solved the problem, and the utilization rate of concentrated water is very low, even causing secondary pollution to the environment. Therefore, it is of great significance to develop an efficient concentrated brine treatment process to make up for the shortcomings of RO and other treatment processes in order to achieve water saving and emission reduction. Vacuum membrane distillation (VMD) is a new type of membrane separation process that combines membrane technology with traditional distillation technology. It has the advantages of low operating temperature, simple equipment, and the retention rate of non-volatile matter such as inorganic salts and macromolecules can reach 100%, which can realize the treatment of high-concentration solutions.

Membrane Distillation (MD) is a new and efficient membrane separation technology that has been rapidly developed in the past decade. It is a membrane separation process that uses the vapor pressure difference on both sides of a hydrophobic microporous membrane as the driving force for mass transfer. The characteristics of the membrane distillation process that are different from other membrane processes are: the membrane is a microporous membrane; the membrane cannot be wetted by the liquid being processed; no capillary condensation occurs in the membrane pores; only steam can transfer mass through the membrane pores. The membrane cannot change the vapor-liquid equilibrium of each component in the operating liquid; at least one side of the membrane must be in direct contact with the operating liquid; for each component, the driving force of the membrane operation is the gas phase partial pressure gradient of the component. Compared with other separation processes, membrane distillation has the following advantages: ① high rejection rate (up to 100% if the membrane is not wetted); ② the operating temperature is much lower than the traditional distillation operation, which can effectively use geothermal, industrial Cheap energy sources such as waste heat from waste water reduce energy consumption; ③ The operating pressure is lower than other membrane separations; ④ It can handle high-concentration wastewater that cannot be treated such as reverse osmosis.

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