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Introduction to pre-coating filtration

The so-called pre-coating filtration is to add a certain amount of filter aid in the filtration process, and after a short period of time, a stable filtration pre-coating is formed on the filter element, which turns simple media surface filtration into deep filtration, resulting in Strong purifying and filtering effect. Commonly used filter aids are perlite, cellulose, diatomaceous earth, carbon black and asbestos. Diatomite filter aid has been widely used due to its comprehensive advantages in performance, price, source and other aspects.

Principle of pre-coating filtration

A filter pump is used to pass the suspension containing the filter aid into the filter tank, and after a period of circulation, the filter aid is bridged on the surface of the filter medium to form a filter pre-coating layer with complex and fine pores. Due to the presence of the pre-coating, a higher filtration accuracy is obtained in the initial stage of the next step of filtration, and it can also prevent dirt particles from clogging the pores of the filter element. During the filtration process, the solid particles in the suspension are mixed with diatomaceous earth particles that are continuously added in a quantitative manner and then accumulated on the filter element to form a loose filter cake, so that the filtration rate is basically stable.

Characteristics of diatomite filter aid

Diatomite filter aid products come in a variety of colors. Its basic component is a porous siliceous shell wall. The main performance indicators are particle size, bulk density, specific surface area, and component content. Among them, particle size distribution is one of the most important performance indicators. It directly determines the size of the filter pores and the distribution of micropores. The coarse-grained particles have better water permeability, but the filtration accuracy is lower, so the required flow rate and filtration accuracy should be met. , Choose the appropriate thickness of diatomaceous earth. Domestically produced products are divided into two types of thickness, which can be used alone or in combination with different thickness and particle size to obtain extremely high filtration accuracy. The bulk density of diatomite also has a great influence on the filtering effect. The smaller the bulk density, the larger the pore volume of the filter aid particles, and its permeability and adsorption should be controlled during the pre-coating operation. The concentration of the medium diatomite and the circulating flow rate of the pre-coating solution enable the diatomite particles to bridge the formation of a uniform pre-coating. The concentration of diatomite is generally 0.3 to 0.6%, and the circulating flow rate can be set to 1 to 2 times the normal flow rate. The pre-coating pressure is generally about 0.1MPa.