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What is the working mechanism and characteristics of the filter bag

March 10,2023

(1) When dusty gas passes through the filter cloth, the gap between the filter cloth fibers or the gap between the dust adsorbed on the filter cloth surface will separate the dust larger than the gap diameter, which is called shielding effect. For the new filter cloth, this effect is not obvious, and the dust removal efficiency is low due to the large fiber spacing. Only after a period of time, there is a certain thickness of dust layer on the surface of the filter bag, can the screening effect be more significant. After dedusting, the surface and interior of the filter bag have a fixed amount of dust, so it can still maintain a good dedusting efficiency. For needle felt or velvet filter cloth, as the felt or velvet filter cloth itself forms a thick porous filter layer, it can give full play to the filtering function, rather than relying on the dust layer to maintain high dust removal efficiency.

(2) When the dust containing gas can pass through the filter cloth fiber, the dust larger than 1m will be captured due to the inertial effect, and the inertial technology will still maintain a linear management movement and impact the fiber. The larger the diameter of dust particles, the greater the degree of inertia effect. The higher the filtration gas velocity is, the greater the risk of inertia effect is. However, if the gas velocity is too high, the air flow through the filter cloth will also increase, and the air flow will penetrate from the weakness and part of the filter cloth, so as to achieve the dust removal efficiency at a reduced speed. The higher the gas velocity, the more serious the historical phenomenon of penetration.

(3) When the dust particles diffuse below 0.2m, the extremely fine dust will generate Brownian motion, such as the thermal motion of gas molecules, which increases the chance of dust contacting with the filter cloth, thus leading to dust capture. Contrary to the inertia effect, this diffusion effect increases with the decrease of the filtered gas velocity and the dust particle size. Take glass fiber as an example, the finer the fiber, the higher and the dust removal efficiency. The pressure loss of fine diameter fiber is greater than that of coarse diameter fiber. The thinner the fiber, the worse the corrosion resistance.

(4) When the dusty gas is close to the filter cloth, the fine dust still flows with the air. If the dust radius is greater than the distance from the dust center to the edge of the filter cloth, the dust is bound and captured by the filter cloth. The smaller the filter cloth gap is, the more obvious the effect is.

(5) The electrostatic interaction between dust particles will generate static electricity. If the filter cloth is an insulator, it will manage electricity. When the charge of the dust is opposite to that of the filter cloth, the dust is adsorbed on the filter cloth, which improves the dust removal efficiency and brings difficulties to the dust removal. On the contrary, if the two charges are the same, the repulsive force will be generated, so that the dust cannot be adsorbed on the filter cloth, thus reducing the dust removal efficiency. Therefore, the electrostatic effect can improve or hinder the dust removal efficiency of the filter cloth. In order to ensure dust removal efficiency, it is necessary to select filter cloth according to the charging characteristics of dust. Generally speaking, only when the dust particle size is less than 1m, the filtering gas speed is very low, can the electrostatic effect be displayed. When the electric field is applied, the electrostatic effect can be enhanced and the dust removal efficiency can be improved.

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