1. The filter mechanism of bag filter
There is a saying that “particles larger than the surface of the filter material are deposited on the surface of the filter material, and particles smaller than the surface of the filter material enter the inside of the filter material.”
This is due to the intuitive understanding of screening. In fact, the filtering mechanism of filter media is by no means a simple screening effect, but includes the synergistic effects of inertia, interception, diffusion, static electricity, and gravity. The inertial collision and interception effects are dominant for dust particles larger than 1 μm, and less than 0.2 μm dust particles. Diffusion and electrostatic effects dominate. Therefore, particles smaller than the pores (mesh) on the surface of the filter can also accumulate on the surface of the filter.
2. Several statements on surface filtration and deep filtration
There is a saying in the industry: We call the filtration of coated media as “surface filtration” and the filtration of conventional filter media as “deep filtration”.
The second argument is that the surface of the film covered with a layer of PTFE microporous film has changed the inherent filtration method of the filter material from the “deep layer filter” to the “surface filter”.
Argument 3: “The filtration stage of the filter media can be divided into three states: deep filtration, transient filtration, and surface filtration.”
Browsing related papers, all sorts of expressions about this kind of filter characteristic, cannot agree. Dust removal and purification are the two major areas involved in dust removal. Bag filter is suitable for the treatment of high concentration industrial dust. It is characterized by surface filtration. It can be cleaned and regenerated. Long-term use: The air filter is suitable for low-concentration gas purification. It is characterized by body filtration, or deep filtration. Recycled, disposable. Therefore, I always believe that “bag dust filter material belongs to surface filtration” has been repeatedly advocated, and it is more appropriate to rely on the “surface filtration” of the primary dust layer on the surface of the filter material. To a certain extent, the filter material is only used to support the role of a dust layer, whether it is conducive to the establishment of a stable primary dust layer as soon as possible, and clear the secondary dust, which is the key to evaluating the quality of the filter structure.
According to this point of view to explain the above statement. The so-called conventional filter material is not used as a “raw filter” made of woven fabrics, but also subjected to surface treatment such as singeing, calendering, coating, heat setting, etc. to form a microporous structure and control a certain aperture and Air permeability. For clean filter media, a small amount of fine dust particles do penetrate the inner layer through the surface, but as a qualified filter media, it is only a transient process during the entire life cycle. It quickly becomes balanced, and a stable primary dust layer is established to realize the surface. filter. This is completely different from the deep filtration of air filters. Of course, low quality filters are another matter. The so-called film-covered filter only has a fine surface pore structure, and the process of establishing a dust layer to achieve surface filtration is faster, more stable, more efficient, and cleaner. In addition, Evonik’s P84 trilobal fiber filter and recently heated ultra-fine surface gradient structure filter media are used to create a more stable and uniform surface pore structure, establish a good dust layer, and achieve high efficiency and low resistance filtration. .
In short, the overall characteristics of the dedusting filter material are “surface filtration”. It should be said that there is no absolute “surface filtration”, but there are differences in the process and proximity of achieving “surface filtration.”
3. Definition and Classification of Fine Denier Fibers
It is mentioned that “microfibers, also known as ultra-fine deniers, are currently not uniformly stipulated internationally. China Textile Industry Ministry Chemical Fiber Industry Co., Ltd. has made the following stipulations on the fineness range of microfibers: 0.5 to 1.3 dtex is microfiber; The Japanese chemical fiber industry generally refers to fibers with a monofilament density less than 0.3 dtex as ultra-fine fibers.”
There are also mentioned in the paper “There is still no uniform standard for the classification of fine denier and microfibers. The German Textile Association calls single fibers with a polyester fiber linear density of less than 1.Zdtex as microfiber, and AKZO The company classifies microfibers as less than 0.3dtex, while Montefibre calls microfibers with a linear density less than 0.55dtex as microfibers, while other countries and regions classify fine fibers as fine as 1.0- 2.4dtex is a fine denier fiber; 0.3-1.0dtex is a superfine denier fiber, and 0-0.3dtex is a superfine fiber.”