Comparison of five materials for filtering dust
Due to the decrease in air quality, especially in some northern cities, you cannot go out without a smog mask in winter. The reason why the smog mask has the effect of preventing smog is because of the filtering material inside. There are currently five main types of filter materials.
1. Glass fiber material
The most prominent features of glass fiber are high temperature resistance, good dimensional stability, and high tensile strength at break. In terms of chemical resistance, glass fiber is very stable to other media except hydrofluoric acid and high temperature and strong alkali. The disadvantage of glass fiber is its poor folding resistance, and it is generally not used on oscillation or pulse systems.
2. Polypropylene material
Polypropylene has good abrasion resistance, high elastic recovery rate, acid and alkali resistance, good moisture resistance, and weak oxidation resistance. It is also an excellent thermoplastic fiber. Polypropylene felt is often used in low-temperature pulse filter bags in melting plants and chemical, In the pulse filter bag of a pharmaceutical factory. Polypropylene is specially used in damp places, and it is limited by low temperature resistance.
3. Polyester material
The most common reason for polyester damage is the hydrolysis of water vapor or the increase of water temperature, especially the hydrolysis corrosion in alkaline environment. It can withstand the operating temperature of 130 ℃ under dry conditions; it will become hard when continuously working above 130 ℃; Fading; brittle, temperature will weaken its strength
4. PTFE (polytetrafluoroethylene) fiber and membrane filter material
Features: PTFE is a neutral polymer compound with a unique molecular structure, that is, a completely symmetrical structure. The special structure makes it have good thermal stability, chemical stability, insulation, lubricity, water resistance, etc.
Filtration performance: high temperature resistance, wide operating temperature range, can be used continuously at 260℃ (long-term continuous use at high temperature, the instantaneous temperature can reach 280℃; strong chemical stability, corrosion resistance; good self-lubrication, very low friction coefficient, very low filter wear Small; the surface tension of the PTFE membrane is very low, with good non-stick and water repellency.
The PTFE coated filter material can achieve surface filtration. This is because the PTFE coated filter material has a microporous structure and has no through holes on the surface, so that dust cannot enter the inside of the membrane or the substrate through the surface of the membrane, so that only gas passes through. Keep dust or materials on the surface of the membrane. At present, the coated filter material has been widely used in many fields such as industrial dust removal and precision filtration.
The surface of the polytetrafluoroethylene (PTFE) film is smooth and resistant to chemical substances. It is laminated to the surface of the ordinary filter material to act as a disposable dust layer, trapping all the dust on the surface of the film, and achieving surface filtration; The film has a smooth surface, excellent chemical stability, non-aging, and hydrophobic, so that the dust trapped on the surface is easily peeled off, and at the same time, the service life of the filter material is improved.
Compared with ordinary filter media, its advantages are:
1). The membrane pore size is between 0.23μm, the filtration efficiency can reach more than 99.99%, and almost zero emission is achieved. After cleaning, the porosity is not changed, and the dust removal efficiency is always high.
2). The pressure loss of the membrane filter material at the beginning of use is higher than that of the ordinary filter material, but after it is put into operation, the pressure loss changes little with the increase of the use time, and the pressure loss of the ordinary filter material will change with the use time The lengthening and getting bigger and bigger.
3). Dust can easily enter the inside of ordinary filter media in use, and it accumulates more and more, until the pores are blocked and the use cannot be continued. With the use of PTFE coated filter material, the filtered dust can be easily removed from the surface of the membrane. The dust removal effect is good, the cycle is long, and the cleaning pressure intensity used is low, which improves the service life of the filter material and reduces the operating cost of the product. .
5. Antistatic fiber
Stainless steel fiber and carbon or other antistatic elements are mixed with the fiber to help reduce the risk of static electricity accumulation. This kind of antistatic fiber is often used in the occasions where the bag filter has the risk of explosion.
It is generally hoped that when the filter material guarantees the same filtration efficiency, the greater the air permeability, the lower the resistance, the better, because this can save a lot of energy. In a dust collector that uses airflow to blow back the dust, the same pressure and the same air volume are used. When the airflow is used for dust removal, the dust removal effect when using a woven material with a large air permeability as a filter bag is better than selecting a woven material with a small air permeability. How to improve the filter material under the condition that the filter material reaches a higher filtration accuracy The air permeability of the filter media, the improvement of the surface finish, the reduction of dust adhesion, and the reduction of running resistance are the first topics that the filter material manufacturer should study.
The filtration speed is calculated by the following formula:
Where v-filtration speed (apparent filtration air speed), m/min
Q-filter dust collector processing air volume, m3/hour
A－Filter area of filter material of filter dust collector, ㎡
The high filtration rate will increase the pressure difference between the two sides of the filter material, squeeze the fine dust that has been attached to the filter material, and reduce the filtration efficiency to reach the specified emission value or wear the single fiber of the filter material. Especially accelerate the damage of glass fiber filter material. If the filtering speed is small, the volume of the dust collector will be increased, thereby increasing the investment. Filtration speed is one of the main factors affecting the performance of filter dust collectors.
Carbon monoxide catalysts, ozone decomposition catalysts, VOC catalysts, Hopcalite catalysts, manganese dioxide catalysts and copper oxide catalysts
also need to use filter materials at the front and back ends during use to avoid blowing out a little dust in the catalyst.