Summary:The dust filter bag is called the heart of the dust collector. The selection of the filter bag is very important. It directly affects the dust removal effect of  particle size; dust concentration; filtration wind speed;the dust collector. The fabric and design of the dust filter bag should pursue high efficiency filtration, easy dust stripping and durability. The choice of filter bag should be selected from the following aspects:

(1) Selection according to the nature of dusty gas

1. Gas temperature

Dust-containing gas temperature is an important factor in the selection of filter bags. Dust-containing gas below 130 ℃ is usually called normal temperature gas, and dusty gas above 130 ℃ is called high temperature gas, so filter bags can be divided into two categories: normal temperature filter bags below 130 ℃ and those above 130 ℃ High temperature filter bag. For this purpose, a suitable filter bag should be selected according to the flue gas temperature. In actual work, some people call the gas of 130 ～ 200 ℃ as medium temperature gas, but the filter bag chooses high temperature type.

2. Gas humidity

Dust-containing gas is divided into three states according to relative humidity: when the relative humidity is below 30%, it is dry gas, when the relative humidity is between 30% and 80%, it is a general state, and when the relative humidity of the gas is above 80%, it is high humidity gas. For high-humidity gas, when it is in a high temperature state, especially when the dust-containing gas contains SO2, condensation will occur when the gas is cooled. This will not only cause scaling and clogging on the surface of the filter bag, but also corrode the structural materials, so special attention is required.

3. The chemical nature of the gas.

Flue gas and chemical waste gas in various furnaces and kilns often contain a variety of chemical components such as acids, alkalis, oxidants, organic solvents, etc., and are often affected by multiple factors such as temperature and humidity. Therefore, when selecting a filter bag, the main factors must be grasped and comprehensively considered based on the chemical composition of the dust-containing gas.

(2) Choose according to the nature of the dust

1. Dust wettability and adhesion

The wettability and wettability of the dust can be characterized by the wetting angle. Generally, those less than 60° are said to be hydrophilic, while those greater than 90° are called hydrophobic. When the humidity of the hygroscopic dust increases, the cohesive force and viscous force of the particles will increase, and the fluidity and charge will decrease, and it will adhere to the surface of the filter bag. Over time, the dust removal will fail and the dust cake will harden. Some dusts, such as CaO, CaCl, KCl, MgCl2, NaCO3, etc., undergo further chemical reactions after moisture absorption, and deliquescent paste bags, which is the most taboo of bag filter.

2. Dust flammability and chargeability

Some dusts will burn or explode in the air with sparks in a specific concentration state. Dust combustion or explosion fire sources are usually caused by friction sparks, static sparks, hot particulate matter, etc., among which the charging hazard is the greatest. This is because chemical fiber filter bags are usually easy to charge, and if the dust is charged at the same time, it is very easy to produce sparks. Therefore, for flammable and easily charged dusts such as coal powder, coke powder, alumina powder and magnesium powder, it is appropriate to choose flame retardant filter bags and conductive filter bags. Filter bags woven with fibers with an oxygen index greater than 30, such as PVC, PPS, P84, PTEF, etc., and for fibers with an oxygen index less than 30, such as: polypropylene, nylon, polyester, imide and other filter bags can be impregnated with flame retardants deal with.

3. Dust flow and friction

When the flow and friction of the dust are strong, the filter bag will be directly worn out, reducing the service life. Particles with rough surfaces and irregular diamond shapes are 10 times more abrasive than smooth spherical particles. Dust particles with a particle size of 90 μm have the greatest abrasion, but when the particle size is reduced to 5 μm to 10 μm, the abrasion is very weak. Abrasion is directly proportional to the 2nd to 3rd power of airflow velocity and 1.5th power of particle size. Therefore, the airflow velocity and its uniformity must be strictly controlled. Among the common dusts, aluminum powder, silicon powder, coke powder, carbon powder, sintered ore powder, etc. are highly abrasive dusts. For abrasive dusts, filter bags with good wear resistance should be used.

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