Filter bag filter material selection needs to pay attention to aspects
At present, regardless of the bag filter equipment manufacturers or direct users, in the selection of filter material, will be required to provide specific filter material manufacturers technical parameters. Among the required technical parameters, they tend to focus on:
(1) gram weight of filter material (mass per unit area). Because the filter material is a textile product, the measured value and the nominal value must have deviation. According to the national standard, the quality per unit area of needled felt filter can be allowed to have a deviation of +/-5%. But some users, for the purpose of preventing filter suppliers from cutting corners (and possibly for other purposes?) It is often proposed to filter bag manufacturers that the gram weight of filter material must be greater than or equal to 550 g/m2 and other requirements. If the filter material manufacturer made the commitment in response to the request, it means that the filter material in the production must control the filter material gram weight in 580g/m2, that is to say, the nominal value of the filter material is 580 grams and should not be 550 grams.
(2) thickness or density of filter material; In the national standard, the filter material thickness is also allowed to have a deviation of +/- 10%.
(3) air permeability of filter material; Note: there is a correlation between filter density and air permeability. High quality needling equipment and process is the premise to ensure high quality filter material production. If the filter material is not dense enough, the air permeability may be very good, the filter material filtration efficiency and dedusting performance will be poor.
(4) strength and elongation of filter material;
(5) temperature resistance of filter material (temperature that allows continuous operation and instantaneous operating temperature that can be borne). As a filter material manufacturer, it must be responsible to put forward the maximum allowable continuous operating temperature and maximum instantaneous operating temperature of the selected filter material according to the expected service life of the filter bag proposed by the user (such as 30,000 operating hours or 45 months, etc.) and the characteristics of temperature and chemical corrosion resistance (oxidation resistance and hydrolysis resistance) of the fiber raw material. If the actual temperature of flue gas will often exceed the maximum continuous operating temperature allowed by filter material, then the user must consider: or take measures in the system to improve the heat exchange efficiency of system equipment such as air preheater and reduce the smoke exhaust temperature; Or reduce the requirement for the expected service life of the filter bag (such as giving up the requirement of 30,000 running hours). It is also reasonable to propose a maximum instantaneous operating temperature for the filter material, because the system may indeed have instantaneous overtemperature (overtemperature refers to the case that the maximum continuous operating temperature is exceeded). Here also must pay attention to two points: first, the maximum instantaneous working temperature allowed by the filter material is not allowed to exceed; Second, the overtemperature is instantaneous. There is an agreement on time, which generally requires that each overtemperature is allowed for a few minutes, and the annual total overtemperature time cannot exceed hours.
(6) thermal shrinkage of filter material. Because most of the filter material is made of chemical fiber, under certain temperature conditions, the filter material will happen thermal shrinkage, so the filter material production must be heat set. Heat setting process is very critical and is often kept secret by filter manufacturers. At home and abroad, there have been cases of filter bag ejection pattern board (the top of the bag cage is not fixed) or top dedusting at the bottom of the filter bag caused by thermal shrinkage of the filter material. However, the filter bag, especially the filter bag with a length of 8 ~ 9 meters, will be stretched downward by the force of gravity plus the weight of dust accumulated after hanging on the flowered board, so the thermal shrinkage and elongation of the filter material are also factors to be considered in a balance. Excessive heat setting, or excessive requirements for small thermal shrinkage, may also cause the elongation of filter bags in the use process, and thus shorten the actual service life of filter bags.