At present, whether it is a bag filter equipment manufacturer or a direct user, when selecting the filter material, it will request the filter material manufacturer to provide specific filter material technical parameters. The required technical parameters are often focused on:
(1) The weight of the filter material (mass per unit area). Since the filter material is a textile product, there must be a deviation between the measured value and the nominal value. According to the national standard, the mass per unit area of the needle felt filter can allow +/- 5% deviation. However, some users, for the purpose of preventing filter suppliers from cutting corners (may have other purposes?) often ask filter bag manufacturers that the weight of filter media must be 550 g/m2 or more. If the filter manufacturer responds to the request, it means that the filter medium must control the weight of the filter material at 580g/m2, that is, the nominal value of the filter material is 580g instead of 550g. .
(2) The thickness or density of the filter; the national standard also allows a +/- 10% deviation in the thickness of the filter.
(3) Permeability of the filter; Note: The density and permeability of the filter are related. High quality acupuncture equipment and processes are the prerequisite for ensuring the production of high quality filter media. If the filter material is not dense enough, the air permeability may be good, and the filtering efficiency and deliming performance of the filter material will be poor.
(4) The strength and elongation of the filter material;
(5) The temperature resistance of the filter (allows continuous operation of the temperature and can withstand the instantaneous operating temperature). As a filter manufacturer, it must be responsible for the life of the filter bag (such as 30,000 hours or 45 months) based on the user’s expectations. According to the characteristics of the temperature resistance and chemical resistance (oxidation and hydrolysis resistance) of fiber raw materials, comprehensive The permissible maximum continuous operating temperature and maximum instantaneous operating temperature of the selected filter media. If the actual flue gas temperature often exceeds the maximum continuous operating temperature allowed by the filter, then the user must consider: or take measures on the system to increase the heat exchange efficiency of the system equipment such as the air preheater and reduce the exhaust temperature; or reduce the The filter bag’s expected service life requirements (such as abandoning 30,000 hours of operation). It is also reasonable to propose a maximum instantaneous operating temperature for the filter, as the system may indeed experience transient over-temperature (over-temperature means: above the maximum continuous operating temperature). Here we must also pay attention to two points: First, the maximum allowable instantaneous operating temperature of the filter material can not be exceeded; Second, the over-temperature is instantaneous, there is a time agreement, generally requires that each over-temperature allows minutes, each year The total overheating time cannot exceed the number of hours.
(6) Heat shrinkage of the filter material. Since most of the filter material is made of chemical fiber, the heat shrinkage of the filter material occurs at a certain temperature, so the heat-setting treatment must be performed in the production of the filter material. Heat setting processes are critical and are often kept confidential by filter manufacturers. At home and abroad, there have been cases where the top of the filter bag (the top of the bag cage is not fixed) or the bottom of the filter bag is broken due to the thermal shrinkage of the filter material. However, the filter bag is especially like a 8 to 9 meter long filter bag. After hanging on the card board, there will be a self-gravity plus a dust-filled force to pull down the filter bag, so the heat shrinkage of the filter Elongation is also a factor that needs to be balanced. Excessive heat setting, or excessive heat shrinkage, may also result in elongation of the filter bag during use, which in turn may shorten the actual life of the filter bag.
In fact, the functional elements or properties used in the filter media are not only the quality and technical requirements such as the durability (or expected service life, etc.) of these filter media mentioned above. As a material for filtering dust particles, the functionality (performance) of the filter must satisfy:
First, filter material filtration efficiency technical indicators;
Second, filter material deliming performance technical indicators.
When the user selects the filter material, there is often a requirement that the dust emission control must be less than 30 to 50 mg/Nm3, and that the dust collector may have a running resistance of less than 1000 to 1200 Pa. However, whether the selected filter material can be achieved can be achieved. These requirements, but they can not put forward specific indicators such as testing and comparison. In fact, as a good filter manufacturer, the research and development of filter media will pay great attention to the filtration efficiency and de-ashing performance of these specific filter media. The reason why there are a variety of surface treatment filters on the market today, is that filter manufacturers continue to pay attention to the filter efficiency and de-ashing performance results.
For many users of coal-fired boiler flue gas bag filter in domestic power plants, the most concern now is the service life of the filter bag. There are two main factors that affect the life of the dust bag: First, the thermal and chemical properties of the flue gas; second, the mechanical loss of the filter bag during filtration and cleaning. If the thermal and chemical properties of the flue gas have a great influence on the choice of chemical fiber filter media, such as oxidation of PPS filter media, acid condensation, and ultra-high temperature operation, the filter bag may soon lose its effectiveness. At this time, even if the filter’s functionality (filtering efficiency and desulfurization performance) is of good quality, it cannot represent the value of its performance and quality at all. This is determined by the PPS fiber itself or its inherent thermal and chemical resistance. In the face of bad smoke, the fate of each filter manufacturer is the same.
However, the normal operation of the filter material can accept the flue gas conditions, the quality of the filter material will determine the actual life of the filter bag. The functional (performance) quality of the filter media mainly refers to the filtration efficiency and the deliming performance. The good filtering efficiency of the filter material means that the dust can be well blocked on the surface of the filter material and rarely penetrate into the middle of the filter material, which not only reduces the abrasion of the filter material fibers during the filter bag movement, but also The dust on the surface of the filter material can be removed in the largest amount; the de-ashing performance is superior, and the running resistance of the filter material due to the dust layer coalescence is low, and the cycle of setting the deashing pressure after once cleaning the dust will rise. Greatly prolonged; the longer the dedusting cycle, the fewer times the filter bag needs to be cleaned, thus reducing the number of mechanical damage of the filter bag and prolonging the service life of the filter bag. What needs to be pointed out here is that at present, many domestic bag filter users do not use “constant pressure” cleaning and use “timed” cleaning more. The shortcoming of regular cleaning is when the filter bag operation pressure difference may not be high, the filter bag is cleaned, which increases the chance and frequency of mechanical damage to the filter bag.