In fiberglass filter bag dust collectors, most of the filter bags are made of medium-alkali glass fiber, which has good acid resistance but poor alkali resistance. At the end of cement kilns, the alkalinity of dust is relatively strong, and the PH value before dissolving in water is generally around 11. In order to prolong the service life of the filter media, if the price allows, alkali-free glass fiber should be used. It can form a colloid protective film, which is coated on the filter bag to prevent the alkali solution from corroding the glass fiber and play a protective role.
Nowadays, fiberglass-coated filter media is widely used at the end of cement kilns. The advantages of this filter material are obvious. First of all, its filtration efficiency is high, an order of magnitude higher than that of membrane-free filter media, and almost achieves zero emissions. The operating resistance is significantly reduced, about 2/3 of that of membrane-free filter media, and the energy saving effect is significant. The dust cleaning performance is excellent, so that the filtration resistance is always kept at a very low level, especially in situations like the cement kiln tail flue gas temperature is high, contains a certain humidity, and the dust in the flue gas is fine and sticky, etc., the superiority of membrane filter material is particularly obvious. The fiberglass coating is used. Due to the smooth surface of the membrane, the cleaning cycle is long and the cleaning pressure intensity is low, which reduces the friction between dust and filter material and extends the life of the filter bag. To further improve the service life of filter bags, there are mainly the following measures.
Selecting appropriate parameters to extend the service life of filter bags
Currently, most of the glass fiber coated filter bags used at the end of cement kilns are low-pressure long-bag pulse dust collectors. There are many factors that affect the service life of filter bags. We only discuss several important parameters that directly affect the service life.
- Pulse bag filter filter speed
The pulse bag filter filter speed refers to the dust-containing gas load per unit time and per unit area. It is one of the important parameters of the bag filter and is closely related to the dust concentration of the gas being processed, the dust characteristics, the filter cloth material used and the cleaning method. The filter speed directly affects the size of the entire filter and the filter bag resistance of the filter bag, thus affecting the service life of the filter bag. After using the coated glass fiber bag, due to surface filtration, the resistance will not gradually increase due to the accumulation of dust in the deep layer of the filter bag. Therefore, under the same conditions, the filter speed is slightly higher than that of the non-membrane filter bag. The filter bag resistance is in a square relationship with the filter speed. If the wind speed is too high, the initial resistance will be too large, which will cause local “perforation” on the film, and then the base cloth will be worn and affect the emission and service life. Due to the use of surface treatment, dust will not accumulate in the deep layers of the filter bag, and pulse cleaning is used, the kinetic energy is large, the cleaning is more thorough, and the resistance will not increase quickly. This is also the reason why the wind speed of the coated filter is higher than that of the non-film filter.
- Selection of pulse cleaning air volume
During pulse cleaning, in addition to the pressure being lower than the normal pressure and the cycle being longer, the cleaning air volume must also be determined to be appropriate. Too large an air volume can easily reduce the service life, and too small an air volume can also affect the service life if the cleaning pressure is the same and the air volume is the same. Under the condition of the same cleaning pressure and air volume, the pressure during offline cleaning can be lower than that during online cleaning, and the air consumption is small, saving power consumption.
In order to improve the anti-bending, wear resistance, heat resistance, corrosion resistance and filtering performance of glass fiber bags, relevant scientific research and production units in my country have studied a variety of surface treatment methods, mainly using silicone oil, PTFE, and graphite treatment. The technology has become mature. After treatment, the wear resistance, softness, water solubility and temperature resistance of glass fiber bags are improved.
- Gas temperature
The fiberglass scrim in the fiberglass coating is famous for its high temperature resistance. As for the fiberglass itself, its softening point is 650℃~980℃ depending on its composition. As a filter cloth, the long-term working temperature is generally controlled at 250℃ Below, it has good dimensional stability and strength properties. When the temperature exceeds 260℃, the glass fiber itself will not be directly damaged, but the glass fiber material and the chemical surface treatment agent that lubricates between the glass fiber yarns will evaporate, resulting in aggravation and acceleration of the glass fiber. Mechanical wear between filaments and glass fiber yarns affects strength and service life.
- Gas humidity
When the fiberglass filter bags is wet, its strength will decrease. This is because the alkali components in the alkali-containing glass fiber are dissolved by water, which causes erosion on the glass fiber surface and causes the film to fall off, thus affecting its life. Therefore, in addition to limiting the higher temperature of the working gas, special attention should be paid to controlling the humidity of the glass fiber bag in use to prevent condensation. For example, the fiberglass filter bag dust collector at the end of the dry kiln is currently in a mixed working condition, that is, a large amount of raw mill exhaust gas enters, and the humidity increases. If the humidity cannot be controlled and air leakage causes water vapor to condense on the filter bag, it will also affect the life.
- Inlet dust concentration
The dust concentration of the gas treated by the bag dust collector directly affects the resistance and service life of the filter bag. The thicker the dust layer attached to the surface of the filter bag, the greater the resistance and the greater the impact on the service life of the filter bag. On the other hand, in order to clean the thick dust layer in time, it is necessary to strengthen the cleaning of the filter bag, that is, shorten the cleaning cycle (the cleaning cycle of the coated filter material is longer than that of the uncoated filter material), increase the cleaning frequency and extend the cleaning time, which will inevitably increase the wear and damage of the filter bag and affect its service life.
Appropriately reducing the dust concentration at the inlet is beneficial to extending the service life of the filter bag and improving the working condition of the entire dust collector. The measure is to add a level of pre-dust collection before entering the dust collector, such as the exhaust gas from the raw material mill first enters the cyclone dust collector, and some equipment designs have the gas enter the ash hopper first to achieve the effect of pre-dust collection.