3.The structural characteristics and selection of bag filter
(1) Selection of filter bag: bag filter is a kind of filter, inertial collision, interception, diffusion, static electricity, gravity sedimentation, etc. of solid dust in dusty gas in filter bag by using organic fiber or inorganic fiber filter cloth. A high-efficiency dedusting equipment separated from the bottom, the quality of the bag is directly related to the efficiency of the dust removal system. Exquisite sewing technology and the selection of suitable high-quality filter materials are the key to protecting the system’s high efficiency. The development of filter media in China is synchronized with the development of bag filter. The filter material for dust removal in asphalt mixing equipment is mainly NOMEX needle felt filter material and aramid needle felt filter material.
If the asphalt mixing equipment uses heavy oil, coal or other impurity oils as fuel, the NOMEX needle felt filter material should be treated in different ways to suit different application requirements, especially with high sulfur heavy oil and impurity oil. Or the raw material has a high water content, which causes the dust of the asphalt mixing equipment to be viscous, and the smoke component is acidic. NOMEX needle felt filter material with acid, oil and water repellent treatment can greatly improve the wear resistance, high temperature resistance, acid and alkali resistance, hydrolysis resistance and dimensional stability of NOMEX filter material, and improve the filter bag. Gray performance and dust removal efficiency as well as bag life. Therefore, NOMEX (polyaramid) high temperature needle felt filter material is one of the ideal filter materials for asphalt concrete equipment dust collector, and the service life can reach more than 2 years.
(2) Temperature control: Generally, the NOMEX filter bag is subjected to a temperature of 200 ° C, so the inlet temperature of the treatment facility should be controlled below 200 ° C. When the flue gas passing through the pipe reaches the dust collector box, the temperature can be lowered to 200 ° C. the following. In order to protect the bag from accidental burning, a safety valve is installed on the flue of the bag filter, and high and low temperature protection devices are provided to extend the service life of the filter bag.
(3) Fan selection: adopt the suction mode that can adjust the size of the damper to adjust the negative pressure of the equipment and the flame size of the burner or boiler.
(4) According to the cleaning effect and service life of the filter bag, most of the current dust collectors use atmospheric backflushing or pulse cleaning.
(5) Air leakage rate: Theoretically, the dust removal efficiency of the bag filter is up to 99%, but it is not achieved in the actual measurement, mainly due to the influence of air leakage. The lower the air leakage rate, the better the dust removal effect.
(6) Filtration wind speed: the lower the average filtering wind speed, the larger the filtering area, the higher the dust removal efficiency, the longer the bag life, but the cost will increase accordingly. Therefore, according to the working conditions, choose the appropriate filtering wind speed, and the general wind speed is controlled. 1~2m/min, the dust removal effect is also better.
(7) Container type dust removal system: a settling chamber is installed in front of the dust collector box, and a bag filter is arranged at the back to form secondary dust removal. The sedimentation chamber can remove a part of large particle dust, reduce the temperature and reduce the pressure of the precipitator. This part of the large particle dust can be directly reused as fine aggregate; the fine dust collected by the bag filter in the back can be recycled and reused as a powder. The dust removal effect is achieved and the raw materials can be saved.
(8) The dust removal system is also equipped with automatic adjustment of negative pressure to ensure that the operating conditions are always in an optimal state and reduce system energy consumption.
(9) The filter bag should generally be pre-coated to prevent the burner from burning incomplete oil or sticky dust into the bag filter, directly sticking to the filter bag and causing the paste bag phenomenon.
(10) Designed a double-lever gravity control valve: used for ash discharge under the screw conveyor under the first and second stage dust collectors. The dust is sent to the hot aggregate hoist or powder hoist by the screw conveyor for recycling or arranging. The valve cover is controlled by a counterweight of different weights, and the valve can be automatically switched to ensure that the valve is always closed, and the negative pressure of the dust removal system is not affected by the outside world.