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Operation and maintenance of bag filter
Asphalt mixing equipment will produce a large amount of high-temperature gas and dust in the production process. These emissions must be treated to meet the emission requirements. Therefore, the dust removal device equipped on the mixing equipment is very important. Bag filter is widely used in the tail gas treatment of asphalt mixing equipment because of its high dust removal efficiency, strong adaptability, simple structure and stable operation. This paper analyzes some common problems in the production of bag filter commonly used in asphalt mixing station, and puts forward solutions, which can be used as a reference for the operation and maintenance of bag filter equipment.
1. Dust removal principleThe bag filter used in asphalt mixing plant is mainly divided into pulse type and atmospheric back blowing type according to different ash cleaning methods. The basic working principle of pulse ash cleaning system is: when the top of the bag is opened, compressed air (also known as pulse) is introduced into the bag; The compressed air is controlled by a solenoid valve of a timing switch. The solenoid valve puts the air into the spray pipe, and each spray pipe corresponds to a row of cloth bags; The spray pipe with small holes is located directly above the mouth of each cloth bag, and its opening is at one end of the cloth bag; Each cloth bag is sleeved on a metal cage bone, and there is a venturi at the top of each metal cage bone, which is used to increase the amount of air carried by pulse air; When the solenoid valve is opened, the compressed air enters the cloth bag. With the increase of pressure in the cloth bag, the volume expands instantaneously. At this time, the dust attached to the surface of the cloth bag falls into the ash hopper, so as to achieve the purpose of ash removal.
（1）
Hydrocarbon pollutants in the original cloth bag
The first step in solving this problem is to determine the source of hydrocarbons polluting the cloth bag. It is most likely from the fuel. If the fuel is oil, especially heavy oil or waste oil, it may not be fully burned due to the high viscosity caused by low fuel temperature. If this reason is confirmed, the fuel oil can be preheated until the viscosity reaches 90 SSU or lower before combustion.
Insufficient cleaning
High differential pressure due to insufficient cleaning should adjust the pulse pressure and cycle. For example, the conventional initial setting is: pulse duration of 0.25 s, pulse interval of 0.15 s, and air pressure of 0.5-0.6 MPa. Some new systems can set three different pulse intervals, generally 10 s, 15 s or 20 s. If the cleaning is insufficient, the pulse interval can be reduced first. If the air pressure must be increased, it shall not exceed IO MPa, otherwise it is easy to cause cloth bag wear and reduce its service life.
(2) Dust emission occurs every cleaning pulse
This phenomenon may be due to the following two reasons.
Excessive cleaning. Excessive cleaning will hinder the generation of dust on the surface of the bag. At this time, the cleaning intensity should be reduced and the differential pressure should be reduced to 747 ~ 1245 PA.
Aging of cloth bags. Cloth bags may be aged for some reasons, such as overheating, chemical corrosion and wear. No matter what causes the bag aging, the bag should be replaced in time to avoid affecting the normal production.
(3) Corrosion of cloth bag
The corrosion of cloth bags may be caused by the following reasons.
Sulfur in fuel. Any fuel oil generally contains sulfur. The best solution is to find low sulfur fuel. In addition, the condensation of water can be avoided by increasing the temperature of the bag filter, because the sulfur dioxide formed in the burner must be mixed with the condensed water to form sulfuric acid.
Low temperature of bag filter. The low temperature of the bag filter is very likely to condense water in the bag filter, resulting in rust of parts; Moreover, corrosives may become more active after encountering condensed water.
The disordered reading of the differential pressure gauge may be due to the presence of moisture in the differential pressure pipe. If the general differential pressure pipe is lack of protection, as long as there is a slight leakage, it will cause water to be sucked into the pipe. The best solution is to select strong and reliable differential pressure pipe and take protective measures.
3. Summary
Bag filter has been the standard configuration of asphalt mixing equipment. At present, it has also become the mainstream product of high-efficiency dust removal equipment. In the process of use, it is necessary to operate and maintain actively according to the specifications. Once a fault is found, as long as the analysis is accurate and the treatment is timely, it can ensure the smooth operation of the pulse bag filter, effectively reduce the operation resistance, prolong the service life of the filter bag, reduce the gas for ash cleaning, achieve high dust removal efficiency with low operation cost, give full play to the advantages of the pulse bag filter and realize economic Efficient dust removal.
