Fire and explosion prevention of the hottest dry d

2022-07-28
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Fire and explosion prevention of dry dedusting system

factories and mining enterprises will produce different dusts in the production process. These dusts not only pollute the plant environment and atmosphere, endanger people's health, but also seriously threaten the lives of on-site operators. This is because some dusts will explode under certain circumstances. People have been fully aware of the harmfulness of dust pollution, but they do not know enough about the harmfulness of dust deflagration under specific conditions, and even ignore the preventive measures and safety education in this regard. It was not until the big explosion of Harbin flax factory on march15,1987 that the alarm was sounded and attention was paid. Therefore, dust control should be understood and treated not only from the perspective of environmental protection, but also from the perspective of fire prevention and explosion prevention. This is the bounden duty of every enterprise, and it is also an important part of fire education and safety precautions. On march15,1987, an explosion accident occurred in Harbin flax factory, resulting in 58 deaths and 177 injuries. According to the experts of the accident investigation team, the explosion was caused by flax fiber dust. It can be seen that the harm of dust deflagration is very serious. Therefore, it is a very important measure to set up effective dust removal and special fixtures to meet the actual use needs

however, due to the limitations of production conditions and the requirements of process, wet dust collectors cannot be used for the dust generated in grain processing, metallurgical enterprises and some light and chemical production. In order to improve economic benefits, some dust must be recycled. Therefore, dry dust removal has become the only way for these enterprises to prevent dust

at present, industrial and mining enterprises are committed to reducing the dust emission of industrial equipment, vigorously promoting high-efficiency and energy-saving dust removal equipment, generally adopting high-efficiency dust collection devices such as electrostatic dust collection and bag type dust collection, and taking the old centrifugal dust collection device as the first level dust removal equipment. However, when dry dust removal equipment is used, the problems of fire prevention and explosion prevention are often ignored, and there are many deflagration accidents caused by improper operation of dust removal equipment. In 1978, a major magnesium dust explosion accident occurred in the second Xiangyang Chemical Plant of Jinan due to the friction and heating of the filter bag of the bag type dust collector, resulting in heavy casualties. Dust explosion also occurred in the dust removal equipment of a flour mill in Wendeng, Yantai. At the end of 1984, a workshop of Jinan match factory was damaged due to the dust removal equipment, which could not effectively discharge the wood dust in the workshop, and the improper use of fire caused a fire accident. According to reports in foreign journals, the number of explosion and fire accidents related to the use of dust collectors or dust removal devices increased from an average of two a year 10 years ago to six five years ago, and has increased to more than 20 in recent years. Therefore, with the popularization of dust removal devices, people should pay enough attention to such accidents

this paper discusses how to prevent dust explosion and combustion in the operation of the used dust removal facilities, especially the bag type dust removal equipment, for the reference of relevant units

I. conditions and factors of dust ignition and explosion

the dust produced in the production process of some factories and mines, especially the dust produced in the processing of some organic substances, will cause explosion and combustion accidents under certain specific conditions. The research results at home and abroad show that there are generally three kinds of conditions: (1) combustible dust is suspended in the air at an appropriate concentration to form a dust cloud; (2) Sufficient air and oxidant; (3) There is a fire source or strong vibration and friction. It is generally believed that as long as explosive dust meets conditions (1) and (2), it means that it has the potential for accidents

1. classification of explosive and non explosive dusts

generally, the dusts prone to explosion accidents include aluminum powder, zinc powder, ferrosilicon powder, magnesium powder, iron powder, aluminum processing grinding powder, various plastic powders, intermediates of organic synthetic drugs, wheat powder, sugar, sawdust, dyes, bakelite ash, milk powder, tea powder, tobacco powder, coal dust, plant fiber dust, etc. The reason why the dust of these materials is prone to explosive combustion is that there are strong reductants h, C, N, s and other elements. When they coexist with peroxides and explosive dust and get the strong support and enthusiastic participation of enterprises and institutions in the global aluminum industry, they will decompose, and a large amount of gas will be produced by oxidation reaction, or a large amount of combustion heat will be released although the amount of gas is small. For example, aluminum powder has the risk of explosion as long as it is in carbon dioxide atmosphere

the difficulty of dust explosion is related to the physical and chemical properties of dust and environmental conditions. It is generally believed that substances with greater combustion heat are more likely to explode, such as coal dust, carbon, sulfur, etc. Substances with fast oxidation rate are easy to explode, such as magnesium powder, aluminum powder, ferrous oxide, dyes, etc. Dust easy to be charged can also easily cause explosion, such as synthetic resin powder, fiber dust, starch, etc. These poorly conductive substances accumulate due to the static electricity generated by friction with the machine or air. When they reach a certain amount, they will discharge and generate electric sparks, which constitute the fire source of explosion

dust that is not easy to cause explosion includes soil, sand, iron oxide, abrasive materials, cement, quartz dust, and dust similar to that after combustion in case of abnormal conditions in the control system. The dust chemical properties of this kind of material are relatively stable, so it is not easy to burn. However, if such dust is generated in oil mist and combustible gases such as CO, CH4 and coal gas, it is also prone to explosion

2. causes of fire and explosion in the dust removal system

in order to prevent dust pollution and dust explosion, it is necessary to use the dust removal system to timely discharge the dust in the working environment and reduce the dust concentration in the workshop. However, for combustible dust, fire prevention and explosion-proof measures must also be taken for dust removal equipment, otherwise improper use will also cause explosion and fire accidents. The explosion and fire of the dust removal system are mainly caused by the satisfaction of conditions (1) and (2). Since the general dust remover inhales air and then discharges it, the oxygen supply in the dust removal system is sufficient. According to the investigation, the fire possibility of the dust removal system is mainly caused by electrostatic spark, spontaneous combustion, impact friction and open fire. The electrostatic spark is caused by the charged nylon filter cloth and pipeline of the dust collector. Spontaneous combustion is caused by the oxidation heat accumulated due to the slow oxidation reaction of the captured dust in the cloth bag or ash hopper. Impact friction is generally considered to be the collision of iron sheets sucked by the dust removal system, or the sparks caused by the collision when the hammer is used to vibrate the dust attached to the ash hopper or bag during maintenance and cleaning. Open flame is caused by gas welding flame and electric welding spark during maintenance

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