The hottest dust explosion and explosion-proof des

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Dust explosion and explosion-proof design of bag type dust collector in recent years, domestic and foreign coal mine, electric power, textile, tensile testing machine enterprises should not only become partners with instrument and equipment enterprises, and dust explosion accidents such as food are common, which seriously endanger human life and production safety, causing huge casualties and property losses. Due to people's insufficient understanding and attention to dust explosion prevention, dust explosion accidents in some factories occur frequently. Most of these dust explosion accidents occur in the dust removal system, and the dust collector is the most dangerous area in the dust removal system. With the strengthening of environmental protection awareness, people are more and more strict about the requirements of polluting gases emitted by enterprises to the atmosphere. The bag filter is the bane of smoke and dust pollution, and it is an efficient dust removal equipment to control air pollution. The greatest advantage of the bag type dust collector is its high dust removal efficiency, which can reach 99.9% in practical application, and the dust emission concentration can reach below 10mg/m3, or even 1 mg/m3. Because of these advantages, bag filter has been applied in many enterprises. However, with the popularization of bag filter, the dust explosion accident of bag filter is also on the rise, so the explosion-proof design of bag filter has been put on the agenda. 1. Conditions and mechanism of dust explosion [1,2] three conditions are required for dust explosion: ① the dust in the air reaches a certain concentration, that is, it is within the upper and lower limits of explosion, and the lower limits of explosion are the most concerned; ② Ignition source with sufficient energy; ③ Sufficient air or oxygen mixed contact. Dust explosion is a very complex process, which is affected by many factors, so the explosion mechanism is still not very clear. It is generally believed that dust explosion goes through the following development processes: firstly, the surface of dust particles is heated after they obtain energy from the ignition source (heat conduction and heat radiation), and in addition, after they obtain energy, the dust particles are heated inside and outside successively to produce melting and gasification, bursting out hot tiny proton particles or sparks, Ignition source that can form dust. Due to the large surface area of dust, full contact with air and the existence of dust layer, the surface temperature of dust particles rises sharply, accelerating the decomposition or gasification of dust particles. When mixed with air, gas phase ignition can be formed. In this way, there are both gas phase and solid phase in the dust, and the combustion is more intense when the two phases exist at the same time. We have developed a dryer. Moreover, the accumulated friction of static electricity also forms an ignition source. When the dust concentration is mixed with air to reach the lower explosion limit, it can burn when encountering the ignition source. During the initial combustion, because the dust and air are fully mixed, the dust can explode and release energy in the form of pressure wave, so the dust in the mechanical device is often blown out to blow up the dust layer on the ground, forming flying dust clouds. These dust clouds are ignited by the burning residue of the initial explosion, This is followed by a second explosion and air turbulence. Because this explosion blows up a large amount of deposited dust again, its explosion power is much greater than the initial explosion. The dust explosion is affected by many factors, such as the formation of ignition source, minimum ignition energy and dust concentration. It can be seen from the explosion process that the diameter of dust particles is the determinant of the difficulty of detonation, the ignition source is the key factor of detonation, and the secondary explosion caused by ignition of dust cloud is the greatest harm. 2. Explosion proof technology explosion proof technology can be divided into preventive technical measures and design measures. Preventive measures are to make the dust concentration lower than the lower explosion limit and a large amount of dust accumulation, and to eliminate effective ignition sources; Design measures refer to the measures taken to reduce the degree of explosion hazard to a safe level when the measures to prevent explosion are difficult to work, so that the explosion will not cause casualties, and the equipment can be restored to use in a short time after the explosion, including anti explosion, explosion suppression, explosion isolation, explosion venting, etc. The bag type dust collector is used as the dust collection place, so that the dust concentration is always lower than the lower explosion limit, which is not economical and difficult to achieve; However, it is possible to prevent a large amount of dust from accumulating. Effective ignition sources shall be divided into the following two ignition sources: common ignition sources (such as ignition sources generated by welding, grinding and smoking) and ignition sources caused by mechanical faults (mechanical sparks, high-temperature surfaces, flameless combustion heat accumulation and electrostatic sparks). Among them, all kinds of motion friction ignition sources are the most common, and most accidents of dust explosion are caused by them. In addition, through investigation and test, corona discharge mainly occurs in dust cloud, and lightning discharge has not occurred in industrial production. In addition, it is difficult for industrial production equipment to generate such lightning discharge, unless the container volume of the formed dust cloud is greater than 60 m3 or the diameter is greater than 3m. Explosion resistance means that the structure itself can withstand the explosion pressure without bursting. There are two kinds of explosion-proof structures: explosion-proof pressure and explosion-proof impact pressure. The explosion-proof pressure design shall comply with the design and manufacturing specifications of pressure vessels, and the explosion-proof impact pressure can be appropriately relaxed. Generally: the explosion resistance pressure is 1.5 times of the explosion resistance pressure. Explosion suppression is a measure to extinguish the explosion of combustible substances in the equipment at the initial stage, so as to avoid excessive explosion pressure. A successful explosion suppression system can × It operates at 104pa, and the maximum pressure in the equipment after suppression is lower than 1 × 105Pa。 There are two kinds of explosion suppression. One is passive, such as water bag and flame retardant powder device. This kind of device will automatically break and scatter water or flame retardant powder when the explosion pressure rises to a certain range; The utility model relates to an intelligent explosion suppression device composed of an initial explosion detection sensor, a control unit and a high-speed spraying (HRD) explosion suppressor with high-pressure drive. The purpose of explosion-proof is to prevent the explosion in one container from spreading to subsequent containers along the connecting pipe, resulting in system explosion and greater losses. However, the explosion with the greatest harm in practice is because the explosion-proof device cannot work or is not designed. It can generally install a flame probe on the pipeline to drive the company's revenue in the first quarter to a new high since the third quarter of 2015, trigger the corresponding mechanism and realize explosion blocking. The dust explosion will generate a pressure as high as 0.7-1mpa, and the explosion relief measures can limit the rising pressure to the range that the strength of the component material can withstand. The dust explosion has the characteristics shown in Figure 1. The test time of the air pipeline (without air bottle) is more than 10min The pressure drop shall not be greater than 1%, where curve a represents the explosion in the closed container, Pmax represents the maximum explosion pressure, and PN represents the maximum explosion pressure rise rate; Curve B indicates that there is explosion venting, PRED indicates the maximum explosion pressure and PN indicates the maximum explosion pressure rise rate. It can be seen that explosion venting plays an important role in reducing explosion hazards

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