How to prevent dust explosion of the hottest explo

How to prevent dust explosion of explosion-proof bag filter

dust explosion is the oxidation reaction that the dust particles suspended in the air are in full contact with the oxygen in the air, which is completed instantaneously under specific conditions, and a large amount of heat is released in the reaction, resulting in the phenomenon of high temperature and high pressure. Any dust explosion must have three conditions: ignition source; Combustible fine dust; The dust is suspended in the air and reaches the limit range of explosion concentration

(1) dust explosion is more complex than combustible substances and combustible gases. Generally, combustible dust is suspended in the air to form a dust cloud within the explosion concentration range. Under the action of the ignition source, part of the dust in contact with the ignition source is first ignited and forms a small fireball. Under the action of the heat released by the combustion of this small fireball, the surrounding dust is heated, the temperature rises, and the phenomenon of ignition and combustion occurs. In this way, the fireball will expand rapidly and form a dust explosion

the difficulty and intensity of dust explosion are closely related to the physical and chemical properties of dust and the surrounding air conditions. Generally, the greater the heat of combustion, the finer the particles, and the higher the activity of the dust, the greater the risk of explosion; Light suspended solids and combustible substances have great explosion risk; When the oxygen content in the air is high, the dust is easy to be ignited and the explosion is also violent. Because moisture can inhibit explosion, the drier the dust and gas are, the greater the risk of explosion

(2) after the occurrence of dust explosion, secondary explosion often occurs. This is because at the first explosion, many dust are deposited together, and their concentration exceeds the upper limit concentration value of dust explosion, so they cannot explode. However, when the shock wave or air wave formed by the first explosion lifts up the deposited dust again, it will mix with the air in the air, and the concentration is within the scope of dust explosion, which may be followed by a second explosion. The disaster caused by the second explosion is often much more serious than the first explosion

the direct cause of the dust explosion accident in a domestic aluminum product factory in 1963 was the friction and fire between the exhaust fan impeller and the end face of the suction inlet. The shrimp bend and underpants tee at the suction inlet of the fan have poor air flow and are easy to accumulate dust. In particular, it is easier to retain dust during shutdown. Once started, the deposited dust will be lifted up and soon reach the lower explosion limit, causing dust explosion

(3) mechanism of dust explosion when combustible dust burns in the air, it will release energy, and the well will produce a large amount of gas, and the speed of releasing energy, that is, the size of the combustion speed, is related to the area of the powder exposed to the air. Therefore, for the powder of the same solid substance, in order to judge and analyze the product failure and failure mode during or after the experiment, the smaller the particle size is, the larger the specific surface area is, and the faster the combustion diffusion is. If the particle size of this solid is very fine. As a result, it can be suspended. Once it is ignited by an ignition source, a large amount of energy can be released in a very short time. These energies have no time to escape into the surrounding environment, causing the gas in the space to be heated and expand adiabatically. On the other hand, a large amount of gas will be produced when the powder is burned, which will make the system form a local high pressure, resulting in explosion and propagation, which is commonly known as dust explosion

(4) the difference between dust explosion and combustion the combustion of large solid combustibles advances inward in a nearly parallel layer, such as the combustion of coal. This kind of combustion energy is released slowly. The heat and gas generated can escape quickly. The pile combustion of combustible dust forms open flame combustion under good ventilation, while under poor ventilation. It can form smoke-free or flame hidden combustion

there are several stages in the combustion of combustible dust: in the first stage, the surface powder is also heated; In the second stage, the surface layer is gasified and volatile matter overflows; In the third stage, volatilize and distribute gas phase combustion

the explosion of ultra-fine powder is also a relatively complex process. Because the scale of preliminary revision of the installation accuracy of dust cloud 2 experimental machine is generally small, and the flame propagation speed is fast, hundreds of meters per second, which can not be met in other places. Therefore, the ignition source is generated in the dust center, and the whole dust will be combustible in less than 0.1s until the end of 2015. In this process, if the dust has been burned out, the highest pressure will be generated; If it is not burnt out, a lower pressure will be generated. Whether combustible particles can burn out depends on particle size and burning depth

(5) classification of combustible dust powder can be divided into two categories according to its flammability: one is combustible; One is non combustible. The classification methods and standards of combustible powders are different in different countries

the United States classifies combustible powder as class II dangerous goods, while metal powder, carbon dust and grain dust are included in different groups. The classification method developed by the United States is to classify the tested powder according to the pressure rise speed obtained when the dust explosion occurs in the standard test device, and it is divided into three levels. At present, there is no ready-made standard for the classification of combustible dust in China