(1) The dust explosion is more complicated than the combustible material and the combustible gas. The combustible dust is suspended in the air to form a dust cloud within the explosive 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 emitted by the burning of this small fireball, the surrounding dust is heated, the temperature rises, and the burning phenomenon occurs, so that the fireball will rapidly expand to form a dust explosion.
(2) After a dust explosion occurs, a secondary explosion often occurs. This is because during the first explosion, a lot of dust was deposited together, and its concentration exceeded the upper limit of the dust explosion and could not be exploded. However, when the shock wave or gas wave formed by the first explosion re-raises the deposited dust, it is mixed with air in the air, and the concentration is within the dust explosion range, and a secondary explosion may occur next. The disaster caused by the second explosion is often much more serious than the first explosion.
(3) Mechanism of dust explosion: When powdered combustible dust is burned in the air, energy is released, and the well generates a large amount of gas, and the speed at which the energy is released, that is, the burning speed is related to the area in which the powder is exposed to the air. Therefore, for a powder of the same solid substance, the smaller the particle size, the larger the specific surface area, and the faster the combustion diffusion. If the particle size of the solid is so fine that it can be suspended, once the ignition source is ignited, a large amount of energy can be released in a very short time. These energies are too late to dissipate into the surrounding environment, causing the gas in the space to be heated and adiabatically expanded. On the other hand, when the powder is burned, a large amount of gas is generated, which causes the system to form a local high pressure, which causes explosion and propagation. This is usually It is called a dust explosion.
(4) The difference between dust explosion and combustion: the combustion of large solid combustibles is carried out inwardly to the parallel layer, such as the combustion of coal. This release of combustion energy is relatively slow. The heat and gas generated can escape quickly. The pile-like combustion of flammable dust forms an open flame when ventilated well, and forms a smokeless or flame smoldering under poor ventilation.
(5) Combustible dust classification Powders can be classified into two categories according to their flammability: one is flammable; the other is non-combustible. The classification methods and standards for combustible powders vary from country to country.