What is the purpose of the explosion-proof steam used in medium-speed coal mills? Could someone explain this?

I understand it to be this: fine coal powder, combined with the high temperatures generated by the prolonged operation of the coal grinder, can lead to dust explosions. Explosion-proof steam (water) is essentially similar to a shielding gas, serving to displace air. I’m not sure if what I said is correct :)

The following information was found on Baidu; I hope it can help you. Reasons for coal dust explosions: Definition: Coal dust, as a type of dust, refers to dispersed solid particles. Coal dust explosion refers to the explosive phenomenon that occurs when combustible coal dust suspended in the air comes into contact with a heat source such as an open flame or an electric spark. Conditions: For combustible coal powder to explode, three conditions must be met: the coal powder itself must be explosive, it must be suspended in air and mixed with air to reach an explosive concentration, and there must be a heat source sufficient to trigger the explosion of the coal powder. The process of coal dust explosion: The explosion of coal dust can be considered to occur in three stages. The first stage is that the suspended coal dust undergoes rapid pyrolysis or gasification under the influence of a heat source, resulting in the generation of flammable gases ； The second step is the combustion that occurs when the combustible gas mixes with air ； The third step is that the heat released by the combustion of coal powder is transferred, through heat conduction and flame radiation, to the coal powder particles that are suspended in the vicinity or blown around; these particles vaporize when heated, thus allowing the combustion process to continue. As each cycle progresses, its reaction speed gradually increases, and through intense combustion, an explosion is ultimately formed. This explosion reaction, as well as the speed of the explosion flame, the speed of the shock wave, and the explosion pressure, will continue to increase and rise, showing exponential growth. Factors affecting coal dust explosion: The explosion properties of coal dust are influenced by factors such as the particle size of the coal dust, its volatility, moisture content, ash content, and the intensity of the ignition source. Characteristics of dust explosions: (1) Multiple explosions are the most prominent feature of coal dust explosions ； (2) The minimum ignition energy required for coal dust explosion is relatively high, generally above several dozen millijoules. (3) Compared with combustible gas explosions, coal dust explosions see a slower rise in pressure, the higher pressures persist for a longer time, release more energy, and possess greater destructive power. Principles of steam explosion prevention and fire extinguishing: Water vapor is an inert, non-flammable gas, and it is also a cost-effective fire extinguishing medium. It can dilute or displace the combustible gases and oxidizing gases in the combustion zone, reducing their concentrations, thereby achieving an effective smothering effect to extinguish the fire. Experience from actual fire fighting shows that when the air in a confined space contains more than 30% water vapor, it is possible to extinguish most fires. However, to successfully extinguish a fire by submersion, it is not only necessary to spray a sufficient amount of steam into the burning area, but also to rapidly create a steam curtain within that area in a short time, so that the steam reaches an effective concentration for extinguishing the fire. Reasons for spontaneous combustion and explosion in the coal grinding system: 1. Accumulation of coal and powder within the coal grinding system. For example, when the coal grinding system is shut down, if the coal powder in the mill is not completely removed or if there is accumulated coal at the mill’s inlet, etc., the accumulated coal can catch fire regardless of whether the coal grinding system is operating or not. 2. The outlet temperature of the coal grinder is too high. Due to the high temperature at the coal mill outlet, it may ignite the coal powder. 3. Coal supply interruption to the coal mill. If the coal supply to the coal grinder is interrupted, the outlet temperature may rise above the limit. 4. The coal powder is too fine and the moisture content is too low. 5. Severe air leakage from the powder bin. Air leakage from the powder bin may cause the coal powder to self-ignite due to the oxygen that enters the bin. 6. Coal powder with high volatility remains in the powder bin for too long. If coal with a high volatile content is stored for an extended period of time, the heat accumulated may cause the coal dust to catch fire on its own. 7. The coal may contain oils or other explosive substances. 8. The primary air duct leaks powder due to wear, or the flange connection leaks powder. 9. Leakage inside the hot air valve: Due to this leakage, a large amount of hot air enters the coal grinder, causing the coal stored there to catch fire; this can lead to an explosion in the pulverization system when it is restarted. 10. Spontaneous combustion of coal powder accumulated in the coarse powder separator: The annular gap between the lower part of the fine powder cone and the fixed cap cone in the coarse powder separator can sometimes be blocked by debris, resulting in excessive accumulation of coal powder, which may lead to its spontaneous combustion. 11. Ball entrapment or friction in the coal grinder. 12. There are external sources of fire.

Dust explosions and explosion-proof steam: Principles of coal dust explosions