Is Coal Dust Harmful?

Coal dust explosion. Coal is a flammable substance. If its dust floats in the air and reaches a certain concentration and there is a heat source sufficient to ignite the coal dust, a coal dust explosion can occur. Is one of the major disasters in coal mines. The explosion wave produced by the coal dust explosion can raise the coal dust deposited in the roadway, cause a continuous explosion, and even affect the entire mine. When coal dust explodes, the explosion temperature can reach 2300 ~ 2500 , the flame propagation speed can reach above 1120m / s, the shock wave speed can reach 2340m / s, and the destructive force is extremely strong. The explosion of coal dust generates a large amount of carbon monoxide, and its concentration can reach 2% to 3%, which can cause death by poisoning personnel. ^[1]

Volatile matter of coal

The explosion of coal dust is mainly carried out in the combustible gas (volatile matter) decomposed by the dust particles, so the quantity and quality of the volatile matter of coal are the most important factors affecting the dust explosion. Generally speaking, the higher the combustible volatile content of coal dust, the stronger the explosiveness. That is, coal with a low degree of coalification has a strong explosiveness of coal dust, which decreases with the increase of the degree of coalification.

Ash and moisture of coal

Ash in coal is a non-combustible substance, which can absorb energy, block thermal radiation, destroy chain reactions, and reduce the explosiveness of coal dust. The effect of coal ash on explosiveness is also related to the amount of volatile matter. For coal dust with less than 15% volatile content, the effect of ash is more significant. When it exceeds 15%, natural ash has almost no effect on the explosion of fine dust. Moisture can reduce the explosiveness of coal dust, because water has a large heat absorption capacity, which can promote the aggregation of fine dust particles into larger particles, reduce the total surface area of the dust particles, and also reduce the flying ability of falling dust. The natural ash and moisture of coal are very low, and the effect of reducing the explosiveness of coal dust is not significant. Only by artificially adding ash (rock dust) or moisture (sprinkling water) can the explosion of coal dust be prevented.

Coal dust particle size

Granularity has a great impact on explosiveness. All coal dust particles with a particle size of less than 1mm may participate in the explosion, and the risk of explosion increases rapidly with decreasing particle size. Coal dust below 75m, especially coal dust with 30 ~ 75m, is the most explosive, because The smaller the particle size, the larger the total surface area and surface energy. After the particle size is less than 10 m, the tendency of coal dust to increase explosiveness becomes gentle. The particle size of coal dust also has a significant effect on the explosion pressure. Test of Chongqing Branch of China Academy of Coal Science. The results show that under the condition of different particle sizes of the same coal type, the explosion pressure increases as the particle size decreases, and the explosion range also expands, that is, the explosiveness increases. The ignition temperature of coal dust with different particle sizes is also different. The smaller the particle size of coal dust, the lower the required ignition temperature and the faster the flame propagation speed.

Gas concentration in the air

Gas participation lowered the lower limit of coal dust explosion.

The "Procedures" stipulates that the geological inspection report of the new mine must contain all coal dust explosive identification materials. Each time the production mine is deepened to a new level, the coal mine explosion test will be organized by the Bureau of Mines.

There are two methods for the identification of coal dust explosiveness: one is performed in a large coal dust explosion test tunnel. This method is more accurate and reliable, but the work is heavy and complicated, so it is generally used as a standard identification; the other is in the laboratory. It is carried out by using large tubular coal dust explosive identification instrument, and the method is simple. At present, this method is mostly used.

(A) dust prevention measures

1,

The unique sign of coal dust explosion is different from gas explosion

When the coal dust exploded, a part of the coal dust was locally coked, bonded together, and deposited on the support and the wall of the roadway, forming the unique products of the coal dust explosion-"skin" and "sticky". This is a unique sign that a coal dust explosion is different from a gas explosion.

A new technology that can effectively suppress the generation of coal mine dust while preventing coal dust explosion and reducing the incidence of coal lung disease was fully put into use by major coal mine companies across the country at the end of 2010, and has been applied in practical conditions and environmental applications. Welcomed and praised by the majority of industrial and mining enterprises.

Overview of coal dust explosion technology

Mine foam dust suppression technology uses underground dust removal water pipes and compressed air pipes, adds a certain amount of additives to the water pipes, introduces compressed air through a special foaming device, generates high-fold foam, and sprays it to the dust source through a nozzle. The foam acts on the dust by means of good covering, moistening and adhesion, which fundamentally prevents the diffusion of the dust and effectively reduces the dust concentration in the air. Compared with other wet dust suppression, this technology can reduce water consumption by 30 to 80%, and the dust suppression efficiency is 3 to 5 times higher than that of spray water spraying. This technology mainly includes two products: mining foam dust suppression equipment and mining foam dust suppression liquid, which are used together.

Coal dust explosion dust suppression equipment

The product is mainly composed of a box and a foam generating device, a foam distributor, a foam nozzle and a support.

Special liquid for coal dust explosion suppression

This product is an additive specially developed for foam dust suppression technology. It has two functions of strong foaming ability and rapid change of the wettability of dust. The special fluid has two functions:

Generate high-fold foam to cover the dust production point, and fundamentally prevent the diffusion of dust;

Even if dust is diffused into the air, the foam liquid contained in the foam can quickly change the surface structure of the dust, change the dust from hydrophobic to hydrophilic, make the dust quickly wet and be captured, and increase the dust reduction efficiency.

Technical characteristics of coal dust explosion

(1) The foam can cover the cutting drum of the digging machine without voids, so that the cutting is completed in the foam body, which fundamentally prevents the dust from spreading outward;

(2) After the liquid forms foam, the total volume and total surface area are greatly increased, increasing the probability of collision with dust and increasing the efficiency of dust reduction;

(3) The liquid film of the foam contains special additives, which can greatly reduce the surface tension of water and rapidly increase the speed of dust being wetted;

(4) Foam has very good stickiness, and dust and foam will be quickly adhered by foam after contact.

(5) For high-gas mines, foam-covered cutting drums can effectively suppress sparks generated by cutting and prevent gas and coal dust explosions.

(6) The water consumption is small, which avoids the subsidence of the comprehensive excavator caused by the large water consumption of water mist and dust removal, which improves the work efficiency.

(7) The main equipment is fixed with strong magnets, which is easy to install, disassemble and maintain. ^[3]