Many accidents are caused by dust explosions, what is the principle of dust explosions?

Dust is produced when a certain amount of combustible dust is dispersed in the air at a sufficient concentration.

When ignited by flames, sparks, or other ignition sources, it causes a violent reaction. Because combustible dust can be made from many different types of materials, including metals, dust can occur in a variety of operating situations**. Many solid materials become flammable if they are broken down into small particles with a relatively large surface-to-mass ratio.

Dust is caused by the rapid ignition of the material that forms the dust cloud. If the material burns fast enough to consume all the oxygen (or other fuel sources) in the environment before all the material is consumed, there is a chance that a follow-up will occur. Combustible dust** is a serious hazard.

They can be caused by the scattering of dust accumulation (only as thick as paper). From the perspective of daily life experience, this phenomenon called dust ** is actually quite easy to produce. <>

Any solid material that can be burned in air will burn very quickly, and this rate will increase with the degree of subdivision of the material. When the material is cut into small pieces, the rate of combustion increases due to the increase in the total contact area between the material and the air. If it continues to shrink to the level of small particles to millimeters or less, and the particles are suspended in air large enough that each particle has enough space for unrestricted burning, the combustion rate will be very fast and the energy required for ignition will be very small.

In general, the smaller the dust cloud, the easier it will ignite and burn more violently. If the combustion of a dust cloud occurs inside a device or building, the pressure in a completely or partially enclosed space may rise rapidly and the equipment or building may rupture, potentially resulting in loss of life and property. Dust blasting is a proven method of preventing damaging** overpressure and is by far the most popular explosion protection technology.

The exhaust gas during the dust-proof blasting process can safely release the pressure generated in the process inside the container into the environment, thereby preventing the container from rupturing.

Dust** occurs when a certain amount of combustible dust is dispersed in the air at a sufficient concentration and causes a violent reaction when it is ignited by flames, sparks, or other ignition sources. Because combustible dust can be made from many different types of materials, including metals, dust can occur under a wide range of operating conditions**. If many solid materials are broken down into small particles with a relatively large surface-to-mass ratio, they will become flammable.

Combustible dust** has caused a large number of workers** and can destroy entire buildings.

This is because the dust in the air reaches a certain concentration, which will cause dust explosions, and I hope everyone should pay attention to safety to avoid accidents.

A large amount of combustible dust forms a dust cloud in the presence of oxygen or air, floats in the air, and then rubs or burns violently.

Factors influencing coal dust**:

Traditional coal dust is usually studied by using the particle size and mass concentration of pulverized coal as independent variables, ignoring the influence of different factors such as ash content and volatile matter in pulverized coal.

Therefore, according to the concept of pulverized coal ** equivalent ratio, combined with the ash content of each coal sample in industrial analysis, the correspondence between the stoichiometric ratio concentration and the actual pulverized coal mass transfer concentration is obtained, so as to study the influence of different equivalent ratio concentrations on the flame propagation of pulverized coal detonation and quiet explosion.

1.Physicochemical properties of coal.

2.Coal dust particle size.

A dust storm is a storm formed by high winds that sweep large amounts of dust and other fine particles into the air. A large amount of dust and sand particles are blown up by strong gusts of wind or strong winds, flying in the air and causing turbidity in the air, and the horizontal visibility is less than 1 km, also known as sandstorms, and the consequence of this is endless flying sand, which has gradually become one of the common natural disasters in the world. Gao Yuanheng.

Strong sandstorms in southern Xinjiang and the Hexi Corridor in China, which can sometimes bring visibility close to zero, and the day is like night, known locally as the black wind.

A sandstorm is a weather phenomenon in which strong winds blow dust and sand on the ground, making the air very turbid, and the horizontal visibility is less than 1 km. Dust storm is a weather phenomenon in wind erosion desertification, and its formation is affected by both natural factors and human activities due to coercetin.

Natural factors include high winds, reduced precipitation, and their sources of sand. Human activity factors refer to the increase in the frequency of sand and dust storms caused by the destruction of vegetation by humans in the process of economic development.

Sandstorm weather mainly occurs in winter and spring, which is due to the semi-arid and arid areas in winter and spring with little precipitation, the surface is extremely dry and loose, and the resistance to wind erosion is very weak.

Dust**, refers to the dust within the limit range, encountering a heat source (open flame or temperature), the flame instantly spreads in the entire mixed dust space, the chemical reaction speed is extremely fast, and a large amount of heat is released at the same time, forming a very high temperature and a lot of pressure, the energy of the system is converted into mechanical work and light and heat radiation, which has a strong destructive force.

Dust is mostly in the production and processing sites accompanied by aluminum powder, zinc powder, aluminum Jingyu high-grade processing and grinding powder, various plastic dismantling powder, intermediates of organic synthetic drugs, wheat flour, sugar, sawdust, bright ruler dyes, bakelite ash, milk powder, tea powder, tobacco powder, coal dust, plant fiber dust, etc.

Particle size has a great impact on performance. The particle size below 1mm may be involved in the coal dust particles, and the danger of the first is rapidly increased with the decrease of particle size, the coal dust below 75 m, especially the coal dust of 30 75 m, is the strongest, because the smaller the particle size of the coal dust per unit mass coal dust level, the greater the total surface area and surface energy, and the particle size is less than 10 m, the trend of increasing the quality of coal dust becomes flat. The particle size of coal dust also has a significant effect on the pressure.

Experiment of Chongqing Branch of China Coal Research Institute. The results show that under the condition of different particle sizes of the same coal type, the pressure increases with the decrease of particle size, and the range of coal dust increases accordingly, that is, the quality is enhanced, and the coal dust ignition temperature is different for different particle sizes.

The smaller the particle size of the coal dust, the lower the required ignition temperature and the faster the flame propagation.

4 Concentration of gas in the air.

The participation of gas reduces the lower limit of coal dust. When the gas concentration is less than 4%, the lower limit of coal dust can be calculated using the following formula:

Where: - Lower limit of coal dust when there is gas in the air**, g m3

** lower limit of dust blasting, g m3

k - coefficient, see Table 1 below.

Table 1 Influence coefficient of gas concentration on the lower limit of coal dust**.

% of gas depth in the air

0k 1 With the increase of gas concentration, the lower limit of coal dust concentration decreases sharply, which should be paid great attention to in mines with gas and coal dust danger. On the one hand, coal dust is often caused by gas; On the other hand, when coal dust is involved, a small-scale gas accident may evolve into a large-scale dust gas accident, causing serious consequences.

5 The amount of oxygen in the air.

When the oxygen content in the air is high, the temperature at which the coal dust is ignited can be reduced; When the oxygen content is low, it is difficult to ignite the coal dust cloud, and when the oxygen content is less than 17%, the coal dust is no longer **. The ** pressure of coal dust also varies with the amount of oxygen in the air. High oxygen content, high pressure; Low oxygen content, low pressure.

6 Detonate the heat source.

To ignite a cloud of coal dust to cause coal dust**, there must be an initiating heat source that meets or exceeds the minimum ignition temperature and energy. The higher the temperature of the detonating heat source, the greater the energy and the easier it is to ignite the dust cloud. And the intensity of the initial explosion of the dust is also greater; On the contrary, the lower the temperature, the smaller the energy, the more difficult it is to ignite the coal dust cloud, and even if it is caused, the initial intensity of ** is smaller.

Ignition sources that can cause coal dust in mines are common, such as artillery ignition sources, electrical sparks, collision sparks, or localized fires or biogas**.

When the coal dust encounters the fire source, the coal dust around the fire source is quickly gasified to prevent flammable gases, these gases are mixed with air and ignited, and the heat of combustion is transferred to the nearby coal dust and makes them heated and combusted. At the location of the occurrence, the air is heated and expanded, the air density becomes thinner, and a negative pressure area is formed in a very short period of time, and the external air is regurgitated and impacted to the location under the action of the air pressure difference, bringing fresh air.

Coal dust and oxygen reach a certain concentration, and it will be caused by open flame or static electricity.

1 Volatile matter of coal.

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

2 Ash and moisture content of coal.

The ash in the coal is an incombustible substance, which can absorb energy, block heat radiation, destroy the chain reaction, and reduce the quality of coal dust. The impact of coal ash on the first property is also related to the amount of volatile content, the volatile content is less than 15% of the coal dust, the impact of ash is more significant, more than 15%, the natural ash has almost no effect on the dust. Water can reduce the quality of coal dust, because the heat absorption capacity of water is large, which can promote the coalescence of fine dust particles into larger particles, reduce the total surface area of dust particles, and at the same time reduce the flying ability of falling dust.

The natural ash and moisture content of coal are very low, and the effect of reducing the quality of coal dust is not significant.