The essence of mine nitrogen fire prevention is to inject a certain amount of nitrogen into the goaf oxidation zone or fire area to reduce the oxygen content to below 5%, so as to achieve the purpose of preventing fire and suppressing gas explosion. Compared with other fire-fighting methods in mines, nitrogen fire-fighting technology is superior to traditional grouting fire-fighting technology: the nitrogen injection process is quick and rapid. The product's nitrogen temperature is low, and the nitrogen can quickly permeate and fill the corners of the oxidation zone or fire zone in the goaf. In the grouting process, because the flow of the slurry in the oxidation zone or the fire zone in the goaf area is affected by the uneven floor, the roof falling and the uneven accumulation, etc., a "flow channel" will be formed, so it cannot be uniformly and fully covered in the "media On the surface, it failed to truly "isolate" oxygen and prevent coal from oxidizing and spontaneously combusting. Therefore, nitrogen fire-fighting technology has better fire-fighting effects.

Principle of Nitrogen Fire Fighting

Eliminate the danger of gas explosion

In coal mines, once a fire occurs in the goaf, the most harmful one causes the explosion of the mixed gas in it. The explosion limit of the mixed gas depends not only on the percentage of the gas in the air, but also partly on the temperature and pressure of the mixed gas. The increase in temperature and air pressure expands this limit, and vice versa. When the oxygen content is less than 7%, the explosion of the mixture is significantly reduced. It is from this theory that the oxygen content is reduced after nitrogen is injected into the fire area, and as long as the oxygen content is less than 7%, the possibility of explosion can be greatly reduced.

Reduce the effect of air leakage

Air leakage in the goaf is one of the main causes of spontaneous fire, let's talk. For closed or semi-closed goaf areas, theoretically speaking, the total amount of mixed gas in the injected space is increased after nitrogen injection, which can reduce the pressure difference between the closed area and the outside, and reduce the external flow of the closed area. The role of internal air leakage.

If there are cracks in the enclosed wall in the roadway, when the enclosed area is under negative pressure, the air can enter the enclosed area through the wall crack or bypass the enclosed wall. In order to prevent air leakage in the confined area, the necessary flow of nitrogen can be continuously injected into the space between the front and rear walls of the confinement to form a positive pressure in the space to prevent fresh air from entering the confined area.

Cooling effect

For goafs with internal fires, the temperature is greater than the outside temperature. When using nitrogen to extinguish the fire, the temperature of the product nitrogen is between 0～5℃, which is much lower than the gas temperature in the fire area. In addition, the flow range of nitrogen after being injected into the fire area is large, which has a significant cooling effect on the goaf area. effect.

Prevent spontaneous combustion of coal

The three elements of coal spontaneous combustion: coal has a tendency to spontaneous combustion; there is continuous oxygen supply conditions; heat is easy to accumulate. The air leakage in the goaf is not enough to take away the heat generated by coal oxidation, and the coal temperature gradually rises, and the coal is in spontaneous combustion and heating. When the temperature reaches above the critical temperature of coal, rapid oxidation accelerates, a large amount of heat is generated, and the temperature of coal rises rapidly. When it reaches the ignition temperature of coal, it ignites and burns, that is, it enters spontaneous combustion. Based on this coal-oxygen compound theory, a certain flow of nitrogen is injected into the oxidation zone of the goaf to reduce the oxygen content in the zone, which is a factor that destroys the spontaneous combustion of coal and reduces the oxygen content below the critical value of coal spontaneous combustion. The purpose of preventing spontaneous combustion of coal has been achieved.

Reduce burning intensity

Whether it is an external fire or an internal fire, when a certain flow of nitrogen (greater than the air leakage) is quickly injected into the fire area, the oxygen content in the area is gradually reduced from 21% to less than 10%, and the raging fire will gradually self-extinguish.

Precautions for Nitrogen Fire Prevention in Mines

The practice of mine nitrogen fire prevention and extinguishing shows that: this technology has the advantages of fast fire extinguishing speed, not only can prevent fire, but also inhibit gas explosion, and has no pollution to the environment and electromechanical equipment. However, the following issues should be paid attention to when applying mine nitrogen to prevent and extinguish fires:

1. While implementing the nitrogen injection process, it is necessary to strengthen the plugging, reduce the air leakage in the goaf as much as possible, and improve the airtight quality of the goaf so that the nitrogen can be stored.

2. In the selection of the nitrogen production device, a certain "gas production" must be considered. Only when a certain amount is satisfied can the effect of nitrogen injection to prevent fire extinguishing can be effectively achieved. Because there is no impermeable "wall" (airtight). Affected by many factors such as mining, it will cause the destruction of the surrounding rocks in the goaf and form an air leakage channel in the goaf. Assuming that there is an air leakage rate of 10Nm3/min in the goaf, if the gas production rate of the nitrogen generator is 600Nm3/min, then the gas production rate per minute is only 10Nm3, that is, the nitrogen injection rate and the air leakage rate are basically the same. Can it reduce the oxygen content in the goaf? Therefore, only a large amount of nitrogen can truly meet the actual demand for nitrogen fire prevention in mines.

3. When the nitrogen generator is used for fire prevention, high-flow (95-97%) purity nitrogen can be used, and when used to reduce the oxygen content, a small flow and high-purity (99-99.9%) nitrogen can be used.

A fixed nitrogen generator for mine

B Ground vehicle-mounted and underground vehicle-mounted nitrogen making device