The essence of nitrogen injection for fire prevention and extinguishing is to inject a certain flow of nitrogen into the oxidation zone or fire zone of the goaf, reducing its oxygen content to 10% or less than 3%, achieving the purpose of fire prevention, extinguishing fire, and suppressing gas explosion. Its functions include:

1. Eliminate the danger of gas explosion

Once a fire occurs in the goaf of a coal mine, the greatest danger is the explosion of the mixed gas inside it. According to the mixed gas explosion triangle, if the oxygen content in the mixed gas is less than 12%, there is a possibility of reducing the explosion. However, the limit of a mixed gas explosion not only depends on the percentage of this gas in the air, but also partly on the temperature and pressure of the mixed gas. The increase in temperature and pressure expands this boundary, and vice versa. If the mixed gas is heated to 300 ℃ and the oxygen content is 9%, an explosion can occur.

2. Cooling effect

For goafs with internal fires, their temperature is higher than the external temperature. When using nitrogen for fire extinguishing, whether using liquid nitrogen or nitrogen, the temperature of the nitrogen is lower than the gas temperature in the fire area. In addition, the flow range of nitrogen after injection into the fire area is large, which has a significant cooling effect on the goaf.

3. Prevention of natural heating and spontaneous combustion of coal

The three elements of coal spontaneous combustion are: coal has a tendency towards spontaneous combustion; Having continuous oxygen supply conditions; Heat tends to accumulate. The leakage air volume in the oxidation zone of the goaf of the coal mine production face is not enough to carry away the heat generated by coal oxidation, and the coal temperature gradually increases, at which point the coal is in a natural heating state. When the temperature reaches above the critical temperature of coal, rapid oxidation and agglomeration accelerate, generating a large amount of heat, and rapidly increasing the coal temperature. When the ignition temperature of coal is reached, it ignites and burns, entering a state of spontaneous combustion. By injecting a certain flow of nitrogen gas into the oxidation zone of the goaf of the working face, the oxygen content in the zone is reduced to disrupt a factor of coal spontaneous combustion, and the oxygen content is reduced below the critical value of coal spontaneous combustion, thus achieving the goal of preventing coal spontaneous combustion.

Pressure swing adsorption nitrogen production equipment is used for coal mine fire extinguishing, and there are three types of equipment: (1) ground fixed nitrogen production equipment with a nitrogen electricity level of 98% and a production capacity of 200-2000m3/h; (2) ground mobile nitrogen production equipment with a nitrogen purity of 98% and a production capacity of 200-1200m3/h; (3) underground mobile nitrogen production equipment with a nitrogen purity of 98% and a production capacity of 200-800m3/h.

In addition to being widely used in university laboratories and industrial production, high-purity nitrogen plays a more important role in safety protection in coal mine production. The role and application principle of nitrogen in extinguishing are as follows:

The essence of nitrogen injection for fire prevention and extinguishing is to inject a certain flow of nitrogen into the oxidation zone or fire zone of the goaf, reducing its oxygen content to 10% or less than 3%, achieving the purpose of fire prevention, extinguishing fire, and suppressing gas explosion. Its functions include:

1. Eliminate the danger of gas explosion

Once a fire occurs in the goaf of a coal mine, the greatest danger is the explosion of the mixed gas inside it. According to the mixed gas explosion triangle, if the oxygen content in the mixed gas is less than 12%, there is a possibility of reducing the explosion. However, the limit of a mixed gas explosion not only depends on the percentage of this gas in the air, but also partly on the temperature and pressure of the mixed gas. The increase in temperature and pressure expands this boundary, and vice versa. If the mixed gas is heated to 300 ℃ and the oxygen content is 9%, an explosion can occur.

2. Cooling effect

For goafs with internal fires, their temperature is higher than the external temperature. When using nitrogen for fire extinguishing, whether using liquid nitrogen or nitrogen, the temperature of the nitrogen is lower than the gas temperature in the fire area. In addition, the flow range of nitrogen after injection into the fire area is large, which has a significant cooling effect on the goaf.

3. Prevention of natural heating and spontaneous combustion of coal

The three elements of coal spontaneous combustion are: coal has a tendency towards spontaneous combustion; Having continuous oxygen supply conditions; Heat tends to accumulate. The leakage air volume in the oxidation zone of the goaf of the coal mine production face is not enough to carry away the heat generated by coal oxidation, and the coal temperature gradually increases, at which point the coal is in a natural heating state. When the temperature reaches above the critical temperature of coal, rapid oxidation and agglomeration accelerate, generating a large amount of heat, and rapidly increasing the coal temperature. When the ignition temperature of coal is reached, it ignites and burns, entering a state of spontaneous combustion. By injecting a certain flow of nitrogen gas into the oxidation zone of the goaf of the working face, the oxygen content in the zone is reduced to disrupt a factor of coal spontaneous combustion, and the oxygen content is reduced below the critical value of coal spontaneous combustion, thus achieving the goal of preventing coal spontaneous combustion.

Pressure swing adsorption nitrogen production equipment is used for coal mine fire extinguishing, and there are three types of equipment: (1) ground fixed nitrogen production equipment with a nitrogen electricity level of 98% and a production capacity of 200-2000m3/h; (2) ground mobile nitrogen production equipment with a nitrogen purity of 98% and a production capacity of 200-1200m3/h; (3) underground mobile nitrogen production equipment with a nitrogen purity of 98% and a production capacity of 200-800m3/h.