In the coal mine, once the goaf is in fire, it will cause the explosion of mixed gas. The explosion limit of mixed gas depends not only on the percentage of the gas in the air, but also partly on the temperature and pressure of the mixture. The increase of temperature and air pressure enlarges the boundary and narrows it on the contrary. 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 in the fire zone will be reduced after nitrogen injection, and the possibility of explosion will be greatly reduced as long as the oxygen content is less than 7%.
Reduce combustion intensity
Whether it is an external fire or an internal fire, when a certain flow of nitrogen (greater than the air leakage) is rapidly 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 extinguish itself.
Prevention of spontaneous combustion of coal
The three factors of coal spontaneous combustion are: coal has spontaneous combustion tendency; continuous oxygen supply conditions; heat is easy to accumulate. If the leakage air volume in the goaf is not enough to take away the heat generated by coal oxidation, the coal temperature will gradually increase, and the coal is in spontaneous combustion. When the temperature reaches above the critical temperature of coal, the oxidation is accelerated, a large amount of heat is generated, and the temperature of coal rises rapidly. When the temperature reaches the ignition temperature of coal, it will ignite and burn, that is, it will enter into spontaneous combustion state. Based on the coal oxygen compound theory, the oxygen content in the oxidation zone of goaf can be reduced by injecting a certain flow of nitrogen into the oxidation zone of the goaf, so as to destroy an element of coal spontaneous combustion and make the oxygen content lower than the critical value of coal spontaneous combustion, so as to achieve the purpose of preventing coal spontaneous combustion.
Reduce air leakage
Air leakage in goaf is one of the main reasons for spontaneous combustion. For the closed or semi closed goaf, theoretically, nitrogen injection increases the total amount of mixed gas in the injected space, which can reduce the ground pressure difference between the inside and outside of the closed area, and reduce the air leakage from outside to inside of the closed area.
If there are cracks in the closed wall in the roadway, when the closed area is negative pressure, air can enter the closed area through the wall gap or around the closed wall. In order to prevent air leakage in the closed area, the necessary flow of nitrogen can be continuously injected into the space between the closed front and rear walls to form a positive pressure in the space and prevent fresh air from entering the closed area. For the goaf with internal fire, its temperature is higher than the external temperature. When nitrogen is used to extinguish fire, the temperature of product nitrogen is between 0 ℃ and 5 ℃, which is much lower than the gas temperature in the fire area. In addition, the flow range of nitrogen in the fire area is large, which has a significant cooling effect on the goaf.
On 2018-08-08 11:45:46
