Study And Application On The Technique Of Nitrogen Injection Against Fire In Spontaneous Combustion Thick Seam Gob

Presently, 60% of the state-owned coal mines have already been in danger because of the coal spontaneous combustion. The loss of high grade coal due to the coal spontaneous combustion has been up to 4.2 billion tons. Worsely, the loss has been growing by 2000-3000 million tons every year. Moreover, the heavy casualties caused by the fire hazard annually lead to heavy toll of lives and billions of yuan in economic losses. Not only does the coal spontaneous combustion waste coal resources, but also leads to the serious environmental and ecological problems.The fully mechanized sublevel caving mining with high output and efficiency, brings out a serious challenge on the prevention and extinguishment of extra thick seam spontaneous combustion. During caving, the collapsed zone is large, resulting in a lot of loose coal left, which is easy to be oxidized by the oxygen in air leakage flow with a result of gob fire, seriously threatening the safety of miners and production Starting from the mechanism of the coal spontaneous combustion, the characteristics and laws of the spontaneous combustion of a extra thick seam in the gob were studied in the paper; With knowing the characteristics of the coal spontaneous combustion and confirming the prediction index,the early stage prediction system based on the gas index analysis was established; combining the practical situation of the Tashan Coal Mine 8202 caving face, the parameters of the nitrogen injection were calculated to develop a reasonable nitrogen injection system to prevent the gob fire in light of the nitrogen injection theory and technology, which was supported by the beam control monitoring system. The nitrogen injection efficiency was improved by monitoring the gas changes in gob and adjusting the nitrogen injection parameters timely.With the monitoring on the gas changes in Tashan Coal Mine 8202 caving gob almost in one year and the data analysis, the pattern of gob gas changes, the nitrogen injection time and the gob of "three zones" change were studied, obtaining the change pattern of O₂, CO, N₂, CH₄ and CO₂ in gob, initial inerting time, continuous injection time and the change of "Three Zones" before and after the nitrogen injection were obtained. Finally, , based on the statistical analysis of monitoring data and the fir inerting index after the nitrogen injection, the objective evaluation was concluded to guide thefire prevention and ensure the mine safety.The conclusions are as follows:1. The spontaneous combustion of extra thick seam in the gob is of the following characteristics: the spontaneous combustion of coal usually occurs in the certain distance to the surface with the hidden high temperature zone and the large region; the high-temperature point is always going against flow movement; during the coal spontaneous combustion when the coal temperature rising; Gobit is difficult to extinguish the fire in gob, and the fire is easy to take place again after unsealing.2. CO should be used as an indicator for the fire prevention in Tashan Mine 8202 Gob , supplemented by C₂H₆, C₂H₄, C₃H₈ and C₂H₂ to control the spontaneous combustion of coal. The CO concentration rising in a sudden showed that the oxidation of coal has already occurred. The emergence C₂H₄ and C₃H₈ showed the coal temperature over 140℃, while the emergence of C₂H₂ shows the coal temperature higher than 190℃.3. The oxygen concentration decreased with the mining depth increasing and eventually stabilized at around 3% to ensure the smooth progress of the fully mechanized 8202 mining face under the continuous nitrogen injection ; the greater the nitrogen injected, the greater the oxygen concentration gradient declined; the nitrogen injection in gob had a certain influencing range on the oxygen concentration.4. There is a certain amount of CO in the air flow in is an obvious feature when caving the extra thick spontaneous combustion coal with greater mining height .5. Gob inerting time could be divided into two stages such as the first and the second inerting time. The residual mined coal in gob was still in the low-temperature oxidation even if the oxygen concentration decreased rapidly to a safe concentration. Only when the oxygen concentration decreased to about 3% and continued for some time, the low-temperature oxidation of residual coal could be effectively controlled.6. Under continuous nitrogen injection, gob "three zones" width distribution were 20-30m for heat radiation zone, 16-38m for oxidation zone, out of 68m from the mining face for suffocative zone; Because of the great amount of air flow and air leakage, the nitrogen injection had little effect on the width of heat radiation zone, while the width of the oxidation zone shortened about 120m and the suffocative zone shifted forward about 172m or soafter nitrogen injection.