| Fully-Mechanized mining caving technique,has many features, such as large air volume, a large amount of air leakage in goaf and leaving many coal.Goaf spontaneous combustion of coal is not only a short time in the release of large amounts of toxic gases, and endanger the security of the workers, but also will ignite the surrounding gas, which will result in serious consequence. as one of the means of coal seam spontaneous combustion control, Nitrogen injection,can change the distribution of oxygen concentration in the goaf, and narrow the scope of the oxidation zone. Reasonable nitrogen injection position and nitrogen injection rate have important influence on the effect of nitrogen injection.8# coal seam of Wang Jialing coal mine is spontaneous combustion in high gas-rich.18101 working face as the first mining face, lack of experience and the specific parameters of the guidance. This paper through field measurement, and Numerical simulation combined with identified and quantified analysis of themine reasonable parameters of nitrogen injection, to prevent mine goaf fire of nitrogen injection work, which will provide important reference basis. The research contents are as follows:Firstly, through the beam tube monitoring system of 18101 working face,setting up different monitoring points, according to the oxygen concentration as an index,we know the spontaneous combustion "three zones" range without nitrogen injection, the results are as follows : the cooled zone range is 0 to61.5m,oxidation zone is 61.5 to 176.4m,and the suffocation zone is after176.4m.In the middle of the working face which near the air input, the cooled zone is 0 to 46.6m,the oxidation zone is 46.6 to 174.2m,and the suffocation zone is after 174.2m.In the middle of working face near the return air side, the cooled zone is 0 to 32.2m,the oxidation zone is 32.2 to 153.4m,and the suffocation zone is after 153.4m.In the return air side, the cooled zone is 0 to 15.2m,the oxidation zone is 15.2 to 70.6m,and the suffocation zone is after 70.6m.Secondly, using ICEMCFD software to establish the three-dimensional physical model of the 18101 fully mechanized caving face, taking into account the influence of the hydraulic support, a simplified solid model is established.And the user-defined function developed porosity, viscous resistance coefficient,left oxygen consumption rate and other key parameters of buried pipe pumping and nitrogen injection pipeline complex flow field in goaf of three-dimensional flow field numerical simulation research, it is concluded that the not before the injection of nitrogen to oxygen concentration as an index partition mining goafspontaneous combustion "three zones" range has little difference with the beam tube determination result contrast, which shows that the numerical simulation results and measured are basically the same, error satisfies the precision requirement to verify the applicability of the model.Thirdly, with the nitrogen injection quantity is 500m3/h,we chose five different location which are close to air input of goaf: X=25m,X=50m,X=75m,X=100m,X=125m,drawing that X=25m and X=50m,dueing to the nitrogen injection location near into the airway, and the nitrogen can move well with the leakage air flow,the effect of shorten the insidewind oxidized can reaches58 m.Compare the different locations of the maximum oxidation zone width and before the injection of nitrogen. Compared with the In the oxidation zone of the maximum width,it reduce 32.63 m,41.21 m,27.64 m, 20.66 m and 16.22 m. When the location is X=50m,the narrow range of maximum width of oxidation zone can be the biggest, which reaches 31.7%.So the best choice of nitrogen injection position should be X=50m,before a distance of the oxidation zone, which can effectively promote the diffusion of nitrogen oxide and narrow band width.Fourthly, selected X=50m as the position of the nitrogen injection, set six different nitrogen injection quantity:500m3/h, 1000m3/h,1500m3/h,2000m3/h and3000m3/h.Six sets of parameters were simulated, and through simulation analysis, we know that get along with the increase of nitrogen injection flow, the six reduce oxidation zone width amplitude are as follows: from 31.71%,42.56%,55.65%,63.57%, 66.31% and 68.13%,which showing a trend of gradual increase:when the quantity of is 2000m3/h,the increase of injection capacity of nitrogen oxidation with maximum width reduction decreases; when the quantity of nitrogen injection is 3000m3/h,working face appeared oxygen concentration below the safety value, so choose reasonable nitrogen injection flow 2000m3/h.Fively, reasonable nitrogen injection parameters are X=50m and the quantity of nitrogen injection is 2000m3/h,and analysis the change rule of nitrogen concentration and oxygen concentration in goaf. Nitrogen distributions are presented for three concentration regions to nitrogen injection port as the center, a section near the area will be the formation of high concentration nitrogen cloud, nitrogen concentration was maintained at more than90%,nitrogen injection port at both ends of the nitrogen concentration is diminishing. Close to the working face and the inlet air tunnel concentration remained above 70%,close to the concentration of nitrogen in the air, and the closer to the working surface, the lower the concentration. At the same time, it can be seen that the oxygen concentration in the goaf area of 78 m is obviously decreased to below 7%.Lastly, based on the above research, the nitrogen injection rate, the position of the nitrogen injection and the injection pipe of the 18101 working face were designed, the nitrogen injection location of mined out area from the working face of 50 m,the nitrogen injection flow is 2000m3/h,and Nitrogen injection pipeline with seamless steel pipe laying, the length of it about 4200 m. |
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