| The productive coal mines in China is mainly based on underground mines.The number of accidents and casualties caused by gas accidents is higher in the five major disasters in coal mines,the mine gas is the security risk that has been lingering in the ears of coal mine workers.The problem of gas enrichment in goaf is serious during the mining process of hard roof comprehensive mechanized coal mining face,The drainage technology of high-level drilling as an efficient and economical extraction method of controling the goaf gas,the extraction effect mainly depends on the determination of the fissure field's height.The development height of roof fissure varies in each mining area due to the differences of coal seam mining intensity,mining depth,roof lithology and roof management technology in goaf.This paper takes Lu'an group Luning coal industry corporation as the engineering background,The gas source in the No.2coal seam face in Luning Mine,the vertical“three belts”of the goaf,the gas migration law in the goaf and the high-level drilling arrangement parameters were comprehensively analyzed through laboratory tests,theoretical research and on-site field investigations.The problem that the gas gushs from goaf to working face is solved under the condition of hard roof comprehensive mechanized coal mining face.The paper mainly achieve the following results around the optimization and application of the goaf gas drainage technology.(1)In the early stage of the study,the gas basic parameters of the 24102working face,the method of weakening roof and the gas source were analyzed by field measurement analysis.It was determined that the average amount of gas emission of 24102 working face was 11.00m~3/min,and the average amount of gas emission of goaf was 5.76m~3/min,accounting for 52.36%of the total gas emission amount of working face;(2)Combined with the test results of rock mechanics parameters of No.2coal seam roof and floor in Luning coal mine,the development height of roof fissure zone in the goaf of 24102 working face was studied through theoretical analysis,FLAC~3DD simulation and borehole peep technical instrument.The research results show that the development height of the roof fissure zone in the goaf of 24102 working face is 16~52m,and the borehole peeper shows that the crack is well developed about 35m away from the roof of the coal seam during the process of mining face advancing;(3)The FLUENT simulation study was carried out on the migration law of gas in the goaf under different extraction modes according to the distribution height of the vertical"three belts",The study shows that the gas extraction by intubation has a limited horizon.When the gas emission is large,it is necessary to use the combination of intubation and high-level drilling to control the goaf gas in a three-dimensional manner,in order to ensure the gas concentration in the working face is within the controllable range,the necessity of high-level drilling to control gas is proved;(4)Based on the above research,they were tested in the field that the main parameters of the goaf gas control by the high-level borehole that is the layout level of the final hole.By monitoring the gas extraction concentration and flow rate of 8 groups 27 test boreholes in air return tunnel of 24102 working face on site,the dynamic evolution law of roof crack was indirectly analyzed.It is found that the optimal placement of the final hole of the high-level borehole in the goaf is in the middle of the fissure field,which is the final hole was arranged about35m away from the coal seam roof.Based on this,after the application of optimized layout of high-level borehole in the mine,it is known that the gas extraction rate of the working surface has been significantly improved by the continuous monitoring data at the site,which is basically above 30%,and the gas concentration of the upper corner has dropped below 0.5%.Which has achieved the purpose of economic and efficient treatment of goaf gas and created good conditions for the safe production of the coal mine. |
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