Research On Law Of Spontaneous Combustion Of Coal Induced By Bedding Boring Gas Extraction And Prevention Technology In Deep Coal Seam

In order to improve the gas extraction efficiency limited by high gas content,high pressure and low permeability coefficient in deep coal seam,it is necessary to take technical measures to increase negative pressure of extraction,infill drilling and lengthen extraction time.However,these measures can easily cause gas leakage in drilling during extraction,resulting in spontaneous combustion of fractured coal body around drilling hole.Based on the theory and methods of porous media seepage and heat transfer,this paper calculated and analyzed the change laws of seepage and temperature in fractured coal body around the gas extraction borehole,and further developed the technology of preventing spontaneous combustion of the fractured coal body induced by gas extraction.(1)The activation energy of three stages of coal spontaneous combustion was obtained by thermogravimetric analysis,and the shortest spontaneous combustion period was 23.72 days.With the low temperature oxidation experiment,the critical oxygen concentration of coal spontaneous combustion is 8%.The CO,C2H4,C3H6,C2H2 and C2H4/C2H6 were determined as the indicators of predicting coal spontaneous combustion in coal mines.The closed oxygen consumption experiment showed that the oxygen consumption rate of coal is proportional to the oxygen concentration.The above experiments provided parameters for numerical simulation and provide basis for predicting coal spontaneous combustion.(2)The model of coal spontaneous combustion induced by gas extraction in boreholes was established by numerical simulation.The effects of different sealing depth,length,negative pressure and initial ground temperature on seepage field distribution,oxygen concentration distribution and coal temperature distribution around boreholes were studied.The results were as follows:the higher the initial coal seam temperature,or the shallower the sealing depth or the smaller the sealing length or the greater the negative pressure,the earlier the inflection point of rapid decrease of oxygen concentration around the borehole and the greater increase of the heating rate of the coal body.Combining oxygen concentration,seepage velocity and coal temperature,three groups of sealing parameters(fs-fc)for preventing spontaneous combustion of coal body induced by gas extraction were determined,including 23-8,20-10 and 18-13.The regularity of spontaneous combustion in boreholes was revealed,providing a theoretical basis for preventing spontaneous combustion of coal body around boreholes.(3)The four-level orthogonal experiments were carried out on the four factors consist of sealing depth,sealing length,negative pressure of extraction and different ground temperature.The time of coal reaching the shortest rapid oxidation stage was obtained by numerical simulation,and the functions of four factors and time were obtained by stepwise regression analysis.The results showed that the time for coal body to reach the shortest rapid oxidation stage is negatively correlated with the extraction pressure of the second power,and positively linearly correlated with the sealing depth and length.The sealing parameters of seams with different buried depths and negative pressure of gas extraction were determined,which can effectively optimize the parameters to prevent spontaneous combustion of coal around boreholes.(4)Through numerical simulation and theoretical analysis,it was determined that the three zones of Coal Spontaneous Combustion around the extraction borehole are heat radiation zone,oxidation zone and asphyxiation zone.The heat radiation zone and oxidation zone are collectively called "dangerous zone",and the asphyxiation zone is "safe zone".The criterion for dividing dangerous areas is that the oxygen concentration around the borehole is more than 8%and the air leakage velocity is less than 0.004m/s.Other areas are called "safe areas".The division of "dangerous area" is of great significance for preventing spontaneous combustion of coal around boreholes.(5)A set of methods for monitoring,testing and preventing spontaneous combustion of gas extraction in boreholes were developed and effectively applied in the field.It provides technical support for preventing coal spontaneous combustion induced by gas extraction,thus ensuring safe and efficient gas extraction in deep coal seams.The thesis has 106 pictures,21 tables,and 180 references.