Experimental Study On Crush And Spontaneous Combustion Characteristics Of Left Coal In Goaf With Large Dip Angle Working Face

Due to the characteristics of the large dip Angle and unique caving mode of goaf in large dip Angle working face,the spontaneous combustion of the residual coal in the goaf is relatively hidden,which makes it difficult to prevent and control the spontaneous combustion.At the same time,the residual coal in the large dip Angle goaf is in different pressure states and breaking degrees,and the characteristics of the coal's compressive breaking are not clear.In combination with the difficulty and low accuracy of the monitoring of the residual coal 's spontaneous combustion in the large dip Angle goaf,the related theories and experimental results are not accurate enough to describe the related problems.Therefore,it is necessary to carry out experimental research on the characteristics of pressure crushing and spontaneous combustion of residual coal in goaf with large dip Angle,to determine the spontaneous combustion law of residual coal in goaf with large dip Angle,and to provide theoretical support for the prevention and control of spontaneous combustion of residual coal with large dip Angle.Based on this,the numerical simulation study on the stress distribution characteristics of the goaf in the large dip Angle working face was carried out,and the experimental study on the characteristics of pressure crushing was carried out,and then the experimental study on the spontaneous combustion of the coal under pressure crushing and the residual coal in the similar goaf was carried out.Finally,the temperature rising law of the residual coal spontaneous combustion and the distribution characteristics of the spontaneous combustion risk area were determined.The results show that:the average compression ratio of 10-20 mm lumber coal is 17%-40%,the crushing coefficient of lumber coal is 2.15-1.34,the average crushing ratio of lumber coal is 69.5%-86.6%under the condition of vertical stress 2.76-22.06 MPa,and the mass ratio of four ends after crushing is significantly negatively correlated with the load,there is a significant positive correlation between the mass ratio below the particle size and the load.In the process of physical heating and heating in nitrogen environment,the coal sample temperature is divided by 100? with the furnace temperature(air flow temperature),which has a nonlinear growth law of quadratic function first and then cubic function.Nitrogen flow rate has a significant influence on the distribution of temperature in the coal sample.In the air environment,there is an exponential function relationship between the oxygen consumption rate,CO production rate,exothermic intensity of the crushed coal and the mass ratio of crushed particle size during the oxidation process of the residual coal.Under different air leakage conditions,the oxidation temperature of coal samples also has significant spatial location difference characteristics.The apparent activation energy of coal in the stage of 40-70? at air volume of 120-1000 mL/min is 20.13 kJ/mol,23.29 kJ/mol,14.57 kJ/mol,8.92 kJ/mol and 19.29 kJ/mol,respectively.Based on five hypotheses to determine the adiabatic oxidation characteristics of coal conducting rapid temperatures-programmed experiments in nitrogen and air atmospheres,a method was proposed to calculate the temperature rise of adiabatic oxidation and exothermic oxidation based on the temperature difference between air and nitrogen subtracting the temperature rise of oxidation and exothermic oxidation corresponding to nitrogen atmospheres.The calculated adiabatic spontaneous combustion periods under the air volume of 250 mL/min,500 mL/min and 1000 mL/min are respectively 626.3 h,274.4 h and 180.1 h.A similar experimental system for spontaneous combustion of residual coal in goaf based on programmed heating was designed and constructed at a ratio of 1:200.The system mainly includes four subsystems:gas supply system,similar goaf and programmed heating system,negative pressure ventilation system,and temperature monitoring and acquisition system.Through different Angle respectively with nitrogen,but the law of residual coal to heat up the air environment comparison found:large tilt Angle face goaf return air side,compared with the level of working face in return air side is more easy to spontaneous combustion,and in the field and cut the top line of spontaneous combustion risk bigger parts of the area of working face length,1/6-1/2 and open cut on the corner of the eye is the most significant.In addition,compared with the horizontal working face,the tendency center area from the top cutting line to the deep 1/6-1/3 of the goaf and the shallow area are more likely to heat up due to oxidation.At the same time,except for the inlet side(inclined lower)under the condition of large dip Angle working face,the risk of spontaneous combustion is similar to that of the horizontal working face in a small part near the 1/6 working face length of the top cut line,other deep areas of goaf are all difficult spontaneous combustion areas.This thesis has 123 figures,54 tables and 112 references.