Research On The Characteristics And Prevention Technology Of Spontaneous Combustion In High Gassy Mine Gob Of Mining With Gob-side Entry Formed By Cutting Roof

Mining with gob-side entry formed by cutting roof(110 mining method)was referred to as the third exploration of technological change in mining industry of China,which has been promoted nationwide and made great achievements so far.This technology was faced with severe disaster of spontaneous combustion in gob-side entry in its application,coupled with the influence of gas emission and gas drainage on it,which made it much more difficult to prevent and control this disaster.Taking specific project case as engineering background,this thesis systematically studied the characteristics and prevention technology of spontaneous combustion in high gassy mine gob of mining with gob-side entry formed by cutting roof.Through the theoretical analysis,the fracture characteristics and collapse model of the direct roof and the basic roof of mining with gob-side entry formed by cutting roof were determined.The discrete element simulation software PFC was used to simulate the process of mining with gob-side entry formed by cutting roof,and the spatial-temporal changes of the overburden collapse,stress,fracture and porosity under this technical condition were obtained.Then,the gas-guiding zone was determined.The feasibility of PFC simulation of the overburden collapse process of mining with gob-side entry formed by cutting roof was verified by theoretical calculations and field measurements.The spatial distribution of porosity,viscous resistance coefficient and inertial resistance coefficient in gob were obtained by fitting the PFC simulation results of porosity,and the UDF function was used to import them into FLUENT calculation.Thus,the PFC-FLUENT coupling numerical simulation model of 3d gob flow field under the condition of mining with gob-side entry formed by cutting roof was established.The gas emission rate and oxygen consumption rate of gob were obtained by field gas monitoring and low temperature oxidation experiment.The simulation results based on PFC-FLUENT coupling model show that the roof cutting changed the distribution of stress,fracture and porosity,and increased the height of overburden caving zone in the gob.Compared with the traditional gob-side entry,the spatial distribution of gas and oxygen in gob of mining with gob-side entry formed by cutting roof was obviously different.The "Y" type ventilation was beneficial to the prevention and control of gas in the upper corner of the working face,but the gas accumulation point was easy to appear in the end section of the gob-side entry.At the same time,the width and depth of the spontaneous combustion zone increased obviously,and there was a strip of spontaneous combustion zone along the gob-side entry.When "W" ventilation was adopted,the gas in the roadway accumulated obviously near the upper corner of the working face.The width of the spontaneous combustion zone in the gob was obviously reduced.Under the condition of high air pressure of the air inlet at the end of the gob-side entry,the air leakage near the lower corner of the working face was obviously reduced,and the diffusion distance of high concentration oxygen to the gob was also significantly reduced.In the air leakage path of the gob,the gas emission had the effect of "increasing resistance along the way",and the effect of "increasing resistance along the way" increased with the increase of the emission intensity.Under the condition of different gas emission intensity,the spontaneous combustion zone of gob "shrunk" towards the working face,and the larger the gas emission intensity was,the more obvious the "shrinkage effect" was.In the ideal situation without oxygen consumption,gas was used to displace and dilute the oxygen in the air flow in the gob in the way of displacement,so that the oxygen concentration was reduced,that is,the relatively strong outflow of gas was equivalent to oxygen being consumed by adsorption.The influence of high-level gas drainage borehole on spontaneous combustion zone was mainly reflected in the range of support separation zone at the working face side.The closer the distance between the high-level borehole and the gob-side entry was,the more favorable it was to restrain the air leakage from the gob-side entry to the deep part of the gob.The gas concentration in the gob was reduced rapidly and the gas accumulation at the end of the gob-side entry was effectively controlled by buried pipe drainage in the caving zone,but it also significantly increased the width of the spontaneous combustion zone at the side of the gob-side entry,and the spontaneous combustion zone at this position will not gradually enter the suffocation zone with the advance of the working face.The coal-oxygen reaction experiments in a lean-oxygen environment caused by methane with temperature ranging from 30-800? were carried out by thermogravimetry and gas chromatography coupling technology.TG-S/DTG-S calibration curves were introduced to analyse the process of coal-oxygen reaction with considerable accuracy.When the combustion and thermolysis did not occur,the methane,as a kind of inert gas,could delay the formation of CO and CO2 in the process of coal-oxygen reaction,slow down the rate of coal-oxygen reaction as well as increase the ignition temperature of coal samples.The effect mentioned above became more obvious with the decrease of oxygen concentration,and methane performed better in inhabiting coal-oxygen reaction than N2 under the condition of same oxygen concentration.When the temperature exceeded 500?,the combustion and pyrolysis reaction of methane took place.Direct combustion of methane and combustion of H2 and C produced by methane pyrolysis could consume a large amount of oxygen,thus inhabiting and even stopping coal-oxygen reaction.When methane combustion and pyrolysis reactions occurred,the concentration of O2,CO,CO2 and H2 underwent "stepwise" changes,and the mutation process of the above gases could be used as the basis for judging whether methane combustion(explosion)has occurred in the mine fire area.Low-temperature coal-oxygen reactions in a lean-oxygen environment caused by methane with temperature ranging from 30-230? were conducted using programmatic heating equipment.In a lean-oxygen environment caused by methane,different oxygen concentrations played a significant effect in delaying the formation of CO,CO2,H2 and C2H6,thus affecting predictors of spontaneous combustion.When the temperature was below 170?,the relationship between R3 value((+?CO/+?CO2)× 100%)and temperature could be described by using the same exponential function under the condition of different oxygen concentrations.Therefore,R3 value could be used as a predictor of spontaneous combustion of residual coal in a lean-oxygen gob caused by methane.At the same time,the absolute production of indicator gases produced by per unit residual coal in gob was introduced to reduce the impact of air leakage and the amount of residual coal in gob on predictors of spontaneous combustion.According to experimental data,the relationships among temperature,oxygen concentration and CCO,CCO2 and CC2H6 were fitted respectively to obtain the corresponding relation diagrams from which the predictors and their corresponding values of temperature could be obtained,thus accurately determining the extent of spontaneous combustion in high gassy mine gob.On the basis of the research on the characteristics of spontaneous combustion in high gassy mine gob of mining with gob-side entry formed by cutting roof,the prevention and control technologies of air blocking method of stage spraying,N2-inhibitor water mist prevention and fire extinguishing,and monitoring were put forward.The working face of mining with gob-side entry formed by cutting roof was divided into the advance support area,the temporary support area behind the frame and the roadway stabilization area.In this paper,the air blocking method of stage spraying along the gob-side entry was put forward,and the numerical simulation and field application of stage spraying along the gob-side entry were carried out.According to the characteristics of large amount of air leakage and many sources and sinks of air leakage in high gassy mine gob of mining with gob-side entry formed by cutting roof,the N2-inhibitor water mist fire prevention and extinguishing technology was proposed,the corresponding equipment was developed,the N2-inhibitor water mist fire prevention and extinguishing experiments were carried out,and the respective action mechanism and synergistic effect of N2,inhibitor and water mist in the process of fire prevention and extinguishing were determined.According to the distribution of the spontaneous combustion zone in high gassy mine gob of mining with gob-side entry formed by cutting roof,the field layout and use mode of the N2-inhibitor water mist equipment were finally established.Through the arrangement of the monitoring system of the gob bundle pipe,the monitoring of the buried pipe along the gob-side entry,the monitoring of buried pipe drainage borehole and the monitoring of the high-level drainage borehole,the spontaneous combustion in the gob of the high gassy mine was monitored,and the disaster characteristics and stage of the gob are predicted by using corresponding indexes and criteria.The research results of this thesis are of great significance for understanding the characteristics of spontaneous combustion in high gassy mine gob of mining with gob-side entry formed by cutting roof,putting forward effective prevention and control measures,ensuring the smooth popularization of this technology and the safe production of mine.