Study On Oxidation And Spontaneous Combustion Disaster Characteristics Of Coal In Deep Mining

With the gradual depletion of shallow coal resources,more and more coal mines are moving into deep mining.The high temperature of the deep coal deposit environment,which is also thermally affected by gas explosion and surrounding coal spontaneous combustion area,makes the deep coal more obviously affected by temperature.Temperature is a visual representation of the average kinetic energy of molecules,and the increase of temperature will increase the molecular activity of coal itself,reduce the difficulty of coal-oxygen reaction,increase the risk of spontaneous combustion of deep coal,and greatly threaten the safe mining of deep mines.Therefore,this paper takes temperature as the main line and adopts the method of comparative analysis to deeply study the heat release characteristics,the characteristics of active functional groups and macromolecular spatial structure changes,the characteristics of pore-crack development,and the characteristics of coal physical strength changes before and after deep coal oxidation at different temperatures,analyzes the inner correlation between heat-force-chemistry-pore-crack during deep coal oxidation,and elucidates the temperature distribution characteristics during deep coal spontaneous combustion.The dynamic temperature mathematical model of deep coal spontaneous combustion was constructed,and the spreading conditions and directions of high temperature regions during deep coal spontaneous combustion were mastered,revealing the disaster mechanism of deep coal spontaneous combustion.The main research results are as follows:(1)Using C600 high-precision microcalorimeter,the oxidation and exothermic characteristics of coal samples at different heat action temperatures were studied,and the heat flow curves,heat absorption and exothermic changes of coal samples at different heat action temperatures were obtained.The results show that the coal samples first enter the heat absorption state and then gradually enter the exothermic state after a certain time of thermal action and then contact with oxygen,but the duration of the heat absorption state is gradually shortened with the increase of the thermal action temperature,and can directly enter the exothermic state at 200 ℃,indicating that the critical temperature at which the coal-oxygen reaction can directly enter the exothermic stage is between 150 ℃ and200 ℃;the thermal action temperature is between 100 ℃ Before the heat action temperature is 100 ℃,the heat absorption and exothermic changes of coal are relatively small;after the heat action temperature exceeds 100 ℃,the heat absorption decreases sharply and the exothermic heat increases exponentially,and 100 ℃ is the sudden change temperature at which the exothermic heat of coal enters into accelerated growth.(2)The structure of active functional groups and the evolution of macromolecular spatial structure of coal samples at different temperatures before and after the participation of oxygen were comparatively studied using Fourier transform infrared spectrometer and X-ray diffractometer.The results show that: the changes of both temperature and oxygen affect the molecular structure of coal;the content of reactive functional groups shows dynamic alternating changes with the increase of temperature,and the participation of oxygen does not change the overall trend,but affects the period of alternating changes,especially the most obvious effect on the oxygen-containing functional groups;the effect of oxygen on the spacing of aromatic layers is two-sided,and the decrease of interlayer spacing of aromatic layers will inhibit the microscopic contact ability between coal and oxygen.The reduction of the interlayer spacing between aromatic layers inhibits the microscopic contact ability between coal and oxygen,and the phenomenon of temperature increase and oxygen removal induced by the reduction of molecular spacing caused by the oxidation reaction may occur during the oxidation of coal;under the aerobic environment,the size and orderliness of the basic structural units are important factors controlling the oxygen transport in the macromolecular structure;the evolution of the spatial arrangement of the molecular structure is reversible with the increase of temperature.(3)The pore-fissure structure development and evolution characteristics of coal samples at different temperatures before and after oxygen participation were studied comparatively by using scanning electron microscopy and low-field nuclear magnetic resonance instrument,and the pore-fissure structure of coal was characterized quantitatively by using fractal theory.The results show that: with the increase of temperature,the thermal action continuously promotes the development of coal fractures,effectively enhances the connectivity between fractures and forms the internal microfracture network of coal,and the oxidation exacerbates the damage produced by thermal action and promotes the accelerated formation of fracture lattices;in the temperature range of 40 ℃-100 ℃,the pore structure development characteristics of coal samples are not obvious with or without the participation of oxygen,and when the temperature rises above 100 ℃,the pore structure distribution of coal samples changes.The pore distribution of coal samples changed significantly when the temperature increased above 100 ℃,indicating that 100 ℃is the starting temperature for the obvious development of pore structure of coal samples;with the increase of temperature,the change of fractal dimension can be divided into two stages before oxygen participation,from room temperature to 100 ℃ and after 100 ℃;after oxygen participation,the fractal dimension of pore fracture structure showed different degrees of decreasing trend,among which the most obvious effect on small pores.(4)Using the RMT-150 C rock mechanics test system,the evolution of mechanical properties of coal samples at different temperatures before and after oxygen participation was comparatively studied,and the changes of uniaxial compressive strength,Poisson’s ratio and elastic modulus with temperature were obtained.The results show that the stress-strain curves of coal samples before and after oxygen participation basically have pore-fissure compressive stage,linear elastic stage,yield stage and damage stage,but the overall strength of coal samples under oxygen conditions is significantly lower than that under oxygen-free conditions,which indicates that the ability of thermal action on compressive strength is relatively weak,while oxidation can increase the mechanical damage effect produced by thermal action and further aggravate the overall damage of coal body.The Poisson’s ratio increased gradually with the increase of temperature before the oxygen participation,and the average value was between 0.2 and 0.4,while the Poisson’s ratio decreased gradually with the increase of temperature after the oxygen participation,and the average value was between 0.2 and 0.35.Before the oxygen participation,the modulus of elasticity fluctuated with the increase of temperature,but generally decreased,while the modulus of elasticity decreased linearly with the increase of temperature after the oxygen participation,but there were fluctuations at 150 ℃.(5)The catastrophic mechanism of deep coal spontaneous combustion was revealed.Through the comprehensive analysis of deep coal oxidation characteristics,it is found that deep coal oxidation has the characteristics of temperature segmentation,and the segmentation critical temperature is 100 ℃;the connection between heat change-mechanical strength-microscopic active structure-pore fissure is close,which shows that heat weakens the mechanical strength of coal sample and accompanies the change of microstructure,and the mechanical strength of coal sample is weakened and more easily damaged,thus generating new pore structure,and the development of pore structure The development of pore structure facilitates the entry of oxygen,the oxidation reaction releases heat,and heat continues to act on the coal sample,thus forming a reciprocal;the mathematical model of deep coal spontaneous combustion temperature dynamics is constructed,and the regional distribution of temperature in the process of deep coal spontaneous combustion is analyzed theoretically,which clarifies that the temperature distribution region is asymmetric distribution,and can be divided into heat dissipation region and heat storage region,which can be further subdivided into hot spot region,heat acceleration accumulation region and slow heat accumulation region.The temperature and oxygen concentration distribution of coal spontaneous combustion is simulated by Fluent simulation software,and it is found that the overall temperature expansion direction is consistent with the oxygen diffusion direction,but the spreading direction of the high temperature hot spot is opposite to the oxygen horizontal diffusion direction,and proceeds in the direction of increasing oxygen concentration and decreasing oxygen concentration gradient.There are 83 Figures,23 Tables and 157 references in this thesis.