Experimental Study On Oxidation Characteristics Of Crushed Coal Bodies Under Stress-Temperature Action

With the deep mining of coal mines,the high stress and high ground temperature environment in the underground becomes more and more serious,which causes the development of pore fissures of coal and changes the heat storage environment and oxygen absorption capacity of coal body,thus causing the increased risk of spontaneous combustion of coal and the increased difficulty of coal mining.Therefore,this paper carries out the experiments on the permeability characteristics and oxidation warming of broken coal bodies under the stress-temperature effect,analyzes the permeability characteristics and gas transport law of broken coal bodies,and then investigates the change law of oxidation thermal characteristics parameters(peak heat flow,characteristic temperature,heat release)and microstructure of broken coal bodies under the stress-temperature effect,and on this basis,analyzes the influence of different stress and temperature effects on coal oxidation process The following main conclusions were obtained.The following main conclusions were obtained.During the experiment,the change of permeability with stress was relatively drastic at the beginning of loading when the temperature was certain,but with the gradual increase of stress,the trend of change of permeability with stress slowed down.When the stress is constant,the permeability of the coal sample gradually decreases with the increase of temperature,and the temperature,stress and permeability of the coal sample all have a negative correlation.On the basises of calculating the permeability,it is important to realize the prediction of permeability in different locations of different environments in the mining area,which is important to guide the fire prevention in the mining area.The analysis of coal low-temperature oxidation test shows that the oxygen consumption rate of coal is maximum at 10 MPa stress under the same temperature condition.In the low temperature stage(when the temperature is less than 70°C),the oxygen consumption rate of coal changes slowly with the increase of temperature,and after the temperature exceedes 70°C,the effect of low stress(0-10MPa)accelerates the coal-oxygen complex reaction,while the promotion effect produced by the continuously increasing stress on the coal-oxygen reaction is weakened.The thermal stability experiments of coal under the action of stress-temperature shows that: the analysis of thermal stability of coal oxidation can be divided into three stages,initial oxidation stage,slow oxidation stage and rapid oxidation stage.When the coal temperature is lower than the initial exothermic temperature,under the action of low stress(0MPa,5MPa),the initial temperature increase will accelerate the process of coal oxygen reaction progress,and there are differences in the degree of promotion of coal oxygen reaction by different initial temperatures.When the reaction temperature exceeds the initial exothermic temperature,the exothermic coal oxidation under high stress(15-20MPa)is enhanced with the increase of initial temperature,and the inflection point of its exothermic heat maximum is delayed.The microstructure analysis of the coal samples revealed that the coal molecules started to generate a large number of hydroxyl groups at 40°C under 0MPa and 10 MPa stresses,and the increase in temperature promoted the generation of oxygen-containing functional groups in the coal under 10 MPa stress;at the temperature of 70°C,the increase in stress promoted the oxidation of the coal and accelerated the participation of multiple functional groups in the reaction,which were consumed.The combined stress-temperature effect exposes more active sites in the coal and accelerates the consumption of active functional groups.