Study Of Spontaneous Combustion Characteristics Of Secondary Oxidation Of Relic Coal

With the change of mining trend from shallow to deep,the deep mine coal rock is in a complex geological environment,and it is subjected to significantly different stress states.The coal left in the mining area occupies a major proportion of the spontaneous coal combustion fires in the underground mine.Due to the complex wind leakage environment of deep mining,which leads to the increasing prominence of spontaneous coal combustion in the mining area and the consequent reignition phenomenon,the oxidation and warming of unoxidized coal from room temperature to 200°C is defined as primary oxidation,and the process of cooling down to room temperature and oxidation and warming again is defined as secondary oxidation.This paper takes coal under different stress and air leakage conditions as the research object,analyzes the laws of heat release and gas generation from coal oxidation on a macroscopic level,and studies the microcrystalline structure,content and type of functional groups and void rate of coal under different stress and air leakage conditions on a microscopic level.From both macroscopic and microscopic aspects,the spontaneous combustion characteristics of secondary oxidation of legacy coal are studied to reveal the reasons for the variability of the spontaneous combustion characteristics of primary and secondary oxidation of legacy coal under complex conditions,and the experimental results have important practical significance for the prevention and control of secondary oxidation of legacy coal in the mining area.The following main conclusions were obtained from the above study.（1）The changes of oxygen consumption rate,index gas,initial exothermic temperature,heat release and activation energy of coal under different stress conditions were obtained by testing and analyzing the oxidation characteristics and thermal properties of coal under different stress conditions.The results showed that the oxygen consumption rate and the concentration of indicator gas were the highest at the stress of9 MPa;the initial exothermic temperature and activation energy decreased first and then increased with the increase of stress,and 9 MPa was the turning stress for the change of exothermic heat,and the stress and oxidation capacity were non-linearly positively correlated.（2）From the study of stress on the spontaneous combustion characteristics of coal,it is concluded that the oxidation degree is most intense at 9 MPa.The oxidation and thermal characteristics of coal under different air leakage were measured with 9 MPa as the base stress,and the changes of oxygen consumption rate,index gas and thermal characteristics parameters of coal under different air leakage conditions were obtained.The results showed that the oxygen consumption rate and the concentration of indicator gas were the highest at the leakage volume of 150 m L/min;the initial exothermic temperature and activation energy decreased first and then increased with the increase of stress,and the exothermic heat was the highest at the secondary oxidation of 150m L/min;the strongest oxidation and the highest risk of spontaneous combustion were observed at the leakage volume of 150 m L/min at the stress of 9 MPa.（3）The microscopic activity structure change pattern of secondary oxidation of legacy coal was obtained by FTIR,XRD and void fraction test analysis.The results showed that:the stress was almost compacted near 9 MPa;the stress did not change the types of the main functional groups in the coal,but only affected the level of their contents,and the secondary oxidation of oxygen-containing functional groups increased,aromatic hydrocarbons increased,aliphatic hydrocarbons decreased and hydroxyl groups decreased;the spacing d₀₀₂of coal molecular lamellae under different air leakage did not change much and did not change the nature of the microcrystalline structure,L_achanged to a large extent and L_cchanged to a small extent,indicating that the oxidation changes the morphological characteristics of coal molecule aromatic layer structural units through the effect on L_aThis paper has 38 pictures,13 tables,and 93 references.