Mechanisms of igneous intrusion on coal physical and chemical structure and low-temperature oxidation

QIN Botao; SHAO Xu; LI Ziwei; QU Bao

doi:10.13247/j.cnki.jcumt.20240404

Abstract：Coal seams intruded by igneous rocks are more prone to spontaneous combustion,which is closely related to the physical and chemical structure modification of coal by magma,thus it is necessary to explore the intrinsic impact mechanisms of igneous rock intrusion on the physical and chemical structure and low-temperature oxidation of coal.First,based on nitro-gen and carbon dioxide isothermal adsorption and Fourier infrared spectroscopy testing,the pore structure and chemical structure characteristics of tectonic coal in the igneous rock intru-sion area were studied,and it was found that the contact metamorphism of magma is higher than the thermal metamorphism on the modification of the coal structure;the coal samples af-fected by the contact metamorphism had an increase of 237.6％in specific surface area,and both the surface roughness and network complexity of the pores increased,the content of aro-matic rings,oxygen-containing functional groups,and alkanes in the coal decreased,while the content of hydroxyl groups and minerals increased,and the parameters of the chemical struc-ture characteristics significantly increased.Secondly,the replacement process of methane and oxygen was investigated by combining programmed heating experiment of the gas-containing coal and the numerical simulation of gas diffusion in granular coal,and the results show that the thermal metamorphism of magma strengthens the replacement of methane and oxygen in the coal,but the contact metamorphism slows down the replacement of both.A new method for quantitative calculation of the physical and chemical oxygen absorption of coal was pro-posed,and the transformation process from physical to chemical adsorption of oxygen in the coal was analyzed,the coal samples subjected to magmatic metamorphism showed a higher physical oxygen absorption,and the main control transition temperature of physical-chemical adsorption of coal samples affected by thermal metamorphism was only 55.22 ℃,which re-duced by almost 20 ℃.The apparent activation energy of the coal-oxygen reaction was accu-rately calculated based on the Arrhenius formula and the chemical reaction rate formula,the thermal metamorphism reduced the apparent activation energy of the coal-oxygen reaction,while the contact metamorphism made the apparent activation energy higher than that of nor-mal coal samples.Finally,the correlation between the physical and chemical structure of tec-tonic coal and its low-temperature oxidation was explored using gray correlation analysis,and it was found that the increase in the surface roughness,network complexity,and branching degree of the tectonic coal not only promoted the displacement of methane and oxygen inside the coal body,making the low-temperature oxidation process quickly shift from physical ad-sorption control to chemical adsorption control,but also promoted the breaking of aromatic hydrocarbons to form more short-chain branches,resulting in a reduction in the activation en-ergy of the coal-oxygen reaction and easy evolution into a strong oxidation reaction.