Study On The Microstructure-Desorption Characteristics Of Gas-Bearing Coal Under High Temperature-Pressure And Application

With the mining level increasing,the gas-fire complex disaster has gradually become one of the major hazards limiting the safe production of high gas-prone and spontaneously combustible coal seams.The mechanism of gas-fire complex hazards in the goaf is invisible,complex,dynamic and coupled,which makes it difficult to study,resulting in a lack of systematic research on the mechanism of combined disaster.This thesis is set in a high temperature and pressure environment with high gas pressure and high ground temperature characteristics,and lean and fat coal are selected for study.Pore and surface area testing and thermogravimetric Fourier infrared spectroscopy coupling（TG-FTIR）tests on raw coal samples and high temperature and pressure pretreated coal samples to characterize the microscopic characteristics of coal under high temperature and pressure environment.Design of an orthogonal tests for gas desorption under different temperature and pressure to determine the influence of gas desorption from legacy coal on the delineation of spontaneously combustible hazard zones.The innovative research results of the thesis are as follows:（1）The coupling test platform of gas ad/de-sorption and coal spontaneous combustion heating and oxidation has been established and consists of three main modules and six component units,which are capable of monitoring parameters such as adsorption,desorption and oxidation gas products during the spontaneous combustion of underground relict coal,and can be used to reveal the spontaneous combustion and oxidation characteristics of gas-bearing coal,while providing instrumentation for subsequent microstructure and desorption experiments.（2）Low-temperature N₂ adsorption experiment and thermogravimetric Fourier coupling tests were carried out on the raw and pretreated coal samples of the two test coals to investigate the effect of high temperature and pressure environment on the microstructure of gas-bearing coals.The test results showed that the proportion of micropores and mesopores pores increased by 24.6%,35.0%and 44.2%,26.6%respectively,indicating that pretreatment increased the proportion of micropores and mesopores in the coals,which would promote the adsorption of oxygen by the coal;Before and after pretreatment,the characteristic temperature points of lean and fat coals in the first stage were 78°C,74°C and 91°C,89°C respectively.The advancement of the characteristic temperature points indicates that the reactivity of the coals has increased;meanwhile,the types of functional groups in the coals before and after pretreatment were the same,but the content showed different degrees of reduction,indicating that some functional groups were already involved in the reaction at this time.The comprehensive analysis indicates that the coal is more prone to spontaneous combustion under high temperature and pressure.（3）Coupled desorption experiments were carried out on lean and fat coals at30～90°C and 0.5MPa～3.0MPa to investigate the desorption pattern of coals under temperature,pressure and combined action.The test results show that desorption is influenced by adsorption,under single conditions,adsorption is negatively correlated with temperature and positively correlated with pressure,thus desorption decreases with increasing temperature and increases with increasing pressure;the effect on desorption is weakened by the rise of both during the compound action,and desorption tends to be the same for both coal types.The reduction in gas desorption is beneficial to the oxidation of the coal left in the mining area.（4）Through the above experimental analysis,the coal is more prone to spontaneous combustion under high temperature and pressure.In order to improve the prevention and control effect,the lean coal desorption data was fitted and the formula for calculating the gas concentration in the mining area was derived based on the division of the air leakage flow and the tri-zone of coal spontaneous combustion in goaf and the hazardous zone under the influence of gas desorption in the coal remains was reduced by 63.5%using the 1304 working face as an example.The results of the study are used to enrich the theory of prevention and control of disasters in high gas-prone spontaneous combustion mines and to provide a reference for the prevention and control of combined gas and fire disasters in the mined area.