Study on evolutionary characteristics of desorption-spontaneous combustion of gas-bearing coal under high temperature and pressure conditions

With the deepening of mine development level, the coal rock storage environment shows high gas pressure and high ground temperature characteristics, and temperature and pressure are important factors affecting the adsorption-desorption-oxidation characteristics of gas-bearing coal. In order to investigate the changes of gas desorption and spontaneous combustion characteristics in relic coal under high temperature and pressure, coal samples with different burial depths in high gas and prone spontaneous combustion mines were selected as test objects, and orthogonal tests for methane desorption from coal under different temperatures and pressures were designed, and pore and surface area tests, TG-FTIR coupling and programmed temperature rise tests were carried out on the original and desorbed coal samples. The results shown that, the inhibition of temperature was significantly greater than the promotion of pressure throughout the desorption experiments. The high temperature and pressure environment mainly changed the microporous structure of the coal, resulting in an increase in the specific surface area and total pore volume. After desorption, the temperature breakpoints of the 320 m and 343 m coal samples were advanced by 8.7% and 4.9%, while the same types of functional groups were present in the coals, but with different decreases in content. The cross-temperature points of CO generation in the desorbed and original coal samples from 320 m and 343 m were 78 ℃ and 74 ℃, respectively, and the concentrations of C₂H₄ and C₂H₆ were consistently lower than those in the original coal samples. Meanwhile, the oxygen consumption of desorbed coal samples decreased at the same coal temperature, and the difference was the largest at 170 ℃. The oxygen contents of coal samples before and after desorption at 320 m and 343 m were 9.3%, 13.1% and 10.3%, 14.3% respectively, and the maximum difference between the two oxygen consumption was 42.3% and 41.2%. The comprehensive analysis shown that, coal samples after high temperature and high pressure desorption were more prone to spontaneous combustion at the initial stage of oxidation and produce more CO, which can be selected as the indicator gas, while the reaction intensity was reduced at the high temperature stage. In addition, the formula of the real-time change of gas environment in the mining area by methane desorption in coal was introduced, and the “oxidation zone” area under the influence of gas desorption in coal left in the mining area under the characteristics of “high gas pressure and high ground temperature” was delineated in more detail using 1304 comprehensive mining face as a model, and the scope was reduced by 63.5%. The research results can provide basic support for the prevention and control of gas-fire coupling disasters in high gas-spontaneous combustion prone coal seams.