Different perspectives and explanations regarding the influence of pre-oxidation on the spontaneous combustion characteristics of coal

LI Jinhu; SUN Jianhong; YANG Zefeng; LI Jinliang; CHEN Liangzhou; ZHUO Hui; ZHANG Qingsong; LU Wei

doi:10.13247/j.cnki.jcumt.20240442

Abstract：Pre-oxidation occurs during coal mining,and pre-oxidized coal is also present in closed fire area.Pre-oxidation leads to the change of the molecular structure of coal and signifi-cantly affects its oxidation activity.At present,there are obvious differences in the research on the influence of pre-oxidation on the secondary oxidation behavior of coal.In order to explore the different reasons for the influence of pre-oxidation on the spontaneous combustion charac-teristics of coal,the oxidation characteristics of coal before and after pre-oxidation were com-pared by low-temperature oxidation experiments and room temperature oxidation experiments after pyrolysis.Then the evolution behavior of active functional groups and free radicals during the oxidation process was analyzed by microscopic means such as FTIR and ESR.The macro-scopic gas and characteristic point temperatures showed that the oxidation activity of pre-oxi-dized coal after Air cooling was lower than that of raw coal,and significantly lower than that of coal samples subjected to N2 cooling.Furthermore,compared with raw coal,pre-oxidized coal after N2 cooling exhibited characteristics of promoting oxidation in the early stage while inhibi-ting it in the later stage.Microscopic analyses of functional groups and free radicals revealed that the simple pre-oxidation process reduced the concentration of alkyl side chains and active free radicals,and significantly inhibited the subsequent secondary oxidation process from the perspective of reactive active substances.However,during N2 cooling,a large number of free radical active sites are generated due to thermal decomposition of the pre-oxidized coal sample,thus improving the coal's self-heating capacity in the early oxidation stage.The results showed that the internal reasons for the different views on the spontaneous combustion characteristics of coal are mainly caused by the different cooling atmospheres.The Air cooling of the pre-oxi-dized coal causes the alkyl functional groups and active radical structures to be consumed by oxidation,which significantly inhibits the oxidation activity of the coal.Conversely,cooling in the N2 environment leads to the thermal decomposition of coal,resulting in a large number of free radical active sites,which greatly increases the oxidation activity of coal in the early stage of spontaneous combustion.The generation and oxidation of active sites from pre-oxidation-de-composed coal affect its spontaneous combustion ability,therefore,inhibiting active site activi-ty and reducing their concentration represent promising strategies to prevent the reignition in closed fire area.