The accurate prediction of coal spontaneous combustion (CSC) in the goaf areas of coal mines is a vital aspect of the migration from passive to active fire prevention and control. However, CSC is highly complicated and existing technologies cannot accurately monitor coal temperatures over wide expanses. Thus, it may be beneficial to assess CSC based on various index gases produced by the reactions of coal. In the present study, the CSC process was simulated by temperature-programmed experiments, and the relationships between index gas concentrations with the coal temperature were determined using logistic fitting functions. CSC was divided into seven stages, and a coal seam spontaneous ignition early warning system involving six criteria was established. Field trials demonstrated that this system is a viable approach to predicting coal seam fires and meets the requirements for the active prevention and control of coal combustion. This work establishes an early warning system based on specific theoretical guidelines that permits the identification of CSC and the implementation of active fire prevention and extinguishing measures.
The functional group structures of coal molecules are one of the most important factors affecting spontaneous combustion. However, it is difficult to determine the exact effects of such structures. Extraction technology is able to modify the functional groups in coal as a means of inhibiting spontaneous combustion reactions. The present work extracted coal from the Caojiatan mine in northern Shaanxi, China, with various solvents. The extraction effectiveness of these solvents was found to decrease in the order of dioctyl sulfosuccinate (AOT) > water > n-hexane > cyclohexane + AOT + ethanol > cyclohexane > ethanol > methanol. With the exception of the AOT, the concentration of functional groups in the extracted coal was decreased compared with that in a control specimen extracted using only water. Ethanol, n-hexane, and methanol provided the optimal extraction efficiencies in terms of capturing coal molecules with aromatic structures, aliphatic structures, and oxygen-containing groups, respectively. The results of this work are expected to assist in future research concerning the extraction of coal molecules with specific functional groups. This work also suggests new approaches to the active prevention and control of spontaneous combustion during the mining, storage, and transportation of coal.
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