Atomic Scale Characterization of the Reaction Mechanism of Moisture in Coal Matrix Acting on Coal Spontaneous Combustion

Abstract

ABSTRACT It is imperative to have an in-depth understanding of the mechanism of action for the role of moisture in a coal matrix during coal spontaneous combustion, not only for preventing fires in the coal industry but also for reducing emissions of hazardous gases. In this study, the method of isotope tracing was first introduced to study the mechanism of moisture in the spontaneous combustion of coal. Moisture in a coal matrix was labeled separately using D2O and H2 18O, and the coal samples with internal moisture and external moisture were prepared by controlling the drying temperature. Coal samples with different isotopic moisture were heated using a spontaneous combustion apparatus. The gaseous products (CO2, CO, and CH4) were measured using a GC-950 gas chromatography equipped with a flame photometric detector, and simultaneously, the isotopic gases (including C18O, C18O2, CH3D) were timely monitored using an online mass spectrometer. The appearance of isotopic gases directly proved that the moisture could participate in the spontaneous combustion of coal in atomic level, and the moisture in the coal matrix is involved in the spontaneous combustion of coal through chemical reaction. Based on the experimental results, the pathways of the oxygen atom and H atom from the moisture participating in the production of isotopic gases were investigated. The reaction mechanism of moisture participating in the spontaneous combustion of coal was also explored based on the migration law of oxygen and hydrogen atoms of H2O molecule in coal matrix.