Risk evaluation of coal spontaneous combustion on the basis of auto-ignition temperature

The spontaneous combustion of coal, if not eradicated immediately, may lead to coal ignition and even a full-blown fire. A new method, DSC Inflection Point (DSCIP), was proposed to determine the coal auto-ignition temperature (CAIT). Heat fluxes and kinetic parameters before and after CAIT were comparatively investigated through TG/DSC analysis and mathematical model construction. Meanwhile, the impacts of temperature rise rate and oxygen concentration on CAIT were studied and two indexes representing the hazard and destructiveness of coal spontaneous combustion, respectively, were proposed. The results demonstrated that the heat flux curve of coal spontaneous combustion can be well fitted using Gaussian mixture model. Compared to the oxidation stage, the released heat during the combustion stage was greatly increased. Furthermore, the activation energy became larger and the reaction order decreased to zero when the temperature exceeded CAIT. The study also found that CAIT was enhanced with the increase of temperature rise rates or the decrease of oxygen concentrations. Changes of heat flux, free radicals, and the activation energy proved the rationality and feasibility of the DSCIP method in determining CAIT. Additionally, under the same environmental conditions, lignite had the largest hazard of coal spontaneous combustion and the anthracite had the biggest destructiveness. Both the hazard and the destructiveness of coal spontaneous combustion became stronger as oxygen concentrations increased.