Coal Secondary Oxidation Thermodynamic Behaviors Affected by Pre-Heating at Different Oxygen Concentrations

To investigate the impact of pre-oxidation oxygen concentration on the propensity of coal spontaneous combustion, thermogravimetric analysis was used to obtain thermal characteristic curves for raw coal and pre-oxidized coal with five different oxygen concentrations. The coal spontaneous combustion process was categorized into three phases: water-loss and weightlessness, oxygenation and weight gain, and combustion phase. It reveals that characteristic temperature points of oxidized coal were lower than that of raw coal, and pre-oxidation plays a role in enhancing the coal oxidation to varying degrees. During the phase of oxygenation and weight gain, the activation energy of oxidized coal decreases from 44% to 84% of that of raw coal. The positive effect on coal secondary oxidation is initially reduced, then increased with the increasing of pre-oxidation oxygen concentration. The sample pre-oxidized with 15% oxygen concentration is the most easily spontaneous combustion, and the total activation energy of its oxidation reaction is 57% of that of the raw coal, the characteristic temperature of which lowered by an average of 7.4°C. It will be conducive to revealing reignition mechanism of coal and preventing coal secondary spontaneous combustion.