ABSTRACT

The intrinsic exothermic reaction of coal with oxygen during low-temperature oxidation is the main heat source responsible for the self-heating and spontaneous combustion of coal. Due to the complexity of low-temperature oxidation of coal with many parallel reactions, it is difficult to directly investigate the heat evolution due to the reaction of coal with oxygen by conventional analytical method. Differential scanning calorimeter (DSC) was introduced in this study to study the intrinsic exothermic reaction of coal with oxygen based on the heat evolution. Using the subtraction analysis method of DSC, the DSC-subtraction curves can be obtained by subtracting the DSC–N₂ curves from the DSC-air curves. Experimental results indicate that the DSC-subtraction curve can better reflect the intrinsic exothermic reaction of coal oxidation than a DSC-air curve by eliminating the influence of evaporation of water and thermal decomposition of inherent functional groups. The experiment factors affecting the intrinsic reaction were also investigated with the subtraction method of DSC. In terms of the kinetics characteristics of heat evolution, the intrinsic reaction of coal with oxygen is divided into three stages: slow oxidation stage, advanced oxidation stage, and rapid oxidation stage. The activation energies and pre-exponent factors at each of the stages were also calculated by oxidative pyrolysis kinetics. The subtraction method applied in this study is a quite promising method to determine the susceptibility of coal to self-heating and spontaneous combustion.

摘要

煤在低温氧化过程中与氧气发生固有的放热反应，是煤自热自燃的主要热源。由于煤低温氧化的复杂性和许多平行反应，很难通过常规分析方法直接研究煤与氧气反应的放热。本研究引入差示扫描量热仪 (DSC)，基于放热研究煤与氧气的本征放热反应。利用DSC的减法分析法，减去DSC-N ₂即可得到DSC-减法曲线来自 DSC-空气曲线的曲线。实验结果表明，通过消除水分蒸发和固有官能团热分解的影响，DSC-减法曲线比DSC-空气曲线更能反映煤氧化的固有放热反应。还用DSC的减法方法研究了影响本征反应的实验因素。从放热动力学特征来看，煤与氧的本征反应分为三个阶段：慢氧化阶段、高级氧化阶段和快速氧化阶段。每个阶段的活化能和指数前因子也通过氧化热解动力学计算。