Insight into the intrinsic reaction of brown coal oxidation at low temperature: Differential scanning calorimetry study

• DSC was introduced to determine the intrinsic reaction of brown coal oxidation at low temperature.
• The optimal test conditions of coal oxidation at low-temperature were 1.0 °C min− 1 heating rate and 5 mg coal mass.
• The exothermic characteristics of the intrinsic reaction can be well expressed by subtracting DSC curve in N2 from air.
• Activation energy obtained from DSC-sub curve can better reflect intrinsic oxidation reaction.

The oxidation of coal at low-temperature involves a series of physical and chemical processes and many parallel reactions. But the intrinsic oxidation reaction between O2 and coal is the main source responsible for the self-heating and spontaneous combustion of brown coal. In this research, differential scanning calorimetry (DSC) was introduced to determine the intrinsic reaction of Ximeng brown coal oxidation at low temperature. The heat evolution of the intrinsic reaction after eliminating the evaporation of water and thermal decomposition of inner oxygen-containing functional groups was obtained by subtracting the DSC curve in N2 from the DSC curve in air. It is considered that the intrinsic reactions between coal and oxygen could be divided into three stages, including the slow oxidation, accelerated oxidation and rapid oxidation stages. Compared with DSC-air curve, the DSC-sub curve based on the subtracting results elucidated the exothermic characteristics of intrinsic oxidation reaction in each stage more clearly. In addition, DSC-sub curve reduced the experimental errors inborn from the heating rate and the sample mass, so it had more practical application value than DSC-air curves. Activation energies obtained from DSC-sub curves can better reflect intrinsic oxidation reaction and be used as important indicators for the evaluation of coal spontaneous combustion tendency.