Thermal decomposition of coal widely exists in the process of coal fire propagation, sealed fire zone, magma erosion and torrefaction of low rank coal. The risk of spontaneous combustion of coal was found to be significantly enhanced after thermal decomposition. In this paper, isothermal flow reactor and infrared spectroscopy were combined to study the thermal decomposition process of coal samples and the oxidation process of coal samples after thermal decomposition. Results showed that the thermal decomposition process of coal sample will lead to the decomposition of oxygen-containing functional group structures such as carboxyl and carbonyl, which can produce a large number of active site structures. These active sites can stably exist and accumulate under inert gas conditions. Once in contact with oxygen, oxidation reaction can occur even at room temperature, release heat and produce a large number of gas products such as CO and CO₂. On this basis, the viewpoint of room temperature oxidation of active sites of thermally decomposed coal is therefore put forward. It is considered that the room temperature oxidation of active sites is the initial heat source leading to self-heating or even uncontrollable spontaneous combustion of thermally decomposed coal. Compared with the raw coal sample, the coal sample after thermal decomposition does not need to go through the preparation period with very slow oxidation rate, but directly enters the self-heating period due to the room temperature oxidation and heat release of the active sites, which is the main reason for higher spontaneous combustion risk of the thermally decomposed coal than the raw coal.
 

thermal decomposition, room temperature oxidation, initial heat source