Effects of thermal boundary conditions on spontaneous combustion of coal under temperature-programmed conditions

[Display omitted] •A method to calculate the key parameters of coal oxidation reaction was proposed.•The course of coal oxidation reaction shows the characteristics of different stages.•Complexity of coal spontaneous combustion were enhanced by substance transfer and temperature-rise.•High-temperature gas and contact wall could heat the surrounding coal. Coal spontaneous combustion (CSC) is one of major disasters that threaten the safety and production of coal mines. A method to calculate the key parameters of coal oxidation reaction based on temperature-programmed tests was proposed. Moreover, a one-step global numerical model for exploring coal oxidation considering the effects of multi-component material was established. The evolution of the oxygen consumption rates (OCRs) in multiple stages of coal oxidation was investigated and the changes in temperature and reaction rate were assessed by changing thermal boundary conditions including gas temperature supplied and wall temperature. The results show that the coal oxidation can be simulated based on the obtained parameters; the process of coal oxidation can be partitioned into three stages (i.e. temperature-dominated, co-dominated by temperature and oxygen, and oxygen-dominated) as the reaction continues. Under thermal conditions involving high-temperature gas, the coal always exhibits a high temperature at the gas inlet and the dimensionless number Φ of the coal self-heating temperature presents three trends including slight variation, a gradual increase, and gradual reduction. Under conditions involving the high-temperature wall of coal-storage tanks in contact with coal (briefly called the contact wall hereinafter), the dimensionless number Φ of the coal self-heating temperature increases exponentially.