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To reveal the influence of pre-oxidation time on coal spontaneous combustion behaviors, temperature-programmed experiments were carried out to analyze the kinetics characteristics of coal primary and secondary spontaneous combustion from the macro viewpoint. By the growth-rate analysis of gaseous compounds, the critical temperature of raw coal (Y 0 ) spontaneous combustion was 70°C. At the critical temperature, isothermal oxidation was performed for 2 h, 4 h, 6 h, and 8 h, and the processed samples were named Y 2 , Y 4 , Y 6 , Y 8 . It was found that the changing trend of CO concentration increased at first and then decreased with the increase in isothermal pre-oxidation time. Two maximum peak values were found near the 1st and 4th hour in the production of CO 2  gas. Spontaneous combustion characteristic parameters and apparent activation energy of oxidized coal showed staged characteristics compared to raw coal. Below 70°C, the order of spontaneous combustion characteristic parameters and the apparent activation energy was Y 0 &lt; Y 2 &lt; Y 4 &lt; Y 6 &lt; Y 8 . Above 70°C, the order was Y 6 &lt; Y 8 &lt; Y 2 &lt; Y 4 &lt; Y 0 . Isothermal pre-oxidation at the critical temperature could slow down coal secondary low-temperature oxidation and speed up high-temperature oxidation. When isothermal pre-oxidation is at the critical temperature, the pre-oxidation time has double effects on the high-temperature oxidation of oxidized coal.

Influences of the pre-oxidation time on coal secondary spontaneous combustion behaviors by temperature-programmed technique