Secondary Spontaneous Combustion Characteristics of Coal Based on Programed Temperature Experiments

In this report, the influence of pre-oxidation degree and ventilation flow on the parameters of spontaneous combustion of coal (temperature, gas concentration, and exothermic intensity) was studied in six sets of programed temperature experiments. The experimental results showed that the pre-oxidation exerted a positive effect on the spontaneous combustion parameters of coal in the early stage of coal-oxygen recombination reaction, but exerted an inhibitory effect in the later stage of coal-oxygen oxidation reaction. Air supply rate had a positive correlation with the initial oxidation of coal samples and 90 degrees C pre-oxidation spontaneous combustion parameters. Air supply rate had negative correlation with 140 degrees C pre-oxidation of coal samples. Meanwhile, secondary oxidation significantly reduced the characteristic temperature of coal. The critical temperature of each coal sample was 83.7 degrees C (coal sample 1-Y), 68.3 degrees C (coal sample 1-L), 69.6 degrees C (coal sample 1-G), 82.1 degrees C (Coal sample 2-Y), 70.4 degrees C (coal sample 2-L), and 70.0 degrees C (coal sample 2-G), and dry cracking temperature was 142.6 degrees C (coal sample 1-Y), 134.8 degrees C (coal sample 1-L), 136.2 degrees C (coal sample 1-G), 147.2 degrees C (coal sample 2-Y), 136.5 degrees C (coal sample 2-L), and 134.4 degrees C (coal sample 2-G). The curves of the characteristic parameters of primary and secondary oxidized coal showed exponential growth. And the oxidation process can be divided into three stages, the first stage (30 degrees C similar to critical temperature), the second stage (critical temperature similar to dry cracking temperature), and the third stage (over the dry temperature).