Effect of low-temperature pre-oxidation on the self-heating of coal

In order to investigate the effect of low-temperature pre-oxidation on the self-heating of coal, research was made on the temperature rise characteristics of coal samples with different pre-oxidation temperatures, duration and numbers. Besides, in situ FTIR and ESR experiments were also carried out to study changes in active groups and free radicals of raw and pre-oxidized coal. Results show that the pre-oxidation in the 30-60 degrees C temperature range markedly reduces the oxidation activity of coal and inhibits the oxidation reaction. TTR (total temperature rise) of the pre-oxidized coal is inversely proportional to pre-oxidation temperature, duration and number. The hydroxyl and aliphatic hydrocarbons continue to decrease in content during the oxidation reaction. The C-O group and carbonyl group, as the main oxidation products, show an increasing trend. The trend of group content in the pre-oxidized coal samples is significantly smaller than that of the raw coal, indicating the activity of active groups is weakened. The variation in Ng for coal samples decreases eventually after pre-oxidation, suggesting that initial oxidation makes the coal molecular structure more stable. This study helps to understand further the effect of low-temperature pre-oxidation on the self-heating of coal and provides a theoretical basis to use the preoxidation method to prevent coal spontaneous combustion.