Characteristics of polycyclic aromatic hydrocarbon release during spontaneous combustion of coal and gangue in the same coal seam

Based on the influence of temperature, coal quality, oxygen supply and other factors, the formation characters of PAHs during spontaneous combustion of coal and gangue in the same coal seam were experimentally studied. The results showed that the amount of PAHs released from coal and gangue first increased and then decreased with the rising of coal and gangue spontaneous combustion temperature. And it reached a peak value about 5.76-7.17 times of the minimum value at 400 °C-500 °C. The types of PAHs released during the high temperature stage of spontaneous combustion were up to 9. The release amount of PAHs generally increased with the rising of the volatile content, sulfur content, carbon content, fixed carbon content and calorific value of coal and gangue, but decreased with the rising of ash content. The amount of PAHs produced by spontaneous combustion of raw coal was generally higher than that of gangue, and the difference was more obvious at high-temperature stage. The total toxicity amount of PAHs produced by spontaneous combustion of raw coal was higher than that of gangue, up to 9.93 times. Its law of change with temperature was consistent with the total amount of PAHs, which increased and then decreased with the rising of temperature; and reached the peak at 300 °C-400 °C with a peak value of 6.72-14.60 times of the minimum value.