Prediction indices and limiting parameters of coal spontaneous combustion in the Huainan mining area in China

Hazards due to spontaneous combustion of coal seriously threaten coal mining safety. To explore and evaluate the prediction indices and limiting parameters of coal self-ignition, seven samples from the Huainan mining area in Anhui Province, China were tested. Experiments were conducted using an oil-bath temperature-programmed system. The experimental results indicated that the oxygen consumption rates and CO production increased slowly initially and then rapidly with the increase in temperature. The plots of CO/CO2 ratio versus temperature exhibited an exponential property. The C2H4/C2H6 ratios exhibited an unstable alternation when the temperature was in the range of 100-130 degrees C. However, the ratios became steady after the temperature increased above 130 degrees C. The low-temperature oxidation process was divided into three stages according to the Delta C-CO/Delta C-O2 ratios. The oxidation index D-O, a new indicator, was used to precisely forecast the point of spontaneous combustion. The limiting parameter analysis indicated that the minimum float coal thicknesses h(min) and limiting oxygen concentrations C-min first increased and then decreased constantly with an increase in temperature. The parameters reached their maximum value at 50 degrees C. The maximum air leakage intensity Q(max) followed a trend opposite to that of the two aforementioned parameters. With an increase in temperature, Q(max) first decreased and then increased. The results provide valuable information for predicting spontaneous combustion of coal, which can help prevent or mitigate risks in industrial mining.