Effects of oxygen supply on low-temperature oxidation of coal: A case study of Jurassic coal in Yima, China

Low-temperature oxidation of coal is the fundamental process for self-heating and self-ignition in the mining, storage, and transportation of coal, and mostly occurs in oxygen-depleted air. However, little is known about the effects of oxygen supply on risk determination of coal self-ignition using the representative indicators. Four Jurassic coal samples from Yima were selected, and experiments on low-temperature oxidation of coal with different oxygen concentrations ranging from 6% to 21% were conducted to determine the characteristics and gas-release trends of coal oxidation at low temperatures (<= 190 degrees C). It was shown that the direct burn-off reaction began to play a major role at a temperature above 80 degrees C regardless of oxygen concentration; the changes in the oxygen consumption rate with temperature at oxygen concentrations of 16% and 11.7% were not significantly different; and when the temperature reached 95 degrees C, there was a visible increase in the CO production with increasing oxygen concentration and C2H4 was detected. The ratios of gaseous products were studied to determine the effects of oxygen supply on risk determination. They showed that the same logarithmic growth trend existed for the CO/CO2 ratio under different oxygen concentrations; the C2H4/C2H6 ratio rose steadily at temperatures above 130 degrees C, and there may be a decreasing linear trend for the C3H8/C2H6 ratio with a threshold temperature between 110 and 130 degrees C. Finally, an improved method was proposed for accurate risk determination of coal self-ignition in situ. (C) 2017 Elsevier Ltd. All rights reserved.