Thermokinetic analysis of low-rank bituminous coal during low-temperature oxidation: A case study of the Jurassic coal in Shendong coalfield, Ordos Basin, China

Abstract

Coal spontaneous combustion, accompanying with coal mining, storage, and utilization processes, has always been a worldwide hazard to cause energy resource waste, worker health risk, and atmospheric environmental pollution. The coal temperature and indicator gases are the most crucial parameters to precisely judge the degree of coal spontaneous combustion at the initial period through assessing the coal oxidized properties. Temperature-programmed and Fourier Transform Infrared Spectroscopy experiments were implemented to simulate the macro- and micro-characterizations of four Jurassic coals in Shendong coalfield, Ordos Basin, China. Based on the second derivative of the oxygen concentration, a novel method was proposed to determine the critical and cracking temperatures of coal during low-temperature oxidization. T1 and T2 of the Jurassic coal with different particle sizes were about 65 °C and 120 °C, respectively. The produce of CO concentration represents the beginning of Jurassic coal oxidization, and the occurrence of C2H4 implies more than 100 °C of coal temperature. Ea of Jurassic samples with different particle sizes from stages Ⅰ to Ⅲ were 63.2, 44.3, and 29.7 kJ/mol, respectively. Hydroxyl groups are the dominant in coal with strong activity, and primarily affect the rate of coal oxidation at low temperature. Aliphatic hydrocarbon groups reduced as the temperature increasing after 90 °C. Oxygen-containing groups and aromatic hydrocarbons displayed a slightly decrease during low-temperature oxidization process. A theoretical basis was provided for forecasting the disasters of coal spontaneous combustion.