Study on the Influence of Water Immersion on the Characteristic Parameters of Spontaneous Combustion Oxidation of Low-Rank Bituminous Coal

Abstract

ABSTRACT To understand the effects of water immersion on the spontaneous combustion of low-rank bituminous coal, and the underlying mechanism, the pore size distributions and active functional groups of water-immersed coal samples were studied. Characterization data were acquired by liquid nitrogen adsorption and Fourier transform infrared spectroscopy. The spontaneous combustion behaviors of the experimental coal samples were assessed based on oxidation kinetics obtained using a programmable temperature device. Water immersion promotes pore development and enhances the activity of functional groups, which in turn stimulates spontaneous combustion. A lower metamorphic degree of coal yields a more obvious effect. Water immersion causes existing pores to expand or forms new pores, such that the specific surface area and total pore volume of the coal increase. Pores with a radius value near 20 nm grew to the greatest extent. The activities of hydroxyl, ether and carbonyl functional groups and of multi-substituted aromatic hydrocarbons in the coal molecules increase, whereas the activities of methyl and methylene groups decrease. The expanded pores provide more space for the coal–oxygen reaction and enhance the functional group activities. These changes increase the risk for spontaneous combustion by increasing the oxygen consumption rate, decreasing the associated activation energy and increasing the pre-exponential factor.