Spontaneous Combustion Characteristics and Inhibition of Air-Dried Coal with Varying Water Soaking Times

Abstract

ABSTRACT Coal left in the goaf is prone to oxidation reactions when soaked in water and air-dried, which can cause a temperature increase and potentially lead to a mine fire. The spontaneous combustion characteristics of residual coal soaked in the goaf differ significantly from those of dry coal. Analyzing the variation rules of functional groups in coals with different water soaking times (WSTs) during low-temperature oxidation and exploring the inhibitory effect of an inhibitor on coals with different WSTs are vital in preventing and controlling fires in soaked and air-dried coal seams in the goaf. This paper analyzes the variation rules of functional groups in raw coal samples and samples soaked for one, three, and five months, as well as the corresponding samples under the influence of the inhibitor, MgCl2, using an experimental system of coal low-temperature oxidation and a Fourier transform infrared spectrometer. The following findings were obtained: as the WST increases, the aliphatic hydrocarbon content increases, the low-temperature oxidation activity becomes higher, and the inhibition effect of the inhibitor weakens gradually. As the WST increases, the -CH2, -CH3, -OH, and -COOH contents fall gradually, while the C=O content rises. At the beginning of the oxidation temperature rise (30–70°C), the inhibitor, MgCl2, slows down the consumption of oxygen-containing functional groups and aliphatic hydrocarbon functional groups. However, when the temperature exceeds 130°C, its inhibitory effect on coal oxidation weakens gradually. In this case, a growing number of functional groups are involved in coal oxidation, and the inhibitor fails to effectively prevent coal oxidation. Therefore, it is necessary to strengthen temperature monitoring in the goaf and regularly replenish inhibitors in soaked and air-dried coal seams to enhance the inhibitory effect and prevent the SC of such seams.