Influence of granularity on thermal behaviour in the process of lignite spontaneous combustion

Abstract

Granularity is one of the primary extrinsic factors that can influence the process of coal spontaneous combustion. Lignite was selected for studying the influence of granularity. A self-developed temperature-programmed oil bath experimental system was adopted to capture the changes in the spontaneous combustion characteristic parameters for different particle sizes. Moreover, the microcrystalline structure and functional group distribution of different granularities were obtained using an X-ray diffractometer and Fourier transform infrared spectrometer. The results show that the microcrystalline structure, the types of functional groups and the release order of gases of different granularities have equal influence during the process of coal spontaneous combustion. A smaller granularity has a lower aromatic group content and a higher content of high-activity hydroxyl groups, aliphatic hydrocarbons and oxygen-containing functional groups. Moreover, a smaller particle size results in a lower critical temperature. The distributions of coal granularity also affect the characteristic of coal spontaneous combustion. A wide particle size distribution produces a larger surface area for contact between coal and oxygen than a narrow distribution, which results in a coal with a stronger spontaneous combustion tendency.