Study on the kinetics and reaction mechanism of low-temperature oxidation of lignite with different coalification

Abstract

The differences in the coalification of lignite result in noticeable variations in the processes of its low-temperature oxidation. Consequently, this study utilizes thermogravimetric analysis and in-situ FTIR to investigate the oxidation kinetics and reaction mechanisms of lignite with different transmittance (PM). For lignite with PM < 30 %, the mechanism function is observed to transition from the three-dimensional diffusion Z–L–T equation to the Avrami–Erofeev equation during the accelerated oxidation stage. The study of the trends in the alterations of active functional groups revealed that the reaction mechanism for type Ⅰ lignite (PM < 30 %) consists of –OH, –CH2–, and –CH3 to glycol structures, and subsequently to –CHO. In contrast, the primary mechanism for type Ⅱ lignite (PM ≥ 30 %) involves the conversion of –OH, –CH2–, and –CH3 to –OOH, and then to –COOH, with its validity confirmed through Pearson correlation coefficients. These research findings contribute to a comprehensive understanding of the mechanisms and development of lignite spontaneous combustion, offering substantial guidance for the advancement of monitoring, warning, and targeted prevention of such disasters.