Low-temperature oxidation and self-heating accelerated spontaneous combustion properties of a Yima formation bituminous coal with various moisture contents

Abstract

By thermogravimetry (TG) experiments, evolution behaviors and properties of thermal oxidation processes at low temperature (< 230.0 °C) of a bituminous coal with five moisture contents were investigated. A novel Acceleration Temperature Point Method (ATPM), defined as the transition point from low-temperature oxidation to rapid self-sustained heating-up period, was proposed to determine the role of moisture content in accelerating such process. Results show that segments of water evaporation and gas desorption dominate in stage 1 (65.0–150.0 °C), while segments of generation of coal-oxygen complex and structure oxidation dominate in stage 2 (150.0–275.0 °C). In the moisture range of 9.16–12.06%, the promoted effect of physical desorption capacity becomes weak with increasing moisture content. This is owing to five aspects: the equilibrium of vapor pressure and wetting capability of physically bound water, the change of mass and heat transfer between gas phase (water vapor)-condensed phase (bulk coal particle), the diffusing effect of gaseous water, the heat from dissolving and swelling of gaseous water into bulk coal pores, and the heat of pyrolysis derived from coal particles. Taking Acceleration Temperature Point (ATP) as a barometer to evaluate the spontaneous combustion susceptibility, the critical moisture content of Gengcun bituminous coal is 9.16%.