A comparison of spontaneous combustion susceptibility of coal from the Benue trough according to rank

Abstract

This study investigated spontaneous combustion susceptibility of coal according to the rank. To estimate the spontaneous combustion susceptibility of coal, both crossing-point temperature (CPT) measurement and gas analysis by using gas chromatography (GC) were performed. For the experiment, Ihuoma coal, Orlu lignite, and Onyeama coal and Owukpa coal that are sub- bituminous coal, Obi/Lafia bituminous coal was used. The lignite such as Ihuoma coal contains more functional groups that easily react to oxygen more so than Onyeama and Owukpa coals. Also, Onyeama and Owukpa coal more functional groups than Obi/Lafia coal. For this reason, the lignite is more easily oxidized than sub-bituminous coal and sub-bituminous more easily oxidized than bituminous at low temperature, which results in high O₂ consumption, increase in CO and CO₂ generation, and low CPT. Although the CPT of Onyeama coal and Owukpa coal is identical to each other as they are the sub-bituminous, Owukpa coal has a lower initial oxidation temperature (IOT) and maximum oxidation temperature (MOT) than those of Onyeama coal. This means that although each coal has the same rank and CPT, spontaneous combustion susceptibility of coal may vary because the initial temperature of the coal at which oxidation begins may be different due to the substances that participate in oxidation.

Key Words: Coal rank, cross-point-temperature, spontaneous combustion, low temperature oxidation.