Reduction of spontaneous combustibility and analysis of oxidation reaction kinetics by oxidation treatment of lignite upgraded coal

Abstract

To effectively utilize lignite coals, methods of reducing the spontaneous combustion of upgraded lignite coal were studied. In previous research, we have demonstrated that using an upgraded Loy Yang coal from Australia, a representative lignite (brown coal), the controlled oxidation treatment at 200℃-240℃ enables to chemically stabilize the functional groups of the upgraded coal, giving rise to a sufficient reduction of the ignition potential to the level of bituminous coal. However, the effect of the oxidation treatment conditions on reducing the spontaneous combustion potential of upgraded coal were not fully evaluated.

In this study, the exothermic reaction rate during oxidation treatment of upgraded Loy Yang coal was carefully examined. Weight change and heat generation rates of upgraded Loy Yang coal during the oxidation treatment were measured at temperatures of 140°C-300°C using oxygen concentrations of 1-15 vol.% by thermogravimetry-differential scanning calorimetry. The exothermic reaction was considered as an apparent first-order reaction in the temperature range of 140°C-240°C, and the heat generation rate was expressed by an Arrhenius-type equation. The activation energy was approximately 60 kJ/mol, and it was found that the O₂ concentration affects the frequency factor. Based on these findings, an estimation equation was newly proposed, allowing a prediction of the oxidation conditions of upgraded brown coal.