Investigation into the Role of Inherent Inorganic Matter and Additives in Low-Temperature Oxidation of a Victorian Brown Coal

Abstract

This paper reports a laboratory investigation into the role of inherent inorganic matter and additives in the low-lemperatures oxidation and spontaneous combustion of a Victorian brown coal. The raw coal, water-washed coal, acid-washed coal, and acid-washed coal respectively doped with fourteen additives, are prepared. Each of the samples is then tested in a wire-mesh reactor to obtain its critical ambient temperature, above which a thermal runaway occurs. The critical ambient temperatures of the acid-washed sample and water-washed coal are higher than that of the raw coal, indicating that the inherent inorganic matter in the coal catalyses the low-temperature oxidation. The relative effectiveness of the additives is determined by comparing their critical ambient temperatures with that of the acid-washed coal. Magnesium acetate (Mg(Ac)2). calcium acetate (Ca(Ac)2). magnesium carbonate (MgCO3). sodium hydroxide (NaOH). calcium chloride (CaC12), and sodium chloride (NaCI) arc found lo inhibit spontaneous combustion, while copper acetate (Cu(Ac)2), potassium acetate (KAc), sodium acetate(NaAc). copper carbonate (CuCO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3). calcium carbonate (CaCO3), and calcium hydroxide (Ca(OH)2) promote the spontaneous combustion. The effect of additive loading is also investigated for an inhibition agent (Ca(Ac)2) and a promotion agent (NaAc). Low-temperature oxidation kinetics are estimated by a transient energy balance approach and compared with the spontaneous combustion potential of the samples.