The effect of inherent and added inorganic matter on low-temperature oxidation reaction of coal

The influence of inherent and added inorganic matter on low-temperature oxidation reactions of coal and the effectiveness of the additives to affect the oxidation reactions are examined in this paper. A Victorian brown coal was selected for this study. Samples of the raw coal, water-washed coal, and acid-washed coal were prepared. The acid-washed coal was also doped with seven additives, respectively, by both wet-mixing (5% wt.) and ion-exchanging with the additives. Each of the samples was then tested in a wire-mesh reactor to determine its critical ambient temperature, above which thermal runaway occurred. The critical ambient temperatures of the acid-washed and water-washed coals were higher than that of the raw coal, indicating that the inherent inorganic matter in the coal catalysed low-temperature oxidation. Of the seven additives used, Cu(Ac)2, KAc, and NaAc were found to promote the oxidation reaction, while NaCl, CaCl2, and Mg(Ac)2 inhibit the reaction. Ca(Ac)2 showed a very little effect. Furthermore, it was observed that the promotion effects of Cu(Ac)2 and KAc were stronger when they were ion-exchanged into the coal, while the inhibition effect of Ca(Ac)2 was stronger when it was wet-mixed with the coal. Low-temperature oxidation kinetics of various samples were also estimated and compared. Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) quantitative analysis of the samples respectively wet-mixed and ion-exchanged with Cu(Ac)2 indicated that the pore volume of the ion-exchanged sample was greater than that of wet-mixed sample, and the amount of copper ion absorbed in the ion-exchanged coal particle was higher and more uniformly distributed in the coal matrix than that in the wet-mixed coal particle.