Proximate analysis of New Zealand and Australian coals by thermogravimetry

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Abstract
A technique has been developed at The University of Auckland for proximate analysis of coals by thermogravimetry using sample weights of <20 mg. Samples from three New Zealand coalfields and the Bowen Basin of Queensland, Australia, have been analysed. Coals tested range in rank from subbituminous to semianthracite, and have ash contents from 3.1 to 21.4% on a dry basis. Results obtained using the technique are within acceptable precision limits of the standard procedure. Volatile matter content of the coal shows a logarithmic increase with decreasing sample weight. To minimise this effect on repeatability, and to optimise the equipment capabilities, sample weights of 15.5 ± 0.5 mg should be used. The technique is ideally suited to (1) analysing samples where insufficient material is available for standard proximate analysis, and (2) correlation with microstudies of coal.