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Kinetic parameters associated with self-heating of New Zealand coals under adiabatic conditions

¹ Division of Mining and Minerals Process Engineering, The University of Queensland, Brisbane 4072, Australia
² Department of Civil and Resource Engineering, The University of Auckland, Auckland, New Zealand

^* E-mail: b.beamish{at}minmet.uq.edu.au

Adiabatic self-heating tests were carried out on five New Zealand coal samples ranging in rank from lignite to high-volatile bituminous. Kinetic parameters of oxidation were obtained from the self-heating curves assuming Arrhenius behaviour. The activation energy E (kJ mol^–1) and the pre-exponential factor A (s^–1) were determined in the temperature range of 70–140°C. The activation energy exhibited a definite rank relationship with a minimum E of 55 kJ mol^–1 occurring at a Suggate rank of ~6.2 corresponding to subbituminous C. Either side of this rank there was a noticeable increase in the activation energy indicating lower reactivity of the coal. A similar rank trend was also observed in the R₇₀ self-heating rate index values that were taken from the initial portion of the self-heating curve from 40 to 70°C. From these results it is clear that the adiabatic method is capable of providing reliable kinetic parameters of coal oxidation.

KEYWORDS: coal, self-heating, adiabatic oven, activation energy