Spontaneous Combustion Liability Indices of Coal

ABSTRACT

The self-heating of coal due to oxidation potentially leading to its ignition is called “spontaneous combustion.” The liability of coal to undergo spontaneous combustion for selected coal obtained from the Witbank Coalfields was examined using different spontaneous combustion tests. The simple indices [crossing point temperature (XPT) and Stage II Slope] obtained from differential thermal analysis and composite indices [FCC (Feng, Chakravorty, Cochrane) and Wits-Ehac Indices] were used to examine the liabilities of 30 coal samples. Two characteristics produced from a differential thermogram (XPT and Stage II Slope) were evaluated as indicative of the liability of coal to self-heat. This study compared the results of various spontaneous combustion tests to assess the liability of coal to undergo spontaneous combustion. It was found that these simple indices provide inconsistent predictions of spontaneous combustion liability, while the composite liability indices provide more reliable results than the simple indices. The physicochemical properties of the samples were found to have impacts on the liability indices and vary from one sample point to another.

KEYWORDS:

• Coal
• coalfield
• crossing point temperature
• liability indices
• intrinsic properties and Wits-Ehac Index

Acknowledgments

This paper is part of a Master study in the School of Mining, Metallurgy and Chemical Engineering, University of Johannesburg, South Africa.