Abstract
Coal and coal-shales tend to undergo spontaneous combustion under favourable atmospheric conditions. Spontaneous combustion liability index and intrinsic properties of coals and coal-shales varies between (above and below) coal seams. The spontaneous combustion liability index (obtained from the Wits-Ehac Index) and intrinsic properties (obtained from proximate, ultimate, and petrographic analysis) of fourteen samples representative of in situ coal (bituminous) and fourteen coal-shales obtained in Witbank coalfield, South Africa were experimentally studied. Comparative analysis of the relationships between the spontaneous combustion liability index and intrinsic properties of coals and coal-shales were established to evaluate their effects on self-heating potential. The intrinsic properties show linear relationship with spontaneous combustion liability and therefore, identifies the factors affecting spontaneous combustion of these materials. The influence of coal-shales intrinsic properties towards spontaneous combustion liability shows higher correlation coefficients than the coals. Both coals and coal-shales show inertinite maceral as major constituents than the vitrinite and liptinite macerals, hence the reactivity of inertinite macerals may show greater influence on spontaneous combustion liability. A definite positive or negative trends exists between the intrinsic properties and spontaneous combustion liability index. This research is part of a larger project which is considering the influence of intrinsic properties of coals and coal-shales on spontaneous combustion liability.
Highlights
Spontaneous combustion causes an increase in the temperature of a thermally segregated accumulation of coal or other combustible materials due to the chemical reactions between this material and oxygen (Davidson 1990)
The spontaneous combustion liability index and intrinsic properties of fourteen samples representative of in situ coal and fourteen coal-shales obtained in Witbank coalfield, South Africa were experimentally studied
Comparative analysis of the relationships between the spontaneous combustion liability index and intrinsic properties of coals and coalshales were established to evaluate their effects on self-heating potential
Summary
Spontaneous combustion causes an increase in the temperature of a thermally segregated accumulation of coal or other combustible materials due to the chemical reactions between this material and oxygen (Davidson 1990). The recent challenge faced by a number of coalfields in South Africa is spontaneous combustion of coals and coalshales (Onifade et al 2018; Onifade and Genc 2018d, e; Fig. 1), which frequently causes loss of revenue and at several intervals it has led to loss of precious resources, increase in production cost, loss of properties, and an increase in rehabilitation cost. Sedimentary rocks such as coals and coal-shales contain different volumes of organic and inorganic matter in which pore spaces are embedded in the solid together with carbon-rich matter
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