Abstract
ABSTRACTPetrographic studies are commonly used to categorize the potential utilization of coals. Eleven coal samples from the Jharia coalfield (JCF), India, were studied using petrographic techniques to investigate maceral content, reflectance, and textural characteristics. Multiple test samples of each coal were slowly oxidized under controlled laboratory conditions from an ambient temperature of 30°c to 300°c to investigate the morphology of oxidized coals. The petrographic characterization of coals before and after oxidation showed significant changes in both morphology and vitrinite reflectance. The oxidation of coal particles produced three predominant textural changes: particles with homogeneous change of reflectance (HCv), particles with oxidation rims (ORv), and particles with no changes were observed (Uv), respectively. These textural characteristics were used to indicate how particles had interacted with oxygen at low temperatures during the early stages of oxidation. The morphological classification developed provides an alternative method to confirm the susceptibility of a coal to spontaneous combustion. Conventional thermal parameters such as crossing point temperature (CPT) were unable to identify the coals prone to spontaneous combustion. However, certain petrographic parameters could be combined with CPT values to provide a much more accurate measure for susceptibility to spontaneous combustion.
Highlights
Spontaneous combustion of coal is a very complex physico-chemical reaction caused by several intrinsic (density, calorific value (CV), moisture content (M), volatile matter (VM), fixed carbon (FC), ash (A), maceral content and rank, total iron, non-pyritic iron, total sulphur, pyritic sulphur, organic sulphur and sulphate sulphur contents of coal) and extrinsic factors
The changes observed in the petrographic texture of an oxidised coal may be due to the reaction temperature and chemical changes, which may be determined by a study of the changes observed in reflectance and morphology of the samples [9, 18,19,20,21,22,23]
This paper outlines the experimental studies performed to provide a petrographic characterization of eleven coal samples collected from mines within the Jharia Coal Field (JCF), Northeast India, some of which are known to be prone to spontaneous combustion
Summary
Spontaneous combustion of coal is a very complex physico-chemical reaction caused by several intrinsic (density, calorific value (CV), moisture content (M), volatile matter (VM), fixed carbon (FC), ash (A), maceral content and rank, total iron, non-pyritic iron, total sulphur, pyritic sulphur, organic sulphur and sulphate sulphur contents of coal) and extrinsic factors (particle size, geological condition, mining methods and environmental condition). Among all the macerals vitrinite is the most vulnerable, whereas the inertinite and liptinite groups are more resistant to oxidation [14,15,16,17,18] Both artificial oxidation and natural weathering may cause changes to the petrographic textures of coal. This paper outlines the experimental studies performed to provide a petrographic characterization of eleven coal samples collected from mines within the Jharia Coal Field (JCF), Northeast India, some of which are known to be prone to spontaneous combustion These studies identify the macerals, vitrinite reflectance and morphological characteristics of fresh and artificial oxidised coals to assess the susceptibility of these coals to spontaneous combustion
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