South African coal and its abrasiveness index determination: An account of challenges

Industry end users of coal like electricity generating stations have specifications on coal required in terms of reactive, chemical and physical properties; this includes the ash content, moisture, composition, hardgrove grindability index and abrasiveness index amongst many other properties. These properties affect each other including the overall coal properties and performance required during its specified usage. Some South African coals are known to be very abrasive, this causes operational challenges during the electricity generation combustion process as the coal abrades the plant equipment at a faster rate. Various South African coal samples were tested for abrasiveness index using the Yancey, Geer and Price (YGP) method. Results from these tests showed a lack of repeatability and reproducibility on the abrasiveness index values of coal samples. This lack of repeatability and reproducibility was observed in all coal samples tested. The same was found when either the same sample was tested in different laboratories or even when a mother sample was divided and tested repeatedly in one laboratory. Proximate and Ultimate analysis were conducted on the same South African coal samples for coal characterisation and classification. The size of the analysed sample; the size and shape, the degree of liberation of the abrasive coal component, and the interface between the abrasive component of coal and the blade surface are additional contributing factors. This study gives an account of challenges experienced and observed during the abrasiveness index determination of different South African coal samples. An attempt to holistically integrate the impact of main coal components contributing to the abrasiveness of coal will be presented.