Effect of chemical, mineralogical and petrographic properties on the grindability behaviour of a South African Highveld feed-coal and its density- separated fractions
DOI:
https://doi.org/10.17159/Abstract
In this study, coal properties which are associated with the wear and damage of costly grinding equipment during pulverization for fuel (pf) combustion were investigated. A South African Highveld feed-coal (<120 >6.7 mm) and its beneficiated fractions were crushed to <1 >0.25 mm particles for the grindability tests. These particles were milled for 60 minutes and screened using a 75 µm sieve to produce <75 µm and >75 µm sized fractions. These samples were analyzed by different techniques for the correlation with the conventional Hardgrave Grindability Index (HGI). The <1.5 g.cm-3 float which contains 93 vol %(mineral-matter free) total-macerals, 9% kaolinite and the lowest HGI (57) (hardest to grind) were pulverized for 15, 30, 60 and 120 minutes for the particle size distribution analysis. This analysis indicates that the <75 µm particles % increase with an increase in the grinding-time. While, the >1.9 g.cm-3 sink with the highest HGI (76), 44% kaolinite and 20 vol% total-macerals grinds easily to generated the highest % <75 µm particles. Based on higher correlation-coefficients (R2) (0.77-0.91), the ash-yield, mineral-matter, petrographic-composition and fixed-carbon have significant effects on the HGI. Conversely, the inherent-moisture and total-sulphur with smaller R2 values (0.48 - 0.62) have only minor effects on the HGI. Results from this investigation could be implemented in the preparation of a suitable pf with low equipment wear propensity from the blending of various feed-coals, utilizing mineralogical and petrographic compositions. Finally, the effect of microlithotypes in Highveld feed-coals on the HGI should be investigated in further studies.
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