Technical Market Support » Metallurgical Coal
Three Australian coals from different coal measures were washed to produce a vitrinite rich fraction (VRF) and an inertinite rich fraction (IRF). Five blend samples of each coal with the same overall bulk quality and grind but different VRF and IRF grinds were produced. These blends were then coked under the same conditions in the BMA Research Coke Oven (RCO).
The grind of the IRF was found to impact coke strength. For Coal A (a high rank German Creek Formation coal) and Coal B (a mid vol Illawarra Coal Measures coal) the finer the grind of the IRF, the stronger the coke. Coal C (a high rank Rangal Coal Measures coal) showed the reverse tendency.
Optical imaging techniques were used to analyse the coke oven feeds. The amount and size of liberated vitrinite, inertinite, liptinite and minerals were determined. In addition, the amount, size and type of composite grains were also determined (vitrinite dominant, vitrinite rich, inertinite, inertinite dominant, inertinite rich, mineral dominant, mineral rich and liptinite dominant, liptinite rich). For Coals A and B the finer the size of the inert rich grains, the stronger the coke. Further the relationship between strength and inertinite grain size measured by coal grain analysis was more linear than the relationship between coke strength and IRF grind. Predictions would be expected to be more reliable using coal grain analysis results than IRF grind. For Coal C there was also a positive correlation between coke volume breakage strength and the amount of large composite grains in the coal sample. It is speculated that the low dilatation of Coal C requires very close association between the inerts and the vitrinite during coking to effectively bond the inerts into the structure. Further work is planned to better define the mechanism.