Technical Market Support » Metallurgical Coal
Previous projects C16047 and C20008 identified some coals from different Australian coal measures exhibited a different sensitivity to fine grinding of the inert rich fraction during coking. The previous work speculated that the differences were due to different dilatation characteristics requiring different coal grain compositions but still left some uncertainty in the mechanisms involved. The main objective of this project was to extend and improve the characterisation of the previous coals and cokes in order to attempt to develop mechanistic understanding for the different behaviour observed.
This project characterised coals and cokes from project C16047 in which each of three coals were washed to produce an inert rich fraction (IRF) and a vitrinite rich fraction (VRF). For each coal the VRF and IRF were blended together to produce five blends with the same overall composition and overall grind but different IRF and VRF grinds. This produced samples that had differing size distributions of the macerals and different mixes of grain types present. Each of these samples were then coked under the same conditions. The general trends were that for coals A and B coke strength increased with increasing fineness of the IRF grind while for coal C the coke strength decreased with increasing fineness of the IRF grind. Traditional wisdom is that, for most cokes, coke strength should increase as the inerts are made finer. The anomalous behaviour of coal C is therefore of interest and may be important to understand in order to optimise the use of this coal.
To help understand the mechanisms underpinning the variation in coke strength with grind for each of the three coals from C16047 a number of advanced characterisation tests were performed and the results examined for mechanistic insights as well as correlations. The CT structures were used as input for finite element analysis of the response of the structures to load. This allowed calculation of the number and distribution of high stress points in the structures. Correlations between the number of high stress points and strength were only partly successful which needs further investigation to understand the significance. The CT also allowed coke porosity and wall size to be characterised in 3D. In general good correlations with strength measures were not found.
Fractographic analysis showed that the features associated with the fractures of cokes from coals A and B were different from those for cokes from coal C. Within the coke series, trends were observed between fractographic parameters and changes in coke strength.
Measuring the size of the fusibles and infusibles in the parent coals with CGA showed that different parameters for the coals were associated with the strength indices.