ACARP Project Number: C13066      Published: August 08

The aim of this project is was to develop a simple tool that allows the determination of the fusibility of inertinite in Australian coals.  The first step in determining the fusible inertinite component is to convert the petrographic analysis to a mass basis. This requires relationships between the rank of the coal and the densities of the maceral groups. To determine these relationships eight coals were subjected to float sink analysis using eight liquid densities. In determining the densities of the maceral groups assumptions must be made relating to the mineral (vol %) and the ash content of the coal. Using mineralogical data determined by QEMSCAN on selected float sink samples of the each coal it was possible to determine a relationship between the ash (%d) with minerals (mass %) and also with minerals (vol %). Using minimisation techniques the best estimates were derived for the densities of the vitrinite and inertinite of the eight coals. Due to the small or zero amount of liptinite in the coals it was not possible to determine the density of liptinite.

The calculated densities of vitrinite and inertinite for the eight coals showed very similar relationships with rank (carbon %daf) as those given by van Krevelen (1961). It is recommended the relationships derived by curve fit to the data of van Krevelen be used to determine the density of the maceral groups.

The next step in determining the fusible inertinite is to estimate the loss of volatile components during carbonisation. Degassing experiments were conducted in small cast iron pots (mini pots) to determine the yield of coke and to prepare coke samples for coke microtexture analysis. A mini pot was packed with 110g of coal to a bulk density of 900 kg/m3. Two mini pots were prepared for each of the four float sink fractions of the eight coals. Ten mini pots were then place into a 7kg bench scale oven for carbonisation.

The mini pot coke tests shows that more of the inertinite can be fused when in close proximity to vitrinite (finely crushed coal packed densely and then coked).

As the mini pot coke results have a higher coke yield and higher fused inertinite than would be normally found for pilot scale data it was decided to extend this project to include the examination of the data from ACARP project C12057 (Bennett et al., 2008). In project C12057 twelve coals were coked in a pilot scale oven and coke microtexture analysis was conducted on the cokes.

There is good agreement between the calculated coke yields and the actual pilot scale coke yield using the coke yield determinations approaches given above. The predicted coke yield based on the pilot scale correlation and the measured volatile matter is, as expected, very good. The two predicted coke yields using petrographic analysis (Diessel & Wolff-Fischer and fitted relationships) do vary slightly from the actual results but the variation is different for different coals, indicating the variation is not just due to errors relating to the petrographic analyses.

All pilot oven cokes show that more than 50% of the semifusinite is fusible with some having more than 90% of the semifusinite fusible.

Several different methods for the prediction of fused carbon in coke were evaluated using the pilot scale data.

A good prediction of fused carbon includes the vitrinite and liptinite in the coke and also the amount of inertinite with a reflectance close to the Romax of the vitrinite. Though there is still an influence of how the inertinite is distributed in the coal matrix - more inertinite in the microlithotype inertite then the less fused carbon in the coke.

The minerals in the coal do seem to have a slight influence on fused carbon when dispersed evenly through the coal as shown by the mini pot coke tests. This influence is not seen in the pilot scale tests. This may be due to the minerals being mostly associated with the inertinite and that the large inertinite pieces do not play a large role in the formation of fused carbon.