Stage 3: A Coke Analogue to Examine the Effect of Mineralogy on Coke Reactivity

This project has had three stages.  The three stages are a series of studies, focusing on understanding the effects of mineralogy on the reactivity of metallurgical coke, by using a coke analogue material in a pseudo-CRI test. All three report stages are published as a complete set. Stage three is the most recent and final stage.

In stage three there were two main objectives, the first was to develop a model to help predict the reactivity of the coke analogue, and the second being to further understand the effects of Fe and Ca on the reactivity of coke.

A model (Cumulative Oxide Model, or COM) was developed principally based on the reactivity measurements of coke analogues containing single minerals. It used a deviation approach, deviation of the reactivity from a standard analogue in CO2 gas at 1100°C, to deal with changes in reactivity due to the mineral content of the analogue. The standard analogue used contained no mineral addition. Reactivity data from stages one and two, as well as newly measured data in stage three, were used in the model to predict the reactivity of the coke analogue. The main findings were:

• The COM model was shown to represent the reactivity of binary systems well, for mineral systems originally containing magnetite, quartz, corundum, magnesia, spinel, monticellite and kaolinite, and the ternary system magnetite, quartz and corundum.
• Approaches have been developed or proposed that allow for non-linear effects of ash minerals, porosity and particle size to be incorporated into the COM model.

The effect of Fe and Ca on the reactivity of coke was studied using both the coke analogue and sole heated oven cokes. Sole heated oven cokes were prepared from washed Australian coal samples, in collaboration with the University of Newcastle.

The main findings from the study into the effects of changes in Fe content in the coke were:

• Using coke analogues containing coke ash with differing Fe contents, the reactivity of the coke analogue increased with increasing Fe content, as expected. Although the increase in the reactivity was small, this may reflect the fact that the increase in Fe content was actually rather small.
• Using sole heated oven cokes containing different contents of Fe, the reactivity increased with increasing Fe content as expected. Fe was added to the sole heated oven cokes in the form of magnetite to the washed coal prior to coking.

The effect of changes in Ca content on the reactivity of coke using the sole heated oven cokes. The main findings were:

• Increasing addition of Ca to the sole heated oven increased the reactivity. Ca was added in the form of lime to the coal prior to coking. The Ca addition had almost double the effect on coke reactivity compared to additions of Fe.
• Ca in the sole heated oven coke had a similar mobility as reported previously for the coke analogue. The behaviour of Ca in coke was more complex, forming complex Ca-Al/Si oxy sulphides. In contrast, there is little S in the analogues.
• Similar to that found in the coke analogue, there is evidence that the Ca added as lime dispersed throughout the coke. This breaking up/dispersion is thought to be at least in part the explanation for the greater effects of Ca than Fe on the sole heated oven cokes reactivity.

The primary validation of the coke analogue reactivity was carried out in stage one where it was shown the analogue reactivities aided understanding and were consistent with the ash effects on reactivity in metallurgical coke. In stage three it was found that similar trends in coke reactivity behaviour were obtained whether the base carbon material was from coal in the sole heated oven cokes or graphite and phenolic resin material in the fired coke analogue. This adds further evidence to the suitability of the analogue for use in the study of mineral effects on metallurgical coke reactivity.

ALL THREE FINAL REPORTS ARE AVAILABLE AS A SET