Understanding Coal Interactions in Coking Blends

• A tool that could accurately define the carrying capacity of a coal was not produced. In this regard, the program was unsuccessful. However, the program did provide sufficient information that would allow development of this tool in the future using different breeze parameters.
• The program was not able to demonstrate that the transfer of plasticising material played a major role in improving the quality of blended coals. Rather, the data indicated that synergistic effects were improving the quality of the blends.

Carrying Capacity
The findings were:

• In this program, some coals were found to have carrying capacity.
• Only a small sub-set of coals exhibited ability to carry the inert material at 10% coke breeze substitution. Should this experimentation be revisited, substitution rates on 0%, 3%, 6%, 9% and 12% would provide better resolution of the effect.
• Ideally, a finer coke breeze would be used (<100µm).
• The carrying capacity varied depending on whether a volume breakage or abrasion index was examined. Coals can carry more coke breeze, without deterioration in volume breakage values, compared to abrasion resistance values.
• The ability of a coal to carry inert substances appears to vary from rank to rank with lower rank, higher volatile coals having superior carrying capacity. However, with only 4 samples examined this may simply be a function of the coals examined.

Transfer of Plasticising Material
The findings were:

• In the boundaries between fusible coke components, there is some evidence for modification of the coke’s fused carbon domain sizes, which has been suggested to be a response to hydrogen transfer. This type of bonding was of the order of only a few microns thick.
• There was no evidence for a more pervasive textural alteration of the coke. Wider transition zones are considered to be a function of the angle of intersection of the transition zone with the surface of the petrographic block.
• Blending coals of differing rank produced coke indices that were superior to that which would be expected based on computation of the results obtained from coke quality of the end members.
• No compelling evidence was found to suggest a significant role for the modified interface bonding mechanism (or transfer of plasticising material) in improving the coke quality of blends. An adhesion-type bonding mechanism was considered to be more common.
• The blend coke quality outcomes that were superior could be explained by a combination of mechanisms where the two components acted in a complimentary manner to minimise the limitations of each individual component.