A Fractographic Approach to Understanding the Mechanisms of Coke Breakage

The prediction of strength of coke produced from a coal (either singly or in a blend) is a key input into valuing the coal. Current models are largely empirical and often fail when used for coal with properties outside the data used to develop the model. This project aims to take techniques used to understand the root cause of mechanical failure in other model systems and apply them to metallurgical coke. This will allow us to build a picture of the root causes of coke fracturing / breakage and ultimately through this approach we should be able to better target the parameters to use in models to predict coke strength from coal properties.

Fractographic techniques have been applied to the study of the breakage of metallurgical coke. Two series of cokes were studied. Each series consisted of two single coals and binary blends of the two coals. The fractographic approach consists of breaking the coke, either by dropping the coke or compressing the coke in a Shimadzu universal tester. The fracture surface formed is then examined to develop an understanding of where the fracture occurred and the mechanism of fracturing. This has allowed us to successfully build a picture of the nature and amount of weaker microstructural features in the coke. These were summarized using "radar graphs".

These radar graphs provide a unique failure profile for each of the metallurgical cokes and blends tested. They provide both a visual and statistical representation of the failure mechanisms for each of the analysed cokes, and have a high degree of reproducibility not only because of the large number of fractured samples analysed but also because they are the physical representation of the actual cokes tested and how they were processed.  To summarize, this research work has shown that cokes formed from different binary coal blends show different failure mechanisms to cokes prepared from the individual component coals in the blend. Significantly, the breakage behaviour of coke blends also differs from that predicted by averaging the breakage behaviour of the parent single coal cokes.

A preliminary analysis was done on the links between fractography results and coal properties and fractography results and coke strength indices. The current data available suggests it should be possible to use the fractography results in developing better understanding of how to predict coke strength. Further it may be possible to build links between the failure mechanisms and the coal properties to allow improved coking models to be developed.