Characterisation of Australian and Indian Coals and their Cokes from Stamp and Top Charged Coke Ovens

Due to strong demand and declining reserves of premium coking coals, new coal reserves are being developed, which are often perceived to be of low premium on the basis of relatively lower coke strength after reaction (CSR) values. In India and China, low premium coals have been used in coke blends using stamp-charging in conventional and heat recovery coke ovens. Stamp charging technology appears to be a promising approach for improved utilization of such resources. In this project, the advanced properties of a number of Australian and Indian coals were characterized using semi-automated microscopy and X-ray diffraction with emphasis on composition variation with coal grain size. The same set of coals were used to prepare gravity charge cokes in 400 kg pilot-scale gravity charge oven and stamp charge cokes in an industrial heat recovery coke oven. Various properties of two sets of cokes were compared, and also related to the parent coal properties. Key findings of this study are primarily based on Australian coal and coke data.

This study implies that coke quality of gravity charge cokes can be improved by optimizing coal grain size composition, which is consistent with previous ACARP studies. This study further shows that the grain size information could also useful for the optimization of size distribution of feed coal of stamp charge cokes.

The study implies that coal minerals particularly clay composition could influence coke properties physically as well as chemically due to impact on cake bulk density and rheology.

The study suggests that during stamp charging, the effect of long storage on mechanical and reactive coke strength of extreme fluidity coals may be less severe.   

Recommendations:

· A systematic parametric study is required to confirm the role of kaolinite on the improvement of coke strength during stamp charging particularly to establish the mechanistic link on the modification of microstructure and fluidity and hence strength; and

· Further work is also required to verify the link between nature and the percentage of highly fusible and non-fusible coarse and fine coal grains and resultant coke quality and the implications of these findings to coal blends.