Characterization of Coal and Coke

Summary

The manufacture of coke to meet given requirements presents the problem of the blend formula for the coal charge and more often than not the answer lies in the utilization of experimental correlations between the properties of the constituents and the usual mechanical strength indices of the coke. As regards coal characterization we have to distinguish between identification tests in relation to origin and genesis and evaluation tests which are more directly linked to the use and the utilization capacity of the coal. Petrographic analysis belongs to the former of the two, although it is being used more and more for the purpose of monitoring consignments and for forecasting coke quality, as a complement to the conventional types of analysis aimed at determining plastic properties. In practical terms, the uniformity of the quality of the supplies is an important factor and we know that coking coals are very sensitive to atmospheric oxidation, which may occur during transportation or stocking. We cannot always be one hundred per cent certain that changes in plastic properties and chemical composition are a result of oxidation. We solved this problem by developing a simple, original test, applicable to the whole range of coals and which can be used in the control laboratories of coking plants.

Coke characteristics depend primordially on the nature of the coal being charged and the carbonization conditions. We also know that it is possible, regardless of the blend involved, to have an effect upon conventional mechanical strength indices by altering the coking parameters or changing the method of charging. However, the increasing interest of the blast furnace operators in the behaviour of the coke when hot, has given rise to new and numerous research projects in this field. As our contribution, we developed, in conjunction with the IRSID and with Community aid, a dual-purpose gasification test, aimed at determining the temperature in the reserve heat zone and assessing the coke’s mechanical strength on arrival in the blast-nozzle zone. The results obtained are interpreted in the light of the properties of the original coal feedstock and in terms of manufacturing factors.