Coke Degradation under Simulated Blast Furnace Conditions

Three metallurgical cokes made from coking coals over a significant range in rank were subjected to treatment with blast furnace-like gas composition-temperature profile to 1 673 K, annealing under N-2 to 2 273 K and gasification with subsequent annealing at 1 873 and 2 273 K. The degradation of cokes after reaction and annealing was characterised using I-drum tumbling, tensile testing, ultra-micro indentation and X-ray diffraction. Both gasification and annealing decreased the mechanical strength of coke. Compared with annealing at 1 673 K, gasification at same temperature caused larger degradation for all three cokes, and the effect was more significant on more reactive coke. In the annealing process, degradation of the cokes occurred through the entire coke lump and resulted in both tensile strength and I-drum tumbling strength decreasing simultaneously. In the process of gasification under the blast furnace-like conditions, degradation took place through the whole piece of coke with high reactivity; however, the degradation of coke with low reactivity was more severe at the periphery than in the core and therefore gasification had a minimal effect on the core of the coke and its tensile strength, but had a much stronger effect on I-600. Microstrength of coke decreased significantly with increasing annealing temperature. The change of microstrength of coke upon gasification, which occurred at relatively low temperatures, was marginal. The cokes after gasification with subsequent annealing had similar microstrength and graphitisation degree compared to those subjected only to annealing at the same temperature.