8th International Congress on Science and Technology of Ironmaking - ICSTI 2018

The present study was undertaken to find out whether or not there is an optimum distribution for nut coke and metallurgical coke over the ferrous layer and coke layer respectively. To this end a model for degradation of coke in the blast furnace was developed. It was verified with data from tuyere raking experiments. The tuyere raking result can be estimated based on degradation as a consequence of abrasion and direct reduction. Subsequently the model was used to analyze the optimum quantity and size for coke and nut coke. For operation at high PCI rates a large part of char is consumed in the direct reduction of FeO. Therefore, the higher the PCI rate, the lower the “consumable” nut coke rate. At a PCI level of 200 kg/tHM, the direct reduction consumes about 55 kg of coke. Since coke reacts on the surface of the particle, the direct reduction can be expressed as a diameter decrease, which corresponds with about 2 mm decrease of diameter. This means that all particles < 2 mm will be consumed by direct reduction. The model indicates that the voidage available for draining the liquid (“primary”) slag increases if more coke is put in the coke layer and less nut coke is used in the ferrous layer, which means, that at higher PCI rates the coke screen size has to be reduced. A strategy for setting the coke screen size is proposed.