Abstract

In the final 20% of the oxygen blow in a BOF, bath stirring decreases due to the drop in CO evolution. To help sustain slag-metal mixing and enhance thermal and chemical homogeneity in the melt, the bath is agitated by injecting inert gas through stirring elements in the vessel bottom – the Bath Agitation Process (BAP). Element designs include tuyeres and various configurations of single- and multi-hole plug, all of which promote localized wear which in many cases will limit the service life of the lining. Wear arises from a combination of thermo-mechanical stresses associated with, for example, the operational vessel thermal cycle, local cooling by the injected gas, and molten bath circulation induced by the injected gas stream, often compounded by accretion growth, localized lining erosion and metal penetration. A comprehensive post mortem study of used BAP injection plugs shows in addition that steel bath wetting effects in current element designs may be a significant factor in the wear process. A new injection element design is proposed in an attempt to reduce the magnitude of these effects and thereby extend vessel lining life. The design is based on slotted gas channel geometry with materials selection optimized for the specific task. A prototype was tested by water modelling to establish its gas injection behaviour. The results and analysis of these tests are discussed, with indications for future work including in-plant trials.