The effect of bottom nozzle configuration on the bath behaviour in the BOF

The blowing behaviour of the BOF is affected in many ways by the behaviour of molten bath. Bottom blowing and its interaction with top blowing have a strong influence on splashing and spitting behaviour, bath homogenisation and bath oscillation. Therefore, three selected bottom nozzle configurations were studied by physical modelling, and the results were compared regarding splashing, homogenisation and oscillation of the bath. According to model tests, bottom nozzle positioning has a great influence on the amount and direction of splashing and spitting. Moreover, at lower lance gaps, the direction of splashes was changed because of bath oscillation. At low lance gap, when type A oscillation is dominant, correlation between the degree of overlap and stability of the bath was found. The bigger the degree of overlap, the more unstable the system as far as type A oscillation and splashing is concerned. The amplitude and oscillation frequency of the bath changed as a function of lance height. Blowing through bottom nozzles prevented the onset of so called type A oscillation. Bottom nozzle configuration of three nozzles resulted in shortest mixing time, lowest total splashing on model walls and longest starting time of type A oscillation.