Modeling Study of Nitrogen Removal from the Vacuum Tank Degasser

Low nitrogen content in liquid steel is required for most of the steelmaking companies, where vacuum degassing of liquid steel is usually carried out to remove nitrogen as well as other impurity elements during ladle treatment. This paper presents an integrated computational fluid dynamics (CFD) model for simulating the nitrogen removal in an industrial vacuum tank degasser (VTD). In the CFD model, oxygen and sulfur are considered as surface-active elements decreasing the denitrogenation rate at the gas–steel interface. An activity coefficient and a desulfurization sub-model are implemented to compute the effective activity coefficients of the related elements and the evolution of sulfur content in liquid steel during the process, respectively. The effect of various elements on denitrogenation rate in the VTD is studied with the developed model. For the used steel compositions the denitrogenation rate decreases with an increase in the content of [S], [O], [Cr], [Nb], [V], [Ti], or [Mn], whereas it increases with an increase in the content of [C], [Si], [P], [Ni], or [Al]. The model is validated by comparing final nitrogen contents measured from the industrial plant with the ones predicted by the model and good agreements were found. The model has proven to be a useful and accurate tool for predicting final nitrogen content of liquid steel in the plant.