Effect of Bottom Stirring Gas on Kinetics of Nitrogen Removal in Oxygen Steelmaking Process

The current BF–BOF practice is well suited to produce grades with varying nitrogen levels; however, it is still possible to optimize BOF bottom stirring schemes. In contrast, nitrogen control is a less understood topic in the future green steelmaking routes. Hence, it is important to identify the process parameters that control nitrogen behavior in both the current and future steelmaking routes. The present study focuses on understanding nitrogen kinetics in liquid steel through a combination of full‐scale plant trials and dynamic model simulations. A set of dedicated trials were performed with extra intermediate sampling to understand the dynamic variation of nitrogen during the converter steelmaking process. From the trial results, four major stages and the dominant rate control factors in these stages were identified. A dynamic nitrogen control model for a BOF was developed and the transient trial data points were used to validate and tune the model. The model predictions and plant trials show that in the current converter practice, switching the bottom blowing gas from N 2 to Ar in the first 50% of the blow has limited influence on final [ N ] in steel. By using the [ N ] prediction model, the effect of a future scenario—with low [ C ] concentration in the hot metal—on nitrogen refining was simulated. With a 3% [ C ] hot metal, the [ N ] in final steel was predicted to be ≈35 ppm which is about 15 ppm higher than the current operations with 4.5% [ C ] hot metal, typically obtained from BFs. Based on the current findings, bottom blowing practices in BOFs are modified to reduce their argon consumption.