Numerical study of dephosphorisation kinetics for different bottom tuyere configuration for combined blowing converters with a single-flow post-combustion oxygen lance

In combined blown converter steelmaking, bottom stirring plays an important role in bath mixing. Better mixing in the bath improves the stirring capacity of the bath and the mass transfer between the slag and metal, which leads to a near-equilibrium steel–slag reaction and improves the dephosphorisation efficiency. Numerical simulations were employed to explore the impact of the bottom-blow configuration, comprising the bottom-blowing flow rate, bottom-blowing distribution diameter, and the ST (star type) configuration distribution on the flow dynamics, mixing characteristics, and dephosphorisation efficiency within the molten pool of a full-scale 250 t converter model. The findings indicated that as the flow rate increased, the mixing time was reduced, and the dephosphorisation efficiency was enhanced. At the same time, three PCDs (pitch circle diameters) were discussed, and it was concluded that, when the PCD of the 12 bottom tuyeres was reduced from 0.63 to 0.43, the mixing time was shortened by 21 s, and the dephosphorisation rate was increased by 19%. In addition, a new type of ST configuration tuyere distribution (12 bottom tuyeres staggered on a circumference with PCDs of 0.43 and 0.63, respectively) was proposed. Compared to the uniform scheme, the STA (angle of adjacent bottom tuyeres 15°) and STB (angle of adjacent bottom tuyeres 30°) mixing times were reduced by 7% and 16%, respectively. Among them, the dephosphorisation rates of the uniform, STA, and STB scheme were 69%, 74%, and 82%, respectively.