# Control of Slag Carryover from the BOF Vessel During Tapping: BOF Cold Model Studies

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## Abstract

In a modern integrated steel plant, slag-free tapping during transfer of liquid steel from the BOF vessel to the ladle is prerequisite to produce ultraclean steel for high-end critical applications. The present investigation aims to examine the drain vortices during the liquid steel tapping process. The tapping experiments were conducted in a geometrical down-scaled Perspex BOF cold model, which was more akin to the industrial practice than the other geometries previously reported in the literature. The study highlights the influence of the complex BOF shape on drain vortices during the tapping process. It is observed that vorticity behavior during liquid steel tapping from the BOF vessel is different from the earlier observations reported for the teeming process. The parametric study of the tapping process and its analysis confirmed that the threshold height for drain vortices is strongly influenced by the nozzle diameter (ND) and marginally influenced by the residual inertia of the liquid. The carryover ratio (COR) for the water-oil experiments is in agreement with the values obtained in industrial practice. Yield loss tends to increase with the increase in ND. The onset of drain vortices in the presence of overlying phase (oil/slag) during the BOF tapping process could be principally controlled by the vessel design. The physical properties of the overlying phase had negligible influence on the drain vortices. The critical times for vortex and drain sink formation were predicted based on dimensional analysis coupled with the mathematical formulation for the tapping process. A strategy to control the slag carryover during the tapping process in industry is also discussed and postulated based on the understanding developed from water modeling experiments.

## Nomenclature

*H*_{i}(LH)Initial liquid height (m)

*d*(ND)Nozzle/tap hole diameter (m)

*Q*(FR)Initial water filling flow rate (lpm/kg s

^{−1})*t*(DT)Dwell/waiting time (s)

- COR
Carryover ratio (—)

*H*_{v}Critical LH for vortex formation (m)

*H*_{d}Critical LH for drain sink formation (m)

*w*_{m}Weight of water/liquid steel tapped during tapping (kg)

*W*_{s}Weight of oil/slag carried over during tapping (kg)

*D*Distance from rear end of LD vessel to the tap hole (m)

*V*Initial water filling velocity (m s

^{−1})*H*Instantaneous LH in LD vessel during tapping (m)

*g*Acceleration due to gravity (m

^{2}s^{−1})*ρ*Density (kg m

^{−3})*μ*Dynamic viscosity (kg m

^{−1}s^{−1})*σ*Surface tension (N m

^{−1})*γ*Kinematic viscosity (m

^{2}s^{−1})*σ*_{s–m}Interfacial tension of liquid steel and slag (N m

^{−1})*C*_{d}Discharge coefficient (—)

*a*_{o}Cross-sectional area of tap hole/nozzle (m

^{2})- Fr
Froude number (—)

- Re
Reynolds number (—)

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