The Fluid Mechanics of Slag-Metal Interactions in Ladle Metallurgy

In Ladle Metallurgy operations following steelmaking, the control of the interactions between slag and metal is crucial for the production of high-quality steel. While the chemical aspects of the refining have been well studied, the fluid dynamic aspects have received less attention. Ladles are often gas-stirred by porous plugs pushing the slag to the periphery of the ladle and opening “eyes” of steel exposed to the atmosphere. The nominal slag-metal contact area is reduced, but there may be entrainment of slag in metal and vice versa which increases the effective interfacial area. Experiments were conducted with water models and the work of others in metallic systems has been included in the study. The eye size has been found to be quite different for thin and thick slag layers, and mathematical models of the controlling factors for the eye size has been determined for these two regimes. The models show that the important factor is the balance between the inertia from the gas-liquid plume and the height of the slag, so the governing equations are based on Froude number control. The conditions for closure of the eye have been identified and mathematically modeled. At higher gas flow rate, droplets of slag are entrained into metal which is quantitatively linked to Kelvin-Helmholtz instability. The role that physical properties of the slag play in these phenomena is discussed.