Mixing models for slag covered, argon stirred ladles

Abstract

Ninety-five percent bulk mixing times were determined experimentally in water models (D=0.30 m and D=0.60m respectively) of a 140T industrial ladle fitted with dual 'plugs' (located diametrically opposite at mid bath radius position) in the presence of an overlying, second phase liquid. Experiments were conducted to investigate the influences of gas flow rate, liquid depth, thickness of the upper phase liquid together with the latter's physical properties on mixing time. Within the range of variables studied, it is observed that besides gas flow rate, liquid depth and vessel radius, thickness of the upper phase liquid has the most significant bearing on mixing times. In contrast, considerably less pronounced effect of density and viscosity on mixing was noted. Dimensional analysis and regression of the experimental data show that 95% bulk mixing times in slag covered, dual plug fitted ladles can be described, in terms of relevant dimensionless groups, via: (τ mix,95%Q/R3) = 196 (Q2/gR5) -0.33 (L/R)-1.0 (ΔL/R)0.3 (Δρ/ρL)-0.044 (vs2/gR3)0.016 in which, Q is the gas flow rate, L is the depth of liquid, R is the vessel radius, ΔL is the thickness of the overlying liquid, ρL is the density of the bulk liquid and vs is the kinematic viscosity of the upper or slag phase. Mixing correlations applicable to slag covered, dual plug fitted ladle and its slag free counterpart were found to bear striking similarity. This, as a possibility, suggests that embodying an additional factor, (≈6(ΔL/L) 0.3vs0.033(Δρ/ρL) -0.044) into a mixing correlation applicable to a slag free, gas stirred ladle, a correlation for an equivalent slag covered system can be derived. The hypothesis has been tested against axi-symmetrical gas stirred ladle system and towards this, relevant experimental measurements, mixing correlations ere. reported on such systems were applied. These suggest that 95% bulk mixing time in slag covered, axisymmetrical ladles can indeed be predicted reasonably well embodying the aforementioned addition factor into an existing correlation applicable to an equivalent slag free system. © 2010 ISIJ.