Hydrodynamic modeling of some gas injection procedures in ladle metallurgy operations
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I.
INTRODUCTION
THEchemical efficiencies of typical processing operations carried out in steelmaking ladles are intrinsmally related to their hydrodynamic performance. Practically all ladle techniques presently used have one thing in common: most in one way or another employ gas, injected through a submerged lance, plug, or nozzle, to stir the contents of the ladle. The gas, rising through the liquid steel, effects mixing, promotes chemical reactions, minimizes temperature and composition inhomogenemes and, through the generation of turbulence, may aid inclusmn agglomeration and float-out. Typical examples include the desulfurization of iron or steel, the modification of inclusion morphology and composition by the injection of powders or pellets, the decarburization of steel by argon in combination blowing practices, and so forth. To date many investigations ~ 4 have been carried out to identify the hydrodynamic phenomena at work during ladle refining by gas injection. The recirculatorv flow fields, as well as the turbulence energy fields, can now be predicted with reasonable degrees of certainty. in industrial injection processes, such as the external desulfurization of molten iron by powdered calcium carbide, powder, in dense phase, is pneumatically transported and injected into the liquid metal through a submerged lance. The carrier gas while rising as a plume to the free surface induces recirculatory flow's of fluid within the vessel, thereby helping to promote metal homogeneity. The way in which the injected gases and powders interact is important in determining the movement of such particles within the melt and the intrinsic efficiencies of a given procedure. This paper presents a theoretical and experimental study of a 150 ton teeming ladle, in which a 0.30 scale water model was used to explore flow patterns generated by partially and fully submerged gas rejection lances.
cy'lindrical ladle, This allowed significant simplification to be made in arriving at .solutions, since the flow, be it turbulent or laminar, becomes two-dimensional, in terms of the cylindrical polar coordinate system chosen. In the present work. the elliptic turbulent flow computer model developed by Gosman et al. 5 was adapted and extended. For the case of turbulence, the two equation steady state turbulent tlo~ mode/ proposed by Launder and Spalding" {z.e., the k-/~ two equation model of turbulence) was used, together with an alternate algebraic model developed at McGill University for submerged gas Injection systems.
A. The Flow Equations For the situation of axisymmetric gas injection, the flow variables considered were assumed to obey axial symmetry li.e., there is no variation of flow properties in the 0 direction). Then in cyhndrical polar coordinates, the governing differential equations max' be represented as. Equation of continuity', Ou --+ O-
1 /~(rv)
r
-0
hr
Ill
Equation of motion in axial direction,
i)
1 6)
7(Dltl)_
4-
--1. 7iF ( p F l t V )
--
i~p o: 1
-4- - - -
i) [ O [.
Ou ~ itu~
r r ~'#""/~7"] + S,,
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