Environmental Engineering Reference
In-Depth Information
1 Introduction
In the metallurgical industry the liquid steel is stirred to promote homogenization by
percolating argon gas through a single refractory stir plug arrangement in the bottom
of the ladle. For example, gas injection is used to enhance the speed of chemical reac-
tions, eliminate thermal and/or composition gradients, and remove inclusions among
other tasks (Bird et al. 1960 ). Submerged gas injection also plays an important role
in copper and aluminium refining processes. However, experimental observations of
the dynamics of liquid metal processing operations are very limited due to the high
temperatures, visual opacity, and large sizes of the processing units. Consequently,
most studies of the hydrodynamics of gas stirred ladles have been restricted to numer-
ical and experimental models of simple gas injection configurations, i.e., injection
of air into a cylindrical water vessel, where the vessel is some scaled model of an
industrial steel-making ladle.
The mathematical models describing fluid motion in gas-stirred ladle systems can
be classified into two main groups: (a) the quasi-single phase models based on the
continuum approach (Grevet et al. 1982 ; Sahai and Guthrie 1982 ; Woo et al. 1990 ;
Balaji and Mazumdar 1991 ; Sheng and Irons 1992 ; Goldschmit and Coppola Owen
2001 ; Taniguchi et al. 2002 ), where the combined gas-liquid fluid is treated as a
mixture and so the form of the mass and momentum conservation equations reduce
to those of a homogeneous fluid in terms of the mixture density and velocity, and
(b) the two-phase fluid models (Schwarz and Turner 1988 ; Xia et al. 1999 , 2002 ;
Ramírez-Argáez 2007 ; De Felice et al. 2012 ), where there is a separate solution field
for each phase and inter-phase transfer terms are employed to simulate the interaction
between the two phases. In essence, the two-fluid models are based on the concept of
unequal phase velocities. However, they will show a tendency to equalize because of
the inter-phase interaction forces. For instance, the main interaction between phases
is provided by the drag forces, which act in the direction opposite to the relative
motion. Other forces may also influence the flow as the lift force, the virtual mass
force, and the turbulent dispersion force. While most early two-fluid scaled models
of gas-stirred ladles are two-dimensional models with axial symmetry, full three-
dimensional (3-D) calculations have also started to appear (Pan et al. 1997 ; Zhang
2000 ; Aoki et al. 2004 ; Olsen and Cloete 2009 ; Cloete et al. 2009 ), with some of
them reporting model calculations of full-scale gas-stirred ladles (Aoki et al. 2004 ;
Cloete et al. 2009 ).
In this paper, we report further two-fluid model calculations of a gas-stirred
ladle in three-space dimensions to study the characteristics of fluid flow and the
influence of the wall on plume development. The numerical results are compared
with visualization experiments on water models in the literature to get an insight
into the plume behaviour and the mixing process. The physical model consists of
an off-centred, submerged air injection in water to simulate argon and molten steel
in a cylindrical vessel, corresponding to a 1:7 scale model of an industrial 35 tons
steel-making ladle. We solve the two-phase transport equations in Eulerian form
using the commercial code FLUENT 6.3 . Turbulent effects are accounted for using a
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