A 2D Axisymmetric Mixture Multiphase Model for Bottom Stirring in a BOF Converter
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THE primary goal in basic oxygen furnace is to remove carbon from a high-carbon iron melt to produce low-carbon steel melt. This is achieved by blowing oxygen into the iron melt. As the majority of oxygen converters is using top-blowing through a lance, mixing in the liquid iron bath remains very poor. Therefore, argon (or nitrogen) gas injection through porous plugs in the furnace bottom is commonly used. The plugs are in many cases set in a way to produce overall axisymmetric flow phenomena in the melt. Bottom gas stirring of the iron melt in the BOF converter is important for advancing the oxidation reactions and also for achieving homogeneity for composition and temperature. Recycled steel (scrap) is charged into the converter in solid form. The scrap melts and mixes with iron melt during the process. The flow and the mixing of the melt are usually taken into account in process models by empirical formulas for mass transfer with a mixing tank or flow sheet approach. Commonly process models are made to be quick simulation tools that can estimate the evolution of the process. In many cases, computational fluid dynamics (CFD) is seen as computationally too costly and cumbersome to be applied to the process models due to complicated physics. However, inclusion of CFD to process model would be a significant improvement over the existing ones.
ARI KRUSKOPF is with the Department of Materials Science and Engineering, Aalto University, P. O. Box 16200, Vuorimiehentie 2, Espoo, 00076 Aalto, Finland. Contact e-mail: ari.kruskopf@aalto.fi Manuscript submitted May 24, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
A. Literature Review of Modeling of Bottom Gas Stirring Many publications have been done over the years on the CFD of gas-stirred systems. According to review article of Mazumdar and Guthrie,[1] mathematical modeling of vertical bubbling gas jet can be divided into three categories: (1) quasi-single-phase formulation, (2) Lagrangian-Eulerian two-phase approach, and (3) Eulerian two-phase models. The review article of Jacobsen et al.[2] considers only the second and third groups. In the quasi-single-phase category, conservation equations for continuity and momentum are solved only for gas/liquid mixture. The gas phase distribution is assumed according to some empirical formula suitable for the problem in question. This means that the method cannot be directly applied to general two-phase flow problems. Still quasi-single-phase formulation has been a fairly popular approach in the literature.[3–14] In the second group, bubble trajectories originating from the nozzle are calculated in a Lagrangian reference frame and continuity and momentum equations for the liquid phase are solved in an Eulerian frame.[15–20] The bubble distribution data affect the liquid flow field and vice versa. In the third group, mass and momentum conservation are solved for both phases in an Eulerian reference frame.[21–35] The first approach is the least accurate description of the twophase flow. Jacobsen et al.[2] note that while the second and
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