Numerical Investigation of Desulfurization Kinetics in Gas-Stirred Ladles by a Quick Modeling Analysis Approach
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sulfurization efficiency has become one of the main objectives in ladle refining process because of the increasing demand for low-sulfur steel. The desulfurization efficiency in the ladle metallurgical furnace (LMF) can be affected by many factors,[1–3] such as the compositions of the molten steel and slag, slag layer thickness, gas-stirring rate, the interaction behavior of the slag-steel phases, slag viscosity, slag optical basicity, liquid steel temperature, etc. It is desired to develop a mathematical model that can effectively predict the
QING CAO and LAURENTIU NASTAC are with the Department of Metallurgical and Materials Engineering, The University of Alabama, Box 870202, Tuscaloosa, AL, 35487. Contact e-mail: [email protected] APRIL PITTS-BAGGETT and QIULIN YU are with Nucor Steel Tuscaloosa, Inc., Tuscaloosa, AL, 35404. Manuscript submitted August 21, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
sulfur refining evolution in the LMF to assist in the optimization/performance improvement of the industrial process control. There are two important factors that affect the accuracy of the desulfurization simulation: (1) the computation of the interfacial thermodynamic equilibrium, and (2) the kinetic mass transfer coefficients. A lot of mathematical models were developed to predict sulfur removal during the ladle refining process.[4–7] Basically, these models can be separated into two types: (1) Computational fluid dynamics (CFD)-simultaneous thermodynamic reaction (STR) coupled model. In this modeling approach, the simultaneous reaction rates of multi-components at the slag-metal interface are computed by the simultaneous reaction model, and then they are added into the source terms of the CFD model to compute the mass transport and distribution of each species in the melt, which makes this model more accurate.[7–10] However, the main limitation of this CFD-STR coupled model is that it
requires highly specialized software, long computational time, and a big number of microprocessors. (2) The other approach is based on the experimental estimation of the mass transfer rate. The slag-metal reactions are described via the mass transfer of each species from the bulk steel and slag phases to the slag-steel interface. The computational time is in the order of seconds and the prediction can be easily performed, for example, in Microsoft Excel. In this approach, the interfacial area is usually calculated as the area of the static slag-steel interface. The mass transfer rate or kinetic constant can be obtained by employing the empirical correlation with the specific stirring energy e, which can be determined experimentally.[11] There are various empirical correlations to compute e based on the experimentally measured data under gas-stirring conditions.[4,6,12] Table I lists some empirical correlations to obtain the e and the kinetic constant. However, the accuracy of these correlations is affected by the amount and position of the porous plugs at the bottom of the ladle, slag/ steel weight, ladle dimensions, etc. These correlatio
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