Development of a Reliable Kinetic Model for Ladle Refining
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THE aim of ladle metallurgical furnace (LMF) operations is to achieve the right steel composition and temperature, and to obtain the desired level of steel cleanliness. The compositions of steel, slag, and inclusions change during ladle refining due to reactions between steel, slag, inclusions, and refractory lining (affected by stirring of the steel bath), and additions to steel and slag. A kinetic model that can predict these changes will be helpful in optimizing ladle refining process. Such a model can also be used to develop a better understanding of the process itself. For example, a comparison of predicted and observed changes in steel chemistry and cleanliness would help in understanding transient reaction products. Figure 1 shows a schematic of all phenomena occurring in ladle refining and considered in the model used in the current study.
DEEPOO KUMAR and PETRUS CHRISTIAAN PISTORIUS are with the Center for Iron and Steelmaking Research, Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213. Contact e-mail: pistorius@ cmu.edu KEVIN C. AHLBORG is with ArcelorMittal Steel Cleveland, 3060 Eggers Avenue, Cleveland, OH 44105-1012. Manuscript submitted December 21, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
In the past, the focus has been the kinetics of steel–slag reactions to achieve the right level of dephosphorization[1] and desulfurization.[2–7] The recent focus has been to expand the kinetic models to include changes in inclusion composition and concentration. An underlying assumption is that reactions are under mass-transfer control, with local equilibrium at the reaction interfaces. Calculation of the local equilibrium can use thermodynamic data from literature or software like FactSageä with solution chemistry fitted to the available thermodynamic data.[5,8–10] An alternate approach is to link the kinetic model directly to FactSageä[11] using ChemApp[12–14] or the macro-processing feature of FactSageä[15] for thermodynamic calculations. As an example, Harada et al.[12] developed a kinetic model to predict compositions of steel, slag, and inclusions using a coupled reaction model proposed by Ohguchi et al.[16] In the coupled reaction model, mass-transfer-controlled reactions between two phases are modeled using equilibrium at the reaction interface. The amount of individual species transported to the interface was calculated using individual mass-transfer coefficients of species in that phase. Mass-transfer coefficients for steel–slag and slag–refractory reactions were experimentally determined.[1,17] The model also considered inclusions originating from slag, agglomeration of inclusions originating from slag with deoxidation inclusions and the flotation of inclusions to the slag. A sensitivity analysis was carried out to find appropriate parameters for inclusion agglomeration and flotation to
fit the model for a plant operation. Experiments were conducted with different stirring conditions to validate the model and further refine flotation behavio
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