Ladle and Continuous Casting Process Models for Reduction of SiO 2 in SiO 2 -Al 2 O 3 -CaO Slags by Al in Fe-Al(-Si) Mel
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TION
IN the previous article by the authors, a mixed control or two-phase mass transfer control model considering mass transport in both metal and slag phases was developed to describe kinetics of the reduction of SiO2 in SiO2-Al2O3-CaO slag by Al in Fe-Al melts. The validity of the model was assessed by comparing predicted compositional changes with laboratory experiments. The metalonly control model, which is a sub-model of the mixed control model considering the mass transport only in the metal phase, was not valid at the high Al contents.[2,3] The mixed control model predicts that the rate of reaction in terms of the normalized rate decreases with the initial Al content in the metal because the mass transport in the slag phase adds an additional resistance to the overall rate. The model was validated through the experiments of the reaction between Fe-melts containing 0.057 to 0.45 wt pct Al and 5.31 wt pct SiO2-46.67 wt pct Al2O3-34.44 wt pct CaO-13.58 wt pct MgO slag at 1873 K (1600 C); the results confirmed that the rate of reaction follows the mixed control model at the low SiO2 content in the slag, and consideration of the mass transport in the slag phase is critical in the kinetic model which is valid in wide range of the Al contents. In this paper, process models for ladle and continuous caster are developed using the mixed control model to predict composition changes due to the reduction of SiO2 by Al as [1]
JIWON PARK, Staff Member, is with the Department of Materials Science and Engineering, Center for Iron and Steelmaking Research, Carnegie Mellon University 5000 Forbes Avenue, Pittsburgh PA 15213, and also with the Korea Institute of Materials Science, Changwon, Korea. RICHARD J. FRUEHAN, U.S. Steel Professor, is with the Department of Materials Science and Engineering, Center for Iron and Steelmaking Research, Carnegie Mellon University. Contact e-mails: [email protected], [email protected] S. SRIDHAR, Professor, TATA Steel and Royal Academy of Engineering Joint Chair for Research into Low C Materials Technologyis with the International Digital Laboratory, WMG, The University of Warwick, Coventry CV4 7AL U.K. Manuscript submitted July 25, 2014. Article published online October 9, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
in Reaction [1]. The temperature in all cases is 1873 K (1600 C), unless otherwise noted. 8 unknowns—bulk and interface concentrations of 4 involving components—are considered as time-dependent variables and solved from the flux equations, mass-balance equations, and local equilibrium condition. 4Al þ 3ðSiO2 Þ ¼ 2ðAl2 O3 Þ þ 3Si
II.
½1
LADLE PROCESS MODEL
In a ladle process, the reaction conditions in ladle are similar to the kinetic experimental conditions conducted in the previous article.[1] The expected composition changes of the metal and the slag would be close to the results in the mixed control model, but the mass ratio of slag to metal is less than the previous kinetic experimental condition. The modified mass transfer coefficient, m¢=mA, will vary with the gas
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