Modeling of the vacuum oxygen decarburization refining process
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I. INTRODUCTION
THE vacuum oxygen decarburization (VOD) process can be used to produce stainless steel. Only scarce literature was found on the modeling of the VOD process. Takawa et al.[1] have developed a mathematical model based on statistical considerations that, however, does not allow a full description of the evolution of each element’s concentration in metal and slag. As the VOD process is a converter process operating under reduced total pressure, it is of interest to consider previously developed mathematical models for other steelmaking processes (e.g., AOD, LDAC convertor, etc.). We have found six types of dynamic models (Table I). For each type, numerous examples have been documented in the open literature, of which we have listed only a limited number. Type (1) models are still too complex for industrial use. They contain many parameters that are difficult to determine. Type (2) models disregard the thermodynamic and kinetic aspects of the reactions and therefore are less realistic. Type (3) models are the most widespread. Their main difficulty is the determination of mass-transfer coefficients and the reaction interfacial areas. Type (4) models consider that all oxidation reactions in the metal/gas reaction zone reach equilibrium. In actual production processes, it is difficult for all reactions to reach equilibrium synchronously in the metal/gas reaction zone. Type (5) models differ from type (3) and (4) models in that they assume an intermixed reaction zone as opposed to a reaction interface reaches an equilibrium condition. Type (6) models are statistical and empirical and thus not flexible. The model presented in this work is a dynamic model for an industrial VOD process. It is based on a thermodynamic and kinetic analysis of the reactions and should be sufficiently fast and accurate to be useful as a simulation tool in an R. DING, formerly Research Fellow, Department of Metallurgy and Materials Engineering, K.U. Leuven, is Research Assistant with the Department of Materials, Queen Mary and Westfield College, University of London, London E1 4NS. B. BLANPAIN, Postdoctoral Fellow (FWO-Flanders) and Part-Time Professor, P.T. JONES, Graduate Student, and P. WOLLANTS, Professor, are with the Department of Metallurgy and Materials Engineering, K.U. Leuven, B-3001 Heverlee, Belgium. Manuscript submitted January 21, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
industrial environment. For this reason, a novel and simple approach was developed to describe the metal/gas reactions. The model was evaluated through a series of simulations of the VOD process at the ALZ Company. Some suggestions for process improvement are made based on calculation results obtained with this model.
II. THE VOD PROCESS AS OPERATED AT ALZ The VOD process consists of three stages. Actual processing conditions are a function of the initial metal conditions and the steel grade. (1) Oxygen blowing. In the first stage, oxygen is blown to decarburize the metal. Alloys and fluxes are added in advance. The oxygen flow rate is betwe
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