The Use of Fundamental Process Models in Studying Ladle Refining Operations.

Abstract

Existing fundamental models of ladle refining operations have been reviewed. No fundamental model that takes all the individual parts of ladle refining into account has been found in the open literature. Nor does a model exist which considers all refining in only one part of a refining step such as vacuum treatment. However, separate fundamental models for prediction regarding alloying, temperature, hydrogen, sulfur, reoxidation, and inclusion growth and removal do exist. In one case, a reoxidation model has also been combined with a sulfur-refining model. Predicted values from the separate models for alloying, temperature, sulfur and hydrogen have been found to agree well with corresponding measured data. The verification of the models for reoxidation and the growth and removal of inclusions is currently lacking and separate models for refining operations such as nitrogen or carbon removal need to be developed. Also, more complex models of parts of ladle refining such as vacuum treatment need to be developed, incorporating the sulfur, hydrogen, reoxidation and inclusion growth and removal models. The ultimate goal is, of course, one overall model that can predict desired parameter values for all steps of ladle refining. Even though such a model does not exist today, the usefulness of existing fundamental models is exemplified. This is to illustrate the potential of more complex and more realistic ladle models in process optimization.KEY WORDS: secondary refining; ladle; modeling; fundamental; steel; slag and gas.tration gradient of the element exists at the interface between two phases. This can, for example, be in the steel phase, if the diffusion of the solutes to be removed or added in steel is the rate controling step. Furthermore, it is assumed that the phases on each side of the concentration boundary layer, the steel phase and the refining phase (gas for hydrogen removal and slag for sulfur removal), are steadily and completely mixed. Therefore, the removal rate of an impurity elements from steel can, for example, be described as follows: 5) ................. (1) where x is the element to be refined (i.e. S or H), k is the total mass-transfer coefficient, r is the steel density, M is the steel mass, and [%x] is the actual concentration of the element to be refined. The parameter [%x] e is the hypothetical concentration of the refined element in the steel phase in equilibrium with the actual concentration in the refining phase. "A" is the interfacial area between the steel and the phase to which the element is refined. In the cases of hydrogen refining and sulfur refining, this is the gas phase and slag phase, respectively.One disadvantage with this traditional approach is that due to the assumptions mentioned, more often than not the coefficients in Eq. (1) can only be valid for one specific case at a time. Therefore, this equation tends to be of limited usefulness in prediction for refining processes in general. For example, the interfacial area A, to be used in prediction of desulfurization during gas...

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