A Mathematical Model for Reactions During Top-Blowing in the AOD Process: Derivation of the Model
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INTRODUCTION
THE argon–oxygen decarburization (AOD) process is the most common process for the refining of stainless steel.[1] Owing to violent agitation caused by the high blowing rates, the AOD vessel has very good mixing characteristics.[2–5] Nowadays, top-blowing is employed in conjunction with side-blowing in the early part of the decarburization stage in order to maximize oxygen delivery into the melt.[6] As illustrated in Figure 1, two main reaction areas can be identified during combined blowing: (1) inside the gas plume, and (2) on the surface of the bath, including metal droplets.[7,8] Numerous reaction models have been proposed for the decarburization[8–37] and nitrification[7,38–40] of steel in an AOD vessel. The majority of the models applicable for side-blowing decarburization have been reviewed elsewhere.[21,41] Despite the vast number of reaction models available, there are only a few models that explicitly address the reactions during top-blowing in the AOD process. Arguably the most relevant examples found in the literature are those proposed by Watanabe and Tohge,[9] Tohge et al.,[17] Kikuchi et al.,[23,42] and Wei et al.[8,21,22,26,28] Some similarities in the modeling setting can be found in the reaction models proposed for the VOD process.[41,43] To summarize, it can be stated that the top-blowing models proposed so far are capable of predicting the decarburization with a reasonable
VILLE-VALTTERI VISURI, AKI KA¨RNA¨, PETRI SULASALMI, EETU-PEKKA HEIKKINEN, and TIMO FABRITIUS are with the Process Metallurgy Research Unit, University of Oulu, PO Box 4300, 90014 University of Oulu, Finland. Contact e-mail: ville-valtteri.visuri@oulu.fi MIKA JA¨RVINEN is with the Department of Mechanical Engineering, Aalto University, PO Box 14440, 00076 Aalto, Finland. PENTTI KUPARI is with the Outokumpu Stainless Oy, 95490 Torne, Finland. Manuscript submitted June 11, 2015. Article published online March 27, 2017. 1850—VOLUME 48B, JUNE 2017
degree of accuracy and have laid the basic foundations for further investigations. However, more research is required along these lines in order to obtain information on the related reaction interfaces and chemical reaction rate phenomena. In our previous work,[29,30] a fundamental model was proposed and validated for the reactions inside the bath during side-blowing in the AOD process. Consequently, the aim of this work was to extend the original model by developing a mathematical model for reactions during top-blowing. In order to provide more information on the controlling mechanisms and dynamics of decarburization during top-blowing, the model combines the transient solution of multicomponent equilibria with a description of the constraining mass transfer. This paper presents the description of the model, while validation and preliminary results are presented in the second part of this work.[44]
II.
DERIVATION OF THE MODEL
The model was programmed using C++, and the main assumptions can be summarized as follows: 1. The top-blown oxygen may react with iron and the species
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