Dephosphorization Kinetics between Bloated Metal Droplets and Slag Containing FeO: The Influence of CO Bubbles on the Ma
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UCTION
IN basic oxygen steelmaking, metal droplets created by the impact of the oxygen jet are ejected into the slag, where they are decarburized and dephosphorized by reaction with iron oxide. Those droplets which swell because of internal nucleation of CO bubbles are termed bloated droplets. The behavior of bloated droplets in terms of decarburization has been studied extensively,[1–7] although several of these studies predate the coining of the term ‘‘bloated droplet’’ which was first used by researchers in the authors’ laboratory.[8] Models for predicting residence time in the emulsion zone of the BOF based on droplet bloating behavior have also been developed.[8,9] Workers at Swinburne University in Australia[10,11] have developed an overall BOF model considering the behavior of bloated droplets. The development of the bloated droplet concept and its influence on BOF modeling has recently been reviewed
KEZHUAN GU, NESLIHAN DOGAN, and KENNETH S. COLEY are with the Department of Materials Science and Engineering, McMaster Steel Research Centre, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L7, Canada. Contact e-mails: [email protected]; [email protected] Manuscript submitted January 26, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
in detail by Brooks et al.[12] All of these studies were focused on decarburization kinetics and the causes of droplet swelling. There are very few studies on bloated droplet refining kinetics related to elements other than carbon. One example of this is dephosphorization, which occurs in competition with decarburization in the emulsion zone of the BOF. Based on pilot plant data, Hewage et al.[13] attempted to model dephosphorization in the emulsion zone, however, these workers found that dephosphorization could not be explained by a simple first order equation with either static equilibrium or dynamic equilibrium values, due to the transient behavior of rate parameters such as instantaneous area, residence time, and mass transfer coefficient. It is well established that dephosphorization is controlled by mass transfer in the metal, slag or both simultaneously. Therefore, it should be possible to describe the reaction using a rate equation that is first order with respect to phosphorus concentration in the metal. The terms dynamic and static used by Hewage et al.[13] refer to the equilibrium partition of phosphorus which exists at the slag metal interface. It is common practice in kinetic studies to assume that this value is constant; static equilibrium. This approach is often adequate, however, the oxygen potential at the interface will change with time, because of changes in the balance between oxygen supply and consumption; dynamic oxygen potential. Although equilibrium with respect to phosphorus is
maintained at the slag metal interface, this equilibrium is set by the oxygen potential which changes with time, leading to a changing or dynamic equilibrium with respect to phosphorus. The concepts of dynamic oxygen potential and dynamic equilibrium with respect to pho
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