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|Title:||DEPHOSPHORIZATION KINETICS FOR REACTION OF BLOATED METAL DROPLETS WITH OXIDIZING SLAG|
|Department:||Materials Science and Engineering|
|Abstract:||Dephosphorization is one of the most important refining reactions in Steelmaking in the Basic Oxygen Furace (BOF). Dephosphorization can only occur by reaction between the metal and the slag and is linked in a rather complex way to the decarburization of droplets in the gas-slag-metal emulsion zone. Decarburization affects dephosphorization of metal droplets by influencing the following: residence time, driving force and mass transfer of phosphorus. Residence time is the contact time of metal droplets with slag, which is determined based on the bloating behavior of metal droplets. This particular aspect of dephosphorization has been studied recently by researchers in the author’s laboratory and others. Therefore, the influence of decarburization on driving force for dephosphorization and mass transfer of phosphorus in the metal phase was the main focus of this study. The effect of decarburization on driving force for dephosphorization was studied in detail by varying decarburization rates which are a function of metal sulfur content, and determining the dynamic interfacial oxygen potential. The dephosphorization driving force was found to have a strong inverse relationship with increasing decarburization rate because the associated oxygen consumption decreases the interfacial oxygen potential. The decreased driving force further affected dephosphorization kinetics by shifting the rate controlling step, to include a greater influence of mass transport in the slag. This observation showed a good agreement with other work on dephosphorization kinetics in the published literature. The dynamic interfacial oxygen potential, controls dephosphorization driving force, between an iron carbon alloy and oxidizing slag was calculated based on a mathematical model, which combines measured decarburization rates with mass transfer of FeO in the slag. With this model, the mass transfer coefficient of “FeO” in slag, k_FeO, was firstly determined as a function of the fraction of liquid slag and total iron oxide in the slag. The influence of dynamic interfacial oxygen potential on dephosphorization kinetics was sequentially analyzed by determining the time dependent interfacial phosphorus partition ratio. The agreement with literature observations confirmed the reliability of the interfacial oxygen potential model developed in this study. Comparing the experimentally observed dephosphorization behaviour of carbon containing droplets with that of carbon free droplets, mass transfer coefficient for phosphorus in the metal for carbon containing droplets was found to be two orders of magnitude higher than that for carbon free droplets because of the stirring effect provided by CO gas generation inside the metal droplet. By combining a theoretical analysis of CO bubble nucleation kinetics with surface renewal theory, the predicted mass transfer coefficient of phosphorus in the metal phase was in good agreement with experimentally measured results. Extension of this analysis to results from a number of published studies on dephosphorization, showed an excellent qualitative agreement with experimental observations, i.e., the effect of silicon in the metal and the effect of iron oxide in the slag. The combined effect of silicon and temperature also showed agreement but the effect of temperature for silicon free metal was not fully explained.|
|Appears in Collections:||Open Access Dissertations and Theses|
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