The Influence of Sulfur on Dephosphorization Kinetics Between Bloated Metal Droplets and Slag Containing FeO
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TRODUCTION
DURING 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 reducible oxides. Several researchers have studied aspects of droplet behavior relevant to steelmaking including, decarburization,[1–6] droplet generation,[7–16] size distribution,[17,18] and residence time.[19] Other workers have developed models[20–23] and conducted plant trials,[24–28] which considered the role of droplets in the overall process kinetics. Previous work in the authors’ laboratory[6] showed that droplet swelling, caused by CO formation inside the droplet, increased the droplet residence time in the slag, thereby favoring decarburization. This work formed the basis of the Bloated Droplet Model, which has since been employed in an overall BOF model by workers at
KEZHUAN GU, NESLIHAN DOGAN, and KENNETH S. COLEY are with the McMaster Steel Research Centre, Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L7, Canada. Contact e-mails: [email protected], [email protected] Manuscript submitted November 2, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Swinburne University in Australia.[20,21] Notwithstanding very recent work, which suggests bubbles formed on the outer surface of droplets can offer similar increases in residence time, convincing experimental evidence for bloated droplets has been reported by several researchers.[5,6,29] Given the importance of droplet swelling in controlling residence time and the fact that dephosphorization is only favored when slag and metal are in contact, data on dephosphorization of bloated droplets are required for the proper inclusion of dephosphorization in BOF process models. Dephosphorization of hot metal has been studied extensively but for brevity only a subset of this work will be reviewed here. Research on phosphorus partitioning in the BOF has been reviewed by Basu et al.[30] More recently, phosphorus equilibrium between liquid iron and BOF type slag has been investigated by Assis et al.,[31] who further developed a corrected phosphorus partition correlation by combining other researchers’ work. Several studies have been conducted on the dephosphorization kinetics of iron–carbon melts using oxidizing slag.[32–35] Mori et al.[32] and Wei et al.[33] suggested that the rate of dephosphorization was under mixed control by mass transport in both slag and metal phase. Monaghan et al.[34] proposed that the rate determining step was mass transfer in the slag. Assuming mass transfer in both slag and metal was rate
controlling, Manning and Fruehan[35] showed that the mass transfer parameter (kA) decreased as the reaction proceeded and appeared to be a function of interfacial tension, which changed with respect to time. Employing IMPHOS pilot plant data, Hewage et al.[36] investigated the dephosphorization kinetics in the BOF and found that dephosphorization cannot be explained by a simple first-order equation with either
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