Investigation of Freeze-Linings in a Nonferrous Industrial Slag
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FREEZE-LININGS are increasingly used in hightemperature pyrometallurgical smelting reactors to ensure furnace integrity that is maintained in chemically aggressive and vigorously agitated bath environments. In earlier studies, air or water-cooled probes have been used to deliberately form freeze-linings on the cold surface of the probe.[1–14] Freeze-lining formation has mainly been investigated from the point of view of the heat transfer so as to predict the deposit thickness as function of process time and also at steady-state conditions. In heat transfer modeling of the freezelining, it has been widely assumed that the bath/deposit interface temperature is equal to the liquidus of the bulk bath at steady-state conditions[12,13,15–21] and that the reactors cannot be operated below this temperature. There is increasing evidence to show, however, that the interface temperature of the freeze-lining and bath is below the liquidus temperature of the bulk bath. Guevara and Irons[22] have used a low temperature physical model to create a freeze-lining under controlled laboratory conditions. At steady-state conditions particles of the primary phase (300 to 500 lm in diameter) ATA FALLAH-MEHRJARDI, Postdoctoral Research Fellow, PETER C. HAYES, Xstrata Professor, and EVGUENI JAK, Professor in Pyrometallurgy, are with the PYROSEARCH, School of Chemical Engineering, The University of Queensland, St Lucia, QLD 4072, Australia. Contact e-mail: [email protected] STEPHANIE VERVYNCKT, Project Leader Recycling & Extraction Technology, is with the Umicore, Olen, Belgium. Manuscript submitted June 18, 2013. Article published online April 23, 2014. 850—VOLUME 45B, JUNE 2014
were observed to circulate between the stable deposit and the superheated bulk liquid. The temperature measurements across the section show that for the set of process conditions studied, the temperature at the interface is that of the solidus for this system, not the liquidus. Subsequently, solidus temperature was used as the interface temperature in the heat transfer modeling of the freeze-lining.[23] A recent study by authors[1,2] investigated the effects of chemistry-related parameters, phase equilibria, and bath movement on the interface temperature between the freeze-lining and bath at steady-state conditions for a silicate-based slags. The experimental results clearly indicated that the interface temperature is lower than the liquidus temperature of the bulk bath at steady-state conditions. A conceptual framework was proposed to explain the effects of chemistry and shear intensity of the bath on the interface temperature and deposit thickness at steady-state conditions.[2] The framework assumed that nucleation of solids can occur in a subliquidus region ahead of the actual deposit interface, and deposit thickness at steady state is determined by the balance between the net addition and removal of material from the steady-state-deposit interface. If this is the case, then this provides opportunities to operate the smelters at temperatures below the
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