The Importance of Slag Engineering in Freeze-Lining Applications
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FREEZE linings are extensively used to protect refractory walls from corrosion. A major advantage of the freeze-lining concept is that the freeze lining consists of solidified process material and, therefore, is selfregenerating and can resist aggressive process materials. To apply the freeze-lining concept in a reactor, its formation and its stability have to be assured. As a result, it is important to control the freeze-lining behavior. In previous research, the freeze-lining behavior was often studied in modeling work[1–3] or in experimental observations of the freeze-lining microstructure[4,5] while considering the composition of the process material as fixed. However, for the zinc fuming process, Verscheure et al. showed that a proper selection of bath composition and the corresponding liquidus temperature minimize the heat loss and improve the process output.[6,7] For slag splashing,[8] it was indicated that the freezelining behavior can be improved by adjusting the slag composition and splashing temperature to obtain a MIEKE CAMPFORTS, formerly Research Assistant, Materials Science Department, Katholieke Universiteit Leuven, is Project Leader, Umicore Research, 2250 Olen, Belgium. Contact e-mail: mieke. [email protected] BART BLANPAIN and PATRICK WOLLANTS, Professors, are with the Centre for High Temperature Processes, Metallurgy and Refractory Materials, Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, 3001 Leuven, Belgium. Manuscript submitted February 13, 2009. Article published online July 22, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
proper ratio between high-melting and low-melting phases. The high-melting phases protect the refractory from corrosion, while the low-melting phases attach the high-melting phases to the refractory. Also, in the studies of the microstructure evolution of an industrial nonferrous slag[9,10] and a synthetic lead slag,[11,12] slag properties such as the temperature stability range of a phase, the type of phase dominating the freeze-lining microstructure (forming a closed structure or not, interlocking or not), the crystallization behavior, and the mass transfer are suggested to affect the freeze-lining formation. Thus, when optimizing the freeze-lining behavior, changes in process parameters, such as the composition of the process material and the process temperature, also have to be considered. Thus, the process material can be adapted to optimize both the freeze-lining formation and the process output. In the present article, the authors explore the freezelining formation of six different slags to illustrate the importance of slag engineering for a freeze lining in continuous contact with the slag bath. Furthermore, microstructural characteristics of a protective freeze lining are indicated and the freeze-lining formation of the six slags is evaluated accordingly.
II.
EXPERIMENTAL
A. Cooled-Probe Technique In previous experiments, a water-cooled probe technique was used, as is described extensively VOLUME 40B, OCTOBER 2009
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