Slag layer

The interelectrode insulators, an integral part of the electrode wall stmcture, are required to stand off interelectrode voltages and resist attack by slag. Well cooled, by contact with neighboring copper electrodes, thin insulators have proven to be very effective, particularly those made of alumina or boron nitride. Alumina is cheaper and also provides good anchoring points for the slag layer. Boron nitride has superior thermal conductivity and thermal shock resistance. 

The reacting particles melt rapidly, and the droplets fall to the slag layer. The sulfide drops settle through it to form the matte phase. Any oxidi2ed copper is reduced to the matte by the following reaction ... 

Since a detailed discussion of the factors listed in Table 4 is beyond the scope of this review, the reader is referred to the listed references for further information. Several of the factors affecting the PCR also affect the slag layer and these are discussed in more detail in Sec. 2.4. 

The heat transfer efficiency is significantly affected by the slag layer properties and behavior therefore, those factors other than slag phenomena that affect HTE are presented in Table 5. As for the PCR, it is desirable to keep the HTE as high as possible. An increase in HTE at the same PCR decreases fuel consumption (Fruehan et al., 1989 Keogh et al.,... 

The slag layer plays important roles in heat transfer and the reduction of iron oxide. The role of the slag layer in heat transfer was described in Sec. 2.3. Katayama et al. (1992) proposed that the reduction of iron oxide occurred at the following three locations... 

Katayama, H., Ibaraki, T., Ohno, T., Yamauchi, M., Hirata, H., and Inomoto, T., The Characteristics and the Function of a Thick Slag Layer in the Smelting Reduction Process, ISIJ Int., 33 124 (1993a)... 

Reactions such as the above have been used for the large-scale commercial production of WC by Kenna-metal, Inc. in a process called the Macro Process [28]. Thermodynamics for the analogous molybdenum reaction show that the reaction is highly exothermic (Table 3). The solid reactants are metered into a carbon-lined kiln to develop a self-sustained exothermic reaction. The reaction occurs in a pool of molten metal at temperatures above 2800 K. At the end of the run the kiln contents solidify into a lower heavy layer of carbide crystals and an upper slag layer of oxides. 

---