Insights into the potential for reduced refractory wear in silicomanganese smelters

Abstract

arc furnace (SAF) used for silicomanganese (SiMn) production, it was found that the taphole and hearth were high refractory wear areas (Steenkamp, 2014). In both these highwear areas, carbon-based cold ramming paste formed the hot face refractory lining (crucible). The wear profile of this SAF is presented in Figure 1. The hot face refractory lining was formed by cold ramming of high-grade carbon ramming material. This material consisted of 50–70% anthracite, 15–25% graphite, 6–12% resin, 2–7% tar, 1–5% clay, and 1–5% alumina. The tap-hole was built using SiC bricks, consisting of 75% SiC, 23.4% Si3N4, 0.3% Fe2O3, 0.3% Al2O3, and 0.2% CaO. In the tap-hole area, the wear of the SiC refractory material was estimated at 0.4 t, and that of the high-grade carbon ramming material, at 1.9 t (Steenkamp, Pistorius, and Tangstad, 2015). The amounts of slag and metal tapped during six years of operation of the tap-hole (September 2007 to April 2013) were estimated at 33 088 t (Steenkamp et al., 2015) and 41 360 t, respectively. The original thickness of the high-grade carbon ramming paste installed in the hearth was 850 mm, of which a minimum of 600 mm was seen to remain after ten years of operation (April 2003 to April 2013). Over the lifetime of the hearth refractory, 384 000 t of SiMn metal was tapped from the furnace (Gous, 2015). The difference in metal exposure of hearth and tap-hole is due to the fact that the furnace had two single-level tap-holes, and that the tap-holes were rebuilt during the lifetime of the hearth refractory. Further details of the refractory design, and history of operations have been discussed elsewhere (Steenkamp et al, 2014, 2015; Steenkamp, 2014). Analysis of the potential for chemical wear in the tap-hole area of the SAF excavated in 2013 (Figure 1) was included in a larger study on tap-hole wear in SAFs producing SiMn (Steenkamp, 2014). In that study the potential for chemical reaction between slag (and metal) and refractory materials being responsible for wear in a single-level tap-hole where slag and metal are tapped typically at 1600°C was tested. It was previously established that reaction between silicomanganese slag and carbonbased tap-hole refractory is possible (Steenkamp, 2014). Predictions by thermodynamic calculations were supported by laboratory-scale experiments with nominally pure materials as well as industrial materials (Steenkamp, 2014), as reaction products SiC and SiMn droplets formed. For the reaction of C-based refractory with slag, if the SiC Insights into the potential for reduced refractory wear in silicomanganese smelters by J.D. Steenkamp*, P.C. Pistorius, and J. Muller