Control of silicon in high carbon ferrochromium produced in submerged arc furnace through redistribution of quartzite in the charge bed

Abstract

High carbon ferrochromium produced in a submerged arc furnace may contain as much as 4%Si. A high level of silicon in this alloy is not desired. In addition to bringing down the value of the alloy, a high level of silicon increases the specific energy consumption during production of the alloy. Controlling the proportion of silica and coke in the charge can help in bringing down the level of silicon in the hot metal. This strategy is adopted by some ferrochromium manufacturers. However, these practices lead to difficulties in tapping, and to reduced recovery of chromium. A thermochemical analysis of the process showed that silicon in the hot metal was at equilibrium with the slag only at high temperatures, which usually prevailed in regions close to the electrodes. Based on this analysis, a strategy was devised to control silicon in the hot metal by appropriate redistribution of quartzite at the top of the charge bed. Trials were carried out at an industrial plant to control the silicon level using this strategy. Results showed that the silicon level in the hot metal was drastically reduced on redistribution of quartzite. This method can result in a reduction of specific energy and specific coke consumption.