The Importance of Controlling the Chemistry of Pre-Oxidized Chromite Pellets for Submerged Arc Furnace FeCr Smelting: a Study on Furnace Si Control

Abstract

South African FeCr operations have over time moved to running furnaces on predominantly pelletized concentrate feeds. This has brought about several changes in how submerged arc FeCr furnaces are operated. In particular, raw material management has become a critical factor to ensure that maximum value is derived from the material, and to minimize the impact of process upsets when they occur. When pre-oxidized pellets are produced, variations in the SiO2 fraction of the pellets will influence the liquidus temperature of the pellet material. Lower liquidus temperatures are undesirable when smelting pellets, since this can lead to impaired pre-reduction of iron oxides in the upper parts of the furnace. Further to this, if for example the furnace electrodes are positioned incorrectly, an excess amount of heat may be generated in the upper parts of the furnace – this can lead to excessive reduction of SiO2 to Si, which in turn reports to the FeCr product as a contaminant. In this paper, the effect of the chemistry of the pellet, electrode control and slag chemistry is studied. It was found that no one factor can fully explain the Si content of the alloy, however, with more modern tools, the industry is one step closer to fully predictive control. Some practical aspects of ensuring that the alloy Si specification is met.