Chemical wear of carbon-based refractory materials in a silicomanganese furnace tap-hole

Abstract

The aim of the study presented here was to investigate the potential for chemical wear of carbon-based refractory materials in a silicomanganese furnace tap-hole. In the study, three research questions were addressed: 1. Is chemical reaction between refractory and slag or refractory and metal a potential wear mechanism? 2. Is the choice in carbon-based refractory material important from a tap-hole refractory life perspective? 3. What are the implications for the life of the tap-hole in a SiMn furnace? To study the potential for chemical wear, thermodynamic calculations were conducted to determine the potential for the formation of SiC and SiMn at 1600°C through reduction of SiO2 and MnO and dissolution of C (and subsequent reaction with Si) in metal. The thermodynamic calculations were based on published [1] metal and slag composition and carbon. Cup test experiments based on synthetic slag and graphite proved SiC formation conclusively, but not SiMn formation. To study the effect of the choice in carbon-based refractory material, two types of refractory materials – carbon block and ramming paste – available commercially and industrial slag were sourced, prepared and characterised. Wettability studies proved the formation of SiC at 1588°C with slag being wetting towards refractory in an argon atmosphere and non-wetting in a CO-atmosphere. Under wetting conditions, the wetting angle of slag on carbon block was slightly higher (50°) at holding temperature compared to that of ramming paste (30°). Under non-wetting conditions the angles were 160° and 150° respectively. Cup test experiments based on industrial slag and carbon-based refractory material proved both SiC and SiMn formation at 1600°C conclusively and confirmed the wetting behaviour of slag towards refractory at larger scale. To study the implications for the life of the tap-hole in a SiMn furnace, the tap-hole of a 48 MVA SiMn furnace was excavated and profiled. The wear predicted by thermodynamic modelling was supported by mass flow calculations. It was concluded that chemical reaction between carbon-based refractory materials and slag and metal is one of the mechanisms responsible for wear in the tap-hole of a silicomanganese furnace.