Investigating the effect of slag bath conditions on the existence of multiphase emulsion zones in PGM smelting furnaces using computation fluid dynamics

The presence of chrome in electric arc furnaces smelting platinum group metals (PGM’s) has a number of potentially negative consequences. In cases where the slag chrome content is above the saturation limit the existence of near-stagnant conditions near the slag/matte interface increases the risk of chromite spinels settling and consolidating into a “mushy layer”, a three-phase suspension of slag, chromite and matte. The hold-up of matte above the elevation of the slag/matte interface can lead to the attack of freeze linings and copper cooling elements potentially causing failures of the furnace lining and significant downtimes as well as major safety risks. This paper investigates the relationship between typical furnace operating parameters and the behavior of the slag bath with respect to the formation of the “mushy” layer at the slag/matte interface using computational fluid dynamics (CFD). The extent of the potential “mushy” layer is seen to increase with decreasing electrode immersion and furnace power. Electrode immersion is, however, a considerably stronger driver is this regard. The CFD modelling results have aided in selecting appropriate furnace electrode immersion/power combinations intended to minimize “mushy” layer formation.

Research highlights
► A CFD model has been built an extended for a circular 3 electrode PGM smelting furnace used to smelt chromite rich PGM concentrates.
► The extent of the multiphase “mushy” layer is seen to increase with decreasing electrode immersion due to poor stirring in the deeper regions of the slag bath.
► A unique approach to calculating the CO bubble momentum transfer and mixing performance is presented.
► Insight into the 3D nature of low velocity zones and slag flows within the bath is greatly improved.
► Equivalent mixing power is introduced as a new calculated parameter to quantify the mixing energy in electrical smelting furnaces.