The tapping of slag and metal is a key operational aspect in high-carbon ferromanganese (HCFeMn) and silicomanganese (SiMn) production. Tapping behaviour can be influenced by taphole design and the physicochemical properties of the tapped slag and metal. Unfavourable behaviour includes difficulties during taphole opening, and sluggish or intermittent slag flow. The slags of interest here consist mostly of components in the CaO-MnO-SiO2-Al2O3-MgO system, but differ greatly in MnO content and basicity due to the different operating practices.
To evaluate the flow behaviour of these slags from submerged arc furnaces (SAFs) the latest physicochemical property models were applied to model viscosity, thermal conductivity, density, and heat capacity as functions of temperature and typical HCFeMn and SiMn slag compositions. These property values were applied in a simplified model of flow through the coke bed and taphole with an inlet pressure specified. Based on a model from the literature (Iida et al. 2008), a model was formulated with spherical-radial flow through the coke bed, being independent of the length of the fluid path through the coke bed.
The effect of variation in the slag-metal ratio was investigated, with the focus on tap streams consisting of only slag. The estimated flow rates were comparable to those reported elsewhere (Kadkhodabeigi 2011) and found to be dependent mostly on slag viscosity, which was generally lower for the typical SiMn slags due to their composition and higher operating temperature. Furthermore, in most of the cases considered it was estimated that the flow through the taphole would develop into laminar flow, with the pressure drop predominantly over the coke bed. Flow rates were found to be highly dependent on the taphole diameter and coke bed void fraction, and to lesser extent on the taphole length and coke bed particle diameter.