Modeling of Manganese Ferroalloy Slag Properties and Flow During Tapping
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A. Background
FURNACE tapping is a key aspect in stable operation of submerged-arc furnaces (SAFs) producing high-carbon ferromanganese (HCFeMn) and silicomanganese (SiMn). These manganese ferroalloys are mostly produced in SAFs through carbothermic reduction of manganese-oxidebearing ores using carbonaceous reductants (typically coke) and fluxes, with silica also being added to produce SiMn. The stable operation of SAFs requires that consistent amounts of liquid slag and alloy are tapped, and reasonable flow rates should be initiated and sustained with minimal effort in order to maximize the operational efficiency and refractory life. Operational problems can be experienced during tapping, such as difficulties during taphole opening and sluggish or intermittent slag flow. Tapping difficulties are typically compensated for by increasing the operating temperature, changing slag composition, or lancing to open tapholes. These practices cause JACQUES MULLER, formerly Master’s Degree Student with the Department of Materials Science and Metallurgical Engineering, University of Pretoria, Pretoria, South Africa, is now Senior Process Engineer with Exxaro Resources, Pretoria, South Africa. Contact e-mail: [email protected] JOHANNES HENDRIK ZIETSMAN, Senior Lecturer, is with the Department of Materials Science and Metallurgical Engineering, University of Pretoria. PETRUS CHRISTIAAN PISTORIUS, POSCO Professor, is with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA and also Extraordinary Professor with the Department of Materials Science and Metallurgical Engineering, University of Pretoria. Manuscript submitted February 6, 2015. Article published online July 25, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
increased refractory damage over time, as well as other adverse effects on the process and equipment. The operation has to be able to tolerate fluctuations in especially slag chemical composition and temperature. Process differences also have to be accommodated when furnaces are converted between the production of HCFeMn and SiMn with minimal changes to the equipment. The behavior of slag and alloy in the taphole region and in contact with associated refractory sub-systems is related to physicochemical properties, which are determined by the temperature and chemical composition of the slag and alloy. Slag properties such as viscosity, thermal conductivity, density, and surface tension are important process variables that also influence operational aspects such as reaction kinetics, slag-alloy separability, and overall process operability. Slag chemical compositions and temperatures differ notably between the HCFeMn and SiMn processes and the production practice followed. In the discard slag practice, HCFeMn alloy is produced from ores, reductants, and basic fluxes (CaO, MgO). The product slag contains low MnO contents of 15 to 20 pct MnO that is discarded onto slag dumps. In South Africa, HCFeMn is mostly produced by smelting ores and reductants in SAFs following the discard sl
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