MELTING BEHAVIOUR OF Mn SOURCES-EFFECT ON FURNACE PERFORMANCE

During production of Mn alloys in Submerged Arc Furnaces (SAF) most of the reduction takes place at the top of the coke bed. The conditions in this zone are crucial. Results of several studies of melting and reduction in this zone are presented and discussed. The temperature at the top of the coke bed is assumed to be determined by the temperature where the slag has viscosity low enough to drain into the coke bed. It is shown that this temperature will increase when the temperature for initial melting of the charge mixture increases. Charge mixtures with a high temperature for initial melting will thus give a high temperature at the top of the coke bed. The temperature for initial melting has been measured for several Mn sources. The investigations show that the temperature where the Mn sources start to melt, the softening temperature vary between the different sources from around 1250 o C to nearly 1600 o C. It decreases with increasing amount of acidic oxides in the ore. Heat-treated ores will have lower melting temperatures than the ores they are made from. Addition of quartz will decrease the melting temperature while it will increase when dolomite is added. Materials that soften at lower temperatures will be reduced at lower temperatures. When produced slag from two pilot experiments with HCFeMn production were compared, % MnO in slag was higher in the experiment where low melting Mn-source was used. A high temperature at the top of the coke bed is believed to be beneficial for SiMn production, but this has not been further discussed.