Iron ore pellets are commonly used in the modern blast furnace process. The use of MgO in pellets, added as dunite or olivine, shortens the temperature range between the softening and melting zones in the blast furnace. This, in fact, leads to a better gas permeability. Other benefits of magnesium addition are the higher productivity, lower coke rate and better desulphurisation. The MgO plays two major roles in the slag's physico-chemical properties: (I) promotes changes in slag viscosity and (II) modifies the slag saturation. Blast furnace slags richer in MgO usually have low viscosities which results in greater refractory wettability. Such slags cause intensive wear at the slag line due to erosion and corrosion, but they are considered safer for the slag-metal interface. The main reason might be associated to the shorter than usual dwell time of such slags in the main trough, which may affect the FeO formation. In order to improve refractory performance by minimizing FeO corrosion, Al_2O_3-SiC-C or Al_2O_3-Spinel-SiC-C ultra-low-cement castables (both low SiC content) have been used in the metal zone as alternatives to single line castables. This study reports the slag attack results, carried out in induction and rotary drum furnaces, with different refractory castables and industrial blast furnace slags with different MgO contents. The results pointed out that the increase in the MgO content of slag decreases the castable wear index in the induction furnace, however, it increases when performed in rotary drum furnace. Phase diagram analysis suggests that the slags richer in MgO could induce a SiC protection mechanism against FeO attack based on spinel (Al_2O_3-MgO) formation at the slag-metal interface. On the other hand, the drop of slag viscosity, caused by MgO increase, would increase erosion, infiltration and corrosion of the refractory castables at the slag line.
展开▼
