Abstract
Reducible oxides containing iron in iron ore sinter are hematite, magnetite and quaternary calcium ferrite (abbreviated by CF), which is the complex crystalline mineral produced from Fe2O3, CaO, SiO2 and Al2O3. Equilibrium diagram for CF reduction with CO-CO2 gas mixture is a little but significantly different from the one for pure iron oxides. In previous analyses for reduction reaction of iron oxides in a blast furnace, however, sinter has been treated as pure iron oxides; existence of CF has been ignored. Reduction steps for CF can be written as
CF (= ‘Fe2O3’) → ‘Fe3O4’ → ‘FeO’ → ‘Fe’,
which are much the same as pure iron oxides, where ‘Fe2O3’, ‘Fe3O4’, ‘FeO’ and ‘Fe’ designate hematite, magnetite, wustite and iron stages of CF, respectively. However, a reported variation of gas composition with temperature measured in a blast furnace shows that the gas composition in the thermal reserve zone is a little higher than the wustite / iron equilibrium, the reduction potential of which is less than that of ‘FeO’ / ‘Fe’ equilibrium and hence ‘FeO’ cannot be reduced to ‘Fe’. In the present work, gaseous reduction model for sinter is developed in consideration of CF reaction process; unreacted-core shrinking model for six interfaces is proposed to take into account reaction process of CF as well as pure iron oxides. Trial comparison of the calculated reduction curve with our previously reported experimental data under simulated blast furnace conditions shows rather good agreement.
