カルシウムフェライトの反応過程を考慮した焼結鉱ガス還元モデル(6界面未反応核モデル)

摘要

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 Fe_2O_3, CaO, SiO_2 and Al_3O_3. Equilibrium diagram for CF reduction with CO-CO_2 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(='Te_2O_3')→'Fe_3O_4'→'FeO'→'Fe'，which are much the same as pure iron oxides, where 'Fe_2O_3，, 'Fe_3O_4，'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.%実機焼結鉱中の4成分系カルシウムフxライト(以下，CFと略記する)は，Sugiyamaらが示したように難還元性鉱物すなわち2FeO•SiO_2,CaO•FeO•SiO_2などを生成する原因となるSiO_2を相当量取り込んで無害化し，酸化鉄の次に還元性の良い鉱物相となったもので，その還元速度の評価は，鉄鉱石原料の劣質化に伴い，ますます重要となってきている。すなわち，CFはSiO_2を取り込んで，がうまく結晶化したものであり，焼結鉱中のCFの割合が増えることは，難還元性鉱物相の減少を通じて，焼結鉱の被還元性の向上に寄与する。