| In order to investigate stepwise reduction behaviors of iron ore pellets, CVRD pellets were reduced stepwise from Fe₂O₃ to Fe₃O₄, Fe₃O₄, to FeO and finally FeO to Fe with H₂-H₂O gas mixtures at 700-900℃. Chemical reaction rate constant(k_(ci))and effective diffusivity(D_(ei)) calculated from the mixed control plots based on the unreacted core model were decreased with proceeding of the reduction step and increased with the increase of the temperature, respectively. In the case of 900℃, k_(ij) was increased with proceeding of the reduction step. k_(ij), for each reduction steps are expressed by following equations, respectively. k_(cm) ＝ exp(3.262－3.563×10³/RT) (㎝/sec) k_(cw) ＝ exp(5.261－6.496×10³/RT) (㎝/sec) k_(efe) ＝ exp(11.979－13.616×10³/RT) (㎝/sec) In the intermediate model, Thiele`s modulus(Φ`) was increased with proceeding of the reduction step, but effectiveness factor(E_f) was decreased contrary to Φ`. Reduction curves calculated by using the rate parameters for stepwise reduction were agreed with experiments in the intermediate model than in the unreacted core model. |
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