Engineering company TOREX, Yekaterinburg, Russia¹ ; Cherepovets State University, Cherepovets, Russia²

I. S. Bersenev, Cand. Eng., Head of the Research and Analysis Department¹, Researcher², e-mail: i.bersenev@torex-npvp.ru

Engineering company TOREX, Yekaterinburg, Russia
E. S. Bersenev, Group Leader, e-mail: e.bersenev@torex-npvp.ru

Engineering company TOREX, Yekaterinburg, Russia¹ ; Ural Federal University named after the first President of Russia B. N. Yeltsin, Yekaterinburg, Russia²
E. R. Sabirov, Senior Engineer¹, Postgraduate Student², e-mail: e.sabirov@torex-npvp.ru

Ural Federal University named after the first President of Russia B. N. Yeltsin, Yekaterinburg, Russia

N. A. Spirin, Dr. Eng., Prof., Head of the Dept. of Thermophysics and Informatics in Metallurgy, e-mail: n.a.spirin@urfu.ru

The paper examines the interrelation between two critical phenomena occurring during the reduction of iron ore pellets: abnormal swelling in the blast furnace and clustering in shaft metallization furnaces. It is shown that both phenomena are caused by the growth of iron whiskers at the wüstite reduction stage, and pellet swelling further accelerates their sintering by increasing the contact area and pressure gradient in the contact zone. Based on a review of literature data and original research results, technical solutions are proposed to limit whisker growth: addition of inhibitor oxides (MgO, Al₂O₃, SiO₂), control of basicity (CaO/SiO₂ <0.2 or >0.8), two-stage reduction (first stage at temperature <900 °C to a reduction degree of 60 %), application of protective coatings (limestone, cement, bentonite, mixed compositions), increase of open porosity (>25 % with predominant pore size of 10-100 μm), control of alkali content (Na₂O + K₂O ≤0.15 % for blast furnace burden and ≤0.08 % for metallization burden), and reducing gas composition (H₂/CO >1,5). It is demonstrated that two-stage reduction can reduce the reduction swelling index of ultra-high-grade pellets from 99.4 % to less than 15 % without loss of reduction rate, while limestone or cement coating reduces clustering by 60–80 %. The proposed solutions do not require radical modernization of existing technologies and can be implemented at the burden preparation stage or by adjusting thermal regimes.

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