Investigations of selected influences on the hydrogen-based reduction of iron ore ultra-fines in a fluidized bed

Thomas Wolfinger

Research output: ThesisDoctoral Thesis


The hydrogen-based reduction of iron ore is considered to be a key technology in transforming the iron and steel industry towards climate neutrality. The combination of hydrogen-based reduction with the fluidized bed technology leads to a promising approach to lower greenhouse gas emissions and energy consumption. This preference is given due to the direct feeding of iron ore fines without a prior agglomeration step and the use of hydrogen. The present thesis introduces an approach for the analysis of the hydrogen-based reduction of iron ore fines and ultra-fines in a conventional low-velocity fluidized bed. Therefore, using a cold fluidization testing model, mathematical correlations were established to describe the fluidization behavior, including the carried-out material. In the case of magnetite-based ultra-fines, the effect of prior oxidation on the reduction kinetics using hydrogen as reducing agent was investigated in a thermogravimetric analyzer. Oxidized iron ore fines and ultra-fines were analyzed regarding their fluidization and reduction behavior in a hot fluidized bed reactor using hydrogen as reducing and fluidizing gas. The results showed controversial restrictions to fluidize iron ore fines and ultra-fines. High gas velocities were required to avoid partly fluidization and channeling, and low gas velocities to avoid gas by-passing and high entrainment rates. A prior oxidation of magnetite-based ultra-fines increased the reduction rate, whereby a moderate degree of oxidation of 50 % was sufficient. The high reduction rate of the solid material and the low gas velocities led to a limitation of the hydrogen supply up to 70 to 80 % degree of reduction. Two effects led to an additional decrease in gas utilization; first, due to the occurrence of a dense iron shell around the particles and thus solid-state diffusion as the rate-limiting mechanism; second, due to the moderate gas interchange between gas bubbles and particles. Therefore, iron ore fines and ultra-fines are suitable under certain restrictions for hydrogen-based reduction in a conventional low-velocity fluidized bed.
Translated title of the contributionUntersuchung ausgewählter Einflüsse auf die Reduktion von Feinst-Eisenerz mit Wasserstoff in der Wirbelschicht
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Schenk, Johannes, Supervisor (internal)
  • Raupenstrauch, Harald, Co-Supervisor (internal)
  • Krammer, Gernot, Assessor B (external), External person
  • Honeyands, Tom, Assessor A (external), External person
Publication statusPublished - 2024

Bibliographical note

embargoed until 08-02-2029


  • hydrogen-based reduction
  • low-velocity fluidized bed
  • iron ore fines and ultra-fines
  • magnetite-based ultra-fines

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