Development of characterization methods for the evaluation of the kinetic behavior and the fluidization of iron ore fines during hydrogen-induced fluidized bed reduction

Daniel Spreitzer

Research output: ThesisDoctoral Thesis

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Abstract

The hydrogen-induced fluidized bed reduction of iron ore fines might be a promising process technology for future-minded ironmaking. Recently, conventional ironmaking processes have typically been based on fossil energy carriers. As a result, the production of iron and crude steel ends in the emission of enormous amounts of carbon dioxide, which is in fact not sustainable. To decrease the emissions of carbon dioxide to an acceptable level, the use of hydrogen as an energy carrier and reducing agent might be the only solution for the long-term, sustainable production of iron and crude steel. In general, conventional ironmaking processes, such as the blast furnace, cannot be operated with pure hydrogen because of the process concept used. The use of fluidized bed reactors for the reduction of iron ores makes an exclusive input of hydrogen probable. Aside from that it is also possible to treat iron ore fines directly without prior agglomeration steps. This ends in the avoidance of these energy-intensive process steps. In the present study, the kinetic behaviors of different iron ore fines during hydrogen-induced fluidized bed reduction are investigated by using a developed approach based on the model designed by Johnson, Mehl and Avrami. The results show that the total reduction process, from hematite to metallic iron, can be described well by using the defined approach. It is shown that the rate-limiting mechanisms chemical reaction and nucleation are the most important steps during hydrogen-induced fluidized bed reduction. Because of the widespread availability of magnetite-based iron ore fines on the market, different opportunities for the treatment of such iron ores without troubles regarding de-fluidization and reducibility are investigated and possible process concepts for successful treatment are presented. It is shown that a prior oxidation of the magnetite still has an influence on the fluidization behavior and the reducibility but a successful operation is only possible with an addition of MgO to the material. The best combination of the properties can be attained with partial prior oxidation. A direct use of hematite and magnetite-based ultra-fines for hydrogen-induced fluidized bed reduction is also examined regarding its suitability for direct ironmaking. In contrast to results reported in literature, a stable fluidization of this fine-grained material is also possible at high metallization degrees without any sticking troubles for hematite-based ores. Different reduction experiments with different laboratory fluidized bed reactors were carried out in combination with morphological investigations of the raw materials as well as the reduced samples after reduction.
Translated title of the contributionEntwicklung neuer Methoden zur Evaluierung des kinetischen Verhaltens und der Fluidisierung von Feineisenerzen während der wasserstoffbasierten Reduktion mittels Wirbelschichttechnologie
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Hofbauer, Hermann, Assessor B (external), External person
  • Schenk, Johannes, Assessor A (internal)
Publication statusPublished - 2020

Bibliographical note

embargoed until null

Keywords

  • fluidized bed
  • reduction
  • iron ore fines
  • hydrogen

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