Reduction of hematite using hydrogen plasma smelting reduction

Masab Naseri Seftejani

Research output: ThesisDoctoral Thesis

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Abstract

Hydrogen plasma smelting reduction (HPSR) of iron ore, which is an alternative to conventional iron- and steel-making processes and reduces the emission of greenhouse gases, was introduced at the Montanuniversitaet Leoben in 1992. In HPSR, hydrogen is activated in the plasma arc zone and becomes partially atomized and ionized. Activated hydrogen particles are strong reducing agents for iron oxides. HPSR offers advantages in terms of thermodynamics and kinetics over the conventional carbo-thermic reduction of iron ores. The work for this thesis has been carried out in the framework of the SuSteel project to obtain data and knowledge by the means of laboratory-scale facilities for the development of a testing HPSR plant at voestalpine Stahl Donawitz GmbH. This thesis provides an overview of generating hydrogen plasma in an arc plasma reactor by collisional processes and discusses the reduction ability of hydrogen species in terms of kinetics and thermodynamics. Furthermore, thermodynamics calculations have been carried out to study the reduction of iron oxide using hydrogen. The reduction behavior of iron oxides was assessed by carrying out a series of experiments. Therefore, the main parameters of reduction namely degree of reduction, degree of hydrogen utilization, reduction rate, and produced amount of metallic iron, and slag were studied. The thermodynamic aspect of the hematite reduction was considered, and the pertinent calculations were carried out using FactSageTM 7.2. All reduction parameters were calculated using the off-gas chemical composition measured by mass spectrometry. Carbon from the hollow graphite electrode, steel crucible, and ignition pin was introduced to the melt and contributed to the reduction process of iron oxides. Hence, the amount of CO and CO2 were the components of off-gas. The degree of reduction of hematite, regarding H2O, CO, and O2 as the gaseous reduction products, was determined. The results showed that at the beginning of the experiments, the degree of reduction and hydrogen utilization was high, and then decreased over the operation time because the concentration of iron oxide was gradually decreased. Conducting experiments with CaO caused a decrease in the phosphorus concentration in the produced iron. The slag formation during the reduction process and the reduction behavior of iron oxides were investigated. Furthermore, the reduction behavior of iron ore during continuous feeding was assessed. For this purpose, the fines of iron oxide and calcined lime were mixed to achieve a basicity of 0, 0.8, 1.6, 2.3, and 2.9, and then the mixtures were charged, melted, and reduced in the hydrogen plasma reactor. The results showed that in the batch process, the degree of hydrogen utilization and reduction rate was gradually decreased during the reduction process. In contrast, during the continuous-feeding experiment, the degree of hydrogen utilization could be kept approximately constant. The highest degrees of reduction and hydrogen utilization were obtained upon the application of slag with a basicity of 2.3. As a main result, the continuous feeding of iron oxides could apply the best conditions for the reduction of iron oxide using hydrogen thermal plasma. The temperature of the hydrogen plasma arc was measured using the spectroscopic method. A fiber of optical spectrometer was installed on the side of the plasma reactor to monitor the arc, capture the light from the arc, and send it to the optical spectrometer. Then, the arc temperature was calculated using the intensity of two main lines of hydrogen in the spectrum. The results showed that the maximum temperature of the arc was 13,435 K.
Translated title of the contributionReduktion von Hämatit mittels Wasserstoffplasma-Schmelzreduktion
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Weiß, Christian, Assessor B (internal)
  • Schenk, Johannes, Assessor A (internal)
Publication statusPublished - 2020

Bibliographical note

embargoed until null

Keywords

  • Hydrogen
  • Plasma
  • Hematite
  • Iron oxide reduction

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