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Fundamental Studies Related to Gaseous Reduction of Iron Oxide
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. (Processes)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The demands for increasing the efficiency and lowering the environmental effects in iron and steelmaking industries have given rise to interests in application of direct reduction (DR) processes for production of iron by different gases. These advancements require comprehensive models for better control of the process conditions and the product properties. In the present thesis fundamental aspects in reduction of iron oxide were investigated.

The experimental studies on reduction of iron oxide pellets were performed under well-controlled conditions in a setup designed for thermogravimetric investigations. The results indicated that the reaction rates by the applied procedure are higher compared to the procedure similar to conventional thermogravimetric analysis (TGA). This difference was caused by the time required for replacing the inert gas by the reaction gases. Reduction by H2-CO mixtures was accompanied by deposition of carbon and formation of cementite. The variations of cementite contents in the industrial iron ore pellets reduced isothermally for different durations, showed that cementite formation starts from the initial stages of reduction. The experimental conditions such as reaction temperature, carbon activity in the reaction gas and reaction time have a large impact on carbide content of the reduced samples.

The kinetics of reduction of iron ore powder by H2 and CO gas mixtures with different compositions were studied using a commercial TGA setup. The results showed that the apparent rates of reaction vary linearly with the H2 and CO contents of the gas. Larger amount of H2 resulted in higher reaction rates. The data were employed in the developed reduction model for pellets. The model was based on the mechanism observed in the commercial iron ore pellets reduced by pure hydrogen. The microstructure of reacted pellets showed that reduction of the examined industrial samples is controlled by both chemical reaction and gaseous diffusion. The reduction model was developed by combining computations for the flow and mass transfer in the gas phase, diffusion of gases in the solid phase and chemical reaction at the reaction sites. The modelling and experimental results were in reasonably good agreement. The present model provides a good foundation for a dynamic multi-particle process model. The results highlighted the importance of considering the reduction mechanisms in different types of pellets prior to modelling.

Experiments were undertaken to investigate the selective reduction of iron oxide in zinc ferrite. It was observed that gaseous reduction by hydrogen at temperatures up to 873 K is a potential method for reduction of iron oxide to metallic iron, while the zinc oxide remains in the product and losses of metallic zinc are negligible. Using this primary step in the hydrometallurgical processing of EAFD can overcome the difficulties for leaching of zinc ferrite.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2016. , 43 p.
Keyword [en]
Direct reduction, iron ore, cementite, reduction model
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-191021ISBN: 978-91-7729-061-2OAI: oai:DiVA.org:kth-191021DiVA: diva2:954514
Public defence
2016-09-16, Kollegisalen, Brinellvägen 8, Stockholm, 18:56 (English)
Opponent
Supervisors
Note

QC 20160823

Available from: 2016-08-24 Created: 2016-08-22 Last updated: 2016-08-26Bibliographically approved
List of papers
1. Study on Direct Reduction of Hematite Pellets Using a New TG Setup
Open this publication in new window or tab >>Study on Direct Reduction of Hematite Pellets Using a New TG Setup
2014 (English)In: Steel Research International, ISSN 1611-3683, Vol. 85, no 4, 718-728 p.Article in journal (Refereed) Published
Abstract [en]

A new thermogravimetric setup was developed to study direct reduction of iron oxide under well-controlled experimental conditions. Pure and industrial hematite samples were isothermally reduced by hydrogen and carbon monoxide gaseous mixtures. Influences of gas composition, gas flow rate, and temperature on reduction were investigated. Reduction rates obtained using the new setup were higher compared to conventional thermogravimetric method. This difference was due to the time required to replace the inert gas with the reactant gas in the conventional method, which led to lower reduction rate at the initial stage. Carbon deposited on the surface of the pellets at relatively high gas flow rates and at low temperatures. The presence of pure iron and high carbon potential in the gas phase were the cause for carbon deposition. Study of partially reduced samples illustrated that the outer layer of pellet with high iron content thickened as reduction proceeded inside the pellet. Closure of micro-pores and formation of dense iron phase in this layer decelerated diffusion of reactant and product gases, and led to decrease of reduction rate at later stages of reaction. At lower temperatures, this effect was coupled with carbon deposition. Therefore, the reduction was seriously hindered.

Keyword
direct reduction, thermogravimetric analysis, reduction mechanism, carbon deposition
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-146156 (URN)10.1002/srin.201300197 (DOI)000333909700024 ()2-s2.0-84898070777 (ScopusID)
Note

QC 20140609

Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2016-08-24Bibliographically approved
2. Effect of Experimental Conditions on Cementite Formation During Reduction of Iron Ore Pellets
Open this publication in new window or tab >>Effect of Experimental Conditions on Cementite Formation During Reduction of Iron Ore Pellets
2016 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Refereed) Published
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-191116 (URN)
External cooperation:
Note

QC 20160825

Available from: 2016-08-23 Created: 2016-08-23 Last updated: 2016-08-25Bibliographically approved
3. Kinetics of Reduction of Hematite by H2 and CO
Open this publication in new window or tab >>Kinetics of Reduction of Hematite by H2 and CO
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-191118 (URN)
External cooperation:
Note

QC 20160825

Available from: 2016-08-23 Created: 2016-08-23 Last updated: 2016-08-25Bibliographically approved
4. Experimental and Modelling Study on Reduction of Hematite Pellets by Hydrogen Gas
Open this publication in new window or tab >>Experimental and Modelling Study on Reduction of Hematite Pellets by Hydrogen Gas
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-191119 (URN)
External cooperation:
Note

QC 20160825

Available from: 2016-08-23 Created: 2016-08-23 Last updated: 2016-08-25Bibliographically approved
5. Investigation of Selective Reduction of Iron Oxide in Zinc Ferrite by Carbon and Hydrogen
Open this publication in new window or tab >>Investigation of Selective Reduction of Iron Oxide in Zinc Ferrite by Carbon and Hydrogen
2016 (English)In: Journal of Sustainable MetallurgyArticle in journal (Refereed) Published
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-191117 (URN)
External cooperation:
Note

QC 20160825

Available from: 2016-08-23 Created: 2016-08-23 Last updated: 2016-08-25Bibliographically approved

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