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Functions of Mg and Mg-CaO mixtures in hot metal desulfurization
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.ORCID iD: 0000-0002-3548-8638
2014 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 85, no 1, 76-88 p.Article in journal (Refereed) Published
Abstract [en]

The mechanisms of hot metal desulfurization using Mg and Mg-CaO mixtures were studied in a newly designed set-up. It was found that most of the added Mg quickly escaped in 2 s. MgS was not formed by homogeneous nucleation but by its formation on the MgO particles originated from oxide shell of the Mg particles. When tiny CaO particles were added together with Mg, the particles efficiently transformed to CaS. It was found that Mg-gas helped the distribution of the CaO particles in the hot metal and improved the kinetic condition. Most of the CaO particles smaller than 10 μm were completely transformed to CaS whereas CaO particles >10 μm still had CaO in the center after 20 s. The CaO particles as nuclei were also found to help Mg gas in forming MgS. The ratio of CaO and Mg added was found to have strong impact on the kinetic conditions of desulfurization. This ratio would need further study in any reactor of interest, as the kinetic conditions would differ considerably. The optimized ratio is expected to be a function of the size and geometry of the reactor, the position and the depth of the addition, the manner of addition and more. The hot metal desulfurization mechanisms using Mg and Mg-CaO mixtures were studied. Most added Mg quickly escaped in 2 s. MgS was not formed by homogeneous nucleation but by formation on oxide particles. When tiny CaO particles were added together with Mg, Mg-gas helped distribution of CaO particles in hot metal and improved kinetics. Most CaO particles sized <10 μm were completely transformed to CaS whereas CaO particles >10 μm still had CaO in the center after 20 s.

Place, publisher, year, edition, pages
2014. Vol. 85, no 1, 76-88 p.
Keyword [en]
CaO, hot metal desulfurization, Mg, reaction mechanisms, Homogeneous nucleation, Hot metal, Kinetic conditions, Oxide particles, Oxide shell, Reaction mechanism, Desulfurization, Kinetics, Magnesium, Mixtures, Nucleation, Metals
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-143068DOI: 10.1002/srin.201300071ISI: 000334354000010Scopus ID: 2-s2.0-84892153729OAI: oai:DiVA.org:kth-143068DiVA: diva2:705581
Note

QC 20140317

Available from: 2014-03-17 Created: 2014-03-17 Last updated: 2017-12-05Bibliographically approved
In thesis
1. A Study on Desulfurization of Hot Metal Using Different Agents
Open this publication in new window or tab >>A Study on Desulfurization of Hot Metal Using Different Agents
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with desulfurization of hot metal using different agents. The aim of this study was to improve the understanding of commonly used desulfurization agents such as fluidized CaO, CaC2, commercial-CaO, Mg, and mixtures of commercial-CaO-Mg. The possibility to use ZnO for desulfurization of hot metal was also investigated. The desulfurization mechanisms and kinetics of these agents were studied. A broad comparison of the desulfurization abilities of the agents was performed under the same experimental conditions. The experimental studies were carried out in a high temperature resistance furnace at 1773 K with good quenching ability and precise control of the oxygen partial pressure.

The influence of ZnO in blast furnace slag on the sulfur removal potential was studied. It was found that ZnO does not stay in blast furnace slag under relevant oxygen potentials and consequently has no influence on its sulfur removal capacity.

The reaction mechanism of Mg was studied by adding pure Mg into hot metal. It was found that most Mg (about 90 %) escaped as gas in less than two seconds, only providing a little desulfurization. MgS is not formed by homogenous nucleation, but on MgO particles originating from the surface of the added Mg metal.

The growth of CaS around CaC2, fluidized CaO and commercial-CaO were measured and compared. The parabolic rate constants were evaluated to be 2.4∙10-7 [cm s-1] for CaC2, and 5∙10-7 [cm s-1] for fluidized CaO particles. The bigger parabolic rate constant of fluidized CaO explains why fluidized CaO achieved a much better desulfurization of hot metal than CaC2 under the same experimental conditions. Commercial-CaO performed less satisfactory in comparison to fluidized CaO powder. This was due to both its less reactive surface and agglomeration of the particles.

Agglomerates and large CaO particles lead to 2CaO.SiO2 formation which hindered further utilization of CaO for desulfurization. The 2CaO.SiO2 formation was favored by a high oxygen potential. Since the desulfurization reaction of CaO not only produced CaS but also oxygen, the local oxygen concentration around big CaO particles was higher than around small particles.

When small CaO particles were added together with Mg they quickly transformed to CaS. The Mg-gas helped to distribute the CaO particles in the hot metal and improved the kinetic conditions.

The desulfurization abilities of some commonly used agents, namely fluidized CaO, CaC2, commercial-CaO, Mg, mixtures of commercial-CaO-Mg, and ZnO were studied and compared under the same experimental conditions. While fluidized CaO showed the best performance, commercial-CaO mixed with 20 mass % Mg achieved the second best desulfurization. Mg-granules performed slightly better than CaC2 and commercial-CaO, but somewhat less satisfactory compared to fluidized CaO and commercial-CaO-Mg mixtures. ZnO does not influence the sulfur concentration of hot metal.

Place, publisher, year, edition, pages
stockholm: KTH Royal Institute of Technology, 2014. viii, 43 p.
Keyword
desulfurization, hot metal, CaO, Mg, CaC2, ZnO, reaction mechanism, desulfurization abilities
National Category
Engineering and Technology
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-144025 (URN)978-91-7595-041-9 (ISBN)
Public defence
2014-04-25, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20140404

Available from: 2014-04-04 Created: 2014-04-04 Last updated: 2014-04-04Bibliographically approved

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