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A Study on Desulfurization of Hot Metal Using Different Agents
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling. (Micro-Modelling and Experimental Kinetics)
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 [en]
desulfurization, hot metal, CaO, Mg, CaC2, ZnO, reaction mechanism, desulfurization abilities
National Category
Engineering and Technology
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-144025ISBN: 978-91-7595-041-9 (print)OAI: oai:DiVA.org:kth-144025DiVA: diva2:710128
Public defence
2014-04-25, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140404

Available from: 2014-04-04 Created: 2014-04-04 Last updated: 2014-04-04Bibliographically approved
List of papers
1. Study on the Possibility of Using ZnO for Hot Metal Desulfurization
Open this publication in new window or tab >>Study on the Possibility of Using ZnO for Hot Metal Desulfurization
2013 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 5, 419-425 p.Article in journal (Refereed) Published
Abstract [en]

The possibility of using ZnO for desulfurization in hot metal was evaluated. A lab scale experimental setup was designed so that different desulfurizing agents could be added to hot metal for evaluation of their desulfurizing power. The setup had good control of both temperature and the gaseous atmosphere. It also provided stirring of the metal bath with an impeller as well as quenching facility to maintain the metal composition at high temperature. Desulfurization of hot metal using CaO powder showed evidently the applicability of the new setup. On the other hand, additions of ZnO into the hot metal under various experimental conditions showed no effect on desulfurization. The results were in contradiction to the suggestion found in literature. A thorough examination of the thermodynamic data employed by the previous work was carried out. The data used in the literature were found to be subjected to fundamental mistakes. The present experimental results convincingly rule out the possibility of using ZnO as a desulfurization agent.

Keyword
desulfurization, hot metal, ZnO, CaO, stirring
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-123424 (URN)10.1002/srin.201200154 (DOI)000318357100002 ()2-s2.0-84877254051 (Scopus ID)
Note

QC 20130610

Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
2. Study on the Possibility of Using ZnO to Increase the Desulfurization Potential of Blast Furnace Slag and Sulfide Capacities
Open this publication in new window or tab >>Study on the Possibility of Using ZnO to Increase the Desulfurization Potential of Blast Furnace Slag and Sulfide Capacities
2013 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 1, 48-55 p.Article in journal (Refereed) Published
Abstract [en]

Zinc oxide has recently been suggested to be a potential material for hot metal desulfurization. The present work was carried out to examine whether ZnO could help the remaining blast furnace (BF) slag to capture sulfur. For this purpose, slags prepared with relatively high ZnO content was equilibrated with either liquid silver or liquid copper under controlled oxygen potential at 1773?K. It was found that most of the ZnO escaped during the experiment, indicating thereby that ZnO could not increase the desulfurization potential of the BF slag in the case of hot metal. The experimental data were used to evaluate the sulfide capacities of the studied slags. In some of the slags equilibrated with silver, the MgO activities were evaluated.

Keyword
desulfurization, hot metal, MgO activity, slag, sulfide capacity, ZnO
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-116727 (URN)10.1002/srin.201200122 (DOI)000312988500008 ()2-s2.0-84872023293 (Scopus ID)
Note

QC 20130125

Available from: 2013-01-25 Created: 2013-01-25 Last updated: 2017-12-06Bibliographically approved
3. Functions of Mg and Mg-CaO mixtures in hot metal desulfurization
Open this publication in new window or tab >>Functions of Mg and Mg-CaO mixtures in hot metal desulfurization
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.

Keyword
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:nbn:se:kth:diva-143068 (URN)10.1002/srin.201300071 (DOI)000334354000010 ()2-s2.0-84892153729 (Scopus ID)
Note

QC 20140317

Available from: 2014-03-17 Created: 2014-03-17 Last updated: 2017-12-05Bibliographically approved
4. Kinetic study on desulfurization of hot metal using CaO and CaC2
Open this publication in new window or tab >>Kinetic study on desulfurization of hot metal using CaO and CaC2
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The kinetics and reaction mechanisms of hot metal desulfurization using CaO and CaC2 were studied in a well-controlled atmosphere with a lab scale high temperature furnace. The growths of CaS around CaO and CaC2 were measured and compared at 1773 K. The parabolic rate constant was evaluated to be 5∙10-7 [cm s-1] on CaO particles, and 2.4∙10-7 [cm s-1] on CaC2. The bigger parabolic constant of CaO resulted in more efficient desulfurization. Agglomerates and big CaO particles led to 2CaO.SiO2 formation which hindered further utilization of CaO for desulfurization. The 2CaO.SiO2 formation was favoured 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.

Keyword
Hot metal, Desulfurization, CaO, CaC2, reaction mechanisms
National Category
Engineering and Technology
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-144018 (URN)
Note

QS 2014

Available from: 2014-04-04 Created: 2014-04-04 Last updated: 2014-04-04Bibliographically approved
5. Study on Desulfurization Abilities of Some Commonly Used Desulfurization Agents
Open this publication in new window or tab >>Study on Desulfurization Abilities of Some Commonly Used Desulfurization Agents
2015 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 86, no 1, 73-83 p.Article in journal (Refereed) Published
Abstract [en]

The desulfurization abilities of some commonly used agents, namely fluidized CaO, CaC2, commercial-CaO, Mg, MgO, CaO center dot MgO, and mixtures of commercial-CaO-Mg were studied and compared under the same experimental conditions in a laboratory furnace at 1773 K. The desulfurization mechanisms of CaO center dot MgO, commercial-CaO, and mixtures of commercial-CaO and Mg were also studied. 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. Since only the CaO portion in CaO center dot MgO functioned to take up sulfur, additional 70% mass had to be added to achieve the same desulfurization level. The poor ability of commercial-CaO in comparison to fluidized CaO powder was due to both its less reactive surface and agglomeration of the particles.

Keyword
Hot metal desulfurization, Desulfurization abilities, CaO, CaC2, Mg, CaO-Mg mixtures.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-144023 (URN)10.1002/srin.201400031 (DOI)000347541200010 ()2-s2.0-84923031074 (Scopus ID)
Note

QC 20150209. Updated from manuscript to article in journal.

Available from: 2014-04-04 Created: 2014-04-04 Last updated: 2017-12-05Bibliographically approved

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