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Study on the dissolution of lime and dolomite in converter slag
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the present study, the dissolution mechanism and rate of lime, limestone and dolomite in converter slag was studied. Lime dissolution in stagnant slag was studied first and dissolution of lime, limestone and dolomite under forced convection were carried out by new experimental setup.

Dissolution of different CaO samples into stagnant converter slags was carried out in a closed tube furnace at 1873K. In the case of CaO-‘FeO’-SiO2 slag, the dissolution of CaO rod in the stagnant slag was retarded after the initial period (2 minutes). A dense layer of 2CaO∙SiO2 was found to be responsible for the total stop of the dissolution. It could be concluded that constant removal of the 2CaO∙SiO2 layer would be of essence to obtain high dissolution rate of lime. In this connection, it was found necessary to study the dissolution of lime in moving slag.

In order to obtain reliable information of lime dissolution under forced convection, the commonly used rotating rod method was examined. Both CFD calculation and cold model experiments showed evidently that the mass transfer due to radial velocity introduced by forced convection was zero if the rod was centrally placed in a cylindrical container. A new experimental design was therefore developed. A cube was placed in the crucible and stirred by Mo rod along with slag. The whole system could be quenched in order to maintain the state of the system at high temperature. A linear relationship between normalized length and time was obtained for lime dissolution. Different lime samples showed big difference in dissolution rate. It was found that the main mechanism of CaO dissolution in slag was due to the removal of 2CaO∙SiO2 layer.

Decomposition and dissolution of limestone and dolomite in slag at 1873 K were studied. The decomposition was carried out both in argon and in slag under argon atmosphere. The decomposition process was simulated using Comsol. The results showed evidently that the decomposition of limestone and dolomite was controlled mostly by heat transfer.

It was also found that the decomposition of limestone product: CaO had very dense structure, no matter the sample was decomposed in slag or in argon. The slow decomposition and the dense CaO layer would greatly hinder the dissolution of lime in the slag. The present results clearly indicate that addition of limestone instead of lime would not be beneficial in converter process.

Discontinuous 2CaO∙SiO2 layer along with MgO∙Fe2O3 particles was found on the surface of the dolomite sample. Some 2CaO∙SiO2 islands were found in the vicinity of the sample in the slag, which revealed therefore that the dissolution was dominated by the peeling-off of the layer of 2CaO∙SiO2-MgO∙Fe2O3 mixture. 2CaO∙SiO2, (Mg, Fe)Oss along with super cooled liquid phases were found inside dolomite sample close to the surface. 2CaO∙SiO2 phase was replaced gradually by 3CaO∙SiO2 towards the centre of the decomposed sample.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 45 p.
Keyword [en]
dissolution, lime, limestone, dolomite, converter slag
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-101461ISBN: 978-91-7501-454-8 (print)OAI: oai:DiVA.org:kth-101461DiVA: diva2:547848
Public defence
2012-09-28, B1, Brinellvägen 23, Kungliga Tekniska Högskolan, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20120829

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2013-03-20Bibliographically approved
List of papers
1. Dissolution of Lime in Synthetic 'FeO'-SiO2 and CaO-'FeO'-SiO2 Slags
Open this publication in new window or tab >>Dissolution of Lime in Synthetic 'FeO'-SiO2 and CaO-'FeO'-SiO2 Slags
2010 (English)In: Steel Research International, ISSN 1611-3683, Vol. 81, no 5, 347-355 p.Article in journal (Refereed) Published
Abstract [en]

Dissolution of different CaO samples into molten synthetic 'FeO'-SiO2 and 'FeO'-SiO2-CaO slags was carried out in a closed tube furnace at 1873K. The slag was kept stagnant. It was found that the dissolution rate was very fast when CaO rod was dipped into 'FeO'-SiO2 slag. In the case of 'FeO'-SiO2-CaO slag, the dissolution of CaO rod in the stagnant slag was retarded after the initial period (2 minutes). Only less than 16 percent CaO reacted with the slag, irrespective of the type of lime. Three phase-regions were identified in the reacted part of the lime rod by SEM-EDS analysis. The formation of these regions was explained thermodynamically. A dense layer of 2CaO center dot SiO2 was found to be responsible for the total stop of the dissolution. It could be concluded that constant removal of the 2CaO center dot SiO2 layer would be of essence to obtain a high dissolution rate of lime. In this connection, it was found necessary to study the dissolution of lime in moving slag to reach a reliable conclusion regarding the relevance of the reactivity obtained by water ATSM test to the real reactivity of lime in high temperature slag.

Keyword
Lime, Slag, Dissolution
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-27521 (URN)10.1002/srin.201000017 (DOI)000278292200003 ()2-s2.0-77953955982 (Scopus ID)
Note
QC 20101217Available from: 2010-12-17 Created: 2010-12-13 Last updated: 2012-08-29Bibliographically approved
2. Experimental Design for the Mechanism Study of Lime Dissolution in Liquid Slag
Open this publication in new window or tab >>Experimental Design for the Mechanism Study of Lime Dissolution in Liquid Slag
2012 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 83, no 3, 259-268 p.Article in journal (Refereed) Published
Abstract [en]

The applicability of rotating rod technique in the study of lime dissolution in slag was investigated. Both computational fluid dynamic (CFD) and cold model experiments showed that the mass transfer due to radial velocity introduced by forced convection was zero if the rod was long. The mass transfer by forced convection was also less important in comparison with natural convection and diffusion when the rod was half length of the height of the bath. This finding was in accordance with the criteria put forward by the original work that the method could only be applicable when a thin disk (instead of rod) with big diameter and big liquid bath were used. To study the lime dissolution by forced convection a new experimental technique was developed. A cube was placed in the slag that was eccentrically stirred. The whole system, viz. the sample along with the slag could be quenched. The new technique could study the effect of forced convection on the dissolution. The microscopic study on the quenched slag-lime samples could reveal the dissolution mechanism successfully.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-67466 (URN)10.1002/srin.201100258 (DOI)000300990400007 ()2-s2.0-84858052204 (Scopus ID)
Note
QC 20120411Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2017-12-08Bibliographically approved
3. Study of Lime Dissolution Under Forced Convection
Open this publication in new window or tab >>Study of Lime Dissolution Under Forced Convection
2012 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 43, no 3, 578-586 p.Article in journal (Refereed) Published
Abstract [en]

Dissolution of different CaO cubes under force convection in liquid CaO-"FeO"-SiO2 slag was studied at 1873 K (1600 A degrees C). A linear relationship between normalized lengths and time was obtained after the experiment. It was evidently observed that the removal of the interface layer(s) including 2CaO center dot SiO2 by shear stress was the main mechanism for the dissolution. A stirring rate of approximately 100 rpm was found to be efficient to remove the interface layer(s). The limes with different structures had different dissolution rates.

Keyword
Cao-Feo-Sio2 Slags, Reactivity, Rates
National Category
Physical Chemistry Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-66968 (URN)10.1007/s11663-011-9629-8 (DOI)000304159700017 ()2-s2.0-84861856003 (Scopus ID)
Note
QC 20120613Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2017-12-08Bibliographically approved
4. Limestone Dissolution in Converter Slag at 1873 K (1600 degrees C)
Open this publication in new window or tab >>Limestone Dissolution in Converter Slag at 1873 K (1600 degrees C)
2013 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 44, no 1, 98-105 p.Article in journal (Refereed) Published
Abstract [en]

Decomposition and dissolution of limestone in slag at 1873 K (1600 A degrees C) were studied. The limestone samples were in the shape of cubes (11 mm x 11 mm x 11 mm approximately). The decomposition was carried out both in argon and in slag under argon atmosphere. In order to gain an insight into the phenomenon of slow decomposition, the decomposition process of CaCO3 was simulated using Comsol. The results showed evidently that the decomposition of calcium carbonate was controlled mostly by heat transfer. It was also found that the decomposition product CaO had very dense structure, whether the sample was decomposed in slag or in argon. The slow decomposition and the dense CaO layer would greatly hinder the dissolution of lime in the slag. The present results clearly indicate that the addition of limestone instead of lime would not be beneficial in the converter process.

Keyword
Calcium-Carbonate, Thermal-Decomposition, Lime, Heat, Dissociation, Mechanism, Pressure, Kinetics
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101412 (URN)10.1007/s11663-012-9761-0 (DOI)000314909000013 ()2-s2.0-84874001227 (Scopus ID)
Note

QC 20130320. Updated from submitted to published. Previous title: Limestone dissolution in converter slag at 1873K

Available from: 2012-08-29 Created: 2012-08-28 Last updated: 2017-12-07Bibliographically approved
5. Dissolution mechanism of dolomite in converter slag at 1873K
Open this publication in new window or tab >>Dissolution mechanism of dolomite in converter slag at 1873K
2014 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, no 1, 75-80 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism of dolomite dissolution in converter slag was studied and found to proceed by two steps: decomposition of dolomite into CaO and MgO and dissolution of the product into the slag. The first step was found to be controlled by heat transfer, which was confirmed by theoretical calculation. The decomposed dolomite had many pores, which allowed easy slag penetration. A discontinuous 2CaO.SiO2 layer along with MgO.Fe2O3 particles was found on the surface of the samples. Some 2CaO.SiO2 islands were found in the vicinity of the samples in the slag, revealing that the dissolution was dominated by peeling-off of the layer of 2CaO.SiO2- MgO.Fe2O3 mixture. 2CaO.SiO2, (Mg, Fe)Oss along with super cooled liquid phases were found inside dolomite samples close to the surface. 2CaO.SiO2 phase was replaced gradually by 3CaO.SiO2 towards the centre of the decomposed sample. While addition of small amounts of dolomite directly into the slag could be considered in steelmaking converter, too much would result in slow dissolution and waste of the raw materials.

Keyword
Converter slag, Decomposition, Dissolution, Dolomite
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101416 (URN)10.1179/1743281212Y.0000000101 (DOI)000334114700012 ()2-s2.0-84893223301 (Scopus ID)
Note

QC 20140317. Updated from submitted to published.

Available from: 2012-08-29 Created: 2012-08-28 Last updated: 2017-12-07Bibliographically approved

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