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Study on some phenomena of slag in steelmaking process
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present work is to study slag phenomena in steelmaking process. In order to attain thegoal, a number of high temperature experiments and simulation experiments were carried out.

Four master slags were used to study the effect of CaF2 on slag viscosity. Experimentalresults indicated the effect of CaF2 on slag viscosity depended strongly on the composition ofmaster slag. For high basicity slags, CaF2 mainly suppressed the precipitation of solid phasesat lower temperatures, leading to a lower viscosity compared to CaF2-free slags. For slagswith higher SiO2 contents, CaF2 both lowered the viscosity of the liquid phase and suppressedthe precipitation of solid phases.

The viscosities of solid-liquid mixtures were experimentally determined for silicon oilparaffinsystem at room temperature and solid-liquid oxide mixture at steelmakingtemperature. The results of both measurements indicated that the increasing trend of mixturesviscosity with particle fraction can be described by Einstein-Roscoe equation.Silicone oils of different viscosities were used to simulate slag foaming. The experimentalresults showed, at a constant viscosity, the foaming height increased first with superficialvelocity before reaching a maximum value. Thereafter, the foaming height decreased with thefurther increase of the superficial velocity. Similar, a maximum foaming height was observedat an optimum viscosity when a constant superficial gas velocity was applied. Based on theexperimental data, a semi-empirical equation of foaming height was developed. Thepredictions of the model agreed well with experiment data. The model could also reasonablywell explain the industrial pilot trial experiments.

Water-silicon oils model and liquid alloy (Ga-In-Sn)- 12% HCl acid model were employed tosimulate the formation of open-eyes in a gas stirred ladle. The experimental results indicatedthat the viscosity of the top liquid and the interfacial tension between the two liquids had onlylittle effect on the open-eye size. A semi-empirical model was developed to describe the sizeof open-eye as functions of the gas flow rate, bath height and slag height. The two sets ofparameters obtained for the water and Ga-In-Sn models were very different. Industrial trialswere also conducted to examine the applicability of the models. Liquid alloy model couldwell predict the formation of an open-eye during ladle treatment.

Two cold models, sodium tungstate-oil model and water-oil model, were carried out tosimulate the formation of droplets in a gas stirred ladle. The experimental results showed thatthe gas flow rate and interfacial tension had strong impact on the size of droplets. A semiempiricalmodel was developed to describe the size of droplets for water model. Meanwhile,the parameter obtained for water model can be used for sodium tungstate-silicone oil system.The results indicate the model has strong compatibility.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 46 p.
Keyword [en]
Slag viscosity, calcium fluoride, fluid viscosity with particles, mixture viscosity
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-32740ISBN: 978-91-7415-955-4OAI: oai:DiVA.org:kth-32740DiVA: diva2:411615
Public defence
2011-05-12, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110419Available from: 2011-04-19 Created: 2011-04-19 Last updated: 2011-04-19Bibliographically approved
List of papers
1. The effect of calcium fluoride on slag viscosity
Open this publication in new window or tab >>The effect of calcium fluoride on slag viscosity
2011 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 5, 928-931 p.Article in journal (Refereed) Published
Abstract [en]

The effect of CaF(2) on the viscosity of high-basicity Al(2)O(3)-CaO-MgO-SiO(2) (-CaF(2)) slags for secondary steelmaking was studied using a Brookfield digital viscometer. The addition of approximately 3 mass pct CaF(2) could decrease the liquidus temperature substantially in the case of high CaO containing slags, leading to good flowability of the slag at the temperature of the ladle treatment. The addition of CaF(2) had the strongest effect on the viscosity of liquid slag with high SiO(2) content.

Keyword
Brookfield digital viscometer, Flowability, Ladle treatment, Liquidus temperature, Secondary steelmaking, Slag viscosity, Calcium fluoride, Silicon compounds, Viscometers, Viscosity
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-32729 (URN)10.1007/s11663-011-9546-x (DOI)000297251300003 ()2-s2.0-80054924863 (ScopusID)
Note
QC 20110419. Updated from submited to published.Available from: 2011-04-19 Created: 2011-04-18 Last updated: 2011-12-19Bibliographically approved
2. The effect of solid particles on liquid viscosity
Open this publication in new window or tab >>The effect of solid particles on liquid viscosity
2011 (English)In: Steel research, ISSN 0177-4832, Vol. 82, no 4, 388-397 p.Article in journal (Refereed) Published
Abstract [en]

The viscosities of solid-liquid mixtures were experimentally determined for silicon oil-paraffin system at room temperature and solid-liquid oxide mixture at steelmaking temperature. The use of oil-paraffin systems was to confirm the results of high temperature measurements, the experimental conditions being very difficult to control. The silicon oil- paraffin mixtures behaved Newtonian until the particle fraction reached 0.15. At this fraction, the mixture started deviate from Newtonian flow; though some average values could still be collected with very high uncertainty. Liquid-2CaO.SiO2 mixtures and liquid-MgO mixtures were studied at steelmaking temperature with carefully prepared particle fractions and well controlled conditions. Liquid-2CaO.SiO2 mixture behaved Newtonian even when the particle fraction reached 0.1. The results of both room temperature measurements and steelmaking temperature measurements were used to examine the applicability of the existing models. Einstein-Roscoe equation was found to be the only model applicably for the systems studied. No modification of the model parameter was found necessary, though the particles were not spherical.

Keyword
Slag, Two-phase mixture, Viscosity, Einstein-Roscoe model
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-32731 (URN)10.1002/srin.201000207 (DOI)000290050900011 ()2-s2.0-79953686509 (ScopusID)
Note
QC 20110419 QC 20110609Available from: 2011-04-19 Created: 2011-04-18 Last updated: 2011-06-09Bibliographically approved
3. Modelling of slag foaming
Open this publication in new window or tab >>Modelling of slag foaming
2010 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, Vol. 37, no 8, 612-619 p.Article in journal (Refereed) Published
Abstract [en]

In this work, silicone oils of different viscosities were used to simulate slag foaming. The experimental results showed that the variations of foaming height with superficial gas velocity and liquid viscosity do not show simple increasing trends. At a constant viscosity, foaming height increased first and then started decreasing with increasing superficial velocity. Similarly, a maximum foaming height was observed at an optimum viscosity when a constant gas flowrate was applied. The foaming height started decreasing with further increasing viscosity. Based on the experimental data, a semiempirical equation of foaming height was developed. The predictions of the model agreed well with experimental data. The model could also reasonably well explain the industrial pilot trial experiments. The experimental results with paraffin particle additions indicated that a small amount of particle addition moved the onset of foaming to lower superficial velocity. However, the increase in viscosity due to the presence of solid particles was found not the main reason for the increase in foaming height.

Keyword
Slag foaming, Mathematical modelling, Physical modelling
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27973 (URN)10.1179/030192310X12690127076550 (DOI)000285043500010 ()2-s2.0-78649600385 (ScopusID)
Note
QC 20110103 Available from: 2011-01-03 Created: 2011-01-03 Last updated: 2011-04-19Bibliographically approved
4. Study of Open Eye Formation in an Argon Stirred Ladle
Open this publication in new window or tab >>Study of Open Eye Formation in an Argon Stirred Ladle
2010 (English)In: STEEL RES INT, ISSN 1611-3683, Vol. 81, no 7, 508-515 p.Article in journal (Refereed) Published
Abstract [en]

Two cold models were employed to simulate the formation of open-eyes in a gas stirred ladle. In the first model, water and silicon oils were employed to simulate liquid steel and slag respectively. In the second one, liquid Ga-In-Sn alloy was used to simulate liquid steel, while 12% hydrochloric acid simulated the top slag. The experimental results indicated that the gas flow rate, height of the lower liquid and height of the top liquid has a strong impact on the open-eye size. On the other hand, the viscosity of the top liquid and the interfacial tension between the two liquids had only little effect on the open-eye size. A semi-empirical model was developed to describe the size of open-eye as a function of the heights of the two adults and the gas flow rate. The two sets of parameters obtained for the the water and Ga-In-Sn models were very different Industrial trials were also conducted to examine the applicability of the models. The model developed based on the Ga-In-Sn model could well predict the formation of an open-eye during ladle treatment. The model could be adopted by the industry to estimate the real gas flow rate by measuring the size of the open-eye online. On the other hand, the mathematical model based on water model experiments was unsatisfactory when applied to the industrial ladle process.

Keyword
ladle treatment, open-type, modelling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-26865 (URN)10.1002/srin.201000063 (DOI)000280782000003 ()2-s2.0-77956590384 (ScopusID)
Note
QC 20101201Available from: 2010-12-01 Created: 2010-11-29 Last updated: 2011-04-19Bibliographically approved
5. Study of slag droplet formation in a gas-stirred ladle using cold models
Open this publication in new window or tab >>Study of slag droplet formation in a gas-stirred ladle using cold models
2011 (English)In: Steel Grips - Journal of Steel and Related Materials, ISSN 1611-4442, Vol. 9, 51-55 p.Article in journal (Refereed) Published
Abstract [en]

Two cold models were employed to simulate the formation of slag droplets in a gas-stirred ladle. How do gas flow rate and interfacial tension between bath liquid and top liquid effect droplet size? Further, a semi-empirical model was developed to describe the size of the droplets of the water model. What else can it be used for with reasonably good agreement?

Keyword
Droplet size, water model, tungstate-silicone oil model, ladle, semi-empirical model
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-32734 (URN)
Note
QC 20120328Available from: 2011-04-19 Created: 2011-04-18 Last updated: 2012-03-28Bibliographically approved

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