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A study of some aspects of gas-slag-metal interactions: Towards dynamic process model and control
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis deals with the development of a new type of dynamic model for metallurgical reactors. It also covers some of the theoretical aspects of steelmaking that is necessary to include in such an application. The thesis consists of modeling work, high temperature experiments and cold model experiments.

Two different aspects of slags in the oxygen steelmaking were investigated. In the first study, slag samples were equilibrated with copper at 1923K in order to study their capacities in capturing phosphorous. Some of the samples were liquid-solid mixtures. The solid phases in these samples were identified by SEM analysis. The identified phases were found to agree well with Thermocalc calculations while the amount of solid fractions didn’t. The phosphorous distribution between the different phases was examined. The phosphate capacities of the samples were evaluated. The MgO content didn’t show any appreciable impact on the phosphate capacity. Furthermore the activities of FeO in the liquid slag samples were calculated and were found to deviate positively from ideality. In the second study the foaming height of CaO-SiO2-FeO slags by the reaction with hot metal was investigated. It was found that the foaming height increased with increasing FeO content up to 20-25%. The foaming height was seen to decrease with increased viscosity. The present results indicated that simply using foaming index for converter slag might lead to wrong conclusion.

Simulation experiments using cold model at room temperature were conducted. Cold model experiments were carried out in order to study the penetration depth due to an impinging gas jet on the surface of a liquid metal. The liquid alloy Ga-In-Sn was used to simulate steel. And an HCl solution was used to simulate the slag. A comparison with predictions of existing models was made and a new model parameter was suggested. The observation of the movement of metal droplets generated by the gas jet was also made. The low velocity of droplets suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag.

Furthermore a study of the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was carried out. Both industrial trials and cold model experiments were conducted. As an auxiliary tool CFD was used to predict the mixing times and was found to agree well with both the model experiments and industrial data. The increase of flow rate of inert gas would not improve the mixing substantially at higher flow rates. The water model study showed also that the gas flow rate had negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that low gas flow rate should be applied in the ladle treatment.

Lastly a new approach to a dynamic process model of 300 ton BOF converter was made. The main feature was to utilize the velocity vectors obtained by CFD simulation. In the standalone model, the steel melt domain was sliced into 1000 cells. Based on the imported velocity vectors from the CFD calculation, the mass transfer of carbon and phosphorus was calculated taking into account the slag metal reactions. The mass exchange between slag and metal was considered to be dominated by the metal droplet formation due to oxygen jet. The convergence of the model calculation and the promising comparison between the model prediction and the industrial data strongly suggested that the proposed approach would be a powerful tool in dynamic process control. However, more precise descriptions of other process aspects need to be included before the model can be practically employed in a dynamic controlling system.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 59 p.
Keyword [en]
BOF, process modeling, phosphorous capacity, penetration depth, slag foaming, mixing time, inclusion removal
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-101460ISBN: 978-91-7501-456-2 (print)OAI: oai:DiVA.org:kth-101460DiVA: diva2:547841
Public defence
2012-09-27, H1, Teknikringen 33, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20120829

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2012-08-29Bibliographically approved
List of papers
1. Capacities of some CaO-SiO2-FeO-MnO-MgO slags and slag-solid mixtures in capturing phosphorous
Open this publication in new window or tab >>Capacities of some CaO-SiO2-FeO-MnO-MgO slags and slag-solid mixtures in capturing phosphorous
2013 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 4, 305-311 p.Article in journal (Refereed) Published
Abstract [en]

Slag is of great importance for dephosphorisation in converter steelmaking. In the present study, slag samples were equilibrated with copper at 1923 K to study their capacities in capturing phosphorous. The phosphate capacities of the slags were calculated. Some of the samples were liquid-solid mixtures. The solid phases in these samples were identified by SEM analysis, and the identified phases were found to agree well with Thermocalc calculations. On the other hand, the fractions of the solid phase did not agree with the Thermocalc calculation. Phosphorous distributions in the different phases were examined, and the phosphate capacities of the samples were evaluated. The MgO content did not show any appreciable impact on the phosphate capacity. The activities of FeO in the pure liquid slag samples were calculated and found to deviate positively from ideality.

Place, publisher, year, edition, pages
Maney Publishing, 2013
Keyword
Phosphate capacity, Converter, Slag, Activity of FeO, Solid particles
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101409 (URN)10.1179/1743281212Y.0000000039 (DOI)000318680800011 ()2-s2.0-84877130980 (Scopus ID)
Note

QC 20130618

Available from: 2012-08-29 Created: 2012-08-28 Last updated: 2017-12-07Bibliographically approved
2. Study of Penetration Depth and Droplet Behavior in the Case of a Gas Jet Impinging on the Surface of Molten Metal using Liquid Ga-In-Sn
Open this publication in new window or tab >>Study of Penetration Depth and Droplet Behavior in the Case of a Gas Jet Impinging on the Surface of Molten Metal using Liquid Ga-In-Sn
2012 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 83, no 7, 678-685 p.Article in journal (Refereed) Published
Abstract [en]

To study the penetration depth in the case of a gas jet impinging on the surface of liquid steel, cold model experiments were carried out using a liquid alloy GaInSn, which had similar physical properties as liquid steel. A HCl solution was used to simulate the top slag. The top phase was found to have appreciable effect on the penetration depth. Comparison of the experimental data with the predictions of the existing models indicated that most the model predictions deviated from the experimental results at higher lance heights and gas flow rates. New model parameter was suggested based on the present experimental data. The observation of the formation and movement of metal droplets generated by the gas jet was also made. The velocity of the droplet was found to be at a level only about 1% of the terminal velocity. This low velocity suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag.

Keyword
BOF, penetration depth, droplet, residence time
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-99413 (URN)10.1002/srin.201100336 (DOI)000305967700008 ()2-s2.0-84863682755 (Scopus ID)
Funder
EU, European Research Council
Note
QC 20120731Available from: 2012-07-31 Created: 2012-07-30 Last updated: 2017-12-07Bibliographically approved
3. Study on foaming of CaO-SiO2-FeO slag by the reaction with hot metal
Open this publication in new window or tab >>Study on foaming of CaO-SiO2-FeO slag by the reaction with hot metal
2012 (English)Manuscript (preprint) (Other academic)
Abstract [en]

In the present study the foaming of CaO-SiO2-FeO slags is investigated. The foaming height induced by the reaction between slag and hot metal were carried out. It was found that the foaming height increases with increased FeO content up to 20-25%. The foaming height was seen to decrease with increased viscosity. The present results indicated that simply using foaming index for converter slag might lead to wrong conclusion.

Publisher
7 p.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101417 (URN)
Note

QC 20120829

Available from: 2012-08-29 Created: 2012-08-28 Last updated: 2012-08-29Bibliographically approved
4. Effect of Inert Gas Flow Rate on Homogenization and Inclusion Removal in a Gas Stirred Ladle
Open this publication in new window or tab >>Effect of Inert Gas Flow Rate on Homogenization and Inclusion Removal in a Gas Stirred Ladle
2010 (English)In: STEEL RES INT, ISSN 1611-3683, Vol. 81, no 12, 1056-1063 p.Article in journal (Refereed) Published
Abstract [en]

In the present study, the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was investigated. Both industrial trials and cold model experiments were conducted. CFD calculation was also carried out as an auxiliary tool. The mixing times predicted by CFD simulation agreed well with both the model experiments and industrial data. 99% mixing could be achieved in about 2-3 minutes. The increase of flow rate of inert gas would not improve the mixing substantially, while the mixing time decreased somewhat with the increase of gas flow rate. The water model study showed also that the gas flow rate had a negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that a low gas flow rate should be applied in the ladle treatment.

Keyword
MIXING PHENOMENA, NONMETALLIC INCLUSIONS, NUMERICAL-SIMULATION, LIQUID REACTIONS, FLUID-FLOW, OPEN-EYE
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-30250 (URN)10.1002/srin.201000102 (DOI)000285896000003 ()2-s2.0-78649813495 (Scopus ID)
Funder
EU, European Research Council
Note

QC 20110222

Available from: 2011-02-22 Created: 2011-02-21 Last updated: 2012-08-29Bibliographically approved
5. A new approach towards dynamic modelling of dephosphorisation in converter process
Open this publication in new window or tab >>A new approach towards dynamic modelling of dephosphorisation in converter process
2012 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 39, 77-84 p.Article in journal (Refereed) Published
Abstract [en]

A new approach was made to model the dephosphorisation process in a 300 tons basic oxygen furnace converter with three argon gas inlets. The main feature of the new approach was to utilise the velocity vectors obtained by computational fluid dynamics (CFD) simulation in a standalone model. The CFD simulation was carried out using commercial software COMSOL Multiphysics. In the standalone model, the steel melt domain was sliced into 1000 cells. The calculated velocity vector in each cell was assumed constant. Based on the imported velocity vectors from the CFD calculation, the mass transfer of carbon and phosphorus was calculated by taking into account the slag-metal reactions. The mass exchange between slag and metal was considered to be dominated by the metal droplet formation due to the oxygen jet. The convergence of the model calculation and the promising comparison between the model prediction and the industrial data strongly suggested that the proposed approach would be a powerful tool in dynamic process control. As a preliminary step, the model only simulated the process after the formation of slag-metal-gas emulsion. Note that the present work is intended to establish a structure of the model. More precise descriptions of other process aspects need to be included before the model can be practically employed in a dynamic controlling system.

Keyword
BOF, Dynamic model, CFD, Dephosphorisation
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-66978 (URN)10.1179/1743281211Y.0000000057 (DOI)000298489400001 ()2-s2.0-84855361235 (Scopus ID)
Note

QC 20120127

Available from: 2012-01-27 Created: 2012-01-27 Last updated: 2017-12-08Bibliographically approved

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