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Fundamental Experimental and Numerical Investigation Focusing on the Initial Stage of a Top-Blown Converter Process
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of this thesis work is to increase the knowledge of phenomena taking place during the initial stage in a top blown converter. The work has been done in a few steps resulting in four different supplements. Water model experiments have been carried out using particle image velocimetry (PIV) technology. The system investigated was a fundamental top blown converter where an air jet was set to impinge on a water surface. The flow field of the combined blown case, where an air jet was introduced through a bottom nozzle, was also captured by the PIV. The work clearly showed that the flow field caused by an impinging top blown jet alone could not match that of the bottom blown case. The main re-circulation loop (or vortex) was investigated with respect to position and it was found that an increased flow rate pushes the center of the re-circulation loop downwards into the bath. However, for the top-blown case there is a point when the flow rate is too large to cause a distinguishable re-circulation loop since the jet becomes more plunging (i.e. penetrates deep into the bath) than impinging, with large surface agitation and splashing as a result.A numerical model with the same dimensions as the experimental system was then created. Three different turbulence models from the same family were tested: standard-, realizable- and a modified-(slight modification of one of the coefficients in order to produce less spreading of the air jet) k-ε turbulence model. It could be shown that for the family of k-ε turbulence models the difference in penetration depth was small and that the values corresponded well to literature data. However, when it comes to the position of the re-circulation loop it was shown that the realizable k-ε model produced better results when comparing the results to the experimental data produced from the PIV measurements, mentioned earlier.It was then shown how the computational fluid dynamics (CFD) model could be coupled to thermodynamics databases in order to solve for both reactions and transport in the system. Instead of an air-water system, a gas-steel-slag system was created using the knowledge obtained in the previous simulation step described above. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag were considered. Extrapolation of data from a few seconds of simulation was used for comparison to experimental data from the literature and showed reasonable agreement. The overall conclusion was that it is possible to make a coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.A parametric study was then undertaken where two different steel grades were tested; one with high initial carbon content (3.85 mass-%) and one with lower carbon content (0.5 mass-%). The initial silicon content was held constant at 0.84 mass-%. Different initial temperatures were tested and also some variation in initial dissolved oxygen content was tried. It was found that the rate of decarburization/desiliconization was influenced by the temperature and carbon concentration in the melt, where a high temperature as well as a high carbon concentration favors decarburization over desiliconization. It was also seen that the region affected by a lower concentration of alloys (or impurities) was quite small close to the axis where the impinging jet hits the bath. Add the oscillating nature of the cavity and it was realized that sampling from this region during an experiment might be quite difficult.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , viii, 43 p.
Keyword [en]
numerical modeling, top-blown converter, BOF, CFD, Thermodynamics, slag, dynamic simulations
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-9310ISBN: 978-91-7415-150-3 (print)OAI: oai:DiVA.org:kth-9310DiVA: diva2:54647
Public defence
2008-11-07, B2, Brinellvägen 23, 10044 Stockholm, KTH, 10:00 (English)
Opponent
Supervisors
Note
QC 20100720Available from: 2008-10-21 Created: 2008-10-17 Last updated: 2010-07-20Bibliographically approved
List of papers
1. Fluid Flow in a Combined Top and Bottom Blown Reactor
Open this publication in new window or tab >>Fluid Flow in a Combined Top and Bottom Blown Reactor
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2006 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 8, 1137-1142 p.Article in journal (Refereed) Published
Abstract [en]

Physical modeling was done to study the flow field in a cylindrical bath agitated by bottom purging, top lance blowing and a combination of both injection types. A particle image velocimetry (PIV) system has been used to capture the velocity field of all three cases mentioned above. Special attention was paid to the recirculation loop. Top blowing creates a re-circulation loop in a relatively small volume close to the surface, compared to bottom- and combined-blowing. Increasing bottom flow rate moves the center of the re-circulation loop downwards into the liquid. When top blowing is combined with bottom blowing the center of the re-circulation loop is moved downwards into the liquid with increasing top lance flow rate.

Keyword
fluid flow, reactor, bottom purging, lance blowing
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-9305 (URN)10.2355/isijinternational.46.1137 (DOI)000240083800004 ()2-s2.0-33750090365 (Scopus ID)
Note
QC 20100720Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-07Bibliographically approved
2. A Mathematical Model of an Impinging Air Jet on a Water Surface
Open this publication in new window or tab >>A Mathematical Model of an Impinging Air Jet on a Water Surface
2008 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, no 4, 377-384 p.Article in journal (Refereed) Published
Abstract [en]

A fundamental mathematical model of the flow field and surface deformation caused by an impinging jet in a top blown reactor has been developed. The results have been validated against water model experiments. More specifically, the predicted penetration depth has been found to agree well with surface deformation measurements and predictions using analytical equations. Furthermore, the predictions of the location of a vortex have been found to agree fairly well with PIV measurements. Calculations were also done to compare the widely used standard k-ε model against the realizable extension of the standard k-ε model to calculate the turbulent conditions of the flow. It was found that the penetration depth caused by the impinging jet on the liquid surface is relatively unaffected by the choice of turbulence model employed. However, when the main re-circulation loop in the bath was investigated there was a clear distinction in the flow fields produced when the two different turbulence models were used.

Keyword
CFD; top blowing; BOF; impinging jet; k-ε model; mathematical modeling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-9307 (URN)10.2355/isijinternational.48.377 (DOI)000255321600001 ()2-s2.0-46749136887 (Scopus ID)
Note
QC 20100720Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-07Bibliographically approved
3. Dynamic Coupling of Computational Fluid Dynamics and Thermodynamics Software: Applied on a Top Blown Converter
Open this publication in new window or tab >>Dynamic Coupling of Computational Fluid Dynamics and Thermodynamics Software: Applied on a Top Blown Converter
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2008 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, no 2, 147-153 p.Article in journal (Refereed) Published
Abstract [en]

A novel modeling approach is presented where a computational fluid dynamics software is coupled to thermodynamic databases to obtain dynamic simulations of metallurgical process phenomena. The modeling approach has been used on a fundamental model of a top-blown converter. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag have been considered. The results show that the mass transport in the surface area is totally controlled by convection. Also, that a large amount of CO produced during the decarburization might slow down the rate of decarburization in droplets ejected from the bath. For the present simulation conditions reflecting laboratory experiments, it was also seen that the amount of slag (FeO and/or SiO2) created is close to zero, i.e. only gas (CO+CO2) is created as the oxygen jet hits the steel bath. It was also illustrated how an extrapolation of the decarburization rate, sampled from a few seconds of simulation, could be done to get a rough estimate of the carbon content at a later stage in the process as long as the carbon content is relatively high. The overall conclusion is that it is possible to make a dynamic coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.

Keyword
BOF; CFD; thermodynamics; modeling; slag and dynamic simulations.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-9308 (URN)10.2355/isijinternational.48.147 (DOI)000253367000005 ()2-s2.0-42349113835 (Scopus ID)
Note
QC 20100720Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-07Bibliographically approved
4. Dynamic Modeling of Steel, Slag and Gas Reactions during Initial Blowing in a Top-Blown Converter
Open this publication in new window or tab >>Dynamic Modeling of Steel, Slag and Gas Reactions during Initial Blowing in a Top-Blown Converter
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2008 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Article in journal (Other academic) Submitted
Abstract [en]

A dynamic modeling approach is presented where a computational fluid dynamics software is coupled to a thermodynamics software to obtain simulations of reactions between steel, slag and gas in a top-blown converter. For each simulation the transport of momentum, energy and mass of species as well as the thermodynamic equilibrium in each cell containing at least two phases was treated. The overall conclusion is that the present calculation procedure is successful for dynamic simulations of interaction between an oxygen gas jet with a melt and a slag. The predicted rate of decarburization was found to agree well with experimental data from laboratory trials. In addition, four cases where simulated for which the temperature, the dissolved carbon content and the dissolved oxygen content were varied. The most important findings from these comparisons were that: i) a higher initial oxygen concentration in the melt yields a larger decarburization rate, ii) carbon content also plays a big role for the desiliconization where a low carbon content is required for desiliconization to take place, iii) decarburization and desiliconization is largely influenced by the temperature at which reactions take place, where low temperature favors desiliconization and iv) the region affected by a lower carbon/silicon concentration (hot-spot region) directly below the jet was approximately 10 mm for the current setup.

Keyword
converter, CFD, thermodynamics, modeling, slag, gas
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9309 (URN)
Note
QS 20120314Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-07Bibliographically approved

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