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Dynamic Modeling of Steel, Slag and Gas Reactions during Initial Blowing in a Top-Blown Converter
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0003-1919-9964
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
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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.

Place, publisher, year, edition, pages
2008.
Keyword [en]
converter, CFD, thermodynamics, modeling, slag, gas
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-9309OAI: oai:DiVA.org:kth-9309DiVA: diva2:54645
Note
QS 20120314Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Fundamental Experimental and Numerical Investigation Focusing on the Initial Stage of a Top-Blown Converter Process
Open this publication in new window or tab >>Fundamental Experimental and Numerical Investigation Focusing on the Initial Stage of a Top-Blown Converter Process
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
numerical modeling, top-blown converter, BOF, CFD, Thermodynamics, slag, dynamic simulations
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-9310 (URN)978-91-7415-150-3 (ISBN)
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

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