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Modelling Decarburization in the AOD Converter: A Practical CFD-Based Approach with Chemical Reactions
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Process.ORCID iD: 0000-0001-6200-1920
Outokumpu Stainless AB.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.ORCID iD: 0000-0001-8797-4585
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Process.ORCID iD: 0000-0003-4384-7984
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Gas blowing technology is widely used in converter steelmaking to homogenize liquid steel and accelerate chemical reactions, with Argon oxygen decarburization (AOD) being the dominant process for stainless steelmaking. Due to the harsh environment, it is advisable to study the phenomenon using small-scale physical models and numerical simulations before conducting industrial-scale trials. This paper presents a practical computational fluid dynamics (CFD) approach for simulating the AOD process, with chemical reactions considered. This approach can simulate the entire process in a reasonable time using a standard workstation. The simulation employs a Finite Volume Method CFD approach to handle mass, momentum and energy transfer, and a local equilibrium assumption is utilized. The study shows that a practical approach can be used to model the initial stage of decarburization in the AOD process with a reduced accuracy in mass transport calculations. The accuracy of the simulation is validated using industrial data, and good agreement is found.

Keywords [en]
AOD process, decarburization reactions, coupled model, CFD
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-339864OAI: oai:DiVA.org:kth-339864DiVA, id: diva2:1813611
Note

QC 20231122

Available from: 2023-11-21 Created: 2023-11-21 Last updated: 2023-11-22Bibliographically approved
In thesis
1. Mixing Time and Decarburization Reactions in Side-blown Metallurgical Converters: A Practical Approach using CFD and Thermodynamics
Open this publication in new window or tab >>Mixing Time and Decarburization Reactions in Side-blown Metallurgical Converters: A Practical Approach using CFD and Thermodynamics
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The side-blowing Argon Oxygen converter (AOD), known for its intense gas stirring and turbulentnature, poses complex fluid dynamics and thermodynamic challenges. Modeling has played asubstantial role in the development of metallurgical converters, particularly in understanding jetbehavior, mixing, flow patterns, and chemical reactions. Flow characteristics and mixing time arerecognized as crucial factors that enhance the efficiency and decarburization rate in metallurgicalreactors. However, to the best of the author's knowledge, no prior study has investigated the impactof mixing time on the decarburization reaction. While most studies suggest that reducing mixing timeis beneficial, it is reasonable to assume that there might be a point at which further reduction inmixing time does not lead to an increase in reaction rates. Adjustments like tilting the converter orrepositioning the nozzles could improve decarburization efficiency by altering pressure conditions andmixing. This study aims to explore how these factors affect the decarburization reaction in side-blownconverters through modeling. The work has been done in a few steps resulting in differentsupplements.Side-blowing water model experiments were carried out to investigate how a vessel inclination wouldaffect the mixing time. The results showed a clear increase in mixing time when higher inclinationangles (14°) were applied. However, studying the non-reacting water models could only give insightto mixing efficiency and not provide information about decarburization efficiency.A numerical model capable of integrating mass and heat transfer with high temperature chemicalreactions was developed to aid in this investigation. First, the model was applied to an ascending gasbubble in liquid steel. The effect of pressure was investigated by injecting the bubble in different bathdepths. It was shown that a mere oxygen bubble injected at the nozzle position under industrialconditions did not decarburize efficiently, rather dissolved into the steel. Only pressure levels at thebath surface could maintain gas as a stable phase and decarburize efficiently.With high grid resolutions the model consumed a lot of computational time calculating equilibriumlocally in each cell with gas and liquid present. Therefore, a more practical approach was taken tostudy the AOD converter that showed high agreement to the first decarburization step whencomparing against two industrial heats. It was shown that with a coarse Computational Fluid Dynamic(CFD) solution the model could be practical, yet fundamental. In the study it was also found that nochromium oxidation was found in one of the heats at the beginning of the process when the initialcarbon content was high. The trends were compared against an industrial online process model andshowed similar behavior.With further developments, the model was tested with different treatments of the thermodynamiccoupling, including reactions limited by turbulence in an intensely stirred side-blown reactor. Themixing time was shown to have an insignificant effect on the decarburization rate. The system wasgoverned by thermodynamics and gas supply rate.Overall, this work developed a general model capable of coupling chemical reactions with CFD. Theuse of this model led to the conclusion that an inclination of the vessel within practical operationalangles would not benefit the decarburization rate in the early stages of decarburization. Withincreased mixing times and small pressure variations from the lowered bath height, the benefits todecarburization might not be worth compared to the engineering challenges posed by such changes.Even relocating the nozzle would require large and unpractical height differences to acquire thepressure decrease needed to benefit thermodynamically.

Abstract [sv]

AOD konvertern, känd för sin intensiva gasomrörning och turbulenta natur, ställer komplexautmaningar inom fluidmekanik och termodynamik. Modellering har spelat en betydande roll iutvecklingen av metallurgiska konvertrar, särskilt för att förstå jetbeteende, omrörning, flödesmönsteroch kemiska reaktioner. Flödesegenskaper och omrörningstid betraktas som avgörande faktorer somförbättrar effektiviteten och kolfärskningshastigheten i metallurgiska reaktorer. Men enligtförfattarens kännedom har ingen tidigare studie undersökt effekten av omrörningstid på kolfärskning.Även om de flesta studier föreslår att en minskning av omrörningstiden är fördelaktig, är det rimligtatt anta att det kan finnas en punkt där ytterligare minskning av omrörningstiden inte leder till enökning av reaktionshastigheten. Justeringar som att luta konvertern eller omplacera dysorna kanförbättra kolfärskningseffektiviteten genom att ändra tryckförhållandena och omrörningen. Måletmed denna studie är att utforska hur dessa faktorer påverkar kolfärskningsreaktionen i sidoblåstakonvertrar genom modellering. Arbetet har utförts i flera steg med olika tillägg.Experiment med vattenmodeller av sidoblåst gas utfördes för att undersöka hur en lutning avbehållaren skulle påverka omrörningstiden. Resultaten visade tydligt en ökning av omrörningstidennär högre lutningsvinklar (14°) användes. Dock kunde studier av icke-reaktiva vattenmodeller bara geinsikt om omrörningseffektivitet och inte ge information om hur effektiv kolfärskningen är.En numerisk modell som kan integrera mass- och värmetransport med kemiska reaktioner vid högatemperaturer utvecklades för att hjälpa till med denna undersökning. Först tillämpades modellen påen stigande gasbubbla i smält stål. Effekten av trycket undersöktes genom att injicera bubblan på olikabadnivåer. Det visades att en enkel bubbla injicerad vid dys positionen under industriella förhållandeninte kolfärskade effektivt, utan löstes in i stålet. Endast trycknivåer vid badytan kunde behålla gasensom en stabil fas och kolfärska effektivt.Med hög upplösning på beräknings celler krävde modellen mycket tid för att beräkna jämvikt lokalt ivarje cell med gas och vätska närvarande. Därför användes ett mer praktiskt tillvägagångssätt för attstudera AOD-konvertern, som visade bra överensstämmelse med det första färsknings stegetgentemot två industriella charger. Det visades att med grova lösningar inom beräkningsfluidmekanikkunde modellen vara praktisk men grundläggande. Resultaten visade även att Ingen kromoxidationhittades i en av omgångarna i början av processen när den initiala kolhalten var hög. Trendernajämfördes med en industriell online-processmodell och visade liknande beteende.Med ytterligare utveckling testades modellen med olika behandlingar av termodynamisk koppling,inklusive reaktioner begränsade av turbulens i en intensivt omrörd sidoblåst reaktor. Omrörningstidenvisade sig ha en obetydlig effekt på kolfärsknings hastigheten; istället styrdes systemet avtermodynamik och gasleveranshastighet.Sammanfattningsvis utvecklades en generell modell i detta arbete som kan koppla samman kemiskareaktioner med fluiddynamiska beräkningar. Användningen av denna modell ledde till slutsatsen atten lutning av behållaren inom praktiska driftsvinklar inte skulle gynna färskningshastigheten i detidiga stadierna av kolfärskning. Med ökade omrörningstider och små tryckvariationer från sänktbadnivå skulle fördelarna med kolfärskning vara små jämfört med de tekniska utmaningar somsådana förändringar medför. Även omplacering av dysan skulle kräva stora och opraktiskahöjdskillnader för att uppnå den trycksänkning som behövs för att gynna termodynamiken.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2023. p. 156
Series
TRITA-ITM-AVL ; 2023:32
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-339867 (URN)978-91-8040-757-1 (ISBN)
Public defence
2023-12-15, F3 / https://kth-se.zoom.us/j/63405242900, Lindstedtsvägen 26, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

Paper 3 of the thesis is published after the posting of the thesis, but before the defence as: https://doi.org/10.1007/s11663-023-02971-6

QC 20231205

Available from: 2023-11-21 Created: 2023-11-21 Last updated: 2023-12-11Bibliographically approved

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Chanouian, SergLarsson, HenrikErsson, Mikael

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