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O aço é um insumo de usos diversos que variam desde a construção civil, até a confecção de bens de consumo. Sob a perspectiva ambiental, as transformações que ocorrem nessa cadeia produtiva se destacam pelos elevados consumos de insumos e de energia - nas formas elétrica e térmica -, e por emissões para o Meio Ambiente. Assim, o grande desafio das siderúrgicas é encontrar alternativas que reduzam os impactos ambientais associados aos seus processos. Esta busca requer porém, uma análise sistêmica e integrada que considere o produto final em todo seu ciclo de vida. Este estudo tem por finalidade a avaliação do desempenho ambiental da produção de aço líquido para um arranjo tecnológico médio no país. Para tanto, utilizou-se a ferramenta de Análise de Ciclo de Vida (ACV). Embora o diagnóstico tenha sido efetuado sobre todas as etapas de processamento, optou-se por evidenciar etapas que fossem inerentes do processamento do aço líquido. O diagnóstico inicial, então, revelou que as principais etapas responsáveis pelos impactos ambientais inerentes ao processo são: a) produção de energia elétrica do Grid brasileiro, b) a manufatura do aço e c) captação e transporte de água. A partir desta vistoria de etapas inerentes pôde-se propor cenários de melhoria de desempenho ambiental para o processo de produção do aço líquido, a saber: I) Aproveitamento de Gás de Aciaria para produção de Energia Elétrica e II) Instalação de Tecnologia de apagamento a seco do coque. Embora o Cenário III não esteja contemplado nas cargas inerentes de processo, o mesmo foi efetuado a partir de solicitação da empresa: III) Substituição do fornecimento de Minério de Manganês. A técnica de ACV foi novamente aplicada com o intuito de verificar a validade das ações propostas. O estudo concluiu que houve melhorias relevantes no desempenho ambiental principalmente nos modelos CED e USEtox, em todas a categorias de impacto apresentadas (Fósseis Não Renováveis, Nuclear Não Renovável, Biomassa Não Renovável, Biomassa Renovável, Energia decorrente de efeitos naturais, Água Renovável, Toxidade Humana a Câncer, Toxidade Humana Não Câncer e Ecotoxidade Aquática) para os Cenário I e II. Pouco impacto foi observado no modelo ReCiPe Midpoint (H) para o Cenário I e II a não ser pela piora na categoria de impacto de Formação de Oxidantes Fotoquímicos para o Cenário II. Isso aconteceu por um aumento na emissão de monóxido de carbono descrito pela proposição. O Cenário III apresentou melhoria significativa apenas de uma categoria de impacto: Depleção de Metais, devido redução da depleção manganês, explicada pela melhoria de qualidade na troca de fornecedores. / Steel is an input for various uses ranging from construction, to the production of consumer goods. From an environmental perspective the changes that occur in the production chain are highlighted by high consumption of raw materials and energy - in electric and thermal forms - and emissions to the environment. So the great challenge of the steel is to find alternatives that reduce environmental impacts associated with their processes. This search, however, requires a systemic and integrated analysis that considers the final product throughout its life cycle. This study aims to evaluate the environmental performance of the liquid steel production to an average technological arrangement in the country. For this, we used the Life Cycle Analysis Tool (ACV). Although the diagnosis has been made on all processing stages, we chose to highlight steps that were inherent in the liquid steel processing. The initial diagnosis then revealed that the main stages responsible for the environmental impacts inherent in the process are: a) electricity production of the Brazilian Grid, b) the manufacture of steel and c) uptake and transport of water. From this survey inherent steps could be proposed improvement scenarios of environmental performance for the liquid steel production process, as follows: I) Steelmaking Gas Utilization for Production of Electricity and II) Coke Dry Quenching Tecnology. Although Scenario III is not contemplated in the process of inherent charges, the same was made on request from the company: III) Replacing the supply of manganese ore. The LCA technique was applied again in order to verify the validity of the proposed actions. The study concluded there were significant improvements in the environmental performance mainly in CED and USEtox models in all the presented impact categories (Fossils Renewable Not Nuclear Renewable No Biomass Renewable Non Renewable Biomass Energy from natural effects, Renewable Water, Toxicity Human to Cancer, Human Toxicity Ecotoxicity not Cancer and Frashwater Ecotoxity) for Scenario I and II. Little impact was observed in the model ReCiPe Midpoint (H) for Scenario I and II unless the worsening Photochemical Oxidant Formation impact category for Scenario II. This happened by an increase in carbon monoxide emission described by the proposition. Scenario III showed significant improvement only in a depletion impact category metals due reducing manganese depletion, explained by the improvement of quality of switching suppliers.

Abstract Non-metallic inclusions are unavoidable particles in steel and are often detrimental to the steelmaking process and the mechanical properties of the steel. While it is not feasible to remove all inclusions, in the well-established calcium treatment of aluminium-killed steel, solid aluminium oxides are transformed into less harmful liquid calcium aluminates. The main objective of this work was to develop a new inclusion identification and classification method. The presented method offers valuable information on phases of the inclusions. This data is often buried within simple inclusion classification criteria. The method offers the best approximation of the phases in each inclusion detected with minimal time, if no time-consuming elemental map analyses are available. In this work, applications for the inclusion phase identification method are presented. Utilising the method, the dispersion and evolution of inclusions during the sampling of liquid steel in lollipop samples is investigated, as well as the evolution of inclusions during continuous casting. New information is obtained on the elongation of inclusions and formation of oxide–sulphide stringers during hot rolling. The results for the investigated steels show that with sulphur contents higher than 10 ppm, calcium aluminates were back-modified to alumina and spinel inclusions during casting. However, with decreasing sulphur contents, and adequate simultaneous calcium treatment of oxides, Al₂O₃ and spinel formation is hindered or even avoided. The most elongated inclusions are often also found in stringers. According to the results of this study, low melting calcium aluminate inclusions are not the most elongated oxide inclusions in the hot rolled product. With moderate calcium treatment, an optimal oxide composition can be obtained, found within the C12A7–CA–MgO composition. These liquid inclusions ensure good castability, while they do not easily elongate or fragment into detrimental stringers after continuous casting. / Tiivistelmä Epämetalliset sulkeumat ovat väistämättä osa terästä, ja ne aiheuttavat ongelmia prosessille ja teräksen mekaanisille ominaisuuksille. Sulkeumien poiston sijaan niiden koostumusta muokataan kalsiumkäsittelyllä. Tällöin kiinteät alumiinioksidit muuttuvat vähemmän ongelmallisiksi suliksi kalsiumaluminaateiksi. Tämän työn päätavoitteena oli kehittää uusi sulkeumien tunnistus- ja luokittelumenetelmä. Sulkeuma-analyysien data voi jäädä hyödyntämättä, jos luokitteluun käytetään yksinkertaisia kriteerejä. Työssä esitetty menetelmä antaa parhaan arvion sulkeumissa olevista faaseista, mikäli sulkeumista ei ole alkuainekarttoja, joiden muodostaminen vie huomattavasti aikaa. Väitöskirjassa esitetään sulkeumien tunnistus- ja luokittelumenetelmän soveltamiskohteita. Menetelmän avulla tutkitaan sulkeumien muutosta ja jakaantumista sulan teräksen näytteenotossa ja sulkeumakuvan muutosta jatkuvavalun aikana. Uutta tietoa esitetään oksidi-sulfidiketjujen muodostumisesta kuumavalssauksen aikana. Tutkituilla teräksillä rikkipitoisuuden noustessa yli 10 ppm:n sulat kalsiumaluminaatit takaisinmuokkautuvat kiinteiksi alumiinioksideiksi tai spinelleiksi jatkuvavalun aikana. Riittävän matalalla rikkipitoisuudella ja kohtuullisella kalsiumkäsittelyllä alumiinioksidien ja spinellien muodostumista voidaan hillitä tai jopa estää se. Tutkimuksessa esitetään, että kuumavalssauksessa venyvimmät sulkeumat muodostavat myös lukuisten sulkeumien oksidi-sulfidiketjuja, jotka ovat tuotteen ominaisuuksien kannalta haitallisia. Tulosten mukaan kalsiumaluminaatit, jotka sulavat matalimmissa lämpötiloissa, eivät kuitenkaan ole taipuvaisimpia venymään valssauksessa. Maltillisella kalsiumkäsittelyllä saavutetaan optimaalinen oksidikoostumus C12A7–CA–MgO-faasiseurueesta. Nämä sulkeumat ovat sulia jatkuvavalussa varmistaen teräksen valettavuuden. Toisaalta ne eivät helposti veny tai rikkoonnu ketjuiksi valssauksessa jatkuvavalun jälkeen.

Lors du traitement en poche de l’acier liquide, les inclusions sont transportées vers l’interface métal liquide/laitier où elles sont capturées. Près de l’interface, le mouvement des inclusions est ralenti sous l’effet des interactions hydrodynamiques avec celle-ci. Afin d’étudier ces interactions, deux maquettes froides ont été mises en œuvre, où les inclusions sont modélisées par des billes millimétriques de densité intermédiaire entre celles de deux liquides transparents. Ces dispositifs nous ont permis de mesurer les variations du coefficient de frottement fen fonction de d/R (d est la distance du centre de la bille à l’interface non déformée et R est le rayon de la bille) pour différentes valeurs du nombre de Bond particulaire Bop, du rapport de différences de densités β et du rapport de viscosités λ. Lorsque d⁄(R>2), les points expérimentaux sont en accord avec le modèle de Bart pour une interface indéformable. fdépend fortement de λ et faiblement de  et Bop.Lorsque d⁄(R≤2), on distingue deux modes de relaxation vers l’équilibre. Lorsque 〖Bo〗_p≪1, la déformation reste faible et le régime de Bart est suivi par le régime de Taylor où (f~R)⁄h (h est l’épaisseur du film de liquide séparant la particule de l’interface). Lorsque 〖Bo〗_p≳1, l’interface se déforme significativement pour atteindre localement la courbure de la bille et le drainage du film s’effectue en régime de Reynolds où f~(R⁄h)^3. Les variations de 1/f en fonction de l’écart à l’équilibre présentent une inflexion que nous attribuons à la transition vers le régime de Reynolds et qui apparaît d’autant plus tôt lors de la relaxation vers l’équilibre que λ est élevé. Dans le régime de transition, fne dépend que de l’écart à la position d’équilibre et de λ. En régime de Reynolds, fest une fonction croissante de λ, 〖Bo〗_p et β, en accord avec le modèle de drainage de Hartland. / In liquid steel ladle treatment, inclusions are transported towards the steel-slag interface before being captured. Near the interface, the inclusions rise up under the effect of gravity but their movement is delayed by the hydrodynamic interaction with the interface. An experimental study has been carried out, using two physical models. In both devices, the variations of the particle velocity are measured as a function of the distance d from the particle center to the non-deformed interface. Then, the friction coefficient f (i.e. the correction to the Stokes steady drag) is deduced. The dependence of f on the density difference ratio β, the particle Bond number 〖Bo〗_p and the viscosity ratio λ is examined. When d⁄R≳2, the experimental results agree well with Bart’s curves established for a non-deformable interface. f essentially depends on the viscosity ratio and weakly depends on β and 〖Bo〗_p. When d⁄R≲2, depending on the value of 〖Bo〗_p, two relaxation modes can be distinguished. When 〖Bo〗_p≪1, the deformation of the interface is weak and the Bart regime is followed by the Taylor regime. This regime is characterized by f~(R⁄h) where h is the film thickness separating the particle from the interface. When 〖Bo〗_p≳1, the interface is significantly deformed and its curvature tends locally to the particle curvature and the film drains in the Reynolds regime characterized by f~(R⁄h)^3. The variations of the experimental friction coefficient as a function of the deviation from the equilibrium position have an inflection point: it is attributed to the transition to the Reynolds regime. This transition appears earlier when the λ is higher. In the transition regime, fonly depends on the equilibrium deviation and on the viscosity ratio. In the Reynolds regime, the friction coefficient is an increasing function of λ, β and 〖Bo〗_p as predicted by Hartland drainage model.

O aço é um insumo de usos diversos que variam desde a construção civil, até a confecção de bens de consumo. Sob a perspectiva ambiental, as transformações que ocorrem nessa cadeia produtiva se destacam pelos elevados consumos de insumos e de energia - nas formas elétrica e térmica -, e por emissões para o Meio Ambiente. Assim, o grande desafio das siderúrgicas é encontrar alternativas que reduzam os impactos ambientais associados aos seus processos. Esta busca requer porém, uma análise sistêmica e integrada que considere o produto final em todo seu ciclo de vida. Este estudo tem por finalidade a avaliação do desempenho ambiental da produção de aço líquido para um arranjo tecnológico médio no país. Para tanto, utilizou-se a ferramenta de Análise de Ciclo de Vida (ACV). Embora o diagnóstico tenha sido efetuado sobre todas as etapas de processamento, optou-se por evidenciar etapas que fossem inerentes do processamento do aço líquido. O diagnóstico inicial, então, revelou que as principais etapas responsáveis pelos impactos ambientais inerentes ao processo são: a) produção de energia elétrica do Grid brasileiro, b) a manufatura do aço e c) captação e transporte de água. A partir desta vistoria de etapas inerentes pôde-se propor cenários de melhoria de desempenho ambiental para o processo de produção do aço líquido, a saber: I) Aproveitamento de Gás de Aciaria para produção de Energia Elétrica e II) Instalação de Tecnologia de apagamento a seco do coque. Embora o Cenário III não esteja contemplado nas cargas inerentes de processo, o mesmo foi efetuado a partir de solicitação da empresa: III) Substituição do fornecimento de Minério de Manganês. A técnica de ACV foi novamente aplicada com o intuito de verificar a validade das ações propostas. O estudo concluiu que houve melhorias relevantes no desempenho ambiental principalmente nos modelos CED e USEtox, em todas a categorias de impacto apresentadas (Fósseis Não Renováveis, Nuclear Não Renovável, Biomassa Não Renovável, Biomassa Renovável, Energia decorrente de efeitos naturais, Água Renovável, Toxidade Humana a Câncer, Toxidade Humana Não Câncer e Ecotoxidade Aquática) para os Cenário I e II. Pouco impacto foi observado no modelo ReCiPe Midpoint (H) para o Cenário I e II a não ser pela piora na categoria de impacto de Formação de Oxidantes Fotoquímicos para o Cenário II. Isso aconteceu por um aumento na emissão de monóxido de carbono descrito pela proposição. O Cenário III apresentou melhoria significativa apenas de uma categoria de impacto: Depleção de Metais, devido redução da depleção manganês, explicada pela melhoria de qualidade na troca de fornecedores. / Steel is an input for various uses ranging from construction, to the production of consumer goods. From an environmental perspective the changes that occur in the production chain are highlighted by high consumption of raw materials and energy - in electric and thermal forms - and emissions to the environment. So the great challenge of the steel is to find alternatives that reduce environmental impacts associated with their processes. This search, however, requires a systemic and integrated analysis that considers the final product throughout its life cycle. This study aims to evaluate the environmental performance of the liquid steel production to an average technological arrangement in the country. For this, we used the Life Cycle Analysis Tool (ACV). Although the diagnosis has been made on all processing stages, we chose to highlight steps that were inherent in the liquid steel processing. The initial diagnosis then revealed that the main stages responsible for the environmental impacts inherent in the process are: a) electricity production of the Brazilian Grid, b) the manufacture of steel and c) uptake and transport of water. From this survey inherent steps could be proposed improvement scenarios of environmental performance for the liquid steel production process, as follows: I) Steelmaking Gas Utilization for Production of Electricity and II) Coke Dry Quenching Tecnology. Although Scenario III is not contemplated in the process of inherent charges, the same was made on request from the company: III) Replacing the supply of manganese ore. The LCA technique was applied again in order to verify the validity of the proposed actions. The study concluded there were significant improvements in the environmental performance mainly in CED and USEtox models in all the presented impact categories (Fossils Renewable Not Nuclear Renewable No Biomass Renewable Non Renewable Biomass Energy from natural effects, Renewable Water, Toxicity Human to Cancer, Human Toxicity Ecotoxicity not Cancer and Frashwater Ecotoxity) for Scenario I and II. Little impact was observed in the model ReCiPe Midpoint (H) for Scenario I and II unless the worsening Photochemical Oxidant Formation impact category for Scenario II. This happened by an increase in carbon monoxide emission described by the proposition. Scenario III showed significant improvement only in a depletion impact category metals due reducing manganese depletion, explained by the improvement of quality of switching suppliers.

[pt] O pó de aciaria (fração Fina-F e fração Grossa-G) gerado no sistema de despoeiramento à seco dos gases de exaustão do conversor LD, e o pó de alto forno-AF recuperado pelo sistema de tratamento de gases do setor de redução (coletor de gases), têm papel relevante entre os materiais secundários gerados nos vários elos da cadeia produtiva de uma siderúrgica integrada, seja pelas quantidades produzidas, seja por suas composições. Por serem portadores principalmente de unidades de ferro e carbono e algumas vezes zinco, esses resíduos são sempre alvo de iniciativas tecnológicas que objetivem recuperá-los ou reciclá-los. Além disso, os materiais particulados gerados pelo sistema de despoeiramento a seco, diferentemente dos à úmido, ainda carecem de estudos aprofundados para suas reciclagens. Embora antiga, a briquetagem atualmente vem se tornando uma tecnologia cada vez mais importante entre os processos de aglomeração. Assim, nesta Tese foi estudado, numa primeira etapa, a viabilidade de fabricação dos chamados briquetes F-G simples, constituídos apenas pelos pós Finos e Grossos, nas proporções percentuais de 50-50 e 70-30, respectivamente, e o exame teórico e experimental de seus usos como carga ferrosa nos processos de redução e como materiais alternativos às sucatas e pelotas, quando adicionados ao aço líquido do conversor LD para o controle de sua temperatura. Na fabricação dos briquetes F-G simples, também buscou-se testar os aglomerantes cimento ARI e melaço de cana de açúcar, isoladamente ou quando misturados, atendendo às relações água/cimento de 0,5 e água/melaço de 0,7. O processo experimental de cura a frio dos aglomerados se estendeu até 28 dias. A resistência à compressão obtida em prensa hidráulica instrumentada foi o principal parâmetro para avaliar a qualidade mecânica dos briquetes. A metodologia experimental envolveu a técnica do planejamento fatorial, 2(k), níveis (mínimo e máximo), com três variáveis (resíduos, aglomerantes e água). Nos resultados verificou-se que a resistência à compressão dos briquetes F-G simples, usando o binômio cimento-melaço sempre apresentou valores mais elevados do que os briquetes quando aglutinados com as duas substancias isoladamente. Além disso, dentre os aglomerados produzidos os de teores mais elevados de fração Grossa (briquetes 50-50), apresentaram maior resistência mecânica que os briquetes tipo 70-30. Em relação aos efeitos de resfriamento que provocam quando adicionados ao aço liquido, os balanços térmicos mostraram que os briquetes do tipo 70-30 apresentariam melhores índices no controle da temperatura do banho de aço, que os do tipo 50-50. A fim de verificar como se comportariam os briquetes F-G anteriores, quando se adicionava o pó de coletor de AF nas suas constituições como fonte supridora de carbono e apenas o cimento ARI como aglutinante, foram produzidos os denominados briquetes autorredutores, também dos tipos F-G, 50-50 e 70-30. Além da viabilidade de fabricação desses aglomerados, foram determinadas suas qualidades mecânicas e levantadas suas metalizações em ensaios de redução nas temperaturas de 1100 graus Celsius e 1150 graus Celsius. O estudo cinético da autorredução foi realizado avaliando-se o grau de conversão a ferro metálico e examinada a fenomenologia de sua evolução. Os resultados evidenciaram que o grau de conversão metálica cresceu com o aumento da temperatura e com a quantidade da fonte de carbono, que a metalização apresentou uma morfologia final do tipo shell layer e que o modelo cinético testado, tipo reação continua, apresentou uma correlação acima de 99 por cento. Além disso, os balanços de energia mostraram que o efeito de resfriamento imposto ao aço liquido pelos briquetes F-G autorredutores, sempre se mostrou superior aos dos briquetes F-G simples. Adicionalmente, afim de melhor interpretar os resultados obtidos foram realizados testes adicionais, como o de reatividade do coque metalúrgico, via a norma ASTM D5341-99 e por aná / [en] The steel dusts (fine-F and coarse-G fractions) generated in the dry dedusting equipment of the LD converter exhaust system, and in the blast furnace-AF dust collector, play a relevant role among secondary materials generated in the various steps of the integrated steelmaking chain, either by the quantities produced and their compositions. Because they mainly contain iron and carbon units and sometimes zinc in their compositions, actually these wastes are being the target of several technological initiatives, aiming to recover or recycle them. Moreover, the particulate materials generated by the LD dry dedusting system, unlike those collected in the wet system of the same LD processes, still lack in-depth studies for recycling. Nowadays briquetting is increasing in importance among agglomeration processes, mainly due to its feature in treat particulate materials with a wide range of size. This thesis studied, in a first stage, the feasibility of manufacturing the so-called simple F-G briquettes, in the proportions of 50-50 and 70-30, respectively, as well as their theoretically and experimentally possibilities to be charged as a ferrous burden in reduction processes and as an alternative material to the scrap and pellets, when used to control the liquid steel temperature in LD converters. In the manufacture of the simple F-G briquettes, was also tested the binders ARI cement and sugarcane molasses, alone or when mixed, taking into account the water / cement ratio of 0,5 and the water / molasses ratio of 0,7. For the briquettes studied in this research, all cure operations lasted for up to 28 days and the compressive strength parameter obtained to evaluate the mechanical quality of the briquettes. The experimental methodology involved the technique of factorial planning, 2(k) levels (minimum and maximum), with three variables (residues, agglomerates and water). The results showed that the compressive strengths of the simple F-G briquettes, when using the cement-molasses mixture, always achieved higher values than that for briquettes using the cement or molasses separately. Moreover, the higher content of coarser fraction (briquettes 50-50) always leads to higher mechanical resistance than the finer one (70-30). On the other hand, the energy balances showed that the simple F-G briquettes 70-30, have presented the better cooling indexes for the liquid steel temperature control than the 50-50 briquettes. Regarding the second part of the thesis, two types of F-G self-reducing briquettes were also produced, containing stoichiometric and 10 percent excess of BF-collector dusts. After curing, they were tested on compression and reduced in temperatures of 1100 Celsius degrees and 1150 Celsius degrees. The kinetic study of the self-reducing briquettes was carried out evaluating the metallic iron conversion and the metallic iron phenomenology and morphology formation. The results showed: a) that the iron conversion increased as higher the temperature and amount of carbon; b) that the iron metallization presented a shell-layer type morphology and, c) that the continuous-reaction type kinetic model, adjusted very well the experimental reduction results, with a correlation factor above 99 percent. Additionally, in order to better understand the experiment results, the metallurgical coke reactivity was obtained using the ASTM D5341-99 test and the Differential Thermogravimetric analyzes (DTG), as well as confirmed the hydrated water amount in the passivated F and G dusts, also using the DTG methodology. Finally, considering the manufacturing feasibility of the both, simple and self-reducing F-G briquettes, the following could be also marked: I) The use of both briquettes type for liquid steel temperature control in LD converters, as effective alternative materials to scraps and pellets, considering the following comparative cooling indexes: a) 2,1 and 2,4 times the scrap, for the self-reducing briquettes 50-50 and 70-30, respectively, both with 10 percent excess; b) 1,7 and 1,9 times the scrap, for the simple briquettes, 50-50 and 70

<p>The electric arc furnace (EAF) is a critical steelmaking facility that melts the scrap by the heat produced from electrodes and burners. The migration to EAF steelmaking has accelerated in the steel industry over the past decade owing to the consistent growth of the scrap market and the goal of "green" steel production. The EAF production already hit a new high in 2018, contributing to 67% of total short tons of U.S. crude steel produced. The EAF steelmaking process involves dynamic complex multi-physics, in which electric arc plasma and coherent jets coexist resulting in an environment with local high temperature and velocity. Different heat transfer mechanisms are closely coupled and the phase change caused by melting and re-solidification is accompanied by in-bath chemical reactions and freeboard post-combustion, which further creates a complicated gas-liquid-solid three-phase system in the furnace. Therefore, not all conditions and phenomena within the EAF are well-understood. The traditional experimental approach to study the EAF is expensive, dangerous, and labor-intense. Most of the time, direct measurements and observations are impossible due to the high temperature within the furnace. To this fact, the numerical model has aroused great interest worldwide, which can help to gain fundamental insights and improve product quality and production efficiency, greatly benefiting the steel industry. However, due to the complexity of the entire EAF steelmaking process, the relevant computational fluid dynamics (CFD) modeling and investigations of the whole process have not been reported so far. </p> <p><br></p> <p>The present study was undertaken with the aim of developing the modeling methodologies and the corresponding comprehensive EAF CFD models to simulate the entire EAF steelmaking process. Two state-of-the-art comprehensive EAF CFD models have been established and validated for both the lab-scale direct current (DC) EAF and the industry-scale alternating current (AC) EAF, which were utilized to understand the physical principles, improve the furnace design, optimize the process, and perform the trouble-shootings.</p> <p><br></p> <p>For the lab-scale DC EAF, a direct-coupling methodology was developed for its comprehensive EAF CFD model which includes the solid steel melting model based on the enthalpy-porosity method and the electric arc model (for lab-scale DC arc) based on the Magneto Hydrodynamics (MHD) theory, so that the dynamic simulation of the steel ingot melting by DC arc in the lab-scale furnace can be achieved, which considered the continuous phase changing of solid steel, the ingot surface deformation, and the phase-to-phase interaction. Both stationary DC arc and the arc-solid steel interface heat transfer and force interaction were validated respectively against the experimental data in published literature. For the given lab-scale furnace, the DC arc behavioral characteristics with varying arc lengths generated by the moving electrode were analyzed, and the effects of both the initial arc length and the dynamic electrode movement on the steel ingot melting efficiency were revealed.</p> <p><br></p> <p>For the industry-scale AC EAF, an innovative integration methodology was proposed for its comprehensive EAF CFD model, which relies on the stage-by-stage approach to simulate the entire steelmaking process. Six simulators were developed for simulating sub-processes in the industry-scale AC EAF, and five models were developed for the above four simulators, including the scrap melting model, the electric arc model (for industry-scale AC arc), the coherent jet model, the oxidation model, and the slag foaming model, which can be partially integrated according to the mass, energy, and momentum balance. Specifically, the dual-cell approach and the stack approach were proposed for the scrap melting model to treat the scrap pile as the porous medium and simulate the scrap melting together with its dynamic collapse process. The statistical sampling method, the CFD-compatible Monte Carlo method, and the electrode regulation algorithm were proposed for the electric arc model to estimate the total AC arc power delivery, the arc radiative heat dissipation, and the instantaneous electrode movement. The energetic approach was proposed to determine the penetration of the top-blown jet in the molten bath based on the results from the coherent jet model. The source term approach was proposed in the oxidation model to simulate the in-bath decarburization process, where the oxidation of carbon, iron, and manganese as well as the effect of those exothermic reactions on bath temperature rising was considered. Moreover, corresponding experiments were performed in the industry-scale EAF to validate the proposed simulators. The quantitative investigations and analyses were conducted afterward to explore and understand the coherent jet performance, the AC arc heat dissipation, the burner preheating characteristics, the scrap melting behavior, the in-bath decarburization efficiency, and the freeboard post-combustion status.</p> <p><br></p>

En cas d' accident grave de réacteur nucléaire, la perte de réfrigérant peut conduire à la formation d'un mélange liquide à haute température (T>2500K) constitué majoritairement du combustible nucléaire et des matériaux de structure (corium). En cas de rupture de la cuve, le corium est susceptible d'interagir avec le béton de l'enceinte de confinement. Au contact du béton, la présence d'acier liquide modifie les processus d'ablation du béton et entraine une production de H2 et CO. Les objectifs de cette thèse étaient de déterminer la cinétique d'oxydation de l'acier liquide dans ces conditions, et d'identifier les mécanismes prépondérants. Pour répondre à ces objectifs, trois volets ont été développés: une approche à l'équilibre thermodynamique, des expériences analytiques à effets séparés et des expériences intégrales avec du corium prototypique. L'analyse des expériences intégrales montre que les gaz relâchés par le béton ne sont pas les seules sources d'oxydation, mais qu'une source d'oxydation extérieure au béton participe aux mécanismes d'oxydation. Les expériences analytiques ainsi que les calculs à l'équilibre thermodynamique ont montré que le corium, par sa capacité à devenir sur-stoechiométrique, est une source d'oxydation supplémentaire. Au contraire, les oxydes du béton ne participent pas au mécanisme d'oxydation. Le mécanisme d'oxydation de l'acier liquide est basé sur une oxydation relativement forte du chrome et du fer. Le nickel n'est pas oxydé, et serait consommé préférentiellement par Évaporation d'après les calculs thermodynamiques. L'étude cinétique de l'oxydation a permis d'une part d'établir deux lois cinétiques d'oxydation par O2 et CO2 et d'autre part de proposer une modélisation de la cinétique d'oxydation de l'acier lors des essais intégraux. / In case of severe nuclear accident, the loss of coolant leads to the formation of a high temperature liquid mixture (T>2500K) of nuclear fuel and structural materials inside the vessel. After the vessel failure, the corium could interact with the concrete of the reactor pit. The metallic phase inside the corium during corium-concrete interaction, changes the ablation processes and release H2 and CO. The aim of the PhD thesis was to study the kinetics and mechanisms of the liquid steel oxidation during corium-concrete interaction. In this way, the study was divided in three parts: with calculations at the thermodynamic equilibrium, with analytical experiments and with prototypical experiments. The results of oxidation analyses during prototypical experiments show that gases inside the concrete are not the only one source of oxidation and that another source outside the concrete have to participate to the oxidation mechanism. The analytical experiments and the thermodynamic approach show that the corium can oxidize the metallic phase whereas the concrete oxides cannot. The oxidation mechanism of liquid steel is based on high chromium and iron oxidation leading to their depletion. Oxidation of nickel does not occur, it would be mainly evaporated according to the thermodynamic calculations. Thanks to the kinetic study, the rates of the liquid steel oxidation by O2 et CO2 have been found and a phenomenological model have been proposed to estimate the steel oxidation during the prototypical experiments.