Extensive computer predictions have been carried out by the author to study flow, addition dispersion and particle motion during central gas injection into cylindrical vessels. In conjunction with numerical computations, experiments were conducted in a 0.30 scale water model of a 150 ton steel processing ladle, using a Froude number scaling criterion. Two typical gas injection configurations (i.e., conventional central injection and C.A.S. alloy addition procedure) were investigated. / Flow visualization studies were carried out using a suspended network of silken threads, mean velocity vectors and overall flow patterns were determined by video recording techniques, while mean velocity vectors and associated turbulence level were also measured with laser doppler velocimetry. These measurements show very reasonable agreement with equivalent numerical predictions. / To simulate the subsurface motion of additions, spherical wooden balls of various densities were dropped from typical heights, and their subsurface trajectories, immersion times, etc., recorded by means of a video recorder. Frame by frame analysis of the video tapes showed trends which are in good accord with computed trajectories. / Mixing times of simulated molten additions were measured by the conductivity measurement technique. These were compared with prediction from an equivalent tracer dispersion model and excellent agreement achieved. / For industrial application, flow, particle motion, and mixing times in a 150 ton steel processing ladle have been predicted and their technological significance discussed.

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Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008. / A full scale, three dimensional, transient, mathematical model was developed to simulate fluid flow and mixing in gas stirred ladles. The volume of fluid (VOF) and discrete phase (DPM) models were used in combination to account for multiphase aspects, and a slightly modified version of the standard - model was employed for turbulence modelling. The model was validated to compare well against published physical modelling results. Model results were interpreted from the fundamental grounds of kinetic energy transport within the ladle. This approach led to the specification of three key measures of mixing efficiency: The rate and efficiency of kinetic energy transfer from the buoyant gas to the bulk steel as well as the total kinetic energy holding capacity of the ladle. These measures describe the quantity of mixing in any specific ladle setup, whereas the traditional measure of mixing time reflects mixing quality, i.e. the degree of kinetic energy distribution through the entire ladle. The model was implemented in designed experiments to assess various operating and design variables pertaining to mixing quantity and quality. Considerable time was invested in finding the correct balance between numerical accuracy and computational time so that the model could be used to generate the required data within the given time frame. Experiments on the operating variables drew an important distinction between factors influencing the shape and the strength of gas induced flow patterns. Flow pattern strengthening variables, such as gas purge rate, significantly affected the quantity of mixing, but had a limited effect on mixing quality. Variables such as mass loading that influence the shape of the flow patterns had much larger potential to influence both the quantity and quality of mixing. Minimization of turbulence losses in the region of the plume eye was identified as the primary outcome of ladle design. It was shown that a taller vessel allowed more distance over which the plume could disperse, thereby reducing velocity gradients and subsequent turbulence generation at the free surface. Multiple tuyere systems yielded similar improvements by dividing the gas flow into several weakened plumes. Surface wave formation was investigated as an added mixing mechanism and demonstrated to be impractical for application in full scale gas stirred ladles. The conditions for resonance between the surface wave and the bubble plume were met only in vessels with a very low aspect ratio. Performance improvements offered by swirl in these ladles could easily be replicated in more practical ways. This study demonstrated the potential of mathematical modelling as a tool for in-depth investigation into fluid flow and mixing in the hostile environment of a full scale gas stirred ladle. Scaled-down cold models are the only alternative and can offer no more than a reasonably reliable predictive framework. The ease of flow data extraction from the numerical model also proved invaluable in facilitating a fundamental understanding of the effects of various important independent variables on ladle hydrodynamics. At this stage of development, however, the model is recommended for use on a comparative basis only. Two important developments are required for complete quantitative agreement: The inclusion of turbulence modulation by the bubbles and the increased turbulence kinetic energy dissipation rate in the vicinity of the free surface. A general strategy was developed to account for these effects and it compared favourably with published cold model results. Further research is required to generalize this approach for application in full scale gas stirred ladles.

O aumento da demanda por aços cada vez mais exigentes, em termos de composição química e limpidez interna, faz com que as condições de refino nas aciarias sejam cada vez mais severas. Ao mesmo tempo, o aumento dos tempos de tratamento do aço, aliado às outras variáveis operacionais como quantidades e tipos de adições químicas, etc. fazem com que haja um aumento no tempo de contato entre o revestimento refratário das panelas de transporte de aço e escórias com conseqüente redução do desempenho (vida) de tais revestimentos refratários. Apesar dos esforços no intuito de redução de custos com redução de consumos de refratários, é cada vez maior a pressão sobre os custos de produção e de segurança operacional. Neste sentido, a construção de modelos de previsão de vida em função de tais variáveis é de extrema importância para a gestão de processos e contratos, estabilidade operacional e segurança. Além disso, os estudos de post-mortem podem contribuir no sentido de compreensão física e química de tais fenômenos e mecanismos de desgaste, contribuindo assim para a validação de tais modelos determinísticos. Neste estudo, buscou-se verificar quais variáveis operacionais influem no desempenho (vida) das panelas através de correlações estatísticas. O modelamento levou em consideração os dados de 6 meses de operação da aciaria de uma usina integrada com capacidade de 4,5 Mt/ano. O estudo post-mortem realizado em uma das panelas, após o final de sua campanha, mostrou-se eficiente na validação de tais correlações e no entendimento físico e químico dos possíveis fenômenos e mecanismos de desgaste. As análises mostraram que as variáveis que impactam a vida das panelas de aço são a temperatura de vazamento do aço, temperatura do aço na panela pós vazamento, quantidade de aço chapas grossas (CG) produzido, rota de tratamento dessulfurado, tempo de panela cheia, participação do forno panela no refino secundário, condições da panela, carga de aço na panela, adições de nefelina, escória sintética, fios de cálcio silício (CaSi) e ferro alumínio cálcio (FeAlCa), ligas de manganês e tempos de tratamento no refino secundário. O estudo de post-mortem de amostras de refratário da linha de escória extraída de uma das panelas revelou que o principal mecanismo de desgaste desta região é a corrosão química pela escória que é facilitada pelas adições de nefelina. / The increased demand for increasingly demanding steels, in terms of chemical composition and internal sanity, makes the conditions of refining in steelmaking plants are increasingly stringent and select. At the same time, increasing metallurgical treatment times, combined with the various other operating variables such as the quantities and types of chemical additions, etc. makes that there is an increase in contact time between the refractory coating of steel transport ladles and slag with a consequent reduction in performance (life) of such refractory linings. Despite efforts in order to reduce costs with a reduction of refractory consumption, it is increasing the pressure on the costs of production and operational safety. In this sense, the construction of life prediction models according to such variables is extremely important for cost reduction, process management and procurement, operational stability and safety. Moreover, post-mortem studies can contribute towards chemical and physical understanding of such phenomena and wear mechanisms, thus contributing to the validation of such deterministic models. In this study, we sought to determine which operating variables really influence the performance (life) of the ladles through statistics correlations. The modeling took into account data from 6 months of operation of an integrated steelmaking plant with capacity of 4.5 Mt / year. The study post-mortem conducted on some ladles, after the end of their campaigns, was effective in the validation of such correlations and in the physical and chemical understanding of possible phenomena and wear mechanisms. The analysis showed that the variables that impact in the life of steel\'s ladles are the steel taping temperature, the steel taping temperature in the ladle after taping, amount of produced plate mill (CG) steel, desulfurized treatment route, ladle full time, participation of the ladle furnace in the secondary refining, ladle conditions, steel load in the ladle, nepheline additions, synthetic slag, calcium silicon (CaSi) and iron aluminium calcium (FeAlCa) wires, manganese alloys and treatment times in the secondary refining. The post-mortem study of slagline\'s refractory samples extracted from ladles in operation revealed that the main wear mechanism in this region is the chemical corrosion by slag and is facilitated by additions of nepheline.

O aumento da demanda por aços cada vez mais exigentes, em termos de composição química e limpidez interna, faz com que as condições de refino nas aciarias sejam cada vez mais severas. Ao mesmo tempo, o aumento dos tempos de tratamento do aço, aliado às outras variáveis operacionais como quantidades e tipos de adições químicas, etc. fazem com que haja um aumento no tempo de contato entre o revestimento refratário das panelas de transporte de aço e escórias com conseqüente redução do desempenho (vida) de tais revestimentos refratários. Apesar dos esforços no intuito de redução de custos com redução de consumos de refratários, é cada vez maior a pressão sobre os custos de produção e de segurança operacional. Neste sentido, a construção de modelos de previsão de vida em função de tais variáveis é de extrema importância para a gestão de processos e contratos, estabilidade operacional e segurança. Além disso, os estudos de post-mortem podem contribuir no sentido de compreensão física e química de tais fenômenos e mecanismos de desgaste, contribuindo assim para a validação de tais modelos determinísticos. Neste estudo, buscou-se verificar quais variáveis operacionais influem no desempenho (vida) das panelas através de correlações estatísticas. O modelamento levou em consideração os dados de 6 meses de operação da aciaria de uma usina integrada com capacidade de 4,5 Mt/ano. O estudo post-mortem realizado em uma das panelas, após o final de sua campanha, mostrou-se eficiente na validação de tais correlações e no entendimento físico e químico dos possíveis fenômenos e mecanismos de desgaste. As análises mostraram que as variáveis que impactam a vida das panelas de aço são a temperatura de vazamento do aço, temperatura do aço na panela pós vazamento, quantidade de aço chapas grossas (CG) produzido, rota de tratamento dessulfurado, tempo de panela cheia, participação do forno panela no refino secundário, condições da panela, carga de aço na panela, adições de nefelina, escória sintética, fios de cálcio silício (CaSi) e ferro alumínio cálcio (FeAlCa), ligas de manganês e tempos de tratamento no refino secundário. O estudo de post-mortem de amostras de refratário da linha de escória extraída de uma das panelas revelou que o principal mecanismo de desgaste desta região é a corrosão química pela escória que é facilitada pelas adições de nefelina. / The increased demand for increasingly demanding steels, in terms of chemical composition and internal sanity, makes the conditions of refining in steelmaking plants are increasingly stringent and select. At the same time, increasing metallurgical treatment times, combined with the various other operating variables such as the quantities and types of chemical additions, etc. makes that there is an increase in contact time between the refractory coating of steel transport ladles and slag with a consequent reduction in performance (life) of such refractory linings. Despite efforts in order to reduce costs with a reduction of refractory consumption, it is increasing the pressure on the costs of production and operational safety. In this sense, the construction of life prediction models according to such variables is extremely important for cost reduction, process management and procurement, operational stability and safety. Moreover, post-mortem studies can contribute towards chemical and physical understanding of such phenomena and wear mechanisms, thus contributing to the validation of such deterministic models. In this study, we sought to determine which operating variables really influence the performance (life) of the ladles through statistics correlations. The modeling took into account data from 6 months of operation of an integrated steelmaking plant with capacity of 4.5 Mt / year. The study post-mortem conducted on some ladles, after the end of their campaigns, was effective in the validation of such correlations and in the physical and chemical understanding of possible phenomena and wear mechanisms. The analysis showed that the variables that impact in the life of steel\'s ladles are the steel taping temperature, the steel taping temperature in the ladle after taping, amount of produced plate mill (CG) steel, desulfurized treatment route, ladle full time, participation of the ladle furnace in the secondary refining, ladle conditions, steel load in the ladle, nepheline additions, synthetic slag, calcium silicon (CaSi) and iron aluminium calcium (FeAlCa) wires, manganese alloys and treatment times in the secondary refining. The post-mortem study of slagline\'s refractory samples extracted from ladles in operation revealed that the main wear mechanism in this region is the chemical corrosion by slag and is facilitated by additions of nepheline.