EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

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A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

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Autor: search.filters.author.Silva, Itavahn Alves da

Resultados da Pesquisa

Agora exibindo 1 - 10 de 30
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    Steel desulfurization on RH degasser : physical and mathematical modeling.
    (2022) Silva, Antonio Marlon Barros; Peixoto, Johne Jesus Mol; Silva, Carlos Antônio da; Silva, Itavahn Alves da
    Due to the high-quality steel demand, especially for ultra-low Sulfur steel, RH desulfurization has been practiced. Based on this, mathematical and physical modeling have been applied to study steel desulfurization by reagent addition in the RH degasser vacuum chamber. The main result of cold modeling, using water and oil emulating steel and slag, respectively, was to assess the influence of density difference between the continuous and disperse phases on oil droplet behavior. It is shown that its flow tends to be more restricted near the down snorkel when the density difference increases. Moreover, these results provide the basis for CFD modeling validation, which enabled the determination of slag drop residence time inside steel on RH and the average value of the rate of dissipation of turbulent kinetic energy inside the RH ladle. These two pa- rameters were used to develop a kinetic model, which reaches a good agreement with industrial trial results available in literature. The optimum desulfurization degree of 31.44% was achieved for a gas flow rate of 90 Nm3 /h, according to the kinetic model. This value can be useful in some steel grade production, where the required S content is less than 10 ppm. Even in common steel grade production, if some punctual chemical adjustment is necessary, this technique is also useful. The main kinetic parameter for steel desulfurization is the steel circulation rate. For best results, it should be reduced in the desulfurization stage, and after that, the normal operation can be resumed, so that the production cycle is not affected.
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    Influence of synthetic slag added during the tapping on inclusion features of a vacuum degassed LCAK steel grade.
    (2020) Melo, Gilberson Mendonça Storck de; Silva, Carlos Antônio da; Peixoto, Johne Jesus Mol; Oliveira, José Roberto; Silva, Caio Vaccari; Silva, Itavahn Alves da
    Synthetic slag has been added during BOF tapping in order to modify the physicochemical properties of resulting slag with the aim of assessing the influence on inclusion density, composition and size distribution. Viscosities and activities of slag oxides were calculated by FactSage 7.2, using the FToxid database and Viscosity module. All heats were treated under vacuum in an RH degasser for 15 minutes. A comparative analysis of top slags with two levels of FeO+MnO (> 10% and ≤ 10%) was carried out. The higher level of FeO+MnO led to almost thrice more inclusion than the lower level. Top slags after treatment with synthetic slag brought the best result of inclusions features thanks to their higher CaO activity, lower viscosity and lower activity of Al2O3. These heats presented smaller inclusions and lower initial inclusion density at ladle arrival at RH. Based on these evidences, top slags with synthetic slags added during the tapping and FeO+MnO content ≤ 10% conferred the best condition in steel cleanliness.
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    Modeling of two-phase flow in blast furnace trough.
    (2020) Oliveira, Marivaldo Junior Monteiro de; Rodrigues, Gustavo Fernando Ribeiro; Silva, Itavahn Alves da; Peixoto, Johne Jesus Mol; Silva, Carlos Antônio da
    Almost 95% of the world's hot metal production is from blast furnaces, reaching a production of 1.2 billions tons in 2018 according to the World Steel Association. The trough is an important equipment within the blast furnace production process, promoting the separation between hot metal and slag after casting. However, the flow pattern inside the runner is understudied due to its complexity. Due to the turbulence in the trough during the casting, there is metal loss in the slag and also slag entrainment in the hot metal. The metal loss in the slag is the most critical situation as it directly affects the efficiency. The influence of flow rate as well as of geometrical parameters on the flow pattern inside the runner is analyzed by physical and numerical simulation. In the physical simulations, particle image velocimetry (PIV) as well as dye injection using HD cameras and residence time distribution (RTD) curves are used to characterize the flow. These techniques allow to validate the mathematical model created in CFX-Ansys. This work stresses the changing flow features as the slag–metal ratio changes during the casting operation and the role of geometry as far as metal separation from the slag is concerned.
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    Bubble behavior in the slab continuous casting mold : physical and mathematical model.
    (2020) Santos Júnior, Paulo Luiz; Peixoto, Johne Jesus Mol; Silva, Carlos Antônio da; Silva, Itavahn Alves da; Galinari, Clenice Moreira
    A two-phase population balance is used to predict the polydispersed bubble flow and size distribution in a slab continuous casting mold and Submerged Entry Nozzle (SEN) system. Multiple Size Group (MUSIG) with a suitable breakage and coalescence model (Ansys CFX) was adopted to account for the polydispersed gas flow. Initial bubble size distribution as determined for two industrial refractories have been taken in consideration. A two way coupling model including the effect of the drag force and non-drag forces such as virtual mass force and turbulent dispersion force was considered. The results are compared with gas distribution in a 1:1 scale water — air mold model running under conditions of fluidynamic similarity to validate the model. The simulations have then been extended to describe the actual steel — argon flow, considering a thermal expansion factor for argon bubbles. The effect of gas distribution on the flow field of liquid inside the mold and other metallurgical aspects are discussed.
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    Comparative study of inclusion removal from liquid steel in the RH and argon purging processes.
    (2020) Campos, Marina Braga; Peixoto, Johne Jesus Mol; Silva, Carlos Antônio da; Silva, Itavahn Alves da
    In order to improve steel quality, it is necessary to increase the cleanliness of the liquid steel; that is, to reduce the number and size of the inclusions in the liquid steel, as well as to control their chemical composition. For this purpose, processes (with different operating costs) are used, such as the bubbling of inert gas in the steel ladle and its treatment in the vacuum degasser RH. This article deals with inclusion removal through an argon purging process and RH treatment, and provides a comparison of their effectiveness using industrial data and a mathematical model. The inclusion count shows a strong exponential decay for RH treated heats with chemical heating, as expected. The same behavior is not seen for RH treated heats without chemical heating as well as an argon purging process. It is suggested that in the later cases, there could exist competition between inclusion removal and inclusion generation from sources, such as refractory-slag-metal interaction and open eye atmosphere metal interaction. It has been concluded that the RH and the argon purging processes are both able to reduce the amount of inclusions. However, the bubbling process would require a much smaller gas flow rate to avoid open eye formation.
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    Numerical and physical simulation of steel ladle draining operation with different well block design.
    (2019) Conceição, Paulo Vinícius Souza da; Silva, Carlos Antônio da; Silva, Itavahn Alves da; Ananias, João Víctor Gomes Guimarães; Resende, Alexandre Dolabella
    At the end of a ladle draining operation a structure called drain sink forms at the top surface of the liquid steel allowing slag carry over from the ladle to the tundish and causing metallic losses. On this study, the effect of different well block configuration on the critical height for drain sink formation (HC) was investigated using numerical and physical modeling. The modified well block configuration showed lower HC in most of the cases when compared with the standard design. It could represent almost 50% of metallic lost savings during the continuous casting process. Air injection was also investigated and increased significantly the HC value. The numerical model showed good agreement with the physical model and was used to help undertanding this behavior.
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    Analysis of the fluid flow behavior within a beam blank mold using submerged-entry nozzle with three exit ports.
    (2019) Gabriel, Weslei Viana; Peixoto, Johne Jesus Mol; Alves, Gesiane Letícia; Silva, Carlos Antônio da; Silva, Itavahn Alves da; Seshadri, Varadarajan
    Through the use of physical and mathematical modeling techniques, liquid flow inside a beam blank mold with a submerged valve consisting of three exit ports has been analyzed. The behavior of the slag metal interface was evaluated using water and an aqueous NaCl solution to simulate steel. Slag simulation was done using silicon oil. Increased casting speed results in increased free surface oscillation. For the fluid density of 1,000 kg/m3, oil entrainment started at a casting velocity of 0.98 m/minute. For a fluid density of 1,170 kg/m3, no entrainment was observed in any of the conditions studied.
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    The influence of flow asymmetry on refractory erosion in the vacuum chamber of a RH degasser.
    (2019) Melo, Pedro Henrique Resende Vaz de; Peixoto, Johne Jesus Mol; Galante, Gustavo Santos; Loiola, Bruna Helena Malovini; Silva, Carlos Antônio da; Silva, Itavahn Alves da; Seshadri, Varadarajan
    Nozzle blockage in RH reactors is a serious operational problem since it can cause an asymmetric distribution of the steel flow in both the up-leg as well as the lower region of the vacuum chamber. This anomaly can alter the circulation rate in addition to affecting the erosion profile of the lower part of vacuum chamber refractory lining. In this study, the effect of nozzle obstruction on liquid circulation rate, wall shear stress, velocity profiles and flow pattern have been evaluated. In addition, refractory erosion in the vacuum chamber has been estimated through physical modeling and mathematical simulation results. Four blockage conditions were studied for different gas flow rates. There was a good agreement in physical and mathematical models results. Asymmetric flow was observed in vacuum chamber lower region in asymmetric blockage cases, which resulted in preferential wear on one chamber side in physical modeling experiments. The wall shear stress analysis in the vacuum chamber using a fluid dynamic model also indicates preferential erosion. When compared, refractory erosion results in physical modeling and shear stress in mathematical modeling presented good correlation.
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    Numerical and physical simulation of the fluid flow in a beam blank mold fed through the center of the web.
    (2019) Gabriel, Weslei Viana; Peixoto, Johne Jesus Mol; Queiroz, Guilherme Santiago; Silva, Carlos Antônio da; Silva, Itavahn Alves da; Seshadri, Varadarajan
    Fluid flow inside a beam blank mold fed through a three-port SEN (two lateral ports and one bottom port), positioned at the center of the mold, has been investigated. Literature survey shows that this kind of configuration is not frequently used. It had been shown that it is possible to get a symmetrical flow with this configuration. The downward inclination of the ports should influence the transient fluid flow. The greater the downward inclination, the greater is the instability of the jet and of the interface between the immiscible fluids that simulate the slag/metal behavior. The flow characterization was made by dye dispersion, PIV technique, measurement of the meniscus oscillation using ultrasonic sensors, and CFD simulations. The slag/metal behavior was simulated using water and oils with different physical properties. The results from PIV as well as from observations of the water–oil interface have been used to validate the CFD simulations. Oils with density close to water resulted in more instability at the interface with entrainment starting from fluid flow rate of 125 L/min (equivalent to casting speed of 1 m/min). Decreasing the viscosity of slag (oils) and increasing the casting velocity (water flow rate) result in reduction of the interfacial stability.
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    A study of intermix in a six-strand billet caster.
    (2018) Amorim, Laudinei Las Casas; Silva, Carlos Antônio da; Resende, Alexandre D.; Silva, Itavahn Alves da; Oliveira, Marivaldo Júnior Monteiro de
    The purpose of this study was to develop an integrated intermix model suitable for a six-strand billet caster. Mathematical and physical simulations were performed in order to compare intermixing under the current procedure with alternative approaches. Plant data were collected, including different operational strategies regarding the tundish weight at holding level, to validate the findings. Additionally, samples were taken from the billets to understand the nature of strand mixing in small sections. The effect of tundish level during the holding procedure was evaluated. It was determined that the most pronounced effect on intermixing was caused by the difference in superheat between the old and new grades. The model will be used to reduce steel downgrade resulting from grade intermixing and for scheduling of intermix sequences.