Itavahn Alves da Silva

LIME-BASED FLUX INJECTION FOR PIG IRON REFINING IN INDUSTRIAL LADLES

A software for lime-based flux injection for desulfurization of pig iron in ladle has been developed with the objective of predicting end sulfur content and temperature in one of the steel plants situated in the Minas Gerais State, Brazil, namely Belgo Mineira S.A. The software is also capable of assessing the influence of various process parameters such as flow rate, flux composition, depth of injection, amount of carry-over slag, initial temperatures of the charging materials, etc., on the process of refining. The mathematical model on which the computer code and the software are based, takes into consideration the contribution of the top slag, the injected particles, and the particles adhering to the bubbles, in the process of desulfurization. Transport phenomena parameters used in the model were chosen after an extensive literature survey. The thermodynamic parameters involved in the various exothermic and endothermic reactions have been considered in the thermal balance. A comparison between the results obtained from injection trials with 30-ton ladle showed that the predicted values using the software are reasonably in agreement with the actually observed values with respect to end sulfur content.

STUDY OF FLOW MODIFICATION AND INCLUSION REMOVAL IN SLAB TUNDISH DUE TO BOTTOM GAS INJECTION

Com o intuito de quantificar o papel da remocao de inclusoes, avalia-se o padrao de fluxo no interior do distribuidor. Modelos matematicos de separacao de inclusao, incluindo a influencia da coalescencia de inclusoes tambem sao discutidos. A presente analise sugere que no tocante a inclusoes de pequenas dimensoes, parâmetros operacionais como fracao de fluxo pistonado deixam de ser criticos, uma vez que a probabilidade de separacao e desprezivel. Entretanto, tecnicas como o uso de cortina de gas sao relevantes para melhor controle do conteudo de inclusao. Resultados de modelamento fisico e matematico sao apresentados considerando a associacao de uma barreira porosa e um plugue anelar de injecao posicionado ao redor do veio. Os resultados confirmam as expectativas ja que a modificacao de fluxo, exposta pela simulacao matematica, permite que inclusoes fiquem retidas no reator, registrando valores de saida abaixo de 3% no caso do veio com aspersao de gas.

Hybrid model associating thermodynamic calculations and artificial neural network in order to predict molten steel temperature evolution from blowing end of a BOF for secondary metallurgy

The developed model is an association of thermodynamic calculations for dissolution of alloys, slag formers and the deoxidation reaction in the molten steel with two artificial neural network (ANN) models trained with industrial data, to predict the molten steel temperature drop from the blowing end of the BOF until the first measurement at secondary metallurgy. To calculate the associated energy for deoxidation, an experiment was designed to set up the parameters for oxygen partitioning among deoxidants, with timed aluminum addition during teeming being the main parameter. The temperature control in the teeming stage presented a standard deviation for the error of prediction of 5.46 oC, for transportation from the rinsing station to the secondary metallurgy of 2.79 oC. The association of all calculations presented an error standard deviation of 7.49 oC. The operational validation presented superior accuracy compared with the current method for controlling the temperature, resulting in a reduction in the aluminum consumption for heating at secondary metallurgy with a potential economy of U

Replacement of fluorspar in the desulfurization of hot metal

4.07 million per year for a steel shop producing 5 million tons of steel yearly. The artificial neural network model confirmed its capacity for modeling a complex multivariable process and the separation of thermodynamic calculation provides a better adaptability to different steel grades with different teeming strategies.

Numerical Simulation of Recirculating Flow and Physical Model of Slag–Metal Behavior in an RH Reactor: Application to Desulfurization

In the steel industry, lime is used as a desulfurizing agent and fluorspar as flux in the hot metal desulfurization process. However there are environmental concerns regarding the use of fluorspar, even when its harmful effects are not fully known. In order to reduce such risks and also to anticipate possible future restrictions, which could undermine the sustainability of steel production, it is proposed to replace the fluorspar for alternative materials in the composition of the desulfurizing lime based mixture. For this purpose new mixtures using aluminum dross, ilmenite, sodalite and ulexite were tested, comparing them with a reference mixture containing fluorspar. The impact of these mixtures on the refractories commonly used in hot metal pretreatment was also checked, since this is an important cost parameter for the steel industries. The laboratory tests showed ulexite as a feasible substitute since the lime (84.03%) – ulexite (10.97%) – graphite (5%) mixture presented the highest desulfurization ratio and low refractory wear (less than the standard fluorspar mixture). The sodalite mixture was the worst by comparison. The ilmenite and aluminum dross mixtures showed similar behavior when compared to the fluorspar mixture.

A Study of Intermix in a Six-Strand Billet Caster

Computational fluid dynamics (CFD) techniques and a 1:7.5 physical model of an RH degasser have been used to evaluate the flow of gas and metal inside an RH reactor for vacuum degassing of liquid steel. The effect of gas injection on the gas spatial distribution, steel circulation rate and flow field inside the ladle, snorkels and vacuum chamber have been assessed. N-pentane oil was employed to evaluate the average residence time as well as the slag droplet size distribution. The predicted radial gas distribution and liquid circulation rate have been validated against experimental data from a physical model. The results with incorporation of the virtual mass force coefficient of 0.25 and the turbulence dispersion force showed better predictions of gas distribution in the up-snorkel as well as circulation rate. Full-scale simulations were performed, and the predicted circulation rate was significantly affected by the argon bubble expansion. Data from these simulations were used to analyze the degree of desulfurization performed by the addition of desulfurizing agents inside the vacuum chamber. A model of the kinetics of desulfurization based on the results from the physical model and CFD simulation and on slag dispersion inside liquid steel yields degrees of desulfurization similar to the industrial trials reported in the literature.

AN EVALUATION OF GAS INJECTION EFFECTS IN A MECHANICALLY STIRRED HOT METAL DESULFURIZATION SYSTEM

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.

Assessment of Slag Entrainment in a RH Degasser Through Physical Modelling Using Circulating Fluids of Different Densities/Oil Systems for Simulating Steel Melt/Slag

Tecnicas de simulacao fisica foram utilizadas para analisar os efeitos da injecao de gas como modo de otimizacao de processos de dessulfuracao mecanicamente agitados. Um modelo em escala 1/7, correspondente a um reator de 315ton de capacidade, foi desenvolvido. O estudo foi realizado por meio da analise do tempo de mistura, cinetica de interacao interfacial e qualidade da dispersao de escoria. Resultados satisfatorios foram observados, como uma reducao de ate 20% do tempo de mistura e um aumento de 40% na dispersao de escoria para o fundo da panela. A interacao gas – liquido e altamente dependente do local de injecao de gas. A tecnica possui grande potencial de otimizacao do processo.

Analysis of Jet Behavior and Surface Fluctuations in the Meniscus of Fluid in a Physical Model of a Beam Blank Mold and CFD Modelling

In this work the circulation rates have been determined in a 1:7.5 scale physical model of RH reactor (Ruhrstal Heraeus) and using oil/water and oil/zinc chloride solution to simulate steel melt/slag in the prototype with the objective of evaluating the influence of density and viscosity on the entrainment of oil simulating slag. A technique based on strain gage bridge and particle image velocimetry was developed to assess the circulation rate, as the usual tracer method is not feasible due to the presence of chloride ions in ZnCl2. The critical velocity and critical diameter of oil drops for slag (oil) entrainment in water/oil and ZnCl2/oil systems were estimated using equations from the literature. Due to the difference in density, the ZnCl2/oil system, showed a critical velocity that is 28% higher than the silicone oil/water system while the maximum size of the entrained droplets was about 65% lower than that for water/oil system.

COMPORTAMENTO METAL-ESCÓRIA EM MODELO FÍSICO DE UM REATOR RH: APLICAÇÃO À DESSULFURAÇÃO

In this study, the influence of the immersion depth, casting speed on the flow characteristics in a beam blank mold with two tubular nozzles have been investigated using a physical model as well as CFD simulations. The results of CFD simulations were found to be consistent with the results of experiments in the physical model. The liquid jet spreads faster the flange region compared to the web region. This can lead to a non-uniform shell thickness along the cross section resulting in uneven solidification of the skin. The jet penetration depth ranged between 66 and 77 cm. The average intensity of meniscus fluctuation was 0.22 mm, and the maximum fluctuation was found to be 0.85 mm. Based on these results, the suggested optimum operating parameters for immersion depth and casting speed were 75 mm and maximum casting speed of 1 m/min.