Varadarajan Seshadri

Decarburisation rates in RH–KTB degasser of CST steel plant through physical modelling study

Abstract A physical model based on similarity principles was constructed to simulate the RH (Ruhrstahl–Heraeus) degasser of CST (Companhia Siderúrgica Tubarão, Vitória, Brazil) to evaluate the influence of metal circulation rate, which essentially defines the degree of exposure of the metal to the vacuum in the chamber, on the decarburisation rate. The circulation rate in addition influences the removal of dissolved gases such as nitrogen, and hence it is essential to optimise this parameter to achieve maximum refining efficiency with minimum refining time, thus improving the productivity of the secondary refining process. In the present work, simulation experiments investigating the kinetics of decarburisation have been carried out using the CO2 adsorption–desorption process in sodium hydroxide solution as the circulating fluid. The effect of bottom gas flowrate and snorkel diameter in this case was also evaluated. Bottom gas injection practice, under the upleg, improves the circulation rate. Increasing the circulation rate by bottom injection leads to an increased degassing rate. However, degasification efficiency does not remain at the same level. The circulation and degasification rates can be improved by an increase in diameter of the downleg snorkel. The relative gain in degasification seems to be higher at the higher flowrate range. The results have been translated to a prototype, to optimise the process.

Fluid flow and mixing characteristics in RH degasser of Companhia Siderúrgica de Tubarão, and influence of bottom gas injection and nozzle blockage through physical modelling study

Abstract A physical model based on similarity principles has been constructed for simulating the RH degasser of Companhia Siderúrgica de Tubarão (CST), Vitória, ES, Brazil. The influence of gas injection through nozzles in the upleg with simultaneous bottom injection of gas, as well as the influence of nozzle blockage, on the circulation rate has been investigated. In addition, mathematical relationships for mixing characteristics in the process have been evaluated.

Avaliação técnica de minérios de ferro para sinterização nas siderúrgicas e minerações brasileiras: uma análise crítica

This paper provides a critical analysis of the methodology used in Brazil for routine technical evaluation of iron ore fines used in the sintering process based uniquely on chemical and granulometric parameters. The mineralogical characterization of adherents, intermediates and nucleantes particles of sinter feed and the main attributes that should constitute its microstrutural identity have been highlighted. It should contribute a great deal to optimize the process parameters during the various stages of the sintering process as well as promote better intrinsic sinter quality. Based on these concepts, it is expected that in future years, significant criterias will be developed for technical analysis of iron ores fines used in agglomeration industry.

PROCESS CONTROL MODEL FOR CHARCOAL BLAST FURNACES IN BRAZIL

Abstract In the present paper, a simple process control model for charcoal blast furnaces is presented. The main feature of the model is that it is based on carbon balance and requires low investment in instrumentation. The process model described in the present work has been tested through trial runs and has proved to be an important tool to maintain a stable furnace operation.

Applying virtual reality model to green ironmaking industry and education: ‘a case study of charcoal mini-blast furnace plant’

ABSTRACT A virtual reality (VR) model has been developed in the case of a generic green ironmaking industrial unit, namely a typical charcoal mini-blast furnace (CMBF) plant in Brazil. The VR prototype construction of the CMBF plant has been implemented through integration of data in different softwares and hardwares, including detailed engineering design of various auxiliary units and major equipments with realistic project parameters. Through the VR technology, one can actually have the unique experience visiting all parts of the CMBF plant, promote technical discussions on engineering and process control with users and improve information handling, communication, safety, maintenance procedures and development of advanced engineering projects in the field. VR industry-professional education platform can be used in universities, museums and industries with great benefits to students, workers and users.

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.

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

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.

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

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.

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 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.

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

Resumo Utilizando um modelo físico de um reator RH em escala 1:7,5, simulou-se o processo de injeção de material dessulfurante na câmara de vácuo, buscando evidenciar a influência da vazão de gás e da diferença de densidade entre as fases sobre o tempo de residência e sobre o tamanho das gotas de escória arrastadas pelo metal, parâmetros essenciais para uma estimativa da taxa de dessulfuração. O aumento na densidade do fluido similar ao aço resultou em considerável prolongamento no tempo de residência e diminuição do diâmetro médio das gotas de óleo arrastadas. Para a solução salina (NaCl) como fluido de circulação, observou-se que a redução da vazão de gás aumenta o tempo de residência das partículas de dessulfurante. Tais resultados sugerem que existe uma vazão ótima de gás para alcançar maior eficiência de dessulfuração no RH, isto é, maior tempo de residência do material dessulfurante e arraste de gotas de escória de menor diâmetro. Palavras-chave: Desgaseificador RH; Dessulfuração; Modelamento Físico.