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V V Chuikov - One of the best experts on this subject based on the ideXlab platform.

Seppo Louhenkilpi - One of the best experts on this subject based on the ideXlab platform.

  • Mathematical Modeling of Nitrogen Removal from the Vacuum Tank Degasser
    Steel Research International, 2014
    Co-Authors: Shan Yu, Jyrki Miettinen, Lei Shao, Seppo Louhenkilpi
    Abstract:

    The removal of nitrogen from an industrial vacuum tank degasser depends on a series of operational parameters, steel composition, and contents of surface-active elements in liquid steel, e.g., oxygen and sulfur. The effect of some specific elements on nitrogen removal in the vacuum degasser has been (well) examined. Still, it is quite challenging to assess the overall effect of the whole steel composition on the process. The focus of the present work was to predict nitrogen removal from the vacuum degasser specially taking into account the multi-component effect of steel composition. An integrated computational fluid dynamics (CFD) model for simulating nitrogen (and hydrogen) removal in industrial vacuum tank Degassers was therefore developed based on theories and methods that are relatively separate in the literature. In order to include the multi-component effect, the model is coupled with an in-house thermodynamics code that can be used to determine the activity coefficient of nitrogen, oxygen, or sulfur as a function of steel composition and temperature. The code was verified by comparing the calculated activity coefficients against experimental measurements from various sources. Efforts were also put into developing an on-line use concept to control the nitrogen removal. The gas plume, flow field, and evolutions of nitrogen and hydrogen during vacuum treatment were predicted and the on-line concept was demonstrated by presenting two operating diagrams. The results showed that the final nitrogen content decreases with an increase in the chemical reaction rate constant and a decrease in the initial nitrogen content. By contrary, the final nitrogen content increases with a decrease in the chemical reaction rate constant and an increase in the initial nitrogen content. Finally, the operating diagrams were validated by industrial data and observations.

  • Modeling Study of Nitrogen Removal from the Vacuum Tank Degasser
    Steel Research International, 2014
    Co-Authors: Shan Yu, Jyrki Miettinen, Seppo Louhenkilpi
    Abstract:

    Low nitrogen content in liquid steel is required for most of the steelmaking companies, where vacuum degassing of liquid steel is usually carried out to remove nitrogen as well as other impurity elements during ladle treatment. This paper presents an integrated computational fluid dynamics (CFD) model for simulating the nitrogen removal in an industrial vacuum tank degasser (VTD). In the CFD model, oxygen and sulfur are considered as surface-active elements decreasing the denitrogenation rate at the gas–steel interface. An activity coefficient and a desulfurization sub-model are implemented to compute the effective activity coefficients of the related elements and the evolution of sulfur content in liquid steel during the process, respectively. The effect of various elements on denitrogenation rate in the VTD is studied with the developed model. For the used steel compositions the denitrogenation rate decreases with an increase in the content of [S], [O], [Cr], [Nb], [V], [Ti], or [Mn], whereas it increases with an increase in the content of [C], [Si], [P], [Ni], or [Al]. The model is validated by comparing final nitrogen contents measured from the industrial plant with the ones predicted by the model and good agreements were found. The model has proven to be a useful and accurate tool for predicting final nitrogen content of liquid steel in the plant.

  • Numerical study on the removal of hydrogen and nitrogen from the melt of medium carbon steel in vacuum tank degasser
    Materials Science Forum, 2013
    Co-Authors: Shan Yu, Jyrki Miettinen, Seppo Louhenkilpi
    Abstract:

    The steelmaking field has been seeing an increased demand of reducing hydrogen and nitrogen in liquid steel before casting. This is often accomplished by vacuum treatment. This paper focuses on developing a numerical model to investigate the removal of hydrogen and nitrogen from the melt of medium carbon steel in a commercial vacuum tank degasser. An activity coefficient model and the eddy-cell expression are implemented in the ANSYS FLUENT code to compute the activities of related elements and mass transfer coefficients of hydrogen and nitrogen in liquid steel. Several cases are simulated to assess the effect of gas flow rate and initial nitrogen content in liquid steel on degassing process and the calculated results are compared with industrial measured data.

  • Numerical Simulation of Dehydrogenation of Liquid Steel in the Vacuum Tank Degasser
    Metallurgical and Materials Transactions B, 2013
    Co-Authors: Shan Yu, Seppo Louhenkilpi
    Abstract:

    Vacuum tank Degassers are often utilized to remove hydrogen from liquid steel. A new comprehensive numerical model, which has been developed to simulate hydrogen removal in the vacuum Degassers, is presented in this paper. The degassing model consists of two sub-models, which calculate the gas-steel flow field and the species transport of hydrogen. An extended k – ε turbulence model is adopted to consider the effect of gas injection on the turbulent properties and an interfacial area concentration model is introduced to compute the interfacial area density between liquid steel and the bubbles. The fluid dynamic sub-model is validated with a physical gas stirred tank, which is believed to have similar flow phenomena as the studied vacuum degasser based on the modified Froude number. Two fundamental expressions for mass transfer coefficient, which have been paid little attention by the researchers concentrating on vacuum degassing, are evaluated with a simulation case corresponding to practical operation. The effect of vacuum pressure on the dehydrogenation process is investigated and, moreover, the integrated model is verified with industrial measurements. The predicted final hydrogen contents in liquid steel show good agreement with the measured ones. The model and the main results are presented.

  • Numerical Simulation of Dehydrogenation of Liquid Steel in the Vacuum Tank Degasser
    Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2012
    Co-Authors: Shan Yu, Seppo Louhenkilpi
    Abstract:

    Vacuum tank Degassers are often utilized to remove hydrogen from liquid steel. A new comprehensive numerical model, which has been developed to simulate hydrogen removal in the vacuum Degassers, is presented in this paper. The degassing model consists of two sub-models, which calculate the gas-steel flow field and the species transport of hydrogen. An extended k–e turbulence model is adopted to consider the effect of gas injection on the turbulent properties and an interfacial area concentration model is introduced to compute the interfacial area density between liquid steel and the bubbles. The fluid dynamic sub-model is validated with a physical gas stirred tank, which is believed to have similar flow phenomena as the studied vacuum degasser based on the modified Froude number. Two fundamental expressions for mass transfer coefficient, which have been paid little attention by the researchers concentrating on vacuum degassing, are evaluated with a simulation case corresponding to practical operation. The effect of vacuum pressure on the dehydrogenation process is investigated and, moreover, the integrated model is verified with industrial measurements. The predicted final hydrogen contents in liquid steel show good agreement with the measured ones. The model and the main results are presented.

H.-t. Hu - One of the best experts on this subject based on the ideXlab platform.

  • Mathematical modelling of molten steel flow in a whole degasser during RH refining process
    Ironmaking & Steelmaking, 2020
    Co-Authors: H.-t. Hu
    Abstract:

    AbstractA three-dimensional mathematical model for molten steel flow in a whole degasser during the RH (Ruhrstahl–Heraeus) refining process is proposed. The model has been developed considering the physical characteristics of the process, particularly the behaviour of gas–liquid two phase flow in the up snorkel and the momentum exchange between the two phases. The fluid flow fields and gas holdups of liquid phases, among other parameters, in a 90 t RH degasser and a water model unit of one-fifth linear scale have been computed using this mathematical model. The results show that the flow pattern of molten steel in a whole RH degasser can be well represented by the mathematical model. Apart from the area close to the free surface and the zone between the two snorkels in the ladle, the molten steel in an RH degasser, especially in the vacuum vessel, is reasonably fully mixed during the refining process. However, there is a boundary layer between the descending liquid stream from the down snorkel and the sur...

  • Mathematical modelling of molten steel flow process in a whole RH degasser during the vacuum circulation refining process : Application of the model and results
    Steel Research International, 2020
    Co-Authors: H.-t. Hu
    Abstract:

    A three-dimensional mathematical model for the molten steel flow during the RH refining process has been applied to the circulatory flow processes in both a practical RH degasser and its water model unit. The model was presented earlier [1] and one of its characteristics is that ladle, snorkels and vacuum vessel are regarded as a whole. Using this model, the fluid flow field and the gas holdups of liquid phases and others have been computed respectively for a 90 t RH degasser and its water model unit with a 1/5 linear scale. The results show that the mathematical model can properly describe the flow pattern of molten steel during the refining process in an RH degasser. Except in the area close to the liquid's free surface and in the zone between the two snorkels in the ladle, a strong mixing of the molten steel occurs, especially in the vacuum vessel. However, there is a boundary layer between the descending liquid stream from the down-snorkel and its surrounding liquid, which is a typical liquid-liquid two-phase flow, and the molten steel in the ladle is not in a perfect mixing state. The lifting gas blown is ascending mostly near the up-snorkel wall, which is more obvious under the conditions of a practical RH degasser, and the flow pattern of the bubbles and molten steel in the up-snorkel is closer to an annular flow. The calculated circulation rates for the water model unit at different lifting gas rates are in good agreement with experimentally determined values.

  • Mathematical Modelling of Molten Steel Flow Process in a Whole RH Degasser during the Vacuum Circulation Refining Process: Mathematical Model of the Flow
    Steel Research International, 2020
    Co-Authors: H.-t. Hu
    Abstract:

    A three-dimensional mathematical model for the molten steel flow in a degasser during the RH refining process has been proposed and developed. The physical characteristics of the process, particularly the behaviour of gas-liquid two-phase flow in the up-snorkel and the momentum exchange between the two phases are considered. The ladle, snorkels and vacuum vessel are regarded as a whole in the model, and the gas-liquid two-phase flow is treated and described on the basis of the two-fluid model and using the especially modified two-equation K-E model. The details of the model are presented.

Muhammad Reza Firmansyah - One of the best experts on this subject based on the ideXlab platform.

  • Effect of addition of sodium chloride in sodium nitrate-sodium fluoride-based degasser in aluminum casting
    IOP Conference Series: Materials Science and Engineering, 2019
    Co-Authors: Donanta Dhaneswara, Jaka Fajar Fatriansyah, Muhammad Reza Firmansyah
    Abstract:

    The effect of addition of Sodium Chloride (NaCl) in increasing degasser efficiency on Al-Si12% casting has been carried out. Al-Si 12% casting product mechanical properties are a very important parameter that indicates the quality of the casting product. However, it is a very common phenomenon that the properties of the casting product was reduced by gas porosity defects, which is formed due to high solubility of H2 at melt temperature of Al-Si 12%. In this investigation, we used NaF and NaNO3 as degasser with the addition of NaCl in the casting process. The addition of NaCl was variated to see the capability of NaCl as a degasser. The casting process were conducted at melting temperature of 800 °C and pouring temperature of 690 °C. The mechanical properties between casting products that use NaF-NaNO3 degasser with variated ratio of NaCl addition were measured and compared. The result shows that mechanical properties of Al-Si12 cast product in this research will be decreased along with increasing number of NaCl addition ratio in degasser composition.

  • Effect of Sodium Nitrate-Sodium Fluoride Ratio as Degasser in Al-7Si-2Cu Casting Product
    IOP Conference Series: Materials Science and Engineering, 2019
    Co-Authors: Donanta Dhaneswara, Jaka Fajar Fatriansyah, Naila Hanandhira, Agatha Rona Basa, Muhammad Reza Firmansyah
    Abstract:

    Effect of Sodium Nitrate-Sodium Fluoride Ratio as degasser in Al-7Si-2Cu Casting product has been investigated. Degassing is one of the methods used in the casting process to remove gases, such as hydrogen gases, in the molten metal. The most commonly used degassing method is by injecting an inert gas such as argon. In this experiment, a conventional degassing method with degasser-based sodium nitrate-sodium fluoride was used with changes in sodium nitrate to sodium fluoride ratio variables are 3:5, 4:4, and 5:3. The type of material used is Al-7Si-2Cu material with additional scrap. The material melted first at 800°C, then the degasser was added into the furnace and held for 3 minutes. High temperature was used to melt the material due to the solubility of hydrogen gases in liquid metal at high temperature is high. The molten metal then poured into the dies at approximately 690°C. The casting process results are then prepared for mechanical testing, such as tensile test, impact test, and hardness test, and microstructure testing. The results show that at the ratio of 1:1.5 (normal ratio), the porosity was lower (0.8 at average) and the mechanical strength was higher (1.2 at average).

Roger Thiffault - One of the best experts on this subject based on the ideXlab platform.

  • The Alcan Compact Degasser: A Trough-Based Aluminum Treatment Process
    Essential Readings in Light Metals, 2020
    Co-Authors: Peter D. Waite, Roger Thiffault
    Abstract:

    In-line degassing processes, employing rotary gas injectors, are used extensively in the aluminum industry for removing unwanted impurities from the liquid metal just prior to casting.

  • Essential Readings in Light Metals: Cast Shop for Aluminum Production, Volume 3 - The Alcan Compact Degasser: A Trough‐based Aluminum Treatment Process. Part I: Metallurgical Principles and Performance
    Essential Readings in Light Metals, 2013
    Co-Authors: Peter D. Waite, Roger Thiffault
    Abstract:

    In-line degassing processes, employing rotary gas injectors, are used extensively in the aluminum industry for removing unwanted impurities from the liquid metal just prior to casting. Although these processes are efficient, and provide the required level of metal treatment, a significant quantity of between one and three tons of metal is retained within the degassing unit between casts. Metal retention is a serious drawback for multi-alloy cast shops, due to the scrap metal produced by draining the degassing unit at alloy changes. The Alcan compact degasser is a new multi-stage in-line degassing process which treats the metal directly in the trough. Following the initial development period in the laboratory, about two years of process development and optimization in the plant has proven that the Alcan compact degasser provides metal treatment efficiencies equivalent to or better than existing technologies, while eliminating metal retention between casts. The metallurgical principles of this process are described and quantitative plant data are presented which characterize the metallurgical performance with respect to degassing, metal cleanliness, and alkali removal.