Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 90 (2004), No. 6

  • Evaluation Method of Mixing Characteristics in Chemical Reactors

    pp. 296-300

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    The tracer response method was widely used to study the mixing properties of steelmaking reactors. In this study, by applying the indexes of fluid mixing based on information entropy, the local mixing properties in vessels were simulated under two different conditions. Especially the two important roles of mixing, distributor and blender, were discussed based on the simulated results. It was also shown that the results obtained by the tracer response method could be correlated to the index based on information entropy. The indexes of fluid mixing based on information entropy were confirmed to be quite useful to analyze the mixing properties of chemical reactors for the improvement of the mixing efficiency.
  • Novel Mixing and Separation Method through Vortex Stirrer

    pp. 301-305

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    There is a strong demand for innovation of steel-making processes, because the preservation of global-environment, energy and resource saving as well as productivity cost and quality on steel are important issues for sustainable-development of steel industry. Without imparting artificial energy, vortex stirrer using only a gravitational energy is invented and studied. Obtained results are as follows: The refining reagent can be completely sucked into the hot metal through the vortex effect. The tangential velocity decreases inversely with increasing radially the distance from the free surface. The calculated results coincide well with the experimental results.
  • Effect of Funnel Angle and Wettability on Swirling Flow of Liquid in the Funnel

    pp. 306-311

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    The application of the swirling flow by funnel to the steel refining process has been expected. In order to generate the swirling flow effectively and to maintain stably, it is necessary to examine the optimum conditions from various viewpoints, such as the shape of the funnel. In addition, it is necessary to clarify the effect of the wettability between the solid surface and the liquid on the swirling flow. Using mercury or water, the swirling flow in the funnel has been observed, and the effect of the funnel angle and the wettability on the swirling flow has been investigated. The swirling flow by funnel is formed stably when the funnel angle against the horizontal surface is larger than 60° in spite of the wettability of the funnel with the liquid. When the funnel angle becomes smaller, such as 30°, the swirling flow is affected by the wettability of the funnel. When the wettability between the funnel and the liquid is poor, the stable swirling flow cannot be obtained because of the slip of the liquid on the inner-surface of the funnel. A model calculation for molten iron has also been conducted on the effect of the wettability on the swirling flow. In regard to the liquid flow of the vertical direction, the liquid flows downward at the surface side of the liquid and upward at the vicinity of the funnel. When the wettability of the inner surface of the funnel with the liquid is poor, the liquid flows more intensely. This may be one of the causes that the swirling flow is difficult to be stabilized when the wettability is poor.
  • Separation of Inclusion through Swirl Flow in Immersion Nozzle Using Water Model Experiment

    pp. 312-316

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    This study aims to separate the inclusion through the centrifugal force acting on the inclusion. The results obtained through the water model experiments and numerical calculations shows as follows: (1) The swirling motion works effectively to separate the inclusions. (2) The magnitudes of most affecting factors for pushing the inclusion towards the central area from the wall through the swirling flow are in the order of swirl velocity of balk flow, diameter of inclusion, axial velocity, radius of nozzle and density of inclusion.
  • Relaxation of Uneven Velocity through Swirl Blade in Immersion Nozzle

    pp. 317-321

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    The flow pattern of the molten flow in the immersion nozzle have a important effect on the quality of the slab, billets, or blooms produced. Uneven flow in the nozzle developed after passing through a sliding gate, sometimes result in formation of vortex near the nozzle and entrapment of CC powder in the molten steel. The purpose is to suppress those uneven flow as soon as possible after passing through the sliding gate. We proposed a new type nozzle with the swirling blade. Numerical and water model studies revealed that rectification was accelerated significantly using the nozzle with the swirl blade, which would lead to the suppression of the vortex generation and turbulence on the meniscus.
  • Effect of Hot Metal Temperature and Rotation Speed on the Rate of Desulfurization Rate by Mechanical Stirring Process

    pp. 322-328

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    The effect of hot metal temperature and rotation speed on the desulfurization rate in mechanical stirring process was investigated with laboratory scale (30 kg), pilot plant scale (4 ton) and commercial plant (270 ton) tests. The results obtained were summarized as follows.
    1) Desulfurization rate of the experiments started at 1250°C was 0.7 times lower, than that started at 1350°C.
    2) Activation energy of the desulfurization rate was 43.9-143.9 kJ/mol. The observed rate of desulfurization was interpreted in terms of the rate controlled by sulfer transfer in hot metal and the entrainment of desulfurization flux into the hot metal.
    3) Difference of the desulfurization rate between the experiments at 1250°C and at 1350°C was decreased by increasing the stirring energy in pilot plant scale tests.
    4) In the commercial plant test, sulfer content could be reduced less than 0.001 wt% by high speed rotation (>120 rpm) in spite of low hot metal temperature below 1250°C.
  • Effect of Baffles on the Mixing of Liquid and Particles in a Mechanically Stirred Vessel

    pp. 329-333

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    For the application of the mechanical stirring method currently used in KR process to the new refining processes, the effect of baffles on the mixing of bath liquid and solid particles was investigated using a water model. The baffle whose width is 1/10 of the vessel diameter was enough to enhance the liquid-particles mixing. The LDV measurement showed the formation of the unsteady vertical flow by the baffle. The same effect on the mixing was observed by injecting gas from the bottom into the mechanically stirred vessel.
  • Effect of Immersion Cylinder on the Dispersion of Low Density Particles by Mechanical Agitation

    pp. 334-338

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    Water model experiments were carried out to promote the dispersion of fine particle into a molten steel bath agitated by an impeller. The dispersion was significantly promoted by immersing a circular cylinder at a radial position between the center of the bath and side wall of the vessel. This is because the liquid flow on the bath surface becomes asymmetrical with respect to the center line of the bath in the presence of the cylinder and, as a result, a large scale vortex is formed in the bath.
  • Behavior of Stratified Two Liquid Layers Contained in a Baffled Vessel Suddenly Set in Rotation

    pp. 339-344

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    A cylindrical baffled vessel containing two liquids of different densities was rotated suddenly around its vertical axis. The interfacial area between the two liquids increased significantly through the effect of the baffle in the initial stage of rotation and the two liquids returned nearly to the initial state in the final stage of rotation. This phenomenon is very beneficial for promoting mixing of molten steel and slag and later separation of them. The maximum penetration depth of the upper liquid into the lower layer and the flow establishment time of the flow in the vessel were measured. Empirical equations were proposed for these quantities.
  • Conditions for the Generation of Swirl Motion of a Gas-Liquid Two-phase Jet in a Cylindrical Vessel

    pp. 345-350

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    A swirl motion of a gas-liquid two-phase jet in a cylindrical vessel appeared under certain injecting conditions, and the bath was strongly agitated in the presence of the swirl motion. This phenomenon is beneficial for the refining of steel and the treatment of waste water. The critical conditions for the generation of the swirl motion were revealed in this study. Correlation methods were proposed for the critical conditions as functions of the water flow rate, gas flow rate, and the aspect ratio of the bath.
  • The Characteristics of Swirl Motion in a Cylindrical Vessel Induced by a Gas-Liquid Two-phase Jet

    pp. 351-356

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    A cylindrical bath was agitated by a bottom blowing gas-liquid two-phase jet. A swirl motion of the bath appeared under certain blowing conditions. The bath was highly agitated in the presence of the swirl motion. Therefore the swirl motion is beneficial for the promotion of bath mixing. The starting time, the period and the amplitude of the swirl motion were measured. These quantities fell between their respective values for baths agitated by a bubbling jet and a liquid jet. The gas flow rate ratio was defined as the ratio of gas flow rate to the total flow rate of gas and liquid. This ratio was found to be useful for predicting the three quantities.
  • Transient Characteristics of Swirling Liquid Jet in a Cylindrical Bath

    pp. 357-362

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    When liquid was injected through a nozzle settled on the bottom of a cylindrical bath, a liquid jet was formed above the nozzle. The jet swirled around the bath axis under a certain injection condition. The bath was highly agitated in the presence of the swirl motion. Therefore the swirl motion is very beneficial for the agitation of a molten steel bath. Considering these circumstances, the authors previously proposed a novel refining process using the swirl motion and investigated the basic characteristics of the swirl motion such as the preferable condition for its occurrence, the period, and the amplitude. In its practical applications, the transient characteristics of the swirl motion are necessary in addition to the basic characteristics. Water model experiments were carried out in this study to understand the starting time and damping time of the swirl motion in the bath. Empirical equations were derived for the two representative time scales.
  • Effect of Top Slag on the Swirl Motion of Cylindrical Bath Agitated by Bottom Blowing Liquid Jet

    pp. 363-370

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    Model experiments were carried out to understand the effects of slag on the swirl motions of a molten steel jet generated through a centered bottom nozzle. Two types of swirl motions were observed. One appeared when the silicone oil layer was thin, while the other appeared when the silicone oil layer was thick. The starting time, damping time, period and amplitude of the two swirl motions were investigated and correlation methods of them were proposed.
  • Water Model Experiment on Mixing Time in a Cylindrical Bath Agitated by Swirling Molten Steel Jet

    pp. 371-378

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    Water model experiments were carried out on a continuous refining process using swirl motion of a molten steel jet. Mixing time was measured by the electric conductivity method. The mixing time was strongly affected by the volume of the liquid flowing in the circulation system. The effect of swirl motion on the mixing time became significant as the aspect ratio of the bath decreased and the inner diameter of the bath increased. The mixing time in a bath agitated by swirling liquid jet was shorter than that of the same scale bath agitated by swirling bubbling jet because of smaller energy loss. An empirical equation was proposed for the mixing time as a function of the aspect ratio, the inner diameter of the bath, and the volume of the liquid in the circulation system.
  • The Swirl Motion of Vertical Bubbling Jet in a Spherical Vessel at Low Weber Numbers

    pp. 379-386

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    A spherical bath agitated by bottom gas injection showed two types of swirl motions, shallow and deep water wave types, under certain blowing conditions. The swirl motions were very similar to those observed for a cylindrical bath. The conditions under which the swirl motions appeared were experimentally determined. Empirical equations were proposed for the period, amplitude, starting time, and damping time of the swirl motions.
  • Mixing Time in a Spherical Vessel Agitated by Bottom Gas Injection

    pp. 387-393

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    Mixing time in a spherical bath agitated by bottom gas injection was measured in the presence of a swirl motion of the deep water wave type. The mixing time was shorter than that of a cylindrical bath because the so-called dead zone was absent in the spherical bath. An empirical equation was proposed forthe mixing time.
  • Effect of Lorentz Force on Instability of the Interface between Two Liquid Layers

    pp. 394-400

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    Recently, in the field of refining reactors of steel making processes, new technologies for obtaining high process efficiency are strongly required. Upward Lorentz force due to stationary magnetic field and direct electric current can make rapid mixing between two liquid layers. And it is expected as one of key technologies in developping innovative refining processes. In this process. Lorentz force appears only in the lower liquid by the difference of electrical conductivity, and a part of the lower loquid scatters upward to disperse as small droplets into the upper liquid. This scattering behavior of the lower liquid is important and dominant phenomena to explain the rapid mixing of two liquids.
    From the results of experiments using mercury-silicone oil system, it is found that Kelvin-Helmholts instability on the interface causes the first scattering, and successive scattering occur in terms of Rayleagh-Taylor instability. Scattering frequency increases with increasing electric current density. And it also increases the volume of the reservoir even if the lower liquid has suffered the same Lorentz force.
  • Effect of Oxide Additives on Desulfurization Efficiency of Hot Metal by CaO-based Powders

    pp. 401-407

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    Utilization of CaO-CaF2 fluxes provides an efficient and inexpensive method for the dusulfurization of hot metal and has been used extensively. However, it is an urgent necessity to develop an effective desulfurization treatment without CaO-CaF2 fluxes from the environmental point of view. Experiments were carried out mainly at 1400°C to clarify the effect of oxide additives on the desulfurization behavior of hot metal by using CaO-based powders and synthesized CaO-Al2O3 slags. The desulfurization efficiency of CaO-based powders increased by the addition of Al2O3 and Na2CO3. However, as the amount of Al2O3 addition increased up to 30 mass%, the initial desulfurization rate was decreased, although the formation of liquid slag at the early stage of reaction was promoted. CaO-Al2O3-TiO2 fluxes were found to have the largest promoting effect on the desulfurization, due to low melting point and low viscosity of such slags. According to the EPMA mapping analysis, it was found that the flux powders near the slag-metal interface were sintered or partly melted, and that the sulfur removed was concentrated in this flux. As the result, the desulfurization rate was considered to be considerably accelerated by Ar blowing into the metal bath. Consequently, CaO-Al2O3-TiO2 fluxes was regarded to be very useful for hot metal treatment.
  • Effect of Flux Composition on the Rate of Desulfurization of Hot Metal by CaO-Al2O3 Flux

    pp. 408-413

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    Study was made on the desulfurization of hot metal by CaO and Al2O3 powder mixture fluxes. The optimum Al2O3 content to gain maximum rate of desulfurization was observed. These phenomena could be qualitatively considered by equilibrium between solid slag and hot metal. Difference in the desulfurization rate among different Al2O3 content could not explained by a simple diffusion model in solid phase. There was a difference in pore distribution of CaO immersed into different hot metal composition. Thick reacted region was formed and large pore was found in it when aluminum content of hot metal was high and it suggest that desulfurization was promoted by increment of specific reaction surface area with hot metal. In contrast, when silicon content of hot metal was high, a silicon rich film was observed at the surface of CaO, and this was identified as gehlenite. Formation of gehlenite film may reduce the rate of desulfurization and this was consistent with previous study.
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    2. Dephosphorization and Desulfurization Pretreatment of Molten Iron with CaO-SiO2-CaF2-FeO-Na2O Slags ISIJ International Vol.38(1998), No.2
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  • Mechanism of Simultaneous Decarburization and Nitrogen Removal by Blasting Iron Ore Powder on to Molten Steel Surface

    pp. 414-421

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    In order to develop the effective way of nitrogen removal from molten steel in the electric arc furnace steelmaking, an attempt was made to accelerate the reaction by the simultaneous decarburization. The iron ore powder was blasted on to the molten steel surface with Ar carrier gas under atmospheric pressure. The melt was 20 kg. The temperature was 1850 to 1950K. The gas flow rate was 3.33 and 4.17×10-4m3/s (STP). The ore blasting rate was 0.167, 0, 417 and 0.500 g/s. The results are summarized as follows;
    (1) By the blasting of iron ore, the decaburization occurs resulting in the acceleration of nitrogen removal several times than the mere Ar blasting.
    (2) Under the hard blasting condition, the nitrogen content decreased from 70 to 28 ppm for 1, 000 s, while the carbon content decreased from 0.55 to 0.12 wt%.
    (3) When the carbon content is larger than 0.09 wt%, the decarburization was controlled by the oxygen transfer and CO bubbles are formed in the melt. When it is less than 0.09 wt%, however, the decarburization was controlled by the carbon transfer and the reaction occurs only on the melt surface.
    (4) It is concluded that the effective nitrogen removal is possible even under atmospheric pressure, in the ranger where the decarburization reaction is controlled by the oxygen transfer.
    (5) The effective interfacial area is 7 times at most as much as the cross sectional area of furnace.
  • Possibility of Several Steelmaking Reactions by the Injection of H2 into Molten Steel

    pp. 422-428

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    An attempt was made to utilize H2 for the secondary refining in steelmaking process, because H2 would react with [O] and [S] without any inclusions and accelerate the nitrogen removal from the molten steel. The 20 kg of plain carbon steel was melted in the induction furnace. The gases of Ar, N2 and H2 were injected from the bottom. The temperature was ca. 1880K. The gas flow arte was 2.50 and 3.33×104m3/s (stp). The results are summarized as follows.
    (1) The rate of nitrogen remove by H2, injection was 1.5 to 2.6 times larger than by Ar injection. The mechanism was (i) reduction of poisoning effect of [O], (ii) acceleration of mass transfer in the gas phase and (iii) finer bubble dispersion due to Marangoni effect.
    (2) The deoxidation proceeded down to 6.0 ppm by H2 injection. But this result was the sum of deoxidation by [C] and H2. Taking into account of oxygen penetration from the outside of furnace, deoxidation by H2 was evaluated. The H2 bubbles leave the molten steel far from water vapor saturation. One reason is that the deoxidation process should be controlled not only by mass transfer in the molten steel but also that in gas phase. The other reason is the shallow molten steel bath.
    (3) Neither desulfurization nor methane formation occurred by H2 injection.
    (4) The [H] content decreased down to less than 1 ppm by Ar injection for 420 s.
  • Penetration Behavior of Molten Metal into Porous Oxides

    pp. 429-438

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    This paper reviews recent developments on experimental methods and results of molten metal penetration into porous media and its theoretical achievements. Several selected topics are focused on, including experimental procedure, threshold pressure, penetration behavior, time dependence of penetration height, etc. studied by authors. And several interesting results of some researcher, including spontaneous penetration, influence of atmosphere or surface treatment on the penetration behavior are also highlighted. On the experimental method, authors have recently developed a new observation method of penetration of molten metal into porous refractory. The penetration behavior was observed by using X-ray radiographic apparatus. On the theoretical achievements, the data for penetration height were analyzed based on a capillary model in which a labyrinth (or tortuosity) factor was introduced, that is, a modified capillary model. The penetration behavior of molten metal was predictable based on penetration behavior of mercury. And some countermeasures to suppress or accelerate the penetration of molten metal into porous media was suggested.
  • Behavior of Gas Curtain Formed at the Boundary between Container Wall and Liquid by Injection Gas

    pp. 439-444

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    An almost continuous gas film, which may be called gas curtain, was formed at the boundary between water solution and solid wall with poor wettability when nitrogen gas was injected into the water solution from the bottom end of the solid wall trough porous brick.
    Length of the gas curtain was observed and briefly discussed in relation to gas injection rate, inclined angle of the solid wall, NaCI concentration, concentration of surface active agent (C8H17SO3N3), roughness of the solid wall and porosity of the porous brick.
  • Electrochemical Sensor for Liquid Alloys using Solid Electrolyte

    pp. 445-450

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    The techniques for electrochemical sensors with solid electrolytes for process control are reviewed. Cell construction, principle of emf measurements, application of oxygen sensors for liquid nickel, silicon and iron at normal and/or low oxygen potentials are explained. Si-sensor in liquid iron by use of tri-phasic zirconia based solid electrolyte, S-sensor in liquid iron with Laβ-alumina+(La2O2S+La2O3) solid electrolyte, Cu-sensor in Cu-Sn alloys and Cu-matte with Cusicon solid electrolyte, and Al-sensor in Zn bath are explained.

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