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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 104 (2018), No. 10

  • Effective Utilization Technique for Coal Having High Fluidity and Long Maximum Permeation Distance by Coal Size Adjustment

    pp. 525-534

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    DOI:10.2355/tetsutohagane.TETSU-2018-014

    In our previous paper, a new measurement method for coal thermoplasticity, “permeation distance method”, was devised. Permeation distance of thermally plastic coal into glass beads layer adjacently placed on the coal sample was measured as a unique caking property. The maximum permeation distance measured is roughly correlated with Gieseler fluidity, however large deviation is observed especially in high fluidity coals. Moreover, it was revealed that high MF coal having longer maximum permeation distance forms thinner pore-wall structures in coke and that coke strength deteriorated when the coal blend included longer maximum permeation distance coal. Therefore, technique for reducing the adverse effects of long maximum permeation distance coal on coke strength is necessary so as to utilize the coal more efficiently.In this paper, influence of grain size mainly of high MF coal on permeation distance and coke strength were investigated for clarifying possibility of controlling permeation distance. As a result, measured maximum permeation distance became shorter with decreasing coal size. Moreover, the coke strength deterioration caused by long maximum permeation distance coal in coal blend was suppressed as the size of the long maximum permeation distance coal became smaller. Consequently, designs and control techniques of coal size were proposed for more effective utilization of long maximum permeation distance coal.
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    Readers Who Read This Article Also Read

    1. Development of Numerical Thermo-fluid Simulator of Ferro Coke Shaft Furnace Tetsu-to-Hagané Vol.104(2018), No.10
    2. Influence of Injection Distance on Water Droplet Behavior in High Pressure Descaling Tetsu-to-Hagané Vol.104(2018), No.10
    3. Influence of P2O5 on Dissolution Behavior of Lime in Molten Slag Tetsu-to-Hagané Vol.104(2018), No.10
  • Simulation of Powder Motion with Particle Contact Model Including Intervening Liquid

    pp. 535-542

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    DOI:10.2355/tetsutohagane.TETSU-2018-024

    The control of packed bed permeability in blast furnace is an important issue to realize highly efficient and stable operation of blast furnace under low carbon condition. The powder accumulation in the packed bed deteriorates the permeability, thus it is necessary to understand the powder behavior in the packed bed. Recently it was revealed that the existence of liquid in the bed had drastic effect on the motion and the accumulation of powder in the bed. In this study a mathematical model to describe the behavior of powder particle under liquid existing condition was developed using discrete element method. The model took into account cohesive force, normal viscous force, sheer viscous force and lubrication due to the liquid film. The model was validated by the comparison of the particle trajectories under various liquid properties. The model was applied to the simulation of passing behavior of the powder particles through the opening among three coarse spherical particles, and successfully reproduced the accumulation behavior under wetting condition.
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    Readers Who Read This Article Also Read

    1. Influence of Injection Distance on Water Droplet Behavior in High Pressure Descaling Tetsu-to-Hagané Vol.104(2018), No.10
    2. Influence of P2O5 on Dissolution Behavior of Lime in Molten Slag Tetsu-to-Hagané Vol.104(2018), No.10
    3. Development of Numerical Thermo-fluid Simulator of Ferro Coke Shaft Furnace Tetsu-to-Hagané Vol.104(2018), No.10
  • Development of Numerical Thermo-fluid Simulator of Ferro Coke Shaft Furnace

    pp. 543-550

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    DOI:10.2355/tetsutohagane.TETSU-2018-042

    For the sake of reduction of reducing agent in blast furnace and making use of low-quality iron ore and coals, the use of ferro coke containing metallic iron as a catalyst was proposed to control the thermal reserve zone temperature. In the production of ferro coke, a vertical shaft furnace is used to realize the optimum carbonizing and pre-reduction process. To optimize the heating process of the shaft furnace, visualization of the temperature distributions inside the shaft furnace is important. In this study, a new simulation technology is developed to visualize the gas flow and the temperature distribution of the briquettes inside the shaft furnace. In the simulation method, both gas flows and solid flows are modeled by the finite volume method so that we can obtain simulation results within a reasonable computation time. Simulation results show that we achieved a good temperature profile in the shaft furnace in the final test campaigns in Keihin works.
  • Influence of P2O5 on Dissolution Behavior of Lime in Molten Slag

    pp. 551-558

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    DOI:10.2355/tetsutohagane.TETSU-2018-053

    Dissolution of lime into molten slag is an important phenomenon in hot-metal dephosphorization treatment and should be suitably promoted in order to obtain an effective refining reaction and to recycle slag as some environmental resources. A lot of research has been conducted on the phenomenon, but the influence of P2O5 on the dissolution behavior of lime has never been studied despite the presence of P2O5 in the slag obtained during actual operation.In this study, the dissolution behavior of lime in CaO-SiO2-FeO or CaO-SiO2-FeO-5.2 mass% P2O5 molten slag was investigated via a high-temperature laser microscope, an optical microscope, and a scanning electron microscope /energy dispersive spectroscopy (SEM/EDS) in order to clarify the influence of P2O5 on the dissolution behavior of lime. We conclude that the addition of P2O5 to the slag accelerates the dissolution of lime in the molten slag mainly by increasing the CaO equilibrium content in the liquid slag saturated with 2CaO·SiO2.P2O5 is a product of the dephosphorization reaction, and basically, its content is preferred to maintain low content for dephosphorization based on equilibrium theory. However, the experimental results obtained in this study clarify that the presence of P2O5 in molten slag is effective for the promotion of the dephosphorization reaction when the reaction is limited by the dissolution of lime.
  • Introduction of Dendrite Fragmentation to Microstructure Calculation by Cellular Automaton Method

    pp. 559-566

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    DOI:10.2355/tetsutohagane.TETSU-2018-026

    Control of solidification microstructure is necessary because the microstructure affects material characters. In order to predict solidification microstructure, effect of fragmentation was indirectly introduced to the cellular automaton method using Vcrit, which is threshold of molten steel flow. Calculations were carried out with various Vcrit (200 μms–1Vcrit≦1 mms–1) and the results were compared with the results of casting experiment using high carbon steel. Observed specimens were extracted from upper part and lower part of casting. Equiaxed grains and branched columnar grains were observed in the microstructure of upper specimen and just columnar grains were observed in the microstructure of lower specimen. Calculation results with Vcrit which is greater than 400 μms–1 show good agreement with microstructure of both observed specimens qualitatively. The microstructures were calculated because flow velocity of molten steel around upper specimen was much greater than flow velocity around lower specimen. There is a possibility that solute transportation which induces the fragmentation occurs even if velocity of molten steel flow was in the order of 10–4 ms–1.
  • Microwave Time Domain Measurements for Measuring Thicknesses of Mold Powder Layers

    pp. 567-576

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    DOI:10.2355/tetsutohagane.TETSU-2018-002

    In a continuous casting process, a mold powder layer consisting of a powder layer and a molten layer on molten steel is important to ensure a quality of steel. Therefore, measuring the thicknesses of the powder and molten layers is needed. In this study, a method to measure the thicknesses of each layer with microwave time domain measurement using VNA (Vector Network Analyzer) is proposed. Because a microwave is insensitive to dust and high temperature, the method has the possibility to measure the thicknesses of the powder and molten layers stably in a real field environment around the continuous casting process. Moreover, VNA can measure wideband frequency signals with high SN ratio. Thus, the method has high range resolution and SN ratio. The measurements of thicknesses of the powder layer on an aluminum plate and the mold powder layer consisting of the powder and molten layers were attempted using the method. As the results, it was shown that the method can measure the thickness of the powder layer on the aluminum plate with the error of 0.56 mm. It was also shown that the method has the ability to measure the thickness of the powder layer on the molten layer. Since the measurements were performed in a laboratory, the investigation of the applicability of the method to the real field environment is future work. The ability of the method to measure the thickness of the molten layer, on which the powder layer exists, should also be evaluated in the future.
  • Influence of Injection Distance on Water Droplet Behavior in High Pressure Descaling

    pp. 577-584

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    DOI:10.2355/tetsutohagane.TETSU-2018-035

    Hydraulic descaling is used in hot rolling mills in order to remove scale and prevent surface defects. Because the impact pressure of the descaling jet is one important factor from the viewpoint of mechanically breaking and applying thermal shock to scale layers, the water jet structure and the droplet velocity should have large effects on scale breaking properties. However, the influence of the injection distance on the jet structure and the droplet velocity has not been clearly understood. In this work, the behavior of changes in the descaling jet structure and attenuation of the water droplet velocity along the injection distance were investigated experimentally. High pressure descaling nozzles with pressures up to 25 MPa were used, and the injection distance was varied in the range from 30 to 400 mm. The jet structure was observed with a high speed camera, and the water droplet velocity and diameter were measured with a phase Doppler analyzer. It was confirmed that the jet structure changes continuously through a process of continuous flow, break-up, water lump, and water droplet. It was found that a continuous flow can be kept for a long distance by using a low injection pressure and large flow rate, and the water droplet diameter also becomes larger, which reduces velocity attenuation. These deformation properties of the jet structure are related to the Weber number expressed by the relative velocity between a water droplet and the surrounding air. A smaller Weber number is effective for reducing velocity attenuation over a long injection distance.
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    Readers Who Read This Article Also Read

    1. Development of Numerical Thermo-fluid Simulator of Ferro Coke Shaft Furnace Tetsu-to-Hagané Vol.104(2018), No.10
    2. Simulation of Powder Motion with Particle Contact Model Including Intervening Liquid Tetsu-to-Hagané Vol.104(2018), No.10
    3. Influence of P2O5 on Dissolution Behavior of Lime in Molten Slag Tetsu-to-Hagané Vol.104(2018), No.10
  • Effects of Electrolyte Composition and Additives on the Formation of Invar Fe-Ni Alloys with Low Thermal Expansion Electrodeposited from Sulfate Bath

    pp. 585-593

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    DOI:10.2355/tetsutohagane.TETSU-2018-051

    The effects of solution composition and additives on the formation of electrodeposited invar Fe-Ni alloys with low thermal expansion was investigated. In all the solutions, with increasing the current density from 10 A·m–2, the Ni content in deposits significantly decreased and showed the anomalous codeposition in which electrochemically less noble Fe deposits preferentially. With increasing current density further, Fe deposition reached the diffusion limitation of Fe2+ ions, as a result, the Ni content in deposits increased with current density. The current density for initiating to increase the Ni content in deposits shifted to higher value with increasing the concentration of Fe2+ ions because of increase in diffusion-limited current density of Fe. With increasing the concentration of malonic acid, the current density region in which the Ni deposition was suppressed, extended and the potential which Fe deposition reached to the diffusion limitation of Fe2+ ions shifted to the less noble direction. As a result, the curve which showed the relationship between the Ni content in deposits and current density, shifted to higher current density region with increasing the malonic acid. The current efficiency for alloy deposition greatly decreased due to promotion of hydrogen evolution with the concentration of malonic acid above 0.05 mol·dm–3. The Ni content in deposits significantly increased with thiourea. With boric acid, the Ni content in deposits somewhat increased in the lower current density region. With both boric acid and saccharin, the invar alloy of Fe-36 mass% Ni was obtained in the wider current density region.
  • Effect of Crystal Structure of Surface Compound Layer on Fatigue Strength of Nitrided SCM 435 Steel

    pp. 594-601

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    DOI:10.2355/tetsutohagane.TETSU-2018-011

    Effect of crystal structure of surface compound layer on the fatigue strength of nitrided SCM 435 steel was investigated. Specimens in which the crystal structure of the surface compound layer was controlled to γ’-Fe4N phase or ε-Fe2-3N phase were prepared by gas nitriding treatment capable of changing nitriding potential (KN). Axial fatigue test were conducted to the specimens. Even in each test specimen which has different crystal structure of the compound layer, distribution of residual stress and hardness in the nitrogen diffusion layer exhibited almost same values. It is revealed that fatigue strength significantly depends on crystal structure of surface compound layer. Specimens with γ’-Fe4N phase dominant shows substantially high fatigue strength comparing to specimens with ε-Fe2-3N phase dominant. In the fatigue test under stress ratio R=0, the specimen from which the surface compound layer was removed showed the highest strength. The fatigue strength is considered to be governed by the fracture strength of each compound layer. Namely, in the specimen with ε-Fe2-3N phase dominant, fatigue cracks are induced by fracture of brittle ε-Fe2-3N phase layer and progress into nitrogen diffusion layer due to stress intensity factor (ΔK) at crack tip exceeds the threshold of stress intensity factor range (ΔKth) in the matrix. On the other hand, in the case of γ’-Fe4N phase dominant, γ’-Fe4N phase with high toughness showed high fatigue strength due to suppress the crack initiation up to a higher stress level.
  • Influence of Heat Collection Plate Structure on Thermoelectric Generation Unit Performance for Radiant Waste Heat Recovery in Continuous Casting Process

    pp. 602-611

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    DOI:10.2355/tetsutohagane.TETSU-2018-029

    In recent years, environmental issues such as global warming and the energy resource depletion have become serious matters. Waste heat recovery can be one of the key technologies to solve these issues. Thermoelectric generator (TEG) is one of the promising technologies expected to play an important role for steel plant’s waste heat recovery, particularly radiant heat from steel products which had not been used yet efficiently. Despite the improved performances of thermoelectric materials, more effort on a TEG unit is needed to maximize TEG system performance. In optimizing the TEG unit performance, the influence of the surface shape of the TEG units has been investigated. Two types of the heat collection plate have tested. The first one was with a fin structure and the second one was with plain plate structure. Based on the results of the simulation and the experiments, it can be concluded that a better performance will be achieved by the TEG unit which has plain type heat collection plate because of larger total heat flux input to TEG modules of the TEG unit with plain type heat collection plate structure compared to the fin type heat collection structure.

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