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

Tetsu-to-Hagané Vol. 87 (2001), No. 5

  • Basic Research on Ironmaking Process in Blast Furnace and Development in Near Future

    pp. 207-220

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    For the last decade, ISIJ organized several collaborative committees in the field of ironmaking such as "Transport phenomena of four fluids", "Enhanced processing technology in lower part of BF", "Advanced approach to intelligent agglomeration", and so on. From 1999, new research project for innovative ironmaking reaction has started to aim at halving energy consumption and load for environment of BF by the promotion of Science and Technology Agency of Japan. Advanced research results of those collaboration were introduced and the significance of basic research has been disccussed.
  • Overview of New Direct Reduced Iron Technology

    pp. 221-227

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    The technology of direct reduced iron production is reviewed for a look at the future trend of alternative iron source out of the blast furnace route. High productivity direct reduced iron based on the demand on mini-mills has been established by the enlargement of furnace size and high temperature reduction. New technical development in the alternative iron world is a conjunction with rotary hearth furnace and iron ore agglomerate with incorporated carbon. The carbon composite agglomerate is reduced in the time less than 10 min at 1300-1400°C in the rotary hearth furnace. The carbon composite agglomerate and rotary hearth furnace technology allows the recycling of residues due to the next century.
  • Behavior of Dioxins in the Sintering Process of Iron Ores

    pp. 228-237

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    The new "law concerning special measures against dioxins" is promulgated in January, 2000 in Japan and the emission control of dioxins has been enforced to the iron are sintering plants and some other plants/processes for metals recycling.
    In 1997, a collaborative research project was formed by the researchers and engineers of Japanese integrated steel makers and universities, in order to investigate the behaviors of dioxins and relating substances in the sintering process of iron ores and to search for new technological principles for suppression of the emissions rather than waste gas treatments. The project has carried out the examination of previous literatures and data, several plant measurements and tests, experiments using process simulators (sinter-pots) and fundamental researches.
    The present paper reports a part of the results of the measurements and analyses of a sintering plant equipped with several waste gas treatment processes. Characteristics of behaviors and flows of dioxins in the sintering bed, windboxes and gas treatment processes are discussed. Further, the effect of additives to raw materials, especially chlorine-bearing materials, on the discharged amount of dioxins in exhaust gas is examined based on the results of sinter-pot tests.
  • Effect of Coal Interaction on Coke Strength

    pp. 238-244

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    To investigate the mechanism of coal interactions for the coke strength, the coke strength for various binary blends was measured. The interaction coefficient a(i, j) for coke strength in equation (1) is defined using S(i, j), the strength of the combination of two different coals, i and j, and Say, the averaged strength of coal i and coal j.
    a(i, j)=(S(i, j)-Sav)/Sav…(1)
    The interaction coefficient a(i, j) increases with the difference of softening point ΔTsp and shows its maximum at the resolidification point ΔTrs of two constituent coals, about 30°C. These changes of the interaction coefficient, a(i, j) were explained by change of coke porosity. Then, the change of coke porosity is caused by the changes of dilatation and contraction.
    For the process control of the coal blends, the interaction coefficients were correlated to the rank (reflectance of vitrinite (Ro)) and fluidity (Gieseler fluidity (MF)) of the constituent coals and the differences in these properties. A method of estimating coke strength based on the coal interaction has been used in coal blending design at coke plant.
  • Analysis of the Influence of Crack in Coke on the Fracture

    pp. 245-251

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    Homogenization method and s-version FEM are proposed to estimate the strength of coke in the view of its microstructure.
    It is important for improvement of permeability in a blast furnace to estimate the condition for making high-strength coke by evaluating its strength. To evaluate the strength of brittle materials with complex microstructual geometry such as coke, it is required to develop analytical procedures that can consider microscopic fractures. Stress intensity factor considering influence of microscopic cracks and inclusions can be estimated by using homogenization method and s-version FEM.
    To evaluate the strength of macroscopic base, we use homogenization method and estimate the stress intensity factor. Then the influence of the crack distribution on the stress intensity factor is considerd. The stress intensity factor is estimated in the case when inclusions exist.
    On the other hand, s-version FEM is used to estimate the stress intensity factor of macrocracks that are a principal factor of coke's brittle fracture considering the influence of microstructure.
    Numerical results calculated by those two methods are in good agreement with analytical result, and the performances of these methods are verified.
    When the Young's modulus of includes is higher than that of the matrix, the stress intensity factor of the microcrack decreases and increases in case inclusions locate ahead of the microcrack-tip and aback of the microcrack-tip, respectively.
    Macrocrack will propagate easily when microcracks lay ahead of macrocrack, and it will be hard for macrocrack to propagate when microcrack lay aback of macrocrack.
  • Reactivity of Coke with CO2 and Evaluation of Strength after Reaction

    pp. 252-258

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    For the investigation on coke degradation in the blast furnace, reactivity of coke with CO2, the morphological change after reaction and the change in its strength were examined. Five kinds of cokes were used. They were machined in the spherical form of 20 mmφ and reacted with pure CO2 at 1073 to 1673K. After the reaction, the specimen were visually observed and the porosity distribution was estimated. Further, they were pressed by universal test machine to estimate the strength after reaction.
    The reaction mode changed at 1373K. At lower temperature, the reaction proceeded homogeneously throughout the specimen, while restricted near the surface at higher temperature. The porosity was almost uniform at lower temperature, but increased near the surface at higher temperature. The tensile strength was estimated indirectly from the results of compression test. The tensile strength was 0.85 to 1.77 MPa before the reaction. It decreased to 0.51 MPa after 50% reaction at 1273K. At 1573K, however, the strength did not decrease so much for the blast furnace coke and highly reactive coke. The strength of formed coke increased after 25% reaction. These changes in strength at 1573K can be attributed to the reaction mode where the reaction did not proceed to the core of specimen, and the crystallization proceeded in the core at higher temperature. The fracture energy, which might show the strength of matrix, decreased by the reaction in all cases.
  • Change of Coke Structure and Behavior of Fine Generation during Gasification of Coke Sphere in High Temperature Region

    pp. 259-266

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    According to the pulverized coal injection (PCI) into blast furnace (BF), the fine generation of coke in the lower part of BF especially around raceway has come to an important problem for stable operation.
    In this study, three kind of spherical cokes were used for gasification experiment simulated to the lower part of BF (1500-1700°C). Each cokes before and after experiments were examined the fine generation using I type tumbler for single particle which was developed by authors. The behavior of fine generation in high temperature can not predict from the conventional industrial tests such as CSR, DI, CRI and JIS-RI, because the industrial tests are carried out around 1000°C and the apparent reaction rate of coke consist of not only a chemical reaction rate but also a diffusion of gas in pore, depending on the reaction temperature. Especially in higher temperature than 1500°C, graphitization behavior will affect significantly on the apparent reaction rate. Then, structure change of coke after experiment was investigated using fluorescent resin and the change of porosity from the surface was clarified. The reaction zone from the surface to the inside was determined by computer aided image analysis. It was found that the amount of coke remained in the reaction zone was in good agreement with that of fine generated from coke.
  • Mechanism of Coke Deterioration by Shear Stress

    pp. 267-273

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    To clarify the generation behavior of fine coke by shear stress in the lower part of blast furnace, coke degradation behavior was investigated using the shear stress tester. Furthermore the theory of tribology was applied to estimate the resistance of wear. The main results obtained are as follows;
    1) The generation rate of coke fine was basically proportional to sliding distance. Shear conditions (shear rate and vertical stress) had a great effect on coke deterioration behavior.
    2) The coke fine ratio increased rapidly with the vertical pressure or the decrease of coke strength. It was assumed that plastic deformation of coke surface layer resulted in the expand of real contact area among lump coke.
    3) The wear resistance of coke could be described by the specific wear rate and breaking energy which were approximately 0.1kJ-1 and 200 kJ/kg respectively for normal metallurgical coke.
  • The Effect of Defects on Surface-breakage Strength of Coke

    pp. 274-281

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    Single coals were carbonized at different bulk densities in a pilot coke oven. DI6150, micro-strength indices and porosities of cokes were measured and polished coke samples were observed under a low magnification microscope. It is shown that the strength of coke matrix does not depend on the rank of parent coal and that the surface-breakage strength of coke is determined by defects such as non-adhesion grain boundaries and connected pores. The formation mechanism of these defects are discussed.
  • Improvement of Strength of Preheated Pellet with Small Addition of Sodium Silicate

    pp. 282-289

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    In the iron are pelletizing process of grate-kiln system for induration, pellets are indurated at about 1000°C within a traveling grate and then at about 1 200°C within a rotary kiln. It is very important for pelletizing process to increase strength of preheated pellet, which means the pellet crushing strength before a rotary kiln, in order to prevent the collapse of pellets in a rotary kiln. Therefore, to strengthen pellets sufficiently within a traveling grate with shorter time, an application of liquid phase sintering method to palletizing process was studied experimentally with addition of sodium silicate solution. The results are summarized as following:
    ( 1 ) The strength of preheated pellets was increased by addition of dilute sodium silicate solution with low melting temperature.
    ( 2 ) The strength of preheated pellets with addition of sodium silicate solution for granulating water, was much more increased than that with addition of solid sodium silicate.
    ( 3 ) Addition of sodium silicate solution did not influence on reducibility, reduction degradation index and reduction test under load of pellets.
  • Effect of Moisture Distribution of Sinter Mixture on Granulating Particles

    pp. 290-297

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    For increase of sinter productivity, it is important to design sinter mixture granulation methods of moisture content, moisture distribution, and mixing method.
    In order to design them, especially moisture distribution and its transformation with mixing, laboratory granulation tests were carried out. These tests were moisture absorption rate for a coarse iron ore (4-6 mm), adhesion of low moisture content fine iron ore (-0.25 mm) and one pseudo-particle coated with high moisture content fine ore, and granulation of coarse and fine ores with varying initial and adding moisture distribution and mixing method with a drum mixer and a high speed agitating mixer.
    The main results obtained are as follows:
    ( 1 ) It took over 5 h to absorb moisture to coarse ore surrounded by raw sinter materials with 6 mass% moisture.
    ( 2 ) When adhering low moisture content fine to pseudo-particles coated with high moisture content adherent fine ores, final moisture content of total adherent fine converged to a constant value.
    ( 3 ) With mixing by a drum mixer, high moisture content fine adhered first to coarse. Next, low moisture content fine adhered to the coarse coated with high moisture content adherent fine. Then, pseudo-particle size distribution depended on moisture distribution of fine as well as ratio of coarse and fine. Pseudo-particle size distribution was sharper, when moisture distribution of fine was sharper and ratio of fine was lower.
    On the other hand, with mixing by a high speed agitating mixer, moisture distribution of fine went homogeneous before adhering. This result suggests that adhering and collapse occurred at a same time. With mixing by a drum mixer after mixing by a high speed agitating mixer, pseudo-particle size distribution was sharpest.
  • Effect of Mineralogical Properties of Iron Ore on Pore Formation of Sinter

    pp. 298-304

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    The effects of mineralogical properties of iron ores on the pore formation in the sintering process have been examined from view points of partical size, combined water content and structure of iron oxide.
    Quasi-particles consist of nulear ores coated with limestone (-0.5 mm and the ratio of CaO to ore (CaO/Ore) was 0.1 and 0.2) have been made by granulating with water, and heat treated by the electric furnace that simulated the heating pattern in an actual sintering process. The porosity of sintered specimen was determined by using the image analysis.
    It was found that the porosity of sinterd specimen was increased with the increase in the combined water contents significantly, whereas was not affected by the particle size in the range of 1.0-4.75 mm. However, Indian high-goethite ore had low porosity of sintered specimen in spite of high combined water contents. It was presumed that the martite was converted into the dense structure and the melts penetrated into the cracks of goethite during heating.
    It was concluded that, in order to control of the pore formation of sinter, the ratio of CaO/Ore should be determinted by the combined water contents of the iron ores as nuclei of quasi-particles and the sturcture of iron oxides.
  • Operation Conditions of Iron Ore Sintering Process Combined with Oxygen Enrichment and Exhaust Gas Recirculation System

    pp. 305-312

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    An advanced sintering process was proposed on the basis of mathematical models and was verified by pot tests. This process is characterized by combining exhaust gas recirculation with oxygen enrichment in order to meet the future environmental regulations as well as to keep the productivity. The main results obtained are as follows:
    (1) The models clarify that the introduction of the oxygen enrichment in the first half and the exhaust gas recirculation in the latter half of the sintering process gives better coke combustion rate and sinter quality than other possible alignments.
    (2) The models also show that with the constant O2 quantity provided, the concentrated O2 supply in a short time helps reduce the sintering time because of the balance between combustion rate and cooling rate of the sinter bed.
    (3) The pot test results were in good agreement with the models. The suitable O2 content of 2830% and O2 injection time of 23 min were consequently obtained.
    (4) The proposed process did not cause the deterioration of sinter qualities such as reducibility although the change in O2 content would affect the occurrence of hematite/magnetite phase in sinter microstructures.
  • Cold Strength Enhancement Mechanism of Carbon Composite Iron Ore Hot Briquet

    pp. 313-319

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    Hot briquetting process was proposed as a new manufacturing method of carbon composite iron are briquet. The process was a binder-less briquetting in use of thermal plasticity of coal. The briquet by hot briquetting was higher apparent density and lower porosity than a cold bonded briquet.
    In order to enhance a cold strength and an apparent density of the briquet, the briquet was made by a double roll type briquetting machine at various conditions. Effects of hot briquetting conditions and coal properties on the briquet properties were investigated and the cold strength was discussed relating to pore structure of the briquet.
    Porosity and crushing strength of the briquet changed with hot briquetting temperature. Crushing strength of the briquet had a maximum value at near temperature standing at maximum fluidity of coal measured by Gieseler plastometer. Increasing maximum fluidity as caking property of coal, crushing strength of the briquet increased with decreasing in the briquet porosity and increasing in coherence to coal and iron ore.
  • Measurement of Hydrogen Reduction Rates of FeO in 2FeO ·SiO2 and CaO · FeO ·SiO2

    pp. 320-326

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    Hydrogen reduction rates of FeO in 2FeO · SiO2 and CaO · FeO ·SiO2 powder are measured at 1173K. The reduction behavior of 2FeO ·SiO2 and CaO · FeO · SiO2 is not affected by the particle size and the reaction advances almost linearly with time in the early stage of reduction.The reduced iron may aggregate and retard the progress of the reduction in the later stage.The derived values for chemical reaction rate constants under the conditions of aFeO= 1 and true density are 0.6 to 0.8 and 0.7 to 1.3 [mol/(s · m3 ·atm)] for 2FeO ·SiO2 and CaO · FeO · SiO2, respectively. The values are very small and it is confirmed that the reducibilities of both 2FeO ·SiO2 and CaO · FeO ·SiO2 are very low. The formation of these compounds causes the adverse effect in the sintering process with respect to the reducibility and therefore minimization of SiO2 content is important in this respect as well as minimum slag in order to realize the improvement in the reducibility of sinters in the blast furnace.
  • Effect of SiO2 and Al2O3 on High Temperature Reduction of Iron Ore

    pp. 327-334

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    Five kinds of iron ores that had different SiO2 and Al2O3 content were reduced at temperature range from 1000°C to 1200°C. The effects of SiO2 and Al2O3 on the final stage of the reduction with CO gas were studied. The results obtained are summarized as follows:
    1) Ores D (0.64 mass% SiO2, 0.8 mass% Al2O3) and E (0.58 mass% SiO2, 0.6 mass% Al2O3) were reduced faster than Ores A (4.64 mass% SiO2, 2.6 mass% Al2O3), B (5.61 mass% SiO2, 2.62 mass% Al2O3) and C (8.46 mass% SiO2, 0.83 mass% Al2O3).
    2) Ores A and B were reduced slower than Ore C at 1100°C because the formation rate of 2FeO · SiO2 was different among them. The amount of 2FeO · SiO2 phase in Ores A and B was lager than Ore C because the distribution of SiO2 particle was different among them. In the case of Ores A and B, the SiO2 particle was distributed inside or at the edge of hematite particle. On the other hand, the large SiO2 particle in Ore C was separated from hematite particle.
    3) Ores D and E were reduced to almost 100% reduction degree at 1200°C, but Ores A, B and C were retarded at low reduction degree at 1200°C because of the melting of 2FeO · SiO2 which was formed during reduction.
  • Influence of Gangue and Micro Pore in Agglomerates on Reducibility and Permeability in Blast Furnace

    pp. 335-341

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    In order to clarify the influence of gangue and micro pore in agglomerates on the reducibility and permeability in the blast furnace, the high temperature properties under load of the native lump are and the pellet produced in the laboratory were measured by use of the past-presented apparatus with the adiabatic heat control.
    The solid phase reduction below 1473K before the pressure drop of ore layer goes abruptly up is controlled by the micro pore volume under 15μm. Gangue plays as a prevention factor to reduction and the influence of CaO/SiO2 is large.
    The reduction and permeation under the melt formation over 1473K are controlled by the micro pore volume under 1μm. Gangue is also a prevention factor to reduction and the influence of CaO/SiO2 is the largest and exceeds that of micro pore.
    The dropping temperature receives the influence of gangue directly, and the influence of SiO2, CaO/SiO2, Al2O3 and MgO was detected.
    The influence of gangue on the reduction and permeation under the melt formation, on the dropping temperature and on the micro pore generation under 1μm can be explained by the melt formation due to the low eutectic temperature on the equilibrium phase diagram.
    As for the main two mineral structures in sinter, hematite and calcium ferrite, it is important to produce the sinter having a large amount of hematite that can secure the micro pore volume under 15 μm and the minimum amount of calcium ferrite with low CaO/SiO2 and low Al2O3 that maintains the cold strength and prevents the reduction degradation.
  • High Rate PCI Operation by Sinter Quality Improvement and Burden Distribution Adjustment

    pp. 342-349

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    Since the beginning of 1998 the high PC injection and low FR operation is realized under high productivity (about 2.2 t/d/m3) and without decrease of Al2O3 in sinter in Muroran No. 2 blast furnace. By sinter quality improvement and burden distribution adjustment by new-type charging chute, inverse v-shape cohesive zone is formed under high O/C (more than 5), and gas flow stabilization and improvement of gas permeability and packing characteristic of dead man are observed. One of main tasks from now on is clarifying phenomena of reaction and assimilation between ash from pulverized coal and dripping slag under cohesive zone and its control.
  • Effect of Burden Properties on Permeability in Blast Furnace

    pp. 350-356

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    Experimental and theoretical studies were made to clarify the effect of raw burden properties, such as high temperature properties, so called KS, and JIS-RI of sinter and the slag rate in blast furnace, on permeability in blast furnace with an experimental blast furnace operation and a 3-dimensional blast furnace mathematical model.
    Obtained results are summarized as follows:
    (1) By analyzing the experimental blast furnace operation using the sinter of low SiO2 contents, it was shown that KS of sinter was more effective on permeability in the experimental blast furnace than slag rate.
    (2) By modeling of permeability evaluation of cohesive-zone based on KS, it was also confirmed that KS of sinter was more effective on permeability in the actual blast furnace than slag rate.
  • Improvement of Blast Furnace Reaction Efficiency by Use of High Reactivity Coke

    pp. 357-364

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    The temperature control technology of the thermal reserve zone is examined as a technology which drastically improves reaction efficiency in the blast furnace, and the usage technology of high reactivity coke is proposed.
    The adaibatic blast furnace simulator which is able to simulate the temperature transition and the gas volume change according to the coke reaction under ore and coke coexistence is developed.
    Following findings are obtained.
    The starting temperature of coke reaction corresponds to the temperature of the thermal reserve zone (Ttrz).
    Ttrz has decreased along with the rise of the coke reactivity. The blast furnace reaction efficiency improves by using high reactivity coke voluminously and by mixing using the small-size high reactivity coke and sinter.
    The decrease of the fuel ratio of about 25-35 kg/t can be expected by using the high reactivity coke.
    The factors of reaction efficiency improvement by using the high reactivity coke are shown as follows.
    (1) Transition of FeO-Fe reduction equilibrium point (W point), that is, decrease of thermal reserve zone temperature, (2) Improvement of the gas reduction ability by the coke reaction, (3) Increase of micro-pore volume according to reduction from wustite to iron, (4) Decrease of melt generation and control of pore decrease by reduction of CW (calcio-wustite), (5) Gas reduction promotion by increase of porosity.
  • Reaction and Consumption Behavior of Unburnt Char in Lower Part of Blast Furnace

    pp. 365-372

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    To clarify the gasification and consumption behavior of unburnt char ascending in the coke packed bed in the lower part of the blast furnace, char reaction-consumption model has been newly developed considering the average residence time and co-gasification with coke particles. The chemical reaction rate constant has been determined based on the high temperature experiments on the char injection into the coke packed bed.
    From the analyses using this model, the following results were obtained.
    ( 1 ) The mean ascending velocity of char particles with the diameter of 20 μm was approximately 0.3 m/s, and it was smaller than the actual gas velocity by one order of magnitude, suggesting the char particles had fairly long residence time in the blast furnace.
    ( 2 ) The consumption rate of char became lower with the increase in the solid-gas loading ratio. This was considered to be caused by the higher ascending velocity which resulted from the successive renewal of stagnant particles in the packed bed by supplied char particles.
    ( 3 ) According to the examination of char consumption behavior along the blast furnace height, char discharge rate from the top of the thermal reserve zone could be reduced considerably by decreasing char exhaust rate from the raceway. This phenomenon resulted from the increase in the consumption rate throughout the height, due to the decrease in the solid-gas loading ratio. Therefore, to suppress the char exhaustion from the top, it was necessary to improve the combustion efficiency in the raceway at higher injection rate of pulverized coal.
  • Deadman Renewal Motion in a Cold Model of Blast Furnace

    pp. 373-379

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    Permeability in coke bed in the lower part of blast furnace is believed to have important functions to affect the operation. Accordingly, elucidation of the renewal mechanism and packed structure of deadman coke is expected. The renewal motion may be related with such a motion that the coke bed floats due to the buoyancy force when the molten liquid is stored beyond a critical depth in the hearth. In the present study, a semi-three dimensional model of blast furnace with semicircular cross section was used. The model can approximate more adequately practical furnace in the stress field than two-dimensional model. The moving trajectory of individual particle of deadman packed bed was observed under the repetition of floating to sinking motion of the bed, using water and model particles in place of molten liquid, coke and ore, respectively. The following results were obtained. The height of particle-free space formed above the hearth when the bed floated, had a close correlation with the total depth of water within the bed. The particle renewal did not take place in the whole deadman region, but was restricted within a particular region determined depending on the free space height. The two renewal paths were recognized. First, the particles forced up due to buoyancy towards the deadman surface, joined with the fast moving particles in the funnel flow region to move into the raceway. Second, the particles which descended within the deadman, turned gradually to the direction to move towards the raceway.
  • Unsteady State Heat Transfer Analysis of Lower Part of Blast Furnace with Liquid Flow

    pp. 380-387

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    Stable operation of the blast furnace much owes to satisfactory heat maintenance in lower part of it.
    To make clear heat transfer behavior in lower part of the blast furnace, a new mathematical model has been developed. The feature of the model is (1) treating as unsteady phenomena, (2) considering mass flow, heat transfer, and direct reduction of slag (FeO), (3) handling gas, solid, and especially metal and slag separately with respect to accurate analysis of liquid behavior.
    By the estimation of effects of various operational conditions on the temperature in lower part of the blast furnace, the following results have been obtained.
    (i) Change of slag (FeO) at cohesive zone makes much influence on temperature in the lower part. To keep stable operation, less than 20 wt% of slag (FeO) at cohesive zone is required.
    (ii) The factors keeping coke temperature at center of deadman are (1) decreasing of slag (FeO) at cohesive zone, (2) decreasing of void fraction of deadman, (3) increasing of temperature of cohesive zone, (4) increasing of temperature of raceway gas, and (5) decreaseng of O/C at center. And the factors keeping coke temperature under raceway are (1) decreasing of slag (FeO) at cohesive zone, (2) increasing of diameter of deadman coke, (3) increasing of void fraction of deadman, (4) increasing of temperature of cohesive zone, (5) increasing of temperature of raceway gas.
  • Liquid Flow in Blast Furnace Hearth Concentrated on Inner Packed Structure

    pp. 388-395

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    The warm water model experiment that assumed the blast furnace hearth has been performed, and the liquid flow and the heat transfer property have been examined. The experimental result was considered using the calculation based on the mathematical model, and the flow and the heat transfer of a real furnace were presumed.
    First, the taphole height and the deadman floating height were changed. The flow was not uniform in the direction of coke free layer height when the deadman floating height was large, there existed fast flow region in the right under part of the deadman bottom and stagnation region in the furnace bottom part. Second, the liquid flow rate and the packed particle diameter were changed. When the liquid flow rate increased or the particle diameter decreased, the stream line took a roundabout way and the stagnation region reduced. Third, the deadman bottom shape was changed. When the bowl shape deadman floated entirely, the liquid flow under the deadman turned round under on the sidewall side. Fourth, the effect of the furnace bottom upheaval and the deadman permeability were examined. Not the furnace bottom upheaval but the deadman low permeability did strengthen circulating flow near the sidewall.
    The last, a real furnace flow measurement using radio isotope was considered based on experimental results, it was verified that the deadman packing structure greatly influenced the liquid flow.
  • Carbidization Behavior of Reduced Limonite Iron Ore with CO-H2-H2S Mixtures in Fluidized Bed: Influence of Reduction Temperature and Carbidization Temperature

    pp. 396-402

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    Iron ore particles of a limonite were completely reduced with H2 at temperatures from 973 to 1273K in a laboratory scale fluidized bed. Then, at temperatures from 873 to 1073K, mainly at 973K, the reduced iron was exposed to H2-H2S mixtures (sulfur activity, as=0.5 or 0.1) for 3.6 ks and carbidized with 80%CO-H2-H2S mixtures at the atmospheric pressure. The integrated rate equation for first-order reaction, -ln(1-fθ)=g(pi, T)t; can be fitted very well to the carbidization curves. It is found that the carburization rate per reduced iron unit surface area g(pi, T)/ap0 slightly increases with increasing the reduction temperature. The value of g(pi, T)/ap0 decreases with increasing the specific surface area of reduced iron, ap0, which increases with decreasing the reduction temperature, and increases with increasing the carbidization temperature. The specific surface area and sulfur content of the reduced iron does not largely change during most period of the carbidization, but both of them start simultaneously to increase just after free carbon deposition starts at the latest stage for the carbidization of reduced iron at 973K. The best temperatures for producing iron carbide are concluded to be 1123-1173K for reducing limonite iron ore and 973K for carbidizing the reduced iron.
  • Reduction of Fine Iron Ore with Circulating Fluidized Bed

    pp. 403-409

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    By means of pre-reduction of iron ore fines, productivity of a blast furnace can be increased and iron ore unsuitable for sintering process can be easily used in the blast furnace. As a pre-reduction process a circulating fluidized bed (CFB) has been developed with a pilot plant.
    The riser of CFB is 550 mm in inside diameter and 10 m in height. The CFB pilot plant processed iron ore of wide size distribution in the feed rate range of 0.5-1.0 t/h. Test result shows that the reduction degree ranges from 60 to 90% at the reduction temperature of 850-900°C with no sticking problem. The degree of gas utilization (the increase of oxidation degree of gas) was 10% at the superficial gas velocity until 10 m/s. The pressure drop in the riser was 30 kPa at the same condition.
    From the analysis of reduction rate the retention time for reducing iron ore to the reduction degree of 60 and 90% are 20 and 120 min at 880°C respectively. The productivity at the reduction degree of 60% is expected to be about 6 times higher than that of the reduction degree of 90%.
  • Numerical Simulation of the Moving Bed Furnace for Reduction and Melting of Oxidized Iron-scrap Briquette Containing Coke Breeze

    pp. 410-417

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    Briquettes of oxidized iron-scrap containing coke breeze are attracting much attention as a new raw material for ironmaking from the viewpoints of energy saving, recycling and environmental protection. The reduction and melting of the oxidized iron-scrap briquettes in a moving bed reactor has been proposed for hot metal production. The aim of this study is to investigate the reduction and melting behavior of the briquette in the reduction-melting furnace. For this purpose, a total mathematical model of the reduction-melting furnace has been developed considering the rates of briquette reduction, iron melting and carburization to molten iron.
    The model was applied to the reduction-melting furnace, of which inner shape is a cylinder of 1 m in inner diameter, 4.5 m in effective height and the tuyere opening is 10% of the cross-sectional area of the furnace. Computations were performed under the conditions of air flow rate of 1.7 kg/s, air preheating 673K and coke ratio of 350 kg/thm. The numerical simulation describes flow of three phases (gas, solid and liquid), chemical reactions and phase changes; specifically, the distributions of temperature of the three-phase, gas concentration, reduction degree and carbon content of molten iron in the furnace. From the calculated distribution of temperature and melting ratio, it was proven that the briquette could be melted with preheated air blowing at 673K. The reduction degree distribution showed that sufficient carbon content of coke breeze in the briquette is necessary in order to obtain higher reduction degree.
  • Total Model with Zinc and Iron Reduction Kinetics for Simulation of a Coke Packed Bed Furnace

    pp. 418-425

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    A new mathematical model of the smelting reduction process with coke packed bed has been developed for recycling the dust containing zinc oxide.
    Kinetic experiments of the zinc reduction were carried out in the temperature range between 1643 and 1823K in order to determine the rate constants and activation energy. It is observed that zinc is reduced faster for slag containing iron. The rate constant of zinc reduction by iron oxide was determined.
    The mathematical model of zinc reduction is composed of one-dimensional flows of solid, liquid and gas phases. It is formulated in terms of heat and mass balances in the furnace, coupled with reduction kinetics of iron/zinc oxides and heat transfer among the components. Operation conditions of pilot plant tests with a scale of 10 tons per day are simulated with the model. It is found that the temperature and CO2/CO ratio of gas at the furnace top must be controlled by the post combustion to prevent zinc accretion.
    The operation results of the pilot plant are compared with those of the simulation ones. It is confirmed that zinc and iron oxide is reduced between two stage-tuyeres and that zinc accretion at the wall of furnace top is decreased by the post combustion.

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