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

Tetsu-to-Hagané Vol. 92 (2006), No. 12

  • Technological Progresses and Researches on Blast Furnace Ironmaking in The New Century

    pp. 694-702

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    Philosophy and business circumstances of Japanese steel industry have drastically changed in the new century. New standpoint of steel industry has to be in responsible consideration for raw material resources, energy and environmental protection. With ratification of the Kyoto Protocol, Japanese Steel Federation has set a voluntary reduction plan of CO2 emission by 10.5% to the one in 1990. Therefore, new process developments and researches for CO2 reduction have been promoted in the ironmaking field as a major contributor of energy consumption. Furthermore, recycling use of waste materials, such as blast furnace dust, mill scale and waste plastic, were proceeded in the ironmaking process for construction of the materials recycling system. Advanced process developments and research results were introduced and future prospects of the basic research have been discussed to reinforce ironmaking technology.
  • Examination of Resolidification and Carbonization Mechanism of Coking and Non- or Slightly-caking Coals during Coke Production

    pp. 703-712

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    Under the recent tight supply-demand situation for caking coal, it is important and urgent to develop technologies which enable the utilization of low grade coal as much as possible for the production of metallurgical coke. To meet with the urgent and important demand, members of the Iron and Steel Institute of Japan (ISIJ) have been actively engaging in the development of new technologies utilizing low grade coal as metallurgical coke feedstock. The research workshop "Research and Development for Low Grade Coal Utilization Technology for Cokemaking", which lasted 2002-2005, has examined the mechanism of resolidification and carbonization of coking and non- or slightly-caking coals by using sophisticated analytical techniques that are widely employed in the field of carbon science. In this review the results obtained are briefly introduced, and the difference and similarity of the mechanism of resolidification and carbonization between caking and slightly caking coals are discussed.
  • Classification of Iron Ore Particle and Relationship between Those Mineral Characteristics and Sintering Properties

    pp. 713-720

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    Australian hematite iron are particles were rinsed with clear water, and classified from its color into three types; yellow particles, intermediates particles, and black particles. Then (1) investigation of the basic properties of the particle according to the iron ore type, (2) the melt examination, and (3) the sintering pot test were executed.
    As a result, each classified type of iron are particle showed a similar mineral characteristic and sintering result was controlled greatly by their ratios.
    It was clarified that the inferior sintering result for the MarraMamba ore was mainly caused by the higher ratio of the yellow particles.
  • Effect of Adding Moisture and Wettability on Granulation of Iron Ore

    pp. 721-727

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    As the fundamental study for determining the optimum moisture content for granulated particle, the contact angle between iron oxide and water was measured by the sessile drop method using reagent hematite samples that have different porosity and five kinds of iron ores. The granulation experiment was conducted by using five kinds of iron ores and the effects of adding moisture and wettability on the granulation property were investigated. The contact angle of reagent hematite sample and iron ore became large as the surface roughness becomes large. Therefore, the wettability between iron oxide and water greatly influenced the surface roughness of iron oxide. When iron are with high wettability was used for nuclei particles, it can be granulated under all conditions in this study. On the other hand, when iron ore with low wettability was used for the nuclei particles, it was remained some fine iron ore particles without granulating. Therefore, when iron ore with low wettability was used for the nuclei particles, it was necessary to increase the adding moisture in order to improve the granulation property of fine particles. The fracture strength increased with decreasing the contact angle without regard to the kind of iron ore using for nuclei particles. Consequently, It was necessary to increase the adding moisture in order to improve the fracture strength.
  • Influence of the Nuclei Particle Properties on Granulability of Marra Mamba Iron Ore by High Speed Agitating Mixer

    pp. 728-734

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    The newly developed brand Marra Mamba ore from Australia has a comparatively high water absorptivity, and since a large amount of fine ore is contained, if it is used as a raw material of sintered ore, it will cause the deterioration of the permeability of the ore bed, and the productivity fall of a sintered ore by the fall of the granulability. By blending nuclei particles with this Marra Mamba ore, the granulability and the permeability of the ore bed have improved sharply by processing them in a high-speed agitating mixer. It was considered that the ratio about 25 mass% was suitable for nuclei particle mixture ratio to a high-speed agitated material.
    Moreover, the granulability was improved by using the ore of 1-3 mm particles as nuclei. As for this, it is considered that the granulation of a middle size ore is accelerated, because of the consistency of the particle size composition of the material and proprrties of high-speed agitating mixer.
  • Influence of Polymer Dispersant on the Granulation of Raw Materials for Sintering Process

    pp. 735-741

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    The influence of the anionic polymer dispersing agent (APD) on the granulation of raw materials was investigated to improve the sintering productivity. This APD has the characteristic that helps the dispersion of fine particles into water and disperses the fine particles that are cohesive. Fundamental examinations showed that the APD increased the adhesion strength of pseudo-particles and increased the pellet strength after drying. Granulation examinations with raw materials showed the good relationship between dispersed ratio and GI-0.5, and the considerable improvement of the granulation was recognized clearly. It was also confirmed that this APD had increased the sintering productivity more greatly than the burnt lime depending on the pot test results.
  • Numerical Simulation Model for Granulation Kinetics of Iron Ores Based on Discrete Element Method

    pp. 742-747

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    A numerical simulation model was developed to analyze the granulation kinetics by using the Discrete Element Method (DEM). The experiment of granulation was performed to understand the actual granulation behavior of iron ore particles. The granulation rate goes up with a decrease in a particles charge ratio and with an increase in a rotational speed of a drum mixer in the experiment. The granulation could be consisted of two processes: One is "a growing process" and the other is "a breaking process". The former would be related to the rotation of granules and the latter would be dependent on the impact, which granules receive from others and/or a drum mixer wall. Then the rotational kinetic energy and the impact energy of a granule were calculated by using the DEM simulation. A granulation energy composed of both the impact energy and the rotational kinetic energy was proposed for analyzing the granulation kinetics. It increases as the rotational speed of the drum mixer rises and as the granule charge ratio drops. The granulation energy would be correlated with the actual granulation process. When the drum mixer diameter becomes large, the granulation energy decreases. When the drum mixer is leaned, the granulation energy becomes larger than at the lean of 0 degrees. That is, the drum mixer has a possibility to improve a granulation process. When the drum mixer is leaned further, the granulation energy rapidly decreases at the lean of 60 degrees. This means that the optimum leaning angle must exist.
  • Effect of Al2O3 and MgO Additions on Liquidus for the CaO-SiO2-FeOx System at 1573K

    pp. 748-754

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    Phase diagrams for the CaO-SiO2-FeOx-Al2O3 or-MgO systems at various oxygen partial pressures are necessary for the design of raw material for ironmaking, the analysis of smelting reaction and sintering process. To clarify the effect of Al2O3 or MgO content on the formation of melts in the sintering process is important for the development of new sinter. In this study, liquidus for the CaO-SiO2-FeOx-Al2O3 or -MgO systems at various oxygen partial pressures were observed at 1573K by using chemical equilibration technique. The liquid phase area changed with adding Al2O3 or MgO. The effect of the Fe3+/Fe2+ ratio on the melting mechanism is discussed.
  • Experimental Evaluation of Chemical Composition and Viscosity of Melts Formed during Iron Ore Sintering

    pp. 755-762

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    The viscosity of the melts formed in the sintering reaction was measured for evaluating the fluidity of the melts, which play a crucial role in the sintering process. Using the sphere draw-up method carried out the measurements of high temperature viscosity. With low-melting point compositions of the Fe2O3-CaO-SiO2 system, the viscosity of high SiO2 content melts (Fe2O3/CaO/SiO2=38.5/34.5/27.0 weight basis) was 5 times higher than that of low SiO2 content melts (Fe2O3/CaO=80/20). The viscosity of low SiO2 content increased with addition of Al2O3 and SiO2. Similarly, with melt compositions generated from actual ores, viscosity depended on the contents of Al2O3 and SiO2.
    Based on the results, the viscosity of the melted liquid was estimated from the chemical composition, and the viscosity of the solid-liquid coexistence phase was also evaluated using a viscosity calculatinge quation for suspensions. The viscosity distribution of the solid-liquid coexistence phase at 1300°C in the ternary composition system Fe2O3-CaO-SiO2 was obtained.
  • Properties of Core Ore Required for Sinter Mixture under Large Amounts Usage of Limonitic Ores

    pp. 763-768

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    The fluidity of melt formed in the sintering process of iron ores is an important factor for producing a high-strength sinter. When using a large amount usage of limonitic ores as core ore of the quasi-particle of sinter mix, it is predicted that the fluidity of formed melt decreases, because the solid ratio in the melt increases by an acceleration of the assimilation of the core ore with the melt.
    In order to control the assimilation of limonitic ore, basic researches were conducted using a modeled briquette, which consisted of a diskshaped iron ore core and a shell layer of fine mixture composed of Fe2O3 and CaCO3 reagents. Assimilation rate of various iron ores was measured, and then solid phase ratio in the melt was calculated based on the phase diagram of CaO-Fe2O3 system. According to the calculated solid phase ratio in the melt, the fluidity of melt was discussed. The results obtained are summarized as follows:
    Fair linear relations were obtained between the porosity of core ore after dehydration and the combined water content of the ore. The assimilation rate of core ore at a specified temperature was represented as a function of the porosity of core ore after dehydration and the holding time at the temperature. The diameter and the apparent density of core ore influenced the calculated solid phase ratio in the melt. It was suggested that an optimal sinter structure was achieved by mixing a large and dense core ore at about 20 mass% in raw mix.
  • Development of a 3 Dimensional Mathematical Simulation Model for Iron Ore Sintering Process

    pp. 769-778

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    A 3 dimensional sinter process mathematical simulation model has been developed for the purpose to make it possible the designs of sinter process from the stereoscopic viewpoint. This sinter process model can calculate not only the progress of sintering reactions and the resultant changes in the bed structures such as pore ratio and minerals composition but also the qualities of produced sinter. Through a pot sintering test, this sinter process model was confirmed authentic and able to calculate also the distributions of sinters property such as minerals composition inside sinter cake. This sinter process model was used for the analysis of the effects of gas flow plate on the sintering performance.
  • The Sintering Behavior of Raw Material Bed Placing Large Particles

    pp. 779-787

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    The pot tests, under the condition that large particles were placed in the sintering bed, were carried out for improvement of permeability. The large particles include green balls made from Marra Mamba ore, fired pellet, sinter, dense alumina ball and pisolite lump ore. In the course of pot tests, permeability before ignition and during sintering, bulk density and yield were measured. Also the cross sections of sinter cakes were observed. As a result, the permeability before ignition and during sintering was both increased regardless of the increase in the bulk density of sintering bed. When the large particles were placed, the calculated bulk density of sinter mixture (the rest part of bed excluding the large particles) decreased in inverse proportion to the surface area of large particles. Therefore, the effect of placing large particles was concluded to cause the permeability increase. Placing large particles occasionally decreased yield owing to void formation under the alumina balls in the sinter cake, which was confirmed the visual observation. It is proposed that the increase of coke and/or CaO contents in fine layer and adding carbon in the green balls are effective for yield recovery.
  • Design of Bed Structure Aiming the Control of Void Structure Formed in the Sinter Cake

    pp. 788-793

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    Design of bed structure is a promising approach to maintain/increase the productivity of sinter under the condition of increasing use of iron ores with high combined water content and fine particle size. In this paper, a process image of the above proposal, MEBIOS, is outlined and further in situ observation of the change in the void structure of the sintering bed by using X-ray CTS and a thermo-fluid dynamic simulation have been conducted in order to preliminary evaluate the possibility of this process.
    X-ray CTS observation suggests that the existence of pellets of 15 mm in particle size does not significantly affect the formation of macroscopic void network in the sintering bed and not lead to inhomogeneous sintering. A series of the laboratory-scale of sinter pot experiment was also carried out to obtain parameters for the numerical simulation. The gas flow near the pellet surface and the differences in the temperature profiles among the pellet center and surface were simulated by using the numerical model although further studies are necessary, e.g., on the considering ways of structural changes of void in the sintering bed, reduction and oxidation reactions and a mesh generation method properly representing the contraction of bed height.
  • Effect of Insertion of Burning Down Materials on Sinter Cake Property and Permeability

    pp. 794-801

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    To increase the utilization of the high combined water ores in sinter production, the improvement of gas permeability of the sintering bed is required.
    It was attempted for permeability improvement that the burning down materials; paper briquette (PB) would be inserted into the lower half of sintering bed up to 5 vol% at pot test. The permeability of the bed was almost equal to that of normal bed during sintering of the upper bed, but at the lower half of the bed permeability increased in proportion of PB insertion volume.
    The reason of permeability improvement is that the flow resistance at combustion zone decreases with formation of macro void caused by PB combustion just before ignition of the coke breeze.
    The ratio of large particle in the product sinter reduced as increase of PB insertion. It is considered that thin parts of sinter; "bridge" between macro voids formed by PB insertion, and these bridges break preferentially during sizing process. Therefore, the large sinter particle could decrease as PB insertion increases.
  • The Preparation and Reduction Behavior of Carbon Composite Iron Oxide Pellets Using Semi-coal-char

    pp. 802-808

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    Carbon composite iron oxide pellets intentionally including residual volatile matter (V.M.) were proposed to decrease the initial temperature for reduction reaction of carbon composite iron ore agglomerate under a rising temperature condition, such as in a blast furnace shaft. The carbonization of coal (Newcastle blend coal) under a rising temperature condition was interrupted at a certain temperature, TC, max =823, 873, 973, 1073 and 1273K, to obtain semi-coal-char containing some residual V.M. Furthermore, to investigate the behavior of gas evolution from the coal char, the semi-coal-char obtained at TC, max(1)=873K was heated from room temperature up to TC, max(2)=1273K at 200Kh-1 in nitrogen atmosphere. In carbonizing at TC, max(1)=1273K, V.M. was almost emitted from TC, max(1)=873K. Total gas volume of two step carbonization (TC, max(1)=873K and TC, max(2)=1273K) almost agreed with that of one step carbonization (TC, max= 873K).
    The semi-coal-char including residual V.M. was mixed with reagent grade hematite in the mass ratio of one to four. Then, Bentonite was added to the mixture as a binder, and the carbon composite iron oxide pellets including residual V.M. were prepared and reduced under rising temperature conditions in nitrogen atmosphere. It was confirmed by the XRD analysis of the reduced pellets that the carbon composite iron oxide pellets using the semi-coal-char at TC, max=823K have the fastest reducibility of the iron oxide.
  • Carbothermic Reduction of the Composite Pellet of Iron Ore and Coal in the Packed Bed with Air Flow

    pp. 809-814

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    In order to examine the feasibility of the carbothermic reduction process using the composite pellets of iron ore and coal fines in their combustion packed bed, laboratory scale experiments were conducted. To prevent the reoxidation of the reduced pellets, attempts were made by coating the composite pellets with different fine materials such as iron ore, limestone, dolomite, serpentine and SiO2 reagent. The isothermal reduction experiment using a single composite pellet shows that SiO2 bearing material, such as serpentine fine and SiO2 reagent, give a reasonable suppression effect on the reoxidation at high temperature. The metallization degree of about 70% has been attained. On the basis of this result, the carbothermic reduction experiment in the combustion packed bed was conducted using the composite pellet coated with SiO2 reagent powder. In this case, the maximum metallization degree was as much as 45% because of the reoxidation of metallic iron could not be perfectly suppressed during the process. Further reduction experiment was carried out using the composite pellet coated by the fine mixture of CaO-SiO2-Al2O3 system to form a melt of the coating layer in high temperature. It gives the maximum metallization degree of about 60%. It suggests that the proposed carbothermic reduction process has a possibility to produce the partially-reduced iron burdens for the blast furnace, although its production rate is necessary to be improved.
  • Development of Production Process for Pre-reduced Agglomerates and Evaluation of Its Quality

    pp. 815-824

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    To achieve the greatly decrease in CO2 emission at iron making process, the production process of the pre-reduced agglomerates (the following: PRA), which are partially reduced simultaneously with agglomeration of iron ore on the existing sintering machine, was proposed. In this paper, the basic studies to produce PRA examined with the test pot and the results of estimations for using PRA as the main raw material of blast furnace were described. At the basic studies, the optimum conditions for producing PRA such as the particle size of coke as reducing agent, the structure of quasi-particles and the oxygen concentration in suction gas during sintering were examined. Then the maximum reduction degree of 40% was achieved for the PRA made from quasi-particles produced by tumbling granulation. Moreover the possibility of attaining reduction degree of 60% was confirmed for the PRA made from briquettes as raw material particles. Whereas it became obvious that prevention of generating excess melt caused by the disintegration of quasi-particle or briquette was indispensable. From the results of estimations to use PRA at blast furnace, the pressure drop in blast furnace was confirmed to decrease as compared with usual sintered ore, and the permeability in blast furnace was improved as the reduction degree of PRA was increased.
  • Influence of Ore and Coal Brand on the Reduction of the Carbon Composite Iron Ore Sheet

    pp. 825-832

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    A new DRI process named SMIMET (Sheet Material Insertion Metallization Method), which a wet and dense sheet material of coal and iron ore mixture is reduced in RHF (rotary hearth furnace), was proposed. Binder addition and pelletizing process were omitted in this process. The fundamental and bench scale tests of it were carried out. In these tests, the raw materials were formed into the sheet shape samples by hand or sheet forming machine. Then, sheets were reduced at 1573K in air atmosphere. The produced DRI formed into briquettes at 1273K in Ar atmosphere or at room temperature. After that, the softening-melting down tests were carried out. As a result, sheets contained higher F.C. coal smashed when they were heated rapidly. Sheet smash was controlled by decrease of the apparent density of the sample. Also, higher metallization degree DRI were produced when hematite are and/or higher F.C. coal was used. The influence of sheet thickness on the productivity was greater than that of apparent density of it. Therefore, the sheet thickness should be decreased when the higher F.C. coal was used to increase the productivity. In addition, the permeability of the softening-melting down tests was affected by the porosities of briquettes. It is believed that the strength of DRI increased when it was formed into briquette so that the temperature, which DRI began to soften and melted, was raised.
  • Effect of Inert Size on Coke Strength

    pp. 833-840

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    In order to improve coke strength by technique of coal size control, it is essential to understand relationship between inert size and coke strength. The size and area of inert in coke was measured with a microscope and an image analysis technique and the effect of inert size on coke strength was investigated. Moreover the reason why DI150-6 leveled off at inert size of 1.5 mm was investigated.
    The results are follows.
    (1) When the inert size is between about 1.5 mm and 5 mm, surface breakage product (DI150-6) decreases as the size of inert in coke becomes smaller. When the inert size is over about 5.0 mm, volume breakage product(DI1506-15) decreases as the inert size becomes smaller.
    (2) The effect of 1% inert in coke on DI150-6 and DI1506-15 was clarified.
    (3) According to Hertzian contact theory and Griffith equation, it is estimated that the crack under 0.5 mm doesn't grow by fall of coke in drum tester. Critical inert size (1.5 mm) is appropriate values for this critical crack size (0.5 mm), because size of the crack around inert particle is equal to the inert size or is smaller than it.
  • Effects of Gasification and Smelting Reduction on Coke Degradation

    pp. 841-848

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    Decreasing of the reducing agent rate can be expected by using the high reactivity coke to the blast furnace. However, it is predicted that the reaction form of the coke and permeability in the blast furnace change.
    In this study, three kinds of coke were used for the solution-loss reaction and the smelting reduction experiments. The coke strength which was evaluated by using 1-type tumbler after each reaction was different, even if these reaction quantities were equivalent. In addition, the effect of the solution-loss reaction on the coke degradation was larger than that of the smelting reduction.
    On the basis of these experiments, the coke strength after direct reduction and results of the blast furnace operation with high reactivity coke were quantitatively estimated. According to the calculation of the operation with high reactivity coke, decreasing the coke rate and in-creasing the productivity by decreasing pressure drop in the blast furnace are expected.
  • Some Fundamental Aspects of Highly Reactive Iron Coke Production

    pp. 849-856

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    The development of production and utilization technology of highly reactive coke is significant in order to improve blast furnace reaction efficiency. In this report, some fundamental aspects of highly reactive iron coke produced in a coke oven chamber were investigated. First, the effects of catalytic Fe powder addition to coal before carbonization on coke strength were investigated. The addition of Fe powder decreased coal caking property and hence resultant coke drum index (DI15015). On the other hand it increased coke reactivity (JIS coke reactivity index and CRI) to a great extent. This means that caking property of blended coals needs to be adjusted higher to produce the iron coke with properstrength and high reactivity. Secondly, it was shown that the iron ore reacts with silica brick at 1200°C in a condition similar to that in a cokeoven chamber. The iron ore and silica reacted to produce fayalite (2FeO·SiO2) and the brick was damaged. On the other hand, it was proved that the iron ore does not react with silica brick at 1 100°C in the above condition. Based on this fundamental study, the iron coke with proper strength and high reactivity was successfully produced in coke ovens on a commercial scale by adjusting the coal blend composition and the coke oven temperature. Furthermore it was revealed that about 70% of iron in iron ore powder added to coal was reduced to metallic iron during carbonization in coke ovens.
  • Development of New Cokemaking Process by Blending of Coal Particles Coated by Caking Coal

    pp. 857-864

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    New cokemaking by blending of agglomerated coal particles was developed for making high strength and high reactivity coke. Agglomerated coal particles were produced by coating the slightly caking coal particles with caking coal particles. In the case of conventional cokemaking process, at the high blending ratio of the slightly caking coal, coke reactivity is raised, however, coke strength reduces. Cracks can be easily generated at the interface between coke textures, because the slightly caking coal particles have low fluidity at the carbonization and the semi-coke has high contraction.
    The slightly caking coal particles (1-5 mm) coated with the caking coal were carbonized in coal blend. From microfocus X ray CT images, the generation of the cracks at the interface between coke textures was not observed. When the -0.5 mm of Ro =1.1% caking coal was used as a coating coal and the slightly caking coal (MF value; 2 ddpm) was used as a central coal, coke strength and coke size were enhanced. At 1373-1773K, the CO2 reaction rate of the coke blended with 20% agglomerated particles was higher than that of coke without adding agglomerated particles.
  • Effects of Mineral Matrix on Softening Property and Reducibility at Dolomite Sinter

    pp. 865-874

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    Increasing permeability of packed burdens and decreasing reducing agent rate in a blast furnace process take an important role to improve productivity. Especially, the softening property during reduction and reducibility of sinter are important. Effects of blending dolomite as raw materials at low SiO2 sinter (SiO2<5 mass%) on these properties were examined by using variously prepared sinter samples. The softening property was estimated by vertical pressure drop of sinter packed bed (70mmφ×100mm) during reduction with elevating temperature up to 1600°C under vertical loading force (0.098×106 Pa). The reducibility was estimated on the basis of the reduction degree obtained by CO/N2(30/70 vol%) gas at constant temperature conditions (900°C, 1100°C).
    Results were summarized as follows:
    (1) Sinter using dolomite instead of serpentine and increasing MgO concentration in sinter with dolomite shows superior sinter reducibility.
    (2) Increasing MgO concentration in sinter with dolomite also shows both superior sinter reducibility and sinter softening property.
    (3) Superiority of sinter reducibility described in (1) and (2) is based on decreasing silicate slag in sinter. Decreasing silicate slag is considered to be caused by increasing both Si and Mg concentration in calcium ferrite with chemical reaction between calcium ferrite and MgO in dolomite.
    (4) Superiority of sinter softening property described in (2) is based on decreasing temperature range of high pressure drop. Decreasing the temperature range is considered to be caused by decreasing liquid phase ratio at high temperature (>1100°C) with MgO addition.
  • Effect of High Al2O3 Slag on the Blast Furnace Operations

    pp. 875-884

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    Increasing the Al2O3 content in the blast furnace slag, the blast furnace operations tend to make troubles such as excess accumulation of molten slag in the blast furnace hearth and increasing pressure drop at the lower part of the blast furnace. So, it will be important to keep good slag fluidity at the blast furnace operations such as, drainage of tapping and keeping good permeability. In order to clarify the effect of high Al2O3 slag fluidity on the blast furnace, high Al2O3 slag (20%) test operations of experimental blast furnace have been carried out. In-vestigation results of the test operation are as follows;
    1) Slag MgO improves the hearth drainage rate at high Al2O3 slag operation.
    2) Permeability of the dripping zone is improved by decreasing slag CaO/SiO2, at high Al2O3 slag operation of the blast furnace.
    3) It was verified that the slag drainage phenomena were able to described by the fluid model.
    4) The optimum composition of high Al2O3 slag of the blast furnace is high MgO and low CaO/SiO2.
  • Characteristics of Liquid Hold-ups in a Soaked and Unsoaked Fixed Bed

    pp. 885-892

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    In most previous works, liquid hold-ups were studied by using a cold model of a fixed bed soaked prior to experiments. However, they did not consider that the dripping zone of a blast furnace is saturated with liquids or with evenly distributed droplets. In the present study, the characteristics of liquid hold-ups and liquid flow were investigated by using a one-dimensional cold model of a fixed bed soaked and unsoaked prior to experiments (initially soaked and unsoaked beds). Packed balls were five kinds, the diameters (Dp) of which ranged from 5.4 to 30 mm. Tap water was used as liquid. Contact angles (θ) for these particle/liquid systems were about 70° and 10° for fluorine-coated particles and non-coated particles, respectively.
    Although, under bad wettability condition (θ_??_70°), total and static hold-ups for initially unsoaked bed packed with small balls are remarkably smaller than those for initially soaked bed, the difference in their hold-ups between initially unsoaked and soaked beds decreases with increasing ball size in the bed. In initially soaked bed, total and static hold-ups increase monotonically as ball size decreases, which means the specific surface area increases. On the other hand, in initially unsoaked bed, total and static hold-ups under bad wettability condition indicate maximum values at about Dp=10 mm and decrease abruptly in proportion to a decrease in particle size, despite an increase in the specific surface area. Only restricted liquid droplets and/or liquid rivulets are formed within the packed bed with good wettability condition ( θ_??_10°) for initially unsoaked bed, nevertheless liquid is easy to spread out on the solid surface. The influence of the initial bed condition, soaked or unsoaked bed, on liquid hold-ups is great under bad wettability condition.
  • Influence of Channeling Factor on Liquid Hold-ups in an Initially Unsoaked Bed

    pp. 893-900

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    One of the important factors for minimum energy consumption and CO2 emission of a blast furnace (BF) is to elucidate the liquid flow phenomena and liquid hold-ups in the dripping zone of BF. Liquid hold-ups were studied by using a cold model of a fixed bed soaked prior to experiments (hereinafter called initially soaked bed), but the existing correlation equations derived from liquid hold-ups under initially soaked bed do not agree with liquid hold-ups under initially unsoaked bed such as the dripping zone of BF.
    In the present study, correlation equations for liquid hold-ups in initially unsoaked bed were experimentally derived by a new approach, in which channeling factor (FC) was proposed and defined as follows: FC is the ratio of the number of liquid paths per one horizontal line to the number of voids between particles per the same horizontal line, and was measured by using the moving image of liquid paths photographed by a CCD video camera.
    By using empirical equation for FC, hold-ups in initially unsoaked bed were described as the following correlation equations.
    Static hold-up HS(I-UB) (%)= 0.9 ·HS(I SB) ·FC0.8·Ncm-1
    Dynamic hold-up Hd(I UB)(%)= 0.9 ·Hd(I SB) ·F0.5C
    Total hold-up is the sum of Hs and Hd Ht (%)=Hs+Hd
    where, Ncm=1+(cosθ)3, and subscripts I-SB and I-UB designate quantities associated with initially soaked and unsoaked beds, respectively.
    The comparison with the previous liquid hold-ups shows that the estimated hold-ups are in good agreement with the experimental values for any particle diameters used and both contact angles of 10° and 70° under initially unsoaked bed.
  • Development of High Ratio Coke Mixed Charging Technique to the Blast Furnace

    pp. 901-910

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    Technique for high ratio coke mixed charging was developed and applied at JFE Steel's East Japan Works (Chiba District) No. 6 blast furnace as the first case of application to a large blast furnace. Simultaneous discharging of ore and coke from the top bunkers, and the precise control of burden distribution technique with the mathematical model considering the segregation behabior of mixed layer have made it possible. Since April 2002, high productivity operation with the world's lowest level of sinter ratio has been conducted using high ratio coke mixed charging technique.
  • Development of a Visual Information Technique of Nonstationary Fluctuations in a Blast Furnace Process

    pp. 911-918

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    By turning stave temperature and shaft pressure data, collected by a numbers of sensors spatially located circumferentially and vertically in the blast furnace, into images distributed in two dimensions, we have succeeded in quantitatively and objectively visualizing shaft pressure variations and spatial changes caused by slipping in the blast furnace. In addition, combining the two-dimensional distribution of secondarily processed data of changes in space and time with the progress of operation data enables early detection of shaft pressure fluctuations. The conjecture that the uneven distribution of voids in the blast furnace may be the cause of shaft pressure fluctuations has been confirmed by our model experiments. It has been also found that there exists a relationship between the cohesive zone root position, assumed by the visualized two-dimensional image of the stave temperature change over time, and the origins of shaft pressure fluctuations.
  • Analyses on Blast Furnace Raceway Formation by Micro Wave Reflection Gunned through Tuyere

    pp. 919-925

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    The blast furnace raceway formation under the intensive coal injection by measurement of micro wave reflection gunned through a tuyere is discussed. As the flow rate of coke as the momentum of coke into raceway decreases by combustion of coal injected into tuyeres, the depth of raceway defined as the maximum position of micro wave reflection is easy to contract. It is expected that this new technology could detect the raceway collapse phenomena in short time and that the stability of raceway in coal injection is different from that in all coke operation. Finally the paper ends by summarizing the effect of raceway formation on unsteady phenomena forcing functional disorder on blast furnace performance of burden distribution for high productivity performance.
  • Stabilization of Tapping Hole Length by Controlling Blast Furnace Raceway Depth

    pp. 926-931

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    On facing the high productivity and elongation of life time in blast furnace iron-making, it is essential to protect the peripheral iron flow formed by a free space in the hearth in addition to maintaining the gas and liquid permeability of deadman. Therefore, it is important to stabilize the length of mud (tapping hole length) which is plugged and formed by hole closing refractory (mud materials), but the phenomena of fluctuation of tapping hole length are not clarified. In this paper, variables affecting the tapping hole length including the raceway depth measured by micro wave reflection struck tuyere are discussed under dimension analysis. As the burden weight above the raceway are balanced to upwind gas, the load to the hearth under the raceway is less than that in the furnace center and a high void ratio area or free space is easy to be formed under the raceway. As the result, it is clarified and quantified that the tapping hole length is recovered from shortage of distance by decreasing raceway depth which promotes deadman to sink further into bottom or increase the void ratio of peripheral area in the hearth.
  • Analyses on Dynamic Solid Flow in Blast Furnace Lower Part by Deadman Shape and Raceway Depth Measurement

    pp. 932-938

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    As one of the factors of frequent troubles that occur in the transition period from all-coke operation to PC injection operation in blast furnace as well as increased troubles in recent years, increased size of the blast furnace and high-productivity operation are pointed out. Consequently, great importance is attached to burden distribution control and burden descent condition, or control of melting zone, deadman shape, solid flow at the lower part of furnace and others. In the present study, the reduced stockline surface profile was measured by the reflection intensity of microwave struck from the furnace top after blow-off with stockline reduced, and investigation was made on the countermeasures for changes in the raceway depth and furnace body profile during operation. As a result, it has been clarified that flow-down of coke into the lower part of blast furnace and inflow into the raceway are greatly subject to the existence of deadman which is the packed structure of the lower part of furnace, and further, they are closely related to dynamic behavior of the raceway and affect changes of the furnace body profile.
  • Mechanical Analyses on Stability of Particle Flows Near Raceway of Blast Furnace

    pp. 939-947

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    Stability of particle flows near raceway in blast furnace has been mechanically analyzed using model experiments and simulations using Discrete Element Method (DEM). Results obtained are as follows.
    (1) Unstable raceway shows that particles above raceway near wall periodically hang and slip.
    (2) Unstable raceway has long periodical changes about several seconds in addition to short periodical change about several 10 ms that stable raceway exhibits.
    (3) Unstable raceway shows the ratio of the height to the depth is greater than about 1 on the average.
    (4) Excess enlargement of tuyere diameter or blast volume could lead to unstable raceway.
    (5) Although increase of input energy from gas into bed raises efficiency of energy transfer from gas to particles, the efficiency is independent on raceway stability.
    (6) With the objective raceway stability and decreasing generation of fine coke in the raceway, there is appropriate range of conditions in the input gas energy.
  • Numerical Analysis on Behavior of Unburned Char and Fine Coke in Blast Furnace

    pp. 948-954

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    A mathematical model of blast furnace operation, which is able to estimate the behaviors of the unburned char and the fine coke simultane-ously, has been developed. The model based on the multi-fluid theory treats dynamic powders that are moving entrained by the gas stream as individual phases and static powders as solid components. The former takes conservation equations of momentum, thermal energy, chemical species and continuity. The latter takes only mass balance equations of chemical species, and shares fields of flow and temperature with the other solid components, such as lump coke, sinter, and so on. In the simulations, the unburned char is derived from the pulverized coal injected from the tuyere, and there is no difference in model treatment between the unburned char and the pulverized coal. The fine coke is generated uniformly in the raceway region from the coke particles, and the generation rate is determined by a kinetic treatment. The simulation of the blast furnace operation by this model revealed that the unburned char and the fine coke having different diameters and densities show different flow patterns especially in the cohesive zone and deadman. Consequently these two powders formed different areas of accumulation and reactions while large amount of powders were deposited in the deadman zone regardless of difference in flow patterns.
  • Stress Field and Solid Flow Analysis of Coke Packed Bed in Blast Furnace Based on DEM

    pp. 955-960

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    The stability of blast furnace operation, such as blast pressure, burden descending, liquid holdup and residual amount of slag in hearth, are dominated by the permeability of coke packed bed. The coke degradation in packed bed is caused by abrasion. Then the stress field is calculated by simulation based on discrete element method (DEM) to make clear the abrasion mechanism. Coke free space shape affects on the liquid drainage efficiency and hearth refractory erosion. Then the effects of hearth depth, burden load and coke consumption on the coke free space shape is considered by using the DEM simulation also.
    The calculated results show that a force network is formed in the whole of BF and supports the load of burden. The stress of particle in the network is much larger than the average, which can be estimated by continuous simulation. A coke in force network is abraded until the contact cross section larger and contact stress is less than the compressive stress. After then another coke particle participates in force network. Coke abrasion is caused by such force network reconstructions. Coke free space shape is dominated by the solid flow caused by coke consumption in hearth. The coke free space shape, hearth refractory erosion and drainage efficiency can be affected by the hearth depth, burden load and coke consumption in hearth.
  • Effects of Operation Condition and Casting Strategy on Drainage Efficiency of the Blast Furnace Hearth

    pp. 961-966

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    A mathematical model is developed to quantify the effect of operation conditions and casting strategy on residual amount of slag and metal in hearth. The model is validated by a physical scale model experiment. Calculated results show that the residual amount of slag increases in proportion to the square of production. The effect of hearth permeability on the residual amount of slag is larger than slag viscosity. Then high permeability is necessary under high productivity operation condition. Although a load is not small, increasing tapping rod diameter and shortening cast duration are the effective way to decease maximum slag level. High durability filling mud is necessary to keep cast duration.
  • A Three-dimensional Mathematical Modelling of Drainage Behavior in Blast Furnace Hearth

    pp. 967-975

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    Stable blast furnace operation is required to reduce energy consumption in iron and steelmaking industry. For the stable blast furnace operation, precise controlled drainage is one of the important factors. However, the effects of the various in-furnace conditions on the stable operation were not examined well. Therefore, in this work, basic characteristic features of drainage in a blast furnace hearth were examined.
    Two- and three-dimensional mathematical model were developed based on the finite difference method to simulate molten iron and slag flow in a hearth of a blast furnace. Pressure drop evaluation model in a taphole was developed to reflect pressure variation in a blast furnace hearth on drainage rate of molten iron and slag for the three-dimensional mathematical model.
    The two-dimensional mathematical model results were validated with measured interfaces shapes obtained using an experimental model.The three-dimensional mathematical model results were validated with measured total, iron and slag drainage rate of Chiba No. 6 blast furnace. The results indicate that the drainage behavior and residual iron and slag volume were affected by the conditions in the hearth. The taphole conditions dominate the total drainage rate under the term of assumed blast furnace conditions. In order to reduce the residual slag volume, the taphole diameter change during the tap should be controlled. The decrease of the coke diameter causes increase of the residual slag volume, decrease of the residual iron volume.
  • Effect of Various In-furnace Conditions on Blast Furnace Hearth Drainage

    pp. 976-985

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    Stable blast furnace operation is required to reduce energy consumption and CO2 emission in iron and steelmaking industry. For the stable blast furnace operation, precise controlled drainage is one of the important factors. Therefore, in this work, the effect of coke diameter, void fraction, coke diameter distribution, coke free space, impermeable zone, slag viscosity in a blast furnace hearth on drainage rates, gas-slag and slag-iron interfaces shapes and maximum gas-slag interfaces height were examined with a three-dimensional mathematical model.
    The results indicate that the conditions of the peripheral region at the taphole level determine the residual slag volume. The packed bed in the region 2.0 m from the taphole has about 50% of contribution to the residual slag volume. The void fraction change has the largest effect on the gas-slag interfaces height. The coke diameter distribution has little effect on the total drainage rate as well as the coke diameter of the uniform packed bed, coke free space, and impermeable zone bellow the taphole level. The taphole conditions dominate the total drainage rate under the terms of the assumed blast furnace conditions. The conditions of the peripheral region in the hearth determine the drainage rate patterns of the iron and slag. The peripheral region's permeability can be predicted from the drainage rate patterns of iron and slag, if precise measurement of the drainage rate patterns can be achieved. A drainage pattern, whether iron drains prior to slag or slag drains prior to iron, is largely affected by a drainage interval.
  • Effect of FeO in Dripping Slag on Blast Furnace Hearth Drainage

    pp. 986-995

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    Japanese iron and steelmaking industry has to reduce CO2 emission by 10.5% in 2010 relative to the level of emissions in 1990. Stable blast furnace operation is required to reduce energy consumption and CO2 emission in iron and steelmaking industry. For the stable blast furnace operation, precise controlled drainage is one of the important factors. However, there are many unrevealed phenomena in the hearth to perform the stable operation. Therefore, in this work, the effect of iron and slag dripping pattern, FeO concentration in the dripping slag on the iron and slag surfaces, thermal properties of refractory and brick on drainage temperature, temperature distribution in the hearth, temporal variation of iron and slag drainage rates and interfaces shapes were investigated by using three-dimensional mathematical model.
    The results indicate that more than 2 mass% FeO in dripping slag will cause deterioration of slag drainage ability due to high slag viscosity around tapholes. Continuous monitoring of FeO concentration in the tapping slag is effective to prevent deterioration of slag drainage ability. The trends of the other side of tapping taphole temperature were varied dramatically according with FeO concentration in the dripping slag. Even in the case of 0 mass% FeO in the dripping slag, there is a solidified slag near the hearth wall except around the tapholes. A peripheral distribution pattern will result in a stable drainage. Slag, which dripped on near the other side of the tapping taphole, stays around the taphole, and does not drain from the tapping taphole located opposite side.
  • Two Dimensional Cold Model Study on Unstable Solid Descending Motion and Control in Blast Furnace Operation with Low Reducing Agents Rate

    pp. 996-1005

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    Unsteady behavior with bridging/slipping of solid bed in low reducing agents operation of blast furnace was simulated using a two dimensional cold model. Alumina sphere was used as representative particle of coke/ore packed bed. Two kinds of deadman particles different in gas permeability was examined. To simulate the effect of cohesive zone on unsteady behavior, a sand layer of lower gas-permeability was charged with a certain thickness at the top of the bed, which descended with a form of cohesive zone when it reached at the lower part. Further, a fine coke layer was set at the shaft bottom with a certain size assuming accumulation of fines. Unsteady phenomenon with the fine coke accumulation was also observed with another thin sand layers, charged in the shaft assuming increase of gas-permeability resistance in reducing coke supply operation. It was revealed that the ratio of peripherally flowing rate of tuyere gas had a considerable effect on the discontinuous behavior of both solid descending motion and gas static pressure. The ratio increased with decline in deadman gas-permeability, approach of the simulated cohesive zone to deadman surface and inflow of small particles into raceway. There was a lowest critical position of the simulated cohesive zone for the rapid increase of discontinuity. The bridging/slipping behavior with fines accumulation was significantly affected by the low gas-permeability layers charged in shaft. Setting up the chimney zone of high gas-permeability at the central part was effective to decrease the discontinuous motion.
  • Control of Peripheral Gas Flow and Design of Burden Quality for Low Reducing Agent Rate Operation of Blast Furnace

    pp. 1006-1014

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    Concepts and targets of operational conditions and burden qualities for reduction of exhaust carbon dioxide (CO2) are discussed with consideration of an energy balance at Steel works. Lowering a reducing agent rate (RAR) with reduction of a heat loss and increase in a shaft efficiency is desirable measures to decrease in the exhaust CO2. Suppressed gas flow at a peripheral part of furnace contributes to improvement of both heat loss and shaft efficiency, however, promoted gas flow at that part is necessary for a stable state of gas permeability with low quality burden against degradation behavior. To apply for the operational design, effects of sinter RDI and coke TI on the RAR and exhaust CO2 through the changes in peripheral gas flow are clarified on the basis of analyses of the operational results and simulations by using of the mathematical model. For example, improvement with -10.4% of RDI and 0.69% of TI contributes the reduction of RAR by 10 kg/t through changes of heat loss by 78.3 MJ/t and shaft efficiency by 0.014.
  • Subjects for Achievement of Blast Furnace Operation with Low Reducing Agent Rate

    pp. 1015-1021

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    The technology which reduces the reducing agent rate by the improvement in the reaction efficiency of blast furnace leads to reduction of hot metal manufacturing cost, but also solution of recent CO2 emission reduction. The subjects for achievement of the blast furnace operation with low reducing agent rate were described on reduction measures of the carbon consumption and problem of the measures referring to the example of reducing agent rate of the present state blast furnace concerning blast operation and reactive improvement. And, carried out concrete measures were introduced in order to aim at the low reducing agent rate operation. The following results were obtained.
    1) Since it has reached the already high reaction efficiency in present state blast furnace, it is not easy to attempt further reduction of the reducing agent rate.
    2) The blast furnace use of high reactivity coke or reduced iron is equal level or over it in comparison with the reduction effect by the assumed blast operation in this paper.
    3) The promotion of coke reaction load with the gasification is worried, when it aims at the low reducing agent rate operation by the high reactivity coke use.
    4) It is estimated that the threshold also exists for the reducibility of competing ore, when it aims at the low reducing agent rate operation using the high reactivity coke.
    5) The use of the low SiO2 sinter is effective for the improvement on the permeability in the blast furnace, when it aims at the low fuel rate operation. However, the new technology of the permeability improvement is desired, since there is some a limit for low SiO2 of the sintered ore, when future raw material supply and demand is considered.
  • HBI Production through Coal-based Direct Reduction and Its Application in Blast Furnace

    pp. 1022-1028

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    In order to reduce CO2, emission and cope with the shortage of agglomerated ore due to the use of low-grade iron ore for a sintering process, which are key issues in the ironmaking field, it was proved that direct reduced iron can be manufactured using comparatively cheap fine iron ore and coal, or steel mill waste as the raw material. By using coal-based direct reduced iron, hot briquetted iron (HBI) which has sufficient strength for blast furnace use was manufactured in the demonstration plant. The use of this HBI in the blast furnace could contribute to reduce CO2, emission and dealing with the shortage of agglomerated ore.

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