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

Tetsu-to-Hagané Vol. 100 (2014), No. 2

  • Preface to the 100th Volume Memorial Special Issue on Ironmaking

    pp. 109-109

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    DOI:10.2355/tetsutohagane.100.109

  • Coal Utilization Technologies for Improvement of Coke Strength Control

    pp. 110-117

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    DOI:10.2355/tetsutohagane.100.110

    Coking coal necessary for cokemaking process is exhausted in progress; increasing the ratio of non- or slightly-coking coal is required. However, non-or-slightly coking coal causes a lot of structural defects in the coke lump and decreases coke strength because of its low dilatation and high shrinkage.
    For increasing the ratio of non- or slightly-coking coal, pre-treatment technology of coal such as the coal size control, increasing the coal bulk density and the rapid preheating reforming etc. have been developed and a new cokemaking process SCOPE21 that consists of those technologies have already started and high quality of coke is produced using over 50% of non- or slightly-coking coal. In addition, knowledge of coke structure formation mechanism and degradation mechanism of coke were remarkably developed.
    This paper reviews the past research on coal utilization technologies, carbonization mechanism and coke structure and degradation behavior of coke, and describes future direction of research and development for increasing the ratio of non- or slightly-coking coal.
  • Evaluation of Coal Thermoplastic and Dilatation Behavior with Coke Pore Structure Analysis

    pp. 118-126

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    DOI:10.2355/tetsutohagane.100.118

    Coke strength is depends on coal thermoplastic and dilatation behavior, so it is very important to understand the behaviors for making high strength coke. In this study, change of coke pore structure were investigated with image analysis of coke cross section when coal combination of blended coal changed and ASP was added to blended coal.
    (1) When thermoplastic temperature between low rank coal and high rank coal widely differed, low circularity pore increased in the both texture derived from low rank coal and high rank coal. It was concluded that when low rank coal particle dilated, high rank coal particle didn’t dilate, so low rank coal particle reached free expansion. Meanwhile, dilatation of high rank coal neighboring low rank coal decreased. As a result, high rank coal not neighboring low rank coal reached free expansion, and low circularity pore area increased in the texture derived from high rank coal.
    (2) When ASP was added to blended coal, low circularity pore decreased in the texture derived from high rank coal. It was thought that ASP lowered softening temperature of high rank coal, so high rank coal could fill void between coal particles before low rank coal solidified.
    As above, investigation of coke pore structure is effective to understand coal thermoplastic and dilatation behavior.
  • Prediction of Coking Behavior of Coking Coals and Binder through Characterization Utilizing High Temperature Solvent Fractionation

    pp. 127-133

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    DOI:10.2355/tetsutohagane.100.127

    Steel industries need to increase the use of low-grade coals in coke making due to the recent rapid increase in coking coal price. To do so, it is necessary to effectively use binders, and it is desired to develop a theory on how to blend coals and binders effectively. In this work the coal fractionation method proposed by the authors was applied to characterize coals and binders. Nine different-rank coals and two binders (HPC developed by Kobe Steel and ASP) that were heat-treated at 400°C in advance were separated into three fractions having different molecular weight by solvent extraction at 350°C. The chemical and physical properties of each fraction were found to be almost independent of the coal and binder types. Based on these results, it was clarified that the thermoplastic behaviors of the mixture of several coals and binders and the strength of their resulting coke can be correlated to the relative abundance of the fractions in the mixture. It is therefore possible to determine an appropriate blending ratio of coals and binders to obtain high-strength coke. This approach can be expected as a new blending theory which is applicable even to the low-grade coals that have not been used and newly-developed binders.
  • Relationship between Chemical Structure of Caking Additives Produced from Low Rank Coals and Coke Strength

    pp. 134-139

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    DOI:10.2355/tetsutohagane.100.134

    Coke strength can be enhanced by adding HyperCoals (HPC). HPC can be produced from different rank of coals including low rank coals. The aim of this study is to investigate and evaluate the usability of HPC from low rank coals as caking additive. In this paper,1H-NMR, solid state 13C-NMR analysis, and elemental analysis were carried out to investigate the molecular structure of HPC prepared from low rank coals. The results showed that the number of aromatic rings in a unit structure increased from 1-2 in original coals to 2-3 in HPC extracted at 360°C. Effect of extraction temperature was also investigated and it was found that fraction of 3 aromatic rings increased in HPC extracted at 400°C in comparison to HPC extracted at 360°C. The strength of cokes produced by adding HPC was directly a function of number of aromatic rings in the HPC and increased with increasing number of rings.
  • Effect of Random Pore Shape, Arrangement and Non-adhesion Grain Boundaries on Coke Strength

    pp. 140-147

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    DOI:10.2355/tetsutohagane.100.140

    The coke strength is determined by coke microstructure and non-adhesion grain boundaries. The aim of this study was to investigate the effects of pore structure and non-adhesion grain boundaries on fracture behavior by RBSM (Rigid Bodies-Spring Model). In regard to pore structure, randomly-shaped pores were generated, and the pores were randomly-arranged. The randomly-shaped pores were controlled by equivalent circle diameters and pore roundness. The non-adhesion grain boundaries were randomly-located in coke matrix. First, coke with realistic pore structure was calculated. As a result, large and distorted pores affected decreasing of the coke strength. Furthermore, a coke model which was composed of coke matrix, pores, and non-adhesion grain boundaries was analyzed. The coke strength was decreased, resulting in an increase of existence of non-adhesion grain boundaries. The numerical data was corresponded to the experimental result. The coke strength was decreased when there are a little bit of non-adhesion grain boundaries. This is because that a non-adhesion grain boundary becomes an origin of the fracture if the non-adhesion grain boundary is in a stress concentration region. It was shown that non-adhesion grain boundaries were the factor of decreasing of the coke strength with low-quality coal.
  • Development of Sinter Quality and the Technology with Corresponding to the Change of Iron Ore Resources: 100 years of Sintering Process and to the Future

    pp. 148-159

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    DOI:10.2355/tetsutohagane.100.148

    For purpose of recycling dust generated in the integrated steel works, sintering process has been applied and developed from dust treatment technology in non-ferrous metal industry in 1910’s. Additional to dust low Fe grade ore has also been utilized as raw material in sintering process.
    In 1960’s, increasing demand of iron and steel products caused shortage of lump iron ore, which was the driving force for full-blown development of sintering process. At last "Self-flux sinter" which has higher reducibility compared to lump iron ore has been invented. "Self-flux sinter" is utilized the phenomenon of forming liquid phase from fine iron ore with lime stone.
    After "Self-flux sinter" invention, this process has been researched and developed eagerly for view point of chemical compositions, texture (mineral, pore), and sinter quality. Furthermore, standard method of sinter quality evaluation has been established, which was utilized for process advance by texture control in divided region.
    Based on previous research, further development theme in future will be introduced in personal vision.
  • Promotion Effect of Melt-formation in the Sintering Bed on the Oxidation Reaction of Metallic Iron Particle Usedas Agglomeration Agent

    pp. 160-169

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    DOI:10.2355/tetsutohagane.100.160

    This study has been performed to understand the reactions of metallic iron and ferrous components in the iron ore sintering bed for utilizing them as agglomeration agent, which relates to the reduction of CO2 emissions. Effects of size of metallic iron particles and pre-heating temperature on sintering phenomena were examined. Changes in the structure and pressure drop of the bed were observed by using laboratory-scale sintering simulator.
    When using larger size of metallic iron particles, pressure drop of the bed did not significantly change. On the contrary, it changed drastically when using metallic iron with smaller particle sizes. Such behaviors are attributed to formation of dense iron oxide layer on the surface of the coarse iron particles, which does not melt due to the shortage of heat. In the case using medium metallic iron particles at higher preheating temperature than 900°C, formed iron oxide tended to melt and oxidation reaction of metallic iron was proceeded. In the case of lower preheating temperature than 900°C, however, the oxidation of metallic iron was suppressed by the oxide layer formed on the surface. Melting of such layer is necessary to be continuously oxidized for metallic iron particle. The additional heat by other agglomeration agents such as coke was required enhance the melting of the iron oxide layers formed on the surface of metallic iron particles with larger size. This suggests that the melting of formed oxide layer is essential for further oxidation of metallic iron oxide particles used as agglomeration agent.
  • "Continuous Cooling Transformation (CCT)" Concept for Iron Ore Sintering Using in situ Quick X-ray Diffraction and Confocal Laser Microscope

    pp. 170-179

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    DOI:10.2355/tetsutohagane.100.170

    In this study, the formation of calcium ferrites during heating and cooling was investigated by in situ and real-time observation using a newly developed system, i.e., in situ "quick X-ray diffraction (Q-XRD)," and an in situ laser microscope. In the new Q-XRD, a specimen was heated up to 1773 K, and X-ray diffraction patterns were measured using a pixel-array area detector with an interval as short as a few seconds. In situ observation both of crystal structure and microstructure successfully revealed the effects of heating and cooling rates on the sintering reaction in the CaO-Fe2O3 system with special attention to overheating and overcooling phenomena. The first continuous cooling transformation (CCT) concept for iron ore sintering was proposed to understand overcooling phenomena when the molten oxide cooled down to room temperature and magnetite (Fe3O4), hematite (Fe2O3), and various types of calcium ferrites were formed. The CCT diagram for sintering provides crucial and fundamental information on the sintering accompanying solidification, precipitation, and formation of calcium ferrites from the molten oxide, and can be used as a guideline for controlling sintering processes.
  • Improvement of Sinter Productivity by Adding Return Fine on Raw Materials after Granulation Stage

    pp. 180-188

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    DOI:10.2355/tetsutohagane.100.180

    In order to increase the permeability of the sintering bed for sinter ore productivity, RF-MEBIOS (Return Fine - Mosaic Embedding Iron Ore Sintering) process, in which return fine as dry particle is added on granulated raw materials and then they are charged into sintering machine, is proposed. In RF-MEBIOS, it is demonstrated by pot tests that productivity increases at the same moisture content in sinter mixture at charging. This productivity increase is caused by higher permeability in sinter packed bed due to two major phenomena. One is increasing the pseudo-particle size at granulation and the other is decreasing the bulk density of sinter packed bed after charging. The former is achieved by a higher moisture content in the raw materials at granulation, which has the role of decreasing small size of pseudo-particle (-0.25mm). The latter is achieved by higher friction in the packed bed composed of dry and wet particles compound, which has a role of decreasing bulk density. In the development of RF-MEBIOS, return fine was chosen as the dry particle because it is dry when produced by the sintering machine. The sinter productivity increases with the increase of the quantity of the return fine added after granulation stage. The effect of pseudo-particle (-0.25mm) ratio andεon flame front speed were evaluated as 55% and 41% to increase of frame front speed, respectively.
    Effect of RF-MEBIOS on sinter productivity is confirmed in No.3 sinter plant in Kashima Steel Works. Under the condition of constant moisture content in sinter mixture at charging, this improvement degree is proportioning to the ratio of bypass return fine which is added to granulated the other sinter materials without granulation. It means granulation at higher moisture has superiority compared to increase of fine material in bypass return fine.
    Finally, RF-MEBIOS method is installed on three commercial sintering machines (Kashima, Wakayama, and Kokura) belonging Sumitomo Metals. In all three sinter plants, productivity increase has been confirmed. Therefore, introducing RF-MEBIOS has been demonstrated to cause a universal improvement of sinter productivity.
  • Effect of Oxygen Enrichment on Sintering with Combined Usage of Coke Breeze and Gaseous Fuel

    pp. 189-197

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    DOI:10.2355/tetsutohagane.100.189

    The temperature in the sintering bed is preferably maintained between 1200°C and 1400°C during sintering to produce high strength and reducibility sintered ore. To achieve this condition, the technology of combined usage of coke breeze and gaseous fuel, which is fed properly from the top surface of the sintering bed, was developed. In this paper, the effect of oxygen enrichment with combined usage of coke breeze and gaseous fuel on the heat pattern in sintering bed and cold strength of sintered ore was investigated. The cold strength of sintered ore was improved by the oxygen enrichment in the pot test. Then, the holding time over 1200°C during sintering was extended and improvement of strength would be attributed to promotion of the sintering reaction. By the simulation model calculations based on chemical kinetics, it is considered that the further extension of the holding time over 1200°C due to oxygen enrichment is caused of an increase in the distance between the combustion points of the coke breeze and gaseous fuel. However, improvement of the cold strength reached saturation over 32vol.% of the oxygen concentration in suction air. It is also considered that the excessive increase of the distance between the combustion points of coke breeze and gaseous fuel decreases overlap of respective heat transfer and doesn’t contribute to the expansion of holding time over 1200°C.
  • Recent Progress on Advanced Blast Furnace Mathematical Model Based on Discrete Method

    pp. 198-210

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    DOI:10.2355/tetsutohagane.100.198

    From the backgrounds of the recent trend towards low reducing agent operation of large blast furnace and application of diversified charging modes of various burdens, an advanced mathematical model of blast furnace is required. Although conventional models based on the continuum model have been widely used, these models are not suitable for the recent demands. The discrete models such as discrete element model (DEM) and particle method are expected to precisely simulate the discontinuous and inhomogeneous phenomena in the recent operation conditions. With the discrete model, the microscopic information on each particle in the packed bed can be obtained besides the overall phenomena in blast furnace. The visual information can be obtained to understand the in-furnace phenomena with high spatial resolution. The liquid dripping and movement of fines in the lower part of blast furnace can be well simulated with DEM and particle method such as Moving Particle Semi-implicit Method (MPS). Moreover, the optimum bed structure for low reducing agent operation is being clarified by application of Eulerian-Lagrangian method. This review summarizes the recent progress on the mathematical model based on the discrete model.
  • Agenda for Low Reducing Agent Operation of Blast Furnace: Thermophysical Properties of Molten Slags on the Gas Permeability at the Dripping Zone of Blast Furnace

    pp. 211-226

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    DOI:10.2355/tetsutohagane.100.211

    Currently, low reducing agent operation of blast furnace is actively investigated in order to reduce CO2 emission. However, low reducing agent operation accelerates coke wear, resulting in the decrease in the void fraction in the blast furnace. Particularly, at the dripping zone, the decrement in the void fraction increases the hold-up amount of liquid burden. As a consequence, the gas permeability at the dripping zone becomes lower dramatically. In the present paper, we have focused on the effect of thermophysical properties of molten slags on the gas pressure drop and the liquid hold-up, the measures of the gas permeability, in the counter-current region of gas-liquid flow. It has been considered from the results of hold-up experiments and/or simulations that the surface tensions of molten slags and their contact angles against carbonaceous materials are the most significant properties for the gas pressure drop as well as the liquid hold-up. The previous studies with respect to their properties have been reviewed for the slag compositions and the temperatures close to those at the dripping zone.
  • Aspects from Powder Behavior to Ensure Burden Bed Permeability for Low Carbon Operation of Blast Furnace

    pp. 227-245

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    DOI:10.2355/tetsutohagane.100.227

    Low reducing agent rate (RAR) operation of blast furnace is a key technology to reduce carbon dioxide emission from the steel industry. To realize stable and highly effective operation of blast furnace under low RAR condition, permeability in the furnace has to be kept in sufficient level. Keeping bed permeability is an essential issue in blast furnace operation especially from the viewpoint of prospective change in circumstance of raw material resources. This paper focuses on powder behavior that deteriorates bed permeability in blast furnace. It is known that excessive accumulation of powder in the burden bed causes serious operation troubles like slip, hanging and so on, therefore the powder accumulation should be suppressed as little as possible. To suppress powder accumulation it is necessary to understand the powder behavior in packed bed, thus this paper summarizes three mechanisms of powder formation, flow and accumulation in blast furnace. Regarding powder generation, numerous research works on ore degradation with progress of reduction, un-burnt char formation in raceway zone and coke degradation have been made and revealed their characteristics in detail. As for powder flow and accumulation, their macroscopic characteristics have been elucidated. It is expected that the profiles of temperature, gas concentration and material flows in the blast furnace under low RAR operation is drastically different from the ones under current operating conditions. Thus further discussions taking into account such differences in conditions and microscopic viewpoints are required for comprehensive understanding of powder behavior under low RAR blast furnace operation.
  • Diffusion Behaviors of He and CH4 in Air Flow through Packed Bed

    pp. 246-250

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    DOI:10.2355/tetsutohagane.100.246

    When practical utilization of hydrogen in blast furnace will be tried, mass transfer behavior of hydrogen under the upward gas flow should be correctly understood. The purpose of this study is to clarify that diffusion behavior of several kinds of gases in air flow through packed bed in order to understand diffusion behavior of hydrogen in blast furnace. Cold model experiments at room temperature were carried out to investigate the diffusion behavior of He and CH4 gases in air flow through the packed bed. Experimental results were analyzed by R.W.FAHIEN’s method and following conclusion was obtained. Effect of molecular species difference on gas diffusion behavior was appeared clearer in the condition of smaller air flow velocity than bigger one from this comparison. In other words, gas diffusion behavior could ignore difference of molecular species under enough large gas flow condition.
  • Simulation of Blast Furnace Operation with Hydrogen Injection

    pp. 251-255

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    DOI:10.2355/tetsutohagane.100.251

    Recent years various trials to decrease carbon dioxide emission from iron and steelmaking industries have been made. One of these trials is utilization of hydrogen in blast furnace process, and this study performed numerical simulation of blast furnace operation with hydrogen injection through tuyere. The simulations were carried out under the conditions of constant bosh gas flow rate, adiabatic flame temperature and hot metal temperature. The simulation results showed that the temperature level in the stack part was decreased with increase in the hydrogen injection ratio. This resulted in the lowering of the top gas temperature and retarded the reduction of iron oxide especially one of magnetite. The injection of the hydrogen remarkably decreased the coke rate. The converted reducing agent rate, that is sum of coke rate and six times (molecular weight ratio of carbon to hydrogen gas) as hydrogen rate showed small change. Although this decrease in coke rate deteriorated the permeability of the burden materials in the furnace, pressure drop in the furnace was reduced. Since the molar flow rate of the reducing gas was kept constant, the decrease in the gas density due to the increase in the hydrogen content was mainly considered to lead the decrease in the pressure drop. The water gas shift reaction played an important role in the generation of the field of gas composition, thus this reaction has to be carefully discussed for further utilization of hydrogen in blast furnace.
  • Measurement of Three-Dimensional Raceway Structure in Small Scale Cold Model by X-ray Computed Tomography

    pp. 256-261

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    DOI:10.2355/tetsutohagane.100.256

    Raceway zone in blast furnace is important region which closely relates to distributions of reducing gas and thermal energy, combustion efficiency of auxiliary reducing agents, degradation of coke particles, and so on. Although numerous works have been made on raceway phenomena, there still are ambiguities such as three-dimensional shape, structure, internal motion, etc.. This paper developed a new method to measure three-dimensional shape and structure of raceway by utilizing X-ray computed tomography. This method used differences between two successive CT images to distinguish regions with and without particle motion. The raceway shape was determined by the boundary of these regions. This method was applied to cold model experiments with alumina spheres of 3.2 mm in diameter. With this measurement, three-dimensional shape of the raceway was successfully revealed, and particles in the upstream region of tuyere actively moved. The results obtained by different measuring intervals show that the region in which the particles actively moved was surrounded by the region with relatively slow particle motion. It is expected that the discussion on the measuring interval and the particle size enables to classify spatially the raceway zone by the rapidity of particle motion.
  • Reaction Behavior of Ca-Loaded Highly Reactive Coke

    pp. 262-269

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    DOI:10.2355/tetsutohagane.100.262

    Usage of highly reactive coke in order to decrease the thermal reserve zone temperature in a blast furnace is considered promising to increase the reaction efficiency in the blast furnace and to decrease the reducing agent rate. In order to develop a new method to produce highly reactive coke by adding a Ca catalyst other than Ca-rich coal, in this paper, firstly the effects of Ca compounds pre-addition to coal on coke qualities were investigated. It was shown that carbonizing the mixture of coal and Ca compounds (CaO, CaCO3) greatly increased coke reactivity and that it was possible to produce Ca-loaded highly reactive coke with high coke strength by adding 3% of Ca compounds under such conditions as high strength coke was produced. Furthermore, the reaction behavior of Ca-loaded highly reactive coke when mixed with conventional coke in the presence of an alkali was investigated. It was shown that when a mixture of Ca-loaded highly reactive coke and conventional coke was heated in a reaction gas, Ca-loaded coke selectively and preferentially reacted. It was also confirmed that Ca acted as catalyst in the existence of K. This shows that the reactivity of Ca-loaded coke is higher than that of conventional coke in an actual blast furnace whereby coke reactivity is promoted by condensed alkali vapor.
  • Quantitative Estimation of Gas Permeability of Softening Sinter Layer with Liquid Phase

    pp. 270-276

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    DOI:10.2355/tetsutohagane.100.270

    Quantifying gas permeability of softening sinter layer was studied with the aim of increasing the precision of gas permeability in cohesive zone.In this study, the effect of liquid in packed bed on gas permeability was evaluated by a cold model experiment, which simulated sinter melting behavior by using sponge ball absorbed glycerin solution. As a result, gas permeability of packed bed with liquid was expressed by formula (a), based on Sugiyama’s formula.
    Δp/L={1/C(ε−ht)}2(1/ϕDp(1−Sr))ρu2/2………(a)
    Formula (a) was adapted to actual softening sinter experiment result, and was confirmed to be good agreement.
  • Influence of a Large Amount of Hydrogen and Traces of Sulfur on Reaction Behavior of a Coke Mixed Bed Under Blast Furnace Simulated Condition

    pp. 277-286

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    DOI:10.2355/tetsutohagane.100.277

    Influence of a large amount of hydrogen and traces of sulfur on reaction behavior of the bed with ore pellet and coke particles were examined in a laboratory reaction apparatus with the blast furnace simulated conditions under load until 1400°C.
    On the later metallization stage around 1000°C, hydrogen half substitute into base gas N2-CO-CO2 enhanced the reduction and sulfur addition to hydrogen (sulfur chemisorption on iron) enhanced it more. Coke mixing into the bed enlarged further these metallization due to the spacer effect and facilitating the water gasification. These results influenced structures of products to provide more swelling of pellets and those topochemical reaction types for sulfur added reaction gas relatively to the gas without sulfur.
    Beyond around 1100°C, reduction processes mostly terminated independently of reaction gas conditions and coke mixing.
    The shrinkage with softening of bed was lessened by hydrogen substitute and coke mixing, because of less FeO bearing slag and spacer effect of coke. Sulfur addition enlarged the shrinkage due to promoting iron sintering derived from sulfur bearing slag.
    Both conditions of base gas and hydrogen substituted gas with coke mixed bed made the bed melt through iron carburization with CO gas and coke, while sulfur addition suppressed the melting.
    Moreover, the reaction behaviors of the bed were overall investigated along with the results of gas pressure drop through the bed and exit gas analysis.
  • Effects of Charcoal Carbon Crystallinity and Ash Content on Carbon Dissolution in Molten Iron and Carburization Reaction in Iron-Charcoal Composite

    pp. 287-293

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    DOI:10.2355/tetsutohagane.100.287

    Charcoal use instead of fossil fuel is one of the possible technologies for mitigation of CO2 emission in the steel industry because charcoal can be considered as "carbon-neutral" material. In this study, the possibility of utilization of charcoal as carbon source for carburization reaction was examined; more specifically effects of carbon crystalinity and ash in charcoal on carbon dissolution into molten iron and iron carburization reaction in iron-charcoal composite were investigated. Two kinds of experiments were carried out. One is measurement of charcoal carbon dissolution rate in iron bath. Another is observation of isothermal reaction between iron and charcoal in a composite sample. Several kinds of charcoal with relatively low ash content were applied as experimental samples. Charcoal samples were treated with several heating patterns to control their carbon crystallinity. Additionally, charcoal samples were treated with acid solutions, HCl and HF, to control the ash content in them. From these investigations, following results were revealed. Charcoal heat-treated at low temperature, 1273K, has advantage for carbon dissolution reaction into iron bath. Charcoal ash strongly prevents the carburization reaction between iron and carbon in the composite sample.
  • Gaseous Reduction Model for Sinter in Consideration of Calcium Ferrite Reaction Process (Unreacted-core Shrinking Model for Six Interfaces)

    pp. 294-301

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    DOI:10.2355/tetsutohagane.100.294

    Reducible oxides containing iron in iron ore sinter are hematite, magnetite and quaternary calcium ferrite (abbreviated by CF), which is the complex crystalline mineral produced from Fe2O3, CaO, SiO2 and Al2O3. Equilibrium diagram for CF reduction with CO-CO2 gas mixture is a little but significantly different from the one for pure iron oxides. In previous analyses for reduction reaction of iron oxides in a blast furnace, however, sinter has been treated as pure iron oxides; existence of CF has been ignored. Reduction steps for CF can be written as
    CF (= ‘Fe2O3’) → ‘Fe3O4’ → ‘FeO’ → ‘Fe’,
    which are much the same as pure iron oxides, where ‘Fe2O3’, ‘Fe3O4’, ‘FeO’ and ‘Fe’ designate hematite, magnetite, wustite and iron stages of CF, respectively. However, a reported variation of gas composition with temperature measured in a blast furnace shows that the gas composition in the thermal reserve zone is a little higher than the wustite / iron equilibrium, the reduction potential of which is less than that of ‘FeO’ / ‘Fe’ equilibrium and hence ‘FeO’ cannot be reduced to ‘Fe’. In the present work, gaseous reduction model for sinter is developed in consideration of CF reaction process; unreacted-core shrinking model for six interfaces is proposed to take into account reaction process of CF as well as pure iron oxides. Trial comparison of the calculated reduction curve with our previously reported experimental data under simulated blast furnace conditions shows rather good agreement.
  • Thermodynamics of Impurities in Pure Iron Obtained by Hydrogen Reduction

    pp. 302-311

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    DOI:10.2355/tetsutohagane.100.302

    Hydrogen itself is not a primary energy and needs an energy for its production, which means that CO2 will be exhausted during the production process, more or less. However, when a Green Hydrogen can be produced, it is a best way to use the hydrogen instead of carbon.
    In this study, two kinds of iron ore were reduced and melted both under hydrogen and carbon atmosphere. The obtained iron metal under hydrogen atmosphere was quite pure one. The impurities in the metal were chemically and thermodynamically analyzed. The characteristics and benefits of hydrogen reduction were discussed in comparison with the carbon reduction.
    The content of silicon in the metal under hydrogen atmosphere was one tenth to the iron obtained by carbon reduction. Manganese was about one third to one tenth against the carbon reduction. However, phosphorus in the hydrogen reduction was almost the same level to the carbon reduction. Sulfur content became half in the hydrogen reduction. Moreover, the content of hydrogen in the metal was the same level between the hydrogen reduction and the carbon reduction. It was found that the rate of hydrogen evolution from a molten metal during solidification was fast significantly. The activities of elements in the metal were calculated through the thermochemical data, and the relationships among those elements were elucidated.
    From the thermodynamic analysis, a high oxygen activity in the metal obtained under hydrogen atmosphere caused to a low content of impurities and high activity of oxides related.
  • Effect of Hydrogen Addition on Reduction Behavior of Ore Layer Mixed with Coke

    pp. 312-318

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    DOI:10.2355/tetsutohagane.100.312

    Low RAR (reducing agent rate) operation of the blast furnace is one of effective techniques for reducing CO2 emissions. Coke mixed charging is a well-known and available measure to achieve low RAR operation by improving permeability and reducibility. Utilization of hydrogenous reducing agents is also an efficient measure. A reduction test under load was performed to investigate the effect of coke mixing with hydrogen addition on reduction behavior of the ore. Simultaneous use of coke mixing and hydrogen addition accelerated the reduction rate through the carbon gasification rate, and it was also decreased pressure drop. The effect of coke mixing and hydrogen addition on blast furnace operation was examined using a two-dimensional mathematical simulation model. In case of the ore layer mixed with coke, hydrogen addition in the reduction gas increased the hydrogen reduction ratio and decreased the direct reduction ratio. As a result, RAR decreased and permeability improved.
  • Reduction Potential Evaluation Index of Various Reducing Agents in Blast Furnace

    pp. 319-324

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    DOI:10.2355/tetsutohagane.100.319

    In blast furnace operation, reducing agent ratio (RAR) is an important index. The RAR is defined as only sum of weight, without considering the kind of reducing material. Here the author proposes a new reducing potential index, "ReP", which considers the difference of reducing material composition under the real blast furnace condition that gas utilization ratios (ηco, ηH2) are 50%. Namely, ReP is set as
    C=3, H=0.5, O=–2, (N=0) (ReP/kmol).
    This index evaluates reduction potentials of various reducing materials in a uniformed manner. Latter part of this report includes an example of blast furnace operation analysis using "ReP". Extended case studies which concern utilization of partially reduced ore, utilization of mixture of ferrous and carbonous materials, and gas utilization ratio changes far from 50%, are performed. When gas utilization ratios change from 50%, "ReP" is available if extended ReP is set as C=2+2ηco, H=ηH2, O=–2, (N=0) (ReP/kmol).
  • Direct Dephosphorization from Iron Ore Containing Higher Concentration of Phosphorus

    pp. 325-330

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    DOI:10.2355/tetsutohagane.100.325

    Iron ore containing higher concentration of phosphorus is reduced by hydrogen gas containing water vapor. 13% of removing yield of phosphorus is obtained. It is observed that removing rate of phosphorus can be expressed as apparent 1st order reaction equation. The reaction rate equation is divided into two parts. Rate constant of the former reaction is about 10 time larger than that of the latter equation. It is estimated on the basis of a previous research result that phosphorus removed from iron oxide is gaseous phosphorus and form of remained phosphorus is Fe2P.
  • Introduction to Selected Papers Introduction to “On the Top Gas Recycled Reforming Process and the Injected Gas Distribution, Tetsu-to-Hagane, 59(1973), pp.1506-1521 by Hiroaki Nishio and Tsuneo Miyashita”

    pp. R1-R2

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    DOI:10.2355/tetsutohagane.100.R1

  • Introduction to “Dissection of Blast Furnaces and Their Inside State (Report on the Dissection of Blast Furnaces-1), Tetsu-to-Hagane, 62 (1976), pp.535-546 by Kenjiro Kanbara, Tomoro Hagiwara, Akitoshi Shigemi, Shin-ichi Kondo, Yuji Kanayama, Ken-ichi Wakabayashi and Nobuyoshi Hiramoto”

    pp. R3-R4

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    DOI:10.2355/tetsutohagane.100.R3

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