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

Tetsu-to-Hagané Vol. 78 (1992), No. 7

  • 高炉技術考

    楯岡 正毅

    pp. 957-959

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  • Iron Ore Deposits and Future Properties of Iron Ore Products in Western Australia

    Yukihiro HIDA, Nobuji NOSAKA

    pp. 960-968

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  • Prospect of Cokemaking Technology in Next Generation

    Yuzuru TAKIZAWA

    pp. 969-976

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  • New Coal Policy Related with the Global Environmental Problem

    Hisanori NEI

    pp. 977-981

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  • Influence of CO Ratio and Reduction Temperature upon the Reducibility of Calcium Ferrite in Sinter in the Initial Stage of Reduction with CO-CO2-N2 Gas Mixture

    Tateo USUI, Hirotoshi KAWABATA, Toshio FUJIMORI, Isao FUKUDA, Zen-ichiro MORITA

    pp. 982-989

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    Abstract

    The reduction behavior of calcium ferrite (CF) in commercial sinter in the initial stage was examined by the gravimetric method.
    In a previous work, final fractional reduction, Ff, obtained in the reduction stage from hematite to magnetite at GR ≡ VCO/(VCO + VCO2) = 0.2 (V: flow rate) and EPMA, X-ray and microscopic analyses clarified that at 1003 K and more CF was reduced to magnetite but below about 1003 K CF was hardly reduced and Ff_??_0.7 when the oxygen reducible in this stage was assumed to come from hematite and Fe2O3 in CF.
    In the present work, influence of both CO ratio GR and reduction temperature T upon the reducibility was studied by changing either GR or T while keeping the counterpart constant. The following "quasiequilibrium line" below which CF was not reduced was found out within the magnetite stable region in the equilibrium diagram for Fe-C-O system:
    T = 1030 - 10.2GR - 801GR2 (873≅T≅1023 K)
    When GR or T were decreased after CF was reduced, "re-oxidation" took place below this line. Long term reduction curve in twice as much as the period for ordinary experiments demonstrated that eight hours were long enough to judge the reducibility of CF and determine Ff.

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  • Effectiveness Factor of Porous Reduced Iron Pellets in Water Gas Shift Reaction

    Fengman SHEN, Reijiro TAKAHASHI, Jun-ichiro YAGI

    pp. 990-997

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    Abstract

    In the process of the gas phase reaction on porous catalysts, all the surface area is not used for the reaction because of the gaseous diffusion resistance inside the particle of catalysts. For the rate expression of such reaction, the effectiveness factor of porous catalyst is often used. However, in some cases it is difficult to obtain the value of effectiveness factor.
    In this study, the non-linear expression of reaction rate for water gas shift reaction was converted into linear form by introducing Taylor's expansion and the equation for calculating the effectiveness factor of porous reduced iron pellets was derived.
    The effect of the following factors on the effectiveness factor was discussed. They were the temperature at which the porous reduced iron pellets were prepared, the pressure and the temperature under which the water gas shift reaction took place, the pore structure and impurity of the pellet. The observed and calculated effectiveness factors showed similar trend. Namely, the effectiveness factor increased with increasing the temperature for the preperation of porous reduced pellets, with increasing the reaction pressure and with decreasing the temperature for water gas shift reaction.
    In the measurement of the effectiveness factor with industrial pellets, about 10 times larger value than the theoretical one was obtained. This discrepancy was reasonably explained by the effect of impurity in the pellet.

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  • Effect of Water Gas Shift Reaction on the Reduction of Wustite Pellets in a Fixed Bed with H2-CO and H2-CO2 Gas Mixtures

    Takeaki MURAYAMA, Koichiro HIGASHI, Kohei IMANISHI, Yoichi ONO

    pp. 998-1004

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    Abstract

    The effect of water gas shift reaction on the reduction was investigated theoretically and experimentally in the fixed bed reduction of wustite pellets with H2-CO and H2-CO2 gas mixtures at 900°C.
    In the model analysis, the water gas shift reaction, the effect of high void fraction in the peripheral part of the fixed bed next to the reaction tube wall on the gas flow, the effect of the gas composition on the parameters, the oxygen diffusion in the dense iron layer, and the heat of reactions were taken into account.
    Following results were obtained;
    1) The calculated results by the present model agreed well with the observed data of fractional reduction, gas composition and temperature.
    2) In the reduction with H2-CO, the effect of water gas shift reaction on the reduction curves was not so significant. However, the temperature in the bed was lowered slightly by the effect of heat of the reaction.
    3) In the reduction with H2-CO2, the effect of water gas shift reaction on the reduction became significant with an increase of CO2 composition in the inlet gas. The temperature in the bed was lowered remarkably.

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  • Combustion Rate and NO Emission during Combustion of Coke Granules in Packed Beds

    Eiki KASAI, Shengli WU, Takeshi SUGIYAMA, Shinichi INABA, Yasuo OMORI

    pp. 1005-1012

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    Abstract

    Combustion experiments of coke granules were conducted using a sintering simulator in order to examine fundamentally a way to reduce NOx emission from the iron are sintering process. Existing state of coke and kind of adhering materials were variously changed in the experiment.
    For any coke granules, conversion ratio of N in coke into NO in outlet gas was high in the early stage of combustion because of relatively low temperature of the coke surface. Therefore, depression of combustion rate in the early stage can be a key to suppress overall NO emission. In the case of the coke granulated with fine materials which would not become to be melt, however, not only the conversion ratio but also combustion rate of coke decreased comparing with coke particles without adhering fine materials. On the other hand, in the case of the coke granulated with fine materials having the composition of calciumferrite, CF, combustion rate did not decrease much because melt formed in the early stage of combustion removed quickly from coke surface and the conversion ratio was vanishingly small.
    On the basis of these results, sintering tests was carried out with a laboratory-scale sinter pot using pregranulated coke with fine mixtures of iron ores, limestone and burnt lime. Reduction of the conversion ratio into NOx in outlet gas was obtained by about 30% for P type coke and more than 40% for S type.

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  • Effect of Mineralogical Properties of Iron Ore on Its Assimilation with Lime

    Yukihiro HIDA, Jun OKAZAKT, Kaoru ITO, Shunichi HIRAKAWA

    pp. 1013-1020

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    Abstract

    In order to clarify the influences of iron ores on their sintering performance based on their mineralogical properties, assimilation experiments of iron ores and artificial ores prepared from reagents were carried out. The assimilation rate of are and the microstructure of assimilated portion differed greately among ores. Dense quartz-bearing Ore-A, a representative one of group-(a) classified according to mineralogical properties, was difficult to assimilate and porous pisolite Ore-D containing clay as gangue minerals (group-(d)), by contrast, assimilated very rapidly. While the assimilated portion of Ore-A consisted of acicular calcium ferrite that had adhered firmly on the surface of unmelted ore particle, that of Ore-D comprised of very small granular hematite grains, glassy silicate and very large pores and seemed very brittle. Ore-C containing clay (medium group (c)) showed the intermediate behavior between those of Ore-A and Ore-D. By the assimilation experiment of artificial ores, an assimilation rate equation expressed as functions of temperature, pore volume of ore and phase composition of gangue minerals was developed. On the basis of such a relationship between mineralogical prorerties of ore and its assimilation behavior, the deterioration in sintering operation as the various ore brands were interchanged could be clearly explained.

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  • Development of High-goethite Ore Self-densification Sintering Process

    Yukihiro HIDA, Jun OKAZAKI, Keiichi NAKAMURA, Kiyota UEKAWA, Naoki KASAI

    pp. 1021-1028

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    Abstract

    In order to develop techniques to counter the deterioration in sintering operation when using a large volume usage of high-goethite ore, basic research was first conducted on the self-densification conditions of the representative pisolite Ore-D. The result showed that Ore-D is densified when heated to 1350°C or above for practical purposes. Next, the pseudo-particle structure of Ore-D fines required to densify the nucleus Ore-D particle at a high temperature before contact with calcium ferrite system melt was clarified by the assimilation tests of tablets.
    On the basis of these basic research results, a new sintering process, tentatively called the "High-goethite ore self-densification sintering process" was proposed. This process is characterized by the pregranulation of high-goethite ore, serpentine and a small amount of solid fuel fines and by the formation of a protective layer on the coarse ore particles. The results of sintering pot test and short-term sinter plant test confirmed that the new process can be a powerful tool to successfully use a large volume of highgoethite ore in sinter production.

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  • Commercial Production of Agglomerates for Blast Furnace Burdens Using a Large Amount of High Grade Iron Ore Fines

    Yasuo NIWA, Noboru SAKAMOTO, Osamu KOMATSU, Hidetoshi NODA, Akira KUMASAKA

    pp. 1029-1036

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    Abstract

    In order to improve present iron are agglomeration processes drastically and correspond to the future trend of iron are resources suitably, a new agglomeration process named the Hybrid Pelletized Sinter process was studied. On the basis of the fundamental study and the semi-commercial plant trial, a commercial plant of the HPS process with annual capacity of 6 million tons was constructed by remodeling the No. 5 Sinter Plant in Fukuyama Steel Works, NKK. Through the long term operation using a large amount of high grade fine ores, the superiority of the process was confirmed in both productivity and properties of the products. According to the evaluation of balst furnace operation charging the products, reduction of the fuel consumption was also achieved by about 12 kg/t due to their improved properties.

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  • Achievement of High Productivity at a Semi-strand Cooling Type Sinter Plant

    Kenji KITAMURA, Takahisa MIYAKE, Kazuyoshi YANAGISAWA, Keiyu ONO, Tsuyoshi SHOUHO

    pp. 1037-1044

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    Abstract

    A semi-strand cooling method and a high temperature boiler exhaust gas circulation method were employed at the Wakayama No. 4 sintering plant in 1985. Since then, the productivity has increased and the medium pressure steam recovery has been achieved. However the productivity of the Wakayama No. 4 sintering plant was primarily affected by the cooling speed of the sinter cake, so the following countermeasures were taken : the reduction of melting index of the sinter feed, the operation with high basicity and the usage of coarse limestone. Through these improvements, Wakayama No. 4 sintering plant has been in stabl operation with high productivity (_??_37 t/m2/d).

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  • Modeling for Control Knowledge in Sintering Process Using Neural Network and Fuzzy Inference

    Kouichi MATSUDA, Naoki TAMURA, Kazuo NOSE, Takashi NODA, Toshihito OKATA, Katsuji OSUZU

    pp. 1045-1052

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    Abstract

    This paper describes the modeling of two control knowledge in a sintering process which aims to stabilize the state of sintering and yield variation. One control knowledge for return fine ratio which includes nonlinear data evaluation is modeled by fuzzy inference. The other control knowledge which selects the action variables by a two dimensional heat pattern of the sintering process is modeled by using neural network in the extraction of typical heat pattern. The fuzzy control system that uses operator's knowledge of return fine ratio control leads to uniform operation and improvement of yield. The neural network system makes possible the analysis of the relationship between the two dimensional heat pattern and yield and other sensing data.

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  • Effect of Al2O3 Content on Sinter Cake Structure

    Takuya KAWAGUCHI, Shunji KASAMA, Tadahiro INAZUMI

    pp. 1053-1060

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    Abstract

    It has been known empirically that increasing the Al2O3 content in raw material makes the yield, productivity, and sinter quality worse in the sintering process. To solve the Al2O3 problem, a study was made on the nature of sintering by assuming it to be a series of reactions in the sintering bed, such as the formation of stem pores and integration of solid bonds to form a sintercake structure.
    It was found that the adverse effects of increased Al2O3 content in raw material for sintering are ascribable to the change in sintercake structure. It is that the bonding of solid particles and the integration of stem pores were cheked. The changes are caused by the deterioration of the fluidity of the melt. When a flux to increase fluidity was added to a high-Al2O3 raw material having low melt fluidity, the yield improved due to improvement of the sintercake structure.

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  • Agglomeration and Densification Processes during Iron Ore Sintering

    Tadahiro INAZUMI, Shunji KASAMA

    pp. 1061-1068

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    Abstract

    Agglomeration and densification processes during sintering reaction have been analyzed through the use of X-ray tomography. Agglomeration and densification degrees were quantified by calculating the X-ray transparency of 0.25 × 0.25 mm pixels. Evaluation of sintered part in the bed whether the part is weakly, appropriately or excessively bonded and clustering degree are possible with the technique. When excess fuel is used for sintering reaction, uneven sintering phenomonon occurs, resulting larger and denser lump of sintered parts and unsintered parts generated simultaneously. It is recognized to be possible to describe agglomeration and densification processes by the percolation model of fractal theory.

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  • Development of an Evaluation Method for the Pore Structure of Sinter Cake and Its Application to the Permeability Analysis

    Shunji KASAMA, Tadahiro INAZUMI, Tsutomu NAKAYASU

    pp. 1069-1076

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    Abstract

    Pore structure of sinter cake was observed three-dimensional with high energy X-ray computerized tomography. Most of pores of 5 mm or more in two-dimensional size were three-dimensional stem pores composing a complicated network linked with each other.
    A new analysis method employing the X-ray computerized tomography has been developed for evaluating the sinter cake pore structure, based on a network model. This method has successfully made it possible to quantify the complexities of the pore network and pore thickness.
    Applying this method to the analysis of the sinter cakes having the different permeability, importance of pore branch structure for the permeability was elucidated. Promoting the coalescence of iron ore particles securing stem pores improves the permeabilty of sinter cake because of producing a permeable pore network.

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  • The Relation between Fine Ratio and Particle Size of Sinter Product in Sinter Cake Sizing Process

    Takazo KAWAGUCHI, Kazuyoshi KURIYAMA

    pp. 1077-1084

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    Abstract

    The breakage process of sinter cake was investigated to find the most efficient sizing method that minimizes the -5 mm fraction in crushed cakes. Sinter cakes with various initial sizes were crushed with a jaw-crusher, shatter and tumble testers to compare the -5 mm fines generation processes. The results showed that the dominant factor that decides the amount of -5 mm fines is the final size of the crushed +5 mm products. Under a specific crushing mode, the -5 mm fines mass is decided by the mean particle size of the residual +5 mm products, independent of the cake strength. The second dominant factor is the crushing mode and the jaw-crusher yields the least -5 mm fines mass among the three crushing modes. Thus the most efficient process is to crush sinter cake with jaw-crushers to a size which is small enough as a feed for blast furnaces. The reason why a jaw-crusher yields the least -5 mm fines mass was considered to be due to a volume breakage included in this mode where the applied energy is used for the size reduction, while the other breakage mode, surface breakage is not preferable to crush sinter cakes because the size reduction takes place by surface grinding that leads to a high -5 mm fines mass.

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  • Analyses of Pyrolytic Gas and Steam Flow during Carbonization

    Hiroshi NOGAMI, Hiroyuki NAKASHIMA, Takatoshi MIURA

    pp. 1085-1092

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    Abstract

    The outflow rates of pyrolytic gas are measured in a small-sized coke oven which is heated from only one side. The pyrolytic gas flows out only from the heated side until the heated walltemperature reaches 1000 K, the flow-out direction of the pyrolytic gas then switches over, and most of the pyrolytic gas flows out from the insulated side.
    A one-dimensional mathematical model is developed to estimate the pyrolytic gas behavior including the conservation equations of mass and energy and the releasing rates of pyrolytic gases. The flow patterns of pyrolytic gas from the heated and the insulated sides and the temperature distribution in the coke oven are well estimated comparing with the experimental ones. The total coking period is estimated being longer than the case without the gas flow since the pyrolytic gas flow having a lower temperature decreases the heat transfer rate at the heated side. Furthermore, in case of wet coals containing 10% moisture, the coking time is lengthened by about 3% than that of dry coal because the heat is consumed as the latent heat of evaporation on the higher temperature side in the boiling zone.

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  • Mathematical Models for Coke and by-product Quality Control

    Katsutoshi IGAWA, Shizuki KASAOKA, Hironobu OHSHIMA

    pp. 1093-1100

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    Abstract

    Mathematical models for predicting coke strength and tar quality were developed. The features of these models are as follows :
    (1) Coke porosity and the abrasion index of the coke pore wall are factors affecting coke strength. Those two indices are correlated with the operating conditions of the coke oven and the properties of the blended coal.
    (2)Tar quality is determined by the secondary decomposition reaction, which is a function of temperature in the space above the charge and off gas velocity.
    The models, because of thier good agreement with operational date, can be utilized for the better control of coke strength and tar quality, and thus contribute to stable coke oven operation.

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    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Mechanism of Coke Size Degradation by Mechanical Impact

    Takashi ARIMA, Tetsu NISHI, Toshiaki OKUHARA

    pp. 1101-1108

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    Abstract

    The rates of the volume breakage and surface breakage of lump coke and the particle size distribution of the resultant products were investigated using a shatter tester and a drum tester. It was found that the change in the probability of the volume breakage of coke could be expressed by the Weibull function and that the surface breakage rate of coke was basically proportional to the weight of the particles.
    Based on the experimental results and applying the concept of the theory of comminution kinetics, the size degradation process of coke was analyzed. It was found that the size degradation process of coke could be described by the above two mechanisms and the effect of the volume breakage on the apparent surface breakage rate and that parameters of the volume breakage and the intrinsic surface breakage could be estimated from data on the size degradation behavior.

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    3. An Analysis on Exergy Consumption and CO2 Discharge in Ironmaking Systems Tetsu-to-Hagané Vol.77(1991), No.8

  • Change in Size and Tensile Strength of Coke during Conveyance

    Tsunao KAMIJO, Haruhisa IWAKIRI, Junpei KIGUCHI, Takeshi YABATA, Hidetoshi TANAKA, Masaji KITAMURA, Humio NOMA

    pp. 1109-1115

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    Abstract

    One of the required properties of coke for blast furnace is it's size to maintaine permeability. Then, authors investigated changes in the size and the tensile strength of coke during a conveyance process, and calculated the size distribution of coke after breakage by using the initial size and the tensile strength of coke. The main results are summarized as follows.
    (1) Change in size of coke and the effect of positions in the coke oven on coke properties are clarified by the sampling and the simulation of the conveyance process.
    (2) The tensile strength of coke is analysed by the Weibull's distribution function and the stabilized effect is quantitatively clarified.
    (3) The calculation of the effect of the initial size and the tensile strength of coke on the size distribution makes it possible to estimate the size of coke charged in blast furnace.

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  • The Estimation of Strength and Fracture of Metallurgical Coke by Thermal Shock

    Nobuo SUZUKI, Shozo ITAGAKI, Shigeyasu MITANI, Sennosuke SATO, Takayuki SUZUKI, Tsuneo OIKAWA

    pp. 1116-1123

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    Abstract

    A fracture mechanism due to thermal stress of metallurgical coke in a blast furnace is investigated by nonlinear transient finite element analysis of heat transfer and thermal stress, as follows;
    (1) Thermal stress distribution in a coke disk heated locally by Joule's method.
    (2) Effect of initial temperature, thermal expansivity and diameter of coke on thermal stress distribution in a coke sphere.
    The strength of coke during rapid heating at high temperature can be estimated. The possibility of thermal schock fracture is deduced to occur in a lower part of a blast furnace.

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  • A Simulation Model on Fluid Flow and Heat Transfer in Packed Bed with Melting Phenomenon

    Jiabing WANG, Reijiro TAKAHASHI, Jun-ichiro YAGI

    pp. 1124-1131

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    Abstract

    In order to elucidate the mechanisms of flow and heat transfer in the cohesive zone in a blast furnace, model experiments at low temperature were carried out for the melting phenomenon, gas and liquid flow and heat transfer in the packed bed. Glass beads were packed and paraffin particles were charged on the top of the packed bed, which corresponded to the coke particle and are respectively.
    A mathematical formulation was proposed for the simulation on simultaneous flow, heat transfer and melting phenomenon in the packed bed. The vectorial form of Ergun's equation was used for the gas flow. For the liquid flow, a dispersion-probability model was applied to obtain the flowing region, in which flow vector was computed from the modified Darcy's equation. Equations of heat balance on gas, solid and liquid were composed of the terms for convection, conduction, heat exchange between three phases and phase transformation. The finite difference method was used to compute flow and heat transfer in the packed bed. The grids for the computation were generated by the use of body-fitted coordinate.
    The experimental results showed good agreement with the values computed.

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  • Movement and Accumulation of Fines Generated in the Blast Furnace

    Morimasa ICHIDA, Takeshi NAKAYAMA, Kenji TAMURA, Haruyuki SHIOTA, Kyouich ARAKI, Yoichi SUGISAKI

    pp. 1132-1139

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    Abstract

    Using a half section three-dimensional model of a blast furnace, a tuyere-injection experiment of coke fines was conducted. The following findings were obtained from the analysis of the influence of the injection rate and particle size of the fines on the burden descent and gas permeability and the study of the movement and accumulation behaviors of the fines in the blast furnace. With an increase in the injection rate of fines, the frequency of slips, the gas pressure, and the frequency and extent of the raceway shape variation increased. But the influence of the fines injection was limited when their particle size was much smaller than the size of the charged materials. The injected fines are to be deposited at the surface of the dead-man and near the furnace wall where the burden descent velocity is low. When the high-concentration regions of fines are formed at the surface of the dead-man and near the furnace wall, the burden descent region in the lower part of the furnace reduced and the retention time of the burden decreased. With the V-shaped stock and inadequate central gas flow, fines are likely to be deposited in the center and they descend with the burden.

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  • Analysis of Si Transfer Reaction in the Lower Part of Blast Furnace by Kinetics Theory

    Takashi SUGIYAMA, Shinroku MATSUZAKI, Hiroji SATO

    pp. 1140-1147

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    Abstract

    Fundamental experiments and development of 2 dimensional mathematical model were carried out to clarify Si transfer mechanism in the lower part of blast furnace by the reaction kinetics theory. According to experiments and calculation results, SiO gas generation from coke and slag near the raceway zone was controlled not by equilibrium theory, but by reaction kinetics. Especially, SiO generation rate from coke is the most important factor for controlling Si concentration in molten iron. Decreasing of gas temperature in the region near raceway and improvement of permeability in the deadman is effective for the decreasing of Si concentration in molten iron.

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  • Estimation of Silicon Transfer Based on Radially Sampled Slag and Metal at Tuyere Level

    Hiroyuki MITSUFUJI, Masaaki SAKURAI, Akira MAKI, Takashi SUMIGAMA, Yasuo NIWA

    pp. 1148-1155

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    Abstract

    A probe capable of measuring radially from tuyere nose to the deadman was installed at a low silicon operation blast furnace. The mechanism of silicon transfer was investigated by using the probe. Molten metal dripps mainly in the region between the end of the raceway and the position of 2.3 m from tuyere nose. [Si] content of the dripping metal in the region controls that of tapped metal.
    [ Si] content at the tuyere level is dependent on (FeO) and (Al2O3) generated from low reduction degree ore and coke ash respectively.
    [Si] content in the region of 0.91.3 m from tuyere nose reaches 0.51% which is higher than the tapped value of 0.23%. However, [Si] content in the region of 1.52.3 m is 0.16%. Totally, average [Si] content at the tuyere level is 0.28%. Consequently, the region which mainly control the overall silicon transfer is above the tuyere level.
    Amout of desiliconization below the tuyere level is 0.05%, which is the difference between the [Si] content at the tuyere level and the tapped value. The desiliconization reaction occurs mainly below the region of 0.91.3 m from tuyere nose.

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  • Size Degradation of Dead-man Coke by Reaction with Molten FeO in Blast Furnace

    Kohei SUNAHARA, Takanobu INADA, Yuji IWANAGA

    pp. 1156-1163

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    Abstract

    Since particle size of deadman coke greatly affects the permeability of gas and liquid in the lower part of a blast furnace, elucidation of the behavior the replacement of deadman coke is an important subject. This paper describes the degradation of deadman coke by the reaction with molten FeO. With use of a one-dimensional reaction model in which two kinetic parameters were determined from a fundamental experiment, the degradation of the deadman coke in an actual blast furnace was simulated. The effect of FeO in molten slag on the degradation of deadman coke concerns reduction ratio on the melting down of ore temperature, and productivity. It takes about 2 weeks that vertical size distribution of degrading deadman coke is stationary pattern.

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  • Main Factors Affecting Static Holdup of Molten Slag in Coke-packed Bed

    Hiroshi OHGUSU, Yutaka SASSA, Yukio TOMITA, Katuhiro TANAKA, Morihiro HASEGAWA

    pp. 1164-1170

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    Abstract

    Fundamental experiments under high temperature were carried out to clarify the dropping behavior and residual mechanism of molten slag in the lower part of blast furnace.
    According to the result of experiment, it was verified that residual phenomenon of molten slag in the coke-packed bed was controlled by capillarity caused by immersion wetting. Static holdup of molten slag was able to be shown by dimensionless empirical formula considering balance between static pressure and that based on immersion work.
    Void diameter affected the quantity of slag droplet that residued in graphite funnel, that is to say, the quasi-packed bed, and its residue was present only under critical void diameter. It is estimated that static holdup indicates almost zero under the condition that coke diameter in the deadman is more than about 20 mm.

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  • Influence of Low Permeability Zone in Blast Furnace Hearth on Temperature Distribution in Furnace Bottom and on Iron and Slag Tapping Indices

    Yoshitaka SAWA, Kanji TAKEDA, Seiji TAGUCHI, Toshiyuki MATSUMOTO, Youichi WATANABE, Hideyuki KAMANO

    pp. 1171-1178

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    Abstract

    Heat transfer behavior and the state of the coke packing zone in the blast furnace hearth were investigated by laboratory experiment and plant data analyses. It was found that the heat transfer coefficient between the flowing molten iron and brick surface is too large to form solidification layer of molten iron at the brick surface; hence, a zone of low permeability against the molten iron and slag flow was expected to exist in the hearth when the brick temperature is low. The concept of the low permeability zone has enabled us to interpret such phenomena observed in operation as (1) the periodical temperature changes of the bottom bricks, (2) differences in the metal and slag conditions at respective tap holes, (3) and the correlation between the flow-out index of slag and the bottom brick temperature.

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  • Development of a Stave Cooler with High Stability of Blast Furnace's Working Profile and without Brick Laying Work

    Fumio ITO, Akitsugu HANAFUSA, Yoshio TAKEI, Takuzi MITSUYASU, Yasuyoshi MIZUNO

    pp. 1179-1186

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    Abstract

    A total of 25 stave-cooled blast furnaces has been put into operation at Nippon Steel Corp. since 1969. NSC has been making to improve the campaign life of each stave-cooled BF to a extent. This paper refers to a new type stave cooler which can eliminate brick laying work. Aimed at reducing both the capital cost and the changing ratio of working profiel in the course of the wear of brick work through a campaign life, this stave was developed. As a result of the finite element method analysis of stave cooler's temperature distribution and thermal stress, it was drawn an inference that 600 mm including 200 mm cast-in brick layer replacing the function of conventional brick wall of 600 mm in thickness would be equivalent in the life of BF's campaign, and that under the high heat flux tapered rib would be useful for supporting cast-in brick.
    This stave was put into practical use in the belly and shaft part of Kamaishi No. 1BF and Tobata No. 1BF, and is functioning satisfactorily.

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  • Outlook of Pulverized Coal Injection into a Blast Furnace

    Shinichi INABA, Jun-ichiro YAGI

    pp. 1187-1197

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  • Temperature Measurement in Pulverized Coal Combustion Fields

    Kazutomo OHTAKE

    pp. 1198-1205

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  • Analysis of Pyrolysis and Combustion Behavior of Pulverized Coal through Fundamental Experiments

    Hiromitsu UENO, Kazuyoshi YAMAGUCHI, Kenji TAMURA

    pp. 1206-1213

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    Abstract

    Experiments concerning the combustion of pulverized coal in a free space was conducted using a vertical cylindrical furnace in order to make clear the combustion behavior of pulverized coal inside tuyeres of the blast furnace.
    First, the influence of blast conditions and properties of pulverized coal on its combustion behavior were analyzed.
    Secondly, the generated char from pulverized coal in stage of the pyrolysis were investigated.
    (1) The amount of ultimate pyrolysis of pulverized coal increases with a rise in the blast temperature and a rise in the oxygen concentration accelates the pyrolysis rate. Accordingly, rising the blast temperature and oxygen concentration is conductive to the improvement of combustion efficiency inside tuyeres. Besides, the use of coarser coal and low volatile matter coal lowers combustion efficiency inside tuyeres. These are conceivably due to the lower pyrolysis rate caused by slow heat up and lower amount of ultimate pyrolysis, respectively.
    (2) With the progress of pylorysis, pulverized coal became spherical and a lot of pores formed inside the particles. Moreover, the coal particles expanded as the pyrolysis proceeded with some kinds of coal. Accordingly, the reactivity of char is estimated to be higher than that of coke.
    (3) Q-factor that fixes the amount of ultimate pyrolysis can be shown by the carbon content in coal, consequently the formula of pyrolysis rate with several different kinds of coal were presented.

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  • Maximum Injection Rate of Pulverized Coal into Blast Furnace with Consideration of Unburnt Char

    Kazuyoshi YAMAGUCHI, Hiromitsu UENO, Kenji TAMURA

    pp. 1214-1221

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    Abstract

    Experiments concerning the combustion and consumption of pulverized coal (PC) with high volatile matter content were conducted using an experimental apparatus capable of simulating the heat transfer and reaction in the lower part of the blast furnace.
    First, the calculating method of PC combustion efficiency in the raceway was proposed and the effects of blast conditions on the efficiency were investigated.
    Secondly, the calculating method of PC consumption efficiency at the apparatus top was proposed and the effects of blast conditions on the efficiency were investigated.
    Thirdly, the unburnt char weight accumulating in the apparatus was measured and the limited char weight not to cause the permeability deterioration in the apparatus was found.
    As a result of these analyses, the following conclusion was obtained concerning the maximum PC injection rate:
    Under the conditions of blast temperature of 1300°C, blast humidity of 5 × 10-3 kg/Nm3 and oxygen enrichment of 2%, the limited PC injection rate is 245 × 10 -3 kg/Nm3 in the apparatus that prevents the discharge of char from the apparatus top, and the limited PC injection rate is 190 × 10-3 kg/Nm3 that does not cause the permeability deterioration even when char accumulates in the apparatus.

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  • Simulation of Transport Phenomena around Raceway Zone in the Lower Part of Blast Furnace

    Hiroshi NOGAMI, Takatoshi MIURA, Takeshi FURUKAWA

    pp. 1222-1229

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    Abstract

    A two dimensional mathematical model was developed to describe transport phenomena in a packed bed of coke in front of blast furnace tuyere including pulverized coal combustion. The model consists of two submodels, one is pulverized coal combustion model in a blow pipe and the other is combustion model in packed bed of coke. In this model coke particles in a raceway are treated as a kind of fluid and flow patterns of gas and solid phase are calculated by using two phase flow approach.
    This model was applied to practical operation conditions. When pulverized coal injected into tuyere, more oxygen is consumed and higher temperature rise appears at the region more close to tuyere tip in the raceway and lower temperature is represented in the coke bed than those of all coke operation. Residence time of pulverized coal particles in a blow pipe is quite short, so burning rates in a blow pipe are very low and the pulverized coal particles mainly burn in raceway cavity. The burning rate of pulverized coal particle increases with volatile matter content of original coal, but some particles reach to inner wall of tuyere when high volatile coal is used.

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  • Mathematical Model of Blast Furnace Raceway Zone with Pulverized Coal and Fine Ore Injection

    Xiao XINGGUO, Kentarou NOZAWA, Shigeki SASAHARA, Masakata SHIMIZU, Shin-ichi INABA

    pp. 1230-1237

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    Abstract

    A mathematical model of blast furnace raceway zone with pulverized coal (PC) and fine ore injection was developed to describe the reaction behaviors of injected PC and fine ore. The model is based on differential balances of mass and heat taking account of the reaction kinetics and heat transfer of PC, coke. fine ore and gases.
    The kinetic parameters of thermal decomposition and reduction of fine ore were determined by the laboratory test. The kinetic parameters of PC and coke combustions were determined by applying the model to a experimental combustion furnace and to a actual blast furnace with all coke and PCI operations, respectively.
    Furthermore, the raceway phenomena with simultaneous injection of PC and fine ore were predicted and the effects of operating conditions on reaction in a raceway were studied using the model. The results were summerized as follows.
    1) The combustion of PC and reduction of fine ore are restrained by the temperature drop of gas occured by the complex injection of PC and fine ore.
    2) The final combustion degree of PC in the raceway is slightly affected by injection rate of fine ore.
    3) Increase of blast temperature can make higher reduction degree of ore than oxygen enrichment.

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  • Current State of Iron Ore Smelting Reduction Technology

    Tomio MIYAZAKI

    pp. 1238-1249

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  • Numerical Analysis of Combustion Mechanism in Iron Bath Type Smelting Reduction Furnace

    Akihiko SHINOTAKE, Yasushi TAKAMOTO

    pp. 1250-1257

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    Abstract

    A numerical analysis based on the mathematical model has been made on the combustion phenomena in an iron bath type smelting reduction furnace. This model deals with seven components: C, CO, CO2, O2, H2, H2O, N2. Gas flow, temperature distribution in smelting reduction furnace were calculated.
    The change of post combustion ratio by coal species and coal feed rate into smelting reduction furnace was calculated and compared with 5 t scale experiment.
    The model was also used to calculate material and heat balance when heat loss amount and prereduction degree of ore changed. It was found that the material and heat balance point was determined uniquely by coal species, heat loss amount, and prereduction degree of ore. In this balance point, ore and coal feed rates are determined uniquely, post combustion ratio and heat efficiency are also determined, so coal and oxygen consumption and productivity at this point can be calculated.

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  • Sticking and Its Prevention in Fluidized Bed Reduction of Iron Ores

    Kazuya MIYAGAWA, Tsunao KAMIJO, Mikio DEGUCHI

    pp. 1258-1265

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    Abstract

    Reduction of iron ore in a fluidized bed is limited by the agglomeration tendency of the bed particles, which causes defluidization. This defluidization is called 'Sticking phenomenon'.
    In this paper, experimental studies using a batch-fluidized bed reactor are carried out to clarify the mechanism and the prevention method of sticking.
    Following results are obtained.
    1) Metallic iron wiskers which ore generated on the surface of iron are entangle the other particles and lead to sticking.
    2) Sticking can be prevented by the carbon coating which restrains the growth of metallic iron whiskers.
    3) If the metallic iron whiskers should grow, sticking can be prevented by controling the ratio of iron ore particles with wiskers below 50%.

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  • Circulation and Reduction Behavior of Iron Ore in Circulating Fluidized Bed

    Masahiko SATO, Hiroshi ITAYA, Seiji TAGUCHI

    pp. 1266-1273

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    Abstract

    The circulation and reduction behavior of iron ores in a circulating fluidized bed prereduction furnace were studied under hot and cold experimental conditions as a part of fundamental study for the development of a smelting reduction process. Three kinds of ore with different particle size and silica sand were used as the circulation materials. The circulation rate of ore was controlled to keep a constant solid hold up in the cold experiments. On the other hand, for the case of hot experiments the circulation rate of ore was not controlled and the solid hold-up was kept constant by supplying a small amount of ore to compensate the dust loss. The results obtained are as follows:
    1) The circulation rate of iron ore increased as the particle size decreased and the average solid hold-up in the riser increased. The circulation rate also increased as the gas velocity in the riser increased.
    2) The gas velocity and solid hold-up were considered to affect the carrying over of particles as the driving force and the probability, respectively. The ore circulation rate, Gs, was proportional to the product of Fr number and the average solid hold-up (1-ε) in the riser.
    3) The rate controlling step in the reduction of very fine ore was considered to be chemical reaction. On the other hand, the reduction of larger ore was affected by both chemical reaction and diffusion in the particles.

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  • © 1992 The Iron and Steel Institute of Japan

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