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

Tetsu-to-Hagané Vol. 66 (1980), No. 13

  • Influence of Potassium on the Rate of Boudouard Reaction of Coke

    pp. 1781-1790

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    In order to reveal influence of potassium, taken up by coke particles from N2-K(g) gas mixture, on the overall rate of Boundouard reaction of coke, a mathematical model is developed. The three unknown parameters for the catalytic action of potassium, contained in this model, are fitted to the experimental data of the overall rate. The temperature dependences of these parameters show that the catalytic action lowers with raising temperature. Potassium reduces both the apparent activation energy and the frequency factor for the reaction; the former lowers considerably with increase in potassium content in the range less than 1 wt%.
    The model is able to make estimation on extent of the reaction zone in the particles. The local concentration of the reaction on the outer shell of particle, due to the rate-enhancing effect of potassium, is considered to reduce the strength of carbon matrix in this portion. Although non-homogenity of the concentration profiles of potassium and carbon dioxide within coke particles complicates quantitative relationship between the overall rate and amount of potassium taken up, a simple empircal expression representing the relation is obtained.
  • Rate of Potassium Uptake of Coke from N2-K(g) Gas Mixture

    pp. 1791-1800

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    It is well known that potassium circulates in blast furnaces and that potassium taken up by coke reduces the strength and enhances the reactivity of coke. The kinetics of potassium uptake by coke from gases is fundamental to elucidate accumulation of potassium in coke and contribution of coke to the circulation. The experimental results on the rate of the potassium uptake from N2-K(g) gas mixtures with 10-4 to 10-3 atm as partial pressures of potassium, in the temperature range from 900 to 1 100°C, have proved that the rate depends on size of coke particle and partial pressure of potassium, and has maximum values in the vicinity of 1000 °C.
    The mathematical analysis of the experimental results, assuming the first reversible reaction as the chemical process and taking into account the diffusion of potassium vapor within coke particle, shows that, with raising temperature, the reverse rate constant increases significantly and the equilibrium constant decreases in the similar extent, while the other factors have no significant dependence on temperature. The mathematical model developed here is able to represent, in good agreement with experimental results, not only the overall rate of the potassium uptake but also the concentration profile of potassium within coke particle.
  • Consideration on the CO and NO Formation around the Coke Specimen during Combustion

    pp. 1801-1809

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    An apparatus was deviced for the analysis of CO2, CO and NO in the small amount of the gas sampled around the coke specimen during combustion. The conversion ratio of organic nitrogen in coke to NO was calculated from the analytical results of these gases.
    According to the analysis of the conversion ratio, the reaction of NO formation was indicated to proceed both on the coke surface and within the boundary layer. The former reaction on the surface gave the most of NO. The reduction of NO formation was brought with elevating the CO/O2 ratio at the coke surface.
  • Development of a Method for Testing the Disintegration Property of Coke during Gasification

    pp. 1810-1819

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    A new test method for the evaluation of disintegration property of coke during the progress of gasification has been developed in order to simulate the state of coke at the raceway in blast furnace.
    This method uses a spouted bed reactor into which heated CO2 gas or perfect combustion gas containing CO2 and H2O is injected at the flow rate enough for fluidizing the specimen coke particles. The cokes which are shot into the reactor react with CO2 or H2O, and thereby the strength deterioration progresses at their surfaces. The fine coke particles are generated by the impact or abrasion of fluidizing particles and carried over to the outside by the stream of gas. The fine cokes are collected by a cyclone and the total mass of them is measured continuously.
    The curve of showing the amount of fine coke collected against reaction time represents the disintegration property of coke and this seems to be well corresponded to the burning character of coke in the raceway. The two indexes are defined to indicate the test result. One is mean disintegration rate and the other is fine coke ratio. The former shows good correlation to the reactivity of coke matrix with CO2 and this is well corresponded also to the test value of CSR (coke strength after reaction in a small scale reactor). The latter is correlated to the minimum gasification degree where disintegration of coke surface starts under a certain condition and that seems to be related to the macro-structure of coke.
  • Relation between Shape of Race-way and Production Rate of Blast Furnace Taking Account of Properties of Coke Sampled at Tuyere Level

    pp. 1820-1829

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    When the productivity of No. 2 blast furnace at Sakai Works, Nippon Steel Corporation, was cut down from 2.08 t/d.m3 to 1.34 t/d.m3 because of the economic deterioration in Japan in the latter half of 1970's, coke was sampled at tuyere level seven times in the course of the cutdown.
    On the basis of the test result of the properties of the sampled coke, the followings were concluded:
    (1) As the production rate decreases, the point of the maximum temperature in the race-way moves toward the tuyere and the temperature of the dead-man decreases.
    (2) Coke becomes fragile because of the long time exposure to high temperatures at the lower part of the furnace. Therfore, the amount of coke fines in the race-way increases with increasing the kinetic energy of blast, and in consequence, gas flows upward rather along the wall side than in the center.
    On the other hand, the decrease of the amount of coke fine, which is brought about by the decrease of the kinetic energy of blast, results in a smooth operation which is attributed to the uniform gas distribution. However, in the case of the lower kinetic energy of blast, the temperature of the dead-man decreases and, consequently, softened and half-melted materials form in the region.
  • Changes of Mineral Phases in MgO-added Self-fluxed Pellets during Indurating Process

    pp. 1830-1839

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    The changes of mineral phases in MgO-added self-fluxed pellets during indurating process, were investigated through quantitative analysis by means of EPMA and a microscopic observation.
    Sampled pellets with the variation of 0, 1, 2, and 4% of MgO contents and 0.5, 1.5, 2.0 of CaO/SiO2 ratios, were made by laboratory-scale electric furnace at 1 200, 1 250, and 1 300°C of indurating temperature.
    The results are as follows :
    (1) Major change of mineral phase by adding MgO component to lime-fluxed pellets is the formation of a magnesio-ferrite phase. Forming amounts of magnesio-ferrite and MgO contents in this phase are increased or decreased respectively with the increase of CaO/SiO2 ratio and indurating temperature. The chemical formula of this phase is showed as (Mg0.50.8·Fe0.20.5) Fe2O4 in pellet outer portion, and as (Mg0.30.5·Fe0.70.5) Fe2O4 in pellet center portion.
    (2) Mineral phases except iron oxide are a calcium ferrite and three kinds of slags with about 0.5, 1.0 and 1.42.0 of CaO/SiO2 ratio. The formation of these phases changes by CaO/SiO2 ratio and indurating temperature. MgO and Fe2O3 contents in slag phases decrease with the increase of CaO/SiO2 ratio of slag. MgO contents in calcium ferrite increase to 2.53.0% by adding MgO component.
  • Effect of MgO-component on Various Metallurgical Properties of Self-fluxed Pellets

    pp. 1840-1849

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    Effects of MgO component on metallurgical properties of fluxed pellets with 0.5, 1.5 and 2.0 of CaO/SiO2, were evaluated from a laboratory-scale reduction test, high temperature reduction test, and softening test under load with one pellet.
    The results are as follows:
    (1) Reduction degree at 900°C1 100°C increases with the increase of MgO contents in pellets with 0.5 of CaO/SiO2, and with 1.52.0 of CaO/SiO2 indurated at 1200°C. However that of the latter pellet indurated at 1 2501 300°C does not change or decreases slightly.
    (2) Swelling index of pellets with 0.5 of CaO/SiO2 shows higher values of 2045% at of MgO contents, and that of pellets with MgO 4% lowers to 1015%. The index of pellets with 1.5 of CaO/SiO2 decreases with the increase of MgO contents.
    (3) Softening properties during reduction test under load areimproved with the addition of MgO component, especially with more than 4% MgO than 2% MgO in case of 0.5 and 1.5 of CaO/SiO2 respectively, because magnesio-ferrite and/or MgO-c ontained calcium ferrite phases with a better softening property are generated in pellets by adding MgO.
    High temperature properties are better in the pellets that showed higher forming temperatures of preliminary liquidus slag from DTA curves of wastite powder of pellets.
  • Testing Method of High Temperature Properties of Blast Furnace Burdens

    pp. 1850-1859

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    Regarding the reduction under load test for measuring high temperature properties of blast furnace burdens, the test conditions, i.e. the load, gas flow rate, particle size and bed height were examined through tests and calculations based on a reduction model for fixed bed. Examinations covered also evaluation criteria of test results for high temperature properties.
    The results obtained are summarized as follows :
    (1) Test results are influenced by each of the load, gas flow rate, particle size and bed height conditions.
    (2) It is desirable to minimize the longitudinal difference of degree of reduction and the dependence on load of test results. The optimal test conditions (Fig. 2) were decided from such a point of view.
    (3) The following evaluation criteria of test results for high temperature properties were proposed : i) the temperatures at the beginning of softening and melt-down are high, with a small temperature difference; ii) the integral and average values of index of permeability resistance between softening and melt-down are small; and iii) the degree of reduction achieved at 1 000 to 1 200°C is high.
  • Behaviors of Pellets and Sinter in the Cohesive Zone of Blast Furnace

    pp. 1860-1869

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    An investigation has been carried out into physical and chemical behaviors of sinter and pellets taken from the cohesive zone of Amagasaki No. 1 BF.
    The results obtained are summarized as follows :
    1) The cohesion of burden materials in the early stage takes place by sintering of M·Fe particles formed on their surfaces.
    2) Wustite remaining mainly in central part of pellets melts at 1 350° 400°C and exudes to the outside.
    3) Sinter tends to have higher values of reduction degree, alkali and S contents than pellets because of the easier contact with ascending gas.
    4) Alkali content in burden materials becomes higher with the progress of cohesion and kalsilite is formed in slag phase. Furthermore, glassy silicate as the main slag phase in lumpy ore contains a large amount of alkali.
    5) With the progress of reduction of wustite to M·Fe, MgO content in residual wustite becomes higher and a part of MgO forms merwinite in slag phase.
  • Test Use of Cold Bond Pellet in an Experimental Blast Furnace

    pp. 1870-1877

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    From July to August in 1977, a test on the use of cold bond pellet as burden was carried out with an experimental blast furnace in the Institute of Industrial Science, University of Tokyo.
    Following results were obtained :
    1) The experimental blast furnace was operated almost successfully when self-fluxed sinter of 4.9 mm mean diameter was replaced completely with cold bond pellet of 9.2 mm mean diameter at the same Fe(ore)/C(coke) ratio.
    2) The cold bond pellet retained its original shape and did not show any tendency of swelling and disintegration in the shaft.
    3) By the replacement with cold bond pellet, the permeability in the shaft was improved, but in the lower part of the furnace, it became worse on account of the increase of slag viscosity, which was overcome by the use of serpentine as flux.
    4) The reducibility of cold bond pellet was good enough, but its softening and melting properties were not satisfactory compared with those of self-fluxed sinter.
    5) The sulfer analysis of hot metal increased, because of high sulfer content of cold bond pellet and low slag ratio.
  • Influence of Gas Flow on Burden Distribution in Blast Furnace

    pp. 1878-1887

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    The surface angle of burden and the process of formation of burden distribution were studied under conditions of gas flow with the aid of experiments and theoretical calculations. The following results were obtained:
    (1) The gas flow affects the burden distribution in three ways, namely, the decrease in surface angle of burden, the collapse of surface coke and the transient fluidization of coke at furnace center, when ore is charged.
    (2) The surface angle depends on the value of ρ u2 of gas and is 2 to 7 degree lower with normal gas flow in blast furnace than without gas flow.
    (3) The collapse of surface coke in charging are becomes considerable with increasing gas flow rate.
    (4) When are moves from the periphery toward the center, gas flows avoiding ore bed because of its low permeability, collects at the center and fluidizes the coke there, blocking the ore motion.
    (5) Such a phenomenon to form coke pillar at the center is to be rather observed with pellets than sinter.
  • Two-dimensional Mathematical Analysis on Gas Flow and Heat Transfer in Blast Furnace by the Application of Finite Element Method

    pp. 1888-1897

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    This paper deals with two-dimensional gas flow in the blast furnace which has complicated structure of the bed by the application of the finite element method. Besides this, simultaneous analysis on the gas flow and heat transfer is also carried out for the simplified conditions in which solid flow is approximated reasonably to potential flow.
    As for the gas flow, multi-dimensional Ergun's equation is solved together with the equation of continuity by using the variational principle. However, heat balance equations for gas and solid are solved on the basis of the Galerkin method. In order to consider the layered structure and also the properties of cohesive and raceway zones in the blast furnace, the finite elements for the numerical computation are corresponded to the ore and coke layers.
    Computed results indicate that the drastic changes in gas flow occur arround the cohesive and raceway zones which have extremely different properties on gas flow. Zig-zag flow of gas appears in the lumpy region which is caused by the different permeability of are and coke layers and also by the inclination of the layers. Computed results for the simultaneous analysis on gas flow and heat transfer give correctly the principal characteristics of heat exchange, which proves the mathematical formulation and the numerical technique to be sound.
  • A Mathematical Model of Blast Furnace Considering Radial Distribution of Gas Flow, Heat Transfer and Reactions

    pp. 1898-1907

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    In consideration of the radial distribution of materials in the blast furnace, a new mathematical model of the blast furnace has been developed. This model consists of heat and mass balance equations at the existence of three phases (gas-solid-liquid) and the equation of motion for gas. Assuming streamline of solid and liquid, the characteristic method has been employed to solve these equations.
    By the mathematical model, the following results have been obtained.
    1. Calculated isothermal line (1 400°C) is similar to that of quenched blast furnace.
    2. The distributions of temperature, composition and mass velocity in the upper part of the shaft is strongly affected by the O/C distribution.
    3. In the lower part of the blast furnace, the dead zone plays as a heat reserved zone and has the influence of the formation of the inverted V-shaped cohesive zone.
    x

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  • Mechanism of Flow Resistance of Gas through the Fused Packed Bed

    pp. 1908-1917

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    An experiment and theoretical analysis on the flow resistance of gas through the fused packed bed were carried out for the calculation of gas flow near the cohesive zone in the blast furnace. The pressure drop was measured for the packed bed of prereduced pellets and sinter which were prepared to be various degree of shrinkage.
    In the case of unfused packed bed, the observed value of the pressure drop showed good agreement with the value calculated by Ergun equation. However in the case of fused packed bed, the observed pressure drop showed a trend to deviate largely from Ergun equation as the degree of shrinkage increased. It was found that the experimental results were expressed well by the equation derived on the basis of the new mechanism proposed here that the pressure drop was caused by flow resistance of gas passed through the narrow slit between fused particles, just like the oliffice.
    On the other hand, an attempt was made to express the shrinkage obtained by experiments as the equation, in order to predict the degree of shrinkage of iron are under various degree of reduction and temperature in the blast furnace.
  • A Kinetic Model of Coke Combustion in the Tuyere Zone of Blast Furnace

    pp. 1918-1927

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    A mathematical model is developed to describe the behaviours of coke combustion in the tuyere zone of blast furnace. The model is based on the reaction kinetics, the differential balances of heat and mass, and the mechanics of gas flows.
    Regarding the axial distribution of gas composition in the tuyere zone, good agreement is obtained between the model prediction and the data observed in a working furnace by the other investigators. Calculated results show that the maximum consumption of coke occurs at the intermediate region of the raceway.
    At the blowing of oxygen-enriched or high-humidity blast, the position at which the maximum consumption of coke occurs is shifted toward tuyere nose. Similar effect is accompanied with the decrease in particle diameter of coke in the tuyere zone.
  • Analysis of Blast Furnace Operation Based on the Mathematical Model for Estimating the Profile of Softening-melting Zone

    pp. 1928-1936

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    A methematical model for estimating the profile of softening-melting zone and the radial gas distribution in the furnace in operation has been developed by use of the measured shaft gas pressures in the furnace.
    Close agreement was obtained between the results of this estimation and the data obtained with other instruments in the furnace, and the accuracy of this estimation was satisfactory.
    Indices representing the operation state in the furnace have been derived based on the results of this estimation, and the usefulness of these indices was confirmed for the control of the heat efficiency, reducibility, molten metal quality, permeability, material descending state, and so on.
    Further, operation states were analysed in the case of a decrease in production and an increase in pellet ratio in burden based on the results of this estimation, and it was showed that the actual phenomena in the furnace could be analysed sufficiently and accurately.
  • Liquid Holdups and Abnormal Flow Phenomena of the Gas-liquid Counter-current Flow in Packed Beds under Simulating Conditions of the Flow in the Dropping Zone of a Blast Furnace

    pp. 1937-1946

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    Experiments were conducted to measure the total holdup, gas pressure drop, flooding velocities and liquid distribution at low superficial velocities of liquid for various degree of wetting between liquids and solids.
    Correlations for both static and dynamic holdups and a flooding diagram that are valid for non-wetting as well as wetting flow were obtained.
    Instability of the bed, in which a transition from a stable to a fluidized bed occurred, was observed before the onset of flooding in some of the experiments. A diagram was developed to discriminate the fluidization from the flooding in relation to the flow conditions. This diagram indicated that in blast furnaces the fluidization of the coke bed is likely to start before the onset of flooding by the slag.
    x

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    2. Influence of Gas Flow on Burden Distribution in Blast Furnace Tetsu-to-Hagané Vol.66(1980), No.13
    3. Modeling of Gas and Liquid Flow in Two Dimensional Packed Bed and Analysis of Dropping Zone in Blast Furnace Tetsu-to-Hagané Vol.80(1994), No.12
  • Empirical Formulae for the Gas Pressure Drop and the Liquid Holdup for the Counter-current Region of Gas-liquid Flow in the Dropping Zone of a Blast Furnace

    pp. 1947-1955

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    The Ergun-type pressure loss equation was extended to the flows in irrigated packed beds on the basis of the assumption that, in the case of irrigated beds, the bed is composed of solid particles and hypothetical liquid droplets. Dimensionless empirical formulae for the quantity and the size of liquid in the bed were obtained by using experimental data on gas pressure drop and liquid holdup obtained under simulating flow conditions of the dropping zone of a blast furnace.
    Flooding gas velocities as well as gas pressure drop and liquid holdup over entire region of gas velocity up to the flooding could be calculated by use of the above formulae with reasonable accuracy.
    The pressure loss equation was further extended to the flow of two liquid phases in the dropping zone of a blast furnace. A sample calculation confirmed the result of earlier study that the fluidization of the coke bed would start before the onset of flooding of the slag.
  • Lower Fuel Rate Operation by a Large Blast Furnace Equipped with Bell-less Top

    pp. 1956-1965

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    A large blast furnace of Kawasaki Steel Corporation, No. 6 furnace at Chiba Works, was blown in as the largest bell-less top equipped furnace in Japan in June, 1977. At the initial stage after the blowing-in the operators experienced such troubles as tuyere bending and burning-out which were attributed to inappropriate gas flow distribution in the furnace. However, a series of operational experiments made it possible to improve the internal furnace condition. Especially the trials to find out the better charging sequence for coke and are burdening have brought about the followings :
    i) CO gas utilization ratio in the top gas has been improved up to about 54 per cent.
    ii) There has been no tuyere burning-out since April, 1979.
    iii) The thermal load on the furnace shell has considerably decreased.
    Those improvements were followed by very low fuel rate records :
    418.4 kg/t-p as a monthly averaged value in March, 1980 and 436.1 kg/t-p as a yearly avearged value for the period between April, 1979 and March, 1980.
  • Low Fuel Rate Operation of a Blast Furnace

    pp. 1966-1974

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    For further decrease of fuel consumption of a blast furnace, which was considerably closed to a lower limitation under a present operational condition, following two additional studies to traditional improvements have been carried out;
    (1) An advanced control technique of burden distribution at a furnace throat to achieve a stable furnace condition and an ideal gas utilization, and
    (2) an operational technique to decrease Si-content and temperature of hot metal without any troublesome using high MgO containing sinter.
    These technique were applied to Fukuyama No. 3 BF (inner volume : 3 223 m3) in order to approach to the minimum fuel consumption under a practical operational condition. 428.2 kg/t-hot metal of a monthly fuel ratio was recorded in January 1979. Not only the increase of gas utilization but also the decrease of heat output in melting zone contributed to achieve this low fuel ratio.
    405 kg/t-hot metal was estimated as a lower limitation of fuel ratio, which might be achieved in near future under a practical operational condition in Nippon Kokan, from the above results.
  • Report on Dissection of Amagasaki No. 1 Blast Furnace

    pp. 1975-1984

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    In order to investigate the internal state of blast furnace, Amagasaki No. 1 B.F., having the inner volume of 721 m3, was blown down and quenched with water on 5th November 1976, after a normal operating condition.
    In this paper, the results of dissection such as the general views of burden distribution, temperature distribution, change in physical and chemical properties of burden materials in the furnace are described.
  • Hydrogen Reduction of Iron Oxide Pellets in Laboratory Scale High Pressure Moving Bed

    pp. 1985-1994

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    In order to clarify the effect of the pressure on the hydrogen reduction of iron oxide pellets by a laboratory moving bed, the experiments were performed under the conditions of pressure at 0.117, 0.304 and 0.507 MPa by using the apparatus which was 0.13 m in internal diameter of reaction tube and 2.0 m in availble height. The results obtained were analysed by the one dimentional mathematical model considering both heat and material transfer.
    Final fractional reduction, gas utilization and production rate of reduced iron were increased by pressure increase and pressure drop in the moving bed were decreased. The rate parameters in the reduction rate equation were determined by the stepwise reduction experiments of a single iron oxide pellet and overall heat transfer coefficient of the moving bed was obtained by the heat transfer experiments of a fixed bed. The distribution of calculated process variables such as gas temperature, fractional reduction and mol fraction of hydrogen are well agreed with the observed data at 0.117 MPa. However, both calculated distributions and observed data at high pressure were not in agreement sufficiently. Furthermore, observed pressure drops in the moving bed were represented by the Ergun's equation.
  • Countercurrent Reduction of Powder Ore in a Drum-type Rotary Fluidized Bed

    pp. 1995-2003

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    In order to increase the gas utilization coefficient and to prohibit the sintering phenomena in fluidized bed, the experiments of the countercurrent reduction of powder are with CO gas in a drum-type rotary fluidized bed at the temperature of 900°C and 750°C were carried out.
    In a modelling vessel (diameter : 30 cm), the rotary fluidized state could be obtained on the conditions that the filling ratio of powder are was in the range of 30 to 50% and the dimensionless rotary speed (F) was 1.0 to 1.2.
    The motion of powder are in the drum-type rotary fluidized bed was seemed to be a completely mixing state. The gas utilization coefficient was maximum under the condition that F was 1.0, and it could be increased up to the stoichiometric equilibrium concentration for the reduction of ore. The results of a mathematical calculation on dimensionless numbers (Gc and Ot) for countercurrent reduction based on the three-interface model were in good agreement with observed data.
  • 抄録

    pp. 2009-2014

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