泥炭の賦存量,前処理技術および流動層燃焼技術について概観した.この分野での研究報告は少なく,また,泥炭を工業的な規模で利用している国はまだ少ないようである.しかし,泥炭の産出と利用は資源として意味があるばかりでなく,土地の有効利用という点でもメリットを生ずるので,特に国土の狭いわが国や広大な泥炭地を持つ国においては重要な課題であろう.
泥炭を都市における集中暖房を含めて工業的な燃料として使用する場合の燃焼器としては流動層方式(広義のそれ)が望ましく,特に循環流動層型のボイラーは多くの使用実績がある.流動層方式の最大の利点は,重油,石炭,木材チップ,バークあるいは都市系廃棄物などの多様な燃料と混焼できること,炉内脱硫が可能で窒素酸化物の発生量を低く抑え得ること,などにある.多様な燃料の使用を可能にしている最大の理由は,流動層が気体と固体の激しい混合状態を創出できることにある.その意味では同じ流動層方式でも,気泡流動層型よりも(高速)循環流動層型の方が泥炭ボイラーに適しているとも考えられるが,循環型では高温集塵あるいは熱交換器の摩耗など固有の問題をかかえているので,現時点では安易に優劣をつけがたい.
本文でも述べたように,泥炭の燃料化にあたって問題になるのは,燃焼器(ボイラー)よりも輸送と貯蔵を含めた前処理操作である.天日乾燥は,コストの上では優位性を持っているが,大量使用を考えた場合には無理がある.一方,現在操業中あるいは商業化されつつある乾燥(前処理)プロセスもコスト面で問題をかかえているといわれる.しかがつて泥炭の燃料化にあたっては,乾燥,貯蔵,輸送,ボイラー,エネルギー利用,採掘地の利用などを合理的に組み合わせた総合的なシステムを考えねばならない.細田らはその一つの例として,泥炭産出地域での農用熱利用と発電によるコジェネレーション・システムを想定し,泥炭の新しい乾燥技術および重質油などを混合・粒状化させてエネルギーに転換するための研究を行っている.

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Several kinds of coal were carbonized by using the coke oven with X-ray computerized tomography scanner (CT oven). Estimation of apparent density distribution of the coal charge during carbonization was successfully carrried out by using the scanner.
(1) The coal charge expands owing to the swelling pressure in the plastic layer during the early carbonization period.
(2) The density distribution of the plastic layer is V-shape.
The estimation model of the coke porosity distribution is developed based on these phenomena. The validity of the model is confirmed through the CT oven.

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The deterioration of coke in the blast furnace has been evaluated as the change in coke size due to reaction between coke and CO₂ gas. To clarify the deterioration mechanism, a series of experiment has been carried out at each reaction temperature using apparatus for high temperature CO₂ reaction.
The findings obtained are as follows :
(1) The deterioration of coke by CO₂ gasification reaction was largely changed with the temperature for CO₂ reaction.
(2) Reaction up to 1300°C : Due to the selective reaction by the anisotropic texture of coke, reaction proceeded to the central core of the lump and weight loss affected the decrease of coke strength.
(3) Reaction between 1300°C and 1500°C : Coke lump reacted uniformly on its surface, thereby holding very low reaction rate in the core of the coke lump. Weight loss did not affect the decrease of coke strength.
(4) As CO₂ reaction below 1300°C decreased remarkably the coke strength, if weight loss caused by the reaction lower than 1300°C could be decreased, this countermeasure would become an important method for the control of coke deterioration.
(5) A good quality coke at high temperature showed uniform microstructure and high reactivity with CO₂ gas at pore-wall.

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2000°C hot drum tester was developed successfully for the evaluation of the thermal deterioration of metallurgical coke. It was observed that the thermal deterioration were occurred by the increase in porosity due to the weight losses as well as to the development of micro cracks. It is considered that above 1800°C the graphitization of coke and the change in volume of mineral matters in coke such as Si and Ca compounds make many micro cracks in coke structure with few weight losses and that micro crack development changes closed pores to open ones about 10%.
Both the thermal shock resistance and fracture toughness of coke were measured by the Joule heating method. It was found that these properties could be estimated roughly from the coke properties at room temperature and that coke with high strength in 2000°C hot drum tester gave high thermal shock resistance.

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The reduction of CaO·2Fe₂O₃(CF₂) in which SiO₂, Al₂O₃ were added separately or simultaneously and resultant expansion have been studied in CO-N₂ (4 : 6) mixed gas at 550 °C.
The main results obtained are as follows :
1) In melted material of CF₂-SiO₂ (SiO₂ : 0.52.0 wt%) system, the addition of SiO₂ into CF₂ promotes the formation of 2CaO·SiO₂(C₂S), CaO·Fe₂O₃(CF) and Fe₂O₃. SiO₂ is insoluble in CF₂. The formed Fe₂O₃ increases the reduction and resultant expansion.
2) In melted material of CF₂-CaO (1.87 wt%)-SiO₂ (SiO₂ : 0.52.0 wt%) system, the combined addition of SiO₂ and CaO promotes the formation of CF₂, CF and C₂S. SiO₂ is only slightly soluble in CF. Consequently, the formation of C₂S and the disappearance of Fe₂O₃ restrains the reduction and resultant expansion.
3) In melted material of CF₂-CaO (1.87 wt%)-SiO₂ (1.0 wt%)-Al₂O₃ (Al₂O₃ : 0.58.0 wt%) system, the combined addition of SiO₂, CaO and Al₂O₃ promotes the formation of CF₂-α (SiO₂ : 1.51.8 wt%, Al₂O₃ : ≤8.2 wt%) and CF₂-β (SiO₂ : 1.51.8 wt%, Al₂O₃ :>8.2 wt%).
Both CF₂-α and CF₂-β restrain the reduction, and the former promotes the resultant expansion, inversely, the latter restrains it.

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The formation mechanism of acicular calcium ferrite which is indispensable for improving the sinter quality was studied by use of a newly developed scanning electron microscope having a sintering furnace in it.
The in-situ observation results of the iron ore particle coated with CaO powder during heating and the microstructure of the sample quenched in sintering process showed that (1) small granular compounds similar to monocalcium ferrite are first generated on ore surface by solid state reaction and (2) immediately fuse to be a primary melt above 1 205°C, and then (3) acicular calcium ferrites are quickly formed by the interactive reaction between hematite in ore and high-CaO melt, absorbing a small amount of SiO₂, Al₂O₃ etc. from the melt as solid solutions.

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In order to make clear the mechanism of the reduction degradation of iron ore sinter, the macro strain in the skeletal hematite during reduction was measured.
The results obtained are as follows :
(1) The strain is scarcely remained in the skeletal hematite in the iron ore sinter.
(2) The difference of the mechanism of the reduction degradation of iron ore sinter is made clear in some kinds of reducing gas such as carbon monoxide, hydrogen and the gas mixture of carbon monoxide and carbon dioxide (35%).
(3) In the case of the reduction by CO and CO + CO₂ (35%), the crack is formed immediately after reaching the maximum strain, 0.50.6, in the crystal, but the strain curve is not obtained during reduction by H₂ gas.

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The immersion of sinter into CaCl₂ aqueous solution and subsequent drying have been carried out. The immersion treatment of sinter was carried out at room temperature under the normal pressure and in vacuum. The CaCl₂ concentration of aqueous solution was changed from 1.0 to 10.0 wt%. The effect of immersion treatment on the reducibility index (RI) and reduction degradation index (RDI) of sinter have been studied.
The main results obtained are as follows :
1) On the immersion under the normal pressure, RI decreased only slightly and RDI decreased remarkably with increase of CaCl₂ concentration in solution.
2) On the immersion in vaccum, RI maintained the value of original sinter and RDI decreased more than the value on the immersion under the normal pressure.
3) Decrease of RDI of sinter was caused by the delay of the reduction rate due to adhered CaCl₂ layer in pore surface and resultant decrease of the amount of cracked magnetite particles.

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The effect of use of preheated air suction and pseudo-particle mix made from raw materials on the sintering behavior and properties of the self-fluxing sinter was studied.
The results obtained are as follows :
1) The exchange to cool air during the process of sintering in preheated air suction technique was very beneficial in decreasing the amount of coke, lowering sintering temperature and decreasing FeO content in sinter.
2) The coating of flux fines on coarse ores in the use of sinter mix decreased the sintering time, and further decreased FeO content in sinter.
3) The combined use of the preheated air suction which included the cool air exchange at the middle of sintering and the pseudo-particled sinter mix for sintering decreased sintering temperature, FeO, magnetite and skeletal hematite content, and increased acicular and fine acicular calcium ferrite content in sinter. As a results, the degradation of sinter was obviously improved, and good strength and reducibility were simultaneously maintained.

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As a means of improving sinter qualities, various granulation methods have been studied. This report presents the minerals formation during heating in "the separated granulation method" and its effect on reduction properties of sintered body. Tests were carried out with specimens which consisted of two types of pseudo-particles : one contained high CaO content and the other low CaO content. The particles were mixed and sintered together in a electric furnace. Then reduction degradation, reducibility, strength, and microstructure were examined on the sintered specimens.
The results showed that CaO segregation in raw materials by the separated granulation improved RDI without worsening of reducibility. The RDI improvement was considered to depend on decrease in secondary hematite and in co-existence area of secondary hematite and calcium ferrite.

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In order to clarify the basic designs and determinations of optimum operating conditions of pelletizers for sinter raw materials, a study has been made on particle flow in pelletizers and granulation.
Following results are obtained :
(1) The granulating characteristic is determined by the rolling length of particles in the pelletizer.
(2) Basic designs of the pelletizers are found from the rolling length.
(3) An optimum operating condition of a drum mixer is on a boundary line between normal cascade zone and cataract zone. There is Froude number that gives an optimum operating condition of a disc pelletizer.

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An integrated simulation model for sintering of iron ore was developed to evaluate the effect of various controlling factors on sinter quality and was applied to commercial sintering process. The model consists of 6 submodels, which are permeability, heat pattern, melting, pore, mineral and quality models. By using the informations on ore qualities, characteristics of sintering machine and operating conditions as input data, the model can predict sinter quality, energy consumption, productivity and other operation performance in sintering process. The predicted values were in good agreement with the observed ones obtained by both pot tests and actual tests in commercial plants. The model was introduced into sinter plants in Kashima Steel Works as operation guidance system. The fluctuation of sinter qualities was decreased by about 20% through the application of the model. The total energy cost on sintering operation was decreased by 5.5%. The economical feasibility studies were performed prior to the construction of a new sintering plant under the condition of the planned production capacity and sinter qualities. In accordance with the specification of productivity and sinter qualities required from blast furnace, new sinter feeds of iron ores were evaluated to obtain optimum operating conditions by the model.

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An approximate simulation model of sintering process has been developed. With this model, which is self-concluded type, the calculation time is markedly shortened in comparison with that of conventional theoretical model expressed by partial differential equations. Characteristics of bed permeability, which are important at simulation with self-concluded model, has been studied by systematic sintering pot test. Based on results of the test, statistical equations have been obtained and included in the model. These equations give permeability resistance of each zone at sintering bed from raw materials and sintering conditions.
As a result of verification of the model both by sintering pot test and sintering machine operation, it has been confirmed that the model works effectively in practical use. The model can be used for evaluating and controlling sintering operation in actual process.

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Stepwise reduction experiments of commercial sinter under the same conditions were repeated more than 4 times over a temperature range of 700° to 1000°C.
In the analysis, reduction of calcium ferrite was not taken into consideration. Mass transfer rate from naphthalene-coated sinter was measured and the following correlation equation for estimating mass-transfer coefficient in a gas film of sinter, k_f (cm/s), was derived in consideration of shape factor :
k_f d_p^*/ D=4+0.82(ν /D)^1/3(ud_p^*/ν)^1/2
where D: diffusivity (cm²/s), d_p^* : volume equivalent diameter (cm), u : gas velocity (cm/s), ν: kinematic viscosity (cm²/s),
Values of chemical reaction rate constant k_c and effective diffusivity D_e in the unreacted-core shrinking model for one interface were so determined by trial and error that the calculated reduction curve might agree well with the experimental one. Their temperature dependencies are
k_c(^h/m)=exp[6.88-16000/(RT)](cm/s) D_e^m=exp[-0.721-4130/(RT)](cm²/s)
k_c(^m/w)=exp[5.34-12200/(RT)] D_e(^w)=exp[0.609-5470/(RT)]
k_c(^w/Fe)=exp[3.39-8560/(RT)] D_e(^Fe)=exp[3.23-9060/(RT)]
whereR: gas constant [cal/(mol·K)], T: temperature (K), h, m, w: abbreviations for hematite, magnetite and wustite.
Although microscopic observation of partially reduced samples showed the application of the single interface model was rather not suitable from the viewpoint of reduction fashion, it was good enough for evaluating the reduction rate because of satisfactory agreement between the calculated and the measured reduction curves.

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Laboratory tests on the reduction degradation behavior of sinter were carried out to clarify the influence of each factor, which includes reduction degradation index (RDI), reducibility index (RI), and temperature profile. Furthermore, the materials were extracted from the shaft of the working blast furnace to ascertain the validity of the tests results. Based on these information, the sinter degradation model was formulated to describe the sinter breakdown. The findings obtained are as follows ;
1) Sinter breakdown occurs significantly in the temperature range of 600 to 800°C. This range coincides with that of hematite being reduced.
2) Maximum amount of fines degraded during reduction depends on RDI, RI and temperature profile, under which reduction reaction occurs.
3) Increase of RDI leads to the deteriorating gas permeability originated by the increasing amount of fines and it exerts adverse effects on the gas flow distribution in the radial direction of the blast furnace.

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For the purpose of utilization of the residual oil for ironmaking as a new energy resource, the development of an injection technique of petroleum coke-oil slurry into a blast furnace was undertaken.
First, from the laboratory test, it became clear that the viscosity and the settling velocity of petroleum coke-oil slurries were much dependent on the brand of petroleum coke ; delayed coke (DC) and fluid coke (FC). Namely, DC slurry has much higher viscosity than FC slurry and the settling velocity of FC in the slurry is higher than that of DC.
Next, transportation characteristics of slurries in the pipelines were studied by the use of the pilot plant. The results obtained are as follows. (1) Petroleum coke-oil slurries may be treated as a Newtonian fluid under these experimental conditions. (2) On planning the injection system, the viscosity for calculating pressure loss can be adopted 0.8-1.0 times as high as the viscosity measured by the viscometer according to the brand of petroleum coke.

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Using a two-dimensional model of the lower part of a blast furnace and a raceway hot model, the formation of raceway and furnace core and the coke degradation have been studied to clarify the desirable blast velocity of a blast furnace. The results obtained are summarized as follows.
(1) The reliable raceway penetration DR(m) is derived as shown by the equation below, and it is estimated that the penetration in large blast furnaces is about 1.4 m.
D_R=5.00 D_t·u_t√(P_b+1)/{ρ_c·d_p·(T_b+273)}
In the equation, D_t, is tuyere diameter (m), u_t is blast velocity (m/s), P_b is blast pressure (kgf/cm², gage), ρ_c is apparent density of coke (kg/m³), d_p is mean size of coke (m), and T_b is blast temperature (°C).
(2) The amount of fine coke deposit in the raceway increases to a great extent and the temperature in the lower part of a blast furnace decreases when the raceway penetration exceeds 1.3 m.
(3) The upper limit of blast velocity u_t (m/s) is estimated by the equation under below any conditions of equipments and operations of a blast furnace. According to the calculation based on this equation, the decrease of blast velocity in about 30 m/s causes the reduction of the raceway penetration of 0.1 m, and blast velocity should be decreased in inverse proportion to productivity when productivity increases.
u_t≤920(804-M_b)·ρ_c·d_p·N_t·D_R²/(γ·v_p·V_i)
In this equation, M_b is blast moisture (g/Nm₃), ρ_c is apparent density of coke (kg/m³), dp is mean size of coke (m), N, is number of tuyeres (-), D_R is raceway penetration (m), γ is productivity (t·d^-1·m^-3), v_p is blast volume per ton of hot metal (Nm³/t), and V_i is inner volume of a blast furnace (m³).

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For the clarification of the mechanism of the desiliconization reaction by the MnO containing slag under pressurized and coke-coexisting condition of blast furnace, fundamental experiments were performed by the use of a pressurized high frequency furnace. Based on the experimental results, a mathematical simulation model with consideration of the direct reduction reaction as the coupled reaction was developed and applied to the quantitative evaluation of the desiliconization reaction by the MnO and FeO containing slag.
The following knowledge was obtained.
1) Under the existence of coke, MnO and FeO are partly consumed by the coupled reaction of direct reduction reaction and the desiliconization reaction is restrained.
2) The increase of pressure, with the presence of coke, results in the indirect enhancement of the desiliconization reaction through the restraint of the direct reduction reaction.
3) The effect of the charging of Mn ore on both the increase of Mn content and the decrease of Si content in pig iron was quantitatively evaluated by a simulation model for blast furnace hearth.

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Imbalanced descending behavior of solids in a blast furnace was studied using a three dimensional model furnace, considering the circumferential imbalance of the coke consumption at the raceway zone and the inner surface profile of the furnace wall. Results are summarized as follows ;
1) In case that there were some closed tuyeres or the local wall scab at the middle part of the shaft in blast furnace, it was found that the descending velocity above them became larger than that at the other part at the throat.
2) The erosion of the furnace wall only at the upper part of the shaft (h/D<0.4) increased the descending velocity at the throat above the eroded part, where h is the distance from the top of the shaft and D is the diameter of the throat.
3) The peripheral dead zone was formed just above the closed tuyeres, of which geometry was different from that of the central dead zone. Stress analysis made it clear that the stress field in the lower part had the relation of σθ<σ_v<σ_h and the shape of the peripheral dead zone was determined by σθ and σ_v where σ_v, is the vertical stres, σ_h is the horizontal stress and σθ is the circumferential stress.

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Influence of injected ore fines on the chemical and physical phenomena in and around the raceway was examined and the mechanism of silicon decrease in iron melt was experimentally investigated by using a small-scale hot furnace.
(1) The temperature in the raceway decreases with increasing the amount of injected ore fines mainly due to the endothermic reaction
(2) A part of injected ore fines remains inside of the raceway and shows high fractions of melting and reduction. Both fractions of sample increase with the increase of the injection rate, as the proportion of remaining ore also increases.
(3) SiO content in the gas and Si content in the metal in the dripping region above the raceway decrease with increasing the injection rate, since SiO gas generated in the raceway can be absorbed by injected iron ore at the molten state.
(4) Decrease of Si content in the metal by the reaction with FeO in slag formed by injected ore is negligibly small in the dripping region below the raceway.

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The deadman coke was sampled by the core probe from Kobe No. 3BF at shutdown. On the basis of the sampling results, the decrease of coke size by solution loss reaction was evaluated from the coke degradation model considering the strength distribution.
The main results obtained are as follows.
1) The coke size decreases by the degradation of reacted layer near the coke surface by solution loss reaction.
2) The accumulation of fine coke in the deadman is derived from the solution loss reaction zone rather than the raceway by evaluating temperature hystory. This affects the permeability in the blast furnace.
3) The decrease in coke size calculated from the coke degradation model, which takes into account the critical strength of 20 × 10⁵ Pa, results in the average of 10 × 10^-3 m and is similar to the sampling results in the blast furnace. Consequently, this model is possibly applied to the criterion of estimating coke degradation in the blast furnace.

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An attempt was made on the simultaneous analysis of the gas flow and heat transfer in the blast furnace by a mathematical model which considered complex structure and nonuniform sink and source terms for both heat and mass. ERGUN'S equation was used for the equation of motion of gas and potential flow approximation was used for the equation of solid flow. Two dimensional distribution for the velocities of gas and solid was obtained numerically by applying the finite element method with quadratic elements. Fundamental equations of heat transfer on gas and solids were composed of the terms for convection, heat exchange and heat source. Numerical computation of the fundamental equations was carried out in accordance with the method of characteristics. In this analysis, sink and source terms regarding fusion of ore in the cohesive zone and combustion of coke in the raceway were incorporated in the mathematical model as well as radial distributions of particle size and void fraction. It was consequently found that the temperature distribution was affected principally by nonuniform gas flow and thermal flow ratio. Within the cohesive zone, strong consumption of heat by fusion of ore and decrease in the solids velocity appeared. These phenomena affected significantly the temperature distribution in the lower region of the blast furnace together with the generation of heat in the raceway region.

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A mathematical model of three-dimensional gas flow in packed beds has been developed to be applied for the analysis of gas flow in packed bed reactor, blast furnace and so on.
Basic equation of the motion of fluid in packed beds was derived on the basis of the mechanics of continua.
In case of gas flow in iso-tropic packed beds, the equation of motion is simplified to the vectorial form of the ERGUN'S equation. Equation of pressure, derived from the locally linearized equation of motion and equation of continuity, is computed by the finite element method with three-dimensional iso-parametric second order elements of 20 nodes. Gas velocity is calculated from pressure gradient in each element.
Computed results were compared with the analytical solution and the experimental results. Good agreement among them confirms the adequateness of this mathematical model.

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A mathematical model of three-dimensional gas flow in a blast furnace has been developed in which three-dimensional layer structure and permeability distribution are considered, using the finite element method.
Cohesive zone profile and pressure distribution were simultaneously measured in an actual blast furnace and compared with the computed results.
Good correspondence between them confirms the adequateness of the mathematical model analysis.
The principal results of the circumferential distribution analysis are as follows.
(1) On the side of high stockline, pressure increases and gas flow rate decreases.
(2) Gas flow rate varies with the permeability distribution that depends on thickness ratio of ore and coke layeres, but pressure is almost constant.
(3) With deviated cohesive zone profile, the level of the maximal variance of pressure distribution corresponds to the sectional average level of the cohesive zone, where pressure is high on the side of high melting level. In the lumpy zone, gas flow rate is low on the side of high melting level.
(4) Blast rate distribution is smoothed through the dropping zone and has no effect on the gas flow distribution in the lumpy zone. On the other hand, pressure drop through tuyere is important to equalize the blast rate distribution.

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Model experiment and mathematical modeling were carried out to elucidate the liquid flow and liquid holdup in the lower part of blast furnace.
Slag viscosity was measured in some ranges of temperature and slag composition in the dripping zone, and computer program for the estimation of slag viscosity was developed. According to the results of model experiment, it was verified that DARCY-type equation can be practically used for the analysis of liquid flow resistance in irrigated packed bed. Molten slag can not flow through the 'deadmann' zone under the condition that coke diameter in the 'deadmann' decreases less than 35 percent of initial coke diameter or void fraction in the 'deadmann' decreases less than 65 percent of initial void fraction of coke bed, or slag viscosity raises more than 6-10 poise, i.e. 'deadmann' temperature falls to lower than 1 400°C.

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Based on the results of profile meter measurements in the blast furnace, an advanced burden distribution model was developed. The simulated results were used as input data to the two dimensional blast furnace model, which was developed by considering radial distributions of gas flow, heat transfer, and reactions.
The effects of burden distribution on the condition inside of blast furnace were numerically studied. The burden distribution investigated was the radial distribution of ore to coke ratio (O/C) and the radial distribution of particle diameter.
It was clarified that the condition inside of blast furnace was strongly affected by the radial distribution of O/C. For example, by moving the armor position of the ore to the furnace center, O/C at the wall was decreased and the shape of the cohesive zone was changed from a inverted V type to a W type. The changes in gas composition and temperature distributions at the top and also in gas pressure at the furnace wall in the stack, which were caused by O/C distribution change, were in good agreement with the simulated results.

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The effects of sinter qualities and coke qualities on the condition inside of the blast furnace are theoretically investigated by the two-dimensional mathematical model of blast furnace which was coupled with the degradation model of sinter and coke.
The following results are obtained ;
(1) Effect of sinter quality.
1) The pressure drop in the blast furnace increases with the increase of RDI or the decrease of the particle diameter of charged sinter.
2) The increase in RDI increases ore to coke ratio (O/C) and also gas utilization ratio because it increases the reduction rate of sinter. As the result, gas and solid temperature in the upper part of the blast furnace decreases.
(2) Effect of coke quality.
1) Coke degradation rate below the solution loss zone in the blast furnace decreases with the increase of CSR.
2) The decrease of the solution loss reaction causes the increases of the gas utilization ratio and gas and solid temperature in the blast furnace.
The simulated results agreed with the observed results of an actual blast furnace.

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A method of estimating thermal conditions of a hearth has been developed, by using boundary element method for thermal analysis and experimental regression analysis for optimization. This method can evaluate hearth conditions in a reasonable computing time and supply useful information, such as heat flux distribution and effective volume of a hearth, which are closely connected with the operation.
The erosion line estimated by the method is in good agreement with the one measured by boring in the hearth of Mizushima No. 1 blast furnace blown out in 1982. The solidified layer distribution is changed to a great extent by the operation which has an effect on the thermal load to a hearth. In order to make the operation stable and to protect hearth refractories, it is important to continually monitor and control the hearth condition.

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Sintering technology with decreasing SiO₂ content from 5.6% to 4.9% at Kobe Works has been achieved based on the following concept. The desirable structure of quasi-particles for low SiO₂ sinter should consist of limonite ores as nucleus and fine ores of low SiO₂ and Al₂O₃ contents as adhering particles. In addition, basicity and MgO content of sinter should be increased.
Consequently, the RDI value of sinter became high and its yield slightly became low, though the reducibility and high temperature property of sinter were improved.
The use of low SiO₂ sinter at Kobe No. 3 blast furnace has increased overall permeability by increasing permeability at the lower part of the furnace in spite of lower permeability at the upper part of the furnace, which has contributed to appreciable increases in ore/coke ratio and injection rate of pulverized coal.

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Lowering of gas temperature at center of upper shaft was observed by decreasing sinter ratio in Mizushima No. 4 blast furnace and the stable operation was disturbed.
The burden distribution in case of the low gas temperature at center has been studied through quantitative analysis of the furnace operation data and model experiments. The ore layer collapse during ore charging was observed by the scale model experiments. The ore layer collapse could be treated quantitatively by use of a simulation model adopting a theory on the stability of the piled layer. The stability of ore layer was discussed by the model study in terms of operation variables, such as ore diameter, throat gas velocity and bell stroke. The results revealed that decrease in bell stroke and bell descending velocity could effectively prevent the burden distribution in case of low gas temperature at center.

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By the use of a descending probe set on the burden surface and equipped with thermo-couples at a given interval, temperature distribution in vertical and radial direction in a blast furnace can be measured as it goes down with burden material.
To estimate the location of the probe in the furnace, an experiment was carried out by a small-sized cylindrical model, and it was found that the middle point of the probe descended in accordance with a stream line of the burden material at the same radial. From this result, a method was presented to estimate the location of the probe in the furnace.
The isotherms were obtained by analyzing the temperature distributions measured at Kakogawa No. 1 blast furnace. The 1200°C isotherm was in a good agreement with the outer profile of melting zone observed after the dissection of the furnace. At Kobe No. 2 blast furnace, the change of isotherms was investigated with the change of coke rate and 1200°C isotherm in the peripheral part was kept at a constant level by the burden distribution control to maintain the stable operation.

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A blast furnace operation control expert system (BAISYS) making use of artificial intelligence (Al) was developed and applied to the commercial operation of Fukuyama No. 5 blast furnace.
BAISYS gathers real-time information from numerous sensors installed on the blast furnace, and by using both this information and knowledge base in Al processor, which consists of knowledge and experience of operaters and engineers (experts), inference and judgement concerning furnace condition are performed and the optimum action is indicated.
The abnormal furnace condition diagnosis expert system, one of the two sub-system in BAISYS, predicts the probability of channeling and slip every two minutes and provides the forecast and action. The furnace heat control expert system, the other sub-system which is designed to constantly control the furnace heat level represented by the hot metal temperature, executes inference every 20 minutes.
This system is very effective for the stable operation of blast furnace.

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In order to make a clear evaluation of overall energy requirement for the production system of directly reduced iron through pellet from iron ore powders, exergy analysis was applied to the two systems. The first one consists of pelletizing, firing and reduction processes (Fired pellets method) and the second one includes pellets curing process instead of firing process (Cement bonded pellets method).
Being compared with enthalpy balance, exergy analysis has two advantages in that the exergy expresses the quality of energy and evaluates different kinds of energy like chemical, thermal, pressure, mixing energies and so on by a unified measure.
As a result of exergy analysis, fired pellets lose less exergy than cement bonded pellets in the reduction process in a shaft furnace. As the overall system, however, exergy requirement in the cement bonded pellets method is about 50% of that in the fired pellets method. This marked difference is caused by the large exergy loss in the firing process. Furthermore, exergy loss in the production of cement bonded pellets will be decreased by decreasing the amount of cement added as binder.

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The direct reduction process is now playing an important role, not only as a supplemental ironmaking procedure in the natural gas or coal producing regions of the world, but also as a technology to provide new iron source free of residual elements to iron and steelmakers, particularly those using electric arc furnace technology.
Continuous charging and slag forming operation of directly reduced iron in electric arc furnace can decrease tap to tap time and refractory wear and lowers electrode consumption.
Recentry, new technical improvements of the hot briquetted iron has been completed which is hardly reoxidized and pulverized during transportation and storage.
Commercial application of this research will permit further increase of market demand for the hot briquetted iron.

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The new ironmaking process, named SC process, has been developed, which is characterized by the division of two functions, reduction and smelting. This process consists of a shaft type reduction furnace and a coke bed type melting furnace using a large amount of pulverized coal and oxgen gas blowing.
Through operation tests with a pilot plant of 8 t per day in production capacity ; SC process has been technically verified to be consistent as an ironmaking process.
Based on the operational results of the pilot plant, a commercial plant of 2 400 t per day with following features was designed.
1) High productivity, 2.5 times as much as that of blast furnace.
2) High heat efficiency, competitive to blast furnace.
3) Wide use of non-coking coal, as much as 70% of total coal consumption.

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Gaseous reduction tests of the fine chromium ore with hydro-carbon were carried out in the temperature range from 900 to 1 150°C by use of a laboratory scale fluidized bed.
The obtained results are as follows :
1) Reduction degree of 60% is easily obtained by use of methane and propane gases in the temperature range from 1 000 to 1 100°C.
2) The addition of calcium hydroxide enhances the gaseous reduction of the chromium ore.
3) The reduction degree increases with the increase of methane or propane content in the gas. The optimum gas content exists because the reduction rate of chromium ore is deteriorated by carbon deposited from excessive reducing gas.

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Experiments have been made to measure the chromium and sulphur distributions between carbon-saturated Cr-Fe-C alloy and CaO-MgO-Al₂O₃-SiO₂ slag at 1 550 and 1 598 °C. The reduction of SiO₂ proceeds very slowly, so that its equilibrium is not attained within the present duration of run. However, the following reactions are so fast that the local equilibria corresponding to the progress of the SiO₂ reduction are attained.
[Cr]+1/2(SiO₂)=(CrO)+1/2[Si]
[S]+(MO)+1/2[Si]=(MS)+1/2(SiO₂)
Based on the above reactions, the chromium and sulphur distributions between metal and slag have been analyzed with respect to temperature, slag composition and optical basicity (Λ). The main equations obtained are as follows :
log(%Cr)[%Si]^1/2/[%Cr]=-3.59(N_CaO+0.5N_MgO-0.1N_Al2O323-N_SiO2)4260/T-0.02
log[%S][%Si]^1/2/(%S)=-3.69(N_CaO+0.6N_MgO-0.3N_Al2O3-N_SiO2)-29840/T+14.62
log[%S][%Si]^1/2/(%S)=14.9Λ-31270/T+24.96
The validity of these equations have been discussed in comparison with the data reported by the other investigators.

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The extraction of Nb from the pig iron containing Nb, which is produced in Baotou, Inner Mongolia, China has been jointly investigated by National Research Institute for Metals, Japan and Beijing University of Iron and Steel Technology, China. By the use of 2 stage tank type continuous selective oxidation furnaces in series, where the most of Si and a part of Mn were removed in the 1st stage and Nb was selectively oxidized in the 2nd stage, the optimum refining conditions to obtain high Nb content slag in the 2nd stage were found out. Through the operations of 11 times the slag holding Nb₂O₅ of as high as 7 to 10% was constantly produced at the recovery rate over 70%. This is due to the adoption of continuous refining process.

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