Recent studies from many different points of view have remarkably improved ironmaking technology. Fundamental studies on the solid flow, behavior of powders, heat exchange between gas and particles in a packed bed clarified substantially the essential mechanisms of the phenomena. These studies contributed to the correct estimation of internal state of a blast furnace, specifically to high injection of pulverized coal. Comprehensive investigations on the oxygen blast furnace process and the SC process showed capability to develop new processes for ironmaking. Studies on mathematical models and artificial intelligence increased the reliability for the estimation of internal state and the control method. The development of a sideway tuyere probe proved the phenomena occurring in and around the raceway. Exergy analysis elucidated the way for the energy savings and compared different ironmaking systems from the energy efficiency.
This review outlines such excellent papers recently reported in Japan for further progress of ironmaking technology.

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A survey on blast furnace practices in American and Canadian steel companies in 1989 was conducted and aggregate data were reported. Recent developments in raw materials which contribute to improvements in blast furnace ironmaking are reviewed. Five blast furnaces, two large and three medium size, are described in more detail as examples. Comments are made on future developments in ironmaking in North America.

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Prior to 1974, the evolution of the ironmaking sector in Western Europe was strongly marked, on one hand by the rapid growth of steel industry, and on the other hand by the replacement of lean local ores by iron-rich imports from overseas. The former evolution was abruptly stopped by the energy crisis and was followed by a period of contracting production and streamlining of the existing installations.
The few new blast furnaces built replaced a larger number of small obsolete units, and the production was concentrated on the most performing furnaces. New ecological constraints put further pressure on the ironmaking sector. The necessity to reduce or completely suppress tuyere injection of oil also had an adverse effect on furnace productivity and on the smoothness of the operation.
Today, all these difficulties have been overcome and the West European blast furnaces achieve excellent performances. The typical plant has two blast furnaces in the range of 8-11 m of hearth diameter, with modern equipment for controlling and monitoring the burden distribution at the top and computerized control rooms. The mean productivity is about 50 t/m²·24 h and the average total fuel rate lies below 500 kg/tHM. Coal injection has been a rapid expansion over the past five years, and end of 1991 the total installed coal injection capacity will exceed 10 Mio t of coal/annum. High injection rates above 170 kg/tHM have been reached on several blast furnaces, reducing the coke rate below 330 kg/tHM and, in at least one case, even below 300 kg/tHM. Trials presently in progress aim at coal injection rates above 300 kg/tHM.

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This review presents some of the recent advances in ironmaking technology in Australia. The first part of the paper summarises blast furnace operations in terms of productivity, fuel rate and hot metal chemistry in BHP. It is shown that in the recent past Australian furnace operations have been characterised by high productivity and low fuel rate. In the second part of the review, the main blast furnace research and development topics are presented. The first of two research streams, which is shorter term in focus, is associated with the development and implementation of computer models and associated sensors to assist present operations. Some of the developments which are reviewed in this field include burden distribution studies, models of the momentum, heat and mass transfer processes occurring in the furnace, raceway studies, opto-electronic and other sensor developments, and studies associated with hearth liquid drainage. The second stream, which addresses longer term strategies, is associated with studies on future blast furnace operations. In this stream, research work on the combustibility of pulverised coals in the blast furnace environment is described. The results shown indicate that Australian research has made a substantial contribution to knowledge in blast furnace ironmaking, and that the studies undertaken are of considerable benefit to Australian blast furnace operations.

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Transport rate of gaseous phosphorus into solid iron under reducing atmosphere was observed by a gravimetric procedure to obtain fundamental data to discuss transport mechanism of phosphorus into reduced iron in a blast furnace.
A kind of killed and rolled steel sheet and non worked electrolytic iron sheet were used as samples. Partial pressure of phosphorus vapor was controlled by using equilibrium relation between P_P2, Ca₃ (PO₄)₂, SiO₂, C, CaSiO₃ and CO. Phosphorus partial pressure and temperature were every one order between 4×10^–6 and 4×10^–2 atm, and every 50°C between 900 and 1050°C, respectively.
Experimental results are as follows:
(1) Transport rate obeyed a parabolic rate law.
(2) Relations between the rate constants of the parabolic rate law, k, the phosphorus partial pressure, P_P2, and the temperature, T, are as follows:
In the case of killed steel, log k=0.14 log P_P2+5.68–15.6 ×10³/T
In the case of the electrolytic iron, log k=0.14 log P_P2+4.94–15.6×10³/T
(3) Reaction product on a surface of solid iron was Fe₂P.

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In a previous work, single particles of commercial sinter were reduced stepwise with CO-CO₂-N₂ gas mixtures. In the analysis, the reduction of calcium ferrite (CF) was not taken into consideration. Values of chemical reaction rate constants k_c and effective diffusivities D_e in the unreacted-core shrinking model were determined by trial and error so that the calculated reduction curve might agree with the experimental one.
In the present work, the method of the kinetic analysis are re-examined:
(1) A new method to obtain the rate parameter values in a prescribed way has been developed and the experimental data have been statistically analyzed; values of k_c and D_e have been determined so as to minimize the difference area between calculated and experimental reduction curves.
(2) Final fractional reduction in the hematite to magnetite stage under rising temperature conditions up to 1 173 K, F_f', was measured after measuring the one at a predetermined temperature, F_f ; below about 1 003 K, CF is hardly reduced and practically F_f =0.7 when oxygen reducible in this stage is assumed to be come from hematite and CF. The ratio F_f /F_f' is also given as a function of reduction temperature.
(3) Some additional experiments on single particle stepwise reduction to the previous work were done in a temperature range from 753 to 1 333 K and rate parameter values have been re-evaluated by the above-stated method in consideration of the facts in (2); temperature dependencies of k_c and D_e are presented.

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Flow characteristics of gas-powder two phase flow in packed beds were experimentally examined for clarifying the aerodynamic behavior of powders in a blast furnace. It was found that two phase flow showed higher pressure loss compared with clean gas flow. Based on the experimental results, a mathematical model for gas-powder two phase flow in packed beds was developed. In this model, three kinds of interaction forces were considered, including:
1) the interaction force between gas and packed particles (F_g-b)
2) the interaction force between gas and powders (F_g-p), and
3) the restraint force of powder motion due to (i) the gravitational force of powders and (ii) the collision and the friction between powders and packed particles F_p-k.
F_g-b could be given by the Ergun type gas flow resistance, and (F_g-p) could be expressed by the Stokes flow law and the Richardson-Zaki's voidage function. Finally, F_p-k could be empirically correlated by using the Fanning equation and the Froude number. This model allows satisfactory prediction of the pressure loss and the hold-up of powders in the packed bed. Furthermore, it was confirmed that the increase in the pressure loss was mainly caused by the increase in the hold-up of powders in the region of low gas velocity and by the interaction force between powders and packed particles in the region of high gas velocity.

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Gasification of metallurgical coke was studied at 1 000, 1 200 and 1 400°C with Ar-CO-CO₂ mixtures. Reaction of coke in blast furnace is dominant from 1 000°C. And at the same time, growth of graphite crystal in coke begins around the temperature.
In present paper, two types of carbon structure were classified by means of X-ray diffraction. One is crystallite that contributes to X-ray diffraction, the other is noncrystalline carbon that contributes to background intensity alone. In this study, reaction model that the two kinds of carbon have different reactivity and react simultaneously and independently, was developed and kinetic analysis was performed. The following results were obtained.
(1) Lc is linear function of temperature and there is no influence of reaction.
(2) La is linear function of temperature in Ar atmosphere. But in existence of reaction, the size of La becomes to be smaller. From this result, it was considered that the gasification reaction proceeds such as mode of decreasing La. Reaction mechanism combining to characteristic of crystallographic structure is proposed.

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Recently, reserves of good coking coals have become less available and comparatively more expensive. Resources are being extended by the use of coal blends with different coking properties and/or selective additive. Coal preheating technology emerged as a technique to overcome some of these problems. It has several advantages including: increases in coke oven productivity, improvements in quality of metallurgical coke, greater uniformity of charge, less air pollution by using a closed charging system, levelling of the charge, a saving in energy because dry coal is more efficient in the preheater than in a coke oven, and the possibility of using poorer and cheaper coking coals. The disadvantages of this technique are the handling of fine and hot coal, the carry-over and the preheater fines.
Currently, the preheating process is being re-considered in combination with dry-cooling of coke in a European Research Project called "Jumbo Coking Reactor", which is based on past and current experience of development of modern cokemaking technology.
This study reviews preheating technology as a means to widen the range of coking coals including not only the high-volatile coals which are more abundant, but also semi-anthracite and petroleum coke. A 6 t Experimental Coke Oven and a 2 t/h Preheating Pilot Plant (Precarbon Process) were used.

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The deviation in the carbonization rate in the coke oven chamber has been investigated with the use of test coke ovens and a 2-dimensional mathematical model.
In the measurement using a 250 kg test coke oven, in the case of using a wet coal charge, there were several points of delay in the carbonization rate at random times, but in the case of a dry coal charge, there were no points of delay and the carbonization progressed uniformly. It was confirmed that the deviation in the carbonization rate was affected by the moisture content of the charged coal.
In order to evaluate flow pattern and heat transfer caused by the steam and the decomposition gas during carbonization, a 2-dimensional gas flow mathematical model was developed. This model consists of mass, energy involving terms of convection and momentum balance equations in both the gas and solid phases. It was confirmed that temperature change, changes in gas pressure and steam flow pattern in a test coke oven with the heating wall at the upper portion were estimated by this model. In the model calculation, the coke fissures and a local distribution of the bulk density affected the steam flow and caused a deviation in the carbonization rate.

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The fundamental pore formation mechanism in iron ore sinter and pellets was investigated, using iron ore/limestone tablets with and without addition of coke. The results showed that pores were formed at the sites of limestone and coke particles, and that the particle size and amount of limestone and coke particle size all had strong effect on the pore structure. Different types of pores in sinter and pellets were classified in terms of their origins. These results are useful in understanding the sintering and pelletizing process.

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To meet the demand for increased production, higher productivity has been carried out based on the following targets at Chiba No. 4 Sinter Plant of Kawasaki Steel Corp.:
1) Maintenance of high bed height operation by ensuring stable permeability in the sinter bed,
2) Cost saving sinter production through improvement of sinter yield, and
3) Maintenance of low SiO₂ operation.
The following results were obtained from the implementation of various countermeasures.
(1) A highly productive operation of 1.8 t/hm² without adding any binders.
(2) The total amount of return fine has been decreased from 400–450 to 260–300 kg/t-sinter.
(3) Sinter production cost has been decreased and the minimum cost per unit has shifted to a higher output.

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The low silicon operation with the silicon content of less than 0.2 % was performed for 16 months from January, 1988 to April, 1989 at Fukuyama No. 5 blast furnace of NKK Corp. The following are the factors attributable to this longterm low Si performance.
1) Prevention of temperature drop of hot metal in the hearth by the decrease in heat loss from the hearth associated with the improvement of tapping conditions
2) Decrease in heat loss from the shaft and prevention of inactivated state in the lower part of the furnace by the improvement of burden distribution
3) Stable operation based on an expert system for furnace heat control and burden distribution control
Low Si content operation was accomplished by lower flame temperature which resulted in the restraint of SiO gas formation and higher thermal flow ratio which contributed to lowering the cohesive zone level.

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In order to clarify the combustion reaction when PC (Pulverized Coal) is blown into the tuyeres of a blast furnace and the effects of resultant unburnt PC on reactions, in the furnace, some fundamental experiments were carried out. The main results obtained are as follows:
(1) Most of PC blown through the tuyeres rapidly burns in the raceway.
(2) Unburnt PC tends to adhere to the softened and fused ore bed.
(3) Unburnt PC adhering to the ore bed is consumed by the direct reduction of FeO and improves the softening and melting-down properties of ores effectively.
In this way, PC entering inside the blast furnace without burning was found to be consumed effectively.

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Some fundamental experiments were carried out concerning the combustion reaction of PC (Pulverized Coal) blown into the tuyeres of a blast furnace and the effects of resultant unburnt PC on in-furnace reactions. The main results obtained are as follows:
(1) The gasification reaction rate of UPC is about 7 times as fast as that of coke. The presence of H₂ promotes the reaction, while CO works oppositely.
(2) As UPC (Unburnt Pulverized Coal) is gasified more quickly than lump coke, the degradation of coke in the raceway becomes less.
In this way, PC blown into the blast furnace without burning was found to be effectively consumed.

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The influence of ore/coke distribution on the descending and melting behaviors of burden was analyzed by using a three-dimensional semicircular warm model of the blast furnace under conditions set as similar as possible to the physical phenomena in the furnace. It is confirmed that the ore/coke largely influences the descending velocity of burden and gas flow. It is estimated that an increase of +0.1 in the heat-flow ratio in the wall region of bosh results in a decrease of about 5°C in the temperature near the reaceway and in the wall temperature of bosh. It corresponds about 80°C in the value converted into that of the actual blast furnace based on the Stanton number. In Tobata No. 1 blast furnace of Nippon Steel Corp., it is verified that an increase of the ore/coke in wall region results in an increase of the descending velocity in wall region, and the ore/coke and the descending velocity are ones of the main factors which decrease the temperature in the lower part of the furnace. At the all coke operation, as the wall temperature in the lower part of the furnace tends to decrease, the ore/coke near the wall should preferably be decreased by the charging of ore closer to the furnace center. At the operation by injecting a large quantity of pulverized coal, as the melting capacity near the wall is large, the ore/coke in the wall region should preferably be increased and the ore/coke in the center region should preferably be decreased by the charging of ore farther from the furnace center.

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The influences of the inner wall profile and ore/coke distribution on the descending and melting behaviors of burden were analyzed by using a three-dimensional semicircular warm model of the blast furnace under conditions set as similar as possible to the physical phenomena in the furnace. It is confirmed that in the case of a profile with blocks installed on the belly where the horizontal stress acting to wall is at its maximum, a sluggishly descending zone of a thickness 2-5 times of the projecting length of the blocks is formed near the wall just above the blocks. It is estimated that the thickness of sluggishly descending zone near the wall increases with increasing projecting length of the blocks on the wall and with decreasing installation interval of distance between the blocks and it decreases with increasing ore/coke near the wall. It is estimated that the height of the dead man decreases with the formation of the wall sluggishly descending zone due to the blocks on the wall. For decreasing the thickness of the sluggishly descending zone near the wall, the ore/coke near the wall should preferably be increased as far as the heat-flow ratio is permitted. Such a burden distribution is effective for pulverized coal injection operation in which the melting capacity near the wall is large.

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