Global warming is a common subject in steel industry in every country. International cooperation will be required using the Kyoto Mechanism from global aspect. In the integrated steel works, there are various means to decrease reducing agent at blast furnace, however, preferable way to reduce CO 2 emissions must be chosen considering energy balance in whole steel works, and energy saving must be actively pursued. Injection of waste plastics and carbon neutral materials such as biomass is better alternative. In the near future, hydrogen will attract attention as a clean energy source even in the steel works. Regarding oxygen blast furnace and smelting reduction, the possibility of CO 2 reduction is dependent on optimum system design of total process including outside process. Charge of prereduced sinter and high reactivity coke to blast furnace leads to reduction of CO 2 , keeping current blast furnace facility and capability.

Review Reduction of CO 2 Emissions from Integrated Steel Works and Its Subjects for a Future StudyReduction of CO 2 emissions has been discussed using newly developed precise model based on carbon and energy balance in large-scale integrated steel works as a whole. Although there are various means to decrease reducing agent rate (RAR) at blast furnace, preferable way to reduce CO 2 emissions must be chosen considering energy balance in whole steel works. Reduction of RAR at blast furnace together with energy saving at downstream processes is important. Maintaining competitiveness in global steel market must be also considered. Simple reduction of RAR such as improvement of shaft efficiency at blast furnace without energy saving at downstream processes leads to increase in production cost because of increment of purchased energy. Injection of waste plastics and carbon neutral materials such as biomass is better alternative.Regarding blast furnace operation, under the use of inferior raw materials such as low strength coke as well as high productivity condition, there are many problems to be solved to achieve low RAR operation. It has been reported that drastic change of lower part situation such as increase in coke degradation and accumulation of coke fine causes operation instability at actual blast furnace. Therefore, to attain stable low RAR operation, it is confirmed that new control measures based on fundamental researches to solve various problems should be developed.KEY WORDS: CO 2 emissions; integrated steel works; blast furnace; reducing agent rate; carbon neutral; energy saving.

At Keihin No. 1 Blast Furnace, waste plastics recycling system was installed in Oct. 1996. Before the installation of that system, the behavior of waste plastics injected into the blast furnace has been studied with the raceway hot model and the commercial blast furnace so as to investigate the possibility of effective waste plastics utilization in the blast furnace. From the observation of plastics particle injected into the raceway of blast furnace, it was estimated that combustibility of coarse plastics was much different from that of pulverized coal. The combustion point of coarse plastics located to deep domain in raceway compared with that of pulverized coal. Although C 1 -C 4 hydrocarbons due to the decomposition of plastics was detected in in-furnace, the decomposition products of plastics in the blast furnace top gas and dust were the same as that of pulverized coal injection. The preparation method of plastics had an influence on the combustion and gasification behavior in the raceway. The coarse plastics gave high combustion and gasification efficiency compared with fine plastics and pulverized coal, and CO 2 gasification rate of unburnt char derived from waste plastics was much higher than that of pulverized coal. Thus, it was concluded that coarse waste plastics could be effectively utilized as a reducing agent in the blast furnace. On the basis of above results, the waste plastics recycling system was designed.

JFE Steel Corporation developed the hydrogen-based gas fuel injection technology for sintering machines to improve sinter quality without increasing coke breeze ratio. With the technology, it is possible to extend the temperature zone between 1 200°C and 1 400°C by injecting the gaseous fuel from the top surface of the sintering machine as a partial substitute for coke breeze. Theoretical and experimental studies were carried out to verify the effect of the gaseous-fuel injection technology on pore structure in the sinter cake with the X-ray CT scanner and sintering pot test.It is important to hold the temperature between 1 200°C and 1 400°C in order to produce high strength and high reducibility sinter. The liquid phase ratio can be increased with extending the proper temperature zone by applying the gaseous fuel injection technology. The increase in liquid phase ratio promotes the combination of pores (1-5 mm) and sinter strength is improved. At the same time, the pores over 5 mm growth are promoted and the permeability is improved in the sintering bed. Moreover, the low-temperature sintering process depresses the iron ore self-densification. Micro pores under 1 μm remain in unmelted ores and improve sinter reducibility. As a result, the technology enables to improve the pore structure in the sinter cake and sinter quality.The technology was put into commercial operation at Keihin No. 1 sinter plant in January 2009 and stable operation has continued up to the present. As a result, the energy efficiency in the sintering process is greatly improved, and it has been achieved to reduce CO2 emissions by a maximum of approximately 60 000 t/year at Keihin No. 1 sinter plant.

The concept of innovative ironmaking process for aiming at energy half consumption has been proposed based on the basic experiments and mathematical calculations. For innovative ironmaking process, intensive combustion technology around raceway was examined by hot model experiments and three-dimensional mathematical simulation so as to utilize solid fuel such as plastics effectively. As results, it became clear that simultaneous injection of pulverized coal/plastics or pulverized coal/gas fuels is favorable to improve combustion efficiency remarkably. Decrease in thermal reserve zone temperature and top gas recycling besides plastics injection are found to be effective for lowering coke rate. In this process, productivity can be also improved owing to relaxation of flooding condition in the lower part of blast furnace. Productivity of 3.5 and more, that is determined by fluidization condition at top, can be expected in this innovative ironmaking process. Totally, it is evaluated that amount of carbon emission would be reduced by eighty-six percent provided sequestration of carbon dioxide is implemented. Finally, integrated ironmaking process with co-generating oxygen production process was proposed.

A mathematical model is developed to quantify the effect of operation conditions and casting strategy on residual amount of slag and metal in hearth. The model is validated by a physical scale model experiment. Calculated results show that the residual amount of slag increases in proportion to the square of production. The effect of hearth permeability on the residual amount of slag is larger than slag viscosity. Then high permeability is necessary under high productivity operation condition. Although a load is not small, increasing tapping rod diameter and shortening cast duration are the effective way to decease maximum slag level. High durability filling mud is necessary to keep cast duration.KEY WORDS: blast furnace; hearth; liquid; tow-phase flow; drainage; residual; slag; mathematical mode; scale model; coke; packed bed; tapping; casting. volumes are measured. Procedures of experiment are same as BF tapping operation. At first, drainage velocity is smaller than liquid supply velocities. As the flow control valve opens, drainage velocity increases When nitrogen gas in the vessel comes out through the flow control valve, the valve is closed and another valve is opened. Liquid sampling is carried out after reaching steady cyclic condition of the alternative casting. Scale condition focused to reproduce liquid surface shape in a blast furnace hearth, because it affects on stability of operation as described in the former section. Figure 2 shows the schematic diagram of the slag surface. When slag velocities of supply and drainage are same, slag surface shape is constant, and the pressures at P and PЈ should be same. The pressure drop between P and PЈ caused by liquid flow DP flow should be compensated by hydrostatic pressure DP gravity · DP flow can be described by Kozeny-Carman equation:.............. (1) where d p (m), e (Ϫ), m slag (Pa · s) and v (m/s) are particle diameter, packed bed porosity, slag viscosity and liquid velocity respectively. To keep the inclination q, the pressure drop has to be compensated by the hydraulic pressure DP gravity , which can be described as following equation: Experimental Result and DiscussionMeasured drainage velocities, HCFC ratio and liquid levels are shown in Fig. 3. HCFC velocity increases in first 60 s and saturates. On the other hand, paraffin velocity increases after 60 s. Consequently the ratio of HCFC to total liquid velocity becomes the maximum at 60 s. Although the liquid level of paraffin becomes the maximum at 90 s, which is half cast duration 180 s, the level of HCFC is the maximum at 60 s. HCFC ratio and level are the maximum at same time under all of other experimental condition. These results show that the HCFC ratio is in proportion to the level of itself. Although it is omitted in this paper, this relation is confirmed by many other condition experiments. Measured casting velocity of an actual BF, which production is 10 000 t/d and hearth diameter is 15 m, is shown in Fig. 4. Although time scale is 85 times larger than the scale model (Table 1), the fea...

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