Decrease of carbon dioxide emission is a serious subject in the steel works. Utilization of biomass as a carbon-neutral agent is an attractive one for iron ore sintering. Sinter pot tests were carried out with using raw biomass and biomass carbonized char. It is not good on yield and exhaust gas that raw biomass is used directly as carbon material for iron ore sintering. While, it is good on the productivity and the exhaust gas (NOx, SOx, dust, dioxins) that biomass carbonized char is used as carbon material. With using biomass char for the sintering, it is necessary to optimize operation (size control and moisture control of the biomass char), because combustion rate of the biomass char is too high. Biomass carbonized char is evaluated on sinter yield as similar as anthracite or coke. The biomass char is effective to decrease CO2, NOx, SOx, dust etc. emission in sinter exhaust gas.

In order to increase the permeability of the sintering bed for sinter ore productivity, RF-MEBIOS (Return Fine -Mosaic Embedding Iron Ore Sintering) process, in which return fine as dry particle is added on granulated raw materials and then they are charged into sintering machine, is proposed. In RF-MEBIOS, it is demonstrated by pot tests that productivity increases at the same moisture content in sinter mixture at charging. This productivity increase is caused by higher permeability in sinter packed bed due to two major phenomena. One is increasing the pseudo-particle size at granulation and the other is decreasing the bulk density of sinter packed bed after charging. The former is achieved by a higher moisture content in the raw materials at granulation, which has the role of decreasing small size of pseudo-particle (-0.25 mm). The latter is achieved by higher friction in the packed bed composed of dry and wet particles compound, which has a role of decreasing bulk density. In the development of RF-MEBIOS, return fine was chosen as the dry particle because it is dry when produced by the sintering machine. The sinter productivity increases with the increase of the quantity of the return fine added after granulation stage. The effect of pseudo-particle (-0.25 mm) ratio and ε on flame front speed were evaluated as 55% and 41% to increase of frame front speed, respectively.Effect of RF-MEBIOS on sinter productivity is confirmed in No.3 sinter plant in Kashima Steel Works. Under the condition of constant moisture content in sinter mixture at charging, this improvement degree is proportioning to the ratio of bypass return fine which is added to granulated the other sinter materials without granulation. It means granulation at higher moisture has superiority compared to increase of fine material in bypass return fine.Finally, RF-MEBIOS method is installed on three commercial sintering machines (Kashima, Wakayama, and Kokura) belonging Sumitomo Metals. In all three sinter plants, productivity increase has been confirmed. Therefore, introducing RF-MEBIOS has been demonstrated to cause a universal improvement of sinter productivity.

Fig. 1. Principle of the simulation model. model for granulation should be discussed. There are two models for the simulation of granulation process. One is trace movement of all particles. The other is trace movement of granulated particle only as one particle. The former might be better to analyze granulation mechanism. However, it is not realistic to simulate them because particles traced are enormous and it would take a long time to simulate the behavior of granules. Therefore the latter is adopted in this work. The assumptions in this simulation model are follows; 1) Granules are treated as one particle. 2) Particle shape is sphere. 3) Particle diameter is uniformly. 4) Particle diameter and other parameter is fixed in the simulation. 5) Effect of moisture is ignored.Physical constants and simulation conditions are shown in Table 1. Figure 2 shows the schematic diagram of a continuous drum mixer used in the simulation. Table 2 lists the size of drum mixer. Drum length and gradient angle were changed to investigate their effects on the granule behavior. The granules are fed at the extreme right of the drum mixer and granules drop from the extreme left (Fig. 2). Feeding rate is fixed at 100 kg/min. Continuous Drum Mixer Determination of ParametersThe simulation parameters are needed to be determined so that the granules behavior simulated correspond to the experimental results. Particularly the frictional coefficient has to be determined carefully since it strongly affects granules behavior. The simulation of granules behavior was performed to investigate the frictional coefficient on the behavior. The snapshots are shown in Fig. 3. The granules behavior is influenced by the frictional coefficient and a rising angle increases with an increase in the frictional coefficient. The rising angle was defined as shown in Fig. 4(a) to evaluate the granule behavior and to compare to experimental results. Figure 4 (b) shows relationship between the friction coefficient used in the simulation and the rising angle. The rising angle obtained from the experiment was also shown in Fig. 3. The rising angle increases with an increase in the ISIJ International, Vol. 49 (2009) frictional coefficient until the coefficient is 0.5, and then, the rising angle is going to be constant value about 100 degrees. The frictional coefficient was determined as 0.7, at which the rising angle obtained from the simulation is the closest to experimental one, although the rising angle obtained from the simulation does not agree with experimental results completely. This difference between them could be due to the assumption of sphere in the granules. The reason of this difference will be investigated more detail in the future. ExperimentGranulation experiment has been performed by using the continuous dram mixer. Granulator consists of rotating drum mixer, water nozzle and feed hopper (Fig. 5). The raw materials used in the actual process are supplied continuously at the extreme right of the drum mixer. Water is sprinkled by a nozzle, and ...

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Recently, an increase in the amount of fine ore, such as Marra Mamba or Brazilian concentrated ultra fine, in raw material of sinter ore lowers the permeability of sintering bed and the yield of the sinter ore. The collapse of voids in the sintering bed will cause these problems although the bed has a porous structure. Therefore, controlling the bed structure by including loosely packed regions and densely packed regions in the same packed bed has been discussed. This new idea is named MEBIOS (Mosaic Embedding Iron Ore Sintering). In this report, permeability improvement techniques based on MEBIOS concept were studied. In order to granulate large dense green balls with ordinary sinter feed ore, mathematical simulation and granulation tests by using pan pelletizers were carried out. The influence of rim height and pan diameter on movement of raw material in pan was investigated. Also, influence of rim height and slope angle on hold-up and influence of residence time on diameter of green balls were studied. Finally, this technique was installed in Wakayama No. 5 sinter plant. As a result, yearly average productivity of 1.41 t/m 2 /h and the use of 135 kg/t-sinter Brazilian concentrated ultra fine ore were achieved with 1 350 MJ/t-sinter heat consumption for sintering in 2011.