FLUIDIZED BED TYPE REDUCING SYSTEM FOR REDUCING FINE IRON ORE

Abstract: A fluidized bed type reducing system (20) for reducing fine iron ore consisting of a lower upper-wide-narrow-lower shape tapered portion (212) and an upper cylindrical portion (211). The extremely fine iron ore discharged together with the reducing gas is recycled by a duct (115) connected to the upper part of the cylindrical portion (211), a capturing device (12) for separation of the extremely fine iron ore from the reducing gas and further duct (121) for refeeding the separated extremely fine iron ore to the system (20). The upper iron ore outlet (113) for discharging fine iron ore particles, the iron ore inlet (112) for charging iron ore with wide particle size distribution and the lower iron ore outlet (114) for discharging coarse iron ore particles are connected to the tapered portion (212) of the system. The extremely fine iron ore supplying tube (121) is installed on another side of the said tapered portion (212).

Description: FLUIDIZED BED TYPE REDUCING SYSTEM FOR REDUCING FINE IRON ORE FIELD OF THE INVENTION The present invention relates to a fluidized bed type reducing system for reducing a fine iron ore. More specifically, the present invention relates to a fluidized bed type reducing system for a fine iron ore, in which the structure of the fluidized bed type reducing furnace is improved such that a fine iron ore having a wide particle size distribution can be made to undergo a fluidized bed reduction in an optimum manner. DESCRIPTION OF THE PRIOR ART A fluidized bed type reducing system for reducing a fine iron ore is disclosed in Japanese Patent Laid-open No. Hei-6-10021. As shown in FIG. 1, this fluidized bed type reducing system 10 is characterized in that a reducing gas is supplied through a lower portion of a cylindrical reducing furnace 11 so as to fluidize a fine iron ore supplied through an iron ore supplying inlet 112. -Further, the fine iron ore which is discharged while being carried by the reducing gas from an upper portion of the reducing furnace through a circulating duct 115 is separated from the reducing gas by a particle capturing device 12 so as to refeed it through an extremely fine iron ore supplying duct 121 into the reducing furnace 11. The upper diameter of the reducing furnace is made larger than the lower diameter of it, so that the elutriation of the fine iron ore can be reduced. Further, iron ore outlets 113 and 114 are formed on the upper and lower portions of the reducing furnace respectively. The upper iron ore outlet 113 is for discharging fine iron ore particles whereas the lower iron ore outlet 114 is for discharging coarse particles, so that the average residence time of the iron ore in the reducing furnace can be controlled for each particle size, and thus both the fine iron ore and the coarse iron ore can be simultaneously reduced with a high efficiency. However, the iron ore has a wide particle size distribution from several scores of microns to several thousand micron. In the conventional fluidized bed type reducing system, if this iron ore is to be maintained in a fluidized state in an efficient manner, the operation should be carried out based on the superficial gas velocity of the coarse iron ore which is, otherwise distributed mostly in the lower level. In this high-gas-velocity operation with the conventional fluidized bed (cylindrical bed) in which the gas velocity is constant along the height of the bed, the coarse particles move upward to the upper level to be mixed with the fine iron ore particles, and therefore, these coarse iron ore particles which need more reducing time than the fines are discharged through the upper iron ore outlet without being sufficiently reduced, this being the problem of the conventional technigue. SUMMARY OF THE INVENTION The present inventors carried out a series of researches and experiments to solve the problem of the conventional fluidized bed type reducing furnace, and the present invention is proposed based on the results of the researches and experiments . Therefore it is an object of the present invention to provide a fluidized bed type reducing system for reducing a fine iron ore, in which the structure of the fluidized bed type reducing furnace is improved such that the coarse iron ore particles are made to be distributed in the lower portion of the fluidized bed within the furnace, whereas the fine iron ore particles to be in the upper portion of the fluidized bed, so that the reducing can be done in a stable fluidized state, that only the coarse iron ore particles can be discharged through the lower iron ore outlet, whereas only the fine iron ore particles can be discharged through the upper iron ore outlet. Thus the average residence time of the particles in the furnace are adjusted differently for different sizes, so that the reducing efficiency can be improved, and that the residence time of the reducing gas in the furnace can be extended, thereby improving the gas utilization degree. In achieving the above object, the fluidized bed type reducing system for reducing a fine iron ore of wide particle size distribution according to the present invention includes: an upper iron ore outlet for discharging fine iron ore particles; a lower iron ore outlet for discharging coarse iron ore particles; a gas distributor installed in a lower portion of a reducing furnace; a gas inlet formed on a lower portion of the reducing furnace for introducing a reducing gas; an iron ore inlet for supplying an fine iron ore of wide particle size distribution; a circulating duct connected to an upper portion of the fluidized bed type reducing furnace for discharging extremely fine iron ore particles together with the reducing gas; a particle capturing device for separating the extremely fine iron ore particles from the reducing gas; an extremely fine iron ore recycling duct for refeeding the separated extremely fine iron ore particles into the fluidized bed type reducing furnace so as to reduce the elutriation of a fine iron ore of a wide particle size distribution. The fluidized bed type reducing furnace includes: a cylindrical upper portion and a tapered lower portion, the tapered portion being in a wide-upper-narrow-lower shape; and the tapered portion includes : the upper iron ore outlet, the iron ore inlet and the lower iron ore outlet on a side thereof in the mentioned seguence, and the extremely fine iron ore recycling duct installed on another side of the tapered portion. BRIEF DESCRIPTION OF THE DRAWINGS The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with reference to the attached drawings in which: FIG. 1 is a schematic diagram showing the conventional fluidized bed type reducing system; FIG. 2 is a schematic diagram showing the fluidized bed type reducing system for reducing a fine iron ore according to the present invention; FIG. 3 is a graphical illustration showing the particle segregation and the reduction degree of iron ore for the case when fine iron ore is reduced using the present invention; FIG. 4 is a graphical illustration showing the particle segregation and the reduction degree of iron ore for the case when fine iron ore is reduced using a conventional fluidized bed type reducing system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 2, a fluidized bed type reducing system 20 for reducing a fine iron ore according to the present invention includes: a fluidized bed type reducing furnace 21 for reducing a fine iron ore of a wide particle size distribution, and a particle capturing device 12 for separating extremely fine iron ore particles from a reducing gas so as to recycle them into the fluidized bed type reducing furnace 21. The fluidized bed type reducing furnace 21 includes: a cylindrical upper portion 211 and a tapered lower portion 212. The tapered portion 212 is in such a shape that its upper portion is wide and its lower portion is narrow. The inclination angle of the tapered portion 212 should be preferably 3-25°, and more preferably 5-10°. The upper portion of the cylindrical portion 211 is connected with the particle capturing device 12 through a circulating duct 115. Through this circulating duct 115, there is discharged the reducing gas in which the extremely fine iron ore particles are entrained. The tapered portion 212 includes: an upper iron ore outlet 113, an iron ore inlet 112 and a lower iron ore outlet 114 on a side thereof in the mentioned seguence. The upper iron ore outlet 113 and the lower iron ore outlet 114 discharge reduced fine iron ore and coarse iron ore respectively, and the iron ore inlet 112 is connected to an iron ore source (not shown in the drawings). The upper iron ore outlet 113 is formed preferably on the widest level of the tapered portion, while the lower iron ore outlet 114 is formed preferably just above the gas distributor 21a. The lower portion of the other side of the tapered portion 212 is connected to the particle capturing device 12 through an extremely fine iron ore recycling duct 121. The extremely fine iron ore particles which are captured by the particle capturing device 12 are recycled through the extremely fine iron ore supplying duct 121 into the fluidized bed type reducing furnace 21. A gas distributor 21a is installed in the lower part of the tapered portion 212, and a reducing gas inlet 21b is formed on the bottom of the tapered portion 212. Further, a exhaust gas outlet 122 is formed on the top of the particle capturing device 12. Now the method for reducing a fine iron ore by using the above described fine iron ore reducing system of the present invention will be described. The reducing gas is introduced into the fluidized bed type reducing furnace 21 through the gas inlet 21b of the bottom of the fluidized bed type reducing furnace 21 via the gas distributor 21a. The fine iron ore is supplied through the iron ore inlet 112, and is fluidized by the reducing gas . The extremely fine iron ore particles which are discharged with the exhaust gas are captured by the particle capturing device 12 so as to be refeed through the extremely fine iron ore supplying duct 121 into the fluidized bed type reducing furnace 21. The fine iron ore which has been reduced in the fluidized bed type reducing furnace 21 is discharged through the upper iron ore outlet 113, while the coarse iron ore being discharged through the lower iron ore outlet 114. Meanwhile the exhaust gas is discharged through the gas outlet 122 which is formed in the top of the particle capturing device 12. In the present invention, the lower portion of the fluidized bed type reducing furnace is in a wide-upper- narrow-lower shape. Therefore, the average residence time of the fine iron ore particles and the coarse iron ore particles are naturally adjusted for the different particle sizes. As the result, the reducing efficiency is improved and the residence time of the gas in the fluidizing bed is extended, thereby improving the gas utilizing degree. Now the present invention will be understood more readily with reference to the following example. <Example> The dimension of a fluidized bed type reducing furnace as can be seen in FIG. 2 is listed in Table 1 below. A fine iron ore having the size and chemical composition as listed in Table 2 was reduced under the operating conditions as listed in Tables 2 to 4. After the reduction, the particle size segregation and the reduction degree for different particle sizes (of the reduced iron discharged through the upper iron ore outlet and the lower iron ore outlet) were evaluated, and the results are shown in FIG. 3. Further, for the sake of comparison, a reducing of fine ore was also carried out in the conventional fluidized bed type reducing furnace. The experimental results of this case are shown in FIG. 4. Table 1 Table 2 Table 3 (Carrying gas) Composition CO: 65%, H 2 : 25%, C0 2 +H 2 0: 10% Temperature About 850°C Pressure 3.3 Kgf/cm 2 Table 4 (Superficial gas velocity in reducing furnace) As shown in FIGs. 3 and 4, compared with the conventional method, the result from the present invention showed that the reduction degree was uniform independent of particle size, and that the average reduction degree was higher than that obtained from the conventional fluidized bed reducing furnace. Further, a much better regregation between the reduced iron particles of 250 μm or less (which are injected into a melter by means of an pneumatic injector) and the reduced iron particles of 250 μm or more (which are fed into the melter by gravity) was observed when the present invention was employed.

Claims: WHAT IS CLAIMED IS: 1. A fluidized bed type reducing system for reducing a fine iron ore, comprising: an upper iron ore outlet for discharging fine iron ore particles; a lower iron ore outlet for discharging coarse iron ore particles; a gas distributor installed in a lower portion of a reducing furnace; a gas inlet formed on a lower portion of said reducing furnace for introducing a reducing gas; an iron ore inlet for supplying an iron ore of wide particle size distribution; a circulating duct connected to an upper portion of said fluidized bed type reducing furnace for discharging extremely fine iron ore particles together with the reducing gas; a particle capturing device for separating the extremely fine iron ore particles from the reducing gas; an extremely fine iron ore recycling duct for refeeding the separated extremely fine iron ore particles into said fluidized bed type reducing furnace so as to reduce the elutriation of a fine iron ore of a wide particle size distribution, said fluidized bed type reducing furnace comprising: a cylindrical upper portion and a tapered lower portion, said tapered portion being in a wide-upper-narrow-lower shape; said tapered portion comprising: said upper iron ore outlet, said iron ore inlet and said lower iron ore outlet on a side thereof in mentioned seguence, said extremely fine iron ore supplying tube installed on another side of said tapered portion. 2. The fluidized bed type reducing system as claimed in claim 1, wherein said tapered portion has an inclination angle of 3-25°. 3. The fluidized bed type reducing system as claimed in any one of claims 1 and 2, wherein said tapered portion has an inclination angle of 5-10°.

Inventors: KIM HANG GOO, KIM YONG HA, LEE IL OCK, KIM, HANG, GOO;, KIM, YONG, HA;, LEE, IL, OCK;
Applicants: KIM HANG GOO, KIM YONG HA, LEE IL OCK, PO HANG IRON & STEEL, RES INST IND SCIENCE & TECH, VOEST ALPINE IND ANLAGEN, KIM, HANG, GOO;, KIM, YONG, HA;, LEE, IL, OCK;, POHANG IRON & STEEL CO., LTD., RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE & TECHNOL, VOEST-ALPINE INDUSTRIEANLAGENBAU GMBH
Application year: 1996
Main classification: C21B13
IPC codes: C21B13, F27B15