2-STAGE FLUIDIZED BED FURNACE FOR PRE-REDUCING FINE IRON ORE AND METHOD FOR PRE-REDUCING FINE IRON ORE USING THE FURNACE

Abstract: The 2-stage fluidized bed furnace for prereducing a fine iron ore of the present invention comprises a first stage fluidized bed furnace for receiving the fine iron ore from storage hopper, discharging medium/small particles to the upper part thereof, and reducing a coarse particle ore while forming a bubbling fluidized bed; a second stage fluidized bed furnace for receiving the medium/small particles discharged from the upper part of the first stage and reducing it while forming a turbulent fluidized bed; and a first hot cyclone for collecting the small particles contained in the discharged gas from the second stage fluidized bed furnace, the first stage furnace being in an upper narrowed-lower-expanded shape and comprising a narrow upper portion, a slant portion and a wide lower portion, the second stage furnace being in an upper-expanded-lower-narrowed shape and comprising a wide upper portion, a slant portion and a narrow lower portion.

Description: 2-STAGE FLUIDIZED BED FURNACE FOR PRE-REDUCING FINE IRON ORE AND METHOD FOR PRE-REDUCING FINE IRON ORE USING THE FURNACE FIELD OF THE INVENTION The present invention relates to a pre-reduction furnace for pre-reducing iron ore fines having a wide particle size distribution in a smelting reduction process for producing molten pig iron directly from iron ores and coal, without sintering machines and coke ovens, and a method and, more particularly to a 2-stage fluidized bed furnace for pre-reducing fine iron ores which include much contents of fine particles ores or is readily decomposed by reaction heat at a pre-reduction temperature as one of physical characteristics of raw iron ores and a method for pre-reducing fine iron ore using the furnace. DESCRIPTION OF THE PRIOR ART Generally, a method of reducing iron ores so as to producing a molten iron includes a blast furnace, direct reduction process by which reduced iron is obtained in a solid form by using a shaft furnace, a rotary kiln and fluidized bed furnace, and other methods using electric f rnace. Burden materials of the blast furnace which is a prevailing iron-making method at present time is charged into it a massive sintered ore with using iron ore fines and a massive coke with using high quality coking coal as a heat source and reducing agents, respectively, so as to improve its permeability and reducibility at the shaft part. Therefore, it raises some serious problems of an immense facility investment, a lack in flexibility of operation due to mass production and a industrial pollution of environments from the pre-treatment facilities because it requires a coke oven for distilling the coking coal and facilities for manufacturing sintering ores. A direct reduction process by which iron is obtained by using a high-quality iron ore and a reducing gas from a natural gas, has been limitedly employed in the area that is easy to be supplied with the high-quality iron ore and the natural gas. Its ratio is very low in the crude steel production quantity of the world. However, there is gradually increasing the production quantity by the demand increase with the structural demand change of various kinds of steels and the deterioration of a quality of scrap. However, the above method is used through pre- treatments such as pelletizing and sintering to enlarge an permeability when iron ores of raw materials are charged in a furnace. This is very important in attaining a normal operation. In case of a smelting reduction precess which makes molten iron by directly using fine iron having largely varying grain sizes without pre-treatment as using coal, it has a importance as a new method of producing irons capable of replacing a blast furnace. There was studied the smelting reduction method for charging a conventional iron ore in a simple reactor and reducing it after directly melting it. However, there is recently developed a smelting reduction process for charging it in a melting furnace after pre-reducing a proper quantity in a solid state and finally reducing it, since it is practical in an energy efficient aspect. It takes interests in developing a technique of a fluidized bed type pre-reduction furnace which fluidizeε fine iron ore by supplying a off-gas of smelting reduction furnace in the fluidized bed reduction furnace which is known as a method of processing fine iron ores for pre- reduction of this process. In a conventional fluidized bed type direct reduction process related to such techniques, special fine particle iron ores which a particle size distribution of materials used is narrow are practical. The fluidized bed reduction process using fine iron ores having a wide distribution (i.e. pre-reduction step of smelting reduction process producing molten iron using coals as a heat source and reducing agent and iron ores without pre-treatment) has been recently developed, but not yet practical because of technical difficulty. In case of the smelting reduction process producing molten iron by directly using fine iron ore and coal without pre-treatment, it is composed of a smelting reduction furnace and a pre-reduction furnace as shown in FIG. 1, the smelting reducing furnace is generated pre-reduction gas by a gasification reaction of charging coals, and then supplies it to the pre-reduction furnace through a gas duct after collection of dust containing pre- reduction gas in hot cyclone. It pre-reduces iron ores charged in pre-reduction furnace up to high reduction degree by validly using a reducing force and heat which a off-gas of smelting reduction furnace has, and pre-reduced iron ores are charged in the smelting reduction furnace and discharges into molten metal by finally being reduced in the molten state. On the other hand, as is shown in FIG. 2, in a method of reducing fine iron ores which have a wide particle size distribution by a fluidized bed pre-reduction process, there is shown a circulating fluidized bed pre-reduction process that coarse particle iron ores which a particle size is large are reduced by fluidization in the lower zone thereof, and small particle iron ores which a particle size is small are discharged by elutriating to the outer through a freeboard area of the top of the furnace and then collects in the hot cyclone and part of the portion of the reducing gas supplied to the hot cyclone is feed into a fluidized bed formed in the lower part through a downcomer. However, it is not easy to control the state of fluidization of charging materials with fraction of different grain sizes. To operate the fluidized bed with fraction of different grain sizes, there is required an operation in a base of coarse particle iron ores existing in the lower of layer in a wide size distribution of the charging ore. The fluidization velocity of such conditions brings about discharge by segregation of medium and small particle ores with coarse particle ores, and it rises a problem of ore collection due to deteriorating the collected efficiency of the cyclone fixed at the rear stage. In FIG. 2, reference numbers 1, 2 and 3 indicate a pre-reduction furnace, a hot cyclone, and a gas distributing plate fixed in pre-reduction furnace, respectively. As described above, to solve the problem in a conventional fluidized reduction furnace using fine iron ore which has a wide particle size distribution, a circulating fluidized bed pre-reduction furnace for pre- reducing fine iron ores composed of 2-staged fluidized bed f rnaces is disclosed in Korean patent publication Nos. 94- 1137 and 94-1138. In the process of the fluidized bed furnace, if burden iron ores with wide particle size distribution are charged in a first fluidized bed reduction furnace, medium and small particle ores are separately supplied to a second fluidized bed furnace by fluidizing gas. The coarse particle ores are stably reduced by fluidizing in the first fluidized bed pre-reduction furnace, and the medium and small particle ores in the second fluidized bed pre-reduction furnace, under different particle size distribution. When the fine iron ores are reduced as fluidizing by continuously charging the fine ores having a wide size distribution in the first fluidized bed reduction furnace. a gas fluidizing velocity for fluidized bed should be operated in a basis of large particle ores in the process of 2-staged fluidized bed furnaces. Accordingly, in the case of the circulating fluidized bed pre-reduction furnace for pre-reducing the fine iron ores, a large quantity of coarse particle iron ores can be transferred to the top of the first fluidized bed reduction furnace by elutriating with small particle ore. There is a problem that deteriorates fluidization of the fine iron ores in the second fluidized bed reduction furnace due to existence of the coarse particle iron ores. Furthermore, in the case of a fluidized bed reduction furnace having 2 reactors, the reducing gas supplied to the first fluidized bed reduction furnace has a problem that deteriorates a reducing force of the fluidizing gas in the second fluidized bed stage according to being supplied to the second fluidized bed reduction furnace in the state that an oxidizing degree is high, because the coarse particle ores are reduced by fluidizing in the course that small particle ores separately are supplied to the second fluidized bed reduction furnace. The present inventor has studied to solve various problems of the conventional method as above, as a result, to provide the present invention. SUMMARY OF THE INVENTION The object of the present invention is to provide a 2- staged fluidized bed pre-reduction furnace of fine iron ores which can prevent elutriating medium/small particle ores as well as improve an efficiency of segregation and a method for pre-reducing the fine iron ores using it, since a first stage fluidized bed reduction furnace is in a upper-narrowed-lower-expanded shape and a second stage fluidized bed reduction furnace is in a upper-expanded- lower-narrowed shape. To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a 2-stage fluidized bed furnace for pre-reducing a fine iron ores which have a wide size distribution according to the present invention comprises: a first stage fluidized bed reduction furnace for receiving the fine iron ores from a iron ore storage hopper, discharging by elutriating a medium/small particle ore to the upper portion thereof, and reducing a coarse particle ore while forming a bubbling fluidized bed in the lower portion thereof; a second stage fluidized bed reduction furnace for receiving medium/small particle ores discharged by elutriating from the upper part of the first stage fluidized bed reduction furnace and reducing them while forming a turbulent fluidized bed; and a first hot cyclone for collecting small particle ores contained in the discharged gas from the second stage fluidized bed reduction furnace. Further, the present invention relates to a method for pre-reducing the fine iron ores using it. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the drawings; In the drawings: FIG. 1 is a sche atical view of a smelting reduction process for producing molten iron. FIG. 2 is schematic diagram of a fluidized bed pre- reduction furnace of a conventional fine iron ore. FIG. 3 is schematic diagram of 2-stage fluidized bed pre-reduction furnace fine iron ore according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawing. Referring to FIG. 3, the 2-stage fluidized bed pre- reduction furnace comprises: a first stage fluidized bed reduction furnace(20) for receiving the fine iron ores from a iron ore storage hopper(10), discharging by elutriating a medium/small size ore to the upper portion thereof, and reducing a coarse particle ore while forming a bubbling fluidizing bed; a second stage fluidizing bed reduction furnace(30) for receiving the medium/small size ores discharged by elutriating from the upper part of the first staged fluidized bed reduction furnace(20) and reducing them while forming a turbulent fluidized bed; and a first hot cyclone(40) for collecting a small size ores contained in the discharged gas from the second stage fluidized bed reduction furnace(30). The first stage fluidized bed reduction furnace(20) is in a upper-narrowed-lower-expanded shape and comprises a narrow upper portion(20a), a slant portion(20b) and a wide lower portion(20c). A first gas distribution plate(21) is installed in the wide lower portion(20c) of the first fluidized bed reduction furnace(20). The side wall of the wide lower portion(20c) is connected to the iron ore storage hopper(10) via an ore feed tube(11)for supplying the iron ore stored in the hopper(10) into the furnace(20). Also, a first reduced gas inlet tube(24) for introducing a reduced gas into the first furnace(20) and a coarse particle ore outlet tube(22) for discharging the pre-reduced coarse particle ores are connected to the side wall of the wide lower portion(20c) . Further, a first medium/small ore outlet tube(23) is connected to the upper side wall of said narrow upper portion(20a) to discharge the medium/small ores in said second stage fluidized bed furnace(30). And, the second stage fluidized bed reduction furnace(30) is in a upper-expended-lower-narrowed shape and comprises a wide upper portion(30a), a slant portion(30b) and a narrow lower portion(30c) . A second gas distribution plate(21) is installed in the narrow lower portion(30c) . The side wall of the narrow lower portion(30c) is connected to the first stage fluidized bed reduction furnace(20) via a first medium/small particle ore outlet tube(23) for introducing the medium/small particle ore discharged from the first furnace(20) and the small particle ores collected in the first hot cyclone(40). Further, a second reducing gas inlet tube(31) for introducing the reduced gas into the furnace(30) and a second medium/small particle ore outlet tube(32) for discharging the pre-reduced medium/small particle ores are connected to the side wall of the narrow lower portion (30c). In addition, the wide upper portion(30a) of the second stage fluidized bed reduction furnace(30) is connected to a first hot cyclone(40) via a third gas outlet tube(43). The bottom of the first hot cyclone(40) is connected to the first medium/small particle ore outlet tube(23) through a first small particle ore feed tube(42) for circulating the small particle ore contained in the discharged gas of the second stage fluidized bed reduction furnace(30) back to the furnace(30). A first gas outlet tube(41) for discharging the gas separated from the small particle ores is connected to the top of the first hot cyclone(40). The first small particle ore feed tube(42) is connected to the first medium/small ore outlet tube(23). Preferably, the present invention further comprises a second hot cyclone(50) for collecting a fine particle ore contained in a discharged gas from the first hot cyclone(40) . The bottom of the second hot cyclone is connected to the narrow lower portion(30c) of the second furnace(30) via a second small particle ore feed tube(52). Further, a second gas outlet tube(51) for discharging the gas separated from the small particle ore is connected to the top of the second hot cyclone(50). A fine reduced iron ore outlet tube(53) for discharging a reduced fine iron ore is preferably connected to the second small particle ore feed tube(52). If the second hot cyclone(50) is not provided, it is desirable to connect the fine reduced iron ore outlet tube(53) to the first small particle ore feed tube(42) . Meanwhile, in the first stage fluidized bed reduction furnace(20), the inner diameter of the narrow upper portion (20a) has preferably 0.8-0.9 times that of the wide lower portion(20c) and the slant portion(20b) preferably has a slant angle of 8-10 degrees. In the second stage fluidized bed reduction furnace (30), the inner diameter of the wide upper portion(30a) preferably has 1.5-1.8 times as large as that of the narrow lower portion(30c) and the slant portion(30b) preferably has a slant angle of 8-10 degrees. On the other hand, the small particle ore discharged from the second stage fluidized bed reduction furnace(30) together with the gas is collected in the first hot cyclone(40) and then recirculated to the second stage fluidized bed reduction furnace(30). A part of the small particle ores collected in the first hot cyclone(40) is discharged to the outside via the fine reduced iron ore outlet tube(53). If the furnace has the second hot cyclone(50), the small particle ore contained in the gas discharged from the first hot cyclone(40) is collected in the second hot cyclone(50), and then recirculated to the second stage fluidized bed reduction furnace(30). A part of the small particle ore collected in the second hot cyclone(50) is discharged to the outside via the fine reduced iron outlet tube(53). It is preferable that coarse particle reduced iron of more than 0.5 mm is discharged through the coarse particle ore outlet tube(22), medium/small particle reduced iron of less than 0.5 mm through the second medium/small particle ore outlet tube(32), and small particle reduced iron of less than 0.125 mm through the fine reduced iron outlet tube(53). When a fine iron ore is introduced into the first stage fluidized bed reduction furnace(20), the fine iron ore in the furnaces forms a fluidizing bed in a various form according to the velocity of the fluidizing gas. If a reducing gas is supplied through the first gas distribution plate(21) at fluidizing velocity lower than that of the coarse particle iron ore, the coarse particle iron ore forms a dense phase in the lower part of the fluidized bed reduction furnace, the small particle iron ore forms a dilute phase in the upper part of it and is separated to a second stage fluidized bed reduction furnace(30) via the first medium/small particle ore outlet tube(23) but the medium particle iron ore is accumulated in the first furnace(20) between the top of the coarse particle ores and the portion to which the first medium/small particle ores outlet tube(23) is connected. In the conventional first fluidized bed furnace, the reaction furnace has cylindrical structure, and therefore the superficial velocity of the reducing gas in a vertical direction is constant. Thus, the medium particle iron ore remaining between the tope of the dense phase of coarse particle ore and the dilute phase of the small particle ore may be accumulated without being discharged to outside. Accordingly, the present invention prevents the coarse particle ore from being discharged to the second stage fluidized bed reduction furnace(30) together with the small particle ore by relatively decreasing the fluidizing velocity of the first fluidized bed furnace(20). Further, in the first reduction furnace(20) according to the present invention, the gas fluidizing velocity to the upper part of the coarse particle dense phase is increased by providing a slant portion(20a) between the narrow upper portion(20a) and the wide lower portion(20c) of the first stage fluidized bed reduction furnace(20) so as to make the upper part of the coarse particle dense phase to be narrower than the lower part thereof, thereby improving separating efficiency of the medium particle ores remaining in the upper and middle region of the first stage bed reduction furnace(30). Therefore, in the present invention, the first and second stage fluidized bed furnaces(20,30) has an optimum condition of fluidized bed reduction for the medium/small ores. In the present invention, the lower superficial velocity of the first stage fluidized bed reduction furnace(20) is preferably 2.0-2.5 m/sec and that of the second stage fluidized bed reduction furnace(30) is preferably 0.2-0.5 m/sec. Now the present invention will be described based on an actual examples. Example The reduction furnace as constructed as FIG. 3 was prepared. A fine iron ore having a wide particle size distribution and a particle size of -10 mm is charged into the first stage fluidized bed reduction furnace(20) and the reducing gas of about 3 Kgf/cm 2 and 850°C is supplied in the first and the second furnaces via the gas distribution plate(21) (31) of the first and the second stage fluidized bed reduction furnaces from the reducing gas feed tube (24) (33) so as to reduce the fine iron ore. Then, the coarse particle reduced iron ores are discharged from the coarse particle ore outlet tube(22) of the first stage fluidized bed reduction furnace(20), the medium/small particle iron ores are discharged from the medium/small particle ore outlet tube(32) of the second stage fluidized bed reduction furnace(30), and the fine reduced iron ores are discharged from the second small particle ore feed tube(52) of the second hot cyclone(50) via the reduced iron outlet tube(53). The present embodiment employed the following experimental device and conditions: (1) Iron ore source 1 ) composition : T . Fe 62 . 5 % , FeO 0 . 51 % , Si0 2 5 . 22 % , A1 2 0 3 2 . 54% , S 0 . 012% , and P 0 . 067% 2) particle size distribution particle size +5 1-5 0.5-1 0.25-0.5 0.25-1.25 -0.125 (mm) fraction (wt%) 12 42.5 10.2 10.1 10.2 15.0 3) charged amounts: 6.5 Kg/min (2) Reducing gas: removing C0 2 contained in by-product gas produced in an iron and steel work by using an absorption tower, adding hydrogens, heating with an electric heater, and supplying. 1) gas composition : CO 65%, H 2 25%, C0 2 5%, H 2 0 5% 2) temperature and pressure : about 850°C, 3Kgf/cm 2 (3) Processing conditions of fluidized bed reduction furnace l)The sizes of facilities in fuidized bed reduction furnace are as follow: - inner diameter of the lower portion of first stage fluidized bed furnace: 0.20m - height of the upper portion of first stage fluidized bed furnace(height from distribution plate to the upper end of slant portion): 2.00 mm - inner diameter of the upper portion of first fluidized bed furnace: 0.17 m - height of the upper portion of first fluidized bed furnace: 4.00 m inner diameter of lower portion of second fluidized bed furnace : 0.50 m - height of the lower portion of second fluidized bed furnace(height from gas distribution plate to the lower end of slant portion): 4.00 - inner diameter of the upper portion of second fluidized bed furnace: 0.80 m - height of the upper portion of second fluidized bed furnace: 2.50 2) gas fluidizing velocity in fluidized bed furnace - superficial velocity of the lower portion of first fluidized bed furnace: 2.20 m/sec - superficial velocity of the upper portion of second fluidized bed furnace: 3.04 m/sec - superficial velocity of the lower portion of first fluidized bed furnace: 0.25 m/sec - superficial velocity of the upper portion of second fluidized bed furnace: 0.28 m/sec 3) discharging rate of reduced iron: 5.81 kg/ in - lower portion of first fluidized bed furnace: 1.74 kg/min (reduced iron of more than 0.5 mm, about 95%) - lower portion of second fluidized bed furnace: 3.49 kg/min (reduced iron of less than 0.5 mm, about 90%) - lower portion of second cyclone: 0.58 kg/min (reduced iron of less than 0.125 mm) As a result of the above-conditioned experiment with the fine iron ore charged into the first stage fluidized bed reduction furnace(20), the discharging ratio of the reduced iron ore was 3:7 and at least about 95% of the medium particle ores(0.25-0.5 mm) was discharged to the second fluidized bed stage reducing furnace. Therefore, in present invention, separating efficiency was improved more than about 20% compared with that of a cylindrical furnace. The gas consumption was 1280 Nm 3 /t-ore and the average reduction percentage was about 65% even when the pre-heating step of ores was omitted. The present invention can reduce a fine iron ore having a wide particle size distribution without any preliminary treatment such as grinding or a separation by a screen. Further, in the present invention, the amount of fine iron ores reduced in the first stage fluidized bed reduction furnace is decreased and thus leads to a high efficiency in the reducing force of the reducing gas in the second stage fluidized bed reduction furnace, thereby improving reducing velocity. In addition, the pre-reduced ore can be easily introduced into a smelting reduction furnace because the pre-reduced small particle ore, the medium/small particle ore and the coarse particle ore are classified during fluidized bed reduction process and each of them are discharged through separate discharging tubes. It will be apparent to those skilled in the art that various modification and variations can be made in a 2- staged fluidized bed pre-reduction furnace of fine iron ores and its method of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and this invention provided they come within the scope of the appended claims and their equivalents.

Claims: What is claimed is: 1. A 2-stage fluidized bed furnace for pre-reducing a fine iron ore, comprising: a first stage fluidized bed furnace(20) for receiving the fine iron ore from a fine iron ore storage hopper(10) via an ore feed tube(11), discharging by elutriating a medium/small particle ore to the upper portion thereof, and reducing a coarse particle ore while forming a bubbling fluidized bed; a second stage fluidized bed furnace(30) for receiving the medium/small particle ore discharged from the upper portion of the first stage fluidized bed reduction furnace(20) and reducing it while forming a turbulent fluidized bed; and a first hot cyclone(40) for collecting a small particle ore contained in the discharged gas from the second stage fluidized bed reduction furnace(30), the first stage fluidized bed reduction furnace(20) being a upper-narrowed-lower-expanded shape and comprising a narrow upper portion. (20a), a slant portion and a wide lower portion(20c), the wide lower portion(20c) having a first gas distribution plate(21) therein, a first reduced gas inlet tube(24) and a coarse particle ore outlet tube(22) connected to the side wall of the wide lower portion(20c), the second stage fluidized bed reduction furnace(30) being a upper-expanded-lower-narrowed shape and comprising a wide upper portion(30a), a slant portion(30b) and a narrow lower portion(30c) , the narrow lower portion(30c) having a second gas distribution plate(31) therein, a second reduced gas inlet tube(33) and a second medium/small particle ore outlet tube(32) connected to the side wall of the narrow lower portion(30c), the first stage fluidized bed reduction furnace(20) connected to the second stage fluidized bed reduction furnace via a first medium/small particle ore outlet tube(23), the second stage fluidized bed reduction furnace connected to the first hot cyclone(40) via a third gas outlet tube(43), the first hot cyclone(40) having a first gas outlet tube(41) in the upper portion thereof and a first small particle ore feed tube(42) in the bottom thereof, the first small particle ore feed tube(42) connected to the first medium/small particle ore outlet tube(33). 2. The fluidized bed furnace as claimed in claim 1, further comprising a second hot cyclone(50) for collecting a fine particle ore contained in a discharged gas from the first hot cyclone(40), the first hot cyclone(40) connected to the second hot cyclone(50) via the first gas outlet tube(41), the second hot cyclone(50) connected to the second stage fluidized bed reduction furnace(30) via a second small particle ore feed tube(52), and having a second gas outlet tube(51) in the upper portion thereof. 3. The fluidized bed furnace as claimed in claim 2, wherein the second small particle ore feed tube(52) has a reduced fine iron ore outlet tube(53) for discharging a reduced fine iron ore. 4. The fluidized bed furnace as claimed in any one of claims 1 to 3, wherein the inner diameter of the narrow upper portion(20a) of the first stage fluidized bed reduction furnace(20) is 0.8-0.9 times that of the wide lower portion(20c) of the first stage fluidized bed reduction furnace(20), the slant portion(20b) of the first stage fluidized bed reduction furnace(20) has a slant angle of 8-10 degrees, the inner diameter of the wide upper portion(30a) of the second stage fluidized bed reduction furnace(30) is 1.5-1.8 times as large as that of the narrow lower portion(30c) of the second stage fluidized bed reduction furnace(30), and the slant portion(30b) of the second stage fluidized bed reduction furnace has a slant angle of 8-10 degrees. 5. A method of pre-reducing a fine iron ore using a 2-stage fluidized bed pre-reduction furnace comprising the steps of, dividing a fine iron ore into a medium/small particle ore whose a particle size distribution is less than 0.5 mm and a coarse particle ore whose a particle size distribution is more than 0.5 mm in a first stage fluidized bed reduction furnace(20); discharging the medium/small particle ore to a second stage fluidized bed reduction furnace(30); pre-reducing the coarse particle ore while forming a bubbling fluidized bed of a coarse particle iron ore in the first stage fluidized bed reduction furnace; and pre-reducing the medium/small particle ore furnace while forming a turbulent fluidized bed of a medium and small size iron ore in the second stage fluidized bed reduction. 6. The method as claimed in claim 5, wherein the medium/small particle ore of less than 0.5 mm which is discharged from the first stage fluidized bed reduction f rnace to the second stage fluidized bed reduction furnace is at least 90%. 7. The method as claimed in claim 6, wherein the fluidizing superficial velocity is 2.0-2.5m/sec in the lower portion of the first stage fluidized bed reduction furnace and 0.2-0.5m/sec in the lower portion of the second stage fluidized bed reduction furnace. 8. A method of pre-reducing a fine iron ore using a 2- stage fluidized bed pre-reduction furnace comprising the steps of: dividing a fine iron ore into a medium/small particle ore whose a particle distribution is less than 0.5mm and a coarse particle ore whose a particle size distribution is more than 0.5mm in a first stage fluidized bed reduction furnace(20); discharging the medium/small particle ore to a second stage fluidized bed reduction furnace(30); pre-reducing the large particle ore while forming a bubbling fluidized bed of a coarse particle ore in the first stage fluidized bed reduction(20); pre-reducing the medium/small particle ore while forming a turbulent fluidized bed of a medium/small particle ore in the second fluidized bed reduction furnace(30); and discharging the small particle ore of less than 0.125mm through a reduced fine iron ore outlet tube(53). 9. The method as claimed in claim 8, wherein the medium/small particle ore of less than 0.5mm which is discharged from the first stage fluidized bed reduction furnace to the second stage fluidized bed reduction furnace is at least 90%. 10. The method as defined in claim 8 or 9, wherein the fluidizing superficial velocity is 2.0-2.5m/sec in the lower portion of the first stage fluidized bed reduction furnace and 0.2-0.5m/sec in the lower portion of the second stage fluidized bed reduction furnace.

Inventors: LEE IL OCK, PARK DAE GYU, PARK SUK IN, LEE, IL, OCK;, PARK, DAE, GYU;, PARK, SUK, IN;
Applicants: LEE IL OCK, PARK DAE GYU, PARK SUK IN, PO HANG IRON & STEEL, RES INST IND SCIENCE & TECH, VOEST ALPINE IND ANLAGEN, LEE, IL, OCK;, PARK, DAE, GYU;, PARK, SUK, IN;, POHANG IRON & STEEL CO., LTD., RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE & TECHNOL, VOEST-ALPINE INDUSTRIEANLAGENBAU GMBH
Application year: 1996
Main classification: C21B13
IPC codes: C21B11, C21B13, F27B15