Abstract:
A two-stage fluidized bed reducing apparatus and a reducing method for fine iron ore of a wide particle size distribution with an increased degree of utilization of the reducing gas. Fine iron particles dropping through the holes of a gas distributor can be recycled into the fluidized bed furnace, thereby preventing an impediment of the reducing gas flow due to abnormal defluidizing or channeling. A first fluidized bed furnace dries, pre-heats and pre-reduces the fine iron ore, and a second fluidized bed furnace finally reduces the pre-reduced iron ore. Downstream of the respective fluidized beds are installed intermediate hoppers and gas/solid sealing valves. Thus, the fine iron ore particles which drop through the holes of gas distributors during the abnormal operation are recycled to the furnaces. Accordingly, the gas flow is not impeded.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a 2-stage fluidized bed fine iron ore reducing apparatus and a reducing method using the apparatus, for reducing a fine iron ore of a wide particle size distribution. More specifically, the present invention relates to a 2-stage fluidized bed fine iron ore reducing apparatus and a reducing method using the apparatus, in which a fine iron ore of a wide particle size distribution can be reduced in an economical and efficient manner, and impediment of the reducing gas flow due to the abnormal phenomena such as defluidizing and channeling can be effectively avoided during the operation. 
     BACKGROUND OF THE INVENTION 
     In the conventional blast furnace method, the size of solid particles are very large, and therefore, the iron ore can be reduced within a fixed bed type furnace. However, in the case of a fine particle iron ore, if the gas velocity is low as in the fixed bed type furnace, low gas permeability and the sticking phenomenon occur, with the result that the operation may be halted. Therefore, a fluidized bed type method has to be necessarily adopted, so that the movements of solid particles can be made brisk with excellent gas permeability. 
     An example of the fluidized bed type furnace is disclosed in Japanese Utility Model Publication No. Sho-58-217615. This is illustrated in FIG.  1 . As shown in FIG. 1, this furnace includes a cylindrical reducing furnace  91  and a cyclone  95 . The reducing furnace  91  is provided with a raw iron ore feeding hole  92 , a high temperature reducing gas injecting hole  93 , and a reduced iron discharge hole  94 . Further, in the lower portion of the reducing furnace, there is disposed a gas distributor  96 . A reducing gas is supplied through the gas distributor  96 , and a fine iron ore is supplied through the feeding hole  92 . Then the reducing furnace is agitated, so that the fine iron ore and the reducing gas can be mixed so as for the iron ore to be reduced in a fluidized state. After the elapsing of a time period, if the fluidized bed rises up to the height of the discharge hole  94 , then the reduced iron is discharged through the discharge hole  94 . Here, the fluidized bed takes the form of a bubbling fluidized bed in which the reducing gas forms bubblings, and the bubblings grow while passing through the particle layer. 
     In the above described reducing furnace, however, in view of the productivity and economy, if the elutriation loss of the fine iron ore particles is to be diminished, if the gas consumption rate is to be minimized, and if the gas utilization degree is to be maximized, then the particle sizes of the raw iron ore particles have to be strictly limited. Accordingly, a fine iron ore having a wide particle size distribution cannot be handled. That is, the above described fluidized bed type furnace cannot treat an iron ore of a wide particle size distribution, but can use only 0-0.5 mm, 0.5-1 mm, 1-2 mm and the like. However, the actually available fine iron ore particles have a size of 8 mm or less. Therefore, if the naturally available fine iron ore is to be used, the fine iron ore has to be sorted by sieving, or it has to be crushed into the rated sizes. The result is that the productivity is lowered, and the production cost is increased, because it requires additional process steps and additional facilities. 
     In an effort to solve this problem, Korean Patent No. 117065 (1997) proposes a 3-stage fluidized bed type reducing apparatus having tapered furnaces as shown in FIG.  2 . In this apparatus, a stable fluidizing of an iron ore of a wide particle size distribution is aimed at, and for this purpose, tapered furnaces are employed. Further, in order to improve the reduction rate and the gas utilization rate, first the iron ore is pre-heated, second pre-reduced and then finally reduced, thereby forming a 3-stage reducing process. That is, as shown in FIG. 2, an upper reaction vessel  10  pre-heats the iron ore in a bubbling fluidizing state. A middle reaction vessel  20  pre-reduces the iron ore in a bubbling fluidizing state. A lower reaction vessel  30  finally reduces the pre-reduced iron ore in a bubbling fluidizing state, thereby completing a continuous 3-stage fluidized bed type process. 
     In FIG. 2, reference codes  40 ,  50  and  60  indicate cyclones, reference code  70  indicates a hopper, and  80  indicates a melter-gasifier. 
     In this 3-stage tapered fluidized bed type reducing furnace, an iron ore of a wide particle size distribution can be stably fluidized, and the reduction degree and the gas utilization degree can be considerably improved, compared with the conventional single type cylindrical fluidized bed type furnace. However, this furnace employs 3 stages, and therefore, the facility cost is very high. Further, if a problem occurs in any one of the plurality of the reaction vessels, then other reaction vessels are affected, with the result that the total process is adversely affected. Thus if an abnormal phenomenon such as defluidizing or channelling occurs which is actually very frequent, then the fine iron ore particles drop through the holes of the gas distributor to be agglomerated at the bottom of the reaction chamber. Therefore, the gas flow is impeded, and this cannot be prevented. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to overcome the above described disadvantages of the conventional techniques. 
     Therefore, it is an object of the present invention to provide a 2-stage fluidized bed fine iron ore reducing apparatus, and a reducing method using the apparatus, in which the degree of utilization of the reducing gas is increased, an iron ore of a wide particle size distribution can be reduced in an efficient and economical manner, and fine iron particles dropping through the holes of a gas distributor can be circulated back into the fluidized bed furnace, thereby preventing an impediment of the reducing gas flow due to abnormalities such as defluidizing or channeling. 
     In achieving the above object, the 2-stage fluidized bed type apparatus for drying, pre-heating and pre-reducing a fine iron ore in a first fluidized bed type furnace, and for finally reducing the fine iron ore (thus pre-reduced) in a second fluidized bed type furnace according to the present invention includes: 
     a first tapered fluidized bed type furnace for receiving a raw fine iron ore and a reducing gas to form a turbulent or bubbling fluidized bed so as to pre-heat and pre-reduce the raw iron ore; 
     a first cyclone for separating fine iron ore particles from a discharge gas of the first fluidized bed type furnace to recycle the separated fine iron ore particles into the first fluidized bed type furnace, the separated discharge gas of the first fluidized bed type furnace being discharged to external atmosphere; 
     a second fluidized bed type furnace for finally reducing the fine iron ore (thus pre-heated and pre-reduced) of the first fluidized bed type furnace, by forming a bubbling or turbulent fluidized bed by utilizing a discharge gas (reducing gas) of a melter-gasifier; 
     a second cyclone for separating fine iron ore particles from a discharge gas of the second fluidized bed type furnace to recycle the fine iron ore particles into the bottom of the second fluidized bed type furnace, the separated discharge gas of the second fluidized bed type furnace being supplied to the first fluidized bed type furnace as a reducing gas; 
     a first intermediate hopper positioned between the first and second fluidized bed type furnaces, for storing fine iron ore particles (dropped through the holes of a gas distributor of the first fluidized bed type furnace) to recycle them into the lower portion of the second fluidized bed type furnace; and 
     a second intermediate hopper positioned beneath the second fluidized bed type furnace, for storing fine iron ore particles (dropped through the holes of a gas distributor of the second fluidized bed type furnace) to recycle them into the lower portion of the second fluidized bed type furnace. 
     In another aspect of the present invention, the method for reducing a fine iron ore by using the above reducing apparatus according to the present invention is characterized in that: a first fluidized bed type furnace dries, pre-heats and pre-reduces the fine iron ore under a reducing atmosphere; a second fluidized bed type furnace finally reduces the pre-reduced fine iron ore; a hopper and a gas/solid particle sealing valve are installed beneath each of the fluidized bed type furnaces; and the fine iron ore particles dropping through the holes of the gas distributors during an abnormality of operation are circulated back into the fluidized bed type furnaces, whereby impediment of the gas flow is avoided. 
    
    
     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 illustrates a conventional single stage fluidized bed type furnace; 
     FIG. 2 illustrates the conventional 3-stage fluidized bed type furnace; and 
     FIG. 3 illustrates the 2-stage fluidized bed type fine iron ore reducing furnace according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 3, the 2-stage fluidized bed type fine iron ore reducing apparatus according to the present invention includes: 
     a first tapered fluidized bed type furnace  100  for receiving raw fine iron ore from a hopper  700  and for receiving a reducing gas to form a turbulent or bubbling fluidized bed so as to pre-heat and pre-reduce the raw iron ore; 
     a first cyclone  300  for separating fine iron ore particles from a discharge gas of the first fluidized bed type furnace  100  to recycle the fine iron ore particles into the first fluidized bed type furnace  100 , the separated discharge gas of the first fluidized bed type furnace being discharged to the external atmosphere; 
     a second fluidized bed type furnace  200  for finally reducing the fine iron ore (thus pre-heated and pre-reduced) of the first fluidized bed type furnace  100 , by forming a bubbling or turbulent fluidized bed by utilizing a discharge gas (reducing gas) of a melter-gasifier  800 ; 
     a second cyclone  400  for separating fine iron ore particles from an exhaust gas of the second fluidized bed furnace  200  to recycle the fine iron ore particles into the bottom of the second fluidized bed furnace  200 , the separated discharge gas of the second fluidized bed furnace  200  being supplied to the first fluidized bed furnace  100  as a reducing gas; 
     a first intermediate hopper  500  positioned between: the first and second fluidized bed type furnaces  100  and  200 , for storing fine iron ore particles (dropped through the holes of a gas distributor  102  of the first fluidized bed type furnace  100 ) to recycle them into the lower portion of the second fluidized bed type furnace  200 ; and 
     a second intermediate hopper  600  positioned beneath the second fluidized bed type furnace  200 , for storing fine iron ore particles (dropped through the holes of a gas distributor  202  of the second fluidized bed type furnace  200 ) to recycle them into the lower portion of the second fluidized bed type furnace  200 . 
     The first fluidized bed type furnace  100  includes a lower tapered portion  100   a  and an upper cylindrical portion  100   b . Further, a first gas supply hole  101  is formed on the lower portion of the furnace  100   a , for receiving a reducing gas, and within the lower portion of the furnace  100   a , there is installed a first gas distributor  102 . Further, a first iron ore discharge hole  106  is formed on the side wall of the tapered portion, and the first iron ore discharge hole  106  communicates through a second pipe  103  to the lower portion of the second fluidized bed type furnace  200 . 
     Further, an iron ore supply hole  105  is formed on the side wall of the tapered portion  100   a , and the iron ore supply hole  105  is connected through a first pipe  701  to a hopper  700  to supply the fine iron ore into the first fluidized bed type furnace  100 . Further, a first gas discharge hole  107  is formed on the top of the furnace  100 , and this first gas discharge hole  107  communicates through a third pipe  301  to the upper portion of the first cyclone  300 . 
     The first cyclone  300  separates the fine iron ore particles from the discharge gas of the first fluidized bed furnace  100 . On the bottom of the first cyclone  300 , there is connected a fourth pipe  302  through which the separated fine iron ore particles are circulated back to the lower portion of the first fluidized bed furnace  100 . A fifth pipe  303  is connected to the top of the first cyclone  300  which finally exhausts the discharge gas from the first fluidized bed furnace  100 . 
     The fourth pipe  302  is deeply buried into the first fluidized bed type furnace  100  to recycle the separated fine iron ore particles deeply into the first fluidized bed type furnace  100 . 
     The second fluidized bed type furnace  200  includes a lower tapered portion  200   a  and an upper cylindrical portion  200   b . A second gas supply hole  201  is formed on the lower portion of the tapered portion  200   a , for receiving a reducing gas, and a gas distributor  202  is disposed in the lower portion of the tapered portion  200   a . 
     A second iron ore discharge hole  206  is formed on the side wall of the tapered portion  200   a , and the second iron ore discharge hole  206  communicates through an eighth pipe  203  into the melter-gasifier  800 . 
     Further, a pre-reduced iron ore supply hole  205  is formed on the side wall of the tapered portion  200   a , and the pre-reduced iron ore supply hole  205  is connected through the second pipe  103  to the first fluidized bed type furnace  100  to receive the dried, pre-heated and pre-reduced iron ore into the second fluidized bed type furnace  200 . A second gas discharge hole  207  is formed on the top of the furnace  200 , and this second gas discharge hole  207  communicates through a 10th pipe  401  to the second cyclone  400 . 
     The second cyclone  400  separates the fine iron ore particles from the discharge gas of the second fluidized bed type furnace  200 . A 9th pipe  402  is connected from the bottom of the second cyclone  400  to the lower portion of the furnace  200 , for circulating the separated fine iron ore particles into the furnace  200 . A 6th pipe  403  is connected to the top of the second cyclone  400 , for supplying the discharge gas of the second fluidized bed type furnace  200  to the first fluidized bed type furnace  100 . 
     The 9th pipe  402  should be preferably buried deeply into the second fluidized bed type furnace  200  to recycle the separated fine iron ore particles deeply into its interior. 
     The first intermediate hopper  500  is disposed between the first fluidized bed type furnace  100  and the second fluidized bed type furnace  200 . The hopper  500  is connected through a seventh pipe  502  to the bottom of the first fluidized bed type furnace  100 , and is connected through an 11th pipe  504  into the second fluidized bed type furnace  200 . 
     On the 7th pipe  502  and the 11th pipe  504 , there are installed one or more of gas/solid sealing type high temperature valves  501  and  503 . In this way, during an emergency situation such as a sudden stop of operation or the like, the fine iron ore particles which have been dropped through the holes of the gas distributor  102  of the first fluidized bed type furnace  100  can be temporarily stored, and then transported by an inactive gas such as nitrogen into the second fluidized bed type furnace  200 . 
     The 11th pipe  504  should be preferably deeply buried into the second fluidized bed type furnace  200 , and thus, the fine iron ore particles which have been dropped through the holes of the gas distributor  102  of the first fluidized bed type furnace  100  can be recycled deeply into the second fluidized bed type furnace  200 . 
     The second intermediate hopper  600  is disposed beneath the second fluidized bed type furnace  200 , and is connected through a 13th pipe  602  to the bottom of the second fluidized bed type furnace  200 , while the hopper  600  is connected through a 12th pipe  604  to the lower portion of the second fluidized bed type furnace  200 . 
     On the 13th pipe  602  and the 12th pipe  604  (i.e., upstream and downstream of the hopper  600 ), there are installed one or more gas/solid sealing type high temperature valves  601  and  603 . In this way, during an emergency situation such as a sudden stop of operation or the like, the fine iron ore particles which have been dropped through the holes of the gas distributor  202  of the second fluidized bed type furnace  200  can be temporarily stored, and then transported by an inactive gas such as nitrogen into the second fluidized bed type furnace  200 . 
     Now the method for reducing a fine iron ore by using the above described reducing apparatus will be described. 
     A fine iron ore which is supplied to the first fluidized bed type furnace  100  is pre-heated and pre-reduced by using a discharge gas (reducing gas) of the second fluidized bed type furnace  200 , while forming a bubbling or turbulent fluidized bed. The iron ore thus reacted is transferred through a second pipe  103  to the lower portion of the second fluidized bed type furnace  200 . Then a final reduction occurs within the second fluidized bed type furnace  200  by forming a bubbling fluidized bed by using a discharge gas (a discharge gas of the melter-gasifier) which is supplied through the second gas supply hole  201 . The finally reduced iron is discharged through the second iron ore discharge hole  206 . The fine iron ore particles which are entrained in the discharge gas of the first fluidized bed type furnace  100  are separated from the gas by the first cyclone  300  to be circulated back to the lower portion of the first fluidized bed type furnace  100 . The fine iron ore particles which are entrained in the discharge gas of the second fluidized bed type furnace  200  are separated from the gas by the second cyclone  400  to be circulated back to the lower portion of the second fluidized bed type furnace  200 . 
     In the present invention, if an abnormality such as defluidizing or channelling occurs during the operation of the fluidized bed type furnaces, the fine iron ore particles drop through the holes of the gas distributor to impede the flow of the reducing gas. Therefore, periodically during the operation and at an emergency such as the blocking of the reducing gas, first the high temperature valves  501  and  601  (upstream of the first and second intermediate hoppers  500  and  600 ) are opened. Thus the fine iron ores which are accumulated beneath the gas distributors of the first and second fluidized bed type furnaces  100  and  200  are transferred to the first and second intermediate hoppers  500  and  600 , respectively, to be stored there. Then the upstream valves  501  and  601  are closed, and the valves  503  and  603  (downstream of the first and second intermediate hoppers  500  and  600 ) are opened. Then an inactive gas such as nitrogen is injected to circulate back the stored iron ore into the second fluidized bed type furnace  200 . 
     When the 2-stage fluidized bed type reducing furnace is used to reduce a fine iron ore, the pre-heating and the pre-reducing within the first fluidized bed type furnace  100  should be carried out preferably at 700-850° C., and the final reaction within the second fluidized bed type furnace  200  should be carried out preferably at 750-900° C. The operating pressure should be preferably 1-5 atmospheres in the absolute pressure. The superficial gas velocity right above the gas distributors within the first and second fluidized bed type furnaces  100  and  200  should be preferably 1.2-2.5 times as fast as the minimum fluidization velocity of the fine iron ore staying within the furnaces, in view of the efficient fluidizing and the elutriation loss of the iron ore particles. The angle of the tapered portions should be preferably 5-20° C. relative to the vertical line. The height of the tapered portions  100   a  and 200 a  above the gas distributors should be preferably 5-10 times as large as the diameter of the gas distributors. The height of the cylindrical portions  100   b  and  200   b  should be preferably 3-5 times as large as their own inner diameter. 
     Now the present invention will be described in detail based on an actual example. 
     EXAMPLE 
     A reduction of a fine iron ore was carried out by using a reducing apparatus having a size as shown in Table 1 and at conditions set forth in Tables 2 to 4. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Height and ID of fluidized bed type furnace 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 First fluidized 
                 ID of tapered portion (at the surface 
               
               
                   
                 bed type furnace 
                 of gas distributor): 0.6 m 
               
               
                   
                   
                 Angle of tapered portion: 5° 
               
               
                   
                   
                 Height of tapered portion (from 
               
               
                   
                   
                 gas distributor): 3 m 
               
               
                   
                   
                 ID of cylindrical portion: 1.1 m 
               
               
                   
                   
                 Height of cylindrical portion: 3.5 m 
               
               
                   
                 Second fluidized 
                 ID of tapered portion (at the surface 
               
               
                   
                 bed type furnace 
                 of gas distributor): 0.6 m 
               
               
                   
                   
                 Angle of tapered portion: 5° 
               
               
                   
                   
                 Height of tapered portion (from 
               
               
                   
                   
                 gas distributor): 3 m 
               
               
                   
                   
                 ID of cylindrical portion: 1.1 m 
               
               
                   
                   
                 Height of cylindrical portion: 3.5 m 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Chemical composition and particle size distribution of the iron ore 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1. Chemical composition: 
                 62.17 of T.Fe, 
               
               
                   
                   
                 0.51 of FeO, 
               
               
                   
                   
                 5.5 of SiO 2 , 
               
               
                   
                   
                 0.11 of TiO 2 , 
               
               
                   
                   
                 0.05 of Mn, 0.012 of S, 
               
               
                   
                   
                 0.65 of P, 
               
               
                   
                   
                 2.32 of moisture 
               
               
                   
                 2. particle size distribution: 
                 4.6% of −0.05 mm, 
               
               
                   
                   
                 5.4% of 0.05-0.15 mm, 
               
               
                   
                   
                 16.8% of 0.15-0.5 mm, 
               
               
                   
                   
                 59.4% of 0.5-4.75 mm, 
               
               
                   
                   
                 13.8% of 4.75-8 mm 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Ingredients, temperature and pressure of reducing gas 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. Gas ingredients: 
                 65% of CO, 25% of H 2 , 5% of CO 2 , 
               
               
                   
                 5% of N 2   
               
               
                 2. Temperature: 
                 800° C. for pre-heating and pre-reducing 
               
               
                   
                 850° C. for final reduction 
               
               
                 3. Pressure: 
                 1.8 Kgf/cm 2  for pre-heating and pre-reducing 
               
               
                   
                 2.0 Kgf/cm 2  for final reduction 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Superficial Gas velocity in fluidized bed type furnace 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 First fluidized 
                 Velocity at the surface of gas 
               
               
                   
                 bed type furnace 
                 distributor: 1.4 m/s 
               
               
                   
                   
                 Velocity in cylindrical portion 
               
               
                   
                   
                 (superficial velocity): 0.4 m/s 
               
               
                   
                 Second fluidized 
                 Velocity at the surface of gas 
               
               
                   
                 bed type furnace 
                 distributor: 1.4 m/s 
               
               
                   
                   
                 Velocity in cylindrical portion 
               
               
                   
                   
                 (superficial velocity): 0.4 m/s 
               
               
                   
                   
               
             
          
         
       
     
     After reducing the fine iron ore by using the above specified apparatus and at conditions set forth in the above tables, the average gas utilization degree and the gas consumption rate were evaluated. The result showed that the gas utilization degree was about 30-35%, and the gas consumption rate was 1200-1500 Nm 3 /ton-ore. Further, the reduction rates of the reduced irons which were discharged through the first and second discharge holes were respectively 30-40% and 85-95%. The iron ore discharge was possible after 60 minutes from feeding the iron ore through the hopper. This shows that the reducing speed is very excellent. 
     According to the present invention as described above, intermediate hoppers and gas/solid sealing valves are installed beneath the fluidized bed type furnaces. Thus the fine iron ore particles which drop through the holes of the gas distributors during an abnormality of operation can be circulated back to the fluidized bed type furnaces. Therefore, the flow of the reducing gas is never impeded, and therefore, the operation can be carried out for a long time without a halt. 
     Further, with only the 2-stage process, the present invention ensures a sufficient reduction rate and a superior gas consumption rate, and is not inferior to Korean Patent 117065 (1997). Further, the present invention is superior over Korean Patent 117065 (1997) in the facility cost and the production cost. 
     Further, in the present invention, a relatively uniformly reduced iron can be obtained regardless of the particle sizes of the iron ore. Further, the discharge amounts and particle sizes can be adjusted for the respective discharge holes, and the reduction rate can be adjusted by controlling the residence time of the iron ore within the furnace.