AU1693499A

AU1693499A - Complex fluidized bed type fine iron ore reducing apparatus, and method therefor

Info

Publication number: AU1693499A
Application number: AU16934/99A
Authority: AU
Inventors: Sun Kwang Jeong; Heung Won Kang; Hang Goo Kim; Il Ock Lee
Original assignee: Voest Alpine Industrienlagenbau GmbH; Research Institute of Industrial Science and Technology RIST; Pohang Iron and Steel Co Ltd
Current assignee: Primetals Technologies Austria GmbH; Research Institute of Industrial Science and Technology RIST; Posco Holdings Inc
Priority date: 1998-12-22
Filing date: 1998-12-22
Publication date: 2000-07-12
Also published as: CA2322130A1; EP1060273A1; WO2000037687A1; JP2002533642A

Description

WO 00/37687 PCT/KR98/00451 COMPLEX FLUIDIZED BED TYPE FINE IRON ORE REDUCING APPARATUS, AND METHOD THEREFOR FIELD OF THE INVENTION 5 The present invention relates to a fluidized bed type reducing apparatus and a reducing method, in which a fine iron ore of a wide particle size distribution is reduced by fluidized bed type furnaces into directly reduced iron of 85% or more of reduction degree, so that a melter 10 gasifier can melt it to manufacture a molten iron. More specifically, the present invention relates to a complex fluidized bed type fine iron ore reducing apparatus and a reducing method, in which a high temperature reducing gas having 60~100% of CO + H2 at 800-900 0 C is utilized in the 15 consideration of the wide particle size distribution, the degradation and the reducibility at a high temperature, so that the reaction rate of the solid fine iron ore, the gas utilization degree and the gas consumption rate can be most advantageously improved, thereby making it possible 20 to achieve a good economy and the optimum operation. BACKGROUND OF THE INVENTION Generally, the iron particles used in the blast furnace are of large size, and therefore, the iron ore 25 can be reduced with the fixed bed type furnaces. In the case of a fine iron ore, if the gas velocity is very slow like that in the fixed bed type furnace, sticking may occur, and therefore, the operation may be interrupted. Therefore, in the case of a fine iron ore, the fluidized 30 bed type furnaces are necessarily used in order to ensure a good gas permeability and a brisk movement of fine iron ore particles in the bed. Japanese Utility Model Gazette Sho-58-217615 is an WO 00/37687 PCT/KR98/00451 2 example of the fluidized bed type furnace which is for reducing a fine iron ore. This fluidized bed type furnace is divided into a cylindrical reducing furnace and a cyclone. The cylindrical reducing furnace includes: a 5 raw iron ore charging inlet; a reducing gas inlet for introducing a reducing gas; and a discharging outlet for discharging a reduced iron ore. Within the lower portion of the reducing furnace, there is installed a gas distributor. The reducing gas is introduced through gas 10 distributor, while the fine iron ore is fed through the charging inlet. Then the iron ore is reacted with the reducing gas while being agitated. When the fluidized bed level reached a out level after a certain time, the reduced iron ore is discharged through the outlet. Here, 15 the form of the fluidized bed is such that the reducing gas forms bubbles above the gas distributor, and that the bubbles pass through an iron ore particle layer while increasing in their size. In order to improve the economy and the productivity, 20 this conventional fluidized bed type furnace aims at reducing the elutriation loss of the fine iron ore out of the furnace, at minimizing the gas consumption rate, and at maximizing the gas utilization degree. For this purpose, the particle size is sternly restricted, and 25 therefore, it cannot cope with an iron ore having a wide particle size distribution. That is, the particle size distribution cannot be wide, but should be limited to 0 0.5 mm, 0-1 mm, or 1-2 mm. However, in reality, the particle size of the raw fine iron ore in the world is 30 mostly 8 mm or less. Therefore, the raw iron ore has to be screened by means of a sieve to exclude the coarse particles, or the iron ore has to be crushed. As a result, the production rate is lowered, and the WO 00/37687 PCT/KR98/00451 3 additional process and facilities are required, thereby aggravating the economy. Meanwhile, in an attempt to overcome the above described disadvantages, Korean Patent No. 074056 5 discloses a twin type fluidized bed furnaces for reducing fine iron ore. FIG. 1 illustrates the twin type fluidized bed reducing furnace. As shown in FIG. 1, the twin type fluidized bed reducing furnace includes: a first 10 fluidized bed furnace 10 for reducing a coarse iron ore; a second fluidized bed furnace 20 for reducing medium/fine iron ores; and a cyclone 30 for capturing extremely fine iron ore particles. A reducing gas supplying hole 11 is formed on the 15 bottom of the first fluidized bed furnace 10, and a gas distributor 12 is installed in the lower part of the furnace 10. Further, a first discharging hole 13 is formed on a side wall of the furnace 10, and a second discharging hole 15 is formed on an upper portion of the 20 side wall of the furnace 10. The second discharging hole 15 is connected through a first conduit 16 to a lower portion of the second fluidized bed furnace 20. Further, an iron ore supplying hole 14 is formed on a lower portion of the other side of the first furnace 10. 25 Further, a reducing gas supplying hole 21 is formed on the bottom of the second fluidized bed furnace 20, and a gas distributor 22 is installed within the lower portion of the furnace 20. A third discharging hole 23 is formed on a side of the furnace 20, and the top of the furnace 30 20 is connected to the cyclone 30. The bottom of the cyclone 30 is connected through a 6th conduit 35 to a lower portion of the furnace 20. A gas discharging hole 33 is formed on the top of the cyclone 30 so as to exhaust WO 00/37687 PCT/KR98/00451 4 the gas. The reducing process using the above described twin type fluidized bed furnaces will be described below. That is, a fine iron ore is supplied through the 5 iron ore supplying hole 14 into the first fluidized bed furnace 10, Under this condition, a reducing gas is supplied through the first reducing gas supplying hole 11, and the gas velocity of the reducing gas is adjusted, so that only the coarse iron ore particles would remain 10 within the first fluidized bed furnace 10. In this manner, a bubbling or turbulent fluidized bed is formed, and the coarse particles are reduced within the fluidized bed of the first furnace 10. Meanwhile, the medium/fine iron ore particles are 15 carried(elutriated) through the first conduit 16 into the second fluidized bed furnace 20. Within the second furnace 20, a reducing gas is supplied through the second gas supplying hole 21 into the second furnace 20 so as to form a bubbling or turbulent fluidized bed. Therefore, 20 the medium/fine iron ores are reduced by the turbulent fluidized bed within the second furnace 20. In this apparatus of Korean Patent No. 074056, the iron ore is reduced after being separated into the coarse iron ore and the medium/fine iron ores by adjusting the 25 gas velocity. In this apparatus, a fine iron ore having a wide particle size distribution is stabilized, and the concentrations of the iron ore are made uniform in the fluidized bed. Therefore, by the separation the reduction degree can be improved, and the particle 30 elutriation loss can be decreased, while the gas consumption rate is also decreased. However, in this conventional twin type fluidized bed furnace, since the two furnaces, i.e., the first and WO 00/37687 PCT/KR98/00451 5 second fluidized bed reducing furnaces 10 and 20 are used and the reducing gas which also serves as a heating means is divided into two streams, the heat loss is very high accordingly. As a result, the heat supply to the 5 furnaces is insufficient, and therefore, additional heat has to be supplied for supplement. Furthermore, a large space is required compared with the conventional single type fludized bed furnace. 10 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 15 provide a complex fluidized bed type apparatus for reducing a fine iron ore, and a method therefore, in which the reactivity of the fine iron ore particles, the gas utilization degree and the gas consumption rate are most efficiently optimized by taking into account the particle 20 size distribution, and the degradation and the reducibility at a high temperature, thereby making it possible to reduce a fine iron ore of a wide particle size distribution in an optimal manner. In achieving the above object, the complex fluidized 25 bed type apparatus for reducing a fine iron ore according to the present invention includes: first and second fluidized bed furnaces and a cyclone, with a gas distributor being installed in the lower portion of each of the furnaces, and with a reducing gas supplying hole 30 being formed on the bottom of each of them; the fine iron ore being separated into coarse iron ore particles and medium/fine iron ore particles within the first fluidized bed furnace, the coarse iron ore particles being reduced WO 00/37687 PCT/KR98/00451 6 within the furnace; the medium /fine iron ore particles being transported through a second discharging hole into the second fluidized bed furnace so as to be reduced while forming a fluidized bed, before being discharged through 5 an iron ore discharging hole; and the cyclone separating extremely fine iron ore particles from a exhaust gas of the second fluidized bed furnace to circulate the fine iron ore particles back to the second fluidized bed furnace, 10 characterized in that: the first fluidized bed furnace is installed within a freeboard zone (upper portion of the second fluidized bed furnace) within the second fluidized bed furnace; the second discharging hole for discharging the medium/fine iron ore particles and the 15 gas from the first fluidized bed furnace is connected through a first conduit into a lower portion of the second fluidized bed furnace; and the cyclone is connected from its bottom through a 6th conduit (which passes through an upper portion of the second fluidized bed furnace) into 20 the lower portion of the second fluidized bed furnace. In the method for reducing a fine iron ore using a complex fluidized bed type apparatus, the gas velocity within the first fluidized bed furnace is 1.2-2.5 times as fast as the minimum fluidization velocity of the iron ore 25 staying within the furnace. Further, the gas velocity within the second fluidized bed furnace is 1.2-1.8 times as fast as the minimum fluidization velocity of the iron ore staying within the furnace. 30 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 WO 00/37687 PCT/KR98/00451 7 with reference to the attached drawings in which: FIG. 1 illustrates the conventional twin type fluidized bed furnaces for reducing fine iron ore; and FIG. 2 illustrates the constitution of the complex 5 fluidized bed apparatus for reducing a fine iron ore according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The complex fluidized bed type apparatus for reducing 10 a fine iron ore according to the present invention includes: a complex fluidized bed furnace consisting of first and second fluidized bed furnaces 100 and 200, the first furnace 100 being for separating the fine iron ore into coarse iron ore particles and medium/fine iron ore 15 particles and for reducing the coarse iron ore particles while forming a bubbling fluidized bed; the second furnace 200 being for reducing the medium/fine iron ore particles transported from the furnace 100 while forming a bubbling fluidized bed; and a cyclone 300 for separating the 20 extremely fine iron ore particles from a exhaust gas of the second fluidized bed furnace 200 to circulate the fine particles back to the second fluidized bed furnace 200. The first fluidized bed furnace 100 is installed within the second fluidized bed furnace 200, so that the heat 25 loss and the installation space can be drastically decreased. FIG. 2 illustrates the constitution of the complex fluidized bed type apparatus for reducing a fine iron ore according to the present invention. 30 As shown in this drawing, the apparatus for reducing a fine iron ore according to the present invention includes: a first fluidized bed furnace 100 installed within a freeboard zone above a fluidized bed of WO 00/37687 PCT/KR98/00451 8 medium/fine iron ore particles within a second fluidized bed furnace 200, for separating the fine iron ore into coarse iron ore particles and medium/fine iron ore particles by the means of an adjusted gas velocity in the 5 furnace 100, to reduce the coarse particles remained within the first fluidized bed furnace 100 while forming a bubbling or turbulent fluidized bed by a reducing gas supplied through a first gas supplying hole 101, and to transport the medium/fine particles through a first 10 conduit 106 into a lower portion of the second fluidized bed furnace 200; the second fluidized bed furnace 200 being for reducing the medium/fine iron ore particles (transported from the first fluidized bed furnace with a exhaust gas) by a reducing gas of a low gas velocity 15 supplied through a second gas supplying hole 201 while forming a bubbling or turbulent fluidized bed; and a cyclone 300 for separating the extremely fine iron ore particles from a exhaust gas of the second fluidized bed furnace 200 to circulate the fine particles back to the 20 second fluidized bed furnace 200. The first fluidized bed furnace 100 has an approximately cylindrical shape, and has a first gas supplying hole 101 on its bottom. A gas distributor 102 is installed within the lower portion of the furnace 100. 25 The side wall of the furnace 100 has a first discharging hole 103 which is connected to a third conduit 108. On another side of the furnace 100, there is formed an iron ore supplying hole 104 which is connected to a second conduit 107. Above the hole 104, there is formed a 30 second discharging hole 105 for discharging the iron ore and the gas, and the hole 105 is connected through a first conduit 106 into the lower portion of the second fluidized bed furnace 200.

WO 00/37687 PCT/KR98/00451 9 The second fluidized bed furnace 200 consists of two cylindrical parts, a wide upper portion and a narrow lower portion. That is, the second furnace 200 includes: an expanded portion 200c having a large inner diameter, 5 a narrow portion 200a having a small inner diameter, and a tapered portion 200b for connecting the expanded portion 200c to the narrow portion 200a. Within the narrow portion 200a, the iron ore particles are made to move briskly by the help of the bubbling gas flow, and in this 10 manner, the gas utilization degree is improved. Further, owing to the large diameter of the expanded portion 200c, the flying of the extremely fine iron ore particles are slowed, thereby inhibiting the elutriation loss of the particles. 15 A second gas supplying hole 201 is formed on the bottom of the narrow portion 200a, for receiving the reducing gas. Further, a second gas distributor 202 is installed within the lower portion of the narrow portion 200a. On a side of the furnace 200, there is formed a 20 third discharging hole 203 which is connected to a 5th conduit 205 for discharging the reduced iron ore. A fourth discharging hole 204 is formed on the top of the expanded portion 200c, and from this top, a 7th conduit 306 extends to the cyclone 300. 25 The cyclone 300 separates the extremely fine iron ore particles from the exhaust gas of the second fluidized bed furnace 200, the exhaust gas being introduced through the 7th conduit 306 into the inlet 301. These separated particles are circulated back into the lower portion of 30 the furnace 200. For this purpose, a 6th conduit 305 is connected into a hole 302. On the top of the cyclone 300, there is formed a gas discharging hole 303 which is connected to a discharge pipe 304 to discharge the exhaust WO 00/37687 PCT/KR98/00451 10 gas to the external atmosphere after its reducing reaction. In the meantime, the height of the first fluidized bed furnace 100 above the distributor 102 should be 5 preferably 10 - 15 times as large as its inner diameter. The reason is as follows. That is, if its height is less than 10 times as large as its inner diameter, the fluidizing of the iron ore within the furnace cannot be smoothly carried out, with the result that even 10 medium/coarse iron particles are flown to be sent to the second fluidized furnace. On the other hand, if its height is more than 15 times as large as its inner diameter, then the elutriation loss of the fine iron ore is very large. The height of the narrow portion 200a above the 15 distributor 202 should be preferably 5 - 10 times as large as its inner diameter, so that a sufficient fluidizing space can be secured, and that the elutriation loss of the fine iron ore can be lowered. The height of the expanded portion 200c should be 20 preferably 2 - 4 times as large as its inner diameter, so that the gas velocity can be reduced within the furnace while lowering the elutriation loss of the fine iron ore. The first fluidized bed furnace 100 should be installed within the freeboard zone of the second 25 fluidized bed furnace 200. Further, the bottom of the first furnace 100 should be preferably placed at a position higher than the third iron ore discharging hole 203. Now the method for reducing the fine iron ore by 30 using the complex fluidized bed type reducing apparatus according to the present invention will be described. The reducing gas which is supplied into the first fluidized bed furnace 100 is maintained at a gas velocity WO 00/37687 PCT/KR98/00451 11 higher than the terminal velocity of medium size iron ore particles, and thus, the raw fine iron ore which is supplied into the first fluidized bed furnace 100 is separated into coarse iron ore particles and medium/fine 5 iron ore particles. The coarse iron ore particles are remained within the first fluidized bed furnace 100, so that they will be reduced while forming a bubbling or turbulent fluidized bed. The medium/fine particles are carried through the first conduit 106 into the lower 10 portion of the second fluidized bed furnace 200. These particles are reduced by a reducing gas (which is supplied through the second gas supplying hole 201), while forming a bubbling fluidized bed. Then the reduced iron ores are discharged through the first discharge hole 103 and the 15 third discharge hole 203 respectively. The extremely fine iron ore particles which are loaded in the exhaust gas of the second fluidized bed furnace 200 are supplied through the 7th conduit 306 into the cyclone 300. The cyclone 300 separates the extremely fine particles from the exhaust 20 gas to circulate the extremely fine particles back to the second fluidized bed furnace 200. In the complex fluidized bed type reducing furnace of the present invention, the gas velocity within the first fluidized bed furnace 100 should be preferably 1.2 - 2.5 25 times as fast as the minimum fluidization velocity of the iron ore particles staying within the furnace, considering the fluidizing and elutriation. The gas velocity within the second fluidized bed type furnace 200 should be preferably 1.2 - 1.8 times as fast as the minimum 30 fluidization velocity of the iron ore particles. Now the present invention will be described based on an actual example.

WO 00/37687 PCT/KR98/00451 12 <Example> The reducing apparatus of FIG. 2 having the dimensions listed in Table 1 was used, and a tests were carried out at conditions set forth in Tables 2 to 4. 5 <Table 1> Heights and inner diameters of fluidized bed type furnaces First furnace Inner diameter: 0.2 m 10 Height: 3.0 m (above gas distributor) Second furnace ID of narrow portion: 0.5 m ID of expanded portion: 0.75 m Height of tapered portion: 4.0 m (above 15 gas distributor) Height of expanded portion: 2.5 m <Table 2> Chemical composition and particle size 20 distribution of raw fine iron ore Chemical composition: T.Fe: 62.17 wt% FeO: 0.51 wt% SiO2: 5.5 wt% 25 TiO 2 : 0.11 wt% Mn: 0.05 wt% S: 0.12 wt% P: 0.65 wt% Crystal water: 2.32 wt% 30 Particle size 0-0.05 mm: 4.6% distribution 0.05-0.15 mm: 5.4% 0.15-0.5 mm: 16.8% WO 00/37687 PCT/KR98/00451 13 0.5-4.75 mm: 59.4% 4.75-8 mm: 13.8% 5 <Table 3> Chemical composition, temperature and pressure of reducing gas Gas composition CO: 65%

H

2 : 25% 10 C0 2 : 5%

N

2 : 5% Temperature About 850 0 C 15 Pressure About 2.0 Kgf/cm 2 <Table 4> Superficial gas velocity within furnaces 20 First furnace Gas velocity: 3.0 m/s Second furnace Velocity within expanded portion: 0.14 m/s Gas velocity at dispersing plate: 0.32 m/s 25 After the reduction of the fine iron ore, the average gas utilization degree and the gas consumption rate were evaluated. The result showed that the gas 30 utilization degree was about 30 - 35%, and the gas consumption rate was 1200 - 1300 Nm 3 /ton-ore. Further, the reduced iron ores which were discharged through the first discharging hole 103 and the third discharging hole WO 00/37687 PCT/KR98/00451 14 203 showed a reduction degree of 88 - 95%. The fine iron ore particles showed somewhat higher reduction degree. The reduced iron ore could be discharged within 60 minutes after the feeding of the raw iron ore from the hopper, 5 thus it was seen that the production rate was excellent. Particularly, the internal temperature of the reaction chambers could be maintained at 850 0 C without any additional heat from the outside. 10 According to the present invention as described above, the reduction of the fine iron ore is carried out after segregation the particle sizes. Therefore, the gas consumption rate can be reduced like in the conventional method, but unlike in the conventional method, the heat 15 loss can be reduced, and a sufficient heat can be secured without any external heat, because the first fluidized bed furnace is installed within the second fluidized bed furnace. Thus the conventional problems can be solved, while the installation space can be decreased. 20 Further, an uniform reduction degree can be obtained regardless of the particle sizes, and the reduced fine iron ores of different particle size classes can be obtained. Therefore, when they are fed into a melting furnace, they can be fed through different feeding 25 devices. Further, the amount and particle sizes of the reduced iron ores which are discharged through each discharging hole can be controlled by the adjustment of the height of the second discharging hole and gas velocity. Further, the residence time of the iron ore can 30 be controlled, and therefore, the reduction degree can be controlled for the different particle sizes.

Claims

1. A complex fluidized bed type apparatus for reducing a fine iron ore, comprising: 5 first and second fluidized bed furnaces and a cyclone, with a gas distributor being installed in a lower portion of each of said furnaces, and with a reducing gas supplying hole being formed on a bottom of each of said furnaces; 10 the charged fine iron ore being separated into coarse iron ore particles and medium/fine iron ore particles within said first fluidized bed furnace, the coarse iron ore particles being reduced within the furnace while forming a bubbling fluidized bed ; 15 the medium /fine iron ore particles being supplied through a second discharging hole into said second fluidized bed furnace so as to be reduced while forming a bubbling fluidized bed, before being discharged through an iron ore discharging hole; and 20 said cyclone being for separating extremely fine iron ore particles from a exhaust gas of said second fluidized bed furnace to circulate the fine iron ore particles back to said second fluidized bed furnace, characterized in that: 25 said first fluidized bed furnace 100 is installed within a freeboard zone (upper portion of said second fluidized bed furnace 200) within said second fluidized bed furnace 200; said second discharging hole 105 for discharging the 30 iron ore and the gas from said first fluidized bed furnace 100 is connected through a first conduit 106 into a lower portion of said second fluidized bed furnace 200; and said cyclone 300 is connected from its bottom through WO 00/37687 PCT/KR98/00451 16 a 6th conduit 302 (passing through an upper portion of said second fluidized bed furnace 200) into a lower portion of said second fluidized bed furnace 200. 5

2. The complex fluidized bed type reducing apparatus as claimed in claim 1, wherein said second fluidized bed furnace 200 comprises: a tapered portion 200b; a narrow portion 200a having an inner diameter same as that of a lowermost portion of said tapered portion 10 200b; and an expanded portion 200c having an inner diameter same as that of an uppermost portion of said tapered portion 200b.

3. The composite fluidized bed type reducing 15 apparatus as claimed in any one of claims 1 to 2, wherein said first fluidized bed furnace 100 has a height above said distributor 102 10 - 15 times as large as its inner diameter. 20

4. The complex fluidized bed type reducing apparatus as claimed in any one of claims 1 to 2, wherein said narrow portion 200a of said second fluidized bed furnace 200 has a height above said distributor 202 5 - 10 times as large as its inner diameter, and said expanded 25 portion 200c has a height 2 - 4 times as large as its inner diameter.

5. The complex fluidized bed type reducing apparatus as claimed in claim 1, wherein said first 30 fluidized bed furnace 100 has a bottom disposed higher than a third discharging hole 203, said discharging hole 203 being for discharging a reduced iron ore from said second fluidized bed furnace 200. WO 00/37687 PCT/KR98/00451 17

6. A method for reducing a fine iron ore by using a complex fluidized bed type reducing apparatus of claim 1, characterized in that: 5 a gas velocity within a first fluidized bed furnace 100 is 1.2 - 2.5 times as fast as the fine iron ore staying within said furnace; and a gas velocity within a second fluidized bed furnace 200 is 1.2 - 1.8 times as fast as the fine iron ore 10 staying within said furnace.

7. The method as claimed in claim 6, wherein said second fluidized bed furnace 200 comprises: a tapered portion 200b; a narrow portion 200a having an inner 15 diameter same as that of a lowermost portion of said tapered portion 200b; and an expanded portion 200c having an inner diameter same as that of an uppermost portion of said tapered portion 200b. 20

8. The method as claimed in any one of claims 6 to 7, wherein said first fluidized bed furnace 100 has a height above said distributor 102 10 - 15 times as large as its inner diameter. 25

9. The method as claimed in any one of claims 6 to 7, wherein said narrow portion 200a of said second fluidized bed furnace 200 has a height above said distributor 202 5 - 10 times as large as its inner diameter, and said expanded portion 200c has a height 2 - 4 times as large as 30 its inner diameter.

10. The method as claimed in claim 6, wherein said first fluidized bed furnace 100 has a bottom disposed WO 00/37687 PCT/KR98/00451 18 higher than a third discharging hole 203, said discharging hole 203 being for discharging a reduced iron ore from said second fluidized bed furnace 200. 5 10 15 20 25 30