WO2003056039A1

WO2003056039A1 - An apparatus and method for recycling dust and sludge containing iron in ironmaking process using coal and fine ore

Info

Publication number: WO2003056039A1
Application number: PCT/KR2002/002370
Authority: WO
Inventors: Hang-Goo Kim; Heung-Won Kang; Sun-Kwang Jeong; Nag-Joon Choi
Original assignee: Posco Co Ltd; Research Institute of Industrial Science and Technology RIST
Current assignee: Research Institute of Industrial Science and Technology RIST; Posco Holdings Inc
Priority date: 2001-12-21
Filing date: 2002-12-17
Publication date: 2003-07-10
Anticipated expiration: 2004-06-21
Also published as: RU2260624C2; CN1509339A; KR20030055357A; CN1242075C; RU2003133738A; KR100584745B1

Abstract

An apparatus and method for recovering Zn component contained in dust and sludge by vaporization and Fe component in the form of molten iron by reduction to reduce cost of sludge treatment and to prevent environmental pollution. A plurality of raw material feed bins (110a, 110b and 110c) respectively store and discharge dust/sludge (which is dewatered, dried and crushed), binder and fine iron ore by fixed quantities. An agitator (100) mixes and agitates a certain quantity of dust/sludge, binder and fine iron ore fed from the raw material feed bins (110a, 110b and 110c). A pelletizer (90) coarsens raw material mixture from the agitator (100) into certain particle sizes of pellets. A drier (80) dries the pellets supplied from the pelletizer (90). A shaft furnace (70) is connected to the melter gasifier (40) via a fifth gas duct (44) for receiving the pellets from the drier (80) and vaporizing Zn component contained in the pellets by reduction gas, and includes a sixth gas duct (71) in an upper portion thereof for emitting exhaust gas containing vaporized Zn component and a screw feeder (72) for outwardly discharging reduced iron pellets which are reduced by reduction gas. A hot enclosed screen (60) sorts the reduced iron pellets discharged from the screw feeder (72) into large and small (disintegrated) ones according to particle sizes and has fifth and sixth ore ducts (61 and 62) for selectively feeding the sorted pellets into a melter gasifier (40) and a briquetting machine (50).

Description

AN APPARATUS AND METHOD FOR RECYCLING DUST AND SLUDGE CONTAINING

IRON IN IRONMAKING PROCESS USING COAL AND FINE ORE

Technical Field The present invention relates to recycling of dust and sludge produced in an ironworks which performs an ironmaking process using non-coking coal and fine iron ore, and more particularly, to an improved apparatus and method for recycling iron-containing dust and sludge, which recovers Zn component contained in dust and sludge via gasification and Fe component in the form of molten iron via reduction, thereby reducing cost of sludge treatment and preventing environmental pollution.

Background Art: Up to the present, the art has not developed yet any ironmaking process which exceeds a blast furnace process regarding energy efficiency or productivity. However, the blast furnace process generally depends on coke obtained through treatment of specific raw coal as a carbon source, which is used as fuel and reducing agent, and sintered ore obtained through agglomeration processes as an iron source.

As a result, the current blast furnace process necessarily accompanies pretreatment facilities such as coke producing and sintering facilities. However, establishment of such facilities consumes excessive amount of cost, whereas these facilities produce massive quantities of environmental contaminants such as SOx, NOx and dust, which confront more severe worldwide regulations. In order to overcome these regulations, massive treatment facilities are also invested thereby consuming excessive amount of cost. Accordingly, the current blast furnace is gradually losing its competitiveness.

Therefore, the nations of the world are making every endeavor to develop advanced ironmaking processes which can overcome the above-mentioned drawbacks of the blast furnace process. As one of the most prominent advanced ironmaking processes currently under development, the coal-based smelting reduction process directly uses non-coking coal as fuel and reducing agent and fine iron ore as iron source, which occupies about 80% or more of the worldwide ore yield. An iron making system related to such a technology which uses non-coking coal and fine iron ore is disclosed in US Patent No. 5,785,733, granted on July 28, 1998.

As shown in Fig. 1, the entire ironmaking system comprises a 3 fluidized-bed reduction furnaces having a preheating furnace 10, a pre-reduction furnace 20 and a final reduction furnace 30, and a melter gasifier 40 having a char bed.

According to this document, fine iron ore is continuously charged via a first ore duct 12 into the preheating furnace 10 where it is preheated by reduction gas fed via a third gas duct 21 while forming a bubbling or turbulence fluidized bed. In succession, fine iron ore preheated in the preheating furnace 10 is discharged via a second ore duct 22 into the preheating reduction furnace 20 where it is pre-reduced by reduction gas fed via a second gas duct 31 while forming a bubbling or turbulence fluidized bed. Pre-reduced fine iron ore is discharged via a third ore duct 32 into the final reduction furnace 30 where it is final-reduced by reduction gas fed via a first gas duct 41 while forming a bubbling or turbulence fluidized bed. Final-reduced fine iron ore is continuously discharged via a fourth ore duct 42 to a following process.

Fine iron ore which is final-reduced in the final reduction furnace 30 and discharged via the fourth ore duct 42 is supplied into a briquetting machine 50 where it is formed into Hot

Briquetted Iron (HBI) . HBI is charged via an HBI transport line 51 into the melter gasifier 40 where it is melted in a char bed to convert into molten pig iron or hot metal. Then, hot metal is discharged out of the melter gasifier 40.

Each of the first to fourth ore ducts 12, 22, 32 and 42 is provided with each of hot gas-tight valves 13, 23, 33 and 43 performing an opening/closing operation to regulate the flow of fine iron ore so that the flow of fine iron ore can be interrupted if necessary.

Non-coking coal lumps are continuously supplied via an opening in the upper portion of the melter gasifier 40 to form a certain height of char bed in the furnace. When oxygen is blown into the char bed via a plurality of tuyeres in a lower portion of the melter gasifier 40, char is burnt in the char beds.

The gas produced from the combustion of char, which becomes reducing gas in the fluidized bed, rises through the char bed to be discharged out of the melter gasifier 40. The discharged reduction gas passes through the first to third gas ducts 41, 31 and 21 in succession to feed each of the 3 fluidized bed reduction furnaces 10, 20 and 30, and then is finally dischsrged out of the process via the fourth gas duct 11. In the meantime, the ironmaking process using non-coking coal and fine iron ore produces large quantities of dust and sludge, which is dried and then injected into the melter gasifier 40 or the preheating furnace 10 without any further treatment. However, since dust/sludge has a extremely small particle size (maximum particle size of about several tens micrometer) , it is directly flown upward as soon as charged into the final reduction furnace 30 in which fine iron ore having a particle size (generally of about 10mm) relatively larger than that of dust/sludge are used. As a result, this process shows a low actual recovery rate and thus is ineffective.

Further, if dust/sludge contains a large quantity of Zn component, Zn component is vaporized at a high temperature of about 1000^°C or higher in the melter gasifier 40. Vaporized Zn component is re-oxidized and condensed into ZnO in the preheating furnace 10 which has a relatively low temperature of about 600 to 700°C. Condensed ZnO sticks to and grows on a furnace wall, thereby creating severe hindrance to the operation.

The present invention has been made to solve the foregoing problems of the prior art and it is therefore an object of the present invention to provide a recycling apparatus and method for iron-containing dust and sludge in an ironmaking process using non-coking coal and fine iron ore, which can raise recovery rate while preventing condensed Zn component from sticking to the furnace wall, thereby improving productivity.

Disclosure of the Invention

According to an aspect of the invention for realizing the above objects, it is provided a recycling apparatus for iron-containing dust and sludge in an ironmaking system using non-coking coal and fine iron ore which includes 3 fluidized-bed reduction furnaces having a preheating furnace, a pre-reduction furnace and a final reduction furnace, a melter gasifier with a char bed in side and a briquetting machine, the recycling apparatus comprising: a plurality of raw material feed bins for respectively storing dust/sludge (which is dewatered, dried and crushed) , binder and fine iron ore and discharging the same by fixed quantities; an agitator for mixing and agitating a certain quantity of dust/sludge, binder and fine iron ore fed from the raw material feed bins; a pelletizer for coarsening raw material mixture from the agitator into certain particle sizes of pellets; a drier for drying the pellets supplied from the pelletizer; a shaft furnace connected to the melter gasifier via a fifth gas duct for receiving the pellets from the drier and vaporizing Zn component contained in the pellets by reduction gas, wherein the shaft furnace includes a sixth gas duct in an upper portion thereof for exhausting exhaust gas containing vaporized Zn component and a screw feeder for outwardly discharging reduced iron pellets which are reduced via reduction gas; and a hot enclosed screen for sorting the reduced iron pellets discharged from the screw feeder into large and small ones according to particle sizes and having fifth and sixth ore ducts for selectively feeding the sorted pellets into the melter gasifier and the briquetting machine.

According to another aspect of the invention for realizing the above objects, it is provided a recycling method for iron-containing dust and sludge in an ironmaking process using non-coking coal and fine iron ore which includes 3 fluidized-bed reduction furnaces having a preheating furnace, a pre-reduction furnace and a final reduction furnace, a melter gasifier with a char bed inside and a briquetting machine. The recycling method comprises the following steps of: agitating, in an agitator, certain quantities of dust/sludge, binder and fine iron ore supplied from raw material feed bins; coarsening, in a pelletizer, raw material mixture supplied from the agitator into certain particle sizes of pellets; drying the pellets in a drier, charging the dried pellets into a shaft furnace, vaporizing Zn component contained in the charged pellets by reduction gas fed through a fifth gas duct of a melter gasifier, exhausting Zn component on exhaust gas, and outwardly discharging reduced iron pellets reduced via reduction gas with a screw feeder of the shaft furnace; and sorting, by a hot enclosed screen, the reduced iron pellets fed from the screw feeder into large and small (disintegrated) pellets to selectively feed into each of the melter gasifier and the briquetting machine.

Brief Description of the Drawings

Fig. 1 schematically illustrates a general ironmaking process using non-coking coal and fine iron ore;

Fig. 2 schematically illustrates a construction of a recycling apparatus of iron-containing dust and sludge in an ironmaking process using non-coking coal and fine iron ore; and Fig. 3 illustrates an equilibrium diagram between Zn (G) and ZnO (S) which is calculated applying thermochemistry in a reduction gas atmosphere.

Best Mode for Carrying out the Invention

The following detailed description will present a preferred embodiment of the invention in reference to the accompanying drawings. As shown in Fig.2, a recycling apparatus 1 of the invention recycles sludge/dust which is produced from an ironmaking process. To that end, the recycling apparatus removes Zn component contained in sludge/dust by vaporizing with reduction gas, and charges sludge/dust of reduced iron into a melter gasifier 40. The apparatus 1 includes raw material feed bins 110a, 110b and 110c, an agitator 100, a pelletizer 90, a drier 80, a shaft furnace 70 and a hot enclosed screen 60.

That is, the raw material feed bins 110a, 110b and 110c store dust/sludge mixture, binder and fine iron ore having particle sizes of 1mm or less. Sludge is mixed with dust containing Fe component after dewatered, dryed and crushed, before stored in a feed bin (110). Discharging/feeding machines

(not shown) are installed respectively in lower portions of the feed bins 110a, 110b and 110c to discharge/feed dust/sludge mixture, binder and fine iron ore by fixed quantities. Upon being discharged from the feed bins 110a, 110b and 110c, raw material is discharged via a transport means such as belt conveyer (not shown) into the agitator 100 in a next process.

The agitator 100 mixes and agitates a certain ratio of dust/sludge mixture, binder and fine iron ore which are discharged from the feed bins 110a, 110b and 110c by fixed quantities. The mixing ratio is varied depending on Fe content in dust/sludge mixture.

The pelletizer 90 receives raw material mixture containing dust/sludge, binder and fine iron ore mixed in the agitator 100, and coarsens the mixture into pellets having certain particle sizes .

Preferably, the pellets from the pelletizer 90 have particle sizes of about 30mm or less regarding the reaction rate thereof in the shaft furnace 70.

Upon supplied with the pellets from the pelletizer 90, the drier 80 heats and dries the pellets in order to remove moisture which is provided while the pelletizer 90 coarsens the raw material mixture into the pellets having certain particle sizes. After dried in the drier 80, the pellets are charged into the shaft furnace 70 which is connected to the melter gasifier 40 via a fifth gas duct 44 to receive reduction gas therefrom. In the shaft furnace 70, Zn component is vaporized and Fe component is reduced via reduction gas supplied through the fifth gas duct 44. A screw feeder 72 is mounted on a lower portion of the shaft furnace 70 to discharge the reduced iron pellets from the shaft furnace 70.

A sixth gas duct 71 is connected between an upper portion of the shaft furnace 70 and a scrubber 120, in which the scrubber 120 uses cooling water to scrub and condense Zn component from exhaust gas which is vaporized by hot reduction gas. Clean exhaust gas, which is cleared of Zn component in the scrubber 120, is exhausted to the outside via an exhaust pipe 121 and a flare stack. A cyclone-type de-Zn bath 130 is installed under and connected to the scrubber 120 via a lower duct 122 in order to discharge high concentrated Zn sludge made from Zn-containing sludge/dust.

The hot enclosed screen 60 installed between the shaft furnace 70 and the melter gasifier 40 sorts the reduced iron pellets from the screw feeder 72 of the furnace 70 into small and large ones according to their particle sizes, and feeds them into the melter gasifier 40 and a briquetting machine 50, respectively, via fifth and sixth ore ducts 61 and 62. Preferably, the reduced iron pellets supplied to the hot enclosed screen 60 are sorted according to a reference particle size of about 5 to 10mm regarding an existing fluidized bed reducing process which utilizes sinter feed having a particle size of about 8mm or less.

Also, the hot enclosed screen 60 may be connected with an inert gas line 69 of feeding inert gas such as Ar or N₂ gas to maintain a hot inert atmosphere thereby preventing cooling and re-oxidation of the pellets.

Accordingly, when the reference particle size is set to 8mm for sorting the reduced iron pellets from the shaft furnace 70 into the large and small (disintegrated) pellets, the reduced iron pellets are sorted into the large pellets having a particle size of about 8mm or more and the small (disintegrated) pellets having a particle size of about 8mm or less in a hot enclosed condition. Those pellets sorted as the large ones by the screen 60 are charged into the melter gasifier 40 via the sixth ore duct 62 connected with a transport line 51 under the briquetting machine 50, on the other hand, those pellets sorted as small ones by the screen 60 are charged into the briquetting machine 50 via the fifth ore duct 61 connected to a fourth ore duct 42 over the briquetting machine 50 where the small (disintegrated) pellets are briquetted into large ones. The briquetted large pellets are charged into the melter gasifier 40.

The following detailed description will present the operation and effect of the invention having the above construction.

Iron-containing dust and sludge produced in the ironmaking process using non-coking coal and fine iron ore is dewatered, dried and crushed. Then, the pre-treated sludge/dust mixture is stored in a feed bin together with binder and fine iron ore but stored in separate feed bins. The sludge/dust mixture, binder and fine iron ore is discharged by fixed quantities from the raw material feed bins 110a, 110b and 110c to feed into the agitator 100 where sludge/dust mixture, binder and fine iron ore are mixed into raw material mixture at a proper mixing ratio, and then raw material mixture is supplied into the pelletizer 90.

In the pelletizer 90, raw material mixture is coarsened into pellets having particle sizes of 30mm or less. The coarsened pellets are charged into the drier 80 where remaining moisture is removed, and the dried pellets are charged into the shaft furnace 70. Then, when the mixed raw material pellets from the pelletizer 90 are fully charged into the furnace 70, reduction gas is supplied to the furnace 70 via the fifth gas duct 44 which has one end connected to the upper portion of the melter gasifier 40 and the other end connected to the lower portion of the furnace 70.

As a result, Zn component is vaporized and removed from the pellets by reduction gas supplied through the lower portion of the furnace 70, and then is discharged as being entrained in the exhaust gas via the sixth gas duct 71. On the other hand, Fe component remained in the pellets is reduced into ferrous oxide or metallic iron while staying in the furnace 70.

Preferably, the shaft furnace 70 maintains an internal pressure of about 4bar,g or less and an internal temperature of about 800 to 1100°C in an ironmaking process using non-coking coal and fine iron ore.

The above conditions are required because reaction rate is low at an internal temperature under 800^°C and sticking readily occurs at an internal temperature over 1100^°C. Fig. 3 shows an equilibrium state between Zn (Gas) and ZnO (Solid) which is thermodynamically calculated in an reducing gas atmosphere containing CO 65wt%, C0₂5wt%, H₂25wt% and H₂02wt% under a gas pressure of about 3bar,g.

Exhaust gas from the furnace 70 is supplied via the sixth gas duct 71 into the water cooling scrubber 120, in which gaseous Zn component in exhaust gas is condensed into Zn or ZnO by cooling water injected in the scrubber 120. Condensed Zn component is discharged in the form of slurry via the lower duct 122 into the cyclone-type de-Zn bath 130. While passing through the dezincification bath 130, sludge is concentrated and recovered into high Zn sludge.

Whereas exhaust gas is emitted via the sixth gas duct 71 from the shaft furnace 70, the pellets remaining in the furnace 70 contain oxidized iron component (mainly Fe₃0₃) which is generally reduced near to metal iron.

The reduced pellets are discharged via the screw feeder 72 installed in the lower portion of the reduced furnace 70 to feed into the hot enclosed screen 60, which sorts the pellets into large and small (disintegrated) ones based upon a reference particle size.

Among the reduced iron pellets sorted in the screen 60, the large pellets are directly charged into the melter gasifier 40 via the sixth ore duct 62 connected to the formed iron line 51 since they would not fly away (not be elutriated) owing to their particle sizes exceeding the reference particle size. On the other hand, in order to prevent elutriation, the small (disintegrated) pellets are fed into the fifth ore duct 61 connected to the fourth ore duct 42 so that they are briquetted in the machine 50 and then charged into the melter gasifier 40 via the formed iron line 51. A mixture having components reported in Table 1 was coarsened into pellets having particle sizes of about 10 to 30mm. The pellets were dried and reduced in reduction gas (CO 65wt%,

C0₂ 5wt%, H₂ 25wt% and H₂0 2wt%) at about 900 ^°C under 3bar,g pressure for about 1 hour. As a result, reduction degree of Fe component was at least 90% and removal ratio of Zn was at least 80%, thereby proving effects of the invention.

Table 1

Chemical Component of Mixture Obtained after Agitation of

Fe-Containing Sludge, Dust and Inorganic Binder

Industrial Applicability

As set forth above in the ironmaking process using non-coking coal and fine iron ore, the present invention coarsens raw material mixture containing sludge/dust (which is dewatered, dried and crushed in previous processes) , binder and fine iron ore into pellets so as to recover Zn component in sludge/dust by vaporizing sludge/dust with reducing gas and then Fe component remaining in sludge/dust in the form of hot metal by reducing and charging sludge/dust into the melter gasifier, thereby improving the recovery rate of Fe component in the iron making equipment while preventing condensed deposits of Zn component from sticking to the furnace wall to ensure a stable process. Furthermore, productivity can be also enhanced since fine ore is mixed with sludge/dust.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions can be made without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A recycling apparatus for iron-containing dust and sludge in an ironmaking system using non-coking coal and fine iron ore which includes 3 fluidized-bed reduction furnaces having a preheating furnace, a pre-reduction furnace and a final reduction furnace, a melter gasifier with a char bed and a briquetting machine, the recycling apparatus comprising: a plurality of raw material feed bins for respectively storing dust/sludge (which is dewatered, dried and crushed) , binder and fine iron ore and discharging the same by fixed quantities; an agitator for mixing and agitating a certain quantity of dust/sludge, binder and fine iron ore fed from the raw material feed bins; a pelletizer for coarsening raw material mixture from the agitator into certain particle sizes of pellets; a drier for drying the pellets supplied from the pelletizer; a shaft furnace connected to the melter gasifier via a fifth gas duct for receiving the pellets from the drier and vaporizing Zn component contained in the pellets by reduction gas, wherein the shaft furnace includes a sixth gas duct in an upper portion thereof for exhausting exhaust gas containing vaporized Zn component and a screw feeder for outwardly discharging reduced iron pellets which are reduced by reduction gas; and a hot enclosed screen for sorting the reduced iron pellets discharged from the screw feeder into large and small

(disintegrated) ones according to particle sizes and having fifth and sixth ore ducts for selectively feeding the sorted pellets into the melter gasifier and the briquetting machine.

2. The recycling apparatus for iron-containing dust and sludge in accordance with claim 1, further comprising: a scrubber connected to the sixth gas duct for injecting cooling water to condense Zn component in exhaust gas; an exhaust pipe connected to the scrubber for exhausting clean exhaust gas cleared of Zn component to a flare stack; and a de-Zn bath connected to a lower portion of the scrubber via a lower duct for condensing a high Zn sludge.

3. The recycling apparatus for iron-containing dust and sludge in accordance with claim 1, further comprising an inert gas line for feeding inert gas into the hot enclosed screen to maintain a hot inert gas atmosphere to prevent cooling and re-oxidation of the pellets.

4. A recycling method for iron-containing dust and sludge in an ironmaking process using non-coking coal and fine iron ore which includes 3 fluidized-bed reduction furnaces having a preheating furnace, a pre-reduction furnace and a final reduction furnace, a melter gasifier with a char bed and a briquetting machine, the recycling method comprising the following steps of: agitating, in an agitator, certain quantities of dust/sludge, binder and fine iron ore supplied from raw material feed bins; coarsening, in a pelletizer, raw material mixture supplied from the agitator into certain particle sizes of pellets; drying the pellets in a drier, charging the dried pellets into a shaft furnace, vaporizing Zn component contained in the charged pellets by reduction gas fed through a fifth gas duct of a melter gasifier, exhausting Zn component on exhaust gas, and outwardly discharging reduced iron pellets reduced via reduction gas with a screw feeder of the shaft furnace; and sorting, by a hot enclosed screen, the reduced iron pellets fed from the screw feeder into large and small pellets to selectively feed into each of the melter gasifier and the briquetting machine.

5. The recycling method for iron-containing dust and sludge in accordance with claim 4, wherein the pellets coarsened in the pelletizer have a reference particle size of about 30mm regarding reaction rate in the shaft furnace.

6. The recycling method for iron-containing dust and sludge in accordance with claim 4, further comprising the steps of: feeding exhaust gas via a sixth gas duct connected to the shaft furnace into a scrubber, injecting cooling water into the scrubber to clear Zn component from exhaust gas by condensation, and emitting exhaust gas cleared of Zn component via a flare stack; and condensing, in a cyclone type de-Zn bath, sludge discharged from the scrubber into a high Zn sludge to recover Zn component.

7. The recycling method for iron-containing dust and sludge in accordance with claim 4, wherein the shaft furnace maintains an internal pressure of about 4bar,g or less and an internal temperature of about 800 to 1100^°C.

8. The recycling method for iron-containing dust and sludge in accordance with claim 4, wherein the hot enclosed screen is fed with inert gas for maintaining a hot inert gas atmosphere to prevent cooling and re-oxidizing of the pellets.

9. The recycling method for iron-containing dust and sludge in accordance with claim 4, wherein the hot enclosed screen has a reference particle size of about 5 to 10mm for sorting the pellets into the small and large pellets regarding a fluidized bed reducing process.

10. The recycling method for iron-containing dust and sludge in accordance with claim 9, wherein the large pellets sorted in the screen are charged into the melter gasifier via a sixth ore duct connected to an HBI feed line under the briquetting machine.

11. The recycling method for iron-containing dust and sludge in accordance with claim 9, wherein the small (disintegrated) pellets sorted in the screen are charged into the briquetting machine via a fifth ore duct connected to a fourth ore duct over the briquetting machine, briquetted in the machine, and then charged into the melter gasifier.