CN1242075C - Apparatus and method for recycling iron laden dust and sludge in ingot iron manufacturing process using semi-soft coking coal and fine iron ore - Google Patents

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

Apparatus and method for recovering iron-containing dust and sludge during ironmaking using coal and fine ore

technical field

The present invention relates to the recovery of dust and sludge from iron processing in the ironmaking process using non-coking coal and fine iron ore. In particular, the invention relates to improved apparatus and methods for the recovery of iron-containing dust and sludge, i.e. by vaporization Zn components contained in dust and sludge are recovered and Fe components in the form of molten iron are recovered by reduction, thereby reducing the cost of sludge treatment and preventing environmental pollution.

technical background

So far, no ironmaking process has been developed in the art that surpasses the blast furnace process in terms of energy efficiency or productivity. However, the blast furnace method generally relies on coke obtained by processing specific raw coal as a carbon source, which is used as a fuel and reducing agent, and sinter obtained through a coagulation process as an iron source.

As a result, the current blast furnace method must be accompanied by the use of pretreatment equipment such as coke production and sintering equipment. However, it takes excessive costs to build these facilities, and these facilities generate a large amount of environmental pollutants, such as SOx, NOx and dust, and are facing stricter regulations worldwide. In order to overcome these limitations, a large amount of processing equipment is also required to consume a larger amount of cost. As a result, the current blast furnace method gradually loses its competitiveness.

Therefore, various efforts are being made in various countries in the world to develop an advanced ironmaking method which can overcome the disadvantages of the above-mentioned blast furnace method. As one of the most prominent advanced ironmaking methods currently in development, the coal-based smelting reduction method directly utilizes non-coking coal as a fuel and reducing agent and fine iron ore as an iron source, which accounts for approximately 80% or more.

U.S. Patent No. 5,785,733, issued July 28, 1998, relates to such an ironmaking system using non-coking coal and fine iron ore technology.

As shown in Figure 1, the entire ironmaking system includes three fluidized bed reduction furnaces, namely a preheating furnace 10, a pre-reduction furnace 20, a final reduction furnace 30, and a furnace vaporizer 40 with a carbon bed.

According to the present invention, the fine iron ore continuously flows into the preheating furnace 10 through the first ore channel 12, where it is pretreated by reducing gas fed through the third gas channel 21, and simultaneously forms a fluidized bed or a turbulent fluidized bed.

Subsequently, the fine iron ore pretreated in the preheating furnace 10 is discharged to the pretreatment reduction furnace 20 through the second ore channel 22, where it is pre-reduced by the reducing gas added through the second gas channel 31, and simultaneously forms an ebullated bed or Turbulent fluidized bed. The pre-reduced fine iron ore is discharged to the final reduction furnace 30 through the third mine channel 32, where it is finally reduced by the reducing gas added through the first gas channel 41, and at the same time forms an ebullated bed or a turbulent fluidized bed. Finally, the reduced fine iron ore is continuously discharged to the following process through the fourth mine road 42.

The fine iron ore that is finally reduced in the final reduction furnace 30 and discharged through the fourth tunnel 42 is supplied to a briquetting machine 50 where hot briquetted iron (HBI) is formed. The HBI is injected through the HBI transfer line 51 into the furnace vaporizer 40 where it is melted in a bed of charcoal to be converted into molten iron ingots or hot metal. The hot metal then exits the furnace vaporizer 40 .

The first to fourth mine passages 12, 22, 32 and 42 provide respective thermal airtight valves 13, 23, 33 and 43 for on/off operation to regulate the flow of the fine iron ore so that the flow of the fine iron ore can be controlled blocking, if necessary.

Non-coke lumps are continuously supplied through openings located in the upper portion of the furnace vaporizer 40 to form a char bed of a specified height in the furnace. When oxygen is blown into the char bed through a plurality of tuyeres located at the lower part of the furnace vaporizer 40, the char burns in the char bed.

The gas generated from the combustion of the char becomes reducing gas in the fluidized bed, which rises through the char bed and exits the furnace vaporizer 40 . The exhausted reducing gas is fed to the three fluidized bed reduction furnaces 10 , 20 and 30 through the first to third gas channels 41 , 31 and 21 in sequence, and finally discharged out of the process through the fourth gas channel 11 .

Meanwhile, the ironmaking process using non-coking coal and fine iron ore generates a large amount of dust and sludge, which is dried and injected into the furnace vaporizer 40 or the preheating furnace 10 without any further treatment. However, because the particle size of the dust/silt is very small (the maximum particle size is about tens of microns), the dust/silt flows directly upward when it is fed into the final reduction furnace 30, and in the final reduction furnace, it has a particle size (usually about 10 mm) relatively Fine iron ore larger than dust/silt is used. As a result, this process exhibits low actual recovery and is therefore ineffective.

In addition, if the dust/sludge contains a large amount of Zn components, the Zn components are vaporized in the furnace vaporizer 40 at a temperature of about 1000° C. or higher. The vaporized Zn components are re-oxidized and condensed to form ZnO in the preheating furnace 10, which has a relatively low temperature of about 600 to 700°C. Condensed ZnO sticks and grows on the furnace walls, thus posing a serious obstacle to operation.

The implementation of the present invention is in order to solve the above-mentioned problems existing in the prior art, so an object of the present invention is exactly to provide, in utilizing non-coking coal and fine iron ore ironmaking process, the recovery equipment and method of iron-containing dust and silt, described The apparatus and method increase recovery while preventing the condensed Zn component from sticking to the furnace walls, thereby increasing productivity.

Contents of the invention

In order to achieve the above object, one aspect of the present invention provides a recovery device for iron-containing dust and sludge in an ironmaking system utilizing non-coking coal and fine iron ore. The ironmaking system includes three fluidized bed reduction furnaces, namely a preheating furnace , a pre-reduction furnace and a final reduction furnace, a furnace vaporizer with a carbon bed in it, and a briquetting machine, and the recovery device includes: a plurality of raw material feeding hoppers, respectively used to store and discharge dust/silt in a certain amount ( which are dehydrated, dried and crushed), binder and fine iron ore; a mixer is used to mix and stir a certain amount of dust/sludge, binder and fine iron ore fed from the raw material hopper; a manufacturing A granulator to coarsen the raw material mixture from the mixer to form pellets of a certain particle size; a dryer to dry the pellets supplied by the granulator; a shaft furnace connected to the furnace through a fifth air duct a vaporizer for recovering the pellets from the drier, and vaporizing the Zn component contained in the pellets by reducing gas, wherein the shaft furnace includes a sixth gas channel above it for removing waste gas containing the vaporized Zn component, and A screw feeder is used to discharge the reduced iron pellets reduced by reducing gas; and a heat-closed sieve is used to classify the reduced iron pellets discharged from the screw feeder into large and small iron pellets according to the particle size, and the fifth and The sixth tunnel is used to selectively feed sorted shot to the furnace vaporizer and briquetting press.

In order to achieve the above object, another aspect of the present invention provides a method for recycling iron-containing dust and sludge in an ironmaking system utilizing non-coking coal and fine iron ore. The ironmaking system includes three fluidized bed reduction furnaces, namely a preheating furnace, a pre-reduction furnace and a final reduction furnace, a furnace vaporizer with a carbon bed and a briquetting machine. The recycling method comprises the steps of: stirring a certain amount of dust/silt, binder and fine iron ore provided by a raw material hopper in a mixer; coarsening the raw material mixture provided by the mixer to form a certain Pellets of particle size; dried in a dryer, the dried pellets are fed into a shaft furnace, the reducing gas fed through the fifth gas channel of the furnace vaporizer vaporizes the Zn component contained in the pellets, and is discharged in the waste gas The Zn component of the Zn component, with a screw feeder of the shaft furnace, the reduced iron pellets that are reduced by reducing gas are discharged outwards; and the reduced iron pellets fed by the screw feeder are classified into large and small (fragmented ) iron shot, selectively fed to each furnace vaporizer and briquetting machine.

Brief description of the drawings

Figure 1 schematically shows a general ironmaking process utilizing non-coking coal and fine iron ore;

Fig. 2 schematically shows the construction of iron-containing dust and sludge recovery plant in ironmaking process using non-coking coal and fine iron ore; and

Figure 3 shows an equilibrium diagram between Zn(gas) and ZnO(solid) obtained by applying thermochemical calculations in a reducing gas environment.

Best Mode for Carrying Out the Invention

The following detailed description will provide preferred embodiments of the present invention with reference to the accompanying drawings.

As shown in Fig. 2, the recovery device 1 of the present invention recovers the sludge/dust generated from the ironmaking process. As a result, the recovery unit removes the Zn component contained in the sludge/dust by vaporization with the reducing gas, and feeds the sludge/dust of reduced iron to the vaporizer 40 of the furnace. Apparatus 1 includes raw material feed hoppers 110 a , 110 b and 110 c , agitator 100 , granulator 90 , dryer 80 , shaft furnace 70 and heat-enclosed screen 60 .

That is, the raw material hoppers 110a, 110b, and 110c store dust/sludge, binder, and fine iron ore with a particle size of 1 mm or less. The sludge is dehydrated, dried and crushed before being stored in the feed hopper (110), and mixed with dust containing Fe components. Discharging/feeding machines (not shown) are respectively installed at the lower parts of the feeding hoppers 110a, 110b and 110c to discharge/feed fixed amounts of dust/sludge mixture, binder and fine iron ore. After being discharged from the feed hoppers 110a, 110b, and 110c, the raw materials are discharged into the agitator 100 in a subsequent step through conveying means such as a conveyor belt (not shown).

The agitator 100 mixes and agitates the dust/sludge mixture, binder and fine iron ore, which are discharged in fixed amounts from the feed hoppers 110a, 110b, and 110c, in a specific ratio. The mixing ratio is changed according to the content of Fe in the dust/sludge mixture.

The granulator 90 receives a raw material mixture containing dust/sludge, binder and fine iron ore mixed in the mixer 100 and coarsens the mixture into pellets of a specific size.

Preferably, the pellets from pelletizer 90 have a particle size of about 30 mm or less, depending on the reaction rate in shaft furnace 70 .

Based on the pellets supplied by the pelletizer 90, the dryer 80 heats and dries the pellets in order to remove the moisture introduced during the coarsening of the raw material mixture by the pelletizer 90 into pellets of a specific particle size.

After drying in the dryer 80, the pellets are fed into the shaft furnace 70 connected to the furnace vaporizer 40 through the fifth gas channel 44 to receive its reducing gas. In the shaft furnace 70 , the Zn component is vaporized, and the Fe component is reduced by the reducing gas supplied from the fifth gas channel 44 . A screw feeder 72 is installed to a lower portion of the shaft furnace 70 to discharge reduced iron pellets from the shaft furnace 70 .

The sixth gas passage 71 is connected between the upper part of the shaft furnace 70 and the scrubber 120, wherein the scrubber 120 uses cooling water to wash and condense Zn components from the exhaust gas vaporized by the hot reducing gas. The purified exhaust gas from which the Zn component was removed in the scrubber 120 is discharged outside through an exhaust gas pipe 121 and a flare chimney. Cyclone type de-Zn bath 130 is installed in the lower part, and is connected to scrubber 120 through a lower pipe 122 to discharge highly concentrated Zn sludge from Zn-containing sludge/dust.

The heat-enclosed sieve 60 is installed between the shaft furnace 70 and the furnace vaporizer 40, and the reduced iron pellets from the shaft furnace 70 screw feeder 72 are classified into large and small iron pellets according to the particle size, and they are passed through the fifth and the second Six ore passes 61 and 62 feed into furnace vaporizer 40 and briquetting machine 50 respectively. Preferably, the reduced iron pellets supplied to the heat-enclosed sieve 60 are classified according to a reference particle size of about 5 to 10 mm in consideration of the presence of a fluidized bed reduction process using a sinter feed having a particle size of about 8 mm or less.

Also, the heat-sealed screen 60 may be connected to an inert gas line 69 fed with an inert gas such as Ar or _N2 gas to maintain a hot inert atmosphere to prevent cooling and re-oxidation of the pellets.

Therefore, when the reference grain size is set to 8mm for sorting the reduced iron pellets from the shaft furnace 70 into large and small (fragmented) pellets, the reduced iron pellets are sorted to have a grain size of Large pellets of about 8mm or larger and small (fragmented) pellets with a particle size of about 8mm or smaller. These pellets classified into large pellets by the sieve 60 are fed into the furnace vaporizer 40 through the sixth tunnel 62 connected with the transfer pipe 51 below the briquetting machine 50, and these pellets classified into small pellets by the sieve 60 The pellets are fed into the briquetting machine 50 through a fifth tunnel 61 connected to the fourth tunnel 42 located above the briquetting machine 50, where small (fragmented) pellets are compacted into large pellets. The large pellets of briquettes are fed to the furnace vaporizer 40 .

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

Iron-bearing dust and sludge generated during ironmaking from non-coking coal and fine iron ore are dewatered, dried and ground. The pretreated sludge/dust mixture is then stored into a feed hopper together with binder and fine iron ore, but into a different feed hopper. The sludge/dust mixture, binder and fine iron ore are discharged in fixed amounts from the raw material hoppers 110a, 110b and 110c and fed to the agitator 100, where the sludge/dust mixture, binder and fine iron ore are properly mixed The ratio is mixed into a raw material mixture, and then the raw material mixture is provided to the granulator 90.

In the pelletizer 90, the raw material mixture is coarsened into pellets with a particle size of 30 mm or less. Coarsened pellets are fed to dryer 80 where remaining moisture is removed and dried pellets are fed to shaft furnace 70 .

Then, when the mixed raw material pellets from the granulator 90 are completely added to the shaft furnace 70, the shaft furnace 70 is supplied with reducing gas through the fifth air passage 44, one end of which is connected to the furnace vaporizer 40, and the other end is connected to the lower part of the shaft furnace 70.

As a result, the Zn component is vaporized and removed from the pellets by the reducing gas supplied from the lower part of the shaft furnace 70, and then carried away by the exhaust gas through the sixth gas passage 71. In addition, Fe components present in the pellets are reduced to ferrous oxide or metallic iron while being kept in the shaft furnace 70 .

Preferably, the shaft furnace 70 maintains an internal pressure of about 4 bar, g (4×10 ⁵ Pa, g) or less during ironmaking using non-coking coal and fine iron ore, and an internal temperature of about 800 to 1100 ℃.

The above conditions are necessary because the reaction rate is low at an internal temperature lower than 800°C, and sticking tends to occur at an internal temperature higher than 1100°C. Figure 3 shows an equilibrium state between Zn(gas) and ZnO(solid), which is calculated thermodynamically in a reducing gas atmosphere including CO6 5wt%, _CO2 5wt%, _H2 5wt% and water 2 wt%, the gas pressure is about 3 bar, g (3×10 ⁵ Pa, g).

The exhaust gas from the shaft furnace 70 is supplied to the water-cooled scrubber 120 through the sixth gas passage 71 , wherein the Zn component in the exhaust gas is condensed into Zn or ZnO by the cooling water injected into the scrubber 120 . The condensed Zn component is discharged to the cyclonic type de-Zn bath 130 in the form of slurry through the lower line 122 . As it passes through the dezincification bath 130, the sludge is concentrated and recycled into high Zn content sludge.

Although the exhaust gas emanates from the shaft furnace 70 through _the sixth gas channel 71, the pellets kept in the shaft furnace 70 contain iron oxide components (mainly _Fe3O3 ), which are generally reduced to close to metallic iron.

The reduced pellets are discharged through a screw feeder 72 installed to the lower part of the reduction furnace 70 and fed to a heat-enclosed sieve 60 that will classify the pellets into large and small (cracked) pellets based on a reference particle size.

Among the reduced iron pellets classified by the sieve 60, the large pellets are directly injected into the furnace vaporizer 40 through the sixth tunnel 62 connected to the formed iron channel 51, because the large pellets whose size exceeds the reference particle size cannot fly away (not detected elutriation). In addition, to prevent elutriation, small (fragmented) pellets are fed into a fifth tunnel 61 connected to the fourth tunnel 42 so that the briquettes are briquetted in the briquetting machine 50 and injected through the iron channel 51 formed to furnace vaporizer 40.

The mixture having the composition described in Table 1 was coarsened into pellets with a particle size of about 10 to 30 mm. The pellets were dried and reduced in reducing gas (CO6 5wt%, _CO2 5wt%, _H2 5wt% and water 2wt%) at about 900 °C, 3 bar, g (3 x ¹⁰⁵ Pa, g) for about 1 hour . As a result, the degree of reduction of the Fe component was at least 90%, and the removal rate of Zn was at least 80%, thus demonstrating the effect of the present invention.

Table 1

Chemical composition of the mixture obtained after stirring iron-containing sludge, dust and inorganic binders T.Fe C CaO SiO ₂ Zn ratio(%) 32.4 18.6 9.2 5.9 1.9

Industrial Applicability

As mentioned above, in the ironmaking process utilizing non-coking coal and fine iron ore, the present invention will contain the raw material of sludge/dust (dewatered, dried and crushed in previous processing), binder and fine iron ore The mixture is coarsened into pellets, thereby recovering the Zn component in the sludge/dust by vaporizing the sludge/dust with reducing gas, and recovering the Fe present in the sludge/dust in the form of hot iron by reducing and feeding the sludge/dust to the furnace vaporizer Components, thereby increasing the recovery rate of Fe components in ironmaking equipment, while preventing the condensation deposits of Zn components from adhering to the furnace wall to ensure a stable process. In addition, productivity is increased due to fine ore and sludge/dust mixing.

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 may be made without departing from the scope and spirit of the invention as disclosed in the appended claims.

Claims (11)

1. A recovery device for recycling iron-containing dust and sludge in the ironmaking system of non-coking coal and fine iron ore. The ironmaking system includes a preheating furnace, a prereduction furnace and a final reduction furnace. A furnace vaporizer for the charcoal bed and a briquetting machine, the recovery unit consists of: A plurality of raw material feed hoppers for respectively storing and discharging dust/sludge, binder and fine iron ore in fixed quantities, said dust/sludge being dewatered, dried and crushed; An agitator for mixing and agitating a quantity of dust/sludge, binder and fine iron ore fed from the raw material hopper; a granulator for coarsening the raw material mixture from the mixer to form pellets; a dryer for drying the pellets supplied by the granulator; A shaft furnace, connected to the furnace vaporizer through a fifth gas channel, for receiving the pellets from the drier and vaporizing the Zn component contained in the pellets by reducing gas, wherein the shaft furnace includes a sixth The air passage is used to remove waste gas containing vaporized Zn components, and a screw feeder is used to discharge reduced iron pellets reduced by reducing gas to the outside; and A heat-enclosed sieve for classifying the reduced iron shot discharged from the screw feeder according to size, and fifth and sixth tunnels for selectively feeding the sorted shot to the furnace vaporizer and briquetting machine. 2. The recovery device of iron-containing dust and sludge according to claim 1, further comprising: A scrubber connected to the sixth air passage for injecting cooling water to condense Zn components in the exhaust gas; an exhaust gas line connected to the scrubber for discharging the purified exhaust gas from which the Zn component has been removed to the flare chimney; and A de-Zn bath connected to the lower part of the scrubber via a lower pipe, used to coagulate high-Zn sludge. 3. The recovery device of ferrous dust and sludge according to claim 1, further comprising an inert gas channel for adding inert gas to the heat-enclosed sieve to maintain a hot inert gas atmosphere to prevent cooling and re-oxidation of the pellets . 4. A recovery method, used to recycle iron-containing dust and sludge in non-coking coal and fine iron ore ironmaking system, ironmaking system includes a preheating furnace, a prereduction furnace and a final reduction furnace, one with A furnace vaporizer of a charcoal bed and a briquetting machine, the recovery method comprises the steps of: Mixing a certain amount of dust/sludge, binder and fine iron ore fed from the raw material hopper in a mixer; coarsening in a granulator the raw material mixture supplied by the mixer to form pellets; Dry the pellets in a drier, feed the dried pellets to a shaft furnace, vaporize the Zn component contained in the fed pellets with the reducing gas fed through the fifth gas channel of the furnace vaporizer, and remove the Zn in the waste gas Components, and use a screw feeder of the shaft furnace to discharge the reduced iron pellets reduced by the reducing gas; The reduced iron shot fed by the screw feeder is sorted by a heat-enclosed screen for selective feeding to each furnace vaporizer and briquetting machine. 5. The recovery method of iron-containing dust and sludge according to claim 4, wherein the pellets coarsened in the granulator have a reference particle size of 30mm according to the reaction rate in the shaft furnace. 6. The recovery method of iron-containing dust and sludge according to claim 4, further comprising the steps of: Feed the exhaust gas to the scrubber through the sixth gas channel connected to the shaft furnace, inject cooling water into the scrubber to remove the Zn component in the exhaust gas by condensation, and discharge the purified exhaust gas from the Zn component removal through the chimney of the torch; as well as The sludge discharged from the scrubber is condensed in a cyclone-type de-Zn bath to form high-Zn sludge to recover Zn components. 7. The recovery method of iron-containing dust and sludge according to claim 4, wherein the shaft furnace maintains an internal pressure of about 4×10 ⁵ Pa, g or lower, and an internal temperature of 800 to 1100° C. 8. The recovery method of iron-containing dust and sludge according to claim 4, wherein the heat-enclosed sieve is fed with inert gas for maintaining a hot inert gas atmosphere to prevent cooling and re-oxidation of the pellets. 9. The recovery method of iron-containing dust and sludge according to claim 4, wherein the heat-enclosed sieve is used to classify the pellets with a reference particle size of 5 to 10 mm according to the fluidized bed reduction process. 10. The iron-containing dust and sludge recovery method according to claim 9, wherein the sieve-classified large pellets are fed to the furnace vaporizer through the sixth mine channel connected to the hot briquette iron feed channel located below the briquetting machine . 11. The recovery method of iron-containing dust and silt according to claim 9, wherein the small pellets classified by the sieve are fed to the briquetting machine through the fifth mine channel connected with the fourth mine channel located above the briquetting machine, Briquettes are compacted in a briquetting machine and then fed to a furnace vaporizer.

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