WO2003025230A1

WO2003025230A1 - Byproduct sludge recycling apparatus in ironmaking system

Info

Publication number: WO2003025230A1
Application number: PCT/KR2002/001519
Authority: WO
Inventors: Myoung-Kyun Shin; Sang-Hoon Joo; Jun-Hyuk Lee
Original assignee: Posco; Research Institute Of Industrial Science & Technology
Priority date: 2001-08-09
Filing date: 2002-08-09
Publication date: 2003-03-27
Also published as: CN1269975C; RU2248401C2; KR100435443B1; CN1498279A; KR20030014618A

Abstract

In an ironmaking system using non-coking coal and fine iron or directly in furnace operations without any additional treatment, a byproduct sludge recycling apparatus powders wet byproduct sludge which is by-produced in water treatment of discharge gas and then re-blows sludge powder into fluidized-bed reduction reactors so that byproduct sludge can be recycled. In the ironmaking system including the fluidized-bed reduction reactor (10, 20 and 30) and an HBI making apparatus (50), the byproduct sludge recycling apparatus (1) comprises: a sludge powder preparing unit (120) for preparing sludge powder by dewatering, drying and crushing byproduct sludge discharged from a water treatment unit (70) for treating process water from scrubbers (60) connected to discharge gas ducts (14); a storage unit (160, 160a) for storing prepared sludge powder; and a sludge powder feeder unit (190, 190a) for feeding sludge powder discharged from the sludge powder storage unit via a pneumatic conveying duct (200a, 200b) to a distributor (210a, 210b). The distributors (210) are connected to the final reduction reactor (30) and the preheating reactor (10), respectively, via sludge powder ducts (300 and 400) for blowing treated sludge powder. The invention reduces the amount of final sludge discharge and the treatment cost according to aftertreatment processes of sludge to enhance the productivity of the ironmaking system.

Description

BYPRODUCT SLUDGE RECYCLING APPARATUS IN IRONMAKING SYSTEM

Technical Field

The present invention relates to an ironmaking system for producing molten iron by using non-coking coal and fine iron ore without any additional treatment. In particular, a byproduct sludge recycling apparatus in the iron making system utilizes iron-containing wet sludge which is by-produced from process water produced during discharge gas scrubbing in the operation of the ironmaking system so that sludge can be recycled in the system itself to reduce the amount of final sludge discharge and the treatment cost of sludge in the ironmaking system as well as enhance the productivity of the ironmaking system.

Background Art

In general, the blast furnace process occupying an important position in the ironmaking system mainly depends on raw coal in the form of processed coke as carbon source used as fuel and reducing agent and on sintered ore obtained from a series of agglomeration process as iron source. This is because raw material which has a strength of at least a predetermined level and a particle size which can ensure permeability in the furnace are needed according to characteristics of its reactor.

The currently popular blast furnace process consuming the above coke and sintered ore needs pretreatment facilities of source such as coke manufacturing facilities and sintering facilities. This creates enormous cost for construction and maintenance of the facilities as well as maintenance operations will be continuously accompanied. Also additional facilities are required for preventing environmental pollution to cope with regulations against facility-related environmental pollution. As a result, the blast furnace process is currently losing its competitive edge because of enormous production cost.

In order to avoid such pretreatment facilities of source for manufacturing coke and sintered ore, a new ironmaking process has been studied which directly utilizes non-coking coal as fuel and reducing source and fine iron ore that occupies at least 80% of global iron ore production as iron source to produce molten iron, and an example thereof is disclosed in US Patent No.5, 534, 046. That is, as shown in FIG.1, an ironmaking system disclosed in the above US Patent comprises 3 fluidized-bed reduction reactors, i.e. a preheating reactor 10, the pre reduction reactor 20 and the final reduction reactor 30, and a melter gasifier 40 having coke fluidized beds therein, in which fine ore at a room temperature are continuously charged via a charging duct 12 from the uppermost reactor (not shown) , pass through the 3 fluidized-bed reduction reactors 10, 20 and 30 in sequence, and then are fed into the melter gasifier 40.

Further, fine ore is transformed into hot reduced fine ore which is heated and reduced for at least 90% in contact with hot reducing gas which passes through the 3 fluidized-bed reduction reactors 30, 20 and 10 in sequence. Hot reduced fine ore is continuously charged into the melter gasifier 40 having the char bed therein, melted in the char bed, and converted into molten pig iron which will be discharged out of the melter gasifier 40.

In the melter gasifier 40, non-coking coal lumps are continuously fed through an upper portion of the gasifier 40 to form a certain level of char beds within the gasifier 40. Oxygen is blown into the char beds through a plurality of tuyeres in a lower portion of the peripheral wall around the fluidized beds to burn char in the char beds.

Combustion gas generated from combustion of char is transformed into hot reducing gas flow while rising through the char beds . Reducing gas is discharged out of the melter gasifier 40 with a portion thereof being fed into the 3 fluidized-bed reduction reactors 10, 20 and 30. In order to maintain the melter gasifier 40 under a predetermined level of pressure, reducing gas is discharged outward via a reducing gas duct 44 and gas discharge ducts 14 of the preheating reactor 10 into scrubbers 60a and 60b communicating therewith, where dust is scrubbed from gas with process water. That is, final discharge gas from the 3 fluidized-bed reduction reactors 10, 20 and 30 flows via one of the gas discharge ducts 14 to the scrubber 60b where discharge gas contacts with process water which is continuously supplied into the scrubber removing dust from gas, and discharge gas from the melter gasifier 40 for pressure adjustment flows via the other one of the gas discharge ducts 14 into the scrubber 60a contacting with process water which is continuously supplied to the scrubber removing dust from gas. Gas is separated from process water and then discharged, whereas process water separated from gas is discharged from the scrubbers 60a and 60b flows via process water ducts 62a and 62b to a water treatment unit 70, where process water is cleared of dust and then re-circulated for reuse.

Ore is carried through the 3 fluidized-bed reduction reactors 10, 20 and 30 via ore charging ducts 22, 32 and 42 which communicate with one another in upper and lower ends of the reduction reactors. Within the ore charging ducts 22, 32 and 42, hot reducing gas and ore flows are formed opposed to each other, in which reducing gas flows from the lower fluidized-bed reduction reactor 30 up to the upper fluidized-bed reduction reactor 10 owing to the pressure difference between the lower and upper ends, and ore flows from the upper fluidized-bed reduction reactor 10 to the lower fluidized-bed reduction reactor 30 under the gravity. In the meantime, fine reduced iron discharged from the final reduction reactor 30 is charged into the melter gasifier

40 according to the following methods: A portion of hot reduction gas fed from the 3 fluidized-bed reduction reactors 10, 20 and 30 is utilized as carrier gas to convey and load fine reduced iron toward and into the melter gasifier 40. Fine reduced iron is prepared into the form of Hot Briquetted Iron

(HBI) or agglomerated iron in a press roll or an HBI making apparatus 50 provided on the last ore charging duct 42, and prepared HBI is carried and loaded with an additional carrier equipment into the melter gasifier 40. At present, the latter is generally applied utilizing the HBI making apparatus 50.

In the ironmaking process via the 3 fluidized-bed reduction reactors 10, 20 and 30, it is necessary to maintain the temperature of fluidized bed (refer to T in FIG. 3) over gas distribution plates within the reduction reactors 10, 20 and 30 at desired levels so that fine reduced iron discharged from the final reduction reactor 30 maintains the reduction rate of at least 85%. In particular, it is most preferred if the preheating reactor 10 is controlled at a temperature of 680 to 700°C.

Well known are methods that control the fluidized beds(T) within the reduction reactors 10, 20 and 30 so that fine reduce iron discharged from the final reduction reactor 30 may maintain the reduction rate in a high level, and examples thereof are disclosed, for example, in Japan Laid-Open Patent Application Nos. H8-337806 and H10-280021.

In the meantime, as shown in FIG. 1, oxidizing agent is blown into the fluidized bed in the preheating reactor 10 to burn a portion of the reduction gas introduced into the fluidized bed so that the preheating reactor 10 can be maintained at a predetermined level or higher. For the purpose of this, the preheating reactor 10 is equipped with oxidizing agent ducts 16 so that the temperature via combustion heat can regulate the fluidized bed in the preheating reactor 10.

Further, in the ironmaking system as above, thermal decrepitation of non-coking coal in the melter gasifier 40 and fine iron ore in the fluidized-bed reduction reactors 10, 20 and 30 causes gas generated in operation of the system to contain a large amount of dust as dust is collected via the scrubbers 60a and 60b, the water treatment unit 70 produces a large amount of sludge, i.e. wet dust, as byproduct during treatment of process water which collects dust in the scrubbers 60a and 60b. Sludge is by-produced for about 200t a day on the basis of a system having a daily productivity of 2,000t.

Such byproduct sludge mainly contains carbon, iron (T. Fe) and ash by a large quantity as reported in Table 1.

Table 1. Component Ratio of Sludge (Dry Base)

Up to the present, byproduct sludge produced in operation of the ironmaking system has been buried for at least 90% consuming enormous cost for treating byproduct sludge as well as increasingly contaminating the environment. In particular, carbon and iron components contained in sludge by a large quantity are almost discarded even though cost can be reduced if they are recycled.

Disclosure of the Invention

Accordingly the present invention has been made to solve the foregoing problems of the prior art. It is therefore an object of the present invention to provide a byproduct sludge recycling apparatus in an ironmaking system capable of powdering wet sludge by-produced from process water used in discharge gas scrubbers and then loading sludge powder into reduction reactors. This enhances productivity of the ironmaking system and decreases the quantity of sludge output reducing aftertreatment cost. Furthermore, carbon and iron contained in sludge by a large quantity can be recycled to reduce maintenance cost.

According to an aspect of the invention to obtain the above objects, in an ironmaking system for producing molten iron by using non-coking coal and fine iron ore and which includes fluidized-bed reduction reactors for reducing introduced fine iron ore, a melter gasifier connected thereto via an HBI making apparatus, a scrubber connected to gas discharge ducts of the melter gasifier and the preheating reactor and a process water treatment unit connected to the scrubber for treating process water, it is provided a byproduct sludge recycling apparatus comprising: a sludge powder preparing unit connected to the water treatment unit for dewatering, drying and crushing byproduct sludge discharged from the water treatment unit to prepare sludge powder; a storage unit connected to the sludge powder preparing unit for storing sludge powder prepared from the sludge powder preparing unit; a sludge powder feeder unit for feeding sludge powder discharged from the sludge powder storage unit via a pneumatic conveying duct to a distributor; and a sludge powder duct connected between the distributor and the final reduction reactor with a plurality of sludge powder flows for re-blowing sludge powder into the final reduction reactor.

According to another aspect of the invention to obtain the above objects, in an ironmaking system for producing molten iron by using non-coking coal and fine iron ore and which includes fluidized-bed reduction reactors for reducing introduced fine iron ore, a melter gasifier connected thereto via an HBI making apparatus, a scrubber connected to gas discharge ducts of the melter gasifier and the preheating reactor and a process water treatment unit connected to the scrubber for treating process water, it is provided a byproduct sludge recycling apparatus comprising: a sludge powder preparing unit connected to the water treatment unit for dewatering, drying and crushing byproduct sludge discharged from the water treatment unit to prepare sludge powder; a storage unit connected to the sludge powder preparing unit for storing sludge powder prepared from the sludge powder preparing unit; a sludge powder feeder unit for feeding sludge powder discharged from the sludge powder storage unit via a pneumatic conveying duct to a distributor; and a sludge powder duct connected between the distributor and an oxidizing agent duct disposed to the preheating reactor and with a plurality of sludge powder flows for re-blowing sludge powder into the preheating reactor.

According to other aspect of the invention to obtain the above objects, in an ironmaking system for producing molten iron by using non-coking coal and fine iron ore and which includes fluidized-bed reduction reactors for reducing introduced fine iron ore, a melter gasifier connected thereto via an HBI making apparatus, a scrubber connected to gas discharge ducts of the melter gasifier and the preheating reactor and a process water treatment unit connected to the scrubber for treating process water, it is provided a byproduct sludge recycling apparatus comprising: a sludge powder preparing unit connected to the water treatment unit for dewatering, drying and crushing byproduct sludge discharged from the water treatment unit to prepare sludge powder; a storage unit connected to the sludge powder preparing unit for storing sludge powder prepared from the sludge powder preparing unit; a sludge powder feeder unit for feeding sludge powder discharged from the sludge powder storage unit via a pneumatic conveying duct to a distributor; and a first sludge powder duct connected between the distributor and the final reduction reactor with a plurality of sludge powder flows for re-blowing sludge powder into the final reduction reactor; and a second sludge powder duct connected between the distributor and an oxidizing agent duct disposed to the preheating reactor with a plurality of sludge powder flows for re-blowing sludge powder into the preheating reactor.

Brief Description of the Drawings

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of an ironmaking process using non-coking coal and fine iron ore;

FIG. 2 is a schematic view of an ironmaking process using non-coking coal and fine iron ore including the first byproduct sludge recycling apparatus according to the first preferred embodiment of the invention;

FIGS. 3a and 3b show a connecting structure between ducts in the first byproduct sludge recycling apparatus and the final reduction reactor in an ironmaking system, in which FIG. 3a is a plan sectional view thereof, and FIG.3b is a vertical sectional view of important parts thereof;

FIG. 4 is a schematic view of an ironmaking process using non-coking coal and fine iron ore including the second byproduct sludge recycling apparatus according to the second embodiment of the invention;

FIG. 5 is a vertical sectional view of a connecting structure between a duct in the second byproduct sludge recycling apparatus and the final reduction reactor in an ironmaking system; FIG. 6 is a graph showing result of combustion test of sludge powder according to the second byproduct sludge recycling apparatus of the invention; and

FIG. 7 is a schematic view of an ironmaking process using non-coking coal and fine iron ore including the third byproduct sludge recycling apparatus according to the third embodiment of the invention.

Best Mode for Carrying out the Invention

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

FIG. 2 shows an ironmaking system including the first byproduct sludge recycling apparatus la of the invention, and FIGS.3a and 3b specifically show a connecting structure between the final reduction reactor 30 and sludge powder blowing ducts 300 in the first byproduct sludge recycling apparatus la, in which the same reference numerals are used to designate the same or similar components in the ironmaking system as in the conventional art.

As shown in FIG.2, the ironmaking system of the invention comprises 3 fluidized-bed reduction reactors 10, 20 and 30: the preheating reactor 10 for reducing fine iron ore introduced therein via the first ore charging duct 12; the pre reduction reactor 20 communicating with the preheating reactor 10 via the second ore charging duct 22; and the final reduction reactor 30 communicating with the final reduction reactor 20 via the third ore charging duct 32. The final reduction reactor 30 communicates via the fourth ore charging duct 42 with a melter gasifier 40 which produces molten pig iron through substantial melting of fine iron ore, in which an HBI making apparatus 50 is equipped on the fourth charging duct 42. The reduction reactors 10, 20 and 30 and the melter gasifier 40 communicate with one another via the second to fourth reducing gas ducts 10, 20 and 30. The fourth reducing gas duct 44 is connected via a gas discharge duct 14 to a scrubber 60a for washing dust from discharge gas, while the preheating reactor 10 is connected via another gas discharge duct 14 to a scrubber 60b for washing dust from discharge gas. The scrubbers 60a and 60b are connected in common to a water treatment unit 70 for treating process water which is supplied via process water ducts 62a and 62b from the scrubbers 60a and 60b.

As indicated with flows (arrows) in FIG. 2, fine iron ore is reduced while passing through the 3 fluidized-bed reduction reactors 10, 20 and 30, agglomerated through the HBI making apparatus 50, and then loaded into the melter gasifier 40. Reducing gas generated therefrom is cleared of dust with process water in the scrubbers 40 after flowing through the ducts, and dust containing process water flows to the water treatment unit 70. Sludge by-produced like this is treated and then re-blown into the ironmaking system.

FIGS. 2 and 3 show the first byproduct sludge recycling apparatus la of the invention which comprises a sludge powder preparing unit 120, a sludge powder storage unit 160, a sludge powder feeder unit 190, a distributor 210a connected via a pneumatic conveying duct 200a with the feeder unit 190 and sludge powder ducts 300 connected between the distributor 210a and the final reduction reactor 30, which will be described in more detail as follows.

As shown in FIG.2, in the first byproduct sludge recycling apparatus la of the invention, the sludge powder preparing unit 120 has a dewaterer 80 connected to the water treatment unit 70 for solidifying wet sludge discharged therefrom, a sludge drier 90 connected to the dewaterer 80 for drying solidified sludge, a crusher 100 connected to the drier 90 for crushing solidified dry sludge into sludge powder of a fine grain size and a sludge powder classifier 110 connected to the crusher 100 for classifying crushed sludge powder.

As schematically shown in FIG. 2, the dewaterer 80 has a drum using centrifugal force and driving means thereof, and is connected to a discharge duct for discharging process water contained in byproduct sludge. Since the moisture content is about 50% when discharged from the water treatment unit 70, byproduct sludge solidifies as soon as dewartered to a moisture content of about 10% by the dewaterer 80.

The drier 90 of the sludge powder preparing unit 120 is connected to the dewaterer 80 in sequence for drying solidified sludge so as to reduce the moisture content thereof to 1% or less from 10%. As not shown in the drawings, it will be more preferred if hot discharge gas from the melter gasifier 40 is utilized as a heat source of the drier 90.

After reduced in the moisture content to 1% or less via the dewaterer 80 and the drier 90, sludge is crushed in the crusher 100 which is connected in sequence to the drier 90.

Solidified dry sludge is crushed and powdered into a fine grain size of about 1mm or less while passing through the crusher

100. This procedure is important since the grain size of crushed sludge has an effect on conveyance of sludge powder S via the pneumatic conveying duct 200a which will be described hereinafter.

As not shown in detail in the drawing, the crusher 100 of the invention may properly utilize a general crusher which compresses dry sludge with a screw blade in a vessel into a predetermined grain size to crush the same.

As the sludge classifier 110 is connected to the crusher 100, crushed sludge powder S is classified into a uniform grain size and then stored into a storage tank 130 of the sludge powder storage unit 160 which will be described later. It is preferred if sludge powder S having a large grain size, e.g. 1mm or more, will be re-charged into the crusher 110 where it will be crushed again as shown in FIG. 2.

In the sludge powder storage unit 160, the storage tank 130 is connected to the classifier 110 of the sludge powder preparing unit 120, and equipped with an inert gas feeding duct 134 for imparting inert atmosphere to an internal space of the storage tank 130 and a dust collector 132 disposed in a discharge port of inert gas in the internal space. A compensator 140 is connected to a lower portion of the storage tank 130, and a cutout valve 150 is disposed on the compensator 140 for regulating supply of sludge powder from the storage tank 130.

The storage tank 130 is connected to the classifier 110 for storing sludge powder S which is crushed and classified in a fine grain size of 1mm or less, and also to the inert gas feeding duct 134 which feeds an inert gas, e.g. nitrogen gas, into the storage tank 130 to maintain the internal space at inert atmosphere. N₂ gas is fed into the storage tank 130 via the inert gas feeding duct 134 in order to prevent self-ignition of carbon component contained in sludge powder S.

The dust collector 132 is installed in an upper portion of the storage tank 130 to capture and recover sludge powder from inert gas when inert gas is discharged from the storage tank 130.

In the meantime, the storage tank 130 is connected to the compensator 140, which is provided with the cutout valve 150 for regulating the flow of sludge powder S discharged from a discharge port 130a of the storage tank 130. As schematically shown in the drawing, the cutout valve 150 is electrically connected via a control unit (not shown) with upper and lower level switches 172 and 174 installed in a feeder tank 170 of the sludge powder feeder unit 190 which will be described as follows:

In the sludge powder feeder unit 190 of the invention connected to the cutout valve 150, the feeder tank 170 is connected downstream of the sludge storage unit 160. The feeder tank 170 is quipped in upper and lower portions with upper and lower level switches 172 and 174 for detecting the level of sludge powder stored therein and in a lower portion with a weight detector 176 for detecting weight variation of sludge powder. The storage tank 170 is connected to a rotary dispenser 180 which adjusts revolution rate in response to a signal from the weight detector 176 to regulate the amount of sludge powder fed from the storage tank 170.

That is to say, as the cutout valve 150 of the sludge powder storage unit 160 is opened, sludge powder S discharged through the discharge port 130a of the storage tank 130 is charged into the sludge powder feeder tank 170, in which sludge powder S introduced into the feeder tank 170 is regulated with the upper and lower level switches 172 and 174 in the feeder tank 170. Therefore, if the level of sludge powder introduced into the feeder tank 170 is lower than the lower level switch 174, the lower level switch 174 detects it and then opens the cutout valve 150 which is electrically connected thereto so as to additionally charge sludge powder S into the feeder tank 170. On the contrary, if the upper level switch 172 detects sludge powder S introduced into the feeder tank 170, the cutout valve 150 is shut. In this manner, the amount of sludge S introduced into the feeder tank 170 is uniformly maintained always.

Also since the weight detector 176 is installed in a lower portion of the feeder tank 170, the rotary dispenser 180 is selectively connected to the feeder tank 170 in a cooperative manner in response to a signal from the weight detector 176 for substantially discharging sludge powder S into the pneumatic conveying duct 200a. That is to say, the rotary dispenser 180 is cooperatively regulated in the dispensing amount by the weight detector 176 which continuously detects the weight variation of the feeder tank 170. The rotary dispenser 180 is electrically connected with the weight detector 176 via a control unit (not shown) .

Sludge powder S is fed via the rotary dispenser 180 of the feeder unit 190 and into the pneumatic conveying duct 200a which is connected between the rotary dispenser 180 and the distributor 210a disposed adjacent to the final reduction reactor 30 side.

The pneumatic conveying duct 200a is connected to an inert gas duct 202 so that inert gas, e.g. N₂ gas, is fed under a predetermined pressure to force sludge powder S, which is fed into the pneumatic conveying duct 200a, to the distributor 210. The inert gas such as N₂ gas is fed into the pneumatic conveying duct 200a since it can prevent self-ignition of carbon component contained in sludge powder by a large quantity.

The sludge powder ducts 300 are provided in plurality between the final reduction reactor 30 and the distributor 210a adjacent thereto creating a plurality of sludge powder flows.

As shown in FIG. 2, after discharged via the rotary dispenser 180 of the powder sludge feeder unit 190 and conveyed on N₂ gas via pneumatic conveying duct 200a into the dispenser

210a, sludge powder S is blown into the final reduction reactor 30 in the plurality of flows from the dispenser 210a.

FIGS.3a and 3b specifically show the connecting structure of the sludge powder ducts 300 to the final reduction reactor 30. As shown in FIG. 3b, the fluidized bed T is formed over the gas distribution plate 30b in a lower portion of the final reduction reactor 30, and the gas distribution plate 30b has nozzles for forming gas jet layers in the fluidized bed T.

Therefore, it is preferred that the sludge powder ducts 300 are extended by the ends 300a into the fluidized bed T within the final reduction reactor 30 rather than simply connected to a reactor wall 30a of the final reduction reactor 30. When sludge powder S is re-blown into the reactor to raise the recycling rate of byproduct sludge, this connecting structure more uniformly mixes sludge powder S with reduced iron (not shown) during discharge of sludge powder S through the ends 300a of the ducts 300. The connecting structure of the sludge powder ducts 300 to the final reduction reactor 30 will be more specifically described as follows: As shown in detail in FIG. 3b, it is preferred that the sludge powder ducts 300 are designed to maintain an insertion angle Al, e.g. 55 to 65 deg. and preferably 60 deg. in respect to a horizontal line from the reactor wall 30a so that sludge powder S from the distributor 210a can be re-blown in the plurality of flows into the final reduction reactor 30 to be recycled therein.

Where the sludge powder ducts 300 have the insertion angle Al smaller than 55 deg., blown sludge powder S is centrally segregated in an upper portion of the fluidized bed T within the reactor. On the other hand, where the insertion angle Al is larger than 65 deg., blown sludge powder S is segregated in a lower portion of the fluidized bed T. Therefore, it is most preferable that the sludge powder ducts 300 are maintained with an insertion angle Al of 60 deg. As a result, sludge powder S may not be uniformly mixed across the fluidized bed T in the final reduction reactor 30 according to the insertion angle, and this has an effect to the recycling rate of byproduct sludge.

As shown in FIGS. 3a and 3b, the sludge powder ducts 300 are inserted into the final reduction reactor 30 with an insertion depth HI, which is about 20 to 30% and most preferably about 25% from the side wall 30a of the final reduction reactor

30. The insertion depth HI is indicated with percentage or % of the reactor radius since the reactor radius is variable.

Where the sludge powder ducts 300 has the insertion depth Hi smaller than 20% of the reactor radius, sludge powder S is segregated in a lateral portion of the fluidized bed T in the final reduction reactor 30 as in the insertion angle Al of the sludge powder ducts. On the other hand, where the insertion depth HI is larger than 30% of the reactor radius, the ends 300a are extended into the reactor too farther so that sludge powder S may not smoothly blown into the final reduction reactor owing to gas resistance in the gas jet layer J or particles in the fluidized bed T within the reactor. Therefore, it is most preferred if the insertion depth HI of the sludge powder ducts 300 is about 25% of the reactor radius.

As shown in FIG. 3b, the ends 300a of the sludge powder ducts 300 are properly distanced from the distribution plate 30b in a lower portion of the final reduction reactor 30 considering the distribution length of the inner gas jet layers J of the fluidized bed T within the final reduction reactor 30. Preferably, the ends 300a are distanced from the distribution plate 30b with a height L of about 400 to 500mm, and most preferably about 450mm.

Where the height L of the ends 300a from the gas distribution plate 30b is smaller than 400mm or larger than 500mm, blown sludge powder S is not properly introduced into the final reduction reactor 30 owing to resistance of high speed gas in the gas jet layers J over the gas distribution plate 30b.

Therefore, as shown in FIGS. 3a and 3b, the ends of the sludge powder ducts 300 are extended through the reactor wall 30a of the final reduction reactor 30 with predetermined ranges of insertion depth H, insertion angle Al and height L from the distribution plate. This is intended to raise the recycling rate of sludge by blowing sludge powder S into the fluidized bed T without segregation in the reactor as well as uniformly mixing sludge within the fluidized bed T. Beyond the above-mentioned ranges, sludge powder S is segregated in the fluidized bed T when blown via the sludge powder ducts 300. This deteriorates the quality of HBI produced by the HBI making apparatus 50 which is on the ore charging duct 42 between the final reduction reactor 30 and the melter gasifier 40. Then, as shown in FIG. 3a, the plurality of sludge powder ducts 300 diverging from the distributor 310a and connected to the final reduction reactor 30 may preferably number in 3 to 6, even though they may be variously numbered according to the size of the final reduction reactor 30. It is preferred that the sludge powder ducts 300 are arranged with the same interval in a radial direction of the final reduction reactor 30 so that sludge powder S can be smoothly blown into the fluidized bed T and uniformly mixed with fine reduced iron in the fluidized bed T.

In this case, it is preferred that the amount of sludge powder S blowing into the final reduction reactor is restricted to about 4 to 6% and preferably about 5% in respect to the amount of fine iron ore charged into the preheating reactor 10 of the 3 fluidized-bed reduction reactors. If sludge powder S is blown into the final reduction reactor 30 and then mixed in the HBI making apparatus 50 which is on the ore charging duct 42 between the final reduction reactor 30 and the melter gasifier 40, carbon component contained in blown sludge powder S may have effect on the quality of HBI.

That is, since sludge powder S is mixed with fine reduced iron and agglomerated in the fluidized bed T without combustion of carbon component in sludge powder as in the second byproduct sludge recycling apparatus (refer to FIG. 4) which will be described later, sludge powder S is preferably blown into the final reduction reactor 30 with a ratio of 5% in respect to the quantity of fine iron ore which are charged into the preheating reactor 10. The quantity of sludge powder can be adjusted with the rotary dispenser 180. Table 2 reports experiment result about byproduct sludge recycling, in which sludge powder S prepared through dewatering, drying and crushing is mixed with the weight ratio of about 5% into fine reduced iron. The result represents experimented values associated with qualities of HBI such as density, compressive strength and fracture rate at drop test. Also Table 2 compares quality standards of HBI necessary for stable adjustment in the ironmaking system of the invention.

Table 2. Quality Standards of sludge-Mixed Reduced Iron Agglomeration

As can be seen in Table 2 and FIG.2, it would be understood that quality standards of HBI required for a normal ironmaking process is satisfied by HBI of the invention which is made in the HBI making apparatus 50 by blowing sludge powder S into the final reduction reactor 30 and mixing the same with fine reduced iron, wherein sludge powder S is prepared in the first byproduct recycling apparatus la of the invention by dewatering, drying and crushing byproduct sludge produced from the water treatment unit 70.

As shown in FIGS.2 and 3, according to the first byproduct sludge recycling apparatus la of the invention, sludge powder S is prepared from byproduct sludge produced in the ironmaking process, re-blown into the fluidized bed T in the final reduction reactor 30, and mixed with fine reduced iron within the final reduction reactor 30. Mixture of sludge and iron is discharged from the final reduction reactor 30 and loaded into the HBI making apparatus 50, and then in the form of HBI charged into the melter gasifier 40. As a result, the ironmaking process yields a decreased amount of byproduct sludge to reduce sludge treatment cost and recycling C and F components in sludge decreases raw material loss so that productivity of the ironmaking process can be elevated and environmental pollution can be reduced.

FIGS.4 to 6 show an ironmaking system including the second byproduct sludge recycling apparatus lb according to another embodiment of the invention, in which the same or similar components as in the first byproduct recycling apparatus la are designated with the same reference numerals without any further detailed description. Hereinafter detailed description will be made about the second byproduct sludge recycling apparatus lb of the invention. As shown in FIG.1 and set forth above, well know is a method for controlling the temperature of the fluidized bed T within the fluidized-bed reduction reactors 10, 20 and 30, and examples thereof are disclosed in Japan Laid-Open Patent Application Nos. H8-337806 and H10-280021. According to these documents, the preheating reactor 10 is provided with oxidizing agent ducts 16 for blowing oxidizing agent into the fluidized bed T (refer to FIG. 5) formed within the preheating reactor 10 to partially burn reduction gas introduced into the fluidized bed T so as to maintain the temperature of the preheating reactor 10 at a predetermined temperature or higher.

As shown in FIGS. 4 and 5, the second byproduct sludge recycling apparatus lb of the invention is characterized in that sludge powder ducts 400 for blowing sludge powder S are connected to the oxidizing agent ducts 16 to recycle byproduct sludge from the ironmaking system.

According to the second byproduct sludge recycling apparatus lb of the invention shown in FIG. 4, as in the first sludge recycling apparatus la, the sludge powder preparing unit 120 dewaters, dries and crushes wet sludge discharged from the water treatment unit 70 to produce sludge powder S having a grain size of about 1mm. Sludge powder S produced like this is conveyed via the storage unit 160, the feeder unit 190 and a pneumatic conveying duct 200b into a distributor 210b disposed adjacent to the preheating reactor 10, in which the pneumatic conveying duct 200b is differently constructed from that in the first sludge recycling apparatus la. The sludge powder ducts 400 are connected between the distributor 210b and the oxidizing agent ducts 16 so that sludge powder S is blown via the sludge powder ducts 400 and then the oxidizing agent ducts 16 into the preheating reactor 10 so as to perform recycling of byproduct sludge.

Therefore, as shown in FIG. 5, together with oxidizing agent fed via the oxidizing agent ducts 16 into the fluidized bed T in the preheating reactor 10, sludge powder S is blown into the fluidized bed T. Blown sludge powder S is burnt in a combustion zone formed in the fluidized bed T in front of the oxidizing agent ducts 16 and thus melted and condensed therein so as to recycle sludge powder S which is obtained by treating byproduct sludge by-produced in the ironmaking process.

As shown in FIG. 5, it is preferred that the sludge powder ducts 400 are extended through the oxidizing agent ducts 16 with predetermined values of angle A2 and insertion depth H2 in order to have smooth feed of sludge powder S.

That is, the sludge powder ducts 400 are connected to the oxidizing agent ducts 16 with an insertion angle A2 of about 60 to 75 deg., and preferably of about 67 deg. This insertion angle A2 is obtained since the angle of repose meaning the minimum angle allowing free drop of sludge powder S is 60 deg. and sludge powder S can be freely dispersed at the maximum angle of 75 deg. into the flow of oxidizing agent without segregation in the oxidizing agent ducts 16. The ends 400 of the sludge powder ducts 400 are extended into the oxidizing agent ducts 16 with a proper penetration depth H2. The depth H2 is about 30 to 60%, preferably about 45%, in respect to the diameter of the oxidizing agent ducts 16. Where the depth H2 is under 30% or over 60% in respect to the diameter D of the oxidizing agent ducts 16, sludge powder S is segregated rather than smoothly mixed into the feeding flow of oxidizing agent which is fed into the preheating reactor via the oxidizing agent ducts 16. So it is needed that sludge powder ducts 400 are penetrated into the oxidizing agent ducts 16 in the above range.

When sludge powder S is fed together with oxidizing agent into the combustion zone in the fluidizing bed T within the preheating reactor 10 via the oxidizing agent ducts 16, carbon component in sludge powder S is gasified together with oxygen component in oxidizing agent by reducing gas which is fed from the pre reduction reactor 20 via a reducing gas duct 24 and a gas distribution plate 10b and blown from a lower portion to an upper portion in the preheating reactor 10. C and 0₂ components are gasified according to Equation 1:

C + λ0₂ -> (2 - 2λ)CO + (2λ - 1)C0₂ ... Equation 1, wherein "λ" in Equation 1 means mole ratio of oxygen in oxidizing agent consumed in combustion of C component contained in sludge powder S. As can be seen from combustibility test of sludge powder S shown in FIG. 6, the optimum combustion is performed where the mole ratio λ of 0₂/C is about 0.6 to 0.7.

Also as can be seen from Table 1, since C component contained in sludge reaches about 38wt%, the molecular number in sludge 1kg is 1X0.01X38/12 = 0.032, wherein 12 is the molecular weight of C.

As a result, since the optimum combustion is obtained when the mole ratio λ of 0₂/C is 0.6 to 0.7 as shown in FIG. 6, it can be understood that the optimum molecular number of 0₂ is 0.6

X0.032 to 0.7X0.032 = 0.0192 to 0.0224. The optimum oxygen Nm³ is 0.0192X22.4 to 0.0224X22.4 = 0.43 to 0.50, wherein 22.4 is a value calculated from the molecular weight of 0₂ 1kg = 22.4 Nm³.

As shown in FIG. 5, in combustion of sludge powder S blown via the sludge powder ducts 400, it can be understood that oxygen is necessary as much as 0.43 to 0.50 Nm³ per sludge powder 1kg. So the quantity of oxidizing agent blown via the oxidizing agent ducts 16 should be increased as much as necessary for combustion of sludge powder S over the quantity of oxidizing agent consumed for temperature control in the fluidized bed T of the preheating reactor 10.

That is, it is preferred that the quantity of oxidizing agent blown into the oxidizing agent ducts 16 of the preheating reactor 10 is increased for about 0.43 to 0.50 Nm³ for every 1kg of sludge powder S which is blown via the sludge powder ducts 400 in order to raise the combustion rate of the combustion zone formed in the reactor Other components such as iron and ash are contained in sludge powder which is blown into the combustion zone of the fluidized bed in the preheating reactor 10 as shown in FIG. 5. Iron and ash components are melted and condensed in the combustion zone, grow up to a grain size that is sufficient not to be splashed upward from the fluidized bed T of the preheating reactor 10, and then are mixed with fine iron ore (not shown) in the fluidized bed T while being dispersed therein. Mixture is fed through the first reduction reactor 20 connected to the preheating reactor 10 via the second ore duct 20 and through the final reduction reactor 30 into the HBI making apparatus 50, where mixture is agglomerated and loaded into the melter gasifier 40 for recycling. Table 3 reports result of melting condensation evaluation of iron and ash contained in sludge powder in combustion test thereof, in which iron and ash undergo melting agglomeration at the ratio of about at least 80% with a grain size of about at least 1mm, i.e. the size that agglomerated particles may not be splashed out of the fluidized bed T in the preheating reactor 10, at the optimum combustion condition of C component contained in sludge powder. It can be understood from this that sludge powder can be recycled for about 90% thereof by the second byproduct sludge recycling apparatus lb.

Table 3. Ratio of Melting agglomeration of Fe and Ash according to Sludge Powder Combustion

According to the second byproduct sludge recycling apparatus lb of the invention as set forth above, sludge powder having a grain size of 1mm or less is prepared from byproduct sludge by-produced in the ironmaking process, and blown together with oxidizing agent via the oxidizing agent ducts 16 into the preheating reactor 10 in order to control the temperature of the fluidized bed T of the fluidized-bed reduction reactor. Then, C component in sludge powder is gasified together with oxidizing agent via combustion reaction in the combustion zone within the fluidized bed. Other components such as iron and ash are melted and agglomerated under combustion heat in the fluidized bed to be mixed with fine iron ore. Mixture thereof is loaded via the pre and final reduction reactors 20 and 30 and as agglomerated via the HBI making apparatus 50 into the melter gasifier 40. This decreases the quantity of byproduct sludge in the ironmaking process thereby reducing sludge treatment cost. Furthermore, recycling of C and Fe components in sludge decreases raw material loss so as to enhance productivity of the ironmaking process as well as reduces environmental pollution.

FIG. 7 shows the third byproduct sludge recycling apparatus lc according to the third embodiment of the invention, in which the same or similar components as in the first and second byproduct recycling apparatuses la and lb are designated with the same reference numerals without any further detailed description. Hereinafter detailed description will be made about the second byproduct sludge recycling apparatus lc of the invention.

According to technical features, the third byproduct sludge recycling apparatus lc of the invention has both of the sludge powder ducts 300 and 400 of the first and second byproduct sludge recycling apparatuses la and lb in the ironmaking system. As shown in FIG. 7, the third byproduct sludge recycling apparatus lc of the invention, like the first and second byproduct sludge recycling apparatuses la and lb, dewaters, dries and crushes wet sludge discharged from the process water treatment unit 70 to prepare sludge powder S having a grain size of 1mm. Sludge powder S prepared like this is conveyed via a storage unit 160a, a feeder unit 190a and in part the first pneumatic conveying duct 200a into the first distributor 210a which is disposed adjacent to the final reduction reactor 30. The other portion of prepared sludge powder S is conveyed from the feeder unit 190a via the pneumatic conveying duct 200b into the second distributor 210b which is disposed adjacent to the preheating reactor 10. The first portion of sludge powder is blown from the first distributor 210a via the first sludge powder ducts 300 into the final reduction reactor 10, while the second portion of sludge powder is blown from the second distributor 210a via the second sludge powder ducts 400 and then oxidizing agent ducts 16 into the preheating reactor 10. These procedures enable byproduct sludge to be recycled.

As shown in FIG. 7, the sludge powder storage unit 160a of the third byproduct sludge recycling apparatus lc of the invention is equipped with a storage tank 130 having dual discharge ports 130a and 130b to which pairs of compensators 140a and 140b and cutout valves 150a and 150b are connected respectively.

The cutout valve 150a is connected to a sludge feeder tank 170a which is equipped with upper and lower level switches 172a and 174a and a weight detector 176a for detecting the weight variation of charged sludge powder in a lower portion of the feeder tank 170a. The cutout valve 150b is connected to a sludge feeder tank 170b which is equipped with upper and lower level switches 172b and 174b and a weight detector 176b for detecting the weight variation of charged sludge powder in a lower portion of the feeder tank 170b. Each of the feeder tanks 170a and 170b also has a rotary dispenser 180a or 180b for adjusting its revolution rate in response to a signal from the weight detector 176a or 176b to adjust the amount of sludge powder S fed through the same. It is preferred that the rotary dispensers 180a and 180b are electrically connected in a cooperative manner with a control unit (not shown) for regulating the amount of sludge powder S blown into the oxidizing agent ducts 16 and the final reduction reactor 30. The rotary dispenser 180a is connected with the first pneumatic conveying duct 200a so that sludge powder S is fed via the same and the first distributor 210a into the first sludge powder ducts 300. Also the rotary dispenser 180b is connected with the second pneumatic conveying duct 200b so that sludge powder S is fed via the same and the second distributor 210b to the second sludge powder ducts 400.

As shown in FIG. 7, sludge powder S blown into the final reduction reactor 30 is dispersed in the fluidized bed T and then discharged as mixed with fine reduced iron into the HBI making apparatus 50, in which mixture of sludge powder and fine reduced iron is agglomerated, and from which agglomerated mixture is loaded into the melter gasifier 40. At the same time, sludge powder S is blown into the preheating reactor 10 together with oxidizing agent which is fed via the oxidizing agent ducts 16 into the fluidized bed T of the preheating reactor 10, and then burnt in the combustion zone in the fluidized bed T so that C component in sludge powder S is burnt and gasified and Fe and ash components are melted and agglomerated mixing with fine reduced iron. Mixture of Fe and ash components and fine reduced iron is loaded via the reduction reactors and as agglomerated via the HBI making apparatus 50 into the melter gasifier 40. In this manner, byproduct sludge can be recycled. Also as shown in FIGS. 3, 5 and 7, the first sludge powder ducts 300 are connected to the final reduction reactor 30 having an insertion depth HI in the range of 20 to 30% in respect to the radius of the final reduction reactor 30 and a connection angle Al in the range of 55 to 65 deg. in respect to the reactor wall 30a, and by their ends 300a having an insertion depth L of 400 to 500mm from the gas distribution plate 30b inside the final reduction reactor 30. These numerical values are determined according to the same reason as described in respect to the first sludge recycling apparatus la. Further, the second sludge powder ducts 400 are connected to the oxidizing agent ducts 16 having an insertion depth H2 of 30 to 60% in respect to the diameter D of the oxidizing agent ducts 16 and a connection angle A2 of 60 to 75 deg. These numerical values are determined according to the same reason as described in respect to the second sludge recycling apparatus lb.

As shown in FIG. 7, it is preferred that the quantity of sludge powder S fed into the final reduction reactor 30 via the first sludge powder ducts 300 is about 4 to 6% and preferably about 5% of the quantity of fine iron ore blown into the preheating reactor 10. These numerical values are determined according to the same reason as described in respect to the second sludge recycling apparatus la.

Therefore, after the quantity of sludge powder to be blown into the final reduction reactor 30 via the first sludge powder ducts 300 is set corresponding to the quantity of fine reduced iron loaded into the preheating reactor 10, the remainder of total feedable sludge powder is blown via the second sludge powder ducts 400 into the oxidizing agent ducts 16.

Also as shown in FIGS. 5 and 7, the quantity of oxidizing agent blown via the oxidizing agent ducts 16 is adjusted corresponding to the quantity of sludge powder blown into the second sludge powder ducts 400, i.e. increased for about 0.43 to 0.50 Nm³ as sludge powder is increased for 1kg, according to the same reason as described in respect to the second sludge recycling apparatus lb.

The third byproduct sludge recycling apparatus lc of the invention is more complicated than the first and second byproduct sludge recycling apparatuses la and lb since the third recycling apparatus lc comprises both of the first and second sludge powder ducts 300 and 400. However, where any of the first and second sludge powder ducts 300 and 400 and the first and second distributors 210a and 210b of the first and second byproduct sludge recycling apparatuses la and lb has a trouble, the recycling operation of byproduct sludge can be still carried out via other normal sludge powder ducts. Therefore, this structure will be more useful considering the operation of the overall ironmaking system.

In the first to third byproduct sludge recycling apparatuses la to lc shown in FIGS. 2, 4 and 7, inert gas ducts 202 are respectively connected to the pneumatic conveying ducts 200a and 200b so that sludge powder S can be more smoothly conveyed from the rotary dispensers 180, 180a and 180b of the sludge powder feeder unit 190 and 190a to the distributors 210a and 210b in the side of the final reduction reactor 30 and the preheating reactor 10.

Of course, as not shown specifically in FIGS. 2, 4 and 7, in each of the pneumatic conveying ducts 200a and 200b, the sludge powder ducts 300 and 400, the ore ducts 12, 22, 32 and 42, the reducing gas ducts 44, 34 and 24, the gas discharge duct 14 and the process water ducts 62a and 62b between the water treatment unit 70 and the scrubbers 60a and 60b, a cutout valve is equipped for adjusting fluid flowing through the same, i.e. flow of sludge powder, ore, reducing gas, discharge gas and process water.

Further, as not shown in FIGS. 2, 4 and 7, a control unit electrically connects the upper and lower level switches 172, 174, 172a, 174a, 172b, 174b of the feeder units 190 and 190b in cooperation with the cutout valves 150, 150a and 150b of the storage units 160 and 160a, the weight detectors 176, 176a and 176b and the rotary dispensers 180, 180a and 180b in cooperation therewith so that these components are cooperative in their operation. In particular, in the third byproduct sludge recycling apparatus lc, the rotary dispensers necessarily operate in a cooperative manner via a control unit so as to feed sludge powder to the first and second sludge powder ducts 300 and 400 by proper quantities.

Industrial Applicability

According to the first and second byproduct sludge recycling apparatuses la and lb of the invention as set forth above, byproduct sludge generated in the ironmaking process is powdered, re-blown into the fluidized beds T in the final reduction reactor 30 and the preheating reactor 10, mixed with fine reduced iron, and then therewith agglomerated into the form of HBI, which is loaded into the melter gasifier 40. Generation of byproduct sludge is reduced owing to the ironmaking process and thus sludge treatment cost is reduced also. Recycling C and Fe components in sludge decreases raw material loss to provide excellent effects of enhancing productivity of the ironmaking process and reducing environmental pollution.

Moreover, in addition to the effects owing to the first and second byproduct sludge recycling apparatuses la and lb, the third byproduct sludge recycling apparatus lc of the invention is provided with both of the sludge powder ducts 300 and 400 according to the first and second byproduct sludge recycling apparatuses la and lb. Even if a trouble occurs to any of the distributors and sludge powder ducts, the byproduct sludge recycling operation can be continuously carried out by selecting a normal line so as to impart a practical effect excellent in system operability.

Although the invention has been shown and described with reference to certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. In an ironmaking system for producing molten iron by using non-coking coal and fine iron ore and which includes fluidized-bed reduction reactors 10, 20, 30 for reducing introduced fine iron ore, a melter gasifier 40 connected thereto via an HBI making apparatus 50, a scrubber 60 connected to gas discharge ducts 14 of the melter gasifier 40 and the preheating reactor 10 and a process water treatment unit 70 connected to the scrubber 60 for treating process water, a byproduct sludge recycling apparatus comprising: a sludge powder preparing unit 120 connected to the water treatment unit 70 for dewatering, drying and crushing byproduct sludge discharged from the water treatment unit 70 to prepare sludge powder; a storage unit 160 connected to the sludge powder preparing unit 120 for storing sludge powder S prepared from the sludge powder preparing unit 120; a sludge powder feeder unit 190 for feeding sludge powder discharged from the sludge powder storage unit 160 via a pneumatic conveying duct 200a to a distributor 210a; and a sludge powder duct 300 connected between the distributor 210a and the final reduction reactor 30 with a plurality of sludge powder flows for re-blowing sludge powder S into the final reduction reactor 30.

2. A byproduct sludge recycling apparatus in accordance with claim 1, wherein the sludge powder duct 300 has an end 300a which is inserted into the final reduction reactor 30 via a reactor wall 30a with an insertion depth HI of about 20 to 30% in respect to the diameter of the final reduction reactor 30, and wherein the sludge powder duct 300 has a penetration angle Al of about 55 to 65 deg. in respect to the reactor wall 30a.

3. A byproduct sludge recycling apparatus in accordance with claim 1, wherein the sludge powder duct 300 has an end 300a which is connected to the final reduction reactor 30 and distanced for about 400 to 500mm from a distribution plate 30b which is disposed in a lower portion in the final reduction reactor 30.

4. A byproduct sludge recycling apparatus in accordance with claim 1, wherein the quantity of sludge powder S blown into the final reduction reactor 30 via the sludge powder duct 300 is about 4 to 6% in respect to the quantity of fine iron ore blown into the preheating reactor 10.

5. In an ironmaking system for producing molten iron by using non-coking coal and fine iron ore and which includes fluidized-bed reduction reactors 10, 20, 30 for reducing introduced fine iron ore, a melter gasifier 40 connected thereto via an HBI making apparatus 50, a scrubber 60 connected to gas discharge ducts 14 of the melter gasifier 40 and the preheating reactor 10 and a process water treatment unit 70 connected to the scrubber 60 for treating process water, a byproduct sludge recycling apparatus comprising: a sludge powder preparing unit 120 connected to the water treatment unit 70 for dewatering, drying and crushing byproduct sludge discharged from the water treatment unit 70 to prepare sludge powder; a storage unit 160 connected to the sludge powder preparing unit 120 for storing sludge powder S prepared from the sludge powder preparing unit 120; a sludge powder feeder unit 190 for feeding sludge powder discharged from the sludge powder storage unit 160 via a pneumatic conveying duct 200b to a distributor 210b; and a sludge powder duct 400 connected between the distributor 210b and an oxidizing agent duct 16 disposed to the preheating reactor 10 with a plurality of sludge powder flows for re-blowing sludge powder S into the preheating reactor 10.

6. A byproduct sludge recycling apparatus in accordance with claim 5, wherein the sludge powder duct 400 is connected in a penetrating manner to the oxidizing agent duct 16 with an insertion depth H2 of about 30 to 60% in respect to the diameter

D of the oxidizing agent duct 16, and wherein the sludge powder duct 400 is connected to the oxidizing agent duct 16 with a connection angle A2 of about 60 to 75 deg.

7. A byproduct sludge recycling apparatus in accordance with claim 5, wherein the quantity of oxidizing agent blown via the oxidizing agent duct 16 is increased for about 0.43 to 0.50 Nm³ for every 1kg of sludge powder S.

8. In an ironmaking system for producing molten iron by using non-coking coal and fine iron ore and which includes fluidized-bed reduction reactors 10, 20, 30 for reducing introduced fine iron ore, a melter gasifier 40 connected thereto via an HBI making apparatus 50, a scrubber 60 connected to gas discharge ducts 14 of the melter gasifier 40 and the preheating reactor 10 and a process water treatment unit 70 connected to the scrubber 60 for treating process water, a byproduct sludge recycling apparatus comprising: a sludge powder preparing unit 120 connected to the water treatment unit 70 for dewatering, drying and crushing byproduct sludge discharged from the water treatment unit 70 to prepare sludge powder; a storage unit 160 connected to the sludge powder preparing unit 120 for storing sludge powder S prepared from the sludge powder preparing unit 120; a sludge powder feeder unit 190a for feeding sludge powder discharged from the sludge powder storage unit 160 via first and second pneumatic conveying ducts 200a and 200b to first and second distributors 210a and 210b; and a first sludge powder duct 300 connected between the first distributor 210a and the final reduction reactor 30 with a plurality of sludge powder flows for re-blowing sludge powder S into the final reduction reactor 30; and a second sludge powder duct 400 connected between the second distributor 210b and an oxidizing agent duct 16 disposed to the preheating reactor 10 with a plurality of sludge powder flows for re-blowing sludge powder S into the preheating reactor

10.

9. A byproduct sludge recycling apparatus in accordance with claim 8, wherein the first sludge powder duct 300 is connected to the final reduction reactor 30, and has an end 300a which is inserted with an insertion depth HI of about 20 to 30% in respect to the diameter of the final reduction reactor 30 and with a connection angle Al of about 55 to 65 deg. in respect to the reactor wall 30a, and wherein the end 300a of the each first sludge powder duct 300 has an insertion height L of about 400 to 500mm from a reaction distribution plate 30b which is disposed within the final reduction reactor 30.

10. A byproduct sludge recycling apparatus in accordance with claim 8, wherein the second sludge powder duct 400 has an end 400a which is connected in a penetrating manner to the oxidizing agent duct 16 with an insertion depth H2 of about 30 to 60% in respect to the diameter D of the oxidizing agent duct 16, and wherein the second sludge powder duct 400 is connected to the oxidizing duct 16 with a connection angle A2 of about 60 to 75 deg.

11. A byproduct sludge recycling apparatus in accordance with claim 8, wherein the quantity of sludge powder S blown into the final reduction reactor 30 via the sludge powder duct 300 is about 4 to 6% in respect to the quantity of fine iron ore blown into the preheating reactor 10, and wherein the quantity of oxidizing agent blown via the oxidizing agent duct 16 is increased for about 0.43 to 0.50 Nm³ for every 1kg of sludge powder S which is blown via the second sludge powder duct 400.

12. A byproduct sludge recycling apparatus in accordance with one of the preceding claims 1, 5 and 8, wherein the sludge powder preparing unit 120 comprises: a dewaterer 80 connected to the water treatment unit 70 for solidifying wet sludge discharged from the water treatment unit 70; a sludge drier 90 connected to the dewaterer 80 for drying solidified sludge; a crusher 100 connected to the drier 90 for crushing solidified dry sludge into a fine grain size; and a sludge powder classifier 110 connected to the crusher 100 for classifying crushed sludge powder.

13. A byproduct sludge recycling apparatus in accordance with claim 1 or 5, wherein the sludge powder storage unit 160 comprises: a storage tank 130 connected to the sludge powder preparing unit 120, the storage tank 130 having an inert gas feeding duct 134 which is connected for internally imparting inert atmosphere and a dust collector 132 disposed to a discharge port of inert gas fed therein; an compensatorl40 connected downstream of the storage tank 130; and a cutout valve 150 disposed to the compensator 140 for adjusting feed of stored sludge powder.

14. A byproduct sludge recycling apparatus in accordance with claim 8, wherein the sludge powder storage unit 160a comprises: a storage tank 130 connected to the sludge powder preparing unit 120, the storage tank 130 having an inert gas feeding duct 134 which is connected for internally imparting inert atmosphere, a dust collectors 132 disposed to a discharge port of inert gas fed therein and dual discharge ports 130a and 130b; compensators 140a and 140b connected respectively to the dual discharge ports 130a and 130b of the storage tank 130; and cutout valves 150a and 150b disposed to the compensators for adjusting feed of stored sludge powder.

15. A byproduct sludge recycling apparatus in accordance with claim 1 or 5, wherein the sludge feeder unit 190 comprises: a sludge powder feeder tank 170 connected downstream of the sludge storage unit 160, the sludge powder tank 170 having upper and lower level switches 172 and 174 in upper and lower portions for detecting the level of sludge powder stored therein. and a weight detector 176 in a lower portion for detecting the weight variation of sludge therein; and a rotary dispenser 180 connected to the feeder tank 170 for adjusting revolution rate in response to a signal from the weight detector 176 to regulate the feeding quantity of sludge powder S.

16. A byproduct sludge recycling apparatus in accordance with claim 8, wherein the sludge feeder unit 190a comprises: sludge powder feeder tanks 170a and 170b connected downstream of the sludge storage unit 160a, the sludge powder tanks 170a and 170b having upper and lower level switches 172a, 174b; 172b, 174b in upper and lower portions for detecting the level of sludge powder stored therein and weight detectors 176a and 176b in lower portions for detecting weight variation of sludge therein; and rotary dispensers 180a and 180b connected respectively to the feeder tanks 170a and 170b for adjusting revolution rate in response to a signal from the weight detectors 176a and 176b to regulate the feeding quantity of sludge powder S.

17. A byproduct sludge recycling apparatus in accordance with one of the preceding claims 1, 5 and 8, wherein the pneumatic conveying ducts 200a and 200b are connected with an inert gas duct 202 for feed of sludge powder.