US20100242683A1 - Process for treating exhaust gas generated during water-granulation of slag and system for said treatment - Google Patents

Process for treating exhaust gas generated during water-granulation of slag and system for said treatment Download PDF

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US20100242683A1
US20100242683A1 US12/625,686 US62568609A US2010242683A1 US 20100242683 A1 US20100242683 A1 US 20100242683A1 US 62568609 A US62568609 A US 62568609A US 2010242683 A1 US2010242683 A1 US 2010242683A1
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exhaust gas
water
granulation
slag
metal
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US12/625,686
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Tetsuo Yamaki
Atsushi Kurosaka
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Pan Pacific Copper Co Ltd
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Pan Pacific Copper Co Ltd
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Assigned to PAN PACIFIC COPPER CO., LTD. reassignment PAN PACIFIC COPPER CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KUROSAKA, ATSUSHI, YAMAKI, TETSUO
Priority to US12/728,861 priority Critical patent/US20100243454A1/en
Publication of US20100242683A1 publication Critical patent/US20100242683A1/en
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22BPRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B15/00Obtaining copper
    • C22B15/0026Pyrometallurgy
    • C22B15/0054Slag, slime, speiss, or dross treating
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22BPRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/04Working-up slag
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27DDETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D17/00Arrangements for using waste heat; Arrangements for using, or disposing of, waste gases
    • F27D17/008Arrangements for using waste heat; Arrangements for using, or disposing of, waste gases cleaning gases
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21BMANUFACTURE OF IRON OR STEEL
    • C21B2400/00Treatment of slags originating from iron or steel processes
    • C21B2400/02Physical or chemical treatment of slags
    • C21B2400/022Methods of cooling or quenching molten slag
    • C21B2400/024Methods of cooling or quenching molten slag with the direct use of steam or liquid coolants, e.g. water
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21BMANUFACTURE OF IRON OR STEEL
    • C21B2400/00Treatment of slags originating from iron or steel processes
    • C21B2400/05Apparatus features
    • C21B2400/066Receptacle features where the slag is treated
    • C21B2400/072Tanks to collect the slag, e.g. water tank
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28Manufacture of steel in the converter
    • C21C5/38Removal of waste gases or dust
    • C21C5/40Offtakes or separating apparatus for converter waste gases or dust
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22BPRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/02Working-up flue dust
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/20Recycling
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/25Process efficiency

Definitions

  • the present invention relates to a process for treating the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal. Particularly, it relates to a process for treating metal fumes contained in the exhaust gas.
  • the present invention relates to a system for treating the exhaust gas which is generated when the slag discharged from a smelting furnace for non-ferrous metal is water-granulated. Particularly, it relates to the system for treating metal fumes contained in the exhaust gas.
  • the smelting process of non-ferrous metals such as copper, lead, zinc and nickel forms matte, which is the mixture of impure metal sulfides, and slag, which is the dreg of non-metal composition, by the smelting reaction in the smelting furnace.
  • the matte and slag are separated and discharged from the smelting furnace.
  • the concentrate of copper sulfide minerals is charged into the smelting furnace such as a blast furnace, a reverberatory furnace, a flash furnace and the like, and then heated and melted to form the matte containing high copper value and the slag mainly containing iron and silicic acid, subsequently, which are then separated and discharged.
  • the matte is smelted by oxidizing blowing in a converter to produce crude copper.
  • the slag is generally water-granulated using high-pressure brine or industrial water to the size which is easy to handle, and then subjected to landfill, or effectively used as construction materials and the like.
  • Patent document 1 describes a method for removing H 2 S gas and/or SO 2 gas, which is generated and mixed at the quenching reaction of the molten dreg with cold water, from a large amount of exhaust gas, which is generated when the molten dreg is water-granulated by adding cold water to the molten dreg discharged from a blast furnace.
  • the above method comprises reducing the temperature of the exhaust gas containing H 2 S gas and SO 2 gas by scattering cooling water to the exhaust gas so that water vapor in the exhaust gas is condensed, and then saturating the exhaust gas by separating the condensed water, and then removing fine water droplets suspending in the exhaust gas to form a gas body of the saturated vapor, and then returning the gas body to the blast furnace so that H 2 S gas and SO 2 gas may form slag by desulfurization reaction in the blast furnace (claim 1 ).
  • a wet electrostatic precipitator is mentioned as a means for removing the fine water droplets suspending in the exhaust gas to obtain a gas body of the saturated vapor.
  • Patent document 2 describes a method for treating the vapor and gas containing H 2 S and SO 2 generated during water-granulation of the slag from the blast furnace, the method comprising spraying alkaline water.
  • one problem to be solved by the present invention is to provide a process for treating the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal. Further, another problem to be solved by the present invention is to provide a system for treating the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal.
  • the present inventor analyzed the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal and found that a trace amount of metal fumes such as iron and arsenic and the like were contained in a large amount of water vapor.
  • the metal fumes which are fine particles produced from condensation of metal vapor, should be prevented from being exhausted to the air from the viewpoint of preservation of the working environment and surrounding environment.
  • Metal fumes generally have a very small particle diameter, most of which are thought to be 1 ⁇ m or less. It is hard to collect the submicron particles in water droplets by inertia collisions. They are merely expected to be collected by Brownian diffusing motion. Accordingly, it is generally difficult to collect 90% or more of the particles by a spray tower with water droplets having a fine particle diameter. Further, the diameter of water droplets may not be maintained due to suspended substance (SS) contained in spray water and therefore, it is possible that the efficiency of collection may be reduced. In addition, scales may be deposited in the piping, and therefore, there is apprehension that the maintenance of the spray tower may be frequently required.
  • SS suspended substance
  • the metal fumes may be removed by using a wet electrostatic precipitator. It has been known that the metal fumes may be collected by the wet electrostatic precipitator. However, as far as the present inventors' knowledge, there has not been the case where the wet electrostatic precipitator is applied to the treatment of the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal. Further, the necessity of such treatment also has not been recognized.
  • the present invention is a process for treating an exhaust gas, which is generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal, containing the water vapor as a major component and metal fumes, the process comprising a step of treating the exhaust gas by a wet electrostatic precipitator.
  • the non-ferrous metal is copper
  • the exhaust gas contains one or more of metal fumes selected from Cu, Zn, Ni and Fe.
  • the process further comprises a step of neutralizing and then filtrating waste water containing metal components discharged from the wet electrostatic precipitator to obtain a residue and returning the residue to the smelting furnace.
  • the present invention is a system for treating an exhaust gas, which is generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal, containing the water vapor as a major component and metal fumes, the system comprising a means for collecting the exhaust gas, an exhaust gas duct and a wet electrostatic precipitator, wherein the means for collecting the exhaust gas is located above a spot where the exhaust gas is generated, and the means for collecting the exhaust gas and the wet electrostatic precipitator is connected via the exhaust gas duct.
  • the non-ferrous metal is copper
  • the exhaust gas contains one or more of metal fumes selected from Cu, Zn, Ni and Fe.
  • the present invention makes it possible to remove the metal fumes from the exhaust gas which is generated when the slag discharged from the smelting furnace for non-ferrous metal is water-granulated.
  • FIG. 1 indicates one example of the scheme, related to the present invention, for treating the exhaust gas.
  • Slag discharged from the smelting furnace 1 such as an electric slag cleaning furnace is flowed, through the slag runner 3 , into the water-granulation runner 4 and then water-granulated by granulating water 2 flowed down through the water-granulation runner, and then fell into the water-granulation tank 6 as the water-granulated slag.
  • the water-granulated slag is picked up by a bucket elevator (not indicated) provided in the water-granulation tank and carried away from the system.
  • the composition of the slag discharged from the smelting furnace differs depending on the kind of non-ferrous metal to be smelted.
  • non-ferrous metal which is an object of the present invention, include, but not particularly limited to, copper, zinc and nickel.
  • the slag before water-granulation is usually at a high-temperature of about 1150-1300° C.
  • a large amount of water vapor is generated as the exhaust gas 5 .
  • the generated water vapor which contains a very small amount of the metal fumes is recovered by a hood for collecting smoke 7 (a means for collecting the exhaust gas) which covers over the water-granulation runner 4 and water-granulation tank 6 , desirably the hood can move vertically and horizontally.
  • the exhaust gas resulting from water-granulation contains metal fumes such as Cu, Zn and Fe generally at a concentration of about 0.1-10 mg/m 3 .
  • the composition of metal fumes is different depending on the metal to be smelted.
  • the concentration of Zn is higher compared to other metals, which is usually about 1-10 mg/m 3 .
  • the temperature of the exhaust gas in the hood for collecting the smoke is typically about 80-90° C.
  • the exhaust gas 5 recovered by the hood for collecting the smoke 7 , including water vapor as a main component is introduced, through a flue 8 (the exhaust gas duct), into the wet electrostatic precipitator 9 .
  • the water vapor is partially condensed spontaneously as it passes through the flue 8 .
  • the temperature of the exhaust gas at the entrance of the wet electrostatic precipitator 9 is typically about 30-80° C.
  • a means for scattering cooling water to the exhaust gas (cooling tower and the like) between the hood for collecting smoke and the wet electrostatic precipitator is not required.
  • the wet electrostatic precipitator 9 is a device which provides a high voltage between a discharging electrode and a dust collecting electrode to generate corona discharge, charging the particles suspending in the gas, and the particles being recovered by the dust collecting electrode by Coulomb force caused by electric field, and then discharges the recovered particles as waste water by washing them out with spray water.
  • Metal fumes are fine particles, made by aggregation of metal vapor, which can be recovered by the wet electrostatic precipitator. However, it is desirable for obtaining a sufficient recovery to operate at a high voltage because most of them are a fine particle equal to or less than 1 ⁇ m.
  • the wet electrostatic precipitator is typically operated at a voltage of about 10-50 kV and a current of about 30-100 mA.
  • wet electrostatic precipitator 9 Any known wet electrostatic precipitator 9 may be used as appropriate.
  • the wet electrostatic precipitator include a parallel type where a discharging electrode and a dust collecting electrode are arranged so that they are placed in parallel with gas flow, and a cross-flow type where a collecting electrode and a dust discharging electrode are arranged so that they are placed at a right angle to the gas flow (Ex. Neueluft type).
  • the exhaust gas 10 discharged from the wet electrostatic precipitator 9 can be released into the air.
  • the temperature of the exhaust gas at the exit of the wet electrostatic precipitator 9 is about 20-40° C.
  • the waste water 11 containing the recovered metal discharged from the wet electrostatic precipitator 9 is recovered by the waste water tank 12 , and then pumped out to a combined waste water treatment facility where the waste water is subjected to neutralizing treatment and then filtrated with a filter press.
  • the metal recovered as a residue can be returned to the smelting furnace as mixed minerals.
  • the treatment of the exhaust gas which was generated during water-granulation of high-temperature slag discharged from an electric slag cleaning furnace attached to a flash furnace was performed.
  • a system for treating the exhaust gas was constructed according to the scheme for treating the exhaust gas depicted in FIG. 1 .
  • the slag discharged from the electric slag cleaning furnace flows, through the slag runner, into the water-granulation runner, and then water-granulated by granulating water flowed down through the water-granulation runner, and then fell into the water-granulation tank as water-granulated slag.
  • the exhaust gas containing a large amount of water vapor resulting from water-granulation was recovered by a hood for collecting smoke that covers over the water-granulation runner and water-granulation tank.
  • the temperature of the exhaust gas in the hood for collecting the smoke is about 80-90° C.
  • the exhaust gas recovered by the hood for collecting the smoke enters the flue, through the entrance of the flue which is placed at the top of the hood and travels to the wet electrostatic precipitator.
  • the temperature of the exhaust gas flowed into the wet electrostatic precipitator was about 30-80° C.
  • the temperature of the exhaust gas discharged from the wet electrostatic precipitator was about 20-40° C.
  • the amount of slag to be water-granulated 2.5 t/min
  • the amount of the exhaust gas recovered by the hood for collecting the smoke 300 m 3 /min
  • the concentration of metals in the exhaust gas recovered by the hood for collecting the smoke (the concentration at the entrance of the precipitator), the concentration of metals in the exhaust gas after the treatment by the wet electrostatic precipitator (the concentration at the exit of the precipitator), and the recovery rate (%) are shown in Table 2.
  • the measurement of the concentration of the metals was carried out by methods for determination of metals in flue gas according to JIS K0083.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Environmental & Geological Engineering (AREA)
  • Organic Chemistry (AREA)
  • Metallurgy (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
  • Manufacture Of Iron (AREA)
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  • Electrostatic Separation (AREA)

Abstract

The present invention provides a process for treating a exhaust gas which is generated when slag discharged from a smelting furnace for non-ferrous metal is water-granulated. There is provided a process for treating an exhaust gas, which is generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal, containing the water vapor as a major component and metal fumes, the process comprising a step of treating the exhaust gas by a wet electrostatic precipitator.

Description

    BACKGROUND OF THE INVENTION
  • 1. Field of the Invention
  • The present invention relates to a process for treating the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal. Particularly, it relates to a process for treating metal fumes contained in the exhaust gas. In addition, the present invention relates to a system for treating the exhaust gas which is generated when the slag discharged from a smelting furnace for non-ferrous metal is water-granulated. Particularly, it relates to the system for treating metal fumes contained in the exhaust gas.
  • 2. Description of the Related Art
  • The smelting process of non-ferrous metals such as copper, lead, zinc and nickel forms matte, which is the mixture of impure metal sulfides, and slag, which is the dreg of non-metal composition, by the smelting reaction in the smelting furnace. The matte and slag are separated and discharged from the smelting furnace. For example, in the smelting process of copper, the concentrate of copper sulfide minerals is charged into the smelting furnace such as a blast furnace, a reverberatory furnace, a flash furnace and the like, and then heated and melted to form the matte containing high copper value and the slag mainly containing iron and silicic acid, subsequently, which are then separated and discharged. The matte is smelted by oxidizing blowing in a converter to produce crude copper. The slag is generally water-granulated using high-pressure brine or industrial water to the size which is easy to handle, and then subjected to landfill, or effectively used as construction materials and the like.
  • When the high-temperature slag discharged from the smelting furnace is water-granulated, exhaust gas containing a large amount of water vapor is generated. As a method for treating the exhaust gas generated during the water-granulation of slag, several methods are known for treating the exhaust gas generated when the slag discharged from the blast furnace for smelting iron is water-granulated.
  • For example, Japanese Patent Application Public Disclosure No. 8-245243 (Patent document 1) describes a method for removing H2S gas and/or SO2 gas, which is generated and mixed at the quenching reaction of the molten dreg with cold water, from a large amount of exhaust gas, which is generated when the molten dreg is water-granulated by adding cold water to the molten dreg discharged from a blast furnace.
  • The above method comprises reducing the temperature of the exhaust gas containing H2S gas and SO2 gas by scattering cooling water to the exhaust gas so that water vapor in the exhaust gas is condensed, and then saturating the exhaust gas by separating the condensed water, and then removing fine water droplets suspending in the exhaust gas to form a gas body of the saturated vapor, and then returning the gas body to the blast furnace so that H2S gas and SO2 gas may form slag by desulfurization reaction in the blast furnace (claim 1). A wet electrostatic precipitator is mentioned as a means for removing the fine water droplets suspending in the exhaust gas to obtain a gas body of the saturated vapor.
  • In U.S. Pat. No. 5,540,895 (Patent document 2) describes a method for treating the vapor and gas containing H2S and SO2 generated during water-granulation of the slag from the blast furnace, the method comprising spraying alkaline water.
  • All of the methods described above are directed to the treatment of the exhaust gas generated at water-granulation of the slag produced at the process for smelting iron and no method for treating the exhaust gas generated at water-granulation of the slag discharged from the smelting furnace for non-ferrous metal is disclosed. To date, the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal has been usually released to the air without any treatment since it has not been thought that any component to be treated is contained in the exhaust gas. Thus, the components have not yet been analyzed in detail, and therefore, the components to be treated have not yet been revealed.
  • SUMMARY OF THE INVENTION
  • Accordingly, one problem to be solved by the present invention is to provide a process for treating the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal. Further, another problem to be solved by the present invention is to provide a system for treating the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal.
  • The present inventor analyzed the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal and found that a trace amount of metal fumes such as iron and arsenic and the like were contained in a large amount of water vapor. The metal fumes, which are fine particles produced from condensation of metal vapor, should be prevented from being exhausted to the air from the viewpoint of preservation of the working environment and surrounding environment.
  • Metal fumes generally have a very small particle diameter, most of which are thought to be 1 μm or less. It is hard to collect the submicron particles in water droplets by inertia collisions. They are merely expected to be collected by Brownian diffusing motion. Accordingly, it is generally difficult to collect 90% or more of the particles by a spray tower with water droplets having a fine particle diameter. Further, the diameter of water droplets may not be maintained due to suspended substance (SS) contained in spray water and therefore, it is possible that the efficiency of collection may be reduced. In addition, scales may be deposited in the piping, and therefore, there is apprehension that the maintenance of the spray tower may be frequently required.
  • On the other hand, in the collection by a wet electrostatic precipitator (mist Cottrell precipitator), efficiency of dust collection of 80% or more may be attained even when the diameter of the dust particle is submicron. Therefore, the metal fumes may be removed by using a wet electrostatic precipitator. It has been known that the metal fumes may be collected by the wet electrostatic precipitator. However, as far as the present inventors' knowledge, there has not been the case where the wet electrostatic precipitator is applied to the treatment of the exhaust gas generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal. Further, the necessity of such treatment also has not been recognized.
  • Accordingly, in one aspect, the present invention is a process for treating an exhaust gas, which is generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal, containing the water vapor as a major component and metal fumes, the process comprising a step of treating the exhaust gas by a wet electrostatic precipitator.
  • In one embodiment of the process related to the present invention, the non-ferrous metal is copper.
  • In another embodiment of the process related to the present invention, the exhaust gas contains one or more of metal fumes selected from Cu, Zn, Ni and Fe.
  • In yet another embodiment of the process related to the present invention, the process further comprises a step of neutralizing and then filtrating waste water containing metal components discharged from the wet electrostatic precipitator to obtain a residue and returning the residue to the smelting furnace.
  • In another aspect, the present invention is a system for treating an exhaust gas, which is generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal, containing the water vapor as a major component and metal fumes, the system comprising a means for collecting the exhaust gas, an exhaust gas duct and a wet electrostatic precipitator, wherein the means for collecting the exhaust gas is located above a spot where the exhaust gas is generated, and the means for collecting the exhaust gas and the wet electrostatic precipitator is connected via the exhaust gas duct.
  • In one embodiment of the system related to the present invention, the non-ferrous metal is copper.
  • In another embodiment of the system related to the present invention, the exhaust gas contains one or more of metal fumes selected from Cu, Zn, Ni and Fe.
  • The present invention makes it possible to remove the metal fumes from the exhaust gas which is generated when the slag discharged from the smelting furnace for non-ferrous metal is water-granulated.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 indicates one example of the scheme, related to the present invention, for treating the exhaust gas.
  • DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION
  • Preferred embodiments of the process for treating the exhaust gas related to the present invention is described below, referring to FIG. 1. Slag discharged from the smelting furnace 1 such as an electric slag cleaning furnace is flowed, through the slag runner 3, into the water-granulation runner 4 and then water-granulated by granulating water 2 flowed down through the water-granulation runner, and then fell into the water-granulation tank 6 as the water-granulated slag. The water-granulated slag is picked up by a bucket elevator (not indicated) provided in the water-granulation tank and carried away from the system.
  • The composition of the slag discharged from the smelting furnace differs depending on the kind of non-ferrous metal to be smelted. For example, in the process for smelting copper, it is in general, Fe: 35-45 mass %, Fe3O4: 3-15 mass %, SiO2: 25-35 mass %, Cu: 0.5-3 mass %. Examples of non-ferrous metal, which is an object of the present invention, include, but not particularly limited to, copper, zinc and nickel.
  • The slag before water-granulation is usually at a high-temperature of about 1150-1300° C. From the vicinity of the water-granulation runner 4 and water-granulation tank 6 where the slag is contacted with water, a large amount of water vapor is generated as the exhaust gas 5. The generated water vapor, which contains a very small amount of the metal fumes is recovered by a hood for collecting smoke 7 (a means for collecting the exhaust gas) which covers over the water-granulation runner 4 and water-granulation tank 6, desirably the hood can move vertically and horizontally. The exhaust gas resulting from water-granulation contains metal fumes such as Cu, Zn and Fe generally at a concentration of about 0.1-10 mg/m3. However, the composition of metal fumes is different depending on the metal to be smelted. For example, in case where copper is smelted, the concentration of Zn is higher compared to other metals, which is usually about 1-10 mg/m3. The temperature of the exhaust gas in the hood for collecting the smoke is typically about 80-90° C.
  • Subsequently, the exhaust gas 5, recovered by the hood for collecting the smoke 7, including water vapor as a main component is introduced, through a flue 8 (the exhaust gas duct), into the wet electrostatic precipitator 9. The water vapor is partially condensed spontaneously as it passes through the flue 8. The temperature of the exhaust gas at the entrance of the wet electrostatic precipitator 9 is typically about 30-80° C. In the present invention, a means for scattering cooling water to the exhaust gas (cooling tower and the like) between the hood for collecting smoke and the wet electrostatic precipitator is not required.
  • The wet electrostatic precipitator 9 is a device which provides a high voltage between a discharging electrode and a dust collecting electrode to generate corona discharge, charging the particles suspending in the gas, and the particles being recovered by the dust collecting electrode by Coulomb force caused by electric field, and then discharges the recovered particles as waste water by washing them out with spray water. Metal fumes are fine particles, made by aggregation of metal vapor, which can be recovered by the wet electrostatic precipitator. However, it is desirable for obtaining a sufficient recovery to operate at a high voltage because most of them are a fine particle equal to or less than 1 μm.
  • The wet electrostatic precipitator is typically operated at a voltage of about 10-50 kV and a current of about 30-100 mA.
  • Any known wet electrostatic precipitator 9 may be used as appropriate. Examples of the wet electrostatic precipitator include a parallel type where a discharging electrode and a dust collecting electrode are arranged so that they are placed in parallel with gas flow, and a cross-flow type where a collecting electrode and a dust discharging electrode are arranged so that they are placed at a right angle to the gas flow (Ex. Neueluft type).
  • The exhaust gas 10 discharged from the wet electrostatic precipitator 9 can be released into the air. The temperature of the exhaust gas at the exit of the wet electrostatic precipitator 9 is about 20-40° C. On the other hand, the waste water 11 containing the recovered metal discharged from the wet electrostatic precipitator 9 is recovered by the waste water tank 12, and then pumped out to a combined waste water treatment facility where the waste water is subjected to neutralizing treatment and then filtrated with a filter press. The metal recovered as a residue can be returned to the smelting furnace as mixed minerals.
  • EXAMPLES
  • Working example for the present invention will be explained below, which is only for illustrative purpose and it is not intended for restricting the present invention.
  • In this working example, the treatment of the exhaust gas which was generated during water-granulation of high-temperature slag discharged from an electric slag cleaning furnace attached to a flash furnace was performed. A system for treating the exhaust gas was constructed according to the scheme for treating the exhaust gas depicted in FIG. 1. The slag discharged from the electric slag cleaning furnace flows, through the slag runner, into the water-granulation runner, and then water-granulated by granulating water flowed down through the water-granulation runner, and then fell into the water-granulation tank as water-granulated slag. The exhaust gas containing a large amount of water vapor resulting from water-granulation was recovered by a hood for collecting smoke that covers over the water-granulation runner and water-granulation tank. The temperature of the exhaust gas in the hood for collecting the smoke is about 80-90° C. The exhaust gas recovered by the hood for collecting the smoke enters the flue, through the entrance of the flue which is placed at the top of the hood and travels to the wet electrostatic precipitator. The temperature of the exhaust gas flowed into the wet electrostatic precipitator was about 30-80° C. The temperature of the exhaust gas discharged from the wet electrostatic precipitator was about 20-40° C.
  • The conditions for the water-granulation of the slag were as follows:
  • The amount of slag to be water-granulated 2.5 t/min
    The temperature of slag before water-granulation 1150-1300° C.
    The amount of water for water-granulation  20 t/min
  • The result of the concentration of the metals (mass %) in the slag measured by methods for determination of metals in flue gas according to JIS K0083 is shown in Table 1.
  • TABLE 1
    Element Cu Zn Fe
    Conc. (%) 0.83 0.76 39.2

    The operation conditions of the system for treating the exhaust gas were as follows.
  • The amount of the exhaust gas recovered by the hood for collecting the smoke 300 m3/min
  • The specification of the wet electrostatic precipitator
      • maker: Erdec company Neueluft type
      • voltage: 15-25 kV
      • current: 60-100 mA
      • amount of spray water: about 20 L/min
  • The concentration of metals in the exhaust gas recovered by the hood for collecting the smoke (the concentration at the entrance of the precipitator), the concentration of metals in the exhaust gas after the treatment by the wet electrostatic precipitator (the concentration at the exit of the precipitator), and the recovery rate (%) are shown in Table 2. The measurement of the concentration of the metals was carried out by methods for determination of metals in flue gas according to JIS K0083.
  • TABLE 2
    (mg/m3)
    Element Cu Zn Fe
    The concentration at the entrance of 0.18 5.33 0.67
    the precipitator
    The concentration at the exit of 0.03 0.21 0.04
    the precipitator
    The recovery rate (%) 80.7 96.0 94.1

Claims (7)

1. A process for treating an exhaust gas, which is generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal, containing the water vapor as a major component and metal fumes, the process comprising a step of treating the exhaust gas by a wet electrostatic precipitator.
2. The process according to claim 1, wherein the non-ferrous metal is copper.
3. The process according to claim 1, wherein the exhaust gas contains one or more of metal fumes selected from Cu, Zn, Ni and Fe.
4. The process according to claim 1, further comprising a step of neutralizing and then filtrating waste water containing metal components discharged from the wet electrostatic precipitator to obtain a residue and returning the residue to the smelting furnace.
5. A system for treating an exhaust gas, which is generated during water granulation of slag discharged from a smelting furnace for non-ferrous metal, containing the water vapor as a major component and metal fumes, the system comprising a means for collecting the exhaust gas, an exhaust gas duct and a wet electrostatic precipitator, wherein the means for collecting the exhaust gas is located above a spot where the exhaust gas is generated, and the means for collecting the exhaust gas and the wet electrostatic precipitator is connected via the exhaust gas duct.
6. The system according to claim 5, wherein the non-ferrous metal is copper.
7. The system according to claim 5, wherein the exhaust gas contains one or more of metal fumes selected from Cu, Zn, Ni and Fe.
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WO2018157450A1 (en) * 2017-02-28 2018-09-07 西安交通大学 Granulator system for granulating liquid-state slags
WO2018157452A1 (en) * 2017-02-28 2018-09-07 西安交通大学 Secondary liquid-state slag temporary storage system with flow temperature monitoring and controlling functions
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WO2012136478A1 (en) * 2011-04-08 2012-10-11 Oce-Technologies B.V. Device for ejecting droplets of an electrically conductive fluid, vapor suppressing means in said device and a method for suppressing vapor of an electrically conductive fluid
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WO2018157452A1 (en) * 2017-02-28 2018-09-07 西安交通大学 Secondary liquid-state slag temporary storage system with flow temperature monitoring and controlling functions
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