US20250179594A1 - Method for producing molten pig iron - Google Patents

Method for producing molten pig iron Download PDF

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US20250179594A1
US20250179594A1 US18/842,513 US202318842513A US2025179594A1 US 20250179594 A1 US20250179594 A1 US 20250179594A1 US 202318842513 A US202318842513 A US 202318842513A US 2025179594 A1 US2025179594 A1 US 2025179594A1
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Prior art keywords
carbon
containing gas
gas
molten pig
pig iron
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Yuji Iwami
Takahide Higuchi
Taichi MURAKAMI
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JFE Steel Corp
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JFE Steel Corp
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Assigned to JFE STEEL CORPORATION reassignment JFE STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HIGUCHI, TAKAHIDE, IWAMI, YUJI, MURAKAMI, TAICHI
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B5/00—Making pig-iron in the blast furnace
    • C21B5/06—Making pig-iron in the blast furnace using top gas in the blast furnace process
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B11/00—Making pig-iron other than in blast furnaces
    • C21B11/02—Making pig-iron other than in blast furnaces in low shaft furnaces or shaft furnaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B5/00—Making pig-iron in the blast furnace
    • C21B5/008—Composition or distribution of the charge
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B7/00—Blast furnaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B7/00—Blast furnaces
    • C21B7/002—Evacuating and treating of exhaust gases
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/02—Roasting processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B2100/00—Handling of exhaust gases produced during the manufacture of iron or steel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B2100/00—Handling of exhaust gases produced during the manufacture of iron or steel
    • C21B2100/20—Increasing the gas reduction potential of recycled exhaust gases
    • C21B2100/22—Increasing the gas reduction potential of recycled exhaust gases by reforming
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B2100/00—Handling of exhaust gases produced during the manufacture of iron or steel
    • C21B2100/20—Increasing the gas reduction potential of recycled exhaust gases
    • C21B2100/26—Increasing the gas reduction potential of recycled exhaust gases by adding additional fuel in recirculation pipes
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B2100/00—Handling of exhaust gases produced during the manufacture of iron or steel
    • C21B2100/20—Increasing the gas reduction potential of recycled exhaust gases
    • C21B2100/28—Increasing the gas reduction potential of recycled exhaust gases by separation
    • C21B2100/282—Increasing the gas reduction potential of recycled exhaust gases by separation of carbon dioxide

Definitions

  • the present invention relates to a method for producing molten pig iron in the steel industry.
  • Reducing carbon dioxide emissions is required across all industries, as mandated by the SDGs and the Paris Agreement, for example.
  • the steel industry emitting large amounts of CO 2 is particularly required to reduce CO 2 emissions.
  • the molten pig iron production process accounts for 60% or more of the CO 2 emissions of all processes.
  • the molten pig iron production process involves reducing and melting iron ores using a carbon source to produce molten pig iron.
  • the reason that the molten pig iron production process involves very high CO 2 emissions is considered to be the use of coke or coal for the reduction and melting.
  • Non Patent Literature 1 describes a review of the technological prospects for achieving the long-term goal of carbon dioxide reduction in the steel industry.
  • Non Patent Literature 1 introduces a method (CCS: Caron dioxide Capture and Storage) of separating CO 2 from an exhaust gas generated through a reduction reaction, and storing CO 2 in an isolated manner so as to reduce CO 2 emissions to the outside.
  • CCS Caron dioxide Capture and Storage
  • Another known method is a technology (CCU: Carbon dioxide Capture and Utilization) for separating CO 2 from an exhaust gas to reuse it.
  • the technology involves synthesizing CH 4 using CO 2 in an exhaust gas and blowing the synthesized CH 4 into a blast furnace through its tuyere so as to use the synthesized CH 4 for a reduction reaction again.
  • the existing technologies have the following problems. That is, although applying the CCS method can contribute to the reduction of CO 2 emissions, the process would consume lots of energy. The method also has problems in that the C source should be moved to the outside of the system and the storage capacity is limited. Meanwhile, when CH 4 is synthesized from CO 2 to blow the synthesized CH 4 into a blast furnace through its tuyere, a line for blowing CH 4 into the tuyere would be needed, which is problematic.
  • the present invention has been made in view of the above circumstances and aims to provide a method for producing molten pig iron by circulating a C source through a process and feeding the recovered C source into a shaft furnace through its throat as a carbon-material-containing agglomerated ore to produce molten pig iron.
  • a method for producing molten pig iron according to the present invention that advantageously solves the above problems includes a first step of producing a carbon-material-containing agglomerated ore from an iron-containing raw material and a carbon-containing raw material; a second step of blowing an oxygen-containing gas into the carbon-material-containing agglomerated ore to reduce and melt the carbon-material-containing agglomerated ore, thereby producing molten pig iron; and a third step of bringing a carbon-containing gas containing carbon monoxide and carbon dioxide produced as a by-product of the reduction into contact with a porous material, thereby recovering carbon, in which in the first step, the carbon recovered in the third step is used for a part of or an entirety of the carbon-containing raw material.
  • the method for producing molten pig iron according to the present invention may have more preferable solutions as follows.
  • molten pig iron can be produced by charging a carbon-material-containing agglomerated ore using the recovered carbon into a shaft furnace through its throat.
  • the recovered carbon can be circulated through a process without the need to modify the shaft furnace.
  • FIG. 1 is a schematic view showing an example of a method for producing molten pig iron according to the present invention.
  • FIG. 2 is a schematic view showing an example of a process for producing a carbon-material-containing agglomerated ore according to a first step of the present invention.
  • FIG. 3 is a schematic view showing an example of a facility in which a countercurrent reduction layer is used according to a second step of the present invention.
  • FIG. 4 ( a ) is a schematic view showing an example of a carbonization apparatus according to a third step of the present invention
  • FIG. 4 ( b ) is an enlarged photograph of a porous material used in the carbonization apparatus.
  • FIG. 5 is a graph showing the influence of carbon species on the reducibility of iron ores.
  • FIG. 6 ( a ) is an SEM photograph of recovered carbon to be used in the present invention
  • FIG. 6 ( b ) is an enlarged photograph of a portion indicated by a broken line in FIG. 6 ( a ) .
  • FIG. 7 is a SEM photograph of carbon black used in a comparative example.
  • FIG. 1 is a schematic view showing an example of a method for producing molten pig iron according to the present embodiment.
  • FIG. 2 is a schematic view showing an example of a process for producing a carbon-material-containing agglomerated ore.
  • FIG. 3 is a schematic view showing an example of a facility in which a countercurrent reduction layer is used.
  • molten pig iron 36 is produced by reducing an iron-containing raw material 4 contained in a carbon-material-containing agglomerated ore 26 in a countercurrent reduction layer.
  • a vertical shaft furnace is preferably used, for example.
  • the following embodiment will describe a method for producing molten pig iron according to the present invention with reference to an example in which a blast furnace 32 is used as the vertical shaft furnace. Note that there has been no vertical shaft furnace for producing molten pig iron without using coke.
  • an iron-containing raw material 4 and a carbon-containing raw material 6 are mixed to produce the carbon-material-containing agglomerated ore 26 .
  • the iron-containing raw material 4 is composed mainly of crushed iron ores, and may also contain dust generated in a steel mill, for example.
  • the obtained carbon-material-containing agglomerated ore 26 is charged into the blast furnace 32 , and a blow gas 34 is blown into the furnace to allow a reduction reaction to proceed and thus produce the molten pig iron 36 .
  • an exhaust gas 38 which has been produced as a by-product of the reduction reaction in the second step, is recovered, and the carbon monoxide contained in the exhaust gas 38 is brought into contact with a porous material so that a process of precipitating solid-state carbon and thus recovering it is performed.
  • the exhaust gas 38 treated herein preferably contains an exhaust gas 40 produced as a by-product of a refining process of molten iron.
  • a part of or all of the carbon-containing raw material 6 used in the first step is the solid-state carbon recovered in the third step. If the carbon content of the recovered solid-state carbon alone is insufficient, a carbon source such as biomass may be used to supplement the deficiency. In such a case, the carbon-containing raw material 6 contains a carbon source such as biomass. Further, the particle size of the carbon-containing raw material 6 is preferably 100 ⁇ m or less. If the iron-containing raw material 4 used in the first step is crushed iron ores and contains a large amount of crystal water, it is preferable to apply a heat treatment step of subjecting the iron-containing raw material 4 to heat treatment in the temperature range of 300° C. to 1000° C. before the first step. Hereinafter, each step will be described in detail.
  • the first step is a step of mixing an iron-containing raw material and a carbon-containing raw material to produce a carbon-material-containing agglomerated ore.
  • the iron-containing raw material 4 and the carbon-containing raw material 6 which contains solid-state carbon recovered from the carbon monoxide contained in the exhaust gas 38 , stored in a storage tank 2 , and cement powder 10 stored in a storage tank 8 are respectively cut in predetermined amounts out of the storage tanks 2 and 8 to be delivered to a conveyor 12 .
  • the iron-containing raw material 4 , the carbon-containing raw material 6 , and the cement powder 10 are conveyed to a kneader 14 by the conveyor 12 .
  • the thus conveyed iron-containing raw material 4 , carbon-containing raw material 6 , and cement powder 10 are mixed in the kneader 14 together with an appropriate amount of water 16 to form mixed powder 20 .
  • the mixed powder 20 is conveyed to a granulator 24 by a conveyor 22 and granulated in the granulator 24 together with an appropriate amount of water 16 to produce the carbon-material-containing agglomerated ore 26 .
  • the carbon-material-containing agglomerated ore 26 is preferably obtained by cold forming because it is necessary to avoid combustion and gasification of carbon.
  • the cold forming method include a method of adding a cement-based solidification agent, for example, and then granulating the mixture with a pelletizer or a drum mixer, and a method of performing compression forming using a briquette machine, for example.
  • the carbon mass percent of each particle of the carbon-material-containing agglomerated ore it is preferable to set the carbon mass percent of each particle of the carbon-material-containing agglomerated ore to 15 mass % or less to maintain the strength after a reduction process.
  • the carbon mass percent of each particle of the carbon-material-containing agglomerated ore exceeds 15 mass %, the crushing strength of the agglomerated material as measured with an autograph (1 mm/min) will be less than the threshold (2.5 MPa), which is not preferable.
  • the second step is a process of producing molten pig iron by reducing and melting the iron-containing raw material 4 contained in the carbon-material-containing agglomerated ore 26 , which has been produced in the first step, using a countercurrent reduction layer.
  • an iron-containing lumpy raw material 30 containing the carbon-material-containing agglomerated ore 26 produced by the above method for producing a carbon-material-containing agglomerated ore and another raw material 28 is fed into the blast furnace 32 through its throat, and a reducing gas is flowed upward from below.
  • the blow gas 34 may contain hydrogen, and when hydrogen is contained, direct reduction of the iron-containing raw material 4 with hydrogen proceeds.
  • the hydrogen is preferably derived from renewable energy.
  • the method for producing molten pig iron it is possible to produce molten pig iron by feeding the carbon-material-containing agglomerated ore, which has been obtained with carbon recovered from the exhaust gas 38 , into the blast furnace 32 through its throat. Therefore, the existing blast furnace 32 can be used as is without the need to modify the blast furnace 32 .
  • the third step is a step of precipitating solid-state carbon from an exhaust gas or the like, which has been produced as a by-product of the reduction reaction in the second step, for recovery purposes.
  • the exhaust gas 38 produced as a by-product of the reduction reaction and the exhaust gas 40 produced as a by-product of a refining step of molten iron contain carbon monoxide, carbon dioxide, hydrogen, and water.
  • it is acceptable as long as each of the exhaust gases 38 and 40 contains at least carbon monoxide and carbon dioxide.
  • the exhaust gases 38 and 40 are treated in a carbonization apparatus 100 , a gas reforming furnace 110 , and a water removal device 120 .
  • the exhaust gas it is also possible to use an exhaust gas discharged from an automobile, a gas turbine, an incinerator, a thermal power station, or a plant other than the foregoing gas.
  • the volume percent of each gas component in the exhaust gas can be adjusted in accordance with the combustion conditions for a fuel that is the raw material of the exhaust gas.
  • the exhaust gas is a blast furnace gas
  • the blast furnace gas contains 21 to 23 volume % of carbon monoxide gas, 19 to 22 volume % of carbon dioxide gas, 2 to 3 volume % of hydrogen, and 53 to 56 volume % of nitrogen gas, and thus is preferable.
  • blast furnace gas is generated as coke, heavy oil, and pulverized coal fed into the blast furnace are partially combusted with air to produce a reducing gas that is composed mainly of carbon monoxide and nitrogen, and then iron ores are reduced with the reducing gas
  • Each of the exhaust gases 38 and 40 used in the present embodiment contains carbon monoxide, carbon dioxide, hydrogen, and water.
  • the exhaust gases 38 and 40 are caused to fill the gas reforming furnace 110 .
  • a hydrogen gas supplied from a hydrogen supply unit is added to the gas reforming furnace 110 to form a mixed gas.
  • An internal space of the gas reforming furnace 110 filled with the mixed gas is then heated to 800 to 1200° C.
  • carbon dioxide in the mixed gas that is present within the gas reforming furnace undergoes a water-gas shift reaction with hydrogen in accordance with the following chemical equation (I), thereby generating carbon monoxide and water.
  • a water-gas shift reaction between carbon dioxide and hydrogen is reversible.
  • the reaction temperature is above 500° C.
  • the chemical equilibrium of the water gas shift reaction shifts in the direction in which carbon monoxide is generated.
  • setting the temperature in the gas reforming furnace 110 to 800 to 1200° C. can efficiently convert carbon dioxide into carbon monoxide, and thus generate carbon monoxide as a raw material of solid-state carbon. That is, in the gas reforming step, setting the temperature in the gas reforming furnace 110 to 800 to 1200° C. can efficiently reform the mixed gas.
  • the water-gas shift reaction that proceeds in the gas reforming furnace 110 is a reaction between carbon dioxide contained in the mixed gas, hydrogen contained in the mixed gas, and hydrogen in the hydrogen gas supplied from the hydrogen supply unit.
  • a hydrogen concentration of 58 volume % or more in the mixed gas has been determined by taking into consideration the conditions under which a carbon monoxide gas would increase through a water-gas shift reaction in the temperature range of 800 to 1200° C.
  • the conditions under which a carbon monoxide gas would increase can be determined based on the relationship between the temperature of the water-gas shift reaction and an equilibrium constant.
  • the upper limit of the hydrogen concentration in the mixed gas may be less than 100 volume %, and the upper limit of the hydrogen concentration in the mixed gas may be determined in accordance with the carbon dioxide concentration.
  • a hydrogen gas derived from renewable energy is preferably used as the hydrogen gas supplied from the hydrogen supply unit disposed outside of the gas reforming furnace 110 . This can further reduce carbon dioxide emissions, which is preferable.
  • the amount of the hydrogen gas supplied from the hydrogen supply unit can be set by taking into consideration the amount of hydrogen contained in the exhaust gases 38 and 40 .
  • the reformed gas after the water-gas shift reaction of the mixed gas is supplied to the water removal device 120 .
  • the reformed gas contains water (water vapor) generated through the water-gas shift reaction.
  • the water contained in the reformed gas is removed while passing through the water removal device 120 .
  • the removal of the water herein can be effected by a method of passing the reformed gas containing the water through a layer filled with an adsorbent in the water removal device 120 , or a method of passing the reformed gas through a separating film, for example.
  • the reformed gas preferably has the water removed therefrom so as to satisfy the relationship of the following expression (1).
  • An adsorbent or a separating film can be used to remove the water from the reformed gas, as described above.
  • oxide such as silica, zeolite, or alumina
  • calcium chloride such as magnesium sulfate; and so on
  • the separating film for water in the gas include a carbon film, a resin film, and an inorganic film. Such films have pores with a diameter on the order of subnanometers.
  • the water in the gas is recovered as liquid water at room temperature by the water removal device 120 .
  • the dehumidified gas with the water removed therefrom becomes a raw material of solid-state carbon.
  • the solid-state carbon is separated from the carbon monoxide in the carbonization apparatus 100 by a bimolecular decomposition reaction (II) that occurs when two carbon monoxide molecules are decomposed as represented by the following chemical equation (II), or by a monomolecular decomposition reaction (III) that occurs when one carbon monoxide molecule reacts with hydrogen, as represented by the following chemical equation (III).
  • the carbon monoxide contained in the dehumidified gas preferably satisfies CO/(CO+CO 2 ) of 0.5 or more, more preferably 0.7 or more.
  • CO/(CO+CO 2 ) 0.5 or more, more preferably 0.7 or more.
  • the dehumidified gas is supplied to a carbon separating unit in the carbonization apparatus 100 , which includes a porous material, at a predetermined supply rate.
  • a method for recovering carbon from the dehumidified gas includes a step of bringing the dehumidified gas into contact with the porous material to separate solid-state carbon. Bringing the dehumidified gas into contact with the porous material and separating carbon from the dehumidified gas are performed within the carbon separating unit in the carbonization apparatus 100 .
  • a filled layer filled with a porous material 102 is provided in the carbon separating unit in the carbonization apparatus 100 as shown in an example of FIG. 4 .
  • the carbon that constitutes the carbon monoxide contained in the dehumidified gas is separated from the carbon monoxide gas in the carbonization apparatus 100 .
  • the carbon monoxide contained in the dehumidified gas is separated as a solid-state carbon by the bimolecular decomposition reaction (II) of the carbon monoxide as represented by the above chemical equation (II), or through the monomolecular decomposition reaction (III) of the carbon monoxide as represented by the above chemical equation (III).
  • the solid-state carbon separated from the carbon monoxide is adsorbed on the surface of the porous material 102 to be precipitated.
  • An off-gas which results from the contact between the dehumidified gas and the porous material 102 and thus has carbon separated therefrom, is discharged from the carbonization apparatus 100 .
  • the off-gas contains carbon dioxide, and it is therefore preferable to mix all or part of the off-gas with the mixed gas.
  • the contact between the dehumidified gas and the porous material 102 is preferably effected under an atmosphere in the temperature range of 500 to 800° C.
  • the temperature at which the reformed gas is brought into contact with the porous material 102 is preferably 500° C. or higher because the decomposition reaction of the carbon monoxide is promoted, while the temperature is preferably 800° C. or lower because thermal energy generated by the decomposition reaction of the carbon monoxide can be effectively utilized.
  • the temperature at which the reformed gas is brought into contact with the porous material 102 is within the range of 500 to 800° C.
  • the contact between the dehumidified gas and the porous material may be effected by passing the dehumidified gas through the layer filled with the porous material 102 provided within the carbon separating unit. Accordingly, a decomposition reaction of carbon monoxide represented by the above chemical equation proceeds. As the decomposition reaction of carbon monoxide proceeds, the solid-state carbon that constitutes the carbon monoxide is precipitated on the surface of the porous material 102 . When a porous iron material is used, solid-state carbon precipitated on its surface partially or entirely causes carburizing to form iron carbide.
  • the contact between the dehumidified gas and the porous material 102 is preferably effected under an atmosphere where the pressure of the dehumidified gas is 1.0 to 10 atm.
  • the pressure of 1.0 atm or more at which the dehumidified gas is brought into contact with the porous material 102 corresponds to the pressurization condition, and allows the equilibrium of a decomposition reaction of the carbon monoxide to shift rightward, thus promoting the decomposition reaction of the carbon monoxide, which is preferable.
  • the pressure of 10 atm or less can ensure the safety of the carbon separating unit of the carbonization apparatus 100 with respect to the legal restraints, which is preferable.
  • the open porosity, as measured by the Archimedes' method, of the porous material 102 with which the dehumidified gas is brought into contact is preferably 50 to 99%, more preferably 80 to 95%.
  • the open porosity of the porous material is 50% or more, the dehumidified gas passes through the pores of the porous material to promote the decomposition reaction of the carbon monoxide and also absorb the decomposed carbon, which is preferable.
  • the open porosity of the porous material 102 is 99% or less, the thermal shock resistance to the dehumidified gas supplied to the porous material 102 can be maintained, which is preferable.
  • the pore diameter of the porous material 102 is preferably 10 ⁇ m or more.
  • the open porosity of the porous material 102 is measured by the Archimedes' method. Specifically, a value measured by a measurement method defined by the Japanese Industrial Standards (JIS R2205; 1992) can be used as the open porosity of the porous material.
  • the porous material 102 with which the dehumidified gas is brought into contact preferably contains at least one element selected from the group consisting of iron, platinum, nickel, cobalt, rhodium, and palladium. That is, the porous material may contain one metal element selected from the group consisting of iron, platinum, nickel, cobalt, rhodium, and palladium, or a combination of two or more of such metal elements. Further, the porous material may be a metal compound containing one metal element selected from the group consisting of iron, platinum, nickel, cobalt, rhodium, and palladium as carbide, oxide, carbonate, sulfate, or the like.
  • iron, platinum, and nickel are preferable.
  • platinum or nickel is used as the porous material, each element functions as a decomposition reaction catalyst for the carbon monoxide, and the catalyst would undergo little deterioration, which is preferable.
  • solid-state carbon generated by a decomposition reaction of the carbon monoxide is precipitated as graphite alone, which is preferable.
  • the porous material 102 with which the dehumidified gas is brought into contact is more preferably iron.
  • the use of iron as the porous material 102 causes the porous material 102 to be carburized by carbon generated by the decomposition reaction of the carbon monoxide to thus obtain austenite (i.e., Y iron) with the carbon being dissolved as a solid-solution.
  • the use of iron as the porous material 102 also causes the porous material 102 to be carburized by carbon generated by the decomposition reaction of the carbon monoxide to obtain cementite (i.e., iron carbide (Fe 3 C)) through a reaction between the carbon and the iron, which is preferable.
  • Austenite and cementite resulting from the carburizing of the porous material 102 by carbon generated by a decomposition reaction of carbon monoxide have almost the same hardness as quenching steel and thus can be directly used as iron-making raw materials.
  • the porous material 102 with which the dehumidified gas is brought into contact is preferably one or more types of iron selected from iron oxide and reduced iron.
  • the porous material 102 with which the dehumidified gas is brought into contact is particularly preferably an iron whisker.
  • An iron whisker is a crystal that grows on the surface of a crystal in an outward direction like a beard and is formed such that, when compression stress is generated around the surface of the crystal, a new crystal grows on the original crystal in an outward direction in an attempt to relax the stress. Since such an iron whisker has a small start point of crystal growth and tends to keep growing continuously, it is formed as a single crystal in the shape of an extremely long and thin beard and has a length of 1 mm or more relative to a diameter of about 1 ⁇ m.
  • the iron whisker as the porous material 102 with which the dehumidified gas is brought into contact can be produced by a method of producing an iron whisker described in Non Patent Literature 2, for example. According to the method of producing an iron whisker, it is possible to obtain an iron whisker as a porous material with an open porosity of 90% or more and a pore diameter of 10 ⁇ m or more.
  • the iron whisker obtained by the method of producing an iron whisker also has a high open porosity and thus can be preferably used as the porous material 102 used for a carbon recovery method. It should be noted that even when a metal other than iron is used as the metal for forming the porous material 102 with which the dehumidified gas is brought into contact, the porous material 102 can be produced in the same manner.
  • the carbon adsorbed on the porous material 102 is recovered within a carbon recovery unit 130 .
  • “recovering the carbon adsorbed on the porous material” includes recovering the solid-state carbon precipitated on the surface of the porous material 102 or recovering the carbon causing carburizing inside of the porous material as a solid solution or a metal carbide compound of the carbon and the metal element contained in the porous material.
  • the carbon obtained by the decomposition reaction of the carbon monoxide contained in the dehumidified gas is precipitated on the surface of the porous material 102 .
  • the carbon obtained by the decomposition reaction of the carbon monoxide contained in the dehumidified gas also causes carburizing inside of the porous material 102 and reacts with the metal element forming the porous material, thereby forming a carbon solid solution or a metal carbide compound. Further, the carbon obtained by a decomposition reaction of the carbon monoxide contained in the dehumidified gas is precipitated on the surface of the carbon solid solution or the metal carbide compound.
  • the carbon precipitated on the surface of the porous material 102 can be recovered by subjecting the porous material 102 containing the carbon to an operation of separating powder and granular materials using a sieve mesh, for example.
  • an operation of separating powder and granular materials using a sieve mesh for example.
  • to recover the carbon that has become a carbon solid solution or a metal carbide compound by reacting with the metal element forming the porous material after carburizing the inside of the porous material 102 it is possible to directly recover the carbon solid solution or the metal carbide compound.
  • the recovered carbon is to be used as an iron-making raw material, using iron as the porous material 102 can collectively use them as the iron-making raw material, which is preferable, without performing an operation of separating the recovered carbon from the porous material 102 .
  • bringing the carbon monoxide contained in the dehumidified gas into contact with the porous material 102 can promote the decomposition reaction of the carbon monoxide and separate solid-state carbon, recovering the carbon as the solid-state carbon, or as a carbon solid solution or a carbon metal compound containing the carbon.
  • the recovered carbon can be circulated through a process, reducing CO 2 emissions to the outside of the system.
  • the exhaust gases 38 and 40 , the mixed gas, and the dehumidified gas of the present embodiment are examples of a carbon-containing gas containing carbon monoxide and carbon dioxide.
  • molten pig iron may be produced by performing a reduction step of heating the carbon-material-containing agglomerated ore to 1160 to 1450° C. using a rotary hearth furnace, instead of the blast furnace 32 , to reduce and melt them, and then cooling them to obtain reduced iron, and a melting step of melting the reduced iron using an electric furnace, for example. Even when a rotary hearth furnace is used, it is possible to use the existing rotary hearth furnace as is as long as the carbon-material-containing agglomerated ore obtained with the recovered carbon is used.
  • FIG. 4 ( a ) shows an example of a carbonization apparatus according to the present embodiment.
  • the carbonization apparatus 100 includes a tubular reaction tower 101 in which a carbon separation reaction from carbon monoxide contained in a carbon-containing gas occurs, a supply pipe 104 for supplying a carbon-containing gas from a lower portion of the reaction tower 101 , a layer of the porous material 102 provided in the reaction tower, and an exhaust gas pipe 105 for discharging an off-gas generated after the carbon separation reaction.
  • the reaction tower 101 contains a silica tube 101 a and a sample holder 101 b .
  • porous material 102 equipped in the carbonization apparatus 100 it is preferable to use a plurality of materials as shown in FIG. 4 ( b ) each made by forming iron whiskers having an open porosity of 97.7% into a tablet shape.
  • the porous material 102 is disposed on a layer of granular alumina balls 103 (with a particle size of 10 mm). Note that the porous material 102 is produced in accordance with the method of producing an iron whisker described in Non Patent Literature 2.
  • Table I shows the ingredient compositions of the iron ores used. “T ⁇ Fe” in Table I represents the total iron content. “LOI” represents the loss on ignition when the iron ores are heated to 1000° C. for 60 minutes, most of which is crystal water in the case of iron ores.
  • the recovered carbon was found to contain C: 38.35 mass % as cementite and solid-state carbon, with the balance being Fe. Of the entire portion of carbon, the content of C existing as the cementite was found to be 18.7 mol %, and the content of C existing as the solid-state carbon was found to be 81.3 mol %.
  • the particle size of iron ore A and the particle size of the recovered carbon were each set to ⁇ 105 ⁇ m.
  • “ ⁇ 105 ⁇ m” herein represents the particle size of the iron ore A that has passed through a sieve with a mesh size of 105 ⁇ m.
  • a sample was obtained by mixing the iron ore A and the weighed powder of the recovered carbon in a mortar without pressing a pestle against each other for 3 minutes. Thus, uniform mixed powder was formed without changing the particle size during mixing.
  • carbon was added in an amount of 0.8 times the oxygen molar content in the iron oxide, and further added in an amount of 0.2 times the iron molar content in the iron oxide or the iron carbide, and then, the sample was mixed.
  • carbon By adding carbon in an amount of 0.8 times the oxygen molar content in the iron oxide, the carbon was used as a reducing material, and by adding carbon in an amount of 0.2 times the iron molar content in the iron oxide or the iron carbide, the effect of carburizing the metallic iron was attempted to be achieved. That is, carbon was provided with two functions that are a reducing material and a carburizing material.
  • the uniformly mixed sample was press-formed with an applied pressure of 98 MPa for 30 seconds into a cylindrical shape with a diameter of 10 mm and a height of 10 mm.
  • the formed sample was heated to 1300° C. at a heating rate of 10° C./min in an atmosphere where 5 volume % of N 2 —Ar mixed gas was supplied at a flow rate of 0.5 NL/min.
  • the generated gas was analyzed with an infrared spectrophotometer to calculate the reduction rate of the iron ores.
  • FIG. 5 shows the results.
  • FIG. 5 also shows the results of a similar test conducted using carbon black instead of the recovered carbon as a comparative example. As is obvious from FIG. 5 , the recovered carbon (indicated by a solid line) increases the reducibility of the iron ore A more than the carbon black (indicated by a broken line).
  • the inventors consider it due to the difference in the particle size of the carbon-containing materials.
  • the recovered carbon is in the form of fibers of about several nm as shown in FIGS. 6 ( a ) and 6 ( b )
  • the carbon black contains particles with a particle size of about several ten ⁇ m as shown in FIG. 7 .
  • solid-state carbon recovered from carbon monoxide is extremely small, it is considered that using such carbon for the carbon-material-containing agglomerated ore can increase the contact area with an iron-containing raw material and a gas, and thus obtain the carbon-material-containing agglomerated ore with high reducibility.
  • the method for producing molten pig iron according to the present invention has the effect of reducing CO 2 emissions to the outside of the system.
  • the method can, by recovering CO 2 from an exhaust gas as solid-state carbon, and producing a carbon-material-containing agglomerated ore by combining the recovered solid-state carbon with an iron-containing raw material, increase the reducibility of the agglomerated ores. This can reduce the unit consumption of carbon required for reduction and contribute to reducing environmental burdens in the steel industry.
  • the present invention is industrially quite advantageous.

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