US20060021469A1 - Process for producing molten iron - Google Patents

Process for producing molten iron Download PDF

Info

Publication number
US20060021469A1
US20060021469A1 US10/537,861 US53786105A US2006021469A1 US 20060021469 A1 US20060021469 A1 US 20060021469A1 US 53786105 A US53786105 A US 53786105A US 2006021469 A1 US2006021469 A1 US 2006021469A1
Authority
US
United States
Prior art keywords
hearth
furnace
melting furnace
iron
amount
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US10/537,861
Other languages
English (en)
Inventor
Shuzo Ito
Itsuo Miyahara
Koji Tokuda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kobe Steel Ltd
Original Assignee
Kobe Steel Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kobe Steel Ltd filed Critical Kobe Steel Ltd
Assigned to KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL LTD.) reassignment KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL LTD.) ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ITO, SHUZO, MIYAHARA, ITSUO, TOKUDA, KOJI
Publication of US20060021469A1 publication Critical patent/US20060021469A1/en
Abandoned legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/008—Use of special additives or fluxing agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B13/00—Making spongy iron or liquid steel, by direct processes
    • C21B13/10—Making spongy iron or liquid steel, by direct processes in hearth-type furnaces
    • C21B13/105—Rotary hearth-type furnaces
    • Y—GENERAL 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/10—Reduction of greenhouse gas [GHG] emissions
    • Y02P10/134—Reduction of greenhouse gas [GHG] emissions by avoiding CO2, e.g. using hydrogen

Definitions

  • the present invention relates to a method of producing a molten iron, more specifically, a method of producing a molten iron by heat-reducing an iron oxide-containing material such as iron ore together with a carbonaceous reducing agent such as carbonaceous material in a moving-hearth reducing furnace and then melting a reduced iron obtained in a melting furnace in particular, which is improved to produce a high purity of molten iron efficiently at a higher productivity.
  • iron source iron oxide-containing material
  • carbonaceous reducing agent such as carbonaceous material
  • This method is effective to some extent, because heat of high-temperature exhaust gas generated in the melting furnace can be used efficiently by introducing the heated gas into the moving-hearth reducing furnace, and this enhances a thermal efficiency of the facilities as a whole.
  • the inventors have been engaged in studies on practical application of this kind of direct iron making method, and this time especially studied a method from various aspects aiming at improvement of smooth operations in a series of processes from solid-phase reduction of iron sources by using a moving-hearth reducing furnace such as a rotary, hearth furnace to melting in a melting furnace, as well as improvement of the quality of molten iron obtained, further suppression of degradation of processing facilities, in particular refractory, and extension of lifetime of the facilities.
  • a moving-hearth reducing furnace such as a rotary, hearth furnace to melting in a melting furnace
  • a method of producing a molten iron having a carbon content of 3.0 mass % or more comprises: feeding a raw material mixture containing a carbonaceous reducing agent, an iron oxide-containing material and a CaO-containing material onto a hearth of a moving-hearth reducing furnace; heating the raw material mixture in the reducing furnace and thus reducing an iron oxide in the raw material mixture; generating a solid reduced iron having a metallization ratio of 80% or more; feeding the solid reduced iron in the state kept at high temperature into a melting furnace and further heating the solid reduced iron therein; and reducing the partially remaining iron oxide and melting the solid reduced iron; wherein a blending amount of the CaO-containing material in the raw material mixture is adjusted in such a manner that another feeding of the CaO-containing material into the melting furnace makes a basicity of a slag generated in the melting furnace 1.1 or more and that an feeding amount of the CaO-containing material becomes 40 kg or less per ton of the
  • the CaO-containing material whose entire amount is sufficient for making the basicity of the slag generated in the melting furnace 1.1 or more, with the raw material mixture and thus eliminate an amount of the CaO-containing material separately added into the melting furnace in result, for a smoother melting operation in the melting furnace; and it is further preferable to adjust the feeding amount of the carbonaceous material for hearth material in such a manner that an amount of the carbonaceous material of a non-combustion state fed into the melting furnace together with the solid reduced iron discharged from the reducing furnace becomes not less than an amount of the carbon aqueous material to be consumed in the melting furnace, for further reliable improvement in the metallization ratio of the solid reduced iron obtained in the reducing furnace, and for a more efficient and faster melting operation in the melting furnace.
  • a MgO content in the raw material mixture or to add MgO additionally into the melting furnace in such a manner that the slag generated in the melting furnace has a MgO content of 6 mass % or more, preferably 8 to 13 mass %, for effective suppression of refractory wear in using magnesia bricks as an inner lining refractory for the melting furnace.
  • FIG. 1 is a process flow chart showing one embodiment of the present invention.
  • FIG. 2 is a graph showing a relationship between a metallization ratio of a solid reduced iron obtained in a rotary-hearth reducing furnace and a residual carbon amount in raw materials in practicing the method according to the present invention and a conventional method.
  • a molten iron is produced continuously by solid-phase reduction of an iron oxide-containing material and melting the reduced material thereof in a series of facilities comprising a moving-hearth reducing furnace and a melting furnace installed next thereto in the present invention.
  • a grate-type reducing furnace as a moving-hearth reducing furnace in the present invention
  • a rotary-hearth reducing furnace is most efficient and practical, considering an area for installation and an operating efficiency of the facility; and thus, embodiments employing a rotary-hearth reducing furnace will be mainly described below.
  • the present invention is not limited thereto, and use of any other reducing furnace is possible, if it is a reducing furnace wherein heat-reduction is carried out on its moving hearth.
  • FIG. 1 is a schematic flow chart illustrating a series of facilities used in practicing the present invention, wherein (A) represents a rotary-hearth reducing furnace, (B) an electric melting furnace and (C) an iron-bath melting furnace; and a production method according to the present invention is carried out by using facilities in combination of a rotary-hearth reducing furnace (A) and an electric melting furnace (B), or in combination of a rotary-hearth reducing furnace (A) and an iron-bath melting furnace (C).
  • A represents a rotary-hearth reducing furnace
  • B an electric melting furnace
  • C an iron-bath melting furnace
  • a powdery carbonaceous material ( 1 ) to be supplied as a hearth material and a raw material mixture ( 2 ) which contains an iron oxide-containing material and a carbonaceous reducing agent, further which is added with CaO, MgO, etc. or as needed with a small amount of a binder, (or, a compact or semi-compact formed of these in a shape of pellet and the like as the raw material mixture) are fed preferably continuously onto a rotary hearth ( 4 ) of the rotary-hearth reducing furnace (A) via a raw material-feeding hopper ( 3 ).
  • the powdery carbonaceous material ( 1 ) is fed onto the rotary hearth ( 4 ) from one hopper, and then the raw material mixture ( 2 ) is fed from another hopper adjacent to the one.
  • the powdery carbonaceous material ( 1 ) to be fed as the hearth material may be eliminated.
  • the rotary hearth ( 4 ) of the rotary-hearth reducing furnace (A) shown in the figure rotates counterclockwise, normally in a rotation period of approximately 8 minutes to 16 minutes, although the frequency varies according to operational conditions.
  • a plurality of combustion burners ( 5 ) are placed in the sidewall above the rotary hearth ( 4 ) and/or in the ceiling in the reducing furnace (A), and heat is supplied to the hearth area from the combustion or radiation heat of the burners ( 5 ).
  • the raw material mixture ( 2 ) fed onto the rotary hearth ( 4 ) consisted of refractory is heated by combustion or radiation heat of the combustion burners. ( 5 ) while the mixture moves in a circumferential direction on the hearth ( 4 ) in the reducing furnace (A), and an iron oxide in the raw material mixture ( 2 ) is reduced to a solid reduced iron while the mixture goes through a heated zone in the reducing furnace (A).
  • the raw material mixture ( 2 ) is less affected by oxidizing gases present in the furnace atmosphere in the earlier stage of heat-reducing the raw material mixture ( 2 ), because strongly reducing gases mainly containing CO gas arc emitted from the carbonaceous reducing agent blended in the raw material mixture ( 2 ) in a great amount to the area surrounding the raw material mixture ( 2 ).
  • the amount of the reducing gases emitted from inside the raw material mixture ( 2 ) decreases in the later stage of reduction, and the raw material mixture ( 2 ) becomes affective to the surrounding oxidizing gases (generated;by burner combustion, e.g.
  • the powdery carbonaceous material ( 1 ) on the rotary hearth ( 4 ) as a hearth material and feed the raw material mixture ( 2 ) thereon, because the oxidizing gases such as CO 2 generated by burner combustion are reduced again by the carbonaceous material ( 1 ) on the hearth ( 4 ), even in the later stage of heat-reduction, and thus, it is possible to make an environmental gas surrounding the raw material mixture ( 2 ) retain a high level of reduction potential and to produce a solid reduced iron having a desirable metallization ratio more consistently and reliably.
  • the solid reduced iron produced in the rotary hearth reducing furnace (A) as described above is discharged by a discharge device ( 6 ), together with a slag generated in the heat-reduction process as a by product or the carbonaceous material ( 1 ) used as a hearth: material remaining after combustion.
  • ( 7 ) represents an exhaust gas duct.
  • the solid reduced iron generated in the reducing furnace (A) is discharged in a state kept at high temperature possibly without cooling by the discharge device ( 6 ) out of the furnace, together with the carbonaceous material ( 1 ) remaining on the hearth ( 4 ), and fed into the melting furnace placed directly connected or close to the rotary-hearth reducing furnace (A).
  • (B) represents an electric melting furnace and (C) an iron-bath melting furnace, and one of these melting furnaces is used suitably selected as needed.
  • the solid reduced iron and the residual carbonaceous material at high temperature discharged from the reducing furnace (A) are fed into the furnace through a feed chute ( 8 ) placed at the top part of the furnace.
  • An auxiliary material (slag-conditioning agent) containing CaO Or MgO, if supplied, is fed via a chute identical with or different from the chute for the solid reduced iron into the melting furnace ( 1 ).
  • heat is supplied into the furnace from electrodes ( 9 ), and unreduced iron oxide remaining in the solid reduced iron is reduced and the solid reduced iron is melted by the heat, finally a molten slag (S) and a molten iron (Fe) are separated and accumulated in the furnace.
  • these molten iron (Fe) and molten slag (S) are discharged at a suitable timing respectively via a molten slag outlet ( 10 ) and a molten iron outlet ( 11 ) out of the furnace.
  • FIG. ( 12 ) represents an exhaust gas duct.
  • the solid reduced iron and the carbonaceous material are fed into the furnace from the upper part of the melting furnace (C).
  • An oxygen-containing gas for combustion of the carbonaceous material in the furnace is generally blown at high speed downward onto the slag (S) or the molten iron (Fe) by a top-blowing lance ( 13 ) inserted from the top part of the furnace.
  • the oxygen-containing gas may be blown into the furnace from a bottom-blowing nozzle ( 14 ) placed in the furnace bottom, from a side-blowing nozzle ( 15 ) placed in the furnace wall, or from these two or more lance and nozzles in a suitable combination.
  • this kind of melting furnace it is necessary to supply a certain amount of needed heat into the furnace by combusting a carbonaceous material in the furnace, and thus a certain amount of fuel is needed; and if no hearth material is fed or if only using an unburned carbonaceous material (hearth material) fed from the reducing furnace (A) to the melting furnace involves scarcity of fuel, the carbonaceous material in short supply may be added alone or in combination with other auxiliary materials (CaO, MgO and the like) from the top part of the furnace.
  • auxiliary materials CaO, MgO and the like
  • the basicity of the slag generated in the melting furnace is adjusted to 1.1 or more, more preferably 1.3 or more, and the [C] content in the molten iron obtained to 3.0 mass % or more in the present invention.
  • the amount of CaO component contained as a gangue component of iron oxide sources (iron ore and others) in the raw material mixture is not sufficient, and an additional amount of CaO component to cover shortfall should be added separately into the melting furnace for adjusting the basicity of the slag generated in the melting furnace to 1.1 or more.
  • an additional amount of CaO component to cover shortfall should be added separately into the melting furnace for adjusting the basicity of the slag generated in the melting furnace to 1.1 or more.
  • MgO-based refractory is commonly used as an inner lining refractory of the melting furnace, which is exposed to the slag having a higher basicity; and it is desirable to add an MgO-containing material separately into the melting furnace such as dolomite, preferably to a MgO content in the slag generated of 6 mass % or more, preferably 8 to 13 mass %, for increasing the MgO content relatively in the generated slag during melting of the solid reduced iron and prevention of the wearing damage of the MgO-based refractory, but in such a case, supply of MgO, which has a high-melting point, directly into the melting furnace may cause similar problems caused by supply of CaO.
  • the content or the composition of the gangues (slag composition) contained in an iron oxide-containing raw material vary significantly according to grade or properties of an iron source contained in a raw material mixture (iron ore, etc.), and the amount of the slag finally generated in the melting furnace is normally approximately 80 to 300 kg per ton of molten iron although it varies slightly depending on the desired basicity, and reaches a level of 400 kg per ton of molten iron when an iron oxide-containing material lower in iron purity is used as a raw material.
  • the amount of the slag generated in the melting furnace varies significantly depending on a grade or kind of iron sources (iron oxide-containing material) used as the raw material, and thus, the amount of a CaO-containing material (burnt lime, etc.) to be added into a melting furnace for controlling the slag basicity, for example, in the range of 20 to 150 kg per ton of molten iron.
  • iron sources iron oxide-containing material
  • CaO-containing material burnt lime, etc.
  • the inventors have conducted studies on the effects of the amount of a slag-conditioning agent added together with the solid reduced iron into the melting furnace on the melting inhibition described above and the measures to overcome the effects, and found the followings: said melting inhibition becomes more significant, resulting in the significant adverse effects on the operation of the furnace when the amount of a slag-conditioning agent added together with the solid reduced iron into the melting furnace exceeds 40 kg per ton of molten iron; the amount of a slag-conditioning agent such as CaO (or CaO and MgO) added into the melting furnace at the time should be reduced to 40 kg per ton of molten iron or less for prevention thereof; a slag-conditioning agent component needed in excess should be blended previously into a raw material mixture to be fed into a rotary-hearth reducing furnace as raw material; and in this manner, it is possible to accelerate the melting of the solid reduced iron and the slag-conditioning agent in the melting furnace.
  • CaO or CaO and MgO
  • the present invention employs the method of alleviating the abovementioned melting inhibition drastically: by mixing all or most part of the additional one to the raw material mixture in advance; then by sintering or partially melting these slag compositions in the raw material mixture by using the heat for heat-reduction of the iron oxide in the rotary-hearth reducing furnace (A) and changing it into a low melting-point complex oxide; and thus by increasing the melting rate (slagging rate) of the slag conditioning materials fed together with the solid reduced iron into the melting furnace and the slag-generating rate drastically.
  • the method accelerates the melting of the slag in the melting furnace and also the melting of the solid reduced iron: by mixing the excess amount thereof with the raw material mixture to be fed into the rotary-hearth reducing furnace (A) in advance; then by sintering or partially melting the slag compositions in the raw material mixture (containing the added CaO— or MgO-containing material) at the same time during heat-reduction of the iron oxide in the raw material mixture; and thus by changing it into complex oxides such as CaO—SiO 2 , 2CaO—SiO 2 , 3CaO-2SiO 2 , 2CaO—Al 2 O 3 —SiO 2 , 3CaO-2SiO 2 , CaO—MgO—SiO 2 , 3CaO—MgO-2SiO 2 ,
  • the melting point of burnt lime (CaO) per se is 2,572° C.
  • the CaO-containing material when the CaO-containing material is mixed in advance into the raw material mixture and heat-reduced at a temperature in the range of 1,250 to 1,400° C., these form the complex oxides as described above by sintering or partially melting together with the other slag components in the raw material mixture.
  • These complex oxides have melting points significantly lower than that of CaO itself, and melt rapidly when fed subsequently into a melting furnace.
  • the melting point of CaO—SiO 2 is 1,544° C.; that of CaO—MgO—SiO 2 , 1,610° C.; that of 3CaO—MgO-2SiO 2 , 1,575° C.; that of 2CaO—SiO 2 , 2,130° C.; that of CaO—Al 2 O 3 -2SiO 2 , 1,550° C.; and that of Al 2 O 3 —SiO 2 , 1,810° C., although these melting points may vary according to the raw material and the blending ratio used, and all of these melting points are notably lower than that of CaO itself.
  • the operation by previously blending the total amount of the slag-conditioning agents with the raw material mixture and adding no slag-conditioning agents such as CaO or MgO into the melting furnace is also a favorable embodiment of the present invention, and this method is particularly effective when an electric furnace, which demands a greater amount of electric power for heating, is used as a melting furnace.
  • the metallization ratio of the solid reduced iron produced by heat-reduction in the rotary-hearth reducing furnace is preferably controlled to 80% or more, preferably 85% or more, and still more preferably 90% or more.
  • the metallization ratio is lower than that, the amount of the unreduced iron oxide (FeO) remaining in the solid reduced iron generated by heat-reduction becomes larger, and when the solid reduced iron is fed into the melting furnace, a greater amount of CO gas is generated due to reduction of the residual iron oxide, resulting in drastic slag foaming.
  • the solid reduced iron generated by heat-reduction in the rotary-hearth reducing furnace (A) preferably has a metallizalion ratio of 80% or more, more preferably 85% or more, and still more preferably 90% or more.
  • the present invention in a series of processes which includes: producing a solid reduced iron by heat-reduction in a rotary-hearth reducing furnace; feeding and heating the solid reduced iron obtained subsequently in the melting furnace directly connected or placed close to the reducing furnace; and thus reducing the residual unreduced iron oxide and melting the reduced iron generated into a molten iron, it becomes possible to perform the series of processes from the production of a solid reduced iron to the heat melting of the reduced iron efficiently, by developing solid-phase reduction of the iron source (iron oxide) intensively as possible in the rotary-hearth reducing furnace (A) and focusing on melting the solid reduced iron in the melting furnace.
  • the heat needed for heat-reduction in the rotary-hearth reducing furnace is supplied to the raw material mixture On the rotary hearth by burner heating.
  • the reduced iron once formed may be re-oxidized by oxidizing gases such as CO 2 gas generated by burner combustion, also, the reduction ratio will be difficult to increase when the reduction potential above the hearth [generally represented by (CO+H 2 )/(CO+CO 2 +H 2 +H 2 O) ⁇ 100(%) or more simply represented by CO/(CO+H 2 O) ⁇ 100(%)] decreases in the last stage of reduction; but it becomes possible to keep the reduction potential of the environmental gas surrounding the raw material mixture high even in the last stage of reduction by laying a powdery carbonaceous material on the hearth as a hearth material, because the atmosphere of the furnace, especially the CO 2 gas diffused into the atmosphere surrounding the raw material mixture on the hearth as a hearth material is changed once again to CO gas having reducing power by the carbonaceous material present. As a result, it becomes possible to ensure a high level
  • the consumption amount of the carbonaceous material varies according to the scale, properties, operational condition and others of the rotary-hearth reducing furnace used, but the amount is approximately 20 to 30 kg per ton (dry base) of raw material mixture fed into the rotary-hearth reducing furnace, or approximately 30 to 60 kg per ton of molten iron obtained in the melting furnace by heat-melting, according to the estimation based on many experiments by the inventors.
  • the amount of the powdery carbonaceous material fed as the hearth material is preferably at least 30 kg or more, more preferably 50 kg or more, and still more preferably 100 kg or more per ton of molten iron obtained in the melting furnace.
  • a powdery carbonaceous material is laid as a hearth material on the rotary hearth as described above, it is effective to form a hearth material layer having a certain thickness for elongating a lifetime of the hearth refractory, because the hearth material layer becomes a buffer between the raw material mixture and the hearth refractory or a protective material of the hearth refractory against a byproduct slag, etc.
  • the excessive amount of carbonaceous material discharged without combustion in the rotary-hearth reducing furnace (A) becomes a highly active high-temperature carbonaceous material eliminated volatile components by heating.
  • the method is also advantageous in smoother operation of the melting furnace from this viewpoint.
  • the iron-bath melting furnace (C) that is, a melting furnace having no heating means by electrodes and using the combustion heat of carbonaceous material as heat source, it is preferable to supply 100 kg or more per ton of molten iron of carbonaceous material previously into the rotary-hearth reducing furnace, because 200 kg or more of carbonaceous material per ton of molten iron is needed for heating and melting in the melting furnace.
  • the carbonaceous material in an amount of 200 kg or more results in a layer thickness of about 5 mm or more), and, for example, a layer thickness of more than about 7.5 mm leads to penetration of the raw material mixture into the hearth material layer on the hearth, causing problems such as inhibition of the progress of reduction.
  • 100 kg of powdery carbonaceous material per ton of molten iron is normally equivalent to a thickness of 2.5 mm, although the thickness depends on the loading density of the raw material mixture laid thereon.
  • the kind of the carbonaceous material to be laid on the hearth of the rotary-hearth reducing furnace is not particularly limited; general coal, coke, etc., which is pulverized into particles, preferably which has a suitable diameter, may be used.
  • anthracite which is less fluid and which is less swelling or viscous on the hearth, is favorable.
  • a molten iron having a carbon content, [C], of 3.0 mass % or more is produced by: feeding a solid reduced iron with a high metallization ratio in a rotary-hearth reducing furnace without cooling in a state kept at a temperature as high as possible, preferably at 900° C. or more, into the melting furnace; reducing the iron oxide remaining in the raw material mixture and melting the solid reduced iron rapidly; and separating a molten iron and a molten slag.
  • a carbonaceous material into the rotary-hearth reducing furnace in an amount slightly larger than an amount finally needed, by previously estimating the amount of the additional carbonaceous material needed in the melting furnace, and by taking into consideration an amount of the carbonaceous material consumed at the previous stage for improvement of the reduction potential of the atmospheric gas in the rotary-hearth reducing furnace and a carbon amount remaining in the solid reduced iron after reduction of the carbonaceous reducing agent blended in the raw material mixture.
  • the amount of carbonaceous material needed in the melting furnace differ significantly between when an arc-heating electric furnace (B) is used as the melting furnace and when heating is performed by using the combustion heat of carbonaceous material as in the iron-bath melting furnace (C).
  • the amount of the carbonaceous material consumed in all processes is preferably controlled as grossly classified into the followings.
  • One is a carbonaceous material (a) which is blended with a raw material mixture (or its compact, etc.) as a carbonaceous reducing agent, an amount of the carbonaceous material (a) is the amount of the carbon consumed if the raw material mixture is completely reduced; this carbon amount varies according to the operational condition of rotary-hearth reducing furnace, in particular its atmospheric gas composition.
  • Another is a carbonaceous material (b) which is fed onto the moving hearth as a hearth material; this amount of the carbon, which converts oxidizing gases, such as, CO 2 generated by burner combustion in the reducing furnace, back into CO gas by reduction (CO 2 +C 2CO) in the neighborhood of the hearth, prevents re-oxidation of the solid reduced iron generated over the rotary hearth, and thus enables production of a solid reduced iron having a high metallization ratio and a low fluctuation in the metallization ratio, and is critical for stabilized melting operation of the solid reduced iron and the slag component in a melting furnace.
  • oxidizing gases such as, CO 2 generated by burner combustion in the reducing furnace
  • Still others are a carbonaceous material (c) ensuring the recarburization (carburization) needed for melting a solid reduced iron in a melting furnace and producing a molten iron having a desired carbon content, and a carbonaceous material (d) consumed as a fuel of the melting furnace when an iron-bath melting furnace using the combustion heat of carbonaceous material for heating therein is used.
  • the carbonaceous material (d) is unnecessary when an arc-heating electric furnace is used, and such a system is controlled based on three kinds of carbonaceous materials (a), (b) and (c).
  • the carbonaceous material (a) used as a carbonaceous reducing agent in a raw material mixture which is blended in an amount for efficient promotion of reduction of the iron oxide in the raw material mixture, is preferably blended in an amount up to that needed for production of a molten iron having a desired carbon content in the melting furnace in general. In this way, it is not necessary to add an additional carbonaceous material into the melting furnace and it is possible to concentrate only on the melting of the solid reduced iron. In such a case, the amount equivalent to the carbonaceous material (b) consumed in the rotary-hearth reducing furnace is fed into the furnace, but in either case, the carbonaceous material is allocated suitably so that the total amount of the carbonaceous materials (a) and (b) becomes constant.
  • the carbonaceous material consumed for combustion in the melting furnace should be added additionally, compared with a case when an arc-heating melting furnace is used; and thus, when coke, for example, is used as the carbonaceous material, the carbonaceous material in an amount of about 250 kg per ton of the molten iron finally obtained or more should be added into the melting furnace, although the amount varies to some extent according to the operational condition.
  • recommended is an operation by blending an amount of carbonaceous material needed for carburization for ensuring a carbon content of final molten iron, in principle, previously with a raw material mixture and laying about 130 to 230 kg/ton (molten iron) of the carbonaceous material on the hearth of the reducing furnace, In this case, approximately 50 to 150 kg/ton (molten iron) of additional carbonaceous material should be added into the melting furnace.
  • Raw material compacts (pellets) having the composition shown in Table 3 were formed by using the two kinds of iron ores and one kind of carbonaceous material shown in Tables 1 and 2. As described in FIG. 1 , each pellet was first subjected to solid-phase reduction in a rotary-hearth reducing furnace aiming at producing a solid reduced iron at a metallization ratio of 92%, and the resulting solid reduced iron was fed without particular cooling into an arc-heating electric furnace located close thereto for production of a carbon-saturated molten iron ([C]: 4.6 mass %) approximately at 1,525° C. Operational results are summarized in Table 4. The binder used was wheat flour.
  • the iron ore used in this experiment was a high-grade ore containing a small amount of gangue components, but if the targeted basicity of slag generated in the melting furnace is set to 1.6, the amount of burnt lime to be added additionally to the melting furnace became approximately 44.9 kg per ton of molten iron, which is a slight beyond the range specified in the present invention. As a result, a phenomenon that a part of the slag aggregates in a block shape was observed when burnt lime was added to the melting furnace in the melting process, leading to instability of; the operation for melting burnt lime and reduced iron and to elongation of the period needed for complete melting.
  • the carbonaceous material amount needed for heating in the melting furnace was supplied not onto the rotary hearth of the rotary-hearth reducing furnace on an upstream side but directly into the melting furnace, and thus, the reduction potential of hearth atmosphere declined to some extent at the last stage of reduction in the rotary-hearth reducing furnace. Consequently, the solid reduced iron discharged from the reducing furnace has a relatively low metallization ratio in the range of 78% to 88% and has a larger fluctuation therein (average: 84%), and thus the molten iron finally obtained has a relatively lower carbon content of 4.2 mass %.
  • the molten iron temperature also dropped to 1,475° C., lower by approximately 50° C. than the desired value, and the operation period was also elongated.
  • the theoretical value for the amount of carbonaceous material to be added additionally into the melting furnace is 18.5 kg per ton of molten iron in this case, but 24.1 kg per ton of molten iron of carbonaceous material, greater by approximately 30% than the theoretical value, was added to the melting furnace as fuel, because the operational condition of the melting furnace was slightly unstable.
  • the combustion ratio of the carbonaceous material in the rotary-hearth reducing furnace depends on the operational condition of the reducing furnace, and was approximately 69% in this experiment.
  • the solid reduced iron obtained in the reducing furnace had an almost desirable metallization ratio of 92% and an extremely low fluctuation thereof of ⁇ 1.5%.
  • a slag-conditioning agent burnt lime
  • the [C] value of the molten iron finally obtained in this example was almost desirable 4.5 mass %, and it was also possible to control the molten iron temperature after treatment almost accurately to a desired value.
  • the ore (B) contains a great amount of silicon oxide (SiO 2 ) in the gangue components as shown in Table 1, and when this kind of ore is used, it is necessary to add CaO in an amount greater than that to the ore (A) for generation of a slag having a desirable basicity in the melting furnace, and the slag consumption generated in the melting furnace reaches approximately 180 kg per ton of molten iron.
  • SiO 2 silicon oxide
  • the amount of a slag-conditioning agent (burnt lime) to be added into the melting furnace is approximately 54 kg per ton of molten iron, which is beyond the range specified in the present invention. Consequently, a phenomenon that the slag became partially aggregated in the melting furnace was observed, although serious troubles leading to interruption of the process for melting solid reduced iron did not occur.
  • the amount of the slag-conditioning agent added additionally to the melting furnace seems to be approximately 40 kg per ton of molten iron or less.
  • the entire CaO source to be added for controlling the slag basicity in the melting furnace was blended previously with the raw material pellet, and no CaO source was added into the melting furnace.
  • all of the carbonaceous material needed in the entire process was added in advance into the reducing furnace as a hearth material. A part of the carbonaceous material fed as a hearth material was consumed for preservation of the reduction potential in the reducing furnace, but another part, approximately 18 kg per ton of molten iron, thereof was fed into the melting furnace together with the solid reduced iron.
  • the solid reduced iron discharged from the rotary-hearth reducing furnace had a very high metallization ratio of 92% close to the desired value and a very small fluctuation thereof of ⁇ 1.0%; and melting of the byproduct slag and the solid reduced iron in the melting furnace proceeded rapidly in a more stabilized manner, allowing stabilized operation even though the slag consumption was higher at about 180 kg per ton of molten iron.
  • an iron-bath melting furnace that uses the combustion heat of carbonaceous material as a heat source for melting a solid reduced iron.
  • a furnace similar to oxygen top-blowing converter was used as the melting furnace, and oxygen for combustion of the carbonaceous material in the melting furnace was blown onto the molten iron from above by using a top-blowing lance.
  • the amount of CaO needed for adjusting the basicity of the slag generated in the melting furnace to 1.6 was relatively smaller at about 73 kg per ton of molten iron, because a high-quality iron ore containing a smaller amount of SiO 2 in gangue components was used as an iron oxide source; the amount, which is larger than 40 kg per ton of molten iron i.e., the upper limit of the addition amount of the slag-conditioning agent specified in the present invention, was added to the melting furnace; and no powdery carbonaceous material was added onto the hearth of the rotary-hearth reducing furnace for production of solid reduced iron.
  • the method allowed relatively smoother melting of the burnt lime added into the melting furnace, because it is possible to agitate the molten iron and the slag vigorously by the oxygen blown from the top-blowing lance.
  • the metallization ratio of the solid reduced iron obtained after heat-reduction was significantly higher at an average of 90%, but the fluctuation thereof was extremely larger at ⁇ 4.5%; thus, the molten iron temperature fluctuated significantly in the range of 1,400 to 1,560° C. during melting; and it was difficult to control the molten iron temperature to the desired value of 1,525° C.
  • a raw material pellet having a composition identical with that of the used in Example 1 was prepared, and the pellet and approximately 210 kg per ton of molten iron of a carbonaceous material were fed onto the hearth of the rotary-hearth reducing furnace as a hearth material for heat-reduction.
  • Approximately 30 kg per ton of molten iron of the carbonaceous material supplied onto the hearth of the reducing furnace is consumed by combustion for preservation of the reduction potential in the reducing furnace, and the other, approximately 180 kg per ton of molten iron, of the carbonaceous material was supplied together with the solid reduced iron into the melting furnace.
  • the insufficient amount, 74 kg per ton of molten iron, of the carbonaceous material was added additionally to the melting furnace.
  • All burnt lime needed to adjust the basicity of the slag generated in the melting furnace to a desired value (1.6) was blended with the raw material pellet in advance, and no burnt lime was added to the melting furnace.
  • a solid reduced iron at approximately 900° C. was fed into the melting furnace in a similar manner to the conventional method (1); because the fluctuation of the metallization ratio of the solid reduced iron was very small at 90 to 93%, the solid reduced iron melted very smoothly in the melting furnace, giving a molten iron having a carbon content, [C], of 4.7 mass % (almost identical with the desired value of 4.6 mass %) at a molten iron temperature of 1,530° C. (desired value: 1,525° C.); the [S] content thereof is sufficiently low at 0.028 mass %, and the fluctuation in molten iron temperature was also very small at 1,500 to 1,550° C.
  • a typical method of,producing a solid reduced iron smaller in fluctuation and higher in metallization ratio by using a rotary-hearth reducing furnace Namely, one case that the heat-reduction carried out by feeding 30 kg or more of a powdery carbonaceous material (per ton of molten iron obtained in the next melting furnace) onto the rotary hearth of a rotary-hearth reducing furnace as a hearth material and then by feeding the raw material pellet over the carbonaceous hearth material layer; and another case that the heat-reduction carried out by feeding only the raw material pellet directly onto the hearth without laying the powdery carbonaceous material onto the rotary-hearth; were compared. In either case, the residual carbon amount of the pellet and the metallization ratio were determined by collecting the raw material pellet under reduction from the sampling holes placed at different sites of the furnace, while maintaining the atmospheric temperature in the reducing furnace to a constant temperature of 1,340° C.
  • the reason for setting the metallization ratio of the solid reduced iron to 80% or more is that when the metallization ratio of solid reduced iron is less than 80%, the load for reducing the residual FeO in solid reduced iron in the melting furnace becomes greater and vigorous foaming of the slag caused by the CO gas bubbles generated during the reduction of the residual FeO makes the operation more unstable.
  • the scope of the present invention is determined.
  • the present invention described so far in detail allows smoother melting of the slag and the solid reduced iron in the melting furnace in a shorter period of time, in particular, by adjusting the addition amount of the CaO-containing material in such a manner that the basicity of the slag generated in the melting furnace becomes 1.1 or more and adjusting the amount of the CaO-containing material fed into the melting furnace to 40 kg per ton of molten iron or less, adding the balance of the CaO-containing material to the raw material mixture, or preferably adding the total amount of the CaO-containing material to the raw material mixture and eliminating the CaO-containing material added into the melting furnace.
  • the present invention provides various advantages in industrial application, such as decrease in the iron oxide content of the molten slag generated in melting furnace, control of the wearing damage of the inner lining refractory of melting furnace, increase in the partition ratio of sulfur toward slag, drastic decrease in the sulfur content of molten iron, and others.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture Of Iron (AREA)
  • Manufacture And Refinement Of Metals (AREA)
US10/537,861 2002-12-05 2003-12-04 Process for producing molten iron Abandoned US20060021469A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2002-353525 2002-12-05
JP2002353525A JP4116874B2 (ja) 2002-12-05 2002-12-05 溶鉄の製法
PCT/JP2003/015509 WO2004050921A1 (fr) 2002-12-05 2003-12-04 Procédé de production de fer fondu

Publications (1)

Publication Number Publication Date
US20060021469A1 true US20060021469A1 (en) 2006-02-02

Family

ID=32463302

Family Applications (2)

Application Number Title Priority Date Filing Date
US10/537,861 Abandoned US20060021469A1 (en) 2002-12-05 2003-12-04 Process for producing molten iron
US11/944,753 Expired - Fee Related US8157888B2 (en) 2002-12-05 2007-11-26 Process for producing molten iron

Family Applications After (1)

Application Number Title Priority Date Filing Date
US11/944,753 Expired - Fee Related US8157888B2 (en) 2002-12-05 2007-11-26 Process for producing molten iron

Country Status (4)

Country Link
US (2) US20060021469A1 (fr)
JP (1) JP4116874B2 (fr)
AU (1) AU2003289162A1 (fr)
WO (1) WO2004050921A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070227301A1 (en) * 2001-05-15 2007-10-04 Midrex International B.V. Zurich Branch Metallic iron nuggets
US20070295165A1 (en) * 2004-10-29 2007-12-27 Kabushiki Kaisha Kobe Seiko Sho ( Kobe Steel Ltd.) Process for Producing Molten Iron and Apparatus Therefor
US20100180723A1 (en) * 2007-09-19 2010-07-22 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Method for manufacturing molten iron
US20100229685A1 (en) * 2007-09-19 2010-09-16 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Process for producing molten iron
CN113462840A (zh) * 2021-06-07 2021-10-01 吉立鹏 一种转炉渣和脱硫渣的铁、热和渣的综合利用方法

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4630031B2 (ja) * 2004-10-01 2011-02-09 新日本製鐵株式会社 酸化鉄含有鉄原料の還元・溶解方法
JP4214157B2 (ja) * 2006-04-25 2009-01-28 株式会社神戸製鋼所 溶鉄製造方法および溶鉄製造装置
JP4603626B2 (ja) 2008-03-31 2010-12-22 新日本製鐵株式会社 還元鉄の製造方法
JP2010196148A (ja) * 2009-02-27 2010-09-09 Nippon Steel Corp 鉄原料およびその製造方法
JP2011252226A (ja) * 2010-05-06 2011-12-15 Kobe Steel Ltd 金属鉄の製造方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6251156B1 (en) * 1998-10-30 2001-06-26 Midrex Technologies, Inc. Method of producing molten iron in duplex furnaces
US20010027701A1 (en) * 2000-03-30 2001-10-11 Midrex International B. V. Method of producing metallic iron and raw material feed device
US20010037703A1 (en) * 2000-04-10 2001-11-08 K. K. Kobe Seiko Sho (Kobe Steel, Ltd.) Method for producing reduced iron
US20010054329A1 (en) * 1998-10-30 2001-12-27 Hoffman Glenn E. Method for producing molten iron in duplex furnaces
US6648942B2 (en) * 2001-01-26 2003-11-18 Midrex International B.V. Rotterdam, Zurich Branch Method of direct iron-making / steel-making via gas or coal-based direct reduction and apparatus

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3254831B2 (ja) * 1993-07-20 2002-02-12 日本鋼管株式会社 金属酸化物の溶融還元方法
US5567224A (en) * 1995-06-06 1996-10-22 Armco Inc. Method of reducing metal oxide in a rotary hearth furnace heated by an oxidizing flame
US6413295B2 (en) 1998-11-12 2002-07-02 Midrex International B.V. Rotterdam, Zurich Branch Iron production method of operation in a rotary hearth furnace and improved furnace apparatus
JP3502064B2 (ja) * 2000-08-30 2004-03-02 株式会社神戸製鋼所 製鉄原料の塊成化物製造方法

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6251156B1 (en) * 1998-10-30 2001-06-26 Midrex Technologies, Inc. Method of producing molten iron in duplex furnaces
US20010054329A1 (en) * 1998-10-30 2001-12-27 Hoffman Glenn E. Method for producing molten iron in duplex furnaces
US20010027701A1 (en) * 2000-03-30 2001-10-11 Midrex International B. V. Method of producing metallic iron and raw material feed device
US6630010B2 (en) * 2000-03-30 2003-10-07 Midrex International B.V. Zurich Branch Method of producing metallic iron
US20010037703A1 (en) * 2000-04-10 2001-11-08 K. K. Kobe Seiko Sho (Kobe Steel, Ltd.) Method for producing reduced iron
US6648942B2 (en) * 2001-01-26 2003-11-18 Midrex International B.V. Rotterdam, Zurich Branch Method of direct iron-making / steel-making via gas or coal-based direct reduction and apparatus

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070227301A1 (en) * 2001-05-15 2007-10-04 Midrex International B.V. Zurich Branch Metallic iron nuggets
US7806959B2 (en) 2001-05-15 2010-10-05 Midrex International B.V. Zurich Branch Metallic iron nuggets
US20070295165A1 (en) * 2004-10-29 2007-12-27 Kabushiki Kaisha Kobe Seiko Sho ( Kobe Steel Ltd.) Process for Producing Molten Iron and Apparatus Therefor
US20100180723A1 (en) * 2007-09-19 2010-07-22 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Method for manufacturing molten iron
US20100229685A1 (en) * 2007-09-19 2010-09-16 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Process for producing molten iron
US7993428B2 (en) 2007-09-19 2011-08-09 Kobe Steel, Ltd. Method for manufacturing molten iron
US8012237B2 (en) 2007-09-19 2011-09-06 Kobe Steel, Ltd. Process for producing molten iron
CN101796199B (zh) * 2007-09-19 2012-07-04 株式会社神户制钢所 铁水制造方法
CN113462840A (zh) * 2021-06-07 2021-10-01 吉立鹏 一种转炉渣和脱硫渣的铁、热和渣的综合利用方法

Also Published As

Publication number Publication date
US20080127778A1 (en) 2008-06-05
JP2004183070A (ja) 2004-07-02
JP4116874B2 (ja) 2008-07-09
AU2003289162A1 (en) 2004-06-23
US8157888B2 (en) 2012-04-17
WO2004050921A1 (fr) 2004-06-17

Similar Documents

Publication Publication Date Title
US8157888B2 (en) Process for producing molten iron
US6630010B2 (en) Method of producing metallic iron
US20060105901A1 (en) Slag conditioner composition, process for manufacture and method of use in steel production
US7160353B2 (en) Process for producing molten iron
EP2210959B1 (fr) Procédé pour produire du fer fondu
WO2008059691A1 (fr) Procédé de fabrication de fer métallique granulaire et équipement pour sa fabrication
JP5420935B2 (ja) 粒状金属鉄の製造方法
JP2002517607A (ja) 酸化鉄の強化された直接還元による持続的製鉄及び固体廃棄物の最小化
JP4984488B2 (ja) 半還元焼結鉱の製造方法
JP5210555B2 (ja) 粒状金属鉄の製造方法
JP2016023319A (ja) 回転炉床炉
JP2004176170A (ja) 溶鉄の製法
RU2186854C1 (ru) Способ доменной плавки
WO2023054345A1 (fr) Procédé de production de fer fondu
JP5096811B2 (ja) 粒状金属鉄の製造方法
JP4015873B2 (ja) 微粉炭吹き込み操業における溶銑Ｓｉ制御方法
JPH07146072A (ja) キュポラ型スクラップ溶融炉
RU2127316C1 (ru) Способ выплавки высококремнистого чугуна
JP2009007619A (ja) 粒状金属鉄の製造方法
JPH0625365B2 (ja) 非焼成塊成鉱を配合装入した高炉操業方法
JPH08260012A (ja) 溶融金属の製造方法
JPH0873916A (ja) 竪型炉を用いた鉄スクラップの溶解方法
JPH03183714A (ja) 治金炉における耐火物損耗抑制方法
JPS63169311A (ja) 酸素高炉における低Ｓｉ銑の製造方法
JPH0762163B2 (ja) 流動層鉱石予備還元炉

Legal Events

Date Code Title Description
AS Assignment

Owner name: KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL LTD.),

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ITO, SHUZO;MIYAHARA, ITSUO;TOKUDA, KOJI;REEL/FRAME:016874/0846

Effective date: 20050401

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION