CN112004947B - Method for producing molten steel - Google Patents
Method for producing molten steel Download PDFInfo
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- CN112004947B CN112004947B CN201980023386.9A CN201980023386A CN112004947B CN 112004947 B CN112004947 B CN 112004947B CN 201980023386 A CN201980023386 A CN 201980023386A CN 112004947 B CN112004947 B CN 112004947B
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 48
- 239000010959 steel Substances 0.000 title claims abstract description 48
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 26
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 123
- 229910052742 iron Inorganic materials 0.000 claims abstract description 58
- 239000002184 metal Substances 0.000 claims abstract description 52
- 229910052751 metal Inorganic materials 0.000 claims abstract description 52
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 38
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 38
- 239000002893 slag Substances 0.000 claims abstract description 34
- 238000005261 decarburization Methods 0.000 claims abstract description 30
- 238000006477 desulfuration reaction Methods 0.000 claims abstract description 15
- 230000023556 desulfurization Effects 0.000 claims abstract description 15
- 238000010079 rubber tapping Methods 0.000 claims abstract description 10
- 238000003723 Smelting Methods 0.000 claims abstract description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 9
- 238000007599 discharging Methods 0.000 claims abstract description 9
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 9
- 239000001301 oxygen Substances 0.000 claims abstract description 9
- 239000000463 material Substances 0.000 claims abstract description 4
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 46
- 238000002844 melting Methods 0.000 description 35
- 230000008018 melting Effects 0.000 description 35
- 238000000034 method Methods 0.000 description 30
- 239000003575 carbonaceous material Substances 0.000 description 21
- 238000001465 metallisation Methods 0.000 description 14
- 229910052717 sulfur Inorganic materials 0.000 description 14
- 239000011593 sulfur Substances 0.000 description 13
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 12
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- 239000003245 coal Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 4
- 238000007664 blowing Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 229910052698 phosphorus Inorganic materials 0.000 description 4
- 239000011574 phosphorus Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 3
- 238000010891 electric arc Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- 238000005255 carburizing Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- -1 iron ore Chemical compound 0.000 description 2
- 239000003345 natural gas Substances 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 239000002028 Biomass Substances 0.000 description 1
- 229910017112 Fe—C Inorganic materials 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000002076 thermal analysis method Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric 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
- Y02P10/20—Recycling
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
- Manufacture Of Iron (AREA)
- Carbon Steel Or Casting Steel Manufacturing (AREA)
Abstract
The method for producing molten steel of the present invention comprises the steps of: a step 1 of adding a carbon source to molten steel remaining in the electric furnace as a molten metal species during tapping of the previous pass ch to obtain molten iron containing carbon; a step 2 of adding DRI to the molten carbon-containing iron produced in the step 1 to perform smelting reduction; next, a step 3 of adding a deoxidizing material to perform desulfurization treatment; a 4 th step of discharging the desulfurized slag produced by the desulfurization treatment in the 3 rd step; next, oxygen is blown in to perform a decarburization treatment; a step 6 of discharging the decarburized slag generated by the decarburization treatment in the step 5; and a 7 th step of tapping after the decarburized slag is discharged in the 6 th step and the molten metal seed portion of the next pass ch remains.
Description
Technical Field
The present invention relates to a method for producing molten steel by reducing and melting reduced iron (DRI) produced by prereducing iron oxide (e.g., iron ore) in a melting furnace.
Background
Conventionally, since a great cost is required for newly constructing a blast furnace, a process for directly producing molten steel by reducing iron oxide such as iron ore, which is agglomerated by a pellet or the like, by a shaft furnace such as the MIDREX method to produce reduced iron (DRI) having a metallization ratio of 90% or more and melting the DRI by an electric furnace has been the mainstream in countries where natural gas is produced.
In addition, a process for producing reduced iron using a carbon material such as coal as a reducing agent for replacing natural gas has been developed and put into practical use. The reduced iron production process includes a method of heating and reducing sintered pellets such as iron ore together with pulverized coal in a rotary kiln (SL/RN method), a method of mixing and agglomerating carbon material and powdery iron oxide and heating and reducing the mixture in a rotary kiln to produce reduced iron (RHF method), and the like. In these methods, it is difficult to produce DRI having a high metallization rate, generally about 85% higher metallization rate, as compared with the shaft furnace method. Therefore, when using the DRI, it is necessary to melt metallic iron in a melting furnace such as an electric furnace and reduce the remaining iron oxide component.
Patent document 1 describes a method in which DRI having a metallized iron content of 60% or more is produced by the RHF method, then molten iron having a carbon content of 1.5 to 4.5 mass% is produced by an arc heating type melting furnace, and after the molten iron is discharged outside the furnace, desulfurization, dephosphorization and decarburization are performed by another melting furnace. In this method, a carbon material is added to a smelting furnace in order to reduce the remaining iron oxide component. However, with this method, heat loss becomes large due to transfer of the molten iron to another furnace. In addition, in order to ensure a heat source, carbon material is further added and molten iron with high carbon content is decarburized to produce molten steel, resulting in CO 2 The amount of production becomes large. Further, patent document 2 discloses a technique of melting an iron-based raw material while supplying a hydrocarbon gas. However, this method requires a lot of costs because hydrocarbon gas is used as a premise.
Prior art literature
Patent literature
Patent document 1: japanese patent application laid-open No. 2001-515138
Patent document 2: japanese patent laid-open publication No. 2016-108575
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing CO which has high productivity and little heat loss when a smelting furnace such as an electric furnace, particularly DRI having a low metallization ratio is melted and reduced 2 A method for producing molten steel with a small amount of produced molten steel.
Means for solving the problems
In the present invention, in order to produce molten steel by melting and reducing DRI having a low metallization ratio, a part of molten steel is left in the furnace and used as a molten metal seed (japanese text "" or may be referred to as a starting molten iron) for the next ch. However, if the molten metal species is molten steel, the reduction of DRI by melting is delayed, and therefore, only the carbon source is first supplied to the molten metal species before DRI is supplied, thereby increasing the C concentration of the molten metal species. The C concentration is preferably 0.5 mass% or more and 1.5 mass% or less as described later.
The present invention is as follows.
(1) A method for producing molten steel, characterized by comprising the steps of:
a step 1 of adding a carbon source to molten steel remaining in the electric furnace as a molten metal species at the time of tapping of the previous charge (hereinafter referred to as "previous ch") to obtain carbon-containing molten iron;
a step 2 of adding DRI to the molten iron containing carbon produced in the step 1 to perform smelting reduction;
next, a step 3 of adding a deoxidizing material to perform desulfurization treatment;
a 4 th step of discharging the desulfurized slag produced by the desulfurization treatment in the 3 rd step;
next, oxygen is blown in to perform a decarburization treatment;
a step 6 of discharging the decarburized slag generated by the decarburization treatment in the step 5; and
and a 7 th step of tapping the molten metal portion remaining after the decarburized slag is discharged in the 6 th step (hereinafter referred to as "next ch").
(2) The method for producing molten steel according to the above (1), wherein, when D (m) is the furnace diameter of the electric furnace, the amount W (t) of molten metal remaining in the 7 th step is set to 0.3 XD 2 ＜W＜1.6×D 2 。
(3) The method for producing molten steel according to (1) or (2), wherein in the step 1, molten iron containing carbon is obtained, the concentration of C being 0.5 mass% or more and 1.5 mass% or less.
Effects of the invention
According to the present invention, it is possible to provide a method of producing CO with high productivity and less heat loss and capable of reducing DRI having a low metallization ratio by melting and reducing the DRI in a melting furnace such as an electric furnace 2 A method for producing molten steel with a small amount of produced molten steel.
Drawings
Fig. 1 is a diagram for explaining each step of producing molten steel in the embodiment of the present invention.
Fig. 2 is a graph showing a relationship between C concentration and a melting point of molten iron.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a view for explaining a method of producing molten steel by melting and reducing DRI having a particularly low metallization ratio in a melting furnace such as an electric furnace according to the present embodiment.
As shown in fig. 1, the manufacturing method according to the present embodiment includes at least 7 steps, i.e., 1 st to 7 th steps.
First, for convenience of explanation, the description will be given starting from step 7. The 7 th step is a step of discharging molten steel in which the concentration of C is reduced to, for example, less than 0.1 mass% by decarburization in the 5 th step. At this time, the molten steel is not discharged in its entire amount, but the molten steel used as the molten metal species of the next ch remains in the furnace.
In the case of using a direct current electric furnace as the smelting furnace, in step 2 described later, an electric arc is generated by applying a voltage between the upper electrode and the lower electrode provided at the hearth, and the electric arc is used for smelting reduction of DRI by heat. When no molten metal species is present at the time of applying the voltage, the electric current flows through the DRI, and therefore, the contact resistance between the DRI and the lower electrode of the hearth is large, and the arc becomes unstable at the initial stage of melting, and the melting time becomes long. In addition, when DRI having a low reduction rate and a large content of iron oxide is used, electricity becomes difficult to flow, and the melting time increases.
On the other hand, when the molten metal species is present at the time of voltage application, the arc is stabilized and the melting time can be shortened because the lower electrode of the hearth is in close contact. Therefore, it is important to leave a part of the molten metal seed without tapping the entire amount. In addition, when the inner diameter of the melting furnace is D (m), the molten metal seed amount W (t) preferably satisfies the following formula (1).
0.3×D 2 ＜W＜1.6×D 2 (1)
Here, if the molten metal seed amount W is 0.3 XD 2 In the following, as described above, the contact resistance between the DRI and the lower electrode of the furnace bottom tends to be large, and the arc may be unstable. In addition, if the molten metal seed amount W is 1.6XD 2 As described above, the load of the decarburization treatment in step 5 described later increases. The values "0.3" and "1.6" are the bath depth (m) in the electric furnace and the density (t/m) of the molten iron 3 ) And (3) a value obtained by integrating the values.
Next, step 1 will be described. Before adding DRI in step 2 described later, in step 1, a carbon material such as coal (ordinary carbon) or smokeless carbon is added to the furnace to prepare molten steel as a molten metal species into molten iron having a predetermined C concentration. The method of supplying the carbon material is not particularly limited, and there are a method of adding the carbon material by free fall from a hopper provided at the upper part of the furnace, a method of supplying the upper electrode as a hollow electrode from the hollow part, a method of blowing the carbon material into the molten steel using a dedicated lance, a method of directly blowing the carbon material into the molten steel using an immersion lance, a method of blowing the carbon material into the molten steel from a bottom blowing port provided for stirring of molten metal, and the like.
Here, when the C concentration of the molten metal species is less than 0.1 mass%, etc., the DRI added in step 2 cannot be melted unless it is equal to or higher than the melting point of iron. Therefore, when the C concentration of the molten metal species is lower than 0.1 mass%, a large amount of energy is required for melting the molten steel as it is. In addition, if the operating temperature is equal to or higher than the melting point of iron and the overheat temperature is set to 100 ℃ in order to stabilize the operation, it is necessary to maintain a high temperature state of 1650 ℃. Therefore, the load on the refractory is large. In addition, when the C concentration of the molten metal species is lower than 0.1 mass%, etc., the iron oxide component remaining in the DRI is not reduced, and slag with a high iron oxide concentration is produced, which adversely affects the refractory. Particularly in the case of using DRI with a low metallization rate.
In the present embodiment, carbon is added in step 1, and the molten metal is produced into a C-containing molten metal. Thus, the metallic iron of the DRI added is carburized by C in the molten metal, the melting point is lowered, the melting speed is promoted, and the productivity is improved. In addition, the operating temperature can be reduced according to the C concentration of the molten metal species, and the load on the refractory can be reduced. In addition, since iron oxide in DRI also reacts with C in the molten metal species to promote reduction, the concentration of iron oxide in the produced slag also becomes low. Further, since denitrification is promoted with the decarburization reaction in the 5 th step, the nitriding can be reduced. As described above, the productivity can be improved by forming the molten metal into the C-containing molten metal, and the load on the refractory can be reduced.
Here, the C concentration of the molten iron as the molten metal species is preferably set to 0.5 mass% or more before the step 2 is performed. This is because, when the C concentration is less than 0.5 mass%, the carburizing and melting rate of metallic iron in DRI and the reduction rate of iron oxide are lowered, and productivity is deteriorated. In contrast, when the C concentration of the molten iron becomes too high, the load of the decarburization treatment increases and CO increases in step 5 described later 2 The amount of production increases. Therefore, the C concentration of the molten iron as the molten metal species is preferably set to 1.5 mass% or less.
Next, step 2 will be described. In step 2, DRI produced by a shaft furnace or RHF is supplied to a smelting furnace, and an electric arc is generated by applying a voltage between an upper electrode and a lower electrode provided at the hearth, so that metallic iron in the DRI is melted and the reduction of iron oxide components remaining in the DRI is performed. The DRI may be supplied by, for example, the following methods: the lump DRI is added into the furnace from a hopper arranged at the upper part through free fall; the pulverized DRI was blown from the hollow by setting the upper electrode as a hollow electrode. The DRI supplied in step 2 is, for example, DRI having the composition shown in Table 1 below. Regarding the slag component, siO 2 、Al 2 O 3 As a main component, in addition to this, caO, mgO, S, P 2 O 5 MnO. In addition, regarding the metallization ratio, when the mass% of the pure iron component in the DRI is defined as mass% m.fe and the mass% of the FeO component in the DRI is defined as mass% FeO, the metallization ratio can be determined by the metalThe conversion was calculated as =mass% m.fe/(mass% m.fe+mass% feo×55.75/71.85).
TABLE 1
| FeO(mass％) | M.Fe(mass％) | C(mass％) | Slag component (mass%) | Metallization Rate (%) |
| 13.7～39.3 | 13.7～78.8 | 0～6 | 4～20 | 65～85 |
In step 2, a carbon material such as coal or smokeless carbon is further charged in accordance with the DRI feeding rate, with respect to the C concentration in the molten iron adjusted in step 1. The amount of carbon material to be charged here is based on the sum of the amount required for carburizing the iron component in the DRI to the C concentration of molten iron and the amount required for reducing iron oxide (FeO, etc.) in the DRI. The carbon material charged in step 2 may be plain carbon, smokeless carbon, or the like, as in the carbon material charged in step 1. Table 2 below shows examples of the composition of plain carbon, and table 3 shows examples of the composition of smokeless carbon. FC in tables 2 and 3 represents Fixed Carbon (Fixed Carbon), and VM represents volatile component (volatile Matter). In the 1 st and 2 nd steps, ordinary carbon and smokeless carbon may be used alone or in combination. As the carbon material other than this, a carbon source such as waste plastics or biomass may be used.
TABLE 2
| FC (mass%) | VM (mass%) | Ash (mass%) |
| 50～60 | 30～40 | 8～12 |
TABLE 3 Table 3
| FC (mass%) | VM (mass%) | Ash (mass%) |
| 70～80 | 5～10 | 12～20 |
The operating temperature is determined by the C concentration in the molten iron, which depends on the difference between the amount of carbon material charged in step 2 relative to the C concentration in the molten iron adjusted in step 1, and the sum of the amount required to carburize the iron component in the DRI to the C concentration of the molten iron and the amount required to reduce iron oxide (FeO, etc.) in the DRI. FIG. 2 is a Fe-C system state diagram showing the change in the melting point of iron due to the concentration of C. It is said that the overheat is required to be 100 ℃ or more for operation stabilization, for example, the operation temperature is 1530 ℃ because the melting point is 1430 ℃ in the case of molten iron having a C concentration of 1.5 mass% for operation at the overheat 100 ℃. In step 2, in order to maintain the operation temperature determined according to the C concentration in the molten iron, a voltage is applied according to the supply rates of the carbon material and DRI.
The C concentration of the carbon-containing molten iron before the start of the 2 nd step is preferably 0.5 mass% or more and 1.5 mass% or less as described above, and more preferably is controlled to be in the range of 0.5 mass% or more and 1.5 mass% or less until the end of the 2 nd step.
Next, step 3 will be described. Although the content varies depending on the place of production, sulfur is contained in iron ore or coal. Since iron oxide in the DRI is not instantaneously reduced, the concentration of iron oxide in the slag is high immediately after the end of DRI input. In a state where the iron oxide concentration in the slag is high, the sulfur distribution between the molten iron (hereinafter, sometimes referred to as metal) and the slag is low, and sulfur is present in the metal more than in the slag. Since sulfur in the metal is difficult to remove in the decarburization treatment in step 5 described later, the sulfur concentration in the molten steel after the completion of the decarburization treatment is high when step 3 and step 4 described later are omitted, and the demand for low-sulfur steel production is not satisfied. In addition, sulfur is a surface active component, and therefore, the adsorption sites are exclusively used. Therefore, if the sulfur concentration in the metal is high, it becomes difficult to remove nitrogen from the metal, and the demand for low nitrogen steel production is not satisfied. Therefore, it is important to perform desulfurization treatment after the end of step 2.
After the completion of step 2 (the end of the DRI supply), in step 3, a deoxidizer such as metallic Al or a metallic Al-containing material is added to the furnace to reduce the iron oxide component in the slag and remove oxygen in the molten iron. In this state, the sulfur distribution between the slag and the metal becomes high, sulfur is transferred from the metal to the slag, and the sulfur concentration in the metal decreases. In addition, when the direct current electric furnace is used as the smelting furnace, the upper electrode is usually used as the negative electrode, and the lower electrode of the hearth is used as the positive electrode, but when the upper electrode is used as the positive electrode, and the lower electrode of the hearth is used as the negative electrode, the apparent sulfur distribution can be electrochemically improved, and desulfurization can be further promoted.
Next, step 4 will be described. When the desulfurization slag formed by the desulfurization in step 3 is directly left for decarburization, sulfur is again transferred from the slag to metal (resulfurization), and thus the desulfurization slag is discharged from the slag hole in step 4.
Next, step 5 will be described. In step 5, an oxygen lance is inserted into the furnace from the upper part of the furnace, and oxygen is blown into the molten iron to perform dephosphorization and decarburization, thereby lowering the phosphorus concentration and the carbon concentration to predetermined values. In the decarburization treatment, oxygen reacts with carbon in the molten iron to generate CO gas, but at this time, nitrogen dissolved in the molten iron is taken into the CO gas, and the nitrogen is removed from the molten iron.
Next, the 6 th step will be described. The 6 th step is a step of discharging the decarburized slag generated in the 5 th step. In the dephosphorization and decarburization in step 5, phosphorus in the molten iron is transferred to the slag. If phosphorus is discharged to the outside of the system without discharging decarburized slag, phosphorus is concentrated, and low-P steel cannot be produced. Therefore, the decarburized slag needs to be discharged as much as possible.
As described above, in the steps 1 to 7 in the present embodiment, heat loss can be suppressed and CO can be suppressed 2 The amount of the produced molten steel was produced. In particular, in step 1, a carbon source is added to the molten metal seed to produce a carbon-containing molten iron, whereby the DRI melting rate and the reduction rate can be increased to reduce heat loss. This can reduce the addition of carbon material for securing a heat source, and as a result, CO can be suppressed as well 2 Production amount. The metal composition and slag composition in each step are shown in tables 4 and 5 below.
TABLE 4 Table 4
| C | Si | Mn | P | S | |
| Seed of molten metal | 0.03～0.07 | ＜0.05 | ＜0.1 | 0.005～0.02 | 0.03～0.2 |
| After adding carbon | 0.1～1.5 | ＜0.2 | ＜0.5 | 0.03～0.15 | 0.1～0.5 |
| After DRI reduction and melting | 0.1～1.5 | ＜0.2 | ＜0.5 | 0.05～0.12 | 0.1～0.5 |
| After S removal | 0.1～1.5 | ＜0.2 | ＜0.5 | 0.03～0.15 | 0.03～0.2 |
| After decarburization (molten metal seed) | 0.03～0.07 | ＜0.05 | ＜0.1 | 0.005～0.02 | 0.03～0.2 |
Units: mass percent of
TABLE 5
Units: mass percent of
As shown in table 4, in the present embodiment, in step 2, a carbon material such as coal or smokeless carbon is further charged in accordance with the DRI supply rate, and the C concentration in the molten iron is in the range of 0.1 to 1.5 mass%. By suppressing the C concentration, CO caused by the decarburization treatment can also be suppressed 2 Production amount.
Examples
Next, an embodiment of the present invention will be described, but the conditions in the embodiment are one example of conditions employed for confirming the operability and effect of the present invention, and the present invention is not limited to this one example of conditions. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
First, in the previous ch, molten steel was tapped from a dc electric furnace having a furnace diameter of 6m and a hollow electrode, and 20t of molten steel was left in the dc electric furnace as a molten metal seed. The concentration of C in the molten steel produced in the previous pass ch was 0.05 mass%. In step 1, a carbon material is added from the hollow electrode, and carbon is added until the C concentration of the molten metal seed becomes 1.0 mass% while the C concentration is measured by a sublance probe having a C sensor incorporated therein for measuring the C concentration by thermal analysis.
Next, in step 2, DRI having a metallization ratio of 75% is added together with the carbon material, and melt reduction is performed. At this time, the C concentration in the metal was controlled so as to be 1.0 mass%, and the operating temperature was controlled so as to be 1570 ℃. The melting reduction time was 30 minutes, the amount of molten metal at the end of the DRI addition was 300t, and the slag amount was 40t.
Next, al ash was added as a deoxidizer to perform desulfurization in step 3, and after desulfurization, slag was discharged for 30t from the slag discharge hole of the dc furnace in step 4. Thereafter, in step 5, oxygen is supplied from an oxygen lance provided in the upper part of the furnace to perform decarburization treatment, thereby producing molten steel having a C concentration of 0.05 mass%. In step 5, denitrification and decarburization are promoted, and the N concentration of the produced molten steel is 30ppm. In step 6, slag produced by the decarburization is discharged from the slag discharge hole. Thereafter, in step 7, molten steel 20t is left in the furnace as the molten metal species of the next ch, and the remaining molten steel of 280t is tapped.
On the other hand, in the case of the 2-furnace system in which the tapping to decarburization, tapping of molten iron after reduction and decarburization treatment in the other furnace are not performed in the 1-furnace, a temperature decrease of at least 100 ℃ is generated by tapping from the melting furnace and charging of molten iron into the decarburization furnace. In contrast, in the present embodiment, the heat loss is not generated, and the energy consumption rate can be reduced. Further, since decarburization is started from a state where the C concentration is 1.0 mass%, the decarburization amount is small as compared with the 2-furnace method, and CO is reduced 2 Production amount. Specifically, the following is described.
At the bookIn the examples, 300× (1-0.05)/100/12×22.4=5.3 Nm was produced because 300t of molten iron having a C concentration of 1.0 mass% was decarburized to 0.05 mass% 3 CO of (c) 2 。
On the other hand, in the case of the 2-furnace method, the reduction of DRI is performed at a C concentration of 3.0 mass%, and the molten iron is tapped and decarburized in another furnace. The reason why the C concentration is set to 3.0 mass% is that if it is lower than 3.0 mass%, heat loss occurs during transition, and therefore the heat generation caused by the combustion of C in the decarburization process alone does not reach the predetermined temperature at the end of the decarburization process. In this example, in order to tap 280t of molten steel, the molten iron of 280t may be decarburized in the 2-furnace method. Thus, CO 2 The production amount was 280× (3-0.05)/100/12×22.4=16.5 Nm 3 。
As described above, in the case of the present embodiment, it was confirmed that CO can be reduced as compared with the 2-furnace system 2 Production amount.
Comparative example
First, in the previous ch, molten steel was tapped from a dc electric furnace having a furnace diameter of 6m and a hollow electrode, and 20t of molten steel was left in the dc electric furnace as a molten metal seed. The concentration of C in the molten steel produced in the previous pass ch was 0.05 mass%. Next, step 1 was omitted, and in step 2, DRI having a metallization ratio of 75% was added to perform melt reduction. At this time, the operation temperature needs to be set to a temperature up to 1640 ℃, and the melting reduction time takes 60 minutes. Thereafter, desulfurization treatment, decarburization treatment and the like were performed under the same conditions as in the examples.
As described above, in the comparative example, since the melting reduction time takes twice as long as in the example, the productivity is lowered.
Industrial applicability
According to the present invention, it is possible to provide a method of producing CO with high productivity and less heat loss and capable of reducing DRI having a low metallization ratio by melting and reducing the DRI in a melting furnace such as an electric furnace 2 The method for producing molten steel with small production amount has great industrial value.
Claims (2)
1. A method for producing molten steel, characterized by comprising the steps of:
a step 1 of adding a carbon source to molten steel having a C concentration of 0.5 mass% or more and 1.5 mass% or less, which is remained as a molten metal species in the electric furnace at the time of tapping of the previous charge, to obtain a molten iron containing carbon;
a step 2 of adding DRI to the molten iron containing carbon produced in the step 1 to perform smelting reduction;
next, a step 3 of adding a deoxidizing material to perform desulfurization treatment;
a 4 th step of discharging the desulfurized slag generated by the desulfurization treatment in the 3 rd step;
next, oxygen is blown in to perform a decarburization treatment;
a step 6 of discharging the decarburized slag generated by the decarburization treatment in the step 5; and
a 7 th step of tapping the molten metal seed portion remaining after the decarburized slag is discharged in the 6 th step,
and (2) charging a carbon source so that the C concentration of the molten carbon-containing iron is in a range of 0.5 mass% or more and 1.5 mass% or less from the start to the end of the step (2), and further, in the step (2), applying a voltage according to the supply rates of the carbon source and DRI so as to maintain an operation temperature corresponding to the C concentration of the molten carbon-containing iron.
2. The method for producing molten steel according to claim 1, wherein when D (m) is the furnace diameter of the electric furnace, the amount W (t) of molten metal remaining in the 7 th step is set to 0.3 xd 2 <W<1.6×D 2 。
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| PCT/JP2019/016502 WO2019203278A1 (en) | 2018-04-17 | 2019-04-17 | Molten steel production method |
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| JP7211454B2 (en) * | 2021-06-11 | 2023-01-24 | Ｊｆｅスチール株式会社 | Method for denitrifying molten steel, method for simultaneous denitrification and desulfurization, and method for manufacturing steel |
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| TW201943856A (en) | 2019-11-16 |
| JPWO2019203278A1 (en) | 2021-02-12 |
| JP6923075B2 (en) | 2021-08-18 |
| WO2019203278A1 (en) | 2019-10-24 |
| TWI698532B (en) | 2020-07-11 |
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| CN112004947A (en) | 2020-11-27 |
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