Shaped refractory, method for producing shaped refractory, method for constructing shaped refractory, and lining structure for electric furnace

Abstract

To provide a shaped refractory used in an electric furnace for producing molten iron by melting an iron-containing raw material containing iron, the shaped refractory being excellent in erosion resistance. The shaped refractory contains at least one selected from the group consisting of aluminum oxide, silicon carbide, and carbon, and the content of magnesium oxide is 10 mass% or less. The apparent porosity of the shaped refractory is preferably 10.0 vol% or less. The content of aluminum oxide in the shaped refractory is preferably 70 mass% or more. The shaped refractory is preferably an electrocast brick. The iron-containing raw material is preferably reduced iron obtained by direct reduction ironmaking. The electric furnace is preferably a submerged-arc furnace.

Description

Shaped refractory, manufacturing method of shaped refractory, construction method of shaped refractory, and lining structure of electric furnace

[0001] The present invention relates to a shaped refractory, a method for manufacturing a shaped refractory, a method for installing a shaped refractory, and a lining structure for an electric furnace.

[0002] The conventional steelmaking method, the blast furnace method (a method of reducing iron ore using coke), uses CO ２ In recent years, CO2 emissions have increased worldwide. ２ As efforts are being made to reduce CO ２ As an ironmaking method that can significantly reduce the amount of generated iron, direct reduction ironmaking (also referred to as "direct reduction method" or "direct ironmaking process") has attracted attention. The direct reduction ironmaking process is a method in which raw materials containing iron oxide (such as iron ore) are introduced into a vertical furnace such as a shaft furnace, a reducing gas is blown in to reduce the raw materials, and reduced iron is produced, and then the reduced iron is melted in an electric furnace (Patent Document 1).

[0003] International Publication No. 2023 / 171486

[0004] In an electric furnace, electric energy is applied to iron-containing raw materials to generate heat, which is used to melt the iron-containing raw materials. Examples of iron-containing raw materials include reduced iron produced by a direct reduction ironmaking process. When such reduced iron is melted in an electric furnace, slag is generated. This slag differs from conventional slag (e.g., blast furnace slag) in that it has low basicity and contains FeO, and is completely liquid at the internal temperature of the electric furnace (e.g., 1500 to 1600°C) when melting the reduced iron. Shaped refractories used in electric furnaces are required to have excellent resistance to corrosion caused by such slag (corrosion resistance).

[0005] The present invention has been made in consideration of the above points, and aims to provide a shaped refractory to be used in an electric furnace that melts an iron-containing raw material containing iron to produce molten iron, the shaped refractory having excellent resistance to melt damage.

[0006] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have thus completed the present invention. That is, the present invention provides the following [1] to

[11] . [1] A shaped refractory for use in an electric furnace for producing molten iron by melting an iron-containing raw material, the shaped refractory containing at least one selected from the group consisting of aluminum oxide, silicon carbide, and carbon, and having a magnesium oxide content of 10% by mass or less. [2] The shaped refractory according to [1] above, having an apparent porosity of 10.0% by volume or less. [3] The shaped refractory according to [1] or [2] above, having an aluminum oxide content of 70% by mass or more. [4] The shaped refractory according to any one of [1] to [3] above, containing aluminum oxide and carbon. [5] The shaped refractory according to any one of [1] to [4] above, which is an electrocast brick. [6] The shaped refractory according to any one of [1] to [5] above, wherein the iron-containing raw material is reduced iron obtained by a direct reduction ironmaking process. [7] The shaped refractory according to any one of [1] to [6] above, wherein the electric furnace is a submerged arc furnace. [8] A method for producing a shaped refractory, comprising molding a kneaded material containing a refractory raw material to obtain a molded product, and at least drying the molded product to produce the shaped refractory according to any one of [1] to [7] above. [9] A method for installing a shaped refractory, comprising installing the shaped refractory according to any one of [1] to [7] above on the inside of the steel shell of an electric furnace.

[10] A lining structure for an electric furnace, comprising the shaped refractory according to any one of [1] to [7] above installed on the inside of the steel shell of an electric furnace.

[11] The lining structure for an electric furnace according to

[10] above, wherein the shaped refractory is installed on the side wall of the electric furnace in a position in contact with slag.

[0007] According to the present invention, a shaped refractory having excellent resistance to melt damage can be provided.

[0008] 1 is a schematic diagram showing an electric furnace; FIG. 2 is a cross-sectional view showing a part of a side wall portion;

[0009] [Shaped refractory] The shaped refractory of this embodiment is a shaped refractory that is applied to the inside of a steel shell in a lining structure (see FIG. 2) of an electric furnace (see FIG. 1) that melts iron-containing raw materials containing iron to produce molten iron.

[0010] The shaped refractory of this embodiment is made of aluminum oxide (Al ２ O ３ ), silicon carbide (SiC), and carbon (C), and the magnesium oxide (MgO) content is 10 mass % or less. As a result, the shaped refractory of this embodiment has excellent resistance to melting damage. The reason for this is not clear, but is presumed as follows. That is, the slag generated in an electric furnace that melts iron-containing raw materials to produce molten iron has a relatively high acidity (SiO ２ If the shaped refractory material in contact with such acidic slag contains a large amount of magnesium oxide, for example, SiO ２ In contrast, the shaped refractory of the present embodiment contains at least one of aluminum oxide, silicon carbide, and carbon, which are amphoteric oxides, and is therefore considered to have high resistance to corrosion by acidic slag.

[0011] The basicity of the slag is determined by the amount of CaO and SiO ２ Mass ratio (CaO / SiO ２ ) The basicity of the acidic slag is, for example, 2.20 or less, and in some cases 1.70 or less, taking into account factors such as gangue components derived from iron ore and the amount of lime added as a flux. The shaped refractory of this embodiment exhibits high resistance to corrosion caused by acidic slag having such a basicity. The basicity of the acidic slag may be 0.50 or more, or 0.75 or more.

[0012] <Component Composition> Next, the component composition (content of each component) of the shaped refractory will be described.

[0013] 《Al ２ O ３ 》 Shaped refractories are aluminum oxide (Al ２ O ３), the content is, for example, 50% by mass or more, and is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, because the corrosion resistance is more excellent.

[0014] The upper limit is not particularly limited and may be 100 mass %, but from the viewpoint of cost etc., the Al content in the shaped refractory material is ２ O ３ The content is preferably 98 mass % or less.

[0015] <<SiC>> When the shaped refractory contains silicon carbide (SiC), the content thereof is, for example, 1 mass % or more, preferably 5 mass % or more, and more preferably 8 mass % or more.

[0016] In particular, Al ２ O ３ When the content of SiC is small (for example, less than 50 mass%), the content of SiC is preferably 15 mass% or more, more preferably 25 mass% or more, and even more preferably 35 mass% or more.

[0017] On the other hand, the content of silicon carbide (SiC) in the shaped refractory is preferably 70 mass % or less, more preferably 60 mass % or less, and even more preferably 50 mass % or less.

[0018] In particular, the shaped refractory is aluminum oxide (Al ２ O ３ When both SiC and carbon (C) are contained, the content of SiC is preferably 20 mass% or less, more preferably 12 mass% or less, still more preferably 7 mass% or less, particularly preferably 3 mass% or less, and most preferably 0 mass%.

[0019] <<C>> Carbon (C) is contained in the shaped refractory, for example, in the form of graphite. When the shaped refractory contains carbon (C), the content is, for example, 3 mass% or more, preferably 5 mass% or more, more preferably 7 mass% or more, and even more preferably 10 mass% or more.

[0020] In particular, Al ２ O ３When the content of Al is small (for example, less than 50 mass%), the content of C is preferably 25 mass% or more, more preferably 35 mass% or more, even more preferably 45 mass% or more, and particularly preferably 55 mass% or more. ２ O ３ When the total content of SiC is small (for example, less than 10 mass %), the content of C is preferably 90 mass % or more.

[0021] On the other hand, the C content in the shaped refractory is, for example, 99% by mass or less, preferably 75% by mass or less, and more preferably 65% ​​by mass or less. The C content may be 20% by mass or less.

[0022] <<MgO>> As described above, the content of magnesium oxide (MgO) in the shaped refractory is 10% by mass or less, and is preferably 7% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, because this provides better corrosion resistance. The lower limit is not particularly limited, and may be 0% by mass.

[0023] Other Components In addition to the above-mentioned components, the shaped refractory may contain, for example, silicon dioxide (SiO ２ ), calcium oxide (CaO), zirconium oxide (ZrO ２ ) (for convenience, referred to as "other components"). ２ The content of the other components is, for example, preferably 20% by mass or less, more preferably 16% by mass or less, and even more preferably 13% by mass or less.

[0024] <<Measurement Method>> The content of each of the above-mentioned components is measured in accordance with JIS R 2216 (Method for fluorescent X-ray analysis of refractory products). When the shaped refractory contains silicon carbide (SiC) and / or carbon (C) as other components, the content is measured in accordance with JIS R 2011 (Method for chemical analysis of refractories containing carbon and silicon carbide).

[0025] <Apparent Porosity> For reasons of superior resistance to corrosion, the apparent porosity of the shaped refractory is preferably 10.0 vol% or less, more preferably 8.0 vol% or less, even more preferably 6.0 vol% or less, and particularly preferably 4.0 vol% or less. The shaped refractory may be an electrocast brick, in which case the apparent porosity of the shaped refractory is easily reduced. The apparent porosity of the shaped refractory is measured in accordance with JIS R 2205 (Method for measuring apparent porosity, water absorption, and specific gravity of refractory bricks).

[0026] <Method for manufacturing shaped refractory> Next, an example of a method for manufacturing a shaped refractory (firebrick) will be described. First, a refractory raw material is mixed with a binder as needed to obtain a kneaded product. As the refractory raw material, for example, mullite (3Al ２ O ３ 2SiO ２ ), corundum (Al ２ O ３ ) and other minerals; alumina (Al ２ O ３ ), silica (SiO ２ ), carbide powder such as silicon carbide (SiC), carbon powder such as graphite (C), etc. The refractory raw materials are selected and blended so that the content of each component in the final shaped refractory product falls within the above-mentioned range.

[0027] The particle size of the refractory raw material is appropriately selected. The particle size of the mineral is adjusted by crushing or the like (for example, to 5 mm or less). The particle size is determined by sieving.

[0028] Although shaped refractories can be produced without using a binder, a binder is added as necessary. The binder is not particularly limited, and conventionally known binders used in the production of shaped refractories can be appropriately used. Examples include phenolic resin (base) and hexamine (hardening agent); polyvinyl alcohol; lignin sulfonic acid or its salts; silicates such as sodium silicate; phosphoric acid or its salts; carbon bond; ceramic bond; and the like. The amount of binder added is, for example, 0.1 to 6.0 mass% based on the refractory raw material. Specifically, when phenolic resin and hexamine are used, the amount of phenolic resin added is preferably 1.0 to 5.0 mass%, more preferably 2.0 to 4.0 mass%, based on the refractory raw material. The amount of hexamine added is preferably 0.1 to 1.0 mass%, more preferably 0.2 to 0.6 mass%.

[0029] The kneaded mixture is then molded (for example, by press molding) into a brick shape to obtain a molded body. In press molding, a device such as a friction press, an oil press, or a rubber press is used, and pressing is performed at a desired pressure.

[0030] The compact is then dried to obtain a dried product. Drying conditions (temperature, time, atmosphere, etc.) include a drying temperature of 180 to 260°C and a drying time of 12 to 48 hours. The drying atmosphere is, for example, a reducing atmosphere. When the firing step described below is not performed, the obtained dried product is used as a shaped refractory.

[0031] After drying, the dried product may be fired to obtain a fired product. The firing conditions (temperature, time, atmosphere, etc.) are, for example, a firing temperature of 1200 to 1600°C and a firing time of 3 to 5 hours. The firing atmosphere is, for example, a reducing atmosphere. When firing is performed, the obtained fired product is used as a shaped refractory.

[0032] The shaped refractory may be an electrocast brick. In this case, for example, the refractory raw material is heated to 1900 to 2500°C in an arc melting furnace to completely melt it, and the resulting melt is poured into a mold and slowly cooled to solidify, thereby obtaining a shaped refractory.

[0033] [Electric Furnace] Next, an electric furnace 1 will be described with reference to FIG. 1 . FIG. 1 is a schematic diagram of the electric furnace 1. The electric furnace 1 includes a furnace shell 2, a furnace lid 3, and electrodes 4. The furnace shell 2 is a container-shaped member with an open top, and is composed of a sidewall 5 and a furnace bottom 6. The furnace bottom 6 is provided with a bottom blowing nozzle (not shown) for blowing a stirring gas such as argon. An iron-containing raw material (not shown) is charged into the furnace shell 2. The iron-containing raw material may be, for example, reduced iron produced by a direct reduction ironmaking process. The furnace lid 3 is a member that covers the opening of the furnace shell 2, and an electrode 4 is attached thereto so as to be movable up and down. The electrode 4 is, for example, a graphite electrode. An arc is generated between the electrode 4 and the iron-containing raw material charged into the electric furnace 1 by power supplied from a power source (not shown). This heats (arc-heats) and melts the iron-containing raw material. The electric furnace 1 is, for example, a submerged arc furnace, in which the electrode 4 is heated while embedded in the iron-containing raw material. At this time, in order to promote melting of the iron-containing raw materials, heating with a burner (not shown) may be performed in parallel with the arc heating. A reducing agent may be added while continuing the arc heating. In this way, the iron-containing raw materials are melted to produce molten iron 7, and further, slag 8 is produced on the surface of the molten iron 7.

[0034] [Lining Structure of Electric Furnace] Next, the lining structure of the electric furnace 1 will be described with reference to Figure 2. The following description also includes a description of a method for applying the shaped refractory. Figure 2 is a cross-sectional view showing a portion of the side wall 5, and more specifically, shows a portion of the side wall 5 when the electric furnace 1 is viewed from above. As shown in Figure 2, the side wall 5 of the electric furnace 1 has a five-layer structure. That is, the lining structure of the electric furnace 1 is manufactured by applying, in this order, a monolithic refractory 10 and a monolithic refractory 11 to the inside of the steel shell 9 (the right side in Figure 2).

[0035] A stamped material or a castable refractory is preferably used as the monolithic refractory 10. The two differ in composition and construction method. Specifically, a stamped material is mainly composed of a carbon material and is tamped using a rammer, whereas a castable refractory is mainly composed of alumina cement and is hardened by drying.

[0036] The shaped refractory material of the present embodiment described above is used as the shaped refractory material 11.

[0037] When reduced iron produced by a direct reduction ironmaking process is used as the iron-containing raw material charged into the electric furnace 1, the resulting slag 8 (see FIG. 1 ) contains FeO, as described above. In this case, conventional shaped refractories (e.g., MgO—C bricks containing a large amount of MgO) may have insufficient resistance to corrosion (erosion resistance) caused by the slag 8. Therefore, it is preferable to apply the shaped refractory of this embodiment as the shaped refractory 11, particularly to a position in the side wall 5 that contacts the slag 8 (the so-called slag line). This suppresses corrosion of the shaped refractory 11 caused by the slag 8.

[0038] The FeO content of the slag 8 may vary depending on the amount of gangue components in the reduced iron charged into the electric furnace 1, the degree of reduction rate, and the like, but is, for example, 0.10 mass% or more, and may be 0.20 mass% or more. The shaped refractory of this embodiment used as the shaped refractory 11 exhibits high resistance to corrosion caused by the slag 8 having such an FeO content. The FeO content of the slag 8 may be 10.00 mass% or less, or may be 5.00 mass% or less.

[0039] Conventionally, in an electric furnace 1 (particularly a submerged arc furnace), cooling (water cooling) may be performed by providing a water cooling system (not shown) on the outside of the steel shell 9. In this case, while melting damage to the shaped refractory 11 can be reduced, heat radiation (heat loss) occurs due to the cooling. However, by using the shaped refractory of this embodiment as the shaped refractory 11, melting damage is suppressed, so that the degree of cooling can be weakened to reduce heat loss, or the water cooling system itself can be omitted.

[0040] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0041] <Production of shaped refractory> A shaped refractory was produced having the component composition and apparent porosity shown in Table 1. First, minerals (mullite, corundum, etc.), oxide powders (silica, alumina, etc.), carbide powders, and graphite were blended as refractory raw materials to obtain the component composition shown in Table 1. The particle size of the refractory raw materials was appropriately selected.

[0042] In the composition of the components in Table 1 below, if the total is not 100 mass %, this means that components not listed in Table 1 below are contained.

[0043] Next, the refractory raw material was kneaded with a binder to obtain a kneaded product. The binders used were a phenolic resin and hexamine, and the amount of the phenolic resin added was 3.0 mass % and the amount of the hexamine added was 0.3 mass %, based on the total mass of the refractory raw material.

[0044] The kneaded mixture was then press-molded into a brick shape to obtain a molded body. 2 The pressure was applied six times.

[0045] The compact was then dried to obtain a dried product. The drying temperature was 230°C, the drying time was 18 hours, and the drying atmosphere was a reducing atmosphere (H ２ : 30% by volume, N ２ After drying, the dried product was fired at 1400°C for 4 hours in a reducing atmosphere (H ２ : 30% by volume, N ２ : 70% by volume) to obtain a shaped refractory material.

[0046] Only the shaped refractory of Example 5 was an electrocast brick. That is, the refractory raw material was heated to 2100°C in an arc melting furnace without being kneaded with a binder, and the resulting molten material was poured into a mold and solidified to obtain a shaped refractory.

[0047] <Evaluation of the shaped refractory> The obtained shaped refractory was applied to the entire surface of the furnace shell (including the side wall) of an electric furnace (not a submerged arc furnace) as described with reference to Figures 1 and 2. No water cooling equipment was installed. Then, reduced iron (hereinafter also simply referred to as "reduced iron") produced by a direct reduction ironmaking method was charged into the electric furnace as the iron-containing raw material, and molten iron was produced by melting it. Five tons of iron-containing raw material (reduced iron) was charged at a time, and molten iron was produced multiple times. Each time, slag was produced on the surface of the molten iron. Analysis of the component composition of the produced slag revealed that it contained 25.6 mass% CaO, SiO ２ : 16.0% by mass, Al ２ O ３ : 25 mass%, MgO: 19.7 mass%, FeO: 0.54 mass%, CaO and SiO ２ Mass ratio (CaO / SiO ２ ) was 1.60, which was lower in basicity and higher in FeO content than, for example, blast furnace slag (which contains almost no FeO).

[0048] <<Wear Rate>> The wear rate (unit: mm / ch) of the shaped refractory material was calculated from the number of charges (ch) until the shaped refractory material installed in the slag line of the side wall was reduced by a certain thickness (unit: mm). The smaller the wear rate value, the better the resistance to corrosion. The results are shown in Table 1 below.

[0049] The molten iron yield (unit: mass %) was calculated from the mass of the iron-containing raw material (reduced iron) charged into the electric furnace and the mass of the molten iron produced. The results are shown in Table 1 below.

[0050]

[0051] <Summary of Evaluation Results> As is clear from the results in Table 1 above, inventive examples 1 to 5, the molten iron yield was high in all cases, and the shaped refractories thereof had a lower wear rate value than comparative example 1, and were found to have excellent resistance to melt damage.

[0052] Reference Examples 1 to 5 and Reference Comparative Example 1 A submerged arc furnace was used as the electric furnace, and the furnace shells were fitted with the shaped refractories of Invention Examples 1 to 5 and Comparative Example 1, respectively. Molten iron was produced from an iron-containing raw material (reduced iron) in the same manner as described above. Only in Reference Comparative Example 1, which used the shaped refractory of Comparative Example 1, water-cooling equipment was installed on the outside of the steel shell to ensure resistance to erosion, and cooling was carried out when producing molten iron. As a result, Reference Comparative Example 1 showed improved resistance to erosion, but also experienced more heat radiation (heat loss) than Reference Examples 1 to 6, which did not employ cooling. In addition, problems caused by the water-cooling equipment occurred once every two years.

[0053] 1: Electric furnace 2: Furnace shell 3: Furnace cover 4: Electrode 5: Side wall 6: Furnace bottom 7: Molten iron 8: Slag 9: Steel shell 10: Monolithic refractory 11: Monolithic refractory

Claims

1. A shaped refractory used in an electric furnace for melting an iron-containing raw material containing iron to produce molten iron, the shaped refractory containing at least one selected from the group consisting of aluminum oxide, silicon carbide, and carbon, and having a magnesium oxide content of 10% by mass or less.

2. The shaped refractory according to claim 1, having an apparent porosity of 10.0% by volume or less.

3. The shaped refractory according to claim 1 or 2, wherein the aluminum oxide content is 70% by mass or more.

4. The shaped refractory according to any one of claims 1 to 3, containing the aluminum oxide and the carbon.

5. The shaped refractory according to any one of claims 1 to 4, which is an electroformed brick.

6. The shaped refractory according to any one of claims 1 to 5, wherein the iron-containing raw material is reduced iron obtained by the direct reduction ironmaking method.

7. The shaped refractory according to any one of claims 1 to 6, wherein the electric furnace is a submerged arc furnace.

8. A method for manufacturing a shaped refractory, comprising molding a mixture containing a refractory raw material to obtain a molded article, and subjecting the molded article to at least drying to manufacture the shaped refractory according to any one of claims 1 to 7.

9. A method for installing a shaped refractory, comprising installing the shaped refractory according to any one of claims 1 to 7 inside the iron shell of an electric furnace.

10. A lining structure of an electric furnace, comprising the shaped refractory according to any one of claims 1 to 7 installed inside the iron shell of the electric furnace.

11. The lining structure of the electric furnace according to claim 10, wherein the shaped refractory is provided at a position in the side wall portion of the electric furnace that comes into contact with slag.

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