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

Abstract

This invention provides a shaped refractories with excellent resistance to melting loss, suitable for use in electric furnaces where iron-containing raw materials are melted to produce molten iron. The shaped refractories contain at least one material selected from the group consisting of alumina, silicon carbide, and carbon, and the magnesium oxide content is 10% by mass or less. The apparent porosity of the shaped refractories is preferably 10.0% by volume or less. The alumina content of the shaped refractories is preferably 70% by mass or more. The shaped refractories are preferably cast bricks. The iron-containing raw materials are preferably reduced iron obtained by direct reduction ironmaking. The electric furnace is preferably a submerged arc furnace.

Description

Technical Field

[0001] This invention relates to shaped refractories, methods for manufacturing shaped refractories, methods for constructing shaped refractories, and furnace lining structures for electric furnaces. Background Technology

[0002] The blast furnace method, a traditional ironmaking process (using coke to reduce iron ore), produces a large amount of CO2.

[0003] In recent years, as global efforts have been made to reduce CO2 emissions, the direct reduction ironmaking process (also known as the "direct reduction method" or "direct ironmaking process") has attracted attention as an ironmaking method that can significantly reduce CO2 production.

[0004] The direct reduction ironmaking method is as follows: raw materials containing iron oxide (such as iron ore) are introduced into a vertical furnace such as a shaft furnace, reducing gas is blown in, the raw materials are reduced to produce reduced iron, and then the reduced iron is melted in an electric furnace (Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2023 / 171486 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In an electric furnace, electrical energy is applied to iron-containing raw materials to generate heat, which melts the iron-containing raw materials.

[0010] As an iron-containing raw material, reduced iron produced by the direct reduction ironmaking process can be cited as an example.

[0011] When such reduced iron is melted in an electric furnace, slag is produced. This slag differs from conventional slag (such as blast furnace slag) in that it has lower basicity, contains FeO, and is completely liquid at the internal temperature of the electric furnace (e.g., 1500–1600 °C) when the reduced iron is melted.

[0012] The shaped refractories used in electric furnaces are required to have excellent resistance to melting loss caused by such slag (melting loss resistance).

[0013] The present invention was made in view of the above aspects, and its object is to provide a shaped refractory for use in an electric furnace for producing molten iron by melting iron-containing raw materials, and the shaped refractory has excellent resistance to melting loss.

[0014] Methods for solving problems

[0015] The inventors conducted in-depth research and found that the above-mentioned objectives could be achieved by adopting the following configuration, thus completing the present invention.

[0016] That is, the present invention provides the following [1] to

[11] .

[0017] [1] A shaped refractory used in an electric furnace for producing molten iron by melting an iron-containing raw material containing iron, wherein the refractory contains at least one of the following: selected from the group consisting of alumina, silicon carbide and carbon, and the content of magnesium oxide is less than 10% by mass.

[0018] [2] According to the shaped refractory described in [1] above, the apparent porosity is less than 10.0% by volume.

[0019] [3] According to the shaped refractory described in [1] or [2] above, the content of the above alumina is 70% by mass or more.

[0020] [4] The shaped refractory according to any one of [1] to [3] above, wherein it contains the above-mentioned alumina and the above-mentioned carbon.

[0021] [5] The shaped refractory according to any one of [1] to [4] above is a fused cast brick.

[0022] [6] The shaped refractory according to any one of [1] to [5] above, wherein the iron-containing raw material is reduced iron obtained by direct reduction ironmaking.

[0023] [7] The shaped refractory according to any one of [1] to [6] above, wherein the electric furnace is a submerged arc furnace.

[0024] [8] A method for manufacturing a shaped refractory, wherein a mixture containing refractory raw materials is shaped to obtain a shaped article, and the shaped article is at least dried, thereby manufacturing the shaped refractory as described in any one of [1] to [7].

[0025] [9] A method for constructing a shaped refractory, wherein the shaped refractory described in any one of [1] to [7] is constructed onto the inner side of the sheet metal of an electric furnace.

[0026]

[10] A furnace lining structure for an electric furnace, comprising a shaped refractory material as described in any one of [1] to [7] above, which is applied to the inner side of the sheet metal of the electric furnace.

[0027]

[11] According to the furnace lining structure of the electric furnace described in

[10] above, the shaped refractory is applied to the side wall of the electric furnace and is in contact with the slag.

[0028] Invention Effects

[0029] According to the present invention, shaped refractory materials with excellent resistance to melting can be provided. Attached Figure Description

[0030] Figure 1 This is a schematic diagram showing an electric furnace.

[0031] Figure 2 This is a cross-sectional view showing a portion of the sidewall. Detailed Implementation

[0032] [Shaped refractory materials]

[0033] The shaped refractory in this embodiment is used in an electric furnace (see reference) to produce molten iron by melting iron-containing raw materials. Figure 1 The furnace lining structure (refer to) Figure 2 A shaped refractory material that is installed on the inside of the sheet metal.

[0034] The shaped refractory of this embodiment contains at least one element selected from the group consisting of alumina (Al2O3), silicon carbide (SiC) and carbon (C), and the content of magnesium oxide (MgO) is 10% by mass or less.

[0035] Therefore, the shaped refractory of this embodiment exhibits excellent resistance to melting. While the reason is unclear, it is speculated as follows.

[0036] That is, the slag produced in the electric furnace that melts iron-containing raw materials to produce molten iron is highly acidic (high in SiO2). When shaped refractory materials in contact with this acidic slag, such as those containing a large amount of magnesium oxide, react with SiO2 to form low-melting-point compounds that are easily dissolved.

[0037] In contrast, the shaped refractory of this embodiment is considered to have high resistance to melting loss caused by acidic slag because it contains at least one of alumina, silicon carbide and carbon, which are amphoteric oxides.

[0038] The basicity of slag is expressed as the mass ratio of CaO to SiO2 (CaO / SiO2). Regarding the basicity of acidic slag, considering factors such as gangue composition from the iron ore and the amount of lime added as flux, it is typically below 2.20, and sometimes below 1.70.

[0039] The shaped refractory of this embodiment exhibits high resistance to melting loss caused by acidic slag with this alkalinity.

[0040] It should be noted that the alkalinity of acidic slag can be above 0.50 or above 0.75.

[0041] <Ingredients and Composition>

[0042] Next, the composition of the shaped refractories (the content of each component) will be explained.

[0043] Al2O3

[0044] When the shaped refractory contains alumina (Al2O3), its content is, for example, 50% by mass or more, 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, for the sake of better resistance to melting and loss.

[0045] There is no specific upper limit, and it can be 100% by mass. However, from the perspective of cost and other factors, the content of Al2O3 in shaped refractories is preferably below 98% by mass.

[0046] SiC

[0047] When the shaped refractory contains silicon carbide (SiC), its content is, for example, 1% by mass or more, preferably 5% by mass or more, and more preferably 8% by mass or more.

[0048] In particular, when the Al2O3 content is low (e.g., less than 50% by mass), the SiC content is preferably 15% by mass or more, more preferably 25% by mass or more, and even more preferably 35% by mass or more.

[0049] On the other hand, the silicon carbide (SiC) content in the shaped refractories is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0050] In particular, when the shaped refractory contains both alumina (Al2O3) and carbon (C), the SiC content is preferably 20% by mass or less, more preferably 12% by mass or less, even more preferably 7% by mass or less, particularly preferably 3% by mass or less, and most preferably 0% by mass.

[0051] 《C》

[0052] Carbon (C) is contained, for example, in shaped refractories in the form of graphite.

[0053] When the shaped refractory contains carbon (C), its content is, for example, 3% by mass or more, preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more.

[0054] In particular, when the content of Al2O3 is low (e.g., less than 50% by mass), the content of C is preferably 25% by mass or more, more preferably 35% by mass or more, even more preferably 45% by mass or more, and especially preferably 55% by mass or more.

[0055] Furthermore, when the combined content of Al2O3 and SiC is low (e.g., less than 10% by mass), the content of C is preferably 90% by mass or more.

[0056] On the other hand, the C content in the shaped refractories 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 also be 20% by mass or less.

[0057] MgO

[0058] The magnesium oxide (MgO) content in the shaped refractory is 10% by mass or less as described above, and preferably 7% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, for the sake of better resistance to melting and loss.

[0059] The lower limit is not specifically defined and can be 0% (mass).

[0060] Other Ingredients

[0061] In addition to the above-mentioned components, shaped refractories may also contain components such as silicon dioxide (SiO2), calcium oxide (CaO), and zirconium oxide (ZrO2) (for convenience, these are referred to as "other components").

[0062] The content of other components (e.g., SiO2) in the shaped refractory is, for example, 1% by mass or more, more preferably 3% by mass or more.

[0063] On the other hand, the content of other components is preferably 20% by mass or less, more preferably 16% by mass or less, and even more preferably 13% by mass or less.

[0064] Determination Method

[0065] The content of the above components was determined according to JIS R 2216 (fluorescent X-ray analysis method for refractory products).

[0066] It should be noted that when shaped refractories contain silicon carbide (SiC) and / or carbon (C) as other components, the determination shall be performed in accordance with JIS R 2011 (chemical analysis method for refractories containing carbon and silicon carbide).

[0067] Apparent porosity

[0068] Based on the reason of better resistance to melting loss, the apparent porosity of the shaped refractory is preferably 10.0% by volume or less, more preferably 8.0% by volume or less, even more preferably 6.0% by volume or less, and particularly preferably 4.0% by volume or less.

[0069] It should be noted that shaped refractories can also be cast bricks, in which case the apparent porosity of the shaped refractories is likely to be low.

[0070] The apparent porosity of shaped refractories was determined according to JIS R 2205 (Methods for determining apparent porosity, water absorption and specific gravity of refractory bricks).

[0071] <Methods for manufacturing shaped refractories>

[0072] Next, an example of a method for manufacturing shaped refractory materials (refractory bricks) will be described.

[0073] First, the refractory raw materials are mixed with the binder as needed to obtain a mixture.

[0074] As refractory raw materials, the following can be used: minerals such as mullite (3Al2O3·2SiO2) and corundum (Al2O3); oxide powders such as alumina (Al2O3) and silicon dioxide (SiO2); carbide powders such as silicon carbide (SiC); carbon powders such as graphite (C); etc.

[0075] Select and combine refractory raw materials to ensure that the content of each component in the final shaped refractory reaches the above-mentioned levels.

[0076] The particle size of refractory raw materials can be selected appropriately.

[0077] Minerals can have their particle size adjusted (e.g., below 5 mm) through crushing or other methods.

[0078] Particle size can be determined by sieving.

[0079] While shaped refractories can also be manufactured without the use of adhesives, adhesives may be added as needed.

[0080] As an adhesive, there are no particular limitations, and existing known adhesives used in the manufacture of shaped refractories may be appropriately used, such as: phenolic resin (main agent) and hexamethylenetetramine (curing agent); polyvinyl alcohol; lignosulfonic acid or its salts; silicates such as sodium silicate; phosphoric acid or its salts; carbon binders; ceramic binders; etc.

[0081] Regarding the amount of binder added, relative to the refractory raw material, as an external admixture, it is, for example, 0.1 to 6.0% by mass. Specifically, for example, when using phenolic resin and hexamethylenetetramine, relative to the refractory raw material, the amount of phenolic resin added is preferably 1.0 to 5.0% by mass, more preferably 2.0 to 4.0% by mass. The amount of hexamethylenetetramine added is preferably 0.1 to 1.0% by mass, more preferably 0.2 to 0.6% by mass.

[0082] Next, the resulting mixture is shaped (e.g., pressed) into a brick shape to obtain a molded body. In pressing, devices such as friction brick presses, hydraulic presses, and rubber presses are used to press the material at any pressure.

[0083] Then, the shaped body is dried to obtain a dried product.

[0084] Drying conditions (temperature, time, atmosphere, etc.) include, for example, a drying temperature of 180–260°C and a drying time of 12–48 hours. The drying atmosphere may be, for example, a reducing atmosphere.

[0085] Without performing the firing process described later, the resulting dried product is used as a shaped refractory.

[0086] After drying, the dried product can also be fired to obtain a fired product.

[0087] The firing conditions (temperature, time, atmosphere, etc.) include, for example, a firing temperature of 1200–1600°C and a firing time of 3–5 hours. The firing atmosphere is, for example, a reducing atmosphere.

[0088] When firing is carried out, the resulting fired product is used as a shaped refractory.

[0089] It should be noted that shaped refractory materials can also be cast bricks.

[0090] In this case, for example, an electric arc melting furnace is used to heat the refractory material to 1900-2500°C to completely melt it, and the resulting melt is poured into a mold and slowly cooled and solidified to obtain a shaped refractory.

[0091] [Electric Furnace]

[0092] Next, based on Figure 1 Instructions for electric furnace 1.

[0093] Figure 1 This is a schematic diagram showing electric furnace 1.

[0094] The electric furnace 1 has a furnace shell 2, a furnace cover 3, and electrodes 4.

[0095] The furnace shell 2 is a container-shaped component with an opening at the top, consisting of a side wall 5 and a furnace bottom 6. A bottom-blowing nozzle (not shown) is provided at the furnace bottom 6 for introducing stirring gases such as argon. Iron-containing raw materials (not shown) are loaded inside the furnace shell 2. For example, reduced iron produced by the direct reduction ironmaking process is used.

[0096] The furnace cover 3 is a component that covers the opening of the furnace shell 2, and the electrode 4 is mounted on it in a manner that allows it to move freely in the vertical direction.

[0097] Electrode 4 is, for example, a graphite electrode, which generates an electric arc between itself and the iron-containing raw material loaded inside the electric furnace 1 using electricity supplied from a power source (not shown). This heats the iron-containing raw material (arc heating) and melts it. The electric furnace 1 is, for example, a submerged arc furnace, in which case heating is performed with electrode 4 embedded in the iron-containing raw material.

[0098] At this point, to promote the melting of the iron-containing raw materials, heating can also be carried out simultaneously with arc heating using a burner (not shown). Alternatively, a reducing agent can be added while continuously heating with an electric arc.

[0099] In this way, the iron-containing raw material melts, thereby generating molten iron 7, and slag 8 is generated on the surface of the molten iron 7.

[0100] [Electric Furnace Lining Structure]

[0101] Next, based on Figure 2 This section describes the furnace lining structure of electric furnace 1. The following description also serves as an explanation of the construction method for shaped refractory materials.

[0102] Figure 2 This is a cross-sectional view showing a portion of the sidewall portion 5, and more specifically, a portion of the sidewall portion 5 as viewed from above when the electric furnace 1 is viewed from above.

[0103] like Figure 2 As shown, the side wall 5 of the electric furnace 1 has a 5-layer structure.

[0104] That is, the furnace lining structure of electric furnace 1 is manufactured in the following manner: unshaped refractories 10 and shaped refractories 11 are sequentially constructed onto the inner side of sheet metal 9. Figure 2 (The right side of the middle).

[0105] As the unshaped refractories 10, ramming mixes or castables are preferred. The compositions and construction methods of the two are different. Specifically, ramming mixes are mainly composed of carbonaceous materials and are compacted using a tamping hammer, while castables are mainly composed of high-alumina cement and are cured by drying.

[0106] Furthermore, the shaped refractory of this embodiment described above is used as the shaped refractory 11.

[0107] However, when using reduced iron produced by direct reduction ironmaking as the iron-containing raw material charged into electric furnace 1, the resulting slag 8 (refer to...) Figure 1 As described above, it contains FeO and other characteristics. In this case, conventional shaped refractories (e.g., MgO-C bricks containing a large amount of MgO) may not be sufficiently resistant to melting loss caused by slag 8.

[0108] Therefore, it is preferable to use the shaped refractory of this embodiment as the shaped refractory 11, especially to be applied to the side wall portion 5 at the position in contact with the slag 8 (the so-called slag line). As a result, the shaped refractory 11 can suppress melting loss caused by the slag 8.

[0109] The FeO content of slag 8 varies depending on the amount of gangue components in the reduced iron charged into electric furnace 1 and the degree of reduction, but it is, for example, more than 0.10% by mass, and sometimes more than 0.20% by mass.

[0110] The shaped refractories of this embodiment, used as shaped refractories 11, exhibit high resistance to melting loss caused by slag 8 with such FeO content.

[0111] It should be noted that the FeO content of slag 8 can be below 10.00% by mass or below 5.00% by mass.

[0112] It should be noted that in the past, in electric furnaces 1 (especially submerged arc furnaces), water cooling equipment (not shown) was sometimes installed on the outside of the sheet metal 9 to implement cooling (water cooling). At this time, the melting loss of the shaped refractory 11 can be reduced, but on the other hand, heat loss will occur due to cooling.

[0113] However, by using the shaped refractory of this embodiment as the shaped refractory 11, melting loss is suppressed. Therefore, the degree of cooling can be reduced to decrease heat loss, or the water cooling equipment itself can be omitted.

[0114] Example

[0115] The present invention will now be described in detail with examples. However, the present invention is not limited to the examples described below.

[0116] <Manufacturing of Shaped Refractory Materials>

[0117] To manufacture shaped refractories having the composition and apparent porosity shown in Table 1 below.

[0118] First, minerals (mullite, corundum, etc.), oxide powders (silicon dioxide, alumina, etc.), carbide powders, and graphite, used as refractory raw materials, are combined in accordance with the composition shown in Table 1 below. The particle size of the refractory raw materials is appropriately selected.

[0119] It should be noted that when the total of the components in Table 1 below is not 100% by mass, it indicates that the product contains components not listed in Table 1 below.

[0120] Next, the refractory raw materials and binder are mixed to obtain a mixture. As binders, phenolic resin and hexamethylenetetramine are used, and the amount of phenolic resin added is set to 3.0% by mass and the amount of hexamethylenetetramine added is set to 0.3% by mass relative to the refractory raw materials (external admixture).

[0121] The resulting mixture is then pressed into a brick shape to obtain the molded body. During the pressing process, a friction brick press is used, applying 2 t / cm twice. 2 The pressure.

[0122] The molded body was then dried to obtain a dried product. The drying temperature was set to 230℃, the drying time was set to 18 hours, and the drying atmosphere was set to a reducing atmosphere (H2: 30% by volume, N2: 70% by volume).

[0123] After drying, the dried product is fired. The firing temperature is 1400℃, the firing time is set to 4 hours, and the firing atmosphere is set to a reducing atmosphere (H2: 30% by volume, N2: 70% by volume).

[0124] Thus, shaped refractory materials are obtained.

[0125] It should be noted that the shaped refractory in Invention Example 5 is a cast brick.

[0126] That is, the refractory material is heated to 2100°C in an electric arc melting furnace without mixing with the binder, and the resulting molten material is poured into a mold to solidify, thereby obtaining a shaped refractory.

[0127] <Evaluation of Shaped Refractory Materials>

[0128] The obtained shaped refractory material is then applied to the entire surface based on... Figures 1-2 The furnace shell (including the side walls) of the electric arc furnace (but not a submerged arc furnace) is described. No water cooling equipment is installed. Then, reduced iron (hereinafter also referred to as "reduced iron"), an iron-containing raw material produced by direct reduction ironmaking, is charged into the electric furnace and melted to produce molten iron. Five tons of iron-containing raw material (reduced iron) are charged at a time, and molten iron is produced multiple times. Slag is formed on the surface of the molten iron each time.

[0129] The analysis of the composition of the generated slag showed that CaO: 25.6% by mass, SiO2: 16.0% by mass, Al2O3: 25% by mass, MgO: 19.7% by mass, and FeO: 0.54% by mass. The mass ratio of CaO to SiO2 (CaO / SiO2), i.e., the basicity, was 1.60. Compared with blast furnace slag (which contains almost no FeO), the basicity was low and the FeO content was high.

[0130] Rate of wear and tear

[0131] The number of times (ch) of shaped refractory material is added from construction to the slag line of the side wall until a certain thickness (unit: mm) is reduced, and the wear rate of the shaped refractory material (unit: mm / ch) is calculated.

[0132] The smaller the loss rate value, the better the resistance to melting. The results are shown in Table 1 below.

[0133] Iron yield

[0134] The iron yield (unit: mass%) is 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.

[0135] [Table 1]

[0136] <Summary of Evaluation Results>

[0137] As can be clearly seen from the results in Table 1 above, the molten iron yield of Examples 1 to 5 is high, and their shaped refractory has a lower loss rate and better resistance to melting compared with Comparative Example 1.

[0138] <Refer to Examples 1-5 and Comparative Example 1>

[0139] Using a submerged arc furnace as an electric furnace, shaped refractory materials of Invention Examples 1 to 5 and Comparative Example 1 were respectively constructed on its furnace shell. These were used as Reference Examples 1 to 5 and Reference Comparative Example 1, respectively. Molten iron was produced from iron-containing raw materials (reduced iron) in the same manner as described above.

[0140] At this time, only for the reference comparative example 1 which uses the shaped refractory of comparative example 1, in order to ensure resistance to melting, a water cooling device was installed on the outside of the iron sheet, and cooling was implemented during the production of molten iron.

[0141] As a result, while improved resistance to melting was observed in Reference Comparative Example 1, more heat dissipation (heat loss) was observed compared to Reference Examples 1-6, which did not implement cooling, and failures caused by water cooling equipment occurred at a rate of once every two years.

[0142] Symbol Explanation

[0143] 1: Electric furnace

[0144] 2: Furnace shell

[0145] 3: Furnace lid

[0146] 4: Electrode

[0147] 5: Side wall portion

[0148] 6: Bottom of the furnace

[0149] 7: Molten Iron

[0150] 8: Slag

[0151] 9: Sheet metal

[0152] 10: Unshaped refractories

[0153] 11: Shaped refractory

Claims

1. A shaped refractory used in an electric furnace for producing molten iron by melting iron-containing raw materials, wherein, Contains at least one of the following: selected from the group consisting of alumina, silicon carbide, and carbon. The magnesium oxide content is less than 10% by mass.

2. The shaped refractory according to claim 1, wherein, The apparent porosity is less than 10.0% by volume.

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

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

5. The shaped refractory according to any one of claims 1 to 4, wherein it is a fused cast 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 direct reduction ironmaking.

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, wherein, The mixture containing refractory materials is shaped to obtain a molded product. The shaped article is at least dried, thereby producing the shaped refractory according to any one of claims 1 to 7.

9. A construction method for shaped refractory materials, wherein, The shaped refractory material according to any one of claims 1 to 7 is applied to the inside of the sheet metal of the electric furnace.

10. A furnace lining structure for an electric furnace, comprising a shaped refractory as described in any one of claims 1 to 7, which is incorporated into the inner side of the sheet metal of the electric furnace.

11. The furnace lining structure of the electric furnace according to claim 10, wherein, The shaped refractory is applied to the side wall of the electric furnace at the location where it contacts the slag.

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