Shaped refractory, method for manufacturing shaped refractory, method for constructing shaped refractory, and lining structure of vertical furnace

Abstract

To provide a shaped refractory which is used for a vertical furnace for producing reduced iron by using a hydrogen-containing gas and has excellent hydrogen gas resistance.SOLUTION: A shaped refractory used for a vertical furnace for producing reduced iron by using a hydrogen-containing gas comprises aluminum oxide of 40 mass% or more. The total content of iron oxide and titanium oxide in the shaped refractory is preferably 5.0 mass% or less. The content of free silica in the shaped refractory is preferably 10.0 mass% or less. The shaped refractory preferably comprises mullite.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to shaped refractories, a method for manufacturing shaped refractories, a method for constructing shaped refractories, and a lining structure of a shaft furnace.

Background Art

[0002] In the blast furnace method, which is a conventional ironmaking method (a method of reducing iron ore using coke), a large amount of CO2 is generated. In recent years, globally, efforts have been made to reduce CO2, and thus, as an ironmaking method that significantly reduces the amount of CO2 generated, the direct reduction ironmaking method (also referred to as the "direct reduction method" or the "direct ironmaking method") has attracted attention. The direct reduction ironmaking method is a method in which a raw material containing iron oxide (such as iron ore) is introduced into a shaft furnace such as a blast furnace, a reducing gas is blown in, the raw material is reduced to produce reduced iron, and then the reduced iron is melted in an electric furnace (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a shaft furnace such as a blast furnace, a shaped refractory (refractory brick) is constructed as a refractory that constitutes the refractory lining structure on the inner side of the scale. Generally, for shaped refractories, as basic performances, good stability (thermal shock resistance) and heat insulation are required. Also, at this time, cost is also considered.

[0005] By the way, in the global movement towards carbon neutrality, in the direct reduction ironmaking method, it has been considered to use a hydrogen-containing gas containing H2 (hydrogen gas) as the reducing gas blown into the shaft furnace. When reducing iron ore using a shaft furnace, the interior of the shaft furnace reaches a high temperature close to 1000 °C. In such a high-temperature environment, when using a hydrogen-containing gas as the reducing gas, there are concerns about the impact of hydrogen gas (H2) on the shaped refractory. That is, for the shaped refractory used in the shaft furnace, it is required to have excellent resistance to hydrogen gas (also referred to as "hydrogen gas resistance").

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a shaped refractory for use in a shaft furnace for producing reduced iron using a hydrogen-containing gas, which has excellent hydrogen gas resistance.

Means for Solving the Problems

[0007] As a result of intensive studies, the present inventors have found that the above object can be achieved by adopting the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [7]. [1] A shaped refractory for use in a shaft furnace for producing reduced iron using a hydrogen-containing gas, the shaped refractory containing 40% by mass or more of aluminum oxide. [2] The shaped refractory according to [1] above, wherein the total content of iron oxide and titanium oxide is 5.0% by mass or less. [3] The shaped refractory according to [1] or [2] above, wherein the content of free silica is 10.0% by mass or less. [4] The shaped refractory according to any one of [1] to [3] above, containing mullite. [5] 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 [1] to [4] above. [6] A method for constructing a shaped refractory, comprising constructing the shaped refractory according to any one of [1] to [4] above inside the iron skin of a shaft furnace. [7] A lining structure of a shaft furnace, comprising the shaped refractory according to any one of [1] to [4] above constructed inside the iron skin of the shaft furnace.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a shaped refractory excellent in hydrogen gas resistance.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] [Shaped Refractory] The shaped refractory of the present embodiment is a shaped refractory constructed inside the iron skin in the lining structure (see FIG. 2) of a vertical furnace (see FIG. 1) for producing reduced iron using a hydrogen-containing gas containing hydrogen gas (H2).

[0011] The shaped refractory of the present embodiment contains 40 mass% or more of aluminum oxide (Al2O3). Thereby, for example, in a high-temperature environment of 1000 to 1200 ° C., it is excellent in resistance to hydrogen gas (hydrogen gas resistance).

[0012] The reason is presumed as follows. For example, when the shaped refractory contains silicon dioxide (SiO2), inside the vertical furnace, the reaction shown in the following formula (1) occurs, and due to this reaction, the shaped refractory deteriorates. SiO2 + H2 → SiO + H2O ··· (1) On the other hand, when the shaped refractory contains a large amount of Al2O3 instead of SiO2, the above reaction is suppressed. That is, it is excellent in hydrogen gas resistance.

[0013] 〈Component Composition〉 Next, the component composition (content of each component) of the shaped refractory will be described.

[0014] 《Al2O3》 As described above, the content of aluminum oxide (Al2O3) in the shaped refractory is 40% by mass or more, and preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, and particularly preferably 80% by mass or more because of the better hydrogen gas resistance.

[0015] The upper limit is not particularly limited and may be 100% by mass. However, from the viewpoint of cost reduction, the content of Al2O3 in the shaped refractory is preferably 90% by mass or less, more preferably 85% by mass or less, and still more preferably 80% by mass or less.

[0016] 《SiO2》 Considering the estimated mechanism of hydrogen gas resistance generation, the content of silicon dioxide (SiO2) in the shaped refractory is preferably low. That is, for the reason of better hydrogen gas resistance, the content of SiO2 in the shaped refractory is preferably 40% by mass or less, more preferably 36% by mass or less, still more preferably 32% by mass or less, and particularly preferably 28% by mass or less.

[0017] The lower limit is not particularly limited and may be 0% by mass. However, if SiO2 is less, instead, Al2O3 will increase and the cost will tend to be high. From the viewpoint of cost reduction, the content of SiO2 in the shaped refractory is preferably 10% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more.

[0018] 《Fe2O3 and TiO2》 For the reason of better hydrogen gas resistance, the total content of iron oxide (Fe2O3) and titanium oxide (TiO2) in the shaped refractory is preferably low. The reason for this is not clear, but it is considered that in the shaped refractory, Fe2O3 and TiO2 are preferentially reduced by hydrogen gas (H2) rather than silicon dioxide (SiO2). Specifically, the total content of Fe2O3 and TiO2 in the shaped refractory is preferably 5.0% by mass or less, more preferably 3.5% by mass or less, still more preferably 1.0% by mass or less, particularly preferably 0.7% by mass or less, and most preferably 0.5% by mass or less.

[0019] 《Other Components》 In addition to the components described above, the shaped refractory may contain components such as magnesium oxide (MgO), calcium oxide (CaO), zirconium oxide (ZrO2), silicon carbide (SiC), carbon (C), etc. (conveniently referred to as "other components"). However, from the viewpoint of obtaining good hydrogen gas resistance, the content of other components in the shaped refractory is preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 6% by mass or less, particularly preferably 4% by mass or less, and most preferably 2% by mass or less.

[0020] 《Measurement Method》 The content of each component described above is measured in accordance with JIS R 2216 (Fluorescent X-ray Analysis Method for Refractory Products). In addition, when the shaped refractory contains silicon carbide (SiC) and / or carbon (C) as other components, the measurement is carried out in accordance with JIS R 2011 (Chemical Analysis Method for Carbon and Silicon Carbide Containing Refractories).

[0021] 〈Content of Free Silica〉 Free silica is generally silicon dioxide (SiO2) in the shaped refractory that is not combined with the above-mentioned components, etc., and is easily detached from the shaped refractory.

[0022] For the reason that the hydrogen gas resistance is more excellent, the content of free silica in the shaped refractory is preferably low. Although the reason for this is not clear, it is considered that in the shaped refractory, free silica is preferentially reduced by hydrogen gas (H2) rather than silicon dioxide (SiO2) chemically bonded to each component. Specifically, the content of free silica in the shaped refractory is preferably 10.0% by mass or less, more preferably 7.5% by mass or less, still more preferably 5.0% by mass or less, and particularly preferably 3.0% by mass or less.

[0023] Free silica is derived from, for example, silica (SiO2) used as a raw material (refractory raw material) of the shaped refractory. In addition, minerals such as mullite (3Al2O3·2SiO2) used as refractory raw materials may also contain silica (SiO2), which can also become free silica.

[0024] The content of free silica is measured in accordance with the "Quantification Method of Free Silicon Dioxide" described in JIS R 1616 (Chemical Analysis Method for Silicon Carbide Fine Powder for Fine Ceramics).

[0025] 〈Mineral Phase〉 The shaped refractory preferably contains minerals such as mullite (3Al2O3·2SiO2) and corundum (Al2O3) because of better hydrogen gas resistance, and more preferably contains mullite.

[0026] For example, a shaped refractory containing mullite can be obtained by using mullite as at least a part of its raw material (refractory raw material).

[0027] The mineral phase of the shaped refractory can be confirmed using an X-ray diffractometer (XRD) of the shaped refractory. That is, minerals such as mullite and corundum are crystallized and have unique XRD patterns, so the presence or absence of each mineral can be confirmed based on the XRD pattern of the shaped refractory.

[0028] 〈Manufacturing Method of Shaped Refractory〉 Next, an example of a method for manufacturing a shaped refractory (refractory brick) will be described. First, the refractory raw material is kneaded with a binder as necessary to obtain a kneaded product. As refractory raw materials, for example, minerals such as mullite (3Al2O3·2SiO2) and corundum (Al2O3); oxide powders such as alumina (Al2O3) and silica (SiO2); etc. are used. The refractory raw materials are selected and blended so that the content of each component in the finally obtained shaped refractory becomes the content described above.

[0029] In addition, minerals such as mullite may contain, as impurities, in addition to silica (SiO2), iron oxide (Fe2O3) and titanium oxide (TiO2). The content of impurities varies depending on the source of acquisition, etc., even for the same mineral.

[0030] The particle size of the refractory raw material is appropriately selected. The particle size of the mineral is adjusted by crushing, etc. (for example, 5 mm or less). The particle size is determined by sieving.

[0031] It is possible to manufacture a shaped refractory without using a binder, but a binder is added as necessary. The binder is not particularly limited, and conventionally known binders used in the manufacture of shaped refractories can be appropriately used. For example, polyvinyl alcohol; lignin sulfonic acid or its salt; silicates such as sodium silicate; phosphoric acid or its salt; carbon bond; ceramic bond; etc. can be mentioned. The addition amount of the binder is an external addition to the refractory raw material, for example, 0.1 to 6.0% by mass.

[0032] Next, the obtained kneaded material is formed into a brick shape (for example, press molding) to obtain a formed body. In press molding, known devices such as friction presses and hydraulic presses are used, and it is pressed at an arbitrary pressure.

[0033] Thereafter, the formed body is dried to obtain a dried product. As the drying conditions (temperature, time, atmosphere, etc.), for example, the drying temperature is 180 to 260 °C, and the drying time is 12 to 48 hours. The drying atmosphere is, for example, an air atmosphere. When the firing described below is not carried out, the obtained dried product is used as a shaped refractory.

[0034] After drying, the dried product may be fired to obtain a fired product. As the firing conditions (temperature, time, atmosphere, etc.), for example, the firing temperature is 1200 to 1600 °C, and the firing time is 3 to 5 hours. The firing atmosphere is, for example, an air atmosphere. When firing is carried out, the obtained fired product is used as a shaped refractory.

[0035] [Shaft furnace] Next, based on FIG. 1, the shaft furnace 1 used in the direct reduction ironmaking method will be described. FIG. 1 is a schematic diagram showing the shaft furnace 1. Generally speaking, from the top 2 of the shaft furnace 1, a raw material 3 containing iron oxide (for example, iron ore pellets) is introduced into the interior of the shaft furnace 1. The raw material 3 is reduced by a reducing gas while descending inside the shaft furnace 1. In this way, reduced iron 4 is produced.

[0036] On the furnace wall 5 of the shaft furnace 1, a gas discharge port 6 and a gas injection port 7 are provided. The gas injection port 7 is provided at a substantially middle position in the vertical direction of the shaft furnace 1 and supplies a reducing gas into the interior of the shaft furnace 1.

[0037] In this embodiment, as the reducing gas, a hydrogen-containing gas containing hydrogen gas (H2) is used. The hydrogen gas concentration in the hydrogen-containing gas is, for example, 10% by volume or more, preferably 50% by volume or more, more preferably 80% by volume or more, still more preferably 90% by volume or more, particularly preferably 95% by volume or more, and most preferably 98% by volume or more. On the other hand, the upper limit is not particularly limited, and the hydrogen gas concentration in the hydrogen-containing gas may be 100% by volume. The remaining gas other than hydrogen gas in the hydrogen-containing gas is, for example, nitrogen gas (N2).

[0038] The reducing gas (hydrogen-containing gas) blown from the gas injection port 7 reduces the raw material 3 introduced from the furnace top 2. At this time, including the temperature of the reducing gas itself, the inside of the vertical furnace 2 becomes a high temperature of 1000 to 1200 °C. The reducing gas after reducing the raw material 3 is exhausted as exhaust gas from the gas discharge port 6.

[0039] A gas suction port 9 and a gas injection port 10 are provided on the furnace wall 5 of the cooling zone 8 which is the lower part of the vertical furnace 1. From the gas injection port 10, a cooling gas and a carburizing gas are blown into the inside of the vertical furnace 1. The gas suction port 9 sucks these gases so as not to invade toward the furnace top 2. The product (reduced iron) generated by the reduction of the raw material 3 is cooled by the cooling gas and carburized (carbon is added) by the carburizing gas in the cooling zone 8. Generally, N2 is used as the cooling gas. As the carburizing gas, mainly CH4 is used, and it may partly contain CO.

[0040] A reduced iron discharge port 11 is provided at the lowermost part of the vertical furnace 1. The reduced iron 4 after cooling and carburizing is discharged from the reduced iron discharge port 11.

[0041] Note that as a measure against clustering (a phenomenon in which the raw material 3 fuses to form a large lump of clusters), a cluster breaker (not shown) for mechanically breaking the generated clusters may be installed inside the vertical furnace 1.

[0042] [Lining structure of the vertical furnace] Next, based on FIG. 2, the lining structure of the vertical furnace 1 will be described. The following description also serves as an explanation of the construction method of the shaped refractory. FIG. 2 is a cross-sectional view showing a part of the furnace wall 5, and more specifically, shows a part of the furnace wall 5 when the vertical furnace 1 is viewed from the upper (furnace top 2) side. As shown in FIG. 2, the furnace wall 5 of the vertical furnace 1 has a five-layer structure. That is, the lining structure of the vertical furnace 1 is manufactured by successively constructing the amorphous refractory 13 and the shaped refractory 14 inside the iron skin 12 (the right side in FIG. 2).

[0043] As the amorphous refractory 13, a stamp material or a castable refractory is preferably used. The two differ in composition and construction method. Specifically, the stamp material has a carbon material as the main component and is tamped using a rammer, while the castable refractory has alumina cement as the main component and is hardened by drying.

[0044] As the shaped refractory 14, the shaped refractory of the present embodiment described above is used. Since the shaped refractory of the present embodiment is excellent in hydrogen gas resistance, even when a hydrogen-containing gas is used as the reducing gas when producing reduced iron 4 in the vertical furnace 1, deterioration of the shaped refractory 14 due to reaction with hydrogen gas is suppressed. Thereby, effects such as stable operation of the vertical furnace 1 and reduction of the production cost of reduced iron 4 can also be expected.

[0045] Note that the shaped refractory of the present embodiment can be used as the shaped refractory 14 of the furnace wall 5 at any part of the vertical furnace 1. However, since the reaction with hydrogen gas is most likely to occur in the vicinity of the gas injection port 7, it is particularly preferably constructed at a part including the gas injection port 7.

Example

[0046] Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples described below.

[0047] 〈Manufacture of shaped refractory〉 A shaped refractory having the component composition, free silica content, and mineral phase shown in Table 1 below (hereinafter also collectively referred to as "component composition, etc.") was manufactured. First, as the component composition and the like shown in Table 1 below, minerals (mullite, corundum, etc.) and oxide powders (silica, alumina, etc.) were blended as refractory raw materials. The particle size of the refractory raw materials was appropriately selected.

[0048] In addition, regarding the component composition in Table 1 below, if the total is not 100% by mass, it means that components not described in Table 1 below are contained.

[0049] Next, the refractory raw material and the binder were kneaded to obtain a kneaded product. Sodium silicate was used as the binder, and it was externally added to the refractory raw material, with the addition amount being 3.0% by mass.

[0050] Next, the obtained kneaded product was press-molded into a brick shape to obtain a molded body. In the press molding, a hydraulic press was used, and a pressure of 2 t / cm 2 was applied 6 times.

[0051] Thereafter, the molded body was dried to obtain a dried product. The drying temperature was 230 °C, the drying time was 18 hours, and the drying atmosphere was an air atmosphere. After drying, the dried product was fired. The firing temperature was 1400 °C, the firing time was 4 hours, and the firing atmosphere was an air atmosphere. Thereby, a shaped refractory was obtained.

[0052] 〈Evaluation of Shaped Refractory〉 The obtained shaped refractory was entirely installed on the furnace wall of the vertical furnace described with reference to FIGS. 1 to 2. Then, while introducing raw materials (iron ore pellets) from the top of the vertical furnace, a hydrogen-containing gas containing 99.8% by volume of H2 (the remaining gas: N2) was blown in from the gas injection port of the vertical furnace to start the production of reduced iron. When producing reduced iron, the temperature inside the vertical furnace was adjusted to 1000 °C. After 15 days (360 hours) had elapsed since the start of the production of reduced iron, the shaped refractory was recovered and the evaluation described below was carried out. The results are shown in Table 1 below.

[0053] 《Mass Reduction Rate》 Based on the mass (A) of the shaped refractory before construction in the vertical furnace and the mass (B) of the recovered shaped refractory, the mass reduction rate (unit: mass %) was determined according to the formula 100×(A - B) / A. The smaller the value of the mass reduction rate, the more the reaction with hydrogen gas is suppressed, and it can be evaluated that the hydrogen gas resistance is excellent.

[0054] 《Ratio (Residual Strength / Initial Strength)》 The ratio (residual strength / initial strength) of the strength (residual strength) of the recovered shaped refractory to the strength (initial strength) of the shaped refractory before construction in the vertical furnace was determined. The strength (initial strength and residual strength) is the compressive strength determined in accordance with JIS R 2206 (Test Method for Compressive Strength of Refractory Bricks). The larger the value of the ratio (residual strength / initial strength), the more the reaction with hydrogen gas is suppressed, and it can be evaluated that the hydrogen gas resistance is excellent.

[0055] 《Cost Index》 Based on the refractory raw materials used, the cost of the shaped refractory was calculated, and the cost index with Comparative Example 1 taken as "1.00" was determined. The smaller the cost index, the lower the cost.

[0056]

Table 1

[0057] 〈Summary of Evaluation Results〉 As is clear from the results in Table 1 above, it was found that the shaped refractories of Invention Examples 1 to 6 are superior in hydrogen gas resistance, with a smaller value of the mass reduction rate and a larger value of the ratio (residual strength / initial strength) than the shaped refractories of Comparative Examples 1 to 3.

Explanation of Reference Signs

[0058] 1: Vertical furnace 2: Furnace top 3: Raw material 4: Reduced iron 5: Furnace wall 6: Gas discharge port 7: Gas injection port 8: Cooling zone 9: Gas suction port 10: Gas injection port 11: Reduced iron discharge port 12: Iron sheet 13: Unshaped refractory 14: Shaped refractory

Claims

1. A shaped refractory used in a vertical furnace for producing reduced iron using a hydrogen-containing gas, The shaped refractory containing 40% by mass or more of aluminum oxide.

2. The shaped refractory according to claim 1, wherein the total content of iron oxide and titanium oxide is 5.0% by mass or less.

3. The shaped refractory according to claim 1, wherein the content of free silica is 10.0% by mass or less.

4. The shaped refractory according to claim 1, containing mullite.

5. A method for producing a shaped refractory, comprising molding a mixture containing a refractory raw material to obtain a molded article, And manufacturing the shaped refractory according to any one of claims 1 to 4 by subjecting the molded article to at least drying.

6. A method for installing a shaped refractory, comprising installing the shaped refractory according to any one of claims 1 to 4 inside the iron skin of a vertical furnace.

7. A lining structure of a vertical furnace, comprising the shaped refractory according to any one of claims 1 to 4 installed inside the iron skin of the vertical furnace.

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