Method for operating blast furnace

Abstract

Provided is a method for operating a blast furnace with which it is possible to reduce the reduction material ratio by using coke having an appropriate reactivity. Provided is a method for operating a blast furnace in which an iron-based starting material and coke are charged in layers from the top of the blast furnace and an oxygen-containing gas and a reducing material containing a hydrocarbon gas are blown into the interior of the blast furnace from the tuyere of the blast furnace, the method being characterized in that: when the oxygen concentration of the oxygen-containing gas is 80 vol% or more, the oxygen-containing gas is introduced into the blast furnace; coke having a reactivity index CRI of 35 or less is used as the coke to operate. The hydrocarbon gas is preferably a gas of hydrogen and / or a hydrogen-containing compound.

Description

Technical Field

[0001] The present invention relates to a method for operating a blast furnace capable of reducing the ratio of reduced materials during blast furnace operation. Background Art

[0002] Typically, a blast furnace is charged with iron-based raw materials and coke in layers from the top of the furnace, and hot air (high-temperature air) and reducing agents such as pulverized coal are blown in from the tuyeres below. Pig iron is produced by reducing the iron-based raw materials descending through the furnace with reducing gases rising from the bottom.

[0003] As mentioned above, blast furnace operations use reducing materials such as coke and pulverized coal to reduce the iron source within the furnace. The total weight of reducing materials required to produce one ton of pig iron is called the reducing materials ratio. Reducing the reducing materials ratio can reduce CO2 emissions from the blast furnace and pig iron production costs. Therefore, reducing the reducing materials ratio is a key issue in blast furnace operations, and extensive technological development is underway.

[0004] For example, as disclosed in Patent Documents 1 and 2, there is a technology that uses highly reactive coke to reduce the reducing material ratio. If the reactivity of the coke is high, the gasification reaction of the coke represented by C+CO2=2CO starts at a low temperature. The gasification reaction is a significant endothermic reaction, so when the gasification reaction starts at a low temperature, the temperature of the heat preservation zone in the blast furnace decreases. As a result, the reduction equilibrium point of FeO-Fe moves to the side with a low reducing gas concentration. As a result, the difference between the reducing gas concentration in the furnace and the reducing gas concentration at the reduction equilibrium point increases, thereby promoting indirect reduction, thereby reducing the amount of molten reduction (reaction formula: FeO+C=Fe+CO), and thus reducing the reducing material ratio.

[0005] Iron coke is a well-known representative of highly reactive coke. Iron coke is produced by mixing iron ore powder with coal and then dry distilling it. The iron contained in the coke acts as a catalyst for the coke's gasification reaction, thereby increasing its reactivity. Patent Documents 3 and 4, as well as Non-Patent Document 1, describe the use of iron coke as a way to reduce the ratio of reducing materials.

[0006] However, in recent years, the steel industry has been developing technologies to significantly reduce CO2 emissions in pursuit of a carbon-neutral society. Blast furnaces, which emit significant amounts of CO2, are no exception. For example, research is underway into blast furnaces using a nearly 100% oxygen-containing gas as blast gas and methane as a reducing agent, as described in Patent Document 5. This blast furnace differs from conventional blast furnaces in that it uses a high-concentration oxygen-containing gas rather than hot air and injects a large amount of methane rather than pulverized coal as a reducing agent. This significantly changes the operating conditions of conventional blast furnaces.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-206982

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2007-231326

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2011-162845

[0012] Patent Document 4: Japanese Patent Application Laid-Open No. 2012-140691

[0013] Patent Document 5: International Publication No. 2021 / 106578

[0014] Patent Document 6: Japanese Patent Application Laid-Open No. 2022-149214

[0015] Non-patent literature

[0016] Non-Patent Document 1: Tetsuya Yamamoto and seven others, "Reaction Behavior of Ferrocoke and Evaluation in Blast Furnaces," Iron and Steel, Vol. 97 (2011), No. 10, pp. 501-509

[0017] Non-patent document 2: Takeru Sato et al., Kawasaki Steel Corporation Technical Report (Kawasaki Steel Corporation Technical Report), Vol. 29, 1997, No. 1, pp. 30-36 Summary of the Invention

[0018] Problems to be solved by the invention

[0019] Blast furnace operating methods that use highly reactive coke, such as iron-based coke, to reduce the reducing material ratio are known to be effective for conventional blast furnaces that inject hot air and a reducing material primarily composed of pulverized coal through the tuyere. However, detailed research has not been conducted on blast furnaces such as those described in Patent Document 5, which inject oxygen-containing gas with a concentration of nearly 100% as the blast gas and inject a hydrocarbon-based reducing material containing a large amount of hydrogen other than pulverized coal through the tuyere. Therefore, it is unclear whether the use of highly reactive coke in such blast furnaces can achieve the same effect of reducing the reducing material ratio as conventional conventional blast furnaces. Furthermore, the reactivity of coke suitable for reducing the reducing material ratio is also unclear.

[0020] In this regard, for example, Patent Document 6 discloses that injecting a large amount of hydrogen-containing gas into a blast furnace effectively reduces the reactivity of coke by suppressing the heat absorption caused by the coke gasification reaction. However, Patent Document 6 targets a blast furnace that blows hot air with a high nitrogen concentration through the tuyere. Therefore, there is no understanding of the reactivity of coke suitable for reducing the reducing material ratio in a blast furnace that injects oxygen-containing gas with a concentration close to 100% as the blast gas and injects a hydrocarbon-based reducing material other than pulverized coal through the tuyere.

[0021] The present invention aims to solve the above-mentioned problems and to propose a blast furnace operating method that can reduce the reducing material ratio by using coke with appropriate reactivity in a so-called oxygen blast furnace in which an oxygen-containing gas with a concentration of 80% by volume or more is blown from the tuyere as the blast gas.

[0022] Methods used to solve problems

[0023] The blast furnace operating method of the present invention has been developed to solve the above-mentioned problems. It is a blast furnace operating method in which iron-based raw materials and coke are charged in layers from the top of the blast furnace, and oxygen-containing gas and reducing materials containing hydrocarbon gases are blown into the interior of the blast furnace from the tuyere of the blast furnace. The method is characterized in that, when the oxygen concentration of the above-mentioned oxygen-containing gas is 80 volume % or more, coke having a reactivity index (CRI) of 35 or less is used as the above-mentioned coke for operation.

[0024] It should be noted that, in the blast furnace operating method of the present invention constructed as described above, the following is considered to be a more preferable solution: (1) the hydrocarbon gas is hydrogen and / or a gas containing a hydrogen compound.

[0025] Effects of the Invention

[0026] According to the blast furnace operating method of the present invention, when an oxygen-containing gas having a concentration of 80 volume % or more is blown from the tuyere as blast gas, blast furnace operation with a reduced material ratio can be achieved by using coke with appropriate reactivity having a reactivity index (CRI) of 35 or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a graph showing the relationship between CRI and the reduced material ratio in the blast furnace of the present invention.

[0028] Figure 2 This is a graph showing the relationship between CRI and consumed C with respect to the amount of smelting reduction and the amount of coke gasification in the blast furnace of the present invention. DETAILED DESCRIPTION

[0029] The following describes embodiments of the present invention in detail. It should be noted that the following embodiments illustrate devices and methods for embodying the technical concept of the present invention and do not specify the following configuration. That is, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0030] First, the blast furnace operating method of this embodiment will be described. In the blast furnace operating method of this embodiment, iron-based raw materials and coke are charged in layers from the blast furnace roof, oxygen-containing gas having a concentration of 80% by volume or greater is blown as blast gas from the tuyere of the blast furnace, and reducing materials containing hydrocarbon gas are blown in from the tuyere.

[0031] The blast furnace operating method of the present invention utilizes oxygen-containing gas as the blast gas, rather than hot air. When hot air (air heated to approximately 1200°C) is used as the blast gas, the combustion gas contains approximately 50% by volume of nitrogen, which does not contribute to the combustion reaction. Therefore, the flame temperature in the whirlpool is difficult to reach a high temperature. Consequently, when a large amount of reducing material containing hydrocarbon gas is blown into the blast furnace, the temperature before the tuyere drops, causing operational problems.

[0032] On the other hand, in the blast furnace operating method of the present invention, by using an oxygen-containing gas as the blast gas, the incorporation of nitrogen that does not contribute to the combustion reaction can be suppressed, thereby allowing the temperature before the tuyere to be raised to a sufficient temperature. In other words, the flame temperature in the raceway can be raised to a higher temperature than when using hot air.

[0033] The oxygen concentration in the oxygen-containing gas is set to be 80% by volume or more. If the oxygen concentration in the oxygen-containing gas is low, it is impossible to ensure a sufficient temperature before the tuyere when a large amount of hydrocarbon gas is blown in, and operational failure may occur. Therefore, the oxygen concentration in the oxygen-containing gas needs to be 80% by volume or more, preferably 90% by volume or more, and more preferably 95% by volume or more. The oxygen concentration can be 100% by volume. It should be noted that, as the residual gas other than the oxygen in the oxygen-containing gas, for example, nitrogen, carbon dioxide, argon, water vapor, etc. can be included. Water vapor reduces the temperature before the tuyere, so the lower the concentration in the oxygen-containing gas, the better, per 1Nm 3 The concentration of water vapor in the oxygen-containing gas is preferably set to 10 g / Nm 3 Below, it is more preferably set to 5g / Nm 3 the following.

[0034] The hydrocarbon gas is preferably a gas containing hydrogen and / or a hydrogen-containing compound. For example, it can be methane, ethane, propane, ethylene, propylene, methanol, ethanol, etc. Alternatively, it can be a gas composed of a portion of these gases, such as externally supplied natural gas, city gas, coke oven gas, etc. Furthermore, it can be a regeneration gas generated using blast furnace gas. For example, it can be regenerated methane gas obtained by reacting carbon monoxide and / or carbon dioxide contained in blast furnace gas with hydrogen using the method described in Patent Document 5. By using the regeneration gas as a hydrocarbon gas, CO2 emissions can be significantly reduced.

[0035] In addition, other blowing reducing materials, such as pulverized coal, waste plastics, carbon monoxide gas and other reducing gases can also be used together with hydrocarbon gas. It should be noted that the amount of other blowing reducing materials blown into the blast furnace is preferably less than 20 weight% relative to the total amount of blowing reducing materials including hydrocarbon gas. Here, the unit "kg / t" is the amount of other blowing reducing materials blown into the blast furnace when producing 1t of molten iron. When other blowing reducing materials are used, the other blowing reducing materials can also be introduced into the hydrocarbon gas supply part. In addition, when pulverized coal and waste plastics are used as other blowing reducing materials, it is preferred to set another reducing material supply part (road) for circulating pulverized coal and waste plastics separately from the hydrocarbon gas supply part.

[0036] The inventors used the two-dimensional blast furnace numerical model shown in non-patent document 2, which takes into account reactions, heat transfer, and material flows, to investigate changes in the reducing material ratio when using cokes with different reactivities and operating the blast furnace at a constant molten iron temperature and iron output.

[0037] The reactivity of coke is studied using the Coke Reaction Index (CRI), which is also used as an actual operational management indicator. The CRI is calculated as follows. Specifically, 200g of coke, adjusted to a particle size of 20±1mm, is reacted under the conditions of a gas composition of CO2 (100 mol%), a reaction temperature of 1100°C, and a reaction time of 2 hours. The mass of the sample after the reaction is then measured, and the result is (mass before reaction - mass after reaction) / mass before reaction × 100. This is referred to as the CRI.

[0038] Methane was used as the hydrocarbon reducing material, and the study was conducted at a methane ratio of 148 kg / t.

[0039] According to the calculation results of the blast furnace numerical model, in a blast furnace where an oxygen-containing gas with a concentration of 100% by volume is blown from the tuyere as the blast gas and methane is blown from the tuyere, the lower the CRI, the lower the reducing material ratio (refer to Figure 1). Therefore, the high reactivity coke preferred in conventional blast furnaces is not conducive to reducing the ratio of reduced materials in the blast furnace of the present invention. On the contrary, the low reactivity coke is conducive to reducing the ratio of reduced materials. Figure 1 In the graph shown, the slope of the curve for a reduced material ratio of 485 kg / t or less is steeper than the slope of the curve for a reduced material ratio of 487 kg / t or more. Therefore, in the present invention, a reduced material ratio of 485 kg / t or less is targeted.

[0040] This is due to the following reasons. An oxygen-containing gas with a concentration of 100% by volume is blown from the tuyere as the blast gas, and a large amount of hydrocarbon reducing materials containing a large amount of hydrogen are blown in, thereby increasing the hydrogen concentration in the furnace. Furthermore, the concentration of reducing gas becomes relatively high due to the nitrogen-free blast air. As a result, the reduction efficiency is improved and the amount of molten reduction is reduced. Therefore, when the reactivity of coke decreases, the amount of coke gasification decreases by more than the increase in the amount of molten reduction, and the reducing material ratio decreases (refer to Figure 2 ). Both molten reduction and coke gasification are significant endothermic reactions and are the main reasons for the increase in the ratio of reducing materials.

[0041] Based on the above, in a blast furnace in which an oxygen-containing gas having a concentration of 80% by volume or more is blown as a blast gas from the tuyere and a reducing material containing hydrocarbon gas is blown into the tuyere, from the viewpoint of reducing the reducing material ratio, the reactivity of the coke should be as low as possible. Furthermore, in order to make the reducing material ratio during blast furnace operation below a prescribed amount, the CRI is required to be below a certain value.

[0042] Example

[0043] Based on the pulverized coal ratio (0 kg / t), methane ratio (148 kg / t), oxygen-containing gas unit consumption (316-318 Nm 3 / t), oxygen concentration in the oxygen-containing gas (100%), oxygen-containing gas temperature (25°C), oxygen-containing gas moisture content (0g / Nm 3 ) operating factors, so that the CRI of the coke used changes, and the blast furnace is operated. It should be noted that the above operating factors are based on Figure 1 The result is set. To obtain the iron output ratio (2.2t / day / m 3 ) and molten iron temperature (1510℃) to adjust the coke ratio (331~342kg / t).

[0044]

[0045] The following can be seen from the results of Table 1. First, in Table 1, which is the operating result of a blast furnace in which the oxygen concentration of the air supplied from the tuyere is 100% by volume and methane as a hydrocarbon gas is blown into the tuyere, attention is paid to the reducing material ratio (coke ratio + pulverized coal ratio + methane ratio). As a result, it can be seen that, among the examples in Table 1, Invention Example 1-1 (reducing material ratio 479 kg / t), Invention Example 1-2 (reducing material ratio 481 kg / t), and Invention Example 1-3 (reducing material ratio 483 kg / t) meet the target reducing material ratio of 485 kg / t or less. On the other hand, it can be seen that Comparative Example 1-1 (reducing material ratio 487 kg / t), Comparative Example 1-2 (reducing material ratio 489 kg / t), and Comparative Example 1-3 (reducing material ratio 490 kg / t) do not meet the target reducing material ratio of 485 kg / t or less. From Figure 1 As can be seen from the above results, in the present invention, the CRI needs to be 35 or less.

Claims

1. A method for operating a blast furnace, wherein an iron-based raw material and coke are charged in layers from the top of the blast furnace, and an oxygen-containing gas and a reducing material containing a hydrocarbon gas are blown into the interior of the blast furnace from the tuyere of the blast furnace, characterized in that: When the oxygen concentration of the oxygen-containing gas is 80% by volume or more, the operation is performed using coke having a reactivity index (CRI) of 35 or less as the coke.

2. The blast furnace operating method according to claim 1, characterized in that: The hydrocarbon gas is hydrogen and / or a gas containing hydrogen compounds.

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