Blast furnace operation method

Abstract

Proposed is a blast furnace operation method through which the reduction material ratio can be decreased by using coke having suitable reactivity. The blast furnace operation method includes charging an iron-based raw material and coke through the top of a blast furnace in a layered manner, and blowing an oxygen-containing gas and a reduction material containing a hydrocarbon-based gas into the blast furnace through the tuyere of the blast furnace. When the oxygen concentration of the oxygen-containing gas is 80 vol% or higher, operation is performed using coke having a chemical reactivity index CRI of 35 or lower. The hydrocarbon-based gas is preferably hydrogen and / or a compound including hydrogen.

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace that can reduce the reducing agent rate in blast furnace operation. [Background technology]

[0002] Generally, in a blast furnace, iron-based raw materials and coke are charged in layers from the top of the furnace, and hot air (high-temperature air) and reducing agents such as pulverized coal are blown in through tuyeres at the bottom of the furnace. In this way, the iron-based raw materials descending inside the furnace are reduced by the reducing gas rising from the bottom of the furnace, producing pig iron.

[0003] As mentioned above, in blast furnace operation, reducing agents such as coke and pulverized coal are used to reduce the iron source inside the furnace. The total weight of reducing agents required to produce one ton of pig iron is called the reducing agent ratio. Reducing the reducing agent ratio can reduce CO2 emissions from the blast furnace and the cost of producing pig iron, so reducing the reducing agent ratio is an important issue in blast furnace operation, and numerous technological developments have been made.

[0004] For example, as disclosed in Patent Documents 1 and 2, there is a technology for reducing the reducing agent ratio by using highly reactive coke. When the reactivity of coke is high, the coke gasification reaction, expressed as C + CO2 = 2CO, starts at a low temperature. Because the gasification reaction is a large endothermic reaction, when the gasification reaction starts at a low temperature, the thermal reserve zone temperature in the blast furnace decreases. This causes the reduction equilibrium point of FeO-Fe to shift toward the side with lower 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, promoting indirect reduction, which reduces the amount of smelting reduction (reaction formula: FeO + C = Fe + CO), and therefore reduces the reducing agent ratio.

[0005] Ferro-coke is well known as a representative example of highly reactive coke. Ferro-coke is produced by carbonizing a mixture of coal and iron ore powder, and the Fe contained in the coke acts as a catalyst for the gasification reaction of the coke, thereby increasing its reactivity. Patent Document 3, Patent Document 4, and Non-Patent Document 1 describe that the reducing agent ratio can be reduced by using ferro-coke.

[0006] In recent years, the entire steel industry has been developing technologies to significantly reduce CO2 emissions in order to realize a carbon-neutral society. Blast furnaces, which emit large amounts of CO2, are no exception. For example, as shown in Patent Document 5, a blast furnace in which an oxygen-containing gas with a concentration of nearly 100% is blown from the tuyere as a blast gas and methane is blown in as a reducing agent is being considered. This blast furnace differs from conventional general blast furnaces in that it blows a high-concentration oxygen-containing gas rather than hot air from the tuyere and blows in large amounts of methane rather than pulverized coal as a reducing agent from the tuyere, resulting in significant changes in operating conditions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-206982 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-231326 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-162845 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-140691 [Patent Document 5] International Publication No. 2021 / 106578 [Patent Document 6] Patent Publication No. 2022-149214 [Non-patent literature]

[0008] [Non-Patent Document 1] Tetsuya Yamamoto and seven others, "Reaction Behavior of Ferro-Coke and Evaluation in Blast Furnace", Iron and Steel, Vol. 97 (2011), No. 10, pp. 501-509 [Non-patent document 2] Takeru Sato et al., Kawasaki Steel Technical Report, Vol. 29, 1997, No. 1, pp. 30-36 Summary of the Invention [Problem to be solved by the invention]

[0009] A blast furnace operating method that reduces the reducing agent ratio (RAR) using a high-reactivity coke, such as ferro-coke, is known to be effective for conventional blast furnaces in which hot air and a reducing agent consisting mainly of pulverized coal are blown through the tuyere. However, no detailed studies have been conducted on blast furnaces in which an oxygen-containing gas with a concentration close to 100% is blown through the tuyere as a blast gas, and a hydrocarbon-based reducing agent other than pulverized coal that contains a large amount of hydrogen is blown through the tuyere, as shown in Patent Document 5. Therefore, it is unclear whether the use of high-reactivity coke in such a blast furnace can achieve the same reducing agent ratio reduction effect as that achieved in conventional blast furnaces, and the reactivity of coke suitable for reducing the RAR is also unclear.

[0010] In this regard, for example, Patent Document 6 discloses that when a large amount of hydrogen-containing gas containing hydrogen gas is injected into a blast furnace, it is effective to reduce the reactivity of the coke in order to suppress the endothermic heat caused by the gasification reaction of the coke. However, Patent Document 6 targets a blast furnace that blows hot air with a high nitrogen gas concentration from the tuyeres. Therefore, there has been no knowledge about the reactivity of coke suitable for reducing the reducing agent rate for a blast furnace that blows an oxygen-containing gas with a concentration of nearly 100% as the blast gas from the tuyeres and blows a hydrocarbon-based reducing agent other than pulverized coal that contains a lot of hydrogen from the tuyeres.

[0011] The object of the present invention is to solve the above problems and to propose a method of operating a blast furnace in which an oxygen-containing gas having an oxygen concentration of 80 vol% or more is blown from the tuyere as a blast gas, thereby enabling a reduction in the reducing agent rate by using coke with appropriate reactivity. [Means for solving the problem]

[0012] The blast furnace operation method of the present invention was developed to solve the above-mentioned problems, and is a method of operating a blast furnace in which iron-based raw materials and coke are charged in layers from the top of the blast furnace, and an oxygen-containing gas and a reducing agent containing a hydrocarbon gas are injected into the blast furnace from the tuyere of the blast furnace, characterized in that when the oxygen concentration of the oxygen-containing gas is 80 vol% or more, operation is performed using coke having a reactivity index CRI of 35 or less as the coke.

[0013] In the method for operating a blast furnace according to the present invention configured as described above, (1) The hydrocarbon gas is a gas of hydrogen and / or a compound containing hydrogen; This is considered to be a more preferable solution. [Effects of the Invention]

[0014] According to the blast furnace operation method of the present invention, when an oxygen-containing gas having a concentration of 80 vol% or more is blown from the tuyere as a blast gas, by using a coke with an appropriate reactivity having a reactivity index CRI of 35 or less, it is possible to realize blast furnace operation that reduces the reducing agent ratio. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a graph showing the relationship between CRI and reducing agent rate in a blast furnace according to the present invention. [Figure 2] 1 is a graph showing the relationship between CRI and consumed C for the amount of smelting reduction and the amount of coke gasification in a blast furnace according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following describes in detail the embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to that described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0017] First, a method for operating a blast furnace according to this embodiment will be described. In the method for operating a blast furnace according to this embodiment, iron-based raw materials and coke are charged in layers from the top of the blast furnace, an oxygen-containing gas with a concentration of 80 vol% or more is blown as a blast gas from the tuyere of the blast furnace, and a reducing agent containing a hydrocarbon gas is blown from the tuyere.

[0018] Here, the blast furnace operating method of the present invention uses an oxygen-containing gas as the blast gas instead of hot air. When hot air (air heated to about 1200°C) is used as the blast gas, the combustion gas contains about 50 vol% nitrogen, which does not contribute to the combustion reaction, so the flame temperature in the raceway is unlikely to reach a high temperature. Therefore, if a reducing agent containing a large amount of hydrocarbon gas is injected into the blast furnace, the tuyere temperature drops, causing operational problems.

[0019] On the other hand, in the blast furnace operation method of the present invention, by using an oxygen-containing gas as the blast gas, it is possible to suppress the inclusion of nitrogen gas that does not contribute to the combustion reaction, and therefore it is possible to raise the temperature at the tuyere tip to a sufficient temperature. In other words, the temperature of the flame in the raceway can be made higher than when hot air is used.

[0020] The oxygen concentration in the oxygen-containing gas is set to 80 vol% or more. If the oxygen concentration in the oxygen-containing gas is low, a sufficient tuyere temperature cannot be ensured when a large amount of hydrocarbon gas is blown in, which may cause operational problems. Therefore, the oxygen concentration in the oxygen-containing gas needs to be 80 vol% or more, preferably 90 vol% or more, and more preferably 95 vol% or more. The oxygen concentration may be 100 vol%. Note that the remaining gas other than oxygen in the oxygen-containing gas may contain, for example, nitrogen, carbon dioxide, argon, water vapor, etc. Water vapor lowers the tuyere temperature, so the concentration in the oxygen-containing gas should be low, and it is preferable that the oxygen concentration in the oxygen-containing gas is 80 vol% or more, and .... 3 The concentration of water vapor per unit area is preferably 10 g / Nm 3 Less than 5g / Nm 3 It is preferable to have the following:

[0021] The hydrocarbon gas is preferably a gas containing hydrogen and / or a compound containing hydrogen. Examples include methane, ethane, propane, ethylene, propylene, methanol, and ethanol. Gases containing at least a portion of these gases, such as externally supplied natural gas, city gas, and coke oven gas, may also be used. Furthermore, the hydrocarbon gas may be a regenerated gas produced using blast furnace gas. For example, the regenerated methane gas may be obtained by reacting carbon monoxide and / or carbon dioxide contained in blast furnace gas with hydrogen, as described in Patent Document 5. By using the regenerated gas as a hydrocarbon gas, CO2 emissions can be significantly reduced.

[0022] Other reducing agents, such as pulverized coal, waste plastics, or reducing gases such as carbon monoxide gas, may also be used together with the hydrocarbon gas. The amount of the other reducing agents injected into the blast furnace is preferably 20 wt% or less of the total amount of reducing agents, including the hydrocarbon gas. Here, the unit "kg / t" refers to the amount of the other reducing agents injected into the blast furnace when producing 1 ton of molten pig iron. When using other reducing agents, the other reducing agents may also be introduced into the hydrocarbon gas supply section. When pulverized coal or waste plastics are used as the other reducing agents, it is preferable to provide a separate reducing agent supply section (path) for circulating the pulverized coal or waste plastics, separate from the hydrocarbon gas supply section.

[0023] The inventors used a two-dimensional blast furnace numerical model shown in Non-Patent Document 2, which takes into account reactions, heat transfer, and material flow, to investigate changes in the reducing agent ratio when a blast furnace was operated using cokes with different reactivities so that the molten iron temperature and iron production rate were constant.

[0024] The coke reactivity was measured using the Coke Reaction Index (CRI), which is also used as an operational management index. The CRI was calculated as follows: 200 g of coke adjusted to a particle size of 20 ± 1 mm was reacted under the following conditions: gas composition: CO2 (100 mol%), reaction temperature: 1100°C, reaction time: 2 hours. The mass of the sample after the reaction was then measured, and the formula (mass before reaction - mass after reaction) / mass before reaction x 100 was calculated. This was taken as the CRI.

[0025] Methane was used as the hydrocarbon reducing agent, and a methane ratio of 148 kg / t was used for the study.

[0026] According to the calculation results of the blast furnace numerical model, in a blast furnace in which 100 vol% oxygen-containing gas is blown from the tuyere as a blast gas and methane is blown in, the lower the CRI, the lower the reducing agent ratio (see Figure 1). Therefore, high-reactivity coke, which has been considered preferable in conventional blast furnaces, is disadvantageous for reducing agent ratio reduction in the blast furnace of the present invention. Conversely, low-reactivity coke is advantageous for reducing agent ratio reduction. In the graph shown in Figure 1, the slope of the graph for reducing agent ratios of 485 kg / t or less is steeper than the slope of the graph for reducing agent ratios of 487 kg / t or more. Therefore, in the present invention, a reducing agent ratio of 485 kg / t or less is targeted.

[0027] This is due to the following reasons: The hydrogen concentration in the furnace increases when 100 vol% oxygen-containing gas is blown from the tuyere as the blast gas and a large amount of hydrocarbon reducing agent containing a lot of hydrogen is blown in. Furthermore, the nitrogen-free blast air makes the reducing gas concentration relatively high. This improves reduction efficiency and reduces the amount of smelting reduction. If the reactivity of the coke decreases, the amount of coke gasification decreases more than the increase in the amount of smelting reduction, and the reducing agent ratio decreases (see Figure 2). Both smelting reduction and coke gasification are large endothermic reactions and are factors that increase the reducing agent ratio.

[0028] From the above, in a blast furnace in which an oxygen-containing gas with a concentration of 80 vol% or more is blown from the tuyere as the blast gas and a reducing agent containing a hydrocarbon gas is blown from the tuyere, the reactivity of the coke is preferably as low as possible from the viewpoint of reducing the reducing agent rate, and furthermore, in order to keep the reducing agent rate in blast furnace operation below a specified amount, the CRI is required to be below a certain level. [Example]

[0029] As shown in Table 1 below, the pulverized coal ratio (0 kg / t), methane ratio (148 kg / t), and oxygen-containing gas consumption rate (316-318 Nm 3 / t), oxygen concentration in oxygen-containing gas (100%), oxygen-containing gas temperature (25°C), oxygen-containing gas moisture (0g / Nm 3The blast furnace was operated under the operating parameters of 2.2t / day / m2, varying the CRI of the coke used. The operating parameters were set based on the results shown in Figure 1. 3 The coke rate was adjusted (331-342 kg / t) to obtain a high molten iron temperature (1510°C).

[0030] [Table 1]

[0031] The results in Table 1 reveal the following. First, we focused on the reducing agent ratio (coke rate + pulverized coal rate + methane rate) in Table 1, which shows the operation results of a blast furnace in which the oxygen concentration of the blast air from the tuyere was 100 vol% and methane, a hydrocarbon gas, was injected from the tuyere. As a result, it was found that, among the examples in Table 1, Invention Example 1-1 (reducing agent ratio 479 kg / t), Invention Example 1-2 (reducing agent ratio 481 kg / t), and Invention Example 1-3 (reducing agent ratio 483 kg / t) satisfied the target reducing agent ratio of 485 kg / t or less. On the other hand, it was found that Comparative Example 1-1 (reducing agent ratio 487 kg / t), Comparative Example 1-2 (reducing agent ratio 489 kg / t), and Comparative Example 1-3 (reducing agent ratio 490 kg / t) did not satisfy the target reducing agent ratio of 485 kg / t or less. From FIG. 1 and the above results, it was found that, in the present invention, the CRI must be 35 or less.

Claims

1. A method for operating a blast furnace, comprising charging iron-based raw materials and coke in layers from the top of the blast furnace, and injecting an oxygen-containing gas having an oxygen concentration of 80 vol% or more and a reducing agent containing a hydrocarbon-based gas into the interior of the blast furnace through the tuyeres of the blast furnace, characterized in that the blast furnace is operated using coke having a reactivity index (CRI) of 35 or less as the coke.

2. 2. The method for operating a blast furnace according to claim 1, wherein the hydrocarbon gas is a gas of hydrogen and / or a compound containing hydrogen.

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