Blast furnace operation method

Abstract

Provided is a blast furnace operating method capable of reducing CO2 emissions.　In the blast furnace operating method, agglomerated ore is charged from the top of the blast furnace and a gas reducing material is supplied from a lower portion of the blast furnace so as to produce molten iron. The phase fraction of the calcium ferrite phase or secondary hematite phase in the agglomerate ore is set within a predetermined range while the supply amount of the gas reducing agent is set to 100 Nm3 / t or more.

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace in which agglomerated ore as an iron raw material is charged from the top of the blast furnace and a gas reducing agent is supplied from the lower part of the blast furnace to produce molten iron. [Background technology]

[0002] The blast furnace method (a method of producing molten iron using a blast furnace) is a highly efficient steelmaking process suitable for mass production, accounting for more than 70% of crude steel production in Japan. However, the blast furnace method consumes large amounts of coal as a solid reducing agent for melting and reducing the iron oxide in iron ore, which means it is also a process that emits a lot of CO2. Given the current social climate regarding environmental issues, reducing CO2 emissions from the blast furnace method is an urgent issue for the steel industry.

[0003] There are several ways to reduce CO2 emissions in the blast furnace process, one of which is to use hydrogen as a gas reducing agent.Methods that have been proposed for utilizing hydrogen include simply injecting hydrogen into the tuyere together with the blast air, injecting hydrogen into the tuyere as a specific compound (for example, a hydrocarbon such as methane), or injecting a hydrogen-based reducing gas from a location other than the tuyere.

[0004] Here, one of the main reasons why CO2 emissions from a blast furnace can be reduced by injecting a gas reducing agent such as hydrogen into the furnace is that the gas reduction rate of iron oxide in the agglomerated ore increases.

[0005] Agglomerates charged into a blast furnace are reduced in two main ways. The first is gas reduction using gaseous reducing agents such as CO or hydrogen. The second is smelting reduction using carbon (C) in coke, a solid reducing agent. In the blast furnace method, gas reduction progresses as the raw materials (agglomerates and solid reducing agents) descend from the top to the bottom of the blast furnace. After that, the agglomerates that were not reduced by gas reduction melt and are melted and reduced by the solid reducing agent, completing the reduction reaction.

[0006] The difference between gas reduction and smelting reduction lies in the amount of heat generated by the reduction reaction. Gas reduction is a reduction reaction that generates a small amount of heat (or endotherm). In contrast, smelting reduction is a reduction reaction that generates a large amount of heat (endotherm). Increasing the proportion of gas reduction using a gas reducing agent (such as hydrogen gas) can reduce the proportion of smelting reduction using a solid reducing agent. This makes it possible to reduce the amount of heat required per ton of molten iron in a blast furnace, reducing the amount of solid reducing agent (carbon) used and lowering CO2 emissions.

[0007] As mentioned above, in the blast furnace process in which a gaseous reducing agent (such as hydrogen gas) is injected, improving the rate of gaseous reduction of agglomerated ore is essential to reducing the amount of solid reducing agent (carbon). However, it is known that even when gaseous reduction of agglomerated ore (pellets or sintered ore) using a gaseous reducing agent is carried out at a temperature (e.g., 900°C) at which the agglomerated ore does not begin to melt, the reduction reaction based on the gaseous reduction stagnates when the reduction reaction reaches a predetermined state (reduction rate of 70%). Specifically, the presence of a structure within the agglomerated ore that inhibits gaseous reduction causes the gaseous reduction reaction to stagnate due to the influence of this structure. Furthermore, the stagnation of the reduction reaction refers to a sudden decrease in the rate of change of the reduction rate per hour (reduction rate).

[0008] For this reason, methods have been proposed for improving the rate of gas reduction in agglomerates by adjusting the properties of the agglomerates. Patent Document 1 discloses a method for suppressing stagnation of the reduction reaction at high temperatures by adding dolomite or limestone to pellets to increase the melting point of the pellets. Patent Document 2 discloses a method for producing high-quality, low-SiO2, highly reducible sintered ore by adjusting the blending ratio of CaO-containing auxiliary raw material powder to suppress the formation of granular hematite and form a structure mainly composed of acicular calcium ferrite. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 3-77853 [Patent Document 2] Special Publication No. 5-59972 [Patent Document 3] Patent No. 5790468 [Patent Document 4] Japanese Patent Publication No. 2021-165429 [Non-patent literature]

[0010] [Non-Patent Document 1] Iron and Steel, Vol.79(1993)9, N618 [Non-patent document 2] Iron and Steel, Vol.79(1993)10, N711 [Non-patent document 3] Iron and Steel, Vol.73(1987)15, p.1956 [Non-patent document 4] Iron and Steel, Vol.69(1983)3, p.363 Summary of the Invention [Problem to be solved by the invention]

[0011] However, the method disclosed in Patent Document 1 is suitable for suppressing stagnation of the reduction reaction when the agglomerates are in a high-temperature state, but is difficult to apply to stagnation of the reduction reaction at temperatures where the agglomerates do not start to melt. Furthermore, while the method disclosed in Patent Document 2 can produce sintered ore with excellent reduction properties, it does not disclose any temperature-related stagnation of the reduction reaction, making it difficult to apply to stagnation of the reduction reaction at temperatures where the agglomerates do not start to melt. Furthermore, in Patent Document 2, the reduction rate in the examples is at most 72.3%, which is similar to the reduction rate (70%) at which stagnation of the reduction reaction based on gas reduction is observed. This also means that the aforementioned stagnation of the reduction reaction based on gas reduction is not considered.

[0012] The present invention has been made in view of the above circumstances, and has an object to provide a blast furnace operation method that can reduce CO2 emissions. [Means for solving the problem]

[0013] The gist and configuration of the present invention to solve the above problems are as follows. [1] A blast furnace operating method in which agglomerated ore is charged from the top of the blast furnace and a gas reducing agent is supplied from the lower part of the blast furnace to produce molten iron, wherein the supply amount of the gas reducing agent is 100 Nm 3 / t or more, and the phase fraction of calcium ferrite phase or secondary hematite phase in the agglomerate ore is within a predetermined range. [2] The method for operating a blast furnace according to [1], wherein the agglomerate ore has a calcium ferrite phase fraction of 40% by volume or more. [3] The method for operating a blast furnace according to [1], wherein the agglomerate ore has a secondary hematite phase fraction of 20% by volume or more. [Effects of the Invention]

[0014] According to the present invention, CO2 emissions can be reduced. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the charging state of a gas reducing agent and a solid reducing agent in blast furnace operation. [Figure 2] FIG. 2 is a diagram showing the relationship between the amount of gas reducing agent and the optimum gas reduction rate. [Figure 3] FIG. 3 is a diagram showing the relationship between the phase fraction of calcium ferrite in the agglomerates and the stagnant gas reduction rate. [Figure 4] FIG. 4 is a diagram showing the relationship between the phase fraction of the secondary hematite phase in the agglomerates and the stagnant gas reduction rate. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the present invention will be described through embodiments of the present invention.

[0017] As shown in FIG. 1 , the present invention relates to a blast furnace operation method in which a reduction reaction of agglomerated ore and lump ore (hereinafter referred to as "agglomerated ore"), which are iron raw materials, is carried out using a solid reducing agent (coke, pulverized coal) charged from the top and tuyere of the blast furnace and a gas reducing agent charged from the lower part of the furnace, thereby obtaining molten iron from a taphole.

[0018] The present inventors first focused on the relationship between the amount of gas reducing agent (hereinafter referred to as "gas reducing agent amount") injected into the blast furnace and the gas reduction rate. In particular, they focused on the relationship between the amount of gas reducing agent and the gas reduction rate when the total amount of the solid reducing agent (hereinafter referred to as "solid reducing agent amount") and the gas reducing agent amount is minimized (hereinafter referred to as "optimum gas reduction rate"). Then, the amount of gas reducing agent Nm 3 The optimum gas reduction rate % for molten iron / t was calculated based on a heat and mass balance calculation for a blast furnace, taking into consideration the reduction equilibrium of wüstite with carbon monoxide (CO) and hydrogen gas (see Non-Patent Documents 1 and 2). Here, the optimum gas reduction rate refers to a value calculated each time based on the amount of each reducing agent (amount of solid reducing agent and amount of gas reducing agent) used, as a value for minimizing the total amount of reducing agent (total amount of solid reducing agent and amount of gas reducing agent) from the viewpoint of the function of heat supply and reducing agents in the furnace.

[0019] Here, the gas reduction rate refers to the rate at which gas reduction occurs among all reduction reactions (gas reduction and smelting reduction) of the agglomerate ore charged into the blast furnace. The gas reducing agent may include not only gases that function as gas reducing agents themselves, such as hydrogen and carbon monoxide (CO), but also gases that function as gas reducing agents via oxidation reactions or thermal decomposition reactions in the blast furnace, such as methane and ammonia.

[0020] The amount of gas reducing agent is, for example, 1 Nm 3 When methane is blown into the blast furnace, it reacts with the oxygen in the blast, resulting in a reaction of 1Nm 3 of carbon monoxide and 2Nm 3 In this case, the total amount of gas reducing material is 3 Nm 3 The amount of 1Nm 3When methane is injected into a blast furnace, the amount of gas reducing agent is 3 Nm 3 and count it.

[0021] Also, for example, 1 Nm 3 When ammonia is injected into the blast furnace, the ammonia 3 of hydrogen and 0.5Nm 3 Nitrogen does not function as a reducing agent, so it is 3 The amount of gas reducing agent when injecting ammonia into a blast furnace is 1.5 Nm 3 and count it.

[0022] Similarly, when the gaseous reducing agent contains impurities such as nitrogen, the amount of the gaseous reducing agent is counted based on the amount of the gaseous reducing agent generated in the blast furnace. Therefore, the gaseous reducing agent may be a mixture of multiple types of gases.

[0023] The temperature of the gas reducing agent is preferably 1300°C or less, which is the hot air temperature in a blast furnace. In order to increase the optimum gas reduction rate above the state where the reduction reaction by gas reduction stagnates (reduction rate of 70%), the temperature is more preferably 500°C or less, and even more preferably 100°C or less.

[0024] Furthermore, the concentration of the gaseous reducing agent that actually contributes to gaseous reduction among the gaseous reducing agents injected into the blast furnace is preferably 90% by volume or more, and more preferably 95% by volume or more.

[0025] The optimum gas reduction rate for the amount of gas reducing material was calculated using the following conditions: thermal reserve zone temperature 1000°C, blast temperature 1100°C, blast moisture 20g / Nm 3 In a blast furnace with a heat loss of 100 Mcal / t, the gas reduction ratio was calculated to minimize the amount of solid reducing agent when gas reducing agent (assuming 100% by volume of room temperature hydrogen) was injected. In this case, the maximum shaft efficiency was set to 0.95 [-: dimensionless number].

[0026] Figure 2 shows the gas reducing agent amount Nm 3As shown in Figure 2, the relationship between the gas reducing agent and the optimum gas reduction rate is shown. 3 It can be seen that the optimum gas reduction rate exceeds 75% when the gas reducing agent amount exceeds 100 Nm 3 When the gas reduction rate exceeds 800 Nm / t, it can be confirmed that the optimum gas reduction rate exceeds the state where the reduction reaction due to the gas reduction of the agglomerate ore stagnates (70% reduction rate). A similar phenomenon can also be confirmed when a gas reducing agent is injected into a blast furnace that can supply room temperature oxygen gas from the tuyere (for example, blast temperature 25°C, oxygen concentration 100%, heat loss 100 Mcal / t). Furthermore, although the amount of CO2 reduction in blast furnace operation increases with an increase in the amount of gas reducing agent, taking into account the point at which no change in CO2 reduction is observed, the amount of gas reducing agent is set to 800 Nm / t. 3 / t or less, and 600 Nm 3 It is more preferable that the ratio is 1 / t or less.

[0027] Next, the present inventors prepared various agglomerates and closely observed the changes in the reduction reaction of the prepared agglomerates during gas reduction, thereby clarifying the state of the texture in the agglomerates that causes the stagnation of the reduction reaction, and also investigated a method for adjusting the agglomerates that can suppress the stagnation of the reduction reaction.

[0028] Specifically, agglomerates with an adjusted calcium ferrite phase fraction were prepared, and gas reduction was performed using a gas reducing agent with a fixed composition at a fixed temperature, and the change in mass during gas reduction was measured. Here, the calcium ferrite phase may be a structure formed by dissolving gangue components such as silica and alumina.

[0029] The phase fraction of calcium ferrite in the agglomerates was measured by carrying out XRD-Rietveld analysis on a powdered sintered ore sample, and calculating the phase fraction of the structure (see Patent Document 3).

[0030] Here, the phase fraction of the calcium ferrite phase in the agglomerates may be calculated by observing the structure in the agglomerates with an optical microscope or an electron microscope and using a point counting method based on the brightness and morphology of the structure determined by the observation.

[0031] Specifically, the calculation of the calcium ferrite phase fraction based on the structural morphology may be performed by first identifying the calcium ferrite phase based on the structural morphology characteristics from an image of the structure in the agglomerate, and then applying a point counting method to the identified calcium ferrite phase to calculate the structural phase fraction.

[0032] The calculation of the calcium ferrite phase fraction based on the brightness of the texture may be performed by first identifying the calcium ferrite phase based on a preset brightness threshold for each texture from a histogram of the brightness values ​​of each pixel in the image of the texture in the agglomerate, and then applying a point counting method to the identified calcium ferrite phase to calculate the phase fraction of the texture.

[0033] The phase fraction of the calcium ferrite phase may be calculated by using an image of the structure in the agglomerate as learning data (teacher image), generating a learning model using the learning data (teacher image), and applying the learning model to a new structure image to calculate the phase fraction of the structure (see Patent Document 4).

[0034] In addition, agglomerates with an adjusted secondary hematite phase fraction in the hematite structure were prepared, and gas reduction was carried out using a gas reducing agent of a fixed composition at a fixed temperature, and the change in mass during gas reduction was detected.

[0035] The phase fraction of the secondary hematite phase in the agglomerates was calculated by observing the texture of the agglomerates with an optical microscope or an electron microscope, separating the secondary hematite phase from other hematite phases based on the brightness and skeletal morphology of the texture ascertained by the observation, and using the point counting method.

[0036] The agglomerates were produced by mixing the raw materials, granulating them, and firing them in a pot test. The calcium ferrite phase fraction or secondary hematite phase fraction in the agglomerates was adjusted by changing the heat pattern during sintering.

[0037] The gas reduction conditions using the gas reducing agent were as follows: reduction temperature: 900°C, gas reducing agent flow rate: 10 L / min, agglomerate mass: 100 g, agglomerate particle size: 10-15 mm, and gas reduction time: 2 hours. The composition of the gas reducing agent was 95% by volume of carbon monoxide (CO) and 5% by volume of carbon dioxide (CO2).

[0038] Based on the time-series changes in the mass of the agglomerates detected during the experiment, the time-series changes in the gas reduction rate R during the experiment were calculated. Specifically, the gas reduction rate R was calculated based on "JIS M 8713:2021 Iron ore - Measurement method for reducibility," by expressing the proportion of oxygen removed from iron oxide (agglomerates) as a mass fraction % and converting the change in mass into the reduction rate R using the following formula (1):

[0039]

number

[0040] Based on the reduction curves obtained in gas reduction experiments, it was revealed that the higher the phase fraction of calcium ferrite in the agglomerated ore, the less likely the reduction reaction stagnation during gas reduction occurs, and the higher the final reduction rate after gas reduction. Here, the reduction curve refers to a curve on a graph showing the time-series change in the gas reduction rate R, with the horizontal axis representing time and the vertical axis representing the gas reduction rate R.

[0041] Observation of agglomerates during gas reduction experiments revealed that the cause of stagnation in the reduction reaction during gas reduction in agglomerates is the formation of iron oxide surrounded by a metallic iron shell within the agglomerate structure. It is believed that the iron oxide surrounded by the metallic iron shell prevents contact with the gas reducing agent, slowing down the reduction reaction rate, which is determined by the diffusion rate of oxygen ions within the agglomerates.

[0042] Furthermore, observations of the agglomerates before and after gas reduction confirmed that iron oxide surrounded by a metallic iron shell was not generated from the calcium ferrite phase. This is consistent with the experimental results showing that the higher the calcium ferrite phase fraction in agglomerates, the less likely the reduction reaction to stagnate.

[0043] Next, the reduction curve obtained in the gas reduction experiment was analyzed using a reduction model that does not consider stagnation of the reduction reaction (unreacted nucleus model: see Non-Patent Document 3), to calculate the gas reduction rate at which the reduction reaction begins to stagnate (hereinafter referred to as the "stagnation gas reduction rate"). That is, fitting of the reduction model was performed using the reduction curve obtained from the experiment, and it was considered that the reduction began to stagnate at the reduction rate at which the reduction curve and the value of the reduction model began to diverge.

[0044] Figure 3 shows the relationship between the calcium ferrite phase fraction in the agglomerates and the stagnant gas reduction rate. As shown in Figure 3, the calcium ferrite phase fraction in the agglomerates and the stagnant gas reduction rate are directly proportional to each other. In other words, it can be confirmed that the higher the calcium ferrite phase fraction in the agglomerates, the higher the stagnant gas reduction rate.

[0045] Specifically, when the stagnant gas reduction rate is adjusted to exceed 70%, the calcium ferrite phase fraction in the agglomerates is preferably 40% by volume or more. Furthermore, when the stagnant gas reduction rate is adjusted to exceed 79%, the calcium ferrite phase fraction in the agglomerates is more preferably 47% by volume or more. Although an increase in the calcium ferrite phase fraction increases the amount of CO2 reduction in blast furnace operation, taking into account the point at which no change in CO2 reduction is observed, the calcium ferrite phase fraction is preferably 65% ​​or less.

[0046] Based on the experimental results shown in Fig. 3, the phase fraction of calcium ferrite in the agglomerates charged into the blast furnace may be adjusted to increase the stagnation gas reduction rate of gas reduction in the blast furnace. That is, in a blast furnace operation method in which agglomerates are charged from the top of the blast furnace and a gas reducing agent is supplied from the lower part of the blast furnace to produce molten pig iron, the supply rate of the gas reducing agent is adjusted to 100 Nm 3 / t or more, and the phase fraction of calcium ferrite in the agglomerates may be adjusted to 40% by volume or more.

[0047] Furthermore, based on the reduction curves obtained in gas reduction experiments, it was revealed that the higher the phase fraction of the secondary hematite phase in the agglomerated ore, the less likely the reduction reaction to stagnate during gas reduction, and the higher the final reduction rate after gas reduction.

[0048] Specifically, observations of the agglomerates before and after gas reduction confirmed that iron oxide surrounded by a metallic iron shell was not generated from the secondary hematite phase. This is consistent with experimental results showing that the higher the fraction of the secondary hematite phase in agglomerates, the less likely the reduction reaction to stagnate.

[0049] The phase fraction of the secondary hematite phase was also analyzed using a reduction model (unreacted nucleus model: see Non-Patent Document 3) that does not consider stagnation of the reduction reaction for the reduction curve obtained in the gas reduction experiment, and the gas reduction rate at which the reduction reaction begins to stagnate (hereinafter referred to as the "stagnation gas reduction rate") was calculated. That is, the reduction model was fitted using the reduction curve obtained from the experiment, and the reduction was deemed to have begun to stagnate at the reduction rate at which the reduction curve and the reduction model value began to diverge.

[0050] Figure 4 shows the relationship between the phase fraction of the secondary hematite phase in the agglomerates and the stagnant gas reduction rate. As shown in Figure 4, the phase fraction of the secondary hematite phase in the agglomerates and the stagnant gas reduction rate are directly proportional to each other. In other words, it can be confirmed that the higher the phase fraction of the secondary hematite phase in the agglomerates, the higher the value of the stagnant gas reduction rate.

[0051] Specifically, when the stagnant gas reduction rate is adjusted to exceed 70%, the secondary hematite phase fraction in the agglomerates is preferably 20% by volume or more. Furthermore, when the stagnant gas reduction rate is adjusted to exceed 80%, the secondary hematite phase fraction in the agglomerates is more preferably 30% by volume or more. Furthermore, although an increase in the secondary hematite phase fraction increases the amount of CO2 reduction in blast furnace operation, taking into account the point at which no change in CO2 reduction is observed, the secondary hematite phase fraction is preferably 55% or less.

[0052] Based on the experimental results shown in Fig. 4, the phase fraction of the secondary hematite phase in the agglomerates charged into the blast furnace may be adjusted to increase the stagnation gas reduction rate of the gas reduction in the blast furnace. That is, in a blast furnace operation method in which agglomerates are charged from the top of the blast furnace and a gas reducing agent is supplied from the lower part of the blast furnace to produce molten pig iron, the supply rate of the gas reducing agent is adjusted to 100 Nm 3 / t or more, and the phase fraction of the secondary hematite phase in the agglomerates may be adjusted to 20% by volume or more.

[0053] Although the gas reduction experiment of the agglomerates described in this embodiment was performed under the above conditions, it is not necessary to limit the experiment to these conditions. That is, other reduction test methods (e.g., "JIS M 8713:2021 Iron Ore - Measurement Method of Reducibility") may be used. Then, the relationship between the calcium ferrite phase fraction or secondary hematite phase fraction in the agglomerates and the stagnant gas reduction rate may be calculated to find the calcium ferrite phase fraction or secondary hematite phase fraction that can suppress stagnation of the gas reduction reaction.

[0054] As described above, according to the blast furnace operation method of this embodiment, the stagnant gas reduction rate at which the reduction reaction begins to stagnate can be increased by adjusting the phase fraction of the calcium ferrite phase or the secondary hematite phase in the agglomerates within a predetermined range. In addition, in a blast furnace process using a gaseous reducing agent, the usage rate of the gaseous reduction of the agglomerates is increased and the usage rate of the solid reducing agent is reduced, thereby reducing CO2 emissions. [Example]

[0055] Hereinafter, examples carried out based on the blast furnace operation method according to this embodiment will be described.

[0056] In the examples, we first confirmed the change in coke ratio when a room-temperature gas reducing agent (hydrogen gas) was injected from the bottom of the furnace using a virtual physical blast furnace implemented in cyberspace. Here, the coke ratio refers to the amount of coke charged from the top of the blast furnace to produce 1 ton of molten pig iron. We also confirmed the change in coke ratio when agglomerated ores with different calcium ferrite phase fractions were used for the gas reducing agent with different injection rates into the blast furnace.

[0057] The reduction reaction of the agglomerates was modeled assuming that the calcium ferrite phase fraction in the agglomerates only affects the stagnation of the gas reduction reaction. Regarding the reduction behavior after the stagnation of the gas reduction reaction, Non-Patent Document 4 was referred to, and calculation parameters were determined to be consistent with the experimental results, assuming that the reduction rate of the agglomerates is determined by the diffusion rate of oxygen ions in the metallic iron covering them.

[0058] The standard operation that serves as the basis for the CO2 reduction rate is Standard Operation 1, with the blast temperature set to 1100°C, the oxygen concentration set to 21% by volume, and the blast moisture content set to 20g / Nm 3 The operation conditions were a heat loss of 100 Mcal / t and a coke rate of 487 kg / t. Reference operation 2 was performed under the same conditions as reference operation 1, except that the gas reducing agent amount (0 Nm 3 / t), the gas reducing agent was 200Nm 3 / t. Reference operation 3 was carried out with the gas reducing agent amount (0 Nm 3 / t), the gas reducing agent was 400Nm 3 / t. The phase fraction of calcium ferrite in the agglomerates in each standard operation was 35.1% by volume. The proportion of agglomerates in the main raw materials was 70% by mass. The results of the examples are shown in Table 1. The proportion of agglomerates in the main raw materials is preferably 60% by mass or more, and more preferably 70% by mass or more. This is because having the proportion of agglomerates in the main raw materials be 60% by mass or more can contribute to improving the CO2 reduction rate.

[0059] [Table 1]

[0060] In Table 1, except for standard operations 1 to 3, the "CO2 reduction rate" was evaluated as "good (○)" when the result was 1% or more. The CO2 reduction rate was calculated based on the value of "0" for standard operation 1.

[0061] As shown in Table 1, in Comparative Example 1, the amount of gas reducing agent was 0 Nm 3 / t, and the optimum gas reduction rate is lower than the stagnant gas reduction rate. Therefore, although the stagnant gas reduction rate improved compared to standard operation 1, the CO2 reduction rate was 0%.

[0062] In contrast, in Example 1, the amount of gas reducing agent was 400 Nm 3 By increasing the optimum gas reduction rate to 1 / t, the calcium ferrite phase fraction in the agglomerates was increased to 40% by volume or more, and the stagnation gas reduction rate of the agglomerates was increased to over 70%, thereby improving the CO2 reduction rate.

[0063] In Examples 2 and 3, the amount of gas reducing agent was 200 Nm 3 By increasing the optimum gas reduction rate to 1 / t, the calcium ferrite phase fraction in the agglomerates was increased to 47% by volume or more, and the stagnation gas reduction rate of the agglomerates was increased to over 79%, thereby improving the CO2 reduction rate.

[0064] Furthermore, in Examples 4 and 5, the calcium ferrite phase fraction in the agglomerates was set to 47 mass% or more, and the amount of gas reducing agent was set to 400 Nm 3 / t, the stagnation gas reduction rate of the gas reduction in the agglomerated ore could be increased to more than 79%. In addition, the amount of gas reducing agent could be increased compared to Invention Examples 2 and 3, so the CO2 reduction rate could be further increased.

[0065] Next, using a virtual physical blast furnace implemented in cyberspace, we confirmed the change in coke ratio when room temperature gas reducing agent (hydrogen gas) was injected from the bottom of the furnace. At the same time, we also confirmed the change in coke ratio when using agglomerated ore with different secondary hematite phase fractions for gas reducing agent with different injection rates into the blast furnace.

[0066] The reduction reaction of the agglomerates was modeled assuming that the phase fraction of the secondary hematite phase in the agglomerates only affects the stagnation of the gas reduction reaction. Regarding the reduction behavior after the stagnation of the gas reduction reaction, Non-Patent Document 4 was referred to, and calculation parameters were determined to be consistent with the experimental results, assuming that the reduction rate of the agglomerates is determined by the diffusion rate of oxygen ions in the metallic iron covering them.

[0067] The standard operation that serves as the basis for the CO2 reduction rate is Standard Operation 1, with the blast temperature set to 1100°C, the oxygen concentration set to 21% by volume, and the blast moisture content set to 20g / Nm 3 The operation conditions were a heat loss of 100 Mcal / t and a coke rate of 487 kg / t. Reference operation 2 was performed under the same conditions as reference operation 1, except that the gas reducing agent amount (0 Nm 3 / t), the gas reducing agent was 200Nm 3 / t. Reference operation 3 was carried out with the gas reducing agent amount (0 Nm 3 / t), the gas reducing agent was 400Nm 3 / t. The phase fraction of the secondary hematite phase in the agglomerates in each standard operation was 10.5% by volume. The proportion of the agglomerates in the main raw materials was 70% by mass. The results of the examples are shown in Table 2. Note that even in this case, the proportion of the agglomerates in the main raw materials is preferably 60% by mass or more, and more preferably 70% by mass or more. This is because having the proportion of the agglomerates in the main raw materials be 60% by mass or more can contribute to improving the CO2 reduction rate.

[0068] [Table 2]

[0069] In Table 2, the "CO2 reduction rate" was evaluated as "good (○)" when the result was 1% or more, except for standard operations 1 to 3. The CO2 reduction rate was calculated based on the value of "0" for standard operation 1.

[0070] As shown in Table 2, in Comparative Example 1, the amount of gas reducing agent was 0 Nm 3 / t, and the optimum gas reduction rate is lower than the stagnant gas reduction rate. Therefore, although the stagnant gas reduction rate improved compared to standard operation 1, the CO2 reduction rate was 0%.

[0071] In contrast, in Example 1, the amount of gas reducing agent was 400 Nm 3 By increasing the optimal gas reduction rate to 1 / t, the secondary hematite phase fraction in the agglomerates was increased to 20% by volume or more, and the stagnation gas reduction rate of the agglomerates was increased to over 70%, thereby improving the CO2 reduction rate.

[0072] In Examples 2 and 3, the amount of gas reducing agent was 200 Nm 3 By increasing the optimal gas reduction rate to / t, the secondary hematite phase fraction in the agglomerates was increased to 30% by volume or more, and the stagnation gas reduction rate of the agglomerates was increased to over 80%, thereby improving the CO2 reduction rate.

[0073] Furthermore, in Examples 4 and 5, the phase fraction of the secondary hematite phase in the agglomerates was set to 30% by volume or more, and the amount of gas reducing agent was set to 400 Nm 3 / t, the stagnation gas reduction rate of the gas reduction in the agglomerated ore could be increased to more than 80%. In addition, the amount of gas reducing agent could be increased compared to Invention Examples 2 and 3, so the CO2 reduction rate could be further increased.

Claims

[Claim 1] A blast furnace operating method for producing molten iron by charging agglomerated ore from a top of the blast furnace and supplying a gas reducing agent from a lower part of the blast furnace, comprising: The supply amount of the gas reducing agent was 100 Nm ３ / t or more, and the phase fraction of the calcium ferrite phase in the agglomerate is 40.8 vol% or more and 55.2 vol% or less, or the phase fraction of the secondary hematite phase is 20 vol% or more and 39.7 vol% or less.

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