Blast furnace operation methods

Abstract

The furnace body temperature and gas flow near the furnace wall will be optimized. [Solution] In a blast furnace operation method including a furnace wall ore dump, the slag content of the furnace wall ore dump is defined as the slag amount, and the ratio of basic oxides to acidic oxides in the iron raw material charged in the furnace wall ore dump is defined as the slag basicity. First relationship information, which is the relationship between furnace body temperature and slag amount, second relationship information, which is the relationship between furnace body temperature and slag basicity, third relationship information, which is the relationship between skin flow temperature and slag amount, and fourth relationship information, which is the relationship between skin flow temperature and slag basicity are obtained. An appropriate range for the slag amount is determined from the first and third relationship information, and an appropriate range for the slag basicity is determined from the second and fourth relationship information. The iron raw material composition of the furnace wall ore dump is determined so that the slag amount and slag basicity fall within the appropriate range.

Description

Technical Field

[0001] The present invention relates to a method for operating a blast furnace.

Background Art

[0002] In blast furnace operation, sintered ore, pellets, lump ore, etc. (hereinafter collectively also referred to as "iron raw materials") as iron sources, as well as coke as a reducing agent and fuel are alternately charged from the top of the furnace, and hot air is blown from the tuyere at the lower part of the furnace, and auxiliary fuels such as pulverized coal are blown in. The iron raw materials and coke charged from the top of the furnace form alternately stacked iron raw material layers and coke layers, and as the load of the iron raw materials and coke in the blast furnace (hereinafter collectively also referred to as "charged materials") decreases, they gradually descend in the blast furnace toward the lower part of the furnace while being heated by the gas rising from the lower part of the furnace and the temperature is increased.

[0003] In blast furnace operation, the distribution of the charged materials is a dominant factor that determines the gas flow distribution and the shape of the cohesive zone in the blast furnace, and has a great influence on the reduction and melting of ore. In addition, the distribution of the charged materials near the furnace wall part is highly important because it also affects the heat load of the blast furnace body and the formation of deposits on the furnace wall, and many prior arts have been reported so far.

[0004] In Patent Document 1, in controlling the gas flow distribution in the radial direction of the furnace radius of a blast furnace, the thickness of the furnace wall deposit is estimated from the heat balance near the furnace wall, and the ratio Lo / Lc of the iron raw material deposit thickness to the coke deposit thickness near the furnace wall is controlled so that the estimated thickness of the furnace wall deposit falls within the set range. A method for controlling the distribution of charged materials in a blast furnace is disclosed.

[0005] In Patent Document 2, the charged materials of both coke and iron raw materials are each divided into two or more according to particle size, and the divided coke and iron raw materials according to particle size are mixed with fine particles with fine particles and coarse particles with coarse particles, and the mixture of the coarse particles is charged into the central and intermediate regions of the furnace, and the mixture of the fine particles is charged into the furnace wall region. A method for charging blast furnace raw materials is reported. As described above, adjusting the ratio of iron raw materials to coke, or the particle size distribution, near the furnace wall is a common method for controlling the distribution of charge materials near the furnace wall, thereby changing the particle size and porosity of the packed bed.

[0006] Focusing on the area near the furnace wall at the bottom of the blast furnace, it is believed that the dripping properties of the iron raw material, as well as the amount and viscosity of the slag, have a significant impact on the formation of the fusion zone (also called the fusion zone root) near the furnace wall, and on the aeration and liquid permeability of the dripping zone below the fusion zone root. The fusion zone root refers to the lower end of the fusion zone. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 3646361 [Patent Document 2] Japanese Unexamined Patent Publication No. 63-140006 [Patent Document 3] Japanese Patent Publication No. 2023-57594 [Patent Document 4] Japanese Patent Application Publication No. 11-92808 [Non-patent literature]

[0008] [Non-Patent Document 1] M. Matsumura et al., ISIJ international, Vol. 45 (2005), No.4, pp. 594-602 [Overview of the project] [Problems that the invention aims to solve]

[0009] The inventors focused on the amount of slag and the slag basicity of the iron raw material charged toward the ore terrace, and diligently investigated methods to optimize the furnace temperature and gas flow near the furnace wall by appropriately adjusting these factors. [Means for solving the problem]

[0010] The blast furnace operation method of the present invention includes (1) an ore dump for charging iron raw materials toward an ore terrace formed in the furnace, wherein the slag content in the iron raw materials charged by the ore dump is defined as the slag amount, and the ratio of basic oxides to acidic oxides in the iron raw materials charged by the ore dump is defined as the slag basicity, and in advance, based on the blast furnace operation record, a first relationship information which is the relationship between the furnace body temperature and the slag amount, a second relationship information which is the relationship between the furnace body temperature and the slag basicity, and a third relationship information which is the relationship between the skin flow temperature and the slag amount. The invention is characterized by comprising: a relationship information acquisition step of acquiring relationship information and a fourth relationship information which is the relationship between skin flow temperature and slag basicity; an appropriate range determination step of determining an appropriate range for the amount of slag from the first relationship information and the third relationship information, and determining an appropriate range for the slag basicity from the second relationship information and the fourth relationship information; and an iron raw material configuration determination step of determining the iron raw material configuration of the ore dump so that the amount of slag and the slag basicity fall within the appropriate range determined in the appropriate range determination step.

[0011] (2) The method for operating a blast furnace according to (1) above, characterized in that the furnace body temperature is the furnace body temperature obtained by a temperature measuring unit installed in the middle section of the Bosch of the blast furnace, or by a temperature measuring unit installed in the lower section of the shaft.

[0012] (3) The method for operating a blast furnace according to (1) or (2) above, characterized in that, in the step of determining the appropriate range, the lower limit of the appropriate range for the amount of slag is determined from the first relational information, the upper limit of the appropriate range for the amount of slag is determined from the third relational information, the lower limit of the appropriate range for the basicity of the slag is determined from the second relational information, and the upper limit of the appropriate range for the basicity of the slag is determined from the fourth relational information.

[0013] (4) The method for operating a blast furnace according to (1) or (2) above, characterized in that the amount of slag is the sum of the ratios (mass%) of CaO, SiO2, Al2O3, and MgO contained in the iron raw material charged in the ore dump.

[0014] (5) The slag basicity is the ratio of CaO to SiO2 contained in the iron raw material charged in the ore dump, and the operation method of the blast furnace according to (1) or (2) above is characterized by this.

[0015] (6) The slag amount is 12% by mass or more and 17% by mass or less, and the operation method of the blast furnace according to (4) above is characterized by this.

[0016] (7) The slag basicity is 1.5 or more and 1.8 or less, and the operation method of the blast furnace according to (5) above is characterized by this.

Advantages of the Invention

[0017] According to the present invention, since the iron raw material with appropriately adjusted slag amount and slag basicity can be charged toward the ore terrace, the furnace body temperature and the gas flow near the furnace wall can be optimized.

Brief Description of the Drawings

[0018] [Figure 1] It is the test result obtained from the load softening test of the relationship between the dropping detection temperature and the slag amount. [Figure 2] It is the analysis result of the relationship between the slag basicity and the slag liquid phase ratio analyzed by thermodynamic calculation. [Figure 3] It is a flowchart for explaining the operation method of the blast furnace. [Figure 4] It is a scatter diagram corresponding to the first relationship information (Example). [Figure 5] It is a scatter diagram corresponding to the second relationship information (Example). [Figure 6] It is a scatter diagram corresponding to the third relationship information (Example). [Figure 7] It is a scatter diagram corresponding to the fourth relationship information (Example).

Embodiments for Carrying Out the Invention

[0019] The present invention aims to solve the problem of appropriately adjusting the amount of slag and the basicity of the slag of the iron raw material charged near the furnace wall. In this specification, the iron raw material charged near the furnace wall is defined as "iron raw material charged toward the ore terrace". An ore terrace refers to the surface layer of the iron raw material that forms near the furnace wall and has a slope angle smaller than the angle of repose of the iron raw material. The meaning of an ore terrace is common technical knowledge (see, for example, Patent Documents 3 and 4), so a detailed explanation is omitted. Note that an ore terrace may be a positive ore terrace that rises towards the furnace wall, or a negative ore terrace that descends towards the furnace wall.

[0020] Furthermore, an ore dump that charges iron raw materials toward the ore terrace is specifically defined as a "furnace wall ore dump." The area in which iron raw materials fall by the furnace wall ore dump may be the entire ore terrace, or a part of it. The number of ore dumps in this invention is at least two. Therefore, there may be one or more ore dumps other than the furnace wall ore dump. A "dump" refers to one charging operation, and multiple dumps that charge one set of iron raw material and coke layers are called one charge.

[0021] The inventors discovered the above-mentioned solution through load softening tests and thermodynamic calculations described below. Multiple samples with different slag amounts were prepared by mixing various combinations of sintered ore, pellets, and lump ore. Each sample was subjected to a load softening test, and the drop detection temperature was measured. The method of the load softening test is described in Non-Patent Literature 1, so a detailed explanation is omitted. Figure 1 shows the test results of the load softening test, with the vertical axis representing the drop detection temperature (°C) and the horizontal axis representing the slag amount (mass%).

[0022] Here, the slag amount refers to the percentage (mass) of slag contained in the iron raw material. The slag amount (mass%) may be defined as the sum of the ratios (mass%) of CaO, SiO2, Al2O3, and MgO contained in the iron raw material, or as the sum of the ratios (mass%) of the representative components CaO and SiO2, or as the ratio (mass%) obtained by removing iron oxides from the iron raw material. In Figure 1, the slag amount (mass%) is defined as the sum of the ratios (mass%) of CaO, SiO2, Al2O3, and MgO.

[0023] Referring to the figure, as the amount of slag (mass%) decreases, carburization of the metal is promoted, and the drip detection temperature decreases (in other words, the dripping characteristics improve). This improvement in dripping characteristics leads to a thinner layer at the base of the fusion zone, improving air permeability.

[0024] The relationship between slag basicity (-) and slag liquid phase fraction (%) was obtained by thermodynamic calculation for multiple iron raw materials with different slag basicity (-). The thermodynamic calculation was performed using Factsage (software). Figure 2 shows the results of the analysis, with the vertical axis representing slag liquid phase fraction (%) and the horizontal axis representing slag basicity (-). The slag liquid phase fraction (%) was analyzed at temperatures of 1400°C and 1500°C.

[0025] Here, slag basicity (-) refers to the ratio of basic oxides to acidic oxides in the iron raw material. The ratio of CaO (mass%) to SiO2 (mass%), i.e., CaO / SiO2, may be used as the slag basicity (-), or the ratio of CaO + MgO (mass%) to SiO2 + Al2O3 (mass%), i.e., CaO + MgO / SiO2 + Al2O3, may be used as the slag basicity (-). In Figure 2, CaO / SiO2 is used as the slag basicity.

[0026] Referring to the figure, at all temperatures, the slag liquid phase percentage (%) increased with decreasing slag basicity (-). This increase in liquid phase percentage (%) improves slag fluidity from the root of the fusion zone to just below the root, and suppresses the formation of deposits on the furnace wall.

[0027] Based on the findings obtained from the load softening tests and analysis described above, by adjusting the raw materials of the iron raw material so that the amount of slag (mass%) and the slag basicity (-) of the iron raw material charged in the furnace wall ore dump dock do not exceed the upper limit (the upper limit will be described later), it is possible to improve air permeability by thinning the fusion zone root, improve the slag fluidity from the fusion zone root to just below the root, and suppress the formation of deposits on the furnace wall.

[0028] On the other hand, an excessive decrease in slag amount (mass%) and a decrease in slag basicity (-) may lead to an excessive increase in the heat load at the bottom of the furnace and gas flow fluctuations due to gas flow bias towards the lower furnace wall. Therefore, it is necessary to adjust the raw materials so that the slag amount (mass%) and slag basicity (-) of the iron raw materials charged in the furnace wall ore dump do not fall below the lower limit (the lower limit will be described later). In other words, there is an appropriate range for the amount of slag (mass%) and the slag basicity (-).

[0029] An embodiment of the blast furnace operation method of the present invention, based on the above-mentioned findings, will now be described. Figure 3 is a flowchart illustrating the blast furnace operation method of this embodiment.

[0030] (Step S101: Step to obtain related information) In blast furnace operation, information on slag quantity (mass%), slag basicity (-), furnace body temperature (°C), and skin flow temperature (°C) is generally obtained. Slag content (mass%) refers to the percentage of slag contained in the iron raw material charged by the furnace wall ore dump as described above, and slag basicity (-) refers to the ratio of basic oxides to acidic oxides in the iron raw material charged by the furnace wall ore dump as described above, but these will not be explained again. In normal blast furnace operation, the blast furnace raw materials charged into the furnace are sampled and subjected to component analysis. From the results of this component analysis, the slag amount (mass%) and slag basicity (-) are calculated. In other words, the slag amount (mass%) and slag basicity (-) are obtained for each blast furnace as operational data.

[0031] The furnace body temperature (°C) is the temperature obtained by a temperature sensor installed in the lower part of the blast furnace, and the heat load in the lower part of the furnace can be determined based on the furnace body temperature (°C). In this specification, the lower part of the furnace is defined as the lower section of the shaft and the part below that lower section of the furnace body. For example, the temperature measured by a temperature sensor installed in the middle section of the Bosch and a temperature sensor located in the lower section of the shaft are considered to be the furnace body temperature. A typical example of a temperature sensor is a thermocouple. Needless to say, furnace body temperature is a parameter that is monitored during normal blast furnace operation and is not specially measured to realize this invention. In other words, furnace body temperature is obtained for each blast furnace as part of the operational record.

[0032] Skin flow temperature refers to the temperature of the gas flowing near the furnace wall. Skin flow temperature can be obtained by a temperature sensor installed protruding into the furnace from the furnace wall directly above the stock line of the blast furnace. A typical example of a temperature sensor for skin flow temperature is a thermocouple. Needless to say, skin flow temperature is a parameter that is monitored during normal blast furnace operation and is not specially measured to realize the present invention. In other words, skin flow temperature is obtained for each blast furnace as part of the operational record.

[0033] In the relationship information acquisition step, based on the aforementioned operational results, the following relationship information is acquired: the first relationship information, which is the relationship between furnace body temperature and slag amount (mass%); the second relationship information, which is the relationship between furnace body temperature and slag basicity (-); the third relationship information, which is the relationship between skin flow temperature and slag amount (mass%); and the fourth relationship information, which is the relationship between skin flow temperature and slag basicity (-). The form of this relationship information is not particularly limited, but in the embodiment described later, the relationship information is acquired in the form of a scatter plot.

[0034] (Step S102: Step to determine the appropriate range) The appropriate range for the slag amount (mass%) is determined from the first and third related information, and the appropriate range for the slag basicity (-) is determined from the second and fourth related information. As mentioned above, if the slag amount (mass%) and slag basicity (-) become excessively low, the heat load at the bottom of the furnace body will increase excessively. Therefore, the lower limit of the appropriate range for slag amount (mass%) and slag basicity (-) can be determined based on the furnace body temperature.

[0035] As described above, if the slag amount (mass%) and slag basicity (-) become excessively high, phenomena such as deterioration of air permeability due to thickening of the fusion zone root, deterioration of slag fluidity from the fusion zone root to just below the root, and growth of deposits on the furnace wall occur, causing the skin flow temperature to rise. Therefore, the upper limit of the appropriate range for slag amount (mass%) and slag basicity (-) can be determined based on the skin flow temperature. In other words, whether or not the gas flow near the furnace wall is appropriate can be evaluated based on the skin flow temperature.

[0036] The following explains in detail the steps for determining the appropriate range (S102), divided into methods for determining the lower limit and methods for determining the upper limit.

[0037] (Regarding the method for determining the lower limit of the appropriate range) The lower limit of the appropriate range for the amount of slag (mass%) can be determined from the first relationship information, which is the relationship between the furnace temperature and the amount of slag (mass%). Since the amount of slag (mass%) when the furnace temperature changes from a low-temperature trend to a high-temperature trend can be determined from the first relationship information, this amount of slag can be set as the lower limit of the appropriate range for the amount of slag (mass%) (hereinafter also referred to as the lower limit of the amount of slag).

[0038] The lower limit of the appropriate range for slag basicity (-) can be determined from the second relationship information, which is the relationship between furnace temperature and slag basicity (-). Since the slag basicity (-) when the furnace temperature changes from a low-temperature trend to a high-temperature trend can be determined from the second relationship information, this slag basicity can be set as the lower limit of the appropriate range for slag basicity (-) (hereinafter also referred to as the slag basicity lower limit).

[0039] As described above, the furnace body temperature can be detected at multiple locations, but it is sufficient to use the temperature measurement data that clearly shows a change in the furnace body temperature from a low-temperature trend to a high-temperature trend. Therefore, the locations of the temperature measurement units considered when determining the lower limit of slag amount and the lower limit of slag basicity do not necessarily have to be the same. In the embodiment described later, the lower limit of slag amount is determined based on relationship information (first relationship information) between the furnace body temperature and the amount of slag (mass%) acquired at the Bosch middle temperature measurement unit, and the lower limit of slag basicity is determined based on relationship information (second relationship information) between the furnace body temperature and slag basicity (-) acquired at the shaft lower temperature measurement unit.

[0040] (Regarding the method for determining the upper limit of the appropriate range) The upper limit of the appropriate range for slag amount (mass%) can be determined from the third relationship information, which is the relationship between skin flow temperature and slag amount (mass%). Since the slag amount (mass%) when the skin flow temperature changes from a low-temperature trend to a high-temperature trend can be determined from the third relationship information, this slag amount can be set as the upper limit of the appropriate range for slag amount (mass%) (hereinafter also referred to as the slag amount upper limit).

[0041] The upper limit of the appropriate range for slag basicity (-) can be determined from the fourth relationship information, which is the relationship between skin flow temperature and slag basicity (-). Since the slag basicity (-) when the skin flow temperature changes from a low-temperature trend to a high-temperature trend can be determined from the fourth relationship information, this slag basicity can be set as the upper limit of the appropriate range for slag basicity (-) (hereinafter also referred to as the upper limit of slag basicity).

[0042] Here, it is desirable to set the appropriate range for slag amount (mass%) and slag basicity (-) for each blast furnace based on operational performance. The furnace body temperature and skin flow temperature are not determined solely by the composition of the iron raw materials deposited on the ore terrace, but are also affected by the layer structure of the iron raw materials deposited below them (in other words, the iron raw materials directly below the ore terrace). In other words, even if the composition of the iron raw materials deposited on the ore terrace is the same, the appropriate range may differ if the layer structure of the iron raw materials directly below the ore terrace is different. Therefore, it is desirable to set the appropriate range for each blast furnace based on operational performance.

[0043] (Step S103: Step to determine the composition of iron raw materials) The composition of the iron raw materials for the furnace wall ore dump is determined so that the slag amount and slag basicity fall within the appropriate range determined in the appropriate range determination step (S102). The composition of the iron raw materials, such as sintered ore, pellets, and lump ore, and their mixing ratios are adjusted as parameters to find mixing conditions that satisfy the appropriate range.

[0044] (Examples) Next, the present invention will be specifically described with reference to an example. In this example, the sum of the ratios of CaO, SiO2, Al2O3, and MgO was defined as the slag amount (mass%), and CaO / SiO2 was defined as the slag basicity (-). Average daily data (operating performance) of blast furnace A was collected over approximately three months, and the first relationship information (relationship between furnace body temperature and slag amount), the second relationship information (relationship between furnace body temperature and slag basicity), the third relationship information (relationship between skin flow temperature and slag amount), and the fourth relationship information (relationship between skin flow temperature and slag basicity) were obtained in the form of scatter plots (see Figures 4 to 7).

[0045] Referring to Figure 4 (First Relationship Information), it was determined that the furnace temperature (temperature of the Bosch middle section) changed from a low-temperature trend to a high-temperature trend at a slag amount of 12 mass%, and the lower limit of the slag amount was set to 12 mass% (see dotted line in Figure 4). As mentioned above, the dripping properties of the fusion zone root improve with decreasing slag amount, which is thought to have caused the furnace temperature to rise. However, below the lower limit of the slag amount, the furnace temperature tends to rise excessively, leading to overactivity in the lower part of the furnace. Overactivity in the lower part of the furnace increases the risk of gas flow fluctuations and furnace wall abrasion in the lower part of the furnace.

[0046] Referring to Figure 5 (Second Relationship Information), it was determined that the furnace body temperature (temperature of the lower part of the shaft) changed from a low-temperature trend to a high-temperature trend at a slag basicity of 1.5, and the lower limit of the slag basicity was set at 1.5 (see dotted line in Figure 5). As mentioned above, a decrease in slag basicity is thought to improve the slag fluidity from the root of the fusion zone directly below it, and to suppress the generation of deposits on the furnace wall. However, below the lower limit of the slag basicity, a tendency was observed for the furnace body temperature to rise excessively and for the lower part of the furnace to become overactive.

[0047] Referring to Figure 6 (Third Relationship Information), it was determined that the skin flow temperature changed from a low-temperature trend to a high-temperature trend at a slag amount of 17 mass%, and the upper limit for the slag amount was set to 17 mass% (see the dotted line in Figure 6). Referring to Figure 7 (Fourth Relationship Information), it was determined that the skin flow temperature changed from a low-temperature trend to a high-temperature trend at a slag basicity of 1.8, and the upper limit for slag basicity was set at 1.8 (see dotted line in Figure 7).

[0048] Summarizing the results in Figures 6 and 7, it was found that excessive increases in skin flow temperature can be prevented by setting the upper limit of slag amount to 17 mass% and the upper limit of slag basicity to 1.8. Since the ratio of iron raw material to coke (O / C) near the furnace wall was not changed, it is considered that the heat load at the bottom of the furnace increased, promoting heat exchange between the gas and the furnace wall, resulting in a decrease in the gas temperature (skin flow temperature) near the furnace wall.

[0049] Based on the above considerations, in this embodiment, the appropriate range for the iron raw material in the furnace wall ore dump was determined to be "slag amount: 12% to 17% by mass, slag basicity: 1.5 to 1.8". The effects of slag quantity and slag basicity on skin flow temperature and furnace body temperature were evaluated by performing furnace wall ore dumping. Two ore dumps were performed. In the first dump, an iron raw material layer (with ore terraces) was formed in the region of the blast furnace dimensionless radius 0.1 to 1.0. Then, furnace wall ore dumping was performed toward the ore terraces of this iron raw material layer (in this example, the region of the blast furnace dimensionless radius 0.7 to 1.0). Table 1 shows the main specifications of the example, comparative example 1, and comparative example 2. [Table 1]

[0050] In the example, iron raw materials with both slag content and slag basicity within the appropriate range were used as furnace wall ore dumps. In Comparative Example 1, iron raw materials with both slag content and slag basicity exceeding the upper limit of the appropriate range were used as furnace wall ore dumps. In Comparative Example 2, iron raw materials with both slag content and slag basicity below the lower limit of the appropriate range were used as furnace wall ore dumps. Comparative Example 1 had excessively high slag content and slag basicity, resulting in a higher skin flow temperature compared to the Example and Comparative Example 2. Furthermore, its reduction index (ηCO, ηH2, CSL) and aeration index (K value) were also inferior. In Comparative Example 2, the furnace body temperature at the bottom of the furnace was higher compared to the Example and Comparative Example 1 because the amount of slag and the slag basicity were excessively low. As a result, the examples were able to lower the CR (coke ratio) and RAR (reducing agent ratio) compared to Comparative Examples 1 and 2.

Claims

1. In a blast furnace operation method including an ore dump for charging iron raw materials toward an ore terrace formed inside the furnace, When the slag content in the iron raw material charged by the ore dump truck is defined as the slag amount, and the ratio of basic oxides to acidic oxides in the iron raw material charged by the ore dump truck is defined as the slag basicity, A relationship information acquisition step involves first acquiring relationship information, which is the relationship between furnace body temperature and slag quantity, second relationship information, which is the relationship between furnace body temperature and slag basicity, third relationship information, which is the relationship between skin flow temperature and slag quantity, and fourth relationship information, which is the relationship between skin flow temperature and slag basicity, based on the blast furnace's operating history. An appropriate range determination step in which an appropriate range for the amount of slag is determined from the first and third related information, and an appropriate range for the basicity of the slag is determined from the second and fourth related information, In the Iron Raw Material Composition Determination Step, the iron raw material composition of the ore dump is determined so that the amount of slag and the basicity of the slag fall within the appropriate range determined in the appropriate range determination step. A method for operating a blast furnace, characterized by having [a certain feature].

2. The furnace body temperature is the temperature obtained by a temperature measuring unit installed in the middle section of the Bosch of the blast furnace, or by a temperature measuring unit installed in the lower section of the shaft. The method for operating a blast furnace according to feature 1.

3. In the appropriate range determination step, the lower limit of the appropriate range for the slag amount is determined from the first relational information, the upper limit of the appropriate range for the slag amount is determined from the third relational information, the lower limit of the appropriate range for the slag basicity is determined from the second relational information, and the upper limit of the appropriate range for the slag basicity is determined from the fourth relational information. A method for operating a blast furnace according to claim 1 or 2, characterized by the above.

4. The amount of slag is the amount of CaO and SiO2 contained in the iron raw material charged in the ore dump truck. ２ , Al ２ O ３ The sum of the ratios of MgO (mass%) A method for operating a blast furnace according to claim 1 or 2, characterized by the above.

5. The slag basicity is determined by the SiO2 contained in the iron raw material charged in the ore dump truck. ２ This is the ratio of CaO to , A method for operating a blast furnace according to claim 1 or 2, characterized by the above.

6. The amount of slag is 12% by mass or more and 17% by mass or less. The method for operating a blast furnace according to feature 4.

7. The slag basicity is 1.5 or more and 1.8 or less. The method for operating a blast furnace according to feature 5.

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