Blast furnace operation methods

Abstract

This invention provides a blast furnace operation method that enables stable operation by maintaining good air permeability within the furnace and the average temperature of the blast furnace raw materials when using reduced iron as a blast furnace raw material. [Solution] In blast furnace operation, blast furnace raw materials are charged into the furnace in such a way that coke layers and ore layers containing reduced iron and iron ore are alternately stacked inside the furnace, and pulverized coal is blown in by air blown from tuyeres, the amount of moisture in the air blown in is adjusted to satisfy equation (1) based on the amount of pulverized coal blown in from the tuyeres and the amount of reduced iron charged into the blast furnace. H≦DA×PCR-B×MR×(1-x)-C×MR×x ···(1) Here, H is the amount of moisture (g / Nm³). 3 ), PCR represents the amount of pulverized coal blown in from the tuyeres (kg / t), MR represents the amount of reduced iron in the blast furnace raw material (mass%), and x represents the amount of particles in the reduced iron with a particle size greater than 40 mm (mass%). A, B, C, and D represent coefficients, satisfying the relationship C > B.

Description

Technical Field

[0001] The present invention relates to a blast furnace operation method using reduced iron as a blast furnace raw material and blowing pulverized coal through tuyeres by blowing air.

Background Art

[0002] In recent years, from the perspective of preventing global warming, reduction of carbon dioxide emissions has been demanded. In the steel industry, out of the carbon dioxide emissions in all processes from pig iron production to steel product shipment, about 70% is emitted from blast furnaces that produce pig iron. Therefore, it can be said that reducing carbon dioxide emissions in blast furnace operation is an urgent task. In particular, it is necessary to reduce the charging amount of reducing materials (such as coke and pulverized coal) as blast furnace raw materials.

[0003] Here, from the perspective of improving productivity in blast furnaces, development of methods to reduce the charging amount of reducing materials by using reduced iron (DRI: Direct Reduced Iron) has been conventionally carried out. Note that HBI (Hot Briqetted Iron) and CBI (Cold Briqetted Iron) obtained by hot-forming and cold-forming reduced iron are easily crushed by the impact during handling and transportation. Therefore, studies have also been conducted on the adjustment of reduced iron considering the variation in particle size during charging into the blast furnace.

[0004] For example, Patent Document 1 discloses a method of charging reduced iron into the furnace of a blast furnace and controlling the oxygen enrichment rate of the blowing air and the amount of pulverized coal blown through tuyeres in order to improve the tapping ratio. Furthermore, Patent Document 1 discloses a method of adjusting the particles of reduced iron with a particle size of less than 5 mm to 10% by mass or less in order to prevent deterioration of the air permeability in the furnace due to the powder of reduced iron. This can be said to be the same technical idea as the conventional method of adjusting the particle size of sintered ore, coke, etc.

[0005] Patent Document 2 discloses a method for improving the pigstriking ratio by charging reduced iron into the blast furnace, monitoring the ratio between the air pressure blown in from the tuyeres and the pressure loss inside the furnace, and controlling the amount of pulverized coal blown in and the amount of reduced iron charged. Furthermore, Patent Document 2 proposes the use of reduced iron with an average particle size of 25 mm or more from the viewpoint of improving the pressure loss inside the furnace. That is, both Patent Documents 1 and 2 disclose a method for adjusting reduced iron particles having particle size variations so that they have a predetermined particle size distribution. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5693768 [Patent Document 2] Patent No. 3589016 [Non-patent literature]

[0007] [Non-Patent Document 1] Challenges toward a low reducing agent ratio in blast furnaces, Ujisawa et al., Iron and Steel Vol. 92 No. 12 (2006) [Non-Patent Document 2] Development of a blast furnace operation simulator and its application to reducing silicon content in molten iron, Sato et al., Kawasaki Steel Technical Report Vol. 29 No. 1 (1997) [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, the methods disclosed in Patent Documents 1 and 2 do not take into account the effect of moisture in the air blown in from the tuyeres. The moisture content of the air is greatly affected by the humidity of the air in the atmosphere. Therefore, if the moisture content of the air is not adjusted, the air permeability (pressure loss) and the average temperature of the blast furnace raw materials will fluctuate, affecting the stabilization of blast furnace operation. As a result, even if reduced iron is used as the blast furnace raw material, it will be difficult to reduce carbon dioxide emissions. In other words, although the methods disclosed in Patent Documents 1 and 2 focus on the technical concept of improving productivity in blast furnaces, they are technical concepts that lack a perspective on reducing carbon dioxide emissions, which is an urgent issue.

[0009] The present invention has been made in view of the above circumstances, and its objective is to provide a blast furnace operation method that can maintain good air permeability inside the furnace and the average temperature of the blast furnace raw material, thereby enabling stable operation when reduced iron is used as the blast furnace raw material. [Means for solving the problem]

[0010] [1] A blast furnace operation method comprising charging blast furnace raw materials into the furnace in such a manner that a coke layer and an ore layer containing reduced iron and iron ore are alternately stacked inside the furnace, and blowing in pulverized coal by air blowing from tuyeres, wherein the amount of moisture in the air blowing is adjusted to satisfy equation (1) based on the amount of pulverized coal blown in from the tuyeres and the amount of reduced iron charged into the blast furnace. H≦DA×PCR-B×MR×(1-x)-C×MR×x ···(1) Here, H is the amount of moisture (g / Nm³). 3 ), PCR represents the amount of pulverized coal blown in from the tuyeres (kg / t), MR represents the amount of reduced iron in the blast furnace raw material (mass%), and x represents the amount of particles in the reduced iron with a particle size greater than 40 mm (mass%). A, B, C, and D represent coefficients, satisfying the relationship C > B. [2] The blast furnace operation method according to [1], wherein the amount of particles with a particle size exceeding 40 mm in the reduced iron is 40% by mass or more. [Effects of the Invention]

[0011] According to the present invention, when using reduced iron as a blast furnace raw material, the air permeability in the furnace and the average temperature of the blast furnace raw materials can be maintained well, and stable operation can be achieved.

Brief Description of the Drawings

[0012] [Figure 1] It is a diagram showing an example of the schematic configuration of a verification device for measuring the temperature of reduced iron, which is a molded product, using a thermocouple. [Figure 2] It is a diagram showing the relationship between the particle size of reduced iron and the temperature of reduced iron. [Figure 3] It is a diagram showing the relationship between the amount of reduced iron and the average temperature of blast furnace raw materials. [Figure 4] It is a diagram showing the relationship between the amount of moisture and the amount of pulverized coal when reduced iron is not used. [Figure 5] It is a diagram showing the relationship between the amount of moisture and the amount of pulverized coal when all reduced iron has particles with a particle size exceeding 40 mm. [Figure 6] It is a diagram showing the relationship between the amount of moisture and the amount of pulverized coal when 50% by mass of the particles of reduced iron have a particle size exceeding 40 mm and 50% by mass of the particles have a particle size of 40 mm or less. [Figure 7] It is a diagram showing the relationship between the ratio of particles with a particle size exceeding 40 mm in reduced iron and the pressure loss. [Figure 8] It is a diagram showing the relationship between the ratio of particles with a particle size exceeding 40 mm in reduced iron and the reducing agent ratio.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described. In the following description, "blast furnace raw materials" means a general term for iron ore, reduced iron, coke, etc. charged into the blast furnace. "Moisture" means the amount of moisture contained per unit volume in the blast air blown from the tuyere.

[0014] In blast furnace operation, hot air (blast air) heated to a high temperature is blown into the tuyere. At this time, fine coal and oxygen-enriched gas are also blown in together with the blast air having moisture. Then, in the vicinity of the tuyere tip (the region near the tuyere in the blast furnace), the moisture in the blast air reacts with coke, generating hydrogen and carbon monoxide as reducing gases. Thereafter, the reduction of blast furnace raw materials proceeds due to the generated reducing gas. The inventors of the present invention focused on the moisture in the blast air and the fine coal to be blown in and conducted studies from the viewpoint of stable blast furnace operation.

[0015] In the furnace, the reaction rate of hydrogen with iron oxide (blast furnace raw material) is faster than the reaction rate of carbon monoxide with iron oxide. Therefore, by using hydrogen, the efficiency of the reduction reaction of blast furnace raw materials in the furnace can be increased. On the other hand, when the moisture content of the blast air blown into the furnace is high, the combustion temperature at the tuyere tip decreases, leading to a decrease in the furnace temperature and a decrease in the reaction rate related to the reduction reaction of blast furnace raw materials. And as the furnace temperature decreases, it also causes a decrease in the molten iron temperature, inducing operation troubles that affect the tapping from the blast furnace. Thus, from the viewpoint of stabilizing blast furnace operation, the moisture content of the blast air blown into the furnace is an important factor. Note that the moisture content of the blast air is greatly affected by the humidity in the atmosphere, especially by seasonal variations. Therefore, it is preferable to adjust it to an appropriate amount of moisture by using a dehumidifying device or the like.

[0016] The fine coal burns at the tuyere tip, mainly generating carbon monoxide. When unburned matter (unburned char) is generated due to insufficient combustion, the unburned matter remains in the furnace in a fine powder state, deteriorating the air permeability in the furnace. Also, the unburned matter is generated under the influence of factors such as a decrease in the combustion temperature at the tuyere tip, oxygen deficiency, and coarsening of the particle size of the fine coal. Since the combustion temperature at the tuyere tip is affected by the moisture content of the blast air blown in, the combustion temperature can be increased by reducing the amount of moisture. Also, since the combustion temperature at the tuyere tip greatly contributes to the temperature rise of blast furnace raw materials, the higher the combustion temperature, the higher the temperature of blast furnace raw materials can be maintained, enabling the promotion of the reduction reaction. That is, from the viewpoint of the combustion of fine coal, the moisture content of the blast air blown into the furnace can also be an important factor.

[0017] By using reduced iron as a blast furnace raw material, the amount of reducing agent used can be reduced, resulting in a reduction in carbon dioxide emissions. Furthermore, in order to efficiently reduce the reducing agent ratio by using reduced iron, it is necessary to consider the behavior of reduced iron in relation to heat absorption within the furnace.

[0018] Therefore, the inventors then focused on the heat transfer efficiency of reduced iron and proceeded with their investigation. Reduced iron has a higher thermal conductivity compared to coke and sintered ore. For this reason, reduced iron has a higher heat transfer efficiency per unit volume compared to coke and sintered ore. However, even if it is reduced iron, molded products such as HBI have larger particle sizes compared to coke and sintered ore used as blast furnace raw materials, and may contain components other than metallic iron (such as iron oxide and gangue). For this reason, molded products of reduced iron (such as HBI) have poor heat transfer efficiency to the center and poor heat transfer efficiency.

[0019] Furthermore, when charging reduced iron into the furnace, it is necessary to reduce the amount of reducing agent charged into the furnace. In other words, it is necessary to reduce the amount of pulverized coal blown in, and this reduction in the amount of pulverized coal blown in will lower the combustion temperature at the tuyere. Therefore, in order to raise the temperature of the raw materials in the furnace without excess or deficiency, it is necessary to adjust the combustion temperature at the tuyere by reducing the amount of moisture in the blown air. Moreover, as mentioned above, reduced iron as a molded product has poor heat transfer efficiency, and the required combustion temperature at the tuyere will differ depending on the size of the molded product. For this reason, moisture in the blown air can be an important factor from the standpoint of the heat transfer efficiency of reduced iron in the furnace.

[0020] Here, the inventors conducted a verification regarding the heating of molded reduced iron according to the size of the molded product. First, sieves with mesh sizes of 25 mm, 35 mm, 45 mm, and 55 mm were prepared for the molded reduced iron. Then, when sieving was performed using these sieves, the particle size of reduced iron that was sieved up when the mesh size was 25 mm and down when the mesh size was 35 mm was set to 30 mm, the particle size of reduced iron that was sieved up when the mesh size was 35 mm and down when the mesh size was 45 mm was set to 40 mm, and the particle size of reduced iron that was sieved up when the mesh size was 45 mm and down when the mesh size was 55 mm was set to 50 mm, and one reduced iron sample was selected for each particle size.

[0021] Subsequently, a verification device was prepared to measure the temperature of the selected reduced iron. Figure 1 shows an example of the schematic configuration of the verification device for measuring the temperature of molded reduced iron using thermocouples. In the verification, a hole was drilled to the center of each selected reduced iron, a thermocouple was inserted, and the reduced iron with the inserted thermocouple was set inside a heating furnace. Furthermore, another thermocouple was also installed inside the heating furnace.

[0022] Reduced iron was heated by blowing nitrogen gas heated to 1000°C at a flow rate of 30 NL / min into a heating furnace for 15 minutes. During this process, no heat was transferred to the heating furnace itself; the reduced iron was heated solely through heat exchange with the nitrogen gas. The temperature of each piece of reduced iron was measured using a thermocouple inserted into it. The temperature inside the heating furnace was also measured using a separate thermocouple. The temperature measured with the separate thermocouple was used to measure the temperature outside (around) the reduced iron, i.e., the temperature of the nitrogen gas.

[0023] Figure 2 shows the relationship between the particle size of the molded reduced iron and the measured temperature of the reduced iron. As shown in Figure 2, reduced iron with a particle size of 40 mm or less could be heated to a temperature similar to that of nitrogen gas (1000°C). On the other hand, for reduced iron with a particle size of 50 mm, a significant decrease in the heating rate was observed. This can be presumed to be because, for larger particle sizes of reduced iron, there was a greater amount of residual iron oxide and gangue components inside the molded product, resulting in a deterioration of heat transfer efficiency.

[0024] Based on the results shown in Figure 2, the inventors focused on a particle size of "40 mm" for reduced iron from the viewpoint of the heat transfer efficiency of reduced iron as a molded product. Based on the heat transfer efficiency of reduced iron, they further diligently investigated reduced iron with a particle size of "40 mm or less" and reduced iron with a particle size exceeding 40 mm. In the following explanation, regarding the particle size of reduced iron, when sieving is performed using a sieve with a sieve mesh size of 40 mm, reduced iron that passes through the sieve is defined as "reduced iron with a particle size of 40 mm or less," and reduced iron that passes through the sieve is defined as "reduced iron with a particle size exceeding 40 mm."

[0025] Next, the inventors conducted a more detailed investigation to find the relationship between moisture content, the amount of reduced iron, and particle size in the blast furnace. Specifically, they performed a simulation of blast furnace operation using a model that incorporated the effects of reduced iron particle size and heat transfer behavior into the blast furnace model described in Non-Patent Document 2.

[0026] In the simulation, the amount of reduced iron was varied from 0 to 200 kg / t while keeping the heat loss, coke ratio, tapping ratio, oxygen enrichment rate, and amount of pulverized coal constant. The amount of air blown in from the tuyeres was adjusted to keep the tapping ratio and heat loss constant. The simulation was then used to confirm the relationship between the average temperature of the blast furnace raw materials in the furnace and the moisture content, amount of reduced iron, and particle size in the air. The average temperature of the blast furnace raw materials was calculated using the average value of the raw materials at a height of 12 to 15 m from the tapping port. The results of the simulation are shown in Table 1. Furthermore, Figure 3 shows the relationship between the amount of reduced iron and the average temperature of the blast furnace raw materials as a result of the simulation.

[0027] [Table 1]

[0028] The simulation first assumed that the reduced iron particle size was over 40 mm and the amount of moisture in the airflow was 30 g / Nm³. 3 "Simulation 1" was conducted. Furthermore, in "Simulation 1," the amount of moisture in the airflow was set to 15 g / Nm³.3 In "Simulation 2," which was modified to the same specifications as "Simulation 1," the particle size of reduced iron was set to 40 mm or less, while the amount of moisture in the airflow was set to 30 g / Nm³. 3 We conducted "Simulation 3," which involved the following:

[0029] As shown in Table 1 and Figure 3, in all simulations, a tendency was observed for the average temperature of the blast furnace raw materials to decrease as the amount of reduced iron increased. Furthermore, as shown in the results of "Simulation 2" and "Simulation 3," a tendency was observed for the average temperature of the blast furnace raw materials to increase by reducing the amount of moisture in the blast air. In addition, as shown in the results of "Simulation 3," a tendency was observed for the average temperature of the blast furnace raw materials to increase by reducing the particle size of the reduced iron to 40 mm or less. Therefore, from the simulation results of blast furnace operation shown in Table 1 and Figure 3, it was confirmed that a relationship exists between the average temperature of the blast furnace raw materials and the amount of moisture in the blast air, the amount of reduced iron, and the particle size.

[0030] Based on these considerations, the inventors concluded that, in light of the relationship between the amount of moisture in the blast air, the amount of pulverized coal blown in, the amount of reduced iron, and the particle size, a relationship also exists between these parameters. Based on this premise, they considered that, regarding the amount of moisture in the blast air, which can be an important factor in blast furnace operation, it would be possible to calculate a value that can maintain the average temperature of the blast furnace raw materials well and enable stable operation, based on information on the amount of pulverized coal, the amount of reduced iron, and the particle size.

[0031] The inventors then found the following equation (1) for the amount of moisture in the blast air that can enable stable operation of a blast furnace. H≦DA×PCR-B×MR×(1-x)-C×MR×x ···(1) Here, H is the amount of moisture (g / Nm³). 3 PCR represents the amount of pulverized coal blown in from the tuyeres (kg / t), MR represents the amount of reduced iron in the blast furnace raw material (mass%), and x represents the amount of particles with a particle size greater than 40 mm in the reduced iron (mass%). A, B, C, and D represent coefficients, and the relationship C > B is satisfied.

[0032] As mentioned above, the inventors found that the amount of moisture in the blown air is related to the amount of pulverized coal, the amount of reduced iron, and the particle size. Based on this, they found a formula by multiplying the values ​​of each parameter (amount of pulverized coal, amount of reduced iron, and particle size) by coefficients (A to C), and using this formula, they found formula (1) which can calculate the maximum amount of moisture that will enable stable operation of the blast furnace.

[0033] Furthermore, the inventors added a coefficient D to equation (1) to improve its versatility. More specifically, coefficient D is a coefficient that depends on the blast furnace volume, the number of tuyeres, the blown air temperature, the tapping ratio, etc., and corresponds to the maximum moisture content of the blown air that enables stable operation of the blast furnace when reducing agents such as pulverized coal are not blown in from the tuyeres and reduced iron is not used. When pulverized coal is blown in from the tuyeres, it is necessary to maintain the combustion temperature at the tip of the tuyeres, i.e., reduce the moisture content of the blown air, in order to suppress the generation of unburned material, so the value of coefficient D needs to be reduced. When reduced iron is used, the value of coefficient D needs to be further reduced in order to maintain a good average temperature of the blast furnace raw materials.

[0034] Furthermore, as previously stated using Table 1 and Figure 3, it can be seen that the effect on the average temperature of the blast furnace raw material is greater for "reduced iron with a particle size greater than 40 mm" than for "reduced iron with a particle size of 40 mm or less". Therefore, the coefficients B and C in equation (1) have the relationship "C > B".

[0035] Here, A, B, C, and D in equation (1) are coefficients determined by the size and ancillary equipment of each blast furnace. For this reason, they may be determined in advance by simulation or other means prior to blast furnace operation. Below, we will explain a method for calculating the coefficients A, B, C, and D in advance by simulating the operation of the blast furnace in question, prior to blast furnace operation. As the simulation model to be applied to this method, we will use a model that incorporates the effects of the particle size and heat transfer behavior of reduced iron into the blast furnace model described in Non-Patent Literature 2.

[0036] First, a simulation of blast furnace operation will be conducted based on parameters obtained from operational records where reduced iron was not used as blast furnace raw material. Then, the data for each combination of the amount of moisture and the amount of pulverized coal obtained from the simulation will be plotted on a graph.

[0037] Figure 4 shows the relationship between the amount of moisture and the amount of pulverized coal when reduced iron is not used. As shown in Figure 4, regression processing is performed on the data obtained from the simulation to calculate equation P. Equation P shown in Figure 4 corresponds to equation (1) when reduced iron is not used. By calculating equation P for the operation of the blast furnace targeted in the simulation, the value of coefficient A related to equation (1) is determined to be "30", and the value of coefficient D is determined to be "110".

[0038] In the simulation results shown in Figure 4, results indicating unsuccessful blast furnace operation are shown with "●", and results indicating stable blast furnace operation are shown with "◇". As shown in Figure 4, it can be confirmed that stable blast furnace operation is possible by adjusting the amount of moisture, which is the value on the vertical axis, to a value below the value calculated by formula P. Unsuccessful blast furnace operation, indicated by "●", refers to results in unsuccessful blast furnace operation due to deterioration of permeability inside the furnace, a decrease in the average temperature of the blast furnace raw materials, etc. Specifically, based on the values ​​obtained from the simulation using the results of actual operation as a baseline, it is determined that blast furnace operation is unsuccessful if the pressure loss is +5.0% or more, or if the average temperature of the raw materials inside the furnace is -3.0% or less.

[0039] Next, a simulation is performed based on parameters obtained from operational results when the amount of reduced iron in the blast furnace raw material is set to 20% by mass, and all reduced iron particles are larger than 40 mm (size at the time of briquetting). Then, the data for each combination of values ​​for the amount of moisture and the amount of pulverized coal obtained from the simulation are plotted on a graph. At this time, the simulation is performed with the amount of moisture adjusted to be less than or equal to the value in equation P relative to the amount of pulverized coal.

[0040] Figure 5 shows the relationship between the amount of moisture and the amount of pulverized coal as a result of the simulation. For the simulation results, "●" indicates that blast furnace operation is unsuccessful, and "◇" indicates that blast furnace operation can be carried out stably. Furthermore, the P-equation calculated from the simulation results when reduced iron is not used as a blast furnace raw material is also shown on the graph (Figure 5).

[0041] Here, as shown in Figure 5, although simulations were performed to keep the amount of moisture below the value based on equation P, the result shows that the blast furnace operation is unsuccessful (●). For this reason, equation Q is calculated, which takes into account the amount of reduced iron in the blast furnace raw materials. That is, equation Q corresponds to equation (1) when all the reduced iron particles used are larger than 40 mm.

[0042] By calculating equation Q, the value of coefficient C in equation (1) for the operation of the blast furnace being simulated is determined to be "0.6". Therefore, as shown in Figure 5, when reduced iron is used as the blast furnace raw material and all reduced iron particles used have a particle size exceeding 40 mm, it can be confirmed that stable blast furnace operation can be carried out by adjusting the amount of moisture in the blast air to a value below the value calculated by equation Q.

[0043] Furthermore, simulations will be conducted based on parameters obtained from operational records regarding the particle size of reduced iron in blast furnace raw materials, where 50% by mass consists of particles larger than 40 mm and 50% by mass consists of particles smaller than or equal to 40 mm. The data obtained from the simulations, along with the combinations of moisture content and pulverized coal content, will then be plotted on a graph. In this case, the simulation will be performed with the moisture content adjusted to be less than or equal to the value in equation P relative to the amount of pulverized coal.

[0044] Figure 6 shows the relationship between the amount of moisture and the amount of pulverized coal as a result of the simulation. For the simulation results, "●" indicates that blast furnace operation is unsuccessful, and "◇" indicates that blast furnace operation can be carried out stably. Furthermore, the Q equation calculated from the simulation results when all reduced iron used as blast furnace raw material has a particle size exceeding 40 mm is also shown on the graph (Figure 6).

[0045] Here, as shown in Figure 6, when the amount of moisture exceeds the value based on equation Q, which is calculated considering the amount of reduced iron, stable blast furnace operation can be achieved (◇). For this reason, equation R is calculated for the amount of reduced iron in the blast furnace raw material, taking into account multiple particle sizes. That is, equation R corresponds to equation (1), which is constructed by dividing the coefficients to consider multiple particle sizes of the reduced iron used. Specifically, in equation (1), coefficients B and C correspond to coefficients that are divided to consider multiple sizes.

[0046] By calculating equation R, the value of coefficient B in equation (1) is determined to be "0.2" and the coefficient C is determined to be "0.6" for the operation of the blast furnace being simulated. Therefore, even when reduced iron is used as the blast furnace raw material, and when reduced iron containing particles of multiple particle sizes is adopted, the amount of moisture that can be used to stably operate the blast furnace can be calculated using equation (1).

[0047] Specifically, the reduced iron charged into the blast furnace can be divided into "reduced iron with a particle size of 40 mm or less" and "reduced iron with a particle size exceeding 40 mm" and applied to equation (1). In other words, even if there is variation in the particle size of the reduced iron charged into the blast furnace during operation, it becomes unnecessary to exclude the charging of reduced iron of a specific particle size (for example, reduced iron with a small particle size). Furthermore, it can be confirmed that stable blast furnace operation can be achieved by adjusting the amount of moisture in the blast air to a value below the value calculated by equation R, which takes into account multiple particle sizes.

[0048] As described above, the blast furnace operation method according to the present invention may be implemented in blast furnace operation in which blast furnace raw materials are charged in such a manner that coke layers and ore layers containing reduced iron and iron ore are alternately stacked inside the blast furnace, and pulverized coal is blown in by air blown from tuyeres. Specifically, in said blast furnace operation, the amount of moisture in the air blown in may be adjusted based on the amount of pulverized coal blown in from the tuyeres and the amount of reduced iron charged into the blast furnace.

[0049] Furthermore, by implementing the blast furnace operation method according to the present invention, when using reduced iron as a blast furnace raw material, it is possible to maintain good air permeability within the furnace and the average temperature of the blast furnace raw material, thereby achieving stable operation.

[0050] Furthermore, it is preferable to adjust the amount of moisture in the airflow based on a value that satisfies equation (1). This is because adjusting it to a value below the value calculated based on equation (1) allows for more efficient maintenance of the airflow within the furnace and the average temperature of the blast furnace raw materials.

[0051] Here, regarding the reduced iron used as a blast furnace raw material, it is preferable that the proportion of particles with a particle size exceeding 40 mm, while satisfying equation (1), be 40% by mass or more. By making the proportion of particles with a particle size exceeding 40 mm in the reduced iron 40% by mass or more, the permeability inside the blast furnace is improved, allowing for a significant reduction in pressure loss and a substantial reduction in the amount of reducing agent used. This makes it possible to more effectively reduce carbon dioxide emissions.

[0052] Furthermore, with respect to reduced iron, when the proportion of particles with a particle size exceeding 40 mm is increased to 40% by mass or more, the average temperature of the blast furnace raw materials decreases due to the effect of heat transfer efficiency. However, by adjusting the amount of moisture calculated from equation (1), stable operation of the blast furnace can be maintained. In other words, in this case, it becomes possible to reduce the reducing agent ratio by using reduced iron with a large particle size, while also maintaining stable operation of the blast furnace. [Examples]

[0053] Examples of the blast furnace operation method of the present invention will be described. In these examples, a simulation model of blast furnace operation was used to evaluate the stabilization of blast furnace operation by changing the amount of reduced iron in the blast furnace raw material, the amount of pulverized coal blown in from the tuyeres, and the amount of moisture in the blast air.

[0054] As a simulation model, a model incorporating elements related to the particle size and heat transfer mode of reduced iron was used. In the evaluation using the simulation model, the airflow rate was adjusted so that the heat loss, oxygen enrichment rate, and tapping ratio remained constant. The simulation model used was a blast furnace model described in Non-Patent Literature 2, with the influence of the particle size and heat transfer behavior of reduced iron incorporated.

[0055] For the evaluation, pressure drop (kPa / m) was used to assess the permeability inside the furnace, and the average furnace raw material temperature (°C) was used to assess the temperature of the blast furnace raw materials inside the furnace. In the evaluation based on pressure drop, it was determined that blast furnace operation would be unsuccessful if the pressure drop value obtained by simulation was +5.0% or more compared to the pressure drop value in the example where reduced iron was not used as a blast furnace raw material (Comparative Example 1). In the evaluation based on the average furnace raw material temperature, it was determined that blast furnace operation would be unsuccessful if the average furnace raw material temperature obtained by simulation was -3.0% or less compared to the average furnace raw material temperature in the example where reduced iron was not used as a blast furnace raw material (Comparative Example 1). Therefore, in each example, it was determined that blast furnace operation would be unsuccessful (indicated as "×" in the "Judgment" column of Tables 2 and 3) if the pressure drop was +5.0% or more, or the average furnace raw material temperature was -3.0% or less, and in all other cases, it was determined that stabilization of blast furnace operation was possible (indicated as "○" in the "Judgment" column of Tables 2 and 3).

[0056] Furthermore, the reason for using the conditions of "pressure loss value of +5.0% or higher" and "average raw material temperature inside the furnace of -3.0% or lower" as thresholds for evaluating the stabilization of blast furnace operation is based on the fact that in actual operating results, blast furnace operation becomes unsuccessful when either of these thresholds is met.

[0057] Furthermore, in each example, the coke ratio (indicated as "reducing agent ratio" in Tables 2 and 3) when reduced iron was used as a blast furnace raw material was also calculated.

[0058] Here, the average furnace raw material temperature was defined as the average value of the temperature of the blast furnace raw materials in a specific region within the furnace at a predetermined height in the furnace radius direction. In all examples, the same region was used.

[0059] In the examples, first, a specific blast furnace (labeled "Blast Furnace S" in Table 2) was selected as the target of operation, and the coefficients A, B, C, and D in equation (1) were determined in advance. Specifically, coefficient A was set to "0.3", coefficient B to "0.2", coefficient C to "0.6", and coefficient D to "110". Then, for each example, simulations were performed by changing the amount of reduced iron in the blast furnace raw material, the particle size of the reduced iron, the amount of pulverized coal blown in from the tuyeres, and the amount of moisture in the blown air. In addition, for each example, the "actual amount of moisture in the blown air" was set separately from the "upper limit of blown air moisture" which corresponds to the amount of moisture calculated based on equation (1), and simulations were performed. The results of the simulations performed with this specific blast furnace (Blast Furnace S) as the target of operation are shown in Table 2.

[0060] [Table 2]

[0061] In Comparative Example 1, reduced iron was not used as a blast furnace raw material, which increased the reducing agent ratio and prevented a reduction in carbon dioxide emissions. Furthermore, in Comparative Examples 2 to 4, the "actual amount of moisture in the blown air" applied to the simulation was increased compared to the "upper limit of blown air moisture" calculated by equation (1), resulting in either a "pressure loss value of +5.0% or more" or an "average temperature of the furnace raw material of -3.0% or less," and in all of these examples, the judgment was "×".

[0062] In contrast, in Invention Examples 1 to 9, the "actual amount of moisture in the blown air" applied to the simulation was reduced compared to the "upper limit of blown air moisture" calculated by equation (1), resulting in pressure loss and average temperature of the furnace raw materials falling within a normal range. Therefore, it was confirmed that the judgment was "○", meaning that stabilization of blast furnace operation is possible. Furthermore, it was confirmed that the reducing agent ratio could be reduced compared to Comparative Example 1, in which reduced iron was not used as a blast furnace raw material, and that carbon dioxide emissions could be reduced.

[0063] Next, another blast furnace (labeled "Blast Furnace T" in Table 3) was chosen as the target for operation, and the coefficients A, B, C, and D in equation (1) were determined in advance. Specifically, coefficient A was set to "0.4", coefficient B to "0.2", coefficient C to "0.7", and coefficient D to "100". Then, for each example, simulations were performed by changing the amount of reduced iron in the blast furnace raw material, the particle size of the reduced iron, the amount of pulverized coal blown in from the tuyeres, and the amount of moisture in the blown air. In addition, for each example, the "actual amount of moisture in the blown air" was set separately from the "upper limit of blown air moisture" which corresponds to the amount of moisture calculated based on equation (1), and simulations were performed. The results of the simulations performed with this other blast furnace (Blast Furnace T) as the target for operation are shown in Table 3.

[0064] [Table 3]

[0065] In Comparative Example 5, reduced iron was not used as a blast furnace raw material, which increased the reducing agent ratio and prevented a reduction in carbon dioxide emissions. Furthermore, in Comparative Examples 6 to 8, the "actual amount of moisture in the blown air" applied to the simulation was increased compared to the "upper limit of blown air moisture" calculated by equation (1), resulting in either a "pressure loss value of +5.0% or more" or an "average temperature of the furnace raw material of -3.0% or less," and in all of these examples, the judgment was "×".

[0066] In contrast, in Invention Examples 10 to 19, the "actual amount of moisture in the blown air" applied to the simulation was reduced compared to the "upper limit of blown air moisture" calculated by equation (1), resulting in pressure loss and average temperature of the furnace raw materials falling within a normal range. Therefore, it was confirmed that the judgment was "○", meaning that stabilization of blast furnace operation is possible. Furthermore, it was confirmed that the reducing agent ratio could be reduced compared to Comparative Example 5, in which reduced iron was not used as a blast furnace raw material, and that carbon dioxide emissions could be reduced.

[0067] Here, Figure 7 shows the relationship between the pressure loss value and the proportion of particles with a particle size exceeding 40 mm in the reduced iron for Invention Examples 15 to 19. As shown in Figure 7, it was confirmed that in blast furnace operation, a significant reduction in pressure loss is possible by ensuring that the amount of particles with a particle size exceeding 40 mm in the reduced iron used as blast furnace raw material is 40% by mass or more.

[0068] Furthermore, Figure 8 shows the relationship between the reducing agent ratio and the proportion of particles with a particle size exceeding 40 mm in the reduced iron for Invention Examples 15 to 19. As shown in Figure 8, it was confirmed that in blast furnace operation, a significant reduction in the reducing agent ratio is possible by setting the amount of particles with a particle size exceeding 40 mm in the reduced iron used as blast furnace raw material to 40% by mass or more. From the above, it is preferable to set the amount of particles with a particle size exceeding 40 mm in the reduced iron used as blast furnace raw material to 40% by mass or more in order to significantly reduce pressure loss and the reducing agent ratio.

Claims

1. In blast furnace operation, blast furnace raw materials are charged into the furnace in such a manner that coke layers and ore layers containing reduced iron and iron ore are alternately stacked, and pulverized coal is blown in by air from tuyeres, A blast furnace operation method, which involves adjusting the amount of moisture in the air supply to satisfy equation (1) based on the amount of pulverized coal blown in from the tuyeres and the amount of reduced iron charged into the blast furnace. H≦D-A×PCR-B×MR×(1-x)-C×MR×x...(1) Here, H is the amount of moisture (g / Nm³). ３ PCR represents the amount of pulverized coal blown in from the tuyeres (kg / t), MR represents the amount of reduced iron in the blast furnace raw material (mass%), and x represents the amount of particles in the reduced iron with a particle size exceeding 40 mm (mass%). A, B, C, and D represent coefficients, and the relationship C > B is satisfied.

2. The blast furnace operation method according to claim 1, wherein the amount of particles with a particle size exceeding 40 mm in the reduced iron is 40% by mass or more.

Images