Blast furnace operation methods

Abstract

Provided is a blast furnace operation method with which it is possible to suppress gas blow-by near the furnace wall of shaft gas blown from the shaft of the blast furnace and disperse the shaft gas toward the center in the furnace.　Provided is a blast furnace operation method in which coke and ore are alternately charged from the blast furnace top, coke layers and ore layers are alternately formed within the blast furnace, blast gas is blown from a tuyere provided in the lower part of the blast furnace, and shaft gas is blown from a blow-in pipe provided in the shaft of the blast furnace, wherein, when the amount of shaft gas blown in is taken as V1 (Nm3 / t), the amount of bosh gas generated by blast gas blown in from the tuyere is taken as V2 (Nm3 / t), the center position of the blast furnace is taken as 0.00, and the wall position of the blast furnace is taken as 1.00, the ratio of the ore layer thickness to the coke layer thickness charged when the normalized radius of the blast furnace is within the range of (V2 / (V1+V2))0.5 to 1.00 is set to 0.7 times or more the ratio of the ore layer thickness to the coke layer thickness charged when the normalized radius is within the range of 0.00-1.00.

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace, which involves injecting shaft gas from an injection pipe provided in the shaft of the blast furnace. [Background technology]

[0002] In recent years, there has been a strong demand to reduce carbon dioxide (CO2) emissions due to global environmental problems. Therefore, blast furnaces within steel mills are required to operate with a low reducing agent ratio (low RAR).

[0003] In a typical blast furnace, hot air (air heated to approximately 1200°C) is blown into the furnace as a blast gas from tuyeres located at the bottom of the furnace. This causes the oxygen in the hot air to react with coke or pulverized coal, which act as reducing agents, producing carbon monoxide (CO) gas and hydrogen (H2) gas. This carbon monoxide and hydrogen gas then reduces the iron ore charged into the blast furnace. Carbon dioxide (CO2) gas is generated as a result of the reduction reaction of the iron ore. The blast gas is the gas blown into the blast furnace from the tuyeres and plays a role in gasifying the coke and pulverized coal inside the furnace.

[0004] As a technology for reducing carbon dioxide emissions in blast furnace operations, a known technique involves reforming carbon monoxide and carbon dioxide contained in by-product gases emitted from blast furnaces to produce hydrocarbons such as methane and ethanol, and then reintroducing these hydrocarbons into the blast furnace as reducing agents.

[0005] Patent Document 1 discloses a technology for reintroducing methane gas, which is produced by reforming by-product gases discharged from blast furnaces, back into the blast furnace. According to Patent Document 1, by using an oxygen blast furnace instead of a hot-air blast furnace when reintroducing methane gas into the blast furnace, the amount of methane gas injected can be increased, and carbon dioxide emissions can be significantly reduced.

[0006] Thus, increasing the oxygen concentration in the blast gas allows for an increase in the amount of reducing agent such as methane gas injected, which is considered effective in reducing carbon dioxide emissions. However, increasing the oxygen concentration in the blast gas reduces the nitrogen content. When the nitrogen content decreases, the flow rate of the blast gas flowing through the blast furnace becomes lower than that of a hot-air blast furnace, so the ratio of the heat capacity of the charge to the heat capacity of the furnace gas (hereinafter, the ratio of the heat capacity of the charge to the heat capacity of the furnace gas will be referred to as the "heat flow ratio") increases. When the heat flow ratio increases, the amount of heat supplied from the blast gas to the raw materials also decreases, which raises concerns that the heating of the raw materials will be insufficient and lead to insufficient molten iron temperature.

[0007] Generally, it is considered preferable to maintain a molten iron temperature of 1500°C or higher for stable operation of a blast furnace. If the molten iron temperature falls below 1500°C, the blast furnace may become unstable or even impossible to operate. To address this, increasing the amount of coke charged into the blast furnace can achieve a low heat flow ratio even under high oxygen concentration conditions, but this results in increased carbon dioxide emissions, which is undesirable.

[0008] To address the problems of low heat flow ratio oxygen blast furnaces, Patent Document 2 discloses a technique for promoting the heating of raw materials in the shaft by injecting preheating gas from the shaft of the blast furnace. Patent Document 3 discloses a technique for maximizing the use of reducing gas in a blast furnace in which reducing gas is injected from the shaft by charging small iron ore near the wall. Patent Document 4 discloses a technique for eliminating deposits on the furnace wall by lowering the layer thickness ratio (O / C) between the ore layer and the coke layer near the furnace wall. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2021 / 106578 [Patent Document 2] Japanese Patent Application Publication No. 63-169310 [Patent Document 3] Japanese Patent Publication No. 2015-199984 [Patent Document 4] Japanese Patent Application Publication No. 10-280014 [Non-patent literature]

[0010] [Non-Patent Document 1] Ken Sato, et al., "Development of a Blast Furnace Operation Simulator and its Application to Molten Iron Silicon Reduction," Kawasaki Steel Technical Report, Vol. 29 (1997), No. 1. [Overview of the project] [Problems that the invention aims to solve]

[0011] In a blast furnace, the gas generated by the combustion of coke and other materials in the lower part of the furnace (hereinafter referred to as "Bosch gas") penetrates deep into the furnace core and rises across the entire furnace cross-section. In contrast, shaft gas injected from the shaft of the blast furnace is difficult to penetrate into the furnace and tends to rise near the furnace walls. Therefore, even if preheating gas is injected from the shaft, as in the technology disclosed in Patent Document 2, it flows only along the furnace walls, failing to promote the heating of the raw materials in the shaft and making stable blast furnace operation impossible. In particular, when operations are carried out to suppress deposits on the furnace walls by lowering the layer thickness ratio (O / C) between the ore layer and the coke layer on the furnace wall, as in Patent Document 4, the ventilation resistance near the furnace walls decreases, making it easier for the shaft gas to flow only along the furnace walls.

[0012] On the other hand, it is believed that by applying the technology disclosed in Patent Document 3, the injected reducing gas can permeate into the furnace, thereby achieving a high molten iron temperature. However, in the technology disclosed in Patent Document 3, small iron ore particles are charged near the wall surface, which may cause the small iron ore particles to enter the gas injection nozzles provided in the shaft, potentially leading to nozzle blockage. Therefore, even if the technology disclosed in Patent Document 3 is applied, there is a problem in that stable blast furnace operation cannot be achieved.

[0013] The present invention has been made in view of such problems, and an object thereof is to provide an operation method for a blast furnace that suppresses the phenomenon in which the shaft gas blown from the shaft portion of the blast furnace flows only near the furnace wall and disperses the shaft gas in the central direction in the furnace.

Means for Solving the Problems

[0014] The means for solving the above problems are as follows. [1] A method for operating a blast furnace in which coke and ore are alternately charged from the top of the blast furnace to alternately form a coke layer and an ore layer in the furnace of the blast furnace, blast gas is blown from tuyeres provided at the lower part of the blast furnace, and shaft gas is blown from a blowing pipe provided in the shaft portion of the blast furnace, wherein the blowing amount of the shaft gas is V1 (Nm / t), and the amount of bosh gas generated by the blast gas blown from the tuyeres is V2 (Nm 3 / t), taking the center position of the blast furnace as 0.00 and the furnace wall surface position of the blast furnace as 1.00, the normalized radius of the blast furnace is (V2 / (V1 + V2)) 0.5 The ratio of the ore layer thickness to the coke layer thickness charged in the range of 1.00 or less and 0.00 or more of the normalized radius is made not less than 0.7 times the ratio of the ore layer thickness to the coke layer thickness charged in the range of 1.00 or less and 0.00 or more of the normalized radius. [2] The method for operating a blast furnace according to [1], wherein V2 / (V1 + V2) is 0.5 or more. [3] The method for operating a blast furnace according to [1] or [2], wherein the heat flow ratio in the furnace below the height where the blowing pipe is provided is 0.9 or more. [4] The method for operating a blast furnace according to [1] or [2], wherein the temperature of the shaft gas is 850°C or higher. [5] The method for operating a blast furnace according to [1] or [2], wherein the total of the CO2 concentration and the H2O concentration contained in the shaft gas is 5% by volume or more. [6] The method for operating a blast furnace according to [1] or [2], wherein the shaft gas is produced by partial combustion of a reducing gas. [7] The method for operating a blast furnace according to [6], wherein the reducing gas is blast furnace gas.

Advantages of the Invention

[0015] By implementing the operation method of the blast furnace according to the present invention, the shaft gas blown from the shaft part of the blast furnace can be dispersed in the central direction inside the furnace.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view of a blast furnace and its auxiliary equipment.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, the present invention will be specifically described through embodiments of the present invention. The following embodiments show a preferred example of the present invention, and the present invention is not limited by these embodiments.

[0018] FIG. 1 is a schematic cross-sectional view of a blast furnace 10 and its auxiliary equipment where the operation method of the blast furnace according to the present embodiment can be implemented. In the operation of the blast furnace 10 for producing pig iron, ore raw materials as raw materials and coke as a reducing agent are alternately charged from a revolving chute 12 provided at the top of the blast furnace 10. As a result, a coke layer 14, which is a layer of coke, and an ore layer 16, which is a layer of ore raw materials, are alternately formed inside the blast furnace 10.

[0019] A tuyere 18 is provided at the lower part of the blast furnace 10. Blast gas and various tuyere-injected reducing agents are blown into the blast furnace 10 from the tuyere 18 at the lower part of the furnace. The blast gas, the tuyere-injected reducing agent, and the coke inside the blast furnace are charged into the blast furnace 10 by a gas containing carbon monoxide gas and hydrogen gas generated by combustion in a raceway 19 in front of the tuyere 18, and the ore raw materials charged into the blast furnace 10 are reduced to produce pig iron. Carbon dioxide is generated in this reduction reaction of the ore raw materials. This carbon dioxide is discharged from the top of the blast furnace 10 as blast furnace gas together with carbon monoxide and hydrogen that did not react with the ore raw materials.

[0020] The top of the blast furnace is under high pressure of approximately 2.5 atmospheres. As the blast furnace gas discharged from the top of the blast furnace 10 returns to atmospheric pressure, expansion and cooling cause the water vapor to condense. The condensed water produced by the condensation of water vapor is removed by the dewatering device 26.

[0021] A portion of the blast furnace gas from which condensed water has been removed is used as shaft gas. The shaft gas is partially combusted by the burner 22 to raise its temperature to approximately 800-1000°C and is then injected into the blast furnace through an inlet pipe 20 located in the shaft section of the blast furnace 10. The remaining blast furnace gas may be stored in a gas holder.

[0022] The shaft gas is blown in to promote the heating of the raw materials in the shaft. By blowing in the shaft gas, the oxygen concentration of the blown gas from the tuyeres 18 is increased, which allows the raw materials in the shaft to be heated even when the amount of gas in the furnace is reduced. In particular, if the heat flow ratio in the furnace below the height where the blowing pipe 20 is installed is 0.9 or higher, the heating of the raw materials in the shaft will be insufficient, resulting in a delay in the reduction of the ore raw materials. Furthermore, the insufficient heating of the raw materials will also lower the molten iron temperature, making it impossible to achieve stable blast furnace operation. For this reason, it is preferable to apply the blast furnace operation method according to this embodiment when the heat flow ratio in the furnace below the height where the blowing pipe 20 is installed is 0.9 or higher.

[0023] In the operation of a blast furnace in which shaft gas is injected from such a shaft section, the shaft gas and the Bosch gas produced by combustion in the raceway 19 exist almost separately without mixing. The shaft gas is located in the annular region near the furnace wall, while the Bosch gas is located in the region inside the annular region. The Bosch gas is a high-temperature gas composed only of CO, H2, and N2 gasified by the combustion of the blast gas injected from the tuyeres 18, the reducing agent, and the coke in front of the tuyeres 18 in the raceway 19.

[0024] The shaft gas and Bosch gas rise within the blast furnace 10 while remaining separate. As a result, the Bosch gas can penetrate into the center of the furnace and contribute to raising the temperature of the raw materials, while the shaft gas rises near the furnace walls and is unable to promote the temperature rise of the raw materials in the shaft section.

[0025] Therefore, in the blast furnace operation method according to this embodiment, the distribution in the radial direction of the furnace of the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 is adjusted according to the flow rate ratio of the Bosch gas amount to the sum of the shaft gas injection amount and the Bosch gas amount. The ratio of the Bosch gas amount to the sum of the shaft gas injection amount and the Bosch gas amount is the ratio expressed by the following equation (1).

[0026] V2 / (V1+V2)···(1) (1) In equation (1), V1 is the amount of shaft gas injected (Nm 3 V2 is the Bosch gas volume (Nm³ / t). 3 / t) is the case.

[0027] In the blast furnace 10, the area ratio of the annular region near the furnace wall where shaft gas exists to the area inside the annular region where Bosch gas exists is the same as the ratio of the amount of shaft gas injected to the amount of Bosch gas. Therefore, the annular region where shaft gas exists is defined as (V2 / (V1+V2)) in the normalized radius of the blast furnace 10, where the radial center position of the blast furnace 10 is 0.00 and the radial furnace wall position is 1.00. 0.5 The range is between 1.00 and above.

[0028] In the blast furnace operation method according to this embodiment, the radial distribution of the ratio is adjusted so that the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 in the annular region where shaft gas exists is high. Specifically, the normalized radius of the blast furnace 10 is (V2 / (V1+V2)) 0.5The ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 charged in the range of 1.00 or less is made 0.7 times or more of the ratio in the range where the normalized radius of the blast furnace 10 is 0.00 or more and 1.00 or less. In the following description, the range where the normalized radius of the blast furnace 10 is 0.00 or more and 1.00 or less is described as "range A of the whole furnace", and the normalized radius of the blast furnace 10 is (V2 / (V1+V2)) 0.5 The range of 1.00 or more and 1.00 or less is described as "range B on the furnace wall side".

[0029] Thus, by making the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 in the range B on the furnace wall side 0.7 times or more of the ratio in the range A of the whole furnace, the ventilation resistance of the annular region where the shaft gas exists can be increased. It is preferable to make the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 in the range B on the furnace wall side 0.8 times or more of the ratio in the range A of the whole furnace, and more preferably 1.0 times or more. As a result, the shaft gas that has been rising in the region can be dispersed in the central direction of the furnace. As a result, the temperature rise of the raw materials in the shaft section is promoted, and even in the operation of a blast furnace with a high heat flow ratio such as an oxygen blast furnace, the decrease in the molten iron temperature is suppressed, and stable operation of the blast furnace can be realized. When using a mixture of ore and small lump coke as the ore layer, the layer thickness of the mixture of ore and small lump coke may be regarded as the ore layer thickness, and the layer thickness of only lump coke may be regarded as the coke layer thickness.

[0030] Furthermore, the range B on the furnace wall side where the shaft gas exists changes depending on the amount of bosch gas and the amount of shaft gas blown in. By changing the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 in response to this change, the shaft gas can be effectively dispersed in the central direction of the furnace, and the temperature rise of the raw materials in the shaft section can be further promoted.

[0031] The amount of shaft gas blown in V1 is the standard state flow rate (Nm of the shaft gas blown from the blowing pipe 20 after partial combustion by the burner 22 3The standard flow rate per unit time (Nm³) is used as the shaft gas injection amount V1 if there are multiple injection pipes 20. If the amount of molten iron produced by the blast furnace 10 is unknown, the shaft gas injection amount is the standard flow rate per unit time (Nm³). 3 You may also use / min).

[0032] The Bosch gas volume V2 is calculated as a standard-state flow rate (Nm³) assuming that the blown gas from the tuyere 18, the reducing agent, and the coke in front of the tuyere 18 are combusted and gasified in the raceway 19, resulting in a high-temperature gas composed only of CO, H2, and N2. 3 The Bosch gas amount is calculated from the airflow conditions, the reducing agent injection conditions from tuyere 18, and the coke ratio. The amount of shaft gas injected is the standard flow rate per unit time (Nm³). 3 When using ( / min), the Bosch gas flow rate is also the standard-condition flow rate per unit time (Nm³). 3 Use / min).

[0033] Since the volume of shaft gas and Bosch gas changes with temperature and pressure, it is preferable to use flow rates corrected for the actual temperature and pressure. However, if the shaft gas and Bosch gas are at the same temperature and pressure, V2 / (V1+V2) will be the same value whether the flow rate is corrected for temperature and pressure or the standard-condition flow rate. If the temperature and flow rate of the shaft gas are set to adequately raise the temperature of the raw materials in the shaft section, the temperature and pressure of the shaft gas and Bosch gas will inevitably be approximately the same, so even if a simple standard-condition flow rate is used, the impact on the present invention is sufficiently small and there is no problem.

[0034] The ratio of the thickness of the coke layer 14 to the thickness of the ore layer 16 can be adjusted, for example, by measurement using a laser profiler installed at the top of the blast furnace 10, which can measure the surface height of the coke layer 14 and the ore layer 16, and by charging control using a swirling chute 12. The laser profiler scans the surface of the coke layer 14 and the ore layer 16 inside the blast furnace 10 with a detection wave whose frequency changes continuously, and obtains distance data between the laser profiler and each position on the surface by receiving reflected waves from each position on the surface. The laser profiler uses this distance data to create surface profile data of the coke layer 14 and the ore layer 16 inside the furnace.

[0035] This laser profiler is used to measure the radial distribution of the coke layer 14's thickness, and the charging of ore raw materials from the swirling chute 12 is controlled using this distribution and the radial distribution of the target thickness ratio. This makes it possible to adjust the radial distribution of the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 to the target distribution.

[0036] The radial distribution of the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 may be adjusted not only as described above, but also by identifying charging conditions that can achieve the target thickness ratio distribution using a model experimental apparatus of the blast furnace 10. Alternatively, the radial distribution of the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 may be adjusted by identifying charging conditions that can achieve the target thickness ratio distribution using numerical simulation of the charge distribution.

[0037] It is preferable that V2 / (V1+V2), expressed in equation (1) above, be 0.5 or greater. If V2 / (V1+V2) is less than 0.5, the amount of shaft gas injected may become too large, increasing pressure loss and potentially reducing the amount of molten iron produced, which is undesirable. Furthermore, if the amount of shaft gas injected becomes too large, the raw materials near the injection pipe 20 may become fluidized, causing the layered structure of the raw materials, such as the coke layer 14 and the ore layer 16, to collapse, which is also undesirable. It is even more preferable that V2 / (V1+V2), expressed in equation (1) above, be 0.7 or greater.

[0038] The shaft gas temperature is preferably 850°C or higher. Maintaining a shaft gas temperature of 850°C or higher promotes the heating of the raw materials within the shaft and suppresses delays in the reduction of the ore raw materials. Conversely, if the shaft gas temperature falls below 850°C, the heating of the raw materials within the shaft slows down, potentially causing delays in the reduction of the ore raw materials, which is undesirable. A shaft gas temperature of 900°C or higher is more preferable, and 1000°C or higher is even more preferable. This further suppresses delays in the reduction of the ore raw materials.

[0039] It is preferable that the total concentration of CO2 and H2O in the shaft gas is 5% by volume or more. If the total concentration of CO2 and H2O in the shaft gas is 5% by volume or more, the precipitation of solid carbon from components such as CO and hydrocarbons in the shaft gas is suppressed, thereby suppressing the occurrence of equipment problems such as pipe blockages. On the other hand, if the total concentration of CO2 and H2O in the shaft gas is less than 5% by volume, the amount of components such as CO and hydrocarbons in the shaft gas increases, and solid carbon may precipitate from these components, which may cause equipment problems such as pipe blockages, so this is undesirable. It is even more preferable that the total concentration of CO2 and H2O in the shaft gas is 10% by volume or more.

[0040] It is preferable to produce shaft gas by partially combusting a reducing gas such as blast furnace gas. This increases the temperature of the shaft gas and allows the total concentration of CO2 and H2O to be 5% by volume or more through this partial combustion. In this embodiment, an example is shown in which a gas obtained by partially combusting a portion of blast furnace gas in burner 22 is used as shaft gas, but this is not the only example. Various reducing gases other than blast furnace gas may be used as shaft gas. [Examples]

[0041] <Example 1> Next, we will describe the examples. In Example 1, the operating conditions of a blast furnace were set such that pure oxygen was blown in as the blowing gas from the tuyer and methane as the reducing agent. In Invention Example 1, the coke ratio was set to 340 kg / t, the ore ratio to 1600 kg / t, and the blowing rate to 320 Nm³.3 Let / t be used, and set the shaft gas injection volume V1 to 500 Nm 3 The ratio was set to / t. The shaft gas composition was N2: 1 vol%, CO: 20 vol%, CO2: 40 vol%, H2: 24 vol%, H2O: 15 vol%, and the shaft gas temperature was 1000°C.

[0042] In Example 1, a cylindrical blast furnace filled with raw materials was used, with an inner shaft diameter of 16 m and a height of 16.8 m. The raw materials were arranged in alternating layers of coke and ore, with the ore layer thickness / coke layer thickness distributed radially as shown in the lower row of Table 1. The coke particle size was 50 mm and the ore particle size was 11 mm. Bosch gas at 600°C was assumed to flow in from the bottom of the cylindrical packed bed, and shaft gas was assumed to be blown into the cylindrical packed bed from a height of 5 m from the bottom.

[0043] Under these conditions, numerical simulations of the gas flow in the furnace were performed to evaluate the diffusion behavior of the shaft gas. The numerical simulation of the gas flow was performed using the numerical simulation method described in Non-Patent Literature 1. To evaluate the diffusion range of the shaft gas, simulations were performed under conditions in which a small amount of tracer chemical species (N2) was mixed with the shaft gas, and the diffusion range of the shaft gas was calculated by determining the radial flow rate distribution of the tracer chemical species. The operating conditions and simulation results for Example 1 are shown in Table 1 below.

[0044] [Table 1]

[0045] First, a numerical simulation was performed under the conditions shown in Invention Example 1. Next, without changing the ore layer thickness and coke layer thickness from Invention Example 1, only the shaft gas injection amount V1 was changed to 300 Nm 3 Conditions reduced to / t (Comparative Example 1) and 1000Nm 3Numerical simulations were performed under the condition of increasing the value to / t (Inventive Example 2). Then, the radial flow rate distribution of tracer chemical species at the furnace top was calculated for Inventive Example 1, Comparative Example 1, and Inventive Example 2, respectively. As mentioned above, the shaft gas was made to contain 1% tracer chemical species (N2), so the radial flow rate distribution of the shaft gas can be calculated from the radial flow rate distribution of tracer chemical species at the furnace top.

[0046] The amount of shaft gas that diffused into the furnace interior was evaluated using the calculated radial flow rate distribution of shaft gas at the furnace top. In this example, the area with a normalized radius of less than 0.9 was defined as the furnace interior. The ratio of the shaft gas flow rate that flowed out from the furnace interior area to the furnace top (the ratio of shaft gas diffusion flow rate in the furnace) to the total shaft gas flow rate calculated using equation (2) below was evaluated as an indicator of shaft gas diffusion in the furnace.

[0047] Shaft gas diffusion flow rate within the furnace (%) = (Shaft gas flow rate (Nm³) that has flowed out to the top of the furnace from within the range of normalization radius < 0.9) 3 (Total shaft gas flow rate (Nm)) × 100 / (Total shaft gas flow rate (Nm) 3 / ton))···(2)

[0048] Invention Example 1 is an operational example in which the average ratio of the ore layer to the coke layer thickness in area B on the furnace wall side (hereinafter referred to as "average O / C") is 0.7 times the average O / C of area A of the entire furnace. In Invention Example 1, the diffusion flow rate of shaft gas inside the furnace was 43%. Comparative Example 1 is an example in which the ore layer thickness and coke layer thickness remain the same as in Invention Example 1, but the shaft gas injection amount V1 is set to 300 Nm 3 This is an example of operation under conditions where the O / C was reduced to / t, and the average O / C in area B on the furnace wall side was 0.6 times the average O / C in area A of the entire furnace. As shown in Table 1, in Comparative Example 1, the average O / C in area B on the furnace wall side became 0.6 times the average O / C in area A of the entire furnace, and the in-furnace diffusion flow rate of shaft gas decreased to 33%.

[0049] In Invention Example 2, the ore layer thickness and coke layer thickness remain the same as in Invention Example 1, but the shaft gas injection amount V1 is set to 1000 Nm 3This is an example of operation under conditions where the O / C was increased to / t, and the average O / C in area B on the furnace wall side was 0.8 times the average O / C in area A of the entire furnace. By making the average O / C in area B on the furnace wall side 0.8 times the average O / C in area A of the entire furnace, the diffusion flow rate of shaft gas inside the furnace increased to 51%.

[0050] These results confirm that increasing the average O / C ratio in area B on the furnace wall side to 0.7 times or more the average O / C ratio in area A of the entire furnace increases the diffusion flow rate of shaft gas within the furnace. This increase in the diffusion flow rate of shaft gas within the furnace increases the amount of shaft gas dispersed towards the center of the furnace. This promotes the heating of the raw materials within the shaft, suppressing the decrease in molten iron temperature even in blast furnaces with high heat flux ratios, such as oxygen blast furnaces, and enabling stable blast furnace operation.

[0051] <Example 2> Example 2 is an operational example in which, compared to Comparative Example 1 where the diffusion flow rate of shaft gas inside the furnace decreased, the ore layer thickness and coke layer thickness were changed to achieve an appropriate ratio between the average O / C in area B on the furnace wall side and the average O / C in area A of the entire furnace. The operating conditions and simulation results for Example 2 are shown in Table 2 below.

[0052] [Table 2]

[0053] Invention Example 3 is an operating example in which the average O / C of area B on the furnace wall side is 0.8 times the average O / C of area A of the entire furnace. As shown in Table 2, by setting the average O / C of area B on the furnace wall side to 0.8 times the average O / C of area A of the entire furnace, the in-furnace diffusion flow rate of shaft gas became 36%, which is an increase compared to Comparative Example 1. Invention Example 4 is an operating example in which the average O / C of area B on the furnace wall side is 1.0 times the average O / C of area A of the entire furnace. As shown in Table 2, by setting the average O / C of area B on the furnace wall side to 1.0 times the average O / C of area A of the entire furnace, the in-furnace diffusion flow rate of shaft gas became 38%, which is a further increase.

[0054] Example 1 is an example in which the amount of shaft gas injected was changed while keeping the layer thickness distribution of ore and coke, i.e., the charge distribution, constant. Changing the amount of shaft gas injected also changes the area B on the furnace wall side where the shaft gas is present. Therefore, as shown in Comparative Example 1 in Table 1, if the charge distribution is kept the same as in Invention Example 1, it was confirmed that the ventilation resistance in area B on the furnace wall side where the shaft gas is present cannot be adequately increased, and the proportion of shaft gas diffusion flow rate inside the furnace decreases.

[0055] In contrast to Comparative Example 1, in Invention Examples 3 and 4 of Example 2, the charge distribution was adjusted so that the ratio of the average O / C in the furnace wall area B to the average O / C in the entire furnace area A was appropriate, corresponding to the area B on the furnace wall side where the shaft gas is present after changing the shaft gas injection amount. As a result, the in-furnace diffusion flow rate of the shaft gas in Invention Examples 3 and 4 increased compared to the in-furnace diffusion flow rate of the shaft gas in Comparative Example 1. These results confirm that adjusting the ratio of the average O / C in the furnace wall area B to the average O / C in the entire furnace area A, corresponding to the area B on the furnace wall side where the shaft gas is present, increases the in-furnace diffusion flow rate of the shaft gas. [Explanation of symbols]

[0056] 10 blast furnace 12. Swinging Shot 14. Coke layer 16 Ore layer 18 Tuyere 19 Raceway 20 Inlet pipe 22 burners

Claims

1. A method of operating a blast furnace, comprising alternately charging coke and ore from the top of the blast furnace to alternately form coke and ore layers inside the furnace, blowing in blast gas from tuyeres located in the lower part of the blast furnace, and blowing in shaft gas from blowing pipes located in the shaft of the blast furnace, The amount of shaft gas injected is V1 (Nm ３ Let V2 (Nm) be the amount of Bosch gas generated by the blown gas from the tuyere. ３ If we assume / t, V2 / (V1+V2) is 0.5 or greater, Depending on the change in the Bosch gas volume and the amount of shaft gas injected, the normalized radius of the blast furnace, with the center position of the blast furnace set to 0.00 and the furnace wall position of the blast furnace set to 1.00, is (V2 / (V1+V2)) ０．５ A method for operating a blast furnace, wherein the average ratio of the ore layer thickness to the coke layer thickness charged in the range of 1.00 or less is adjusted to be at least 0.7 times the average ratio of the ore layer thickness to the coke layer thickness charged in the range of 0.00 or more and 1.00 or less with a normalization radius.

2. A method for operating a blast furnace, comprising: alternately charging coke and ore from the top of the blast furnace to alternately form coke layers and ore layers inside the blast furnace; blowing in blast gas from tuyeres provided in the lower part of the blast furnace; and blowing in shaft gas from blowing pipes provided in the shaft section of the blast furnace, If the amount of shaft gas blown in is V1 (Nm³ / t), and the amount of Bosch gas generated by the blown gas from the tuyere is V2 (Nm³ / t), V2 / (V1+V2) is between 0.5 and 0.68, A method for operating a blast furnace, wherein the normalization radius of the blast furnace, with the center position of the blast furnace set to 0.00 and the furnace wall position of the blast furnace set to 1.00, is such that the average value of the ratio of the ore layer thickness to the coke layer thickness charged in the range of (V2 / (V1+V2)) 0.5 to 1.00 is 0.7 times or more the average value of the ratio of the ore layer thickness to the coke layer thickness charged in the range of normalization radius 0.00 to 1.

00.

3. The method for operating a blast furnace according to claim 1 or claim 2, wherein the heat flow ratio in the furnace below the height at which the blowing pipe is provided is 0.9 or more.

4. The method for operating a blast furnace according to claim 1 or claim 2, wherein the temperature of the shaft gas is 850°C or higher.

5. CO contained in the aforementioned shaft gas ２ Potential and H ２ A method for operating a blast furnace according to claim 1 or claim 2, wherein the total concentration of oxygen is 5% by volume or more.

6. The method for operating a blast furnace according to claim 1 or claim 2, wherein the shaft gas is produced by partial combustion of a reducing gas.

7. The method for operating a blast furnace according to claim 6, wherein the reducing gas is blast furnace gas.

Images