Blast furnace operation method

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

Blast furnace operation method

[0001] The present invention relates to a method for operating a blast furnace in which shaft gas is injected from an injection pipe provided in the shaft portion of the blast furnace.

[0002] In recent years, against the backdrop of global environmental issues, carbon dioxide (CO ２ Therefore, it is required to operate blast furnaces in steel works at low reducing agent ratios (low RAR).

[0003] In a typical blast furnace, hot air (air heated to about 1200°C) is blown into the blast furnace as a blast gas from a tuyere located at the bottom of the furnace. This causes the oxygen in the hot air to react with the coke and pulverized coal that act as reducing agents, producing carbon monoxide (CO) gas and hydrogen (H ２ The iron ore charged into the blast furnace is reduced by the carbon monoxide gas and hydrogen gas. The reduction reaction of the iron ore produces carbon dioxide (CO ２ Blast gas is a gas that is blown into the blast furnace through the tuyere and serves to gasify the coke and pulverized coal inside the blast furnace.

[0004] One known technology for reducing carbon dioxide emissions in blast furnace operations involves reforming the 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 the hydrocarbons into the blast furnace as reducing agents.

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

[0006] In this way, 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 thought to be effective in reducing carbon dioxide emissions. However, increasing the oxygen concentration in the blast gas reduces the nitrogen content in the blast gas. When the nitrogen content in the blast gas decreases, the blast gas flow rate in the blast furnace becomes lower than in a hot-blast blast furnace, increasing the ratio of the heat capacity of the charge material to the heat capacity of the furnace gas (hereinafter, the ratio of the heat capacity of the charge material to the heat capacity of the furnace gas is referred to as the "heat flow ratio"). When the heat flow ratio increases, the amount of heat supplied from the blast gas to the raw materials also decreases, resulting in insufficient temperature rise of the raw materials, which raises concerns about insufficient hot metal temperature.

[0007] Generally, for stable operation of a blast furnace, it is considered preferable to maintain the molten iron temperature at 1500° C. or higher, and if the molten iron temperature is lower than 1500° C., the operation of the blast furnace may become unstable or even impossible. To address this issue, if the amount of coke charged into the blast furnace is increased, a low heat flow ratio can be achieved even under high oxygen concentration conditions, but this undesirably results in increased carbon dioxide emissions.

[0008] To solve the problems of oxygen blast furnaces with low heat flow ratios, Patent Document 2 discloses a technique for injecting preheat gas from the shaft of the blast furnace to promote the temperature rise of the raw materials in the shaft. 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 thickness ratio O / C of the ore layer to the coke layer near the furnace wall.

[0009] International Publication No. 2021 / 106578 Japanese Patent Application Laid-Open No. 63-169310 Japanese Patent Application Laid-Open No. 2015-199984 Japanese Patent Application Laid-Open No. 10-280014

[0010] Takeru Sato and two others, "Development of a Blast Furnace Operation Simulator and Its Application to Reducing Silicon in Molten Iron," Kawasaki Steel Technical Report, Vol. 29 (1997), No. 1

[0011] In a blast furnace, gas generated by the combustion of coke and other materials in the lower part of the furnace (hereinafter referred to as "bosh gas") penetrates deep into the furnace core and rises across the entire cross section of the furnace. In contrast, shaft gas injected from the shaft of the blast furnace has difficulty penetrating into the furnace and rises near the furnace wall. For this reason, even if preheat gas is injected from the shaft, as in the technology disclosed in Patent Document 2, it flows only through the furnace wall, failing to promote the temperature rise of the raw materials in the shaft, resulting in the problem of not being able to achieve stable blast furnace operation. In particular, when an operation is performed to suppress deposition on the furnace wall by reducing the thickness ratio O / C of the ore layer to the coke layer on the furnace wall, as in Patent Document 4, the airflow resistance near the furnace wall is reduced, making it more likely that shaft gas will flow only through the furnace wall.

[0012] On the other hand, it is believed that application of the technology disclosed in Patent Document 3 allows the injected reducing gas to penetrate into the furnace, thereby realizing a high molten iron temperature. However, with 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 get into the gas injection nozzle provided in the shaft and cause nozzle clogging. Therefore, there is a problem in that stable blast furnace operation cannot be achieved even with application of the technology disclosed in Patent Document 3.

[0013] The present invention has been made in consideration of these problems, and its object is to provide a method for operating a blast furnace that can suppress the phenomenon in which shaft gas blown into the shaft portion of the blast furnace flows only near the furnace wall, and can disperse the shaft gas toward the center of the furnace.

[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 form alternate coke layers and ore layers inside the blast furnace, blast gas is blown in from a tuyere provided in the lower part of the blast furnace, and shaft gas is blown in from an injection pipe provided in the shaft part of the blast furnace, wherein the blowing amount of the shaft gas is V1 (Nm ３ / t), and the amount of bosh gas generated by the blast gas blown in from the tuyere is V2 (Nm ３ / t), the normalized radius of the blast furnace, with the center position of the blast furnace being 0.00 and the furnace wall position of the blast furnace being 1.00, is (V2 / (V1+V2)) ０．５ [1] A method for operating a blast furnace, wherein a ratio of the ore layer thickness to the coke layer thickness charged within a normalized radius range of 0.00 to 1.00 is set to 0.7 times or more the ratio of the ore layer thickness to the coke layer thickness charged within a normalized radius range of 0.00 to 1.00. [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 a heat flow ratio in the furnace below a height at which the injection pipe is provided is 0.9 or more. [4] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more. [5] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more. [6] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more. [7] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more. [8] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more. [9] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more.

[10] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more.

[11] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 850°C or more.

[12] The method for operating a blast furnace according to [1] or [2], wherein a temperature of the shaft gas is 8 ２ Concentration and H ２ [6] The method for operating a blast furnace according to [1] or [2], wherein the total of the shaft gas and the O concentration is 5% by volume or more. [7] The method for operating a blast furnace according to [6], wherein the shaft gas is produced by partial combustion of a reducing gas. [8] The method for operating a blast furnace according to [6], wherein the reducing gas is blast furnace gas.

[0015] By carrying out the method for operating a blast furnace according to the present invention, shaft gas injected from the shaft portion of the blast furnace can be dispersed toward the center of the furnace.

[0016] FIG. 1 is a cross-sectional schematic diagram of a blast furnace and its associated facilities.

[0017] The present invention will be specifically described below through embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments.

[0018] 1 is a cross-sectional schematic diagram of a blast furnace 10 and its associated facilities, in which a blast furnace operating method according to this embodiment can be implemented. In operation of the blast furnace 10 for producing pig iron, raw ore and coke, a reducing agent, are alternately charged into the blast furnace 10 through a rotating 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 raw ore, are alternately formed inside the blast furnace 10.

[0019] Tuyere 18 is provided at the lower part of the blast furnace 10. Blast gas and, as necessary, various tuyere-injected reducing materials are injected into the blast furnace 10 through the tuyere 18 at the lower part of the furnace. The blast gas, tuyere-injected reducing materials, and coke in the blast furnace are combusted in a raceway 19 in front of the tuyere 18, resulting in gases containing carbon monoxide and hydrogen, which reduce the ore raw material charged into the blast furnace 10 to produce pig iron. Carbon dioxide is produced by this reduction reaction of the ore raw material. This carbon dioxide, together with carbon monoxide, hydrogen, and other materials that did not react with the ore raw material, is discharged from the top of the blast furnace 10 as blast furnace gas.

[0020] The top of the blast furnace is under high pressure of about 2.5 atmospheres. When the blast furnace gas discharged from the top of the blast furnace 10 returns to normal pressure, it expands and cools, causing the steam to condense. The condensed water produced by the condensation of the steam is removed by a dehydrator 26.

[0021] A portion of the blast furnace gas from which the condensed water has been removed is used as shaft gas. The shaft gas is partially combusted by a burner 22 to be heated to about 800 to 1000°C, and is then blown into the blast furnace 10 through an injection pipe 20 provided in the shaft portion of the blast furnace 10. The remainder of the blast furnace gas may be stored in a gas holder.

[0022] The shaft gas is injected to promote the temperature rise of the raw materials in the shaft section. By injecting the shaft gas, the oxygen concentration of the blast gas injected from the tuyere 18 is increased, thereby enabling the temperature rise of the raw materials in the shaft section 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 injection pipe 20 is installed is 0.9 or more, the temperature rise of the raw materials in the shaft section is insufficient, resulting in a delay in the reduction of the ore raw materials. Furthermore, the insufficient temperature rise of the raw materials also reduces the temperature of the molten pig iron, making stable blast furnace operation impossible. Therefore, 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 injection pipe 20 is installed is 0.9 or more.

[0023] In the operation of a blast furnace in which shaft gas is injected from the shaft portion, the shaft gas and bosh gas generated by combustion in the raceway 19 exist separately without being mixed together. The shaft gas exists in an annular region near the furnace wall, and the bosh gas exists in an area inside the annular region. The bosh gas is a mixture of blast gas injected from the tuyere 18, reducing material, and CO and H gasified by combustion in the raceway 19 of the coke in front of the tuyere 18. ２ , N ２ It is a high-temperature gas composed only of

[0024] The shaft gas and the bosh gas remain separated as they rise inside the blast furnace 10. For this reason, the bosh gas penetrates into the center of the furnace and contributes to raising the temperature of the raw materials, whereas the shaft gas rises near the furnace wall and is unable to promote the temperature rise of the raw materials inside the shaft.

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

[0026] V2 / (V1+V2) (1) In equation (1), V1 is the amount of shaft gas injected (Nm ３ / t), and V2 is the amount of Bosh gas (Nm ３ / t).

[0027] In the blast furnace 10, the area ratio between the annular region near the furnace wall where shaft gas exists and the region inside the annular region where bosh gas exists is the same as the ratio between the amount of shaft gas injected and the amount of bosh gas. Therefore, the annular region where shaft gas exists is expressed as (V2 / (V1+V2)) in the normalized radius of the blast furnace 10, where the center position in the radial direction of the blast furnace 10 is 0.00 and the furnace wall surface position in the radial direction is 1.00. ０．５ The range is from 1.00 to 1.00.

[0028] In the blast furnace operation method according to the present embodiment, the radial distribution of the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 in the annular region where the shaft gas exists is adjusted so that the ratio becomes high. Specifically, when the normalized radius of the blast furnace 10 is (V2 / (V1+V2)) ０．５ The ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 charged in the range of a normalized radius of 0.00 to 1.00 is set to 0.7 times or more of the ratio when the ore layer 16 is charged in the range of a normalized radius of 0.00 to 1.00. In the following description, the range of the normalized radius of the blast furnace 10 of 0.00 to 1.00 is referred to as "range A of the entire furnace," and the normalized radius of the blast furnace 10 is set to (V2 / (V1+V2)) ０．５ The range of 1.00 or more and 1.00 or less is referred to as "range B on the furnace wall side."

[0029] In this way, by setting the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 in the furnace wall-side region B to be 0.7 times or more of the ratio in the entire furnace region A, the airflow resistance in the annular region where shaft gas exists can be increased. The ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 in the furnace wall-side region B is preferably 0.8 times or more, more preferably 1.0 times or more, of the ratio in the entire furnace region A. This allows the shaft gas that would otherwise rise in this region to be dispersed toward the center of the furnace. As a result, the temperature rise of the raw materials in the shaft is promoted, and even in the operation of a blast furnace with a high heat flow ratio, such as an oxygen blast furnace, a decrease in the molten iron temperature is suppressed, thereby achieving stable blast furnace operation. When a mixture of ore and small lump coke is used as the ore layer, the thickness of the layer containing the mixture of ore and small lump coke can be defined as the ore layer thickness, and the thickness of the layer containing only the lump coke can be defined as the coke layer thickness.

[0030] Furthermore, the range B on the furnace wall side where the shaft gas exists varies depending on the amount of bosh gas and the amount of shaft gas injected. 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 toward the center of the furnace, further accelerating the temperature rise of the materials in the shaft section.

[0031] The shaft gas injection amount V1 is the standard flow rate (Nm m) of the shaft gas injected from the injection pipe 20 after partial combustion by the burner 22. ３ / t). When there are multiple injection pipes 20, the total flow rate is the shaft gas injection amount V1. When the production rate of the blast furnace 10 is unknown, the standard state flow rate per unit time (Nm ３ / min) may also be used.

[0032] The bosh gas amount V2 is the amount of CO, H, and the amount of the blast gas blown in from the tuyere 18, the reducing agent, and the coke in front of the tuyere 18 combust in the raceway 19 and undergo a gasification reaction. ２ , N ２ The standard state flow rate (Nm ３ The amount of bosh gas can be calculated from the blast conditions, the conditions for injecting the reducing agent from the tuyere 18, and the coke ratio. The amount of shaft gas injected is expressed as the standard flow rate (Nm ３ / min), the Bosch gas amount is also calculated as the standard state flow rate per unit time (Nm ３ / min) is used.

[0033] Since the volumes of the shaft gas and bosh gas change depending on the temperature and pressure, it is preferable to use flow rates corrected for the actual temperature and pressure. However, if the shaft gas and bosh gas are at the same temperature and pressure, V2 / (V1+V2) will be the same whether the flow rate is corrected for the temperature and pressure or the standard state flow rate. If the temperature and flow rate of the shaft gas are set so that the raw material in the shaft section can be appropriately heated, the temperature and pressure of the shaft gas and the bosh gas will inevitably be approximately the same, so even if a simple standard state flow rate is used, the effect on the present invention is sufficiently small and there is no problem.

[0034] The adjustment of the ratio of the thickness of the coke layer 14 to the thickness of the ore layer 16 can be achieved, for example, by measurements using a laser profile meter that is installed at the top of the blast furnace 10 and can measure the surface heights of the coke layer 14 and the ore layer 16, and by burden control using the rotating chute 12. The laser profile meter scans the surface of the coke layer 14 and the ore layer 16 inside the blast furnace 10 with detection waves that change continuously in frequency, and receives reflected waves from each position on the surface to obtain distance data between the laser profile meter and each position on the surface. The laser profile meter uses this distance data to create surface profile data of the coke layer 14 and the ore layer 16 inside the furnace.

[0035] The radial distribution of the thickness of the coke layer 14 is measured using this laser profile meter, and the radial distribution and the target radial distribution of the layer thickness ratio are used to control the charging of the ore raw material from the rotating chute 12. 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 adjustment of the radial distribution of the ratio of the thickness of the ore layer 16 to the thickness of the coke layer 14 is not limited to the above, and may be adjusted by specifying charging conditions that can realize a target distribution of layer thickness ratios using a model testing device of the blast furnace 10. 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 specifying charging conditions that can realize a target distribution of layer thickness ratios using a numerical simulation of burden distribution.

[0037] V2 / (V1+V2) represented by the above formula (1) is preferably 0.5 or more. If V2 / (V1+V2) is less than 0.5, the amount of shaft gas injected becomes too large, which may increase pressure loss and reduce the production of molten pig iron, which is undesirable. Furthermore, if the amount of shaft gas injected becomes too large, the raw materials near the injection tube 20 may become fluidized, which may cause the layered structure of the raw materials, such as the coke layer 14 and the ore layer 16, to collapse, which is undesirable. It is even more preferable that V2 / (V1+V2) represented by the above formula (1) is 0.7 or more.

[0038] The temperature of the shaft gas is preferably 850°C or higher. By setting the temperature of the shaft gas to 850°C or higher, the temperature rise of the raw materials in the shaft section can be promoted, and the delay in reduction of the ore raw materials can be suppressed. On the other hand, if the temperature of the shaft gas is less than 850°C, the temperature rise of the raw materials in the shaft section slows down, which may cause a delay in reduction of the ore raw materials, and this is not preferable. The temperature of the shaft gas is more preferably 900°C or higher, and even more preferably 1000°C or higher. This makes it possible to further suppress the delay in reduction of the ore raw materials.

[0039] CO contained in shaft gas ２ and H ２ The total concentration of CO in the shaft gas is preferably 5% by volume or more. ２ and H ２ If the total concentration of O is 5% by volume or more, the precipitation of solid C from components such as CO and hydrocarbons contained in the shaft gas is suppressed, thereby suppressing the occurrence of equipment troubles such as pipe clogging. ２ and H ２ If the total concentration of O is less than 5% by volume, the amount of components such as CO and hydrocarbons contained in the shaft gas increases, and solid C may precipitate from these components, causing equipment problems such as pipe clogging, which is not preferable. ２ and H ２ The total concentration of O is more preferably 10% by volume or more.

[0040] The shaft gas is preferably produced by partially burning a reducing gas such as blast furnace gas. This increases the temperature of the shaft gas and reduces CO ２ and H ２ The total concentration of O can be 5% by volume or more. In the present embodiment, an example has been shown in which the gas obtained by partially burning a part of the blast furnace gas in the burner 22 is used as the shaft gas, but the present invention is not limited to this. The shaft gas is not limited to the blast furnace gas, and various reducing gases may be used.

[0041] <Example 1> Next, an example will be described. In Example 1, the blast furnace was operated under the following conditions: pure oxygen was blown from the tuyere as blast gas and methane was blown as a reducing agent. In Example 1, the coke rate was 340 kg / t, the ore rate was 1600 kg / t, and the blast rate was 320 Nm ３ / t, and the shaft gas injection amount V1 is 500 Nm ３ The shaft gas composition was N ２ : 1 vol%, CO: 20 vol%, CO ２ : 40% by volume, H ２ : 24% by volume, H ２ O: 15% by volume, and the shaft gas temperature was 1000°C.

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

[0043] Under these conditions, a numerical simulation of the gas flow in the furnace was carried out to evaluate the diffusion behavior of the shaft gas. The numerical simulation of the gas flow was carried out using the numerical simulation method described in Non-Patent Document 1. In order to evaluate the diffusion range of the shaft gas, a tracer chemical species (N ２ The simulation was carried out under the condition that a small amount of tracer species was mixed, and the radial flow rate distribution of the tracer species was obtained to calculate the diffusion range of the shaft gas. The operating conditions and simulation results of Example 1 are shown in Table 1 below.

[0044]

[0045] First, a numerical simulation was carried out under the conditions shown in Example 1. Next, the ore layer thickness and the coke layer thickness were not changed from Example 1, and only the shaft gas injection amount V1 was changed to 300 Nm ３ / t (Comparative Example 1) and 1000 Nm ３ A numerical simulation was carried out under the condition that the flow rate of the tracer species was increased to 1 / t (Example 2 of the invention). Then, the radial flow rate distribution of the tracer species at the furnace top was calculated for each of Example 1 of the invention, Comparative Example 1, and Example 2 of the invention. As described above, the shaft gas contained tracer species (N ２ ) is set to 1%, so that the radial flow distribution of the shaft gas can be calculated from the radial flow distribution of the tracer species at the furnace top.

[0046] The amount of shaft gas that diffused into the inner blast furnace was evaluated using the calculated value of the radial flow rate distribution of shaft gas at the furnace top. In this example, the range of less than 0.9 in normalized radius was defined as the inner blast furnace. The ratio of the shaft gas flow rate that flowed out from the inner blast furnace range to the furnace top to the total shaft gas flow rate calculated using the following formula (2) (the ratio of the shaft gas flow rate that diffused into the furnace) was evaluated as an index of the shaft gas diffusion into the furnace.

[0047] Shaft gas diffusion flow rate in the furnace (%) = (shaft gas flow rate flowing out to the furnace top from the range of normalized radius < 0.9 (Nm ３ / ton) × 100 / (total shaft gas flow rate (Nm ３ / ton))...(2)

[0048] Inventive Example 1 is an operating example in which the average value of the ratio of the ore layer to the coke layer thickness in the range B on the furnace wall side (hereinafter referred to as "average O / C") is 0.7 times the average O / C in the range A of the entire furnace. In Inventive Example 1, the in-furnace diffusion flow rate ratio of the shaft gas was 43%. In Comparative Example 1, the ore layer thickness and the coke layer thickness were the same as in Inventive Example 1, but the shaft gas injection rate V1 was increased to 300 Nm ３ / t, and the average O / C in the range B on the furnace wall side was 0.6 times the average O / C in the range A of the entire furnace. As shown in Table 1, in Comparative Example 1, the average O / C in the range B on the furnace wall side was 0.6 times the average O / C in the range A of the entire furnace, and the in-furnace diffusion flow rate ratio of the shaft gas was reduced to 33%.

[0049] In Example 2, the ore layer thickness and the coke layer thickness were the same as in Example 1, but the shaft gas injection amount V1 was increased to 1000 Nm ３ / t, and the average O / C in the range B on the furnace wall side is 0.8 times the average O / C in the range A of the entire furnace. By making the average O / C in the range B on the furnace wall 0.8 times the average O / C in the range A of the entire furnace, the diffusion flow rate of the shaft gas in the furnace increased to 51%.

[0050] These results confirmed that the in-furnace diffusion flow rate of shaft gas increases when the average O / C in the furnace wall area B is set to 0.7 times or more the average O / C in the entire furnace area A. Increasing the in-furnace diffusion flow rate of shaft gas increases the amount of shaft gas dispersed toward the center of the furnace. This promotes the temperature rise of the raw materials in the shaft section, suppresses the drop in the molten iron temperature even when operating a blast furnace with a high heat flow ratio, such as an oxygen blast furnace, and enables stable blast furnace operation.

[0051] Example 2 In Example 2, the ore layer thickness and the coke layer thickness were changed to optimize the ratio of the average O / C in the range B on the furnace wall side to the average O / C in the range A of the entire furnace, as compared to Comparative Example 1, in which the in-furnace diffusion flow rate ratio of the shaft gas was reduced in Example 1. The operating conditions and simulation results of Example 2 are shown in Table 2 below.

[0052]

[0053] Inventive Example 3 is an operational example in which the average O / C in the furnace wall-side range B is 0.8 times the average O / C in the entire furnace range A. As shown in Table 2, by setting the average O / C in the furnace wall-side range B to 0.8 times the average O / C in the entire furnace range A, the in-furnace diffusion flow rate of the shaft gas was 36%, which was higher than that of Comparative Example 1. Inventive Example 4 is an operational example in which the average O / C in the furnace wall-side range B is 1.0 times the average O / C in the entire furnace range A. As shown in Table 2, by setting the average O / C in the furnace wall-side range B to 1.0 times the average O / C in the entire furnace range A, the in-furnace diffusion flow rate of the shaft gas was 38%, which was a further increase.

[0054] Example 1 is an example in which the shaft gas injection rate was changed while the ore and coke layer thickness distribution, i.e., the burden distribution, was kept constant. Changing the shaft gas injection rate also changes the range B on the furnace wall where the shaft gas is present. Therefore, as shown in Comparative Example 1 in Table 1, if the burden distribution is kept the same as in Example 1, it is not possible to appropriately increase the airflow resistance in the range B on the furnace wall where the shaft gas is present, and it was confirmed that the diffusion flow rate of the shaft gas within 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 furnace wall area B where the shaft gas exists after changing the shaft gas injection rate. As a result, the in-furnace diffusion flow rate ratio of the shaft gas in Invention Examples 3 and 4 was increased compared to the in-furnace diffusion flow rate ratio of the shaft gas in Comparative Example 1. From these results, it was confirmed that the in-furnace diffusion flow rate ratio of the shaft gas was increased by 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 furnace wall area B where the shaft gas exists.

[0056] 10 Blast furnace 12 Swivel chute 14 Coke layer 16 Ore layer 18 Tuyere 19 Raceway 20 Injection tube 22 Burner

Claims

1. A method for operating a blast furnace, in which coke and ore are alternately charged from the top of the blast furnace to form alternate coke layers and ore layers inside the blast furnace, blast gas is blown in from a tuyere provided in the lower part of the blast furnace, and shaft gas is blown in from an injection pipe provided in the shaft part of the blast furnace, ３ / t), and the amount of bosh gas generated by the blast gas blown in from the tuyere is V2 (Nm ３ / t), the normalized radius of the blast furnace, with the center position of the blast furnace being 0.00 and the furnace wall position of the blast furnace being 1.00, is (V2 / (V1+V2)) ０．５ a ratio of the ore layer thickness to the coke layer thickness charged in a range of a normalized radius of 0.00 to 1.00 is set to 0.7 times or more the ratio of the ore layer thickness to the coke layer thickness charged in a range of a normalized radius of 0.00 to 1.

00.

2. The method for operating a blast furnace according to claim 1, wherein V2 / (V1+V2) is 0.5 or more.

3. A method for operating a blast furnace as set forth in claim 1 or claim 2, wherein the heat flow ratio within the furnace below the height at which the injection pipe is installed is 0.9 or more.

4. A 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 shaft gas ２ Concentration and H ２ The method for operating a blast furnace according to claim 1 or 2, wherein the total of the concentration of sintered steel and the concentration of O is 5% by volume or more.

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

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

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