Blast furnace operation method

Abstract

To propose a blast furnace operation method configured to suspend an operation, stop blasting at a blast furnace, and then resume blasting, the blast furnace operation method capable of smoothly loading new coke into a volume-decreased region where coke has burned, and capable of stably starting a blast furnace.SOLUTION: A blast furnace operation method is for stopping blasting while reducing a height of a surface of a raw material packed bed directly above a tuyere of a blast furnace to be lower than a height of a bosh part top edge of the blast furnace, and thereafter resuming blasting. The blast furnace operation method is configured to: after stopping blasting at the blast furnace, blow at least oxygen by a burner inserted from a tap hole into the furnace; burn coke remaining inside the furnace to reduce a volume of a residual material inside the furnace; and after charging new coke to a region where the volume is decreased, conduct blasting from the tuyere. The blast furnace is configured to, before charging the new coke to the region where the volume is decreased, break a residual coke surface layer which will be an obstacle of the charging of the new coke, by breaking means.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for operating a blast furnace for stopping operation, shutting down the blast furnace, and then restarting blasting. [Background technology]

[0002] A blast furnace is a facility that heats, reduces, and melts iron ore using high-temperature reducing gas generated by the reaction between high-temperature air and oxygen blown in from numerous tuyere ports arranged in the direction of the blast and coke charged from the top of the furnace together with the raw materials, and discharges the molten iron and molten slag from a tap hole installed below the tuyere. During normal operation of a blast furnace, the reaction heat inside the furnace and the heat supply from the tuyere are balanced, allowing for stable operation of the blast furnace.

[0003] Here, when the blast furnace is shut down or stopped for a long time, the heat supply to the blast furnace is stopped. On the other hand, because the heat radiation continues due to the temperature difference between the inside of the blast furnace and the atmosphere, the cooling inside the furnace progresses and some of the molten material solidifies. When the blast furnace is restarted, the solidified layer inside the furnace must be melted, and for that, the coke packed layer through which the solidified material passes must be heated. For this reason, when the blast furnace is shut down for a long time or when it is expected to be restarted, the coke ratio in the furnace is increased to shut down the furnace, and thermal compensation is performed until the injection of pulverized coal can be started after the blast. At the same time, all but one or two tuyere openings above the tap hole are blocked with refractories, etc., to limit the amount of molten iron and slag generated with the blast, and a cycle of smooth discharge of a small amount of molten material is established. After that, the adjacent tuyere is opened, and the number of open tuyere openings is gradually increased, and normal operation is restored.

[0004] As a method for restoring a blast furnace to normal operation after cessation of blowing, Patent Document 1 discloses that a burner is inserted from the tap hole and oxygen or the like is blown in from the burner to burn the coke between the tap hole and the tuyere and reduce the volume of the solidified material, and then new coke is poured into the area of ​​reduced volume from the top of the furnace and blown in air from the tuyere, thereby restoring the blast furnace to normal operation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6947345 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, it is said that in order to reduce pressure loss and ensure the air and liquid permeability of the coke packed bed, it is desirable to set the coke replacement rate to 0.65 or more. It is necessary to fill the volume reduction area where the coke is burned with the burner with new coke to ensure air and liquid permeability. However, with the method of Patent Document 1, there is a risk that the upper part of the combustion space will be covered with residue, making it impossible to fill the volume reduction area where the coke is burned with new coke.

[0007] The object of the present invention is to propose a blast furnace operation method in which operation is stopped, the blast furnace is tuned down, and then blasted again, which enables new coke to be smoothly filled into the volume-reduced area where coke has been burned, thereby enabling the blast furnace to be started up stably. [Means for solving the problem]

[0008] The blast furnace operation method of the present invention was developed to solve the above-mentioned problems, and is a blast furnace operation method for reducing the height of the surface of the raw material packed bed directly above the tuyere to be lower than the height of the upper end of the blast furnace morning glory, shutting down the blast furnace, and then starting air blowing again. After shutting down the blast furnace, at least oxygen is blown in from a burner inserted from the tap hole toward the inside of the furnace to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace, and after new coke is charged into the volume reduction area, air is blown from the tuyere. In this blast furnace operation method, before new coke is charged into the volume reduction area, the surface layer of the residual coke that would hinder the charging of the new coke is destroyed by a destruction means.

[0009] In addition, in the blast furnace operation method of the present invention, (1) The destruction is carried out by dropping a destruction means suspended from the upper part of the blast furnace onto the surface layer of the residual coke; (2) The destruction is carried out by a destruction means suspended from the upper part of the blast furnace lifting up the surface layer of the residual coke; (3) The destruction means is a dummy cooling stave (dummy CS), are each considered to be a preferred embodiment. Effect of the Invention

[0010] According to the blast furnace operation method of the present invention, in blast furnace operation in which the surface of the raw material packed bed directly above the blast furnace tuyere is lowered below the upper end of the blast furnace morning glory to stop blowing air, and then blowing air again, new coke can be smoothly charged into the volume-reduced section where the coke has been burned, making it possible to perform a stable start-up. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a part of a cross section of a furnace body of a blast furnace. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the lower part of a blast furnace showing the state in which a burner is inserted from the tap hole. [Diagram 3] FIG. 2 is a schematic diagram showing an example of a burner. [Figure 4] FIG. 2 is a schematic cross-sectional view showing a state in which the volume of the residue in the furnace is reduced by burning the remaining coke using a burner. [Diagram 5] FIG. 2 is a schematic cross-sectional view illustrating a method for destroying the surface layer of the residual coke by suspending a destruction means from the top of the furnace and dropping it onto the surface layer of the residual coke. [Figure 6] FIG. 2 is a schematic cross-sectional view illustrating a method for destroying the residual coke surface layer by lowering a destruction means from the furnace top and lifting up the residual coke surface layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present invention will be described in detail. Note that the following embodiments are merely examples of devices and methods for embodying the technical idea of ​​the present invention, and the configuration is not limited to the one described below. In other words, the technical idea of ​​the present invention can be modified in various ways within the technical scope described in the claims. In addition, in the following embodiments, an example of a blast furnace operation method that is the subject of the present invention will be described, and then the features of the blast furnace operation method of the present invention will be described.

[0013] <One example of a blast furnace operation method to which the present invention is applied> FIG. 1 is a schematic cross-sectional view showing a part of the cross section of the furnace body of a blast furnace. As shown in FIG. 1, the blast furnace according to this embodiment has a shaft, a furnace belly, a morning glory, a hearth, and a tuyere. In the embodiment shown in FIG. 1, when the blast furnace is shut down for a long period of time, the height of the surface of the raw material packed bed directly above the tuyere of the blast furnace is reduced below the upper end of the morning glory of the blast furnace to shut down the blast furnace. After that, in order to blow hot air from the tuyere to return the blast furnace to normal operation, first, a burner is inserted from the tap hole, and oxygen or oxygen and nitrogen are blown from the burner to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace. Instead of nitrogen, LNG may be blown in.

[0014] Fig. 2 is a schematic cross-sectional view of the lower part of a blast furnace showing a state where a burner is inserted from the tap hole. In the embodiment shown in Fig. 2, the tap hole is blocked with a material called mud material when the blast furnace is not blown, so in order to insert a burner into the furnace, the tap hole blocked with mud material is first opened. A known tap hole opening machine can be used to open the tap hole. After the tap hole is opened, a burner is inserted from the tap hole into the lower part of the blast furnace.

[0015] 3(a) and (b) are schematic diagrams showing an example of a burner. In the embodiment shown in FIG. 3(a) and (b), the burner has a double-tube structure of an inner tube and an outer tube through which gas flows, and has a cap covering the ends of the inner tube and the outer tube, and a thermocouple for measuring the burner temperature outside the outer tube. When the cap is present as shown in FIG. 3(a), the gas blown in from the gas inlet of the inner tube is discharged from the gas outlet of the outer tube without leaking to the outside. On the other hand, when the cap is not present as shown in FIG. 3(b), the gas blown in from the gas inlet of the inner tube is supplied into the furnace. Therefore, the burner has a function of cooling the burner by flowing gas from the inner tube to the outer tube with the cap present, so that the burner can be stably inserted into the furnace.

[0016] In addition, the combustion is started by stopping the cooling caused by the flow of gas from the inner tube to the outer tube, dissolving and removing the cap, and for example, blowing oxygen into the furnace from the inner tube of the burner and blowing nitrogen into the lower part of the furnace from the outer tube. The blowing of nitrogen is performed to prevent wear due to cooling of the tip of the burner. If only oxygen is blown in, the burner will wear out in a short time. Blowing of nitrogen is also effective in preventing explosions. After the blast furnace is stopped, combustion is performed by blowing in a mixed gas of oxygen and nitrogen so that the ratio of nitrogen / oxygen blown in from the inner tube and the outer tube is 1 to 2. It is desirable to blow the mixed gas of oxygen and nitrogen into the red-hot coke at 800°C to 1000°C immediately after the cessation of the blast furnace. By blowing it in immediately after the cessation of the blast furnace, early combustion of the residual coke can be expected. Even if the coke has not reached 800°C immediately after the cessation of the blast furnace, the temperature is raised by blowing in the mixed gas of oxygen and nitrogen, and then combustion is started. Note that LNG may be blown in instead of nitrogen.

[0017] Fig. 4 is a schematic cross-sectional view showing a state in which the volume of the residue in the furnace is reduced by burning the remaining coke using a burner. In the embodiment shown in Fig. 4, when the coke is burned off by combustion, more coke rolls into the space vacated by the burning according to the angle of repose, and the volume of the residue in the furnace is reduced as the coke is burned off one by one.

[0018] <Features of the blast furnace operation method of the present invention> The feature of the blast furnace operation method of the present invention is that new coke is charged after the surface layer of the residual coke, which becomes an obstacle when new coke is charged into the volume-reduced area of ​​the furnace residue where the volume has been reduced, is destroyed by a destruction means.

[0019] Fig. 5 is a schematic cross-sectional view illustrating a method for breaking the surface of the residual coke by lowering a breaking means from the furnace top and dropping it onto the surface of the residual coke. In the embodiment shown in Fig. 5, the breaking means is suspended by a furnace top crane to above the volume reduction region of the furnace residue. After positioning the breaking means in this manner, the breaking means is dropped onto the surface layer of the volume reduction region. This breaks the surface layer of the volume reduction region, and prevents any obstacles from being impeded when new coke is charged into the volume reduction region.

[0020] Fig. 6 is a schematic cross-sectional view illustrating a method for breaking the surface of the residual coke by lowering a breaking means from the furnace top and lifting the surface layer of the residual coke. In the embodiment shown in Fig. 6, the breaking means is suspended above the volume reduction region of the furnace residue by a furnace top crane. After positioning the breaking means in this manner, the breaking means is dropped onto the surface layer of the volume reduction region. Thereafter, as shown in Fig. 6, the surface layer of the residual coke is lifted by the breaking means, breaking the surface layer of the volume reduction region, and eliminating the obstacle when new coke is charged into the volume reduction region.

[0021] A dummy CS was used as a destruction tool to remove the surface residues using an actual machine. A dummy CS is a device of the same weight and size but does not have the function of a CS. A dummy CS is used when suspending or lifting the CS in a blast furnace during a pre-test of CS renewal. CS is also an abbreviation for cooling stave. By attaching a CS to the inside of a blast furnace and passing water through the CS, it serves to protect the steel shell on the outside of the blast furnace body from powder breakage due to thermal expansion. The dummy CS can be used as a destruction tool to suspend the residual coke surface layer as shown in Figure 5 or lift it up as shown in Figure 6, thereby destroying the residual coke surface layer.

[0022] In addition, when surface residues were removed by suspending and lifting a dummy CS, there were cases where the suspending speed of a 5t hoist was too slow to destroy the surface residues by suspending. In such cases, since a 5t hoist has a strong lifting force, it is preferable to weld a 500mm plate to the dummy CS as a claw and destroy it by suspending. Note that an example of using a dummy CS as a destruction means when suspending and lifting is shown here. However, any destruction means when suspending can be used as long as it has a certain amount of weight. In addition, any destruction means when suspending can be used as long as it has a certain amount of weight and has a claw. EXAMPLES

[0023] Internal volume 5000m 3 In the blast furnace, the height of the top surface of the packed bed of raw materials in the furnace directly above the tuyere was reduced to 1 m below the top end of the blast furnace morning glory and the furnace was shut down. Immediately after shutting down the blast furnace, a burner as shown in Figure 3(a) was installed at the tap hole so that its tip was at 0.4 of the dimensionless radius inside the furnace, and a mixture of oxygen and nitrogen was blown into the red-hot coke at 800°C and burned. The mixed gas was blown so that the nitrogen / oxygen ratio was 1 to 2. When coke was present at the tip of the burner, the blown oxygen was almost entirely consumed by combustion, but when the coke at the tip of the burner disappeared and the state became like the coke packed bed in Figure 4, the amount of oxygen consumed decreased. Therefore, the extent to which the coke was consumed can be determined by measuring the oxygen concentration in the furnace. After confirming that the oxygen concentration in the furnace had increased, the blowing of oxygen from the tap hole burner was stopped. The residue that formed a skin on the surface of the burned and reduced volume was destroyed by a dummy CS that was inserted and hung from the top of the blast furnace. After that, unused coke was charged from the top of the blast furnace. The tap hole burner was fired again to heat the newly charged coke, and when the temperature of the coke at the tip of the tuyere exceeded 2000°C, hot air at 1100°C was blown from the tuyere, and heating was switched to the tuyere to start up the blast furnace. The molten material in the furnace was discharged smoothly, and steady operation was achieved without any problems. [Industrial Applicability]

[0024] According to the blast furnace operation method of the present invention, a stable operation method can be provided not only for restarting a blast furnace, but also for various vertical melting furnaces other than a blast furnace.

Claims

1. A blast furnace operation method for reducing the height of the surface of the raw material packed bed directly above the tuyere to below the height of the upper end of the blast furnace morning glory, shutting down the blast furnace, and then starting blowing again, in which after shutting down the blast furnace, at least oxygen is blown in from a burner inserted from the tap hole toward the inside of the furnace to burn the coke remaining in the furnace, reducing the volume of the residue in the furnace and forming a volume reduction region, and new coke is charged into the volume reduction region before blowing air from the tuyere, in which, before charging new coke into the volume reduction region, a surface layer of the residual coke that would hinder the charging of the new coke is destroyed by a destruction means.

2. The blast furnace operating method according to claim 1 , wherein the destruction is carried out by dropping a destruction means suspended from an upper portion of the blast furnace onto a surface layer of the residual coke.

3. The blast furnace operating method according to claim 1 , wherein the destruction is carried out by a destruction means suspended from an upper portion of the blast furnace lifting up the surface layer of the residual coke.

4. The blast furnace operation method according to any one of claims 1 to 3, wherein the destructive means is a dummy cooling stave (dummy CS).

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