Blast furnace operation method

Abstract

To provide a blast furnace operation method for, when charging new coke into a furnace and then charging a raw material, preventing breakage of a tuyere and occurrence of fittg.SOLUTION: There is provided a blast furnace operation method configured so that: a height of a raw material charging layer surface is lowered to a tuyere height of a blast furnace and wind supply is stopped, then wind supply is started again, the blast furnace operation method is configured to: blow an oxygen-containing gas from a burner which is inserted into a tap hole after stop of wind supply to the blast furnace; burn coke which is left in the furnace for reducing volume of a residue in the furnace; charge new coke from a throat to a front side of the blast furnace, in a volume reduction region of the residue in the furnace; then, when using a revolving chute for charging the raw material into the blast furnace, at the time, charge the raw material into the furnace without using a tilt angle at which, a raw material falling position of the raw material charged from the revolving chute, is a position of the tuyere or lower angle, then supply wind from the tuyere.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for operating a blast furnace when the operation is stopped, the blast furnace is shut down, and then blasting is started again. [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 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 and becomes a solidified material. When restarting the blast from this state, the solidified material in 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 blast, 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 a blast shutdown, 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 to reduce the volume of the solidified material, new coke is poured into the reduced volume area from the top of the furnace to the tip of the tuyere, and then the raw materials are loaded into the blast furnace using a rotating chute, and then air is blown in from the tuyere, thereby restoring the blast furnace to normal operation.

[0005] Furthermore, Patent Document 2 discloses that when performing reduction operation or reduction return operation to lower the raw material charging level of a blast furnace, the tilting angle of the rotating chute is adjusted in accordance with the raw material charging level, since the falling position of the raw materials will differ if the raw material charging level changes, even if the tilting angle of the rotating chute is the same. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6947345 [Patent Document 2] Japanese Patent Application Publication No. 9-157711 Summary of the Invention [Problem to be solved by the invention]

[0007] In both Patent Documents 1 and 2, a burner is inserted from the tap hole, and oxygen or the like is blown from the burner to burn the coke between the tap hole and the tuyere to reduce the volume of the solidified material, after which new coke is charged in front of the tuyere, and then raw materials are charged using a rotating chute. Since the surface height of the raw material packed bed is reduced to the tuyere height before the air is stopped, when the raw materials are charged from the rotating chute, part or all of the tuyere is exposed. For this reason, there was a problem that the raw materials charged into the furnace from the rotating chute directly collided with the tuyere that protruded from the furnace wall bricks into the furnace, causing damage or displacement of the tuyere (a phenomenon in which the mating surfaces of the large tuyere and the small tuyere are misaligned to create a gap, resulting in air leakage, etc.).

[0008] The object of the present invention is to propose a blast furnace operation method in which operation is stopped, the blast furnace is tuned off, and then blasted again, which can prevent damage or displacement of the tuyere when new coke is charged into the furnace and then raw materials are charged. [Means for solving the problem]

[0009] The blast furnace operation method of the present invention was developed to solve the above-mentioned problems, and is a blast furnace operation method in which the height of the surface of the raw material packed bed is reduced to the height of the tuyere of the blast furnace, air is stopped, and then air is blown again. After the blast furnace is stopped, oxygen-containing gas is blown in from a burner inserted into the tap hole to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace, new coke is charged into the area where the volume of the residue in the furnace has decreased from the throat to the front of the tuyere of the blast furnace, and then, when charging raw materials into the blast furnace using a rotating chute, the raw materials are charged into the furnace without using a tilting angle less than that which causes the raw materials to fall from the rotating chute to the tuyere position, and then air is blown from the tuyere.

[0010] In addition, in the blast furnace operation method of the present invention, (1) Charging the raw materials into the furnace without using the tilting angle until the raw materials pile up on the tuyere reaches a thickness of 1 m; (2) Charging the raw materials so that the inclination angle of the pile surface of the raw materials is 35° or less with respect to the horizontal plane; are each considered to be a preferred embodiment. Effect of the Invention

[0011] 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 reduced to the tuyere height, air is stopped, and then air is blown again, it is possible to stably restart the blast furnace while suppressing the occurrence of tuyere damage or displacement. [Brief description of the drawings]

[0012] [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 showing a situation in which raw materials are charged while avoiding the tuyere. [Figure 6] 1 is a schematic cross-sectional view showing the state after the raw materials are charged so that the inclination angle of the raw material stacking surface is 35° or less with respect to the horizontal plane. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] <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. 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 to the height of the tuyere of the blast furnace and the blast furnace is shut down. To return the blast furnace to normal operation by blowing hot air from the tuyere, a burner is first inserted from the tap hole, and oxygen-containing gas or oxygen-containing gas and combustible gas are blown from the burner to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace.

[0015] 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.

[0016] 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 outside the outer tube for measuring the burner temperature. 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.

[0017] Combustion is started by stopping the cooling caused by the gas flow from the inner tube to the outer tube, dissolving and removing the cap, and then, for example, blowing a combustible gas into the furnace from the inner tube of the burner, and blowing an oxygen-containing gas into the lower part of the furnace from the outer tube as a combustion supporting gas. When the temperature at the tip of the burner exceeds the combustion start temperature of the surrounding coke (approximately 800°C), the gas blown from the burner is switched to only the oxygen-containing gas to burn the coke. It is preferable to blow pure oxygen as the oxygen-containing gas, but a gas with an oxygen concentration lower than 100% may be used as long as the coke combustion can be sustained.

[0018] Fig. 4 is a schematic cross-sectional view showing a state in which the volume of the furnace residue is reduced by burning the remaining coke using a burner. In the embodiment shown in Fig. 4, when the coke is burned away by combustion, further coke rolls into the space where the burned coke has disappeared according to the angle of repose, and the coke is burned away. In this way, the remaining coke is burned away one after another, and the volume of the furnace residue is reduced as shown in Fig. 4. In the process of reducing the volume of the furnace residue, the furnace residue remaining on the tuyere is also eliminated.

[0019] Fresh coke is charged into the volume reduction area where the volume of the furnace residue has decreased, as shown in Figure 4. Fresh coke is charged from the furnace throat until the coke is filled in front of the tuyere. This forms a highly permeable coke layer in front of the tuyere.

[0020] After that, the raw materials are charged into the blast furnace using a rotating chute. From the rotating chute, raw ore materials such as sintered ore and lump ore and coke are alternately charged, and ore layers and coke layers are alternately formed in the blast furnace. As the raw ore materials, for example, sintered ore having a harmonic mean of 9 mm and an arithmetic mean diameter of 16 mm can be used. As the coke, for example, coke having a harmonic mean of 43 mm and an arithmetic mean diameter of 56 mm can be used. After a predetermined amount of raw materials is charged into the blast furnace, hot air is blown from the tuyere to resume blast furnace operation.

[0021] <Features of the blast furnace operation method according to this embodiment> A feature of the blast furnace operation method according to this embodiment is that when raw materials are charged into a blast furnace using a rotating chute, the raw materials are charged into the furnace without using a tilting angle that would cause the raw materials to fall from the rotating chute to the tuyere position.

[0022] FIG. 5 is a schematic cross-sectional view showing a situation in which raw materials are charged while avoiding the tuyere. Each line shown in FIG. 5 shows the falling trajectory of the raw materials from the rotating chute at each tilting angle. When the tilting angle of the rotating chute is increased, the raw materials are charged toward the center of the furnace, and when the tilting angle of the rotating chute is decreased, the raw materials are charged toward the furnace wall. In the blast furnace operation method according to the present embodiment, when raw materials are charged from the rotating chute, the raw materials are charged into the blast furnace without using a tilting angle of the rotating chute below which the falling position of the raw materials supplied from the rotating chute becomes the tuyere position. As described above, in the process of burning the remaining coke using a burner, the residue in the furnace on the tuyere disappears, so even if new coke is charged up to the front of the tuyere, the upper surface of the tuyere is exposed. For this reason, if the raw materials supplied from the rotating chute directly collide with the tuyere, the impact may damage the tuyere or cause the tuyere to shift. In response to this, by charging raw materials without using the tilt angle of the rotating chute below the tilt angle at which the falling position of the raw materials supplied from the rotating chute is the tuyere position, it is possible to stably resume blast furnace operation while suppressing the occurrence of tuyere damage and tuyere misalignment. The tilt angle of the rotating chute that is not used can be determined in advance by determining the falling position of the raw materials at each tilt angle at the tuyere height. For example, if the internal volume is 5000 m 3 In the case of using a blast furnace in which a tuyere is provided at the lower end of the morning glory of the blast furnace, if the tilt angle of the rotating chute is set to 26.3°, the falling position of the raw material charged from the rotating chute will be the tuyere position, so the raw material is charged into the furnace without using a tilt angle of 26.3° or less among the tilt angles of the rotating chute. The tilt angle of the rotating chute is controlled by notches 1 to 25. The tilt angle of 1 notch is 52.5°, the tilt angle of 20 notches is 26.3°, and the tilt angle of 25 notches is 12.0°. Therefore, in the blast furnace operation method according to this embodiment, the raw material is charged into the furnace from the rotating chute using a tilt angle of 1 to 19 notches without using notches 20 to 25.

[0023] On the other hand, even if the tilt angle is not used, some of the raw materials charged near the tuyere will flow onto the tuyere. If the raw materials are piled up to a height of 1m on the tuyere by this flow, the raw materials will cushion the impact even if the raw materials are charged at the tuyere position, so damage to the tuyere is suppressed. Therefore, until the raw materials pile up on the tuyere reaches 1m in thickness, the raw materials are charged without using a tilt angle of the rotating chute below which the raw materials fall to the tuyere position. On the other hand, if the raw materials are continuously charged into the furnace without using a tilt angle (for example, a tilt angle of 26.3° or less as mentioned above) that prevents the raw materials from falling to the periphery even after the raw materials pile up on the tuyere reaches 1m in thickness, unintended segregation of coke, sintered ore, and lump ore will occur due to the flow caused by the gradient of the raw materials surface in the furnace. If there is an area where sintered ore and lump ore are distributed excessively, (1) the furnace heat will decrease due to poor reduction, and (2) the permeability will deteriorate due to the expansion of the cohesive zone, which may hinder smooth start-up operation. Therefore, after the thickness of the raw material pile above the tuyere reaches 1m, the normal tilt angle of the rotating chute is used to prevent a gradient from forming on the surface of the raw materials inside the furnace (for example, a tilt angle of 26.3° or less as mentioned above), and the raw material charging is controlled to prevent unintended segregation of the raw materials, enabling the blast furnace to be started up stably. The raw material pile thickness above the tuyere can be found by determining the height of the raw material pile surface at the tuyere position using sauging, and subtracting the height from that height to the top surface of the tuyere.

[0024] FIG. 6 is a schematic cross-sectional view showing the state after the raw materials are charged so that the inclination angle of the raw material pile surface is a horizontal plane. In the embodiment shown in FIG. 6, the combustion of the remaining coke using a burner does not burn off the furnace residues at the center of the furnace, so the raw material pile surface in the furnace at the start-up after a long period of cooling is higher at the center of the furnace and lower at the periphery. If sintered ore is charged in this state where the raw material pile surface in the furnace is inclined, it will flow excessively to the periphery, causing poor ventilation and making the operation of the blast furnace unstable. For this reason, it is preferable to charge the raw materials so that the inclination angle of the raw material pile surface in the furnace is 35° or less with respect to the horizontal plane. This suppresses excessive flow of the raw materials to the periphery at the start-up, which can contribute to the stabilization of blast furnace operation by suppressing poor ventilation. [Industrial Applicability]

[0025] According to the blast furnace operation method of the present invention, a smooth start-up of the blast furnace can be realized even after a long period of blast shutdown.

Claims

1. A blast furnace operation method in which the height of the surface of the raw material packed bed is reduced to the height of the tuyere of the blast furnace, air is stopped, and then air is blown again, A method for operating a blast furnace, comprising the steps of: after shutting down the blast furnace, blowing in oxygen-containing gas from a burner inserted into the tap hole, burning the coke remaining in the furnace and reducing the volume of the residue in the furnace; charging new coke into the area where the volume of the residue in the furnace has decreased from the throat to the front of the tuyere of the blast furnace; and then, when charging raw materials into the blast furnace using a rotating chute, not using a tilting angle less than that which causes the raw materials to fall from the rotating chute to the tuyere position, and then blowing air from the tuyere.

2. The method for operating a blast furnace according to claim 1, wherein the raw materials are charged into the furnace without using the tilting angle until the raw materials pile up on the tuyere reaches a thickness of 1 m.

3. The method for operating a blast furnace according to claim 2, wherein the raw materials are charged so that an inclination angle of a pile surface of the raw materials is 35° or less with respect to a horizontal plane.

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