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 accurately obtaining a progress of coke burning and accurately knowing completion of the burning, 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 if it is determined that burning of the coke near the burner is completed according to a gas configuration of CO and CO2 inside the furnace, after charging new coke to a region where the volume is decreased, conduct blasting from the tuyere.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

[0002] A blast furnace heats, reduces, and melts iron ore by the reaction of high-temperature air or oxygen blown from a large number of tuyeres arranged in the blowing direction with coke charged together with raw materials from the furnace top, and discharges hot metal and molten slag to the outside of the furnace through the taphole installed below the tuyere. During normal operation of the blast furnace, since the reaction heat in the furnace and the heat supply from the tuyere are balanced, stable operation of the blast furnace is possible.

[0003] Here, when the blast furnace is shut down or stopped for a long time, the heat supply into the blast furnace stops. On the other hand, since heat dissipation continues due to the temperature difference between the inside of the blast furnace and the atmosphere, cooling inside the furnace progresses, and some of the melt solidifies. When restarting the blast, the solidified layer inside the furnace must be melted, and for this purpose, it is necessary to heat the coke-packed layer through which the solidified matter passes. Therefore, when the blast furnace is shut down for a long time or during a stoppage when restart is expected, the coke ratio inside the furnace is increased before shutting down the blast, and heat compensation is performed until the injection of pulverized coal can be started after the blast. At the same time, except for one or two tuyeres above the taphole, the others are blocked with refractories or the like to limit the amount of hot metal slag generated with the blast and establish a cycle for smooth discharge of a small amount of melt. Then, the tuyeres in the adjacent part are opened, and the number of opened tuyeres is gradually increased to restore normal operation.

[0004] As a method for restoring the blast furnace to normal operation after shutting down the blast, Patent Document 1 discloses that a burner is inserted from the taphole, oxygen or the like is blown from the burner to burn the coke between the taphole and the tuyere to reduce the volume of the solidified matter, and then new coke is charged from the furnace top into the volume reduction region, and by blowing air from the tuyere, the blast furnace can be restored to normal operation.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Patent Document 1, in order to consume the in-furnace residue as much as possible, the rise of O 2 gas is used to judge the combustion of the remaining coke. However, Patent Document 1 does not provide a clear threshold for the O 2 concentration, and moreover, it is impossible to accurately judge the progress of combustion only by the gentle rise of O 2 gas, and it is impossible to accurately know the completion of the combustion of the remaining coke. Therefore, it is impossible to accurately know the formation time of the volume reduction region and the charging time of the new coke in the next process, and it is impossible to smoothly start up the blast furnace. Furthermore, since the range of the remaining coke that the burner can burn is limited, it may be necessary to push the burner into the furnace several times to expand the combustion region and form a volume reduction region. Also in this case, since it is impossible to accurately know the completion of the combustion of the remaining coke, there is a risk of delaying the expansion of the combustion region in a state where the temperature in the furnace is high after the blast is stopped.

[0007] An object of the present invention is to propose a blast furnace operation method in which the operation is stopped, the blast furnace is stopped from blowing, and then blowing is resumed again, and in which the progress of the combustion of coke can be accurately determined and the completion of combustion can be accurately known, and a smooth and stable start-up of the blast furnace can be performed.

Means for Solving the Problems

[0008] The blast furnace operation method of the present invention is a blast furnace operation method in which the height of the surface of the raw material charging layer directly above the tuyere of the blast furnace is reduced below the height of the upper end of the morning glory part of the blast furnace, and then the blast is restarted. After the blast furnace is shut down, at least oxygen is blown from a burner inserted into the furnace from the tapping hole, and the coke remaining in the furnace is burned to reduce the volume of the residues in the furnace. When the combustion of the coke near the burner is judged to be completed from the gas composition of CO and CO 2 in the furnace, after newly charging coke into the volume reduction region where the volume of the residues in the furnace has been reduced, the blast is carried out from the tuyere. This is the blast furnace operation method.

[0009] In the blast furnace operation method of the present invention, (1) When the gas composition of CO and CO 2 in the furnace becomes less than 1%, it is judged that the combustion of the coke near the burner is completed. (2) When it is judged that the combustion of the coke near the burner is completed, the burner is further pushed into the furnace to burn the remaining coke at least once, thereby forming the volume reduction region. are considered to be preferable embodiments respectively.

Advantages of the Invention

[0010] According to the blast furnace operation method of the present invention, in the blast furnace operation in which the surface of the raw material charging layer directly above the tuyere of the blast furnace is reduced below the upper end of the morning glory part of the blast furnace and then the blast is restarted, the progress of the combustion of the coke can be accurately determined and the completion of the combustion can be accurately known. Since new coke can be smoothly charged into the volume reduction region where the coke has been burned, stable startup can be achieved.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be specifically described. Note that the following embodiments illustrate devices and methods for embodying the technical idea of the present invention, and do not specify the configuration to be the following. That is, the technical idea of the present invention can be variously modified within the technical scope described in the claims. Further, in the following embodiments, after explaining an example of the blast furnace operation method targeted by the present invention, the features of the blast furnace operation method of the present invention will be explained.

[0013] <Regarding an example of the blast furnace operation method targeted by the present invention> FIG. 1 is a schematic cross-sectional view showing a part of the cross-section of a blast furnace body. As shown in FIG. 1, the blast furnace according to the present embodiment has a shaft section, a hearth section, a tuyere section, a furnace bottom, and a tuyere. In the embodiment shown in FIG. 1, when the blast furnace is shut down for a long period, the height of the surface of the raw material charging layer directly above the tuyere of the blast furnace is reduced below the upper end of the tuyere section of the blast furnace before shutting down. Thereafter, to return the blast furnace to normal operation by blowing hot air from the tuyere, first, a burner is inserted from the tapping hole, oxygen or oxygen and nitrogen are blown from the burner, and the coke remaining in the furnace is burned to reduce the volume of the furnace residues. Instead of nitrogen, LNG may be blown in.

[0014] Figure 2 is a schematic cross-sectional view of the lower part of a blast furnace showing the state where a burner is inserted from the taphole. In the embodiment shown in Figure 2, since the taphole is closed with a material called mud material during the blast furnace shutdown, in order to insert the burner into the furnace, first, the taphole closed with the mud material is opened. A known taphole opening machine can be used for opening the taphole. After the taphole is opened, the burner is inserted from the taphole into the lower part of the blast furnace.

[0015] Figures 3(a) and (b) are schematic views showing an example of the burner. In the embodiment shown in Figures 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 exists as shown in Figure 3(a), the gas blown 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 does not exist as shown in Figure 3(b), the gas blown from the gas inlet of the inner tube is supplied into the furnace. Therefore, since the burner has a function of cooling the burner by flowing gas from the inner tube to the outer tube with the cap present, the burner can be stably inserted into the furnace.

[0016] Also, for combustion start, the cooling by the gas flow from the inner tube to the outer tube is stopped, the cap is melted and removed, for example, oxygen is blown into the furnace from the inner tube of the burner, and nitrogen is blown into the lower part of the furnace from the outer tube. The blowing of nitrogen is performed to prevent wear due to cooling at the tip of the burner. If only oxygen is blown, the burner will be worn out in a short time. Also, the blowing of nitrogen is effective for explosion prevention. After the blast furnace shutdown, combustion is carried out by blowing a mixed gas of oxygen and nitrogen so that the ratio of nitrogen / oxygen blown from the inner tube and the outer tube becomes 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 shutdown. By blowing immediately after the shutdown, early combustion of the residual coke can be expected. Even if the coke immediately after the shutdown has not reached 800°C, the temperature is raised by blowing the mixed gas of oxygen and nitrogen, and then combustion is started. Note that LNG may be blown instead of nitrogen.

[0017] FIG. 4 is a schematic cross-sectional view showing a state in which residual coke is burned using a burner to reduce the volume of the in-furnace residue. In the embodiment shown in FIG. 4, when the coke is burned out by combustion, the coke rolls into the space where the combustion has disappeared according to the angle of repose, and as the coke is sequentially burned out, the volume of the in-furnace residue decreases.

[0018] Here, the oxygen blown from the burner is almost consumed by combustion when coke exists at the tip of the burner. However, when the coke at the tip of the burner disappears and a state like the coke packed bed in FIG. 4 is reached, the consumption of oxygen decreases. Therefore, by measuring the oxygen concentration in the furnace, it is possible to know to what extent the coke has been consumed. However, since the oxygen concentration rises gradually, it is impossible to accurately grasp the progress of combustion, and there may be an error in judging the completion of combustion of the residual coke.

[0019] <Regarding the 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, in order to quickly expand the further combustion region in a state where the in-furnace temperature is high after the blast is stopped, the judgment of the completion of combustion of the residual coke is carried out based on the CO, CO 2 gas composition.

[0020] Conventionally, as shown in FIG. 5, in the furnace body opening 1, the two riser pipes 2-1 and 2-2 connected to the furnace body opening 1, and the dust catcher 3 (DC) connected to the riser pipes 2-1 and 2-2, there have been problems in judgment in the following points (a) and (b). (a) Since the suction of O 2 (air) from the furnace body opening 1 through the riser pipes 2-1 and 2-2 occurs and the oxygen concentration rises, an error occurs in judging the completion of combustion of the residual coke. (b) During combustion by the burner, for example, a temperature difference may occur between the north side inside the furnace (the side where the riser pipe 2-1 is connected to the furnace body opening 1) and the south side inside the furnace (the side where the riser pipe 2-2 is connected to the furnace body opening 1). In that case, the gas heated on the north side rises through the north riser pipe 2-1, and while drawing in air from DC3, a gas flow is generated where the gas descends from the south riser pipe 2-2. When the gas descends through the south riser pipe 2-2 while drawing in air from DC3, the oxygen concentration rises at the south furnace top gas analyzer 4-2, and a deviation occurs between the measured value of the north furnace top gas analyzer 4-1 and the measured value of the south furnace top gas analyzer 4-2. As a result, due to the deviation in the measured values between the furnace top gas analyzers 4-1 and 4-2 caused by the increase in oxygen concentration, an error occurs in the judgment of the completion of the combustion of the remaining coke.

[0021] As shown in (a) and (b) above, O 2 Since it is not possible to notice the progress of combustion only from the gentle rise of the gas, by observing the changes in CO, CO 2 gases, the staged progress of combustion, namely, (1) the initial stage of combustion, (2) the mid-stage of combustion, (3) the final stage of burning, and (4) the end of combustion, is grasped. Hereinafter, the states of CO and CO 2 in each combustion stage will be described.

[0022] (1) In the initial stage of combustion, the blown-in O 2 causes the red-hot coke to burn and CO 2 is generated. Since the remaining coke layer is thick, CO 2 + C → 2CO proceeds, and CO >> CO 2 ≒ 0%. (2) In the mid-stage of combustion, the blown-in O 2 causes the red-hot coke to burn and CO 2 is generated. As the remaining coke layer becomes thinner, CO 2 + C → 2CO proceeds, but CO 2 can also be confirmed. (3) In the final stage of combustion, the blown-in O2 causes the red-hot coke to burn and CO 2 is generated. As the remaining coke layer almost disappears, CO 2 + C → 2CO no longer proceeds, and CO 2 >> CO ≒ 0%. (4) At the end of combustion, the residual coke layer near the burner disappears, and even if O 2 is blown in, the coke no longer burns, and CO 2 becomes CO≈0%. In the process shown in the above (1) to (4), by checking the CO and CO 2 concentrations, it is possible to determine how far the combustion has progressed.

[0023] Also, from the end stage of combustion to the end of combustion, due to the sharp decrease in the CO 2 concentration, by setting a threshold of CO, CO 2 <1% to determine the completion of combustion, when further operating by pushing the burner into the furnace to burn the residual coke, it is possible to quickly expand the further combustion area while the furnace is hot.

[0024] In the blast furnace operation method of the present invention, after determining the completion of combustion as described above, the oxygen injection from the taphole burner is stopped and the unused coke is filled from the upper part of the blast furnace.

Example

[0025] In a blast furnace with an internal volume of 5000 m 3 , the upper surface height of the raw material filling layer in the furnace directly above the tuyere was reduced by 1 m below the upper end of the blast furnace morning glory part, and the blast was stopped. Immediately after the blast was stopped in the blast furnace, the burner shown in Fig. 3 was installed at the taphole so that the tip position was at a dimensionless radius of 0.4 in the furnace, and a mixed gas of oxygen and nitrogen was blown into the red-hot coke at 800 °C for combustion. The mixed gas was blown in so that the ratio of nitrogen / oxygen was 1 to 2. The blown-in oxygen is consumed by combustion when coke exists at the burner tip. Also, due to combustion, CO 2 and CO are generated step by step, so by measuring the gas composition with a gas sensor provided at the furnace top as shown in Fig. 6, the progress of combustion was judged step by step as described above. The gas compositions of CO 2 and CO are CO and CO 2After the gas composition became less than 1% and the completion of combustion was confirmed, the oxygen blowing from the tapping burner was stopped, and the unused coke was charged from the upper part of the blast furnace. The tapping burner was burned again to heat the newly charged coke. 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 the heating from the tuyere was switched to start up the blast furnace. As a result, the discharge of the molten material in the furnace could be carried out smoothly, and stable operation could be achieved smoothly.

[0026] Considering that in most cases, the discharge of the molten material in the furnace can be carried out smoothly by the blast furnace operation method of the present invention, the method of the present invention is judged to contribute to the smooth start-up of the blast furnace.

Industrial Applicability

[0027] According to the blast furnace operation method of the present invention, not only the restart of the blast furnace but also stable operation methods can be provided in various shaft melting furnaces other than the blast furnace.

Claims

1. A blast furnace operation method for reducing the height of the surface of the raw material charging layer directly above the tuyere of the blast furnace below the height of the upper end of the morning glory part of the blast furnace and then shutting down the blast, and then restarting the blast. After shutting down the blast of the blast furnace, at least oxygen is blown in from a burner inserted into the furnace from the taphole, and the coke remaining in the furnace is burned to reduce the volume of the residues in the furnace, and the CO and CO ２ in the furnace. When the gas composition is judged to be less than 1% and the combustion of the coke near the burner is completed, after newly charging coke into the volume reduction region where the volume of the residues in the furnace has been reduced, the blast is blown from the tuyere. A blast furnace operation method.

2. The blast furnace operation method according to claim 1, wherein when it is determined that the combustion of the coke near the burner has been completed, the burner is further pushed into the furnace at least once to burn the residual coke, thereby forming the volume reduction region.

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