Blast furnace operation method and blast furnace

Abstract

Provided are a blast furnace operation method and a blast furnace with which it is possible to smoothly perform re-operation of a blast furnace by suppressing a reduction in diameter due to combustion consumption of coke and preventing deterioration of discharge properties of a melt. A blast furnace operation method for stopping operation, damping down the blast furnace, and then restarting blowing, the blast furnace operation method comprising: a combustion step in which after damping down, an oxygen-containing gas is blown in by a burner inserted in a tap hole, coke remaining in the furnace is combusted, and the volume of the furnace residue is reduced; a charging step in which coke is recharged into the reduced-volume region; and a blowing step in which blowing from the tuyere is restarted, the blast furnace operation method having an introduction step in which an inert gas is introduced into the furnace after the blowing down and before the blowing step.

Description

Technical Field

[0001] The present invention relates to a blast furnace operating method for stopping operation to shut down the blast furnace and then restarting the blast, and a blast furnace used in the blast furnace operating method. Background Art

[0002] In the past, the premise of blast furnace operation was that after ignition, the operation would not be stopped except for a short stop for regular equipment maintenance, and the operation itself would continue even if the operation adjustment such as reducing the production volume was made. The reasons for this include the huge cost of restarting the operation accompanying the stop, which was economically unreasonable, and the fact that once the operation was stopped, it took about half a year to restart the operation, so there was no upward elasticity in production volume.

[0003] On the other hand, unlike the past when global steel demand maintained a high growth trend, the current world economic situation is unstable and steel demand has changed greatly in a short period of time. As a result, blast furnace operation also needs to be flexible to large changes in production volume, and the importance of shutting down the furnace in a state where it can be operated again has increased.

[0004] In the shutdown accompanying the repair of the blast furnace, since the shutdown is premised on a certain period of time, the furnace bottom is usually disassembled to remove the coke, molten iron and slag trapped at the bottom of the furnace. On the other hand, in the case of closing the furnace based on the premise of flexible restart according to economic conditions, since this operation leads to an extension of the shutdown period, it is best not to implement it. However, if the residue in the furnace is not removed, the remaining coke in the furnace is consumed by combustion and becomes smaller in diameter, and as the porosity decreases, the discharge of molten iron and slag during restarting deteriorates. In addition, as the furnace heat decreases, the fluidity of the remaining molten iron and slag deteriorates. Therefore, if the discharge operation is not performed, there is a high risk of poor discharge of molten iron and slag when the operation is restarted, and in the worst case, it cannot be operated again.

[0005] In view of the above problems, for example, in Patent Document 1, the deterioration of discharge performance during re-operation is suppressed by making the incombustibles put into the furnace low-melting-point incombustibles for the purpose of preventing troubles during maintenance operations. In addition, in Patent Document 2, it is found that not only the diameter is reduced due to the combustion and consumption of the residual coke, but also the pig iron, slag, etc. attached to the coke are re-melted during re-operation, resulting in an increase in the amount of melt. As a result, the amount of melt is prevented from increasing during re-operation by intentionally burning out the coke using a burner and then charging new coke.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2005-248293

[0009] Patent Document 2: Japanese Patent No. 6947345 Summary of the invention

[0010] Problems to be solved by the invention

[0011] However, in Patent Document 1, in addition to the furnace slag originally generated with the restart of operation, low-melting-point incombustibles are added from outside the system, resulting in an increase in the amount of slag that must be discharged, which still has problems. In addition, Patent Document 2 is more advanced than the prior art in suppressing the increase in the amount of molten material, but it cannot prevent the reduction in diameter caused by the combustion of the newly charged coke. The longer the furnace is closed, the more difficult it is to avoid the reduction in diameter caused by the combustion and consumption of coke and the resulting deterioration in dischargeability.

[0012] The object of the present invention is to provide a blast furnace operating method and a blast furnace which can smoothly resume operation of the blast furnace by suppressing the reduction in diameter caused by the combustion and consumption of coke and preventing the deterioration of the dischargeability of the molten material, which has not been achieved in the prior art.

[0013] Methods used to solve problems

[0014] The blast furnace operating method of the present invention is developed to solve the above-mentioned problems. It is a blast furnace operating method for stopping operation to shut down the blast furnace and then restarting air supply, and it comprises: a combustion process, wherein after the air supply is shut down, oxygen-containing gas is blown into the blast furnace using a burner inserted in the iron outlet to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace; a loading process, wherein coke is reloaded into the volume reduction area; and an air supply process, wherein air supply from the air port is restarted. In the blast furnace operating method, there is a process of introducing inactive gas into the furnace after the above-mentioned air supply process and before the above-mentioned air supply process.

[0015] It should be noted that the following is considered to be a more preferred solution in the blast furnace operating method of the present invention configured as described above:

[0016] (1) further comprising a determination step of determining whether the combustion of the coke in the blast furnace is still continuing after the introduction step;

[0017] (2) in the determination step, the concentration of the gas in the blast furnace is analyzed, and when the concentration of CO gas is equal to or higher than a threshold value, it is determined that the combustion of coke in the blast furnace is still continuing;

[0018] (3) when it is determined in the above determination step that the combustion of the coke in the blast furnace is still continuing, there is further provided a step of adding coke to the upper portion of the tuyere;

[0019] (4) in the above-mentioned introduction step, the amount of the inert gas introduced into the blast furnace is in a range of 7% to 13% of the volume of the blast furnace per hour;

[0020] (5) In the above-mentioned introduction step, the inert gas is introduced into the blast furnace from an introduction port formed at an upper portion of the tuyere of the blast furnace.

[0021] Furthermore, the blast furnace of the present invention is a blast furnace for implementing the above-mentioned blast furnace operating method, wherein an inlet for introducing an inert gas is formed at an upper portion of the tuyere.

[0022] Effects of the Invention

[0023] According to the blast furnace operation method and blast furnace of the present invention, by introducing inert gas into the blast furnace, the reduction in diameter caused by the combustion and consumption of coke in the blast furnace can be suppressed. Thus, by preventing the deterioration of the discharge property of the molten material, the blast furnace can be smoothly re-operated. In addition, the present invention does not need to maintain the pressure in the furnace as a positive pressure, so there is no risk of leakage of the furnace gas to the outside of the furnace accompanying the introduction of the inert gas, and various operations around the blast furnace can be performed in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic cross-sectional view showing a part of the cross section of the furnace body of the blast furnace.

[0025] Figure 2 It is a schematic cross-sectional view of the lower part of the blast furnace showing a state in which a burner is inserted from a tapping hole.

[0026] Figure 3 It is a schematic diagram showing an example of a burner.

[0027] Figure 4 This is a schematic cross-sectional view showing a state in which the volume of the residue in the furnace is reduced by burning the residual coke using a burner.

[0028] Figure 5 This is a schematic diagram for explaining one embodiment of a furnace body of a blast furnace for carrying out the blast furnace operating method of the present invention.

[0029] Figure 6 It is a graph showing the relationship between the amount of N 2 gas introduced into the furnace and the CO gas concentration in the furnace. DETAILED DESCRIPTION

[0030] The following is a detailed description of the embodiments of the present invention. It should be noted that the following embodiments illustrate the apparatus and method for implementing the technical concept of the present invention, and do not define the structure as the following apparatus and method. That is, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0031] <About an example of a blast furnace operating method and a blast furnace to which the present invention is directed>

[0032] Figure 1 1 is a schematic cross-sectional view showing a portion of a blast furnace body cross section. Figure 1 In the embodiment shown, when the blast furnace is shut down for a long time, the height of the surface of the raw material filling layer just above the tuyere of the blast furnace is lowered than the upper end of the belly of the blast furnace to shut down the blast furnace. Then, in order to restart the air supply from the tuyere and return the blast furnace to normal operation, first, a burner is inserted into the furnace from the tapping hole, and oxygen-containing gas or oxygen-containing gas and combustible gas are blown in from the burner to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace (combustion process).

[0033] Figure 2 1 is a schematic cross-sectional view of the lower part of a blast furnace showing a burner inserted from a tap hole. Figure 2 In the embodiment shown, when the blast furnace is shut down, the tap hole is blocked by a material called taphole mud, so in order to insert the burner into the furnace, the tap hole blocked by the taphole mud is first opened. The tap hole can be opened using a known tap hole opening machine. After the tap hole is opened, the burner is inserted into the lower part of the blast furnace from the tap hole.

[0034] Figure 3 (a) and (b) are schematic diagrams showing examples of burners. Figure 3 In the embodiments shown in (a) and (b), the burner has a double tube structure of an inner tube and an outer tube for gas circulation, and has a cover covering the ends of the inner tube and the outer tube and a thermocouple provided outside the outer tube for measuring the temperature of the burner. Figure 3 In the case where the cover is present as shown in (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. Figure 3 In the case where there is no cover as shown in (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 causing the gas to flow from the inner tube to the outer tube when the cover is present, so the burner can be stably inserted into the furnace.

[0035] In addition, at the beginning of combustion, the cooling caused by the circulation of gas from the inner tube to the outer tube is stopped, and the cover is melted and removed by utilizing furnace heat, for example, a combustible gas is blown into the furnace from the inner tube of the burner, and an oxygen-containing gas as a combustion-supporting gas is blown into the lower part of the furnace from the outer tube. If the temperature at the front end of the burner exceeds the combustion start temperature (about 800°C) of the coke present in the surroundings, the gas blown from the burner is switched to only oxygen-containing gas to burn the coke. As the oxygen-containing gas, pure oxygen is preferably blown in, but if the combustion of the coke can be sustained, a gas having an oxygen concentration of less than 100% may also be used. It should be noted that in the present embodiment, an example of blowing a combustible gas and an oxygen-containing gas from a burner is shown, but it is not limited thereto, and only oxygen-containing gas may also be blown from the burner.

[0036] Figure 4 Schematic cross-sectional view showing a state where the volume of the residue in the furnace is reduced by burning the residual coke using a burner. Figure 4 In the illustrated embodiment, when the coke disappears due to combustion, the coke further rolls into the burned-out space according to the angle of repose, and the coke is successively burned out, thereby reducing the volume of the residue in the furnace.

[0037] Then, the blowing of oxygen from the burner is stopped, and unused coke is charged from the upper part of the blast furnace into the space in the furnace, i.e., the volume reduction area, which is created by reducing the volume of the residue in the furnace (charging process). Then, oxygen is blown from the burner again to heat the newly charged coke, and when the temperature of the coke at the front end of the tuyere exceeds, for example, 2000°C, hot air of, for example, 1100°C is blown from the tuyere (air supply process), and the heating from the tuyere is switched to start the blast furnace.

[0038] <About the characteristics of the blast furnace operating method and blast furnace of the present invention>

[0039] The blast furnace operation method and the blast furnace of the present invention are characterized in that they have an introduction process of introducing an inert gas into the blast furnace after the above-mentioned wind stop and before the air supply process. Here, "after the wind stop and before the air supply process" refers to any of the moments after the wind stop and (1) before the combustion process, (2) after the combustion process and before the charging process, and (3) after the charging process and before the air supply process. Among them, (2) is preferred. In the case of (1) introducing an inert gas, the process is delayed because the combustion of coke is hindered. In the case of (3) introducing an inert gas, since the temperature in the furnace rises in (2), a part of the unused coke charged in the charging process reacts, and thus the effect of the present invention is reduced.

[0040] In the blast furnace operation method of the present invention, inert gas is introduced into the blast furnace in the introduction step to suppress the contact between the coke charged into the volume reduction area between the tuyere and the tap hole and the air, thereby suppressing the combustion of the coke. It should be noted that various inert gases such as argon and nitrogen can be used as the inert gas, but nitrogen (N2) is the best from the perspective of cost.

[0041] Figure 5 Schematic diagram of one embodiment of a blast furnace body for illustrating the blast furnace operating method of the present invention. Figure 5 As shown in FIG. 1 , a pipe as an inlet is provided on the blast furnace at an upper portion than the tuyere, and inert gas is introduced into the blast furnace from the inlet. Figure 5 In the example shown, an inlet is provided just above the tuyere, but an inlet may also be provided near the roof of the blast furnace (for example, at a position about 5 m below the roof of the blast furnace when the blast furnace height is set to 100 m). By providing the inlet above the tuyere, it is possible to prevent the coke loaded into the volume reduction area between the tuyere and the tap hole from obstructing the introduction of the inert gas. In addition, by providing the inlet for introducing the inert gas separately from other openings such as the raw material loading port, the tuyere, and the tap hole, the inert gas introduction operation can be performed without interfering with other operations and equipment, compared with a structure in which the inert gas is introduced from other openings.

[0042] Here, the amount of inert gas introduced into the blast furnace is determined by the volume of the blast furnace. Specifically, it is preferably in the range of 7% or more and 13% or less per hour relative to the volume of the blast furnace. This range is preferred because, when the amount introduced is less than 7%, the amount is too small to suppress the combustion of coke, and even if the amount introduced is greater than 13%, the combustion suppression effect remains unchanged.

[0043] It should be noted that in the blast furnace operation method of the present invention, it is preferred to add a determination step after the introduction step of the inert gas into the blast furnace, in which it is determined whether the combustion of the coke in the blast furnace is still continuing. Specifically, a gas analyzer is provided on a recovery pipe (not shown) for recovering the gas discharged from the furnace top, and the gas analyzer is used to analyze the gas concentration in the furnace (the gas concentration discharged from the furnace top). Furthermore, when the concentration of CO gas is high (above the threshold), it is determined that the combustion of the coke is still continuing, and when the concentration of CO gas is low (less than the threshold), it is determined that the combustion of the coke is not continuing. The CO gas concentration serving as the threshold is, for example, 1%.

[0044] In addition, in the determination process, when it is determined that the combustion of coke is still continuing, it is preferred to further add coke to the upper part of the tuyere, thereby causing the oxygen remaining in the furnace to react (combust) with the coke added to the upper part of the tuyere. In this way, the combustion consumption of coke existing between the tuyere and the tapping hole can be suppressed, and the reduction in the diameter of coke between the tuyere and the tapping hole and the deterioration of discharge performance thereof can be avoided.

[0045] Example

[0046] According to the above embodiment, the actual internal volume is 5000m 3 In a blast furnace, N2 gas is introduced into the furnace by changing the amount of CO gas introduced into the furnace, and the change in the CO gas concentration in the furnace is calculated. Figure 6 Graph showing the relationship between the amount of N2 gas introduced into the furnace and the CO gas concentration in the furnace. Figure 6 In the figure shown, the drawing is omitted for the case where the N2 gas introduction amount is less than 7%, but when it is less than 7%, the CO gas concentration increases significantly (for example, becomes 8% or more) compared with the case of more than 7%. In the embodiment, when the N2 gas introduction amount is 7%, the CO gas concentration becomes about 0.8%, and it is confirmed that the CO gas concentration is sufficiently reduced. In addition, for the purpose of thoroughly suppressing the combustion and consumption of coke, the N2 gas introduction amount is increased to 10%. As a result, compared with the case where the N2 gas introduction amount is 8%, the N2 gas introduction amount increases by 25%, and the CO gas concentration is reduced to about 0.1%, which is reduced by 80%, and the combustion and consumption of coke can be fully suppressed. By using the present invention, the discharge of the molten material at the time of blast furnace startup can be ensured, and after re-operation without removing the residue in the furnace, it can be restored to engineering operation in 21 days.

Claims

1. A blast furnace operating method for stopping operation to shut down the blast furnace and then restarting the blast furnace, comprising: a combustion step, in, After the air is shut down, oxygen-containing gas is blown into the furnace using a burner inserted in the tap hole to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace; a charging step, in which coke is recharged into the volume reduction area; and an air supply step, in which air supply from the air port is restarted. The blast furnace operating method includes a step of introducing an inert gas into the furnace after the blast stop and before the blast supply step.

2. The blast furnace operating method according to claim 1, in, The method further comprises a determination step of determining whether the combustion of the coke in the blast furnace is still continuing after the introduction step.

3. The blast furnace operating method according to claim 2, in, In the determination step, the concentration of the gas in the blast furnace is analyzed, and when the concentration of CO gas is equal to or higher than a threshold value, it is determined that the combustion of coke in the blast furnace is still continuing.

4. The blast furnace operating method according to claim 2 or 3, in, If it is determined in the determination step that the combustion of the coke in the blast furnace is still continuing, the method further includes a step of charging additional coke to the upper portion of the tuyere.

5. The blast furnace operating method according to claim 1, in, In the introduction step, the amount of the inert gas introduced into the blast furnace is in a range of 7% to 13% with respect to the volume of the blast furnace per hour.

6. The blast furnace operating method according to claim 1, in, In the introduction step, the inert gas is introduced into the blast furnace from an introduction port formed at an upper portion of the tuyere of the blast furnace.

7. A blast furnace, which is a blast furnace implementing the blast furnace operating method according to claim 1, in, An inlet for introducing an inert gas is formed at an upper portion of the tuyere.

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