Blast furnace operation method and blast furnace

Abstract

A blast-furnace operation method and a blast furnace are proposed with which it is possible to smoothly reoperate a blast furnace by preventing the coke from decreasing in diameter due to combustion and consumption and preventing the melt from deteriorating in dischargeability. The blast-furnace operation method is for suspending an operation of a blast furnace to stop the blasting and thereafter restarting blasting, and comprises a combustion step in which after the stopping of blasting, an oxygen-containing gas is blown into the furnace with a burner inserted into the tapping hole to burn the coke remaining in the furnace and reduce the volume of in-furnace residues, a charging step in which coke is newly charged into the volume reduction region, and a blasting step in which blasting through the tuyeres is restarted. The blast-furnace operation method further includes an introduction step in which an inert gas is introduced into the furnace during the period from after the stopping of blasting to before the blasting step.

Description

[Technical field]

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

[0002] Traditionally, blast furnace operations have not been stopped after blow-in, except for short stoppages for periodic equipment repairs, and operations are adjusted, such as reducing production volume, but the premise is that operations themselves continue. This is because the cost of restarting operations due to shutdowns is enormous and economically unreasonable, and because once operations are shut down, it takes about six months to restart, so there is no upward flexibility in terms of production volume.

[0003] On the other hand, unlike the past, when global steel demand was consistently high and production was on the rise, the current world economic situation is unstable, and steel demand has changed significantly in a short period of time. As a result, blast furnace operations are now required to be flexible in response to large fluctuations in production volume, and banking, which shuts down furnaces when they can be operated again, is becoming increasingly important.

[0004] In the case of a blast furnace shutdown for repair, it is common to dismantle the hearth and remove the coke, molten iron, and slag that have accumulated in the hearth, since the shutdown is assumed to last for a certain period of time. On the other hand, in the case of banking, which assumes flexible restart depending on the economic situation, it is desirable not to carry out such work, as it will lead to an extension of the shutdown period. However, if the remains in the furnace are not removed, the remaining coke in the furnace will be burned and consumed, becoming smaller in diameter, and the porosity will decrease, which will worsen the dischargeability of the molten iron and slag when the furnace is restarted. In addition, the fluidity of the remaining molten iron and slag will deteriorate as the furnace heat decreases, so if the discharge work is not carried out, there is a high risk of poor discharge of the molten iron and slag when operations are resumed, and in the worst case, restarting the furnace will be impossible.

[0005] In response to the above-mentioned problems, for example, in Patent Document 1, the incombustible material charged into the furnace has a low melting point composition in order to prevent the repair work from being hindered, thereby preventing the dischargeability from worsening when the furnace is restarted. In addition, in Patent Document 2, it was discovered that not only does the remaining coke become smaller in diameter by burning and consuming it, but pig iron, slag, etc. attached to the coke remelt when the furnace is restarted, leading to an increase in the amount of molten material. As a result, the coke is intentionally burned off using a burner, and then new coke is charged, preventing an increase in the amount of molten material when the furnace is restarted. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-248293 A [Patent Document 2] Patent No. 6947345 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in Patent Document 1, low-melting-point incombustible materials were added from outside the system in addition to the slag generated in the furnace when operation was restarted, which led to an increase in the amount of molten slag that had to be discharged, and this still left a problem. In addition, Patent Document 2 is more advanced than the conventional technology in that it suppresses the increase in the amount of molten material, but it is unable to prevent the diameter reduction caused by the combustion of the newly charged coke, and there was a problem in that the longer the banking period, the smaller the diameter due to the combustion and consumption of the coke and the accompanying deterioration in dischargeability are unavoidable.

[0008] The object of the present invention is to propose a blast furnace operation method and a blast furnace which can smoothly restart the blast furnace by suppressing the reduction in diameter due to the combustion consumption of coke, which was not possible in the prior art, and preventing a deterioration in the dischargeability of the molten material. [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 for stopping operation, suspending ventilation of the blast furnace, and then restarting ventilation, the blast furnace operation method having a combustion process in which oxygen-containing gas is blown in from a burner inserted into the tap hole after the suspending ventilation, and the coke remaining in the furnace is burned to reduce the volume of the material remaining in the furnace, a charging process in which new coke is charged into the area of ​​reduced volume, and a ventilation process in which ventilation is resumed from the tuyere, and the blast furnace operation method further has an introduction process in which an inert gas is introduced into the furnace after the suspending ventilation and before the ventilation process.

[0010] In the blast furnace operation method according to the present invention configured as described above, (1) Further comprising a determination step of determining whether or not the combustion of coke in the blast furnace is continuing after the introduction step; (2) in the determination step, a concentration of gas in the blast furnace is analyzed, and when a 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 continuing; (3) The method further includes an additional step of charging additional coke up to an upper part of the tuyere when it is determined in the determination step that the combustion of coke in the blast furnace is continuing. (4) In the introduction step, the amount of the inert gas introduced into the blast furnace is in the range of 7% to 13% of the blast furnace volume per hour; (5) In the introducing step, the inert gas is introduced into the blast furnace from an inlet formed above the tuyere of the blast furnace; is considered to be a more preferable solution.

[0011] The blast furnace of the present invention is a blast furnace for carrying out the above-mentioned blast furnace operating method, and is a blast furnace in which an inlet for introducing an inert gas is formed above the tuyere. Effect of the Invention

[0012] According to the blast furnace operation method and blast furnace of the present invention, by introducing an inert gas into the blast furnace, it is possible to suppress the diameter reduction caused by the combustion consumption of coke in the blast furnace. This prevents the dischargeability of the molten material from deteriorating, and allows the blast furnace to be smoothly restarted. In addition, since the present invention does not require the furnace pressure to be kept positive, there is no risk of the gas in the furnace leaking outside the furnace due to the introduction of the inert gas, and various tasks around the blast furnace can be performed in parallel. [Brief description of the drawings]

[0013] [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 a state in which a burner is inserted through a 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 remaining material in the furnace is reduced by burning the remaining coke using a burner. [Diagram 5] FIG. 1 is a schematic diagram for explaining one embodiment of a furnace body of a blast furnace in which a blast furnace operating method according to the present invention is carried out. [Figure 6] 1 is a graph showing the relationship between the amount of N2 gas introduced into a furnace and the CO gas concentration in the furnace. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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 ideas of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims.

[0015] <An example of a blast furnace operation method and a blast furnace 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 below the upper end of the morning glory part of the blast furnace to shut down the blast furnace. After that, in order to resume blowing from the tuyere and return the blast furnace to normal operation, first, a burner is inserted into the furnace 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 material remaining in the furnace (combustion process).

[0016] 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.

[0017] 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, a cap 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. 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.

[0018] At the start of combustion, the cooling caused by the flow of gas from the inner tube to the outer tube is stopped, the cap is dissolved and removed by furnace heat or the like, and, for example, combustible gas is blown into the furnace from the inner tube of the burner, and oxygen-containing gas is blown into the lower part of the furnace from the outer tube as a combustion-supporting gas. When the temperature of the tip of the burner exceeds the combustion start temperature (approximately 800°C) of the coke present in the vicinity, the gas blown from the burner is switched to only 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 combustion of the coke can be sustained. In this embodiment, an example in which combustible gas and oxygen-containing gas are blown from the burner is shown, but the present invention is not limited to this, and only oxygen-containing gas may be blown from the burner.

[0019] Fig. 4 is a schematic cross-sectional view showing a state in which the remaining coke is burned using a burner to reduce the volume of the material remaining in the furnace. In the embodiment shown in Fig. 4, when the coke disappears due to combustion, more coke rolls into the space where the coke has disappeared according to the angle of repose, and the volume of the material remaining in the furnace decreases as the coke is burned and disappeared one by one.

[0020] After that, the blowing of oxygen from the burner is stopped, and unused coke is charged from the top of the blast furnace into the volume reduction area, which is the space created in the furnace by reducing the volume of the remaining material in the furnace (charging process).Oxygen is then blown again from the burner to heat the newly charged coke, and when the temperature of the coke at the tip of the tuyere exceeds, for example, 2000°C, hot air of, for example, 1100°C is blown from the tuyere (blowing process), and heating is switched back to the tuyere to start up the blast furnace.

[0021] <About the blast furnace operation method and features of the blast furnace of the present invention> The blast furnace operation method and the blast furnace of the present invention are characterized in that they include an introduction step of introducing an inert gas into the blast furnace after the above-mentioned cessation of airflow and before the blasting step. Here, "after the cessation of airflow and before the blasting step" means any of the following points after the cessation of airflow: (1) a point before the combustion step, (2) a point after the combustion step and before the charging step, and (3) a point after the charging step and before the blasting step. Of these, (2) is preferable. When an inert gas is introduced in (1), the process is delayed because coke combustion may be inhibited. When an inert gas is introduced in (3), the temperature inside the furnace rises in (2), causing a part of the unused coke charged in the charging step to react, thereby reducing the effect of the present invention.

[0022] In the blast furnace operation method of the present invention, in the introduction step, an inert gas is introduced into the blast furnace to suppress contact between the coke charged in the volume reduction region between the tuyere and the tap hole and the air, thereby suppressing combustion of the coke. As the inert gas, various inert gases such as argon and nitrogen can be used, but nitrogen (N2) is optimal from the viewpoint of cost.

[0023] FIG. 5 is a schematic diagram for explaining one embodiment of a furnace body of a blast furnace in which a blast furnace operating method according to the present invention is implemented. As shown in FIG. 5, a piping serving as an inlet is provided above the tuyere in the blast furnace, and an inert gas is introduced into the blast furnace from this inlet. In the example shown in FIG. 5, the inlet is provided directly above the tuyere, but the inlet may be provided near the top of the blast furnace (for example, at a position about 5 m below the top of the blast furnace when the blast furnace height is 100 m). By providing the inlet above the tuyere, it is possible to suppress the introduction of the inert gas being hindered by the coke charged in the volume reduction region between the tuyere and the tap hole. In addition, by providing the inlet for introducing the inert gas separately from other openings such as a raw material charging port, tuyere, and tap hole, the inert gas introduction work can be performed without interfering with other work or equipment, compared to a configuration in which the inert gas is introduced from other openings.

[0024] Here, the amount of inert gas introduced into the blast furnace is determined by the volume of the blast furnace. Specifically, it is preferable to set the amount to be in the range of 7% to 13% per hour of the volume of the blast furnace. This range is preferable because if the amount is less than 7%, the amount is too small to suppress the combustion of coke, and even if the amount is more than 13%, the combustion suppression effect remains the same.

[0025] In the blast furnace operation method of the present invention, it is preferable to add a determination step of determining whether or not the combustion of coke in the blast furnace is continuing after the introduction step of introducing an inert gas into the blast furnace. Specifically, a gas analyzer is installed in a recovery pipe (not shown) that recovers the gas discharged from the top of the furnace, and the gas concentration in the furnace (the gas concentration discharged from the top of the furnace) is analyzed by this gas analyzer. If the concentration of CO gas is high (above a threshold), it is determined that the combustion of coke is continuing, and if the concentration of CO gas is low (below the threshold), it is determined that the combustion of coke is not continuing. The threshold CO gas concentration is, for example, 1%.

[0026] Furthermore, if it is determined in the determination step that the coke combustion is continuing, it is preferable to charge additional coke up to the top of the tuyere to react (burn) the oxygen remaining in the furnace with the coke above the added tuyere. This makes it possible to suppress the combustion and consumption of the coke present between the tuyere and the tap hole, and to avoid the reduction in the diameter of the coke between the tuyere and the tap hole and the associated deterioration in dischargeability. EXAMPLES

[0027] According to the above-mentioned embodiment, the internal volume is actually 5000 m 3The blast furnace was used, and N2 gas was introduced into the furnace at different amounts to obtain the change in the CO gas concentration in the furnace. FIG. 6 is a graph showing the relationship between the amount of N2 gas introduced into the furnace and the CO gas concentration in the furnace. In the graph shown in FIG. 6, plots for N2 gas introduction amounts of less than 7% are omitted, but the CO gas concentration is orders of magnitude higher (for example, 8% or more) when the amount of N2 gas introduced is less than 7% compared to when the amount is 7% or more. In the embodiment, the CO gas concentration was about 0.8% when the amount of N2 gas introduced was 7%, and a sufficient decrease in the CO gas concentration was confirmed. Furthermore, the amount of N2 gas introduced was increased to 10% in order to thoroughly suppress the combustion consumption of coke. As a result, compared to the case of the amount of N2 gas introduced of 8%, the amount of N2 gas introduced increased by 25%, while the CO gas concentration decreased by 80% to about 0.1%, and the combustion consumption of coke could be sufficiently suppressed. By using the present invention, it is possible to ensure the dischargeability of the molten material at the time of starting up the blast furnace, and it was possible to return to process operation in 21 days after restarting without removing the remaining material in the furnace.

Claims

1. A blast furnace operation method for stopping operation, suspending ventilation of a blast furnace, and then restarting ventilation, the method comprising: a combustion step in which oxygen-containing gas is blown in from a burner inserted into a tap hole after the suspending of ventilation, thereby burning coke remaining in the furnace and reducing the volume of materials remaining in the furnace; a charging step in which new coke is charged into the area of ​​reduced volume; and a ventilation step in which ventilation is resumed from a tuyere, the method further comprising an introduction step in which an inert gas is introduced into the furnace after the suspending of ventilation, after the combustion step, and before the charging step.

2. The blast furnace operating method according to claim 1, further comprising a determination step of determining whether or not combustion of coke in the blast furnace continues after the introducing step.

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

4. The blast furnace operating method according to claim 2 or 3, further comprising an additional step of charging additional coke up to an upper part of the tuyere when it is determined in the determination step that the combustion of coke in the blast furnace is continuing.

5. The blast furnace operating method according to claim 1, wherein an amount of the inert gas introduced into the blast furnace in the introducing step is in the range of 7% to 13% of the blast furnace volume per hour.

6. The blast furnace operating method according to claim 1 , wherein in the introducing step, the inert gas is introduced into the blast furnace from an inlet formed above a tuyere of the blast furnace.

7. A blast furnace for carrying out the blast furnace operating method according to claim 1, wherein an inlet for introducing an inert gas is formed above the tuyere.

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