JP7626237B2 - Blast furnace operation method and blast furnace - Google Patents

Description

The present invention relates to a blast furnace operation method for stopping operations, shutting down the blast furnace, and then restarting blasting, and to a blast furnace used in the blast furnace operation method.

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 assumption is that operations themselves will continue. This is because the costs of restarting operations due to shutdowns are enormous and economically unreasonable, and because once operations are stopped, it takes about six months to restart, meaning there is no upward flexibility in terms of production volume.

On the other hand, unlike the past, when global demand for steel was consistently high and production was on the rise, the current global economic situation is unstable, and steel demand has begun to fluctuate significantly in a short period of time. As a result, blast furnace operations are now required to be more flexible in dealing with large fluctuations in production volume, and banking, which allows furnaces to be shut down when they can be operated again, is becoming increasingly important.

In the case of a blast furnace shutdown involving renovation, it is assumed that the shutdown will last for a certain period of time, so it is common to dismantle the hearth and remove the coke, molten iron, and molten slag that have accumulated in the hearth. 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 this work, as it will lead to an extension of the shutdown period. However, if the remaining material in the furnace is not removed, the remaining coke in the furnace will be burned and consumed, becoming smaller in diameter, and the porosity will decrease, making it difficult to discharge 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.

In response to the above-mentioned problems, for example, in Patent Document 1, the non-combustible material charged into the furnace has a low melting point composition in order to prevent any hindrance to repair work, thereby preventing the deterioration of dischargeability 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 the pig iron, slag, etc. adhering to the coke remelts 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 new coke is then charged, preventing an increase in the amount of molten material when the furnace is restarted.

JP 2005-248293 A Patent No. 6947345

However, in Patent Document 1, low-melting-point incombustible materials are added from outside the system in addition to the slag generated in the furnace when operations are restarted, which leads to an increase in the amount of molten slag that must be discharged, and this still poses a problem. In addition, Patent Document 2 is more advanced than conventional technology in that it prevents an 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 is a problem in that the longer the banking period, the more the diameter reduction caused by the combustion and consumption of coke and the associated deterioration in dischargeability become unavoidable.

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 preventing the reduction in diameter due to the combustion consumption of coke, which was not possible in the prior art, and by preventing a deterioration in the dischargeability of the molten material.

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, shutting down the blast furnace, and then restarting the blowing process, which includes a combustion process in which oxygen-containing gas is blown in from a burner inserted into the tap hole after the shutting down process to burn the coke remaining in the furnace and 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 blowing process in which blowing from the tuyere is resumed, and which further includes an introduction process in which an inert gas is introduced into the furnace after the shutting down process and before the blowing process.

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 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;
This is believed to be a more preferable solution.

Furthermore, the blast furnace of the present invention is a blast furnace that carries out the above-mentioned blast furnace operation method, and is a blast furnace in which an inlet for introducing an inert gas is formed above the tuyere.

According to the blast furnace operation method and blast furnace of the present invention, by introducing inert gas into the blast furnace, it is possible to suppress the diameter reduction caused by the combustion and 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 inert gas, and various tasks can be performed in parallel around the blast furnace.

FIG. 2 is a schematic cross-sectional view showing a part of a cross section of a furnace body of a blast furnace. 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. FIG. 2 is a schematic diagram showing an example of a burner. 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. 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. 1 is a graph showing the relationship between the amount of N ₂ gas introduced into a furnace and the CO gas concentration in the furnace.

The following is a detailed description of the embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods for embodying the technical ideas of the present invention, and are not intended to specify the configurations 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.

<An example of a blast furnace operation method and a blast furnace according to the present invention>
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 immediately 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).

Figure 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. In the embodiment shown in Figure 2, when the blast furnace is shut down, the tap hole is blocked with a material called mud material, 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.

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.

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, etc., 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 supporting gas. When the temperature of 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 oxygen-containing gas to burn the coke. It is preferable to blow pure oxygen as the oxygen-containing gas, but as long as the coke combustion can be sustained, a gas with an oxygen concentration lower than 100% may be used. In this embodiment, an example of blowing combustible gas and oxygen-containing gas from the burner is shown, but this is not limited to this, and only oxygen-containing gas may be blown from the burner.

Figure 4 is a schematic cross-sectional view showing the 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 Figure 4, when the coke disappears due to combustion, further 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 after another.

After that, the blowing of oxygen from the burner is stopped, and unused coke is charged from the top of the blast furnace to fill the volume reduction area, which is the space created in the furnace by reducing the volume of the material remaining 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 at, 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.

<Features of the blast furnace operation method and 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 preferred. 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 some of the unused coke charged in the charging step to react, thereby reducing the effect of the present invention.

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.

5 is a schematic diagram for explaining one embodiment of a furnace body of a blast furnace in which the blast furnace operation method according to the present invention is implemented. As shown in FIG. 5, the blast furnace is provided with a pipe serving as an inlet above the tuyere, and 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 prevent the introduction of the inert gas from being hindered by the coke charged in the volume reduction area between the tuyere and the tap hole. In addition, by providing the inlet for introducing the inert gas separately from other openings such as the raw material charging inlet, 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.

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 introduced is less than 7%, the amount is too small to suppress coke combustion, and even if the amount introduced is more than 13%, the combustion suppression effect remains the same.

In addition, in the blast furnace operation method of the present invention, it is preferable to add a judgment step of judging whether or not the combustion of coke in the blast furnace is continuing after the introduction step of introducing 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. Then, if the concentration of CO gas is high (above a threshold value), it is judged that the combustion of coke is continuing, and if the concentration of CO gas is low (below the threshold value), it is judged that the combustion of coke is not continuing. The threshold CO gas concentration is, for example, 1%.

In addition, if it is determined in the determination process that 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.

According to the above-mentioned embodiment, a blast furnace with an internal volume of 5000 m ³ was actually used, and N ₂ 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 N ₂ gas introduced into the furnace and the CO gas concentration in the furnace. In the graph shown in FIG. 6, plots are omitted for N ₂ gas introduction amounts of less than 7%, but the CO gas concentration is orders of magnitude higher (for example, 8% or more) when the amount of N 2 gas introduced is less than 7% compared to when the amount is 7% or more. In the example, the CO gas concentration was about 0.8% when the amount of N ₂ gas introduced was 7%, and a sufficient decrease in the CO gas concentration was confirmed. Furthermore, the amount of N ₂ gas introduced was increased to 10% in order to thoroughly suppress the combustion consumption of coke, and as a result, compared to the case of an N ₂ gas introduction amount of 8%, the amount of N ₂ gas introduced increased by 25%, while the CO gas concentration decreased by 80% to about 0.1%, and the combustion consumption of coke was sufficiently suppressed. By using the present invention, it is possible to ensure the discharge of molten material when starting up a blast furnace, and after restarting the furnace, process operation could be resumed in 21 days without removing residual material in the furnace.

Claims (7)

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 . The blast furnace operation method according to claim 1, further comprising a determination step of determining whether or not the combustion of coke in the blast furnace continues after the introduction step. The blast furnace operation method according to claim 2, wherein in the determination step, the concentration of gas in the blast furnace is analyzed, and if the concentration of CO gas is equal to or greater than a threshold value, it is determined that the combustion of coke in the blast furnace is continuing. The blast furnace operation method according to claim 2 or 3, further comprising an additional step of charging additional coke up to the top of the tuyere if it is determined in the determination step that the combustion of coke in the blast furnace is continuing. The blast furnace operation method according to claim 1, wherein the amount of inert gas introduced into the blast furnace in the introduction step is in the range of 7% to 13% of the blast furnace volume per hour. The blast furnace operating method according to claim 1, wherein in the introduction step, the inert gas is introduced into the blast furnace from an inlet formed above the tuyere of the blast furnace. 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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