JP2024012113A - Blast furnace operation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blast furnace operation method capable of preventing a decrease in a furnace internal temperature against a local decrease in a raw material surface level and appropriately suppressing a furnace top gas temperature.

SOLUTION: In a blast furnace operation method in which air blowing is resumed by opening at least a part of a tuyere after closing the tuyere due to a long period of wind rest, the control upper limit of a furnace top gas temperature is raised from an upper limit temperature in the normal operation to a predetermined temperature within the upper limit temperature for equipment protection when water is sprinkled into the furnace based on the furnace top gas temperature against a local decrease in a raw material surface level in a blast furnace.

SELECTED DRAWING: Figure 5

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method of operating a blast furnace for effectively cooling the top of the furnace when the blast furnace is shut down, the blast furnace is put into air rest, and then restarted.

In a blast furnace, high-temperature reducing gas is generated by the reaction between high-temperature air and oxygen blown into the furnace through ventilation holes called tuyeres, and coke and pulverized coal in the furnace. A blast furnace is a facility that uses generated high-temperature reducing gas to raise the temperature, reduce, and melt iron ore, and then discharges pig iron and slag out of the furnace through a taphole installed at the bottom of the tuyere. During normal operation of a blast furnace, the reaction heat within the furnace and the heat supply from the tuyere are balanced, so stable operation of the blast furnace is possible.

Here, the high-temperature reducing gas generated by the reaction inside the furnace heads toward the top of the blast furnace, but if the raw material surface level drops below the standard, the reduction reaction time with the raw material becomes shorter, and the top gas temperature increases. It will rise. At this time, equipment such as blast furnace gas cleaning equipment through which high-temperature reducing gas passes may be damaged. To prevent such damage, water is sprayed into the furnace using a water sprinkler installed at the top of the furnace. The function required of this cooling device is to lower the gas temperature at the top of the furnace without cooling the blast furnace raw material itself that is charged into the furnace.

When the blast furnace is closed for a long period of time or stopped, the heat supply to the inside of the blast furnace is stopped. On the other hand, heat radiation continues due to the temperature difference between the temperature inside the blast furnace and the atmosphere, so cooling inside the furnace progresses and some of the molten material solidifies. Therefore, when restarting operation of the blast furnace, that is, when restarting air blowing, it is necessary to melt the solidified layer in the furnace and heat the coke packed bed through which the solidified material passes until the molten material can pass through.

Therefore, when a blast furnace is shut down for a long period of time or when it is expected to restart, first, after normal operation ends, a reduced-scale operation is carried out to reduce the raw material level, and the blast furnace enters the wind-down period with the raw material level reduced. After the period ends, startup operations will be carried out to increase raw material levels and return to normal operations.

In scale reduction operations, the scale reduction level is lowered. That is, the raw material level is uniformly lowered in the circumferential direction with the tuyere open all around the tuyere without charging the raw material while blowing hot air. Therefore, the amount of water sprinkled at the top of the furnace is only adjusted to the value of the rise in the gas temperature at the top of the furnace. At that time, the blast furnace increases the coke ratio in the furnace and enters a period of rest to compensate for the heat until the injection of pulverized coal can begin after the blast of air. At the same time, all but one or two tuyeres on the taphole are blocked with refractories, etc., to limit the amount of hot metal slag generated due to air blowing, and to establish a cycle for smooth discharge of small amounts of molten material. . In subsequent start-up operations, the reduction level will be increased. That is, when raising the raw material level, a method is used in which adjacent tuyeres are opened and the number of opened tuyeres is gradually increased to restore normal operation (Patent Document 1).

Patent No. 6947345

During start-up operation, which starts air blowing by partially opening the tuyeres mentioned above, high-temperature air can only be blown into the furnace through the open tuyeres, so the temperature rise, reduction, and melting of iron ore is done through the open tuyeres. This is done only in the area where the hot air blown from the tuyeres reaches. Therefore, the reaction within the blast furnace becomes non-uniform in the circumferential direction, causing a local drop in the surface level of the raw material at the top of the furnace. This phenomenon causes a local furnace top gas temperature rise, and water is sprayed into the furnace from the furnace top watering device. At that time, there was a problem that a large amount of cooling water landed directly on the raw material itself in areas where the surface level of the raw material had not been lowered, resulting in overcooling, resulting in a decrease in the temperature inside the furnace.

An object of the present invention is to provide a blast furnace operating method capable of solving the above-mentioned problems, preventing a decrease in the furnace temperature in response to a local decrease in the raw material surface level, and appropriately suppressing the furnace top gas temperature. It's about making suggestions.

The blast furnace operating method of the present invention was developed to solve the above-mentioned problem, and after the tuyere is closed for a long period of air suspension, at least a portion of the tuyere is opened to resume blowing air. In the blast furnace operating method at the time, when water is sprinkled into the furnace based on the top gas temperature in response to a local drop in the surface level of the raw material inside the blast furnace, the upper limit for controlling the top gas temperature is set to the upper limit temperature during normal operation. This is a method of operating a blast furnace in which the temperature is raised from

In addition, in the blast furnace operating method of the present invention,
(1) In the present invention, the predetermined temperature within the upper limit temperature for equipment protection is a temperature near the upper limit temperature for equipment protection;
(2) In (1) above, the temperature near the upper limit temperature for equipment protection is a temperature in the range of -20°C to 0°C of the upper limit temperature;
(3) In the present invention, in any of (1) and (2) above, charging the raw material into the blast furnace and sprinkling water into the blast furnace are performed alternately;
(4) In any of the above present invention, (1), (2), and (3) above, if the furnace top gas temperature decreases to the control upper limit during normal operation without watering, the control upper limit is Returning the temperature from near the upper limit for equipment protection to the upper limit for normal operation;
is considered to be a more preferable solution.

According to the blast furnace operating method of the present invention, when the tuyere is partially opened to re-air the blast furnace after a long period of air suspension or suspension, it is possible to prevent a decrease in the temperature inside the furnace and damage to the furnace top equipment. As a result, it is possible to stabilize the startup operation of the blast furnace and reduce the risk of equipment damage.

It is a cross-sectional schematic diagram showing a part of the furnace body cross section of a blast furnace. It is a top view of the tuyere level of a blast furnace for explaining an open tuyere and a closed tuyere. FIG. 2 is a schematic diagram showing a state where a local decrease in the raw material surface level occurs in a blast furnace. (a) and (b) are schematic diagrams each showing a state of water sprayed by a water spray nozzle of a water sprinkler provided at the top of the furnace. It is a graph showing data on the number of tuyere openings, the amount of water sprinkled, the furnace top gas temperature, and the hot metal temperature at the time of starting up the blast furnace after a long-term wind break.

Embodiments of the present invention will be specifically described below. Note that the following embodiments are intended to exemplify an apparatus and method for embodying the technical idea of the present invention, and the configuration is not limited to the following. That is, the technical idea of the present invention can be modified in various ways within the technical scope described in the claims.

As described above, when the tuyere is partially opened to start blowing air, the reaction within the blast furnace becomes non-uniform in the circumferential direction. As a result, the raw material that remained at the top of the blast furnace before the blast furnace was shut down or stopped reacts locally, causing a phenomenon in which the height of the raw material surface locally decreases, and the top gas temperature locally increases. do. On the other hand, if water is sprayed by a water sprinkler, there will be areas that become supercooled. As a result, the viscosity of the slag decreases at that location, causing operational problems such as difficulty in discharging the slag. According to an embodiment of the present invention, the control upper limit of the furnace top gas temperature is raised to a temperature close to the upper limit temperature for equipment protection. Thereby, the amount of water sprinkled into the blast furnace can be suppressed, the furnace temperature can be prevented from decreasing due to a local decrease in the raw material surface level, and the furnace top gas temperature can be appropriately suppressed.

FIG. 1 is a schematic cross-sectional view showing a part of the cross-section of the furnace body of a blast furnace. As shown in FIG. 1, the blast furnace according to this embodiment has a shaft part, a furnace top part, a furnace part, a morning glory part, a hearth, and a tuyere. Although only one tuyere is shown in the cross-sectional view shown in FIG. 1, the blast furnace body has a plurality of tuyeres in the circumferential direction. Since the tuyere is clogged with clay when the blast furnace is at rest, the tuyere clogged with clay is first opened when the blast furnace starts operating. As mentioned above, since there are multiple tuyeres, they are partially open. A known tuyere opening machine can be used to open the tuyeres. High-temperature air is sequentially blown through the partially opened tuyeres.

FIG. 2 is a top view of the tuyere level of the blast furnace for explaining open tuyeres and closed tuyeres. As shown in FIG. 2, there are a plurality of tuyeres in the circumferential direction of the blast furnace body, and these tuyeres are partially opened. Thus, in operations where the tuyeres are partially opened to begin blowing, hot air is blown into the furnace only through the open tuyeres. Therefore, heating, reduction, and dissolution of iron ore occur only in the area where the high-temperature air blown through the tuyeres reaches. That is, the reaction caused by the high temperature air blown from the tuyere occurs only around the open tuyere shown in FIG. 2. Therefore, the reaction within the blast furnace becomes non-uniform in the circumferential direction between the upper part of the open tuyere and the upper part of the closed tuyere, causing a local drop in the raw material surface level at the top of the furnace.

FIG. 3 is a schematic diagram showing a state in which a local decrease in the raw material surface level occurs in the blast furnace. As shown in FIG. 3, since the reaction of the high temperature air occurs only around the partially opened tuyere, the height of the raw material surface locally decreases. The position where the height locally decreases on the raw material surface basically corresponds to the upper part of the open tuyere. However, the high temperature air rising from the tuyere does not necessarily correspond to the upper part of the open tuyere because it passes through the raw material and rises. Therefore, it is difficult to identify a position on the raw material surface where the height is locally reduced.

FIGS. 4(a) and 4(b) are schematic diagrams each showing a state of water sprayed by a watering nozzle of a watering device provided at the top of the furnace. As shown in FIG. 4(a), the top of the furnace is provided with a plurality of water spray nozzles in the circumferential direction. In FIG. 4, the water spray range by each water spray nozzle is illustrated. In the embodiment shown in FIGS. 4(a) and 4(b), there are two types of water nozzles, A and B, and the angles at which water is sprayed are different (the angle of water nozzle A is 40 degrees, and the angle of water spray nozzle B is 40 degrees). angle is set to 30 degrees). The water sprinkling device sprays water all at once from a plurality of water sprinkling nozzles when the furnace top gas temperature exceeds a temperature near a predetermined control upper limit.

Here, it is theoretically possible to locally reduce the furnace top gas temperature by spraying water from the water nozzle locally only on the part corresponding to the position where the height of the raw material surface has decreased. be. However, as described above, it is difficult to specify the position where the height of the raw material surface has decreased. Therefore, it is generally difficult to target localized drop positions with some water spray nozzles. As a result, in order to suppress the rise in the furnace top gas temperature, it is necessary to spray water all at once from a plurality of water spray nozzles. In that case, partial supercooling occurs in a portion corresponding to a position where the height of the raw material surface is not lowered.

Therefore, in this embodiment, the control upper limit temperature of the furnace top gas temperature is increased from the upper limit temperature during normal operation to a predetermined temperature within the upper limit temperature for equipment protection. The predetermined temperature within the upper limit temperature for equipment protection is preferably a temperature near the upper limit temperature for equipment protection. As a result, the amount of water sprinkled into the blast furnace by the water sprinkler can be suppressed, suppressing the rise in the furnace top gas temperature within a necessary range, and preventing the occurrence of partial supercooling. Here, the temperature near the upper limit temperature for equipment protection is preferably a temperature in the range of -20 to 0°C of the upper limit temperature for safety reasons. It is more preferable that the upper limit temperature is the same as above.

In addition, if water is sprinkled when charging raw materials into the blast furnace, cooling water will be directly splashed onto the raw materials being charged. When charging into the rotating chute), it stops. It is preferable that the water spraying be carried out for a relatively short period of time, such as 5 seconds, 6 seconds, or 30 seconds, and that the water spraying and the charging of the raw material be repeated alternately. By doing so, it is possible to prevent cooling water from directly splashing on the raw material, and as a result, it is possible to further suppress the occurrence of supercooling.

The blast furnace was actually started up after a long period of wind shutdown, and data on the number of tuyere openings, amount of water sprinkled, top gas temperature, and hot metal temperature were obtained. FIG. 5 is a graph showing data on the number of tuyere openings, the amount of water sprayed, the furnace top gas temperature, and the hot metal temperature at the time of starting up the blast furnace after a long-term wind break.

In this example, the upper limit temperature for equipment protection is 350°C, and it is dangerous if it exceeds 350°C even a little. When the blast furnace was restarted after a long period of hiatus, the upper limit for controlling the top gas temperature was initially set at 260°C, the same as the upper limit for normal operation. During normal operation, a mist spraying device is used instead of the watering device shown in FIGS. 4(a) and 4(b). In that case, the cooling effect (effect of suppressing temperature rise) is weak, so for safety reasons, it is necessary to set the upper limit temperature at a sufficiently low temperature. Therefore, during normal operation, the upper limit temperature is set at 260°C. .

When starting up the blast furnace after a long period of wind shutdown, we set the upper limit temperature to 260°C and proceeded with partial opening of the tuyeres, but the temperature approached the upper limit as soon as the blast furnace started. Therefore, in order to suppress the temperature rise, a water sprinkler sprayed a large amount of water (6 to 14 tons). As a result, the hot metal temperature decreased and supercooling occurred. Supercooling is unfavorable in terms of operation because it leads to a decrease in the viscosity of the slag. Therefore, in order to stop the occurrence of supercooling, the upper limit of the control temperature of the furnace top gas was raised to the upper temperature limit (350° C.) for equipment protection at the time position indicated by the arrow in the graph of the furnace top gas temperature.

As a result, the amount of water sprinkled was suppressed (reduced to about 3 tons), and the furnace top gas temperature and hot metal temperature became stable. As the tuyere opening was advanced, a balanced condition was achieved in the furnace, water spraying was no longer required, and the top gas temperature stabilized. Note that the higher the upper limit of the control temperature of the furnace top gas is, the closer to the upper limit of the temperature for equipment protection, the more water sprinkling is suppressed, which is preferable from the viewpoint of preventing overcooling. On the other hand, for safety reasons, it is necessary to avoid exceeding the upper temperature limit for equipment protection. Therefore, it is desirable to set the upper limit of the control temperature of the furnace top gas to a temperature in the range of -20°C to 0°C, which is the upper limit of the temperature for equipment protection.

As mentioned above, the upper limit of the control of the furnace top gas temperature is raised to a temperature close to the upper limit temperature for equipment protection (350°C in the above example), and the upper limit of control is used as the threshold of the furnace temperature control. The blast furnace is operated by repeatedly sprinkling water into the furnace and charging raw materials into the furnace without watering. In such a state, if the furnace top gas temperature falls to the control upper limit during normal operation (260° C. in the above example) without watering, it is preferable to return the control upper limit to the original value. That is, it is preferable to return the control upper limit from 350° C. to 260° C., use the returned control upper limit as the threshold for furnace temperature control, and operate the blast furnace without watering from the watering nozzle of the watering device. The reason for this is that as the opening of the tuyere progresses, the circumferential balance of reduction becomes stable, and the circumferential balance of the raw material level becomes uniform, so even if the control upper limit is returned to its original value, the amount of water sprinkled into the blast furnace will be kept to a minimum. This is because it can be kept to a minimum. Note that the timing for restoring the management upper limit is not limited to the example described above, and it is also possible to restore the management upper limit at a timing based on other criteria.

According to the blast furnace operating method according to the present invention, it is possible to provide a stable operating method not only for restarting a blast furnace but also for various vertical melting furnaces other than blast furnaces.

Claims (5)

In a blast furnace operating method when the tuyeres are closed for a long period of air suspension, at least a portion of the tuyere is opened to resume air blowing,
When sprinkling water into the furnace based on the top gas temperature in response to a local drop in the raw material surface level inside the blast furnace, the upper limit for controlling the furnace top gas temperature is changed from the upper limit temperature during normal operation to the upper limit temperature for equipment protection. A method of operating a blast furnace that raises the temperature to a specified temperature within The blast furnace operating method according to claim 1, wherein the predetermined temperature within the upper limit temperature for equipment protection is a temperature near the upper limit temperature for equipment protection. The blast furnace operating method according to claim 2, wherein the temperature near the upper limit temperature for equipment protection is a temperature in the range of -20° C. to 0° C. of the upper limit temperature. The blast furnace operating method according to any one of claims 1 to 3, wherein charging of raw materials into the blast furnace and sprinkling of water into the blast furnace are performed alternately. If the furnace top gas temperature drops to the control upper limit during normal operation without watering, the control upper limit is returned from a predetermined temperature within the upper limit temperature for equipment protection to the control upper limit temperature during normal operation. 3. The blast furnace operating method according to any one of 3.

Images