Blast furnace operation method

Abstract

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

Description

[Technical field]

[0001] The present invention relates to a blast furnace operation method for effectively cooling the furnace top when the operation is stopped, the blast furnace is quenched, and then the furnace is started up again. [Background technology]

[0002] In a blast furnace, high-temperature reducing gas is generated by the reaction between the high-temperature air and oxygen blown into the furnace through a blast hole called a tuyere and the coke and pulverized coal inside the furnace. The high-temperature reducing gas generated in a blast furnace heats, reduces, and melts the iron ore, and the pig iron and slag are discharged from the tap hole installed below the tuyere to the outside of the furnace. During normal operation, the reaction heat inside the furnace and the heat supply from the tuyere are balanced, allowing the blast furnace to operate stably.

[0003] Here, the high-temperature reducing gas generated by the reaction in the furnace heads toward the top of the blast furnace. If the surface level of the raw materials drops below the standard, the time for the reduction reaction with the raw materials becomes shorter, and the top gas temperature rises. At this time, there is a risk of damage to equipment through which the high-temperature reducing gas passes, such as blast furnace gas cleaning equipment. To prevent such damage, a sprinkler system installed at the top of the furnace sprays water into the furnace. The function required of this cooling system is to lower the gas temperature at the top of the furnace without cooling the blast furnace raw materials themselves that are charged into the furnace.

[0004] When a blast furnace is shut down or shut down for an extended period of time, the heat supply to the furnace is stopped. However, heat continues to be released due to the temperature difference between the inside of the furnace and the atmosphere, causing the furnace to cool and some of the molten material to solidify. Therefore, when the blast furnace is restarted, that is, when blowing is restarted, it is necessary to melt the solidified layer in the furnace and heat the coke packed layer through which the solidified material passes until the molten material can pass through.

[0005] Therefore, when a blast furnace is shut down for an extended period or when it is expected to be restarted, first, after normal operation is completed, reduced-scale operation is carried out to lower the raw material level, and then the shutdown period is started with the raw material level lowered. After the shutdown period is completed, start-up operation is carried out to raise the raw material level and return to normal operation.

[0006] In the reduced scale operation, the reduced scale level is lowered. That is, without charging raw materials while blowing hot air, the tuyere is opened all around, and the raw material level is uniformly lowered in the circumferential direction. Therefore, the amount of water sprayed at the top of the furnace is adjusted only according to the rise in the furnace top gas temperature. At that time, the coke ratio in the furnace is increased and the blast furnace is stopped, and thermal compensation is performed until the injection of pulverized coal can be started after the blast. At the same time, all but one or two tuyere above the tap hole are blocked with refractories or the like to limit the amount of molten iron and slag generated with the blast, and a cycle of smooth discharge of a small amount of molten material is established. In the subsequent start-up operation, the reduced scale level is raised. That is, when the raw material level is raised, the tuyere in the adjacent area is opened, and the number of open tuyere is gradually increased, and normal operation is restored (Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6947345 Summary of the Invention [Problem to be solved by the invention]

[0008] In the start-up operation where the tuyere is partially opened and the blowing of air is started, the high-temperature air is blown into the furnace only from the open tuyere, so the temperature rise, reduction, and melting of the iron ore are only performed in the area where the high-temperature air blown in from the open tuyere reaches. As a result, the reaction in the blast furnace becomes uneven in the circumferential direction, and the surface level of the raw materials at the top of the furnace is locally lowered. This phenomenon causes a localized rise in the top gas temperature, and water is sprayed into the furnace from the top water sprinkler system. At that time, there was a problem that the cooling water was directly deposited on the raw materials themselves in large amounts in the areas where the surface level of the raw materials was not lowered, causing them to be overcooled, leading to a drop in the temperature inside the furnace.

[0009] The object of the present invention is to propose a blast furnace operation method that can solve the above problems, prevent a decrease in the furnace temperature due to a local decrease in the surface level of the raw materials, and appropriately suppress the furnace top gas temperature. [Means for solving the problem]

[0010] The blast furnace operation method of the present invention was developed to solve the above-mentioned problems, and is a blast furnace operation method in which the tuyere is closed for a long period of time due to a blast furnace shutdown, and then at least a portion of the tuyere is opened to resume blasting, in which, in response to a local drop in the surface level of the raw materials in the blast furnace, water is sprayed into the furnace based on the top gas temperature, and the upper limit of the control of the top gas temperature is raised from the upper limit temperature during normal operation to a predetermined temperature within the upper limit temperature for equipment protection.

[0011] In addition, in the blast furnace operation method of the present invention, (1) In the present invention, the predetermined temperature within the upper limit temperature for equipment protection is a temperature in the vicinity of the upper limit temperature for equipment protection; (2) In the above (1), 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, (1) or (2), the charging of raw materials into the blast furnace and the spraying of water into the blast furnace are alternately performed; (4) In any of the present invention, (1), (2) and (3), when the furnace top gas temperature falls to the upper control limit during normal operation without water spraying, returning the upper control limit from a temperature close to the upper limit temperature for equipment protection to the upper control limit temperature during normal operation; This is believed to be a more preferable solution. Effect of the Invention

[0012] According to the blast furnace operation method of the present invention, when the tuyere is partially opened to resume blasting after a long period of blasting or shutdown, it is possible to prevent a drop in the furnace temperature and damage to the furnace top equipment. As a result, it is possible to stabilize the blast furnace start-up operation and reduce the risk of equipment damage. [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 top view of a blast furnace at tuyere level to illustrate open and closed tuyere. [Diagram 3] FIG. 2 is a schematic diagram showing a state in which a local drop in the surface level of raw materials occurs in a blast furnace. [Figure 4] 1(a) and 1(b) are schematic diagrams showing the state of water sprayed by the sprinkler nozzles of the sprinkler device installed at the top of the furnace. [Diagram 5] 1 is a graph showing data on the number of open tuyeres, the amount of water sprayed, the furnace top gas temperature, and the molten iron temperature at the time of starting up a blast furnace after a long period of blast shutdown. 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] As described above, when the tuyere is partially opened to start blowing, the reaction in the blast furnace becomes non-uniform in the circumferential direction. As a result, the raw materials remaining at the top of the furnace before the blast furnace is stopped or stopped react locally, causing a phenomenon in which the height position of the raw material surface is locally lowered, and the furnace top gas temperature rises locally. In contrast, when water is sprayed by a water sprinkler, there are places where the slag becomes supercooled. As a result, the viscosity of the slag decreases at those places, and operational problems such as difficulty in discharging the slag occur. According to an embodiment of the present invention, the upper limit of the top gas temperature is raised to a temperature near the upper limit temperature for equipment protection. This makes it possible to reduce the amount of water sprayed into the blast furnace, prevent a drop in the furnace temperature due to a local drop in the raw material surface level, and appropriately suppress the furnace top gas temperature.

[0016] 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 portion, a furnace top portion, a furnace belly portion, a morning glory portion, a hearth, and a tuyere. In the cross-sectional view shown in FIG. 1, only one tuyere is shown, but the blast furnace body has multiple tuyere in the circumferential direction. Since the tuyere is blocked with clay when the blast furnace is stopped, the tuyere blocked with clay is first opened when the operation starts. As described above, since there are multiple tuyere, they are partially opened. A known tuyere opening machine can be used to open the tuyere. High-temperature air is blown in order from the partially opened tuyere.

[0017] FIG. 2 is a top view of the tuyere level of a blast furnace for explaining an open tuyere and a closed tuyere. As shown in FIG. 2, there are a plurality of tuyere in the circumferential direction of the blast furnace body, and they are partially opened. In this way, in an operation in which the tuyere is partially opened and blowing is started, high-temperature air is blown into the furnace only from the open tuyere. Therefore, the temperature rise, reduction, and melting of the iron ore are only performed in the part where the high-temperature air blown from the open tuyere reaches. In other words, 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 in the blast furnace becomes uneven in the circumferential direction between the upper part of the open tuyere and the upper part of the closed tuyere, and a local drop in the raw material surface level at the top of the furnace occurs.

[0018] FIG. 3 is a schematic diagram showing a state in which a local drop in the raw material surface level occurs in a blast furnace. As shown in FIG. 3, the reaction of high-temperature air occurs only around the partially opened open tuyere, so the height of the raw material surface drops locally. The position where the height drops locally on the raw material surface basically corresponds to the upper part of the open open tuyere. However, since the high-temperature air rising from the tuyere rises through the raw material, it does not necessarily correspond to the upper part of the open tuyere. Therefore, it is difficult to identify the position where the height drops locally on the raw material surface.

[0019] 4(a) and 4(b) are schematic diagrams showing the state of water sprayed by the sprinkler nozzles of the sprinkler device installed at the furnace top. As shown in FIG. 4(a), the furnace top is provided with multiple sprinkler nozzles in the circumferential direction. FIG. 4 illustrates the range of water sprayed by each sprinkler nozzle. In the embodiment shown in FIG. 4(a) and 4(b), there are two types of sprinkler nozzles, A and B, which have different angles for spraying water (the angle of sprinkler nozzle A is set to 40 degrees, and the angle of sprinkler nozzle B is set to 30 degrees). When the furnace top gas temperature exceeds a temperature near a predetermined upper limit of control, the sprinkler device sprays water from multiple sprinkler nozzles at the same time.

[0020] Here, it is theoretically possible to locally lower the top gas temperature by spraying water from the water sprinkler nozzles only at the portion corresponding to the position where the height of the raw material surface has decreased. However, as described above, it is difficult to identify the position where the height of the raw material surface has decreased. Therefore, it is generally difficult to target the localized position of the decrease with a certain water sprinkler nozzle. As a result, in order to suppress the rise in the top gas temperature, it is necessary to spray water from multiple water sprinkler nozzles at the same time. In that case, partial supercooling will occur in the portion corresponding to the position where the height of the raw material surface has not decreased.

[0021] Therefore, in this embodiment, the upper limit of the furnace gas temperature is increased from the upper limit of normal operation to a predetermined temperature within the upper limit of equipment protection. The predetermined temperature within the upper limit of equipment protection is preferably a temperature close to the upper limit of equipment protection. As a result, the amount of water sprinkled into the blast furnace by the sprinkler device is reduced, and the increase in the furnace gas temperature is suppressed within a necessary range, and the occurrence of partial supercooling can be prevented. Here, the temperature close to the upper limit of equipment protection is preferably a temperature in the range of −20 to 0° C. of the upper limit for safety reasons, and more preferably the upper limit of equipment protection itself from the viewpoint of preventing supercooling.

[0022] If water is sprayed when the raw materials are charged into the blast furnace, the cooling water will directly splash onto the raw materials being charged, so water spraying from the sprinkler system is stopped when the raw materials are being charged (when the iron ore and coke are being charged into the rotating chute). It is preferable to spray water for a relatively short period of time, such as 5, 6, or 30 seconds each time, and to alternate between spraying water and charging the raw materials. In this way, it is possible to prevent the cooling water from splashing directly onto the raw materials, and as a result, the occurrence of supercooling can be further suppressed. EXAMPLES

[0023] In fact, a blast furnace was started up after a long period of shutdown, and data on the number of open tuyeres, the amount of water sprayed, the top gas temperature, and the molten iron temperature were obtained. Figure 5 is a graph showing data on the number of open tuyeres, the amount of water sprayed, the top gas temperature, and the molten iron temperature at the time of starting up a blast furnace after a long period of shutdown.

[0024] In this embodiment, the upper limit temperature for equipment protection is 350°C, and even a slight increase above 350°C is dangerous. When starting up a blast furnace after a long period of shutdown, the upper limit of the furnace gas temperature was initially set to 260°C, the same as the upper limit temperature during normal operation. During normal operation, a device that sprinkles water in a mist form is used instead of the sprinkler device shown in Figures 4(a) and (b). In this case, the cooling effect (the effect of suppressing temperature rise) is weak, so for safety reasons, it is necessary to set the upper limit temperature at a sufficiently low level, and therefore the upper limit temperature during normal operation is set to 260°C.

[0025] When the blast furnace was started up after a long period of shutdown, the upper limit of the temperature control was set at 260°C, and partial opening of the tuyeres was carried out, but the temperature approached the upper limit soon after starting. Therefore, in order to suppress the temperature rise, the sprinkler system sprayed large amounts of water (6 to 14 tons). As a result, the temperature of the molten iron dropped, and supercooling occurred. Supercooling is undesirable from an operational standpoint, as 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 top gas temperature control was raised to the upper limit for equipment protection (350°C) at the time position indicated by the arrow on the graph of the top gas temperature.

[0026] As a result, the amount of water sprayed was reduced (to about 3 tons), and the top gas temperature and molten iron temperature stabilized. As the tuyere opening was advanced, a balanced state was achieved inside the furnace, water spraying became unnecessary, and the top gas temperature stabilized. Note that the higher the upper limit of the top gas temperature control is, the closer it is to the upper limit of the temperature for equipment protection, and the more water spraying 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 limit of the temperature for equipment protection. Therefore, it is desirable to set the upper limit of the top gas temperature control to a temperature in the range of -20℃ to 0℃, which is the upper limit of the temperature for equipment protection.

[0027] As described 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 the control is used as the threshold value of the furnace temperature control, and the blast furnace is operated by repeating water sprinkling into the furnace and charging the raw materials into the furnace without sprinkling. In such a state, if the furnace top gas temperature falls to the upper limit of the control during normal operation (260 ° C. in the above example) without sprinkling water, it is preferable to return the upper limit of the control to its original state. That is, it is preferable to return the upper limit of the control from 350 ° C. to 260 ° C., and use the returned upper limit of the control as the threshold value of the furnace temperature control, and operate the blast furnace without sprinkling water from the sprinkler nozzle of the sprinkler device. The reason for this is that the opening of the tuyere progresses, the circumferential balance of the reduction is stabilized, and the circumferential balance of the raw material level becomes uniform, so that even if the upper limit of the control is returned to its original state, the amount of water sprinkled into the blast furnace can be minimized. The timing of returning the upper limit of the control to its original state is not limited to the above example, and it is also possible to return the upper limit of the control to its original state based on other criteria. [Industrial Applicability]

[0028] According to the blast furnace operation method of the present invention, a stable operation method can be provided not only for restarting a blast furnace, but also for various vertical melting furnaces other than a blast furnace.

Claims

1. A method for operating a blast furnace when at least a part of the tuyere is opened to resume blowing after the tuyere has been closed for a long period of time due to a blast furnace shutdown, the method comprising the steps of: in a process of sequentially opening the tuyere, in response to a local drop in the surface level of raw materials in the blast furnace, alternately sprinkling water into the furnace and charging raw materials into the furnace based on a furnace top gas temperature; First, the upper limit of the furnace gas temperature is set as the threshold value, and the tuyere opening is performed sequentially without water spraying. When the temperature of the furnace gas reaches near the upper limit of the control, the first amount of water is sprayed. When the temperature of the molten iron is lowered by the spraying of the first amount of water, the upper limit of the furnace gas temperature as a threshold value is set to a predetermined temperature in the range of −20° C. to 0° C., which is the upper limit temperature for equipment protection, and the spraying of water is switched to a second amount of water less than the first amount of water; When the furnace gas temperature and molten iron temperature stabilized, water spraying was stopped. When the furnace top gas temperature falls to the upper limit of normal operation without water spraying, the temperature is returned to the upper limit of normal operation, which is a predetermined temperature close to the upper limit of equipment protection as a threshold value. Blast furnace operating methods.

2. A blast furnace operation method as described in claim 1, wherein the first water rate of the water spray is 6 to 14 t / h, and the second water rate of the water spray is 3 t / h or less.

3. A blast furnace operation method as described in claim 1 or 2, wherein the upper control limit temperature of the top gas is 260°C and the upper limit temperature for equipment protection is 350°C.

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