Blast furnace operation method

Abstract

To quickly recover the temperature of molten iron changed by the increase or decrease of the blowing amount of hydrogen gas.SOLUTION: In a blast furnace operation method capable of injecting pulverized coal and hydrogen gas, a first action for increasing the blowing amount of hydrogen gas from a second blowing amount to a third blowing amount is started during the blast furnace operation for blowing the pulverized coal at a first blowing amount. After a predetermined time has elapsed from the start of the first action, a second action of reducing the blowing amount of the pulverized coal from the first blowing amount to a fourth blowing amount is started. The predetermined time is preferably at least one hour or more.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for operating a blast furnace capable of injecting pulverized coal and hydrogen gas. [Background technology]

[0002] In recent years, in order to curb global warming, the CO generated in steelworks has been 2 There is a demand for reduction in CO2 emissions, and in blast furnace operation, there is a shift from an operation method in which pulverized coal is injected to an operation method in which pulverized coal and hydrogen gas are injected. As this replacement progresses, the reducing agent ratio decreases and CO 2 This can reduce emissions.

[0003] In a conventional blast furnace operation method, a reduction action for reducing the amount of pulverized coal injected and an increase action for increasing the amount of hydrogen gas injected were simultaneously carried out. However, this operating method had a problem in that the molten iron temperature dropped significantly after the reduction action and the increase action were carried out, and it took a long time for this dropped molten iron temperature to recover. The reason for the drop in the molten iron temperature is thought to be that the heat balance in the furnace is temporarily disrupted due to an increase in hydrogen gas. When the molten iron temperature decreases, the slag removal property of the molten iron slag decreases.

[0004] Furthermore, in the conventional blast furnace operation method, an increase action for increasing the amount of pulverized coal injected and a decrease action for decreasing the amount of hydrogen gas injected were simultaneously carried out. However, this operating method has a problem in that the molten iron temperature increases significantly after the increase action and decrease action are performed, and it takes a long time for this increased molten iron temperature to recover.

[0005] Patent Document 1 discloses a method for controlling molten iron temperature, which executes a first control loop for calculating a target value of the pulverized coal ratio so that the molten iron temperature predicted by a physical model capable of calculating the conditions inside the blast furnace falls within a preset target range, and a second control loop for calculating an operation amount of the pulverized coal flow rate to compensate for the deviation between the target value of the pulverized coal ratio and the current actual value of the pulverized coal ratio.

[0006] In Patent Document 2, a high-concentration hydrogen-containing gas containing 80 mol% or more of hydrogen gas is blown in at a predetermined temperature and amount, and the resulting gas is cooled to 100° C. 2 A method for operating a blast furnace to reduce CO2 emissions is disclosed. Patent Document 3 discloses a technology for ensuring a high molten iron temperature by keeping the ratio D / R, which is the distance D from the tip of the raceway formed in front of the tuyere to the furnace wall and the furnace body radius R at the tuyere height, within a predetermined range under conditions where the heat flow ratio β in the lower part of the furnace is 0.8 or more. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7107444 [Patent Document 2] Patent No. 7297091 [Patent Document 3] Patent No. 7276612 [Non-patent literature]

[0008] [Non-Patent Document 1] Nishioka, Ujizawa, Takaya, Nippon Steel & Sumitomo Metal Technical Review, No. 410 (2018) Summary of the Invention [Problem to be solved by the invention]

[0009] It is desirable to have a means for quickly restoring the molten iron temperature that has changed due to an increase or decrease in the amount of hydrogen gas injected. [Means for solving the problem]

[0010] In order to solve the above problems, one aspect of the blast furnace operation method of the present invention is characterized in that (1) in a blast furnace operation method capable of injecting pulverized coal and hydrogen gas, during blast furnace operation in which pulverized coal is injected at a first injection rate, a first action is initiated to increase the injection rate of hydrogen gas from a second injection rate to a third injection rate, and after a predetermined time has elapsed from the start of the first action, a second action is initiated to decrease the injection rate of pulverized coal from the first injection rate to a fourth injection rate.

[0011] (2) The method for operating a blast furnace according to (1) above, characterized in that the predetermined time is at least one hour or more.

[0012] (3) The method for operating a blast furnace according to (1) or (2) above, characterized in that, when a blast furnace operation in which an injection amount of pulverized coal is a first injection amount and an injection amount of hydrogen gas is a second injection amount is defined as a base operation and a cohesive zone height in the base operation is defined as 1, the specified time is set so that the cohesive zone height after start of the second action does not become 1.05 or more.

[0013] (4) The method for operating a blast furnace according to (1) or (2) above, characterized in that the predetermined time is less than 6 hours.

[0014] (5) A method of operating a blast furnace as described in (1) or (2) above, characterized in that, when a blast furnace operation in which the amount of pulverized coal injected is a first injection amount and the amount of hydrogen gas injected is a second injection amount is defined as a base operation, the third injection amount is set so that the furnace temperature in the base operation is the same as the furnace temperature after the start of the first action, and the fourth injection amount is set so that the furnace temperature in the base operation is the same as the furnace temperature after the start of the second action, and the furnace temperature is either the furnace top gas temperature or the temperature before the tuyere.

[0015] (6) The method for operating a blast furnace according to (5) above, characterized in that the third injection amount and the fourth injection amount are determined in advance using a blast furnace mathematical model capable of simulating an actual blast furnace.

[0016] From another viewpoint, the method for operating a blast furnace of the present invention is characterized in that (7) in a method for operating a blast furnace capable of injecting pulverized coal and hydrogen gas, during operation of the blast furnace injecting pulverized coal at a fifth injection amount, a third action is initiated to reduce the injection amount of hydrogen gas from a sixth injection amount to a seventh injection amount, and after a predetermined time has elapsed from the start of the third action, a fourth action is initiated to increase the injection amount of pulverized coal from the fifth injection amount to an eighth injection amount. Effect of the Invention

[0017] According to the invention of (1) above, since the action of reducing the amount of pulverized coal injection is started after the action of increasing hydrogen gas is started, the molten iron temperature that has decreased due to the increase in hydrogen gas can be quickly restored. In other words, since the amount of pulverized coal injection is maintained high for a predetermined time after the action of increasing hydrogen gas is started, the molten iron temperature can be quickly restored. According to the invention of (7) above, the amount of pulverized coal injected is maintained low for a predetermined time after the start of the action to reduce hydrogen gas, so that the molten iron temperature that was increased by such action can be quickly restored. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of a blast furnace. [Diagram 2] 1 is a flowchart for explaining a method of operating a blast furnace. [Diagram 3] 4 shows the simulated results of the molten iron temperature and the cohesive zone height. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (First embodiment) The first embodiment corresponds to a method for operating a blast furnace in which the amount of hydrogen gas injected is increased during an operation in which pulverized coal is injected. <Outline of blast furnace structure> FIG. 1 is a schematic diagram of a blast furnace in this embodiment. The blast furnace 1 is a bell-less type blast furnace, and includes a normal tuyere (in other words, a tuyere for blowing hot air) 2, a shaft tuyere 3, a circulating gas blowing section 4, an external gas blowing section 5, a pulverized coal blowing section 6, a swivel chute 7, and a tap hole 8. The present invention can also be applied to a bell-type blast furnace that does not have a swivel chute.

[0020] Typically, tuyere 2 is an inlet for blowing hot air generated in a hot stove (not shown) into blast furnace 1, and multiple tuyere are provided along the circumferential direction of blast furnace 1. An annular pipe (not shown) is disposed so as to surround the lower part of blast furnace 1, and multiple blowpipes (not shown) are provided on this annular pipe at predetermined intervals in the circumferential direction. The annular pipe supplies hot air sent from the hot stove to the blowpipes.

[0021] Each blowpipe is connected to an annular pipe and is also connected to a different normal tuyere 2. The blowpipe blows hot air sent from the annular pipe into the blast furnace 1 through the normal tuyere 2. The shaft tuyere 3 is a tuyere provided in the shaft portion of the blast furnace, and a plurality of shaft tuyere 3 are provided along the circumferential direction of the blast furnace 1. The blast furnace shaft has a shape that expands in diameter from top to bottom.

[0022] The circulating gas blowing section 4 can blow reformed gas obtained by reforming BFG (blast furnace gas) into the furnace from at least one of the normal tuyere 2 and the shaft tuyere 3 . Specifically, BFG to CO 2 The reformed gas from which the water vapor has been removed can be injected into the blast furnace 1 as a second reducing gas. The second reducing gas is at least N, H 2 , a gas containing CO, the gas containing CO gas being at least 20% by volume. In other words, by blowing the second reducing gas (reformed gas obtained by reforming BFG) into the furnace from at least one of the normal tuyere 2 and the shaft tuyere 3, hydrogen gas (pure hydrogen) contained in the second reducing gas is blown in. For this reason, there is a correlation between the amount of the second reducing gas and the amount of hydrogen gas contained in the second reducing gas, and therefore, by increasing or decreasing the amount of the second reducing gas, it is possible to increase or decrease the amount of hydrogen gas contained in the second reducing gas.

[0023] The external gas injection section 5 stores hydrogen-based reducing gas procured from outside the steelworks in a tank or the like, and can inject this hydrogen-based reducing gas as the first reducing gas into the furnace from at least one of the normal tuyere 2 and the shaft tuyere 3. The hydrogen-based reducing gas injected from the external gas injection part 5 is a gas containing hydrogen gas as a main component. Hydrogen gas includes pure hydrogen gas and hydrogen compound gas. The proportion of hydrogen gas in the gas in terms of volume fraction should be as high as possible, and is preferably 50% or more. Specifically, the first reducing gas may be any reducing gas introduced from outside the blast furnace system, such as pure hydrogen, COG, NG, city gas, NH 3 , C.H. 4 , C 2 H 4 , C 2 H 6 Examples include: When COG is injected, the pure hydrogen gas and CH 4 (Hydrogen compound gas) corresponds to "hydrogen gas". When blowing in city gas or NG, CH 4 (Hydrogen compound gas) etc. are equivalent to "hydrogen gas". NH 3 When blowing in NH 3 (Hydrogen compound gas) itself corresponds to "hydrogen gas" (CH 4 , C 2 H 4 and C 2 H 6 The same applies to . That is, by blowing the first reducing gas (hydrogen-based reducing gas) into the furnace from at least one of the normal tuyere 2 and the shaft tuyere 3, the hydrogen gas contained in the first reducing gas is blown in. Therefore, there is a correlation between the amount of the first reducing gas and the amount of hydrogen gas contained in the first reducing gas, and therefore, by increasing or decreasing the amount of the first reducing gas, it is possible to increase or decrease the amount of hydrogen gas contained in the first reducing gas.

[0024] The manner in which hydrogen gas is blown in will be exemplified below. (A) The first reducing gas (hydrogen-based reducing gas) is normally injected from the tuyere 2. The second reducing gas (reformed gas obtained by reforming BFG) is not normally injected from the tuyere 2. The first reducing gas and the second reducing gas are not injected from the shaft tuyere 3. As a result, hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) is normally blown in from the tuyere 2 . (B) A mixed gas of a first reducing gas (hydrogen-based reducing gas) and a second reducing gas is normally injected from the tuyere 2. Injection of the first reducing gas and the second reducing gas from the shaft tuyere 3 is not performed. As a result, hydrogen gas contained in the first reducing gas and the second reducing gas is normally blown in from the tuyere 2 . (C) The first reducing gas is normally injected through tuyere 2, and the second reducing gas is injected through shaft tuyere 3. As a result, hydrogen gas contained in the first reducing gas is normally blown in from the tuyere 2, Hydrogen gas contained in the second reducing gas is blown in from the shaft tuyere 3 . (D) The second reducing gas is normally injected from tuyere 2, and the first reducing gas (hydrogen-based reducing gas) is injected from shaft tuyere 3. As a result, hydrogen gas contained in the second reducing gas is normally blown in from the tuyere 2, Hydrogen gas contained in the first reducing gas is blown in from the shaft tuyere 3 . (E) A first reducing gas (hydrogen-based reducing gas) is injected from both the normal tuyere 2 and the shaft tuyere 3. No second reducing gas is injected. As a result, the hydrogen gas contained in the first reducing gas is blown in from the normal tuyere 2 and the shaft tuyere 3 . (F) The second reducing gas is injected from both the normal tuyere 2 and the shaft tuyere 3. The first reducing gas (hydrogen-based reducing gas) is not injected. As a result, the hydrogen gas contained in the second reducing gas is blown in from the normal tuyere 2 and the shaft tuyere 3 . (G) The second reducing gas is injected from the normal tuyere 2. The first reducing gas (hydrogen-based reducing gas) is not injected from the normal tuyere 2. The first reducing gas (hydrogen-based reducing gas) and the second reducing gas are not injected from the shaft tuyere 3. As a result, the hydrogen gas contained in the second reducing gas is injected from the normal tuyere 2. In addition, modes (A) to (C) have a higher carbon consumption reduction effect than modes (D) to (G).

[0025] The pulverized coal injection section 6 injects pulverized coal into the furnace from a lance extending into the inside of the blowpipe, usually via the tuyere 2 .

[0026] The injection amounts of the first reducing gas and the second reducing gas can be controlled, for example, by adjusting the pressure of a blower or the like. The injection amount of pulverized coal can be adjusted, for example, by the amount of injected air. As described above, by changing the injection amounts of the first reducing gas and the second reducing gas, the injection amount of hydrogen gas contained in these reducing gases is adjusted. The adjustment may be performed by remote control from an operator's room or manually by an operator. Here, the amount of hydrogen gas injected is the amount of hydrogen gas (Nm 3 / t). The amount of pulverized coal injected is the weight of pulverized coal (kg / t) required to produce 1 ton of molten iron.

[0027] The rotating chute 7 charges the iron raw materials and coke alternately in layers while rotating around an axis extending in the vertical direction. The iron raw materials may be lump ore, sintered ore, pellets, unburned carbon-containing agglomerated ore, etc. The iron raw materials may also contain a reduction aid such as small lump coke. The coke may also contain ferro coke. By controlling the drive method (forward tilting / reverse tilting), tilting angle, and rotation speed of the rotating chute 7, the blast furnace raw materials can be charged at a desired position. Note that forward tilting refers to a drive method in which the rotating chute 7 is driven from the furnace wall side toward the furnace center side, and reverse tilting refers to a drive method in which the rotating chute 7 is driven from the furnace center side toward the furnace wall side.

[0028] The tap hole 8 is provided at the bottom of the blast furnace 1, and taps the molten iron produced by reducing the iron raw material. A plurality of tap holes 8 are provided around the periphery of the furnace, and the molten iron can be tapped continuously or intermittently.

[0029] The blast furnace operation method of this embodiment will be described in detail with reference to the flowchart of Fig. 2. The reducing gas injection mode in this flowchart is, as an example, in accordance with the above-mentioned mode (A) in which only the first reducing gas (hydrogen-based reducing gas) is injected. In S101, the blast furnace is operated while injecting pulverized coal from the pulverized coal injection section 6. This blast furnace operation is a proven conventional blast furnace operation, and is hereinafter also referred to as base operation. It goes without saying that the base operation is stable operation. Stable operation refers to an operating state in which the gas flow in the furnace and the temperature distribution of the packed bed are appropriately controlled. For convenience of explanation, the amount of pulverized coal injected in S101 is defined as a first injection amount. The first injection amount is a value greater than 0 and does not fluctuate over a long period of time (e.g., 24 hours or more) (however, small fluctuations are considered to be no fluctuation).

[0030] Here, an operation in which the first reducing gas (hydrogen-based reducing gas) is injected together with the pulverized coal may be the base operation. In other words, when the injection amount of the hydrogen gas contained in the first reducing gas in S101 (base operation) is defined as the second injection amount, the second injection amount may be 0 or may be greater than 0. When the second injection amount is greater than 0, a value that does not fluctuate over a long period of time (e.g., 24 hours or more) (however, small fluctuations are considered to be no fluctuation) is defined as the second injection amount.

[0031] In S102, an action (hereinafter also referred to as the "first action") is started to increase the amount of hydrogen gas contained in the first reducing gas injected from the second amount to a third amount (in other words, the target amount of hydrogen gas contained in the first reducing gas injected) while maintaining the amount of pulverized coal injected at the first amount. The third injection amount can be appropriately set in consideration of the operating conditions of the base operation, the furnace volume, etc. For example, an operating condition can be set to "the furnace top gas temperature in the base operation is the same as the furnace top gas temperature after increasing the injection amount of the hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas)," and the injection amount of the hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) that satisfies such an operating condition can be set to the third injection amount. In addition, the operating condition is that "the temperature before the tuyere in the base operation is the same as the temperature before the tuyere after the injection amount of the hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) is increased," and the injection amount of the hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) that satisfies the operating condition can be set as the third injection amount. The injection amount of the hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) can be searched based on a blast furnace mathematical model (see, for example, Non-Patent Document 1) that can simulate an actual blast furnace. The blast furnace mathematical model searches for an injection amount of hydrogen gas that satisfies the above-mentioned operating condition while adjusting the blast amount and the oxygen enrichment amount. Then, the searched injection amount can be set as the third injection amount. The third injection amount is a value that does not change over a long period of time (for example, 24 hours or more) (however, small fluctuations are considered to be no fluctuation). In addition, if the temperature difference from the top gas temperature (temperature before the tuyere) during base operation is within 3°C, it can be considered to be "the same" (the same applies below).

[0032] When the first reducing gas (hydrogen-based reducing gas) and the second reducing gas are blown together as exemplified in the above-mentioned modes (B) to (D), the sum of the blown amounts of hydrogen gas contained in these gases may be set as the second blown amount and the third blown amount. When increasing the blown amount of hydrogen gas from the second blown amount to the third blown amount, only the blown amount of hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) may be increased, only the blown amount of hydrogen gas contained in the second reducing gas may be increased, or both the blown amounts of hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) and the second reducing gas may be increased.

[0033] The furnace top gas temperature is the temperature of the CO gas and N gas discharged from the furnace top. 2 This refers to the temperature of gas, etc., and can be measured using a furnace top gas thermometer, etc. The temperature before the tuyere generally refers to the temperature inside the furnace at the tip of the tuyere 2, and for example, the theoretical combustion temperature calculated based on a known calculation method (for example, Ram's calculation formula) can be taken as the temperature before the tuyere.

[0034] Increasing the amount of hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) injected causes the heat balance in the furnace to be disrupted, and the molten iron temperature temporarily drops (the same applies when the amount of hydrogen gas contained in the second reducing gas is increased). The amount of hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) that is blown in reaches the target value in about a few minutes (the same applies when the amount of hydrogen gas contained in the second reducing gas that is blown in is increased).

[0035] In S103, it is determined whether a predetermined time has elapsed since the start of the first action. The predetermined time may be counted automatically by a control device that controls the blast furnace, or may be counted by an operator using a timing device such as a time watch. The "predetermined time" will be described later. If the elapsed time has not reached the predetermined time (S103 No), the first action is continued without changing the injection amount of pulverized coal from the first injection amount. If the predetermined time has elapsed (S103 Yes), the process proceeds to S104.

[0036] In S104, an action (hereinafter also referred to as a second action) is started to reduce the amount of pulverized coal injected from the first amount to a fourth amount. The fourth amount can be appropriately set in consideration of the operating conditions of the base operation, the furnace volume, and the like. For example, an operating condition can be set as "the furnace gas temperature during base operation is the same as the furnace gas temperature after the amount of pulverized coal injection is reduced," and the amount of pulverized coal injection that satisfies such an operating condition can be set as the fourth injection amount. In addition, the operating condition is set to "the temperature in front of the tuyere during base operation is the same as the temperature in front of the tuyere after the amount of pulverized coal injection is reduced," and the amount of pulverized coal injection that satisfies this operating condition can be set to the fourth injection amount. The injection amount of the pulverized coal can be searched for based on a blast furnace mathematical model (see, for example, Non-Patent Document 1) capable of simulating an actual furnace. The blast furnace mathematical model searches for an injection amount of the pulverized coal that satisfies the above-mentioned operating conditions while adjusting the blast amount and the oxygen enrichment amount. Then, the searched injection amount can be set as the fourth injection amount. Even after the second action is started, the blowing amount of the hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) is not changed and the third blowing amount is maintained.

[0037] In this way, by starting the second action with a delay from the start of the first action, the molten iron temperature that has been reduced by increasing the amount of hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) can be quickly restored. In other words, the amount of pulverized coal injected immediately after starting the process of increasing the injection amount of hydrogen gas contained in the first reducing gas (hydrogen-based reducing gas) is maintained at a high level (first injection amount), so that a large amount of pulverized coal can be burned. This enables the molten iron temperature to be quickly restored to the level during base operation, compared to the conventional method (in which the action of injecting hydrogen-based reducing gas and the action of reducing the amount of pulverized coal injected are initiated simultaneously). It goes without saying that the same effect can also be obtained in the blowing modes (B) to (G) different from the blowing mode (A).

[0038] The "predetermined time" in S103 may be any value greater than 0, and is preferably one hour or greater. As the "predetermined time" becomes longer, the effect of early recovery of the molten iron temperature increases. Therefore, there is no particular limit on the upper limit of the "predetermined time". However, if the "predetermined time" becomes too long, excessive pulverized coal will be charged, resulting in large fluctuations in the cohesive zone height. If the fluctuations in the cohesive zone height become large, the gas flow in the furnace will change significantly, which may lead to gas flow fluctuations. Therefore, it is desirable to set an upper limit on the predetermined time so as to prevent gas flow fluctuations.

[0039] Here, when the cohesive zone height in the base operation is defined as 1 (a dimensionless value), it is desirable to set the upper limit of the "predetermined time" so that the cohesive zone height after the start of the second action (the action of reducing the amount of pulverized coal injection) does not become 1.05 or more. If the cohesive zone height is suppressed to less than 1.05, the occurrence of gas flow fluctuations can be effectively prevented. An appropriate upper limit value of the predetermined time cannot be uniquely defined because it varies depending on the furnace volume, the operating conditions of the blast furnace, etc., but can be appropriately searched for based on the above-mentioned blast furnace mathematical model. In the examples described later, the height of the cohesive zone is kept below 1.05 by keeping the predetermined time below 6 hours. The main object of the present invention is to "quickly recover the molten iron temperature", not to "keep the cohesive zone height below 1.05". For the above reasons, claim 1 does not state an "upper limit of the predetermined time". As is well known, in a blast furnace, there is a temperature range where the temperature of the iron raw material is about 1200 (a temperature range where the iron raw material softens). In this embodiment, the height from the center of a tap hole 8 located in a certain furnace radial direction to this temperature range is defined as the "cohesive zone height."

[0040] Second embodiment The second embodiment corresponds to a method for operating a blast furnace in which the amount of hydrogen gas injected during an operation in which pulverized coal is injected is reduced. The method for operating a blast furnace according to the second embodiment can be realized by the blast furnace shown in FIG. During blast furnace operation in which pulverized coal is injected at the fifth injection rate, the injection rate of hydrogen gas is reduced from the sixth injection rate to the seventh injection rate (corresponding to the third action). The seventh injection rate is set by the same method as that of the first embodiment. The injection mode of hydrogen gas is also set by the same method as that of the first embodiment. After a predetermined time has elapsed from the start of the third action, the injection amount of pulverized coal is increased from the fifth injection amount to the eighth injection amount (corresponding to the fourth action). The method of setting the eighth injection amount is the same as that of the second embodiment.

[0041] In this way, by starting the fourth action with a delay from the start of the third action, the molten iron temperature that has risen due to the reduction in the amount of hydrogen gas injection can be quickly restored. In other words, by maintaining the amount of pulverized coal injection at a low level (the fifth injection amount) immediately after the amount of hydrogen gas injection is reduced, the increase in the molten iron temperature due to the combustion of a large amount of pulverized coal can be suppressed. This enables the molten iron temperature to be quickly restored to the level during base operation, compared to the conventional method (which simultaneously initiates an action to reduce the amount of hydrogen-based reducing gas injected and an action to increase the amount of pulverized coal injected).

[0042] The present invention will be specifically described with reference to an example. This example corresponds to the first embodiment. The hydrogen gas was blown in in the manner (A) described above. The molten metal temperature and the cohesive zone height when pulverized coal and the first reducing gas (hydrogen gas contained in the first hydrogen gas) were injected in the injection patterns of Example 1, Example 2, and Comparative Example 1 were simulated using the blast furnace mathematical model described in Non-Patent Document 1. The first reducing gas was city gas. In Example 1, the amount of the first reducing gas injected was varied from 0 to 12 Nm 3 / t (increasing the amount of hydrogen gas injected from the second injection rate to the third injection rate), and three hours after the start of this action, an action was started to decrease the amount of pulverized coal injected from the first injection rate (219.4 kg / t) to the fourth injection rate (208.7 kg / t). In Example 2, the amount of the first reducing gas injected was varied from 0 to 12 Nm 3 / t (increasing the amount of hydrogen gas injected from the second rate to the third rate), and six hours after the start of this action, an action was started to decrease the amount of pulverized coal injected from the first rate (219.4 kg / t) to the fourth rate (208.7 kg / t). In Comparative Example 1, the first reducing gas injection amount was changed from 0 to 12 Nm 3 / t (an action to increase the amount of hydrogen gas contained in the first reducing gas from the second amount to the third amount), and an action to decrease the amount of pulverized coal injected from the first amount (219.4 kg / t) to the fourth amount (208.7 kg / t) were simultaneously started.

[0043] The third and fourth injection rates were determined so that the furnace top gas temperature was the same as that in the base operation. Table 1 shows the operating parameters for base operation and the operating parameters after reducing the amount of pulverized coal injection (also called high NG operation). [Table 1]

[0044] FIG. 3 shows the simulation results of Examples 1 and 2 and Comparative Example 1. The time when the injection of the first reducing gas (hydrogen gas contained in the first hydrogen gas) started was set to "0". Comparative Example 1 is shown by a solid line, Example 1 (after 3 hours) by a dashed line, and Example 2 (after 6 hours) by a dotted line. As described above, it takes several minutes for the injection amount to switch to the target injection amount, but this is omitted in FIG. 3. In other words, the injection amount of the first reducing gas and the injection amount of pulverized coal are shown as set values ​​displayed on a screen or the like.

[0045] In Comparative Example 1, it took about 20 hours for the molten iron temperature to recover to the level during base operation, but in Examples 1 and 2, this time could be shortened to about 3 hours. Furthermore, the maximum value of the cohesive zone height was 8.5 m in Example 2, but it was possible to suppress it to about 8.3 m in Example 1. Since the cohesive zone height during base operation is about 8.1 m, when this is taken as "1", the cohesive zone height in Example 1 is about "1.02", and the cohesive zone height in Example 2 is about "1.05". It was found that by setting the predetermined time to less than 6 hours, the cohesive zone height can be suppressed while hastening the recovery of the molten pig iron temperature. [Explanation of symbols]

[0046] 1 blast furnace 2 Normal tuyere 3 Shaft tuyere 4 Circulating gas blowing section 5 External gas inlet 6. Pulverized coal injection section 7 Swivel Shot 8 Taphole

Claims

1. A method for operating a blast furnace capable of injecting pulverized coal and hydrogen gas, comprising: During operation of the blast furnace injecting pulverized coal at a first injection rate, a first action is started to increase an injection rate of hydrogen gas from a second injection rate to a third injection rate; a second action is started to reduce the injection amount of the pulverized coal from the first injection amount to a fourth injection amount after a predetermined time has elapsed since the start of the first action; A method for operating a blast furnace comprising the steps of:

2. The predetermined time is at least 1 hour.

2. The method for operating a blast furnace according to claim 1 .

3. When a blast furnace operation in which the amount of pulverized coal injected is the first injection amount and the amount of hydrogen gas injected is the second injection amount is defined as a base operation, and the height of the cohesive zone in the base operation is defined as 1, The predetermined time is set so that the height of the cohesive zone after the start of the second action does not become 1.05 or more.

3. The method for operating a blast furnace according to claim 1 or 2.

4. The predetermined time is less than 6 hours.

3. The method for operating a blast furnace according to claim 1 or 2.

5. When the blast furnace operation in which the amount of pulverized coal injected is the first injection amount and the amount of hydrogen gas injected is the second injection amount is defined as the base operation, The third blowing amount is set so that the furnace temperature during the base operation is equal to the furnace temperature after the start of the first action, The fourth blowing amount is set so that the furnace temperature during the base operation is equal to the furnace temperature after the start of the second action; The furnace temperature is either the furnace top gas temperature or the temperature before the tuyere; 3. The method for operating a blast furnace according to claim 1 or 2.

6. The method for operating a blast furnace according to claim 5, characterized in that the third injection amount and the fourth injection amount are grasped in advance by using a blast furnace mathematical model capable of simulating an actual blast furnace.

7. A method for operating a blast furnace capable of injecting pulverized coal and hydrogen gas, comprising: During operation of the blast furnace injecting pulverized coal at the fifth injection rate, a third action is started to reduce the injection rate of hydrogen gas from the sixth injection rate to a seventh injection rate; After a predetermined time has elapsed from the start of the third action, a fourth action is started to increase the injection amount of the pulverized coal from a fifth injection amount to an eighth injection amount. A method for operating a blast furnace comprising the steps of:

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