Blast furnace operation method

Abstract

A blast furnace operation method according to one aspect of the present disclosure comprises: a parameter estimation step for estimating blast parameters and a pulverized coal ratio in a second operation, such that the amount molten iron produced, the molten iron temperature, and the furnace top gas temperature in the second operation match those in a reference operation; a change information acquisition step for acquiring information on a temporal change in one or both of the molten iron temperature and the amount of molten iron produced when performing the second operation based on the blast parameters and the pulverized coal ratio estimated in the parameter estimation step with a delay of a predetermined time after switching from the reference operation to the first operation; a repeating step for performing the change information acquisition step a plurality of times while changing the predetermined time; and an optimum delay time acquisition step for determining, as an optimum delay time, a predetermined time such that the temporal change in the molten iron temperature or the amount of molten iron produced is the smallest, on the basis of the information acquired in the repeating step. After switching from the reference operation to the first operation, the second operation based on the blast parameters and the pulverized coal ratio estimated in the parameter estimation step is started with a delay of the optimum delay time.

Description

Blast furnace operation method

[0001] This application claims priority to Japanese Patent Application No. 2024-027364, filed on February 27, 2024, the contents of which are incorporated herein by reference.

[0002] In blast furnace operation, iron sources such as sintered ore, pellets, and lump ore (collectively referred to as "iron raw materials") and coke as a reducing agent and fuel are alternately charged from the top of the furnace, and hot air is blown through tuyeres in the lower part of the furnace, along with an auxiliary fuel such as pulverized coal. The iron raw materials and coke (collectively referred to as "burden materials") charged from the top of the furnace form alternating ore and coke layers. As the burden materials are lowered, they gradually descend within the blast furnace toward the lower part of the furnace, where they are heated by gases rising from the lower part of the furnace and their temperature is raised. The iron raw materials descend while being heated and reduced within the blast furnace, melting and separating into pig iron and slag, which drip onto the hearth.

[0003] To date, blast furnace operation methods have been studied in which a portion of the iron raw material is replaced with reduced iron for the purposes of lowering the reducing agent ratio (RAR), improving the permeability of the ore layer, and improving the air and liquid permeability of the deadman coke by increasing its temperature. Examples of reduced iron include scrap, pig iron, direct reduced iron (DRI) pellets, and hot briquette reduced iron (HBI). The pig iron is cold pig iron cast into a lump weighing approximately 10 to 30 kg for ease of handling.

[0004] Blast furnace operation methods for replacing a portion of the iron raw material with reduced iron are disclosed in, for example, Patent Documents 1 to 3. Patent Document 1 proposes a blast furnace operation method for increasing the amount of scrap charged from the furnace top to the periphery of the furnace interior in order to maintain the reduction efficiency and high-temperature properties of the ore layer when the alumina content in sintered ore increases. Patent Document 2 proposes a blast furnace operation method for maintaining permeability within the furnace by replacing a portion of the iron raw material with scrap when the reduction degradation index (RDI) of sintered ore or the drum strength (DI) of coke deteriorates below a reference value. Patent Document 3 proposes a blast furnace operation method for measuring the increase in pressure drop (deterioration in permeability) associated with an increase in the amount of pulverized coal injection and increasing the amount of reduced iron charged according to the increase.

[0005] Japanese Patent No. 3017009 Japanese Patent Application Laid-Open No. 2008-240028 Japanese Patent No. 3589016

[0006] :Kouji TAKATANI, Takanobu INADA, Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace", ISIJ International, Vol. 39 (1999), No. 1, p. 15-22) Iron and Steel, Vol. 79 (1993) N618

[0007] However, when reduced iron is used instead of a portion of the iron raw materials, operational parameters such as the pig iron production rate, molten iron temperature, and top gas temperature change unsteadily. The greater the change in the amount of reduced iron charged, the greater the change in the operational parameters. By appropriately adjusting the blast parameters (blast rate, oxygen enrichment amount) and the pulverized coal ratio, changes in the pig iron production rate, molten iron temperature, and top gas temperature can be suppressed. However, depending on the values ​​of the blast parameters (blast rate, oxygen enrichment amount) and the pulverized coal ratio, and the timing of their changes, the pig iron production rate and molten iron temperature may fluctuate significantly, potentially resulting in unstable blast furnace operation.

[0008] In view of the above, an object of the present disclosure is to stably operate a blast furnace while suppressing fluctuations in the iron production rate and molten iron temperature when increasing or decreasing the amount of reduced iron charged in reduced iron production operations, which are operations in which reduced iron is charged in place of a portion of iron raw materials.

[0009] The gist of the present disclosure is as follows: (1) A method of operating a blast furnace according to one aspect of the present disclosure includes: defining a first operation as an operation in which blast parameters and a pulverized coal ratio are the same as those of a reference operation but a different amount of reduced iron charged from those of the reference operation; and defining a second operation as an operation in which the amount of reduced iron charged from those of the first operation is the same as those of the first operation but a different amount of blast parameters and a pulverized coal ratio from those of the first operation; a change information acquiring step of acquiring information on changes over time in one or both of the molten iron temperature and the tapping rate when the second operation based on the reference operation is performed; a repeating step of performing the change information acquiring step a plurality of times while changing the predetermined time; and an optimal delay time acquiring step of determining, based on the information acquired in the repeating step, the predetermined time at which the change over time in the molten iron temperature or the tapping rate is minimized as an optimal delay time, wherein after switching from the standard operation to the first operation, the second operation based on the blast specifications and the pulverized coal ratio estimated in the specification estimating step is started with a delay of the optimal delay time. (2) Preferably, in the method for operating a blast furnace described in (1) above, an amount of reduced iron charged in the first operation is greater than that in the reference operation. (3) Preferably, in the method for operating a blast furnace described in (1) or (2) above, a blending ratio of reduced iron contained in the iron raw material in the second operation is 0.5 mass% or more and 50 mass% or less. (4) Preferably, in the blast furnace operation method described in any one of (1) to (3) above, in the change information acquisition step, information on the time-dependent changes in both the molten iron temperature and the amount of iron tapped is acquired, and in the optimal delay time acquisition step, the predetermined time at which the time-dependent change in the molten iron temperature or the amount of iron tapped, whichever is more sensitive to delay time, is minimized is determined as the optimal delay time.(5) Preferably, in the method for operating a blast furnace according to any one of (1) to (4) above, when an operation in which the blast specifications and the pulverized coal ratio are the same as those of the second operation and the charged amount of reduced iron is larger than those of the second operation is defined as a third operation, and an operation in which the charged amount of reduced iron is the same as those of the third operation and the blast specifications and the pulverized coal ratio are different from those of the third operation is defined as a fourth operation, the fourth operation has the same blast specifications and the pulverized coal ratio as those of the second operation, and the fourth operation has the same blast specifications and the pulverized coal ratio as those of the second operation, the fourth operation has the same blast specifications and the pulverized coal ratio as those of the second operation, and the fourth operation has the same blast specifications and the pulverized coal ratio as those of the second operation. The method further includes a second change information acquisition step of acquiring information regarding changes over time in one or both of the molten iron temperature and the amount of molten iron tapped when the fourth operation is carried out, a second repetition step of performing the second change information acquisition step a plurality of times while changing the predetermined time, and a second optimal delay time acquisition step of determining, based on the information acquired in the second repetition step, the predetermined time at which the change over time in the molten iron temperature or the amount of molten iron tapped is minimized, as a second optimal delay time, and after switching from the second operation to the third operation, the fourth operation is started based on the air blowing specifications and pulverized coal ratio estimated in the second specification estimation step with a delay of the second optimal delay time. (6) Preferably, the blast furnace operation method according to any one of (1) to (5) above further includes a second parameter estimation step of estimating blast parameters and a pulverized coal ratio in the fourth operation such that the output rate, molten iron temperature, and furnace top gas temperature in the fourth operation are the same as those in the second operation, when a third operation is defined as an operation having the same blast parameters and a pulverized coal ratio as those in the second operation and a larger amount of reduced iron charged than those in the second operation, and a fourth operation is defined as an operation having the same amount of reduced iron charged as those in the third operation but a different blast parameters and pulverized coal ratio. After switching from the second operation to the third operation, the fourth operation is started after a delay of the optimal delay time, based on the blast parameters and the pulverized coal ratio estimated in the second parameter estimation step.

[0010] According to the present disclosure, when the amount of reduced iron charged is increased or decreased in a reduced iron operation, the blast furnace can be stably operated while suppressing fluctuations in the pig iron production rate and molten iron temperature, thereby making it possible to fully enjoy the effects of reduced iron charging, such as improved reduction efficiency and permeability, and a reduced reducing agent ratio (RAR).

[0011] 1 is a schematic diagram of a blast furnace. 2 is a flowchart showing a method for operating a blast furnace. 3 is a result of acquiring information on changes in molten iron temperature and iron tapping rate over time (embodiment). 4 is a graph for explaining a method for determining an optimal delay time according to determination method 1. 5 is a graph for explaining a method for determining an optimal delay time according to determination method 1. 6 is a graph for explaining a method for determining an optimal delay time according to determination method 2. 7 is a graph for explaining a method for determining an optimal delay time according to determination method 2. 8 is a graph corresponding to determination method 1, with the horizontal axis representing the "timing for switching from the first operation to the second operation" and the vertical axis representing the "maximum difference from the iron tapping rate reference value." 9 is a graph corresponding to determination method 1, with the horizontal axis representing the "timing for switching from the first operation to the second operation" and the vertical axis representing the "maximum difference from the iron tapping rate reference value." 10 is a graph corresponding to determination method 1, with the horizontal axis representing the "timing for switching from the first operation to the second operation" and the vertical axis representing the "maximum difference from the iron tapping rate reference value." 1 is a graph corresponding to determination method 1, with the horizontal axis representing the "timing of switching from the first operation to the second operation" and the vertical axis representing the "maximum value of the difference from the molten iron temperature reference value." This is a graph corresponding to determination method 2, with the horizontal axis representing the "timing of switching from the first operation to the second operation" and the vertical axis representing the "integral value of the difference from the molten iron temperature reference value." This is a graph corresponding to determination method 2, with the horizontal axis representing the "timing of switching from the first operation to the second operation" and the vertical axis representing the "integral value of the difference from the molten iron temperature reference value." This is a graph corresponding to determination method 2, with the horizontal axis representing the "timing of switching from the first operation to the second operation" and the vertical axis representing the "integral value of the difference from the molten iron temperature reference value."

[0012] <Schematic configuration of blast furnace> 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 tuyere 2, an annular pipe 3, a blowpipe 4, a pulverized coal injection lance 5, a swivel chute 6, and a tap hole 7. Note that the present disclosure can also be applied to a bell-type blast furnace that does not have a swivel chute.

[0013] The tuyere 2 is an inlet for blowing hot air generated in a hot stove (not shown) into the blast furnace 1, and a plurality of tuyere 2 are provided along the circumferential direction of the blast furnace 1. From the tuyere 2, pulverized coal, which will be described later, can be blown into the furnace together with the hot air.

[0014] The annular pipe 3 is disposed so as to surround the lower part of the blast furnace 1. A plurality of blowpipes 4 are provided at predetermined intervals in the circumferential direction of the annular pipe 3. The annular pipe 3 supplies hot air sent from the hot stove to the blowpipes 4.

[0015] Each blowpipe 4 is connected to the annular pipe 3 and to a different tuyere 2. The blowpipe 4 blows the hot air sent from the annular pipe 3 into the blast furnace 1 through the tuyere 2.

[0016] The pulverized coal injection lance 5 is provided to inject pulverized coal into the furnace from the tuyere 2. The pulverized coal injection lance 5 penetrates the wall surface of each blowpipe 4 and extends into the interior of each blowpipe 4. The pulverized coal injected from the pulverized coal injection lance 5 into the blowpipe 4 is blown into the furnace through the tuyere 2 together with hot air that has flowed into the blowpipe 4 from the annular pipe 3.

[0017] The rotating chute 6 rotates around an axis extending vertically, charging iron raw materials and coke alternately in layers. The iron raw materials can be lump ore, sintered ore, pellets, unburned carbon-containing agglomerated ore, etc., but when reduced iron operation is performed, some of the iron raw materials can be replaced with reduced iron. The iron raw materials may also contain a reduction aid such as small coke. The coke may also contain ferrocoke. The driving method (forward tilting / reverse tilting) of the rotating chute 6, the tilting angle, and the rotation speed can be controlled to charge the blast furnace raw materials at the desired position. Forward tilting refers to a driving method in which the rotating chute 6 is driven from the furnace wall side toward the furnace center, and reverse tilting refers to a driving method in which the rotating chute 6 is driven from the furnace center side toward the furnace wall side.

[0018] The tap hole 7 is provided at the hearth of the blast furnace 1, and taps the molten iron produced by reducing the iron raw materials. A plurality of tap holes 7 are provided along the circumferential direction of the furnace, and the molten iron can be tapped continuously or intermittently.

[0019] When reduced iron is added to the iron raw materials charged into a blast furnace, operational parameters such as the pig iron production rate, molten iron temperature, and top gas temperature change non-steadily. To accommodate these changes in operational parameters, during normal blast furnace operation, the blast parameters and pulverized coal ratio are also changed a predetermined time after the reduced iron charge rate is changed. This aims to keep the pig iron production rate, molten iron temperature, and top gas temperature approximately the same before and after the change in the reduced iron charge rate. However, when the pig iron production rate and molten iron temperature fluctuate significantly, inappropriate timing for changing the blast parameters and pulverized coal ratio may result in unstable blast furnace operation.

[0020] In the blast furnace operation method according to this embodiment, the state before the reduced iron charging amount is changed is referred to as the reference operation. The reference operation refers to operation performed under operational specifications that are prerequisites for analysis. The state after all of the reduced iron charging amount, blast specifications, and pulverized coal ratio are changed from the reference operation values ​​is referred to as the second operation. The state in which the reduced iron charging amount is changed from the reference operation values ​​but the blast specifications and pulverized coal ratio are not changed from the reference operation values ​​is referred to as the first operation. Detailed definitions of the reference operation, the first operation, and the second operation will be described later. In the blast furnace operation method according to this embodiment, the first operation is provided to delay changes in the blast specifications and pulverized coal ratio.

[0021] Table 1 is a comparison table outlining the standard operation, the first operation, and the second operation. When switching from the standard operation to the first operation, the amount of reduced iron charged is increased or decreased by α, but the blast specifications and the pulverized coal ratio conditions are not changed. When switching from the first operation to the second operation, the amount of reduced iron charged is not changed, but the blast specifications and the pulverized coal ratio conditions are changed.

[0022]

[0023] The inventors have discovered that blast furnace operation can be stabilized by optimizing the delay time for changing the blast parameters and pulverized coal ratio in response to a change in the amount of reduced iron charged, i.e., the length from the start of the first operation to the start of the second operation. The delay time, i.e., the length from the start of the first operation to the start of the second operation, can be optimized by the parameter estimation step, change information acquisition step, repetition step, and minimum delay time acquisition step described below. The optimal delay time is a value acquired by simulation before the start of the second operation. The start of the first operation refers to the time when the amount of reduced iron charged is changed from the value in the standard operation. The start of the second operation refers to the time when one or both of the blast parameters and the pulverized coal ratio are changed from the value in the first operation.

[0024] <Flow of blast furnace operation method> One embodiment of the blast furnace operation method of the present disclosure will be described with reference to Fig. 2. Fig. 2 is a flowchart for explaining the blast furnace operation method of this embodiment. The blast furnace operation method of this embodiment has a standard operation, a first operation, and a second operation.

[0025] The method includes a specification estimation step (S1), a change information acquisition step (S2), a repeat step (S3), and a minimum delay time acquisition step (S4). Each step will be described in detail below.

[0026] (S1: Parameter Estimation Step) The blast furnace operation method of this embodiment is an operation system in which a standard operation is switched to a first operation, and then the first operation is switched to a second operation. Therefore, before describing the content of the parameter estimation step, the definitions of the standard operation, the first operation, and the second operation will be described.

[0027] "Reference operation" refers to operation performed under the operating specifications that are prerequisites for analysis. The reference operation may be an operation that does not include reduced iron as an iron raw material, or an operation that includes reduced iron. Furthermore, the reference operation is preferably an operation performed during a stable operation period. A stable operation period refers to a period during which blast furnace operation is stable, avoiding periods immediately before and after blast shutdown, periods in which a rapid increase in skeletal mass occurs, periods in which a rapid increase or decrease in pig iron production occurs, and periods in which blast specifications fluctuate significantly.

[0028] In the present disclosure, the blast specifications and pulverized coal ratio in the standard operation are applied to the first operation, which will be described later. Furthermore, in the present disclosure, the pig iron production rate, molten iron temperature, and top gas temperature in the standard operation are used in the specification estimation step. These values ​​can be set to be approximately constant during the stable operation period. The blast specifications and pulverized coal ratio, as well as the pig iron production rate, molten iron temperature, and top gas temperature at any time during the stable operation period, can be used in the subsequent operation. Preferably, the blast specifications and pulverized coal ratio, as well as the pig iron production rate, molten iron temperature, and top gas temperature immediately after the standard operation is completed and the first operation is started are used in the subsequent operation. "Immediately before the start of the first operation" refers to, for example, the period up to 8 hours before the start of the first operation.

[0029] "First operation" refers to a blast furnace operation that has the same blast specifications and pulverized coal ratio as the reference operation but has a different reduced iron charging amount from the reference operation. The first operation may be an operation in which the reduced iron charging amount is greater than that of the reference operation, or may be an operation in which the reduced iron charging amount is less than that of the reference operation. An operation in which the reduced iron charging amount is not substantially the same as that of the reference operation is considered to be the first operation. "Blast specifications" refer to the blast volume, oxygen enrichment rate, and blast moisture content. Therefore, if the reduced iron charging amount in the reference operation is 0, the reduced iron charging amount in the first operation is greater than 0. Furthermore, if the reduced iron charging amount in the reference operation is k (k > 0), the reduced iron charging amount in the first operation is greater than k or less than k.

[0030] However, it is desirable to set the blending ratio of reduced iron in the first operation and the second operation to 0.5 mass % or more and 50 mass % or less.

[0031] If the blending ratio in the first operation is 0.5% by mass or more, the fluctuations in the tapping rate and the molten iron temperature tend to be large at the start of the first operation and the second operation. Therefore, the effects of the operating method according to the present disclosure are more preferably exhibited. The blending ratio of reduced iron in the first operation may be 1% by mass or more, 5% by mass or more, or 10% by mass or more.

[0032] On the other hand, the reason why it is preferable to set the upper limit of the blending ratio in the first operation to 50 mass% is that if the amount of reduced iron is excessively large, the amount of oxygen to be reduced decreases, resulting in a decrease in the amount of reducing gas in terms of operational design, which has the disadvantage of making it impossible to maintain the furnace top gas temperature, etc. The blending ratio of reduced iron in the first operation may be set to 45 mass% or less, 40 mass% or less, or 30 mass% or less.

[0033] In normal operation, the higher the blending ratio of reduced iron in the first operation, the greater the fluctuations in the iron production rate and molten iron temperature, which may result in unstable blast furnace operation. However, the blast furnace operation method according to the present disclosure can stably operate the blast furnace while suppressing fluctuations in the iron production rate and molten iron temperature. Therefore, the higher the blending ratio of reduced iron in the first operation, the more pronounced the effects of the blast furnace operation method according to the present disclosure, which is preferable.

[0034] The "second operation" refers to an operation in which the amount of reduced iron charged is the same as that in the first operation, but the blast specifications and pulverized coal ratio are different. Therefore, the example of the blending ratio of reduced iron in the first operation described above can also be applied to the second operation. The purpose of the "parameter estimation step" described below is to search for the optimal blast specifications and pulverized coal ratio for this second operation.

[0035] In the parameter estimation step, the blast parameters and pulverized coal ratio in the second operation are estimated so that the pig iron production rate, molten iron temperature, and furnace top gas temperature in the second operation are the same as those in the standard operation.

[0036] "The same as the standard operation" also includes "substantially the same." For example, if the difference in pig iron production rate between the standard operation and the second operation is approximately ±100 (t / d), this is not considered an operational variation that requires operational action, and therefore can be considered "the same pig iron production rate." If the difference in molten iron temperature between the standard operation and the second operation is approximately ±2°C, this is not considered an operational variation that requires operational action, and therefore can be considered "the same molten iron temperature." If the difference in furnace top gas temperature between the standard operation and the second operation is approximately ±10 (°C), this is not considered an operational variation that requires operational action, and therefore can be considered "the same molten iron temperature."

[0037] The parameter estimation step can be realized, for example, by analytical processing using a blast furnace mathematical model. Specifically, a process for estimating the pig iron production rate, molten iron temperature, and furnace top gas temperature for the standard operation and a process for estimating the blast parameters and pulverized coal ratio for the second operation are realized by analytical processing using the blast furnace mathematical model. The blast furnace mathematical model (see, for example, Non-Patent Document 1) is a mathematical model that divides the internal region of a blast furnace into a mesh and performs calculations by substituting preset conditions into calculation formulas for material balance, momentum balance, and energy balance to estimate state variables (output values) and comprehensively simulate the state inside the furnace.

[0038] A method for estimating the pig iron production rate, molten iron temperature, and top gas temperature for standard operation using a blast furnace mathematical model is described below. Setting conditions for standard operation, such as the blast parameters, pulverized coal ratio (PC), reduced iron blending ratio, reduced iron consumption rate, blast moisture, and O / C, are input into the blast furnace mathematical model to estimate state variables. The estimated state variables include at least the pig iron production rate, molten iron temperature, and top gas temperature. The reduced iron blending ratio (mass%) refers to the ratio of the mass of reduced iron to the mass of iron raw materials. The reduced iron consumption rate (kg / t) refers to the weight of reduced iron consumed to produce one ton of molten iron. O / C refers to the weight ratio of the ore layer to the coke layer. The estimated state variables may further include the theoretical combustion temperature at the tuyere tip, the bosh gas volume, the reducing agent ratio, the coke ratio, the PCI ratio, the slag ratio, ηCO, ηH, SLC, and furnace pressure loss.

[0039] In the standard operation, the state variables are estimated in a steady state (operation time is set to infinity).

[0040] A method for obtaining the blast parameters and pulverized coal ratio for the second operation using a blast furnace mathematical model will be described. The set conditions for the second operation, such as the reduced iron blending ratio, reduced iron consumption rate, blast moisture, and O / C, are input into the blast furnace mathematical model. Furthermore, the simulation conditions are set to "the same iron production rate, molten iron temperature, and top gas temperature as in the standard operation." This allows the blast parameters and pulverized coal ratio that satisfy these conditions to be searched for. The iron production rate, molten iron temperature, and top gas temperature for the second operation can also be estimated as state variables. In this case, the output iron production rate, molten iron temperature, and top gas temperature may be completely identical to or substantially identical to the iron production rate, molten iron temperature, and top gas temperature for the standard operation. The range of substantially identical values ​​can be appropriately set by adjusting the parameters of the blast furnace mathematical model. The meaning of "substantially identical" will not be repeated. The operating conditions of the second operation, such as the blast moisture content and O / C, may or may not be the same as those of the standard operation.

[0041] In the second operation, the state variables in the steady state (operation time set to infinity) are estimated.

[0042] In this embodiment, the specification estimation step is realized by analytical processing using a blast furnace mathematical model, but the present disclosure is not limited to this, and the specification estimation step may be realized by a method other than a blast furnace mathematical model.

[0043] For example, the parameter estimation step may be performed by analytical processing using the RIST model. The RIST model is known as a partial balance model based on thermodynamics, and its details are disclosed in, for example, Non-Patent Document 2, so a detailed description thereof will be omitted.

[0044] (S2: Change information acquisition step) In the change information acquisition step, information is acquired regarding changes over time in one or both of the molten iron temperature and the tapping rate when the second operation is carried out based on the blast specifications and pulverized coal ratio estimated in the specification estimation step, with a delay of a predetermined time after switching from the standard operation to the first operation. Preferably, in the change information acquisition step, information regarding changes over time in both the molten iron temperature and the tapping rate is acquired. The "predetermined time" is, for example, a candidate value for the optimal delay time, and is any value greater than 0. The predetermined time is, for example, within a range of 1 hour to 10 hours. The time point of switching from the standard operation to the first operation refers to the time point when the first operation starts.

[0045] In the parameter estimation step, by inputting the following as setting conditions: "the blast parameters, pulverized coal ratio, blast moisture, and O / C of the first operation are the same as those of the reference operation," "the reduced iron blending ratio of the first operation is the same as that of the second operation," and "a predetermined time (delay time)," it is possible to acquire, as a state variable, "information regarding the change over time in one or both of the molten iron temperature and the amount of molten iron produced when switching to the second operation based on the blast parameters and pulverized coal ratio estimated in the parameter estimation step after a predetermined time has elapsed since the first operation."

[0046] In the present embodiment, the change information acquisition step is realized by an analysis process using a blast furnace mathematical model, but the present disclosure is not limited to this, and a method other than the blast furnace mathematical model may be used. For example, information on changes over time when the first operation is switched to the second operation after a predetermined time has elapsed may be acquired based on the operational performance.

[0047] (S3: Repeating step) The change information acquiring step is performed multiple times by changing the predetermined time, and "information regarding the change over time in the molten iron temperature and the tapping rate" is acquired for each "predetermined time." The repeating step estimates the results brought about by each of multiple candidate values ​​for the optimal delay time. The change information acquiring step is preferably repeated three or more times, four or more times, or five or more times, for example.

[0048] (S4: Optimum Delay Time Acquisition Step) Based on the information acquired in the repetition step, a predetermined time from among the "predetermined times" at which the change over time in one or both of the molten iron temperature and the tapping rate is minimized is determined as the optimum delay time. Whether or not it is "minimum" can be determined by comparing it with the molten iron temperature during standard operation (hereinafter also referred to as the molten iron temperature reference value) and the tapping rate during standard operation (hereinafter also referred to as the tapping rate reference value). Hereinafter, the molten iron temperature reference value and the tapping rate reference value will be collectively referred to as the "reference values". An example of a method for determining the optimum delay time is given below.

[0049] Determination method 1: The molten iron temperature and / or the amount of tapped iron is calculated from the start of the first operation until the operation is stabilized, and the predetermined time in the second operation at which the maximum value of the difference between the molten iron temperature and the reference value for the molten iron temperature or the maximum value of the difference between the amount of tapped iron and the reference value for the amount of tapped iron is minimized is defined as the "optimum delay time." Note that "operation is stabilized" means that the amount of tapped iron and the molten iron temperature have recovered to the levels of the reference operation, which means, for example, 24 hours after the start of the first operation.

[0050] Determination method 2: The difference between the molten iron temperature and / or the amount of iron tapped and their respective reference values ​​is calculated from the start of the first operation until the operation stabilizes, and the predetermined time of the second operation at which the integral value of the difference between the molten iron temperature and the molten iron temperature reference value or the integral value of the difference between the amount of iron tapped and the amount of iron tapped and the reference value for the amount of iron tapped is minimized is determined to be the “optimum delay time.”

[0051] Determination method 3: Calculate the average values ​​of the molten iron temperature and the amount of iron tapped from the start of the first operation until the operation stabilizes, and determine the predetermined time of the second operation at which the difference between the average value of the molten iron temperature and the reference value of the molten iron temperature or the difference between the average value of the amount of iron tapped and the reference value of the amount of iron tapped is the smallest.

[0052] Determination Method 1, Determination Method 2, and Determination Method 3 can be selected as appropriate depending on the operational state. For example, since a sudden change in the molten iron temperature or the amount of iron tapped, even for a short period of time, carries a high risk of destabilizing the operation, it is desirable to select Determination Method 1 when such a phenomenon is observed.

[0053] By carrying out the above steps S1 to S4, it is possible to estimate the optimal delay time from the start of the first operation until switching to the blast specifications and pulverized coal ratio estimated in the specification estimation step. By operating the blast furnace based on such an estimation result, it is possible to operate the blast furnace stably while suppressing fluctuations in the pig iron production rate and molten iron temperature.

[0054] That is, by switching from the standard operation to the first operation and then starting the second operation after the lapse of the optimal delay time, the blast furnace can be operated stably while suppressing fluctuations in the pig iron tapping rate and molten iron temperature. Note that "starting the second operation after the lapse of the optimal delay time after switching from the standard operation to the first operation" means that the length of the first operation is made to match the optimal delay time. Here, the length of the first operation and the optimal delay time may be substantially the same. For example, if the length of the first operation is within a range of, for example, the optimal delay time ±30 minutes, the length of the first operation and the optimal delay time are considered to be substantially the same, and the blast furnace operating method characterized by "starting the second operation after the lapse of the optimal delay time after switching from the standard operation to the first operation" is considered to be implemented. If the sensitivity of the pig iron tapping rate or the molten iron temperature to the delay time is small, a large difference between the optimal delay time and the actual delay time is permitted.

[0055] As explained by exemplifying Determination Method 1, Determination Method 2, and Determination Method 3, in the optimal delay time acquisition step, the optimal delay time may be determined based on a change in the molten iron temperature over time, or the optimal delay time may be determined based on a change in the amount of iron tapped over time. When a change in the molten iron temperature over time is used, it is not essential to acquire a change in the amount of iron tapped over time in the change information acquisition step. When a change in the amount of iron tapped over time is used, it is not essential to acquire a change in the molten iron temperature over time in the change information acquisition step.

[0056] On the other hand, in the change information acquisition step, information on changes over time of both the molten iron temperature and the amount of tapped iron may be acquired, and in the optimum delay time acquisition step, any one of the changes over time of the molten iron temperature and the amount of tapped iron may be used to determine the optimum delay time. For example, of the changes over time of the molten iron temperature and the amount of tapped iron, the one that is more sensitive to the delay time may be used to determine the optimum delay time.

[0057] For example, in the change information acquisition step of the embodiment described below, both the change in the molten iron temperature and the change in the amount of tapped iron over time were acquired. An example of the results is shown in Figures 4A and 4B. A more preferable method for determining the optimum delay time will be described with reference to this data.

[0058] In this example, both the graph showing the change in the tapping rate over time shown in Figure 4A and the graph showing the change in the molten iron temperature over time shown in Figure 4B have a downwardly convex shape. On the other hand, the graph showing the change in the molten iron temperature over time shown in Figure 4B has a steeper downward curve than the graph showing the change in the tapping rate over time shown in Figure 4A. In other words, the sensitivity of the change in the molten iron temperature over time to the delay time is higher than that of the change in the tapping rate over time. In the examples shown in Figures 4A and 4B, it is preferable to determine the predetermined time at the data point where the change in the molten iron temperature over time is minimum as the optimal delay time.

[0059] In the blast furnace operation method described above, the reduced iron charging amount is increased only once during standard operation. When switching from standard operation to first operation, the reduced iron charging amount is increased, but when switching from second operation to third operation, the reduced iron charging amount is not increased. However, in the blast furnace operation method according to the present disclosure, the reduced iron charging amount may be increased two or more times. For example, if the second operation satisfies the definition of standard operation, the second operation can be regarded as the standard operation, and the above-described procedure can be performed again, thereby increasing the reduced iron charging amount two times. Naturally, the above-described procedure can also be performed further. This further facilitates stable operation of the blast furnace while suppressing fluctuations in the iron production rate and molten iron temperature. A specific example of an embodiment in which the reduced iron charging amount is increased two or more times is described below.

[0060] (A. Embodiment of Recalculating Optimal Delay Time) In the blast furnace operating method according to the present disclosure, a third operation and a fourth operation may be further performed. The third operation is defined as an operation having the same blast specifications and pulverized coal ratio as the second operation and a larger amount of reduced iron charged than the second operation. The fourth operation is defined as an operation having the same amount of reduced iron charged as the third operation and different blast specifications and pulverized coal ratio. When the second operation is considered to be the reference operation, the definition of the third operation is substantially the same as the first operation, and the definition of the fourth operation is substantially the same as the second operation.

[0061] Furthermore, the blast furnace operation method according to the present disclosure may include: (S11) a second parameter estimation step of estimating blast parameters and a pulverized coal ratio in the fourth operation, which will result in the same pig iron output, molten iron temperature, and top gas temperature as those in the second operation; (S12) a second change information acquisition step of acquiring information on changes over time in one or both of the molten iron temperature and the pig iron output when the fourth operation is carried out based on the blast parameters and the pulverized coal ratio estimated in the second parameter estimation step, with a predetermined delay after switching from the second operation to the third operation; (S13) a second repetition step of performing the second change information acquisition step a plurality of times, each time changing the predetermined time; and (S14) a second optimum delay time acquisition step of determining, based on the information acquired in the second repetition step, a predetermined time at which the change over time in the molten iron temperature or the pig iron output is minimized, as a second optimum delay time. When the second operation is regarded as the reference operation, the configurations of the second parameter estimation step, the second change information acquisition step, the second repetition step, and the second optimum delay time acquisition step are substantially the same as the configurations of the parameter estimation step, the change information acquisition step, the repetition step, and the optimum delay time acquisition step described above. In other words, in the blast furnace operation method according to the present disclosure, these steps may be repeated again.

[0062] In the second optimal delay time acquisition step, a second optimal delay time is calculated. Then, after switching from the second operation to the third operation, a fourth operation based on the blast parameters and pulverized coal ratio estimated in the second parameter estimation step is started with a delay of the second optimal delay time. This increases the number of opportunities to increase the amount of reduced iron charged to two. Naturally, the fourth operation can be regarded as the reference operation, and the above procedure can be carried out again. By gradually increasing the amount of reduced iron charged, it becomes easier to stably operate the blast furnace while suppressing fluctuations in the iron production rate and molten iron temperature.

[0063] (B. Embodiment in which the optimal delay time for the second operation is used for the fourth operation) In the blast furnace operating method according to the present disclosure, a third operation and a fourth operation may be further carried out. The third operation is defined as an operation in which the blast specifications and pulverized coal ratio are the same as those of the second operation, but the amount of reduced iron charged is greater than that of the second operation. The fourth operation is defined as an operation in which the amount of reduced iron charged is the same as those of the third operation, but the blast specifications and pulverized coal ratio are different. When the second operation is considered to be the reference operation, the definition of the third operation is substantially the same as that of the first operation, and the definition of the fourth operation is substantially the same as that of the second operation.

[0064] Furthermore, the blast furnace operation method according to the present disclosure may include: (S21) a second parameter estimation step of estimating blast parameters and a pulverized coal ratio in a fourth operation in which the iron tapping rate, molten iron temperature, and furnace top gas temperature in the fourth operation are the same as those in the second operation. When the second operation is considered to be the reference operation, the configuration of the second parameter estimation step is substantially the same as the configuration of the parameter estimation step described above.

[0065] Then, after switching from the second operation to the third operation, a fourth operation based on the blast specifications and pulverized coal ratio estimated in the second specification estimation step is started with a delay of the optimal delay time. Here, the optimal delay time applied to the fourth operation is the same as the optimal delay time applied to the second operation. In other words, the optimal delay time applied to the second operation is diverted to the fourth operation.

[0066] Comparing Embodiment A, in which the optimum delay time is recalculated, with Embodiment B, in which the optimum delay time for the second operation is diverted to the fourth operation, the second change information acquisition step, the second repetition step, and the second optimum delay time acquisition step are omitted in Embodiment B. Therefore, the calculation process in Embodiment B is simpler than that in Embodiment A.

[0067] Embodiment A is suitable for the case where the blending ratio of reduced iron is increased non-uniformly. For example, if the blending ratio of reduced iron in the reference operation is 0%, the blending ratios of reduced iron in the first and second operations are 10%, and the blending ratio of reduced iron in the third and fourth operations is 40%, it is preferable to recalculate the optimal delay time to be applied to the fourth operation.

[0068] Embodiment B is suitable for the case where the blending ratio of reduced iron is increased uniformly. For example, if the blending ratio of reduced iron in the reference operation is 0%, the blending ratio of reduced iron in the first and second operations is 20%, and the blending ratio of reduced iron in the third and fourth operations is 40%, it is preferable to apply the optimal delay time applied to the second operation to the fourth operation.

[0069] (Example) Hereinafter, the present disclosure will be described in detail with reference to an example. According to the method described in the embodiment, a parameter estimation step was carried out by carrying out an analysis process using a blast furnace mathematical model. The setting values ​​given to the blast furnace mathematical model and the output state variables are shown in Table 2. In this example, an operation in which reduced iron was not included in the iron raw material was set as the reference operation, and the blending ratio of reduced iron in the second operation was set to about 10 mass % (10.3 mass %).

[0070] Through the analysis process, the blast specifications and pulverized coal ratio in the second operation were estimated to be blast volume: 5235 (Nm3 / min), oxygen enrichment rate: 2.95 (%), and pulverized coal ratio (PC): 47.1 (t / hr).

[0071] The predetermined time for the "change information acquisition step" was set to three patterns: 4 hours, 6 hours, and 8 hours, and "information on time-dependent changes in hot metal temperature and tapping rate" was acquired for each pattern. Figure 3 shows the acquired results, and is a graph with time on the horizontal axis and the tapping rate or hot metal temperature on the vertical axis. The time when the first operation started is set to "0."

[0072] The graphs of FIGS. 4A, 4B, 5A, and 5B were obtained from FIG. 3. FIG. 4A is a graph with the horizontal axis representing the timing of switching from the first operation to the second operation and the vertical axis representing the maximum difference from the reference value for the iron tapping rate, and corresponds to Determination Method 1. FIG. 4B is a graph with the horizontal axis representing the timing of switching from the first operation to the second operation and the vertical axis representing the maximum difference from the reference value for the iron tapping rate, and corresponds to Determination Method 1. FIG. 5A is a graph with the horizontal axis representing the timing of switching from the first operation to the second operation and the vertical axis representing the integral of the difference from the reference value for the iron tapping rate, and corresponds to Determination Method 2. FIG. 5B is a graph with the horizontal axis representing the timing of switching from the first operation to the second operation and the vertical axis representing the integral of the difference from the reference value for the iron tapping rate, and corresponds to Determination Method 2. The definitions of Determination Methods 1 and 2 will not be repeated.

[0073] Furthermore, in addition to the patterns in which the predetermined time was set to 4 hours, 6 hours, and 8 hours shown in FIG. 3 , patterns in which the predetermined time was set to 5 hours and 7 hours were also examined. From the results, the graphs shown in FIGS. 6A to 5B were obtained. These graphs are explained below. Note that the markers in FIGS. 6A to 6B with the caption "X% → Y%" represent data for an operation in which the charged amount of reduced iron in the reference operation was X% and the charged amount of reduced iron in the first and second operations was Y%. For example, the markers with the caption "0% → 5%" represent data for an operation in which the charged amount of reduced iron in the reference operation was 0% and the charged amount of reduced iron in the first and second operations was 5%.

[0074] 6A and 6B are graphs in which the horizontal axis represents "the timing of switching from the first operation to the second operation" and the vertical axis represents "the maximum value of the difference from the reference value for the iron tapping rate," and correspond to determination method 1. Note that Fig. 6A is a vertically expanded version of Fig. 6B, with "0% → 50%" omitted from the five data series shown in Fig. 6B.

[0075] 7A and 7B are graphs in which the horizontal axis represents the "switching timing for switching from the first operation to the second operation" and the vertical axis represents the "maximum difference from the reference value for the molten iron temperature," and correspond to Determination Method 1. Note that Fig. 7A is a vertically expanded version of Fig. 7B, with the "0% → 50%" data series omitted from the five data series shown in Fig. 7B.

[0076] 8A and 8B are graphs in which the horizontal axis represents "the timing of switching from the first operation to the second operation" and the vertical axis represents "the integrated value of the difference from the reference value of the iron tapping rate," and correspond to determination method 2. Note that Fig. 8A is a vertically expanded version of Fig. 8B, with "0% → 50%" omitted from the five data series shown in Fig. 8B.

[0077] 9A and 9B are graphs with the horizontal axis representing the "switching timing from the first operation to the second operation" and the vertical axis representing the "integral value of the difference from the reference value of the molten iron temperature," and correspond to determination method 2. Note that Fig. 9A is a vertically expanded version of Fig. 9B, with the "0% → 50%" data series omitted from the five data series shown in Fig. 9B.

[0078] As shown in Table 2, when the operation in which reduced iron is not included in the iron raw material is defined as the reference operation and the blending ratio of reduced iron in the second operation is set to approximately 10 mass % (10.3 mass %), it was found that the maximum value and the integrated value were smallest for "6 hours" regardless of whether determination method 1 or 2 was used, as shown in Figures 4A to 5B. Therefore, it was found that by setting "6 hours" as the optimal delay time, the changes in the molten iron temperature and the amount of tapped iron over time were minimized.

[0079] 4A to 5B also show the results of similar analysis performed under the conditions shown in Table 2, except that the blending ratio of reduced iron contained in the iron raw material in the reduced iron production operation was changed to approximately 2 mass % (2.1 mass %). Even when the blending ratio of reduced iron contained in the iron raw material was changed to approximately 2 mass %, the optimal delay time was 6 hours.

[0080] The results of similar analysis performed under a plurality of conditions in which the blending ratio of reduced iron in the reference operation and the blending ratio of reduced iron in the second operation were changed are shown in Figures 6A, 6B, 7A, and 7B, as well as Figures 8A, 8B, 9A, and 9B. The optimal delay time changed depending on the conditions under which the blending ratio of reduced iron was changed. When the optimal delay time was determined using Determination Method 1 (see Figures 7A and 7B) with a focus on the molten iron temperature, the optimal delay time under each condition was as shown in Table 3.

[0081]

[0082] 1. Blast furnace 2. Tuyere 3. Annular pipe 4. Blowpipe 5. Pulverized coal injection lance 6. Swivel chute 7. Taphole

Claims

1. When an operation having the same blast specifications and pulverized coal ratio as a reference operation but a different reduced iron charging amount from the reference operation is defined as a first operation, and an operation having the same reduced iron charging amount as the first operation but a different blast specifications and pulverized coal ratio from the first operation is defined as a second operation, the operation includes: a parameter estimation step of estimating blast specifications and pulverized coal ratio in the second operation such that the pig iron output, molten iron temperature, and furnace top gas temperature in the second operation are the same as those in the reference operation; a change information acquisition step of acquiring information on changes over time in one or both of the molten iron temperature and the pig iron output when the second operation is carried out based on the blast specifications and pulverized coal ratio estimated in the parameter estimation step after a predetermined time delay after switching from the reference operation to the first operation; and a repeating step of performing the change information acquisition step a plurality of times while changing the predetermined time. an optimal delay time acquisition step of determining, as an optimal delay time, the predetermined time at which a change in molten iron temperature or a pulverized coal rate over time is minimized based on the information acquired in the repeating step, wherein after switching from the standard operation to the first operation, the second operation based on the blast specifications and the pulverized coal ratio estimated in the specification estimation step is started with a delay of the optimal delay time.

2. The method of operating a blast furnace according to claim 1, wherein the amount of reduced iron charged in the first operation is greater than that in the standard operation.

3. A method of operating a blast furnace according to claim 1 or 2, characterized in that in the second operation, the blending ratio of reduced iron contained in the iron raw material is 0.5 mass% or more and 50 mass% or less.

4. A method for operating a blast furnace according to claim 1 or 2, characterized in that in the change information acquisition step, information on changes over time in both the molten iron temperature and the amount of molten iron tapped is acquired, and in the optimum delay time acquisition step, the predetermined time at which the change over time in either the molten iron temperature or the amount of molten iron tapped, whichever is more sensitive to delay time, is minimized is determined as the optimum delay time.

5. When an operation having the same blast parameters and pulverized coal ratio as the second operation and a larger amount of reduced iron charged than the second operation is defined as a third operation, and an operation having the same amount of reduced iron charged as the third operation but different blast parameters and pulverized coal ratio is defined as a fourth operation, the operation includes: a second parameter estimation step of estimating blast parameters and pulverized coal ratio in the fourth operation such that the iron output, molten iron temperature, and furnace top gas temperature in the fourth operation are the same as those in the second operation; a second change information acquisition step of acquiring information regarding changes over time in one or both of the molten iron temperature and the iron output when the fourth operation is carried out based on the iron output parameters and pulverized coal ratio estimated in the second parameter estimation step with a predetermined delay after switching from the second operation to the third operation; and a second repetition step of carrying out the second change information acquisition step a plurality of times while changing the predetermined time. a second optimum delay time acquisition step of determining, based on information acquired in the second repetition step, the predetermined time at which a change in molten iron temperature or a tapping rate over time is minimized as a second optimum delay time, wherein after switching from the second operation to the third operation, the fourth operation based on the blast parameters and the pulverized coal ratio estimated in the second parameter estimation step is started with a delay of the second optimum delay time.

6. The method for operating a blast furnace according to claim 1 or 2, further comprising: a second parameter estimation step of estimating blast parameters and pulverized coal ratio in the fourth operation such that the output, molten iron temperature, and furnace top gas temperature in the fourth operation are the same as those in the second operation, when a third operation is defined as an operation having the same blast parameters and pulverized coal ratio as those in the second operation but a larger amount of reduced iron charged than those in the second operation, and a fourth operation is defined as an operation having the same amount of reduced iron charged as those in the third operation but a different blast parameters and pulverized coal ratio, and wherein, after switching from the second operation to the third operation, the fourth operation is started with a delay of the optimal delay time, based on the blast parameters and pulverized coal ratio estimated in the second parameter estimation step.

Images