Blast furnace operation methods

Abstract

This invention provides a method for operating a blast furnace that enables stable operation with a low reducing agent ratio. [Solution] A method for operating a blast furnace in which a hydrogen-based reducing gas and an auxiliary reducing agent are injected into the blast furnace, wherein the ratio of the auxiliary reducing agent is adjusted based on the change in the amount of solution loss carbon caused by fluctuations in the amount of hydrogen-based reducing gas injected.

Description

Technical Field

[0001] The present invention relates to a method for operating a blast furnace.

Background Art

[0002] In the steel industry, the blast furnace method is the mainstream in the pig iron manufacturing process. In the blast furnace method, while charging blast furnace iron-based raw materials (raw materials containing iron oxide. mainly sintered ore. hereinafter also simply referred to as "iron-based raw materials") and coke into the blast furnace alternately and in layers from the top of the blast furnace, hot air is blown into the blast furnace from the tuyere at the lower part of the blast furnace. The hot air reacts with pulverized coal blown in together with the hot air and coke in the blast furnace to generate high-temperature reducing gas (here mainly CO gas). That is, the hot air gasifies coke and pulverized coal. The reducing gas rises in the blast furnace and reduces the iron-based raw materials while heating them. The iron-based raw materials descend in the blast furnace while being heated and reduced by the reducing gas. Thereafter, the iron-based raw materials melt and drip in the blast furnace while being further reduced by coke. The iron-based raw materials are finally stored as hot metal (pig iron) containing less than 5% by mass of carbon in the hearth part. The hot metal in the hearth part is taken out from the tapping hole and subjected to the next steelmaking process. Therefore, in the blast furnace method, carbon materials such as coke and pulverized coal are used as reducing agents.

[0003] In recent years, prevention of global warming has been called for, and reduction of emissions of carbon dioxide (CO2 gas), which is one of the greenhouse gases, has become a social issue. As described above, in the blast furnace method, since carbon materials are used as reducing agents, a large amount of CO2 gas is generated. Therefore, the steel industry is one of the major industries in terms of CO2 gas emissions and must respond to the social demands. Specifically, there is an urgent need to further reduce the reducing agent ratio (the amount of reducing agent used per ton of hot metal) in blast furnace operation.

[0004] As a technology for reducing the reducing agent ratio, for example, as disclosed in Patent Document 1, a technology for improving the reducing gas potential in the furnace by blowing a high-concentration hydrogen-containing gas together with hot air from the tuyere is known.

Prior Art Documents

[0005] [Patent Document 1] International Publication No. 2021 / 107091 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, using a hydrogen-based reducing gas reduces the solution loss reaction compared to conventional operation without a hydrogen-based reducing gas. This reduces the amount of carbon powder consumed in the furnace, which could lead to an increase in the accumulation of carbon powder and a decrease in furnace permeability. Therefore, one of the objectives of the present invention is to provide a method for operating a blast furnace that enables stable operation with a low reducing agent ratio. [Means for solving the problem]

[0007] The gist of this invention is as follows:

[0008] (1) A method for operating a blast furnace, comprising injecting a hydrogen-based reducing gas and an auxiliary reducing agent into the blast furnace, wherein the ratio of the auxiliary reducing agent is adjusted based on the change in the amount of solution loss carbon caused by fluctuations in the amount of hydrogen-based reducing gas injected. (2) In (1), the coke ratio may be adjusted according to the amount of adjustment of the auxiliary reducing agent ratio. (3) In (1) or (2), after adjusting the auxiliary reducing agent ratio, the auxiliary reducing agent ratio may be readjusted based on the permeability index of the blast furnace. (4) In any one of (1) to (3), the change in the amount of solution loss carbon may be a predicted value based on at least one of the operating performance of the blast furnace and the simulation. In (5)(4), after adjusting the auxiliary reducing agent ratio based on the predicted value, the amount of solution loss carbon in the blast furnace may be obtained, and the auxiliary reducing agent ratio may be readjusted based on the obtained amount of solution loss carbon. [Effects of the Invention]

[0009] According to one aspect of the present invention, a method for operating a blast furnace that enables stable operation at a low reducing agent ratio is provided. [Brief explanation of the drawing]

[0010] [Figure 1] This is a flowchart showing the overall configuration of the blast furnace system used in the embodiment. [Figure 2] This is a functional block diagram of the entire blast furnace system according to the embodiment. [Figure 3] This is a flowchart of the operation method of the blast furnace according to the embodiment. [Figure 4] This is a flowchart of the operation method for the first modified blast furnace. [Figure 5] This is a functional block diagram of the entire blast furnace system in the first modified example. [Figure 6] This is a flowchart of the operation method for the second modified blast furnace. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, thus omitting redundant explanations.

[0012] <Blast Furnace System> First, the overall configuration of the blast furnace system 1 according to this embodiment, including the hydrogen-based reducing gas supply system 2 and control device 3 connected to the blast furnace system 1, will be described based on Figure 1. The blast furnace system 1 comprises a blast furnace 10, a CO2 separation and recovery device 20, a buffer tank 30, a compressor 40, and a heater 50.

[0013] The blast furnace 10 comprises a blast furnace body 10a, a normal tuyere 11, a shaft tuyere 12, and a blower 13. Inside the blast furnace body 10a, the reduction reaction of iron-based raw materials by the blast furnace method takes place. Specifically, iron-based raw materials and coke are charged into the blast furnace 10 alternately and in layers from the top of the blast furnace 10, while hot air supplied from the blower 13, auxiliary reducing agent, and enriched oxygen gas are blown into the blast furnace 10 from the normal tuyere 11. In the following description, "tuyere tip combustion temperature" refers to the temperature at the gas outlet of the normal tuyere 11.

[0014] The hot air reacts with the auxiliary reducing agent blown in with the hot air and the coke in the blast furnace 10 to generate high-temperature reducing gas (primarily CO gas in this case). In other words, the hot air gasifies the coke and auxiliary reducing agent. The reducing gas rises within the blast furnace 10, heating and reducing the iron-based raw materials. The iron-based raw materials descend within the blast furnace 10, being heated and reduced by the reducing gas. Subsequently, the iron-based raw materials melt and drip down the blast furnace 10 while being further reduced by the coke. The iron-based raw materials are ultimately accumulated in the hearth as molten pig iron containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is removed from the tap and used in the next steelmaking process.

[0015] Auxiliary reducing agents refer to substances such as pulverized coal, powdered coke, and waste plastics, either individually or in combination, that are blown into the blast furnace through the tuyeres.

[0016] Typically, the tuyeres 11 are located at the bottom of the blast furnace 10. The tuyeres 11 are inlets for blowing heated hydrogen-based reducing gas and auxiliary reducing agents into the blast furnace 10, in addition to the hot air mentioned above. In this embodiment, reducing gas separated from the top exhaust gas (blast furnace exhaust gas) can also be blown into the blast furnace 10 through the tuyeres 11.

[0017] The shaft tuyere 12 is attached at a position higher than the normal tuyere 11 and is a tuyere for blowing gas into the shaft section 10b of the blast furnace 10. In the present embodiment, the shaft tuyere 12 is provided in the shaft section 10b of the blast furnace 10. The shaft tuyere 12 may be attached to the bosh section or the belly section of the blast furnace 10. The shaft tuyere 12 is an injection port for blowing the reformed top gas circulation gas obtained by reforming the top gas into the shaft section 10b of the blast furnace 10. In FIG. 1, only one shaft tuyere 12 is depicted on the left side of the shaft section 10b, but a plurality of shaft tuyeres 12 may be provided. The plurality of shaft tuyeres 12 are, for example, evenly arranged in the circumferential direction of the shaft section 10b.

[0018] The CO2 separation and recovery device 20 is a device that recovers the top gas and separates it into a reducing gas (CO gas and hydrogen gas) and nitrogen gas, and CO2 gas and H2O gas. The method of separation is not particularly limited, and examples include chemical adsorption method and physical adsorption method (PSA), etc. In the following description, the reducing gas and nitrogen gas separated from the top gas are referred to as reformed top gas circulation gas (Returned Blast Furnace Gas; RBFG). The reformed top gas circulation gas (secondary reducing gas) contains at least 20% by volume fraction of CO gas. The secondary reducing gas is, for example, a gas recovered and separated from the top gas, or a gas containing CO gas and H2 gas obtained by reforming a hydrocarbon-based gas by a general method such as partial oxidation. It is preferable that the content rates of CO2 gas and H2O gas in the secondary reducing gas are low. For example, the H2O gas is preferably 10% or less, more preferably 5% or less by volume fraction. Also, the CO2 gas is preferably 5% or less, more preferably 3% or less by volume fraction. By being below this numerical value, the influence of the gasification reaction, which is an endothermic reaction, can be suppressed. The secondary reducing gas may be blown into the blast furnace at room temperature, but in order to provide heat supply to the blast furnace, it is desirable to be blown in a heated state. Depending on the injection position of the secondary reducing gas, the appropriate temperature conditions of the secondary reducing gas change, but for example, it is preferably 600 °C or higher, more preferably 800 °C or higher. The CO2 gas and H2O gas separated by the CO2 separation and recovery device 20 are discharged outside the system. Note that the CO2 separation and recovery device 20 does not necessarily have to recover the entire amount of the top gas of the furnace. For example, the CO2 separation and recovery device 20 may recover only the amount of the top gas corresponding to the flow rate of the reformed top circulation gas blown into the blast furnace.

[0019] The buffer tank 30 is a tank that temporarily stores the reformed top circulation gas. A desired amount of the reformed top circulation gas is introduced from the buffer tank 30 into the compressor 40. The remaining reformed top circulation gas is used, for example, as a heat source in the steelworks.

[0020] The compressor 40 pressurizes the reformed top circulation gas. Here, the compressor 40 pressurizes the reformed top circulation gas to about the internal pressure of the blast furnace 10 (about 4.5 atmospheres), for example. The pressurized reformed top circulation gas is introduced into the heater 50.

[0021] The heater 50 heats the reformed top circulation gas. The heater 50 can be sufficiently realized by an electric heater or the like. The heating temperature is arbitrarily set according to the operating conditions of the blast furnace 10. However, for example, when the reformed top circulation gas is blown from the tuyere 12 of the shaft section into the shaft section 10b of the blast furnace 10, it is preferably set to 800 °C or higher. The blowing temperature of the reformed top circulation gas is measured, for example, by thermometers provided at the normal tuyere 11 and the tuyere 12 of the shaft section. The reformed top circulation gas heated by the heater 50 is blown into the blast furnace 10 from the normal tuyere 11 or is blown into the shaft section 10b of the blast furnace 10 from the tuyere 12 of the shaft section. The reformed top circulation gas may be blown into the blast furnace 10 from both the normal tuyere 11 and the tuyere 12 of the shaft section.

[0022] The hydrogen-based reducing gas supply system 2 comprises a hydrogen-based reducing gas tank 70 and a heater 71. The hydrogen-based reducing gas supply system 2 is a system that supplies hydrogen-based reducing gas to the blast furnace system 1 from outside the system. The hydrogen-based reducing gas (first reducing gas) is a gas in which H is present in an elemental composition ratio of 30 mol% or more and which exists as a gas under standard conditions (0°C, 1 atm). For example, it is H2 gas, unsaturated hydrocarbon gases (C2H4, C2H2, C3H6, etc.), saturated hydrocarbon gases (CH4, C2H6, etc.), NH3 gas, coke oven gas, city gas, natural gas, etc. and mixtures thereof. Particularly preferred are H2 gas and unsaturated hydrocarbon gases (C2H4, C2H2, C3H6, etc.). H2 gas is preferred from the viewpoint of reducing carbon consumption per unit area because it does not contain carbon and does not cause a thermal decomposition reaction at the tuyeres. Furthermore, because the gas has low viscosity and density, it is also preferable from the viewpoint of permeability in the blast furnace. Unsaturated hydrocarbon gases are preferable because they contain double and triple bonds in their gas molecules, resulting in a relatively large heat of combustion per mole of oxygen, and they also serve as a heat source at the tuyeres. It is more preferable that the elemental composition ratio of H in the first reducing gas is 50 mol% or more. The first reducing gas may also be a mixed gas with other gases (e.g., N2 gas) (without impairing the effects of this embodiment).

[0023] The hydrogen-based reducing gas tank 70 is a tank for storing hydrogen-based reducing gas. Here, hydrogen-based reducing gas is a concept that includes not only hydrogen gas but also mixed gases of hydrogen gas and other gases. Any gas other than hydrogen gas that does not impair the effects of this embodiment can be used as the hydrogen-based reducing gas; for example, nitrogen gas can be used. The heater 71 heats the hydrogen-based reducing gas supplied from the hydrogen-based reducing gas tank 70. The heater 71 can easily be implemented with an electric heater or the like. The heater 71 is usually connected to the tuyere 11, and the heated hydrogen-based reducing gas is usually blown into the blast furnace 10 from the tuyere 11. The heater 71 may be used in combination with the heater 50.

[0024] The control unit 3 is comprised of, for example, a computer. The control unit 3 includes, for example, a processor such as a CPU (Central Processing Unit) connected by a bus, and memory, and executes programs. The computer functions as the control unit 3 by executing programs. Furthermore, all or part of the functions of the control device 3 may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. The program may also be transmitted via a telecommunications line.

[0025] As shown in Figure 2, the control device 3 comprehensively controls the blast furnace system 1 and the hydrogen-based reducing gas supply system 2. The control device 3 controls the operation of the blast furnace 10. The control device 3 controls the group of devices that generate reformed top circulation gas from the top exhaust gas and injects the reformed top circulation gas into the blast furnace 10 from the normal tuyeres 11 or shaft tuyeres 12 of the blast furnace 10. The control device 3 controls the hydrogen-based reducing gas supply system 2 and injects the hydrogen-based reducing gas into the blast furnace 10 from the normal tuyeres 11 of the blast furnace 10.

[0026] The control device 3 acquires temperature, gas flow rate, amount of discharged dust, etc., at various parts of the blast furnace system 1 via various measuring devices (not shown) installed in the blast furnace system 1, and controls the blast furnace system 1 based on the obtained measurement values. In this embodiment, the control device 3 includes a solution loss carbon amount acquisition unit 31 that acquires the amount of solution loss carbon in the blast furnace 10 based on information obtained via the measuring device, and an air permeability index acquisition unit 32 that acquires an air permeability index in the blast furnace 10 based on information obtained via the measuring device. The control device 3 controls the amount of auxiliary reducing agent blown into the blast furnace 10 based on the acquired solution loss carbon amount and air permeability index. Note that Figure 2 only illustrates the characteristic functions of the control device 3 of this embodiment, and does not illustrate the basic functions of blast furnace control.

[0027] <Blast furnace operation method> According to the blast furnace system 1 of this embodiment, at least four types of operation as shown below are possible. The blast furnace operation method of this embodiment, described later, is applicable to the following operations (2) to (4) in which hydrogen-based reducing gas is injected into the blast furnace 10.

[0028] (1) Normal operation: Normal operation is an operation in which hydrogen-based reducing gas is not injected into the blast furnace 10, and the reforming furnace top circulation gas is also not injected into the blast furnace 10. (2) Hydrogen injection operation: Hydrogen-based reducing gas supplied from the hydrogen-based reducing gas tank 70 via the heater 71 is normally injected into the blast furnace 10 from the tuyeres 11, and the reformed furnace top circulation gas is not injected into the blast furnace 10. (3) Reformed furnace top circulation gas injection operation (normal tuyere): Operation in which hydrogen-based reducing gas is injected into the blast furnace 10 from the normal tuyere 11, and reformed furnace top circulation gas is also injected into the blast furnace 10 from the normal tuyere 11. (4) Reformed furnace top circulation gas injection operation (shaft tuyere): Operation in which hydrogen-based reducing gas is injected into the blast furnace 10 from the normal tuyere 11, and reformed furnace top circulation gas is injected into the blast furnace 10 from the shaft tuyere 12.

[0029] The following will provide a detailed explanation of how the blast furnace is operated. Figure 3 is a flowchart showing the operation method of the blast furnace in this embodiment. The blast furnace operation method of this embodiment includes the steps of: step S1 adjusting the amount of hydrogen-based reducing gas injected; step S2 obtaining the amount of solution loss carbon in the blast furnace 10; step S3 determining whether the operating conditions can be adjusted; step S4 adjusting the ratio of auxiliary reducing agent injected into the blast furnace 10; step S5 obtaining the permeability index or the amount of solution loss carbon in the blast furnace 10; and step S6 determining whether the operating conditions can be readjusted.

[0030] The following describes a case where the control device 3 executes a program including the above steps, but it is not limited to this configuration. The operation method of this embodiment can also be performed by an operator in some steps or all of them.

[0031] In step S1, the control device 3 adjusts the amount of hydrogen-based reducing gas injected into the blast furnace 10 based on the operator's instructions. Specific examples of step S1 include: (1) starting or stopping hydrogen injection operations, in which hydrogen-based reducing gas supplied from the hydrogen-based reducing gas supply system 2 is normally injected into the blast furnace 10 from the tuyeres 11; (2) changing the amount of hydrogen-based reducing gas injected into the blast furnace 10 during hydrogen injection operations; (3) starting or stopping the injection of reformer top circulation gas into the blast furnace 10; and (4) changing the amount of reformer top circulation gas injected into the blast furnace 10. Furthermore, the adjustment of the amount of hydrogen-based reducing gas injected in step S1 also includes cases where the effective amount of reducing gas components injected is changed due to a change in the type of hydrogen-based reducing gas.

[0032] In step S2, the control device 3 acquires the amount of solution loss carbon in the blast furnace 10. The amount of solution loss carbon can be acquired by observing the flow rate of CO gas discharged from the top of the blast furnace 10. The amount of solution loss carbon is the sum of gasification reactions in the blast furnace 10 other than the gasification reaction that normally reacts with oxygen at the tip of the tuyere 11 (C + 1 / 2CO2 = CO), and is calculated by subtracting the amount of carbon gasified at the tip of the tuyere from the amount of carbon in the top gas. The amount of carbon in the top gas is calculated from the amount of top gas and the concentrations of CO and CO2 in the top gas. The amount of carbon gasified at the tip of the tuyere is calculated from the amount of oxygen in the blown air.

[0033] In step S3, the control device 3 compares the amount of solution loss carbon obtained in step S2 with the amount of solution loss carbon before adjusting the hydrogen-based reducing gas injection amount in step S1, and determines whether or not adjustment of the auxiliary reducing agent ratio is necessary. For example, when switching from normal operation to hydrogen injection operation, the amount of CO2 gas in the blast furnace 10 decreases due to the increase in the hydrogen reduction rate, and the solution loss reaction decreases. As a result, the consumption of auxiliary reducing agent and coke generated powder in the blast furnace 10 decreases, and carbon powder tends to accumulate in the blast furnace 10. This reduces the permeability of the blast furnace 10, hindering stable operation.

[0034] In step S3, the control device 3 determines whether the change in the amount of solution loss carbon is within an acceptable range. The change in the amount of solution loss carbon is calculated from the difference in the amount of solution loss carbon before and after adjusting the amount of hydrogen-based reducing gas injected. If the change in the amount of solution loss carbon exceeds a preset allowable value (S3-NO), the control device 3 determines that adjustment of the auxiliary reducing agent ratio is necessary and proceeds to step S4. On the other hand, if the change does not exceed the above allowable range (S3-YES), the control device 3 proceeds to step S3A and performs a program termination determination. The above tolerance range in step S3 is set based on the relationship between the amount of carbon powder that increases due to the reduction in solution loss carbon and the permeability of the blast furnace 10. The relationship between the amount of carbon powder accumulated and permeability can be derived from operational data or blast furnace simulations.

[0035] If the process proceeds to step S3A, the control device 3 determines whether to terminate execution based, for example, on a prediction of the fluctuations in the amount of solution loss carbon. If the change in the amount of solution loss carbon is small and well below the allowable limit (S3A-YES), the control device 3 determines that the amount of solution loss carbon is generally stable and terminates execution. On the other hand, if the change in the amount of solution loss carbon is relatively close to the allowable limit (S3A-NO), the process returns to step S2 and repeats the acquisition of the amount of solution loss carbon. A predetermined waiting time may be provided between restarting step S2 from step S3A.

[0036] Furthermore, the judgment criterion in step S3 may include the time during which the change in the amount of solution loss carbon exceeds the allowable value. In other words, the condition for determining whether an adjustment of the auxiliary reducing agent ratio is necessary may be set as follows: when the change in the amount of solution loss carbon exceeds the allowable value, and the cumulative value of the time during which the allowable value is exceeded exceeds a predetermined cumulative time. This makes it possible to determine whether or not an adjustment of the auxiliary reducing agent ratio is necessary without being affected by temporary fluctuations in the amount of solution loss carbon.

[0037] In step S4, the control device 3 adjusts the auxiliary reducing agent ratio based on the change in the amount of solution loss carbon obtained in step S2. The auxiliary reducing agent ratio is the amount of auxiliary reducing agent injected per ton of molten iron produced (unit: kg / t-pig). Specifically, the control device 3 decreases the auxiliary reducing agent ratio if the change in the amount of solution loss carbon is negative, and increases the auxiliary reducing agent ratio if the change in the amount of solution loss carbon is positive. Based on the change in the amount of solution loss carbon, the control device 3 calculates the amount of auxiliary reducing agent to be injected from the blower 13 into the blast furnace 10 and adjusts the operating conditions of the blower 13. For example, if the amount of solution loss carbon decreases (a negative change) due to an increase in the amount of hydrogen-based reducing gas injected, the control device 3 reduces the amount of auxiliary reducing agent injected by an amount corresponding to the decrease in the amount of solution loss carbon. This suppresses the increase in the accumulation of carbon powder in the blast furnace 10 and prevents deterioration of the permeability inside the blast furnace 10. Regarding the adjustment amount of auxiliary reducing agent, it can be determined by considering that the change in solution loss carbon corresponds to the change in carbon powder consumed in the blast furnace, and that this change is equivalent to the change in carbon powder brought into the blast furnace from the auxiliary reducing agent. The amount of carbon powder brought into the blast furnace from the auxiliary reducing agent can be calculated as the amount of unburned carbon powder using, for example, the combustion rate of the auxiliary reducing agent in the combustion reaction at the tuyeres. The combustion rate of the auxiliary reducing agent can be derived from actual results or simulations.

[0038] In step S4, the coke ratio (amount of coke used per ton of molten iron) may be adjusted according to the amount of adjustment to the auxiliary reducing agent ratio. The amount of adjustment to the auxiliary reducing agent ratio is calculated from the difference in the auxiliary reducing agent ratio before and after the adjustment. If the auxiliary reducing agent ratio is decreased, the coke ratio is increased, and if the auxiliary reducing agent ratio is increased, the coke ratio is decreased. The amount of adjustment to the coke ratio can be determined, for example, so that the reducing agent ratio remains constant. Alternatively, the coke ratio may be adjusted as appropriate so that the molten iron temperature remains constant. If the reducing agent ratio is decreased in accordance with the increase in the amount of hydrogen-based reducing gas injected, there is a risk of insufficient heat inside the blast furnace 10. By adjusting the coke ratio to increase the heat inside the blast furnace 10, it becomes easier to maintain the furnace temperature of the blast furnace 10.

[0039] In step S5, the control device 3 acquires the permeability index of the blast furnace 10. The permeability index is, for example, the pressure loss inside the furnace, the permeability resistance index, or the measurement values ​​from each pressure gauge installed in various parts of the blast furnace. Permeability can also be determined from the increase or decrease in top dust discharged from the top of the furnace or the increase or decrease in the amount of carbon discharged from the taphole. The control device 3 acquires the permeability index through the equipment of the blast furnace system 1 or an external observation device. By acquiring the permeability index, it is possible to determine whether or not the permeability inside the blast furnace 10 has deteriorated.

[0040] In step S6, the control device 3 determines whether the permeability inside the blast furnace 10 is within an acceptable range based on the permeability index obtained in step S5. If the permeability inside the blast furnace 10 exceeds the acceptable range (S6-NO), the control device 3 returns to step S4 and re-executes the adjustment of the auxiliary reducing agent ratio. If the permeability inside the blast furnace 10 is within an acceptable range (S6-YES), the control device 3 terminates the execution of the program.

[0041] According to the blast furnace operation method of this embodiment described above, even when a hydrogen-based reducing gas is injected to achieve a low reducing agent ratio, the accumulation of carbon powder due to a decrease in the amount of solution loss reaction can be suppressed, enabling stable operation.

[0042] (First variation) Figure 4 is a flowchart showing the operation method of the first modified blast furnace, and Figure 5 is a functional block diagram of the entire blast furnace system that implements the operation method of the first modified blast furnace. The first modified blast furnace operation method includes the steps of: adjusting the amount of hydrogen-based reducing gas injected (S1); obtaining a predicted value for the change in the amount of solution loss carbon in the blast furnace 10 (S2); determining whether or not to adjust the operating conditions (S3); adjusting the ratio of auxiliary reducing agent injected into the blast furnace 10 (S4); obtaining the amount of solution loss carbon in the blast furnace 10 (S5); and determining whether or not to readjust the operating conditions (S6). The control device 3 of the first modified example shown in Figure 5 has a solution loss carbon amount change prediction value acquisition unit 33.

[0043] The blast furnace operation method of the first modified example differs from the blast furnace operation method of the previous embodiment shown in Figure 3 in that, in step S2, a predicted value of the change in the amount of solution loss carbon is used, and in step S5, the amount of solution loss carbon is obtained, and in step S6, it is determined whether the auxiliary reducing agent ratio is appropriate based on the amount of solution loss carbon. Descriptions of configurations and methods common to the previous embodiment will be omitted as appropriate.

[0044] The following describes a case where the control device 3 executes a program including the above steps, but it is not limited to this configuration. The operation method of this embodiment can also be performed by an operator in some steps or all of them.

[0045] In step S1, the control device 3 adjusts the amount of hydrogen-based reducing gas injected into the blast furnace 10 based on the operator's instructions.

[0046] In step S2, the control device 3 obtains a predicted value for the change in the amount of solution loss carbon in the blast furnace 10. The predicted value for the amount of solution loss carbon is obtained from a pre-prepared relationship between the amount of hydrogen-based reducing gas injected and the amount of solution loss carbon. The relationship between the amount of hydrogen-based reducing gas injected and the amount of solution loss carbon can be derived from operational records or blast furnace simulations. In the solution loss carbon change prediction acquisition unit 33, the control device 3 obtains a predicted value for the change in the amount of solution loss carbon from the difference between the predicted values ​​of the amount of solution loss carbon before and after changing the amount of hydrogen-based reducing gas injected.

[0047] In the first modified example, it is unnecessary to obtain an actual value of the solution loss carbon amount in step S2, and a predicted value of the change in the solution loss carbon amount can be obtained immediately according to the amount of hydrogen-based reducing gas injected, allowing subsequent steps to be executed quickly.

[0048] In step S3, the control device 3 determines whether the predicted value of the change in the amount of solution loss carbon obtained in step S2 is within an acceptable range. If the change in the amount of solution loss carbon exceeds a preset acceptable range (S3-NO), the control device 3 determines that adjustment of the auxiliary reducing agent ratio is necessary and proceeds to step S4. On the other hand, if the change in the amount of solution loss carbon does not exceed the above acceptable range (S3-YES), the control device 3 terminates the execution of the program.

[0049] In step S4, the control device 3 adjusts the auxiliary reducing agent ratio based on the change in the amount of solution loss carbon obtained in step S2.

[0050] In step S5, the control device 3 acquires the amount of solution loss carbon from the blast furnace 10. The amount of solution loss carbon can be acquired by observing the flow rate of CO gas emitted from the top of the blast furnace 10.

[0051] In step S6, the control device 3 compares the measured amount of solution loss carbon obtained in step S5 with the predicted amount of solution loss carbon obtained in step S2, and determines whether the difference between the measured and predicted amounts of solution loss carbon is within an acceptable range. Since the auxiliary reducing agent ratio set in step S4 is based on the predicted change in the amount of solution loss carbon, the control device 3 determines whether the adjustment of the amount of auxiliary reducing agent injected in step S4 is appropriate by measuring the amount of solution loss carbon after adjusting the auxiliary reducing agent ratio.

[0052] If the adjustment of the auxiliary reducing agent ratio is insufficient and the difference between the measured and predicted values ​​of the solution loss carbon amount exceeds the acceptable range (S6-NO), the control device 3 returns to step S4 and re-executes the adjustment of the auxiliary reducing agent ratio. If the difference between the measured and predicted values ​​of the solution loss carbon amount is within the acceptable range (S6-YES), the control device 3 terminates the execution of the program.

[0053] Even in the first modified blast furnace operation method described above, when a hydrogen-based reducing gas is injected to achieve a low reducing agent ratio, the accumulation of carbon powder due to the reduction in solution loss reaction volume can be suppressed, enabling stable operation. Furthermore, steps S5 and S6 of the operating method in the first modified example can be omitted if it is possible to accurately adjust the auxiliary reducing agent ratio in step S4 based on the predicted value of the change in the amount of carbon loss in the solution.

[0054] (Second variation) Figure 6 is a flowchart showing the operation method of the blast furnace in the second modified example. The second modified blast furnace operation method includes the steps of: adjusting the amount of hydrogen-based reducing gas injected (S1); obtaining a predicted value for the change in the amount of solution loss carbon in the blast furnace 10 (S2); determining whether or not to adjust the operating conditions (S3); adjusting the ratio of auxiliary reducing agent injected into the blast furnace 10 (S4); obtaining the amount of solution loss carbon in the blast furnace 10 (S5); determining whether or not to readjust the operating conditions (S6); and adjusting the tuyere combustion temperature or the properties of the auxiliary reducing agent (S7).

[0055] The blast furnace operation method of the second modified example differs from the blast furnace operation method of the first modified example shown in Figure 4 in that it includes a step S7 for adjusting the tuyere combustion temperature or the properties of the auxiliary reducing agent. Descriptions of components and methods common to both the first modified example and the second modified example will be omitted as appropriate.

[0056] The following describes a case where the control device 3 executes a program including the above steps, but it is not limited to this configuration. The operation method of this embodiment can also be performed by an operator in some steps or all of them.

[0057] Steps S1 to S5 are the same as in the first modified example.

[0058] In step S6, the control device 3 compares the measured amount of solution loss carbon obtained in step S5 with the predicted amount of solution loss carbon obtained in step S2, and determines whether the difference between the measured and predicted amounts of solution loss carbon is within an acceptable range. If the difference between the measured and predicted amounts of solution loss carbon exceeds the acceptable range (S6-NO), the control device 3 determines that the adjustment of the auxiliary reducing agent ratio is insufficient and proceeds to step S7. If the difference between the measured and predicted amounts of solution loss carbon is within an acceptable range (S6-YES), the control device 3 terminates the execution of the program.

[0059] In step S7, the control device 3 adjusts either the tuyere combustion temperature or the properties of the auxiliary reducing agent. In step S7, either the tuyere combustion temperature adjustment or the auxiliary reducing agent properties adjustment may be performed alone, or both may be performed in combination.

[0060] The tuyere combustion temperature is typically the temperature at the tip of the tuyere 11 (gas outlet), and if it is difficult to measure, it can be determined by simulating blast furnace operation. As a simulation model, the so-called "blast furnace mathematical model," such as that shown in Kouji TAKATANI, Takanobu INADA, Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace", ISIJ International, Vol.39(1999), No.1, p.15-22, can be used. In this blast furnace mathematical model, the internal region of the blast furnace is divided in the height, radial, and circumferential directions to define multiple meshes (small regions), and the behavior of each mesh is simulated.

[0061] In step S6, if the difference between the measured and predicted amounts of solution loss carbon exceeds the acceptable range and carbon powder accumulation is predicted, the tuyere combustion temperature is increased. This increases the combustion rate of the auxiliary reducing agent in the blast furnace 10, suppressing the accumulation of carbon powder in the lower part of the blast furnace 10. This also suppresses a decrease in the permeability of the blast furnace 10.

[0062] The properties of the auxiliary reducing agent include, for example, if the auxiliary reducing agent is pulverized coal, its particle size, shape, and composition, which are elements of the auxiliary reducing agent that affect how easily the pulverized coal burns. In step S6, if the difference between the measured and predicted amounts of solution loss carbon exceeds the acceptable range and carbon powder accumulation is predicted, the properties of the auxiliary reducing agent are changed to increase the combustion rate. For example, the particle size of the pulverized coal is made finer. This increases the combustion rate of the auxiliary reducing agent in the blast furnace 10, suppressing the accumulation of carbon powder in the lower part of the blast furnace 10. This also suppresses the decrease in permeability within the blast furnace 10.

[0063] In step S7, the control device 3 determines the amount to adjust the tuyere combustion temperature or the degree to adjust the auxiliary reducing agent properties based on the difference between the measured and predicted values ​​of the solution loss carbon amount, and then performs the adjustment of the tuyere combustion temperature or the auxiliary reducing agent properties. After the execution of step S7, the control device 3 repeats steps S5 and S6. In the second and subsequent steps S6, if the difference between the measured and predicted values ​​of the solution loss carbon amount is within an acceptable range (S6-YES), the control device 3 terminates the execution of the program.

[0064] Even in the second modified blast furnace operation method described above, when a hydrogen-based reducing gas is injected to achieve a low reducing agent ratio, the accumulation of carbon powder due to the reduction in solution loss reaction volume can be suppressed, enabling stable operation.

[0065] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0066] 1. Blast furnace system 2. Hydrogen-based reducing gas supply system 10 blast furnace 10a Blast furnace body 10b Shaft section 11 Normal tuyere 12 Shaft section tuyere 20 CO2 Separation and Recovery Device 30 buffer tanks 40 Compressors 50, 71 heater 60 Blower 70 Hydrogen-based reduction gas tank

Claims

1. A method for operating a blast furnace, comprising injecting a hydrogen-based reducing gas and an auxiliary reducing agent into the blast furnace, Based on the change in the amount of solution loss carbon caused by fluctuations in the amount of hydrogen-based reducing gas injected, the auxiliary reducing agent ratio is adjusted. The operation method of a blast furnace.

2. The coke ratio is adjusted according to the amount of adjustment of the auxiliary reducing agent ratio. The method for operating a blast furnace according to claim 1.

3. After adjusting the auxiliary reducing agent ratio, the auxiliary reducing agent ratio is readjusted based on the permeability index of the blast furnace. A method for operating a blast furnace according to claim 1 or 2.

4. As the change in the amount of solution loss carbon, a predicted value based on at least one of the operating results of the blast furnace and simulations is used. A method for operating a blast furnace according to claim 1 or 2.

5. After adjusting the auxiliary reducing agent ratio based on the predicted value, the amount of solution loss carbon in the blast furnace is obtained, and the auxiliary reducing agent ratio is readjusted based on the obtained amount of solution loss carbon. The method for operating a blast furnace according to claim 4.

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