Blast furnace operation method

Abstract

This blast furnace operation method is characterized in that a hydrogen-based reducing gas is blown into a blast furnace, a CO2 gas and a H2O gas are separated and removed from a furnace top exhaust gas to generate a reformed furnace top circulating gas, and the reformed furnace top circulating gas is blown into the blast furnace, the method including a step of acquiring a target range of the iron tapping ratio during operation on the basis of the previously acquired relationship between the blowing amount of hydrogen based reducing gas and the total pressure loss, the operating condition being adjusted so that the range of the iron tapping ratio during operation is within the target range of the iron tapping ratio.

Description

Blast furnace operation method

[0001] This application claims priority to Japanese Patent Application No. 2024-035001, filed on March 7, 2024, the contents of which are incorporated herein by reference.

[0002] In the steel industry, the blast furnace process is the mainstream of pig iron production. In the blast furnace process, ferrous materials (materials containing iron oxide, mainly sintered ore, hereinafter simply referred to as "ferrous materials") and coke are alternately and in layers charged into the blast furnace from the top of the furnace, while hot air is blown into the blast furnace from tuyere openings at the bottom. The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace to generate high-temperature reducing gas (mainly CO gas). That is, the hot air gasifies the coke and pulverized coal. The reducing gas rises within the blast furnace, heating and reducing the ferrous materials. The ferrous materials then descend within the blast furnace, where they are heated and reduced by the reducing gas. The ferrous materials then melt and drip down the blast furnace, where they are further reduced by the coke. The iron-based raw materials are finally stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is then removed from the taphole and used in the subsequent steelmaking process. Therefore, in the blast furnace process, carbonaceous materials such as coke and pulverized coal are used as reducing agents.

[0003] Recently, there has been a growing demand to prevent global warming, and carbon dioxide (CO ２ As mentioned above, the blast furnace method uses carbonaceous material as a reducing agent, which produces a large amount of CO ２ Therefore, the steel industry produces CO ２ As the industry is one of the major sources of gas emissions, it is necessary to respond to social demands. Specifically, there is an urgent need to further reduce the reducing agent ratio (amount of reducing agent used per ton of molten iron) in blast furnace operation.

[0004] The reducing agent has the role of generating heat in the furnace to raise the temperature of the charge material and the role of reducing the iron-based raw materials in the furnace, and in order to reduce the reducing agent ratio, it is necessary to increase the reduction efficiency in the furnace. The reduction reactions in the furnace can be expressed by various reaction formulas. Of these reduction reactions, the direct reduction reaction by coke (reaction formula: FeO + C → Fe + CO) is an endothermic reaction that involves a large heat absorption. Therefore, it is important to prevent this reaction from occurring as much as possible in order to reduce the reducing agent ratio. Since this direct reduction reaction occurs in the lower part of the blast furnace, CO, H are generated by the time the iron-based raw materials reach the lower part of the furnace. ２ If the iron-based raw material can be sufficiently reduced with a reducing gas such as the above, the amount of the iron-based raw material that is the target of the direct reduction reaction can be reduced.

[0005] As a conventional technique for solving the above-mentioned problems, a technique is known in which the reducing gas potential in the furnace is improved by performing a hydrogen gas injection operation in which hydrogen gas is injected together with hot air from a tuyere, as disclosed in Patent Document 1. In this technique, the reducing agent ratio is reduced by using hydrogen gas as a reducing gas for the iron-based raw materials.

[0006] International Publication No. 2021 / 107091

[0007] In order to further reduce the reducing agent rate, it was necessary to increase the productivity and improve the efficiency of molten iron production. However, achieving stable high productivity operation posed problems, such as ensuring good permeability in the furnace and stabilizing the tuyere combustion temperature.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for operating a blast furnace that can further improve the efficiency of producing molten iron.

[0009] The gist of the present invention is as follows: (1) A hydrogen-based reducing gas is injected into a blast furnace, and CO is removed from the top exhaust gas. ２ Gas and H ２(2) A method for operating a blast furnace, comprising: separating and removing O gas to generate a reformed furnace top circulation gas; and injecting the reformed furnace top circulation gas into the blast furnace, the method comprising the steps of: obtaining a target range of productivity during operation from a relationship between the injection amount of the hydrogen-based reducing gas and total pressure drop obtained in advance; and adjusting operating conditions so that the range of productivity during operation falls within the target range of productivity. ３ Over 3.7t / d / m ３ (3) The method for operating a blast furnace according to (1), characterized in that the range of the productivity is set to 3.0 t / d / m or less. ３ (4) The method for operating a blast furnace according to any one of (1) to (3), characterized in that the tuyere combustion temperature is maintained at 2100°C or higher.

[0010] According to the present invention, it is possible to provide a method for operating a blast furnace that can further improve the efficiency of producing molten iron.

[0011] FIG. 1 is a flow diagram showing the overall configuration of a blast furnace system used in this embodiment; FIG. 2 is a graph for verifying the effect of this embodiment; FIG. 3 is a graph for verifying the effect of this embodiment; FIG. 4 is a graph for verifying the effect of this embodiment; FIG. 5 is a graph for verifying the effect of this embodiment; FIG. 6 is a graph for verifying the effect of this embodiment; FIG. 7 is a graph for verifying the effect of this embodiment;

[0012] The inventors conducted a simulation of hydrogen gas injection operation and analyzed the internal state of the blast furnace in detail, and found that the pressure loss (total pressure loss) inside the blast furnace was significantly reduced compared to base operation (operation without hydrogen gas injection).

[0013] As will be explained in detail in the Examples, when the productivity (amount of molten iron produced per unit volume of the blast furnace and per unit time (day)) is increased in hydrogen gas injection operation, the total pressure drop increases while the amount of carbon charged to the blast furnace (carbon consumption per ton of molten iron) decreases. Therefore, by increasing the productivity, not only does the production efficiency of molten iron increase, but the carbon consumption also decreases. Furthermore, the productivity can be increased to at least the total pressure drop close to that of base operation.

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0015] 1, the overall configuration of a blast furnace system 1 according to this embodiment and a hydrogen-based reducing gas supply system 2 connected to the blast furnace system 1 will be described. The blast furnace system 1 includes a blast furnace 10 and a CO ２ The system includes a separation and recovery device 20, a buffer tank 30, a compressor 40, and a heater 50.

[0016] The blast furnace 10 includes a blast furnace body 10a, a normal tuyere 11, and a shaft tuyere 12. Inside the blast furnace body 10a, a reduction reaction of iron-based raw materials is carried out by the blast furnace process. Specifically, iron-based raw materials and coke are charged alternately and in layers into the blast furnace 10 from the top of the blast furnace 10, while hot air, pulverized coal, and enriched oxygen gas are blown into the blast furnace 10 through the normal tuyere 11. Furthermore, as described below, a hydrogen-based reducing gas is also blown into the blast furnace 10 through the normal tuyere 11 or the shaft tuyere 12. In the following description, the "tuyere combustion temperature" refers to the temperature at the gas outlet of the normal tuyere 11. From the viewpoint of stable operation of the blast furnace, it is preferable that the tuyere combustion temperature be high and constant. In this regard, as shown in the examples described below, in this embodiment, the tuyere combustion temperature can be maintained at 2100°C or higher. The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace 10 to generate high-temperature reducing gas (mainly CO gas in this case). That is, the hot air gasifies the coke and pulverized coal. Note that, as will be described in detail later, there are cases where pulverized coal is not blown into the blast furnace 10. As a result, the hot air becomes bosh gas, which is mainly composed of hydrogen gas, CO gas, and nitrogen gas. The bosh gas and hydrogen-based reducing gas rise inside the blast furnace 10 and reduce the iron-based raw materials while heating them. More specifically, the hydrogen gas and CO gas in the bosh gas and hydrogen-based reducing gas reduce the iron-based raw materials. These gases are then discharged from the top of the blast furnace as furnace top exhaust gas. The furnace top exhaust gas contains unreacted hydrogen gas, CO gas, CO ２ Gas, H ２ The iron-based raw materials are heated and reduced by bosh gas and hydrogen-based reducing gas while descending through the blast furnace 10. The iron-based raw materials are then melted and dripped through the blast furnace 10 while being further reduced by coke. The iron-based raw materials are finally stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is taken out through a tap hole and is used in the next steelmaking process. The productivity (t / d / m) in this embodiment is ３ ) means the amount of molten iron produced per unit volume of the blast furnace 10 and per unit time (day).

[0017] The normal tuyere 11 is provided at the bottom of the blast furnace 10 and blows heated hydrogen-based reducing gas into the blast furnace 10 in addition to the hot air described above, as will be described later. In this embodiment, the pressure loss from the gas outlet (tuyere tip) of the normal tuyere 11 to the top of the furnace is referred to as the "pressure loss in the blast furnace" (in the following explanation, the "pressure loss in the blast furnace" will be referred to as the "total pressure loss"). Note that, although FIG. 1 shows normal tuyere 11 only at both ends of the blast furnace 10, three or more normal tuyere 11 may be provided at regular intervals around the circumferential direction. Furthermore, reformed furnace top circumferential circulation gas may be blown into the blast furnace 10 through the normal tuyere 11.

[0018] The shaft tuyere 12 is provided in the shaft 10b of the blast furnace 10, and injects reformed top recirculating gas (RBFG) obtained by reforming the top exhaust gas into the shaft 10b of the blast furnace 10. Although the shaft tuyere 12 is depicted only on the left side of the shaft 10b in FIG. 1 , a shaft tuyere 12 may also be provided on the right side of the shaft 10b, or three or more shaft tuyere 12 may be provided at regular intervals around the circumference. Furthermore, a hydrogen-based reducing gas may be injected into the blast furnace 10 from the shaft tuyere 12.

[0019] CO ２ The separation and recovery device 20 recovers the top flue gas and separates CO ２ Gas and H ２ The reformer top circulation gas (RBFG) is generated by separating the CO gas from the reformer top exhaust gas. The reformer top circulation gas is a gas containing 20% ​​or more CO gas by volume. The reformer top circulation gas is, for example, a gas recovered and separated from the furnace top exhaust gas, or a gas containing CO gas and H gas obtained by reforming a hydrocarbon gas by a general method such as partial oxidation. ２ The CO in the reformer top circulation gas is ２ Gas and H ２ The lower the O gas content, the better. ２ The volume fraction of O gas is preferably 10% or less, more preferably 5% or less. ２ The volume fraction of the gas is preferably 5% or less, more preferably 3% or less. By keeping the volume fraction below this value, the influence of the gasification reaction, which is an endothermic reaction, can be suppressed. ２The separation and recovery device 20 does not necessarily recover the entire amount of the top exhaust gas. ２ The separation and recovery device 20 may recover only an amount of furnace top flue gas corresponding to the flow rate of the reformed furnace top recycle gas (RBFG) injected into the blast furnace. The remaining furnace top flue gas is used as a heat source for the steelworks. The separation method is not particularly limited, but examples thereof include chemical adsorption and physical adsorption (PSA). ２ Gas and H ２ The O gas is discharged to the outside of the system. In the following description, the reforming furnace top recirculation gas may also be referred to as "RBFG."

[0020] The buffer tank 30 is a tank for temporarily storing RBFG. A desired amount of RBFG is introduced from the buffer tank 30 into the compressor 40.

[0021] The compressor 40 pressurizes the RBFG. Here, the compressor 40 pressurizes the RBFG to, for example, the internal pressure of the blast furnace 10 (approximately 4.5 atmospheres). The pressurized RBFG is introduced into the heater 50.

[0022] The heater 50 heats the RBFG. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. For example, when RBFG is injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12, it is preferably set to 800°C or higher. The heater 50 can be sufficiently realized by an electric heater or the like. The RBFG heated by the heater 50 is injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12. In FIG. 1 , RBFG is injected into the blast furnace 10 from the shaft tuyere 12 on the left side, but RBFG may also be injected into the blast furnace 10 from the shaft tuyere 12 on the right side (not shown). RBFG may be injected into the blast furnace 10 from both the normal tuyere 11 and the shaft tuyere 12, or may be injected into the blast furnace 10 from the normal tuyere 11.

[0023] Amount of RBFG injected into the blast furnace 10 (Nm ３ / t) may be set arbitrarily depending on the operating conditions of the blast furnace 10.

[0024] The hydrogen-based reducing gas supply system 2 includes a hydrogen-based reducing gas tank 70 and a heater 71. The hydrogen-based reducing gas tank 70 stores a hydrogen-based reducing gas. Here, the hydrogen-based reducing gas refers to a gas containing 30 mol % or more of H as an elemental composition ratio, and existing as a gas under standard conditions (0°C, 1 atmosphere). For example, H ２ Gas, unsaturated hydrocarbon gas (C ２ H ４ , C ２ H ２ , C ３ H ６ etc.), saturated hydrocarbon gases (CH ４ , C ２ H ６ , etc.), NH ３ Gas, coke oven gas, city gas, natural gas, etc., and mixtures thereof are particularly preferred. ２ Gas, unsaturated hydrocarbon gas (C ２ H ４ , C ２ H ２ , C ３ H ６ etc.) H ２ The gas does not contain carbon and does not cause a thermal decomposition reaction at the tip of the tuyere, so it is preferable from the viewpoint of reducing the carbon consumption unit. Furthermore, the gas has low viscosity and density, so it is also preferable from the viewpoint of gas permeability inside the blast furnace. Furthermore, the hydrogen-based reducing gas may be injected into the blast furnace at room temperature, but is preferably injected in a heated state in order to supply heat to the blast furnace. The heating temperature of the hydrogen-based reducing gas is, for example, 500°C or higher, 1000°C or higher, or 1200°C or higher. It is more preferable that the elemental composition ratio of H in the hydrogen-based reducing gas is 50 mol% or higher. Furthermore, the hydrogen-based reducing gas may be mixed with other gases (such as N) (which do not impair the effect of this embodiment). ２ The hydrogen-based reducing gas tank 70 supplies the hydrogen-based reducing gas to the heater 71.

[0025] The heater 71 heats the hydrogen-based reducing gas. The hydrogen-based reducing gas heated by the heater 71 is injected into the blast furnace 10. Therefore, in this embodiment, a hydrogen gas injection operation is performed. The heater 71 can be sufficiently realized by an electric heater or the like. The heating temperature and injection amount (Nm３ / t) may be set arbitrarily depending on the operating conditions of the blast furnace 10. In FIG. 1, the heater 71 is shown as being normally connected to the tuyere 11, but the heater 71 may be connected to the shaft tuyere 12.

[0026] Although details will be described later, when a hydrogen-based reducing gas is injected into the blast furnace 10, the total pressure drop is significantly reduced compared to base operation (operation in which a hydrogen-based reducing gas is not injected into the blast furnace 10) (see FIG. 2). On the other hand, when the productivity is increased, the total pressure drop tends to increase (see FIG. 3). Furthermore, when the productivity is increased, the amount of carbon per ton of molten iron charged into the blast furnace 10 (hereinafter also referred to as carbon consumption) decreases. Therefore, by increasing the productivity, not only does the production efficiency of molten iron increase, but the carbon consumption also decreases. Furthermore, the productivity can be increased to at least the total pressure drop close to that of base operation. Specifically, when the productivity is increased to 2.7 t / d / m ３ Over 3.7t / d / m ３ It can be set to 2.7 t / d / m or less. ３ The following productivity rates are achievable even in base operation: ３ If the productivity exceeds 3.0 t / d / m, the total pressure loss will be worse than in the base operation. ３ In this case, the total pressure loss is particularly low.

[0027] Possible methods for increasing the productivity include, for example, increasing the amount of hot blast blown, increasing the amount of hydrogen-based reducing gas blown, or increasing the amount of RBFG blown. Furthermore, since the total pressure drop is reduced, fine iron-based raw materials and coke that could not be used in base operation due to the increased pressure drop can be used. This allows for effective use of resources.

[0028] <2. Blast Furnace Operation Method> Next, a blast furnace operation method will be described. First, iron-based raw materials and coke are alternately and layeredly charged into the blast furnace 10 from the top of the blast furnace 10, while hot air, pulverized coal, and enriched oxygen gas are normally blown into the blast furnace 10 from the tuyere 11. Here, in the blast furnace operation method according to this embodiment, the total pressure drop is reduced, so that fine iron-based raw materials and coke that could not be used in base operation due to the increased pressure drop can be used. This allows for effective utilization of resources.

[0029] On the other hand, the hydrogen-based reducing gas tank 70 supplies the hydrogen-based reducing gas to the heater 71. The heater 71 heats the hydrogen-based reducing gas. Here, the heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10, but may be, for example, a temperature similar to that of hot air (for example, about 1200°C). Next, the heated hydrogen-based reducing gas is injected into the blast furnace 10. By injecting the hydrogen-based reducing gas into the blast furnace 10, the total pressure drop can be reduced. Furthermore, by increasing the injection amount of the hydrogen-based reducing gas, the productivity can be increased to a level close to the total pressure drop in base operation. The injection amount of the hydrogen-based reducing gas into the blast furnace may be set arbitrarily depending on the operating conditions of the blast furnace 10 based on the productivity range obtained in the process of obtaining the target productivity range described below.

[0030] (Step of Obtaining Target Range of Productivity Ratio) In this embodiment, it is desirable to obtain in advance the relationship between the injection amount of hydrogen-based reducing gas and the total pressure drop, for example, by simulation. The operable productivity range can be obtained from the difference between the value of the total pressure drop corresponding to the injection amount of hydrogen-based reducing gas and the value of the total pressure drop in base operation. Specifically, when the productivity is set to 2.7 t / d / m ３ Over 3.7t / d / m ３ The "operable productivity range" refers to a range of operating conditions where stable operation is possible without excessively increasing the tuyere combustion temperature, for example. In this embodiment, the above-mentioned operable productivity range is set as the "target productivity range during operation," and the operating conditions are adjusted to operate the blast furnace. This can further improve the efficiency of molten iron production.

[0031] The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace 10 to generate high-temperature reducing gas (mainly CO gas in this case). That is, the hot air gasifies the coke and pulverized coal. As a result, the hot air becomes bosh gas, which is mainly composed of hydrogen gas, CO gas, and nitrogen gas. The bosh gas and hydrogen-based reducing gas rise inside the blast furnace 10 and reduce the iron-based raw materials while heating them. More specifically, the hydrogen gas and CO gas in the bosh gas and hydrogen-based reducing gas reduce the iron-based raw materials. These gases are then discharged from the top of the blast furnace as furnace top exhaust gas. The furnace top exhaust gas contains unreacted hydrogen gas, CO gas, CO ２ Gas, H ２ The gases contained in the blast furnace 10 include O gas and nitrogen gas. As the iron-based raw materials descend through the blast furnace 10, they are heated and reduced by bosh gas and hydrogen-based reducing gas. The iron-based raw materials are then melted and dripped through the blast furnace 10 while being further reduced by coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is removed from the taphole and used in the next steelmaking process.

[0032] The top exhaust gas is CO ２ The CO is introduced into the separation and recovery device 20. ２ The separation and recovery device 20 recovers the top flue gas and separates CO ２ Gas and H ２ The O gas is separated and removed to generate RBFG. The RBFG is temporarily stored in the buffer tank 30. A desired amount of RBFG is introduced from the buffer tank 30 into the compressor 40.

[0033] The compressor 40 pressurizes the RBFG. Here, the compressor 40 pressurizes the RBFG to, for example, the internal pressure of the blast furnace 10 (approximately 4.5 atmospheres). The pressurized RBFG is introduced into the heater 50.

[0034] The heater 50 heats the RBFG. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10, but for example, when the RBFG is blown into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12, it is preferable to set the heating temperature to 800°C or higher. The RBFG heated by the heater 50 is blown into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12.

[0035] Amount of RBFG injected into the blast furnace 10 (Nm ３ / t) may be arbitrarily set depending on the operating conditions of the blast furnace 10. By increasing the amount of RBFG injected into the blast furnace 10, the productivity can be increased.

[0036] As explained above, according to this embodiment, since a hydrogen-based reducing gas is injected into the blast furnace 10, the total pressure drop can be reduced. Furthermore, if the productivity rate is increased, the total pressure drop increases, but the carbon consumption decreases. Therefore, the productivity rate can be increased until the total pressure drop becomes the same as that in base operation. In this way, an operating method is possible in which the target range of the productivity rate during operation is obtained from the relationship between the injection amount of the hydrogen-based reducing gas and the total pressure drop obtained in advance, and the operating conditions are adjusted so that the productivity rate during operation falls within the target range of the productivity rate. Specifically, in this embodiment, the productivity rate is set to 2.7 t / d / m ３ Over 3.7t / d / m ３ This allows for a further increase in the production efficiency of molten iron. ３ It is preferable that the total pressure drop is less than 100°C. Furthermore, by reducing the total pressure drop, it is possible to use iron-based raw materials and coke with particle sizes that could not be used in base operation. Furthermore, in this embodiment, the tuyere tip combustion temperature can be maintained at 2100°C or higher. Furthermore, the operating conditions are adjusted by, for example, the blast rate, oxygen enrichment rate, coke ratio, and pulverized coal injection rate.

[0037] Next, an example of this embodiment will be described. In this example, a simulation of blast furnace operation was performed to verify the effects of this embodiment. Here, the simulation model used was the so-called "blast furnace mathematical model" shown in Kouji TAKATANI, Takanobu INADA, and Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace," ISIJ International, Vol. 39 (1999), No. 1, pp. 15-22, etc. This blast furnace mathematical model roughly defines a plurality of meshes (small regions) by dividing the internal region of the blast furnace in the height direction, radial direction, and circumferential direction, and simulates the behavior of each mesh.

[0038] As the blast furnace operation, a base operation (operation without hydrogen gas injection) and a hydrogen injection operation (Example) in which hydrogen gas is injected into the blast furnace 10 from the normal tuyere 11 while RBFG is injected into the blast furnace 10 from the shaft tuyere 12 were assumed. The specifications common to each operation are as follows:

[0039] The distribution of iron-based raw materials and coke charged from the furnace top was constant. ２ The separation and recovery device 20 separates CO contained in the top exhaust gas. ２ Gas and H ２ The furnace temperature was set to 1535°C. The furnace temperature (adjustment of the molten iron temperature) was adjusted by adjusting the pulverized coal ratio and coke ratio. Other specifications are as shown in Table 1 below.

[0040]

[0041] The results are shown in Figures 2 to 8. Figure 2 shows the results for a production rate of 2.75 t / d / m ３ The horizontal axis shows the relationship between the hydrogen injection amount (Nm ３ / t), and the vertical axis represents the total pressure loss (kPa). ３ / t), the total pressure drop was 90 kPa. However, it can be seen that the total pressure drop decreased by increasing the hydrogen injection rate. In particular, when the hydrogen injection rate was 700 Nm３ It can be seen that during operation at 1 / t, the total pressure drop is reduced to approximately 46 kPa. This is due to two main effects: (1) the low density and low viscosity of the hydrogen-based reducing gas reduces gas resistance, and (2) the direct reduction reaction caused by the hydrogen-based reducing gas improves the melt-down properties of the ore in the cohesive zone. Due to the above effects, the total pressure drop can be reduced by injecting the hydrogen-based reducing gas into the blast furnace. This study provides a relationship between the amount of hydrogen-based reducing gas injected and the total pressure drop.

[0042] Next, Fig. 3 and Fig. 4 will be considered. Fig. 3 shows the results when the injection rate of hydrogen-based reducing gas was 600 Nm ３ The horizontal axis of Figure 3 shows the relationship between the productivity (t / d / m ３ ), and the vertical axis represents total pressure drop (kPa). Point P1 shows the relationship between the productivity and total pressure drop in the example, and graph L1 is an approximate straight line of point P1. Graph L2 shows the total pressure drop in base operation. In base operation, the productivity (Po) was 2.7 t / d / m ３ As shown in graph L1, in the example, when the productivity is increased, the total pressure drop also increases, but there is a region where the total pressure drop is lower than in the base operation. Specifically, when the productivity is 3.7 t / d / m ３ In the region below (the intersection of graphs L1 and L2), the total pressure drop in the example becomes lower than the total pressure drop in the base operation. ３ Over 3.7t / d / m ３ In this way, the target range of the productivity during operation is obtained from the relationship between the injection amount of the hydrogen-based reducing gas and the total pressure drop that has been obtained in advance.

[0043] FIG. 4 shows the results of the experiment using a hydrogen-based reducing gas injection rate of 600 Nm ３ The horizontal axis of Figure 4 shows the relationship between the productivity and the carbon consumption when the boiler is operated at a constant productivity (t / d / m ３), and the vertical axis represents the carbon consumption per ton of molten iron (carbon amount input to the blast furnace) (kg / t). Point P3 shows the relationship between the productivity and carbon consumption in the example, and graph L3 is an approximate straight line of point P3. As graph L3 shows, increasing the productivity reduces the carbon consumption. Therefore, 2.7 t / d / m ３ Over 3.7t / d / m ３ By setting the target range for the productivity below and increasing the productivity up to the target range, it is possible to further improve the efficiency of molten iron production and reduce carbon consumption. In this way, carbon consumption can be reduced by adjusting the operating conditions of the blast furnace so that the productivity falls within the target range.

[0044] 5 to 7 show the results of the experiment using a hydrogen-based reducing gas injection rate of 600 Nm ３ The horizontal axis of Figure 5 shows the results of investigating why carbon consumption decreased with increasing productivity when the boiler was operated at a constant productivity (t / d / m ３ ), and the vertical axis shows various reduction ratios (the proportion of reduction reactions of each gas in all reduction reactions) (%). Point P4 shows the relationship between productivity and the reduction ratio of hydrogen gas in the example, and graph L4 is an approximation curve of point P4. Point P5 shows the relationship between productivity and the reduction ratio of CO gas in the example, and graph L5 is an approximation curve of point P5. Point P6 shows the relationship between productivity and the reduction ratio of carbon (reduction ratio of direct reduction) in the example, and graph L6 is an approximation curve of point P6. Table 2 shows the relationship between productivity and the reduction ratio of carbon (reduction ratio of direct reduction) in the example. ３ The figures in the upper row of Table 2 show the productivity.

[0045]

[0046] As shown in Fig. 5 and Table 2, as the productivity increases, the ratio of the reduction reaction of hydrogen gas and carbon (i.e., the ratio of endothermic reactions) increases and the ratio of the reduction reaction by CO gas (i.e., the ratio of exothermic reactions) decreases, so the required heat quantity increases as the productivity increases, i.e., the carbon consumption increases.

[0047] The horizontal axis of Figure 6 is the productivity (t / d / m ３), and the vertical axis represents the Si content (mass%) in the molten iron. Point P7 shows the relationship between the productivity and the Si content in the molten iron in the example, and graph L7 is an approximate curve of point P7. Table 3 shows the results for a molten iron with a productivity of 2.7 t / d / m ３ SiO based on ２ The required heat quantity (MJ / t) for the reduction reaction of SiO ２ is the SiO in the iron-based raw material ２ The figures in the top row of Table 3 are productivity rates.

[0048]

[0049] As shown in FIG. 6 and Table 3, as the productivity increases, the Si content in the molten iron decreases, and therefore, as the productivity increases, the SiO ２ The amount of heat required for the reduction of the carbon dioxide is reduced, which means that the carbon consumption is reduced.

[0050] The horizontal axis of Figure 7 is the productivity (t / d / m ３ ), and the vertical axis indicates the heat loss of the blast furnace (value per ton of molten iron) (MJ / t). Here, heat loss is the amount of heat extracted from the blast furnace. Point P8 shows the relationship between productivity and heat loss in the example, and graph L8 is an approximation curve of point P8. Graph L9 shows the heat loss in base operation (productivity ratio 2.7). Table 4 shows the heat loss in the case where the productivity ratio is 2.7 t / d / m ３ The figures in the top row of Table 4 are productivity ratios.

[0051]

[0052] As shown in Figure 7 and Table 4, the higher the productivity, the smaller the heat loss, i.e., the smaller the carbon consumption.

[0053] 5 to 7 and Tables 2 to 4, it can be said that the carbon consumption decreases as the productivity increases. Therefore, it is thought that the results shown in Figure 3 were obtained.

[0054] Figure 8 shows the results of the investigation of the tuyere combustion temperature. The horizontal axis of Figure 8 is the productivity (t / d / m ３) and the vertical axis represents the tuyere tip combustion temperature (°C). Point P10 represents the relationship between the productivity and the tuyere tip combustion temperature in the example, and graph L11 represents the tuyere tip combustion temperature in base operation (production rate of 2.7). As shown in Figure 8, in the example, the tuyere tip combustion temperature can be maintained at 2100°C or higher.

[0055] As described above, according to this embodiment, the total pressure drop can be reduced by injecting a hydrogen-based reducing gas into the blast furnace 10. Furthermore, if the productivity is increased, the total pressure drop increases, but the carbon consumption decreases. Therefore, the productivity can be increased until the total pressure drop becomes the same as that in base operation. Specifically, when the productivity is increased to 2.7 t / d / m ３ Over 3.7t / d / m ３ This allows for a further increase in the production efficiency of molten iron. ３ It is preferable that the total pressure drop is less than 2100°C. In addition, by reducing the total pressure drop, it is possible to use iron-based raw materials and coke with particle sizes that could not be used in the base operation. In addition, in this embodiment, the tuyere combustion temperature can be maintained at 2100°C or higher.

[0056] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0057] REFERENCE SIGNS LIST 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 CO ２ Separation and recovery device 30 Buffer tank 40 Compressor 50, 71 Heater 70 Hydrogen-based reducing gas tank

Claims

1. Hydrogen-based reducing gas is blown into the blast furnace, and CO is removed from the top exhaust gas. ２ Gas and H ２ a step of separating and removing O gas to generate a reformed furnace top circulating gas, and injecting the reformed furnace top circulating gas into the blast furnace, the step of obtaining a target range of productivity during operation from a relationship between an injection amount of the hydrogen-based reducing gas and a total pressure drop obtained in advance, and adjusting operating conditions so that the range of productivity during operation falls within the target range of productivity.

2. The above-mentioned productivity range is 2.7t / d / m ３ Over 3.7t / d / m ３ 2. A method for operating a blast furnace according to claim 1, characterized in that:

3. The range of the productivity is 3.0 t / d / m ３ 3. The method for operating a blast furnace according to claim 2, characterized in that:

4. A method for operating a blast furnace according to any one of claims 1 to 3, characterized in that the tuyere combustion temperature is maintained at 2100°C or higher.

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