WO2025187531A1 - Blast furnace operation method - Google Patents

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

The present invention relates to a method for operating a blast furnace. This application claims priority from Japanese Patent Application No. 2024-035001, filed on March 7, 2024, the contents of which are incorporated herein by reference.

In the steel industry, the blast furnace method is the mainstream process for producing pig iron. In this method, iron-based raw materials (raw materials containing iron oxide, mainly sintered ore; hereafter simply referred to as "iron-based raw materials") and coke are charged alternately and in layers into the blast furnace from the top of the furnace, while hot air is blown into the furnace from tuyere openings at the bottom. The hot air reacts with the pulverized coal blown in with it and the coke in the blast furnace to generate high-temperature reducing gas (mainly CO gas in this case). In other words, the hot air gasifies the coke and pulverized coal. The reducing gas rises within the blast furnace, heating and reducing the iron-based raw materials. As the iron-based raw materials descend within the blast furnace, they are heated and reduced by the reducing gas. The iron-based raw materials then melt and drip down the blast furnace, being further reduced by the coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing just under 5% carbon by mass. The molten pig iron in the hearth is 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.

In recent years, there has been a growing call for the prevention of global warming, and reducing emissions of carbon dioxide ( _CO2 gas), one of the greenhouse gases, has become a social issue. As mentioned above, the blast furnace process uses carbonaceous material as a reducing agent, which generates large amounts of _CO2 gas. Therefore, the steel industry is one of the major industries in terms of _CO2 gas emissions, and must respond to this social demand. 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.

The reducing agent serves two purposes: to generate heat in the furnace, thereby raising the temperature of the charge material, and to reduce the iron-based raw materials in the furnace. Therefore, 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. Among these reduction reactions, the direct reduction reaction by coke (reaction formula: FeO + C → Fe + CO) is an endothermic reaction accompanied by a large heat absorption. Therefore, minimizing the occurrence of this reaction is important in reducing the reducing agent ratio. Because this direct reduction reaction occurs in the lower part of the blast furnace, if the iron-based raw materials can be sufficiently reduced with reducing gases such as CO and _H2 before they reach the lower part of the furnace, the amount of iron-based raw materials subject to the direct reduction reaction can be reduced.

As a conventional technique for solving the above problems, for example, as disclosed in Patent Document 1, a technique is known in which hydrogen gas is blown in from the tuyere along with hot air to increase the reducing gas potential inside the furnace. With this technique, hydrogen gas is used as a reducing gas for the iron-based raw materials, thereby reducing the reducing agent ratio.

International Publication No. 2021/107091

In order to further reduce the reducing agent rate, it was necessary to increase the productivity rate and improve efficiency, in other words, to further improve the efficiency of molten iron production. However, achieving stable high productivity operation presented problems such as ensuring good ventilation within the furnace and stabilizing the tuyere combustion temperature.

The present invention was made in consideration of the above problems, and its object is to provide a method of operating a blast furnace that can further improve the efficiency of molten iron production.

The gist of the present invention is as follows.
(1)
Hydrogen-based reducing gas is blown into the blast furnace,
_CO2 gas and _H2O gas are separated and removed from the top exhaust gas to generate a reformed top circulation gas;
A method for operating a blast furnace, comprising injecting the reformed furnace top circulating gas into the blast furnace,
obtaining a target range of productivity during operation from the relationship between the injection amount of the hydrogen-based reducing gas and the total pressure drop obtained in advance,
A method for operating a blast furnace, comprising adjusting operating conditions so that a range of productivity during operation falls within a target range of productivity.
(2)
The method for operating a blast furnace according to (1), characterized in that the productivity range is more than 2.7 t/d/m ³ and not more than 3.7 t/d/m ^{3 .}
(3)
The method for operating a blast furnace according to (2), characterized in that the productivity range is 3.0 t/d/ ^m3 or less.
(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.

The present invention provides a method for operating a blast furnace that can further improve the efficiency of molten iron production.

FIG. 1 is a flow diagram showing the overall configuration of a blast furnace system used in this embodiment. 10 is a graph verifying the effect of this embodiment. 10 is a graph verifying the effect of this embodiment. 10 is a graph verifying the effect of this embodiment. 10 is a graph verifying the effect of this embodiment. 10 is a graph verifying the effect of this embodiment. 10 is a graph verifying the effect of this embodiment. 10 is a graph verifying the effect of this embodiment.

The inventors conducted a simulation of hydrogen gas injection operation and conducted a detailed analysis of the internal state of the blast furnace, 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).

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

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that in this specification and drawings, components having substantially the same functional configuration will be assigned the same reference numerals, and redundant explanations will be omitted.

<1. Overall configuration of the blast furnace system>
1 , a description will be given of 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. The blast furnace system 1 includes a blast furnace 10, a _CO2 separation and capture device 20, a buffer tank 30, a compressor 40, and a heater 50.

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 in which 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 ascend within 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 flue gas. The furnace top flue gas contains unreacted hydrogen gas and CO gas as well as _CO2 gas, _H2O gas, and nitrogen gas. While descending within the blast furnace 10, the iron-based raw materials are heated and reduced by the bosh gas and hydrogen-based reducing gas. The iron-based raw materials are then melted and dripped into 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 removed from the tap hole and is used in the next steelmaking process. In this embodiment, the productivity (t/d/m ³ ) refers to the amount of molten pig iron produced per unit volume and unit time (day) of the blast furnace 10.

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

The shaft tuyere 12 is provided in the shaft 10b of the blast furnace 10 and injects reformed top recirculating gas (RBFG), which is reformed top exhaust gas, into the shaft 10b of the blast furnace 10. While the shaft tuyere 12 is shown only on the left side of the shaft 10b in Figure 1, a shaft tuyere 12 may also be provided on the right side of the shaft 10b, or three or more 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.

The _CO2 separation and capture unit 20 recovers the top flue gas and separates _CO2 gas and _H2O gas from the top flue gas to generate reformer top recycle gas (RBFG). The reformer top recycle gas is a gas containing 20% or more CO gas by volume. The reformer top recycle gas is, for example, a gas recovered and separated from the top flue gas, or a gas containing CO gas and _H2 gas obtained by reforming a hydrocarbon gas using a general method such as partial oxidation. The _CO2 gas and _H2O gas contents in the reformer top recycle gas are preferably low. For example, the volume fraction of _H2O gas is preferably 10% or less, more preferably 5% or less. The volume fraction of _CO2 gas is preferably 5% or less, more preferably 3% or less. By keeping the volume fraction below this value, the effects of the gasification reaction, which is an endothermic reaction, can be suppressed. Here, the _CO2 separation and capture unit 20 does not necessarily recover the entire amount of the top flue gas. For example, the _CO2 separation and capture device 20 may recover only an amount of furnace top flue gas corresponding to the flow rate of 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, and examples include chemical adsorption and physical adsorption (PSA). The separated _CO2 gas and _H2O gas are discharged outside the system. In the following description, reformed furnace top recycle gas may also be referred to as "RBFG".

The buffer tank 30 is a tank that temporarily stores RBFG. The desired amount of RBFG is introduced from the buffer tank 30 into the compressor 40.

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.

The heater 50 heats the RBFG. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10; however, for example, when RBFG is injected into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12, it is preferable to set it to 800°C or higher. The heater 50 can be adequately realized by an electric heater or the like. The RBFG heated by the heater 50 is injected into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12. In FIG. 1, RBFG is injected into the blast furnace 10 from the shaft section tuyere 12 on the left side, but RBFG may also be injected into the blast furnace 10 from the shaft section 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 section tuyere 12, or may be injected into the blast furnace 10 from the normal tuyere 11.

The 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 .

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 ). _Examples of _{the hydrogen-based reducing gas include H2 gas, unsaturated hydrocarbon gases (C2H4, C2H2 , C3H6 , etc. )} , saturated hydrocarbon gases ( _CH4 , _C2H6 , etc.), _NH3 gas, coke oven gas, city gas, _natural gas, and _mixtures thereof. Particularly preferred are _H2 gas and unsaturated hydrocarbon gases ( _{C2H4 , C2H2} , _C3H6 , etc.). _H2 gas is preferable from the viewpoint of reducing carbon consumption unit because it does not contain carbon and does not cause a thermal decomposition reaction at the tuyere tip. Furthermore, because the gas has low viscosity and density, it is also preferable from the viewpoint of gas permeability inside the blast furnace. The hydrogen-based reducing gas may be injected into the blast furnace at room temperature, but is preferably injected in a heated state 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. The elemental composition ratio of H in the hydrogen-based reducing gas is more preferably 50 mol% or higher. The hydrogen-based reducing gas may also be a mixed gas with other gases (e.g., _N2 gas) (without impairing the effects of this embodiment). 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. 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 rate (Nm ³ /t) of the hydrogen-based reducing gas may be set arbitrarily depending on the operating conditions of the blast furnace 10. Note that, although the heater 71 is shown in FIG. 1 as being normally connected to the tuyere 11, the heater 71 may also be connected to the shaft tuyere 12.

As will be described in detail 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, increasing the productivity tends to increase the total pressure drop (see FIG. 3). Furthermore, increasing the productivity reduces the amount of carbon per ton of molten iron charged into the blast furnace 10 (hereinafter also referred to as carbon consumption). Therefore, increasing the productivity not only increases the molten iron production efficiency but also reduces carbon consumption. Furthermore, the productivity can be increased to at least near the total pressure drop of base operation. Specifically, the productivity can be set to be greater than 2.7 t/d/m ³ and not more than 3.7 t/d/m ³ . A productivity of 2.7 t/d/m ³ or less is also achievable in base operation. If the productivity exceeds 3.7 t/d/m ³ , the total pressure drop becomes worse than that in base operation. The productivity is preferably 3.0 t/d/m ³ or less. In this case, the total pressure drop becomes particularly low.

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, because the total pressure drop is reduced, it becomes possible to use fine iron-based raw materials and coke that could not be used under base operation due to the increased pressure drop. This allows for more effective use of resources.

<2. Blast furnace operation method>
Next, a method for operating a blast furnace will be described. First, 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 from the normal 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.

Meanwhile, 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. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10, but may be set, for example, to a temperature similar to that of hot air (for example, approximately 1200°C). The heated hydrogen-based reducing gas is then injected into the blast furnace 10. Injecting the hydrogen-based reducing gas into the blast furnace 10 can reduce the total pressure drop. Furthermore, increasing the amount of hydrogen-based reducing gas injected can increase the productivity to a level close to that of base operation. The amount of hydrogen-based reducing gas injected into the blast furnace can 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.

(Step of obtaining target range of productivity)
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, the productivity can be set to more than 2.7 t/d/m ³ and not more than 3.7 t/d/m ³ . The "operable productivity range" refers to a range of operating conditions that allows stable operation without excessively increasing the tuyere combustion temperature, for example. In this embodiment, the above-mentioned operable productivity range is defined 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.

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. This turns the hot air into bosh gas, primarily composed of hydrogen gas, CO gas, and nitrogen gas. The bosh gas and hydrogen-based reducing gas ascend within the blast furnace 10, heating and reducing the iron-based raw materials. 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 flue gas. The furnace top flue gas contains unreacted hydrogen gas and CO gas, as well as _CO2 gas, _H2O gas, and nitrogen gas. While descending within the blast furnace 10, the iron-based raw materials are heated and reduced by the bosh gas and hydrogen-based reducing gas. The iron-based raw materials then melt and drip down the blast furnace 10, where they are further reduced by the coke. The iron-based raw materials are eventually stored in the hearth as molten pig iron (pig iron) containing just under 5% by mass of carbon. The molten pig iron in the hearth is removed from the tap hole and used in the subsequent steelmaking process.

The top flue gas is introduced into a _CO2 separation and capture unit 20. The _CO2 separation and capture unit 20 recovers the top flue gas and separates and removes _CO2 gas and _H2O gas from the top flue gas to generate RBFG. A buffer tank 30 temporarily stores the RBFG. A desired amount of RBFG is introduced from the buffer tank 30 into a compressor 40.

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.

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 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 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.

The 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. By increasing the amount of RBFG injected into the blast furnace 10, the productivity can be increased.

As described 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, increasing the productivity increases the total pressure drop, but reduces carbon consumption. Therefore, the productivity can be increased until the total pressure drop is comparable to that of base operation. In this way, an operating method is possible in which a target range of the productivity during operation is obtained from the relationship between the injection rate of the hydrogen-based reducing gas and the total pressure drop, and the operating conditions are adjusted so that the productivity during operation falls within the target range. Specifically, in this embodiment, the productivity can be increased to more than 2.7 t/d/m ³ and not more than 3.7 t/d/m ³ . This further improves the efficiency of molten iron production. In addition, the productivity is preferably not more than 3.0 t/d/m ³ . Furthermore, the reduction in total pressure drop allows the use of iron-based raw materials and coke with particle sizes that could not be used in base operation. In addition, in this embodiment, the tuyere tip combustion temperature can be maintained at or above 2100° C. Furthermore, the operating conditions are adjusted by, for example, the blast rate, oxygen enrichment rate, coke ratio, and amount of pulverized coal injected.

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 is 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 multiple meshes (small regions) by dividing the internal region of the blast furnace in the vertical, radial, and circumferential directions, and simulates the behavior of each mesh.

The blast furnace operations assumed were base operation (operation without hydrogen gas injection) and hydrogen injection operation (example) in which hydrogen gas is normally injected into the blast furnace 10 through the tuyere 11 while RBFG is injected into the blast furnace 10 through the shaft tuyere 12. The specifications common to each operation are as follows:

- The distribution of iron-based raw materials and coke charged from the furnace top was kept constant.
The CO ₂ separation and capture device 20 was designed to separate and remove 100% of the CO ₂ gas and H ₂ O gas contained in the furnace top flue gas.
The molten iron temperature was set to 1535°C.
- Furnace heat adjustment (adjustment of molten iron temperature) was carried out by adjusting the pulverized coal ratio and coke ratio.
Other specifications are as shown in Table 1 below.

The results are shown in Figures 2 to 8. Figure 2 shows the relationship between the hydrogen injection rate and the total pressure drop when the productivity was constant at 2.75 t/d/ ^m3 . The horizontal axis represents the hydrogen injection rate ( ^Nm3 /t), and the vertical axis represents the total pressure drop (kPa). Under base operation (hydrogen injection rate: 0 ^Nm3 /t), the total pressure drop was 90 kPa. However, it can be seen that increasing the hydrogen injection rate reduced the total pressure drop. In particular, it can be seen that the total pressure drop decreased to approximately 46 kPa during operation with a hydrogen injection rate of 700 ^Nm3 /t. 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 progress of the direct reduction reaction by the hydrogen-based reducing gas improves the melt-through properties of the ore in the cohesive zone. Due to the above effect, the total pressure loss can be reduced by injecting a hydrogen-based reducing gas into a blast furnace. This provides a relationship between the amount of hydrogen-based reducing gas injected and the total pressure loss.

Next, Figures 3 and 4 will be considered. Figure 3 shows the relationship between productivity and total pressure drop when operation was performed at a constant injection rate of hydrogen-based reducing gas of 600 Nm ³ /t. The horizontal axis of Figure 3 shows productivity (t/d/m ³ ), and the vertical axis shows total pressure drop (kPa). Point P1 shows the relationship between 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 , and the total pressure drop was 90 kPa. As graph L1 shows, in the example, increasing the productivity also increases the total pressure drop, but there is a region where the total pressure drop is lower than in base operation. Specifically, in the region where the productivity is 3.7 t/d/m ³ or less (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. Therefore, in the example, the productivity can be increased to more than 2.7 t/d/m ³ and 3.7 t/d/m ³ or less. In this way, the target range of the productivity during operation is obtained from the relationship between the injection amount of hydrogen-based reducing gas and the total pressure drop obtained in advance.

Figure 4 shows the relationship between productivity and carbon consumption when the hydrogen-based reducing gas injection rate is kept constant at 600 Nm ³ /t. The horizontal axis of Figure 4 represents productivity (t/d/m ³ ), and the vertical axis represents carbon consumption per ton of molten iron (blast furnace carbon input) (kg/t). Point P3 shows the relationship between productivity and carbon consumption in the example, and graph L3 is an approximate straight line to point P3. As graph L3 shows, increasing productivity reduces carbon consumption. Therefore, by setting the target productivity range to greater than 2.7 t/d/m ³ and not more than 3.7 t/d/m ³ and increasing the productivity up to the target range, it is possible to further improve the molten iron production efficiency and reduce carbon consumption. In this way, carbon consumption can be reduced by adjusting the operating conditions of the blast furnace so that the obtained productivity falls within the target range.

5 to 7 show the results of investigating why carbon consumption decreased with increasing productivity when the hydrogen-based reducing gas injection rate was kept constant at 600 Nm ³ /t. The horizontal axis of FIG. 5 represents productivity (t/d/m ³ ), and the vertical axis represents various reduction ratios (the proportion of each gas's reduction reaction to the total reduction reaction) (%). Point P4 shows the relationship between productivity and the hydrogen gas reduction ratio in the example, and graph L4 is an approximation curve for point P4. Point P5 shows the relationship between productivity and the CO gas reduction ratio in the example, and graph L5 is an approximation curve for point P5. Point P6 shows the relationship between productivity and the carbon reduction ratio (reduction ratio for direct reduction) in the example, and graph L6 is an approximation curve for point P6. Table 2 shows the heat required for all reduction reactions (MJ/t) based on a productivity of 2.7 t/d/m ³ . The figures in the upper row of Table 2 are productivity rates.

As shown in Figure 5 and Table 2, as the productivity increases, the ratio of reduction reactions with hydrogen gas and carbon (i.e., the ratio of endothermic reactions) increases, and the ratio of reduction reactions with CO gas (i.e., the ratio of exothermic reactions) decreases. Therefore, as the productivity increases, the required heat quantity increases. In other words, carbon consumption increases.

The horizontal axis of Figure 6 represents the productivity (t/d/ ^m3 ), 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 approximation curve of point P7. Table 3 shows the heat quantity (MJ/t) required for the reduction reaction of _SiO2 based on a productivity of 2.7 t/d/ ^m3 . Note that _SiO2 here refers to _SiO2 in the iron-based raw material. The values in the upper row of Table 3 are productivity rates.

As shown in Figure 6 and Table 3, as the productivity increases, the Si content in the molten iron decreases, and therefore the heat required for reducing _SiO2 decreases as the productivity increases. In other words, the carbon consumption decreases.

The horizontal axis of Figure 7 shows the productivity (t/d/ ^m3 ), and the vertical axis shows 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 2.7). Table 4 shows the heat quantity (MJ/t) of heat loss when the productivity is 2.7 t/d/ ^m3 . The values in the upper row of Table 4 are productivity.

As shown in Figure 7 and Table 4, the higher the productivity, the lower the heat loss. In other words, the amount of carbon consumption decreases.

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

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

As described 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, increasing the productivity increases the total pressure drop, but reduces carbon consumption. Therefore, the productivity can be increased until the total pressure drop is comparable to that of base operation. Specifically, the productivity can be increased to more than 2.7 t/d/m ³ and not more than 3.7 t/d/m ³ . This further improves the efficiency of molten iron production. The productivity is preferably not more than 3.0 t/d/m ³ . Furthermore, the reduction in total pressure drop makes it 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 combustion temperature can be maintained at 2100°C or higher.

The above describes in detail preferred embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to such examples. It is clear that a person with ordinary skill in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas set forth in the claims, and it is understood that these naturally fall within the technical scope of the present invention.

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 capture device 30 Buffer tank 40 Compressor 50, 71 Heater 70 Hydrogen-based reducing gas tank

Claims (4)

Hydrogen-based reducing gas is blown into the blast furnace,
_CO2 gas and _H2O gas are separated and removed from the top exhaust gas to generate a reformed top circulation gas;
A method for operating a blast furnace, comprising injecting the reformed furnace top circulating gas into the blast furnace,
obtaining a target range of productivity during operation from the relationship between the injection amount of the hydrogen-based reducing gas and the total pressure drop obtained in advance,
A method for operating a blast furnace, comprising adjusting operating conditions so that a range of productivity during operation falls within a target range of productivity. The method for operating a blast furnace according to claim 1, characterized in that the productivity range is more than 2.7 t/d/ ^m³ and not more than 3.7 t/d/ ^m³ . The method for operating a blast furnace according to claim 2, characterized in that the productivity range is set to 3.0 t/d/ ^m3 or less. 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.