Blast furnace operation method

Abstract

This blast furnace operation method is characterized by comprising: a step for heating a hydrogen-based reducing gas supplied from outside the blast furnace system; a step for blowing the heated hydrogen-based reducing gas into the blast furnace; a step for separating the reducing gas from the furnace top exhaust gas; a step for heating the separated reducing gas; and a step for blowing the reducing gas into the blast furnace.

Description

Blast furnace operation method

[0001] This application claims priority to Japanese Patent Application No. 2023-101584, filed on June 21, 2023, 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 layeredly charged into the blast furnace from the top of the furnace, while hot air is blown into the blast furnace through tuyere openings located in the lower part of the furnace below the bosh. 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, for example, a technique for increasing the reducing gas potential in the furnace by blowing hydrogen gas together with hot air from the tuyere is known, as disclosed in Patent Document 1. In this technique, hydrogen gas is used as a reducing gas for the iron-based raw materials, thereby reducing the reducing agent ratio.

[0006] International Publication No. 2021 / 107091

[0007] As disclosed in Patent Document 1, the present inventors have defined a parameter called the reduction rate of carbon consumption intensity (Input ΔC) as a parameter that serves as an index for reducing the reducing agent rate. "Carbon consumption intensity (Input C)" is the carbon required to produce one ton of molten iron (i.e., the amount of carbon consumed per ton of molten iron). "Reduction rate of carbon consumption intensity Input ΔC" means the reduction rate of carbon consumption intensity compared to base operation, which is operation without hydrogen gas injection. If Input C of base operation in units of kg / t is A and Input C during a certain operation in units of kg / t is B, Input ΔC is expressed by the following formula: Input ΔC = (A - B) / A × 100 (%) The larger the reduction rate of carbon consumption intensity Input ΔC, the greater the reduction in reducing agent rate, and ultimately the reduction in CO ２ Emissions are reduced.

[0008] The inventors have studied the technology described in Patent Document 1 in detail and found that if the Input ΔC is to be increased by the technology described in Patent Document 1, it is necessary to inject a large amount of hydrogen gas heated to a high temperature into the blast furnace. For example, if the Input ΔC is to be increased to 40% or more, the injection rate of hydrogen gas is 650 Nm ３ / t or more, and the temperature of the hydrogen gas had to be 1200°C or more. In this case, it was necessary to prepare a large amount of hydrogen gas, as well as to prepare a heating device for heating the hydrogen gas to a high temperature, and further to construct the blast furnace equipment from materials that could withstand the high temperature of hydrogen gas.

[0009] As described above, the technique disclosed in Patent Document 1 has a problem in that it requires a great deal of effort to increase Input ΔC.

[0010] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a method for operating a blast furnace that can increase Input ΔC even when the amount of hydrogen-based reducing gas (details of the hydrogen-based reducing gas will be described later) injected is reduced and the heating temperature of the hydrogen-based reducing gas is lowered.

[0011] The present inventors have studied the technology described in Patent Document 1 in detail and found that a large amount of hydrogen gas is emitted as furnace top exhaust gas during blast furnace operation. Therefore, the present inventors attempted to separate reducing gas (including hydrogen gas and CO gas) from the furnace top exhaust gas and inject the separated reducing gas into the blast furnace. As a result, they found that even when the amount of hydrogen gas injected was reduced and the heating temperature of the hydrogen gas was lowered compared to the technology described in Patent Document 1, an Input ΔC value comparable to that of the technology described in Patent Document 1 could be obtained. The present invention was made based on this finding.

[0012] The gist of the present invention is as follows: (1) A method for operating a blast furnace, comprising the steps of heating a hydrogen-based reducing gas supplied from outside the blast furnace system, injecting the heated hydrogen-based reducing gas into a blast furnace, separating the reducing gas from a furnace top exhaust gas, heating the separated reducing gas, and injecting the reducing gas into the blast furnace. (2) The method for operating a blast furnace according to (1), wherein the reducing gas is injected into the blast furnace from a normal tuyere provided in the lower part of the blast furnace. (3) The method for operating a blast furnace according to (1) or (2), wherein the reducing gas is injected into the shaft part of the blast furnace. (4) The method for operating a blast furnace according to any one of (1) to (3), wherein operating conditions are adjusted based on a tuyere-end combustion temperature and a furnace top exhaust gas temperature. (5) The method for operating a blast furnace according to (4), characterized in that the operating conditions include the amount of the reducing gas injected, the amount of hot air blown, and the amount of oxygen contained in the hot air. (6) The method includes the steps of: heating a hydrogen-based reducing gas supplied from outside the blast furnace system; injecting the heated hydrogen-based reducing gas into the blast furnace from at least one of a normal tuyere and a shaft tuyere provided at a position higher than the normal tuyere; separating the reducing gas from the top exhaust gas; heating the separated reducing gas; and injecting the heated reducing gas into the blast furnace from at least one of the normal tuyere and the shaft tuyere. The method for operating a blast furnace according to any one of (1) to (5), characterized in that at least one of the operating conditions of the reducing gas injection amount, the hot air blowing amount, and the oxygen content contained in the hot air is adjusted based on the tuyere tip combustion temperature and the furnace top exhaust gas temperature at at least one of the timings of injecting the heated hydrogen-based reducing gas into the blast furnace from at least one of the normal tuyere and the shaft tuyere and of injecting the heated reducing gas into the blast furnace from at least one of the normal tuyere and the shaft tuyere. (7) The method for operating a blast furnace according to (1) to (6), characterized in that the reducing gas contains CO gas separated from the furnace top exhaust gas and hydrogen gas.

[0013] According to the present invention, even when the amount of hydrogen-based reducing gas blown in is reduced and the heating temperature of the hydrogen-based reducing gas is lowered, the Input ΔC can be increased.

[0014] Fig. 1 is a flow diagram showing the overall configuration of a blast furnace system used in this embodiment; Fig. 2 is a graph verifying the effect of the first embodiment; Fig. 3 is a graph verifying the effect of the first embodiment; Fig. 4 is a graph verifying the effect of the second embodiment; Fig. 5 is a graph verifying the effect of the second embodiment; Fig. 6 is a graph verifying the effect of the second embodiment;

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, 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 description will be omitted.

[0016] 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, a heater 50, and flow meters 61 and 62.

[0017] 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 occurs using a blast furnace process. Specifically, 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 blown into the blast furnace 10 from the normal tuyere 11. In the following description, the "tuyere tip combustion temperature" refers to the temperature at the gas outlet of the normal tuyere 11. 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 other words, the hot air gasifies the coke and pulverized coal. As will be described in detail later, pulverized coal may not be blown into the blast furnace 10. The reducing gas rises within the blast furnace 10 and reduces the iron-based raw materials while heating them. The iron-based raw materials are heated and reduced by reducing gas while descending through the blast furnace 10. The iron-based raw materials then melt and drip 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 is used in the next steelmaking process.

[0018] The normal tuyere 11 is provided below the bosh portion of the blast furnace 10, and in addition to the hot air described above, as will be described later, a heated hydrogen-based reducing gas and a reducing gas separated from the furnace top exhaust gas (blast furnace exhaust gas) are blown into the blast furnace 10. Note that although normal tuyere 11 is depicted at two locations, one on the left and one on the right, of the blast furnace 10 in Fig. 1, three or more normal tuyere 11 may be attached at a predetermined interval around the entire circumference of the blast furnace 10.

[0019] The shaft tuyere 12 is provided at a position higher than the normal tuyere 11 of the blast furnace 10, and injects reducing gas separated from the top exhaust gas into the shaft 10b of the blast furnace 10. Although the shaft tuyere 12 is depicted in two locations, one on the left and one on the right of the shaft 10b in Fig. 1, three or more shaft tuyere 12 may be attached at a predetermined interval around the entire circumference of the blast furnace 10. Although the shaft tuyere 12 is depicted in Fig. 1 on the shaft 10b, it may be attached at a position lower than the shaft 10b, such as the belly portion, the bosch portion, or a lower position, as long as it can inject reducing gas separated from the top exhaust gas into the shaft 10b and is higher than the installation position of the normal tuyere 11.

[0020] CO ２ The separation and recovery device 20 recovers the top exhaust gas and separates the reducing gas (CO gas and hydrogen gas), nitrogen gas, and CO ２ Gas and H ２ The separation method is not particularly limited, but examples thereof include chemical adsorption and physical adsorption (PSA). In the following description, the reducing gas and nitrogen gas separated from the furnace top exhaust gas are also referred to as RBFG (Returned Blast Furnace Gas). ２ Gas and H ２ O gas is discharged outside the system. ２ The 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 the amount of furnace top exhaust gas corresponding to the flow rate of the RBFG injected into the blast furnace.

[0021] The buffer tank 30 is a tank that temporarily stores RBFG. A desired amount of RBFG is introduced from the buffer tank 30 to the compressor 40. The remaining RBFG is used as a heat source in, for example, a steel mill.

[0022] 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.

[0023] 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 blast furnace 10, for example, from the normal tuyere 11, or from the shaft tuyere 12 into the shaft 10b of the blast furnace 10. In FIG. 1 , RBFG is injected into the blast furnace 10 from the normal tuyere 11 and the shaft tuyere 12 on the left side, but RBFG may also be injected into the blast furnace 10 from the normal tuyere 11 and the shaft tuyere 12 on the right side. RBFG may be injected into the blast furnace 10 from both the normal tuyere 11 and the shaft tuyere 12.

[0024] The flow meter 61 measures the flow rate of RBFG injected into the blast furnace 10 from the normal tuyere 11. The flow meter 62 measures the flow rate of RBFG injected into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12. In this embodiment, by adjusting the flow rate of RBFG introduced from the buffer tank 30 to the compressor 40, it is possible to arbitrarily adjust the flow rate of RBFG injected into the blast furnace 10 from the normal tuyere 11 and the flow rate of RBFG injected into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12.

[0025] The hydrogen-based reducing gas supply system 2 includes a hydrogen-based reducing gas tank 70, a heater 71, and a flow meter 72. The hydrogen-based reducing gas supply system 2 is a system that supplies a hydrogen-based reducing gas to the blast furnace system 1 from outside the blast furnace system 1.

[0026] The hydrogen-based reducing gas tank 70 is a tank that stores a hydrogen-based reducing gas. Here, the hydrogen-based reducing gas is a concept that includes not only hydrogen gas but also a mixed gas of hydrogen gas and another gas (such as nitrogen gas) (which does not impair the effects of this embodiment). The heater 71 heats the hydrogen-based reducing gas supplied from the hydrogen-based reducing gas tank 70. The heater 71 can be sufficiently realized by an electric heater or the like. The heater 71 is connected to the normal tuyere 11, and the heated hydrogen-based reducing gas is injected into the blast furnace 10 from the normal tuyere 11. The heater 71 may be used in combination with the heater 50. The flow meter 72 measures the flow rate of the hydrogen-based reducing gas injected into the blast furnace 10 from the normal tuyere 11. Furthermore, as will be described later, even when the injection amount of the hydrogen-based reducing gas is reduced and the heating temperature of the hydrogen-based reducing gas is lowered, the Input ΔC can be increased. Furthermore, in this embodiment, the hydrogen-based reducing gas is normally injected from the tuyere 11 , but the hydrogen-based reducing gas may also be injected into the blast furnace 10 from the shaft tuyere 12 .

[0027] 2. First embodiment (2-1. Blast furnace operating method according to the first embodiment) Next, a first embodiment of the present invention will be described. In the first embodiment, RBFG is normally injected into a blast furnace 10 from a tuyere 11. In the first embodiment, the shaft tuyere 12 and the flow meter 62 may be omitted.

[0028] The method of operating the blast furnace 10 according to the first embodiment is generally as follows: That is, 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 heated hydrogen-based reducing gas is supplied from the hydrogen-based reducing gas supply system 2 to the normal tuyere 11. Then, hot air, pulverized coal, oxygen-enriched gas, heated hydrogen-based reducing gas, and heated CO and H are supplied from the normal tuyere 11. ２The RBFG containing the hydrogen-based reducing gas is blown into the blast furnace 10. 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. The reducing gas rises within the blast furnace 10 and reduces the iron-based raw materials while heating them. The hydrogen-based reducing gas and RBFG rise within the blast furnace 10 and reduce the iron-based raw materials while heating them. While the iron-based raw materials descend within the blast furnace 10, they are heated and reduced by the reducing gas, hydrogen-based reducing gas, and RBFG. The iron-based raw materials then 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 (pig iron) containing slightly less than 5% by mass of carbon. The molten iron in the hearth is taken out through a tap hole and is used in the next steelmaking process.

[0029] On the other hand, the top exhaust gas of the blast furnace 10 is discharged. ２ The separation and recovery device 20 recovers the top exhaust gas and separates it into reducing gas (CO gas and hydrogen gas) and nitrogen gas (i.e., RBFG), and CO ２ Gas and H ２ O and CO gases. ２ Gas and H ２ The O gas is discharged to the outside of the system.

[0030] The RBFG is temporarily stored in a buffer tank 30. A desired amount of RBFG is introduced from the buffer tank 30 into a compressor 40. The remaining RBFG is discharged outside the system and used, for example, as a heat source in a steel mill.

[0031] Next, the RBFG is pressurized by the compressor 40. 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.

[0032] The RBFG is then heated by the heater 50. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. The RBFG heated by the heater 50 is injected into the blast furnace 10 from the normal tuyere 11. A flow meter 61 measures the flow rate of the RBFG injected into the blast furnace 10 from the normal tuyere 11. The RBFG is mainly injected into the blast furnace 10 from the normal tuyere 11, but may also be injected into the blast furnace 10 from the shaft tuyere 12 as an auxiliary. Details will be described later.

[0033] Here, in blast furnace operation, it is preferable to maintain the tuyere combustion temperature, furnace top exhaust gas temperature, and molten pig iron temperature within a predetermined range for reasons such as ensuring stable operation. For example, the tuyere combustion temperature is preferably maintained at approximately 2000 to 2300°C, the furnace top exhaust gas temperature is preferably maintained at approximately 105°C or higher, and the molten pig iron temperature is preferably maintained at approximately 1520°C or higher. Note that the upper limit of the tuyere combustion temperature is an upper limit assuming normal operation (operation without injection of hydrogen-based reducing gas or RBFG). If the tuyere combustion temperature exceeds the upper limit, it is preferable to take measures such as strengthening the cooling capacity of the tuyere equipment or using materials with higher heat resistance to prevent wear on the tuyere equipment. The specifications of the blast furnace operation are preferably determined so that the tuyere combustion temperature, furnace top exhaust gas temperature, and molten pig iron temperature are maintained within a predetermined range. As long as the tuyere combustion temperature, the furnace top exhaust gas temperature, and the molten iron temperature are maintained within predetermined ranges, the blast furnace operation specifications can be freely designed. Although the tuyere combustion temperature may exceed the upper limit as a result of the design, it is preferable to take the above-mentioned measures separately.

[0034] For example, the injection temperature of the hydrogen-based reducing gas (usually the temperature of the hydrogen-based reducing gas injected from the tuyere 11) is preferably about 800 to 1000°C, and the injection amount of hydrogen gas in the hydrogen-based reducing gas is 300 to 600 Nm ３ / t. Both of these ranges are lower than those in Patent Document 1. The RBFG injection temperature (usually the temperature of the RBFG injected from the tuyere 11, i.e., the heating temperature by the heater 50) is preferably about 800 to 1000°C, and the RBFG injection rate is 400 to 800 Nm ３In particular, the amount of RBFG blown is preferably about 600 Nm ３ / t or more is preferable. As will be described later, in this case, the Input ΔC exceeds 40%. Other adjustable parameters include the amount of hot air injected and the amount of oxygen contained in the hot air (oxygen injection amount). The molten pig iron temperature can also be adjusted by the amount of pulverized coal injected into the blast furnace 10 or the coke ratio (amount of coke used per ton of molten pig iron). For example, the molten pig iron temperature is first adjusted by the amount of pulverized coal injected, and if the molten pig iron temperature exceeds the predetermined range even when the amount of pulverized coal injected becomes zero, the coke ratio is adjusted. The molten pig iron temperature is a value that reflects the total heat (furnace heat) in the blast furnace 10. During blast furnace operation, the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature are monitored periodically (preferably constantly), and if any of the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature falls outside the above-mentioned ranges, the operating conditions (for example, as described above, at least one of the hydrogen-based reducing gas injection temperature, the injection amount of hydrogen gas in the hydrogen-based reducing gas, the RBFG injection temperature, the RBFG injection amount, the hot blast injection amount, and the oxygen content in the hot blast (injection amount of oxygen-enriched gas)) can be adjusted. Note that, since the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature are prone to fluctuate when injecting a hydrogen-based reducing gas or RBFG, it is preferable to monitor the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature when injecting these gases.

[0035] (2-2. Specific Examples of Operation Method) Some specific examples of operation methods will be described below. Note that the specific examples listed below can also be applied to the second embodiment described later.

[0036] (2-2-1. When the molten iron temperature drops) The amount of RBFG blown into the blast furnace 10 from the normal tuyere 11 is increased. At the same time, the amount of enriched oxygen gas blown is increased and the amount of hot air blown (blowing rate) is reduced to maintain the tuyere tip combustion temperature. Furthermore, if this causes the furnace top exhaust gas temperature to fall below a predetermined range, the amount of RBFG blown from the shaft tuyere 12 is further increased.

[0037] (2-2-2. When the tuyere tip combustion temperature drops) The amount of oxygen-enriched gas blown is increased and the amount of hot air blown is reduced to raise the tuyere tip combustion temperature. This may reduce the amount of bosh gas, causing the furnace top exhaust gas temperature to fall below the specified range. In this case, the amount of RBFG blown from the shaft tuyere 12 is simultaneously increased to address the issue.

[0038] (2-2-3. When the furnace top exhaust gas temperature drops) The amount of RBFG blown from the shaft tuyere 12 is increased.

[0039] (2-2-4. When both the tuyere tip combustion temperature and the furnace top exhaust gas temperature decrease) The amount of enriched oxygen gas blown in is increased and the amount of hot air blown in is decreased to increase the tuyere tip combustion temperature, while at the same time increasing the amount of RBFG blown in from the shaft tuyere 12.

[0040] (2-2-5. When the tuyere tip combustion temperature decreases and the top exhaust gas temperature increases) If the top exhaust gas temperature is too high, the gas flow rate in the furnace increases, increasing the possibility of causing operational fluctuations, so an excessive increase in the top exhaust gas temperature is undesirable. The amount of enriched oxygen gas blown in is increased and the amount of hot air blown in is reduced. This causes the tuyere tip combustion temperature to tend to increase and the top exhaust gas temperature to tend to decrease. If the top exhaust gas temperature falls below the specified range, the amount of RBFG blown in from the shaft tuyere 12 is simultaneously increased to control the top exhaust gas temperature.

[0041] (2-2-6. When the tuyere tip combustion temperature rises and the top exhaust gas temperature falls) The amount of enriched oxygen gas blown in is reduced and the amount of hot air blown in is increased. This reduces the tuyere tip combustion temperature and causes the top exhaust gas temperature to tend to rise. When the top exhaust gas temperature exceeds the specified range, the amount of RBFG blown in from the shaft tuyere 12 is simultaneously reduced to control the top exhaust gas temperature.

[0042] (2-2-7. When both the tuyere tip combustion temperature and the furnace top exhaust gas temperature increase) Reduce the amount of enriched oxygen gas blown in, increase the amount of hot air blown in, and reduce the amount of RBFG blown in from the shaft tuyere 12.

[0043] (2-3. Verification of Effects) Next, the verification of the effects performed by the present inventors will be described. In this verification, a simulation of blast furnace operation was performed to verify the effects of the blast furnace operation method according to the first embodiment. 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. The prerequisites for the simulation are as follows. Hydrogen gas is used as the hydrogen-based reducing gas. ２ The separation and recovery device 20 is a device for recovering CO contained in the top exhaust gas. ２ Gas and H ２ 100% O2 gas is separated and removed. - The iron production rate and molten iron temperature are kept constant at all levels (12,350 t / d, 1,535°C). - The furnace top exhaust gas temperature is kept close to the lower limit (105°C). - Furnace heat adjustment (adjustment of molten iron temperature) is performed by adjusting the amount of pulverized coal injected. If the molten iron temperature exceeds 1,535°C even when the amount of pulverized coal injected is zero, the coke rate is adjusted. - The amounts of hot air and oxygen injected were adjusted so that the above preconditions were met.

[0044] Under the above preconditions, simulations were carried out for the following levels. Levels 1-5 correspond to the first embodiment. (Level 1-1) No hydrogen gas injection, hot air injection temperature of 1200°C, RBFG injection operation (injection temperature of 1200°C) (H2-0 BT 1200°C in Figures 2 and 3. Note that H2-0 BT 1200°C indicates no hydrogen gas injection and hot air injection temperature of 1200°C). (Level 1-2) With hydrogen gas injection (injection temperature of 1200°C, injection rate of 650 Nm ３ / t), the hot air blowing temperature was 1200°C, and RBFG blowing operation (blowing temperature was 1000°C) (H2-650 1200°C, BT 1200°C in Figures 2 and 3. Note that H2-650 1200°C was operated with a hydrogen gas blowing rate of 650 Nm ３ / t indicates that the blowing temperature is 1200°C, and BT1200°C indicates that the blowing temperature of the hot air is 1200°C.) (Level 1-3) With hydrogen gas blowing (blowing temperature 1000°C, blowing amount 650 Nm ３ / t), the hot air blowing temperature was 1200°C, and RBFG blowing operation (blowing temperature was 1000°C) (H2-650 1000°C, BT 1200°C in Figures 2 and 3. Note that H2-650 1000°C was operated with a hydrogen gas blowing rate of 650 Nm ３ / t indicates that the blowing temperature is 1000°C, and BT1200°C indicates that the blowing temperature of the hot air is 1200°C.) (Level 1-4) With hydrogen gas blowing (blowing temperature is 1000°C, blowing amount is 650 Nm ３ / t), the hot air blowing temperature was 1300°C, and RBFG blowing operation (blowing temperature was 1000°C) (H2-650 1000°C, BT 1300°C in Figures 2 and 3. Note that H2-650 1000°C was operated with a hydrogen gas blowing rate of 650 Nm ３ / t indicates that the blowing temperature is 1000°C, and BT1300°C indicates that the hot air blowing temperature is 1300°C.) (Level 1-5) With hydrogen gas blowing (blowing temperature 1000°C, blowing amount 325 Nm ３ / t), the hot air blowing temperature was 1300°C, and RBFG blowing operation (blowing temperature was 1000°C) (H2-325 1000°C, BT 1300°C in Figures 2 and 3. Note that H2-325 1000°C was blown at a hydrogen gas blowing rate of 325 Nm ３ / t indicates that the blowing temperature is 1000°C, and BT1300°C indicates that the hot air blowing temperature is 1300°C.)

[0045] The results are shown in Figures 2 and 3. The horizontal axis of Figure 2 (RBFG tuyere injection amount) represents the injection amount (Nm m ３The horizontal axis of FIG. 3 (RBFG tuyere injection amount) represents the amount of RBFG injected into the blast furnace 10 from the tuyere 11 (Nm ３ / t), and the vertical axis (hydrogen gas utilization rate of the entire system) represents the utilization rate (%) of hydrogen gas in the entire system. Here, the utilization rate of hydrogen gas in the entire system is expressed by the following formula: n Ｈ２ ＊ =100×a / (a+b) n Ｈ２ ＊ : Hydrogen gas utilization rate (%) a: CO ２ H discharged from the separation and recovery device 20 to the outside of the system ２ Amount of O gas (Nm ３ / t) b: Amount of hydrogen gas discharged from the buffer tank 30 to the outside of the system (Nm ３ / t)

[0046] 2 and 3, the following findings can be obtained. The greater the amount of hydrogen gas injected from the hydrogen-based reducing gas supply system 2 (i.e., not contained in RBFG), the greater the Input ΔC. However, since a large amount of hydrogen gas needs to be prepared, the above-mentioned problems arise. The greater the amount of RBFG injected, the greater the Input ΔC. In level 1-5, the amount of RBFG injected was 600 Nm ３ By setting the hydrogen gas injection rate at 1.5 Nm / t, the Input ΔC exceeds 40% (43.2%, the point surrounded by the dashed circle in Figure 2). This value is comparable to levels 1-2 to 1-4, in which a large amount of hydrogen gas is injected. Furthermore, the hydrogen gas injection rate in level 1-5 is 325 Nm ３ / t, which is 50% lower than in levels 1-2 to 1-4, and the hydrogen gas injection temperature is also low at 1000°C. The hydrogen gas utilization rate in level 1-5 was 77% (a = 253 Nm ３ / t, b = 76 Nm ３ / t) (the point surrounded by the dashed circle in FIG. 3).

[0047] As described above, according to the first embodiment, even when the amount of hydrogen-based reducing gas blown from the hydrogen-based reducing gas supply system 2 is reduced and the heating temperature of the hydrogen-based reducing gas is lowered, the Input ΔC can be increased.

[0048] 3. Second embodiment (3-1. Blast furnace operating method according to second embodiment) Next, a second embodiment of the present invention will be described. In the second embodiment, RBFG is injected into the blast furnace 10 from the shaft tuyere 12. In the second embodiment, the flow meter 61 may be omitted.

[0049] The operation method of the blast furnace 10 according to the second embodiment is generally as follows. Specifically, 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 heated hydrogen-based reducing gas is supplied from the hydrogen-based reducing gas supply system 2 to the normal tuyere 11. Then, hot air, pulverized coal, oxygen-enriched gas, and heated hydrogen-based reducing gas are blown into the blast furnace 10 from the normal tuyere 11. Meanwhile, RBFG is blown into the shaft 10b of the blast furnace 10 from the shaft tuyere 12. 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). Specifically, the hot air gasifies the coke and pulverized coal. The reducing gas rises within the blast furnace 10 and reduces the iron-based raw materials while heating them. The hydrogen-based reducing gas and RBFG rise within the blast furnace 10, heating and reducing the iron-based raw materials. While descending within the blast furnace 10, the iron-based raw materials are heated and reduced by the reducing gas, hydrogen-based reducing gas, and RBFG. The iron-based raw materials then melt and drip down within 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 a taphole and used in the next steelmaking process.

[0050] On the other hand, the top exhaust gas of the blast furnace 10 is discharged. ２ The separation and recovery device 20 recovers the top exhaust gas and separates it into reducing gas (CO gas and hydrogen gas) and nitrogen gas (i.e., RBFG), and CO ２ Gas and H ２ O and CO gases. ２ Gas and H ２ The O gas is discharged to the outside of the system.

[0051] The RBFG is temporarily stored in a buffer tank 30. A desired amount of RBFG is introduced from the buffer tank 30 into a compressor 40. The remaining RBFG is discharged outside the system and used, for example, as a heat source in a steel mill.

[0052] Next, the RBFG is pressurized by the compressor 40. 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.

[0053] The RBFG is then heated by the heater 50. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. The RBFG heated by the heater 50 is injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12. A flow meter 62 measures the flow rate of the RBFG injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12. The RBFG is mainly injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12, but may also be injected into the blast furnace 10 from the normal tuyere 11 as an auxiliary. A specific example of the operating method is as described in the first embodiment.

[0054] Here, in blast furnace operation, it is preferable to maintain the tuyere combustion temperature, furnace top exhaust gas temperature, and molten pig iron temperature within a predetermined range for reasons such as stable operation. For example, the tuyere combustion temperature is preferably maintained at approximately 2000 to 2300°C, the furnace top exhaust gas temperature is preferably maintained at approximately 105°C or higher, and the molten pig iron temperature is preferably maintained at approximately 1520°C or higher. Note that the upper limit of the tuyere combustion temperature is an upper limit assuming normal operation (operation without injection of hydrogen-based reducing gas or RBFG). If the tuyere combustion temperature exceeds the upper limit, it is preferable to take measures such as strengthening the cooling capacity of the tuyere equipment or using materials with higher heat resistance to prevent wear on the tuyere equipment. The specifications of the blast furnace operation are determined so that the tuyere combustion temperature, furnace top exhaust gas temperature, and molten pig iron temperature are maintained within the predetermined range. As long as the tuyere combustion temperature, the furnace top exhaust gas temperature, and the molten iron temperature are maintained within predetermined ranges, the blast furnace operation specifications can be freely designed. Although the tuyere combustion temperature may exceed the upper limit as a result of the design, it is preferable to take the above-mentioned measures separately.

[0055] For example, the injection temperature of the hydrogen-based reducing gas (usually the temperature of the hydrogen-based reducing gas injected from the tuyere 11) is preferably about 600 to 1000°C, and the injection amount of hydrogen gas in the hydrogen-based reducing gas is 400 to 600 Nm ３ / t. Both of these ranges are lower than those in Patent Document 1. The RBFG injection temperature (the temperature of the RBFG injected from the shaft tuyere 12, i.e., the heating temperature by the heater 50) is preferably set to about 800 to 1000°C, and the RBFG injection rate is set to 200 to 600 Nm ３ / t. This is because, as will be described later, in this case, the Input ΔC exceeds 40%. Other adjustable parameters include the amount of hot air injected and the amount of oxygen contained in the hot air (oxygen injection amount). The molten pig iron temperature can also be adjusted by the amount of pulverized coal injected into the blast furnace 10 or the coke ratio (the amount of coke used per ton of molten pig iron). For example, the molten pig iron temperature is first adjusted by the amount of pulverized coal injected, and if the molten pig iron temperature exceeds the predetermined range even when the amount of pulverized coal injected becomes zero, the coke ratio is adjusted accordingly. The molten pig iron temperature is a value that reflects the total heat (furnace heat) in the blast furnace 10. During blast furnace operation, the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature are monitored periodically (preferably constantly), and if any of the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature falls outside the above-mentioned ranges, the operating conditions (for example, as described above, at least one of the hydrogen-based reducing gas injection temperature, the injection amount of hydrogen gas in the hydrogen-based reducing gas, the RBFG injection temperature, the RBFG injection amount, the hot blast injection amount, and the oxygen content in the hot blast (injection amount of oxygen-enriched gas)) can be adjusted. Note that, since the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature are prone to fluctuate when injecting a hydrogen-based reducing gas or RBFG, it is preferable to monitor the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature when injecting these gases.

[0056] (3-2. Verification of Effects) Next, the verification of effects carried out by the present inventors will be described. In this verification, a simulation of blast furnace operation was carried out to verify the effects of the blast furnace operation method according to the second embodiment. The simulation model is the same as that of the first embodiment. The preconditions for the simulation are as follows: Hydrogen gas is used as the hydrogen-based reducing gas. CO ２ The separation and recovery device 20 is a device for recovering CO contained in the top exhaust gas. ２ Gas and H ２100% O2 gas is separated and removed. The hydrogen gas injection temperature and RBFG injection temperature are 800°C for all levels. However, the hydrogen gas injection temperature for level 2-1 is 1200°C. The hot air injection temperature (blast temperature) is 1200°C for all levels. The iron production rate and molten iron temperature are constant for all levels (12,350 t / d, 1535°C). The furnace top exhaust gas temperature is 135°C for all levels. Furnace heat adjustment (molten iron temperature adjustment) is performed by adjusting the amount of pulverized coal injection. If the molten iron temperature exceeds 1535°C even when the pulverized coal injection rate is zero, the coke rate is adjusted. The hot air injection rate and oxygen injection rate were adjusted so that the above preconditions were met.

[0057] Under the above preconditions, simulations were carried out for the following levels. Levels 2-2 to 2-4 correspond to the second embodiment. (Level 2-1) Hydrogen gas injection amount: 650 Nm ３ / t, hot air blowing temperature 1200°C, no RBFG blowing (H2: 650 Nm ３ / t, BT1200°C). (Level 2-2) Hydrogen gas injection amount 600 Nm ３ / t, hot air blowing temperature 1200°C, RBFG blowing operation (H2: 600 Nm ３ / t, BT1200 ° C) (Level 2-3) Hydrogen gas injection amount 500 Nm ３ / t, hot air blowing temperature 1200°C, RBFG blowing operation (H2: 500 Nm ３ / t, BT1200 ° C) (Level 2-4) Hydrogen gas injection amount 400 Nm ３ / t, hot air blowing temperature 1200°C, RBFG blowing operation (H2: 400 Nm ３ / t, BT1200℃)

[0058] The results are shown in Figures 4 and 5. The horizontal axis of Figure 4 (shaft tuyere RBFG injection amount) represents the injection amount (Nm m) of RBFG injected into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12. ３ / t), and the vertical axis represents Input ΔC (%). The horizontal axis of FIG. 5 (RBFG injection amount from shaft tuyere) represents the injection amount (Nm ３ / t), and the vertical axis (hydrogen gas utilization rate of the entire system) represents the hydrogen gas utilization rate (%) of the entire system. The method for calculating the hydrogen gas utilization rate of the entire system is as described above.

[0059] 4 and 5, the following findings can be obtained: The greater the amount of hydrogen gas injected from the hydrogen-based reducing gas supply system 2 (i.e., not contained in RBFG), the greater the Input ΔC. The greater the amount of RBFG injected, the greater the Input ΔC. In level 2-4, the amount of RBFG injected was 600 Nm ３ By setting the hydrogen gas injection rate at 400 Nm / t, the Input ΔC exceeds 40% (40.5%, the point surrounded by the dashed circle in Figure 4). This value is comparable to Level 2-1, in which a large amount of hydrogen gas is injected, and Levels 2-2 and 2-3, in which the amount of hydrogen gas injected is slightly larger. Furthermore, the amount of hydrogen gas injected in Level 2-4 is 400 Nm ３ / t, which is lower than levels 2-1 to 2-3, and the hydrogen gas injection temperature is also low at 800°C. The hydrogen gas utilization rate in level 2-4 was 63% (a = 260 Nm ３ / t, b=151Nm ３ / t) (the point surrounded by the dashed circle in FIG. 5).

[0060] As described above, according to the second embodiment, even when the injection amount of the hydrogen-based reducing gas is reduced and the heating temperature of the hydrogen-based reducing gas is lowered, the Input ΔC can be increased.

[0061] The inventors also studied the degree of freedom in operation. The results are shown in Figures 6 and 7. The horizontal axis of Figure 6 (RBFG injection amount from shaft tuyere) represents the injection amount (Nm m) of RBFG injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12. ３ / t), and the vertical axis represents the tuyere combustion temperature (°C). ΔC represents Input ΔC. In FIG. 6, the group of points where Input ΔC is 29% or more and less than 33%, the group where Input ΔC is 33% or more and less than 38%, and the group where Input ΔC is more than 40% are surrounded by dashed lines. The "normal upper limit" (= 2300°C) of the tuyere combustion temperature in FIG. 6 is the upper limit assuming normal operation (operation without injection of hydrogen-based reducing gas or RBFG). The horizontal axis of FIG. 7 represents the tuyere combustion temperature (°C), and the vertical axis represents the furnace top exhaust gas temperature (°C). As a reference example, FIGS. 6 and 7 also show an example in which the blast temperature is 1300°C (BT 1300°C) and the hydrogen gas injection temperature is 1000°C in Level 2-4.

[0062] 6 and 7 reveal the following: The tuyere combustion temperature increases when the injection rate of hydrogen-based reducing gas from the hydrogen-based reducing gas supply system 2 (i.e., not included in the RBFG) is reduced or when the injection rate of RBFG is increased. In blast furnace operation, it is necessary to operate the furnace so that both the top exhaust gas temperature and the tuyere combustion temperature are within appropriate ranges. The top exhaust gas temperature is highly dependent on the flow rate of gas supplied into the blast furnace, and the top exhaust gas temperature increases as the gas flow rate per unit of iron production increases. On the other hand, the tuyere combustion temperature is highly dependent on the oxygen enrichment ratio, which is a combustion condition at the tuyere. The tuyere combustion temperature increases as the oxygen enrichment ratio increases. In blast furnace operation, increasing the oxygen enrichment ratio means a decrease in the hot air blow rate and a decrease in the gas flow rate supplied from the tuyere. Therefore, increasing the oxygen enrichment ratio and raising the tuyere combustion temperature reduces the gas flow rate supplied into the furnace and lowers the top exhaust gas temperature. Therefore, assuming an operation in which gas is injected from the normal tuyere 11, it is difficult to independently control the furnace top exhaust gas temperature and the tuyere tip combustion temperature (because moving one of them will move the other in the opposite direction). When RBFG is injected into the normal tuyere as in the first embodiment, it is possible to adjust the amount of gas injected into the furnace by adjusting the RBFG injection rate. However, since gas at a temperature lower than the tuyere tip combustion temperature is supplied into the blast furnace, increasing the RBFG injection rate will result in a decrease in the tuyere tip combustion temperature. Therefore, it is not possible to independently control the furnace top exhaust gas temperature and the tuyere tip combustion temperature. The second embodiment is similar to the first embodiment in that gas at a temperature lower than the tuyere tip combustion temperature is supplied into the furnace. However, since RBFG is injected from the shaft 10b rather than from the tuyere where coke is burning (the end of the normal tuyere 11), the tuyere tip combustion temperature does not decrease even if the RBFG injection rate is adjusted. Therefore, it is possible to adjust the top exhaust gas temperature by increasing the amount of RBFG injection, while separately adjusting the oxygen enrichment rate at the tuyere section to set the tuyere combustion temperature to an appropriate value. This is one of the advantages of the second embodiment (the advantage is that the gas is injected into a location separate from the normal tuyere 11). Therefore, the tuyere combustion temperature at level 2-4 is higher than the tuyere combustion temperatures at levels 2-1 to 2-3.The tuyere combustion temperature in level 2-4 is sufficiently higher than the lower limit (2000°C). Furthermore, the furnace top exhaust gas temperature in level 2-4 is also sufficiently higher than the lower limit (105°C).

[0063] Therefore, in the second embodiment, the degree of freedom in operation is increased (the range in which the operational parameters can be designed is wide). Note that, if the Input ΔC of Level 2-4 exceeds 40%, the tuyere tip combustion temperature will exceed the upper limit (2300°C) (the point indicated by the dashed circle A in Figure 6), but operation can be continued if the above-mentioned measures are taken.

[0064] 4. Third embodiment (4-1. Blast furnace operating method according to the third embodiment) Next, a third embodiment of the present invention will be described. In the third embodiment, RBFG is injected into the blast furnace 10 from both the normal tuyere 11 and the shaft tuyere 12.

[0065] The operation method of the blast furnace 10 according to the third embodiment is generally as follows. Specifically, 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 heated hydrogen-based reducing gas is supplied from the hydrogen-based reducing gas supply system 2 to the normal tuyere 11. Then, hot air, pulverized coal, oxygen-enriched gas, and heated hydrogen-based reducing gas are blown into the blast furnace 10 from the normal tuyere 11. Meanwhile, RBFG is blown into the blast furnace 10 from the normal tuyere 11 and the shaft tuyere 12. 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). Specifically, the hot air gasifies the coke and pulverized coal. The reducing gas rises within the blast furnace 10 and reduces the iron-based raw materials while heating them. The hydrogen-based reducing gas and RBFG rise within the blast furnace 10, heating and reducing the iron-based raw materials. While descending within the blast furnace 10, the iron-based raw materials are heated and reduced by the reducing gas, hydrogen-based reducing gas, and RBFG. The iron-based raw materials then melt and drip down within 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 a taphole and used in the next steelmaking process.

[0066] On the other hand, the top exhaust gas of the blast furnace 10 is discharged.２ The separation and recovery device 20 recovers the top exhaust gas and separates it into reducing gas (CO gas and hydrogen gas) and nitrogen gas (i.e., RBFG), and CO ２ Gas and H ２ O and CO gases. ２ Gas and H ２ The O gas is discharged to the outside of the system.

[0067] The RBFG is temporarily stored in a buffer tank 30. A desired amount of RBFG is introduced from the buffer tank 30 into a compressor 40. The remaining RBFG is discharged outside the system and used, for example, as a heat source in a steel mill.

[0068] Next, the RBFG is pressurized by the compressor 40. 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.

[0069] Next, the RBFG is heated by the heater 50. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. The RBFG heated by the heater 50 is injected into the blast furnace 10 from the normal tuyere 11 and the shaft tuyere 12. A flow meter 61 measures the flow rate of the RBFG injected into the blast furnace 10 from the normal tuyere 11. A flow meter 62 measures the flow rate of the RBFG injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12. A specific example of the operating method is as described in the first embodiment.

[0070] Here, in blast furnace operation, it is preferable to maintain the tuyere combustion temperature, furnace top exhaust gas temperature, and molten pig iron temperature within a predetermined range for reasons such as stable operation. For example, the tuyere combustion temperature is preferably maintained at approximately 2000 to 2300°C, the furnace top exhaust gas temperature is preferably maintained at approximately 105°C or higher, and the molten pig iron temperature is preferably maintained at approximately 1520°C or higher. Note that the upper limit of the tuyere combustion temperature is an upper limit assuming normal operation (operation without injection of hydrogen-based reducing gas or RBFG). If the tuyere combustion temperature exceeds the upper limit, it is preferable to take measures such as strengthening the cooling capacity of the tuyere equipment or using materials with higher heat resistance to prevent wear and tear on the tuyere equipment. The specifications of the blast furnace operation are determined so that the tuyere combustion temperature, furnace top exhaust gas temperature, and molten pig iron temperature are maintained within the predetermined ranges. As long as the tuyere combustion temperature, the furnace top exhaust gas temperature, and the molten iron temperature are maintained within predetermined ranges, the blast furnace operation specifications can be freely designed. Although the tuyere combustion temperature may exceed the upper limit as a result of the design, it is preferable to take the above-mentioned measures separately.

[0071] For example, the injection temperature of the hydrogen-based reducing gas (usually the temperature of the hydrogen-based reducing gas injected from the tuyere 11) is preferably about 800 to 1000°C, and the injection amount of hydrogen gas in the hydrogen-based reducing gas is 300 to 600 Nm ３ / t. Both of these ranges are lower than those of Patent Document 1. The normal tuyere injection temperature of RBFG (the temperature of RBFG normally injected from the tuyere 11, i.e., the heating temperature by the heater 50) is preferably about 800 to 1000°C, and the normal tuyere injection rate of RBFG is 100 to 300 Nm ３ The RBFG shaft tuyere blowing temperature (the temperature of the RBFG blown from the shaft tuyere 12, i.e., the heating temperature by the heater 50) is usually the same as the tuyere blowing temperature, and the RBFG shaft tuyere blowing amount is 200 to 600 Nm ３ In particular, the RBFG injection amount is preferably about 600 Nm3 / t in total of the normal tuyere injection amount and the shaft tuyere injection amount. ３ / t or more is preferable. As will be described later, in this case, the Input ΔC exceeds 40%. Other adjustable parameters include the amount of hot air injected and the amount of oxygen contained in the hot air (oxygen injection amount). The molten pig iron temperature can also be adjusted by the amount of pulverized coal injected into the blast furnace 10 or the coke ratio (amount of coke used per ton of molten pig iron). For example, the molten pig iron temperature is first adjusted by the amount of pulverized coal injected, and if the molten pig iron temperature exceeds the predetermined range even when the amount of pulverized coal injected becomes zero, the coke ratio is adjusted. The molten pig iron temperature is a value that reflects the total heat (furnace heat) in the blast furnace 10. During blast furnace operation, the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature are monitored periodically (preferably constantly), and if any of the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature falls outside the above-mentioned ranges, the operating conditions (for example, as described above, at least one of the hydrogen-based reducing gas injection temperature, the injection amount of hydrogen gas in the hydrogen-based reducing gas, the RBFG injection temperature, the RBFG injection amount, the hot blast injection amount, and the oxygen content in the hot blast (injection amount of oxygen-enriched gas)) can be adjusted. Note that, since the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature are prone to fluctuate when injecting a hydrogen-based reducing gas or RBFG, it is preferable to monitor the tuyere combustion temperature, top exhaust gas temperature, and molten pig iron temperature when injecting these gases.

[0072] (3-2. Verification of Effects) Next, the verification of effects carried out by the present inventors will be described. In this verification, a simulation of blast furnace operation was carried out to verify the effects of the blast furnace operation method according to the third embodiment. The simulation model is the same as that of the first embodiment. The preconditions for the simulation are as follows: Hydrogen gas is used as the hydrogen-based reducing gas. CO ２ The separation and recovery device 20 is a device for recovering CO contained in the top exhaust gas. ２ Gas and H ２100% O2 gas is separated and removed. - The hydrogen gas injection temperature and RBFG injection temperature are 800°C. - The hot air injection temperature (blast temperature) is 1200°C. - The iron production rate and molten iron temperature are 12,350 t / d and 1,535°C. - The furnace top exhaust gas temperature is 132°C, and the tuyere combustion temperature is 2,196°C. - Furnace heat adjustment (molten iron temperature adjustment) is performed by adjusting the amount of pulverized coal injected. If the molten iron temperature exceeds 1,535°C even when the amount of pulverized coal injected is zero, the coke rate is adjusted. - The hot air injection rate and oxygen injection rate were adjusted so that the above preconditions were met.

[0073] Under the above preconditions, the simulation was carried out at the following levels: At this level, the hydrogen gas injection amount was 400 Nm ３ / t, RBFG shaft tuyere injection rate is 400 Nm ３ / t, and the normal tuyere injection rate is 200 Nm ３ As a result, the Input ΔC was 42.2%.

[0074] As described above, according to the third embodiment, even when the amount of hydrogen gas blown in is reduced and the heating temperature of the hydrogen gas is lowered, the Input ΔC can be increased.

[0075] Next, examples of this embodiment will be described. In these examples, a blast furnace operation simulation was performed using a blast furnace mathematical model to confirm the effects of the first to third embodiments. Example 1 corresponds to the first embodiment, Example 2 corresponds to the second embodiment, and Example 3 corresponds to the third embodiment.

[0076] <1. Example 1> (1-1. Main specifications) Hydrogen gas is used as the hydrogen-based reducing gas. CO ２ The separation and recovery device 20 separates CO contained in the top exhaust gas. ２ Gas and H ２100% of O gas is separated and removed. - The iron production rate and molten iron temperature are 12,350 t / d and 1,535°C, respectively. - The furnace top exhaust gas temperature is set to near the lower limit (105°C) to maximize the carbon reduction effect. - Furnace heat adjustment (adjustment of molten iron temperature) is performed by adjusting the amount of pulverized coal injected. If the molten iron temperature exceeds 1,535°C even when the amount of pulverized coal injected is zero, the coke ratio is adjusted. - The amount of hot air injected and the amount of oxygen injected are adjusted so that the above preconditions are met. - Hydrogen gas is injected (injection temperature 1,000°C, injection amount 325 Nm ３ / t), hot air blowing temperature 1300°C, RBFG blowing temperature 1000°C, blowing amount 600 Nm ３ / t

[0077] (1-2. Simulation Results) As a result of the simulation, in Example 1, Input ΔC was 43.2%.

[0078] 2. Example 2 (2-1. Main specifications) Hydrogen gas was used as the hydrogen-based reducing gas. CO ２ The separation and recovery device 20 separates CO contained in the top exhaust gas. ２ Gas and H ２ 100% of O gas is separated and removed. - The hydrogen gas injection temperature and RBFG injection temperature are 800°C. - The hot air injection temperature (blast temperature) is 1200°C. - The iron production rate and molten iron temperature are 12,350 t / d and 1,535°C, respectively. - The furnace top exhaust gas temperature is 135°C. - Furnace heat adjustment (adjustment of molten iron temperature) is performed by adjusting the amount of pulverized coal injected. If the molten iron temperature exceeds 1,535°C even when the amount of pulverized coal injected is zero, the coke ratio is adjusted. - The amount of hot air injection and the amount of oxygen injection were adjusted so that the above preconditions were met. - Hydrogen gas injection rate: 400 Nm ３ / t, RBFG injection amount 600 Nm ３ / t

[0079] (2-2. Simulation Results) As a result of the simulation, in Example 2, Input ΔC was 40.5%.

[0080] 3. Example 3 (3-1. Main specifications) Hydrogen gas is used as the hydrogen-based reducing gas. CO ２The separation and recovery device 20 separates CO contained in the top exhaust gas. ２ Gas and H ２ 100% of O2 gas is separated and removed. - The hydrogen gas injection temperature and RBFG injection temperature are set to 800°C. - The hot air injection temperature (blast temperature) is set to 1200°C. - The iron production rate and molten iron temperature are set to 12,350 t / d and 1,535°C. - The furnace top exhaust gas temperature is set to 132°C, and the tuyere tip combustion temperature is set to 2,196°C. - Furnace heat adjustment (adjustment of molten iron temperature) is performed by adjusting the amount of pulverized coal injected. If the molten iron temperature exceeds 1,535°C even when the amount of pulverized coal injected is zero, the coke ratio is adjusted. - The hot air injection rate and oxygen injection rate were adjusted so that the above preconditions were met. - The hydrogen gas injection rate is set to 400 Nm ３ / t, RBFG shaft tuyere injection rate is 400 Nm ３ / t, and the normal tuyere injection rate is 200 Nm ３ / t.

[0081] (3-2. Simulation Results) As a result of the simulation, in Example 3, Input ΔC was 42.2%.

[0082] Therefore, according to the first to third embodiments, even when the amount of hydrogen-based reducing gas blown in is reduced and the heating temperature of the hydrogen-based reducing gas is lowered, the Input ΔC can be increased.

[0083] 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 or 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.

[0084] 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 ２Separation and recovery device 30: Buffer tank 40: Compressor 50, 71: Heater 61, 62, 72: Flow meter 70: Hydrogen-based reducing gas tank

Claims

1. A method for operating a blast furnace, comprising: a step of heating a hydrogen-based reducing gas supplied from outside a blast furnace system; a step of injecting the heated hydrogen-based reducing gas into a blast furnace; a step of separating the reducing gas from a top exhaust gas; a step of heating the separated reducing gas; and a step of injecting the reducing gas into the blast furnace.

2. A method for operating a blast furnace as claimed in claim 1, characterized in that the reducing gas is injected into the blast furnace through a normal tuyere provided in the lower part of the blast furnace.

3. A method for operating a blast furnace as claimed in claim 1 or 2, characterized in that the reducing gas is injected into the shaft of the blast furnace.

4. The method for operating a blast furnace according to claim 1, characterized in that the operating conditions are adjusted based on the tuyere combustion temperature and the furnace top exhaust gas temperature.

5. A method for operating a blast furnace as described in claim 4, characterized in that the operating conditions include the amount of reducing gas blown, the amount of hot air blown, and the amount of oxygen contained in the hot air.

6. A method for operating a blast furnace according to claim 1 or 2, comprising: a step of heating a hydrogen-based reducing gas supplied from outside the blast furnace system; a step of injecting the heated hydrogen-based reducing gas into the blast furnace from at least one of a normal tuyere and a shaft tuyere installed at a position higher than at least the normal tuyere; a step of separating a reducing gas from a top exhaust gas; a step of heating the separated reducing gas; and a step of injecting the heated reducing gas into the blast furnace from at least one of the normal tuyere and the shaft tuyere, wherein at least one of the operating conditions is adjusted based on the tuyere tip combustion temperature and the top exhaust gas temperature at at least one of the timings when the heated hydrogen-based reducing gas is injected into the blast furnace from at least one of the normal tuyere and the shaft tuyere and when the heated reducing gas is injected into the blast furnace from at least one of the normal tuyere and the shaft tuyere.

7. A method for operating a blast furnace according to claim 1 or 2, characterized in that the reducing gas contains CO gas separated from the top exhaust gas and hydrogen gas.