Operating method of blast furnace

Abstract

An operating method for a blast furnace, comprising blowing a first reducing gas, which has a hydrogen-based reducing gas as the main component, into the blast furnace; blowing a second reducing gas, which is a gas recovered and separated from the top gas of the blast furnace and contains at least 50% by volume of CO gas, into the blast furnace; heating the second reducing gas to the blowing temperature before blowing the second reducing gas into the blast furnace; and determining the blowing temperature of the second reducing gas based on the blowing amount of the first reducing gas blown into the blast furnace and the blowing amount of the second reducing gas blown into the blast furnace.

Description

Technical Field

[0001] The present invention relates to a method for operating a blast furnace. This application claims priority based on Japanese Patent Application No. 2023-189486 filed in Japan on November 6, 2023, and incorporates its content herein by reference.

Background Art

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

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

[0004] The reducing agent has the role of heating the charged material to raise its temperature in the furnace and the role of reducing the iron-based raw materials in the furnace. 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 amount of heat absorption. Therefore, it is important not to generate this reaction as much as possible in reducing the reducing agent ratio. Since this direct reduction reaction occurs in the lower part of the blast furnace, if the iron-based raw materials can be sufficiently reduced by reduction gases such as CO and H2 before reaching the lower part of the furnace, the amount of iron-based raw materials targeted by the direct reduction reaction can be reduced.

[0005] As a conventional technique for solving the above problems, for example, as disclosed in Patent Document 1, there is a known technique of improving the reduction gas potential in the furnace by blowing a hydrogen-based reduction gas together with hot air from the tuyere. In this technique, the reducing agent ratio is reduced by using a hydrogen-based reduction gas such as LNG (liquefied natural gas) as the reduction gas for the iron-based raw materials.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] When a large amount of hydrogen-based reducing gas is blown into a blast furnace, the heat balance between the upper part of the furnace and the lower part of the furnace (here, the lower part of the furnace refers to the region where the furnace temperature is higher than the starting temperature of the solution loss reaction (C + CO2 → 2CO). The upper part of the furnace is the region above the lower part of the furnace.) changes significantly. Therefore, it is necessary to appropriately control the operating parameters so that the heat balance between the upper part and the lower part of the furnace is compatible. That is, when a large amount of hydrogen-based reducing gas is blown into the blast furnace to enjoy a significant carbon reduction effect, the combustion temperature at the tuyere tip decreases. To suppress such a decrease in the combustion temperature at the tuyere tip, increasing the oxygen enrichment rate increases the heat flow ratio. For this reason, the top gas temperature decreases, falling below the lower limit of the top gas temperature as an operating management standard, and there is concern that the ventilation deterioration due to the delay in heating the charged materials in the upper part of the furnace and the insufficient discharge of dust outside the furnace will become prominent.

[0008] Thus, simply increasing the oxygen enrichment rate alone makes it difficult to maintain both the combustion temperature at the tuyere tip and the top gas temperature within an appropriate range. This is because the blast furnace process is a process in which the reduction and heat balance in the upper part of the furnace are established using the exhaust gas (the exhaust gas after the solution loss reaction is completed in the lower part of the furnace) after establishing the heat balance in the lower part of the furnace, which has the largest reduction and heat load. In normal operation without using hydrogen-based reducing gas, the operation is carried out with appropriate parameters so that the heat balances of the upper and lower parts of the furnace are satisfied simultaneously. On the other hand, in the operation of blowing a large amount of hydrogen-based reducing gas into the blast furnace, the ore reduction rate becomes almost 100% at the cohesive zone level and the amount of molten reduction becomes almost zero, so the reduction and heat load in the lower part of the furnace are significantly alleviated. Therefore, the carbon consumption is reduced. However, since the temperature of the exhaust gas generated from the lower part of the furnace decreases, establishing the heat balance in the upper part of the furnace becomes the rate-determining step of the blast furnace operation.

[0009] Therefore, in the technology disclosed in Patent Document 1, as the reducing gas supplied to the upper part of the furnace, a reducing gas preheated in the shaft part is supplied separately from the hydrogen-based reducing gas supplied from the lower part of the furnace. By this, it is considered that the heat balance of the upper part of the furnace and the heat balance of the lower part of the furnace can be controlled almost independently.

[0010] On the other hand, from the viewpoint of further reducing the ratio of reducing agent, there was room for improvement in the type of reducing gas blown into the blast furnace and the temperature of the reducing gas.

[0011] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an operation method of a blast furnace capable of further reducing the ratio of reducing agent.

Means for Solving the Problems

[0012] The gist of the present invention is as follows. (1) An operation method of a blast furnace, blowing a first reducing gas mainly composed of a hydrogen-based reducing gas into the blast furnace Including the act of charging, blowing a second reducing gas, which is a gas recovered and separated from the top gas of the blast furnace and contains at least 50% by volume of CO gas, into the blast furnace Including the act of charging, before blowing the second reducing gas into the blast furnace, raising the second reducing gas to the blowing temperature Including the act of heating, and When the blowing rate of the first reducing gas is 0 Nm 3 / min, determining the blowing temperature of the second reducing gas the blowing of the second reducing gas blown into the blast furnace quantity to based on make, When the blowing rate of the first reducing gas exceeds 0 Nm 3 / min, the blowing temperature of the second reducing gas is determined based on the blowing rate of the first reducing gas blown into the blast furnace, the blowing temperature of the first reducing gas blown into the blast furnace, and the blowing rate of the second reducing gas blown into the blast furnace

Figure 1

Advantages of the Invention

[0013] According to the present invention, it is possible to provide an operating method for further reducing the reduction material ratio and reducing the carbon consumption per unit. The "carbon consumption per unit (Input C)" is the carbon required to produce one ton of hot metal (that is, the carbon consumption per ton of hot metal).

Brief Description of the Drawings

[0014]

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0016] <1. Overall Configuration of Blast Furnace System> First, based on FIG. 1, the overall configuration of the blast furnace system 1 according to the present embodiment and the primary 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, a CO2 separation and recovery device 20, a buffer tank 30, a compressor 40, a heater 50, and a flow meter 61.

[0017] The blast furnace 10 includes a blast furnace main body 10a, a normal tuyere 11, and a shaft section tuyere 12. Inside the blast furnace main body 10a, a reduction reaction of iron-based raw materials is carried out by the blast furnace method. Specifically, while charging iron-based raw materials and coke into the blast furnace 10 alternately and layer by layer from the top of the blast furnace 10, 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" shall mean 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 a high-temperature reducing gas (here mainly CO gas). The hot air gasifies the coke and pulverized coal. Note that the pulverized coal may not be contained in the hot air. The reducing gas rises in the blast furnace 10 and reduces the iron-based raw materials while heating them. The iron-based raw materials are heated and reduced by the reducing gas while descending in the blast furnace 10. Thereafter, the iron-based raw materials melt and drip in the blast furnace 10 while being further reduced by the coke. The iron-based raw materials are finally accumulated in the hearth part as hot metal (pig iron) containing less than 5% by mass of carbon. The hot metal in the hearth part is taken out from the tapping hole and supplied to the next steelmaking process.

[0018] The normal tuyere 11 is provided below the bosh part of the blast furnace 10. The above-described hot air and the secondary reducing gas are blown into the blast furnace 10 from the normal tuyere 11. In FIG. 1, the normal tuyere 11 is depicted only at both ends of the blast furnace 10, but two or more normal tuyeres 11 may be provided at equal intervals in the circumferential direction. Also, the primary reducing gas may be blown into the blast furnace 10 from the normal tuyere 11.

[0019] The shaft section tuyere 12 is provided at a position higher than the normal tuyere 11 of the blast furnace 10. The above-described gas is blown into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12. In FIG. 1, the shaft section tuyere 12 is depicted only at both ends of the shaft section 10b, but two or more shaft section tuyeres 12 may be provided at equal intervals in the circumferential direction of the shaft section 10b, and they may be attached to the bosh part or the belly part. Also, the secondary reducing gas may be blown into the blast furnace 10 from the shaft section tuyere 12.

[0020] The CO₂ separation and recovery device 20 is a device that recovers top-of-furnace exhaust gas (BFG, Blast Furnace Gas) and separates it into CO gas, hydrogen gas, nitrogen gas, and CO₂ gas and H₂O gas. The separation method is not particularly limited, and examples include chemical adsorption method and physical adsorption method (PSA). It is preferable that the energy required for separation is covered by renewable energy. The CO₂ gas and H₂O gas are discharged outside the system. Note that the CO₂ separation and recovery device 20 does not necessarily have to recover the entire amount of top-of-furnace exhaust gas. For example, the CO₂ separation and recovery device 20 may recover only a portion of the top-of-furnace exhaust gas corresponding to the flow rate of the gas blown into the blast furnace.

[0021] The buffer tank 30 is a tank that temporarily stores the second reducing gas containing CO gas, hydrogen gas, and nitrogen gas separated and recovered from the top-of-furnace exhaust gas. A desired amount of the second reducing gas is introduced from the buffer tank 30 into the compressor 40. The remaining gas that has not been introduced into the compressor 40 is used, for example, as a heat source in the steelworks. Note that the hydrogen gas may be reused as part of the first reducing gas described later.

[0022] The second reducing gas is a gas separated from the top-of-furnace exhaust gas and contains at least 50% by volume of CO gas. Specifically, it is preferable to satisfy CO / (CO + CO₂ + H₂ + H₂O + N₂) ≥ 0.50. Also, the total content of the impurity CO₂ gas and H₂O gas contained in the second reducing gas is preferably less than 10% by volume. Further, the CO / CO₂ gas concentration ratio of the second reducing gas is preferably 9 or more. Similarly, the H₂ / H₂O gas concentration ratio is preferably 9 or more. Note that the CO / CO₂ gas concentration ratio preferably further satisfies the following conditions.

[0023]

Number

[0024] The left side of the above formula (1) is the CO / CO2 gas concentration ratio, and T on the right side is the temperature of the second reducing gas when the second reducing gas is blown into the blast furnace 10.

[0025] The compressor 40 pressurizes the second reducing gas. Here, the compressor 40 pressurizes the second reducing gas to about the internal pressure of the blast furnace 10 (about 4.5 atmospheres), for example. The pressurized second reducing gas is introduced into the heater 50. In this embodiment, the second reducing gas is obtained by separating and recovering the top gas, but the second reducing gas may be obtained from outside the system.

[0026] The heater 50 heats the second reducing gas to a predetermined temperature. Here, the predetermined temperature is preferably determined based on, for example, the blowing amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the blowing amount of the second reducing gas blown into the blast furnace 10. As shown in the examples, depending on the blowing amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the blowing amount of the second reducing gas blown into the blast furnace 10, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is determined. Therefore, based on the blowing amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the blowing amount of the second reducing gas blown into the blast furnace 10, a simulation of the blast furnace operation can be performed to determine the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value. Thereby, the carbon consumption per unit can be reduced.

[0027] For example, when the blowing amount of the first reducing gas blown into the blast furnace 10 is 0 Nm 3 / t, the predetermined temperature is determined as follows. That is, when the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, the predetermined temperature is set to room temperature. In this embodiment, room temperature generally means 25°C or more and 30°C or less. When the blowing amount of the second reducing gas blown into the blast furnace 10 is more than 100 Nm 3 / t and less than 200 Nm 3 / t If the following conditions are met, set the predetermined temperature to be higher than 200°C and lower than or equal to 400°C. When the injection amount of the second reducing gas blown into the blast furnace 10 is more than 200 Nm 3 / t and less than or equal to 300 Nm 3 / t, set the predetermined temperature to be higher than 400°C and lower than or equal to 600°C.

[0028] On the other hand, when the normal-temperature first reducing gas is blown into the blast furnace 10 at 150 Nm 3 / t or more and 250 Nm 3 / t or less, determine the predetermined temperature as follows. That is, when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, set the predetermined temperature to be normal temperature. When the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t and more than 200 Nm 3 / t or less, set the predetermined temperature to be higher than 200°C and lower than or equal to 400°C. When the injection amount of the second reducing gas blown into the blast furnace 10 is 200 Nm 3 / t and more than 300 Nm 3 / t or less, set the predetermined temperature to be higher than 400°C and lower than or equal to 600°C.

[0029] On the other hand, when the high-temperature first reducing gas is blown into the blast furnace 10 at 500 Nm 3 / t or more and 800 Nm 3 / t or less, determine the predetermined temperature as follows. Here, the high temperature means, for example, a temperature of 500°C or higher. That is, when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, set the predetermined temperature to be 200°C or higher. When the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t and more than 200 Nm 3 / t or less, set the predetermined temperature to be higher than 500°C and lower than or equal to 800°C. When the injection amount of the second reducing gas blown into the blast furnace 10 is 200 Nm 3 / t and more than 300 Nm 3 / t or less, set the predetermined temperature to be higher than 700°C and lower than or equal to 900°C.

[0030] As shown in the embodiments described below, when the secondary reducing gas is heated under the above temperature conditions and blown into the blast furnace 10, the carbon consumption per unit becomes the minimum value or a value in the vicinity thereof, so that the carbon consumption per unit can be further reduced.

[0031] The heating method of the secondary reducing gas is not particularly limited, but a direct heating method of heating the secondary reducing gas by burning a part of the secondary reducing gas is preferable. This method is a method of heating by bringing the secondary reducing gas into direct contact with the gas on the fuel side. According to this method, the equipment can be downsized compared to indirect heating (for example, a method of heating by heat exchange using the sensible heat of the top gas). Therefore, the pipe length of the secondary reducing gas after temperature rise can be shortened, and heat loss is reduced.

[0032] In the direct heating method, since a part of the secondary reducing gas is burned, CO2 gas and H2O gas are generated. The higher the heating temperature, the higher the CO2 gas concentration and H2O gas concentration contained in the secondary reducing gas. The graph L1 shown in FIG. 5 shows the correlation between the temperature of the secondary reducing gas blown into the blast furnace 10 and the CO gas concentration and CO2 gas concentration in the secondary reducing gas. It is considered that the reduction potential decreases as the CO2 gas concentration and H2O gas concentration increase. However, as described above, by determining a predetermined temperature based on the blowing amount of the primary reducing gas blown into the blast furnace 10, the temperature of the primary reducing gas, and the blowing amount of the secondary reducing gas blown into the blast furnace 10, the decrease in the reduction potential can be suppressed, and thus the carbon consumption per unit can be reduced.

[0033] Even when the secondary reducing gas is heated by the direct heating method, the main component of the secondary reducing gas blown into the blast furnace 10 is preferably CO gas. That is, the content of CO2 gas and H2O gas, which are impurities contained in the secondary reducing gas, is preferably less than 10% by volume, respectively. Similarly, the content of hydrogen gas is also preferably less than 10% by volume. Further, the CO / CO2 gas concentration ratio of the secondary reducing gas is preferably 9 or more.

[0034] Furthermore, the CO / CO2 gas concentration ratio of the second reducing gas is preferably determined based on the injection amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the injection amount of the second reducing gas blown into the blast furnace 10. That is, according to the injection amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the injection amount of the second reducing gas blown into the blast furnace 10, the CO / CO2 gas concentration ratio at which the carbon consumption per unit reaches the minimum value is determined. Therefore, based on the injection amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the injection amount of the second reducing gas blown into the blast furnace 10, a simulation of the blast furnace operation can be performed to determine the CO / CO2 gas concentration ratio at which the carbon consumption per unit reaches the minimum value. Thereby, the carbon consumption per unit can be reduced.

[0035] For example, when the injection amount of the first reducing gas blown into the blast furnace 10 is 0 Nm 3 / t, or when the first reducing gas at normal temperature is blown into the blast furnace 10 at 150 Nm 3 / t or more and 250 Nm 3 / t or less, the CO / CO2 gas concentration ratio is determined as follows. That is, when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, the CO / CO2 gas concentration ratio of the second reducing gas is set to 40 or more. When the injection amount of the second reducing gas blown into the blast furnace 10 is more than 100 Nm 3 and 200 Nm 3 / t or less, the CO / CO2 gas concentration ratio of the second reducing gas is set to 20 or more. When the injection amount of the second reducing gas blown into the blast furnace 10 is more than 200 Nm 3 and 300 Nm 3 / t or less, the CO / CO2 gas concentration ratio of the second reducing gas is set to 15 or more.

[0036] On the other hand, when the high-temperature first reducing gas in the blast furnace 10 is 500 Nm 3 / t or more and 800 Nm 3 / tWhen blown in as follows, the CO / CO2 gas concentration ratio is determined as follows. That is, when the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, the CO / CO2 gas concentration ratio of the second reducing gas is set to 50 or more. When the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t exceeding 200 Nm 3 / t or less, the CO / CO2 gas concentration ratio of the second reducing gas is set to 10 or more. When the blowing amount of the second reducing gas blown into the blast furnace 10 is 200 Nm 3 / t exceeding 300 Nm 3 / t or less, the CO / CO2 gas concentration ratio of the second reducing gas is set to 8 or more.

[0037] By adjusting the CO / CO2 gas concentration ratio of the second reducing gas as described above, the carbon consumption per unit can be further reduced. The second reducing gas heated by the heater 50 is blown into the blast furnace 10. The flow meter 61 measures the blowing amount of the second reducing gas blown into the blast furnace 10.

[0038] The first reducing gas supply system 2 includes a first reducing gas tank 70, a heater 71, and a flow meter 72. The first reducing gas supply system 2 is a system that supplies the first reducing gas from outside the system of the blast furnace system 1 to the blast furnace system 1.

[0039] The first reducing gas tank 70 is a tank for storing the first reducing gas. Here, the first reducing gas is a gas mainly composed of a hydrogen-based reducing gas, and it is sufficient that the proportion of the hydrogen-based reducing gas in the gas is the highest in terms of volume fraction, preferably 50% or more. The hydrogen-based reducing gas is a hydrogen-containing gas containing hydrogen as an element in the gas, and it is preferable that H is 50 mol% or more in terms of elemental composition ratio. Also, it refers to those existing as a gas under standard conditions (0 °C, 1 atm). The hydrogen-based reducing gas is, for example, in addition to hydrogen gas, a mixed gas of hydrogen gas and other gases (unsaturated hydrocarbon-based gases (C2H4, C2H2, C3H6, etc.), saturated hydrocarbon-based gases (CH4, C2H6, etc.), NH3, coke oven gas, blast furnace gas, town gas, natural gas, etc.) that do not impair the effects of this embodiment. Note that the first reducing gas may also be a mixed gas of a hydrogen-based reducing gas and other gases (for example, nitrogen gas) that do not impair the effects of this embodiment. The heater 71 heats the first reducing gas supplied from the first 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 blast furnace 10, and the heated first reducing gas is blown into the blast furnace 10. The heater 71 may be used in combination with the heater 50. The flow meter 72 measures the flow rate of the first reducing gas (the blowing amount of the first reducing gas) blown into the blast furnace 10.

[0040] <2. Operating Method of Blast Furnace> Next, the operation method of the blast furnace 10 according to the present embodiment will be described. In the operation method of the blast furnace 10 according to the present embodiment, while alternately and layerwise charging iron-based raw materials and coke into the blast furnace 10 from the furnace top of the blast furnace 10, the first reducing gas heated by the first reducing gas supply system 2 is supplied to the blast furnace 10. In addition to the heated first reducing gas, hot air, pulverized coal, and enriched oxygen gas are 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 a high-temperature reducing gas (here mainly CO gas). That is, the hot air gasifies the coke and pulverized coal. The reducing gas and the first reducing gas rise in the blast furnace 10 and reduce the iron-based raw materials while heating them. The iron-based raw materials are reduced while descending in the blast furnace 10 by the reducing gas and the first reducing gas. Thereafter, the iron-based raw materials melt and drip in the blast furnace 10 while being further reduced by the coke. The iron-based raw materials are finally accumulated as hot metal (pig iron) containing less than 5% by mass of carbon in the hearth part. The hot metal in the hearth part is taken out from the taphole and supplied to the next steelmaking process.

[0041] On the other hand, the top gas of the blast furnace 10 is discharged. The CO2 separation and recovery device 20 recovers the top gas and separates it into CO gas, hydrogen gas, and nitrogen gas, and CO2 gas and H2O gas. The CO2 gas and H2O gas are discharged outside the system.

[0042] The CO gas, hydrogen gas, and nitrogen gas are temporarily stored in the buffer tank 30. A desired amount of the second reducing gas is introduced from the buffer tank 30 into the compressor 40. The second reducing gas introduced into the compressor 40 is the gas recovered and separated from the top gas and contains at least 50% by volume fraction of CO gas. The specific composition is as described above. The remaining gas is discharged outside the system and used, for example, as a heat source in the steelworks.

[0043] Next, the second reducing gas is pressurized by the compressor 40. Here, the compressor 40 pressurizes the second reducing gas to about the internal pressure of the blast furnace 10 (about 4.5 atmospheres), for example. The pressurized second reducing gas is introduced into the heater 50.

[0044] Next, the second reducing gas is heated to a predetermined temperature by the heater 50. That is, before blowing the second reducing gas into the blast furnace 10, the second reducing gas is heated to a predetermined temperature. The predetermined temperature is preferably determined based on the blowing amount of the first reducing gas blown into the blast furnace 10 and the blowing amount of the second reducing gas blown into the blast furnace 10. After heating the second reducing gas to the determined predetermined temperature, the second reducing gas is blown into the blast furnace 10. The specific method for determining the predetermined temperature is as described above. Further, it is preferable to determine the CO / CO2 gas concentration ratio of the second reducing gas based on the blowing amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the blowing amount of the second reducing gas blown into the blast furnace 10. The specific determination method is as described above. The flow meter 61 measures the flow rate of the second reducing gas blown into the blast furnace 10.

[0045] Here, in blast furnace operation, for reasons such as performing stable operation, it is preferable to maintain the tuyere tip combustion temperature, the top gas temperature, and the hot metal temperature within a predetermined range. For example, the tuyere tip combustion temperature is preferably maintained at about 2000 °C or higher and 2300 °C or lower, the top gas temperature is preferably maintained at about 105 °C or higher, and the hot metal temperature is preferably maintained at about 1520 °C or higher. The upper limit value of the tuyere tip combustion temperature is the upper limit value assumed for normal operation (operation without blowing the first reducing gas and the second reducing gas into the blast furnace 10). When the tuyere tip combustion temperature exceeds the upper limit value, it is preferable to take measures such as strengthening the cooling capacity of the tuyere equipment to prevent wear of the tuyere equipment and using a material with higher heat resistance. The specifications of blast furnace operation are preferably determined so that the tuyere tip combustion temperature, the top gas temperature, and the hot metal temperature are maintained within a predetermined range. As long as the tuyere tip combustion temperature, the top gas temperature, and the hot metal temperature are maintained within a predetermined range, the specifications of blast furnace operation can be freely designed. Also, as a result of the design, the tuyere tip combustion temperature may exceed the upper limit value, but it is preferable to take the above-mentioned measures separately.

Example

[0046] Next, an example of this embodiment will be described. In this example, a simulation of the operation method of the blast furnace according to this embodiment was performed to verify the effects of the operation method of the blast furnace according to this embodiment. The simulation model used the so-called "blast furnace mathematical model" shown in Kouji TAKATANI, Takanobu INADA, Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace", ISIJ International, Vol. 39 (1999), No. 1, p. 15-22, etc. This blast furnace mathematical model generally 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.

[0047] In this simulation, hydrogen gas was used as the first reducing gas, and simulations of blast furnace operations were carried out for three patterns: hydrogen gas injection volume: 0 Nm 3 / t, injection of 200 Nm 3 / t of normal-temperature hydrogen gas, and injection of 650 Nm 3 / t of high-temperature hydrogen gas. The specifications of the blast furnace operation are as shown in Table 1. Note that the reduction material ratio indicates the amount of reduction materials such as coke and pulverized coal-containing carbon materials per ton of hot metal without including the injected gas. The carbon consumption per unit is the amount of carbon required to produce one ton of hot metal, which is approximately the same as the reduction material ratio. The injection volumes of hydrogen gas (the first reducing gas) and the second reducing gas are the injection volumes per ton of hot metal, and are measured by the flow meters 61 and 72 provided between the sources of the respective gases and the connection to the blast furnace 10. Also, the injection temperatures of hydrogen gas and the second reducing gas are set as the temperatures of the gases when they are injected into the blast furnace 10.

[0048]

Table 1

[0049] In blast furnace operation, the pulverized coal ratio, oxygen enrichment rate, and hot blast injection volume were adjusted so that the hot metal output, hot metal temperature, and top gas temperature would be constant. However, when the pulverized coal ratio becomes zero, the coke ratio is adjusted. Then, the temperature of the reducing gas (secondary reducing gas) (predetermined temperature) and the injection volume of the secondary reducing gas blown into the blast furnace 10 were varied, and the influence of these parameters on the carbon consumption per unit was examined. The results are shown in FIGS. 2 to 4.

[0050] FIG. 2 is a graph L10 to L30 showing the correlation between the temperature (° C.) of the secondary reducing gas and the carbon consumption per unit (kg / t) when the injection volume of the primary reducing gas (hydrogen gas) blown into the blast furnace 10 is 0 Nm 3 / t. Graph L10 corresponds to the case where the injection volume of the secondary reducing gas is 100 Nm 3 / t, graph L20 corresponds to the case where the injection volume of the secondary reducing gas is 200 Nm 3 / t, and graph L30 corresponds to the case where the injection volume of the secondary reducing gas is 300 Nm 3 / t.

[0051] FIG. 3 is a graph L10 to L30 showing the correlation between the temperature (° C.) of the secondary reducing gas and the carbon consumption per unit (Nm 3 / t) when injecting 200 Nm of normal temperature primary reducing gas (hydrogen gas) into the blast furnace 10. Graph L10 corresponds to the case where the injection volume of the secondary reducing gas is 100 Nm 3 / t, graph L20 corresponds to the case where the injection volume of the secondary reducing gas is 200 Nm 3 / t, and graph L30 corresponds to the case where the injection volume of the secondary reducing gas is 300 Nm 3 / t. 3 / t.

[0052] FIG. 4 is a graph showing the correlation between the temperature (° C.) of the secondary reducing gas and the carbon consumption per unit (Nm 3 / t) when injecting 650 Nm of high temperature primary reducing gas (hydrogen gas) into the blast furnace 10. Graph L10 is the injection volume of the secondary reducing gas at 100 Nm 3 / t. 3Corresponding to the case where it becomes / t, the graph L20 shows that the blowing amount of the second reducing gas is 200 Nm 3 Corresponding to the case where it becomes / t, the graph L30 shows that the blowing amount of the second reducing gas is 300 Nm 3 Corresponds to the case where it becomes / t.

[0053] As shown in FIGS. 2 to 4, according to the blowing amount of the first reducing gas blown into the blast furnace 10, the temperature of the first reducing gas, and the blowing amount of the second reducing gas blown into the blast furnace 10, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is different. For example, when the blowing amount of the first reducing gas blown into the blast furnace 10 is 0 Nm 3 / t, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is as follows. That is, when the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is normal temperature. When the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t and more than 200 Nm 3 / t or less, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is more than 200°C and 400°C or less. When the blowing amount of the second reducing gas blown into the blast furnace 10 is 200 Nm 3 / t and more than 300 Nm 3 / t or less, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is more than 400°C and 600°C or less.

[0054] On the other hand, when the first reducing gas at normal temperature is blown into the blast furnace 10 at 200 Nm 3 / t, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is as follows. That is, when the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, the temperature range of the second reducing gas at which the carbon consumption per unit becomes the minimum value is normal temperature. When the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t and more than 200 Nm 3 / tWhen the following conditions are met, the temperature range of the second reducing gas at which the carbon consumption per unit is minimized is above 200°C and below 400°C. When the injection amount of the second reducing gas blown into the blast furnace 10 is more than 200 Nm 3 / tand less than 300 Nm 3 / t, the temperature range of the second reducing gas at which the carbon consumption per unit is minimized is above 400°C and below 600°C.

[0055] On the other hand, when the high-temperature first reducing gas is blown into the blast furnace 10 at 1200 Nm 3 / t, the temperature range of the second reducing gas at which the carbon consumption per unit is minimized is as follows. That is, when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, the temperature range of the second reducing gas at which the carbon consumption per unit is minimized is 200°C or higher. When the injection amount of the second reducing gas blown into the blast furnace 10 is more than 100 Nm 3 and less than 200 Nm 3 / t, the temperature range of the second reducing gas at which the carbon consumption per unit is minimized is above 500°C and below 800°C. When the injection amount of the second reducing gas blown into the blast furnace 10 is more than 200 Nm 3 and less than 300 Nm 3 / t, the temperature range of the second reducing gas at which the carbon consumption per unit is minimized is above 700°C and below 900°C.

[0056] Therefore, as described above, by determining a predetermined temperature and heating the second reducing gas to the determined predetermined temperature and then blowing it into the blast furnace 10, the carbon consumption per unit can be further reduced.

[0057] Next, the hydrogen gas injection amount is 0 Nm 3 / t, the injection of normal temperature hydrogen gas is 200 Nm 3 / t, and the injection of high-temperature hydrogen gas is 650 Nm 3Regarding the three patterns of blowing, the influence of the CO / CO2 gas concentration ratio on the carbon consumption unit was investigated. The results are shown in Tables 2A to 2C. Table 2A shows the correlation between the CO / CO2 gas concentration ratio and the carbon consumption unit when the first reducing gas is not blown into the blast furnace 10. In Table 2A, NH-1 indicates the case where the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less, and NH-2 indicates the case where the blowing amount of the second reducing gas blown into the blast furnace 10 is more than 100 Nm 3 / t and 200 Nm 3 / t or less, and NH-3 indicates the case where the blowing amount of the second reducing gas blown into the blast furnace 10 is more than 200 Nm 3 / t and 300 Nm 3 / t or less. As shown in Table 2A, when the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / t or less (NH-1), the CO / CO2 gas concentration ratio of the second reducing gas is set to 400 or more, and when the blowing amount of the second reducing gas blown into the blast furnace 10 is more than 100 Nm 3 / t and 200 Nm 3 / t or less (NH-2), the CO / CO2 gas concentration ratio of the second reducing gas is set to 20 or more, and when the blowing amount of the second reducing gas blown into the blast furnace 10 is more than 200 Nm 3 / t and 300 Nm 3 / t or less (NH-3), it can be seen that by setting the CO / CO2 gas concentration ratio of the second reducing gas to 15 or more, the carbon consumption unit is reduced (the value of the carbon consumption unit is decreased compared to the carbon consumption unit shown in Table 1).

[0058] Table 2B shows the correlation between the CO / CO2 gas concentration ratio and the carbon consumption unit when 200 Nm of normal-temperature hydrogen gas is blown into the blast furnace 10. In Table 2B, RH-1 indicates the case where the blowing amount of the second reducing gas blown into the blast furnace 10 is 100 Nm3 / t or less, and RH-2 indicates the case where the blowing amount of the second reducing gas blown into the blast furnace 10 is more than 100 Nm 3 / t and 200 Nm 3 / t or less, and RH-2 indicates the case where the blowing amount of the second reducing gas blown into the blast furnace 10 is more than 100 Nm 3 / tIndicates the case where RH-3 is such that the injection amount of the second reducing gas blown into the blast furnace 10 is 200 Nm 3 / tOver 300 Nm 3 / tIndicates the case where it is below. As shown in Table 2B, when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / tOr less (RH-1), the CO / CO2 gas concentration ratio of the second reducing gas is set to 400 or more, and when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / tOver 200 Nm 3 / tOr less (RH-2), the CO / CO2 gas concentration ratio of the second reducing gas is set to 20 or more, and when the injection amount of the second reducing gas blown into the blast furnace 10 is 200 Nm 3 / tOver 300 Nm 3 / tOr less (RH-3), it can be seen that by setting the CO / CO2 gas concentration ratio of the second reducing gas to 15 or more, the carbon consumption unit is reduced (the value of the carbon consumption unit is decreased compared to the carbon consumption unit shown in Table 1).

[0059] Table 2C shows the correlation between the CO / CO2 gas concentration ratio and the carbon consumption unit when 650 Nm of high-temperature hydrogen gas is blown into the blast furnace 10 3 / tIn Table 2C, HH-1 indicates the case where the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / tOr less, HH-2 indicates the case where the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / tOver 200 Nm 3 / tOr less, and HH-3 indicates the case where the injection amount of the second reducing gas blown into the blast furnace 10 is 200 Nm 3 / tOver 300 Nm 3 / tOr less. As shown in Table 2C, when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / tOr less (HH-1), the CO / CO2 gas concentration ratio of the second reducing gas is set to 50 or more, and when the injection amount of the second reducing gas blown into the blast furnace 10 is 100 Nm 3 / tOver 200 Nm 3 / tWhen the following conditions are met (HH-2), the CO / CO2 gas concentration ratio of the second reducing gas is set to 10 or more, and the injection amount of the second reducing gas injected into the blast furnace 10 is 200 Nm 3 / tOver 300 Nm 3 / tWhen the following conditions are met (HH-3), by setting the CO / CO2 gas concentration ratio of the second reducing gas to 8 or more, it can be seen that the carbon consumption per unit is reduced (the value of the carbon consumption per unit is decreased compared to the carbon consumption per unit shown in Table 1).

[0060]

Table 2A

[0061]

Table 2B

[0062]

Table 2C

[0063] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and these are naturally understood to belong to the technical scope of the present invention.

Description of Reference Numerals

[0064] 1 Blast furnace system 2 First reducing gas supply system 10 Blast furnace 10a Blast furnace body 10b Shaft section 11 Normal tuyere 12 Shaft section tuyere 20 CO2 separation and recovery device 30 Buffer tank 40 Compressor 50, 71 Heater 61, 72 Flowmeter 70 First Reduction Gas Tank

Claims

1. A method for operating a blast furnace, comprising: injecting a first reducing gas, which has a hydrogen-based reducing gas as a main component, into the blast furnace; injecting a second reducing gas, which is a gas recovered and separated from the top gas of the blast furnace and contains at least 50% by volume of CO gas, into the blast furnace; heating the second reducing gas to a blowing temperature before injecting the second reducing gas into the blast furnace; when the injection rate of the first reducing gas is 0 Nm3 / min, the blowing temperature of the second reducing gas is determined based on the injection rate of the second reducing gas to be injected into the blast furnace; when the injection rate of the first reducing gas exceeds 0 Nm3 / min, the blowing temperature of the second reducing gas is determined based on the injection rate of the first reducing gas to be injected into the blast furnace, the blowing temperature of the first reducing gas to be injected into the blast furnace, and the injection rate of the second reducing gas to be injected into the blast furnace.

2. In the blast furnace provided with a normal tuyere attached below the bosh part and a shaft part tuyere attached at a position higher than the normal tuyere, injecting the first reducing gas into the blast furnace from the normal tuyere, injecting the second reducing gas into the blast furnace from the shaft part tuyere. The method for operating a blast furnace according to Claim 1.

3. When the injection amount of the first reducing gas injected into the blast furnace is 0 Nm ３ / t, When the injection amount of the second reducing gas blown into the blast furnace is 100 Nm ３ / t or less, the injection temperature of the second reducing gas is set to normal temperature, When the blowing rate of the second reducing gas blown into the blast furnace is more than 100 Nm ３ / t and less than or equal to 200 Nm ３ / t, the blowing temperature of the second reducing gas is set to more than 200°C and less than or equal to 400°C, When the blowing amount of the second reducing gas blown into the blast furnace is more than 200 Nm ３ / t and less than or equal to 300 Nm ３ / t, the blowing temperature of the second reducing gas is set to be more than 400°C and less than or equal to 600°C. The operation method of the blast furnace according to claim 1 or 2 is characterized by this.

4. when the first reducing gas at normal temperature is injected into the blast furnace, When the injection amount of the second reducing gas blown into the blast furnace is 100 Nm ３ / t or less, the injection temperature of the second reducing gas is set to normal temperature, When the blowing rate of the second reducing gas blown into the blast furnace is more than 100 Nm ３ / t and less than or equal to 200 Nm ３ / t, the blowing temperature of the second reducing gas is set to more than 200°C and less than or equal to 400°C, The blowing amount of the second reducing gas blown into the blast furnace is more than 200 Nm ３ / t and less than or equal to 300 Nm ３ / t. When this is the case, the blowing temperature of the second reducing gas is more than 400°C and less than or equal to 600°C. The method for operating a blast furnace according to claim 1 or 2, characterized in that

5. when the first reducing gas at high temperature is injected into the blast furnace, When the blowing amount of the second reducing gas blown into the blast furnace is 100 Nm ３ / t or less, the blowing temperature of the second reducing gas is set to 200°C or higher, When the injection amount of the second reducing gas blown into the blast furnace is more than 100 Nm ３ / t and less than or equal to 200 Nm ３ / t, the injection temperature of the second reducing gas is set to more than 500°C and less than or equal to 800°C, The injection amount of the second reducing gas blown into the blast furnace is more than 200 Nm ３ / t and not more than 300 Nm ３ / t. When this is the case, the injection temperature of the second reducing gas is more than 700°C and not more than 900°C. The method for operating a blast furnace according to claim 1 or 2, characterized by this.

6. When the blowing amount of the second reducing gas blown into the blast furnace is 100 Nm ３ / t or less, the CO / CO ２ gas concentration ratio of the second reducing gas is set to 400 or more, The blowing amount of the second reducing gas blown into the blast furnace is more than 100 Nm ３ / t and less than or equal to 200 Nm ３ / t. In this case, the CO / CO ２ gas concentration ratio of the second reducing gas is set to 20 or more, When the injection amount of the second reducing gas blown into the blast furnace exceeds 200 Nm ３ / t and is 300 Nm ３ / t or less, the CO / CO ２ gas concentration ratio of the second reducing gas is 15 or more. The operation method of the blast furnace according to claim 3, characterized in that.

7. When the injection amount of the second reducing gas blown into the blast furnace is 100 Nm ３ / t or less, the CO / CO ２ gas concentration ratio of the second reducing gas is set to 400 or more, The injection amount of the second reducing gas blown into the blast furnace is more than 100 Nm ３ / t and less than or equal to 200 Nm ３ / t, the CO / CO ２ gas concentration ratio of the second reducing gas is set to 20 or more, When the injection amount of the second reducing gas blown into the blast furnace is more than 200 Nm ３ / t and not more than 300 Nm ３ / t, the CO / CO ２ gas concentration ratio of the second reducing gas is set to 15 or more. The operation method of the blast furnace according to claim 4, characterized in that.

8. When the blowing amount of the second reducing gas blown into the blast furnace is 100 Nm ３ / t or less, the CO / CO ２ gas concentration ratio of the second reducing gas is set to 50 or more, The blowing amount of the second reducing gas blown into the blast furnace is more than 100 Nm ３ / t and less than or equal to 200 Nm ３ / t. In this case, the CO / CO ２ gas concentration ratio of the second reducing gas is set to 10 or more, When the blowing amount of the second reducing gas blown into the blast furnace is more than 200 Nm ３ / t and not more than 300 Nm ３ / t, the operation method of the blast furnace according to claim 5, characterized in that the CO / CO ２ gas concentration ratio of the second reducing gas is set to 8 or more.

Images