Blast furnace operation method

Abstract

This blast furnace operation method comprises: isolating CO2 gas and H2O gas from a furnace top exhaust gas and removing the same to generate a reformed furnace top circulating gas; and blowing the reformed furnace top circulating gas into a blast furnace (10) from a shaft tuyere (12). The method is characterized by blowing a cracked gas generated through cracking of a NH3-containing gas into the blast furnace (10) from a normal tuyere (11).

Description

Blast furnace operation method

[0001] This application claims priority to Japanese Patent Application No. 2024-033898, filed on March 6, 2024, the contents of which are incorporated herein by reference.

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

[0003] Recently, there has been a growing demand to prevent global warming, and carbon dioxide (CO ２ As mentioned above, the blast furnace method uses carbonaceous material as a reducing agent, which produces a large amount of CO ２ Therefore, the steel industry ２ As it is one of the major industries in terms of CO2 emissions, ２ We must respond to the social demand for reducing gas emissions. 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 problem, for example, as disclosed in Patent Document 1, a method for producing a hot air stream from a tuyere using H ２ A technique is known in which the reducing gas potential in the furnace is increased by blowing in a gas. ２ The gas is used as a reducing gas for iron-based raw materials, thereby reducing the reducing agent ratio.

[0006] International Publication No. 2021 / 107091

[0007] However, the technology described in Patent Document 1 does not include CO ２ There was room for further improvement in gas emissions.

[0008] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to ２ To provide a method for operating a blast furnace that can further reduce gas emissions compared to conventional techniques.

[0009] The gist of the present invention is as follows: (1) CO from the top exhaust gas ２ Gas and H ２ A method for operating a blast furnace, comprising separating and removing O gas to generate a reformed furnace top circulation gas, and injecting the reformed furnace top circulation gas into a blast furnace through a shaft tuyere, the method comprising: ３ A method for operating a blast furnace, characterized in that cracking gas produced by cracking contained gas is injected into the blast furnace through a normal tuyere. ３The contained gas is NH ３ (3) The method for operating a blast furnace according to (1), characterized in that the cracking gas is heated and then injected into the blast furnace. (4) The method for operating a blast furnace according to (1), characterized in that the amount of the reformed furnace top circulating gas injected into the blast furnace is 350 Nm3. ３ (5) The method for operating a blast furnace according to any one of (1) to (3), characterized in that the amount of cracking gas injected into the blast furnace is 350 Nm3 / t-pig or more. ３ The method for operating a blast furnace according to any one of (1) to (3), characterized in that the blast furnace is operated at a temperature of 10 ...

[0010] According to the present invention, CO ２ It is possible to provide a method for operating a blast furnace that can further reduce gas emissions compared to conventional techniques.

[0011] It is a flow diagram showing the overall configuration of a blast furnace system used in this embodiment. It is a graph verifying the effect of this embodiment. It is a graph verifying the effect of this embodiment.

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0013] 1, the overall configuration of a blast furnace system 1 according to this embodiment and a cracking gas supply system 2 connected to the blast furnace system 1 will be described. The blast furnace system 1 includes a blast furnace 10 and a CO ２ The system includes a separation and recovery device 20, a buffer tank 30, a compressor 40, and a heater 50.

[0014] The blast furnace 10 includes a blast furnace body 10a, a normal tuyere 11, and a shaft tuyere 12. Inside the blast furnace body 10a, a reduction reaction of iron-based raw materials is carried out by the blast furnace method. Specifically, iron-based raw materials and coke are charged into the blast furnace 10 alternately and in layers from the top of the blast furnace 10, while hot air, pulverized coal, and oxygen-enriched gas are blown into the blast furnace 10 from the normal tuyere 11. Furthermore, as will be described later, cracking gas (NH ３ N produced by cracking (pyrolyzing) the contained gas ２ Gas and H ２ A mixed gas containing CO gas is also blown into the blast furnace 10. In the following description, the "tuyere tip combustion temperature" usually means the temperature at the gas outlet of the 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 this case). In other words, the hot air gasifies the coke and pulverized coal. In addition, as will be described in detail later, there are cases where the pulverized coal is not blown into the blast furnace 10. As a result, the hot air is converted into H ２ gas, CO gas, and N ２ The bosh gas and cracking gas rise in the blast furnace 10 and reduce the iron-based raw materials while heating them. More specifically, the H in the bosh gas and cracking gas ２ The iron-based raw materials are reduced by the CO gas and the H gas. These gases are then discharged from the top of the blast furnace as top exhaust gas. The top exhaust gas contains unreacted H ２ Gas, CO gas, CO ２ Gas, H ２ O gas, N ２ The iron-based raw materials are heated and reduced by the bosh gas and cracking gas while descending through the blast furnace 10. The iron-based raw materials are then melted and dripped through the blast furnace 10 while being further reduced by coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is removed from the taphole and used in the next steelmaking process.

[0015] The normal tuyere 11 is provided below the bosh portion of the blast furnace 10, and in addition to the hot air described above, heated cracking gas is blown into the blast furnace 10 as will be described later. Note that part or all of the hot air may be replaced with cracking gas. Note that although normal tuyere 11 is depicted only at both ends of the blast furnace 10 in FIG. 1, three or more normal tuyere may be provided around the circumferential direction of the blast furnace 10.

[0016] The shaft tuyere 12 is provided in the shaft 10b of the blast furnace 10, and injects reformed top recirculating gas (RBFG) obtained by reforming the top exhaust gas into the shaft 10b of the blast furnace 10. Although the shaft tuyere 12 is depicted only on the left side of the shaft 10b in FIG. 1 , two or more shaft tuyere 12 may be provided at equal intervals around the circumference of the shaft 10b. RBFG may be injected into any of the shaft tuyere 12.

[0017] CO ２ The separation and recovery device 20 recovers the top flue gas and separates CO ２ Gas and H ２ O gas is separated to produce RBFG, where CO 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 top flue gas corresponding to the flow rate of RBFG injected into the blast furnace. The remaining top flue gas is used as a heat source for the steelworks. The separation method is not particularly limited, but examples include chemical adsorption and physical adsorption (PSA). ２ Gas and H ２ The O gas is discharged to the outside of the system.

[0018] The buffer tank 30 is a tank for temporarily storing RBFG. A desired amount of RBFG is introduced from the buffer tank 30 into the compressor 40.

[0019] 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.

[0020] The heater 50 heats the RBFG. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. For example, when RBFG is injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12, it is preferably set to 800°C or higher. The heater 50 can be sufficiently realized by an electric heater or the like. The RBFG heated by the heater 50 is injected into the shaft 10b of the blast furnace 10 from the shaft tuyere 12. In FIG. 1 , RBFG is injected into the blast furnace 10 from the shaft tuyere 12 on the left side, but RBFG may also be injected into the blast furnace 10 from the shaft tuyere 12 on the right side (not shown). RBFG may be injected into the blast furnace 10 from both the normal tuyere 11 and the shaft tuyere 12, or may be injected into the blast furnace 10 from the normal tuyere 11.

[0021] Amount of RBFG injected into the blast furnace 10 (Nm ３ / t-pig) may be arbitrarily set depending on the operating conditions of the blast furnace 10. However, as will be shown in the examples described later, the more the amount of RBFG injected into the blast furnace 10 increases, the more CO ２ In the example, the amount of RBFG injected into the blast furnace 10 is 350 Nm ３ / t-pig or more, H ２ The CO ２ The emission reduction rate is large. Therefore, the amount of RBFG injected into the blast furnace 10 is 350 Nm ３ It is preferable that the ratio is / t-pig or more.

[0022] On the other hand, the more the amount of RBFG injected into the blast furnace 10 increases, the higher the furnace top exhaust gas temperature (°C) becomes (see Figure 2). An excessive increase in the furnace top exhaust gas temperature may cause instability in the operation of the blast furnace 10. From this perspective, the amount of RBFG injected into the blast furnace 10 is set to 400 Nm ３ It is preferable that the total weight is 1 / t-pig or less.

[0023] The cracking gas supply system 2 includes a liquid ammonia tank 70, a cracking device 71, and a heater 72. The liquid ammonia tank 70 contains NH ３ is stored in a liquid state. ３ Is H ２It has a higher boiling point and is more stable than NH 3 , so it can be easily liquefied and stored. ３ The density of NH ３ Gas cracking produces H ２ It generates gas, so a large amount of H ２ In other words, in this embodiment, the H ２ The gas is transported as liquid ammonia. The liquid ammonia tank 70 contains liquid NH ３ NH ３ The NH3-containing gas is supplied to the cracking device 71. ３ may be stored in a gaseous state.

[0024] The cracking device 71 is a NH ３ The cracking of the contained gas produces cracking gas, i.e., N ２ Gas and H ２ The heater 72 heats the cracking gas. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10, but may be set to, for example, a temperature similar to that of hot air (for example, about 1200°C). The heater 72 can be sufficiently realized by an electric heater or the like. This makes it possible to suppress a drop in the tuyere tip combustion temperature, thereby enabling stable operation of the blast furnace 10. Furthermore, since the cracking gas has sensible heat, it is at a certain temperature (generally 900°C or higher). Therefore, the burden on the heater 72 can be reduced. The heater 72 is usually connected to the tuyere 11, and the heated cracking gas is usually blown into the blast furnace 10 from the tuyere 11. The amount of cracking gas blown in (Nm ３ / t-pig) may be arbitrarily set depending on the operating conditions of the blast furnace 10. For example, the amount of cracking gas injected is 350 Nm ３ It may be / t-pig or more.

[0025] The cracking gas is usually H in the gas injected into the blast furnace 10 from the tuyere 11. ２ The cracking gas is preferably a gas having a concentration of 70% or more by volume fraction. ３ The contained gas is a pyrolyzed gas, and NH３ The decomposition rate is not limited by the

[0026] As mentioned above, the cracking gas has sensible heat, so the cracking gas may be directly injected into the blast furnace 10 without being heated. Even in this case, the blast furnace 10 can be operated without significantly changing the environment inside the furnace. However, the temperature of the cracking gas (especially N ２ Since the temperature of the cracking gas is lower than that of the hot air, if an excessive amount of cracking gas is injected into the blast furnace, the combustion temperature at the tuyere tip will be excessively reduced, and the operation design may not be viable. For this reason, when room temperature cracking gas is injected into the blast furnace 10, the cracking gas should be within a range where blast furnace operation can be maintained (for example, 700 Nm ３ The amount of cracking gas injected can be adjusted by adjusting the temperature (up to 1000 kJ / t-pig or less). Note that room temperature generally means a temperature between 25°C and 30°C.

[0027] 2. Blast Furnace Operation Method Next, a blast furnace operation method will be described. First, iron-based raw materials and coke are alternately and layer-wise charged into the blast furnace 10 from the top of the blast furnace 10, while hot air, pulverized coal, and oxygen-enriched gas are usually blown into the blast furnace 10 from the tuyere 11.

[0028] On the other hand, the liquid ammonia tank 70 contains liquid NH ３ NH ３ The cracking device 71 is supplied with NH ３ The cracking of the contained gas produces cracking gas, i.e., N ２ Gas and H ２ The heater 72 heats the cracking gas. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10, but is preferably 800°C or higher, and may be set to a temperature similar to that of hot air (for example, about 1200°C). The heated cracking gas is then blown into the blast furnace 10 from the normal tuyere 11. NH ３ Since the decomposition temperature of the gas is 950°C, NH ３ The cracking gas may be blown into the blast furnace 10 without passing through the heater 72 while maintaining the temperature at about 950° C., which is the decomposition temperature of the molten iron.

[0029] The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace 10 to generate high-temperature reducing gas (mainly CO gas in this case). That is, the hot air gasifies the coke and pulverized coal. Note that, as will be described in detail later, there are cases where pulverized coal is not blown into the blast furnace 10 (pulverized coal ratio = 0). As a result, the hot air is converted into H ２ gas, CO gas, and N ２ The bosh gas and cracking gas rise in the blast furnace 10 and reduce the iron-based raw materials while heating them. More specifically, the H in the bosh gas and cracking gas ２ The iron-based raw materials are reduced by the CO gas and the H gas. These gases are then discharged from the top of the blast furnace as top exhaust gas. The top exhaust gas contains unreacted H ２ Gas, CO gas, CO ２ Gas, H ２ O gas, N ２ The iron-based raw materials are heated and reduced by the bosh gas and cracking gas while descending through the blast furnace 10. The iron-based raw materials are then melted and dripped through the blast furnace 10 while being further reduced by coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is removed from the taphole and used in the next steelmaking process.

[0030] The top exhaust gas is CO ２ The CO is introduced into the separation and recovery device 20. ２ The separation and recovery device 20 recovers the top flue gas and separates CO ２ Gas and H ２ The O gas is separated and removed to generate RBFG. The RBFG is temporarily stored in the buffer tank 30. A desired amount of RBFG is introduced from the buffer tank 30 into the compressor 40.

[0031] 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.

[0032] The heater 50 heats the RBFG. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10, but for example, when the RBFG is blown into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12, it is preferable to set the heating temperature to 800°C or higher. The RBFG heated by the heater 50 is blown into the shaft section 10b of the blast furnace 10 from the shaft section tuyere 12.

[0033] Amount of RBFG injected into the blast furnace 10 (Nm ３ / t-pig) may be arbitrarily set depending on the operating conditions of the blast furnace 10. However, as will be shown in the examples described later, the more the amount of RBFG injected into the blast furnace 10 increases, the more CO ２ In the example, the amount of RBFG injected into the blast furnace 10 is 350 Nm ３ / t-pig or more, H ２ The CO ２ The emission reduction rate is large. Therefore, the amount of RBFG injected into the blast furnace 10 is 350 Nm ３ It is preferable that the ratio is / t-pig or more.

[0034] On the other hand, the more the amount of RBFG injected into the blast furnace 10 increases, the higher the furnace top exhaust gas temperature (°C) becomes (see Figure 2). An excessive increase in the furnace top exhaust gas temperature may cause instability in the operation of the blast furnace 10. From this perspective, the amount of RBFG injected into the blast furnace 10 is set to 400 Nm ３ It is preferable that the total weight is 1 / t-pig or less.

[0035] As described above, according to this embodiment, NH ３ H produced by cracking of contained gases ２ Gas and N ２ A mixed gas containing H is usually injected into the blast furnace from the tuyere 11. ２ Compared with the case where gas is simply injected into the blast furnace 10 through the normal tuyere 11, ２ It is possible to reduce the amount of NH ３ Is H ２ It has a higher boiling point and is more stable than NH 3 , so it can be easily liquefied and stored. ３The density of NH ３ Gas cracking produces H ２ It generates gas, so a large amount of H ２ The gas can be easily transported to the blast furnace.

[0036] Furthermore, since the cracking gas is heated before being injected into the blast furnace 10, a decrease in the combustion temperature at the tuyere tip is suppressed, and the blast furnace 10 can be operated stably.

[0037] In this embodiment, NH ３ NH as a contained gas ３ Although the gas (100% purity) has been described, it is not limited to this. For example, NH ３ The contained gas is NH ３ The main component (NH ３ The mixed gas may contain 50% or more of the above-mentioned elements.

[0038] Next, an example of this embodiment will be described. In this example, a simulation of blast furnace operation was performed to verify the effects of this embodiment. Here, the simulation model used was the so-called "blast furnace mathematical model" shown in Kouji TAKATANI, Takanobu INADA, and Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace," ISIJ International, Vol. 39 (1999), No. 1, pp. 15-22, etc. This blast furnace mathematical model roughly defines a plurality of meshes (small regions) by dividing the internal region of the blast furnace in the height direction, radial direction, and circumferential direction, and simulates the behavior of each mesh.

[0039] As blast furnace operation, base operation (H ２ (Operation without gas injection), high temperature (800°C) H ２ Gas is usually injected into the blast furnace 10 from the tuyere 11. ２ The cracking gas injection operation (comparative example) and the cracking gas injection operation (example) in which the cracking gas is injected into the blast furnace 10 from the normal tuyere 11 were assumed. ３ As a contained gas, pure NH ３The specifications common to each operation are as follows:

[0040] The distribution of iron-based raw materials and coke charged from the furnace top was constant. ２ The separation and recovery device 20 is a device for recovering CO contained in the top exhaust gas. ２ Gas and H ２ The furnace temperature was adjusted by adjusting the pulverized coal ratio and coke ratio. Other specifications are as shown in Table 1 below.

[0041]

[0042] The results are shown in Figures 2 and 3. Figure 2 shows the RBFG injection amount (Nm ３ / t-pig) and the furnace top exhaust gas temperature (°C), and Fig. 3 shows the correlation between the RBFG injection amount (Nm ３ / t-pig) and CO in blast furnaces ２ 2 is a graph showing the correlation between the RBFG injection amount (Nm m) and the emission reduction rate (%). ３ / t-pig) and the furnace top exhaust gas temperature (°C), and "●" indicates the H ２ The graph shows the furnace top exhaust gas temperature when the gas is injected into the blast furnace 10 from the normal tuyere 11. The "▲" in Figure 3 indicates the RBFG injection amount (Nm m) when RBFG is injected while 900°C cracking gas is injected into the blast furnace 10 from the normal tuyere 11. ３ / t-pig) and CO in blast furnaces ２ The plot (graph) shows the correlation with the emission reduction rate (%). The "●" indicates the H ２ CO in the blast furnace when gas is injected into the blast furnace 10 from the normal tuyere 11 ２ The emission reduction rate (%) is shown. ２The emission reduction rate (%) was calculated by (carbon consumption intensity in base operation - carbon consumption intensity in each case) / carbon consumption intensity in base operation x 100. Here, carbon consumption intensity is the amount of carbon required to produce 1 ton of molten pig iron (kg / t-pig). The value in parentheses in each plot in Figure 2 is the oxygen enrichment rate (%).

[0043] As shown in FIG. 3, in the example, the CO ２ The emission reduction rate increased, and the RBFG injection volume increased to 350 Nm ３ / t-pig or more, H ２ The CO ２ The emission reduction rate increases (circled area in Figure 3). However, as the RBFG injection rate increases, the furnace top exhaust gas temperature also increases (circled area in Figure 2). From the viewpoint of stable blast furnace operation, the furnace top exhaust gas temperature is preferably 160°C or less. Therefore, the RBFG injection rate is set to 400 Nm ３ / t-pig or less is preferred.

[0044] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0045] 1 Blast furnace system 2 Cracking gas supply system 10 Blast furnace 10a Blast furnace body 10b Shaft section 11 Normal tuyere 12 Shaft section tuyere 20 CO ２ Separation and recovery device 30 Buffer tank 40 Compressor 50, 72 Heater 70 Liquid ammonia tank 71 Cracking device

Claims

1. CO from the top exhaust gas ２ Gas and H ２ A method for operating a blast furnace, comprising separating and removing O gas to generate a reformed furnace top circulation gas, and injecting the reformed furnace top circulation gas into a blast furnace through a shaft tuyere, the method comprising: ３ A method for operating a blast furnace, characterized in that cracking gas produced by cracking contained gas is injected into said blast furnace through a normal tuyere.

2. Said NH ３ The contained gas is NH ３ 2. The method for operating a blast furnace according to claim 1, wherein the fuel is gas.

3. The method for operating a blast furnace according to claim 1, characterized in that the cracking gas is heated before being injected into the blast furnace.

4. The amount of the reformed furnace top circulating gas injected into the blast furnace is 350 Nm ３ The method for operating a blast furnace according to any one of claims 1 to 3, characterized in that the blast furnace is operated at a temperature of 10 ...

5. The amount of cracking gas injected into the blast furnace is 350 Nm ３ The method for operating a blast furnace according to any one of claims 1 to 3, characterized in that the blast furnace is operated at a temperature of 10 ...

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