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

[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. 2024-033898, filed on March 6, 2024, the contents of which are incorporated herein by reference. [Background technology]

[0002] In the steel industry, the blast furnace process is the mainstream method for producing pig iron. In this process, iron-based raw materials (raw materials containing iron oxide, mainly sintered ore, hereinafter simply referred to as "iron-based raw 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 tuyeres 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). In other words, the hot air gasifies the coke and pulverized coal. The reducing gas rises within the blast furnace, heating and reducing the iron-based raw materials. As the iron-based raw materials descend within the blast furnace, they are heated and reduced by the reducing gas. The iron-based raw materials then melt and drip down the blast furnace, where they are further reduced by the coke. The iron-based raw materials are eventually stored in the hearth as molten pig iron (pig iron) containing just under 5% by mass of carbon. The molten pig iron in the hearth is removed from the 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] In recent years, there has been a growing call to prevent global warming, and reducing emissions of carbon dioxide (CO2 gas), a greenhouse gas, has become a social issue. As mentioned above, the blast furnace process uses carbonaceous material as a reducing agent, which generates large amounts of CO2 gas. Therefore, the steel industry, which is one of the major industries in terms of CO2 gas emissions, must respond to the social demand for reducing CO2 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 serves two purposes: to generate heat in the furnace, raising the temperature of the charge, and to reduce the iron-based raw materials in the furnace. In order to reduce the reducing agent rate, it is necessary to increase the reduction efficiency in the furnace. The reduction reactions in the furnace can be expressed by various reaction equations. Among these reduction reactions, the direct reduction reaction with coke (reaction equation: FeO + C ⇒ Fe + CO) is an endothermic reaction that involves a large heat absorption. Therefore, minimizing this reaction is important in reducing the reducing agent rate. Because this direct reduction reaction occurs in the lower part of the blast furnace, if the iron-based raw materials can be sufficiently reduced with reducing gases such as CO and H2 before they reach the lower part of the furnace, the amount of iron-based raw materials subject to the direct reduction reaction can be reduced.

[0005] As a conventional technique for solving the above problems, a technique for increasing the reducing gas potential in the furnace by blowing H gas together with hot air from the tuyere is known, as disclosed in Patent Document 1. In this technique, H gas is used as a reducing gas for the iron-based raw materials, thereby reducing the reducing agent ratio. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2021 / 107091 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology described in Patent Document 1 leaves room for further improvement in terms of CO2 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 provide a method for operating a blast furnace that can further reduce CO2 gas emissions compared to conventional techniques. [Means for solving the problem]

[0009] The gist of the present invention is as follows. (1) CO2 gas and H2O gas are separated and removed from the top exhaust gas to generate reformed top circulation gas. In the method for operating a blast furnace, the reformed furnace top circulating gas is injected into the blast furnace through a shaft tuyere, A method for operating a blast furnace, characterized in that cracking gas produced by cracking an NH3-containing gas is injected into the blast furnace through a normal tuyere. (2) The method for operating a blast furnace according to (1), wherein the NH3-containing gas is NH3 gas. (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 amount of the reforming furnace top circulating gas injected into the blast furnace was 350 Nm 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 1 / t-pig or more. (5) The amount of cracking gas injected into the blast furnace was 350 Nm 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 1 / t-pig or more. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for operating a blast furnace that can further reduce CO2 gas emissions compared to conventional techniques. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a flow diagram showing the overall configuration of a blast furnace system used in this embodiment. [Figure 2] 10 is a graph verifying the effect of this embodiment. [Figure 3] 10 is a graph verifying the effect of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[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. Overall configuration of the blast furnace system> 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, a CO2 separation and capture 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 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 oxygen-enriched gas are blown into the blast furnace 10 through the normal tuyere 11. Furthermore, as described below, cracking gas (a mixed gas containing N2 gas and H2 gas obtained by cracking (pyrolyzing) NH3-containing gas) is also blown into the blast furnace 10 through 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. This results in the hot air becoming bosh gas, primarily composed of H2 gas, CO gas, and N2 gas. The bosh gas and cracking gas rise within the blast furnace 10, heating and reducing the iron-based raw materials. More specifically, the H2 gas and CO gas in the bosh gas and cracking gas reduce the iron-based raw materials. These gases are then discharged from the top of the blast furnace as furnace top exhaust gas. The furnace top exhaust gas contains unreacted H2 gas and CO gas, as well as CO2 gas, H2O gas, and N2 gas. As the iron-based raw materials descend within the blast furnace 10, they are heated and reduced by the bosh gas and cracking gas. The iron-based raw materials then melt and drip down the blast furnace 10 while being further reduced by coke. The iron-based raw materials ultimately accumulate 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.

[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 furnace top recirculating gas (RBFG) obtained by reforming furnace 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] The CO2 separation and capture unit 20 recovers the top flue gas and separates CO2 gas and H2O gas from the top flue gas to generate RBFG. Here, the CO2 separation and capture unit 20 does not necessarily recover the entire amount of the top flue gas. For example, the CO2 separation and capture unit 20 may recover only an 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, and examples include chemical adsorption and physical adsorption (PSA). The separated CO2 gas and H2O gas are discharged outside the system.

[0018] The buffer tank 30 is a tank that temporarily stores 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 (about 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 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 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 section 10b of the blast furnace 10 from the shaft section tuyere 12. In FIG. 1 , RBFG is injected into the blast furnace 10 from the shaft section tuyere 12 on the left side, but RBFG may also be injected into the blast furnace 10 from the shaft section tuyere 12 on the right side (not shown). RBFG may be injected into the blast furnace 10 from both the normal tuyere 11 and the shaft section tuyere 12, or may be injected into the blast furnace 10 from the normal tuyere 11.

[0021] RBFG injection amount into blast furnace 10 (Nm 3 / t-pig) may be arbitrarily set depending on the operating conditions of the blast furnace 10, but as will be shown in the examples described later, the CO2 emission reduction rate increases as the amount of RBFG injected into the blast furnace 10 increases. In the examples, the amount of RBFG injected into the blast furnace 10 is set to 350 Nm 3 / t-pig or more, the CO2 emission reduction rate is greater than when H2 gas is normally injected into the blast furnace 10 from the tuyere 11. Therefore, the amount of RBFG injected into the blast furnace 10 is 350 Nm 3 It is preferable that it 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 it is / 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 stores NH3 in a liquid state. NH3 has a higher boiling point and is more stable than H2, so it can be easily liquefied and stored. Liquefaction also increases the density of NH3. Since H2 gas is produced by cracking NH3 gas, a large amount of H2 gas can be easily transported to a blast furnace. That is, in this embodiment, H2 gas is transported as liquid ammonia. The liquid ammonia tank 70 supplies liquid NH3 to the cracking device 71 as an NH3-containing gas. NH3 may also be stored in a gaseous state.

[0024] The cracking device 71 generates cracking gas, i.e., a mixed gas containing N2 gas and H2 gas, by cracking NH3-containing gas. 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, for example, a temperature similar to that of hot air (e.g., about 1200°C). The heater 72 can be sufficiently realized by an electric heater or the like. This makes it possible to suppress a decrease 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 injected into the blast furnace 10 from the tuyere 11. The injection amount of cracking gas (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 set to / t-pig or higher.

[0025] The cracking gas is preferably a gas in which the H concentration in volume fraction of the gas injected into the blast furnace 10 from the tuyere 11 is 70% or more. The cracking gas is a gas obtained by thermal decomposition of an NH3-containing gas, and is not limited by the decomposition rate of NH3.

[0026] As mentioned above, cracking gas has sensible heat, so it may be injected into the blast furnace 10 as is without heating it. Even in this case, the blast furnace 10 can be operated without significantly changing the environment inside the furnace. However, since the temperature of cracking gas (particularly the temperature of N2 gas) is lower than that of hot air, injecting excessive cracking gas into the blast furnace may result in an excessive drop in the tuyere combustion temperature, which may make the operational design unrealistic. For this reason, when room temperature cracking gas is injected into the blast furnace 10, it is recommended to inject the cracking gas within a range where blast furnace operation can be maintained (for example, 700 Nm 3 The amount of cracking gas injected can be adjusted to the temperature (below 1 / t-pig). Note that room temperature generally means a temperature between 25°C and 30°C.

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

[0028] Meanwhile, the liquid ammonia tank 70 supplies liquid NH3 to the cracking device 71 as an NH3-containing gas. The cracking device 71 generates cracking gas, i.e., a mixed gas containing N2 gas and H2 gas, by cracking the NH3-containing gas. 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, for example, and may be set to a temperature similar to that of hot air (e.g., approximately 1200°C). The heated cracking gas is then blown into the blast furnace 10 from the normal tuyere 11. Furthermore, since the decomposition temperature of NH3 gas is 950°C, the cracking gas may be blown into the blast furnace 10 from the cracking device 71 without passing through the heater 72, while being maintained at approximately 950°C, the decomposition temperature of NH3.

[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. 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). This causes the hot air to become bosh gas, primarily composed of H2 gas, CO gas, and N2 gas. The bosh gas and cracking gas ascend within the blast furnace 10, heating and reducing the iron-based raw materials. More specifically, the H2 gas and CO gas in the bosh gas and cracking gas reduce the iron-based raw materials. These gases are then discharged from the top of the blast furnace as furnace top flue gas. The furnace top flue gas contains unreacted H2 gas and CO gas, as well as CO2 gas, H2O gas, and N2 gas. The iron-based raw materials are heated and reduced by the bosh gas and cracking gas while descending within the blast furnace 10. The iron-based raw materials are then melted and further reduced by coke as they drip inside the blast furnace 10. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing just under 5% by mass of carbon. The molten pig iron in the hearth is then removed from the tap hole and used in the next steelmaking process.

[0030] The top flue gas is introduced into a CO2 separation and capture unit 20. The CO2 separation and capture unit 20 recovers the top flue gas and separates and removes CO2 gas and H2O gas from the top flue gas to generate RBFG. A buffer tank 30 temporarily stores the RBFG. A desired amount of RBFG is introduced from the buffer tank 30 into a compressor 40.

[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 (about 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] RBFG injection amount into blast furnace 10 (Nm 3 / t-pig) may be arbitrarily set depending on the operating conditions of the blast furnace 10, but as will be shown in the examples described later, the CO2 emission reduction rate increases as the amount of RBFG injected into the blast furnace 10 increases. In the examples, the amount of RBFG injected into the blast furnace 10 is set to 350 Nm 3 / t-pig or more, the CO2 emission reduction rate is greater than when H2 gas is normally injected into the blast furnace 10 from the tuyere 11. Therefore, the amount of RBFG injected into the blast furnace 10 is 350 Nm 3 It is preferable that it 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 it is / t-pig or less.

[0035] As described above, according to this embodiment, a mixed gas containing H gas and N gas produced by cracking an NH3-containing gas is injected into the blast furnace from the normal tuyere 11. As described below, this reduces CO2 gas emissions compared to when H2 gas is simply injected into the blast furnace 10 from the normal tuyere 11. Furthermore, NH3 has a higher boiling point and is more stable than H2, so it can be easily liquefied and stored. Furthermore, liquefaction can increase the density of NH3. Furthermore, because H2 gas is produced by cracking NH3 gas, large amounts of H2 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, NH3 gas (purity 100%) is described as the NH3-containing gas, but this is not limiting. For example, the NH3-containing gas may be a mixed gas containing NH3 as the main component (NH3 content of 50 vol% or more). [Example]

[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 divides the internal region of a blast furnace in the height direction, radial direction, and circumferential direction to define a plurality of meshes (small regions), and simulates the behavior of each mesh.

[0039] The blast furnace operations assumed were base operation (operation without H gas injection), H gas injection operation (comparison example) in which high-temperature (800°C) H gas is injected into the blast furnace 10 through the normal tuyere 11, and cracking gas injection operation (example) in which cracking gas is injected into the blast furnace 10 through the normal tuyere 11. Pure NH was used as the NH-containing gas. The specifications common to each operation are as follows:

[0040] The distribution of the iron-based raw materials and coke charged from the furnace top was assumed to be constant. The CO2 separation and capture device 20 was designed to separate and remove 100% of the CO2 gas and H2O gas contained in the furnace top exhaust gas. The iron production rate and hot metal temperature were set at 12,350 t / d and 1,535°C. Furnace heat adjustment (adjustment of molten iron temperature) was carried out by adjusting the pulverized coal ratio and coke ratio. Other specifications are shown in Table 1 below.

[0041] [Table 1]

[0042] The results are shown in Figures 2 and 3. Figure 2 shows the RBFG injection rate (Nm 3 / t-pig) and the furnace top exhaust gas temperature (℃), and Fig. 3 shows the correlation between the RBFG injection rate (Nm 3 2 shows the correlation between the amount of RBFG injected (Nm m ) and the CO2 emission reduction rate (%) in the blast furnace. 3 3 is a plot (graph) showing the correlation between the amount of RBFG injected (Nm / t-pig) and the furnace top exhaust gas temperature (°C), and "●" indicates the furnace top exhaust gas temperature when 800°C H2 gas is injected into the blast furnace 10 from the normal tuyeres 11 while RBFG is being injected. "▲" in Fig. 3 indicates the amount of RBFG injected (Nm / t-pig) when 900°C cracking gas is injected into the blast furnace 10 from the normal tuyeres 11 while RBFG is being injected. 3 This is a plot (graph) showing the correlation between the CO2 emission reduction rate (%) in the blast furnace when 800°C H2 gas is injected into the blast furnace 10 through the normal tuyeres 11 while RBFG is being injected. The CO2 emission reduction rate (%) in the blast furnace 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 iron (kg / t-pig). The numbers in parentheses in each plot in Figure 2 are the oxygen enrichment rate (%).

[0043] As shown in Figure 3, in the example, the CO2 emission reduction rate increased as the RBFG injection rate increased, and when the RBFG injection rate was 350 Nm 3When the RBFG injection rate is 1 / t-pig or more, the CO2 emission reduction rate is greater than when H2 gas is normally injected into the blast furnace 10 from the tuyere 11 (circled area in Figure 3). However, the more the RBFG injection rate increases, the higher the furnace top exhaust gas temperature becomes (circled area in Figure 2). From the viewpoint of stable operation of the blast furnace, it is preferable that the furnace top exhaust gas temperature is 160°C or less. Therefore, the RBFG injection rate is set to 400 Nm 3 / t-pig or lower 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. [Explanation of symbols]

[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 tuyere 20 CO2 separation and capture equipment 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 Separating and removing O gas to generate reforming furnace top circulation gas; In the method for operating a blast furnace, the reformed furnace top circulating gas is injected into the blast furnace through a shaft tuyere, NH ３ The cracking gas produced by cracking the contained gas is injected into the blast furnace through a normal tuyere; The amount of the reformed furnace top circulating gas injected into the blast furnace is 350 Nm 3 / t-pig or more; A method for operating a blast furnace, characterized in that the amount of cracking gas injected into the blast furnace is 350 Nm 3 / t-pig or more.

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. 2. The method for operating a blast furnace according to claim 1, wherein the cracking gas is heated before being injected into the blast furnace.

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