JP7817658B2 - Blast furnace operation method - Google Patents

Description

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.

In the steel industry, the blast furnace method is the mainstream process for producing pig iron. In this method, ferrous raw materials (raw materials containing iron oxide, primarily sintered ore; hereafter simply referred to as "ferrous 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 furnace from tuyere openings at the bottom. The hot air reacts with the pulverized coal blown in 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 ferrous raw materials. As the ferrous raw materials descend within the blast furnace, they are heated and reduced by the reducing gas. The ferrous raw 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.

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

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. Therefore, in order to reduce the reducing agent ratio, it is necessary to increase the reduction efficiency in the furnace. The reduction reactions in the furnace can be expressed by various reaction formulas. Among these reduction reactions, the direct reduction reaction by coke (reaction formula: FeO + C ⇒ Fe + CO) is an endothermic reaction accompanied by a large heat absorption. Therefore, minimizing the occurrence of this reaction is important in reducing the reducing agent ratio. Because this direct reduction reaction occurs in the lower part of the blast furnace, if the iron-based raw materials can be sufficiently reduced with reducing gases such as CO and _H2 before reaching the lower part of the furnace, the amount of iron-based raw materials subject to the direct reduction reaction can be reduced.

As a conventional technique for solving the above problem, for example, a technique disclosed in Patent Document 1 is known in which _H2 gas is blown together with hot air from the tuyere to increase the reducing gas potential in the furnace. In this technique, _H2 gas is used as a reducing gas for the iron-based raw material, thereby reducing the reducing agent ratio.

International Publication No. 2021/107091

However, the technology described in Patent Document 1 leaves room for further improvement in terms of _CO2 gas emissions.

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.

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 a 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 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 method for operating a blast furnace according to any one of (1) to (3), characterized in that the amount of the reformed furnace top circulating gas injected into the blast furnace is 350 Nm ³ /t-pig or more.
(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 Nm ³ /t-pig or more.

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.

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

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

<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.

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 alternately and in layers into the blast furnace 10 from the top of the blast furnace 10, while hot air, pulverized coal, and enriched oxygen gas are blown into the blast furnace 10 from the normal tuyere 11. Furthermore, as described below, cracking gas (a mixed gas containing _N2 gas and _H2 gas obtained by cracking (thermally decomposing) _NH3 -containing gas) is also blown into the blast furnace 10 from the normal tuyere 11. In the following description, the "tuyere tip combustion temperature" refers to the temperature at the gas outlet of the normal tuyere 11. The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace 10 to generate high-temperature reducing gas (mainly CO gas). 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. As a result, the hot air becomes bosh gas, mainly 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 flue gas. The furnace top flue gas contains unreacted _H2 gas and CO gas as well as _CO2 gas, _H2O gas, and _N2 gas. While descending within the blast furnace 10, the iron-based raw materials are heated and reduced by the bosh gas and cracking gas. The iron-based raw materials then melt and drip down within the blast furnace 10 while being further reduced by the coke. The iron-based raw materials are eventually stored in the hearth as molten pig iron (pig iron) containing just under 5% by mass of carbon. The molten pig iron in the hearth is removed from the tap hole and used in the subsequent steelmaking process.

Normal tuyere 11 is installed below the bosh section of blast furnace 10, and in addition to the hot air described above, heated cracking gas is blown into blast furnace 10 as described below. Note that some or all of the hot air may be replaced with cracking gas. Note that while normal tuyere 11 is shown only at both ends of blast furnace 10 in Figure 1, three or more normal tuyere may be installed around the circumference of blast furnace 10.

The shaft tuyere 12 is provided in the shaft 10b of the blast furnace 10 and injects reformed top recirculating gas (RBFG), which is reformed top exhaust gas, into the shaft 10b of the blast furnace 10. Although the shaft tuyere 12 is shown only on the left side of the shaft 10b in Figure 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.

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.

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

The compressor 40 pressurizes the RBFG. Here, the compressor 40 pressurizes the RBFG, for example, to the internal pressure of the blast furnace 10 (approximately 4.5 atmospheres). The pressurized RBFG is introduced into the heater 50.

The heater 50 heats the RBFG. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. For example, when RBFG is injected into the shaft section 10b of the blast furnace 10 through the shaft section tuyere 12, it is preferable to set the temperature to 800°C or higher. The heater 50 can be implemented as 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 through the shaft section tuyere 12. In FIG. 1, RBFG is injected into the blast furnace 10 through 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 through both the normal tuyere 11 and the shaft section tuyere 12, or it may be injected into the blast furnace 10 through the normal tuyere 11.

The amount of RBFG injected into the blast furnace 10 (Nm ³ /t-pig) may be set arbitrarily depending on the operating conditions of the blast furnace 10, but as shown in the examples described below, the CO ₂ emission reduction rate increases as the amount of RBFG injected into the blast furnace 10 increases. In the examples, when the amount of RBFG injected into the blast furnace 10 is 350 Nm ³ /t-pig or more, the CO ₂ emission reduction rate is greater than when H ₂ gas is normally injected into the blast furnace 10 from the tuyere 11. Therefore, it is preferable that the amount of RBFG injected into the blast furnace 10 is 350 Nm ³ /t-pig or more.

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 lead to instability in the operation of the blast furnace 10. From this viewpoint, it is preferable that the amount of RBFG injected into the blast furnace 10 is 400 Nm ³ /t-pig or less.

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. Note that _NH3 may also be stored in a gaseous state.

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. Here, 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., approximately 1200°C). The heater 72 can be sufficiently realized by an electric heater or the like. This can suppress a decrease in the tuyere 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 normally connected to the tuyere 11, and the heated cracking gas is normally injected into the blast furnace 10 from the tuyere 11. The amount of cracking gas injected ( ^Nm3 /t-pig) can be set arbitrarily depending on the operating conditions of the blast furnace 10. For example, the amount of cracking gas injected may be 350 Nm ³ /t-pig or more.

The cracking gas is preferably a gas in which the _H2 concentration in the gas injected into the blast furnace 10 from the tuyere 11 is 70% or more by volume fraction. 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 .

As mentioned above, since cracking gas has sensible heat, 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, 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 unfeasible. Therefore, when room temperature cracking gas is injected into the blast furnace 10, the amount of cracking gas injected may be adjusted within a range in which blast furnace operation can be maintained (for example, 700 ^Nm3 /t-pig or less). Room temperature generally means a temperature between 25°C and 30°C.

<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.

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. Here, the heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10, but is preferably, for example, 800°C or higher, 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, which is the decomposition temperature of NH3.

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). As a result, the hot air becomes bosh gas, primarily composed of _H2 gas, CO gas, and _N2 gas. The bosh gas and cracking gas rise within the blast furnace 10 and reduce the iron-based raw materials while heating them. 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 through the blast furnace 10. The iron-based raw materials then melt and drip through the blast furnace 10 while being further reduced by coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is removed from the taphole and is used in the next steelmaking process.

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

The compressor 40 pressurizes the RBFG. Here, the compressor 40 pressurizes the RBFG, for example, to the internal pressure of the blast furnace 10 (approximately 4.5 atmospheres). The pressurized RBFG is introduced into the heater 50.

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

The amount of RBFG injected into the blast furnace 10 (Nm ³ /t-pig) may be set arbitrarily depending on the operating conditions of the blast furnace 10, but as shown in the examples described below, the CO ₂ emission reduction rate increases as the amount of RBFG injected into the blast furnace 10 increases. In the examples, when the amount of RBFG injected into the blast furnace 10 is 350 Nm ³ /t-pig or more, the CO ₂ emission reduction rate is greater than when H ₂ gas is normally injected into the blast furnace 10 from the tuyere 11. Therefore, it is preferable that the amount of RBFG injected into the blast furnace 10 is 350 Nm ³ /t-pig or more.

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 lead to instability in the operation of the blast furnace 10. From this viewpoint, it is preferable that the amount of RBFG injected into the blast furnace 10 is 400 Nm ³ /t-pig or less.

As described above, according to this embodiment, a mixed gas containing _H2 gas and _N2 gas produced by cracking NH3 _- containing gas is injected into the blast furnace from the normal tuyere 11. As described below, this reduces the amount of _CO2 gas emitted compared to when _H2 gas is simply injected into the blast furnace 10 from the normal tuyere 11. Furthermore, since _NH3 has a higher boiling point and is more stable than _H2 , it can be easily liquefied and stored. Furthermore, liquefaction can increase the density of _NH3 . Furthermore, since _H2 gas is produced by cracking _NH3 gas, large amounts of _H2 gas can be easily transported to the blast furnace.

In addition, 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, thereby enabling stable operation of the blast furnace 10.

In this embodiment, _NH3 gas (100% purity) is described as the _NH3- containing gas, but the _NH3 -containing gas is not limited to this. For example, the NH3-containing gas may be a mixed gas containing _NH3 as the main component ( _NH3 content of 50 vol% or more).

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. The simulation model used here is the so-called "blast furnace mathematical model" shown in Kouji Takatani, Takanobu Inada, and Yutaka Ujisawa, "Three-dimensional Dynamic Simulator for Blast Furnace," ISIJ International, Vol. 39 (1999), No. 1, pp. 15-22. This blast furnace mathematical model, broadly speaking, defines multiple meshes (small regions) by dividing the internal region of the blast furnace in the vertical, radial, and circumferential directions, and simulates the behavior of each mesh.

As blast furnace operations, the following were assumed: base operation (operation without _H2 gas injection), _H2 gas injection operation (comparative example) in which high-temperature (800°C) _H2 gas is injected into the blast furnace 10 from the normal tuyere 11, and cracking gas injection operation (example) in which cracking gas is injected into the blast furnace 10 from the normal tuyere 11. Pure _NH3 was used as the _NH3- containing gas. The specifications common to each operation are as follows:

- The distribution of iron-based raw materials and coke charged from the furnace top was kept constant.
The CO ₂ separation and capture device 20 was designed to separate and remove 100% of the CO ₂ gas and H ₂ O gas contained in the furnace top flue gas.
The iron production rate and molten iron temperature were 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 as shown in Table 1 below.

The results are shown in Figures 2 and 3. Figure 2 is a graph showing the correlation between the RBFG injection rate (Nm ³ /t-pig) and the furnace top exhaust gas temperature (°C), and Figure 3 is a graph showing the correlation between the RBFG injection rate (Nm ³ /t-pig) and the CO ₂ emission reduction rate (%) in the blast furnace. In Figure 2, "▲" is a plot (graph) showing the correlation between the RBFG injection rate (Nm ³ /t-pig) and the furnace top exhaust gas temperature (°C) when RBFG is injected while 900°C cracking gas is injected into the blast furnace 10 from the normal tuyere 11, and "●" indicates the furnace top exhaust gas temperature when 800°C H ₂ gas is injected into the blast furnace 10 from the normal tuyere 11 while RBFG is injected. In Figure 3, "▲" is a plot (graph) showing the correlation between the RBFG injection rate ( ^Nm3 /t-pig) and the _CO2 emission reduction rate (%) in the blast furnace when 900°C cracking gas is injected into the blast furnace 10 through the normal tuyere 11 while RBFG is being injected, and "●" indicates the _CO2 emission reduction rate (%) in the blast furnace when 800°C _H2 gas is injected into the blast furnace 10 through the normal tuyere 11 while RBFG is being injected. The _CO2 emission reduction rate (%) in the blast furnace was calculated by (carbon consumption rate in base operation - carbon consumption rate in each case) / carbon consumption rate in base operation x 100. Here, carbon consumption rate is the amount of carbon (kg/t-pig) required to produce 1 ton of molten iron. The value in parentheses in each plot in Figure 2 is the oxygen enrichment rate (%).

As shown in Figure 3, in the example, the _CO2 emission reduction rate increases as the RBFG injection rate increases, and when the RBFG injection rate is 350 ^Nm3 /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 (the circled part in Figure 3). However, the furnace top exhaust gas temperature also increases as the RBFG injection rate increases (the circled part in Figure 2). From the viewpoint of stable operation of the blast furnace, the furnace top exhaust gas temperature is preferably 160°C or less, and therefore the RBFG injection rate is preferably 400 ^Nm3 /t-pig or less.

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

1 Blast furnace system 2 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 (3)

_CO2 gas and _H2O gas are separated and removed from the top exhaust gas to generate a 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,
The cracking gas produced by cracking the _NH3- containing gas is usually injected into the blast furnace through a 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 . The method for operating a blast furnace according to claim 1, wherein the _NH3- containing gas is _NH3 gas. 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.