Blast furnace operation method

Abstract

To provide a method for operating a blast furnace with which Input▵C can efficiently be lowered.SOLUTION: The gist of the present invention is as follows. (1) A method for operating a blast furnace in which a mixed reducing gas containing at least a hydrogen-based reducing gas and a CO gas is injected into the blast furnace. A simulation of blast furnace operation is performed to obtain a relation between CO / (CO+H2) and a reduction rate of a carbon consumption basic unit in the blast furnace, and a composition of the mixed reducing gas is adjusted based on the relation, wherein CO represents a volume% of the CO gas contained in the mixed reducing gas, and H2 represents a volume% of the hydrogen-based reducing gas contained in the mixed reducing gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace. [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 is one of the major industries in terms of CO2 gas emissions, and it must respond to this social demand. 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 hydrogen gas together with hot air from the tuyere is known, as disclosed in Patent Document 1. In this technique, hydrogen gas is used as a reducing gas for the iron-based raw materials, thereby reducing the reducing agent ratio. [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] As disclosed in Patent Document 1, the present inventors have defined a parameter called the reduction rate of carbon consumption intensity (Input △C) as a parameter that serves as an index for reducing the reducing agent rate. "Carbon consumption intensity (Input C)" is the carbon required to produce one ton of molten iron (i.e., the amount of carbon consumed per ton of molten iron). "Reduction rate of carbon consumption intensity Input △C" means the reduction rate of carbon consumption intensity compared to base operation, which is operation without hydrogen gas injection. If Input C of base operation in units of kg / t is A and Input C during a certain operation in units of kg / t is B, Input △C can be expressed by the following formula. Input △C=(AB) / A×100(%) The larger the reduction rate of carbon consumption intensity, Input △C, the more the reducing agent rate is reduced, and ultimately the amount of CO2 emissions is reduced.

[0008] Although the reduction reaction of iron-based raw materials using hydrogen gas proceeds very quickly, it is an endothermic reaction. Therefore, simply injecting hydrogen gas into a blast furnace requires the use of a large amount of carbon to maintain the furnace temperature, which may actually decrease the input ΔC. On the other hand, CO gas is known as a reducing gas commonly used in blast furnace operation. Since most reduction reactions using CO gas are exothermic, they rarely decrease the furnace temperature. Although the reaction rate is slower than that of hydrogen gas, this does not pose any particular problems. However, because CO gas contains carbon, it contributes little to reducing the input ΔC. Furthermore, after detailed studies of blast furnace operation, the inventors found that nitrogen gas also affects the input ΔC. This is likely due to the significant impact of the sensible heat of nitrogen gas.

[0009] Therefore, in order to efficiently reduce the Input ΔC, it is necessary to set the compositions of the hydrogen gas, CO gas, and nitrogen gas injected into the blast furnace within appropriate ranges, but such knowledge has not been available in the past.

[0010] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a method for operating a blast furnace that can more efficiently reduce Input ΔC. [Means for solving the problem]

[0011] The gist of the present invention is as follows. (1) A method for operating a blast furnace, comprising injecting a mixed reducing gas containing at least a hydrogen-based reducing gas and a CO gas into the blast furnace, A simulation of blast furnace operation is performed to determine the relationship between CO / (CO+H) (CO: volume % of the CO gas contained in the mixed reducing gas, H: volume % of the hydrogen-based reducing gas contained in the mixed reducing gas) and a reduction rate of carbon consumption intensity in the blast furnace, A method for operating a blast furnace, comprising adjusting the composition of the mixed reducing gas based on the relationship. (2) the mixed reducing gas contains nitrogen gas, The method for operating a blast furnace according to (1), characterized in that the volume percentage of the nitrogen gas contained in the mixed reducing gas is adjusted based on the value of CO / (CO+H), or the value of CO / (CO+H) is adjusted based on the volume percentage of the nitrogen gas contained in the mixed reducing gas. (3) The method for operating a blast furnace according to (2), characterized in that when the volume percentage of the nitrogen gas contained in the mixed reducing gas is 5 volume percent or less, CO / (CO+H2) is set to 0.3 or more. (4) The method for operating a blast furnace according to (2), characterized in that when the volume percentage of the nitrogen gas contained in the mixed reducing gas is 20 volume % or more and 30 volume % or less, CO / (CO+H2) is set to 0.2 or more. (5) The method for operating a blast furnace according to (2), characterized in that when the volume percentage of the nitrogen gas contained in the mixed reducing gas is 45 volume % or more and 55 volume % or less, CO / (CO+H2) is set to an arbitrary value. (6) The method for operating a blast furnace according to any one of (1) to (5), wherein the mixed reducing gas is injected into the blast furnace from a normal tuyere or a shaft tuyere. [Effects of the Invention]

[0012] According to the present invention, Input ΔC can be reduced more efficiently. [Brief explanation of the drawings]

[0013] [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. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] <1. Overall configuration of the blast furnace system> 1, a description will be given of the overall configuration of a blast furnace system 1 according to this embodiment and a mixed reducing gas supply system 2 connected to the blast furnace system 1. The blast furnace system 1 includes a blast furnace 10, a CO2 separation and capture device 20, a buffer tank 30, a compressor 40, a heater 50, and a flow meter 61.

[0016] The blast furnace 10 includes a blast furnace body 10a and a normal tuyere 11. 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 enriched oxygen gas are blown into the blast furnace 10 from the normal tuyere 11. In the following description, the "tuyere tip combustion temperature" refers to the temperature at the gas outlet of the normal tuyere 11. The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace 10 to generate high-temperature reducing gas (mainly CO gas). In other words, the hot air gasifies the coke and pulverized coal. In some cases, pulverized coal is not blown into the blast furnace 10, as will be described in detail later. The reducing gas rises within the blast furnace 10 and reduces the iron-based raw materials while heating them. The iron-based raw materials are heated and reduced by reducing gas while descending through the blast furnace 10. The iron-based raw materials then melt and drip through the blast furnace 10 while being further reduced by coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing just under 5% by mass of carbon. The molten pig iron in the hearth is removed from the taphole and used in the next steelmaking process.

[0017] The tuyere 11 is usually provided at the bottom of the blast furnace 10, and in addition to the hot air mentioned above, a heated mixed reducing gas is blown into the blast furnace 10 as will be described later.

[0018] The CO2 separation and capture device 20 is a device that recovers top flue gas and separates it into reducing gas (CO gas and hydrogen gas) and nitrogen gas, and CO2 gas and HO gas. The separation method is not particularly limited, and examples include chemical adsorption and physical adsorption (PSA). In the following description, the reducing gas and nitrogen gas separated from the top flue gas are also referred to as RBFG (Returned Blast Furnace Gas). CO2 gas and HO gas are discharged outside the system. The CO2 separation and capture device 20 does not necessarily recover the entire amount of top flue gas. For example, the CO2 separation and capture device 20 may recover only an amount of top flue gas corresponding to the flow rate of RBFG injected into the blast furnace.

[0019] 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. The remaining RBFG is used, for example, as a heat source in a steel mill. The composition of the RBFG stored in the buffer tank 30 (volume percentage of each gas) is measured, for example, by gas chromatography.

[0020] 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.

[0021] The heater 50 heats the RBFG. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. The heater 50 can be sufficiently realized by an electric heater or the like. The RBFG heated by the heater 50 is mixed with an external mixed reducing gas, which will be described later, to form a mixed reducing gas, which is then injected into the blast furnace 10 from the normal tuyere 11. In FIG. 1 , the mixed reducing gas is injected into the blast furnace 10 from the normal tuyere 11 on the left side, but the mixed reducing gas may also be injected into the blast furnace 10 from the normal tuyere 11 on the right side. The heater 50 may be omitted. Furthermore, the RBFG does not have to be injected into the blast furnace 10. In this case, an external mixed reducing gas, which will be described later, is injected into the blast furnace 10.

[0022] The flow meter 61 normally measures the flow rate of the RBFG injected into the blast furnace 10 from the tuyere 11. In this embodiment, by adjusting the flow rate of the RBFG introduced from the buffer tank 30 to the compressor 40, the flow rate of the RBFG normally injected into the blast furnace 10 from the tuyere 11 can be adjusted as desired.

[0023] The mixed reducing gas supply system 2 includes a hydrogen-based reducing gas tank 70a, a CO gas tank 70b, a nitrogen gas tank 70c, flow meters 71a to 71c, and a heater 71. The mixed reducing gas supply system 2 is a system that supplies an external mixed reducing gas to the blast furnace system 1 from outside the blast furnace system 1.

[0024] The hydrogen-based reducing gas tank 70a is a tank that stores a hydrogen-based reducing gas and can supply a desired amount of the hydrogen-based reducing gas to the heater 72. Here, the hydrogen-based reducing gas is a concept that includes not only hydrogen gas but also a mixed gas of hydrogen gas and another gas (such as a noble gas) (which does not impair the effects of this embodiment).

[0025] The CO gas tank 70b is a tank that stores CO gas and can supply a desired amount of CO gas to the heater 72. The nitrogen gas tank 70c is a tank that stores nitrogen gas and can supply a desired amount of nitrogen gas to the heater 72. In this embodiment, at least a hydrogen-based reducing gas and CO gas are supplied to the heater 72.

[0026] The flow meter 71a measures the flow rate of the hydrogen-based reducing gas supplied to the heater 72. The flow meter 71b measures the flow rate of CO gas supplied to the heater 72. The flow meter 71c measures the flow rate of nitrogen gas supplied to the heater 72. The gases discharged from each tank are mixed to form an external mixed reducing gas, which is then introduced into the heater 72. The external mixed reducing gas contains at least a hydrogen-based reducing gas and CO gas. The external mixed reducing gas may further contain nitrogen gas. The heater 72 heats the external mixed reducing gas. The heating temperature is set arbitrarily depending on the operating conditions of the blast furnace 10. The heater 72 can be sufficiently realized by an electric heater or the like. The external mixed reducing gas heated by the heater 72 is mixed with RBFG to form a mixed reducing gas, which is then usually injected into the blast furnace 10 through the tuyere 11. The heater 72 may be omitted.

[0027] <2. Blast furnace operation method> Next, a method for operating a blast furnace will be described. First, the specifications of base operation (operation without injecting external mixed reducing gas into the blast furnace 10) are determined, and a simulation of blast furnace operation is performed based on these specifications to determine Input C. Here, an example of the simulation model 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 roughly divides the internal region of the blast furnace in the vertical, radial, and circumferential directions to define multiple meshes (small regions), and simulates the behavior of each mesh.

[0028] Next, a simulation of blast furnace operation is performed by arbitrarily changing the composition of the external mixed reducing gas and the amount of RBFG injected (i.e., by arbitrarily changing the composition of the mixed reducing gas), and the Input C at this time is calculated. The relationship between CO / (CO+H2) (CO: volume % of CO gas contained in the mixed reducing gas (volume % relative to the total volume of the mixed reducing gas), H2: volume % of hydrogen-based reducing gas contained in the mixed reducing gas (volume % relative to the total volume of the mixed reducing gas) and the reduction rate of carbon consumption intensity in the blast furnace (i.e., Input △C) is calculated. An example of the results is shown in Figure 2. The horizontal axis of Figure 2 shows CO / (CO+H2) of the mixed reducing gas, and the vertical axis shows the blast furnace carbon reduction effect, i.e., Input △C (%). Graph L1 shows the relationship between CO / (CO+H2) and Input ΔC when the volume percent of nitrogen gas contained in the mixed reducing gas (volume percent relative to the total volume of the mixed reducing gas) is 0 volume percent, graph L2 shows the relationship between CO / (CO+H2) and Input ΔC when the volume percent of nitrogen gas contained in the mixed reducing gas is 25 volume percent, and graph L3 shows the relationship between CO / (CO+H2) and Input ΔC when the volume percent of nitrogen gas contained in the mixed reducing gas is 50 volume percent. In particular, as shown in graph L1, when the volume percent of nitrogen gas is 0 volume percent, if CO / (CO+H2) is low (i.e., if a lot of hydrogen gas is injected into the blast furnace 10), it can be seen that Input ΔC actually becomes lower.

[0029] Next, the composition of the reducing gas mixture is adjusted based on the above relationship. Specifically, the composition of the reducing gas mixture is adjusted so that the Input ΔC reaches a target value. For example, the volume percentage of nitrogen gas contained in the reducing gas mixture is adjusted based on the value of CO / (CO+H2), or the value of CO / (CO+H2) is adjusted based on the volume percentage of nitrogen gas contained in the reducing gas mixture. This makes it possible to more efficiently reduce the Input ΔC. Furthermore, favorable results are obtained in terms of the reaction rate and reaction heat.

[0030] If the results shown in Figure 2 are obtained, it is preferable to carry out the following process. That is, when the volume percent of the nitrogen gas contained in the mixed reducing gas is 5 volume percent or less, it is preferable to set CO / (CO+H2) to 0.3 or more (graph L1). This makes it possible to more efficiently reduce the Input ΔC.

[0031] When the volume percent of the nitrogen gas contained in the mixed reducing gas is 20 volume percent or more and 30 volume percent or less, it is preferable to set CO / (CO+H2) to 0.2 or more (graph L2), which makes it possible to more efficiently reduce the input ΔC.

[0032] When the volume percent of the nitrogen gas contained in the mixed reducing gas is 45 volume percent or more and 55 volume percent or less, it is preferable to set CO / (CO+H2) to an arbitrary value (graph L3). This makes it possible to more efficiently reduce the input ΔC. By performing the above process, a good input ΔC can be obtained regardless of the volume percent of nitrogen gas.

[0033] In actual operation, the actual operation is carried out based on the composition of the mixed reducing gas determined by the above-mentioned method in addition to the specifications of the base operation.

[0034] In the above-described embodiment, RBFG and the external mixed reducing gas are injected into the blast furnace 10 through the normal tuyere 11. However, for example, a shaft tuyere may be provided in the shaft section, and the RBFG and the external mixed reducing gas may be injected into the blast furnace 10 through the shaft tuyere. Alternatively, the injection location of the RBFG and the injection location of the external mixed reducing gas may be different. For example, RBFG may be injected into the blast furnace 10 through the shaft section, and the external mixed reducing gas may be injected into the blast furnace 10 through the normal tuyere 11. In this case, too, the sum of RBFG and the external mixed reducing gas is defined as the mixed reducing gas, and the composition of the mixed reducing gas (in other words, the amount of RBFG injected and the composition of the external mixed reducing gas) is determined by the above-described method. In addition, in the above-described embodiment, the furnace top flue gas is circulated as RBFG, but the furnace top flue gas may be discharged to the outside without being circulated. [Example]

[0035] <1.Main specifications> Hydrogen gas was used as the hydrogen-based reducing gas. The distribution of the iron-based raw materials and coke charged from the furnace top was assumed to be constant. Pulverized coal injection was not performed. 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. The furnace top exhaust gas temperature was set to around 135°C to be the same as in normal operation. The tuyere combustion temperature was left free. Furnace heat adjustment (adjustment of molten iron temperature) was carried out by adjusting the coke ratio. The amounts of hot air and oxygen blown in were adjusted so that the above preconditions were met. The hot air blowing temperature was kept constant at 1300℃, and the RBFG blowing temperature was kept constant at 1000℃. The flow rate of the external mixed reducing gas is 400Nm 3 It was kept constant at / t. The volume percentage of nitrogen gas contained in the mixed reducing gas was set to 0 volume%, 25 volume%, or 50 volume%.

[0036] Based on the above main parameters, blast furnace operation was simulated by arbitrarily changing the composition of the external mixed reducing gas and the amount of RBFG injected (i.e., arbitrarily changing the composition of the mixed reducing gas), and the resulting Input C was calculated. The simulation model for blast furnace operation was a so-called "blast furnace mathematical model" as shown, for example, 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. Meanwhile, Input C for base operation (operation without external mixed reducing gas injected into the blast furnace 10) was calculated, and Input ΔC was calculated. The relationship between CO / (CO + H2) (CO: volume % of CO gas contained in the mixed reducing gas, H2: volume % of hydrogen-based reducing gas contained in the mixed reducing gas) and the reduction rate of carbon consumption intensity in the blast furnace (i.e., Input ΔC) was then calculated. As a result, the relationship shown in Figure 2 was obtained. Therefore, it became clear that the Input ΔC can be reduced more efficiently by carrying out the above-mentioned processing.

[0037] Furthermore, when pulverized coal is injected, higher oxygen enrichment operation is required than in base operation, which further reduces the amount of heat transfer medium (nitrogen gas). For this reason, it becomes even more important to control the distribution behavior of hydrogen-based reducing gas and CO gas.

[0038] 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]

[0039] 1 Blast Furnace System 2. External mixed reducing gas supply system 10 blast furnace 10a Blast furnace body 11 Normal tuyere 20 CO2 separation and capture equipment 30 Buffer Tank 40 Compressor 50, 72 heater 61, 71a~71c flow meter 70a Hydrogen-based reducing gas tank 70b CO gas tank 70c Nitrogen Gas Tank

Claims

1. A method for operating a blast furnace, comprising injecting a mixed reducing gas containing at least a hydrogen-based reducing gas and a CO gas into the blast furnace, Simulation of blast furnace operation was carried out, and CO / (CO + H ２ ) (CO: volume % of the CO gas contained in the mixed reducing gas, H ２ : determining the relationship between the volume % of the hydrogen-based reducing gas contained in the mixed reducing gas and the reduction rate of the carbon consumption intensity in the blast furnace, A method for operating a blast furnace, comprising adjusting the composition of the mixed reducing gas based on the relationship.

2. the mixed reducing gas contains nitrogen gas, CO / (CO+H ２ ), or adjust the volume percentage of the nitrogen gas contained in the mixed reducing gas based on the volume percentage of the nitrogen gas contained in the mixed reducing gas. ２ 2. The method of operating a blast furnace according to claim 1, wherein the value of .lambda.

3. When the volume percent of the nitrogen gas contained in the mixed reducing gas is 5 volume percent or less, the CO / (CO+H ２ 3. The method for operating a blast furnace according to claim 2, wherein the ratio of the total number of blast furnaces to the total number of blast furnaces is 0.3 or more.

4. When the volume percentage of the nitrogen gas contained in the mixed reducing gas is 20 volume percent or more and 30 volume percent or less, CO / (CO+H ２ 3. The method for operating a blast furnace according to claim 2, wherein the ratio of the total number of blast furnaces to the total number of blast furnaces is 0.2 or more.

5. When the volume percentage of the nitrogen gas contained in the mixed reducing gas is 45 volume percent or more and 55 volume percent or less, CO / (CO+H ２ 3. The method for operating a blast furnace according to claim 2, wherein the value of the temperature is set to any value.

6. The method for operating a blast furnace according to any one of claims 1 to 5, characterized in that the mixed reducing gas is injected into the blast furnace from a normal tuyere or a shaft tuyere.

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