Operation method of blast furnace

Abstract

To provide an operation method of a blast furnace capable of further decreasing a reducing material ratio.SOLUTION: The gist of the present invention is as follows. In an operation method of a blast furnace, a hydrogen-based reducing gas is blown into the blast furnace, CO2 gas and H2O gas are separated and removed from a furnace top exhaust gas to generate a reforming furnace top circulating gas, and the reformed furnace top circulating gas is blown into the blast furnace. The operation method of a blast furnace includes a determination step of determining a target value of a blowing temperature of the reforming furnace top circulating gas and a target value of a CO2 separation ratio of the furnace top exhaust gas based on a target value of a reducing material ratio, a separation step of separating and removing the CO2 gas and the H2O gas from the top exhaust gas based on the target value of the CO2 separation ratio of the top exhaust gas determined in the determination step, and a blowing step of raising the temperature of the reforming furnace top circulating gas based on the target value of the blowing temperature of the reforming furnace top circulating gas determined in the determination step and blowing the reforming furnace top circulating gas into the blast furnace.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for operating a blast furnace.

Background Art

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

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

[0004] As a technique for reducing the ratio of reducing agent, for example, as disclosed in Patent Documents 1 to 5, a technique has been proposed in which reformed top circulation gas obtained by reforming top gas is blown into a blast furnace from tuyeres in the shaft section of the blast furnace. Since the reformed top circulation gas contains unreacted reducing gas, according to this technique, reduction of the reducing agent ratio can be expected.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the techniques disclosed in Patent Documents 1 to 5, the reducing agent ratio could not be sufficiently reduced. Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an operating method for a blast furnace capable of further reducing the reducing agent ratio.

Means for Solving the Problems

[0007] The inventor of the present invention has examined in detail the technique of blowing reformed top circulation gas into a blast furnace from tuyeres in the shaft section, and has found that there is a correlation between the reducing agent ratio and the blowing temperature of the reformed top circulation gas and the CO2 separation rate. The present invention has been made based on this finding.

[0008] The gist of the present invention is as follows. (1) Inject a hydrogen-based reducing gas into a blast furnace, In an operating method of a blast furnace that separates and removes CO2 gas and H2O gas from the top gas of the furnace to produce a reformed top-circulation gas and injects the reformed top-circulation gas into the blast furnace, A determination step of determining a target value of the injection temperature of the reformed top-circulation gas and a target value of the CO2 separation rate of the top gas based on a target value of the reducing material ratio; A separation step of separating and removing the CO2 gas and the H2O gas from the top gas based on the target value of the CO2 separation rate of the top gas determined in the determination step; A blowing step of heating the reformed top-circulation gas based on the target value of the injection temperature of the reformed top-circulation gas determined in the determination step and injecting it into the blast furnace. The operating method of the blast furnace is characterized by comprising the above steps. (2) Inject the hydrogen-based reducing gas into the blast furnace from a normal tuyere, The operating method of the blast furnace according to (1), characterized in that the reformed top-circulation gas is injected into the blast furnace from a shaft-section tuyere. (3) In the determination step, Create a relationship 1 between the estimated value of the reducing material ratio and the estimated value of the injection temperature of the reformed top-circulation gas for each estimated value of the CO2 separation rate of the top gas, Based on the created relationship 1 and the target value of the reducing material ratio, determine a combination of the target value of the injection temperature of the reformed top-circulation gas and the target value of the CO2 separation rate of the top gas. The operating method of the blast furnace according to (1) or (2) is characterized by this. (4) In the determination step, Create a relationship 2 between the estimated value of the reducing material ratio and the estimated value of the CO2 separation rate of the top gas for each estimated value of the injection temperature of the reformed top-circulation gas, Based on the created relationship 2 and the target value of the reducing material ratio, determine a combination of the target value of the injection temperature of the reformed top-circulation gas and the target value of the CO2 separation rate of the top gas. The operating method of the blast furnace according to (1) or (2) is characterized by this. (5) In the determination step, For each estimated value of the CO2 separation rate of the top gas, create Relationship 3 between the estimated value of the top temperature and the estimated value of the injection temperature of the reformed top circulating gas. Based on the created Relationships 1 and 3, and the target value of the reducing agent ratio and the target value of the top temperature, determine the target value of the injection temperature of the reformed top circulating gas and the target value of the CO2 separation rate of the top gas. The operation method of the blast furnace according to (3) is characterized by this. (6) In the determination step, For each estimated value of the injection temperature of the reformed top circulating gas, create Relationship 4 between the estimated value of the top temperature and the estimated value of the CO2 separation rate of the top gas. Based on the created Relationships 2 and 4, and the target value of the reducing agent ratio and the target value of the top temperature, determine the target value of the injection temperature of the reformed top circulating gas and the target value of the CO2 separation rate of the top gas. The operation method of the blast furnace according to (4) is characterized by this.

Effect of the Invention

[0009] According to the present invention, it is possible to provide an operation method of a blast furnace capable of further reducing the reducing agent ratio.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0012] <1. Overall Configuration of Blast Furnace System> First, based on FIG. 1, the overall configuration of the blast furnace system 1 according to the present embodiment and the hydrogen-based reducing gas supply system 2 connected to the blast furnace system 1 will be described. The blast furnace system 1 includes a blast furnace 10, a CO2 separation and recovery device 20, a buffer tank 30, a compressor 40, and a heater 50.

[0013] The blast furnace 10 includes a blast furnace body 10a, a normal tuyere 11, and a shaft section 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, while charging iron-based raw materials and coke into the blast furnace 10 alternately and in layers from the top of the blast furnace 10, hot air, pulverized coal, and enriched oxygen gas are blown into the blast furnace 10 from the normal tuyere 11. In the following description, the "tuyere tip combustion temperature" shall mean the temperature at the gas outlet of the normal tuyere 11. The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace 10 to generate a high-temperature reducing gas (here mainly CO gas). That is, the hot air gasifies the coke and pulverized coal. Although details will be described later, there may be cases where pulverized coal is not blown into the blast furnace 10. The reducing gas rises in the blast furnace 10 and reduces the iron-based raw materials while heating them. The iron-based raw materials are reduced while descending in the blast furnace 10 and are heated and reduced by the reducing gas. Thereafter, the iron-based raw materials melt and drip in the blast furnace 10 while being further reduced by the coke. The iron-based raw materials are finally stored as hot metal (pig iron) containing less than 5% by mass of carbon in the hearth section. The hot metal in the hearth section is taken out from the taphole and supplied to the next steelmaking process.

[0014] The normal tuyere 11 is provided at the lower part of the blast furnace 10. In addition to the hot air described above, as will be described later, heated hydrogen-based reducing gas or reformed top circulation gas is blown into the blast furnace 10. Although only the normal tuyeres 11 are depicted at both ends of the blast furnace 10 in FIG. 1, three or more may be provided at regular intervals over the circumferential direction.

[0015] The shaft section tuyere 12 is provided in the shaft section 10b of the blast furnace 10, and reformed top circulation gas or hydrogen-based reducing gas obtained by reforming the top exhaust gas is blown into the shaft section 10b of the blast furnace 10. Although only the shaft section tuyere 12 is depicted on the left side of the shaft section 10b in FIG. 1, a shaft section tuyere 12 may also be provided on the right side of the shaft section 10b, and three or more may be provided at regular intervals over the circumferential direction.

[0016] The CO2 separation and recovery device 20 recovers the top-of-furnace exhaust gas, separates and removes CO2 gas and H2O gas from the top-of-furnace exhaust gas, and generates reformed top-of-furnace recycle gas. Here, the CO2 separation and recovery device 20 does not necessarily have to recover the entire amount of the top-of-furnace exhaust gas. For example, the CO2 separation and recovery device 20 may recover only an amount of the top-of-furnace exhaust gas corresponding to the flow rate of the reformed top-of-furnace recycle gas blown into the blast furnace. The remaining top-of-furnace exhaust gas is used as a heat source in the steelworks. The separation method is not particularly limited, and examples include chemical adsorption method and physical adsorption method (PSA), etc. Here, the CO2 separation and recovery device 20 separates and removes CO2 gas and H2O gas from the top-of-furnace exhaust gas based on the target value of the CO2 separation rate determined in the determination process described later. The CO2 separation rate is represented by the following mathematical formula. In the following mathematical formula, the top-of-furnace exhaust gas used in the circulation process means the top-of-furnace exhaust gas actually reformed by the CO2 separation and recovery device 20, that is, the top-of-furnace exhaust gas that becomes the reformed top-of-furnace recycle gas and is circulated to the blast furnace 10. Note that the gas content in the mathematical formula is based on volume. The CO2 content is measured by a gas analyzer such as a gas chromatograph, for example. It is preferable that as much H2O gas as possible is separated.

[0017]

Number

[0018] The separated CO2 gas and H2O gas are discharged outside the system.

[0019] The buffer tank 30 is a tank that temporarily stores the reformed top-of-furnace recycle gas. A desired amount of the reformed top-of-furnace recycle gas is introduced from the buffer tank 30 into the compressor 40.

[0020] The compressor 40 pressurizes the reformed top-of-furnace recycle gas. Here, the compressor 40 pressurizes the reformed top-of-furnace recycle gas to about the internal pressure of the blast furnace 10 (about 4.5 atmospheres), for example. The pressurized reformed top-of-furnace recycle gas is introduced into the heater 50.

[0021] The heater 50 heats the reformer top recycle gas. Here, the heater 50 heats the reformer top recycle gas to the target value of the injection temperature of the reformer top recycle gas determined in the determination step described later. The heater 50 can be sufficiently realized by an electric heater or the like. The reformer top recycle gas heated by the heater 50 is blown into the shaft portion 10b of the blast furnace 10 from the shaft portion tuyere 12. The injection temperature of the reformer top recycle gas is measured by, for example, a thermometer provided at the shaft portion tuyere 12. In FIG. 1, the reformer top recycle gas is blown into the blast furnace 10 from the left shaft portion tuyere 12, but the reformer top recycle gas may also be blown into the blast furnace 10 from the right shaft portion tuyere 12 (not shown).

[0022] The hydrogen-based reducing gas supply system 2 includes a hydrogen-based reducing gas tank 70 and a heater 71. The hydrogen-based reducing gas supply system 2 is a system that supplies hydrogen-based reducing gas from outside the blast furnace system 1 to the blast furnace system 1.

[0023] The hydrogen-based reducing gas tank 70 is a tank for storing hydrogen-based reducing gas. Here, the hydrogen-based reducing gas refers to a gas containing 30 mol% or more of H as an elemental composition ratio in the gas and existing as a gas under standard conditions (0 °C, 1 atm). For example, it is H2 gas, unsaturated hydrocarbon-based gas (C2H4, C2H2, C3H6, etc.), saturated hydrocarbon-based gas (CH4, C2H6, etc.), NH3 gas, coke oven gas, city gas, natural gas, etc., and a mixed gas thereof. Particularly preferably, it is H2 gas or unsaturated hydrocarbon-based gas (C2H4, C2H2, C3H6, etc.). H2 gas does not contain carbon and does not cause a thermal decomposition reaction at the tuyere tip, so it is preferable from the viewpoint of reducing the carbon consumption per unit. Also, since the viscosity and density of the gas are small, it is also preferable from the viewpoint of the air permeability in the blast furnace. Unsaturated hydrocarbon-based gas contains double bonds or triple bonds in the gas molecule, so the heat of combustion per mole of oxygen is relatively large, and it is preferable because it becomes a heat source at the tuyere tip. Also, the hydrogen-based reducing gas (excluding unsaturated hydrocarbon-based gas) may be blown into the blast furnace at room temperature, but it is preferably blown in a heated state for heat supply to the blast furnace. The heating temperature of the hydrogen-based reducing gas is, for example, 500 °C or higher, 1000 °C or higher, or 1200 °C or higher. In addition, it is more preferable that the elemental composition ratio of H in the gas of the hydrogen-based reducing gas is 50 mol% or more. Also, the hydrogen-based reducing gas may be a mixed gas with other gases (for example, N2 gas) (as long as the effects of the present embodiment are not impaired). The heater 71 heats the hydrogen-based reducing gas supplied from the hydrogen-based reducing gas tank 70. The heater 71 can be sufficiently realized by an electric heater or the like. The heater 71 is usually connected to the tuyere 11, and the heated hydrogen-based reducing gas is blown into the blast furnace 10 from the tuyere 11. The heater 71 may be used in combination with the heater 50.

[0024] <2. Consideration by the Inventor of the Present Invention> Next, the consideration by the inventor of the present invention will be described. The inventor examined the operation of the blast furnace using the above-described blast furnace system 1 and hydrogen-based reducing gas supply system 2, and succeeded in finding a method for reducing the reducing agent ratio.

[0025] In this study, a simulation of blast furnace operation was conducted. The simulation model used the so-called "blast furnace mathematical model" shown in Kouji TAKATANI, Takanobu INADA, Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace", ISIJ International, Vol.39(1999), No.1, p.15-22, etc. This blast furnace mathematical model generally defines a plurality of meshes (small regions) by dividing the internal region of the blast furnace in the height direction, radial direction, and circumferential direction, and simulates the behavior of each mesh.

[0026] In blast furnace operation, it is preferable to maintain the tuyere tip combustion temperature, the top gas temperature, and the hot metal temperature within a predetermined range for reasons such as stable operation. For example, the tuyere tip combustion temperature is preferably maintained at about 2000°C or higher and 2300°C or lower, the top gas temperature is preferably maintained at about 105°C or higher, and the hot metal temperature is preferably maintained at about 1520°C or higher. The upper limit value of the tuyere tip combustion temperature is the upper limit value assumed for normal operation (operation without blowing hydrogen-based reducing gas and reformed top circulating gas into the blast furnace 10, and blowing pulverized coal and hot air). The above normal operation was defined as the "base operation" in this simulation, and various parameters were changed with respect to the base operation. The parameters of the base operation are as shown in Table 1.

[0027]

Table 1

[0028] Specifically, the shaft part tuyere height position, the injection temperature of the reformed furnace top circulating gas, and the CO2 separation rate of the furnace top exhaust gas were each changed in four ways: 0 m, 2 m, 4 m, and 6 m from the lower end of the shaft part; in four ways: 800 °C, 900 °C, 1000 °C, and 1100 °C; and in five ways: 60%, 70%, 80%, 90%, and 100% (see Table 2), and the specifications were determined for each case. Here, the shaft part tuyere height position means the height position where the shaft part tuyere is installed when an arbitrary height position is used as a reference. Gas is blown in from the shaft part tuyere arranged at this height position.

[0029]

Table 2

[0030] Specifically, as shown in Table 3, for all cases, the injection temperature of hydrogen gas from the normal tuyere 11, the injection amount of hydrogen gas from the normal tuyere 11, the injection amount of the reformed furnace top circulating gas from the shaft part tuyere 12, and the H2O separation rate of the furnace top exhaust gas were made constant. In this study, hydrogen gas was used as the hydrogen-based reducing gas. During the calculation, the hot metal temperature and the tapping amount were the same as those in the base operation shown in Table 1, and the specifications of the hot blast blowing amount, oxygen enrichment amount (oxygen enrichment rate), and reducing agent ratio were adjusted so that the tuyere tip combustion temperature was constant.

[0031]

Table 3

[0032] Regarding the influence of the shaft part tuyere height position, the injection temperature of the reformed furnace top circulating gas, and the CO2 separation rate of the furnace top exhaust gas on the reducing agent ratio or the carbon reduction effect, a part of the calculation results is shown in FIGS. 2A to 4B. Here, the carbon reduction effect represents the reduction rate of the carbon used from the base operation (as described above, no injection of hydrogen gas from the normal tuyere 11, no injection of the reformed furnace top circulating gas from the shaft part tuyere, and there is injection of pulverized coal from the normal tuyere), and the carbon usage amount [kg / t] is calculated from the carbon contained in the coke and the pulverized coal.

[0033] Figure 2A is a graph showing the relationship between the shaft tuyere height position and the estimated value of the reducing material ratio obtained from the blast furnace simulation results for each estimated value of the injection temperature of the reformed furnace top circulating gas. Figure 2B is a graph showing the relationship between the shaft tuyere height position and the carbon reduction effect for each estimated value of the injection temperature of the reformed furnace top circulating gas. Here, the CO2 separation rate is set to 100%. From Figures 2A and 2B, it can be seen that when the shaft tuyere height position is increased, the estimated value of the reducing material ratio increases (the carbon reduction effect decreases). Since the effect of the reformed furnace top circulating gas blown from the shaft tuyere 12 appears strongly on the wall side of the blast furnace 10, when the position of the shaft tuyere 12 is raised, the reformed furnace top circulating gas blown into the blast furnace 10 is discharged from the wall side to the furnace top without being fully utilized, while the temperature rise and reduction in the radial middle part of the blast furnace 10 are delayed, resulting in a decrease in the reduction gas utilization rate and an increase in the direct reduction rate, and it is considered that the estimated value of the reducing material ratio increases (the carbon reduction effect decreases).

[0034] Furthermore, it can be seen that when the injection temperature of the reformed furnace top circulating gas is increased, the estimated value of the reducing material ratio decreases (the carbon reduction effect increases). When the injection temperature of the reformed furnace top circulating gas increases, the sensible heat input into the furnace increases, thereby improving the temperature rise situation in the furnace and facilitating the progress of reduction in the lump zone. Therefore, it is considered that the estimated value of the reducing material ratio decreases (the carbon reduction effect increases).

[0035] FIG. 3A is a graph showing the relationship between the estimated value of the blowing temperature of the reforming furnace top circulating gas and the estimated value of the reducing material ratio for each estimated value of the CO2 separation rate of the top gas. FIG. 3B is a graph showing the relationship between the estimated value of the blowing temperature of the reforming furnace top circulating gas and the carbon reduction effect for each estimated value of the CO2 separation rate of the top gas. Here, the shaft part tuyere height position is taken as the lower end of the shaft. Here, the lower end of the shaft is the lower end part of the shaft part 10b where the furnace diameter is the largest in the shaft part 10b. When there is a belly part with a constant furnace diameter in the lower part of the shaft part 10b, the lower end of the shaft is also the upper end of the belly part. From FIGS. 3A and 3B, it can be seen that when the blowing temperature of the reforming furnace top circulating gas is increased, the estimated value of the reducing material ratio decreases. When the blowing temperature of the reforming furnace top circulating gas rises, the sensible heat input into the furnace increases, thereby improving the temperature rise situation in the furnace and facilitating the progress of reduction in the lump zone. Therefore, the estimated value of the reducing material ratio is considered to decrease (the carbon reduction effect increases).

[0036] Furthermore, it can be seen that when the CO2 separation rate of the top gas decreases, the estimated value of the reducing material ratio increases (the carbon reduction effect decreases). When the CO2 separation rate of the top gas decreases, a large amount of CO2 gas is mixed into the reforming furnace top circulating gas. As a result, the concentration of reducing gases (CO gas, hydrogen gas) in the reforming furnace top circulating gas decreases, making it difficult to promote reduction in the shaft part 10b. Furthermore, the CO2 gas mixed into the reforming furnace top circulating gas causes an endothermic reaction, the gasification reaction (CO2 + C = CO), in the furnace. From these facts, it is considered that the estimated value of the reducing material ratio increases (the carbon reduction effect decreases).

[0037] FIG. 4A is a graph showing the relationship between the estimated value of the CO2 separation rate of the top-of-furnace exhaust gas and the estimated value of the reducing material ratio for each estimated value of the blowing temperature of the reformed top-of-furnace circulating gas. FIG. 4B is a graph showing the relationship between the estimated value of the CO2 separation rate of the top-of-furnace exhaust gas and the carbon reduction effect for each estimated value of the blowing temperature of the reformed top-of-furnace circulating gas. Here, the tuyere height position in the shaft section is set as the lower end of the shaft. From FIGS. 4A and 4B, it can be seen that when the CO2 separation rate of the top-of-furnace exhaust gas decreases, the estimated value of the reducing material ratio increases (the carbon reduction effect decreases). When the CO2 separation rate decreases, a large amount of CO2 gas is mixed into the reformed top-of-furnace circulating gas, so the concentration of reducing gas (CO gas, hydrogen gas) in the reformed top-of-furnace circulating gas decreases accordingly, making it difficult to promote reduction in the shaft section 10b. Furthermore, the CO2 gas mixed into the reformed top-of-furnace circulating gas causes an endothermic reaction, the gasification reaction (CO2 + C = 2CO), in the furnace. From these facts, it is considered that the estimated value of the reducing material ratio increases (the carbon reduction effect decreases).

[0038] That is, in order to lower the estimated value of the reducing material ratio, it is desirable to lower the tuyere height position in the shaft section, raise the blowing temperature of the reformed top-of-furnace circulating gas, and raise the CO2 separation rate of the top-of-furnace exhaust gas. Although only a part of the calculation results is shown in FIGS. 2A to 4B, it has been found that within the range of conditions for which the calculations were performed this time, the estimated value of the reducing material ratio changes almost linearly with respect to any of the tuyere height position in the shaft section, the blowing temperature of the reformed top-of-furnace circulating gas, and the CO2 separation rate of the top-of-furnace exhaust gas.

[0039] On the other hand, in order to stably conduct blast furnace operation, it is preferable that the top-of-furnace exhaust gas temperature (top-of-furnace temperature) be within a predetermined range. For example, if the top-of-furnace exhaust gas temperature decreases excessively, H2O gas may condense at the top of the furnace to form water and enter the blast furnace.

[0040] FIG. 5 is a graph showing the relationship between the estimated value of the injection temperature of the reforming furnace top circulating gas and the estimated value of the furnace top exhaust gas temperature (furnace top temperature) for each estimated value of the CO2 separation rate of the furnace top exhaust gas. FIG. 6 is a graph showing the relationship between the estimated value of the CO2 separation rate of the furnace top exhaust gas and the estimated value of the furnace top exhaust gas temperature (furnace top temperature) for each estimated value of the injection temperature of the reforming furnace top circulating gas. Here, the shaft part tuyere height position is the lower end of the shaft. As shown in FIGS. 5 and 6, it can be seen that the higher the injection temperature of the reforming furnace top circulating gas and the higher the CO2 separation rate of the furnace top exhaust gas, the lower the furnace top temperature. Conditions where the sensible heat utilization from the reforming furnace top circulating gas such as high circulating gas injection temperature or high CO2 separation rate and the utilization of reducing gas derived from the reforming furnace top circulating gas are more likely to result in a smaller amount of Bosch gas (gas generated usually at the tuyere tip) required for the reduction of the iron-based raw material. As a result, the amount of gas for heating the solids (iron-based raw material and coke) in the blast furnace decreases, making it difficult to heat the solids and leading to a temperature drop in the upper part of the furnace.

[0041] Note that FIG. 7 is a graph showing the relationship between the shaft part tuyere height position and the estimated value of the furnace top exhaust gas temperature (furnace top temperature) for each estimated value of the injection temperature of the reforming furnace top circulating gas. As shown by an example in FIG. 7, as the shaft part tuyere height position increases, the change in the furnace top temperature when changing the injection temperature of the reforming furnace top circulating gas and the CO2 separation rate of the furnace top exhaust gas tends to be smaller, and the change in the furnace top temperature with respect to each condition change is not linear. However, in actual operation, the shaft part tuyere height position is fixed, and the injection temperature of the reforming furnace top circulating gas and the CO2 separation rate of the furnace top exhaust gas are considered to be factors that can be changed. Therefore, the results of this study suggest the possibility of determining the appropriate ranges of these two conditions from the perspective of the furnace top temperature. In addition, in this embodiment, the hydrogen-based reducing gas is blown into the blast furnace 10 from the normal tuyere 11, and the reformed furnace top circulating gas is blown into the blast furnace 10 from the shaft tuyere 12. However, the tuyere into which each gas is blown is not limited. For example, the hydrogen-based reducing gas may be blown into the blast furnace 10 from the shaft tuyere, or the reformed furnace top circulating gas may be blown into the blast furnace 10 from the normal tuyere 11. In any case, by determining the appropriate range of the blowing temperature of the reformed furnace top circulating gas and the CO2 separation rate of the top gas from the top temperature, the operation of the blast furnace with a reduced reducing material ratio is possible. Specific examples of the operation method of the blast furnace based on the above findings are as follows.

[0042] <3. Specific Example 1> Specific Example 1 is an operation method of a blast furnace in which a hydrogen-based reducing gas is blown into the blast furnace 10 from the normal tuyere 11, CO2 gas and H2O gas are separated and removed from the top gas to generate a reformed furnace top circulating gas, and the reformed furnace top circulating gas is blown into the blast furnace 10 from the shaft tuyere 12. Further, Specific Example 1 includes a determination step of determining a target value of the blowing temperature of the reformed furnace top circulating gas and a target value of the CO2 separation rate based on a target value of the reducing material ratio, a separation step of separating and removing CO2 gas and H2O gas from the top gas based on the target value of the CO2 separation rate determined in the determination step, and a blowing step of heating the reformed furnace top circulating gas based on the target value of the blowing temperature of the reformed furnace top circulating gas determined in the determination step and blowing it into the blast furnace 10 from the shaft tuyere 12.

[0043] In Specific Example 1, for example, after installing the shaft part tuyere 12 at the lower end of the shaft, the operation is carried out according to the specifications shown in Table 3. Then, based on any one of FIGS. 3A to 4B, the target value of the blowing temperature of the reforming furnace top circulating gas corresponding to the target value of the reducing agent ratio and the target value of the CO2 separation rate are determined. And based on the target value of the CO2 separation rate, CO2 gas and H2O gas are separated and removed from the top gas of the furnace, and the reforming furnace top circulating gas is heated up based on the target value of the blowing temperature of the reforming furnace top circulating gas (heated up so that the blowing temperature of the reforming furnace top circulating gas coincides with the target value), and blown into the blast furnace 10 from the shaft part tuyere 12. For example, when it is desired to set the target value of the reducing agent ratio to 300 kg / t using FIG. 3A, combinations of conditions such as (850 °C, 90%), (910 °C, 80%), (1010 °C, 70%) etc. can be selected as the combination of the blowing temperature of the reforming furnace top circulating gas and the CO2 separation rate of the top gas of the furnace.

[0044] <4. Specific Example 2> In Specific Example 2, in the determination step of Specific Example 1, Relationship 1 between the estimated value of the reducing agent ratio and the estimated value of the blowing temperature of the reforming furnace top circulating gas is created for each estimated value of the CO2 separation rate, and based on the created Relationship 1 and the target value of the reducing agent ratio, a combination of the target value of the blowing temperature of the reforming furnace top circulating gas and the target value of the CO2 separation rate is determined.

[0045] Relationship 1 is shown, for example, in FIG. 3A. Therefore, for example, when it is desired to set the target value of the reducing agent ratio to 300 kg / t using FIG. 3A, combinations of conditions such as (850 °C, 90%), (910 °C, 80%), (1010 °C, 70%) etc. can be selected as the combination of the blowing temperature of the reforming furnace top circulating gas and the CO2 separation rate of the top gas of the furnace.

[0046] <5. Specific Example 3> In Specific Example 3, in Specific Example 1, Relationship 2 between the estimated value of the reducing agent ratio and the estimated value of the CO2 separation rate is created for each estimated value of the blowing temperature of the reforming furnace top circulating gas, and based on the created Relationship 2 and the target value of the reducing agent ratio, a combination of the target value of the blowing temperature of the reforming furnace top circulating gas and the target value of the CO2 separation rate is determined.

[0047] Relationship 2 is shown in, for example, FIG. 4A. Therefore, when it is desired to set the target value of the reducing agent ratio to 300 kg / t using FIG. 4A, combinations of conditions of the blowing temperature of the reforming furnace top circulating gas and the CO2 separation rate of the furnace top exhaust gas, such as (1100°C·60%), (1000°C·70%), (900°C·81%), (800°C·97%), etc., may be selected.

[0048] <6. Specific Example 4> In Specific Example 4, in Specific Example 2, Relationship 3 between the estimated value of the furnace top temperature and the estimated value of the blowing temperature of the reforming furnace top circulating gas is created for each estimated value of the CO2 separation rate, and based on the created Relationships 1 and 3, the target value of the reducing agent ratio, and the target value of the furnace top temperature, the target value of the blowing temperature of the reforming furnace top circulating gas and the target value of the CO2 separation rate of the furnace top exhaust gas are determined.

[0049] Relationship 3 is shown in, for example, FIG. 5. Therefore, using the relationship between the estimated value of the reducing agent ratio shown in FIG. 3A and the blowing temperature of the reforming furnace top circulating gas and the relationship between the estimated value of the furnace top temperature shown in FIG. 5 and the blowing temperature of the reforming furnace top circulating gas, the target value of the blowing temperature of the reforming furnace top circulating gas and the target value of the CO2 separation rate of the furnace top exhaust gas that achieve the target value of the reducing agent ratio and the target value of the furnace top temperature are determined.

[0050] Therefore, when it is desired to set the target value of the reducing agent ratio to 300 kg / t and the target value of the furnace top temperature to 115°C using FIGS. 3A and 5, the blowing temperature of the reforming furnace top circulating gas may be set to 910°C and the CO2 separation rate of the furnace top exhaust gas may be set to 80%.

[0051] <7. Specific Example 5> In Specific Example 5, in Specific Example 3, Relationship 4 between the estimated value of the furnace top temperature and the estimated value of the CO2 separation rate is created for each estimated value of the blowing temperature of the reforming furnace top circulating gas, and based on the created Relationships 2 and 4, the target value of the reducing agent ratio, and the target value of the furnace top temperature, the target value of the blowing temperature of the reforming furnace top circulating gas and the target value of the CO2 separation rate of the furnace top exhaust gas are determined.

[0052] Relationship 4 is shown, for example, in FIG. 6. Therefore, using the relationship between the estimated value of the reducing material ratio shown in FIG. 4A and the CO2 separation rate, and the relationship between the estimated value of the furnace top temperature shown in FIG. 6 and the CO2 separation rate, the target value of the reformed furnace top circulating gas injection temperature and the target value of the CO2 separation rate of the furnace top exhaust gas are determined so as to achieve the target value of the reducing material ratio and the target value of the furnace top temperature.

[0053] Therefore, when it is desired to set the target value of the reducing material ratio to 300 kg / t and the target value of the furnace top temperature to 115°C using FIGS. 4A and 6, the injection temperature of the reformed furnace top circulating gas may be set to 900°C and the CO2 separation rate of the furnace top exhaust gas may be set to 81%.

[0054] According to the above-described Specific Examples 1 to 5, it is possible to further reduce the reducing material ratio.

[0055] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and these are also naturally understood to belong to the technical scope of the present invention.

Explanation of Reference Numerals

[0056] 1 Blast furnace system 2 Hydrogen-based reducing gas supply system 10 Blast furnace 10a Blast furnace body 10b Shaft section 11 Normal tuyere 12 Shaft section tuyere 20 CO2 separation and recovery device 30 Buffer tank 40 Compressor 50, 71 Heater 70 Hydrogen-based reducing gas tank

Claims

1. Inject a hydrogen-based reducing gas into the blast furnace, CO from the top gas of the furnace ２ gas and H ２ In the operation method of a blast furnace that separates and removes O gas to generate reformed top-circulation gas and blows the reformed top-circulation gas into the blast furnace, Based on the target value of the reducing agent ratio, the target value of the blowing temperature of the reformer top circulating gas and the CO ２ A determination step of determining the target value of the separation rate; CO of the top gas determined in the determination step ２ Based on the target value of the separation rate, the CO ２ gas and the H ２ separation step of separating and removing O gas, and a blowing step of heating the reformed top circulating gas based on the target value of the blowing temperature of the reformed top circulating gas determined in the determination step and blowing it into the blast furnace. A method for operating a blast furnace, characterized by comprising:

2. Inject the hydrogen-based reducing gas into the blast furnace from a normal tuyere, and the method for operating a blast furnace according to claim 1, characterized in that the reformed top circulating gas is blown into the blast furnace from a shaft section tuyere.

3. In the determination step, Relationship 1 between the estimated value of the reducing material ratio and the estimated value of the blowing temperature of the reformer top recycle gas is created for each estimated value of the CO ２ separation rate of the top exhaust gas, Based on the created relationship 1 and the target value of the reducing agent ratio, determine the combination of the target value of the blowing temperature of the reformed furnace top circulating gas and the target value of the CO ２ separation rate of the furnace top exhaust gas, which is a method for operating a blast furnace according to claim 1 or 2.

4. In the determination step, The estimated value of the reducing material ratio and the CO ２ Relationship 2 with the estimated value of the separation rate is created for each estimated value of the blowing temperature of the reforming furnace top recycle gas, Based on the created relationship 2 and the target value of the reducing agent ratio, determine the target value of the blowing temperature of the reformed furnace top circulating gas and the CO ２ The operation method of a blast furnace according to claim 1 or 2, characterized by determining a combination of the target value of the separation rate.

5. In the determination step, The relationship 3 between the estimated value of the top-furnace temperature and the estimated value of the blowing temperature of the reforming top-furnace circulating gas is based on the CO of the top-furnace exhaust gas ２ created for each estimated value of the separation rate, Based on the created relationships 1 and 3, the target value of the reducing agent ratio, and the target value of the furnace top temperature, determine the target value of the blowing temperature of the reformed furnace top circulating gas and the CO ２ The method for operating a blast furnace according to claim 3, characterized in that a target value of the separation rate is determined.

6. In the determination step, The estimated value of the furnace top temperature and the CO ２ Relationship 4 with the estimated value of the separation rate of the furnace top exhaust gas is created for each estimated value of the injection temperature of the reformed furnace top recycle gas, Based on the created relationships 2 and 4, the target value of the reducing agent ratio, and the target value of the furnace top temperature, determine the target value of the blowing temperature of the reformed furnace top circulating gas and the CO ２ The operation method of a blast furnace according to claim 4, characterized in that a target value of the separation rate is determined.

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