Operation method for blast furnace

Abstract

To provide an operation method for a blast furnace capable of achieving a low reduction agent ratio and low pressure loss.SOLUTION: A blast furnace operation method comprises blowing hydrogen-based reduction gas into the interior of the blast furnace through ordinary tuyere, blowing reformer top circulation gas into the interior of the blast furnace through shaft part tuyere, where the furnace center is 0.0 and the furnace wall is 1.0, the region from the furnace center to a position where the dimensionless radius is 0.3 is defined as the central part, the region from the position where the dimensionless radius is 0.3 to the position where the dimensionless radius is r as the intermediate part, and the region from the position where the dimensionless radius is r to the position where the dimensionless radius is 1.0 as the furnace wall part, when r is set to be greater than 0.3 and less than 1.0, and where the control range is the uppermost layer of the ferrous raw material layer and the uppermost layer of the coke layer, and where the O / C index, which is the ratio of the O / C of the furnace wall part to the O / C of the intermediate part, is set to exceed 1.0 in the intermediate part and the furnace wall part of the control range.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 for producing pig iron. In this process, iron-based raw materials and coke are alternately and layeredly charged into the blast furnace from the top, while hot air is blown into the blast furnace through tuyere openings at the bottom. The hot air reacts with the pulverized coal blown in 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, further reduced by the coke. The iron-based raw materials ultimately accumulate in the hearth as molten pig iron (pig iron), containing just under 5% carbon by mass. The molten iron in the hearth is taken out through a taphole and is 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 must respond to the societal demand for CO2 gas reduction. Therefore, 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] In addition, reducing pressure loss inside the furnace is also an important issue in blast furnace operation. This is because if pressure loss inside the furnace increases, that is, if the permeability inside the furnace deteriorates, the risk of operational instability increases. Conversely, if pressure loss inside the furnace is reduced, not only will stable operation be possible, but it will also be possible to aim for high productivity operation, so it is desirable to reduce pressure loss as much as possible.

[0005] As a technique for reducing the reducing agent ratio, for example, as disclosed in Patent Documents 1 and 2, a technique has been proposed in which reformed furnace top circulating gas obtained by reforming furnace top exhaust gas is injected into a blast furnace from a tuyere in the shaft portion of the blast furnace.

[0006] However, in the techniques of Patent Documents 1 and 2, since the reforming furnace top circulation gas contains unreacted reducing gas, although a certain degree of reduction in the reducing agent ratio can be expected, it is difficult to sufficiently reduce the reducing agent ratio to meet the increasing demand in recent years for reduction in CO2 gas emissions.

[0007] Patent Document 3 discloses a technique for improving the reducing gas potential in a furnace by blowing hydrogen gas together with hot air from the tuyere. Patent Document 3 defines a parameter called the reduction rate of the carbon consumption intensity (Input △C) as a parameter that serves as an index for reducing the reducing agent rate, and discloses that the greater the reduction rate of the carbon consumption intensity, Input △C, the more the reducing agent rate is reduced, and ultimately the amount of CO2 emissions is reduced.

[0008] However, with the technology described in Patent Document 3, if the Input ΔC is to be increased, a large amount of hydrogen gas needs to be heated to a high temperature and injected into the blast furnace, which requires not only the preparation of a large amount of hydrogen gas, but also the preparation of a heating device for heating the hydrogen gas to a high temperature, and the construction of the blast furnace equipment from materials that can withstand high-temperature hydrogen gas. In other words, there is a problem in that a great deal of effort is required to increase the Input ΔC.

[0009] Furthermore, Patent Document 4 proposes a blast furnace operation method that enables appropriate ore reduction and permeability in the furnace radial direction when a reducing gas containing hydrogen gas is injected into the lower shaft of the blast furnace. Furthermore, Patent Document 5 proposes controlling the weight ratio of coke to ore (O / C) in each region as a method of operating a blast furnace that can further enhance the effect of reducing CO2 while reducing pressure loss inside the furnace when hydrogen gas is injected from the tuyere.

[0010] However, even the technique of Patent Document 4 is unable to sufficiently reduce the reducing agent ratio. Furthermore, the technology of Patent Document 5 does not sufficiently consider the case where gas is simultaneously blown in from the shaft portion. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2015 / 105107 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-129325 [Patent Document 3] International Publication No. 2021 / 107091 [Patent Document 4] Patent No. 5770124 [Patent Document 5] Japanese Patent Application Publication No. 2023-177114 Summary of the Invention [Problem to be solved by the invention]

[0012] As described above, a method for operating a blast furnace in which a hydrogen-based reducing gas is injected into the interior of the blast furnace from a normal tuyere and gas is injected into the interior of the blast furnace from a shaft tuyere has not been proposed that can achieve a low reducing agent ratio and low pressure loss. Therefore, an object of the present invention is to provide a method for operating a blast furnace that can achieve a low reducing agent rate and low pressure loss. [Means for solving the problem]

[0013] The present inventors have conducted studies on reducing the reducing agent ratio and reducing the pressure loss inside the furnace. As a result, the following findings were obtained. a) When hydrogen-based reducing gas is injected into the inside of a blast furnace from a normal tuyere and the reformed top circulation gas obtained by separating and removing CO2 gas and H2O gas from the top exhaust gas is injected into the inside of the blast furnace from a shaft tuyere, by controlling the distribution of the charged coke and iron-based raw materials inside the furnace (charge distribution), it is possible to further reduce pressure loss without worsening the reducing agent ratio.

[0014] The present invention has been made in view of the above problems. The gist of the present invention is as follows. [1] A method for operating a blast furnace in which iron-based raw materials and coke are alternately charged from the top of the furnace so that they are layered, wherein a hydrogen-based reducing gas is blown into the inside of the blast furnace from a normal tuyere, and a modified furnace top circulation gas obtained by separating and removing at least a part of CO gas and H O gas from the furnace top exhaust gas is blown into the inside of the blast furnace from a shaft tuyere, and in the dimensionless radius of the blast furnace, where the furnace center is 0.0 and the furnace wall is 1.0, the furnace center to the position where the dimensionless radius is 0.3 is the central part, and the position where the dimensionless radius is 0.3 to the dimensionless radius is the center. a furnace wall section extending up to a position where the radius is r, and a furnace wall section extending from a position where the dimensionless radius is r to a position where the dimensionless radius is 1.0, and when r is greater than 0.3 and less than 1.0, a control range is defined as an uppermost layer of the iron-based raw material layers and an uppermost layer of the coke layers, and an O / C ratio, which is a ratio of the mass of the iron-based raw materials to the mass of the coke, is controlled in the center, intermediate section, and furnace wall section within the control range, so that an O / C index, which is a ratio of O / C of the furnace wall section to O / C of the intermediate section, exceeds 1.0. [2] The method for operating a blast furnace according to [1], wherein the O / C index is greater than 1.0 and less than 2.5. [3] The method for operating a blast furnace according to [1] or [2], wherein r is 0.4 or more and 0.6 or less. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for operating a blast furnace that can achieve a low reducing agent rate and low pressure loss. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a half cross section of a blast furnace, which is used to explain the method of operating a blast furnace of the present invention. [Figure 2] FIG. 10 is a diagram showing simulation results when the O / C index is changed. [Figure 3] FIG. 10 is a diagram showing simulation results when the O / C index is changed. [Figure 4] FIG. 10 is a diagram showing the results of a simulation when the dimensionless radius that is the boundary between the intermediate portion and the furnace wall portion is changed. [Figure 5] FIG. 10 is a diagram showing the results of a simulation when the dimensionless radius that is the boundary between the intermediate portion and the furnace wall portion is changed. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, a method for operating a blast furnace according to one embodiment of the present invention (sometimes referred to as an operating method according to this embodiment) will be described with reference to the drawings.

[0018] The operating method according to this embodiment is a method for operating a blast furnace, using a blast furnace 1 equipped with a normal tuyere 10 and a shaft tuyere 11 provided in the shaft 3, in which iron-based raw materials and coke are alternately charged in layers from the furnace top 4, as shown in Fig. 1. The operating method according to this embodiment is also a method for operating a blast furnace, in which a hydrogen-based reducing gas is injected into the inside of the blast furnace 1 through the normal tuyere 10, and a reformed furnace top circulating gas obtained by separating and removing at least a portion of CO2 gas and HO gas from the furnace top flue gas is injected into the inside of the blast furnace 1 through the shaft tuyere 11. Hereinafter, in the non-dimensional radius of the blast furnace 1, the furnace center FC is 0.0 and the furnace wall 2 is 1.0, and in each layer, the furnace center FC to the position where the non-dimensional radius is 0.3 is referred to as the center portion R1, the position where the non-dimensional radius is 0.3 to the position where the non-dimensional radius is r is referred to as the middle portion R2, and the position where the non-dimensional radius is r to the position where the non-dimensional radius is 1.0 is referred to as the furnace wall portion R3.

[0019] [Injection of hydrogen-based gas from normal tuyere] Generally, hot air, pulverized coal, and oxygen-enriched gas are blown into the blast furnace 1 through the normal tuyere 10. The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace 1 to generate high-temperature reducing gas (mainly CO gas in this case). In other words, the hot air gasifies the coke and pulverized coal. In some cases, the pulverized coal is not blown into the blast furnace 1. The generated reducing gas rises inside the blast furnace 1, heating and reducing the iron-based raw materials. The iron-based raw materials are heated and reduced by the reducing gas while descending inside the blast furnace 1. The iron-based raw materials then melt and drip inside the blast furnace 1 while being further reduced by 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 next steelmaking process.

[0020] In the operating method according to this embodiment, in addition to the hot air described above, a hydrogen-based reducing gas is blown into the blast furnace 1. By blowing hydrogen-based reducing gas together with hot air from the tuyere, the reducing gas potential inside the furnace can be improved, and the reducing agent rate can be reduced.

[0021] (hydrogen-based reducing gas) The hydrogen-based reducing gas may be pure hydrogen, or may be a hydrogen-containing gas such as COG, or may be a mixed gas of a hydrogen-containing gas and another gas (such as nitrogen gas). The amount of hydrogen-based reducing gas blown in is 400 to 600 Nm 3The hydrogen-based reducing gas is preferably blown in at a heated state to prevent a drop in the furnace top temperature, for example, at 600°C or higher. The hydrogen-based reducing gas is supplied from outside the blast furnace system. For example, the hydrogen-based reducing gas can be heated as needed by a heater connected to the normal tuyere 10 from a tank that stores the hydrogen-based reducing gas, and then blown into the blast furnace 1 through the normal tuyere 10.

[0022] [Injection of reformer top circulating gas from the shaft tuyere] In the operating method according to this embodiment, the reformed furnace top circulating gas is blown into the inside of the blast furnace 1 from the shaft tuyere 11. This has the effect of promoting reduction and temperature rise inside the furnace.

[0023] (reforming furnace top circulation gas) The reformed furnace top circulation gas blown in from the shaft tuyere 11 is a gas obtained by separating and removing at least a part of CO2 gas and H2O gas from the furnace top exhaust gas. The reformed furnace top circulation gas is injected into the inside of the blast furnace 1 from the shaft tuyere 11 by any method. For example, the reformed furnace top circulation gas can be temporarily stored in a buffer tank, the reformed furnace top circulation gas introduced from the buffer tank can be pressurized by a compressor to the internal pressure of the blast furnace 1 (about 4.5 atmospheres), heated by a reformed furnace top circulation gas heater introduced from the compressor, and the reformed furnace top circulation gas heated by the heater can be injected into the inside of the blast furnace 1 from the shaft tuyere 11. There may be a plurality of shaft tuyere 11, and in that case, the reformed furnace top circulating gas may be injected into the inside of the blast furnace 1 from a plurality of shaft tuyere.

[0024] The amount of reformer top circulating gas injected is 200 to 600 Nm 3 The temperature of the reforming furnace top circulating gas when it is blown in is preferably 800°C or higher.

[0025] The reformer top circulation gas generally consists of CO, H2, N2, and CO2 and H2O that were not completely separated. Although it is difficult to completely separate and remove CO2 gas and HO gas from the top exhaust gas, it is preferable to separate and remove as much as possible. This is because, if the CO2 separation rate decreases, a large amount of CO2 gas will be mixed into the reformer top circulation gas, which will reduce the concentration of reducing gases (CO gas, hydrogen gas) in the reformer top circulation gas, making it difficult to promote reduction in the shaft, and the CO2 gas mixed into the reformer top circulation gas will cause an endothermic gasification reaction (CO2 + C = CO) in the furnace, which will increase the reducing agent ratio. Preferably, the CO2 separation rate is 80% or more by volume. The CO2 content is measured by a gas analyzer such as a gas chromatograph. The separation rate of H2O gas is preferably 90% or more by volume. The separated CO2 gas and H2O gas are discharged outside the system. The separation method is not particularly limited, and examples thereof include chemical adsorption and physical adsorption (PSA).

[0026] When CO2 gas and HO gas are separated and removed from the top flue gas to generate the reformed top circulation gas, it is not necessary to separate and remove all of the top flue gas. For example, only an amount of the top flue gas corresponding to the flow rate of the reformed top circulation gas injected into the blast furnace may be recovered and the CO2 gas and HO gas may be separated and removed. The remaining top flue gas can be used as a heat source for the steelworks.

[0027] [Charging iron-based raw materials and coke from the furnace top] In the operating method according to this embodiment, iron-based raw materials and coke are alternately charged from the furnace top so that they form layers. At this time, the distribution of the charged materials forming the layers is controlled. Here, known iron-based raw materials and coke may be used. The iron-based raw materials are raw materials containing iron oxide, and mainly include sintered ore.

[0028] (Charge distribution) In the operating method according to this embodiment, the uppermost layer of the iron-based raw material layers and the uppermost layer of the coke layers are set as the control range, and the burden distribution within this control range is controlled. For example, as shown in Figure 1, when the coke layers are designated C1, C2, C3, ... Cn from the side closest to the furnace top 4, and the iron-based raw material layers are designated Or1, Or2, Or3, ... Orn from the side closest to the furnace top 4, the control range S is the range consisting of C1 and Or1. In the figure, C1 is closer to the furnace top than Or1, but even if Or1 is closer to the furnace top than C1, the control range is similarly the range consisting of C1 and Or1.

[0029] Regarding the distribution of the burden, the O / C, which is the ratio of the mass of iron-based raw materials to the mass of coke, is controlled in the center portion R1, the intermediate portion R2, and the furnace wall portion R3 within the control range S, and the O / C index, which is the ratio of the O / C in the furnace wall portion to the O / C in the intermediate portion within the control range S, is controlled. The O / C in each of the center portion R1, the intermediate portion R2, and the furnace wall portion R3 may be set appropriately according to the operating conditions within a range that satisfies the O / C index described below.

[0030] (O / C index) Specifically, the O / C index, which is the ratio of the O / C in the furnace wall section R3 to the O / C in the middle section R2 in the control range S, is set to exceed 1.0. By setting the O / C index in a range exceeding 1.0 (increasing the O / C in the furnace wall section R3), it is possible to reduce the pressure loss in the furnace (the difference between the pressure at the tip of the tuyere and the pressure at the top of the blast furnace). This is presumably because increasing the O / C in the furnace wall section R3 relatively strengthens the central flow. If the O / C index is 1.0 or less, sufficient effect cannot be obtained. On the other hand, although there is no upper limit to the O / C index, when reformer top circulating gas is injected from the shaft tuyere 11, a high O / C index tends to improve the temperature rise on the wall side due to the sensible heat of the circulating gas, but also increase the reducing agent ratio. Therefore, when the reducing agent ratio is set in a lower range, the O / C index is preferably greater than 1.0 and equal to or less than 2.5.

[0031] (Middle position) In the operating method according to this embodiment, as described above, the O / C ratio between the intermediate portion R2 and the furnace wall portion R3 is controlled. In this embodiment, in the dimensionless radius of the blast furnace 1, the furnace center FC is 0.0 and the furnace wall 2 is 1.0, and in each layer, the furnace center FC to the position where the dimensionless radius is 0.3 is the center R1, the position where the dimensionless radius is 0.3 to the position where the dimensionless radius is r is the middle R2, and the position where the dimensionless radius is r to the position where the dimensionless radius is 1.0 is the furnace wall R3. If r is 0.3 or less, the middle R2 does not exist. Also, if r is 1.0, the furnace wall R3 does not exist. Therefore, r is greater than 0.3 and less than 1.0. If the range of the intermediate portion R2 or the furnace wall portion R3 is too narrow, it will be difficult to control the O / C within that range in actual operation, so r may be set to 0.4 or more and 0.9 or less.

[0032] Furthermore, if the position of the boundary between the intermediate portion R2 and the furnace wall portion R3 is changed, the degree of the effect changes. That is, if r is less than 0.4, there is a concern that the pressure loss will increase. Therefore, it is preferable that r is 0.4 or more. This is because if the region with a high O / C becomes wide, the region through which gas can easily flow will become narrow, and there is a concern that the overall ventilation resistance will increase. On the other hand, by widening the region with a high O / C ratio to a certain extent, the reduction load is dispersed, the central flow is strengthened, and the pressure drop in the furnace is reduced. To obtain this effect, r is preferably 0.6 or less. For example, r is 0.5 (in this case, the dimensionless radius is in the range of 0.0 to 0.3 at the center, 0.3 to 0.5 at the middle, and 0.5 to 1.0 at the furnace wall).

[0033] (Charging method) The control of the O / C index, i.e., the control of the radial distribution of the charging, is not limited and may be performed by any known method. For example, the radial distribution of the accumulated material can be controlled by charging the material using a bell-less top charging device while changing the tilt angle of the rotating chute in the furnace over time. O / C is the ratio of the mass of iron-based raw materials to the mass of coke, and is calculated for the entire region, i.e., the center region R1, the middle region R2, and the furnace wall region R3. For example, in the middle region R2, O / C is the ratio of the mass of iron-based raw materials to the mass of coke in the entire middle region R2. However, if the charging amounts and charging locations of the iron-based raw materials and coke are known, O / C can be calculated using the actual charging amounts of each. [Example]

[0034] A simulation was performed using a mathematical model of a blast furnace to examine the influence of the burden distribution conditions (O / C index) in the blast furnace and the dimensionless radius that forms the boundary between the middle part and the furnace wall part on the pressure drop and the reducing agent rate in the furnace, assuming that a hydrogen-based reducing gas is injected into the blast furnace from a normal tuyere, and that the reformed top circulation gas obtained by separating and removing at least a portion of the CO2 gas and HO gas from the top exhaust gas is injected into the blast furnace from a shaft tuyere.

[0035] The blast furnace mathematical model is based on the work of Kouji TAKATANI, Takanobu INADA, and Yutaka UJISAWA, entitled "Three-dimensional Dyna The model used was that described in "IC Simulator for Blast Furnace," ISIJ International, Vol. 39 (1999), No. 1, pp. 15-22. The simulation specifications are shown in Table 1.

[0036] [Table 1]

[0037] (Experimental Example 1) The dimensionless radius that is the boundary between the middle part and the furnace wall part was set to 0.5, and the O / C index was changed. The results are shown in Figures 2 and 3.

[0038] As can be seen from FIG. 2, compared to when the O / C index is set to 1.0, by setting the O / C index to more than 1.0, the pressure loss inside the furnace is reduced. Furthermore, as can be seen from Figure 3, a lower reducing agent rate can be obtained compared to normal operation by injecting hydrogen gas and reformed furnace top recycle gas into the blast furnace. In particular, it is clear that keeping the O / C index at 2.5 or less is preferable because it can keep the reducing agent rate low.

[0039] (Experimental Example 2) The O / C index was set to 1.5, and the dimensionless radius that was the boundary between the middle part and the furnace wall part was changed. The results are shown in Figures 4 and 5.

[0040] As can be seen from FIG. 4, the pressure loss inside the furnace can be reduced by setting the dimensionless radius that is the boundary between the intermediate portion and the furnace wall portion to 0.4 or more and 0.6 or less. Furthermore, as shown in Fig. 5, when the dimensionless radius that forms the boundary between the intermediate section and the furnace wall section is in the range of 0.4 to 0.9, the reducing agent rate is also lower than in normal operation. [Explanation of symbols]

[0041] 1 blast furnace 2 Furnace wall 3 Shaft section 4 Hearth top 10 Normal tuyeres 11 Shaft tuyere R1 center R2 middle part R3 Furnace wall S Control Range C Coke layer Or ore layer FC furnace center

Claims

1. A method for operating a blast furnace in which iron-based raw materials and coke are alternately charged from the top of the furnace so that they form layers, A hydrogen-based reducing gas is usually injected into the inside of the blast furnace through a tuyere, From the top exhaust gas, CO ２ Gas and H ２ a reformed furnace top circulating gas obtained by separating and removing at least a portion of the O gas is injected into the interior of the blast furnace through a shaft tuyere; In the dimensionless radius of the blast furnace, the furnace center is represented as 0.0 and the furnace wall is represented as 1.

0. When the furnace center to the position where the dimensionless radius is 0.3 is defined as a central portion, the position where the dimensionless radius is 0.3 to the position where the dimensionless radius is r is defined as an intermediate portion, and the position where the dimensionless radius is r to the position where the dimensionless radius is 1.0 is defined as a furnace wall portion, and the r is greater than 0.3 and less than 1.0, a control range including the uppermost layer of the iron-based raw material layers and the uppermost layer of the coke layers, and controlling O / C, which is the ratio of the mass of the iron-based raw materials to the mass of the coke, in the center portion, the intermediate portion, and the furnace wall portion of the control range; The O / C index, which is the ratio of O / C of the furnace wall portion to O / C of the intermediate portion, is greater than 1.0; A method for operating a blast furnace, comprising:

2. The O / C index is greater than 1.0 and less than 2.

5.

2. The method for operating a blast furnace according to claim 1 .

3. The r is set to 0.4 or more and 0.6 or less.

3. The method for operating a blast furnace according to claim 1 or 2.

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