Operating method of blast furnace

Abstract

The operation method of a blast furnace according to one aspect of the present disclosure is an operation method of a blast furnace for charging an iron raw material containing reduced iron into the furnace, including: an acquisition step of previously acquiring the ηCO distribution in a reference operation in which the charged iron raw material does not contain reduced iron; a high ηCO region specifying step of defining the average value of ηCO in the ηCO distribution or the ηCO calculated from the top gas as the average ηCO, and previously specifying a high ηCO region where the relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO is 1.0 or more; and a charging step of charging 75 mass% or more of the reduced iron into the high ηCO region.

Description

Technical Field

[0001] The present invention relates to an operation method of a blast furnace for charging an iron raw material containing reduced iron into a furnace. This application claims priority based on Japanese Patent Application No. 2024-001753 filed in Japan on January 10, 2024, and incorporates its content herein by reference.

Background Art

[0002] In a blast furnace, an iron raw material, and coke as a reducing material and a fuel are alternately charged from the top of the furnace. Further, a tuyere is formed at the lower part of the blast furnace, and hot air is blown from this tuyere, and an auxiliary fuel such as pulverized coal is blown in.

[0003] Patent Document 1 describes a technique of charging reduced iron or the like at a position where the ratio of the coke layer thickness Lc to the average particle diameter Dc of coke, Lc / Dc, is 2 or less (a thin region of the coke layer with two or less coke particles).

[0004] Patent Document 2 discloses a technique of measuring the gas composition distribution in the furnace diameter direction at the top of the furnace and charging reduced iron or the like through a sub-hopper in a region where ηCO (CO2% / (CO%+CO2%)) is 0.57 or more.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The charging positions of reduced iron and the like in Patent Document 1 and Patent Document 2 are both in regions with a high ηCO (regions with a high reduction load).

[0008] However, the method of Patent Document 1 requires identifying a region with a thin coke layer thickness, which is difficult to identify.

[0009] In addition, in the method of Patent Document 2, since the range in the furnace diameter direction for charging reduced iron and the like is small, it is necessary to prepare a sub-hopper. Also, depending on the operating conditions, there may be no region where ηCO (CO2% / (CO% + CO2%)) is 0.57 or more, resulting in low versatility. Furthermore, there is also a problem in that the upper limit of the charging amount of reduced iron and the like is low.

Means for Solving the Problems

[0010] The gist of the present disclosure is as follows.

[0011] (1) The operation method of a blast furnace according to one aspect of the present disclosure is an operation method of a blast furnace for charging iron raw materials containing reduced iron into the furnace, including an acquisition step of previously acquiring the ηCO distribution in a reference operation in which the iron raw materials to be charged do not contain reduced iron, defining the average value of ηCO in the ηCO distribution or the ηCO calculated from the top gas as the average ηCO, and a high ηCO region specifying step of previously specifying a high ηCO region where the relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO is 1.0 or more, and a charging step of charging 75 mass% or more of the reduced iron into the high ηCO region. (2) Preferably, in the operation method of the blast furnace described in (1) above, in the high ηCO region specifying step, a relative ηCO distribution, which is the distribution of relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO, is acquired, and the high ηCO region is specified based on the relative ηCO distribution. (3) Preferably, in the operation method of the blast furnace according to the above (1) or (2), the blast furnace has a charging hopper for charging the reduced iron, and the charging hopper is a combined charging hopper for charging the reduced iron and iron raw materials other than the reduced iron. (4) Preferably, in the operation method of the blast furnace according to any one of the above (1) to (3), when the iron raw materials are 100% by mass, the ratio of the reduced iron contained in the iron raw materials is 0.5% by mass or more and 50% by mass or less. (5) Preferably, in the operation method of the blast furnace according to any one of the above (1) to (4), in the charging step, 80% by mass or more of the reduced iron is charged into the high ηCO region. (6) Preferably, in the operation method of the blast furnace according to any one of the above (1) to (5), in the high ηCO region specifying step, a region where the relative ηCO is 1.2 or more is regarded as the high ηCO region.

Advantages of the Invention

[0012] According to the present invention, the high ηCO region can be specified and the reduced iron can be intensively deposited in such a region. Thereby, the reduction material ratio (RAR) can be more effectively reduced.

Brief Description of the Drawings

[0013]

Fig. 1

Fig. 2

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Fig. 5

Embodiments for Carrying Out the Invention

[0014] The operation method of a blast furnace according to the present invention is an operation method of a blast furnace for charging iron raw materials containing reduced iron into the furnace, and includes an acquisition step, a high ηCO region identification step, and a charging step. Hereinafter, each step will be described item by item.

[0015] >Regarding the acquisition step< The acquisition step is a step of acquiring in advance the ηCO distribution in the reference operation. The reference operation is an operation in which the iron raw materials to be charged do not contain reduced iron, and is the operation during the period from the time when the charging conditions were last changed to the time when reduced iron is charged. When the charging conditions are changed, the furnace conditions fluctuate immediately thereafter but eventually stabilize. In the acquisition step, it is preferable to acquire in advance the ηCO distribution in a state where the furnace conditions are stable. More preferably, in the acquisition step, the ηCO distribution at a time as close as possible to the time when reduced iron is charged is acquired.

[0016] ηCO is the ratio of CO to CO2 and is calculated by the following formula. ηCO = CO2% / (CO% + CO2%)

[0017] The measurement methods of CO2% and CO% are not particularly limited. For example, CO2% and CO% can be measured using gas chromatography or the like.

[0018] When the reduced iron is defined by the metallic iron conversion rate, it is preferably 70% by mass or more. The metallic iron conversion rate is the relative ratio of the amount of metallic iron in the total iron content of the reduced iron. Metallic iron is iron that is not combined with oxygen or does not exist as pyrite.

[0019] The reduced iron may be iron scrap, pig iron, reduced iron pellets, reduced iron briquettes, etc. Pig iron refers to cold iron cast into lumps of about 10 to 30 kg for easy handling.

[0020] The iron raw material (excluding reduced iron) is one or more of sintered ore, lump ore, pellets, etc., and these may contain auxiliary raw materials (for example, limestone, silica, serpentine, etc.). It is desirable that the reference operation is a stable operation. The stable operation refers to an operation state in which the gas flow in the furnace, the pressure drop of the charged material packed bed, the temperature distribution, etc. are properly controlled. For example, an operation state in which all of the following conditions are satisfied is regarded as a stable operation. · There is no uneven gas flow in the furnace and the gas is supplied relatively uniformly to the packed bed, or the fluctuation of the gas flow is small. · The fluctuation of the pressure drop of the charged material packed bed (for example, stagnation of the pressure drop, slip, etc.) is small. · Heat is supplied to the furnace without excess or deficiency, or the temperature fluctuation is small.

[0021] The ηCO distribution can be obtained by analyzing the gas composition measured by the upper zone probe of the blast furnace. In the shaft part of the blast furnace, a plurality of probes extending into the furnace (for example, upper probe, middle probe, lower probe) are installed, and the probe located closest to the furnace top among these probes is the upper probe. The number of measurement points by the upper probe is generally about 7 to 15. The ηCO distribution refers to a graph representing the distribution of ηCO in the furnace diameter direction.

[0022] The ηCO distribution may be obtained by giving the operating parameters of the reference operation to the blast furnace mathematical model (see Non-Patent Document 1) for analysis. That is, the ηCO distribution may be obtained based on the measurement results of the upper zone probe of the actual blast furnace, or may be obtained based on the blast furnace mathematical model.

[0023] In addition, the blast furnace mathematical model described below refers to the blast furnace mathematical model of Non-Patent Document 1 unless otherwise specified.

[0024] The blast furnace mathematical model is a mathematical model that divides the internal region of the blast furnace into a plurality of small regions, substitutes the preset blast furnace operating conditions and raw material properties in each small region into the arithmetic expressions of material balance, momentum balance, and energy balance for calculation processing, thereby calculating state variables such as the reduction reaction rate between solids (ore raw materials, etc.) and in-furnace gas (CO gas, H2 gas, etc.), in-furnace gas flow, in-furnace gas temperature, in-furnace gas composition, and ηCO in each small region, and comprehensively simulating the in-furnace state.

[0025] >High ηCO Region Identification Step< The high ηCO region identification step is a step of preliminarily identifying a high ηCO region where the relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO is 1.0 or more.

[0026] The average ηCO may be the average value of ηCO in the ηCO distribution (hereinafter, also referred to as "distribution average ηCO"), or may be ηCO calculated from the top gas (hereinafter, also referred to as "top gas ηCO"). The distribution average ηCO may be the arithmetic average value or the median of ηCO at each furnace diameter position measured by the upper sonde. Since the top gas is the gas collected at the top of the furnace, the top gas ηCO is uniquely determined. The distribution average ηCO and the top gas ηCO are generally the same value. Therefore, the relative ηCO calculated from the distribution average ηCO and the relative ηCO calculated from the top gas ηCO are generally the same value.

[0027] Note that the top gas ηCO may be obtained by analyzing the top gas of an actual blast furnace, or may be obtained based on the analysis results by the blast furnace mathematical model.

[0028] Also, according to the research results of the present inventors, the average value of ηCO in the ηCO distribution is often about 50%. Therefore, in the high ηCO region identification step, the average ηCO in the ηCO distribution may be regarded as 50%. In this case, it is not necessary to measure and calculate the distribution average ηCO and the top gas ηCO.

[0029] In the step of specifying the high ηCO region, a region where the relative ηCO is 1.1 or more is regarded as the high ηCO region. On the other hand, the region regarded as the high ηCO region may be a region where the relative ηCO is 1.1 or more, a region where the relative ηCO is 1.2 or more, or a region where the relative ηCO is 1.3 or more.

[0030] In addition, according to the findings of the present inventors, the high ηCO region usually exists continuously. However, there may be a case where the high ηCO region exists discontinuously. In this case, reduced iron may be charged into each of the plurality of discontinuous high ηCO regions.

[0031] >Charging step< The charging step is a step of charging 75 mass% or more of the reduced iron into the high ηCO region. That is, when the reduced iron contained in the iron raw material layer is 100 mass%, 75 mass% or more of the reduced iron is charged into the high ηCO region. The charging amount of the reduced iron is preferably 77 mass% or more, 80 mass% or more, 82 mass% or more, or 85 mass% or more.

[0032] In the present embodiment, since the high ηCO region is specified based on the average ηCO (in other words, with the furnace diameter position where the relative ηCO is 1.0 as the boundary), the high ηCO region can be defined in a relatively wide range. Therefore, it has excellent versatility compared to the method of Patent Document 2 in which the position for charging the reduced iron (the furnace diameter region where ηCO is 57% or more) is narrow or cannot be specified. In many cases, the furnace diameter region where ηCO is 57% or more described in Patent Document 2 does not exist in the furnace. Therefore, there are many cases where the operation method of Patent Document 2 cannot be implemented. On the other hand, the furnace diameter position where the relative ηCO is 1.0 always exists in the furnace in principle. The operation method of the blast furnace according to the present embodiment is applicable to various charge distributions.

[0033] In addition, in the operation illustrated in FIG. 1 described later, since it is difficult to specify the furnace diameter region where ηCO is 57% or more, it is difficult to specify the position for charging the reduced iron by the method of Patent Document 2.

[0034] By charging 75 mass% or more of the reduced iron contained in the iron raw material layer into the high ηCO region, the reduced iron can be intensively deposited in the region with a high reduction load, so that the reduction material ratio (RAR) can be reduced. The "iron raw material layer" means the ore layer located between the coke layers, and this ore layer may be formed by one dump or a plurality of dumps. In addition, although it is possible to intensively charge reduced iron into a part of the specified high ηCO region, there is a risk that the gas flow will change and the operation will become unstable due to the local improvement of the air permeability at the charging position. Therefore, it is desirable to charge reduced iron into the entire high ηCO region. Moreover, it is more desirable to uniformly charge reduced iron into the entire high ηCO region.

[0035] The raw material charging method for realizing this iron raw material layer can be explored using a model experiment device simulating a blast furnace or a numerical simulation model such as DEM (Discrete Element Method). In such an experimental device, the iron raw material is charged into the furnace while changing the arrangement of the reduced iron in the charging hopper, etc., to form an iron raw material layer. After forming the iron raw material layer, by evaluating the distribution of the reduced iron in the iron raw material layer, a raw material charging method for realizing the above layer structure can be explored. In the numerical simulation model, the processing performed in the above experimental device is simulated by information processing using software.

[0036] Here, the charging hopper can store reduced iron and iron raw materials other than reduced iron. That is, since the high ηCO region can be specified in a relatively wide range, reduced iron and iron raw materials other than reduced iron can be charged into the furnace from the same charging hopper (in other words, a combined charging hopper). Therefore, as described in Patent Document 2, it is not necessary to provide a sub-hopper dedicated to reduced iron.

[0037] When the iron raw material (including reduced iron) forming the iron raw material layer is 100% by mass, the proportion of reduced iron is preferably 0.5% by mass or more and 50% by mass or less. The proportion of reduced iron with respect to the iron raw material may be 0.8% by mass or more, 1.0% by mass or more, or 3% by mass or more. The proportion of reduced iron with respect to the iron raw material may be 40% by mass or less, 35% by mass or less, or 30% by mass or less. If the amount of reduced iron is excessively small, the effect of reducing the reducing agent ratio (RAR) cannot be fully exhibited. If the amount of reduced iron is excessively large, the amount of oxygen to be reduced decreases, so that the reducing gas decreases in terms of operation design, and there are disadvantages such as the furnace top gas temperature cannot be maintained.

[0038] The present inventors obtained the knowledge regarding the appropriate charging position of the above-described reduced iron from the analysis results of the blast furnace mathematical model. That is, using the blast furnace mathematical model, the influence of the charging position of reduced iron in the furnace diameter direction on the reducing agent ratio (RAR) was evaluated.

[0039] First, for a large blast furnace A with a furnace volume of about 4500 m 3 as an analysis target, the parameters of the blast furnace mathematical model were fitted so as to reproduce the operating conditions during the stable operation period without using reduced iron (in other words, the operating conditions of the reference operation) and the measurement values of the upper sonde. The ηCO distribution in the furnace diameter direction at the upper sonde position at this time (corresponding to the ηCO distribution obtained in the acquisition step) is shown in FIG. 1.

[0040] ηCO (50.3%) shown by the broken line in the figure is the average ηCO (furnace top gas ηCO) calculated based on the gas composition of the furnace top gas. As described above, the average ηCO may be the distribution average ηCO calculated based on the measurement results of the upper sonde.

[0041] FIG. 2 is a relative ηCO distribution in which ηCO in the ηCO distribution of FIG. 1 is replaced with relative ηCO. The relative ηCO was obtained by dividing ηCO in the ηCO distribution by the average ηCO. It can be confirmed that both ηCO and relative ηCO are low in the furnace center and near the furnace wall.

[0042] In the central part of the furnace and near the furnace wall, in order to ensure the air permeability inside the furnace, the weight ratio of ore raw material to coke, i.e., O / C (Ore by Coke), is low, and generally ηCO is also low. The analysis results in Figure 1 are consistent with this.

[0043] The region where the relative ηCO is 1.0 or more was defined as the high ηCO region, and the influence of the reduction iron charging position was analyzed using a blast furnace mathematical model. In the illustrated example, when the high ηCO region is defined by the dimensionless radius of the furnace diameter, it is from 0.38 to 0.89. Each charging condition was represented by Roman numerals (I to XV). The metallization rate of the reduction iron was 96 mass%, and the particle size was 42 mm. 10 mass% of the iron raw material during the reference operation was replaced with reduction iron (that is, iron raw material other than reduction iron: reduction iron = 90 mass%: 10 mass%), and the influence of the charging position of reduction iron in the furnace diameter direction on the reduction material ratio (RAR) was evaluated. The charging amount (mass%) of reduction iron for each furnace diameter position under each charging condition I to XV is shown in Tables 1 to 4. The furnace diameter position was shown by the dimensionless radius of the furnace diameter.

[0044] [Table 1]

[0045] [Table 2]

[0046] [Table 3]

[0047] [Table 4]

[0048] For any charging condition, the O / C distribution in the furnace diameter direction under the given conditions was assumed to be constant. Note that this ore (O) was defined as the sum of the weights of reduced iron and other iron raw materials. In the case of charging condition II, the amount charged to the center side of the furnace was larger than that in the high ηCO region, and in the case of charging condition XI, the amount charged to the furnace wall side was larger than that in the high ηCO region. The blast volume and oxygen enrichment amount were kept constant, and only the amount of PC injection was adjusted so that the hot metal temperature was constant, and the reduction material ratio (RAR) was compared.

[0049] Fig. 3 shows the influence of the reduced iron charging condition on the reduction material ratio (RAR). The reduction material ratio (RAR) deteriorated significantly between the case where reduced iron was concentrated near the furnace center (charging condition II) and the case where it was concentrated near the furnace wall (charging condition XI). This is due to the deterioration of ηCO and ηH2. From these results, it can be said that it is not desirable to concentrate the reduced iron near the furnace center or furnace wall with a low O / C. Also, in charging conditions XII, XIII, and XIV, the reduction material ratio (RAR) deteriorated significantly, similar to charging condition II.

[0050] Table 5 and Fig. 4 show the mixing ratio of reduced iron in the high ηCO region for each charging condition (the ratio of the reduced iron arranged in the high ηCO region when the total amount of reduced iron is 100 mass%) and the reduction material ratio (RAR). Fig. 4 is a scatter diagram of the data shown in Table 5, with the horizontal axis being the mixing ratio of reduced iron in the high ηCO region and the vertical axis being the reduction material ratio (RAR). Note that the mixing ratio of reduced iron is the ratio of the amount of reduced iron charged to the high ηCO region to the total amount of reduced iron charged into the furnace when charging the iron raw material containing reduced iron into the furnace. When the reduction material ratio was 442.0 kg / t or less, it was judged as qualified.

[0051]

Table 5

[0052] Under the charging conditions II, XI, XII, XIII, and XIV where the reducing agent ratio (RAR) deteriorated, it was found that the mixing ratio of reduced iron in the high ηCO region was low. Also, the reducing agent ratio (RAR) tended to decrease as the amount of reduced iron in the high ηCO region increased. From these analysis results, it became clear that when the mixing ratio of reduced iron in the high ηCO region is less than 75% by mass, the reducing agent ratio (RAR) increases significantly.

[0053] (Example) The present invention will be described in detail while showing examples.

[0054] Furnace volume 4000m 3 In the above large blast furnace B, for several days targeting a certain period (hereinafter also referred to as the operation period) during which the operation without using reduced iron (i.e., the reference operation) was stable, the ηCO distribution in the furnace diameter direction was obtained by gas analysis of the upper sonde, and the furnace top gas ηCO was measured by gas analysis at the furnace top, and the relative ηCO distribution was calculated. The results are shown in Fig. 5.

[0055] From the relative ηCO distribution, the region from a dimensionless radius of 0.33 to 0.94 in the furnace diameter (i.e., the region where the relative ηCO is 1.0 or more) was defined as the high ηCO region. Note that the period for specifying the high ηCO region is arbitrary, but it is more desirable to use the period during stable operation. Regarding stable operation, the explanation will not be repeated.

[0056] Without changing the charging conditions of the iron raw material and coke during the operation period, 10% by mass of the iron raw material was replaced with reduced iron having a metallization rate of 96%. In the examples, the aim was to charge reduced iron relatively uniformly into the specified high ηCO region. In the comparative examples, the aim was to concentrate the placement of reduced iron near the furnace wall.

[0057] From the results of preliminary studies by simulation, the mixing ratios of reduced iron in the high ηCO region in the examples and comparative examples were 84% by mass and 73% by mass, respectively. A comparison of the main blast furnace operating parameters of the examples and comparative examples is shown in Table 6.

[0058]

Table 6

[0059] It can be seen that there is no significant difference in the amount of molten iron discharged and the temperature of molten iron between the examples and the comparative examples. It was confirmed that in the examples, ηCO and ηH2 were higher than those in the comparative examples, and due to the improvement in the reduction efficiency, the reduction material ratio (RAR) could be made lower.

Claims

1. A method for operating a blast furnace in which iron raw materials including reduced iron are charged into the furnace, comprising the steps of: An acquisition step of acquiring in advance an ηCO distribution in a furnace radial direction in a standard operation in which the charged iron raw material does not contain reduced iron; A high ηCO region specifying step of specifying in advance a high ηCO region in which a relative ηCO obtained by dividing the ηCO in the ηCO distribution by the average ηCO is 1.0 or more, the average ηCO being defined as an average ηCO in the ηCO distribution or an average ηCO calculated from a furnace top gas; A charging step of charging 75 mass% or more of the reduced iron into the high ηCO region; having A method for operating a blast furnace comprising the steps of:

2. In the high ηCO region identification step, a relative ηCO distribution is obtained, which is a distribution of relative ηCO obtained by dividing ηCO in the ηCO distribution by the average ηCO, and the high ηCO region is identified based on the relative ηCO distribution.

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

3. The blast furnace has a charging hopper for charging the reduced iron, and the charging hopper is a dual-purpose charging hopper for charging the reduced iron and iron raw materials other than the reduced iron.

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

4. When the iron raw material is taken as 100 mass%, the proportion of reduced iron contained in the iron raw material is 0.5 mass% or more and 50 mass% or less.

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

5. In the charging step, 80 mass% or more of the reduced iron is charged into the high ηCO region.

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

6. In the high ηCO region identification step, a region in which the relative ηCO is 1.2 or more is regarded as the high ηCO region.

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

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