Particle size distribution evaluation method of reduced iron and gas permeability evaluation method in blast furnace

Abstract

To provide a particle size distribution evaluation method of reduced iron capable of accurately evaluating the particle size distribution of the reduced iron.SOLUTION: A particle size distribution evaluation method of reduced iron according to the present invention includes: a first step of acquiring image data of reduced iron; a second step of acquiring shape data of reduced iron particles using the image data of the reduced iron acquired in the first step; a third step of evaluating shape anisotropy of the reduced iron particles using the shape data of the reduced iron particles acquired in the second step; a fourth step of calculating a particle size using the shape data acquired in the second step for a reduced iron particle determined to have large shape anisotropy in the third step; and a fifth step of calculating a particle size distribution of the reduced iron using the particle size of the reduced iron particle calculated in the fourth step.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the particle size distribution of reduced iron and a method for evaluating the permeability inside a blast furnace. [Background technology]

[0002] In recent years, reducing CO2 emissions has been required to prevent global warming. In the steel industry, CO2 emissions from blast furnaces used to produce pig iron account for approximately 70% by mass of all CO2 emissions. Therefore, reducing CO2 emissions in blast furnace operation has become an urgent issue. In blast furnace operation, CO2 emissions can be reduced by reducing the amount of reducing material (e.g., coke, pulverized coal, natural gas) used. One method for doing so is the use of reduced iron (see Non-Patent Document 1). Furthermore, maintaining good permeability within the blast furnace promotes the reduction of iron oxide in the raw materials, thereby reducing the amount of reducing material used. The reduction reaction between iron oxide and reducing gas mainly occurs in the upper part of the blast furnace, known as the lumpy zone. Against this background, a method for evaluating the permeability of the lumpy zone has been proposed, in which the harmonic mean diameter and porosity of the raw materials are calculated from the particle size distribution of the raw materials, and the pressure drop in the raw material layer is evaluated (see Non-Patent Document 2). When this method is used, the particle size distribution of raw materials such as sintered ore and coke is measured before charging, and the shape of each raw material is controlled based on the harmonic mean diameter, which approximates a spherical shape. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Ujizawa et al., Iron and Steel Vol.92(2006) No.12 [Non-patent document 2] Yamada et al., Kawasaki Steel Technical Report Vol.6 (1974) No.1 Summary of the Invention [Problem to be solved by the invention]

[0004] The shape of reduced iron, especially compressed reduced iron, depends on the type of molding machine. From the perspective of molding efficiency, the shape is often close to a rectangular parallelepiped rather than a sphere. Therefore, when reduced iron is used as a raw material, the pressure drop evaluation formula described in Non-Patent Document 2 cannot be used. Furthermore, raw materials containing reduced iron break and partially pulverize during handling and transportation, resulting in variations in particle size and shape (particle size distribution). For this reason, the particle size distribution of raw materials such as sintered ore, lump ore, pellets, and coke is measured by sieving (JIS M 8706). However, when the particle size distribution of reduced iron is measured by sieving, the smallest surface of the reduced iron particle is classified as the particle size due to the large variations in size and shape (anisotropy) of the reduced iron particles. As a result, reduced iron particles with different volumes cannot be sieved, and the particle size distribution of reduced iron cannot be accurately evaluated. The inability to accurately evaluate the particle size distribution of reduced iron means that the porosity and pressure drop of the raw material layer, and ultimately the permeability inside the blast furnace, cannot be accurately evaluated.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for evaluating the particle size distribution of reduced iron, which can accurately evaluate the particle size distribution of reduced iron. Another object of the present invention is to provide a method for evaluating the permeability inside a blast furnace, which can accurately evaluate the permeability inside the blast furnace. [Means for solving the problem]

[0006] A method for evaluating the particle size distribution of reduced iron according to the present invention is a method for evaluating the particle size distribution of reduced iron to be charged into a blast furnace, and includes: a first step of acquiring image data of the reduced iron; a second step of acquiring shape data of the reduced iron particles using the image data of the reduced iron acquired in the first step; a third step of evaluating the shape anisotropy of the reduced iron particles using the shape data of the reduced iron particles acquired in the second step; a fourth step of calculating the particle size of reduced iron particles determined to have large shape anisotropy in the third step using the shape data acquired in the second step; and a fifth step of calculating the particle size distribution of the reduced iron using the particle size of the reduced iron particles calculated in the fourth step.

[0007] The method for evaluating the permeability inside a blast furnace according to the present invention includes the steps of calculating a pressure drop in a raw material packed bed using the particle size distribution of reduced iron calculated by the method for evaluating the particle size distribution of reduced iron according to the present invention, and evaluating the permeability inside the blast furnace based on the calculated pressure drop.

[0008] The method may further include a step of calculating the weight of the reduced iron particles determined to have large shape anisotropy by substituting the area of ​​the reduced iron particles obtained in the second step into a relational expression showing the relationship between the area and weight of the reduced iron particles, and calculating the void fraction of the raw material packed bed using the calculated weight. [Effects of the Invention]

[0009] According to the method for evaluating the particle size distribution of reduced iron of the present invention, the particle size distribution of reduced iron can be evaluated with high accuracy. Also, according to the method for evaluating the permeability inside a blast furnace of the present invention, the permeability inside a blast furnace can be evaluated with high accuracy. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the length and width of a reduced iron particle. [Figure 2] FIG. 2 is a diagram for explaining a method for calculating the width of a reduced iron particle. [Figure 3]FIG. 3 is a diagram showing the relationship between the measured weight and area of ​​reduced iron particles. [Figure 4] FIG. 4 is a diagram showing the measured and calculated values ​​of the porosity of reduced iron with small shape anisotropy. [Figure 5] FIG. 5 is a diagram showing the measured and calculated values ​​of the porosity of reduced iron with large shape anisotropy. [Figure 6] FIG. 6 shows particle size distributions of sintered ore and reduced iron. [Figure 7] FIG. 7 is a diagram showing the results of measuring the void ratio using the sintered ore shown in FIG. 6 and reduced iron. [Figure 8] FIG. 8 is a flowchart showing the flow of a method for evaluating the permeability inside a blast furnace according to one embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing a container used for measuring pressure loss. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a method for evaluating particle size distribution of reduced iron and a method for evaluating permeability inside a blast furnace according to the present invention will be described with reference to the drawings.

[0012] Reduced iron, particularly shaped reduced iron, cracks occur during handling and transportation, resulting in anisotropy in size and shape, particularly shape anisotropy. The inventors of the present invention have conducted extensive research to accurately evaluate the particle size distribution of reduced iron taking into account this shape anisotropy, and have found that the particle size distribution of reduced iron can be accurately evaluated by using image data of the reduced iron. The findings of the inventors of the present invention will be described in detail below with reference to the drawings.

[0013] The inventors of the present invention first left the reduced iron at rest and photographed it from above to obtain image data of the surface of the reduced iron particle with the largest area on a two-dimensional plane. Next, as shown in Fig. 1, a rectangular shape was created circumscribing the planar shape of the reduced iron particle RI, and the longer side of the rectangular shape was calculated as the length L of the reduced iron particle RI, and the diameter of the inscribed circle R centered at the center of gravity G of the reduced iron particle RI was calculated as the width W of the reduced iron particle RI. Here, the reason why the diameter of the inscribed circle R centered at the center of gravity G of the reduced iron particle RI is used as the width W of the reduced iron particle RI will be explained.

[0014] As shown in Figure 2, feathers formed during molding may remain on the outer periphery of reduced iron particles RI. However, because these feathers are fragile, they often break during material handling and transportation, and they often disappear after charging into the blast furnace. Therefore, to accurately predict the void fraction and pressure loss of the mixed raw material layer after charging into the blast furnace, it is necessary to evaluate the width of reduced iron particles RI excluding the feathers, rather than the width W' of reduced iron particles RI including the feathers shown in Figure 2. For this reason, in the present invention, the diameter of the inscribed circle R centered on the center of gravity G of the reduced iron particle RI is calculated as the width W of the reduced iron particle RI.

[0015] Next, the calculated length L and width W of the reduced iron particle RI were used to calculate the particle size of the reduced iron with a large anisotropy in shape. Specifically, the shape of a single particle of reduced iron was considered to be a rectangular parallelepiped, and the length L and width W of the reduced iron particle RI calculated from the image data of the reduced iron were used to calculate the briquette size of the reduced iron particle RI (thickness of the mold of the molding machine) T. b The surface area of ​​the reduced iron particles RI was calculated from the above equation. Then, the diameter of a sphere having the same surface area as the surface area of ​​the reduced iron particles RI was calculated as the single particle diameter d of the reduced iron using the following equation (1). M_i Here, the subscript i is an identification number of reduced iron with large shape anisotropy that does not satisfy the condition shown in the following formula (3). For example, if the total number of reduced iron with large shape anisotropy that does not satisfy the condition shown in the following formula (3) is N, then i = 1, 2, 3, ..., N.

[0016]

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[0017] Next, we evaluated the variation in the weight of reduced iron particles RI relative to their area. Figure 3 shows a graph in which the horizontal axis represents the area S of reduced iron particles RI obtained from reduced iron image data, and the vertical axis represents the measured weight per reduced iron particle. As shown in Figure 3, the measured weight per reduced iron particle is proportional to the area S of the reduced iron particle. This indicates that the anisotropy of the shape of reduced iron particles RI in the thickness direction is small.

[0018] Generally, the weight of a single particle of reduced iron is calculated by determining the volume of the single particle of reduced iron and multiplying it by its specific gravity. In this case, however, it is necessary to obtain data on the thickness of the single particle using a three-dimensional scanner or the like. However, as described above, the anisotropy of the shape of the formed reduced iron particles in the thickness direction is small. In other words, the formed reduced iron particles have the characteristic of being less likely to crack in the thickness direction.

[0019] Therefore, if a calibration curve showing the relationship between the area S and weight of reduced iron particles as shown in Figure 3 is created, the weight per single particle of reduced iron x can be calculated by substituting the area S of the reduced iron particles obtained from the 2D image data into the following equation (2): M_i can be calculated. Note that the parameter α in formula (2) indicates the slope of the calibration curve shown in Figure 3 and is obtained for each reduced iron molding machine. Here, the subscript i is the identification number of reduced iron with large shape anisotropy that does not satisfy the condition shown in formula (3) below. For example, if the total number of reduced iron with large shape anisotropy that does not satisfy the condition shown in formula (3) below is N, then i = 1, 2, 3, ..., N.

[0020]

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[0021] Next, for raw materials such as sintered ore, lump ore, and pellets, the shape of each particle is nearly spherical, so particle size classification by sieving (JIS M 8706) and weight measurement for each particle size are possible, and the porosity can be calculated from the particle size distribution using the method described in Non-Patent Document 2. Similarly, for reduced iron, reduced iron with small shape anisotropy, i.e., satisfying the condition shown in the following formula (3), was mixed with sintered ore, and the porosity ε was calculated using the method described in Non-Patent Document 2. As a result, as shown in Figure 4, the measured value and calculated value of porosity ε were almost identical. Note that W in formula (3) b indicates the width of the mold of the molding machine, but the width W of the reduced iron particles RI described above may also be used.

[0022]

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[0023] Next, reduced iron with large shape anisotropy, i.e., iron not satisfying the condition shown in Equation (3), was mixed with sinter, and the porosity ε was calculated using the method described in Non-Patent Document 2. As a result, as shown in Figure 5, it was confirmed that the measured and calculated values ​​of porosity ε differed significantly. This is thought to be because the porosity estimation formula described in Non-Patent Document 2 was constructed assuming spherical particles. For this reason, it is necessary to construct a porosity estimation formula that takes into account the influence of particles with large shape anisotropy, i.e., particles not satisfying the condition shown in Equation (3).

[0024] Therefore, the inventors of the present invention prepared sintered ore and reduced iron having the particle size distribution shown in Figure 6 and measured the porosity by changing the weight ratio of each. The porosity measurement results are shown in Figure 7. Note that the black plots in Figure 6 represent the representative diameter and weight of particles classified by sieving, while the white plots represent the representative diameter and weight calculated from image data. The porosity shown in Figure 7 was calculated from the weight and height of the sample packed into a container with a diameter of 1 m, after mixing sintered ore and reduced iron and filling it.

[0025] As a result, as shown in Figure 7, it was confirmed that the weight fraction of reduced iron with large shape anisotropy is proportional to the void fraction ε. In other words, as shown in the following mathematical formula (4), it was found that the void fraction ε of the raw material packed bed can be calculated by calculating the void fraction ε0 of raw material with small shape anisotropy and adding the result obtained by multiplying the weight fraction of raw material with large shape anisotropy by a coefficient. Note that x in mathematical formula (4) M is the sum of the weight of reduced iron particles with large shape anisotropy relative to the total weight of the filling material, Σx M_i The percentage of is shown.

[0026]

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[0027] Subsequently, the inventors of the present invention conducted extensive research into an estimation formula for pressure drop in a raw material packed bed containing a mixture of reduced iron and sintered ore. In order to calculate the estimation formula for pressure drop described in Non-Patent Document 2, it is necessary to determine the harmonic mean diameter and porosity obtained from the particle size distribution. In contrast, in the present invention, the harmonic mean diameter is determined from the particle size distribution of particles with small shape anisotropy. p ' and the harmonic mean diameter D calculated from the particle size distribution including particles with large shape anisotropy. p In addition, the porosity is expressed as the harmonic mean diameter D p After calculating the porosity ε0 from ', the value calculated using the above formula (4) and the harmonic mean diameter D p The value ε obtained from B Therefore, the pressure loss ΔP / L was calculated using the following formulas (5) to (7) and compared with the measured value. As a result, the harmonic mean diameter D p The pressure drop ΔP / L calculated from the formula (7) using the void fraction ε and the pressure drop ΔP / L was closest to the measured value. Therefore, in the present invention, the pressure drop ΔP / L of the raw material packed bed is calculated using the formula (7) shown below. Note that in the formulas (5) to (7), g c is the gravity conversion coefficient (-), μ is the gas viscosity (Pa·sec), u0 is the gas flow velocity (cm / sec), and ρ is the gas density (g / cm 3 ) is shown.

[0028]

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[0029]

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[0030]

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[0031] Hereinafter, a method for evaluating the permeability inside a blast furnace, which is one embodiment of the present invention, will be described, which has been conceived based on the above-mentioned studies.

[0032] Fig. 8 is a flowchart showing the flow of a method for evaluating the permeability inside a blast furnace according to one embodiment of the present invention. As shown in Fig. 8, in the method for evaluating the permeability inside a blast furnace according to one embodiment of the present invention, first, sampled reduced iron is left stationary for each brand, and the reduced iron is photographed from above to obtain image data of the reduced iron (step S1). Note that image data of the reduced iron transported by a belt conveyer may be obtained online. Next, shape data of a single reduced iron particle included in the obtained image data is obtained (step S2). Specifically, the length L, width W, and area S of a single reduced iron particle are calculated from the image data of the reduced iron.

[0033] Next, the shape anisotropy of the reduced iron particles is evaluated by determining whether the calculated length L of the reduced iron particles satisfies the condition shown in the above formula (3) (step S3). If the result of the determination is that the calculated length L of the reduced iron particles satisfies the condition shown in the above formula (3), the shape anisotropy of the reduced iron particles is determined to be small, and the process proceeds to step S6. On the other hand, if the calculated length L of the reduced iron particles does not satisfy the condition shown in the above formula (3), the shape anisotropy of the reduced iron particles is determined to be large, and the process proceeds to step S4.

[0034] Next, for reduced iron particles determined to have a large anisotropy of shape, the area S calculated in the process of step S2 is substituted into the above formula (2) to obtain the weight x of the reduced iron particles. M_i (Step S4). Then, by substituting the length L and width W calculated in the process of Step S2 into the above formula (1), the particle diameter d of the reduced iron particles is calculated. M_i On the other hand, for reduced iron particles determined to have small shape anisotropy, the harmonic mean diameter D p ' and weight are measured (step S6), and the harmonic mean diameter D p The porosity ε0 is calculated from (step S7).

[0035] Next, the weight x of the reduced iron particles calculated in the process of step S4 is M_i The weight fraction of reduced iron particles with large shape anisotropy x M Calculate the calculated weight ratio x M The void ratio ε of the raw material packed bed is calculated by substituting the void ratio ε0 and the void ratio ε0 into the above formula (4). Next, the harmonic mean diameter D p (Step S9). Finally, the pressure drop ΔP / L of the raw material packed bed is calculated using the above formula (7) (Step S10). Thereafter, the permeability inside the blast furnace is evaluated based on the calculated pressure drop ΔP / L. [Example]

[0036] Table 1 shows the weight of each representative diameter of reduced iron (HBI (Hot Briquetted Iron)) and sintered ore. The representative diameter and weight of sintered ore were determined by sieving (JIS M 8706) using the sieve mesh shown in Table 2. As shown in Table 3, the representative diameter and weight of reduced iron with small shape anisotropy that satisfied the condition shown in formula (3) were determined by sieving. On the other hand, with large shape anisotropy that did not satisfy the condition shown in formula (3), the values ​​obtained from the image data were calculated by substituting them into formulas (1) and (2). T in formula (1) b The value of is 30 mm, and W in formula (3)b The value was set to 55 mm.

[0037] As shown in Table 3, the reduced iron was classified into the following categories based on the particle diameter of a single reduced iron particle: 80.4 mm or more and 93 mm or less, 63.5 mm or more and less than 80.4 mm, 53.3 mm or more and less than 63.5 mm, 25 mm or more and less than 53.3 mm, 15 mm or more and less than 25 mm, 4.8 mm or more and less than 15 mm, and 0.1 mm or more and less than 4.8 mm. The average of the lower and upper limits of each category was used as the representative diameter, and the weight of each representative diameter was calculated.

[0038] [Table 1]

[0039] [Table 2]

[0040] [Table 3]

[0041] As shown in Table 1, the porosity ε0 was calculated from the particle size distribution of reduced iron particles with small shape anisotropy that satisfied the condition shown in Equation (3) and sintered ore using the method described in Non-Patent Document 2. Next, the weight ratio x M was obtained, and the void ratio ε of the raw material packed bed in which sintered ore and reduced iron particles were mixed was calculated using Equation (4). Table 4 also shows comparative examples. The comparative examples are obtained by using the conventional method described in Non-Patent Document 2 to obtain the void ratio ε B The harmonic mean diameter D p is the harmonic mean diameter calculated from the particle size distribution of the total reduced iron and sintered ore combined, and the porosity ε B was calculated using the formula described in Non-Patent Document 2. A comparison between the formula of the present invention and the conventional formula is shown in Table 5, and it was confirmed that the use of the formula of the present invention makes it possible to significantly reduce errors compared to the conventional formula. The relative error was calculated using the formula (8) shown below.

[0042]

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[0043] [Table 4]

[0044] [Table 5]

[0045] Next, to investigate the pressure drop in a raw material packed bed containing a mixture of sintered ore and reduced iron particles, samples with the particle size distribution shown in Table 6 were prepared. Iron chips were prepared to simulate reduced iron, with the sizes shown in Table 7. The samples shown in Table 6 were packed into a container shown in Figure 9, and air was allowed to flow at a flow rate of 5 cm / sec to measure the pressure drop. The harmonic mean diameter Dp' is the harmonic mean diameter found from the particle size distribution of particles with small shape anisotropy, and the void fraction ε was calculated using the above formula (4). Furthermore, the harmonic mean diameter D p is calculated from the particle size distribution of the total iron chips and sintered ore, and the porosity ε B was calculated using the method described in Non-Patent Document 2. Table 8 shows a comparison of the obtained harmonic mean diameter, porosity, and pressure loss. In the above formulas (5) to (7) used to calculate the pressure loss, the gas flow velocity u0 is 5 cm / sec, and the gas density ρ is 1.166×10 -3 g / cm 3 , the gas viscosity μ is 1.8×10 -5 Pa·sec, g c was set to 980. As shown in Table 8, it was confirmed that the pressure loss can be calculated more accurately by using the formula (7) compared to the formulas (5) and (6).

[0046] [Table 6]

[0047] [Table 7]

[0048] [Table 8]

[0049] Although the present invention has been described above as an embodiment, the present invention is not limited to the descriptions and drawings that form part of the disclosure of the present invention. In other words, other embodiments, examples, and operational techniques that can be made by those skilled in the art based on the present invention are all included in the scope of the present invention. [Explanation of symbols]

[0050] RI reduced iron particles

Claims

1. A method for evaluating the particle size distribution of reduced iron to be charged into a blast furnace, comprising: a first step of acquiring image data of the reduced iron; a second step of acquiring shape data of reduced iron particles using the image data of the reduced iron acquired in the first step; a third step of evaluating the shape anisotropy of the reduced iron particles using the shape data of the reduced iron particles acquired in the second step; a fourth step of calculating particle sizes of reduced iron particles determined to have large shape anisotropy in the third step using the shape data acquired in the second step; a fifth step of calculating a particle size distribution of the reduced iron using the particle sizes of the reduced iron particles calculated in the fourth step; A method for evaluating the particle size distribution of reduced iron, comprising:

2. 10. A method for evaluating the permeability inside a blast furnace, comprising the steps of: calculating a pressure drop in a raw material packed bed using the particle size distribution of reduced iron calculated by the method for evaluating the particle size distribution of reduced iron according to claim 1; and evaluating the permeability inside the blast furnace based on the calculated pressure drop.

3. 3. The method for evaluating permeability inside a blast furnace according to claim 2, further comprising a step of calculating a weight of the reduced iron particles determined to have large shape anisotropy by substituting the area of ​​the reduced iron particles obtained in the second step into a relational expression showing the relationship between the area and weight of the reduced iron particles, and calculating the void fraction of the raw material packed bed using the calculated weight.

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