Blast furnace operation method

Abstract

To suppress an increase in the thickness of a mixed layer in a cohesive zone and to enhance the air permeability in a furnace.SOLUTION: The present invention provides an operation method for a blast furnace for producing pig iron by alternately forming coke layers and ore layers. With a furnace diameter position included in the range of 0.1 or more and 0.3 or less in the blast furnace dimensionless radius as a boundary, the area on the furnace center side of this boundary is defined as the furnace center part and the area on the furnace wall side of this boundary is defined as the non-furnace center part. The coke layer in the non-furnace center part is divided into an upper layer and a lower layer, respectively, and the upper layer and the lower layer are defined as a coke upper layer and a coke lower layer, respectively. In this case, the operation method charges coke so that the hydrodynamic radius of the coke upper layer is smaller than the hydrodynamic radius of the coke lower layer and the hydrodynamic radius of the coke layer in the furnace center part.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace in which coke layers and ore layers are alternately formed. [Background technology]

[0002] Iron-containing ore raw materials (sinter, pellets, lump ore, etc.) and coke as a reducing agent and fuel are alternately charged into the blast furnace from the top. Tuyere is formed at the bottom of the blast furnace, and hot air is blown in from this tuyere, and auxiliary fuel such as pulverized coal is also blown in.

[0003] The ore raw material and coke (hereinafter collectively referred to as "burden") are alternately charged from the top of the furnace to form an ore layer and a coke layer, respectively. As the burden material descends in the blast furnace, it gradually descends toward the bottom of the furnace and is heated by the gas rising from the bottom of the furnace, thereby increasing its temperature. The ore materials that are heated and reduced while descending in the blast furnace begin to soften and fuse when they reach the bottom of the furnace, forming a fusion zone, which ultimately drips onto the hearth. In the fusion zone, the gaps between the ore materials decrease, reducing gas permeability. As a result, gas passes through the coke layer between the fusion zones and rises toward the furnace top. Therefore, the shape of the fusion zone has a significant impact on the permeability of the blast furnace.

[0004] In a blast furnace, the area before the ore begins to soften and melt is generally defined as the lumpy zone, the area where the ore melting layer exists (including the coke layer between the ore melting layers) is the melting zone, and the area after the ore starts to drip is defined as the dripping zone.

[0005] To ensure smooth discharge of burden materials during blast furnace operation, it is important to ensure permeability within the furnace. It is known that the particle size of the burden materials and the porosity of the burden packed bed significantly affect permeability within the furnace. It is also known that larger particle sizes improve permeability, and coke with a sharper particle size distribution has a higher porosity. Therefore, increasing the lower particle size limit of the burden is desirable as a means of ensuring permeability within the furnace. However, this would result in a decrease in yield due to an increase in the amount of return ore and small and medium-sized lump coke sent to the sintering process. This would result in a decrease in productivity of the sintering furnace and coke oven, an increase in production costs, and an imbalance in the material balance between processes. For this reason, it is difficult to increase the lower particle size limit of the burden materials beyond the current level.

[0006] Therefore, particle size-specific charging has been proposed as a method for improving the permeability of the ore layer and coke layer while maintaining the particle size distribution of the ore raw material and coke. Patent Document 1 describes a blast furnace operation method characterized by dividing the charge of either or both of raw ore material and coke into two or more portions based on particle size, and then charging the divided portions of the same type of charge in an order of decreasing particle size from the bottom to the top, and such that all of these layers reach from the center of the furnace to the furnace wall surface. According to this blast furnace operation method, the particle size distribution of each divided portion becomes sharp and the porosity increases, thereby improving permeability.

[0007] As mentioned above, ore raw materials and coke are charged alternately into a blast furnace, and a mixed layer where ore and coke coexist is formed at the boundary between the ore and coke layers. Because the average particle size of sintered ore, a typical ore raw material, is about 1 / 2 to 1 / 3 of the average particle size of coke, the particle size distribution of the mixed layer becomes broader and the porosity decreases. Therefore, from the viewpoint of permeability, the formation of a mixed layer is undesirable. The following factors (1) to (3) are thought to be factors in the formation of this mixed layer at the boundary between the ore and coke layers. (1) When ore materials are charged onto the coke layer, the kinetic energy of the falling ore materials causes the coke layer to collapse and form a mixed layer. (2) In the shaft of a blast furnace, the cross-sectional area of ​​the furnace increases as the burden material is lowered. This increases the thickness of the mixed layer due to the difference in particle size between the ore and coke, especially the fine ore particles penetrating into the coke layer. (3) In the cohesive zone, the ore materials soften and melt, and the load of the accumulated burden causes the molten ore materials to penetrate into the coke layer, increasing the thickness of the mixed layer.

[0008] According to the charging method described in Patent Document 1, not only the porosity of the ore layer and the coke layer is increased to improve permeability, but also the difference in particle size near the boundary between the ore layer and the coke layer is reduced, which is expected to suppress the formation of a mixed layer due to the difference in particle size described above in (2).

[0009] On the other hand, in the cohesive zone region of the blast furnace, the ore raw materials form a softened cohesive layer, which makes the gas permeability very poor, and gas flows unevenly into the coke layer between the cohesive layers. At this time, as described in (3) above, the molten ore raw materials penetrate into the coke layer, blocking the voids in the coke layer that serve as gas flow paths, further worsening the gas permeability. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 55-110708 Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, ensuring the permeability of the cohesive zone is essential for stable operation of a blast furnace. However, the charging method described in Patent Document 1 cannot sufficiently suppress the formation of a mixed layer derived from molten ore (i.e., the case of (3) above) when particle-size-specific charging is performed only on ore raw materials. [Means for solving the problem]

[0012] The present invention focuses on the hydraulic radius of the coke layer, and aims to operate a blast furnace with a relatively small hydraulic radius of the coke layer distributed in the non-furnace center upper layer. By reducing the hydraulic radius of the coke layer distributed in the non-furnace center upper layer, it becomes difficult for molten ore to penetrate the coke layer in the cohesive zone, and therefore it is possible to suppress an increase in the thickness of the mixed layer formed between the coke layer and the molten ore layer. On the other hand, the center of the furnace, where sufficient gas flow must be ensured, generally has a smaller amount of ore charged than the non-center of the furnace, so there is no problem of deterioration in permeability due to an increase in the thickness of the mixed layer.Instead, it is desirable to increase the hydraulic radius of the coke layer and improve permeability.

[0013] That is, one aspect of the method for operating a blast furnace according to the present invention is characterized in that (1) in a method for operating a blast furnace that produces pig iron by alternately forming coke layers and ore layers, the boundary is a furnace diameter position within the range of 0.1 to 0.3 inclusive of the dimensionless radius of the blast furnace, the area closer to the furnace center than this boundary is defined as the furnace center area, and the area closer to the furnace wall than this boundary is defined as the non-furnace center area, and the coke layer in the non-furnace center area is divided into an upper layer and a lower layer, which are defined as the upper coke layer and the lower coke layer, respectively, and coke is charged so that the hydraulic radius of the upper coke layer is smaller than the hydraulic radius of the lower coke layer and the hydraulic radius of the coke layer in the furnace center area. However, the hydraulic radius is defined by the following formula (A).

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[0014] (2) The method for operating a blast furnace according to (1) above, wherein the thickness of the upper coke layer is not more than twice the average particle size of the coke used in the blast furnace.

[0015] (3) The method for operating a blast furnace according to (1) or (2) above, characterized in that the hydraulic radius of the upper coke layer is 80% or less of the hydraulic radius of the lower coke layer.

[0016] (4) A method of operating a blast furnace according to any one of (1) to (3) above, characterized in that the particle size of the coke distributed to the upper coke layer is smaller than the particle size of the coke distributed to the lower coke layer and the particle size of the coke distributed to the coke layer at the center of the furnace.

[0017] (5) A method of operating a blast furnace according to (4) above, characterized in that the coke to be charged into the non-furnace center is divided into two parts by particle size in advance, and a coarse coke is charged into the furnace, followed by a fine coke, thereby forming a coke layer in the non-furnace center, and a coke having a particle size larger than that of the fine coke is charged into the furnace, thereby forming a coke layer in the furnace center.

[0018] (6) The method for operating a blast furnace according to (1) above, wherein the upper coke layer has a smaller porosity than the lower coke layer and the coke layer in the center of the furnace.

[0019] (7) A method of operating a blast furnace according to (6) above, characterized in that the upper coke layer is filled with stock coke, and the lower coke layer and the coke layer at the center of the furnace are filled with home-made coke.

[0020] (8) From another perspective, the method for operating a blast furnace according to the present invention is a method for operating a blast furnace that produces pig iron by alternately forming coke layers and ore layers, wherein a furnace diameter position within the range of 0.1 to 0.3 inclusive of the dimensionless radius of the blast furnace is used as a boundary, and the area closer to the furnace center than the boundary is defined as the furnace center, and the area closer to the furnace wall than the boundary is defined as the non-furnace center, and the coke layer in the non-furnace center is divided into an upper layer and a lower layer, which are defined as the upper coke layer and the lower coke layer, respectively, and the hydraulic radius of the upper coke layer is smaller than the hydraulic radius of the lower coke layer and the hydraulic radius of the coke layer in the furnace center. However, the hydraulic radius is defined by the following formula (A).

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[0021] According to the blast furnace operation method of the present invention, an increase in the thickness of the mixed layer in the cohesive zone is suppressed and permeability in the center of the furnace is ensured, thereby improving permeability in the entire blast furnace. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2 is an explanatory diagram for explaining the mechanism of formation of a mixed layer. [Figure 2] FIG. 10 is a graph showing the relationship between the interfacial grain size ratio and the thickness of the mixed layer. [Figure 3] FIG. 1 is an explanatory diagram for explaining the concept of hydraulic radius. [Figure 4] FIG. 2 is a diagram showing the relationship between the hydraulic radius of the coke layer and the mixed layer thickness. [Figure 5] The graph shows the relationship between the apparent particle size and porosity of coke and the hydraulic radius. [Figure 6] 1 shows the relationship between the mixed layer and the effective coke layer thickness in Examples and Comparative Examples. [Figure 7] FIG. 10 is a graph showing the relationship between gas flow rate and pressure loss in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0023] First, for the purpose of understanding the present invention, the mechanism by which a mixed layer is formed in the cohesive zone will be described in detail with reference to Fig. 1. Fig. 1 is an explanatory diagram for explaining the mechanism by which a mixed layer is formed.

[0024] Referring to the figure, ore layers O and coke layers C are alternately stacked in the blast furnace, and in the cohesive zone P, cohesive ore layers OF, which are softened and melted ore and have high airflow resistance, and coke slits, which are derived from the coke and have relatively low airflow resistance, are alternately formed. The arrows in the figure indicate the direction of gas flow. Reducing gas injected from the tuyere 11 passes through the coke slits in the cohesive zone P and flows to the furnace top. Molten iron HM and slag SL accumulate at the furnace bottom.

[0025] The mixed layer in the cohesive zone P is formed when the molten ore in the ore cohesive zone OF penetrates into the coke layer C under the load of the blast furnace burden. As described above, the mixed layer is formed from ore and coke with large particle size differences, and the particle size distribution is broad, resulting in a low porosity and impaired permeability. Therefore, in order to ensure permeability in the blast furnace, it is necessary to aim for a layer structure that makes it difficult for the mixed layer to thicken.

[0026] The inventors have demonstrated through the following experiments that the penetration of molten ore into the coke layer C can be effectively suppressed by reducing the hydraulic radius of the upper layer of the coke layer C in the non-furnace center area (hereinafter also referred to as the upper layer of the non-furnace center coke layer). Here, when the boundary between the furnace center area and the non-furnace center area is defined as boundary R, ​​boundary R is the dimensionless radius of the blast furnace and is 0.2. However, boundary R may be in the range of 0.1 to 0.3 and is not limited to 0.2. In other words, the furnace diameter region below boundary R is defined as the furnace center area, and the furnace diameter region above boundary R is defined as the non-furnace center area.

[0027] (load softening test) To identify the controlling factors for the thickness of the mixed layer in the cohesive zone, we conducted multiple load-softening tests. A sample consisting of an upper coke layer 40 mm high, a middle ore layer 120 mm high, and a lower coke layer 80 mm high was placed in a black smoke crucible and heated using a heater under specified conditions. The heater heating rate was 5°C / min in the temperature range from 25°C to 500°C, 6°C / min in the temperature range from 500°C to 800°C, and 7°C / min in the temperature range from 800°C to 1500°C. The test was terminated when the heater temperature reached 1500°C. The atmospheric gas was N2 gas (N2:100% by mass) in the temperature range up to 750°C, and a mixture of N2 and CO (N2:CO = 75% by mass:25% by mass) in the temperature range from 750°C to 1500°C. At the end of the test, the gas was switched back to N2 gas (N2:100% by mass). A load of 98 kPa was applied in the temperature range from 600°C to 1500°C. All conditions were based on a coke ratio (CR) of 301 kg / t and a pulverized coal ratio (PCR) of 190 kg / t. The final slag basicity was 1.26, equivalent to that of a commercial plant. The basicity was adjusted with limestone for levels 8 and 9. Table 1 shows the type and particle size of the samples used at each level. [Table 1]

[0028] (Filling structure analysis using X-ray CT images) Next, X-ray CT images of the sample-packed layer were taken after the test, and the thickness of the mixed layer at each level was evaluated by image analysis. The pixel size was 0.4 mm x 0.4 mm, and the slice pitch was 1.0 mm. The CT images were processed to calculate the ore ratio, porosity, and apparent particle size. Specifically, the CT images were first tri-valued based on brightness values ​​and classified into three regions: raw ore, coke, and voids.

[0029] Next, for each horizontal cross-sectional image, the number of pixels of the ore material (I o), the number of pixels of the coke (I c ), the number of void pixels (I v ), and the number of pixels on the solid side of the boundary between the void and the solid (ore raw material and coke) (I s-v ) were counted, and the ore ratio OR [%], porosity ε [-], and apparent particle size d were calculated using the following equations (1) to (3). e [mm] was calculated. Note that the particle size determined from the horizontal cross-sectional image is π / 4 times the actual size if the particles are assumed to be spherical, and this was corrected.

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[0030] (Governing factors for mixed layer formation in the cohesive zone) At all levels, the sample temperature at the end of the test was approximately 1440°C, which corresponds to the temperature range at the bottom of the cohesive zone (just before dripping). The particle size ratio (interface particle size ratio) of the coke / ore raw material and the mixed layer thickness are shown in Table 1 above, and their relationship is summarized in Figure 2. The interfacial particle size ratio and mixed layer thickness were determined by analyzing CT images of the packed bed before softening and fusion.

[0031] As mentioned above, in the lumpy zone (shaft), the cross-sectional area of ​​the furnace increases as the burden material descends, and the thickness of the mixed layer increases due to the difference in particle size between the ore raw material and the coke, but no clear correlation was observed in the cohesive zone. Specifically, the correlation coefficient was about 0.289. From this, it can be inferred that in the cohesive zone P, where the liquid phase ratio of the ore becomes high and melt penetration into the coke layer C occurs, the physical properties of the generated liquid phase and the permeability of the coke layer C are the dominant factors affecting the thickness of the mixed layer.

[0032] Furthermore, in this test or in actual blast furnace operation, the final basicity of the slag is constant, so there is no significant change in the physical properties of the resulting liquid phase, and it is thought that the liquid permeability of the coke layer C is the controlling factor. Therefore, the present inventors focused on the hydraulic radius of the coke layer C. Figure 3 is an explanatory diagram for explaining the concept of hydraulic radius, and shows a schematic diagram of the interface between the coke layer C and the ore layer O in the cohesive zone P. The coke particles constituting the coke layer C are designated by the symbol C. P The ore particles that make up the ore layer O are denoted by O. P Referring to the figure, the adjacent coke particle C P Between the particles, voids G of various sizes are formed. When we consider that fluids (gas or liquid) flow through pipes formed by the voids G between particles, the concept corresponding to the average value of the radii of each pipe corresponds to the hydraulic radius. In other words, the hydraulic radius corresponds to the width of the flow path for gas or liquid in the coke layer C, and is defined mathematically as follows:

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[0033] The calculated hydraulic radius for each level is shown in Table 1, and the relationship between the hydraulic radius and the mixed layer thickness is shown in Figure 4. In the high-temperature region corresponding to the lower end of the cohesive zone P, a correlation was found between the hydraulic radius of coke layer C and the amount of molten ore penetration (correlation coefficient: 0.763), and it was found that the amount of molten ore penetration increases as the hydraulic radius of coke layer C increases. From the above test results, it was found that by charging coke so that the hydraulic radius of the upper coke layer becomes smaller, the formation of a mixed layer can be suppressed and the permeability of the cohesive zone P can be improved.

[0034] (Coke charging) From the above findings, it can be said that in order to improve the permeability of the blast furnace, coke should be charged so that the hydraulic radius of the upper layer of the coke layer in the non-furnace center area becomes smaller. Specifically, the coke is charged so that the hydraulic radius of the upper non-furnace-center coke layer is smaller than that of the lower non-furnace-center coke layer (hereinafter also referred to as the "lower non-furnace-center coke layer"). Preferably, the coke is charged so that the hydraulic radius of the upper non-furnace-center coke layer is 80% or less of that of the lower non-furnace-center coke layer. There is no particular restriction on the lower limit, but it is desirable to charge the coke so that the hydraulic radius of the upper non-furnace-center coke layer is 10% or more of that of the lower non-furnace-center coke layer. This takes into consideration the ratio between the upper limit particle size (100 mm) and the lower limit particle size (10 mm) of the coke particle size distribution (10 mm or more and 100 mm or less) described below. The non-furnace-center lower coke layer refers to a portion of the non-furnace-center coke layer excluding the non-furnace-center upper coke layer. Note that the non-furnace-center lower coke layer may have a substantially constant or variable hydraulic radius within the layer.

[0035] Here, the coke layer in the center of the furnace needs to have a larger hydraulic radius than the upper coke layer in the non-center area of ​​the furnace. This is because the amount of ore charged in the center of the furnace, where sufficient gas flow must be ensured, is generally smaller than that in the non-center area of ​​the furnace. Therefore, it is more desirable to increase the hydraulic radius of the coke layer to improve permeability than to address the issue of thickening the mixed layer due to the penetration of molten ore.

[0036] Here, the coke used in the blast furnace operating method of this embodiment is the oversized coke used in a normal blast furnace, and is not the coke from which the fine particle side has been removed in advance as described in the background art. In other words, the blast furnace operating method of this embodiment is based on the premise that, instead of distributing to desired locations coke with a narrow particle size distribution from which fine coke has been removed in advance (for example, coke with a particle size distribution of 30 mm to 75 mm from which coke with a particle size less than 30 mm has been removed in advance), as explained in the background art, coke with a broad particle size distribution used in ordinary blast furnaces is distributed to appropriate locations. The particle size distribution of the broad coke is preferably 10 mm to 100 mm, more preferably 25 mm to 75 mm. This eliminates problems such as a decrease in yield due to an increase in the amount of return ore and small and medium-sized lump coke to the sintering process.

[0037] As is clear from the above equation (4), the hydraulic radius is determined by the apparent particle size of the coke (d e,c ) and the porosity of the coke layer (hereinafter also referred to as packed porosity). In equation (4), the apparent particle size of the coke (d e,c Instead of the above, the arithmetic mean diameter of the coke, the harmonic mean diameter of the coke, or the corrected mean particle size obtained by multiplying the arithmetic mean diameter of the coke or the harmonic mean diameter of the coke by a shape factor can be used. The packing void ratio is influenced by the particle size distribution, particle shape, fineness ratio, etc. of the coke, and by charging coke with a small packing void ratio, the hydraulic radius can be reduced.

[0038] The relationship between the apparent particle size and porosity of coke and the hydraulic radius is shown in Figure 5. As is clear from the figure, the hydraulic radius decreases as the porosity decreases and the apparent particle size decreases.

[0039] Comparing the coke particle size and mixed layer thickness with Table 1, the thickness of the mixed layer for each level is approximately twice the median coke particle size for each level. In this test, the coke particle size was adjusted to a range of 5 mm, and the median particle size was not significantly different from the average particle size. Therefore, it is desirable to set the upper layer thickness of the non-furnace center coke layer at approximately twice the average particle size of the charged coke. If the thickness of the upper layer of the non-furnace center coke layer exceeds twice the average coke particle size, the thickness of the coke layer with a small hydraulic radius will increase beyond the limit at which the molten ore can penetrate, which will actually increase the obstruction to gas permeability. That is, when the upper non-furnace-center coke layer is defined as a coke layer included in a region from the top surface of the non-furnace-center coke layer to a predetermined depth, the predetermined depth is included in the range of not less than the lower limit of the coke particle diameter but not more than twice the average particle diameter of the charged coke. Therefore, the predetermined depth may be the lower limit of the coke particle diameter, or may be twice the average particle diameter of the coke, or any value therebetween. The remaining coke layer of the non-furnace-center coke layer located below the upper non-furnace-center coke layer can be defined as the lower non-furnace-center coke layer.

[0040] A coke layer with a small hydraulic radius has the effect of inhibiting the penetration of molten ore, but it can also be a factor that inhibits gas permeability, so it is desirable to limit the thickness range within which molten ore penetration can occur. For example, when the average particle size of the coke is 50 mm, the upper layer of the non-furnace center coke layer is preferably set to an upper limit of about 100 mm from the upper surface of the coke layer.

[0041] The following is an example of a method for reducing the hydraulic radius of the upper layer of the non-furnace-center coke layer. (1) A method in which fine coke and coarse coke are separated into separate hoppers, the coarse coke is charged to form a lower non-furnace center coke layer, and then the fine coke is charged to form an upper non-furnace center coke layer. However, a method may be used in which the arrangement of coke in one hopper is set so as to achieve this charging sequence (a so-called method of controlling the discharge time sequence). The fine coke and the coarse coke can be obtained by pre-screening the coke used in the blast furnace. The particle size of the coke distributed in the furnace-center coke layer may be larger than that of the fine coke distributed in the upper non-furnace-center coke layer, regardless of its size relative to the coarse coke distributed in the lower non-furnace-center coke layer. However, from the viewpoint of improving the permeability of the furnace center, it is desirable that the particle size of the coke distributed in the furnace-center coke layer be equal to or larger than that of the coke distributed in the lower non-furnace-center coke layer. (2) A method in which cokes with different packing characteristics are separated into separate hoppers, and the coke with a larger packing void ratio is charged to form a lower layer of the non-furnace-center coke layer, and then the coke with a smaller packing void ratio is charged to form an upper layer of the non-furnace-center coke layer. However, a method may be used in which the arrangement of coke in one hopper is set so as to achieve this charging sequence (a so-called method of controlling the discharge time sequence). For example, stock coke can be used as a coke with a small packing void ratio, while for example, self-produced coke can be used as a coke with a large packing void ratio. Stock coke includes wet coke and purchased coke, and generally has a smaller particle size, higher sphericity, and a higher fineness rate than self-produced coke, resulting in a smaller packing void ratio. As shown in Figure 5, coke with a small particle size and low porosity packing characteristics has a small hydraulic radius, so using stock coke can reduce the hydraulic radius of the upper layer of the non-furnace center coke layer. Self-produced coke is described, for example, in JP 2021-167447 A. Stock coke is described, for example, in JP 2018-172734 A.

[0042] (Example) The present invention will be described in detail with reference to examples. Using cokes having the particle size distribution shown in Table 2, the effect of the coke layer structure on pressure drop (permeability) was evaluated based on a theoretical calculation method. Note that [%] in Table 2 is mass %. [Table 2] In the example, the coke was divided into fine particles (25 mm or more and 50 mm or less) and coarse particles (more than 50 mm and 75 mm or less), and the fine particles were distributed in the upper layer and the coarse particles in the lower layer. In Comparative Example 1, a method was used in which mixed coke of coarse particles and fine particles was charged (that is, a charging method similar to that used in normal blast furnace operation). In Comparative Example 2, a charging method was used in which fine particles were distributed in the lower layer and coarse particles in the upper layer (that is, a layer structure opposite to that of the Example). The packing characteristics of fine, coarse, and mixed coke are shown in Table 3. [Table 3] The shape factor and porosity were assumed based on the method in Non-Patent Document 1 (Ichida et al., Iron and Steel, Vol. 77 (1991), p. 1561-). The hydraulic radii of fine and coarse particles were calculated by substituting the mean particle size, shape factor, and porosity into Equation (4). That is, d in Equation (4) e,c The hydraulic radius of each particle was calculated by substituting the mean particle size × shape factor into ε and substituting the porosity into ε in equation (4). Note that the particle size distribution of each fine particle and coarse particle was assumed to have a skewness of 0 (i.e., mean particle size = average particle size), and the mean particle size × shape factor was substituted into equation (4). The hydraulic radius of the mixed coke was calculated by substituting the harmonic mean diameter, shape factor, and porosity into equation (4). The thickness of the mixed layer was estimated by linearly approximating the relationship between hydraulic radius and mixed layer thickness shown in Figure 4.

[0043] In Comparative Example 1, the coke layer thickness in each case was determined so that the coke charging amount was constant, based on the charging conditions where the coke layer thickness in the belly was 200 mm. Since it is thought that almost no gas can pass through the mixed layer where the molten ore has penetrated, the difference between the coke layer thickness and the mixed layer thickness was defined as the effective coke layer thickness. The graph of the comparison results is shown in Figure 6. In the examples, it was confirmed that by arranging the fine particles with a small hydraulic radius in the upper layer of the coke layer, the thickness of the mixed layer can be kept low, and the effective coke layer thickness can be increased.

[0044] Next, the pressure loss (air permeability) of the examples and comparative examples was compared. Assuming that no gas flows through the mixed layer, the height is the effective coke layer thickness, and the flow rate is 0.56 m in the horizontal direction for a coke layer with a depth of 1 m. 3 / s] or more than 1.68[m 3 The pressure drop was evaluated when a reducing gas of less than [kJ / s] was passed through the bed. The pressure drop was calculated using the Ergun equation, a general method for estimating pressure drop in packed beds. In the case where the reducing gas was charged separately into the fine particle section and the coarse particle section, the pressure drop was calculated assuming that the reducing gas was distributed so that the pressure drop in the coarse particle section and the fine particle section was equal. A comparison of the pressure drops is shown in Fig. 7.

[0045] It can be seen that the pressure drop in the Example is the lowest regardless of the gas flow rate. In addition, since the difference in pressure drop from the Comparative Example increases as the gas flow rate through the coke layer increases, it can be inferred that the effect of the present invention is more pronounced in low coke rate operation and high productivity operation. On the other hand, in Comparative Example 2, although the particle size distribution of the fine particle portion and the coarse particle portion is sharp due to particle size-specific charging, it is understood that the pressure loss increases compared to normal operation due to the increase in the thickness of the melt penetration layer. [Explanation of symbols]

[0046] 11 Tuyere Ore layer C Coke layer P cohesive zone SL Slug HM molten iron C P Coke particles O P Ore particles H molten ore penetration depth

Claims

1. A method for operating a blast furnace to produce pig iron by alternately forming coke layers and ore layers, comprising: When the furnace diameter position within the range of 0.1 to 0.3 in the dimensionless radius of the blast furnace is defined as a boundary, the furnace center side of the boundary is defined as the furnace center part, and the furnace wall side of the boundary is defined as the non-furnace center part, and the coke layer in the non-furnace center part is divided into an upper layer and a lower layer, which are defined as the upper coke layer and the lower coke layer, respectively, 1. A method for operating a blast furnace, comprising charging coke so that the hydraulic radius of the upper coke layer is smaller than the hydraulic radius of the lower coke layer and the hydraulic radius of the coke layer in the center of the furnace. Here, the hydraulic radius is defined by the following formula (A). [Equation 1] However, R ｈ : hydraulic radius [mm], ε: porosity of coke layer (-), d e,c : Coke particle size [mm]

2. 2. The method for operating a blast furnace according to claim 1, wherein the thickness of the upper coke layer is not more than twice the average particle size of the entire charged coke.

3. 3. The method for operating a blast furnace according to claim 1, wherein the hydraulic radius of the upper coke layer is 80% or less of the hydraulic radius of the lower coke layer.

4. 3. The method for operating a blast furnace according to claim 1, wherein the particle size of the coke distributed to the upper coke layer is smaller than the particle size of the coke distributed to the lower coke layer and the particle size of the coke distributed to the coke layer in the center of the furnace.

5. The coke to be charged into the non-furnace center portion is divided into two parts according to particle size in advance, and the coarse coke is charged into the furnace, and then the fine coke is charged into the furnace, thereby forming a coke layer in the non-furnace center portion; 5. The method for operating a blast furnace according to claim 4, wherein a coke layer is formed in the center of the furnace by charging coke having a particle size larger than that of the fine coke into the furnace.

6. 2. The method for operating a blast furnace according to claim 1, wherein the upper coke layer has a smaller porosity than the lower coke layer and the coke layer in the center of the furnace.

7. The upper layer of the coke is filled with stock coke, The coke lower layer and the coke layer in the center of the furnace are filled with homemade coke.

7. The method for operating a blast furnace according to claim 6.

8. A method for operating a blast furnace to produce pig iron by alternately forming coke layers and ore layers, comprising: When the furnace diameter position within the range of 0.1 to 0.3 in the dimensionless radius of the blast furnace is defined as a boundary, the furnace center side of the boundary is defined as the furnace center part, and the furnace wall side of the boundary is defined as the non-furnace center part, and the coke layer in the non-furnace center part is divided into an upper layer and a lower layer, which are defined as the upper coke layer and the lower coke layer, respectively, A method for operating a blast furnace, characterized in that the hydraulic radius of the upper coke layer is smaller than the hydraulic radius of the lower coke layer and the hydraulic radius of the coke layer in the center of the furnace. Here, the hydraulic radius is defined by the following formula (A). [Equation 2] However, R ｈ : hydraulic radius [mm], ε: porosity of coke layer (-), d e,c : Coke particle size [mm]

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