Method for charging raw material into blast furnace and method for producing molten iron

Abstract

To provide a method for charging a raw material into a blast furnace and a method for producing molten iron that can charge reduced iron into a portion of the furnace having a large reduction load in the radial direction without providing a dedicated hopper at the top of the furnace.　Provided is a method for mixing an ore raw material and reduced iron and introducing the mixture into the furnace in a bell-less blast furnace. When the ore raw material is charged into one of the furnace top bunkers by a charging conveyor, reduced iron is cut out on top of the ore raw material on the charging conveyor, reduced iron is layered onto the ore raw material over a length range of 4% to 32% and / or a length range of 61% to 96% of the distance from the leading edge in the transport direction, and the raw material is charged into the furnace top bunker in this state. In the furnace top bunker, the falling direction of the raw material is changed toward the furnace center axis x by a segregation control plate set in a prescribed direction. When the raw material in the furnace top bunker is charged into the furnace by a turning chute, charging of the raw material is performed while the turning chute is turned and tilted and the raw material charging position is moved from the furnace wall to the furnace center periphery side.

Description

Blast furnace raw material charging method and molten iron manufacturing method

[0001] The present invention relates to a method for charging raw materials in a bell-less blast furnace to obtain a desired burden distribution, and to a method for producing molten iron.

[0002] In recent years, CO ２ Global warming caused by increased CO emissions has become a problem, and the steel industry is also increasing its CO emissions. ２ The reduction of CO emissions from steelworks is an important issue. ２ Most of the CO is emitted from blast furnaces. ２ Emissions can be reduced by reducing the amount of reducing materials (coke, pulverized coal, natural gas, etc.) used in blast furnaces.

[0003] Coke serves as a heat source for melting raw ore, a reducing agent for raw ore, a recarburizer for carburizing molten iron to lower its melting point, and a spacer to ensure gas permeability within the blast furnace. Maintaining gas permeability with this coke stabilizes the unloading of the burden and ensures stable operation of the blast furnace.

[0004] where CO ２ From the viewpoint of reducing emissions, it is desirable to keep the ratio of coke charged to the blast furnace low. However, if the ratio of coke is reduced, the role of coke as described above also decreases, so it is necessary to improve the permeability of the ore layer as well as the reduction efficiency.

[0005] To address this problem, the use of metallic iron raw materials such as reduced iron and iron scrap has been considered, and various proposals have been made regarding the charging method, etc. Among them, Patent Document 1 discloses a method in which reduced iron and iron scrap held in a sub-hopper at the top of the furnace are charged, together with ore held in the main hopper, by a rotating chute to a portion where the gas utilization rate of the exhaust gas is high, which indicates a high reduction load of the ore. The following describes an example in which reduced iron is used as the metallic iron raw material.

[0006] According to the method of Patent Document 1, reduced iron can be charged only to a portion of the blast furnace where the reduction load is large in the radial direction thereof, and therefore the reduction state of the ore in the furnace can be effectively stabilized, and the gas flow can also be stabilized.

[0007] JP 2019-183270 A

[0008] Shinroku Matsuzaki and Yoshihiro Taguchi, "Analysis of Segregation Phenomena Considering Both Particle Size and Particle Density," Tetsu-to-Hagané, Vol. 88, No. 12, 2002, pp. 823-830

[0009] However, the method of Patent Document 1 requires the installation of a dedicated sub-hopper at the furnace top for holding reduced iron, which increases the equipment cost. Another problem is that charging reduced iron from a dedicated hopper increases the charging time. While a charging method in which separate batches of reduced iron are set to be charged can be considered to address these problems, this method increases the number of charging batches, thereby increasing the charging time and reducing productivity.

[0010] In order to solve the above-mentioned problems, it is necessary to charge reduced iron discharged onto a charging conveyor from a raw material hopper and ore raw materials discharged onto a separate charging conveyor into one furnace top bunker and then charge them into the furnace through a rotating chute. However, for example, when the ore raw materials are divided into two batches and reduced iron is mixed with the first batch, it has not been found until now how the reduced iron and ore raw materials should be charged into the furnace top bunker so that the reduced iron can be charged to a portion of the blast furnace where the reduction load is large in the radial direction.

[0011] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a raw material charging method and a method for producing molten iron that can charge metallic iron raw materials such as reduced iron into radially heavy reduction load areas of a blast furnace without providing a dedicated hopper for reduced iron or the like at the top of the furnace and without increasing the number of charging batches.

[0012] Taking the case of using reduced iron as the metallic iron raw material as an example, in order to solve the above-mentioned problems, the present inventors have conducted extensive research into the relationship between the burden distribution (distribution of reduced iron) and factors (and combinations thereof), such as (i) a method for cutting out reduced iron on a charging conveyor (the stacking pattern on the ore raw material), (ii) a method for tilting a rotating chute, (iii) the use of segregation control plates in a furnace top bunker, and (iv) a method for mixing reduced iron in two batches of ore raw material charging. As a result, it has been found that by optimizing and combining the above factors (i) to (iii), and preferably further optimizing and combining factor (iv), it is possible to accurately charge reduced iron into a desired position (a portion with a large reduction load) when ore raw materials and reduced iron held in one furnace top bunker are charged into a furnace.

[0013] The present invention was made based on this finding and is summarized as follows: [1] A method for charging a mixture of ore raw material (a) containing at least one of sintered ore, pellets, and lump ore and metallic iron raw material (b) containing reduced iron and / or granulated pig iron into a bell-less blast furnace having a plurality of top bunkers arranged in parallel and a raw material charging device for charging raw materials into the furnace by a revolving chute, the method comprising: conveying the ore raw material (a) to the top of the blast furnace by a charging conveyor and charging it into one of the top bunkers; cutting out the metallic iron raw material (b) on top of the ore raw material (a) conveyed by the charging conveyor; thereby stacking the metallic iron raw material (b) on the ore raw material (a) within the length range of the ore raw material (a) loaded on the charging conveyor within the length range of (i) and / or (ii) below; and charging the raw materials in this state into the top bunker; A method for charging raw materials into a blast furnace, wherein a segregation control plate is installed in the top bunker, and the raw material receiving surface of the segregation control plate faces toward the inside of the furnace in the radial direction of the furnace and is inclined downward relative to the inside of the furnace, and raw materials falling from above are allowed to fall downward via the raw material receiving surface of the segregation control plate, thereby depositing them in the top bunker, and when the raw materials in the top bunker are charged into the furnace using the rotating chute, the rotating chute is rotated and tilted to move the raw material charging position from the furnace wall toward the periphery of the furnace center, thereby charging the raw materials. (i) A length range of 4% or more and 32% or less of the distance from the front side in the conveying direction. (ii) A length range of 61% or more and 96% or less of the distance from the front side in the conveying direction. [2] The raw material charging method for a blast furnace according to [1], wherein, when the ore raw material (a) is transported to the furnace top by the charging conveyor and charged into one of the furnace top bunkers, the metallic iron raw material (b) is stacked on the ore raw material (a) in the length ranges (i) and / or (ii) below of the loading length of the ore raw material (a) loaded on the charging conveyor: (i) a length range of 4% or more and 18% or less of the distance from the front side in the conveying direction; (ii) a length range of 61% or more and 96% or less of the distance from the front side in the conveying direction. [3] The raw material charging method for a blast furnace according to [1] or [2], wherein, when one charge of the ore raw material (a) is charged into the furnace in two batches, the metallic iron raw material (b) is mixed with the ore raw material (a) of the first batch and then charged into the furnace.[4] The raw material charging method for a blast furnace according to [3], wherein the second batch of ore raw material (a) is charged into the furnace without being mixed with the metallic iron raw material (b). [5] The raw material charging method for a blast furnace according to any one of [1] to [4], wherein the average apparent density of the metallic iron raw material (b) is larger than the average apparent density of the ore raw material (a). [6] The raw material charging method for a blast furnace according to [5], wherein the ratio of the average apparent density of the metallic iron raw material (b) to the average apparent density of the ore raw material (a) is 1.25 or more. [7] The raw material charging method for a blast furnace according to any one of [1] to [6], wherein the aspect ratio of the longest side to the shortest side of the metallic iron raw material (b) is 1.4 or more. [8] The raw material charging method for a blast furnace according to any one of [1] to [7], wherein the average particle size of the metallic iron raw material (b) is larger than the harmonic mean particle size of the ore raw material (a). [9] The method for charging raw materials into a blast furnace according to any one of [1] to [8], wherein the ratio of the average particle size of the metallic iron raw material (b) to the harmonic mean particle size of the ore raw material (a) is 3.5 or more.

[10] The method for producing molten iron according to any one of [1] to [9], comprising a step of mixing an ore raw material (a) containing at least one of sintered ore, pellets, and lump ore, and a metallic iron raw material (b) containing reduced iron and / or granulated pig iron, and charging the mixture into a blast furnace.

[0014] According to the raw material charging method of the present invention, metallic iron raw materials such as reduced iron can be accurately charged to a radially large reduction load position of the blast furnace without providing a dedicated hopper for reduced iron or the like at the furnace top or increasing the number of charging batches. This improves productivity and reduces equipment costs in blast furnace operation. Furthermore, according to the present invention, by charging one charge of ore raw materials into the furnace in two batches and mixing the metallic iron raw materials with the ore raw materials of the first batch, the metallic iron raw materials can be charged to a particularly suitable position. Furthermore, according to the molten iron production method of the present invention, raw materials are charged by the above-described raw material charging method, thereby enabling high productivity production of molten iron while keeping equipment costs low.

[0015] FIG. 1 is an explanatory diagram schematically showing the process from when raw materials are released onto a charging conveyor until they are transported to the top of a blast furnace in one embodiment of the present invention. FIG. 2 is an explanatory diagram schematically showing the process from when raw materials are transported to the top of a blast furnace by a charging conveyor to when they are loaded into the furnace by a raw material charging device in one embodiment of the present invention. FIG. 3 is an explanatory diagram schematically showing the use of a segregation control plate installed in a top bunker in one embodiment of the present invention. FIG. 4 is an explanatory diagram schematically showing the charging of raw materials through a rotating chute in one embodiment of the present invention. FIG. 5 is an explanatory diagram showing the layering conditions of metallic iron raw materials b relative to ore raw materials a transported by a charging conveyor in the present invention. FIG. 6 is an explanatory diagram schematically showing a model experimental apparatus of an actual blast furnace used in an experiment to measure the discharge distribution of raw materials (sintered ore and reduced iron) from the top bunker. FIG. 7 is a graph showing the discharge rate of metallic iron raw materials (reduced iron) at each stage of raw material discharge from the top bunker in a test in which raw materials were charged into the top bunker using the experimental apparatus of FIG. 6 according to the conditions of the present invention. FIG. 8 is a graph showing the discharge rate of metallic iron raw material (reduced iron) at each stage of raw material discharge from the top bunker in a test in which raw materials were charged into the top bunker using the experimental apparatus of FIG. 6 under the conditions of the present invention. FIG. 9 is a graph showing an example of the particle size (discharge particle size distribution of the ore raw material) of the ore raw material (sintered ore) at each stage of raw material discharge from the top bunker in a test in which raw materials were charged into the top bunker using the experimental apparatus of FIG. 6 under the conditions of the present invention. FIG. 10 is a schematic diagram showing an HBI discharge experimental apparatus for conducting an experiment to measure the segregation behavior of HBI. FIG. 11 is a graph showing an example of measurement results of the movement distance of HBI in an experiment using the discharge experimental apparatus of FIG. 10. FIG. 12 is a graph showing the relationship between the apparent density of HBI and the representative movement distance in an experiment using the discharge experimental apparatus of FIG. 10. FIG. 13 is a graph showing the relationship between the aspect ratio of HBI and the representative movement distance in an experiment using the discharge experimental apparatus of FIG. 10. Fig. 14 is a graph showing the relationship between the particle size ratio of HBI and the representative moving distance in an experiment using the discharge experimental apparatus shown in Fig. 10. Fig. 15 is an explanatory diagram showing a schematic diagram of the shape (cross section) of the deposit in the furnace when ore raw material a is charged into the furnace in two batches in the present invention.Fig. 16 is a schematic diagram illustrating a model testing apparatus used in an experiment to verify the layering conditions of metallic iron raw materials b relative to ore raw materials a transported by a charging conveyor. Fig. 17 is a diagram illustrating the layering conditions of metallic iron raw materials b relative to ore raw materials a in an experiment using the model testing apparatus of Fig. 16. Fig. 18 is a graph showing the mixing ratio of reduced iron in the furnace radial direction in an experiment using the model testing apparatus of Fig. 16. Fig. 19 is a graph showing the discharge ratio of metallic iron raw materials (reduced iron) when raw materials are discharged from the top bunker in an experiment using the model testing apparatus of Fig. 16. Fig. 20 is a graph showing the discharge ratio of metallic iron raw materials (reduced iron) at each stage of raw material discharge from the top bunker in a test in which raw materials were charged into the top bunker under conditions outside the scope of the present invention.

[0016] In a blast furnace, ore raw materials such as sintered ore and coke (lump coke) are charged alternately from the top of the furnace to form a layered charging layer (packed bed). The amount of one layer of this ore raw material layer and coke layer is called one charge of ore raw material and one charge of coke, respectively. These one charge of ore raw material and coke are not necessarily charged into the furnace in one go; one charge of ore raw material and coke may be divided and charged into the furnace in multiple batches. These divided ore raw material and coke are called one batch of ore raw material and one batch of coke, respectively.

[0017] The raw material charging method of the present invention is applicable to a bell-less top blast furnace having a plurality of furnace top bunkers arranged in parallel and a raw material charging device that charges raw materials into the furnace using a rotating chute. In a bell-less top blast furnace, lump coke and ore raw materials, each removed from a raw material hopper, are charged into separate furnace top bunkers and then alternately introduced into the furnace using a rotating chute. In this type of raw material charging, the present invention mixes ore raw material a and metallic iron raw material b (e.g., reduced iron) and charges them into the furnace. During raw material charging, the metallic iron raw material b is selectively charged into a radially heavy portion (position) of the furnace where the reduction load is large.

[0018] In the present invention, the ore raw material a is a general term for sintered ore, pellets, lump ore, and the like, which are widely used as iron sources for blast furnaces. The ore raw material a used in the present invention includes at least one of sintered ore, pellets, and lump ore. Furthermore, the metallic iron raw material b used in the present invention refers to a raw material containing 80 mass% or more of metallic iron, and includes reduced iron and / or granulated pig iron. Note that the ore raw material a may be mixed with auxiliary materials (e.g., limestone, silica, serpentine, etc.) primarily for the purpose of adjusting the composition of the slag, and this case is also included in the present invention.

[0019] Here, the reduced iron generally used is a molded body of reduced iron, and a representative example is a molded body of reduced iron called HBI (hot briquette iron). HBI is obtained by hot compression molding (molding) of reduced iron obtained by reducing ores (lump ore, pellets, etc.) with a reducing gas. Other examples of reduced iron other than HBI include lump reduced iron obtained by partially reducing ores such as sintered ore, pellets, and lump ore with a reducing gas; and reduced iron molded bodies obtained by molding iron-based dust generated in blast furnaces, converters, electric furnaces, etc. Granulated pig iron is a granular iron material obtained by cooling and solidifying molten pig iron in a dispersed state. Granulated pig iron is generally obtained by dropping dispersed molten pig iron droplets into cooling water and cooling them. The average particle size is typically several millimeters to several tens of millimeters.

[0020] Figures 1 to 4 are explanatory diagrams schematically illustrating one embodiment of the present invention. Figure 1 shows the process from when raw materials are discharged onto a charging conveyor until they are transported to the top of a blast furnace. Figure 2 shows the process from when raw materials are transported to the top of the blast furnace by the charging conveyor to when they are loaded into the furnace by a raw material charging device. Figure 3 shows the use of a segregation control plate installed in a furnace top bunker. Figure 4 shows the charging of raw materials through a rotating chute. Figure 5 is an explanatory diagram showing the stacking conditions for metallic iron raw materials b relative to ore raw materials a transported by a charging conveyor in the present invention. In the figures, 1 denotes the furnace body of a blast furnace, 2 denotes the raw material charging device installed at the top of the furnace, and 3 denotes the charging conveyor that transports raw materials to the top of the furnace and supplies them to the raw material charging device 2.

[0021] The raw material charging device 2 is composed of multiple furnace top bunkers 4 arranged in parallel, a rotating chute 5 that charges the raw materials discharged from each furnace top bunker 4 into the furnace, and a collecting hopper 6 that supplies the raw materials discharged from each furnace top bunker 4 to the rotating chute 5.

[0022] The multiple top bunkers 4 are arranged in parallel around the furnace central axis x. Therefore, when there are two top bunkers 4, they are usually arranged symmetrically around the furnace central axis x, and when there are three or more top bunkers 4, they are arranged at intervals (for example, at equal intervals) in the circumferential direction around the furnace central axis x.

[0023] Each top bunker 4 (bunker body) is composed of an upper cylindrical portion 41 and a lower funnel-shaped portion 42, and a raw material discharge port 40 is provided at the lower end (the lower end of the funnel-shaped portion 42). Here, the raw material discharge port 40 is aligned with the bunker central axis x in the furnace radial direction. Ｂ It is preferable to provide the raw material discharge port 40 at a position eccentric to the furnace central axis x (closer to the furnace central axis x), and more preferably as close to the furnace central axis x as possible. Ｂ When the top bunker 4 is installed above the furnace, the side shape of the furnace top bunker 4 in the furnace radial direction becomes symmetrical. In this case, the diameter of the collecting hopper 6 that receives raw materials from multiple top bunkers 4 becomes large, so the raw materials tend to flow eccentrically with respect to the central axis of the rotating chute 5, and as a result, the center position of charging by the rotating chute 5 tends to shift.

[0024] In this embodiment, the wall (shell) 421 of the funnel-shaped portion 42 on the side opposite to the furnace central axis x (furnace wall side) has an inclination as a funnel-shaped portion, whereas the wall (shell) 420 on the furnace central axis x side is vertical or has a steeper inclination (close to vertical) than the wall 421. As a result, the raw material discharge port 40 is provided at a position eccentric to the furnace central axis x side in the furnace radial direction.

[0025] A flow rate adjusting gate (not shown) is provided at the raw material discharge port 40 at the bottom of each top bunker 4, and the raw materials discharged from the raw material discharge port 40 after having their flow rate adjusted by this flow rate adjusting gate are guided to the rotating chute 5 via a collecting hopper 6 and a top ring 7. This rotating chute 5 rotates around its base end (upper end) located on the furnace central axis x and tilts in the furnace radial direction with the base end (upper end) as a pivot to charge the raw materials into the furnace.

[0026] Reference numeral 9a denotes an ore raw material hopper, 10 denotes a reserving hopper, and 9b denotes a metallic iron raw material hopper that holds metallic iron raw material b such as reduced iron. Reference numeral 11 denotes an ore conveyor that transports the ore raw material a discharged from the ore raw material hopper 9a to the reserving hopper 10.

[0027] The raw materials discharged from the raw material hoppers are transported to the furnace top by the charging conveyor 3 and charged into one of the furnace top bunkers 4. At this time, as shown by the dashed lines in Figures 2 and 3, the raw materials fall diagonally downward away from the furnace central axis x through a receiving chute 12. In the embodiment shown in Figures 1 to 4, the ore raw material a is held in the reserving hopper 10 (and the ore raw material hopper 9a), and the metallic iron raw material b is held in the metallic iron raw material hopper 9b. The raw materials held in these hoppers are discharged onto the charging conveyor 3 as appropriate.

[0028] In the present invention, when ore raw material a is cut out onto the charging conveyor 3 and transported to the furnace top by the charging conveyor 3 to be charged into one of the furnace top bunkers 4, metallic iron raw material b is cut out and piled up on the ore raw material a transported by the charging conveyor 3. At this time, of the loading length L of the ore raw material a loaded on the charging conveyor 3, metallic iron raw material b is piled up on the ore raw material a in the length ranges (i) and / or (ii) below: (i) A length range of 4% or more and 32% or less of the distance from the front side in the conveying direction. (ii) A length range of 61% or more and 96% or less of the distance from the front side in the conveying direction.

[0029] That is, as shown in Figures 5(A) to 5(C), the length range w (w1, w2) for stacking the metallic iron raw material b relative to the stacking length L of the ore raw material a is set to one of the following: - A length range w1 of 0.04L or more and 0.32L or less from the leading end in the conveying direction (Figure 5(A)) - A length range w2 of 0.61L or more and 0.96L or less from the leading end in the conveying direction (Figure 5(B)) - A length range w1 of 0.04L or more and 0.32L or less and a length range w2 of 0.61L or more and 0.96L or less from the leading end in the conveying direction (Figure 5(C)).

[0030] Then, in this state, the ore raw materials a and the metallic iron raw materials b are charged into the top bunker 4. As will be described later, in the stacking configuration (i) above, the discharge rate of the metallic iron raw materials b at the initial stage of raw material discharge from the top bunker 4 is increased when the stacking position of the metallic iron raw materials b is shifted closer to the front side in the conveying direction. For this reason, it is more preferable to stack the metallic iron raw materials b on the ore raw materials a in a length range w from the front side in the conveying direction of 4% (0.04 L) to 18% (0.18 L) of the stacking length L of the ore raw materials a loaded on the charging conveyor 3.

[0031] Here, the stacking position (range) of the metallic iron raw material b in the stacking configuration (i) above can be arbitrarily selected as long as the distance from the leading end in the conveying direction is within a length range of 4% (0.04 L) to 32% (0.32 L) of the stacking length L of the ore raw material a. It is more preferable to arbitrarily select the stacking position (range) from a length range of 4% (0.04 L) to 18% (0.32 L) of the distance from the leading end in the conveying direction. Therefore, as the length range of 4% (0.04 L) to 32% (0.32 L) of the distance from the leading end in the conveying direction, for example, a length range of 10 (0.10 L) to 30% (0.30 L) of the distance from the leading end in the conveying direction can be selected. Alternatively, a length range of 8 (0.08 L) to 25% (0.25 L), etc., can be selected. Furthermore, as the length range of 4% (0.04L) or more and 18% (0.18L) or less of the distance from the leading edge in the conveying direction, for example, a length range of 8 (0.08L) to 15% (0.15L) of the distance from the leading edge in the conveying direction can be selected, or a length range of 10 (0.10L) to 18% (0.18L) can be selected.

[0032] Furthermore, the stacking position (range) of the metallic iron raw material b in the stacking form (ii) above can be selected arbitrarily as long as the distance from the front end in the conveying direction is within a length range of 61% (0.61 L) to 96% (0.96 L) of the loaded length L of the ore raw material a. Therefore, for example, a length range of 65 (0.65 L) to 80% (0.80 L) or 70 (0.70 L) to 85% (0.85 L) of the distance from the front end in the conveying direction can be selected.

[0033] Furthermore, among metallic iron raw materials b, reduced iron briquettes such as HBI are obtained by bridging reduced iron using twin briquettes or the like, but sharp burrs are formed in the gap between the briquettes. If these burrs come into direct contact with the conveyor belt of the charging conveyor 3, they may cause damage to the conveyor belt. Therefore, it is preferable that metallic iron raw materials b are not directly loaded onto the charging conveyor 3, even partially, but are loaded (stacked) only on the ore raw materials a in accordance with the conditions of the present invention.

[0034] As shown in FIG. 3 , the raw materials (ore raw material a + metallic iron raw material b) charged into the top bunker 4 fall downward via a segregation control plate 8 installed in the top bunker 4 and accumulate in the bunker. The segregation control plate 8 is disposed in the upper space of the top bunker 4 and is supported so as to be tiltable up and down around a pivot 81. The front surface of the segregation control plate 8 forms a raw material receiving surface 80 that receives the raw materials falling from above. The segregation control plate 8 is oriented so that the raw material receiving surface 80 faces the furnace inner side (the direction of the furnace central axis x) in the furnace radial direction and is inclined downward relative to the furnace inner side (the direction of the furnace central axis x). Therefore, the raw materials introduced into the top bunker 4 from the receiving chute 12 fall obliquely downward away from the furnace central axis x. However, when the raw materials hit the raw material receiving surface 80 of the segregation control plate 8, their falling direction is changed and they fall obliquely downward toward the furnace central axis x. As a result, the raw material is aligned along the bunker center axis x Ｂ The raw material falls to a position closer to the furnace central axis x than the position (above the raw material discharge port 40 in this embodiment).

[0035] The segregation control plate 8 only needs to receive the raw material falling away from the furnace central axis x, change its direction, and guide it toward the furnace central axis x, so the inclination angle of the segregation control plate 8 (raw material receiving surface 80) can be set to an appropriate angle that enables this. However, if the inclination angle θ of the raw material receiving surface 80 relative to the horizontal plane is too small, the raw material will not slide down properly and will accumulate on the segregation control plate 8. On the other hand, if the inclination angle θ is too large, it will be difficult to guide the raw material toward the furnace central axis x. From the above perspectives, the inclination angle θ should be approximately 30 to 75°, preferably approximately 40 to 60°.

[0036] The falling direction is changed by the segregation control plate 8, and the falling direction is Ｂ The raw materials that fall to a position closer to the furnace central axis x than the ore discharge port 40 are deposited in the bunker as follows. First, the ore raw material a, which is the main raw material, falls to a position closer to the furnace central axis x (a position above the raw material discharge port 40 in this embodiment), and then rolls away from the furnace central axis x, forming a slope as shown in FIG. 3 . At this time, larger particle sizes tend to flow down the slope and segregate toward the lower part of the bunker. That is, the ore raw material a is prone to segregation due to the difference in particle size. In contrast, such segregation due to the difference in particle size is less likely to occur between the ore raw material a and the metallic iron raw material b. That is, the metallic iron raw material b (especially in the case of HBI) generally has a larger particle size than the ore raw material a but also has a higher density. Therefore, the metallic iron raw material b that falls to a position closer to the furnace central axis x in the furnace top bunker 4 sinks into the ore raw material layer and deposits at that position. In other words, the metallic iron raw material b, which has a higher density than the ore raw material a, does not flow down the slope, but sinks and remains at a position closer to the furnace central axis x where it fell (above the raw material discharge port 40 in this embodiment). In this way, segregation due to the density difference occurs preferentially between the ore raw material a and the metallic iron raw material b, and excessive segregation due to the particle size difference is suppressed. This is generally known, and Non-Patent Document 1 reports that when deposition is performed at a low flow rate, such as when charging using a bell-less chute, segregation due to the density difference takes precedence and segregation due to the particle size difference is suppressed.

[0037] To confirm this, the inventors conducted an experiment to measure the discharge distribution of raw materials (sintered ore and reduced iron) from the top bunker using a scale model of a blast furnace charging system. Figure 6 shows a schematic diagram of the 1 / 17.8 scale model experimental apparatus used in this experiment. This simulation apparatus, designed to reproduce the time-dependent changes in raw material discharge from an actual blast furnace, is composed of a bell-less type raw material charging device 22, a charging conveyor 23, and raw material hoppers 29 (a raw material hopper 29a for ore raw materials and a raw material hopper 29b for metallic iron raw materials). The raw material charging device 22 is also composed of a top bunker 24, a collecting hopper 26, a switching chute 30, and other components. A flow rate control gate is installed at the raw material discharge port 240 of the top bunker 24. Two top bunkers 24 are arranged symmetrically about the furnace center axis. A segregation control plate 28, as shown in Figure 3, is installed within the top bunker 24, and the inclination angle θ of its raw material receiving surface is set to 55°. A sampling box 31 movable by a belt conveyor 32 is disposed below the raw material charging device 22, and this moving sampling box 31 is configured to sequentially collect raw materials discharged over time from the furnace top bunker 24. In this experiment, sintered ore was used as the ore raw material a, and reduced iron (HBI) was used as the metallic iron raw material b. Other experimental conditions and raw material conditions were determined in accordance with the law of similarity with an actual blast furnace.

[0038] The apparent density of HBI (reduced iron) is 5.0 to 6.0 t / m ３ and the typical density is 5.2 t / m ３ The apparent density of the sintered ore was 3.0 to 4.0 t / m ３ and the typical density is 3.4 t / m ３The size of the HBI was 5.6 mm x 2.8 mm x 1.7 mm, and the average particle size (defined below) of the HBI was 3.6 mm. The average particle size (defined below) of the sintered ore was 0.7 mm. In this experiment, sintered ore and HBI were cut onto a charging conveyor 23 and charged into a top bunker 24 under the conditions of the present invention, and then discharged from the top bunker 24. The discharge ratio of HBI (reduced iron) relative to the discharge weight ratio of raw materials is shown in Figures 7 and 8 (A) to (D), and the particle size distribution of sintered ore relative to the discharge weight ratio of raw materials is shown in Figure 9. That is, Figures 7 and 8 show the discharge ratio of reduced iron at each stage of raw material discharge from the top bunker in a test in which raw materials were charged into the top bunker under the conditions of the present invention using the experimental apparatus of Figure 6. Figure 9 shows an example of the particle size distribution of sintered ore at each stage of raw material discharge from the top bunker in a test in which raw materials were charged into the top bunker using the experimental apparatus shown in Figure 6 under the conditions of the present invention. The horizontal axis of each graph represents the weight (cumulative value) ratio of raw materials discharged from the top bunker. Comparing Figures 7 and 8(A) to (D) with Figure 9, it can be seen that the sintered ore at the end of raw material discharge is coarse, while the HBI ratio at the end of raw material discharge is small, even though the particle size of the HBI is larger than that of the sintered ore. Therefore, it was confirmed that segregation due to particle size differences in HBI is less likely to occur than in sintered ore.

[0039] In the present invention, metallic iron raw materials b are stacked in a specific form on ore raw materials a loaded on the charging conveyor 3, and by utilizing the action of the segregation control plate 8 and segregation due to the density difference of the raw materials in the top bunker 4, the metallic iron raw materials b are accumulated in a large amount in a specific region in the top bunker 4. As a result, when discharging the raw materials from the top bunker 4, the discharge of the metallic iron raw materials b in the latter or final stage of the raw material discharge can be suppressed, and the discharge rate of the metallic iron raw materials b in the initial or first half of the raw material discharge can be increased.

[0040] Here, FIG. 7(A) shows a case in which HBI is stacked on sintered ore in a length range of 4 to 32% from the front end in the conveying direction of the sintered ore loaded on the charging conveyor, and the sintered ore and HBI are charged into the furnace top bunker in this state (see FIG. 17(b) to be described later). Also, FIG. 7(B) shows a case in which HBI is stacked on sintered ore in a length range of 61 to 96% from the front end in the conveying direction of the sintered ore loaded on the charging conveyor, and the sintered ore and HBI are charged into the furnace top bunker in this state (see FIG. 17(c) to be described later). Also, FIG. 8(C) shows a case in which HBI is stacked on sintered ore in a length range of 4 to 18% from the front end in the conveying direction of the sintered ore loaded on the charging conveyor, and the sintered ore and HBI are charged into the furnace top bunker in this state (see FIG. 17(d) to be described later). 8(D) shows a case in which HBI is stacked on sintered ore in a length range of 4 to 32% and a length range of 61 to 96% from the front end in the conveying direction of the sintered ore loaded on the charging conveyor, and the sintered ore and HBI are charged into the furnace top bunker in this state (configuration (e) shown in FIG. 17 described later). As these graphs show, the discharge of HBI at the end of the raw material discharge is suppressed, and the discharge rate of HBI at the beginning or first half of the raw material discharge is high. In particular, in the case of FIG. 8(C), in which the HBI stacking range is shifted to the front end of the sintered ore loading length, the discharge rate of HBI at the beginning of the raw material discharge is particularly high.

[0041] For comparison, Figure 20 shows the ratio of HBI (reduced iron) discharged relative to the weight ratio of raw materials discharged from the top bunker in a test in which raw materials were charged into the top bunker under conditions outside the scope of the present invention (the test conditions, other than the HBI stacking range, were the same as those in the tests of Figures 7 and 8). In this comparative example, HBI was stacked on sintered ore in a length range from 32 to 61% of the length of the sintered ore loaded on the charging conveyor, from the front end in the conveying direction, and the sintered ore and HBI were charged into the top bunker in this state. In this comparative example, the HBI discharge ratio is relatively high in the latter half or final stage of raw material discharge.

[0042] Furthermore, in the present invention, when the raw materials (ore raw material a + metallic iron raw material b) charged in the furnace top bunker 4 are charged into the furnace using the rotating chute 5, the raw materials are charged while rotating and tilting the rotating chute 5 to move the raw material charging position from the furnace wall toward the furnace center periphery. That is, the raw materials are charged while rotating the rotating chute 5 and gradually shifting (tilting) the direction of the chute from the furnace wall toward the furnace center periphery (forward tilting charging using the rotating chute). Figure 4 shows a schematic diagram of this charging situation. The raw materials are charged using the rotating chute 5 by starting with charging into the furnace wall, then rotating the rotating chute 5 and gradually tilting it from the direction of charging into the furnace wall (furnace wall periphery) (solid line) to the direction of charging into the furnace center periphery (two-dot chain line).

[0043] Here, it is preferable to deposit the metallic iron raw material b from the middle to the furnace wall of the blast furnace for the following reasons. In a blast furnace, ores are reduced by reducing gas rising from the lower furnace side. Typically, the ore raw material layer in a blast furnace increases in thickness from the middle to the furnace wall. This increases reducing gas consumption, resulting in a lower reducing gas concentration and a lower reduction rate from the middle to the furnace wall. This decrease in reduction rate from the middle to the furnace wall leads to a decrease in the reduction rate of the entire ore raw material layer. The ore raw material melts in the lower part of the blast furnace while still in a low reduction state and is finally reduced by a direct reduction reaction accompanied by a large endothermic heat, which increases the amount of fuel required in the blast furnace, i.e., the amount of coke required. In contrast, by depositing the metallic iron raw material b from the middle to the furnace wall as a raw material that has already been reduced, it is possible to compensate for the insufficient reduction in that region. Here, "from the middle of the furnace to the furnace wall" includes not only the area spanning the middle of the furnace and the furnace wall, but also the area consisting only of the middle of the furnace or the area consisting only of the furnace wall.

[0044] As described above, in the present invention, a large amount of metallic iron raw materials b is discharged in the initial stage or first half of the raw material discharge from the top bunker 4, and the raw materials are piled up in the top bunker 4 so that the discharge rate of metallic iron raw materials b is high. Therefore, raw material charging using the rotating chute 5 starts with charging onto the furnace wall, and the direction of the chute is gradually shifted (tilted) from the furnace wall, through the intermediate furnace section, to the furnace center periphery while charging the raw materials (normal tilting charging). This makes it possible to pile the metallic iron raw materials b at a high mixing ratio from the intermediate furnace section to the furnace wall section (particularly in the region of a dimensionless radius of 0.6 to 0.8).

[0045] In the present invention, the peripheral part of the furnace center is the region between the furnace center and the furnace middle part in the furnace radial direction, and is generally expressed by a dimensionless radius (r / R ０ , hereinafter the same) refers to the region of 0.20 to less than 0.30. In general, the furnace center refers to the region of dimensionless radius 0.00 to less than 0.20, the furnace intermediate region refers to the region of dimensionless radius 0.30 to 0.80, and the furnace wall region refers to the region of dimensionless radius over 0.80 to 1.00. Here, the dimensionless radius (r / R ０ ) indicates the position in the furnace in the furnace radial direction, and the distance r from the furnace center to that position is the furnace radius R ０ This is the value divided by .

[0046] In the present invention, the starting position for raw material charging may be determined appropriately within the furnace wall. The starting position for raw material charging is the center of the falling raw material from the rotating chute on the raw material deposition surface inside the furnace. Furthermore, in the present invention, there is no particular limitation on the charging amount (mixing ratio) of metallic iron raw material b. The greater the charging amount of metallic iron raw material b, the more the reducing agent ratio can be reduced. However, as the charging amount of metallic iron raw material b increases, the heat flow ratio decreases. Generally, a blast furnace is preferably operated with a heat flow ratio of 0.9 or less. In a typical blast furnace (with an ore charging rate of approximately 1,600 kg / t), this range is reached at 400 kg / t or more, resulting in a delay in the temperature rise of the raw material, which reduces the effectiveness of reducing agent ratio reduction. Therefore, the charging amount (mixing ratio) of metallic iron raw material b is preferably limited to 25 mass% or less of the ore raw material a.

[0047] Generally, the density of metallic iron raw material b (particularly in the case of HBI) is higher than the density of ore raw material a. In any case, in the present invention, it is preferable that the average apparent density of metallic iron raw material b is higher than the average apparent density of ore raw material a. To confirm this, the inventors conducted an experiment to measure the segregation behavior of HBI using an HBI discharge experimental device. Here, the average apparent density is a value obtained by randomly selecting 20 raw material particles, adding up the apparent densities of each, and then dividing the sum by the total number of raw material particles (20).

[0048] Figure 10 shows the experimental equipment used in the HBI discharge experiment. Sintered ore was used as the ore raw material a, and reduced iron (HBI) was used as the metallic iron raw material b. In this experiment, coke was discharged from a hopper to form a deposition surface, and then a mixed raw material of sintered ore and HBI was discharged from the hopper on top of it. The HBI travel distance was evaluated by setting the point directly below the hopper discharge outlet as the origin and the base of the coke deposition surface as 1. HBI was recovered at each travel distance, and its weight ratio was evaluated.

[0049] Figure 11 shows an example of the measurement results for the distance traveled by HBI. The vertical axis represents the proportion of HBI present at each travel distance out of the total weight of HBI introduced, and the horizontal axis represents the distance traveled by HBI. The greatest number of HBI was found at a position slightly below the outlet. This is presumably because the proportion of HBI present directly below the outlet is low because the inertia of falling is strong and the HBI moves downhill. On the other hand, as mentioned above, HBI tends to sink, and therefore, it remains where the inertia of falling is lost, resulting in a maximum value for the proportion of HBI present.

[0050] FIG. 11 also shows the measurement results for the cases where the apparent density ratio (density ratio), which is the ratio of the apparent density of the charged HBI to the apparent density of the sintered ore, is 1.5 and 2.0. As shown in FIG. 11, the proportion of HBI directly below the discharge port is almost the same for both density ratios. When the density ratio is 2.0, the weight proportion of HBI present at short travel distances is large, and HBI is not present at the base of the coke volume surface. On the other hand, when the density ratio is 1.5, although the weight proportion of HBI present at short travel distances is large, HBI is present at longer travel distances than when the density ratio is 2.0, and HBI is also present at the base of the coke volume surface. Thus, the weight proportion of HBI present at each travel distance changes depending on the density ratio.

[0051] Therefore, the movement distance at the position where the HBI abundance ratio shows a maximum value is called the representative movement distance, and the relationship with the apparent density of HBI was investigated. In other words, the shorter the representative movement distance, the more likely HBI is to remain near the drop point in the top bunker, and as mentioned above, it is thought that it is possible to reduce the HBI ratio at the beginning of discharge (initial flow). Here, the representative movement distance was calculated from the position of the apex of a quadratic function of each plot obtained by the least squares method. The apparent density of the HBI used was 4620 to 8400 kg / m ３ The apparent density of the sintered ore is 4200 kg / m ３ FIG. 12 shows the relationship between the apparent density of HBI and the representative moving distance. The horizontal axis is the ratio of the apparent density of HBI to that of sintered ore (density ratio). The higher the density ratio, the shorter the representative moving distance tends to be, but it can be seen that this tendency changes when the density ratio is 1.25. When the density ratio is smaller than 1.25, the apparent densities of the sintered ore and HBI are similar, making it difficult for the HBI to sink into the sintered ore and remain there. Therefore, it is preferable that the density ratio of the sintered ore to the HBI is 1.25 or more.

[0052] Thus, from the viewpoint of appropriately achieving segregation due to the density difference between the metallic iron raw material b and the ore raw material a, taking into consideration the above-mentioned experimental conditions and results, it is considered desirable that the average apparent density of the metallic iron raw material b be sufficiently greater than the average apparent density of the ore raw material a. However, if the average apparent density is too large, the metallic iron raw material b mixed with the ore raw material a may not be smoothly discharged when the raw materials are discharged from the top bunker 4 and may remain in the top bunker 4. In this case, damage to equipment or an unexpected burden distribution may occur, which may destabilize blast furnace operation. From this viewpoint, the average apparent density of the metallic iron raw material b is preferably about 1.25 to 2.0 times, and more preferably about 1.5 to 2.0 times, the average apparent density of the ore raw material a.

[0053] Furthermore, it is believed that the more complex the shape of the HBI, the more difficult it is for the HBI to roll, and therefore the shorter the migration distance. Similar to the method described above, the device shown in Figure 10 was used to investigate the migration distance when the aspect ratio of the HBI was changed. Here, the aspect ratio of the HBI is the value obtained by dividing the length of the longest side of the HBI by the length of the shortest side. As described above, a maximum value appears in the HBI abundance ratio, and the migration distance at the maximum value was evaluated as the representative migration distance. Figure 13 shows the relationship between the aspect ratio of the HBI and the representative migration distance. The representative migration distance tends to decrease as the aspect ratio increases, but this trend changes when the aspect ratio is 1.4. It is believed that when the aspect ratio is smaller than 1.4, the shape of the HBI is closer to a cube, which weakens the resistance to rolling and makes it more difficult for the HBI to remain in place. Therefore, it is preferable that the aspect ratio of the HBI be 1.4 or greater.

[0054] Generally, metallic iron raw material b (especially in the case of HBI) has a particle size considerably larger than that of ore raw material a. It is considered that the larger the HBI particle, the heavier the HBI becomes and the shorter the travel distance. As in the above-mentioned method, the travel distance was investigated using the apparatus shown in Figure 10 when the particle size ratio of HBI was changed. Here, the average particle size [d Ｏ] is the harmonic mean particle size in the case of any raw material such as sinter, pellets, or lump ore, and is the particle size calculated by the formula: mean particle size = 1 / Σ(Wi / di) (where Wi: weight ratio of particles with particle size di, and di: median diameter of the sieve openings of each sieve).

[0055] In addition, when the ore raw material a is composed of two or more types of raw materials (for example, two or more types of raw materials selected from sintered ore, pellets, and lump ore), the average particle diameter of each raw material is calculated, and then the average particle diameter weighted by the weight ratio is calculated. Ｍ In the case of HBI, the average particle diameter [d r ] of metallic iron raw material b is calculated as follows. The size of HBI sampled from the lot of HBI to be used is measured, and when the size is approximated to a rectangular parallelepiped with length a, width b, and thickness c, the particle diameter dr (diameter equivalent to a sphere of equal volume) is calculated from the following formula. This is performed for 20 HBI samples sampled at random, and the average value of these is taken as the average particle diameter [d Ｍ ] When the metallic iron raw material b is reduced iron or granulated iron other than HBI, its average particle size [d Ｍ ] is the average particle size [d Ｏ ] is calculated in the same way.

[0056] Furthermore, when the metallic iron raw material b consists of two or more types of raw materials (e.g., two or more types of reduced iron, or reduced iron and granulated pig iron), the average particle diameter of each raw material is calculated, and then the average particle diameter weighted by the weight ratio is calculated. The particle diameter ratio of HBI is the value obtained by dividing the average particle diameter of HBI by the average particle diameter of the ore. As mentioned above, a maximum value appears in the HBI abundance ratio, and the migration distance at the maximum value was evaluated as the representative migration distance. Figure 14 shows the relationship between the particle diameter ratio of HBI and the representative migration distance. The representative migration distance tends to decrease as the particle diameter ratio increases, but this tendency changes when the particle diameter ratio is 3.5. When the particle diameter ratio is smaller than 3.5, this is thought to be because the weight of the HBI is small and it becomes difficult for the HBI to remain in place. Therefore, it is preferable that the particle diameter ratio of HBI is 3.5 or more.

[0057] However, although there is no particular limitation on the particle diameters of the ore raw material a and the metallic iron raw material b, if the average particle diameter of the metallic iron raw material b is too large, a sufficient apparent density may not be ensured, and furthermore, there is a risk that the discharge from the bunker may be physically hindered. Therefore, the average particle diameter of the ore raw material a is set to [d Ｏ ], the average particle size of the metallic iron raw material b is [d Ｍ ], then [d Ｏ ] × 7 ≧ [d Ｍ ] is preferable.

[0058] For the following reasons, it is preferable to deposit the metallic iron raw material b in the lower part of the ore raw material layer extending from the middle to the furnace wall of the blast furnace. In a blast furnace, the ore raw material layer descends and softens and melts, but the lower part of the ore raw material layer softens and melts first. This softening and melting of the lower part of the ore raw material layer reduces the air permeability to the upper part of the ore raw material layer, thereby worsening the high-temperature properties of the ore raw material layer. To address this problem, improving the air permeability of the lower part of the ore raw material layer is thought to improve the air permeability and high-temperature properties of the upper part of the ore raw material layer. It is generally known that when reduced iron with a low high-temperature shrinkage rate is mixed with the ore raw material layer, the reduced iron does not melt during ore melting, creating voids around the reduced iron, thereby ensuring air permeability. Therefore, mixing metallic iron raw materials such as reduced iron in the lower part of the ore raw material layer creates voids around the metallic iron raw material with a low high-temperature shrinkage rate during softening and melting. This improves the air permeability of the lower part of the ore raw material layer, making it easier for high-temperature reducing gas to flow to the upper part of the ore raw material layer, improving the high-temperature properties of the upper part of the ore raw material layer and improving the reduction efficiency.

[0059] In the present invention, in order to deposit the metallic iron raw materials b in the lower part of the ore raw material layer from the middle part to the furnace wall part of the blast furnace, it is preferable to divide one charge of the ore raw materials a into two, charge each of them into a separate furnace top bunker 4, and sequentially charge them into the furnace via the rotating chute 5. That is, one charge of the ore raw materials a is charged into the furnace in two batches, and the metallic iron raw materials b are mixed with the ore raw materials a of the first batch and charged into the furnace by the above-mentioned method. If the ore raw materials a of the subsequent second batch are charged in the region from the middle part to the furnace wall part, the metallic iron raw materials b will be below the ore raw materials a of the second batch, so that it is possible to deposit a high proportion of the metallic iron raw materials b in the lower part of the ore raw material layer from the middle part to the furnace wall part of the blast furnace. FIG. 15 is a schematic diagram showing the shape (cross section) of the deposit in the furnace when the raw materials are charged by such a method. The area surrounded by the dotted line is the "lower area of ​​the ore raw material layer extending from the middle part of the furnace to the furnace wall" where the metallic iron raw material b can be deposited at a high rate.

[0060] The second batch of ore raw material a is charged by tilting the rotating chute 5 while rotating. The charging method may be either a method in which the raw material charging position is moved from the furnace wall toward the periphery of the furnace center (normal tilting charging) or a method in which the raw material charging position is moved from the periphery of the furnace center toward the furnace wall (reverse tilting charging). Furthermore, charging may be started with reverse tilting, and once it reaches the furnace wall, it may be further tilted with normal tilting to charge into the middle of the furnace. However, reverse tilting charging is preferred for the second batch because reverse tilting reduces the risk that the metallic iron raw material b charged in the first batch will be entrained in the flow of the second batch of raw material into the furnace center and move to the center of the blast furnace. In this case, it is more preferable not to mix the metallic iron raw material b with the second batch of ore raw material a because the heat generated by the reduction reaction of the ore raw material a is lost by the metallic iron raw material b, thereby preventing an increase in the reducing agent rate due to a lack of heat.

[0061] The inventors conducted the following experiment using a scale model of a blast furnace charging system to verify the stacking conditions of metallic iron raw materials b against ore raw materials a transported by a charging conveyor 3. Figure 16 shows a schematic diagram of the 1 / 17.8 scale model experimental apparatus of an actual blast furnace used in this experiment. This simulation experimental apparatus is composed of a blast furnace body 21, a bell-less type raw material charging device 22, a charging conveyor 23, and raw material hoppers 29 (raw material hopper 29a for ore raw materials and raw material hopper 29b for metallic iron raw materials) in order to reproduce the changes in raw material discharge over time in an actual furnace. The raw material charging device 22 is also composed of a furnace top bunker 24, a rotating chute 25, a collecting hopper 26, a top ring 27, a switching chute 30, and the like. A flow rate control gate is installed at the raw material discharge port 240 of the furnace top bunker 24. Two furnace top bunkers 24 are arranged symmetrically about the furnace axis. In addition, a segregation control plate 28 as shown in FIG. 3 is installed in the furnace top bunker 24, and the inclination angle θ of the material receiving surface is set to 55°.

[0062] In this experiment, sintered ore was used as the ore raw material a, and reduced iron (HBI) was used as the metallic iron raw material b. Other experimental conditions and raw material conditions were determined in accordance with the law of similarity with those of an actual blast furnace. Raw materials discharged from a raw material hopper 29 were transported to the furnace top by a charging conveyor 23 and charged into the top bunker 24. The raw materials were divided into two and charged into separate top bunkers 24, and two batches were charged into the furnace body 21. Reduced iron was mixed only in the first batch, but not in the second batch. For both the first and second batches, the raw materials discharged from the top bunker 24 were charged into the furnace body 21 through a rotating chute 25. For the first batch, in which reduced iron was mixed, the rotating chute 25 was tilted and rotated to move the raw material charging position from the furnace wall, through the middle of the furnace, and toward the periphery of the center of the furnace (tilting pattern: forward tilting). For the second batch, the raw materials were charged while rotating and tilting the rotating chute 25 to move the raw material charging position from the middle of the furnace toward the furnace wall (tilting pattern = reverse tilting). The starting position for charging the first batch of raw materials using the rotating chute 25 was a dimensionless radius of 0.90, and the ending position was a dimensionless radius of 0.20 (the center position of the raw materials falling from the rotating chute on the raw material pile surface inside the furnace). The starting position for charging the second batch of raw materials was a dimensionless radius of 0.50, and the ending position was a dimensionless radius of 0.95 (the center position of the raw materials falling from the rotating chute on the raw material pile surface inside the furnace).

[0063] In this experiment, for the first batch of raw materials, when reduced iron (hereinafter referred to as reduced iron b) was cut out and stacked on the ore raw material a on the charging conveyor 23, the cut lengths of the reduced iron b were set to five patterns, (a) to (e) shown in FIG. 17 , and each was charged into the furnace top bunker 24. Details of each condition are as follows. Pattern (a): Reduced iron b was stacked on the ore raw material a over the entire length of the ore raw material a loaded on the charging conveyor 23. Pattern (b): Reduced iron b was stacked on the ore raw material a at a distance from the front end in the conveying direction of 4 to 32% of the loaded length of the ore raw material a loaded on the charging conveyor 23. Pattern (c): Reduced iron b was stacked on the ore raw material a at a distance from the front end in the conveying direction of 61 to 96% of the loaded length of the ore raw material a loaded on the charging conveyor 23. Form (d): Reduced iron b was layered on the ore raw material a in a length range of 4 to 18% from the front end in the conveying direction of the total length of the ore raw material a loaded on the charging conveyor 23. Form (e): Reduced iron b was layered on the ore raw material a in a length range of 4 to 32% and a length range of 61 to 96% from the front end in the conveying direction of the total length of the ore raw material a loaded on the charging conveyor 23.

[0064] After the charging of the raw materials from the top bunker 24 into the blast furnace was completed, the charged materials were sampled in the radial direction of the furnace, and the mixed proportion of reduced iron was measured. The results are shown in Fig. 18. In Fig. 18, the horizontal axis represents the dimensionless radius of the blast furnace, and the vertical axis represents the mixed proportion of reduced iron by weight. Fig. 19 also shows the results of measuring the discharge proportion of reduced iron when the raw materials were discharged from the top bunker. In Fig. 19, the horizontal axis represents the discharge weight (integrated value) proportion of raw materials, and the vertical axis represents the discharge proportion of reduced iron.

[0065] As shown in Figure 18, the first batch of mixed reduced iron was charged by tilting the furnace wall toward the furnace center, and therefore no mixing of reduced iron was observed in the furnace center in any of the configurations (a) to (e). On the other hand, when the stacking position of the reduced iron on the ore raw materials (position within the stacking length) was shifted to a shorter position toward the front of the ore raw material loading length (configuration (a) → configuration (b)), as in configuration (b), the mixed proportion of reduced iron increased from the middle of the furnace to the furnace wall. This result is thought to be due to the fact that, based on the results of the discharge distribution from the furnace top bunker under the same conditions (Figure 19), the discharge proportion of reduced iron in the initial stage of material discharge from the furnace top bunker increases when the stacking position of the reduced iron is shifted to a shorter position toward the front.

[0066] Furthermore, when the stacking position of the reduced iron on the ore raw materials (position within the stacking length) was changed to a shorter position toward the rear of the stacking length of the ore raw materials (from configuration (a) to configuration (c)), the mixed proportion of reduced iron from the middle of the furnace to the furnace wall also increased. This result is thought to be due to the fact that, based on the results of the discharge distribution from the furnace top bunker under the same conditions ( FIG. 19 ), when the stacking position of the reduced iron was changed to a shorter position toward the rear, the discharge proportion of reduced iron in the middle period of material discharge from the furnace top bunker increased.

[0067] Furthermore, when the stacking position of the reduced iron on the ore raw material (position within the stacking length range) was shifted further forward than in configuration (b) (configuration (b) → configuration (d)), the proportion of reduced iron mixed toward the furnace wall side increased. This result is thought to be due to the fact that, based on the results of the discharge distribution from the furnace top bunker under the same conditions ( FIG. 19 ), when the stacking position of the reduced iron is shifted further forward, the discharge proportion of reduced iron at the initial stage of raw material discharge from the furnace top bunker becomes particularly high.

[0068] Furthermore, configuration (e) combines configurations (b) and (c), with the stacking positions of the reduced iron on the ore raw material (positions within the stacking length range) being both at the front and rear ends of the loading length of the ore raw material. This results in a reduced iron deposition distribution that is exactly intermediate between configurations (b) and (c), with the mixed proportion of reduced iron increasing from the middle of the furnace to the furnace wall. Furthermore, configuration (d), in which reduced iron is stacked on the ore raw material within a length range of 4% to 18% from the front end in the conveying direction, is particularly preferable in terms of the high mixed proportion of reduced iron near the furnace wall, where the reduction load is particularly high.

[0069] As described above, by mixing the ore raw material a and the metallic iron raw material b according to the present invention, it is possible to control the mixing ratio of the metallic iron raw material b when the metallic iron raw material is discharged from the top bunker. This makes it possible to selectively charge a high ratio of the metallic iron raw material b to the region from the middle of the furnace to the furnace wall, where the reduction load is heavy. The method for producing molten pig iron of the present invention also includes a step of mixing the ore raw material a containing at least one of sintered ore, pellets, and lump ore with the metallic iron raw material b containing reduced iron and / or granulated pig iron by the above-described raw material charging method of the present invention, and charging the mixture into a blast furnace.

[0070] In order to confirm the effect of the present invention in an actual furnace, a large bell-less blast furnace (inner volume 5500 m) equipped with the equipment configuration shown in Figs. 1 to 4 was used. ３ The raw material charging device 2 installed at the top of the blast furnace was equipped with three parallel top bunkers 4, which were arranged at equal intervals in the circumferential direction around the central axis x of the blast furnace. A segregation control plate 8 was installed within the top bunker 4, and the inclination angle θ of its raw material receiving surface 80 was set to 55°.

[0071] Sintered ore was used as the ore raw material, and reduced iron (HBI) was used as the metallic iron raw material. Ｏ ] is 12 mm, and the average particle size of reduced iron [d Ｍ ] is 66 mm, and [d Ｍ ] / [d Ｏ ] = 5.5. The average apparent density of the ore raw material (sintered ore) is 3.4 t / m ３ The average apparent density of reduced iron (HBI) is 5.4 t / m３ The mixing ratio of reduced iron was set to 4 mass % of the ore raw material.

[0072] In this example, the ore raw material discharged from the ore raw material hopper 9a via the reserve hopper 10 was transported to the furnace top by the charging conveyor 3 and charged into the top bunker 4. One charge of ore raw material was divided into two and charged into separate top bunkers 4, and two batches were charged into the blast furnace. Reduced iron was discharged from the metallic iron raw material hopper 9b and layered on top of the ore raw material layer of the first batch transported by the charging conveyor 3, and mixed with the ore raw material and charged into one of the top bunkers 4. On the other hand, reduced iron was not mixed with the ore raw material of the second batch. For both the first and second batches, the raw material discharged from the top bunker 4 was charged into the furnace through the rotating chute 5. For the first batch, in which reduced iron was mixed, the materials were charged by tilting and rotating the rotating chute 5 to move the material charging position from the furnace wall toward the furnace center (tilting pattern = forward tilting). The starting position for charging the first batch of materials using the rotating chute 5 was a position with a dimensionless radius of 0.90, and the ending position was a position with a dimensionless radius of 0.20 (the center position of the materials falling from the rotating chute on the material accumulation surface inside the furnace). For the subsequent second batch, the materials were charged by tilting and rotating the rotating chute 5 to move the material charging position from the middle of the furnace toward the furnace wall (tilting pattern = reverse tilting). The starting position for charging the second batch of materials using the rotating chute 5 was a position with a dimensionless radius of 0.50, and the ending position was a position with a dimensionless radius of 0.95 (the center position of the materials falling from the rotating chute on the material accumulation surface inside the furnace).

[0073] In Example 1, when the first batch of ore materials was charged into the top bunker 4, reduced iron was layered on the ore materials loaded on the charging conveyor 3 as follows: 60 kg / t of reduced iron was cut out and layered on the ore materials in a length range from 4 to 32% of the total length of the ore materials loaded on the charging conveyor 3, from the front end in the conveying direction (configuration (b) in FIG. 17 ).

[0074] In Example 2, when the first batch of ore materials was charged into the top bunker 4, reduced iron was layered on the ore materials loaded on the charging conveyor 3 as follows: 60 kg / t of reduced iron was cut out and layered on the ore materials in a length range from 61 to 96% of the length of the ore materials loaded on the charging conveyor 3 from the front end in the conveying direction (configuration (c) in FIG. 17 ).

[0075] In Example 3, when the first batch of ore materials was charged into the top bunker 4, reduced iron was layered on the ore materials loaded on the charging conveyor 3 as follows: 60 kg / t of reduced iron was cut out and layered on the ore materials in a length range of 4 to 32% and a length range of 61 to 96% from the front end in the conveying direction of the loaded length of the ore materials loaded on the charging conveyor 3 (configuration (e) in FIG. 17 ).

[0076] In the comparative example, when the first batch of ore materials was charged into the top bunker 4, reduced iron was layered on the ore materials loaded on the charging conveyor 3 as follows: Reduced iron was cut out at 60 kg / t and layered on the ore materials over almost the entire length of the ore materials loaded on the charging conveyor 3 (configuration (a) in FIG. 17 ).

[0077] The operating conditions for the invention examples and comparative examples, as well as the measurement results of the air permeability index, gas utilization rate, and molten iron temperature, are shown in Table 1. According to this, in invention examples 1 to 3, reduced iron was placed (charged) at a high mixing ratio in the lower part of the raw ore layer from the middle of the furnace to the furnace wall, which improved the insufficient reducing power and stabilized the gas flow distribution, resulting in a lower air permeability index and a lower reducing agent rate compared to the comparative examples.

[0078] From the above, it has been confirmed that the raw material charging method of the present invention is effective for stable operation of a blast furnace because it optimizes the radial distribution of reduced iron mixed with the ore raw material, and is also effective for low reducing agent ratio operation.

[0079]

[0080] REFERENCE SIGNS LIST 1 Furnace body 2 Raw material charging device 3 Charging conveyor 4 Furnace top bunker 5 Swiveling chute 6 Collecting hopper 7 Top ring 8 Segregation control plate 9a Ore raw material hopper 9b Metallic iron raw material hopper 10 Reserving hopper 11 Ore conveyor 12 Receiving chute 21 Furnace body 22 Raw material charging device 23 Charging conveyor 24 Furnace top bunker 25 Swiveling chute 26 Collecting hopper 27 Top ring 28 Segregation control plate 29a, 29b Raw material hopper 30 Switching chute 31 Sampling box 32 Belt conveyor 40 Raw material discharge port 41 Cylindrical portion 42 Funnel-shaped portion 80 Raw material receiving surface 81 Pivot portion 240 Raw material discharge port 420, 421 Wall portion a Ore raw material b Metallic iron raw material x Furnace central axis x Ｂ Bunker center axis

Claims

1. A method for charging a mixture of ore raw material (a) containing at least one of sintered ore, pellets, and lump ore and metallic iron raw material (b) containing reduced iron and / or granulated pig iron into a bell-less blast furnace having a plurality of bunkers arranged in parallel and a raw material charging device for charging raw materials into the furnace using a rotating chute, the method comprising: transporting the ore raw material (a) to the top of the furnace by a charging conveyor and charging it into one of the bunkers; cutting out metallic iron raw material (b) on top of the ore raw material (a) being transported by the charging conveyor; thereby stacking metallic iron raw material (b) on top of the ore raw material (a) within the length range of the ore raw material (a) loaded on the charging conveyor within the length range of (i) and / or (ii) below; and charging the raw material in this state into the bunker; A method for charging raw materials into a blast furnace, comprising: (i) a length range of 4% to 32% of the distance from the front end in the conveying direction; (ii) a length range of 61% to 96% of the distance from the front end in the conveying direction; and (iii) a length range of 61% to 96% of the distance from the front end in the conveying direction.

2. The raw material charging method for a blast furnace according to claim 1, wherein when the ore raw material (a) is transported to the furnace top by the charging conveyor and charged into one of the furnace top bunkers, the metallic iron raw material (b) is layered on the ore raw material (a) in the following length ranges (i) and / or (ii) of the loaded length of the ore raw material (a) loaded on the charging conveyor: (i) a length range of 4% or more and 18% or less of the distance from the front side in the conveying direction, and (ii) a length range of 61% or more and 96% or less of the distance from the front side in the conveying direction.

3. A method for charging raw materials into a blast furnace according to claim 1 or 2, wherein when charging one charge of ore raw material (a) into the furnace in two batches, the first batch of ore raw material (a) is mixed with metallic iron raw material (b) and then charged into the furnace.

4. A method for charging raw materials into a blast furnace according to claim 3, wherein the second batch of ore raw material (a) is charged into the furnace without being mixed with metallic iron raw material (b).

5. A method for charging raw materials into a blast furnace according to claim 1 or 2, wherein the average apparent density of the metallic iron raw material (b) is greater than the average apparent density of the ore raw material (a).

6. A method for charging raw materials into a blast furnace according to claim 5, wherein the ratio of the average apparent density of the metallic iron raw material (b) to the average apparent density of the ore raw material (a) is 1.25 or more.

7. A method for charging raw materials into a blast furnace according to claim 1 or 2, wherein the aspect ratio of the longest side to the shortest side of the metallic iron raw material (b) is 1.4 or more.

8. A method for charging raw materials into a blast furnace according to claim 1 or 2, wherein the average particle size of the metallic iron raw material (b) is larger than the harmonic mean particle size of the ore raw material (a).

9. A method for charging raw materials into a blast furnace according to claim 1 or 2, wherein the ratio of the average particle size of the metallic iron raw material (b) to the harmonic mean particle size of the ore raw material (a) is 3.5 or more.

10. A method for producing molten iron, comprising the step of mixing (a) an ore raw material containing at least one of sintered ore, pellets, and lump ore with (b) a metallic iron raw material containing reduced iron and / or granulated pig iron by the raw material charging method according to claim 1 or 2, and charging the mixture into a blast furnace.

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