Method for charging raw materials into blast furnace

Abstract

To provide a method for charging raw materials into a blast furnace with which reduced iron can be charged into a position having large reducing load in the radial direction of the furnace without arranging an exclusive hopper at the furnace top part.SOLUTION: In a method for mixing an ore raw material and reduced iron and charging the mixture into a blast furnace in a bell-less type blast furnace, when the ore raw material is charged into one of the furnace top bunkers by a charging conveyor, the reduced iron is cut out onto the ore raw material transported by the charging conveyor, so that the reduced iron is stacked on the ore raw material in a length range in which a distance from a head side in a transport direction is 18% or more and 75% or less of a loading length of the ore raw material, and the ore raw material and the reduced iron are charged into the furnace top bunker in this state. When the raw material in the furnace top bunker is charged into the furnace by a turning chute, the raw material is charged while moving a raw material charging position from a furnace center peripheral part to a furnace wall part side by tilting and turning the turning chute.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for charging raw materials in a bell-less blast furnace to obtain a desired burden distribution. [Background technology]

[0002] In recent years, global warming due to increased CO2 emissions has become a problem, and reducing CO2 emissions is also an important issue in the steel industry. Most of the CO2 emitted from steelworks comes from blast furnaces. Reducing CO2 emissions from blast furnaces is possible by reducing the amount of reducing materials (coke, pulverized coal, natural gas, etc.) used in the blast furnace. 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. From the perspective of reducing CO2 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.

[0003] 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, through 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. Below, an example will be described in which reduced iron is used as the metallic iron raw material. According to the method of Patent Document 1, reduced iron can be charged only to the radially large portion of the blast furnace where the reduction load is large, thereby effectively stabilizing the reduction state of the ore in the furnace and stabilizing the gas flow. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-183270 [Non-patent literature]

[0005] [Non-Patent Document 1] 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 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method of Patent Document 1 requires the installation of a dedicated sub-hopper at the furnace top to hold 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 up to address these problems, this method increases the number of charging batches, lengthening the charging time and reducing productivity. To solve the above-mentioned problems, it is necessary to charge reduced iron, which is discharged from a raw material hopper onto a charging conveyor, and ore raw materials, which are separately discharged onto a charging conveyor, into a single furnace top bunker and then into the furnace through a rotating chute. However, for example, when the ore raw materials are divided into two batches and the reduced iron is mixed with the first batch, it has not been known how to charge the reduced iron and ore raw materials 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.

[0007] 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 that can charge metallic iron raw materials such as reduced iron into parts of a blast furnace where the reduction load is large in the radial direction, 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. [Means for solving the problem]

[0008] 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) the method of cutting out reduced iron on the charging conveyor (the stacking pattern on the ore raw material), (ii) the method of tilting the rotating chute, (iii) the use of segregation control plates in the top bunker, and (iv) the method of 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) and (ii), and preferably further optimizing and combining the above factors (iii) and / or (iv), it is possible to accurately charge reduced iron into the desired position (a portion with a large reduction load) when charging the ore raw material and reduced iron held in one top bunker into the furnace.

[0009] The present invention was made based on these findings and has the following gist. [1] A method for charging a bell-less 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, comprising 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, When the ore raw material (a) is transported to the furnace top by a charging conveyor and charged into one of the furnace top bunkers, the metallic iron raw material (b) is cut out on top of the ore raw material (a) transported by the charging conveyor, so that the metallic iron raw material (b) is stacked on the ore raw material (a) in a length range of 18% to 75% of the loading length of the ore raw material (a) loaded on the charging conveyor, from the front side in the conveying direction, and in this state the ore raw material (a) and the metallic iron raw material (b) are charged into the furnace top bunker, When the raw materials in the furnace top bunker are charged into the furnace using the rotating chute, the raw materials are charged while rotating and tilting the rotating chute to move the raw material charging position from the peripheral portion of the furnace center toward the furnace wall.

[0010] [2] In the raw material charging method of the above [1], 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 top of the ore raw material (a) in a length range of 18% to 32% of the loading length of the ore raw material (a) loaded on the charging conveyor, the distance from the front side in the conveying direction. [3] In the raw material charging method of [1] or [2] above, When one charge of ore raw material (a) is charged into the furnace in two batches, A method for charging raw materials into a blast furnace, comprising: mixing a first batch of ore raw material (a) with metallic iron raw material (b) and charging the mixture into the furnace. [4] The raw material charging method for a blast furnace according to the above [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).

[0011] [5] In any of the raw material charging methods [1] to [4] above, A segregation control plate is installed in the top bunker, A method for charging raw materials into a blast furnace, characterized in that, when the ore raw materials (a) and the metallic iron raw materials (b) transported by the charging conveyor are charged into the furnace top bunker, the raw materials falling from above are caused to fall downward via the raw material receiving surfaces of the segregation control plates and deposited in the bunker, with the raw material receiving surfaces of the segregation control plates facing toward the outside of the furnace in the radial direction of the furnace and inclined downward with respect to the outside of the furnace. [6] In any of the raw material charging methods [1] to [5] above, the average apparent density [ρ b ] is the average apparent density [ρ a ] is larger than the raw material charging method for a blast furnace. [7] In the raw material charging method of [6] above, the average apparent density [ρ b ] and the average apparent density of the ore raw material (a) [ρ a ] ratio [ρ b ] / [ρ a ] is 1.25 or more.

[0012] [8] The raw material charging method for a blast furnace according to any one of the above [1] to [7], wherein the metallic iron raw material (b) has an aspect ratio of 1.4 or more. [9] In any of the raw material charging methods [1] to [8] above, the average particle size [d b ] is the average particle size [d a ] is larger than the raw material charging method for a blast furnace.

[10] In the raw material charging method of [9] above, the average particle size [d b ] and the average particle size of the ore raw material (a) [d a ] ratio [d b ] / [d a ] is 3.5 or more.

[11] A method for producing molten iron, comprising a step of mixing (a) an ore raw material containing at least one of sinter, pellets, and lump ore with (b) a metallic iron raw material containing reduced iron and / or granulated pig iron by any one of the raw material charging methods [1] to

[10] above, and charging the mixture into a blast furnace. [Effects of the Invention]

[0013] According to the raw material charging method of the present invention, metallic iron raw materials such as reduced iron can be accurately charged to radially adjacent portions (positions) of the blast furnace where the reduction load is large, without providing a dedicated hopper for reduced iron or the like at the furnace top or increasing the number of charging batches. This allows for improved productivity and reduced equipment costs in blast furnace operation. In the method of the present invention, by using a segregation control plate in the top bunker under predetermined conditions, the metallic iron raw material can be charged at a desired location (position) with particularly high precision. In addition, in the method of the present invention, one charge of ore raw material is charged into the furnace in two batches, and the metallic iron raw material is mixed with the ore raw material of the first batch, so that the metallic iron raw material can be charged at a particularly suitable location (position). Furthermore, according to the method for producing molten pig iron of the present invention, by charging raw materials using the above-mentioned raw material charging method, molten pig iron can be produced with high productivity while keeping equipment costs low. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic diagram of a process from when raw materials are fed onto a charging conveyor to when they are transported to the top of a blast furnace in one embodiment of the method of the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing a schematic diagram of a situation in which raw materials are transported to the top of a blast furnace by a charging conveyor and then charged into the furnace by a raw material charging device in one embodiment of the method of the present invention. [Figure 3] 1 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 according to the conditions of the present invention. [Figure 4] FIG. 1 is an explanatory diagram showing a schematic diagram of a raw material being charged through a rotating chute in one embodiment of the method of the present invention. [Figure 5] Graph showing an example of particle size (discharge particle size distribution of ore raw material) of ore raw material (sintered ore) at each stage of raw material discharge from the furnace top bunker in a test in which raw material was charged into the furnace top bunker according to the conditions of the present invention. [Figure 6] FIG. 10 is an explanatory diagram schematically showing the use of a segregation control plate installed in a furnace top bunker in another embodiment of the method of the present invention. [Figure 7] Schematic diagram of the actual blast furnace model experimental equipment used in experiments to measure the discharge distribution of raw materials (sintered ore and reduced iron) from the furnace top bunker. [Figure 8] An explanatory diagram showing a schematic diagram of the discharge test equipment used in a measurement experiment to estimate the travel distance of reduced iron in the top bunker. [Figure 9] Graph showing the measurement results of the travel distance of reduced iron in an experiment using the discharge experimental device of FIG. [Figure 10] This graph shows the relationship between the density ratio [ρHBI] / [ρore] (the ratio of the average apparent density of reduced iron [ρHBI] to the average apparent density of sintered ore [ρore]) and the representative travel distance, based on the measurement results of the travel distance of reduced iron using the discharge test equipment in Figure 8. [Figure 11] Graph showing the relationship between the aspect ratio of reduced iron and the representative travel distance based on the measurement results of the travel distance of reduced iron using the discharge test equipment in Figure 8. [Figure 12] This graph shows the relationship between the particle size ratio [dHBI] / [dore] (the ratio of the average particle size of reduced iron [dHBI] to the average particle size of sintered ore [dore]) and the representative moving distance, based on the measurement results of the moving distance of reduced iron using the discharge test equipment in Figure 8. [Figure 13] FIG. 1 is an explanatory diagram showing a schematic cross-section of the deposits in the furnace when two batches of ore raw material a are charged into the furnace in the method of the present invention. [Figure 14] An explanatory diagram showing a model experimental device used in an experiment to verify the layering conditions of metallic iron raw material b against ore raw material a transported by a charging conveyor. [Figure 15] An explanatory diagram showing the layering conditions of metallic iron raw material b on ore raw material a in an experiment using the model experimental device of Figure 14. [Figure 16] Graph showing the mixing ratio of metallic iron raw material (reduced iron) in the furnace radial direction in the experiment using the model experimental equipment of Figure 14 [Figure 17] Graph showing the discharge rate of metallic iron raw material (reduced iron) when raw materials are discharged from the furnace top bunker in the experiment using the model experimental equipment of Figure 14. [Figure 18] 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 under conditions outside the scope of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In a blast furnace, ore raw materials such as sintered ore and coke (lump coke) are charged alternately from the top of the furnace, forming a layered charging layer (packed bed). 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 coke, respectively. The raw material charging method of the present invention is applicable to a bell-less 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 blast furnace, lump coke and ore materials are discharged from a raw material hopper and charged into separate furnace top bunkers, and then alternately introduced into the furnace through a rotating chute. In this type of raw material charging in a blast furnace, the present invention mixes ore materials a and metallic iron materials b (e.g., reduced iron) and charges them into the furnace. During the raw material charging, metallic iron materials b are selectively charged into radially adjacent locations of the furnace where the reduction load is large.

[0016] The ore raw material a in the present invention 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. The metallic iron raw material b 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. Here, the reduced iron generally used is a molded body of reduced iron, and a representative example of such a molded body is called HBI (hot briquetted iron). HBI is obtained by hot compression molding (molding) of reduced iron obtained by reducing ores (lump ore, pellets, etc.) with a reducing gas. 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, and is generally obtained by dropping dispersed molten pig iron droplets into cooling water to cool them. The average particle size is usually several mm to several tens of mm.

[0017] Figures 1 and 2 are explanatory diagrams showing a schematic diagram of one embodiment of the method 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, and Figure 2 shows 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 the figure, 1 is a furnace body of a blast furnace, 2 is a raw material charging device installed at the top of the furnace, and 3 is a charging conveyor that transports raw materials to the top of the furnace and supplies them to the raw material charging device 2. 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. The multiple furnace top bunkers 4 are arranged in parallel around the furnace central axis x. Therefore, when there are two furnace top bunkers 4, they are usually arranged symmetrically around the furnace central axis x, and when there are three or more furnace top bunkers 4, they are arranged at intervals (for example, at equal intervals) in the circumferential direction around the furnace central axis x.

[0018] 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 If the top bunker 4 is installed above the furnace, the side shape of the furnace top bunker 4 in the furnace radial direction will be symmetrical. In this case, the diameter of the collecting hopper 6 that receives raw materials from multiple top bunkers 4 will be large, so the raw materials will 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 will tend to shift. 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.

[0019] 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. 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. The raw materials discharged from the raw material hoppers are transported to the furnace top by a charging conveyor 3 and charged into one of the furnace top bunkers 4. At this time, as shown by the dashed line in Figure 2 (and Figure 6 described later), the raw materials fall diagonally downward through a receiving chute 12, away from the furnace center line x, and are deposited in the furnace top bunker 4.

[0020] In the embodiment shown in Figures 1 and 2, 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, and the raw materials held in these hoppers are appropriately discharged onto the charging conveyor 3. In the method of the present invention, when ore raw material a is cut onto a charging conveyor 3 and transported to the furnace top by the charging conveyor 3 and charged into one of the top bunkers 4, metallic iron raw material b is cut and piled on top of the ore raw material a being transported by the charging conveyor 3. At this time, metallic iron raw material b is piled on top of the ore raw material a in a length range w of 18% (0.18 L) to 75% (0.75 L) from the front end in the conveying direction of the loading length L of the ore raw material a loaded on the charging conveyor 3. That is, as shown in FIG. 2, the length range w of the metallic iron raw material b piled on top of the ore raw material a is set to 0.18 L to 0.75 L from the front end in the conveying direction of the loading length L of the ore raw material a. Then, the ore raw material a and metallic iron raw material b are charged into the top bunker 4 in this state.

[0021] The metallic iron raw materials b charged into the top bunker 4 are stacked on the ore raw materials a within the length range w as described above, resulting in a state in which a large amount of the metallic iron raw materials b is deposited in a specific region within the top bunker 4 (this point will be described in detail later). Therefore, when discharging the raw materials from the top bunker 4, the discharge of the metallic iron raw materials b in the initial stage of raw material discharge is suppressed, and the discharge rate of the metallic iron raw materials b in the middle and later stages of raw material discharge can be increased. As will be described later, in the present invention, when the raw materials in the top bunker 4 are charged into the furnace using the rotating chute 5, the rotating chute 5 is rotated and tilted to move the raw material charging position from the furnace center periphery toward the furnace wall (charging by reverse tilting). This allows the metallic iron raw materials b to be charged (deposited) at a high rate in the desired region in the furnace radial direction, i.e., the region from the furnace center to the furnace wall. Here, the region from the furnace middle to the furnace wall includes not only a region spanning the furnace middle and the furnace wall, but also a region consisting only of the furnace middle or only of the furnace wall. In addition, the discharge rate of the metallic iron raw materials b from the middle stage of raw material discharge from the top bunker 4 (especially the final stage of raw material discharge) increases if the stacking position of the metallic iron raw materials b is closer to the front side in the conveying direction of the loaded length L of the ore raw materials a. Therefore, 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 the loaded length L of the ore raw materials a loaded on the charging conveyor 3, which is 18% (0.18 L) to 32% (0.32 L).

[0022] Here, the stacking position (range) of the metallic iron raw material b can be arbitrarily selected as long as the distance from the front end in the conveying direction is within a length range of 18% (0.18 L) to 75% (0.75 L) of the stacking length L of the ore raw material a, preferably within a length range of 18% (0.18 L) to 32% (0.32 L) from the front end. Therefore, the length range of 18% (0.18 L) to 75% (0.75 L) from the front end in the conveying direction can be, for example, a length range of 20% (0.20 L) to 65% (0.65 L) or 25% (0.25 L) to 60% (0.60 L) from the front end in the conveying direction. Furthermore, as a length range in which the distance from the front end in the conveying direction is 18% (0.18L) or more and 32% (0.32L) or less, for example, a length range in which the distance from the front end in the conveying direction is 20% (0.20L) to 30% (0.30L) or 22% (0.22L) to 32% (0.32L) can be selected. Furthermore, among metallic iron raw materials b, reduced iron shaped products such as HBI are obtained by molding reduced iron using twin molding rolls or the like, and sharp burrs are formed in the gap between the molding rolls. If these burrs come into direct contact with the conveyor belt of the charging conveyor 3, it 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.

[0023] Here, how the metallic iron raw material b charged into the furnace top bunker 4 together with the ore raw material a is deposited in the furnace top bunker 4 (deposit form and region) will be briefly described. As described above, the raw materials charged into the top bunker 4 from the charging conveyor 3 fall obliquely downward through the receiving chute 12, away from the furnace centerline x, and are deposited in the top bunker 4. The ore raw material a, which is the main raw material, falls to a position away from the furnace centerline x and then rolls toward the furnace centerline x, forming a slope. Larger particle sizes tend to flow downward and segregate toward the lower part of the bunker (above the raw material discharge port 40). In other words, the ore raw material a is prone to segregation due to particle size differences. In contrast, such segregation due to particle size differences is unlikely to occur between the ore raw material a and the metallic iron raw material b. Generally, the metallic iron raw material b (especially in the case of HBI) has a larger particle size than the ore raw material a, but also a higher density. Therefore, the metallic iron raw material b that falls to a position away from the furnace centerline x in the top bunker 4 sinks into the ore raw material layer and deposits there. In other words, metallic iron raw material b, which has a higher density than ore raw material a, does not flow down the slope but sinks and remains at the position where it fell (a position away from the furnace central axis x). In this way, segregation due to the density difference occurs preferentially between ore raw material a and metallic iron raw material b, and excessive segregation due to 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 density difference occurs preferentially and segregation due to particle size difference is suppressed.

[0024] In the present invention, metallic iron raw materials b are stacked in a specific form on ore raw materials a loaded on a charging conveyor. This utilizes segregation due to differences in raw material density within the top bunker 4, allowing metallic iron raw materials b to accumulate in a specific area within the top bunker 4. This reduces the discharge of metallic iron raw materials b in the early stages of discharge and increases the discharge rate of metallic iron raw materials b from the middle to later stages of discharge. Figure 3 shows the discharge rate of metallic iron raw materials b at each stage of discharge from the top bunker in a test in which raw materials were charged into the top bunker according to the conditions of the present invention (the test conditions will be described in detail later). In this test, sintered ore was used as the ore raw material a, and reduced iron (HBI) was used as the metallic iron raw material b. A segregation control plate, as described below, was installed within the top bunker. The horizontal axis of Figure 3 represents the weight (cumulative value) rate of raw materials discharged from the top bunker. Here, Fig. 3(A) shows a case where metallic iron material b (reduced iron) is stacked on ore material a in a length range from 18% to 75% of the total length of ore material a loaded on a charging conveyor, from the front end in the conveying direction, and then the ore material a and metallic iron material b are charged into the top bunker in this state (see Fig. 15(b) to be described later). Fig. 3(B) shows a case where metallic iron material b (reduced iron) is stacked on ore material a in a length range from 18% to 32% of the total length of ore material a loaded on a charging conveyor, from the front end in the conveying direction, and then the ore material a and metallic iron material b are charged into the top bunker in this state (see Fig. 15(c) to be described later). As shown in Fig. 3(A), the discharge of metallic iron material b is suppressed in the early stage of material discharge, and the discharge rate of metallic iron material b increases from the middle stage of material discharge onward. In particular, in the case of FIG. 3(B) where the stacking range of metallic iron raw material b is shifted to the front side of the stacking length of ore raw material a, the discharge rate of metallic iron raw material b at the end of raw material discharge is high.

[0025] For comparison, Figure 18 shows the discharge ratio of metallic iron raw material b 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 (the test conditions were the same as those in the test in Figure 3 except for the stacking range of metallic iron raw material b). Figure 18(A) shows the case in which metallic iron raw material b was stacked on ore raw material a in a length range from 4% to 18% of the stacking length of ore raw material a loaded on the charging conveyor, from the front end in the conveying direction, and then ore raw material a and metallic iron raw material b were charged into the top bunker in this state. Figure 18(B) shows the case in which metallic iron raw material b was stacked on ore raw material a in a length range from 75% to 96% of the stacking length of ore raw material a loaded on the charging conveyor, from the front end in the conveying direction, and then ore raw material a and metallic iron raw material b were charged into the top bunker in this state. In the case of Figure 18(A), the discharge rate of metallic iron raw material b is relatively high in the early stage of raw material discharge, and in the case of Figure 18(B), the discharge rate of metallic iron raw material b is very high in the first half to middle stage of raw material discharge.

[0026] Furthermore, in the method of the present invention, when the raw materials (ore raw material a and metallic iron raw material b) charged into the furnace top bunker 4 as described above are charged into the furnace using the rotating chute 5, the rotating chute 5 is rotated and tilted to move the raw material charging position from the furnace center periphery toward the furnace wall. That is, the raw materials are charged while the rotating chute 5 is rotated and the direction of the chute is gradually shifted (tilted) from the furnace center periphery toward the furnace wall (reverse tilting charging using the rotating chute). Figure 4 shows a schematic diagram of the charging of raw materials using the rotating chute 5. As shown in the figure, raw materials are charged using the rotating chute 5 starting from the charging direction toward the furnace center periphery, and then the rotating chute 5 is tilted gradually from the direction toward the furnace center periphery (two-dot chain line) to the direction toward the furnace wall (furnace wall periphery) (solid line).

[0027] 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 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.

[0028] As described above, in the method of the present invention, a large amount of metallic iron raw materials b is discharged from the furnace top bunker 4 after the middle stage of raw material discharge, and the raw materials are piled up in the furnace top bunker 4 so that the discharge rate of metallic iron raw materials b becomes high. Therefore, by starting raw material charging using the rotating chute 5 from charging into the periphery of the furnace center, and then gradually shifting (tilting) the direction of the chute from the periphery of the furnace center through the middle part of the furnace to the furnace wall side (reverse tilting charging), it becomes possible to pile up the metallic iron raw materials b from the middle part of the furnace to the furnace wall side at a high mixing ratio. In the present invention, the peripheral region of the furnace center refers to the region between the furnace center and the furnace middle in the furnace radial direction, and generally refers to the region with a dimensionless radius (r / R0, hereinafter the same) of 0.20 to less than 0.30. Generally, the furnace center refers to the region with a dimensionless radius of 0.00 to less than 0.20, the furnace middle refers to the region with a dimensionless radius of 0.30 to 0.80, and the furnace wall refers to the region with a dimensionless radius of more than 0.80 to 1.00. Here, the dimensionless radius (r / R0) indicates a position within the furnace in the furnace radial direction, and is the value obtained by dividing the distance r from the furnace center to that position by the furnace radius R0.

[0029] In the present invention, the starting position for charging raw materials may be appropriately determined within the periphery of the center of the furnace, and the starting position for charging raw materials is the center of the raw material falling from the rotating chute on the raw material pile surface inside the furnace. In the method of the present invention, there is no particular limitation on the amount (mixing ratio) of metallic iron raw material b charged. The more the amount of metallic iron raw material b charged, the more the reducing agent rate can be reduced. However, as the amount of metallic iron raw material b charged increases, the heat flow ratio decreases. Generally, a blast furnace is preferably operated at a heat flow ratio of 0.9 or less. In a typical blast furnace (with an ore charge of approximately 1,600 kg / t), this range is reached at 400 kg / t or more, which causes a delay in the temperature rise of the raw materials, reducing the effectiveness of reducing the reducing agent rate. Therefore, it is preferable to limit the amount (mixing ratio) of metallic iron raw material b charged to 25 mass% or less of ore raw material a.

[0030] As will be described later, in the present invention, segregation of ore raw material a occurs in the top bunker 4 due to particle size differences. As a result, the ore raw material a discharged from the top bunker 4 has a discharge particle size distribution (particle size transition) as shown in Figure 5. That is, Figure 5 shows an example of the particle size of ore raw material a (discharge particle size distribution of ore raw material a) 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 (the test conditions will be described in detail later). In this test, sintered ore was used as the ore raw material a, and reduced iron (HBI) was used as the metallic iron raw material b. A segregation control plate, as described later, was installed in the top bunker. The horizontal axis of Figure 5 represents the weight (cumulative value) ratio of raw materials discharged from the top bunker. As shown in the figure, the particle size of ore material a is particularly large in the early stage of discharge (discharge weight ratio: 0.15 or less). The particle size subsequently becomes smaller, but becomes relatively large in the later stage of discharge (discharge weight ratio: around 0.6 to 0.7). As a result, coarse particles of ore material a accumulate around the center of the furnace and from the middle to the furnace wall, while fine particles accumulate around the furnace wall and from the periphery to the middle of the core. On the other hand, as mentioned above, metallic iron material b is discharged from the furnace top bunker at the discharge ratio shown in Figure 3. In the present invention, in which reverse tilting charging is performed using the rotating chute 5, more metallic iron material is charged from the middle to the furnace wall. Therefore, in the region from the middle to the furnace wall, the difference in particle size between metallic iron material b and ore material a becomes smaller. This increases the porosity of the raw material layer (ore material a + metallic iron material b) before softening and melting, improving permeability and reduction efficiency. Furthermore, by using the segregation control plate under predetermined conditions in the top bunker 4, the ore raw material a can be deposited (segregated) in a more preferable state in the top bunker 4, thereby further enhancing the above-mentioned effects. This point will be described in detail later.

[0031] Next, a more preferred embodiment of the method of the present invention will be described. In the present invention, the particle size distribution of the ore raw material a discharged from the top bunker 4 depends on the segregation behavior due to particle size differences within the top bunker. However, by installing a segregation control plate 8 within the top bunker 4 and allowing the ore raw material a to fall downward via this segregation control plate 8, the segregation state due to particle size differences of the ore raw material a is optimized, and it has been found that the particle size distribution of the ore raw material a discharged from the top bunker 4 becomes particularly suitable for the raw material charging mode (reverse tilting) using the rotating chute 5 of the present invention. FIG. 6 is a schematic diagram showing an embodiment of the present invention in which a segregation control plate 8 is installed in the top bunker 4 and the segregation caused by the particle size difference of the ore raw material a is controlled (optimized) by the segregation control plate 8. The front surface of the segregation control plate 8 forms a raw material receiving surface 80 that receives raw materials falling from above. The segregation control plate 8 is disposed in the upper space of the furnace top bunker 4 and is supported so as to be tiltable up and down around a pivot part 81. The orientation of this segregation control plate 8 is set so that its raw material receiving surface 80 faces the outside of the furnace in the furnace radial direction and is inclined downward with respect to the outside of the furnace. When raw materials (ore raw material a and metallic iron raw material b) are charged from the charging conveyor 3 into the furnace top bunker 4, the raw materials falling from above pass through the raw material receiving surface 80 of the segregation control plate 8 (i.e., after being received by the raw material receiving surface 80 once), and then fall downward and pile up in the bunker.

[0032] Here, we will only discuss ore raw material a, which is charged into the top bunker 4 from the charging conveyor 3 and segregates due to particle size differences. The ore raw material a, which is introduced into the top bunker 4 from the charging conveyor 3 through the receiving chute 12, falls obliquely downward, away from the furnace central axis x. By temporarily receiving the ore raw material a on the raw material receiving surface 80 of the segregation control plate 8 and then allowing it to fall (changing its falling direction), the ore raw material a falls to a position farther away from the furnace central axis x and then rolls toward the furnace central axis x, forming a slope. At this time, ore raw material a with larger particle size tends to flow downward and segregate toward the lower part of the bunker (above the raw material discharge port 40). Furthermore, ore raw material a with smaller particle size tends to accumulate away from the furnace central axis x, while ore raw material a with larger particle size tends to accumulate (segregate) closer to the furnace central axis x. As a result, the segregation state due to particle size differences of the ore raw material a is optimized, and the particle size distribution of the ore raw material a discharged from the top bunker 4 becomes particularly suitable for the raw material charging mode (reverse tilting charging) using the rotating chute of the present invention. Figure 5, which was explained earlier, shows the results of a test using such a segregation control plate 8. On the other hand, the metallic iron raw material b that has passed through the raw material receiving surface 80 of the segregation control plate 8 and fallen to a position away from the furnace central axis x sinks at the falling position due to the density difference with the ore raw material a, and is deposited at that position.

[0033] The segregation control plate 8 only needs to receive the raw materials falling from above and guide them away from 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 allows this. However, if the inclination angle θ of the raw material receiving surface 80 relative to the horizontal plane is too small, the raw materials 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 materials away from the furnace central axis x, which will reduce the effect of promoting segregation due to particle size differences in the ore raw material a. From the above perspectives, the inclination angle θ should be approximately 7 to 47°, preferably approximately 7 to 37°.

[0034] As already mentioned, metallic iron raw materials b (especially in the case of HBI) generally have a higher density (apparent density) than ore raw materials a, so that metallic iron raw materials b charged into the top bunker 4 sink into the raw material layer due to the density difference with ore raw materials a and accumulate. In other words, metallic iron raw materials b segregate preferentially due to the density difference with ore raw materials a, and excessive segregation due to particle size difference is suppressed. To confirm this, the inventors conducted an experiment to measure the discharge distribution of raw materials (sintered ore and reduced iron) from the furnace top bunker using a scale model of a blast furnace charging device. Figure 7 shows a schematic diagram of the 1 / 17.8 scale model experimental equipment used in this experiment. This simulation equipment is composed of 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) to reproduce the time-dependent changes in raw material discharge from an actual furnace. The raw material charging device 22 also comprises a top bunker 24, a collecting hopper 26, and a switching chute 30. 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 6, is installed within the top bunker 24, and the inclination angle θ of its raw material receiving surface is set to 27°. A sampling box 31 that can be moved by a belt conveyor 32 is placed below the raw material charging device 22, and this moving sampling box 31 is configured to sequentially collect raw materials discharged from the furnace top bunker 24 over time. In this experiment, sintered ore was used as ore raw material A, and reduced iron (HBI) was used as metallic iron raw material B. Other experimental and raw material conditions were determined according to the law of similarity with an actual blast furnace.

[0035] The apparent density of reduced iron (HBI) is 5.0 to 6.0 t / m 3 and the typical density is 5.2t / m 3 The apparent density of the sintered ore was 3.0 to 4.0 t / m 3 and the typical density is 3.4t / m 3The size of the reduced iron (HBI) was 5.6 mm × 2.8 mm × 1.7 mm, with an average particle size (defined below) of 3.6 mm. The average particle size (defined below) of the sintered ore was 0.7 mm. According to the method of the present invention, sintered ore and reduced iron were cut onto a charging conveyor 23 and charged into the top bunker 24. Afterwards, the sintered ore was discharged from the top bunker 24. Figure 5 shows the particle size distribution of the sintered ore relative to the weight ratio of the raw materials. Figure 3 also shows the ratio of reduced iron relative to the weight ratio of the raw materials. The horizontal axes of Figures 3 and 5 represent the weight (cumulative) ratio of raw materials discharged from the top bunker. Comparing these figures, it can be seen that the sintered ore at the initial stage of discharge (initial flow) is coarse (Figure 5), whereas the reduced iron fraction at the initial stage of discharge (initial flow) is small (Figure 3), despite its larger particle size. This confirms that segregation due to particle size differences in the reduced iron is less likely to occur than in the sintered ore. Therefore, a higher density of reduced iron can reduce the proportion of reduced iron at the initial stage of discharge (initial flow), and in the reverse tilting charging of the present invention, it is more preferable because it can suppress the charging of reduced iron near the center of the furnace and increase the amount of reduced iron charged to the middle to wall of the furnace. The apparent density of the reduced iron in this case was 1.5 times that of the ore raw material.

[0036] 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. In order to confirm this, the inventors conducted the following experiment to measure the segregation behavior of metallic iron raw material b using a discharge experimental device for metallic iron raw material b. Here, the average apparent density of the raw material 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). Figure 8 shows a schematic diagram of the discharge test equipment used in this experiment. Sintered ore was used as ore raw material a, and reduced iron (HBI) was used as metallic iron raw material b. In this experiment, coke was discharged from the hopper in the discharge test equipment to form a pile surface, and then a mixture of sintered ore and reduced iron was discharged from the hopper onto the pile surface. The distance traveled by reduced iron within the furnace top bunker was evaluated by setting the origin directly below the hopper discharge outlet and the base of the coke pile surface as 1. The reduced iron was recovered at each travel distance, and its weight percentage was evaluated.

[0037] Figure 9 shows an example of the measurement results of the travel distance of reduced iron. This measurement result shows that the average apparent density of reduced iron [ρ b ] and the average apparent density of sinter [ρ a ] ratio [ρ b ] / [ρ a The graphs are for density ratios of 2.0 and 1.5. The vertical axis shows the weight ratio of reduced iron present at each travel distance out of the total weight of reduced iron introduced. The greatest amount of reduced iron is present at a position a little further away from the outlet. This is presumably because the reduced iron present at the position directly below the outlet has a low proportion of reduced iron because the inertia of the fall is strong and it moves down the slope. However, as mentioned above, the reduced iron tends to sink, so it remains at the point where the inertia of the fall is lost, resulting in a maximum value for the proportion of reduced iron present. Here, if the travel distance at the position where the proportion of reduced iron shows a maximum value is called the "representative travel distance," it is thought that the shorter this representative travel distance, the more likely the reduced iron is to remain near the drop point in the top bunker, and as mentioned above, the proportion of reduced iron at the initial stage of discharge (initial flow) is likely to be small. Therefore, the relationship between the representative travel distance and the density of reduced iron was investigated using the same measurement experiment as above. Here, the representative travel distance was calculated from the position of the apex of a quadratic function of each plot obtained by the least squares method. The density of the reduced iron used was 4620 to 8400 kg / m 3 and the density of sinter is 4200 kg / m 3 is.

[0038] Figure 10 shows the relationship between the density of reduced iron (density ratio to sintered ore) and the typical travel distance, which is the result of the investigation. The horizontal axis is the density ratio between reduced iron and sintered ore, i.e., the average apparent density of reduced iron [ρ HBI ] and the average apparent density of sinter [ρ ore ] ratio [ρ HBI ] / [ρ ore ]. Figure 10 shows that the higher the density ratio between reduced iron and sintered ore, the shorter the representative moving distance of reduced iron tends to be, but this tendency changes when the density ratio is 1.25. When the density ratio is smaller than 1.25, the densities of the sintered ore and reduced iron are similar, making it difficult for the reduced iron to sink into the sintered ore and remain there. Therefore, from the results of this investigation, it can be seen that the density ratio between reduced iron and sintered ore (average apparent density of reduced iron [ρ HBI ] and the average apparent density of sinter [ρ ore ] ratio [ρ HBI ] / [ρ ore ]) was found to be preferably 1.25 or higher.

[0039] From the viewpoint of appropriately obtaining segregation due to the density difference between metallic iron raw material b and ore raw material a, and taking into consideration the above-mentioned experimental conditions and results, it is considered desirable that the average apparent density of metallic iron raw material b is sufficiently larger than the average apparent density of ore raw material a. For this reason, the average apparent density [ρ b ] and the average apparent density of ore raw material a [ρ a ] ratio [ρ b ] / [ρ a ] is preferably 1.25 or more, more preferably 1.5 or more, provided that the density ratio [ρ b ] / [ρ a If the density ratio [ρ ] is too large, when the raw materials are discharged from the top bunker 4, the metallic iron raw materials b mixed with the ore raw materials a may not be discharged smoothly and may become stuck in the top bunker 4. In that case, it is expected that equipment damage or unexpected burden distribution will occur, which may destabilize blast furnace operation. For this reason, it is necessary to set the density ratio [ρ b ] / [ρ a ] should preferably be limited to around 2.0.

[0040] Furthermore, although there is no particular limitation on the shape of the metallic iron raw material b in the present invention, it is believed that the shape of the metallic iron raw material b also affects the above-mentioned moving distance. That is, the more complex the shape of the metallic iron raw material b, the more difficult it is for the metallic iron raw material b to roll, and therefore the moving distance is thought to be shorter. Therefore, similar to the above-mentioned measurement experiment, an experiment was conducted using the apparatus shown in FIG. 8 for metallic iron raw materials b with different aspect ratios to investigate the moving distance. In the experiment, sintered ore was used as the ore raw material a, and reduced iron (HBI) was used as the metallic iron raw material b. Here, the aspect ratio of the metallic iron raw material b (HBI in this experiment) is the value obtained by dividing the length of the longest side of the metallic iron raw material b by the length of the shortest side, and is the average aspect ratio of 20 randomly selected raw material particles.

[0041] As mentioned above, the abundance ratio of reduced iron exhibits a maximum value, and the movement distance at the maximum value was evaluated as the representative movement distance. Figure 11 shows the relationship between the aspect ratio of reduced iron and the representative movement distance, which is the measurement result. Figure 11 shows that the representative movement distance tends to decrease as the aspect ratio increases, but this trend changes when the aspect ratio is 1.4. This is thought to be because when the aspect ratio is smaller than 1.4, the shape of the reduced iron is close to a cube, which weakens the resistance to rolling and makes it difficult for the reduced iron to remain in place. Therefore, these survey results indicate that an aspect ratio of 1.4 or more is preferable for reduced iron. For the above reasons, the aspect ratio of the metallic iron raw material b is preferably 1.4 or more. However, if the aspect ratio of the metallic iron raw material b is too large, there is a risk of clogging the discharge port of the top bunker 4. Furthermore, if the difference in shape between the metallic iron raw material b and the ore raw material a is too large, there is a risk of forming an unexpected burden distribution, which may destabilize blast furnace operation. For this reason, it is desirable to set the upper limit of the aspect ratio of the metallic iron raw material b to about 6.5.

[0042] Next, the preferred particle size (average particle size) of the ore raw material a and the metallic iron raw material b will be described. Here, the average particle size of ore raw material a [d a] is the harmonic mean diameter for any raw material, such as sinter, pellets, or lump ore, and is the particle size calculated as average particle size = 1 / Σ(Wi / di) (where Wi is the weight ratio of particles with particle size di, and di is the median diameter of the sieve openings). 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 size of each is determined, and then the average particle size weighted by the weight ratio is determined.

[0043] The average particle size of metallic iron raw material b [d b In the case of HBI, the average particle diameter [d b ].

number

[0044] In the present invention, there are no particular limitations on the particle sizes of the ore raw material a and the metallic iron raw material b. However, the particle size of the metallic iron raw material b (especially in the case of HBI) is generally considerably larger than that of the ore raw material a. In the example of the above experiment, the average particle size of the HBI is 5.1 times that of the ore raw material. It is considered that the larger the particles of the metallic iron raw material b, the heavier the particles are, and the shorter the above-mentioned moving distance. Therefore, similar to the above-mentioned measurement experiment, an experiment was conducted using the apparatus of FIG. 8 for cases where the particle size ratio of the metallic iron raw material b to the ore raw material a was different, and the moving distance was investigated. In the experiment, sintered ore was used as the ore raw material a, and reduced iron (HBI) was used as the metallic iron raw material b, and the relationship between the particle size ratio of the reduced iron to the sintered ore and the moving distance was investigated. Here, the particle size ratio of the reduced iron to the sintered ore is defined as the average particle size [d HBI ] and the average particle size of sinter [d ore ] ratio [d HBI ] / [d ore ].

[0045] As mentioned above, the proportion of reduced iron has a maximum value, so the distance traveled at the maximum value was evaluated as the representative distance traveled. Figure 12 shows the particle size ratio [d HBI ] / [d ore ] and the representative moving distance. HBI ] / [d ore ] tends to decrease the representative movement distance, but the particle size ratio [d HBI ] / [d ore ] is 3.5, the tendency changes. HBI ] / [d ore When the particle size ratio [d HBI ] / [d ore It was found that a value of 3.5 or higher is preferable. From the above results, the average particle size of metallic iron raw material b [d b ] is the average particle size of raw ore a [d a ], and in particular, the average particle size [d b ] and the average particle size of ore raw material a [d a] ratio [d b ] / [d a However, if the average particle size of the metallic iron raw material b is too large, it may not be possible to ensure a sufficient apparent density, and there is a risk that the discharge from the furnace top bunker may be physically hindered. Therefore, it is preferable that the particle size ratio [d b ] / [d a ] should preferably be limited to around 7.0.

[0046] The metallic iron raw material b is preferably deposited in the lower part of the ore raw material layer extending from the middle part of the blast furnace to the furnace wall part for the following reasons. In a blast furnace, the ore raw material layer softens and melts as it descends. 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 of the upper part of the ore raw material layer, worsening the high-temperature properties of the ore raw material layer. 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 low high-temperature shrinkage is mixed into the ore raw material layer, the reduced iron does not melt during ore melting, creating voids around the reduced iron, ensuring air permeability. Therefore, mixing metallic iron raw materials such as reduced iron into the lower part of the ore raw material layer creates voids around the metallic iron raw material with low high-temperature shrinkage during softening and melting, improving the air permeability of the lower part of the ore raw material layer. This facilitates the flow of high-temperature reducing gas 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 reduction efficiency.

[0047] In the method of the present invention, in order to deposit metallic iron raw material 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 ore raw material a into two parts, charge each part into a separate furnace top bunker 4, and sequentially charge them into the furnace via a rotating chute 5. That is, one charge of ore raw material a is charged into the furnace in two batches, and the metallic iron raw material b is mixed with the ore raw material a of the first batch and charged into the furnace by the above-mentioned method. If the ore raw material a of the subsequent second batch is charged in the region from the middle part to the furnace wall part, the metallic iron raw material b will be below the ore raw material a of the second batch, so that it is possible to deposit a high proportion of the metallic iron raw material b in the lower part of the ore raw material layer from the middle part to the furnace wall part of the blast furnace. Figure 13 shows a schematic diagram of the shape (cross section) of the deposits inside the furnace when the raw materials are charged using this method. The area surrounded by the dotted line is the "lower region of the ore raw material layer from the middle part of the furnace to the furnace wall" where a high proportion of metallic iron raw material b can be deposited.

[0048] The second batch of ore raw material a can be charged by either tilting the rotating chute 5 while rotating it, moving the raw material charging position from the furnace wall toward the furnace center periphery (normal tilting charging), or by moving the raw material charging position from the furnace center periphery toward the furnace wall (reverse tilting charging). Furthermore, charging can be started with reverse tilting, and once it reaches the furnace wall, it can be charged to the middle of the furnace with further normal tilting. However, reverse tilting charging is preferable for the second batch because reverse tilting charging reduces the risk that the metallic iron raw material b charged in the first batch will be caught in the flow of the second batch of raw material into the furnace center and move to the furnace center. In this case, heat generated by the reduction reaction of the ore raw material a is lost by the substitution of the metallic iron raw material b, and an increase in the reducing agent rate due to a lack of heat is suppressed. Therefore, it is more preferable not to mix the metallic iron raw material b with the ore raw material a of the second batch.

[0049] The present inventors conducted the following experiment using a scale model of a blast furnace charging device in order to verify the conditions for stacking metallic iron raw materials b on ore raw materials a transported by the charging conveyor 3. Figure 14 shows a schematic diagram of the 1 / 17.8 scale model experimental equipment used in this experiment. This simulation equipment 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) to reproduce the time-dependent changes in raw material discharge from an actual furnace. The raw material charging device 22 is also composed of a top bunker 24, a rotating chute 25, a collecting hopper 26, a top ring 27, and a switching chute 30. 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 6, is installed within the top bunker 24, and the inclination angle θ of its raw material receiving surface is set to 27°.

[0050] In this experiment, sintered ore was used as ore raw material A, and reduced iron (HBI) was used as metallic iron raw material B. Other experimental and raw material conditions were determined according to the law of similarity with an actual blast furnace. The raw materials discharged from the raw material hopper 29 were transported to the furnace top by the charging conveyor 23 and charged into the top bunker 24. The ore raw material (sintered ore) was divided into two batches and charged into separate top bunkers 24. The 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 the rotating chute 25. For the first batch, in which reduced iron was mixed, the raw materials were charged by rotating and tilting the rotating chute 25 to move the raw material charging position from the furnace center periphery to the middle of the furnace and toward the furnace wall (tilting pattern = reverse tilting). For the second batch, the raw materials were charged by 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 of the first batch of raw material charging through the rotating chute 25 was a dimensionless radius of 0.20, and the ending position was a dimensionless radius of 0.90 (the center position of the raw material falling from the rotating chute on the raw material pile surface inside the furnace). The starting position of the second batch of raw material charging was a dimensionless radius of 0.50, and the ending position was a dimensionless radius of 0.95 (the center position of the raw material falling from the rotating chute on the raw material pile surface inside the furnace).

[0051] In this experiment, for the first batch of raw materials, when reduced iron (hereinafter referred to as reduced iron b) was cut out and piled on top of the ore raw material a on the charging conveyor 23, the cut lengths of the reduced iron b were set to three patterns (a) to (c) shown in Fig. 15, and each was charged into the furnace top bunker 24. Details of each condition are as follows. Form (a): Reduced iron (b) was layered on the ore material (a) over the entire length of the ore material (a) loaded on the charging conveyor 23. Form (b): Reduced iron (b) was stacked on the ore material (a) in a length range of 18% to 75% of the length of the ore material (a) loaded on the charging conveyor 23 from the front end in the conveying direction. Form (c): Reduced iron (b) was stacked on the ore material (a) in a length range of 18% to 32% of the total length of the ore material (a) loaded on the charging conveyor 23 from the front end in the conveying direction.

[0052] 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 ratio of reduced iron was measured. The results are shown in Figure 16. In Figure 16, the horizontal axis represents the dimensionless radius of the blast furnace, and the vertical axis represents the mixed ratio of reduced iron by weight. Furthermore, Figure 17 shows the results of measuring the discharge ratio of reduced iron when the raw materials were discharged from the top bunker. In Figure 17, the horizontal axis represents the discharge weight (cumulative value) ratio of raw materials, and the vertical axis represents the discharge ratio of reduced iron. As shown in Figure 16, the first batch of mixed reduced iron was charged with reverse tilting from the furnace center toward the furnace wall, so no mixing of reduced iron was observed in the furnace center in any of the configurations (a) to (c). On the other hand, when the stacking position of the reduced iron on the ore raw materials (position within the stacking length) was shifted toward the middle of the ore raw material loading length (configuration (a) → 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 17), the closer the stacking position of the reduced iron to the middle, the higher the discharge proportion of reduced iron from the middle of the material discharge from the furnace top bunker.

[0053] Furthermore, when the stacking position of the reduced iron on the ore raw materials (position within the stacking length range) was shifted to the front of the middle position of the ore raw materials stacking length (configuration (b) → configuration (c)), the proportion of reduced iron mixed toward the furnace wall 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 (Figure 17), the proportion of reduced iron discharged from the furnace top bunker at the end of the material discharge increases as the stacking position of the reduced iron moves toward the front of the middle position. Furthermore, configuration (c), in which reduced iron is stacked on the ore raw materials within a length range of 18% to 32% from the front end in the transport 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. As described above, by mixing the ore raw material a and the metallic iron raw material b according to the method of the present invention, it is possible to control the mixing ratio of the metallic iron raw material b when it is discharged from the furnace top bunker. This makes it possible to selectively charge a high ratio of the metallic iron raw material b into the region from the middle part of the furnace to the furnace wall part, where the reduction load is large. The method for producing molten pig iron of the present invention also includes a step of mixing an ore raw material a including at least one of sintered ore, pellets, and lump ore with a metallic iron raw material b including reduced iron and / or granulated pig iron by the raw material charging method of the present invention described above, and charging the mixture into a blast furnace. [Example]

[0054] 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 and 2 was used. 3 ) An operational test was conducted. 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 as shown in Figure 6 was installed inside the top bunker 4, and the inclination angle θ of its raw material receiving surface 80 was set to 27°. Sintered ore was used as the ore raw material, and reduced iron (HBI) was used as the metallic iron raw material. a ] is 12 mm, and the average particle size of reduced iron [d b ] is 66 mm, and [d a ] / [d b ]=5.5. The aspect ratio of the reduced iron is 3.7. The average apparent density of the ore raw material (sintered ore) [ρ a ] is 3.4t / m 3 and the average apparent density of reduced iron (HBI) [ρ b ] is 5.4t / m 3 The mixed ratio of reduced iron was set to 4 mass% of the ore raw material.

[0055] The ore raw material discharged from the 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. In this example, 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. In this example, reduced iron was discharged from the 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 materials discharged from the top bunker 4 were charged into the furnace through the rotating chute 5. For the first batch, in which reduced iron was mixed, the rotating chute 5 was rotated and tilted to move the raw material charging position from the periphery of the furnace center toward the furnace wall, and the raw materials were charged (tilting pattern = reverse tilting). The starting position for charging the first batch of raw materials using the rotating chute 5 was a dimensionless radius of 0.20, and the ending position was a dimensionless radius of 0.90 (the center position of the raw materials falling from the rotating chute on the raw material pile surface inside the furnace). For the subsequent second batch, the raw materials were charged while rotating and tilting the rotating chute 5, moving 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 second batch of raw materials using the rotating chute 5 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).

[0056] In Example 1, when the first batch of ore materials was charged into the furnace 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 18% to 75% of the length of the ore materials loaded on the charging conveyor 3 from the front end in the conveying direction (configuration (b) in FIG. 15 ). In Example 2, when the first batch of ore materials was charged into the furnace 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 18% 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 (c) in FIG. 15 ). 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: 60 kg / t of reduced iron was cut out 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. 15 ).

[0057] Table 1 shows the operating conditions for the invention example and the comparative example, as well as the measurement results of the air permeability index, gas utilization rate, and molten iron temperature. According to this, in invention examples 1 and 2, reduced iron was placed (charged) at a high mixing ratio in the lower part of the ore raw material layer from the middle of the furnace to the furnace wall, which improved the insufficient reducing power and stabilized the gas flow distribution. As a result, the air permeability index and the reducing agent rate were lower than in the comparative example. In particular, the effect was greatest in invention example 2, in which the reduced iron was stacked closer to the front of the length of the ore raw material transported by the charging conveyor 3. 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.

[0058] [Table 1] [Explanation of symbols]

[0059] 1 Furnace body 2 Raw material charging device 3 Charging conveyor 4 Furnace Top Bunker 5 Swivel Shot 6. Collection 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 Swivel Shot 26 Collection Hopper 27 Top Ring 28 Segregation control plate 29a, 29b Raw material hopper 30 Switch Shot 31 Sampling Box 32 Conveyor Belt 40 Raw material outlet 41 Cylindrical part 42 Infundibulum 80 Raw material receiving surface 81 Central branch 240 Raw material discharge port 420,421 Wall a. Mineral ore raw materials b. Metallic iron raw materials x Furnace center axis x B Bunker center axis

Claims

1. A method for charging a bell-less 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, comprising 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 resulting mixture into the blast furnace, comprising: When the ore raw material (a) is transported to the furnace top by a charging conveyor and charged into one of the furnace top bunkers, the metallic iron raw material (b) is cut out on top of the ore raw material (a) transported by the charging conveyor, so that the metallic iron raw material (b) is stacked on the ore raw material (a) in a length range of 18% to 75% of the loading length of the ore raw material (a) loaded on the charging conveyor, from the front side in the conveying direction, and in this state the ore raw material (a) and the metallic iron raw material (b) are charged into the furnace top bunker, When the raw materials in the furnace top bunker are charged into the furnace using the rotating chute, the raw materials are charged while rotating and tilting the rotating chute to move the raw material charging position from the peripheral portion of the furnace center toward the furnace wall.

2. 2. The method for charging raw materials into 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 stacked on the ore raw material (a) in a length range of 18% to 32% of the loading length of the ore raw material (a) loaded on the charging conveyor, the distance from the front side in the conveying direction.

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

4. 4. The 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 the metallic iron raw material (b).

5. A segregation control plate is installed in the top bunker, 3. The method for charging raw materials into a blast furnace according to claim 1 or 2, characterized in that, when the ore raw materials (a) and the metallic iron raw materials (b) transported by the charging conveyor are charged into the furnace top bunker, the raw materials falling from above are caused to fall downward via the raw material receiving surfaces of the segregation control plates and deposited in the bunker, with the raw material receiving surfaces of the segregation control plates facing toward the outside of the furnace in the radial direction of the furnace and inclined downward with respect to the outside of the furnace.

6. The average apparent density [ρ ｂ ] is the average apparent density [ρ ａ 3. The method for charging raw materials into a blast furnace according to claim 1, wherein the raw material charging amount is greater than the maximum raw material loading amount.

7. The average apparent density [ρ ｂ ] and the average apparent density of the ore raw material (a) [ρ ａ ]ratio[ρ ｂ ] / [ρ ａ 7. The method for charging raw materials into a blast furnace according to claim 6, wherein the ratio of the raw material content to the total raw material content is 1.25 or more.

8. 3. The method for charging raw materials into a blast furnace according to claim 1, wherein the aspect ratio of the metallic iron raw material (b) is 1.4 or more.

9. The average particle size [d ｂ ] is the average particle size [d ａ 3. The method for charging raw materials into a blast furnace according to claim 1, wherein the raw material charging amount is greater than the maximum raw material loading amount.

10. The average particle size [d ｂ ] and the average particle size [d ａ ] ratio [d ｂ ] / [d ａ 10. The method for charging raw materials into a blast furnace according to claim 9, wherein the ratio of the total raw materials to the total raw materials is 3.5 or more.

11. 3. A method for producing molten iron, comprising the step of mixing an ore raw material (a) containing at least one of sintered ore, pellets, and lump ore with a metallic iron raw material (b) 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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