Method of charging raw materials into a 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 raw material charging method for obtaining a desired charge distribution in a bell-less blast furnace. [Background Art]

[0002] In recent years, global warming caused by the increase in CO₂ emissions has become a problem, and the suppression of CO₂ emissions is an important issue in the steel industry as well. Most of the CO₂ discharged from iron and steel plants is emitted from blast furnaces. Reduction of CO₂ emissions in a blast furnace can be achieved by reducing the amount of reducing agents (coke, pulverized coal, natural gas, etc.) used in the blast furnace. Coke serves as a heat source for melting iron ore raw materials, a reducing agent for iron ore raw materials, a carburizing material for carburizing molten iron to lower its melting point, and a spacer for ensuring air permeability in the blast furnace. By maintaining air permeability with this coke, the descending of the charged material is stabilized, and stable operation of the blast furnace is achieved. Here, from the viewpoint of reducing CO₂ emissions, it is desirable that the proportion of coke charged into the blast furnace is low. However, when the proportion of coke is reduced, the role played by the aforementioned coke is also reduced, so it is necessary to improve the reduction efficiency of the ore layer and also improve air permeability at the same time.

[0003] As a countermeasure for this problem, the use of metallic iron raw materials such as reduced iron and iron scrap has been studied, and various proposals have conventionally been made regarding the charging form thereof. Among these, Patent Document 1 discloses a method of charging reduced iron or iron scrap held in an auxiliary hopper at the top of the furnace, together with ore held in a main hopper, through a rotating chute into a region with a high gas utilization rate of exhaust gas, which indicates a high reduction load of ore. Hereinafter, description will be given with an example of using reduced iron as the metallic iron raw material. According to the method of Patent Document 1, reduced iron can be charged only into a region having a large reduction load in the radial direction of the blast furnace, so the reduction state of ore in the furnace can be effectively stabilized, and the gas flow can also be stabilized. [Prior Art Documents] [Patent Document]

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

[0005] [Non-Patent Document 1] Matsuzaki Shinroku, Taguchi Yoshihiro, "Analysis of Segregation Phenomena Considering Both Particle Diameter and Particle Density", Tetsu-to-Hagané, 2002, Vol.88, No.12, pp.823-830 [Summary of the Invention] [Problem to be Solved by the Invention]

[0006] However, the method disclosed in Patent Document 1 requires providing a dedicated auxiliary hopper for holding reduced iron at the furnace top, which causes a problem of increased equipment cost. In addition, charging reduced iron from the dedicated hopper also causes a problem that the charging time becomes longer. On the other hand, to address such problems, a charging method in which a separate batch for charging reduced iron is set has been considered, but in this method, an increase in the number of charging batches prolongs the charging time, leading to a decrease in productivity. To solve the above problems, it is necessary to charge reduced iron cut out from a raw material hopper onto a charging conveyor and ore raw materials separately cut out onto the charging conveyor into one furnace top bunker, and then charge the mixture into the furnace through a rotating chute. However, for example, when ore raw materials are divided into two portions and reduced iron is mixed in the first batch, no finding has been obtained so far as to how reduced iron and ore raw materials should be charged into the furnace top bunker so that reduced iron can be charged into a region with a large reduction load in the radial direction of the blast furnace.

[0007] Therefore, the object of the present invention is to solve the problems of the prior art described above and to provide a raw material charging method that allows metallic iron raw materials such as reduced iron to be charged into the part of the blast furnace radially where the reduction load is large, without providing a dedicated hopper for reduced iron 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 a metallic iron raw material as an example, the inventors diligently studied the relationship between elements (and their combinations) and the distribution of the charged material (distribution of reduced iron) in order to solve the above problems, including (i) the method of cutting reduced iron on the charging conveyor (stacking form on the ore raw material), (ii) the tilting method of the swivel chute, (iii) the use of segregation control plates in the furnace top bunker, and (iv) the method of mixing reduced iron when charging ore raw materials in two batches. As a result, it was found that by optimizing and combining (i) and (ii) above, and preferably further optimizing and combining (iii) and / or (iv) above, when charging ore raw materials and reduced iron held in a single furnace top bunker into the furnace, the reduced iron can be accurately charged to the desired position (the part with a large reduction load).

[0009] This invention is based on the above findings and is summarized as follows. [1] A method for charging a blast furnace with a bellless blast furnace having a bellless blast furnace in which multiple top bunkers are arranged in parallel and a raw material charging device that charges raw materials into the furnace by a swirling chute, by mixing ore raw materials (a) including at least one of sintered ore, pellets and lump ore, and metallic iron raw materials (b) including reduced iron and / or granular pig iron, When transporting the ore raw material (a) to the top of the furnace by a charging conveyor and charging it into one of the top furnace bunkers, the metallic iron raw material (b) is cut out onto the ore raw material (a) being 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 total length of the ore raw material (a) loaded on the charging conveyor, from the leading edge in the transport direction, and the ore raw material (a) and metallic iron raw material (b) are then charged into the top furnace bunker. A method for charging raw materials into a blast furnace, characterized in that when charging raw materials from the furnace top bunker into the furnace using the rotating chute, the rotating chute is rotated and tilted to move the raw material charging position from the area around the furnace center towards the furnace wall while charging the raw materials.

[0010] [2] A method for charging raw materials into a blast furnace, characterized in that when transporting ore raw materials (a) to the top of the furnace by the charging conveyor and charging them into one of the top bunkers, metallic iron raw materials (b) are stacked on top of the ore raw materials (a) in a length range of 18% to 32% of the total length of the ore raw materials (a) loaded on the charging conveyor, from the leading edge in the transport direction. [3] In the raw material charging method described in [1] or [2] above, When loading one charge's worth of ore raw materials (a) into the furnace in two batches, A method for charging raw materials into a blast furnace, characterized by mixing the first batch of ore raw materials (a) with metallic iron raw materials (b) and charging them into the furnace. [4] A method for charging raw materials into a blast furnace, characterized in that the second batch of ore raw materials (a) is charged into the furnace without being mixed with metallic iron raw materials (b) in the raw material charging method described in [3] above.

[0011] [5] In any of the raw material loading methods described in [1] to [4] above, A segregation control plate is installed inside the furnace top bunker. A method for charging raw materials into a blast furnace, characterized in that when charging the ore raw materials (a) and metallic iron raw materials (b) transported by the charging conveyor into the furnace top bunker, the raw material receiving surface of the segregation control plate faces outward in the furnace radial direction and is inclined downward with respect to the outward direction of the furnace, so that the raw materials falling from above fall downward via the raw material receiving surface of the segregation control plate and accumulate in the bunker. [6] In any of the raw material charging methods described in [1] to [5] above, the average apparent density of the metallic iron raw material (b) [ρ b ] is the average apparent density of the ore raw material (a) [ρ a A method for charging raw materials into a blast furnace, characterized in that it is larger than ]. [7] In the raw material charging method according to the above [6], the average apparent density [ρ b of the metallic iron raw material (b) and the average apparent density [ρ a of the ore raw material (a), the ratio of [ρ b / [ρ a is 1.25 or more. A raw material charging method for a blast furnace, characterized in that:

[0012] [8] In the raw material charging method according to any one of the above [1] to [7], the aspect ratio of the metallic iron raw material (b) is 1.4 or more. A raw material charging method for a blast furnace, characterized in that: [9] In the raw material charging method according to any one of the above [1] to [8], the average particle diameter [d b of the metallic iron raw material (b) is larger than the average particle diameter [d a of the ore raw material (a). A raw material charging method for a blast furnace, characterized in that:

[10] In the raw material charging method according to the above [9], the average particle diameter [d b of the metallic iron raw material (b) and the average particle diameter [d a of the ore raw material (a), the ratio of [d b / [d a is 3.5 or more. A raw material charging method for a blast furnace, characterized in that:

[11] A method for producing hot metal, 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 by the raw material charging method according to any one of the above [1] to

[10] , 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 into a site (position) having a large reduction load in the radial direction of the 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. Therefore, in blast furnace operation, productivity can be improved and equipment costs can be reduced. Furthermore, in the method of the present invention, by using a segregation control plate under predetermined conditions in a top bunker, the metallic iron raw material can be charged into a desired site (position) with particularly high accuracy. Furthermore, in the present invention, the ore raw materials for one charge are loaded into the furnace in two batches, and by mixing metallic iron raw materials with the ore raw materials of the first batch, the metallic iron raw materials can be charged into a particularly suitable location. Furthermore, according to the molten iron manufacturing method of the present invention, by charging raw materials using the above-described raw material charging method, molten iron can be manufactured with high productivity while keeping equipment costs low. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram illustrating the process in one embodiment of the present invention, from cutting the raw materials onto the charging conveyor to transporting them to the top of the blast furnace. [Figure 2] This is a schematic diagram illustrating one embodiment of the present invention, in which raw materials are transported to the top of the blast furnace by a charging conveyor and then loaded into the furnace using a raw material charging device. [Figure 3] This graph shows 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] An explanatory diagram schematically showing the loading of raw materials through a swirling chute in one embodiment of the present invention. [Figure 5] This graph shows an example of the particle size distribution of ore raw materials (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 according to the conditions of the present invention. [Figure 6] This diagram schematically illustrates the usage of a segregation control plate installed in a furnace top bunker in another embodiment of the present invention. [Figure 7] This is a schematic diagram illustrating the model experimental setup of an actual blast furnace used in an experiment to measure the emission distribution of raw materials (sintered ore and reduced iron) from the top bunker. [Figure 8] This is a schematic diagram illustrating the discharge experiment apparatus used in a measurement experiment simulating the distance reduced iron travels within the furnace top bunker. [Figure 9] Figure 8 shows the graph of the measurement results for the distance traveled by reduced iron in an experiment using the discharge experimental apparatus. [Figure 10] Based on the measurement results of the reduced iron migration distance using the discharge experimental apparatus shown in Figure 8, the 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 migration distance. [Figure 11] Based on the measurement results of the reduced iron migration distance using the discharge experimental apparatus shown in Figure 8, the graph shows the relationship between the aspect ratio of reduced iron and its representative migration distance. [Figure 12] Based on the measurement results of the reduced iron migration distance using the discharge experimental apparatus shown in Figure 8, the 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 migration distance. [Figure 13] This is an explanatory diagram schematically showing the shape (cross-section) of the deposits inside the furnace when ore raw material a is loaded into the furnace in two batches according to the method of the present invention. [Figure 14] This is a schematic diagram illustrating a model experimental apparatus used in an experiment to verify the stacking conditions of metallic iron raw material b against ore raw material a being transported by a charging conveyor. [Figure 15] Figure 14 is an explanatory diagram showing the layering conditions of metallic iron raw material b on ore raw material a in an experiment using a model experimental apparatus. [Figure 16] Figure 14 shows a graph illustrating the mixing ratio of metallic iron raw material (reduced iron) in the furnace radial direction in an experiment using a model experimental apparatus. [Figure 17] Figure 14 shows the graph illustrating the discharge rate of metallic iron raw material (reduced iron) when raw material is discharged from the top bunker in an experiment using a model experimental apparatus. [Figure 18] In a test where raw materials were charged into the furnace top bunker under conditions outside the scope of the present invention, this graph shows the discharge rate of metallic iron raw materials (reduced iron) at each stage of raw material discharge from the furnace top bunker. [Modes for carrying out the invention]

[0015] In a blast furnace, ore materials such as sintered ore and coke (lump coke) are alternately charged from the top of the furnace to form a layered charging bed (packing bed). The amount of one layer of these ore material and coke layers is called one charge of ore material and one charge of coke, respectively. These one charge of ore material and coke are not necessarily charged into the furnace in a single charge; sometimes one charge of ore material and coke is divided into multiple charges and charged into the furnace in batches. These divided batches of ore material and coke are called one batch of ore material and one batch of coke, respectively. The raw material charging method of the present invention is applicable to a bellless blast furnace having a raw material charging device that charges raw materials into the furnace via a rotating chute, with multiple top bunkers arranged in parallel. In a bellless blast furnace, lump coke and ore raw materials, each extracted from a raw material hopper, are charged into separate furnace top bunkers and then alternately loaded into the furnace via a swirling chute. In this invention, when charging raw materials into such a blast furnace, ore raw material a and metallic iron raw material b (such as reduced iron) are mixed and charged into the furnace. Furthermore, during the charging of raw materials, the metallic iron raw material b is selectively charged to areas (positions) with a high reduction load in the radial direction of the furnace.

[0016] In this invention, ore raw material a is a general term for sintered ore, pellets, and lump ore, which are widely used as iron sources in blast furnaces, and the ore raw material a used in this invention includes at least one of sintered ore, pellets, and lump ore. Furthermore, metallic iron raw material b used in this invention refers to a raw material with a metallic iron content of 80 mass% or more, and the metallic iron raw material b used in this invention includes reduced iron and / or granular pig iron. In addition, ore raw material a may be mixed with auxiliary raw materials (e.g., limestone, silica, serpentinite, etc.) mainly for the purpose of adjusting the composition of slag, and this invention includes such cases. Here, it is common to use molded bodies of reduced iron as the reduced iron, and among them, molded bodies of reduced iron called HBI (Hot Briquetted Iron) are representative, but the invention is not limited to this. HBI is obtained by reducing ores (lumps of ore, pellets, etc.) with a reducing gas and then hot-compressing (molding) the reduced iron. In addition, as reduced iron other than HBI, for example, lump-shaped reduced iron obtained by partially reducing ores such as sintered ore, pellets, and lumps of ore with a reducing gas; and molded bodies of reduced iron obtained by molding iron-based dust generated in blast furnaces, converters, electric furnaces, etc. may also be used. Granular iron is a granular iron material obtained by cooling and solidifying molten iron in a droplet state. Generally, it is obtained by dropping droplets of dispersed molten iron into cooling water and cooling them. Typically, its average particle size is several millimeters to several tens of millimeters.

[0017] Figures 1 and 2 are schematic explanatory diagrams illustrating one embodiment of the present invention. Figure 1 shows the process from cutting the raw material onto the charging conveyor to transporting it to the top of the blast furnace, while Figure 2 shows the process from transporting the raw material to the top of the blast furnace via the charging conveyor to loading it into the furnace using the raw material charging device. In the diagram, 1 is the furnace body of the blast furnace, 2 is a raw material charging device located 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 consists of multiple furnace top bunkers 4 arranged in parallel, a swirling chute 5 that charges the raw materials discharged from each furnace top bunker 4 into the furnace, and a collection hopper 6 that supplies the raw materials discharged from each furnace top bunker 4 to the swirling chute 5. 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, they are arranged at intervals (for example, at equal intervals) in the circumferential direction around the furnace central axis x.

[0018] Each furnace top bunker 4 (bunker body) is composed of an upper cylindrical part 41 and a lower funnel-shaped part 42, with a raw material discharge port 40 provided at its lower end (the lower end of the funnel-shaped part 42). Here, the raw material discharge port 40 is located along the bunker central axis x in the furnace radial direction. B It is preferable to position it eccentrically towards the furnace center axis x (closer to the furnace center axis x), and preferably as close to the furnace center axis x as possible. For example, if the raw material discharge port 40 is located bunker center axis x B When installed on top, the lateral shape of the furnace top bunker 4 in the furnace radial direction becomes symmetrical. In this case, the diameter of the collection hopper 6 that receives raw materials from multiple furnace top bunkers 4 becomes larger, making it easier for the raw materials to flow eccentrically with respect to the central axis of the swivel chute 5, and as a result, a shift in the charging center position by the swivel chute 5 is likely to occur. In this embodiment, the wall portion (shell portion) 421 of the funnel-shaped portion 42 on the side opposite the furnace center axis x (furnace wall side) has an inclination as a funnel-shaped portion, while the wall portion (shell portion) 420 on the furnace center axis x side is vertical or has a steeper inclination than the wall portion 421 (an inclination close to vertical). As a result, the raw material discharge port 40 is located at a position eccentric to the furnace center axis x side in the furnace radial direction.

[0019] A flow rate adjustment gate (not shown) is provided at the raw material discharge port 40 at the lower end of each furnace top bunker 4. The raw material discharged from the raw material discharge port 40 after its flow rate is adjusted by this flow rate adjustment gate is guided to a swirling chute 5 via a collection hopper 6 and a top ring 7. This swirling chute 5 rotates around its base end (upper end) located on the furnace central axis x, and while tilting in the furnace radial direction with the base end (upper end) as a pivot point, it charges the raw material into the furnace. 9a is an ore raw material hopper, 10 is a reserve hopper, and 9b is a metallic iron raw material hopper that holds metallic iron raw materials b such as reduced iron. Also, 11 is an ore conveyor that transports the ore raw materials a extracted from the ore raw material hopper 9a to the reserve hopper 10. The raw materials cut from the raw material hopper are transported to the top of the furnace by the charging conveyor 3 and charged into one of the top furnace 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 in the direction away from the furnace centerline x through the receiving chute 12 and accumulate in the top furnace bunker 4.

[0020] In the embodiments shown in Figures 1 and 2, the reserve hopper 10 (and the ore raw material hopper 9a) holds the ore raw material a, and the metallic iron raw material hopper 9b holds the metallic iron raw material b. The raw materials held in these hoppers are then dispensed onto the charging conveyor 3 as needed. In the present invention, when cutting out ore raw material a onto a charging conveyor 3 and transporting it to the furnace top via the charging conveyor 3 for charging into one of the furnace top bunkers 4, metallic iron raw material b is cut out and stacked on top of the ore raw material a being transported by the charging conveyor 3. At this time, metallic iron raw material b is stacked on top of the ore raw material a within a length range w of 18% (0.18L) to 75% (0.75L) of the total loading length L of the ore raw material a loaded on the charging conveyor 3, from the leading end in the transport direction. That is, as shown in Figure 2, the length range w for stacking metallic iron raw material b relative to the loading length L of the ore raw material a is set to a range of 0.18L to 0.75L from the leading end in the transport direction. Then, the ore raw material a and metallic iron raw material b are charged into the furnace top bunker 4 in this state.

[0021] Since the metallic iron raw material b charged into the furnace top bunker 4 is layered on top of the ore raw material a over the length range w described above, it accumulates in large quantities in specific areas within the furnace top bunker 4 (this will be explained in detail later). Therefore, when the raw materials are discharged from the furnace top bunker 4, the discharge of metallic iron raw material b is suppressed in the initial stages of discharge, and the discharge rate of metallic iron raw material b is increased from the middle stages of discharge onward. Furthermore, as will be described later, in this invention, when the raw materials in the furnace top bunker 4 are charged into the furnace using the swivel chute 5, the swivel chute 5 is rotated and tilted to move the raw material charging position from the area around the center of the furnace towards the furnace wall while charging the raw materials (charging by reverse tilting). This makes it possible to charge (accumulate) a high proportion of metallic iron raw material b in a desired area in the furnace radial direction, i.e., the area from the middle of the furnace to the furnace wall. Here, the region from the middle of the furnace to the furnace wall includes not only the region that spans both the middle of the furnace and the furnace wall, but also the region consisting only of the middle of the furnace or the region consisting only of the furnace wall. Furthermore, positioning the stacking of metallic iron raw material b closer to the front end in the conveying direction of the stacked length L of ore raw material a increases the discharge rate of metallic iron raw material b from the mid-stage to the end of raw material discharge from the furnace top bunker 4 (especially in the final stage of raw material discharge). For this reason, it is more preferable to stack metallic iron raw material b on top of ore raw material a within a length range w of 18% (0.18L) to 32% (0.32L) of the stacked length L of ore raw material a loaded on the charging conveyor 3, from the front end in the conveying direction.

[0022] Here, the stacking position (range) of the metallic iron raw material b can be arbitrarily selected as long as it is within a length range of 18% (0.18L) to 75% (0.75L) of the stacking length L of the ore raw material a in the transport direction, preferably within a length range of 18% (0.18L) to 32% (0.32L) from the front side. Therefore, as a length range of 18% (0.18L) to 75% (0.75L) from the front side in the transport direction, for example, a length range of 20% (0.20L) to 65% (0.65L) or 25% (0.25L) to 60% (0.60L) from the front side in the transport direction can be selected. Furthermore, as a length range of 18% (0.18L) to 32% (0.32L) from the leading edge in the conveying direction, for example, a length range such as 20% (0.20L) to 30% (0.30L) or 22% (0.22L) to 32% (0.32L) from the leading edge in the conveying direction can be selected. Furthermore, molded products of reduced iron, such as HBI, among the metallic iron raw materials b, are obtained by molding reduced iron with twin molding rolls, but sharp burrs are formed in the portion corresponding to the gap between the molding rolls. If this portion comes into direct contact with the conveyor belt of the charging conveyor 3, it can cause damage to the conveyor belt. Therefore, it is preferable that the metallic iron raw materials b are not loaded directly onto the charging conveyor 3, even partially, and are loaded (stacked) only on the ore raw materials a in accordance with the conditions of the present invention.

[0023] Here, we will briefly explain how the metallic iron raw material b, which is charged into the furnace top bunker 4 along with the ore raw material a, is deposited (depositation morphology and area) within the furnace top bunker 4. As described above, the raw materials charged from the charging conveyor 3 into the furnace top bunker 4 fall diagonally downwards away from the furnace centerline x through the receiving chute 12 and accumulate in the furnace top bunker 4. Here, the main raw material, ore raw material a, falls to a position away from the furnace centerline x, then rolls towards the furnace centerline x, forming a slope. At this time, larger particles tend to flow downwards along the slope and are more likely to segregate towards the lower side of the bunker (above the raw material discharge port 40). In other words, ore raw material a is prone to segregation due to particle size differences. In contrast, such segregation due to particle size differences is less likely to occur between ore raw material a and metallic iron raw material b. That is, metallic iron raw material b (especially in the case of HBI) generally has a larger particle size than ore raw material a, but also a higher density, so metallic iron raw material b that falls to a position away from the furnace centerline x in the furnace top bunker 4 sinks into the ore raw material layer at that position and accumulates. 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 settles at the point where it falls (a position away from the furnace's central axis x). In this way, segregation due to the density difference preferentially occurs 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 Literature 1 reports that in the case of deposition with a low flow rate, such as charging a bellless chute, segregation due to density difference becomes preferential and segregation due to particle size difference is suppressed.

[0024] In this invention, metallic iron raw material b is stacked in a specific form on ore raw material a loaded on a charging conveyor, and segregation due to density differences of the raw materials within the furnace top bunker 4 is utilized to deposit a large amount of metallic iron raw material b in a specific area within the furnace top bunker 4. As a result, when raw materials are discharged from the furnace top bunker 4, the discharge of metallic iron raw material b is suppressed in the initial stages of discharge, and the discharge rate of metallic iron raw material b is increased from the middle stages onward. Figure 3 shows the discharge rate of metallic iron raw material b at each stage of raw material discharge from the furnace top bunker in a test in which raw materials were charged into the furnace top bunker according to the conditions of this invention (test conditions will be described in detail later). In this test, sintered ore was used as ore raw material a, and reduced iron (HBI) was used as metallic iron raw material b. In addition, a segregation control plate, as described later, was installed inside the furnace top bunker. The horizontal axis of Figure 3 represents the percentage of the total weight (cumulative value) of raw materials discharged from the furnace top bunker. Here, Figure 3(A) shows the case where metallic iron raw material b (reduced iron) is stacked on top of the ore raw material a, which accounts for 18% to 75% of the total length of the ore raw material a loaded on the charging conveyor, in the distance from the leading end in the transport direction, and then the ore raw material a and metallic iron raw material b are charged into the furnace top bunker in this state (the configuration (b) in Figure 15 described later). Also, Figure 3(B) shows the case where metallic iron raw material b (reduced iron) is stacked on top of the ore raw material a, which accounts for 18% to 32% of the total length of the ore raw material a loaded on the charging conveyor, in the distance from the leading end in the transport direction, and then the ore raw material a and metallic iron raw material b are charged into the furnace top bunker in this state (the configuration (c) in Figure 15 described later). As shown in the figures, the discharge of metallic iron raw material b is suppressed in the initial stages of raw material discharge, and the discharge rate of metallic iron raw material b increases from the middle stages of raw material discharge onward. In particular, in the case of Figure 3(B), where the stacking range of metallic iron raw material b is shifted towards the front 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 furnace top bunker in a test in which raw materials were charged into the furnace top bunker under conditions outside the scope of the present invention (test conditions other than the stacking range of metallic iron raw material b were the same as in the test in Figure 3). Here, Figure 18(A) shows the case in which metallic iron raw material b is stacked on top of ore raw material a in a length range of 4% to 18% from the leading end in the transport direction of the stacked length of ore raw material a loaded on the charging conveyor, and in this state, ore raw material a and metallic iron raw material b are charged into the furnace top bunker. Figure 18(B) shows the case in which metallic iron raw material b is stacked on top of ore raw material a in a length range of 75% to 96% from the leading end in the transport direction of the stacked length of ore raw material a loaded on the charging conveyor, and in this state, ore raw material a and metallic iron raw material b are charged into the furnace top bunker. In Figure 18(A), the proportion of metallic iron raw material b discharged is relatively high in the initial stages of raw material discharge, while in Figure 18(B), the proportion of metallic iron raw material b discharged is very high in the first half to middle stages of raw material discharge.

[0026] Furthermore, in the present invention, when the raw materials (ore raw materials a and metallic iron raw materials b) charged into the furnace top bunker 4 as described above are charged into the furnace using the swivel chute 5, the swivel chute 5 is rotated and tilted to move the raw material charging position from the area around the furnace center to the furnace wall side while the raw materials are being charged. That is, while the swivel chute 5 is rotated, the direction of the chute is sequentially shifted (tilted) from the area around the furnace center to the furnace wall side while the raw materials are being charged (reverse tilting charging by swivel chute). Figure 4 schematically shows the situation of raw material charging through this swivel chute 5. As shown in the figure, the charging of raw materials by the swivel chute 5 starts with charging to the area around the furnace center, and while the swivel chute 5 is rotated, the raw materials are charged while sequentially tilting from the direction of charging to the area around the furnace center (dotted line) to the direction of charging to the furnace wall side (around the furnace wall) (solid line).

[0027] Here, it is preferable to deposit the metallic iron raw material b from the middle of the blast furnace to the furnace wall for the following reasons. In a blast furnace, the ore is reduced by reducing gas rising from the lower part of the furnace. Normally, the thickness of the ore raw material layer in the blast furnace increases from the middle of the furnace to the furnace wall, and as a result, the consumption of reducing gas increases, so the reducing gas concentration decreases and the reduction rate in the middle of the furnace to the furnace wall decreases. This decrease in the reduction rate in the middle of the furnace 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 in such a low reduction rate state and is finally reduced by a direct reduction reaction accompanied by a large endothermic reaction, which causes an increase in the amount of fuel required in the blast furnace, i.e., the amount of coke required. In contrast, by depositing metallic iron raw material b, which has already undergone reduction, from the middle of the furnace to the furnace wall, 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 region that spans both the middle of the furnace and the furnace wall, but also the region consisting only of the middle of the furnace or the region consisting only of the furnace wall.

[0028] As described above, in the present invention, a large amount of metallic iron raw material b is discharged from the mid-stage of raw material discharge from the top bunker 4, and the raw materials are accumulated in the top bunker 4 in such a way that the discharge ratio of metallic iron raw material b is high. Therefore, by starting the charging of raw materials by the swirling chute 5 from the area around the center of the furnace, and then sequentially shifting (tilting) the direction of the chute from the area around the center of the furnace through the middle of the furnace to the furnace wall side while charging the raw materials (reverse tilt charging), it becomes possible to accumulate metallic iron raw material b from the middle of the furnace to the furnace wall with a high mixing ratio. In this invention, the region around the furnace center refers to the area between the furnace center and the intermediate furnace in the furnace radial direction, and generally refers to the region with a dimensionless radius (r / R0, the same applies hereafter) 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 intermediate furnace 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 greater than 0.80 to 1.00. Here, the dimensionless radius (r / R0) indicates the position inside the furnace in the furnace radial direction, and is the value obtained by dividing the distance r from the furnace center at that position by the furnace radius R0.

[0029] In this invention, the position at which raw material charging begins can be appropriately determined within the area surrounding the center of the furnace. The position at which raw material charging begins is the center of the raw material fall from the swirling chute onto the raw material accumulation surface inside the furnace. In the present invention, there are no special restrictions on the amount (mixing ratio) of metallic iron raw material b charged in, and it is possible to reduce the reducing agent ratio as the amount of metallic iron raw material b charged in increases. However, as the amount of metallic iron raw material b charged in increases, the heat flow ratio decreases. Generally, it is preferable to operate a blast furnace with a heat flow ratio of 0.9 or less, and in a typical blast furnace (ore charging amount of about 1600 kg / t), this range is reached at 400 kg / t or more, causing a delay in the heating of the raw materials, which diminishes the effect of reducing the reducing agent ratio. For this reason, it is preferable to keep the amount (mixing ratio) of metallic iron raw material b charged in (mixing ratio) to 25 mass% or less of the ore raw material a.

[0030] As will be described later, in the present invention, the ore raw material a undergoes segregation due to particle size differences within the furnace top bunker 4, resulting in a particle size distribution (particle size transition) of the ore raw material a discharged from the furnace top bunker 4, as shown in Figure 5. Specifically, Figure 5 shows an example of the particle size distribution of the ore raw material a at each stage of raw material discharge from the furnace top bunker in a test in which raw materials were charged into the furnace top bunker according to the conditions of the present invention (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. In addition, a segregation control plate, as will be described later, was installed inside the furnace top bunker. The horizontal axis of Figure 5 represents the percentage of the discharged weight (cumulative value) of the raw materials from the furnace top bunker. As shown in the figure, the ore raw material a has a particularly large particle size in the initial discharge stage (discharge weight ratio: 0.15 or less), and then the particle size decreases, but in the later discharge stage (discharge weight ratio: around 0.6 to 0.7), the particle size becomes relatively large. As a result, coarse grains of ore raw material a accumulate around the center of the furnace and from the middle of the furnace to the furnace wall, while fine grains accumulate at the furnace wall and from the center of the furnace to the middle. On the other hand, as described above, metallic iron raw material b is discharged from the top bunker at the discharge ratio shown in Figure 3, and in this invention, which uses a reverse tilting charging by a swirling chute 5, a large amount is charged from the middle of the furnace to the furnace wall. Therefore, in this region from the middle of the furnace to the furnace wall, the particle size difference between metallic iron raw material b and ore raw material a becomes smaller, the porosity of the raw material layer (ore raw material a + metallic iron raw material b) before softening and melting increases, and the permeability and reduction efficiency improve. Furthermore, by using a segregation control plate under predetermined conditions within the furnace top bunker 4, the ore raw material a can be deposited (segregated) in a more favorable state within the furnace 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 present invention will be described. In the present invention, the particle size distribution of the ore raw material a discharged from the furnace top bunker 4 depends on the segregation behavior due to particle size differences within the furnace top bunker. However, by installing a segregation control plate 8 inside the furnace 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 furnace top bunker 4 is particularly suitable for the raw material charging method (reverse tilting) using the swirling chute 5 of the present invention. Figure 6 schematically shows one embodiment in which, in the present invention, a segregation control plate 8 is installed in the furnace top bunker 4, and the segregation due to the particle size difference of the ore raw material a is controlled (optimized) by this segregation control plate 8. The front surface of the segregation control plate 8 constitutes a raw material receiving surface 80 that receives raw materials falling from above. The segregation control plate 8 is positioned in the upper space of the furnace top bunker 4 and is supported so as to be able to tilt up and down around a pivot portion 81. The segregation control plate 8 is oriented such that its raw material receiving surface 80 faces outward in the furnace radial direction and is inclined downward with respect to the outward direction. 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 are passed through the raw material receiving surface 80 of the segregation control plate 8 (i.e., received by the raw material receiving surface 80) and then dropped downward, accumulating in the bunker.

[0032] Here, we will only describe the ore material a that undergoes segregation due to particle size differences among the raw materials charged into the furnace top bunker 4 from the charging conveyor 3. The ore material a that is fed into the furnace top bunker 4 from the charging conveyor 3 through the receiving chute 12 falls diagonally downward in the direction away from the furnace central axis x. Then, by receiving this ore material a on the raw material receiving surface 80 of the segregation control plate 8 and then letting it fall (changing the direction of fall), the ore material a falls to a position further away from the furnace central axis x, and then rolls toward the furnace central axis x, forming a slope. At this time, the larger the particle size of the ore material a, the more easily it flows downward down the slope and is more likely to segregate on the lower side of the bunker (above the raw material discharge port 40). Also, the smaller the particle size of the ore material a, the more likely it is to accumulate at a position far from the furnace central axis x, and the larger the particle size of the ore material a, the more likely it is to accumulate (segregate) closer to the furnace central axis x. As a result, the segregation state due to particle size differences in the ore raw material a is optimized, and the particle size distribution of the ore raw material a discharged from the furnace top bunker 4 becomes particularly suitable for the raw material charging method (reverse tilt charging) using the swirling chute of the present invention. Figure 5, described 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 falls to a position away from the furnace central axis x via the raw material receiving surface 80 of the segregation control plate 8 sinks at the point of impact due to the density difference with the ore raw material a, and accumulates at that location.

[0033] The segregation control plate 8 only needs to receive the raw material falling from above and guide it away from the furnace central axis x, so the inclination angle of the segregation control plate 8 (raw material receiving surface 80) should be set to an appropriate angle that makes this possible. However, if the inclination angle θ of the raw material receiving surface 80 with respect 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 away from the furnace central axis x, so the effect of promoting segregation due to the particle size difference of the ore raw material a will decrease. From the above viewpoint, it is best to set the inclination angle θ to about 7 to 47°, preferably to about 7 to 37°.

[0034] As already mentioned, metallic iron raw material b (especially in the case of HBI) generally has a higher density (apparent density) than ore raw material a. Therefore, when metallic iron raw material b is charged into the furnace top bunker 4, it settles into the raw material layer due to the density difference with ore raw material a. In other words, segregation of metallic iron raw material b due to the density difference with ore raw material a occurs preferentially, and excessive segregation due to particle size differences is suppressed. To confirm this, the inventors conducted an experiment to measure the emission distribution of raw materials (sintered ore and reduced iron) from the top bunker using a scale model of the blast furnace charging system. Figure 7 schematically shows a 1 / 17.8 scale model experimental apparatus of the actual blast furnace used in this experiment. This simulated experimental apparatus is composed of a bellless 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 the actual machine. The raw material charging device 22 is composed of a top bunker 24, a collection hopper 26, a switching chute 30, etc., and a flow rate adjustment gate is provided at the raw material discharge port 240 of the top bunker 24. Two top bunkers 24 are arranged symmetrically with respect to the furnace central axis. In addition, a segregation control plate 28 as shown in Figure 6 is installed inside the top bunker 24, and the inclination angle θ of its raw material receiving surface is set to 27°. Below the raw material charging device 22, a sampling box 31 that can be moved by a belt conveyor 32 is positioned, and this movable sampling box 31 is configured to sequentially recover the raw materials discharged from the furnace top bunker 24 over time. In this experiment, sintered ore was used as 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 similarity rules with actual blast furnaces.

[0035] The apparent density of reduced iron (HBI) is 5.0-6.0 t / m³. 3 The typical density is 5.2 t / m³. 3 The apparent density of the sintered ore was 3.0-4.0 t / m³. 3 The typical density is 3.4 t / m³. 3The size of the reduced iron (HBI) particles was 5.6 mm × 2.8 mm × 1.7 mm, and the average particle size (definition as described later) was 3.6 mm. The average particle size (definition as described later) of the sintered ore was 0.7 mm. After the sintered ore and reduced iron were cut onto the charging conveyor 23 according to the method of the present invention and charged into the furnace top bunker 24, the particle size distribution of the discharged sintered ore relative to the discharged weight ratio of the raw materials is shown in Figure 5, and the ratio of reduced iron relative to the discharged weight ratio of the raw materials is shown in Figure 3. The horizontal axis in Figures 3 and 5 represents the ratio of the discharged weight (cumulative value) of the raw materials from the furnace top bunker. Comparing the two figures, it can be seen that the sintered ore is coarse-grained in the initial discharge (first flow) (Figure 5), while the proportion of reduced iron in the initial discharge (first flow) is small despite the particle size of the reduced iron being larger than that of the sintered ore (Figure 3). Therefore, it was confirmed that segregation due to particle size differences in reduced iron is less likely to occur than in sintered ore. Therefore, a higher density of reduced iron allows for a smaller proportion of reduced iron in the initial discharge (initial flow), and in the reverse tilting charging method of the present invention, it is preferable because it suppresses the charging of reduced iron near the center of the furnace and increases the amount of reduced iron charged to the middle and walls of the furnace. The apparent density of reduced iron at this time was 1.5 times the apparent density of the ore raw materials.

[0036] Generally, the density of metallic iron raw material b (especially in the case of HBI) is greater than the density of ore raw material a. However, in any case, in the present invention, it is preferable that the average apparent density of metallic iron raw material b is greater than the average apparent density of ore raw material a. To confirm this, the inventors conducted the following experiment to measure the segregation behavior of metallic iron raw material b using a metallic iron raw material b discharge experimental apparatus. Here, the average apparent density of the above raw material is the value obtained by randomly selecting 20 raw material particles, summing their respective apparent densities, and then dividing by the total number of raw material particles (20). Figure 8 schematically shows the discharge experimental apparatus used 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. In this experiment, coke was discharged from the hopper to form a deposit surface in the discharge experimental apparatus, and then a mixed raw material of sintered ore and reduced iron was discharged from the hopper onto it. To evaluate the distance traveled by reduced iron, which was assumed to move within the furnace top bunker, the origin was set to directly below the hopper outlet, and the base of the coke deposit surface was set to 1. Reduced iron was recovered at each travel distance, and its weight percentage was evaluated.

[0037] Figure 9 shows an example of the measurement results for the migration distance of reduced iron. This measurement result is the average apparent density of reduced iron [ρ b ] and the average apparent density of sintered ore [ρ a ] ratio [ρ b ] / [ρ a This shows the cases where the density ratio is 2.0 and 1.5. The vertical axis represents the proportion of the weight of reduced iron present at each travel distance out of the total weight of reduced iron introduced. Reduced iron is most abundant at a position slightly below the outlet. This is because the proportion of reduced iron is low directly below the outlet due to the strong inertia of the fall and the downward movement down the slope. On the other hand, as mentioned above, reduced iron tends to sink, so it remains where the inertia of the fall is lost, and a maximum value in the proportion of reduced iron appears there. Here, if we define the distance traveled to the point where the proportion of reduced iron is maximum as the "representative travel distance," then the shorter this representative travel distance, the more likely the reduced iron is to remain near the point of impact within the furnace top bunker, and as mentioned above, the proportion of reduced iron in the initial discharge (initial flow) tends to be smaller. Therefore, we investigated the relationship between the representative travel distance and the density of reduced iron using the same measurement experiment as above. Here, the representative travel distance was calculated by obtaining a quadratic function of each plot using the least squares method and determining the position of the peak. The density of reduced iron used was 4620-8400 kg / m³. 3 The density of the sintered ore is 4200 kg / m³. 3 That is the case.

[0038] Figure 10 shows the relationship between the density of reduced iron (density ratio with sintered ore) and the representative migration distance, which is the result of the survey. The horizontal axis represents the density ratio of reduced iron to sintered ore, i.e., the average apparent density of reduced iron [ρ HBI ] and the average apparent density of sintered ore [ρ ore ] ratio [ρ HBI ] / [ρ ore ]. As shown in Figure 10, the representative migration distance of reduced iron tends to decrease as the density ratio of reduced iron to sintered ore increases, but this trend changes at a density ratio of 1.25. When the density ratio is less than 1.25, the densities of sintered ore and reduced iron are close, making it difficult for reduced iron to sink into the sintered ore and thus less likely to remain in place. Therefore, from these survey results, the density ratio of reduced iron to sintered ore (average apparent density of reduced iron [ρ HBI ] and the average apparent density of sintered ore [ρ ore ] ratio [ρ HBI ] / [ρ ore It was found that a value of 1.25 or higher is preferable.

[0039] From the perspective of appropriately obtaining segregation due to the density difference between metallic iron raw material b and ore raw material a, considering the experimental conditions and results described above, it is desirable that the average apparent density of metallic iron raw material b be sufficiently greater than the average apparent density of ore raw material a. Therefore, the average apparent density of metallic iron raw material b [ρ b ] and the average apparent density of ore raw material a [ρ a ] ratio [ρ b ] / [ρ a ] is preferably 1.25 or higher, and more preferably 1.5 or higher. However, the density ratio [ρ b ] / [ρ a If the density ratio [ρ] is too large, when raw materials are discharged from the top bunker 4, the metallic iron raw material b, which is mixed with the ore raw material a, may not be discharged smoothly and may accumulate inside the top bunker 4. In that case, damage to the equipment or an unexpected distribution of charges may occur, which could destabilize blast furnace operation. For this reason, the density ratio [ρ] b ] / [ρ a It is desirable to set the upper limit for ] to around 2.0.

[0040] Furthermore, although there are no particular restrictions on the shape of the metallic iron raw material b in this invention, it is thought that the shape of the metallic iron raw material b also affects the distance traveled as described above. That is, the more complex the shape of the metallic iron raw material b, the less likely it is to roll, and therefore the shorter the distance traveled. So, similar to the measurement experiment described above, we conducted an experiment using the apparatus in Figure 8 with metallic iron raw materials b having different aspect ratios and investigated their distance traveled. 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 metallic iron raw material b (HBI in this experiment) is the value obtained by dividing the length of the longest side of metallic iron raw material b by the length of the shortest side, and is the average of the aspect ratios of 20 randomly selected raw material particles.

[0041] As mentioned above, a maximum value appears in the proportion of reduced iron, so the distance traveled at the maximum value was evaluated as the representative distance traveled. Figure 11 shows the relationship between the aspect ratio of reduced iron and the representative distance traveled, which is the result of the measurement. According to Figure 11, there is a tendency for the representative distance to decrease as the aspect ratio increases, but this trend changes at an aspect ratio of 1.4. When the aspect ratio is smaller than 1.4, the shape of the reduced iron is closer to a cube, and the resistance to rolling is weaker, so it is thought that it does not stay in place easily. Therefore, from the results of this investigation, it was found that an aspect ratio of 1.4 or higher is preferable for reduced iron. For the reasons stated above, it is preferable that the aspect ratio of metallic iron raw material b be 1.4 or greater. However, if the aspect ratio of metallic iron raw material b is too large, it may block the outlet of the furnace top bunker 4. Also, if the difference in shape between metallic iron raw material b and ore raw material a is too large, it may create an unexpected charge distribution and destabilize blast furnace operation. For this reason, it is desirable to limit the aspect ratio of metallic iron raw material b to approximately 6.5.

[0042] Next, we will explain the preferred particle size (average particle size) of the ore raw material a and the metallic iron raw material b. Here, the average particle size of the ore raw material a [d aIn the case of any raw material such as sintered ore, pellets, or lump ore, the particle size is the harmonic mean diameter, 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 midpoint diameter of each sieve). Furthermore, if the ore raw material a consists of two or more types of raw materials (for example, two or more types of raw materials from sintered ore, pellets, and lump ore), the average particle size of each is determined, and then the weighted average particle size is calculated based on the weight ratio.

[0043] Average particle size of metallic iron raw material b [d b In the case of HBI, the average particle size [d] is determined as follows: Measure the size of HBI sampled from the lot of HBI to be used, and approximate this size as a rectangular parallelepiped with length a, width b, and thickness c. Then, calculate the particle size dr (equivalent diameter of an equivolute sphere) from the following formula. Perform this for 20 randomly sampled HBI, and take their average value to determine the average particle size [d] of the metallic iron raw material b. b ]

number

[0044] In this invention, there are no particular restrictions on the particle sizes of the ore raw material a and the metallic iron raw material b, however, generally, the particle size of metallic iron raw material b (especially in the case of HBI) is considerably larger than that of ore raw material a. In the example of the above experiment, the average particle size of HBI is 5.1 times that of the average particle size of the ore raw materials. It is thought that the larger the particles of metallic iron raw material b, the greater the particle weight and the shorter the migration distance described above. Therefore, similar to the measurement experiment described above, experiments were conducted using the apparatus in Figure 8 for cases where the particle size ratio of metallic iron raw material b and ore raw material a was different, and the migration 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 reduced iron and sintered ore and the migration distance was investigated. Here, the particle size ratio of reduced iron and sintered ore is defined as the average particle size of reduced iron [d HBI ] and the average grain size of the sintered ore [d ore ] ratio [d HBI ] / [d ore ]

[0045] As described above, a maximum value appears in the proportion of reduced iron, so the migration distance at the maximum value was evaluated as the representative migration distance. Figure 12 shows the particle size ratio [d HBI ] / [d ore The relationship between ] and representative travel distance is shown. According to Figure 12, particle size ratio [d HBI ] / [d ore The larger the ], the smaller the representative migration distance tends to be, but the particle size ratio [d HBI ] / [d ore It can be seen that the trend changes at 3.5. Particle size ratio [d HBI ] / [d ore If ] is less than 3.5, it is thought that the weight of reduced iron is small and it is less likely to remain in place. Therefore, from the results of this investigation, 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 the metallic iron raw material b [d b ] is the average particle size [d a It is preferable that the average particle size [d b ] and the average particle size of the ore raw material a [d a] ratio [d b ] / [d a It is preferable that the particle size ratio [d b ] / [d a It is desirable to set the upper limit for ] at around 7.0.

[0046] 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 from the middle of the blast furnace to the furnace wall. In a blast furnace, the ore raw material layer descends, causing softening and melting. The first part to soften and melt is the lower part of the ore raw material layer. This softening and melting of the lower part of the ore raw material layer reduces the permeability to the upper part of the ore raw material layer, worsening the high-temperature properties of the ore raw material layer. To address this problem, it is believed that improving the permeability of the lower part of the ore raw material layer will improve the permeability and high-temperature properties of the upper part of the ore raw material layer. Generally, it is known that when reduced iron, which has a low high-temperature shrinkage rate, is mixed into the ore raw material layer, the reduced iron does not melt when the ore melts, creating voids around the reduced iron and ensuring permeability. Therefore, by mixing metallic iron raw materials such as reduced iron into the lower part of the ore raw material layer, voids are created around the metallic iron raw materials, which have a low high-temperature shrinkage rate, when softening and melting. This improves the permeability of the lower part of the ore raw material layer, making it easier for high-temperature reducing gases to flow to the upper part of the ore raw material layer. As a result, the high-temperature properties of the upper part of the ore raw material layer are improved, and the reduction efficiency can be increased.

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

[0048] Furthermore, the charging of the ore raw material a for the second batch can be done either by rotating and tilting the swivel chute 5 to move the raw material charging position from the furnace wall towards the furnace center (forward tilt charging), or by moving the raw material charging position from the furnace center towards the furnace wall (reverse tilt charging). In addition, charging may be started with reverse tilting, and after reaching the furnace wall, charging to the middle of the furnace may be done with forward tilting. However, reverse tilt charging is preferable for the second batch because it reduces the risk of metallic iron raw material b charged in the first batch being caught up in the flow of raw material into the furnace center for the second batch and moving towards the furnace center. In this case, the heat generated by the reduction reaction of ore raw material a is lost when metal iron raw material b is substituted, and to prevent an increase in the reducing agent ratio due to insufficient heat, it is preferable not to mix metal iron raw material b with ore raw material a in the second batch.

[0049] In order to verify the stacking conditions for metallic iron raw material b relative to ore raw material a transported by the charging conveyor 3, the inventors conducted the following experiment using a scale model of a blast furnace charging apparatus. Figure 14 schematically shows a 1 / 17.8 scale model experimental apparatus of the actual blast furnace used in this experiment. This simulated experimental apparatus is composed of a blast furnace body 21, a bellless 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 the actual furnace. The raw material charging device 22 is composed of a top bunker 24, a swivel chute 25, a collection hopper 26, a top ring 27, a switching chute 30, etc., and a flow rate adjustment gate is provided at the raw material discharge port 240 of the top bunker 24. Two top bunkers 24 are arranged symmetrically with respect to the furnace central axis. In addition, a segregation control plate 28 as shown in Figure 6 is installed inside 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 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 similarity rules with actual blast furnaces. The raw materials cut from the raw material hopper 29 were transported to the furnace top by the charging conveyor 23 and charged into the furnace top bunker 24. At this time, the ore raw materials (sintered ore) were divided into two and charged into separate furnace top bunkers 24, and charged into the furnace body 21 in two batches. Reduced iron was mixed only in the first batch and not in the second batch. In both the first and second batches, the raw materials cut from the furnace top bunker 24 were charged into the furnace body 21 through the rotating chute 25. In the first batch, in which reduced iron was mixed, the rotating chute 25 was rotated and tilted to move the raw material charging position from the area around the furnace center through the middle of the furnace to the furnace wall side while the raw materials were being charged (tilting pattern = reverse tilting). In the second batch, the rotating chute 25 was rotated and tilted to move the raw material charging position from the middle of the furnace to the furnace wall side while the raw materials were being charged (tilting pattern = reverse tilting). For the first batch of raw material charging via the rotating chute 25, the starting position was set to a dimensionless radius of 0.20 and the ending position to a dimensionless radius of 0.90 (the center position of the raw material drop from the rotating chute on the raw material accumulation surface inside the furnace). Similarly, for the second batch of raw material charging, the starting position was set to a dimensionless radius of 0.50 and the ending position to a dimensionless radius of 0.95 (the center position of the raw material drop from the rotating chute on the raw material accumulation surface inside the furnace).

[0051] In this experiment, for the first batch of raw materials, when cutting and stacking reduced iron (hereinafter referred to as reduced iron b) on top of the ore raw material a on the charging conveyor 23, the cut lengths of reduced iron b were in three forms as shown in Figure 15 (a) to (c), and each was charged into the furnace top bunker 24. The details of each condition are as follows. Form (a): Reduced iron b was layered on top of the ore raw material a along the entire length of the loading length of the ore raw material a loaded on the charging conveyor 23. Form (b): Reduced iron b was layered on top of the ore raw materials a that were loaded on the charging conveyor 23, in a length range of 18% to 75% of the total loading length of the ore raw materials a, from the leading end in the transport direction. Form (c): Reduced iron b was layered on top of the ore raw material a that was loaded on the charging conveyor 23, in a length range of 18% to 32% from the leading edge in the transport direction.

[0052] After the raw materials were fully charged into the blast furnace from the top bunker 24, the charged material was sampled radially to measure the proportion of reduced iron. 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 weight-based proportion of reduced iron. Figure 17 shows the results of measuring the proportion of reduced iron discharged when the raw materials were discharged from the top bunker. In Figure 17, the horizontal axis represents the proportion of the discharged weight (cumulative value) of the raw materials, and the vertical axis represents the proportion of reduced iron discharged. As shown in Figure 16, in the first batch mixed with reduced iron, the raw materials are charged in a reverse tilting motion from the periphery of the furnace center toward the furnace wall, so no mixing of reduced iron is observed in the center of the furnace in any of the configurations (a) to (c). On the other hand, when the stacking position of reduced iron on the ore raw materials (position within the stacking length range) is shortened toward the middle of the stacking length of the ore raw materials (configuration (a) → configuration (b)), the mixing ratio of reduced iron from the middle of the furnace to the furnace wall increased. This result is thought to be because, as seen from the discharge distribution from the top bunker under the same conditions (Figure 17), the discharge ratio of reduced iron from the top bunker increases from the middle of the raw material discharge period as the stacking position of reduced iron moves toward the middle.

[0053] Furthermore, when the stacking position of reduced iron on the ore raw materials (position within the stacking length range) was changed to shift towards the front of the intermediate position in the stacking length of the ore raw materials (morphology (b) → morphology (c)), the proportion of reduced iron mixed toward the furnace wall increased. This result is thought to be because, as seen from the discharge distribution from the furnace top bunker under the same conditions (Figure 17), the closer the stacking position of reduced iron is to the front of the intermediate section, the higher the proportion of reduced iron discharged toward the end of the raw material discharge from the furnace top bunker. Moreover, in terms of having a high proportion of reduced iron mixed toward the furnace wall side where the reduction load is particularly high, morphology (c), in which reduced iron is stacked on the ore raw materials in a length range of 18% to 32% from the leading end in the transport direction, is particularly preferable. As described above, by mixing ore raw material a and metallic iron raw material b according to the present invention, it becomes possible to control the mixing ratio of metallic iron raw material b during furnace top bunker extraction. This allows for the selective charging of metallic iron raw material b at a high proportion in the region from the middle of the furnace to the furnace wall, where the reduction load is high. Furthermore, the molten iron production method of the present invention includes a step of mixing ore raw material a, which includes at least one of sintered ore, pellets, and lump ore, with metallic iron raw material b, which includes reduced iron and / or granular iron, and charging the mixture into a blast furnace, using the raw material charging method of the present invention described above. [Examples]

[0054] To verify the effects of the present invention in actual equipment, a large bellless blast furnace (internal volume 5500 m³) equipped with the equipment configuration shown in Figures 1 and 2 was constructed. 3 An operational test was conducted. The raw material charging device 2 installed at the top of the blast furnace is equipped with three parallel top bunkers 4, and these three top bunkers 4 are 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, is installed inside the top bunker 4, and the inclination angle θ of its raw material receiving surface 80 is set to 27°. Sintered ore was used as the raw material for the ore, and reduced iron (HBI) was used as the raw material for the metallic iron. The average particle size of the raw materials [d a ] is 12 mm, average particle size of reduced iron [d b ] is 66mm, and [d a ] / [d b ] = 5.5. The aspect ratio of reduced iron is 3.7. Also, the average apparent density of ore raw materials (sintered ore) [ρ a ] is 3.4t / m 3 The average apparent density of reduced iron (HBI) is [ρ b ] is 5.4t / m 3 The mixing ratio of reduced iron was set to 4 mass% of the ore raw materials.

[0055] The ore raw materials, extracted from the raw material hopper 9a via the reserve hopper 10, were transported to the furnace top via the charging conveyor 3 and charged into the furnace top bunker 4. In this embodiment, one charge of ore raw materials was divided into two and charged into separate furnace top bunkers 4, and charged into the blast furnace in two batches. At that time, reduced iron was extracted from the raw material hopper 9b and stacked on top of the ore raw material layer as it was transported by the charging conveyor 3, and then mixed with the ore raw materials and charged into one of the furnace top bunkers 4. On the other hand, reduced iron was not mixed into the ore raw materials of the second batch. For both the first and second batches, the raw materials extracted from the furnace top bunker 4 were charged into the furnace via the swivel chute 5. In the first batch, which was mixed with reduced iron, the swivel chute 5 was rotated and tilted to move the raw material charging position from the area around the furnace center towards the furnace wall while the raw materials were charged (tilting pattern = reverse tilting). For the first batch of raw material charging using the rotating chute 5, the starting position was set to a dimensionless radius of 0.20 and the ending position to a dimensionless radius of 0.90 (the center position of the raw material falling from the rotating chute on the raw material accumulation surface inside the furnace). For the subsequent second batch, the rotating chute 5 was rotated and tilted to move the raw material charging position from the middle of the furnace towards the furnace wall while charging the raw material (tilting pattern = reverse tilting). For the second batch of raw material charging using the rotating chute 5, the starting position was set to a dimensionless radius of 0.50 and the ending position to a dimensionless radius of 0.95 (the center position of the raw material falling from the rotating chute on the raw material accumulation surface inside the furnace).

[0056] In Invention Example 1, when charging the first batch of ore raw materials into the furnace top bunker 4, reduced iron was layered on top of the ore raw materials loaded on the charging conveyor 3 as follows: 60 kg / t of reduced iron was cut and layered on top of the ore raw materials in a length range of 18% to 75% of the total length of the ore raw materials loaded on the charging conveyor 3, from the leading end in the transport direction (Figure 15, form (b)). In Invention Example 2, when charging the first batch of ore raw materials into the furnace top bunker 4, reduced iron was layered on top of the ore raw materials loaded on the charging conveyor 3 as follows: 60 kg / t of reduced iron was cut and layered on top of the ore raw materials in a length range of 18% to 32% of the total length of the ore raw materials loaded on the charging conveyor 3, from the leading end in the transport direction (Figure 15, form (c)). In the comparative example, when charging the first batch of ore raw materials into the furnace top bunker 4, reduced iron was layered on top of the ore raw materials loaded on the charging conveyor 3 as follows: 60 kg / t of reduced iron was cut and layered on top of the ore raw materials over almost the entire length of the loading of the ore raw materials on the charging conveyor 3 (Figure 15, form (a)).

[0057] Table 1 shows the operating conditions for the inventive examples and comparative examples, as well as the measurement results of the airflow resistance index, gas utilization rate, and molten iron temperature. According to this, in inventive examples 1 and 2, the reduced iron was able to be placed (charged) at a high mixing ratio in the lower part of the ore raw material layer from the middle to the furnace wall, resulting in an improvement in the insufficient reducing power and a stable gas flow distribution. As a result, the airflow resistance index was reduced and the reducing agent ratio decreased compared to the comparative example. In particular, inventive example 2, the reduced iron was stacked so that it was concentrated in the length range closer to the front of the loading length of the ore raw materials transported by the charging conveyor 3, and this effect was significant. Based on the above, it has been confirmed that the raw material charging method of the present invention optimizes the radial distribution of reduced iron mixed with ore raw materials, making it effective for stable operation of blast furnaces, and further effective for low reducing agent ratio operation.

[0058] [Table 1] [Explanation of Symbols]

[0059] 1 Furnace body 2 Raw material charging device 3. Loading conveyor 4. Hearthtop Bunker 5. Swinging Shot 6 Collective Hopper 7 Top Ring 8. Segregation control plate 9a Ore raw material hopper 9b Metal Iron Raw Material Hopper 10 Reserve Hopper 11. Ore conveyor 12 Receiving Shoot 21 Furnace body 22 Raw material charging device 23 Loading conveyor 24. Hearthtop Bunker 25. Swinging Shot 26 Collective Hopper 27 Top Ring 28 Segregation control plate 29a, 29b Raw material hopper 30 Switch Shot 31 Sampling Box 32 Belt conveyor 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. Ore raw materials b. Metallic iron raw materials x Furnace center axis x B Bunker central axis

Claims

1. In a bellless blast furnace having multiple top bunkers arranged in parallel and a raw material charging device that charges raw materials into the furnace by a swirling chute, a method for charging a blast furnace by mixing ore raw materials (a) including at least one of sintered ore, pellets and lump ore, and metallic iron raw materials (b) including reduced iron and / or granular pig iron, When transporting the ore raw material (a) to the top of the furnace by a charging conveyor and charging it into one of the top furnace bunkers, the metallic iron raw material (b) is cut out onto the ore raw material (a) being 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 total length of the ore raw material (a) loaded on the charging conveyor, from the leading edge in the transport direction, and the ore raw material (a) and metallic iron raw material (b) are then charged into the top furnace bunker. A method for charging raw materials into a blast furnace, characterized in that when charging raw materials from the furnace top bunker into the furnace using the rotating chute, the rotating chute is rotated and tilted to move the raw material charging position from the area around the furnace center towards the furnace wall while charging the raw materials.

2. A method for charging raw materials into a blast furnace according to claim 1, characterized in that when transporting ore raw materials (a) to the top of the furnace by the charging conveyor and charging them into one of the top bunkers, metallic iron raw materials (b) are stacked on top of the ore raw materials (a) in a length range of 18% to 32% of the total length of the ore raw materials (a) loaded on the charging conveyor, from the leading edge in the transport direction.

3. When loading one charge's worth of ore raw materials (a) into the furnace in two batches, A method for charging raw materials into a blast furnace according to claim 1 or 2, characterized in that the first batch of ore raw materials (a) is mixed with metallic iron raw materials (b) and charged into the furnace.

4. The method for charging raw materials into a blast furnace according to claim 3, characterized in that the second batch of ore raw materials (a) is charged into the furnace without mixing it with metallic iron raw materials (b).

5. A segregation control plate is installed inside the furnace top bunker. The method for charging raw materials into a blast furnace according to claim 1 or 2, characterized in that when charging the ore raw materials (a) and metallic iron raw materials (b) transported by the charging conveyor into the furnace top bunker, the raw material receiving surface of the segregation control plate faces outward in the furnace radial direction and is inclined downward with respect to the outward direction of the furnace, causing the raw materials falling from above to fall downward via the raw material receiving surface of the segregation control plate and accumulate in the bunker.

6. Average apparent density of metallic iron raw material (b) [ρ ｂ ] is the average apparent density of ore raw materials (a) [ρ ａ A method for charging raw materials into a blast furnace according to claim 1 or 2, characterized in that it is larger than ].

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

8. A method for charging raw materials into a blast furnace according to claim 1 or 2, characterized in that the aspect ratio of the metallic iron raw material (b) is 1.4 or more.

9. Average particle size of metallic iron raw material (b) [d ｂ ] is the average particle size of the ore raw material (a) [d ａ A method for charging raw materials into a blast furnace according to claim 1 or 2, characterized in that it is larger than ].

10. Average particle diameter [d of the metallic iron raw material (b) ｂ and the average particle diameter [d of the ore raw material (a) ａ ratio [d ｂ / [d ａ is 3.5 or more, the raw material charging method for a blast furnace according to claim 9.

11. A method for producing molten iron, characterized by comprising the step of charging a blast furnace with a blast furnace using the raw material charging method described in claim 1 or 2, comprising the 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 granular pig iron.

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