Pig iron production method and ore raw material

Abstract

To provide a pig iron production method capable of improving the gas permeability of a blast furnace and ore raw material.SOLUTION: A pig iron production method according to an embodiment of the present invention produces pig iron using a blast furnace having a tuyere and includes: a step of laminating a first layer comprising ore raw material and a second layer comprising cokes alternately at the inside of the blast furnace; and a step of reducing and melting the raw material of the laminated first layer while blowing auxiliary fuel into the blast furnace by hot wind fed from the tuyere. The ore raw material comprises plural reduced iron molded bodies obtained by compression-molding reduced iron, the shape of each reduced iron molded body has swelling in which the central part is thicker than the circumferential part at both faces and is the chamfered rectangular one in a plane view, and the length ratio of the long side with respect to the short side of each reduced iron molded body in a plane view is 1.5 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing pig iron and to an ore feedstock. [Background technology]

[0002] A known method for producing pig iron involves alternately stacking a first layer containing raw ore and a second layer containing coke in a blast furnace, reducing and melting the raw ore with hot air blown through the tuyere while injecting auxiliary fuel into the blast furnace. The coke serves as a heat source for melting the raw ore, a reducing agent for the raw ore, a recarburizer for carburizing the molten iron to lower its melting point, and a spacer for ensuring gas permeability within the blast furnace. Maintaining gas permeability with the coke stabilizes the unloading of the burden and ensures stable operation of the blast furnace.

[0003] In blast furnace operation, a low coke ratio is desirable from the perspective of cost reduction. However, lowering the coke ratio also reduces the role of the coke described above. For example, a blast furnace operation method using reduced iron has been proposed as a method for reducing the coke ratio, i.e., increasing the ratio of raw ore (see JP 2015-199978 A). In this blast furnace operation method, reduced iron and acidic lump ore are mixed in advance and charged into the blast furnace, enabling blast furnace operation without increasing high-temperature airflow resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-199978 Summary of the Invention [Problem to be solved by the invention]

[0005] The conventional blast furnace operation method utilizes the fact that reduced iron is a material that is difficult to pulverize. Even if other ore materials pulverize, the reduced iron maintains its shape and becomes aggregate, thereby maintaining gas flow in the shaft. Therefore, the conventional blast furnace operation method requires reduced iron to be strong, necessitating the production of briquettes with a high apparent density. However, increasing the apparent density tends to cause segregation, meaning that the reduced iron accumulates in the lower layer, thereby preventing the permeability improvement effect of the reduced iron. This effect is more pronounced when the reduced iron is small. Therefore, the conventional blast furnace operation method balances the strength of the reduced iron with the prevention of segregation by increasing the particle size of the reduced iron according to the apparent density. However, the permeability improvement effect is not sufficiently achieved at this balance point, and further improvement of the permeability inside the blast furnace is required.

[0006] The present invention has been made in light of the above-mentioned circumstances, and has as its object to provide a pig iron manufacturing method and ore raw material that can improve the gas permeability inside a blast furnace. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into the segregation of reduced iron and have found that the use of reduced iron having a specific shape makes segregation less likely to occur, leading to the completion of the present invention.

[0008] That is, a method for producing pig iron according to one embodiment of the present invention is a method for producing pig iron using a blast furnace having a tuyere, and includes the steps of alternately stacking first layers containing raw ore and second layers containing coke in the blast furnace, and reducing and melting the stacked raw ore in the first layer while blowing auxiliary fuel into the blast furnace with hot air blown from the tuyere, wherein the raw ore includes a plurality of reduced iron cast bodies formed by compressing reduced iron, the shape of the reduced iron cast bodies having bulges on both sides with a central portion thicker than the peripheral portions, and having a rectangular shape with rounded corners in plan view, and the ratio of the long side to the short side of the reduced iron cast bodies in plan view is 1.5 or less.

[0009] In the method for producing pig iron, the ore raw material of the first layer includes reduced iron casts having a ratio of long sides to short sides in a plan view of not more than the above-mentioned upper limit. The reduced iron casts are less likely to segregate when the first layer is stacked, which makes the gas flow in the blast furnace uniform and improves the gas permeability in the blast furnace.

[0010] The proportion of reduced iron casts with a particle size of 50 mm or more among the plurality of reduced iron casts is preferably 10 mass% or less. The reduced iron casts contained in the ore raw material are less likely to segregate when the first layer is stacked, so segregation can be suppressed without relying on reduced iron casts with a large particle size. Furthermore, reduced iron casts with a large particle size have a high drop impact energy when the first layer is stacked, and tend to be easily pulverized by the impact. Therefore, by setting the proportion of reduced iron casts with a particle size of 50 mm or more to the above upper limit or less, the drop impact energy can be reduced, pulverization or volumetric destruction can be suppressed, the charging yield of reduced iron casts can be improved, and the gas permeability in the blast furnace can be further improved.

[0011] In another embodiment of the present invention, a raw ore material is used for producing pig iron, and includes a plurality of reduced iron molded bodies obtained by compressing reduced iron, the shape of the reduced iron molded bodies being a rectangular shape with rounded corners in plan view, with bulges on both sides that are thicker in the center than in the peripheral parts, and the ratio of the long side to the short side of the reduced iron molded bodies in plan view being 1.5 or less.

[0012] The ore raw material includes reduced iron casts having a ratio of long sides to short sides in a plan view of not more than the above upper limit. The reduced iron casts are less likely to segregate when stacking the ore raw material, and therefore, when used in the production of pig iron, the gas flow in a blast furnace is made uniform, thereby improving the gas permeability in the blast furnace.

[0013] Here, the term "reduced iron casts having a particle size of 50 mm or more" refers to reduced iron casts that are passed through a sieve with 50 mm openings and remain on the sieve. [Effects of the Invention]

[0014] As described above, the pig iron manufacturing method and ore raw material of the present invention can improve the gas permeability inside a blast furnace by using the same. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a flow diagram showing a method for producing pig iron according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the inside of a blast furnace used in the pig iron manufacturing method of FIG. [Figure 3] FIG. 3 is a schematic perspective view illustrating the shape of a reduced iron cast. [Figure 4] FIG. 4 is a schematic enlarged partial view of the area from the cohesive zone to the dripping zone in FIG. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a blast furnace burden distribution experimental device used in the examples. [Figure 6] FIG. 6 is a graph showing the proportions of raw materials at five locations in the radial direction in an example where the iron plate has dimensions of 20 mm×7 mm×4 mm. [Figure 7] FIG. 7 is a graph showing the proportions of raw materials at five locations in the radial direction in an example where the iron plate has dimensions of 10 mm×7 mm×4 mm. [Figure 8] FIG. 8 is a graph showing the relationship between the tumbler rotation speed and the airflow resistance index during the tumbler rotation test in the examples. [Figure 9] FIG. 9 is a graph showing the relationship between the proportion of HBI particles having a particle size of 50 mm or more and the airflow resistance index in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a method for producing pig iron according to each embodiment of the present invention will be described.

[0017] The pig iron manufacturing method shown in FIG. 1 is a pig iron manufacturing method for manufacturing pig iron using a blast furnace 1 shown in FIG. 2, and includes a stacking step S1 and a reducing and melting step S2.

[0018] <Blast furnace> As shown in Figure 2, the blast furnace 1 has a tuyere 1a and a tap hole 1b provided at the bottom of the furnace. A plurality of tuyere 1a is usually provided. The blast furnace 1 is a solid-gas counterflow shaft furnace. Hot air, with high-temperature or room-temperature oxygen added as needed, is blown into the furnace through the tuyere 1a to carry out a series of reactions, such as the reduction and melting of raw ore 11 (described below), and pig iron is then extracted from the tap hole 1b. The blast furnace 1 is also equipped with a Bell-Armor type raw material charging device 2. This raw material charging device 2 will be described later.

[0019] <Lamination process> In the stacking step S1, as shown in Fig. 2, first layers 10 and second layers 20 are alternately stacked in a blast furnace 1. That is, the number of first layers 10 and second layers 20 is two or more.

[0020] (1st layer) The first layer 10 contains a raw ore 11, which is itself an embodiment of the present invention. The raw ore 11 is a raw ore used in the production of pig iron, and is heated and reduced to molten pig iron F by hot air blown in from the tuyere 1a in the reduction and melting step S2.

[0021] [Ore raw materials] The "raw ore" refers to ores that are used as iron raw materials and mainly contains iron ore. The raw ore 11 includes a plurality of reduced iron molded bodies 11a formed by compressing reduced iron. The raw ore 11 may also include other raw ore 11b such as fired ore (iron ore pellets, sintered ore), lump ore, carbon composite agglomerated ore, metal, etc.

[0022] The reduced iron casts 11 a (HBI, Hot Briquette Iron) serve as aggregates that improve the permeability of the cohesive zone D, which will be described later, and allow the hot air to permeate to the center of the blast furnace 1 .

[0023] The reduced iron cast 11a is formed by hot-forming reduced iron (DRI) (direct reduced iron). DRI has a high porosity and is prone to oxidation heat generation during marine transport and outdoor storage, whereas HBI has a low porosity and is less susceptible to reoxidation. After ensuring the permeability of the first layer 10, the reduced iron cast 11a functions as a metal and becomes molten iron. Because the reduced iron cast 11a has a high metallization rate and does not require reduction, it does not require much reducing agent to become this molten iron. This contributes to reducing CO2 emissions. Note that the "metallization rate" refers to the ratio [mass %] of metallic iron to the total iron content.

[0024] The reduced iron cast 11a is generally produced using a twin-roll molder. In this case, the shape of the reduced iron cast 11a is a rectangular shape with bulges on both sides, with the central portion thicker than the peripheral portions, and with the corners rounded in a plan view, as shown in FIG. 3 . Specifically, the outline of the cross section of the reduced iron cast 11a perpendicular to the long sides bulges upward and downward, drawing an arch-like arc. On the other hand, the outline of the cross section parallel to the long sides draws an arch-like arc upward and downward near each short side, and the central portion is substantially parallel to the rectangular surface. The outline of the cross section perpendicular to the long sides may also have a central portion substantially parallel to the rectangular surface. At the positions of the long sides of the outline of the cross section perpendicular to the long sides and the short sides of the outline parallel to the long sides, the end points of the arcs extending upward and downward may coincide, or may be spaced a certain distance apart, as shown in FIG. 3 , and the outline may have a linear portion extending upward and downward between them. Furthermore, the shape in plan view is a rectangular shape with rounded corners, as described above. That is, the corners of the rectangle are rounded. At least the long sides are formed of straight lines and rounded corners, while the short sides may be formed of straight lines and rounded corners, or may be formed of only rounded corners as shown in FIG. 3. The reduced iron cast 11a may have so-called burrs, particularly on the periphery. The reduced iron cast may be chipped due to a molding defect or may be cracked due to an impact during transportation or charging into a blast furnace. Such imperfect reduced iron casts may be included in some of the raw ore. However, the "shape of the reduced iron cast" in this specification refers to the complete reduced iron cast excluding the imperfect reduced iron cast described above, and refers to the shape of the reduced iron cast body itself, excluding burrs.

[0025] The proportion of reduced iron casts 11a having a long side length (L in FIG. 3) of 40 mm or more and 140 mm or less in plan view, a short side length (B in FIG. 3) of 20 mm or more and 70 mm or less in plan view, and a thickness (height of the thick central part, H in FIG. 3) of 20 mm or more and 50 mm or less is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 80 mass% or more.

[0026] The upper limit of the ratio (L / B) of the long side L to the short side B of the reduced iron cast 11a in plan view is 1.5, and more preferably 1.4. If L / B exceeds the upper limit, segregation of the reduced iron cast 11a may occur easily when the raw ore 11 is stacked in the first layer 10. On the other hand, the lower limit of L / B is 1.0 because the long side is greater than or equal to the short side.

[0027] The upper limit of the proportion of the reduced iron casts 11a having a particle size of 50 mm or more among the plurality of reduced iron casts 11a is preferably 10% by mass, more preferably 8% by mass. The reduced iron casts 11a contained in the raw ore 11 are unlikely to segregate when the first layer 10 is stacked, so segregation can be suppressed without relying on reduced iron casts 11a having a large particle size. Furthermore, reduced iron casts 11a having a large particle size are subject to a large drop impact energy when the first layer 10 is stacked, and tend to be easily pulverized by the impact. Therefore, by setting the proportion of the reduced iron casts 11a having a particle size of 50 mm or more to the above upper limit or less, the drop impact energy can be reduced, pulverization or volumetric destruction can be suppressed, the charging yield of the reduced iron casts 11a can be improved, and the permeability in the blast furnace 1 can be further improved.

[0028] The upper limit of the content of the reduced iron casts 11a in the raw ore 11 is preferably 30% by mass, more preferably 25% by mass. By setting the content of the reduced iron casts 11a to the above upper limit or less, segregation can be suppressed, and the ore pile inclination angle can be stabilized at a low level. Therefore, the reduced iron casts 11a are relatively uniformly distributed in the first layer 10, and the hot air can be reliably ventilated to the center of the blast furnace 1. This reduces the amount of coke 21 used. Furthermore, since instability of the first layer 10 due to segregation of the reduced iron casts 11a can be avoided, layer collapse can be suppressed when the upper layer descends as the ore is melted from below in the reduction and melting step S2. The ore pile inclination angle refers to the angle of the inclined surface of the ore pile layer (such as the first layer 10) from the horizontal.

[0029] The lower limit of the amount of the reduced iron casts 11a charged is preferably 100 kg per ton of pig iron, more preferably 150 kg. If the amount of the reduced iron casts 11a charged is less than the above lower limit, the reduced iron casts 11a may not be able to sufficiently ensure gas permeability in the cohesive zone D in the reduction and melting step S2. On the other hand, the upper limit of the amount of the reduced iron casts 11a charged is determined appropriately within a range that does not result in an excess of aggregate and thereby reduce the aggregate effect. For example, the upper limit of the amount of the reduced iron casts 11a charged is set to 700 kg per ton of pig iron.

[0030] The lower limit of the ratio of the average particle size of the reduced iron casts 11a to the average particle size of the other raw ore materials 11b is preferably 1.3, more preferably 1.4. As shown in FIG. 4, when some of the other raw ore materials 11b in the first layer 10 melt and move downward in the blast furnace 1 as dripping slag 12, the high-melting-point reduced iron casts 11a do not soften even when the other raw ore materials 11b soften and shrink. Mixing reduced iron casts 11a larger than the other raw ore materials 11b as aggregate facilitates the aggregate effect of the reduced iron casts 11a, thereby preventing the entire first layer 10 from shrinking. Therefore, by setting the average particle size ratio at or above the lower limit, a hot air flow path can be established as shown by the arrows in FIG. 4, thereby improving the air permeability in the reduction and melting process S2. The upper limit of the average particle size ratio is preferably 10, more preferably 5. If the ratio of the average particle diameters exceeds the upper limit, it becomes difficult to uniformly mix the reduced iron casts 11a into the first layer 10, which may increase segregation. Note that the "average particle diameter" refers to the particle diameter at which the cumulative mass in the particle diameter distribution is 50%.

[0031] Furthermore, when the reduced iron casts 11a contain aluminum oxide, the upper limit of the aluminum oxide content in the reduced iron casts 11a is preferably 1.5% by mass, more preferably 1.3% by mass. If the aluminum oxide content exceeds the upper limit, the melting point of the slag may increase and the viscosity may become higher, which may make it difficult to ensure gas permeability in the lower part of the furnace. Therefore, by setting the aluminum oxide content in the reduced iron casts 11a to the upper limit or less, an increase in the amount of coke 21 used in the second layer 20 (described later) can be suppressed. Note that the aluminum oxide content may be 0% by mass, i.e., the reduced iron casts 11a may not contain aluminum oxide. However, the lower limit of the aluminum oxide content is preferably 0.5% by mass. If the aluminum oxide content is less than the lower limit, the reduced iron casts 11a may become expensive, which may increase the production cost of pig iron.

[0032] In addition to the raw ore material 11, auxiliary materials such as limestone, dolomite, and silica stone may be charged together into the first layer 10. In addition to the raw ore material 11, the first layer 10 generally contains a mixture of undersized coke obtained by sieving coke.

[0033] (2nd layer) The second layer 20 includes coke 21 .

[0034] The coke 21 serves as a heat source for melting the raw ore 11, generates CO gas which is a reducing agent necessary for reducing the raw ore 11, carburizes the molten iron to lower its melting point, and acts as a spacer to ensure air permeability within the blast furnace 1.

[0035] (Lamination method) Various methods can be used to alternately stack the first layers 10 and the second layers 20. Here, the method will be described using as an example a blast furnace 1 equipped with a Bell-Armor type raw material charging device 2 (hereinafter also simply referred to as "raw material charging device 2") as shown in Figure 2.

[0036] The raw material charging device 2 is provided at the top of the furnace. That is, the first layer 10 and the second layer 20 are charged from the top of the furnace. As shown in FIG. 2, the raw material charging device 2 has a bell cup 2a, a lower bell 2b, and an armor 2c.

[0037] Bell cup 2a is filled with the raw materials to be charged. When charging first layer 10, the raw materials for first layer 10 are charged into bell cup 2a, and when charging second layer 20, the raw materials for second layer 20 are charged into bell cup 2a.

[0038] Lower bell 2b has a conical shape that widens downward and is disposed within bell cup 2a. Lower bell 2b is movable up and down (in Figure 2, the upward movement is indicated by a solid line, and the downward movement is indicated by a dashed line). When lower bell 2b is moved upward, it seals the bottom of bell cup 2a, and when moved downward, it forms a gap along the extension of the side wall of bell cup 2a.

[0039] The armor 2c is installed below the lower bell 2b on the furnace wall of the blast furnace 1. When the lower bell 2b is moved downward, raw materials fall through the gap, and the armor 2c is a repulsion plate for repelling the falling raw materials. The armor 2c is also configured to be able to move in and out of the interior of the blast furnace 1.

[0040] Using this raw material charging device 2, the first layer 10 can be stacked as follows. The same applies to the second layer 20. The first layer 10 and the second layer 20 are stacked alternately.

[0041] First, lower bell 2b is positioned upward, and the raw material for first layer 10 is loaded into bell cup 2a. When lower bell 2b is positioned upward, the bottom of bell cup 2a is sealed, so the raw material is filled into bell cup 2a. The amount of material filled is the amount of each layer stacked. If the capacity of bell cup 2a is insufficient to stack each layer, first layer 10 may be stacked in multiple batches. This single stacking of the raw material filled in is also called "one batch."

[0042] Next, the lower bell 2b is moved downward. This creates a gap between the bell cup 2a and the raw materials, which fall through this gap toward the furnace wall and collide with the armor 2c. The raw materials that collide with the armor 2c and are repelled are then charged into the furnace. The raw materials fall while moving toward the furnace interior due to the repulsion from the armor 2c, and are deposited as they flow toward the center of the furnace from the position where they fell. The armor 2c is configured to be able to move in and out toward the interior of the blast furnace 1, so the falling position of the raw materials can be adjusted by moving the armor 2c in and out. This adjustment allows the first layer 10 to be deposited in a desired shape.

[0043] <Reducing dissolution process> In the reducing and melting step S2, the ore raw material 11 in the stacked first layer 10 is reduced and melted while auxiliary fuel is blown into the blast furnace 1 by hot air blown from the tuyere 1a. Note that the blast furnace is a continuous operation, and the reducing and melting step S2 is performed continuously. On the other hand, the stacking step S1 is performed intermittently, and new first layers 10 and second layers 20 to be treated in the reducing and melting step S2 are added depending on the status of the reduction and melting treatment of the first layer 10 and second layer 20 in the reducing and melting step S2.

[0044] Figure 2 shows the state in the reducing and melting step S2. As shown in Figure 2, the hot air from the tuyere 1a causes the coke 21 to swirl around the tuyere 1a, forming a raceway A, which is a hollow area where the coke 21 exists in a very sparse state. The temperature of this raceway A is the highest in the blast furnace 1, at about 2000°C. Adjacent to the raceway A is the deadman B, which is a pseudo-stagnation zone of the coke inside the blast furnace 1. Furthermore, above the deadman B, there are a dripping zone C, a cohesive zone D, and a lumpy zone E, in that order.

[0045] The temperature inside the blast furnace 1 rises from the top toward the raceway A. That is, the temperature increases in the order of lumpy zone E, cohesive zone D, and dripping zone C. For example, lumpy zone E is between 20°C and 1200°C, while deadman B is between 1200°C and 1600°C. The temperature of deadman B varies in the radial direction, and the temperature at the center of deadman B may be lower than that of dripping zone C. In addition, by stably circulating hot air through the center of the furnace, a cohesive zone D with an inverted V-shaped cross section is formed, ensuring breathability and reducibility inside the furnace.

[0046] In the blast furnace 1, the iron ore raw material 11 is first heated and reduced in the lumpy zone E. In the cohesive zone D, the ore reduced in the lumpy zone E softens and shrinks. The softened and shrunk ore descends to become dripping slag and moves to the dripping zone C. In the reduction and melting step S2, the reduction of the ore raw material 11 proceeds mainly in the lumpy zone E, and the melting of the ore raw material 11 occurs mainly in the dripping zone C. In the dripping zone C and the deadman B, direct reduction proceeds, in which the descending liquid iron oxide FeO directly reacts with the carbon in the coke 21.

[0047] The reduced iron casts 11a exert an aggregate effect in the cohesive zone D. That is, even when the ore softens and shrinks, the reduced iron casts 11a, which have a high melting point, do not soften, and an air passage that reliably passes the hot air to the center of the blast furnace 1 is secured.

[0048] In addition, molten pig iron F, which is molten reduced iron, is piled up in the hearth, and molten slag G is piled up on top of the molten pig iron F. This molten pig iron F and molten slag G can be taken out from the tap hole 1b.

[0049] <Advantages> The raw ore 11 includes reduced iron casts 11a having a ratio of long sides to short sides in a plan view of 1.5 or less. The reduced iron casts 11a are less likely to segregate when the raw ore 11 is stacked. Therefore, when used to produce pig iron, the gas flow in the blast furnace 1 is made uniform, and the gas permeability in the blast furnace 1 can be improved.

[0050] Furthermore, in the method for producing pig iron, the raw ore material 11 of the present invention is layered in the first layer 10, so that the flow of gas in the blast furnace 1 is made uniform, and the gas permeability in the blast furnace 1 can be improved.

[0051] [Other embodiments] The present invention is not limited to the above-described embodiment.

[0052] In the above embodiment, the ore raw material of the present invention includes reduced iron casts and other raw ore materials. However, the ore raw material of the present invention may include only reduced iron casts. Such raw ore can be mixed with other types of raw ore as needed and included in the first layer stacked in a blast furnace.

[0053] In the above embodiment, the pig iron manufacturing method of the present invention has been described as including only the laminating step and the reducing and melting step, but the pig iron manufacturing method may include other steps.

[0054] For example, the pig iron production method may include a step of charging a mixture of coke and reduced iron casts into the center of the blast furnace. In this case, it is preferable that the proportion of reduced iron casts with a particle size of 5 mm or more in the mixture is 90 mass % or more, and the content of the reduced iron casts in the mixture is 75 mass % or less. When the hot air reaches the center of the blast furnace, it rises through the center. By including reduced iron casts with a large particle size in the center at a content equal to or less than the upper limit, sensible heat can be effectively utilized without impeding the flow of the hot air. Therefore, the amount of coke used can be further reduced. Here, the "center" of the blast furnace refers to the region at a distance of 0.2Z or less from the center, where Z is the radius of the throat.

[0055] The pig iron production method may also include a step of pulverizing powder derived from the reduced iron cast and coal. In this case, it is preferable to include the fine powder obtained in the pulverization step as the auxiliary fuel. The reduced iron cast is partially crushed and turned into powder during transportation, etc. This powder reduces gas permeability in the blast furnace and is therefore not suitable for use as the first layer. Furthermore, this powder has a large specific surface area and is therefore prone to reoxidation to iron oxide. Injecting the auxiliary fuel containing this iron oxide through the tuyeres can improve gas permeability. Therefore, by pulverizing the powder derived from the reduced iron cast together with coal and using the pulverized powder and the fine powder containing the coal as auxiliary fuel to be injected through the tuyeres, the reduced iron cast can be effectively utilized and the gas permeability in the blast furnace can be improved.

[0056] Although the stacking process in the above embodiment uses the Bell-Armor method, other methods can also be used. One such method is the Bell-Less method. The Bell-Less method uses a rotating chute, allowing stacking to be performed while adjusting its angle. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] <Shape of reduced iron compact> First, an experiment was conducted to examine the effect of the shape of the reduced iron compact on segregation.

[0059] Figure 5 shows the blast furnace burden distribution experimental apparatus 8 used in this experiment. The blast furnace burden distribution experimental apparatus 8 shown in Figure 5 is a two-dimensional slice cold model simulating a Bell-Armor type raw material charging device at a scale of 1 / 10.7. The dimensions of the blast furnace burden distribution experimental apparatus 5 are a height of 1,450 mm (length of L1 in Figure 5), a width of 580 mm (length of L2 in Figure 5), and a depth of 100 mm (length perpendicular to the paper surface in Figure 5).

[0060] The components of the blast furnace burden distribution experimental apparatus 8 are numbered the same as the corresponding components with the same function in the Bell-Armor type raw material charging apparatus 2 in Figure 2. Since the functions are the same, detailed explanations will be omitted. In addition, as shown in Figure 5, the blast furnace burden distribution experimental apparatus 8 has a central charging chute 8a for charging coke, which simulates central charging.

[0061] A base coke layer 81, a center charging coke layer 82, a first ore layer 83, and a second ore layer 84 were charged into this blast furnace burden distribution experimental device 8 in this order.

[0062] The raw materials used in charging the first ore layer 83 and the second ore layer 84 were sintered ore (particle size 2.8 to 4.0 mm) simulating sintered ore and lump ore, alumina balls (φ2 mm) simulating iron ore pellets, coke (particle size 8.0 to 9.5 mm) simulating lump coke, and iron plates simulating reduced iron (HBI). The raw materials were scaled to 2 / 11.2. The mass ratio of HBI / sintered ore / alumina balls was 18.5 mass% / 32.6 mass% / 48.9 mass%.

[0063] Under the above conditions, the size of the steel plate simulating the HBI was set to two sizes: 20mm x 7mm x 4mm (ratio of long side to short side L / B = 2.86) and 10mm x 7mm x 4mm (L / B = 1.43). After charging, ore samples were taken at five locations (A to E) in the radial direction to determine the proportion of each raw material. The results for L / B = 2.86 are shown in Figure 6, and the results for L / B = 1.43 are shown in Figure 7.

[0064] As shown in Figure 5, the first ore layer 83 and the second ore layer 84 are deposited with a downward slope toward the center. In this case, HBI, which has a large individual weight, tends to segregate toward the center, which is the lower part. When L / B = 2.86, as shown in Figure 6, the proportion of HBI near the center increases, indicating the occurrence of segregation. Note that the low proportion of HBI in areas A and B near the periphery is intentional. In other words, this is because the proportion of HBI is controlled to decrease when the raw material is charged, since it is easier to ensure ventilation in the periphery.

[0065] In contrast, even when L / B = 1.43, the individual weight is still sufficiently larger than that of sintered ore and alumina balls, but as shown in Figure 7, the proportion of HBI is relatively stable in C to E, which are close to the middle to the center, and segregation is suppressed more than in L / B = 2.86 in Figure 6.

[0066] From the above, it is clear that segregation during stacking of raw ore can be suppressed by setting the ratio of long sides to short sides of the reduced iron molded bodies to 1.5 or less.

[0067] <Particle size of reduced iron compacts> Next, an experiment was conducted to examine the effect of the particle size of the reduced iron compact on the air permeability index.

[0068] First, we investigated the effect of the drop impact energy difference due to particle size on the air permeability index. Specifically, we conducted a tumbler rotation test to apply an impact to HBI that simulated the transportation conditions.

[0069] The HBI tumbler rotation test was conducted in accordance with JIS-M8712:2000 "Method for measuring rotational strength of iron ores (pellets, sintered ore)." The rotating drum is a 6mm thick steel plate with an inner diameter of 1000mm and a length of 500mm. Two 50mm x 50mm x 6mm equal-leg angle iron blades are attached to the inner surface in symmetrical positions along the axial direction. The attachment surfaces face in the opposite direction to the direction of rotation, making it easier to lift the sample by rotation.

[0070] The sample used was dry HBI, weighing 15±0.15 kg. The size breakdown of the sample was varied (the ratio of large to small sizes was changed) and the test was conducted. Note that large size refers to HBI with a particle size of 40 mm to 100 mm, and small size refers to HBI with a particle size of 20 mm to 40 mm.

[0071] After rotating the tumbler a predetermined number of times at a rotation speed of 25±1 rpm, the airflow resistance index K was calculated as follows. After the tumbler rotation test, the particle size distribution of the reduced iron molded bodies was obtained by sieving. This particle size distribution was calculated by dividing the representative particle size (median) between the sieve openings by d i [cm], representative particle size di The weight fraction of the reduced iron compacts belonging to i Using this particle size distribution, the harmonic mean diameter D p [cm], particle size composition index I sp is calculated using the following formula 1. Furthermore, the gravity conversion coefficient g c [9.807(g·cm) / (G·sec 2 )] and calculate the airflow resistance index K using the following formula 1. The results are shown in Figure 8.

number

[0072] The results in Figure 8 show that as the tumbler rotation speed increases and the cumulative rotational drop impact increases, the HBI is destroyed and the airflow resistance index K increases. On the other hand, when comparing at the same rotation speed, as the proportion of large sizes increases and the proportion of small sizes decreases, the airflow resistance index K increases. This is presumably because the drop impact force increases due to an increase in individual weight.

[0073] Therefore, the proportion of HBI particles with a particle size of 50 mm or more was changed, and the above-mentioned tumbler test was carried out at rotation speeds of 400 and 800 rpm to calculate the airflow resistance index K. The results are shown in Figure 9.

[0074] The results in Figure 9 show that by keeping the proportion of HBI with a particle size of 50 mm or more to 10 mass% or less, powdering and volumetric collapse during transportation and charging into the blast furnace can be suppressed. As a result, the HBI charging yield can be improved, and the permeability inside the blast furnace can also be improved. [Industrial Applicability]

[0075] The pig iron manufacturing method and ore raw material of the present invention can improve the gas permeability inside a blast furnace by using the same. [Explanation of symbols]

[0076] 1 blast furnace 1a tuyere 1b Taphole 2 Raw material charging device 2a Bell Cup 2b Lower Bell 2c Armor 10 1st layer 11. Mineral ore raw materials 11a Reduced iron compact 11b Other mineral raw materials 12 Dripping slag 20 2nd layer 21 Coke 8. Blast furnace burden distribution experimental device 8a Central charging chute 81 Coke layer 82 Central coke layer 83 First Ore Layer 84 Second Ore Layer A Raceway B Furnace core C. dripping zone D Cohesive zone E. Massive zone F molten iron G. Molten slag

Claims

1. A method for producing pig iron using a blast furnace having a tuyere, comprising: stacking first layers containing raw ore and second layers containing coke alternately in the blast furnace; reducing and melting the ore raw material of the first layer stacked while blowing auxiliary fuel into the blast furnace with hot air blown from the tuyere; Equipped with the ore raw material includes a plurality of reduced iron molded bodies obtained by compressing reduced iron, and other ore raw materials including at least one of sintered ore, lump ore, carbonaceous composite agglomerated ore, and metal; the reduced iron cast has a rectangular shape in plan view with rounded corners and bulges on both sides, with the central portion being thicker than the peripheral portions; the outline of a cross section perpendicular to the long sides of the rectangular shape bulges outward in an arch-like arc at both ends, the outline of a cross section parallel to the long sides of the rectangular shape bulges outward in an arch-like arc at both ends near the short sides, and the central portion is substantially parallel to the rectangular shape; a ratio of a long side to a short side of the reduced iron cast body in a plan view is 1.5 or less, the reduced iron cast bodies have a long side length of 40 mm or more and 140 mm or less in plan view, a short side length of 20 mm or more and 70 mm or less in plan view, and a thickness of 20 mm or more and 50 mm or less, and the proportion of the reduced iron cast bodies that have such a length is 50 mass % or more of the total reduced iron cast bodies, A method for producing pig iron, wherein the ratio of the average particle size of the reduced iron cast to the average particle size of the other raw ore material is 1.3 or more and 10 or less.

2. 2. The method for producing pig iron according to claim 1, wherein the proportion of reduced iron casts with a particle size of 50 mm or more in the plurality of reduced iron casts is 10 mass % or less.

3. A raw ore used in the production of pig iron, The method includes a plurality of reduced iron molded bodies obtained by compressing reduced iron, and other ore raw materials including at least one of sintered ore, lump ore, carbonaceous composite agglomerated ore, and metal, the reduced iron cast has a rectangular shape in plan view with rounded corners and bulges on both sides, with the central portion being thicker than the peripheral portions; the outline of a cross section perpendicular to the long sides of the rectangular shape bulges outward in an arch-like arc at both ends, the outline of a cross section parallel to the long sides of the rectangular shape bulges outward in an arch-like arc at both ends near the short sides, and the central portion is substantially parallel to the rectangular shape; a ratio of a long side to a short side of the reduced iron cast body in a plan view is 1.5 or less, the reduced iron cast bodies have a long side length of 40 mm or more and 140 mm or less in plan view, a short side length of 20 mm or more and 70 mm or less in plan view, and a thickness of 20 mm or more and 50 mm or less, and the proportion of the reduced iron cast bodies that have such a length is 50 mass % or more of the total reduced iron cast bodies, The ratio of the average particle size of the reduced iron cast to the average particle size of the other raw ore is 1.3 or more and 10 or less.

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