Pig iron manufacturing method and ore raw materials

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 pig iron manufacturing method and an ore raw material.

Background Art

[0002] A method of manufacturing pig iron is known, in which a first layer containing an ore raw material and a second layer containing coke are alternately laminated in a blast furnace, and while blowing an auxiliary fuel into the blast furnace with hot air blown from a tuyere, the ore raw material is reduced and melted. At this time, the coke serves as a heat source for melting the ore raw material, a reducing agent for the ore raw material, a carburizing agent for lowering the melting point by carburizing molten iron, and a spacer for ensuring air permeability in the blast furnace. By maintaining air permeability with this coke, the settlement of the charged material is stabilized, and stable operation of the blast furnace is achieved.

[0003] In blast furnace operation, it is desirable that the proportion of this coke is low from the viewpoint of cost reduction. However, when the proportion of coke is lowered, the roles played by the above-mentioned coke also decline. For example, as a method of reducing the proportion of coke, that is, increasing the proportion of ore raw material, a blast furnace operation method using reduced iron has been proposed (see Japanese Unexamined Patent Application Publication No. 2015-199978). In the above blast furnace operation method, reduced iron and acidic lump ore are premixed and charged into the blast furnace, enabling blast furnace operation in which the high-temperature air resistance does not increase.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional blast furnace operation method described above, the fact that reduced iron is a raw material that is difficult to pulverize is utilized. Even if other ore raw materials are pulverized, the reduced iron maintains its shape and acts as aggregate, thereby maintaining the gas flow in the shaft. For this reason, the conventional blast furnace operation method requires the reduced iron to have strength, making it essential to form briquettes with high apparent density. However, increasing the apparent density makes it easier for the reduced iron to accumulate in the lower layer, a phenomenon known as segregation, and the effect of improving permeability by the reduced iron is not obtained. This effect is particularly pronounced when the size of the reduced iron is small. Therefore, in the conventional blast furnace operation method, the particle size of the reduced iron is increased according to the apparent density to balance the strength of the reduced iron with preventing segregation. However, at this balance point, it cannot be said that the effect of improving permeability is sufficiently obtained, and further improvement of permeability in the blast furnace is required.

[0006] This invention was made based on the circumstances described above, and aims to provide a pig iron manufacturing method and ore raw materials that can improve the permeability inside a blast furnace. [Means for solving the problem]

[0007] The inventors of this invention conducted thorough research on the segregation of reduced iron and discovered that using reduced iron with a specific shape makes segregation less likely, thus completing the present invention.

[0008] In other words, a pig iron manufacturing method according to one aspect of the present invention is a pig iron manufacturing method that uses a blast furnace having tuyeres to manufacture pig iron, comprising the steps of alternately stacking a first layer containing ore raw materials and a second layer containing coke in the blast furnace, and reducing and dissolving the stacked ore raw materials of the first layer while blowing auxiliary fuel into the blast furnace with hot air blown from the tuyeres, wherein the ore raw materials include a plurality of reduced iron molded bodies formed by compression molding of reduced iron, the shape of the reduced iron molded bodies is a rectangular shape with rounded corners in plan view, and the ratio of the length of the long side to the short side of the reduced iron molded body in plan view is 1.5 or less.

[0009] In this pig iron manufacturing method, the first layer of ore raw material includes a reduced iron molded body in which the ratio of the length of the long side to the short side in a plan view is less than or equal to the above upper limit. Since this reduced iron molded body is less prone to segregation when the first layer is laminated, the gas flow in the blast furnace can be made uniform and the permeability of the blast furnace can be improved.

[0010] The proportion of reduced iron molded bodies with a particle size of 50 mm or larger in the above-mentioned multiple reduced iron molded bodies is preferably 10% by mass or less. Since the reduced iron molded bodies contained in the ore raw material are less likely to segregate when the first layer is laminated, segregation can be suppressed without relying on reduced iron molded bodies with large particle sizes. Furthermore, reduced iron molded bodies with large particle sizes have a large impact energy when the first layer is laminated, and tend to pulverize easily due to this impact. For this reason, by keeping the proportion of reduced iron molded bodies with a particle size of 50 mm or larger below the above upper limit, the impact energy is reduced, pulverization or volume fracture is suppressed, the charging yield of reduced iron molded bodies is improved, and the permeability inside the blast furnace can be further improved.

[0011] Another embodiment of the present invention provides an ore raw material used in the production of pig iron, comprising a plurality of reduced iron molded bodies formed by compression molding of reduced iron, wherein the shape of the reduced iron molded bodies is a rectangular shape with rounded corners in a plan view, and the ratio of the length of the long side to the short side of the reduced iron molded bodies in a plan view is 1.5 or less.

[0012] The ore raw material includes a reduced iron molded body in which the ratio of the length of the long side to the short side in a plan view is less than or equal to the above upper limit. Since this reduced iron molded body is less prone to segregation when the ore raw material is stacked, when used in the production of pig iron, the gas flow in the blast furnace can be made uniform and the permeability of the blast furnace can be improved.

[0013] Here, "reduced iron molded body with a particle size of 50 mm or more" refers to the reduced iron molded body that remains on a sieve with a 50 mm mesh. [Effects of the Invention]

[0014] As described above, the pig iron manufacturing method and ore raw material of the present invention can improve the air permeability in the blast furnace by using them.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a flowchart showing a pig iron manufacturing method according to an 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. 1. [Figure 3] FIG. 3 is a schematic perspective view for explaining the shape of the reduced iron compact. [Figure 4] FIG. 4 is a schematic partial enlarged view from the cohesive zone to the vicinity of the dripping zone in FIG. 2. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a blast furnace charge distribution experiment apparatus used in the examples. [Figure 6] FIG. 6 is a graph showing the ratio of raw materials at five positions in the radial direction in an example where the size of the iron plate is 20 mm × 7 mm × 4 mm. [Figure 7] FIG. 7 is a graph showing the ratio of raw materials at five positions in the radial direction in an example where the size of the iron plate is 10 mm × 7 mm × 4 mm. [Figure 8] FIG. 8 is a graph showing the relationship between the number of tumbler rotations and the air permeability resistance index during the tumbler rotation test in the examples. [Figure 9] FIG. 9 is a graph showing the relationship between the ratio of HBI with a particle size of 50 mm or more and the air permeability resistance index in the examples.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the pig iron manufacturing method 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 the blast furnace 1 shown in FIG. 2, and includes a stacking step S1 and a reduction melting step S2.

[0018] <​​As shown in Figure 2, the blast furnace 1 has tuyeres 1a and tapping port 1b located at the bottom of the furnace. Multiple tuyeres 1a are usually provided. The blast furnace 1 is a solid-gas counter-flow shaft furnace. Hot air, which is high-temperature air with high-temperature or room-temperature oxygen added as needed, is blown into the furnace from the tuyeres 1a to carry out a series of reactions, such as the reduction and melting of the ore raw material 11 (described later), and pig iron can be extracted from the tapping port 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 lamination process S1, as shown in Figure 2, the first layer 10 and the second layer 20 are alternately stacked inside the blast furnace 1. In other words, the number of layers in the first layer 10 and the second layer 20 is two or more.

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

[0021] [Ore raw materials] "Ore raw material" refers to ores that serve as raw materials for iron, and mainly contains iron ore. The ore raw material 11 includes a plurality of reduced iron molded bodies 11a obtained by compression molding of reduced iron. The ore raw material 11 may also include other ore raw materials 11b such as calcined ore (iron ore pellets, sintered ore), lump ore, agglomerated ore with carbon material interior, metal, etc.

[0022] The reduced iron molded body 11a (HBI, Hot Briquette Iron) improves the air permeability of the fusion zone D described later and acts as aggregate to allow the hot air to reach the center of the blast furnace 1.

[0023] The reduced iron molded body 11a is formed from reduced iron (DRI) in a hot state. While DRI has the disadvantage of high porosity and generating heat through oxidation during sea transport or outdoor storage, HBI has low porosity and is less prone to re-oxidation. After ensuring the permeability of the first layer 10, the reduced iron molded body 11a functions as a metal and becomes molten iron. Since the reduced iron molded body 11a has a high metallization rate and does not require reduction, it requires little reducing agent when it becomes molten iron. Therefore, CO2 emissions can be reduced. Note that "metallization rate" refers to the percentage of metallic iron [mass %] of the total iron content.

[0024] The reduced iron molded body 11a is generally manufactured using a twin-roll molding machine. In this case, the shape of the reduced iron molded body 11a is a rectangular shape with rounded corners in a plan view, with a bulge on both sides in the center that is thicker than the periphery, as shown in Figure 3. Specifically, the reduced iron molded body 11a has a rectangular surface as the reference, and the contour of the cross section perpendicular to the long side bulges outwards in an arch-like arc. On the other hand, the contour of the cross section parallel to the long side bulges outwards in an arch-like arc near each short side, and the central part is approximately parallel to the rectangular surface. The contour of the cross section perpendicular to the long side may also have a portion in the middle that is approximately parallel to the rectangular surface. The endpoints of the arcs extending vertically at the positions of the long side of the contour of the cross section perpendicular to the long side and the short side of the contour parallel to the long side may coincide, or, as shown in Figure 3, they may be at a certain distance apart, and the contour may have a straight section extending vertically between them. Furthermore, the plan view shape is a rounded rectangle, as described above, meaning the corners of the rectangle are rounded. At least the longer sides are composed of rounded corners and straight lines, while the shorter sides may be composed of rounded corners and straight lines, or they may be composed only of rounded corners, as shown in Figure 3. Note that the reduced iron molded body 11a may have so-called burrs, particularly around the periphery. In addition, the reduced iron molded body may be partially chipped due to defects during molding, or may crack due to impacts during transportation or blast furnace charging, and such incomplete reduced iron molded bodies may be included in the ore raw material. However, the "shape of the reduced iron molded body" as used herein refers to the shape of the complete reduced iron molded body excluding the aforementioned incomplete reduced iron molded bodies and excluding burrs.

[0025] Preferably, the proportion of the reduced iron molded body 11a is 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, where the length of the long side of the reduced iron molded body 11a in a plan view (L in Figure 3) is 40 mm or more and 140 mm or less, the length of the short side of the reduced iron molded body 11a in a plan view (B in Figure 3) is 20 mm or more and 70 mm or less, and the thickness of the reduced iron molded body 11a (height of the thickest part in the center, H in Figure 3) is 20 mm or more and 50 mm or less.

[0026] Furthermore, the upper limit of the ratio of the long side L to the short side B of the reduced iron molded body 11a in a plan view (L / B) is 1.5, with 1.4 being more preferable. If L / B exceeds the above upper limit, segregation of the reduced iron molded body 11a may easily occur when the ore raw material 11 is laminated on the first layer 10. On the other hand, the lower limit of L / B is 1.0, since the long side ≥ the short side.

[0027] The upper limit for the proportion of reduced iron molded bodies 11a with a particle size of 50 mm or more among the multiple reduced iron molded bodies 11a is preferably 10% by mass, and more preferably 8% by mass. Since the reduced iron molded bodies 11a contained in the ore raw material 11 are less likely to segregate when the first layer 10 is laminated, segregation can be suppressed even without relying on reduced iron molded bodies 11a with large particle sizes. Furthermore, reduced iron molded bodies 11a with large particle sizes tend to have a large impact energy when the first layer 10 is laminated, and are prone to pulverization due to that impact. For this reason, by keeping the proportion of reduced iron molded bodies 11a with a particle size of 50 mm or more below the above upper limit, the impact energy is reduced, pulverization or volume breakdown is suppressed, the charging yield of reduced iron molded bodies 11a is improved, and the permeability inside the blast furnace 1 can be further improved.

[0028] The upper limit for the content of reduced iron molded bodies 11a in the ore raw material 11 is preferably 30% by mass, and more preferably 25% by mass. By keeping the content of reduced iron molded bodies 11a below the above upper limit, segregation can be suppressed, and the ore deposition inclination angle becomes stable at a low position. As a result, the reduced iron molded bodies 11a are distributed relatively uniformly within the first layer 10, and the hot air can be reliably vented to the center of the blast furnace 1. Consequently, the amount of coke 21 used can be reduced. In addition, since instability of the first layer 10 due to segregation of reduced iron molded bodies 11a can be avoided, it is possible to suppress the occurrence of layer collapse when the upper layer descends as it is dissolved from below in the reduction dissolution process S2. The ore deposition inclination angle refers to the angle from the horizontal of the inclined surface of the ore deposition layer (first layer 10, etc.).

[0029] The lower limit of the amount of reduced iron molded body 11a charged is preferably 100 kg per ton of pig iron, and more preferably 150 kg. If the amount of reduced iron molded body 11a charged is less than the above lower limit, the function of ensuring the permeability of the reduced iron molded body 11a in the fusion zone D may not work sufficiently in the reduction melting process S2. On the other hand, the upper limit of the amount of reduced iron molded body 11a charged is determined appropriately within a range where there is an excess of aggregate and the aggregate effect is not reduced, but the upper limit of the amount of reduced iron molded body 11a charged is, for example, 700 kg per ton of pig iron.

[0030] The lower limit of the ratio of the average particle size of the reduced iron molded body 11a to the average particle size of the other ore raw materials 11b is preferably 1.3, and more preferably 1.4. As shown in Figure 4, even when a portion of the other ore raw materials 11b in the first layer 10 melts and moves to the bottom of the blast furnace 1 as dripping slag 12, and this moved other ore raw materials 11b softens and shrinks, the high-melting-point reduced iron molded body 11a does not soften. When reduced iron molded body 11a, which is a certain size or larger than the other ore raw materials 11b, is mixed as aggregate, the aggregate effect of the reduced iron molded body 11a is easily expressed, and layer shrinkage of the entire first layer 10 can be suppressed. Therefore, by setting the above average particle size ratio to or above the lower limit, a hot air flow path as shown by the arrow in Figure 4 can be secured, and the air permeability in the reduction dissolution process S2 can be improved. On the other hand, the upper limit of the above average particle size ratio is preferably 10, and more preferably 5. If the ratio of the average particle sizes exceeds the upper limit, it may become difficult to uniformly mix the reduced iron molded body 11a into the first layer 10, potentially increasing segregation. Note that "average particle size" refers to the particle size at which the cumulative mass in the particle size distribution accounts for 50%.

[0031] Furthermore, if the reduced iron molded body 11a contains aluminum oxide, the upper limit of the aluminum oxide content in the reduced iron molded body 11a is preferably 1.5% by mass, and more preferably 1.3% by mass. If the aluminum oxide content exceeds the upper limit, it may become difficult to ensure permeability at the bottom of the furnace due to an increase in the slag melting point and viscosity. For this reason, by keeping the aluminum oxide content in the reduced iron molded body 11a below the upper limit, it is possible to suppress an increase in the amount of coke 21 used in the second layer 20, which will be described later. Note that the aluminum oxide content may be 0% by mass, that is, the reduced iron molded body 11a may not contain aluminum oxide, but the lower limit of the aluminum oxide content is preferably 0.5% by mass. If the aluminum oxide content is below the lower limit, the reduced iron molded body 11a will be expensive, which may increase the cost of producing pig iron.

[0032] In addition to the ore raw material 11, auxiliary raw materials such as limestone, dolomite, and silica may be charged into the first layer 10. Furthermore, it is common to use fine-grained coke obtained by sieving coke in addition to the ore raw material 11 in the first layer 10.

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

[0034] Coke 21 serves as a heat source for dissolving the ore raw material 11, generates CO gas which is a reducing agent necessary for reducing the ore raw material 11, acts as a carburizing agent to lower the melting point of molten iron, and acts as a spacer to ensure permeability within the blast furnace 1.

[0035] (Lamination method) Various methods can be used to alternately stack the first layer 10 and the second layer 20. Here, we will explain the method using 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 as an example.

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

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

[0038] The lower bell 2b is cone-shaped and widens downwards, and is positioned inside the bell cup 2a. The lower bell 2b is movable up and down (in Figure 2, the upward position is shown by a solid line, and the downward position by a dashed line). When the lower bell 2b is moved upward, it seals the lower part of the bell cup 2a, and when it is moved downward, a gap is formed on the extension of the side wall of the bell cup 2a.

[0039] Armor 2c is located below the lower bell 2b and is installed on the furnace wall of the blast furnace 1. When the lower bell 2b is moved downward, raw materials fall through the gap, and armor 2c is a rebound plate that repels these falling materials. Furthermore, armor 2c is configured to be able to move in and out toward the interior of the blast furnace 1.

[0040] Using this raw material loading device 2, the first layer 10 can be stacked as follows. The same procedure applies to the second layer 20. Furthermore, the stacking of the first layer 10 and the second layer 20 is performed alternately.

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

[0042] Next, the lower bell 2b is moved downward. This creates a gap between it and the bell cup 2a, through which the raw material falls toward the furnace wall and collides with the armor 2c. The raw material, having collided with and been repelled by the armor 2c, is then charged into the furnace. As the raw material falls while moving toward the furnace due to the repulsion from the armor 2c, it flows inward from its landing position and accumulates towards the center of the furnace. Since the armor 2c is configured to move in and out of the blast furnace 1, the landing position of the raw material 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] <Reduction and dissolution process> In the reduction and dissolution process S2, auxiliary fuel is blown into the blast furnace 1 using hot air supplied from the tuyeres 1a, while the ore raw material 11 of the stacked first layer 10 is reduced and dissolved. The blast furnace is operated continuously, and the reduction and dissolution process S2 is carried out continuously. On the other hand, the stacking process S1 is carried out intermittently, and depending on the status of the reduction and dissolution treatment of the first layer 10 and the second layer 20 in the reduction and dissolution process S2, new first layers 10 and second layers 20 to be treated in the reduction and dissolution process S2 are added.

[0044] Figure 2 shows the state during the reduction dissolution process S2. As shown in Figure 2, the hot air from the tuyeres 1a causes the coke 21 to swirl around, forming a raceway A, which is a void where the coke is in a remarkably sparse state. The temperature of this raceway A is the highest inside the blast furnace 1, at approximately 2000°C. Adjacent to raceway A is the furnace core B, which is a pseudo-stagnation zone of coke inside the blast furnace 1. Above the furnace core B are the dripping zone C, the fusion zone D, and the lumpy zone E, in that order.

[0045] The temperature inside blast furnace 1 rises from the top towards raceway A. In other words, the temperature is highest in the order of bulk zone E, fused zone D, and dripping zone C. For example, the temperature in bulk zone E is between 20°C and 1200°C, while the core B is between 1200°C and 1600°C. Note that the temperature of core B varies radially, and the temperature at the center of core B may be lower than that of dripping zone C. In addition, by stably circulating hot air in the center of the furnace, a fused zone D with an inverted V-shaped cross-section is formed, ensuring air permeability and reducing properties within the furnace.

[0046] Inside the blast furnace 1, the iron ore raw material 11 is first heated and reduced in the massive zone E. In the fusion zone D, the ore reduced in massive 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 dissolution process S2, the reduction of the ore raw material 11 mainly proceeds in massive zone E, and the dissolution of the ore raw material 11 mainly occurs in the dripping zone C. In addition, in the dripping zone C and furnace core B, direct reduction proceeds in which the descending liquid iron oxide FeO directly reacts with the carbon of coke 21.

[0047] The reduced iron molded body 11a exhibits an aggregate effect in the fusion zone D. In other words, even when the ore is softened and shrinks, the high-melting-point reduced iron molded body 11a does not soften, ensuring that a ventilation passage is secured that reliably allows the hot air to reach the center of the blast furnace 1.

[0048] Furthermore, molten iron F, which is reduced iron that has melted, is deposited in the hearth, and molten slag G is deposited on top of the molten iron F. This molten iron F and molten slag G can be removed from the tap port 1b.

[0049] <Advantages> The ore raw material 11 includes a reduced iron molded body 11a in which the ratio of the length of the long side to the short side in a plan view is 1.5 or less. Since this reduced iron molded body 11a is less prone to segregation when the ore raw material 11 is stacked, when used in the production of pig iron, the gas flow in the blast furnace 1 can be made uniform and the permeability of the blast furnace 1 can be improved.

[0050] Furthermore, in this pig iron manufacturing method, the ore raw material 11 of the present invention is laminated in the first layer 10, which makes the gas flow inside the blast furnace 1 more uniform and improves the permeability inside the blast furnace 1.

[0051] [Other embodiments] However, the present invention is not limited to the embodiments described above.

[0052] In the embodiments described above, the present invention describes a case in which the ore raw material includes a reduced iron molded body and other ore raw materials. However, the present invention may also include only a reduced iron molded body. In such cases, the ore raw material can be mixed with other types of ore raw materials as needed and included in the first layer that is laminated in the blast furnace.

[0053] In the above embodiment, the pig iron manufacturing method of the present invention was described in which it comprises only a lamination step and a reduction dissolution step, but the pig iron manufacturing method may also include other steps.

[0054] For example, the pig iron manufacturing method may include a step of charging a mixture of coke and reduced iron molded bodies into the center of the blast furnace. In this case, it is preferable that the proportion of reduced iron molded bodies with a particle size of 5 mm or more in the mixture is 90% by mass or more, and the content of reduced iron molded bodies in the mixture is 75% by mass or less. When the hot air reaches the center of the blast furnace, it rises up this center. By including reduced iron molded bodies with a large particle size in the center in a content below the above upper limit, the sensible heat can be effectively utilized without obstructing 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 furnace mouth.

[0055] Furthermore, the pig iron manufacturing method may include a step of finely grinding powder derived from the reduced iron molded body and coal. In this case, it is preferable to include the fine powder obtained in the fine grinding step as the auxiliary fuel. The reduced iron molded body is partially crushed into powder during the transport process, etc. Such powder reduces the permeability inside the blast furnace and is therefore not suitable for use as the first layer. In addition, because this powder has a large specific surface area, it is re-oxidized to iron oxide. By blowing in this auxiliary fuel containing iron oxide from the tuyeres, the permeability can be improved. Therefore, by finely grinding the powder derived from the reduced iron molded body together with coal, and using the finely ground powder containing the coal as an auxiliary fuel blown in from the tuyeres, the reduced iron molded body can be effectively utilized, and the permeability inside the blast furnace can be improved.

[0056] In the above embodiment, the bell-armor method was described as the lamination process, but other methods can also be used. One such other method is the bell-less method. In the bell-less method, lamination can be performed using a rotating chute while adjusting its angle. [Examples]

[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 a reduced iron molded body> First, we experimented with the effect of the shape of the reduced iron molded body on segregation.

[0059] Figure 5 shows the blast furnace charge distribution experimental apparatus 8 used in this experiment. The blast furnace charge distribution experimental apparatus 8 shown in Figure 5 is a two-dimensional sliced ​​cold model that simulates a Bell Armor type raw material charging apparatus at a scale of 1 / 10.7. The dimensions of the blast furnace charge distribution experimental apparatus 5 are a height of 1450 mm (length L1 in Figure 5), a width of 580 mm (length L2 in Figure 5), and a depth of 100 mm (length perpendicular to the plane of the paper in Figure 5).

[0060] Each component of the blast furnace charge distribution experimental apparatus 8 is numbered the same as the corresponding component with the same function in the Bell-Armor type raw material charging apparatus 2 shown in Figure 2. Since the functions are the same, a detailed explanation is omitted. In addition, as shown in Figure 5, the blast furnace charge distribution experimental apparatus 8 has a central charging chute 8a for charging coke, simulating central charging.

[0061] In this blast furnace charge distribution experimental apparatus 8, a base coke layer 81, a central charge coke layer 82, a first ore layer 83, and a second ore layer 84 were charged in this order.

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

[0063] Under the conditions described above, two sizes of iron plates simulating HBI were used: 20mm × 7mm × 4mm (length ratio of long side to short side L / B = 2.86) and 10mm × 7mm × 4mm (L / B = 1.43). After charging, ore samples were taken at five locations (A to E) in the radial direction, and the proportion of each raw material was determined. Figure 6 shows the results for L / B = 2.86, and Figure 7 shows the results for L / B = 1.43.

[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 larger individual weight, is more likely to segregate toward the center. When L / B = 2.86, as shown in Figure 6, the proportion of HBI near the center is increased, indicating that segregation is occurring. Note that the low proportion of HBI in A and B, which are closer to the periphery, is intentional. That is, because permeability is easily ensured in the periphery, the proportion of HBI is controlled to decrease during raw material charging.

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

[0066] From the above, it can be seen that segregation during the stacking of ore raw materials can be suppressed by making the ratio of the length of the long side to the short side of the reduced iron molded body 1.5 or less.

[0067] <Particle size of reduced iron molded material> Next, we experimented with the effect of the particle size of the reduced iron molded body on the air permeability resistance index.

[0068] First, we investigated the effect of differences in impact energy due to particle size variations on the air permeability resistance index. Specifically, we conducted a tumbler rotation test to simulate transport conditions on the HBI.

[0069] HBI's tumbler rotation test was conducted in accordance with JIS-M8712:2000 "Method for measuring the rotational strength of iron ore (pellets, sintered ore)". The rotating drum is made of 6 mm thick steel plate, with an inner diameter of φ1000 mm and a length of 500 mm. Two 50 mm x 50 mm x 6 mm equal-sided angle steel blades are mounted axially in symmetrical positions on the inner surface. The mounting surface is oriented opposite to the direction of rotation to facilitate lifting of the sample by rotation.

[0070] The sample used was dried HBI, weighing 15 ± 0.15 kg. The size breakdown of the above sample was changed (the ratio of large to small sizes was changed), and the test was conducted. 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 material a predetermined number of times at a rotation speed of 25±1 rpm, the air permeability resistance index K was calculated as follows. After the tumbler rotation test, the particle size distribution was obtained by sieving the reduced iron molded body. This particle size distribution was calculated by taking the representative particle size (median) between the sieve meshes. i [cm], representative particle size di The weight fraction of the reduced iron molded body belonging to w i It is expressed as follows. Using this particle size distribution, the harmonic mean diameter D p [cm], particle size composition index I sp The following equation 1 is used to calculate it. Furthermore, the gravity conversion factor g c [9.807 (g·cm) / (G·sec) 2 Using the formula below, the air permeability resistance index K is calculated. 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 air permeability resistance index K increases. On the other hand, when comparing at the same rotation speed, the air permeability resistance index K increases as the proportion of large sizes increases and the proportion of small sizes decreases. This is presumed to be because the drop impact force increases due to the increase in individual weight.

[0073] Therefore, the above-mentioned tumbler test was performed at 400 and 800 rotations, varying the proportion of HBI particles with a particle size of 50 mm or more, and the air permeability resistance index K was calculated. The results are shown in Figure 9.

[0074] The results in Figure 9 show that by limiting the proportion of HBI with a particle size of 50 mm or more to 10% by mass or less, pulverization and volume breakdown during transport and blast furnace charging 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 production method and ore raw materials of the present invention can improve the permeability inside a blast furnace when used. [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. Ore raw materials 11a Reduced iron molded body 11b Other ore raw materials 12. Dropping slag 20 2nd layer 21 Coke 8. Blast Furnace Charge Distribution Experiment Apparatus 8a Central loading chute 81 Coke layer 82. Central Coke Layer 83. First Ore Layer 84. Second Ore Layer A Raceway B Furnace core C. Dropping Zone D Fusion zone E. Blocky zone F Molten iron G Molten slag

Claims

1. A method for producing pig iron using a blast furnace having tuyeres, The process involves alternately stacking a first layer containing ore raw materials and a second layer containing coke within the blast furnace described above. The process involves blowing auxiliary fuel into the blast furnace using hot air supplied from the above-mentioned tuyeres, while simultaneously reducing and dissolving the above-mentioned first layer of ore raw materials that has been stacked. Equipped with, The above ore raw material is a mixture of multiple reduced iron molded bodies obtained by compression molding of reduced iron, and other ore raw materials including at least one of calcined ore, lump ore, agglomerated ore with carbon material content, and metal. The shape of the reduced iron molded body described above is a rectangular shape with rounded corners in plan view, with the central part being thicker than the peripheral part on both sides. Using this rectangular surface as a reference, the contour of the cross section perpendicular to the long side bulges outwards in an arched arc, and the contour of the cross section parallel to the long side forms an arched arc near each short side, with the central part being approximately parallel to the rectangular surface. The ratio of the length of the long side to the short side of the above-mentioned reduced iron molded body in a plan view is 1.5 or less. The reduced iron molded body has a long side length of 40 mm or more and 140 mm or less in a plan view, a short side length of 20 mm or more and 70 mm or less in a plan view, and a thickness of 20 mm or more and 50 mm or less. The proportion of reduced iron molded bodies that account for 50% by mass or more of the total reduced iron molded body is 50% by mass or more. The ratio of the average particle size of the reduced iron molded body to the average particle size of the other ore raw materials is 1.3 or more and 10 or less. A method for producing pig iron, wherein, in the above-mentioned multiple reduced iron molded bodies, the proportion of reduced iron molded bodies remaining on the sieve having a mesh size of 50 mm is 10% by mass or less. Here, the average particle size is defined as the particle size at which the cumulative mass in the particle size distribution accounts for 50%.

2. It is a raw ore used in the production of pig iron. It contains a mixture of multiple reduced iron molded bodies obtained by compression molding of reduced iron, and other ore raw materials including at least one of calcined ore, lump ore, carbonized lump ore, and metal. The shape of the reduced iron molded body described above is a rectangular shape with rounded corners in plan view, with the central part being thicker than the peripheral part on both sides. Using this rectangular surface as a reference, the contour of the cross section perpendicular to the long side bulges outwards in an arched arc, and the contour of the cross section parallel to the long side forms an arched arc near each short side, with the central part being approximately parallel to the rectangular surface. The ratio of the length of the long side to the short side of the above-mentioned reduced iron molded body in a plan view is 1.5 or less. The reduced iron molded body has a long side length of 40 mm or more and 140 mm or less in a plan view, a short side length of 20 mm or more and 70 mm or less in a plan view, and a thickness of 20 mm or more and 50 mm or less. The proportion of reduced iron molded bodies that account for 50% by mass or more of the total reduced iron molded body is 50% by mass or more. The ratio of the average particle size of the reduced iron molded body to the average particle size of the other ore raw materials is 1.3 or more and 10 or less. An ore raw material in which, of the above-mentioned multiple reduced iron molded bodies, the proportion of reduced iron molded bodies remaining on the sieve having a 50 mm mesh is 10% by mass or less. Here, the average particle size is defined as the particle size at which the cumulative mass in the particle size distribution accounts for 50%.

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