Pig iron production method

Abstract

A pig iron manufacturing method of one aspect of the present invention manufactures pig iron using a blast furnace having a tuyere, wherein the pig iron manufacturing method includes: a process of alternately stacking a first layer containing a ore raw material and a second layer containing coke within the blast furnace; and a process of reducing and melting the ore raw material of the stacked first layer while blowing auxiliary fuel into the blast furnace using hot air blown from the tuyere, the first layer being mixed with aggregate containing a reduced iron compact obtained by compression molding a reduced iron, the ore raw material taking iron ore pellets as a main raw material, the reduced iron compact having an average basicity of 0.5 or less, and the ore raw material having an average basicity of 0.9 or more.

Description

Technical Field

[0001] The present invention relates to a method for producing pig iron. Background Art

[0002] The following method is well known: a first layer consisting of raw ore and a second layer consisting of coke are alternately stacked in a blast furnace. The raw ore is reduced and melted while auxiliary fuel is blown into the blast furnace using hot air from the tuyere, thereby producing pig iron. The coke serves as a heat source for melting the raw ore, a reducing agent for the raw ore, a carburizer that is carburized into the molten iron to lower its melting point, and a spacer to ensure air permeability within the blast furnace. Maintaining air permeability through the coke stabilizes the discharge of the charge and ensures stable operation of the blast furnace.

[0003] In blast furnace operation, it is desirable to have a lower proportion of coke from the perspective of cost reduction. However, when the proportion of coke is reduced, the role played by the above-mentioned coke is also reduced. For example, as a method for reducing the proportion of coke even if the proportion of ore raw materials is increased, a blast furnace operation method has been proposed in which the peripheral portion of the blast furnace is limited to the loading of reduced iron with a small particle size (see Japanese Patent Application Laid-Open No. 11-315308). In this blast furnace operation method, the reduced iron that does not need to be reduced is only loaded into the peripheral portion of the furnace, thereby maintaining the role of the coke in the center of the furnace as a heat source, reducing material, recarburizer, and spacer, and improving the filling rate of the raw materials.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 11-315308 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Due to the recent demand for reducing CO2 emissions, further reductions in the use of coke are being sought in blast furnace operations. In the above-mentioned conventional blast furnace operating methods, the functions of coke as a heat source, reducing material, and recarburizer can be replaced by auxiliary fuel blown in through the tuyere. On the other hand, the role of the spacer is solely performed by coke. In the above-mentioned conventional blast furnace operating methods, the location for charging reduced iron is limited to the periphery of the furnace. In addition, the amount of coke used remains relatively reduced by the charging of reduced iron. Therefore, in the above-mentioned conventional blast furnace operating methods, there is a limit to the reduction in the use of coke, and it is difficult to say that it can fully meet the recent demand for CO2 reduction.

[0009] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing pig iron that can maintain stable operation of a blast furnace and reduce the amount of coke used.

[0010] Solutions to Problems

[0011] A method for producing pig iron according to one embodiment of the present invention uses a blast furnace having a tuyere to produce pig iron, wherein the method comprises: a step of alternately stacking a first layer containing ore raw materials and a second layer containing coke in the blast furnace; and a step of reducing and melting the stacked first layer of ore raw materials while blowing auxiliary fuel into the blast furnace using hot air blown from the tuyere, wherein the first layer is mixed with aggregates containing reduced iron formed bodies obtained by compression molding reduced iron, the ore raw materials using iron ore pellets as a main raw material, the average basicity of the reduced iron formed bodies is 0.5 or less, and the average basicity of the iron ore pellets is 0.9 or more.

[0012] In this pig iron manufacturing method, the first layer containing ore raw materials includes reduced iron formed bodies obtained by compression molding reduced iron as aggregate. Through these reduced iron formed bodies, hot air can easily pass through during the softening and remelting of the first layer in the melting process, so the amount of coke used to ensure air permeability can be reduced in this pig iron manufacturing method. In addition, in this pig iron manufacturing method, reduced iron formed bodies with an average basicity of 0.5 or less are used, so reduced iron formed bodies can be obtained relatively cheaply. In addition, in this pig iron manufacturing method, by using iron ore pellets with an average basicity of 0.9 or more as the main raw material, the increase in viscosity of the reduced iron formed bodies with low basicity when melted is suppressed, and burn-through is promoted. This mainly improves the permeability of the remelting zone, and the amount of coke used can be reduced. Therefore, by using this pig iron manufacturing method, stable operation of the blast furnace can be maintained and the amount of coke used can be reduced.

[0013] The content of the iron ore pellets in the ore raw material is preferably 50% by mass or more. By setting the content of the iron ore pellets to be equal to or greater than the lower limit, the air permeability can be further improved.

[0014] Preferably, the iron ore pellets are self-fluxing. By making the iron ore pellets self-fluxing, the burn-through of the reduced iron formed body is promoted, and the air permeability can be further improved.

[0015] Preferably, a ratio R of the unit consumption of the iron ore pellets to the unit consumption of the reduced iron formed body satisfies the following formula 1. Thus, by satisfying the following formula 1, the air permeability improvement effect of the burn-through of the reduced iron formed body can be more reliably exhibited.

[0016] [Mathematical formula 1]

[0017]

[0018] In the above formula 1, (C / S) represents the average basicity, and (%SiO2) represents the content of SiO2 [mass %]. In addition, the subscript HBI refers to the reduced iron shaped body, and the subscript P refers to the iron ore pellet. It should be noted that (C / S) critical Indicates the critical alkalinity of HBI.

[0019] Here, "main raw material" refers to the raw material with the highest mass content. "Basicity" refers to the ratio of the mass of CaO to the mass of SiO2. It should be noted that, when the target material is composed of multiple granular materials, "average basicity" refers to the ratio of the total mass of CaO to the total mass of SiO2 in the granular materials.

[0020] "Critical alkalinity" refers to Figure 3 As shown in FIG, when the pressure loss of the sample filling layer is continuously measured using the average alkalinity of HBI as a parameter and its maximum value (maximum pressure loss) is plotted, the average alkalinity at which the maximum pressure loss begins to decrease is obtained. Figure 5 As shown in FIG, the inner diameter of the graphite crucible 71 filled with the sample is The large-scale load reduction experimental furnace 7 is composed of an upper coke layer 72a (height 20 mm), an ore layer 72b (height 110 mm) and a lower coke layer 72c (height 40 mm) from the top.

[0021] Effects of the Invention

[0022] As described above, by using the pig iron production method of the present invention, it is possible to reduce the amount of coke used while maintaining stable operation of the blast furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flowchart showing a method for producing pig iron according to one embodiment of the present invention.

[0024] Figure 2 It is shown in Figure 1 Schematic diagram of the interior of a blast furnace used in the pig iron manufacturing process.

[0025] Figure 3 This is a graph showing the relationship between the average basicity of the reduced iron formed body and the maximum pressure loss.

[0026] Figure 4 yes Figure 2 A schematic enlarged view of the area from the soft melting zone to the dripping zone.

[0027] Figure 5 Schematic cross-sectional view showing the structure of a large-scale load reduction experimental furnace used in Examples.

[0028] Figure 6 This is a graph showing a temperature profile for heating the sample filling layer in the examples.

[0029] Figure 7 This is a graph showing the relationship between the temperature of the sample filling layer and the flow rate of the supplied gas in Examples.

[0030] Figure 8 It is a graph which shows the result of Example. DETAILED DESCRIPTION

[0031] Hereinafter, the pig iron production method according to each embodiment of the present invention will be described.

[0032] Figure 1 The method of manufacturing pig iron shown is to use Figure 2 The pig iron manufacturing method for manufacturing pig iron in the blast furnace 1 shown includes a lamination step S1 and a reduction melting step S2.

[0033] <Blast Furnace>

[0034] Blast furnace 1 Figure 2 As shown, the blast furnace 1 has a tuyere 1a and a taphole 1b located at the bottom of the furnace. Multiple tuyere 1a are typically provided. The blast furnace 1 is a solid-gas countercurrent vertical furnace. Hot air, with high-temperature or room-temperature oxygen added to high-temperature air as needed, is blown into the furnace through the tuyere 1a, enabling a series of reactions, including the reduction and melting of ore raw materials 11, described later. Pig iron is then removed from the taphole 1b. Furthermore, the blast furnace 1 is equipped with a bell and guard plate type raw material charging device 2. This raw material charging device 2 will be described later.

[0035] <Lamination process>

[0036] In the lamination step S1, Figure 2 As shown, the first layers 10 and the second layers 20 are alternately stacked in the blast furnace 1. That is, the number of the first layers 10 and the number of the second layers 20 are both 2 or more.

[0037] (First floor)

[0038] The first layer 10 contains ore material 11. In addition, aggregate 12 is mixed in the first layer 10. In addition to the ore material 11 and the aggregate 12, auxiliary materials such as limestone, dolomite, and silica may also be added to the first layer 10.

[0039] The ore raw material 11 refers to the ore that becomes the iron raw material. The ore raw material 11 is heated and reduced by the hot air blown in from the tuyere 1a in the reduction and melting step S2 to become molten iron. In this pig iron production method, iron ore pellets are used as the main raw material. "Iron ore pellets" are made by using fine iron ore powder of several tens of μm as raw material and improving its quality according to properties suitable for blast furnace use (such as size, strength, and reducibility). It should be noted that in this pig iron production method, the iron ore pellets preferably do not contain fine sintered ore powder.

[0040] The lower limit of the average basicity of the iron ore pellets is 0.9, more preferably 1.0, and even more preferably 1.4. If the basicity of the iron ore pellets is less than the lower limit, burn-through of the reduced iron shaped body may be difficult to promote, and air permeability may be reduced. There is no particular upper limit on the average basicity of the iron ore pellets, but the average basicity of the iron ore pellets is generally 2.0 or less.

[0041] The lower limit of the content of the iron ore pellets in the ore raw material 11 is preferably 50% by mass, more preferably 90% by mass, and even more preferably 100% by mass, that is, the ore raw material 11 is entirely iron ore pellets. By setting the content of the iron ore pellets to be greater than the lower limit, the air permeability can be further improved.

[0042] The iron ore pellets are preferably self-fluxing. By making the iron ore pellets self-fluxing, the burn-through of the reduced iron formed body is promoted, and the air permeability can be further improved.

[0043] The iron ore pellets preferably have a porosity of 21% or more of coarse open pores with a pore diameter of 4 μm or more. By including iron ore pellets with a porosity of 21% or more of coarse open pores with a pore diameter of 4 μm or more in the ore raw material, the reduction rate of the ore raw material can be improved, thereby further reducing the amount of coke used. Here, the "porosity of coarse open pores with a pore diameter of 4 μm or more" refers to the ratio of the volume of coarse open pores with a pore diameter of 4 μm or more to the apparent volume of the iron ore pellets, which is measured using a mercury intrusion meter (such as "Autopore III 9400" of Shimadzu Corporation) with the open porosity of the iron ore pellets being ε0 [%] and the total micropore volume per unit weight of the iron ore pellets being A [cm 3 / g], the total pore volume of pores with a diameter of 4 μm or more per unit weight of the iron ore pellets is defined as A +4 [cm 3 / g] is given by ε0×A +4 / A[%] is the calculated amount. It should be noted that open pores refer to pores that are communicated with the outside of the iron ore pellets, and closed pores refer to pores that are closed inside the iron ore pellets.

[0044] The iron ore pellets preferably contain MgO. MgO improves the desulfurization capacity of the slag at the hearth level and enhances its reducibility at high temperatures. Therefore, it is believed that the burn-through behavior of the ore raw material 11 is brought close to that of the reduced iron shaped body, thereby promoting the burn-through of the reduced iron shaped body. The lower limit of the MgO content in the ore raw material 11 is preferably 1% by mass, and more preferably 1.5% by mass. On the other hand, the upper limit of the MgO content is preferably 4% by mass, and more preferably 3% by mass. When the MgO content is less than the lower limit, the effect of promoting the burn-through of the reduced iron shaped body may not be fully achieved. Conversely, when the MgO content exceeds the upper limit, the strength of the iron ore pellets may decrease.

[0045] The ore raw material 11 may contain sintered ore, lump ore, carbon-containing lump ore, metal, etc. in addition to the above-mentioned iron ore pellets. It should be noted that from the perspective of improving air permeability, the content of sintered ore in the ore raw material 11 is preferably 10% by mass or less, and more preferably 0% by mass, that is, the ore raw material 11 does not contain sintered ore.

[0046] It should be noted that reduced iron shaped bodies included in the aggregate 12 described later can also serve as the iron raw material, but in this specification, the reduced iron shaped bodies are not included in the ore raw material 11 .

[0047] The aggregate 12 is used to improve the air permeability of the soft melting zone D described later and to allow the hot air to flow to the center of the blast furnace 1. The aggregate 12 includes a reduced iron shaped body (HBI, Hot Briquette Iron) obtained by compression-molding reduced iron.

[0048] HBI is obtained by forming reduced iron (DRI) in a hot state. DRI has the disadvantage of high porosity and heat release during offshore transportation and outdoor storage. In contrast, HBI has low porosity and is difficult to reoxidize. After ensuring the air permeability of the first layer 10, the aggregate 12 functions as a metal and becomes molten iron. Since the aggregate 12 has a high metallization rate and does not require reduction, it does not require too much reducing material when it becomes the molten iron. Therefore, CO2 emissions can be reduced. It should be noted that "metallization rate" refers to the ratio of metallic iron to the total iron amount [mass %].

[0049] The upper limit of the average basicity of the reduced iron shaped body is 0.5, more preferably 0.4. Reduced iron shaped bodies contain SiO2 and Al2O3 as slag components from iron ore, and generally tend to have a low average basicity. In this pig iron production method, reduced iron shaped bodies having an average basicity below the upper limit are used, eliminating the need to prepare high-quality reduced iron shaped bodies that have their basicity increased by removing SiO2 and Al2O3 or adding CaO. Consequently, pig iron can be produced at low cost. On the other hand, the lower limit of the average basicity of the reduced iron shaped body is not particularly limited and may be 0.

[0050] The ratio R of the unit consumption of the iron ore pellets to the unit consumption of the reduced iron formed body preferably satisfies the following formula 1. When the ratio R of the unit consumption of the iron ore pellets to the unit consumption of the reduced iron formed body satisfies the following formula 1, the effect of improving the air permeability of the reduced iron formed body by the burn-through can be more reliably exhibited.

[0051] [Mathematical formula 2]

[0052]

[0053] The above-mentioned formula 1 will be described in detail. Figure 3 This is a graph showing the relationship between the average alkalinity of HBI and the maximum pressure loss of a filling layer formed by alternately stacking the first layer 10 and the second layer 20. It can be judged that the smaller the maximum pressure loss, the higher the air permeability. Figure 3 It can be seen that improved permeability is observed when the average basicity of HBI exceeds a certain value. This certain value is the critical basicity. It is believed that the presence of CaO at a basicity above this critical value causes the SiO2 in HBI to transform into a calcium silicate melt, reducing the viscosity of the molten iron generated from HBI and promoting burn-through. In other words, a CaO basicity above the critical basicity is required to achieve the burn-through-promoting effect of HBI.

[0054] exist Figure 3 In this case, CaO is supplied from HBI, but it can also be supplied from iron ore pellets. It is thought that when the amount of CaO exceeds the critical basicity relative to the amount of SiO2 in the HBI and iron ore pellets combined, burn-through of the HBI is promoted, thereby improving the permeability of the above-mentioned filling layer.

[0055] The SiO2 content and CaO content of HBI and iron ore pellets are calculated by setting the unit consumption of reduced iron shaped bodies as M. HBI [kg] and the unit consumption of iron ore pellets is set as M P [kg], it is represented by the following formula 2.

[0056] [Mathematical formula 3]

[0057] [SiO2 amount]=(%SiO2) HBI ×M HBI +(%SiO2) P ×M P

[0058] [CaO content] = (C / S) HBI ×(%SiO2) HBI ×M HBI +(C / S) HBI ×(%SiO2) P ×M P

[0059] ···2

[0060] Here, it is considered that when the amount of CaO / the amount of SiO2 ≥ (C / S) as mentioned above critical When the above equation 2 is substituted into the inequality, the burn-through of HBI is promoted. P / M HBI When solving, the above formula 1 is obtained.

[0061] The lower limit of the amount of reduced iron shaped bodies charged is preferably 100 kg, and more preferably 150 kg, per ton of pig iron. If the amount of reduced iron shaped bodies charged is less than this lower limit, the air permeability ensuring function of the aggregate 12 in the soft melting zone D may not be fully exerted during the reduction and melting step S2. On the other hand, the amount of reduced iron shaped bodies charged is appropriately determined within a range that does not result in excessive aggregate and a reduction in the aggregate effect. However, the upper limit of the amount of reduced iron shaped bodies charged is, for example, 700 kg per ton of pig iron.

[0062] The lower limit of the ratio of the average particle size of the reduced iron shaped body to the average particle size of the ore raw material 11 is preferably 1.3, more preferably 1.4. Figure 4 As shown, a portion of the ore raw material 11 of the first layer 10 melts and moves as dripping slag 13 toward the bottom of the blast furnace 1. When the ore raw material 11 softens and shrinks, the reduced iron shaped bodies with a high melting point do not soften. When the reduced iron shaped bodies that are larger than the ore raw material 11 by a certain amount are mixed as aggregate 12, the aggregate effect of the reduced iron shaped bodies is more likely to be exhibited, and the layer shrinkage of the entire first layer 10 can be suppressed. Therefore, by setting the ratio of the average particle size to be greater than the lower limit, it is possible to ensure Figure 4The hot air flow path is formed as shown by the arrows, thereby improving the air permeability in the reduction melting step S2. On the other hand, the upper limit of the average particle size ratio is preferably 10, and more preferably 5. If the average particle size ratio exceeds the upper limit, it will be difficult to uniformly mix the reduced iron shaped bodies in the first layer 10, and segregation may increase. It should be noted that the "average particle size" refers to the particle size at which the cumulative mass in the particle size distribution accounts for 50%.

[0063] The upper limit of the air permeability resistance index after the drum rotation test of the above-mentioned reduced iron formed body is preferably 0.1, and more preferably 0.08. The above-mentioned reduced iron formed body is usually transported in a factory different from the factory where it is manufactured. During this period, the volume may be destroyed and the particle size distribution may change. Therefore, by using a reduced iron formed body that ensures that the air permeability resistance index is below a certain value after the above-mentioned drum rotation test, the permeability in the block band E described later can be improved in actual blast furnace operation. On the other hand, the lower limit of the above-mentioned air permeability resistance index is not particularly limited, and can be a value close to 0, which is the theoretical limit value in definition, but is usually about 0.03. It should be noted that the use of a reduced iron formed body having the property that the above-mentioned air permeability resistance index is below the specified value does not mean that a drum rotation test is required in the pig iron manufacturing method.

[0064] Here, the "air permeability resistance index after the drum rotation test" of the reduced iron shaped body is calculated as follows. First, a drum rotation test is performed according to the method for measuring the rotation strength of iron ores (JIS-M8712:2000) to obtain the particle size distribution of the reduced iron shaped body after sieving. In this particle size distribution, the representative particle size (median value) between the sieve holes is expressed as d i [cm], will belong to the representative particle size d i The weight fraction of the reduced iron shaped body is expressed as w i Using this particle size distribution, the harmonic mean diameter D is calculated using the following formula 3: p [cm], particle size structure index I sp And, use the gravity conversion factor g c [9.807(g·cm) / (G·sec 2 )], and the air permeability resistance index K was calculated using the following formula 3. It should be noted that the rotation condition of the drum in the above-mentioned drum rotation test was set to 600 rotations at 24±1 rpm.

[0065] [Formula 4]

[0066]

[0067] Furthermore, when the reduced iron shaped body contains aluminum oxide, the upper limit of the aluminum oxide content in the reduced iron shaped body is preferably 1.5% by mass, and more preferably 1.3% by mass. If the aluminum oxide content exceeds the upper limit, it may be difficult to ensure air permeability in the lower part of the furnace due to the increased melting point and viscosity of the slag. Therefore, by setting the aluminum oxide content in the reduced iron shaped body below the upper limit, it is possible to suppress an increase in the amount of coke used. It should be noted that the aluminum oxide content may be 0% by mass, that is, the reduced iron shaped body does 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 less than the lower limit, the reduced iron shaped body becomes expensive, and the production cost of pig iron may increase.

[0068] (Second floor)

[0069] The second layer 20 contains coke 21 .

[0070] The coke 21 functions as a heat source for melting the raw ore 11 , generating CO gas as a reducing material required for reducing the raw ore 11 , a carburizer for carburizing into molten iron to lower the melting point, and a spacer for ensuring air permeability in the blast furnace 1 .

[0071] (Lamination method)

[0072] Various methods can be used to alternately stack the first layer 10 and the second layer 20. Figure 2 This method will be described by taking as an example a blast furnace 1 having a raw material charging device 2 of the bell and guard plate type (hereinafter, also simply referred to as "raw material charging device 2").

[0073] 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. Figure 2 As shown, there are a bell cup 2a, a discharge bell 2b and a guard plate 2c.

[0074] The bell cup 2a is filled with the raw materials to be charged. When the first layer 10 is charged, the raw materials constituting the first layer 10 are filled into the bell cup 2a, and when the second layer 20 is charged, the raw materials constituting the second layer 20 are filled into the bell cup 2a.

[0075] The material bell 2b is a cone shaped bell that expands downward and is arranged in the material bell cup 2a. Figure 2 In the figure, the state of moving upward is indicated by a solid line, and the state of moving downward is indicated by a dotted line. When the bell 2b moves upward, it seals the lower part of the bell cup 2a, and when it moves downward, a gap is formed on the extension of the side wall of the bell cup 2a.

[0076] The guard plate 2c is installed on the wall of the blast furnace 1 below the charging bell 2b. When the charging bell 2b is moved downward, raw materials fall through the gap. The guard plate 2c acts as a rebound plate to prevent the falling materials from rebounding. Furthermore, the guard plate 2c is configured to be able to advance and retreat toward the interior (center) of the blast furnace 1.

[0077] The first layer 10 can be stacked as follows using the raw material charging device 2. The same applies to the second layer 20. The first layer 10 and the second layer 20 are stacked alternately.

[0078] First, place the bell cup 2a with the first layer 10 of raw materials in the top position of the bell 2b. With the bell cup 2a sealed at the bottom, the raw materials fill the bell cup 2a. Note that the amount of material filled is the amount required to stack each layer.

[0079] Next, the material bell 2b is moved downward. This creates a gap between the bell cup 2a and the material bell cup, so the raw material falls from the gap toward the furnace wall and collides with the guard plate 2c. The raw material that collides with and rebounds from the guard plate 2c is loaded into the furnace. Because the raw material is rebounded by the guard plate 2c, it moves toward the furnace while falling, so it flows from the falling position toward the center of the furnace and accumulates. The guard plate 2c is constructed to be able to move forward and backward toward the center, so the falling position of the raw material can be adjusted by moving the guard plate 2c forward and backward. Through this adjustment, the first layer 10 can be accumulated in the desired shape.

[0080] <Reduction Melting Process>

[0081] In the reduction and melting step S2, while auxiliary fuel is blown into the blast furnace using hot air from the tuyere 1a, the stacked first layer 10 of ore raw material 11 is reduced and melted. It should be noted that the blast furnace is operated continuously, and the reduction and melting step S2 is performed continuously. Meanwhile, the stacking step S1 is performed intermittently, and new first layers 10 and second layers 20 to be processed in the reduction and melting step S2 are added depending on the status of the reduction and melting of the first and second layers 10, 20 in the reduction and melting step S2.

[0082] Figure 2 The state in the reduction melting step S2 is shown. Figure 2As shown, the hot air from the tuyere 1a forms a tuyere circulation zone A near the tuyere 1a. This tuyere circulation zone A is a cavity where coke 21 swirls and exists in a significantly sparse state. Within the blast furnace 1, the temperature of this tuyere circulation zone A reaches a maximum of approximately 2000°C. Adjacent to the tuyere circulation zone A, within the blast furnace 1, lies the core B, which serves as a pseudo-stagnation zone for coke. Furthermore, upward from the core B, there are, in order, a dripping zone C, a soft melting zone D, and a lump zone E.

[0083] The temperature within the blast furnace 1 rises from the top toward the tuyere circulation zone A. Specifically, the temperature increases in the order of the massive zone E, the soft melting zone D, and the dripping zone C. For example, the massive zone E is approximately 20°C to 1200°C, while the core B is approximately 1200°C to 1600°C. It should be noted that the temperature of the core B varies radially, with the center of the core B sometimes being lower than the dripping zone C. Furthermore, by stably circulating hot air within the center of the furnace, the soft melting zone D is formed with an inverted V-shaped cross-section, ensuring air permeability and reducibility within the furnace.

[0084] Inside the blast furnace 1, iron ore raw material 11 is first heated and reduced in the massive zone E. In the softening zone D, the ore reduced in the massive zone E softens and shrinks. The softened and shrunken ore descends to form dripping slag, which then moves toward the dripping zone C. In the reduction and melting step S2, reduction of the ore raw material 11 primarily proceeds in the massive zone E, while melting of the ore raw material 11 primarily occurs in the dripping zone C. It should be noted that direct reduction proceeds in the dripping zone C and the furnace core B, where the descending liquid iron oxide FeO directly reacts with the carbon in the coke 21.

[0085] The aggregate 12 including the reduced iron shaped bodies exerts an aggregate effect in the softening zone D. That is, even when the ore softens and shrinks, the reduced iron shaped bodies with a high melting point do not soften, thereby ensuring an air passage for the hot air to reliably penetrate the center of the blast furnace 1.

[0086] The reduced iron shaped body has a high melting point, but its melting point is lowered by the carburization reaction between carbon monoxide (CO) in the reducing gas and carbon from the coke, turning it into molten iron at a temperature below the soft melting zone D of approximately 1500°C. At this point, the SiO₂, a component of the slag contained in the reduced iron shaped body, is also in a solid state, forming a solid-liquid coexistence with the molten iron from the previously melted reduced iron shaped body, resulting in a high viscosity, and thus hindering burn-through. In the case of a reduced iron shaped body with a high basicity, CaO reacts with SiO₂ to form a calcium silicate melt, eliminating the solid-liquid coexistence and promoting burn-through. Similarly, in the case of a reduced iron shaped body with a low basicity, i.e., one containing a high amount of SiO₂, when SiO₂ supplied from the reduced iron shaped body reacts with CaO supplied from the iron ore pellets with a high basicity, i.e., one containing a high amount of CaO, to form a calcium silicate melt, the solid-liquid coexistence is eliminated, promoting burn-through of the reduced iron shaped body.

[0087] On the hearth, molten iron F formed by melting reduced iron is deposited, and molten slag G is deposited on top of the molten iron F. The molten iron F and the molten slag G can be taken out from the tapping hole 1b.

[0088] Examples of the auxiliary fuel blown in through the tuyere 1a include pulverized coal (coal pulverized to a particle size of approximately 50 μm), heavy oil, and natural gas. These auxiliary fuels function as a heat source, a reducing agent, and a recarburizer. Specifically, they replace the coke 21's role other than as a spacer.

[0089] Advantages

[0090] In this pig iron manufacturing method, the first layer 10, which includes ore raw material 11, includes reduced iron shaped bodies obtained by compression-molding reduced iron as aggregate 12. These reduced iron shaped bodies facilitate the passage of hot air during the softening and remelting of the first layer 10 in the reduction and melting step S2. Therefore, in this pig iron manufacturing method, a relatively small amount of coke is required to ensure air permeability. Furthermore, in this pig iron manufacturing method, reduced iron shaped bodies with an average basicity of 0.5 or less are used, making them relatively inexpensive to obtain. Furthermore, in this pig iron manufacturing method, by using iron ore pellets with an average basicity of 0.9 or greater as the main raw material, the increase in viscosity of the reduced iron shaped bodies with a low average basicity when melted is suppressed, thereby promoting burn-through. This primarily improves the air permeability of the remelting zone D, thereby reducing the amount of coke used. Therefore, by using this pig iron manufacturing method, stable operation of the blast furnace 1 can be maintained while reducing the amount of coke used.

[0091] [Other embodiments]

[0092] It should be noted that the present invention is not limited to the above-mentioned embodiment.

[0093] In the above embodiment, the explanation is based on the premise that the ore raw materials of all the stacked first layers are mainly iron ore pellets, the average basicity of the reduced iron formed bodies is 0.5 or less, and the average basicity of the iron ore pellets is 0.9 or greater. However, the present invention also includes a configuration in which the ore raw materials of at least one first layer are mainly iron ore pellets, the average basicity of the reduced iron formed bodies is 0.5 or less, and the average basicity of the iron ore pellets is 0.9 or greater. However, among all the first layers, preferably 90% or more, more preferably 95% or more, and even more preferably 100%, i.e., all the layers are first layers having the above structure.

[0094] In the above-mentioned embodiment, the case where the pig iron production method of the present invention includes only the lamination step and the reduction melting step has been described, but the pig iron production method may include other steps.

[0095] For example, the pig iron manufacturing method may also include a step of charging a mixture of coke and reduced iron shaped bodies into the center of the blast furnace. In this case, the proportion of reduced iron shaped bodies with a particle size of 5 mm or more in the reduced iron shaped bodies in the mixture is 90% by mass or more, and the content of the reduced iron shaped bodies in the mixture is preferably 75% by mass or less. When the hot air reaches the center of the blast furnace, it rises in the center. By including reduced iron shaped bodies with a larger particle size in the center at a content below the upper limit, sensible heat can be effectively utilized without hindering 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 an area that is less than 0.2Z from the center when the radius of the furnace mouth is set to Z.

[0096] In addition, the pig iron manufacturing method may also include a step of finely pulverizing the powder from the reduced iron mold and coal. In this case, it is preferable to include the fine powder obtained by the above-mentioned fine pulverization step as the above-mentioned auxiliary fuel. The reduced iron mold is partially broken and becomes powder due to the transportation process, etc. Such powder reduces the permeability in the blast furnace and is therefore not suitable for use as the first layer. In addition, the specific surface area of ​​the powder is large, so it is reoxidized into iron oxide. When the auxiliary fuel containing the iron oxide is blown in from the tuyere, the permeability can be improved. Therefore, by finely pulverizing the powder from the reduced iron mold together with the coal and using the fine powder containing the finely pulverized powder and the coal as the auxiliary fuel blown in from the tuyere, the reduced iron mold can be effectively utilized and the permeability in the blast furnace can be improved.

[0097] While the stacking process in the above embodiment uses a bell and guard plate method, other methods can also be used. One such method is a bellless method. In the bellless method, a rotating chute can be used, and stacking can be performed while adjusting its angle.

[0098] [Example]

[0099] Hereinafter, the present invention will be described in further detail with reference to Examples, but the present invention is not limited to these Examples.

[0100] The effect of the basicity of iron ore pellets on the permeability was investigated by conducting a large-scale load reduction experiment simulating the periphery of a blast furnace.

[0101] exist Figure 5 The large-scale load reduction experimental furnace 7 used in this experiment is shown in FIG. The inner diameter of the graphite crucible 71 filled with the sample is set to The sample filling layer 72 consists of, from top to bottom, an upper coke layer 72a (20 mm height), an ore layer 72b (110 mm height), and a lower coke layer 72c (40 mm height). The ore layer 72b corresponds to the first layer 10 of the present invention, while the upper coke layer 72a and the lower coke layer 72c correspond to the second layer 20.

[0102] The ore layer 72b is a mixture of the reduced iron formed body (HBI) and the ore raw material. In addition, the ore layer 72b has a constant total iron content (T.Fe).

[0103] The chemical properties of the HBI used are shown in Table 1. The average basicity of HBI was 0.46. The HBI charge rate was 250 kg per ton of pig iron.

[0104] [Table 1]

[0105]

[0106] As ore raw materials, three types were prepared: (1) iron ore pellets with an average basicity of 0.04 (SiO2 content = 5.44 mass%, MgO content = 0.54 mass%), (2) iron ore pellets with an average basicity of 1.20 (SiO2 content = 4.23 mass%, MgO content = 2.11 mass%), and (3) self-fluxing sintered ore with an average basicity of 2.10 (SiO2 content = 5.40 mass%, MgO content = 1.00 mass%).

[0107] The sample filling layer 72 using the ore raw materials (1) to (3) above was respectively heated in an electric furnace 73 with Figure 6 The temperature curve shown is shown while heating and supplying Figure 7The gas (reducing gas) with the composition shown is supplied from the gas supply pipe 74 provided at the bottom of the large load reduction test furnace 7 and discharged from the gas discharge pipe 75 provided at the top. The total supply rate of the gas is 40 NL / min, and the temperature is controlled by two thermocouples 76. In addition, the load applied to the sample filling layer 72 is set to 1 kgf / cm 2 This load is applied by applying the weight of the hammer 78 via the load bar 77 .

[0108] Under the above conditions, the pressure loss of the sample filling layer 72 is continuously measured and the time integral value of the pressure loss (S value) is calculated. The S value can be used as an evaluation index of the softening and melting behavior of the ore layer 72b. It is believed that the smaller the S value, the higher the permeability. Figure 8 The results are shown in .

[0109] according to Figure 8 The results show that the S value is in the order of iron ore pellets with an average basicity of 1.20 < iron ore pellets with an average basicity of 0.04 < self-fluxing sintered ore with an average basicity of 2.10. By using iron ore pellets with an average basicity of 0.9 or more as ore raw materials, the air permeability is improved.

[0110] The average basicity (=CaO amount / SiO amount) determined from the amount of CaO and SiO calculated using the above formula 2 is 0.10 when (1) iron ore pellets with an average basicity of 0.04 are used, and 1.13 when (2) iron ore pellets with an average basicity of 1.20 are used. The critical basicity of the HBI used is 0.88. It can be said that by setting the basicity determined from the amount of CaO and SiO calculated using the above formula 2 to be greater than the critical basicity of HBI, that is, satisfying the above formula 1, air permeability is improved.

[0111] Industrial Applicability

[0112] By using the pig iron manufacturing method of the present invention, it is possible to maintain stable operation of the blast furnace and reduce the amount of coke used.

[0113] Description of Reference Numerals

[0114] 1 blast furnace

[0115] 1a Air outlet

[0116] 1b taphole

[0117] 2 Raw material loading device

[0118] 2a bell cup

[0119] 2b Cutting clock

[0120] 2c guard plate

[0121] 10 First Floor

[0122] 11 Ore raw materials

[0123] 12 Aggregates

[0124] 13 Dripping slag

[0125] 20 Second Floor

[0126] 21 Coke

[0127] 7 Large load reduction test furnace

[0128] 71 graphite crucible

[0129] 72 Sample filling layer

[0130] 72a Upper coke layer

[0131] 72b Ore Layer

[0132] 72c Lower coke layer

[0133] 73 Electric furnace

[0134] 74 Gas supply pipe

[0135] 75 Gas exhaust pipe

[0136] 76 Thermocouple

[0137] 77 Loading rod

[0138] 78 Hammer

[0139] A. Air circulation area

[0140] B hearth

[0141] C drip zone

[0142] D Soft melting zone

[0143] E blocky band

[0144] F Molten Iron

[0145] G Molten slag.

Claims

1. A method for producing pig iron using a blast furnace having a tuyere, wherein: The pig iron manufacturing method comprises: a step of alternately stacking a first layer containing ore raw materials and a second layer containing coke in the blast furnace; and The process of reducing and melting the first layer of the stacked ore raw materials while blowing auxiliary fuel into the blast furnace using hot air blown from the tuyere, Aggregates including reduced iron compacts obtained by compression-molding reduced iron are mixed in the first layer. The ore raw material uses iron ore pellets as the raw material with the largest content in terms of mass conversion, i.e., the main raw material. The average basicity of the reduced iron shaped body is 0.5 or less, The average basicity of the iron ore pellets is above 0.9, The ratio of the average particle size of the reduced iron formed body to the average particle size of the ore raw material is 1.4 or more and 10 or less, Here, basicity refers to the ratio of the mass of CaO to the mass of SiO2. When the object substance is composed of multiple granules, the average basicity refers to the ratio of the total mass of CaO in the multiple granules to the total mass of SiO2 in the multiple granules.

2. A method for producing pig iron using a blast furnace having a tuyere, wherein: The pig iron manufacturing method comprises: a step of alternately stacking a first layer containing ore raw materials and a second layer containing coke in the blast furnace; and The process of reducing and melting the first layer of the stacked ore raw materials while blowing auxiliary fuel into the blast furnace using hot air blown from the tuyere, Aggregates including reduced iron compacts obtained by compression-molding reduced iron are mixed in the first layer. The ore raw material uses iron ore pellets as the raw material with the largest content in terms of mass conversion, i.e., the main raw material. The average basicity of the reduced iron shaped body is 0.5 or less, The average basicity of the iron ore pellets is above 0.9, Here, basicity refers to the ratio of the mass of CaO to the mass of SiO2. When the target substance is composed of a plurality of granules, the average basicity refers to the ratio of the total mass of CaO in the granules to the total mass of SiO2 in the granules. The ratio R of the unit consumption of the iron ore pellets to the unit consumption of the reduced iron formed body satisfies the following formula 1: [Formula 1] In the above formula 1, (C / S) represents the average basicity, (%SiO2) represents the SiO2 content [mass %], and the subscript HBI refers to the reduced iron shaped body, and the subscript P refers to the iron ore pellet. It should be noted that (C / S) critical The critical basicity of HBI is represented. Here, the critical basicity refers to the average basicity at which the maximum pressure loss starts to decrease when the pressure loss of the sample filling layer is continuously measured using the average basicity of the reduced iron formed body as a parameter and the maximum pressure loss is plotted as the maximum value.

3. The method for producing pig iron according to claim 1 or 2, wherein: The content of the iron ore pellets in the ore raw material is 50% by mass or more.

4. The method for producing pig iron according to claim 1 or 2, wherein: The iron ore pellets are self-fluxing.

5. The method for producing pig iron according to claim 3, wherein: The iron ore pellets are self-fluxing.

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