Pig iron manufacturing method

Abstract

To provide a pig iron production method capable of decreasing a reducing material ratio while maintaining stable operation of a blast furnace.SOLUTION: A pig iron production method for producing pig iron using a blast furnace having a tuyere comprises the steps of: alternately laminating a first layer containing an ore raw material and a second layer containing coke in the blast furnace; and reducing and dissolving the ore raw material in the laminated first layer while blowing auxiliary fuel into the blast furnace by hot air blown from the tuyere. The ore raw material includes a reduced iron molding obtained by compression molding of reduced iron. The auxiliary fuel includes pulverized coal. The amount of the reduced iron is 200 kg or more per 1 ton of pig iron produced. The reducing material ratio of the reducing material including the coke and the pulverized coal is 440 kg / tp or less, and the pulverized coal ratio is 130 kg / tp or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing pig iron. [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 materials charged as the first and second layers, ensuring stable operation of the blast furnace.

[0003] With the recent increase in awareness of environmental issues, there is a demand to reduce emissions of CO2, a greenhouse gas, even in blast furnace operation. As one method for reducing CO2 emissions, a molten iron production method has been proposed that increases productivity by increasing the productivity rate and reduces the amount of coke used (see JP 2014-132108 A).

[0004] The method for producing molten pig iron described in this publication is said to be able to reduce the amount of coke used and lead to a reduction in greenhouse gas emissions by increasing the amount of pulverized coal injected, which serves as auxiliary fuel for the hot air blown from the tuyere, and by increasing the oxygen enrichment rate of the oxygen-enriched air. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-132108 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the conventional hot metal manufacturing method mentioned above achieves a reduction in coke consumption, it also increases the amount of pulverized coal injected. Because pulverized coal is also a source of CO2 emissions, it cannot be said that the overall CO2 emissions have been sufficiently reduced.

[0007] The present invention has been made in light of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing pig iron that can reduce the reducing agent rate while maintaining stable operation of a blast furnace. [Means for solving the problem]

[0008] 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 a first layer containing a raw ore and a second layer 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 reduced iron compacts formed by compressing reduced iron, the auxiliary fuel includes pulverized coal, the blending amount of the reduced iron is 200 kg or more per ton of pig iron to be produced, the reducing agent ratio of the reducing agent containing the coke and the pulverized coal is 440 kg / tp or less, and the pulverized coal ratio is 130 kg / tp or more.

[0009] In this pig iron production method, the reduced iron compacts formed by compressing the reduced iron act as aggregate, and since the total amount of the reduced iron compacts is equal to or greater than the lower limit, hot air can easily pass through the first layer during softening and melting in the reduction and melting process, so less coke is required to ensure permeability. Furthermore, in this pig iron production method, the stable operation of the blast furnace can be improved by using pulverized coal as auxiliary fuel at a pulverized coal ratio equal to or greater than the lower limit. Therefore, by using this pig iron production method, stable operation of the blast furnace can be maintained even at a low reducing agent ratio equal to or less than the upper limit.

[0010] Preferably, the ore raw material includes self-fluxed pellets containing MgO, and the self-fluxed pellets have an MgO content of 1.0% by mass or more and a basicity of 1.0 or more. Self-fluxed pellets have excellent reducibility, and by including self-fluxed pellets having an MgO content of 1.0% by mass or more and a basicity of 1.0 or more in the ore raw material, it is possible to promote the reduction of the ore raw material and the burn-through of the reduced iron cast.

[0011] The lower furnace heat ratio is preferably 0.5 or less. By setting the lower furnace heat ratio to the above upper limit or less in this way, the melting capacity in the lower furnace can be increased, and the operational stability of the blast furnace can be further improved.

[0012] The oxygen enrichment rate of the hot air is preferably 2.5% by volume or less. By setting the oxygen enrichment rate of the hot air to the upper limit or less in this way, it is possible to improve the operational stability of the blast furnace while maintaining a low reducing agent rate.

[0013] The nitrogen enrichment rate of the hot air is preferably 0% by volume or more. By setting the nitrogen enrichment rate of the hot air to the lower limit or more, the sensible heat of the bosh gas is increased, and the melting ability is improved.

[0014] Here, "pulverized coal" refers to coal that has been pulverized to a particle size of approximately 50 μm, and "pulverized coal ratio" refers to the mass [kg] of pulverized coal injected from the tuyere when producing 1 ton of pig iron. "Reducing agent ratio" refers to the total mass [kg] of reducing agent required to produce 1 ton of pig iron, and the reducing agent mentioned above includes all substances that reduce ore raw materials such as coke, pulverized coal, and heavy oil.

[0015] "Basicity" refers to the ratio of the mass of CaO to the mass of SiO2. In the case where the substance in question is composed of multiple granules, it refers to the ratio of the total mass of CaO to the total mass of SiO2 of the multiple granules.

[0016] The "lower furnace heat ratio" refers to the sum of the sensible heat of the molten iron and the slag divided by the sensible heat of the bosh gas. Note that "bosh gas" refers to the gas in the state it is in at the moment when the hot blast air blown in from the tuyere, added oxygen, moisture in the hot blast, and auxiliary fuel containing pulverized coal are gasified in the tuyere.

[0017] Oxygen or nitrogen may be added to the hot air to control the combustion temperature. Adding oxygen increases the oxygen concentration of the hot air above 21% by volume in air, while adding nitrogen decreases it below 21% by volume in air. Adding oxygen is called oxygen enrichment, and adding nitrogen is called nitrogen enrichment. The "oxygen enrichment rate" of hot air refers to the percentage of oxygen enriched relative to the 21% by volume oxygen content of air, assuming that the hot air, including the oxygen blown in from the tuyere, is air. The oxygen enrichment rate RO2 is calculated using the following formula. For example, an oxygen enrichment rate of 2.5% by volume indicates that the oxygen content is 21 + 2.5 = 23.5% by volume relative to the hot air volume (air volume + oxygen volume + nitrogen volume). Note that in the case of nitrogen enrichment, the following formula 1 will show a negative value.

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[0018] Similarly, the "nitrogen enrichment rate" of hot air refers to the proportion of nitrogen enriched relative to the 79% by volume of nitrogen in air, assuming that the hot air, including the nitrogen blown in from the tuyere, is air, and the nitrogen enrichment rate RN2 is calculated using the following formula 2. For example, a nitrogen enrichment rate of 2.5% by volume indicates that the nitrogen is 79 + 2.5 = 81.5% by volume relative to the hot air volume (air volume + oxygen volume + nitrogen volume). Note that in the case of oxygen enrichment, the following formula 2 will show a negative value.

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[0019] As described above, the method for producing pig iron of the present invention can reduce the reducing agent rate while maintaining stable operation of the blast furnace. [Brief explanation of the drawings]

[0020] [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 enlarged partial view of the area from the cohesive zone to the dripping zone in FIG. [Figure 4] FIG. 4 is a diagram showing a schematic diagram of the treatment carried out at the tuyere in the reduction and melting step of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, a method for producing pig iron according to each embodiment of the present invention will be described.

[0022] 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.

[0023] <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 blast furnace 1 through the tuyere 1a to carry out a series of reactions, such as the reduction and melting of the ore raw material 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.

[0024] The lower limit of the furnace volume, which is the volume from the hearth of blast furnace 1 to the specified raw material charging line, is 2000 m 3 is preferred, and 4000m 3The pig iron manufacturing method is particularly suitable for use in the operation of a blast furnace having a furnace volume equal to or greater than the lower limit. The upper limit of the furnace volume of the blast furnace 1 in which the pig iron manufacturing method can be suitably used is not particularly limited, and the larger the furnace volume, the more suitably the pig iron manufacturing method functions. However, the practical upper limit of the furnace volume of the blast furnace 1 is 7000 m 3 That's about it.

[0025] <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.

[0026] (1st layer) The first layer 10 contains raw ore 11. The raw ore 11 is heated and reduced to molten iron F by hot air blown in from the tuyere 1a in the reduction and melting step S2.

[0027] The raw ore 11 refers to ores that are iron raw materials and mainly contains iron ore. Examples of the raw ore 11 include fired ore (iron ore pellets, sintered ore), lump ore, carbon composite agglomerated ore, metal, etc. The raw ore 11 also contains aggregate 11a.

[0028] The aggregate 11a is intended to improve the permeability of the cohesive zone D, which will be described later, and to allow the hot air to reach the center of the blast furnace 1. The aggregate 11a includes reduced iron casts (HBI, Hot Briquette Iron) obtained by compressing and molding reduced iron. That is, the raw ore 11 includes reduced iron casts.

[0029] HBI is made by hot-molten direct reduced iron (DRI). While DRI has a high porosity and generates heat due to oxidation during marine transport or outdoor storage, HBI has a low porosity and is less susceptible to reoxidation. After ensuring the permeability of the first layer 10, the aggregate 11a functions as metal and becomes molten iron. Since the aggregate 11a has a high metallization rate and does not require reduction, not much reducing agent is required to become this molten iron. This reduces CO2 emissions. Note that the "metallization rate" refers to the ratio [mass %] of metallic iron to the total iron content.

[0030] The lower limit of the amount of reduced iron (the total amount of reduced iron constituting the reduced iron cast) is 200 kg, more preferably 250 kg, and even more preferably 300 kg per ton of pig iron to be produced. If the amount of reduced iron is less than the lower limit, the reducing agent rate may not be reduced sufficiently. On the other hand, the upper limit of the amount of reduced iron is appropriately determined 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 reduced iron is set to 700 kg per ton of pig iron to be produced.

[0031] The lower limit of the ratio of the average particle size of the reduced iron casts to the average particle size of the raw ore 11b excluding the aggregate 11a is preferably 1.3, more preferably 1.4. As shown in FIG. 3 , when a portion of the raw ore 11b excluding the aggregate 11a in the first layer 10 melts and moves downward in the blast furnace 1 as dripping slag 12, the raw ore 11b excluding the aggregate 11a softens and shrinks. However, the reduced iron casts, which have a high melting point, do not soften. Mixing the reduced iron casts, which are larger than the raw ore 11b excluding the aggregate 11a, as the aggregate 11a facilitates the aggregate effect of the reduced iron casts, thereby preventing the entire first layer 10 from shrinking. Therefore, by setting the ratio of the average particle size at or above the lower limit, a hot air flow path can be established as shown by the arrows in FIG. 3 , thereby improving the air permeability in the reduction and melting process S2. The upper limit of the ratio of the average particle size 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 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%.

[0032] The upper limit of the air permeability resistance index of the reduced iron casts after the tumbler rotation test is preferably 0.1, more preferably 0.08. The reduced iron casts are generally transported between factories where they are manufactured and where they are used. During this transport, volumetric collapse and changes in particle size distribution may occur. Therefore, by using reduced iron casts that are guaranteed to have an air permeability resistance index of a certain value or less even after the tumbler rotation test, the permeability in the lumpy zone E described below can be improved in actual blast furnace operation. Meanwhile, the lower limit of the air permeability resistance index is not particularly limited and may be a value close to the theoretical limit value of 0 by definition, but is typically about 0.03. It is sufficient to use reduced iron casts that have properties that result in the air permeability resistance index being a predetermined value or less; this does not necessarily mean that the pig iron production method requires a tumbler rotation test.

[0033] Here, the "air permeability index after tumbler rotation test" of the reduced iron cast is calculated as follows. First, a tumbler rotation test is performed in accordance with the rotation strength measurement method for iron ores (JIS-M8712:2000), and the particle size distribution of the reduced iron cast is obtained by sieving. This particle size distribution is calculated by dividing the representative particle size (median) between the sieve openings by d i [cm], representative particle size d i 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 3. 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 3. The tumbler rotation conditions in the tumbler rotation test are 24±1 rpm, 600 rotations.

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[0034] The lower limit of the basicity of the reduced iron cast is preferably 0.9, more preferably 1.0. By setting the basicity of the reduced iron cast at or above the lower limit, the shrinkage initiation temperature of the reduced iron cast increases, thereby suppressing the amount of shrinkage of the first layer 10. This improves the permeability of the cohesive zone D in the reduction and melting step S2, ensuring that the hot air reaches the center of the blast furnace 1. This reduces the amount of coke 21 used. On the other hand, the upper limit of the basicity of the reduced iron cast is preferably 1.4, more preferably 1.3. If the basicity of the reduced iron cast exceeds the upper limit, the strength of the reduced iron cast may decrease. The basicity of the reduced iron cast can be adjusted by adding an auxiliary material such as limestone during production of the reduced iron cast.

[0035] Furthermore, when the reduced iron casts contain aluminum oxide, the upper limit of the aluminum oxide content in the reduced iron casts 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 to the upper limit or less, an increase in the amount of coke 21 used can be suppressed. Note that the aluminum oxide content may be 0% by mass, i.e., the reduced iron casts 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 may become expensive, which may increase the production cost of pig iron.

[0036] The ore material 11 preferably contains self-fluxed pellets. Self-fluxed pellets have excellent reducibility, and by including self-fluxed pellets in the ore material 11 in this manner, the reduction of the ore material 11 is promoted.

[0037] The self-fluxed pellets preferably contain MgO. MgO enhances the desulfurization ability of slag at the hearth level and enhances reducibility at high temperatures. Therefore, it is believed that MgO has the effect of facilitating the burn-through of the reduced iron casts by making the burn-through behavior of the self-fluxed pellets closer to that of the reduced iron casts. The lower limit of the MgO content of the self-fluxed pellets is preferably 1% by mass, more preferably 1.5% by mass. On the other hand, the upper limit of the MgO content of the self-fluxed pellets is preferably 4% by mass, more preferably 3% by mass. If the MgO content of the self-fluxed pellets is less than the lower limit, the effect of promoting the burn-through of the reduced iron casts may not be sufficiently obtained. Conversely, if the MgO content of the self-fluxed pellets exceeds the upper limit, the strength of the self-fluxed pellets may be reduced.

[0038] The lower limit of the basicity of the self-fluxed pellets is preferably 1.0, more preferably 1.4, which is basic. If the basicity of the self-fluxed pellets is below the lower limit, it may be difficult to promote burn-through of the reduced iron cast, and the air permeability may be reduced. Although there is no particular upper limit for the basicity of the self-fluxed pellets, the average basicity of the self-fluxed pellets is usually 2.0 or less.

[0039] From the viewpoint of promoting melt-through of the reduced iron cast, the self-fluxed pellets preferably have an MgO content of 1.0 mass % or more and a basicity of 1.0 or more.

[0040] In addition to the raw ore material 11, auxiliary materials such as limestone, dolomite, silica stone, etc. may be charged together into the first layer 10.

[0041] (2nd layer) The second layer 20 includes coke 21 .

[0042] 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.

[0043] The lower limit of the coke rate is preferably 200 kg / tp, more preferably 230 kg / tp. On the other hand, the upper limit of the coke rate is preferably 290 kg / tp, more preferably 250 kg / tp. If the coke rate is below the lower limit, stable operation of the blast furnace 1 may not be maintained. Conversely, if the coke rate exceeds the upper limit, operation at a low reducing agent rate may become difficult. The "coke rate" refers to the total mass [kg] of coke used as a reducing agent when producing 1 ton of pig iron, and the coke includes coke charged in layers other than the second layer 20.

[0044] (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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The armor 2c is provided 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 toward the interior (center) of the blast furnace 1.

[0049] 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.

[0050] 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.

[0051] 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 blast furnace 1. The raw materials fall while moving toward the furnace interior due to the repulsion from the armor 2c, and are deposited from the position where they fell toward the center of the blast furnace 1. The armor 2c is configured to be able to move in and out toward the center, 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.

[0052] <Reducing dissolution process> In the reduction and melting step S2, the raw ore 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.

[0053] The blast furnace is operated continuously, 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 processed in the reducing and melting step S2 are added depending on the status of the reduction and melting treatment of the first layers 10 and second layers 20 in the reducing and melting step S2.

[0054] Figure 2 shows the state during 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. Within the blast furnace 1, the temperature of this raceway A is the highest, at about 2000°C.

[0055] 4 shows the state of the tuyere 1a and the vicinity of the raceway A of the blast furnace 1 during the reduction melting process S2. The blast furnace 1 is provided with a cylindrical auxiliary fuel inlet 1c connected to the tuyere 1a, and auxiliary fuel 40 is injected into the tuyere 1a from this auxiliary fuel inlet 1c.

[0056] The auxiliary fuel inlet 1c is installed so that its outlet faces downstream of the hot air H so that the auxiliary fuel 40 is carried by the air current of the hot air H blown from the tuyere 1a and the fine powder 41 is blown deep into the raceway A.

[0057] The auxiliary fuel 40 includes pulverized coal 41. In addition to the pulverized coal 41, the auxiliary fuel 40 may also include heavy oil, natural gas, etc. The auxiliary fuel 40 functions as a heat source, a reducing agent, and a recarburizer. In other words, it takes over all roles of the coke 21 except for the role of spacer.

[0058] The pulverized coal 41 is preferably pulverized to a particle size of 500 μm or less, more preferably 100 μm or less. By setting the maximum particle size of the pulverized coal 41 to the above upper limit or less, the specific surface area of ​​the pulverized coal 41 can be increased, thereby improving combustion efficiency.

[0059] The lower limit of the pulverized coal ratio is 130 kg / tp, and more preferably 150 kg / tp. On the other hand, the upper limit of the pulverized coal ratio is preferably 250 kg / tp, and more preferably 220 kg / tp. If the pulverized coal ratio is below the lower limit, it may be difficult to reduce the coke rate while maintaining the stability of the blast furnace operation, and as a result, it may be difficult to reduce the reducing agent rate. Conversely, if the pulverized coal ratio exceeds the upper limit, the amount of pulverized coal 41 may become excessive, making it difficult to reduce the reducing agent rate.

[0060] The injected auxiliary fuel 40 is mainly sprayed onto the coke 21 at the back of the raceway A. This causes an increase in acidic slag derived from ash from melted pulverized coal 41 at the back of the raceway A, and bird's nest slag J, which is a slag layer where slag with increased viscosity and melting point accumulates (holds up).

[0061] When bird's nest slag J grows, the gas permeability in the lower part of the blast furnace 1 near the raceway A deteriorates. To prevent this deterioration in gas permeability, it is preferable that the auxiliary fuel 40 contains reduced iron casts that are pulverized to a particle size of 500 μm or less, preferably 100 μm or less.

[0062] When auxiliary fuel 40 containing the reduced iron casts is blown in through tuyere 1a, the reduced iron casts are heated and melted in raceway A, assimilated with and converted into slag with bird's nest slag J that has formed up to that point, and then promptly drip as dripping slag 12. As a result, bird's nest slag J is less likely to grow, and permeability can be maintained. Maintaining permeability makes it easier for hot blast H to reach the center of blast furnace 1, resulting in a reduction in the amount of coke 21 used.

[0063] The lower limit of the injection amount of the reduced iron casts is preferably 3 kg, more preferably 5 kg, per ton of pig iron. If the injection amount is less than the lower limit, the effect of improving permeability may be insufficient.

[0064] The upper limit of the reducing agent ratio (RAR) of the reducing material containing coke 21 and pulverized coal 41 in the second layer 20 is 440 kg / tp, and more preferably 430 kg / tp. In this pig iron production method, even if the coke rate is kept low, the reduced iron casts (aggregate 11a) contained in the raw ore 11 in the first layer 10 ensure good permeability within the blast furnace 1, and stable blast furnace operation can be maintained at a RAR equal to or lower than the upper limit. Therefore, CO2 emissions can be sufficiently reduced. Meanwhile, the lower limit of the RAR is preferably 400 kg / tp, and more preferably 410 kg / tp. If the RAR is lower than the lower limit, the amount of coke 21 charged in the second layer 20 may be limited, making it difficult to ensure good permeability within the blast furnace 1, or the amount of pulverized coal 41 in the auxiliary fuel 40 may be limited, making it difficult to maintain stable blast furnace operation.

[0065] The hot air H (air and added oxygen) blown in from the tuyere 1a, the moisture contained in the hot air H, and the auxiliary fuel 40 containing pulverized coal 41 are converted into gas (bosh gas) in the tuyere 1a.

[0066] The lower limit of the Bosch gas consumption unit is 1290 Nm 3 / tp is preferred, 1310Nm 3 On the other hand, from the viewpoint of pressure loss in the furnace, the upper limit of the bosh gas ratio is 1350 Nm 3 / tp is preferred, 1330Nm 3 / tp is more preferable. The melting capacity in the lower furnace tends to be proportional to the bosh gas sensible heat and therefore the bosh gas consumption rate. Oxygen enrichment can increase the bosh gas sensible heat by increasing the temperature before the tuyere, but even if nitrogen enrichment reduces the temperature before the tuyere, the melting capacity can be enhanced by increasing the bosh gas consumption rate. Therefore, by controlling the bosh gas consumption rate, the controllability of melting reduced iron in the lower furnace can be improved, further improving the operational stability of the blast furnace 1. Here, the "bosh gas consumption rate" is the value obtained by dividing the total amount of bosh gas per unit time by the amount of pig iron produced per unit time.

[0067] The upper limit of the lower furnace heat ratio is preferably 0.5, with 0.45 being more preferable. By keeping the lower furnace heat ratio below this upper limit, the melting capacity in the lower furnace is increased, further improving the operational stability of the blast furnace 1. This lower furnace heat ratio can be adjusted by controlling the sensible heat of the bosh gas. The lower limit of the lower furnace heat ratio is determined by the flooding limit, where excessive bosh gas flow causes the dripping hot metal and slag to be blown up by the bosh gas, destabilizing operation, and the combustion temperature limit, where plasma formation occurs at approximately 3500°C and no higher temperatures are achieved. For example, it is 0.2. The "lower furnace heat ratio" can be calculated from the sensible heats of the hot metal, slag, and bosh gas using Equation 4 below. The sensible heat values ​​in Equation 4 are calculated under the following conditions: The hot metal temperature is generally considered to be 1500°C, which is the optimum furnace temperature, and the slag temperature is 1550°C, which is 50°C higher than the hot metal temperature. The theoretical combustion temperature before the tuyere is used as the temperature before the tuyere for the bosh gas temperature. The specific heat of the molten iron is 0.75 kJ / kg / K, the specific heat of the slag is 1.26 kJ / kg / K, and the specific heat of the bosh gas component N2 is 1.30 kJ / Nm 3 / K, CO is 1.31kJ / Nm3 / K, H2 is 1.28kJ / Nm 3 / K. The standard for the amount of hot metal is 1000 kg, and the slag and bush gas amounts are calculated using the slag ratio (kg / tp) and the bosh gas consumption rate, with sensible heat = specific heat x temperature x amount. Lower furnace heat ratio = {(molten iron sensible heat) + (slag sensible heat)} / (bosh gas sensible heat) 4

[0068] The lower limit of the inlet temperature of the hot blast H is preferably 2100°C, more preferably 2120°C. On the other hand, the upper limit of the inlet temperature is preferably 2200°C, more preferably 2170°C. If the inlet temperature is below the lower limit, the melting capacity in the lower furnace will be insufficient due to a decrease in the sensible heat of the bosh gas, and the melting of the reduced iron in the lower furnace will not proceed sufficiently, which may result in unstable blast furnace operation. Conversely, if the inlet temperature exceeds the upper limit, the melting capacity in the lower furnace will be too high, which will increase the pressure drop in the lower furnace due to rapid melting of the reduced iron and cause slag to evaporate and resolidify, resulting in poor descent, such as sagging, which may result in unstable blast furnace operation.

[0069] The upper limit of the oxygen enrichment rate of the hot blast H is preferably 2.5% by volume, more preferably 2% by volume. For stable blast furnace operation, it is preferable to operate at a constant pig iron productivity. When the reducing agent ratio is constant, the pig iron productivity decreases as the oxygen content in the hot blast H decreases. Furthermore, when the oxygen content in the hot blast H is constant, the pig iron productivity increases as the reducing agent ratio decreases. Since this pig iron production method aims for operation at a low reducing agent ratio, the oxygen content must be reduced to maintain a constant pig iron productivity. One possible way to reduce the oxygen content is to reduce the amount of hot blast H, i.e., the amount of bosh gas. However, reducing the amount of bosh gas may lead to a decrease in the melting capacity in the lower furnace, which may reduce the operational stability of the blast furnace 1. Therefore, an effective method is to adjust the oxygen content by adjusting the oxygen enrichment rate of the hot blast H. Therefore, by setting the oxygen enrichment rate of the hot blast H below the above upper limit, the operational stability of the blast furnace 1 can be improved while maintaining a low reducing agent ratio. The oxygen enrichment rate and nitrogen enrichment rate of the hot air H are complementary to each other (oxygen enrichment rate + nitrogen enrichment rate = 0). In other words, the lower limit of the oxygen enrichment rate of the hot air H is determined by the upper limit of the nitrogen enrichment rate described below.

[0070] The lower limit of the nitrogen enrichment rate of the hot air H is preferably 0% by volume. In this case, the oxygen enrichment rate is 0% by volume or less. By setting the nitrogen enrichment rate of the hot air H at or above the lower limit, the sensible heat of the bosh gas increases, and the dissolving capacity is improved. On the other hand, the upper limit of the nitrogen enrichment rate of the hot air H is preferably 4% by volume due to constraints such as an increase in pressure drop associated with an increase in the amount of bosh gas and flooding limits, and 2% by volume is more preferable from the viewpoint of dissolving capacity.

[0071] Oxygen enrichment and nitrogen enrichment are explained in more detail below. The sensible heat of the bosh gas, which is the source of melting capacity, is proportional to the product of the inlet temperature of the hot blast H and the bosh gas consumption rate. Furthermore, bosh gas consists of carbon monoxide gas produced by the partial oxidation of coke and pulverized coal with oxygen supplied to the tuyere, and hydrogen and nitrogen produced by the thermal decomposition of pulverized coal. Under a constant oxygen content, the net reaction heat in the combustion field (raceway space) (the difference between the heat generated by partial oxidation and the heat absorbed by the thermal decomposition reaction) is constant. Enriched oxygen and nitrogen are typically heated in a hot stove along with air from the blower and supplied to the tuyere. High oxygen enrichment reduces the amount of nitrogen in the air, thereby decreasing the sensible heat supplied to the combustion field. Conversely, high nitrogen loading increases the sensible heat supplied to the combustion field. As a result, nitrogen enrichment results in a lower inlet temperature than oxygen enrichment, but a higher sensible heat of the bosh gas. In other words, melting capacity can be controlled by oxygen or nitrogen enrichment.

[0072] As shown in Fig. 2, adjacent to the raceway A, there is a deadman B, which is a pseudo-stagnation zone of coke inside the blast furnace 1. Also, above the deadman B, there are a dripping zone C, a cohesive zone D, and a lumpy zone E in this order.

[0073] 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 blast furnace 1, a cohesive zone D with an inverted V-shaped cross section is formed, ensuring breathability and reducibility inside the blast furnace 1.

[0074] 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.

[0075] The aggregate 11a including the reduced iron casts exerts an aggregate effect in the cohesive zone D. In other words, even when the ore softens and shrinks, the reduced iron casts with 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.

[0076] 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.

[0077] <Advantages> In this pig iron manufacturing method, reduced iron compacts formed by compressing reduced iron act as aggregate 11a, and the total amount of aggregate 11a is 200 kg or more per ton of pig iron at the above-mentioned reduced iron blending amount. This allows hot blast H to easily pass through during softening and melting of first layer 10 in the reduction and melting step S2, and therefore requires less coke 21 to ensure permeability. Furthermore, in this pig iron manufacturing method, pulverized coal 41 is used as auxiliary fuel 40 at a pulverized coal ratio of 130 kg / tp or more, thereby improving stable operation of the blast furnace 1. Therefore, by using this pig iron manufacturing method, stable operation of the blast furnace 1 can be maintained even at a low reducing agent ratio of 440 kg / tp or less.

[0078] [Other embodiments] The present invention is not limited to the above-described embodiment.

[0079] 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.

[0080] 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 be 90 mass % or more, and that the content of the reduced iron casts in the mixture be 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 a region that is 0.2Z or less away from the central axis of the blast furnace, where Z is the radius of the throat.

[0081] 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]

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0083] Using operational data from an operating blast furnace, we confirmed the conditions under which the reducing agent rate could be reduced while maintaining stable blast furnace operation. Specifically, we determined the coke rate that would enable stable operation when the pulverized coal rate was set to approximately 175 kg / tp and the blending amount of reduced iron was varied. The results are shown in Table 1.

[0084] [Table 1]

[0085] The results in Table 1 show that in No. 2, where the reduced iron blending rate is less than 200 kg / tp, the reduction load inside the blast furnace increases, causing thermal instability, making stable operation impossible at a reducing agent rate of 440 kg / tp or less. In contrast, in No. 1, where the reduced iron blending rate is 200 kg / tp or more, the aggregate effect of the reduced iron is obtained, improving permeability and allowing a reduction in the coke rate, enabling stable operation at a reducing agent rate of 440 kg / tp or less.

[0086] From the above results, it can be said that the reducing agent rate can be reduced while maintaining stable blast furnace operation by setting the reduced iron blending amount to 200 kg or more per ton of pig iron produced, the pulverized coal rate to 130 kg / tp or more, and the reducing agent rate to 440 kg / tp or less. [Industrial Applicability]

[0087] By using the method for producing pig iron of the present invention, the reducing agent rate can be reduced while maintaining stable operation of the blast furnace. [Explanation of symbols]

[0088] 1 blast furnace 1a tuyere 1b Taphole 1c Auxiliary fuel inlet 2 Raw material charging device 2a Bell Cup 2b Lower Bell 2c Armor 10 1st layer 11. Mineral ore raw materials 11a Aggregate 11b Mineral ore materials excluding aggregates 12 Dripping slag 20 2nd layer 21 Coke 40 Auxiliary fuel 41 Pulverized coal A Raceway B Furnace core C. dripping zone D Cohesive zone E. Massive zone F molten iron G. Molten slag H hot air J Bird's Nest Slug

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 reduced iron molded bodies obtained by compression molding reduced iron, the auxiliary fuel includes pulverized coal; the amount of reduced iron blended is 200 kg or more per ton of pig iron to be produced, a reducing agent ratio of the reducing agent containing the coke and the pulverized coal is 440 kg / tp or less, and a pulverized coal ratio is 130 kg / tp or more; A method for producing pig iron, wherein the lower furnace heat ratio is 0.5 or less.

2. the ore feedstock comprises fluxed pellets containing MgO; 2. The method for producing pig iron according to claim 1, wherein the fluxed pellets have an MgO content of 1.0 mass % or more and a basicity of 1.0 or more.

3. 3. A method for producing pig iron according to claim 1 or claim 2, wherein the oxygen enrichment rate of the hot air is 2.5% by volume or less.

4. 3. The method for producing pig iron according to claim 1 or claim 2, wherein the nitrogen enrichment rate of the hot air is 0% by volume or more.

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