Pig iron manufacturing method

Abstract

This disclosure aims to provide a pig iron manufacturing method that uses biomass while exhibiting excellent operational stability. [Solution] A pig iron manufacturing method according to one aspect of the present disclosure is a pig iron manufacturing method that uses a blast furnace having tuyeres to manufacture pig iron, comprising: a lamination step of alternately stacking a first layer containing ore raw materials and a second layer containing coke in the blast furnace; and a reduction and dissolution step of reducing and dissolving the stacked ore raw materials of the first layer while blowing auxiliary fuel into the blast furnace with hot air blown from the tuyeres, wherein the auxiliary fuel includes pulverized coal obtained by crushing coal and pulverized carbonized biomass obtained by crushing carbonized biomass, and in the reduction and dissolution step, the Bosch gas ratio is 1.6 Nm 3 / min / blast furnace volume m 3 More than 2.3Nm 3 / min / blast furnace volume m 3 The following conditions apply: the heat flow ratio is 0.7 or more and 0.9 or less; the temperature in front of the tuyere of the hot air is 1900°C or more and 2400°C or less; and the oxygen content of the hot air is 21% by volume or more and 26% by volume or less.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing pig iron. [Background technology]

[0002] A known method of producing pig iron involves alternately stacking a first layer containing ore raw materials and a second layer containing coke in a blast furnace, and reducing and melting the ore raw materials while blowing auxiliary fuel into the blast furnace with hot air supplied from tuyeres. In this method, the coke serves as a heat source for melting the ore raw materials, a reducing agent for the ore raw materials, a carburizing agent for carburizing the molten iron and lowering its melting point, and a spacer to ensure ventilation within the blast furnace. Maintaining ventilation with coke stabilizes the loading of the charges in the first and second layers, thereby ensuring stable operation of the blast furnace.

[0003] In addition, as auxiliary fuels (reducing agents), pulverized coal (PC; coal that has been finely ground to about 50 μm) and heavy oil are blown in through the tuyeres.

[0004] On the other hand, from the perspective of preventing global warming, reducing CO2 emissions has become an urgent issue in recent years. In the steel industry, CO2 emitted from blast furnaces accounts for a large proportion, about 70%, of the total CO2 emissions from steel mills, and there is a social demand for CO2 reduction at blast furnaces.

[0005] Specifically, in terms of CO2 reduction, along with the growing demand for the creation of a circular economy, there is a desire to move away from fossil fuels, similar to the energy sector, and the use of biomass, especially carbonized biomass, is attracting attention. Here, "carbonized biomass" refers to biomass in which biomass raw materials are heated in a dilute oxygen atmosphere to release volatile components and increase the carbon content, i.e., the calorific value.

[0006] Carbonized biomass has a CO2 emission factor of 0 t-CO2 / t-biomass and can significantly reduce CO2 emissions, so it has been proposed to use it as a substitute for the pulverized coal used as an auxiliary fuel (for example, Japanese Patent Publication No. 2011-117075). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2011-117075 [Overview of the project] [Problems that the invention aims to solve]

[0008] Carbonized biomass has characteristics such as a high volatile content, high oxygen content, and low calorific value compared to pulverized coal. When carbonized biomass is used as a substitute for pulverized coal, which is used as tuyeres-blown coal material, it is necessary to reduce the hot air supply rate, the amount of oxygen enriched in the hot air, or both, in order to maintain a constant pig iron output. In particular, reducing the air supply rate significantly lowers the Bosch gas amount (Bosch gas ratio). A decrease in the Bosch gas ratio may lead to abnormal raw material descent and other issues, potentially reducing the operational stability of the blast furnace. In addition, because the sensible heat of the air supply decreases, there is a concern that problems such as cooling may occur if the furnace temperature is not adjusted correctly.

[0009] This disclosure is made based on the circumstances described above and aims to provide a pig iron manufacturing method that uses carbonized biomass while exhibiting excellent operational stability. [Means for solving the problem]

[0010] The pig iron manufacturing method according to one aspect of the present disclosure is a pig iron manufacturing method for manufacturing pig iron using a blast furnace having tuyeres, including a stacking step of alternately stacking a first layer containing ore raw materials and a second layer containing coke in the blast furnace, and a reduction and melting step of reducing and melting the ore raw materials in the stacked first layer while blowing auxiliary fuel into the blast furnace with hot air blown from the tuyeres. The auxiliary fuel includes pulverized coal obtained by pulverizing coal and pulverized carbonized biomass obtained by pulverizing carbonized biomass. In the reduction and melting step, the bosh gas ratio is 1.6 Nm 3 / min / blast furnace volume m 3 or more and 2.3 Nm 3 / min / blast furnace volume m 3 or less, the heat flow ratio is 0.7 or more and 0.9 or less, the temperature of the hot air in front of the tuyere is 1900°C or more and 2400°C or less, and the oxygen ratio of the hot air is 21% by volume or more and 26% by volume or less.

Advantages of the Invention

[0011] The pig iron manufacturing method of the present disclosure is excellent in operation stability while using biomass.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a flowchart showing a pig iron manufacturing method according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing the inside of a blast furnace used in the pig iron manufacturing method of FIG. 1. [Figure 3] FIG. 3 is a diagram schematically showing the treatment performed at the tuyere in the reduction and melting step of FIG. 1. [Figure 4] FIG. 4 is a flowchart showing a pig iron manufacturing method according to an embodiment different from FIG. 1. [Figure 5] FIG. 5 is a graph showing the relationship between the bosh gas ratio and the slip number in the examples. [Figure 6] FIG. 6 is a graph showing the relationship between the adhesive force and the pressure loss during conveyance in the examples.

Modes for Carrying Out the Invention

[0013] [Description of Embodiments in this Disclosure] As a result of diligent research into the operational stability of blast furnaces using carbonized biomass, the Discloser discovered that the oxygen content of the hot air is key to operating at a suitable temperature in front of the tuyere, and thus completed the technology described herein.

[0014] In other words, (1) A pig iron manufacturing method according to one aspect of the present disclosure is a pig iron manufacturing method using a blast furnace having tuyeres, comprising: a lamination step of alternately stacking a first layer containing ore raw materials and a second layer containing coke in the blast furnace; and a reduction and dissolution step of reducing and dissolving the stacked ore raw materials of the first layer while blowing auxiliary fuel into the blast furnace with hot air blown from the tuyeres, wherein the auxiliary fuel includes pulverized coal obtained by crushing coal and pulverized carbonized biomass obtained by crushing carbonized biomass, and in the reduction and dissolution step, the Bosch gas ratio is 1.6 Nm 3 / min / blast furnace volume m 3 More than 2.3Nm 3 / min / blast furnace volume m 3 The following conditions apply: the heat flow ratio is 0.7 or more and 0.9 or less; the temperature in front of the tuyere of the hot air is 1900°C or more and 2400°C or less; and the oxygen content of the hot air is 21% by volume or more and 26% by volume or less.

[0015] This pig iron manufacturing method keeps the oxygen content of the hot air within the above range, making it possible to achieve a suitable balance between the Bosch gas ratio and the temperature in front of the hot air tuyeres within the above range. Furthermore, in conjunction with keeping the heat flow ratio within the above range, it is possible to improve the operational stability of the blast furnace when using carbonized biomass.

[0016] (2) In the reduction dissolution step of the pig iron production method described in (1) above, it is preferable to nitrogen-enrich the hot air. When carbonized biomass is used as an auxiliary fuel, the oxygen content tends to become too high due to the oxygen supply from the carbonized biomass itself. In contrast, by nitrogen-enriching the hot air, the hot air can be easily brought to the desired oxygen content.

[0017] (3) In the auxiliary fuel of the above pig iron manufacturing method of (1) or (2), the weight percentage value of the adhesion force between the fine coal and the fine carbonized biomass is 3.0 gf / cm 2 It is preferably below. By setting the weight percentage value of the adhesion force between the fine coal and the fine carbonized biomass to be below the above upper limit, it is possible to prevent fluctuations in the amount blown into the blast furnace due to adhesion to and peeling from the pipe wall when the auxiliary fuel is transported, thereby suppressing a decrease in the operational stability of the blast furnace.

[0018] (4) In any of the pig iron manufacturing methods of (1) to (3) above, the effective calorific value of the fine carbonized biomass is preferably 1400 kcal / kg or more. By setting the effective calorific value of the fine carbonized biomass in this way, the proportion of the fine carbonized biomass in the auxiliary fuel can be increased.

[0019] (5) In any of the pig iron manufacturing methods of (1) to (4) above, it is preferable to include a mixing and grinding process of mixing and grinding coal and carbonized biomass, and to include the mixture obtained in the above fine grinding process as the above auxiliary fuel. By mixing and grinding coal and carbonized biomass simultaneously in this way, it is possible to prevent uneven distribution of fine coal or fine carbonized biomass when blowing into the blast furnace, thereby increasing the operational stability of the blast furnace.

[0020] Here, "bosh gas" refers to the gas in the state at the moment when the hot air, added oxygen, moisture in the hot air, and auxiliary fuel containing fine coal blown from the tuyere are gasified at the tuyere, and "bosh gas ratio" refers to the value obtained by dividing the total amount of the above gas per minute (the theoretical calculated value in the standard state of the total amount of gas when the entire amount reacts to become N2, CO, and H2) by the furnace volume including up to the furnace bottom.

[0021] "Heat flow ratio" refers to the ratio (Ws / Wg) of the heat capacity Ws of the solid particles charged into the blast furnace to the heat capacity Wg of the gas in the furnace, and can be used as an operation index of the blast furnace.

[0022] "Tuyer temperature" refers to the temperature of the combustion zone calculated assuming that theoretical reactions such as the combustion of auxiliary fuels have completely occurred inside the furnace at the tuyer. It is the theoretical temperature Tf obtained by Equation 1 below from the sensible heat of the hot air, the heat of carbon combustion at the tuyer, and the endothermic heat from the water gasification reaction.

number

[0023] The oxygen in "oxygen ratio" includes the amount of oxygen and enriched oxygen in the venting gas, which is the air blown in from the tuyeres; the amount of oxygen contained in the pulverized coal; the amount of oxygen contained in the carbonized biomass; and the amount of oxygen in the transport gas, which is the gas used when transporting pulverized coal or carbonized biomass via pipelines. The total amount used as the basis for the oxygen ratio includes the amount of air or nitrogen as the transport gas, the amount of oxygen contained in the pulverized coal; the amount of nitrogen contained in the pulverized coal; the amount of oxygen contained in the carbonized biomass; the amount of air as the venting gas; the amount of enriched oxygen; and the amount of enriched nitrogen.

[0024] "Nitrogen enrichment" of hot air is an operation that increases the nitrogen concentration in the total gas by blowing in elemental nitrogen in addition to the blast air supplied to the furnace. The nitrogen is blown in along with the blast air from the blast furnace tuyeres.

[0025] [Details of the embodiments of this disclosure] The following describes in detail a pig iron manufacturing method according to one embodiment of this disclosure.

[0026] [First Embodiment] The pig iron manufacturing method shown in Figure 1 is a pig iron manufacturing method that uses the blast furnace 1 shown in Figure 2 to produce pig iron, and comprises a lamination step S1 and a reduction dissolution step S2.

[0027] <Blast furnace> As shown in Figure 2, the blast furnace 1 has tuyeres 1a and tapping port 1b located at the bottom of the furnace. Multiple tuyeres 1a are usually provided. The blast furnace 1 is a solid-gas counter-flow shaft furnace. Hot air, which is high-temperature air with high-temperature or room-temperature oxygen added as needed, is blown into the blast furnace 1 from the tuyeres 1a to carry out a series of reactions, such as the reduction and melting of the ore raw material 11 (described later), and pig iron can be extracted from the tapping port 1b. The blast furnace 1 is also equipped with a Bell Armor type raw material charging device 2. This raw material charging device 2 will be described later.

[0028] The lower limit of the furnace volume, which is the volume from the bottom of blast furnace 1 to the specified raw material charging line, is 2000 m³. 3 Preferably, 4000m 3 This is more preferable. The pig iron production method can be particularly suitably used in the operation of a blast furnace whose furnace volume is 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 production method can be suitably used is not particularly limited, and the larger the furnace volume, the suitably the pig iron production method functions. However, a practical upper limit for the furnace volume of the blast furnace 1 is 7000 m³. 3 It is to that extent.

[0029] <Lamination process> In the lamination process S1, as shown in Figure 2, the first layer 10 and the second layer 20 are alternately stacked inside the blast furnace 1. In other words, the number of layers in the first layer 10 and the second layer 20 is two or more.

[0030] (1st layer) The first layer 10 contains ore raw material 11. In the reduction and dissolution process S2, the ore raw material 11 is heated and reduced by hot air blown in from the tuyeres 1a to become molten iron F.

[0031] The ore raw material 11 refers to ores that serve as raw materials for iron, and mainly contains iron ore. Examples of ore raw material 11 include calcined ore (iron ore pellets, sintered ore), lump ore, agglomerated ore with carbonized interior, and metal (e.g., HBI: Hot Briquette Iron).

[0032] In addition to the ore raw material 11, auxiliary raw materials such as limestone, dolomite, and silica may also be charged into the first layer 10.

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

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

[0035] The lower limit of the coke ratio is preferably 200 kg / tp, and more preferably 230 kg / tp. On the other hand, the upper limit of the coke ratio is preferably 290 kg / tp, and more preferably 250 kg / tp. If the coke ratio is below the lower limit, it may not be possible to maintain stable operation of the blast furnace 1. Conversely, if the coke ratio exceeds the upper limit, it may become difficult to operate with a low reducing agent ratio. "Coke ratio" refers to the total mass (kg) of coke used as a reducing agent when producing 1 ton of pig iron, and the above coke includes coke charged in addition to the second layer 20.

[0036] (Lamination method) Various methods can be used to alternately stack the first layer 10 and the second layer 20. Here, we will explain the method using a blast furnace 1 equipped with a Bell Armor type raw material charging device 2 (hereinafter also simply referred to as "raw material charging device 2") as shown in Figure 2 as an example.

[0037] The raw material charging device 2 is located at the top of the furnace. In other words, the first layer 10 and the second layer 20 are charged from the top of the furnace. As shown in Figure 2, the raw material charging device 2 has a bell cup 2a, a lower bell 2b, and an armor 2c.

[0038] The bell cup 2a is filled with the raw materials to be charged. When charging the first layer 10, the raw materials constituting the first layer 10 are filled into the bell cup 2a, and when charging the second layer 20, the raw materials constituting the second layer 20 are filled into the bell cup 2a.

[0039] The lower bell 2b is cone-shaped and widens downwards, and is positioned inside the bell cup 2a. The lower bell 2b is movable up and down (in Figure 2, the upward position is shown by a solid line, and the downward position by a dashed line). When the lower bell 2b is moved upward, it seals the lower part of the bell cup 2a, and when it is moved downward, a gap is formed on the extension of the side wall of the bell cup 2a.

[0040] Armor 2c is located below the lower bell 2b and is installed on the furnace wall of the blast furnace 1. When the lower bell 2b is moved downward, raw materials fall through the gap, and armor 2c is a rebound plate that repels these falling materials. Furthermore, armor 2c is configured to move in and out toward the interior (center) of the blast furnace 1.

[0041] Using this raw material loading device 2, the first layer 10 can be stacked as follows. The same procedure applies to the second layer 20. Furthermore, the stacking of the first layer 10 and the second layer 20 is performed alternately.

[0042] First, the lower bell 2b is positioned upwards, and the raw material for the first layer 10 is loaded into the bell cup 2a. When the lower bell 2b is positioned upwards, the bottom of the bell cup 2a is sealed, and the above raw material is filled into the bell cup 2a. The amount filled is equal to the stacking amount of each layer.

[0043] Next, the lower bell 2b is moved downward. This creates a gap between it and the bell cup 2a, through which the raw material falls towards the furnace wall and collides with the armor 2c. The raw material, having collided with and been repelled by the armor 2c, is charged into the blast furnace 1. As the raw material falls while moving inward due to the repulsion from the armor 2c, it flows and accumulates towards the center of the blast furnace 1 from its landing position. Since the armor 2c is configured to move in and out toward the center, the landing position of the raw material can be adjusted by moving the armor 2c in and out. This adjustment allows the first layer 10 to be accumulated in a desired shape.

[0044] <Reduction and dissolution process> In the reduction and dissolution process S2, auxiliary fuel 40 is blown into the blast furnace 1 by hot air supplied from the tuyeres 1a, while the ore raw material 11 of the stacked first layer 10 is reduced and dissolved.

[0045] The blast furnace is operated continuously, and the reduction and dissolution process S2 is carried out continuously. On the other hand, the lamination process S1 is carried out intermittently, and depending on the reduction and dissolution status of the first layer 10 and the second layer 20 in the reduction and dissolution process S2, new first layers 10 and second layers 20 to be processed in the reduction and dissolution process S2 are added.

[0046] Figure 2 shows the state during the reduction dissolution process S2. As shown in Figure 2, the hot air from the tuyeres 1a causes the coke 21 to swirl around, forming a raceway A, which is a sparsely populated cavity near the tuyeres 1a. Inside the blast furnace 1, the temperature of this raceway A is the highest, at approximately 2000°C.

[0047] Figure 3 shows the state of the blast furnace 1 near the tuyere 1a and raceway A during the reduction dissolution process S2. The blast furnace 1 is provided with a cylindrical auxiliary fuel injection port 1c connected to the tuyere 1a, and the auxiliary fuel 40 is injected into the tuyere 1a from this auxiliary fuel injection port 1c.

[0048] The auxiliary fuel inlet 1c is positioned so that its outlet faces downstream of the hot air H, allowing the auxiliary fuel 40 to be carried by the hot air H blown in from the tuyere 1a, and the fine powder 41 to be blown deep into the raceway A.

[0049] The auxiliary fuel 40 includes a mixture 41 of pulverized coal 41a, which is obtained by crushing coal, and pulverized carbonized biomass 41b, which is obtained by crushing carbonized biomass. In addition to the mixture 41, heavy oil, natural gas, hydrogen-containing gas, etc., may also be included. The auxiliary fuel 40 functions as a heat source, reducing agent, and carburizing agent. In other words, it replaces the roles of coke 21, except for its role as a spacer.

[0050] The pulverized coal 41a is preferably finely ground to a particle size of 500 μm or less, preferably 100 μm or less. By keeping the maximum particle size of the pulverized coal 41a below the above upper limit, the specific surface area of ​​the pulverized coal 41a can be increased, thereby improving combustion efficiency.

[0051] Examples of carbonized biomass that can be used as the source for pulverized biomass 41b include woody materials (coniferous trees, broad-leaved trees, bamboo, thinned wood, waste wood, forestry waste, construction waste, etc.), agricultural residues (rice straw, sugarcane bagasse, CKS (coconut shells), PKS (palm kernel shells), corn, etc.), food waste (coffee grounds, etc.), and livestock waste. One type of carbonized biomass may be used, or multiple types may be mixed. An example of coal used in blast furnace tuyeres and the properties of the carbonized biomass are shown in Table 1.

[0052] To use biomass as a substitute for pulverized coal, which is used as coal material in blast furnace tuyeres, it is necessary to make the properties of the biomass closer to those of pulverized coal through carbonization and pulverization. For this reason, pulverized biomass 41b is used in this pig iron manufacturing method. In the carbonization process, the biomass raw material is heated in a dilute oxygen atmosphere to release volatile components and increase the carbon content. This increases the calorific value of the biomass. The presence or absence and degree of carbonization result in differences in components (especially carbon, oxygen, and volatile components) and calorific value. Increasing the heating temperature in the carbonization process and increasing the degree of carbonization increases the amount of volatile components released and decreases the weight of the carbonized biomass, but it is possible to improve the CO2 reduction effect in the blast furnace per unit weight of carbonized biomass.

[0053] [Table 1]

[0054] In Table 1, "VM" represents volatile components and "Ash" represents ash content, both as mass percent on an anhydrous basis, determined in accordance with the JIS Industrial Analysis Method for Coal JIS-M-8812 (2004). "C," "H," and "O" represent the carbon, hydrogen, and oxygen content, respectively, as mass percent on an anhydrous basis, determined in accordance with JIS-M-8819 (1997).

[0055] HGI stands for Hardgrove Grindability Index, an index indicating the ease of grinding coal, coke, and other materials. HGI can be measured in accordance with JIS-M-8801 (2008) using the following procedure: The air-dried material is adjusted to a particle size of 0.6 mm to 1.18 mm. 50 g of this material is placed in a sample mill, and a weight is placed on the mill's grinding wheel. After 60 rotations, the ground material is sieved. The percentage of coal that passes through a 200-mesh (74 μm) sieve is denoted as D, and the HGI is calculated from D as follows. Carbonized biomass was also measured in accordance with the above-mentioned JIS-M-8801 for coal. HGI = 13 + 6.93 × D ... 2

[0056] "Effective heat output" is the amount of heat generated in the lower part of the blast furnace when C becomes CO and H becomes H2 (heat output in the raceway). The effective heat output Qef is given by the following formula. Qef[kcal / kg] = Total calorific value - {57 × (%C) + 290 × (%H)} ...3 Here, "total calorific value" is the calorific value when C and H are completely combusted in the lower part of the blast furnace, and %C and %H are the proportions of C and H contained in the carbonized biomass, respectively (mass %; 0 ≤ %C, %H ≤ 100). This total calorific value is measured in accordance with JIS-M-8814 (2003).

[0057] The lower limit of the effective calorific value of pulverized biomass 41b is preferably 1400 kcal / kg, more preferably 1600 kcal / kg, and even more preferably 1800 kcal / kg. Increasing the amount of low-calorific-value carbon material injected into the auxiliary fuel 40 will increase the amount of unburned carbon material, making it impossible to secure sufficient heat. As shown in Table 1, carbonized biomass tends to have a lower effective calorific value than coal, so if the effective calorific value of pulverized biomass 41b is low, the amount of pulverized biomass 41b that can be substituted for pulverized coal 41a will be limited. On the other hand, by setting the effective calorific value of pulverized biomass 41b to be above the lower limit mentioned above, the proportion of pulverized biomass 41b in the auxiliary fuel 40 can be increased. The upper limit of the effective calorific value of pulverized biomass 41b is not particularly limited, but is usually 2000 kcal / kg or less. If multiple brands are used in the pulverized biomass 41b, the effective calorific value shall be the value prorated by weight.

[0058] In the auxiliary fuel 40, the upper limit of the weight-based allocation of cohesion between pulverized coal 41a and pulverized biomass 41b is 3.0 gf / cm². 2 Preferably, 2.5 gf / cm³ 2 This is more preferable. The pulverized coal 41a and pulverized biomass 41b are transported through the piping by air (or nitrogen) and blown into the furnace through the auxiliary fuel inlet 1c and the tuyeres 1a. If the cohesion of the mixture 41 of pulverized coal 41a and pulverized biomass 41b is high, powder adhesion and detachment from the pipe wall are likely to occur during transport, which may cause pressure loss fluctuations during transport. In addition, non-steady adhesion and detachment may cause fluctuations in the amount of fuel blown into the blast furnace, which may make stable operation difficult. By keeping the weight-based cohesion value below the above upper limit, such a decrease in the operational stability of the blast furnace can be suppressed. The lower limit of the weight-based cohesion value is not particularly limited and is 0 gf / cm 2 It may be possible, but theoretically it is 0 gf / cm 2 The adhesion strength can be measured by a shear test of the powder (pulverized coal 41a or pulverized biomass 41b).

[0059] The lower limit of the mixture ratio (the mass of mixture 41 blown in from the tuyeres when producing 1 ton of pig iron) is 130 kg / tp, with 150 kg / tp being more preferable. On the other hand, the upper limit of the mixture ratio is preferably 250 kg / tp, with 220 kg / tp being more preferable. If the mixture ratio is below the above lower limit, it may be difficult to reduce the coke ratio while maintaining the stability of blast furnace operation, and consequently, it may be difficult to reduce the reducing agent ratio. Conversely, if the mixture ratio exceeds the above upper limit, the amount of mixture 41 will be excessive, and it may be difficult to reduce the reducing agent ratio.

[0060] The injected auxiliary fuel 40 is mainly sprayed onto the coke 21 at the back of raceway A. As a result, the acidic slag derived from the molten ash of the mixture 41 at the back of raceway A increases, and a bird's nest slag layer J is formed, which is a slag layer where the slag with increased viscosity and melting point accumulates (holds up).

[0061] The hot air H (air and added oxygen) blown in from the tuyer 1a, the moisture contained in the hot air H, and the auxiliary fuel 40 containing the mixture 41 are converted into gas (Bosch gas) at the tuyer 1a.

[0062] The lower limit of the Bosch gas ratio is 1.6 Nm. 3 / min / blast furnace volume m 3 Therefore, 1.7 Nm 3 / min / blast furnace volume m 3 This is more preferable. On the other hand, the upper limit of the Bosch gas ratio is 2.3 Nm. 3 / min / blast furnace volume m 3 And, 2.2 Nm 3 / min / blast furnace volume m 3This is more preferable. In blast furnace operation, hot air H is blown in from tuyeres 1a attached around the lower part of the blast furnace, and CO gas is generated by burning the coke present in front of the tuyeres and the mixture 41 blown in simultaneously with the hot air H inside the furnace. Pig iron is obtained by heating and reducing the charged ore with the generated CO gas. If the amount of Bosch gas is small, the rising gas preferentially passes through the parts of the first layer 10 and second layer 20 where the voids are large, causing a deviation in the gas flow in the circumferential direction. This causes variation in the height of the fusion zone (the area where the ore layer softens and melts) in the circumferential direction, resulting in unstable operation (drop deviation, increased slip). A certain amount of Bosch gas is necessary to make the distribution of Bosch gas uniform in the circumferential direction, and this can usually be controlled by the Bosch gas ratio. If the Bosch gas ratio falls below the above lower limit, the above-mentioned phenomena may occur. Conversely, if the amount of Bosch gas is too high, an excess of gas is injected into the furnace, resulting in a larger gas pressure relative to the load of the charge, and thus an increase in furnace pressure drop. An increase in furnace pressure drop makes it difficult to maintain a stable load descent of the charge. Therefore, from the perspective of furnace pressure drop, the Bosch gas ratio should be kept below the above upper limit.

[0063] The lower limit of the heat flow ratio used as an operating indicator for blast furnace 1 is preferably 0.7, and more preferably 0.71. On the other hand, the upper limit of the flow ratio is preferably 0.9, and more preferably 0.89. The larger the heat flow ratio, the greater the descent of the ore raw material 11, which is the material to be heated, and the smaller the flow rate of the furnace gas, which is the heating medium. In this case, the heating of the ore raw material 11 is delayed, and fusion of the raw material does not occur until the ore raw material 11 descends to a lower level in the furnace, so the height of the fusion zone D becomes low. As a result, the amount of heat required for the preliminary reduction of the ore becomes insufficient, making ideal operation difficult. Conversely, if the heat flow ratio is small, the heating of the raw material proceeds quickly, and the height of the fusion zone D becomes high. If the height of the fusion zone D becomes too high, there is a risk of increased pressure loss due to the increase in the gas temperature at the top of the furnace (top gas temperature) and deterioration of the top equipment. Considering these factors, the heat flow ratio is set within the above range.

[0064] The lower limit of the temperature in front of the tuyere of the hot air H is 1900°C, with 2000°C being more preferable. On the other hand, the upper limit of the temperature in front of the tuyere is 2400°C, with 2390°C being more preferable. If the temperature in front of the tuyere is below the lower limit, the heat transfer properties to the molten iron may deteriorate. Conversely, if the temperature in front of the tuyere exceeds the upper limit, the reaction of formula 4 below will occur actively in the lower part of the fusion zone D from the raceway A. If the formation of SiO becomes vigorous due to the rise in the temperature in front of the tuyere, the SiO2 slag formed by re-oxidation will become a cause of shelf slag. For this reason, the temperature in front of the tuyere is kept below the upper limit. SiO2(s)+C(s) → SiO(g)+CO(g) ···4

[0065] The lower limit of the oxygen content of the hot air H is 21 vol%, with 22 vol% being more preferable. On the other hand, the upper limit of the oxygen content of the hot air H is 26 vol%, with 24 vol% being more preferable. Raceway A is a combustion space with a diameter of about 1.5 m, and it is desirable that the injected mixture 41 be burned as much as possible during the short time it passes through this narrow combustion space. This is because unburned mixture 41 (unburned pulverized coal 41a and unburned pulverized biomass 41b) accumulates in the furnace as unburned char, which worsens the air permeability and hinders stable operation. There are various methods to efficiently burn the mixture 41 and stabilize operations, but generally, a method of enriching with oxygen to increase the oxygen concentration in the combustion space (improving the reaction rate) is adopted. From the viewpoint of the combustion rate of the mixture 41, it is preferable to operate with an oxygen concentration higher than the normal oxygen concentration in the air. On the other hand, if the amount of injected oxygen is increased too much, the temperature in front of the tuyeres will rise. If the temperature in front of the tuyere is too high (for example, higher than 2400°C), the reaction in equation 4 above will occur actively in the lower part of the fusion zone D from raceway A. When the temperature in front of the tuyere rises and SiO formation becomes vigorous, the SiO2 slag formed by re-oxidation becomes a cause of shelf sagging, leading to deterioration of operation. From this perspective, the oxygen content of the hot air H should be kept below the above upper limit.

[0066] It is advisable to nitrogen-enrich the hot air (H). When using carbonized biomass as the auxiliary fuel (40), the oxygen content tends to become too high due to oxygen supply from the carbonized biomass itself. By nitrogen-enriching the hot air (H), the desired oxygen content can be easily achieved.

[0067] Adjacent to Raceway A, as shown in Figure 2, there is a core B inside the blast furnace 1, which is a pseudo-stagnation zone for coke. Above core B, there are a dripping zone C, a fusion zone D, and a lumpy zone E in that order.

[0068] The temperature inside blast furnace 1 rises from the top towards raceway A. In other words, the temperature is highest in the order of bulk zone E, fused zone D, and dripping zone C. For example, the temperature in bulk zone E is between 20°C and 1200°C, while the core B is between 1200°C and 1600°C. Note that the temperature of core B varies radially, and the temperature at the center of core B may be lower than that of dripping zone C. Furthermore, by stably circulating hot air in the center of blast furnace 1, a fused zone D with an inverted V-shaped cross-section is formed, ensuring air permeability and reducing properties inside blast furnace 1.

[0069] Inside the blast furnace 1, the iron ore raw material 11 is first heated and reduced in the massive zone E. In the fusion zone D, the ore reduced in massive zone E softens and shrinks. The softened and shrunk ore descends to become dripping slag 13 and moves to the dripping zone C. In the reduction and dissolution process S2, the reduction of the ore raw material 11 mainly proceeds in massive zone E, and the dissolution of the ore raw material 11 mainly occurs in the dripping zone C. In addition, in the dripping zone C and furnace core B, direct reduction proceeds in which the descending liquid iron oxide FeO directly reacts with the carbon of the coke 21.

[0070] Molten iron F, which is reduced iron that has melted, is deposited in the hearth, and molten slag G is deposited on top of the molten iron F. Both the molten iron F and the molten slag G can be removed from the tap 1b.

[0071] <Advantages> This pig iron production method maintains an oxygen content of 21% to 26% by volume in the hot air H, allowing the Bosch gas ratio and the temperature in front of the tuyeres of the hot air H to be set at suitable values ​​of 1.6 Nm3 / min / blast furnace volume m3 to 2.2 Nm3 / min / blast furnace volume m3 and 1900°C to 2400°C, respectively. Combined with a heat flow ratio of 0.7 to 0.9, this method enhances the operational stability of blast furnace 1 when using carbonized biomass.

[0072] [Second Embodiment] The pig iron manufacturing method shown in Figure 4 is a pig iron manufacturing method that uses a blast furnace 1 having a tuyeres 1a to produce pig iron, and comprises a lamination step S1 in which a first layer 10 containing ore raw material 11 and a second layer 20 containing coke 21 are alternately stacked in the blast furnace 1, and a reduction and dissolution step S2 in which auxiliary fuel 40 is blown into the blast furnace 1 with hot air H blown from the tuyeres 1a, while reducing and dissolving the ore raw material 11 in the stacked first layer 10, wherein the auxiliary fuel 40 includes pulverized coal 41a obtained by crushing coal and pulverized carbonized biomass 41b obtained by crushing carbonized biomass, and in the reduction and dissolution step S2, the Bosch gas ratio is 1.6 Nm 3 / min / blast furnace volume m 3 More than 2.2Nm 3 / min / blast furnace volume m 3 The following conditions apply: the heat flow ratio is 0.7 or more and 0.9 or less; the temperature in front of the tuyeres of the hot air H is 1900°C or more and 2400°C or less; and the oxygen content of the hot air H is 21% by volume or more and 26% by volume or less. Furthermore, the pig iron manufacturing method includes a mixing and fine grinding step S3.

[0073] <Blast furnace> Since blast furnace 1 is the same as blast furnace 1 in the first embodiment, a detailed explanation will be omitted.

[0074] <Lamination process> The lamination process S1 can be carried out in the same manner as the lamination process S1 of the first embodiment, so a detailed explanation will be omitted.

[0075] <Mixing and grinding process> In the mixing and grinding process S3, coal and carbonized biomass are mixed and ground together. In other words, when the carbonized biomass is ground, it is ground at the same time as the coal.

[0076] Grinding can be carried out using a roller mill, ball mill, or the like. The particle size of the ground coal and carbonized biomass is preferably 500 μm or less, and the average particle size is preferably 100 μm or less.

[0077] <Reduction and dissolution process> The reduction and dissolution step S2 is the same as the reduction and dissolution step S2 of the first embodiment, except that the mixture 41 obtained in the mixing and grinding step S3 is included as auxiliary fuel 40. Further explanation is omitted.

[0078] <Advantages> When pulverized coal 41a and pulverized biomass 41b are injected into the furnace separately using different transport lines, the type and amount of coal injected into each tuyeres will differ, causing deviations in the combustion behavior (combustion rate) in front of tuyeres 1a. This can lead to a deterioration of the blast furnace circumferential balance and, consequently, make it difficult to maintain stable blast furnace operation. In contrast, by mixing coal and biomass and crushing them simultaneously, it is possible to suppress the uneven distribution of pulverized coal 41a or pulverized biomass 41b when injected into the blast furnace 1, thereby increasing the operational stability of the blast furnace 1.

[0079] [Other embodiments] The above embodiments do not limit the configuration of the present invention. Therefore, the above embodiments allow for the omission, substitution, or addition of components of each part of the above embodiments based on the description herein and common technical knowledge, and all such omissions, substitutions, or additions should be interpreted as falling within the scope of the present invention.

[0080] In the above embodiment, the pig iron manufacturing method of the present invention was described in which it comprises only a lamination step and a melting step, but the pig iron manufacturing method may also include other steps.

[0081] For example, the pig iron manufacturing method may include a step of charging a mixture of coke and HBI into the center of the blast furnace. In this case, it is preferable that the proportion of HBI with a particle size of 5 mm or larger in the mixture is 90% by mass or more, and the total HBI content in the mixture is 75% by mass or less. When the hot air reaches the center of the blast furnace, it rises up through this center. By including HBI with a large particle size in the center in a content below the above upper limit, the sensible heat can be effectively utilized without obstructing the flow of the hot air. Therefore, the amount of coke used can be further reduced. Here, the "center" of the blast furnace refers to the region where the distance from the central axis of the blast furnace is 0.2Z or less, when the radius of the furnace mouth is Z.

[0082] In the above embodiment, the bell-armor method was described as the lamination process, but other methods can also be used. One such other method is the bell-less method. In the bell-less method, lamination can be performed while adjusting the angle of a rotating chute. [Examples]

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0084] <Number of slips> Blast furnace operation is continuous, and the stacked first and second layers melt down from the bottom during the reduction dissolution process described above, causing the entire structure to descend. While it is preferable for the descent to occur at a constant rate, abnormal descent can occur. The number of times this abnormal descent occurred was measured by varying the Bosch gas ratio, and this was recorded as the number of slips.

[0085] The number of slips was measured using a finger measuring device (mechanical measuring instrument) installed on top of the furnace to determine the rate at which the raw material descended. An abnormal descent was recorded if, after charging coke or ore and before charging the next material (coke or ore), the material descended at a rate 20% or more faster than the average speed even once. In other words, the number of abnormal descents was equal to the number of times an abnormal descent occurred in each set of materials as described above.

[0086] The Bosch gas ratio is determined by dividing the amount of Bosch gas by the volume of the blast furnace. Since the volume of the blast furnace is constant, the Bosch gas ratio was varied according to the amount of Bosch gas. The amount of Bosch gas was calculated by setting the airflow rate to 5600 Nm³. 3 / min or more 7200Nm 3 Ranges below / min, oxygen enrichment amount 0 Nm³ 3 / min or more 610Nm 3 Ranges below / min, nitrogen enrichment amount 0 Nm³ 3 / min or more 200Nm 3 Within a range of / min or less, with a fan humidity of 4.0 Nm³ 3 / min or more 55.0Nm 3 The range is less than or equal to / min, the amount of pulverized coal and pulverized biomass mixture blown in is in the range of 0 t / hr to 100 t / hr, the oxygen content in the above mixture is in the range of 2.4% to 5.5% by mass, the hydrogen content in the above mixture is in the range of 4.3% to 4.9% by mass, the nitrogen content in the above mixture is in the range of 1.6% to 2.3% by mass, and the amount of conveying air is 3700 Nm³ 3 / min or more 6800Nm 3 The value was adjusted by varying it within a range of / min or less.

[0087] The evaluation results for the number of slips are shown in Figure 5. From the results in Figure 5, the Bosch gas ratio was set to 1.6 Nm 3 / min / blast furnace volume m 3 As described above, it is possible to achieve stable operation with fewer slips.

[0088] <Adhesive strength> By changing the type of pulverized biomass and the mixing ratio with pulverized coal, the weight-based cohesion ratio between pulverized coal and pulverized biomass was altered, and the pressure loss during transport was measured. The results are shown in Figure 6.

[0089] From the results in Figure 6, the adhesive strength is 3.0 gf / cm². 2 It can be seen that the increase in pressure loss becomes significant when it exceeds this value. For this reason, in the auxiliary fuel, the weight-based cohesion ratio of pulverized coal and pulverized biomass is 3.0 gf / cm². 2 The following is preferable.

[0090] <Effective heat output> Based on the operating parameters required for blast furnace operation, a numerical analysis was performed using the RIST model (see Yoichi Ono: Iron and Steel, 1993, Vol.79, No.9, pp.618-624 and Yoichi Ono: Iron and Steel, 1993, Vol.79, No.10, pp.711-715) to determine the replacement rate when the effective calorific value of pulverized biomass is changed.

[0091] Here, the "replacement rate" refers to the amount of pulverized coal reduced relative to the amount of pulverized biomass injected when replacing pulverized coal with pulverized biomass, and is shown by equation 5 below. Replacement rate (%) = (Amount of pulverized coal replaced [kg / tp] × Total calorific value of pulverized coal [kcal / kg]) (Amount of finely ground carbonized biomass replacement [kg / tp]) ×Total calorific value of finely pulverized biomass [kcal / kg]) × 100 ... 5

[0092] When the above replacement rate exceeds 100%, the amount of pulverized coal reduced exceeds the amount of pulverized biomass injected, allowing for efficient CO2 reduction. The numerical analysis results showed that when the effective calorific value of pulverized biomass is 1400 kcal / kg or more, the above replacement rate exceeds 100%. Therefore, it is preferable that the effective calorific value of pulverized biomass be 1400 kcal / kg or more. [Industrial applicability]

[0093] The pig iron production method disclosed herein utilizes carbonized biomass while also offering excellent operational stability. Because it enables the use of carbonized biomass as a substitute for pulverized coal in blast furnaces, it is expected to significantly reduce CO2 emissions under stable operation conditions. [Explanation of Symbols]

[0094] 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. Ore raw materials 13. Dropping slag 20 2nd layer 21 Coke 40 Auxiliary fuel 41 mixture 41a Pulverized coal 41b Finely pulverized biomass A Raceway B Furnace core C. Dropping Zone D Fusion zone E. Blocky zone F Molten iron G Molten slag H hot air J Bird's Nest Slag

Claims

1. A method for producing pig iron using a blast furnace having tuyeres, The lamination process involves alternately stacking a first layer containing ore raw materials and a second layer containing coke within the blast furnace described above. A reduction and dissolution process is performed in which auxiliary fuel is blown into the blast furnace using hot air blown from the above tuyeres, while the stacked first layer of ore raw materials is reduced and dissolved. Equipped with, The above auxiliary fuel includes pulverized coal obtained by crushing coal and pulverized carbonized biomass obtained by crushing carbonized biomass. In the above reduction and dissolution process, The Bosch gas ratio is 1.6 Nm. ３ / min / blast furnace volume m ３ 2.3Nm or more ３ / min / blast furnace volume m ３ The following: The heat flow ratio is 0.7 or more and 0.9 or less. The temperature in front of the tuyer of the hot air mentioned above is between 1900°C and 2400°C. A method for producing pig iron, wherein the oxygen content of the hot air is 21% by volume or more and 26% by volume or less.

2. The method for producing pig iron according to claim 1, wherein the hot air is nitrogen-enriched in the reduction dissolution step described above.

3. In the above auxiliary fuel, the weight-based ratio of the cohesion between the pulverized coal and the pulverized biomass is 3.0 gf / cm². ２ The method for producing pig iron according to claim 1 or claim 2, which is as follows:

4. The pig iron production method according to claim 1 or claim 2, wherein the effective calorific value of the above-mentioned finely powdered carbonized biomass is 1400 kcal / kg or more.

5. It includes a mixed grinding process for mixing and grinding coal and carbonized biomass, A method for producing pig iron according to claim 1 or claim 2, comprising the mixture obtained in the fine grinding step as the auxiliary fuel.

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