Method for producing reduced iron

Abstract

One method for producing reduced iron disclosed herein is a method for producing reduced iron using a vertical shaft furnace, comprising the following steps: an iron oxide charging step of charging iron oxide raw materials into the vertical shaft furnace; and a blowing step of heating a reducing gas, primarily hydrogen, and then blowing it into the vertical shaft furnace, wherein the unit consumption of hydrogen is R (Nm³). 3 / t-DRI) and the blow-in temperature T (K) satisfy R≥0.0051T 2 -15.108T+12188. Preferably, the unit consumption of hydrogen R (Nm³) is... 3 / t-DRI) and the blow-in temperature T (K) satisfy R≤0.0068T 2 -19.792T+15771.

Description

Technical Field

[0001] This invention relates to a method for manufacturing reduced iron.

[0002] This application claims priority based on Japanese Patent Application No. 2023-213395 filed on December 18, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] The vertical shaft furnace method for producing reduced iron, also known as vertical shaft furnace operation, is a representative operation of the direct reduction process that uses iron oxide as raw material to produce reduced iron. Vertical shaft furnace operation is mainly prevalent in oil-producing countries and other regions where natural gas is readily available at low cost.

[0004] Here, a general description of the method for producing reduced iron using a vertical shaft furnace is provided. First, iron oxide raw material is charged into the vertical shaft furnace from the top. The iron oxide raw material is the raw material for reduced iron, with iron oxide as the main component. Examples of iron oxide raw material are iron oxide particles and lump ore. Next, reducing gas is blown into the vertical shaft furnace from the bottom. Here, the reducing gas is heated to a predetermined temperature before being blown into the furnace. The temperature of the reducing gas is, for example, around 900–950°C. Then, the reducing gas blown into the furnace reduces the iron oxide raw material inside. Reduced iron can be produced through this direct reduction process. The reduced iron is discharged from the bottom of the furnace and cooled.

[0005] The exhaust gas discharged from the top of the vertical shaft furnace, containing hydrogen, CO, water vapor, and CO2, is called top gas. After removing water vapor from the top gas, the hydrogen and CO in the top gas are reused as part of the feed gas. In addition, after removing water vapor from the top gas, it is also possible to remove CO2.

[0006] The reducing gas used in a vertical shaft furnace is produced from feed gas containing carbon. Feed gas examples include natural gas and coke oven gas. The reducing gas can be obtained by modifying the feed gas using steam, CO2, or oxygen. Alternatively, sometimes the feed gas is used directly as the reducing gas in the vertical shaft furnace without modification. The main components of a typical reducing gas are hydrogen (H2), CO, and CH4.

[0007] However, in recent years, in order to further reduce CO2 emissions, technologies using pure hydrogen as a reducing gas have been proposed. For example, Patent Document 1 describes a technology that uses hydrogen separated from coke oven gas (COG) via the PSA process as a reducing gas. Patent Document 2 describes a technology that uses hydrogen obtained through electrolysis as a reducing gas.

[0008] Existing technical documents Patent documents Patent Document 1: U.S. Patent No. 9938594B2 Patent Document 2: International Publication No. 2022-169392 Non-patent literature Non-Patent Literature 1: Hara Yukiaki et al., "Mathematical Model of Shaft Furnace for Iron Ore Reduction", Iron and Steel, Japan, Japan Iron and Steel Association, 1976, Vol. 62, No. 3, p. 315 Non-Patent Literature 2: Hideyuki Yamaoka et al., “Three-Dimensional Mathematical Models of Vertical Reduction Furnaces and Cupola-Type Melting Furnaces”, Iron and Steel, Japan, Japan Iron and Steel Association, 1988, Vol. 74, No. 12, p. 2254 Summary of the Invention

[0009] The problem that the invention aims to solve However, when using hydrogen-based gases as the reducing gas, the specific operating conditions for shaft furnace operation are not yet understood. In particular, the unit consumption of hydrogen required to produce reduced iron is unknown.

[0010] Therefore, the present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a method for manufacturing reduced iron that can achieve a high metallization rate.

[0011] Methods for solving problems The main points of this invention are as follows.

[0012] (1) One aspect of the present invention is a method for manufacturing reduced iron using a vertical shaft furnace, comprising the following steps: a step of charging iron oxide raw material into a vertical shaft furnace; and a step of blowing a reducing gas, mainly hydrogen, into the vertical shaft furnace, wherein the unit consumption of the hydrogen is R (Nm³). 3 / t-DRI) and the blow-in temperature T (K) satisfy the following mathematical formula (1).

[0013] R≥0.0051T 2 -15.108T+12000 (1) (2) Preferably, in the method for manufacturing reduced iron described in (1) above, the unit consumption of hydrogen R (Nm³) is... 3 / t-DRI) and the above blow-in temperature T (K) satisfy the following mathematical formula (2).

[0014] R≤0.0068T 2 -19.792T+15771 (2) (3) Preferably, in the method for manufacturing reduced iron described in (1) or (2) above, the unit consumption of hydrogen R (Nm³) is... 3 / t-DRI) and the above blow-in temperature T (K) satisfy the following mathematical formula (3).

[0015] R≥0.0051T 2 -15.108T+12188 (3) (4) Preferably, in the method for manufacturing reduced iron according to any one of (1) to (3) above, the blowing temperature T is controlled based on the unit consumption R of hydrogen gas.

[0016] (5) Preferably, in the method for manufacturing reduced iron according to any one of (1) to (3) above, the unit consumption of hydrogen R is controlled based on the blowing temperature T.

[0017] Invention Effects According to the present invention, a method for manufacturing reduced iron that can achieve a high metallization rate is provided. Attached Figure Description

[0018] Figure 1 The figure shows the unit hydrogen consumption R (Nm³) for each metallization rate (%) of reduced iron. 3 A graph showing the relationship between / t-DRI) and the blow-in temperature T (K).

[0019] Figure 2 This is a schematic diagram showing the configuration of the reduced iron manufacturing apparatus according to this embodiment. Detailed Implementation

[0020] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] <1. Based on the inventor's understanding of this invention> First, the inventors' understanding, which forms the basis of this embodiment, will be explained. The degree of reduction of the iron oxide raw material charged into the shaft furnace is evaluated by the metallization rate of the reduced iron. The metallization rate of the reduced iron can be expressed as a function of the hydrogen concentration of the reducing gas blown into the shaft furnace, the blowing temperature of the reducing gas, the blowing amount of the reducing gas, and the blowing time of the reducing gas. The inventors of this invention have made the following simplifications with the aim of benefiting the design and efficient operation of the shaft furnace.

[0022] • The hydrogen concentration of the reducing gas is 100% by volume. • The amount and time of reducing gas blown in are combined to calculate the unit hydrogen consumption (Nm³). 3 / t-DRI) It should be noted that the metallization rate of reduced iron is the relative ratio of the amount of metallic iron in the reduced iron discharged from the shaft furnace to the total iron content of the reduced iron discharged from the shaft furnace. The total iron content is determined by the test specified in JIS M 8212:2005 "Iron ore - Quantitative method for total iron". Furthermore, the amount of metallic iron is determined by the test specified in ISO 5416:2006 (bromomethanol titration method).

[0023] As a result, the metallization rate of reduced iron becomes the unit hydrogen consumption R (Nm³). 3 The function of / t-DRI) and the blowing temperature T (K) was then derived by the inventors of this invention through simulation using a mathematical model of the shaft furnace. This model was constructed, for example, based on chemical engineering methods described in Non-Patent Documents 1 and 2. This model can theoretically analyze and estimate thermal and mass movement within the shaft furnace, such as chemical reactions and heat transfer phenomena, exemplified by the reduction reaction of hydrogen-based iron oxide feedstock. Using this mathematical model, the operation of a shaft furnace using hydrogen was simulated, and macroscopic thermal and mass movement was evaluated.

[0024] The calculation conditions are as shown in Table 1. The conditions other than the hydrogen reduction rate constant are equivalent to the operating conditions of the shaft furnace and its peripheral equipment.

[0025] The residence time (in minutes) in Table 1 refers to the time that the iron oxide feedstock, charged from the furnace top, remains in the region in contact with hydrogen, which is the reducing gas. Specifically, the residence time is the time that the iron oxide feedstock remains in the region from the hydrogen inlet to the charging position at the furnace top. The region in contact with the hydrogen is the region where the iron oxide feedstock is reduced by the hydrogen.

[0026] The iron oxide raw material is set to be at least 90% by mass of iron oxide particles.

[0027] Unit consumption of hydrogen (Nm³) 3 / t-DRI) is the flow rate of hydrogen required to produce 1 ton of reduced iron (DRI). For example, the unit hydrogen consumption is calculated by dividing the amount of hydrogen used per unit time by the amount of reduced iron produced per unit time. The amount of hydrogen used per unit time can be derived by measuring the flow rate and composition of the reducing gas at the inlet and outlet of the shaft furnace using flow meters and gas chromatography. The amount of reduced iron produced per unit time can be derived by measuring the weight of the reduced iron discharged from the shaft furnace using force sensors. Alternatively, the amount of reduced iron produced can also be calculated using the following formula.

[0028] Reduced iron production rate (t-DRI / hr) = Raw material loading rate (t-Raw material / hr) - {Reducing gas output weight (t-Output gas / hr) - Reducing gas input weight (t-Input gas / hr)} The weight of the reducing gas at the outlet side and the weight of the reducing gas at the inlet side of the vertical shaft furnace can be derived from their flow rate and gas composition.

[0029] The hydrogen blowing temperature (K) is the temperature of the hydrogen gas when it is blown into the vertical shaft furnace.

[0030] The furnace top pressure refers to the gas pressure at the top of the vertical furnace.

[0031] Raw material particle size refers to the particle size (mm) of the iron oxide raw material. Particle size can be determined by sieving.

[0032] Porosity is the ratio of the volume of pores within a particle to the apparent volume of the raw material particles. The method for determining porosity is specified in JISM 8716:1990, "Iron ore particles – Apparent density and porosity calculation method".

[0033] The hydrogen reduction rate constant represents the rate of reduction reaction using hydrogen. It is defined as the velocity (m / s) of the reaction interface within the particle per unit time.

[0034] [Table 1] The simulation results are shown in Figure 1 middle. Figure 1 The horizontal axis represents the temperature (K) at which hydrogen is blown in. Figure 1 The vertical axis represents the unit consumption of hydrogen (Nm³). 3 / t-DRI). Curve L1 represents the unit hydrogen consumption R (Nm³) when the metallization rate of reduced iron reaches 92%. 3 The relationship between / t-DRI) and the blowing temperature T (K). Curve L2 shows the unit hydrogen consumption R (Nm³) when the metallization rate of reduced iron reaches 96%. 3 The relationship between / t-DRI) and the blowing temperature T (K). Curve L3 shows the unit hydrogen consumption R (Nm³) when the metallization rate of reduced iron reaches 100%. 3 The relationship between / t-DRI) and the blowing temperature T (K). Curve L4 shows the unit hydrogen consumption R (Nm³) when the metallization rate of reduced iron reaches 88%. 3 The relationship between / t-DRI) and the blow-in temperature T (K).

[0035] Curve L1 is represented by the following mathematical expression (3'), and curve L3 is represented by the following mathematical expression (2'). In mathematical expressions (3') and (2'), R is the unit consumption of hydrogen (Nm³). 3 / t-DRI), where T is the hydrogen blowing temperature (K). For example, from Figure 1 As indicated, it is known that there is a correlation between the unit consumption of hydrogen and the hydrogen injection temperature, and this correlation varies depending on the metallization rate of the reduced iron.

[0036] R=0.0051T 2 -15.108T+12188 (3') R=0.0068T 2 -19.792T+15771 (2') Considering practical operation, a higher metallization rate of reduced iron is preferred. Therefore, the preferred unit hydrogen consumption R (Nm³) is... 3 / t-DRI) and the blowing temperature T (K) satisfy the following mathematical formula (1). Thus, the metallization rate of reduced iron can be significantly improved.

[0037] R≥0.0051T 2 -15.108T+12000 (1) Furthermore, the unit consumption of hydrogen, R (Nm³), is further optimized. 3 / t-DRI) and the blowing temperature T (K) satisfy the following mathematical formula (3). Therefore, the metallization rate of reduced iron can be further improved. It is believed that by controlling the unit consumption of hydrogen R and the blowing temperature T in accordance with the mathematical formula (3) under the conditions recorded in Table 1, the metallization rate of reduced iron can be set to 92% or more.

[0038] R≥0.0051T 2 -15.108T+12188 (3) On the other hand, if hydrogen is blown in at a metallization rate exceeding 100%, it results in excessive hydrogen being blown into the shaft furnace. Therefore, the preferred unit hydrogen consumption R (Nm³) is... 3 / t-DRI) and the blow-in temperature T (K) further satisfy the following mathematical formula (2).

[0039] R≤0.0068T 2 -19.792T+15771 (2) By adjusting the unit consumption of hydrogen and the blowing temperature in accordance with mathematical formula (1), the metallization rate of reduced iron can be sufficiently improved. Furthermore, by adjusting the unit consumption of hydrogen and the blowing temperature in accordance with mathematical formula (2), excessive hydrogen blowing can be avoided. The method for manufacturing reduced iron in this embodiment is based on the above understanding.

[0040] It should be noted that, instead of mathematical formula (1), the following mathematical formula (4) can also be used to specify the unit consumption R of hydrogen and the blowing temperature T.

[0041] R≥0.0051T 2 -15.108T+X (4) Where X is any number greater than 12000. When X is 12188, mathematical formula (4) becomes the same as mathematical formula (3) above. In mathematical formula (4), X can also be set to 12050, 12100, 12200, 12300, 12500, 12500 or 12600. If X is increased, the lower limit of the unit consumption R of hydrogen increases, and the metallization rate of reduced iron is further improved.

[0042] In addition, instead of mathematical formula (2), the following mathematical formula (5) can also be used to specify the unit consumption R of hydrogen and the blowing temperature T.

[0043] R≤0.0068T 2 -19.792T+Y (5) Where Y is any number below 15771. In mathematical formula (5), Y can also be set to 15700, 15600, 15500, 15400 or 15300. If Y is reduced, the upper limit of the unit consumption R of hydrogen is reduced, which can further reduce the amount of hydrogen used.

[0044] Alternatively, instead of mathematical formula (1), the following mathematical formula (6) can be used to specify the unit consumption R of hydrogen and the blowing temperature T.

[0045] R≥0.0062T 2 -18.066T+14388 (6) In mathematical formula (6), R is the unit consumption of hydrogen (Nm³). 3 / t-DRI), where T is the hydrogen blowing temperature (K). Mathematical formula (6) is related to... Figure 1 The mathematical formula corresponding to the curve L2. By adjusting the unit consumption of hydrogen and the blowing temperature in accordance with the mathematical formula (6), the metallization rate of reduced iron can be set to about 96% or more.

[0046] <2-1. Apparatus for Manufacturing Reduced Iron> Next, based on Figure 2 The apparatus 1A for manufacturing reduced iron according to this embodiment will be described. Figure 2 As shown, the reduced iron manufacturing apparatus 1A of this embodiment includes a vertical shaft furnace 1, a heating furnace 2, and a dehydration device 3. The vertical shaft furnace 1 is the same as conventional ones. That is, iron oxide raw material 4 is charged from the top of the vertical shaft furnace 1. There are no particular restrictions on the type of iron oxide raw material 4, as long as it is operated in the same way as conventional vertical shaft furnaces. Examples of iron oxide raw material 4 include iron oxide particles. The iron oxide raw material 4 preferably contains more than 90% by mass of iron oxide particles, and more preferably consists only of iron oxide particles. Examples of iron oxide raw material 4 other than iron oxide particles include lump ore, sinter, and unburned lump compounds.

[0047] On the other hand, reducing gas 5 is blown into the vertical shaft furnace 1 from the side below. The reducing gas 5 blown into the vertical shaft furnace 1 rises within it. The reducing gas 5 reduces the iron oxide raw material 4 within the vertical shaft furnace 1, generating reduced iron (DRI) 6. The reduced iron 6 is discharged from the bottom of the vertical shaft furnace 1 and cooled. The metallization rate of the reduced iron 6 is preferably set to, for example, 92% or higher. Meanwhile, top gas 7 (exhaust gas) is discharged from the top of the vertical shaft furnace 1. The top gas 7 contains, in addition to unreacted hydrogen, water vapor, dust, CO2 gas, etc. The top gas 7 is dedusted using a dust removal device (not shown), and after further removing CO2 gas by chemical adsorption or the like, it is introduced into a dehydration device 3. The dehydration device 3 dehydrates the top gas 7. This generates hydrogen gas. The generated hydrogen gas is introduced into a heating furnace 2.

[0048] A reducing gas 5 is introduced into the heating furnace 2. The reducing gas 5 is primarily composed of hydrogen, preferably hydrogen. Specifically, the reducing gas 5 preferably contains hydrogen at a proportion of 90% by volume or more. Other gases may also be included in the reducing gas 5 at a proportion of 10% by volume or less. Examples of other gases include CO gas, CO2 gas, H2O gas (water vapor), CH4 gas, etc. The hydrogen can be obtained by electrolysis of hydrogen, separation of hydrogen from coke oven gas (COG) or gas obtained through water gas shift reaction using the PSA method or membrane separation method.

[0049] After heating the reducing gas 5 to a predetermined temperature, the heating furnace 2 blows it into the vertical furnace 1. The temperature of the reducing gas 5 when it is blown into the vertical furnace 1 is called the blowing temperature. The heating furnace 2 can be implemented by existing electric furnaces, etc. The heating furnace 2 heats the reducing gas 5 in a manner that satisfies the above mathematical formula (1), preferably further satisfies mathematical formula (2). That is, the amount of hydrogen introduced into the heating furnace 2 and the heating temperature obtained by the heating furnace 2 are adjusted in a manner that satisfies mathematical formula (1), preferably further satisfies mathematical formula (2).

[0050] The heating furnace 2 and the vertical furnace 1 are connected by piping. Reducing gas 5 is blown into the vertical furnace 1 through this piping. The blowing temperature of the reducing gas 5 is measured, for example, using a thermocouple. The thermocouple is installed at the connection between the piping and the vertical furnace 1. The blowing temperature of the reducing gas 5 is measured using this thermocouple. The thermocouple can also be installed anywhere within the piping or at the outlet of the heating furnace 2.

[0051] <2-2. Methods for manufacturing reduced iron> Next, the method for manufacturing reduced iron using the manufacturing apparatus 1A that uses reduced iron will be described. This manufacturing method includes the following steps: an iron oxide charging step of charging iron oxide raw material 4 into a vertical shaft furnace 1; and a blowing step of heating a reducing gas 5, which is mainly composed of hydrogen, and then blowing it into the vertical shaft furnace 1.

[0052] In the blowing process, one or both of the unit consumption of hydrogen R and the blowing temperature T are controlled in a manner that satisfies the above mathematical formula (1), preferably further satisfies mathematical formula (2). There are no particular limitations on the means of controlling these values.

[0053] For example, the blowing temperature T can be controlled based on the unit consumption R of hydrogen. In this case, only the blowing temperature T is controlled. If the blowing temperature T is increased, the lower limit of the unit consumption R of hydrogen required to ensure a high metallization rate decreases. Therefore, by increasing the blowing temperature T, the amount of reducing gas 5 blown in can be reduced. The blowing temperature T can be set to any value by changing the output power of the heating furnace 2. After being heated by the heating furnace 2, the reducing gas 5 is blown into the vertical furnace 1.

[0054] Furthermore, the unit consumption R of hydrogen can also be controlled based on the blowing temperature T. In this case, only the unit consumption R of hydrogen is controlled. When there are certain constraints on the blowing temperature T, it is preferable to satisfy the above mathematical formula by controlling the unit consumption R of hydrogen. The unit consumption R of hydrogen can be set to any value by changing the blowing rate of reducing gas 5 or the production rate of reduced iron. If the blowing rate of reducing gas 5 is increased, the lower limit of the blowing temperature T required to ensure a high metallization rate decreases. Therefore, by increasing the blowing rate of reducing gas 5, the blowing temperature T of reducing gas 5 can be reduced.

[0055] Of course, the blowing temperature T and the unit consumption of hydrogen R can also be controlled in a way that satisfies the above mathematical formula.

[0056] The reducing gas 5, blown into the vertical shaft furnace 1, rises within the furnace. The reducing gas 5 reduces the iron oxide raw material 4 within the furnace 1, producing reduced iron (DRI) 6. The reduced iron 6 is discharged from the bottom of the furnace 1 and cooled. The metallization rate of the reduced iron 6 is preferably set to, for example, 92% or higher. Meanwhile, top gas 7 (exhaust gas) is discharged from the top of the furnace 1. The top gas 7 is dedusted using a dust removal device (not shown), and after further removing CO2 gas by chemical adsorption or the like, it is introduced into a dehydration device 3. The dehydration device 3 dehydrates the top gas 7, thereby generating hydrogen gas. The generated hydrogen gas is then introduced into a heating furnace 2.

[0057] It should be noted that there are no particular restrictions on other operating conditions. For example, the reduced iron manufacturing apparatus 1A can be operated according to the operating conditions shown in Table 1. On the other hand, it can also be operated under operating conditions other than those shown in Table 1. For example, the residence time can exceed 70 minutes. The longer the residence time, the longer the time required to manufacture reduced iron becomes, and on the other hand, the metallization rate of reduced iron becomes higher. Extending the residence time will not adversely affect the metallization rate of reduced iron.

[0058] According to this embodiment, the reduced iron manufacturing apparatus 1A having a shaft furnace 1 is operated in a manner that satisfies mathematical formula (1), and preferably further satisfies mathematical formula (2). Therefore, the unit consumption amount R of hydrogen required to produce reduced iron 6 can be determined. Thus, the minimum unit consumption amount R of hydrogen required to obtain reduced iron 6 can be determined. By setting the amount of hydrogen blown into the shaft furnace 1 to a minimum, the hydrogen supply mechanism in the shaft furnace 1 and its peripheral equipment can be miniaturized and simplified. Therefore, according to this embodiment, the design and operation of the shaft furnace 1 and its peripheral equipment can be carried out effectively.

[0059] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the examples described. Those skilled in the art will readily conceive of various modifications or alterations within the scope of the technical concept described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0060] Explanation of symbols 1A Apparatus for manufacturing reduced iron 1 Vertical shaft furnace 2 Heating Furnace 3. Dehydration device 4. Iron oxide raw materials 5 Reducing Gas 6. Reduced iron 7. Furnace Top Gas T blow-in temperature R represents the unit consumption of hydrogen gas.

Claims

1. A method for manufacturing reduced iron, characterized in that, It uses a vertical shaft furnace to produce reduced iron, and includes the following steps: The process of charging iron oxide raw materials into a vertical shaft furnace; and The process of blowing a reducing gas, mainly hydrogen, into the vertical furnace. The hydrogen gas in Nm 3 The unit consumption R of the / t-DRI meter and the blow-in temperature T in K satisfy the following mathematical formula (1). R≥0.0051T 2 -15.108T+12000 (1)。 2. The method for manufacturing reduced iron according to claim 1, characterized in that, The hydrogen gas in Nm 3 The unit consumption R of the / t-DRI meter and the blow-in temperature T in K satisfy the following mathematical formula (2). R≤0.0068T 2 -19.792T+15771 (2).

3. The method for manufacturing reduced iron according to claim 1 or 2, characterized in that, The hydrogen gas in Nm 3 The unit consumption R of the / t-DRI meter and the blow-in temperature T in K satisfy the following mathematical formula (3). R≥0.0051T 2 -15.108T+12188 (3)。 4. The method for manufacturing reduced iron according to claim 1 or 2, characterized in that, The blowing temperature T is controlled based on the unit consumption R of the hydrogen.

5. The method for manufacturing reduced iron according to claim 1 or 2, characterized in that, The unit consumption R of hydrogen is controlled based on the blowing temperature T.

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