Method and apparatus for manufacturing reduced iron

Abstract

The method for manufacturing reduced iron includes the following steps: an iron oxide charging step of charging iron oxide raw material into a vertical shaft furnace; a partial combustion step of heating the raw material gas to 800°C or higher by partially burning the raw material gas with oxygen to generate reducing gas; and a blowing step of blowing the reducing gas into the vertical shaft furnace. In the blowing step, when the temperature of the reducing gas after the partial combustion step is 800°C or higher but lower than 900°C, the water vapor concentration of the reducing gas is set to 21% by volume or lower; when the temperature of the reducing gas after the partial combustion step is 900°C or higher but lower than 1000°C, the water vapor concentration of the reducing gas is set to 23% by volume or lower; and when the temperature of the reducing gas after the partial combustion step is 1000°C or higher, the water vapor concentration of the reducing gas is set to 24% by volume or lower.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2023-213399, filed on December 18, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] The method for producing reduced iron using a shaft furnace (shaft furnace operation) is a representative operation of the direct reduction process for producing reduced iron from iron oxide feedstock, and is mainly popular in regions where natural gas is readily available at low cost (oil-producing countries). Here, a general overview of the method for producing reduced iron using a shaft furnace is provided. First, iron oxide feedstock (e.g., iron oxide granules) is charged into the shaft furnace from the top, and reducing gas is blown in from the bottom. The reducing gas is heated to a specified temperature (e.g., around 900–950°C) and then blown into the shaft furnace. The reducing gas blown into the shaft furnace then reduces the iron oxide feedstock within the furnace. Reduced iron can be produced through this direct reduction process. The reduced iron is discharged from the bottom of the shaft furnace and cooled. A top gas (exhaust gas) containing hydrogen, CO, water vapor, and CO2 is discharged from the top of the shaft furnace. After removing water vapor from the top gas, the hydrogen and CO in the top gas are reused as part of the feedstock gas. Furthermore, after removing water vapor from the top gas, it is also possible to remove CO2.

[0004] The reducing gas used in a vertical shaft furnace (blown into the furnace) is obtained by modifying carbon-containing feedstock gases (such as natural gas, coke oven gas, etc.) using steam, CO2, or oxygen. However, when the feedstock gases are modified inside the furnace, they may also be used directly as reducing gases without modification. The main components of the reducing gas are hydrogen (H2), CO (CO), and CH4.

[0005] However, in recent years, in order to further reduce CO2 emissions, technologies to increase the concentration of hydrogen in reducing gases have been studied. For example, Patent Document 1 discloses a technology that uses a reducing gas with a hydrogen concentration of 70% by volume or more. In the technology disclosed in Patent Document 1, the reducing gas is heated by utilizing heat exchange (heat exchange) of waste gas, heating by a heating furnace, and partial combustion of the reducing gas using oxygen.

[0006] Existing technical documents Patent documents Patent Document 1: International Publication No. 2022-169392 Summary of the Invention

[0007] The problem that the invention aims to solve However, when hydrogen is partially burned, water (steam) is generated. Steam generally delays the reduction reaction of iron oxide raw materials in the shaft furnace, thus reducing the reduction rate (productivity) of reduced iron due to the generation of steam.

[0008] The present invention was made in view of the above-mentioned problems. The object of the present invention is to provide a novel and improved method for producing reduced iron with a high reduction rate, even when hydrogen is partially combusted, and an apparatus suitable for producing reduced iron using the method.

[0009] Methods for solving problems The main points of this invention are as follows.

[0010] [1] A method for manufacturing reduced iron according to one aspect of the present invention includes the following steps: an iron oxide charging step of charging iron oxide raw material into a vertical furnace; a partial combustion step of heating the raw material gas to 800°C or higher by partially burning the raw material gas with oxygen to generate a reducing gas; and a blowing step of blowing the reducing gas into the vertical furnace. In the blowing step, when the temperature of the reducing gas after the partial combustion step is 800°C or higher and lower than 900°C, the water vapor concentration of the reducing gas is set to 21% by volume or lower; when the temperature of the reducing gas after the partial combustion step is 900°C or higher and lower than 1000°C, the water vapor concentration of the reducing gas is set to 23% by volume or lower; and when the temperature of the reducing gas after the partial combustion step is 1000°C or higher, the water vapor concentration of the reducing gas is set to 24% by volume or lower.

[0011] [2] In the method for manufacturing reduced iron described in [1], in the blowing process, the water vapor concentration of the reducing gas can be set to 10% by volume or less when the temperature of the reducing gas after the partial combustion process is 800°C or higher and lower than 900°C, the water vapor concentration of the reducing gas can be set to 17% by volume or less when the temperature of the reducing gas after the partial combustion process is 900°C or higher and lower than 1000°C, and the water vapor concentration of the reducing gas can be set to 19% by volume or less when the temperature of the reducing gas after the partial combustion process is 1000°C or higher.

[0012] [3] In the method for manufacturing reduced iron described in [1], the raw material gas may also contain hydrogen as a main component.

[0013] [4] In the method for manufacturing reduced iron described in [2], the raw material gas may also contain hydrogen as a main component.

[0014] [5] In any of the methods for manufacturing reduced iron in [1] to [4], in the partial combustion process described above, the raw material gas and the oxygen may be introduced into a heating furnace and the raw material gas may be partially combusted in the heating furnace.

[0015] [6] In the method for manufacturing reduced iron described in [3] or [4], in the partial combustion process described above, the raw material gas at a temperature below 100°C may be heated to a temperature above 897°C by partial combustion using the oxygen described above.

[0016] [7] In the method for manufacturing reduced iron described in [3] or [4], in the partial combustion process described above, the raw material gas at a temperature below 100°C may be heated to a temperature above 969°C by partial combustion using the oxygen described above.

[0017] [8] In any of the methods for manufacturing reduced iron in [1] to [4], a preheating step may be included to preheat the raw material gas, and in the partial combustion step, the preheated raw material gas is partially combusted using the oxygen.

[0018] [5] In the method for manufacturing reduced iron described in [8], the raw material gas can also be preheated by utilizing the sensible heat contained in the exhaust gas of the vertical furnace in the preheating process described above.

[0019]

[10] In the method for manufacturing reduced iron described in [9], a circulation process may also be included in which hydrogen obtained by dehydrating the waste gas after the above preheating process is introduced into the heating furnace.

[0020]

[11] Another aspect of the present invention provides a method for manufacturing reduced iron, comprising the following steps: an iron oxide charging step of charging iron oxide raw material into a vertical shaft furnace; a partial combustion step of generating a reducing gas by partially burning the raw material gas with oxygen to raise the temperature of the raw material gas to 800°C or higher; and a blowing step of blowing the reducing gas into the vertical shaft furnace, wherein at each temperature of the reducing gas, the relationship between the concentration of water vapor in the reducing gas (in volume fraction) and the reduction rate of the reduced iron is determined, and based on the relationship, the water vapor concentration is controlled according to the target reduction rate and the temperature of the reducing gas, or, based on the relationship, the temperature of the reducing gas is controlled according to the target reduction rate and the water vapor concentration.

[0021]

[12] Another embodiment of the invention is an apparatus for manufacturing reduced iron using the method for manufacturing reduced iron described in [6], comprising: a heating furnace connected to a piping system for heating the introduced raw material gas and oxygen to partially combust them and obtain reducing gas; and a vertical furnace into which the reducing gas obtained in the heating furnace is blown, wherein the heating furnace is configured such that the raw material gas is supplied directly from the raw material gas supply source via a piping system.

[0022] Invention Effects According to the above-described embodiments of the present invention, a method for producing reduced iron with a high reduction rate, and an apparatus suitable for producing reduced iron, are provided, even when hydrogen is partially combusted. Attached Figure Description

[0023] Figure 1 This is a graph showing the correlation between the hydrogen concentration (volume%) in the reducing gas and the reduction rate (%) of reduced iron (DRI) at each temperature of the reducing gas.

[0024] Figure 2 This is a schematic diagram showing the configuration of the reduced iron manufacturing apparatus according to the first embodiment.

[0025] Figure 3 This is a schematic diagram showing the configuration of the reduced iron manufacturing apparatus according to the second embodiment.

[0026] Figure 4 It is a curve showing the correlation between the preheating temperature of the feed gas and the partial combustion rate of the feed gas.

[0027] Figure 5 This is a schematic diagram showing the configuration of the reduced iron manufacturing apparatus according to the third embodiment. Detailed Implementation

[0028] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0029] <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 inventors of this invention studied the correlation between the concentration (volume%) of water vapor in the reducing gas and the reduction rate (%) of reduced iron. Specifically, this study was conducted using a mathematical model of a shaft furnace. This model is constructed based on chemical engineering methods described in non-patent literature (e.g., Hara et al.: Iron and Steel, Vol. 62 (1976), No. 3, p. 315; Yamaoka et al.: Iron and Steel, Vol. 74 (1988), No. 12, p. 2254), and is a model that can theoretically analyze and estimate the thermal / mass movement within the shaft furnace, represented by the reduction reaction of iron oxide raw materials utilizing reducing gas, as well as heat transfer phenomena. Using this mathematical model, the operation of a shaft furnace using a reducing gas containing a high concentration of hydrogen was simulated, and macroscopic thermal / mass movement was evaluated.

[0030] The calculation conditions are as shown in Table 1.

[0031] In this calculation, the reducing gas is set to consist of hydrogen.

[0032] The residence time in Table 1 refers to the time that the iron oxide feedstock charged from the furnace top remains in the region in contact with the reducing gas (the region where the iron oxide feedstock is reduced by the reducing gas). Specifically, this region is the area from the reducing gas inlet to the charging position at the furnace top. Gas flow rate is the total flow rate of reducing gas and water vapor rising within the shaft furnace. Values ​​per ton of reduced iron are shown here. Gas flow rate can vary depending on the reduction rate, etc. Furnace top pressure represents the gas pressure at the top of the shaft furnace. Feedstock particle size represents the particle size (mm) of the iron oxide feedstock. Particle size can be determined by sieving. Porosity is the ratio of the volume of pores within a particle to the apparent volume of the feedstock particles, and its determination method is specified by JIS M8716:1990. The hydrogen reduction rate constant represents the rate of reduction using hydrogen, defined as the velocity (m / s) of the reaction interface within the particle per unit time. When the hydrogen concentration in the reducing gas becomes less than 100% by volume, the gas other than hydrogen is set to water vapor. Therefore, in the hypothetical actual operation, to set the reducing gas temperature to the desired level, the hydrogen used as the feed gas undergoes partial combustion. However, if the heating temperature is insufficient through partial combustion alone, it can be supplied via a separate heating furnace or a heat exchanger utilizing the sensible heat contained in the exhaust gas. The reducing gas temperature is set to 800°C or higher. This is because if the reducing gas temperature falls below 800°C, the time required to achieve the target reduction rate of 80% or 92% (described later) becomes longer, reducing production efficiency.

[0033] The residence time, gas flow rate, furnace top pressure, raw material particle size, and porosity are set to the above ranges because the above ranges are preferred ranges for obtaining a high reduction rate.

[0034] [Table 1] The simulation results are shown below. Figure 1 middle.

[0035] Figure 1 The horizontal axis represents the hydrogen concentration (volume %) in the reducing gas (shown on the bottom) and the water vapor concentration (volume %) in the reducing gas (shown on the top). In this simulation, when the hydrogen concentration in the reducing gas becomes below 100% by volume, the gas other than hydrogen is set as water vapor. Therefore, the denominator of the formula for calculating the hydrogen concentration is the sum of the volumes of hydrogen and water vapor, and the value obtained by subtracting the value on the horizontal axis from 100 is the water vapor concentration (volume %) in the reducing gas.

[0036] The vertical axis represents the reduction rate of reduced iron. The reduction rate is expressed as a percentage (mass of oxygen removed from iron oxide by hydrogen in reduced iron / mass of oxygen originally present in the iron oxide in the raw material).

[0037] On the other hand, the target lower limit for the reduction rate of reduced iron used as a raw material for blast furnaces is 80%. This is because when the reduction rate is below 80%, the improvement effect on the reduction ratio and production volume of the blast furnace is reduced.

[0038] observe Figure 1 It can be seen that the water vapor concentration required to achieve a reduction rate of 80% or higher varies at different temperatures of the reducing gas. Specifically, when the reducing gas temperature (temperature at the time of injection) is above 800°C but below 900°C, a water vapor concentration of 21% by volume is required to achieve a reduction rate of 80% or higher. When the reducing gas temperature is above 900°C but below 1000°C, a water vapor concentration of 23% by volume is required to achieve a reduction rate of 80% or higher. When the reducing gas temperature is above 1000°C, a water vapor concentration of 24% by volume is required to achieve a reduction rate of 80% or higher.

[0039] On the other hand, the lower limit of the target value for the reduction rate of reduced iron used as a raw material for electric furnaces is 92%. This is because if the reduction rate falls below 92%, it becomes difficult to melt the reduced iron in the next process using an electric furnace.

[0040] observe Figure 1It can be seen that the water vapor concentration required to achieve a reduction rate of 92% or higher varies at different temperatures of the reducing gas. Specifically, when the reducing gas temperature (temperature at the time of injection) is above 800°C but below 900°C, a water vapor concentration of less than 10% by volume is required to achieve a reduction rate of 92% or higher. When the reducing gas temperature is above 900°C but below 1000°C, a water vapor concentration of less than 17% by volume is required to achieve a reduction rate of 92% or higher. When the reducing gas temperature is above 1000°C, a water vapor concentration of less than 19% by volume is required to achieve a reduction rate of 92% or higher.

[0041] If the water vapor concentration exceeds 10% by volume when the temperature of the reducing gas is above 800°C but below 900°C, or exceeds 17% by volume when the temperature of the reducing gas is above 900°C but below 1000°C, or exceeds 19% by volume when the temperature of the reducing gas is above 1000°C, the reduction rate decreases. Under the calculation conditions in Table 1, the reduction rate becomes less than 92%.

[0042] There is no particular upper limit to the target reduction rate, but it is preferably 95% when used in either blast furnaces or electric furnaces. This is because when the reduction rate exceeds 95%, the production efficiency of reduced iron decreases and the production cost increases.

[0043] As by Figure 1 As is known, the water vapor concentration required to achieve a reduction rate of 95% or less varies at each temperature of the reducing gas. Specifically, when the reducing gas temperature is above 800°C but below 900°C, the water vapor concentration can be set to 6% by volume or more to achieve a reduction rate of 95% or less. When the reducing gas temperature is above 900°C but below 1000°C, the water vapor concentration can be set to 11% by volume or more to achieve a reduction rate of 95% or less. When the reducing gas temperature is above 1000°C, the water vapor concentration can be set to 17% by volume or more to achieve a reduction rate of 95% or less.

[0044] If the above are summarized, it will look like Table 2.

[0045] [Table 2] Thus, the inventors of this invention discovered that a range of water vapor concentrations at each temperature of the reducing gas, which is practically not a problem (i.e., allows for the achievement of the target reduction rate), can be determined. By designing the operation within such a range of reducing gas temperature and water vapor concentration, the preheating and heating loads on the feed gas can be reduced. Figure 1 In this way, when the relationship between the volumetric concentration of hydrogen and water vapor in the reducing gas and the reduction rate is determined at each temperature of the reducing gas, the water vapor concentration can be controlled based on the target reduction rate and the temperature of the reducing gas during operation, and the temperature of the reducing gas can also be controlled based on the target reduction rate and the water vapor concentration.

[0046] The method for manufacturing reduced iron in this embodiment is based on the above understanding.

[0047] <2. First Implementation> (2-1. Apparatus for manufacturing reduced iron) Next, the first embodiment will be described. Figure 2 As shown, the reduced iron manufacturing apparatus 1A of the first embodiment includes a vertical shaft furnace 1 and a heating furnace 2. The vertical shaft furnace 1 is the same as conventional ones. That is, iron oxide raw material is loaded from the top of the vertical shaft furnace 1. There are no particular restrictions on the type of iron oxide raw material, as long as it is operated in the same way as conventional vertical shaft furnaces. Examples of iron oxide raw materials include iron oxide particles.

[0048] On the other hand, reducing gas, obtained by partially burning the raw material gas, is blown into the vertical shaft furnace 1 from the side below (for example, in the case where the vertical shaft furnace has a reduction zone, a transition zone, and a cooling zone in sequence from the top of the furnace, at a position equivalent to the cooling zone). As the reducing gas blown into the vertical shaft furnace 1 rises within it, it reduces the iron oxide raw material inside the furnace 1. The result is the formation of reduced iron (DRI).

[0049] The generated reduced iron is discharged from the bottom of the shaft furnace 1 and cooled. On the other hand, top gas (exhaust gas) is discharged from the top of the shaft furnace 1. In addition to unreacted hydrogen, the exhaust gas also contains water vapor, dust, etc.

[0050] Raw material gas and oxygen are introduced into heating furnace 2. The raw material gas is a gas containing hydrogen (natural gas, furnace top gas, or hydrogen, etc.). Preferably, it contains hydrogen as a main component (e.g., hydrogen is 90% by volume or more and other gases are 10% by volume or less, hydrogen is 95% by volume or more and other gases are 5% by volume or less, or hydrogen is 99% by volume or more and other gases are 1% by volume or less), and more preferably it is composed of hydrogen. Examples of gases other than hydrogen contained in the raw material gas include CO gas, CO2 gas, CH4 gas, etc. The hydrogen used as the raw material gas can be obtained by electrolysis of hydrogen, or by separating hydrogen from coke oven gas (COG) or gas obtained through water-gas shift reaction using the PSA method or membrane separation method.

[0051] In the heating furnace 2, oxygen is used to partially combust the raw material gas. Specifically, the heating furnace 2 mainly performs partial combustion of hydrogen in the raw material gas. Thus, the heating furnace 2 heats the raw material gas to generate reducing gas. Here, in this embodiment, partial combustion means that when the raw material gas reacts with oxygen, at least 40% by mass of H2 and CO gases remain in the raw material gas.

[0052] Heating furnace 2 heats the raw material gas to at least 800°C. Here, as mentioned above, in order to set the reduction rate of reduced iron to 80% or more or 92% or more, it is necessary to set the water vapor concentration to a value within a specified range according to the temperature range of the reducing gas, or to set the temperature of the reducing gas to a value within a specified range according to the range of water vapor concentration.

[0053] The heating furnace 2 and the vertical furnace 1 are connected by a piping, and the reducing gas is blown into the vertical furnace 1 through the piping.

[0054] Here, the temperature of the reducing gas is measured, for example, by a thermocouple. A thermocouple is installed at the connection between the aforementioned piping and the vertical furnace 1, and this thermocouple is used to measure the temperature of the reducing gas. The water vapor concentration is calculated as the volume of water vapor / the volume of the reducing gas × 100 (volume %). Since water vapor is generated through a chemical reaction represented by the following chemical formula, the volume of water vapor is calculated as 2 × the volume of oxygen.

[0055] 2H₂ + O₂ → 2H₂O The volume of oxygen is measured by installing a flow meter (mass flow meter, etc.) on the oxygen supply pipe connected to the heater 2. Regarding the volume of the reducing gas, the volume of the raw material gas introduced into the heater 2 (heater inlet gas volume) is measured using a flow meter, and the volume of oxygen is derived from the above formula.

[0056] Volume of reducing gas = Gas volume at furnace inlet + Oxygen volume For oxygen, an additional heating mechanism (heater, etc.) can be installed in the heating furnace 2 to heat it, or it can be heated by heat exchange with the exhaust gas.

[0057] (2-2. Methods for manufacturing reduced iron) Next, a method for manufacturing reduced iron using the reduced iron manufacturing apparatus 1A (the reduced iron manufacturing method of the first embodiment) will be described. The reduced iron manufacturing method of the first embodiment includes: an iron oxide charging step of charging iron oxide raw material into a vertical shaft furnace 1; a partial combustion step of heating the raw material gas to 800°C or higher by partially burning the raw material gas with oxygen in a heating furnace 2 to generate reducing gas; and a blowing step of blowing the reducing gas into the vertical shaft furnace 1.

[0058] Here, when the water vapor concentration is controlled according to the temperature of the reducing gas, the water vapor concentration of the reducing gas is set to 21% by volume or less when the temperature of the reducing gas is above 800°C and below 900°C, the water vapor concentration of the reducing gas is set to 23% by volume or less when the temperature of the reducing gas is above 900°C and below 1000°C, and the water vapor concentration of the reducing gas is set to 24% by volume or less when the temperature of the reducing gas is above 1000°C.

[0059] On the other hand, when controlling the temperature of the reducing gas based on the water vapor concentration, if the water vapor concentration of the reducing gas is 21% by volume or less, the temperature of the reducing gas is set to 800°C or more (preferably less than 900°C); if the water vapor concentration of the reducing gas is 23% by volume or less, the temperature of the reducing gas is set to 900°C or more (preferably less than 1000°C); and if the water vapor concentration of the reducing gas is 24% by volume or less, the temperature of the reducing gas is set to 1000°C or more.

[0060] Therefore, the reduction rate of reduced iron can be set to over 80%.

[0061] On the other hand, in order to set the reduction rate of reduced iron to 92% or more, when controlling the water vapor concentration according to the temperature of the reducing gas, it is preferable to set the water vapor concentration of the reducing gas to 10% by volume or less when the temperature of the reducing gas is 800°C or more and less than 900°C, to set the water vapor concentration of the reducing gas to 17% by volume or less when the temperature of the reducing gas is 900°C or more and less than 1000°C, and to set the water vapor concentration of the reducing gas to 19% by volume or less when the temperature of the reducing gas is 1000°C or more.

[0062] On the other hand, when controlling the temperature of the reducing gas based on the water vapor concentration, it is preferable to set the temperature of the reducing gas to 800°C or higher (preferably lower than 900°C) when the water vapor concentration of the reducing gas is 10% by volume or lower, to 900°C or higher (preferably lower than 1000°C) when the water vapor concentration of the reducing gas is 17% by volume or lower, and to 1000°C or higher when the water vapor concentration of the reducing gas is 19% by volume or lower.

[0063] Preferably, when the temperature of the reducing gas is 800°C or higher but lower than 900°C, the water vapor concentration is set to 6% or higher; when the temperature of the reducing gas is 900°C or higher but lower than 1000°C, the water vapor concentration is set to 11% or higher; and when the temperature of the reducing gas is 1000°C or higher, the water vapor concentration is set to 17% or higher. This allows the reduction rate of reduced iron to be set to 95% or lower.

[0064] By controlling the temperature of the reducing gas based on the water vapor concentration, the reduction rate of reduced iron can also be set to below 95%.

[0065] There is no particular upper limit to the temperature of the reducing gas; it can be adjusted appropriately according to the performance of the vertical furnace 1, for example, it can be 1150℃.

[0066] During operation, the water vapor concentration can be controlled by adjusting the mixing ratio of hydrogen and oxygen in the feed gas introduced into furnace 2. The reducing gas temperature can be controlled by adjusting the mixing ratio of hydrogen and oxygen in the feed gas introduced into furnace 2 and by preheating the feed gas as described later.

[0067] Inside the shaft furnace 1, the iron oxide raw material is reduced to produce reduced iron as described above. The reduced iron is discharged from the bottom of the shaft furnace 1 and cooled. On the other hand, top gas (exhaust gas) is discharged from the top of the shaft furnace 1. In addition to unreacted hydrogen, the exhaust gas also contains water vapor, dust, etc.

[0068] In the reduced iron manufacturing apparatus 1A used in this embodiment, the heating furnace is configured such that the raw material gas is supplied directly from the raw material gas supply source (which is outside the system and not shown) via piping. That is, it does not have a preheating furnace as in the reduced iron manufacturing apparatus 1B and 1C used in the embodiments described later.

[0069] Therefore, in the method for manufacturing reduced iron in this embodiment, preheating is not performed, and the raw material gas below 100°C is heated to a temperature at which a sufficient reduction rate can be obtained by partially burning it with oxygen.

[0070] The inventors of this invention discovered that when using natural gas as the primary feedstock gas, a sufficient reduction rate cannot be obtained through partial combustion alone. However, if the feedstock gas is primarily hydrogen or contains hydrogen, a sufficient reduction rate can be obtained even through partial combustion. This is because the reduction reaction using natural gas involves the reduction of carbon monoxide and hydrogen produced in the furnace. Since the reduction reaction using carbon monoxide is exothermic, the higher the temperature, the less the reduction reaction proceeds if the concentration of carbon dioxide and water vapor produced through partial combustion is high. On the other hand, it is believed that the reduction reaction using hydrogen is endothermic, therefore, the higher the temperature, the more the reduction reaction proceeds even if the water vapor concentration is high.

[0071] As a result of a specific study, Table 3 shows the relationship between the temperature of the reducing gas, the water vapor concentration, and the reduction rate of the reduced iron obtained when hydrogen is used as the feed gas and the temperature of the reducing gas is raised only by partial heating with oxygen. In this case, the water vapor concentration is equal to the concentration of hydrogen consumed. The calculation method in Table 3 is as described above.

[0072] [Table 3] As shown in Table 3, to produce reduced iron with a reduction rate of 80% or higher for use as a blast furnace feedstock, it is sufficient to heat the feedstock gas to 897°C or higher through partial combustion (the reducing gas is set to 897°C or higher). In this case, the hydrogen concentration of the reducing gas is 11% by volume or higher. On the other hand, to produce reduced iron with a reduction rate of 92% or higher for use as an electric furnace feedstock, it is sufficient to heat the feedstock gas to 969°C or higher through partial combustion (the reducing gas is set to 969°C or higher). In this case, the water vapor concentration of the reducing gas is 12% by volume or higher.

[0073] As explained above, according to the first embodiment of the reduced iron manufacturing method using the reduced iron manufacturing apparatus 1A, as long as a gas with hydrogen as the main component is used as the raw material gas, even without a preheating process for preheating the raw material gas, reduced iron with a high reduction rate can be manufactured simply by a partial combustion process in which the raw material gas is partially combusted using oxygen.

[0074] <3. Second Implementation> (3-1. Apparatus for manufacturing reduced iron) Next, the second embodiment will be described. Figure 3 As shown, the reduced iron manufacturing apparatus 1B of the second embodiment adds a preheating furnace 3 to the reduced iron manufacturing apparatus 1A of the first embodiment.

[0075] The raw material gas is introduced into the preheating furnace 3. The composition of the raw material gas is the same as in the first embodiment. The raw material gas is preheated in the preheating furnace 3. The preheated raw material gas is then introduced into the heating furnace 2. The preheating furnace 3 is equipped with any heating mechanism (e.g., a heater) for preheating the raw material gas. There are no particular limitations on the preheating temperature, but if heating (partial combustion) of the raw material gas in the preheating furnace 3 is taken into consideration, it is preferably lower than the temperature of the reducing gas blown into the vertical furnace 1.

[0076] Oxygen and preheated raw material gas are introduced into heating furnace 2. Heating furnace 2, similar to the first embodiment, uses oxygen to partially combust the raw material gas. Specifically, heating furnace 2 primarily performs partial combustion of hydrogen in the raw material gas. Thus, the raw material gas is heated in heating furnace 2 to generate a reducing gas. In heating furnace 2, the raw material gas is heated to at least 800°C. In heating furnace 2, similar to the first embodiment, the water vapor concentration is set to a predetermined range based on the temperature range of the reducing gas, or the temperature of the reducing gas is set to a predetermined range based on the water vapor concentration.

[0077] Furthermore, in the second embodiment, the raw material gas introduced into the heating furnace 2 is preheated. Therefore, depending on the degree to which the raw material gas is preheated, the partial combustion rate (water vapor concentration of the reducing gas) of the raw material gas varies. Figure 4 This indicates the correlation between the preheating temperature (°C) of the feed gas and the hydrogen and water vapor concentrations (volume %) in the reducing gas, assuming the feed gas is converted to hydrogen. Figure 4 In this example, the thermal efficiency is set to 100%, and the temperature of the reducing gas is set to 1000℃. Region A represents the partial combustion rate of the raw material gas without preheating, and Region C represents the partial combustion rate (0% by volume) of the raw material gas after preheating to 1000℃. For example, from... Figure 4 As indicated, the higher the preheating temperature of the raw material gas, the lower the partial combustion rate of the raw material gas becomes. That is, the heating load in furnace 2 decreases.

[0078] (3-2. Methods for manufacturing reduced iron) Next, a method for manufacturing reduced iron using the apparatus 1B (the method for manufacturing reduced iron according to the second embodiment) will be described. The method for manufacturing reduced iron according to the second embodiment adds a preheating step to the method for manufacturing reduced iron according to the first embodiment, whereby the raw material gas is preheated. In the partial combustion step, the preheated raw material gas is partially combusted using oxygen. In the preheating step, the raw material gas is preheated in such a way that the partial combustion rate in the partial combustion step exceeds 0% by volume.

[0079] According to the second embodiment, in addition to obtaining the same effects as the first embodiment, the heating load of the heating furnace 2 is reduced because the raw material gas is preheated by the preheating furnace 3. Therefore, the water vapor concentration in the reducing gas used to set the temperature of the reducing gas to the desired temperature can be reduced.

[0080] <4. Third Implementation> (4-1. Apparatus for manufacturing reduced iron) Next, the third embodiment will be described. Figure 5 As shown, the reduced iron manufacturing apparatus 1C of the third embodiment adds a dust removal device 4 and a dehydration device 5 to the reduced iron manufacturing apparatus 1B of the second embodiment.

[0081] The exhaust gas discharged from the vertical shaft furnace 1 is introduced into the dust removal device 4. The dust removal device 4 removes dust and other particles from the exhaust gas using any dust removal mechanism (dust filter, etc.). Furthermore, CO2 gas in the exhaust gas is removed by chemical adsorption, etc. Afterwards, the exhaust gas is introduced into the preheating furnace 3. The preheating furnace 3 is a heat exchanger that preheats the raw material gas introduced into the preheating furnace 3 using the sensible heat contained in the exhaust gas. Afterwards, the raw material gas is introduced into the heating furnace 2, and the exhaust gas is introduced into the dehydration device 5. The dehydration device 5 removes water vapor from the exhaust gas as liquid water by cooling the exhaust gas (i.e., dehydration). As a result, the exhaust gas becomes mainly composed of hydrogen (and may contain CO gas, N2 gas, etc., depending on the situation). This gas is then introduced into the heating furnace 2.

[0082] Preheated raw material gas, hydrogen recovered from waste gas, and (room temperature) oxygen (CO gas, N2 gas, etc. from the waste gas can also be introduced simultaneously) are introduced into heating furnace 2. In heating furnace 2, similar to the first embodiment, the raw material gas (hydrogen recovered from the raw material gas and waste gas) is partially combusted using oxygen. This generates a reducing gas in heating furnace 2. The raw material gas is heated to at least 800°C in heating furnace 2. In heating furnace 2, similar to the first embodiment, the water vapor concentration is set to a value within a specified range based on the temperature range of the reducing gas, or the temperature of the reducing gas is set to a value within a specified range based on the water vapor concentration.

[0083] (4-2. Methods for manufacturing reduced iron) Next, the method for manufacturing reduced iron using the reduced iron manufacturing apparatus 1C (the reduced iron manufacturing method of the third embodiment) will be described. The reduced iron manufacturing method of the third embodiment modifies the preheating step of the second embodiment and further adds a waste gas recirculation step.

[0084] In the waste gas recycling process, the waste gas discharged from the vertical furnace 1 is dedusted by the dust removal device 4, and then introduced into the preheating furnace 3 to preheat the raw material gas using sensible heat (i.e., to perform a preheating process). After that, the waste gas is introduced into the dehydration device 5 to dehydrate the waste gas. The hydrogen obtained is then introduced into the heating furnace 2.

[0085] According to the third embodiment, in addition to obtaining the same effects as the first and second embodiments, the overall thermal efficiency of the system can be improved and the consumption of hydrogen can be reduced by using the sensible heat of the waste gas to preheat the raw material gas and then reusing the hydrogen in the waste gas.

[0086] 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.

[0087] Industrial availability According to the present invention, a method for producing reduced iron with a high reduction rate can be provided even when hydrogen is partially burned, thus providing high industrial applicability.

[0088] Explanation of symbols 1 Vertical shaft furnace 2 Heating Furnace 3. Preheating furnace 4. Dust removal device 5. Dehydration device 1A, 1B, 1C Apparatus for manufacturing reduced iron

Claims

1. A method for manufacturing reduced iron, characterized in that, It has the following processes: The iron oxide charging process of feeding iron oxide raw materials into a vertical shaft furnace; A partial combustion process in which the raw material gas is heated to above 800°C by partially burning it with oxygen to generate a reducing gas; and The blowing process of blowing the reducing gas into the vertical furnace. In the blowing process, when the temperature of the reducing gas after the partial combustion process is above 800°C and below 900°C, the water vapor concentration of the reducing gas is set to below 21% by volume; when the temperature of the reducing gas after the partial combustion process is above 900°C and below 1000°C, the water vapor concentration of the reducing gas is set to below 23% by volume; and when the temperature of the reducing gas after the partial combustion process is above 1000°C, the water vapor concentration of the reducing gas is set to below 24% by volume.

2. The method for manufacturing reduced iron according to claim 1, characterized in that, In the blowing-in process, when the temperature of the reducing gas after the partial combustion process is above 800°C and below 900°C, the water vapor concentration of the reducing gas is set to below 10% by volume; when the temperature of the reducing gas after the partial combustion process is above 900°C and below 1000°C, the water vapor concentration of the reducing gas is set to below 17% by volume; and when the temperature of the reducing gas after the partial combustion process is above 1000°C, the water vapor concentration of the reducing gas is set to below 19% by volume.

3. The method for manufacturing reduced iron according to claim 1, characterized in that, The raw material gas contains hydrogen as its main component.

4. The method for manufacturing reduced iron according to claim 2, characterized in that, The raw material gas contains hydrogen as its main component.

5. The method for manufacturing reduced iron according to any one of claims 1 to 4, characterized in that, In the partial combustion process, the raw material gas and the oxygen are introduced into a heating furnace, where the raw material gas undergoes partial combustion.

6. The method for manufacturing reduced iron according to claim 3 or 4, characterized in that, In the partial combustion process, the raw material gas, which is below 100°C, is heated to above 897°C by partial combustion using the oxygen.

7. The method for manufacturing reduced iron according to claim 3 or 4, characterized in that, In the partial combustion process, the raw material gas, which is below 100°C, is heated to above 969°C by partial combustion using the oxygen.

8. The method for manufacturing reduced iron according to any one of claims 1 to 4, characterized in that, The process includes a preheating step that preheats the raw material gas. In the partial combustion process, the preheated raw material gas is partially combusted using the oxygen.

9. The method for manufacturing reduced iron according to claim 8, characterized in that, In the preheating process, the raw material gas is preheated using the sensible heat contained in the exhaust gas of the vertical furnace.

10. The method for manufacturing reduced iron according to claim 9, characterized in that, It has a circulation process that introduces hydrogen obtained by dehydrating the waste gas after the preheating process into the heating furnace.

11. A method for manufacturing reduced iron, characterized in that, It has the following processes: The iron oxide charging process of feeding iron oxide raw materials into a vertical shaft furnace; A partial combustion process in which the raw material gas is heated to above 800°C by partially burning it with oxygen to generate a reducing gas; and The blowing process of blowing the reducing gas into the vertical furnace. At each temperature of the reducing gas, determine the relationship between the concentration of hydrogen and water vapor in the reducing gas (by volume), i.e., the relationship between the water vapor concentration and the reduction rate of reduced iron. Based on the aforementioned relationship, the water vapor concentration is controlled according to the target reduction rate and the temperature of the reducing gas, or... Based on the aforementioned relationship, the temperature of the reducing gas is controlled according to the reduction rate and the water vapor concentration, which are the targets.

12. An apparatus for manufacturing reduced iron, characterized in that, It is an apparatus for manufacturing reduced iron using the method for manufacturing reduced iron according to claim 6, comprising: A heating furnace, connected to piping, heats the introduced raw material gas and oxygen, causing partial combustion to obtain a reducing gas; and The reducing gas obtained in the heating furnace is blown into a vertical furnace. The heating furnace is configured such that the raw material gas is supplied directly from the raw material gas supply source via piping.

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