Apparatus for producing direct reduced iron and method for producing direct reduced iron

Abstract

The direct reduced iron manufacturing apparatus includes a shaft furnace for manufacturing direct reduced iron using hydrogen gas; a dust removal device for removing dust from exhaust gas of the shaft furnace; a dehydration device for dehydrating the exhaust gas after dust removal to obtain a circulating gas; a hydrogen gas introduction device for introducing the hydrogen gas into the circulating gas to obtain a pre-heating gas containing the circulating gas and the hydrogen gas; a heating device for heating the pre-heating gas to become a reducing gas; and a hydrocarbon gas introduction device for introducing a hydrocarbon gas into at least one of the circulating gas, the pre-heating gas, and the reducing gas.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2024-059691, filed on April 2, 2024, the contents of which are incorporated herein by reference. Background Technology

[0003] Currently, reduced iron is produced in shaft furnaces using natural gas (NG) as the reducing gas, as part of the HyL and Midrex processes. To lower the melting point of the reduced iron and facilitate its dissolution in the electric furnace of the next process, the reduced iron preferably contains about 4% carbon.

[0004] For example, in direct reduced iron (DRI) manufactured without forming and in a cooled state after reduction, the carbon concentration is generally increased by carburizing with gases such as methane during the cooling process in a shaft furnace (Patent Document 1, Non-Patent Document 1). When using reduced iron in pellet form, the pellets need to be cooled, so using methane gas for cooling is not a problem. On the other hand, when transporting reduced iron by sea, there is an obligation to process it into hot-pressed iron blocks (HBI) for disaster prevention. When manufacturing hot-pressed iron blocks (HBI) through hot forming outside the shaft furnace, the iron reduced at a temperature of around 700°C needs to be discharged outside the furnace, making the aforementioned cooling process impossible. Therefore, when manufacturing HBI, it is difficult to increase the carbon concentration in the reduced iron after reduction.

[0005] The carbon concentration of HBI produced from methane gas is typically 0.5% to 1.5%, which is less than half that of DRI produced during the carburizing process in the cooling stage. From the viewpoint of reducing CO2, it is preferable to use H2 as the reducing gas. However, when using H2 as the reducing gas, the reducing gas does not contain carbon, so there is a problem that the carbon concentration does not increase during the reduction process and the HBI contains almost no carbon.

[0006] As a technology for efficiently adding carbon in the cooling zone, Patent Document 1 discloses a technology that leaves methane in the cooling gas without decomposing the natural gas used as the feed gas.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 62-263911 Non-patent literature Non-patent literature 1: ENERGIRON Technology General Overview (2012) Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in the technology disclosed in Non-Patent Document 1, natural gas is used as the feed gas, resulting in low CO2 reduction efficiency.

[0010] The present invention was made in view of the above circumstances, and its object is to provide an apparatus and a method for manufacturing direct reduced iron that can perform carburizing of reduced iron in a direct reduction furnace using hydrogen as a raw material gas, even when discharged at high temperature.

[0011] means for solving problems

[0012] To address the aforementioned issues, the present invention proposes the following methods.

[0013] (1) The direct reduced iron manufacturing apparatus of Scheme 1 of the present invention comprises: Vertical shaft furnace, using hydrogen to produce direct reduced iron; A dust removal device is used to remove dust from the exhaust gas of the vertical furnace; A dehydration device is used to dehydrate the exhaust gas after dust removal to obtain circulating gas. A hydrogen introduction device introduces hydrogen into the circulating gas, resulting in a pre-heating gas containing both the circulating gas and the hydrogen. A heating device is used to heat a pre-heating gas containing the circulating gas and the hydrogen to make it a reducing gas; and A hydrocarbon gas introduction device introduces hydrocarbon gas into at least one of the circulating gas, the pre-heating gas, and the reducing gas.

[0014] (2) Solution 2 of the present invention further comprises, in the direct reduced iron manufacturing apparatus of Solution 1: A gas analysis device is used to determine the concentration of the tracer gas in the circulating gas; and The control device controls the amount of hydrocarbon gas introduced by the hydrocarbon gas introduction device based on the concentration of the tracer gas.

[0015] (3) Solution 3 of the present invention is that, in the direct reduced iron manufacturing apparatus of Solution 2, The tracer gas is CO2.

[0016] (4) Solution 4 of the present invention further comprises, in any one of Solutions 1 to 3, the direct reduced iron manufacturing apparatus, including: A carbon analysis device is used to determine the carbon concentration in the directly reduced iron.

[0017] (5) The direct reduced iron manufacturing method of Scheme 5 of the present invention uses a vertical shaft furnace and hydrogen to manufacture direct reduced iron, the manufacturing method comprising: The dust removal process involves removing dust from the exhaust gas of the vertical furnace. The dehydration process involves dehydrating the exhaust gas after dust removal in the dust removal process to obtain circulating gas. The hydrogen introduction process involves introducing hydrogen into the circulating gas to obtain a pre-heating gas containing the circulating gas and the hydrogen. The heating process involves heating the gas containing the circulating gas and the hydrogen before heating to make it a reducing gas; and The hydrocarbon gas introduction process involves introducing hydrocarbon gas into at least one of the circulating gas, the pre-heating gas, and the reducing gas.

[0018] Invention Effects

[0019] According to the above-described embodiments of the present invention, an apparatus and a method for manufacturing direct reduced iron can be provided, which enable carburizing of reduced iron in a direct reduction furnace using hydrogen even at high temperatures. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating an example of a direct reduced iron manufacturing apparatus according to the first embodiment of the present invention.

[0021] Figure 2 This is a flowchart illustrating an example of a direct reduced iron manufacturing apparatus according to the second embodiment of the present invention.

[0022] Figure 3 This is a graph used to illustrate the relationship between the amount of hydrocarbon gas introduced and the carbon concentration in the reduced iron.

[0023] Figure 4 This is a graph used to illustrate the relationship between the amount of hydrocarbon gas introduced and the carbon concentration not present in the reduced iron.

[0024] Figure 5 This is a graph used to illustrate the relationship between the amount of hydrocarbon gas introduced and the concentration of tracer gas (CO2) in the circulating gas.

[0025] Figure 6 These are graphs illustrating the relationship between the amount of hydrocarbon introduced, the carbon concentration in the reduced iron, and the tracer gas concentration and time. (a) is a graph illustrating the relationship between the amount of hydrocarbon gas introduced and time. (b) is a graph illustrating the relationship between the carbon concentration in the reduced iron and time. (c) is a graph illustrating the relationship between the tracer gas concentration in the circulating gas and time.

[0026] Figure 7 This is a flowchart illustrating an example of a direct reduced iron manufacturing apparatus according to the third embodiment of the present invention. Detailed Implementation

[0027] (First Embodiment)

[0028] Hereinafter, with reference to the accompanying drawings, the apparatus 100 for manufacturing direct reduced iron and the method for manufacturing direct reduced iron according to the first embodiment will be described. Figure 1 This is a flowchart illustrating an example of a direct reduced iron (DRI) manufacturing apparatus according to the first embodiment of the present invention. The DRI manufacturing apparatus 100 includes: a shaft furnace 20 for manufacturing DRI using hydrogen; a dust removal device 30 for removing dust from the exhaust gas of the shaft furnace 20; a dehydration device 40 for dehydrating the dust-removed exhaust gas to obtain circulating gas; a hydrogen introduction device 65 for introducing hydrogen into the circulating gas to obtain a pre-heating gas containing the circulating gas and hydrogen; a heating device 50 for heating the pre-heating gas to become a reducing gas; and a hydrocarbon gas introduction device 60 for introducing a hydrocarbon gas into at least one of the circulating gas, the pre-heating gas, and the reducing gas. It should be noted that the hydrogen may contain impurities such as nitrogen, within a range that does not hinder the reduction reaction. The concentration of hydrogen is, for example, 90 vol% or more.

[0029] (Vertical furnace 20)

[0030] The vertical shaft furnace 20 includes: a raw material charging section 24 for charging iron oxide as raw material; a reduced iron discharge section 25 for discharging reduced iron; a reducing gas inlet 28 located at the lower part of the furnace 20 for blowing in reducing gas; and an exhaust outlet 29 located at the upper part of the furnace 20 for discharging exhaust gas. Iron oxide as raw material is charged into the furnace 20 from the raw material charging section 24 at the top. As the iron oxide descends within the furnace 20, it is reduced by hydrogen to become reduced iron. The reduced iron is discharged from the reduced iron discharge section 25 at a high temperature. The reaction between iron oxide and hydrogen is as shown in equation (1A) below. As shown in equation (1A) below, hydrogen reacts with iron oxide to become water (water vapor). Furthermore, iron oxide is reduced as shown in equation (1B) below by carbon monoxide (CO) produced by the reaction of hydrocarbon gases described later. In this reaction, carbon dioxide (CO2) is produced. Fe₂O₃ + 3H₂ → 2Fe + 3H₂O (1A) Fe₂O₃ + 3CO → 2Fe + 3CO₂ (1B)

[0031] Reducing gas heated by heating device 50 is blown in through reducing gas inlet 28. Iron oxide is reduced by the reducing gas. Furthermore, the reduced iron reacts with hydrocarbon gas introduced by hydrocarbon gas introduction device 60 (described later), increasing the carbon concentration in the directly reduced iron. Here, methane gas is used as an example of the hydrocarbon gas to illustrate the reaction. The reaction between reduced iron and methane gas is shown in equation (2A) below. Hydrogen gas is produced through the reaction of methane gas with reduced iron, as shown in equation (2A) below. The produced hydrogen gas is discharged from exhaust outlet 29. Additionally, methane gas reacts with water and carbon dioxide in the shaft furnace 20, as shown in equations (2B) and (2C) below, producing carbon monoxide and hydrogen. The produced carbon monoxide and hydrogen are discharged from exhaust outlet 29. 3Fe + CH4 → Fe3C + 2H2 (2A) H2O + CH4 → CO + 3H2 (2B) CO2 + CH4 → 2CO + 2H2 (2C)

[0032] (Dust removal device 30)

[0033] Dust removal device 30 removes dust from the exhaust gas discharged from exhaust outlet 29. The dust removal method is not particularly limited; examples include cyclone separators and scrubbers. Preferably, the dust concentration is 5~50 mg / Nm³. 3 Dust removal is performed in a wide range of ways. The exhaust gas after dust removal is sent to the dewatering unit 40.

[0034] (Dehydration device 40)

[0035] The dehydration unit 40 dehydrates the exhaust gas after dust removal by the dust removal unit 30 to obtain recirculating gas. The exhaust gas discharged from the exhaust outlet 29 contains unreacted hydrogen (hydrogen exhaust gas), hydrocarbon gases, water vapor, carbon monoxide, and carbon dioxide produced in the reduction reaction of iron oxide, etc. Water hinders the reduction reaction, so it is preferable that the moisture concentration in the exhaust gas is as low as possible. For example, if the moisture concentration in the exhaust gas is 25 vol%, it is preferable to remove the moisture to a moisture concentration of less than 2 vol% by dehydration. The dehydration unit 40 performs dehydration, for example, by cooling the exhaust gas after dust removal. The dehydrated recirculating gas is pressurized to a pressure above the pressure inside the shaft furnace 20 by a compressor (not shown) and then introduced into the heating unit 50.

[0036] (Hydrogen introduction device 65)

[0037] Hydrogen introduction device 65 introduces hydrogen, which is used as a feed gas, into the circulating gas before the heating device 50, resulting in a pre-heating gas containing both the circulating gas and hydrogen. The introduction of hydrogen into the circulating gas can be carried out using known methods. The hydrogen supplied as the feed gas is, for example, hydrogen produced by the electrolysis of water.

[0038] (Heating device 50)

[0039] The heating device 50 heats the pre-heating gas, which contains recirculated gas and hydrogen, after being dehydrated by the dehydration device 40, to above 700°C, and then blows it into the reducing gas inlet 28 as a reducing gas. In this embodiment, the pre-heating gas consists of recirculated gas and hydrogen as a raw material gas. The temperature of the blown-in reducing gas is approximately 700~1000°C. Furthermore, the blowing rate of the reducing gas is approximately 1000~2200 Nm³. 3 / t-DRI.

[0040] (Hydrocarbon gas introduction device 60)

[0041] The hydrocarbon gas introduction device 60 introduces hydrocarbon gas into the reducing gas blown into the shaft furnace 20 from the reducing gas inlet 28. The reducing gas with introduced hydrocarbon gas is then introduced into the shaft furnace 20 from the reducing gas inlet 28, and the introduced hydrocarbon gas is used in the above-described reaction. The amount of hydrocarbon gas introduced can be appropriately varied depending on the raw material (iron oxide) used. The hydrocarbon gas is pressurized to a pressure above that of the reducing gas and introduced into the reducing gas. The hydrocarbon gas can be introduced from a tank (not shown) for storing hydrocarbon gas, or from a plant other than the direct reduced iron manufacturing unit 100 via piping.

[0042] (The manufacturing method of direct reduced iron)

[0043] The direct reduced iron (DRE) manufacturing method of this embodiment uses a shaft furnace and hydrogen gas to manufacture DRE. The manufacturing method includes: a dust removal process, in which dust is removed from the exhaust gas of the shaft furnace 20; a dehydration process, in which the exhaust gas after dust removal is dehydrated to obtain a circulating gas; a hydrogen introduction process, in which hydrogen gas is introduced into the circulating gas to obtain a pre-heating gas containing the circulating gas and hydrogen; a heating process, in which the pre-heating gas is heated to become a reducing gas; and a hydrocarbon methane gas introduction process, in which a hydrocarbon gas is introduced into at least one of the circulating gas, the pre-heating gas, and the reducing gas. Hereinafter, the DRE manufacturing method using the DRE manufacturing apparatus 100 of the first embodiment will be described. Raw material (iron oxide) is fed into the raw material loading section 24 at the top of the shaft furnace 20. The raw material is reduced to reduced iron by the reducing gas introduced from the reducing gas blowing inlet 28 within the shaft furnace 20, and discharged from the reduced iron discharge section 25 of the shaft furnace 20. The raw material used in the DRE manufacturing apparatus 100 of the first embodiment preferably has a small deviation in composition.

[0044] The reducing gas introduced through the reducing gas inlet 28 of the vertical shaft furnace 20 reduces iron oxide within the furnace and is then discharged as exhaust gas from the exhaust outlet 29. The discharged exhaust gas contains unreacted hydrogen and hydrocarbon gases, as well as water vapor, carbon monoxide, and carbon dioxide produced during the reduction reaction of iron oxide. The exhaust gas discharged from the exhaust outlet 29 is dedusted by the dust removal device 30 (dust removal process), dehydrated by the dehydration device 40 to become circulating gas (dehydration process), and hydrogen is introduced into the circulating gas by the hydrogen introduction device 65 to obtain a pre-heating gas containing both circulating gas and hydrogen (hydrogen introduction process). Next, the pre-heating gas containing both circulating gas and hydrogen is heated by the heating device 50 to become a reducing gas (heating process), which is then introduced into the furnace from the lower part of the vertical shaft furnace 20. Alternatively, a portion of the exhaust gas can be discharged outside the system.

[0045] Before being introduced into the heated reducing gas into the shaft furnace 20, hydrocarbon gas is introduced through the hydrocarbon gas introduction device 60 (hydrocarbon gas introduction process). Examples of hydrocarbon gases include methane gas. The amount of hydrocarbon gas introduced is controlled according to the composition of the raw material, which has been pre-analyzed, to the extent that it is used for the carbonization reaction in formula (2A). Therefore, by appropriately introducing hydrocarbon gas from the hydrocarbon gas introduction device 60, the amount of residual hydrocarbon gas not used for the carbonization reaction can be reduced, thereby reducing the amount of carbon dioxide produced by the reaction of the hydrocarbon gas.

[0046] The apparatus 100 for manufacturing direct reduced iron and the method for manufacturing direct reduced iron according to the first embodiment have been described above. In conventional direct reduction equipment using natural gas as the feed gas, hydrocarbon gases are easily injected because equipment is installed to remove or decompose carbon dioxide from the circulating gas. However, when the feed gas of the present invention is hydrogen, equipment to remove or decompose carbon dioxide is not required. Without equipment to remove or decompose carbon dioxide, excessive injection of hydrocarbons can lead to carbon dioxide accumulation in the circulating gas. According to the apparatus 100 for manufacturing direct reduced iron, carburizing of reduced iron can be performed in a direct reduction furnace using hydrogen, even with high-temperature exhaust. Furthermore, by introducing an appropriate amount of hydrocarbon gas based on pre-analyzed feed gas, the amount of carbon dioxide generated during the reaction of hydrocarbon gases can be reduced. The circulating gas can also be used outside the apparatus 100 for manufacturing direct reduced iron.

[0047] In the first embodiment, the hydrocarbon gas is introduced into the reducing gas heated by the heating device 50, but the hydrocarbon gas may also be introduced into at least one of the circulating gas, the gas before heating, and the reducing gas. The hydrocarbon gas may also be introduced into the circulating gas or the gas before heating by the heating device 50. The hydrocarbon gas may be introduced into the circulating gas and the gas before heating, or into the gas before heating and the reducing gas, or into the circulating gas and the reducing gas, or into the circulating gas, the gas before heating, and the reducing gas. When introducing the hydrocarbon gas, a hydrocarbon gas pressurized to a pressure higher than that of the introduced reducing gas or circulating gas is used.

[0048] In the first embodiment, the reducing gas is obtained by heating a mixture of circulating gas and hydrogen. However, in the first embodiment, hydrocarbon gas is introduced into the reducing gas before it is introduced into the shaft furnace 20. That is, the reducing gas introduced into the shaft furnace 20 includes circulating gas, hydrogen, and hydrocarbon gas.

[0049] (Second Implementation)

[0050] Next, the direct reduced iron manufacturing apparatus 100A of the second embodiment will be described. Figure 2 This is a flowchart illustrating an example of a direct reduced iron (DRI) manufacturing apparatus according to the second embodiment of the present invention. The DRI manufacturing apparatus 100A includes: a shaft furnace 20 for manufacturing DRI using hydrogen; a dust removal device 30 for removing dust from the exhaust gas of the shaft furnace 20; a dehydration device 40 for dehydrating the dust-removed exhaust gas; a hydrogen introduction device 65 for introducing hydrogen into the circulating gas to obtain a pre-heating gas containing the circulating gas and hydrogen; a heating device 50 for heating the pre-heating gas to become a reducing gas; a hydrocarbon gas introduction device 60 for introducing a hydrocarbon gas into at least one of the circulating gas, the pre-heating gas, and the reducing gas; a gas analysis device 80 for measuring the concentration of a tracer gas in the exhaust gas or the circulating gas; and a control device 70 for controlling the amount of hydrocarbon gas introduced by the hydrocarbon gas introduction device 60 based on the concentration of the tracer gas in the exhaust gas or the circulating gas. Hereinafter, the same reference numerals will be used to denote the same constituent elements, and descriptions may be omitted at times.

[0051] (Gas Analysis Apparatus 80)

[0052] The gas analyzer 80 measures the concentration of the tracer gas in the circulating gas. The gas analyzer 80 can be appropriately selected based on the type and concentration of the tracer gas in the exhaust gas. The concentration measurement of the tracer gas is preferably performed continuously. For example, a non-dispersive infrared analyzer or a gas chromatograph can be used as the gas analyzer 80. Here, the tracer gas is the gas produced by the decomposition and reaction of hydrocarbon gases in the furnace, and is a gas other than H2 and water vapor. The tracer gas can be at least one of the following: methane, carbon monoxide, and carbon dioxide. An increase in the gas concentration can sometimes hinder reduction; therefore, carbon dioxide (CO2) is particularly preferred as the tracer gas. The measured concentration of the tracer gas is sent to the control device 70.

[0053] (Control device 70)

[0054] The control device 70 controls the amount of hydrocarbon gas introduced into the hydrocarbon gas introduction device based on the concentration of tracer gas in the exhaust gas measured by the gas analyzer 80. For example, in areas exceeding... Figure 5 At the critical point G, the control device 70, for example, controls valve 62, to reduce the amount of hydrocarbon gas introduced. Additionally, the control device 70 controls the hydrogen introduction device to introduce an amount of hydrogen equivalent to the amount consumed in the reduction process.

[0055] The control device 70 can also be constructed using a processor such as a CPU (Central Processing Unit) and memory. The control device 70 operates the valve 62 by executing a program through the processor, controlling the amount of hydrocarbon gas introduced. It should be noted that all or part of the functions of the control device 70 can also be implemented using hardware such as ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array). The aforementioned program can also be recorded on a computer-readable recording medium. Computer-readable recording media include removable media such as floppy disks, optical disks, ROMs, CD-ROMs, semiconductor storage devices (e.g., SSDs), hard disks built into computer systems, and other storage devices. The aforementioned program can also be transmitted via electrical communication lines.

[0056] (The manufacturing method of direct reduced iron)

[0057] The following describes a method for manufacturing direct reduced iron using the direct reduced iron manufacturing apparatus 100A of the second embodiment. Raw material (iron oxide) is fed into the raw material charging section 24 at the top of the shaft furnace 20. The raw material is reduced to reduced iron by reducing gas introduced through the reducing gas blowing inlet 28 within the shaft furnace 20, and discharged from the reduced iron discharge section 25 of the shaft furnace 20.

[0058] The reducing gas introduced through the reducing gas inlet 28 of the vertical shaft furnace 20 reduces iron oxide in the furnace 20 and is then discharged as exhaust gas from the exhaust outlet 29 of the furnace 20. The discharged exhaust gas contains hydrogen, the aforementioned water vapor, carbon dioxide, carbon monoxide, etc. The exhaust gas discharged from the exhaust outlet 29 is dusted by the dust removal device 30 (dust removal process), dehydrated to become circulating gas (dehydration process), and hydrogen is introduced into the circulating gas to obtain a pre-heating gas containing both circulating gas and hydrogen (hydrogen introduction process). The pre-heating gas is heated by the heating device 50 to become a reducing gas (heating process), and introduced into the furnace from the lower part of the furnace 20. Alternatively, a portion of the exhaust gas can be discharged outside the system. The gas analysis device 80 measures the concentration of the tracer gas in the circulating gas. Preferably, the concentration is equivalent to the amount consumed by the reduction of hydrogen introduced into the circulating gas.

[0059] Before introducing the heated reducing gas into the shaft furnace 20, a hydrocarbon gas corresponding to the concentration of the tracer gas is introduced through the hydrocarbon gas introduction device 60 and the control device 70 (hydrocarbon gas introduction process). Here, the case of using methane gas as the hydrocarbon gas is used as an example to explain each reaction. The methane gas introduced into the reducing gas reacts with the reduced iron based on the above formula (2A). When more than the amount of methane gas consumed in this reaction is introduced, the carbon dioxide concentration in the circulating gas increases, which becomes an obstacle to the reduction reaction of iron oxide. In direct reduction equipment using natural gas as the feed gas, it is easy to inject hydrocarbon gas because equipment for removing or decomposing CO2 in the circulating gas is assembled. However, when the feed gas of the present invention is hydrogen, there is no equipment for removing or decomposing CO2. Therefore, in the direct reduced iron manufacturing apparatus 100A, it is important to control the amount of hydrocarbon gas introduced in order not to accumulate carbon dioxide in the circulating gas.

[0060] The following describes the method for adjusting the amount of hydrocarbon gas introduced based on the concentration of the tracer gas.

[0061] The relationship between the amount of hydrocarbon gas introduced, the carbon concentration in the reduced iron, and the amount of carbon dioxide gas.

[0062] First, the relationship between the amount of hydrocarbon gas introduced, the carbon concentration in the reduced iron, and the amount of carbon dioxide gas is explained.

[0063] Figure 3This is a graph used to illustrate the relationship between the amount of hydrocarbon gas introduced and the carbon concentration in the reduced iron. Figure 3 The horizontal axis represents the amount of hydrocarbon gas introduced, and the vertical axis represents the carbon concentration in the reduced iron. Figure 4 This is a graph used to illustrate the relationship between the amount of hydrocarbon gas introduced and the carbon concentration not present in the reduced iron. Figure 4 The horizontal axis represents the amount of hydrocarbon gas introduced, and the vertical axis represents the carbon concentration not present in the reduced iron. Figure 5 This is a graph used to illustrate the relationship between the amount of hydrocarbon gas introduced and the concentration of tracer gas (CO2) in the circulating gas. Figure 5 The horizontal axis represents the amount of hydrocarbon gas introduced, and the vertical axis represents the concentration of tracer gas in the circulating gas. Up to the critical point G, the carbon concentration in the reduced iron increases along with the amount of hydrocarbon gas introduced. Figure 3 In the absence of external discharge of circulating gas, the amount of hydrocarbon gas introduced is correlated with the carbon concentration in the reduced iron. Above the critical point G, the carbon concentration in the reduced iron increases slowly. When the increase in carbon concentration in the reduced iron becomes slow, even increasing the amount of hydrocarbon gas introduced will not introduce it into the reduced iron; therefore, the concentration of carbon not present in the reduced iron (methane gas, methane decomposition products, etc.) increases. Figure 4 By analyzing the tracer gas, the amount of carbon not introduced into the reduced iron can be determined. On the other hand, carbon dioxide is generated from the remaining hydrocarbon gas, causing a sharp increase in the concentration of tracer gas (e.g., carbon dioxide concentration) within the shaft furnace 20. Figure 5 A certain amount of carbon dioxide is consumed by the above-mentioned (2C) reaction, but the amount of carbon dioxide exceeding this consumption is stored in the circulating gas.

[0064] Next, a graph with the horizontal axis as the time axis will be used to illustrate this process. Figure 6 (a) is a graph illustrating the relationship between the amount of hydrocarbon gas introduced and time. Figure 6 (b) is a graph illustrating the relationship between carbon concentration and time in reduced iron. Figure 6 (c) is a graph illustrating the relationship between the concentration of tracer gas in the circulating gas and time. Here, the amount of hydrocarbon gas introduced proportionally to the elapsed time is increased ( Figure 6 (a) Thus, as the amount of hydrocarbon gas introduced increases, the carbon concentration in the reduced iron increases proportionally. When approaching the critical point of carbon concentration in the reduced iron, the increase in carbon concentration becomes slow even over time. Figure 6 (b) When the increase in carbon concentration in reduced iron becomes slow, carbon dioxide is generated from the remaining hydrocarbon gas that was not introduced into the reduced iron. Therefore, when the increase in carbon concentration in reduced iron becomes slow, the concentration of tracer gas (e.g., carbon dioxide concentration) in the shaft furnace 20 increases sharply over time. Figure 6 (c)).

[0065] The amount of hydrocarbon gas introduced can be adjusted, for example, by the following methods.

[0066] The relationship between the amount of hydrocarbon gas introduced and the concentrations of reduced iron and carbon and tracer gas is predetermined. The amount of hydrocarbon gas introduced, for example, is determined based on the target value A of the reduced iron and carbon concentration. Figure 3 Next, the concentration of the tracer gas in the circulating gas is continuously measured using a gas analyzer 80. If the measured value is within the range assumed based on the hydrocarbon gas introduction rate B... Figure 5 If the measured value is within the range of the assumed value C, it is considered a normal operating condition and operation continues. If the measured value exceeds the range of the assumed value C, it is considered an abnormal operating condition, and the amount of hydrocarbon gas introduced is increased or decreased. Although the tracer concentration can be reduced by discharging the circulating gas outside the system, from the point of view of energy loss, it is preferable not to discharge the circulating gas.

[0067] The amount of hydrocarbon gas introduced can also be adjusted using the following method. The carbon accumulation status within the shaft furnace 20 is estimated based on the amount of hydrocarbon gas introduced, the carbon concentration of the reduced iron, and the tracer concentration of the circulating gas. If it is determined that carbon has accumulated within the shaft furnace 20 (for example, if the tracer gas concentration of the circulating gas rises sharply), the amount of hydrocarbon gas introduced is reduced. Although the tracer concentration can also be reduced by discharging the circulating gas outside the system, from the viewpoint of energy loss, it is preferable not to discharge it. As described above, by controlling the amount of hydrocarbon gas introduced, the carbon concentration in the circulating gas can be kept within a certain range.

[0068] The apparatus 100A for manufacturing direct reduced iron and the method for manufacturing direct reduced iron according to the second embodiment have been described above. According to the apparatus 100A, carburizing of reduced iron can be performed in a direct reduction furnace using hydrogen, even with high-temperature exhaust. Since the amount of hydrocarbon gas introduced is controlled according to the concentration of the tracer gas, the amount of carbon dioxide generated can be reduced even when using raw materials with large compositional deviations.

[0069] In the direct reduced iron manufacturing apparatus 100A, the concentration of the tracer gas is determined using the circulating gas after dehydration in the dehydration unit 40. However, the timing of the measurement is not particularly limited as long as the tracer concentration is measured before heating using the heating unit 50. For example, the exhaust gas after dust removal by the dust removal unit 30 can also be measured.

[0070] In the second embodiment, the hydrocarbon gas is introduced as a reducing gas, but the hydrocarbon gas can also be introduced as a circulating gas or a gas before heating. When introducing the hydrocarbon gas, a hydrocarbon gas pressurized to a pressure higher than that of the introduced reducing gas or circulating gas is used. When the hydrocarbon gas is introduced as a circulating gas, the gas analyzer 80 measures the concentration of the tracer gas in the circulating gas before the hydrocarbon gas is introduced. Additionally, the gas analyzer 80 can also measure the amount of hydrogen.

[0071] (Third implementation)

[0072] Next, the direct reduced iron manufacturing apparatus 100B of the third embodiment will be described. Figure 7 This is a flowchart illustrating an example of a direct reduced iron (DRE) manufacturing apparatus according to the third embodiment of the present invention. The DRE manufacturing apparatus 100B includes: a shaft furnace 20 for manufacturing DRE using hydrogen; a dust removal device 30 for removing dust from the exhaust gas of the shaft furnace 20; a dehydration device 40 for dehydrating the dust-removed exhaust gas to obtain circulating gas; a hydrogen introduction device 65 for introducing hydrogen into the circulating gas to obtain a pre-heating gas containing the circulating gas and hydrogen; a heating device 50 for heating the pre-heating gas to become a reducing gas; a hydrocarbon gas introduction device 60 for introducing a hydrocarbon gas into at least one of the circulating gas, the pre-heating gas, and the reducing gas; a gas analysis device 80 for measuring the concentration of a tracer gas in the exhaust gas or the circulating gas; a control device 70 for controlling the amount of hydrocarbon gas introduced into the hydrocarbon gas introduction device 60 based on the concentration of the tracer gas in the exhaust gas or the circulating gas; and a carbon analysis device 90 for measuring the carbon concentration in the DRE. Hereinafter, the same reference numerals will be used to denote the same constituent elements, and descriptions may be omitted at times.

[0073] (Carbon analysis device 90)

[0074] Carbon analysis device 90 measures the carbon concentration in the direct reduced iron discharged from reduced iron discharge section 25. The carbon concentration in the direct reduced iron can be determined, for example, according to JIS G 1211-3, combustion-infrared absorption method. The measured carbon concentration is sent to control device 70.

[0075] (Control device 70)

[0076] The control device 70 controls the amount of hydrocarbon gas introduced into the hydrocarbon gas introduction device 60 based on the concentration of tracer gas in the circulating gas or exhaust gas and the carbon concentration in the direct reduced iron, as measured by the gas analyzer 80. The control device 70, for example, controls the amount of hydrocarbon gas introduced via the control valve 62. Additionally, the control device 70 controls the hydrogen introduction device to introduce an amount of hydrogen equivalent to the amount consumed in the reduction process.

[0077] (The manufacturing method of direct reduced iron)

[0078] The following describes a method for manufacturing direct reduced iron using the direct reduced iron manufacturing apparatus 100B according to the third embodiment. Raw material (iron oxide) is fed into the raw material charging section 24 at the top of the shaft furnace 20. The raw material is reduced to reduced iron by reducing gas introduced through the reducing gas blowing inlet 28 within the shaft furnace 20, and discharged from the reduced iron discharge section 25 of the shaft furnace 20.

[0079] The reducing gas introduced through the reducing gas inlet 28 of the vertical shaft furnace 20 reduces iron oxide in the furnace 20 and is then discharged as exhaust gas from the exhaust outlet 29 of the furnace 20. The discharged exhaust gas contains hydrogen, the aforementioned water vapor, carbon dioxide, carbon monoxide, etc. The exhaust gas discharged from the exhaust outlet 29 is dedusted by the dust removal device 30 (dust removal process), dehydrated to become circulating gas (dehydration process), and hydrogen is introduced into the circulating gas to obtain a pre-heating gas containing both circulating gas and hydrogen (hydrogen introduction process). The pre-heating gas is heated by the heating device 50 to become a reducing gas (heating process). The reducing gas is introduced into the furnace from the lower part of the furnace. Alternatively, a portion of the exhaust gas can be discharged outside the system. Preferably, this amount is equivalent to the amount of hydrogen consumed in the reduction of the circulating gas.

[0080] In the heated reducing gas, a hydrocarbon gas corresponding to the concentration of the tracer gas and the carbon concentration in the direct reduced iron is introduced through the hydrocarbon gas introduction device 60 and the control device 70 (hydrocarbon gas introduction process). When the hydrocarbon gas introduced into the reducing gas is methane, the introduced methane gas reacts with the reduced iron based on the above formula (2A). When more than the amount of methane gas consumed in this reaction is introduced, the carbon dioxide concentration in the circulating gas increases, becoming an obstacle to the reduction reaction of iron oxide. Therefore, in the direct reduced iron manufacturing apparatus 100B, the concentration of carbon dioxide in the circulating gas is controlled to be within a predetermined range. Furthermore, due to differences in raw materials, the target carbon concentration may not always be achieved; therefore, in the direct reduced iron manufacturing apparatus 100B, the amount of hydrocarbon gas introduced is controlled to be within a predetermined range for the carbon concentration of the direct reduced iron.

[0081] The amount of hydrocarbon gas introduced can be adjusted, for example, by the following methods.

[0082] The relationship between the hydrocarbon gas introduction rate and the concentrations of reduced iron and carbon and tracer gas is predetermined, and the target value A of the reduced iron and carbon concentration is determined accordingly. Figure 3 The amount of hydrocarbon gas introduced is B. Next, the carbon concentration of the direct reduced iron is measured using a carbon analysis device 90. If the measured value is within the range of variation of the target carbon concentration, it is considered to be in normal operation and operation continues. If the measured value is higher than the target carbon concentration, the amount of hydrocarbon gas introduced is reduced; if the measured value is lower than the target carbon concentration, the amount of hydrocarbon gas introduced is increased. By controlling the amount of hydrocarbon gas introduced in this way, the carbon concentration of the direct reduced iron can be controlled within an appropriate range.

[0083] The apparatus 100B for manufacturing direct reduced iron and the method for manufacturing direct reduced iron according to the third embodiment have been described above. According to the apparatus 100B, carburizing of reduced iron can be performed in a direct reduction furnace using hydrogen, even with high-temperature exhaust. Since the amount of hydrocarbon gas introduced is controlled according to the carbon concentration in the direct reduced iron, the carbon concentration in the direct reduced iron can be controlled within an appropriate range.

[0084] It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Furthermore, without departing from the spirit of the present invention, the constituent elements in the above embodiments can be appropriately replaced with known constituent elements, and the above-described variations can also be appropriately combined.

[0085] Industrial availability The direct reduced iron manufacturing apparatus uses a direct reduction furnace with hydrogen, which can perform carburizing of reduced iron even when the exhaust is at high temperature, thus making it highly applicable to industry.

[0086] Explanation of reference numerals in the attached figures 20 Shaft furnace, 30 Dust removal device, 40 Dehydration device, 50 Heating device, 60 Hydrocarbon gas introduction device, 70 Control device, 80 Gas analysis device, 90 Carbon analysis device, 100 Direct reduced iron manufacturing device

Claims

1. An apparatus for manufacturing direct reduced iron, comprising: Vertical shaft furnace, using hydrogen to produce direct reduced iron; A dust removal device is used to remove dust from the exhaust gas of the vertical furnace; A dehydration device is used to dehydrate the exhaust gas after dust removal to obtain circulating gas. A hydrogen introduction device introduces hydrogen into the circulating gas to obtain a pre-heating gas containing the circulating gas and the hydrogen. A heating device heats the gas before heating to make it a reducing gas; as well as A hydrocarbon gas introduction device introduces hydrocarbon gas into at least one of the circulating gas, the pre-heating gas, and the reducing gas.

2. The apparatus for manufacturing direct reduced iron according to claim 1, further comprising: A gas analysis device for determining the concentration of tracer gas in the exhaust gas or the circulating gas; and The control device controls the amount of hydrocarbon gas introduced by the hydrocarbon gas introduction device based on the concentration of the tracer gas.

3. The apparatus for manufacturing direct reduced iron according to claim 2, wherein, The tracer gas is CO2.

4. The apparatus for manufacturing direct reduced iron according to claim 1 or 2, further comprising: A carbon analysis device is used to determine the carbon concentration in the directly reduced iron.

5. A method for manufacturing direct reduced iron, using a shaft furnace and hydrogen gas, the method comprising: The dust removal process involves removing dust from the exhaust gas of the vertical furnace. The process includes a dehydration step, in which the exhaust gas after dust removal is dehydrated to obtain a circulating gas; a hydrogen introduction step, in which hydrogen is introduced into the circulating gas to obtain a pre-heating gas containing the circulating gas and the hydrogen; a heating step, in which the pre-heating gas is heated to become a reducing gas; and a hydrocarbon gas introduction step, in which a hydrocarbon gas is introduced into at least one of the circulating gas, the pre-heating gas, and the reducing gas.

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