Method for producing reduced iron and reduction furnace

Abstract

Provided is a method for producing reduced iron, the method making it possible to accurately control the final carbon content of the reduced iron. The method comprises a reduction step in which iron oxide is reduced with a reducing gas blown into the reduction furnace to obtain reduced iron, a carburization step in which the carbon content of the reduced iron is increased with a carburizing gas blown into the reduction furnace, and a control step in which the amount of the carburizing gas to be blown into is controlled in accordance with the gangue content of the iron oxide.

Description

Method for producing reduced iron and reduction furnace

[0001] This invention relates to a method for producing reduced iron and a reduction furnace.

[0002] In the steelmaking process, for example, a method is used in which iron oxide is reduced in a vertical reduction furnace (shaft furnace) to produce reduced iron. In this method, the reduction furnace is filled with agglomerated iron ore (hereinafter simply referred to as iron oxide) such as sintered ore and pellets as the raw material for iron oxide, from the iron oxide loading inlet at the top of the reduction furnace. Then, CO and H are added to the reduction furnace. ２ Reduced iron is produced by blowing in a reducing gas containing [unspecified element] to reduce iron oxide. In this method, natural gas is used as the raw material gas for the reducing gas. This raw material gas is heated and reformed in a reformer along with the top gas. This generates the reducing gas. The top gas is the gas remaining after the reducing gas has been subjected to the reduction of iron oxide in the reduction furnace, and is generally discharged from the top of the reduction furnace. The generated reducing gas is blown into the reduction furnace and reacts with the iron oxide supplied from the top of the reduction furnace. The iron oxide is then reduced to reduced iron. The reduced iron is then discharged from the reduced iron outlet at the bottom of the reduction furnace.

[0003] As a technology relating to the production of such reduced iron, for example, Patent Document 1 discloses "a method for producing reduced iron by reducing iron oxide, comprising: a reduced iron production step of reducing the iron oxide to produce reduced iron by bringing the iron oxide into contact with a reducing gas while lowering it from the top of a reducing furnace, and discharging the reduced iron from the bottom of the reducing furnace; a reformed gas production step of extracting the top gas of the reducing furnace, adjusting its moisture content and performing dust removal treatment to produce a process gas, and supplying at least the process gas into a reformer to produce a reformed gas containing carbon monoxide and hydrogen in the reformer; a reduction gas supply step of supplying the generated reformed gas to the reducing furnace as the reducing gas; a cooling step of introducing a cooling gas into a cooling region set at the bottom of the reducing furnace to cool the cooling region; and a reformed gas introduction step of extracting a portion of the reformed gas and introducing it into the cooling region to increase the amount of carbon contained in the reduced iron passing through the cooling region."

[0004] Japanese Patent Publication No. 2017-88912

[0005] In the production of reduced iron, as described in Patent Document 1, before the reduced iron is discharged from the reduction furnace, carburizing of the reduced iron may be performed in the area below the reducing gas injection point of the reduction furnace up to the reduced iron discharge port (hereinafter also referred to as the lower part of the reduction furnace; the area above the reducing gas injection point of the reduction furnace up to the iron oxide charging inlet is also referred to as the upper part of the reduction furnace). Here, carburizing is a process that increases the carbon content of the reduced iron using carburizing gas. Carburizing is performed, for example, by adding CH4 to the lower part of the reduction furnace. ４ This is done by blowing in a gas mainly composed of [unspecified substance] and bringing the gas into contact with reduced iron.

[0006] When the carbon content of reduced iron increases, carbon acts as an auxiliary heat source when dissolving the reduced iron. Furthermore, the melting point of reduced iron decreases. As a result, the energy required to dissolve the reduced iron can be reduced. On the other hand, for example, when transporting reduced iron by sea, it is necessary to compress and mold the reduced iron into HBI (Hot Briquetted Iron) to prevent spontaneous combustion. However, if the carbon content of the reduced iron becomes excessively high, its moldability into HBI decreases. Therefore, during carburizing at the bottom of the reduction furnace, it is necessary to control the carbon content of the reduced iron discharged from the furnace (hereinafter also referred to as the final carbon content of reduced iron) to stay within the target range.

[0007] However, with the technology described in Patent Document 1, it is difficult to accurately control the final carbon content of reduced iron, and there is a need for improvement in this regard.

[0008] The present invention was developed in view of the above-mentioned circumstances and aims to provide a method for producing reduced iron that enables precise control of the final carbon content of reduced iron. The present invention also aims to provide a reduction furnace that can be suitably used in the above-mentioned method for producing reduced iron. In this disclosure, any numerical range expressed using "~" means a range that includes the numerical values ​​written before and after "~" as the lower limit and upper limit, respectively.

[0009] The inventors have conducted intensive research to solve the above problems. As a result, the inventors have found that by controlling the amount of blown-in carburizing gas according to the amount of gangue components contained in iron oxide (iron oxide raw materials such as iron ore) (hereinafter also referred to as the gangue amount of iron oxide), the above problems can be solved.

[0010] Based on the above findings, the present invention has been further studied and completed. That is, the gist configuration of the present invention is as follows.

[0011] 1. A method for producing reduced iron, comprising: a reduction step of reducing iron oxide with a reducing gas blown into a reduction furnace to obtain reduced iron; a carburizing step of increasing the carbon amount of the reduced iron with a carburizing gas blown into the reduction furnace; and a control step of controlling the amount of blown-in carburizing gas according to the gangue amount of the iron oxide.

[0012] 2. The method for producing reduced iron according to 1 above, wherein in the control step, the amount of blown-in carburizing gas is increased as the gangue amount of the iron oxide increases, and the amount of blown-in carburizing gas is decreased as the gangue amount of the iron oxide decreases. <00并将其代入式(1)进行计算。

[0013] 3. The method for producing reduced iron according to 1 or 2 above, wherein in the control step, the relationship of the following formula (1) is satisfied. (1 - G ０ ÷100) ÷ ((1 - G ÷ 100) ÷ A) ≤ V Ｃ / V Ｃ０ ≤ (1 - G ０ ÷100) ÷ ((1 - G ÷ 100) × A) ··· (1) In the formula, A: a constant, G: the gangue amount of iron oxide (mass %), G ０ : the reference gangue amount of iron oxide (mass %), V Ｃ : the amount of blown-in carburizing gas (Nm ３ / t), and V Ｃ０ : the reference amount of blown-in carburizing gas (Nm ３ / t). [[ID=-]]

[0014] 4. A reduction furnace, comprising: a reduction section for reducing iron oxide with a reducing gas to obtain reduced iron; a carburizing section for increasing the carbon amount of the reduced iron with a carburizing gas; and a control section for controlling the amount of blown-in carburizing gas according to the gangue amount of the iron oxide.

[0015] 5. The reduction furnace according to item 4, wherein the control unit controls the amount of carburizing gas injected to increase as the amount of iron oxide gangue increases, and to decrease as the amount of iron oxide gangue decreases.

[0016] 6. The reduction furnace according to 4 or 5, wherein the control unit satisfies the following relationship (1). (1-G ０ (÷100)÷((1-G÷100)÷A)≦V Ｃ / V Ｃ０ ≤ (1 - G) ０ (÷100)÷((1-G÷100)×A) ... (1) In the formula, A: constant, G: amount of iron oxide gangue (mass%), G ０ : Reference gangue amount of iron oxide (mass%), V Ｃ : Amount of carburizing gas blown in (Nm ３ / t), and V Ｃ０ : Standard injection rate of carburizing gas (Nm³) ３ / t), which is.

[0017] The present invention's method for producing reduced iron allows for precise control of the final carbon content of the reduced iron, which is extremely advantageous from an industrial standpoint. Furthermore, since the present invention's method for producing reduced iron does not require large-scale equipment expansion, it is also extremely advantageous in terms of cost.

[0018] This is a schematic diagram showing an example of the general configuration of a reduction furnace and its ancillary equipment. This is a schematic diagram showing an example of the general configuration of a reduction furnace with a control unit and its ancillary equipment. This is a schematic diagram showing an example of the functional block of a control unit.

[0019] [1] Method for Producing Reduced Iron Hereinafter, a method for producing reduced iron according to one embodiment of the present invention will be described with reference to Figure 1. Figure 1 is a schematic diagram showing an example of the general configuration of a reduction furnace and its ancillary equipment used in a method for producing reduced iron according to one embodiment of the present invention. In the figure, reference numeral 1 denotes a reduction furnace, 1a denotes iron oxide, 1b denotes reduced iron, 3 denotes a dust removal device, 4 denotes a dewatering device, 5 denotes a natural gas supply unit, 6 denotes an air supply unit, 7 denotes a reforming device, 8 denotes a reduction gas injection device, 9 denotes a carburizing gas injection device, 10 denotes a reduction unit, and 11 denotes a carburizing unit.

[0020] In a method for producing reduced iron according to one embodiment of the present invention, iron oxide is charged into the iron oxide charging inlet of the reduction furnace and gradually lowered. Then, reducing gas is blown in from the reducing gas injection port of the reduction furnace, and the iron oxide is reduced to reduced iron by the reducing gas in the reduction section. In addition, carburizing gas is blown in from the carburizing gas injection port at the bottom of the reduction furnace, and the carbon content of the reduced iron is increased by the carburizing gas in the carburizing section. After that, the reduced iron is discharged from the reduced iron discharge port of the reduction furnace. At this time, mainly CO, CO ２ , H ２ and H ２ O-containing top gas is discharged. This top gas is dust-removed by a dust removal device and its moisture content is adjusted by a dewatering device. Then, a portion of the top gas is sent to the reformer as the first top gas, which will become the raw material gas. The reformer receives the first top gas along with CH ４ The contained gas, for example, natural gas, is supplied from the natural gas supply unit. Then, in the reforming unit, the supplied gas is heated. A reforming reaction then occurs, mainly producing CO and H ２ A high-temperature reducing gas containing CO is generated. This reducing gas is then injected into the reduction furnace. The remaining portion of the furnace top gas is used as a second furnace top gas, for example, as a heating fuel in the combustion chamber of a reformer. The second furnace top gas after combustion as a heating fuel is usually CO ２ The gas containing the carbon dioxide is discharged outside the system. The carbon dioxide gas remaining after carburizing (hereinafter also referred to as post-reaction carbon dioxide gas) is discharged outside the reduction furnace from a carbon dioxide gas outlet located lower than the reduction gas inlet. The post-reaction carbon dioxide gas is then, for example, dedusted by a dust removal device, and then, as appropriate, supplied from the natural gas supply unit, such as CH4. ４ After adding the contained gas, it is again blown into the reduction furnace as a carburizing gas.

[0021] The following describes in more detail each step of the method for producing reduced iron according to one embodiment of the present invention.

[0022] (Reduction Process) In the reduction process, reducing gas is blown into the reduction furnace, and the iron oxide charged into the furnace is reduced by the reducing gas to obtain reduced iron. The conditions for the reduction process are not particularly limited and can be carried out by conventional methods.

[0023] For example, the gas composition of the reducing gas is CO: 1-70% by volume, H ２ Preferably, 30 to 99% by volume, with the remainder being 0 to 10% by volume. The remainder is N ２ Examples of inert gases include the following. The injection temperature of the reducing gas is 800 to 1100°C, and the injection volume of the reducing gas is 1400 to 3000 Nm³. ３ / t is preferred. Also, the amount of iron oxide charged is preferably 1300 to 1500 kg / t. Here, the unit of the amount of reducing gas blown in is (Nm). ３ The units (kg / t) and the amount of iron oxide charged are unit consumption units, respectively, representing the amount of reducing gas injected and the amount of iron oxide charged per ton of reduced iron produced. Similarly, the unit (Nm³) for the amount of carburizing gas injected, which will be discussed later, is also used. ３ Units such as ( / t) are also unit consumption rates. Hereafter, the amount of reducing gas injected and the amount of iron oxide charged may be referred to as the unit consumption rate for the injection of reducing gas and the unit consumption rate for the charging of iron oxide, etc.

[0024] (Carburizing Process) In the carburizing process, carburizing gas is blown into the reduction furnace, and the carbon content of the reduced iron is increased by the carburizing gas blown into the reduction furnace. The amount of carburizing in the carburizing process is the increase in carbon content of the reduced iron (mass %) during the carburizing process, and can be calculated, for example, by the following formula: [Amount of carburizing in the carburizing process (mass %)] = [Final carbon content of reduced iron (mass %)] - [Carbon content of reduced iron at the end of the reduction process (mass %)]

[0025] The composition of the carburizing gas is, for example, CH ４ : 30-100% by volume, H ２ Preferably, 0 to 50% by volume of the active ingredient and 0 to 70% by volume of the remainder. The remainder is N ２ Examples of inert gases include the following. The amount of carburizing gas injected can be determined by control in the control process described later. The amount of carburizing gas injected is, for example, 50 Nm³. ３ / t or more 500Nm ３ The amount should be determined within the range of / t or less. Other than the composition and amount of the carburizing gas injected, the conditions of the carburizing process are not particularly limited. For example, the injection temperature of the carburizing gas is preferably 0°C to 100°C.

[0026] (Control process) In the control process, it is important to control the amount of carburizing gas injected according to the amount of iron oxide gangue.

[0027] In other words, the inventors, through diligent research, obtained the following findings: In the carburizing process, carburizing of reduced iron proceeds by an endothermic reaction according to the following equation (2). This reaction proceeds on the surface of the metallic iron contained in the reduced iron. Therefore, for this reaction to proceed, it is advantageous to have less reduced iron, and consequently less gangue of iron oxide, which is the raw material. That is, the more gangue of iron oxide there is, the more difficult it becomes for this reaction to proceed. On the other hand, the less gangue of iron oxide there is, the easier it becomes for this reaction to proceed. CH ４ →C+2H ２ ... (2)

[0028] Based on the above, the control process controls the amount of carburizing gas injected according to the amount of iron oxide gangue. In the preferred embodiment of 1, the amount of carburizing gas injected is increased as the amount of iron oxide gangue increases, and the amount of carburizing gas injected is decreased as the amount of iron oxide gangue decreases. The amount of iron oxide gangue can be determined, for example, based on the standard amount of iron oxide gangue described later.

[0029] Here, gangue components are elements and compounds that do not contain Fe atoms. Examples of gangue components include CaO and SiO. ２ MgO, Al ２ O ３ and TiO ２ These are some examples. Furthermore, the amount of iron oxide gangue (mass %) can be confirmed, for example, by performing a component analysis of the iron oxide before charging it into the reduction furnace. The component analysis can be performed according to standard methods. It is also possible to calculate the amount of iron oxide gangue from the amount of gangue components contained in the reduced iron.

[0030] Furthermore, it is especially preferable to control the amount of carburizing gas injected according to the amount of iron oxide gangue so as to satisfy the following relationship (1). This is extremely advantageous because it is possible to accurately control the final carbon content of reduced iron even when the amount of iron oxide gangue changes in various ways. In a preferred embodiment of 1, V is formed based on the following equation (1). Ｃ / V Ｃ０Determine the appropriate range (the lower limit to the upper limit of equation (1) below). Then, V Ｃ / V Ｃ０ V Ｃ This process involves changing the parameters to produce reduced iron. (1-G) ０ (÷100)÷((1-G÷100)÷A)≦V Ｃ / V Ｃ０ ≤ (1 - G) ０ (÷100)÷((1-G÷100)×A) ... (1) In the formula, A: constant, G: amount of iron oxide gangue (mass%), G ０ : Reference gangue amount of iron oxide (mass%), V Ｃ : Amount of carburizing gas blown in (Nm ３ / t), and V Ｃ０ : Standard injection rate of carburizing gas (Nm³) ３ / t), which is.

[0031] Here, A is preferably 0.95, and more preferably 0.98.

[0032] Also, G ０ and V Ｃ０ These represent the standard amount of iron oxide gangue and the standard amount of carburizing gas injected, respectively. ０ and V Ｃ０ These represent the amount of iron oxide gangue (mass%) and the amount of carburizing gas injected (Nm³) when the target final carbon content of reduced iron (hereinafter also referred to as the target final carbon content of reduced iron) is obtained under base operating conditions in actual operation. ３ The base operating conditions are the amount of iron oxide charged, the composition of the reducing gas, the injection temperature of the reducing gas, and the injection rate of the reducing gas, which are specified or recommended for the reducing furnace to be used in actual operation (hereinafter also referred to as the reducing furnace to be used). The base operating conditions can be confirmed, for example, by the specifications (instruction manual) of the reducing furnace to be used or by past operating results. Conditions that cannot be confirmed in the specifications, such as the composition of the iron oxide to be used other than the gangue components and the injection temperature of the carburizing gas, should be set according to the conditions planned for actual operation.

[0033] For example, G ０ and V Ｃ０Each of these can be determined by conducting preliminary operation tests of the reduction furnace to be used. Specifically, preliminary operation tests of the reduction furnace to be used are conducted by varying the amount of iron gangue and the amount of carburizing gas injected, according to the base operating conditions of the reduction furnace to be used. Conditions that cannot be confirmed in the specifications, such as the composition of the iron oxide other than the gangue components and the injection temperature of the carburizing gas, are set according to the conditions planned for actual operation. Then, from the results of the preliminary operation tests, the amount of iron gangue and the amount of carburizing gas injected when the target final carbon content of reduced iron is obtained are determined, and G ０ and V Ｃ０ The error in each value is acceptable if it is within a range of ±5%, preferably ±3%. ０ and V Ｃ０ This can take on various values ​​depending on the type of reduction furnace to be used (structure, size, etc.). In the above preliminary operation test, the CH of the carburizing gas ４ and H ２ The remaining portion is N ２ Inert gases such as the following can be used.

[0034] Furthermore, CH in the composition of the carburizing gas ４ and H ２ Among the other gas types, mainly H ２ O, CO ２ CO and hydrocarbons with two or more carbon atoms affect the amount of carburization in the carburizing process. Therefore, the amount of carburization in the carburizing process can also be adjusted by changing the concentration of these gas species.

[0035] For example, H ２ O and CO ２ In particular, when the atmosphere becomes hot, CH follows equations (3) and (4) ４ It reacts with CO and H ２ This generates H in the carburizing gas. In this case, the increase in the amount of carburizing in the carburizing process is due to the H in the carburizing gas. ２ Oxygen and CO2 ２ Reducing the quantity is advantageous. ４ +H ２ O → CO + 3H ２ ... (3) CH ４ +CO ２ → 2CO + 2H２ ... (4)

[0036] In addition, CO and hydrocarbons having two or more carbon atoms generate C according to the following formulas (5), (⑥), and (⑦), increasing the carburizing amount in the carburizing process. CO + H ２ → C + H ２ O... (5) 2CO → C + CO ２ ... (6) C ｎ H ｍ → nC + m / 2H ２ ... (⑦) Here, n in the above formula (⑦) is an integer of 2 or more, and m is an integer corresponding to the number of n (the number of H atoms bonded to n C atoms).

[0037] Further, the target final carbon amount of the reduced iron is set, for example, in the range of 0.50 to 7.00% by mass.

[0038] Note that the blowing amount of the carburizing gas may be the total amount of the carburizing gas blown into the reduction furnace. Also, as the blowing amount of the carburizing gas, the total amount of hydrocarbons such as CH ４ that contribute to the increase in the carburizing amount in the carburizing process and CO among the carburizing gas blown into the reduction furnace may be used. Further, the blowing amount of the carburizing gas can be controlled by, for example, a blower (hereinafter also referred to as a carburizing gas blower) that feeds the carburizing gas, and further, a flow rate adjustment valve (hereinafter also referred to as a carburizing gas adjustment valve) disposed in the flow path of the carburizing gas, which constitutes a carburizing gas blowing device.

[0039] (Distribution process) In the distribution process, as described above, it is preferable to distribute the top gas into the first top gas and the second top gas. The top gas is the gas after the reducing gas is used for the reduction of iron oxide in the reduction process. In one example, the first top gas is fed to the reformer and used as a raw material gas for the reducing gas in the reforming process. The second top gas is used as a heating fuel in the combustion chamber of the reformer. Also, a part of the top gas may be distributed other than the first top gas and the second top gas, and for example, supplied to another device and stored. Also, the distribution amount may be appropriately determined according to the operating conditions.

[0040] Incidentally, the means for distributing and controlling the flow rate of the top gas is not particularly limited, and may follow a conventional method. For example, a mass flow controller or the like may be used.

[0041] (Reforming step) In the reforming step, it is preferable to generate a reducing gas from the first top gas and the CH ４ - containing gas. For example, the above-mentioned first top gas and natural gas, which is a CH ４ - containing gas, are supplied to the reforming apparatus. Then, in the reforming apparatus, the supplied gas is heated. And the reforming reactions of the following formulas (3)' and (4)' occur, and a high-temperature reducing gas mainly containing CO and H ２ is generated. CH ４ + H ２ O → CO + 3H ２ ΔH = 206 kJ / mol... (3)' CH ４ + CO ２ → 2CO + 2H ２ ΔH = 247 kJ / mol... (4)'

[0042] For the conditions other than the above, there is no particular limitation, and a conventional method may be followed.

[0043] [2] Reduction furnace Next, the reduction furnace according to an embodiment of the present invention will be described. The reduction furnace according to an embodiment of the present invention can be suitably used for the method for producing reduced iron according to an embodiment of the present invention described above.

[0044] The reduction furnace according to an embodiment of the present invention includes, for example, a reduction part that reduces iron oxide with a reducing gas to obtain reduced iron, a carburizing part that increases the carbon content of the reduced iron with a carburizing gas, and a control part that controls the blowing amount of the carburizing gas according to the gangue amount of the iron oxide. FIG. 2 is a schematic diagram showing an example of the schematic configuration of a reduction furnace having a control part and its auxiliary equipment. In the figure, reference numeral 12 is the control part. <00002The configuration of the reduction section is not particularly limited, and a general configuration can be used. For example, the reduction section is a region through which reducing gas injected from a reducing gas inlet flows, and which also serves as a filling section (downward path) for iron oxide charged from the iron oxide charging inlet at the top of the reduction furnace. The reduction section is connected to the reducing gas inlet and the furnace top gas outlet, respectively, and constitutes a path through which the reducing gas (furnace top gas) flows. The reduction section is also connected to the upper iron oxide charging inlet and the lower carburizing section, respectively, and constitutes a downward path for iron oxide (reduced iron).

[0046] The configuration of the carburizing section is not particularly limited, and a general configuration can be used. For example, the carburizing section is a region through which carburizing gas injected from the carburizing gas inlet flows, and which also serves as a descent path for reduced iron obtained from iron oxide in the reduction section. The carburizing section is connected to the carburizing gas inlet and the carburizing gas outlet, respectively, and constitutes a path through which the carburizing gas flows. Furthermore, the carburizing section is connected to the upper reduction section and the lower reduced iron outlet, respectively, and constitutes a descent path for reduced iron. That is, in one example, the iron oxide inlet, reduction section, carburizing section, and reduced iron outlet are arranged from top to bottom.

[0047] The control unit controls the amount of carburizing gas injected according to the amount of iron oxide gangue. The preferred control mode in the control unit is as described in [1] above.

[0048] As an example, the control unit may include an input unit that receives various setting values ​​and measurement data such as the amount of iron oxide gangue; a calculation unit that performs calculations on the input setting values ​​and measurement data; a storage unit that stores the setting values ​​and measurement data; and an output unit that outputs an operation signal to the carburizing gas injection device (i.e., an operation signal that changes the amount of carburizing gas injected) based on the calculation results of the calculation unit.

[0049] In this case, specifically, the control unit is an information processing device. Figure 3 shows an example of the functional blocks of the control unit. A reduction furnace may have a control unit as shown in Figure 3. As shown in Figure 3, the control unit has an input unit and an output unit that are connected to external devices for data communication, a calculation unit and a storage unit that stores various types of data, all of which are connected to each other for data communication.

[0050] The input and output sections are, for example, interfaces provided to enable data communication with external devices.

[0051] The arithmetic unit is, for example, a CPU. The arithmetic unit controls the operation of the entire control unit. Based on various setting values ​​and measurement data input from the external input unit or stored in the memory unit, the arithmetic unit calculates how to change the amount of carburizing gas injected and generates an operation signal to the carburizing gas injection device. The output unit outputs this operation signal. The arithmetic unit realizes the above functions, for example, by executing a program stored in the memory unit.

[0052] The storage unit is, for example, a writable non-volatile memory such as EPROM. While not particularly limited, the storage unit can include, for example, an HDD and an SSD.

[0053] For example, the carburizing gas injection device receives an operating signal output from the output unit and adjusts at least one of the following: the airflow rate of the carburizing gas blower that constitutes the device, and the opening degree of the carburizing gas control valve. This controls the amount of carburizing gas injected as described in [1] above.

[0054] Other than the above, there are no particular limitations on the configuration, and it is acceptable to use a configuration similar to that of conventionally known reduction furnaces.

[0055] The following describes some examples. These examples utilize a numerical analysis model capable of simulating heat transfer and reactions in a reduction furnace. The numerical analysis model and analysis conditions used are as follows. (Numerical Analysis Model and Analysis Conditions) ・Numerical analysis model: A one-dimensional model in which the region inside the reduction furnace is divided into 40 equally spaced areas in the vertical (height) direction. ・The regions from 1st to 20th are set as the reduction zone, and regions from 26th to 40th are set as the carburizing zone, starting from the top of the reduction furnace (the upper vertical side of the furnace). (Regions from 21st to 25th are set as transition zones where only the descent of reduced iron occurs (no reduction or carburizing occurs).) ・Using the above numerical analysis model, the mass balance and heat balance of the solid and gas in each region inside the reduction furnace, as well as the heat transfer between the solid and gas, are calculated sequentially at intervals of a small amount of time (1 second). ・Based on the above calculations, the changes in temperature and composition of the solid and gas in each region inside the reduction furnace are analyzed, and the final carbon content of the reduced iron is calculated. ・Source of numerical values ​​used in calculations such as reaction rates: Bechara et al.: Materials 2018, 11(7), 1094 (https: / / doi.org / 10.3390 / ma11071094) • Expected operating conditions: As described below.

[0056] Example 1: A reduction furnace (internal volume: 80 m³) is schematically shown in Figure 1. ３ ) and its ancillary equipment are used to produce reduced iron under the conditions described in Table 1. In other words, in Invention Example 1, reduced iron is produced by controlling the amount of carburizing gas injected according to the amount of iron gangue oxide under each condition. In particular, the amount of carburizing gas injected is changed according to the amount of iron gangue oxide to satisfy the relationship in equation (1) above. On the other hand, in Comparative Example 1, reduced iron is produced without changing the amount of carburizing gas injected from the base operating conditions.

[0057] Under all conditions, the operating period is 7 days, the target final carbon content of reduced iron is 2.50% by mass, G ０ is 4.99% by mass, V Ｃ０ 251 Nm ３ / t.

[0058] Table 1 shows the operating parameters based on the unit cost per ton of reduced iron produced. For example, if 1400 kg of iron oxide pellets are used to produce 1 ton of reduced iron, the amount of iron oxide pellets used is expressed as 1400 kg / ton. If 3000 tons of reduced iron are produced per day, multiply this amount by 3000 to obtain the daily parameters. Note that G ０ and V Ｃ０ This is obtained through preliminary operation tests in accordance with the procedure described above. The amount of iron oxide charged (iron oxide charge rate), the reducing gas injection temperature, the reducing gas injection rate (reducing gas injection rate), and the composition of the reducing gas under base operating conditions are based on the specifications of the reduction furnace used.

[0059] Conditions other than those listed above and in Table 1 shall be governed by conventional methods. The remainder of both the reducing gas and the carburizing gas shall be N ２ Furthermore, the blowing temperature of the carburizing gas was room temperature (25°C) in all cases.

[0060] Next, using the final carbon content of reduced iron calculated for each condition, the accuracy of controlling the final carbon content of reduced iron is evaluated according to the following criteria. The evaluation results are shown in Table 1. Pass (Excellent): In all conditions, the final carbon content of reduced iron is within the range of 2.40 to 2.60 mass% (target final carbon content of reduced iron ± 0.10 mass%). Fail (Poor): In at least one condition, the final carbon content of reduced iron is outside the range of 2.40 to 2.60 mass%.

[0061]

[0062] As shown in Table 1, the inventive example exhibits excellent control accuracy for the final carbon content of reduced iron. On the other hand, the comparative example shows insufficient control accuracy for the final carbon content of reduced iron.

[0063] Furthermore, when producing reduced iron using various reduction furnaces under various operating conditions and target final carbon content of reduced iron, the amount of carburizing gas injected should be controlled according to the amount of iron oxide gangue, and in particular, the H of the carburizing gas should be controlled to satisfy the relationship shown in equation (1) above. ２ By changing the quantity, the same results as above can be obtained. One example of this is described later as Example 2.

[0064] • Example 2 A reduction furnace (internal volume: 100 m³) schematically shown in Figure 1 ３ ) and its ancillary equipment are used to produce reduced iron under the conditions described in Table 2. In other words, in Invention Example 2, the amount of carburizing gas injected is controlled according to the amount of iron gangue oxide under each condition to produce reduced iron. Specifically, the amount of carburizing gas injected is changed according to the amount of iron gangue oxide to satisfy the relationship shown in equation (1) above. On the other hand, in Comparative Example 2, reduced iron is produced with almost no change in the amount of carburizing gas injected from the base operating conditions.

[0065] Under all conditions, the operating period is 7 days, the target final carbon content of reduced iron is 1.70% by mass, G ０ is 5.07 mass%, V Ｃ０ 259 Nm ３ The value is / t. All other conditions are the same as in Example 1, except those described above and in Table 2.

[0066] Next, using the final carbon content of reduced iron calculated for each condition, the accuracy of controlling the final carbon content of reduced iron is evaluated according to the following criteria. The evaluation results are shown in Table 2. Pass (Excellent): In all conditions, the final carbon content of reduced iron is within the range of 1.60 to 1.80 mass% (target final carbon content of reduced iron ±0.10 mass%). Fail (Poor): In at least one condition, the final carbon content of reduced iron is outside the range of 1.60 to 1.80 mass%.

[0067]

[0068] As shown in Table 2, the inventive example exhibits excellent control accuracy for the final carbon content of reduced iron. On the other hand, the comparative example shows insufficient control accuracy for the final carbon content of reduced iron.

[0069] 1. Reduction furnace 1a. Iron oxide 1b. Reduced iron 3. Dust removal device 4. Dehydration device 5. Natural gas supply unit 6. Air supply unit 7. Reforming device 8. Reduction gas injection device 9. Carburizing gas injection device 10. Reduction unit 11. Carburizing unit 12. Control unit

Claims

1. A method for producing reduced iron, comprising: a reduction step of reducing iron oxide with reducing gas blown into a reduction furnace to obtain reduced iron; a carburizing step of increasing the carbon content of the reduced iron with carburizing gas blown into the reduction furnace; and a control step of controlling the amount of carburizing gas blown in according to the amount of gangue in the iron oxide.

2. The method for producing reduced iron according to claim 1, wherein in the control step, the amount of carburizing gas injected is increased as the amount of iron oxide gangue increases, and the amount of carburizing gas injected is decreased as the amount of iron oxide gangue decreases.

3. The method for producing reduced iron according to claim 1 or 2, wherein in the control step, the relationship of the following formula (1) is satisfied. (1 - G ３ , ３ , Ｃ０ , Ｃ ÷ 100) ÷ ((1 - G ÷ 100) ÷ A) ≤ V Ｃ / V Ｃ０ ≤ (1 - G ０ ÷ 100) ÷ ((1 - G ÷ 100) × A) ··· (1) In the formula, A: constant, G: gangue amount of iron oxide (mass%), G ０ : reference gangue amount of iron oxide (mass%), V Ｃ : blowing amount of carburizing gas (Nm ３ / t), and V Ｃ０ : reference blowing amount of carburizing gas (Nm ３ / t), is as follows.

4. A reduction furnace comprising: a reduction section that reduces iron oxide with a reducing gas to obtain reduced iron; a carburizing section that increases the carbon content of the reduced iron with a carburizing gas; and a control section that controls the amount of carburizing gas injected according to the amount of gangue in the iron oxide.

5. The reduction furnace according to claim 4, wherein the control unit controls the amount of carburizing gas injected to increase as the amount of iron oxide gangue increases, and to decrease as the amount of iron oxide gangue decreases.

6. The reduction furnace according to claim 4 or 5, wherein the control unit satisfies the following relationship (1). (1-G ０ (÷100)÷((1-G÷100)÷A)≦V Ｃ / V Ｃ０ ≤ (1 - G) ０ (÷100)÷((1-G÷100)×A) ... (1) In the formula, A: constant, G: amount of iron oxide gangue (mass%), G ０ : Reference gangue amount of iron oxide (mass%), V Ｃ : Amount of carburizing gas blown in (Nm ３ / t), and V Ｃ０ : Standard injection rate of carburizing gas (Nm³) ３ / t), which is.

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