Method for producing reduced iron and reduction furnace

Abstract

Provided is a method for producing reduced iron, the method capable of accurately controlling the final carbon content of the reduced iron. This method includes: a reducing step of reducing iron oxide by a reducing gas blown into a reduction furnace to obtain reduced iron; a carburizing step of increasing the carbon content of the reduced iron by the carburizing gas blown into the reduction furnace; and a controlling step of controlling the H2 content of the carburizing gas according to the CH4 content of the carburizing gas.

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 [a certain 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 diligently conducted research to solve the above problems. As a result, the inventors found that the CH of carburizing gas４ According to the amount, it has been found that the above problems can be solved by controlling the H amount of the carburizing gas. ２

[0010]

[0011]

[0012] 1. 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 CH of the carburizing gas ４ According to the amount, the H amount of the carburizing gas is controlled. A method for producing reduced iron having a control step. ２

[0013] 2. In the control step, the H amount of the carburizing gas is increased as the CH amount of the carburizing gas increases, and the H amount of the carburizing gas is decreased as the CH amount of the carburizing gas decreases. The method for producing reduced iron according to 1 above. ４ ２ ４ ２ Ｈ０ Ｃ Ｃ０ Ｈ Ｈ０ Ｃ Ｃ０ Ｃ ３ Ｃ０ ３ Ｈ ４ ２ Ｈ０ ４ ２ 3. In the control step, the method for producing reduced iron according to 1 or 2 above, which satisfies the relationship of the following formula (1). (1 - (1 - R × A) ÷ (V / V)) ÷ B ≤ R ≤ (1 - (1 - R × B) ÷ (V / V)) ÷ A... (1) In the formula, A: constant, B: constant, V: blowing amount of carburizing gas (Nm / t), V: reference blowing amount of carburizing gas (Nm / t), R: ratio of H amount to CH amount of carburizing gas, and R: ratio of reference H amount to reference CH amount of carburizing gas.​​​​​​​​​​​​​​​​​​​​​​

[0014] 4. In the reduction furnace, H ２ A method for producing reduced iron according to any one of the above 1 to 3, further comprising a hydrogenation step of adding [something].

[0015] 5. In the vertical direction of the reduction furnace, the H of the hydrogen addition step ２ The method for producing reduced iron according to claim 4, wherein the injection position of the carburizing gas is the same as or above the injection position of the carburizing gas, and below the injection position of the reducing gas.

[0016] 6. A reducing 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 the carburizing gas is CH ４ Depending on the amount, the H of the carburizing gas ２ A reduction furnace having a control unit that controls the quantity.

[0017] 7. The control unit controls the CH of the carburizing gas. ４ The amount of H in the carburizing gas increases as the quantity increases. ２ Increase the amount of the carburizing gas CH ４ The amount decreases as the H of the carburizing gas decreases. ２ The reduction furnace according to item 6, which is controlled to reduce the amount.

[0018] 8. The reduction furnace according to 6 or 7, wherein the control unit satisfies the following relationship (1). (1 - (1 - R Ｈ０ ×A)÷(V Ｃ / V Ｃ０ )) ÷ B ≤ R Ｈ ≤ (1 - (1 - R) Ｈ０ ×B)÷(V) Ｃ / V Ｃ０ ))÷A...(1) In the formula, A: constant, B: constant, V Ｃ : Amount of carburizing gas blown in (Nm ３ / t) V Ｃ０ : Standard injection rate of carburizing gas (Nm³) ３ / t), R Ｈ CH4 carburizing gas ４ H in relation to quantity ２ The ratio of quantities, and R Ｈ０ : Standard CH for carburizing gas ４ Reference H for quantity２ It is the ratio of quantities.

[0019] 9. In the reduction furnace, H ２ A reduction furnace according to any one of 6 to 8, further comprising a hydrogen addition section for adding...

[0020] 10. In the vertical direction of the reduction furnace, the H of the hydrogen addition section ２ The reduction furnace according to 9, wherein the injection position of the carburizing gas is the same as or above the injection position of the carburizing gas, and below the injection position of the reducing gas.

[0021] 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.

[0022] 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.

[0023] [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, 11 denotes a carburizing unit, 12 denotes a hydrogen supply unit, and 13 denotes an additional hydrogen injection device.

[0024] 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.

[0025] The following describes in more detail each step of the method for producing reduced iron according to one embodiment of the present invention.

[0026] (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.

[0027] 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.

[0028] (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 %)]

[0029] The composition of the carburizing gas can be determined by control in the control process described later. For example, the composition of the carburizing gas may be CH ４ : 30-100% by volume, H ２ The percentage should be determined within the range of 0-50 volume%, and the remainder within the range of 0-70 volume%. The remainder is N ２ Examples of inert gases include the following. Furthermore, the amount of carburizing gas injected may be constant or determined by control in the control process described later. For example, the amount of carburizing gas injected may be 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.

[0030] (Control Step) In the control step, it is important to control the amount of H in the carburizing gas according to the amount of CH in the carburizing gas. ４ That is, as a result of intensive research, the inventors obtained the following findings. In the carburizing step, carburization of reduced iron proceeds by an exothermic reaction according to the following formula (2). In this reaction, H is generated as a by-product. That is, H affects the reaction equilibrium of formula (2). For example, in the gas present in the carburizing section of the reduction furnace, which is the region where the reaction occurs, that is, the higher the amount of H with respect to the amount of CH in the carburizing gas, the more difficult it is for the reaction to proceed. On the other hand, the lower the amount of H with respect to the amount of CH in the carburizing gas, the easier it is for the reaction to proceed. CH → C + 2H ... (2) ２

[0031] That is, as a result of intensive research, the inventors obtained the following findings. In the carburizing step, carburization of reduced iron proceeds by an exothermic reaction according to the following formula (2). In this reaction, H is generated as a by-product. That is, H affects the reaction equilibrium of formula (2). For example, in the gas present in the carburizing section of the reduction furnace, which is the region where the reaction occurs, that is, the higher the amount of H with respect to the amount of CH in the carburizing gas, the more difficult it is for the reaction to proceed. On the other hand, the lower the amount of H with respect to the amount of CH in the carburizing gas, the easier it is for the reaction to proceed. ２ is generated. That is, H ２ affects the reaction equilibrium of formula (2). For example, in the gas present in the carburizing section of the reduction furnace, which is the region where the reaction occurs, that is, the higher the amount of H with respect to the amount of CH in the carburizing gas, the more difficult it is for the reaction to proceed. On the other hand, the lower the amount of H with respect to the amount of CH in the carburizing gas, the easier it is for the reaction to proceed. ４ amount of H ２ with respect to the amount of CH in the carburizing gas increases, the more difficult it is for the reaction to proceed. On the other hand, the lower the amount of H ４ with respect to the amount of CH in the carburizing gas, the easier it is for the reaction to proceed. CH ２ → C + 2H ４ ... (2) ２ <00​​​​​​​​​​​​​​​​​​​​​​​​​​Ｈ Determine the appropriate range (lower limit to upper limit of the following formula (1)). Then, produce reduced iron so that R Ｈ falls within the appropriate range. For example, the supply amount of H ２ to the carburizing gas before being blown into the reduction furnace, and / or the supply amount of H ２ to the carburizing gas in the hydrogen addition step described later is changed, and R Ｈ is controlled within the appropriate range. (1 - (1 - R Ｈ０ × A) ÷ (V Ｃ / V Ｃ０ )) ÷ B ≤ R Ｈ ≤ (1 - (1 - R Ｈ０ × B) ÷ (V Ｃ / V Ｃ０ )) ÷ A ··· (1) In the formula, A: constant, B: constant, V Ｃ : blowing amount of carburizing gas (Nm ３ / t) V Ｃ０ : reference blowing amount of carburizing gas (Nm ３ / t), R Ｈ : ratio of the amount of H ４ to the amount of CH ２ in the carburizing gas, and R Ｈ０ : ratio of the reference amount of H ４ to the reference amount of CH ２ in the carburizing gas.

[0034] Here, A is preferably 0.36 to 0.42, more preferably 0.39 to 0.42. B is preferably 0.42 to 0.48, more preferably 0.42 to 0.45. As a combination of A and B, preferably A = 0.36, B = 0.48, more preferably A = 0.39, B = 0.45, and still more preferably A = 0.40, B =​​​​​​​​​​​​​​​​​４ Amount (Nm ３ / t) and reference H ２ Amount (Nm ３ The same method can be used to calculate ( / t).

[0036] Also, V Ｃ０ and R Ｈ０ These represent the standard injection rate of carburizing gas and the standard CH, respectively. ４ Reference H for quantity ２ It is the ratio of quantities. That is, V Ｃ０ and R Ｈ０ Each of these values ​​represents 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 in actual operation under base operating conditions. ３ CH4 ( / t) and carburizing gas ４ H in relation to quantity ２ This refers to the ratio of quantities. Base operating conditions are the specified or recommended amount of iron oxide to be charged, the composition of the reducing gas, the injection temperature of the reducing gas, and the injection rate of the reducing gas, etc., for the reducing furnace to be used in actual operation (hereinafter also referred to as the reducing furnace to be used). Base operating conditions can be confirmed, for example, from the specifications (instruction manual) of the reducing furnace to be used or from past operating records. Conditions that cannot be confirmed in the specifications, such as the composition of the iron oxide to be used or the injection temperature of the carburizing gas, should be set according to the conditions planned for actual operation.

[0037] For example, V Ｃ０ and R Ｈ０ These can be determined by conducting preliminary operation tests of the reduction furnace to be used. Specifically, the amount of carburizing gas injected and the CH4 of the carburizing gas can be determined based on the base operating conditions of the reduction furnace to be used. ４ H in relation to quantity ２ Preliminary operation tests of the planned reduction furnace will be conducted by varying the ratio of quantities. Conditions that cannot be confirmed in the specifications, such as the composition of the iron oxide used, the injection temperature and injection volume of the carburizing gas, will be set according to the conditions planned for actual operation. Then, based on the results of the preliminary operation tests, the injection volume of the carburizing gas and the CH4 of the carburizing gas that will yield the target final carbon content of the reduced iron will be determined. ４ H in relation to quantity ２ Find the ratio of the quantities, VＣ０ and R Ｈ０ The error in each value is acceptable if it is within a range of ±5%, preferably ±3%. Ｃ０ and R Ｈ０ 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.

[0038] Also, the H of the carburizing gas ２ The amount is controlled, for example, by adjusting the H2O2 amount to the carburizing gas before it is injected into the reduction furnace. ２ This can be done by adjusting the supply amount. As will be explained in the hydrogen addition process described later, the reduction furnace has a separate inlet for the carburizing gas, H ２ An inlet is provided, and H is added to the carburizing gas in the reduction furnace. ２ You may also add H to the carburizing gas. ２ The amount supplied is, for example, each H that makes up the hydrogen supply unit. ２ Flow control valves (hereinafter referred to as H) placed in the flow path ２ It can be controlled by a control valve (also called a regulating valve).

[0039] 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.

[0040] 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 +H２ O → CO + 3H ２ ... (3) CH ４ +CO ２ → 2CO + 2H ２ ... (4)

[0041] In addition, CO and hydrocarbons with two or more carbon atoms generate C according to the following equations (5), (6), and (7), increasing the amount of carburized material 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, in formula (7) above, n 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). Note that the carburizing gas according to one embodiment of the present invention is basically CH ４ Since it is composed of hydrocarbons such as those shown above, the effect of the reaction equilibrium in formula (5) is hardly observed.

[0042] Furthermore, the target final carbon content of reduced iron is set, for example, within the range of 0.50 to 7.00 mass%.

[0043] (Hydrogen addition process) In the reduction furnace, hydrogen is added to the carburizing gas. ２ The system may further include an optional hydrogen addition step.

[0044] In this case, in the vertical direction of the reduction furnace, H ２ It is preferable that the injection position of the carburizing gas is the same as or above the injection position of the carburizing gas, and below the injection position of the reducing gas.

[0045] Furthermore, when performing the hydrogen addition process, the carburizing gas is H ２ This refers to the carburizing gas after the addition of H. In other words, the amount of carburizing gas injected includes H in the hydrogen addition process. ２ The amount of blown-in gas is added. Also, the CH of the carburizing gas ４ Quantity and H ２ The amounts are as follows: H ２ CH contained in the carburized gas after addition ４ Quantity and H２ It means quantity.

[0046] (Distribution Process) In the distribution process, as described above, it is preferable to distribute the top gas into a first top gas and a second top gas. The top gas is the gas remaining after the reducing gas has been used to reduce iron oxide in the reduction process. In one example, the first top gas is supplied to the reformer and used as the raw material gas for the reducing gas in the reformer. The second top gas is used as heating fuel in the combustion chamber of the reformer. Alternatively, a portion of the top gas may be distributed to other sources besides the first and second top gases, for example, to be supplied to or stored in another device. The distribution amount may be determined as appropriate according to the operating conditions.

[0047] Furthermore, the means for distributing and controlling the flow rate of the top gas are not particularly limited and can be done according to conventional methods. For example, a mass flow controller may be used.

[0048] (Reforming process) In the reforming process, the first top gas and CH ４ It is preferable to generate a reducing gas from the contained gas. For example, in a reformer, the first furnace top gas and CH ４ Natural gas, which is the contained gas, is supplied. Then, the supplied gas is heated in the reforming unit. Then, the reforming reactions shown in equations (3)' and (4)' occur, mainly producing CO and H ２ A high-temperature reducing gas containing CH is generated. ４ +H ２ O → CO + 3H ２ ΔH=206kJ / mol...(3)' CH ４ +CO ２ → 2CO + 2H ２ ΔH=247kJ / mol...(4)'

[0049] Other than the conditions mentioned above, there are no particular limitations; you may follow the usual law.

[0050] [2] Reduction Furnace Next, a reduction furnace according to one embodiment of the present invention will be described. The reduction furnace according to one embodiment of the present invention can be suitably used in the method for producing reduced iron according to the above embodiment of the present invention.

[0051] A reduction furnace according to one embodiment of the present invention includes, for example, 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 the carburizing gas being CH ４ Depending on the amount, the H of the carburizing gas ２ It has a control unit that controls the quantity. Figure 2 is a schematic diagram showing an example of the general configuration of a reduction furnace and its ancillary equipment having a control unit. In the figure, reference numeral 14 denotes the control unit.

[0052] The 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).

[0053] 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.

[0054] In the control unit, the carburizing gas CH ４ Depending on the amount, the H of the carburizing gas ２ The quantity is controlled. The preferred control method in the control unit is as described in [1] above.

[0055] Furthermore, in a reduction furnace according to one embodiment of the present invention, H is added to the carburizing gas in the reduction furnace. ２ It may further have an optional hydrogen addition section to add H. ２The inlet is connected, for example, to the carburizing section through which the carburizing gas flows. In the hydrogen addition section, in the vertical direction of the reduction furnace, H ２ It is preferable that the injection position (inlet) of the carburizing gas is the same as or higher than the injection position (inlet) of the carburizing gas, and lower than the injection position (inlet) of the reducing gas.

[0056] As another example, the control unit can set various values ​​and the CH of the carburizing gas. ４ An input unit for inputting measurement data such as quantity; a calculation unit for processing the input set values ​​and measurement data; a storage unit for storing the set values ​​and measurement data; and a unit for determining the H of carburizing gas based on the calculation results from the calculation unit. ２ One example is a device having an output unit that outputs an operation signal that changes the quantity.

[0057] 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.

[0058] The input and output sections are, for example, interfaces provided to enable data communication with external devices.

[0059] 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 the H of the carburized gas. ２ The calculation determines how to change the amount of H in the carburizing gas. ２ An operating signal that changes the amount, for example, the amount of H supplied to the carburizing gas before it is injected from the hydrogen supply unit into the reduction furnace. ２ An operating signal that changes the supply amount, and / or H from the hydrogen supply unit to the additional hydrogen injection device. ２ The unit generates an operating signal that changes the supply amount. The output unit outputs the operating signal. The calculation unit realizes the above-mentioned functions, for example, by executing a program stored in the memory unit.

[0060] 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.

[0061] For example, the hydrogen supply unit receives the operating signal output from the output unit, and each H ２ The opening of the control valve is adjusted to control the amount of hydrogen supplied to the carburizing gas before it is injected from the hydrogen supply unit into the reduction furnace. ２ The amount of hydrogen supplied, and / or the amount of hydrogen supplied from the hydrogen supply unit to the additional hydrogen injection unit. ２ The supply amount is changed. This changes the H of the carburizing gas as described in [1] above. ２ Control the quantity.

[0062] 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.

[0063] 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 solids and gases in each region inside the reduction furnace, as well as the heat transfer between solids and gases, 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 solids and gases in each region inside the reduction furnace are analyzed, and the final carbon content of 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.

[0064] 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 according to the conditions listed in Table 1. That is, in Invention Example 1, the carburizing gas CH ４ Depending on the amount, the H of the carburizing gas ２ Reduced iron is produced by controlling the quantity. In particular, the carburizing gas CH ４ Depending on the quantity, the H of the carburizing gas should satisfy the relationship shown in equation (1) above. ２ The amount is changed. On the other hand, in Comparative Example 1, the H of the carburizing gas ２ Reduced iron is produced with virtually no change in quantity from the base operating conditions.

[0065] Under all conditions, the operating period is 7 days, the target final carbon content of reduced iron is 3.00% by mass, V Ｃ０ 250 Nm ３ / t, R Ｈ０ It is 0.29.

[0066] 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 get the daily parameters. Note that V Ｃ０ and R Ｈ０ 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.

[0067] 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.

[0068] 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 2.90 to 3.10 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 2.90 to 3.10 mass%.

[0069]

[0070] 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.

[0071] Furthermore, when producing reduced iron using various reduction furnaces under various operating conditions and target final carbon content of reduced iron, the CH4 of the carburizing gas is also a factor. ４ Depending on the amount, the H of the carburizing gas ２ To control the amount, in particular, to satisfy the relationship in equation (1) above, the H of the carburizing gas ２ By changing the quantity, the same results as above can be obtained. One example of this is described later as Example 2.

[0072] • Example 2 A reduction furnace (internal volume: 100 m³) schematically shown in Figure 1 ３ ) and its ancillary facilities produce reduced iron according to the conditions listed in Table 2. That is, in Invention Example 2, the carburizing gas CH ４ Depending on the amount, the H of the carburizing gas ２ Reduced iron is produced by controlling the quantity. In particular, the carburizing gas CH ４ Depending on the quantity, the H of the carburizing gas should satisfy the relationship shown in equation (1) above. ２ The amount is changed. On the other hand, in Comparative Example 2, the H of the carburizing gas ２ Reduced iron is produced with virtually no change in quantity from the base operating conditions.

[0073] Under all conditions, the operating period is 7 days, the target final carbon content of reduced iron is 1.90% by mass, V Ｃ０ 221 Nm ３ / t, R Ｈ０The value is 0.33. All other conditions are the same as in Example 1, except those described above and in Table 2.

[0074] 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 1.80 to 2.00 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 1.80 to 2.00 mass%.

[0075]

[0076] 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.

[0077] 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. Hydrogen supply unit 13. Additional hydrogen injection device 14. Control unit

Claims

1. A reduction step in which iron oxide is reduced to reduced iron by a reducing gas blown into a reduction furnace; a carburizing step in which the carbon content of the reduced iron is increased by a carburizing gas blown into the reduction furnace; and the carburizing gas is CH ４ Depending on the amount, the H of the carburizing gas ２ A method for producing reduced iron, comprising a control step for controlling the quantity.

2. In the control step, the CH of the carburizing gas ４ The amount of H in the carburizing gas increases as the quantity increases. ２ Increase the amount of the carburizing gas CH ４ The amount decreases as the H of the carburizing gas decreases. ２ A method for producing reduced iron according to claim 1, wherein the amount is controlled to decrease.

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 - (1 - R Ｈ０ × A) ÷ (V Ｃ / V Ｃ０ )) ÷ B ≤ R Ｈ ≤ (1 - (1 - R Ｈ０ × B) ÷ (V Ｃ / V Ｃ０ )) ÷ A ··· (1) In the formula, A: constant, B: constant, V Ｃ : injection amount of carburizing gas (Nm ３ / t) V Ｃ０ : reference injection amount of carburizing gas (Nm ３ / t), R Ｈ : ratio of the amount of H ４ to the amount of CH ２ in the carburizing gas, and R Ｈ０ : ratio of the amount of reference H ４ to the amount of reference CH ２ in the carburizing gas.

4. In the reduction furnace, H ２ A method for producing reduced iron according to any one of claims 1 to 3, further comprising a hydrogenation step of adding [a certain substance].

5. In the vertical direction of the reduction furnace, the H of the hydrogen addition step ２ The method for producing reduced iron according to claim 4, wherein the injection position of the carburizing gas is the same as or above the injection position of the carburizing gas, and below the injection position of the reducing gas.

6. A reducing 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 the carburizing gas is CH ４ Depending on the amount, the H of the carburizing gas ２ A reduction furnace having a control unit that controls the quantity.

7. The control unit controls the CH of the carburizing gas. ４ The amount of H in the carburizing gas increases as the quantity increases. ２ Increase the amount of the carburizing gas CH ４ The amount decreases as the H of the carburizing gas decreases. ２ A reduction furnace according to claim 6, which controls the amount to decrease.

8. The reduction furnace according to claim 6 or 7, wherein the control unit satisfies the following relationship (1): (1 - (1 - R Ｈ０ ×A)÷(V Ｃ / V Ｃ０ )) ÷ B ≤ R Ｈ ≤ (1 - (1 - R) Ｈ０ ×B)÷(V) Ｃ / V Ｃ０ ))÷A...(1) In the formula, A: constant, B: constant, V Ｃ : Amount of carburizing gas blown in (Nm ３ / t) V Ｃ０ : Standard injection rate of carburizing gas (Nm³) ３ / t), R Ｈ CH4 carburizing gas ４ H in relation to quantity ２ The ratio of quantities, and R Ｈ０ : Standard CH for carburizing gas ４ Reference H for quantity ２ It is the ratio of quantities.

9. In the reduction furnace, H ２ A reduction furnace according to any one of claims 6 to 8, further comprising a hydrogen addition unit for adding a hydrogen.

10. In the vertical direction of the reduction furnace, the H of the hydrogen addition section ２ The reduction furnace according to claim 9, wherein the injection position of the carburizing gas is the same as or above the injection position of the carburizing gas, and below the injection position of the reducing gas.

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