Method for producing reduced iron and reduction furnace

Abstract

Provided is a method for producing reduced iron, said method making it possible to produce reduced iron having a lower energy requirement for dissolution. The blowing amount of a carburizing gas is modified in accordance with the blowing temperature of a reducing gas.

Description

Method for producing reduced iron and reduction furnace

[0001] The present 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, agglomerated iron ore such as sintered ore or pellets (hereinafter simply referred to as iron oxide) is charged into the reduction furnace through an iron oxide charging port at the top of the reduction furnace as the iron oxide raw material. Then, CO and H ２ Reduced iron is produced by injecting a reducing gas containing the above-mentioned element into the furnace to reduce iron oxide. In this method, natural gas or the like is used as the raw material gas for the reducing gas. This raw material gas is heated and reformed together with the furnace top gas in a reformer. This generates the reducing gas. The furnace top gas is the gas remaining after the reducing gas has been used to reduce iron oxide in the reduction furnace, and is generally discharged from the furnace top. The generated reducing gas is injected into the reduction furnace and reacts with iron oxide supplied from above the reduction furnace. The iron oxide is then reduced to form reduced iron. The reduced iron is then discharged from a reduced iron outlet at the bottom of the reduction furnace.

[0003] As a technology related to the production of such reduced iron, for example, Patent Document 1 discloses the following: "A method for producing reduced iron by reducing iron oxide, comprising: a reduced iron production step of bringing the iron oxide into contact with a reducing gas while causing it to fall from a top of a reduction furnace in order to reduce the iron oxide to produce reduced iron, and discharging the reduced iron from the bottom of the reduction furnace; a reformed gas production step of extracting furnace top gas from the reduction furnace, adjusting the moisture content thereof, and performing dust removal treatment thereon 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 reducing gas supply step of supplying the produced reformed gas to the reduction furnace as the reducing gas; a cooling step of introducing a cooling gas into a cooling region set in a lower part of the reduction 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 carbon content of the reduced iron passing through the cooling region."

[0004] JP 2017-88912 A

[0005] In the production of reduced iron, as in Patent Document 1, there are cases where the reduced iron is carburized in a region below the reducing gas injection position of the reducing furnace up to the reduced iron discharge port (hereinafter also referred to as the lower part of the reducing furnace; the region above the reducing gas injection position of the reducing furnace up to the iron oxide charging port is also referred to as the upper part of the reducing furnace) before the reduced iron is discharged from the reducing furnace. Here, carburization is a process of increasing the carbon content of the reduced iron by using carburizing gas. Carburization can be carried out, for example, by injecting CH ４ The reduction is carried out by blowing in a gas containing CO as a main component and bringing the gas into contact with the reduced iron.

[0006] When the carbon content of reduced iron increases, the carbon acts as an auxiliary heat source when melting the reduced iron. Also, the melting point of the reduced iron decreases. As a result, the energy required to melt the reduced iron (hereinafter also referred to as the required melting energy) can be reduced.

[0007] In recent years, from the viewpoint of protecting the global environment, etc., there has been a demand for further reduction in the energy required for melting. Therefore, there is currently a demand for producing reduced iron that requires less energy to melt.

[0008] The present invention has been developed in view of the above-described current situation, and aims to provide a method for producing reduced iron that enables production of reduced iron with lower melting energy requirements. Another object of the present invention is to provide a reduction furnace that can be suitably used in the above-described method for producing reduced iron. In this disclosure, any numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively.

[0009] The inventors have conducted extensive research to solve the above problems. First, the inventors attempted to reduce the energy required for melting by further increasing the carbon content of reduced iron. However, carbon reacts with oxygen to form carbon dioxide during the melting of reduced iron, generating heat in the process and assisting the melting of the reduced iron. Therefore, simply increasing the carbon content of reduced iron increases emissions of carbon dioxide, a greenhouse gas, which is counter to global environmental protection.

[0010] Therefore, rather than simply increasing the amount of carbon contained in reduced iron, the inventors focused on the form of carbon contained in reduced iron and conducted further intensive research in order to increase the heat generation efficiency per amount of carbon contained in reduced iron. As a result, the inventors obtained the following findings: Carbon contained in reduced iron exists in two forms: as elemental carbon and as Fe ３ C (cementite). ３ When the reduced iron is dissolved, C generates heat through the decomposition reaction according to the following formula (3), and therefore can supply more energy than when carbon exists as a single substance. ３ C = 3Fe + C (3) That is, Fe in reduced iron ３ Increasing the amount of carbon present in C increases the heat generation efficiency per amount of carbon contained in reduced iron, and it is possible to further reduce the energy required for melting while suppressing an increase in carbon dioxide emissions.

[0011] Based on the above findings, the inventors further conducted research and discovered the following: The form of carbon present in reduced iron is affected by the temperature of the carburized part, particularly the temperature of the upper region of the carburized part. There is a correlation between the temperature of the reducing gas injection and the temperature of the carburized part. Therefore, by changing the flow conditions of the carburizing gas, particularly the injection amount of the carburizing gas, depending on the injection temperature of the reducing gas, it is possible to control the Fe content in the reduced iron. ３ It is possible to increase the amount of carbon present in C. As a result, the heat generation efficiency per amount of carbon contained in the reduced iron is increased, and the energy required for melting is further reduced while suppressing an increase in carbon dioxide emissions.

[0012] The present invention has been completed based on the above findings and further investigations. That is, the gist and configuration of the present invention are as follows.

[0013] 1. A method for producing reduced iron, comprising: a reduction step in which iron oxide is reduced to form reduced iron by using a reducing gas blown into a reduction furnace; a carburization step in which the carbon content of the reduced iron is increased by using a carburizing gas blown into the reduction furnace; and a control step in which the amount of carburizing gas blown in is changed depending on the blowing temperature of the reducing gas.

[0014] 2. The method for producing reduced iron according to 1, wherein in the control step, the amount of carburizing gas injected is changed so that the temperature of the upper region of the carburizing section of the reducing furnace is in the range of 550 to 800°C. Here, the upper region of the carburizing section is the region from midway between the carburizing gas inlet and the carburizing gas outlet to the carburizing gas outlet in the height direction of the reducing furnace.

[0015] 3. The method for producing reduced iron according to 1 or 2 above, wherein in the control step, when the blowing temperature of the reducing gas is lower than the standard blowing temperature of the reducing gas minus 80°C, the blowing amount of the carburizing gas satisfies the relationship of the following formula (1), and when the blowing temperature of the reducing gas is higher than the standard blowing temperature of the reducing gas plus 90°C, the blowing amount of the carburizing gas satisfies the relationship of the following formula (2). ０ × (3.7 (T / T ０ )-2.4) ...(1) V ０ × (4.3 (T / T ０ )-3.7)≦V (2) where V: amount of carburizing gas blown in (Nm ３ / h), V ０ : Standard injection amount of carburizing gas (Nm ３ / h) and T: reducing gas blowing temperature (°C) and T ０ : Standard blowing temperature of reducing gas (℃)

[0016] 4. A distribution step in which the furnace top gas discharged from the reduction furnace is distributed into a first furnace top gas and a second furnace top gas, and the furnace top gas is a gas obtained after the reducing gas has been used for reducing the iron oxide in the reduction step; and ４a reforming step of generating the reducing gas from a containing gas.

[0017] 5. A reducing furnace comprising: a reduction section that reduces iron oxide with a reducing gas to produce reduced iron; a carburizing section that increases the amount of carbon contained in the reduced iron with a carburizing gas; and a control section that changes the amount of carburizing gas blown in accordance with the blowing temperature of the reducing gas.

[0018] 6. The reducing furnace according to 5 above, wherein the control unit changes the amount of carburizing gas injected so that the temperature of the upper region of the carburizing section of the reducing furnace is in the range of 550 to 800°C. Here, the upper region of the carburizing section is the region from midway between the carburizing gas inlet and the carburizing gas outlet to the carburizing gas outlet in the height direction of the reducing furnace.

[0019] 7. The reducing furnace according to 5 or 6 above, wherein, under the control of the control unit, when the blowing temperature of the reducing gas is less than the standard blowing temperature of the reducing gas minus 80°C, the blowing amount of the carburizing gas satisfies the relationship of the following formula (1), and when the blowing temperature of the reducing gas is more than the standard blowing temperature of the reducing gas plus 90°C, the blowing amount of the carburizing gas satisfies the relationship of the following formula (2). V≦V ０ × (3.7 (T / T ０ )-2.4) ...(1) V ０ × (4.3 (T / T ０ )-3.7)≦V (2) where V: amount of carburizing gas blown in (Nm ３ / h), V ０ : Standard injection amount of carburizing gas (Nm ３ / h) and T: reducing gas blowing temperature (°C) and T ０ : Standard blowing temperature of reducing gas (℃)

[0020] According to the method for producing reduced iron of the present invention, it is possible to produce reduced iron with an improved heat generation efficiency per carbon amount contained in the reduced iron, thereby further reducing the energy required for melting while suppressing an increase in carbon dioxide emissions, which is extremely advantageous from an industrial perspective. Furthermore, the method for producing reduced iron of the present invention is also extremely advantageous in terms of cost because it does not require large-scale expansion of facilities.

[0021] 1 is a schematic diagram showing an example of a schematic configuration of a reducing furnace and its auxiliary equipment, and FIG. 2 is a schematic diagram showing an example of a schematic configuration of a reducing furnace having a control unit and its auxiliary equipment, and FIG. 3 is a schematic diagram showing an example of a functional block of a control unit.

[0022] [1] Manufacturing method of reduced iron Hereinafter, a manufacturing method of reduced iron according to one embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing an example of the general configuration of a reducing furnace and its auxiliary equipment used in a manufacturing method of reduced iron according to one embodiment of the present invention. In the figure, reference numeral 1 denotes a reducing furnace, 1a denotes iron oxide, 1b denotes reduced iron, 3 denotes a dust removal device, 4 denotes a dehydration device, 5 denotes a natural gas supply section, 6 denotes an air supply section, 7 denotes a reforming device, 8 denotes a reducing gas injection device, 9 denotes a carburizing gas injection device, 10 denotes a reduction section, and 11 denotes a carburizing section.

[0023] In a method for producing reduced iron according to one embodiment of the present invention, iron oxide is charged into a reducing furnace through an iron oxide charging port and gradually lowered. Reducing gas is then blown into the reducing furnace through a reducing gas inlet, and the iron oxide is reduced to produce reduced iron in the reduction zone by the reducing gas. Carburizing gas is then blown into the reducing furnace through a carburizing gas inlet at the bottom of the reducing furnace, and the carbon content of the reduced iron is increased by the carburizing gas in the carburizing zone. The reduced iron is then discharged from the reduced iron outlet of the reducing furnace. At this time, mainly CO and CO are discharged from the top of the reducing furnace. ２ , H ２ and H ２ The furnace top gas containing O is discharged. This furnace top gas is subjected to dust removal in a dust removal device and moisture adjustment in a dehydration device. Then, a part of the furnace top gas is sent to a reformer as a first furnace top gas that becomes a raw material gas. The reformer is supplied with CH 3 O 4 together with the first furnace top gas. ４ A gas containing, for example, natural gas is supplied from a natural gas supply. Then, in the reformer, the supplied gas is heated. Then, a reforming reaction occurs, and mainly CO and H are produced. ２ A high-temperature reducing gas containing CO is generated. This reducing gas is then blown into the reducing furnace. The remaining part of the furnace top gas is used as a second furnace top gas, for example, as a heating fuel in the combustion chamber of the reformer. The second furnace top gas after being combusted as a heating fuel usually contains CO ２The carburizing gas after being used for carburizing (hereinafter also referred to as "reacted carburizing gas") is discharged to the outside of the reducing furnace from a carburizing gas outlet located at a position lower than the reducing gas inlet. Next, the reacted carburizing gas is, for example, dusted by a dust removal device, and then appropriately mixed with CH4 gas such as natural gas supplied from a natural gas supply unit. ４ After adding the containing gas, the gas is blown into the reduction furnace again as carburizing gas.

[0024] Hereinafter, each step of the method for producing reduced iron according to one embodiment of the present invention will be described in more detail.

[0025] (Reduction step) In the reduction step, a reducing gas is blown into a reduction furnace, and the iron oxide charged into the reduction furnace is reduced by the reducing gas blown into the reduction furnace to produce reduced iron. The conditions for the reduction step are not particularly limited, and may be those of a conventional method.

[0026] For example, the gas composition of the reducing gas is CO: 1 to 70% by volume, H ２ The balance is preferably 0 to 10% by volume. ２ The reducing gas blowing temperature is 800 to 1100°C, and the blowing amount of reducing gas is 1400 to 3000 Nm ３ The amount of iron oxide charged is preferably 1,300 to 1,500 kg / t.

[0027] (Carburizing Process) In the carburizing process, carburizing gas is injected into a reducing furnace, and the carbon content of the reduced iron is increased by the carburizing gas injected into the reducing furnace. The amount of carburization in the carburizing process is the amount of carbon increase (mass %) in the reduced iron during the carburizing process, and can be calculated, for example, by the following formula: [Amount of carburization 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 %)] Here, the final carbon content of reduced iron is the carbon content of the reduced iron discharged from the reducing furnace.

[0028] The composition of the carburizing gas is, for example, CH ４ : 30 to 100% by volume, and the balance: 0 to 70% by volume. ２The amount of carburizing gas to be blown may be determined by the control step described later. The amount of carburizing gas to be blown may be, for example, 50 Nm ３ / t or more 500Nm ３ The carburizing gas may be blown at a temperature in the range of 0°C to 100°C.

[0029] (Controlling Step) In the controlling step, it is important to change the amount of carburizing gas blown in accordance with the blowing temperature of the reducing gas.

[0030] As mentioned above, carbon in reduced iron exists either as a single carbon or as Fe ３ C (cementite). ３ When reduced iron is melted, C generates heat through the decomposition reaction according to the above formula (3), and therefore can supply more energy than when carbon exists as a single substance. ３ Increasing the amount of carbon present in C increases the heat generation efficiency per carbon amount contained in reduced iron, thereby enabling a further reduction in the energy required for melting while suppressing an increase in carbon dioxide emissions.

[0031] The form of carbon present in reduced iron is affected by the temperature of the carburized part, especially the temperature of the upper region of the carburized part. ３ To increase the amount of carbon present in C, for example, the temperature in the upper region of the carburized part is increased by (Fe ３ It is effective to control the temperature to a range of 550 to 800°C (at which point the C production reaction progresses). Here, the upper region of the carburized area is the region from midway between the carburizing gas inlet and the carburizing gas outlet in the height direction of the reducing furnace to the carburizing gas outlet. The carburizing gas outlet is located at a higher position than the carburizing gas inlet. Furthermore, when multiple carburizing gas outlets are located in the height direction of the reducing furnace, the highest position among them is used to define the upper region of the carburized area. Similarly, when multiple carburizing gas inlets are located in the height direction of the reducing furnace, the lowest position among them is used to define the upper region of the carburized area.

[0032] In the carburization process, the carburization of the reduced iron progresses through an endothermic reaction according to the above formula (3) or the following formula (4). When the reduced iron descends through the reduction section inside the reduction furnace, its temperature is increased by the sensible heat of the reducing gas. After descending through the reduction section, the reduced iron descends through the carburized section. This creates a correlation between the injection temperature of the reducing gas and the temperature of the carburized section. CH ４ →C+2H ２ ...(4)

[0033] Therefore, it is important to change the amount of carburizing gas blown in accordance with the temperature of the reducing gas blown in.

[0034] In particular, it is preferable to change the amount of carburizing gas injected depending on the temperature of the reducing gas injected so that the temperature of the upper region of the carburized portion is in the range of 550 to 800°C. By controlling the temperature of the upper region of the carburized portion in the range of 550 to 800°C, Fe ３ It is possible to further expand the range in the height direction of the reduction furnace where the C production reaction proceeds. ３ This makes it possible to further increase the amount of carbon present in C. The temperature of the upper region of the carburized part is more preferably 600°C or higher, and even more preferably 700°C or higher. The temperature of the upper region of the carburized part is more preferably 750°C or lower.

[0035] The temperature of the carburized portion generally increases with increasing height in the reducing furnace. Therefore, if both the upper end (at the height of the carburizing gas outlet) and the lower end (at a height midway between the carburizing gas inlet and the carburizing gas outlet) of the upper region of the carburized portion are within the above temperature range, the entire upper region of the carburized portion can be considered to be within the above temperature range. There are no particular restrictions on the method for measuring the temperature of the upper region of the carburized portion. For example, a thermocouple can be embedded in the furnace wall of the reducing furnace located above the upper region of the carburized portion, and the temperature of the upper region of the carburized portion can be measured using this thermocouple.

[0036] Furthermore, when the reducing gas blowing temperature is less than the standard reducing gas blowing temperature minus 80°C, it is more preferable that the amount of carburizing gas blown satisfies the relationship of the following formula (1). In this case, it is particularly preferable to change the amount of carburizing gas blown in accordance with the reducing gas blowing temperature so as to satisfy the relationship of the following formula (1). When the reducing gas blowing temperature is more than the standard reducing gas blowing temperature plus 90°C, it is more preferable that the amount of carburizing gas blown in accordance with the reducing gas blowing temperature so as to satisfy the relationship of the following formula (2). In this case, it is particularly preferable to change the amount of carburizing gas blown in accordance with the reducing gas blowing temperature so as to satisfy the relationship of the following formula (2). V≦V ０ × (3.7 (T / T ０ )-2.4) ...(1) V ０ × (4.3 (T / T ０ )-3.7)≦V (2) where V: amount of carburizing gas blown in (Nm ３ / h), V ０ : Standard injection amount of carburizing gas (Nm ３ / h) and T: reducing gas blowing temperature (°C) and T ０ : Standard blowing temperature of reducing gas (℃)

[0037] In the above formula (1), V is more preferably V ０ × (3.9 (T / T ０ ) -2.7) or less. ０ ×0.95×(3.9(T / T ０ ) -2.7) or greater.

[0038] In the above formula (2), V is more preferably V ０ × (4.6 (T / T ０ ) -3.9) or more. ０ ×1.05×(4.6(T / T ０ ) -3.9) or less.

[0039] When the blowing temperature of the reducing gas is in the range of the reference blowing temperature of the reducing gas −80° C. to the reference blowing temperature of the reducing gas +90° C., V is preferably 0.90×V ０ ~1.10 x V ０ , more preferably 0.95×V０ ~1.05 x V ０、 More preferably, 0.98×V ０ ~1.02 x V ０ is.

[0040] Here, V ０ is the injection amount of carburizing gas (Nm) when the final carbon content of reduced iron targeted in actual operation (hereinafter also referred to as the target final carbon content of reduced iron) is obtained under the base operating conditions. ３ / h). The base operating conditions are the amount of iron oxide charged, the composition of the reducing gas, the reducing gas injection temperature, and the reducing gas injection rate that 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, from the specifications (instruction manual) of the reducing furnace to be used or from past operating records. Note that conditions that cannot be confirmed from specifications, such as the composition of the iron oxide to be used, the composition of the carburizing gas, and the injection temperature, can be set according to the conditions planned for actual operation.

[0041] For example, V ０ can be determined by conducting a preliminary operation test of the reducing furnace to be used. Specifically, a preliminary operation test of the reducing furnace to be used is conducted by varying the amount of carburizing gas injected according to the base operating conditions of the reducing furnace to be used. Conditions that cannot be confirmed in specifications, such as the composition of the iron oxide to be used, the composition of the carburizing gas, and the injection temperature, are set according to the conditions planned for actual operation. Then, from the results of the preliminary operation test, the amount of carburizing gas injected when the target final carbon content of the reduced iron is obtained is determined, and V ０ The error of each value is allowable within the range of ±5%, preferably ±3%. ０ can take various values ​​depending on the type (structure, size, etc.) of the reducing furnace to be used.

[0042] T ０ may be determined based on the base operating conditions. ０ It can be said that this corresponds to the reducing gas injection temperature in the above-mentioned preliminary operation test.

[0043] The target final carbon content of the reduced iron is set, for example, in the range of 0.50 to 7.00 mass %.

[0044] (Distribution Step) In the distribution step, as described above, it is preferable to distribute the furnace gas into a first furnace gas and a second furnace gas. The furnace gas is the gas obtained after the reducing gas has been used to reduce iron oxide in the reduction step. In one example, the first furnace gas is supplied to a reformer and used as a raw material gas for the reducing gas in the reforming step. The second furnace gas is used as heating fuel in the combustion chamber of the reformer. Furthermore, a portion of the furnace gas may be distributed to a location other than the first furnace gas and the second furnace gas, for example, to be supplied to another device or stored. The distribution amount may be determined appropriately depending on the operating conditions.

[0045] The means for distributing and controlling the flow rate of the furnace gas is not particularly limited, and may be any conventional method, such as a mass flow controller.

[0046] (Reforming step) In the reforming step, the first furnace gas and CH ４ For example, the reformer may be configured to generate a reducing gas from the first furnace top gas and CH ４ The natural gas containing gas is supplied to the reformer. The supplied gas is then heated in the reforming device. The reforming reactions of the following formulas (4) and (5) occur, producing mainly CO and H. ２ A hot reducing gas containing CH ４ +CO ２ → 2CO + 2H ２ ΔH=247kJ / mol...(4) CH ４ +H ２ O → CO + 3H ２ ΔH=206kJ / mol...(5)

[0047] The conditions other than those mentioned above are not particularly limited, and may be those according to conventional methods.

[0048] [2] Reduction Furnace Next, a 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 in the above-described method for producing reduced iron according to an embodiment of the present invention.

[0049] A reducing furnace according to one embodiment of the present invention comprises, for example, a reducing section that reduces iron oxide with a reducing gas to produce reduced iron, a carburizing section that increases the amount of carbon contained in the reduced iron with a carburizing gas, and a control section that changes the amount of carburizing gas injected depending on the injection temperature of the reducing gas. Figure 2 is a schematic diagram showing an example of the overall configuration of a reducing furnace having a control section and its associated equipment. In Figure 2, reference numeral 12 denotes the control section.

[0050] The reducing section is not particularly limited in its configuration, and a general configuration can be used. For example, the reducing section is a region through which the reducing gas blown in through the reducing gas blowing port flows and which serves as a charging section (a descending path) for the iron oxide charged through the iron oxide charging port at the top of the reducing furnace. The reducing section is connected to the reducing gas blowing port and the top gas outlet, respectively, and forms a path through which the reducing gas (top gas) flows. The reducing section is also connected to the iron oxide charging port at the top and the carburizing section at the bottom, respectively, and forms a descending path for the iron oxide (reduced iron).

[0051] The carburizing section is not particularly limited, and a common configuration can be used. For example, the carburizing section is a region through which carburizing gas injected through the carburizing gas inlet flows and which serves as a path for the reduced iron obtained from the iron oxide in the reducing section to descend. The carburizing section is connected to the carburizing gas inlet and the carburizing gas outlet, forming a path for the carburizing gas to flow. The carburizing section is also connected to the upper reducing section and the lower reduced iron outlet, forming a path for the reduced iron to descend. That is, in one example, the carburizing section is arranged, in order from top to bottom, with an iron oxide charging inlet, a reducing section, a carburizing section, and a reduced iron outlet. The carburizing section may be provided with a temperature measuring device for measuring the temperature of the carburizing section, particularly the temperature of the upper region of the carburizing section. A thermocouple is an example of a temperature measuring device. For example, a thermocouple can be embedded in the furnace wall of the reducing furnace above the carburizing section to measure the temperature of the upper region of the carburizing section.

[0052] The control unit changes the amount of carburizing gas injected depending on the temperature of the reducing gas injected. The preferred control mode in the control unit is as described in [1] above.

[0053] As an example, the control unit may have an input unit for inputting various set values ​​and measurement data such as the reducing gas injection temperature and preferably the temperature of the upper region of the carburized section; a calculation unit for processing the input set values ​​and measurement data; a memory unit for storing the set values ​​and measurement data; and an output unit for outputting an operation signal for changing the amount of carburizing gas injected based on the processing results of the calculation unit.

[0054] In this case, specifically, the control unit is an information processing device. Fig. 3 shows an example of functional blocks of the control unit. The reducing furnace may have a control unit as shown in Fig. 3. As shown in Fig. 3, the control unit includes an input unit and an output unit connected to external devices so as to be able to communicate data with each other, a calculation unit, and a storage unit that stores various data, all of which are connected to each other so as to be able to communicate data with each other.

[0055] The input unit and the output unit are, for example, interfaces that are provided to enable data communication with external devices.

[0056] The calculation unit is, for example, a CPU. The calculation unit controls the operation of the entire control unit. The calculation unit calculates how to change the amount of carburizing gas to be injected based on various set values ​​and measurement data input from the outside to the input unit or stored in the memory unit, and generates an operation signal to change the amount of carburizing gas to be injected. The output unit outputs the operation signal. The calculation unit realizes the above-mentioned functions by, for example, executing a program stored in the memory unit.

[0057] The storage unit is, for example, a writable nonvolatile memory such as an EPROM, etc. The storage unit is not particularly limited, but may be, for example, an HDD, an SSD, etc.

[0058] The carburizing gas injection device receives the operation signal output from the output section, controls the injection amount of the carburizing gas as described in [1] above, and then injects the carburizing gas into the reducing furnace.

[0059] The configuration other than that described above is not particularly limited, and may be the same as that of a conventionally known reduction furnace.

[0060] Examples will be described below. The examples of the present invention are based on a numerical analysis model that can simulate 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 regions at equal intervals in the height direction. Starting from the top of the reduction furnace (the upper side in the height direction of the reduction furnace), the first to twentieth regions are set as the reduction region, and the 26th to 40th regions are set as the carburization region. (The 21st to 25th regions are set as the transition zone where only reduced iron descends (no reduction or carburization occurs).) Using the above numerical analysis model, the material balance and heat balance of the solids and gases in each region inside the reduction furnace, as well as the solid-gas heat transfer, are calculated sequentially at short time intervals (1 second). Using the above calculations, the changes in the temperature and composition of the solids and gases in each region inside the reduction furnace are analyzed, and the final carbon content of the reduced iron and the Fe content in the reduced iron are calculated. ３ The mass fraction of carbon present in C (hereinafter referred to as Fe ３ ・Source of values ​​used to calculate reaction rate, etc.: Bechara et al.: Materials 2018, 11(7), 1094 (https: / / doi.org / 10.3390 / ma11071094) ・Assumed operating conditions: As described in Examples 1 and 2 below

[0061] Example 1 Furnace volume as shown in Figure 1: 80 m ３ In the reducing furnace and its associated equipment, reduced iron is produced under the conditions listed in Table 1. That is, in Example 1, reduced iron is produced by varying the amount of carburizing gas injected depending on the reducing gas injection temperature under each condition. In particular, the amount of carburizing gas injected is varied depending on the reducing gas injection temperature so that the temperature in the upper region of the carburizing section of the reducing furnace is in the range of 550 to 800°C. The amount of carburizing gas injected is also varied so as to satisfy the relationship of formula (1) or (2) above. On the other hand, in Comparative Example 1, reduced iron is produced under all conditions with the carburizing gas composition and injection amount remaining almost unchanged.

[0062] Under all conditions, the operation period was 7 days, the target final carbon content of the reduced iron was 1.30 mass%, and V ０ is 350Nm３ / h, T ０ is 900°C.

[0063] In Table 1, the operational specifications are listed in terms of the basic unit per ton of reduced iron produced. For example, if 1,400 kg of iron oxide pellets are used to produce 1 ton of reduced iron, the amount of iron oxide pellets used is expressed as 1,400 kg / t. If 3,000 t / day of reduced iron is produced, this amount is multiplied by 3,000 to obtain the specifications per day. ０ is obtained by a preliminary operation test according to the above procedure. ０ is determined based on base operating conditions. ０ can also be said to be the injection temperature of the reducing gas in the above-mentioned preliminary operation test. ０ The reducing gas injection rate and composition are based on the specifications of the reducing furnace used. The carburizing gas composition is based on the conditions planned for actual operation. The temperature of the upper region of the carburized area is listed as the temperature from the bottom of the upper region of the carburized area (at a height midway between the carburizing gas inlet and the carburizing gas outlet) to the top of the upper region of the carburized area (at the height of the carburizing gas outlet). In an actual furnace, the temperatures at the top and bottom of the upper region of the carburized area are measured, for example, using thermocouples embedded in the furnace wall at the top and bottom of the upper region of the carburized area. This is also true for Example 2, which will be described later.

[0064] Conditions other than those described above and in Table 1 were the same as those used in the conventional methods. The remaining parts of the reducing gas and carburizing gas were N ２ The temperature of the carburizing gas blown in was room temperature (25°C) in all cases. The same applies to Example 2 described later.

[0065] Next, the Fe calculated for each condition ３ The carbon mass ratio of C (= [Fe in reduced iron ３The effect of reducing the energy required for melting (the effect of increasing the heat generation efficiency per carbon amount contained in reduced iron and reducing the energy required for melting while suppressing an increase in carbon dioxide emissions) was evaluated using the following criteria using the formula ([mass of carbon present in Fe C] / [total mass of carbon contained in reduced iron] × 100). The evaluation results are also shown in Table 1. Pass (Excellent): Under all conditions, Fe ３ The carbon mass ratio of C is 85.0% or more. Fail (bad): Fe is ３ The carbon mass ratio of C is less than 85.0%. In actual equipment, Fe in reduced iron ３ The mass of carbon present in C and the total mass of carbon contained in the reduced iron can be determined, for example, by subjecting the reduced iron to X-ray diffraction measurement and then subjecting the measurement results to Rietveld analysis.

[0066]

[0067] As shown in Table 1, an excellent effect of reducing the energy required for melting can be obtained in Example 1. On the other hand, in Comparative Example 1, the effect of reducing the energy required for melting is insufficient.

[0068] Example 2 Furnace volume as shown in Figure 1: 100 m ３ In a reducing furnace (having a different furnace volume from that of Example 1) and its associated equipment, reduced iron is produced under the conditions listed in Table 2. That is, in Example 2, reduced iron is produced by varying the amount of carburizing gas injected depending on the reducing gas injection temperature under each condition. In particular, the amount of carburizing gas injected is varied depending on the reducing gas injection temperature so that the temperature in the upper region of the carburizing section of the reducing furnace is in the range of 550 to 800°C. The amount of carburizing gas injected is also varied so as to satisfy the relationship of formula (1) or (2) above. On the other hand, in Comparative Example 2, reduced iron is produced under all conditions with the carburizing gas composition and injection amount remaining almost unchanged.

[0069] Under all conditions, the operation period was 7 days, the target final carbon content of the reduced iron was 1.70 mass%, and V ０ is 380Nm ３ / h, T ０ is 930°C.

[0070] Next, the effect of reducing the energy required for dissolution was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0071]

[0072] As shown in Table 2, an excellent effect of reducing the energy required for melting is obtained in Example 2. On the other hand, the effect of reducing the energy required for melting is insufficient in Comparative Example 2.

[0073] Furthermore, when various reducing furnaces are used to produce reduced iron under various operating conditions and with various target final carbon contents, the same results as those described above can be obtained by changing the amount of carburizing gas injected depending on the reducing gas injection temperature, particularly by changing the amount of carburizing gas injected depending on the reducing gas injection temperature so that the temperature of the upper region of the carburizing section of the reducing furnace is in the range of 550 to 800°C and so that the relationship of formula (1) or (2) above is satisfied.

[0074] REFERENCE SIGNS LIST 1 reduction furnace 1a iron oxide 1b reduced iron 3 dust removal device 4 dehydration device 5 natural gas supply section 6 air supply section 7 reforming device 8 reducing gas injection device 9 carburizing gas injection device 10 reduction section 11 carburizing section 12 control section

Claims

1. The reduction process involves reducing iron oxide to reduced iron using reducing gas blown into a reduction furnace. A carburizing step is performed in which the carbon content of the reduced iron is increased by the carburizing gas blown into the reduction furnace. A control step of changing the amount of carburizing gas injected according to the injection temperature of the reducing gas, A method for producing reduced iron, comprising the characteristics of [the method].

2. The method for producing reduced iron according to claim 1, wherein in the control step, the amount of carburizing gas injected is changed so that the temperature of the upper region of the carburizing section of the reduction furnace is in the range of 550 to 800°C. Here, the upper region of the carburizing section is the area from the intermediate point between the carburizing gas inlet and the carburizing gas outlet to the carburizing gas outlet in the height direction of the reducing furnace.

3. In the control process described above, When the injection temperature of the reducing gas is less than the standard injection temperature of the reducing gas minus 80°C, the amount of carburizing gas injected satisfies the following relationship (1): A method for producing reduced iron according to claim 1 or 2, wherein when the injection temperature of the reducing gas exceeds the standard injection temperature of the reducing gas + 90°C, the amount of carburizing gas injected satisfies the relationship shown in the following equation (2). V≦V ０ ×(3.7(T / T ０ )-2.4) ・・・(1) V ０ ×(4.3(T / T ０ )-3.7)≦V ・・・(2) During the ceremony, V: Amount of carburizing gas blown in (Nm) ３ / h), V ０ : Standard injection rate of carburizing gas (Nm³) ３ / h), T: Injection temperature of reducing gas (°C) and T ０ : Reference injection temperature of reducing gas (°C) That is the case.

4. The top gas discharged from the reduction furnace is divided into a first top gas and a second top gas, and the top gas is the gas remaining after the reduction gas has been subjected to the reduction of iron oxide in the reduction process, in a distribution process, From the first top gas and the CH ４ containing gas, a reforming step of generating the reducing gas, A method for producing reduced iron according to claim 1 or 2, comprising:

5. A distribution step comprising distributing the top gas discharged from the reduction furnace into a first top gas and a second top gas, wherein the top gas is the gas remaining after the reduction gas has been subjected to the reduction of iron oxide in the reduction step, A reforming step is performed to generate the reducing gas from the first furnace top gas and the CH4-containing gas. A method for producing reduced iron according to claim 3, comprising:

6. A reducing unit reduces iron oxide to reduced iron using a reducing gas, A carburized section, in which the amount of carbon contained in the reduced iron is increased by carburizing gas, A control unit that changes the amount of carburizing gas injected according to the injection temperature of the reducing gas, A reduction furnace having

7. The reduction furnace according to claim 6, wherein the control unit changes the amount of carburizing gas injected so that the temperature of the upper region of the carburizing section of the reduction furnace is in the range of 550 to 800°C. Here, the upper region of the carburizing section is the area from the intermediate point between the carburizing gas inlet and the carburizing gas outlet to the carburizing gas outlet in the height direction of the reducing furnace.

8. Under the control of the control unit, When the injection temperature of the reducing gas is less than the standard injection temperature of the reducing gas minus 80°C, the amount of carburizing gas injected satisfies the following relationship (1): The reduction furnace according to claim 6 or 7, wherein when the injection temperature of the reducing gas exceeds the reference injection temperature of the reducing gas + 90°C, the amount of carburizing gas injected satisfies the relationship shown in the following equation (2). V≦V ０ ×(3.7(T / T ０ )-2.4) ・・・(1) V ０ ×(4.3(T / T ０ )-3.7)≦V ・・・(2) During the ceremony, V: Amount of carburizing gas blown in (Nm) ３ / h), V ０ : Standard injection rate of carburizing gas (Nm³) ３ / h), T: Injection temperature of reducing gas (°C) and T ０ : Reference injection temperature of reducing gas (°C) That is the case.