Method for producing reduced iron

Abstract

The present invention is a method for producing reduced iron from iron oxide, which enables energy saving and reduction of CO2 emission. The method for producing reduced iron has the following steps: an iron oxide charging step of charging iron oxide into a reduction furnace; a reducing gas blowing step of blowing reducing gas into the reduction furnace; a reduction step of reducing the iron oxide in the reduction furnace using the reducing gas; a methane synthesis step of synthesizing a gas mainly composed of methane from a part of top gas discharged from the top of the reduction furnace and hydrogen; and a gas reforming step of reforming the reducing gas by heating a raw material gas composed of the methane gas and the top gas from which the part of the top gas supplied to the methane synthesis step is removed; wherein the amount V1 of the top gas supplied to the methane synthesis step and the amount V2 of water vapor in the top gas supplied to the gas reforming step are adjusted in accordance with the variation of the ratio H2 / CO of H2 and CO in the reducing gas blown into the reduction furnace, and the material balance in the process from the iron oxide charging step to the reduction step is controlled. W , control the material balance in the process from the iron oxide charging step to the reduction step.

Description

Technical Field

[0001] This invention relates to a method for manufacturing reduced iron. Background Technology

[0002] In recent years, against the backdrop of global environmental issues and the depletion of fossil fuels, there has been a strong demand for energy conservation in steel plants.

[0003] Furthermore, the main raw material for iron is iron oxide, making a reduction process necessary to reduce this iron oxide. The most common reduction process in the world is the blast furnace. In this type of blast furnace, coke, pulverized coal, and oxygen in hot blast (air heated to about 1200°C) react at the tuyeres to produce CO and H2 gases (reducing gases). These reducing gases are then used to reduce iron ore and other materials in the furnace. Due to improvements in blast furnace operation technology in recent years, the reducing agent ratio (the amount of coke and pulverized coal used to produce 1 ton of molten steel) has been reduced to about 500 kg / t. This reducing agent ratio has essentially reached its lower limit, and a further reduction cannot be expected.

[0004] On the other hand, in regions where natural gas is produced, a method is often used to produce reduced iron by filling a vertical reduction furnace with lumped iron ore such as sintered ore or pellets as iron oxide feedstock, and blowing in a reducing gas containing hydrogen and carbon monoxide to reduce the iron oxide feedstock. In this method, natural gas or similar gases are used as the feedstock gas for the reducing gas. The feedstock gas, together with the top gas discharged from the top of the reduction furnace, is heated and reformed in a heating and reforming unit to generate a reducing gas. The generated reducing gas is blown into the reduction furnace and reacts with the iron oxide feedstock supplied from the top of the reduction furnace, reducing the iron oxide to reduced iron. The produced reduced iron is cooled in a region lower than where the reducing gas was blown into the reduction furnace, and then discharged from the bottom of the reduction furnace.

[0005] It should be noted that the gas supplied to the reduced iron oxide is discharged from the top of the reduction furnace as top gas. After dust collection and cooling, a portion of it is fed into the heating reforming unit as feedstock for reforming gas. The remaining top gas is used as fuel gas for the heating and heating reforming unit. This remaining top gas used as fuel gas for the heating and heating reforming unit is typically discharged outside the system.

[0006] As a process for manufacturing reduced iron as described above, Patent Document 1 describes reforming the exhaust gas from the reduction furnace and natural gas in a reformer to generate a reducing gas mainly composed of CO and H2 gas. This reducing gas is then blown into the reduction furnace to reduce the iron oxide inside the furnace, thereby manufacturing reduced iron.

[0007] In addition, Patent Document 2 describes a method for producing reduced iron by reforming the top gas of a reduction furnace after removing coke oven gas and CO2, and blowing the gas into the reduction furnace.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2017-88912

[0011] Patent Document 2: Japanese Patent Publication No. 2016-529384 Summary of the Invention

[0012] In the reduced iron manufacturing method described in Patent Document 1, natural gas is used to produce reducing gas. Therefore, although it is at a lower level compared to a blast furnace, it is still impossible to avoid a certain degree of CO2 emission, which presents a problem.

[0013] Furthermore, the method described in Patent Document 2 involves using coke oven gas or converter gas generated within a steel plant to produce reducing gas. However, in an integrated steel plant, coke oven gas and converter gas are essential fuel gases for downstream processes such as heating furnaces and annealing furnaces. Therefore, if these gases are diverted to the reduced iron manufacturing process, it will lead to a shortage of fuel gas in downstream processes. Consequently, in order to compensate for the gas shortage in downstream processes, natural gas is supplied from external sources, ultimately failing to reduce CO2 emissions, which remains a challenge.

[0014] In view of the above-mentioned situation, the present invention aims to propose a method that can achieve energy saving and reduce CO2 emissions when producing reduced iron from iron oxide.

[0015] To achieve energy conservation and reduce CO2 emissions, the inventors have developed a system comprising the following steps: an iron oxide filling step, in which iron oxide is filled into a reduction furnace; a reducing gas blowing step, in which reducing gas is blown into the reduction furnace; a reduction step, in which the reducing gas is used to reduce iron oxide within the reduction furnace; a methane synthesis step, in which a portion of the top gas discharged from the top of the reduction furnace is used to synthesize methane with hydrogen; and a gas reforming step, in which methane gas and a portion of the top gas supplied to the methane synthesis step are used as feedstock gases, and the feedstock gases are heated to reform the aforementioned reducing gas. In this system, the top gas is recycled. Furthermore, to achieve practically stable operation in this system, a good material balance is required, that is, the gas balance within the system is maintained in a manner that stably maintains the H2 / CO composition ratio (volume ratio) in the reducing gas supplied to the reduction furnace at a predetermined set value.

[0016] However, when the quality of the iron oxide (lumpy ore) used as a raw material for reduced iron is unstable, the composition of the gas released from the furnace top varies, making it difficult to maintain the aforementioned good material balance. Furthermore, due to performance changes caused by the continuous operation of the methane synthesis unit in the methane synthesis process and the heating reforming unit in the gas reforming process, the gas composition at the outlet of the methane synthesis unit and the heating reforming unit changes, resulting in variations in the H2 / CO ratio in the reducing gas, making it difficult to maintain the aforementioned good material balance.

[0017] Therefore, the inventors conducted in-depth research on methods for maintaining good material balance in the above-mentioned system. The important new discovery is that, based on the compositional changes of the reducing gas blown into the reduction furnace, the gas balance is appropriately maintained between the above-mentioned methane synthesis process and the above-mentioned gas reforming process, thereby completing the present invention.

[0018] That is, the essence of the present invention is as follows.

[0019] 1. A method for manufacturing reduced iron, comprising the following steps:

[0020] The iron oxide filling process involves filling the reduction furnace with iron oxide.

[0021] In the reducing gas blowing process, reducing gas is blown into the aforementioned reduction furnace;

[0022] The reduction process involves reducing the iron oxide using the reducing gas in the reduction furnace.

[0023] The methane synthesis process involves synthesizing a gas with methane as the main component from a portion of the top gas discharged from the top of the aforementioned reduction furnace and hydrogen.

[0024] In the gas reforming process, the above-mentioned methane gas and the furnace top gas (excluding the portion supplied to the above-mentioned methane synthesis process) are used as raw material gas, and the raw material gas is heated to reform the above-mentioned reducing gas.

[0025] Furthermore, based on the variation in the H2 / CO ratio of the reducing gas blown into the reduction furnace, the amount of top gas V1 supplied to the methane synthesis process and the amount of water vapor V in the feed gas supplied to the gas reforming process are adjusted in a manner that suppresses the variation. W Control the material balance of H2 and CO in the process from the above-mentioned iron oxide filling process to the above-mentioned reduction process.

[0026] 2. The method for manufacturing reduced iron according to 1 above, wherein when the change in the H2 / CO ratio is an increase in the value of the H2 / CO ratio, the amount of water vapor V is increased. W The amount of gas at the furnace top, V1, decreases as mentioned above.

[0027] 3. The method for manufacturing reduced iron according to 1 above, wherein when the change in the H2 / CO ratio is such that the value of the H2 / CO ratio decreases, the amount of water vapor V is increased. W The gas volume V1 at the top of the furnace increases as described above.

[0028] According to the present invention, in a method for manufacturing reduced iron that has a closed system for recycling the furnace top gas, in which CO2-free hydrogen is supplied from the outside to the furnace top gas of the reduction furnace to synthesize regenerated methane and the regenerated methane is used to produce reducing gas, operation under material balance can be stably achieved. Attached Figure Description

[0029] Figure 1 This diagram illustrates the reduced iron manufacturing process using a conventional vertical shaft furnace.

[0030] Figure 2 This is a diagram illustrating the reduced iron manufacturing process of the present invention.

[0031] Figure 3 V represents the amount of water vapor adjusted when the composition of the reducing gas changes. W A graph showing the relationship between the amount of gas V1 used in methane synthesis and the amount of gas at the furnace top. Detailed Implementation

[0032] Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings. First, the description will begin with a previous reduced iron manufacturing process compared with the method of the present invention.

[0033] Right now, Figure 1 This diagram illustrates the structure of a reduced iron manufacturing process utilizing a traditional vertical reduction furnace. Figure 1 In the attached diagram, 1 represents a reduction furnace, 1a represents iron oxide, 1b represents reduced iron, 2 represents the top gas discharged from the reduction furnace 1, 3 represents a dust removal device for the top gas 2, 4 represents a dehydration device, 5 represents natural gas supplied from the outside, 6 represents air, 7 represents a heating and reforming device for heating or heating and reforming the top gas 2 and air 6 to produce a reducing gas 8 containing carbon monoxide and hydrogen, and 9 represents a reducing gas blowing device for supplying reducing gas to the reduction furnace 1.

[0034] In reduction furnace 1, which is the core of the reduced iron manufacturing process, lumpy iron oxide raw material 1a, such as sinter or pellets, is charged from the top and slowly descends. The iron oxide raw material 1a is reduced by blowing high-temperature reducing gas 8 into it from the middle of the furnace, and the reduced iron 1b is discharged from the bottom. At this time, top gas 2, mainly containing CO, CO2, H2, and H2O, is discharged from the top of the furnace. This top gas 2 is dedusted by dust removal device 3, and a portion is used as feed gas with moisture adjustment before being sent to heating reforming unit 7. In heating reforming unit 7, a gas containing hydrocarbons, such as natural gas 5, is supplied along with the moisture-adjusted top gas 2 and heated. A reforming reaction occurs in heating reforming unit 7, generating high-temperature reducing gas 8, mainly containing CO and H2, which is then blown into reduction furnace 1. Additionally, the remaining portion of the top gas 2 is dehydrated and used as heating fuel in the combustion chamber of heating reforming unit 7.

[0035] [Implementation Method]

[0036] Compared to the above Figure 1 The prior art process shown is, in this invention, as... Figure 2 As shown, instead of the hydrocarbon gases such as natural gas 5 supplied from the outside, recycled methane generated in the reactor for methane synthesis within the process is used. That is, in Figure 2 In the configuration of the reduced iron manufacturing process shown, a new methane synthesis unit 11 is added, in which methane is synthesized from furnace top gas 2 and hydrogen 10. The regenerated methane generated in this methane synthesis unit 11 is supplied to the heating reforming unit 7 as the raw material gas to form reducing gas 8.

[0037] Here, the raw materials for methane synthesis in the methane synthesis unit 11 are hydrogen 10 supplied from an external source and a gas containing CO, CO2, and hydrocarbons. The gas containing CO, CO2, and hydrocarbons can be any gas obtainable within a steel plant, for example... Figure 2 As shown, the top gas 2 generated from the reduction furnace 1 will be used for the previous Figure 1 The heated portion of the reforming unit 7 flows into the methane synthesis unit 11, where methane is synthesized, as feedstock for regenerated methane. By changing the flow rate of the top gas 2 within this system, the required amount of regenerated methane for the reforming unit 7 can be synthesized. Since there is no fuel supplied for heating the reforming unit 7, an external CO2-free heat source, such as CO2-free electricity, can be used instead. In this method, if CO2-free electricity is used for heating the reforming unit 7 and for hydrogen production, theoretically, zero CO2 emissions can be achieved.

[0038] The regenerated methane synthesized in the methane synthesis unit 11 is mixed with the dehydrated and partially dehydrated furnace top gas 2 and supplied to the heating reforming unit 7. In the heating reforming unit 7, the gas is reformed into a gas mainly containing H2 and CO, and is blown into the reduction furnace 1 as the reducing gas 8 to supply the production of reduced iron.

[0039] In order to make the above Figure 2 The reduction iron manufacturing process in the closed system shown is valid. Crucially, maintaining gas balance between the methane synthesis step and the gas reforming step is essential to prevent fluctuations in the composition (H2 / CO ratio) of the reducing gas blown into the reduction furnace. This allows for immediate suppression of changes in the reducing gas composition. Specifically, as mentioned above, the composition of the furnace top gas released from the furnace top changes when the quality of the raw material iron oxide is unstable. Furthermore, since the ratio of the dust-removed furnace top gas to the raw material gas and the gas used for methane synthesis varies depending on the amount of gas required to generate reducing gas in the subsequent gas reforming step—that is, the amount of regenerated methane gas fed into the gas reforming step and the amount of water vapor in the furnace top gas—it is necessary to estimate the gas volume in each step to achieve the aforementioned material balance.

[0040] Therefore, in this invention, the amount of top gas V1 supplied to the methane synthesis process and the amount of water vapor V in the feed gas supplied to the gas reforming process are adjusted according to the change in the H2 / CO ratio in the reducing gas blown into the reduction furnace. W Thus, reduced iron is produced under the aforementioned favorable material balance. The method of operation under favorable material balance in the present invention will be described in detail below.

[0041] In addition, the H2 and CO in the reducing gas blown into the reduction furnace, Figure 2 In the heating reforming unit 7 near the reduction furnace 1 shown, CH4 is synthesized by reacting with CO2 and H2O. The respective reactions are represented by the following formulas (i) and (ii).

[0042] CH4+CO2→2CO+2H2…(i)

[0043] CH4+H2O→CO+3H2…(ii)

[0044] According to equations (i) and (ii), the feedstock gases for reforming are CH4, CO2, and H2O. H2O is either removed by cooling the gas or added to the gas itself, thereby allowing adjustment of the amount supplied to the heated reforming unit. On the other hand, CH4 is synthesized by supplying a portion of the top gas discharged from the reduction furnace to a methane synthesis unit. According to equation (ii) above, if the amount of water vapor (H2O) supplied to the heated reforming unit is V... W[Nm] 3 If the amount of CH4 reacting with H2O increases, the amount of CH4 also needs to increase. Furthermore, to increase the amount of CH4, the amount of top gas V1 [Nm] supplied from the top gas discharged from the reduction furnace to the methane synthesis unit needs to be increased. 3 / t], therefore, V W It is positively correlated with V1.

[0045] Here, for example, we consider a state where the amount of CH4 produced decreases due to a reduced reaction rate in the methane synthesis unit. If operation continues under this state, the amount of CH4 supplied to the heating reformer also decreases, and therefore the amount of CO in the reducing gas also decreases. As a result, the proportion of H2 in the reducing gas relative to H2 and C (H2 ratio) increases. As mentioned above, since it is necessary to maintain a constant composition ratio (volume ratio) H2 / CO of H2 and CO in the reducing gas blown into the reduction furnace, it is necessary to reduce the H2 ratio. Therefore, in order to suppress the CO and H2 produced by the reaction represented by equation (ii) above, it is necessary to reduce the amount of water vapor V supplied to the heating reformer. W This reduces the amount of top gas V1 supplied to the methane synthesis process.

[0046] Furthermore, consider, for example, the increased CO2 concentration in the furnace top gas Vt due to the unstable quality of the iron oxide agglomerates used as raw materials for reduced iron. If operation continues under this condition, the amount of CO2 supplied to the methane synthesis unit or the heating reforming unit also increases, thus increasing the amount of CO in the reducing gas. As a result, the proportion of CO in the reducing gas relative to H2 and CO (the CO ratio) also increases. As mentioned above, since the composition ratio (volume ratio) H2 / CO of the reducing gas blown into the reduction furnace needs to be maintained constant, it is necessary to increase the H2 ratio. Therefore, in order to promote the production of CO and H2 by the reaction represented by the above formula (ii), it is necessary to increase the amount of steam V supplied to the heating reforming unit. W At the same time, the amount of gas supplied to the top of the furnace in the synthesis process, V1, is increased.

[0047] It should be noted that performing these operations will change the amount of reducing gas supplied to the reduction furnace. However, if the change in the amount of reducing gas is too large, stable operation of the reduction furnace becomes difficult. Therefore, it is necessary to pay attention to changes in the amount of reducing gas. Specifically, if the decrease in the amount of reducing gas is too large, it will lead to a decrease in production and a reduction in product characteristics. On the other hand, if the increase in the amount of reducing gas is too large, the gas flow resistance in the furnace will increase, and the raw material (pelletized ore) in the furnace will no longer decrease.

[0048] The inventors investigated the appropriate amount of reducing gas to avoid the above drawbacks and found that the appropriate flow rate of the reducing gas was 1500 Nm³. 3 / t~3500Nm 3 / t.

[0049] Furthermore, regarding the simple adjustment of the aforementioned water vapor quantity V W The method of using gas V1 for methane synthesis was studied in depth.

[0050] First, using Figure 3 The amount of water vapor V adjusted when the composition of the reducing gas changes, as described above. W The relationship between the amount of gas at the furnace top for methane synthesis and V1 is explained. Figure 3 This indicates that V is used in this process. W V with V1 as the horizontal axis and V as the vertical axis W A diagram illustrating the relationship with V1. As mentioned earlier, in V... W When the reaction increases, a large amount of H2 is produced through the reaction described in equation (ii) above. Therefore, in order to maintain the H2 / CO ratio of the reducing gas, the amount of CO produced through the reaction described in equation (i) above needs to be increased, so the amount of V1 increases. That is, the increase in the amount of gas used for methane synthesis, ΔV1, is relative to the increase in the amount of water vapor, ΔV. W The ratio becomes steeper. On the other hand, in terms of water vapor quantity V... W When the reaction is reduced, the production of a large amount of H2 according to equation (ii) above is suppressed, therefore the amount of CO required to maintain the specified H2 / CO ratio does not change significantly. Therefore, the increase in the amount of gas used for methane synthesis, ΔV1, is relative to the increase in the amount of water vapor, ΔV. W The ratio becomes slower. That is, due to V W The change (differential value) in the relationship with V1 with respect to V W The value of V changes accordingly, therefore the expected value of V is... W The relationship with V1 is represented by a nonlinear function.

[0051] Therefore, the inventors, etc., in order to determine the representation of V W The nonlinear function relating to V1 was used to perform numerical calculations of the material balance within the process. It should be noted that the material balance calculations were performed using commercially available software. The supply gas flow rate and the H2 / CO ratio within the supply gas flow rate were set, and the composition of the top gas was calculated. Then, the amount of water vapor V supplied from the top gas to the heating and reforming unit was arbitrarily determined. W Calculate the amount of methane synthesized in the methane synthesis unit and the amounts of CO and H2 synthesized in the heating reforming unit, respectively, and then change the amount of water vapor supplied, V, in sequence. W Calculations are performed to make the H2 / CO ratio in the reducing gas obtained from these results equal to the initial set value, and the calculations are performed until the H2 / CO ratio based on the calculation is equal to the set H2 / CO ratio.

[0052] Table 1 shows the reducing gas flow rate of 2200 Nm³. 3 The above calculation results are within the range of / t and 0.5≤H2 / CO≤4.

[0053]

[0054] Example

[0055] The following describes the embodiments.

[0056] according to Figure 2 As shown, the reducing gas blowing rate is 2200 Nm³. 3 This process is operated under the condition that the volume ratio (H2 / CO) of the reducing gas is 2.0. Under these stable operating conditions, the gas composition (volume) of the top gas is H2:CO:CO2:H2O = 48:30:9:14. When the grade of the agglomerated ore charged into the reduction furnace decreases, the H2 / CO ratio in the reducing gas increases to 2.2, meaning the H2 ratio increases. Furthermore, the final reduction rate of the product decreases from 91% at the start of operation to 89%. Therefore, to restore the H2 / CO ratio to 2.0, the amount of steam V introduced into the heating reforming unit is increased. W From the previous 374Nm 3 / t reduced to 355Nm 3 The system can maintain operation with a set H2 / CO ratio of 2.0 at a given reducing gas composition. Furthermore, the final reduction rate of the product can be restored to 91% of the initial operating rate.

[0057] Explanation of reference numerals in the attached figures

[0058] 1. Reduction Furnace

[0059] 1a Iron oxide

[0060] 1b Reduced iron

[0061] 2. Furnace top gas

[0062] 3. Dust removal device

[0063] 4. Dehydration device

[0064] 5. Natural Gas

[0065] 6. Air

[0066] 7. Heating and reforming unit

[0067] 8 Reducing Gas

[0068] 9. Reducing gas blowing device

[0069] 10 hydrogen

[0070] 11. Methane Synthesis Unit

Claims

1. A method for manufacturing reduced iron, comprising the following steps: The iron oxide filling process involves filling the reduction furnace with iron oxide. The reducing gas blowing process involves blowing reducing gas into the reduction furnace. The reduction process involves reducing the iron oxide using the reducing gas inside the reduction furnace. The methane synthesis process involves synthesizing a gas with methane as the main component from a portion of the top gas discharged from the top of the reduction furnace and hydrogen. as well as In the gas reforming process, the methane gas and a portion of the furnace top gas (excluding the gas supplied to the methane synthesis process) are used as feed gas, and the feed gas is heated to reform the reducing gas. Specifically, based on the variation in the H2 / CO ratio of the reducing gas blown into the reduction furnace, the amount of top gas V1 supplied to the methane synthesis process and the amount of water vapor V in the feed gas supplied to the gas reforming process are adjusted in a manner that suppresses the variation. W Control the material balance of H2 and CO in the process from the filling process of the iron oxide to the reduction process.

2. The method for manufacturing reduced iron according to claim 1, wherein, The change in the H2 / CO ratio is such that when the value of the H2 / CO ratio increases, the amount of water vapor V... W And the amount of gas at the top of the furnace, V1, decreases.

3. The method for manufacturing reduced iron according to claim 1, wherein, When the change in the H2 / CO ratio is such that the value of the H2 / CO ratio decreases, the amount of water vapor V... W And the amount of gas at the top of the furnace, V1, increases.

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