Method for manufacturing reduced iron

Abstract

We propose a method that enables energy conservation and a reduction in CO2 emissions when manufacturing reduced iron from iron oxide. In a method for manufacturing reduced iron comprising an iron oxide filling process for filling iron oxide into a reduction furnace, a reduction gas injection process for injecting a reduction gas into the reduction furnace, a reduction process for reducing the iron oxide by the reduction gas within the reduction furnace, a methane synthesis process for synthesizing a gas having methane as the main component from a portion of the furnace gas discharged from the furnace furnace and hydrogen gas, and a gas reforming process for using the furnace gas excluding the methane gas and the portion supplied to the methane synthesis process as raw material gas and heating the raw material gas to reform it into the reduction gas, the amount of furnace gas V1 supplied to the methane synthesis process and the amount of water vapor Vw in the furnace gas supplied to the gas reforming process are adjusted according to the variation of the ratio H2 and CO H2 / CO in the reduction gas injected into the reduction furnace, thereby controlling the material balance in the process from the iron oxide filling process to the reduction process.

Description

Technology Field

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

[0002] Recently, there is a strong demand for energy conservation in steel mills, against the backdrop of global environmental issues and the depletion of fossil fuels.

[0003] Therefore, the raw material for iron is mainly iron oxide, and a reduction process to reduce this iron oxide becomes essential. The most widespread and common reduction process in the world is the blast furnace. In this blast furnace, oxygen in the hot air (air heated to about 1200°C) reacts with coke or pulverized coal at the tuyere to produce CO and H2 gases (reducing gases), and these reducing gases are used to reduce iron ore and other materials inside the furnace. Due to recent improvements in blast furnace operation technology, the reducing agent ratio (the amount of coke and pulverized coal used per ton of hot metal produced) has been reduced to about 500 kg / t, but the reducing agent ratio has already reached its lower limit, so further significant reduction in the reducing agent ratio cannot be expected.

[0004] Meanwhile, in regions where natural gas is produced, a method of producing reduced iron is also frequently used in which agglomerated iron ore, such as sintered ore or pellets, is filled into a vertical reduction furnace as an iron oxide raw material, and a reducing gas containing hydrogen and carbon monoxide is blown in to reduce the iron oxide raw material. In this method, natural gas or the like is used as the raw gas for the reducing gas. The raw gas is heated and reformed in a heating reforming device together with the furnace top gas discharged from the furnace top of the reduction furnace to generate reducing gas. The generated reducing gas is blown into the reduction furnace and reacts with the iron oxide raw material supplied from the top of the reduction furnace, thereby reducing the iron oxide to become reduced iron. The produced reduced iron is cooled in an area below the location where the reducing gas is blown into the reduction furnace, and then discharged from the bottom of the reduction furnace.

[0005] In addition, the gas after being supplied for the reduction of iron oxide is discharged from the furnace of the reduction furnace as furnace gas, and after dust collection and cooling, a portion is sent to a heating reforming device as a raw material for reforming gas. In addition, the remaining furnace gas is used as fuel gas for the heating and heating reforming device. The remaining furnace gas used as fuel gas for the heating and heating reforming device is generally discharged outside the system.

[0006] As a process for producing reduced iron as described above, for example, Patent Document 1 describes a method of producing reduced iron by reforming the exhaust gas of a reduction furnace and natural gas in a reformer to generate a reducing gas consisting mainly of CO and H2 gas, and blowing this reducing gas into a reduction furnace to reduce the iron oxide inside the reduction furnace.

[0007] In addition, Patent Document 2 describes a method for producing reduced iron by reforming furnace gas and CO2-removed furnace gas to produce reducing gas, and blowing the gas into the reducing furnace. Prior art literature

[0008] Japanese Published Patent Application No. 2017-88912, Japanese Published Patent Application No. 2016-529384 The problem to be solved

[0009] In the method for producing reduced iron described in Patent Document 1, since natural gas is used to produce reducing gas, there is a problem in that some CO2 emissions cannot be avoided, although they are lower than those of a blast furnace.

[0010] In addition, the method described in Patent Document 2 involves producing reducing gas using coke oven gas or converter gas generated within a steel mill. Here, since coke oven gas or converter gas is indispensable as fuel gas for downstream processes such as heating furnaces or annealing furnaces in an integrated steel mill, if it is diverted to the process of producing reduced iron, it causes a shortage of fuel gas in the downstream processes. As a result, natural gas is eventually supplied externally to compensate for the gas shortage in the downstream processes, and the reduction of CO2 emissions is not realized, leaving it as a challenge.

[0011] The present invention is made in consideration of the above phenomenon and aims to propose a method that enables energy conservation and a reduction in CO2 emissions when producing reduced iron from iron oxide. means of solving the problem

[0012] The inventors have developed a system having an iron oxide filling process for filling iron oxide into a reduction furnace, a reduction gas injection process for injecting reduction gas into the reduction furnace, a reduction process for reducing iron oxide with reduction gas within the reduction furnace, a methane synthesis process for synthesizing methane from a portion of the furnace gas discharged from the furnace furnace and hydrogen gas, and a gas reforming process for using the furnace gas excluding the methane gas and the portion supplied to the methane synthesis process as raw material gas, and heating said raw material gas to reform it into said reduction gas. In this system, the furnace gas is circulated and reused. Furthermore, in order to achieve stable operation in this system, it is required to balance the gas within the above system so that the mass balance in this system is sound, that is, so that the composition ratio (volume ratio) of H2 and CO in the reduction gas supplied into the reduction furnace, H2 / CO, is always maintained at a predetermined set value without fluctuation.

[0013] However, when the grade of iron oxide (massive ore) that serves as the raw material for reduced iron fluctuates, the composition of the furnace gas discharged from the furnace fluctuates, making it difficult to maintain the above material balance sound. In addition, due to changes in performance caused by continuous operation of the methane synthesis device in the methane synthesis process or the heating reforming device in the gas reforming process, the gas composition at the outlet of the methane synthesis device or the heating reforming device fluctuates, causing the ratio of H2 to CO in the reducing gas, H2 / CO, to change, making it difficult to maintain the above material balance sound.

[0014] Therefore, the inventors have identified a method for maintaining a sound material balance in the above-mentioned system, and have newly recognized that it is important to maintain an appropriate gas balance between the methane synthesis process and the gas reforming process according to changes in the composition of the reducing gas blown into the reduction furnace, and have come to complete the present invention.

[0015] In other words, the gist of the present invention is as follows.

[0016] 1. An iron oxide filling process for filling iron oxide into a reduction furnace, and

[0017] A reducing gas injection process for injecting reducing gas into the above-mentioned reduction furnace, and

[0018] A reduction process for reducing the iron oxide by the reduction gas in the above reduction furnace, and

[0019] A methane synthesis process for synthesizing a gas with methane as the main component from a portion of the furnace gas discharged from the furnace furnace of the above-mentioned reduction furnace and hydrogen gas, and

[0020] A gas reforming process that uses furnace gas, excluding the methane gas and the portion supplied to the methane synthesis process, as a raw material gas, and heats the raw material gas to reform it into the reducing gas.

[0021] A method for manufacturing reduced iron having,

[0022] A method for producing reduced iron, wherein the amount of furnace gas V1 supplied to the methane synthesis process and the amount of water vapor Vw in the raw gas supplied to the gas reforming process are adjusted to suppress the variation in the ratio of H2 and CO in the reducing gas blown into the reducing furnace, thereby controlling the material balance of H2 and CO in the process from the iron oxide filling process to the reduction process.

[0023] 2. A method for producing reduced iron as described in 1, wherein if the variation in the above H2 / CO ratio is an increase in the value of the above H2 / CO ratio, the above steam amount Vw and the above furnace gas amount V1 are reduced.

[0024] 3. A method for producing reduced iron as described in 1, wherein if the variation in the above H2 / CO ratio is a decrease in the value of the above H2 / CO ratio, the above steam amount Vw and the above furnace gas amount V1 are increased.

[0025] 4. A method for producing reduced iron as described in any one of 1 to 3, wherein the ratio X (percentage) of the amount of furnace gas V1 supplied to the methane synthesis process to the amount of furnace gas Vt generated above, and the ratio Y (percentage) of the amount of water vapor Vw in the raw gas supplied to the gas reforming process to the amount of furnace gas Vt generated above satisfy the following equation (1).

[0026] aX 2 +bX+c≤Y≤100 … (1)

[0027] However, a, b, and c are arbitrary values ​​determined by the operating conditions of the reduction furnace. Effects of the invention

[0028] According to the present invention, in a method for producing reduced iron having a closed system that recirculates and reuses furnace gas, wherein CO2-free hydrogen is supplied from the outside to the furnace gas of a reduction furnace to synthesize regenerated methane and the regenerated methane is used to produce a reduction gas, stable operation under a sound material balance can be realized. Brief explanation of the drawing

[0029] FIG. 1 is a diagram showing a process for producing reduced iron using a general shaft furnace. FIG. 2 is a diagram showing a process for producing reduced iron according to the present invention. FIG. 3 is a diagram showing the relationship between the amount of steam Vw, which is adjusted when the composition of the reducing gas changes, and the amount of furnace gas V1 for methane synthesis. FIG. 4 is a diagram showing experimental results investigating the relationship between the percentage Y of the amount of steam Vw provided to the reforming process relative to the amount of furnace gas Vt, and the percentage X of the amount of gas V1 provided to methane gas synthesis relative to the amount of furnace gas Vt. Specific details for implementing the invention

[0030] (Form for carrying out the invention)

[0031] Hereinafter, the method of the present invention will be described in detail with reference to the drawings. First, the conventional reduced iron manufacturing process, which is contrasted with the method of the present invention, will be described in order.

[0032] That is, FIG. 1 is a diagram showing the configuration of a process for manufacturing reduced iron using a conventional shaft-type reduction furnace. In FIG. 1, reference numeral 1 is a reduction furnace, 1a is iron oxide, 1b is reduced iron, 2 is furnace gas discharged from the reduction furnace (1), 3 is a dust removal device for furnace gas (2), 4 is a dehydration device, 5 is natural gas supplied from the outside, 6 is air, 7 is a heat reforming device that heats or heat reforms furnace gas (2) and air (6) to produce a reducing gas (8) containing carbon monoxide gas and hydrogen gas, and 9 is a reducing gas injection device that supplies the reducing gas to the reduction furnace (1).

[0033] In the reduction furnace (1), which is the center of the reduced iron manufacturing process, bulk iron oxide raw material (1a), such as sintered ore or pellets, is charged from the top and slowly lowered. Then, by blowing in a high-temperature reducing gas (8) from the middle of the furnace, the iron oxide raw material (1a) is reduced, and reduced iron (1b) is discharged from the bottom of the furnace. At this time, furnace gas (2), mainly containing CO, CO2, H2, and H2O, is discharged from the top of the furnace. This furnace gas (2) is removed by a dust removal device (3), and some of it is sent to a heating and reforming device (7) with moisture adjustment as a raw material gas. In the heating and reforming device (7), a gas containing hydrocarbons, such as natural gas (5), is supplied along with the aforementioned moisture-adjusted furnace gas (2) and heated. In the heating reforming device (7), a reforming reaction occurs, and a high-temperature reducing gas (8) containing mainly CO and H2 gas is produced and blown into the reduction furnace (1). In addition, the remaining portion of the furnace gas (2) is used as a heating fuel in the combustion chamber of the heating reforming device (7) after dehydration.

[0034] [Embodiment]

[0035] Regarding the conventional process shown in FIG. 1 above, in the present invention, as shown in FIG. 2, instead of hydrocarbon gas supplied from the outside, such as natural gas (5), regenerated methane produced in a methane synthesis reactor within the process is used. That is, in the configuration of the reduced iron manufacturing process shown in FIG. 2, a methane synthesis device (11) that synthesizes methane from furnace gas (2) and hydrogen (10) is newly installed. The regenerated methane produced in this methane synthesis device (11) is supplied to a heat reforming device (7) to be used as a raw material gas for the reduction gas (8).

[0036] Here, the raw material for methane synthesis in the methane synthesis device (11) is a gas containing CO, CO2, and hydrocarbons, supplied from the outside and hydrogen gas (10). Any gas containing CO, CO2, and hydrocarbons available within the steel mill may be used, but for example, as shown in FIG. 2, the amount of furnace gas (2) generated from the reduction furnace (1) that was previously used for heating the heating reforming device (7) in FIG. 1 is introduced into the methane synthesis device (11) to perform methane synthesis and serve as the raw material for regenerated methane. By changing the flow of furnace gas (2) within this system, the amount of regenerated methane required for the heating reforming device (7) can be synthesized. At this time, since fuel for heating the heating reforming device (7) is not supplied, it is acceptable to substitute it with an external CO2-free heat source, for example, an external heat source using CO2-free electricity. In this method, if CO2-free power is used for heating the heating reforming device (7) or for hydrogen production, CO2 emissions can be made zero in principle.

[0037] The regenerated methane synthesized in the methane synthesis device (11) is mixed with furnace gas (2) that has undergone dehydration, dust removal, and partial dehydration, and supplied to the heating reforming device (7). In the heating reforming device (7), it is reformed into a gas mainly containing H2 and CO, and then blown into the reduction furnace (1) as a reducing gas (8) to be provided for the production of reduced iron.

[0038] In establishing the manufacturing process of reduced iron in a closed system as shown in Figure 2 above, it is important to suppress the variation in the composition (ratio H2 / CO) of the reducing gas blown into the reduction furnace by maintaining a gas balance between the methane synthesis process and the gas reforming process. That is, as mentioned above, the composition of the furnace gas discharged from the furnace of the reduction furnace varies, such as when the grade of the raw iron oxide changes. Furthermore, since the ratio of splitting the furnace gas after dust removal into raw gas and gas for methane synthesis changes according to the amount of gas required to generate the reducing gas in the subsequent gas reforming process—that is, the amount of regenerated methane gas sent to the gas reforming process and the amount of water vapor in the furnace gas—it is necessary to estimate the amount of gas in each process to satisfy the material balance mentioned above.

[0039] Therefore, in the present invention, reduced iron is produced under the sound material balance described above by adjusting the furnace gas amount V1 supplied to the methane synthesis process and the water vapor amount Vw in the raw gas supplied to the gas reforming process according to the variation in the H2 / CO ratio of the reducing gas blown into the reduction furnace. Below, a method for realizing operation under a sound material balance in the method of the present invention will be explained in detail.

[0040] Thus, H2 and CO in the reducing gas blown into the reducing furnace are synthesized by the reaction of CH4 with CO2 and H2O in the heating reforming device (7) immediately preceding the reducing furnace (1) shown in FIG. 2. Each reaction is represented by the following equations (i) and (ii).

[0041] CH4+CO2→ 2CO+2H2… (i)

[0042] CH4+H2O → CO+3H2… (ii)

[0043] From equations (i) and (ii), it can be seen that the gases serving as raw materials for reforming are CH4, CO2, and H2O. Among these, the amount of H2O supplied to the heating reforming device can be adjusted by removing it through condensation by cooling the gas or by adding H2O itself to the gas. Meanwhile, CH4 is synthesized by supplying a portion of the furnace gas discharged from the reduction furnace to the methane synthesis device. From the above equation (ii), the amount of steam (H2O) supplied to the heating reforming device Vw [Nm 3 It can be seen that if / t] increases, the amount of CH4 reacted with H2O also needs to be increased. Furthermore, in order to increase the amount of CH4, the amount of furnace gas V1 [Nm²] supplied to the methane synthesis unit from the furnace furnace gas discharged from the reduction furnace must be 3 It is necessary to increase [ / t], and therefore, Vw and V1 are in a positive relationship.

[0044] Here, for example, we consider a state in which the amount of CH4 generated decreases due to a decrease in the reaction rate of the methane synthesis unit. If operation continues in this state, the amount of CH4 supplied to the heat reforming unit decreases, and thus the amount of CO in the reducing gas also decreases. As a result, the ratio of H2 to C in the reducing gas (H2 ratio) increases. As mentioned above, since the composition ratio (volume ratio) of H2 and CO in the reducing gas blown into the reduction furnace, H2 / CO, needs to be maintained constant, it is necessary to reduce the H2 ratio. Therefore, in order to suppress the generation of CO and H2 by the reaction represented by the above equation (ii), it is necessary to reduce the amount of steam Vw supplied to the heat reforming unit and reduce the amount of furnace gas V1 supplied to the methane synthesis process.

[0045] In addition, consider a state in which the CO2 concentration in the furnace gas Vt increases due to fluctuations in the grade of the iron oxide lump ore, which is a raw material for reduced iron. If operation continues in this state, the amount of CO2 supplied to the methane synthesis unit or the heat reforming unit also increases, and thus the amount of CO in the reducing gas also increases. As a result, the ratio of CO to H2 and CO in the reducing gas (CO ratio) increases. As mentioned above, since the composition ratio (volume ratio) of H2 and CO in the reducing gas blown into the reducing furnace, H2 / CO, needs to be maintained constant, it is necessary to increase the H2 ratio. Therefore, in order to promote the generation of CO and H2 by the reaction represented by the above equation (ii), it is necessary to increase the amount of steam Vw supplied to the heat reforming unit and the amount of furnace gas V1 supplied to the synthesis process.

[0046] In addition, performing these operations causes the amount of reducing gas supplied to the reduction furnace to fluctuate. However, if the fluctuation range of the reducing gas amount is excessive, stable operation of the reduction furnace becomes difficult, so 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 excessive, it leads to a decrease in production volume and a deterioration in the quality of the product. On the other hand, if the increase in the amount of reducing gas is excessive, the ventilation resistance of the gas inside the furnace increases, and the raw material (pellet) inside the furnace does not fall.

[0047] As a result of the inventor's investigation into the appropriate amount of reducing gas to avoid the above disadvantages, the appropriate flow rate of the reducing gas is 1500 Nm 3 / t or more than 3500Nm 3 / t was less than

[0048] In addition, a detailed examination was conducted regarding a method for easily adjusting the aforementioned amount of steam Vw and the gas V1 for methane synthesis.

[0049] First, using Figure 3, we will explain the relationship between the amount of water vapor Vw, which is adjusted when the composition of the reducing gas described above changes, and the amount of furnace gas V1 for methane synthesis. Figure 3 is a schematic diagram showing the relationship between Vw and V1 when Vw is placed on the horizontal axis and V1 on the vertical axis in the present process. As previously described, when Vw changes to an increase, a large amount of H2 is generated by the reaction described in Equation (ii) above; therefore, in order to maintain the ratio of H2 / CO of the reducing gas, it is necessary to increase the amount of CO generated by the reaction represented by Equation (i) above, and thus the amount of V1 increases. That is, the ratio of the increment of the gas for methane synthesis ΔV1 to the increment of the amount of water vapor ΔVw becomes steep. Meanwhile, when the amount of water vapor Vw changes to a decrease, the generation of a large amount of H2 following the reaction shown in Equation (ii) above is suppressed, so there is no large fluctuation in the amount of CO required to maintain a predetermined ratio of H2 / CO. Therefore, the ratio of the incremental ΔV1 of the gas for methane synthesis to the incremental ΔVw of the amount of water vapor becomes moderate. In other words, since the amount of change (derivative) of the relationship between Vw and V1 changes with the value of Vw, it was expected that the relationship between Vw and V1 would appear as a non-linear function.

[0050] Therefore, the inventors performed numerical calculations of the material balance within the process to determine a non-linear function representing the relationship between Vw and V1. In addition, the calculation of the material balance was performed using commercially available software for simulation. After calculating the composition of the furnace gas by setting the blower gas flow rate and the ratio of H2 / CO in the blower gas flow rate, the amount of steam Vw supplied from the furnace gas to the heating reformer was arbitrarily determined. The amount of methane synthesized in the methane synthesis unit and the amount of CO and H2 synthesized in the heating reformer were each calculated, and calculations were performed by changing the amount of steam supplied Vw one by one so that the ratio of H2 / CO in the reducing gas obtained from these results became the same as the initial set value, and calculations were performed until the ratio of H2 / CO calculated by this was the same as the set ratio of H2 / CO.

[0051] In addition, as with the tactics, the increment ΔV1 of the gas for methane synthesis with respect to the increment ΔVw of the amount of water vapor is estimated to represent a fundamentally positive value, although it may be steep or gradual depending on the range of the amount of water vapor Vw as shown in Fig. 3. Therefore, the ratio of the increment ΔV1 of the gas for methane synthesis with respect to the increment ΔVw of the amount of water vapor, i.e., the derivative value, becomes a positive value as follows.

[0052] dV1 / dVw>0

[0053] For the above equation, furnace gas quantity Vt[Nm 3 X is the percentage (V1 / Vt×100) of the furnace gas volume for methane synthesis (the volume of furnace gas supplied to the methane reaction device) V1 with respect to / t, and the furnace gas volume Vt[Nm 3 If we let Y be the percentage of the amount of water vapor Vw for [ / t] (Vw / Vt×100) and assume that there is no significant change in the amount of gas Vt, the above equation can be expressed as follows.

[0054] dV1 / dVw=dY / dX>0

[0055] Although various functions are considered for the form of the derivative value dY / dX, it is assumed that it always takes a defined value, that periodicity is not assumed in the value, that the increment of ΔV1 with respect to the increment of ΔVw gradually increases as shown in Fig. 3, and for ease of handling, it is given by the following linear equation.

[0056] dY / dX=αX+β(α>0, β>0)

[0057] By integrating the above equation, the functional form of Y is obtained.

[0058] ∫(dY / dX)dX=∫(αX+β)dX

[0059] Y-Y0=α / 2X 2 +βX+γ

[0060] In summary, Y is expected to appear as a quadratic function of X as follows.

[0061] Y = aX 2 +bX + c (a, b, c are defined integers)

[0062] In Table 1, the reducing gas flow rate is 2200 Nm 3 / t, and the above calculation results are shown in the range of 0.5 ≤ H2 / CO ≤ 4. In addition, regarding the calculation results shown in Table 1, furnace gas quantity Vt [Nm 3 Y is the percentage of water vapor Vw with respect to [ / t] (Vw / Vt × 100), and Vt is the furnace gas amount [Nm 3 Figure 4 shows the result of organizing the percentage (V1 / Vt×100) of the furnace gas volume V1 for methane synthesis for [ / t] as X.

[0063]

[0064] As mentioned above, the operating range in this process is furnace gas volume Vt [Nm 3It is estimated that when the percentage of the amount of water vapor Vw (Vw / Vt × 100) for [ / t] is set to Y, it appears as a quadratic function of X. The result of fitting the operating range of FIG. 4 as a quadratic function of X is shown. As described in FIG. 4, it was found that the appropriate operating range in the process is determined using the following equation (1).

[0065] aX 2 +bX+c≤Y≤100 … (1)

[0066] In the equation, a, b, and c are arbitrary values ​​determined by the operating conditions of the reduction furnace.

[0067] For example, the reducing gas temperature is 600°C to 1200°C, and the amount of injected reducing gas is 1500 Nm³ 3 3500Nm at / t 3 If we find the appropriate a, b, and c for operation under the condition / t, they are as follows.

[0068] 0.002≤a≤0.038

[0069] 2.6≤b≤3.3

[0070] 10≤c≤34

[0071] As described above, by determining a, b, and c for each operation and applying them to the above equation (1), an appropriate range of furnace gas amount V1 supplied to the heating reformer is given for the amount of steam (H2O) Vw in the operation. And by adjusting Vw and V1 within this appropriate range, it becomes possible to manufacture reduced iron in a sound material balance in a closed circulation system.

[0072] Examples

[0073] The following describes the embodiments.

[0074] As shown in FIG. 2, the amount of reducing gas injected is 2200 Nm 3 / t, the operation of this process was carried out under the condition that the composition ratio (volume ratio) of H2 / CO in the reducing gas was 2.0. Under these conditions, the gas composition (volume) in the furnace gas during normal operation was H2:CO:CO2:H2O = 48:30:9:14. As the grade of the lump ore charged into the reduction furnace decreased, the ratio of H2 / CO in the reducing gas rose to 2.2, meaning the H2 ratio increased. Furthermore, the reduction rate of the finished product also decreased from 91% at the start of operation to 89%. Therefore, to return the ratio of H2 / CO to 2.0, the amount of steam Vw injected into the heating reforming device was increased from the previous 374 Nm³ 3 355 Nm from / t 3 As the reduction was reduced to / t, it became possible to maintain operation with the reduction gas composition set to a ratio of H2 / CO of 2.0. In addition, the reduction rate of the product could be restored to 91% of the initial operation rate. Explanation of the symbols

[0075] 1 : Reduction furnace 1a : Iron oxide 1b : Reduced iron 2 : Rojeong Gas 3: Vibration damping device 4: Dehydration device 5 : Natural gas 6 : Air 7: Heating reformer 8: Reducing gas 9: Reducing gas injection device 10: Hydrogen 11: Methane Synthesis Unit

Claims

Claim 1 A method for manufacturing reduced iron comprising: an iron oxide filling process for filling iron oxide into a reduction furnace; a reduction gas injection process for injecting a reduction gas into the reduction furnace; a reduction process for reducing the iron oxide by the reduction gas within the reduction furnace; a methane synthesis process for splitting the furnace top gas discharged from the furnace top of the reduction furnace and synthesizing a gas having methane as the main component from one of the split furnace top gases and hydrogen gas; and a gas reforming process for using the methane gas and the other of the split furnace top gas as raw materials and heating the raw materials to reform them into the reduction gas, wherein, in accordance with fluctuations in the ratio of H2 to CO in the reduction gas injected into the reduction furnace, the amount of furnace top gas V1 supplied to the methane synthesis process and the amount of water vapor Vw in the raw materials supplied to the gas reforming process are adjusted to suppress said fluctuations, in a process extending from the iron oxide filling process to the reduction process. A method for producing reduced iron that controls the mass balance of H2 and CO. Claim 2 A method for producing reduced iron according to claim 1, wherein if the variation in the non-H2 / CO is an increase in the value of the non-H2 / CO, the amount of water vapor Vw and the amount of furnace gas V1 are reduced. Claim 3 A method for producing reduced iron according to claim 1, wherein if the variation in the non-H2 / CO is a decrease in the value of the non-H2 / CO, the amount of water vapor Vw and the amount of furnace gas V1 are increased. Claim 4 A method for producing reduced iron according to any one of claims 1 to 3, wherein the ratio X (percentage) of the amount of furnace gas V1 supplied to the methane synthesis process to the amount of furnace gas Vt generated, and the ratio Y (percentage) of the amount of water vapor Vw in the raw gas supplied to the gas reforming process to the amount of furnace gas Vt generated, satisfy the following equation (1). aX 2 +bX+c≤Y≤100 … (1) where a, b and c are arbitrary values ​​determined by the operating conditions of the reduction furnace.

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