Method for producing reduced iron

Abstract

To provide a method that enables energy saving and reduction of an amount of CO2 emissions when producing reduced iron from iron oxide.SOLUTION: A method for manufacturing reduced iron includes an iron oxide filling step for filling iron oxide into a reduction furnace, a reduction gas blowing step for blowing reduction gas into the reduction furnace, a reduction step for reducing the iron oxide using the reduction gas within the reduction furnace, a methane synthesis step for synthesizing gas, the main component of which is methane, from hydrogen gas and a portion of the blast furnace top gas emitted from the blast furnace top of the reduction furnace, and a gas reforming step in which methane and the remainder of the blast furnace top gas are used as raw material gas, and the raw material gas is heated to reform it into reduced gas, wherein these steps are interconnected in a circulatory system, and operation in the circulation system is continued while supplementing carbon deficiency during its circulation, in one or more steps selected from the reduction gas blowing step, the reduction step, the methane synthesis step, and the gas reforming step, or in connection parts between two or more steps selected from the reduction gas blowing step, the reduction step, the methane synthesis step, and the gas reforming step.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing reduced iron, and more particularly to a method for producing reduced iron using a vertical reduction furnace. [Background technology]

[0002] In recent years, steel plants have been strongly required to conserve energy in the context of global environmental issues and the depletion of fossil fuels. Now, the main raw material for iron is iron oxide, and a reduction process is essential to reduce this iron oxide. The most common reduction process in the world is the blast furnace. In this blast furnace, coke or pulverized coal reacts with oxygen in hot air (air heated to about 1200°C) in the tuyeres, producing CO and H. 2 This gas (reducing gas) is used to reduce the iron ore 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 per ton of molten iron produced) has been reduced to around 500 kg / t, but this has already reached its lower limit, and no further significant reduction in the reducing agent ratio can be expected.

[0003] Meanwhile, in regions where natural gas is produced, a method is often used in which a vertical reduction furnace is filled with agglomerated iron ore such as sintered ore or pellets 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 to produce reduced iron. In this method, natural gas or the like is used as the raw material gas for the reducing gas. The raw material gas is heated and reformed in a heating and reforming device 7 together with the top gas discharged from the top of the reduction furnace to produce a reducing gas. The produced reducing gas is blown into the reduction furnace and reacts with the iron oxide raw material supplied from the top of the reduction furnace, reducing the iron oxide to produce reduced iron. The produced reduced iron is cooled in a region below the position where the reducing gas is blown into the reduction furnace, and then discharged from the bottom of the reduction furnace.

[0004] The gas used for the reduction of iron oxide is discharged from the top of the reduction furnace as top gas, and after dust collection and cooling, a portion of the top gas is sent to the heating reformer 7 as a raw material for reformed gas. The remaining top gas (the remainder of the top gas) is used as fuel gas for the heating and thermal reformer 7. The remaining top gas used as fuel gas for the heating and thermal reformer 7 is generally discharged outside the system.

[0005] As an example of the above-mentioned reduced iron production process, Patent Document 1 describes a process in which exhaust gas from a reduction furnace and natural gas are reformed in a reformer to produce mainly CO and H. 2 It is described that a reducing gas consisting of a gas is generated, and this reducing gas is blown into a reduction furnace to reduce iron oxide in the reduction furnace, thereby producing reduced iron. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-88912 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the method for producing reduced iron described in Patent Document 1, natural gas is used to produce reducing gas, so a certain amount of CO is emitted, although it is lower than that in a blast furnace. 2 The problem is that emissions are unavoidable. The gases emitted in this way are called CO 2 This method of producing reduced iron contains a certain amount of CO 2 Although emissions can be reduced to a certain extent, they cannot be reduced to zero.

[0008] The present invention has been made in consideration of the above-mentioned current situation, and aims to realize energy saving and CO 2 The aim is to propose ways in which emissions can be reduced. [Means for solving the problem]

[0009] The inventors have found that in the above-mentioned method for producing reduced iron, 2 In order to reduce emissions to zero, the top gas from the reduction furnace is treated with an external CO 2 Free hydrogen is supplied to synthesize regenerated methane, which is then used to produce reducing gas, resulting in energy savings and reduced CO 2 In other words, this method of producing reduced iron can reduce the amount of CO emissions contained in the exhaust gas from the reduction furnace. 2 All gaseous carbon sources, such as iron oxide and CO, are recycled and reused through the process of synthesizing regenerated methane. For this reason, the system is made up of the iron oxide charging process in the reduction furnace, the process of blowing reducing gas into the reduction furnace, the reduction process in the reduction furnace, the methane synthesis process in which regenerated methane gas is generated from the top gas of the reduction furnace, and the gas reforming process in which reducing gas is generated from regenerated methane gas and the top gas. 2 This will make it possible to reduce carbon emissions to zero.

[0010] Furthermore, the inventors have considered the actual application of the above-mentioned method for producing reduced iron to a steelworks, and have found that it is necessary to secure carbon in the above-mentioned circulation (reuse) system (hereinafter also simply referred to as the system). That is, a certain amount of carbon is discharged outside the system in a form other than gas, such as carbon consumed for carburizing the reduced iron in the reduction furnace, and carbon contained in dust that accompanies the exhaust gas (furnace top gas) from the reduction furnace and is removed from the exhaust gas by a dust collector. Furthermore, during non-steady times such as when operational trouble occurs, carbon may be discharged outside the system in a form that is not performed during steady operation, such as the atmospheric release of exhaust gas from the reduction furnace. Considering such carbon discharge outside the system, the amount of carbon circulating in the system tends to decrease. In such a case, the proportion of the iron oxide reduction reaction by CO in the iron oxide reduction reaction in the reduction furnace decreases, and H 2 The ratio of the reaction by CO to the reduction of iron oxide increases. 2 Since the iron oxide reduction reaction by is an endothermic reaction, if the latter reaction increases, the heat in the reduction furnace becomes insufficient, making it difficult to obtain reduced iron with a sufficiently high reduction rate.

[0011] There is a method of preheating the raw iron oxide for thermal compensation, but if operation is continued without supplying a carbon source and the reducing gas becomes entirely hydrogen, the preheating temperature of the raw iron oxide becomes very high, making it difficult to handle the raw iron oxide. In addition, since the original operation of the reduction furnace did not require preheating of the raw materials, extra equipment is required for preheating the raw materials, making this operation economically disadvantageous. On the other hand, with regard to the method of raising the reducing gas temperature for thermal compensation, if the reducing gas temperature becomes high, the raw materials tend to fuse together in the reduction furnace, making it difficult to properly lower and discharge the raw materials, and more likely to cause problems with the reducing gas injection equipment. In addition, raising the reducing gas temperature compared to the original operation of the reduction furnace requires extra energy, making this operation economically disadvantageous. For the above reasons, the method of raising the reducing gas temperature, like the preheating of the raw iron oxide, is also economically disadvantageous because it requires the use of hydrogen. 2 Therefore, it has been newly discovered that in order to continue producing reduced iron with a sufficiently high reduction rate in the circulation (recycle) system, it is necessary to supply a certain amount of carbon source to compensate for the carbon loss from the carbon circulation / recycle system.

[0012] As described above, the inventors have conducted intensive research to solve the above-mentioned problems associated with the conventional techniques and to realize the production of reduced iron at a high reduction rate in a circulation (reuse) system, and as a result, have developed the following novel method for producing reduced iron.

[0013] The gist of one embodiment of the present invention is as follows.

[0014] 1. An iron oxide charging process in which iron oxide is charged into a reduction furnace; a reducing gas blowing step of blowing a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with the reducing gas in the reduction furnace; a methane synthesis step of mixing a part of a furnace top gas discharged from a top of the reducing furnace with oxygen gas to use as a heating fuel, and synthesizing a gas mainly composed of methane from exhaust gas obtained by burning the heating fuel and hydrogen gas; a gas reforming step of using the methane and the remainder of the furnace gas as a raw material gas and reforming the raw material gas into the reducing gas by heating the raw material gas with the combustion heat of the heating fuel; A method for producing reduced iron in a circulating system in which the operation is continued while compensating for carbon shortage during operation in the circulation system in one or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step, or in a connection portion between two or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step.

[0015] 2. The method for producing reduced iron according to claim 1, wherein the carbon is supplemented at each connection of three processes: either one or both of the methane synthesis process and the gas reforming process, or the reduction process in addition to both of the processes.

[0016] 3. The method for producing reduced iron according to 1 or 2 above, wherein the carbon is a combustion gas of waste plastic.

[0017] 4. The method for producing reduced iron according to 1 or 2 above, wherein the carbon is a combustion gas of biomass.

[0018] 5. The method for producing reduced iron described in 1 or 2 above, wherein when the nitrogen concentration in the circulation system increases to or above a certain level, a portion of the furnace gas to be supplied to the methane synthesis step is discharged outside the circulation system, and natural gas is supplied in place of the synthesized methane to carry out the gas reforming step.

[0019] 6. An iron oxide charging step of charging the iron oxide into the reduction furnace; a reducing gas blowing step of blowing a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with the reducing gas in the reduction furnace; Mainly CO and CO obtained from part of the top gas discharged from the top of the reduction furnace 2 , H 2a methane synthesis step of synthesizing a gas mainly composed of methane from a gas consisting of the above and hydrogen gas; Mainly CO, CO obtained from the methane and the remainder of the furnace gas 2 , H 2 The raw gas is a gas consisting of CO 2 a gas reforming step of heating the gas using free electricity or in combination with a heating fuel to reform the gas into the reducing gas; A method for producing reduced iron in a circulating system in which the operation is continued while compensating for carbon shortage during operation in the circulation system in one or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step, or in a connection portion between two or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step.

[0020] 7. The method for producing reduced iron according to claim 6, wherein the carbon is supplemented at each connection of three steps, namely, the methane synthesis step and / or the gas reforming step, or the reduction step in addition to both steps.

[0021] 8. The method for producing reduced iron according to 6 or 7 above, wherein the carbon is a combustion gas of waste plastic.

[0022] 9. The method for producing reduced iron according to claim 6 or 7, wherein the carbon is a combustion gas of biomass.

[0023] 10. The method for producing reduced iron as described in 6 or 7 above, wherein when the nitrogen concentration in the circulation system rises to a certain level or more, a portion of the furnace gas to be supplied to the methane synthesis step is discharged outside the circulation system, and natural gas is supplied in place of the synthesized methane to carry out the gas reforming step.

[0024] The gist of another embodiment of the present invention is as follows.

[0025] 1. An iron oxide charging process in which iron oxide is charged into a reduction furnace; a reducing gas blowing step of blowing a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with the reducing gas in the reduction furnace; a methane synthesis step of synthesizing a gas mainly composed of methane from a portion of the top gas discharged from a top of the reducing furnace and hydrogen gas; a gas reforming step of using the methane and the remainder of the furnace gas as a raw material gas and heating the raw material gas to reform it into the reducing gas; A method for producing reduced iron in a circulating system in which the operation is continued while compensating for carbon shortage during operation in the circulation system in one or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step, or in a connection portion between two or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step.

[0026] 2. The method for producing reduced iron according to claim 1, wherein the carbon is supplemented at each connection of three processes: either one or both of the methane synthesis process and the gas reforming process, or the reduction process in addition to both of the processes.

[0027] 3. The method for producing reduced iron according to 1 or 2 above, wherein the carbon is a combustion gas of waste plastic.

[0028] 4. The method for producing reduced iron according to 1 or 2 above, wherein the carbon is a combustion gas of biomass. Effect of the Invention

[0029] In the present invention, CO is introduced from the outside into the top gas of the reduction furnace. 2 In a method for producing reduced iron with a closed system that circulates carbon, in which free hydrogen is supplied to synthesize regenerated methane and the regenerated methane is used to produce reducing gas, it is possible to operate the system while supplying a carbon source when necessary. This prevents fluctuations in the amount of carbon circulating in the system, and reduces CO 2It has become possible to stably carry out emission-free operations. Furthermore, when using carbon-neutral raw materials such as waste plastics or biomass as the carbon source, in addition to the above effects, there is also the effect of further reducing the environmental impact of the process. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a diagram showing a process for producing reduced iron using a general shaft furnace. [Diagram 2] FIG. 1 is a diagram showing a process for producing reduced iron according to the present invention. [Diagram 3] 1 is a diagram showing another process for producing reduced iron according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The method of the present invention will be described in detail below with reference to the drawings. First, a conventional process for producing reduced iron will be described in order in comparison with the method of the present invention. [Previous process] That is, Fig. 1 is a diagram showing the configuration of a reduced iron manufacturing process using a conventional shaft-type reduction furnace. In Fig. 1, reference numeral 1 denotes a reduction furnace, 1a denotes iron oxide, 1b denotes reduced iron, 2 denotes top gas discharged from the reduction furnace 1, 3 denotes a dust remover for the top gas 2, 4 denotes a dehydrator, 5 denotes natural gas supplied from the outside, 6 denotes air, 7 denotes a heating reformer that uses heat obtained by mixing a part of the top gas 2 with the air 6 and burning the mixture to heat and reform the remainder of the top gas 2 mixed with the natural gas to produce reducing gas 8 containing carbon monoxide gas and hydrogen gas, and 9 denotes a reducing gas injection device that supplies reducing gas to the reduction furnace 1.

[0032] In the reduction furnace 1, which is the core of the reduced iron manufacturing process, lump iron oxide raw materials 1a such as sintered ore or pellets are charged from the top and gradually lowered. The iron oxide raw materials 1a are reduced by blowing in high-temperature reducing gas 8 from the center of the furnace, and reduced iron 1b is discharged from the bottom of the furnace. At this time, mainly CO, CO 2 , H 2 , H 2The furnace gas 2, which is composed of O, is discharged. This furnace gas 2 is subjected to dust removal in a dust remover 3, and a portion of it is adjusted in moisture as a raw material gas and sent to a thermal reformer 7. In the thermal reformer 7, a gas containing a hydrocarbon, for example, natural gas 5, is supplied together with the moisture-adjusted furnace gas 2 and heated. In the thermal reformer 7, a reforming reaction occurs, and mainly CO, H 2 High-temperature reducing gas 8 composed of gas is generated and blown into the reducing furnace 1. The remaining part of the furnace top gas 2 is dehydrated and then used as heating fuel together with air 6 in the combustion chamber of the thermal reformer 7. The routes for supplying and discharging the heating fuel used for thermal reforming are shown by dotted lines in FIG. 1.

[0033] [First form] In contrast to the conventional process shown in Fig. 1, the present invention uses regenerated methane generated in a methane synthesis reactor within the process, instead of a hydrocarbon gas supplied from outside, such as the natural gas 5, as shown in Fig. 2. That is, the configuration of the reduced iron manufacturing process shown in Fig. 2 is newly provided with a methane synthesis unit 11 that synthesizes a gas mainly composed of methane from a part of the top gas 2 and hydrogen 10. The regenerated methane generated in the methane synthesis unit 11 is supplied to the thermal reformer 7 together with the remainder of the top gas, and used as a raw material gas for the reducing gas 8. In the present invention, the "gas mainly composed of methane" synthesized in the methane synthesis step may include, in addition to methane, water vapor (H 2 O), hydrogen (H 2 ), nitrogen (N 2 ), CO, CO 2 , hydrocarbons, etc.

[0034] The raw materials for methane synthesis in the methane synthesis unit 11 are hydrogen gas 10 supplied from the outside, CO and CO 2 and a gas containing at least one selected from CO and CO 2The gas containing at least one selected from the above may be any gas available in the steelworks. For example, as shown in FIG. 2, exhaust gas obtained by mixing a part of the furnace gas 2 with a combustion support gas in the combustion chamber of the thermal reformer 7 and burning the mixture may be used. When burning the furnace gas 2 in the combustion chamber of the thermal reformer 7, it is preferable to use oxygen gas 12 instead of air as the combustion support gas so as not to mix in nitrogen. Here, the oxygen gas 12 used as the combustion support gas does not necessarily need to be pure oxygen with an oxygen concentration of 100%, and may contain a small amount of gas other than oxygen, such as nitrogen, carbon dioxide, argon, etc. However, if the oxygen concentration is too low, the gas volume increases, which causes a problem that the thermal reformer 7 and the reactor for methane synthesis must be enlarged, so that the oxygen concentration is preferably 80% or more. The routes for supplying the heating fuel used for thermal reforming and using the exhaust gas as a raw material for methane synthesis are shown by dotted lines in FIG. 2.

[0035] The hydrogen gas 10 and oxygen gas 12 are produced using CO 2 In principle, using free electricity would reduce CO 2 Emissions can be reduced to zero. Here, CO 2 As free electricity, for example, electricity generated by solar power generation or nuclear power generation may be used.

[0036] In the above operation shown in FIG. 2, the carbon in the circulation system is gradually reduced due to carburization of the reduced iron, leakage of gas from the furnace body and piping constituting the process, and diffusion of gas in the system during non-steady operation. Therefore, it is necessary to compensate for the reduced amount of carbon. In the present invention, the stable production of reduced iron in the circulation system is realized by performing the operation while compensating for the reduced amount of carbon in one or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step, or in a connection between two or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step. That is, in the closed circulation system of the present invention, the reduced amount of carbon is, for example, at most about 30 kg per ton of reduced iron, so that the carbon can be compensated for without making a major modification to existing equipment. Therefore, the carbon can be compensated for in one or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step, or in a connection between two or more of the steps.

[0037] In the reduced iron production process shown in Fig. 2, carbon can be replenished at, for example, one or more of the refilling points (1) to (3) shown in Fig. 2. The refilling point (1) is a connection between the dehydrator 4 and the thermal reformer 7 on the path extending from the methane synthesis unit 11, the refilling point (2) is a connection between the reduction furnace 1 and the dust remover 3 on the path extending from the reduction furnace 1, and the refilling point (3) is a connection between the dehydrator 4 and the thermal reformer 7 on the path extending from the reduction furnace 1. In other words, the refilling point (1) is a connection between the methane synthesis step and the gas reforming step, the refilling point (2) is a connection between the reduction step and the methane synthesis step and a connection between the reduction step and the gas reforming step, and the refilling point (3) is a connection between the reduction step and the methane synthesis step.

[0038] Here, as described above, if a carbon shortage occurs in the system, the possibility of the operation becoming unstable increases, so it is preferable to replenish carbon continuously rather than intermittently. In other words, it is preferable to start supplementing carbon when a carbon shortage in the system is detected, and to continue supplementing until the carbon shortage is resolved.

[0039] In this case, the method for determining the amount of carbon shortage is not particularly limited, and may be, for example, a method of calculating from the flow rates and compositions of the reducing gas and top gas blown into the reducing furnace, or a method of calculating from the carbon content of the product reduced iron and the production amount of reduced iron. Considering the speed of measurement, the former method of calculating from the flow rates and compositions of the reducing gas and top gas is preferred. The method of calculating from the flow rates and compositions of the reducing gas and top gas is a method of calculating the amount of carbon atoms contained in each gas from the measurement results of the flow rates and compositions of the reducing gas and top gas, and taking the difference as the amount of carbon substance discharged outside the system, i.e., the amount of carbon substance that is insufficient. The method of calculating from the carbon content of the product reduced iron and the production amount of reduced iron is a method of measuring the carbon content of the product reduced iron and the production amount of reduced iron, and taking the amount of carbon discharged as carbon in reduced iron (amount of carburization) calculated from these as the amount of carbon that is insufficient.

[0040] On the other hand, fluctuations in the amount of carbon in the system due to carbon supplementation can be understood, for example, by determining the amount of carbon contained in the reducing gas from the flow rate and composition of the reducing gas and monitoring its change over time. If the amount of carbon in the system is on the rise, the amount of carbon to be supplemented is excessive, so the amount of carbon to be supplemented is reduced. If the amount of carbon in the system is on the decline, the amount of carbon to be supplemented is insufficient, so the amount of carbon to be supplemented is increased. As described above, by monitoring fluctuations in the amount of carbon in the system and adjusting the amount of carbon to be supplemented in response to those fluctuations, it is possible to continue operations while supplementing the system with just the right amount of carbon, without excess or deficiency.

[0041] When varying the amount of carbon supplementation in accordance with the variation in the amount of carbon in the system, it is desirable to set the reference amount of carbon in the system under conditions such that the reduction rate of the product reduced iron (product reduction rate) is equal to or greater than the reference value. In this case, by setting the reference value of the reduction rate to 90% or more, the energy required in the downstream process of melting DRI (direct reduced iron) can be minimized. More preferably, by setting the reference value of the reduction rate to 93% or more, the energy required in the downstream process can be further reduced.

[0042] In addition, the carbon replenishment method may be a method of directly introducing a gaseous carbon source such as natural gas into the system, or a method of combusting a gaseous, liquid or solid carbon source and introducing the resulting combustion gas. When introducing a combustion gas, it is preferable to utilize the combustion heat of the carbon source as a heat source required in the system, for example, as a heat source for the thermal reforming device 7, in order to improve energy efficiency. However, when introducing the combustion gas of the carbon source into the system, it is preferable to remove dust from the combustion gas before introducing it into the system, since the combustion gas may contain unburned solid and liquid components such as soot and tar. When removing dust, a new dust remover may be installed for the carbon source combustion gas, but it is more preferable to effectively utilize existing equipment, for example, by using a dust remover for the furnace gas in combination.

[0043] In particular, when waste plastics are used as a solid carbon source, carbon sources that would otherwise be landfilled or incinerated can be effectively utilized, thereby reducing the environmental impact of the process. The same is true when biomass, a carbon-neutral carbon source, is used as a solid carbon source. For these reasons, using waste plastics or biomass as a carbon source is more suitable as an embodiment of the present invention than using fossil fuels such as natural gas, coal, and petroleum.

[0044] In the conventional reduced iron production process, it has been proposed to supply a carbon source for a purpose other than carbon compensation in the circulation (reuse) system of the present invention, such as to increase the carbon content of the reduced iron. For example, Japanese Patent Laid-Open Publication No. 49-129616 discloses a method in which LPG is injected from below the reducing gas injection position of the reducing furnace, and the reduced iron is carburized while being cooled. In the case of supplying the carbon source from the lower part of the reducing furnace proposed in this publication, the supply position of the carbon source is outside the carbon circulation / reuse system. In other words, the carbon supplied at the lower part of the reducing furnace carburizes into the reduced iron before being supplied to the circulation / reuse system, and therefore the shortage in the circulation / reuse system cannot be compensated for, and therefore this technology cannot be applied to the present invention.

[0045] [Second form] A second embodiment of the present invention is shown in Fig. 3. This second embodiment differs in that the portion of the top gas 2 generated from the reduction furnace 1 that was used to heat the thermal reformer 7 in the first embodiment (Fig. 2) is fed into a methane synthesis unit 11 that synthesizes methane, and used as the raw material for regenerated methane. By changing the flow of the top gas 2 in this system, the amount of regenerated methane required for the thermal reformer 7 can be synthesized. At this time, since no fuel for heating the thermal reformer 7 is supplied, the amount of external CO 2 Free heat source, e.g. CO 2 A heat source 13 using free electricity can be used instead. The heat supply path from the heat source 13 is shown by a dotted line in FIG. 3. In this method, CO is used for heating the thermal reformer 7 and for producing hydrogen. 2 In principle, using free electricity would reduce CO 2 Emissions can be reduced to zero.

[0046] In the second embodiment, it is also necessary to replenish the carbon source from within the system, and thus stable production of reduced iron in the circulation system can be realized by replenishing the carbon source in the same manner as in the first embodiment. In addition, in the second embodiment, the replenishing carbon source is used as the heating fuel for the thermal reformer 7, thereby reducing the amount of CO 2 It is also possible to reduce the amount of free heat used. Furthermore, as in the first embodiment, the environmental impact of the process can be reduced by using supplementary carbon sources such as waste plastics and biomass.

[0047] In the reduced iron production process shown in Fig. 3, carbon can be replenished at one or more of the refilling points (4) to (6) shown in Fig. 3. The refilling point (4) is a connection between the methane synthesis unit 11 and the dehydration unit 4 on the path extending from the methane synthesis unit 11, the refilling point (5) is a connection between the reduction furnace 1 and the dust remover 3 (the same point as (2) in Fig. 2) on the path extending from the reduction furnace 1, and the refilling point (6) is a connection between the dust remover 3 and the dehydration unit 4 on the path extending from the reduction furnace 1. In other words, the refilling point (4) is a connection between the methane synthesis step and the gas reforming step, the refilling point (5) is a connection between the reduction step and the methane synthesis step and a connection between the reduction step and the gas reforming step, and the refilling point (6) is a connection between the reduction step and the methane synthesis step.

[0048] 2 and 3, the carbon filling locations (1) to (6) are exemplified, but the carbon filling locations are not limited to these, and may be any process other than the iron oxide filling process and the connection between processes. However, it is desirable to exclude from the carbon filling locations the portion from the outlet of the thermal reformer 7 to the inlet of the reduction furnace 1, i.e., the reducing gas injection process performed by the reducing gas injection device 9, the reduction process performed in the reduction furnace 1, the connection between the heating reforming process and the reducing gas injection process, and the connection between the reducing gas injection process and the reduction process. This is because, while keeping the composition of the reducing gas constant and suppressing the fluctuation of the iron oxide reduction reaction behavior in the reduction furnace are essential for stable operation of the reduction furnace, the filling of carbon in the portion from the outlet of the thermal reformer 7 to the inlet of the reduction furnace 1 may fluctuate the composition of the reducing gas injected into the reduction furnace.

[0049] When the combustion gas of a liquid or solid carbon source is used as the carbon source, it is more preferable to use the part before the dust collector on the outlet side of the reduction furnace (e.g., (2) in Fig. 2, (5) in Fig. 3) as the carbon supplement part, from the viewpoint that it is not necessary to newly install a dust removal facility. Alternatively, it is more effective to use the heating part of the thermal reformer or the part before that (e.g., (3) in Fig. 2) as the carbon supplement part, and to utilize the sensible heat of the combustion gas of the carbon source as the amount of heat required for the reforming reaction.

[0050] In the configurations of the present invention shown in FIG. 2 and FIG. 3, a small amount of CO, CO 2 , H 2 , H 2 If unnecessary gases other than O and hydrocarbons, such as nitrogen gas for purging, are mixed in, the unnecessary gases gradually accumulate in the process, causing a problem of a decrease in the reducing gas concentration. Therefore, it is advisable to periodically monitor the nitrogen concentration in the system, and when the nitrogen concentration increases to a certain level, for example, when the nitrogen concentration reaches 20% or more, to temporarily discharge the top gas or combustion exhaust gas flowing into the methane synthesis reactor out of the system. At this time, regenerated methane cannot be produced, so it is also possible to temporarily blow in natural gas instead of regenerated methane.

[0051] In addition, H2 supplied from outside as a raw material for methane synthesis is used. 2 Regarding CO 2 It is preferable to use a manufacturing method that generates as little H as possible. For example, water electrolysis can be used. 2 Gas does not necessarily have to be 100% H 2 It does not have to be gas, but in order to keep the methane concentration in the generated regenerated methane gas high, H 2 The higher the concentration, the better. Preferably, H 2 The concentration is 80 vol% or more. EXAMPLES

[0052] Examples of the present invention are described below. Here, the operational specifications are described as the basic unit per ton of reduced iron (DRI) produced. For example, if 1300 kg of sintered ore is used to produce 1 ton of reduced iron (DRI), the amount of sintered ore used is expressed as 1300 kg / t. If a reduced iron plant with a production capacity of 3000 t / day is considered, the following values ​​are multiplied by 3000 to obtain the specifications per day. Here, a product reduction rate of 90% or more is set as a standard for sustaining steady operation, from the viewpoint of the efficiency of melting and smelting DRI in the subsequent process. The product reduction rate is defined as the rate at which all of the total iron content (T.Fe) in the product is Fe. 2 O 3 If we assume that 2 O 3It is an index that expresses the ratio of the amount of oxygen atoms (mass%) derived from iron oxide contained in the product to the amount of oxygen atoms (mass%) derived from iron oxide, expressed as a percentage. Table 1 shows representative specifications of the operating conditions and operating results of Examples 1 to 6 and the Comparative Example.

[0053] [Table 1]

[0054] Examples 1 to 3 according to the present invention are cases in which reduced iron is produced according to the reduced iron production process shown in Fig. 2. That is, 1342 kg / t of sintered ore is charged as a raw material from the top of the reduction furnace 1. 2200 Nm3 of high-temperature reducing gas heated to 800°C is fed from the center of the furnace. 3 / t(H 2 At this time, 2181 Nm3 of CO is blown from the top of the reduction furnace. 3 / t(H 2 :48%, CO:29%, CO 2 :9%, H 2 The volume of the exhausted top gas is smaller than the volume of the injected reducing gas because carbon carburizes the reduced iron in the reduction furnace.

[0055] After dust is removed from the furnace gas, a portion of it is used as raw material gas (shown as "(raw material gas)" in Table 1), and the remainder is used as heating fuel gas for the thermal reformer 7 (shown as "(used for methane regeneration reaction after combustion in heating furnace)" in Table 1). The heating fuel gas is dehydrated and then converted into CO 2 The combustion is performed using pure oxygen produced by a cryogenic separation process driven by free electricity. The exhaust gas from the combustion chamber of the thermal reformer 7 is entirely recovered and dehydrated, and the dehydrated combustion exhaust gas (CO 2 The remaining part (100%) is fed to a methane synthesis unit 11 for methane synthesis. Here, CO 2Hydrogen generated by electrolysis using free electricity (shown as "hydrogen for regenerated methane" in Table 1) is added to synthesize regenerated methane gas. The synthesized regenerated methane gas is dehydrated and then fed into the heating reformer 7 together with the raw material gas to be used as a raw material for reducing gas. In this process, as mentioned above, if there is a shortage of carbon in the system, it is necessary to supply a carbon source.

[0056] [Example 1] In Example 1, natural gas was selected as the carbon source, and natural gas was supplied directly into the system from the position of the supply point (1) shown in Figure 2. As a result of calculations based on the amount of carbon in the product DRI and the amount of carbon in the top gas dust, the necessary supply amount of natural gas was 13.3 kg / t. Under these conditions, the operating conditions were examined so that high-temperature reducing gas having the above-mentioned temperature and composition could be blown into the reduction furnace, and 1576 Nm3 of the top gas was blown into the reduction furnace. 3 / t as raw gas, and the remaining 605Nm 3 The raw material gas was partially dehydrated so that the hydrogen and oxygen atomic balance of the entire system was balanced. The heated fuel gas was combusted with pure oxygen after dehydration and used in the thermal reformer 7. The exhaust gas after combustion was fully recovered and, after dehydration, was blown into the methane synthesis unit 11. A gas with a hydrogen concentration of 918 Nm3 was generated in the methane synthesis unit 11. 3 The gas was dehydrated and then fed into the heating reformer 7 together with the raw material gas and natural gas as a carbon source to be used as a raw material for the reducing gas. The reduced iron produced by the above method achieved a product reduction rate of 92.9%, confirming that the method of Invention Example 1 is capable of continuing steady-state operation.

[0057] [Example 2] In Example 2, biomass made from wood was selected as the carbon source, and the biomass combustion gas was supplied directly into the system from the position of the supplementary point (2) shown in Figure 2. If the supplementary point (2) is located in the position shown in Figure 2, the dust collector for the furnace gas can be used as a dust collector for the biomass combustion gas. As a result of calculations based on the amount of carbon in the product DRI, the amount of carbon in the furnace gas dust, and the amount of carbon in the biomass, the required supply amount of biomass was 11.7 kg / t. Under these conditions, the operating conditions were examined so that high-temperature reducing gas having the above-mentioned temperature and composition could be blown into the reduction furnace, and 1522 Nm3 of the gas obtained by adding the biomass combustion gas to the furnace gas (shown as "flow rate before branching" in Table 1) was blown into the reduction furnace. 3 / t as raw gas, and the remaining 680Nm 3 The raw material gas was partially dehydrated so that the hydrogen and oxygen atomic balance of the entire system was balanced. The heated fuel gas was combusted with pure oxygen after dehydration and used in the thermal reformer 7. The exhaust gas after combustion was fully recovered and dehydrated before being blown into the methane synthesis unit 11. The exhaust gas was blown into the methane synthesis unit 11 at 1046 Nm 3 The gas was reacted with 10000g / t of hydrogen to synthesize a gas mainly composed of methane, and the synthesis gas was dehydrated and then fed into the heating reformer 7 together with the raw material gas to be used as a raw material for the reducing gas. The reduced iron produced by the above method achieved a product reduction rate of 93.1%, confirming that the method of Invention Example 2 can be used for continuous steady-state operation.

[0058] [Example 3] In Example 3, waste plastics mainly composed of urethane were selected as the carbon source, and the combustion gas of the waste plastics was supplied into the post-dust removal system from the position of the supply point (3) shown in Figure 2. As a result of calculations based on the amount of carbon in the product DRI, the amount of carbon in the furnace top gas dust, and the amount of carbon in the waste plastics, the necessary supply amount of waste plastics was 15.7 kg / t. Under these conditions, the operating conditions were examined so that high-temperature reducing gas having the above-mentioned temperature and composition could be blown into the reducing furnace, and 1576 Nm3 of the furnace top gas was blown into the reducing furnace. 3 / t as raw gas, and the remaining 605Nm 3The raw material gas was partially dehydrated so that the hydrogen and oxygen atomic balance of the entire system was balanced. After dehydration, the heated fuel gas was mixed with the combustion gas of waste plastics, combusted with pure oxygen, and used in the thermal reformer 7. The exhaust gas after combustion was fully recovered, dehydrated, and then blown into the methane synthesis unit 11. The exhaust gas was converted to 993 Nm3 in the methane synthesis unit 11. 3 The resulting gas was reacted with 10000g / t of hydrogen to synthesize a gas mainly composed of methane, and the synthesis gas was dehydrated and then fed into the heating reformer 7 together with the raw material gas to be used as a raw material for the reducing gas. The reduced iron produced by the above method achieved a product reduction rate of 93.1%, confirming that the method of Invention Example 3 is capable of continuing steady-state operation.

[0059] As described above, according to the reduced iron production methods of Examples 1 to 3, the target product reduction rate is achieved while reducing CO 2 It is possible to operate with zero emissions.

[0060] Next, Examples 4 to 6 according to the present invention are cases in which reduced iron is produced according to the reduced iron production process shown in Fig. 3. That is, the conditions of the sintered ore charged into the reduction furnace 1, the reducing gas blown into the reduction furnace 1, the top gas discharged from the top of the furnace, and the raw material gas used as the reforming raw material are the same as those of Example 1. The remaining top gas after the raw material gas is extracted is dehydrated and then sent to the methane synthesis unit 11 as the raw material for regenerated methane synthesis (shown as "(amount used for regenerated methane reaction)" in Table 1). Here, CO 2 Hydrogen generated by electrolysis using free electricity is added to synthesize regenerated methane gas. The synthesized regenerated methane gas is fed into the thermal reformer 7 and used as a raw material for reducing gas. Here, in Examples 4 to 6 of the present invention, since fuel for heating the thermal reformer 7 is not supplied, CO is used instead. 2 Free electricity is supplied from the outside to perform electrical heating. In this process, as in the invention examples 1 to 3, if there is a shortage of carbon in the system, it is necessary to supply a carbon source.

[0061] [Example 4] In Example 4, natural gas was selected as the carbon source, and natural gas was supplied directly into the system from the position of the supply point (4) shown in FIG. 3. As in Example 1, the required supply amount of natural gas was 13.3 kg / t. Under these conditions, the operating conditions were examined so that high-temperature reducing gas having the above-mentioned temperature and composition could be blown into the reducing furnace, and 1576 Nm3 of the furnace top gas was blown into the reducing furnace. 3 / t was used as the raw gas. The raw gas was partially dehydrated so that the hydrogen and oxygen atom balance of the entire system was balanced. The remaining 605 Nm 3 The gas was dehydrated and blown into the methane synthesis unit 11 as the raw material gas for the regenerated methane reactor. 3 The gas was reacted with 10000g / t of hydrogen to synthesize a gas mainly composed of methane, and natural gas was mixed with the synthesis gas as a carbon source. After dehydration, the gas was fed into the heating reformer 7 together with the raw material gas and used as a raw material for the reducing gas. The reduced iron produced by the above method achieved a product reduction rate of 93.3%, confirming that steady operation can be continued with the method of Invention Example 4.

[0062] [Example 5] In Example 5, biomass made from wood was selected as the carbon source, and biomass combustion gas was supplied directly into the system from the position of the supplementary point (5) shown in FIG. 3. If the supplementary point (5) is located in the position shown in FIG. 3, the top gas dust collector can be used as a dust collector for the biomass combustion gas. As in Example 2, the required supply amount of biomass was 11.7 kg / t. Under these conditions, the operating conditions were examined so that high-temperature reducing gas having the above-mentioned temperature and composition could be blown into the reducing furnace, and 1522 Nm3 of the gas obtained by adding the biomass combustion gas to the top gas (Table 1, "Flow rate before branching") was blown into the reducing furnace. 3 / t was used as the raw gas. The raw gas was partially dehydrated so that the hydrogen and oxygen atom balance of the entire system was balanced. The remaining 680 Nm 3 The gas was dehydrated and blown into the methane synthesis unit 11 as the raw material gas for the regenerated methane reactor. 3The gas was reacted with 10000g / t of hydrogen to synthesize a gas mainly composed of methane, and the synthesis gas was dehydrated and then fed into the heating reformer 7 together with the raw material gas to be used as a raw material for the reducing gas. The reduced iron produced by the above method achieved a product reduction rate of 92.7%, confirming that the method of Invention Example 5 is capable of continuing steady-state operation.

[0063] [Example 6] In Example 6, waste plastics mainly composed of urethane were selected as the carbon source, and the combustion gas of the waste plastics was supplied into the post-dust removal system from the position of the supply point (6) shown in Figure 3. As in Example 3, the required supply amount of waste plastics was 15.7 kg / t. Under these conditions, the operating conditions were examined so that high-temperature reducing gas having the above-mentioned temperature and composition could be blown into the reducing furnace, and 1576 Nm3 of the furnace top gas was blown into the reducing furnace. 3 / t was used as the raw gas. The raw gas was partially dehydrated so that the hydrogen and oxygen atom balance of the entire system was balanced. The remaining 605 Nm 3 The mixed gas of 1000 / t and the combustion gas of waste plastics was used as the raw material gas for the regenerated methane reactor, and after dehydration, it was blown into the methane synthesis unit 11. 3 The resulting gas was reacted with 10000g / t of hydrogen to synthesize a gas mainly composed of methane, which was then mixed with combustion gas from waste plastics as a carbon source and, after dehydration, was fed into the heating reformer 7 together with the raw material gas and used as a raw material for the reducing gas. The reduced iron produced by the above method achieved a product reduction rate of 93.2%, confirming that the method of Invention Example 6 is capable of continuing steady-state operation.

[0064] As described above, according to the reduced iron production methods of Examples 4 to 6, the target product reduction rate is achieved while reducing CO 2 It is possible to operate with zero emissions. In Examples 4 to 6, electricity was used as the energy source for the heating furnace, but CO 2 If it is free, the energy source does not have to be electricity. For example, 2 Heating may also be achieved by using the heat of combustion of hydrogen produced by electrolysis using free electricity.

[0065] [Comparative Example] A comparative example of the present invention will be described. In the reduced iron production process shown in Fig. 2, the conditions of the sintered ore charged into the reduction furnace, the reducing gas blown into the reduction furnace, the top gas discharged from the top of the furnace, and the raw material gas used as the reforming raw material were the same as those in Example 1. The difference from Example 1 is that the operation was continued without supplying a carbon source, which is actually required. As a result, in the early stage of operation, the composition of the reducing gas was H 2 :CO=62:38, but carbon atoms were gradually expelled from the system, and finally H 2 In this operation where the reducing gas was all hydrogen, the CO, which is the raw material for methane, was reduced. 2 Since no methane is generated, that is, reforming of methane is not required, the methane synthesis unit 11 and the thermal reformer 7 are no longer necessary.

[0066] Specifically, as shown in Table 1, the top gas of the reduction furnace is 2200 Nm 3 / t(H 2 :80%, H 2 O:20%) of which 1821Nm 3 / t as raw gas, 379Nm 3 / t is used as combustion gas for the heating furnace, and CO 2 By supplying hydrogen generated by electrolysis of water using free electricity to the raw gas, the total hydrogen consumption due to the reduction of the raw sintered ore in the reduction furnace and the hydrogen consumption as a heat source in the heating and reforming device 7 is reduced by 742 Nm 3 The operation was carried out while compensating for hydrogen consumption of 10 ...

[0067] As described above, in the reduced iron production method of the comparative example, 2 Although emissions were zero, the target product reduction rate could not be achieved, and it was confirmed that it would be difficult to continue normal operations. [Explanation of symbols]

[0068] 1. Reduction furnace 1a Iron oxide 1b Reduced iron 2. Furnace gas 3 Dust removal equipment 4 Dehydration equipment 5. Natural Gas 6. Air 7. Heating and reforming equipment 8. Reducing Gas 9. Reducing gas injection device 10 Hydrogen 11 Methane synthesis unit 12 Oxygen gas 13 Heat source

Claims

1. an iron oxide charging step of charging the iron oxide into a reduction furnace; a reducing gas blowing step of blowing a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with the reducing gas in the reduction furnace; a methane synthesis step of mixing a part of a furnace top gas discharged from a top of the reducing furnace with oxygen gas to use as a heating fuel, and synthesizing a gas mainly composed of methane from exhaust gas obtained by burning the heating fuel and hydrogen gas; a gas reforming step of using the methane and the remainder of the furnace gas as a raw material gas and reforming the raw material gas into the reducing gas by heating the raw material gas with the combustion heat of the heating fuel; A method for producing reduced iron in a circulating system in which the operation is continued while compensating for carbon shortage during operation in the circulation system in one or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step, or in a connection portion between any two or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step.

2. 2. The method for producing reduced iron according to claim 1, wherein the carbon is supplemented at each connection of one or both of the methane synthesis step and the gas reforming step, or at each connection of three steps including the reduction step and both of the steps.

3. The method for producing reduced iron according to claim 1 or 2, wherein the carbon is a combustion gas of waste plastic.

4. The method for producing reduced iron according to claim 1 or 2, wherein the carbon is a combustion gas of biomass.

5. 3. The method for producing reduced iron according to claim 1, wherein when a nitrogen concentration in the circulation system increases to or above a certain level, a part of the top gas to be supplied to the methane synthesis step is discharged to outside the circulation system, and natural gas is supplied in place of the synthesized methane to perform the gas reforming step.

6. an iron oxide charging step of charging the iron oxide into a reduction furnace; a reducing gas blowing step of blowing a reducing gas into the reduction furnace; a reduction step of reducing the iron oxide with the reducing gas in the reduction furnace; Mainly CO and CO obtained from a part of the top gas discharged from the top of the reduction furnace ２ , H ２ a methane synthesis step of synthesizing a gas mainly composed of methane from a gas consisting of the above and hydrogen gas; Mainly CO, CO obtained from the methane and the remainder of the furnace gas ２ , H ２ The raw gas is a gas consisting of CO ２ a gas reforming step of heating the gas using free electricity or in combination with a heating fuel to reform the gas into the reducing gas; A method for producing reduced iron in a circulating system in which the operation is continued while compensating for carbon shortage during operation in the circulation system in one or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step, or in a connection portion between any two or more of the reducing gas injection step, the reduction step, the methane synthesis step, and the gas reforming step.

7. 7. The method for producing reduced iron according to claim 6, wherein the carbon is supplemented at each connection of one or both of the methane synthesis step and the gas reforming step, or at each connection of three steps including the reduction step and both of the steps.

8. The method for producing reduced iron according to claim 6 or 7, wherein the carbon is a combustion gas of waste plastics.

9. The method for producing reduced iron according to claim 6 or 7, wherein the carbon is a combustion gas of biomass.

10. 8. The method for producing reduced iron according to claim 6 or 7, wherein when a nitrogen concentration in the circulation system increases to or above a certain level, a part of the top gas to be supplied to the methane synthesis step is discharged to outside the circulation system, and natural gas is supplied in place of the synthesized methane to perform the gas reforming step.

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