Direct reduction furnace operation method and method for producing reduced iron

Abstract

Provided is a direct reduction furnace operation method that enables production of reduced iron having excellent energy efficiency when being melted in an electric furnace while reducing CO2 emission. The present invention involves: charging iron oxide and a carbonaceous material into a direct reduction furnace from the top of the furnace; and blowing a reducing gas having a H2 concentration of 80 vol% or more into the direct reduction furnace.

Description

Method for operating a direct reduction furnace and method for producing reduced iron

[0001] The present invention relates to a method for operating a direct reduction furnace and a method for producing reduced iron.

[0002] In recent years, steelworks have been strongly required to save energy against the backdrop of global environmental issues and the depletion of fossil fuels. The raw material for iron is mainly iron oxide such as iron ore, and a reduction process to reduce this iron ore is essential in steelworks. The most common reduction process that is widespread worldwide is the blast furnace. In a blast furnace, coke or pulverized coal reacts with oxygen in hot air (air heated to about 1200°C) in the tuyere. This reaction produces CO and H, which become reducing gases. ２ These reducing gases reduce iron ore and other materials in the furnace. Thanks to recent improvements in blast furnace operation technology, the reducing agent rate (the amount of coke and pulverized coal used to produce 1 ton of molten iron) has been reduced to about 500 kg / t, which is already at its lower limit. Therefore, a further significant reduction in the reducing agent rate cannot be expected.

[0003] On the other hand, direct reduction ironmaking (sometimes called direct reduction or direct ironmaking) has been developed as a reduction process different from that of the blast furnace.

[0004] The direct reduction ironmaking process is as follows. Specifically, a direct reduction furnace is charged with iron oxide raw material (hereinafter simply referred to as iron oxide), such as lump iron ore (lump ore) or pellets (spherical iron ore powder). A reducing gas is then injected into the direct reduction furnace to reduce the iron oxide and obtain reduced iron. The obtained reduced iron is then cooled in a region (cooling zone) below the reducing gas injection position of the direct reduction furnace. The reduced iron is then discharged from the bottom of the direct reduction furnace. The reduced iron discharged from the direct reduction furnace is then melted in an electric furnace.

[0005] Here, a shaft furnace is mainly used as the direct reduction furnace. Furthermore, natural gas, such as Midrex (registered trademark) or Hyl (registered trademark), is generally used as the source of the reducing gas. In this case, the natural gas is reformed with the exhaust gas (hereinafter also referred to as top gas) discharged from the top of the direct reduction furnace to produce CO and H. ２ The reducing gas is then blown into a reduction furnace to reduce the iron oxide according to the following formula, thereby obtaining reduced iron: ２ O ３ +3CO→2Fe+3CO ２ ΔH ２９８ =-247kJ / kg-Fe (i) Fe ２ O ３ +3H ２ → 2Fe + 3H ２ O ΔH ２９８ =858kJ / kg-Fe (ii)

[0006] In this way, in the general direct reduction ironmaking process, CO and H ２ Since a reducing gas containing ２ is produced and excreted.

[0007] In recent years, CO ２ There is a growing need to reduce CO emissions, and the steelmaking process is also ２ Therefore, in the direct reduction ironmaking process, a technology using a reducing gas whose main component is hydrogen is being considered. By using a reducing gas whose main component is hydrogen, the main component of the furnace gas becomes H. ２ O and CO ２ A significant reduction in emissions can be expected.

[0008] As an example of such a technique, Patent Document 1 discloses, "A method for operating a direct reduction furnace using a shaft furnace system for producing reduced iron using a reducing gas mainly containing hydrogen, the method comprising the step of charging a raw material iron oxide that has been preheated in advance into the direct reduction furnace."

[0009] Patent Document 2 discloses "a method for operating a direct reduction furnace using a shaft furnace system to produce reduced iron using a reducing gas mainly composed of hydrogen, the method comprising the step of blowing a portion of the gas discharged from the top of the furnace into the middle of the furnace, and circulating the furnace top gas."

[0010] Patent Document 3 discloses "a method for producing reduced iron by reducing iron oxide charged into a shaft furnace, characterized in that a heated mixed gas containing a reducing gas containing 90% by volume or more of hydrogen gas and nitrogen gas is blown into the shaft furnace."

[0011] JP 2012-102371 A JP 2012-102372 A International Publication No. 2021 / 230307

[0012] As described above, in the direct reduction ironmaking process, it is necessary to discharge the reduced iron obtained in the direct reduction furnace and melt it in an electric furnace. However, when the reduced iron obtained by the techniques of Patent Documents 1 to 3 is melted in an electric furnace, there is a problem that the energy efficiency (hereinafter also referred to as the energy efficiency during melting in an electric furnace) is lower than when the reduced iron obtained by a general direct reduction ironmaking process is melted in an electric furnace.

[0013] The present invention has been developed to solve the above problems, and ２ An object of the present invention is to provide a method for operating a direct reduction furnace that enables production of reduced iron with excellent energy efficiency during electric furnace melting while reducing waste. Another object of the present invention is to provide a method for producing reduced iron, which produces reduced iron using the above-mentioned method for operating a reduction furnace. Note that in this disclosure, any numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively.

[0014] The inventors first conducted extensive research into the causes of the above problems and obtained the following findings. (1) In the techniques of Patent Documents 1 to 3, a reducing gas containing hydrogen as the main component is used. That is, the reducing gas contains almost no CO. (2) On the other hand, in a general direct reduction ironmaking process, the reducing gas contains CO. Therefore, in a direct reduction furnace, the Boudoir reaction (2CO → C + CO ２ ) causes carburization of the reduced iron during the process of reducing the iron ore. ２ When a reducing gas with a concentration of 80% by volume or more is used, carburization of the reduced iron does not occur during the process of reducing iron ore. Here, carburization of the reduced iron has the following effects: - Lowers the melting point of the reduced iron. - Reduces iron oxide remaining in the reduced iron. - When the reduced iron is melted in an electric furnace, carbon is burned by oxygen. This generates a lot of energy and shortens the melting time of the reduced iron. (4) As described in (3) above, while the above effects can be obtained by carburizing the reduced iron, the reduced iron obtained by the techniques of Patent Documents 1 to 3 does not undergo carburization during the process of reducing iron oxide, resulting in reduced energy efficiency during melting in an electric furnace.

[0015] Based on the above findings, the inventors have conducted further research to solve the above problems and have discovered the following: (5) It is important to charge a carbonaceous material, preferably at least one of biomass and plastic, in addition to iron oxide into the direct reduction furnace from the top of the furnace. ２ Even when using a reducing gas with a concentration of 80% by volume or more, carburization of the reduced iron progresses, making it possible to produce reduced iron with excellent energy efficiency when melting in an electric furnace. Furthermore, by using carbon-neutral biomass, particularly semi-carbonized biomass, as the carbonaceous material, CO ２ It is therefore possible to produce reduced iron that is particularly excellent in energy efficiency during melting in an electric furnace, while reducing the amount of discharged iron to substantially zero and achieving excellent reaction efficiency in a direct reduction furnace. The present invention has been completed based on the above findings and further investigations.

[0016] That is, the gist and configuration of the present invention are as follows.

[0017] 1. A method for operating a direct reduction furnace, comprising: a charging step of charging iron oxide and carbonaceous material into the direct reduction furnace from the top of the furnace; ２ A method for operating a direct reduction furnace, comprising: an injection step of injecting a reducing gas having a concentration of 80% by volume or more; and a reduction step of reducing the iron oxide in the direct reduction furnace to obtain reduced iron.

[0018] 2. The method for operating a direct reduction furnace according to 1 above, wherein at least one of biomass and plastic is used as the carbonaceous material.

[0019] 3. The method for operating a direct reduction furnace according to 1 or 2 above, wherein torrefied biomass is used as the carbonaceous material.

[0020] 4. The method for operating a direct reduction furnace according to any one of 1 to 3, wherein the amount of the carbonaceous material charged into the direct reduction furnace is controlled in accordance with the amount of C contained in the reduced iron.

[0021] 5. The method for operating a direct reduction furnace according to any one of 1 to 4, wherein the amount of the carbonaceous material charged into the direct reduction furnace is controlled so that the amount of C contained in the reduced iron is 1.0 mass% or more and 5.0 mass% or less.

[0022] 6. The method for operating a direct reduction furnace according to any one of 1 to 5 above, further comprising a heat supply step of supplying heat to the direct reduction furnace.

[0023] 7. The method for operating a direct reduction furnace according to 6 above, wherein fuel heat from biomass is used as the heat source in the heat supply step.

[0024] 8. A method for producing reduced iron, comprising producing reduced iron by the method for operating a reduction furnace according to any one of 1 to 7 above.

[0025] According to the present invention, CO ２ This makes it possible to produce reduced iron that is highly energy efficient when melted in an electric furnace while reducing emissions to virtually zero.

[0026] The present invention relates to a direct reduction furnace, a process for producing reduced iron, and a method for producing reduced iron.

[0027] A method for operating a direct reduction furnace according to one embodiment of the present invention will now be described.

[0028] A method for operating a direct reduction furnace according to one embodiment of the present invention includes a charging step of charging iron oxide and carbonaceous material into the direct reduction furnace from the top of the furnace; ２ The method includes: an injection step of injecting a reducing gas having a concentration of 80% by volume or more; and a reduction step of reducing the iron oxide in the direct reduction furnace to obtain reduced iron.

[0029] Fig. 1 is a schematic diagram showing an example of the configuration of a shaft furnace, which is a direct reduction furnace. In the figure, reference numeral 1 denotes a shaft furnace, 1a denotes iron oxide, 1b denotes reduced iron, 1c denotes a furnace top, 1d denotes a cooling zone, 2 denotes a reducing gas inlet, 3 denotes a furnace top gas outlet, 4 denotes a cooling gas inlet, 5 denotes a cooling gas suction port, 6 denotes an iron oxide charging port, 7 denotes a reduced iron outlet, and 13 denotes a briquetting machine.

[0030] In the shaft furnace 1, iron oxide 1a is charged through the furnace top 1c, particularly the iron oxide charging port 6, and the iron oxide 1a is gradually allowed to fall. High-temperature reducing gas is blown into the shaft furnace 1 through a reducing gas inlet 2 located in the center of the shaft furnace 1 to reduce the iron oxide 1a and obtain reduced iron 1b. The reduced iron 1b is then discharged through a reduced iron outlet 7 located in the lower part of the shaft furnace 1. Meanwhile, furnace top gas is discharged through a furnace top gas outlet 3. The temperature of the reducing gas blown through the reducing gas inlet 2 is, for example, 700°C to 1200°C.

[0031] In addition, a cooling zone 1d located at the bottom of the shaft furnace 1 is provided with a cooling gas inlet 4 and a cooling gas suction port 5. Cooling gas is blown into the cooling zone 1d from the cooling gas inlet 4. The cooling gas is sucked in from the cooling gas suction port 5 so as not to infiltrate the furnace top 1c. For example, N ２ is used.

[0032] In the method for operating a direct reduction furnace according to one embodiment of the present invention, it is important to charge a carbonaceous material in addition to iron oxide into the direct reduction furnace from the top of the furnace.

[0033] [Charging Step] In a method for operating a direct reduction furnace according to one embodiment of the present invention, in addition to iron oxide, a carbonaceous material is charged into the direct reduction furnace from the top of the furnace, particularly from an iron oxide charging port. ２ Even when using a reducing gas with a concentration of 80% by volume or more, carburization of the reduced iron progresses, making it possible to produce reduced iron with excellent energy efficiency during melting in an electric furnace. That is, the carbonaceous material charged into a direct reduction furnace undergoes thermal decomposition during the process of heating by the gas in the furnace. As a result, the carbonaceous material progresses in carbonization while generating volatile gases. The generated carbon is a mixture of Fe, which is generated during the process of reducing iron oxide. ３ O ４ The carbon material comes into contact with FeO and Fe, and carburization progresses. In addition, CO and CH are contained in the volatile gases generated from the carbon material. ４ , H ２ When the reaction is contained, the Boudoir reaction (CO → C + CO ２ ) plus CH ４ →C+2H ２ Reaction, CO + H ２ →C+H ２ The carburization of the reduced iron is further promoted by the reaction of O. Note that, optionally, carbonaceous material may be additionally charged into the direct reduction furnace from a position other than the top of the furnace.

[0034] Here, the direct reduction furnace is charged with carbonaceous material together with iron oxide through the furnace top 1c, particularly the iron oxide charging port 6 (hereinafter referred to as the first method). In addition to the first method, other methods may be used: charging the carbonaceous material together with cooling gas through the cooling gas inlet 4 (hereinafter referred to as the second method); providing a tuyere in the center of the furnace and transporting the carbonaceous material in a gas phase (hereinafter referred to as the third method); or preheating the solid carbonaceous material to generate volatile gas components containing C and then charging only the volatile gas into the direct reduction furnace 1 (hereinafter referred to as the fourth method). However, in the second method, the volatilization of the volatile gas contained in the carbonaceous material may not proceed sufficiently because the cooling zone has a lower temperature than the upper part of the furnace, resulting in a decrease in the amount of carburization of the reduced iron. Furthermore, in the third method and other methods, additional energy and costs may be required for transporting the carbonaceous material. For these reasons, only the first method may be used as a method for charging the carbonaceous material into the direct reduction furnace. On the other hand, in cases where the amount of carbonaceous material that can be charged from the furnace top is limited, multiple methods may be combined as appropriate. Carbonaceous material is a substance that partially contains C (carbon) atoms. In addition to C atoms, the carbonaceous material may also contain, for example, H (hydrogen) atoms and O (oxygen) atoms. For example, a substance in which the mass of C atoms accounts for 30 to 100% of the total mass of the carbonaceous material, the mass of H atoms accounts for 0 to 30%, and the mass of O atoms accounts for 0 to 60% is preferred.

[0035] From the viewpoint of effectively carburizing reduced iron, examples of suitable carbonaceous materials include biomass and plastics. Among them, biomass is a carbon-neutral carbonaceous material, and therefore, it is preferable to use biomass as a carbon-neutral material. ２ This is particularly advantageous as it makes it possible to reduce emissions to virtually zero. The plastics may be virgin or used plastics. The concept of used plastics includes waste plastics, plastics that are not planned to be disposed of, factory offcuts, etc. When waste plastics are used, it is possible to effectively utilize charcoal that would otherwise be landfilled or incinerated, thereby reducing the environmental load. However, when plastics are used, CO ２ Since emissions cannot be reduced to zero, the CO contained in the furnace gas ２is preferably subjected to CCU or CCS as described below.

[0036] Here, biomass is a general term for a certain amount of accumulated animal and plant resources and waste materials originating from these resources (excluding fossil resources). In a method for operating a direct reduction furnace according to one embodiment of the present invention, any biomass that produces charcoal through pyrolysis, such as agricultural, forestry, livestock, fisheries, and waste, can be used. In particular, biomass with a high effective calorific value is preferred, such as woody biomass.

[0037] An example of woody biomass is forestry biomass.

[0038] Examples of forestry biomass include: Papermaking by-products such as pulp black liquor and chip dust; Lumbering by-products such as bark and sawdust, and forest residues such as branches, leaves, treetops and offcuts; Special-purpose forest products such as thinned timber from cedar, cypress and pine species, and waste logs for edible fungi; Firewood and charcoal forests such as castanopsis, oak and pine, and short-rotation forestry timber such as willow, poplar, eucalyptus and pine.

[0039] Furthermore, some waste-based biomass, for example, general waste such as pruned branches from roadside trees in municipalities and garden trees in private homes, and industrial waste such as pruned branches from roadside trees in national and prefectural governments and garden trees in companies, and construction and building waste, can also be suitably used as woody biomass.

[0040] Some agricultural biomass, such as waste and by-product sources such as rice husks, wheat straw, rice straw, sugarcane residue, palm oil, etc., and energy crop sources such as rice bran, rapeseed, and soybeans, can also be suitably used as woody biomass.

[0041] Biomass is composed of C, O, and H atoms. However, biomass itself has a high moisture content and low density, making it weak. Therefore, if biomass is directly charged into a reduction furnace, it may become pulverized or hang up inside the furnace, causing the reduction reaction to stagnate. Therefore, it is preferable to use semi-carbonized biomass as the carbon material.

[0042] Here, semi-carbonized biomass is biomass that is not completely carbonized but is partially carbonized, and preferably has a density of 700 to 850 kg / m ３ Semi-carbonized biomass is biomass that has been subjected to a heat treatment to reduce the moisture content of biomass, such as woody biomass, and to promote carbonization to increase the density and strength of the biomass.

[0043] Torrefied biomass has excellent storage and transportability. Furthermore, since torrefied biomass is not completely carbonized, volatile gas components remain. Therefore, when torrefied biomass is charged into a furnace and heated, CO, H ２ , CO ２ , C.H. ４ and O ２ Among these volatile gases, CO, CH ４ and H ２ The carburization of reduced iron is promoted by CO and H ２ Because it has reducing properties, it promotes the reduction of iron oxide and prevents reaction stagnation due to endothermic heat during hydrogen reduction. Furthermore, because the heat treatment temperature when producing torrefied biomass is mild, total energy consumption is also reduced. For these reasons, it is preferable to use torrefied biomass as the carbon material. Hereinafter, uncarbonized biomass will also be referred to as raw biomass. Furthermore, completely carbonized biomass will also be referred to as carbonized biomass. Note that since the temperature at the top of the shaft furnace is about 300°C, when raw biomass is charged from the top of the furnace, carbonization will progress to a certain extent within the furnace. However, as mentioned above, there is a concern that powdering and hanging will occur at the top of the furnace. Therefore, it is preferable to use torrefied biomass.

[0044] The method for producing torrefied biomass is not particularly limited. For example, it is preferable to produce torrefied biomass by subjecting raw biomass to low-temperature heat treatment at 200 to 300°C and then compacting it. This makes it possible to further increase the energy density. According to the above production method, for example, density: 200 kg / m ３When woody biomass (raw biomass) is used as the material, the density is 750 kg / m ３ It is possible to produce carbonized biomass to a certain extent.

[0045] It is also preferable to control the amount of carbonaceous material charged into the direct reduction furnace (hereinafter also referred to as the charging amount of carbonaceous material) in accordance with the amount of C contained in the reduced iron. For example, it is preferable to control the charging amount of carbonaceous material so that the amount of C contained in the reduced iron is 1.0 mass % or more and 5.0 mass % or less.

[0046] That is, if the amount of carbonaceous material charged is too small, the carburization of the reduced iron may not proceed sufficiently. On the other hand, if the amount of carbonaceous material charged is too large, the carbonaceous material does not contribute to the carburization reaction, and the amount of carbon discharged together with the reduced iron from the lower part of the furnace increases. Furthermore, reduced iron is often compression-molded into HBI (Hot Briquette Iron) to improve transportability and handling. For the marine transportation of HBI, the international standard (IMSBC: International Maritime Solid Bulk Cargoes) requires that the HBI have an apparent density of 5.0 g / cm3. ３ In this regard, excessive carbon in the reduced iron reduces the apparent density of the HBI and reduces the yield. Furthermore, an increase in the amount of C dissolved in the Fe particles and an increase in the amount of C present at the interfaces between the Fe particles leads to a decrease in the strength of the HBI.

[0047] Therefore, from the viewpoint of achieving both excellent energy efficiency during melting in an electric furnace and excellent HBI performance (apparent density and strength), it is preferable to control the amount of carbonaceous material charged according to the amount of C contained in the reduced iron, particularly so that the amount of C contained in the reduced iron is 1.0 mass% or more and 5.0 mass% or less. Furthermore, the amount of carbonaceous material charged is controlled so that the amount of C contained in the reduced iron is more preferably 2.0 mass% or more, even more preferably 3.0 mass% or more, and even more preferably 4.0 mass% or more. The amount of C contained in the reduced iron may be measured, for example, using reduced iron discharged from a direct reduction furnace according to the procedure described in Evaluation 1 of Example 1 below. Furthermore, the carbonaceous material to be used may be selected according to the amount of C contained in the reduced iron.

[0048] As an example, it is preferable to control the amount of carbonaceous material charged into the direct reduction furnace using the ratio of the amount of C (mass of C atoms) contained in the carbonaceous material to the amount of Fe (mass of Fe atoms) contained in the iron oxide charged into the direct reduction furnace (hereinafter also referred to as the C / Fe charging ratio) so that the amount of C contained in the reduced iron is 1.0 mass% or more and 5.0 mass% or less. In this case, by controlling the amount of carbonaceous material charged into the direct reduction furnace so that the C / Fe charging ratio is preferably in the range of 1.0 to 20.0%, more preferably 3.0 to 15.0%, the amount of C contained in the reduced iron can be 1.0 mass% or more and 5.0 mass% or less. For example, when the iron oxide charged into the direct reduction furnace is Fe ２ O ３ In the case where the carbonaceous material is composed only of carbon atoms and the mass of the carbonaceous material to be charged into the direct reduction furnace is 50%, if the ratio of the charging amount of the carbonaceous material to the charging amount of iron oxide into the direct reduction furnace (= carbonaceous material charging amount [kg / h] / iron oxide charging amount [kg / h]×100) is set in the range of 1.4 to 28.0%, the C / Fe charging ratio will be in the range of 1.0 to 20.0%. The mass of the C atoms to the mass of the entire carbonaceous material is, for example, 30 to 100%.

[0049] Additionally, the iron oxide used in the method for operating a direct reduction furnace according to one embodiment of the present invention is, for example, iron ore. Specific examples include lump iron ore (lump ore) and iron oxide pellets (spherical iron ore powder). The grade of the iron ore used as the iron oxide, i.e., the iron content, is not particularly limited, but from the viewpoint of reduction in a shaft furnace, it is generally preferable that the iron content be 65% by mass or more. However, in recent years, the price of high-grade ore from South America, for example, is expected to rise. For this reason, low-grade ore (Fe content: 63% by mass or less), for example, from Australia, which is an inexpensive and abundant resource, may also be used as needed.

[0050] [Blow-in process] Direct reduction furnace ２ Concentration: Blow in reducing gas of 80% by volume or more. ２ The concentration is preferably 90% by volume or more, more preferably 95% by volume or more. ２ The upper limit of the concentration is not particularly limited, and may be 100% by volume. The type of the remaining gas other than hydrogen is not particularly limited. For example, N２ , H ２ O, CO and CO ２ In addition, gases produced as by-products in the steelmaking process (hereinafter also referred to as by-product gases) can also be used. Examples of by-product gases include blast furnace gas (BFG) and coke oven gas (COG). However, if the remaining gas contains CO or CO ２ If the furnace gas contains CO ２ In this case, the CO contained in the furnace gas ２ is preferably subjected to CCU or CCS as described below.

[0051] [Reduction step] In the reduction step, H ２ The iron oxide is reduced to obtain reduced iron by using a reducing gas having a concentration of 80% by volume or more according to the above formula (i). The iron oxide can also be reduced by a volatile gas generated from the carbonaceous material charged into the direct reduction furnace.

[0052] [Heat Supply Step] The method for operating a direct reduction furnace according to one embodiment of the present invention preferably further includes a heat supply step of supplying heat to the direct reduction furnace. As described above, in a general direct reduction ironmaking process, CO and H ２ A reducing gas containing H ２ On the other hand, in the method for operating a direct reduction furnace according to one embodiment of the present invention, H ２ A reducing gas with a concentration of 80% by volume or more is used. As shown in the above formulas (i) and (ii), the reduction reaction with CO is an exothermic reaction, while the reduction reaction with H ２ The reduction reaction by H is an endothermic reaction. ２ When a gas with a concentration close to 100% by volume is used, the temperature inside the direct reduction furnace may drop. In this case, it is preferable to supply heat to the direct reduction furnace to compensate for the endothermic heat.

[0053] The heat source is not particularly limited. For example, the heat from biomass combustion is suitable as the heat source. By utilizing the heat from biomass combustion, CO emitted from the direct reduction furnace can be reduced. ２ Not only that, but also the CO emitted from the entire manufacturing process ２It is possible to reduce the amount of carbon dioxide emitted from the biomass to substantially zero. As the biomass, the above-mentioned semi-carbonized biomass and tar obtained in the process of pyrolysis of biomass are preferred. Carbonized biomass and tar have a high calorific value per unit volume and are considered promising as alternative fuels to coal.

[0054] The amount of heat supplied to the direct reduction furnace can be determined, for example, by the above formulas (i) and (ii) based on the amount of reducing gas (e.g., H ２ The enthalpy of the reduction reaction calculated from the composition of the reducing gas (for example, H ２ The heat quantity can be determined by calculating the difference in enthalpy due to the reduction reaction calculated from the composition of the gas (CO / CO = 1 to 3) and converting the difference into the heat quantity equivalent to the amount of reduced iron produced.

[0055] [Reduced Iron Manufacturing Process] Next, the overall reduced iron manufacturing process will be described. Fig. 2 is a diagram showing an example of the configuration of a conventional reduced iron manufacturing process. In the figure, reference numeral 1 denotes a shaft furnace, 1a denotes iron oxide, 1b denotes reduced iron, 8 denotes a dust removal device, 9 denotes a dehydration device, 10 denotes a natural gas supply unit, 11 denotes an air supply unit, 12 denotes a heating reformer, and 14 denotes a reducing gas injection device.

[0056] In one example of a reduced iron production process shown in Figure 2, iron oxide is charged from the top of a shaft furnace 1 and gradually lowered. High-temperature reducing gas is blown into the shaft furnace 1 from the middle to reduce the iron oxide 1a. Reduced iron 1b is then discharged from the bottom of the shaft furnace 1. At this time, mainly CO, CO ２ , H ２ , H ２ A furnace top gas containing O is discharged. This furnace top gas is subjected to dust removal in a dust removal device 8, and a portion of the top gas is adjusted in moisture content in a dehydration device 9 as raw material gas and sent to a thermal reforming device 12. A gas containing hydrocarbons, for example, natural gas from a natural gas supply unit, is supplied to the thermal reforming device 12 together with the moisture-adjusted furnace top gas. Next, the supplied gas is heated in the thermal reforming device 12. Then, a reforming reaction occurs, and mainly CO and H are produced. ２This produces a high-temperature reducing gas containing the above-mentioned elements. This reducing gas is then blown into the reducing furnace. The remaining part of the furnace top gas is dehydrated and then used as heating fuel in the combustion chamber of the thermal reformer 12.

[0057] In the method for operating a direct reduction furnace according to one embodiment of the present invention, as described above, H ２ A reducing gas with a concentration of 80% by volume or more is used. Therefore, in the method for operating a direct reduction furnace according to one embodiment of the present invention, a heating reforming device is not required. Instead, as shown in FIG. 3, hydrogen gas (H ２ The hydrogen gas (gas having a concentration of 80% by volume or more, preferably 90% by volume or more, and more preferably 95% by volume or more) is heated by a gas heater 16. The heating temperature of the hydrogen gas is not particularly limited, but is preferably, for example, 900 to 1200°C. Next, the heated hydrogen gas is blown into the shaft furnace 1 as a reducing gas by a reducing gas blowing device 14. After being subjected to a reduction reaction in the furnace, the reducing gas is mainly converted into H ２ and H ２ The H that was not used in the reduction reaction is discharged from the shaft furnace 1 as a furnace top gas containing O. ２ In the example shown in FIG. 3, the furnace gas is dedusted by the dust removal device 8, dehydrated by the dehydration device 9, and then recycled. ２ and blown into the shaft furnace 1 as a reducing gas.

[0058] In addition, CO is added to the furnace gas. ２ When CO is contained in the furnace gas, ２ It is preferable to separate and recover the CO from the furnace gas and use it for basic chemical synthesis (CCU) or storage (CCS). ２ Separation device 17 ２ After separation, CO ２ In particular, when a non-carbon-neutral carbonaceous material such as waste plastic is used as the carbonaceous material, CO ２ Emissions can be reduced to virtually zero.

[0059] The heat source of the gas heater 16 is not particularly limited. For example, the heat from biomass combustion is suitable as the heat source. By utilizing the heat from biomass combustion, the CO emitted from the direct reduction furnace can be reduced. ２ Not only that, but also the CO emitted from the entire manufacturing process ２ It is possible to reduce the carbon dioxide emission to substantially zero. As the biomass, the above-mentioned semi-carbonized biomass and tar obtained in the process of pyrolysis of biomass are preferable.

[0060] The conditions other than those mentioned above are not particularly limited, and may be those according to conventional methods.

[0061] In the method for operating a direct reduction furnace according to one embodiment of the present invention, a method using a shaft furnace has been described in particular. However, the type of direct reduction furnace is not limited to this, and methods using a fluidized bed, rotary kiln, rotary hearth furnace (RHF), etc. are also possible. Note that a shaft furnace is preferred as the direct reduction furnace because of its high production efficiency, availability, and operational stability. Furthermore, the majority of direct reduction furnaces operating worldwide are shaft furnace-type Midrex (registered trademark) and Hyl (registered trademark).

[0062] In addition, a method for producing reduced iron according to one embodiment of the present invention produces reduced iron by the above-described method for operating a direct reduction furnace. Note that conditions other than those described above are not particularly limited and may be those according to conventional methods.

[0063] As described above, according to the present invention, CO ２ It is possible to produce reduced iron with excellent energy efficiency during melting in an electric furnace while reducing CO emissions to substantially zero. ２ It is possible to produce reduced iron that achieves both excellent energy efficiency during melting in an electric furnace and excellent performance as HBI (Hot Briquette Iron) while reducing emissions to substantially zero.

[0064] Hereinafter, a method for operating a direct reduction furnace and a method for producing reduced iron according to one embodiment of the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples described below.

[0065] Example 1 A reduced iron production test was carried out using a bench-scale shaft furnace in the reduced iron production process shown in Figure 3. The test conditions were as follows. Note that conditions not specified were those according to conventional methods or the general description in the specification. Reduced iron production rate: 15 kg / h Operation period: 7 days Reducing gas composition: H ２ Concentration 90% by volume (volume ratio, H ２ :N ２ = 9:1) Amount of reducing gas blown in: 2200 Nm ３ / t-DRI (gas volume per ton of reduced iron) Iron oxide: Brazilian iron oxide pellets with particle size of 10.0 to 15.0 mm Main component composition of iron oxide: In mass %, T. Fe: 66%, FeO: 0.63%, SiO ２ :2.0%, CaO:2.1%, Al ２ O ３ : 0.5%, MgO: 0.16%, C: 0.1%

[0066] In some cases, the carbonaceous material shown in Table 1 was charged together with the iron oxide through the iron oxide charging port at the top of the shaft furnace.

[0067] The energy efficiency of the produced reduced iron during melting in an electric furnace and the reaction efficiency in a direct reduction furnace were evaluated in the following manner.

[0068] [Evaluation of Energy Efficiency During Melting in an Electric Furnace (hereinafter also referred to as Evaluation 1)] Evaluation 1 was performed based on the amount of carbon (carburization amount) contained in the produced reduced iron. That is, the amount of carbon contained in the reduced iron discharged from the lower part of the shaft furnace was measured according to the infrared absorption method specified in JIS G 1211 (2018), "Iron and Steel - Methods for Determination of Carbon." The amount of carbon contained in this reduced iron was measured once a day, and the average value was taken as the amount of carbon contained in the reduced iron. The evaluation results are also shown in Table 1. Note that the meanings of A to E in the column for Evaluation 1 in Table 1 are as follows. Furthermore, cases A to C were evaluated as having excellent energy efficiency during melting in an electric furnace. A: The amount of carbon contained in the reduced iron is 4.0% by mass or more. B: The amount of carbon contained in the reduced iron is 3.0% by mass or more and less than 4.0% by mass. C: The amount of carbon contained in the reduced iron is 1.0% by mass or more and less than 3.0% by mass. D: The amount of carbon contained in the reduced iron is 0.5% by mass or more and less than 1.0% by mass. E: The amount of carbon contained in the reduced iron is less than 0.5% by mass.

[0069] [Evaluation of reaction efficiency in a direct reduction furnace (hereinafter also referred to as evaluation 2)] Evaluation 2 was performed based on the reduction rate. Here, the reduction rate is defined by the following formula: [Reduction rate (unit: %)] = {([Amount of O in iron oxide before reduction (unit: mass %)] - [Amount of O in reduced iron (unit: mass %)]) / [Amount of O in iron oxide before reduction (unit: mass %)]} × 100 Here, the amount of O (oxygen) in iron oxide before reduction (unit: mass %) is the amount of FeO and FeO contained in the iron oxide before reduction. ２ O ３ Here, the Fe content (mass%) in FeO is calculated by subtracting the Fe content (mass%) in FeO from the T.Fe (mass%) of the iron oxide before reduction. ２ O ３ Assuming that it exists as Fe ２ O ３ The total amount of O (mass%) contained in the reduced iron (obtained after reduction) was calculated. ３ O ４ Here, the Fe content (mass%) obtained by subtracting the Fe content (mass%) in FeO and M.Fe from the T.Fe (mass%) of reduced iron is ３ O４ Assuming that it exists as Fe ３ O ４ The total amount of O (mass%) contained in the powder was calculated.

[0070] The evaluation results are also shown in Table 1. The meanings of A to D in the column for Evaluation 2 in Table 1 are as follows. Generally, a reduction rate of 95% or more is required for the subsequent melting in an electric furnace. Therefore, cases A and B were evaluated as having excellent reaction efficiency in a direct reduction furnace. A: Reduction rate of 98% or more B: Reduction rate of 95% or more but less than 98% C: Reduction rate of 90% or more but less than 95% D: Reduction rate less than 90%

[0071]

[0072] As shown in Table 1, in the inventive examples, all of the reduced iron produced had excellent energy efficiency during melting in an electric furnace. In addition, in all of the inventive examples, the CO emissions from the entire process were ２ In particular, in No. 3, which used semi-carbonized biomass as the carbonaceous material, the reduced iron produced was particularly excellent in energy efficiency during melting in an electric furnace, and the reaction efficiency in a direct reduction furnace was also particularly excellent.

[0073] Example 2 Reduced iron was produced under the same conditions as in Example 1, except for the conditions shown in Table 2. The amount of C contained in the produced reduced iron was measured in the same manner as in Evaluation 1 of Example 1. The reaction efficiency in the direct reduction furnace was evaluated in the same manner as in Evaluation 2 of Example 1. The results are also shown in Table 2.

[0074] Furthermore, a detailed evaluation of the energy efficiency during the melting of the produced reduced iron in an electric furnace and an evaluation of the performance of the HBI were carried out as follows. The results are shown in Table 2.

[0075] [Detailed Evaluation of Energy Efficiency During Melting in an Electric Furnace (hereinafter also referred to as Evaluation 1')] In order to perform a more detailed evaluation of the energy efficiency during melting in an electric furnace, in Evaluation 1', the produced reduced iron was used to calculate the energy efficiency during melting in an electric furnace using the following formula (1) in accordance with the method specified in JIS G 0703 (1995), "Heat Balance Method for Arc Furnaces," and the energy efficiency during melting in an electric furnace was evaluated. The meanings of A to E in the Evaluation 1' column in Table 2 are as follows. Furthermore, cases A to C were evaluated as having excellent energy efficiency during melting in an electric furnace. Energy efficiency during electric furnace melting = (heat of molten steel + heat of slag + heat of decomposition reaction - heat of molten iron) / (total heat input - heat of molten iron) x 100 (%) ... (1) A: Energy efficiency during electric furnace melting is 80% or more B: Energy efficiency during electric furnace melting is 70% or more but less than 80% C: Energy efficiency during electric furnace melting is 50% or more but less than 70% D: Energy efficiency during electric furnace melting is 40% or more but less than 50% E: Energy efficiency during electric furnace melting is less than 40%

[0076] [Performance Evaluation of HBI] The produced reduced iron was used to mold HBI under the following conditions: Briquetting machine roll diameter: 500 mmφ Roll linear pressure: 150 kN Roll rotation speed: 9 rpm Charge amount of reduced iron: 60 kg Heating temperature of reduced iron: 700°C

[0077] The molded HBI was then measured for apparent density and crushing strength in the following manner to evaluate its performance. When both of the ratings 3 and 4 described below were A to C (excluding when both of the ratings 3 and 4 were A to B), the HBI was evaluated as having excellent performance. When both of the ratings 3 and 4 described below were A to B, the HBI was evaluated as having particularly excellent performance. The results are also shown in Table 2.

[0078] Evaluation of apparent density of HBI (hereinafter also referred to as Evaluation 3) The apparent density of HBI was measured by the method described in "ISO 15968: Direct reduced iron - Determination of apparent density and water absorption of hot briquette iron (HBI)." The apparent density of HBI was measured once a day. Specifically, 60 kg of reduced iron produced during the operation period was collected every day, and HBI was produced from the collected reduced iron. Five samples of the produced HBI were taken each time, and the apparent density of each HBI was measured. The average value was then calculated to evaluate the apparent density of the HBI. The meanings of A to D in the Evaluation 3 column in Table 2 are as follows: A: The apparent density of HBI is 5.5 g / cm ３ B: Apparent density of HBI is 5.0 g / cm ３ 5.5g / cm or more ３ C: The apparent density of HBI is less than 4.5 g / cm ３ 5.0g / cm or more ３ D: The apparent density of HBI is less than 4.5 g / cm ３ less than

[0079] Evaluation of HBI Strength (hereinafter also referred to as Evaluation 4) Using a general-purpose autograph, the crushing strength of the HBI was measured at an application rate of 1 mm / min. The measurement of the crushing strength of the HBI was also conducted once a day. Specifically, 60 kg of reduced iron produced during the operation period was collected each day, and HBI was produced from the collected reduced iron. Five samples of the produced HBI were taken each time, and the crushing strength of each HBI was measured. The average value was then calculated to evaluate the crushing strength of the HBI. The meanings of A to D in the column for Evaluation 4 in Table 2 are as follows: A: The crushing strength of the HBI was 8,000 kgf or more. B: The crushing strength of the HBI was 6,000 kgf or more but less than 8,000 kgf. C: The crushing strength of the HBI was 4,000 kgf or more but less than 6,000 kgf. D: The crushing strength of the HBI was less than 4,000 kgf.

[0080]

[0081] As shown in Table 2, all of the reduced iron produced in the inventive examples exhibited excellent energy efficiency during melting in an electric furnace. Furthermore, the inventive examples in which the amount of carbonaceous material charged was controlled so that the amount of carburized reduced iron was in the range of 1.0 mass % to 5.0 mass % showed particularly excellent HBI performance.

[0082] DESCRIPTION OF SYMBOLS 1 Shaft furnace 1a Iron oxide 1b Reduced iron 1c Furnace top 1d Cooling zone 2 Reducing gas inlet 3 Furnace top gas outlet 4 Cooling gas inlet 5 Cooling gas suction port 6 Iron oxide charging port 7 Reduced iron outlet 8 Dust removal device 9 Dehydration device 10 Natural gas supply unit 11 Air supply unit 12 Heating reformer 13 Briquetting machine 14 Reducing gas inlet 15 Hydrogen supply unit 16 Gas heater 17 CO ２ Separation unit 18 Methanol synthesis unit

Claims

1. A method for operating a direct reduction furnace, comprising: a charging step of charging iron oxide and carbonaceous material into the direct reduction furnace from the top of the furnace; ２ A method for operating a direct reduction furnace, comprising: an injecting step of injecting a reducing gas having a concentration of 80 volume % or more; and a reducing step of reducing the iron oxide in the direct reduction furnace to obtain reduced iron.

2. The method for operating a direct reduction furnace according to claim 1, wherein at least one of biomass and plastic is used as the carbonaceous material.

3. The method for operating a direct reduction furnace according to claim 1 or 2, wherein semi-carbonized biomass is used as the carbonaceous material.

4. A method for operating a direct reduction furnace according to any one of claims 1 to 3, further comprising controlling an amount of the carbonaceous material charged into the direct reduction furnace in accordance with an amount of C contained in the reduced iron.

5. A method for operating a direct reduction furnace according to any one of claims 1 to 4, comprising controlling the amount of carbonaceous material charged into the direct reduction furnace so that the amount of C contained in the reduced iron is 1.0 mass% or more and 5.0 mass% or less.

6. The method for operating a direct reduction furnace according to any one of claims 1 to 5, further comprising a heat supply step of supplying heat to the direct reduction furnace.

7. The method for operating a direct reduction furnace according to claim 6, wherein fuel heat from biomass is used as a heat source for the heat supply step.

8. A method for producing reduced iron, comprising the steps of: producing reduced iron by the method for operating a reduction furnace according to any one of claims 1 to 7.

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