Method for producing carbon agglomerates

Abstract

Provided is a method for producing a high-strength carbonaceous lump using, as a raw material, a gas containing C in a constituent element. The method for producing a carbonaceous lump according to the present invention has: a carbon precipitation step in which a raw material gas containing a gas containing C in a constituent element is brought into contact with a solid containing Fe in a constituent element to generate a carbon-containing precipitate on a surface of the solid; a step for recovering the carbon-containing precipitate by separating the solid and the carbon-containing precipitate; and then, a lump forming step for obtaining a carbon lump by pressurizing and heating the carbon-containing precipitate.

Description

[Technical Field]

[0001] The present invention relates to a method for producing carbon agglomerates using a gas containing C as a constituent element as a raw material. [Background technology]

[0002] In recent years, there has been a strong demand for reducing carbon dioxide (CO2) emissions against the backdrop of global environmental issues. Therefore, low reducing agent ratio (RAR) operation is also required for blast furnaces installed in steelworks. In a typical blast furnace, hot air (air heated to approximately 1200°C) is blown into the blast furnace through the tuyere as blast gas. This causes the oxygen in the hot air to react with the reducing agents, coke and pulverized coal, to produce carbon monoxide (CO) gas and hydrogen (H2) gas. These carbon monoxide and hydrogen gases reduce the iron ore charged into the blast furnace. Furthermore, carbon dioxide is produced during the reduction reaction of the iron ore. The blast gas, which is blown into the blast furnace through the tuyere, also serves to gasify the pulverized coal and coke within the blast furnace.

[0003] As a technology for reducing carbon dioxide emissions in the operation of such blast furnaces, a technology has been proposed in which carbon monoxide and carbon dioxide contained in by-product gases emitted from blast furnaces and the like are reformed to produce hydrocarbons such as methane and ethanol, which are then reintroduced into the blast furnace as solid reducing agents.

[0004] For example, Patent Document 1 proposes a method of generating solid carbon from CO gas through the Boudouard reaction and reverse water gasification reaction by mixing with hydrogen, and circulating the carbon to a blast furnace. In particular, Patent Document 1 proposes a method of briquetting the solid carbon using a binder (coal-derived binder or tar) and returning the briquettes to the blast furnace. However, it is difficult for briquettes to achieve a strength sufficient for use in a blast furnace. Furthermore, Patent Document 1 lists as a feature that the precipitated solid carbon is pure carbon with a low content of impurities such as ash.

[0005] Patent Document 2 proposes a method of introducing into a blast furnace solid carbon obtained by the thermal decomposition of methane and solid carbon obtained by the reaction of hydrogen generated during the thermal decomposition with carbon dioxide, a by-product gas from the blast furnace. Patent Document 2 also proposes briquetting the solid carbon using a binder. However, as in the case of Patent Document 1, with conventional molding using a conventional binder, there is a concern that the briquettes will volatilize at the high temperatures inside the blast furnace, making it difficult to achieve a strength sufficient for use in the blast furnace. For this reason, an agglomeration method that bonds solid carbon using a mechanism other than a binder is needed.

[0006] Furthermore, Patent Documents 3 and 4 propose methods for producing solid carbon from CO gas and CO gas contained in by-product gas, but do not describe a method for agglomerating this solid carbon. It has also been reported that hydrogen is contained in the gas during solid carbon production. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 54-150388 [Patent Document 2] Patent Publication No. 2021-165214 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-57372 [Patent Document 4] Special Publication No. 2015-516361 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, the conventional method of using solid carbon generated from by-product gases containing C as a constituent element has the problem that it is not possible to produce carbon agglomerates strong enough to withstand use in a blast furnace.

[0009] For example, when solid carbon generated from by-product gas is used in a blast furnace, there are two possible methods: injecting the solid carbon from the tuyere or charging it from the top of the furnace. When injecting solid carbon from the tuyere, the amount of injection is limited, so charging from the top of the furnace allows for a larger amount of solid carbon to be used. However, when charging from the top of the furnace, the solid carbon must have a certain size, similar to the coke normally used, and must have strength that will not break down in the blast furnace. In other words, the solid carbon must be agglomerated before being charged. In particular, when the solid carbon is charged from the 1000m 3 In a blast furnace having an internal volume above this level, the weight of the contents becomes large, and therefore, if the agglomerates have low strength, they may be pulverized and scattered inside the blast furnace, or the generated powder may deteriorate ventilation inside the blast furnace, making it impossible to operate the furnace.

[0010] When agglomerates obtained by agglomerating solid carbon with a binder according to the methods described in Patent Documents 1 and 2 are charged into a blast furnace, the binder volatilizes due to the heat inside the blast furnace, and the volatilized components interfere with the gas recovery process from the blast furnace, or the agglomerates are pulverized by the heat and impact inside the blast furnace. For this reason, it is difficult to use such agglomerates in large quantities in a blast furnace, and they can only be used in very small blast furnaces. Furthermore, while it may be possible to increase the strength of the agglomerates by carbonizing them after agglomeration using a binder, this requires careful selection of the type of binder and carbonization conditions. With typical binders and carbonization conditions, the agglomerates may break down and become pulverized during carbonization. Therefore, unless the binder and carbonization conditions are specified, agglomerates suitable for large-scale use in a blast furnace cannot be obtained. For these reasons, conventional technologies are insufficient for obtaining agglomerates that can be charged into the top of a blast furnace and used, and the obtained agglomerates are not suitable for practical use.

[0011] In view of the above problems, an object of the present invention is to provide a method for producing high-strength carbon agglomerates using a gas containing C as a constituent element as a raw material. [Means for solving the problem]

[0012] The gist of the present invention is as follows.

[0013] [1] a carbon deposition step of contacting a raw material gas containing a gas containing C as a constituent element with a solid containing Fe as a constituent element to generate a carbon-containing precipitate on a surface of the solid; separating the solid from the carbon-containing precipitate and recovering the carbon-containing precipitate; a subsequent agglomeration step of pressurizing and heating the carbon-containing precipitate to obtain carbon agglomerates; A method for producing a carbon agglomerate comprising the steps of:

[0014] [2] The method for producing carbon agglomerates according to [1] above, wherein the gas contains one or both of CO gas and CH4 gas.

[0015] [3] The method for producing carbon agglomerates according to [2] above, wherein the raw material gas contains the CO gas and hydrogen gas.

[0016] [4] The method for producing carbon agglomerates according to [2] above, wherein the raw material gas is CH4 gas.

[0017] [5] The method for producing carbon agglomerates according to any one of the above [1] to [4], wherein the solid contains at least one selected from the group consisting of sintered ore, iron ore, and reduced iron.

[0018] [6] The method for producing carbon agglomerates according to any one of the above [1] to [5], wherein the carbon deposition step is carried out at an atmospheric temperature of 300°C or higher and 1500°C or lower.

[0019] [7] The method for producing carbon agglomerates according to any one of the above [1] to [6], wherein the carbon-containing precipitate contains 1 mass % or more of T. Fe.

[0020] [8] The method for producing carbon agglomerates according to any one of the above [1] to [7], wherein the agglomerating step is a hot pressing step in which pressure and heating of the carbon-containing precipitate are performed simultaneously.

[0021] [9] The method for producing carbon agglomerates according to the above [8], wherein the maximum temperature of the carbon-containing precipitate in the hot pressing step is 750°C or higher.

[0022]

[10] The method for producing carbon agglomerates according to any one of the above [1] to [9], wherein the agglomerating step is carried out without adding a binder to the carbon-containing precipitate.

[0023]

[11] The method for producing carbon agglomerates according to any one of the above [1] to

[10] , wherein the carbon agglomerates have an indirect tensile strength of 5 MPa or more. [Effects of the Invention]

[0024] According to the method for producing carbon agglomerates of the present invention, high-strength carbon agglomerates can be produced using a gas containing C as a constituent element as a raw material. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a reactor used in Examples 1, 2, and 4 of the present invention and Comparative Example 1. [Figure 2] 1A is a photograph of sintered ore after separation of the carbon-containing precipitate deposited in Example 1, and FIG. 1B is a photograph of the carbon-containing precipitate separated from the sintered ore in Example 1. FIG. [Figure 3] 1 is a graph showing a Raman spectrum of the carbon-containing precipitate in Example 1. [Figure 4] 1 is a TEM image of a carbon-containing precipitate in Example 1. [Figure 5] FIG. 1 is a schematic diagram showing the structure of an electric furnace used in Example 3 of the present invention. [Figure 6] 1 is a TEM image of a carbon-containing precipitate in Example 3. [Figure 7] 1 is a TEM image of a carbon-containing precipitate in Example 4. [Figure 8] 1 is a TEM image of a carbon-containing precipitate in Comparative Example 1. [Figure 9]FIG. 1(A) is a diagram showing the procedure for a hot press test, and FIG. 1(B) is a diagram showing the procedure for an indirect tensile test. [Figure 10] 1 is a photograph showing the appearance of a carbon agglomerate obtained from the carbon-containing precipitate of Invention Example 1 at a molding temperature of 1000° C. [Figure 11] 1 is a graph showing the relationship between molding temperature and indirect tensile strength for carbon agglomerates obtained from the carbon-containing precipitates and carbon black of Invention Examples 1 to 3. [Figure 12] 1 is a graph showing the relationship between molding temperature and bulk density for carbon agglomerates obtained from the carbon-containing precipitates and carbon black of Invention Examples 1 to 3. [Figure 13] 1 is a low-magnification TEM image of a carbon agglomerate obtained from the carbon-containing precipitate of Example 3 at a molding temperature of 1000°C. [Figure 14] This is an enlarged TEM image of the frame in Figure 13. [Figure 15] 1 is a TEM image of a carbon agglomerate obtained from the carbon-containing precipitate of Example 2 at a molding temperature of 1000°C. [Figure 16] 15 is an enlarged TEM image of FIG. [Figure 17] FIG. 1 is a diagram illustrating the reaction mechanism by which tubular or spherical carbon-containing precipitates are produced from CO gas, CO gas, and methane gas. DETAILED DESCRIPTION OF THE INVENTION

[0026] A method for producing carbon agglomerates according to one embodiment of the present invention includes a carbon precipitation step of bringing a source gas containing a gas containing C as a constituent element into contact with a solid containing Fe as a constituent element to produce carbon-containing precipitates on a surface of the solid; a step of separating the solid from the carbon-containing precipitates and recovering the carbon-containing precipitates; and an agglomeration step of subsequently pressurizing and heating the carbon-containing precipitates to obtain carbon agglomerates.

[0027] [Source gas] The raw material gas includes a gas containing C as a constituent element. The gas containing C as a constituent element is not particularly limited, but preferably includes one or more selected from the group consisting of CO, CO2, and CH4, and more preferably includes one or both of CO gas and CH4 gas. The raw material gas may consist of a gas containing C as a constituent element, or may consist of a gas containing C as a constituent element and another gas. The content of the gas containing C as a constituent element in the raw material gas may be 1% by volume or more and 100% by volume or less. The other gas preferably consists of one or both of H2 and N2. In particular, the raw material gas preferably contains hydrogen, as this easily generates fibrous carbon. The content of H2 in the raw material gas is preferably 1% by volume or more and 50% by volume or less. Specifically, by-product gases from steelworks, particularly blast furnace gas and converter gas, are advantageously suitable as the raw material gas. The raw material gas preferably contains CO gas and hydrogen gas, and is also preferably composed of CH4 gas.

[0028] [Solids containing Fe as a constituent element] Examples of solids containing Fe as a constituent element include metallic iron and iron oxide. The solid containing Fe as a constituent element preferably includes one or more selected from the group consisting of sintered ore, iron ore, and reduced iron (pure iron). The content of total iron (T.Fe) in the solid is preferably 1% by mass or more, more preferably 50% by mass or more. Even if a large amount of Fe is contained, it is possible to obtain carbon, and this carbon can be agglomerated. The upper limit of the total iron (T.Fe) content in the solid is not particularly limited, but the total iron content can be 99.9% by mass or less. The solid containing Fe as a constituent element includes, as an Fe source, one or more selected from the group consisting of pure iron (M.Fe), FeO, Fe2O3, Fe3O4, and other Fe compounds. Examples of other Fe compounds include metallic iron containing one or both of Si and S in solid solution, and calcium ferrite, a compound of calcium and iron oxide. The solid containing Fe as a constituent element is composed of these Fe sources and other components, such as Si, Ca, Al, Mg, P, S, Na, K, Mn, Ti, Zn, V, and Ni.

[0029] The particle size of the solid containing Fe as a constituent element is not particularly limited, but it is preferable that the particle size be distributed in the range of more than 5 mm to 80 mm or less so that the solid can support an appropriate amount of carbon-containing precipitate. In this specification, "particle size" corresponds to the nominal mesh size of a sieve mesh conforming to JIS Z 8801:2019. That is, a solid having a particle size of more than X mm is a solid that remains on the sieve when sieved through a sieve with a nominal mesh size of X mm. A solid having a particle size of Y mm or less is a solid that passes through a sieve with a nominal mesh size of Y mm and falls below the sieve.

[0030] [Carbon deposition process] A raw material gas containing a gas containing C as one of the constituent elements is brought into contact with a solid containing Fe as one of the constituent elements to form a carbon-containing precipitate on the surface of the solid. That is, when a carbon-containing precipitate is formed from a gas containing C using a solid containing Fe as a catalyst, fibrous carbon is formed in the carbon-containing precipitate. Then, when the carbon-containing precipitate is agglomerated, entanglement of the fibrous carbon occurs, promoting bonding between particles of the carbon-containing precipitate. Furthermore, when the carbon agglomerate fractures, it becomes necessary to cut or pull out the fibers, which is expected to contribute to increasing the strength of the carbon agglomerate.

[0031] The carbon-containing precipitate is composed of solid carbon (C) and other components. The content of solid carbon (C) in the carbon-containing precipitate can be 10% by mass or more and 99% by mass or less. The other components are derived from a solid containing Fe used as a catalyst and can be one or more selected from the group consisting of pure iron (M.Fe), FeO, Fe2O3, Fe3O4, other Fe compounds, and Si, Ca, Al, Mg, P, S, Na, K, Mn, Ti, Zn, V, Ni, and compounds thereof. Examples of the other Fe compounds (Fe compounds other than oxides) include metallic iron containing one or both of Si and S as a solid solution, and calcium ferrite, which is a compound of calcium and iron oxide. The content of T.Fe in the carbon-containing precipitate is preferably 1% by mass or more. This results in a carbon-containing precipitate in which fibrous or tubular carbon grows from iron particles. The upper limit of the content of T.Fe in the carbon-containing precipitate is not particularly limited, but the content of T.Fe can be 50 mass % or less.

[0032] The reaction for producing solid carbon from CO2 gas, CO gas, or CH4 gas is not particularly limited, but examples thereof include the following reactions.

[0033] [Reaction to produce solid carbon from CO gas] Solid carbon can be produced from CO gas by the Boudouard reaction shown in reaction formula (1). The Boudouard reaction can produce solid carbon from CO gas at temperatures below about 700°C. 2CO=C+CO2 (1)

[0034] Solid carbon can be produced from CO gas by the reverse water-gasification reaction shown in reaction formula (2). The reverse water-gasification reaction can produce solid carbon from CO gas at temperatures below approximately 650°C. CO + H2 = C + H2O (2)

[0035] The methanation reaction shown in reaction formula (3) produces CH4 gas from CO gas, and the thermal decomposition reaction shown in reaction formula (4) produces solid carbon from CH4 gas. The methanation reaction can produce CH4 gas from CO gas at temperatures below approximately 650°C, and the thermal decomposition reaction can produce solid carbon from CH4 gas in air at temperatures above approximately 500°C. CO + 3H2 = CH4 + H2O (3) CH4=C+2H2 (4)

[0036] Solid carbon can be produced from CO gas by the decomposition reaction shown in reaction formula (5). The decomposition reaction can produce solid carbon from CO gas under low oxygen partial pressure. 2CO=2C+O2 (5)

[0037] [Reaction to produce solid carbon from CO2 gas] Solid carbon can be produced from CO2 gas by the reverse water-gasification reaction shown in reaction formula (6). The reverse water-gasification reaction can produce solid carbon from CO2 gas at temperatures below approximately 650°C. CO2 + 2H2 = C + 2H2O (6)

[0038] CO gas can be produced from CO gas by the reverse water-gas shift reaction shown in reaction formula (7), and solid carbon can be produced from CO gas by the reverse water-gas conversion reaction shown in reaction formula (2). The reverse water-gas shift reaction can produce CO gas from CO gas at temperatures above about 850°C. CO2 + H2 = CO + H2O (7) CO + H2 = C + H2O (2)

[0039] The methanation reaction shown in reaction formula (8) produces CH gas from CO gas, and the thermal decomposition reaction shown in reaction formula (4) produces solid carbon from CH gas. The methanation reaction can produce CH gas from CO gas at temperatures below approximately 600°C. CO2 + 4H2 = CH4 + 2H2O (8) CH4=C+2H2 (4)

[0040] Solid carbon can be produced from CO2 gas by the decomposition reaction shown in reaction formula (9). The decomposition reaction can produce solid carbon from CO2 gas under low oxygen partial pressure. CO2 = C + O2 (9)

[0041] [Reaction to produce solid carbon from CH4 gas] Solid carbon can be produced from CH4 gas by the pyrolysis reaction shown in reaction formula (4). CH4=C+2H2 (4)

[0042] The carbon deposition step is preferably carried out at an ambient temperature of 300°C or higher and 1500°C or lower. If the ambient temperature is lower than 300°C, the deposition rate of the carbon-containing precipitates is insufficient. Therefore, the ambient temperature is preferably 300°C or higher, and more preferably 400°C or higher. On the other hand, if the ambient temperature exceeds 1500°C, the deposited carbon becomes difficult to bond, making it difficult to obtain carbon agglomerates with high strength. Therefore, the ambient temperature is preferably 1500°C or lower, and more preferably 1000°C or lower.

[0043] In the carbon deposition step, the temperature of the raw material gas supplied to the Fe-containing solid is not particularly limited and can be room temperature (for example, 10°C or higher and 35°C or lower). However, the temperature of the raw material gas is not limited to room temperature and may be heated to any temperature equal to or lower than the ambient temperature.

[0044] The carbon deposition step is preferably carried out in an atmosphere substantially free of oxygen gas. This means that the raw material gas supplied to the Fe-containing solid does not contain oxygen gas (O2), thereby preventing oxidation and combustion of carbon, and that the furnace atmosphere does not contain oxygen, thereby preventing carbon combustion. "An atmosphere substantially free of oxygen gas" means an atmosphere in which the oxygen gas content is reduced to 5% by volume or less.

[0045] The reaction time (flow time of the raw material gas) in the carbon deposition step is not particularly limited, but is preferably 10 minutes or more and 480 minutes or less. If the reaction time is 10 minutes or more, a sufficient amount of carbon-containing deposit can be obtained by ensuring a sufficient reaction time. If the reaction time is 480 minutes or less, the process can be prevented from being prolonged.

[0046] [Separation and recovery process] Next, the solid containing Fe as a constituent element is separated from the carbon-containing precipitate, and the carbon-containing precipitate is recovered. Specifically, the solid to which the carbon-containing precipitate adheres is sieved using a sieve with appropriate mesh size to separate the carbon-containing precipitate from the solid. The carbon-containing precipitate is a fine powder. Therefore, by using a sieve with mesh size smaller than the particle size of the Fe-containing solid but larger than the particle size of the carbon-containing precipitate, the Fe-containing solid can be left on the sieve while the carbon-containing precipitate falls below the sieve. The particle size of the carbon-containing precipitate is not particularly limited, but for example, when laser scattering particle size distribution measurement (wet) is performed, the proportion of particles larger than 0.1 μm and smaller than 100 μm can be more than 90%. The mesh size of the sieve can be selected according to the particle size of the solid containing Fe as a constituent element, and can be selected, for example, from the range of 0.1 mm to 10 mm.

[0047] [Agglomeration process] Next, the carbon-containing precipitate is pressurized and heated to obtain a carbon agglomerate. Since the carbon-containing precipitate obtained in the carbon precipitation step is coarse when generated, it is necessary to pressurize and heat the precipitate to promote bonding and thereby achieve agglomeration.

[0048] Specifically, it is preferable to heat the carbon-containing precipitate to a temperature of 400°C or higher to form an agglomerate. That is, if the heating temperature is 400°C or higher, the bonding reaction rate of carbon is significantly improved. The heating temperature is more preferably 750°C or higher, and even more preferably 1000°C or higher. On the other hand, although there is no particular upper limit to the heating temperature, it is preferable to set the heating temperature to 2000°C or lower from the viewpoint of protecting the device.

[0049] A preferred embodiment of the agglomeration step is a hot-pressing step in which pressure and heating of the carbon-containing precipitate are simultaneously performed. In the hot-pressing step, the carbon-containing precipitate is pressure-molded while being heated in an oxygen-free atmosphere to obtain a carbon agglomerate. The oxygen-free atmosphere is preferably an atmosphere in a space through which an inert gas such as nitrogen flows.

[0050] In the hot pressing step, the temperature of the carbon-containing precipitate at the start of pressing the carbon-containing precipitate is referred to as the "pressing start temperature," and the maximum temperature of the carbon-containing precipitate during pressing is referred to as the "pressing temperature."

[0051] The molding start temperature in the hot pressing step is not particularly limited, but is typically room temperature (for example, 10° C. or higher and 35° C. or lower). This allows the temperature range of the carbon-containing precipitate in the hot pressing step to be widened, and the reaction time to be extended.

[0052] From the viewpoint of realizing high strength of the carbon agglomerates, the maximum temperature (molding temperature) of the carbon-containing precipitate in the hot pressing step is preferably 400° C. or higher, more preferably 750° C. or higher, and even more preferably 1000° C. or higher. From the viewpoint of protecting the hot pressing equipment, the molding temperature is preferably 2000° C. or lower.

[0053] The rate of temperature rise from the molding start temperature to the molding temperature is preferably 1°C / min or more and 30°C / min or less. By setting the rate of temperature rise to 1°C / min or more and 30°C / min or less, a decrease in strength can be avoided.

[0054] In the hot pressing process, the pressure mechanically applied to the carbon-containing precipitate is called the molding pressure. From the viewpoint of realizing high strength of the carbon agglomerate, the molding pressure is preferably 10 kPa or more, more preferably 20 MPa or more. From the viewpoint of production cost, the molding pressure is preferably 300 MPa or less.

[0055] Another embodiment of the agglomeration step is a step of compression-molding the carbon-containing precipitate at room temperature (for example, 10°C or higher and 35°C or lower) to obtain a molded product, and then carbonizing the molded product to obtain a carbon agglomerate. The preferred molding pressure during compression-molding is the same as the molding pressure in the hot-pressing step. The preferred carbonization temperature during carbonization is the same as the molding temperature in the hot-pressing step.

[0056] The agglomeration step is preferably carried out without adding a binder to the carbon-containing precipitate, which prevents the binder from volatilizing due to the heat in the blast furnace, and the volatilized components from interfering with the gas recovery step from the blast furnace, and prevents the carbon agglomerates from being pulverized due to the heat and impact in the blast furnace.

[0057] In this embodiment, the term "carbon agglomerates" refers to agglomerates primarily composed of carbon produced by the production method according to this embodiment, and their composition is the same as that of the carbon-containing precipitate. The shape and size of the carbon agglomerates are not particularly limited, and examples of the shapes include cylindrical, almond-shaped, and pillow-shaped pellets. In this case, the size may be 10 to 100 mm in diameter and 5 to 100 mm in height. The carbon agglomerates obtained by this embodiment preferably have an indirect tensile strength of 1 MPa or more, more preferably 5 MPa or more. An indirect tensile strength of 1 MPa or more can withstand handling when transporting the carbon agglomerates on a belt conveyor or the like. An indirect tensile strength of 5 MPa or more can withstand charging the carbon agglomerates from the top of a blast furnace. The carbon agglomerates can be used not only in blast furnaces but also as a carbon material themselves. Therefore, the method according to the present invention can be effectively utilized as a method for producing carbon materials with low CO2 emissions. [Example]

[0058] [Formation of carbon-containing precipitates] (Example 1) A vertical reactor was used to generate carbon-containing precipitates from CO gas. Figure 1 shows a schematic diagram of the vertical reactor. An alumina support 12, alumina balls, and 500 g of sintered ore were charged, in this order, into a furnace core tube 10 with an inner diameter of 80 mm. The composition of the sintered ore used here is shown in Table 1 below. The particle size of the sintered ore was greater than 15 mm and less than 21 mm (15 mm sieve passing rate: 0%, 21 mm sieve passing rate: 100%). The ambient temperature inside the furnace core tube 10, measured by a thermocouple 16, was set to 800°C by a heater 14. Then, a room temperature raw material gas having a composition by volume of 31% CO, 19% H2, and 50% N2 was flowed from the gas inlet pipe 18 located below the reactor into the furnace core tube 10 at a flow rate of 17 NL / min (flow rate of gas volume per minute converted to standard conditions (0°C, 1 atmosphere)) for 3 hours, bringing the raw material gas into contact with the sintered ore for 3 hours. The alumina balls served to maintain the temperature inside the furnace core tube, and the iron contained in the sintered ore functioned as a catalyst for the formation of carbon-containing precipitates. This process produced carbon-containing precipitates on the sintered ore.

[0059] [Table 1]

[0060] The sintered ore with the carbon-containing precipitates attached was then recovered from the reactor and sieved through a 0.125 mm mesh sieve to separate the carbon-containing precipitates from the sintered ore. The carbon-containing precipitates were a fine powder, and this sieving process allowed for easy separation from the sintered ore. Figure 2(A) shows a photograph of the sintered ore after the carbon-containing precipitates had been separated, and Figure 2(B) shows a photograph of the carbon-containing precipitates separated from the sintered ore. The particle size distribution of the carbon-containing precipitates measured using a laser diffraction particle size distribution analyzer was D10 2.1 μm, D50 6.61 μm, and D90 14.8 μm, in mass%.

[0061] The amount of carbon-containing precipitates was 11 g per 500 g of sinter before treatment. As shown in Table 2, the chemical analysis values of the carbon-containing precipitates show that the carbon content in the carbon-containing precipitates was 72.0 mass %, indicating that the precipitates were mainly composed of C. The amount of carbon generated was 1.5 when the weight of the sinter before treatment was taken as 100.

[0062] [Table 2]

[0063] The carbon content in the carbon-containing deposit relative to the carbon content in the flowing raw material gas (ie, carbon yield) was 1.1%.

[0064] The Raman spectra of three samples (N1, N2, and N3) collected from the carbon-containing deposits were measured using conventional Raman spectroscopy with a nano photon Raman Force. The results are shown in Figure 3. As shown in Figure 3, the G-band, which indicates crystallinity, is observed at 1600 cm -1 The nearby peaks were large and sharply developed, indicating that the carbon-containing precipitates contained highly crystalline carbon.

[0065] Figure 4 shows a TEM image of the carbon-containing precipitates. From Figure 4, it can be seen that the carbon-containing precipitates are mainly iron particles (the black particles in the image below) from which carbon has developed into fibrous forms. Furthermore, the Raman spectrum shown in Figure 3 clearly shows that the carbon has high crystallinity, which suggests that the fibers have excellent strength.

[0066] (Example 2) Except for changing the atmospheric temperature in the furnace core tube from 800°C to 550°C and the reaction time from 3 hours to 40 minutes, a carbon-containing precipitate was formed on the sintered ore in the same manner as in Example 1, and the carbon-containing precipitate and the sintered ore were separated and recovered. The carbon yield in this case was 8.7%.

[0067] (Example 3) Carbonaceous deposits were produced from methane gas using an electric furnace. Methane decomposes at temperatures above 500°C as follows, resulting in the deposition of solid carbon. CH4 → C+2H2

[0068] Figure 5 shows a schematic diagram of an electric furnace. 30 g of reduced iron pellets obtained by reducing iron ore pellets were charged into the electric furnace 20. The composition of the reduced iron pellets used here is shown in Table 3 below. The particle size of the reduced iron pellets was φ10 mm. The atmospheric temperature inside the electric furnace 20 was set to 900°C. Then, a room-temperature raw material gas consisting of 100% by volume of methane gas was flowed into the electric furnace 20 at a flow rate of 10 NL / min for 1 hour. The iron contained in the reduced iron pellets functions as a catalyst for the formation of carbon-containing precipitates. This process caused carbon-containing precipitates to form on the reduced iron pellets.

[0069] [Table 3]

[0070] The reduced iron pellets with the carbon-containing precipitates attached were recovered from the electric furnace and sieved through a 0.125 mm mesh sieve to separate the carbon-containing precipitates from the reduced iron pellets, which were then recovered separately. The carbon-containing precipitates were a fine powder and could be easily separated from the reduced iron pellets by this sieving process. The carbon yield was approximately 1%.

[0071] A TEM image of the carbon-containing precipitate is shown in Figure 6. The black particles in the image are iron particles, from which fibrous carbon has grown.

[0072] (Example 4) Carbon-containing precipitates were formed on iron ore pellets in the same manner as in Example 1, except that a raw material gas having a volumetric composition of 30% CO and 70% N was used, iron ore pellets were used instead of sintered ore, the atmospheric temperature in the furnace tube was set to 550°C, and the reaction time was set to 30 minutes. Chemical analysis values of the iron ore pellets used here are shown in Table 4 below. The particle size of the iron ore pellets was greater than 9 mm and less than 12 mm (9 mm sieve passing rate: 0%, 12 mm sieve passing rate: 100%). The carbon-containing precipitates and iron ore pellets were separated and recovered. Because the amount of carbon-containing precipitates produced by this process was small, this process was repeated 10 times to obtain a sufficient amount for the agglomeration test described below. The same iron ore pellets were used repeatedly.

[0073] [Table 4]

[0074] A TEM image of the carbon-containing precipitate is shown in Figure 7. The carbon-containing precipitate had a morphology in which particulate carbon encompassed iron particles (black particles in the image).

[0075] (Comparative Example 1) Using the reactor shown in Figure 1, carbon-containing precipitates were formed on alumina balls instead of sintered ore. 500 g of alumina balls were placed on the alumina support 12 of a furnace core tube 10 with an inner diameter of φ80 mm to form a soaking zone approximately 50 mm high. The particle size of the alumina balls was φ6 mm. The atmospheric temperature inside the furnace core tube 10 was set to 1400°C, and then a room-temperature raw material gas consisting of 100% methane gas by volume was flowed into the furnace core tube 10 from the gas inlet tube 18 at a flow rate of 1.0 NL / min for 1 hour. This process produced carbon-containing precipitates on the alumina balls.

[0076] The alumina balls with the carbon-containing precipitates attached were recovered from the reactor and sieved through a sieve with 0.125 mm openings to separate the carbon-containing precipitates from the alumina balls, which were then recovered separately. The carbon-containing precipitates were fine powders and could be easily separated from the alumina balls by this sieving operation.

[0077] Figure 8 shows a TEM image of the carbon-containing precipitates. The low-magnification image in the top of Figure 8 shows that the carbon-containing precipitates are particulate, and many of the carbon-containing precipitates have a fluffy ball-like structure. The TEM image in the bottom of Figure 8, which shows an enlargement of this fluffy ball-like carbon-containing precipitate (the boxed area in the top of Figure 8), reveals that the carbon-containing precipitates have a structure with many edges.

[0078] [Agglomeration of carbon-containing precipitates] The following hot pressing step was carried out to agglomerate (coke) the carbon-containing precipitates obtained by the above treatment. Hot pressing is a molding method in which carbon-containing precipitates are heated while being pressurized, and by employing this method, it is possible to produce high-strength carbon agglomerates (coke) from the carbon-containing precipitates. Note that a binder is not necessarily required in the agglomeration method using hot pressing. One of the new features discovered by the inventors is that high-strength carbon agglomerates can be obtained without a binder.

[0079] (Example 1) 9(A) and (B) show an outline of the hot press test. 1.32 g of the carbon-containing precipitate obtained in Example 1 was filled into a mold having a diameter of 12 mm shown in FIG. 9(A), and pressure molding of the carbon-containing precipitate was performed. The molding start temperature was room temperature, and the carbon-containing precipitate was heated at a heating rate of 20°C / min to the maximum temperature (molding temperature) shown in Table 5 while applying a molding pressure of 50 MPa under a nitrogen gas flow. The carbon-containing precipitate was then held at the molding temperature for 5 minutes. The obtained carbon agglomerate was then cooled and collected.

[0080] The indirect tensile strength of the obtained carbon agglomerates was measured as shown in Figure 9(B). Specifically, the indirect tensile strength was measured by the method described in the non-patent document "Miyakawa A. et al., Study on Coke Strength by Indirect Tensile Strength Test Method (I), Journal of the Fuel Association, Vol. 54, No. 584, 1975, pp. 983-993." The indirect tensile strength of ordinary coke (lump coke for steelmaking obtained by carbonizing coal) produced in steelworks was also measured for comparison. The carbon agglomerates obtained at a molding temperature of 1000°C had the appearance shown in Figure 10.

[0081] The visual evaluation of the success or failure of agglomeration and the indirect tensile strength values are shown in Table 5. Agglomeration was successful in all tests at molding temperatures of 1000°C or higher. It was also found that the carbon agglomerates produced according to the present invention, without a binder, exhibited higher indirect tensile strength than ordinary coke.

[0082] [Table 5]

[0083] (Examples 1 to 3) The carbon-containing precipitates and carbon black obtained in Examples 1 to 3 were each hot-pressed under four molding temperatures of 500°C, 750°C, 1000°C, and 1250°C, with the remaining conditions remaining the same as above, to obtain carbon agglomerates. The indirect tensile strength of the obtained carbon agglomerates was measured. Figure 11 shows the measurement results of the indirect tensile strength. It was observed that the indirect tensile strength tended to increase as the molding temperature increased.

[0084] The bulk density of the obtained carbon agglomerates was measured and the results are shown in Figure 12. The bulk density was determined by measuring the diameter and height of the carbon agglomerates to calculate the volume, and then dividing the weight by the volume.

[0085] As shown in Figure 12, the carbon agglomerates of Example 3 produced from CH4 gas have a slightly higher density than the carbon agglomerates of Examples 1 and 2 produced from CO gas. However, as shown in Figure 11, there is no significant difference in indirect tensile strength between Examples 1 to 3, indicating that the method of the present invention can be carried out using a variety of feedstock gases. The carbon black agglomerates had low bulk density and low indirect tensile strength. Carbon black is carbon produced by incomplete combustion in the presence of oxygen, and has a different structure from the carbon-containing deposits of the present invention, which are produced in an atmosphere substantially free of oxygen. This is thought to be why the indirect tensile strength of the carbon black agglomerates was low.

[0086] Figure 13 shows a low-magnification TEM image of a carbon agglomerate obtained by hot pressing the carbon-containing precipitate of Example 3 under the same conditions as above, except that the molding temperature was 1000°C. The black material is iron, which is surrounded by carbon, and it was found that the carbon was bonded to itself, not to itself. Furthermore, Figure 14 shows an enlarged TEM image of the area (frame) where the carbon was bonded to itself. From this observation, it was found that the carbon had a multi-walled carbon nanotube-like structure, with SP in the stacking direction. 2 It was found that they were bonded together.

[0087] Figure 15 shows a TEM image of a carbon agglomerate obtained by hot pressing the carbon-containing precipitate of Example 2 under the same conditions as above, except that the molding temperature was 1000°C. It was found that even in this carbon agglomerate, there were no areas where black iron particles were bonded together, and carbon particles were bonded together. Figure 16 shows an enlarged TEM image of the bonded area between carbon particles. As in Figure 14, carbon particles were bonded together by SP 2 These results indicate that the bonding between particles of carbon-containing precipitates in the carbon agglomerates is due to carbon-carbon bonding.

[0088] The present inventors have investigated why bonding of carbon black particles is insufficient in carbon black agglomerates, whereas bonding of carbon-containing precipitates is sufficient in carbon agglomerates produced according to the present invention. The carbon-containing precipitates of Examples 1 to 3 of the present invention are characterized by their fibrous, tubular, or spherical structure containing iron particles. In the case of tubular or spherical shapes, when carbon-containing precipitate particles approach each other, the faces of the laminated structure always face each other. Therefore, by bringing the particles closer together by applying pressure and promoting bonding by heating, bonding of carbon particles becomes possible. In contrast, carbon black is known to be composed of crystallites within the particles. In other words, carbon black is a material with many edges. At the edges, SP 2 It is presumed that sufficient agglomeration was not achieved due to the inability to bond.

[0089] (Example 4) The carbon-containing precipitate of Example 4 was subjected to hot pressing under two molding temperatures of 750°C and 1000°C, with the other conditions remaining the same as above, to obtain carbon agglomerates. Agglomeration was successful under both conditions. The indirect tensile strength was 7.1 MPa when the molding temperature was 750°C and 13.0 MPa when the molding temperature was 1000°C, indicating a sufficiently high strength.

[0090] (Comparative Example 1) Next, we will explain the necessity of forming carbon-containing precipitates on a solid containing Fe as a constituent element. The reaction by which tubular or spherical carbon-containing precipitates are formed from CO gas, CO gas, and methane gas is thought to have the mechanism shown in Figure 17. First, C carburizes the iron, and then the carbon that is not completely dissolved precipitates from the iron nuclei and grows as fibers. During this process, spherical carbon may also form during the nucleation stage. Because the presence of iron nuclei allows fibers to grow, Fe was necessary in this invention. Such tubular or spherical carbon is difficult to form at high temperatures, and a precipitation reaction from the gas phase to the solid phase occurs.

[0091] On the other hand, when the carbon-containing precipitates according to Comparative Example 1 deposited on alumina balls were hot-pressed under the same conditions as above except for a molding temperature of 500 to 1000°C, agglomeration was not possible at any molding temperature. In other words, since carbon-containing precipitates formed on solids containing Fe have better moldability than carbon-containing precipitates formed on solids not containing Fe, it is necessary to use carbon-containing precipitates formed on solids containing Fe in order to achieve agglomeration.

[0092] (Example 2) An agglomeration method other than hot pressing was also carried out. The carbon-containing precipitate obtained in Example 2 was compression-molded at room temperature (25°C) (without adding a binder), and the molded product was carbonized under atmospheric pressure (carbonization temperature: 1000°C) to obtain a carbon agglomerate. As a result, the carbon agglomerate after carbonization had visible cracks and a low indirect tensile strength of 1.2 MPa. This result demonstrates that hot pressing is an excellent method for agglomeration in the present invention. However, if the carbon agglomerate has an indirect tensile strength of 1 MPa or more, it can withstand handling during transportation on a belt conveyor or the like. Therefore, a method of carbonizing a molded product obtained by compression-molding the carbon-containing precipitate under atmospheric pressure can also be effectively used as a method for producing a carbon agglomerate with excellent handleability. [Industrial Applicability]

[0093] According to the method for producing carbon agglomerates of the present invention, high-strength carbon agglomerates can be produced using a gas containing C as a constituent element as a raw material.

Claims

1. a carbon deposition step of contacting a raw material gas containing a gas containing C as a constituent element with a solid containing Fe as a constituent element to produce a carbon-containing deposit on a surface of the solid, the carbon deposit comprising fibrous, tubular, or spherical carbon developed thereon; separating the solid from the carbon-containing precipitate and recovering the carbon-containing precipitate; thereafter, an agglomeration step of simultaneously pressurizing and heating the carbon-containing precipitate without adding a binder to the carbon-containing precipitate to a maximum temperature of 750°C or higher to obtain a carbon agglomerate having an indirect tensile strength of 5 MPa or higher; A method for producing a carbon agglomerate comprising the steps of:

2. The gas containing C as a constituent element is CO gas and CH ４ 2. The method for producing carbon agglomerates according to claim 1, wherein the method further comprises one or both of a gas.

3. 3. The method for producing carbon agglomerates according to claim 2, wherein the raw material gas contains the CO gas and hydrogen gas.

4. The source gas is ４ 3. The method for producing carbon agglomerates according to claim 2, wherein the gas is a gas.

5. 5. The method for producing carbon agglomerates according to claim 1, wherein the solid comprises at least one selected from the group consisting of sintered ore, iron ore, and reduced iron.

6. The method for producing carbon agglomerates according to any one of claims 1 to 4, wherein the carbon deposition step is carried out at an atmospheric temperature of 300°C or higher and 1500°C or lower.

7. The method for producing carbon agglomerates according to any one of claims 1 to 4, wherein the carbon-containing precipitate contains 1 mass % or more of trivalent iron.

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