Methanation device, methanation method, hydrocarbon direct decomposition device, and hydrocarbon direct decomposition method

Abstract

Provided is a methanation device for removing a saturated hydrocarbon from a raw material gas containing methane and a saturated hydrocarbon through methanation, in which a saturated hydrocarbon having at least two carbon atoms reacts with hydrogen and the saturated hydrocarbon is converted into methane. The methanation device comprises: at least two catalyst layers composed of a catalyst for methanation, the catalyst layers being provided at intervals in the flow direction of a mixed gas containing a raw material gas and a hydrogen-containing gas; a hydrogen supply line for supplying a hydrogen-containing gas to an upstream side of the catalyst layer on the most upstream side in the flow direction of the mixed gas; a raw material gas supply line for supplying the raw material gas to each space between two catalyst layers adjacent to each other in the flow direction of the mixed gas and the upstream side of the catalyst layer on the most upstream side in the flow direction of the mixed gas; and a cooler provided between two catalyst layers adjacent to each other in the flow direction of the mixed gas and cooling the mixed gas discharged from the catalyst layer on the upstream side among the two catalyst layers adjacent to each other.

Description

Methanation device, methanation method, hydrocarbon direct cracking device, and hydrocarbon direct cracking method

[0001] This application claims priority to Japanese Patent Application No. 2023-220345, filed on December 27, 2023, with the Japan Patent Office, the contents of which are incorporated herein by reference.

[0002] Currently, the production of various types of energy is heavily dependent on fossil fuels such as oil, coal, and natural gas, but from the perspective of global environmental conservation, the increase in carbon dioxide emissions released by the combustion of fossil fuels is seen as a problem. The Paris Agreement, agreed upon in 2015, calls for a reduction in carbon dioxide emissions in order to address the issue of climate change, and reducing carbon dioxide emissions from the combustion of fossil fuels is a key issue for thermal power plants and other facilities. While processes for separating and capturing emitted carbon dioxide are being actively studied, technologies for producing energy without emitting carbon dioxide by using alternative fuels to fossil fuels are also being considered.

[0003] Therefore, hydrogen, a clean fuel that does not emit carbon dioxide when burned, has been attracting attention as an alternative to fossil fuels. Hydrogen can be produced, for example, by steam reforming methane contained in natural gas. However, this production method produces carbon monoxide as a by-product, which is ultimately oxidized and emitted as carbon dioxide. Meanwhile, methods such as water electrolysis and photocatalysis have been investigated as methods for producing hydrogen from water without using fossil fuels, but these methods require a large amount of energy and are therefore economically problematic.

[0004] In response to this, methods have been developed to produce hydrogen and carbon by directly decomposing hydrocarbons. The features of direct decomposition of hydrocarbons are that hydrogen fuel can be obtained without emitting carbon dioxide, and that the by-product carbon is solid and can be easily immobilized, and the carbon itself can be effectively used in a wide range of applications, such as electrode materials, tire materials, and building materials. Up until now, methods have been developed to directly decompose hydrocarbons into hydrogen and carbon by contacting a supported catalyst with hydrocarbon gas, but a problem has been that carbon, a product of the direct decomposition reaction of hydrocarbons, adheres to the catalyst, causing a decrease in catalytic activity in a short period of time.

[0005] In response to this, the applicant of the present disclosure has developed a method for directly decomposing hydrocarbons into carbon and hydrogen using a catalyst that is an unsupported catalyst consisting of an aggregate of multiple iron particles, as described in Patent Document 1. With this method, even if carbon, which is a product of the direct decomposition reaction of hydrocarbons, adheres to the catalyst, new active sites are generated to maintain activity, and it was considered that the activity of this reaction can be maintained for a long time.

[0006] When natural gas, for example, is used as a feed gas for the direct cracking reaction of hydrocarbons, natural gas contains saturated hydrocarbons having two or more carbon atoms, such as ethane, propane, and butane (hereinafter referred to as "saturated C2+ hydrocarbons") in addition to methane. Since saturated C2+ hydrocarbons are more reactive than methane, side reactions such as thermal decomposition and polymerization of saturated C2+ hydrocarbons may occur at temperatures required for the direct cracking reaction of methane, which may result in, for example, pipe blockage. When a feed gas containing saturated C2+ hydrocarbons is used as a feed for the direct cracking reaction of hydrocarbons, it is necessary to remove the saturated C2+ hydrocarbons from the feed gas in order to suppress such risks.

[0007] Taking ethane, propane, and butane as examples of saturated hydrocarbons C2+, as shown in the following reaction formulas (1) to (3), each saturated hydrocarbon C2+ reacts with hydrogen to convert each saturated hydrocarbon C2+ into methane, thereby enabling removal from the raw material gas. Generally, the synthesis of methane from hydrogen and carbon dioxide is often called methanation, but in this disclosure, the reaction in which saturated hydrocarbons C2+ react with hydrogen to convert saturated hydrocarbons C2+ into methane, as shown in reaction formulas (1) to (3), is defined as "methanation." C ２ H ６ +H ２ →2CH ４ ... (1) C ３ H ８ +2H ２ →3CH ４ ... (2) C ４ H １０ +3H ２ →4CH ４ ...(3)

[0008] Patent No. 7089235

[0009] However, depending on the temperature conditions of methanation, there is a possibility that methane contained in the feed gas or a portion of the converted methane may be directly decomposed into hydrogen and carbon. In this case, carbon may adhere to the methanation catalyst, deteriorating the methanation catalyst and reducing methanation activity, which may result in a decrease in the ability to remove saturated hydrocarbons (C2+) from the feed gas.

[0010] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a methanation device, a methanation method, a direct cracking device for hydrocarbons, and a direct cracking method for hydrocarbons that can suppress deterioration of a methanation catalyst.

[0011] In order to achieve the above-mentioned object, the methanation device according to the present disclosure is a methanation device that removes saturated hydrocarbons C2+ from a feed gas containing methane and the saturated hydrocarbons C2+ by methanation, in which saturated hydrocarbons C2+ having two or more carbon atoms react with hydrogen to convert the saturated hydrocarbons C2+ to methane. The methanation device includes at least two catalyst layers composed of the methanation catalyst, the at least two catalyst layers being spaced apart in the flow direction of a mixed gas containing the feed gas and a hydrogen-containing gas; a hydrogen supply line for supplying the hydrogen-containing gas upstream of the most upstream catalyst layer in the flow direction of the mixed gas; a feed gas supply line for supplying the feed gas upstream of the most upstream catalyst layer in the flow direction of the mixed gas and between two adjacent catalyst layers in the flow direction of the mixed gas; and a cooler that is provided between the two adjacent catalyst layers in the flow direction of the mixed gas and that cools the mixed gas that has flowed out from the upstream catalyst layer of the two adjacent catalyst layers in the flow direction of the mixed gas.

[0012] a methanation method for removing saturated hydrocarbons C2+ having two or more carbon atoms from a feed gas containing methane and the saturated hydrocarbons C2+ by methanation, in which saturated hydrocarbons C2+ having two or more carbon atoms react with hydrogen to convert the saturated hydrocarbons C2+ to methane; the method includes the steps of: flowing the hydrogen-containing gas through at least two catalyst layers composed of the methanation catalyst, the at least two catalyst layers being spaced apart in a flow direction of a mixed gas containing the feed gas and a hydrogen-containing gas, the at least two catalyst layers being the most upstream catalyst layer; flowing a portion of the feed gas through the most upstream catalyst layer in the flow direction of the mixed gas; supplying the remainder of the feed gas between two adjacent catalyst layers in the flow direction of the mixed gas; cooling the mixed gas flowing out from the upstream catalyst layer of the two adjacent catalyst layers; and flowing the cooled mixed gas and the feed gas supplied between the two adjacent catalyst layers in the flow direction of the mixed gas through the downstream catalyst layer of the two adjacent catalyst layers.

[0013] According to the methanation apparatus and methanation method of the present disclosure, methanation in each catalyst layer increases the temperature of the mixed gas flowing through it, but by dividing the raw material gas and supplying it to each catalyst layer, methanation in each catalyst layer can be moderated, and furthermore, by cooling the mixed gas flowing out of each catalyst layer, the temperature of the mixed gas flowing into the adjacent catalyst layer in the mixed gas flow direction can be lowered. As a result, even if the temperature of the mixed gas increases due to methanation in each catalyst layer, it can be suppressed to a level that does not cause direct decomposition of methane, thereby suppressing carbon deposition on the methanation catalyst and, as a result, suppressing deterioration of the methanation catalyst.

[0014] 1 is a schematic diagram of a hydrocarbon direct cracking apparatus including a methanation device according to an embodiment of the present disclosure; FIG. 2 is a schematic diagram of a methanation device for simulation 1; FIG. 3 is a schematic diagram of a methanation device for simulation 2; and FIG. 4 is a schematic diagram of a methanation device for simulation 3.

[0015] Hereinafter, methanation devices and methanation methods according to embodiments of the present disclosure will be described with reference to the drawings. The embodiments described below illustrate one aspect of the present disclosure, but are not intended to limit the present disclosure and can be modified as desired within the scope of the technical concept of the present disclosure.

[0016] <Configuration of Methanation Device and Hydrocarbon Direct Cracking Device According to an Embodiment of the Present Disclosure> In the following embodiment, a methanation device according to an embodiment of the present disclosure will be described as one component of a hydrocarbon direct cracking device, but the present disclosure is not limited to this configuration and may be used as one component of any device or as a standalone device. As shown in FIG. 1 , a hydrocarbon direct cracking device 1 according to an embodiment of the present disclosure includes a methanation device 2 and a reactor 22. The methanation device 2 and the reactor 22 are connected by a treated gas supply line 5. The direct cracking device 1 may also include a gas chromatograph 16 for sampling a portion of the gas (the treated gas described below) flowing through the treated gas supply line 5 to measure the composition of the gas.

[0017] The methanation device 2 includes a housing 10, which houses a catalyst layer 11 made of a methanation catalyst and a cooler 13. The catalyst layer 11 includes two catalyst layers, i.e., a first catalyst layer 11a and a second catalyst layer 11b, spaced apart between both ends of the housing 10. As described below, gas flows through the housing 10 from one end to the other. The upstream catalyst layer in this gas flow direction is designated the first catalyst layer 11a, and the downstream catalyst layer is designated the second catalyst layer 11b. Any methanation catalyst can be used, including supported catalysts in which nickel, iron, cobalt, or a noble metal element is supported on alumina. The catalyst shape is not particularly limited, and any shape, such as tablet, ring, extruded, or granular pellet, can be used.

[0018] A space 12 is defined between the first catalyst layer 11a and the second catalyst layer 11b within the housing 10, and a cooler 13 is provided within the space 12. The configuration of the cooler 13 is not particularly limited, but the cooler 13 may, for example, have a configuration that cools the gas by heat exchange between the gas and any refrigerant.

[0019] In the configuration of FIG. 1, two catalyst layers (i.e., a first catalyst layer 11 a and a second catalyst layer 11 b) and one cooler 13 provided between them (i.e., in a space 12) are provided within a housing 10, but a configuration in which three or more catalyst layers, i.e., at least two catalyst layers, are provided may also be provided. In a configuration in which three or more catalyst layers are provided, a cooler 13 is provided in each of the spaces 12 between two catalyst layers adjacent to each other in the gas flow direction.

[0020] The methanation device 2 further includes a hydrogen supply line 3 for supplying a hydrogen-containing gas into the housing 10 and a feed gas supply line 4 for supplying a feed gas into the housing 10. The hydrogen supply line 3 is connected to the housing 10 upstream of the first catalyst layer 11a in the direction of gas flow within the housing 10. The hydrogen supply line 3 may be provided with a flow control valve 14 for adjusting the amount of hydrogen-containing gas supplied to the housing 10. The hydrogen-containing gas flowing through the hydrogen supply line 3 may be pure hydrogen gas or a mixed gas of hydrogen and components that do not contribute to methanation (rare gases, nitrogen, methane, etc.). The feed gas is a gas containing methane and saturated hydrocarbons (C2+) having two or more carbon atoms (ethane, propane, butane, etc.). For example, natural gas, compressed natural gas (CNG), city gas, liquefied petroleum gas, naphtha, etc. can be used as the feed gas. Therefore, the above-mentioned gas circulating within the housing 10 is a mixed gas containing a hydrogen-containing gas supplied into the housing 10 via the hydrogen supply line 3 and a raw material gas supplied into the housing 10 via the raw material gas supply line 4.

[0021] The raw material gas supply line 4 branches into branch lines 4a and 4b. One branch line 4a is connected to the casing 10 upstream of the first catalytic layer 11a in the flow direction of the mixed gas within the casing 10, and the other branch line 4b is connected to the casing 10 between the first catalytic layer 11a and the second catalytic layer 11b. The branch line 4a may be connected to the casing 10 without merging with the hydrogen supply line 3, or may merge with the hydrogen supply line 3 as shown in FIG. 1. The branch line 4b only needs to be connected to the casing 10 so as to communicate with the space 12. The raw material gas flowing into the space 12 via the branch line 4b may flow upstream of the cooler 13, downstream of the cooler 13, or into a region where the cooler 13 is provided. The branch lines 4a and 4b may be provided with flow control valves 15a and 15b, respectively, for adjusting the amount of raw material gas supplied into the casing 10 via the branch lines 4a and 4b. The hydrogen supply line 3 may have branch lines like the raw material gas supply line 4, and each of the branch lines of the hydrogen supply line 3 may be connected to the housing 10 upstream of the first catalytic layer 11a and between the first catalytic layer 11a and the second catalytic layer 11b.

[0022] A catalyst 20 for the direct cracking reaction of hydrocarbons is accommodated within the reactor 22. The reactor 22 is provided with a heating device 21 (for example, a jacket through which steam flows) for raising the temperature of the inside of the reactor 22, particularly the catalyst 20. A product gas distribution line 6 is connected to the reactor 22 on the opposite side of the catalyst 20 from the position where the treated gas supply line 5 connects to the reactor 22.

[0023] The catalyst 20 is not particularly limited, and may be, for example, an unsupported catalyst consisting of an aggregate of multiple iron particles. Within the reactor 22, the catalyst 20 particles may be stationary, or the particles may be suspended in the raw material gas by ejecting the treated gas described below upward, forming a fluidized bed. When hydrocarbons react with the catalyst 20, carbon and hydrogen are produced, and the carbon adheres to the catalyst 20 particles. When the catalyst 20 forms a fluidized bed, the particles of the catalyst 20 rub against each other, physically removing the carbon adhered to the catalyst 20 particles. When a fixed-bed reactor, for example, is used as the reactor 22, a carbon removal device may be provided outside the reactor 22 to remove the carbon adhered to the catalyst 20 from the catalyst 20.

[0024] The direct cracking apparatus 1 may further include a hydrogen recycle line 7 that connects the product gas distribution line 6 with the hydrogen supply line 3. The hydrogen recycle line 7 may be provided with a valve 8, which may be either an on-off valve or a flow rate control valve.

[0025] <Operation of the methanation device according to an embodiment of the present disclosure> Next, the operation (methanation method) of the methanation device according to an embodiment of the present disclosure will be described. Hydrogen-containing gas flows into the casing 10 upstream of the first catalytic layer 11a via the hydrogen supply line 3. A portion of the raw material gas flowing through the raw material gas supply line 4 flows into the casing 10 upstream of the first catalytic layer 11a via the branch line 4a.

[0026] The hydrogen-containing gas and the feed gas that have flowed into the casing 10 upstream of the first catalytic layer 11a flow into the first catalytic layer 11a. In the first catalytic layer 11a, the saturated C2+ hydrocarbons in the feed gas react with the hydrogen in the hydrogen-containing gas due to the action of the methanation catalyst to produce methane, and a mixed gas containing methane, unreacted C2+ saturated hydrocarbons, and unreacted hydrogen flows out of the first catalytic layer 11a and into the space 12. Although the temperature of the mixed gas rises due to the reaction heat from this methanation, the above-described operation makes the methanation in the first catalytic layer 11a more moderate (the amount of methanation reaction is reduced) compared to when the entire amount of feed gas flowing through the feed gas supply line 4 is supplied into the casing 10 upstream of the first catalytic layer 11a, thereby suppressing the temperature rise of the mixed gas flowing out of the first catalytic layer 11a.

[0027] 1 , the catalyst layer 11 is divided into two and the feed gas is supplied in two separate streams, but increasing the number of catalyst layers 11 (i.e., the number of feed gas streams) reduces the flow rate of the feed gas flowing through the first catalyst layer 11a, making methanation in the first catalyst layer 11a more gentle and further suppressing the temperature rise of the mixed gas flowing out of the first catalyst layer 11a. If the temperature rise of the mixed gas flowing out of the first catalyst layer 11a can be suppressed to a level that does not cause direct decomposition of methane, the direct decomposition reaction of methane in the first catalyst layer 11a can be suppressed, and carbon deposition on the methanation catalyst constituting the first catalyst layer 11a can be suppressed, thereby suppressing deterioration of the methanation catalyst.

[0028] The mixed gas flowing into the space 12 is cooled by heat exchange with the refrigerant circulating through the cooler 13. The cooled mixed gas and the feed gas flowing through the branch line 4b flow into the second catalyst layer 11b. In the second catalyst layer 11b, saturated hydrocarbons C2+ react with hydrogen to produce methane, based on the same principle as in the first catalyst layer 11a. Because the mixed gas cooled by the cooler 13 flows into the second catalyst layer 11b, even if the temperature of the mixed gas in the second catalyst layer 11b increases due to methanation, the temperature of the mixed gas can be suppressed to a level at which direct decomposition of methane does not occur. As a result, the direct decomposition reaction of methane can be suppressed in the second catalyst layer 11b, and carbon deposition on the methanation catalyst constituting the second catalyst layer 11b can be suppressed, thereby suppressing deterioration of the methanation catalyst.

[0029] According to this methanation method, the temperature of the mixed gas flowing through each of the first and second catalytic layers 11a and 11b increases due to methanation in each of the first and second catalytic layers 11a and 11b. However, by supplying the feed gas to each of the first and second catalytic layers 11a and 11b separately, methanation in each of the first and second catalytic layers 11a and 11b can be moderated. Furthermore, by cooling the mixed gas flowing out of the first catalytic layer 11a, the temperature of the mixed gas flowing into the adjacent second catalytic layer 11b in the direction of flow of the mixed gas can be lowered. As a result, even if the temperature of the mixed gas increases due to methanation in each of the first and second catalytic layers 11a and 11b, it can be suppressed to a level that does not cause direct decomposition of methane. This suppresses carbon deposition on the methanation catalyst, thereby suppressing deterioration of the methanation catalyst.

[0030] In this methanation method, because the feed gas is supplied in separate portions via the branch lines 4a and 4b, the flow rate of the mixed gas flowing through the second catalytic layer 11b is greater than the flow rate of the mixed gas flowing through the first catalytic layer 11a. Therefore, it is preferable to use a larger amount of catalyst in the second catalytic layer 11b than in the first catalytic layer 11a. This allows the amounts of catalyst in the first catalytic layer 11a and the second catalytic layer 11b to be adjusted appropriately according to the amounts of mixed gas flowing through the first catalytic layer 11a and the second catalytic layer 11b, respectively, allowing methanation to be performed under appropriate conditions in each of the first catalytic layer 11a and the second catalytic layer 11b. When the catalytic layer 11 is composed of three or more catalytic layers, the amount of catalyst in each catalytic layer may be increased toward the downstream side in the mixed gas flow direction.

[0031] In this methanation method, when the hydrogen-containing gas contains components that do not contribute to methanation, the concentrations of hydrogen and saturated hydrocarbons (C2+) in each catalyst layer are lower than when the hydrogen-containing gas contains only hydrogen. This suppresses the temperature rise of the mixed gas due to heat generated during methanation in each catalyst layer, thereby enabling gentle methanation in each catalyst layer. As a result, the temperature rise of the mixed gas in each catalyst layer can be suppressed to a level that does not cause direct decomposition of methane, thereby suppressing carbon deposition on the methanation catalyst and suppressing deterioration of the methanation catalyst.

[0032] In such a methanation method, it is preferable to adjust the supply amount of the hydrogen-containing gas so that the concentration ratio of hydrogen to saturated hydrocarbons C2+ in the mixed gas is 1 or more. In order to convert ethane, which has the smallest carbon number among the saturated hydrocarbons C2+, into methane, one molecule of hydrogen is required per molecule of ethane. Therefore, by adjusting the conditions in this way, the saturated hydrocarbons C2+ in the feed gas can be stoichiometrically converted into methane.

[0033] In a configuration equipped with a gas chromatograph 16 and a flow control valve 14, a decrease in methanation activity in the methanation device 2 can be detected from the measurement results of the gas chromatograph 16. When a decrease in methanation activity is detected, the supply rate of the hydrogen-containing gas can be increased by the flow control valve 14. Increasing the supply rate of the hydrogen-containing gas increases the hydrogen concentration in the mixed gas. This facilitates the reaction of carbon, polymerization products, and the like attached to the methanation catalyst with hydrogen, converting the attached carbon, polymerization products, and the like into gases such as methane, thereby removing the deposits from the catalyst. In other words, this can prevent the methanation catalyst from being deteriorated by products generated by side reactions such as the thermal decomposition and polymerization of saturated hydrocarbons (C2+), or it can regenerate a deteriorated catalyst.

[0034] If the raw material gas contains sulfur, the sulfur may deteriorate the methanation catalyst. Therefore, it is preferable to provide a desulfurization device in the raw material gas supply line 4 to remove sulfur from the raw material gas before it flows into the casing 10.

[0035] <Operation of the hydrocarbon direct cracking device according to an embodiment of the present disclosure> Next, the operation of the hydrocarbon direct cracking device according to an embodiment of the present disclosure (hydrocarbon direct cracking method) will be described. The mixed gas flowing out from the second catalyst layer 11b flows out of the housing 10, flows as treated gas through the treated gas supply line 5, and flows into the reactor 22. The treated gas that flows into the reactor 22 passes through the catalyst 20 while coming into contact with the catalyst 20. At this time, the hydrocarbons in the treated gas are directly cracked into hydrogen and carbon. Taking methane as an example of the hydrocarbon in this direct cracking reaction, the reaction represented by the following reaction formula (4) occurs in the reactor 22. CH ４ →2H ２ + C ... (4)

[0036] Carbon produced by the direct cracking method adheres to the catalyst 20, and the produced hydrogen flows out of the reactor 22 as a product gas together with unreacted hydrocarbons and circulates through the product gas distribution line 6. Carbon can be recovered by stopping the supply of treated gas to the reactor 22, recovering the catalyst 20 from the reactor 22, and, if necessary, removing the carbon adhered to the catalyst 20 using a carbon remover. Hydrogen can be recovered by recovering the reaction gas circulating through the product gas distribution line 6. Hydrogen can be purified by providing a hydrogen purification unit in the product gas distribution line 6. In this case, when the hydrocarbon conversion rate is low, the hydrogen concentration in the treated gas will be low, but the hydrogen purification unit can increase the hydrogen concentration in the final product.

[0037] If the treated gas contains saturated C2+ hydrocarbons such as ethane and propane in addition to methane as hydrocarbons, for example, ethane and propane are also directly decomposed into hydrogen and carbon as shown in the following reaction formulas (5) and (6). However, at the temperature (preferably 600°C to 900°C) required for the direct decomposition reaction of methane, side reactions such as thermal decomposition of saturated C2+ hydrocarbons and accompanying polymerization reactions (tar formation) may also occur, and these side reactions may cause, for example, blockage of pipes. ２ H ６ →2C+3H ２ ... (5) C ３ H ８ →3C+4H ２ ...(6)

[0038] However, in a method for direct cracking of hydrocarbons according to an embodiment of the present disclosure, treated gas, from which at least a portion of the saturated C2+ hydrocarbons have been removed by converting them to methane in the feed gas in the methanation device 2, is used as the feed gas for the direct cracking reaction. That is, the concentration of saturated C2+ hydrocarbons in the treated gas used as the feed gas for the direct cracking reaction is lower than in the initial feed gas supplied to the methanation device 2. Therefore, compared to using the initial feed gas supplied to the methanation device 2 as the feed gas for the direct cracking reaction, the method for direct cracking of hydrocarbons according to an embodiment of the present disclosure can suppress side reactions such as polymerization reactions (tar production) associated with the thermal cracking of saturated C2+ hydrocarbons, thereby reducing the risk of pipe blockages and the like.

[0039] When the hydrogen recycle line 7 is provided, at least a portion of the product gas is supplied to the hydrogen supply line 3, and the hydrogen-containing gas flowing through the hydrogen supply line 3 flows into the casing 10 upstream of the first catalyst layer 11a together with the product gas. That is, at least a portion of the product gas can be used as at least a portion of the hydrogen-containing gas. This allows the amount of hydrogen supplied to the direct cracking apparatus 1 to be reduced, thereby reducing the operating cost of the direct cracking apparatus 1.

[0040] If the hydrogen recycle line 7 is provided with an on-off valve 8, the entire amount of the product gas can be transferred to a storage unit or hydrogen consumption facility (not shown) without using the product gas as at least a part of the hydrogen-containing gas by closing the valve 8. If the valve 8 is a flow control valve, the amount of the product gas used as at least a part of the hydrogen-containing gas can be adjusted.

[0041] <Simulation for verifying the effects of the methanation method of the present disclosure> Next, a simulation performed to verify the effects of the methanation method of the present disclosure will be described. According to studies by the inventors of the present disclosure, the preferred temperature range for the above-mentioned methanation is 250°C to 360°C, while the preferred temperature range for the direct decomposition reaction of methane is 600°C to 900°C, as mentioned above. Therefore, in the methanation method of the present disclosure, it is believed that the above-mentioned effects can be appropriately achieved if the temperature of the mixed gas flowing out from each catalyst layer can be controlled to 360°C or less.

[0042] (Simulation 1) As shown in Figure 2, a simulation was performed on a methanation apparatus configured such that five catalyst layers, I to V, were installed in a housing, the feed gas was divided and supplied to each catalyst layer as indicated by (1) to (5), and hydrogen gas was supplied upstream of the most upstream catalyst layer I. The feed gas had a composition of 89 vol% methane, 6 vol% ethane, 4 vol% propane, and 1 vol% butane. When the saturated C2+ hydrocarbons (ethane, propane, and butane) in this feed gas were converted to methane by methanation across all catalyst layers I to V, the adiabatic rise in temperature was approximately 180°C. In Simulation 1, the ratio of the hydrogen concentration to the saturated C2+ hydrocarbon concentration was set to 1.5, and the conditions for each gas flowing into each catalyst layer were calculated so that the adiabatic rise in temperature in each of catalyst layers I to V was 60°C. At this time, the mixed gas, whose temperature has risen due to heat generated during the methanation, is cooled by heat exchange with a refrigerant in the cooler between adjacent catalyst layers, resulting in a temperature drop of 60° C. The results are shown in Table 1 below.

[0043]

[0044] According to Table 1, the supply amounts of the raw material gases (1) to (5) are: (1) 110 Nm ３ / hr, (2) 150Nm ３ / hr, (3) 210Nm ３ / hr, (4) 290Nm ３ / hr, (5) 394Nm ３ / hr, the temperature of the mixed gas flowing out from each catalyst layer can be controlled to 360° C. or less.

[0045] (Simulation 2) As shown in Figure 3, a simulation was performed using a methanation apparatus configured such that two catalyst layers, catalyst layers I and II, were provided in a housing, the feed gas was divided and supplied to each catalyst layer as shown in (1) and (2), and hydrogen gas was supplied upstream of the most upstream catalyst layer I. In Simulation 2, it was assumed that the hydrogen-containing gas contained components that did not contribute to methanation, and 1121 Nm ３ / hr. In Simulation 2, the adiabatic rise in temperature when saturated C2+ hydrocarbons in a feed gas with the same composition as in Simulation 1 are converted to methane by methanation across catalyst layers I and II is approximately 100°C. In Simulation 2, as in Simulation 1, the ratio of hydrogen concentration to saturated C2+ hydrocarbon concentration was set to 1.5, and the conditions for each gas flowing into each catalyst layer were calculated so that the adiabatic rise in temperature in each of catalyst layers I and II would be 60°C. In this case, the mixed gas of feed gas and hydrogen gas is cooled between catalyst layers I and II by heat exchange with a refrigerant in a cooler, resulting in a temperature drop of 60°C. The results are shown in Table 2 below. The hydrogen supply rate in Table 2 is a flow rate excluding the methane supply rate.

[0046]

[0047] According to Table 2, the supply amounts of the raw material gases (1) and (2) are: (1) 463 Nm ３ / hr, (2) 693Nm ３ / hr, the temperature of the mixed gas flowing out from each catalyst layer can be controlled to 360° C. or less.

[0048] (Simulation 3) As shown in Figure 4, a simulation was performed using a methanation apparatus configured such that three catalyst layers, catalyst layers I to III, were provided in a housing, the feed gas was divided and supplied to each catalyst layer as indicated by (1) to (3), and hydrogen gas was supplied upstream of the most upstream catalyst layer I. In Simulation 3, as in Simulation 2, a case was assumed in which the hydrogen-containing gas contained components that did not contribute to methanation, and 720 Nm3 of hydrogen was added to the hydrogen gas supplied upstream of catalyst layer I. ３ / hr. In Simulation 2, the adiabatic rise in temperature when saturated C2+ hydrocarbons in a feed gas with the same composition as in Simulation 1 are converted to methane by methanation across all of the catalyst layers I to III is approximately 120°C. In Simulation 3, the ratio of the hydrogen concentration to the saturated C2+ hydrocarbon concentration is set to 1.5, and the conditions for each gas flowing into each catalyst layer are calculated so that the adiabatic rise in temperature in each of the catalyst layers I to III is 60°C or less. In this case, the mixed gas of the feed gas and hydrogen gas is cooled between adjacent catalyst layers by heat exchange with a refrigerant in a cooler, resulting in a temperature drop of 60°C. The results are shown in Table 3 below. The hydrogen supply rate in Table 3 is a flow rate excluding the methane supply rate.

[0049]

[0050] According to Table 3, the supply amounts of the raw material gases (1) to (3) are: (1) 254 Nm ３ / hr, (2) 391Nm ３ / hr, (3)509Nm ３ / hr, the temperature of the mixed gas flowing out from each catalyst layer can be controlled to 360° C. or less.

[0051] Simulations 1 to 3 show that by dividing a catalyst layer made of a methanation catalyst into multiple layers, supplying the raw material gas to each catalyst layer in separate portions, and cooling the mixed gas flowing out of each catalyst layer with a cooler, even if the temperature of the mixed gas increases due to methanation in each catalyst layer, the increase can be suppressed to a level that does not cause direct decomposition of methane.

[0052] The contents described in each of the above embodiments can be understood, for example, as follows.

[0053] [1] A methanation device according to one embodiment is a methanation device (2) for removing saturated hydrocarbons C2+ from a feed gas containing methane and the saturated hydrocarbons C2+ by methanation, in which saturated hydrocarbons C2+ having two or more carbon atoms react with hydrogen to convert the saturated hydrocarbons C2+ to methane, the methanation device (2) comprising at least two catalyst layers (11a, 11b) made of a catalyst for methanation, the at least two catalyst layers (11a, 11b) being spaced apart in a flow direction of a mixed gas containing the feed gas and a hydrogen-containing gas; a hydrogen supply line (3) for supplying the hydrogen-containing gas upstream of the most upstream catalyst layer (11a) in the flow direction of the mixed gas; and a feed gas supply line (4) for supplying the feed gas upstream of the most upstream catalyst layer (11a) in the flow direction of the mixed gas and between two adjacent catalyst layers (11a, 11b) in the flow direction of the mixed gas, respectively. a cooler (13) provided between two adjacent catalyst layers (11a, 11b) in the direction of flow of the mixed gas, for cooling the mixed gas that has flowed out from the catalyst layer (11a) on the upstream side of the two adjacent catalyst layers (11a, 11b) in the direction of flow of the mixed gas.

[0054] According to the methanation apparatus of the present disclosure, methanation in each catalyst layer increases the temperature of the mixed gas flowing through it, but by dividing the raw material gas and supplying it to each catalyst layer, methanation in each catalyst layer can be moderated, and furthermore, by cooling the mixed gas flowing out of each catalyst layer, the temperature of the mixed gas flowing into the adjacent catalyst layer in the mixed gas flow direction can be lowered. As a result, even if the temperature of the mixed gas increases due to methanation in each catalyst layer, it can be suppressed to a level that does not cause direct decomposition of methane, thereby suppressing carbon deposition on the methanation catalyst and, as a result, suppressing deterioration of the methanation catalyst.

[0055] [2] A methanation device according to another aspect is the methanation device of [1], wherein the amount of catalyst constituting each of the at least two catalyst layers (11a, 11b) is greater in the catalyst layer (11b) located downstream in the flow direction of the mixed gas.

[0056] According to the configuration [1] above, by dividing the raw material gas and supplying it to each catalyst layer, the amount of mixed gas flowing through the catalyst layer on the downstream side increases. Therefore, according to the configuration, the amount of catalyst in each catalyst layer can be adjusted to an appropriate amount according to the amount of mixed gas flowing through each catalyst layer, and methanation can be carried out in each catalyst layer under appropriate conditions.

[0057] [3] A methanation device according to yet another embodiment is the methanation device according to [1] or [2], wherein the catalyst is a supported catalyst in which nickel, iron, cobalt, or a metal element is supported on alumina.

[0058] With this configuration, methanation can be carried out appropriately in each catalyst layer.

[0059] [4] An apparatus for direct cracking of hydrocarbons according to one embodiment includes the methanation apparatus according to any one of [1] to [3], a reactor (22) containing a catalyst (20) for a direct cracking reaction of hydrocarbons, and a treated gas supply line (5) for supplying treated gas, which is a gas flowing out from the methanation apparatus (2), to the reactor (22).

[0060] According to the direct hydrocarbon cracking apparatus disclosed herein, the content of saturated hydrocarbons C2+ in the treated gas is reduced compared to the raw gas, thereby suppressing risks associated with side reactions such as thermal cracking and polymerization reactions of saturated hydrocarbons C2+.

[0061] [5] Another embodiment of the direct cracking apparatus for hydrocarbons is the direct cracking apparatus for hydrocarbons according to [4], further comprising: a product gas distribution line (6) through which a product gas containing hydrogen produced by the direct cracking of hydrocarbons in the reactor (22) flows after flowing out of the reactor; and a hydrogen recycle line (7) communicating between the product gas distribution line (6) and the hydrogen supply line (3).

[0062] According to this configuration, at least a portion of the hydrogen in the product gas is used as at least a portion of the hydrogen supplied to the methanation unit, so the amount of hydrogen supplied to the direct cracking unit can be reduced, and as a result, the operating costs of the hydrocarbon direct cracking unit can be reduced.

[0063] [6] A methanation method according to one aspect is a methanation method for removing saturated hydrocarbons C2+ from a feed gas containing methane and the saturated hydrocarbons C2+ by methanation, in which saturated hydrocarbons C2+ having two or more carbon atoms react with hydrogen to convert the saturated hydrocarbons C2+ to methane, the method comprising the steps of: flowing the hydrogen-containing gas through the most upstream catalyst layer (11a) of at least two catalyst layers (11a, 11b) composed of the methanation catalyst, the at least two catalyst layers (11a, 11b) being spaced apart in a flow direction of a mixed gas containing the feed gas and a hydrogen-containing gas; flowing a part of the feed gas through the most upstream catalyst layer (11a) in the flow direction of the mixed gas; and supplying the remainder of the feed gas between the two catalyst layers (11a, 11b) adjacent to each other in the flow direction of the mixed gas. The method includes the steps of: cooling the mixed gas flowing out from the upstream catalyst layer (11a) of the two adjacent catalyst layers (11a, 11b); and circulating the cooled mixed gas and the raw material gas supplied between the two adjacent catalyst layers (11a, 11b) in the flow direction of the mixed gas through the downstream catalyst layer (11b) of the two adjacent catalyst layers (11a, 11b).

[0064] According to the methanation method of the present disclosure, methanation in each catalyst layer increases the temperature of the mixed gas flowing through it, but by dividing the raw material gas and supplying it to each catalyst layer, methanation in each catalyst layer can be moderated, and furthermore, by cooling the mixed gas flowing out of each catalyst layer, the temperature of the mixed gas flowing into the adjacent catalyst layer in the direction of mixed gas flow can be lowered. As a result, even if the temperature of the mixed gas increases due to methanation in each catalyst layer, it can be suppressed to a level that does not cause direct decomposition of methane, thereby suppressing carbon deposition on the methanation catalyst and, as a result, suppressing deterioration of the methanation catalyst.

[0065] [7] A methanation method according to another aspect is the methanation method according to [6], wherein the supply amount of the hydrogen-containing gas is adjusted so that the concentration ratio of hydrogen to the saturated hydrocarbons C2+ in the mixed gas is 1 or more.

[0066] In order to convert ethane, which has the smallest carbon number among the saturated hydrocarbons C2+, into methane, one molecule of hydrogen is required for one molecule of ethane. Therefore, according to this method, the saturated hydrocarbons C2+ in the feed gas can be converted stoichiometrically into methane.

[0067] [8] A methanation method according to yet another embodiment is the methanation method according to [6] or [7], wherein the hydrogen-containing gas contains hydrogen and a component that does not contribute to the methanation.

[0068] According to this method, the concentrations of hydrogen and saturated hydrocarbons (C2+) in each catalyst layer are lower than when only hydrogen is supplied, and therefore the temperature rise of the mixed gas due to heat generated during methanation in each catalyst layer is suppressed, thereby enabling the methanation in each catalyst layer to be gentle. As a result, the temperature rise of the mixed gas in each catalyst layer can be suppressed to a level that does not cause direct decomposition of methane, thereby suppressing the deposition of carbon on the methanation catalyst and the deterioration of the methanation catalyst.

[0069] [9] A methanation method according to yet another aspect is the methanation method according to any one of [6] to [8], comprising: a step of detecting a decrease in the activity of the methanation; and a step of increasing the supply amount of the hydrogen-containing gas when the decrease in activity is detected.

[0070] According to this method, it is possible to prevent the methanation catalyst from being deteriorated by products produced by side reactions such as thermal decomposition and polymerization of saturated hydrocarbons C2+, or to regenerate a deteriorated catalyst.

[0071]

[10] A methanation method according to yet another embodiment is the methanation method according to any one of [6] to [9], wherein the feed gas is natural gas, compressed natural gas, city gas, liquefied petroleum gas, or naphtha.

[0072] According to this method, a generally available hydrocarbon gas can be used as the source gas without separately preparing the source gas.

[0073]

[11] A method for direct cracking of hydrocarbons according to one embodiment includes the steps of converting the saturated C2+ hydrocarbons in the raw material gas into methane by the methanation method according to any one of [6] to

[10] , and bringing a treated gas, which is a gas obtained after converting the saturated C2+ hydrocarbons into methane, into contact with a catalyst (20) for direct cracking of hydrocarbons, thereby directly cracking the methane in the treated gas into hydrogen and carbon.

[0074] According to the direct cracking method for hydrocarbons disclosed herein, the content of saturated C2+ hydrocarbons in the treated gas is reduced compared to the feed gas, thereby suppressing risks associated with side reactions such as thermal cracking and polymerization reactions of saturated C2+ hydrocarbons.

[0075]

[12] Another embodiment of the method for direct cracking of hydrocarbons is the method for direct cracking of hydrocarbons according to

[11] , wherein at least a portion of a hydrogen-containing product gas produced by directly cracking methane in the treated gas into hydrogen and carbon is used as at least a portion of the hydrogen-containing gas to be supplied to the most upstream catalyst layer (11a) of at least two catalyst layers (11a, 11b) spaced apart in the flow direction of the mixed gas.

[0076] According to this method, at least a portion of the hydrogen in the product gas is used as at least a portion of the hydrogen used in the methanation method, so the amount of hydrogen used in the methanation method can be reduced, and as a result, the operating costs of the hydrocarbon direct cracking unit can be reduced.

[0077] REFERENCE SIGNS LIST 1 Direct decomposition unit 2 Methanation unit 3 Hydrogen supply line 4 Raw material gas supply line 5 Treated gas supply line 6 Product gas distribution line 7 Hydrogen recycle line 11a First catalyst layer (catalyst layer) 11b Second catalyst layer (catalyst layer) 13 Cooler 20 Catalyst 22 Reactor

Claims

1. A methanation apparatus for removing a saturated hydrocarbon from a raw material gas containing methane and the saturated hydrocarbon by methanation in which a saturated hydrocarbon having two or more carbon atoms reacts with hydrogen to convert the saturated hydrocarbon to methane, at least two catalyst layers composed of the catalyst for methanation, at least two catalyst layers provided at intervals in the flow direction of a mixed gas containing the raw material gas and a hydrogen-containing gas; a hydrogen supply line for supplying the hydrogen-containing gas upstream of the catalyst layer on the most upstream side in the flow direction of the mixed gas; a raw material gas supply line for supplying the raw material gas to each of upstream of the catalyst layer on the most upstream side in the flow direction of the mixed gas and between two adjacent catalyst layers in the flow direction of the mixed gas; a cooler provided between two adjacent catalyst layers in the flow direction of the mixed gas, for cooling the mixed gas flowing out from the catalyst layer on the upstream side in the flow direction of the two adjacent catalyst layers.

2. The methanation apparatus according to claim 1, wherein the amount of the catalyst constituting each of the at least two catalyst layers increases toward the catalyst layer on the downstream side in the flow direction of the mixed gas.

3. The methanation apparatus according to claim 1 or 2, wherein the catalyst is a supported catalyst in which nickel, iron, cobalt, or a noble metal element is supported on alumina.

4. A hydrocarbon direct decomposition apparatus comprising: the methanation apparatus according to claim 1 or 2; a reactor containing a catalyst for the direct decomposition reaction of a hydrocarbon; a treated gas supply line for supplying a treated gas, which is a gas flowing out from the methanation apparatus, to the reactor.

5. The hydrocarbon direct decomposition apparatus according to claim 4, further comprising: a product gas flow line through which a product gas containing hydrogen generated by direct decomposition of a hydrocarbon in the reactor flows after flowing out of the reactor; a hydrogen recycle line communicating the product gas flow line and the hydrogen supply line.

6. A method for removing a saturated hydrocarbon from a raw material gas containing methane and the saturated hydrocarbon by methanation in which a saturated hydrocarbon having two or more carbon atoms reacts with hydrogen to convert the saturated hydrocarbon into methane, the method comprising: flowing the hydrogen-containing gas through the catalyst layer on the most upstream side among at least two catalyst layers spaced apart in the flow direction of a mixed gas containing the raw material gas and the hydrogen-containing gas, the at least two catalyst layers being composed of the catalyst for methanation; flowing a part of the raw material gas through the catalyst layer on the most upstream side in the flow direction of the mixed gas; supplying the remainder of the raw material gas between two adjacent catalyst layers in the flow direction of the mixed gas; cooling the mixed gas flowing out from the catalyst layer on the upstream side among the two adjacent catalyst layers; and flowing the cooled mixed gas and the raw material gas supplied between two adjacent catalyst layers in the flow direction of the mixed gas through the catalyst layer on the downstream side among the two adjacent catalyst layers.

7. The methanation method according to claim 6, wherein the supply amount of the hydrogen-containing gas is adjusted so that the concentration ratio of hydrogen to the saturated hydrocarbon in the mixed gas is 1 or more.

8. The methanation method according to claim 6 or 7, wherein the hydrogen-containing gas contains a component that does not contribute to the methanation and hydrogen.

9. The methanation method according to claim 6 or 7, comprising detecting a decrease in the activity of the methanation and increasing the supply amount of the hydrogen-containing gas when the decrease in the activity is detected.

10. The methanation method according to claim 6 or 7, wherein the raw material gas is natural gas, compressed natural gas, town gas, liquefied petroleum gas, or naphtha.

11. A method for direct decomposition of hydrocarbons, comprising converting the saturated hydrocarbon in the raw material gas into methane by the methanation method according to claim 6 or 7, and directly decomposing methane in the treated gas into hydrogen and carbon by bringing the treated gas, which is the gas after the conversion of the saturated hydrocarbon into methane, into contact with a catalyst for direct decomposition reaction of hydrocarbons.

12. The method for direct decomposition of hydrocarbons according to claim 11, wherein at least a part of the product gas containing hydrogen generated by directly decomposing methane in the treated gas into hydrogen and carbon is used as at least a part of the hydrogen-containing gas supplied to the catalyst layer on the most upstream side among at least two catalyst layers provided at intervals in the flow direction of the mixed gas.

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