Gas separation system

Abstract

A gas separation system (1) is a separation system for separating N2 from a mixed gas containing H2O, NH3, CO2, CH4, and N2. The gas separation system (1) includes: a second separation membrane (20); and a third separation membrane (30) disposed on a downstream side of the second separation membrane (20). The second separation membrane (20) generates a second enriched gas in which NH3 is enriched and a second depleted gas in which NH3 is depleted and CO2, CH4, and N2 are enriched by separating NH3. The third separation membrane (30) is configured to selectively transmit N2 as compared with CH4.

Description

Technical Field

[0001] This invention relates to gas separation systems. Background Technology

[0002] Previously, cryogenic separation (e.g., Patent Document 1) was known as a method for separating nitrogen contained in a gas mixture.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-152360 Summary of the Invention

[0006] However, cryogenic separation requires large-scale equipment and has high operating costs. In particular, it is known that the cost is too high if cryogenic separation is used in smaller-scale separation equipment (e.g., LOKHANDWALA, Kaaeid A., et al. Membrane separation of nitrogen from natural gas: A case study from membrane synthesis to commercial deployment. Journal of Membrane Science, 2010, 346.2:270-279.).

[0007] The purpose of this invention is to provide a gas separation system that can efficiently separate nitrogen.

[0008] The first aspect of the present invention relates to a gas separation system that separates nitrogen from a mixture of nitrogen and a first gas and a second gas different from nitrogen. The gas separation system comprises: a separation body; and a nitrogen separation membrane disposed downstream of the separation body. The separation body generates a gas enriched with the first gas and a gas depleted of the first gas and enriched with nitrogen and the second gas by separating the first gas. The nitrogen separation membrane is configured such that nitrogen can selectively permeate compared to the second gas.

[0009] The gas separation system involved in the second aspect of the present invention is based on the first aspect described above, wherein the separator is a gas separation membrane that allows the first gas to selectively permeate.

[0010] The gas separation system involved in the third aspect of the present invention is based on the above-described third aspect, but the composition of the gas separation membrane is different from that of the nitrogen separation membrane.

[0011] The gas separation system of the fourth aspect of the present invention is based on any one of the first to third aspects described above, wherein the nitrogen partial pressure in the gas supplied to the nitrogen separation membrane is higher than the nitrogen partial pressure in the mixed gas.

[0012] Invention Effects

[0013] According to the present invention, a gas separation system capable of efficiently separating nitrogen can be provided. Attached Figure Description

[0014] Figure 1 This is a schematic diagram showing the configuration of the gas separation system according to the first embodiment.

[0015] Figure 2 This is a schematic diagram showing the configuration of the gas separation system according to the second embodiment.

[0016] Figure 3 This is a schematic diagram showing the configuration of the gas separation system according to the third embodiment. Detailed Implementation

[0017] 1. First Implementation Method

[0018] (Gas separation system 1)

[0019] Figure 1 This is a schematic diagram showing the configuration of the gas separation system 1 according to the first embodiment.

[0020] The gas separation system 1 includes: a methanation reactor 5, a first separation membrane 10, a second separation membrane 20, and a third separation membrane 30.

[0021] [Methanation Reactor 5]

[0022] The methanation reactor 5 is located upstream of the first separation membrane 10. The methanation reactor 5 synthesizes CH4 (methane) from CO2 (carbon dioxide) and H2 (hydrogen), thereby generating a mixed gas.

[0023] As a source of H2, for example, the decomposition gas of NH3 can be utilized. Therefore, the mixed gas generated by the methanation reactor 5 may contain undecomposed NH3, unreacted CO2, and H2O (water vapor) or N2 (nitrogen) as byproducts, in addition to CH4.

[0024] In this embodiment, NH3 is an example of a "first gas different from N2" involved in the present invention, and CH4 is an example of a "second gas different from N2" involved in the present invention.

[0025] H₂O and NH₃ are polar gases. The dynamic molecular diameter of H₂O is 0.265 nm. The dynamic molecular diameter of NH₃ is 0.26 nm. N₂, CO₂, and CH₄ are nonpolar gases. The dynamic molecular diameter of N₂ is 0.364 nm. The dynamic molecular diameter of CO₂ is 0.33 nm. The dynamic molecular diameter of CH₄ is ​​0.38 nm.

[0026] Thus, the mixed gas involved in this embodiment includes two polar gases (NH3 and H2O) and three non-polar gases (N2, CO2 and CH4).

[0027] Polar gases are gases composed of polar molecules. That is, polar gases are gases whose constituent molecules have an electric dipole moment. Nonpolar gases are gases composed of nonpolar molecules. That is, nonpolar gases are gases whose constituent molecules do not have an electric dipole moment.

[0028] It should be noted that the mixed gas involved in this embodiment includes two polar gases and three non-polar gases, but is not limited thereto. The mixing ratio of each gas in the mixed gas can be appropriately set.

[0029] [First separation membrane 10]

[0030] The first separation membrane 10 is disposed downstream of the methanation reactor 5. The first separation membrane 10 is disposed upstream of the second separation membrane 20. A mixed gas comprising NH3, H2O, CO2, CH4, and N2 is supplied from the methanation reactor 5 to the first separation membrane 10. The mixed gas supplied to the first separation membrane 10 is preferably pressurized.

[0031] The first separation membrane 10 separates H2O, which is one of the gases different from N2, from the mixed gas. The first separation membrane 10 is an H2O separation membrane capable of selectively permeating H2O from the mixed gas. The material of the first separation membrane 10 is not particularly limited; it can be any membrane capable of selectively permeating H2O. The first separation membrane 10 is preferably a membrane that preferentially adsorbs H2O compared to NH3 (e.g., a hydrophilic membrane). For example, zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes can be used as the first separation membrane 10. In particular, zeolite membranes exhibit high separation performance even under high temperature conditions, and are therefore preferred.

[0032] It should be noted that, in this specification, selective permeation means that the desired component is enriched in the permeation space of the separation membrane.

[0033] The first separation membrane 10 generates a first enriched gas enriched with H2O and a first depleted gas enriched with NH3, CO2, CH4 and N2 by selectively permeating H2O contained in the mixed gas.

[0034] The first enriched gas is discharged to the outside through the permeate side space of the first separation membrane 10. The concentration of H2O in the first enriched gas is not particularly limited; however, the first enriched gas preferably mainly contains H2O. "Mainly contains H2O" means that the highest concentration of H2O in the first enriched gas is H2O.

[0035] A first depleted gas flows out from the non-permeable side space of the first separation membrane 10 and is supplied to the second separation membrane 20. The first depleted gas contains NH3, CO2, CH4, and N2. The first depleted gas may contain H2O.

[0036] The concentration of N2 in the first depleted gas is higher than the concentration of N2 in the mixed gas. In this embodiment, the partial pressure of nitrogen in the first depleted gas is higher than the partial pressure of nitrogen in the mixed gas.

[0037] On the other hand, the concentration of N2 in the first enriched gas is lower than the concentration of N2 in the mixed gas.

[0038] [Second separation membrane 20]

[0039] The second separation membrane 20 is disposed downstream of the first separation membrane 10. The second separation membrane 20 is disposed upstream of the third separation membrane 30. A first depleted gas containing NH3, CO2, CH4, and N2 is supplied from the first separation membrane 10 to the second separation membrane 20.

[0040] The concentration of H2O in the first depleted gas supplied to the second separation membrane 20 is lower than the concentration of H2O in the mixed gas supplied to the first separation membrane 10.

[0041] The second separation membrane 20 separates NH3, which is a first gas different from N2, from the first depleted gas. The second separation membrane 20 is an NH3 separation membrane capable of selectively permeating NH3 from the first depleted gas. The material of the second separation membrane 20 is not particularly limited; for example, zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes can be used as the second separation membrane 20.

[0042] The composition of the second separation membrane 20 is preferably different from that of the first separation membrane 10. The second separation membrane 20 is preferably composed of a structure suitable for the separation of NH3. Different composition refers to concepts including different constituent materials and different pore sizes. For example, it is preferable that the pore size of the second separation membrane 20 is larger than the dynamic molecular diameter of NH3 and smaller than the dynamic molecular diameter of CO2. Furthermore, the second separation membrane 20 may not have water adsorption properties.

[0043] It should be noted that the second separation membrane 20 can have the same structure as the first separation membrane 10. For example, if H2O is depleted and the second separation membrane 20 allows selective permeation of NH3, the first and second separation membranes 10 and 20 can have the same structure.

[0044] The second separation membrane 20 selectively permeates NH3 contained in the first depleted gas to generate a second enriched gas enriched with NH3 and a second depleted gas depleted with NH3 but enriched with CO2, CH4 and N2.

[0045] In this embodiment, the second enriched gas is discharged to the outside through the permeation side space of the second separation membrane 20. The concentration of NH3 in the second enriched gas is not particularly limited; however, the second enriched gas preferably mainly contains NH3. "Mainly contains NH3" means that the highest concentration of NH3 in the second enriched gas is NH3.

[0046] The second lean gas flows out from the non-permeable side space of the second separation membrane 20 and is supplied to the third separation membrane 30. The second lean gas contains CO2, CH4, and N2. If the first lean gas contains H2O, the second lean gas may contain H2O. The second lean gas may contain NH3.

[0047] The concentration of N2 in the second lean gas is higher than the concentration of N2 in the mixed gas. In this embodiment, the partial pressure of nitrogen in the second lean gas is higher than the partial pressure of nitrogen in the mixed gas. Furthermore, the concentration of N2 in the second lean gas is higher than the concentration of N2 in the first lean gas. In this embodiment, the partial pressure of nitrogen in the second lean gas is higher than the partial pressure of nitrogen in the first lean gas.

[0048] On the other hand, the concentration of N2 in the second enriched gas is lower than the concentration of N2 in the first depleted gas.

[0049] In this embodiment, the second separation membrane 20 is an example of the "separator" involved in the present invention, the second enriched gas is an example of the "gas enriched by the first gas" involved in the present invention, and the second depleted gas is an example of the "gas in which the first gas is depleted and nitrogen and the second gas are enriched" involved in the present invention.

[0050] [Third separation membrane 30]

[0051] The third separation membrane 30 is disposed downstream of the second separation membrane 20. A second lean gas containing CO2, CH4 and N2 is supplied from the second separation membrane 20 to the third separation membrane 30.

[0052] The concentration of H2O in the second depleted gas supplied to the third separation membrane 30 is lower than the concentration of H2O in the mixed gas supplied to the first separation membrane 10.

[0053] The concentration of NH3 in the second depleted gas supplied to the third separation membrane 30 is lower than the concentration of NH3 in the first depleted gas supplied to the second separation membrane 20.

[0054] The third separation membrane 30 separates N2 and CO2 from the second depleted gas. The third separation membrane 30 is configured such that N2 and CO2 can selectively permeate compared to CH4, which is the second gas. The material of the third separation membrane 30 is not particularly limited, as long as it is a membrane capable of selectively permeating N2 and CO2. Examples of materials that can be used for the third separation membrane 30 include zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes.

[0055] The third separation membrane 30 is preferably composed differently from the first separation membrane 10. The third separation membrane 30 is preferably composed of a structure suitable for the separation of N2 and CO2. The third separation membrane 30 may not have water adsorption properties. It should be noted that the third separation membrane 30 may also have the same structure as the first separation membrane 10.

[0056] The third separation membrane 30 is preferably composed differently from the second separation membrane 20. For example, it is preferable that the pore size of the third separation membrane 30 is larger than the dynamic molecular diameter of N2 and CO2 and smaller than the dynamic molecular diameter of CH4. It should be noted that the third separation membrane 30 may be composed of the same structure as the second separation membrane 20.

[0057] The third separation membrane 30 selectively permeates N2 and CO2 contained in the second depleted gas to generate a third enriched gas enriched with N2 and CO2, and a third depleted gas depleted with N2 and CO2 and enriched with CH4.

[0058] The third enriched gas flows out from the permeate side space of the third separation membrane 30. The individual concentrations of N2 and CO2 in the third enriched gas are not particularly limited; however, the third enriched gas preferably mainly contains N2 and CO2. "Mainly contains N2 and CO2" means that the combined concentration of N2 and CO2 in the third enriched gas exhibits the highest concentration. The third lean gas flows out from the non-permeate side space of the third separation membrane 30. The concentration of CH4 in the third lean gas is not particularly limited; however, the third lean gas preferably mainly contains CH4. "Mainly contains CH4" means that the highest concentration of CH4 in the third lean gas is CH4.

[0059] The N2 concentration in the third enriched gas is higher than the N2 concentration in the mixed gas. Furthermore, the N2 concentration in the third enriched gas is higher than the N2 concentration in the first lean gas. Additionally, the N2 concentration in the third enriched gas is higher than the N2 concentration in the second lean gas.

[0060] On the other hand, the concentration of N2 in the third depleted gas is lower than the concentration of N2 in the second depleted gas.

[0061] In this embodiment, the third separation membrane 30 is an example of the "nitrogen separation membrane" involved in the present invention.

[0062] (feature)

[0063] (1) Gas separation system 1 is a separation system for separating N2 from a mixture of gases including H2O, NH3, CO2, CH4, and N2. Gas separation system 1 includes: a second separation membrane 20 (separator); and a third separation membrane 30 (nitrogen separation membrane), which is disposed downstream of the second separation membrane 20. The second separation membrane 20 generates a second enriched gas enriched with NH3 and a second depleted gas enriched with CO2, CH4, and N2 by separating NH3 (a first gas different from nitrogen). The third separation membrane 30 is configured such that N2 can selectively permeate compared to CH4 (a second gas different from nitrogen).

[0064] Currently, well-known nitrogen separation membranes have low N2 permeability coefficients, failing to achieve efficient N2 separation. Therefore, in gas separation system 1, a second depleted gas is generated in the second separation membrane 20, where NH3 is depleted and CO2, CH4, and N2 are enriched. This reduces the concentration of components other than N2 upstream of the third separation membrane 30, thereby increasing the N2 concentration in the gas supplied to the third separation membrane 30. Consequently, the N2 removal efficiency in the third separation membrane 30 can be improved.

[0065] (2) The gas separation system 1 includes a second separation membrane 20 that selectively allows NH3 to pass through, serving as the "separator". Therefore, compared to the case where an adsorption tower that separates NH3 by PSA method is used as the separator, the gas separation system 1 can suppress pressure fluctuations in the second lean gas supplied to the third separation membrane 30. Accordingly, complex pressure control of the second lean gas is not required. In addition, the energy required to pressurize the reduced pressure portion of the second lean gas can be reduced. Furthermore, compared to the case where a structure that separates NH3 by temperature variation adsorption (TSA) or absorption method is used as the separator, the gas separation system 1 does not require complex temperature control of the second lean gas. In addition, in the case of temperature variation adsorption (TSA) or absorption method, the gas temperature is sometimes lowered in order to perform adsorption or absorption more effectively. Therefore, the energy required to heat the second lean gas can be reduced.

[0066] (3) The structure of the third separation membrane 30 is preferably different from that of the second separation membrane 20. Therefore, a separation membrane suitable for the separation of N2 can be used as the third separation membrane 30.

[0067] (4) The partial pressure of nitrogen in the second lean gas (the gas supplied to the nitrogen separation membrane) is higher than that in the mixed gas. This means that the first gas, which is different from nitrogen, is removed by the second separation membrane 20 before N2 is separated by the third separation membrane 30. Accordingly, N2 can be separated from the second lean gas with good precision.

[0068] (5) Gas separation system 1 separates CH4 from a mixture of gases containing H2O (first polar gas), NH3 (second polar gas), N2 (first nonpolar gas), CO2 (second nonpolar gas), and CH4 (third nonpolar gas). First separation membrane 10 selectively permeates H2O to generate a first enriched gas enriched with H2O and a first depleted gas depleted with H2O and enriched with components other than H2O. Second separation membrane 20 separates NH3 to generate a second enriched gas enriched with NH3 and a second depleted gas depleted with NH3 and enriched with components other than NH3. Third separation membrane 30 separates CO2 to generate a third enriched gas enriched with CO2 and a third depleted gas depleted with CO2 and enriched with components other than CO2.

[0069] Thus, according to gas separation system 1, when separating CH4 from the mixed gas, it is possible to separate the non-polar gases N2, CO2, and CH4 after pre-separating the polar gases H2O and NH3. Therefore, since the polar gases can be separated before the non-polar gases are separated, there is no need to set up a separate production line for separating the polar gases.

[0070] (A variation of the first embodiment)

[0071] The first embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention.

[0072] [Variation Example 1]

[0073] In the first embodiment described above, the mixed gas includes H2O, NH3, CO2, CH4, and N2, but is not limited to these. It is acceptable as long as the mixed gas includes at least N2 and two gases other than N2 (the first and second gases).

[0074] [Variation Example 2]

[0075] In the first embodiment described above, the third separation membrane 30 selectively allows N2 and CO2 contained in the second depleted gas to pass through; however, it is not necessary to selectively allow CO2 to pass through. In this case, as long as a CO2 separation membrane is disposed between the second separation membrane 20 and the third separation membrane 30, CO2 can be separated in advance by the CO2 separation membrane.

[0076] [Variation Example 3]

[0077] In the first embodiment described above, the mixed gas contains two polar gases and three non-polar gases, but is not limited thereto.

[0078] Furthermore, in the first embodiment described above, H2O is cited as an example of the first polar gas, and NH3 is cited as an example of the second polar gas, but the method is not limited to these. For example, H2O, NH3, CH3OH, C2H5OH, etc., can be used as polar gases.

[0079] Furthermore, in the first embodiment described above, N2 is cited as an example of a first nonpolar gas, CO2 as an example of a second nonpolar gas, and CH4 as an example of a third nonpolar gas, but the method is not limited to these. For example, N2, CO2, CH4, H2, etc., can be used as nonpolar gases.

[0080] [Variation Example 4]

[0081] In the first embodiment described above, the gas separation system 1 includes a methanation reactor 5; however, it may not include a methanation reactor 5. Therefore, the mixed gas is not limited to the gas synthesized by methanation, and any gas containing at least N2 and two gases other than N2 can be used.

[0082] [Variation Example 5]

[0083] In the first embodiment described above, the gas separation system 1 includes a second separation membrane 20 as an example of a separator; however, the separator is not limited to a separation membrane. It is acceptable as long as the separator is a structure capable of separating a first gas different from N2. For example, a structure capable of separating a first gas different from N2 by means of PSA, TSA, or absorption can be used as the separator.

[0084] [Variation Example 6]

[0085] In the first embodiment described above, the polar gases (H2O and NH3) contained in the mixed gas are discharged to the outside; however, at least one polar gas can be reused. For example, NH3 can be reused as a raw material for generating H2 supplied to the methanation reactor 5, or as fuel for combustion in other processes. Furthermore, in the modified example 3 described above, H2, which is one of the non-polar gases, can be reused. This improves the gas utilization efficiency of the entire system.

[0086] [Variation Example 7]

[0087] In the first embodiment described above, N2 is separated after the first gas, which is different from N2, is separated from the mixed gas. However, a portion of N2 can be separated before the first gas, which is different from N2, is separated from the mixed gas.

[0088] For example, a portion of N2 can be pre-separated using an N2 separation membrane disposed upstream of the first separation membrane 10. Alternatively, a portion of N2 can be pre-separated using an N2 separation membrane disposed between the first separation membrane 10 and the second separation membrane 20.

[0089] [Variation Example 8]

[0090] In the first embodiment described above, H2O is separated by the first separation membrane 10 and NH3 is separated by the second separation membrane 20. However, NH3 can be separated by the first separation membrane 10 and H2O can be separated by the second separation membrane 20.

[0091] 2. Second Implementation Method

[0092] (Gas separation system 1a)

[0093] Figure 2 This is a schematic diagram showing the configuration of the gas separation system 1a according to the second embodiment.

[0094] The gas separation system 1a includes a first separation membrane 10a and a second separation membrane 20a.

[0095] [First separation membrane 10a]

[0096] The first separation membrane 10a is disposed upstream of the second separation membrane 20a. The first separation membrane 10a is supplied with a mixed gas containing NH3, CH4 and N2.

[0097] In this embodiment, NH3 is an example of a "first gas different from N2" involved in the present invention, and CH4 is an example of a "second gas different from N2" involved in the present invention.

[0098] NH3 is a deteriorating gas. The dynamic molecular diameter of NH3 is 0.26 nm. N2 and CH4 are non-deteriorating gases. The dynamic molecular diameter of N2 is 0.364 nm. The dynamic molecular diameter of CH4 is 0.38 nm.

[0099] Degrading gases refer to gases that are corrosive to metals, gases that cause brittleness in metals, and gases that exhibit alkalinity when dissolved in aqueous solution. Examples of gases that are corrosive to metals include NH3. Examples of gases that cause brittleness in metals include H2. Examples of gases that exhibit alkalinity when dissolved in aqueous solution include NH3. Furthermore, from the viewpoint that it can dissolve other components to form an aqueous solution, H2O is also considered a degrading gas.

[0100] Non-deteriorating gases refer to all gases other than deteriorating gases.

[0101] It should be noted that the mixed gas involved in this embodiment includes one deteriorating gas and two non-deteriorating gases, but is not limited thereto. The mixing ratio of each gas in the mixed gas can be appropriately set.

[0102] The mixed gas supplied to the first separation membrane 10a is preferably pressurized.

[0103] The first separation membrane 10a separates NH3, which is a first gas different from N2, from the mixed gas. The first separation membrane 10a is an NH3 separation membrane capable of selectively permeating NH3 from the mixed gas. The constituent material of the first separation membrane 10a is not particularly limited, as long as it is a membrane capable of selectively permeating NH3. For example, zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes can be used as the first separation membrane 10a. In particular, zeolite membranes exhibit high separation performance even under high temperature conditions, and are therefore preferred.

[0104] The first separation membrane 10a generates a first enriched gas enriched with NH3 and a first depleted gas enriched with CH4 and N2 by selectively permeating NH3 contained in the mixed gas.

[0105] The first enriched gas is discharged to the outside through the permeate side space of the first separation membrane 10a. The concentration of NH3 in the first enriched gas is not particularly limited; however, it is preferable that the first enriched gas mainly contains NH3. "Mainly contains NH3" means that the highest concentration of NH3 in the first enriched gas is NH3. The first enriched gas may contain CH4.

[0106] A first lean gas flows out from the non-permeable side space of the first separation membrane 10a and is supplied to the second separation membrane 20a. The first lean gas contains CH4 and N2. The first lean gas may contain NH3.

[0107] The concentration of N2 in the first depleted gas is higher than the concentration of N2 in the mixed gas. In this embodiment, the partial pressure of nitrogen in the first depleted gas is higher than the partial pressure of nitrogen in the mixed gas.

[0108] On the other hand, the concentration of N2 in the first enriched gas is lower than the concentration of N2 in the mixed gas.

[0109] In this embodiment, the first separation membrane 10a is an example of the "separator" involved in the present invention, the first enriched gas is an example of the "gas enriched by the first gas" involved in the present invention, and the first depleted gas is an example of the "gas depleted by the first gas and enriched by nitrogen and the second gas" involved in the present invention.

[0110] [Second separation membrane 20a]

[0111] The second separation membrane 20a is disposed downstream of the first separation membrane 10a. A first lean gas containing CH4 and N2 is supplied from the first separation membrane 10a to the second separation membrane 20a.

[0112] The concentration of NH3 in the first depleted gas supplied to the second separation membrane 20a is lower than the concentration of NH3 in the mixed gas supplied to the first separation membrane 10a.

[0113] The second separation membrane 20a separates N2 from the first depleted gas. The second separation membrane 20a is configured such that N2 selectively permeates compared to CH4, which is the second gas. The material of the second separation membrane 20a is not particularly limited, as long as it is a membrane capable of selectively permeating N2. Examples of materials that can be used for the second separation membrane 20a include zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes.

[0114] The second separation membrane 20a is preferably composed differently from the first separation membrane 10a. The second separation membrane 20a is preferably composed of a structure suitable for the separation of N2.

[0115] The second separation membrane 20a generates a second enriched gas enriched with N2 and a second depleted gas enriched with CH4 by selectively permeating N2 contained in the first depleted gas.

[0116] The second enriched gas is discharged to the outside through the permeation side space of the second separation membrane 20a. The concentration of N2 in the second enriched gas is not particularly limited; however, it is preferable that the second enriched gas mainly contains N2. "Mainly contains N2" means that the highest concentration of N2 in the second enriched gas is N2.

[0117] The second lean gas is discharged to the outside from the non-permeable side space of the second separation membrane 20a. The concentration of CH4 in the second lean gas is not particularly limited; however, it is preferable that the second lean gas mainly contains CH4. "Mainly contains CH4" means that the highest concentration of CH4 in the second lean gas is CH4. If the first lean gas contains NH3, the second lean gas may also contain NH3.

[0118] The N2 concentration in the second enriched gas is higher than the N2 concentration in the mixed gas. Furthermore, the N2 concentration in the second enriched gas is higher than the N2 concentration in the first depleted gas.

[0119] On the other hand, the concentration of N2 in the second enriched gas is lower than the concentration of N2 in the first depleted gas.

[0120] In this embodiment, the second separation membrane 20a is an example of the "nitrogen separation membrane" involved in the present invention.

[0121] (feature)

[0122] (1) The gas separation system 1a is a separation system for separating N2 from a mixture of gas containing NH3, CH4, and N2. The gas separation system 1a includes: a first separation membrane 10a (separator); and a second separation membrane 20a (nitrogen separation membrane) disposed downstream of the first separation membrane 10a. The first separation membrane 10a generates a first enriched gas enriched with NH3 and a first depleted gas enriched with CH4 and N2 by separating NH3 (a first gas different from nitrogen). The second separation membrane 20a is configured such that N2 can selectively permeate compared to CH4 (a second gas different from nitrogen).

[0123] In this way, in the gas separation system 1a, a first depleted gas is generated in the first separation membrane 10a, where NH3 is depleted and CH4 and N2 are enriched. As a result, the concentration of components other than N2 can be reduced upstream of the second separation membrane 20a, thereby increasing the N2 concentration in the gas supplied to the second separation membrane 20a. Accordingly, the N2 removal efficiency in the second separation membrane 20a can be improved.

[0124] (2) The gas separation system 1a includes a first separation membrane 10a that selectively allows NH3 to pass through, serving as the "separator". Therefore, compared to the case where an adsorption tower is used as the separator to separate NH3 by PSA, the gas separation system 1a can suppress pressure fluctuations in the first lean gas supplied to the second separation membrane 20a. Accordingly, complex pressure control of the first lean gas is not required, and the energy required to pressurize the reduced pressure portion of the first lean gas can be reduced. Furthermore, compared to the case where NH3 is separated by temperature variation adsorption (TSA) or absorption, the gas separation system 1a does not require complex temperature control of the first lean gas, and the energy required to heat the first lean gas can be reduced.

[0125] (3) The composition of the second separation membrane 20a is preferably different from that of the first separation membrane 10a. Accordingly, a separation membrane suitable for the separation of CH4 can be used as the second separation membrane 20a.

[0126] (4) The partial pressure of nitrogen in the first lean gas (the gas supplied to the nitrogen separation membrane) is higher than the partial pressure of nitrogen in the mixed gas. This means that the first gas, which is different from N2, is separated from N2 by the first separation membrane 10a before N2 is concentrated by the second separation membrane 20a. Accordingly, N2 can be separated from the first lean gas with good precision.

[0127] (5) Gas separation system 1a separates NH3 from a mixture of gas containing NH3 (first deteriorating gas), CH4 (first non-deteriorating gas), and N2 (second deteriorating gas). First separation membrane 10a generates a first enriched gas enriched with NH3 and a first depleted gas enriched with CH4 and N2 by selectively permeating NH3. Second separation membrane 20a generates a second enriched gas enriched with CH4 and a second depleted gas by separating CH4.

[0128] Thus, according to the gas separation system 1a, CH4 and N2 can be separated after NH3 has been pre-separated by passing it through the separation membrane. Therefore, since deteriorating gases can be separated by passing them through the separation membrane before non-deteriorating gases are separated, pressure fluctuations in the first lean gas supplied to the second separation membrane 20a can be suppressed compared to the case where an adsorption tower or absorption tower is used to separate NH3 via PSA. Consequently, complex pressure control of the first lean gas is unnecessary, and the energy required to pressurize the reduced pressure portion of the first lean gas can be reduced. Furthermore, compared to the case where NH3 is separated via TSA or absorption, the gas separation system 1a eliminates the need for complex temperature control of the first lean gas, and the energy required to heat the first lean gas can be reduced.

[0129] (A variation of the second embodiment)

[0130] The second embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention.

[0131] [Variation Example 1a]

[0132] In the second embodiment described above, the mixed gas contains NH3, CH4, and N2, but is not limited to these. The mixed gas may contain at least N2 and two other gases different from N2.

[0133] [Variation Example 2a]

[0134] In the second embodiment described above, the mixed gas contains one deteriorating gas and two non-deteriorating gases, but is not limited thereto.

[0135] Furthermore, in the second embodiment described above, NH3 is cited as an example of a deteriorating gas, but it is not limited to this. For example, NH3, H2, H2O, etc., can be used as deteriorating gases.

[0136] Furthermore, in the second embodiment described above, CH4 is cited as an example of the first non-deteriorating gas, and N2 is cited as an example of the second non-deteriorating gas, but the invention is not limited to these. For example, CO2, N2, CH4, etc., can be used as non-deteriorating gases.

[0137] [Variation Example 3a]

[0138] In the second embodiment described above, the second separation membrane 20a separates CH4, which is an example of a first non-deteriorating gas, contained in the first depleted gas, but is not limited thereto. The separator can separate the deteriorating gas and the first non-deteriorating gas together.

[0139] For example, if the mixed gas supplied to the first separation membrane 10a contains NH3, CH4, N2 and H2, the first depleted gas supplied to the second separation membrane 20a contains CH4, N2 and H2.

[0140] In this case, the second separation membrane 20a can separate the CH4 and H2 contained in the first depleted gas. This generates a first enriched gas containing CH4 and H2 and a second depleted gas containing N2.

[0141] [Variation Example 4a]

[0142] The first separation membrane 10 can separate various deteriorating gases. For example, in the above modified example 3a, the first separation membrane 10 can generate a first enriched gas enriched with NH3 and H2, and a first depleted gas depleted with NH3 and H2 and enriched with CH4 and N2.

[0143] [Variation Example 5a]

[0144] In the second embodiment described above, the gas separation system 1a includes a first separation membrane 10a as an example of a separator; however, the separator is not limited to a separation membrane. The separator can be any structure capable of separating a first gas different from N2. For example, a structure capable of separating a first gas different from N2 by means of PSA, TSA, or absorption can be used as the separator.

[0145] [Variation 6a]

[0146] In the second embodiment described above, the first enriched gas, containing the deteriorated gas separated by the first separation membrane 10a, is discharged to the outside from the permeate side space of the first separation membrane 10a. The deteriorated gas can be reused for the synthesis of desired substances or as fuel. Furthermore, in the modified example 3a described above, H2, which is one of the non-deteriorated gases, can be reused.

[0147] [Variation Example 7a]

[0148] In the second embodiment described above, N2 is separated after the first gas, which is different from N2, is separated from the mixed gas. However, a portion of N2 can be separated before the first gas, which is different from N2, is separated from the mixed gas.

[0149] For example, a portion of N2 can be pre-separated by an N2 separation membrane configured on the upstream side of the first separation membrane 10a.

[0150] 3. Third Implementation Method

[0151] (Gas separation system 1b)

[0152] Figure 3 This is a schematic diagram showing the configuration of the gas separation system 1b.

[0153] The gas separation system 1b includes a first separation membrane 10b and a second separation membrane 20b.

[0154] [First separation membrane 10b]

[0155] The first separation membrane 10b is disposed upstream of the second separation membrane 20b. The first separation membrane 10b is supplied with a mixed gas containing NH3, H2, CH4, and N2. The mixed gas supplied to the first separation membrane 10b is preferably pressurized.

[0156] In this embodiment, NH3 and H2 are examples of "a first gas different from N2" involved in the present invention, and CH4 is an example of "a second gas different from N2" involved in the present invention.

[0157] NH3 is the first condensable gas. The dynamic molecular diameter of NH3 is 0.265 nm. CH4, N2, and H2 are the first non-condensable gases. The dynamic molecular diameter of CH4 is 0.38 nm. The dynamic molecular diameter of N2 is 0.364 nm. The dynamic molecular diameter of H2 is 0.289 nm.

[0158] Thus, the mixed gas involved in this embodiment includes one condensable gas (NH3) and three non-condensable gases (H2, CH4 and N2).

[0159] Condensable gases refer to gases whose saturated vapor pressure is below 2 MPaG at the operating temperature of the separator (in this embodiment, the second separation membrane 20b) used to separate non-condensable gases in the downstream section. Non-condensable gases refer to gases other than condensable gases.

[0160] It should be noted that the mixed gas involved in this embodiment includes one condensable gas and three non-condensable gases, but is not limited thereto. The mixing ratio of each gas in the mixed gas can be appropriately set.

[0161] The first separation membrane 10b separates NH3 and H2, which are first gases different from N2, from the mixed gas.

[0162] The first separation membrane 10b is a separation membrane capable of selectively permeating NH3 and H2 in the mixed gas. As long as the first separation membrane 10b is a membrane capable of selectively permeating NH3 and H2, the constituent material of the first separation membrane 10b is not particularly limited. For example, zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes can be used as the first separation membrane 10b. In particular, zeolite membranes exhibit high separation performance even under high temperature conditions, and are therefore preferred.

[0163] The first separation membrane 10b selectively permeates NH3 and H2 contained in the mixed gas to generate a first enriched gas enriched with NH3 and H2, and a first depleted gas depleted with NH3 and H2 and enriched with CH4 and N2.

[0164] The first enriched gas is discharged to the outside through the permeate side space of the first separation membrane 10b. The individual concentrations of NH3 and H2 in the first enriched gas are not particularly limited; however, the first enriched gas preferably mainly contains NH3 and H2. "Mainly contains NH3 and H2" means that the combined concentration of NH3 and H2 in the first enriched gas exhibits the highest possible concentration. The mixing ratio of NH3 and H2 in the first enriched gas is not particularly limited.

[0165] A first lean gas flows out from the non-permeable side space of the first separation membrane 10b and is supplied to the second separation membrane 20b. The first lean gas contains CH4 and N2. The first lean gas may contain one or both of NH3 and H2.

[0166] The concentration of N2 in the first depleted gas is higher than the concentration of N2 in the mixed gas. In this embodiment, the partial pressure of nitrogen in the first depleted gas is higher than the partial pressure of nitrogen in the mixed gas.

[0167] On the other hand, the concentration of N2 in the first enriched gas is lower than the concentration of N2 in the mixed gas.

[0168] In this embodiment, the first separation membrane 10b is an example of the "separator" involved in the present invention, the first enriched gas is an example of the "gas enriched by the first gas" involved in the present invention, and the first depleted gas is an example of the "gas depleted by the first gas and enriched by nitrogen and the second gas" involved in the present invention.

[0169] [Second separation membrane 20b]

[0170] The second separation membrane 20b is disposed downstream of the first separation membrane 10b. A first lean gas containing CH4 and N2 is supplied from the first separation membrane 10b to the second separation membrane 20b.

[0171] The concentration of NH3 in the first depleted gas supplied to the second separation membrane 20b is lower than the concentration of NH3 in the mixed gas supplied to the first separation membrane 20.

[0172] The second separation membrane 20b separates N2 from the second depleted gas. The second separation membrane 20b is configured such that N2 selectively permeates compared to CH4, which is the second gas. The material of the second separation membrane 20b is not particularly limited, as long as it is a membrane capable of selectively permeating N2. Examples of materials that can be used for the second separation membrane 20b include zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes.

[0173] The second separation membrane 20b is preferably composed differently from the first separation membrane 10b. The second separation membrane 20b is preferably composed of a structure suitable for the separation of CH4.

[0174] The second separation membrane 20b generates a second enriched gas enriched with N2 and a second depleted gas enriched with CH4 by selectively permeating N2 contained in the first depleted gas.

[0175] The second enriched gas is discharged to the outside through the permeate side space of the second separation membrane 20b. The concentration of N2 in the second enriched gas is not particularly limited; however, it is preferable that the second enriched gas mainly contains N2. "Mainly contains N2" means that the highest concentration of N2 in the second enriched gas is N2.

[0176] The second depleted gas is discharged to the outside from the non-permeable side space of the second separation membrane 20b. The concentration of CH4 in the second depleted gas is not particularly limited; however, it is preferable that the second depleted gas mainly contains CH4. "Mainly contains CH4" means that the highest concentration of CH4 in the second depleted gas is CH4. If the first depleted gas contains NH3, the second depleted gas may also contain NH3.

[0177] The N2 concentration in the second enriched gas is higher than the N2 concentration in the mixed gas. Furthermore, the N2 concentration in the second enriched gas is higher than the N2 concentration in the first depleted gas.

[0178] On the other hand, the concentration of N2 in the second enriched gas is lower than the concentration of N2 in the first depleted gas.

[0179] In this embodiment, the second separation membrane 20b is an example of the "nitrogen separation membrane" involved in the present invention.

[0180] (feature)

[0181] (1) Gas separation system 1b is a separation system for separating N2 from a mixture of gas containing NH3, H2, CH4 and N2. Gas separation system 1b includes: a first separation membrane 10b (separator); and a second separation membrane 20b (nitrogen separation membrane) disposed downstream of the first separation membrane 10b. The first separation membrane 10b separates NH3 and H2 (a first gas different from nitrogen) to generate a first enriched gas enriched with NH3 and H2, and a first depleted gas depleted with NH3 and H2 and enriched with CH4 and N2. The second separation membrane 20b is configured such that N2 can selectively permeate compared to CH4 (a second gas different from nitrogen).

[0182] Thus, in the gas separation system 1b, a first depleted gas is generated in the first separation membrane 10b, where NH3 and H2 are depleted and CH4 and N2 are enriched. This reduces the concentration of components other than N2 upstream of the second separation membrane 20b, thereby increasing the N2 concentration in the gas supplied to the second separation membrane 20b. Consequently, the N2 removal efficiency in the second separation membrane 20b can be improved.

[0183] (2) The gas separation system 1b includes a first separation membrane 10b that selectively allows NH3 and H2 to pass through, serving as the "separator". Therefore, compared to the case where an adsorption tower is used as the separator to separate NH3 via PSA, the gas separation system 1b can suppress pressure fluctuations in the first lean gas supplied to the second separation membrane 20b. Accordingly, complex pressure control of the first lean gas is unnecessary. In addition, the energy required to pressurize the reduced pressure portion of the first lean gas can be reduced. Furthermore, compared to the case where NH3 is separated via TSA or absorption, the gas separation system 1b does not require complex temperature control of the first lean gas. In addition, the energy required to heat the first lean gas can be reduced.

[0184] (3) The composition of the second separation membrane 20b is preferably different from that of the first separation membrane 10b. Accordingly, a separation membrane suitable for the separation of CH4 can be used as the second separation membrane 20b.

[0185] (4) The partial pressure of nitrogen in the first lean gas (the gas supplied to the nitrogen separation membrane) is higher than the partial pressure of nitrogen in the mixed gas. This means that the first gas, which is different from N2, is separated from N2 by the first separation membrane 10b before N2 is concentrated by the second separation membrane 20b. Accordingly, N2 can be separated from the first lean gas with good precision.

[0186] (5) Gas separation system 1b separates NH3 from a mixture of gas containing NH3 (first condensable gas), CH4 (first non-condensable gas), and N2 (second condensable gas). First separation membrane 10b generates a first enriched gas enriched with NH3 and a first depleted gas enriched with CH4 and N2 by selectively permeating NH3. Second separation membrane 20b generates a second enriched gas enriched with CH4 and a second depleted gas by separating CH4.

[0187] Thus, according to the gas separation system 1b, CH4 and N2 can be separated after NH3 has been pre-separated by passing it through the separation membrane. Therefore, since condensable gases can be pre-separated before non-condensable gases are separated, the condensation and liquefaction of NH3 in the second separation membrane 20b, which would otherwise reduce the separation performance of the second separation membrane 20b, can be suppressed. Furthermore, compared to the case where an adsorption tower is used to separate NH3 via PSA, pressure fluctuations in the first lean gas supplied to the second separation membrane 20b can be suppressed. Accordingly, complex pressure control of the first lean gas is unnecessary. Additionally, the energy required to pressurize the reduced pressure portion of the first lean gas can be reduced. Moreover, compared to the case where NH3 is separated via TSA or absorption, the gas separation system 1b does not require complex temperature control of the first lean gas. Additionally, the energy required to heat the first lean gas can be reduced.

[0188] (A variation of the third embodiment)

[0189] The third embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention.

[0190] [Variation 1b]

[0191] In the third embodiment described above, the mixed gas includes NH3, H2, CH4, and N2, but is not limited to these.

[0192] [Variation Example 2b]

[0193] In the third embodiment described above, the gas separation system 1b includes a first separation membrane 10b as an example of a separator; however, the separator is not limited to a separation membrane. Any structure capable of separating a first gas different from N2 can be used. For example, a structure that separates a first gas different from N2 using a PSA method, a TSA method, or an absorption method can be used as the separator.

[0194] [Variation 3b]

[0195] In the third embodiment described above, the mixed gas contains one condensable gas and three non-condensable gases, but is not limited thereto.

[0196] Furthermore, in the third embodiment described above, NH3 is cited as an example of the first condensing gas, but it is not limited to this. For example, NH3, H2O, etc., can be used as the condensing gas.

[0197] Furthermore, in the third embodiment described above, CH4 is cited as an example of a first non-condensable gas, N2 is cited as an example of a second non-condensable gas, and H2 is cited as an example of a third non-condensable gas, but the invention is not limited to these examples. For instance, CO2, N2, H2, CH4, etc., can be used as non-condensable gases.

[0198] [Variation 4b]

[0199] In the third embodiment described above, N2 is separated after the first gas, which is different from N2, is separated from the mixed gas. However, a portion of N2 can be separated before the first gas, which is different from N2, is separated from the mixed gas.

[0200] For example, a portion of N2 can be pre-separated by an N2 separation membrane configured on the upstream side of the first separation membrane 10b.

[0201] Explanation of reference numerals in the attached figures

[0202] 1. Gas separation systems 1a and 1b

[0203] 5. Methanation reactor

[0204] 10, 10a, 10b First separation membrane

[0205] 20, 20a, 20b Second separation membrane

[0206] 30 Third separation membrane

Claims

1. A gas separation system for separating nitrogen from a mixture of nitrogen and a first and a second gas different from nitrogen, characterized in that, The separation system comprises: Separators; and A nitrogen separation membrane is disposed downstream of the separator. The separator separates the first gas to generate a gas enriched with the first gas and a gas depleted of the first gas and enriched with nitrogen and the second gas. The nitrogen separation membrane is configured such that nitrogen can selectively permeate compared to the second gas.

2. The gas separation system according to claim 1, characterized in that, The separator is a gas separation membrane that allows the first gas to selectively permeate.

3. The gas separation system according to claim 2, characterized in that, The composition of the gas separation membrane is different from that of the nitrogen separation membrane.

4. The gas separation system according to any one of claims 1 to 3, characterized in that, The partial pressure of nitrogen in the gas supplied to the nitrogen separation membrane is higher than the partial pressure of nitrogen in the mixed gas.

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