Gas separation system, and mixed gas separation method

Abstract

A gas separation system 100 according to the present invention comprises: a first gas separation device 11 that separates a first gas G1 including a gas A and a gas B different from the gas A to obtain a second gas G2 having a higher content percentage of the gas A than the first gas G1; a first vacuum pump 21 that reduces the pressure of an internal space of the first gas separation device 11; and a first circulation path 31 that guides, to the first vacuum pump 21, at least some of the second gas G2 as a seal gas for the first vacuum pump 21.

Description

Gas separation system and method for separating mixed gases

[0001] The present invention relates to a gas separation system and a method for separating a mixed gas.

[0002] In recent years, technologies for separating and recovering individual components from mixed gases have been attracting attention due to environmental regulations and other factors. For example, in factories or power plants, mixed gases containing carbon dioxide, nitrogen, and the like are discharged from combustion equipment. For example, Patent Document 1 describes a process for removing CO2 and SO2 from exhaust gas by separating the exhaust gas from a boiler using a decompression-type membrane separation unit. For example, Patent Document 2 describes a hydrogen separation system that separates hydrogen from an original fuel gas containing hydrogen and flammable gases other than hydrogen, and includes a hydrogen separation means that extracts hydrogen-reduced fuel gas from a primary side and hydrogen-enriched gas from a secondary side. In the separation system described in Patent Document 1, hydrogen is separated from the original fuel gas while the secondary side is decompressed using a decompression means.

[0003] JP 2020-501884 A JP 2013-181068 A

[0004] Vacuum pumps that require a seal gas have superior pumping efficiency compared to other vacuum pumps. However, the present inventors have discovered that when a vacuum pump that requires a seal gas is used as a pressure reducing device in a pressure reducing separation system such as those described in Patent Documents 1 and 2, the separated concentrated gas (hereinafter sometimes simply referred to as separated gas) is diluted by the seal gas. When the separated gas is diluted by the seal gas, it is difficult to recover a highly concentrated separated gas.

[0005] The present invention aims to provide a gas separation system and a method for separating mixed gases that are suitable for recovering high-concentration separated gases while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0006] In one aspect, the present invention provides a gas separation system comprising: a first gas separation device that separates a first gas containing gas A and gas B different from gas A to obtain a second gas having a higher content of gas A than the first gas; a first vacuum pump that reduces the pressure in an internal space of the first gas separation device; and a first circulation path that introduces at least a portion of the second gas to the first vacuum pump as a seal gas for the first vacuum pump.

[0007] From another aspect, the present invention provides a method for separating a mixed gas, comprising: a first gas separation step of supplying a first gas containing gas A and gas B different from gas A to a first gas separation device, and separating the first gas by reducing the pressure in the internal space of the first gas separation device with a first vacuum pump, thereby obtaining a second gas having a higher content of gas A than the first gas; and a first circulation step of supplying at least a part of the second gas to the first vacuum pump as a seal gas for the first vacuum pump.

[0008] According to the present invention, it is possible to provide a gas separation system and a method for separating mixed gases that are suitable for recovering a high concentration of separated gas while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0009] FIG. 1 is a schematic configuration diagram showing an example of a gas separation system according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of a first gas separation apparatus. FIG. 3 is a schematic cross-sectional view showing an example of a first separation membrane. FIG. 4 is a schematic perspective view showing another example of the first gas separation apparatus. FIG. 5 is a schematic configuration diagram showing an example of a gas separation system of Variation 1. FIG. 6 is a schematic cross-sectional view showing an example of a gas separation system of Variation 2. FIG. 7 is a schematic cross-sectional view showing an example of a second gas separation apparatus. FIG. 8 is a schematic cross-sectional view showing an example of a second separation membrane. FIG. 9 is a schematic configuration diagram showing an example of a gas separation system of Variation 3. FIG. 10 is a schematic configuration diagram showing an example of a gas separation system of Variation 4. FIG. 11 is a schematic configuration diagram showing an example of a gas separation system of Variation 5. FIG. 12 is a schematic configuration diagram showing an example of a gas separation system of Variation 6. FIG. 13 is a schematic configuration diagram for explaining the gas separation system used in Calculation Examples 1 to 5. FIG. 14 is a schematic configuration diagram for explaining the gas separation system used in Calculation Example 6. FIG. 15 is a schematic configuration diagram for explaining the gas separation system used in Calculation Example 7. FIG. 16 is a schematic configuration diagram for explaining the gas separation system used in Calculation Example 8. FIG. 17 is a schematic configuration diagram for explaining the gas separation system used in Calculation Example 9.

[0010] A gas separation system according to a first aspect of the present invention comprises: a first gas separation device that separates a first gas containing gas A and gas B different from gas A to obtain a second gas having a higher content of gas A than the first gas; a first vacuum pump that reduces the pressure in an internal space of the first gas separation device; and a first circulation path that guides at least a portion of the second gas to the first vacuum pump as a seal gas for the first vacuum pump.

[0011] In a second aspect of the present invention, for example, the gas separation system according to the first aspect further comprises a second gas separation device that separates a mixed gas containing gas A and gas B to obtain a concentrated gas having a higher content of gas A than the mixed gas, and a second vacuum pump that reduces the pressure inside the second gas separation device, wherein (i) the mixed gas is the second gas discharged from the first gas separation device, or (ii) the concentrated gas is the first gas supplied to the first gas separation device.

[0012] In a third aspect of the present invention, for example, the gas separation system according to the second aspect, when the above (i) is satisfied, further comprises at least one selected from the group consisting of a second circulation path that guides at least a portion of the concentrated gas discharged from the second gas separation device to the second vacuum pump as a seal gas for the second vacuum pump, and a third circulation path that guides at least a portion of the second gas discharged from the first gas separation device to the second vacuum pump as a seal gas for the second vacuum pump; and when the above (ii) is satisfied, further comprises at least one selected from the group consisting of a second circulation path that guides at least a portion of the concentrated gas discharged from the second gas separation device to the second vacuum pump as a seal gas for the second vacuum pump, and a fourth circulation path that guides at least a portion of the second gas discharged from the first gas separation device to the second vacuum pump as a seal gas for the second vacuum pump.

[0013] In a fourth aspect of the present invention, for example, in the gas separation system according to any one of the first to third aspects, the first gas separation device has a first separation membrane that allows the gas A to permeate preferentially.

[0014] In a fifth aspect of the present invention, for example, in the gas separation system according to any one of the second to fourth aspects, the second gas separation device has a second separation membrane that allows the gas A to permeate preferentially.

[0015] In a sixth aspect of the present invention, for example, the gas separation system according to any one of the first to fifth aspects further includes a first booster provided in the first circulation path.

[0016] In a seventh aspect of the present invention, for example, the gas separation system according to the sixth aspect further comprises a first recovery path branching off from the first circulation path downstream of the first booster, and a first recovery section connected to the first recovery path and recovering the second gas.

[0017] In an eighth aspect of the present invention, for example, the gas separation system according to any one of the third to seventh aspects further includes a second booster provided in the second circulation path.

[0018] In a ninth aspect of the present invention, for example, the gas separation system according to the eighth aspect further comprises a second recovery path branching off from the second circulation path downstream of the second booster, and a second recovery section connected to the second recovery path and recovering the first gas.

[0019] In a tenth aspect of the present invention, for example, the gas separation system according to any one of the first to ninth aspects further comprises a drain mechanism that discharges moisture contained in the seal gas.

[0020] In an eleventh aspect of the present invention, for example, in the gas separation system according to any one of the first to tenth aspects, the first gas contains carbon dioxide as the gas A and nitrogen as the gas B.

[0021] A mixed gas separation method according to a twelfth aspect of the present invention includes a first gas separation step of supplying a first gas containing gas A and gas B different from gas A to a first gas separation device, and separating the first gas by reducing the pressure in the internal space of the first gas separation device with a first vacuum pump to obtain a second gas having a higher content of gas A than the first gas, and a first circulation step of supplying at least a portion of the second gas to the first vacuum pump as a seal gas for the first vacuum pump.

[0022] In a thirteenth aspect of the present invention, for example, the mixed gas separation method according to the twelfth aspect further includes a second gas separation step of supplying a mixed gas containing the gas A and the gas B to a second gas separation device, separating the mixed gas by reducing the pressure in the internal space of the second gas separation device with a second vacuum pump, and obtaining a concentrated gas having a higher content of the gas A than the mixed gas, wherein (i) the mixed gas is the second gas discharged from the first gas separation device, or (ii) the concentrated gas is the first gas supplied to the first gas separation device.

[0023] In a fourteenth aspect of the present invention, for example, the mixed gas separation method according to the thirteenth aspect, when the above (i) is satisfied, further includes at least one step selected from the group consisting of a second circulation step in which at least a portion of the concentrated gas discharged from the second gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump, and a third circulation step in which at least a portion of the second gas discharged from the first gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump; and when the above (ii) is satisfied, further includes at least one step selected from the group consisting of a second circulation step in which at least a portion of the concentrated gas discharged from the second gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump, and a fourth circulation step in which at least a portion of the second gas discharged from the first gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump.

[0024] In a fifteenth aspect of the present invention, for example, in the mixed gas separation method according to any one of the twelfth to fourteenth aspects, the first gas contains carbon dioxide as the gas A and nitrogen as the gas B.

[0025] The present invention will be described in detail below, but the following description is not intended to limit the present invention to a specific embodiment.

[0026] <Gas Separation System> FIG. 1 is a schematic diagram of a gas separation system 100 according to one embodiment of the present invention. As shown in FIG. 1, the gas separation system 100 includes a first gas separation device 11, a first vacuum pump 21, and a first circulation path 31. The first gas separation device 11 separates a first gas G1 containing gas A and a gas B different from gas A to obtain a second gas G2 having a higher content of gas A than the first gas G1. The first vacuum pump 21 is a vacuum pump that requires a seal gas and is a decompression device that decompresses the internal space of the first gas separation device 11. The first circulation path 31 is a path that guides at least a portion of the second gas G2 to the first vacuum pump 21 as a seal gas for the first vacuum pump 21.

[0027] Seal gas is a gas supplied to a vacuum pump for the purposes of shaft sealing, improving the degree of vacuum, suppressing the generation of reaction products, suppressing corrosion, and extending the pump's life. Conventionally, an inert gas has been used as the seal gas. Typically, the separated gas from the gas separation device and the seal gas are discharged together from the vacuum pump. Therefore, when a vacuum pump requiring a seal gas is used as the pressure reducing device of a pressure reducing separation system such as those described in Patent Document 1 or 2, the separated gas is diluted by the seal gas (inert gas), making it difficult to recover a highly concentrated separated gas.

[0028] According to the gas separation system 100 of this embodiment, at least a portion of the second gas G2, which has a higher content of gas A than the first gas G1, can be used as a seal gas for the first vacuum pump 21. The second gas G2 is supplied to the first vacuum pump 21 via the first circulation path 31. This makes it possible to suppress a decrease in the content of gas A in the finally recovered separated gas. In this way, according to the gas separation system 100, a high-concentration separated gas can be recovered while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0029] The first gas separation device 11 is not particularly limited as long as it is an apparatus capable of separating the first gas G1 to obtain a second gas G2 having a higher content of gas A than the first gas G1. For example, the first gas separation device 11 may employ a membrane separation method in which the first gas G1 is separated using a separation membrane to obtain a second gas G2, or a physical adsorption method in which the first gas G1 is separated using an adsorbent to obtain a second gas G2. Physical adsorption methods include, for example, a pressure vacuum swing adsorption (PVSA) system, a pressure swing adsorption (PSA) system, a temperature swing adsorption (TSA) system, and a pressure and temperature swing adsorption (PTSA) system. The PVSA system, the PSA system, the TSA system, and the PTSA system are systems for separating gases using an adsorbent in which a chemically adsorbed component such as potassium carbonate or an amine is supported on a carrier such as activated carbon or a porous resin. In the PVSA method, gas is separated by utilizing the difference in adsorption capacity depending on the pressure of the adsorbent by forcibly suctioning with a vacuum pump. In the PSA method, gas is separated by utilizing the difference in adsorption capacity depending on the pressure of the adsorbent. In the TSA method, gas is separated by utilizing the difference in adsorption capacity depending on the temperature of the adsorbent. In the PTSA method, gas is separated by utilizing the difference in adsorption capacity depending on the pressure and temperature of the adsorbent. When the first gas separation device 11 employs a physical adsorption method, the first gas separation device 11 may also employ the PVSA method.

[0030] The first gas G1 includes an acidic gas. The first gas G1 may include, for example, carbon dioxide, methane, hydrogen, nitrogen, oxygen, helium, argon, propane, or propylene. The first gas G1 includes a gas A and a gas B that is different from gas A. Examples of gas A and gas B include nitrogen and carbon dioxide. For example, the first gas G1 may include carbon dioxide as gas A and nitrogen as gas B. The first gas G1 may include nitrogen as gas A and carbon dioxide as gas B.

[0031] When the first gas separation device 11 employs a membrane separation method, the first gas separation device 11 may have a first separation membrane 111 for separating the first gas G1. The first gas G1 can be separated by the first separation membrane 111 to obtain a second gas G2.

[0032] [First Gas Separation Apparatus] Figure 2 is a schematic cross-sectional view showing an example of the first gas separation apparatus 11 included in the gas separation system 100. In the example of Figure 2, the first gas separation apparatus 11 has a first separation membrane 111 that separates the supplied first gas G1. The second gas G2 obtained by the first separation membrane 111 has a higher content of gas A than the first gas G1.

[0033] The first separation membrane 111 of the first gas separation device 11 can be rephrased as a separation membrane that separates the first gas G1 into a first permeable gas S1 and a first non-permeable gas S2. The first permeable gas S1 may be the second gas G2, and the first non-permeable gas S2 may be the second gas G2.

[0034] As shown in Fig. 2, the first gas separation device 11 includes a first separation membrane 111 and a container 112. The container 112 has a first chamber 113 and a second chamber 114. The first chamber 113 functions as a supply space to which a first gas G1 is supplied. The second chamber 114 functions as a permeation space to which a first permeation gas S1 is supplied. The first permeation gas S1 is obtained by the first gas G1 permeating through the first separation membrane 111.

[0035] The first separation membrane 111 is disposed inside the container 112. Inside the container 112, the first separation membrane 111 separates a first chamber 113 and a second chamber 114. The first separation membrane 111 extends from one of a pair of wall surfaces of the container 112 to the other.

[0036] The first chamber 113 has a feed space inlet 113a and a feed space outlet 113b. The second chamber 114 has a permeate space outlet 114b. The feed space inlet 113a is an opening for supplying the first gas G1 to the feed side space (first chamber 113). The permeate space outlet 114b is an opening for discharging the first permeate gas S1 from the permeate side space (second chamber 114). The feed space outlet 113b is an opening for discharging the first non-permeate gas S2 (third gas G3) that did not permeate the first separation membrane 111 from the feed side space (first chamber 113). The feed space inlet 113a, the feed space outlet 113b, and the permeate space outlet 114b are each formed, for example, on a wall surface of the container 112.

[0037] The first gas separation device 11 is suitable for a flow-through (continuous) membrane separation method, but may also be used for a batch-type membrane separation method.

[0038] The configuration of the first separation membrane 111 is not particularly limited. Figure 3 is a schematic cross-sectional view showing an example of the first separation membrane 111 provided in the first gas separation device 11 shown in Figure 2. As shown in Figure 3, the first separation membrane 111 may include a separation functional layer 1, a porous support 3 that supports the separation functional layer 1, and an intermediate layer 2 disposed between the separation functional layer 1 and the porous support 3. The intermediate layer 2 is in direct contact with each of the separation functional layer 1 and the porous support 3, for example.

[0039] The first separation membrane 111 may be a separation membrane that preferentially allows permeation of gas A. For example, when the first gas G1 contains carbon dioxide as gas A and nitrogen as gas B, the first separation membrane 111 may be a carbon dioxide separation membrane that preferentially allows permeation of carbon dioxide (gas A) contained in the first gas G1. For example, when the first gas G1 contains nitrogen as gas A and carbon dioxide as gas B, the first separation membrane 111 may be a nitrogen separation membrane that preferentially allows permeation of nitrogen (gas A) contained in the first gas G1.

[0040] When the first separation membrane 111 is a carbon dioxide separation membrane, the carbon dioxide (gas A) content in the first permeable gas S1 is higher than the carbon dioxide content in the first gas G1. On the other hand, the carbon dioxide content in the first non-permeable gas S2 is lower than the carbon dioxide content in the first gas G1. In other words, when the first separation membrane 111 is a carbon dioxide separation membrane, the first permeable gas S1 corresponds to the second gas G2.

[0041] (Separation Functional Layer) When the first separation membrane 111 is a carbon dioxide separation membrane, the separation functional layer 1 is a layer that allows preferential permeation of carbon dioxide (gas A) contained in the first gas G1. The separation functional layer 1 preferably contains a resin. Examples of resins contained in the separation functional layer 1 include polyether block amide resin, polyamide resin, polyether resin, polyimide resin, polyetherimide resin, cellulose acetate resin, silicone resin, and fluororesin. The separation functional layer 1 preferably contains a polyether block amide resin, polyimide resin, or cellulose acetate resin, and more preferably contains a polyether block amide resin. The separation functional layer 1 is preferably composed essentially of a resin. In this specification, "consisting essentially of" means excluding other components that alter the essential characteristics of the referenced material, and means that the material comprises, for example, 95 wt % or more, or even 99 wt % or more.

[0042] The thickness of the separation functional layer 1 is, for example, 50 μm or less, preferably 25 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 5 μm or less. The thickness of the separation functional layer 1 may be 0.01 μm or more, 0.05 μm or more, or 0.1 μm or more.

[0043] (Intermediate Layer) The intermediate layer 2 may contain, for example, a resin and may further contain nanoparticles dispersed in the resin (matrix). The nanoparticles may be spaced apart within the matrix or may be partially aggregated. The material of the matrix is ​​not particularly limited, and examples thereof include silicone resins such as polydimethylsiloxane; fluororesins such as polytetrafluoroethylene; epoxy resins such as polyethylene oxide; polyimide resins; polysulfone resins; polyacetylene resins such as polytrimethylsilylpropyne and polydiphenylacetylene; and polyolefin resins such as polymethylpentene. The matrix preferably contains a silicone resin.

[0044] The nanoparticles may contain an inorganic material or an organic material. Examples of inorganic materials contained in the nanoparticles include silica, titania, and alumina. The nanoparticles preferably contain silica.

[0045] The thickness of the intermediate layer 2 is not particularly limited and is, for example, less than 50 μm, preferably 40 μm or less, more preferably 30 μm or less, even more preferably 25 μm or less, particularly preferably 10 μm or less, and most preferably 5 μm or less. The lower limit of the thickness of the intermediate layer 2 is not particularly limited and may be 0.01 μm or 1 μm. The intermediate layer 2 is, for example, a layer having a thickness of less than 50 μm.

[0046] (Porous Support) The porous support 3 supports the separation function layer 1 via the intermediate layer 2. Examples of the porous support 3 include nonwoven fabrics, porous polytetrafluoroethylene, aromatic polyamide fibers, porous metals, sintered metals, porous ceramics, porous polyesters, porous nylons, activated carbon fibers, latex, silicone, silicone rubber, polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyether ether ketone, polyacrylonitrile, polyimide, and polyphenylene oxide. Permeable (porous) polymers containing at least one selected from the group consisting of metal foams having open or closed cells, polymer foams having open or closed cells, silica, porous glass, and mesh screens. The porous support 3 may be a combination of two or more of these.

[0047] The porous support 3 has an average pore size of, for example, 0.01 to 0.4 μm. The thickness of the porous support 3 is not particularly limited and is, for example, 10 μm or more, preferably 20 μm or more, and more preferably 50 μm or more. The thickness of the porous support 3 is, for example, 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0048] When the first separation membrane 111 is a nitrogen separation membrane, the carbon dioxide (gas B) content in the first permeable gas S1 is lower than the carbon dioxide content in the first gas G1. On the other hand, the carbon dioxide content in the first non-permeable gas S2 is higher than the carbon dioxide content in the first gas G1. In other words, when the first separation membrane 111 is a nitrogen separation membrane, the first non-permeable gas S2 corresponds to the second gas G2.

[0049] (Separation Functional Layer) When the first separation membrane 111 is a nitrogen separation membrane, the separation functional layer 1 is a layer that allows nitrogen contained in the first gas G1 to preferentially permeate.

[0050] (Intermediate Layer) As the intermediate layer 2, those exemplified as the intermediate layer 2 when the first separation membrane 111 is a carbon dioxide separation membrane can be used.

[0051] (Porous Support) As the porous support 3, those listed as the porous support 3 when the first separation membrane 111 is a carbon dioxide separation membrane can be used.

[0052] The configuration of the first separation membrane 111 is not limited to the example shown in Fig. 3. The first separation membrane 111 may be composed of, for example, a separation functional layer 1 and a porous support 3 that is arranged on one side of the separation functional layer 1 and supports the separation functional layer 1. The first separation membrane 111 may be composed of, for example, a separation functional layer 1, a protective layer that is arranged on one side of the separation functional layer 1 and protects the separation functional layer 1, and a porous support 3 that is arranged on the other side of the separation functional layer 1 and supports the separation functional layer 1. The protective layer may contain the materials described for the intermediate layer 2.

[0053] [First Vacuum Pump] The first vacuum pump 21 is a vacuum pump that requires a seal gas. The first vacuum pump 21 can reduce the pressure in the internal space of the first gas separation device 11. When the first gas separation device 11 has a first separation membrane 111, the first vacuum pump 21 can reduce the pressure in the permeate side space (second chamber 114) of the first gas separation device 11. In other words, the first vacuum pump 21 can generate or increase a pressure difference between the supply side space (first chamber 113) and the permeate side space (second chamber 114) of the first gas separation device 11. The first vacuum pump 21 is typically a gas transport vacuum pump, and examples of the first vacuum pump include a reciprocating vacuum pump and a rotary vacuum pump. Examples of the reciprocating vacuum pump include a diaphragm type and a swinging piston type vacuum pump. Examples of rotary vacuum pumps include liquid ring pumps, oil rotary pumps (rotary pumps), mechanical booster pumps, and various dry pumps such as roots, claw, screw, turbo, and scroll types. Screw-type dry pumps are preferably used because of their excellent pump efficiency. The first vacuum pump 21 may be equipped with a variable speed mechanism for changing the rotation speed, etc. An example of the variable speed mechanism is an inverter that drives the pump motor. By controlling the pump rotation speed, etc. with the variable speed mechanism, the pressure in the internal space of the first gas separation device 11 can be appropriately adjusted.

[0054] The first vacuum pump 21 may be an assembly of multiple vacuum pumps. That is, the first vacuum pump 21 may be configured so that each of the multiple vacuum pumps can reduce the pressure in the permeate side space (second chamber 114) of the first gas separation device 11. With this configuration, the pressure in the permeate side space of the first gas separation device 11 can be appropriately adjusted by adjusting the number of vacuum pumps in operation.

[0055] 1 , the first vacuum pump 21 is disposed in a second gas discharge path 52 for discharging the second gas G2 from the first gas separation device 11. When the first gas separation device 11 has a first separation membrane 111, the second gas discharge path 52 is connected to the permeate space outlet 114b of the first gas separation device 11.

[0056] [Gas Paths] As shown in FIG. 1, in addition to the first circulation path 31, the gas separation system 100 may further include a first gas supply path 51, a second gas discharge path 52, and a third gas discharge path 53 as gas paths.

[0057] The first gas supply path 51 is a path for supplying the first gas G1 to the first gas separation device 11 during operation. When the first gas separation device 11 has a first separation membrane 111, the first gas supply path 51 is connected to a supply space inlet 113a of the first gas separation device 11. The first gas supply path 51 may be connected to a supply source (not shown) such as a combustion device. The first gas G1 may be supplied to the first gas separation device 11 from the supply source such as a combustion device.

[0058] The second gas discharge path 52 is a path for discharging the second gas G2 from the first gas separation device 11 during operation. When the first gas separation device 11 has the first separation membrane 111, the second gas discharge path 52 is connected to the permeate space outlet 114b of the first gas separation device 11. For example, a pump for controlling the flow rate of the second gas G2 may be disposed in the second gas discharge path 52.

[0059] The third gas discharge path 53 is a path for discharging the third gas G3 from the first gas separation device 11 during operation. When the first gas separation device 11 has the first separation membrane 111, the third gas discharge path 53 is connected to the supply space outlet 113b of the first gas separation device 11. For example, a pump that controls the flow rate of the third gas G3 may be disposed in the third gas discharge path 53.

[0060] 1 , the second gas discharge path 52 may have a first portion 521, a second portion 522, and a third portion 523. When the first gas separation device 11 has the first separation membrane 111, the first portion 521 is a portion that connects the permeate space outlet 114b of the first gas separation device 11 and the first vacuum pump 21. The second portion 522 is a portion that connects the first vacuum pump 21 and the branch position 61. The third portion 523 is a portion that connects to the branch position 61.

[0061] The first circulation path 31 is a path that guides at least a portion of the second gas G2 to the first vacuum pump 21 as a seal gas for the first vacuum pump 21. In the example of Fig. 1 , the first circulation path 31 branches off from the second gas exhaust path 52 at a branch position 61 and is connected to a seal gas inlet of the first vacuum pump 21. However, the connection position of the first circulation path 31 is not limited to the example shown in Fig. 1 . For example, the first circulation path 31 may branch off from the exhaust port of the first vacuum pump 21 and be connected to the seal gas inlet of the first vacuum pump 21.

[0062] 1, the gas separation system 100 may include a first booster 71 provided in the first circulation path 31. The first booster 71 pressurizes the second gas G2 as a seal gas supplied to the first vacuum pump 21. By continuously operating the first booster 71, the second gas G2 can be stably obtained.

[0063] The first booster 71 is not particularly limited as long as it can pressurize the second gas G2 as a seal gas supplied to the first vacuum pump 21. The first booster 71 is typically a compressor.

[0064] The gas separation system 100 may include a drain mechanism (not shown) that discharges moisture contained in the second gas G2 serving as the seal gas. With this configuration, for example, when the second gas G2 contains moisture, malfunctions in the components of the gas separation system 100 due to moisture can be suppressed.

[0065] A drain mechanism may be provided in the first booster 71. As shown in Fig. 1 , the moisture collected by the drain mechanism may be discharged to the outside through a first drain path 35 connected to the first booster 71.

[0066] A switching valve (not shown) may be provided at the branch position 61. A flow rate adjustment valve (not shown) may be provided in the first circulation path 31. With this configuration, the flow rate of the second gas G2 introduced into the first circulation path 31 can be adjusted by the switching valve and the flow rate adjustment valve.

[0067] The flow rate of the second gas G2 supplied to the first vacuum pump 21 is preferably 12 NL / min or more. The upper limit of the flow rate of the second gas G2 supplied to the first vacuum pump 21 is not particularly limited.

[0068] Unless otherwise specified, each of the gas paths of the gas separation system 100 is made up of, for example, metal or resin piping.

[0069] The gas separation system 100 may further include a control device 40 that controls each component of the gas separation system 100. The control device 40 is, for example, a DSP (Digital Signal Processor) including an A / D conversion circuit, an input / output circuit, an arithmetic circuit, a storage device, etc. The control device 40 stores a program for appropriately operating the gas separation system 100. For example, the control device 40 may adjust the flow rate of the second gas G2 supplied to the first vacuum pump 21. The control device 40 may adjust the flow rate of the second gas G2 introduced into the first circulation path 31 by controlling a switching valve provided at the branch position 61 and a flow rate adjustment valve provided in the first circulation path 31.

[0070] The gas separation system 100 may further include a recovery unit 82 that recovers the second gas G2. As shown in FIG. 1 , the third portion 523 of the second gas discharge path 52 may be connected to the recovery unit 82. The recovery unit 82 is, for example, a container that stores the second gas G2. The recovery unit 82 may be filled with an adsorbent that can adsorb gas A contained in the second gas G2. Typically, the third portion 523 of the second gas discharge path 52 is provided with a booster (not shown) for recovering the second gas G2 in the recovery unit 82.

[0071] The adsorbent is not particularly limited. The adsorbent may be composed of, for example, a porous material. Examples of porous materials include activated carbon, zeolite, molecular sieve, mesoporous silica, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), metal-organic polyhedra (MOPs), covalent organic polymers (COPs), porous aromatic frameworks (PAFs), hydrogen-bonded organic frameworks (HOFs), and porous organic polymers (POPs). The porous material may contain one or a combination of two or more materials selected from the group consisting of the above materials. The adsorbent may be composed of a polymer having an amino group. Such a polymer is, for example, an amine polymer containing structural units derived from an epoxy monomer.

[0072] The gas separation system 100 may further include a recovery unit 83 that recovers the third gas G3. As shown in Fig. 1 , the third gas discharge path 53 may be connected to the recovery unit 83. The recovery unit 83 is, for example, a container that stores the third gas G3.

[0073] Although not shown, a buffer tank and a pressure reducing valve may be provided downstream of the first booster 71 in the first circulation path 31 .

[0074] [Another Example of First Gas Separation Apparatus] In the gas separation system 100, the first gas separation apparatus 11 having the first separation membrane 111 is not limited to the form shown in Fig. 2. The first gas separation apparatus 11 having the first separation membrane 111 may be, for example, a spiral membrane element or a hollow fiber membrane element. Fig. 4 is a perspective view schematically showing another example of the first gas separation apparatus 11 having the first separation membrane 111. The first gas separation apparatus 15 shown in Fig. 4 is a spiral membrane element and includes a central tube 16 and a laminate 17. The laminate 17 includes the first separation membrane 111.

[0075] The central tube 16 has a cylindrical shape. A plurality of openings are formed on the surface of the central tube 16 to allow the first permeable gas S1 to flow into the interior of the central tube 16. Examples of materials for the central tube 16 include resins such as acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. The inner diameter of the central tube 16 is, for example, in the range of 20 to 100 mm.

[0076] The laminate 17 further includes a feed-side channel material 18 and a permeate-side channel material 19 in addition to the first separation membrane 111. The laminate 17 is wound around a central tube 16. The first gas separation device 15 may further include an exterior material (not shown).

[0077] As the feed-side flow path material 18 and the permeate-side flow path material 19, for example, a resin net, woven fabric, or knitted fabric made of polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0078] Membrane separation using the first gas separation device 15 is performed, for example, by the following method. First, a first gas G1 is supplied to one end of the wound stack 17. As a result, a first permeable gas S1 that has permeated the first separation membrane 111 of the stack 17 moves into the interior of the central tube 16. The first permeable gas S1 is discharged to the outside through the central tube 16. The first gas G1 treated in the first gas separation device 15 is discharged to the outside from the other end of the wound stack 17 as a first non-permeable gas S2.

[0079] <Method for Separating Mixed Gas> Next, a method for separating mixed gas using the gas separation system 100 described above will be described.

[0080] The method for separating the mixed gas includes a first gas separation process in which a first gas G1 containing gas A and gas B different from gas A is supplied to a first gas separation device 11, and the first gas G1 is separated by reducing the pressure in the internal space of the first gas separation device 11 with a first vacuum pump 21 to obtain a second gas G2 having a higher content of gas A than the first gas G1, and a first circulation process in which at least a portion of the second gas G2 is supplied to the first vacuum pump 21 as a seal gas for the first vacuum pump 21.

[0081] According to this mixed gas separation method, in the first circulation step, at least a portion of the second gas G2, which has a higher content of gas A than the first gas G1, is used as a seal gas for the first vacuum pump 21, thereby suppressing a decrease in the content of gas A in the finally recovered separated gas. Therefore, a high-concentration separated gas can be recovered while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0082] For example, the first gas G1 may contain carbon dioxide as gas A and nitrogen as gas B. The first gas G1 may contain nitrogen as gas A and carbon dioxide as gas B.

[0083] The first gas separation step and the first circulation step of this embodiment are performed, for example, as follows. Hereinafter, the first gas separation step and the first circulation step will be described using an example in which the first gas separation device 11 has a first separation membrane 111.

[0084] [First Gas Separation Step] In the first gas separation step, first, the first gas G1 is supplied to the first chamber 113 (supply side space) of the first gas separation device 11 through the first gas supply path 51 .

[0085] Next, with the first gas G1 being supplied to the first chamber 113 of the first gas separation device 11, the second chamber 114 (permeation side space) is depressurized by the first vacuum pump 21. Specifically, the first vacuum pump 21 is used to depressurize the second chamber 114 through the permeation space outlet 114b.

[0086] By reducing the pressure inside the second chamber 114, a pressure difference is generated or increases between the supply-side space and the permeation-side space. As a result, the first gas G1 is separated by the first separation membrane 111, and the first permeation gas S1 is supplied to the second chamber 114. While the separation of the first gas G1 is being performed, the pressure inside the second chamber 114 may continue to be reduced by the first vacuum pump 21.

[0087] The first permeable gas S1 (second gas G2) supplied to the second chamber 114 passes through the first portion 521 of the second gas exhaust path 52 and is sucked by the first vacuum pump 21. The first vacuum pump 21 exhausts the sucked first permeable gas S1 to the second portion 522 of the second gas exhaust path 52.

[0088] [First circulation process] In the first circulation process, at least a portion of the first permeable gas S1 (second gas G2) discharged from the first vacuum pump 21 to the second portion 522 of the second gas discharge path 52 is supplied to the first vacuum pump 21 as a seal gas via the first circulation path 31.

[0089] The flow rate of the first permeable gas S1 supplied to the first vacuum pump 21 may be adjusted by a switching valve provided at the branch position 61 and a flow rate adjustment valve provided in the first circulation path 31 .

[0090] The mixed gas separation method may include a recovery step of recovering the second gas G2 discharged from the third portion 523 of the second gas discharge path 52 in the recovery section 82. The mixed gas separation method may include a second gas recovery step of recovering the first permeable gas S1 (second gas G2) obtained in the first gas separation step in the recovery section 82. The mixed gas separation method may further include a third gas recovery step of recovering the first non-permeable gas S2 (third gas G3) obtained in the first gas separation step in the recovery section 83.

[0091] <Modifications of Gas Separation System> The gas separation system according to this embodiment is not limited to the structure of the gas separation system 100 shown in Fig. 1. Modifications 1 to 6 of the gas separation system according to this embodiment will be described below.

[0092] 5 is a schematic diagram showing an example of a gas separation system 101 according to Modification 1. The gas separation system 101 includes a first recovery path 91 branching off from the first circulation path 31 downstream of the first booster 71, and a first recovery section 92 connected to the first recovery path 91 and recovering the second gas G2. Except for these, the gas separation system 101 has the same configuration as the gas separation system 100 described above.

[0093] In the gas separation system 100 described above, a booster (not shown) for recovering the second gas G2 in the recovery section 82 is typically provided in the third portion 523 of the second gas discharge path 52. On the other hand, in the gas separation system 101 of Modification 1, the first recovery section 92 is connected to the first recovery path 91 that branches off from the first circulation path 31 downstream of the first booster 71, so there is no need to provide a booster for recovering the second gas G2 in the first recovery section 92. Therefore, with the same processing power as the gas separation system 100, the number of devices constituting the system can be reduced.

[0094] 5 , the second gas discharge path 52 has only a first portion 521. When the first gas separation device 11 has the first separation membrane 111, the first portion 521 is a portion that connects the permeate space outlet 114b of the first gas separation device 11 to the first vacuum pump 21. The first recovery path 91 branches off from the first circulation path 31 at a branch position 93 located downstream of the first booster 71, and is connected to a first recovery section 92.

[0095] The first recovery unit 92 is, for example, a container that stores the second gas G2. The first recovery unit 92 may be filled with an adsorbent capable of adsorbing the gas A contained in the second gas G2. The adsorbents listed above for the recovery unit 82 can be used as the adsorbent.

[0096] Although not shown in the drawings, the first recovery path 91 may be provided with a booster for recovering the second gas G2 in the first recovery section 92. In this case, although the number of devices constituting the system increases, the processing power can be reduced.

[0097] The gas separation system according to this embodiment may further include a second gas separation device 12 and a second vacuum pump 22. The second gas separation device 12 is a device that separates a mixed gas Gm containing gas A and gas B to obtain a concentrated gas Gc having a higher content of gas A than the mixed gas Gm. The second vacuum pump 22 reduces the pressure in the internal space of the second gas separation device 12.

[0098] (i) The mixed gas Gm may be the second gas G2 discharged from the first gas separation device 11 (Variation 2), or (ii) the concentrated gas Gc may be the first gas G1 supplied to the first gas separation device 11 (Variation 3). Hereinafter, the gas separation system of Variation 2 will be referred to as a gas separation system 102. The gas separation system of Variation 3 will be referred to as a gas separation system 103.

[0099] (i) When the mixed gas Gm is the second gas G2 discharged from the first gas separation device 11, i.e., in Modification 2, the gas separation system 102 may further include at least one selected from the group consisting of a second circulation path 32 that guides at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22, and a third circulation path 33 that guides at least a portion of the second gas G2 discharged from the first gas separation device 11 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22 (Modification 4). Hereinafter, the gas separation system of Modification 4 will be referred to as gas separation system 104.

[0100] (ii) When the concentrated gas Gc is the first gas G1 supplied to the first gas separation device 11, i.e., in Modification 3, the gas separation system 102 may further include a second circulation path 32 that guides at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22, and a fourth circulation path 34 that guides at least a portion of the second gas G2 discharged from the first gas separation device 11 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22 (Modification 5). Hereinafter, the gas separation system of Modification 5 will be referred to as a gas separation system 105.

[0101] Variation 4 and Variation 5 may be combined (Variation 6). Hereinafter, the gas separation system of Variation 6 will be referred to as gas separation system 106.

[0102] In the following modified examples 2 to 6, the same elements are denoted by the same reference numerals, and the description thereof may be omitted.

[0103] (Variation 2) FIG. 6 is a schematic diagram showing an example of a gas separation system 102 of Variation 2. As shown in FIG. 6, in the gas separation system 102, a second gas separation device 12 is disposed downstream of a first gas separation device 11. According to the gas separation system 101, at least a portion of the second gas G2 discharged from the first-stage first gas separation device 11 can be used as a seal gas for the first-stage first vacuum pump 21. In the gas separation system 102, the second gas G2 corresponds to the mixed gas Gm supplied to the second-stage second gas separation device 12. The second gas G2 is supplied to the first vacuum pump 21 via the first circulation path 31. This configuration further suppresses a decrease in the content of gas A contained in the finally recovered separated gas. According to the gas separation system 102 of Variation 2, a vacuum pump requiring a seal gas with excellent pumping efficiency can be used, while recovering a higher concentration of separated gas.

[0104] The second gas separation device 12 is not particularly limited as long as it is a device that can separate the mixed gas Gm to obtain a concentrated gas Gc having a higher content of gas A than the mixed gas Gm. For example, the second gas separation device 12 may employ a membrane separation method in which the mixed gas Gm is separated using a separation membrane to obtain the concentrated gas Gc, or may employ a physical adsorption method in which the mixed gas Gm is separated using an adsorbent to obtain the concentrated gas Gc. When the second gas separation device 12 employs a physical adsorption method, the second gas separation device 12 may employ a PSA system.

[0105] When the second gas separation device 12 employs a membrane separation method, the second gas separation device 12 may have a second separation membrane 121 that separates the mixed gas Gm. The mixed gas Gm can be separated by the second separation membrane 121 to obtain a concentrated gas Gc.

[0106] [Second Gas Separation Device] Figure 7 is a schematic cross-sectional view showing an example of the second gas separation device 12 included in the gas separation system 102. In the example of Figure 7, the second gas separation device 12 has a second separation membrane 121 that separates the supplied mixed gas Gm. The concentrated gas Gc obtained by the second separation membrane 121 has a higher content of gas A than the mixed gas Gm.

[0107] The second separation membrane 121 of the second gas separation device 12 can be rephrased as a separation membrane that separates the mixed gas Gm into a second permeable gas S3 and a second non-permeable gas S4. The second permeable gas S3 may be the concentrated gas Gc, or the second non-permeable gas S4 may be the concentrated gas Gc.

[0108] 7, the second gas separation device 12 includes a second separation membrane 121 and a container 122. The container 122 has a first chamber 123 and a second chamber 124. The first chamber 123 functions as a supply space to which the mixed gas Gm is supplied. The second chamber 124 functions as a permeation space to which a second permeation gas S3 is supplied. The second permeation gas S3 is obtained by the mixed gas Gm permeating through the second separation membrane 121.

[0109] The second separation membrane 121 is disposed inside the container 122. Inside the container 122, the second separation membrane 121 separates the first chamber 123 and the second chamber 124. The second separation membrane 121 extends from one of a pair of wall surfaces of the container 122 to the other.

[0110] The first chamber 123 has a feed space inlet 123a and a feed space outlet 123b. The second chamber 124 has a permeate space outlet 124b. The feed space inlet 123a is an opening for supplying the first gas G1 to the feed side space (first chamber 113). The permeate space outlet 114b is an opening for discharging the second permeate gas S3 from the permeate side space (second chamber 124). The feed space outlet 123b is an opening for discharging the second non-permeate gas S4 that did not permeate the second separation membrane 121 from the feed side space (first chamber 123). The feed space inlet 123a, the feed space outlet 123b, and the permeate space outlet 124b are each formed on, for example, a wall surface of the container 122.

[0111] Like the first gas separation apparatus 11, the second gas separation apparatus 12 is suitable for a continuous membrane separation method. However, the second gas separation apparatus 12 may also be used for a batch membrane separation method.

[0112] The configuration of the second separation membrane 121 is not particularly limited. Figure 8 is a schematic cross-sectional view showing an example of the second separation membrane 121 provided in the second gas separation device 12 shown in Figure 7. As shown in Figure 8, the second separation membrane 121 may include a separation functional layer 5, a porous support 7 that supports the separation functional layer 5, and an intermediate layer 6 disposed between the separation functional layer 5 and the porous support 7. The intermediate layer 6 is in direct contact with each of the separation functional layer 5 and the porous support 7, for example.

[0113] The second separation membrane 121 may be a separation membrane that preferentially allows permeation of gas A. For example, when the mixed gas Gm contains carbon dioxide as gas A and nitrogen as gas B, the second separation membrane 121 may be a carbon dioxide separation membrane that preferentially allows permeation of carbon dioxide (gas A) contained in the mixed gas Gm. For example, when the mixed gas Gm contains nitrogen as gas A and carbon dioxide as gas B, the second separation membrane 121 may be a nitrogen separation membrane that preferentially allows permeation of nitrogen (gas A) contained in the mixed gas Gm.

[0114] When the second separation membrane 121 is a carbon dioxide separation membrane, the carbon dioxide (gas A) content in the second permeable gas S3 is higher than the carbon dioxide content in the mixed gas Gm. On the other hand, the carbon dioxide content in the second non-permeable gas S4 is lower than the carbon dioxide content in the mixed gas Gm. In other words, when the second separation membrane 121 is a carbon dioxide separation membrane, the second permeable gas S3 corresponds to the concentrated gas Gc.

[0115] (Separation function layer) When the second separation membrane 121 is a carbon dioxide separation membrane, the separation function layer 5 is a layer that allows carbon dioxide (gas A) contained in the mixed gas Gm to preferentially permeate. As the separation function layer 5, those listed as the separation function layer 5 when the first separation membrane 111 is a carbon dioxide separation membrane can be used.

[0116] (Intermediate Layer) As the intermediate layer 6, those exemplified as the intermediate layer 2 when the first separation membrane 111 is a carbon dioxide separation membrane can be used.

[0117] (Porous Support) As the porous support 7, those listed as the porous support 3 when the first separation membrane 111 is a carbon dioxide separation membrane can be used.

[0118] When the second separation membrane 121 is a nitrogen separation membrane, the carbon dioxide (gas B) content in the second permeable gas S3 is lower than the carbon dioxide content in the mixed gas Gm. On the other hand, the carbon dioxide content in the second non-permeable gas S4 is higher than the carbon dioxide content in the mixed gas Gm. In other words, when the second separation membrane 121 is a nitrogen separation membrane, the second non-permeable gas S4 corresponds to the concentrated gas Gc.

[0119] (Separation Functional Layer) When the second separation membrane 121 is a nitrogen separation membrane, the separation functional layer 5 is a layer that allows nitrogen contained in the mixed gas Gm to pass preferentially.

[0120] (Intermediate Layer) As the intermediate layer 6, those exemplified as the intermediate layer 2 when the first separation membrane 111 is a carbon dioxide separation membrane can be used.

[0121] (Porous Support) As the porous support 7, those listed as the porous support 3 when the first separation membrane 111 is a carbon dioxide separation membrane can be used.

[0122] The configuration of the second separation membrane 121 is not limited to the example shown in Fig. 8. The second separation membrane 121 may be composed of, for example, a separation functional layer 5 and a porous support 7 that is disposed on one side of the separation functional layer 5 and supports the separation functional layer 5. The second separation membrane 121 may be composed of, for example, a separation functional layer 5, a protective layer that is disposed on one side of the separation functional layer 5 and protects the separation functional layer 5, and a porous support 7 that is disposed on the other side of the separation functional layer 5 and supports the separation functional layer 5. The protective layer may contain the material described for the intermediate layer 2 of the first separation membrane 111.

[0123] The second gas separation device 12 having the second separation membrane 121 is not limited to the form shown in Fig. 7. The second gas separation device 12 having the second separation membrane 121 may be, for example, a spiral membrane element, a hollow fiber membrane element, etc. Although not shown, the second gas separation device 12 having the second separation membrane 121 may be a spiral membrane element, like the first gas separation device 15 shown in Fig. 4.

[0124] [Second Vacuum Pump] Like the first vacuum pump 21, the second vacuum pump 22 may be a vacuum pump that requires a seal gas. The second vacuum pump 22 can reduce the pressure in the internal space of the second gas separation device 12. When the second gas separation device 12 has a second separation membrane 121, the second vacuum pump 22 can reduce the pressure in the permeate side space (second chamber 124) of the second gas separation device 12. In other words, the second vacuum pump 22 can generate or increase a pressure difference between the supply side space (first chamber 123) and the permeate side space (second chamber 124) of the second gas separation device 12. The second vacuum pump 22 can be any of the pumps listed for the first vacuum pump 21.

[0125] The second vacuum pump 22 may be an assembly of multiple vacuum pumps. That is, the second vacuum pump 22 may be configured so that each of the multiple vacuum pumps can reduce the pressure in the permeate side space (second chamber 124) of the second gas separation device 12. With this configuration, the pressure in the permeate side space of the second gas separation device 12 can be appropriately adjusted by adjusting the number of vacuum pumps in operation.

[0126] 6, the second vacuum pump 22 is disposed in a concentrated gas discharge path 54 for discharging the concentrated gas Gc from the second gas separation device 12. When the second gas separation device 12 has a second separation membrane 121, the concentrated gas discharge path 54 is connected to the permeate space outlet 124b of the second gas separation device 12.

[0127] 6 , in the gas separation system 102 of the second modification, the mixed gas Gm may be supplied to the second gas separation device 12 via the second gas discharge path 52. The mixed gas Gm corresponds to the second gas G2 discharged from the first gas separation device 11. When the second gas separation device 12 has a second separation membrane 121, the second gas discharge path 52 is connected to the supply space inlet 123 a of the second gas separation device 12.

[0128] As shown in FIG. 6, the gas separation system 102 may further include a concentrated gas discharge path 54 and a non-concentrated gas discharge path 55 as gas paths.

[0129] The concentrated gas discharge path 54 is a path for discharging concentrated gas Gc from the second gas separation device 12 during operation. When the second gas separation device 12 has a second separation membrane 121, the concentrated gas discharge path 54 is connected to the permeate space outlet 124b of the second gas separation device 12. For example, a pump for controlling the flow rate of concentrated gas Gc may be disposed in the concentrated gas discharge path 54.

[0130] The non-concentrated gas discharge path 55 is a path for discharging the non-concentrated gas Gs from the second gas separation device 12 during operation. When the second gas separation device 12 has a second separation membrane 121, the non-concentrated gas discharge path 55 is connected to the supply space outlet 123b of the second gas separation device 12. For example, a pump for controlling the flow rate of the non-concentrated gas Gs may be disposed in the non-concentrated gas discharge path 55.

[0131] As shown in Figure 6, in the gas separation system 102 of Modification 2, the non-concentrated gas discharge path 55 may merge with the first gas supply path 51 at a junction position 67. By merging the non-concentrated gas discharge path 55 with the first gas supply path 51, it is possible to reuse, for example, the non-concentrated gas Gs containing gas A that was not completely separated in the second gas separation device 12. However, the non-concentrated gas discharge path 55 does not have to merge with the first gas supply path 51. The non-concentrated gas discharge path 55 may be connected to a recovery unit (not shown in Figure 6) that recovers the non-concentrated gas Gs.

[0132] 6 , in the gas separation system 102 of Modification 2, the concentrated gas discharge path 54 may have a first portion 541 and a second portion 542. When the second gas separation device 12 has the second separation membrane 121, the first portion 541 is a portion that connects the permeate space outlet 124b of the second gas separation device 12 and the second vacuum pump 22. The second portion 542 is a portion that connects to the second vacuum pump 22.

[0133] As shown in FIG. 6 , the gas separation system 102 of the second modification may further include a recovery unit 84 that recovers the concentrated gas Gc. As shown in FIG. 6 , the second portion 542 of the concentrated gas discharge path 54 may be connected to the recovery unit 84. The recovery unit 84 is, for example, a container that stores the concentrated gas Gc. The recovery unit 84 may be filled with an adsorbent capable of adsorbing the gas A contained in the concentrated gas Gc. The adsorbents listed above for the recovery unit 82 can be used as the adsorbent. Typically, the second portion 542 of the concentrated gas discharge path 54 is provided with a booster (not shown) for recovering the concentrated gas Gc in the recovery unit 84.

[0134] Next, a method for separating a mixed gas using the gas separation system 102 of the second modified example described above will be described.

[0135] In addition to the first gas separation step and first circulation step described above, the mixed gas separation method using the gas separation system 102 of Modification 2 further includes a second gas separation step of supplying a mixed gas Gm containing gas A and gas B to the second gas separation device 12, separating the mixed gas Gm by reducing the pressure in the internal space of the second gas separation device 12 with the second vacuum pump 22, and obtaining a concentrated gas Gc having a higher content of gas A than the mixed gas Gm. In this mixed gas separation method, (i) the mixed gas Gm is the second gas G2 discharged from the first gas separation device 11.

[0136] The second gas separation step of Modification 2 is carried out, for example, as follows: Hereinafter, the second gas separation step will be described using an example in which the second gas separation device 12 has the second separation membrane 121.

[0137] [Second Gas Separation Step] In the second gas separation step, first, the second gas G2 is supplied to the first chamber 123 (supply side space) of the second gas separation device 12 through the second gas supply path 52.

[0138] Next, with the second gas G1 being supplied to the first chamber 123 of the second gas separation device 12, the second chamber 124 (permeation side space) is depressurized by the second vacuum pump 22. Specifically, the second chamber 124 is depressurized using the second vacuum pump 22 through the permeation space outlet 124b.

[0139] By reducing the pressure inside the second chamber 124, a pressure difference is generated or increases between the supply-side space and the permeation-side space. As a result, the second gas G2 is separated by the second separation membrane 121, and the second permeation gas S3 is supplied to the second chamber 124. While the separation of the second gas G2 is being performed, the pressure inside the second chamber 124 may continue to be reduced by the second vacuum pump 22.

[0140] The second permeable gas S3 (concentrated gas Gc) supplied to the second chamber 124 passes through the first portion 541 of the concentrated gas discharge path 54 and is sucked into the second vacuum pump 22. The second vacuum pump 22 discharges the sucked second permeable gas S3 into the second portion 542 of the concentrated gas discharge path 54.

[0141] The mixed gas separation method may include a recovery step of recovering the concentrated gas Gc discharged from the second portion 542 of the concentrated gas discharge path 54 in the recovery section 84. The mixed gas separation method may include a second gas recovery step of recovering the first non-permeable gas S2 (third gas G3) obtained in the first gas separation step in the recovery section 83. The mixed gas separation method may further include a circulation step of circulating the second non-permeable gas S4 (non-concentrated gas Gs) obtained in the second gas separation step to the first-stage first gas separation device 11.

[0142] (Variation 3) FIG. 9 is a schematic diagram showing an example of a gas separation system 103 of Variation 3. As shown in FIG. 9, in the gas separation system 103, a first gas separation device 11 is disposed downstream of a second gas separation device 12. According to the gas separation system 103, at least a portion of the second gas G2 discharged from the second-stage first gas separation device 11 can be used as a seal gas for the second-stage first vacuum pump 21. In the gas separation system 103, the first gas G1 corresponds to the concentrated gas Gc supplied to the second-stage first gas separation device 11. The second gas G2 is supplied to the first vacuum pump 21 via the first circulation path 31. This configuration can further suppress a decrease in the content of gas A contained in the finally recovered separated gas. According to the gas separation system 103 of Variation 3, a vacuum pump requiring a seal gas with excellent pumping efficiency can be used, while recovering a higher concentration of separated gas.

[0143] 9 , the second vacuum pump 22 is disposed in a concentrated gas discharge path 54 for discharging concentrated gas Gc from the second gas separation device 12. In the gas separation system 103 of Modification 3, the concentrated gas discharge path 54 corresponds to the first gas supply path 51 for supplying the first gas G1 to the first gas separation device 11. When the second gas separation device 12 has a second separation membrane 121, the concentrated gas discharge path 54 is connected to the permeate space outlet 124b of the second gas separation device 12.

[0144] [Gas Paths] As shown in FIG. 9, the gas separation system 103 of the third modification may further include a mixed gas supply path 56, a concentrated gas discharge path 54, and a non-concentrated gas discharge path 55 as gas paths.

[0145] The mixed gas supply path 56 is a path for supplying the mixed gas Gm to the second gas separation device 12 during operation. When the second gas separation device 12 has a second separation membrane 121, the mixed gas supply path 56 is connected to a supply space inlet 123a of the second gas separation device 12. The mixed gas supply path 56 may be connected to a supply source (not shown) such as a combustion device. The mixed gas Gm may be supplied to the mixed gas supply path 56 from a supply source such as a combustion device.

[0146] As with the gas separation system 102 of Modification 2, the concentrated gas discharge path 54 is a path for discharging concentrated gas Gc from the second gas separation device 12 during operation. When the second gas separation device 12 has a second separation membrane 121, the concentrated gas discharge path 54 is connected to the permeate space outlet 124b of the second gas separation device 12. A pump for controlling the flow rate of concentrated gas Gc may be disposed in the concentrated gas discharge path 54, for example.

[0147] As with the gas separation system 102 of Modification 2, the non-concentrated gas discharge path 55 is a path for discharging the non-concentrated gas Gs from the second gas separation device 12 during operation. When the second gas separation device 12 has a second separation membrane 121, the non-concentrated gas discharge path 55 is connected to the supply space outlet 123b of the second gas separation device 12. For example, a pump for controlling the flow rate of the non-concentrated gas Gs may be disposed in the non-concentrated gas discharge path 55.

[0148] As shown in FIG. 9 , the gas separation system 103 of Modification 3 may further include a recovery unit 85 that recovers the non-concentrated gas Gs. As shown in FIG. 9 , the non-concentrated gas discharge path 55 may be connected to the recovery unit 85. The recovery unit 85 is, for example, a container that stores the non-concentrated gas Gs. However, in the gas separation system 103 of Modification 3, the non-concentrated gas discharge path 55 may merge with the mixed gas supply path 56 at a merging position (not shown in FIG. 9 ). By merging the non-concentrated gas discharge path 55 with the mixed gas supply path 56, for example, it is possible to reuse the non-concentrated gas Gs containing gas A that was not completely separated in the second gas separation device 12.

[0149] Although not shown, Modification 3 and Modification 1 may be combined. That is, the gas separation system 103 may include a first recovery path branching off from the first circulation path 31 downstream of the first booster 71, and a first recovery unit connected to the first recovery path and recovering the second gas G2. In this case, the number of devices constituting the system can be reduced while maintaining the same processing power as the gas separation system 103 shown in FIG. 9.

[0150] 9 , in the gas separation system 103 of the third modification, the concentrated gas discharge path 54 may have a first portion 541 and a second portion 542. When the second gas separation device 12 has the second separation membrane 121, the first portion 541 is a portion that connects the permeate space outlet 124b of the second gas separation device 12 and the second vacuum pump 22. The second portion 542 is a portion that connects the second vacuum pump 22 and the supply space inlet 113a of the first gas separation device 11.

[0151] As shown in Figure 9, in the gas separation system 103 of Modification 3, the third gas discharge path 53 may merge with the mixed gas supply path 56 at a merging position 68. By merging the third gas discharge path 53 with the mixed gas supply path 56, it is possible to reuse, for example, the third gas G3 containing the gas A that was not completely separated in the first gas separation device 11. However, the third gas discharge path 53 does not have to merge with the mixed gas supply path 56. The third gas discharge path 53 may be connected to a recovery section (not shown in Figure 8) that recovers the third gas G3.

[0152] Next, a method for separating a mixed gas using the gas separation system 103 of the third modified example will be described.

[0153] The mixed gas separation method using the gas separation system 103 of the third modification further includes the second gas separation process described above in addition to the first gas separation process and the first circulation process described above. In this mixed gas separation method, (ii) the concentrated gas Gc is the first gas G1 supplied to the first gas separation device 11.

[0154] The mixed gas separation method may include a recovery step of recovering the second gas G2 discharged from the third portion 523 of the second gas discharge path 52 in the recovery section 82. The mixed gas separation method may include a second gas recovery step of recovering the second gas G2 (first permeable gas S1) obtained in the first gas separation step in the recovery section 82. The mixed gas separation method may further include a circulation step of circulating the third gas G3 (first non-permeable gas S2) obtained in the first gas separation step to the first-stage second gas separation device 12.

[0155] 10 is a schematic diagram showing an example of a gas separation system 104 of Modification 4. The gas separation system 104 of Modification 4 has the same configuration as the gas separation system 102 of Modification 2, except that it further includes at least one selected from the group consisting of a second circulation path 32 that guides at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22, and a third circulation path 33 that guides at least a portion of the second gas G2 discharged from the first gas separation device 11 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22.

[0156] As shown in FIG. 10 , in a gas separation system 104, a second gas separation device 12 is disposed downstream of a first gas separation device 11. According to the gas separation system 104, at least a portion of the second gas G2 discharged from the first-stage first gas separation device 11 can be used as a seal gas for the first-stage first vacuum pump 21, and at least a portion of the concentrated gas Gc discharged from the second-stage second gas separation device 12 can be used as a seal gas for the second-stage second vacuum pump 22, and / or at least a portion of the second gas G2 discharged from the first-stage first gas separation device 11 can be used as a seal gas for the second-stage second vacuum pump 22. The second gas G2 is supplied to the first vacuum pump 21 via a first circulation path 31 and / or to the second vacuum pump 22 via a third circulation path 33. The concentrated gas Gc is supplied to the second vacuum pump 22 via a second circulation path 32. This configuration further suppresses a decrease in the content of gas A contained in the finally recovered separated gas. According to the gas separation system 104 of the fourth modification, it is possible to recover a separated gas with a higher concentration while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0157] 10 , in the gas separation system 104 of the fourth modification, the first circulation path 31 may have a first portion 311 and a second portion 312. The first portion 311 is a portion that connects the branch position 61 and the branch position 63. The second portion 312 is a portion that connects the branch position 63 and the first vacuum pump 21.

[0158] The second circulation path 32 is a path that guides at least a portion of the concentrated gas Gc to the second vacuum pump 22 as a seal gas for the second vacuum pump 22. In the example of Fig. 10 , the second circulation path 32 branches off from the concentrated gas discharge path 54 at a branch position 62 and is connected to a seal gas inlet of the second vacuum pump 22. However, the connection position of the second circulation path 32 is not limited to the example shown in Fig. 10 . For example, the second circulation path 32 may branch off from the discharge port of the second vacuum pump 22 and be connected to the seal gas inlet of the second vacuum pump 22.

[0159] 10 , the gas separation system 104 may include a second booster 72 provided in the second circulation path 32. The second booster 72 pressurizes the concentrated gas Gc as a seal gas supplied to the second vacuum pump 22. By continuously operating the second booster 72, the concentrated gas Gc can be obtained stably.

[0160] The second booster 72 is not particularly limited as long as it can pressurize the concentrated gas Gc as the seal gas supplied to the second vacuum pump 22. The second booster 72 is typically a compressor.

[0161] The gas separation system 104 may include a drain mechanism (not shown) that discharges moisture contained in the concentrated gas Gc serving as the seal gas. With this configuration, for example, when the concentrated gas Gc contains moisture, malfunctions of the components of the gas separation system 104 due to moisture can be suppressed.

[0162] A drain mechanism may be provided in the second booster 72. As shown in Fig. 10, the moisture collected by the drain mechanism may be discharged to the outside through a second drain path 36 connected to the second booster 72.

[0163] A switching valve (not shown) may be provided at the branch position 62. A flow rate adjustment valve (not shown) may be provided in the second circulation path 32. With this configuration, the flow rate of the concentrated gas Gc introduced into the second circulation path 32 can be adjusted by the switching valve and the flow rate adjustment valve.

[0164] 10 , in the gas separation system 104 of Modification 4, the concentrated gas discharge path 54 may have a third portion 543 in addition to a first portion 541 and a second portion 542. When the second gas separation device 12 has a second separation membrane 121, the first portion 541 is a portion that connects the permeate space outlet 124b of the second gas separation device 12 to the second vacuum pump 22. The second portion 542 is a portion that connects the second vacuum pump 22 to the branch position 62. The third portion 543 is a portion that connects to the branch position 62.

[0165] The third circulation path 33 is a path that guides at least a portion of the second gas G2 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22. In the example of Fig. 10 , the third circulation path 33 branches off from the first circulation path 31 at a branch position 63 and is connected to the seal gas inlet of the second vacuum pump 22. However, the connection position of the third circulation path 33 is not limited to the example shown in Fig. 10 .

[0166] A switching valve (not shown) may be provided at the branch position 63. A flow rate adjustment valve (not shown) may be provided in the third circulation path 33. With this structure, the flow rate of the second gas G2 introduced into the third circulation path 33 can be adjusted by the switching valve and the flow rate adjustment valve.

[0167] The flow rate of the second gas G2 supplied to the first vacuum pump 21, the flow rate of the second gas G2 supplied to the second vacuum pump 22, and the flow rate of the concentrated gas Gc supplied to the second vacuum pump 22 are preferably 12 NL / min or more. The upper limit of the flow rate of the second gas G2 supplied to the first vacuum pump 21, the upper limit of the flow rate of the second gas G2 supplied to the second vacuum pump 22, and the upper limit of the flow rate of the concentrated gas Gc supplied to the second vacuum pump 22 are not particularly limited.

[0168] Although not shown, Modification 4 and Modification 1 may be combined. That is, the gas separation system 104 may include a second recovery path branching off from the second circulation path 32 downstream of the second booster 72, and a second recovery unit connected to the second recovery path and recovering the concentrated gas Gc. In this case, the number of devices constituting the system can be reduced with the same processing power as the gas separation system 104 shown in FIG. 10.

[0169] In the gas separation system 104, for example, the control device 40 may adjust the flow rate of the second gas G2 supplied to the first vacuum pump 21 and / or the flow rate of the second gas G2 supplied to the second vacuum pump 22. The control device 40 may adjust the flow rate of the concentrated gas Gc supplied to the second vacuum pump 22. The control device 40 may adjust the flow rate of the second gas G2 introduced into the first circulation path 31 and / or the flow rate of the second gas G2 introduced into the third circulation path 33 by controlling the switching valve provided at the branch position 61, the switching valve provided at the branch position 63, the flow rate adjustment valve provided in the first circulation path 31, and the flow rate adjustment valve provided in the third circulation path 33. The control device 40 may adjust the flow rate of the concentrated gas Gc introduced into the second circulation path 32 by controlling the switching valve provided at the branch position 62 and the flow rate adjustment valve provided in the second circulation path 32.

[0170] Although not shown, a buffer tank and a pressure reducing valve may be provided downstream of the second booster 72 in the second circulation path 32 .

[0171] Next, a method for separating a mixed gas using the gas separation system 104 of the fourth modification will be described.

[0172] The mixed gas separation method using the gas separation system 104 of Variation 4 includes, in addition to the first gas separation step, first circulation step, and second gas separation step described above, at least one step selected from the group consisting of a second circulation step in which at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 is introduced to the second vacuum pump 22 as a seal gas for the second vacuum pump 22, and a third circulation step in which at least a portion of the second gas G2 discharged from the first gas separation device 11 is introduced to the second vacuum pump 22 as a seal gas for the second vacuum pump 22. In this mixed gas separation method, (i) the mixed gas Gm is the second gas G2 discharged from the first gas separation device 11.

[0173] The second circulation step and the third circulation step of Modification 4 are performed, for example, as follows. Hereinafter, the second circulation step and the third circulation step will be described using an example in which the second gas separation device 12 has the second separation membrane 121.

[0174] [Second Circulation Step] In the second circulation step, at least a portion of the second permeable gas S3 (enriched gas Gc) discharged from the second vacuum pump 22 to the second portion 542 of the concentrated gas discharge path 54 is supplied to the second vacuum pump 22 as a seal gas via the second circulation path 32.

[0175] The flow rate of the second permeable gas S3 supplied to the second vacuum pump 22 may be adjusted by a switching valve provided at the branch position 62 and a flow rate adjustment valve provided in the second circulation path 32 .

[0176] [Third Circulation Process] In the third circulation process, at least a portion of the first permeable gas S1 (second gas G2) discharged from the first vacuum pump 21 to the second portion 522 of the second gas discharge path 52 is supplied to the second vacuum pump 22 as a seal gas via the third circulation path 33.

[0177] The flow rate of the first permeable gas S1 supplied to the second vacuum pump 22 may be adjusted by a switching valve provided at the branch position 63 and a flow rate adjustment valve provided in the third circulation path 33 .

[0178] The mixed gas separation method may include a recovery step of recovering the concentrated gas Gc discharged from the third portion 543 of the concentrated gas discharge path 54 in the recovery section 84. The mixed gas separation method may include a third gas recovery step of recovering the first non-permeable gas S2 (third gas G3) obtained in the first gas separation step in the recovery section 83. The mixed gas separation method may further include a circulation step of circulating the second non-permeable gas S4 (non-concentrated gas Gs) obtained in the second gas separation step to the first-stage first gas separation device 11.

[0179] 11 is a schematic configuration diagram showing an example of a gas separation system 105 of Modification 5. The gas separation system 105 of Modification 5 has the same configuration as the gas separation system 103 of Modification 3, except that it further includes at least one selected from the group consisting of a second circulation path 32 that guides at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22, and a fourth circulation path 34 that guides at least a portion of the second gas G2 discharged from the first gas separation device 11 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22.

[0180] As shown in FIG. 11 , in the gas separation system 105, the first gas separation device 11 is disposed downstream of the second gas separation device 12. According to the gas separation system 105, at least a portion of the second gas G2 discharged from the second-stage first gas separation device 11 can be used as a seal gas for the second-stage first vacuum pump 21, and at least a portion of the concentrated gas Gc discharged from the first-stage second gas separation device 12 can be used as a seal gas for the first-stage second vacuum pump 22, and / or at least a portion of the second gas G2 discharged from the second-stage first gas separation device 11 can be used as a seal gas for the first-stage second vacuum pump 22. The second gas G2 is supplied to the first vacuum pump 21 via the first circulation path 31 and / or to the second vacuum pump 22 via the fourth circulation path 34. The concentrated gas Gc is supplied to the second vacuum pump 22 via the second circulation path 32. This configuration further suppresses a decrease in the content of gas A contained in the finally recovered separated gas. According to the gas separation system 105 of the fifth modification, it is possible to recover a separated gas with a higher concentration while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0181] 11 , in the gas separation system 105 of the fifth modification, the first circulation path 31 may have a first portion 311 and a second portion 312. The first portion 311 is a portion that connects the branch position 61 and the branch position 64. The second portion 312 is a portion that connects the branch position 64 and the first vacuum pump 21.

[0182] The second circulation path 32 is a path that guides at least a portion of the concentrated gas Gc to the second vacuum pump 22 as a seal gas for the second vacuum pump 22. In the example of Fig. 11 , the second circulation path 32 branches off from the concentrated gas discharge path 54 at a branch position 62 and is connected to a seal gas inlet of the second vacuum pump 22. However, the connection position of the second circulation path 32 is not limited to the example shown in Fig. 11 . For example, the second circulation path 32 may branch off from the discharge port of the second vacuum pump 22 and be connected to the seal gas inlet of the second vacuum pump 22.

[0183] 11 , the gas separation system 105 may include a second booster 72 provided in the second circulation path 32. The second booster 72 pressurizes the concentrated gas Gc as a seal gas supplied to the second vacuum pump 22. By continuously operating the second booster 72, the concentrated gas Gc can be obtained stably.

[0184] The gas separation system 105 may include a drain mechanism (not shown) that discharges moisture contained in the concentrated gas Gc serving as the seal gas. With this configuration, for example, when the concentrated gas Gc contains moisture, malfunctions of the components of the gas separation system 105 due to moisture can be suppressed.

[0185] A drain mechanism may be provided in the second booster 72. As shown in Fig. 11 , the moisture collected by the drain mechanism may be discharged to the outside through a second drain path 36 connected to the second booster 72.

[0186] A switching valve (not shown) may be provided at the branch position 62. A flow rate adjustment valve (not shown) may be provided in the second circulation path 32. With this configuration, the flow rate of the concentrated gas Gc introduced into the second circulation path 32 can be adjusted by the switching valve and the flow rate adjustment valve.

[0187] 11 , in the gas separation system 105 of the fifth modification, the concentrated gas discharge path 54 may have a third portion 543 in addition to a first portion 541 and a second portion 542. When the second gas separation device 12 has a second separation membrane 121, the first portion 541 is a portion that connects the permeate space outlet 124b of the second gas separation device 12 to the second vacuum pump 22. The second portion 542 is a portion that connects the second vacuum pump 22 to the branch position 62. The third portion 543 is a portion that connects to the branch position 62.

[0188] In the gas separation system 105 of the fifth modification, the fourth circulation path 34 is a path that guides at least a portion of the second gas G2 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22. In the example of Fig. 11 , the fourth circulation path 34 branches off from the first circulation path 31 at a branch position 64 and is connected to the seal gas inlet of the second vacuum pump 22. However, the connection position of the fourth circulation path 34 is not limited to the example shown in Fig. 11 .

[0189] A switching valve (not shown) may be provided at the branch position 64. A flow rate adjustment valve (not shown) may be provided in the fourth circulation path 34. With this structure, the flow rate of the second gas G2 introduced into the fourth circulation path 34 can be adjusted by the switching valve and the flow rate adjustment valve.

[0190] The flow rate of the second gas G2 supplied to the first vacuum pump 21, the flow rate of the second gas G2 supplied to the second vacuum pump 22, and the flow rate of the concentrated gas Gc supplied to the second vacuum pump 22 are preferably 12 NL / min or more. The upper limit of the flow rate of the second gas G2 supplied to the first vacuum pump 21, the upper limit of the flow rate of the second gas G2 supplied to the second vacuum pump 22, and the upper limit of the flow rate of the concentrated gas Gc supplied to the second vacuum pump 22 are not particularly limited.

[0191] Although not shown, Modification 5 and Modification 1 may be combined. That is, the gas separation system 105 may include a first recovery path branching off from the first circulation path 31 downstream of the first booster 71, and a first recovery unit connected to the first recovery path and recovering the second gas G2. In this case, the number of devices constituting the system can be reduced with the same processing power as the gas separation system 105 shown in FIG. 11 .

[0192] In the gas separation system 105, for example, the control device 40 may adjust the flow rate of the second gas G2 supplied to the first vacuum pump 21 and / or the flow rate of the second gas G2 supplied to the second vacuum pump 22. The control device 40 may adjust the flow rate of the concentrated gas Gc supplied to the second vacuum pump 22. The control device 40 may adjust the flow rate of the second gas G2 introduced into the first circulation path 31 and / or the flow rate of the second gas G2 introduced into the fourth circulation path 34 by controlling the switching valve provided at the branch position 61, the switching valve provided at the branch position 64, the flow rate adjustment valve provided in the first circulation path 31, and the flow rate adjustment valve provided in the fourth circulation path 34. The control device 40 may adjust the flow rate of the concentrated gas Gc introduced into the second circulation path 32 by controlling the switching valve provided at the branch position 62 and the flow rate adjustment valve provided in the second circulation path 32.

[0193] Next, a method for separating a mixed gas using the gas separation system 105 of the fifth modified example will be described.

[0194] The mixed gas separation method using the gas separation system 105 of variant 5 includes, in addition to the first gas separation step, first circulation step, and second gas separation step described above, at least one step selected from the group consisting of a second circulation step in which at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 is introduced into the second vacuum pump 22 as a seal gas for the second vacuum pump 22, and a fourth circulation step in which at least a portion of the second gas G2 discharged from the first gas separation device 11 is introduced into the second vacuum pump 22 as a seal gas for the second vacuum pump 22. In this mixed gas separation method, (ii) the concentrated gas Gc is the first gas G1 supplied to the first gas separation device 11.

[0195] The second circulation step and the fourth circulation step of the fifth modification are carried out, for example, as follows. Hereinafter, the second circulation step and the fourth circulation step will be described using an example in which the second gas separation device 12 has the second separation membrane 121.

[0196] [Second Circulation Step] In the second circulation step, at least a portion of the second permeable gas S3 (enriched gas Gc) discharged from the second vacuum pump 22 to the second portion 542 of the concentrated gas discharge path 54 is supplied to the second vacuum pump 22 as a seal gas via the second circulation path 32.

[0197] The flow rate of the second permeable gas S3 supplied to the second vacuum pump 22 may be adjusted by a switching valve provided at the branch position 62 and a flow rate adjustment valve provided in the second circulation path 32 .

[0198] [Fourth Circulation Step] In the fourth circulation step, at least a portion of the first permeable gas S1 (second gas G2) discharged from the first vacuum pump 21 to the second portion 522 of the second gas discharge path 52 is supplied to the second vacuum pump 22 as a seal gas via the fourth circulation path 34.

[0199] The flow rate of the first permeable gas S1 supplied to the second vacuum pump 22 may be adjusted by a switching valve provided at the branch position 64 and a flow rate adjustment valve provided in the fourth circulation path 34 .

[0200] The mixed gas separation method may include a recovery step of recovering the second gas G2 discharged from the third portion 523 of the second gas discharge path 52 in the recovery section 82. The mixed gas separation method may further include a circulation step of circulating the first non-permeable gas S2 (third gas G3) obtained in the first gas separation step to the first-stage second gas separation device 12. The mixed gas separation method may include a fourth gas recovery step of recovering the second non-permeable gas S4 (non-concentrated gas Gs) obtained in the second gas separation step in the recovery section 85.

[0201] 12 is a schematic diagram showing an example of a gas separation system 106 of Modification 6. The gas separation system 106 of Modification 6 has the same configuration as the gas separation system 102 of Modification 2, except that it further includes at least one selected from the group consisting of a second circulation path 32 that guides at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22, a third circulation path 33 that guides at least a portion of the second gas G2 discharged from the first gas separation device 11 to the second vacuum pump 22 as a seal gas for the second vacuum pump 22, and a fourth circulation path 34 that guides at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 to the first vacuum pump 21 as a seal gas for the first vacuum pump 21. The gas separation system 106 shown in Figure 12 has the same configuration as the gas separation system 104 shown in Figure 10, except that it further includes a fourth circulation path 34 that guides at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 to the first vacuum pump 21 as a seal gas for the first vacuum pump 21.

[0202] 12 , in a gas separation system 106, a second gas separation device 12 is disposed downstream of a first gas separation device 11. According to the gas separation system 106, at least a portion of the second gas G2 discharged from the first-stage first gas separation device 11 can be used as a seal gas for the first-stage first vacuum pump 21, and at least a portion of the concentrated gas Gc discharged from the second-stage second gas separation device 12 can be used as a seal gas for the second-stage second vacuum pump 22, and / or at least a portion of the second gas G2 discharged from the first-stage first gas separation device 11 can be used as a seal gas for the second-stage second vacuum pump 22, and / or at least a portion of the concentrated gas Gc discharged from the second-stage second gas separation device 12 can be used as a seal gas for the first-stage first vacuum pump 21. The second gas G2 is supplied to the first vacuum pump 21 via a first circulation path 31 and / or to the second vacuum pump 22 via a third circulation path 33. The concentrated gas Gc is supplied to the second vacuum pump 22 via the second circulation path 32 and / or to the first vacuum pump 21 via the fourth circulation path 34. This configuration further suppresses a decrease in the content of gas A in the finally recovered separated gas. The gas separation system 106 of variant 6 can recover a separated gas with an even higher concentration while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0203] 12 , in the gas separation system 106 of the sixth modification, the second circulation path 32 may have a first portion 321 and a second portion 322. The first portion 321 is a portion that connects the branch position 62 and the branch position 65. The second portion 322 is a portion that connects the branch position 65 and the second vacuum pump 22.

[0204] In the gas separation system 106 of the sixth modification, the fourth circulation path 34 is a path that guides at least a portion of the concentrated gas Gc to the first vacuum pump 21 as a seal gas for the first vacuum pump 21. In the example of Fig. 12 , the fourth circulation path 34 branches off from the second circulation path 32 at a branch position 65 and is connected to the seal gas inlet of the first vacuum pump 21. However, the connection position of the fourth circulation path 34 is not limited to the example shown in Fig. 12 .

[0205] A switching valve (not shown) may be provided at the branch position 65. A flow rate adjustment valve (not shown) may be provided in the fourth circulation path 34. With this structure, the flow rate of the concentrated gas Gc introduced into the fourth circulation path 34 can be adjusted by the switching valve and the flow rate adjustment valve.

[0206] The flow rates of the second gas G2 supplied to the first vacuum pump 21, the second vacuum pump 22, the first vacuum pump 21, and the second vacuum pump 22 are preferably 12 NL / min or more. The upper limit of the flow rate of the second gas G2 supplied to the first vacuum pump 21, the second vacuum pump 22, the first vacuum pump 21, and the second vacuum pump 22 is not particularly limited.

[0207] Although not shown, Modification 6 and Modification 1 may be combined. That is, the gas separation system 106 may include a second recovery path branching off from the second circulation path 32 downstream of the second booster 72, and a second recovery unit connected to the second recovery path and recovering the concentrated gas Gc. In this case, the number of devices constituting the system can be reduced with the same processing power as the gas separation system 106 shown in FIG. 12.

[0208] In the gas separation system 106, for example, the control device 40 may adjust the flow rate of the second gas G2 supplied to the first vacuum pump 21 and / or the flow rate of the second gas G2 supplied to the second vacuum pump 22. The control device 40 may adjust the flow rate of the concentrated gas Gc supplied to the first vacuum pump 21 and / or the flow rate of the concentrated gas Gc supplied to the second vacuum pump 22. The control device 40 may adjust the flow rate of the second gas G2 introduced into the first circulation path 31 and / or the flow rate of the second gas G2 introduced into the third circulation path 33 by controlling the switching valve provided at the branch position 61, the switching valve provided at the branch position 63, the flow rate adjustment valve provided in the first circulation path 31, and the flow rate adjustment valve provided in the third circulation path 33. The control device 40 may adjust the flow rate of concentrated gas Gc led to the second circulation path 32 and / or the flow rate of concentrated gas Gc led to the fourth circulation path 34 by controlling the switching valve provided at the branch position 62, the switching valve provided at the branch position 65, the flow rate control valve provided in the second circulation path 32, and the flow rate control valve provided in the fourth circulation path 34.

[0209] In the gas separation system 106 of the sixth modification, the control device 40 may control switching of the circulation path to be used.

[0210] Next, a method for separating a mixed gas using the gas separation system 106 of the sixth modification will be described.

[0211] The mixed gas separation method using the gas separation system 106 of Variation 6 includes, in addition to the first gas separation step, first circulation step, and second gas separation step described above, at least one step selected from the group consisting of the second circulation step, third circulation step, and a fourth circulation step in which at least a portion of the concentrated gas Gc discharged from the second gas separation device 12 is introduced into the first vacuum pump 21 as a seal gas for the first vacuum pump 21. In this mixed gas separation method, (i) the mixed gas Gm is the second gas G2 discharged from the first gas separation device 11.

[0212] The fourth circulation step of Modification 6 is carried out, for example, as follows: Hereinafter, the fourth circulation step will be described using an example in which the second gas separation device 12 has the second separation membrane 121.

[0213] [Fourth Circulation Step] In the fourth circulation step, at least a portion of the second permeable gas S3 (enriched gas Gc) discharged from the second vacuum pump 22 to the second portion 542 of the concentrated gas discharge path 54 is supplied to the first vacuum pump 21 as a seal gas via the fourth circulation path 34.

[0214] The flow rate of the second permeable gas S3 supplied to the first vacuum pump 21 may be adjusted by a switching valve provided at the branch position 65 and a flow rate adjustment valve provided in the fourth circulation path 34 .

[0215] (Other Modifications) The above examples may be combined with each other as long as there is no technical contradiction.

[0216] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0217] Calculation Examples 1 to 5 Simulations were performed for the operation of the gas separation system 200 shown in Fig. 13. As shown in Fig. 13, the gas separation system 200 was equipped with a first gas separation device 211 that separates a first gas F1 containing gas A and a gas B different from gas A to obtain a second gas F2 having a higher content of gas A than the first gas F1, a second gas separation device 212 that separates the second gas F2 to obtain a fourth gas F4 having a higher content of gas A than the second gas F2, a first vacuum pump 221 that depressurizes the permeate side space of the first gas separation device 211, and a second vacuum pump 222 that depressurizes the permeate side space of the second gas separation device 212. The gas separation system 200 was provided with, as circulation paths, a first circulation path 231 that guides at least a portion of the second gas F2 to the first vacuum pump 221 as a seal gas for the first vacuum pump 221, a third circulation path 233 that guides at least a portion of the second gas F2 to the second vacuum pump 222 as a seal gas for the second vacuum pump 222, a second circulation path 232 that guides at least a portion of the fourth gas F4 to the second vacuum pump 222 as a seal gas for the second vacuum pump 222, and a fourth circulation path 234 that guides at least a portion of the fourth gas F4 to the first vacuum pump 221 as a seal gas for the first vacuum pump 221. That is, the gas separation system 200 had the same configuration as the gas separation system 106 of Variation 6 shown in FIG. 12 (some elements are omitted in FIG. 13 ). In the gas separation system 200, it was assumed that a carbon dioxide separation membrane with a CO permeation rate of 500 GPU, an N permeation rate of 16.67 GPU, and a separation coefficient α of 30 was used as the first separation membrane 211a provided in the first-stage first gas separation device 211 and the second separation membrane 212a provided in the second-stage second gas separation device 212. The permeation rates of the second gas F2 permeating through the first separation membrane 211a and the fourth gas F4 permeating through the second separation membrane 212a were both set to 500 GPU. The pump efficiencies of the first vacuum pump 221 and the second vacuum pump 222 were both set to 40%. The supply conditions for the first gas F1 supplied to the first-stage first gas separation device 211 were set as follows:[Supply conditions for first gas F1] CO2 weight: 45.3 kg / hr (4800 NL / min) Composition (volume ratio): Gas A: CO2 8.5%, Gas B: N2 71.5%, Other gases: O2 5%, H2O 15% Pressure: 101.33 kPa Temperature: 25°C.

[0218] For calculation examples 1 to 5, the amount of carbon dioxide recovered (kg / h), carbon dioxide recovery rate (wt%), carbon dioxide concentration (vol%), and carbon dioxide recovery power (kWh / kg-CO2) were calculated when the circulation amounts of the second gas F2 and the fourth gas F4 to the first vacuum pump 221 in the first stage and the circulation amounts of the second gas F2 and the fourth gas F4 to the second vacuum pump 222 in the second stage were set as shown in Table 1. For the calculations, Schlumberger's process modeling software Symmetry was used. The carbon dioxide recovery power is the energy required to operate the gas separation system 200 per kg of carbon dioxide contained in the fourth gas F4 obtained from the second gas separation device 212 in the second stage.

[0219] Calculation Example 6 As Calculation Example 6, a simulation was performed when the gas separation system 500 shown in Figure 14 was operated. As shown in Figure 14, the gas separation system 500 was equipped with a first gas separation device 511 that separates a first gas F1 containing gas A and a gas B different from gas A to obtain a second gas F2 having a higher gas A content than the first gas F1, a second gas separation device 512 that separates the second gas F2 to obtain a fourth gas F4 having a higher gas A content than the second gas F2, a first vacuum pump 521 that depressurizes the permeate side space of the first gas separation device 511, and a second vacuum pump 522 that depressurizes the permeate side space of the second gas separation device 512. The gas separation system 500 had the same configuration as the gas separation system 200 shown in Figure 13, except that it did not have a circulation path. In the gas separation system 500, it was assumed that the same carbon dioxide separation membranes as those used in the gas separation system 200 were used as the first separation membrane 511a provided in the first-stage first gas separation device 511 and the second separation membrane 512a provided in the second-stage second gas separation device 512. Air (N2 / O2 (volume ratio) = 80 / 20) was set as the seal gas for the first-stage first vacuum pump 521 and the second-stage second vacuum pump 522. The permeation rate of the second gas F2 permeating the first separation membrane 511a and the permeation rate of the fourth gas F4 permeating the second separation membrane 512a were both set to 500 GPU. The pump efficiencies of the first vacuum pump 521 and the second vacuum pump 522 were both set to 40%. The supply conditions for the first gas F1 supplied to the first-stage first gas separation device 511 were set to the same as those in the gas separation system 200.

[0220] For calculation example 6, the amount of carbon dioxide recovered (kg / h), carbon dioxide recovery rate (wt%), carbon dioxide concentration (vol%), and carbon dioxide recovery power (kWh / kg-CO2) were calculated when the supply rate of seal gas to the first vacuum pump 521 in the first stage and the supply rate of seal gas to the second vacuum pump 522 in the second stage were set to 60 NL / min. For the calculations, process modeling software Symmetry manufactured by Schlumberger was used.

[0221] The simulation results of calculation examples 1 to 6 are shown in Table 1. In Table 1, the supply amount of the second gas F2 to the first vacuum pump refers to the supply amount of the second gas F2 supplied to the first vacuum pump 221 via the first circulation path 231. The supply amount of the second gas F2 to the second vacuum pump refers to the supply amount of the second gas F2 supplied to the second vacuum pump 222 via the third circulation path 233. The supply amount of the fourth gas F4 to the first vacuum pump refers to the supply amount of the fourth gas F4 supplied to the first vacuum pump 221 via the fourth circulation path 234. The supply amount of the fourth gas F4 to the second vacuum pump refers to the supply amount of the fourth gas F4 supplied to the second vacuum pump 222 via the second circulation path 232.

[0222]

[0223] As shown in Table 1, in Calculation Examples 1 to 5, in which at least a portion of the second gas F2, which has a higher carbon dioxide content than the first gas F1, and / or at least a portion of the fourth gas F4, which has a higher carbon dioxide content than the second gas F2, was used as the seal gas for the vacuum pump that depressurized the internal space of the gas separation apparatus, the concentration of carbon dioxide in the finally recovered separated gas was higher, and a high-concentration separated gas could be recovered, compared to Calculation Example 6, in which air was used as the seal gas for the vacuum pump. Furthermore, a comparison of Calculation Examples 1 to 5 shows that by controlling the supply amounts of the second gas F2 and / or the fourth gas F4 to the first-stage first vacuum pump 221 and the second-stage second vacuum pump 222, the carbon dioxide recovery power could be reduced.

[0224] Calculation Example 7: As Calculation Example 7, a simulation was performed on the range downstream of the second discharge path 254 when the gas separation system 201 shown in FIG. 15 was operated. Elements of the gas separation system 201 common to the gas separation system 200 ( FIG. 13 ) used in Calculation Examples 1 to 5 are designated by the same reference numerals, and descriptions thereof will be omitted. As shown in FIG. 15 , the gas separation system 201 included a booster (compressor) 272 provided in the second circulation path 232 and a recovery unit 284 connected to the third portion 254c of the second discharge path 254. The third portion 254c of the second discharge path 254 included a booster (compressor) 223 for recovering the fourth gas F4 in the recovery unit 284. The pump efficiencies of the first vacuum pump 221 and the second vacuum pump 222 were both set to 40%. The supply conditions of the first gas F1 supplied to the first-stage first gas separation device 211 were set to the same as those of the gas separation system 200. The CO2 concentration of the fourth gas F4 discharged from the second gas separation device 212 was set to 95%. The supply pressure of the compressor 272 was set to 0.5 MPaG. The supply pressure of the compressor 223 was set to 1.0 MPaG, and the power efficiency was set to 70%. The filling processing rate of the recovery section 284 was set to 250 N / min (258 t / year).

[0225] In Calculation Example 7, the amount (circulation flow rate) of the fourth gas F4 that is pressurized by the compressor 272 and returned to the second vacuum pump 222 through the second circulation path 232 is set to 12 NL / min and 60 NL / min, and for each case, the sum of the processing power (kWh / kg-CO2) of the second vacuum pump 222, the compressor 272, and the compressor 223 when attempting to supply 250 NL / min of the fourth gas F4 to the recovery section 284 is calculated. For the calculation, process modeling software Symmetry manufactured by Schlumberger GmbH was used.

[0226] Calculation Example 8: As Calculation Example 8, a simulation was performed on the range downstream of the second discharge path 254 when the gas separation system 202 shown in FIG. 16 was operated. Elements of the gas separation system 202 common to the gas separation system 201 ( FIG. 15 ) used in Calculation Example 7 are designated by the same reference numerals, and a description thereof will be omitted. As shown in FIG. 16 , the gas separation system 202 includes a recovery path 291 branching from the second portion 254b of the second discharge path 254 downstream of the compressor 272, and a recovery section 292 connected to the recovery path 291 and recovering the fourth gas F4. The pump efficiencies of the first vacuum pump 221 and the second vacuum pump 222 were both set to 40%. The supply conditions of the first gas F1 supplied to the first-stage first gas separation device 211 were set to the same as those of the gas separation system 200. The supply pressure of the compressor 272 was set to 1 MPaG. The fourth gas F4 was reduced in pressure to 0.5 MPaG by a pressure reducing valve (not shown) provided downstream of the compressor 272 in the second circulation path 232, and then supplied to the second vacuum pump 222. The filling processing rate of the recovery section 292 was set to 250 N / min (258 t / year).

[0227] In Calculation Example 8, the amount (circulation flow rate) of the fourth gas F4 that was pressurized by the compressor 272 and returned to the second vacuum pump 222 through the second circulation path 232 was set to 12 NL / min and 60 NL / min, and for each case, the sum of the processing power (kWh / kg-CO2) of the second vacuum pump 222 and the compressor 272 was calculated when attempting to supply the fourth gas F4 at 250 NL / min to the recovery section 292. For the calculation, process modeling software Symmetry manufactured by Schlumberger was used.

[0228] Calculation Example 9: As Calculation Example 9, a simulation was performed in the range downstream of the second discharge path 254 when the gas separation system 203 shown in FIG. 17 was operated. The gas separation system 203 had the same configuration as the gas separation system 202 ( FIG. 16 ) used in Calculation Example 8, except that a booster 224 for recovering the fourth gas F4 in the recovery section 292 was provided on the recovery path 291. Elements of the gas separation system 203 common to the gas separation system 202 ( FIG. 16 ) used in Calculation Example 8 are designated by the same reference numerals, and their description will be omitted. The pump efficiencies of the first vacuum pump 221 and the second vacuum pump 222 were both set to 40%. The supply conditions of the first gas F1 supplied to the first-stage first gas separation device 211 were set to the same as those of the gas separation system 200. The supply pressure of the compressor 272 was set to 0.5 MPaG. The supply pressure of the compressor 224 was set to 1.0 MPaG, and the power efficiency was set to 70%. The filling rate of the recovery section 292 was set to 250 N / min (258 t / year).

[0229] In Calculation Example 9, the amount (circulation flow rate) of the fourth gas F4 that is pressurized by the compressor 272 and returned to the second vacuum pump 222 through the second circulation path 232 is set to 12 NL / min and 60 NL / min, and for each case, the sum of the processing power (kWh / kg-CO2) of the second vacuum pump 222, the compressor 272, and the compressor 224 when attempting to supply the fourth gas F4 at 250 NL / min to the recovery section 292 is calculated. For the calculation, process modeling software Symmetry manufactured by Schlumberger was used.

[0230] The simulation results of calculation examples 7 to 9 are shown in Table 2. In Table 2, the number of devices refers to the number of devices provided downstream of the second discharge path 254, excluding the recovery section.

[0231]

[0232] As shown in Table 2, in Calculation Example 8, it was possible to reduce the number of devices constituting the system with the same sum of processing power as in Calculation Example 7 or Calculation Example 9. Note that although the number of devices in Calculation Example 9 was greater than in Calculation Example 8, Calculation Example 9 was able to reduce the sum of processing power compared to Calculation Example 8.

[0233] In the above example, a simulation was performed on an example in which the first gas F1 supplied to the first-stage gas separation apparatus contained carbon dioxide as gas A and nitrogen as gas B. However, the gas supplied to the first-stage gas separation apparatus is not limited to that used in the above example.

[0234] The gas separation system of this embodiment is suitable for separating a mixed gas, for example, a mixed gas containing carbon dioxide and nitrogen. In particular, the gas separation system of this embodiment is suitable for efficiently recovering carbon dioxide from exhaust gas emitted from a combustion device such as a factory or a power plant.

Claims

1. A gas separation system comprising: a first gas separation device that separates a first gas containing gas A and gas B different from gas A to obtain a second gas having a higher content of gas A than the first gas; a first vacuum pump that reduces the pressure inside the first gas separation device; and a first circulation path that introduces at least a portion of the second gas into the first vacuum pump as a seal gas for the first vacuum pump.

2. The gas separation system of claim 1, further comprising: a second gas separation device that separates a mixed gas containing gas A and gas B to obtain a concentrated gas having a higher content of gas A than the mixed gas; and a second vacuum pump that reduces the pressure inside the second gas separation device, wherein (i) the mixed gas is the second gas discharged from the first gas separation device, or (ii) the concentrated gas is the first gas supplied to the first gas separation device.

3. The gas separation system described in claim 2, further comprising at least one selected from the group consisting of a second circulation path that guides at least a portion of the concentrated gas discharged from the second gas separation device to the second vacuum pump as a seal gas for the second vacuum pump when the above (i) is satisfied, and a third circulation path that guides at least a portion of the second gas discharged from the first gas separation device to the second vacuum pump as a seal gas for the second vacuum pump when the above (ii) is satisfied, and a fourth circulation path that guides at least a portion of the second gas discharged from the first gas separation device to the second vacuum pump as a seal gas for the second vacuum pump.

4. The gas separation system according to claim 1, wherein the first gas separation device has a first separation membrane that allows the gas A to permeate preferentially.

5. The gas separation system according to claim 2, wherein the second gas separation device has a second separation membrane that allows the gas A to permeate preferentially.

6. The gas separation system according to claim 1, further comprising a first booster provided in the first circulation path.

7. The gas separation system described in claim 6, further comprising: a first recovery path branching off from the first circulation path downstream of the first booster; and a first recovery section connected to the first recovery path and recovering the second gas.

8. The gas separation system according to claim 3, further comprising a second booster provided in the second circulation path.

9. The gas separation system described in claim 8, further comprising: a second recovery path branching off from the second circulation path downstream of the second booster; and a second recovery section connected to the second recovery path and recovering the first gas.

10. The gas separation system according to claim 1, further comprising a drain mechanism for discharging moisture contained in the seal gas.

11. The gas separation system of claim 1, wherein the first gas comprises carbon dioxide as gas A and nitrogen as gas B.

12. A method for separating a mixed gas, comprising: a first gas separation step of supplying a first gas containing gas A and gas B different from gas A to a first gas separation device, and separating the first gas by reducing the pressure in the internal space of the first gas separation device with a first vacuum pump to obtain a second gas having a higher content of gas A than the first gas; and a first circulation step of supplying at least a portion of the second gas to the first vacuum pump as a seal gas for the first vacuum pump.

13. The method for separating a mixed gas according to claim 12, further comprising a second gas separation step of supplying a mixed gas containing gas A and gas B to a second gas separation device, and separating the mixed gas by reducing the pressure in the internal space of the second gas separation device with a second vacuum pump, thereby obtaining a concentrated gas having a higher content of gas A than the mixed gas, wherein (i) the mixed gas is the second gas discharged from the first gas separation device, or (ii) the concentrated gas is the first gas supplied to the first gas separation device.

14. The method for separating mixed gases described in claim 13, further comprising at least one step selected from the group consisting of a second circulation step in which, when the condition (i) above is met, at least a portion of the concentrated gas discharged from the second gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump, and a third circulation step in which at least a portion of the second gas discharged from the first gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump; and when the condition (ii) above is met, further comprising at least one step selected from the group consisting of a second circulation step in which at least a portion of the concentrated gas discharged from the second gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump, and a fourth circulation step in which at least a portion of the second gas discharged from the first gas separation device is guided to the second vacuum pump as a seal gas for the second vacuum pump.

15. The method for separating a mixed gas according to claim 12, wherein the first gas contains carbon dioxide as the gas A and nitrogen as the gas B.

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