Gas recovery system and gas recovery method

Abstract

A gas recovery system 100 according to the present invention includes: 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 of the gas A than the first gas G1; a recovery unit 20 having an adsorbent 202 for adsorbing the gas A contained in the second gas G2; and a third gas circulation passage 61 for guiding the third gas G3 discharged from the recovery unit 20 to an upstream side of the first gas separation device 11. A gas recovery method according to the present invention includes: a first gas separation step for separating a first gas containing a gas A and a gas B different from the gas A by a first gas separation device to obtain a second gas having a higher content of the gas A than the first gas; an adsorption step for adsorbing the gas A contained in the second gas by an adsorption material included in a recovery unit and discharging a third gas from the recovery unit; and a third gas circulation step for sending the third gas to the upstream side of the first gas separation device.

Description

Gas recovery system and gas recovery method

[0001] The present invention relates to a gas recovery system and a gas recovery method.

[0002] In recent years, in view of environmental regulations and the like, techniques for separating and recovering individual components from mixed gases have been attracting attention. 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 gas storage container for storing recovered gases such as carbon dioxide. The inside of the gas storage container is filled with a porous material as an adsorbent for adsorbing the gas.

[0003] International Publication No. 2019 / 026872

[0004] Adsorbents generate heat of adsorption when they adsorb gas. It is known that the heat of adsorption causes the temperature of the adsorbent to rise, temporarily reducing its adsorption capacity. This reduction in adsorption capacity leads to a decrease in the gas recovery rate.

[0005] An object of the present invention is to provide a new gas recovery system and gas recovery method suitable for improving the gas recovery rate.

[0006] In one aspect, the present invention provides a gas recovery 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 recovery section having an adsorbent that adsorbs gas A contained in the second gas; and a third gas circulation path that guides a third gas discharged from the recovery section to the upstream side of the first gas separation device.

[0007] From another aspect, the present invention provides a gas recovery method including: a first gas separation step of separating a first gas containing gas A and gas B different from gas A in a first gas separation device to obtain a second gas having a higher content of gas A than the first gas; an adsorption step of adsorbing gas A contained in the second gas onto an adsorbent provided in a recovery section and discharging a third gas from the recovery section; and a third gas circulation step of sending the third gas to the upstream side of the first gas separation device.

[0008] According to the present invention, a new gas recovery system and a new gas recovery method suitable for improving the gas recovery rate can be provided.

[0009] FIG. 1 is a schematic configuration diagram showing an example of a gas recovery 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 device. 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 a first gas separation device. FIG. 5 is a schematic configuration diagram showing a gas recovery system of modified example 1. FIG. 6 is a schematic configuration diagram showing a gas recovery system of modified example 2. FIG. 7 is a schematic configuration diagram showing a gas recovery system of modified example 3. FIG. 8 is a schematic configuration diagram showing a gas recovery system of modified example 4. FIG. 9 is a schematic cross-sectional view showing an example of a second gas separation device. FIG. 10 is a schematic cross-sectional view showing an example of a second separation membrane. FIG. 11 is a schematic configuration diagram showing a gas recovery system of modified example 5. FIG. 12 is a schematic configuration diagram showing a gas recovery system of modified example 6.

[0010] A gas recovery 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 recovery section having an adsorbent that adsorbs gas A contained in the second gas; and a third gas circulation path that guides a third gas discharged from the recovery section to the upstream side of the first gas separation device.

[0011] In a second aspect of the present invention, for example, the gas recovery system according to the first aspect further includes a concentration sensor that measures the content of gas A in the third gas, and when the content of gas A in the third gas is equal to or greater than the content of gas A in the first gas, the third gas is sent upstream of the first gas separation device.

[0012] In a third aspect of the present invention, for example, in the gas recovery system according to the first or second aspect, the third gas circulation path guides the third gas to the first gas separation device.

[0013] In a fourth aspect of the present invention, for example, in a gas recovery system according to any one of the first to third aspects, when an adsorption mode is performed in which the gas A contained in the second gas is adsorbed onto the adsorbent, and then a desorption mode is performed in which an adsorbed gas containing the gas A is desorbed from the adsorbent, the content of the gas A in the adsorbed gas is higher than the content of the gas A in the second gas.

[0014] In a fifth aspect of the present invention, for example, in the gas recovery system according to the fourth aspect, the recovery section has a container, a gas inlet, and a gas outlet, and in the adsorption mode, non-adsorbed gas is discharged from the gas outlet.

[0015] In a sixth aspect of the present invention, for example, the gas recovery system according to any one of the first to fifth aspects further includes a fourth gas circulation path that guides a fourth gas discharged from the first gas separation device and having a lower content of gas A than the second gas to the upstream side of the first gas separation device.

[0016] In a seventh aspect of the present invention, for example, in the gas recovery system according to any one of the first to sixth aspects, the first gas separation device has a first separation membrane that allows the gas A to permeate preferentially.

[0017] In an eighth aspect of the present invention, for example, the gas recovery system according to any one of the first to seventh aspects further comprises a second gas separation device that separates a mixed gas containing the gas A and the gas B to obtain a concentrated gas having a higher content of the gas A than the mixed gas, and the concentrated gas is at least a portion of the first gas supplied to the first gas separation device.

[0018] In a ninth aspect of the present invention, for example, in the gas recovery system according to the eighth aspect, the third gas circulation path guides the third gas upstream of the second gas separation device, or downstream of the second gas separation device and upstream of the first gas separation device.

[0019] In a tenth aspect of the present invention, for example, a gas recovery system according to any one of the first to ninth aspects further comprises a vacuum pump for reducing the pressure in the internal space of the first gas separation device, a first circulation path for directing at least a portion of the second gas to the vacuum pump as a seal gas for the vacuum pump, a first booster provided in the first circulation path, and a branch path branching off from the first circulation path downstream of the first booster, and the recovery unit is connected to the branch path.

[0020] In an eleventh aspect of the present invention, for example, the gas recovery system according to any one of the first to ninth aspects further comprises a second booster provided between the first gas separation device and the recovery section, which boosts the pressure of the second gas.

[0021] In a twelfth aspect of the present invention, for example, the gas recovery system according to any one of the first to eleventh aspects further comprises a removal section provided between the first gas separation device and the recovery section, which removes impurities contained in the second gas.

[0022] In a thirteenth aspect of the present invention, for example, in the gas recovery system according to any one of the eighth to twelfth aspects, the second gas separation device has a second separation membrane that allows the gas A to permeate preferentially.

[0023] In a fourteenth aspect of the present invention, for example, in the gas recovery system according to any one of the first to thirteenth aspects, the first gas contains carbon dioxide as the gas A and nitrogen as the gas B.

[0024] A gas recovery method according to a fifteenth aspect of the present invention includes: a first gas separation step of separating a first gas containing gas A and gas B different from gas A in a first gas separation device to obtain a second gas having a higher content of gas A than the first gas; an adsorption step of adsorbing gas A contained in the second gas onto an adsorbent provided in a recovery section and discharging a third gas from the recovery section; and a third gas circulation step of sending the third gas to the upstream side of the first gas separation device.

[0025] In a 16th aspect of the present invention, for example, in the gas recovery method according to the 15th aspect, in the third gas circulation process, if the content of gas A in the third gas is equal to or greater than the content of gas A in the first gas, the third gas is sent to the upstream side of the first gas separation device.

[0026] In a seventeenth aspect of the present invention, for example, in the gas recovery method according to the fifteenth or sixteenth aspect, the third gas is sent to the first gas separation device in the third gas circulation step.

[0027] In an 18th aspect of the present invention, for example, the gas recovery method according to any one of the 15th to 17th aspects further includes a second gas separation step of separating a mixed gas containing the gas A and the gas B in a second gas separation device to obtain a concentrated gas having a higher content of the gas A than the mixed gas, and the concentrated gas is at least a part of the first gas supplied to the first gas separation device.

[0028] In a 19th aspect of the present invention, for example, in the gas recovery method according to the 18th aspect, in the third gas circulation process, the third gas is sent to the upstream side of the second gas separation device, or to the downstream side of the second gas separation device and the upstream side of the first gas separation device.

[0029] In a twentieth aspect of the present invention, for example, in the gas recovery method according to any one of the fifteenth to nineteenth aspects, the first gas contains carbon dioxide as the gas A and nitrogen as the gas B.

[0030] 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.

[0031] <Gas Recovery System> FIG. 1 is a schematic diagram of a gas recovery system 100 according to one embodiment of the present invention. As shown in FIG. 1, the gas recovery system 100 includes a first gas separation device 11, a recovery section 20, and a third gas circulation path 61. The first gas separation device 11 is a device that 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 recovery section 20 has an adsorbent 202 that adsorbs gas A contained in the second gas G2. The third gas circulation path 61 is a path that guides a third gas G3 discharged from the recovery section 20 to the upstream side of the first gas separation device 11.

[0032] Hereinafter, a mode in the recovery unit 20 in which the second gas G2 is brought into contact with the adsorbent 202 to adsorb gas A contained in the second gas G2 onto the adsorbent 202 will be referred to as an adsorption mode. A mode in the recovery unit 20 in which an adsorbed gas containing gas A is desorbed from the adsorbent 202 that has adsorbed gas A will be referred to as a desorption mode. When the desorption mode is performed after the adsorption mode is performed, the content of gas A in the adsorbed gas is higher than the content of gas A in the second gas G2.

[0033] In the adsorption mode, the recovery section 20 discharges non-adsorbed gas that has not been adsorbed by the adsorbent 202. The non-adsorbed gas contains gas A, although the content of gas A is lower than that of the adsorbed gas.

[0034] According to the gas recovery system 100 of this embodiment, the third gas G3 can be guided to the upstream side of the first gas separation device 11 by the third gas circulation path 61. The third gas G3 may be an adsorbed gas or a non-adsorbed gas. The third gas G3 is typically a non-adsorbed gas. Therefore, according to the gas recovery system 100, it is possible to recycle the third gas G3 (e.g., a non-adsorbed gas) having a low content of gas A. This can improve the recovery rate of the gas A finally obtained.

[0035] When the adsorption mode is performed, the pressure in the recovery section 20 is preferably greater than 0.1 MPa and equal to or less than 1.1 MPa. When the desorption mode is performed, the pressure in the recovery section 20 may be reduced. In other words, in the desorption mode, the adsorbed gas may be desorbed from the adsorbent 202 by reducing the pressure in the recovery section 20. When the desorption mode is performed, the pressure in the recovery section 20 may be reduced to 0.1 MPa. In this specification, unless otherwise specified, "pressure" means absolute pressure.

[0036] 1 , in the gas recovery system 100, the third gas circulation path 61 is a path that guides the third gas G3 to the first gas separation device 11. That is, according to the gas recovery system 100, the third gas circulation path 61 can guide the third gas G3 to the first gas separation device 11.

[0037] The gas recovery system 100 preferably includes a concentration sensor 25 that measures the content of gas A in the third gas G3, and when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the first gas G1, the third gas G3 is sent upstream of the first gas separation device 11. The content of gas A in the third gas G3 is monitored by the concentration sensor 25, and when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the first gas G1, the third gas G3 can be sent upstream of the first gas separation device 11.

[0038] In the adsorption mode, the adsorbent 202 generates heat of adsorption by adsorbing gas A. The heat of adsorption causes the temperature of the adsorbent 202 to rise, temporarily reducing the adsorption capacity of the adsorbent 202. As such, the adsorption capacity of the adsorbent 202 fluctuates, and therefore the content of gas A in the third gas G3 (non-adsorbed gas) discharged from the recovery section 20 in the adsorption mode is not necessarily constant. Therefore, if non-adsorbed gas with a low content of gas A is recycled, for example, the content of gas A in the first gas G1 supplied to the first gas separation device 11 will decrease. This may inhibit the improvement in the recovery rate of the gas A finally obtained.

[0039] However, when the content of gas A in the third gas G3 is equal to or higher than the content of gas A in the first gas G1, sending the third gas G3 upstream of the first gas separation device 11 can avoid, for example, a decrease in the content of gas A in the first gas G1 supplied to the first gas separation device 11. Therefore, the recovery rate of the gas A finally obtained can be stably improved.

[0040] The concentration sensor 25 is not particularly limited as long as it can measure the content of gas A in a predetermined gas. As the concentration sensor 25, for example, a gas concentration sensor such as a non-dispersive infrared (NDIR) type, a thermal conductivity detector (TCD) type, or a gas chromatography (GC) type can be used.

[0041] In the gas recovery system 100, when the content of gas A in the third gas G3 is less than the content of gas A in the first gas G1, the third gas G3 may be released to the atmosphere.

[0042] In the gas recovery system 100, the content of gas A in the first gas G1 is, for example, in the range of 1 to 70 vol %. Note that the first gas G1 here refers to the first gas G1 before the third gas G3 joins with it. The content of gas A in the third gas G3 is, for example, in the range of 1 to 95 vol %. In this specification, the content (vol %) of gas A in a specified gas is the volume ratio of a specific gas to the specified gas under standard conditions (0°C, 101.33 kPa).

[0043] 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.

[0044] [Collection Unit] The collection unit 20 has a container 201, a gas inlet 20a, and a gas outlet 20b. The container 201 is filled with an adsorbent 202 capable of adsorbing gas A contained in the second gas G2. In the adsorption mode, the second gas G2 is supplied to the collection unit 20 through the gas inlet 20a, and non-adsorbed gas is discharged from the collection unit 20 through the gas outlet 20b. In the desorption mode, the adsorbed gas is discharged from the collection unit 20 through the gas outlet 20b.

[0045] A pressure regulating valve (not shown) for adjusting the pressure of the gas discharged from the recovery unit 20 may be disposed on the gas discharge port 20b side of the recovery unit 20. In the adsorption mode, the amount of gas A adsorbed to the adsorbent 202 can be increased by adjusting the pressure regulating valve. This makes it possible to increase the content of gas A in the adsorbed gas in the desorption mode. That is, when the desorption mode is performed after the adsorption mode, the content of gas A in the adsorbed gas is higher than the content of gas A in the second gas G2. The content of gas A in the adsorbed gas is, for example, 95 vol% or more.

[0046] The container 201 may be configured to be detachable and movable from the gas recovery system 100. In this case, the gas recovery system 100 can be made more compact. The shape of the container 201 is not particularly limited. The container 201 may have, for example, a cubic shape, a rectangular parallelepiped shape, a cylindrical shape, or a prismatic shape. The container 201 may be used as a storage and transportation container for the gas A. A plurality of containers 201 may be stacked for storage.

[0047] The material of the container 201 is not particularly limited. Examples of materials for the container 201 include metal, alloy, plastic, and combinations thereof. The plastic may be fiber-reinforced plastic. The container 201 may be made of fiber-reinforced plastic. In this case, the weight of the collection unit 20 can be reduced.

[0048] The adsorbent 202 is not particularly limited as long as it can adsorb gas A. The adsorbent 202 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 202 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.

[0049] 1, the gas recovery system 100 includes one recovery unit 20. However, there is no limit to the number of recovery units 20. For example, a plurality of recovery units 20 may be connected in series or in parallel.

[0050] [First Gas Separation Apparatus] The first gas separation apparatus 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 apparatus 11 may employ a membrane separation method in which the first gas G1 is separated using a separation membrane to obtain the second gas G2, or may employ a physical adsorption method in which the first gas G1 is separated using an adsorbent to obtain the second gas G2. Examples of physical adsorption methods include the PVSA (Pressure Vacuum Swing Adsorption) method, the PSA (Pressure Swing Adsorption) method, the TSA (Temperature Swing Adsorption) method, and the PTSA (Pressure and Temperature Swing Adsorption) method. The PVSA method, the PSA method, the TSA method, and the PTSA method are methods 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 due to 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 due to the pressure of the adsorbent. In the TSA method, gas is separated by utilizing the difference in adsorption capacity due to the temperature of the adsorbent. In the PTSA method, gas is separated by utilizing the difference in adsorption capacity due to 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.

[0051] 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.

[0052] Fig. 2 is a schematic cross-sectional view showing an example of a first gas separation device 11 provided in the gas recovery system 100. In the example of Fig. 2, the first gas separation device 11 has a first separation membrane 111 that separates a supplied first gas G1. A second gas G2 obtained by the first separation membrane 111 has a higher content of gas A than the first gas G1.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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 (fourth gas G4) 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] (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.

[0062] 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.

[0063] (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.

[0064] 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.

[0065] 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.

[0066] (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.

[0067] 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.

[0068] 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.

[0069] (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.

[0070] (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.

[0071] (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.

[0072] 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.

[0073] [Gas Paths] As shown in FIG. 1, the gas recovery system 100 further includes a first gas supply path 51, a second gas exhaust path 52, a third gas exhaust path 53, and a fourth gas exhaust path 54 as gas paths.

[0074] 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.

[0075] 1, the third gas circulation path 61 may merge with the first gas supply path 51 at a merging position 81. However, the merging position of the third gas circulation path 61 is not limited to the example shown in Fig. 1. The third gas circulation path 61 may be connected to the supply space inlet 113a of the first gas separation device 11, for example.

[0076] 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.

[0077] The fourth gas discharge path 54 is a path for discharging a fourth gas G4, which has a lower content of gas A than 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 fourth gas discharge path 54 is connected to the supply space outlet 113b of the first gas separation device 11. A pump for controlling the flow rate of the fourth gas G4 may be disposed in the fourth gas discharge path 54, for example.

[0078] 1 , in the gas recovery system 100, the fourth gas discharge path 54 merges with the third gas circulation path 61 at a junction position 82. That is, the fourth gas discharge path 54 is a circulation path that guides the fourth gas G4 to the upstream side of the first gas separation device 11. In this way, the fourth gas discharge path 54 may be a circulation path that guides the fourth gas G4 to the upstream side of the first gas separation device.

[0079] Although the content of gas A in the fourth gas G4 is lower than that in the second gas G2, the fourth gas G4 still contains gas A. By guiding the fourth gas G4 to the upstream side of the first gas separation device 11 through the fourth gas discharge path 54, the fourth gas G4 can be recycled. This makes it possible to improve the recovery rate of the gas A that is ultimately obtained.

[0080] A switching valve (not shown) may be provided at the confluence position 82. A flow rate adjustment valve (not shown) may be provided in the fourth gas discharge path 54. With this configuration, the flow rate of the fourth gas G4 introduced to the upstream side of the first gas separation device 11 can be adjusted by the switching valve and the flow rate adjustment valve.

[0081] The junction position 82 of the fourth gas discharge path 54 is not limited to the example shown in Fig. 1. The fourth gas discharge path 54 may, for example, merge with the first gas supply path 51 at the junction position 81, or may be connected to the supply space inlet 113a of the first gas separation device 11.

[0082] The configuration of the fourth gas discharge path 54 is not limited to the example shown in Fig. 1. That is, the fourth gas discharge path 54 does not have to be a circulation path that guides the fourth gas G4 to the upstream side of the first gas separation device 11. The fourth gas discharge path 54 may be open to the atmosphere, for example.

[0083] The third gas discharge path 53 is a path for discharging the third gas G3 (adsorbed gas or non-adsorbed gas) from the recovery unit 20. The third gas discharge path 53 is connected to the gas discharge port 20b of the recovery unit 20.

[0084] As shown in FIG. 1 , the third gas circulation path 61 may branch off from the third gas discharge path 53 at a branch position 91 .

[0085] A switching valve (not shown) may be provided at the branch position 91. A flow rate adjustment valve (not shown) may be provided in the third gas circulation path 61. With this configuration, the flow rate of the third gas G3 introduced into the third gas circulation path 61 can be adjusted by the switching valve and the flow rate adjustment valve.

[0086] As shown in FIG. 1, the concentration sensor 25 for measuring the content of gas A in the third gas G3 may be provided in the third gas discharge path 53 upstream of the branch position 91.

[0087] When the third gas G3 is released to the atmosphere, the third gas G3 may be released to the atmosphere via a third gas exhaust path 53.

[0088] 1 , the gas recovery system 100 includes a vacuum pump 31 that reduces the pressure in the internal space of the first gas separation device 11, and a first circulation path 71 that is a seal gas circulation path that guides at least a portion of the second gas G2 to the vacuum pump 31 as a seal gas for the vacuum pump 31. The gas recovery system 100 further includes a first booster 34 provided in the first circulation path 71, and a branch path 72 that branches off from the first circulation path 71 downstream of the first booster 34. In the gas recovery system 100, the recovery unit 20 is connected to the branch path 72.

[0089] 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 is 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 a pressure reduction device for reducing the pressure inside the vacuum-type gas separation device, the separated gas is diluted by the seal gas (inert gas), making it difficult to recover a highly concentrated separated gas.

[0090] However, with the above-described configuration, 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 vacuum pump 31. The second gas G2 is supplied to the vacuum pump 31 via the first circulation path 71. Therefore, with the above-described configuration, it is possible to improve the recovery rate of the gas A that is ultimately obtained while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0091] Furthermore, according to the above-described configuration, the recovery unit 20 is connected to the branch path 72 that branches off from the first circulation path 71 downstream of the first booster 34, and therefore the second gas G2 can be recovered in the recovery unit 20 by pressurizing the second gas G2 using the first booster 34. Therefore, there is no need to separately provide a booster for pressurizing the second gas G2 upstream of the recovery unit 20. This makes it possible to reduce the number of devices constituting the system.

[0092] The vacuum pump 31 is a vacuum pump that requires a seal gas. The vacuum pump 31 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 vacuum pump 31 can reduce the pressure in the permeate side space (second chamber 114) of the first gas separation device 11. In other words, the vacuum pump 31 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 vacuum pump 31 is typically a gas transport vacuum pump, and examples thereof include a reciprocating vacuum pump and a rotary vacuum pump. Examples of reciprocating vacuum pumps include diaphragm-type and oscillating piston-type vacuum pumps. Examples of rotary vacuum pumps include liquid ring pumps; oil rotary pumps (rotary pumps); mechanical booster pumps; and various dry pumps such as roots-type, claw-type, screw-type, turbo-type, and scroll-type. A screw-type dry pump is preferably used because of its excellent pumping efficiency. The vacuum pump 31 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 rotation speed, etc. of the pump with the variable speed mechanism, the pressure in the internal space of the first gas separation device 11 can be appropriately adjusted.

[0093] The vacuum pump 31 may be an assembly of multiple vacuum pumps. That is, the vacuum pump 31 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.

[0094] The flow rate of the second gas G2 supplied to the vacuum pump 31 is preferably 12 NL / min or more. The upper limit of the flow rate of the second gas G2 supplied to the vacuum pump 31 is not particularly limited.

[0095] 1 , the second gas discharge path 52 connects the permeate space outlet 114b of the first gas separation device 11 to the inlet of the vacuum pump 31. The first circulation path 71 connects the outlet of the vacuum pump 31 to the seal gas inlet of the vacuum pump 31. The branch path 72 branches off from the first circulation path 71 at a branch position 92.

[0096] A switching valve (not shown) may be provided at the branch position 92. Flow rate adjustment valves (not shown) may be provided in the first circulation path 71 and the branch path 72. With this configuration, the flow rate of the second gas G2 introduced into the first circulation path 71 and the flow rate of the second gas G2 introduced into the recovery unit 20 can be adjusted by the switching valve and the flow rate adjustment valves.

[0097] Although not shown, the branch path 72 may be provided with a buffer tank and a pressure reducing valve.

[0098] 1 , the first booster 34 is provided in the first circulation path 71 upstream of the branch position 92. The first booster 34 pressurizes the second gas G2 as a seal gas supplied to the vacuum pump 31, and also pressurizes the second gas G2 supplied to the recovery section 20.

[0099] The first booster 34 is not particularly limited as long as it can pressurize the second gas G2. The first booster 34 is typically a compressor.

[0100] The gas recovery 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 of the components of the gas recovery system 100 due to moisture can be suppressed.

[0101] A drain mechanism may be provided in the first booster 34. As shown in FIG. 1 , the moisture collected by the drain mechanism may be discharged to the outside through a first drain path 65 connected to the first booster 34.

[0102] Unless otherwise specified, each of the gas paths of the gas recovery system 100 is made up of, for example, metal or resin piping.

[0103] The gas recovery system 100 may further include a switching unit (not shown) that switches between the adsorption mode and the desorption mode. The switching unit may be, for example, a switching valve provided at the gas inlet 20 a of the recovery unit 20.

[0104] The gas recovery system 100 may further include a desorption promotion device (not shown) that promotes desorption of the adsorbed gas from the adsorbent 202 in the desorption mode.

[0105] The desorption promotion device includes, for example, a decompression device that decompresses the inside of the collection section 20 in the desorption mode, and a heating device that heats the adsorbent 202 in the collection section 20. In the desorption mode, decompression of the inside of the collection section 20 by the decompression device can be promoted, thereby facilitating desorption of the adsorbed gas from the adsorbent 202. In the desorption mode, heating the adsorbent 202 by the heating device can be promoted, thereby facilitating desorption of the adsorbed gas from the adsorbent 202. The decompression device is provided, for example, in the third gas discharge path 53. The configuration of the heating device is not particularly limited as long as it is capable of heating the adsorbent 202. The heating device is typically a heater.

[0106] The gas recovery system 100 may further include a control device 40 that controls each component of the gas recovery 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 recovery system 100. For example, the control device 40 may adjust the flow rate of the third gas G3 introduced into the third gas circulation path 61. The control device 40 may adjust the flow rate of the third gas G3 introduced into the third gas circulation path 61 by controlling a switching valve provided at the branch position 91 and a flow rate adjustment valve provided in the third gas circulation path 61. The control device 40 may adjust the flow rate of the second gas G2 supplied to the vacuum pump 31 and the flow rate of the second gas G2 supplied to the recovery unit 20. The control device 40 may control the switching valve provided at the branch position 92, the flow rate control valve provided in the first circulation path 71, and the flow rate control valve provided in the branch path 72, thereby adjusting the flow rate of the second gas G2 supplied to the vacuum pump 31 and the flow rate of the second gas G2 supplied to the recovery section 20.

[0107] [Another Example of First Gas Separation Device] In the gas recovery system 100, the first gas separation device 11 having the first separation membrane 111 is not limited to the form shown in Fig. 2. The first gas separation device 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 schematic perspective view showing another example of the first gas separation device 11 having the first separation membrane 111. The first gas separation device 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.

[0108] 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.

[0109] 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).

[0110] 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.

[0111] 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.

[0112] <Gas Recovery Method> Next, a gas recovery method using the gas recovery system 100 described above will be described.

[0113] The gas recovery method includes a first gas separation process in which a first gas G1 containing gas A and a gas B different from gas A is separated in a first gas separation device 11 to obtain a second gas G2 having a higher content of gas A than the first gas G1; an adsorption process in which gas A contained in the second gas G2 is adsorbed by an adsorbent 202 possessed by a recovery section 20 and a third gas G3 is discharged from the recovery section 20; and a third gas circulation process in which the third gas G3 is sent upstream of the first gas separation device 11.

[0114] According to this gas recovery method, in the third gas circulation step, the third gas G3 is sent to the upstream side of the first gas separation device 11, so that the third gas G3 can be recycled. This makes it possible to improve the recovery rate of the gas A that is finally obtained.

[0115] The first gas separation step, the adsorption step, and the third gas circulation step are performed, for example, as follows. Each step will be described below using an example in which the first gas separation device 11 has a first separation membrane 111.

[0116] [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 .

[0117] Next, while the first gas G1 is 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 vacuum pump 31. Specifically, the vacuum pump 31 is used to depressurize the second chamber 114 through the permeation space outlet 114b.

[0118] 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 a first permeation gas S1 is supplied to and discharged from the second chamber 114. A first non-permeation gas S2 that did not permeate the first separation membrane 111 is discharged from the first chamber 113. While separation of the first gas G1 is taking place, the pressure inside the second chamber 114 may continue to be reduced by the vacuum pump 31.

[0119] The first permeable gas S1 (second gas G2) discharged from the second chamber 114 passes through the second gas discharge path 52 and is sucked into the vacuum pump 31. The vacuum pump 31 discharges the sucked second gas G2 into the first circulation path 71. The second gas G2 passes through the branch path 72 and is supplied to the recovery unit 20 through the gas inlet 20a.

[0120] [Adsorption Process] In the adsorption process, the gas A contained in the second gas G2 is adsorbed by the adsorbent 202 of the recovery section 20, and the non-adsorbed gas that has not been adsorbed by the adsorbent 202 is discharged from the recovery section 20 through the gas discharge port 20b. The adsorption process is a process corresponding to the adsorption mode.

[0121] [Third Gas Circulation Step] In the third gas circulation step, the third gas G3 is sent to the first gas separation device 11.

[0122] In the gas recovery method, in the third gas circulation step, if the content of gas A in the third gas G3 is equal to or higher than the content of gas A in the first gas G1, it is preferable to send the third gas G3 upstream of the first gas separation device 11. By doing so, for example, it is possible to avoid a decrease in the content of gas A in the first gas G1 supplied to the first gas separation device 11. Therefore, it is possible to stably improve the recovery rate of the gas A finally obtained.

[0123] The gas recovery method may include a third gas release step of releasing the third gas G3 to the atmosphere when the content of gas A in the third gas G3 is less than the content of gas A in the first gas G1.

[0124] The gas recovery method may include a fourth gas circulation step of sending the fourth gas G4 discharged from the first gas separation device 11 to the upstream side of the first gas separation device 11. The fourth gas circulation step allows the fourth gas G4 to be recycled, thereby improving the recovery rate of the gas A that is finally obtained.

[0125] The gas recovery method may include a first circulation step of supplying at least a portion of the second gas G2 to the vacuum pump 31 as a seal gas for the vacuum pump 31. According to 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 vacuum pump 31, so that it is possible to improve the recovery rate of the gas A that is ultimately obtained while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0126] In the first circulation step, at least a portion of the second gas G2 discharged from the vacuum pump 31 to the first circulation path 71 is supplied to the vacuum pump 31 as a seal gas via the first circulation path 71.

[0127] The gas recovery method may include a desorption step of desorbing the adsorbed gas containing gas A from the adsorbent 202 of the recovery section 20. The desorption step corresponds to the desorption mode.

[0128] 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.

[0129] <Modifications of the Gas Recovery System> The gas recovery system according to this embodiment is not limited to the configuration of the gas recovery system 100 shown in Fig. 1. Modifications 1 to 6 of the gas recovery system according to this embodiment will be described below. In the following, elements common to the gas recovery system 100 shown in Fig. 1 will be designated by the same reference numerals, and descriptions thereof may be omitted.

[0130] (Variation 1) Fig. 5 is a schematic diagram showing a gas recovery system 101 of Variation 1. The gas recovery system 101 includes a booster 36 that pressurizes the internal space of the first gas separation device 11, instead of the vacuum pump 31. The booster 36 is provided in the first gas supply path 51. The gas recovery system 101 does not include the first circulation path 71, and the recovery unit 20 is connected to the second gas discharge path 52. Except for these, the gas recovery system 101 has the same configuration as the gas recovery system 100 described above.

[0131] The pressure booster 36 is not particularly limited as long as it can pressurize the internal space of the first gas separation device 11 .

[0132] As shown in Figure 5, in the gas recovery system 101, when the first gas separation device 11 has a first separation membrane 111, the second gas exhaust path 52 connects the permeation space outlet 114b of the first gas separation device 11 to the gas inlet 20a of the recovery section 20.

[0133] 5, the second gas discharge path 52 is provided with a booster 37 for recovering the second gas G2 in the recovery section 20. That is, the gas recovery system 101 is further provided with a booster 37 that is provided between the first gas separation device 11 and the recovery section 20 and that boosts the pressure of the second gas G2.

[0134] The pressure booster 37 is not particularly limited as long as it can pressurize the second gas G2 supplied to the recovery section 20. The pressure booster 37 is typically a compressor.

[0135] The gas recovery method using the gas recovery system 101 of the first modification includes a first gas separation step, an adsorption step, and a third gas circulation step, similar to the gas recovery method using the gas recovery system 100 described above.

[0136] The gas recovery method may include a third gas release step, a fourth gas circulation step, and a desorption step, similar to the gas recovery method using the gas recovery system 100 described above.

[0137] (Variation 2) Figure 6 is a schematic diagram showing a gas recovery system 102 of Variation 2. The gas recovery system 102 is provided between the first gas separation device 11 and the recovery section 20 and includes a removal section 26 that removes impurities contained in the second gas G2. Except for this, the gas recovery system 102 has the same configuration as the gas recovery system 100 described above. By providing the removal section 26 between the first gas separation device 11 and the recovery section 20, impurities contained in the second gas G2 can be removed before the gas is supplied to the recovery section 20.

[0138] The removal unit 26 may be filled with an adsorbent capable of removing impurities contained in the second gas G2. As the adsorbent, the adsorbents 202 of the recovery unit 20 described above can be used.

[0139] 6, the removal unit 26 may include a first removal unit 261 and a second removal unit 262. The first removal unit 261 and the second removal unit 262 may be connected in series.

[0140] In the first removal section 261, for example, acidic components such as carbon dioxide gas contained in the second gas G2 are removed. In the second removal section 262, for example, moisture contained in the second gas G2 is removed.

[0141] The gas recovery method using the gas recovery system 102 of the second modification includes a first gas separation step, an adsorption step, and a third gas circulation step, similar to the gas recovery method using the gas recovery system 100 described above.

[0142] The gas recovery method may include a removal step of removing impurities contained in the second gas G2 after the first gas separation step. In the removal step, the impurities contained in the second gas G2 after the first gas separation step are removed by a removal unit 26.

[0143] The gas recovery method may include a third gas release step, a fourth gas circulation step, a first circulation step, and a desorption step, similar to the gas recovery method using the gas recovery system 100 described above.

[0144] 7 is a schematic diagram showing a gas recovery system 103 of Modification 3. In the gas recovery system 103, the recovery unit 20 is connected to the second gas discharge path 52 so that the second gas G2 discharged from the vacuum pump 31 is supplied to the recovery unit 20 without passing through the booster 34. Except for this, the gas recovery system 103 has the same configuration as the gas recovery system 100 described above.

[0145] 7 , in the gas recovery system 103, the second gas discharge path 52 has 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 to the vacuum pump 31. The second portion 522 is a portion that connects the vacuum pump 31 to the branch position 93. The third portion 523 is a portion that connects the branch position 93 to the gas inlet 20a of the recovery section 20. In the gas recovery system 103, the first circulation path 71 branches off from the second gas discharge path 52 at the branch position 93.

[0146] 7, a booster 37 is provided in the second portion 523 of the second gas discharge path 52 to recover the second gas G2 in the recovery section 20. That is, the gas recovery system 103 is further provided with a booster 37 that is provided between the first gas separation device 11 and the recovery section 20 and that boosts the pressure of the second gas G2.

[0147] The gas recovery method using the gas recovery system 103 of the third modification includes a first gas separation step, an adsorption step, and a third gas circulation step, similar to the gas recovery method using the gas recovery system 100 described above.

[0148] The gas recovery method may include a third gas release step, a fourth gas circulation step, a first circulation step, and a desorption step, similar to the gas recovery method using the gas recovery system 100 described above.

[0149] The gas recovery system according to this embodiment may include a second gas separation device 12 in addition to the first gas separation device 11. 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 concentrated gas Gc is at least a part of the first gas G1 supplied to the first gas separation device 11. In other words, when the gas recovery system includes the second gas separation device 12, the first gas separation device 11 is arranged downstream of the second gas separation device 12.

[0150] When the gas recovery system is equipped with a second gas separation device 12, the third gas circulation path 61 may lead the third gas G3 upstream of the second gas separation device 12 (Variant 4, Variant 6), or may lead the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11 (Variant 5).

[0151] (Variation 4) Figure 8 is a schematic diagram showing a gas recovery system 200 of Variation 4. In the gas recovery system 200, the third gas circulation path 61 is a path that guides the third gas G3 to the upstream side of the second gas separation device 12. According to the gas recovery system 200, the third gas circulation path 61 can guide the third gas G3 to the upstream side of the second gas separation device 12, so that the third gas G3 can be recycled. This can improve the recovery rate of the gas A that is finally obtained.

[0152] In the gas recovery system 200, when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm, it is preferable that the third gas G3 be sent upstream of the second gas separation device 12. However, the reason that the third gas G3 is sent upstream of the second gas separation device 12 is not limited to when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm. For example, when the content of gas A in the third gas G3 is approximately the same as the content of gas A in the first gas G1, the third gas G3 may be sent upstream of the second gas separation device 12.

[0153] In the gas recovery system 200, the content of gas A in the mixed gas Gm is, for example, in the range of 1 to 70 vol %. Note that the mixed gas Gm here refers to the mixed gas Gm before the third gas G3 joins. The content of gas A in the third gas G3 is, for example, in the range of 1 to 95 vol %.

[0154] [Second Gas Separation Device] 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.

[0155] 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.

[0156] Fig. 9 is a schematic cross-sectional view showing an example of the second gas separation device 12 included in the gas recovery system 200. In the example of Fig. 9, 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.

[0157] 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.

[0158] 9 , 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] The configuration of the second separation membrane 121 is not particularly limited. Figure 10 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 9. As shown in Figure 10, 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.

[0163] 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.

[0164] 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.

[0165] (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.

[0166] (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.

[0167] (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.

[0168] 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.

[0169] (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.

[0170] (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.

[0171] (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.

[0172] The configuration of the second separation membrane 121 is not limited to the example shown in Fig. 10. 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.

[0173] The second gas separation device 12 having the second separation membrane 121 is not limited to the form shown in Fig. 9. 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.

[0174] 8, the gas recovery system 200 includes a vacuum pump 32 that reduces the pressure in the internal space of the second gas separation device 12, and a second circulation path 73 that is a seal gas circulation path that guides at least a portion of the concentrated gas Gc to the vacuum pump 32 as a seal gas for the vacuum pump 32. The gas recovery system 200 further includes a second booster 35 provided in the second circulation path 73.

[0175] According to the above-described configuration, at least a portion of the concentrated gas Gc, which has a higher content of gas A than the mixed gas Gm, can be used as a seal gas for the vacuum pump 32. The concentrated gas Gc is supplied to the vacuum pump 32 via the second circulation path 73. Therefore, according to the above-described configuration, it is possible to improve the recovery rate of the gas A that is ultimately obtained while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0176] The vacuum pump 32 may be a vacuum pump that requires a seal gas, like the vacuum pump 31. The vacuum pump 32 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 vacuum pump 32 can reduce the pressure in the permeate side space (second chamber 124) of the second gas separation device 12. In other words, the vacuum pump 32 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 vacuum pump 32 can be any of the pumps listed for the vacuum pump 31.

[0177] The vacuum pump 32 may be an assembly of multiple vacuum pumps. That is, the vacuum pump 32 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.

[0178] The flow rate of the concentrated gas Gc supplied to the vacuum pump 32 is preferably 12 NL / min or more. The upper limit of the flow rate of the concentrated gas Gc supplied to the vacuum pump 32 is not particularly limited.

[0179] 8, the vacuum pump 32 is disposed in a concentrated gas discharge path 56 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 56 is connected to the permeate space outlet 124b of the second gas separation device 12.

[0180] 8, the second booster 35 is provided in the second circulation path 73. The second booster 35 pressurizes the concentrated gas Gc as a seal gas to be supplied to the vacuum pump 32. By continuously operating the second booster 35, the concentrated gas Gc can be obtained stably.

[0181] The second booster 35 is not particularly limited as long as it can pressurize the concentrated gas Gc as the seal gas supplied to the vacuum pump 32. The second booster 35 is typically a compressor.

[0182] The gas recovery system 200 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 recovery system 200 due to moisture can be suppressed.

[0183] The second booster 35 may be provided with a drain mechanism. As shown in Fig. 8, the moisture collected by the drain mechanism may be discharged to the outside through a second drain path 66 connected to the second booster 35.

[0184] [Gas Paths] As shown in FIG. 8, the gas recovery system 200 further includes a mixed gas supply path 55, a concentrated gas discharge path 56, and a non-concentrated gas discharge path 57 as gas paths.

[0185] The mixed gas supply path 55 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 55 is connected to a supply space inlet 123a of the second gas separation device 12. The mixed gas supply path 55 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 55 from a supply source such as a combustion device.

[0186] The concentrated gas discharge path 56 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 56 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 56.

[0187] 8 , in the gas recovery system 200, the concentrated gas discharge path 56 has a first portion 561, a second portion 562, and a third portion 563. When the second gas separation device 12 has the second separation membrane 121, the first portion 561 is a portion that connects the permeate space outlet 124b of the second gas separation device 12 to the vacuum pump 32. The second portion 562 is a portion that connects the vacuum pump 32 to the branch position 94. The third portion 563 is a portion that connects the branch position 94 to the supply space inlet 113a of the first gas separation device 11. In the gas recovery system 200, the second circulation path 73 branches off from the concentrated gas discharge path 56 at the branch position 94.

[0188] As shown in FIG. 8 , in the gas recovery system 200 , the third portion 563 of the concentrated gas discharge path 56 corresponds to the first gas supply path 51 .

[0189] The non-concentrated gas discharge path 57 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 57 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 57.

[0190] In the gas recovery system 200, the non-concentrated gas discharge path 57 is open to the atmosphere. However, the configuration of the non-concentrated gas discharge path 57 is not limited to the example shown in FIG.

[0191] In the gas recovery system 200, the third gas circulation path 61 is a path that guides the third gas G3 to the second gas separation device 12 during operation. As shown in Fig. 8 , the third gas circulation path 61 may merge with the mixed gas supply path 55 at a merging position 83. However, the merging position of the third gas circulation path 61 is not limited to the example shown in Fig. 8 . The third gas circulation path 61 may be connected to the supply space inlet 123a of the second gas separation device 12, for example.

[0192] The gas recovery method using the gas recovery system 200 of the fourth modification includes a first gas separation step, an adsorption step, and a third gas circulation step, similar to the gas recovery method using the gas recovery system 100 described above.

[0193] The gas recovery method further includes a second gas separation step of separating a mixed gas Gm containing gas A and gas B in a second gas separation device 12 to obtain a concentrated gas Gc having a higher content of gas A than the mixed gas Gm. In the gas recovery method, the concentrated gas Gc is at least a part of the first gas G1 supplied to the first gas separation device.

[0194] In the gas recovery method, the second gas separation step and the third gas circulation step are performed, for example, as follows. Each step will be described below using an example in which the second gas separation device 12 has a second separation membrane 121.

[0195] [Second Gas Separation Step] In the second gas separation step, first, the mixed gas Gm is supplied to the first chamber 123 (supply side space) of the second gas separation device 12 through the mixed gas supply path 55 .

[0196] Next, with the mixed gas Gm 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 vacuum pump 32. Specifically, the vacuum pump 32 is used to depressurize the second chamber 124 through the permeation space outlet 124b.

[0197] 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 mixed gas Gm is separated by the second separation membrane 121, and a second permeation gas S3 is supplied to the second chamber 124 and discharged from the second chamber 124. A second non-permeation gas S4 that did not permeate the second separation membrane 121 is discharged from the first chamber 123. While separation of the mixed gas Gm is being performed, the pressure inside the second chamber 124 may continue to be reduced by the vacuum pump 32.

[0198] The second permeable gas S3 (concentrated gas Gc) discharged from the second chamber 124 passes through the first portion 561 of the concentrated gas discharge path 56 and is sucked into the vacuum pump 32. The vacuum pump 32 discharges the sucked concentrated gas Gc into the second portion 562 of the concentrated gas discharge path 56. The concentrated gas Gc passes through the third portion 563 of the concentrated gas discharge path 56 and is supplied to the first gas separation device 11 through the supply space inlet 113a. The second non-permeable gas S4 (non-concentrated gas Gs) discharged from the first chamber 123 is released to the atmosphere.

[0199] The second gas separation step is followed by the first gas separation step.

[0200] [Third Gas Circulation Step] In the third gas circulation step, the third gas G3 is sent to the upstream side of the second gas separation device 12.

[0201] In the gas recovery method, in the third gas circulation step, if the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm, it is preferable to send the third gas G3 upstream of the second gas separation device 12. By doing so, for example, a decrease in the content of gas A in the mixed gas Gm supplied to the second gas separation device 12 can be avoided. Therefore, the recovery rate of the gas A finally obtained can be stably improved. However, sending the third gas G3 upstream of the second gas separation device 12 is not limited to cases where the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm. For example, if the content of gas A in the third gas G3 is approximately the same as the content of gas A in the first gas G1, the third gas G3 may be sent upstream of the second gas separation device 12.

[0202] The gas recovery method may include a second circulation step of supplying at least a portion of the second permeable gas S3 (concentrated gas Gc) to the vacuum pump 32 as a seal gas for the vacuum pump 32. According to the second circulation step, at least a portion of the concentrated gas Gc, which has a higher content of gas A than the mixed gas Gm, is used as a seal gas for the vacuum pump 32, so that it is possible to improve the recovery rate of the gas A that is ultimately obtained while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0203] In the second circulation process, at least a portion of the concentrated gas Gc discharged from the vacuum pump 32 to the second portion 562 of the concentrated gas discharge path 56 is supplied to the vacuum pump 32 as a seal gas via the second circulation path 73.

[0204] The gas recovery method may include a third gas release step, a fourth gas circulation step, a first circulation step, and a desorption step, similar to the gas recovery method using the gas recovery system 100 described above.

[0205] 11 is a schematic diagram showing a gas recovery system 210 of Modification 5. In the gas recovery system 210, the third gas circulation path 61 is a path that guides the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11. Except for this, the gas recovery system 210 has the same configuration as the gas recovery system 200 described above.

[0206] In the gas recovery system 210, when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the first gas G1, it is preferable that the third gas G3 be sent downstream of the second gas separation device 12 and upstream of the first gas separation device 11. However, sending the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11 is not limited to when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the first gas G1. For example, when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm, the third gas G3 may be sent downstream of the second gas separation device 12 and upstream of the first gas separation device 11.

[0207] In the gas recovery system 210, the content of gas A in the first gas G1 is, for example, in the range of 40 to 70 vol %. Note that the first gas G1 here refers to the first gas G1 before the third gas G3 joins with it. The content of gas A in the third gas G3 is, for example, in the range of 40 to 95 vol %.

[0208] In the gas recovery system 210, the third gas circulation path 61 is a path that guides the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11 during operation. As shown in Figure 11, the third gas circulation path 61 may merge with the first gas supply path 51 (the third portion 563 of the concentrated gas discharge path 56) at a merging position 84. However, the merging position of the third gas circulation path 61 is not limited to the example shown in Figure 11. The third gas circulation path 61 may be connected, for example, to the supply space inlet 113a of the first gas separation device 11.

[0209] The gas recovery method using the gas recovery system 210 of variant 5 includes a second gas separation process, a first gas separation process, an adsorption process, and a third gas circulation process, similar to the gas recovery method using the gas recovery system 200 described above.

[0210] In the gas recovery method, the third gas circulation step is carried out, for example, as follows.

[0211] [Third Gas Circulation Step] In the third gas circulation step, the third gas G3 is sent downstream of the second gas separation device 12 and upstream of the first gas separation device 11 .

[0212] In the gas recovery method, in the third gas circulation step, if the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the first gas G1, it is preferable to send the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11. By doing so, for example, a decrease in the content of gas A in the first gas G1 supplied to the first gas separation device 11 can be avoided. Therefore, the recovery rate of the gas A finally obtained can be stably improved. However, sending the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11 is not limited to cases where the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the first gas G1. For example, if the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm, the third gas G3 may be sent downstream of the second gas separation device 12 and upstream of the first gas separation device 11.

[0213] This gas recovery method may include a third gas release process, a fourth gas circulation process, a first circulation process, a second circulation process, and a desorption process, similar to the gas recovery method using the gas recovery system 200 described above.

[0214] (Variation 6) FIG. 12 is a schematic diagram showing a gas recovery system 220 of Variation 6. The gas recovery system 220 includes a booster 38 that pressurizes the internal space of the second gas separation device 12 instead of the vacuum pump 32. The booster 38 is provided in the mixed gas supply path 55. The gas recovery system 220 does not include the second circulation path 73, and the first gas separation device 11 is connected to the concentrated gas discharge path 56. In addition, in the gas recovery system 220, the downstream portion of the first gas separation device 11 has the same configuration as the downstream portion of the first gas separation device 11 in the gas recovery system 101 of FIG. 5. Except for these, the gas recovery system 220 has the same configuration as the gas recovery system 200 described above. That is, in the gas recovery system 220, the third gas circulation path 61 is a path that guides the third gas G3 to the upstream side of the second gas separation device 12.

[0215] The pressure booster 38 is not particularly limited as long as it can pressurize the internal space of the second gas separation device 12 .

[0216] In the gas recovery system 220, when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm, it is preferable that the third gas G3 be sent upstream of the second gas separation device 12. However, the reason that the third gas G3 is sent upstream of the second gas separation device 12 is not limited to when the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm. For example, when the content of gas A in the third gas G3 is approximately the same as the content of gas A in the first gas G1, the third gas G3 may be sent upstream of the second gas separation device 12.

[0217] In the gas recovery system 220, the content of gas A in the mixed gas Gm is, for example, in the range of 1 to 70 vol %. Note that the mixed gas Gm here refers to the mixed gas Gm before the third gas G3 joins. The content of gas A in the third gas G3 is, for example, in the range of 1 to 95 vol %.

[0218] The gas recovery method using the gas recovery system 220 of variant 6 includes a second gas separation process, a first gas separation process, an adsorption process, and a third gas circulation process, similar to the gas recovery method using the gas recovery system 200 described above.

[0219] In the gas recovery method, the third gas circulation step is carried out, for example, as follows.

[0220] [Third Gas Circulation Step] In the third gas circulation step, the third gas G3 is sent to the second gas separation device 12.

[0221] In the gas recovery method, in the third gas circulation step, if the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm, it is preferable to send the third gas G3 to the second gas separation device 12. By doing so, for example, a decrease in the content of gas A in the mixed gas Gm supplied to the second gas separation device 12 can be avoided. Therefore, the recovery rate of the gas A finally obtained can be stably improved. However, sending the third gas G3 to the second gas separation device 12 is not limited to cases where the content of gas A in the third gas G3 is equal to or greater than the content of gas A in the mixed gas Gm. For example, if the content of gas A in the third gas G3 is approximately the same as the content of gas A in the first gas G1, the third gas G3 may be sent to the second gas separation device 12.

[0222] This gas recovery method may include a third gas release step, a fourth gas circulation step, and a desorption step, similar to the gas recovery method using the gas recovery system 200 described above.

[0223] (Other Modifications) The above examples may be combined with each other as long as there is no technical contradiction.

[0224] The gas recovery 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 recovery 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 recovery 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 recovery section having an adsorbent that adsorbs gas A contained in the second gas; and a third gas circulation path that guides a third gas discharged from the recovery section to the upstream side of the first gas separation device.

2. The gas recovery system of claim 1, further comprising a concentration sensor for measuring the content of gas A in the third gas, and when the content of gas A in the third gas is equal to or greater than the content of gas A in the first gas, the third gas is sent upstream of the first gas separation device.

3. The gas recovery system according to claim 1, wherein the third gas circulation path guides the third gas to the first gas separation device.

4. A gas recovery system as described in claim 1, wherein, when an adsorption mode is performed in which the gas A contained in the second gas is adsorbed onto the adsorbent, and then a desorption mode is performed in which the adsorbed gas containing the gas A is desorbed from the adsorbent, the content of the gas A in the adsorbed gas is higher than the content of the gas A in the second gas.

5. The gas recovery system according to claim 4, wherein the recovery section has a container, a gas inlet, and a gas outlet, and in the adsorption mode, non-adsorbed gas is discharged from the gas outlet.

6. A gas recovery system as described in claim 1, further comprising a fourth gas circulation path that guides a fourth gas discharged from the first gas separation device and having a lower content of gas A than the second gas to the upstream side of the first gas separation device.

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

8. The gas recovery system according to claim 1, further comprising a second gas separation device that separates a mixed gas containing said gas A and said gas B to obtain a concentrated gas having a higher content of said gas A than said mixed gas, and said concentrated gas is at least a portion of said first gas supplied to said first gas separation device.

9. A gas recovery system as described in claim 8, wherein the third gas circulation path guides the third gas to the upstream side of the second gas separation device, or to the downstream side of the second gas separation device and the upstream side of the first gas separation device.

10. A gas recovery system as described in claim 1, further comprising: a vacuum pump that reduces the pressure in the internal space of the first gas separation device; a first circulation path that guides at least a portion of the second gas to the vacuum pump as a seal gas for the vacuum pump; a first booster provided in the first circulation path; and a branch path that branches off from the first circulation path downstream of the first booster, wherein the recovery unit is connected to the branch path.

11. The gas recovery system according to claim 1, further comprising a second booster provided between the first gas separation device and the recovery section, for boosting the pressure of the second gas.

12. The gas recovery system according to claim 1, further comprising a removal section provided between the first gas separation device and the recovery section, for removing impurities contained in the second gas.

13. The gas recovery system according to claim 8, wherein the second gas separation device has a second separation membrane that allows gas A to permeate preferentially.

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

15. A gas recovery method comprising: a first gas separation step of separating a first gas containing gas A and gas B different from gas A in a first gas separation device to obtain a second gas having a higher content of gas A than the first gas; an adsorption step of adsorbing gas A contained in the second gas onto an adsorbent possessed by a recovery section and discharging a third gas from the recovery section; and a third gas circulation step of sending the third gas to the upstream side of the first gas separation device.

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