Recovery system and recovery method

Abstract

This recovery system 100 comprises: a first gas separation device 11 that separates a first gas G1 including a gaseous substance A and a gaseous substance B different from the gaseous substance A to obtain a second gas G2 in which the substance A content is higher than in the first gas G1; a recovery device 20 that changes the state of the substance A included in the second gas G2 and recovers the substance A; and a third gas circulation path 61 that guides a third gas G3 discharged from the recovery device 20 to the upstream side of the first gas separation device 11. For example, the first gas includes carbon dioxide as the substance A and nitrogen as the substance B.

Description

Collection system and collection method

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

[0002] In recent years, in view of environmental regulations and the like, techniques for separating and recovering components from mixed gases have been attracting attention. For example, in factories, power plants, and the like, mixed gases containing carbon dioxide, nitrogen, and the like are discharged from combustion devices such as boilers. For example, Patent Document 1 proposes a technique for recovering CO2 and SO2 from the exhaust gas by separating the boiler exhaust gas using a membrane separation unit.

[0003] Special Publication No. 2020-501884

[0004] The conventional recovery system as described in Patent Document 1 has room for improvement in terms of reducing the recovery power.

[0005] Therefore, an object of the present invention is to provide a recovery system and a recovery method suitable for reducing the recovery power.

[0006] In one aspect, the present invention provides a recovery system comprising: a first gas separation device that separates a first gas containing a gaseous substance A and a gaseous substance B different from the gaseous substance A to obtain a second gas having a higher content of the substance A than the first gas; a recovery device that changes the state of the substance A contained in the second gas and recovers it; and a third gas circulation path that guides a third gas discharged from the recovery device to the upstream side of the first gas separation device.

[0007] From another aspect, the present invention provides a recovery method including: a first gas separation step of separating a first gas containing a gaseous substance A and a gaseous substance B different from the gaseous substance A in a first gas separation device to obtain a second gas having a higher content of the substance A than the first gas; a recovery step of recovering the substance A contained in the second gas by changing its state in a recovery device and discharging a third gas from the recovery device; 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 recovery system and a recovery method suitable for reducing recovery power can be provided.

[0009] FIG. 1 is a schematic configuration diagram showing an example of a recovery system according to one 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 recovery system of Modified Example 1. FIG. 6 is a schematic cross-sectional view showing a recovery system of Modified Example 2. FIG. 7 is a schematic configuration diagram showing a recovery system of Modified Example 3. FIG. 8 is a schematic cross-sectional view showing an example of a second gas separation device. FIG. 9 is a schematic cross-sectional view showing an example of a second separation membrane. FIG. 10 is a schematic configuration diagram showing a recovery system of Modified Example 4. FIG. 11 is a schematic configuration diagram showing a recovery system of Modified Example 5. FIG. 12 is a schematic configuration diagram showing the recovery system used in Calculation Examples 1 and 4. FIG. 13 is a schematic configuration diagram showing the recovery system used in Calculation Examples 9 and 12.

[0010] A recovery system according to a first aspect of the present invention comprises: a first gas separation device that separates a first gas containing a gaseous substance A and a gaseous substance B different from the gaseous substance A to obtain a second gas having a higher content of the substance A than the first gas; a recovery device that changes the state of the substance A contained in the second gas and recovers it; and a third gas circulation path that guides a third gas discharged from the recovery device to the upstream side of the first gas separation device.

[0011] In a second aspect of the present invention, for example, in the recovery system according to the first aspect, the recovery device includes a liquefaction unit that liquefies the substance A contained in the second gas.

[0012] In a third aspect of the present invention, for example, the recovery system according to the first or second aspect 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 substance A than the second gas to the upstream side of the first gas separation device.

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

[0014] In a fifth aspect of the present invention, for example, the recovery system according to any one of the first to fourth aspects further comprises a second gas separation device that separates a mixed gas containing the gaseous substance A and the gaseous substance B to obtain a concentrated gas having a higher content of the substance 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.

[0015] In a sixth aspect of the present invention, for example, in the recovery system according to the fifth aspect, the third gas circulation path satisfies at least one selected from the group consisting of (i) guiding the third gas to the upstream side of the second gas separation device, and (ii) guiding the third gas to the downstream side of the second gas separation device and the upstream side of the first gas separation device.

[0016] In a seventh aspect of the present invention, for example, in the recovery system according to the fifth or sixth aspect, the second gas separation device has a second separation membrane that allows the substance A of the gas to preferentially permeate.

[0017] In an eighth aspect of the present invention, for example, the recovery system according to any one of the first to seventh aspects further comprises a pressurizing device that pressurizes the internal space of the first gas separation device.

[0018] In a ninth aspect of the present invention, for example, the recovery system according to any one of the first to seventh aspects further comprises a decompression device that decompresses the internal space of the first gas separation device.

[0019] In a tenth aspect of the present invention, for example, in the recovery system according to the ninth aspect, the pressure reducing device is a vacuum pump, and the recovery system further comprises 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 booster provided in the first circulation path, and a branch path that branches off from the first circulation path downstream of the booster, and the recovery device is connected to the branch path.

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

[0021] In a twelfth aspect of the present invention, for example, in the recovery system according to any one of the first to eleventh aspects, the content of the substance A in the second gas is 80 vol % or more.

[0022] In a thirteenth aspect of the present invention, for example, the recovery system according to any one of the first to fourth aspects further comprises a combustion device that is supplied with a fuel gas containing oxygen and that discharges an exhaust gas containing the gaseous substance A and the gaseous substance B, and the exhaust gas is the first gas.

[0023] In a fourteenth aspect of the present invention, for example, in the recovery system according to the thirteenth aspect, the content of the substance A in the exhaust gas is 20 vol % or more.

[0024] A recovery method according to a fifteenth aspect of the present invention includes: a first gas separation step of separating a first gas containing a gaseous substance A and a gaseous substance B different from the gaseous substance A in a first gas separation device to obtain a second gas having a higher content of the substance A than the first gas; a recovery step of changing the state of the substance A contained in the second gas in a recovery device to recover it, and discharging a third gas from the recovery device; and a third gas circulation step of sending the third gas to the upstream side of the first gas separation device.

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

[0026] <Recovery System> FIG. 1 is a schematic diagram showing an example of a recovery system 100 according to one embodiment of the present invention. As shown in FIG. 1, the recovery system 100 includes a first gas separation device 11, a recovery device 20, and a third gas circulation path 61. The first gas separation device 11 is a device that separates a first gas G1 containing a gaseous substance A and a gaseous substance B different from the gaseous substance A to obtain a second gas G2 having a higher content of substance A than the first gas G1. The recovery device 20 is a device that changes the state of the substance A contained in the second gas G2 and recovers it. The recovery device 20 can obtain a recovered material M having a higher content of substance A than the second gas G2.

[0027] According to the recovery system 100 of this embodiment, the third gas G3 can be guided upstream of the first gas separation device 11 via the third gas circulation path 61. The third gas G3 is typically an off-gas generated due to a state change of the substance A contained in the second gas G2 in the recovery device 20. The third gas G3 has a lower content of substance A than the second gas G2. The recovery system 100 can recycle the third gas G3, which has a low content of substance A, with a simple configuration. This reduces the recovery power for the substance A of the entire recovery system 100. In this specification, the "recovery power for the substance A of the entire recovery system" refers to the sum of the power required to operate the entire recovery system per kg of the weight of substance A contained in the recovered material M obtained from the recovery device 20. The power required to operate the entire recovery system includes the separation power of the gas separation device (first gas separation device 11 in FIG. 1).

[0028] 1 , in the 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 recovery system 100, the third gas circulation path 61 can guide the third gas G3 to the first gas separation device 11.

[0029] The first gas G1 contains a gaseous substance A and a gaseous substance B that is different from the gaseous substance A. Note that the substance A and the substance B may be compounds or simple substances. The first gas G1 may contain an acidic gas as the gaseous substance A and the gaseous substance B. Examples of the substance A and the substance B include carbon dioxide, methane, hydrogen, nitrogen, oxygen, helium, argon, propane, and propylene. The substances A and B may be nitrogen and carbon dioxide. For example, the first gas G1 may contain carbon dioxide as the substance A and nitrogen as the substance B. The first gas G1 may contain nitrogen as the substance A and carbon dioxide as the substance B.

[0030] The first gas G1 may contain impurities such as NOx (nitrogen oxides) and SOx (sulfur oxides) in addition to the gaseous substance A and the gaseous substance B.

[0031] The content of substance A in the first gas G1 is, for example, in the range of 1 to 70 vol%. The upper limit of the content of substance A in the first gas G1 may be 50 vol%, 40 vol%, 30 vol%, or even 20 vol%. The lower limit of the content of substance A in the first gas G1 may be 5 vol%, 10 vol%, or even 15 vol%. Note that the first gas G1 here refers to the first gas G1 before the third gas G3 joins with it. In this specification, the content (vol%) of substance A in a specified gas is the volume ratio of the gaseous substance to the specified gas under standard conditions (0°C, 101.33 kPa).

[0032] The content of substance A in the second gas G2 is, for example, 80 vol% or more. The lower limit of the content of substance A in the second gas G2 may be 85 vol%, 90 vol%, or even 95 vol%. A high content of substance A in the second gas G2 can further reduce the recovery power of the substance A in the entire recovery system 100. The upper limit of the content of substance A in the second gas G2 is, for example, 99 vol%.

[0033] The content of the substance A in the third gas G3 is, for example, 80 vol % or less. The upper limit of the content of the substance A in the third gas G3 may be 75 vol %. The lower limit of the content of the substance A in the third gas G3 is, for example, 50 vol %.

[0034] The temperature of the third gas G3 is not particularly limited. For example, when the first gas G1 contains carbon dioxide as substance A and nitrogen as substance B, the temperature of the third gas G3 can be −20° C. or lower. When the temperature of the third gas G3 is −20° C. or lower, it is possible to reduce part of the cooling energy required for membrane separation in the first gas separation device 11 by utilizing the cold energy of the third gas G3. When the first gas G1 contains carbon dioxide as substance A and nitrogen as substance B, the lower limit of the temperature of the third gas G3 is, for example, −30° C.

[0035] The content of substance A in the recovered material M is, for example, 95 vol% or more. The lower limit of the content of substance A in the recovered material M may be 96 vol%, 97 vol%, 98 vol%, or even 99 vol%. The upper limit of the content of substance A in the recovered material M is, for example, 99.99 vol%.

[0036] [Recovery Device] The recovery device 20 is not particularly limited as long as it is a device that can change the state of the substance A contained in the second gas G2 and recover it. As shown in Fig. 1, the recovery device 20 may have a state change unit 21 and a tank 22. The state change unit 21 is for changing the state of the substance A contained in the second gas. The tank 22 is for recovering a recovery material M having a higher content of substance A than the second gas G2 discharged from the state change unit 21.

[0037] The third gas G3 is typically off-gas discharged from the state change unit 21. In this case, as shown in FIG. 1 , the third gas circulation path 61 is connected to the state change unit 21. However, the third gas G3 is not limited to off-gas discharged from the state change unit 21. For example, the third gas G3 may be off-gas discharged from the tank 22. In this case, although not shown in the drawings, the third gas circulation path 61 is connected to the tank 22.

[0038] 1 , the state change unit 21 has a gas inlet 21a, a gas outlet 21b, and a recovered material outlet 21c. A second gas G2 is supplied to the state change unit 21 through the gas inlet 21a, and a third gas G3 is discharged from the state change unit 21 through the gas outlet 21b. The recovered material M is discharged from the state change unit 21 through the recovered material outlet 21c. For example, when the first gas G1 contains carbon dioxide as substance A and nitrogen as substance B, the recovered material M includes liquid carbon dioxide (liquefied carbon dioxide), solid carbon dioxide (dry ice), supercritical fluid carbon dioxide, etc.

[0039] The state change unit 21 changes the state of the substance A contained in the second gas G2 to a state other than gas, thereby obtaining a recovered material M having a higher content of substance A than the second gas G2. A third gas G3 having a lower content of substance A than the second gas G2 is discharged from the state change unit 21. In this specification, "a state other than gas" refers to a non-gaseous state including a liquid, a solid, and a supercritical fluid. The state change unit 21 includes at least one selected from the group consisting of a liquefaction unit that liquefies the substance A contained in the second gas G2, a solidification unit that solidifies the substance A contained in the second gas G2, and a supercritical processing unit that changes the state of the substance A contained in the second gas G2 to a supercritical fluid. The state change unit 21 may be a liquefaction unit that liquefies the substance A contained in the second gas G2.

[0040] The state change unit 21 includes, for example, a pressure adjustment unit that adjusts the pressure of the second gas G2 and a temperature adjustment unit that adjusts the temperature of the second gas G2 after the pressure adjustment. By adjusting the pressure by the pressure adjustment unit and the temperature by the temperature adjustment unit, the substance A contained in the second gas G2 can be changed into a state other than gaseous, thereby obtaining a recovered material M having a higher content of substance A than the second gas G2. That is, the pressure adjustment unit and the temperature adjustment unit can function as a liquefaction unit, a solidification unit, or a supercritical treatment unit. When the pressure adjustment unit and the temperature adjustment unit function as a liquefaction unit, the pressure adjustment unit may adjust the pressure of the second gas G2 to 100 to 3000 kPa. The temperature adjustment unit may adjust the temperature of the second gas G2 to -30 to 50°C. The pressure adjustment unit is typically a pressure booster. The temperature adjustment unit is typically a cooler.

[0041] The recovery device 20 may further include a water vapor removal section that removes water vapor contained in the second gas G2 after temperature adjustment, and a separation section that separates liquid, solid, or supercritical fluid substance A from the second gas G2 from which the water vapor has been removed.

[0042] 1, the collected material M discharged from the state change unit 21 is collected in the tank 22. The tank 22 may be configured to store the collected material M.

[0043] [Combustion Device] The recovery system 100 may further include a combustion device 30 that is supplied with a fuel gas G0 containing oxygen and that discharges exhaust gas containing a gaseous substance A and a gaseous substance B. In this specification, the term "combustion device" refers to a device that burns fuel using the fuel gas and discharges exhaust gas. Examples of the combustion device 30 include a boiler, an incinerator, and an internal combustion engine such as an engine. The combustion device 30 is typically a boiler.

[0044] 1, the exhaust gas discharged from the combustion device 30 is the first gas G1 supplied to the first gas separation device 11. Note that the first gas G1 here refers to the first gas G1 before the third gas G3 is merged therewith.

[0045] The content of substance A in the exhaust gas discharged from the combustion device 30 is preferably 20 vol % or more. In this case, by using the exhaust gas discharged from the combustion device 30 as the first gas G1 supplied to the first gas separation device 11, the separation power of the first gas separation device 11 can be reduced.

[0046] The lower limit of the content of substance A in the exhaust gas discharged from the combustion device 30 may be 25 vol %, or may further be 30 vol %.

[0047] The upper limit of the content of substance A in the exhaust gas discharged from the combustion device 30 is preferably 70 vol %. When the content of substance A in the first gas G1 supplied to the first gas separation device 11 is 70 vol % or less, the separation power of the first gas separation device 11 can be reduced more efficiently.

[0048] The upper limit of the content of substance A in the exhaust gas discharged from the combustion device 30 may be 65 vol%, 60 vol%, 55 vol%, or even 50 vol%.

[0049] There are no particular limitations on the fuel used in the combustion device 30. Examples of fuel include liquid fuels such as petroleum, gaseous fuels such as natural gas, solid fuels such as coal and wood, and special fuels such as waste. A fuel supply device (not shown) that supplies fuel may be connected to the combustion device 30.

[0050] Although not shown, the combustion device 30 may have a burner for burning fuel, a fuel supply pipe for supplying fuel to the burner, and a fuel gas supply pipe for supplying fuel gas G0 to the burner. In this case, in the combustion device 30, the fuel is burned using the fuel gas G0 supplied to the burner, thereby generating exhaust gas containing the gaseous substance A.

[0051] The oxygen content in the fuel gas G0 supplied to the combustion device 30 is preferably 20 vol% or more. If the oxygen content in the fuel gas G0 is 20 vol% or more, the content of substance A in the exhaust gas discharged from the combustion device 30 may increase. Therefore, the separation power of the first gas separation device 11 may be reduced.

[0052] The lower limit of the oxygen content in the fuel gas G0 supplied to the combustion device 30 may be 25 vol %, or may further be 30 vol %.

[0053] There is no particular upper limit to the oxygen content in the fuel gas G0 supplied to the combustion device 30. The upper limit of the oxygen content in the fuel gas G0 is, for example, 100 vol%. The upper limit of the oxygen content in the fuel gas G0 may be 90 vol%, 80 vol%, or even 70 vol%.

[0054] [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 substance 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 a physical adsorption method in which the first gas G1 is separated using an adsorbent to obtain the second gas G2. Physical adsorption methods include, for example, pressure vacuum swing adsorption (PVSA), pressure swing adsorption (PSA), temperature swing adsorption (TSA), and pressure and temperature swing adsorption (PTSA). The PVSA, PSA, TSA, and PTSA methods are methods of 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.

[0055] 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.

[0056] Fig. 2 is a schematic cross-sectional view showing an example of the first gas separation device 11 provided in the recovery system 100. In the example of Fig. 2, the first gas separation device 11 has a first separation membrane 111 that separates the supplied first gas G1. The second gas G2 obtained by the first separation membrane 111 has a higher content of substance A than the first gas G1.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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 space (first chamber 113). The permeate space outlet 114b is an opening for discharging the first permeate gas S1 from the permeate 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 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.

[0061] 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.

[0062] 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.

[0063] The first separation membrane 111 may be a separation membrane that preferentially allows permeation of gaseous substance A. For example, when the first gas G1 contains carbon dioxide as substance A and nitrogen as substance B, the first separation membrane 111 may be a carbon dioxide separation membrane that preferentially allows permeation of gaseous carbon dioxide (gaseous substance A) contained in the first gas G1. For example, when the first gas G1 contains nitrogen as substance A and carbon dioxide as substance B, the first separation membrane 111 may be a nitrogen separation membrane that preferentially allows permeation of gaseous nitrogen (gaseous substance A) contained in the first gas G1.

[0064] When the first separation membrane 111 is a carbon dioxide separation membrane, the carbon dioxide (substance 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.

[0065] (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 gaseous carbon dioxide (gaseous substance 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, for example, that 95 wt % or more, or even 99 wt % or more, is composed of the material.

[0066] 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.

[0067] (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.

[0068] 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.

[0069] 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.

[0070] (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.

[0071] 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.

[0072] When the first separation membrane 111 is a nitrogen separation membrane, the carbon dioxide (substance 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.

[0073] (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.

[0074] (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.

[0075] (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.

[0076] 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.

[0077] [Gas Paths] As shown in FIG. 1, the recovery system 100 further includes a first gas supply path 51, a second gas exhaust path 52, and a fourth gas exhaust path 54 as gas paths.

[0078] 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. As shown in FIG. 1 , the first gas supply path 51 may be connected to an exhaust gas outlet 30b of the combustion device 30. Exhaust gas may be supplied as the first gas G1 from the combustion device 30 to the first gas separation device 11.

[0079] 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.

[0080] 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 flow rate adjustment valve.

[0081] 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 connects the permeate space outlet 114b of the first gas separation device 11 and the gas inlet 21a of the state change section 21. For example, a pump (not shown) for controlling the flow rate of the second gas G2 may be disposed in the second gas discharge path 52.

[0082] The fourth gas discharge path 54 is a path for discharging a fourth gas G4, which has a lower content of substance 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. For example, a pump (not shown) that controls the flow rate of the fourth gas G4 may be disposed in the fourth gas discharge path 54.

[0083] 1 , in the 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.

[0084] Although the content of substance A in the fourth gas G4 is lower than that in the second gas G2, the fourth gas G4 still contains substance A. By guiding the fourth gas G4 to the upstream side of the first gas separation device 11 via the fourth gas discharge path 54 and the third gas circulation path 61, the fourth gas G4 can be recycled. This can improve the recovery rate of the substance A that is ultimately obtained.

[0085] 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 switching valve and the flow rate adjustment valve can adjust the flow rate of the fourth gas G4 introduced to the upstream side of the first gas separation device 11. Furthermore, the switching valve and the flow rate adjustment valve provided in the third gas circulation path 61 can adjust the flow rate of the third gas G3 introduced to the upstream side of the first gas separation device 11.

[0086] 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.

[0087] 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.

[0088] When the combustion device 30 is included, the recovery system 100 may further include a fuel gas supply path 58 and an exhaust gas circulation path 59 as gas paths.

[0089] The fuel gas supply path 58 is a path for supplying the fuel gas G0 from the gas supply unit 31 to the combustion device 30 during operation. The fuel gas supply path 58 connects the outlet 31b of the gas supply unit 31 and the fuel gas inlet 30a of the combustion device 30.

[0090] The exhaust gas circulation path 59 is a path for sending at least a portion of the exhaust gas to the combustion device 30. By sending at least a portion of the exhaust gas to the combustion device 30 via the exhaust gas circulation path 59, the content of substance A in the first gas G1 supplied to the first gas separation device 11 can be increased.

[0091] In the example of FIG. 1 , the first gas supply path 51 has a first portion 51A, a second portion 51B, and a third portion 51C. The first portion 51A connects the exhaust gas outlet 30b of the combustion device 30 and the branching position 95. The second portion 51B connects the branching position 95 and the merging position 81. The third portion 51C connects the merging position 81 and the supply space inlet 113a of the first gas separation device 11. In the example of FIG. 1 , the exhaust gas circulation path 59 branches off from the first gas supply path 51 at the branching position 95 and connects to the fuel gas supply path 58 at the merging position 83. However, the connection position of the exhaust gas circulation path 59 is not limited to the example shown in FIG. 1 . For example, the exhaust gas circulation path 59 may branch off from the exhaust gas outlet 30b of the combustion device 30 and connect to the fuel gas inlet 30a of the combustion device 30.

[0092] The collection system 100 may further include a collection path 53. The collection path 53 connects the collected material discharge port 21c of the state change unit 21 and the inlet of the tank 22 for collecting the collected material M.

[0093] Unless otherwise specified, each of the paths of the recovery system 100 is made up of, for example, metal or resin piping.

[0094] 1, the recovery system 100 further includes a pressurizing device 41 that pressurizes the internal space of the first gas separation device 11. That is, the recovery system 100 is a system that performs gas separation by a pressurization method. In the example shown in FIG. 1, the pressurizing device 41 is provided in the third portion 51C of the first gas supply path 51.

[0095] The pressurizing device 41 is not particularly limited as long as it can pressurize the internal space of the first gas separation device 11 .

[0096] 1 , the junction position 81 in the first gas supply path 51 is located upstream of the pressurizing device 41. Therefore, the third gas G3 discharged from the state change section 21 is supplied to the first gas separation device 11 via the pressurizing device 41. However, the location of the junction position 81 is not limited to the example shown in FIG. 1 . For example, the junction position 81 may be located downstream of the pressurizing device 41 and upstream of the first gas separation device 11.

[0097] As shown in Figure 1, in the recovery system 100, 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 21a of the state change section 21.

[0098] The second gas discharge path 52 may be provided with a booster (not shown) for supplying the second gas G2 to the state change section 21. That is, the recovery system 100 may further include a booster provided between the first gas separation device 11 and the state change section 21 to boost the pressure of the second gas G2.

[0099] The pressure booster is not particularly limited as long as it can pressurize the second gas G2 supplied to the state change unit 21. The pressure booster is typically a compressor.

[0100] The recovery system 100 may include a concentration sensor (not shown) that measures the content of substance A in the third gas G3. If the content of substance A in the third gas G3 is equal to or greater than the content of substance A in the first gas G1, the third gas G3 may be sent upstream of the first gas separation device 11. The content of substance A in the third gas G3 may be monitored by the concentration sensor, and if the content of substance A in the third gas G3 is equal to or greater than the content of substance A in the first gas G1, the third gas G3 may be sent upstream of the first gas separation device 11. If the content of substance A in the third gas G3 is less than the content of substance A in the first gas G1, the third gas G3 may be released to the atmosphere.

[0101] The concentration sensor is not particularly limited as long as it can measure the content of substance A in a predetermined gas. For example, a gas concentration sensor using a non-dispersive infrared (NDIR) method, a thermal conductivity detector (TCD) method, or a gas chromatography (GC) method can be used as the concentration sensor.

[0102] The recovery system 100 may further include a control device 40 that controls each component of the 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. A program for appropriately operating the recovery system 100 is stored in the control device 40. For example, the control device 40 may adjust the flow rate of the third gas G3 introduced to the first gas separation device 11. The control device 40 may adjust the flow rate of the third gas G3 introduced to the first gas separation device 11 by controlling 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 state change unit 21.

[0103] [Another Example of First Gas Separation Apparatus] In the recovery system 100, the first gas separation apparatus 11 having the first separation membrane 111 is not limited to the form shown in Fig. 2. The first gas separation apparatus 11 having the first separation membrane 111 may be, for example, a spiral membrane element, a hollow fiber membrane element, or the like. Fig. 4 is a schematic cross-sectional view showing another example of the first gas separation apparatus 11 having the first separation membrane 111. The first gas separation apparatus 15 shown in Fig. 4 is a spiral membrane element and includes a central tube 16 and a laminate 17. The laminate 17 includes the first separation membrane 111.

[0104] 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.

[0105] 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).

[0106] 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.

[0107] 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.

[0108] <Recovery Method> Next, a recovery method using the above-described recovery system 100 will be described.

[0109] The recovery method in this embodiment (hereinafter sometimes simply referred to as the "recovery method") includes a first gas separation step in which a first gas G1 containing a gaseous substance A and a gaseous substance B different from the gaseous substance A is separated in a first gas separation device 11 to obtain a second gas G2 having a higher content of substance A than the first gas G1, a recovery step in which the substance A contained in the second gas G2 is recovered by changing its state in a recovery device 20 and a third gas G3 is discharged from the recovery device 20, and a third gas circulation step in which the third gas G3 is sent upstream of the first gas separation device 11. In the recovery step, a recovered product M having a higher content of substance A than the second gas G2 can be obtained.

[0110] According to the 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. The third gas G3 is typically an off-gas generated in association with a state change of the substance A contained in the second gas G2 in the state change section 21 of the recovery device 20. That is, the third gas G3 has a lower content of substance A than the second gas G2. This allows the recovery power of the substance A of the entire recovery system 100 to be reduced.

[0111] The first gas separation step, the state change step, and the third gas circulation step are performed, for example, as follows. Each step will be described below using the case where the first gas separation device 11 has the first separation membrane 111 as an example.

[0112] [First Gas Separation Step] In the first gas separation step, first, the first gas G1 is supplied to the first chamber 113 (supply space) of the first gas separation device 11 through the first gas supply path 51 .

[0113] Next, with the first gas G1 being supplied to the first chamber 113 of the first gas separation device 11, the inside of the first chamber 113 (supply space) is pressurized by the pressurizing device 41. More specifically, the inside of the first chamber 113 is pressurized using the pressurizing device 41 through the supply space inlet 113a.

[0114] By pressurizing the first chamber 113, a pressure difference is generated or increases between the supply space and the permeation 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. The first chamber 113 may continue to be pressurized by the pressurizing device 41 while separation of the first gas G1 is being performed.

[0115] The first permeable gas S1 (second gas G2) discharged from the second chamber 114 is discharged to the second gas discharge path 52. The second gas G2 is supplied to the state change unit 21 through the gas inlet 21a.

[0116] [Recovery process] In the recovery process, the state change unit 21 changes the state of the substance A contained in the second gas G2 to a state other than gas, thereby obtaining a recovered material M having a higher content of substance A than the second gas G2, and a third gas G3 having a lower content of substance A than the second gas G2 is discharged from the state change unit 21 through the gas discharge port 21b.

[0117] The recovery step includes, for example, a liquefaction step of liquefying the substance A contained in the second gas G2, a solidification step of solidifying the substance A contained in the second gas G2, and a supercritical processing step of changing the state of the substance A contained in the second gas G2 into a supercritical fluid. The recovery step may be a liquefaction step of liquefying the substance A contained in the second gas G2 to obtain a liquid recovered product M.

[0118] [Third Gas Circulation Step] In the third gas circulation step, the third gas G3 is sent to the first gas separation device 11. By the third gas circulation step, the third gas G3 having a low content of substance A can be recycled. This allows the power required to recover substance A in the entire recovery system 100 to be reduced.

[0119] The recovery method may further 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 final substance A.

[0120] The recovery method may further include a first gas supply step of supplying the exhaust gas discharged from the combustion device 30 to the first gas separation device 11 as a first gas G1.

[0121] The recovery method may further include an exhaust gas circulation step of sending a portion of the exhaust gas discharged from the combustion device 30 back to the combustion device 30 .

[0122] For example, the first gas G1 may contain carbon dioxide as the substance A and nitrogen as the substance B. The first gas G1 may contain nitrogen as the substance A and carbon dioxide as the substance B.

[0123] <Modifications of the Collection System> The collection system according to this embodiment is not limited to the configuration of the collection system 100 shown in Fig. 1. Modifications 1 to 5 of the collection system according to this embodiment will be described below. In the following, elements common to the collection system 100 shown in Fig. 1 will be designated by the same reference numerals, and descriptions thereof may be omitted.

[0124] (Variation 1) Fig. 5 is a schematic diagram showing a recovery system 101 of Variation 1. The recovery system 101 includes a decompression device 45 that decompresses the internal space of the first gas separation device 11 instead of the pressurizing device 41. That is, the recovery system 101 is a system that performs gas separation using a decompression method. Except for this, the recovery system 101 has basically the same configuration as the recovery system 100 described above. In the example shown in Fig. 5, the decompression device 45 is provided in the second gas discharge path 52. However, although not shown, the recovery system 101 may also include an air blower for sending the first gas G1 into the internal space of the first gas separation device 11.

[0125] The pressure reducing device 45 is typically a vacuum pump 45. As shown in Fig. 5 , the recovery system 101 may include a vacuum pump 45 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 45 as a seal gas for the vacuum pump 45. The recovery system 101 may further include a booster 43 provided in the first circulation path 71, and a branch path 72 that branches off from the first circulation path 71 downstream of the booster 43. In this case, the state change unit 21 may be connected to the branch path 72.

[0126] Seal gas is a gas supplied to a vacuum pump for purposes such as 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.

[0127] However, with the above-described configuration, at least a portion of the second gas G2, which has a higher content of substance A than the first gas G1, can be used as a seal gas for the vacuum pump 45. The second gas G2 is supplied to the vacuum pump 45 via the first circulation path 71. Therefore, with the above-described configuration, it is possible to improve the recovery rate of the substance A that is ultimately obtained while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0128] Furthermore, according to the above-described configuration, the state change unit 21 is connected to the branch path 72 that branches off from the first circulation path 71 downstream of the booster 43, so that the second gas G2 can be pressurized using the booster 43 to supply the second gas G2 to the state change unit 21. Therefore, there is no need to separately provide a booster for pressurizing the second gas G2 upstream of the state change unit 21. This allows the number of devices that make up the recovery system 101 to be reduced.

[0129] The vacuum pump 45 is a vacuum pump that requires a seal gas. The vacuum pump 45 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 45 can reduce the pressure in the permeate space (second chamber 114) of the first gas separation device 11. In other words, the vacuum pump 45 can generate or increase a pressure difference between the supply space (first chamber 113) and the permeate space (second chamber 114) of the first gas separation device 11. The vacuum pump 45 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 45 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.

[0130] The vacuum pump 45 may be an assembly of multiple vacuum pumps. That is, the vacuum pump 45 may be configured so that each of the multiple vacuum pumps can reduce the pressure in the permeation space (second chamber 114) of the first gas separation device 11. With this configuration, the pressure in the permeation space of the first gas separation device 11 can be appropriately adjusted by adjusting the number of vacuum pumps in operation.

[0131] 5 , 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 45. The first circulation path 71 connects the outlet of the vacuum pump 45 to the seal gas inlet of the vacuum pump 45. The branch path 72 branches off from the first circulation path 71 at a branch position 92 and is connected to the gas inlet 21a of the state change section 21.

[0132] 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 state change unit 21 can be adjusted by the switching valve and the flow rate adjustment valves.

[0133] Although not shown, the branch path 72 may be provided with a buffer tank and a pressure reducing valve.

[0134] 5 , the booster 43 is provided in the first circulation path 71 upstream of the branch position 92. The booster 43 pressurizes the second gas G2 as a seal gas supplied to the vacuum pump 45, and also pressurizes the second gas G2 supplied to the state change unit 21.

[0135] The pressure booster 43 is not particularly limited as long as it can pressurize the second gas G2, and is typically a compressor.

[0136] The recovery system 101 may include a drain mechanism (not shown) that discharges moisture contained in the second gas G2 serving as a seal gas. With this configuration, for example, when the second gas G2 contains moisture, malfunctions of the components of the recovery system 101 due to the moisture can be suppressed.

[0137] A drain mechanism may be provided in the booster 43. As shown in Fig. 5, the moisture collected by the drain mechanism may be discharged to the outside through a drain path 75 connected to the booster 43.

[0138] In the recovery system 101, 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 45 and the flow rate of the second gas G2 supplied to the state change section 21.

[0139] The recovery method using the recovery system 101 of the first modification includes a first gas separation step, a state change step, and a third gas circulation step, similar to the recovery method using the above-described recovery system 100. This allows the recovery power of the entire recovery system 101 for the substance A to be reduced.

[0140] In the recovery method of Modification 1, the first gas separation step is carried out, 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.

[0141] [First Gas Separation Step] In the first gas separation step, first, the first gas G1 is supplied to the first chamber 113 (supply space) of the first gas separation device 11 through the first gas supply path 51 .

[0142] Next, while the first gas G1 is being supplied to the first chamber 113 of the first gas separation device 11, the pressure inside the second chamber 114 (permeation space) is reduced by the vacuum pump 45. More specifically, the pressure inside the second chamber 114 is reduced by using the vacuum pump 45 through the permeation space outlet 114b.

[0143] By reducing the pressure inside the second chamber 114, a pressure difference is generated or increases between the supply space and the permeation 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 45.

[0144] 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 45. The vacuum pump 45 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 state change unit 21 through the gas inlet 21a.

[0145] The recovery method of the first modification may further include a fourth gas circulation step, similar to the recovery method using the recovery system 100 described above.

[0146] The recovery method of Modification 1 may further include a first gas supplying step, similar to the recovery method using recovery system 100 described above.

[0147] The recovery method of the first modification may further include an exhaust gas circulation step, similar to the recovery method using the recovery system 100 described above.

[0148] The recovery method of Modification 1 may further include a first circulation step of supplying at least a portion of the second gas G2 to the vacuum pump 45 as a seal gas for the vacuum pump 45. According to the first circulation step, at least a portion of the second gas G2, which has a higher content of substance A than the first gas G1, is used as a seal gas for the vacuum pump 45, so that it is possible to improve the recovery rate of the substance A obtained ultimately while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0149] In the first circulation step, at least a portion of the second gas G2 discharged from the vacuum pump 45 to the first circulation path 71 is supplied to the vacuum pump 45 as a seal gas via the first circulation path 71.

[0150] (Variation 2) FIG. 6 is a schematic diagram showing a recovery system 102 of Variation 2. In the recovery system 102, the state change unit 21 is connected to the second gas discharge path 52 so that the second gas G2 discharged from the pressure reducing device (vacuum pump) 45 is supplied to the state change unit 21 without passing through the booster 43. Except for this, the recovery system 102 has basically the same configuration as the recovery system 101 of Variation 1 described above. The recovery system 102 is a system that performs gas separation using a pressure reduction method. The recovery system 102 has a simple configuration and can recycle the third gas G3, which has a low content of substance A. This can reduce the power required to recover substance A throughout the recovery system 102.

[0151] 6 , in the recovery system 102, 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 and the inlet of the vacuum pump 45. The second portion 522 is a portion that connects the outlet of the vacuum pump 45 and the branch position 93. The third portion 523 is a portion that connects the branch position 93 and the gas inlet 21a of the state change section 21. In the recovery system 102, the first circulation path 71 branches off from the second gas discharge path 52 at the branch position 93 and is connected to the seal gas inlet of the vacuum pump 45.

[0152] A switching valve (not shown) may be provided at the branch position 93. A flow rate adjustment valve (not shown) may be provided in the first circulation path 71. With this configuration, the switching valve and the flow rate adjustment valves can adjust 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 state change unit 21.

[0153] 6, the booster 43 is provided in the first circulation path 71. The booster 43 pressurizes the second gas G2 as a seal gas supplied to the vacuum pump 45.

[0154] 6, in the recovery system 102, a booster 47 for supplying the second gas G2 to the state change section 21 is provided in the third portion 523 of the second gas discharge path 52. That is, the recovery system 102 further includes a booster 47 that is provided between the first gas separation device 11 and the state change section 21 and that boosts the pressure of the second gas G2.

[0155] In the recovery system 102, the control device 40 may adjust the flow rate of the second gas G2 supplied to the vacuum pump 45 and the flow rate of the second gas G2 supplied to the state change section 21 by controlling the switching valve provided at the branch position 93 and the flow rate adjustment valve provided in the first circulation path 71.

[0156] The recovery method using the recovery system 102 of the second modification includes a first gas separation step, a state change step, and a third gas circulation step, similar to the recovery method using the above-described recovery system 100. This allows the recovery power of the entire recovery system 102 for the substance A to be reduced.

[0157] In the recovery method of Modification 2, the first gas separation step is carried out, 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.

[0158] [First Gas Separation Step] As in the recovery method of Modification 1, first, the first gas G1 is supplied to the first chamber 113 (supply space) of the first gas separation device 11 through the first gas supply path 51. Next, while the first gas G1 is being supplied to the first chamber 113 of the first gas separation device 11, the pressure inside the second chamber 114 (permeation space) is reduced by the vacuum pump 45. As a result, the first gas G1 is separated by the first separation membrane 111, and a first permeation gas S1 is supplied to the second chamber 114 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.

[0159] The first permeable gas S1 (second gas G2) discharged from the second chamber 114 passes through the first portion 521 of the second gas discharge path 52 and is sucked by the vacuum pump 45. The vacuum pump 45 discharges the sucked second gas G2 to the second portion 522 of the second gas discharge path 52. The second gas G2 passes through the third portion 523 of the second gas discharge path 52 and is supplied to the state change unit 21 through the gas inlet 21a.

[0160] The recovery method of Modification 2 may further include a fourth gas circulation step, similar to the recovery method using the recovery system 100 described above.

[0161] The recovery method of Modification 2 may further include a first gas supplying step, similar to the recovery method using recovery system 100 described above.

[0162] The recovery method of Modification 2 may further include an exhaust gas circulation step, similar to the recovery method using the recovery system 100 described above.

[0163] The recovery method of Modification 2 may further include a first circulation step, similar to the recovery method using the recovery system 101 of Modification 1 described above. In the recovery method of Modification 2, the first circulation step is carried out, for example, as follows.

[0164] In the first circulation process, at least a portion of the second gas G2 discharged from the vacuum pump 45 to the second portion 522 of the second gas discharge path 52 is supplied to the vacuum pump 45 as a seal gas via the first circulation path 71.

[0165] The 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 may be a device that separates a mixed gas Gm containing a gaseous substance A and a gaseous substance B to obtain a concentrated gas Gc having a higher content of substance A than the mixed gas Gm. The concentrated gas Gc may be at least a part of the first gas G1 supplied to the first gas separation device 11. In other words, when the recovery system includes the second gas separation device 12, the first gas separation device 11 may be arranged downstream of the second gas separation device 12.

[0166] When the recovery system is equipped with a second gas separation device 12, the third gas circulation path 61 may satisfy at least one selected from the group consisting of (i) guiding the third gas G3 upstream of the second gas separation device 12, and (ii) guiding the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11.

[0167] The recovery system including the second gas separation device 12 may be a system that performs gas separation by a pressurized method, or may be a system that performs gas separation by a reduced pressure method.

[0168] (Variation 3) Figure 7 is a schematic diagram showing a recovery system 200 of Variation 3. The recovery system 200 includes a second gas separation device 12 and a first gas separation device 11 arranged downstream of the second gas separation device 12. In the recovery system 200, 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 recovery system 100 of Figure 1. The recovery system 200 is a system that performs gas separation using a pressurized method.

[0169] In the recovery system 200, the third gas circulation path 61 satisfies at least one selected from the group consisting of (i) guiding the third gas G3 upstream of the second gas separation device 12, and (ii) guiding the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11. The recovery system 200 has a simple configuration and can recycle the third gas G3 having a low content of substance A. This can reduce the power required to recover substance A throughout the recovery system 200.

[0170] 7 , in the 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 and / or the first gas separation device 11. That is, according to the recovery system 200, the third gas circulation path 61 can guide the third gas G3 to the second gas separation device 12 and / or the first gas separation device 11.

[0171] The mixed gas Gm contains a gaseous substance A and a gaseous substance B that is different from the gaseous substance A. Like the first gas G1, the mixed gas Gm may contain acidic gases as the gaseous substance A and the gaseous substance B. For example, the mixed gas Gm may contain carbon dioxide as the substance A and nitrogen as the substance B. The mixed gas Gm may contain nitrogen as the substance A and carbon dioxide as the substance B. In addition to the gaseous substance A and the gaseous substance B, the mixed gas Gm may contain impurities such as NOx (nitrogen oxides) and SOx (sulfur oxides).

[0172] The content of substance A in the mixed gas Gm is, for example, in the range of 1 to 70 vol%. The upper limit of the content of substance A in the mixed gas Gm may be 50 vol%, 40 vol%, 30 vol%, or even 20 vol%. Note that the mixed gas Gm here refers to the mixed gas Gm before the third gas G3 joins. The content of substance A in the third gas G3 is, for example, in the range of 1 to 95 vol%.

[0173] The content of substance A in the concentrated gas Gc is, for example, 50 vol% or more. The lower limit of the content of substance A in the concentrated gas Gc may be 55 vol%, 60 vol%, or even 65 vol%. The upper limit of the content of substance A in the concentrated gas Gc is, for example, 79 vol%.

[0174] In the example shown in Fig. 7, the exhaust gas discharged from the combustion device 30 (omitted in Fig. 7) is the mixed gas Gm supplied to the second gas separation device 12. Note that the mixed gas Gm here refers to the mixed gas Gm before the third gas G3 is merged.

[0175] [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 substance 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.

[0176] 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.

[0177] Fig. 8 is a schematic cross-sectional view showing an example of the second gas separation device 12 included in the recovery system 200. In the example of Fig. 8, 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 substance A than the mixed gas Gm.

[0178] 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.

[0179] 8, 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.

[0180] 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.

[0181] 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 space (first chamber 113). The permeate space outlet 114b is an opening for discharging the second permeate gas S3 from the permeate 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 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.

[0182] 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.

[0183] The configuration of the second separation membrane 121 is not particularly limited. Figure 9 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 8. As shown in Figure 9, 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.

[0184] The second separation membrane 121 may be a separation membrane that preferentially allows permeation of gaseous substance A. For example, when the mixed gas Gm contains carbon dioxide as substance A and nitrogen as substance B, the second separation membrane 121 may be a carbon dioxide separation membrane that preferentially allows permeation of gaseous carbon dioxide (gaseous substance A) contained in the mixed gas Gm. For example, when the mixed gas Gm contains nitrogen as substance A and carbon dioxide as substance B, the second separation membrane 121 may be a nitrogen separation membrane that preferentially allows permeation of gaseous nitrogen (gaseous substance A) contained in the mixed gas Gm.

[0185] When the second separation membrane 121 is a carbon dioxide separation membrane, the carbon dioxide (substance 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.

[0186] (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 preferential permeation of gaseous carbon dioxide (gaseous substance A) contained in the mixed gas Gm. 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.

[0187] (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.

[0188] (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.

[0189] When the second separation membrane 121 is a nitrogen separation membrane, the carbon dioxide (substance 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.

[0190] (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.

[0191] (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.

[0192] (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.

[0193] The configuration of the second separation membrane 121 is not limited to the example shown in Fig. 9. 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.

[0194] The second gas separation device 12 having the second separation membrane 121 is not limited to the form shown in Fig. 8. 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.

[0195] [Gas Paths] As shown in FIG. 7, the 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.

[0196] 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 the supply space inlet 123a of the second gas separation device 12. The mixed gas supply path 55 may be connected to the exhaust gas outlet 30b of the combustion device 30 (omitted in FIG. 7 ). Exhaust gas may be supplied as the mixed gas Gm from the combustion device 30 to the second gas separation device 12.

[0197] 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 connects the permeate space outlet 124b of the second gas separation device 12 and the supply space inlet 113a of the first gas separation device 11. The concentrated gas discharge path 56 may be provided with, for example, a pump (not shown) that controls the flow rate of concentrated gas Gc.

[0198] 7, in the recovery system 200, the concentrated gas discharge path 56 corresponds to the first gas supply path 51. In the recovery system 200, the first gas separation device 11 is connected to the concentrated gas discharge path 56.

[0199] The non-concentrated gas discharge path 57 is a path for discharging, during operation, non-concentrated gas Gs, which has a lower content of substance A than 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 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 (not shown) for controlling the flow rate of the non-concentrated gas Gs may be disposed in the non-concentrated gas discharge path 57.

[0200] In the 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.

[0201] In the recovery system 200, the third gas circulation path 61 satisfies at least one selected from the group consisting of (i) guiding the third gas G3 upstream of the second gas separation device 12, and (ii) guiding the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11. As shown in FIG. 7 , the third gas circulation path 61 may branch into a first portion 61A and a second portion 61B at a branching position 91. The first portion 61A may merge with the concentrated gas discharge path 56 (first gas supply path 51) at a merging position 81. The second portion 61B may merge with the mixed gas supply path 55 at a merging position 84. However, the merging position of the first portion 61A and the second portion 61B is not limited to the example shown in FIG. 7 . The first portion 61A may be connected to, for example, the supply space inlet 113a of the first gas separation device 11. The second portion 61B may be connected to the feed space inlet 123a of the second gas separation device 12, for example.

[0202] A switching valve (not shown) may be provided at the branch position 91. Flow rate control valves (not shown) may be provided in each of the first portion 61A and the second portion 61B of the first circulation path 71. With this configuration, the flow rates of the third gas G3 guided to the second gas separation device 12 and the first gas separation device 11 can be adjusted by the switching valve and each flow rate control valve.

[0203] 7 , the mixed gas supply path 55 has a first portion 55A and a second portion 55B. The first portion 55A is, for example, a portion that connects the exhaust gas outlet 30b of the combustion device 30 (not shown in FIG. 7 ) and the junction position 84. The second portion 55B is a portion that connects the junction position 84 and the supply space inlet 123a of the second gas separation device 12.

[0204] 7, the recovery system 200 further includes a pressurizing device 42 that pressurizes the internal space of the second gas separation device 12. In the example shown in FIG. 7, the pressurizing device 42 is provided in the second portion 55B of the mixed gas supply path 55.

[0205] The pressurizing device 42 is not particularly limited as long as it can pressurize the internal space of the second gas separation device 12 .

[0206] In the example shown in Figure 7, the junction position 84 in the mixed gas supply path 55 is located upstream of the pressurizing device 42. Therefore, the third gas G3 discharged from the state change section 21 is supplied to the second gas separation device 12 via the pressurizing device 42. However, the location of the junction position 84 is not limited to the example shown in Figure 7. For example, the junction position 84 may be located downstream of the pressurizing device 42 and upstream of the second gas separation device 12.

[0207] In the recovery system 200, when the content of substance A in the third gas G3 is equal to or greater than the content of substance A in the mixed gas Gm, the third gas G3 may be sent upstream of the second gas separation device 12. However, the reason the third gas G3 is sent upstream of the second gas separation device 12 is not limited to when the content of substance A in the third gas G3 is equal to or greater than the content of substance A in the mixed gas Gm. For example, when the content of substance A in the third gas G3 is approximately the same as the content of substance A in the first gas G1, the third gas G3 may be sent upstream of the second gas separation device 12.

[0208] In the recovery system 200, when the content of substance A in the third gas G3 is equal to or greater than the content of substance 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. 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 substance A in the third gas G3 is equal to or greater than the content of substance A in the mixed gas Gm. For example, when the content of substance A in the third gas G3 is approximately the same as the content of substance A in the first gas G1, the third gas G3 may be sent downstream of the second gas separation device 12 and upstream of the first gas separation device 11.

[0209] In the recovery system 200, the control device 40 may adjust the flow rate of the third gas G3 guided to each of the second gas separation device 12 and the first gas separation device 11 by controlling the switching valve provided at the branch position 91 and the flow control valves provided in the first part 61A and the second part 61B of the first circulation path 71.

[0210] The recovery method using the recovery system 200 of the third modification includes a first gas separation step, a state change step, and a third gas circulation step, similar to the recovery method using the above-described recovery system 100. This allows the recovery power of the substance A of the entire recovery system 200 to be reduced.

[0211] The recovery method of Modification 3 further includes a second gas separation step, prior to the first gas separation step, of separating a mixed gas Gm containing gaseous substance A and gaseous substance B in a second gas separation device 12 to obtain a concentrated gas Gc having a higher content of substance A than the mixed gas Gm. In the recovery method of Modification 3, the concentrated gas Gc is at least a portion of the first gas G1 supplied to the first gas separation device.

[0212] In the recovery method of Modification 3, the second gas separation step and the third gas circulation step are performed, for example, as follows. Each step will be described below using the case where the second gas separation device 12 has the second separation membrane 121 as an example.

[0213] [Second Gas Separation Step] In the second gas separation step, first, the mixed gas Gm is supplied to the first chamber 123 (supply space) of the second gas separation device 12 through the mixed gas supply path 55 .

[0214] Next, with the mixed gas Gm being supplied to the first chamber 123 of the second gas separation device 12, the inside of the first chamber 123 (supply space) is pressurized by the pressurizing device 42. In detail, the inside of the first chamber 123 is pressurized using the pressurizing device 42 through the supply space inlet 123a.

[0215] By pressurizing the first chamber 123, a pressure difference is generated or increases between the supply space and the permeation 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 the separation of the mixed gas Gm is being performed, the second chamber 124 may continue to be pressurized by the pressurizing device 42.

[0216] The second permeable gas S3 (concentrated gas Gc) discharged from the second chamber 124 is discharged to the concentrated gas discharge path 56. The concentrated gas Gc passes through 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.

[0217] The second gas separation step is followed by the first gas separation step.

[0218] [Third Gas Circulation Step] In the third gas circulation step, the third gas G3 is sent to at least one selected from the group consisting of the upstream side of the second gas separation device 12, and the downstream side of the second gas separation device 12 and the upstream side of the first gas separation device 11. This makes it possible to reduce the power required to recover the substance A in the entire recovery system 200.

[0219] The recovery method of Modification 3 may further include a fourth gas circulation step, similar to the recovery method using the recovery system 100 described above.

[0220] The recovery method of Modification 3 may further include a first gas supplying step, similar to the recovery method using recovery system 100 described above.

[0221] In the first gas supply step, the exhaust gas discharged from the combustion device 30 is supplied to the first gas separation device 11 as a mixed gas Gm.

[0222] The recovery method of Modification 3 may further include an exhaust gas circulation step, similar to the recovery method using the recovery system 100 described above.

[0223] (Variation 4) FIG. 10 is a schematic diagram showing a recovery system 201 of Variation 4. The recovery system 201 includes a decompression device 46 that decompresses the internal space of the second gas separation device 12 instead of the pressurization device 42. In the recovery system 201, 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 recovery system 101 of FIG. 5. The recovery system 201 is a system that performs gas separation using a decompression method. Except for these, the recovery system 201 has basically the same configuration as the recovery system 200 of Variation 3 described above. In the example shown in FIG. 10, the decompression device 46 is provided in the concentrated gas discharge path 56. However, although not shown, the recovery system 201 may also include an air blower for sending the mixed gas Gm into the internal space of the second gas separation device 12. The recovery system 201 allows for the recycling of a third gas G3 having a low content of substance A with a simple configuration. This allows the recovery power of the entire recovery system 201 for the substance A to be reduced.

[0224] The pressure reducing device 46 is typically a vacuum pump 46. As shown in Fig. 10, the recovery system 201 may include a vacuum pump 46 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 46 as a seal gas for the vacuum pump 46. The recovery system 201 may further include a booster 44 provided in the second circulation path 73.

[0225] According to the above-described configuration, at least a portion of the concentrated gas Gc, which has a higher content of substance A than the mixed gas Gm, can be used as a seal gas for the vacuum pump 46. The concentrated gas Gc is supplied to the vacuum pump 46 via the second circulation path 73. Therefore, according to the above-described configuration, it is possible to improve the recovery rate of the substance A that is ultimately obtained while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0226] The vacuum pump 46 may be a vacuum pump that requires a seal gas, like the vacuum pump 45. The vacuum pump 46 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 46 can reduce the pressure in the permeation space (second chamber 124) of the second gas separation device 12. In other words, the vacuum pump 46 can generate or increase a pressure difference between the supply space (first chamber 123) and the permeation space (second chamber 124) of the second gas separation device 12. The vacuum pump 46 can be any of the pumps listed for the vacuum pump 45.

[0227] The vacuum pump 46 may be an assembly of multiple vacuum pumps. That is, the vacuum pump 46 may be configured so that each of the multiple vacuum pumps can reduce the pressure in the permeation space (second chamber 124) of the second gas separation device 12. With this configuration, the pressure in the permeation space of the second gas separation device 12 can be appropriately adjusted by adjusting the number of vacuum pumps in operation.

[0228] 10 , the vacuum pump 46 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 connects the permeate space outlet 124b of the second gas separation device 12 and the supply space inlet 113a of the first gas separation device 11.

[0229] 10 , the booster 44 is provided in the second circulation path 73. The booster 44 pressurizes the concentrated gas Gc as a seal gas to be supplied to the vacuum pump 46. By continuously operating the booster 44, the concentrated gas Gc can be obtained stably.

[0230] The pressure booster 44 is not particularly limited as long as it can pressurize the concentrated gas Gc as the seal gas supplied to the vacuum pump 46. The pressure booster 44 is typically a compressor.

[0231] The recovery system 201 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 recovery system 201 due to moisture can be suppressed.

[0232] A drain mechanism may be provided in the booster 44. As shown in Fig. 10, the moisture collected by the drain mechanism may be discharged to the outside through a drain path 76 connected to the booster 44.

[0233] 10 , in the recovery system 201, the concentrated gas discharge path 56 has a first portion 561, a second portion 562, a third portion 563, and a fourth portion 564. When the second gas separation device 12 has a second separation membrane 121, the first portion 561 connects the permeate space outlet 124b of the second gas separation device 12 to the inlet of the vacuum pump 46. The second portion 562 connects the outlet of the vacuum pump 46 to the branch position 94. The third portion 563 connects the branch position 94 to the junction position 81. The fourth portion 564 connects the junction position 81 to the supply space inlet 113a of the first gas separation device 11. In the recovery system 201, the second circulation path 73 branches off from the concentrated gas discharge path 56 at the branch position 94 and is connected to the seal gas inlet of the vacuum pump 46.

[0234] 10 , in the recovery system 201, the concentrated gas discharge path 56 corresponds to the first gas supply path 51. In the recovery system 201, the first gas separation device 11 is connected to the concentrated gas discharge path 56.

[0235] A switching valve (not shown) may be provided at the branch position 94. A flow rate control valve (not shown) may be provided in the second circulation path 73. With this configuration, the switching valve and each flow rate control valve can adjust the flow rate of the concentrated gas Gc introduced into the second circulation path 73 and the flow rate of the concentrated gas Gc (first gas G1) introduced into the first gas separation device 11.

[0236] In the recovery system 201, the third gas circulation path 61 satisfies at least one selected from the group consisting of (i) guiding the third gas G3 upstream of the second gas separation device 12, and (ii) guiding the third gas G3 downstream of the second gas separation device 12 and upstream of the first gas separation device 11. As shown in FIG. 10 , the third gas circulation path 61 may branch into a first portion 61A and a second portion 61B at a branching position 91. The first portion 61A may merge with the concentrated gas discharge path 56 (first gas supply path 51) at a merging position 81. The second portion 61B may merge with the mixed gas supply path 55 at a merging position 84. However, the merging position of the third gas circulation path 61 is not limited to the example shown in FIG. 10 . The first portion 61A may be connected to, for example, the supply space inlet 113a of the first gas separation device 11. The second portion 61B may be connected to the feed space inlet 123a of the second gas separation device 12, for example.

[0237] In the recovery system 201, the control device 40 may control the switching valve provided at the branch position 94 and the flow control valve provided in the second circulation path 73 to adjust the flow rate of the concentrated gas Gc supplied to the vacuum pump 46 and the flow rate of the concentrated gas Gc (first gas G1) supplied to the first gas separation device 11.

[0238] The recovery method using the recovery system 201 of Modification 4 includes a second gas separation step, a first gas separation step, a state change step, and a third gas circulation step, similar to the recovery method using the recovery system 200 of Modification 3. This allows the recovery power of the entire recovery system 201 for the substance A to be reduced.

[0239] In the recovery method of Modification 4, the second gas separation step is performed, for example, as follows. Each step will be described below using an example in which the second gas separation device 12 has the second separation membrane 121.

[0240] [Second Gas Separation Step] In the second gas separation step, first, the mixed gas Gm is supplied to the first chamber 123 (supply space) of the second gas separation device 12 through the mixed gas supply path 55 .

[0241] 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 space) is depressurized by the vacuum pump 46. Specifically, the vacuum pump 46 is used to depressurize the second chamber 124 through the permeation space outlet 124b.

[0242] By reducing the pressure inside the second chamber 124, a pressure difference is generated or increases between the supply space and the permeation 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 46.

[0243] 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 46. The vacuum pump 46 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.

[0244] The second gas separation step is followed by the first gas separation step.

[0245] The recovery method of Modification 4 may further include a second circulation step in which at least a portion of the second permeable gas S3 (concentrated gas Gc) is supplied to the vacuum pump 46 as a seal gas for the vacuum pump 46. According to the second circulation step, at least a portion of the concentrated gas Gc, which has a higher content of substance A than the mixed gas Gm, is used as a seal gas for the vacuum pump 46, so that it is possible to improve the recovery rate of the final substance A obtained while employing a vacuum pump that requires a seal gas with excellent pumping efficiency.

[0246] In the second circulation process, at least a portion of the concentrated gas Gc discharged from the vacuum pump 46 to the second portion 562 of the concentrated gas discharge path 56 is supplied to the vacuum pump 46 as a seal gas via the second circulation path 73.

[0247] The recovery method of variant 4 may further include a fourth gas circulation process, a first circulation process, a first gas supply process, and an exhaust gas circulation process, similar to the recovery method using the recovery system 101 of variant 1 described above.

[0248] (Variation 5) Figure 11 is a schematic diagram showing a recovery system 202 of Variation 5. In the recovery system 202, 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 recovery system 102 of Figure 6. Except for this, the recovery system 202 has the same configuration as the recovery system 201 of Variation 4 described above. The recovery system 202 is a system that performs gas separation using a reduced pressure method. The recovery system 202 has a simple configuration and can recycle the third gas G3, which has a low content of substance A. This allows the recovery power of substance A for the entire recovery system 202 to be reduced.

[0249] The recovery method using the recovery system 202 of Modification 5 includes the second gas separation step, the first gas separation step, the state change step, and the third gas circulation step, similar to the recovery method using the recovery system 201 of Modification 4. This makes it possible to reduce the recovery power of the substance A in the entire recovery system 202.

[0250] The recovery method of variant 5 may further include a fourth gas circulation process, a first circulation process, a first gas supply process, and an exhaust gas circulation process, similar to the recovery method using the recovery system 102 of variant 2 described above.

[0251] (Other Modifications) The above examples may be combined with each other as long as there is no technical contradiction.

[0252] The present invention will be explained in more detail below using calculation examples, but the present invention is not limited thereto.

[0253] [Recovery System 300] The recovery system 300 shown in Figure 12 is a system that performs gas separation using a pressurized method. The recovery system 300 does not include a third gas circulation path 61 that guides the third gas G3 discharged from the state change section 21 of the recovery device 20 to at least one selected from the group consisting of the upstream side of the first gas separation device 11 and the downstream side of the second gas separation device 12 and the upstream side of the first gas separation device 11. On the other hand, the recovery system 300 includes a third gas separation device 13 that separates the third gas G3 discharged from the state change section 21 to obtain a fifth gas G5 having a higher content of substance A than the third gas G3, and a fifth gas circulation path 65 that guides the fifth gas G5 discharged from the third gas separation device 13 downstream of the first gas separation device 11 and upstream of the state change section 21. Except for these features, the recovery system 300 had the same configuration as the recovery system 200 shown in Figure 7. Although omitted from Figure 12, the recovery system 300 was equipped with a combustion device 30 connected to the mixed gas supply path 55 and supplying exhaust gas as mixed gas Gm to the first-stage second gas separation device 12, and an exhaust gas circulation path 59 for sending at least a portion of the exhaust gas to the combustion device 30.

[0254] (Calculation Example 1) As Calculation Example 1, a simulation was performed when the recovery system 300 shown in FIG. 12 was operated. However, in Calculation Example 1, it was assumed that the third gas G3 discharged from the state change section 21 was released to the atmosphere. In other words, it was assumed that the fifth gas G5 was not circulated using the fifth gas circulation path 65. It was assumed that the state change section 21 was a liquefaction section that liquefied the substance A contained in the second gas G2 to obtain a liquid recovered material M. It was assumed that the recovered material M discharged from the state change section 21 was recovered in the tank 22. It was also assumed that a portion of the exhaust gas from the combustion device 30 was circulated to the combustion device 30 using the exhaust gas circulation path 59, and that a portion of the exhaust gas was released to the atmosphere.

[0255] In the recovery system 300, it was assumed that a carbon dioxide separation membrane with a CO permeation rate of 400 GPU and a separation factor α of 25 was used as the second separation membrane 121 provided in the first-stage second gas separation device 12. It was assumed that a carbon dioxide separation membrane with a CO permeation rate of 160 GPU and a separation factor α of 35 was used as the first separation membrane 111 provided in the second-stage first gas separation device 11.

[0256] It was assumed that the mixed gas Gm supplied to the first-stage second gas separation device 12 had a carbon dioxide content of 20 vol% as substance A, a nitrogen content of 56 vol% as substance B, an oxygen content of 4 vol%, and a water (HO) content of 20 vol%. It was also assumed that the weight of carbon dioxide in the mixed gas Gm was 414.2 kg / h and the temperature of the mixed gas Gm was 80°C.

[0257] It was assumed that the pumping efficiencies of the first-stage pressurizing device 42 and the second-stage pressurizing device 41 were both 70%. It was assumed that the supply side pressure of the first-stage second gas separation device 12 was 840 kPa, and the supply side pressure of the second-stage first gas separation device 11 was 670 kPa. In this specification, unless otherwise specified, "pressure" means absolute pressure. It was assumed that the permeation side pressure of the first-stage second gas separation device 12 and the permeation side pressure of the second-stage first gas separation device 11 were both 101.3 kPa. It was assumed that the gas supply temperatures to the second separation membrane 121 provided in the first-stage second gas separation device 12 and the first separation membrane 111 provided in the second-stage first gas separation device 11 were both 30°C.

[0258] For Calculation Example 1, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated when the following assumptions were met. The carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system is the sum of the power required to operate the entire recovery system per kg of carbon dioxide contained in the liquid carbon dioxide (liquefied carbon dioxide) obtained from the recovery device 20. The calculation was performed using AVEVA Process Simulation (APS), a process simulation software manufactured by AVEVA. <Assumptions> - The carbon dioxide content of the second gas G2 (first permeate gas S1) discharged from the second-stage first gas separation device 11 is 95 vol%. - The amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 is 2,590 tons per year.

[0259] (Calculation Example 2) As Calculation Example 2, a simulation was performed when the recovery system 200 shown in FIG. 7 was operated. Although omitted from FIG. 7, the recovery system 200 was equipped with a combustion device 30 connected to the mixed gas supply line 55 and supplying exhaust gas as the mixed gas Gm to the first-stage second gas separation device 12, and an exhaust gas circulation line 59 for sending at least a portion of the exhaust gas to the combustion device 30. However, in Calculation Example 2, it was assumed that the third gas G3 was not circulated using the first portion 61A of the third gas circulation line, but only the third gas G3 was circulated using the second portion 61B of the third gas circulation line and the fourth gas G4 was circulated using the fourth gas circulation line 54. Also, under assumed conditions, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 3,000 tons per year. For Calculation Example 2, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated under the same conditions as in Calculation Example 1, except for these.

[0260] (Calculation Example 3) As in Calculation Example 2, a simulation was performed when the recovery system 200 shown in FIG. 7 was operated. However, in Calculation Example 3, it was assumed that the third gas G3 was not circulated using the second portion 61B of the third gas circulation path, but only the third gas G3 was circulated using the first portion 61A of the third gas circulation path and the fourth gas G4 was circulated using the fourth gas circulation path 54. In addition, under assumed conditions, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 3,000 tons per year. For Calculation Example 3, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated under the same conditions as in Calculation Example 1, except for these.

[0261] (Calculation Example 4) As in Calculation Example 1, a simulation was performed when the recovery system 300 shown in FIG. 12 was operated. However, in Calculation Example 4, it was assumed that the fifth gas G5 was circulated using the fifth gas circulation path 65 and the fourth gas G4 was circulated using the fourth gas circulation path 54. In the recovery system 300, it was assumed that a carbon dioxide separation membrane with a CO2 permeation rate of 160 GPU and a separation coefficient α of 35 was used as the third separation membrane 131 provided in the third-stage third gas separation device 13. It was assumed that the supply side pressure of the third-stage third gas separation device 13 was 670 kPaA and the permeation side pressure was 101.3 kPaA. It was assumed that the gas supply temperature to the third separation membrane 131 provided in the third-stage third gas separation device 13 was 30 ° C. It was assumed that the carbon dioxide content of the fifth gas G5 discharged from the third-stage third gas separation device 13 was 95 vol%. In addition, under the assumed conditions, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was 2,910 tons / year. Other than this, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 4 under the same conditions as Calculation Example 1.

[0262] (Calculation Example 5) As in Calculation Example 3, a simulation was performed on the operation of the recovery system 200 shown in FIG. 7 . That is, in Calculation Example 5, the third gas G3 was not circulated using the second portion 61B of the third gas circulation path, and only the third gas G3 was circulated using the first portion 61A of the third gas circulation path and the fourth gas G4 was circulated using the fourth gas circulation path 54. However, under the assumed conditions, the carbon dioxide content of the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was set to 91 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 2,590 tons / year. For Calculation Example 5, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated under the same conditions as in Calculation Example 3, except for these.

[0263] (Calculation Example 6) As in Calculation Example 3, a simulation was performed in which the recovery system 200 shown in FIG. 7 was operated. However, under assumed conditions, the carbon dioxide content of the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was 92 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was 2,697 tons / year. Other than these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 6 under the same conditions as in Calculation Example 3.

[0264] (Calculation Example 7) As in Calculation Example 3, a simulation was performed for operation of the recovery system 200 shown in FIG. 7. However, under assumed conditions, the carbon dioxide content of the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was set to 93 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 2,800 tons / year. Other than these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 7 under the same conditions as in Calculation Example 3.

[0265] (Calculation Example 8) As in Calculation Example 3, a simulation was performed in which the recovery system 200 shown in FIG. 7 was operated. However, under assumed conditions, the carbon dioxide content of the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was 94 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was 2,901 tons / year. Other than these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 8 under the same conditions as in Calculation Example 3.

[0266] The simulation results for Calculation Examples 1 to 4 are shown in Table 1. The simulation results for Calculation Examples 5 to 8 are shown in Table 2. In Tables 1 and 2, the "CO2 capture rate" of each device refers to the ratio (wt%) of the weight (wt) of carbon dioxide contained in the concentrated gas discharged from the device to the weight (wt) of carbon dioxide contained in the feed gas supplied to the device. For example, the "CO2 capture rate" of a combustion device refers to the ratio (wt%) of the weight (wt) of carbon dioxide contained in the exhaust gas (mixed gas Gm) discharged from the combustion device to the weight (wt) of carbon dioxide contained in the fuel gas supplied to the combustion device. In Table 1, the "CO2 capture power" of each device refers to the power required to obtain a gas or substance with a high carbon dioxide content in the device. For example, the "CO2 capture power" of a capture device refers to the power (kWh) required to obtain a capture product M with a higher carbon dioxide content than the second gas G2 in the capture device. Exceptionally, the "CO2 capture power" of the combustion device means the power (kWh) required to circulate a portion of the exhaust gas from the combustion device 30 to the combustion device 30 using the exhaust gas circulation path 59. The same applies to Tables 3 and 4 described below.

[0267]

[0268]

[0269] As can be seen from a comparison of the simulation results of calculation examples 1 and 4 and calculation examples 2, 3, 5 to 8, when a recovery system equipped with a third gas circulation path 61 that guides the third gas G3 discharged from the recovery device 20 to the upstream side of the first gas separation device 11 was operated (calculation examples 2, 3, 5 to 8), the simple configuration made it possible to reduce the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system. Also, as can be seen from a comparison of the simulation results of calculation examples 2 and 3, 5 to 8, when the third gas G3 discharged from the recovery device 20 was circulated downstream of the first-stage second gas separation device 12 and upstream of the second-stage first gas separation device 11 (calculation examples 3, 5 to 8), the third gas G3 was circulated upstream of the first-stage second gas separation device 12 (calculation example 2), and the recovery power could be reduced more than when it was. Furthermore, from the simulation results of calculation examples 3, 5 to 8, it was found that when the carbon dioxide content in the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 is in the range of 90 to 95 vol%, the effect of reducing the recovery power is significant.

[0270] [Recovery System 301] The recovery system 301 shown in Figure 13 is a system that performs gas separation using a decompression method. The recovery system 301 does not include a third gas circulation path 61 that guides the third gas G3 discharged from the state change section 21 of the recovery device 20 to at least one selected from the group consisting of the upstream side of the first gas separation device 11 and the downstream side of the second gas separation device 12 and the upstream side of the first gas separation device 11. On the other hand, the recovery system 301 includes a third gas separation device 13 that separates the third gas G3 discharged from the state change section 21 to obtain a fifth gas G5 having a higher content of substance A than the third gas G3, and a fifth gas circulation path 65 that guides the fifth gas G5 discharged from the third gas separation device 13 downstream of the first gas separation device 11 and upstream of the state change section 21. Except for these features, the recovery system 301 had the same configuration as the recovery system 201 shown in Figure 10. 13 , the recovery system 301 was equipped with a combustion device 30 that was connected to the mixed gas supply line 55 and supplied exhaust gas as mixed gas Gm to the first-stage second gas separation device 12. However, the recovery system 301 did not have an exhaust gas circulation line 59 for sending at least a portion of the exhaust gas to the combustion device 30.

[0271] (Calculation Example 9) As Calculation Example 9, a simulation was performed when the recovery system 301 shown in FIG. 13 was operated. However, in Calculation Example 9, it was assumed that the third gas G3 discharged from the state change section 21 was released to the atmosphere. In other words, it was assumed that the fifth gas G5 was not circulated using the fifth gas circulation path 65. It was assumed that the state change section 21 was a liquefaction section that liquefied the substance A contained in the second gas G2 to obtain a liquid recovered material M. It was assumed that the recovered material M discharged from the state change section 21 was recovered in the tank 22. It was also assumed that a portion of the exhaust gas from the combustion device 30 was released to the atmosphere.

[0272] In the recovery system 301, it was assumed that a carbon dioxide separation membrane with a CO permeation rate of 400 GPU and a separation factor α of 25 was used as the second separation membrane 121 provided in the first-stage second gas separation device 12. It was assumed that a carbon dioxide separation membrane with a CO permeation rate of 160 GPU and a separation factor α of 35 was used as the first separation membrane 111 provided in the second-stage first gas separation device 11.

[0273] It was assumed that the mixed gas Gm supplied to the first-stage second gas separation device 12 had a carbon dioxide content of 8 vol% as substance A, a nitrogen content of 70 vol% as substance B, an oxygen content of 5 vol%, and a water (HO) content of 17 vol%. It was assumed that the weight of carbon dioxide in the mixed gas Gm was 414.2 kg / h and the temperature of the mixed gas Gm was 80°C.

[0274] It was assumed that the pump efficiency of the first-stage vacuum pump 46 and the second-stage vacuum pump 45 was 40%, and the blower efficiency was 70%. It was assumed that the supply side pressure of the first-stage second gas separation device 12 and the supply side pressure of the second-stage first gas separation device 11 were both 115 kPaA. It was assumed that the permeation side pressure of the first-stage second gas separation device 12 was 3 kPaA, and the permeation side pressure of the second-stage first gas separation device 11 was 20 kPaA. It was assumed that the gas supply temperatures to the second separation membrane 121 provided in the first-stage second gas separation device 12 and the first separation membrane 111 provided in the second-stage first gas separation device 11 were both 30°C.

[0275] For Calculation Example 9, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated when the following assumed conditions were met. The calculation was performed using AVEVA Process Simulation (APS), a process simulation software manufactured by AVEVA. <Assumed conditions> - The carbon dioxide content of the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 is 95 vol%. - The amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 is 2,590 tons per year.

[0276] (Calculation Example 10) As Calculation Example 10, a simulation was performed when the recovery system 201 shown in FIG. 10 was operated. Although omitted from FIG. 10, the recovery system 201 was equipped with a combustion device 30 connected to the mixed gas supply line 55 and supplying exhaust gas as the mixed gas Gm to the first-stage second gas separation device 12. However, the recovery system 201 did not include an exhaust gas circulation line 59 for sending at least a portion of the exhaust gas to the combustion device 30. Furthermore, in Calculation Example 10, it was assumed that the third gas G3 was not circulated using the first portion 61A of the third gas circulation line, but only the third gas G3 was circulated using the second portion 61B of the third gas circulation line and the fourth gas G4 was circulated using the fourth gas circulation line 54. Furthermore, under assumed conditions, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was 3,000 tons per year. Other than these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 10 under the same conditions as Calculation Example 9.

[0277] (Calculation Example 11) As in Calculation Example 10, a simulation was performed on the operation of the recovery system 201 shown in FIG. 10. However, in Calculation Example 11, it was assumed that the third gas G3 was not circulated using the second portion 61B of the third gas circulation path, but only the third gas G3 was circulated using the first portion 61A of the third gas circulation path and the fourth gas G4 was circulated using the fourth gas circulation path 54. In addition, under assumed conditions, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 3,000 tons per year. For Calculation Example 11, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated under the same conditions as in Calculation Example 9, except for these.

[0278] (Calculation Example 12) As in Calculation Example 9, a simulation was performed when the recovery system 301 shown in FIG. 13 was operated. However, in Calculation Example 12, it was assumed that the fifth gas G5 was circulated using the fifth gas circulation path 65 and the fourth gas G4 was circulated using the fourth gas circulation path 54. In the recovery system 301, it was assumed that a carbon dioxide separation membrane with a CO2 permeation rate of 160 GPU and a separation coefficient α of 35 was used as the third separation membrane 131 provided in the third-stage third gas separation device 13. It was assumed that the supply side pressure of the third-stage third gas separation device 13 was 670 kPaA and the permeation side pressure was 101.3 kPaA. It was assumed that the gas supply temperature to the third separation membrane 131 provided in the third-stage third gas separation device 13 was 30 ° C. It was assumed that the carbon dioxide content of the fifth gas G5 discharged from the third-stage third gas separation device 13 was 95 vol%. In addition, under the assumed conditions, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was 2,910 tons / year. Other than this, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 12 under the same conditions as in Calculation Example 9.

[0279] (Calculation Example 13) As in Calculation Example 11, a simulation was performed on the operation of the recovery system 201 shown in FIG. 10. That is, in Calculation Example 13, the third gas G3 was not circulated using the second portion 61B of the third gas circulation path, and only the third gas G3 was circulated using the first portion 61A of the third gas circulation path and the fourth gas G4 was circulated using the fourth gas circulation path 54. However, under the assumed conditions, the carbon dioxide content of the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was set to 85 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 1,922 tons / year. For Calculation Example 13, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated under the same conditions as in Calculation Example 11, except for these.

[0280] Calculation Example 14 As in Calculation Example 11, a simulation was performed when the recovery system 201 shown in FIG. 10 was operated. However, under assumed conditions, the carbon dioxide content in the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was set to 90 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 2,494 tons / year. Other than these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 14 under the same conditions as in Calculation Example 11.

[0281] Calculation Example 15: As in Calculation Example 11, a simulation was performed for operation of the recovery system 201 shown in FIG. 10 . However, under assumed conditions, the carbon dioxide content of the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was set to 91 vol %. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 2,600 tons / year. Except for these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 15 under the same conditions as in Calculation Example 11.

[0282] (Calculation Example 16) As Calculation Example 16, a simulation was performed when the recovery system 201 shown in FIG. 10 was operated, similar to Calculation Example 11. However, under assumed conditions, the carbon dioxide content in the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was set to 92 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 2,705 tons / year. Other than these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 16 under the same conditions as Calculation Example 11.

[0283] Calculation Example 17 As in Calculation Example 11, a simulation was performed when the recovery system 201 shown in FIG. 10 was operated. However, under assumed conditions, the carbon dioxide content in the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 was set to 93 vol%. In addition, the amount of liquid carbon dioxide (liquefied carbon dioxide) produced by the recovery device 20 was set to 2,806 tons / year. Other than these, the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system was calculated for Calculation Example 17 under the same conditions as in Calculation Example 11.

[0284] The simulation results of calculation examples 9 to 12 are shown in Table 3. The simulation results of calculation examples 13 to 17 are shown in Table 4.

[0285]

[0286]

[0287] As can be seen from the comparison of the simulation results of calculation examples 9 and 12 with calculation examples 10, 11, 13 to 17, when a recovery system equipped with a third gas circulation path 61 that guides the third gas G3 discharged from the recovery device 20 to the upstream side of the first gas separation device 11 was operated (calculation examples 10, 11, 13 to 17), the simple configuration made it possible to reduce the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system. Also, as can be seen from the comparison of the simulation results of calculation examples 10 and 11, 13 to 17, when the third gas G3 discharged from the recovery device 20 was circulated downstream of the first-stage second gas separation device 12 and upstream of the second-stage first gas separation device 11 (calculation examples 11, 13 to 17), the third gas G3 was circulated upstream of the first-stage second gas separation device 12 (calculation example 10), and the recovery power could be reduced more than when it was circulated. Furthermore, from the simulation results of calculation examples 11, 13 to 17, it was found that when the carbon dioxide content in the second gas G2 (first permeable gas S1) discharged from the second-stage first gas separation device 11 is in the range of 90 to 95 vol%, the effect of reducing the recovery power is significant.

[0288] As can be seen from a comparison of the simulation results of Calculation Examples 2, 3, 5 to 8 in Tables 1 and 2 and Calculation Examples 10, 11, 13 to 17 in Tables 3 and 4, performing gas separation in a gas separation device using a pressurized method rather than a reduced pressure method enabled a reduction in the carbon dioxide recovery power (kWh / kg-CO2) of the entire recovery system with a smaller membrane area.

[0289] The capture system and capture method of this embodiment are suitable for separating a mixed gas, for example, a mixed gas containing carbon dioxide and nitrogen. In particular, the capture system and capture method of this embodiment are suitable for efficiently capturing carbon dioxide from exhaust gas emitted from a combustion device such as a factory or a power plant.

Claims

1. A recovery system comprising: a first gas separation device that separates a first gas containing a gaseous substance A and a gaseous substance B different from said gaseous substance A to obtain a second gas having a higher content of said substance A than said first gas; a recovery device that changes the state of said substance A contained in said second gas and recovers it; and a third gas circulation path that guides a third gas discharged from said recovery device to the upstream side of said first gas separation device.

2. The recovery system according to claim 1, wherein the recovery device includes a liquefaction section that liquefies the substance A contained in the second gas.

3. A 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 substance A than the second gas to the upstream side of the first gas separation device.

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

5. The recovery system described in claim 1, further comprising a second gas separation device that separates a mixed gas containing gaseous substance A and gaseous substance B to obtain a concentrated gas having a higher content of substance 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.

6. The recovery system described in claim 5, wherein the third gas circulation path satisfies at least one selected from the group consisting of (i) guiding the third gas to the upstream side of the second gas separation device, and (ii) guiding the third gas to the downstream side of the second gas separation device and the upstream side of the first gas separation device.

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

8. The recovery system according to claim 1, further comprising a pressurizing device for pressurizing the internal space of the first gas separation device.

9. The recovery system according to claim 1, further comprising a pressure reducing device for reducing the pressure in the internal space of the first gas separation device.

10. A recovery system as described in claim 9, further comprising: a first circulation path that introduces at least a portion of the second gas into the vacuum pump as a seal gas for the vacuum pump; a booster provided in the first circulation path; and a branch path that branches off from the first circulation path downstream of the booster, wherein the recovery system is connected to the branch path.

11. The recovery system of claim 1, wherein the first gas contains carbon dioxide as the substance A and nitrogen as the substance B.

12. The recovery system according to claim 1, wherein the content of substance A in the second gas is 80 vol % or more.

13. The recovery system according to claim 1, further comprising a combustion device to which a fuel gas containing oxygen is supplied and which discharges an exhaust gas containing the gaseous substance A and the gaseous substance B, the exhaust gas being the first gas.

14. The recovery system according to claim 13, wherein the content of substance A in the exhaust gas is 20 vol % or more.

15. A recovery method comprising: a first gas separation step of separating a first gas containing gaseous substance A and gaseous substance B different from said gaseous substance A in a first gas separation device to obtain a second gas having a higher content of said substance A than said first gas; a recovery step of recovering said substance A contained in said second gas by changing its state in a recovery device and discharging a third gas from said recovery device; and a third gas circulation step of sending said third gas to the upstream side of said first gas separation device.

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