Gas separation system, and mixed gas separation method

Abstract

This gas separation system comprises: a first separation membrane unit that accommodates a first separation membrane for separating a mixed gas into a first permeated gas and a first non-permeated gas; and a second separation membrane unit that accommodates a second separation membrane for separating the first permeated gas into a second permeated gas and a second non-permeated gas. The mixed gas includes a first gas and a second gas different from the first gas. The first separation membrane and the second separation membrane are capable of preferentially permeating the second gas. Control is performed so that, when the temperature of the mixed gas supplied to the first separation membrane unit during operation is defined as T1 and the temperature of the first permeated gas supplied to the second separation membrane unit is defined as T2, the temperature T1 and the temperature T2 satisfy T1≥T2.

Description

Gas separation system and method for separating mixed gases

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

[0002] Factories and power plants, for example, emit mixed gases containing carbon dioxide and nitrogen from combustion equipment. From the perspective of environmental regulations, it is desirable to separate and recover each component from the mixed gas.

[0003] Membrane separation is a method developed to separate individual components from a gas mixture. Compared to absorption methods, which separate specific components from a gas mixture by absorbing them with an absorbent, membrane separation allows for efficient separation of individual components while keeping operating costs down.

[0004] In membrane separation methods, gas separation systems combining multiple separation membrane units are sometimes used. For example, Patent Document 1 discloses a two-stage separation membrane system using two-stage reduced-pressure separation membrane units (Figure 7 of Patent Document 1). In the first-stage separation membrane unit, CO2, SO2, and NO are separated from the boiler exhaust gas. x The first stage is removed, and then CO2 / SO2 is separated in the second stage separation membrane unit.

[0005] Special Publication No. 2020-501884

[0006] The two-stage separation membrane system described in Patent Document 1 employs a reduced-pressure separation membrane unit arranged in two stages to separate boiler exhaust gas. According to the system configuration of Patent Document 1, the recovery power required to separate the exhaust gas can be reduced. However, with the system configuration of Patent Document 1, the required total membrane area increases, making it difficult to achieve a compact overall system.

[0007] The present invention aims to provide a novel gas separation system and a method for separating mixed gases that are suitable for achieving both a reduction in recovery power and a reduction in membrane area.

[0008] The inventors investigated whether it was possible to reduce the required membrane area while simultaneously reducing the recovery power in a two-stage gas separation system combining two separation membrane units. As a result, they newly discovered that it is possible to achieve both a reduction in recovery power and a reduction in membrane area by controlling the temperature of the gas supplied to the two separation membrane units. Based on this finding, the inventors furthered their research and completed the present invention.

[0009] In one aspect, the present invention provides a gas separation system comprising: a first separation membrane unit containing a first separation membrane for separating a mixed gas into a first permeate gas and a first non-permeate gas; and a second separation membrane unit containing a second separation membrane for separating the first permeate gas into a second permeate gas and a second non-permeate gas, wherein the mixed gas includes a first gas and a second gas different from the first gas; the first and second separation membranes are capable of preferentially permeating the second gas; and when the temperature of the mixed gas supplied to the first separation membrane unit during operation is defined as T1 and the temperature of the first permeate gas supplied to the second separation membrane unit is defined as T2, the temperatures T1 and T2 are controlled to satisfy T1 ≥ T2.

[0010] From another aspect, the present invention provides a method for separating a mixed gas, comprising: a first separation step of supplying a mixed gas to a first separation membrane unit containing a first separation membrane to separate the mixed gas into a first permeate gas and a first non-permeate gas; a second separation step of supplying the first permeate gas to a second separation membrane unit containing a second separation membrane to separate the first permeate gas into a second permeate gas and a second non-permeate gas; and a temperature control step of controlling temperatures T1 and T2 such that T1 ≥ T2, where T1 is defined as the temperature of the mixed gas supplied to the first separation membrane unit in the first separation step and T2 is defined as the temperature of the first permeate gas supplied to the second separation membrane unit in the second separation step, wherein the mixed gas comprises a first gas and a second gas different from the first gas, and the first and second separation membranes are capable of preferentially permeating the second gas.

[0011] According to the present invention, it is possible to provide a new gas separation system and a method for separating mixed gases that are suitable for achieving both a reduction in recovery power and a reduction in membrane area.

[0012] This is a schematic configuration diagram showing an example of a gas separation system according to one embodiment of the present invention. This is a diagram showing modification 1 of part II of Figure 1. This is a diagram showing modification 2 of part II of Figure 1. This is a diagram showing modification 3 of part II of Figure 1. This is a diagram showing modification 4 of part II of Figure 1. This is an enlarged view showing modification 1 of part III of Figure 1. This is an enlarged view showing modification 2 of part III of Figure 1. This is a schematic cross-sectional view showing an example of a separation membrane unit. This is a schematic cross-sectional view showing an example of a separation membrane. This is a schematic perspective view showing a spiral-type membrane element. This is a schematic configuration diagram showing modification 1 of the gas separation system. This is a schematic configuration diagram showing modification 2 of the gas separation system. This is a graph showing the relationship between the moisture content of the mixed gas in calculation example 6 and the moisture content of the mixed gas discharged from the dehumidification section and the recovery power in calculation examples 26 to 31.

[0013] A gas separation system according to a first aspect of the present invention comprises: a first separation membrane unit containing a first separation membrane for separating a mixed gas into a first permeate gas and a first impermeable gas; and a second separation membrane unit containing a second separation membrane for separating the first permeate gas into a second permeate gas and a second impermeable gas, wherein the mixed gas includes a first gas and a second gas different from the first gas; the first and second separation membranes are capable of preferentially permeating the second gas; and when the temperature of the mixed gas supplied to the first separation membrane unit during operation is defined as T1 and the temperature of the first permeate gas supplied to the second separation membrane unit is defined as T2, the temperatures T1 and T2 are controlled to satisfy T1 ≥ T2.

[0014] In a second embodiment of the present invention, for example, in the gas separation system according to the first embodiment, the first separation membrane and the second separation membrane have the same configuration.

[0015] In a third aspect of the present invention, for example, a gas separation system according to the first or second aspect further comprises a depressurization unit for reducing the pressure of the permeate space of the first separation membrane unit and a pressurization unit for increasing the pressure of the supply space of the second separation membrane unit.

[0016] In a fourth aspect of the present invention, for example, a gas separation system according to any one of the first to third aspects further comprises a first heat exchange unit for adjusting the temperature of the mixed gas supplied to the first separation membrane unit, and a second heat exchange unit for adjusting the temperature of the first permeate gas supplied to the second separation membrane unit.

[0017] In a fifth aspect of the present invention, for example, the gas separation system according to the fourth aspect further comprises a first temperature sensor for measuring the temperature T1 and a second temperature sensor for measuring the temperature T2, and the first heat exchange unit and the second heat exchange unit are controlled so that the temperatures T1 and T2 satisfy T1 ≥ T2 based on the monitoring results from the first temperature sensor and the second temperature sensor.

[0018] In a sixth aspect of the present invention, for example, in a gas separation system according to any one of the first to fifth aspects, the content of the second gas in the mixed gas is 30 vol% or less.

[0019] In a seventh aspect of the present invention, for example, in a gas separation system according to any one of the first to sixth aspects, the mixed gas contains nitrogen as the first gas and carbon dioxide as the second gas.

[0020] In the eighth aspect of the present invention, for example, the gas separation system according to any one of the first to seventh aspects is a continuous system.

[0021] In a ninth aspect of the present invention, for example, a gas separation system according to any one of the third to eighth aspects further comprises a first permeate gas path that guides the first permeate gas discharged from the first separation membrane unit to the second separation membrane unit, wherein the depressurization unit and the pressurization unit are arranged in the first permeate gas path.

[0022] In a tenth embodiment of the present invention, for example, a gas separation system according to any one of the first to ninth embodiments further comprises a mixed gas path that guides the mixed gas to the first separation membrane unit, and a second impermeable gas path that guides the second impermeable gas discharged from the second separation membrane unit to the first separation membrane unit, wherein the second impermeable gas path merges with the mixed gas path.

[0023] In an eleventh aspect of the present invention, for example, a gas separation system according to any one of the first to tenth aspects further comprises a dehumidifier for reducing the moisture content in the mixed gas supplied to the first separation membrane unit.

[0024] In a twelfth aspect of the present invention, for example, in the gas separation system according to the eleventh aspect, when the moisture content in the mixed gas discharged from the dehumidifier during operation is defined as C1, the dehumidifier is controlled so that the moisture content C1 is 5 vol% or less.

[0025] In a thirteenth aspect of the present invention, for example, in the gas separation system according to the twelfth aspect, the dehumidification unit is controlled so that the moisture content C1 is 1 vol% or less.

[0026] In a fourteenth aspect of the present invention, the gas separation system according to the twelfth or thirteenth aspect further comprises a moisture sensor, wherein when the moisture content in the mixed gas supplied to the dehumidifier during operation is defined as C0, the moisture sensor measures at least one selected from the group consisting of the moisture content C0 and the moisture content C1, and the dehumidifier is controlled based on the monitoring results from the moisture sensor.

[0027] In a 15th aspect of the present invention, for example, in a gas separation system according to any one of the 11th to 14th aspects, the dehumidification unit includes at least one selected from the group consisting of a condenser, a vacuum device, a desiccant-equipped dehumidifier, an electrodialysis device equipped with an ion exchange membrane, and a separation membrane device equipped with a water vapor separation membrane.

[0028] A sixteenth aspect of the present invention provides a method for separating a mixed gas, comprising: a first separation step of supplying the mixed gas to a first separation membrane unit containing a first separation membrane to separate the mixed gas into a first permeate gas and a first non-permeate gas; a second separation step of supplying the first permeate gas to a second separation membrane unit containing a second separation membrane to separate the first permeate gas into a second permeate gas and a second non-permeate gas; and a temperature control step of controlling the temperature T1 and the temperature T2 so that T1 ≥ T2, where T1 is defined as the temperature of the mixed gas supplied to the first separation membrane unit in the first separation step, and T2 is defined as the temperature of the first permeate gas supplied to the second separation membrane unit in the second separation step, wherein the mixed gas comprises a first gas and a second gas different from the first gas, and the first separation membrane and the second separation membrane can preferentially permeate the second gas.

[0029] In a 17th aspect of the present invention, for example, the method for separating a mixed gas according to the 16th aspect further includes a dehumidification step of reducing the moisture content in the mixed gas supplied to the first separation membrane unit.

[0030] A gas separation system according to an 18th aspect of the present invention comprises: a first separation membrane unit housing a first separation membrane for separating a mixed gas into a first permeable gas and a first impermeable gas; and a dehumidification unit for reducing the moisture content in the mixed gas supplied to the first separation membrane unit, wherein the mixed gas includes a first gas and a second gas different from the first gas, and the first separation membrane is capable of preferentially permeating the second gas.

[0031] In a 19th aspect of the present invention, for example, in a gas separation system according to the 18th aspect, when the moisture content in the mixed gas discharged from the dehumidifier during operation is defined as C1, the dehumidifier is controlled so that the moisture content C1 is 5 vol% or less.

[0032] In a 20th aspect of the present invention, for example, in the gas separation system according to the 19th aspect, the dehumidification unit is controlled so that the moisture content C1 is 1 vol% or less.

[0033] In a 21st aspect of the present invention, the gas separation system according to the 19th or 20th aspect further comprises a moisture sensor, wherein when the moisture content in the mixed gas supplied to the dehumidifier during operation is defined as C0, the moisture sensor measures at least one selected from the group consisting of the moisture content C0 and the moisture content C1, and the dehumidifier is controlled based on the monitoring results from the moisture sensor.

[0034] In a 22nd aspect of the present invention, for example, in a gas separation system according to any one of the 18th to 21st aspects, the dehumidification unit includes at least one selected from the group consisting of a condenser, a vacuum device, a desiccant-equipped dehumidifier, an electrodialysis device equipped with an ion exchange membrane, and a separation membrane device equipped with a water vapor separation membrane.

[0035] A method for separating a mixed gas according to a 23rd aspect of the present invention includes: a first separation step of supplying a mixed gas to a first separation membrane unit containing a first separation membrane to separate the mixed gas into a first permeable gas and a first non-permeable gas; and a dehumidification step of reducing the moisture content in the mixed gas supplied to the first separation membrane unit, wherein the mixed gas includes a first gas and a second gas different from the first gas, and the first separation membrane is capable of preferentially permeating the second gas.

[0036] The details of the present invention will be described below, but the following description is not intended to limit the present invention to any particular embodiment.

[0037] <Embodiment of the Gas Separation System> Figure 1 is a schematic diagram showing an example of a gas separation system according to this embodiment. The gas separation system 100A in Figure 1 comprises a first separation membrane unit 10 and a second separation membrane unit 20. The first separation membrane unit 10 houses a first separation membrane 11 and uses the first separation membrane 11 to separate the mixed gas G0 into a first permeate gas G1 and a first impermeable gas G2. The second separation membrane unit 20 houses a second separation membrane 21 and uses the second separation membrane 21 to separate the first permeate gas G1 discharged from the first separation membrane unit 10 into a second permeate gas G3 and a second impermeable gas G4.

[0038] The mixed gas G0 processed in the first separation membrane unit 10 contains a first gas and a second gas different from the first gas. Examples of the first gas and the second gas include nitrogen, carbon dioxide, and the like. For example, the mixed gas G0 may contain nitrogen as the first gas and carbon dioxide as the second gas.

[0039] The mixed gas G0 may contain moisture (H₂O). The mixed gas G0 may be a gas in a moisture-saturated state.

[0040] In the present embodiment, both the first separation membrane 11 and the second separation membrane 21 can preferentially permeate the second gas. Therefore, the first permeated gas G1 separated by the first separation membrane 11 has a higher content of the second gas and a lower content of the first gas than the mixed gas G0. The first non-permeated gas G2 has a lower content of the second gas and a higher content of the first gas than the mixed gas G0. The second permeated gas G3 separated by the second separation membrane 21 has a higher content of the second gas and a lower content of the first gas than the first permeated gas G1. The second non-permeated gas G4 has a lower content of the second gas and a higher content of the first gas than the first permeated gas G1.

[0041] The temperature of the mixed gas G0 supplied to the first separation membrane unit 10 during operation is defined as T1. The temperature of the first permeated gas G1 supplied to the second separation membrane unit 20 during operation is defined as T2. At this time, in the gas separation system 100A, the temperature T1 and the temperature T2 are controlled to satisfy T1 ≧ T2.

[0042] The present inventors studied whether the required membrane area can be reduced while reducing recovery power in a two-stage gas separation system combining two separation membrane units. As a result, the inventors newly found that by controlling the temperature T1 and the temperature T2 to satisfy T1 ≧ T2 during operation, both reduction of recovery power and reduction of membrane area can be achieved at the same time. According to the gas separation system 100A, both reduction of recovery power and reduction of membrane area are achieved.

[0043] As long as T1 ≥ T2 is satisfied, the temperature T1 of the mixed gas G0 supplied to the first separation membrane unit 10 and the temperature T2 of the first permeate gas G1 supplied to the second separation membrane unit 20 are not particularly limited. Temperatures T1 and T2 are, for example, in the range of 15°C to 40°C.

[0044] The difference between temperature T1 and temperature T2 is, for example, 0°C or more and 20°C or less. The lower limit of the difference between temperature T1 and temperature T2 may be 1°C, 3°C, or even 5°C. The upper limit of the difference between temperature T1 and temperature T2 may be 15°C, or even 10°C.

[0045] The first separation membrane 11 and the second separation membrane 21 may have the same configuration. In the gas separation system 100A, even if the first separation membrane 11 and the second separation membrane 21 have the same configuration, the reduction of recovery power and the reduction of membrane area can be achieved simultaneously by controlling the temperatures T1 and T2 so that T1 ≥ T2. In this specification, "the two separation membranes have the same configuration" means that the two separation membranes have the same characteristics that are not affected by operating conditions, such as material, shape, and thickness.

[0046] The gas separation system 100A further comprises a depressurization section 31 and a pressurization section 41.

[0047] The pressure reduction unit 31 reduces the pressure in the permeate space of the first separation membrane unit 10. In other words, the pressure reduction unit 31 creates a differential pressure between the supply space and the permeate space of the first separation membrane unit 10. A specific example of the pressure reduction unit 31 is a pump. Preferably, the pressure reduction unit 31 is a vacuum device such as a vacuum pump. A vacuum pump is typically a gas transport type vacuum pump, and examples include reciprocating vacuum pumps or rotary vacuum pumps. Examples of reciprocating vacuum pumps include diaphragm type or oscillating piston type vacuum pumps. Examples of rotary vacuum pumps include liquid-sealed 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. The pump as the pressure reduction unit 31 may be equipped with a variable speed mechanism for changing the rotation speed, etc. An example of a variable speed mechanism is an inverter that drives the motor of the pump. By controlling the rotation speed of the pump with the variable speed mechanism, the pressure in the permeate space of the first separation membrane unit 10 can be appropriately adjusted.

[0048] The pressure reduction section 31 may be an assembly of multiple pumps. That is, the pressure reduction section 31 may be configured so that each of the multiple pumps can reduce the pressure in the permeate space of the first separation membrane unit 10. With this configuration, the pressure in the permeate space of the first separation membrane unit 10 can be appropriately adjusted by adjusting the number of operating pumps.

[0049] The pressurizing unit 41 increases the pressure in the supply space of the second separation membrane unit 20. In other words, the pressurizing unit 41 creates a differential pressure between the supply space and the permeate space of the second separation membrane unit 20. Specific examples of the pressurizing unit 41 are a compressor and a pump. The pressurizing unit 40 may be a compressor that sends high-pressure first permeate gas G1, which is obtained by compressing the first permeate gas G1, toward the supply space of the second separation membrane unit 20, or it may be a pump that pumps the first permeate gas G1 toward the supply space of the second separation membrane unit 20. The pump is typically a gas transport type pressurizing pump, and examples include a reciprocating pressurizing pump or a rotary pressurizing pump. Examples of reciprocating pressurizing pumps include diaphragm pumps and oscillating piston pumps. Examples of rotary pumps include liquid-sealed 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. The pump, which serves as the pressurizing unit 41, may be equipped with a variable speed mechanism for changing the rotational speed, etc. An example of a variable speed mechanism is an inverter that drives the pump's motor. By controlling the rotational speed, etc., of the pump with the variable speed mechanism, the pressure in the supply space of the second separation membrane unit 20 can be appropriately adjusted.

[0050] The pressurizing section 41 may be an assembly of multiple pumps. That is, the pressurizing section 41 may be configured so that each of the multiple pumps can increase the pressure in the supply space of the second separation membrane unit 20. With this configuration, the pressure in the supply space of the second separation membrane unit 20 can be appropriately adjusted by adjusting the number of operating pumps.

[0051] For example, when the supplied mixed gas contains nitrogen and carbon dioxide, the separation power of the separation membrane unit tends to increase as the carbon dioxide content in the mixed gas decreases. According to our studies, when comparing an operating method that generates a differential pressure by reducing the pressure from the permeate space of the separation membrane unit (reduced pressure method) with an operating method that generates a differential pressure by increasing the pressure from the supply space of the separation membrane unit (pressurized method), the difference in required separation power tends to be larger as the carbon dioxide content in the supplied mixed gas decreases. Therefore, if the reduced pressure method is adopted for a separation membrane unit to process a mixed gas with a low carbon dioxide content (e.g., 10 vol% or less), the recovery power can be reduced. On the other hand, the reduced pressure method tends to require a larger membrane area compared to the pressurized method, and this tendency is more pronounced as the carbon dioxide content in the mixed gas decreases. Therefore, by adopting the reduced pressure method for the first stage separation membrane unit and the pressurized method for the second stage separation membrane unit of a two-stage gas separation system combining two separation membrane units, it is possible to achieve both a reduction in recovery power and a reduction in membrane area.

[0052] During operation, the pressure in the permeate space of the first separation membrane unit 10 is, for example, 70 kPa or less, preferably 50 kPa or less, more preferably 30 kPa or less, even more preferably 10 kPa or less, and particularly preferably 5 kPa or less. The upper limit of the pressure in the permeate space of the first separation membrane unit 10 may be 1 kPa, 2 kPa, or even 3 kPa. In this specification, unless otherwise specified, "pressure" means absolute pressure.

[0053] During operation, the pressure in the supply space of the second separation membrane unit 20 is, for example, 101 kPa or more, preferably 150 kPa or more, more preferably 200 kPa or more, even more preferably 300 kPa or more, and particularly preferably 400 kPa or more. The upper limit of the pressure in the supply space of the second separation membrane unit 20 may be 1500 kPa, 1300 kPa, 1100 kPa, 1000 kPa, and even 900 kPa.

[0054] The gas separation system 100A may further include a blower 45. The blower 45 sends the mixed gas G0 toward the supply space of the first separation membrane unit 10. The blower 45 allows the mixed gas G0 to be efficiently moved toward the supply space of the first separation membrane unit 10.

[0055] The airflow pressure of the blower 45 during operation is 101 kPa or higher, preferably 120 kPa or higher. The upper limit of the airflow pressure of the blower 45 is, for example, 150 kPa.

[0056] The gas separation system 100A further comprises a first heat exchange section 51 and a second heat exchange section 52.

[0057] The first heat exchange unit 51 adjusts the temperature T1 of the mixed gas G0 supplied to the first separation membrane unit 10. The first heat exchange unit 51 heats or cools the mixed gas G0 to a range of, for example, 20°C to 35°C.

[0058] The second heat exchange unit 52 adjusts the temperature T2 of the first permeate gas G1 supplied to the second separation membrane unit 20. The second heat exchange unit 52 heats or cools the first permeate gas G1 to a range of, for example, 15°C to 35°C.

[0059] The first heat exchange section 51 and the second heat exchange section 52 may be gas-liquid heat exchangers that generate heat exchange between a cooling medium such as antifreeze and a mixed gas G0 or a first permeate gas G1. A gas-liquid heat exchanger is typically a finned tube heat exchanger.

[0060] The gas separation system 100A further includes a first temperature sensor 51a and a second temperature sensor 52a. The first temperature sensor 51a measures the temperature T1 of the mixed gas G0 supplied to the first separation membrane unit 10. The second temperature sensor 52a measures the temperature T2 of the first permeate gas G1 supplied to the second separation membrane unit 20.

[0061] In the gas separation system 100A, the first heat exchange unit 51 and the second heat exchange unit 52 may be controlled based on the monitoring results from the first temperature sensor 51a and the second temperature sensor 52a so that temperatures T1 and T2 satisfy T1 ≥ T2. With such a configuration, it is easy to achieve both a reduction in recovery power and a reduction in membrane area.

[0062] The gas separation system 100A may further include a dehumidification unit 90. In this specification, "dehumidification" means reducing the moisture (H2O) content in the mixed gas G0, and does not necessarily mean completely removing the moisture contained in the mixed gas G0.

[0063] The dehumidification unit 90 reduces the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10. In this embodiment, the dehumidification unit 90 is positioned between the source of the mixed gas G0 (not shown) and the first separation membrane unit 10, and reduces the moisture content in the mixed gas G0 discharged from the source.

[0064] The higher the moisture content in the mixed gas G0, the more the concentration of the first permeate gas G1 in the first separation membrane unit 10 is inhibited, and the lower the final recovery efficiency. As a result, the recovery power required to operate the gas separation system 100A increases. By including a dehumidification unit 90 in the gas separation system 100A, the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 can be reduced. Therefore, the recovery power required to operate the gas separation system 100A can be reduced.

[0065] C1 is defined as the moisture content in the mixed gas G0 discharged from the dehumidifier 90 during operation. The dehumidifier 90 may be controlled so that the moisture content C1 is 5 vol% or less. When the moisture content C1 is 5 vol% or less, the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 is reduced, thereby reducing the recovery power required to operate the gas separation system 100A.

[0066] The moisture content C1 may be 4 vol% or less, 3 vol% or less, 2 vol% or less, or even 1 vol% or less.

[0067] The dehumidification unit 90 may be controlled so that the moisture content C1 is 1 vol% or less. When the moisture content C1 is 1 vol% or less, the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 is further reduced, thereby further reducing the recovery power required to operate the gas separation system 100A.

[0068] The dehumidification unit 90 may be controlled so that the moisture content C1 is 0.5 vol% or less. When the moisture content C1 is 0.5 vol% or less, the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 is further reduced, thereby further reducing the recovery power required to operate the gas separation system 100A.

[0069] The lower limit of the water content C1 is, for example, 0 vol%.

[0070] The gas separation system 100A may further include a moisture sensor 96. The moisture content of the mixed gas G0 supplied to the dehumidifier 90 during operation is defined as C0. The moisture sensor 96 measures at least one selected from the group consisting of moisture content C0 and moisture content C1. In the gas separation system 100A, the dehumidifier 90 may be controlled based on the monitoring results from the moisture sensor 96. With such a configuration, it is easy to reduce the recovery power required to operate the gas separation system 100A.

[0071] As shown in Figure 1, the moisture sensor 96 may include a moisture sensor 96a that measures the moisture content C0 in the mixed gas G0 supplied to the dehumidification unit 90, and a moisture sensor 96b that measures the moisture content C1 in the mixed gas G0 discharged from the dehumidification unit 90. With such a configuration, both the moisture content C0 and the moisture content C1 can be measured, making it easy to control the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 to a desired range. However, the gas separation system 100A may be equipped with only a moisture sensor 96a that measures the moisture content C0, or only a moisture sensor 96b that measures the moisture content C1. Even with such a configuration, the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 can be controlled to a desired range.

[0072] Based on the monitoring results from the moisture sensor 96, the dehumidification unit 90 may be controlled so that the moisture content C1 is 5 vol% or less. Alternatively, based on the monitoring results from the moisture sensor 96, the dehumidification unit 90 may be controlled so that the moisture content C1 is 1 vol% or less.

[0073] The moisture sensor 96 is not particularly limited, as long as it can measure at least one selected from the group consisting of moisture content C0 and moisture content C1. Examples of moisture sensors 96 include: dew point meters; ceramic sensors such as capacitive and conductive types; phosphate sensors; QCM (quartz crystal microbalance) moisture sensors; mass sensors (MS), FT-IR (Fourier transform infrared spectroscopy) devices; optical fiber moisture sensors; color-changing chemical sensors (indicator method); electrical conductivity moisture sensors; thermal conductivity sensors; and the like. A dew point meter may also be used as the moisture sensor 96. The moisture content in the gas can be calculated from the dew point of the gas measured by the dew point meter.

[0074] The configuration of the dehumidification unit 90 is not particularly limited, as long as it can reduce the moisture content of the mixed gas G0. The dehumidification unit 90 may include at least one selected from the group consisting of a condenser 91, a vacuum device 92, a dehumidifier 93 equipped with a desiccant, an electrodialysis device 94 equipped with an ion exchange membrane, and a separation membrane device 95 equipped with a water vapor separation membrane.

[0075] In the example shown in Figure 1, the gas separation system 100A includes a condenser 91 as a dehumidification unit 90.

[0076] The condenser 91 removes the water contained in the mixed gas G0 as a liquid. The condenser 91 may include at least one selected from the group consisting of a heat exchanger and a compressor.

[0077] The condenser 91 may include a heat exchanger. The heat exchanger cools the mixed gas G0 discharged from the source of the mixed gas G0. When the mixed gas G0 is cooled to below its saturation temperature (dew point), the water contained in the mixed gas G0 condenses. The temperature of the mixed gas G0 discharged from the source is, for example, 100°C. In this case, the heat exchanger cools the temperature of the mixed gas G0 to, for example, a range of 12°C to 21°C. The heat exchanger may be a gas-liquid heat exchanger.

[0078] The condenser 91 may include a compressor. The compressor compresses the mixed gas G0 discharged from the source of the mixed gas G0. Compressing the mixed gas G0 increases the partial pressure of water vapor in the mixed gas G0, making it easier to reach the saturation vapor pressure. When the saturation vapor pressure is exceeded, the water contained in the mixed gas G0 condenses. The compressor is typically a compressor.

[0079] Although not shown in the diagram, if the condenser 91 includes a compressor, a heat exchanger may be placed downstream of the compressor. That is, the condenser 91 may include a compressor and a heat exchanger placed downstream of the compressor. With such a configuration, the cooling by the heat exchanger further promotes the condensation of water. Therefore, the water contained in the mixed gas G0 can be condensed more efficiently.

[0080] If the gas separation system 100A includes a condenser 91 as a dehumidification unit 90, a drain tank 85 may be connected to the condenser 91. As shown in Figure 1, a drain path 75 may be connected to the drain tank 85. The drain tank 85 and drain path 75 allow the condensed moisture to be discharged to the outside.

[0081] The gas separation system 100A may also include a pressure reducing device 92 as the dehumidification unit 90. The case where the gas separation system 100A includes a pressure reducing device 92 as the dehumidification unit 90 will be described below with reference to Figure 2A. Figure 2A is a diagram showing a modified example 1 of part II of Figure 1.

[0082] The depressurization device 92 removes the moisture contained in the mixed gas G0 by converting it into a gas. The depressurization device 92 reduces the pressure of the mixed gas G0 discharged from the source of the mixed gas G0. When the pressure of the mixed gas G0 is reduced, the boiling point of the mixed gas G0 decreases, and the moisture contained in the mixed gas G0 vaporizes. This phenomenon is also called vacuum drying.

[0083] As shown in Figure 2A, the depressurization device 92 may include a depressurizer 92a and a sealed container 92b. First, the mixed gas G0 discharged from the source is supplied to the sealed container 92b. By reducing the pressure inside the sealed container 92b using the depressurizer 92a, the water contained in the mixed gas G0 can be vaporized. The depressurizer 92a is typically a vacuum pump. However, when reducing the pressure inside the sealed container 92b using a vacuum pump, it is not always necessary to reduce the pressure to a vacuum. The pressure inside the sealed container 92b does not need to be a vacuum as long as it is lower than 1 atmosphere.

[0084] If the gas separation system 100A includes a dehumidifying unit 90 and a pressure reducing device 92, a discharge path 72a may be connected to the sealed container 92b of the pressure reducing device 92. The discharge path 72a allows vaporized moisture to be discharged to the outside.

[0085] The gas separation system 100A may include a dehumidifying device 93 equipped with a desiccant 93a as the dehumidifying unit 90. The case where the gas separation system 100A includes a dehumidifying device 93 equipped with a desiccant 93a as the dehumidifying unit 90 will be described below with reference to Figure 2B. Figure 2B shows a modified example 2 of part II of Figure 1.

[0086] The desiccant 93a provided in the desiccant 93 includes a solid desiccant and a liquid desiccant. The desiccant 93a provided in the desiccant 93 may be a solid desiccant or a liquid desiccant.

[0087] The solid desiccant includes a solid desiccant that removes moisture contained in the mixed gas G0 by physical adsorption, and a solid desiccant that removes moisture contained in the mixed gas G0 by chemical reaction. Examples of solid desiccant that remove moisture by physical adsorption include silica gel, molecular sieves, and activated carbon. Examples of solid desiccant that remove moisture by chemical reaction include phosphoric acid (anhydrous phosphoric acid) and calcium chloride.

[0088] Liquid desiccants remove moisture contained in the mixed gas G0 through a chemical hydration reaction. Examples of liquid desiccants include calcium chloride solution, sulfuric acid, and ethylene glycol.

[0089] If the gas separation system 100A includes a dehumidifying device 93 equipped with a desiccant 93a as a dehumidifying unit 90, a discharge path 72b may be connected to the desiccant 93. The discharge path 72b allows the desiccant 93a after moisture absorption, the moisture recovered by the desiccant 93a, and the hydrate of the desiccant 93a and moisture to be discharged to the outside.

[0090] The gas separation system 100A may include an electrodialysis apparatus 94 equipped with an ion exchange membrane as the dehumidification unit 90. The case where the gas separation system 100A includes an electrodialysis apparatus 94 equipped with an ion exchange membrane as the dehumidification unit 90 will be described below with reference to Figure 2C. Figure 2C shows a modified example 3 of part II of Figure 1.

[0091] The ion exchange membrane of the electrodialysis machine 94 includes at least one pair of cation exchange membranes and anion exchange membranes. The electrodialysis machine 94 separates water contained in the mixed gas G0 by utilizing the phenomenon in which water molecules move together with ions when ions move through the ion exchange membrane (electroosmosis). Specifically, when a DC voltage is applied between the electrodes of the electrodialysis machine 94, water contained in the mixed gas G0 is adsorbed and dissolved on the surface of the ion exchange membrane and ionized through the wet layer formed on the surface of the ion exchange membrane. The ionized water moves through the ion exchange membrane due to the action of the electric field. At this time, water molecules move together with the ions. The ion exchange membrane does not allow gas components to pass through, but selectively moves only ions and their water of hydration. In this way, water contained in the mixed gas G0 is separated through the ion exchange membrane.

[0092] If the gas separation system 100A includes an electrodialysis apparatus 94 equipped with an ion exchange membrane as a dehumidification unit 90, the electrodialysis apparatus 94 may also be connected to a discharge path 72c for discharging treated water after ion separation (desalination) treatment.

[0093] The gas separation system 100A may also include a separation membrane device 95 equipped with a water vapor separation membrane 95a as a dehumidification unit 90. The case where the gas separation system 100A includes a separation membrane device 95 equipped with a water vapor separation membrane 95a as a dehumidification unit 90 will be described below with reference to Figure 2D. Figure 2D shows a modified example 4 of part II of Figure 1.

[0094] The water vapor separation membrane 95a in the separation membrane apparatus 95 is a separation membrane that selectively allows water vapor to pass through. The separation membrane apparatus 95 uses the water vapor separation membrane 95a to separate the water contained in the mixed gas G0.

[0095] For example, a polyimide membrane, a polysulfone membrane, a polydimethylsiloxane membrane, etc., can be used as the water vapor separation membrane 95a.

[0096] If the gas separation system 100A includes a separation membrane device 95 equipped with a water vapor separation membrane 95a as a dehumidification unit 90, a discharge path 72c may be connected to the separation membrane device 95. The discharge path 72c allows the separated moisture to be discharged to the outside.

[0097] The gas separation system 100A may further include a third heat exchange section 53 and a fourth heat exchange section 54.

[0098] The third heat exchange unit 53 adjusts the temperature of the first permeate gas G1 discharged from the depressurization unit 31. The temperature of the first permeate gas G1 discharged from the depressurization unit 31 is, for example, 840°C. The third heat exchange unit 53 cools the temperature of the first permeate gas G1 to, for example, a range of 20°C to 50°C.

[0099] The fourth heat exchange unit 54 adjusts the temperature of the first permeate gas G1 discharged from the pressurized unit 41. The temperature of the first permeate gas G1 discharged from the pressurized unit 41 is, for example, 310°C. The fourth heat exchange unit 54 cools the temperature of the first permeate gas G1 to, for example, a range of 9°C to 21°C.

[0100] Similar to the first heat exchange section 51 and the second heat exchange section 52, the third heat exchange section 53 and the fourth heat exchange section 54 may be gas-liquid heat exchangers.

[0101] The gas separation system 100A may further include a first condensation section 56 and a second condensation section 57.

[0102] The first condensation unit 56 cools and condenses the first impermeable gas G2 discharged from the first separation membrane unit 10. According to the first condensation unit 56, for example, the gaseous first impermeable gas G2 is liquefied to obtain liquid first impermeable gas G2.

[0103] The second condensation unit 57 cools and condenses the second permeate gas G3 discharged from the second separation membrane unit 20. According to the second condensation unit 57, for example, the gaseous second permeate gas G3 is liquefied to obtain liquid second permeate gas G3.

[0104] The first condensing section 56 and the second condensing section 57 may be, for example, water-cooled heat exchangers. Water-cooled heat exchangers generate heat exchange between a cooling medium (refrigerant) such as antifreeze and an impermeable or permeable gas. Examples of refrigerants include ethylene glycol, propylene glycol, ethanol, and water. A common refrigerant may be used for both the first condensing section 56 and the second condensing section 57.

[0105] The gas separation system 100A includes a mixed gas path 61, a first permeable gas path 62, a first non-permeable gas path 63, a second permeable gas path 64, and a second non-permeable gas path 65 as gas pathways.

[0106] The mixed gas path 61 is connected to the mixed gas inlet 10a of the first separation membrane unit 10 and is a path for guiding the mixed gas G0 to the first separation membrane unit 10. The mixed gas path 61 may be directly connected to the source of the mixed gas G0, or it may be configured to continuously supply the mixed gas G0 from the source to the first separation membrane unit 10.

[0107] In the gas separation system 100A, a moisture sensor 96a, a dehumidification unit 90, a moisture sensor 96b, a blower 45, a first heat exchange unit 51, and a first temperature sensor 51a are arranged in the mixed gas path 61.

[0108] The mixed gas path 61 has a first portion 61a that connects the source of the mixed gas G0 to the blower 45, and a second portion 61b that connects the blower 45 to the first separation membrane unit 10. The dehumidifying unit 90 is located in the first portion 61a, and the first heat exchange unit 51 is located in the second portion 61b.

[0109] In the gas separation system 100A, the blower 45 can send the mixed gas G0 through the second section 61b toward the supply space of the first separation membrane unit 10. The blower 45, for example, pushes the mixed gas G0 that has passed through the first section 61a toward the second section 61b.

[0110] In the example shown in Figure 1, the drain tank 85 is located in the first section 61a downstream of the dehumidification unit 90 (condenser 91).

[0111] The first permeate gas path 62 connects the first permeate gas outlet 10b of the first separation membrane unit 10 and the first permeate gas inlet 20a of the second separation membrane unit 20, and is a path that guides the first permeate gas G1 to the second separation membrane unit 20.

[0112] In the gas separation system 100A, a depressurization section 31, a third heat exchange section 53, a pressurization section 41, a fourth heat exchange section 54, a second heat exchange section 52, and a second temperature sensor 52a are arranged in the first permeate gas path 62.

[0113] The first permeate gas path 62 has a first portion 62a connecting the first permeate gas outlet 10b of the first separation membrane unit 10 to the depressurization section 31, a second portion 62b connecting the depressurization section 31 to the pressurization section 41, and a third portion 62c connecting the pressurization section 41 to the first permeate gas inlet 20a of the second separation membrane unit 20. The third heat exchange section 53 is located in the second portion 62b, and the fourth heat exchange section 54 and the second heat exchange section 52 are located in the third portion 62c.

[0114] The depressurization unit 31 can reduce the pressure of the permeate space of the first separation membrane unit 10 through the first portion 62a. The depressurization unit 31 can, for example, suck in the first permeate gas G1 that has passed through the first portion 62a and discharge the first permeate gas G1 to the second portion 62b. The depressurization unit 31 is configured, for example, not to discharge the first permeate gas G1 that has passed through the first portion 62a to the outside of the gas separation system 100A. The depressurization unit 31 is connected only to the first portion 62a and the second portion 62b. If the depressurization unit 31 is a collection of multiple pumps, the first portion 62a of the first permeate gas path 62 may branch and be connected to each of the inlets of the multiple pumps. Similarly, the second portion 62b of the first permeate gas path 62 may branch and be connected to each of the outlets of the multiple pumps.

[0115] The pressurizing section 41 can increase the pressure of the supply space of the second separation membrane unit 20 through the third section 62c. The pressurizing section 41, for example, pumps the first permeate gas G1 that has passed through the second section 62b and discharges the first permeate gas G1 to the third section 62c. The pressurizing section 41 is configured, for example, not to discharge the gas that has passed through the second section 62b to the outside of the gas separation system 100A. The pressurizing section 41 is connected, for example, only to the second section 62b and the third section 62c. If the pressurizing section 41 is a collection of multiple pumps, the second section 62b of the first permeate gas path 62 may branch and be connected to each of the inlets of the multiple pumps. Similarly, the third section 62c of the first permeate gas path 62 may branch and be connected to each of the outlets of the multiple pumps.

[0116] As shown in Figure 1, a drain tank 86 may be located in the second portion 62b downstream of the third heat exchange unit 53. A drain path 76 may be connected to the drain tank 86. If the mixed gas G0 processed by the first separation membrane unit 10 contains water (H2O), the first permeate gas G1 is supplied to the third heat exchange unit 53 while still containing water, and may condense due to cooling by the third heat exchange unit 53. The drain tank 86 and drain path 76 allow the condensed water to be discharged to the outside.

[0117] As shown in Figure 1, a drain tank 87 may be located in the third section 62c downstream of the fourth heat exchange section 54. A drain path 77 may be connected to the drain tank 87. If the mixed gas G0 processed by the first separation membrane unit 10 contains water (H2O), the first permeate gas G1 is supplied to the fourth heat exchange section 54 while still containing water, and may condense due to cooling by the fourth heat exchange section 54. The drain tank 87 and drain path 77 allow the condensed water to be discharged to the outside.

[0118] The first impermeable gas path 63 is connected to the first impermeable gas outlet 10c of the first separation membrane unit 10 and is a path for discharging the first impermeable gas G2 from the first separation membrane unit 10. The first condenser 56 is located in the first impermeable gas path 63. Upstream of the first condenser 56 in the first impermeable gas path 63, a blower or pump may be provided to send the first impermeable gas G2 toward the first condenser 56.

[0119] The second permeate gas path 64 is connected to the second permeate gas outlet 20b of the second separation membrane unit 20 and is a path for discharging the second permeate gas G3 from the second separation membrane unit 20. The second condensation unit 57 is located in the second permeate gas path 64.

[0120] As shown in Figure 1, the gas separation system 100A may further include a recovery unit 82 for recovering the liquid second permeate gas G3 condensed by the second condensation unit 57. The recovery unit 82 may be connected to the second permeate gas path 64. The recovery unit 82 is, for example, a container for storing the liquid second permeate gas G3.

[0121] The second impermeable gas path 65 is connected to the second impermeable gas outlet 20c of the second separation membrane unit 20 and is a path for discharging the second impermeable gas G4 from the second separation membrane unit 20.

[0122] As shown in Figure 1, the second non-permeable gas path 65 may merge with the mixed gas path 61 at the merging position 61p. By merging the second non-permeable gas path 65 with the mixed gas path 61, for example, the second non-permeable gas G4 containing the second gas that could not be completely separated by the second separation membrane unit 20 can be reused.

[0123] However, the second non-permeable gas path 65 does not have to merge with the mixed gas path 61. The second non-permeable gas path 65 may also be directly connected to a recovery unit (not shown) for recovering the second non-permeable gas G4.

[0124] Each of the paths in the gas separation system 100A is composed of, for example, metal or resin piping, unless otherwise specified.

[0125] In the gas separation system 100A, the pressure reduction unit 31 may be a vacuum pump that requires a sealing gas. The case where the pressure reduction unit 31 is a vacuum pump that requires a sealing gas will be described below with reference to Figures 3A and 3B.

[0126] Vacuum pumps that require a sealing gas have superior pump efficiency compared to other vacuum pumps. A sealing gas is a gas supplied to a vacuum pump for purposes such as shaft sealing, improving vacuum level, suppressing the generation of reaction products, inhibiting corrosion, and extending the lifespan. Conventionally, inert gases have been used as sealing gases. Normally, the permeate gas from the separation membrane unit and the sealing gas are discharged together from the vacuum pump. Therefore, when a vacuum pump requiring a sealing gas is used as the vacuum pressure section of a vacuum-type separation membrane unit, the permeate gas is diluted by the sealing gas (inert gas), making it difficult to recover high-concentration permeate gas.

[0127] Figure 3A is an enlarged view showing a modified example 1 of part III in Figure 1. When the depressurization section 31 is a vacuum pump that requires a seal gas, the gas separation system 100A may include a circulation path 71 that guides at least a portion of the first permeate gas G1 to the depressurization section 31 as a seal gas for the depressurization section 31. With such a configuration, it is possible to suppress the decrease in the content of the second gas contained in the permeate gas that is ultimately recovered. Therefore, it is possible to recover a high concentration of permeate gas while employing a vacuum pump that requires a seal gas with excellent pump efficiency.

[0128] The circulation path 71 is a path that guides at least a portion of the first permeate gas G1 to the vacuum pump 31 as a sealing gas for the vacuum pump 31. In the example shown in Figure 3A, the circulation path 71 branches off from the first portion 62a of the first permeate gas path 62 at branching position 71q and is connected to the sealing gas inlet of the vacuum pump 31. However, the connection position of the circulation path 71 is not limited to the example shown in Figure 3A. For example, the circulation path 71 may branch off from the outlet of the vacuum pump 31 and be connected to the sealing gas inlet of the vacuum pump 31.

[0129] A switching valve may be provided at the branching position 71q. A flow rate control valve may be provided in the circulation path 71. With this configuration, the flow rate of the first permeate gas G1 led to the circulation path 71 can be adjusted by the switching valve and the flow rate control valve. The flow rate of the first permeate gas G1 supplied to the pressure reducing section 31 is preferably 12 NL / min or more. There is no particular upper limit to the flow rate of the first permeate gas G1 supplied to the pressure reducing section 31.

[0130] As shown in Figure 3A, if the depressurization unit 31 is a vacuum pump that requires a sealing gas, the gas separation system 100A may include a booster 47 provided in the circulation path 71. The booster 47 pressurizes the first permeate gas G1, which is supplied to the depressurization unit 31 as a sealing gas. By continuously operating the booster 47, the first permeate gas G1 can be obtained stably. The booster 47 is not particularly limited as long as it can pressurize the first permeate gas G1, which is supplied to the depressurization unit 31 as a sealing gas. The booster 47 is typically a compressor.

[0131] The gas separation system 100A may be equipped with a drain mechanism (not shown) for discharging moisture contained in the first permeate gas G1, which acts as a sealing gas. With such a configuration, for example, if the first permeate gas G1 contains moisture, it is possible to suppress malfunctions of each component of the gas separation system 100A due to moisture. The booster 47 may also be equipped with a drain mechanism. As shown in Figure 3A, moisture recovered by the drain mechanism may be discharged to the outside through a drain path 79 connected to the booster 47.

[0132] Figure 3B is an enlarged view showing a modified example 2 of part III in Figure 1. If the pressure reduction section 31 is a vacuum pump that requires a sealing gas, the booster 47 may be provided between the pressure reduction section 31 and the branching position 71q. This configuration also makes it possible to suppress the decrease in the content of the second gas contained in the permeate gas that is ultimately recovered.

[0133] The gas separation system 100A may further include a control unit 80 that controls each component of the gas separation system 100A. The control unit 80 is, for example, a DSP (Digital Signal Processor) that includes an A / D conversion circuit, input / output circuits, arithmetic circuits, a memory device, etc. The control unit 80 stores a program for properly operating the gas separation system 100A. In detail, the control unit 80 can control the operation of, for example, the depressurization unit 31, the pressurization unit 41, the first heat exchange unit 51, the second heat exchange unit 52, the dehumidification unit 90, etc. The control unit 80 may receive information from each sensor and determine the operating conditions of the depressurization unit 31, the pressurization unit 41, the first heat exchange unit 51, the second heat exchange unit 52, the dehumidification unit 90, etc., based on this information.

[0134] For example, when mixed gas G0 is supplied to the first separation membrane unit 10 from the mixed gas path 61, the control unit 80 controls the depressurization unit 31 so that the permeate space of the first separation membrane unit 10 is depressurized. More specifically, the control unit 80 controls the depressurization unit 31 so that the permeate space of the first separation membrane unit 10 remains depressurized while mixed gas G0 is supplied to the first separation membrane unit 10. Similarly, when the first permeate gas G1 is supplied to the second separation membrane unit 20 from the first permeate gas path 62, the control unit 80 controls the pressurization unit 41 so that the supply space of the second separation membrane unit 20 is pressurized. More specifically, the control unit 80 controls the pressurization unit 41 so that the supply space of the second separation membrane unit 20 remains pressurized while the first permeate gas G1 is supplied to the second separation membrane unit 20. Note that the gas separation system 100A does not necessarily have a control unit 80. In the gas separation system 100A, an operator may control the operation of the depressurization unit 31 and the pressurization unit 41 by switching them on and off, respectively.

[0135] The gas separation system 100A of this embodiment is, for example, a continuous system. In this specification, a continuous system means a system that can continuously process a mixed gas G0 without closing the paths constituting the gas separation system 100A by on-off valves or the like. In other words, the gas separation system 100A processes the mixed gas G0 in the first separation membrane unit 10, and the first permeate gas G1 obtained in the first separation membrane unit 10 can be immediately processed in the second separation membrane unit 20 without being collected in a recovery unit or the like. Thus, the gas separation system 100A of this embodiment is capable of continuous operation. The gas separation system 100A, which functions as a continuous system, is suitable for applications where the mixed gas G0 is supplied continuously, particularly for the treatment of exhaust gas from factories or power plants.

[0136] In the gas separation system 100A, for example, at least one of the following is satisfied: (I) separating the mixed gas G0 into a first permeate gas G1 and a first non-permeate gas G2 while reducing the pressure of the permeate space of the first separation membrane unit 10 by the depressurization unit 31, and (II) separating the first permeate gas G1 into a second permeate gas G3 and a second non-permeate gas G4 while increasing the pressure of the supply space of the second separation membrane unit 20 by the pressurization unit 41. In the gas separation system 100A, it is preferable that both of the above requirements (I) and (II) are satisfied.

[0137] In the gas separation system 100A, the content of the second gas in the mixed gas G0 may be 30 vol% or less. As described above, in the pressurized method, the recovery power tends to increase as the content of the second gas in the supplied mixed gas G0 decreases, while the required membrane area tends to decrease. By keeping the content of the second gas in the mixed gas G0 at 30 vol% or less, the required membrane area for the entire gas separation system 100A can be reduced. In this specification, unless otherwise specified, "content" refers to the value at standard conditions (0°C, 101 kPa).

[0138] In the gas separation system 100A, the content of the second gas in the mixed gas G0 may be less than 30 vol%. The content of the second gas in the mixed gas G0 may be 25 vol% or less, 20 vol% or less, or even 15 vol% or less. The lower limit of the content of the second gas in the mixed gas G0 is, for example, 10 vol%.

[0139] The permeation rate of the second gas permeating through the first separation membrane 11 is not particularly limited. The permeation rate of the second gas permeating through the first separation membrane 11 is, for example, 1 GPU or more, and may be 5 GPU or more, 10 GPU or more, 50 GPU or more, or even 100 GPU or more. The upper limit of the permeation rate of the second gas permeating through the first separation membrane 11 is not particularly limited, and is, for example, 1000 GPU. However, GPU is 10 -6 ·cm 3 (STP) / (sec・cm 2 This means cmHg. 3(STP) represents the volume of the gas at 1 atmosphere and 0°C. The permeation rate of the second gas permeating through the first separation membrane 11 can be calculated based on the results of the following separation operation using a test piece made from the first separation membrane 11.

[0140] The permeation rate of the second gas permeating through the second separation membrane 21 is not particularly limited. The permeation rate of the second gas permeating through the second separation membrane 21 is, for example, 1 GPU or more, and may be 5 GPU or more, 10 GPU or more, 50 GPU or more, or even 80 GPU or more. The upper limit of the permeation rate of the second gas permeating through the second separation membrane 21 is not particularly limited, and is, for example, 1000 GPU. The permeation rate of the second gas permeating through the second separation membrane 21 can be calculated based on the results of the following separation operation using a test piece made from the second separation membrane 21.

[0141] (Separation Operation) A test specimen is prepared from the first separation membrane 11 or the second separation membrane 21. A test gas consisting of the first gas and the second gas is supplied to a space adjacent to one side of the test specimen, and a separation operation is performed by reducing the pressure in the space adjacent to the other side of the test specimen. Based on the results of the separation operation, the permeation rate of the second gas permeating through the first separation membrane 11 and the permeation rate of the second gas permeating through the second separation membrane 21 are determined. In the separation operation, the content of the second gas in the test gas is 50 vol% under standard conditions, the test gas supplied to the space adjacent to one side is at a temperature of 30°C and a pressure of 0.1 MPa, and the space adjacent to the other side is reduced to a pressure of 0.1 MPa less than the atmospheric pressure in the measurement environment.

[0142] In detail, the separation operation can be carried out, for example, by the following method. First, a test specimen is prepared from the first separation membrane 11 or the second separation membrane 21. The test specimen can be prepared, for example, by cutting the first separation membrane 11 or the second separation membrane 21 into a disc shape with a diameter of 20 mm. The size of the disc-shaped test specimen may be larger than 20 mm in diameter. The test specimen is set in a metal cell and sealed with an O-ring to prevent leakage. Next, the test gas is injected into the space (supply space) inside the metal cell so that the test gas contacts one main surface of the test specimen. As described above, the content of the second gas in the test gas injected into the supply space is 50 vol% under standard conditions (0°C, 101 kPa). The test gas is at a temperature of 30°C and a pressure of 0.1 MPa. Next, the space (permeation space) inside the metal cell adjacent to the other main surface of the test specimen is depressurized with a vacuum pump. At this time, the permeation space is depressurized so that the pressure within the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment. As a result, the permeated fluid that has permeated through the test specimen is obtained in the permeation space.

[0143] [Separation Membrane Unit] Figure 4 is a schematic cross-sectional view showing an example of the first separation membrane unit 10. As shown in Figure 4, the first separation membrane unit 10 comprises a first separation membrane 11 and a container 12. The container 12 has a first chamber 13 and a second chamber 14. The first chamber 13 functions as a supply space to which the mixed gas G0 is supplied. The second chamber 14 functions as a permeation space to which the first permeate gas G1 is supplied. The first permeate gas G1 is obtained by the mixed gas G0 permeating through the first separation membrane 11. In this embodiment, the configuration of the second separation membrane unit 20 is the same as that of the first separation membrane unit 10, so its description is omitted.

[0144] The first separation membrane 11 is located inside the container 12. Inside the container 12, the first separation membrane 11 separates the first chamber 13 and the second chamber 14. The first separation membrane 11 extends from one of a pair of walls of the container 12 to the other.

[0145] The first chamber 13 has a mixed gas inlet 10a and a first impermeable gas outlet 10c. The second chamber 14 has a first permeable gas outlet 10b. The mixed gas inlet 10a of the first chamber 13 is an opening for supplying the mixed gas G0 to the first separation membrane unit 10. The first permeable gas outlet 10b of the second chamber 14 is an opening for discharging the first permeable gas G1 obtained by the mixed gas G0 permeating through the first separation membrane 11 from the first separation membrane unit 10. The first impermeable gas outlet 10c of the first chamber 13 is an opening for discharging the mixed gas G0 (first impermeable gas G2) that did not permeate through the first separation membrane 11 from the first separation membrane unit 10. Each of the mixed gas inlet 10a, the first permeable gas outlet 10b, and the first impermeable gas outlet 10c is formed, for example, on the wall surface of the container 12.

[0146] The first separation membrane unit 10 is suitable for a continuous flow membrane separation method. However, the first separation membrane unit 10 may also be used in a batch membrane separation method.

[0147] (Separation Membrane) As described above, the first separation membrane 11 can preferentially permeate the second gas contained in the mixed gas G0. Below, the first separation membrane 11 when the second gas is carbon dioxide, that is, the first separation membrane 11 that preferentially permeates carbon dioxide, will be described. In this specification, a separation membrane that preferentially permeates carbon dioxide may be called a "carbon dioxide permeable membrane".

[0148] Figure 5 is a schematic cross-sectional view showing an example of the first separation membrane 11. As shown in Figure 5, the first separation membrane 11 as a carbon dioxide permeable membrane includes, for example, a separation functional layer 1. The first separation membrane 11 may further include 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, for example, in direct contact with the separation functional layer 1 and the porous support 3, respectively. Although not shown, the first separation membrane 11 may further include a protective layer that protects the separation functional layer 1. The protective layer is, for example, in direct contact with the separation functional layer 1.

[0149] (Separation Functional Layer) The separation functional layer 1 is a layer that can preferentially permeate carbon dioxide contained in the mixed gas G0. In a preferred embodiment, the separation functional layer 1 includes a resin. Examples of resins included in the separation functional layer 1 include polyether block amide resins, polyamide resins, polyether resins, polyimide resins, cellulose acetate resins, silicone resins, and fluororesins. The separation functional layer 1 preferably includes a polyether block amide resin. In this embodiment, the separation functional layer 1 preferably consists substantially of a resin. In this specification, "substantially consisting of" means excluding other components that alter the essential characteristics of the material mentioned, for example, that 95 wt% or more, and more precisely 99 wt% or more, is composed of the material.

[0150] In another preferred embodiment, the separation functional layer 1 comprises an ionic liquid. The ionic liquid is a salt (ionic compound) that is liquid at 25°C. The separation functional layer 1 comprising the ionic liquid is typically an ionic gel membrane. The separation functional layer 1 may comprise the ionic liquid and a hydrophilic polymer A that forms a crystalline structure in the ionic liquid. The separation functional layer 1 may further comprise a polymer B different from polymer A. The separation functional layer 1 may be hydrophobic or hydrophilic. When the separation functional layer 1 is hydrophobic, polymers A and B can be, for example, those described in International Publication 2023 / 032744, in which the present applicant is the applicant. When the separation functional layer 1 is hydrophilic, polymers A and B can be, for example, those described in International Publication 2024 / 166604, in which the present applicant is the applicant.

[0151] In this embodiment, specific ionic liquids include, for example, ionic liquids having imidazolium, pyridinium, ammonium, or phosphonium and substituents having one or more carbon atoms.

[0152] In an ionic liquid having imidazolium and a substituent having one or more carbon atoms, examples of substituents having one or more carbon atoms include alkyl groups having one to 20 carbon atoms, cycloalkyl groups having three to 14 carbon atoms, and aryl groups having six to 20 carbon atoms. These may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc. (for example, hydroxyalkyl groups having one to 20 carbon atoms).

[0153] Examples of alkyl groups having 1 to 20 carbon atoms include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, and n-eicosadecyl. Examples include hydroxyl groups, i-propyl groups, sec-butyl groups, i-butyl groups, 1-methylbutyl groups, 1-ethylpropyl groups, 2-methylbutyl groups, i-pentyl groups, neopentyl groups, 1,2-dimethylpropyl groups, 1,1-dimethylpropyl groups, t-pentyl groups, 2-ethylhexyl groups, and 1,5-dimethylhexyl groups, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0154] The alkyl groups described above may be substituted with cycloalkyl groups. The number of carbon atoms in the alkyl groups substituted with cycloalkyl groups is, for example, 1 to 20. Examples of alkyl groups substituted with cycloalkyl groups include cyclopropylmethyl group, cyclobutylmethyl group, cyclohexylmethyl group, and cyclohexylpropyl group, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0155] Examples of cycloalkyl groups having 3 to 14 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, norbornyl, bornyl, and adamantyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0156] Examples of aryl groups having 6 to 20 carbon atoms include phenyl, toluyl, xylyl, mesityl, anisyl, naphthyl, and benzyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0157] Compounds having imidazolium and substituents with one or more carbon atoms may further have substituents such as alkyl groups and may form salts with counter anions. Examples of counter anions include alkyl sulfates, tosylates, methanesulfonates, acetates, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, thiocyanates, dicyanamides, tricyanomethanides, tetracyanoborates, hexafluorophosphates, tetrafluoroborates, and halides. From the viewpoint of gas separation performance, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, dicyanamides, tricyanomethanides, and tetracyanoborates are preferred.

[0158] Ionic liquids having imidazolium and substituents with one or more carbon atoms include, specifically, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium tetrachloroferate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1 -Butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate, 1-butyl-3-methylimidazolium tribromide, 1,3-dimethylimidazolium chloride, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, 1,3-diisopropylimidazolium tetrafluoroborate, 1,3-di-tert-butylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium chloride, 1,2-dimethyl-3-propylimidazolium iodide, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium bromide, 1-methyl-3-propylimidazolium iodide, 1-methyl-3-n-octylimidazolium bromide, 1-methyl-3-n-octylimidazolium Examples include dazolium chloride, 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate, 1-ethyl-3-methylimidazolium tricyanomethanide, 1-ethyl-3-methylimidazolium tetracyanoborate, and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0159] In particular, from the viewpoint of gas separation performance, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI][FSI]), 1-ethyl-3-methylimidazolium dicyanamide ([EMI][DCA]), 1-ethyl-3-methylimidazolium tricyanomethanide ([EMI][TCM]), 1-ethyl-3-methylimidazolium tetracyanoborate ([EMI][TCB]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4m][TF2N]), and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2OHim][TF2N]) are especially preferred.

[0160] The ionic liquid content in the separation functional layer 1 is, for example, 5 wt% or more, and may be 30 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, or even 80 wt% or more, from the viewpoint of gas separation performance. The higher the ionic liquid content, the higher the separation functional layer 1 tends to have separation performance. The upper limit of the ionic liquid content is not particularly limited and may be, for example, 95 wt% or less, or 90 wt% or less. The independence of the separation functional layer 1 tends to be easily ensured when the ionic liquid content is 95 wt% or less.

[0161] The thickness of the separation functional layer 1 is, for example, 50 μm or less, preferably 25 μm or less, and more preferably 15 μm or less. The thickness of the separation functional layer 1 may, in some cases, be 10 μm or less, 5.0 μm or less, or 2.0 μm or less. The thickness of the separation functional layer 1 may be 0.05 μm or more, or 0.1 μm or more.

[0162] (Intermediate layer) The intermediate layer 2 may, for example, contain a resin and further contain nanoparticles dispersed in the resin (matrix). The nanoparticles may be spaced apart from each other in the matrix or partially aggregated. The material of the matrix is ​​not particularly limited and includes, for example, 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.

[0163] Nanoparticles may contain inorganic materials or organic materials. Examples of inorganic materials that can be included in nanoparticles include silica, titania, and alumina. It is preferable that the nanoparticles contain silica.

[0164] The thickness of the intermediate layer 2 is not particularly limited, and is, for example, less than 50 μm, preferably 40 μm or less, and more preferably 30 μm or less. The lower limit of the thickness of the intermediate layer 2 is not particularly limited, and is, for example, 0.1 μm. The intermediate layer 2 is, for example, a layer having a thickness of less than 50 μm.

[0165] (Porous Support) The porous support 3 supports the separation functional layer 1 via the intermediate layer 2. Examples of the porous support 3 include nonwoven fabric; porous polytetrafluoroethylene; aromatic polyamide fiber; porous metal; sintered metal; porous ceramic; porous polyester; porous nylon; activated carbon fiber; latex; silicone; silicone rubber; permeable (porous) polymer containing at least one selected from the group consisting of polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyetheretherketone, polyacrylonitrile, polyimide, and polyphenylene oxide; metal foam having open or closed cells; polymer foam having open or closed cells; silica; porous glass; mesh screen, etc. The porous support 3 may be a combination of two or more of these.

[0166] The porous support 3 has an average pore diameter of, for example, 0.01 to 0.4 μm. The thickness of the porous support 3 is not particularly limited, but 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.

[0167] (Protective Layer) The protective layer protects the separation functional layer 1 and improves the strength of the first separation membrane 11. As the protective layer, a hydrophobic membrane, a dense membrane, a porous material, etc., can be used. A dense membrane is typically a layer in which no pores can be observed when viewed with an SEM at a magnification of 5000x (a non-porous layer). From the viewpoint of suppressing carrier elution, a hydrophobic membrane composed of polydimethylsiloxane (PDMS) is preferably used as the hydrophobic membrane. The hydrophobic membrane may also be a hydrophobic membrane having a porous structure. Examples of porous materials include nonwoven fabrics, woven fabrics, nets, and meshes. From the viewpoint of having excellent heat resistance and being resistant to hydrolysis, polyolefins such as PP; nonwoven fabrics containing PTFE, etc., are preferably used as the porous material.

[0168] The thickness of the protective layer is not particularly limited, and is, for example, less than 50 μm, preferably 40 μm or less, and more preferably 30 μm or less. The lower limit of the thickness of the protective layer is not particularly limited, and is, for example, 0.1 μm.

[0169] The first separation membrane 11 is typically a flat membrane. However, the first separation membrane 11 may have a shape other than a flat membrane, for example, it may be a hollow fiber membrane.

[0170] (Method for manufacturing a separation membrane) The first separation membrane 11 can be manufactured, for example, by the following method. First, a coating solution containing the material for the intermediate layer 2 is prepared. Next, the coating solution containing the material for the intermediate layer 2 is applied to the porous support 3 to form a coating film. The method of applying the coating solution is not particularly limited, and for example, a wire bar can be used. The thickness of the formed intermediate layer 2 can be adjusted by adjusting the wire diameter of the wire bar and the concentration of the material for the intermediate layer 2 in the coating solution. Alternatively, the coating film may be formed by immersing the porous support 3 in the coating solution. Next, the coating film is dried to form the intermediate layer 2. Drying of the coating film can be carried out, for example, under heating conditions. The heating temperature of the coating film is, for example, 50°C or higher. The heating time of the coating film is, for example, 1 minute or more, and may be 5 minutes or more.

[0171] The surface of the intermediate layer 2 may be treated to facilitate adhesion as needed. This may include surface treatments such as applying a primer, corona discharge treatment, or plasma treatment.

[0172] Next, a coating solution containing the material for the separation functional layer 1 is prepared. The coating solution containing the material for the separation functional layer 1 is applied onto the intermediate layer 2 to obtain a coating film. This coating film is dried to form the separation functional layer 1. The coating method and drying conditions for the coating solution can be the same as those described above for the intermediate layer 2. The coating of the coating solution containing the material for the separation functional layer 1 may be performed by spin coating. This yields the first separation film 11.

[0173] The method for producing the first separation membrane 11 is not limited to the method described above. For example, the first separation membrane 11 can also be produced by the following method. For example, a coating solution containing the material for the separation functional layer 1 is applied onto a transfer film to obtain a coating film. The separation functional layer 1 is formed by drying the coating film. Next, an intermediate layer 2 is formed by coating a coating solution containing the material for the intermediate layer 2 onto the separation functional layer 1 and drying it. The laminate of the intermediate layer 2 and the separation functional layer 1 is transferred to a porous support 3. This gives the first separation membrane 11.

[0174] [Modifications of the Separation Membrane Unit] The first separation membrane unit 10 and the second separation membrane unit 20 provided in the gas separation system 100A are not limited to the form shown in Figure 4. The first separation membrane unit 10 and the second separation membrane unit 20 may include, for example, a spiral-shaped membrane element, a hollow fiber membrane element, etc. Figure 6 is a schematic exploded perspective view showing a spiral-shaped membrane element. The first separation membrane unit 10 and the second separation membrane unit 20 may include a spiral-shaped membrane element as shown in Figure 6.

[0175] In the following, the case in which the first separation membrane unit 10 and the second separation membrane unit 20 of the gas separation system 100A described above each include a spiral-type membrane element will be further explained with reference to Figure 6. In the following, only the case in which the first separation membrane unit 10 includes a spiral-type membrane element will be explained, and the case in which the second separation membrane unit 20 includes a spiral-type membrane element will be omitted.

[0176] The spiral-shaped membrane element 15 shown in Figure 6 comprises a central tube 16 and membrane leaves 19 that have a first separation membrane 11 and are wound around the central tube 16.

[0177] The central tube 16 has a cylindrical shape. Through holes 16h are formed on the surface of the central tube 16 to allow the mixed gas G0 to flow into the interior of the central tube 16. The number of through holes 16h is not particularly limited and may be one or two or more. 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.

[0178] The membrane element 15 has a plurality of membrane leaves 19. Each membrane leaf 19 includes a first separation membrane 11 and a permeate-side flow channel material 17. For example, a membrane leaf 19 has two first separation membranes 11. The two first separation membranes 11 are overlapped and sealed on three sides to form a bag-like structure. The permeate-side flow channel material 17 is positioned between the two first separation membranes 11 so as to be located inside the bag-like structure. The permeate-side flow channel material 17 secures a space (permeate space) between the two first separation membranes 11 as a flow channel for the first permeate gas G1. In this way, the permeate-side flow channel material 17 is used in combination with the first separation membrane 11. The number of membrane leaves 19 is not particularly limited and can be, for example, 2 to 30.

[0179] The membrane element 15 further includes a supply-side flow channel material 18. The supply-side flow channel material 18 is located outside the bag-like structure described above and is stacked on the membrane leaf 19. More specifically, multiple supply-side flow channel materials 18 and multiple membrane leaf 19 are stacked alternately. The supply-side flow channel material 18 secures a space (supply space) between the membrane leaf 19 that serves as a flow path for the mixed gas G0.

[0180] For the supply-side channel material 18 and the permeate-side channel material 17, for example, a net, woven fabric, or knitted fabric made of a resin such as polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0181] The outer surface of the membrane element 15 is composed of a shell (not shown) made of a material that prevents gas from passing through. The shell may be made of FRP (fiber-reinforced plastic). The membrane element may be housed in a casing (not shown).

[0182] The first separation membrane unit 10, which includes the membrane element 15 shown in Figure 6, can be operated, for example, in the following way. First, a mixed gas G0 is supplied to one end of the wound membrane leaf 19. The space inside the central tube 16 is depressurized. Depressurization can be performed by the depressurization unit 31. As a result, the first permeate gas G1 that has permeated through the first separation membrane 11 of the membrane leaf 19 moves into the central tube 16. The first permeate gas G1 is discharged to the outside through the central tube 16. The mixed gas G0 (first non-permeate gas G2) processed in the first separation membrane unit 10 is discharged to the outside from the other end of the wound membrane leaf 19.

[0183] <Embodiment of Mixed Gas Separation Method> Next, an example of a mixed gas separation method using the gas separation system 100A described above will be explained with reference to Figure 1.

[0184] The method for separating a mixed gas using the gas separation system 100A includes a first separation step, a second separation step, and a temperature control step. In the first separation step, the mixed gas G0 is supplied to a first separation membrane unit 10 containing a first separation membrane 11, and the mixed gas G0 is separated into a first permeate gas G1 and a first impermeable gas G2. In the second separation step, the first permeate gas G1 is supplied to a second separation membrane unit 20 containing a second separation membrane 21, and the first permeate gas G1 is separated into a second permeate gas G3 and a second impermeable gas G4. In the temperature control step, when the temperature of the mixed gas G0 supplied to the first separation membrane unit 10 in the first separation step is defined as T1, and the temperature of the first permeate gas G1 supplied to the second separation membrane unit 20 in the second separation step is defined as T2, temperatures T1 and T2 are controlled to satisfy T1 ≥ T2. As described above, the mixed gas G0 includes a first gas and a second gas different from the first gas. The first separation membrane 11 and the second separation membrane 21 can preferentially permeate the second gas. With a mixed gas separation method having such a configuration, it is possible to achieve both a reduction in recovery power and a reduction in membrane area.

[0185] In the mixed gas separation method of this embodiment, the first separation step includes reducing the pressure of the permeate space of the first separation membrane unit 10. The second separation step includes increasing the pressure of the supply space of the second separation membrane unit 20.

[0186] (First Separation Step) The first separation step is carried out, for example, as follows: First, the mixed gas G0 is supplied to the supply space of the first separation membrane unit 10 through the mixed gas path 61. The mixed gas G0 is supplied to the supply space by, for example, a blower 45.

[0187] Next, with the mixed gas G0 supplied to the supply space of the first separation membrane unit 10, the permeate space is depressurized. Specifically, the permeate space is depressurized through the first permeate gas outlet 10b using the depressurization unit 31. As an example, the pressure in the permeate space of the first separation membrane unit 10 is 3 kPa.

[0188] By reducing the pressure in the permeate space, a pressure difference is created between the supply space and the permeate space. As a result, the mixed gas G0 is separated by the first separation membrane 11, and the first permeate gas G1 is supplied to the permeate space. While the separation of the mixed gas G0 is taking place, the permeate space may be continuously reduced in pressure by the pressure reduction unit 31. The pressure difference between the supply space and the permeate space of the first separation membrane unit 10 is adjusted to, for example, 500 kPa or less, preferably 400 kPa or less, more preferably 300 kPa or less, even more preferably 200 kPa or less, and particularly preferably 100 kPa or less, from the viewpoint of reducing the energy consumed by the gas separation system 100A. The lower limit of the pressure difference between the supply space and the permeate space of the first separation membrane unit 10 is not particularly limited, and is, for example, 10 kPa.

[0189] The first permeate gas G1 supplied to the permeation space passes through the first portion 62a of the first permeate gas path 62 and is drawn into the depressurization section 31. The depressurization section 31 discharges the drawn-in first permeate gas G1 into the second portion 62b of the first permeate gas path 62. Since the first permeate gas G1 is supplied to the second portion 62b, the pressure in the second portion 62b is normally maintained at approximately atmospheric pressure in the measurement environment. The first permeate gas G1 is supplied to the pressurization section 41 through the second portion 62b.

[0190] As described above, the first separation membrane 11 of the first separation membrane unit 10 preferentially allows the second gas contained in the mixed gas G0 to permeate. Therefore, the first permeate gas G1 obtained by the first separation step has a higher content of the second gas compared to the mixed gas G0. The content of the second gas (e.g., carbon dioxide) in the first permeate gas G1 obtained by the first separation step is not particularly limited, and is, for example, 40 vol% to 70 vol%. The ratio of the content of the second gas in the first permeate gas G1 (vol%) to the content of the second gas in the mixed gas G0 (vol%) is not particularly limited, and is, for example, 2 to 6.

[0191] Meanwhile, the concentration of the first gas in the mixed gas G0 gradually increases from the mixed gas inlet 10a of the supply space toward the first impermeable gas outlet 10c. The content of the first gas (e.g., nitrogen) in the mixed gas G0 (first impermeable gas G2) processed in the supply space is, for example, 95 vol% to 99 vol%. The first impermeable gas G2 is discharged to the outside of the first separation membrane unit 10 through the first impermeable gas outlet 10c. The first impermeable gas G2 is discharged, for example, through the first impermeable gas path 63.

[0192] (Second Separation Step) The second separation step is carried out, for example, as follows: First, the first permeate gas G1 is supplied to the supply space of the second separation membrane unit 20 through the second portion 62b and the third portion 62c of the first permeate gas path 62.

[0193] Next, with the first permeate gas G1 supplied to the supply space of the second separation membrane unit 20, the supply space is pressurized. Specifically, the supply space is pressurized through the first permeate gas inlet 20a using the pressurizing unit 41. As an example, the pressure in the supply space of the second separation membrane unit 20 is 900 kPa.

[0194] By increasing the pressure of the supply space, a differential pressure is created between the supply space and the permeate space. As a result, the first permeate gas G1 is separated by the second separation membrane 21, and the second permeate gas G3 is supplied to the permeate space. While the separation of the first permeate gas G1 is taking place, the supply space may be continuously pressurized by the pressurizing unit 41. The differential pressure between the supply space and the permeate space of the second separation membrane unit 20 is adjusted to, for example, 1000 kPa or less, preferably 800 kPa or less, more preferably 600 kPa or less, even more preferably 500 kPa or less, and particularly preferably 400 kPa or less, from the viewpoint of reducing the energy consumed by the gas separation system 100A. The lower limit of the differential pressure between the supply space and the permeate space of the second separation membrane unit 20 is not particularly limited, and is, for example, 100 kPa.

[0195] The second permeate gas G3 supplied to the permeate space is sent to, for example, the recovery unit 82 via the second permeate gas path 64.

[0196] As described above, the second separation membrane 21 of the second separation membrane unit 20 preferentially allows the second gas contained in the first permeate gas G1 to permeate. Therefore, the second permeate gas G3 obtained by the second separation step has a higher content of the second gas compared to the first permeate gas G1. The content of the second gas (e.g., carbon dioxide) in the second permeate gas G3 obtained by the second separation step is not particularly limited, but is for example 95 vol%. The ratio of the content of the second gas (vol%) in the second permeate gas G3 to the content of the second gas (vol%) in the first permeate gas G1 is not particularly limited, but is for example 1.3 to 2.5.

[0197] Meanwhile, the concentration of the first gas in the first permeate gas G1 gradually increases from the first permeate gas inlet 20a to the second non-permeate gas outlet 20c in the supply space. The content of the first gas (e.g., nitrogen) in the first permeate gas G1 (second non-permeate gas G4) processed in the supply space is not particularly limited, but is, for example, 70 vol% to 97 vol%. The second non-permeate gas G4 is discharged to the outside of the second separation membrane unit 20 through the second non-permeate gas outlet 20c.

[0198] In the mixed gas separation method of this embodiment, it is preferable that the first separation step and the second separation step be performed consecutively. That is, it is preferable that the first permeate gas G1 separated in the first separation step is not collected in a tank or the like, but is immediately used in the second separation step. By performing the first separation step and the second separation step consecutively, the processing amount of mixed gas G0 per unit time can be easily increased.

[0199] (Temperature control process) The temperature control process is carried out together with the first separation process and the second separation process. In the first separation process, the temperature T1 of the mixed gas G0 is adjusted by the first heat exchange unit 51 so that temperatures T1 and T2 satisfy T1 ≥ T2, and in the second separation process, the temperature T2 of the first permeate gas G1 is adjusted by the second heat exchange unit 52.

[0200] The temperature control process may be performed based on the monitoring results from the first temperature sensor 51a and the second temperature sensor 52a.

[0201] The mixed gas separation method of this embodiment may further include a dehumidification step to reduce the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10. By performing the dehumidification step, the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 can be reduced. As a result, the recovery power required to operate the gas separation system 100A can be reduced.

[0202] In the dehumidification process, the dehumidification unit 90 may be controlled so that the moisture content C1 in the mixed gas G0 discharged from the dehumidification unit 90 is 5 vol% or less.

[0203] In the dehumidification process, the dehumidification unit 90 may be controlled so that the moisture content C1 in the mixed gas G0 discharged from the dehumidification unit 90 is 1 vol% or less.

[0204] The dehumidification process may be carried out based on the monitoring results from the moisture sensor 96.

[0205] (Other steps) The mixed gas separation method of this embodiment may further include a recovery step of recovering the first non-permeable gas G2 obtained in the first separation step into a recovery unit 81, and a recovery step of recovering the second permeable gas G3 obtained in the second separation step into a recovery unit 82.

[0206] The separation method of this embodiment may further include a mixing step of mixing the second impermeable gas G4 and the mixed gas G0. The mixing step can be carried out by sending the second impermeable gas G4 to the confluence point 61p of the mixed gas path 61 through the second impermeable gas path 65. The mixing step allows the second impermeable gas G4 to be reused and tends to improve the recovery rate of the first and second gases.

[0207] As described above, the mixed gas G0 includes a first gas and a second gas. Typically, the mixed gas G0 includes nitrogen as the first gas and carbon dioxide as the second gas. The mixed gas G0 is typically exhaust gas from a factory or power plant. However, the gas separation system 100A of this embodiment can also be used to separate mixed gas G0 with a composition other than that described above. For example, the first gas and the second gas may be one gas selected from nonpolar gases such as nitrogen, methane, oxygen, and hydrogen, inert gases such as helium, and acidic gases other than carbon dioxide. Examples of acidic gases other than carbon dioxide include hydrogen sulfide, carbonyl sulfide, and sulfur oxides (SO4). x ), hydrogen cyanide, nitrogen oxides (NO x ) are some examples.

[0208] According to the mixed gas separation method of this embodiment, for example, a second permeate gas G3 in which the second gas is concentrated and a first impermeate gas G2 in which the first gas is concentrated can be recovered. The recovery rate of the second gas (e.g., carbon dioxide) by this separation method is not particularly limited, but is, for example, 80 wt% or more, preferably 90 wt% or more. The recovery rate of the first gas is not particularly limited, but is, for example, 90 wt% or more, preferably 95 wt% or more. The second permeate gas G3 in which carbon dioxide is concentrated can be used, for example, in the production of dry ice. The first impermeate gas G2 in which nitrogen is concentrated can be used, for example, in industrial applications.

[0209] The gas separation system 100A and the method for separating mixed gases using the gas separation system 100A of this embodiment make it possible to achieve both a reduction in recovery power and a reduction in membrane area. The gas separation system 100A and the method for separating mixed gases using the gas separation system 100A of this embodiment are suitable for achieving both a reduction in recovery power and a reduction in membrane area.

[0210] <Modifications of the Gas Separation System> The gas separation system of this embodiment is not limited to the gas separation system 100A shown in Figure 1. Hereinafter, modifications 1 and 2 of the gas separation system of this embodiment will be described with reference to Figures 7 and 8. In the following, elements common to the gas separation system 100A described above will be given the same reference numerals, and detailed explanations will be omitted.

[0211] [Modified Gas Separation System 1] Figure 7 is a schematic diagram showing modified gas separation system 1 of this embodiment. The gas separation system 100B of modified gas separation system 1 shown in Figure 7 is equipped with a depressurization unit 32 that depressurizes the permeate space of the second separation membrane unit 20, instead of a pressurization unit 41 that pressurizes the supply space of the second separation membrane unit 20. Except for this, the gas separation system 100B of modified gas separation system 1 has basically the same configuration as the gas separation system 100A (Figure 1) described above. The gas separation system 100B also makes it possible to achieve both a reduction in recovery power and a reduction in membrane area.

[0212] The pressure reduction unit 32 can be the same as the pressure reduction unit 31 described above.

[0213] In the gas separation system 100B, a moisture sensor 96a, a dehumidification unit 90, a moisture sensor 96b, a blower 45, a first heat exchange unit 51, and a first temperature sensor 51a are arranged in the mixed gas path 61. A pressure reduction unit 31, a third heat exchange unit 53, a fourth heat exchange unit 54, a second heat exchange unit 52, and a second temperature sensor 52a are arranged in the first permeate gas path 62. A pressure reduction unit 32 is arranged in the second permeate gas path 64. However, the gas separation system 100B does not necessarily have to include a fourth heat exchange unit 54, a drain tank 87, and a drain path 77 connected to the drain tank 87.

[0214] The depressurization unit 32 can reduce the pressure in the permeation space of the second separation membrane unit 20 through the second permeation gas path 64. The depressurization unit 32 can, for example, suck in the second permeation gas G3 that has passed through the second permeation gas path 64 and discharge the second permeation gas G3 back into the second permeation gas path 64. The depressurization unit 32 is configured, for example, not to discharge the second permeation gas G3 that has passed through the second permeation gas path 64 to the outside of the gas separation system 100B. The depressurization unit 32 is connected only to the second permeation gas path 64. If the depressurization unit 32 is a collection of multiple pumps, the second permeation gas path 64 may branch and be connected to each of the inlets of the multiple pumps.

[0215] In the gas separation system 100B, the pressure in the permeate space of the second separation membrane unit 20 during operation is, for example, 70 kPa or less, preferably 50 kPa or less, more preferably 30 kPa or less, even more preferably 10 kPa or less, and particularly preferably 5 kPa or less. The upper limit of the pressure in the permeate space of the second separation membrane unit 20 may be 1 kPa, 2 kPa, or even 3 kPa.

[0216] In the gas separation system 100B, the content of the second gas in the mixed gas G0 may be 20 vol% or less. The content of the second gas in the mixed gas G0 may be 15 vol% or less, and even more so, 10 vol% or less. The lower limit of the content of the second gas in the mixed gas G0 is, for example, 5 vol%.

[0217] In the example shown in Figure 7, the gas separation system 100B includes a condenser 91 as the dehumidification unit 90. However, the gas separation system 100B may also include a vacuum device 92, a dehumidifier 93 equipped with a desiccant, an electrodialysis device 94 equipped with an ion exchange membrane, or a separation membrane device 95 equipped with a water vapor separation membrane as the dehumidification unit 90. For these modifications, the embodiments described with reference to Figures 2A to 2D can be applied.

[0218] In the gas separation system 100B, the pressure reduction unit 32 may be a vacuum pump that requires a sealing gas. When the pressure reduction unit 32 is a vacuum pump that requires a sealing gas, the embodiments described with reference to Figures 3A to 3B can be applied.

[0219] In the method for separating mixed gases using the gas separation system 100B, in the second separation step, the first permeate gas G1 is supplied to the second separation membrane unit 20 containing the second separation membrane 21, and the permeate space of the second separation membrane unit 20 is depressurized to separate the first permeate gas G1 into the second permeate gas G3 and the second non-permeate gas G4.

[0220] [Modified Gas Separation System 2] Figure 8 is a schematic diagram showing modified gas separation system 2 of this embodiment. The gas separation system 100C of modified gas separation system 2 shown in Figure 8 is equipped with a pressurizing unit 42 that increases the pressure of the supply space of the first separation membrane unit 10, instead of a blower 45 that sends the mixed gas G0 toward the supply space of the first separation membrane unit 10. The gas separation system 100C is not equipped with a depressurizing unit 31 that reduces the pressure of the permeate space of the first separation membrane unit 10. Except for these, the gas separation system 100C of modified gas separation system 2 has basically the same configuration as the gas separation system 100A (Figure 1) described above. The gas separation system 100C also makes it possible to achieve both a reduction in recovery power and a reduction in membrane area.

[0221] The pressurizing section 42 can be the same as the pressurizing section 41 described above.

[0222] The gas separation system 100C may further include a fifth heat exchange section 55. The fifth heat exchange section 55 adjusts the temperature of the mixed gas G0 discharged from the first heat exchange section 51. Similar to the first heat exchange section 51, the fifth heat exchange section 55 may be a gas-liquid heat exchanger.

[0223] As shown in Figure 8, a drain tank 88 may be placed between the first heat exchange unit 51 and the fifth heat exchange unit 55. A drain path 78 may be connected to the drain tank 88. If the mixed gas G0 processed by the first separation membrane unit 10 contains water (H2O), the mixed gas G0 containing water is supplied to the first heat exchange unit 51 and may be condensed by cooling by the first heat exchange unit 51. The drain tank 88 and drain path 78 allow the condensed water to be discharged to the outside.

[0224] In the gas separation system 100C, a moisture sensor 96a, a dehumidification unit 90, a moisture sensor 96b, a pressurization unit 42, a first heat exchange unit 51, a fifth heat exchange unit 55, and a first temperature sensor 51a are arranged in the mixed gas path 61. In the first permeate gas path 62, a third heat exchange unit 53, a pressurization unit 41, a fourth heat exchange unit 54, a second heat exchange unit 52, and a second temperature sensor 52a are arranged. However, the gas separation system 100C does not necessarily have to include a third heat exchange unit 53, a drain tank 86, and a drain path 76 connected to the drain tank 86.

[0225] The pressurizing unit 42 can increase the pressure in the supply space of the second separation membrane unit 20 through the second portion 61b of the mixed gas path 61. The pressurizing unit 42, for example, pumps the mixed gas G0 that has passed through the first portion 61a and discharges the mixed gas G0 to the second portion 61b. The pressurizing unit 42 is configured, for example, not to discharge the gas that has passed through the first portion 61a to the outside of the gas separation system 100A. The pressurizing unit 42 is connected, for example, only to the first portion 61a and the second portion 61b. If the pressurizing unit 42 is a collection of multiple pumps, the first portion 61a of the mixed gas path 61 may branch and be connected to each of the inlets of the multiple pumps. Similarly, the second portion 61b of the mixed gas path 61 may branch and be connected to each of the outlets of the multiple pumps.

[0226] In the gas separation system 100C, the pressure in the supply space of the first separation membrane unit 10 during operation is, for example, 101 kPa or more, preferably 150 kPa or more, more preferably 200 kPa or more, even more preferably 300 kPa or more, and particularly preferably 400 kPa or more. The upper limit of the pressure in the supply space of the first separation membrane unit 10 may be 1500 kPa, 1300 kPa, 1100 kPa, 1000 kPa, or even 900 kPa.

[0227] In the gas separation system 100C, the content of the second gas in the mixed gas G0 may be 20 vol% or more. The content of the second gas in the mixed gas G0 may be 25 vol% or more, and may be even 30 vol% or more. The upper limit of the content of the second gas in the mixed gas G0 is, for example, 70 vol%.

[0228] In the method for separating a mixed gas using the gas separation system 100C, in the first separation step, the mixed gas G0 is supplied to the first separation membrane unit 10 which houses the first separation membrane 11, and the supply space of the first separation membrane unit 10 is pressurized to separate the mixed gas G0 into a first permeate gas G1 and a first impermeable gas G2.

[0229] The above-described embodiments are mutually applicable, insofar as they do not conflict with technical standards. The above embodiments and their variations may be combined with each other, insofar as they do not conflict with technical standards. Furthermore, the components of the gas separation system and the steps of the mixed gas separation method described above may be substituted, added to, or combined with each other, insofar as they do not conflict with technical standards. For example, the components described in relation to the gas separation system may be used in embodiments of the mixed gas separation method, and the steps described in relation to the mixed gas separation method may be performed by the gas separation system. These combined forms are also included within the scope of the present invention.

[0230] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0231] (Calculation Examples 1-19) As calculation examples 1-19, simulations were performed when the gas separation system 100A shown in Figure 1 was operated using a cross-flow model. Specifically, it was assumed that the above-mentioned carbon dioxide permeable membranes were used as the first separation membrane 11 provided in the first separation membrane unit 10 and the second separation membrane 21 provided in the second separation membrane unit 20 in the gas separation system 100A. The temperature of the mixed gas G0 was set to 15°C, 20°C, 25°C, 30°C, 35°C, and 40°C, and the permeation rates of CO2 (GPU), N2 (GPU), O2 (GPU), and H2O (GPU) permeating through the first separation membrane 11 and the second separation membrane 21 in each case were set as shown in Table 1.

[0232]

[0233] The supply conditions for mixed gas G0 were set as follows: [Supply conditions for mixed gas] Composition (volume ratio): CO2 / N2 / O2 / H2O = 10 / 80 / 4 / 6 CO2 weight: 489 kg / hr Pressure: 101.33 kPa Temperature T1: 100°C

[0234] In the operation of the gas separation system 100A in calculation examples 1 to 19, it was assumed that the mixed gas G0 was sent to the supply space of the first separation membrane unit 10 at 120 kPa by the blower 45, the permeate space of the first separation membrane unit 10 was reduced to 3 kPa by the depressurization unit 31 (vacuum pump), and the supply space of the second separation membrane unit 20 was pressurized to 900 kPa by the pressurization unit 41 (compressor). In calculation examples 1 to 19, it was not assumed that the moisture content of the mixed gas G0 supplied to the first separation membrane unit 10 would be reduced by the dehumidification unit 90. The operating efficiency of the blower 45 was set to 60%, the operating efficiency of the depressurization unit 31 to 40%, and the operating efficiency of the pressurization unit 41 to 70%. The cooling energy efficiency (COP) was set to 3.

[0235] For calculation examples 1 to 19, assuming the following conditions are met, what is the carbon dioxide capture power (kWh / kg-CO2) and the required total membrane area (m²)? 2 The calculation was performed using Symmetry, a process modeling software from Schlumberger. The carbon dioxide recovery power is the energy required to operate the gas separation system per 1 kg of carbon dioxide contained in the second permeate gas G3. [Assumptions] The carbon dioxide content in the second permeate gas G3 discharged from the second separation membrane unit is 95 vol%. The carbon dioxide recovery rate by the gas separation system is 70 wt%. The amount of carbon dioxide recovered by the gas separation system is 3000 tons / year.

[0236] Table 2 shows the simulation results for calculation examples 1 to 19.

[0237]

[0238] As shown in Table 2, among Calculation Examples 1 to 19 assuming the gas separation system 100A shown in FIG. 1, Calculation Examples 1, 2, 6 to 8, 10 to 13, and 15 to 19 in which temperature T1 and temperature T2 satisfy T1≧T2 have a recovery power of 1.74 kWh / kg-CO2 or less and a total membrane area of 3302 m 2 or less, achieving both reduction in recovery power and reduction in membrane area.

[0239] (Calculation Examples 20 to 22) As Calculation Examples 20 to 22, simulations were performed when operating the gas separation system 100B shown in FIG. 7. The gas separation system 100B had the same configuration as the gas separation system 100A shown in FIG. 1, except that the permeation space of the second separation membrane unit 20 is depressurized by a pressure reducing unit 32. That is, the gas separation system 100B was not provided with a pressurizing unit that pressurizes the supply space of the second separation membrane unit 20. Specifically, in the gas separation system 100B, it was assumed that a carbon dioxide permeable membrane is used as the first separation membrane 11 provided in the first separation membrane unit 10 and the second separation membrane 21 provided in the second separation membrane unit 20, in the same manner as in Calculation Examples 1 to 19. The temperature of the mixed gas G0 was set to 15°C, 20°C, 25°C, 30°C, 35°C, and 40°C, and the permeation rates (GPU) of CO2, the permeation rates (GPU) of N2, the permeation rates (GPU) of O2, and the permeation rates (GPU) of H2O that permeate through the first separation membrane 11 and the second separation membrane 21 in each case were set as shown in Table 1. The supply conditions of the mixed gas G0 supplied to the first separation membrane unit 10 were the same as those in Calculation Examples 1 to 19.

[0240] In the operation of the gas separation system 100B of Calculation Examples 20 to 22, the mixed gas G0 is sent out at 120 kPa by the blower 45 toward the supply space of the first separation membrane unit 10, the permeation space of the first separation membrane unit 10 is depressurized to 3 kPa by the pressure reducing unit 31 (vacuum pump), and the permeation space of the second separation membrane unit 20 is depressurized to 3 kPa by the pressure reducing unit 32 (vacuum pump). The operation efficiency of the blower 45 was set to 60%, the operation efficiency of the pressure reducing unit 31 was set to 40%, and the operation efficiency of the pressurizing unit 41 was set to 70%. The cooling energy efficiency (COP) was set to 3.

[0241] For calculation examples 20 to 22, assuming the same assumptions as in calculation examples 1 to 19 are met, the carbon dioxide capture power (kWh / kg-CO2) and the required total membrane area (m²) are calculated. 2 The following calculations were performed. The simulation results for calculation examples 20 to 22 are shown in Table 3.

[0242]

[0243] As shown in Table 3, among calculation examples 20 to 22 assuming the gas separation system 100B shown in Figure 7, in calculation examples 20 to 21 where temperatures T1 and T2 satisfy T1 ≥ T2, the recovered power is 1.86 kWh / kg-CO2 or less, and the total membrane area is 4585 m². 2 The following results were achieved, allowing for both a reduction in recovery power and a reduction in film area.

[0244] (Calculation Examples 23-25) As calculation examples 23-25, simulations were performed when the gas separation system 100C shown in Figure 8 was in operation. The gas separation system 100C had the same configuration as the gas separation system 100A shown in Figure 1, except that the supply space of the first separation membrane unit 10 was pressurized by the pressurizing unit 42. That is, the gas separation system 100C did not have a blower 45 that sent the mixed gas G0 toward the supply space of the first separation membrane unit 10. In detail, in the gas separation system 100C, it was assumed that carbon dioxide permeable membranes were used as the first separation membrane 11 in the first separation membrane unit 10 and the second separation membrane 21 in the second separation membrane unit 20, as in calculation examples 1-19. The temperature of the mixed gas G0 was set to 15°C, 20°C, 25°C, 30°C, 35°C, and 40°C, and the permeation rates of CO2 (GPU), N2 (GPU), O2 (GPU), and H2O (GPU) permeating through the first separation membrane 11 and the second separation membrane 21 in each case were set as shown in Table 1. The supply conditions for the mixed gas G0 supplied to the first separation membrane unit 10 were the same as in calculation examples 1 to 19.

[0245] In the operation of the gas separation system 100C in calculation examples 23 to 25, it was assumed that the supply space of the first separation membrane unit 10 was pressurized to 900 kPa by the pressurizing unit 42 (compressor), and the supply space of the second separation membrane unit 20 was pressurized to 900 kPa by the pressurizing unit 41 (compressor). The operating efficiency of the pressurizing units 42 and 41 was set to 70%. The cooling energy efficiency (COP) was set to 3.

[0246] For calculation examples 23 to 25, assuming the same assumptions as in calculation examples 1 to 19 are met, the carbon dioxide capture power (kWh / kg-CO2) and the required total membrane area (m²) are calculated. 2 The calculations were performed. The simulation results for calculation examples 23 to 25 are shown in Table 4.

[0247]

[0248] As shown in Table 4, among calculation examples 23 to 25 assuming the gas separation system 100C shown in Figure 8, in calculation examples 23 to 24 where temperatures T1 and T2 satisfy T1 ≥ T2, the recovery power is 1.03 kWh / kg-CO2 or less, and the total membrane area is 1575 m². 2 The following results were achieved, allowing for both a reduction in recovery power and a reduction in film area.

[0249] (Calculation Examples 26-31) In calculation examples 26-31, it was assumed that the moisture content in the mixed gas G0 supplied to the first separation membrane unit 10 in the gas separation system 100A shown in Figure 1 is reduced by the dehumidification unit 90. Specifically, it was assumed that the moisture content C1 in the mixed gas G0 discharged from the dehumidification unit 90 is changed as shown in Table 5. Except for this, the simulation was performed when the gas separation system 100A shown in Figure 1 was operated as a cross-flow model under the same operating conditions as in calculation example 6.

[0250] For calculation examples 26 to 31, the carbon dioxide capture power (kWh / kg-CO2) was calculated assuming the same assumptions as in calculation examples 1 to 19.

[0251] Table 5 shows the simulation results for calculation examples 26 to 31, along with the simulation results for calculation example 6. Figure 9 is a graph showing the relationship between the moisture content (vol%) of the mixed gas G0 in calculation example 6 and the moisture content C1 (vol%) of the mixed gas G0 discharged from the dehumidification unit 90 and the recovered power (kWh / kg-CO2) in calculation examples 26 to 31.

[0252]

[0253] As shown in Table 5 and Figure 9, in calculation examples 26 to 31, which assume that the moisture content of the mixed gas G0 supplied to the first separation membrane unit 10 is reduced by the dehumidification unit 90 in the gas separation system 100A shown in Figure 1, the recovery power could be reduced compared to calculation example 6, which does not assume that the moisture content of the mixed gas G0 supplied to the first separation membrane unit 10 is reduced by the dehumidification unit 90. In calculation examples 28 to 31, where the moisture content C1 in the mixed gas G0 is 1 vol% or less, the recovery power could be reduced to 1.03 kWh / kg-CO2 or less.

[0254] In the above embodiment, a simulation was conducted in which the mixed gas G0 contains nitrogen as the first gas and carbon dioxide as the second gas. However, the mixed gas G0 is not limited to that used in the above embodiment.

[0255] The gas separation system of this embodiment is suitable for separating mixed gases, such as a mixed gas containing carbon dioxide and nitrogen. In particular, the gas separation system of this embodiment is suitable for efficiently recovering carbon dioxide from exhaust gases discharged from combustion equipment such as factories or power plants.

Claims

1. A gas separation system comprising: a first separation membrane unit containing a first separation membrane for separating a mixed gas into a first permeate gas and a first non-permeate gas; and a second separation membrane unit containing a second separation membrane for separating the first permeate gas into a second permeate gas and a second non-permeate gas, wherein the mixed gas includes a first gas and a second gas different from the first gas; the first and second separation membranes are capable of preferentially permeating the second gas; and when the temperature of the mixed gas supplied to the first separation membrane unit during operation is defined as T1, and the temperature of the first permeate gas supplied to the second separation membrane unit is defined as T2, the system is controlled so that temperatures T1 and T2 satisfy T1 ≥ T2.

2. The gas separation system according to claim 1, wherein the first separation membrane and the second separation membrane have the same configuration.

3. The gas separation system according to claim 1, further comprising: a depressurization unit for reducing the permeation space of the first separation membrane unit; and a pressurization unit for increasing the pressure of the supply space of the second separation membrane unit.

4. The gas separation system according to claim 1, further comprising: a first heat exchange unit for adjusting the temperature T1; and a second heat exchange unit for adjusting the temperature T2.

5. The gas separation system according to claim 4, further comprising: a first temperature sensor for measuring the temperature T1; and a second temperature sensor for measuring the temperature T2, wherein the first heat exchange unit and the second heat exchange unit are controlled based on the monitoring results from the first temperature sensor and the second temperature sensor so that the temperatures T1 and T2 satisfy T1 ≥ T2.

6. The gas separation system according to claim 1, wherein the content of the second gas in the mixed gas is 30 vol% or less.

7. The gas separation system according to claim 1, wherein the mixed gas contains nitrogen as the first gas and carbon dioxide as the second gas.

8. The gas separation system according to claim 1, wherein it is a continuous system.

9. The gas separation system according to claim 3, further comprising a first permeation gas path that guides the first permeation gas discharged from the first separation membrane unit to the second separation membrane unit, wherein the depressurization unit and the pressurization unit are arranged in the first permeation gas path.

10. The gas separation system according to claim 1, further comprising: a mixed gas path for guiding the mixed gas to the first separation membrane unit; and a second non-permeable gas path for guiding the second non-permeable gas discharged from the second separation membrane unit to the first separation membrane unit, wherein the second non-permeable gas path merges with the mixed gas path.

11. The gas separation system according to claim 1, further comprising a dehumidifier for reducing the moisture content in the mixed gas supplied to the first separation membrane unit.

12. The gas separation system according to claim 11, wherein, when the moisture content of the mixed gas discharged from the dehumidifier during operation is defined as C1, the dehumidifier is controlled so that the moisture content C1 is 5 vol% or less.

13. The gas separation system according to claim 12, wherein the dehumidification unit is controlled so that the moisture content C1 is 1 vol% or less.

14. The gas separation system according to claim 12, further comprising a moisture sensor, wherein when the moisture content in the mixed gas supplied to the dehumidifier during operation is defined as C0, the moisture sensor measures at least one selected from the group consisting of the moisture content C0 and the moisture content C1, and the dehumidifier is controlled based on the monitoring results from the moisture sensor.

15. The gas separation system according to claim 11, wherein the dehumidification unit includes at least one selected from the group consisting of a condenser, a vacuum device, a dehumidifier equipped with a desiccant, an electrodialysis device equipped with an ion exchange membrane, and a separation membrane device equipped with a water vapor separation membrane.

16. A method for separating a mixed gas, comprising: a first separation step of supplying a mixed gas to a first separation membrane unit containing a first separation membrane to separate the mixed gas into a first permeate gas and a first non-permeate gas; a second separation step of supplying the first permeate gas to a second separation membrane unit containing a second separation membrane to separate the first permeate gas into a second permeate gas and a second non-permeate gas; and a temperature control step of controlling the temperature T1 and the temperature T2 so that T1 ≥ T2, where T1 is defined as the temperature of the mixed gas supplied to the first separation membrane unit in the first separation step and T2 is defined as the temperature of the first permeate gas supplied to the second separation membrane unit in the second separation step, wherein the mixed gas comprises a first gas and a second gas different from the first gas, and the first separation membrane and the second separation membrane are capable of preferentially permeating the second gas.

17. The method for separating a mixed gas according to claim 16, further comprising a dehumidification step of reducing the moisture content in the mixed gas supplied to the first separation membrane unit.

Images