Gas separation system and gas separation method

Abstract

Provided are a gas separation system and a gas separation method with which it is possible to improve content ratio of a first gas in a recovery gas and improve recovery rate of the first gas with a simple configuration. The gas separation system according to one embodiment includes first to third separation units each equipped with a separation membrane, a permeate gas recovery unit, a return unit, a non-permeate gas recovery unit, and a permeate gas supply unit. The permeate gas recovery unit recovers a recovery gas containing a first permeate gas that has permeated a first separation membrane. The return unit returns, to a mixed gas supply unit, a return gas containing a third permeate gas that has permeated a third separation membrane. The permeable gas supply unit can be switched between at least two modes among a recovery mode, a return mode, and a stop mode. In the recovery mode, a second permeate gas that has permeated a second separation membrane is combined with a recovery gas. In the return mode, the second permeate gas is combined with the return gas. In the stop mode, supply of the second permeable gas to the permeable gas recovery unit and the return unit is stopped.

Description

Gas separation system and gas separation method

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

[0002] Conventionally, gas separation methods are known that use a separation membrane to separate specific gas components from a mixed gas containing multiple gas components. In gas separation methods, it is desirable to separate desired gas components from a mixed gas at high concentration and high yield. For example, a gas separation method has been proposed that includes a raw material flow separation step in which the raw material flow as a mixed gas is separated into a first permeate flow and a first concentrated flow by a separation membrane, a concentrated material separation step in which the first concentrated flow is separated into a second permeate flow and a second concentrated flow by a separation membrane, and a return step in which the second permeate flow is returned to the raw material flow (see Patent Document 1). In such a gas separation method, the concentration of specific gas components is improved in both the first permeate flow and the second concentrated flow by returning the second permeate flow to the raw material flow. Furthermore, a gas separation apparatus has been proposed in which supply gas channels and non-permeable gas channels are connected to all separation membrane modules, and the number of separation membrane modules constituting the first and second separation membrane units can be adjusted by opening and closing valves provided in the supply gas channels between separation membrane modules and valves provided in the non-permeable gas channels between separation membrane modules (see Patent Document 2). In such a gas separation apparatus, the number of separation membrane modules in the first and second separation membrane units can be adjusted according to the demand for the composition and quantity of raw materials and the quality and quantity of the product gas.

[0003] Japanese Patent Publication No. 2013-534863, Japanese Patent Publication No. 2013-017939

[0004] However, in the gas separation method described in Patent Document 1, the composition of the raw material flow used in the raw material flow separation process may fluctuate over time. In this case, the optimal area ratio between the separation membrane used in the raw material flow separation process and the separation membrane used in the concentrate separation process changes, which may cause a decrease in the concentration of a specific gas component and / or the recovery rate of a specific gas component in the first permeate flow (recovered gas). Furthermore, in the gas separation apparatus described in Patent Document 2, the area ratio between the first separation membrane unit (for example, the separation membrane used in the raw material flow separation process) and the second separation membrane unit (for example, the separation membrane used in the concentrate separation process) can be adjusted. However, since the separation membranes are arranged in parallel in both the first and second separation membrane units, the concentration polarization caused by the reduced flow velocity of the gas supplied to each separation membrane may cause a decrease in the concentration of a specific gas component and / or the recovery rate of a specific gas component in the recovered gas. In addition, the large number of valves required for the entire apparatus may make operation complicated and increase component costs. The main objective of the present invention is to provide a gas separation system and a gas separation method that can improve the content ratio of the first gas in the recovered gas and the recovery rate of the first gas with a simple configuration.

[0005] [1] A gas separation system according to one embodiment of the present invention comprises a first separation unit, a second separation unit, a third separation unit, a mixed gas supply unit, a permeate gas recovery unit, a return unit, a non-permeate gas recovery unit, and a permeate gas supply unit. The first separation unit is supplied with a mixed gas containing a first gas and a second gas. The first separation unit is equipped with a first separation membrane permeable to the first gas. The second separation unit is supplied with a first non-permeate gas that has passed through the first separation unit without permeating the first separation membrane. The second separation unit is equipped with a second separation membrane permeable to the first gas. The third separation unit is supplied with a second non-permeate gas that has passed through the second separation unit without permeating the second separation membrane. The third separation unit is equipped with a third separation membrane permeable to the first gas. The mixed gas supply unit is configured to supply the mixed gas to the first separation unit. The permeate gas recovery unit is configured to recover a recovered gas containing the first permeate gas that has permeated through the first separation membrane. The return unit is configured to return the return gas containing the third permeate gas that has permeated through the third separation membrane to the mixed gas supply unit for integration with the mixed gas. The non-permeate gas recovery unit is configured to recover the third non-permeate gas that has passed through the third separation unit without permeating through the third separation membrane. The permeate gas supply unit is switchable to at least two of the following modes: recovery mode, return mode, and stop mode. In recovery mode, the permeate gas supply unit supplies the second permeate gas that has permeated through the second separation membrane to the permeate gas recovery unit for integration with the recovered gas. In return mode, the permeate gas supply unit supplies the second permeate gas to the return unit for integration with the return gas. In stop mode, the permeate gas supply unit stops supplying the second permeate gas to the permeate gas recovery unit and the return unit. [2] In the gas separation system described in [1] above, the permeate gas supply unit may be switchable between the recovery mode, the return mode, and the stop mode. [3] In the gas separation system described in [1] or [2] above, the first separation unit may comprise a plurality of first separation membranes. The third separation unit may comprise a plurality of third separation membranes. In this case, the permeate gas recovery unit is configured to recover the first permeate gas that has permeated through the plurality of first separation membranes in one go.The return unit is configured to return the third permeate gas that has permeated through the plurality of third separation membranes to the mixed gas supply unit in one unit. [4] In the gas separation system according to any one of [1] to [3] above, the second separation unit may be provided with a plurality of second separation membranes. In this case, the permeate gas supply unit may be provided in a plurality corresponding to the plurality of second separation membranes. [5] The gas separation system according to any one of [1] to [4] above may further be provided with a gas measuring instrument. The gas measuring instrument is capable of measuring the flow rate and / or composition of at least one of the gases among the mixed gas supplied to the first separation unit by the mixed gas supply unit, the recovered gas recovered in the permeate gas recovery unit, the returned gas returned to the mixed gas supply unit in the return unit, and the third non-permeate gas recovered in the non-permeate gas recovery unit. The permeate gas supply unit is configured to select one of the recovery mode, the return mode, and the stop mode according to the measurement result of the gas measuring instrument. [6] A gas separation method according to another aspect of the present invention includes a first supply step, a second supply step, a third supply step, a permeate gas recovery step, a return step, a non-permeate gas recovery step, and a mode selection step. In the first supply step, a mixed gas containing a first gas and a second gas is supplied to a first separation unit equipped with a first separation membrane permeable to the first gas. In the second supply step, the first non-permeate gas that has passed through the first separation unit without permeating the first separation membrane is supplied to a second separation unit equipped with a second separation membrane permeable to the first gas. In the third supply step, the second non-permeate gas that has passed through the second separation unit without permeating the second separation membrane is supplied to a third separation unit equipped with a third separation membrane permeable to the first gas. In the permeate gas recovery step, a recovered gas containing the first permeate gas that has permeated the first separation membrane is recovered. In the return process, the return gas containing the third permeate gas that has permeated through the third separation membrane is merged with the mixed gas. In the non-permeate gas recovery process, the third non-permeate gas that has passed through the third separation section without permeating through the third separation membrane is recovered. In the mode selection process, one of the recovery mode, return mode, or stop mode is selected. In the recovery mode, the second permeate gas that has permeated through the second separation membrane is merged with the recovered gas. In the return mode, the second permeate gas is merged with the return gas.In the stop mode, the confluence of the second permeate gas with the recovered gas and the return gas is stopped. [7] The gas separation method described in [6] above may further include a measurement step. In the measurement step, the flow rate and / or composition of at least one of the mixed gas, the recovered gas, the return gas, and the third non-permeate gas is measured. In this case, in the mode selection step, one of the recovery mode, the return mode, and the stop mode is selected according to the measurement results obtained in the measurement step.

[0006] According to embodiments of the present invention, it is possible to improve the content ratio of the first gas in the recovered gas and the recovery rate of the first gas.

[0007] Figure 1 is a schematic diagram of a gas separation system according to one embodiment of the present invention. Figure 2 is a schematic diagram of a gas separation system according to another embodiment of the present invention. Figure 3 is a schematic diagram of a gas separation system according to yet another embodiment of the present invention. Figure 4 is a perspective view of the first separation membrane composite comprising the gas separation system of Figure 1. Figure 5 is a schematic cross-sectional view of the first separation membrane composite of Figure 4. Figure 6 is a partially enlarged view of the separation membrane composite of Figure 5.

[0008] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Furthermore, in order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments; however, these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overview of the gas separation system: Figure 1 is a schematic diagram of a gas separation system according to one embodiment of the present invention; Figure 2 is a schematic diagram of a gas separation system according to another embodiment of the present invention.

[0010] As shown in Figure 1, in one embodiment, the gas separation system 100 includes a first separation unit 1, a second separation unit 2, a third separation unit 3, a mixed gas supply unit 4, a permeate gas recovery unit 5, a return unit 6, a permeate gas supply unit 7, and a non-permeate gas recovery unit 8. The first separation unit 1 is supplied with a mixed gas containing a first gas and a second gas. The first separation unit 1 is equipped with a first separation membrane 12 that is permeable to the first gas. The second separation unit 2 is supplied with a first non-permeable gas that has passed through the first separation unit 1 without permeating the first separation membrane 12. The second separation unit 2 is equipped with a second separation membrane 22 that is permeable to the first gas. The third separation unit 3 is supplied with a second non-permeable gas that has passed through the second separation unit 2 without permeating the second separation membrane 22. The third separation unit 3 is equipped with a third separation membrane 32 that is permeable to the first gas. The mixed gas supply unit 4 is configured to supply the mixed gas to the first separation unit 1. The permeate gas recovery unit 5 is configured to recover the recovered gas, which includes the first permeate gas that has permeated through the first separation membrane 12. The return unit 6 is configured to return the return gas, which includes the third permeate gas that has permeated through the third separation membrane 32, to the mixed gas supply unit 4 and combine it with the mixed gas. The non-permeate gas recovery unit 8 is configured to recover the third non-permeate gas that has passed through the third separation unit 3 without permeating through the third separation membrane 32. The permeate gas supply unit 7 is switchable to at least two of the following modes: recovery mode, return mode, and stop mode. In other words, the permeate gas supply unit 7 may be switchable to recovery mode and return mode, or to recovery mode and stop mode, or to return mode and stop mode, or to recovery mode, return mode, and stop mode. In recovery mode, the permeate gas supply unit 7 supplies the second permeate gas that has permeated through the second separation membrane 22 to the permeate gas recovery unit 5 and combines it with the recovered gas. In return mode, the permeate gas supply unit 7 supplies the second permeate gas to the return unit 6 and merges it with the return gas. In stop mode, the permeate gas supply unit 7 stops supplying the second permeate gas to the permeate gas recovery unit 5 and the return unit 6.With this configuration, the permeate gas supply unit can be switched to at least two of the recovery mode, return mode, and stop mode, so that the area ratio of the separation membrane used for collecting the recovered gas and the separation membrane used for collecting the return gas can be adjusted in a balanced manner according to the composition of the mixed gas supplied by the mixed gas supply unit to the first separation unit. More specifically, in recovery mode, the permeate gas supply unit supplies the second permeate gas to the permeate gas recovery unit and merges it with the recovered gas. Therefore, in recovery mode, the first and second separation membranes are used for collecting the recovered gas, and the third separation membrane is used for collecting the return gas. In return mode, the permeate gas supply unit supplies the second permeate gas to the return unit and merges it with the return gas. Therefore, in return mode, the first separation membrane is used for collecting the recovered gas, and the second and third separation membranes are used for collecting the return gas. Furthermore, in stop mode, the permeate gas supply unit stops supplying the second permeate gas to the permeate gas recovery unit and the return unit. Therefore, in stop mode, the first separation membrane is used for collecting the recovered gas, the third separation membrane is used for collecting the return gas, and the second separation membrane is not used for collecting either the recovered gas or the return gas. Thus, even if the composition of the mixed gas supplied to the first separation unit fluctuates, by appropriately switching the mode of the permeate gas supply unit, it is possible to improve the proportion of the first gas in the recovered gas and the recovery rate of the first gas as a whole gas separation system. The recovery rate of the first gas is the ratio of the amount of first gas contained in the recovered gas to the amount of first gas contained in the mixed gas per unit time (i.e., the amount of first gas contained in the mixed gas minus the amount of first gas contained in the third non-permeate gas). Furthermore, even if the performance of the first, second, and third separation membranes (e.g., gas permeability and selectivity) changes, the recovered gas containing a sufficient amount of the first gas can be efficiently recovered by appropriately switching the mode of the permeate gas supply unit. Note that the mode of the permeate gas supply unit may also be switched to efficiently recover the third non-permeate gas containing a sufficient amount of the second gas.

[0011] In one embodiment, the permeate gas supply unit 7 is switchable between recovery mode, return mode, and stop mode. Therefore, even if the composition of the mixed gas fluctuates, the area ratio of the separation membrane used for collecting the recovered gas and the separation membrane used for collecting the return gas can be precisely adjusted. As a result, the content ratio of the first gas in the recovered gas and the recovery rate of the first gas can be stably improved.

[0012] The first separation unit 1 typically includes a flow path 15 through which the mixed gas passes (see Figure 5). In one embodiment, the first separation membrane 12 provided in the first separation unit 1 faces the flow path 15. The number of first separation membranes 12 is 1 or more, preferably 2 or more, and more preferably 4 or more. On the other hand, the number of first separation membranes 12 is, for example, 10,000 or less, and preferably 5,000 or less. When the number of first separation membranes is within this range, the first gas can be stably separated from the mixed gas.

[0013] In one embodiment, the first separation unit 1 includes a plurality of first separation membranes 12. When the first separation unit 1 includes a plurality of first separation membranes 12, the permeate gas recovery unit 5 may be configured to recover the first permeate gas that has permeated through the plurality of first separation membranes 12 all at once, and may be provided in multiple units corresponding to the plurality of first separation membranes 12.

[0014] In one embodiment, the permeate gas recovery unit 5 is configured to recover the first permeate gas that has permeated through multiple first separation membranes 12 all at once. This allows for efficient recovery of the first permeate gas with a simple configuration.

[0015] The second separation section 2 typically includes a flow path 15 through which the first non-permeable gas passes (see Figure 5). In one embodiment, the second separation membrane 22 provided in the second separation section 2 faces the flow path 15. The number of second separation membranes 22 is, for example, 0.1 to 10 times, preferably 0.3 to 3 times, the number of first separation membranes 12. The number of second separation membranes 22 is, for example, 0.1 to 10 times, preferably 0.3 to 3 times, the number of third separation membranes 32. The number of second separation membranes 22 is 1 or more, preferably 2 or more, and more preferably 4 or more. On the other hand, the number of second separation membranes 22 is, for example, 10,000 or less, preferably 5,000 or less. When the number of second separation membranes is within this range, the area ratio of the separation membrane used for collecting the recovered gas and the separation membrane used for collecting the return gas can be adjusted more precisely according to the composition of the mixed gas.

[0016] As shown in Figure 2, in one embodiment, the second separation unit 2 is equipped with a plurality of second separation membranes 22. When the second separation unit 2 is equipped with a plurality of second separation membranes 22, the permeate gas supply unit 7 may be configured to supply the second permeate gas that has permeated through the plurality of second separation membranes 22 to the permeate gas recovery unit 5 or the return unit 6 all at once, and there may be multiple units provided corresponding to the plurality of second separation membranes 22.

[0017] In the illustrated example, multiple permeate gas supply units 7 are provided, corresponding to multiple second separation membranes 22. Each of the multiple permeate gas supply units 7 is configured to individually supply the second permeate gas that has permeated through the corresponding second separation membrane 22 to the permeate gas recovery unit 5 or the return unit 6. With this configuration, the modes of the multiple permeate gas supply units can be switched individually, so the area ratio of the separation membrane used for collecting the recovered gas and the separation membrane used for collecting the return gas can be precisely adjusted. As a result, the content ratio of the first gas in the recovered gas and the recovery rate of the first gas can be improved more stably.

[0018] The third separation section 3 typically includes a flow path 15 through which the second non-permeable gas passes (see Figure 5). In one embodiment, the third separation membrane 32 provided in the third separation section 3 faces the flow path 15. The number of third separation membranes 32 is 1 or more, preferably 2 or more, and more preferably 4 or more. On the other hand, the number of third separation membranes 32 is, for example, 10,000 or less, and preferably 5,000 or less. When the number of third separation membranes is within this range, the third permeable gas can be stably returned to the return section. Therefore, the recovery rate of the first gas can be sufficiently improved.

[0019] As shown in Figure 1, in one embodiment, the third separation unit 3 includes a plurality of third separation membranes 32. When the third separation unit 3 includes a plurality of third separation membranes 32, the return unit 6 may be configured to return the third permeate gas that has permeated through the plurality of third separation membranes 32 to the mixed gas supply unit 4 in one unit, and there may be multiple return units corresponding to the plurality of third separation membranes 32.

[0020] In one embodiment, the return unit 6 is configured to return the third permeate gas that has permeated through multiple third separation membranes 32 to the mixed gas supply unit 4 in one go. This allows for efficient return of the third permeate gas with a simple configuration.

[0021] In one embodiment, the gas separation system 100 further includes a gas measuring instrument 9. The gas measuring instrument 9 is capable of measuring the flow rate and / or composition of at least one of the following gases: the mixed gas supplied to the first separation unit 1 by the mixed gas supply unit 4, the recovered gas recovered in the permeate gas recovery unit 5, the returned gas returned to the mixed gas supply unit 4 in the return unit 6, and the third non-permeate gas recovered in the non-permeate gas recovery unit 8. The permeate gas supply unit 7 is configured to select one of the above recovery mode, return mode, or stop mode according to the measurement result of the gas measuring instrument 9. With this configuration, the mode of the permeate gas supply unit can be switched based on the flow rate and / or composition of one or more of the mixed gas, recovered gas, returned gas, and third non-permeate gas. Therefore, the area ratio of the separation membrane used for collecting the recovered gas and the separation membrane used for collecting the returned gas can be appropriately adjusted according to the flow rate and / or composition of those gases.

[0022] In one embodiment, the gas separation system 100 further includes a control unit 10. Typically, the control unit 10 is communicatively connected to the gas measuring instrument 9 and the permeate gas supply unit 7. In the illustrated example, the control unit 10 is configured to calculate the mode of the permeate gas supply unit 7 based on the measurement results received from the gas measuring instrument 9. Based on the calculation results, the control unit 10 can control the mode switching of the permeate gas supply unit 7.

[0023] B. Details of the Gas Separation System Next, the details of the gas separation system 100 will be described with reference to Figures 1 to 6. As shown in Figure 1, the gas separation system 100 includes a first separation unit 1, a second separation unit 2, a third separation unit 3, a mixed gas supply unit 4, a permeate gas recovery unit 5, a return unit 6, a permeate gas supply unit 7, a non-permeate gas recovery unit 8, a gas measuring instrument 9, and a control unit 10.

[0024] B-1. First Separation Unit The first separation unit 1 is configured to separate a raw material gas containing a first gas and a second gas into a first permeate gas and a first impermeate gas. As described above, the first separation unit 1 includes at least one first separation membrane 12. The first separation membrane 12 has any suitable configuration.

[0025] In one embodiment, the first separation unit 1 includes a first separation membrane composite 11 containing a first separation membrane 12, a first housing (not shown) that houses the first separation membrane composite 11, and a sealing member (not shown). As shown in Figure 4, the first separation membrane composite 11 typically has a columnar shape extending in a predetermined direction. As shown in Figure 5, the first separation membrane composite 11 has a first end face E1, a second end face E2, and a side surface S. The first end face E1 and the second end face E2 are end faces in the axial direction of the first separation membrane composite 11 and are located apart from each other in a predetermined direction. The side surface S is located between the first end face E1 and the second end face E2. The axial dimension of the first separation membrane composite 11 is, for example, 0.1 m to 10 m, preferably 0.5 m to 2 m.

[0026] The first separation membrane composite 11 typically comprises a support 13 and a first separation membrane 12. The support 13 has a columnar shape with one or more through-holes. Examples of the overall shape of the support 13 include a cylindrical shape with a circular base, an elliptical columnar shape with an elliptical base, a prismatic columnar shape with a polygonal base, and a columnar shape with an irregular base. The outer diameter of the support 13 can be appropriately set depending on the purpose. In one embodiment, the support 13 has a monolithic shape with multiple through-holes 13a. The monolithic shape refers to a columnar shape with multiple through-holes, and is a concept that includes a honeycomb shape in which each of the multiple through-holes is defined by a cell.

[0027] Each of the multiple through-holes 13a extends in the axial direction of the support 13 from the first end face E1 (inlet end face) to the second end face E2 (outlet end face) of the first separation membrane composite 11. The axial direction of the support 13 and the direction in which the through-holes 13a extend are typically substantially parallel.

[0028] Each of the multiple through-holes 13a has an arbitrary appropriate shape in a cross-section perpendicular to the axial direction of the support 13. Examples of cross-sectional shapes of the through-holes 13a include triangles, quadrilaterals, pentagons, polygons with hexagons or more, circles, and ellipses. Among these cross-sectional shapes of the through-holes 13a, circular and elliptical shapes are preferred, and circular shapes are more preferred.

[0029] The cross-sectional shape and size of the through-holes 13a may all be the same, or at least some may differ. If the cross-sectional shape of the through-hole 13a is circular, the inner diameter of the through-hole 13a is, for example, 1 mm to 20 mm. The distance between the centers of adjacent through-holes 13a is, for example, 1.1 mm to 50 mm. The distance between the centers of adjacent through-holes is measured, for example, as the length of the line segment connecting the centers of adjacent through-holes in a cross-section perpendicular to the axial direction of the support.

[0030] The support 13 typically has a porous structure that allows fluid to permeate. More specifically, the support 13 comprises a three-dimensional, continuous mesh-like framework and interconnected pores partitioned by the framework. The framework of the support 13 is made of any suitable material. Typical materials for the support include ceramic materials. Examples of ceramic materials include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide, and cordierite. Ceramic materials can be used alone or in combination. Among ceramic materials, alumina is preferred.

[0031] The support 13 may consist of a single layer or have a multilayer structure in which multiple layers are stacked. As shown in Figure 6, in one embodiment, the support 13 has a multilayer structure having multiple layers with different pore sizes. In this case, it is preferable that the pore size is smaller closer to the first separation membrane 12.

[0032] Regarding the distribution of pore sizes throughout the support 13, including its surface and interior, D5 is, for example, 0.01 μm to 50 μm, D50 is, for example, 0.05 μm to 70 μm, and D95 ​​is, for example, 0.1 μm to 2000 μm. D50 is preferably 0.05 μm to 25 μm. The average pore size of the support 13 on the first separation membrane 12 side is 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. The porosity of the support 13 on the first separation membrane 12 side is, for example, 15% to 70%. The average pore size of the support is measured, for example, by a mercury porosimeter, palm porometer, or nanopalm porometer.

[0033] Such a support 13 is prepared by any suitable method. In one embodiment, first, the raw material powder containing the ceramic material described above is molded into a desired shape by any suitable molding method (e.g., vacuum extrusion). This typically yields an unfired molded body having a monolithic shape. Next, the unfired molded body is fired by any suitable method. The firing temperature is, for example, 900°C to 1800°C, preferably 1200°C to 1500°C. The firing time is, for example, 1 hour to 100 hours.

[0034] Typically, sealing portions (not shown) are provided at both ends of the support 13 in the longitudinal direction (axial direction). The sealing portions are attached to both ends of the support 13 in the longitudinal direction and are members that cover and seal the longitudinal end faces of the support 13 and the outer peripheral surfaces near those end faces. The sealing portions suppress the inflow and outflow of fluid from the end faces of the support 13. The sealing portions are, for example, plate-shaped members made of glass or resin. The material and shape of the sealing portions may be changed as appropriate. Since the sealing portions are provided with multiple openings that overlap with the multiple through-holes 13a of the support 13, the longitudinal ends of each through-hole 13a of the support 13 are not covered by the sealing portions. Therefore, it is possible for fluid to flow in and out of the through-holes 13a from both ends. In this way, a support 13 having a monolithic shape is prepared.

[0035] As shown in Figure 5, the first separation membrane 12 is typically provided on the surface of the support 13. In one embodiment, the first separation membrane 12 is provided on the inner surface of each of the multiple through-holes 13a in the support 13. In the illustrated example, a flow path 15 is formed inside the through-hole 13a. More specifically, in a cross-section perpendicular to the axial direction of the support 13, the flow path 15 is formed in the portion of the through-hole 13a where the first separation membrane 12 is not formed (typically the central portion). The first separation membrane 12 may be formed over the entire inner surface of the through-hole 13a (i.e., surrounding the flow path 15), as in the illustrated example, or it may be formed on a part of the inner surface of the through-hole 13a. When the separation membrane is formed to surround the flow path, the fluid passing through the flow path can be efficiently brought into contact with the separation membrane, thereby improving the separation efficiency of the desired gas components.

[0036] The first separation membrane 12 typically has micropores. The first separation membrane 12 separates specific components from a mixture by permeating them, for example, by utilizing differences in molecular size and / or differences in adsorption properties.

[0037] The first separation membrane 12 is composed of any suitable material. Examples of materials for the first separation membrane 12 include zeolite, alumina, titania, silica, zirconia, carbon, metal-organic frameworks (MOFs), and organic polymers such as silicone and polyimide. The materials for the first separation membrane 12 can be used individually or in combination.

[0038] The average pore size of the first separation membrane 12 can be arbitrarily and appropriately selected depending on the material to be separated. The average pore size of the first separation membrane 12 is, for example, 0.2 nm to 1 nm, preferably 0.3 nm to 0.8 nm. By setting the average pore size of the first separation membrane 12 within this range, selectivity can be increased. The average pore size of the first separation membrane 12 is smaller than the average pore size of the support 13.

[0039] In one embodiment, the first separation membrane 12 is a zeolite membrane 12a. The zeolite membrane 12a is prepared by forming zeolite in a film shape on the surface of a support 13. The zeolite membrane 12a may contain a single zeolite or may contain two or more types of zeolites having different structures and / or compositions.

[0040] When the first separation membrane 12 is a zeolite membrane 12a, taking the maximum ring number of the zeolite constituting the zeolite membrane 12a as n, the arithmetic mean of the short diameter and the long diameter of the n-member ring pores is defined as the average pore diameter. The n-member ring pores are pores in which the number of oxygen atoms forming a cyclic structure by bonding with T atoms (to be described later) is n. When there are a plurality of n-member ring pores with the same n, the arithmetic mean of the short diameter and the long diameter of all the n-member ring pores is defined as the average pore diameter of the zeolite. The average pore diameter of the zeolite membrane is determined by the framework structure of the zeolite. For example, it can be obtained from the values disclosed in the "Database of Zeolite Structures" [online] of the International Zeolite Association, Internet <URL: http: / / www.iza-structure.org / databases / >.

[0041] Examples of the zeolite constituting the zeolite membrane 12a include zeolites in which the atom (T atom) located at the center of the oxygen tetrahedron (TO ４ ) is only Si or consists of Si and Al; AlPO-type zeolites in which the T atom consists of Al and P; SAPO-type zeolites in which the T atom consists of Si, Al, and P; MAPSO-type zeolites in which the T atom consists of magnesium (Mg), Si, Al, and P; and ZnAPSO-type zeolites in which the T atom consists of zinc (Zn), Si, Al, and P. A part of the T atom may be substituted with another element.

[0042] The maximum ring number of the zeolite is, for example, 12 or less, preferably 10 or less, more preferably 8 or less. On the other hand, the lower limit of the maximum ring number of the zeolite is typically 6.

[0043] Examples of the zeolite include zeolites of AEI type, AEN type, AFN type, AFV type, AFX type, BEA type, CHA type, DDR type, ERI type, ETL type, FAU type (X type, Y type), GIS type, LEV type, LTA type, MEL type, MFI type, MOR type, PAU type, RHO type, SAT type, and SOD type. When the zeolite is an 8-member ring zeolite, examples thereof include zeolites of AEI type, AFN type, AFV type, AFX type, CHA type, DDR type, ERI type, ETL type, GIS type, IHW type, LEV type, LTA type, LTJ type, RHO type, SAT type, etc.

[0044] When the zeolite membrane 12a contains Si and Al, the zeolite membrane 12a may further contain an alkali metal. Examples of the alkali metal include sodium (Na) and potassium (K).

[0045] The molar ratio of Si / Al in the zeolite membrane 12a is, for example, 1 or more and 100,000 or less, preferably 1 or more and 1000 or less. When the molar ratio of Si / Al in the zeolite membrane 12a is within such a range, breakage of the zeolite membrane 12a can be stably suppressed. The molar ratio of Si / Al is measured, for example, by scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX; X-ray acceleration voltage 10 kV).

[0046] The thickness of the first separation membrane 12 is, for example, 0.05 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.5 μm to 10 μm. When the thickness of the first separation membrane 12 is within such a range, selectivity and permeation rate can be adjusted in a well-balanced manner.

[0047] The surface roughness (Ra) of the first separation membrane 12 is, for example, 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less. The surface roughness (Ra) is measured, for example, in accordance with JIS B 0601.

[0048] The first separation membrane 12 is formed by any suitable method depending on the material constituting the membrane. For example, a zeolite membrane 12a is obtained by coating a zeolite as a seed crystal onto a support 13, immersing the support 13 with the attached seed crystal in a raw material solution, and growing the zeolite using the seed crystal as a nucleus by hydrothermal synthesis. The raw material solution includes, for example, a silica source, an alumina source, organic matter, an alkali source, and water. The heating temperature in hydrothermal synthesis is, for example, 60°C to 200°C. The heating time is, for example, 1 hour to 240 hours. If the first separation membrane 12 is not a zeolite membrane, the first separation membrane 12 can be formed by known methods. For example, a separation membrane can also be formed using a raw material slurry obtained by mixing an organic binder, a ceramic raw material, and a solvent.

[0049] The range of the number of first separation membrane complexes 11 provided in the first separation unit 1 is the same as the range of the number of first separation membranes 12 described above. The first separation membrane complex 11 may have one first separation membrane 12 or may have multiple first separation membranes 12.

[0050] The first housing contains the first separation membrane composite 11 described above. In one embodiment, the first housing is a substantially cylindrical tubular member. The longitudinal direction of the first housing is substantially parallel to the longitudinal direction of the first separation membrane composite 11. Ports are provided at both ends in the longitudinal direction and on the sides of the first housing. A mixed gas supply line 41 and a first non-permeable gas supply line 16, described later, are connected to the ports at the longitudinal ends of the first housing. A first recovery line 51, described later, is connected to the ports on the sides of the first housing. The first housing is made of any suitable metal. Examples of metals that make up the first housing include stainless steel and carbon steel. Each member of the first housing may be made of the same metal or different metals. Depending on the shape of the first separation membrane composite 11, the shape of the first housing and the connection positions of the various lines (i.e., the positions of each port), etc., may be appropriately changed. The first housing may contain one first separation membrane composite 11 or multiple first separation membrane composites 11.

[0051] In one embodiment, the sealing member is arranged longitudinally between the side surface S of the first separation membrane composite 11 and the inner surface of the first housing. The sealing member is a substantially annular member formed of a material that is impermeable to fluids. The sealing member is in close contact with the side surface S of the first separation membrane composite 11 and the inner surface of the first housing over the entire circumference in the circumferential direction around the central axis of the first separation membrane composite 11. The sealing member is, for example, an O-ring or packing formed of a flexible resin such as rubber. The material of the sealing member may be carbon, metal, or other inorganic material other than resin.

[0052] In one embodiment, the first separation unit 1 comprises a plurality of first housings. Each of the plurality of first housings houses one or more first separation membrane composites 11. The plurality of first housings housing the first separation membrane composites 11 may be arranged in series as shown in Figure 1, or in parallel as shown in Figure 3.

[0053] As shown in Figure 1, when a plurality of first housings containing the first separation membrane complex 11 are arranged in series, the first separation unit 1 further includes a first connection line 14. The first connection line 14 connects adjacent first housings among the plurality of first housings containing the first separation membrane complex 11. In the following, among the adjacent first housings, the first housing located on the mixed gas supply unit side may be referred to as the upstream first housing, and the first housing located on the second separation unit side may be referred to as the downstream first housing. The first connection line 14 is typically a pipe through which fluid can pass. The upstream end of the first connection line 14 in the direction of fluid passage is connected to the end on the second end face side of the first separation membrane complex 11 in the upstream first housing. The downstream end of the first connection line 14 in the direction of fluid passage is connected to the end on the first end face side of the first separation membrane complex 11 in the downstream first housing.

[0054] In the illustrated example, the first separation unit 1 is connected to the second separation unit 2 via a first impermeable gas supply line 16. The first impermeable gas supply line 16 is typically a pipe for supplying the first impermeable gas that has passed through the first separation unit 1 to the second separation unit 2. The upstream end of the first impermeable gas supply line 16 in the direction of supply of the first impermeable gas is connected to the end on the second end face side of the flow path 15 of the first separation membrane complex 11. The downstream end of the first impermeable gas supply line 16 in the direction of supply of the first impermeable gas is connected to the end on the first end face side of the flow path 15 of the second separation membrane complex 21, which will be described later.

[0055] B-2. Second Separation Section The second separation section 2 is configured to separate the first non-permeable gas into a second permeable gas and a second non-permeable gas. In one embodiment, the second separation section 2 includes a second separation membrane complex 21, a second housing (not shown) that houses the second separation membrane complex 21, and a sealing member (not shown). The second separation membrane complex 21 will be described in the same manner as the first separation membrane complex 11. Therefore, a detailed description of the second separation membrane complex 21 will be omitted as appropriate. Also, the second housing and sealing member of the second separation section 2 will be described in the same manner as the first housing and sealing member of the first separation section 1. Therefore, a detailed description of the second housing and sealing member will be omitted as appropriate.

[0056] The second separation membrane composite 21 typically comprises a support 13 and a second separation membrane 22. The support 13 of the second separation membrane composite 21 is described in the same way as the support 13 of the first separation membrane composite 11. The support 13 of the second separation membrane composite 21 and the support 13 of the first separation membrane composite 11 may be made of the same material or different materials. The support 13 of the second separation membrane composite 21 and the support 13 of the first separation membrane composite 11 may have the same shape or different shapes. The second separation membrane 22 is described in the same way as the first separation membrane 12. The second separation membrane 22 and the first separation membrane 12 may be made of the same material or different materials.

[0057] The second housing contains the second separation membrane complex 21 described above. In one embodiment, ports are provided at both ends in the longitudinal direction and on the sides of the second housing. The ports at the longitudinal ends of the second housing are connected to the first non-permeable gas supply line 16 and the second non-permeable gas supply line 26, which will be described later. The ports on the sides of the second housing are connected to the switching line 71, which will be described later. Depending on the shape of the second separation membrane complex 21, the shape of the second housing and the connection positions of the various lines may be changed as appropriate. The second housing may contain one second separation membrane complex 21, or it may contain multiple second separation membrane complexes 21.

[0058] In one embodiment, the sealing members are arranged longitudinally between the side surface S of the second separation membrane composite 21 and the inner surface of the second housing. The sealing members are in close contact with the side surface S of the second separation membrane composite 21 and the inner surface of the second housing over the entire circumference in the circumferential direction around the central axis of the second separation membrane composite 21.

[0059] The second separation unit 2 may comprise one second housing as shown in Figure 1, or it may comprise multiple second housings as shown in Figure 2. One or more second separation membrane composites 21 are housed in the second housing. As shown in Figure 2, when the second separation unit 2 comprises multiple second housings housing the second separation membrane composites 21, the multiple second housings may be arranged in series or in parallel. In the illustrated example, the multiple second housings are arranged in series.

[0060] When a plurality of second housings containing the second separation membrane complex 21 are arranged in series, the second separation unit 2 further includes a second connection line 24. The second connection line 24 connects adjacent second housings among the plurality of second housings containing the second separation membrane complex 21. In the following, among adjacent second housings, the second housing located on the first separation unit side may be referred to as the upstream second housing, and the second housing located on the third separation unit side may be referred to as the downstream second housing. The second connection line 24 is typically a pipe through which fluid can pass. The upstream end of the second connection line 24 in the direction of fluid passage is connected to the end on the second end face side of the second separation membrane complex 21 in the upstream second housing. The downstream end of the second connection line 24 in the direction of fluid passage is connected to the end on the first end face side of the second separation membrane complex 21 in the downstream second housing.

[0061] In the illustrated example, the second separation section 2 is connected to the third separation section 3 via a second impermeable gas supply line 26. The second impermeable gas supply line 26 is typically a pipe for supplying the second impermeable gas that has passed through the second separation section 2 to the third separation section 3. The upstream end of the second impermeable gas supply line 26 in the direction of supply of the second impermeable gas is connected to the end on the second end face side of the flow path 15 of the second separation membrane complex 21. The downstream end of the second impermeable gas supply line 26 in the direction of supply of the second impermeable gas is connected to the end on the first end face side of the flow path 15 of the third separation membrane complex 31, which will be described later.

[0062] B-3. ​​Third Separation Section As shown in Figure 1, the third separation section 3 is configured to separate the second non-permeable gas into a third permeable gas and a third non-permeable gas. In one embodiment, the third separation section 3 includes a third separation membrane composite 31, a third housing (not shown) that houses the third separation membrane composite 31, and a sealing member (not shown). The third separation membrane composite 31 will be described in the same manner as the first separation membrane composite 11. Therefore, a detailed description of the third separation membrane composite 31 will be omitted as appropriate. Also, the third housing and sealing member of the third separation section 3 will be described in the same manner as the first housing and sealing member of the first separation section 1. Therefore, a detailed description of the third housing and sealing member will be omitted as appropriate.

[0063] The third separation unit 3 typically comprises a support 13 and a third separation membrane 32. The support 13 of the third separation membrane composite 31 is described in the same way as the support 13 of the first separation membrane composite 11. The support 13 of the first separation membrane composite 11, the second separation membrane composite 21, and the third separation membrane composite 31 may be made of the same material or different materials. The support 13 of the first separation membrane composite 11, the second separation membrane composite 21, and the third separation membrane composite 31 may have the same shape or different shapes. The third separation membrane 32 is described in the same way as the first separation membrane 12. The first separation membrane 12, the second separation membrane 22, and the third separation membrane 32 may be made of the same material or different materials.

[0064] The third housing contains the third separation membrane composite 31 described above. In one embodiment, ports are provided at both longitudinal ends and on the sides of the third housing. The ports at the longitudinal ends of the third housing are connected to the second non-permeable gas supply line 26 and the second recovery line 81, which will be described later. The ports on the sides of the third housing are connected to the return line 61, which will be described later. Depending on the shape of the third separation membrane composite 31, the shape of the third housing and the connection positions of the various lines may be changed as appropriate. The third housing may contain one third separation membrane composite 31, or it may contain multiple third separation membrane composites 31.

[0065] In one embodiment, the sealing member is arranged longitudinally between the side surface S of the third separation membrane composite 31 and the inner surface of the third housing. The sealing member is in close contact with the side surface S of the third separation membrane composite 31 and the inner surface of the third housing over the entire circumference in the circumferential direction centered on the central axis of the third separation membrane composite 31.

[0066] In one embodiment, the third separation unit 3 comprises a plurality of third housings. Each of the plurality of third housings contains one or more third separation membrane composites 31. The plurality of third housings may be arranged in series as shown in Figure 1, or in parallel as shown in Figure 3.

[0067] As shown in Figure 1, when a plurality of third housings containing the third separation membrane complex 31 are arranged in series, the third separation unit 3 further includes a third connection line 34. The third connection line 34 connects adjacent third housings among the plurality of third housings containing the third separation membrane complex 31. In the following, among adjacent third housings, the third housing located on the second separation unit side may be referred to as the upstream third housing, and the third housing located on the non-permeable gas recovery unit side may be referred to as the downstream third housing. The third connection line 34 is typically a pipe through which fluid can pass. The upstream end of the third connection line 34 in the direction of fluid passage is connected to the end on the second end face side of the third separation membrane complex 31 in the upstream third housing. The downstream end of the third connection line 34 in the direction of fluid passage is connected to the end on the first end face side of the third separation membrane complex 31 in the downstream third housing.

[0068] B-4. Mixed Gas Supply Unit In one embodiment, the mixed gas supply unit 4 includes a mixed gas supply line 41. The mixed gas supply line 41 is piping for supplying a mixed gas, including a first gas and a second gas, to the first separation unit 1. The upstream end of the mixed gas supply line 41 in the direction of supplying the mixed gas is connected to various industrial products or industrial facilities that can discharge the mixed gas. Examples of various industrial products or industrial facilities include CO２ Examples include oil fields such as EOR (Enhanced Operating Refinement) oil fields, natural gas fields, biogas plants, petrochemical plants, chemical plants, thermal power plants, waste incineration facilities, and cracking plants. The downstream end of the mixed gas supply line 41 in the direction of mixed gas supply is connected to the end on the first end face side of the flow path 15 of the first separation membrane complex 11. The mixed gas supply line 41 may be equipped with pretreatment equipment or filters to remove impurities and solids from the mixed gas.

[0069] B-5. Permeate Gas Recovery Section In one embodiment, the permeate gas recovery section 5 includes a first recovery line 51 and a first recovery section 52. The first recovery line 51 is typically a pipe through which the recovered gas, including the first permeate gas, can pass. As will be described in detail later, in one embodiment, the first permeate gas flows out from the side surface S of the first separation membrane complex 11. Therefore, the upstream end of the first recovery line 51 in the direction of passage of the recovered gas is connected to the space facing the side surface S of the first separation membrane complex 11. The downstream end of the first recovery line 51 in the direction of passage of the recovered gas is connected to the first recovery section 52. The first recovery section 52 has any suitable configuration, such as a tank or blower, that can store or pump the recovered gas.

[0070] B-6. Return Section In one embodiment, the return section 6 comprises a return line 61 and a compressor 62. The return line 61 is typically a pipe through which the return gas, including the third permeate gas, can pass. As will be described in detail later, in one embodiment, the third permeate gas flows out from the side surface S of the third separation membrane complex 31. Therefore, the upstream end of the return line 61 in the direction of return gas passage is connected to the space facing the side surface S of the third separation membrane complex 31. The downstream end of the return line 61 in the direction of return gas passage is connected to the mixed gas supply line 41. The compressor 62 is provided in the return line 61. The compressor 62 is configured to pressurize the return gas passing through the return line 61.

[0071] B-7. Permeate Gas Supply Unit In one embodiment, the permeate gas supply unit 7 includes a switching line 71, a first on-off valve 72, and a second on-off valve 73. The switching line 71 is typically a pipe through which the second permeate gas can pass. In one embodiment, the switching line 71 includes a main section 711, a first branch section 712, and a second branch section 713. The main section 711 is the upstream portion of the switching line 71 in the direction of passage of the second permeate gas. As will be described in detail later, in one embodiment, the second permeate gas flows out from the side surface S of the second separation membrane complex 21. Therefore, the upstream end of the main section 711 in the direction of passage of the second permeate gas is connected to the space facing the side surface S of the second separation membrane complex 21. The first branch section 712 and the second branch section 713 branch off and extend from the downstream end of the main section 711 in the direction of passage of the second permeate gas. In the illustrated example, the downstream end of the first branch section 712 in the direction of passage of the second permeate gas is connected to the first recovery line 51. The downstream end of the second branch section 713 in the direction of passage of the second permeate gas is connected in the return line 61 between the third separation membrane complex 31 and the compressor 62. The first on-off valve 72 is typically provided in the first branch section 712 of the switching line 71. The first on-off valve 72 can open and close the first branch section 712. The second on-off valve 73 is typically provided in the second branch section 713 of the switching line 71. The second on-off valve 73 can open and close the second branch section 713. Examples of the first on-off valve 72 and the second on-off valve 73 include ball valves, gate valves, and butterfly valves, respectively. Instead of the first on-off valve 72 and the second on-off valve 73, a three-way valve may be provided in the section where the main section 711 branches into the first branch section 712 and the second branch section 713. The three-way valve can open and close the first branch section 712 and the second branch section 713.

[0072] B-8. Impermeable Gas Recovery Unit In one embodiment, the impermeable gas recovery unit 8 comprises a second recovery line 81 and a second recovery tank 82. The second recovery line 81 is typically a pipe through which the third impermeable gas can pass. The upstream end of the second recovery line 81 in the direction of passage of the third impermeable gas is connected to the end on the second end face side of the flow path 15 of the third separation membrane complex 31. The downstream end of the second recovery line 81 in the direction of passage of the third impermeable gas is connected to the second recovery tank 82. The second recovery tank 82 has any suitable configuration, such as a tank or blower, that can store or pump the third impermeable gas.

[0073] B-9. Gas Measuring Instrument The gas measuring instrument 9 has any suitable configuration. In one embodiment, the gas measuring instrument 9 is provided in at least one of the mixed gas supply line 41, the first recovery line 51, the return line 61, and the second recovery line 81. In the illustrated example, the gas measuring instrument 9 is provided upstream of the connection portion of the return line 61 in the mixed gas supply line 41. The gas measuring instrument 9 may also be provided downstream of the connection portion of the return line 61 in the mixed gas supply line 41. This allows the gas measuring instrument 9 to measure the flow rate and / or composition of the mixed gas passing through the mixed gas supply line 41. Alternatively, the gas measuring instrument 9 may be provided downstream of the connection portion of the first branch section 712 in the first recovery line 51. This allows the gas measuring instrument 9 to measure the flow rate and / or composition of the recovered gas passing through the first recovery line 51. Alternatively, the gas measuring instrument 9 may be provided downstream of the connection portion of the second branch section 713 in the return line 61. This allows the gas measuring instrument 9 to measure the flow rate and / or composition of the return gas passing through the return line 61. Alternatively, the gas measuring instrument 9 may be installed in the second recovery line 81. This allows the gas measuring instrument 9 to measure the flow rate and / or composition of the third non-permeable gas passing through the second recovery line 81.

[0074] B-10. Control Unit The control unit 10 can control the operation of the gas separation system 100. The control unit 10 includes, for example, a central processing unit (CPU), a ROM, and a RAM. The control unit 10 stores threshold data that serves as a criterion for switching the mode of the permeate gas supply unit 7. In one embodiment, the control unit 10 is communicably connected to the gas measuring device 9, the first on-off valve 72, and the second on-off valve 73.

[0075] C. Gas Separation Method Next, a gas separation method according to one embodiment will be described with reference to FIG. 1. Typically, the gas separation method is implemented by the gas separation system 100. In one embodiment, the gas separation method includes a first supply step, a second supply step, a third supply step, a permeate gas recovery step, a return step, a non-permeate gas recovery step, and a mode selection step. The gas separation method preferably includes a measurement step before the mode selection step.

[0076] C-1. First Supply Step In the first supply step, the mixed gas is supplied to the first separation unit 1 described above. The mixed gas includes a first gas (high-permeability gas) that can permeate through the first separation membrane 12 and a second gas (low-permeability gas) that is less permeable through the first separation membrane 12 than the first gas. The combination of the first gas and the second gas is appropriately changed according to the use of the first separation membrane 12. As gas components included in the mixed gas, for example, carbon dioxide (CO ２ ), hydrocarbons of C1 to C8, hydrogen (H ２ ), helium (He), nitrogen (N ２ ), oxygen (O ２ ), water vapor (H ２ O), carbon monoxide (CO), nitrogen oxides, ammonia (NH ３ ), sulfur oxides, hydrogen sulfide (H ２ S), sulfur fluoride, mercury (Hg), arsine (AsH ３ ), hydrogen cyanide (HCN), carbonyl sulfide (COS), organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes can be mentioned. The mixed gas can contain these components alone or in combination.

[0077] The content of the first gas in the mixed gas is, for example, 1% to 99% by volume, preferably 10% to 90% by volume. The temperature of the mixed gas supplied to the first separation unit 1 is, for example, 0°C to 200°C, preferably 20°C to 100°C. The pressure of the mixed gas supplied to the first separation unit 1 is, for example, 0 MPaG (gauge pressure) to 20 MPaG (gauge pressure), preferably 0.5 MPaG (gauge pressure) to 10 MPaG (gauge pressure).

[0078] As a result, when the mixed gas passes through the first separation section 1, at least a portion of the first gas contained in the mixed gas permeates through the first separation membrane 12 and is separated from the mixed gas as the first permeate gas. The remaining portion of the mixed gas that did not permeate through the first separation membrane 12 is discharged from the first separation section 1 as the first non-permeate gas. The content of the first gas in the first permeate gas is, for example, 50% to 100% by volume, or for example, 70% to 99% by volume.

[0079] In the illustrated example, the mixed gas is supplied to the flow path 15 of the first separation membrane complex 11 via the mixed gas supply line 41. As shown in Figure 5, when the mixed gas passes through the flow path 15 of the first separation membrane complex 11, at least a portion of the first gas permeates through the first separation membrane 12 and the support 13 in sequence and flows out from the side surface S of the first separation membrane complex 11 as the first permeate gas. On the other hand, the remaining portion of the mixed gas that did not permeate the first separation membrane 12 is discharged from the flow path 15 of the first separation membrane complex 11 as the first non-permeate gas.

[0080] C-2. Second Supply Process As shown in Figure 1, in the second supply process, the first non-permeable gas that has passed through the first separation section 1 without permeating the first separation membrane 12 is supplied to the second separation section 2 described above. The temperature range of the first non-permeable gas supplied to the second separation section 2 is, for example, the same as the temperature range of the mixed gas described above. The pressure range of the first non-permeable gas supplied to the second separation section 2 is, for example, the same as the pressure range of the mixed gas described above.

[0081] As a result, when the first impermeable gas passes through the second separation section 2, at least a portion of the first gas remaining in the first impermeable gas permeates through the second separation membrane 22 and is separated from the first impermeable gas as the second permeable gas. The remaining portion of the first impermeable gas that did not permeate through the second separation membrane 22 is discharged from the second separation section 2 as the second impermeable gas.

[0082] In the illustrated example, the first impermeable gas is supplied to the flow path 15 of the second separation membrane complex 21 via the first impermeable gas supply line 16. As shown in Figure 5, when the first impermeable gas passes through the flow path 15 of the second separation membrane complex 21, at least a portion of the first gas remaining in the first impermeable gas permeates through the second separation membrane 22 and the support 13 in sequence, and flows out as the second permeable gas from the side surface S of the second separation membrane complex 21. On the other hand, the remainder of the first impermeable gas that did not permeate the second separation membrane 22 is discharged from the flow path 15 of the second separation membrane complex 21 as the second impermeable gas.

[0083] C-3. Third Supply Process As shown in Figure 1, in the third supply process, the second non-permeable gas that has passed through the second separation section 2 without permeating the second separation membrane 22 is supplied to the third separation section 3 described above. The temperature range of the second non-permeable gas supplied to the third separation section 3 is, for example, the same as the temperature range of the mixed gas described above. The pressure range of the second non-permeable gas supplied to the third separation section 3 is, for example, the same as the pressure range of the mixed gas described above.

[0084] As a result, when the second impermeable gas passes through the third separation section 3, the first gas remaining in the second impermeable gas permeates through the third separation membrane 32 and is separated from the second impermeable gas as the third permeable gas. In addition, the remaining portion of the second impermeable gas that did not permeate through the second separation membrane 22 is discharged from the third separation section 3 as the third impermeable gas.

[0085] In the illustrated example, the second impermeable gas is supplied to the flow path 15 of the third separation membrane complex 31 via the second impermeable gas supply line 26. As shown in Figure 5, when the third impermeable gas passes through the flow path 15 of the third separation membrane complex 31, the first gas remaining in the second impermeable gas permeates through the third separation membrane 32 and the support 13 in sequence, and flows out as the third permeable gas from the side surface S of the third separation membrane complex 31. On the other hand, the remaining portion of the second impermeable gas that did not permeate through the third separation membrane 32 is discharged from the flow path 15 of the third separation membrane complex 31 as the third impermeable gas.

[0086] C-4. Permeate Gas Recovery Process In the permeate gas recovery process, the recovered gas containing the first permeate gas is recovered. In the illustrated example, the recovered gas is sent to the first recovery unit 52 via the first recovery line 51 for storage or pumping. The content of the first gas in the recovered gas is, for example, 50% to 100% by volume, and also, for example, 70% to 99% by volume.

[0087] C-5. Return Process In the return process, the return gas containing the third permeate gas is merged with the mixed gas. In the illustrated example, the return gas is sent to the mixed gas supply line 41 via the return line 61. As a result, the return gas merges with the mixed gas and is supplied again to the first separation unit 1. The return gas passing through the return line 61 is pressurized by the compressor 62 as needed. The pressure range of the pressurized return gas is, for example, the same as the pressure range of the mixed gas described above.

[0088] C-6. Impermeable Gas Recovery Process In the impermeable gas recovery process, the third impermeable gas is recovered. In the illustrated example, the third impermeable gas is recovered by the impermeable gas recovery unit 8. More specifically, the third impermeable gas is sent to the second recovery tank 82 via the second recovery line 81 for storage or pumping. The content of the first gas in the third impermeable gas is, for example, 10% by volume or less, preferably 5% by volume or less.

[0089] C-7. Measurement Process In the measurement process, the flow rate and / or composition of at least one of the mixed gas, recovered gas, return gas, and third non-permeable gas described above is measured. In the illustrated example, the gas measuring instrument 9 measures the flow rate and / or composition of at least one of the mixed gas passing through the mixed gas supply line 41, the recovered gas passing through the first recovery line 51, the return gas passing through the return line 61, and the third non-permeable gas passing through the second recovery line 81. The gas measuring instrument 9 then transmits the measurement results to the control unit 10.

[0090] C-8. Mode Selection Process In the mode selection process, one of the following modes is selected: recovery mode, return mode, or stop mode. In recovery mode, the second permeate gas is merged with the recovered gas. In return mode, the second permeate gas is merged with the return gas. In stop mode, the merging of the second permeate gas with the recovered gas and the return gas is stopped. In other words, if recovery mode is selected, the recovered gas contains the first and second permeate gases, and the return gas contains the third permeate gas. Also, if return mode is selected, the recovered gas contains the first permeate gas, and the return gas contains the second and third permeate gases. Also, if stop mode is selected, the recovered gas contains the first permeate gas, and the return gas contains the third permeate gas.

[0091] In one embodiment, during the mode selection step, one of the recovery mode, return mode, or stop mode is selected according to the measurement results obtained in the measurement step described above. In the illustrated example, the control unit 10 compares the measurement results received from the gas measuring instrument 9 with threshold data to determine the appropriate mode for the permeate gas supply unit 7. Based on this determination, the control unit 10 opens and closes the first on-off valve 72 and the second on-off valve 73, respectively. More specifically, if the control unit 10 selects the recovery mode, the control unit 10 opens the first on-off valve 72 and closes the second on-off valve 73. If the control unit 10 selects the return mode, the control unit 10 closes the first on-off valve 72 and opens the second on-off valve 73. If the control unit 10 selects the stop mode, it closes the first on-off valve 72 and the second on-off valve 73. Alternatively, one of the recovery mode, return mode, or stop mode may be selected by human judgment according to the measurement results obtained in the measurement step described above.

[0092] As described above, in the gas separation method according to one embodiment, it is possible to select from recovery mode, return mode, and stop mode. Therefore, even if there are fluctuations in the composition of the mixed gas and / or changes in the performance of the separation membrane, the area ratio of the separation membrane used for collecting the recovered gas and the separation membrane used for collecting the return gas can be adjusted in a balanced manner. As a result, the content of the first gas in the recovered gas can be improved and the first gas can be recovered efficiently, or the content of the second gas in the third non-permeable gas can be improved and the second gas can be recovered efficiently.

[0093] The gas separation system and gas separation method according to embodiments of the present invention are used for separating specific gas components from a mixed gas, and are particularly suitable for separating specific gas components from a mixed gas whose composition is prone to fluctuation.

[0094] 1. First separation section 12. First separation membrane 2. Second separation section 22. Second separation membrane 3. Third separation section 32. Third separation membrane 4. Mixed gas supply section 5. Permeate gas recovery section 6. Return section 7. Permeate gas supply section 8. Non-permeate gas recovery section 9. Gas measuring instrument 10. Control unit

Claims

1. A first separation unit to which a mixed gas containing a first gas and a second gas is supplied, the first separation unit comprising a first separation membrane permeable to the first gas; a second separation unit to which a first impermeable gas that has passed through the first separation unit without passing through the first separation membrane is supplied, the second separation unit comprising a second separation membrane permeable to the first gas; a third separation unit to which a second impermeable gas that has passed through the second separation unit without passing through the second separation membrane is supplied, the third separation unit comprising a third separation membrane permeable to the first gas; a mixed gas supply unit configured to supply the mixed gas to the first separation unit; a permeable gas recovery unit configured to recover recovered gas containing the first permeable gas that has passed through the first separation membrane; a return unit configured to return returned gas containing the third permeable gas that has passed through the third separation membrane to the mixed gas supply unit and merge it with the mixed gas; and an impermeable gas recovery unit configured to recover a third impermeable gas that has passed through the third separation unit without passing through the third separation membrane. A gas separation system comprising a permeate gas supply unit that can switch between at least two of the following modes: a recovery mode in which the second permeate gas that has permeated through the second separation membrane is supplied to the permeate gas recovery unit and merged with the recovered gas; a return mode in which the second permeate gas is supplied to the return unit and merged with the return gas; and a stop mode in which the supply of the second permeate gas to the permeate gas recovery unit and the return unit is stopped.

2. The gas separation system according to claim 1, wherein the permeate gas supply unit is switchable between the recovery mode, the return mode, and the stop mode.

3. The gas separation system according to claim 1 or 2, wherein the first separation unit comprises a plurality of first separation membranes, the third separation unit comprises a plurality of third separation membranes, the permeate gas recovery unit is configured to recover the first permeate gas that has permeated through the plurality of first separation membranes in a single unit, and the return unit is configured to return the third permeate gas that has permeated through the plurality of third separation membranes in a single unit to the mixed gas supply unit.

4. The gas separation system according to claim 1 or 2, wherein the second separation unit comprises a plurality of second separation membranes, and the permeate gas supply unit is provided in a plurality corresponding to the plurality of second separation membranes.

5. The gas separation system according to claim 1 or 2, further comprising a gas measuring instrument capable of measuring the flow rate and / or composition of at least one of the gases among the mixed gas supplied to the first separation unit by the mixed gas supply unit, the recovered gas recovered in the permeate gas recovery unit, the returned gas returned to the mixed gas supply unit in the return unit, and the third non-permeate gas recovered in the non-permeate gas recovery unit, wherein the permeate gas supply unit is configured to select one of the recovery mode, the return mode, and the stop mode according to the measurement result of the gas measuring instrument.

6. A first supply step of supplying a mixed gas containing a first gas and a second gas to a first separation section equipped with a first separation membrane permeable to the first gas; a second supply step of supplying a first non-permeable gas that has passed through the first separation section without passing through the first separation membrane to a second separation section equipped with a second separation membrane permeable to the first gas; a third supply step of supplying a second non-permeable gas that has passed through the second separation section without passing through the second separation membrane to a third separation section equipped with a third separation membrane permeable to the first gas; a permeable gas recovery step of recovering a recovered gas containing the first permeable gas that has passed through the first separation membrane; a return step of combining a return gas containing a third permeable gas that has passed through the third separation membrane with the mixed gas; and a non-permeable gas recovery step of recovering a third non-permeable gas that has passed through the third separation section without passing through the third separation membrane. A gas separation method comprising a mode selection step of selecting one of the following: a recovery mode in which the second permeate gas that has permeated through the second separation membrane is combined with the recovered gas; a return mode in which the second permeate gas is combined with the return gas; and a stop mode in which the combination of the second permeate gas with the recovered gas and the return gas is stopped.

7. The gas separation method according to claim 6, further comprising a measurement step of measuring the flow rate and / or composition of at least one gas among the mixed gas, the recovered gas, the return gas, and the third non-permeable gas, wherein in the mode selection step, one of the recovery mode, the return mode, and the stop mode is selected according to the measurement results obtained in the measurement step.

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