Separation system and separation method

Abstract

A separation system (1) comprises: a condensable component remover (41) that removes a portion of a condensable component from a mixed gas containing the condensable component and two or more components other than the condensable component, and obtains low-condensable gas in which the concentration of the condensable component has been reduced; a separation membrane complex (21) that has a separation membrane (20) and separates the low-condensable gas into membrane permeate gas that has permeated through the separation membrane (20), and membrane non-permeate gas that does not permeate through the separation membrane (20); and a heat exchanger (31) that cools the mixed gas by exchanging heat between the mixed gas before being introduced into the condensable component remover (41) and the membrane permeate gas or the membrane non-permeate gas. The membrane permeate gas or the membrane non-permeate gas, the temperature of which has been lowered by passing through the separation membrane complex (21), can be used to preliminarily cool the mixed gas before introduction into the condensable component remover (41), thereby reduce the energy consumption in the separation of the mixed gas.

Description

Separation system and separation method

[0001] The present invention relates to a technique for separating mixed gases. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2024-147981, filed on August 29, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] Conventionally, separation systems have been proposed for recovering carbon dioxide from combustion exhaust gas containing carbon dioxide. For example, the separation systems disclosed in Japanese Patent Laid-Open Nos. 6-99013 and 6-99034 disclose, as an example of a carbon dioxide concentrator, a membrane separation device in which a pressure difference is established between both sides of a gas separation membrane and high-concentration carbon dioxide is recovered from the low-pressure side. International Publication No. 2022 / 255055 discloses that when a separation membrane separates a mixed gas under high differential pressure conditions in which the difference between the supply-side pressure and the permeation-side pressure is large, the temperature of the gas permeating the separation membrane decreases due to the Joule-Thomson effect. In this case, the temperature of the separation membrane composite including the separation membrane also decreases.

[0003] Incidentally, mixed gases such as combustion exhaust gas contain not only carbon dioxide but also condensable components such as water. When carbon dioxide is separated from combustion exhaust gas using a separation membrane composite, if the surface temperature of the separation membrane decreases due to the Joule-Thomson effect, a large amount of water, a condensable component, may be adsorbed onto the separation membrane, resulting in a decrease in the carbon dioxide permeation rate. Therefore, it is conceivable to remove water from the mixed gas using a condenser or a condensable component remover such as a TSA (Thermal Swing Adsorption) before separation using the separation membrane composite. However, the condensable component remover requires cooling the mixed gas to a predetermined temperature or below, which results in a large amount of energy consumption.

[0004] The present invention aims to reduce the energy consumption in cooling a mixed gas when the mixed gas is separated using a separation membrane.

[0005] A first aspect of the invention is a separation system for separating a mixed gas, comprising: a condensable component remover that removes a portion of the condensable components from a mixed gas containing a condensable component and two or more components other than the condensable components to obtain a low-condensable gas in which the concentration of the condensable components has been reduced; a separation membrane composite that has a separation membrane and separates the low-condensable gas into a membrane-permeable gas that has permeated the separation membrane and a membrane-non-permeable gas that does not permeate the separation membrane; and a heat exchanger that cools the mixed gas by exchanging heat between the mixed gas before being introduced into the condensable component remover and the membrane-permeable gas or the membrane-non-permeable gas.

[0006] According to the present invention, the energy consumption in the separation of a mixed gas can be reduced by pre-cooling the mixed gas before it is introduced into the condensable component remover using a membrane-permeable gas or a membrane-non-permeable gas whose temperature has been reduced by passing through a separation membrane composite.

[0007] The invention of aspect 2 is the separation system of aspect 1, further comprising another separation membrane composite having another separation membrane and separating the membrane permeable gas or the membrane non-permeable gas heated by heat exchange with the mixed gas in the heat exchanger into a membrane permeable gas and a membrane non-permeable gas for the other separation membrane.

[0008] A third aspect of the invention is the separation system of the second aspect, further comprising a temperature measurement unit that measures the temperature of the gas introduced into or discharged from the heat exchanger, and an introduction gas amount adjustment unit that adjusts the amount of gas introduced into the heat exchanger based on the temperature measured by the temperature measurement unit.

[0009] A fourth aspect of the present invention is the separation system of the third aspect, wherein the temperature measuring unit measures the temperature of the gas that is led out of the heat exchanger and introduced into the other separation membrane.

[0010] A fifth aspect of the invention is the separation system of any one of the first to fourth aspects, further comprising another heat exchanger that performs heat exchange between the mixed gas before being introduced into the condensable component remover and the low-condensable gas before being introduced into the separation membrane composite, thereby heating the low-condensable gas and cooling the mixed gas.

[0011] A sixth aspect of the present invention is the separation system according to any one of the first to fifth aspects, wherein the low-condensable gas introduced into the separation membrane composite has a temperature of 40° C. or higher.

[0012] A seventh aspect of the present invention is the separation system according to any one of the first to sixth aspects, wherein the mixed gas contains at least one selected from the group consisting of hydrogen, carbon dioxide, oxygen, nitrogen, and methane as a component other than the condensable components.

[0013] An eighth aspect of the invention is a method for separating a mixed gas, comprising the steps of: removing a portion of the condensable components from a mixed gas containing a condensable component and two or more components other than the condensable components in a condensable component remover to obtain a low-condensable gas in which the concentration of the condensable components has been reduced; supplying the low-condensable gas to a separation membrane of a separation membrane composite to separate the low-condensable gas into a membrane-permeable gas that has permeated the separation membrane and a membrane-non-permeable gas that has not permeated the separation membrane; and cooling the mixed gas by performing heat exchange between the mixed gas before being introduced into the condensable component remover and the membrane-permeable gas or the membrane-non-permeable gas.

[0014] A ninth aspect of the invention is the separation method of the eighth aspect, further comprising the step of heating the low-condensable gas and cooling the mixed gas by performing heat exchange between the mixed gas before being introduced into the condensable component remover and the low-condensable gas before being introduced into the separation membrane composite.

[0015] A tenth aspect of the present invention is the separation method according to the eighth or ninth aspect, wherein the low-condensable gas introduced into the separation membrane composite has a temperature of 40° C. or higher.

[0016] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings.

[0017] Fig. 1 is a diagram showing the configuration of a separation system; Fig. 2 is a diagram showing the separation flow of a mixed gas; Fig. 3 is a diagram showing another example of a separation system; Fig. 4 is a diagram showing another example of a separation system; Fig. 5 is a diagram showing another example of a separation system.

[0018] FIG. 1 is a diagram showing the configuration of a separation system 1 according to one embodiment of the present invention. The separation system 1 is a facility for separating a mixed gas using a separation membrane composite. The mixed gas includes a condensable component and two or more components other than the condensable component. The condensable component is a component having a boiling point of 25° C. (room temperature) or higher at atmospheric pressure (1 atmosphere). The mixed gas may include two or more condensable components. The two or more components other than the condensable component (components to be separated by the separation membrane composite, hereinafter referred to as "target components") are components that differ from the condensable components and have a boiling point lower than 25° C. at atmospheric pressure. As described below, in the separation system 1, after reducing the condensable components in the mixed gas, at least one of the two or more target components is separated from the other target components. Separation using the separation membrane composite may be performed, for example, for the purpose of extracting a component that is highly permeable to the separation membrane composite from the mixed gas, or for the purpose of concentrating a component that is less permeable to the separation membrane composite.

[0019] The mixed gas in this embodiment is, for example, a combustion exhaust gas. In this case, the mixed gas contains water (H ２ O) and carbon dioxide (CO ２ ) and nitrogen (N ２ ) and the like. The mixed gas may be other than combustion exhaust gas. The condensable component may be other than water, and the target component may be other than carbon dioxide and nitrogen. A preferred mixed gas is hydrogen (H ２ ), carbon dioxide, oxygen (O ２ ), nitrogen and methane (CH ４ ) as a target component other than the condensable component.

[0020] The separation system 1 includes a first separation membrane assembly 21, a second separation membrane assembly 22, a first heat exchanger 31, a second heat exchanger 32, a third heat exchanger 33, a condensable component remover 41, and a cooler 42. Each of the first separation membrane assembly 21 and the second separation membrane assembly 22 has a separation membrane 20. The separation membrane 20 is typically formed on a porous support. The support is made of, for example, ceramic, resin, or metal. The support may have any shape, such as a monolith, honeycomb, flat plate, or tubular shape.

[0021] The separation membrane 20 is a membrane having micropores and free volume through which substances can permeate. The separation membrane 20 separates a specific substance from a mixture of multiple substances by utilizing molecular sieving or the like. Other substances are less likely to permeate the separation membrane 20 than the specific substance. In other words, the amount of other substances that permeates the separation membrane 20 is smaller than the amount of the specific substance that permeates the separation membrane 20. The separation membrane 20 may be an inorganic membrane such as a zeolite membrane, MOF membrane, silica membrane, or carbon membrane, or an organic membrane such as a polyimide membrane or silicone membrane. In this embodiment, the separation membrane 20 of the first separation membrane composite 21 and the separation membrane 20 of the second separation membrane composite 22 are of the same type. Depending on the design of the separation system 1, the two membranes may be of different types. Furthermore, the first separation membrane composite 21 and the second separation membrane composite 22 may each be a single membrane or multiple membranes. When the first separation membrane composite 21 or the second separation membrane composite 22 is made up of a plurality of membranes, the respective separation membranes 20 may be of the same type or different types.

[0022] In the separation system 1, each separation membrane assembly 21, 22 is housed in a housing, and the separation membrane 20 divides the housing into a supply-side space (primary space) and a permeate-side space (secondary space). In the separation membrane assemblies 21, 22, the pressure in the permeate-side space is set lower than the pressure in the supply-side space, and the feed gas supplied to the supply-side space is separated into a membrane-permeated gas that has permeated the separation membrane 20 and a membrane-non-permeated gas that has not permeated the separation membrane 20. When the pressure of the membrane-permeated gas is lower than the pressure of the feed gas, the temperature of the membrane-permeated gas decreases due to the Joule-Thomson effect. This decreases the surface temperature of the separation membrane 20, and also decreases the temperature of the membrane-non-permeated gas that has not permeated the separation membrane 20. The pressure difference between the supply-side space and the permeate-side space is, for example, 0.1 MPa to 20.0 MPa. When this pressure difference is large, the temperature decrease of the membrane-permeated gas and the membrane-non-permeated gas is likely to be significant. The pressure of the membrane-non-permeated gas is approximately the same as the pressure of the feed gas.

[0023] Each of the first heat exchanger 31, the second heat exchanger 32, and the third heat exchanger 33 is a device for transferring thermal energy from one gas to another gas, and is typically a gas-gas heat exchanger. Each of the heat exchangers 31, 32, and 33 has, for example, two gas flow paths, and heat exchange occurs between the two gases without direct contact between the two gases. Various well-known structures may be employed for the heat exchangers 31, 32, and 33. The cooler 42 cools the gas using a refrigerant such as water. Various well-known structures may be employed for the cooler 42. Furthermore, the cooler 42 may be provided in another portion of the first flow path 51 (described later) or may be omitted.

[0024] The condensable component remover 41 is a device that utilizes temperature changes to remove some of the condensable components from the mixed gas, thereby obtaining a low-condensable gas in which the concentration of the condensable components is reduced. In the condensable component remover 41, the condensable components are more easily removed when the mixed gas is cooled. For example, the condensable component remover 41 in FIG. 1 is a condenser that condenses some of the condensable components contained in the mixed gas by cooling the mixed gas to a predetermined temperature or lower, and discharges the condensable components as liquid to the outside. The condensable component remover 41 has a discharge flow path that discharges the liquid condensable components to the outside. Typically, of the gases in all the flow paths (first to third flow paths 51 to 53 described below) of the separation system 1, the temperature of the gas flowing through the condensable component remover 41, which is a condenser, is the lowest.

[0025] The condensable component remover 41 may be a TSA (Thermal Swing Adsorption) device. Typically, a TSA device is provided with two adsorption tanks containing an adsorbent. A mixed gas is introduced into one of the adsorption tanks, and the condensable components are adsorbed onto the adsorbent. At this time, the mixed gas is cooled to a predetermined temperature or lower to efficiently adsorb the condensable components onto the adsorbent. In the other adsorption tank, the adsorbent to which the condensable components have been adsorbed is heated without introducing the mixed gas, thereby desorbing the condensable components. The desorbed condensable components are discharged to the outside. In each adsorption tank, adsorption and desorption of the condensable components are alternately performed. The number of adsorption tanks may be three or more. The condensable component remover 41 may be something other than a condenser or a TSA device.

[0026] In the separation system 1, a mixed gas is introduced from the outside. In FIG. 1 , a flow path 51 for the mixed gas (hereinafter referred to as the "first flow path 51") is indicated by a thick solid line. The first flow path 51 is provided with, in order from upstream to downstream in the flow direction of the mixed gas, a first heat exchanger 31, a third heat exchanger 33, a second heat exchanger 32, and a cooler 42, and its downstream end is connected to the condensable component remover 41. As described above, the condensable component remover 41 produces a low-condensable gas in which a portion of the condensable components in the mixed gas have been removed. Another flow path 52 (hereinafter referred to as the "second flow path 52") is connected to the condensable component remover 41, and the low-condensable gas flows through the second flow path 52 in a direction away from the condensable component remover 41. In FIG. 1 , the second flow path 52 is indicated by a thick dashed line.

[0027] The second flow path 52 is provided with a second heat exchanger 32 and a third heat exchanger 33, arranged in this order from upstream to downstream in the flow direction of the low-condensable gas, and its downstream end is connected to the first separation membrane composite 21. In the first separation membrane composite 21, the low-condensable gas serves as a feed gas and is separated into a membrane-permeable gas and a membrane-non-permeable gas. Another flow path 53 (hereinafter referred to as the "third flow path 53") is connected to the first separation membrane composite 21, and the membrane-non-permeable gas flows through the third flow path 53 in a direction away from the first separation membrane composite 21. In FIG. 1, the third flow path 53 is indicated by a thick dashed line. The third flow path 52 is provided with a first heat exchanger 31, and its downstream end is connected to the second separation membrane composite 22. In the second separation membrane composite 22, the membrane-non-permeable gas in the first separation membrane composite 21 serves as a feed gas and is separated into a membrane-permeable gas and a membrane-non-permeable gas.

[0028] 1, each of the flow paths 51 to 53 is appropriately provided with a pressure-boosting mechanism such as a compressor, a pressure-reducing mechanism such as a vacuum pump, and / or a blower mechanism such as a fan, and gas flows continuously from the upstream side of the first flow path 51 to the downstream side of the third flow path 53. In the example of FIG. 1, no heating unit (excluding heat exchangers 31 to 33) is provided that directly or indirectly heats the gas flowing through each of the flow paths 51 to 53 using electricity, fuel, or the like, but such a heating unit may be provided as necessary.

[0029] FIG. 2 is a diagram showing the flow of mixed gas separation in the separation system 1. The dashed blocks in FIG. 2 (steps S21 and S22) are processes performed in other separation systems 1 described below, but are not performed in the separation system 1 of FIG. 1. Although steps S11 to S17 are depicted as sequential processes in FIG. 2, in reality, steps S11 to S17 are performed in parallel. Steps S11 to S13 focus on the mixed gas flowing through the first flow path 51, steps S14 and S15 focus on the low-condensable gas flowing through the second flow path 52, and steps S16 and S17 focus on the gas flowing through the third flow path 53 (in this process example, the membrane-non-permeable gas of the first separation membrane assembly 21). Also, in FIG. 1, examples of the temperature of the gas flowing through each portion of the flow paths 51 to 53 are shown near the corresponding portion. While the following description refers to these temperatures, the temperature of the gas flowing through the flow paths 51 to 53 may be varied.

[0030] In the separation system 1, a high-temperature (e.g., 170°C) mixed gas is introduced from the outside into the first flow path 51. Typically, of all the gases in all the flow paths (i.e., the first to third flow paths 51 to 53) in the separation system 1, the temperature of the mixed gas immediately after introduction into the first flow path 51 is the highest. In the first heat exchanger 31, heat exchange occurs between the mixed gas and the gas flowing through the third flow path 53 (hereinafter simply referred to as the "gas in the third flow path 53"). The gas in the third flow path 53 is a membrane-non-permeable gas of the first separation membrane composite 21, and as described below, has a temperature sufficiently lower than that of the mixed gas, e.g., 30°C. This cools the mixed gas to a temperature lower than the temperature at which it was introduced into the first flow path 51, e.g., 130°C (step S11).

[0031] The mixed gas that has passed through the first heat exchanger 31 passes sequentially through the third heat exchanger 33 and the second heat exchanger 32. In each of the third heat exchanger 33 and the second heat exchanger 32, heat exchange occurs between the mixed gas and the gas flowing through the second flow path 52. The gas flowing through the second flow path 52 is a low-condensable gas that has been cooled to a low temperature (e.g., −30°C) in the condensable component remover 41. As described below, the low-condensable gas passes sequentially through the second heat exchanger 32 and the third heat exchanger 33. In the third heat exchanger 33, the mixed gas is cooled by heat exchange with the low-condensable gas that has been heated in the second heat exchanger 32. Subsequently, in the second heat exchanger 32, the mixed gas is further cooled by heat exchange with the low-condensable gas before the temperature increase (step S12). The temperature of the mixed gas immediately after passing through the third heat exchanger 33 is, for example, 80°C, and the temperature of the mixed gas immediately after passing through the second heat exchanger 32 is, for example, 30°C. The mixed gas that has passed through the second heat exchanger 32 is further cooled by the cooler 42 and introduced into the condensable component remover 41. The temperature of the mixed gas immediately after passing through the cooler 42 is, for example, 10°C.

[0032] In the condensable component remover 41, a refrigerant (e.g., ammonia (NH ３ The mixed gas is further cooled using a condensable gas (e.g., chlorofluorocarbons, carbon dioxide, hydrocarbons, chlorofluorocarbons, etc.). As a result, most of the condensable components (here, water) contained in the mixed gas are condensed into liquid and removed from the mixed gas. As a result, a low-condensable gas having a lower concentration of condensable components than the mixed gas is obtained (step S13). The cooling temperature of the mixed gas in the condensable component remover 41 is determined appropriately depending on the type of condensable components. In the example of FIG. 1, a low-condensable gas at −30° C. is discharged from the condensable component remover 41. The low-condensable gas flows through the second flow path 52.

[0033] The low-condensable gas passes through the second heat exchanger 32 and the third heat exchanger 33 in this order. In the second heat exchanger 32, the low-condensable gas is heated by heat exchange with the mixed gas whose temperature has been lowered in the third heat exchanger 33, and then, in the third heat exchanger 33, the low-condensable gas is further heated by heat exchange with the mixed gas before the temperature is lowered (step S14). As described above, step S14 focuses on the low-condensable gas and is the same process as step S12, which focuses on the mixed gas. The temperature of the low-condensable gas immediately after passing through the second heat exchanger 32 is, for example, 20°C, and the temperature of the low-condensable gas immediately after passing through the third heat exchanger 33 is, for example, 70°C. The low-condensable gas that has passed through the third heat exchanger 33 is introduced into the first separation membrane assembly 21.

[0034] The low-condensable gas is supplied to the supply space of the first separation membrane composite 21 and separated into a membrane-permeated gas that has permeated the separation membrane 20 and a membrane-non-permeated gas that has not permeated the separation membrane 20 (step S15). In this processing example, in which the mixed gas contains carbon dioxide and nitrogen, the amount of carbon dioxide permeated through the separation membrane 20 is greater than the amount of nitrogen permeated. Therefore, the membrane-permeated gas from the first separation membrane composite 21 has a higher carbon dioxide concentration than the low-condensable gas. This membrane-permeated gas is discharged to the outside and used as high-concentration carbon dioxide gas. On the other hand, the membrane-non-permeated gas from the first separation membrane composite 21 has a lower carbon dioxide concentration than the low-condensable gas. This membrane-non-permeated gas flows through the third flow path 53. As described above, the first separation membrane composite 21 is cooled by the Joule-Thomson effect, so the temperature of the membrane-non-permeated gas is lower than the temperature of the low-condensable gas introduced into the first separation membrane composite 21. The temperature of the membrane non-permeating gas immediately after passing through the first separation membrane assembly 21 is, for example, 30°C.

[0035] The membrane non-permeating gas, which is the gas in the third flow path 53, passes through the first heat exchanger 31. In the first heat exchanger 31, the membrane non-permeating gas is heated by heat exchange with the mixed gas immediately after being introduced into the first flow path 51 (the mixed gas that has not passed through any of the heat exchangers 31 to 33) (step S16). As described above, step S16 focuses on the gas in the third flow path 53, and is the same process as step S11, which focuses on the mixed gas. The temperature of the membrane non-permeating gas immediately after passing through the first heat exchanger 31 is, for example, 70°C. The membrane non-permeating gas that has passed through the first heat exchanger 31 is introduced into the second separation membrane assembly 22.

[0036] The membrane non-permeating gas is supplied to the supply space of the second separation membrane composite 22 and separated into a membrane permeating gas that has permeated the separation membrane 20 and a membrane non-permeating gas that has not permeated the separation membrane 20 (step S17). As with the first separation membrane composite 21, the membrane permeating gas of the second separation membrane composite 22 has a higher carbon dioxide concentration than the feed gas (membrane non-permeating gas of the first separation membrane composite 21). The membrane non-permeating gas of the second separation membrane composite 22 has a lower carbon dioxide concentration than the feed gas. In this processing example, the membrane non-permeating gas is high-concentration nitrogen gas. The membrane permeating gas and membrane non-permeating gas of the second separation membrane composite 22 are discharged to the outside. As described above, steps S11 to S17 are performed in parallel with each other.

[0037] In the separation system 1, the membrane permeate gas from the first separation membrane composite 21 may be introduced into the third flow path 53. In this case, in the first heat exchanger 31, heat exchange occurs between the membrane permeate gas and the mixed gas flowing through the first flow path 51, heating the membrane permeate gas and cooling the mixed gas. The membrane permeate gas is introduced into the second separation membrane composite 22. The membrane permeate gas from the second separation membrane composite 22 has a higher carbon dioxide concentration than the membrane permeate gas from the first separation membrane composite 21, and a higher-concentration carbon dioxide gas is obtained.

[0038] As described above, the separation system 1 includes the condensable component remover 41, the first separation membrane assembly 21, and the first heat exchanger 31. The condensable component remover 41 removes some of the condensable components from a mixed gas containing condensable components and two or more components other than the condensable components, thereby obtaining a low-condensable gas in which the concentration of the condensable components is reduced. The first separation membrane assembly 21 has a separation membrane 20 and separates the low-condensable gas into a membrane-permeated gas that has permeated the separation membrane 20 and a membrane-non-permeated gas that has not permeated the separation membrane 20. The first heat exchanger 31 cools the mixed gas by exchanging heat between the mixed gas before being introduced into the condensable component remover 41 and the membrane-permeated gas or the membrane-non-permeated gas.

[0039] Here, a separation system of the comparative example is assumed. In the separation system of the comparative example, the mixed gas is introduced directly into the cooler and the condensable component remover. In this case, the temperature of the mixed gas needs to be significantly lowered in the cooler and the condensable component remover, resulting in a large amount of energy consumption. In contrast, in the separation system 1, the mixed gas is pre-cooled before being introduced into the cooler 42 and the condensable component remover 41 using the membrane permeable gas or membrane non-permeable gas whose temperature has been lowered by passing through the first separation membrane assembly 21. This allows the energy consumption of the separation system 1 to be reduced compared to the separation system of the comparative example.

[0040] As described above, the temperatures of the membrane permeant gas and membrane non-permeant gas in the first separation membrane composite 21 are lower than the temperature of the supply gas (low-condensable gas) in the first separation membrane composite 21. If another comparative example is considered in which the gas introduced into the second separation membrane composite 22 is heated using electricity, fuel, or the like, this other comparative example makes it possible to suppress adsorption of condensable components (e.g., water) in the separation membrane 20 of the second separation membrane composite 22, but increases the energy consumption in the separation system.

[0041] In contrast, in a preferred separation system 1, the membrane permeable gas or membrane non-permeable gas heated by heat exchange with the mixed gas in the first heat exchanger 31 is introduced into the second separation membrane composite 22 and separated into the membrane permeable gas and the membrane non-permeable gas for the separation membrane 20 of the second separation membrane composite 22. In this way, by using the mixed gas to heat the gas introduced into the second separation membrane composite 22, energy consumption in the separation system 1 can be further reduced.

[0042] A preferred separation system 1 further includes another heat exchanger (the second heat exchanger 32 or the third heat exchanger 33 in the above example) that heats the low-condensable gas and cools the mixed gas by performing heat exchange between the mixed gas before being introduced into the condensable component remover 41 and the low-condensable gas before being introduced into the first separation membrane assembly 21. This makes it possible to further cool the mixed gas and heat the low-condensable gas.

[0043] Preferably, the temperature of the low-condensable gas introduced into the first separation membrane composite 21 is 40°C or higher. This allows for appropriate separation by suppressing condensation of condensable components in the separation membrane 20 of the first separation membrane composite 21. Similarly, the temperature of the gas introduced into the second separation membrane composite 22 is also preferably 40°C or higher. However, depending on the type and concentration of condensable components contained in the mixed gas, the temperature of the gas introduced into the separation membrane composites 21, 22 may be less than 40°C.

[0044] The separation method includes the steps of removing a portion of the condensable components from the mixed gas in the condensable component remover 41 to obtain a low-condensable gas (step S13), separating the low-condensable gas into a membrane-permeable gas and a membrane-non-permeable gas by supplying the low-condensable gas to the separation membrane 20 of the first separation membrane composite 21 (step S15), and cooling the mixed gas by performing heat exchange between the mixed gas before being introduced into the condensable component remover 41 and the membrane-permeable gas or the membrane-non-permeable gas (steps S11 and S16). This separation method can reduce the energy consumption in cooling the mixed gas when separating the mixed gas using a separation membrane.

[0045] A preferred separation method further includes steps (steps S12 and S14) of heating the low-condensable gas and cooling the mixed gas by performing heat exchange between the mixed gas before being introduced into the condensable component remover 41 and the low-condensable gas before being introduced into the first separation membrane assembly 21. This makes it possible to further cool the mixed gas and heat the low-condensable gas.

[0046] A preferred separation method further includes a step (step S17) of supplying the membrane permeable gas or membrane non-permeable gas heated by heat exchange with the mixed gas in steps S11 and S16 to the separation membrane 20 of the second separation membrane composite 22, thereby separating the gas into a membrane permeable gas and a membrane non-permeable gas for the second separation membrane composite 22. This allows for further reduction in energy consumption when the second separation membrane composite 22 is used.

[0047] Fig. 3 is a diagram showing another example of the separation system 1. The separation system 1 of Fig. 3 further includes a temperature measurement unit 61 and an introduction gas amount adjustment unit 62. Other configurations are similar to those of the separation system 1 of Fig. 1, and the same components are denoted by the same reference numerals.

[0048] The temperature measurement unit 61 is attached in the third flow path 53 between the first heat exchanger 31 and the second separation membrane composite 22 and measures the temperature of the gas discharged from the first heat exchanger 31 and introduced into the second separation membrane composite 22 (i.e., the gas in the third flow path 53 after passing through the first heat exchanger 31; in FIG. 3 , it is the membrane non-permeable gas of the first separation membrane composite 21). The introduced gas amount adjustment unit 62 includes a bypass flow path 621, a distribution unit 622, and a flow rate control unit (not shown). One end of the bypass flow path 621 is connected to a position upstream of the first heat exchanger 31 in the first flow path 51 (hereinafter referred to as the "branch position"), and the other end is connected to a position between the first heat exchanger 31 and the third heat exchanger 33 in the first flow path 51. The distribution unit 622 is provided near the branch position and includes a flow meter, a flow rate adjustment valve, etc. The distribution unit 622 is capable of adjusting the ratio between the amount (flow rate) of the mixed gas introduced from the branch position into the first heat exchanger 31 and the amount of the mixed gas introduced into the bypass flow path 621. The flow rate control unit is, for example, a computer having a CPU or a dedicated electric circuit, and is electrically connected to the temperature measurement unit 61 and the distribution unit 622.

[0049] Next, a portion of the flow of mixed gas separation in the separation system 1 of Figure 3 will be described with reference to Figure 2. In this processing example, the dashed blocks in Figure 2 (steps S21 and S22) are executed. In the first heat exchanger 31, the gas in the third flow path 53 is heated by heat exchange with the mixed gas immediately after introduction into the first flow path 51 (step S16). Subsequently, the temperature measurement unit 61 measures the temperature of the gas in the third flow path 53 (step S21). The temperature measured by the temperature measurement unit 61 is input to the flow rate control unit. The gas in the third flow path 53 is separated into a membrane-permeated gas and a membrane-non-permeated gas by the second separation membrane composite 22 (step S17).

[0050] Meanwhile, the flow rate control unit controls the distributor 622 based on the temperature measured by the temperature measurement unit 61, and adjusts the amount of mixed gas introduced into the first heat exchanger 31 (step S22). For example, if the measured temperature is higher than a set value, the amount of mixed gas introduced into the first heat exchanger 31 is reduced, and the amount of mixed gas introduced into the bypass flow path 621 is increased. On the other hand, if the measured temperature is lower than a set value, the amount of mixed gas introduced into the first heat exchanger 31 is increased, and the amount of mixed gas introduced into the bypass flow path 621 is reduced. As a result, the temperature of the gas in the third flow path 53, which is heated using the mixed gas in step S16, is adjusted to be approximately constant. Other processes in FIG. 2 are similar to those in the separation system 1 of FIG. 1.

[0051] As described above, the separation system 1 of FIG. 3 includes a temperature measurement unit 61 that measures the temperature of the gas introduced into the second separation membrane composite 22 and an introduced gas amount adjustment unit 62 that adjusts the amount of mixed gas introduced into the first heat exchanger 31 based on the temperature measured by the temperature measurement unit 61. The separation method for the separation system 1 of FIG. 3 also includes a step of measuring the temperature of the gas introduced into the second separation membrane composite 22 (step S21) and a step of adjusting the amount of mixed gas introduced into the first heat exchanger 31 based on the temperature measured in step S21 (step S22). The separation system 1 and the separation method can appropriately control the temperature of the gas introduced into the second separation membrane composite 22, thereby stabilizing the separation performance of the second separation membrane composite 22. Note that gas temperature control similar to that performed in the first heat exchanger 31 may also be performed in the second heat exchanger 32 or the third heat exchanger 33.

[0052] The separation system 1 and the separation method described above can be modified in various ways.

[0053] In the separation system 1 of Fig. 1 , the first heat exchanger 31 is disposed upstream of the third heat exchanger 33 in the first flow path 51, but as shown in Fig. 4 , the third heat exchanger 33 may be disposed upstream of the first heat exchanger 31. In the example of Fig. 4 , the low-condensable gas immediately before being introduced into the first separation membrane composite 21 is heated in the third heat exchanger 33 by the mixed gas immediately after being introduced into the first flow path 51, and the gas immediately before being introduced into the second separation membrane composite 22 (in the example of Fig. 4 , the membrane-non-permeating gas of the first separation membrane composite 21) is heated in the first heat exchanger 31 by the mixed gas after passing through the third heat exchanger 33.

[0054] Furthermore, the separation system 1 of FIG. 4 may be provided with a temperature measurement unit 61 and an introduction gas amount adjustment unit 62, as in FIG. 3 . In this case, as shown in FIG. 5 , the temperature measurement unit 61 is attached to the second flow path 52 between the third heat exchanger 33 and the first separation membrane assembly 21. One end of a bypass flow path 621 of the introduction gas amount adjustment unit 62 is connected to a branch position upstream of the third heat exchanger 33 in the first flow path 51, and the other end is connected to a position in the first flow path 51 between the third heat exchanger 33 and the first heat exchanger 31. The distribution unit 622 is provided near the branch position and is capable of adjusting the ratio between the amount of mixed gas introduced from the branch position into the third heat exchanger 33 and the amount of mixed gas introduced into the bypass flow path 621. The flow rate control unit controls the distribution unit 622 based on the temperature measured by the temperature measurement unit 61. Note that the amount of mixed gas introduced into the third heat exchanger 33 may be adjusted by a method other than using the bypass flow path. Furthermore, gas temperature control similar to that performed in the third heat exchanger 33 may be performed in the first heat exchanger 31 or the second heat exchanger 32. In the separation system 1 of Figure 5, the temperature of the gas introduced into the first separation membrane composite 21 can be appropriately controlled, and the separation performance of the first separation membrane composite 21 can be stabilized.

[0055] 3 and 5, a mechanism for adjusting the amount of mixed gas introduced into the heat exchanger is provided, but a mechanism for adjusting the amount of gas introduced into the heat exchanger with respect to the gas that exchanges heat with the mixed gas may also be provided. Also, the temperature measurement unit 61 may be provided in a different location as long as it can measure the temperature of the gas introduced into or discharged from the heat exchanger (which may be either the mixed gas or the gas that exchanges heat with the mixed gas).

[0056] In the separation system 1, the membrane permeate gas (or membrane non-permeate gas) of the second separation membrane composite 22 may be returned to the second flow path 52. In the second separation membrane composite 22, the temperature of the membrane permeate gas also drops below the temperature of the supply gas, so the membrane permeate gas is preferably returned to the second flow path 52 upstream of the third heat exchanger 33 (for example, to a position between the second heat exchanger 32 and the third heat exchanger 33). In addition, heat exchange may be performed between the membrane permeate gas or membrane non-permeate gas of the second separation membrane composite 22 and the mixed gas, thereby cooling the mixed gas. Heat exchange may be performed between the mixed gas and the gas (membrane permeate gas or membrane non-permeate gas) that does not flow through the third flow path 53 after passing through the first separation membrane composite 21, thereby cooling the mixed gas.

[0057] In the separation system 1, the second separation membrane assembly 22 may be omitted. Furthermore, the second heat exchanger 32 and the third heat exchanger 33 may be a single heat exchanger, or both may be omitted depending on the design of the separation system 1.

[0058] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0059] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention.

[0060] The separation system and separation method of the present invention can be used in a variety of fields to separate a variety of substances.

[0061] REFERENCE SIGNS LIST 1 Separation system 20 Separation membrane 21, 22 Separation membrane complex 31, 32, 33 Heat exchanger 41 Condensable component remover 61 Temperature measurement unit 62 Introduced gas amount adjustment unit S11 to S17, S21, S22 Steps

Claims

1. A separation system for separating a mixed gas, comprising: a condensable component remover that removes a portion of a condensable component from a mixed gas containing a condensable component and two or more components other than the condensable component, thereby obtaining a low-condensable gas in which the concentration of the condensable component has been reduced; a separation membrane complex that has a separation membrane and separates the low-condensable gas into a membrane-permeable gas that has permeated the separation membrane and a membrane-non-permeable gas that has not permeated the separation membrane; and a heat exchanger that cools the mixed gas by exchanging heat between the mixed gas before being introduced into the condensable component remover and the membrane-permeable gas or the membrane-non-permeable gas.

2. A separation system according to claim 1, further comprising another separation membrane complex which has another separation membrane and separates the membrane permeable gas or the membrane non-permeable gas heated by heat exchange with the mixed gas in the heat exchanger into a membrane permeable gas and a membrane non-permeable gas for the other separation membrane.

3. A separation system according to claim 2, further comprising: a temperature measuring unit that measures the temperature of the gas introduced into or discharged from the heat exchanger; and an introduced gas amount adjusting unit that adjusts the amount of gas introduced into the heat exchanger based on the temperature measured by the temperature measuring unit.

4. A separation system according to claim 3, wherein the temperature measuring unit measures the temperature of the gas that is led out of the heat exchanger and introduced into the other separation membrane.

5. A separation system according to any one of claims 1 to 4, further comprising another heat exchanger that performs heat exchange between the mixed gas before being introduced into the condensable component remover and the low-condensable gas before being introduced into the separation membrane composite, thereby heating the low-condensable gas and cooling the mixed gas.

6. A separation system according to any one of claims 1 to 4, wherein the temperature of the low-condensable gas introduced into the separation membrane composite is 40°C or higher.

7. A separation system according to any one of claims 1 to 4, wherein the mixed gas contains at least one component selected from the group consisting of hydrogen, carbon dioxide, oxygen, nitrogen and methane as a component other than the condensable components.

8. A method for separating a mixed gas, comprising the steps of: removing a portion of the condensable components from a mixed gas containing a condensable component and two or more components other than the condensable components in a condensable component remover to obtain a low-condensable gas in which the concentration of the condensable components has been reduced; supplying the low-condensable gas to a separation membrane of a separation membrane composite to separate the low-condensable gas into a membrane-permeable gas that has permeated the separation membrane and a membrane-non-permeable gas that does not permeate the separation membrane; and cooling the mixed gas by performing heat exchange between the mixed gas before being introduced into the condensable component remover and the membrane-permeable gas or the membrane-non-permeable gas.

9. A separation method according to claim 8, further comprising the step of heating the low-condensable gas and cooling the mixed gas by performing heat exchange between the mixed gas before being introduced into the condensable component remover and the low-condensable gas before being introduced into the separation membrane composite.

10. A separation method according to claim 8 or 9, wherein the temperature of the low-condensable gas introduced into the separation membrane composite is 40°C or higher.

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