Gas separation systems, and hydrocarbon production systems

Abstract

To provide a technique for improving efficiency of carbon dioxide desorption by purge gas in a gas separation system.SOLUTION: A gas separation system comprises: connection flow passages that can connect a first adsorber and a second adsorber in series among a plurality of adsorbers; a purge gas supply flow passage that can supply a purge gas to the first adsorber; and a control unit that can simultaneously execute a first desorption step of causing the purge gas to be supplied to the first adsorber through the purge gas supply flow passage in a state where carbon dioxide is adsorbed on the first and second adsorbers, so as to desorb the carbon dioxide from the first adsorber, and a second desorption step of causing the first adsorber to connect with the second adsorber through the connection passages, causing the purge gas circulating in the first adsorber to flow into the second adsorber through the connection flow passages, so as to desorb the carbon dioxide from the second adsorber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas separation system for separating carbon dioxide from a carbon dioxide-containing gas. [Background technology]

[0002] Conventionally, in a methane production apparatus for producing methane from carbon dioxide and hydrogen, a technology has been proposed in which the apparatus is provided with two adsorption towers containing an adsorbent having carbon dioxide adsorption performance, and each adsorption tower repeatedly adsorbs and desorbs carbon dioxide to separate the carbon dioxide from a carbon dioxide-containing gas, and methane is produced using the separated carbon dioxide and the hydrogen used during the desorption (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-142806 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the technology described in Patent Document 1, the inside of the adsorption tower is purged with hydrogen to desorb carbon dioxide, and then the hydrogen used in the purge is used to generate methane, so the amount of hydrogen used for purging is limited. Therefore, there are cases where the efficiency of desorption of carbon dioxide from the adsorption tower by the purge gas cannot be sufficiently obtained. This problem is not limited to methane production devices that use hydrogen as a purge gas, but is a common issue in carbon dioxide separation systems that separate carbon dioxide using an adsorbent.

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide a technique for improving the efficiency of desorption of carbon dioxide by a purge gas in a gas separation system. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, there is provided a gas separation system including a plurality of adsorbers housing an adsorbent capable of adsorbing carbon dioxide therein. The gas separation system includes a connection flow path capable of connecting a first adsorber and a second adsorber among the plurality of adsorbers in series, a purge gas supply flow path capable of supplying a purge gas to the first adsorber, and a control unit capable of simultaneously executing a first desorption step of supplying the purge gas to the first adsorber via the purge gas supply flow path and desorbing carbon dioxide from the first adsorber in a state in which carbon dioxide is adsorbed in the first adsorber and the second adsorber, and a second desorption step of connecting the second adsorber to the first adsorber via the connection flow path, causing the purge gas that has circulated in the first adsorber to flow into the second adsorber via the connection flow path and desorbing carbon dioxide from the second adsorber.

[0008] According to this configuration, the purge gas that has passed through the first adsorption device is Second Since the first adsorption vessel can be made to flow into the adsorption vessel, the second adsorption vessel can also be desorbed at the same time. The mixed gas containing the purge gas from which the carbon dioxide in the first adsorption vessel has been desorbed has a high carbon dioxide concentration immediately after the start of the desorption process, but the carbon dioxide concentration thereafter gradually decreases. By making this mixed gas flow into the second adsorption vessel, the carbon dioxide in the second adsorption vessel can also be desorbed. This makes it possible to improve the efficiency of carbon dioxide desorption by the purge gas.

[0009] (2) The gas separation system of the above-mentioned form may further include a carbon dioxide-containing gas supply flow path capable of supplying a carbon dioxide-containing gas containing carbon dioxide to a third adsorber different from the first adsorber and the second adsorber, and the control unit may be capable of simultaneously executing an adsorption process, in which the carbon dioxide-containing gas is supplied to the third adsorber via the carbon dioxide-containing gas supply flow path to adsorb carbon dioxide, and the adsorption / desorption process including the first desorption process, the second desorption process, and the adsorption process, which are executed simultaneously, may be repeatedly executed by changing the first adsorber, the second adsorber, and the third adsorber in which the first desorption process, the second desorption process, and the adsorption process are executed, respectively.

[0010] According to this configuration, the carbon dioxide adsorbed in the first and second adsorbers can be desorbed while the carbon dioxide-containing gas is being supplied to the third adsorber and the carbon dioxide is being adsorbed in the third adsorber. That is, since the desorption process of the first and second adsorbers is performed during the adsorption process, it is possible to artificially increase the amount of purge gas and extend the desorption time. As a result, the carbon dioxide desorption efficiency in a limited time can be improved by using a limited amount of purge gas.

[0011] (3) In the gas separation system of the above aspect, the control unit may cause the purge gas that has circulated through the first adsorber to flow into the second adsorber via the connecting flow path during a portion of the second desorption step. In this way, the purge gas can be appropriately reused, for example, by causing the purge gas that has circulated through the first adsorber to flow into the second adsorber only during a period when the carbon dioxide concentration of the mixed gas discharged from the first adsorber is low and it is expected that the carbon dioxide desorption from the second adsorber will be sufficiently performed by the purge gas that has circulated through the first adsorber.

[0012] (4) In the gas separation system of the above embodiment, the purge gas may be hydrogen. In this case, for example, it is possible to produce hydrocarbons using hydrogen as the purge gas coming out of the adsorber and the desorbed carbon dioxide. In this case, it is possible to improve the purity of the hydrocarbons compared to the case where other purge gases are used.

[0013] (5) According to another aspect of the present invention, a hydrocarbon production system is provided. This hydrocarbon production system includes the gas separation system of the above aspect, and a hydrocarbon production section connected to the gas separation system, which produces hydrocarbon compounds using a mixed gas of carbon dioxide separated by the gas separation system and hydrogen used as the purge gas. According to this configuration, the hydrocarbon production section can produce hydrocarbon compounds using a mixed gas having a high concentration of carbon dioxide and hydrogen. This makes it possible to produce hydrocarbon compounds with high purity. Furthermore, the gas separation system can improve the efficiency of carbon dioxide desorption by the purge gas by reusing the purge gas, thereby improving the efficiency of hydrocarbon production in the hydrocarbon production section. Furthermore, the amount of excess hydrogen in the production of methane in the hydrocarbon production section can be reduced.

[0014] The present invention can be realized in various aspects, for example, in the form of a gas separation method, a hydrocarbon production method, a method for controlling a gas separation system, a method for controlling a hydrocarbon production system, computer programs for causing a computer to execute these control methods, a server device for distributing the computer program, a non-transitory storage medium storing the computer program, a carbon dioxide circulation system, a fuel production system using hydrocarbons as fuel, etc. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of a gas separation system according to a first embodiment. [Diagram 2] FIG. 4 is an explanatory diagram of the timing of switching the adsorber in the gas separation system. [Diagram 3] FIG. 1 is an explanatory diagram of step 1 in a gas separation system. [Figure 4] FIG. 2 is an explanatory diagram of step 2 in the gas separation system. [Diagram 5] FIG. 2 is an explanatory diagram of step 3 in the gas separation system. [Figure 6] FIG. 2 is an explanatory diagram conceptually showing the amount of adsorbed carbon dioxide at the start of steps 1 to 3. [Figure 7] FIG. 2 is an explanatory diagram showing a schematic configuration of a gas separation system of a comparative example. [Figure 8] FIG. 4 is an explanatory diagram of the switching timing of the adsorber in the gas separation system of the comparative example. [Figure 9] FIG. 4 is a graph showing a change in the amount of adsorbed carbon dioxide in a desorption process of the gas separation system of the first embodiment. [Figure 10] FIG. 4 is a graph showing the change in the amount of carbon dioxide adsorbed in the desorption process of the gas separation system of the comparative example. [Figure 11] FIG. 4 is an explanatory diagram showing a schematic configuration of a gas separation system according to a second embodiment. [Figure 12] FIG. 11 is an explanatory diagram of the switching timing of the adsorber in the gas separation system of the second embodiment. [Figure 13] FIG. 1 is an explanatory diagram of step 1A in a gas separation system according to a second embodiment. [Figure 14] FIG. 11 is an explanatory diagram of the switching timing of the adsorber in the gas separation system of the third embodiment. [Figure 15] FIG. 11 is an explanatory diagram of the second desorption step in step 1B of the third embodiment. [Figure 16] FIG. 11 is an explanatory diagram showing a schematic configuration of a gas separation system according to a fourth embodiment. [Figure 17] FIG. 13 is an explanatory diagram of the switching timing of the adsorber in the gas separation system of the fourth embodiment. [Figure 18] FIG. 13 is an explanatory diagram of the second desorption step in step 1C of the fourth embodiment. [Figure 19] FIG. 11 is an explanatory diagram showing a schematic configuration of a hydrocarbon production system according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] First Embodiment 1 is an explanatory diagram showing a schematic configuration of a gas separation system 1 of a first embodiment. The gas separation system 1 separates and recovers carbon dioxide contained in exhaust gas discharged from a combustion furnace, an internal combustion engine, or the like. The gas separation system 1 includes a plurality of adsorbers 11, 12, and 13 (when the adsorbers 11, 12, and 13 are not distinguished from one another, they are also simply referred to as adsorbers 10), a carbon dioxide-containing gas supply flow path 20, a purge gas supply flow path 70 that supplies hydrogen as a purge gas, a connection flow path 80 (connection flow paths 81, 82, and 83) that connects the two adsorbers 10 in series, a heat medium flow path 30, a mixed gas flow path 60, a surge tank 40, and a control unit 55.

[0017] The plurality of adsorbers 11, 12, 13 are formed in a cylindrical shape, and adsorbents 11a, 12a, 13a are accommodated therein. The adsorbents 11a, 12a, 13a are materials having carbon dioxide occlusion performance, such as zeolite, activated carbon, silica gel, etc. A carbon dioxide-containing gas supply passage 20, a purge gas supply passage 70, a mixed gas passage 60, and a heat medium passage 30 are connected to each of the adsorbers 11, 12, 13. A refrigerant passage (not shown) is also formed in each of the plurality of adsorbers 11, 12, 13.

[0018] The carbon dioxide-containing gas supply flow passage 20 is connected to an external exhaust gas supply device (for example, a combustion furnace or an internal combustion engine) that discharges exhaust gas as carbon dioxide-containing gas, and exhaust gas discharged from the exhaust gas supply device flows through the carbon dioxide-containing gas supply flow passage 20. The exhaust gas flowing through the carbon dioxide-containing gas supply flow passage 20 is supplied to the adsorbers 11, 12, and 13 via exhaust gas branch flow passages 21, 22, and 23. Exhaust gas inlet valves 21a, 22a, and 23a are provided in the exhaust gas branch flow passages 21, 22, and 23, respectively. The exhaust gas inlet valves 21a, 22a, and 23a each control the supply of exhaust gas to the inside of the adsorbers 11, 12, and 13 in response to a command from the control unit 55. In this embodiment, exhaust gas is exemplified as the carbon dioxide-containing gas, but the carbon dioxide-containing gas does not have to be exhaust gas.

[0019] As shown in FIG. 1, the mixed gas flow path 60 is connected to each of the adsorbers 11, 12, and 13 via mixed gas branch paths 61, 62, and 63. A mixed gas containing carbon dioxide desorbed from the adsorbents 11a, 12a, and 13a and hydrogen as a purge gas flows through the mixed gas flow path 60. The mixed gas may contain, for example, nitrogen, oxygen, and the like. The mixed gas branch paths 61, 62, and 63 are provided with mixed gas outlet valves 61a, 62a, and 63a. The mixed gas outlet valves 61a, 62a, and 63a control the flow of the mixed gas from the adsorbers 11, 12, and 13, respectively, in response to a command from the control unit 55.

[0020] The purge gas supply passage 70 supplies purge gas to the inside of the adsorber 11, 12, 13. The purge gas supply passage 70 connected to an external purge gas supply unit (e.g., a hydrogen tank) is provided with a flow rate controller 70a that adjusts the flow rate of hydrogen flowing through the purge gas supply passage 70 in response to a command from the control unit 55. The hydrogen flowing through the purge gas supply passage 70 is supplied to the adsorber 11, 12, 13 via purge gas branch passages 71, 72, 73. The purge gas branch passages 71, 72, 73 are provided with purge gas inlet valves 71a, 72a, 73a, respectively. The purge gas inlet valves 71a, 72a, 73a each control the flow of hydrogen into the adsorber 11, 12, 13 in response to a command from the control unit 55.

[0021] The connection flow path 80 connects two adsorbers 10 in series, and supplies the mixed gas (mixed gas containing purge gas and carbon dioxide) discharged from one of the adsorbers 10 to the other adsorber 10. In detail, the connection flow path 81 connects the mixed gas branch flow path 61 and the purge gas branch flow path 72 to connect the adsorber 11 and the adsorber 12 in series. The connection flow path 82 connects the mixed gas branch flow path 62 and the purge gas branch flow path 73 to connect the adsorber 12 and the adsorber 13 in series. The connection flow path 83 connects the mixed gas branch flow path 63 and the purge gas branch flow path 71 to connect the adsorber 13 and the adsorber 11 in series. That is, the connection flow path 80 is a bypass flow path. The connection flow paths 81, 82, and 83 are provided with connection flow path valves 81a, 82a, and 83a, respectively. The connection flow path valves 81a, 82a, and 83a each control the flow of gas in the connection flow path 80 in response to a command from the control unit 55.

[0022] The heat medium passage 30 is connected to a heat medium tank (not shown), and the heat medium flows through the heat medium passage 30. The heat medium flowing through the heat medium passage 30 is supplied to the adsorbers 11, 12, and 13 via the heat medium distribution passages 31, 32, and 33. This causes heat to be input to the adsorbers 11, 12, and 13 by the heat medium. A heater 30a for heating the heat medium is provided in the heat medium passage 30, and the temperature of the heat medium is controlled by the control unit 55 controlling the heater 30a. In this embodiment, oil is used as the heat medium, but in other embodiments, water, steam, gas, and the like may be used.

[0023] The heat medium distribution passages 31, 32, and 33 are provided with heat medium inlet valves 31a, 32a, and 33a. The heat medium inlet valves 31a, 32a, and 33a control the flow of the heat medium to the adsorber 11, 12, and 13 in response to a command from the control unit 55. The adsorber 11, 12, and 13 in this embodiment are double-shell tanks (double pipes), and the heat medium flows into the gap between the outer shell and the inner shell. As a result, heat is input into the adsorber 11, 12, and 13 by the heat medium. In another embodiment, for example, the heat medium distribution passages 31, 32, and 33 may be wound around the outer periphery of the adsorber 11, 12, and 13, respectively. Even in this manner, heat can be input into the adsorber 11, 12, and 13 by the heat medium. In another embodiment, the adsorber 10 may be heated using a heater (for example, a heating wire, hot air, light irradiation, etc.) provided in the adsorber 10.

[0024] A mixed gas flow path 60 is connected to the surge tank 40. The surge tank 40 stores the mixed gas flowing through the mixed gas flow path 60.

[0025] The control unit 55 is a computer including a ROM, a RAM, and a CPU, and performs overall control of the gas separation system 1, such as switching between the adsorbers 11, 12, and 13 in the gas separation process described below, and controlling the opening and closing of valves. Details of the control content of the control unit 55 will be described later.

[0026] The program for realizing the above-mentioned gas separation process may be stored in advance in the control unit 55. The program may be provided by a program provider via a communication network. The program may be stored in a portable storage medium that is commercially available and distributed. In this case, the portable storage medium may be set in an external or built-in reading device, and the program may be read and executed by the control unit 55. As the portable storage medium, various types of storage media such as CD-ROM, DVD-ROM, flexible disk, optical disk, magneto-optical disk, IC card, USB memory device, etc. may be used. The program stored in such a storage medium is read by the reading device.

[0027] FIG. 2 is an explanatory diagram of the switching timing of the adsorber 10 in the gas separation system 1 of this embodiment. In the gas separation process of this embodiment, as shown in the figure, step 1, step 2, and step 3 constitute one cycle, and this cycle is repeated multiple times. In each step, the adsorption step, the second desorption step (heating + desorption), and the first desorption step are each performed in one of the three adsorber 11, 12, and 13. Specifically, in step 1, the adsorption step is performed in the adsorber 13, the first desorption step is performed in the adsorber 11, and the second desorption step is performed in the adsorber 12. In step 2, the adsorption step is performed in the adsorber 11, the first desorption step is performed in the adsorber 12, and the second desorption step is performed in the adsorber 13. In step 3, the adsorption step is performed in the adsorber 12, the first desorption step is performed in the adsorber 13, and the second desorption step is performed in the adsorber 11. In this manner, in the gas separation system 1 of the present embodiment, carbon dioxide in the exhaust gas is adsorbed in one of the adsorbers, and at the same time, the adsorbed carbon dioxide is desorbed in the other two adsorbers. This makes it possible to steadily supply a carbon dioxide-containing gas (exhaust gas). Each of steps 1, 2, and 3 in the present embodiment is also referred to as an "adsorption / desorption step."

[0028] Focusing on one adsorber 10, the adsorption step, the second desorption step, and the first desorption step are repeated in this order. The following will be described taking the adsorber 13 as an example. In the adsorption step, exhaust gas as a carbon dioxide-containing gas is supplied to the adsorber 13, and a refrigerant is also supplied. By cooling the adsorber 13, the carbon dioxide in the exhaust gas is adsorbed by the adsorbent 13a. When a predetermined adsorption time has elapsed, the process proceeds to the second desorption step. In this embodiment, the adsorption time is set to the time required for the adsorbent 13a of the adsorber 13 to adsorb a full amount of carbon dioxide. The adsorption time can be obtained by experiment, calculation, simulation, or the like. In the gas separation process of this embodiment, the length of each step is set to the same adsorption time.

[0029] In the second desorption step, the adsorber 13 is supplied with a heat medium and hydrogen as a purge gas. When the adsorber 13 is supplied with a heat medium and the adsorbent 13a is heated, the carbon dioxide trapped in the adsorbent 13a is easily desorbed from the adsorbent 13a. In the second desorption step, a mixed gas containing carbon dioxide discharged from the adsorber 12 (step 2 in FIG. 2) in which the first desorption step is being performed and a purge gas (hydrogen in this embodiment) is supplied to the adsorber 13. That is, the purge gas is supplied through the connection flow path 82 (FIG. 1). When the mixed gas containing the purge gas is supplied to the adsorber 13, the partial pressure of carbon dioxide inside the adsorber 13 decreases, so that the carbon dioxide adsorbed to the adsorbent 13a is desorbed from the adsorbent 13a. After the adsorption time has elapsed, the process proceeds to the first desorption step.

[0030] In the first desorption step, a purge gas is supplied to the adsorber 13 via the purge gas supply passage 70. That is, in the first desorption step, a purge gas is supplied from an external purge gas supply unit (e.g., a hydrogen tank). Since the adsorber 13 is heated in the second desorption step (FIG. 2), it is in a state in which carbon dioxide is easily desorbed from the adsorbent 13a. When the purge gas is supplied to the adsorber 13, the partial pressure of carbon dioxide inside the adsorber 13 decreases, and the carbon dioxide adsorbed to the adsorbent 13a is desorbed from the adsorbent 13a. After the adsorption time has elapsed, the process returns to the adsorption step.

[0031] FIG. 3 is an explanatory diagram of step 1 in the gas separation system 1, FIG. 4 is an explanatory diagram of step 2 in the gas separation system 1, and FIG. 5 is an explanatory diagram of step 3 in the gas separation system 1. In the gas separation system 1, exhaust gas (carbon dioxide-containing gas) is sequentially supplied to each of the three adsorbers 11, 12, and 13 to separate carbon dioxide from the exhaust gas. In the gas separation system 1, two adsorbers 10 are connected in series via a connection flow path 80. Then, the purge gas that has flowed through the adsorber 10 in which the first desorption step is performed is supplied to the adsorber 10 in which the second desorption step is performed. Here, in the adsorber 10 in the second desorption step, a heat medium is supplied and heated, and a purge gas (mixed gas) is supplied. In FIGS. 3 to 5, the flows of the exhaust gas, heat medium, and purge gas (hydrogen) are indicated by thick solid lines.

[0032] As shown in Fig. 3, in step 1 (Fig. 2), an adsorption step is performed in the adsorber 13, and exhaust gas is supplied to the adsorber 13. Specifically, the controller 55 opens the exhaust gas inlet valve 23a and closes the exhaust gas inlet valve 21a and the exhaust gas inlet valve 22a, and exhaust gas is supplied to the adsorber 13 via the carbon dioxide-containing gas supply passage 20 and the exhaust gas branch passage 23. In the adsorber 13, carbon dioxide contained in the exhaust gas is trapped by the adsorbent 13a, and most of the gases such as nitrogen and moisture that are not trapped by the adsorbent 13a are released as off-gas to the outside of the gas separation system 1, for example, to the atmosphere.

[0033] The first desorption step is performed in the adsorber 11, and the purge gas is supplied to the adsorber 11. Specifically, the control unit 55 opens the purge gas inlet valve 71a, closes the purge gas inlet valve 72a and the purge gas inlet valve 73a, and supplies the purge gas to the adsorber 11 through the purge gas supply passage 70 and the purge gas branch passage 71. When the purge gas is supplied to the adsorber 11, the carbon dioxide adsorbed in the adsorbent 11a is desorbed from the adsorbent 11a. The carbon dioxide desorbed from the adsorbent 11a is mixed with the purge gas (hydrogen) inside the adsorber 11. In step 1, the mixed gas outlet valve 61a is closed, and the connection passage valve 81a is opened, so that the mixed gas discharged from the adsorber 11 flows into the adsorber 12 through the mixed gas branch passage 61, the connection passage 81, and the purge gas branch passage 72.

[0034] The second desorption step is performed in the adsorber 12, and the heat medium and the mixed gas described above are supplied to the adsorber 12. Specifically, the controller 55 controls the heater 30a so that the heat medium reaches a predetermined temperature (amount of heat input), and opens the heat medium inlet valve 32a. As a result, the heat medium flowing through the heat medium passage 30 is supplied to the adsorber 12 via the heat medium branch passage 32. When the heat medium is supplied to the adsorber 12 and the mixed gas containing the purge gas is supplied, the carbon dioxide adsorbed in the adsorbent 12a is desorbed from the adsorbent 12a. The carbon dioxide desorbed from the adsorbent 12a is mixed with the mixed gas containing the purge gas inside the adsorber 12. In step 1, since the mixed gas outlet valve 62a is open, the mixed gas discharged from the adsorber 12 passes through the mixed gas branch passage 62 and the mixed gas passage 60 and is stored in the surge tank 40. When the adsorber 10 in which the first desorption process is performed is called the "first adsorber", the adsorber 10 in which the second desorption process is performed is called the "second adsorber", and the adsorber 10 in which the adsorption process is performed is called the "third adsorber", in process 1, adsorber 11 is the "first adsorber", adsorber 12 is the "second adsorber", and adsorber 13 is the "third adsorber".

[0035] As shown in FIG. 4, in step 2, an adsorption step is performed in the adsorber 11, and exhaust gas is supplied to the adsorber 11 through the carbon dioxide-containing gas supply passage 20 and the exhaust gas branch passage 21. A first desorption step is performed in the adsorber 12, and purge gas is supplied to the adsorber 12 through the purge gas supply passage 70 and the purge gas branch passage 72. A second desorption step is performed in the adsorber 13, and a mixed gas containing carbon dioxide and purge gas discharged from the adsorber 12 is supplied to the adsorber 13 through the mixed gas branch passage 62, the connection passage 82, and the purge gas branch passage 73. The mixed gas discharged from the adsorber 13 is stored in the surge tank 40 through the mixed gas branch passage 63 and the mixed gas passage 60. In step 2, the adsorber 11 is the "third adsorber", the adsorber 12 is the "first adsorber", and the adsorber 13 is the "second adsorber".

[0036] As shown in FIG. 5, in step 3, the adsorption step is performed in the adsorber 12, and the adsorber 12 is supplied with exhaust gas via the carbon dioxide-containing gas supply passage 20 and the exhaust gas branch passage 22. The adsorber 13 is performed with a first desorption step, and the adsorber 13 is supplied with purge gas via the purge gas supply passage 70 and the purge gas branch passage 73. The adsorber 11 is performed with a second desorption step, and the adsorber 11 is supplied with a mixed gas containing carbon dioxide and purge gas discharged from the adsorber 13 via the mixed gas branch passage 63, the connection passage 83, and the purge gas branch passage 71. The mixed gas discharged from the adsorber 11 is stored in the surge tank 40 through the mixed gas branch passage 61 and the mixed gas passage 60. In step 3, the adsorber 11 is the "second adsorber", the adsorber 12 is the "third adsorber", and the adsorber 13 is the "first adsorber". That is, in the gas separation system 1 of the present embodiment, the control unit 55 repeatedly executes the adsorption / desorption process by changing the first adsorption device, the second adsorption device, and the third adsorption device.

[0037] FIG. 6 is an explanatory diagram conceptually showing the amount of carbon dioxide adsorption at the start of steps 1 to 3. In FIG. 6, the amount of carbon dioxide adsorption is shown with dot hatching. In FIG. 6, when the entire adsorber 10 is hatched, it indicates that the amount of carbon dioxide adsorption is 100%, and when the adsorber 10 is not hatched, it indicates that the amount of carbon dioxide adsorption is 0%. Here, 100% is the amount adsorbed in the adsorber 10 at the end of the adsorption step. As described above, in the gas separation system 1 of this embodiment, when one adsorber 10 is focused on, multiple cycles are repeated, with one cycle being the adsorption step → second desorption step → desorption step (FIG. 2). FIG. 6 illustrates one cycle after multiple cycles have been performed.

[0038] 6(A), at the start of step 1, no carbon dioxide is adsorbed to the adsorbent 13a of the adsorber 13 (amount of adsorbed carbon dioxide: 0%), and carbon dioxide is adsorbed to the adsorbent 11a of the adsorber 11 and the adsorbent 12a of the adsorber 12. The amount of carbon dioxide adsorbed in the adsorber 12 is 100%, and the amount of adsorption in the adsorber 11 is less than that in the adsorber 12 (for example, about 10%). The adsorber 11 has undergone the second desorption step in the immediately preceding step 3, and is in a state in which the adsorbent 11a has been heated and a portion of the carbon dioxide has been desorbed.

[0039] In step 1, a purge gas is supplied to the adsorber 11, and a carbon dioxide-containing gas is supplied to the adsorber 13. The adsorber 11 and the adsorber 12 are connected in series, and a mixed gas containing the purge gas that has flowed through the adsorber 11 and the carbon dioxide desorbed from the adsorbent 11a in the adsorber 11 flows into the adsorber 12.

[0040] In step 1, all of the carbon dioxide adsorbed to the adsorbent 11a of the adsorber 11 is desorbed, so that the amount of carbon dioxide adsorbed in the adsorber 11 is 0% at the start of step 2. That is, no carbon dioxide is adsorbed in the adsorber 11 (FIG. 6(B)). In addition, the mixed gas supplied to the adsorber 12 in step 1 contains a purge gas, and a portion of the carbon dioxide adsorbed to the adsorbent 12a of the adsorber 12 in step 1 is desorbed, so that the amount of carbon dioxide adsorbed in the adsorber 12 is small (for example, about 10%) at the start of step 2 (FIG. 6(B)). In addition, in step 1, a carbon dioxide-containing gas is supplied to the adsorber 13, and carbon dioxide is adsorbed to the adsorbent 13a, so that the amount of carbon dioxide adsorbed in the adsorber 13 is 100% at the start of step 2 (FIG. 6(B)).

[0041] 6(B), in step 2, a purge gas is supplied to the adsorber 12, and a carbon dioxide-containing gas is supplied to the adsorber 11. The adsorber 12 and the adsorber 13 are connected in series, and a mixed gas containing the purge gas that has flowed through the adsorber 12 and the carbon dioxide desorbed from the adsorbent 12a in the adsorber 12 flows into the adsorber 13.

[0042] In step 2, all of the remaining carbon dioxide adsorbed in the adsorbent 12a of the adsorber 12 is desorbed. 12 The amount of carbon dioxide adsorbed in the adsorbent is 0%. 12 (FIG. 6(C)). In addition, the mixed gas supplied to the adsorber 13 in step 2 contains a purge gas, and a portion of the carbon dioxide adsorbed to the adsorbent 13a of the adsorber 13 in step 2 is desorbed, so that at the start of step 3, the amount of carbon dioxide adsorbed in the adsorber 13 is small (for example, about 10%) (FIG. 6(C)). In addition, in step 2, a carbon dioxide-containing gas is supplied to the adsorber 11, and carbon dioxide is adsorbed to the adsorbent 11a, so that at the start of step 3, the amount of carbon dioxide adsorbed in the adsorber 11 is 100% (FIG. 6(C)).

[0043] In this way, steps 1, 2, and 3 are repeated as one cycle, and the adsorption step → second desorption step (heating + desorption) → first desorption step is repeated in each adsorber 10. As described above, most of the carbon dioxide adsorbed in the adsorber 10 can be desorbed in the second desorption step (heating + desorption), and the remaining carbon dioxide can be desorbed in the subsequent first desorption step, so that all of the carbon dioxide adsorbed in each adsorbent can be desorbed.

[0044] As described above, in the gas separation system 1 of the present embodiment, two adsorbers 10 are connected in series, and the purge gas that has been circulated through one of the adsorbers 10 and from which carbon dioxide has been desorbed is used to desorb carbon dioxide in the subsequent adsorber 10. In other words, since the purge gas is reused, it is possible to improve the efficiency of carbon dioxide desorption by the purge gas.

[0045] Next, the effects of this embodiment will be described in comparison with a comparative example. 7 is an explanatory diagram showing a schematic configuration of a gas separation system 1P of a comparative example. The gas separation system 1P of the comparative example does not have the connection flow path 80 (connection flow paths 81, 82, 83) in the gas separation system 1 of the present embodiment. The other configurations of the gas separation system 1P are the same as those of the gas separation system 1 of the present embodiment. Hereinafter, the same reference numerals are used for the same configurations as those of the gas separation system 1, and the preceding description is to be referred to.

[0046] FIG. 8 is an explanatory diagram of the switching timing of the adsorber 10 in the gas separation system 1P of the comparative example. In the gas separation process of the comparative example, as in the above embodiment, step 1P, step 2P, and step 3P are one cycle, and this cycle is repeated multiple times. In each step performed in the gas separation system 1P of the comparative example, the adsorption step, the heating step, and the desorption step are each performed in one of the three adsorber 11, 12, and 13. Specifically, in step 1P, the adsorption step is performed in the adsorber 13, the heating step is performed in the adsorber 12, and the desorption step is performed in the adsorber 11. In step 2P, the adsorption step is performed in the adsorber 11, the heating step is performed in the adsorber 13, and the desorption step is performed in the adsorber 12. In step 3P, the adsorption step is performed in the adsorber 12, the heating step is performed in the adsorber 11, and the desorption step is performed in the adsorber 13. In the comparative gas separation system 1P, carbon dioxide in a carbon dioxide-containing gas (exhaust gas) is adsorbed in one of the adsorbers 10, while another of the adsorbers 10 is heated to raise the temperature of the adsorbent, and the adsorbed carbon dioxide is desorbed in the other of the heated adsorbers 10.

[0047] FIG. 9 is a diagram showing a change in the amount of carbon dioxide adsorption in the desorption process of the gas separation system 1 of this embodiment. FIG. 9 illustrates the amount of carbon dioxide adsorption in the adsorber 11 (first desorption process) and the adsorber 12 (second desorption process) in process 1 shown in FIG. 2. In FIG. 9, the first desorption process is indicated by a solid line, and the second desorption process is indicated by a dashed line. In this example, the time for one process is designed to be 2000 seconds. Since the adsorber 12 has performed the adsorption process in the previous process (process 3), the amount of adsorption at the start of process 1 shown in FIG. 9 is 100%. Since the adsorber 11 has performed the second desorption process (heating + desorption) in the previous process (process 3) and about 90% has been desorbed, the amount of carbon dioxide adsorption is about 10%. In this example, a purge gas in an amount that reacts with the full amount of carbon dioxide without excess or deficiency is flowed into the adsorber 11. Adsorber 11 and adsorber 12 were connected in series, and the mixed gas discharged from adsorber 11 was supplied to and discharged from adsorber 12. As a result, as shown in the figure, the amount of carbon dioxide adsorption in adsorber 11 became almost 0, and the amount of carbon dioxide adsorption in adsorber 12 became about 10%.

[0048] In this manner, by reusing the purge gas used for desorbing carbon dioxide in the adsorber 11 to desorb carbon dioxide in the adsorber 12, all of the carbon dioxide could be desorbed from the adsorber 12.

[0049] FIG. 10 is a diagram showing the change in the amount of carbon dioxide adsorption in the desorption process of the gas separation system 1P of the comparative example. FIG. 10 illustrates the amount of carbon dioxide adsorption in the adsorber 11 in the process 1P shown in FIG. 8. In this example, as in the example shown in FIG. 9, the time for one process is designed to be 2000 seconds. In the adsorber 11, the adsorption process is performed in the process 2, and then the heating process is performed in the process 3. The amount of adsorption at the start of the process 1 shown in FIG. 10 is 100%, and the carbon dioxide is in a state in which it is easy to desorb. In this example, a purge gas in an amount that reacts with the full amount of carbon dioxide without excess or deficiency is flowed into the adsorber 11 for one process time (2000 seconds), and the same amount of purge gas is subsequently flowed and discharged for the one process time (2000 seconds). As shown in the figure, the amount of carbon dioxide adsorption in the adsorber 11 becomes 0% from 3500 seconds to 4000 seconds, but about 7% of carbon dioxide remains at 2000 seconds (at the end of one process). As described above, in the gas separation system 1P of the comparative example, steps 1 to 3 are executed sequentially in each adsorber 10 (FIG. 8), and therefore the time of the desorption step cannot be extended. Therefore, at the end of the desorption step, about 7% of carbon dioxide remains in the adsorber 10. In order to desorb all of the carbon dioxide in the desorption step without changing the time of one step, it is necessary to input further external energy to hasten the desorption, for example, by increasing the energy for heating the adsorber 10 from the outside or connecting the outlet of the adsorber 10 to a vacuum pump.

[0050] As described above, according to the gas separation system 1 of the present embodiment, the purge gas that has passed through one adsorber 10 can be reused and flowed into another adsorber 10, so that the two adsorber 10 can simultaneously perform desorption. The mixed gas containing the purge gas and carbon dioxide that is discharged after desorbing the carbon dioxide in the first adsorber 10 has a high carbon dioxide concentration immediately after the start of the desorption process, but the carbon dioxide concentration gradually decreases thereafter. When this mixed gas is flowed into the second adsorber 10, the carbon dioxide in the second adsorber 10 can also be desorbed. Focusing on one adsorber 10, the amount of purge gas was increased in a pseudo manner and the desorption time was extended by performing desorption of carbon dioxide in two steps, the second desorption step and the first desorption step. In the gas separation system 1 of the present embodiment, the amount of purge gas and the time for one step are actually the same as those in the comparative example, so it can be said that the desorption efficiency of carbon dioxide by the purge gas was improved compared to the comparative example.

[0051] Furthermore, according to the gas separation system 1 of this embodiment, by connecting two adsorbers 10 and reusing the purge gas, the carbon dioxide desorption efficiency can be improved without inputting additional external energy, such as by increasing the energy for heating the adsorber 10 from the outside or connecting the outlet of the adsorber 10 to a vacuum pump, and therefore a decrease in energy efficiency can be suppressed.

[0052] According to the gas separation system 1 of this embodiment, carbon dioxide desorption can be completed efficiently and in a short period of time using a limited amount of purge gas, thereby making it possible to reduce the size of the gas separation system 1 and achieve energy savings.

[0053] <Second embodiment> FIG. 11 is an explanatory diagram showing a schematic configuration of a gas separation system 1A of the second embodiment. In addition to the configuration of the gas separation system 1 of the first embodiment, the gas separation system 1A of the present embodiment further includes two adsorbers 14, 15 and two connection flow paths 84, 85. The adsorbers 14, 15 have the same configuration as the adsorbers 11 to 13. The adsorber 13 is connected to the adsorber 14 via a connection flow path 83, the adsorber 14 is connected to the adsorber 15 via a connection flow path 84, and the adsorber 15 is connected to the adsorber 11 via a connection flow path 85. In the embodiment described below, the same components as those of the gas separation system 1 are denoted by the same reference numerals, and the preceding description is referred to.

[0054] FIG. 12 is an explanatory diagram of the switching timing of the adsorber 10 in the gas separation system 1A of the second embodiment. In the gas separation process of this embodiment, as shown in the figure, step 1A, step 2A, step 3A, step 4A, and step 5A are set as one cycle, and this cycle is repeated multiple times. In each step, the adsorption step, the heating step, the first desorption step, the second desorption step, and the cooling step are each performed in one of the five adsorber 11, 12, 13, 14, and 15. In this embodiment, each of steps 1A, 2A, 3A, 4A, and 5A is also called an "adsorption / desorption step." In addition, the adsorber 10 in which the first desorption step is performed is also called a "first adsorber," the adsorber 10 in which the second desorption step is performed is also called a "second adsorber," and the adsorber 10 in which the adsorption step is performed is also called a "third adsorber."

[0055] Specifically, in step 1A, an adsorption step is performed in the adsorber 11, a heating step is performed in the adsorber 12, a first desorption step is performed in the adsorber 13, a second desorption step is performed in the adsorber 14, and a cooling step is performed in the adsorber 15. In steps 2A, 3A, 4A, and 5A, the adsorber 10 targeted in each of the adsorption step, heating step, first desorption step, second desorption step, and cooling step is changed, and an adsorption / desorption step is performed. In the gas separation system 1A of this embodiment, carbon dioxide in the exhaust gas is adsorbed in any one of the adsorber 10, and at the same time, the other one of the adsorber 10 is heated, and the adsorbed carbon dioxide is desorbed in the other two adsorber 10, and the other one of the adsorber 10 is cooled.

[0056] Focusing on one adsorber 10, the adsorption process, heating process, first desorption process, second desorption process, and cooling process are repeatedly performed in this order. In this embodiment, the heating process is provided independently of the desorption process, and heating is not performed in the second desorption process. In addition, the cooling process is provided independently of the adsorption process.

[0057] FIG. 13 is an explanatory diagram of step 1A in the gas separation system 1A. In the gas separation system 1A, exhaust gas (carbon dioxide-containing gas) is sequentially supplied to each of five adsorbers 11, 12, 13, 14, and 15 to separate carbon dioxide from the exhaust gas. In the gas separation system 1A, similarly to the first embodiment, two adsorbers 10 are connected in series via a connection flow path 80, and the purge gas that has flowed through the adsorber 10 as the first adsorber in which the first desorption step is performed is supplied to the adsorber 10 as the second adsorber in which the second desorption step is performed. In FIG. 13, the flows of the exhaust gas, heat medium, and purge gas (hydrogen) are indicated by thick solid lines.

[0058] As shown in Fig. 13, in step 1A (Fig. 12), an adsorption step is performed in the adsorber 11, and exhaust gas is supplied to the adsorber 11. Specifically, the controller 55 opens the exhaust gas inlet valve 21a and closes the exhaust gas inlet valves 22a to 25a, and exhaust gas is supplied to the adsorber 11 via the carbon dioxide-containing gas supply passage 20 and the exhaust gas branch passage 21. In the adsorber 11, carbon dioxide contained in the exhaust gas is trapped by the adsorbent 11a, and most of the gases such as nitrogen and moisture that are not trapped by the adsorbent 11a are released as off-gas to the outside of the gas separation system 1, for example, to the atmosphere.

[0059] A heating step is performed in the adsorber 12, and the heat medium is supplied to the adsorber 12. Specifically, the controller 55 controls the heater 30a so that the heat medium reaches a predetermined temperature (input heat amount), opens the heat medium inlet valve 32a, and closes the heat medium inlet valves 31a, 33a, 34a, and 35a to supply the heat medium. As a result, the heat medium flowing through the heat medium flow path 30 is supplied to the adsorber 12 via the heat medium branch flow path 32. When the heat medium is supplied to the adsorber 12, the temperature of the adsorbent 12a increases, and the carbon dioxide adsorbed in the adsorbent 12a becomes easily desorbed.

[0060] The first desorption step is performed in the adsorber 13, and the purge gas is supplied to the adsorber 13. Specifically, the control unit 55 opens the purge gas inlet valve 73a and closes the purge gas inlet valves 71a, 72a, 74a, and 75a, and the purge gas is supplied to the adsorber 13 through the purge gas supply passage 70 and the purge gas branch passage 73. When the purge gas is supplied to the adsorber 13, the carbon dioxide adsorbed in the adsorbent 13a is desorbed from the adsorbent 13a. The carbon dioxide desorbed from the adsorbent 13a is mixed with the purge gas (hydrogen) inside the adsorber 13. In step 1A, the mixed gas outlet valve 63a is closed and the connecting passage valve 83a is opened, so that the mixed gas discharged from the adsorber 13 flows into the adsorber 14 through the mixed gas branch passage 63, the connecting passage 83, and the purge gas branch passage 74.

[0061] The second desorption step is performed in the adsorber 14, and the above-mentioned mixed gas is supplied to the adsorber 14. When the mixed gas containing the purge gas is supplied to the adsorber 14, the carbon dioxide adsorbed to the adsorbent 14a is desorbed from the adsorbent 14a. The carbon dioxide desorbed from the adsorbent 14a is mixed with the mixed gas containing the purge gas inside the adsorber 14. In step 1A, since the mixed gas outlet valve 64a is open, the mixed gas discharged from the adsorber 14 passes through the mixed gas branch passage 64 and the mixed gas passage 60 and is stored in the surge tank 40.

[0062] A cooling step is performed in the adsorber 15, and a refrigerant is supplied to the adsorber 15 (not shown). When a relatively low-temperature heat medium is supplied to the heat medium flow path of the adsorber 15, the adsorbent 15a is cooled, and the temperature of 15a decreases. This makes the adsorbent 15a more likely to adsorb carbon dioxide. In step 1A of this embodiment, the adsorber 11 is the "third adsorber", the adsorber 13 is the "first adsorber", and the adsorber 13 is the "second adsorber". In the gas separation system 1A of this embodiment as well, the control unit 55 repeatedly performs the adsorption and desorption step by changing the first adsorber, the second adsorber, and the third adsorber.

[0063] As described above, the gas separation system 1A of this embodiment also makes it possible to reuse purge gas that has passed through one adsorbent 10 and flow it into another adsorbent 10, thereby improving the efficiency of carbon dioxide desorption by the purge gas.

[0064] <Third embodiment> The gas separation system of the third embodiment has the same configuration as the gas separation system 1A of the second embodiment, but the gas separation process by the control unit 55 is different from that of the second embodiment.

[0065] FIG. 14 is an explanatory diagram of the switching timing of the adsorber 10 in the gas separation system of the third embodiment. In the gas separation process of this embodiment, as in the second embodiment, step 1B, step 2B, step 3B, step 4B, and step 5B are set as one cycle, and this cycle is repeated multiple times. In each step, the adsorption step, the heating step, the first desorption step, the second desorption step, and the cooling step are each performed in one of the five adsorber 11, 12, 13, 14, and 15. In this embodiment, each of steps 1B, 2B, 3B, 4B, and 5B is also called an "adsorption / desorption step". In addition, the adsorber 10 in which the first desorption step is performed is also called a "first adsorber", the adsorber 10 in which the second desorption step is performed is also called a "second adsorber", and the adsorber 10 in which the adsorption step is performed is also called a "third adsorber".

[0066] The gas separation process of this embodiment differs from the gas separation process of the second embodiment in that, during a part of the second desorption step, the purge gas that has flowed through the first adsorption device is caused to flow into the second adsorption device through the connection flow path 80. In this embodiment, only during the latter half of the second desorption step, the purge gas that has flowed through the first adsorption device is caused to flow into the second adsorption device through the connection flow path 80. In FIG. 14, the first half of the second desorption step is illustrated as "disconnected," indicating that the first adsorption device and the second adsorption device are not connected, and that the purge gas is not supplied to the second adsorption device. In addition, the second half of the second desorption step is illustrated as "connected," indicating that the first adsorption device and the second adsorption device are connected, and that the purge gas is supplied to the second adsorption device.

[0067] Fig. 15 is an explanatory diagram of the second desorption step of step 1B of the third embodiment. Fig. 15 illustrates a part of the gas separation system of the third embodiment. Fig. 15(A) illustrates the first half (non-connection step) of the second desorption step, and Fig. 15(B) illustrates the second half (connection step) of the second desorption step. In Fig. 15, the flow of the purge gas (hydrogen) is indicated by a thick solid line.

[0068] As shown in FIG. 14, in the step 1B, the first desorption step is performed in the adsorber 13, and the second desorption step is performed in the adsorber 14. As in the second embodiment, a purge gas is supplied to the adsorber 13 (FIG. 15). When the purge gas is supplied to the adsorber 13, the carbon dioxide adsorbed in the adsorbent 13a is desorbed from the adsorbent 13a, and the carbon dioxide desorbed from the adsorbent 13a is mixed with the purge gas (hydrogen) inside the adsorber 13. As shown in FIG. 15(A), in the first half of the second desorption step of the step 1B, the mixed gas outlet valve 63a is opened and the connection flow path valve 83a is closed. That is, since the adsorber 13 as the first adsorber and the adsorber 14 as the second adsorber are not connected, the mixed gas discharged from the adsorber 13 passes through the mixed gas branch flow path 63 and the mixed gas flow path 60 and is stored in the surge tank 40.

[0069] In step 1B, when a predetermined time has elapsed, the process proceeds to the connection step of the second desorption step. As shown in FIG. 15(B), in the latter half of the second desorption step of step 1B, the mixed gas outlet valve 63a is closed and the connection flow path valve 83a is opened. That is, since the adsorber 13 as the first adsorber and the adsorber 14 as the second adsorber are connected, the mixed gas discharged from the adsorber 13 flows into the adsorber 14 through the mixed gas branch flow path 63, the connection flow path 83, and the purge gas branch flow path 74. When the mixed gas containing the purge gas is supplied to the adsorber 14, the carbon dioxide adsorbed in the adsorbent 14a is desorbed from the adsorbent 14a and mixed with the mixed gas containing the purge gas inside the adsorber 14. In the latter half of step 1B, since the mixed gas outlet valve 64a is opened, the mixed gas discharged from the adsorber 14 passes through the mixed gas branch flow path 64 and the mixed gas flow path 60 and is stored in the surge tank 40.

[0070] In the first half of the first desorption step, the carbon dioxide concentration of the mixed gas discharged from the first adsorption device is high, so that the effect of desorption of carbon dioxide is small even if the mixed gas is passed through the second adsorption device. Therefore, as in the gas separation process of this embodiment, in the first half of the second desorption step, the first adsorption device and the second adsorption device are not connected, and the mixed gas with a high carbon dioxide concentration is stored in the surge tank 40, and in the second half when the carbon dioxide concentration of the mixed gas discharged from the first adsorption device has decreased, the first adsorption device and the second adsorption device may be connected to reuse the purge gas. In this way, the efficiency of desorption of carbon dioxide by the purge gas can be improved.

[0071] <Fourth embodiment> 16 is an explanatory diagram showing a schematic configuration of a gas separation system 1C of the fourth embodiment. The gas separation system 1C of the present embodiment includes a vacuum pump 45 in addition to the configuration of the gas separation system 1A of the second embodiment. In the embodiments described below, the same components as those of the gas separation systems 1 and 1A are denoted by the same reference numerals, and the preceding description is to be referred to.

[0072] The vacuum pump 45 is provided in a pressure reduction flow passage 46, both ends of which are connected to a mixed gas flow passage 60 between the adsorber 15 and the surge tank 40. The pressure reduction flow passage 46 is provided with a switching valve 47 for controlling the flow of the pressure reduction flow passage 46 in response to a command from the control unit 55. As shown in FIG. 16, a switching valve 48 for controlling the flow of the mixed gas flow passage 60 in response to a command from the control unit 55 is provided between the mixed gas flow passage 60 and the connecting ends of the pressure reduction flow passage 46. When the switching valve 48 is closed and the switching valve 47 is opened, the vacuum pump 45 is driven in response to a command from the control unit 55 to reduce the pressure inside the adsorber 10. In the gas separation system 1C of this embodiment, the vacuum pump 45 reduces the pressure inside the adsorber 10 during a part of the second desorption step.

[0073] In the fourth embodiment, similarly to the third embodiment, during a part of the second desorption step, the purge gas that has circulated through the first adsorption unit is caused to flow into the second adsorption unit via the connection flow path 80. In this embodiment, unlike the third embodiment, the purge gas that has circulated through the first adsorption unit is caused to flow into the second adsorption unit via the connection flow path 80 only during the first half of the second desorption step.

[0074] FIG. 17 is an explanatory diagram of the switching timing of the adsorber 10 in the gas separation system of the fourth embodiment. In the gas separation process of this embodiment, as in the third embodiment, steps 1C, 2C, 3C, 4C, and 5C are set as one cycle, and this cycle is repeated multiple times. In each step, the adsorption step, the heating step, the first desorption step, the second desorption step, and the cooling step are each performed in one of the five adsorber 11, 12, 13, 14, and 15. Each of steps 1C, 2C, 3C, 4C, and 5C in this embodiment is also called an "adsorption / desorption step." In addition, the adsorber 10 in which the first desorption step is performed is also called a "first adsorber," the adsorber 10 in which the second desorption step is performed is also called a "second adsorber," and the adsorber 10 in which the adsorption step is performed is also called a "third adsorber."

[0075] In FIG. 17, as in FIG. 14, the step in which the purge gas is supplied to the second adsorber is indicated as "connected" and the step in which the purge gas is not supplied to the second adsorber is indicated as "disconnected". In this embodiment, as described above, the first adsorber and the second adsorber are connected in the first half of the second desorption step, and the purge gas is supplied to the second adsorber. At this time, the vacuum pump 45 is not driven. In the second half of the second desorption step, the first adsorber and the second adsorber are not connected, and the purge gas is not supplied to the second adsorber. At this time, the vacuum pump 45 is driven. Thus, in this embodiment, the vacuum pump 45 is not driven in the first half of the second desorption step, and the vacuum pump 45 is driven in the second half of the second desorption step.

[0076] FIG. 18 is an explanatory diagram of the second desorption step of step 1C of the fourth embodiment. FIG. 18 illustrates a part of the gas separation system 1C. FIG. 18(A) illustrates the first half (connection step) of the second desorption step, and FIG. 18(B) illustrates the second half (disconnection step) of the second desorption step. As illustrated, in the first half of the second desorption step, the vacuum pump 45 is not driven, and in the second half of the second desorption step, the vacuum pump 45 is driven. In FIG. 18, the flow of the purge gas (hydrogen) is indicated by a thick solid line.

[0077] As shown in FIG. 17, in step 1C, the first desorption step is performed in the adsorber 13, and the second desorption step is performed in the adsorber 14. As in the second embodiment, a purge gas is supplied to the adsorber 13 (FIG. 18). When the purge gas is supplied to the adsorber 13, the carbon dioxide adsorbed in the adsorbent 13a is desorbed from the adsorbent 13a, and the carbon dioxide desorbed from the adsorbent 13a is mixed with the purge gas (hydrogen) inside the adsorber 13. As shown in FIG. 18(A), in the first half of the second desorption step of step 1C, the mixed gas outlet valve 63a is closed and the connection passage valve 83a is opened. In addition, the switching valve 47 is closed, the vacuum pump 45 is stopped, and the switching valve 48 is opened. That is, since the adsorber 13 as the first adsorber and the adsorber 14 as the second adsorber are connected, the mixed gas discharged from the adsorber 13 flows into the adsorber 14 through the mixed gas branch path 63, the connection path 83, and the purge gas branch path 74. When the mixed gas containing the purge gas is supplied to the adsorber 14, the carbon dioxide adsorbed to the adsorbent 14a is desorbed from the adsorbent 14a and mixed with the mixed gas containing the purge gas inside the adsorber 14. In the first half of the step 1C, since the mixed gas outlet valve 64a is open, the mixed gas discharged from the adsorber 14 passes through the mixed gas branch path 64 and the mixed gas path 60 and is stored in the surge tank 40.

[0078] In step 1C, when a predetermined time has elapsed, the process proceeds to the connection step of the second desorption step. As shown in FIG. 18(B), in the latter half of the second desorption step of step 1C, the mixed gas outlet valve 63a is opened and the connection flow path valve 83a is closed. In addition, the switching valve 47 is opened, the vacuum pump 45 is driven, and the switching valve 48 is closed. That is, since the adsorber 13 as the first adsorber and the adsorber 14 as the second adsorber are not connected, the mixed gas discharged from the adsorber 13 passes through the mixed gas branch flow path 63, the mixed gas flow path 60, and the pressure reduction flow path 46 and is stored in the surge tank 40.

[0079] In this embodiment, in the latter half of the second desorption step, the desorption of carbon dioxide is assisted by using the vacuum pump 45. In this case, if the adsorber 13 and the adsorber 14 are connected, the desorption of carbon dioxide in the adsorber 14 as the second adsorber is assisted, and the desorption of carbon dioxide in the adsorber 13 as the first adsorber cannot be efficiently performed. In this embodiment, in the first half of the second desorption step, the first adsorber and the second adsorber are connected to reuse the purge gas to improve the desorption efficiency of carbon dioxide by the purge gas, and in the latter half of the second desorption step, the first adsorber and the second adsorber are not connected, and the carbon dioxide desorption rate of the first adsorber is improved by using the vacuum pump 45. Even in this way, the desorption efficiency of carbon dioxide by the purge gas can be improved.

[0080] <Fifth embodiment> 19 is an explanatory diagram showing a schematic configuration of a hydrocarbon production system 5 of the fifth embodiment. The hydrocarbon production system 5 of the present embodiment is an apparatus for producing methane (CH4) using a mixed gas of carbon dioxide (CO2) and hydrogen (H2), and includes a gas separation system 1 and a hydrocarbon production unit 8. Note that the present embodiment is also applicable to a hydrocarbon production apparatus for producing hydrocarbon compounds other than methane, and is also applicable to a "hydrocarbon production apparatus" for producing, for example, compounds composed of carbon and hydrogen such as ethane and propane, and compounds mainly composed of carbon and hydrogen such as methanol, as "hydrocarbon compounds."

[0081] In this embodiment, the surge tank 40 temporarily stores the mixed gas flowing through the mixed gas passage 60. The mixed gas stored in the surge tank 40 is sent to the hydrocarbon production unit 8. The hydrocarbon production unit 8 produces methane using the mixed gas of carbon dioxide and hydrogen supplied by the surge tank 40. The produced methane is supplied to a device external to the hydrocarbon production system 5.

[0082] As described above, the hydrocarbon production system 5 of this embodiment includes the gas separation system 1, and produces methane as a hydrocarbon using carbon dioxide separated from the exhaust gas by the gas separation system 1 and hydrogen as a purge gas. Therefore, it is possible to produce hydrocarbon compounds with high purity. Also, as described above, the gas separation system 1 improves the efficiency of desorption of carbon dioxide by the purge gas by reusing the purge gas, and therefore it is possible to improve the efficiency of hydrocarbon production in the hydrocarbon production section 8. Also, it is possible to reduce the amount of excess hydrogen in the production of methane in the hydrocarbon production section 8.

[0083] <Modifications of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the invention. For example, the following modifications are also possible.

[0084] In the above embodiment, a gas other than hydrogen may be used as the purge gas. For example, rare gases such as helium and neon, water vapor, methane, and mixed gases containing at least one of them may be used. When a gas other than hydrogen is used as the purge gas in the hydrocarbon production system 5 of the fifth embodiment, a hydrogen supply unit that supplies hydrogen to the hydrocarbon production unit 8 may be provided. However, using hydrogen as the purge gas is preferable because it allows the hydrocarbon production unit 8 to produce high-purity hydrocarbons.

[0085] The number of adsorber 10 is not limited to that in the above embodiment, and may be four or less, or six or more.

[0086] In the above embodiment, an example has been shown in which the purge gas is supplied to the first adsorber, the mixed gas containing the purge gas and carbon dioxide discharged from the first adsorber is supplied to the second adsorber, and the mixed gas discharged from the second adsorber is stored in the surge tank 40. However, a configuration in which a plurality of adsorbers are further connected in series to the second adsorber may be used. For example, when a fourth adsorber, a fifth adsorber, and a sixth adsorber are connected in series subsequent to the second adsorber, the mixed gas discharged from the second adsorber is supplied to the fourth adsorber, the mixed gas discharged from the fourth adsorber containing the carbon dioxide desorbed in the fourth adsorber is supplied to the fifth adsorber, the mixed gas discharged from the fifth adsorber containing the carbon dioxide desorbed in the fifth adsorber is supplied to the sixth adsorber, and the mixed gas discharged from the sixth adsorber containing the carbon dioxide desorbed in the sixth adsorber is stored in the surge tank 40. In this way, although the amount of carbon dioxide desorbed in one step decreases in the later stages, the purge gas can be reused to desorb carbon dioxide in the adsorber 10, thereby improving the efficiency of carbon dioxide desorption by the purge gas. However, if the mixed gas discharged from the upper-stage adsorber 10 is saturated with carbon dioxide, carbon dioxide cannot be desorbed in the later-stage adsorber 10, so it is preferable to appropriately set the number of adsorbers 10 connected in series in the desorption step so that carbon dioxide can be desorbed in the later-stage adsorber 10 as well, depending on the supply amount of purge gas and the time for one step.

[0087] In the above embodiment, an example was shown in which the temperature of the adsorbent was increased by flowing a purge gas, i.e., a so-called temperature swing was performed to desorb carbon dioxide, but carbon dioxide may be desorbed only by flowing a purge gas without performing a temperature swing. Also, in addition to supplying a purge gas, the pressure may be reduced using a vacuum pump, and a temperature swing may also be performed.

[0088] In the third embodiment, in the latter half of the second desorption step, the purge gas that has flowed through the first adsorber is made to flow into the second adsorber through the connecting flow path, and in the fourth embodiment, in the first half of the second desorption step, the purge gas that has flowed through the first adsorber is made to flow into the second adsorber through the connecting flow path, but the period during which the first adsorber and the second adsorber are connected to each other and the purge gas is reused is not limited to the above embodiments. For example, the second desorption step may be divided into three periods, namely, an early period, a middle period, and a late period, in which the first adsorber and the second adsorber are not connected to each other and carbon dioxide is desorbed only by the first adsorber in the early period, the first adsorber and the second adsorber are connected (multi-staged) and carbon dioxide is desorbed by the first adsorber and the second adsorber in the middle period, and the first adsorber and the second adsorber are connected to each other (multi-staged) and carbon dioxide is desorbed by the first adsorber and the second adsorber in the late period.

[0089] In the above third and fourth embodiments, the connection / non-connection of the adsorber in the second desorption step is switched according to the passage of time, but the present invention is not limited to this. For example, the connection / non-connection may be switched according to the carbon dioxide concentration of the mixed gas discharged from the first adsorber, such as connecting the adsorber when the carbon dioxide concentration of the mixed gas discharged from the first adsorber is low (multi-stage). Also, the connection / non-connection may be switched according to the carbon dioxide desorption rate, such as disconnecting the adsorber when the carbon dioxide desorption rate from the adsorber is high (single adsorber).

[0090] In the above embodiment, the mixed gas branch path and the purge gas branch path are connected by the connection flow path 80 as a bypass flow path, but the connection flow path is not limited to the above embodiment. For example, the connection flow path 80 may be provided separately from the mixed gas branch path and the purge gas branch path. When the connection flow path 80 is provided separately from the mixed gas branch path and the purge gas branch path, they may be connected so that the flow direction of the purge gas in the first adsorber is the same as that in the above embodiment (for example, the first adsorber and the lower side of the second adsorber in the drawing are connected by the connection flow path 80), or the flow direction of the purge gas in the first adsorber and the flow direction of the purge gas in the second adsorber are different and may be connected to turn (for example, the lower side of the first adsorber and the lower side of the second adsorber in the drawing are connected by the connection flow path 80).

[0091] The surge tank in the above embodiment does not have to be provided. If a surge tank is provided, it is preferable because it can stabilize the ratio of hydrogen to carbon dioxide in the mixed gas and can keep the ratio of hydrogen to carbon dioxide within a target range without having to adjust the flow rate of hydrogen successively.

[0092] As another embodiment, a carbon dioxide circulation system or a fuel production system using hydrocarbons as fuel may be configured. For example, the carbon dioxide circulation system includes the hydrocarbon production system 5 of the fifth embodiment, a combustor that uses methane supplied from the hydrocarbon generation unit 8 of the hydrocarbon production system 5, carbon dioxide supplied from the surge tank 40 of the hydrocarbon production system 5, and air in the atmosphere, and circulates carbon dioxide by supplying exhaust gas discharged from the combustor to the hydrocarbon production system 5. In addition, the fuel production system includes the hydrocarbon production system 5 of the fifth embodiment, and a fuel production unit, and produces fuel using the hydrocarbons produced by the hydrocarbon production system 5.

[0093] The present invention has been described above based on the embodiments and modifications, but the above-mentioned embodiments are intended to facilitate understanding of the present invention and do not limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0094] 1, 1A, 1C, 1P...Gas separation system 5. Hydrocarbon production system 8...Hydrocarbon production section 10, 11, 12, 13, 14, 15...Adsorber 11a, 12, 13a, 14a, 15a...Adsorbent 20...Carbon dioxide-containing gas supply passage 21, 22, 23...Exhaust gas distribution channel 21a, 22a, 23a...Exhaust gas inlet valve 30…Heat medium passage 30a…Heater 31, 32...heat medium distribution channel 31a, 32a... Heat medium inlet valve 40…Surge tank 45…Vacuum pump 46…Pressure reduction channel 47, 48...Switching valve 55...Control section 60...Mixed gas flow path 61, 62, 63, 64...Mixed gas distribution channels 61a, 62a, 63a, 64a...Mixed gas outlet valve 70...Purge gas supply passage 70a...Flow rate controller 71, 72, 73, 74... Purge gas distribution channels 71a, 72a, 73a...Purge gas inlet valve 80, 81, 82, 83, 84, 85...Connecting flow paths 81a, 82a, 83a, 84a, 85a... Connection passage valve

Claims

1. A gas separation system including a plurality of adsorbers each containing an adsorbent capable of adsorbing carbon dioxide, a connection flow path capable of connecting a first adsorption device and a second adsorption device in series among the plurality of adsorption devices; a purge gas supply passage capable of supplying a purge gas to the first adsorption device; a control unit capable of simultaneously executing a first desorption step of supplying the purge gas to the first adsorber via the purge gas supply flow path in a state in which carbon dioxide is adsorbed in the first adsorber and the second adsorber, and desorbing carbon dioxide from the first adsorber, and a second desorption step of connecting the second adsorber to the first adsorber via the connecting flow path during at least a portion of the step, causing the purge gas that has circulated inside the first adsorber to flow into the second adsorber via the connecting flow path, and desorbing carbon dioxide from the second adsorber; Equipped with The purge gas is hydrogen. Gas separation systems.

2. 2. The gas separation system of claim 1, a carbon dioxide-containing gas supply flow path capable of supplying a carbon dioxide-containing gas to a third adsorption device different from the first adsorption device and the second adsorption device; The control unit is An adsorption step of supplying the carbon dioxide-containing gas to the third adsorption device through the carbon dioxide-containing gas supply passage to adsorb carbon dioxide can be carried out simultaneously with the first desorption step, an adsorption / desorption process including the first desorption process, the second desorption process, and the adsorption process, which are simultaneously performed, can be repeatedly performed by changing the first adsorption device, the second adsorption device, and the third adsorption device in which the first desorption process, the second desorption process, and the adsorption process are performed, respectively; Gas separation systems.

3. 3. A gas separation system according to claim 1 or claim 2, The control unit is during a part of the second desorption step, the purge gas that has circulated through the first adsorption device is caused to flow into the second adsorption device via the connecting flow path; Gas separation systems.

4. 1. A hydrocarbon production system comprising: A gas separation system according to any one of claims 1 to 3; A hydrocarbon production unit is connected to the gas separation system and produces a hydrocarbon compound using a mixed gas of carbon dioxide separated by the gas separation system and hydrogen used as the purge gas. Hydrocarbon production systems.

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