Gas separation system

Abstract

To provide a technique capable of suppressing a decrease in the concentration of carbon dioxide in a mixed gas even when the desorption amount of carbon dioxide decreases with the lapse of time.SOLUTION: A gas separation system includes a first adsorption device, a second adsorption device, a mixed gas delivery flow path through which a mixed gas containing carbon dioxide and a purge gas delivered from the first adsorption device and the second adsorption device can flow when the purge gas is supplied to the first adsorption device and the second adsorption device, and a control unit that controls the gas separation system such that an adsorption process and a desorption process are repeatedly performed in the first adsorption device and the second adsorption device. The controller performs control such that the mixed gas is delivered from the second adsorption device to the mixed gas delivery flow path in a case where the concentration of the carbon dioxide in the mixed gas delivered from the first adsorption device is lower than a first set concentration set in advance in a state where the second adsorption device has undergone the adsorption process and the desorption process is being performed in the first adsorption device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas separation system. [Background technology]

[0002] Conventionally, there have been known techniques for separating carbon dioxide from exhaust gases, etc., using an adsorbent that adsorbs carbon dioxide. For example, Patent Documents 1 and 2 disclose a methane production apparatus that produces methane using a mixed gas containing carbon dioxide and hydrogen that is delivered from an adsorber after carbon dioxide adsorbed to an adsorbent housed in the adsorber is desorbed by supplying a purge gas to the adsorber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-142806 [Patent Document 2] Japanese Patent Publication No. 2022-97832 Summary of the Invention [Problem to be solved by the invention]

[0004] In the desorption process in which carbon dioxide is desorbed from the adsorbent, the amount of carbon dioxide desorbed tends to decrease over time as the amount of adsorbed carbon dioxide decreases. As a result, even if the supply amount of purge gas is kept constant with the intention of maintaining the H2 / CO2 ratio in the mixed gas at an appropriate value from the perspective of hydrocarbon synthesis efficiency, if the amount of carbon dioxide desorbed decreases over time, the H2 / CO2 ratio in the mixed gas will deviate from the appropriate value. For this reason, there has been a demand for technology that can suppress the decrease in the carbon dioxide concentration in the mixed gas even if the amount of carbon dioxide desorbed decreases over time.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and aims to provide a technology that can suppress a decrease in the concentration of carbon dioxide in a mixed gas even if the amount of carbon dioxide desorption decreases over time. [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 aspects.

[0007] (1) According to one aspect of the present invention, there is provided a gas separation system for separating carbon dioxide from a raw material gas containing carbon dioxide, the gas separation system including: a first adsorber accommodating a first adsorbent capable of adsorbing carbon dioxide therein; a second adsorber accommodating a second adsorbent capable of adsorbing carbon dioxide therein; a mixed gas delivery flow path through which a mixed gas containing carbon dioxide and the purge gas delivered from the first adsorber and the second adsorber can flow when a purge gas is supplied to the first adsorber and the second adsorber; an adsorption step of supplying the raw material gas to the first adsorber or the second adsorber to adsorb carbon dioxide onto the first adsorbent or the second adsorbent; and a control unit that controls the gas separation system so that a desorption process, in which the purge gas is supplied to the first adsorbent or the second adsorbent and carbon dioxide is desorbed from the first adsorbent or the second adsorbent, is repeatedly performed in the first adsorbent and the second adsorbent, and the control unit controls the second adsorbent to send out the mixed gas to the mixed gas delivery passage when the concentration of carbon dioxide in the mixed gas sent out from the first adsorbent is lower than a predetermined first set concentration when the second adsorbent has undergone the adsorption process and the desorption process is being performed in the first adsorbent.

[0008] According to this configuration, when the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device undergoing the desorption process is lower than the first set concentration, the mixed gas is delivered from the second adsorption device that has undergone the adsorption process to the mixed gas delivery path. This prevents the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery path from becoming further lower than the first set concentration. In other words, even if the amount of carbon dioxide desorbed in the first adsorption device decreases over time, it is possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery path from decreasing.

[0009] (2) In the gas separation system of the above form, the control unit may control the mixed gas not to be sent from the second adsorption device to the mixed gas delivery path when the concentration is higher than a second set concentration that is pre-set to a value equal to or higher than the first set concentration when in the above state. According to this configuration, when the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device in which the desorption process is being performed is higher than the second set concentration, delivery of the mixed gas from the second adsorption device to the mixed gas delivery path is stopped. This makes it possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery path from becoming further higher than the second set concentration. In other words, according to this configuration, the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery path is prevented from becoming further lower than the first set concentration while being prevented from becoming further higher than the second set concentration, making it possible to prevent large fluctuations in the concentration of carbon dioxide in the mixed gas.

[0010] (3) In the gas separation system of the above form, a mixed gas supply flow path can supply the mixed gas discharged from the first adsorbent to the second adsorbent, and the control unit may control the mixed gas to be discharged from the second adsorbent to the mixed gas discharge flow path by supplying the mixed gas discharged from the first adsorbent to the second adsorbent via the mixed gas supply flow path when the concentration is lower than the first set concentration in the above state. According to this configuration, when the mixed gas is delivered from the second adsorbent to the mixed gas delivery passage, the mixed gas flowing downstream of the mixed gas delivery passage corresponds to the mixed gas delivered from the first adsorbent to which carbon dioxide desorbed from the second adsorbent that has undergone the adsorption process has been added. This makes it possible to prevent the carbon dioxide concentration in the mixed gas flowing downstream of the mixed gas delivery passage from becoming further lower than the first set concentration.

[0011] (4) In the gas separation system of the above form, a purge gas supply flow path capable of supplying the purge gas to the first adsorbent and the second adsorbent may be further provided, and when the concentration is lower than the first set concentration in the above state, the control unit may control the mixed gas to be delivered from the second adsorbent to the mixed gas delivery flow path by supplying a portion of the purge gas delivered via the purge gas supply flow path to the second adsorbent. According to this configuration, when the mixed gas is delivered from the second adsorption device to the mixed gas delivery passage, the mixed gas flowing downstream of the mixed gas delivery passage corresponds to a mixture of the mixed gas delivered from the first adsorption device and the mixed gas delivered from the second adsorption device in a state that has undergone the adsorption process. Therefore, it is possible to prevent the carbon dioxide concentration in the mixed gas flowing downstream of the mixed gas delivery passage from becoming further lower than the first set concentration.

[0012] (5) According to another aspect of the present invention, there is provided a gas separation system for separating carbon dioxide from a raw material gas containing carbon dioxide, the gas separation system including: a first adsorber accommodating a first adsorbent capable of adsorbing carbon dioxide therein; a second adsorber accommodating a second adsorbent capable of adsorbing carbon dioxide therein; a mixed gas delivery flow path through which a mixed gas containing carbon dioxide and the purge gas delivered from the first adsorber and the second adsorber can flow when a purge gas is supplied to the first adsorber and the second adsorber; an adsorption step of supplying the raw material gas to the first adsorber or the second adsorber to adsorb carbon dioxide onto the first adsorbent or the second adsorbent; and a control unit that controls the gas separation system so that a desorption process, in which the purge gas is supplied to the first adsorbent or the second adsorbent to desorb carbon dioxide from the first adsorbent or the second adsorbent, is repeatedly performed in the first adsorbent and the second adsorbent, and the control unit controls the amount of the mixed gas delivered from the second adsorbent to the mixed gas delivery flow path to be increased when the second adsorbent has undergone the adsorption process and the desorption process is being performed in the first adsorbent and the concentration of carbon dioxide in the mixed gas delivered from the first adsorbent is lower than a predetermined first set concentration.

[0013] According to this configuration, when the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device undergoing the desorption process is lower than the first set concentration, the amount of mixed gas delivered from the second adsorption device that has undergone the adsorption process to the mixed gas delivery passage is increased. This makes it possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage from becoming further lower than the first set concentration. In other words, even if the amount of carbon dioxide desorbed in the first adsorption device decreases over time, it is possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage from decreasing.

[0014] (6) In the gas separation system of the above form, when the state is such that the concentration is higher than a second set concentration that is set in advance to a value equal to or higher than the first set concentration, the control unit may control the amount of the mixed gas sent from the second adsorption device to the mixed gas delivery passage to be reduced. According to this configuration, when the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device in which the desorption process is being performed is higher than the second set concentration, the amount of mixed gas delivered from the second adsorption device to the mixed gas delivery passage is reduced. This makes it possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage from becoming even higher than the second set concentration. In other words, according to this configuration, the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage is prevented from becoming even lower than the first set concentration while also being prevented from becoming even higher than the second set concentration, making it possible to prevent large fluctuations in the concentration of carbon dioxide in the mixed gas.

[0015] (7) The gas separation system of the above aspect may further include a mixed gas supply flow path capable of supplying the mixed gas discharged from the first adsorber to the second adsorber, and the control unit may, when the concentration is lower than the first set concentration in the above state, control to increase a second mixed gas flow rate, which is the flow rate of the mixed gas discharged from the first adsorber that is supplied to the second adsorber via the mixed gas supply flow path, and control to decrease a first mixed gas flow rate, which is the flow rate of the mixed gas discharged from the first adsorber that is not supplied to the second adsorber, and when the concentration is higher than the second set concentration in the above state, control to decrease the second mixed gas flow rate and control to increase the first mixed gas flow rate. According to this configuration, the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage is adjusted by controlling the first mixed gas flow rate and the second mixed gas flow rate based on a comparison of the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device with the first set concentration and the second set concentration. This makes it possible to suppress large fluctuations in the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage.

[0016] (8) The gas separation system of the above aspect may further include a purge gas supply flow path capable of supplying the purge gas to the first adsorption device and the second adsorption device, and the control unit may, when the concentration is lower than the first set concentration in the above state, control a first purge gas flow rate, which is the flow rate of the purge gas supplied via the purge gas supply flow path and is supplied to the first adsorption device, to decrease, and control a second purge gas flow rate, which is the flow rate of the purge gas supplied via the purge gas supply flow path and is supplied to the second adsorption device, to increase, and when the concentration is higher than the second set concentration in the above state, control the first purge gas flow rate to increase, and control the second purge gas flow rate to decrease. According to this configuration, the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage is adjusted by controlling the first purge gas flow rate and the second purge gas flow rate based on a comparison of the concentration of carbon dioxide in the mixed gas delivered from the first adsorber with the first set concentration and the second set concentration. This makes it possible to prevent large fluctuations in the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage.

[0017] The present invention can be realized in various forms, for example, a carbon dioxide separation method, a gas separation system control method, a computer program for controlling a gas separation system, a hydrocarbon production system, a control method for these systems, a computer program for controlling these systems, a server device for distributing these computer programs, a non-transitory storage medium on which the computer program is stored, and the like. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is an explanatory diagram illustrating the configuration of a gas separation system according to a first embodiment. [Figure 2] FIG. 10 is an explanatory diagram showing a state in which carbon dioxide is not added to the mixed gas. [Figure 3] FIG. 10 is an explanatory diagram showing a state in which carbon dioxide is being added to a mixed gas. [Figure 4] FIG. 2 is an explanatory diagram showing switching between various processes performed in the adsorber. [Figure 5] 10 is a flowchart showing the procedure of a route switching process executed by a control unit. [Figure 6] FIG. 10 is an explanatory diagram of the effect of the route switching process. [Figure 7] FIG. 10 is an explanatory diagram of a route added by the route addition process. [Figure 8] 10 is a flowchart showing the procedure of a route addition process according to the second embodiment. [Figure 9] FIG. 4 is an explanatory diagram showing a first mixed gas flow rate and a second mixed gas flow rate. [Figure 10] 10 is a flowchart showing the procedure of a flow rate adjustment process according to a third embodiment. [Figure 11] FIG. 10 is an explanatory diagram of the effect of the flow rate adjustment process. [Figure 12] FIG. 4 is an explanatory diagram showing a first purge gas flow rate and a second purge gas flow rate. [Figure 13] 13A and 13B are diagrams illustrating the effect of the flow rate adjustment process in the fourth embodiment. [Figure 14] FIG. 10 is an explanatory diagram illustrating the configuration of a gas separation system according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] First Embodiment FIG. 1 is an explanatory diagram illustrating the configuration of a gas separation system 1 according to one embodiment of the present invention. The gas separation system 1 is a system that separates carbon dioxide from a feed gas containing carbon dioxide. The gas separation system 1 includes a first adsorber 10, a second adsorber 20, a combustion facility EG, an exhaust gas supply flow path 50, an exhaust gas discharge flow path 60, a hydrogen supply source HY, a hydrogen supply flow path 70, a mixed gas delivery flow path 80, a hydrocarbon synthesis unit 90, and a control unit 100. The first and second adsorber 10, 20 may also be collectively referred to simply as "adsorbers."

[0020] The first adsorber 10 is a device for separating carbon dioxide from a raw material gas. The first adsorber 10 accommodates therein a first adsorbent 12 capable of adsorbing carbon dioxide. In the gas separation system 1, exhaust gas discharged from the combustion equipment EG flows into the first adsorber 10 as the raw material gas. Examples of the first adsorbent 12 include zeolite, activated carbon, and silica gel. The second adsorber 20 is an adsorbent similar to the first adsorber 10. The second adsorber 20 accommodates therein a second adsorbent 22 similar to the first adsorber 10. The first and second adsorbents 12 and 22 may also be collectively referred to simply as adsorbents.

[0021] The combustion equipment EG is a combustion furnace in a factory. The exhaust gas discharged from the combustion equipment EG contains oxygen, nitrogen, water, and the like in addition to carbon dioxide adsorbed by the first and second adsorbents 12 and 22. The exhaust gas supply flow path 50 connects the combustion equipment EG to the first and second adsorbers 10 and 20, respectively, and is a gas flow path capable of supplying the exhaust gas discharged from the combustion equipment EG to the first and second adsorbers 10 and 20. The exhaust gas supply flow path 50 includes branch flow paths 51 and 52 for supplying the exhaust gas to the first and second adsorbers 10 and 20, respectively. Each of the branch flow paths 51 and 52 is provided with a first exhaust gas supply valve 51v and a second exhaust gas supply valve 52v. By controlling the opening and closing of these valves, it is possible to switch between performing and stopping the supply of exhaust gas to each of the first and second adsorbers 10 and 20.

[0022] The exhaust gas discharge flow path 60 connects each of the first and second adsorber 10, 20 to the outside of the gas separation system 1, and is a gas flow path that can discharge the exhaust gas that has been discharged from the combustion equipment EG and then passed through each of the first and second adsorber 10, 20 to the outside of the gas separation system 1. The exhaust gas discharge flow path 60 includes branch flow paths 61, 62 for discharging the exhaust gas from each of the first and second adsorber 10, 20. A first exhaust gas discharge valve 61v and a second exhaust gas discharge valve 62v are provided in each of the branch flow paths 61, 62. By controlling the opening and closing of these valves, it is possible to switch between performing and stopping the exhaust gas discharge from each of the first and second adsorber 10, 20.

[0023] In the exhaust gas supplied from the combustion equipment EG to the first and second adsorbers 10 and 20 via the exhaust gas supply flow path 50, carbon dioxide contained in the exhaust gas is adsorbed by the first and second adsorbents 12 and 22. The remaining exhaust gas that is not adsorbed by the first and second adsorbents 12 and 22 is discharged to the outside of the gas separation system 1 via the exhaust gas discharge flow path 60.

[0024] The hydrogen supply source HY is a water electrolysis device. The hydrogen supply passage 70 is a gas passage that connects the first adsorption device 10 and the second adsorption device 20 in parallel and can supply hydrogen supplied from the hydrogen supply source HY to the first adsorption device 10 and the second adsorption device 20. The hydrogen supply passage 70 includes branch passages 71 and 72 for supplying hydrogen to the first and second adsorption devices 10 and 20, respectively. A first hydrogen supply valve 71v and a second hydrogen supply valve 72v are provided in each of the branch passages 71 and 72. By controlling the opening and closing of these valves, it is possible to switch between starting and stopping the supply of hydrogen to each of the first and second adsorption devices 10 and 20. The hydrogen supplied from the hydrogen supply source HY through the hydrogen supply passage 70 to the first and second adsorption devices 10 and 20 is used as a purge gas for desorbing carbon dioxide adsorbed in the first and second adsorbents 12 and 22. In other words, the hydrogen supply passage 70 corresponds to a purge gas supply passage.

[0025] The mixed gas delivery passage 80 connects the first adsorber 10 and the second adsorber 20 in parallel and is a passage through which the mixed gas delivered from the first and second adsorber 10, 20 to the hydrocarbon synthesis apparatus 90 (described later) can flow when purge gas is supplied to the insides of the first and second adsorber 10, 20. The mixed gas contains carbon dioxide and hydrogen as a purge gas. The mixed gas delivery passage 80 includes branch passages 81, 82 for delivering the mixed gas from each of the first and second adsorber 10, 20. Each of the branch passages 81, 82 is provided with a first mixed gas delivery valve 81v and a second mixed gas delivery valve 82v. By controlling the opening and closing of these valves, it is possible to switch between starting and stopping the delivery of the mixed gas from each of the first and second adsorber 10, 20.

[0026] The mixed gas supply flow path S1 connects a portion of the mixed gas delivery flow path 80 downstream of the position where the first mixed gas delivery valve 81v is provided with a portion of the hydrogen supply flow path 70 upstream of the position where the second hydrogen supply valve 72v is provided. The mixed gas supply flow path S1 is a gas flow path that can supply the mixed gas delivered from the first adsorber 10 to the second adsorber 20. A mixed gas supply valve V12 is provided in the mixed gas supply flow path S1. By controlling the opening and closing of the mixed gas supply valve V12, it is possible to switch between executing and stopping the supply of the mixed gas from the first adsorber 10 to the second adsorber 20.

[0027] Furthermore, a mixed gas delivery valve V11 is provided in a portion of the mixed gas delivery passage 80 downstream of position C where the mixed gas supply passage S1 is connected. By controlling the opening and closing of the mixed gas delivery valve V11, it is possible to switch between running and stopping the flow of mixed gas to the portion of the mixed gas delivery passage 80 downstream of position C.

[0028] The hydrocarbon synthesis unit 90 is connected to the downstream end of the mixed gas delivery passage 80, and synthesizes methane by a methanation reaction using the mixed gas supplied from the first and second adsorbers 10, 20 via the mixed gas delivery passage 80. The control unit 100 is a computer including a ROM, a RAM, and a CPU, and performs overall control of the gas separation system 1. The control unit 100 controls various valves and the like provided in each of the above-mentioned passages. The control unit 100 controls the gas separation system 1 so that the adsorption process, desorption process, and additional standby process, which will be described below, are performed in each of the first and second adsorbers 10, 20.

[0029] The control unit 100 controls the gas separation system 1 so that, in each of the first and second adsorbers 10, 20, the following steps are repeatedly performed: an adsorption process in which exhaust gas, which is a raw material gas, is supplied to the adsorber to adsorb carbon dioxide onto the adsorbent; a desorption process in which hydrogen, which is a purge gas, is supplied to the adsorber after the adsorption process to desorb carbon dioxide from the adsorbent; and an additional standby process in which an adsorber other than the adsorber undergoing the desorption process is placed on standby, and carbon dioxide is desorbed from the other adsorber and added to the mixed gas delivered from the adsorber undergoing the desorption process, as necessary. The adsorber undergoing the additional standby process has already undergone the adsorption process. The state after the adsorption process refers to a state in which carbon dioxide has been sufficiently adsorbed onto the adsorbent after the adsorption process.

[0030] When the adsorption step is being performed in the first adsorber 10, the first exhaust gas supply valve 51v and the first exhaust gas discharge valve 61v are in an open state, and the first hydrogen supply valve 71v and the first mixed gas delivery valve 81v are in a closed state. In this state, carbon dioxide contained in the exhaust gas supplied from the combustion equipment EG to the first adsorber 10 is adsorbed by the first adsorbent 12. The remaining exhaust gas that is not adsorbed by the first adsorbent 12 is discharged to the outside of the gas separation system 1 via the exhaust gas discharge flow path 60 (branch flow path 61).

[0031] FIG. 2 is an explanatory diagram showing a state in which carbon dioxide is not added from the second adsorber 20 to the mixed gas discharged from the first adsorber 10 during the desorption process when the additional standby process is being performed in the second adsorber 20. At this time, the mixed gas discharged from the first adsorber 10 flows through the path indicated by the bold line in FIG. 2. That is, the first exhaust gas supply valve 51v and the first exhaust gas discharge valve 61v are closed, and the first hydrogen supply valve 71v and the first mixed gas discharge valve 81v are open. The mixed gas discharge valve V11 is open, and the mixed gas supply valve V12 is closed. The second exhaust gas supply valve 52v, the second exhaust gas discharge valve 62v, the second hydrogen supply valve 72v, and the second mixed gas discharge valve 82v are closed.

[0032] In this state, hydrogen supplied from the hydrogen supply source HY to the first adsorber 10 acts as a purge gas to desorb the carbon dioxide adsorbed in the first adsorbent 12. The desorbed carbon dioxide is sent together with hydrogen as a mixed gas to the mixed gas delivery flow path 80 (branch flow path 81) and then reaches the hydrocarbon synthesis system 90. In Fig. 2, the path taken by hydrogen delivered from the hydrogen supply source HY to reach the first adsorber 10 and the path taken by the mixed gas delivered from the first adsorber 10 to pass through the mixed gas delivery valve V11 and reach the hydrocarbon synthesis system 90 are each shown by thick lines. The path shown by thick lines in Fig. 2 is called path R1.

[0033] FIG. 3 is an explanatory diagram showing a state in which carbon dioxide is added from the second adsorption device 20 to the mixed gas discharged from the first adsorption device 10 during the desorption process while the second adsorption device 20 is performing an additional standby process. If the carbon dioxide concentration in the mixed gas discharged from the first adsorption device 10 becomes low while the first adsorption device 10 is performing a desorption process, carbon dioxide is added to the mixed gas from the second adsorption device 20, which is performing an additional standby process. At this time, the mixed gas discharged from the first adsorption device 10 flows through the path indicated by the bold line in FIG. 3. That is, the mixed gas discharge valve V11 is closed, and the mixed gas supply valve V12 is open. In addition, the second exhaust gas supply valve 52v, the second exhaust gas exhaust valve 62v, and the second hydrogen supply valve 72v are closed, and the second mixed gas discharge valve 82v is open.

[0034] In this state, the mixed gas supplied from the first adsorber 10 to the second adsorber 20 via the mixed gas supply passage S1 desorbs the carbon dioxide adsorbed in the second adsorbent 22. The mixed gas supplied to the second adsorber 20 is delivered to the mixed gas delivery passage 80 (branch passage 82) while the carbon dioxide desorbed in the second adsorber 20 is added thereto, and then reaches the hydrocarbon synthesis unit 90. In Fig. 3, the path taken by hydrogen delivered from the hydrogen supply source HY to reach the first adsorber 10 and the path taken by the mixed gas delivered from the first adsorber 10 to pass through the mixed gas supply valve V12 and reach the hydrocarbon synthesis unit 90 are each shown by thick lines. The path shown by thick lines in Fig. 3 is referred to as path R2. That is, by controlling the opening and closing of the mixed gas discharge valve V11 and the mixed gas supply valve V12, it is possible to switch whether the mixed gas discharged from the first adsorption device 10 passes through the second adsorption device 20 before reaching the hydrocarbon synthesis device 90 (whether it passes through route R1 or route R2).

[0035] 1, similar to the mixed gas supply flow path S1, mixed gas delivery valve V11, and mixed gas supply valve V12 in the first adsorption device 10, the gas separation system 1 also includes a mixed gas supply flow path that can supply the mixed gas discharged from the second adsorption device 20 to the first adsorption device 10, and two valves that can switch whether or not the mixed gas discharged from the second adsorption device 20 passes through the first adsorption device 10 on its way to the hydrocarbon synthesis device 90. When the adsorption step, desorption step, and additional standby step are performed in the second adsorption device 20, each step is carried out by opening and closing the various valves corresponding to the second adsorption device 20, in the same way as when the adsorption step, desorption step, and additional standby step are performed in the first adsorption device 10 described above.

[0036] 2 and 3 , when the second adsorber 20 has undergone the adsorption process and the first adsorber 10 is performing the desorption process, if the concentration of carbon dioxide in the mixed gas delivered from the first adsorber 10 is low, the control unit 100 controls the mixed gas delivered from the first adsorber 10 to be supplied to the second adsorber 20 via the mixed gas supply flow path S1, thereby delivering the mixed gas from the second adsorber 20 to the mixed gas delivery flow path 80. At this time, the control unit 100 controls the opening and closing of various valves to supply the mixed gas from the first adsorber 10 to the second adsorber 20 and to deliver the mixed gas from the second adsorber 20 to the mixed gas delivery flow path 80.

[0037] FIG. 4 is an explanatory diagram showing the switching of various processes performed in the first and second adsorption devices 10 and 20. In the gas separation system 1, each of the first and second adsorption devices 10 and 20 performs a standby process in addition to the adsorption process, desorption process, and additional standby process described above. The standby process is a process in which an adsorption device other than the adsorption device undergoing the adsorption process is placed on standby. The adsorption device undergoing the standby process is in a state in which no supply or discharge of exhaust gas, no supply of hydrogen, or delivery of mixed gas is performed. As shown in FIG. 4, each of the first and second adsorption devices 10 and 20 repeats various processes in the order of cycles 1 to 4.

[0038] 5 is a flowchart showing the steps of the route switching process executed by the control unit 100. The route switching process is repeatedly executed when one adsorber has undergone the adsorption process and the other adsorber is undergoing the desorption process. The route switching process switches between route R1 and route R2 depending on the concentration of carbon dioxide in the mixed gas delivered from the other adsorber. Here, an example of the route switching process executed when the desorption process is being carried out in the first adsorber 10 and the additional standby process is being carried out in the second adsorber 20 will be described. Note that at the start of the route switching process that is executed for the first time after the desorption process is started in the first adsorber 10, the route through which hydrogen delivered from the hydrogen supply source HY becomes mixed gas and reaches the hydrocarbon synthesis unit 90 (hereinafter referred to as the used route) is route R1.

[0039] When the path switching process is started, first, the control unit 100 determines whether the carbon dioxide concentration Cc in the mixed gas delivered from the first adsorption device 10 is lower than a preset first set concentration C1 (step S11). The concentration Cc is measured by a concentration sensor (not shown) provided in a portion of the mixed gas delivery flow path 80 upstream of position C (see FIG. 1, etc.). In the gas separation system 1, the first set concentration C1 is set in consideration of the H2 / CO2 ratio in the mixed gas that is suitable for hydrocarbon synthesis.

[0040] If it is determined that the concentration Cc is lower than the first set concentration C1 (step S11: YES), the control unit 100 switches the route to be used to route R2 (step S12). Thereafter, the control unit 100 ends the route switching process. Note that if the route to be used was already route R2 before step S12 was executed, the execution of step S12 keeps the route to be used as route R2.

[0041] On the other hand, if it is determined that the concentration Cc is equal to or greater than the first set concentration C1 (step S11: NO), the control unit 100 determines whether the concentration Cc is higher than a second set concentration C2, which is preset to a value equal to or greater than the first set concentration C1 (step S13). The second set concentration C2, like the first set concentration C1, is set in consideration of the H2 / CO2 ratio in the mixed gas that is suitable for hydrocarbon synthesis. For example, the concentration Cc may become higher than the second set concentration C2 if the concentration Cc rises excessively due to the route R2 being maintained for a long period of time. If the concentration Cc is equal to or less than the second set concentration C2 (step S13: NO), the control unit 100 terminates the route switching process.

[0042] If the concentration Cc is higher than the second set concentration C2 (step S13: YES), the control unit 100 switches the route to be used to route R1 (step S14). In other words, the control unit 100 controls the second adsorption unit 20 not to send out the mixed gas to the mixed gas delivery passage 80. Thereafter, the control unit 100 ends the route switching process. Note that if the route to be used was already route R1 before step S14 was executed, the execution of step S14 causes the route to remain as route R1. Thereafter, the control unit 100 ends the route switching process.

[0043] FIG. 6 is an explanatory diagram of the effect of the path switching process. In FIG. 6, the horizontal axis represents the elapsed time since the start of the desorption process, and the vertical axis represents the concentration Cc. The solid line L1 represents the fluctuation of the concentration Cc in the gas separation system 1. The dashed line L2 represents the fluctuation of the concentration Cc in the gas separation system of the comparative example. The gas separation system of the comparative example includes only one adsorber. That is, in the gas separation system of the comparative example, the adsorption process and the desorption process are performed in one adsorber, and the concentration Cc refers to the concentration of carbon dioxide in the mixed gas delivered from that one adsorber. Note that in the gas separation system of the comparative example, the desorption process is performed on an adsorber in which carbon dioxide has been sufficiently adsorbed by the adsorbent after the adsorption process. In contrast, in the gas separation system 1, the desorption process is performed (via the standby process) after an additional standby process in which carbon dioxide can be desorbed from an adsorber in which carbon dioxide has been sufficiently adsorbed by the adsorbent after the adsorption process (see FIG. 4). Therefore, the maximum value of the concentration Cc on the solid line L1 is lower than the maximum value of the concentration Cc on the dashed line L2.

[0044] As shown by the dashed line L2, in the gas separation system of the comparative example, the concentration Cc increases for approximately 100 seconds after the start of the desorption process, but then continues to decrease over time. This is because the amount of carbon dioxide desorbed decreases as the amount of carbon dioxide adsorbed decreases over time. On the other hand, as shown by the solid line L1, in the gas separation system 1 of this embodiment, the concentration Cc increases for approximately 50 seconds after the start of the desorption process and then decreases over time for 100 seconds, but thereafter the concentration Cc repeatedly increases and decreases, remaining within a certain range. This is because when the concentration Cc becomes lower than the first set concentration C1, the concentration Cc is increased by switching the use route to route R2, and when the concentration Cc becomes higher than the second set concentration C2, the concentration Cc is decreased by switching the use route to route R1. That is, the first set concentration C1 and the second set concentration C2 used in the path switching process are set as the lower and upper limits of a desired range in order to keep the concentration Cc within that range.

[0045] As described above, according to the gas separation system 1 of the above-described embodiment, when the concentration Cc is lower than the first set concentration C1, the mixed gas delivered from the first adsorption device 10 is supplied to the second adsorption device 20 via the mixed gas supply flow path S1, thereby delivering the mixed gas from the second adsorption device 20 in a state of having undergone the adsorption process to the mixed gas delivery flow path 80. At this time, the mixed gas flowing downstream of the mixed gas delivery flow path 80 corresponds to the mixed gas delivered from the first adsorption device 10 to which carbon dioxide desorbed from the second adsorption device 20 in a state of having undergone the adsorption process has been added. Therefore, it is possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery flow path 80 from becoming further lower than the first set concentration C1. In other words, even if the amount of carbon dioxide desorbed in the first adsorption device 10 decreases over time, it is possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery flow path 80 from decreasing.

[0046] Furthermore, in the gas separation system 1 of the above-described embodiment, when the concentration Cc is higher than the second set concentration C2, the delivery of the mixed gas from the second adsorption device 20 to the mixed gas delivery passage 80 is stopped. This makes it possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage 80 from becoming even higher than the second set concentration C2. That is, according to the gas separation system 1, the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage 80 is prevented from becoming even lower than the first set concentration C1 while being prevented from becoming even higher than the second set concentration C2, making it possible to prevent large fluctuations in the concentration of carbon dioxide in the mixed gas.

[0047] Second Embodiment The gas separation system 1a of the second embodiment is the same as the gas separation system 1 of the first embodiment except that, compared to the gas separation system 1 of the first embodiment, it performs a route addition process (described in Figure 8) instead of the route switching process described in Figure 5.

[0048] FIG. 7 is an explanatory diagram of routes added by the route addition process described later. The route added by the route addition process is route R3, which is different from route R1 among the bold lines in FIG. 7. In the gas separation system 1a of the second embodiment, when the mixed gas is delivered from the second adsorber 20 to the mixed gas delivery passage 80 when the concentration Cc is lower than the first set concentration C1, instead of supplying the mixed gas delivered from the first adsorber 10 to the second adsorber 20 via the mixed gas supply passage S1 as in the first embodiment, a portion of the purge gas supplied via the hydrogen supply passage 70 is supplied to the second adsorber 20. Here, the portion of the purge gas refers to a portion of the purge gas supplied for the first adsorber 10 during the desorption step. The hydrogen purge gas supplied to the second adsorber 20 from the branch position Ca (shown in FIG. 7) via the branch passage 72 desorbs the carbon dioxide adsorbed by the second adsorbent 22. The desorbed carbon dioxide is delivered to the branch passage 82 together with hydrogen as a mixed gas. This series of routes is referred to as route R3.

[0049] In the gas separation system 1 of the first embodiment, the route used was switched between route R1 (FIG. 2) and route R2 (FIG. 3) depending on the concentration Cc. On the other hand, in the gas separation system 1a of the second embodiment, the route used is switched between route R1 and whether route R3 is added. When route R3 is added as the route used, the second exhaust gas supply valve 52v and the second exhaust gas discharge valve 62v are closed, and the second hydrogen supply valve 72v and the second mixed gas delivery valve 82v are open.

[0050] FIG. 8 is a flowchart showing the steps of the path addition process executed in the gas separation system 1a of the second embodiment. Similar to the path switching process (FIG. 5), the path addition process is repeatedly executed when one adsorber has undergone the adsorption process and the other adsorber is undergoing the desorption process. The path addition process is a process for switching whether or not to add path R3 to path R1 depending on the carbon dioxide concentration in the mixed gas delivered from the other adsorber. Here, as with the explanation in FIG. 5, an example of the path addition process executed in a state in which the first adsorber 10 is undergoing the desorption process and the second adsorber 20 is undergoing the additional standby process will be described. It should be noted that at the start of the first path addition process executed after the desorption process has started in the first adsorber 10, only path R1 is used.

[0051] When the route addition process is started, first, the control unit 100 determines whether the concentration Cc is lower than the first set concentration C1 (step S21), similar to step S11 in FIG. 5. If the concentration Cc is lower than the first set concentration C1 (step S21: YES), the control unit 100 adds route R3 to the used route (step S22). Thereafter, the control unit 100 ends the route addition process. Note that if route R3 had already been added to the used route before step S22 was executed, the execution of step S22 maintains the used route as route R1 and route R3.

[0052] On the other hand, if the concentration Cc is equal to or greater than the first set concentration C1 (step S21: NO), the control unit 100 determines whether the concentration Cc is greater than the second set concentration C2 (step S23), similar to step S13 in FIG. 5. If the concentration Cc is equal to or less than the second set concentration C2 (step S23: NO), the control unit 100 terminates the path addition process. On the other hand, if the concentration Cc is greater than the second set concentration C2 (step S23: YES), the control unit 100 removes the path R3 from the used paths (step S24). In other words, the control unit 100 controls the second adsorber 20 not to send the mixed gas to the mixed gas delivery path 80. Specifically, the control unit 100 closes the second hydrogen supply valve 72v and the second mixed gas delivery valve 82v. Then, the control unit 100 terminates the path addition process. If the route to be used is already route R1 only before step S24 is executed, the route to be used remains route R1 after step S24 is executed. Thereafter, the control unit 100 ends the route addition process.

[0053] As described above, according to the gas separation system 1a of the second embodiment, when the concentration Cc is lower than the first set concentration C1, a portion of the purge gas supplied via the hydrogen supply passage 70 is supplied to the second adsorbent 20, thereby delivering the mixed gas that has undergone the adsorption process from the second adsorbent 20 to the mixed gas delivery passage 80. At this time, the mixed gas flowing downstream of the mixed gas delivery passage 80 corresponds to a mixed gas obtained by mixing the mixed gas delivered from the first adsorbent 10 and the mixed gas delivered from the second adsorbent 20 that has undergone the adsorption process. Therefore, similar to the gas separation system 1 of the first embodiment, it is possible to prevent the carbon dioxide concentration in the mixed gas flowing downstream of the mixed gas delivery passage 80 from becoming further lower than the first set concentration C1.

[0054] Third Embodiment The gas separation system 1b of the third embodiment is the same as the gas separation system 1 of the first embodiment except that, compared to the gas separation system 1 of the first embodiment, it performs a flow rate adjustment process (Figure 10) instead of the path switching process described in Figure 5.

[0055] FIG. 9 is an explanatory diagram showing the first mixed gas flow rate M1 and the second mixed gas flow rate M2. In the gas separation system 1 of the first embodiment, the path R1 and the path R2 are switched depending on the concentration Cc. On the other hand, in the gas separation system 1b of the third embodiment, depending on the concentration Cc, the flow rate of the mixed gas delivered from the first adsorption device 10 that is supplied to the second adsorption device 20 via the mixed gas supply passage S1 (hereinafter referred to as the second mixed gas flow rate M2) and the flow rate of the mixed gas delivered from the first adsorption device 10 that is not supplied to the second adsorption device 20 (hereinafter referred to as the first mixed gas flow rate M1) are adjusted. In detail, the control unit 100 adjusts the first mixed gas flow rate M1 and the second mixed gas flow rate M2 by controlling the aperture of the mixed gas delivery valve V11 and the aperture of the mixed gas supply valve V12 depending on the concentration Cc. The first mixed gas flow rate M1 can also be said to be the flow rate of the mixed gas flowing downstream of position C in route R1. The second mixed gas flow rate M2 can also be said to be the flow rate of the mixed gas flowing downstream of position C in route R2.

[0056] FIG. 10 is a flowchart showing the procedure of the flow rate adjustment process executed in the gas separation system 1b of the third embodiment. Similar to the path switching process (FIG. 5), the flow rate adjustment process is repeatedly executed when one adsorber has undergone the adsorption process and the other adsorber is undergoing the desorption process. The flow rate adjustment process adjusts the first mixed gas flow rate M1 and the second mixed gas flow rate M2 according to the concentration of carbon dioxide in the mixed gas delivered from the other adsorber. When the flow rate of the mixed gas flowing through the portion of the mixed gas delivery flow path 80 upstream of position C (see FIG. 9, etc.) is Q, the first mixed gas flow rate M1 is expressed as ηQ, and the second mixed gas flow rate M2 is expressed as (1−η)Q. Here, as with the explanations in FIGS. 5 and 8, the flow rate adjustment process will be described as an example, which is executed when the first adsorber 10 is undergoing the desorption process and the second adsorber 20 is undergoing the additional standby process. At the start of the flow rate adjustment process that is executed for the first time after the desorption process is started in the first adsorption device 10, η is set to 1 (the first mixed gas flow rate M1=Q, and the second mixed gas flow rate M2=0).

[0057] When the flow rate adjustment process is started, the control unit 100 first determines whether the concentration Cc is lower than the first set concentration C1 (step S31), similar to steps S11 and S21 in FIGS. 5 and 8. If the concentration Cc is lower than the first set concentration C1 (step S31: YES), the control unit 100 decreases η by Δη (step S32). At this time, the value obtained by decreasing Δη from the η immediately before step S32 is executed is stored in the control unit 100 as the new η. Next, the control unit 100 determines whether the new η is equal to or less than 0 (step S33: NO). If the control unit 100 determines that the new η is not equal to or less than 0 (step S33: NO), the control unit 100 terminates the flow rate adjustment process. On the other hand, if the control unit 100 determines that the new η is equal to or less than 0 (step S33: YES), the control unit 100 stores the new η as 0 (step S34) and then terminates the flow rate adjustment process. Therefore, if the new η is not a value equal to or less than 0 (step S33: NO), the first mixed gas flow rate M1 represented by ηQ decreases and the second mixed gas flow rate M2 represented by (1-η)Q increases by the amount of decrease due to Δη. On the other hand, if the new η is a value equal to or less than 0 (step S33: YES), η is set to 0, and the first mixed gas flow rate M1 represented by ηQ is set to 0, and the second mixed gas flow rate M2 represented by (1-η)Q is set to Q.

[0058] On the other hand, if the concentration Cc is equal to or greater than the first set concentration C1 (step S31: NO), the control unit 100 determines whether the concentration Cc is greater than the second set concentration C2 (step S35), similar to steps S13 and S23 in FIGS. 5 and 8. If the concentration Cc is equal to or less than the second set concentration C2 (step S35: NO), the control unit 100 terminates the flow rate adjustment process. On the other hand, if the concentration Cc is greater than the second set concentration C2 (step S35: YES), the control unit 100 increases η by Δη (step S36). At this time, the value obtained by increasing η by Δη from the value just before step S36 was executed is stored in the control unit 100 as the new η. Next, the control unit 100 determines whether the new η is equal to or greater than 1 (step S37). If it is determined that the new η is not equal to or greater than 1 (step S37: NO), the control unit 100 terminates the flow rate adjustment process. On the other hand, if it is determined that the new η is 1 or greater (step S37: YES), the control unit 100 stores the new η as 1 (step S38) and then terminates the flow rate adjustment process. Therefore, if the new η is not 1 or greater (step S37: NO), the first mixed gas flow rate M1 represented by ηQ increases and the second mixed gas flow rate M2 represented by (1-η)Q decreases by the amount of increase due to Δη. On the other hand, if the new η is 1 or greater (step S37: YES), η is set to 1, and the first mixed gas flow rate M1 represented by ηQ is set to Q, and the second mixed gas flow rate M2 represented by (1-η)Q is set to 0.

[0059] As described with reference to FIG. 10 , when the second adsorption device 20 has undergone the adsorption process and the first adsorption device 10 is performing the desorption process, if the concentration Cc is lower than the first set concentration C1, the control unit 100 controls the second mixed gas flow rate M2 to increase and the first mixed gas flow rate M1 to decrease. As a result, the amount of mixed gas delivered from the second adsorption device 20 to the mixed gas delivery path 80 increases. On the other hand, when the concentration Cc is higher than the second set concentration C2 in the same state, the control unit 100 controls the second mixed gas flow rate M2 to decrease and the first mixed gas flow rate M1 to increase. As a result, the amount of mixed gas delivered from the second adsorption device 20 to the mixed gas delivery path 80 decreases.

[0060] FIG. 11 is an explanatory diagram of the effect of the flow rate adjustment process. In FIG. 11, the horizontal axis represents the elapsed time since the start of the desorption process, and the vertical axis represents the concentration Cc. The solid line L3 shows the fluctuation of the concentration Cc in the gas separation system 1b of the third embodiment. The dashed line L2, similar to FIG. 6, shows the fluctuation of the concentration Cc in the gas separation system of the comparative example. As shown by the solid line L3, in the gas separation system 1b of the third embodiment, similar to the solid line L1 in FIG. 6, the concentration Cc increases for about 50 seconds after the start of the desorption process and then decreases over time until 100 seconds. However, unlike the solid line L1 in FIG. 6, the concentration Cc thereafter remains at an approximately constant value. This result confirms that the flow rate adjustment process (FIG. 9) is superior to the route switching process (FIG. 5) in terms of converging the concentration Cc to a constant value.

[0061] As described above, according to the gas separation system 1b of the third embodiment, when the concentration Cc is lower than the first set concentration C1, the second mixed gas flow rate M2 is controlled to increase and the first mixed gas flow rate M1 is controlled to decrease, thereby increasing the amount of mixed gas that has undergone the adsorption process and is delivered to the mixed gas delivery flow path 80 from the second adsorption device 20. This makes it possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery flow path 80 from becoming further lower than the first set concentration C1. In other words, even if the amount of carbon dioxide desorbed in the first adsorption device 10 decreases over time, it is possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery flow path 80 from decreasing.

[0062] Furthermore, in the gas separation system 1b of the third embodiment described above, when the concentration Cc is higher than the second set concentration C2, the second mixed gas flow rate M2 is controlled to decrease and the first mixed gas flow rate M1 is controlled to increase, thereby reducing the amount of mixed gas delivered from the second adsorption device 20 to the mixed gas delivery passage 80. This makes it possible to prevent the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage 80 from becoming even higher than the second set concentration C2. That is, according to the gas separation system 1b of the third embodiment, the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery passage 80 is prevented from becoming even lower than the first set concentration C1 while being prevented from becoming even higher than the second set concentration C2, thereby making it possible to prevent large fluctuations in the concentration of carbon dioxide in the mixed gas.

[0063] <Fourth embodiment> The gas separation system 1c of the fourth embodiment is the same as the gas separation system 1b of the third embodiment except that, in addition to adjusting the first mixed gas flow rate M1 and the second mixed gas flow rate M2 according to the concentration Cc, the gas separation system 1c of the fourth embodiment adjusts the first purge gas flow rate P1 and the second purge gas flow rate P2 according to the concentration Cc.

[0064] FIG. 12 is an explanatory diagram showing the first purge gas flow rate P1 and the second purge gas flow rate P2. In the gas separation system 1c of the fourth embodiment, as described above, the flow rate of the purge gas supplied through the hydrogen supply channel 70 to the first adsorption device 10 (first purge gas flow rate P1) and the flow rate of the purge gas supplied through the hydrogen supply channel 70 to the second adsorption device 20 (second purge gas flow rate P2) are adjusted in accordance with the concentration Cc. Specifically, the control unit 100 adjusts the first purge gas flow rate P1 and the second purge gas flow rate P2 by controlling the aperture of the first hydrogen supply valve 71v and the aperture of the second hydrogen supply valve 72v in accordance with the concentration Cc. The first purge gas flow rate P1 can also be said to be the flow rate of the purge gas flowing downstream of the branch position Ca (shown in FIG. 12) in the path R1. The second purge gas flow rate P2 can also be said to be the flow rate of the purge gas that flows downstream of the branch position Ca in the path R3.

[0065] In the gas separation system 1c of the fourth embodiment, when the second adsorption device 20 has undergone the adsorption process and the first adsorption device 10 is performing the desorption process, if the concentration Cc is lower than the first set concentration C1, the control unit 100 controls the first purge gas flow rate P1 to decrease and the second purge gas flow rate P2 to increase. As a result, the amount of mixed gas delivered from the second adsorption device 20 to the mixed gas delivery path 80 increases. On the other hand, when the concentration Cc is higher than the second set concentration C2 in the same state, the control unit 100 controls the first purge gas flow rate P1 to increase and the second purge gas flow rate P2 to decrease. As a result, the amount of mixed gas delivered from the second adsorption device 20 to the mixed gas delivery path 80 decreases. That is, in the gas separation system 1c of the fourth embodiment, the control unit 100 adjusts the first mixed gas flow rate M1, the second mixed gas flow rate M2, and the first purge gas flow rate P1 and the second purge gas flow rate P2 in accordance with the concentration Cc. At this time, the first purge gas flow rate P1 and the second purge gas flow rate P2 are adjusted by a process similar to the flow rate adjustment process described with reference to FIG.

[0066] 13 is an explanatory diagram of the effect of the flow rate adjustment process in the fourth embodiment. In FIG. 13, the horizontal axis represents the elapsed time since the start of the desorption process, and the vertical axis represents the concentration Cc. The solid line L4 represents the fluctuation of the concentration Cc in the gas separation system 1c of the fourth embodiment. The dashed line L2 represents the fluctuation of the concentration Cc in the gas separation system of the comparative example, as in FIG. 6.

[0067] As described above, according to the gas separation system 1c of the fourth embodiment, when the concentration Cc is lower than the first set concentration C1, the second purge gas flow rate P2 is controlled to increase and the first purge gas flow rate P1 is controlled to decrease, thereby increasing the amount of mixed gas that has undergone the adsorption process and is delivered to the mixed gas delivery flow path 80 from the second adsorption device 20. When the concentration Cc is higher than the second set concentration C2, the second purge gas flow rate P2 is controlled to decrease and the first purge gas flow rate P1 is controlled to increase, thereby decreasing the amount of mixed gas that is delivered from the second adsorption device 20 to the mixed gas delivery flow path 80. Therefore, the concentration of carbon dioxide in the mixed gas that flows downstream of the mixed gas delivery flow path 80 is prevented from becoming lower than the first set concentration C1 and from becoming higher than the second set concentration C2, thereby preventing large fluctuations in the concentration of carbon dioxide in the mixed gas.

[0068] Fifth Embodiment 14 is an explanatory diagram illustrating the configuration of a gas separation system 1d according to a fifth embodiment. The gas separation system 1d according to the fifth embodiment is the same as the gas separation system 1 according to the first embodiment, except that it includes a third adsorption device 30, as compared with the gas separation system 1 according to the first embodiment.

[0069] The third adsorber 30 is an adsorber similar to the first and second adsorber 10, 20, and accommodates therein a second adsorbent 32 similar to the first and second adsorbents 12, 22. In addition to the third adsorber 30, the gas separation system 1d of the fifth embodiment is equipped with a branch flow path 53, a branch flow path 63, a branch flow path 73, a branch flow path 83, a third exhaust gas supply valve 53v, a third exhaust gas discharge valve 63v, a third hydrogen supply valve 73v, a third mixed gas delivery valve 83v, a mixed gas supply flow path S2, a mixed gas delivery valve V21, and a mixed gas supply valve V22.

[0070] In the gas separation system 1d of the fifth embodiment, when the second adsorption device 20 has undergone the adsorption process and the first adsorption device 10 is performing the desorption process, if the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device 10 is low, the control unit 100 controls the third adsorption device 30 to deliver the mixed gas to the mixed gas delivery flow path 80 in addition to the second adsorption device 20. At this time, the delivery of the mixed gas from the third adsorption device 30 is performed according to the concentration of carbon dioxide in the mixed gas at a position in the mixed gas delivery flow path 80 downstream of the position to which the branch flow path 82 is connected and upstream of the position to which the mixed gas supply flow path S2 is connected. The gas separation system 1d of the fifth embodiment as described above can also suppress large fluctuations in the concentration of carbon dioxide in the mixed gas flowing downstream of the mixed gas delivery flow path 80.

[0071] <Modification 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 of the invention. For example, the following modifications are also possible.

[0072] In the above-described embodiment, the mixed gas supply flow path S1 connects a portion of the mixed gas delivery flow path 80 downstream of the position where the first mixed gas delivery valve 81v is provided and a portion of the hydrogen supply flow path 70 upstream of the position where the second hydrogen supply valve 72v is provided, but this is not limited to this. The mixed gas supply flow path S1 may be provided at any position as long as it is possible to supply the mixed gas delivered from the first adsorber 10 to the second adsorber 20. For example, the mixed gas supply flow path S1 may be directly connected to at least one of the first adsorber 10 and the second adsorber 20.

[0073] In the above-described embodiment, the first set concentration C1 and the second set concentration C2 are described as different values, but this is not limited thereto. The second set concentration C2 can be set to a value equal to or greater than the first set concentration C1, and therefore the first set concentration C1 and the second set concentration C2 may be the same value. When the first set concentration C1 and the second set concentration C2 are the same value and this value is set as the concentration target value, for example, in the route switching process (FIG. 5), if the concentration Cc is lower than the concentration target value (step S11: YES), the control unit 100 switches the route to be used to route R2 (step S12), and if the concentration Cc is higher than the concentration target value (step S13: YES), the control unit 100 switches the route to be used to route R1 (step S14).

[0074] In the third embodiment described above, the decrease amount in step S32 and the increase amount in step S36 in the flow rate adjustment process (FIG. 10) are both Δη, but the decrease amount in step S32 and the increase amount in step S36 may be different values.

[0075] In the fourth embodiment described above, the control unit 100 adjusts both the first mixed gas flow rate M1 and the second mixed gas flow rate M2 and the first purge gas flow rate P1 and the second purge gas flow rate P2 in accordance with the concentration Cc, but this is not limiting. The control unit 100 may adjust only the first purge gas flow rate P1 and the second purge gas flow rate P2 in accordance with the concentration Cc.

[0076] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0077] The present invention can also be realized in the following forms. [Application example 1] A gas separation system for separating carbon dioxide from a raw material gas containing carbon dioxide, comprising: a first adsorption device that accommodates a first adsorbent capable of adsorbing carbon dioxide; a second adsorbent housing a second adsorbent capable of adsorbing carbon dioxide therein; a mixed gas delivery flow path through which a mixed gas containing carbon dioxide and the purge gas delivered from the first adsorption device and the second adsorption device can flow when the purge gas is supplied to the first adsorption device and the second adsorption device; a control unit that controls the gas separation system so that an adsorption step of supplying the raw material gas to the first adsorbent or the second adsorbent to cause the first adsorbent or the second adsorbent to adsorb carbon dioxide, and a desorption step of supplying the purge gas to the first adsorbent or the second adsorbent after the adsorption step to cause the carbon dioxide to be desorbed from the first adsorbent or the second adsorbent are repeatedly performed in the first adsorbent and the second adsorbent, the control unit controls the mixed gas to be delivered from the second adsorber to the mixed gas delivery passage when the concentration of carbon dioxide in the mixed gas delivered from the first adsorber is lower than a predetermined first set concentration when the second adsorber has undergone the adsorption process and the desorption process is being performed in the first adsorber. [Application example 2] The gas separation system according to Application Example 1, The control unit, when in the state, controls the mixed gas not to be sent from the second adsorption device to the mixed gas delivery passage when the concentration is higher than a second set concentration that is set in advance to a value equal to or higher than the first set concentration. [Application example 3] The gas separation system according to Application Example 1 or Application Example 2, further comprising: a mixed gas supply flow path capable of supplying the mixed gas delivered from the first adsorption device to the second adsorption device, When the concentration is lower than the first set concentration in the above state, the control unit controls the mixed gas delivered from the first adsorption device to be supplied to the second adsorption device via the mixed gas supply flow path, thereby delivering the mixed gas from the second adsorption device to the mixed gas delivery flow path. [Application example 4] The gas separation system according to any one of Application Examples 1 to 3, further comprising: a purge gas supply passage capable of supplying the purge gas to the first adsorption device and the second adsorption device; When the concentration is lower than the first set concentration in the above state, the control unit controls the second adsorbent to deliver the mixed gas from the second adsorbent to the mixed gas delivery line by supplying a portion of the purge gas supplied via the purge gas supply line to the second adsorbent. [Application example 5] A gas separation system for separating carbon dioxide from a raw material gas containing carbon dioxide, comprising: a first adsorption device that accommodates a first adsorbent capable of adsorbing carbon dioxide; a second adsorbent housing a second adsorbent capable of adsorbing carbon dioxide therein; a mixed gas delivery flow path through which a mixed gas containing carbon dioxide and the purge gas delivered from the first adsorption device and the second adsorption device can flow when the purge gas is supplied to the first adsorption device and the second adsorption device; a control unit that controls the gas separation system so that an adsorption step of supplying the raw material gas to the first adsorbent or the second adsorbent to cause the first adsorbent or the second adsorbent to adsorb carbon dioxide, and a desorption step of supplying the purge gas to the first adsorbent or the second adsorbent after the adsorption step to cause the carbon dioxide to be desorbed from the first adsorbent or the second adsorbent are repeatedly performed in the first adsorbent and the second adsorbent, the control unit controls the amount of the mixed gas delivered from the second adsorption device to the mixed gas delivery passage to be increased when the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device is lower than a predetermined first set concentration when the second adsorption device has undergone the adsorption process and the desorption process is being performed in the first adsorption device. [Application Example 6] The gas separation system according to Application Example 5, The control unit, when in the state, controls the amount of the mixed gas delivered from the second adsorption device to the mixed gas delivery passage to be reduced when the concentration is higher than a second set concentration that is pre-set to a value equal to or greater than the first set concentration. [Application Example 7] The gas separation system according to Application Example 6, further comprising: a mixed gas supply flow path capable of supplying the mixed gas delivered from the first adsorption device to the second adsorption device, The control unit When the concentration is lower than the first set concentration in the above state, a second mixed gas flow rate, which is a flow rate of the mixed gas delivered from the first adsorber that is supplied to the second adsorber via the mixed gas supply passage, is controlled to increase, and a first mixed gas flow rate, which is a flow rate of the mixed gas that is not supplied to the second adsorber, is controlled to decrease, a gas separation system that, when in the state, if the concentration is higher than the second set concentration, controls the flow rate of the second mixed gas to decrease and controls the flow rate of the first mixed gas to increase. [Application Example 8] The gas separation system according to Application Example 6, further comprising: a purge gas supply passage capable of supplying the purge gas to the first adsorption device and the second adsorption device; The control unit When the concentration is lower than the first set concentration in the above state, a first purge gas flow rate, which is the flow rate of the purge gas supplied via the purge gas supply flow path and is supplied to the first adsorption device, is controlled to decrease, and a second purge gas flow rate, which is the flow rate of the purge gas supplied via the purge gas supply flow path and is supplied to the second adsorption device, is controlled to increase, When the concentration is higher than the second set concentration in the above state, the gas separation system controls the first purge gas flow rate to increase and the second purge gas flow rate to decrease. [Explanation of symbols]

[0078] 1, 1a, 1b, 1c, 1d...Gas separation system 10...First adsorption device 12...First adsorbent 20…Second adsorption device 22…Second adsorbent 30...Third adsorption device 32…Second adsorbent 50...Exhaust gas supply passage 51,52,53…Diversion channel 51v...First exhaust gas supply valve 52v...Second exhaust gas supply valve 53v...Third exhaust gas supply valve 60...Exhaust gas discharge passage 61,62,63…Diversion channel 61v...First exhaust gas discharge valve 62v...Second exhaust gas discharge valve 63v...Third exhaust gas discharge valve 70...Hydrogen supply channel 71,72,73…Diversion channel 71v…First hydrogen supply valve 72v…Second hydrogen supply valve 73v…Third hydrogen supply valve 80...mixed gas delivery passage 81,82,83…Diversion channel 81v...First mixed gas delivery valve 82v...Second mixed gas delivery valve 83v...Third mixed gas delivery valve 90...Hydrocarbon synthesis unit 100...Control unit EG: Combustion equipment HY...Hydrogen supply source S1, S2...Mixed gas supply passage V11, V21...Mixed gas delivery valve V12, V22...Mixed gas supply valve

Claims

1. A gas separation system for separating carbon dioxide from a raw material gas containing carbon dioxide, comprising: a first adsorption device that accommodates a first adsorbent capable of adsorbing carbon dioxide; a second adsorbent housing a second adsorbent capable of adsorbing carbon dioxide therein; a mixed gas delivery flow path through which a mixed gas containing carbon dioxide and the purge gas delivered from the first adsorption device and the second adsorption device can flow when the purge gas is supplied to the first adsorption device and the second adsorption device; a control unit that controls the gas separation system so that an adsorption step of supplying the raw material gas to the first adsorbent or the second adsorbent to cause the first adsorbent or the second adsorbent to adsorb carbon dioxide, and a desorption step of supplying the purge gas to the first adsorbent or the second adsorbent after the adsorption step to cause the carbon dioxide to be desorbed from the first adsorbent or the second adsorbent are repeatedly performed in the first adsorbent and the second adsorbent, the control unit controls the mixed gas to be delivered from the second adsorption device to the mixed gas delivery passage when the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device is lower than a predetermined first set concentration when the second adsorption device has undergone the adsorption process and the desorption process is being performed in the first adsorption device.

2. 10. The gas separation system of claim 1, The control unit, when in the above state, controls the mixed gas not to be sent from the second adsorption device to the mixed gas delivery passage when the concentration is higher than a second set concentration that is pre-set to a value equal to or greater than the first set concentration.

3. 3. The gas separation system of claim 1 or claim 2, further comprising: a mixed gas supply passage capable of supplying the mixed gas delivered from the first adsorption device to the second adsorption device, When the concentration is lower than the first set concentration in the above state, the control unit controls the mixed gas discharged from the first adsorption device to be supplied to the second adsorption device via the mixed gas supply flow path, thereby discharging the mixed gas from the second adsorption device to the mixed gas discharge flow path.

4. 3. The gas separation system of claim 1 or claim 2, further comprising: a purge gas supply passage capable of supplying the purge gas to the first adsorption device and the second adsorption device; When the concentration is lower than the first set concentration in the above state, the control unit controls the second adsorbent to deliver the mixed gas to the mixed gas delivery line by supplying a portion of the purge gas supplied via the purge gas supply line to the second adsorbent.

5. A gas separation system for separating carbon dioxide from a raw material gas containing carbon dioxide, comprising: a first adsorption device that accommodates a first adsorbent capable of adsorbing carbon dioxide; a second adsorbent housing a second adsorbent capable of adsorbing carbon dioxide therein; a mixed gas delivery flow path through which a mixed gas containing carbon dioxide and the purge gas delivered from the first adsorption device and the second adsorption device can flow when the purge gas is supplied to the first adsorption device and the second adsorption device; a control unit that controls the gas separation system so that an adsorption step of supplying the raw material gas to the first adsorbent or the second adsorbent to cause the first adsorbent or the second adsorbent to adsorb carbon dioxide, and a desorption step of supplying the purge gas to the first adsorbent or the second adsorbent after the adsorption step to cause the carbon dioxide to be desorbed from the first adsorbent or the second adsorbent are repeatedly performed in the first adsorbent and the second adsorbent, the control unit controls the amount of the mixed gas delivered from the second adsorption device to the mixed gas delivery passage to be increased when the concentration of carbon dioxide in the mixed gas delivered from the first adsorption device is lower than a predetermined first set concentration when the second adsorption device has undergone the adsorption process and the desorption process is being performed in the first adsorption device.

6. 6. The gas separation system of claim 5, The control unit, when in the above state, controls the amount of the mixed gas sent from the second adsorption device to the mixed gas delivery passage to be reduced when the concentration is higher than a second set concentration that is pre-set to a value equal to or greater than the first set concentration.

7. 7. The gas separation system of claim 6, further comprising: a mixed gas supply passage capable of supplying the mixed gas delivered from the first adsorption device to the second adsorption device, The control unit When the concentration is lower than the first set concentration in the above state, a second mixed gas flow rate, which is a flow rate of the mixed gas delivered from the first adsorption device that is supplied to the second adsorption device via the mixed gas supply passage, is controlled to increase, and a first mixed gas flow rate, which is a flow rate of the mixed gas delivered from the first adsorption device that is not supplied to the second adsorption device, is controlled to decrease, When the concentration is higher than the second set concentration in the above state, the gas separation system controls the second mixed gas flow rate to decrease and the first mixed gas flow rate to increase.

8. 7. The gas separation system of claim 6, further comprising: a purge gas supply passage capable of supplying the purge gas to the first adsorption device and the second adsorption device; The control unit When the concentration is lower than the first set concentration in the above state, a first purge gas flow rate, which is a flow rate of the purge gas supplied to the first adsorption device among the flow rates of the purge gas supplied via the purge gas supply flow path, is controlled to decrease, and a second purge gas flow rate, which is a flow rate of the purge gas supplied to the second adsorption device among the flow rates of the purge gas supplied via the purge gas supply flow path, is controlled to increase, When the concentration is higher than the second set concentration in the above state, the gas separation system controls the first purge gas flow rate to increase and the second purge gas flow rate to decrease.

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