Gas separation system

Abstract

To provide a technique which can suppress accumulation of moisture in an adsorbent.SOLUTION: A gas separation system separating carbon dioxide from raw material gas including carbon dioxide comprises: a plurality of adsorbers accommodating inside adsorbent which can adsorb carbon dioxide; and a control unit which controls to perform adsorption process where the raw material gas is supplied to the adsorber so that the adsorbent adsorbs carbon dioxide and desorption process where purge gas is supplied to the adsorber so that carbon dioxide is desorbed from adsorbent for each of adsorbers. The control unit controls a part of sending-out gas after adsorption that is gas fed from the adsorber during adsorption process is discharged, when passing through the adsorber in a state that after the desorption process and before the next adsorption process, to outside of the gas separation system.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, techniques for separating carbon dioxide from exhaust gases and the like using adsorbents that adsorb carbon dioxide have been known. For example, Patent Document 1 discloses a gas adsorption device that adsorbs carbon dioxide using an adsorbent containing zeolite. Patent Document 2 discloses an adsorbent containing polyamine. Patent Document 3 discloses a carbon dioxide capture device that desorbs carbon dioxide by heating water and bringing the generated steam into contact with an adsorbent. Patent Document 4 discloses the use of a metal-organic framework (MOF) for adsorption and desorption of carbon dioxide. Patent Document 5 discloses a carbon dioxide separation and capture system that performs a purification reflux, in which a portion of the gas discharged from an adsorption tower during an adsorption step is supplied to an adsorption tower during a desorption step, and a concentration reflux, in which a portion of the gas discharged from an adsorption tower during a desorption step is supplied to an adsorption tower during an adsorption step. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7185433 [Patent Document 2] Patent No. 6300457 [Patent Document 3] Japanese Patent Application Publication No. 2023-108268 [Patent Document 4] Special Publication No. 2021-522226 [Patent Document 5] Patent No. 4189344 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, when moisture accumulates in an adsorbent, the adsorption capacity of the adsorbent tends to decrease. In Patent Document 5, as moisture in the refluxed gas accumulates due to reflux, the degree of decrease in the adsorption capacity of the adsorbent increases. For this reason, there has been a demand for technology that can suppress moisture accumulation in the adsorbent. However, Patent Documents 1 to 5 do not take into consideration the decrease in the adsorption capacity of the adsorbent due to moisture accumulation.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to provide a technique that can suppress the accumulation of moisture in an adsorbent. [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 carbon dioxide-containing raw material gas, the gas separation system including: a plurality of adsorbers each containing an adsorbent capable of adsorbing carbon dioxide; and a control unit that controls each of the adsorbers so that an adsorption step of supplying the raw material gas to the adsorbers to cause the adsorbent to adsorb carbon dioxide, and a desorption step of supplying the purge gas to the adsorbers to desorb carbon dioxide from the adsorbent, are performed in each of the adsorbers, and the control unit controls so that a portion of a post-adsorption delivery gas, which is a gas delivered from the adsorbers during the adsorption step, passes through the adsorbers in a state in which the desorption step has been completed and the next adsorption step is not yet performed, and is then discharged to the outside of the gas separation system.

[0008] According to this configuration, the passage of gas discharged from the adsorber during the adsorption step removes moisture from the adsorbent housed in the adsorber after the desorption step and before the next adsorption step, while discharging the moisture to the outside of the gas separation system. This prevents moisture from accumulating in the adsorbent, thereby preventing a decrease in the adsorption capacity of the adsorbent.

[0009] (2) In the gas separation system of the above form, the plurality of adsorbers may include three or more adsorbers, and the control unit may control, when refluxing the adsorbed delivery gas from one adsorber to the other adsorber in two adsorbers while refluxing the refluxed delivery gas, which is the adsorbed delivery gas that has passed through the other adsorber, from the other adsorber to the one adsorber, so that a portion of the adsorbed delivery gas passes through the adsorber in the above state and is then discharged outside the gas separation system. According to this configuration, even when the reflux of the post-adsorption delivery gas and the reflux of the post-reflux delivery gas are carried out in parallel, moisture can be removed from the adsorbent housed in an adsorbent that is not included in the path through which the gas circulates by these refluxes, and the moisture can be discharged outside the gas separation system.

[0010] 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]

[0011] [Figure 1] 1 is an explanatory diagram illustrating the configuration of a gas separation system according to a first embodiment. [Figure 2]FIG. 2 is an explanatory diagram showing switching between various processes performed in each adsorber. [Figure 3] FIG. 2 is an explanatory diagram showing the state of the gas separation system in cycle 1. [Figure 4] FIG. 1 is an explanatory diagram showing the state of the gas separation system in cycle 2. [Figure 5] FIG. 10 is an explanatory diagram showing the state of the gas separation system in cycle 3. [Figure 6] FIG. 4 is an explanatory diagram illustrating the configuration of a gas separation system according to a second embodiment. [Figure 7] FIG. 2 is an explanatory diagram showing switching between various processes performed in each adsorber. [Figure 8] FIG. 2 is an explanatory diagram showing the state of the gas separation system in cycle 1. [Figure 9] FIG. 1 is an explanatory diagram showing the state of the gas separation system in cycle 2. [Figure 10] FIG. 10 is an explanatory diagram showing the state of the gas separation system in cycle 3. [Figure 11] FIG. 10 is an explanatory diagram illustrating the configuration of a gas separation system according to a third embodiment. [Figure 12] FIG. 2 is an explanatory diagram showing the state of the gas separation system in cycle 1. [Figure 13] FIG. 1 is an explanatory diagram showing the state of the gas separation system in cycle 2. [Figure 14] FIG. 10 is an explanatory diagram showing the state of the gas separation system in cycle 3. [Figure 15] FIG. 2 is an explanatory diagram showing switching between various processes performed in each adsorber. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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 raw material 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 recirculation flow path 60, an exhaust gas discharge flow path 70, a mixed gas delivery flow path 80, and a control unit 100. The first and second adsorber 10, 20 may also be collectively referred to simply as "adsorbers."

[0013] The first adsorber 10 is a device for separating carbon dioxide from a raw material gas. The first adsorber 10 accommodates an adsorbent capable of adsorbing carbon dioxide therein. 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 adsorbents include activated carbon, zeolite, alkali metal-containing inorganic solids, solid amines (solids formed by supporting amines on a porous support), metal organic frameworks (MOFs), and covalent organic frameworks (COFs). The second adsorber 20 is an adsorbent similar to the first adsorber 10. The second adsorber 20 accommodates an adsorbent similar to the first adsorber 10 therein.

[0014] 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 adsorbent. The exhaust gas supply flow path 50 connects the combustion equipment EG to each of the first and second adsorbers 10 and 20, and is a gas flow path that can supply 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 that can supply the exhaust gas to each of the first and second adsorbers 10 and 20. Valves 51v and 52v are provided in the branch flow paths 51 and 52, respectively. 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.

[0015] The exhaust gas reflux flow path 60 is connected to each of the first and second adsorbers 10 and 20 and is a gas flow path that can reflux the exhaust gas sent from one adsorber to the other adsorber. Reflux means supplying the gas sent from one adsorber to another adsorber. In this embodiment, the exhaust gas reflux flow path 60 also serves as a gas flow path that can discharge the exhaust gas sent from the adsorbers to the outside of the gas separation system 1. The exhaust gas reflux flow path 60 includes branch flow paths 61 and 62 that can discharge the exhaust gas from one adsorber and reflux the exhaust gas to the other adsorber. In this embodiment, the branch flow paths 61 and 62 are also gas flow paths that can discharge the exhaust gas to the outside of the gas separation system 1. The exhaust gas reflux flow path 60 also includes a reflux flow path 60R. The reflux flow path 60R is a flow path that connects the branch flow path 61 and the branch flow path 62 to reflux the exhaust gas sent from one adsorber to the other adsorber. Valves 61v and 61ev are provided in the branch path 61 on the near side and the far side, respectively, of the position where the return path 60R is connected, as viewed from the first adsorber 10. Similarly, valves 62v and 62ev are provided in the branch path 62 on the near side and the far side, respectively, of the position where the return path 60R is connected, as viewed from the second adsorber 20. In addition, a valve Rav is provided in the return path 60R. By controlling the opening and closing of these valves, it is possible to switch between performing and stopping the discharge of exhaust gas from the adsorber to the outside of the gas separation system 1 and the return flow of exhaust gas from one adsorber to the other adsorber.

[0016] The exhaust gas discharge flow path 70 is a gas flow path that connects each of the first and second adsorber 10, 20 to the outside of the gas separation system 1 and is capable of discharging exhaust gas that has been returned from one adsorber to the other adsorber to the outside of the gas separation system 1 (see FIG. 5, described later). The exhaust gas discharge flow path 70 includes branch flow paths 71, 72 that can discharge exhaust gas from each of the first and second adsorber 10, 20. The branch flow paths 71, 72 are provided with valves 71v, 72v, respectively. By controlling the opening and closing of these valves, it is possible to switch between performing and stopping exhaust gas discharge from the adsorber to the outside of the gas separation system 1.

[0017] Carbon dioxide contained in the exhaust gas supplied from the combustion equipment EG to the adsorber via the exhaust gas supply passage 50 is adsorbed by the adsorbent. The remaining exhaust gas that is not adsorbed by the adsorbent is sent from one adsorber to the other adsorber via the exhaust gas reflux passage 60 (see FIGS. 4 and 5, which will be described later), or is discharged to the outside of the gas separation system 1 via the exhaust gas reflux passage 60 (or the exhaust gas discharge passage 70) (see FIGS. 3 to 5, which will be described later).

[0018] Hydrogen can be supplied as a purge gas from a hydrogen supply source (not shown) to each of the first adsorption devices 10 and 20. The supply of hydrogen to each of the first and second adsorption devices 10 and 20 can be switched on and off by controlling the opening and closing of a valve (not shown). When hydrogen is supplied to the adsorption devices, carbon dioxide is desorbed from the adsorbent.

[0019] The mixed gas delivery flow path 80 connects the first adsorber 10 and the second adsorber 20 in parallel and is a flow path capable of delivering the mixed gas delivered from the first and second adsorber 10, 20 when hydrogen 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 flow path 80 includes branch flow paths 81, 82 that can deliver the mixed gas from each of the first and second adsorber 10, 20. Valves 81v, 82v are provided in the branch flow paths 81, 82, respectively. 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.

[0020] A vacuum pump 85 is provided in a portion of the mixed gas delivery flow path 80 downstream of the positions where the valves 81v and 82v are provided. The vacuum pump 85 can reduce the pressure inside either the first or second adsorber 10, 20 that is spatially connected to the vacuum pump 85 when either the valve 81v or 82v is opened. The lower the pressure inside the adsorber, the more rapidly the desorption of carbon dioxide from the adsorbent is promoted.

[0021] Furthermore, a valve Cv is provided in the mixed gas delivery passage 80 at a portion downstream of the position where the return passage 80R, which will be described later, is connected. By controlling the opening and closing of the valve Cv, it is possible to switch between executing and stopping the delivery of the mixed gas to the downstream end of the mixed gas delivery passage 80. The downstream end of the mixed gas delivery passage 80 is connected to, for example, a tank that stores the mixed gas or a synthesis device that synthesizes hydrocarbons using the mixed gas.

[0022] The reflux path 80R is connected from between the position of the mixed gas delivery path 80 where the vacuum pump 85 is provided and the position of the valve Cv to a portion of the exhaust gas supply path 50 upstream of the positions where the valves 51v and 52v are provided. The reflux path 80R is a path that can reflux the mixed gas delivered from one adsorber to the other adsorber (see FIG. 4, which will be described later). The reflux path 80R is provided with a valve Rcv. By controlling the opening and closing of the valve Rcv, it is possible to switch between starting and stopping the reflux of the mixed gas from one adsorber to the other adsorber.

[0023] 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 flow paths. The control unit 100 also controls the gas separation system 1 so that each adsorber performs an adsorption process in which exhaust gas, which is a raw material gas, is supplied to the adsorber to cause carbon dioxide to be adsorbed onto the adsorbent, and a desorption process in which hydrogen, which is a purge gas, is supplied to the adsorber to cause carbon dioxide to be desorbed from the adsorbent.

[0024] 2 is an explanatory diagram illustrating an example of switching between various processes performed in each of the adsorbers. As shown in FIG. 2, each of the first and second adsorbers 10, 20 repeats various processes in the order of cycles 1 to 6 (returning to cycle 1 after cycle 6). In the gas separation system 1, each of the first and second adsorbers 10, 20 performs a lean reflux process, a concentrated reflux process, and a drying process in addition to the adsorption process and desorption process described above. Details of these processes will be described later.

[0025] FIG. 3 is an explanatory diagram showing the state of the gas separation system 1 in cycle 1. The thick lines in FIG. 3 indicate gas flows, and this also applies to FIGS. 4, 5, 8 to 10, and 12 to 14 described below. For convenience of explanation, the descriptions of FIGS. 3 to 5 will generally refer to only the valves in the open state among the various valves provided in the gas separation system 1. In cycle 1, the first adsorber 10 performs an adsorption process, and the second adsorber 20 performs a desorption process. In the state shown in FIG. 3, valves 51v, 61v, and 61ev are open. When the first adsorber 10 is performing the adsorption process, carbon dioxide contained in the flue gas supplied from the combustion equipment EG via the flue gas supply flow path 50 (branch flow path 51) is adsorbed by the adsorbent. The remaining flue gas not adsorbed by the adsorbent is discharged to the outside of the gas separation system 1 via the flue gas reflux flow path 60 (branch flow path 61). Hereinafter, the gas delivered from the adsorber during the adsorption process may be referred to as the "delivered gas after adsorption."

[0026] 3, valves 82v and Cv are open. Also, in the state shown in Fig. 3, hydrogen is supplied to the second adsorption device 20 from a hydrogen supply source (not shown). When the second adsorption device 20 is in the desorption process, the vacuum pump 85 is operated to reduce the pressure inside the second adsorption device 20, and hydrogen is supplied to the second adsorption device 20 from the hydrogen supply source as a purge gas, thereby desorbing the carbon dioxide adsorbed on the adsorbent. The desorbed carbon dioxide is then sent as a mixed gas together with hydrogen to the mixed gas delivery path 80 (branch path 81), and then sent to the end downstream of the valve Cv.

[0027] FIG. 4 is an explanatory diagram showing the state of the gas separation system 1 in cycle 2. In cycle 2, the first adsorber 10 performs an adsorption process and a rich reflux process, and the second adsorber 20 performs a lean reflux process. In the state shown in FIG. 4, valves 51v, 61v, 61ev, Rav, and 62v are open. When the first adsorber 10 is performing the adsorption process, as in FIG. 3, carbon dioxide is adsorbed onto the adsorbent from the supplied exhaust gas, and the post-adsorption delivery gas (exhaust gas that has passed through the first adsorber 10) is discharged to the outside of the gas separation system 1. When the second adsorber 20 is performing the lean reflux process, a portion of the post-adsorption delivery gas is refluxed to the second adsorber 20 via the reflux path 60R and the branch path 62. The post-adsorption delivery gas refluxed to the second adsorber 20 is used as a purge gas to desorb the carbon dioxide adsorbed on the adsorbent. The post-adsorption send gas is a gas that has undergone carbon dioxide adsorption by an adsorbent, and therefore has a low (dilute) carbon dioxide concentration, and can therefore be used for carbon dioxide desorption. When the second adsorber 20 is in the lean reflux step, the valve 82v is open, and the vacuum pump 85 is operating to reduce the pressure inside the second adsorber 20. Comparing the desorption step and the lean reflux step, the difference is that in the former, purge gas is supplied to the adsorber, while in the latter, the post-adsorption send gas is refluxed (supplied) to the adsorber.

[0028] 4, the valves 82v and Rcv are open. When the first adsorber 10 is in the concentrated reflux step, the adsorbed delivery gas returned to the second adsorber 20 is mixed with the desorbed carbon dioxide inside the second adsorber 20 and then returned as a mixed gas to the first adsorber 10 via the mixed gas delivery flow path 80 (branch flow path 81), the reflux flow path 80R, and the exhaust gas supply flow path 50 (branch flow path 51). Hereinafter, the gas delivered from the adsorber to which the adsorbed delivery gas has been returned (the second adsorber 20 in FIG. 4) may be referred to as the post-reflux delivery gas. The post-reflux delivery gas returned to the first adsorber 10 contains carbon dioxide desorbed from the adsorbent, and therefore has a high (rich) carbon dioxide concentration. The post-recirculation discharge gas returned to the first adsorbent 10 has carbon dioxide adsorbed by the adsorbent, and is then discharged again as post-adsorption discharge gas to the outside of the gas separation system 1 via the exhaust gas return flow path 60 (branch flow path 61), and a portion of it is returned to the second adsorbent 20 via the return flow path 60R and the branch flow path 62.

[0029] The reflux of the refluxed send-out gas via the reflux path 80R and the reflux of the adsorbed send-out gas via the reflux path 60R are carried out in parallel, thereby circulating the gas within the gas separation system 1 (see Figure 4). Of the gas circulation processes, the process in which the adsorbed send-out gas with a low (dilute) carbon dioxide concentration is refluxed corresponds to the lean reflux process, and the process in which the refluxed send-out gas with a high (rich) carbon dioxide concentration is refluxed corresponds to the rich reflux process. The execution of the lean reflux process and the rich reflux process increases the carbon dioxide concentration in the gas circulating within the gas separation system 1, thereby improving the purity and recovery rate of the carbon dioxide recovered from the gas separation system 1.

[0030] 5 is an explanatory diagram showing the state of the gas separation system 1 in cycle 3. In cycle 3, an adsorption process is performed in the first adsorber 10, and a drying process is performed in the second adsorber 20. In the state shown in FIG. 5, valves 51v, 61v, and 61ev are open. When the first adsorber 10 is performing the adsorption process, carbon dioxide is adsorbed from the exhaust gas onto the adsorbent, as in FIG. 3, and the post-adsorption output gas (exhaust gas that has passed through the first adsorber 10) is sent out of the gas separation system 1.

[0031] In the state shown in FIG. 5 , the valves Rav, 62v, and 72v are open. When the second adsorber 20 is performing the drying process, a portion of the adsorbed send gas is returned to the second adsorber 20 via the return path 60R and the branch path 62. The adsorbed send gas returned to the second adsorber 20 is used to remove moisture from the adsorbent and then discharged as a returned send gas to the outside of the gas separation system 1 via the exhaust gas discharge path 70 (branch path 72). When moisture accumulates in the adsorbent, the adsorption capacity of the adsorbent tends to decrease. The drying process is performed to prevent moisture from accumulating in the adsorbent. The difference between the lean return process and the drying process is that in the former, the returned send gas is returned to the adsorber from which the adsorbed send gas was originally sent, while in the latter, the returned send gas is discharged to the outside of the gas separation system 1.

[0032] Here, the drying process is performed in the second adsorber 20, which has just completed the desorption process and is about to begin the next adsorption process. Furthermore, when the second adsorber 20 is undergoing the drying process, the vacuum pump 85 is not operating, and the pressure inside the second adsorber 20 is not reduced. In other words, the drying process is performed under atmospheric pressure when the adsorbent has completed the desorption process and carbon dioxide has been desorbed from it. Therefore, the amount of carbon dioxide desorbed from the adsorbent is extremely small. Furthermore, the post-adsorption delivery gas used in the drying process has undergone carbon dioxide adsorption in the adsorber from which the post-adsorption delivery gas is delivered, and therefore the carbon dioxide concentration in this gas is low. Therefore, the amount of carbon dioxide leaking outside the gas separation system 1 during the drying process is extremely small. The low carbon dioxide leakage rate was experimentally confirmed by measuring the carbon dioxide concentration in the gas discharged from the adsorber during the drying process to the outside of the gas separation system 1 via the exhaust gas discharge path 70.

[0033] 2, in cycles 1 to 3, the first adsorber 10 performs the adsorption process, the adsorption process and the concentrated reflux process, and the adsorption process in that order, while the second adsorber 20 performs the desorption process, the lean reflux process, and the drying process in that order. On the other hand, in cycles 4 to 6, the first adsorber 10 performs the desorption process, the lean reflux process, and the drying process in that order, while the second adsorber 20 performs the adsorption process, the adsorption process and the concentrated reflux process, and the adsorption process in that order. That is, in cycles 4 to 6, compared to cycles 1 to 3, the process performed in the first adsorber 10 and the process performed in the second adsorber 20 are interchanged. In cycles 4 to 6, as in cycles 1 to 3, each process is performed in the first adsorber 10 and the second adsorber 20 by opening and closing various valves.

[0034] As shown in Fig. 2, the drying step is performed in the adsorber after the desorption step and before the next adsorption step is performed. For example, in the second adsorber 20, the drying step is performed in cycle 3, after the desorption step is completed in cycle 1 and before the next adsorption step is performed in cycle 4. In this way, as shown in Fig. 5, the control unit 100 controls the adsorbent so that a portion of the post-adsorption delivery gas, which is the gas delivered from the adsorber during the adsorption step (the first adsorber 10 in cycle 3), passes through the adsorber after the desorption step and before the next adsorption step is performed (the second adsorber 20 in cycle 3), and is then discharged to the outside of the gas separation system 1. In other words, the control unit 100 controls the adsorbent so that the drying step is performed in the adsorber after the desorption step and before the next adsorption step is performed.

[0035] As described above, according to the gas separation system 1 of the above-described embodiment, the passage of gas delivered from the adsorber during the adsorption step can remove moisture from the adsorbent housed in the adsorber that has completed the desorption step and is about to undergo the next adsorption step, while discharging the moisture to the outside of the gas separation system 1. Therefore, it is possible to prevent moisture from accumulating in the adsorbent, and therefore possible to prevent a decrease in the adsorption capacity of the adsorbent.

[0036] Second Embodiment 6 is an explanatory diagram illustrating the configuration of a gas separation system 1a according to a second embodiment. The gas separation system 1a according to the second embodiment has the same configuration as the gas separation system 1 according to the first embodiment, except that it further includes a third adsorption device 30, a branch channel 53, a branch channel 63, a branch channel 73, and a branch channel 83 in addition to the configuration of the gas separation system 1 according to the first embodiment.

[0037] The third adsorber 30 is an adsorber similar to the first and second adsorber 10, 20 and contains the same adsorbent therein. The branch channel 53 is included in the exhaust gas supply channel 50 and is a branch channel capable of supplying exhaust gas to the third adsorber 30. The branch channel 63 is included in the exhaust gas reflux channel 60 and is a branch channel capable of sending exhaust gas from the third adsorber 30 and returning exhaust gas to the third adsorber 30. The branch channel 63 is connected to each of the branch channels 61 and 62 via the reflux channel 60R. The branch channel 73 is included in the exhaust gas discharge channel 70 and is a gas channel capable of discharging the exhaust gas returned to the third adsorber 30 via the branch channel 63 to the outside of the gas separation system 1. The branch channel 83 is included in the mixed gas delivery channel 80 and is a branch channel capable of sending out the mixed gas from the third adsorber 30. Valves 53v, 63v, 73v, and 83v are provided in the branch channels 53, 63, 73, and 83, respectively. By controlling the opening and closing of these valves, gas flow in the branch channels 53, 63, 73, and 83 can be switched between on and off.

[0038] 7 is an explanatory diagram illustrating an example of switching between various processes performed in each of the adsorbers. As shown in FIG. 7, each of the first to third adsorbers 10, 20, and 30 repeats various processes in the order of cycles 1 to 9 (returning to cycle 1 after cycle 9). In the gas separation system 1a, a pressure recovery process is performed in addition to the adsorption process, desorption process, lean reflux process, rich reflux process, and drying process described in the first embodiment. The pressure recovery process will be described in detail later.

[0039] FIG. 8 is an explanatory diagram showing the state of the gas separation system 1a in cycle 1. For convenience of explanation, in the explanations of FIGS. 8 to 10, only the valves in the open state among the various valves provided in the gas separation system 1a will be basically referred to. In cycle 1, the first adsorber 10 performs an adsorption process, the second adsorber 20 performs a drying process, and the third adsorber 30 performs a desorption process. In the state shown in FIG. 8, the valves 51v and 61v are open. When the first adsorber 10 is performing the adsorption process, carbon dioxide contained in the flue gas supplied from the combustion equipment EG via the flue gas supply passage 50 (branch passage 51) is adsorbed by the adsorbent.

[0040] 8, the valves Rav, 62v, and 72v are open. When the second adsorber 20 is in the drying process, the post-adsorption delivery gas (exhaust gas that has passed through the first adsorber 10) is refluxed to the second adsorber 20 via the branch path 61, the return path 60R, and the branch path 63. The post-adsorption delivery gas that has been refluxed to the second adsorber 20 is used to remove moisture from the adsorbent, and then is discharged as post-reflux delivery gas to the outside of the gas separation system 1 via the exhaust gas discharge path 70 (branch path 72).

[0041] 8, valves 83v and Cv are open, and hydrogen is supplied from a hydrogen supply source (not shown) to the third adsorption device 30. When the third adsorption device 30 is in the desorption process, the vacuum pump 85 is operated to reduce the pressure inside the third adsorption device 30, and hydrogen is supplied from the hydrogen supply source to the second adsorption device 20 as a purge gas, thereby desorbing the carbon dioxide adsorbed on the adsorbent. The desorbed carbon dioxide is then sent together with hydrogen as a mixed gas to the mixed gas delivery path 80 (branch path 83), and then sent to the end downstream of valve Cv.

[0042] FIG. 9 is an explanatory diagram showing the state of the gas separation system 1a in cycle 2. In cycle 2, the first adsorber 10 performs the adsorption process and the rich reflux process, the second adsorber 20 continues to perform the drying process, and the third adsorber 30 performs the lean reflux process. As in FIG. 8, the first adsorber 10 is performing the adsorption process and the second adsorber 20 is performing the drying process. Therefore, carbon dioxide is adsorbed onto the adsorbent from the exhaust gas supplied to the first adsorber 10, and the adsorbed discharge gas (exhaust gas that has passed through the first adsorber 10) is refluxed to the second adsorber 20 and then discharged to the outside of the gas separation system 1. In addition, in the state shown in FIG. 9, the valves Rbv and 63v are open. When the third adsorber 30 is performing the lean reflux process, a portion of the adsorbed discharge gas is refluxed to the third adsorber 30 via the reflux path 60R and the branch path 63. In addition, in the state shown in FIG. 9, the valves 83v and Rcv are open. When the first adsorber 10 is in the concentrated reflux process, the adsorbed delivery gas returned to the second adsorber 20 is mixed with the desorbed carbon dioxide inside the second adsorber 20, and then returned as a mixed gas (refluxed delivery gas) to the first adsorber 10 via the mixed gas delivery flow path 80 (branch flow path 81), the reflux flow path 80R, and the exhaust gas supply flow path 50 (branch flow path 51).

[0043] FIG. 10 is an explanatory diagram showing the state of the gas separation system 1a in cycle 3. In cycle 3, the first adsorber 10 performs an adsorption process, the second adsorber 20 subsequently performs a drying process, and the third adsorber 30 performs a pressure recovery process. As in FIGS. 8 and 9 , the first adsorber 10 is performing the adsorption process, and the second adsorber 20 is performing the drying process. Therefore, carbon dioxide is adsorbed onto the adsorbent from the exhaust gas supplied to the first adsorber 10, while the adsorbed discharge gas (exhaust gas that has passed through the first adsorber 10) is refluxed to the second adsorber 20 and then discharged to the outside of the gas separation system 1. In addition, in the state shown in FIG. 10 , the valves Rbv and 63v are open. When the third adsorber 30 is performing the pressure recovery process, a portion of the adsorbed discharge gas is refluxed to the third adsorber 30 via the reflux path 60R and the branch path 63, similar to when the third adsorber 30 is performing the lean reflux process (see FIG. 9 ). On the other hand, in the state shown in FIG. 10 , the valve 83v is not open. Specifically, as shown in FIG. 9 , when the third adsorber 30 is in the lean reflux step and the first adsorber 10 is in the rich reflux step, the valve 83v is open. However, as shown in FIG. 10 , when the third adsorber 30 is in the pressure recovery step, the valve 83v is not open. Therefore, unlike in the lean reflux step, the adsorbed delivery gas returned to the third adsorber 30 is retained inside the third adsorber 30, thereby increasing the internal pressure of the third adsorber 30. That is, the pressure recovery step is a step of restoring the internal pressure of the adsorber that was reduced by the vacuum pump 85 during the desorption step. Comparing the pressure recovery step and the drying step, the former differs in that the adsorbed delivery gas is retained inside the adsorber, while the latter differs in that the adsorbed delivery gas passes through the adsorber and is discharged to the outside of the gas separation system 1 as a reflux delivery gas.

[0044] As shown in FIG. 7 , in cycles 1 to 3, the first adsorber 10 performs the adsorption process, the adsorption process and the concentrated reflux process, and the adsorption process in that order, while the third adsorber 30 performs the desorption process, the lean reflux process, and the pressure recovery process in that order, during which the second adsorber 20 performs the drying process. On the other hand, in cycles 4 to 6, instead of the third adsorber 30, the first adsorber 10 performs the desorption process, the lean reflux process, and the pressure recovery process in that order, while the second adsorber 20 performs the adsorption process, the adsorption process and the concentrated reflux process, and the adsorption process in that order, during which the third adsorber 30 performs the drying process in place of the second adsorber 20. That is, in cycles 4 to 6, the processes performed in the first to third adsorber 10, 20, and 30 are interchanged compared to cycles 1 to 3. In cycles 4 to 6, as in cycles 1 to 3, each process is performed in the first to third adsorber 10, 20, and 30 by opening and closing various valves. The same is true for cycles 7 to 9.

[0045] As shown in Fig. 7, the drying step is performed in the adsorber after the desorption step and before the next adsorption step is performed, as in the first embodiment. For example, as shown in Fig. 7, in the second adsorber 20, the drying step is performed in cycles 1 to 3 after the desorption step is completed in cycle 7 and before the next adsorption step is performed in cycle 4. Of the drying steps in cycles 1 to 3, in the drying steps in cycles 1 and 3, as in the first embodiment, the second adsorber 20 is dried by the post-adsorption delivery gas delivered from the first adsorber 10 during the adsorption step (see Figs. 8 and 10). On the other hand, in the drying step in cycle 2, unlike the first embodiment, the second adsorber 20 is dried by the post-adsorption delivery gas delivered from the first adsorber 10 during the adsorption step and the concentrated reflux step. That is, in a gas separation system 1a equipped with three control units 100, as shown in FIG. 9, when the post-adsorption delivery gas is refluxed from one of the two adsorbers (the first adsorber 10 in cycle 2) to the other adsorber (the third adsorber 30 in cycle 2) while the post-adsorption delivery gas, which is the post-adsorption delivery gas that has passed through the other adsorber, is refluxed from the other adsorber (the third adsorber 30 in cycle 2) to one of the adsorbers (the first adsorber 10 in cycle 2), the control unit 100 controls the gas separation system 1 so that a portion of the post-adsorption delivery gas (the gas delivered from the first adsorber 10 in cycle 2) passes through the adsorber (the second adsorber 20 in cycle 2) in a state that has completed the desorption process and is before the next adsorption process is performed, and then is discharged outside the gas separation system 1.

[0046] A test was conducted to verify the moisture removal effect from the adsorbent by the drying process using the gas separation system 1a of the second embodiment. The gas separation system 1a used in the test was equipped with an adsorber constructed by filling a stainless steel container with a diameter of 25 mm and a length of 100 mm with 2 mm diameter pellets as the adsorbent. In the test, the gas separation system 1a equipped with three such adsorber was used. Ten cycles of various processes, each consisting of cycles 1 to 9 shown in FIG. 7, were performed in each adsorber. Then, in the 11th cycle, cycles 1 to 3, the average dew point of the adsorbed gas discharged from the first adsorber 10 during the adsorption process was measured using a chilled mirror dew point meter. The lower the average dew point, the more moisture can be considered to have been removed from the adsorbent. Cycles 1, 4, and 7 were performed for 100 seconds, cycles 2, 5, and 8 for 395 seconds, and cycles 3, 6, and 9 for 5 seconds. Furthermore, the carbon dioxide-containing raw gas to be adsorbed into the adsorbent was not the exhaust gas described above, but gas with a carbon dioxide concentration of 10% and a dew point of 20° C. As a comparative example, after 10 cycles of various processes excluding the drying process were performed in each of the adsorbers, the average dew point of the adsorbed gas discharged from the first adsorber 10 during the adsorption process was measured in cycles 1 to 3 of the 11th cycle.

[0047] As a result of the above-described test, the average dew point was 5.2°C in the comparative example, while the average dew point was −2.7°C in the gas separation system 1a of the second embodiment. In both cases, because gas with a dew point of 20°C was supplied to the adsorber, it was confirmed that a larger amount of moisture was adsorbed from the gas onto the adsorbent in the gas separation system 1a of the second embodiment. The larger amount of moisture adsorbed onto the adsorbent means that the amount of moisture accumulated in the adsorbent at the start of the 11th cycle 1 was smaller, which can be considered to be the effect of moisture removal from the adsorbent by the drying process. Furthermore, the average dew point of the refluxed delivery gas delivered from the second adsorbent 20 during the drying process in the 11th cycle 1 to 3 was measured and found to be 8.2°C. That is, when the post-adsorption delivery gas transitioned to the refluxed delivery gas, the average dew point increased by 10.9°C (= 8.2 − (−2.7)). This increase can be considered to be the amount of moisture removed from the adsorbent by the drying process.

[0048] As described above, in the gas separation system 1a of the second embodiment, as in the first embodiment, moisture can be removed from the adsorbent housed in the adsorber while the moisture is discharged to the outside of the gas separation system. In particular, in the gas separation system 1a of the second embodiment, not only when only the reflux of the adsorbed send-out gas is being performed (see FIGS. 8 and 10 ), but also when the reflux of the adsorbed send-out gas and the reflux of the refluxed send-out gas are being performed in parallel (see FIG. 9 ), moisture can be removed from the adsorbent housed in the adsorber (the second adsorber 20 in cycle 2) that is not included in the path through which the gas is circulated by the reflux, while the moisture can be discharged to the outside of the gas separation system 1a.

[0049] Third Embodiment FIG. 11 is an explanatory diagram illustrating the configuration of a gas separation system 1b of the third embodiment. In the gas separation system 1a of the second embodiment (FIG. 6), the exhaust gas supply flow path 50, the exhaust gas discharge flow path 70, and the mixed gas delivery flow path 80 were connected to the same side of the adsorber (the lower side in FIG. 6). However, in the gas separation system 1b of the third embodiment, the side of the adsorber to which the exhaust gas supply flow path 50 and the mixed gas delivery flow path 80 are connected (the lower side in FIG. 11) is different from the side to which the exhaust gas discharge flow path 70 is connected (the upper side in FIG. 11). Furthermore, the gas separation system 1b of the third embodiment differs from the configuration of the gas separation system 1a of the second embodiment in that it includes branch flow paths 64, 65, and 66 and does not include valves Rav and Rbv.

[0050] The branch channels 64, 65, and 66 are included in the exhaust gas reflux channel 60 and are capable of refluxing the exhaust gas (post-adsorption delivery gas) delivered from each of the first to third adsorbers 10, 20, and 30. The branch channels 64, 65, and 66 are connected to each of the branch channels 61, 62, and 63 via the reflux channel 60R. The sides of the adsorbers to which the branch channels 64, 65, and 66 are connected are different from the sides to which the branch channels 61, 62, and 63 are connected. Valves 64v, 65v, and 66v are provided in the branch channels 64, 65, and 66, respectively. By controlling the opening and closing of these valves, it is possible to switch between enabling and disabling gas flow in the branch channels 64, 65, and 66.

[0051] In the gas separation system 1b of the third embodiment, similarly to the gas separation system 1a of the second embodiment, the first to third adsorption units 10, 20, and 30 each repeat various steps in the order of cycles 1 to 9 shown in FIG.

[0052] FIG. 12 is an explanatory diagram showing the state of the gas separation system 1b in cycle 1. For convenience of explanation, in the explanations of FIGS. 12 to 14, only the valves in the open state among the various valves provided in the gas separation system 1b will be basically referred to. In cycle 1, the first adsorber 10 performs an adsorption process, the second adsorber 20 performs a drying process, and the third adsorber 30 performs a desorption process. In the state shown in FIG. 12, the valves 51v and 61v are open. When the first adsorber 10 is performing the adsorption process, carbon dioxide contained in the flue gas supplied from the combustion equipment EG via the flue gas supply passage 50 (branch passage 51) is adsorbed by the adsorbent.

[0053] 12, the valves 65v and 72v are open. When the second adsorber 20 is in the drying process, the post-adsorption delivery gas (exhaust gas that has passed through the first adsorber 10) is returned to the second adsorber 20 via the branch path 61, the return path 60R, and the branch path 65. The post-adsorption delivery gas returned to the second adsorber 20 is used to remove moisture from the adsorbent, and then is discharged as post-return delivery gas to the outside of the gas separation system 1 via the exhaust gas discharge path 70 (branch path 72).

[0054] 12, valves 83v and Cv are open, and hydrogen is supplied from a hydrogen supply source (not shown) to the third adsorption device 30. When the third adsorption device 30 is in the desorption process, the vacuum pump 85 is operated to reduce the pressure inside the third adsorption device 30, and hydrogen is supplied from the hydrogen supply source to the second adsorption device 20 as a purge gas, thereby desorbing the carbon dioxide adsorbed on the adsorbent. The desorbed carbon dioxide is then sent together with hydrogen as a mixed gas to the mixed gas delivery path 80 (branch path 83), and then sent to the end downstream of valve Cv.

[0055] FIG. 13 is an explanatory diagram showing the state of the gas separation system 1a in cycle 2. In cycle 2, the first adsorber 10 performs the adsorption process and the rich reflux process, the second adsorber 20 subsequently performs the drying process, and the third adsorber 30 performs the lean reflux process. As in FIG. 12, the first adsorber 10 is performing the adsorption process and the second adsorber 20 is performing the drying process. Therefore, carbon dioxide is adsorbed onto the adsorbent from the exhaust gas supplied to the first adsorber 10, and the adsorbed discharge gas (exhaust gas that has passed through the first adsorber 10) is refluxed to the second adsorber 20 and then discharged to the outside of the gas separation system 1. In addition, in the state shown in FIG. 13, the valve 63v is open. When the third adsorber 30 is performing the lean reflux process, a portion of the adsorbed discharge gas is refluxed to the third adsorber 30 via the reflux path 60R and the branch path 63. In addition, in the state shown in FIG. 13, the valves 83v and Rcv are open. When the first adsorber 10 is in the concentrated reflux process, the adsorbed delivery gas returned to the second adsorber 20 is mixed with the desorbed carbon dioxide inside the second adsorber 20, and then returned as a mixed gas (refluxed delivery gas) to the first adsorber 10 via the mixed gas delivery flow path 80 (branch flow path 81), the reflux flow path 80R, and the exhaust gas supply flow path 50 (branch flow path 51).

[0056] FIG. 14 is an explanatory diagram showing the state of the gas separation system 1b in cycle 3. In cycle 3, the first adsorber 10 performs an adsorption process, the second adsorber 20 subsequently performs a drying process, and the third adsorber 30 performs a pressure recovery process. As in FIGS. 12 and 13, the first adsorber 10 is performing the adsorption process, and the second adsorber 20 is performing the drying process. Therefore, carbon dioxide is adsorbed onto the adsorbent from the exhaust gas supplied to the first adsorber 10, while the adsorbed discharge gas (exhaust gas that has passed through the first adsorber 10) is returned to the second adsorber 20 and then discharged to the outside of the gas separation system 1. In addition, in the state shown in FIG. 14, the valve 63v is open. When the third adsorber 30 is performing the pressure recovery process, a portion of the adsorbed discharge gas is returned to the third adsorber 30 via the return path 60R and the branch path 63, as in the lean reflux process (see FIG. 13). On the other hand, in the state shown in Fig. 14, the valve 83v is not open. In detail, as shown in Fig. 13, when the third adsorber 30 is in the lean reflux step and the first adsorber 10 is in the rich reflux step, the valve 83v is open, but as shown in Fig. 14, when the third adsorber 30 is in the pressure recovery step, the valve 83v is not open. Therefore, unlike in the lean reflux step, the adsorbed discharge gas that has been refluxed to the third adsorber 30 is retained inside the third adsorber 30 without passing through it, and this increases the pressure inside the third adsorber 30.

[0057] As described above, in the gas separation system 1b of the third embodiment, as in the first and second embodiments, moisture can be removed from the adsorbent housed in the adsorber while the moisture is discharged to the outside of the gas separation system. Specifically, as in the gas separation system 1a of the second embodiment in which the return of the adsorbed send-out gas and the return of the returned send-out gas are performed, moisture can be removed from the adsorbent housed in the adsorber (the second adsorber 20 in cycle 2) that is not included in the path through which the gas is circulated by the return, while the moisture can be discharged to the outside of the gas separation system 1a. Therefore, in the gas separation system 1b of the third embodiment, as in the first and second embodiments, moisture can be prevented from accumulating in the adsorbent, and therefore a decrease in the adsorption capacity of the adsorbent can be prevented.

[0058] <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.

[0059] In the second and third embodiments described above, the gas separation systems 1a and 1b each include three adsorbers, but this is not limited thereto. The gas separation system may include four or more adsorbers. FIG. 15 is an explanatory diagram illustrating an example of switching between various processes performed in each of the adsorbers when the gas separation system includes four adsorbers. In FIG. 15, the fourth adsorber 40 corresponds to the fourth adsorber included in the gas separation system. As shown in FIG. 15, each of the first to fourth adsorbers 10, 20, 30, and 40 may repeat various processes, including a drying process, in the order of cycles 1 to 8 (returning to cycle 1 after cycle 8), thereby separating carbon dioxide from the raw material gas while removing moisture from the adsorbent, thereby preventing moisture from accumulating in the adsorbent.

[0060] In the second and third embodiments described above, the pressure recovery step restores the pressure inside the adsorber using the post-adsorption delivery gas, but this is not limited to this. The pressure recovery step may also restore the pressure inside the adsorber using the feed gas. Note that, because the drying step is performed after the pressure recovery step (see FIGS. 7 and 15), the gas that remained in the adsorber during the pressure recovery step is discharged to the outside of the gas separation system. Therefore, from the viewpoint of carbon dioxide recovery efficiency, it is preferable to perform the pressure recovery step using the post-adsorption delivery gas, which has a lower carbon dioxide concentration than the feed gas.

[0061] 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. [Explanation of symbols]

[0062] 1...Gas separation system 1a...Gas separation system 1b...Gas separation system 10...First adsorption device 20…Second adsorption device 30…Third adsorption device 40…4th adsorption device 50...Exhaust gas supply passage 51~53…Diversion channel 51v~53v...bulb 60...Exhaust gas recirculation passage 60R...Reflux path 61~66…Diversion channel 61v~66v...bulb 61ev, 62ev... valve 70...Exhaust gas discharge flow path 71~73…Diversion channel 71v~73v...bulb 80...mixed gas delivery passage 80R...Reflux path 81~83…Diversion channel 81v~83v...bulb 85...Vacuum pump 100...Control unit Cv...valve EG: Combustion equipment Rav… Valve Rbv...valve Rcv...valve

Claims

1. A gas separation system for separating carbon dioxide from a raw material gas containing carbon dioxide, comprising: a plurality of adsorbents each containing an adsorbent capable of adsorbing carbon dioxide; a control unit that controls each of the adsorbers so that an adsorption step of supplying the raw material gas to the adsorbent and causing the adsorbent to adsorb carbon dioxide, and a desorption step of supplying the purge gas to the adsorbent and causing the adsorbent to desorb carbon dioxide, are performed in each of the adsorbers; The control unit controls a portion of the post-adsorption discharge gas, which is the gas discharged from the adsorber during the adsorption process, to pass through the adsorber in a state after the desorption process has completed and before the next adsorption process is performed, and then be discharged outside the gas separation system.

2. 10. The gas separation system of claim 1, The plurality of adsorbers include three or more adsorbers, a control unit that, when refluxing the post-adsorption delivery gas from one of the two adsorbers to the other adsorber while refluxing the post-adsorption delivery gas, which is the post-adsorption delivery gas that has passed through the other adsorber, from the other adsorber to the one adsorber, controls the gas separation system so that a portion of the post-adsorption delivery gas passes through the adsorber in the state and then is discharged outside the gas separation system.

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