Carbon dioxide recovery system

Abstract

To improve system efficiency in a carbon dioxide recovery system which decompresses the inside of a recovery device when CO2 is recovered.SOLUTION: In a carbon dioxide recovery system, a plurality of recovery devices 11, 12 which can switch its function between adsorption and desorption of CO2, and a decompression device 13 which vacuum-suctions and decompresses the inside of the recovery device are provided. Each recovery device can be operated in each of modes including an adsorption mode in which CO2 contained in a CO2-containing gas is adsorbed at a normal pressure, a desorption mode in which CO2 adsorbed in the adsorption mode is desorbed, a gas removal mode in which the inside of the recovery device is vacuum-suctioned and decompressed by the decompression device to remove a gas from the inside of the recovery device, and a pressure equalization mode in which the recovery device is connected to another recovery device in such a manner that the gas existing therein may move therebetween. In the pressure equalization mode, the recovery device at the normal pressure and the recovery device decompressed by the decompression device are connected. In the recovery device connected in the pressure equalization mode, the pressure is lower than the normal pressure when the pressure equalization mode ends.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a carbon dioxide capture system that captures CO2 from a CO2-containing gas that contains CO2. [Background technology]

[0002] Patent Document 1 proposes a carbon dioxide capture system that captures CO2 from a mixed gas containing CO2 by an electrochemical reaction. The carbon dioxide capture system of Patent Document 1 is provided with a capture device equipped with an electrochemical cell having a working electrode and a counter electrode, and the adsorption and desorption of CO2 can be switched by changing the potential difference between the working electrode and the counter electrode. In this carbon dioxide capture system, in order to capture high-purity CO2, CO2 is adsorbed in the electrochemical cell, and then desorbed and captured from the electrochemical cell while the inside of the capture device is depressurized by a vacuum pump. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-46607 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional technology, the inside of the capture device is depressurized every time CO2 is desorbed and captured, which increases the power of the vacuum pump and reduces the system efficiency.

[0005] In view of the above, an object of the present invention is to improve the system efficiency in a carbon dioxide capture system that reduces the pressure inside a capture device when capturing CO2. [Means for solving the problem]

[0006] In order to achieve the above object, the invention described in claim 1 provides a carbon dioxide capture system that captures CO2 from a CO2-containing gas, and includes a plurality of capture devices (11, 12) capable of switching between adsorption and desorption of CO2, and a pressure reduction device (13) that reduces the pressure inside the capture devices by vacuum suction.

[0007] The capture device can operate in various modes, including an adsorption mode in which it adsorbs CO2 contained in a CO2-containing gas at normal pressure, a desorption mode in which it desorbs the CO2 adsorbed in the adsorption mode, a gas removal mode in which it reduces the pressure by vacuum-suctioning the gas from inside the capture device using a pressure reducing device, and removes the gas from inside the capture device, and a pressure equalization mode in which it connects to other capture devices so that the gas present inside can be moved.

[0008] In the pressure equalization mode, the recovery device at normal pressure is connected to a recovery device depressurized by a depressurization device. The recovery device connected in the pressure equalization mode is at a pressure lower than normal pressure when the pressure equalization mode ends.

[0009] In this way, the pressure in the recovery device can be reduced in advance before the start of the gas removal mode by using the recovery device depressurized by the depressurizing device. Therefore, in the gas removal mode after the pressure equalization mode ends, the power of the depressurizing device can be reduced compared to the case where the gas removal mode is executed following the adsorption mode, and the system efficiency can be improved.

[0010] The reference characters in parentheses for each of the above components indicate the corresponding relationship with the specific means described in the embodiments described later. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing an overall configuration of a carbon dioxide capture system according to a first embodiment. [Diagram 2] FIG. 1 is a perspective view showing a schematic diagram of an electrochemical cell. [Diagram 3] FIG. 4 is a diagram showing a control pattern of the carbon dioxide capture system of the first embodiment. [Figure 4]FIG. 13 is a diagram showing a state in which the first recovery device is operating in an adsorption mode. [Diagram 5] FIG. 13 is a diagram showing a state in which the first recovery device is operating in a gas removal mode and the second recovery device is operating in an adsorption mode. [Figure 6] FIG. 13 shows the first and second recovery devices operating in a pressure equalization mode. [Figure 7] FIG. 13 shows a state in which the first collection device is operating in a desorption mode and the second collection device is operating in a gas removal mode. [Figure 8] FIG. 13 is a diagram showing a state in which the first recovery device is operating in an adsorption mode and the second recovery device is operating in a desorption mode. [Figure 9] FIG. 11 is a diagram showing a control pattern of the carbon dioxide capture system of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a number of embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, the same reference numerals may be used to designate parts corresponding to matters described in the preceding embodiment, and duplicated descriptions may be omitted. In each embodiment, when only a part of the configuration is described, other embodiments described previously may be applied to other parts of the configuration. In addition to combinations of parts that are specifically indicated as being possible in each embodiment, it is also possible to partially combine embodiments even if not indicated, as long as there is no particular problem with the combination.

[0013] (First embodiment) A first embodiment of the present invention will be described below with reference to the drawings. As shown in Fig. 1, a carbon dioxide capture system 1 of this embodiment is provided with a blower 10, capture devices 11 and 12, pressure reduction devices 13 and 14, a CO2 utilization device 15, a control device 16, on-off valves 20-27, and flow path switching valves 30-33. The devices other than the control device 16 are connected by gas pipes 100-107.

[0014] Gas can pass through the gas pipes 100 to 107. The gas pipes 100 to 107 include supply pipes 100 to 102, off-gas pipes 103 to 105, and recovery pipes 106 and 107.

[0015] The first supply pipe 100 passes through the CO2-containing gas supplied to the recovery devices 11 and 12. The CO2-containing gas contains CO2 and gases other than CO2 (e.g., N2, O2, etc.). For example, the atmosphere, exhaust gas from a factory, exhaust gas from an internal combustion engine, etc., can be used as the CO2-containing gas. In this embodiment, a CO2-containing gas with a low CO2 concentration is used.

[0016] The first supply pipe 100 is provided with a blower 10. The blower 10 supplies a CO2-containing gas to the capture devices 11 and 12, and discharges off-gas from the capture devices 11 and 12 after CO2 is captured from the CO2-containing gas. The blower 10 operates in an adsorption mode, which will be described later. The off-gas mainly contains N2 and O2.

[0017] In this embodiment, a fan or a blower is used as the blower 10. In this embodiment, the blower 10 does not perform a pressure increase operation to increase the pressure inside the capture devices 11 and 12 above atmospheric pressure. Therefore, in the adsorption mode, the inside of the capture devices 11 and 12 is at "normal pressure" and CO2 adsorption is performed at normal pressure. However, inside the capture devices 11 and 12, the blowing of air by the blower 10 may cause a pressure increase of, for example, about 10 kPaG relative to atmospheric pressure. In this embodiment, the normal pressure is set within the range of 101 kPa to 110 kPa, taking into account a slight pressure increase due to the blowing of air by the blower 10.

[0018] The first supply pipe 100 branches into a second supply pipe 101 and a third supply pipe 102. The second supply pipe 101 and the third supply pipe 102 are provided in parallel. The second supply pipe 101 is connected to the first recovery device 11, and the third supply pipe 102 is connected to the second recovery device 12.

[0019] A first flow path switching valve 30 is provided at the branch point of the second supply pipe 101 and the third supply pipe 102. The first flow path switching valve 30 connects the first supply pipe 100 to either the second supply pipe 101 or the third supply pipe 102, and switches the flow path of the CO2-containing gas that has passed through the first supply pipe 100 to either the second supply pipe 101 or the third supply pipe 102. The first flow path switching valve 30 switches the flow path of the CO2-containing gas, and connects the blower 10 to either the first recovery device 11 or the second recovery device 12.

[0020] The second supply pipe 101 is provided with a first on-off valve 20. The first on-off valve 20 can close the second supply pipe 101 to interrupt the flow of the CO2-containing gas supplied to the first recovery device 11.

[0021] The third supply pipe 102 is provided with a second on-off valve 21. The second on-off valve 21 can close the third supply pipe 102 to interrupt the flow of the CO2-containing gas supplied to the second recovery device 12.

[0022] The capture devices 11 and 12 are devices that separate and capture CO2 from a CO2-containing gas. A plurality of the capture devices 11 and 12 are provided, and the plurality of capture devices 11 and 12 are provided in parallel. In this embodiment, two capture devices 11 and 12 are provided.

[0023] The capture devices 11 and 12 are electrochemical gas capture devices that switch between adsorption and desorption of CO2 by electrochemical reaction, and separate and capture CO2 from the CO2-containing gas. The first capture device 11 and the second capture device 12 have the same configuration.

[0024] The capture devices 11 and 12 of this embodiment can operate at least in an adsorption mode, a desorption mode, a gas removal mode, and a pressure equalization mode. The adsorption mode is a mode in which the capture devices 11 and 12 adsorb CO2 contained in the CO2-containing gas. The desorption mode is a mode in which the CO2 adsorbed in the adsorption mode is desorbed from the capture devices 11 and 12. The gas removal mode is a mode in which off-gas is sucked and removed from the inside of the capture devices 11 and 12 after the adsorption mode and before the desorption mode. The pressure equalization mode is a mode in which multiple capture devices 11 and 12 with different internal pressures are connected to each other, and the gas present inside each capture device is made movable to equalize the pressure of the multiple capture devices 11 and 12.

[0025] The recovery devices 11 and 12 operate by switching between the various modes. Each mode may be started immediately after the previous mode is finished, before the previous mode is finished, or after a predetermined time has elapsed after the previous mode is finished.

[0026] The recovery devices 11 and 12 each include an electrochemical cell 50 shown in Fig. 2. In the recovery devices 11 and 12, the electrochemical cell 50 is housed in a housing (not shown). The electrochemical cell 50 is capable of switching between adsorption and desorption of CO2 by electrochemical reaction.

[0027] The electrochemical cell 50 has a working electrode 51, a counter electrode 52, and an insulating layer 53. In Fig. 2, the working electrode 51, the counter electrode 52, and the insulating layer 53 are illustrated with a gap between them for convenience, but in reality, these components are arranged in contact with each other.

[0028] The working electrode 51 and the counter electrode 52 are disposed with an insulating layer 53 sandwiched therebetween. The working electrode 51, the counter electrode 52, and the insulating layer 53 are configured, for example, in a plate shape. The working electrode 51 is a negative electrode, and the counter electrode 52 is a positive electrode. In the electrochemical cell 50, a predetermined voltage is applied to the working electrode 51 and the counter electrode 52 by a power source 54, and the potential difference between the working electrode 51 and the counter electrode 52 can be changed.

[0029] The electrochemical cell 50 can be operated in a switchable manner between an adsorption mode in which the working electrode 51 adsorbs CO2, and a desorption mode in which the working electrode 51 desorbs CO2 from the working electrode 51, by changing the potential difference between the working electrode 51 and the counter electrode 52. The adsorption mode is a charge mode in which the electrochemical cell 50 is charged, and the desorption mode is a discharge mode in which the electrochemical cell 50 is discharged.

[0030] In the adsorption mode, a first voltage V1 is applied between the working electrode 51 and the counter electrode 52, and electrons are supplied from the counter electrode 52 to the working electrode 51. At the first voltage V1, the working electrode potential is smaller than the counter electrode potential.

[0031] In the desorption mode, a second voltage V2 is applied between the working electrode 51 and the counter electrode 52, and electrons are supplied from the working electrode 51 to the counter electrode 52. The second voltage V2 is a voltage different from the first voltage V1. The second voltage V2 may be any voltage lower than the first voltage V1, and the magnitude relationship between the working electrode potential and the counter electrode potential is not limited. That is, in the desorption mode, the working electrode potential may be less than the counter electrode potential, the working electrode potential may be equal to the counter electrode potential, or the working electrode potential may be greater than the counter electrode potential.

[0032] The electrochemical capture devices 11 and 12 can selectively adsorb CO2 from CO2-containing gas in response to the applied electric energy. For example, a pressure-type capture device that adsorbs CO2 by pressure adsorbs CO2 from a CO2-containing gas with a low CO2 concentration, and in addition to CO2, also adsorbs a considerable amount of gases other than CO2, such as N2. The electrochemical capture devices 11 and 12 can more efficiently capture CO2 from a CO2-containing gas with a low CO2 concentration than a pressure-type capture device.

[0033] The electrochemical capture devices 11 and 12 are suitable for capturing CO2 from a CO2-containing gas having a low CO2 concentration. For this reason, in this embodiment, a CO2-containing gas having a low CO2 concentration is supplied to the capture devices 11 and 12, and the CO2 concentration of the off-gas after the CO2 is adsorbed in the capture devices 11 and 12 is set to less than 1000 ppm. It is more preferable that the CO2 concentration of the off-gas is less than 500 ppm.

[0034] In this embodiment, the CO2 concentration of the CO2-containing gas is 400 ppm to 5%. The CO2 concentration of the CO2-containing gas is more preferably 1000 ppm to 3%, further preferably 1500 ppm to 3%, and particularly preferably 5000 ppm to 1.5%.

[0035] Returning to FIG. 1, off-gas pipes 103 and 104 for discharging off-gas are connected to the recovery devices 11 and 12. A first off-gas pipe 103 is connected to the first recovery device 11, and a second off-gas pipe 104 is connected to the second recovery device 12. The first off-gas pipe 103 is connected to the off-gas obtained after CO2 has been removed from the CO2-containing gas in the first recovery device 11. The second off-gas pipe 104 is connected to the off-gas obtained after CO2 has been removed from the CO2-containing gas in the second recovery device 12.

[0036] The first off-gas pipe 103 and the second off-gas pipe 104 are each connected on the downstream side of the gas flow to a third off-gas pipe 105. The off-gas flowing through the third off-gas pipe 105 is discharged to the atmosphere.

[0037] The first off-gas piping 103 is provided with a third on-off valve 22. The second off-gas piping 104 is provided with a fourth on-off valve 23. The third on-off valve 22 can close the first off-gas piping 103. The fourth on-off valve 23 can close the second off-gas piping 104.

[0038] A second flow path switching valve 31 is provided at the junction of the first off-gas piping 103 and the second off-gas piping 104. The second flow path switching valve 31 connects either the first off-gas piping 103 or the second off-gas piping 104 to a third off-gas piping 105. The second flow path switching valve 31 switches between a state in which the first recovery device 11 communicates with the outside via the off-gas piping 103, 105 and a state in which the second recovery device 12 communicates with the outside via the off-gas piping 104, 105.

[0039] The capture devices 11 and 12 are connected to capture pipes 106 and 107 for capturing CO2 separated from the CO2-containing gas. The first capture device 11 is connected to a first capture pipe 106, and the second capture device 12 is connected to a second capture pipe 107.

[0040] The first recovery pipe 106 is provided with a fifth on-off valve 24. The second recovery pipe 107 is provided with a sixth on-off valve 25. The fifth on-off valve 24 is capable of closing the first recovery pipe 106. The sixth on-off valve 25 is capable of closing the second recovery pipe 107.

[0041] The downstream gas flow ends of the first recovery pipe 106 and the second recovery pipe 107 are connected to either the first pressure reducing device 13 or the second pressure reducing device 14. A seventh on-off valve 26 is provided on the upstream side of the gas flow path of the first pressure reducing device 13. An eighth on-off valve 27 is provided on the upstream side of the gas flow path of the second pressure reducing device 14. The first pressure reducing device 13 and the second pressure reducing device 14 are vacuum pumps that suction the insides of the recovery devices 11, 12. The first pressure reducing device 13 and the second pressure reducing device 14 exhaust the gas present inside the recovery devices 11, 12 from the recovery devices 11, 12.

[0042] The first recovery pipe 106 is connected to the first pressure reducing device 13 or the second pressure reducing device 14 by the third flow path switching valve 32. The third flow path switching valve 32 switches whether the first recovery device 11 is connected to the first pressure reducing device 13 or the second pressure reducing device 14.

[0043] The second recovery pipe 107 is connected to the first pressure reducing device 13 or the second pressure reducing device 14 by the fourth flow path switching valve 33. The fourth flow path switching valve 33 switches whether the second recovery device 12 is connected to the first pressure reducing device 13 or the second pressure reducing device 14.

[0044] The first pressure reducing device 13 is used in a gas removal mode in which the off-gas remaining inside the capture devices 11 and 12 is sucked in and removed. The gas removal mode is performed after the adsorption mode in which the capture devices 11 and 12 adsorb CO2 is completed and before the desorption mode in which the capture devices 11 and 12 desorb CO2 is started.

[0045] In the gas removal mode, the first pressure reducing device 13 evacuates the inside of the recovery devices 11, 12, and reduces the pressure inside the recovery devices 11, 12 to a pressure lower than normal pressure. In this embodiment, the pressure inside the recovery devices 11, 12 after being reduced in the gas removal mode is called a "high vacuum." In this embodiment, the high vacuum is in the range of 10 Pa to 10 kPa, preferably in the range of 100 Pa to 5 kPa. The central value of the high vacuum is, for example, 500 Pa.

[0046] The level to which the pressure inside the capture devices 11, 12 is reduced by the first pressure reducing device 13 depends on the amount of CO2 adsorbed by the capture devices 11, 12, the amount of off-gas remaining inside the capture devices 11, 12, the purity of the CO2 to be captured, etc.

[0047] The second pressure reducing device 14 is used in a desorption mode in which the CO2 desorbed by the capture devices 11 and 12 is sucked in and captured. The desorption mode is performed after the gas removal mode.

[0048] A CO2 utilization device 15 is provided downstream of the second pressure reducing device 14 in the gas flow direction. The CO2 utilization device 15 is a device that utilizes CO2. The CO2 absorbed and captured by the second pressure reducing device 14 from the capture devices 11 and 12 is supplied to the CO2 utilization device 15.

[0049] The CO2 utilization device 15 may be, for example, a storage tank for storing CO2 or a conversion device for converting CO2 into fuel. The conversion device may be a device for converting CO2 into a hydrocarbon fuel such as methane. The hydrocarbon fuel may be a gas fuel at normal temperature and pressure, or may be a liquid fuel at normal temperature and pressure.

[0050] The first recovery device 11 and the second recovery device 12 are connected by a connection pipe 108. The internal spaces of the first recovery device 11 and the second recovery device 12 are connected by the connection pipe 108, and the gases present in the internal spaces of the first recovery device 11 and the second recovery device 12 can move between them via the connection pipe 108.

[0051] When there is a pressure difference between the internal spaces of the first recovery device 11 and the second recovery device 12, the pressures in the internal spaces of the first recovery device 11 and the second recovery device 12 can be equalized by connecting them with the connection pipe 108 and enabling gas movement. In other words, by connecting the first recovery device 11 and the second recovery device 12 with the connection pipe 108, a pressure equalization mode can be executed to equalize the pressures of the first recovery device 11 and the second recovery device 12.

[0052] In the pressure equalization mode, the recovery devices 11, 12 at normal pressure are connected to the recovery devices 11, 12 depressurized by the first depressurization device 13. Regarding the start and end timing of other modes performed before and after the pressure equalization mode, the end of the previous mode and the start of the subsequent mode may be simultaneous, the subsequent mode may be started before the end of the previous mode, or the subsequent mode may be started a predetermined time after the end of the previous mode.

[0053] If the latter mode is started a predetermined time after the end of the former mode, for example, the mode can be switched to the equalization mode after sufficient CO2 adsorption in the adsorption mode, thereby increasing the purity of the captured CO2. If the former mode ends and the latter mode starts at the same time, or if the latter mode starts before the former mode ends, the CO2 capture speed can be improved.

[0054] In this embodiment, the recovery devices 11, 12 after the adsorption mode and before the gas removal mode is started are connected to the recovery devices 11, 12 after the gas removal mode and before the adsorption mode is started by the connection pipe 108 to perform the pressure equalization mode. The insides of the recovery devices 11, 12 after the adsorption mode are at normal pressure, and the insides of the recovery devices 11, 12 after the gas removal mode are at high vacuum. By performing the pressure equalization mode, the pressure in the recovery devices 11, 12, which were at normal pressure, decreases, and the pressure in the recovery devices 11, 12, which were at high vacuum, increases. The pressures inside the two recovery devices 11, 12 become equal through the pressure equalization mode, and become intermediate pressure between normal pressure and high vacuum. At the end of the pressure equalization mode, the pressure in the recovery devices 11, 12 is lower than normal pressure.

[0055] In this embodiment, the intermediate pressure generated by the pressure equalization mode is referred to as a "medium vacuum." A medium vacuum is a pressure lower than normal pressure and higher than a high vacuum. In this embodiment, the medium vacuum is in the range of 10 kPa to 60 kPa. The median value of the medium vacuum is, for example, 50 kPa. The specific value of the medium vacuum varies depending on the number of recovery devices to be pressure equalized, and when two recovery devices 11 and 12 are pressure equalized, the value is an intermediate value between normal pressure and high vacuum.

[0056] The connecting pipe 108 is provided with a ninth on-off valve 28. The ninth on-off valve 28 can close the connecting pipe 108 to block the movement of gas between the first recovery device 11 and the second recovery device 12. The connecting pipe 108 is closed by the ninth on-off valve 28 in modes other than the pressure equalization mode.

[0057] The carbon dioxide capture system 1 is provided with a control device 16. The control device 16 is composed of a well-known microcomputer including a CPU, ROM, RAM, etc., and its peripheral circuits. The control device 16 performs various calculations and processing based on a control program stored in the ROM, and controls the operation of various controlled devices. The control device 16 in this embodiment controls the operation of the blower 10, the operation of the capture devices 11 and 12, the operation of the pressure reducing devices 13 and 14, the opening / closing switching control of the on-off valves 20-28, the flow path switching control of the flow path switching valves 30-33, etc.

[0058] Next, the operation of the carbon dioxide capture system 1 of this embodiment will be described. As described above, the first capture device 11 and the second capture device 12 operate by switching between the adsorption mode, the gas removal mode, the pressure equalization mode, and the desorption mode. The first capture device 11 and the second capture device 12 operate in different orders of the modes.

[0059] 3 is an example of a control pattern of the collection devices 11, 12, and shows the execution order of each mode of the collection devices 11, 12. The collection devices 11, 12 switch between and execute each mode according to a preset control pattern.

[0060] As shown in Fig. 3, the first recovery device 11 and the second recovery device 12 regularly execute each mode in a different order. The modes of the first recovery device 11 and the second recovery device 12 are switched in the order of the first stage (1), the second stage (2), the third stage (3), ..., and the ninth stage (9) shown in Fig. 3. Even after the ninth stage (9), the recovery devices 11 and 12 execute each mode according to the control pattern.

[0061] Figure 4 shows the gas flow in the first stage (1), Figure 5 shows the gas flow in the second stage (2), Figure 6 shows the gas flow in the third stage (3), Figure 7 shows the gas flow in the fourth stage (4), and Figure 8 shows the gas flow in the fifth stage (5). In Figures 4 to 8, the pipes through which gas flows at each stage are indicated by thick lines.

[0062] In a first stage (1) shown in FIG. 4, the first recovery device 11 operates in adsorption mode and the second recovery device 12 is deactivated.

[0063] In the first stage (1), the blower 10 is operating, and the pressure reducing devices 13 and 14 are not operating. The first flow path switching valve 30 connects the blower 10 and the first recovery device 11 via the supply pipes 100 and 101. The second flow path switching valve 31 connects the first recovery device 11 to the outside via the off-gas pipes 103 and 105. The on-off valves 20 and 22 are in an open state, and the on-off valves 21, 23, 24 to 28 are in a closed state.

[0064] In the adsorption mode, the first recovery device 11 is supplied with a CO2-containing gas and adsorbs CO2. A first voltage V1 is applied to the electrochemical cell 50 of the first recovery device 11, and CO2 contained in the CO2-containing gas introduced into the first recovery device 11 is adsorbed by the electrochemical cell 50. The off-gas from which CO2 has been removed in the first recovery device 11 is exhausted from the first recovery device 11 and released into the atmosphere via the off-gas pipes 103 and 105. At the end of the adsorption mode, the inside of the first recovery device 11 is at normal pressure, and off-gas remains.

[0065] In the second stage (2) shown in FIG. 5, the first recovery device 11 operates in gas removal mode and the second recovery device 12 operates in adsorption mode.

[0066] In the second stage (2), the blower 10 and the first pressure reducing device 13 are operating, and the second pressure reducing device 14 is not operating. The first flow path switching valve 30 connects the blower 10 and the second recovery device 12 via the supply pipes 100 and 102. The second flow path switching valve 31 connects the second recovery device 12 to the outside via the off-gas pipes 104 and 105. The third flow path switching valve 32 connects the first recovery device 11 and the first pressure reducing device 13 via the first recovery pipe 106. The on-off valves 21, 23, 24, and 26 are in the open state, and the on-off valves 20, 22, 25, 27, and 28 are in the closed state.

[0067] In the gas removal mode, the first recovery device 11 is vacuum-suctioned by the first pressure reducing device 13, and the off-gas remaining inside is discharged from the first recovery device 11. The off-gas sucked by the first pressure reducing device 13 is released into the atmosphere. When the gas removal mode ends, the inside of the first recovery device 11 is at a high vacuum, and no off-gas remains.

[0068] In the adsorption mode, the second recovery device 12 is supplied with a CO2-containing gas and adsorbs CO2. A first voltage V1 is applied to the electrochemical cell 50 of the second recovery device 12, and CO2 contained in the CO2-containing gas introduced into the second recovery device 12 is adsorbed by the electrochemical cell 50. The off-gas from which CO2 has been removed in the second recovery device 12 is exhausted from the second recovery device 12 and released into the atmosphere via the off-gas pipes 104 and 105. At the end of the adsorption mode, the inside of the second recovery device 12 is at normal pressure, and off-gas remains.

[0069] In the third stage (3) shown in FIG. 6, both the first recovery device 11 and the second recovery device 12 operate in pressure equalization mode.

[0070] In the third stage (3), the blower 10 and the pressure reducing devices 13 and 14 are not in operation. The on-off valve 28 is in an open state, and the on-off valves 20 to 27 are in a closed state.

[0071] In the third stage (3), the on-off valve 28 is opened, thereby connecting the first recovery device 11 and the second recovery device 12 via the connecting pipe 108, allowing gas to move between the first recovery device 11 and the second recovery device 12.

[0072] In the second stage (2) before the third stage (3), the first recovery device 11 is in a high vacuum in gas removal mode, and the second recovery device 12 is in an adsorption mode and is at normal pressure. Therefore, in the pressure equalization mode, the off-gas remaining inside the second recovery device 12 flows into the first recovery device 11. As a result, the pressure in the first recovery device 11 increases and the pressure in the second recovery device 12 decreases, and the two recovery devices 11, 12 are equalized in pressure. At the end of the pressure equalization mode, the insides of the first recovery device 11 and the second recovery device 12 are at a medium vacuum. In the pressure equalization mode of the third stage (3), the first recovery device 11 in a high vacuum can be used to reduce the pressure of the second recovery device in normal pressure to a medium vacuum without using power.

[0073] In a fourth stage (4) shown in FIG. 7, the first collection device 11 operates in a desorption mode and the second collection device 12 operates in a gas removal mode.

[0074] In the fourth stage (4), the blower 10 is stopped, and the pressure reducing devices 13 and 14 are operating. The third flow path switching valve 32 connects the first recovery device 11 and the second pressure reducing device 14 via the first recovery pipe 106. The fourth flow path switching valve 33 connects the second recovery device 12 and the first pressure reducing device 13 via the second recovery pipe 107. The on-off valves 24 to 27 are in an open state, and the on-off valves 20 to 23 and 28 are in a closed state.

[0075] In the first recovery device 11 in the desorption mode, a second voltage V2 is applied to the electrochemical cell 50, and the CO2 adsorbed in the electrochemical cell 50 is desorbed. The CO2 desorbed in the first recovery device 11 is supplied to the CO2 utilization device 15 by vacuum suction by the second pressure reducing device 14.

[0076] In the gas removal mode, the second recovery device 12 is vacuum-suctioned by the first pressure reducing device 13, and the off-gas remaining inside is discharged from the first recovery device 11. The off-gas sucked by the first pressure reducing device 13 is released into the atmosphere. When the gas removal mode ends, the inside of the second recovery device 12 is at a high vacuum, and no off-gas remains.

[0077] The second recovery device 12 is depressurized in advance from normal pressure to medium vacuum in the pressure equalization mode of the third stage (3) before performing the gas removal mode in the fourth stage (4). Therefore, in the gas removal mode of the fourth stage (4), it is only necessary to depressurize the second recovery device 12 from medium vacuum to high vacuum, and the power required for depressurization of the first depressurization device 13 can be reduced compared to the case of depressurizing from normal pressure to high vacuum.

[0078] In the fifth stage (5) shown in FIG. 8, the first recovery device 11 operates in adsorption mode and the second recovery device 12 operates in desorption mode.

[0079] In the fifth stage (5), the blower 10 and the second pressure reducing device 14 are operating, and the first pressure reducing device 13 is not operating. The first flow path switching valve 30 connects the blower 10 and the first recovery device 11 via the supply pipes 100 and 101. The second flow path switching valve 31 connects the first recovery device 11 to the outside via the off-gas pipes 103 and 105. The fourth flow path switching valve 33 connects the second recovery device 12 and the second pressure reducing device 14 via the second recovery pipe 107. The on-off valves 20, 22, 25, and 27 are in the open state, and the on-off valves 21, 23, 24, 26, and 28 are in the closed state.

[0080] In the adsorption mode, the first recovery device 11 is supplied with a CO2-containing gas and adsorbs CO2. A first voltage V1 is applied to the electrochemical cell 50 of the first recovery device 11, and CO2 contained in the CO2-containing gas introduced into the first recovery device 11 is adsorbed by the electrochemical cell 50. The off-gas from which CO2 has been removed in the first recovery device 11 is exhausted from the first recovery device 11 and released into the atmosphere via the off-gas pipes 103 and 105. At the end of the adsorption mode, the inside of the first recovery device 11 is at normal pressure, and off-gas remains.

[0081] In the second capture device 12 in the desorption mode, a second voltage V2 is applied to the electrochemical cell 50, and the CO2 adsorbed in the electrochemical cell 50 is desorbed. The CO2 desorbed in the second capture device 12 is supplied to the CO2 utilization device 15 by vacuum suction by the second pressure reducing device 14.

[0082] As shown in FIG. 3, the modes of the recovery devices 11, 12 are switched in sequence from the sixth stage (6) onwards. In the sixth stage (6), the first recovery device 11 operates in the gas removal mode, and the second recovery device 12 operates in the adsorption mode. In the seventh stage (7), the first recovery device 11 and the second recovery device 12 operate in the pressure equalization mode. In the eighth stage (8), the first recovery device 11 operates in the desorption mode, and the second recovery device 12 operates in the gas removal mode. In the ninth stage (9), the first recovery device 11 operates in the adsorption mode, and the second recovery device 12 operates in the desorption mode.

[0083] In the pressure equalization mode of the seventh stage (7), similarly to the third stage (3), the pressure in the first recovery device 11 increases and the pressure in the second recovery device 12 decreases, and the two recovery devices 11, 12 are equalized. At the end of the pressure equalization mode, the insides of the first recovery device 11 and the second recovery device 12 are at a medium vacuum. And, the second recovery device 12 is depressurized from normal pressure to a medium vacuum in advance in the pressure equalization mode of the seventh stage (7) before the gas removal mode is performed in the eighth stage (8). Therefore, in the gas removal mode of the eighth stage (8), it is only necessary to depressurize the second recovery device 12 from a medium vacuum to a high vacuum, and the power of the first depressurization device 13 required for depressurization can be reduced.

[0084] According to the present embodiment described above, in the carbon dioxide capture system including the multiple capture devices 11 and 12, a pressure equalization mode is provided in which the second capture device 12 after the adsorption mode and before the gas removal mode is started is connected to the first capture device 11 after the gas removal mode and before the adsorption mode is started to equalize the pressure. In the pressure equalization mode, the first capture device 11 at high vacuum can be used to reduce the pressure of the second capture device 12 at normal pressure to a medium vacuum, which is an intermediate pressure between high vacuum and normal pressure. As a result, the second capture device 12 is depressurized from normal pressure to a medium vacuum in advance of the gas removal mode after the pressure equalization mode. Therefore, in the gas removal mode after the pressure equalization mode, the second capture device 12 only needs to reduce the pressure from a medium vacuum to a high vacuum, and compared to the case where the gas removal mode is executed following the adsorption mode, the power of the first pressure reduction device 13 can be reduced, and the system efficiency can be improved.

[0085] In addition, in this embodiment, after the first recovery device 11 reaches a high vacuum in the gas removal mode, the pressure equalization mode is performed immediately after the gas removal mode without going through any other mode. Therefore, the first recovery device 11 can transition to the pressure equalization mode while maintaining as high a vacuum as possible, and when the second recovery device 12 is depressurized to a medium vacuum in the pressure equalization mode, the pressure can be as low as possible. As a result, in the second recovery device 12, the power of the first depressurization device 13 required for depressurization in the gas removal mode after the pressure equalization mode can be further reduced.

[0086] In addition, this embodiment uses capture devices 11 and 12 that electrochemically adsorb CO2 using an electrochemical cell 50. This allows CO2 to be adsorbed and desorbed with lower energy than when, for example, a pressure-type capture device is used.

[0087] In addition, the electrochemical capture devices 11 and 12 are advantageous in capturing CO2 from a CO2-containing gas having a low CO2 concentration, as compared with, for example, a pressure-type capture device. For this reason, in this embodiment, a CO2-containing gas having a low CO2 concentration is supplied to the capture devices 11 and 12, and the CO2 concentration of the off-gas after CO2 adsorption in the capture devices 11 and 12 is set to less than 1000 ppm, preferably less than 500 ppm.

[0088] In this embodiment, since the electrochemical recovery devices 11 and 12 are used, the pressure is not increased above atmospheric pressure in the adsorption mode, and the recovery devices 11 and 12 are at normal pressure when the adsorption mode ends. Therefore, the pressure in the recovery devices 11 and 12 becomes lower than normal pressure when the pressure equalization mode ends.

[0089] Second embodiment Next, a second embodiment of the present invention will be described below, focusing only on the differences from the first embodiment.

[0090] As shown in FIG. 9, in the second embodiment, the control pattern of the recovery devices 11, 12 is different from that in the first embodiment, and the execution order of the modes is different.

[0091] 9, in a first stage (1), the first recovery device 11 operates in an adsorption mode and the second recovery device 12 is deactivated. In a second stage (2), the first recovery device 11 operates in a gas removal mode and the second recovery device 12 operates in an adsorption mode.

[0092] In a third stage (3), the first recovery device 11 operates in a desorption mode and the second recovery device 12 operates in an adsorption mode. In a fourth stage (4), the first recovery device 11 and the second recovery device 12 operate in a pressure equalization mode. In a fifth stage (5), the first recovery device 11 operates in an adsorption mode and the second recovery device 12 operates in a gas removal mode.

[0093] In the pressure equalization mode of the fourth stage (4), the pressure in the first recovery device 11, which was at high vacuum, increases, and the pressure in the second recovery device 12, which was at normal pressure, decreases, resulting in a medium vacuum in the first recovery device 11 and the second recovery device 12. In the fifth stage (5), when the gas removal mode is performed in the second recovery device 12, the second recovery device 12 has been depressurized in advance from normal pressure to a medium vacuum in the pressure equalization mode, so that the power of the first depressurization device 13 required to depressurize the second recovery device 12 in the gas removal mode can be reduced.

[0094] Subsequently, in a sixth stage (6), the first recovery device 11 operates in adsorption mode and the second recovery device 12 operates in desorption mode. In a seventh stage (7), the first recovery device 11 and the second recovery device 12 operate in pressure equalization mode.

[0095] In the pressure equalization mode of the seventh stage (7), the pressure in the first recovery device 11, which was at normal pressure, drops, and the pressure in the second recovery device 12, which was at high vacuum, rises. In the eighth stage (8), when the gas removal mode is performed in the first recovery device 11, the first recovery device 11 has been previously depressurized from normal pressure to a medium vacuum in the pressure equalization mode, so that the power of the first depressurization device 13 required to depressurize the first recovery device 11 in the gas removal mode can be reduced.

[0096] In the second embodiment described above, similarly to the first embodiment, a pressure equalization mode is provided for equalizing the pressure in the recovery devices 11, 12, which are at normal pressure after the adsorption mode is completed, and the recovery devices 11, 12, which are at high vacuum after the gas removal mode is completed. This allows the power of the first pressure reduction device 13 required for depressurizing the recovery devices 11, 12 to be reduced in the gas removal mode after the pressure equalization mode.

[0097] Furthermore, in the second embodiment, when the gas removal mode is executed after the pressure equalization mode in both the first recovery device 11 and the second recovery device 12, the power reduction effect of the first pressure reducing device 13 can be obtained.

[0098] In addition, in the second embodiment, the desorption mode is performed after the gas removal mode and before the pressure equalization mode in the capture devices 11 and 12. Therefore, the desorption mode can be performed in a state where the inside of the capture devices 11 and 12 is in high vacuum and there is as little off-gas as possible, and the purity of the CO2 captured in the desorption mode can be increased.

[0099] (Other embodiments) The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. Furthermore, the means disclosed in each of the above-described embodiments may be appropriately combined within the scope of feasibility.

[0100] For example, in each of the above embodiments, an example has been described in which the carbon dioxide capture system 1 is provided with two capture devices 11, 12, but three or more capture devices may be provided in the carbon dioxide capture system 1. When three or more capture devices are provided, in the pressure equalization mode, all of the capture devices may be connected to perform pressure equalization, or only some of the capture devices may be connected to perform pressure equalization.

[0101] In addition, in each of the above embodiments, an example in which the electrochemical capture devices 11 and 12 are provided in the carbon dioxide capture system 1 has been described, but a pressure-type capture device may be provided downstream of the gas flow of the electrochemical capture devices 11 and 12. The pressure-type capture device may be provided downstream of the gas flow of the capture pipes 106 and 107 through which the CO2 captured by the electrochemical capture devices 11 and 12 flows. Compared to the electrochemical capture devices 11 and 12, the pressure-type capture device can efficiently capture CO2 from a CO2-containing gas with a high CO2 concentration. For this reason, by recovering CO2 from a low-concentration CO2-containing gas with the electrochemical capture devices 11 and 12 and supplying the gas with an increased CO2 concentration to the pressure-type capture device, two-stage CO2 capture can be performed, and the purity of CO2 can be efficiently increased. [Explanation of symbols]

[0102] 11 First recovery device 12 Second recovery device 13 First pressure reducing device 14 Second pressure reducing device 50 Electrochemical Cells

Claims

1. CO ２ CO containing ２ CO from contained gas ２ A carbon dioxide capture system for capturing CO ２ A plurality of recovery devices (11, 12) capable of switching between adsorption and desorption of a pressure reducing device (13) for reducing the pressure inside the recovery device by vacuum suction; Equipped with The recovery device is configured to recover the CO ２ CO contained in the gas ２ and an adsorption mode for adsorbing CO adsorbed in the adsorption mode. ２ a desorption mode in which the inside of the recovery device is desorbed, a gas removal mode in which the inside of the recovery device is depressurized by vacuum suction using the decompression device to remove gas from the inside of the recovery device, and a pressure equalization mode in which the recovery device is connected to another recovery device so that gas present therein can be moved, In the pressure equalization mode, the recovery device at normal pressure is connected to the recovery device decompressed by the decompression device, A carbon dioxide capture system in which the capture device connected in the pressure equalization mode is at a pressure lower than normal pressure when the pressure equalization mode ends.

2. 2. The carbon dioxide capture system according to claim 1, wherein in the pressure equalization mode, the capture device after the adsorption mode ends and before the gas removal mode starts is connected to the capture device after the gas removal mode ends and before the adsorption mode starts.

3. The recovery device generates CO by electrochemical reaction. ２ The carbon dioxide capture system of claim 1, further comprising an electrochemical cell (50) for switching between adsorption and desorption of

4. In the adsorption mode, the recovery device ２ After adsorption, the off-gas is CO ２ 2. The carbon dioxide capture system of claim 1, wherein the concentration is less than 1000 ppm.

5. The off-gas is CO ２ 5. The carbon dioxide capture system of claim 4, wherein the concentration is less than 500 ppm.

6. 6. The carbon dioxide capture system according to claim 4 or 5, wherein in the pressure equalization mode, the off-gas is transferred from the capture device after the adsorption mode ends and before the gas removal mode starts to the capture device after the gas removal mode ends and before the adsorption mode starts.

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