Carbon dioxide collection system

Abstract

To provide a carbon dioxide collection system with which energy costs decrease and in which an adsorbent hardly deteriorates.SOLUTION: A carbon dioxide collection system 1 includes: an adsorption apparatus 2 for causing an adsorbent to adsorb carbon dioxide contained in air; an air supply path 3 for supplying air to the adsorption apparatus 2; and a recovery path 6 for recovering the carbon dioxide adsorbed in the adsorbent A of the adsorption apparatus 2. The air supply path 3 comprises a heat exchanger 31 capable of circulating a cooling medium C, and thus the air is cooled by the heat exchanger 31.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide capture system that captures carbon dioxide contained in air. [Background technology]

[0002] Global warming caused by carbon dioxide released during the combustion of fossil fuels has become a problem, and there is an urgent need to curb the release of carbon dioxide into the atmosphere as a result of fossil fuel combustion. On the other hand, there are applications where the use of fossil fuels is technically or economically unavoidable, and so there are growing expectations for technology called Direct Air Capture, which directly captures carbon dioxide from the atmosphere.

[0003] Carbon dioxide can be converted into hydrocarbons such as methane by reacting it with hydrogen. If the hydrogen is produced using electricity derived from renewable energy sources such as solar or wind power, and the carbon dioxide is collected from the atmosphere, the resulting hydrocarbons, even when burned, will not increase the atmospheric carbon dioxide concentration throughout the entire process from fuel production to use, making them carbon-neutral hydrocarbons.

[0004] In conventional carbon dioxide capture systems, the following steps are generally repeated in sequence: an adsorption step in which carbon dioxide contained in the air is adsorbed onto an adsorbent in an adsorption device, a depressurization step in which the air pressure in the adsorption device is reduced to below atmospheric pressure, a desorption step in which the adsorbent is heated to desorb carbon dioxide, and a cooling step in which the adsorbent is cooled.This carbon dioxide capture system adsorbs carbon dioxide onto the adsorbent in the adsorption step, and then performs a depressurization step and a desorption step in which the adsorbent with adsorbed carbon dioxide is heated under reduced pressure to desorb the carbon dioxide from the adsorbent, thereby making it possible to capture high-concentration carbon dioxide.

[0005] As such a conventional carbon dioxide recovery system, for example, as disclosed in Patent Document 1 below, a system equipped with an adsorption device having a carbon dioxide adsorption plate on which an amine compound is supported is known. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-13169 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional carbon dioxide capture systems, a large amount of energy is required to heat the adsorbent in the desorption step, leaving room for improvement in terms of reducing energy costs. Furthermore, in the desorption step, adsorbents, particularly those carrying amine compounds, have the problem of being prone to oxidation and rapid deterioration when exposed to air at high temperatures.

[0008] An object of the present invention is to provide a carbon dioxide recovery system that reduces energy costs and that does not easily deteriorate an adsorbent. [Means for solving the problem]

[0009] The carbon dioxide capture system according to the present invention is configured to include an adsorption device that adsorbs carbon dioxide contained in air onto an adsorbent, an air supply path that supplies air to the adsorption device, and a capture path that captures the carbon dioxide adsorbed by the adsorbent of the adsorption device, The air supply path is provided with a heat exchanger through which a cooling medium can flow, and the air is cooled by the heat exchanger.

[0010] According to this configuration, the air supplied to the adsorption device is cooled by the heat exchanger, and carbon dioxide is adsorbed onto the adsorbent in a thermodynamically favorable environment, making it possible to achieve a temperature swing with air at room temperature, for example. This reduces the energy required for heating in the desorption process and makes it easier to suppress deterioration of the adsorbent.

[0011] In the carbon dioxide recovery system according to the present invention, it is preferable that the cooling medium is liquefied natural gas or a refrigerant that has undergone heat exchange with liquefied natural gas.

[0012] With this configuration, liquefied natural gas is used as the cooling medium, making it possible to adsorb carbon dioxide in a sub-zero environment where adsorption is thermodynamically favorable, and enabling a more reliable temperature swing with room temperature air.

[0013] In the carbon dioxide recovery system according to the present invention, it is preferable that the air supply path has a first path that communicates with the adsorption device and a second path that does not communicate with the adsorption device, is switchable between the first path and the second path, and is configured so that in the case of the first path, the cooling medium is circulated through the heat exchanger, and in the case of the second path, the cooling medium is not circulated through the heat exchanger.

[0014] According to this configuration, even if frost forms inside the heat exchanger due to the flow of cooling medium, causing a pressure loss, the air supply path can be switched from the first path to the second path, allowing room temperature air to flow through the second path and be discharged outside the adsorption device, thereby defrosting the heat exchanger.

[0015] In the carbon dioxide recovery system according to the present invention, it is preferable that the heat exchanger is further capable of circulating a heating medium, is configured to be switchable between cooling medium circulation and heating medium circulation, and is configured to circulate the heating medium in the case of the second path.

[0016] According to this configuration, in the case of the second path, the heating medium is circulated in the heat exchanger, so that the heat exchanger can be defrosted more reliably.

[0017] In the carbon dioxide capture system according to the present invention, it is preferable to provide two air supply paths having the first path and the second path.

[0018] According to this configuration, since two air supply paths are provided, the adsorption process and defrosting can be performed by alternately switching between the two air supply paths, such as switching one air supply path to the first path to perform the adsorption process and switching the other air supply path to the second path to defrost the heat exchanger. Therefore, according to this embodiment, it is not necessary to interrupt the adsorption process for defrosting, and the adsorption process can be performed continuously.

[0019] In the carbon dioxide recovery system according to the present invention, it is preferable that the recovery path is equipped with a condenser, and that a heating medium generated in the condenser is circulated to the heat exchanger.

[0020] According to this configuration, by circulating the heating medium generated in the condenser through the heat exchanger, it is possible to circulate the heating medium more efficiently and without waste, thereby reducing operating costs.

[0021] In the carbon dioxide recovery system according to the present invention, it is preferable that the adsorbent is made of a porous material containing an amine compound.

[0022] According to this configuration, the adsorbent is made of a porous material containing an amine compound, so that carbon dioxide can be adsorbed more efficiently. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram showing a configuration of a carbon dioxide capture system (first embodiment). [Figure 2] FIG. 1 is a diagram showing the configuration of a carbon dioxide capture system (second embodiment). [Figure 3] FIG. 10 is a diagram showing the configuration of a carbon dioxide capture system (third embodiment). [Figure 4] FIG. 10 is a diagram showing the configuration of a carbon dioxide capture system (fourth embodiment). [Figure 5] FIG. 10 is a diagram showing the configuration of a carbon dioxide capture system (fifth embodiment). DETAILED DESCRIPTION OF THE INVENTION

[0024] First Embodiment Hereinafter, an embodiment of the present invention will be described. (Carbon dioxide capture system) As shown in FIG. 1, the carbon dioxide capture system 1 includes an adsorption device 2 that adsorbs carbon dioxide contained in the air onto adsorbent material A, an air supply path 3 that supplies air to the adsorption device 2, an air discharge path 4 that discharges air from the adsorption device 2, a capture path 6 that captures the carbon dioxide adsorbed by the adsorbent material A of the adsorption device 2, and a heating / cooling means (not shown) that heats or cools the adsorbent material A.

[0025] In this embodiment, the air supply path 3 includes a blower 30 (such as a blower), a heat exchanger 31 through which the cooling medium C can flow, and a first switching valve V1. The air discharge path 4 includes a second switching valve V2. The recovery path 6 includes a third switching valve V3, a condenser 60, and a pressure reducing device 61 (such as a vacuum pump).

[0026] The cooling medium C used in the heat exchanger 31 may be, for example, liquefied natural gas (for example, -160°C) or a refrigerant that has been heat exchanged with liquefied natural gas. The air introduced into the air supply path 3 is cooled by the cooling medium C in the heat exchanger 31 to, for example, below freezing point.

[0027] Examples of the heating means include an electric heater and a heat exchanger. The heating means is preferably configured to generate a heating medium by utilizing waste heat, geothermal heat, or solar heat. Examples of the cooling means include a cooling water circulation device. Examples of devices that integrally include a heating means and a cooling means include a heat pump. Examples of the heating medium include air at a predetermined temperature, hot water, saturated steam, and superheated steam. Examples of the cooling medium include air at room temperature, water at room temperature, and cold water.

[0028] The adsorption device 2 contains an adsorbent A. The adsorbent A is heated or cooled by a heating / cooling means (not shown).

[0029] The adsorbent A is a component capable of adsorbing and desorbing carbon dioxide contained in air, and is preferably composed of a porous material containing an amine compound. By combining the amine compound with an appropriate carrier, carbon dioxide can be desorbed at relatively low temperatures. Examples of applicable amine compounds include tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and polyethyleneimine (PEI). Examples of porous materials include metal-organic frameworks (MOFs), zeolites, activated carbon, mesoporous silica, silica, and alumina. In particular, by using MIL-101(Cr), the adsorbent can be used at temperatures as low as -20°C.

[0030] (Carbon dioxide capture method) Next, a carbon dioxide recovery method using the carbon dioxide recovery system 1 will be described.

[0031] The carbon dioxide recovery method includes an adsorption process in which carbon dioxide contained in the air is adsorbed onto adsorbent A in adsorption device 2, a depressurization process in which the air pressure in adsorption device 2 is reduced to below atmospheric pressure, a desorption process in which adsorbent A is heated to desorb carbon dioxide, and a cooling process in which adsorbent A is cooled, and these processes are carried out repeatedly in sequence.

[0032] In the adsorption step, the first switching valve V1 and the second switching valve V2 are opened, and the third switching valve V3 is closed. At this time, the temperature inside the adsorption device 2 is approximately room temperature, and the air pressure is approximately atmospheric pressure. Air introduced into the air supply path 3 by operating the blower 30 is cooled, for example, to below freezing point by the cooling medium of the heat exchanger 31. The cooled air flows into the adsorption device 2, and at least a portion of the carbon dioxide is adsorbed by the adsorbent A. The air with a reduced carbon dioxide concentration is discharged from the adsorption device 2 via the air discharge path 4.

[0033] In the depressurization step, the first switching valve V1 and the second switching valve V2 are closed, and the third switching valve V3 is opened. Then, the depressurization device 61 is operated to remove air from the adsorption device 2. At this time, the temperature inside the adsorption device 2 is below room temperature (for example, below freezing), but the air pressure is below atmospheric pressure. The processing time of the depressurization step and the output of the depressurization device 61 may be set appropriately depending on the purity required for the carbon dioxide obtained in the subsequent desorption step. Also, in the depressurization step, the condenser 60 may be operated as needed to liquefy water vapor contained in the sucked air and discharge it as drain water.

[0034] In the desorption step, following the depressurization step, the first selector valve V1 and the second selector valve V2 are closed, and the third selector valve V3 is opened. Then, with the depressurization device 61 operating, the adsorbent A is heated by the heating / cooling means. This allows high-concentration carbon dioxide to be recovered via the recovery path 6. The recovered carbon dioxide is, for example, filled into a cylinder or the like while being pressurized by a compressor as needed. Note that, also in the desorption step, the condenser 60 may be operated as needed to liquefy water vapor contained in the sucked air and discharge the liquefied water as drain water.

[0035] In the cooling step, the first selector valve V1, the second selector valve V2, and the third selector valve V3 are all closed. Then, the adsorbent A is cooled by the heating / cooling means. As a result, the adsorbent A is cooled under conditions where the oxygen partial pressure is low. At this time, the pressure inside the adsorption device 2 is lower than atmospheric pressure.

[0036] Second Embodiment The second embodiment of the present invention will be described below with reference to the drawings. Here, only the configurations that differ from the first embodiment described above will be described, and the same symbols will be used for the configurations that are similar to those in the first embodiment, and the description will be omitted.

[0037] (Carbon dioxide capture system) 2, the air supply path 3 in this embodiment has a first path 32 that communicates with the adsorption device 2 and a second path 33 that does not communicate with the adsorption device 2, and a fourth selector valve V4 is provided in the second path 33. The first path 32 or the second path 33 can be switched by switching the first selector valve V1 and the fourth selector valve V4, respectively. That is, two paths are provided for circulating air. When the first selector valve V1 is opened and the fourth selector valve V4 is closed, switching to the first path 32 allows the cooling medium to circulate through the heat exchanger 31. When the first selector valve V1 is closed and the fourth selector valve V4 is opened, switching to the second path 33 stops the flow of the cooling medium through the heat exchanger 31.

[0038] (Carbon dioxide capture method) In the adsorption process, the first and second switching valves V1 and V2 are opened, and the third and fourth switching valves V3 and V4 are closed. At this time, the air supply path 3 is switched so as to communicate with the first path 32 by switching the first and fourth switching valves V1 and V4. The temperature inside the adsorption device 2 is approximately room temperature, and the air pressure is approximately atmospheric pressure. Air introduced into the air supply path 3 by operating the blower 30 is cooled to, for example, below freezing point by the cooling medium of the heat exchanger 31. The cooled air flows into the adsorption device 2, and at least a portion of the carbon dioxide is adsorbed by the adsorbent A. The air with a reduced carbon dioxide concentration is discharged from the adsorption device 2 via the air discharge path 4.

[0039] If the adsorption process is performed for a while, the flow of the cooling medium may cause frost to form inside the heat exchanger 31, increasing pressure loss. To prevent this, after the adsorption process is performed in the first path 32 for a predetermined time, the first switching valve V1 and the fourth switching valve V4 are switched to switch the air supply path 3 to the second path 33, and the flow of the cooling medium in the heat exchanger 31 is stopped. Room temperature air is circulated through the second path 33 and discharged outside the adsorption device 2, thereby defrosting the heat exchanger 31.

[0040] Third Embodiment Hereinafter, the third embodiment of the present invention will be described with reference to the drawings. Here, only the configurations that are different from the first and second embodiments described above will be described, and the same reference numerals will be used to designate the same configurations as the first and second embodiments, and the description thereof will be omitted.

[0041] (Carbon dioxide capture system) As shown in FIG. 3, the carbon dioxide capture system 1 in this embodiment is configured to include another air supply path 3 having a first path 32 and a second path 33 in addition to the configuration in the second embodiment.

[0042] (Carbon dioxide capture method) In the carbon dioxide capture method of the present embodiment, the adsorption process and the defrosting process are performed in the same manner as in the second embodiment. However, in the present embodiment, two air supply paths 3 are provided, and therefore the adsorption process and defrosting can be performed by alternately switching between the two air supply paths 3, such as switching one air supply path 3 to the first path 32 to perform the adsorption process and switching the other air supply path 3 to the second path 33 to defrost the heat exchanger 31. Therefore, according to the present embodiment, unlike the second embodiment, there is no need to interrupt the adsorption process for defrosting, and the adsorption process can be performed continuously.

[0043] Fourth Embodiment The fourth embodiment of the present invention will be described below with reference to the drawings. Here, only the configurations that differ from the first to third embodiments described above will be described, and the same symbols will be used for the configurations that are similar to the first to third embodiments, and the description will be omitted.

[0044] (Carbon dioxide capture system) As shown in Figure 4, in addition to the configuration of the second embodiment, the carbon dioxide recovery system 1 in this embodiment is configured so that the heat exchanger 31 can further circulate a heating medium and can be switched between circulating a cooling medium and circulating a heating medium, and is configured to circulate the heating medium when the air supply path 3 is switched to the second path 33.

[0045] As the heating medium supply device, for example, a device such as a heater may be separately prepared, but as shown in Fig. 4, a configuration may also be used in which hot water produced in a condenser 60 is used as the heating medium. In this configuration, the condenser 60 is connected to the heat exchanger 31 via a pipe P2, and the hot water produced in the condenser 60 is circulated as the heating medium H. Furthermore, although not shown, two carbon dioxide capture systems 1 may be prepared, and the condenser 60 in one carbon dioxide capture system 1 may be connected to the heat exchanger 31 in the other carbon dioxide capture system 1 via a pipe, so that the hot water produced in the condenser 60 can be circulated as the heating medium H.

[0046] (Carbon dioxide capture method) In the adsorption process, the first and second switching valves V1 and V2 are opened, and the third and fourth switching valves V3 and V4 are closed. At this time, the air supply path 3 is switched so as to communicate with the first path 32 by switching the first and fourth switching valves V1 and V4. The temperature inside the adsorption device 2 is approximately room temperature, and the air pressure is approximately atmospheric pressure. Air introduced into the air supply path 3 by operating the blower 30 is cooled to, for example, below freezing point by the cooling medium of the heat exchanger 31. The cooled air flows into the adsorption device 2, and at least a portion of the carbon dioxide is adsorbed by the adsorbent A. The air with a reduced carbon dioxide concentration is discharged from the adsorption device 2 via the air discharge path 4.

[0047] If the adsorption process is performed for a while, the flow of the cooling medium may cause frost to form in the heat exchanger 31, increasing pressure loss. To prevent this, after the adsorption process is performed in the first path 32 for a predetermined time, the first selector valve V1 and the fourth selector valve V4 are switched to switch the air supply path 3 to the second path 33, the flow of the cooling medium in the heat exchanger 31 is stopped, and the heating medium H, such as hot water produced in the condenser 60, is circulated through the heat exchanger 31. In this way, room-temperature air is circulated through the second path 33 and discharged to the outside of the adsorption device 2, and the heating medium H is circulated in the heat exchanger 31 through the pipe P2, thereby more effectively defrosting the heat exchanger 31.

[0048] Although not shown, when two carbon dioxide capture systems 1 are used, if the desorption process is performed in one carbon dioxide capture system 1 and the adsorption process is performed in the other carbon dioxide capture system 1, the hot water from the condenser 60 in one carbon dioxide capture system 1 can be circulated to the heat exchanger 31 in the other carbon dioxide capture system 1 to defrost the heat exchanger 31 in the other carbon dioxide capture system 1.

[0049] Fifth Embodiment (Carbon dioxide capture system) Hereinafter, the fifth embodiment of the present invention will be described with reference to the drawings. Here, only the configurations that differ from the first to fourth embodiments described above will be described, and the same symbols will be used for the configurations that are similar to the first to fourth embodiments, and the description will be omitted.

[0050] As shown in Fig. 5, the carbon dioxide capture system 1 in this embodiment has the same configuration as the fourth embodiment, but the capture paths are configured to include a main capture path 6A and a sub-recovery path 6B. The main recovery path 6A includes a third switching valve V3, a fifth switching valve V5, a second heat exchanger 62, and a pressure reducing device 61 (such as a vacuum pump). The sub-recovery path 6B includes a sixth switching valve V6 and a condenser 60. The second heat exchanger 62 is configured to be able to reuse the cooling medium C after it has been used in the heat exchanger 31 of another carbon dioxide capture system 1.

[0051] (Carbon dioxide capture method) In the desorption step, following the depressurization step, the first and second switching valves V1 and V2 are closed, and the third and fifth switching valves V3 and V5 of the main recovery path 6A are opened. Then, with the depressurization device 61 in operation, the heating / cooling means is operated to supply a heating medium to the adsorption device 2 via the pipe P1 to heat the adsorbent A. The heating temperature is a temperature suitable for desorption of carbon dioxide, preferably 60°C to 100°C. This allows high-concentration carbon dioxide to be recovered via the recovery path 6. The recovered carbon dioxide is filled into a cylinder or the like, for example, while being pressurized by a compressor as necessary.

[0052] At this time, the water vapor contained in the sucked air is cooled in the second heat exchanger 62 by reusing the cooling medium C that has been used in the heat exchanger 31 in the adsorption step of another carbon dioxide capture system 1. If the cooling capacity of the second heat exchanger 62 alone is insufficient, the sixth switching valve V6 is opened and the condenser 60 is operated to liquefy the water vapor contained in the sucked air. Then, as in the fourth embodiment, the heating medium H, such as hot water, produced in the condenser 60 is circulated via the pipe P2, thereby more effectively defrosting the heat exchanger 31.

[0053] Other Embodiments In each of the above-described embodiments, the cooling medium supplied to the heat exchanger 31 may be configured to cool the water vapor, for example, by being supplied to the condenser 60 in the recovery path 6, as long as it still has a cooling effect thereafter.

[0054] In the above-described embodiment, the heating medium H passing through the pipe P2 is preferably circulated if it is hot water, but if air is used, it may be circulated.

[0055] Furthermore, the configurations disclosed in the above embodiments can be applied in combination with configurations disclosed in other embodiments as long as no contradictions arise, and the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0056] The present invention can be suitably used in the technical field relating to an apparatus and method for recovering low-concentration carbon dioxide contained in the atmosphere to obtain high-purity carbon dioxide, for example. [Explanation of symbols]

[0057] 1. Carbon dioxide capture system 2 Adsorption device 3 Air supply path 30 Blower 31 Heat exchanger 32 First Route 33 Secondary Route 4 Air exhaust route 6. Recovery route 6A Main Recovery Route 6B Secondary Recovery Route 60 Condenser 61 Pressure reducing device 62 Second heat exchanger V1 First switching valve V2 Second switching valve V3 Third switching valve V4 Fourth switching valve V5 Fifth switching valve V6 Sixth switching valve P2 piping A. Adsorbent C Cooling medium H Heating medium

Claims

1. A carbon dioxide capture system including an adsorption device that adsorbs carbon dioxide contained in air onto an adsorbent, an air supply path that supplies air to the adsorption device, and a capture path that recovers the carbon dioxide adsorbed by the adsorbent of the adsorption device, A carbon dioxide recovery system, wherein the air supply path is provided with a heat exchanger through which a cooling medium can flow, and the air is cooled by the heat exchanger.

2. 2. The carbon dioxide recovery system according to claim 1, wherein the cooling medium is liquefied natural gas or a refrigerant heat-exchanged with liquefied natural gas.

3. 3. The carbon dioxide recovery system according to claim 1, wherein the air supply path has a first path that is connected to the adsorption device and a second path that is not connected to the adsorption device, and is switchable between the first path and the second path, and is configured so that in the case of the first path, the cooling medium is circulated through the heat exchanger, and in the case of the second path, the cooling medium is not circulated through the heat exchanger.

4. The carbon dioxide capture system according to claim 3 , comprising two air supply paths, each of which includes the first path and the second path.

5. The carbon dioxide recovery system described in claim 3, wherein the heat exchanger is further capable of circulating a heating medium, is configured to be switchable between cooling medium circulation and heating medium circulation, and is configured to circulate the heating medium in the case of the second path.

6. The carbon dioxide recovery system according to claim 5 , wherein the recovery path includes a condenser, and the heating medium generated in the condenser is circulated to the heat exchanger.

7. 3. The carbon dioxide recovery system according to claim 1, wherein the adsorbent is made of a porous material containing an amine compound.

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