Carbon dioxide capture method

Abstract

To provide a carbon dioxide recovery method capable of highly efficiently recovering high concentration carbon dioxide from a gas mixture with a low carbon dioxide concentration.SOLUTION: Provided is a carbon dioxide recovery method having a carbon dioxide recovery cycle including: an adsorbing step in which two or more carbon dioxide adsorbing towers, in which any one or more of A-type, X-type and Y-type zeolites are filled as an adsorbent (s) of carbon dioxide, are disposed, and a gas mixture is introduced to one of the carbon dioxide adsorbing towers by a pressure equal to or greater than the atmospheric pressure and equal to or lower than 0.2 Mpa to adsorb carbon dioxide in the gas mixture; a non-adsorbed gas delivery step for delivering non-adsorbed gas; a de-pressure step for discharging residual non-adsorbed gas; a residual non-adsorbed gas purge step for introducing the concentrated carbon dioxide gas to push out the residual non-adsorbed gas; and a desorption step for desorbing the carbon dioxide in the adsorbent(s) by suction using a pressure lower than the atmospheric pressure to recover the concentrated carbon dioxide. The carbon dioxide gas in the residual non-adsorbed gas purge step is obtained by the desorption step in another carbon dioxide adsorbing tower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering carbon dioxide from a mixed gas, and more particularly to a method for recovering carbon dioxide by concentrating carbon dioxide from a mixed gas containing carbon dioxide at a low concentration. [Background technology]

[0002] In recent years, efforts to capture carbon dioxide, which is considered to be the main cause of global warming, from industrial exhaust gases and the atmosphere, and to reuse or store it have been actively promoted in addition to reducing emissions. Carbon dioxide capture is carried out, for example, by pressure swing adsorption (PSA).

[0003] In a carbon dioxide recovery method using the PSA method, a mixed gas containing carbon dioxide is introduced into an adsorption tower containing an adsorbent, the carbon dioxide is adsorbed onto the adsorbent, non-adsorbed gas is discharged from the adsorption tower, and then the pressure inside the adsorption tower is reduced to below atmospheric pressure to desorb the carbon dioxide from the adsorbent, thereby concentrating and recovering the carbon dioxide in the mixed gas (see, for example, Patent Document 1). This carbon dioxide recovery method treats mixed gases with high carbon dioxide concentrations, such as blast furnace gas, and adsorbs carbon dioxide at a medium pressure of about 0.1 to 0.4 MPa, and separates and recovers it by vacuum regeneration. Therefore, the higher the carbon dioxide concentration in the mixed gas and the greater the pressure difference between adsorption and desorption, the easier it is to concentrate and purify the carbon dioxide.

[0004] Incidentally, combustion exhaust gases emitted from boilers, power generators, and the like are mixed gases with a low carbon dioxide concentration (10 vol% or less) compared to blast furnace gas. Mixed gases containing low concentrations of carbon dioxide have a lower carbon dioxide recovery efficiency than mixed gases such as blast furnace gas containing high concentrations of carbon dioxide. Furthermore, when recovering carbon dioxide from such mixed gases, the above-mentioned carbon dioxide recovery method requires a higher-than-normal adsorption pressure to adsorb the low-concentration carbon dioxide from the mixed gas onto an adsorbent. However, increasing the adsorption pressure requires the use of a compressor or other device, which inevitably results in excessive power consumption and lower energy efficiency and work efficiency required for recovery compared to mixed gases with high concentrations of carbon dioxide. Therefore, mixed gases containing low concentrations of carbon dioxide do not achieve a carbon dioxide recovery efficiency commensurate with the treatment efficiency, and are generally discarded as is. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5647388 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above points, and provides a carbon dioxide recovery method capable of recovering carbon dioxide at a high concentration and with high efficiency from a mixed gas having a low carbon dioxide concentration. [Means for solving the problem]

[0007] That is, the first invention is a gas containing carbon dioxide at 10 vol% or less. Combustion exhaust gas, etc.A carbon dioxide recovery method for concentrating and recovering the carbon dioxide from a mixed gas, comprising: a plurality of carbon dioxide adsorption towers filled with one or more of A-type zeolite, X-type zeolite, and Y-type zeolite as an adsorbent for the carbon dioxide; an adsorption step of introducing the mixed gas into one of the carbon dioxide adsorption towers at a pressure of not less than atmospheric pressure and not more than 0.2 MPa to adsorb the carbon dioxide in the mixed gas onto the adsorbent; a non-adsorbed gas delivery step of delivering non-adsorbed gas that was not adsorbed in the adsorption step; a depressurization step of discharging the remaining non-adsorbed gas present in a dead volume inside the carbon dioxide adsorption tower from the carbon dioxide adsorption tower after the adsorption step; and and a desorption step of suctioning at a pressure lower than atmospheric pressure to desorb the carbon dioxide adsorbed by the adsorbent in the carbon dioxide adsorption tower after the residual non-adsorbed gas purging step, thereby recovering concentrated carbon dioxide gas, wherein the carbon dioxide gas used in the residual non-adsorbed gas purging step is the carbon dioxide gas obtained in the desorption step in another of the carbon dioxide adsorption towers.

[0008] A second invention relates to the carbon dioxide recovery method of the first invention, in which a plurality of the carbon dioxide adsorption towers repeat the carbon dioxide recovery cycle to continuously recover the concentrated carbon dioxide gas from the mixed gas.

[0009] The third invention relates to a carbon dioxide recovery method according to the first or second invention, wherein the mixed gas is a moisture-containing mixed gas containing moisture, and the carbon dioxide recovery cycle includes a moisture removal step of removing the moisture contained in the moisture-containing mixed gas prior to the adsorption step.

[0010] A fourth invention relates to the carbon dioxide capture method of the third invention, wherein the moisture removal step includes a moisture removal cycle including a plurality of moisture adsorption towers filled with a moisture adsorbent, the moisture adsorption step comprising: a moisture adsorption step of delivering the moisture-containing mixed gas to one of the moisture adsorption towers at a pressure of not less than atmospheric pressure and not more than 0.2 MPa to cause the moisture to be adsorbed onto the moisture adsorbent, thereby obtaining a dry mixed gas from which the moisture has been removed; a dry mixed gas delivery step of delivering the dry mixed gas to the adsorption step of the carbon dioxide capture cycle; a moisture washing step of introducing the non-adsorbed gas delivered by the non-adsorbed gas delivery step of the carbon dioxide capture cycle into the moisture adsorption tower after the moisture adsorption step, and washing the moisture adsorbed by the moisture adsorbent in the moisture adsorption tower; a moisture discharge step of discharging the moisture-mixed non-adsorbed gas that has contained moisture after the moisture washing step; and a pressurization step of introducing the non-adsorbed gas delivered by the non-adsorbed gas delivery step of the carbon dioxide capture cycle into the moisture adsorption tower after the moisture discharge step, and raising the pressure inside the moisture adsorption tower to above atmospheric pressure.

[0011] A fifth invention relates to the carbon dioxide recovery method of the fourth invention, in which a plurality of the carbon dioxide adsorption towers repeat the carbon dioxide recovery cycle and a plurality of the moisture adsorption towers repeat the moisture removal cycle to continuously recover the concentrated dry carbon dioxide gas from the moisture-containing mixed gas. [Effects of the Invention]

[0012] According to the carbon dioxide recovery method of the first invention, the carbon dioxide content is 10 vol% or less. Combustion exhaust gas, etc.A carbon dioxide recovery method for concentrating and recovering the carbon dioxide from a mixed gas, comprising: a plurality of carbon dioxide adsorption towers filled with one or more of A-type zeolite, X-type zeolite, and Y-type zeolite as an adsorbent for the carbon dioxide; an adsorption step of introducing the mixed gas into one of the carbon dioxide adsorption towers at a pressure of not less than atmospheric pressure and not more than 0.2 MPa to adsorb the carbon dioxide in the mixed gas onto the adsorbent; a non-adsorbed gas delivery step of delivering non-adsorbed gas that was not adsorbed in the adsorption step; a depressurization step of discharging the remaining non-adsorbed gas present in a dead volume inside the carbon dioxide adsorption tower from the carbon dioxide adsorption tower after the adsorption step; and a depressurization step of discharging the remaining non-adsorbed gas present in a dead volume inside the carbon dioxide adsorption tower after the depressurization step. The carbon dioxide recovery cycle includes a residual non-adsorbed gas purging step in which concentrated carbon dioxide gas is introduced into a tower and the residual non-adsorbed gas remaining inside the carbon dioxide adsorption tower even after the depressurization step is pushed out, and a desorption step in which concentrated carbon dioxide gas is recovered by suctioning at a pressure lower than atmospheric pressure to desorb the carbon dioxide adsorbed by the adsorbent in the carbon dioxide adsorption tower after the residual non-adsorbed gas purging step, and the carbon dioxide gas used in the residual non-adsorbed gas purging step is the carbon dioxide gas obtained in the desorption step in another carbon dioxide adsorption tower. Therefore, carbon dioxide can be recovered at a high concentration and with high efficiency from a mixed gas with a low carbon dioxide concentration.

[0013] According to the carbon dioxide recovery method of the second invention, in the first invention, the multiple carbon dioxide adsorption towers repeat the carbon dioxide recovery cycle to continuously recover the concentrated carbon dioxide gas from the mixed gas, thereby making it possible to recover carbon dioxide more efficiently.

[0014] According to the carbon dioxide recovery method of the third invention, in the first or second invention, the mixed gas is a moisture-containing mixed gas containing moisture, and a moisture removal process for removing the moisture contained in the moisture-containing mixed gas is provided prior to the adsorption process of the carbon dioxide recovery cycle, so that a dry mixed gas from which moisture has been removed can be supplied to the carbon dioxide recovery cycle.

[0015] According to a fourth aspect of the present invention, in the carbon dioxide capture method of the third aspect, the moisture removal step includes a moisture adsorption step in which a plurality of moisture adsorption towers filled with a moisture adsorbent are arranged, the moisture-containing mixed gas is delivered to one of the moisture adsorption towers at a pressure of atmospheric pressure or higher but 0.2 MPa or lower to adsorb the moisture onto the moisture adsorbent, thereby obtaining a dry mixed gas from which the moisture has been removed; a dry mixed gas delivery step in which the dry mixed gas is delivered to the adsorption step of the carbon dioxide capture cycle; and a dry mixed gas delivery step in which the non-adsorbed gas delivered by the non-adsorbed gas delivery step of the carbon dioxide capture cycle is desorbed from the moisture. Since the system has a moisture removal cycle including a moisture washing step of introducing the non-adsorbed gas into the moisture adsorption tower after the adsorption step to wash the moisture adsorbed by the moisture adsorbent in the moisture adsorption tower, a moisture discharging step of discharging a moisture-mixed non-adsorbed gas containing the moisture by the moisture washing step, and a pressurization step of introducing the non-adsorbed gas delivered by the non-adsorbed gas delivery step of the carbon dioxide capture cycle into the moisture adsorption tower after the moisture discharging step to raise the pressure inside the moisture adsorption tower to above atmospheric pressure, it is possible to achieve efficient workability and power savings, and to remove moisture from a moisture-containing mixed gas with high efficiency.

[0016] According to the carbon dioxide recovery method of the fifth invention, in the fourth invention, multiple carbon dioxide adsorption towers repeat the carbon dioxide recovery cycle, and multiple moisture adsorption towers repeat the moisture removal cycle, thereby continuously recovering the concentrated dry carbon dioxide gas from the moisture-containing mixed gas, thereby making it possible to recover dry carbon dioxide more efficiently. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of a carbon dioxide capture device used in a carbon dioxide capture method according to one embodiment of the present invention. [Figure 2] FIG. 2 is a first schematic diagram showing gas flow paths in the carbon dioxide capture device of FIG. 1 corresponding to each step of the carbon dioxide capture cycle. [Figure 3] FIG. 2 is a second schematic diagram showing gas flow paths in the carbon dioxide capture device of FIG. 1 corresponding to each step of the carbon dioxide capture cycle. [Figure 4] FIG. 2 is a schematic diagram of a carbon dioxide capture device used in a carbon dioxide capture method according to another embodiment. [Figure 5] FIG. 5 is a first schematic diagram showing gas flow paths in the moisture removal means of the carbon dioxide recovery device of FIG. 4 corresponding to each step of the moisture removal cycle. [Figure 6] FIG. 5 is a second schematic diagram showing gas flow paths in the moisture removal means of the carbon dioxide recovery device of FIG. 4 corresponding to each step of the moisture removal cycle. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1 shows a carbon dioxide capture device 10 used in a carbon dioxide capture method according to one embodiment of the present invention. The carbon dioxide capture device 10 has a plurality of carbon dioxide adsorption towers 20 (20A, 20B, 20C) and a carbon dioxide capture unit 30 that captures carbon dioxide, and a mixed gas containing carbon dioxide is introduced into each of the carbon dioxide adsorption towers 20 (20A, 20B, 20C), where the carbon dioxide is separated and concentrated, and then sent to the carbon dioxide capture unit 30 for capture.

[0019] The mixed gas to be treated is a gas containing a relatively low concentration of carbon dioxide (low carbon dioxide concentration gas), such as combustion exhaust gas emitted from a boiler or generator. The carbon dioxide concentration contained in this mixed gas is 10 vol% or less. The mixed gas also includes a moisture-containing mixed gas containing moisture. The gases other than carbon dioxide contained in the mixed gas are not particularly limited, but examples include gas components mainly contained in the atmosphere, such as nitrogen and oxygen. Other components contained in combustion exhaust gas, such as NOx and SOx, are preferably removed from the mixed gas by pretreatment because they may cause deterioration of the adsorbent.

[0020] The carbon dioxide adsorption tower 20 is a treatment device filled with a carbon dioxide adsorbent, which adsorbs, separates, and concentrates carbon dioxide from the mixed gas. The carbon dioxide adsorbent is selected from one or more of A-type zeolite, X-type zeolite, and Y-type zeolite. A-type zeolite, X-type zeolite, and Y-type zeolite have the property of easily and selectively adsorbing carbon dioxide. In particular, X-type zeolite is more preferred because of its excellent carbon dioxide adsorption properties.

[0021] In the carbon dioxide adsorption tower 20, the introduced mixed gas is separated into carbon dioxide gas that has been adsorbed and concentrated by the adsorbent and non-adsorbed gas that has not been adsorbed in the adsorption process, and these are sequentially discharged. The carbon dioxide gas adsorbed by the adsorbent is allowed to contain trace amounts of impurities (other gas components, etc.). The non-adsorbed gas may also contain trace amounts of carbon dioxide that were not completely adsorbed by the adsorbent. When the non-adsorbed gas is discharged from the carbon dioxide adsorption tower 20, a portion of it temporarily remains in the dead volume inside the carbon dioxide adsorption tower 20 as residual non-adsorbed gas.

[0022] A plurality of pipes are connected to the carbon dioxide adsorption tower 20, and these pipes are used to supply a mixed gas, etc., and to deliver each gas separated from the mixed gas, etc. In the figure, reference numeral 11 denotes a first pipe section for supplying the mixed gas to the carbon dioxide adsorption tower 20, 12 a second pipe section for delivering a non-adsorbed gas from the carbon dioxide adsorption tower 20, 13 a third pipe section for delivering a remaining non-adsorbed gas from the carbon dioxide adsorption tower 20, 14 a fourth pipe section for supplying carbon dioxide gas to the carbon dioxide adsorption tower 20, 15 a fifth pipe section for delivering carbon dioxide gas from the carbon dioxide adsorption tower 20, and 16a to 16e valves for opening and closing the respective pipe sections 11, 12, 13, 14, and 15.

[0023] The carbon dioxide adsorption tower 20 can be connected to each piping section as appropriate, but it is preferable to share a connection section and arrange the piping sections by branching from the connection section in order to simplify the structure. In the example shown, the first piping section 11, the fourth piping section 14, and the fifth piping section 15 branch off and are connected to one side of the carbon dioxide adsorption tower 20 via a connection section 17, and the second piping section 12 and the third piping section 13 branch off and are connected to the other side via a connection section 18. In each of the piping sections 11 to 15 connected in this manner, the flow of the corresponding gas is controlled or stopped by opening or closing an on-off valve 16. Although not shown, various sensors, such as pressure gauges, for detecting the pressure, concentration, etc. of the corresponding gas may be appropriately installed in each of the carbon dioxide adsorption towers 20, the carbon dioxide capture section 30, the piping sections 11, 12, 13, 14, and 15, the connection sections 17 and 18, etc., as needed.

[0024] The multiple carbon dioxide adsorption towers 20 (20A, 20B, 20C) are arranged in parallel. There is no particular limitation on the number of carbon dioxide adsorption towers 20 as long as there is more than one, but from the viewpoints of processing efficiency, installation space, cost, etc., it is preferable to have about three. Furthermore, the piping sections 11 to 15 connected to the carbon dioxide adsorption towers 20A, 20B, 20C are connected to the same type of piping sections as shown in the figure.

[0025] The carbon dioxide capture unit 30 is a device that captures the carbon dioxide gas separated and concentrated from the mixed gas in the carbon dioxide adsorption tower 20. This carbon dioxide capture unit 30 has the function of supplying a portion of the captured carbon dioxide gas to the carbon dioxide adsorption tower 20 via the fourth piping unit 14. The carbon dioxide gas captured in the carbon dioxide capture unit 30 is transferred to an appropriate capture process, such as being liquefied and stored, with reuse in mind. The carbon dioxide capture unit 30 may be appropriately equipped with a device for measuring the carbon dioxide concentration, such as a gas chromatograph, or a device for measuring the amount of carbon dioxide gas, such as a flow meter, as necessary. From the perspective of reuse, it is preferable that the carbon dioxide concentration of the captured carbon dioxide gas be 90 vol% or more so that it can be easily liquefied.

[0026] The carbon dioxide recovery method of the present invention, which is carried out using the carbon dioxide recovery apparatus 10, is a method for concentrating and recovering carbon dioxide from a mixed gas containing a low concentration of carbon dioxide, and has a carbon dioxide recovery cycle including an adsorption step, a non-adsorbed gas delivery step, a depressurization step, a residual non-adsorbed gas purging step, and a desorption step.

[0027] The adsorption process is a process in which a mixed gas is introduced into one of the carbon dioxide adsorption towers 20 at a pressure equal to or higher than atmospheric pressure and equal to or lower than 0.2 MPa, causing the adsorbent to adsorb carbon dioxide in the mixed gas. In the adsorption process, the supplied mixed gas is introduced into the carbon dioxide adsorption tower 20 via the first piping section 11, and the mixed gas is brought into contact with the adsorbent packed in the carbon dioxide adsorption tower 20, causing the carbon dioxide in the mixed gas to be adsorbed by the adsorbent. In the adsorption process, the longer the time for which the adsorption process is performed (adsorption time), the easier it is to ultimately recover carbon dioxide at a higher concentration. The adsorption time is appropriate depending on conditions such as the type of adsorbent used, the carbon dioxide concentration in the mixed gas, and the supply flow rate of the mixed gas.

[0028] In this adsorption step, the carbon dioxide adsorption tower 20 is filled with an adsorbent selected from one or more of A-type zeolite, X-type zeolite, and Y-type zeolite, which have high selectivity for carbon dioxide adsorption. X-type zeolite is particularly preferred because of its excellent adsorption performance for gases with low carbon dioxide concentrations. By using these adsorbents, carbon dioxide can be efficiently adsorbed into the adsorbent at a relatively low pressure (above atmospheric pressure and below 0.2 MPa) without having to increase the adsorption pressure using a compressor or the like. The mixed gas treated in this manner is separated into carbon dioxide adsorbed into the adsorbent and non-adsorbed gas that is not adsorbed into the adsorbent.

[0029] The non-adsorbed gas delivery process is a process in which a non-adsorbed gas, which is a gas of the mixed gas that was not adsorbed in the adsorption process, is delivered from the carbon dioxide adsorption tower 20. In the non-adsorbed gas delivery process, the second piping section 12 is opened, and the process is performed integrally with the adsorption process. That is, the mixed gas introduced from the first piping section 11 is brought into contact with the adsorbent to adsorb carbon dioxide (adsorption process), and the gas that was not adsorbed by the adsorbent is delivered as a non-adsorbed gas from the carbon dioxide adsorption tower 20 to the second piping section 12. In the adsorption process and the non-adsorbed gas delivery process, for example, the first piping section 11 and the second piping section 12 are closed after a predetermined adsorption time has elapsed, and the supply of the mixed gas and the delivery of the non-adsorbed gas are stopped.

[0030] The depressurization step is a step of discharging the remaining non-adsorbed gas present in the dead volume inside the carbon dioxide adsorption tower 20 from the carbon dioxide adsorption tower 20 after the adsorption step. During the depressurization step, at the end of the adsorption step and the non-adsorbed gas delivery step, the first piping section 11 and the second piping section 12 are closed to make the inside of the carbon dioxide adsorption tower 20 a closed space, and the inside of the carbon dioxide adsorption tower 20 is pressurized higher than the outside. Therefore, in the depressurization step, the third piping section 13 is opened to reduce the pressure inside the carbon dioxide adsorption tower 20, and the remaining non-adsorbed gas is delivered to the third piping section 13 and discharged as appropriate. Note that, although the remaining non-adsorbed gas is discharged via the third piping section 13 in the depressurization step, it may also be discharged from the second piping section 12 side instead of the third piping section 13.

[0031] The remaining non-adsorbed gas purging step is a step in which concentrated carbon dioxide gas is introduced into the carbon dioxide adsorption tower 20 after the depressurization step, and the remaining non-adsorbed gas that remains inside the carbon dioxide adsorption tower 20 after the depressurization step is pushed out. The concentrated carbon dioxide gas introduced into the carbon dioxide adsorption tower 20 is a portion of the carbon dioxide gas recovered in the carbon dioxide recovery unit 30, which will be described later, and is supplied from the carbon dioxide recovery unit 30 via the fourth piping unit 14.

[0032] In the remaining non-adsorbed gas purging step, the third piping section 13, which was opened in the depressurization step, continues to be open, and the pressure inside the carbon dioxide adsorption tower 20 is reduced by the depressurization step, and the internal pressures of the carbon dioxide adsorption tower 20 and the third piping section 13 become substantially uniform, after which the supply of carbon dioxide gas is started. Because the third piping section 13 is open, the remaining non-adsorbed gas remaining after the depressurization step is smoothly discharged from the carbon dioxide adsorption tower 20 by the supply of carbon dioxide gas. By discharging the remaining non-adsorbed gas with carbon dioxide gas in this way, the carbon dioxide adsorption tower 20 becomes filled with carbon dioxide. When the discharge of the remaining non-adsorbed gas inside the carbon dioxide adsorption tower 20 is completed, the fourth piping section 14 and the third piping section 13 are closed, the supply of carbon dioxide gas is stopped, and the remaining non-adsorbed gas purging step is terminated.

[0033] The desorption step is a step of suctioning at a pressure lower than atmospheric pressure to desorb the carbon dioxide adsorbed by the adsorbent in the carbon dioxide adsorption tower 20 after the residual non-adsorbed gas purging step, thereby recovering concentrated carbon dioxide gas. In the desorption step, the fifth piping section 15 is opened, and the pressure inside the carbon dioxide adsorption tower 20 is reduced to below atmospheric pressure by a gas suction means 40, such as a suction pump, arranged in the fifth piping section 15. The carbon dioxide adsorbed by the adsorbent is desorbed as carbon dioxide gas from the adsorbent by reducing the pressure inside the carbon dioxide adsorption tower 20. In particular, since the carbon dioxide adsorption tower 20 is filled with carbon dioxide and contains almost no other gases due to the residual non-adsorbed gas purging step, the carbon dioxide is concentrated at a high concentration and recovered in the carbon dioxide recovery section 30. When desorption of carbon dioxide from the adsorbent is complete, the fifth piping section 15 is closed, and the desorption step is terminated.

[0034] In one carbon dioxide adsorption tower 20, the adsorption step, non-adsorbed gas delivery step, depressurization step, residual non-adsorbed gas purging step, and desorption step are sequentially performed as described above. This constitutes one carbon dioxide capture cycle, which is repeatedly performed in each of the multiple carbon dioxide adsorption towers 20 (20A, 20B, 20C). In this case, it is preferable that the carbon dioxide capture cycles of the carbon dioxide adsorption towers 20 (20A, 20B, 20C) be performed at different times in order to avoid interference between the gases flowing through the respective piping sections 11 to 15. By repeatedly performing the carbon dioxide capture cycle in this manner, concentrated carbon dioxide gas can be continuously recovered from the mixed gas, allowing for more efficient carbon dioxide recovery.

[0035] 2 and 3, the flow of the carbon dioxide capture cycle performed in the multiple carbon dioxide adsorption towers 20A, 20B, and 20C will be described, focusing on the carbon dioxide adsorption tower 20A. In each of the piping sections 11 to 15 in Figures 2 and 3, the solid lines indicate paths through which gas flows when the corresponding on-off valves 16a to 16e are open, and the dashed lines indicate piping sections through which gas does not flow when the on-off valves 16a to 16e are closed.

[0036] 2(a), the first piping section 11 and the second piping section 12 connected to the carbon dioxide adsorption tower 20A are opened, and the mixed gas is supplied to the first piping section 11. The mixed gas is introduced into the carbon dioxide adsorption tower 20A via the first piping section 11, and the carbon dioxide in the mixed gas is adsorbed by the adsorbent packed in the carbon dioxide adsorption tower 20A (adsorption step). Then, the non-adsorbed gas that was not adsorbed by the adsorbent is discharged from the carbon dioxide adsorption tower 20A via the second piping section 12 (non-adsorbed gas delivery step).

[0037] Next, as shown in FIG. 2(b), the first piping section 11 and the second piping section 12 connected to the carbon dioxide adsorption tower 20A are closed, while the third piping section 13 is opened, and the remaining non-adsorbed gas in the carbon dioxide adsorption tower 20A is discharged (depressurization process).

[0038] 3(a), while the third piping section 13 connected to the carbon dioxide adsorption tower 20A is kept open, the fourth piping section 14 is opened and concentrated carbon dioxide gas is supplied from the carbon dioxide recovery section 30. This concentrated carbon dioxide gas is introduced into the carbon dioxide adsorption tower 20A via the fourth piping section 14, and the remaining non-adsorbed gas remaining in the carbon dioxide adsorption tower 20A is pushed out and discharged via the third piping section 13 (residual non-adsorbed gas purging step).

[0039] At this time, the carbon dioxide gas introduced into the carbon dioxide adsorption tower 20A is carbon dioxide gas obtained in the desorption step in the other carbon dioxide adsorption tower. In the example shown, in the carbon dioxide adsorption tower 20C, the carbon dioxide gas desorbed from the adsorbent in the desorption step is recovered in the carbon dioxide capture unit 30 via the fifth piping section 15. The recovered carbon dioxide gas is then introduced from the carbon dioxide capture unit 30 into the carbon dioxide adsorption tower 20A via the fourth piping section 14. In this way, using the carbon dioxide gas obtained in the desorption step in the other carbon dioxide adsorption tower in the remaining non-adsorbed gas purging step means that the carbon dioxide gas obtained from the mixed gas to be treated is used to discharge the remaining non-adsorbed gas from the carbon dioxide adsorption tower 20A, and therefore the mixed gas to be treated is used without waste, making it possible to concentrate the carbon dioxide in the carbon dioxide adsorption tower 20A to a higher concentration.

[0040] After the remaining non-adsorbed gas is discharged from the carbon dioxide adsorption tower 20A, as shown in FIG. 3(b), the third piping section 13 connected to the carbon dioxide adsorption tower 20A is closed, and the fifth piping section 15 is opened, and the pressure inside the carbon dioxide adsorption tower 20A is reduced, thereby desorbing carbon dioxide from the adsorbent. The desorbed carbon dioxide is then recovered as carbon dioxide gas in the carbon dioxide recovery section 30 via the fifth piping section 15 (desorption step). The recovered carbon dioxide gas is transferred to an appropriate recovery process. In addition, a portion of the recovered carbon dioxide gas is also used as gas to push out the remaining non-adsorbed gas from the other carbon dioxide adsorption towers 20B, 20C when the remaining non-adsorbed gas purging step is performed in the other carbon dioxide adsorption towers 20B, 20C.

[0041] As described above, in the carbon dioxide capture cycle, carbon dioxide is efficiently adsorbed from a mixed gas with a low carbon dioxide concentration in the adsorption step, and therefore carbon dioxide can be efficiently captured from a mixed gas with a low concentration. In particular, by supplying concentrated carbon dioxide gas obtained in the desorption step of another carbon dioxide adsorption tower in the remaining non-adsorbed gas purging step, and filling the carbon dioxide adsorption tower 20A with carbon dioxide while discharging the remaining non-adsorbed gas, the carbon dioxide obtained from the mixed gas to be treated can be effectively utilized, and carbon dioxide can be captured at a higher concentration and with higher efficiency.

[0042] When the carbon dioxide capture cycle is being carried out in the carbon dioxide adsorption tower 20A as described above, other steps of the carbon dioxide capture cycle that do not interfere with the gas flow path of the carbon dioxide adsorption tower 20A are carried out appropriately in the other carbon dioxide adsorption towers 20B and 20C, as shown in Figures 2(a) to 3(b). For example, when the adsorption step and non-adsorbed gas delivery step are being carried out in the carbon dioxide adsorption tower 20A shown in Figure 2(a), the carbon dioxide adsorption tower 20B carries out a desorption step in which carbon dioxide gas is recovered, and the carbon dioxide adsorption tower 20C carries out a residual non-adsorbed gas purging step in which carbon dioxide gas is introduced and residual non-adsorbed gas is pushed out.

[0043] 2(b), for example, an adsorption process for adsorbing carbon dioxide from the mixed gas and a non-adsorbed gas discharge process for discharging non-adsorbed gas are performed in the carbon dioxide adsorption tower 20B, and a desorption process for recovering carbon dioxide gas is performed in the carbon dioxide adsorption tower 20C, and the gas flow paths of the carbon dioxide adsorption towers 20A, 20B, and 20C are controlled so as not to interfere with each other. The carbon dioxide gas recovered in the carbon dioxide recovery unit 30 is transferred to an appropriate recovery process.

[0044] During the remaining non-adsorbed gas purging step in the carbon dioxide adsorption tower 20A shown in FIG. 3(a), the adsorption step and non-adsorbed gas delivery step are continuously performed in the carbon dioxide adsorption tower 20B, and the desorption step is continuously performed in the carbon dioxide adsorption tower 20C, and the carbon dioxide gas obtained from the carbon dioxide adsorption tower 20C as described above is used in the remaining non-adsorbed gas purging step in the carbon dioxide adsorption tower 20A.

[0045] Furthermore, when the desorption process is being carried out in the carbon dioxide adsorption tower 20A shown in FIG. 3(b), the carbon dioxide adsorption tower 20B is performing a depressurization process of discharging the remaining non-adsorbed gas, and the carbon dioxide adsorption tower 20C is performing an adsorption process of adsorbing carbon dioxide from the mixed gas and a non-adsorbed gas delivery process of discharging the non-adsorbed gas, and the gas flow paths of the carbon dioxide adsorption towers 20A, 20B, and 20C are controlled so as not to interfere with each other.

[0046] The implementation pattern of the carbon dioxide capture cycle of each of the carbon dioxide adsorption towers 20A, 20B, 20C is not limited to the example shown in the figure, and can be implemented within a range that does not interfere with each carbon dioxide capture cycle.

[0047] Mixed gases containing carbon dioxide, such as combustion exhaust gas, usually contain moisture. When recovering carbon dioxide from a mixed gas containing moisture, the moisture inhibits the separation of carbon dioxide, reducing the carbon dioxide recovery efficiency. In addition, since the recovered carbon dioxide also contains moisture, a separate moisture removal process is required. Therefore, in the carbon dioxide recovery method of the present invention, particularly when the mixed gas is a moisture-containing mixed gas, it is preferable to perform a moisture removal process to remove moisture contained in the moisture-containing mixed gas prior to the adsorption process in the carbon dioxide recovery cycle.

[0048] FIG. 4 shows a carbon dioxide capture device 50 used in a carbon dioxide capture method having a moisture removal step, which includes a carbon dioxide capture means 10A corresponding to the carbon dioxide capture device 10 described above, and a moisture removal means 60 in which the moisture removal step is carried out.

[0049] The moisture removal means 60 has multiple moisture adsorption towers 70 (70A, 70B). The moisture adsorption towers 70 are filled with a moisture adsorbent, and are treatment devices that adsorb moisture from a moisture-containing mixed gas using the moisture adsorbent to separate the gas into a dry mixed gas. The moisture adsorbent is not particularly limited as long as it is a material that can easily and selectively adsorb moisture, but preferred examples include zeolites such as molecular sieves and activated alumina. The dry mixed gas is a mixed gas containing carbon dioxide that has been dried by removing moisture.

[0050] A plurality of pipes are connected to the moisture adsorption tower 70, and these pipes are used to supply a moisture-containing mixed gas and to deliver a dry mixed gas obtained by removing moisture from the moisture-containing mixed gas. In the figure, reference numeral 71 denotes a first moisture pipe section for supplying the moisture mixed gas, 72 denotes a second moisture pipe section for delivering the dry mixed gas, 73 denotes a third moisture pipe section for supplying a non-adsorbed gas from the carbon dioxide capture means 10A, 74 denotes a fourth moisture pipe section for delivering a moisture-mixed non-adsorbed gas described below, and 76a to 76d denote on-off valves for opening and closing the moisture pipe sections 71, 72, 73, and 74. Each moisture adsorption tower 70 and each moisture pipe section 71, 72, 73, and 74 may be provided with various sensors for detecting the moisture content of the corresponding gas, as needed.

[0051] In the moisture adsorption tower 70, each moisture piping section can be connected as appropriate, but it is preferable to share a connection section and arrange each moisture piping section by branching off from the connection section in order to simplify the structure. In the illustrated example, a first moisture piping section 71 and a fourth moisture piping section 74 branch off and are connected to one side of the moisture adsorption tower 70 via a connection section 77, and a second moisture piping section 72 and a third moisture piping section 73 branch off and are connected to the other side via a connection section 78. In each of the piping sections 71, 72, 73, and 74 connected in this manner, the flow of the corresponding gas is controlled or stopped by opening or closing an on-off valve 76.

[0052] The multiple moisture adsorption towers 70 (70A, 70B) are arranged in parallel. There is no particular limitation on the number of moisture adsorption towers 70 as long as there is more than one, but from the viewpoints of processing efficiency, installation space, cost, etc., it is preferable to have about two. Furthermore, the moisture piping sections 71 to 74 connected to the moisture adsorption towers 70A, 70B are connected to the same type of moisture piping sections as shown in the figure.

[0053] In the carbon dioxide capture device 50 of the embodiment, the first piping section 11 of the carbon dioxide capture means 10A and the second moisture piping section 72 of the moisture removal means 60 are connected, and the second piping section 12 of the carbon dioxide capture means 10A and the third moisture piping section 73 of the moisture removal means 60 are connected, thereby connecting the carbon dioxide capture means 10A and the moisture removal means 60.

[0054] The moisture removal process carried out by the moisture removal means 60 is a process of supplying a dry mixed gas obtained by removing moisture from a moisture-containing mixed gas containing moisture to the carbon dioxide capture means 10A, and has a moisture removal cycle including a moisture adsorption process, a dry mixed gas delivery process, a moisture washing process, a moisture discharge process, and a pressure increase process.

[0055] The moisture adsorption step is a step in which the moisture-containing mixed gas is sent to one of the moisture adsorption towers 70 at a pressure of atmospheric pressure or higher and 0.2 MPa or lower, and the moisture is adsorbed by the moisture adsorbent to obtain a dry mixed gas from which the moisture has been removed. In the moisture adsorption step, the supplied moisture-containing mixed gas is introduced into the moisture adsorption tower 70 via the first moisture piping section 71, and the moisture-containing mixed gas is brought into contact with the moisture adsorbent filled in the moisture adsorption tower 70, thereby causing the moisture in the moisture-containing mixed gas to be adsorbed by the moisture adsorbent. The moisture-containing mixed gas is separated into the moisture adsorbed by the moisture adsorbent and the dry mixed gas from which the moisture has been removed.

[0056] The dry mixed gas delivery process is a process in which the dry mixed gas is delivered to the adsorption process of the carbon dioxide capture cycle. In the dry mixed gas delivery process, the second moisture piping section 72 is opened and the process is performed integrally with the moisture adsorption process. That is, the moisture-containing mixed gas introduced from the first moisture piping section 71 passes through a moisture adsorbent to remove moisture and become a dried dry mixed gas (moisture adsorption process), which is delivered as is from the moisture adsorption tower 70 to the second moisture piping section 72. In the moisture adsorption process and dry mixed gas delivery process, the first moisture piping section 71 and the second moisture piping section 72 are closed after a predetermined moisture adsorption time has elapsed, and the supply of the mixed gas and the delivery of the non-adsorbed gas are stopped.

[0057] The dry mixed gas delivered in the dry mixed gas delivery step is supplied to the carbon dioxide capture means 10A from the second moisture piping section 72 via the first piping section 11, because the second moisture piping section 72 is in communication with the first piping section 11. Therefore, in the carbon dioxide capture means 10A, it becomes possible to perform the carbon dioxide capture process using a mixed gas that does not contain moisture, and dry carbon dioxide can be recovered at a high concentration and with high efficiency without being affected by factors such as a decrease in carbon dioxide recovery efficiency due to moisture.

[0058] The moisture washing step is a step in which the non-adsorbed gas discharged in the non-adsorbed gas discharge step of the carbon dioxide capture cycle is introduced into the moisture adsorption tower 70 after the moisture adsorption step to wash away the moisture adsorbed by the moisture adsorbent in the moisture adsorption tower 70. In the moisture washing step, the non-adsorbed gas is brought into contact with the moisture adsorbent to absorb moisture into the non-adsorbed gas, thereby producing a moisture-mixed non-adsorbed gas. The non-adsorbed gas discharged in the non-adsorbed gas discharge step is a dry gas that is not adsorbed by the adsorbent, and therefore moisture can be easily desorbed from the moisture adsorbent by contacting it with the moisture adsorbent. The non-adsorbed gas is supplied to the moisture adsorption tower 70 via the third moisture piping section 73 by connecting the second piping section 12 of the carbon dioxide capture means 10A to the third moisture piping section 73 of the moisture removal means 60.

[0059] The moisture discharge step is a step of discharging the moisture-mixed non-adsorbed gas that has been absorbed by the moisture washing step from the moisture adsorption tower 70. In the moisture discharge step, the fourth moisture piping section 74 is opened and the moisture discharge step is performed integrally with the moisture washing step. That is, the non-adsorbed gas introduced from the third moisture piping section 73 passes through the moisture adsorbent to become a moisture-mixed non-adsorbed gas that contains moisture (moisture washing step), and is sent as is from the moisture adsorption tower 70 to the fourth moisture piping section 74 and discharged as appropriate. When the amount of moisture adsorbed by the moisture adsorbent reaches a predetermined amount, the fourth moisture piping section 74 is closed and the delivery of the moisture-mixed non-adsorbed gas is stopped.

[0060] The pressurization step is a step in which the non-adsorbed gas delivered in the non-adsorbed gas delivery step of the carbon dioxide capture cycle is introduced into the moisture adsorption tower 70 after the moisture discharge step, thereby raising the pressure inside the moisture adsorption tower 70 to atmospheric pressure or higher. In the pressurization step, the supply of non-adsorbed gas from the third moisture piping section 73 to the moisture adsorption tower 70 continues, while the fourth moisture piping section 74 is closed, thereby raising the pressure inside the moisture adsorption tower 70. By raising the pressure inside the moisture adsorption tower 70 to atmospheric pressure or higher, the pressure inside the carbon dioxide capture apparatus 50 can be maintained when the moisture adsorption step, etc. is performed again in the moisture adsorption tower 70, allowing each step to be carried out smoothly. When the pressure inside the moisture adsorption tower 70 reaches a predetermined pressure, the third moisture piping section 73 is closed, the supply of non-adsorbed gas is stopped, and the pressurization step is terminated.

[0061] In the moisture removal process, moisture is removed from the moisture-containing mixed gas in the moisture adsorption process, and the moisture removed from the moisture-containing mixed gas can be easily discharged in the moisture cleaning process and the pressurization process by utilizing the non-adsorbed gas of the carbon dioxide capture cycle, thereby making it possible to improve the efficiency of the work required for moisture removal and reduce power consumption.

[0062] In each moisture adsorption tower 70, a moisture adsorption process, a dry mixed gas delivery process, a moisture washing process, a moisture discharge process, and a pressure increase process are sequentially performed, and this process is repeated to form one moisture removal cycle. In this case, it is preferable that the moisture removal cycles of the moisture adsorption towers 70 (70A, 70B) be performed at different times to avoid interference between the gases flowing through the moisture piping sections 71-74. Furthermore, by repeatedly performing the carbon dioxide capture cycle and the moisture removal cycle in conjunction with each other, concentrated dry carbon dioxide gas can be continuously recovered from the moisture-containing mixed gas. Therefore, dry carbon dioxide can be recovered more efficiently.

[0063] 5 and 6, the flow of the moisture removal cycle performed in the multiple moisture adsorption towers 70A and 70B will be described, focusing on the moisture adsorption tower 70A. In each moisture piping section 71-74 in Figures 5 and 6, the solid lines indicate the paths through which gas flows when the corresponding on-off valves 76a-76d are open, and the dashed lines indicate the moisture piping sections through which gas does not flow when the on-off valves 76a-76d are closed.

[0064] As shown in FIG. 5(a), the first moisture piping section 71 and the second moisture piping section 72 connected to the moisture adsorption tower 70A are opened, and the moisture-containing mixed gas is supplied to the first moisture piping section 71. The moisture-containing mixed gas is introduced into the moisture adsorption tower 70A via the first moisture piping section 71, and the moisture in the moisture-containing mixed gas is adsorbed by the moisture adsorbent packed in the moisture adsorption tower 70A (moisture adsorption step). The dry mixed gas from which the moisture has been removed by the moisture adsorbent is then discharged from the moisture adsorption tower 70A via the second moisture piping section 72 (dry mixed gas delivery step). The dry mixed gas discharged from the moisture adsorption tower 70A is supplied from the second moisture piping section 72 to the carbon dioxide capture means 10A via the first piping section 11, and a carbon dioxide capture cycle using a moisture-free mixed gas is performed.

[0065] 5(b), the first moisture piping section 71 and the second moisture piping section 72 connected to the moisture adsorption tower 70A are closed, while the third moisture piping section 73 and the fourth moisture piping section 74 are opened, and the dry non-adsorbed gas delivered in the non-adsorbed gas delivery step is supplied from the second piping section 12 of the carbon dioxide capture means 10A to the third moisture piping section 73. This non-adsorbed gas is introduced into the moisture adsorption tower 70A via the third moisture piping section 73, where the moisture adsorbed by the moisture adsorbent is desorbed to produce a moisture-mixed non-adsorbed gas (moisture washing step). The moisture-mixed non-adsorbed gas is discharged from the moisture adsorption tower 70A via the fourth moisture piping section 74 (moisture discharge step).

[0066] 6, the third moisture piping section 73 is kept open to continuously supply dry non-adsorbed gas, and the fourth moisture piping section 74 is closed, thereby increasing the pressure inside the moisture adsorption tower 70A (pressurization step). Note that by increasing the pressure inside the moisture adsorption tower 70A, the pressure inside the carbon dioxide recovery device 50 is maintained when the moisture piping section is opened again during the moisture adsorption step or the like.

[0067] As described above, in the moisture removal cycle, moisture is removed from the moisture-containing mixed gas and the resulting dry mixed gas is supplied to the carbon dioxide capture cycle, making it possible to perform the carbon dioxide capture process using a moisture-free mixed gas, and dry carbon dioxide can be captured at a high concentration and with high efficiency. Furthermore, the dry non-adsorbed gas generated in the carbon dioxide capture cycle can be used in the moisture removal cycle to discharge moisture, making it possible to improve the efficiency of the work required for moisture removal, reduce power consumption, and achieve highly efficient moisture removal from the moisture-containing mixed gas.

[0068] While the moisture removal cycle is being performed in the moisture adsorption tower 70A as described above, other steps of the moisture removal cycle that do not interfere with the gas flow path of the moisture adsorption tower 70A are appropriately performed in the other moisture adsorption tower 70B, as shown in Figures 5(a) to 6. For example, while the moisture adsorption tower 70A shown in Figure 5(a) is performing the moisture adsorption step and the dry mixed gas delivery step, the moisture adsorption tower 70B is performing a moisture washing step in which moisture is desorbed from the moisture adsorbent and a moisture discharge step in which a moisture-containing non-adsorbed gas is discharged. Furthermore, although not shown, the moisture adsorption tower 70B may also perform a pressurization step.

[0069] 5(b) to 6, while the moisture adsorption tower 70A is performing the moisture washing step, moisture discharge step, and pressurization step, the moisture adsorption tower 70B is performing, for example, a moisture adsorption step of removing moisture from a moisture-containing mixed gas and a dry mixed gas delivery step of discharging a dry mixed gas from the moisture adsorption tower 70B and supplying it to a carbon dioxide capture cycle. Note that the implementation pattern of the moisture removal cycle of each moisture adsorption tower 20A, 20B is not limited to the example shown in the figures, and can be implemented within a range that does not interfere with each moisture removal cycle. [Example]

[0070] [Carbon dioxide capture processing] In the carbon dioxide recovery process of prototype examples 1 to 12, three carbon dioxide adsorption towers (20A, 20B, 20C) were arranged in parallel as shown in Fig. 1, and a carbon dioxide recovery system (10) having connected piping sections (11 to 15) was used to recover carbon dioxide from the mixed gas by carrying out a carbon dioxide recovery cycle (adsorption step, non-adsorbed gas delivery step, depressurization step, residual non-adsorbed gas purging step, desorption step) based on treatment conditions 1 to 3 described below. In this carbon dioxide recovery system, the volume of each of the three carbon dioxide adsorption towers was set to 174 ml, and they were filled with one of the adsorbents listed below.

[0071] [Adsorbent] Adsorbent 1: Type A zeolite (Resonac Universal Co., Ltd., "5A") Adsorbent 2: X-type zeolite (Li-LSX, manufactured by Resonac Universal Co., Ltd.) Adsorbent 3: Y-type zeolite (Tosoh Corporation, "320NAD1C") Adsorbent 4: Activated carbon (Futamura Chemical Co., Ltd., "15MH")

[0072] [Processing condition 1] For treatment condition 1, a simulated gas containing 3 vol% carbon dioxide and other gas components such as nitrogen and oxygen was used as the mixed gas, the supply flow rate of the mixed gas was 6 L / min, the internal pressure of the carbon dioxide adsorption tower in the adsorption step was 0.2 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption step was below atmospheric pressure.

[0073] [Processing condition 2] For treatment condition 2, a simulated gas containing 5 vol% carbon dioxide and other gas components such as nitrogen and oxygen was used as the mixed gas, the supply flow rate of the mixed gas was 4 L / min, the internal pressure of the carbon dioxide adsorption tower in the adsorption step was 0.2 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption step was below atmospheric pressure.

[0074] [Processing condition 3] For treatment condition 3, a simulated gas containing 10 vol% carbon dioxide and other gas components of nitrogen and oxygen was used as the mixed gas, the supply flow rate of the mixed gas was 4 L / min, the internal pressure of the carbon dioxide adsorption tower in the adsorption step was 0.2 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption step was atmospheric pressure or less.

[0075] [Prototype 1] In prototype example 1, each carbon dioxide adsorption tower was filled with adsorbent 1, and carbon dioxide recovery treatment was carried out under treatment condition 1.

[0076] [Prototype 2] In prototype example 2, each carbon dioxide adsorption tower was filled with adsorbent 2, and the carbon dioxide recovery process was carried out under process condition 1.

[0077] [Prototype 3] In prototype example 3, each carbon dioxide adsorption tower was filled with adsorbent 3, and carbon dioxide recovery treatment was carried out under treatment condition 1.

[0078] [Prototype 4] In prototype example 4, each carbon dioxide adsorption tower was filled with adsorbent 4, and carbon dioxide recovery treatment was carried out under treatment condition 1.

[0079] [Prototype 5] In prototype example 5, the adsorbent 1 was packed into each carbon dioxide adsorption tower, and the carbon dioxide recovery process was carried out under process condition 2.

[0080] [Prototype 6] In prototype example 6, each carbon dioxide adsorption tower was filled with adsorbent 2, and carbon dioxide recovery treatment was carried out under treatment condition 2.

[0081] [Prototype 7] In prototype example 7, each carbon dioxide adsorption tower was filled with adsorbent 3, and carbon dioxide recovery treatment was carried out under treatment condition 2.

[0082] [Prototype 8] Prototype example 8 is a carbon dioxide recovery process carried out under process condition 2, with each carbon dioxide adsorption tower packed with adsorbent 4.

[0083] [Prototype 9] Prototype example 9 is a carbon dioxide recovery process carried out under process condition 3, with each carbon dioxide adsorption tower packed with adsorbent 1.

[0084] [Prototype 10] Prototype example 10 is a carbon dioxide recovery process carried out under process condition 3, with adsorbent 2 packed in each carbon dioxide adsorption tower.

[0085] [Prototype 11] Prototype example 11 is a carbon dioxide recovery process carried out under process condition 3, with adsorbent 3 packed in each carbon dioxide adsorption tower.

[0086] [Prototype 12] Prototype example 12 is a carbon dioxide recovery process carried out under process condition 3, with each carbon dioxide adsorption tower packed with adsorbent 4.

[0087] [CO2 concentration and CO2 recovery rate] In the carbon dioxide recovery process of Prototype Examples 1 to 12, a device for measuring the concentration of recovered carbon dioxide gas and a device for measuring the gas amount were installed in the carbon dioxide recovery section (30) of the carbon dioxide recovery device. A gas chromatograph (manufactured by Shimadzu Corporation, "GC-2014"), a detector (manufactured by Shimadzu Corporation, "TCD"), and a column (manufactured by GL Sciences Inc., "Active Carbon 60 / 80") were used as the device for measuring the carbon dioxide concentration. A mass-quantity integrating flow meter (manufactured by Shinagawa Co., Ltd.) was used as the device for measuring the carbon dioxide gas amount.

[0088] In the carbon dioxide recovery process of Prototype Examples 1 to 12, a predetermined adsorption time was set, and the carbon dioxide recovery cycle was repeatedly performed during the set treatment time, and the concentration and amount of recovered carbon dioxide gas were measured. If the measured carbon dioxide gas concentration did not reach a value close to 90 vol%, the adsorption time was increased and the same treatment was performed again. The treatment was continued with successively increased adsorption times until the carbon dioxide gas concentration reached a value close to 90 vol%. From the carbon dioxide concentration and gas amount obtained in each treatment, the CO2 recovery rate (%) of Prototype Examples 1 to 12 was calculated based on the following formula (i). The recovered CO2 concentration and CO2 recovery rate of each Prototype Example 1 to 12 are shown in Tables 1 to 3 below. Note that in formula (i), the gas to be treated is the mixed gas supplied to the carbon dioxide recovery device, and the recovered gas is the carbon dioxide gas recovered by the carbon dioxide recovery device.

[0089]

number

[0090] [Table 1]

[0091] [Table 2]

[0092] [Table 3]

[0093] [Results and Discussion (1)] The carbon dioxide recovery processes of prototypes 1 to 4 shown in Table 1 compare the carbon dioxide recovery efficiency when a mixed gas with a lower carbon dioxide concentration (3 vol%) among mixed gases containing low concentrations (10 vol% or less) of carbon dioxide (low carbon dioxide concentration gas) was used under process condition 1 in carbon dioxide recovery devices filled with adsorbents 1 to 4, respectively. The carbon dioxide recovery processes of prototypes 5 to 8 shown in Table 2 compare the carbon dioxide recovery efficiency when a mixed gas with a higher carbon dioxide concentration (5 vol%) than that under process condition 1 was used. The carbon dioxide recovery processes of prototypes 9 to 12 shown in Table 3 compare the carbon dioxide recovery efficiency when a mixed gas with an even higher carbon dioxide concentration (10 vol%) than that under process condition 2 was used.

[0094] In prototypes 4, 8, and 12, which used adsorbent 4 (activated carbon), the concentration of the recovered carbon dioxide gas did not rise to around 90 vol% even when the adsorption time was gradually increased, so the recovery process was discontinued. This showed that activated carbon is not suitable as an adsorbent for recovering carbon dioxide from gases with low carbon dioxide concentrations.

[0095] In Prototype Examples 1-3, 5-7, and 9-11, which used adsorbents 1-3 (zeolites), carbon dioxide gas was recovered at high concentrations (near 90 vol%). This indicates that A-type zeolite, X-type zeolite, and Y-type zeolite can all be suitably used as adsorbents for recovering carbon dioxide from gases with low carbon dioxide concentrations. Furthermore, when comparing Prototype Examples 1-3, 5-7, and 9-11, Prototype Examples 2, 6, and 10, which used adsorbent 2 (X-type zeolite), had better carbon dioxide recovery rates than the other adsorbent examples 1 and 3. Furthermore, when comparing Prototype Examples 1-3 under treatment condition 1 (3 vol%), Prototype Example 2, which used adsorbent 2, was able to recover carbon dioxide more efficiently than Prototype Examples 1 and 3. Therefore, it is believed that X-type zeolite is the optimal adsorbent for recovering carbon dioxide from gases with low carbon dioxide concentrations.

[0096] [Low adsorption pressure carbon dioxide capture process] Next, a carbon dioxide recovery process of Prototype Example 13 was carried out under Process Condition 4 described below as a process for recovering carbon dioxide from a mixed gas using low adsorption pressure. As with Prototype Examples 1 to 12, the carbon dioxide recovery process of Prototype Example 13 was carried out by gradually increasing the adsorption time until the measured carbon dioxide gas concentration reached a value close to 90 vol%. The results are shown in Table 4.

[0097] [Processing condition 4] For treatment condition 4, a simulated gas containing 10 vol% carbon dioxide and other gas components such as nitrogen and oxygen was used as the mixed gas, the supply flow rate of the mixed gas was 4 L / min, the internal pressure of the carbon dioxide adsorption tower in the adsorption step was 0.1 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption step was atmospheric pressure or less.

[0098] Prototype example 13 is a carbon dioxide recovery treatment carried out under treatment condition 4, with each carbon dioxide adsorption tower packed with adsorbent 1 (A-type zeolite).

[0099] [Table 4]

[0100] [Results and Discussion (2)] As shown in Table 4, it was possible to recover carbon dioxide at a high concentration even when the adsorption pressure was set low. In addition, the carbon dioxide recovery rate was good, at approximately 50%. Therefore, it was found that the carbon dioxide recovery method of the present invention can efficiently recover carbon dioxide from gas with a low carbon dioxide concentration even at a low adsorption pressure.

[0101] [Carbon dioxide recovery process for water-containing mixed gases] As a process for recovering carbon dioxide from a moisture-containing mixed gas, a carbon dioxide recovery apparatus (50) equipped with a carbon dioxide recovery means (10A) and a moisture removal means (60) as shown in FIG. 4 was used, and the carbon dioxide recovery process of prototype example 14 was carried out under process condition 5 described below. In the carbon dioxide recovery process of prototype example 14, the moisture removal means performed a moisture removal cycle (moisture adsorption process, dry mixed gas delivery process, moisture washing process, moisture discharge process, and pressure increase process) to supply the dry mixed gas to the carbon dioxide recovery means, and the carbon dioxide recovery means performed a carbon dioxide recovery cycle to recover carbon dioxide from the dry mixed gas, and the concentration and gas flow rate were measured. In prototype example 14, the adsorption time was gradually increased until the measured carbon dioxide gas concentration approached 99 vol%. The results are shown in Table 5.

[0102] [Processing condition 5] For treatment condition 5, a simulated gas in a wet state (dew point 0°C) consisting of 10 vol% carbon dioxide and other gas components such as nitrogen and oxygen was used as the moisture-containing mixed gas; the supply flow rate of the moisture-containing mixed gas was 4 L / min; the internal pressure of the moisture adsorption tower in the moisture adsorption step and the internal pressure of the carbon dioxide adsorption tower in the adsorption step were 0.2 MPa; the internal pressure of the moisture adsorption tower in the pressurization step was above atmospheric pressure; and the internal pressure of the carbon dioxide adsorption tower in the desorption step was below atmospheric pressure.

[0103] [Prototype 14] Prototype example 14 is a carbon dioxide recovery process carried out under process condition 5, in which each moisture adsorption tower was filled with activated alumina ("Neobead SA" manufactured by Mizusawa Industrial Chemicals Co., Ltd.) and each carbon dioxide adsorption tower was filled with adsorbent 2 (X-type zeolite).

[0104] [Table 5]

[0105] [Results and Discussion (3)] In prototype 14, as shown in Table 5, highly concentrated carbon dioxide was able to be recovered extremely efficiently. This is thought to be because carbon dioxide was recovered in a carbon dioxide recovery cycle from a dry mixed gas that had been dried through a moisture removal process, which suppressed the effect of moisture during carbon dioxide adsorption and improved carbon dioxide recovery efficiency.

[0106] Furthermore, although the treatment conditions for Prototype Example 14 were the same as those for Prototype Example 10 except that the gas to be treated was a moisture-containing mixed gas, the carbon dioxide recovery rate was slightly lower than that of Prototype Example 10. This is thought to be because, after the dry mixed gas is supplied from the moisture adsorption tower to the carbon dioxide capture means, some of the dry mixed gas remains in the dead volume of the moisture adsorption tower and is discharged, or the moisture adsorbent adsorbs carbon dioxide in the moisture mixed gas, resulting in some of the carbon dioxide in the moisture-containing mixed gas being discharged without being supplied to the carbon dioxide capture means. Therefore, the carbon dioxide-containing gas discharged from the moisture removal means may be returned to the first moisture piping section (71) that supplies the moisture-containing mixed gas. This improves the carbon dioxide recovery rate. [Industrial Applicability]

[0107] The carbon dioxide recovery method of the present invention can recover carbon dioxide at a high concentration and with high efficiency from a mixed gas with a low carbon dioxide concentration. Therefore, it becomes possible to recover carbon dioxide from gases with low carbon dioxide concentrations, such as combustion exhaust gas, which have conventionally been discarded, thereby contributing to reducing the environmental load. [Explanation of symbols]

[0108] 10,50 Carbon dioxide capture device 10A Carbon dioxide capture measures 11 First piping section 12 Second piping section 13 Third piping section 14 Fourth piping section 15 Fifth piping section 16a~16e On-off valve 17,18 Connection 20, 20A, 20B, 20C Carbon dioxide adsorption tower 30 Carbon Dioxide Capture Section 40 Gas suction means 60 Moisture removal means 70,70A,70B Moisture adsorption tower 71 First moisture piping section 72 Second moisture piping section 73 Third moisture piping section 74 Fourth moisture piping section 76a~76d On-off valve 77,78 Connection

Claims

1. A carbon dioxide recovery method for concentrating and recovering carbon dioxide from a mixed gas such as a combustion exhaust gas containing carbon dioxide at 10 vol % or less, comprising: a plurality of carbon dioxide adsorption towers are provided, each filled with one or more of A-type zeolite, X-type zeolite, and Y-type zeolite as the carbon dioxide adsorbent; an adsorption step of introducing the mixed gas into one of the carbon dioxide adsorption towers at a pressure of atmospheric pressure or more and 0.2 MPa or less, and causing the adsorbent to adsorb the carbon dioxide in the mixed gas; a non-adsorbed gas delivery step of delivering a non-adsorbed gas that has not been adsorbed in the adsorption step; a depressurization step of discharging the remaining non-adsorbed gas present in a dead volume inside the carbon dioxide adsorption tower from the carbon dioxide adsorption tower after the adsorption step; a residual non-adsorbed gas purging step in which concentrated carbon dioxide gas is introduced into the carbon dioxide adsorption tower after the depressurization step, and the residual non-adsorbed gas remaining inside the carbon dioxide adsorption tower after the depressurization step is pushed out; a desorption step of suctioning at a pressure lower than atmospheric pressure to desorb the carbon dioxide adsorbed by the adsorbent in the carbon dioxide adsorption tower after the residual non-adsorbed gas purging step, thereby recovering concentrated carbon dioxide gas, The carbon dioxide gas used in the residual non-adsorbed gas purging step is the carbon dioxide gas obtained in the desorption step in another carbon dioxide adsorption tower. A carbon dioxide recovery method characterized by:

2. 2. The carbon dioxide recovery method according to claim 1, wherein a plurality of the carbon dioxide adsorption towers repeat the carbon dioxide recovery cycle to continuously recover the concentrated carbon dioxide gas from the mixed gas.

3. The mixed gas is a moisture-containing mixed gas containing moisture, 3. The carbon dioxide recovery method according to claim 1, further comprising a moisture removal step of removing the moisture contained in the moisture-containing mixed gas prior to the adsorption step in the carbon dioxide recovery cycle.

4. The moisture removal step A plurality of moisture adsorption towers filled with moisture adsorbent are arranged, a moisture adsorption step of delivering the moisture-containing mixed gas to one of the moisture adsorption towers at a pressure of atmospheric pressure or higher and 0.2 MPa or lower to allow the moisture to be adsorbed by the moisture adsorbent, thereby obtaining a dry mixed gas from which the moisture has been removed; a dry mixed gas delivery step of delivering the dry mixed gas to the adsorption step of the carbon dioxide capture cycle; a moisture washing step of introducing the non-adsorbed gas delivered in the non-adsorbed gas delivery step of the carbon dioxide recovery cycle into the moisture adsorption tower after the moisture adsorption step, and washing the moisture adsorbed by the moisture adsorbent in the moisture adsorption tower; a moisture discharging step of discharging the moisture-mixed non-adsorbed gas containing the moisture obtained by the moisture washing step; and a pressurization step of introducing the non-adsorbed gas delivered in the non-adsorbed gas delivery step of the carbon dioxide recovery cycle into the moisture adsorption tower after the moisture discharge step, and raising the pressure inside the moisture adsorption tower to atmospheric pressure or higher.

5. 5. The carbon dioxide recovery method according to claim 4, wherein a plurality of the carbon dioxide adsorption towers repeat the carbon dioxide recovery cycle and a plurality of the moisture adsorption towers repeat the moisture removal cycle to continuously recover the concentrated dry carbon dioxide gas from the moisture-containing mixed gas.

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