Carbon dioxide recovery 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 it 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 is captured, 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 having an adsorbent to adsorb the carbon dioxide to the adsorbent, non-adsorbed gas is discharged from the adsorption tower, and then the pressure inside the adsorption tower is reduced to less than 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 larger the pressure difference during adsorption and desorption, the easier it is to concentrate and refine the carbon dioxide.

[0004] Incidentally, combustion exhaust gases discharged from boilers, generators, etc. are mixed gases with a low carbon dioxide concentration (10 vol% or less) compared to blast furnace gas. A mixed gas containing a low concentration of carbon dioxide has a lower carbon dioxide recovery efficiency compared to a mixed gas containing a high concentration of carbon dioxide, such as blast furnace gas. In addition, when recovering carbon dioxide from this mixed gas, in the above-mentioned carbon dioxide recovery method, the adsorption pressure needs to be higher than usual in order to adsorb the low concentration of carbon dioxide from the mixed gas to the adsorbent. However, in order to increase the adsorption pressure, the adsorption pressure is increased using a compressor or other compressor, and therefore excessive power consumption is unavoidable, and the energy efficiency and work efficiency required for recovery are also worse than those of a high concentration mixed gas. Therefore, a mixed gas containing a low concentration of carbon dioxide does not have a carbon dioxide recovery efficiency commensurate with the treatment efficiency, and it has been common to discard it as it 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 consideration of the above-mentioned 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 carbon dioxide recovery method for concentrating and recovering carbon dioxide from a mixed gas containing carbon dioxide at 10 vol % or less, 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 atmospheric pressure or more and 0.2 MPa or less to adsorb the carbon dioxide in the mixed gas onto the adsorbent; a non-adsorbed gas delivery step of delivering the non-adsorbed gas that was not adsorbed in the adsorption step; and a residual 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 of introducing concentrated carbon dioxide gas into the carbon dioxide adsorption tower after the depressurization step and pushing out the remaining non-adsorbed gas remaining inside the carbon dioxide adsorption tower even after the depressurization step; 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 remaining non-adsorbed gas purging step, thereby recovering concentrated carbon dioxide gas, wherein the carbon dioxide gas used in the remaining non-adsorbed gas purging step is the carbon dioxide gas obtained by the desorption step in another carbon dioxide adsorption tower.

[0008] A second invention relates to the carbon dioxide recovery method according to 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] A third invention relates to a carbon dioxide capture method according to the first or second invention, wherein the mixed gas is a moisture-containing mixed gas containing moisture, and the carbon dioxide capture 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 a carbon dioxide capture method according to the third invention, wherein the moisture removal step includes a moisture adsorption cycle in which a plurality of moisture adsorption towers filled with a moisture adsorbent are provided, the moisture adsorption step being a moisture adsorption step of delivering the moisture-containing mixed gas to one of the moisture adsorption towers at a pressure of more than atmospheric pressure and not more than 0.2 MPa to cause the moisture to be adsorbed by the moisture adsorbent to obtain 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 nonadsorbed gas delivered by the nonadsorbed gas delivery step of the carbon dioxide capture cycle into the moisture adsorption tower after the moisture adsorption step to wash the moisture adsorbed by the moisture adsorbent in the moisture adsorption tower; a moisture discharge step of discharging the moisture-mixed nonadsorbed gas containing the moisture by the moisture washing step; and a pressurization step of introducing the nonadsorbed gas delivered by the nonadsorbed gas delivery step of the carbon dioxide capture cycle into the moisture adsorption tower after the moisture discharge step to raise the pressure inside the moisture adsorption tower to more than 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. Effect of the Invention

[0012] According to a first aspect of the present invention, there is provided a carbon dioxide recovery method for concentrating and recovering carbon dioxide from a mixed gas containing carbon dioxide at 10 vol% or less, the method 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 atmospheric pressure or more and 0.2 MPa or less 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; and 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 of introducing concentrated carbon dioxide gas into the carbon dioxide adsorption tower after the depressurization step and pushing out the remaining non-adsorbed gas remaining inside the carbon dioxide adsorption tower even after the depressurization step; 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 remaining non-adsorbed gas purging step, thereby recovering concentrated carbon dioxide gas, wherein the carbon dioxide gas used in the remaining non-adsorbed gas purging step is the carbon dioxide gas obtained in the desorption step in another carbon dioxide adsorption tower, so that 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, 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, thereby making it possible to recover carbon dioxide more efficiently.

[0014] According to the carbon dioxide capture method of the third invention, in the first or second invention, the mixed gas is a moisture-containing mixed gas that contains 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 capture cycle, so that a dry mixed gas from which moisture has been removed can be supplied to the carbon dioxide capture cycle.

[0015] According to a fourth aspect of the present invention, in the third aspect of the present invention, the moisture removal step includes a moisture adsorption step in which a plurality of moisture adsorption towers filled with a moisture adsorbent are provided, 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 to the moisture adsorbent, thereby obtaining a dry mixed gas in a dry state 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 moisture removal step in which the non-adsorbed gas delivered by the non-adsorbed gas delivery step of the carbon dioxide capture cycle is delivered to the moisture adsorption step. Since the system has a moisture removal cycle that includes a moisture washing step of introducing a 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 discharge 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 discharge step to raise the pressure inside the moisture adsorption tower to above atmospheric pressure, efficiency of operation and power saving can be achieved, and moisture can be removed from the moisture-containing mixed gas with high efficiency.

[0016] According to the carbon dioxide recovery method of the fifth invention, in the fourth invention, 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, 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 description of the drawings]

[0017] [Figure 1] FIG. 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. [Diagram 2] FIG. 2 is a first schematic diagram illustrating gas flow paths in the carbon dioxide capture device of FIG. 1 corresponding to each step of the carbon dioxide capture cycle. [Diagram 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. [Diagram 5] FIG. 5 is a first schematic diagram showing gas flow paths in the moisture removal means of the carbon dioxide capture 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 capture device of FIG. 4 corresponding to each step of the moisture removal cycle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 section 30 that captures carbon dioxide, and introduces a mixed gas containing carbon dioxide into each of the carbon dioxide adsorption towers 20 (20A, 20B, 20C) to separate and concentrate the carbon dioxide, and sends it to the carbon dioxide capture section 30 for capture.

[0019] The mixed gas to be treated is a gas containing a relatively low concentration of carbon dioxide, such as combustion exhaust gas discharged from a boiler or a generator (low carbon dioxide concentration gas). 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 gas other than carbon dioxide contained in the mixed gas is not particularly limited, but examples include gas components mainly contained in the atmosphere, such as nitrogen and oxygen. Other components such as combustion exhaust gas contain NOx and SOx, but since there is a risk of deterioration of the adsorbent, it is desirable to remove them from the mixed gas by pretreatment.

[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 selectively adsorbing carbon dioxide. In particular, X-type zeolite is more preferable because it has 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 permitted to contain trace amounts of impurities (other gas components, etc.). The non-adsorbed gas may contain trace amounts of carbon dioxide that have not been 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 mixed gases and the like are supplied, and each gas separated from the mixed gas is delivered, etc. In the figure, reference numeral 11 denotes a first piping section for supplying the mixed gas to the carbon dioxide adsorption tower 20, 12 denotes a second piping section for delivering the non-adsorbed gas from the carbon dioxide adsorption tower 20, 13 denotes a third piping section for delivering the remaining non-adsorbed gas from the carbon dioxide adsorption tower 20, 14 denotes a fourth piping section for supplying carbon dioxide gas to the carbon dioxide adsorption tower 20, 15 denotes a fifth piping section for delivering the carbon dioxide gas from the carbon dioxide adsorption tower 20, and 16a to 16e denote on-off valves for opening and closing the respective piping sections 11, 12, 13, 14, and 15.

[0023] In the carbon dioxide adsorption tower 20, each piping section can be appropriately connected, but it is preferable to share the connection section and arrange each piping section by branching from the connection section in order to simplify the structure. In the illustrated example, the first piping section 11, the fourth piping section 14, and the fifth piping section 15 are branched and 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 are branched and connected to the other side via a connection section 18. In each of the piping sections 11 to 15 connected in this manner, the corresponding gas is allowed to flow or stopped by opening and closing the on-off valve 16. Although not illustrated, various sensors such as pressure gauges that detect the pressure, concentration, etc. of the corresponding gas are appropriately provided in each of the carbon dioxide adsorption towers 20, the carbon dioxide capture section 30, each of the piping sections 11, 12, 13, 14, 15, the connection sections 17, 18, etc., as necessary.

[0024] The multiple carbon dioxide adsorption towers 20 (20A, 20B, 20C) are arranged in parallel. The number of carbon dioxide adsorption towers 20 is not particularly limited as long as there is more than one, but about three is preferable from the viewpoints of processing efficiency, installation space, cost, etc. 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 a 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 liquefying and storing, in consideration of reuse. The carbon dioxide capture unit 30 is appropriately equipped with a device for measuring the concentration of carbon dioxide, such as a gas chromatograph, and a device for measuring the amount of carbon dioxide gas, such as a flow meter, as necessary. Note that, from the viewpoint of reuse, it is preferable that the carbon dioxide concentration of the captured carbon dioxide gas is 90 vol% or more so that it can be easily liquefied.

[0026] The carbon dioxide recovery method of the present invention carried out using the above-mentioned 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 the 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, and carbon dioxide in the mixed gas is adsorbed by the adsorbent. 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 filled in the carbon dioxide adsorption tower 20, and a process in which carbon dioxide in the mixed gas is adsorbed by the adsorbent is performed. 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 high 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. In particular, X-type zeolite is preferred because it has excellent adsorption performance for low carbon dioxide concentration gas. 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 increasing 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 nonadsorbed gas delivery process is a process in which a nonadsorbed 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 nonadsorbed gas delivery process, the second piping section 12 is opened, and the nonadsorbed gas delivery process is performed integrally with the adsorption process. That is, the mixed gas introduced from the first piping section 11 is contacted with the adsorbent to adsorb carbon dioxide (adsorption process), and the gas that was not adsorbed by the adsorbent is delivered as it is from the carbon dioxide adsorption tower 20 to the second piping section 12 as a nonadsorbed gas. In the adsorption process and nonadsorbed 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 nonadsorbed 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. In 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, so that the inside of the carbon dioxide adsorption tower 20 is under a higher pressure 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 appropriately. Note that, although the remaining non-adsorbed gas is discharged through the third piping section 13 in the depressurization step, it may 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 remaining inside the carbon dioxide adsorption tower 20 even after the depressurization step is pushed out. The concentrated carbon dioxide gas introduced into the carbon dioxide adsorption tower 20 is a part of the carbon dioxide gas recovered in the carbon dioxide recovery section 30, which will be described later, and is supplied from the carbon dioxide recovery section 30 via the fourth piping section 14.

[0032] In the remaining non-adsorbed gas purging step, the third piping section 13 that was opened in the depressurization step continues to be open, and the inside of the carbon dioxide adsorption tower 20 is depressurized by the depressurization step, and the internal pressures of the carbon dioxide adsorption tower 20 and the third piping section 13 become substantially uniform, and then the supply of carbon dioxide gas is started. Since 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 manner, the carbon dioxide adsorption tower 20 becomes filled with carbon dioxide. When the discharge of the remaining non-adsorbed gas in 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 desorbing the carbon dioxide adsorbed by the adsorbent in the carbon dioxide adsorption tower 20 after the residual non-adsorbed gas purging step by sucking at a pressure lower than atmospheric pressure, and 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 less than 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 by the residual non-adsorbed gas purging step and contains almost no other gases, the carbon dioxide is concentrated at a high concentration and recovered in the carbon dioxide recovery section 30. When the desorption of carbon dioxide from the adsorbent is completed, the fifth piping section 15 is closed, and the desorption step is terminated.

[0034] In one carbon dioxide adsorption tower 20, the adsorption step, the non-adsorbed gas delivery step, the depressurization step, the residual non-adsorbed gas purging step, and the 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) are performed at different times in order to avoid interference between the gases flowing through the respective piping sections 11 to 15. In this way, by repeatedly performing the carbon dioxide capture cycle, concentrated carbon dioxide gas can be continuously captured from the mixed gas, and carbon dioxide can be more efficiently captured.

[0035] Here, the flow of the carbon dioxide capture cycle performed in the multiple carbon dioxide adsorption towers 20A, 20B, and 20C will be described mainly with reference to carbon dioxide adsorption tower 20A with reference to Figures 2 and 3. In each of piping sections 11-15 in Figures 2 and 3, the solid line sections indicate paths through which gas flows when the corresponding on-off valves 16a-16e are open, and the dashed line sections indicate piping sections through which gas does not flow when the on-off valves 16a-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 filled 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 maintained in an open state, 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 the carbon dioxide gas obtained by the desorption step in the other carbon dioxide adsorption tower. In the illustrated example, in the carbon dioxide adsorption tower 20C, the carbon dioxide gas desorbed from the adsorbent by the desorption step is recovered in the carbon dioxide capture unit 30 via the fifth piping section 15. Then, the recovered carbon dioxide gas is introduced from the carbon dioxide capture unit 30 to 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 of 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 within the carbon dioxide adsorption tower 20A, so that the mixed gas to be treated is utilized without waste, and the carbon dioxide in the carbon dioxide adsorption tower 20A can be concentrated 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 a gas for pushing out the remaining non-adsorbed gas from the other carbon dioxide adsorption towers 20B, 20C when a remaining non-adsorbed gas purge 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 purge step and filling the carbon dioxide adsorption tower 20A with carbon dioxide while discharging the remaining non-adsorbed gas, it is possible to effectively utilize the carbon dioxide obtained from the mixed gas to be treated and capture carbon dioxide 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 appropriately carried out 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 captured, and the carbon dioxide adsorption tower 20C carries out a residual non-adsorbed gas purging step in which carbon dioxide gas is introduced and the 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 section 30 is transferred to an appropriate recovery process.

[0044] When the remaining non-adsorbed gas purging step is being carried out in the carbon dioxide adsorption tower 20A shown in FIG. 3(a), the adsorption step and non-adsorbed gas delivery step are continuously carried out in the carbon dioxide adsorption tower 20B, and the desorption step is continuously carried out 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 for the remaining non-adsorbed gas purging step of the carbon dioxide adsorption tower 20A.

[0045] Furthermore, during the desorption process of the carbon dioxide adsorption tower 20A shown in FIG. 3(b), the carbon dioxide adsorption tower 20B performs a depressurization process for discharging remaining non-adsorbed gas, and the carbon dioxide adsorption tower 20C performs an adsorption process for adsorbing carbon dioxide from the mixed gas and a non-adsorbed gas delivery process for discharging 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 as long as it does not interfere with each carbon dioxide capture cycle.

[0047] A mixed gas containing carbon dioxide, such as a combustion exhaust gas, usually contains moisture. When recovering carbon dioxide from a mixed gas containing moisture, the moisture hinders the separation of carbon dioxide, reducing the efficiency of recovering the carbon dioxide, which is a problem. In addition, the recovered carbon dioxide also contains moisture, so 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 containing moisture, it is preferable to perform a moisture removal process for removing moisture contained in the moisture-containing mixed gas prior to the adsorption process of the carbon dioxide recovery cycle.

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

[0049] The moisture removal means 60 has a plurality of moisture adsorption towers 70 (70A, 70B). The moisture adsorption towers 70 are filled with a moisture adsorbent, and are processing devices that adsorb moisture from a moisture-containing mixed gas using the moisture adsorbent and separate the moisture into a dry mixed gas in a dry state. The moisture adsorbent is not particularly limited as long as it is a material that can selectively adsorb moisture easily, but for example, zeolite such as molecular sieves, activated alumina, and the like are preferably used. 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 the moisture-containing mixed gas and the like are supplied, and the dry mixed gas obtained by removing moisture from the moisture-containing mixed gas and the like are delivered. In the figure, reference numeral 71 denotes a first moisture piping section for supplying the moisture mixed gas, 72 denotes a second moisture piping section for delivering the dry mixed gas, 73 denotes a third moisture piping section for supplying the non-adsorbed gas from the carbon dioxide capture means 10A, 74 denotes a fourth moisture piping section for delivering the moisture-mixed non-adsorbed gas described below, and 76a to 76d denote opening and closing valves for opening and closing the moisture piping sections 71, 72, 73, and 74. Each moisture adsorption tower 70 and each moisture piping section 71, 72, 73, and 74 may be appropriately provided with various sensors for detecting the moisture content of the corresponding gas, as necessary.

[0051] In the moisture adsorption tower 70, each moisture piping section can be connected as appropriate, but in order to simplify the structure, it is preferable to share a connection section and arrange each moisture piping section by branching off from the connection section. In the illustrated example, a first moisture piping section 71 and a fourth moisture piping section 74 are branched and 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 are branched and 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 or stop of the corresponding gas is performed by opening or closing an on-off valve 76.

[0052] The multiple moisture adsorption towers 70 (70A, 70B) are arranged in parallel. The number of moisture adsorption towers 70 is not particularly limited as long as there is more than one, but about two is preferable from the viewpoints of processing efficiency, installation space, cost, etc. Furthermore, the moisture piping sections 71-74 connected to the moisture adsorption towers 70A, 70B are linked 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 of sending the moisture-containing mixed gas to one of the moisture adsorption towers 70 at a pressure of atmospheric pressure or more and 0.2 MPa or less to adsorb moisture to the moisture adsorbent, thereby obtaining a dry mixed gas from which 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 performing a process in which the moisture in the moisture-containing mixed gas is 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 that has been dried by removing the moisture.

[0056] The dry mixed gas delivery process is a process of delivering the dry mixed gas 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 the 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 the 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 captured at a high concentration and with high efficiency without being affected by a decrease in carbon dioxide capture efficiency due to moisture.

[0058] The moisture washing step is a step of introducing the non-adsorbed gas sent out by the non-adsorbed gas sending out step of the carbon dioxide capture cycle into the moisture adsorption tower 70 after the moisture adsorption step, and washing out 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 which moisture has been adsorbed, and the non-adsorbed gas is made to contain moisture to form a moisture-mixed non-adsorbed gas. The non-adsorbed gas sent out by the non-adsorbed gas sending out step is a dry gas that has not been adsorbed by the adsorbent out of the dry mixed gas, and therefore moisture can be easily desorbed from the moisture adsorbent by contacting it with the moisture adsorbent that has adsorbed moisture. The non-adsorbed gas is supplied to the moisture adsorption tower 70 through the third moisture piping section 73 by communicating the second piping section 12 of the carbon dioxide capture means 10A with 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 contained moisture due to 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 appropriately. 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 of introducing the non-adsorbed gas sent out by the non-adsorbed gas sending step of the carbon dioxide capture cycle into the moisture adsorption tower 70 after the moisture discharge step, thereby increasing 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, so that the pressure inside the moisture adsorption tower 70 is increased. By increasing the pressure inside the moisture adsorption tower 70 to atmospheric pressure or higher, the pressure inside the carbon dioxide capture device 50 can be maintained when the moisture adsorption step or the like is performed again in the moisture adsorption tower 70, and each step can be performed 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 one 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 these processes are repeated as one moisture removal cycle. In this case, it is preferable that the moisture removal cycle of each moisture adsorption tower 70 (70A, 70B) is performed at different timings from the viewpoint of avoiding interference between gases flowing through each moisture piping section 71-74. In addition, by repeatedly processing the carbon dioxide capture cycle and the moisture removal cycle in conjunction with each other, it is possible to continuously recover concentrated dry carbon dioxide gas from the moisture-containing mixed gas. Therefore, it is possible to recover dry carbon dioxide with higher efficiency.

[0063] Here, the flow of the moisture removal cycle performed in the multiple moisture adsorption towers 70A, 70B will be described mainly with reference to Figures 5 and 6, with the moisture adsorption tower 70A as the main focus. 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 through the first moisture piping section 71, and the moisture in the moisture-containing mixed gas is adsorbed by the moisture adsorbent filled in the moisture adsorption tower 70A (moisture adsorption step). Then, the dry mixed gas in a dry state from which the moisture has been removed by the moisture adsorbent is discharged from the moisture adsorption tower 70A through the second moisture piping section 72 (dry mixed gas delivery step). The dry mixed gas in a dry state discharged from the moisture adsorption tower 70A is supplied to the carbon dioxide capture means 10A through the second moisture piping section 72 via the first piping section 11, and a carbon dioxide capture cycle is performed using a mixed gas that does not contain moisture.

[0065] Next, as shown in Fig. 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, and the moisture adsorbed in 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, while the third moisture piping section 73 is maintained in an open state to continuously supply dry non-adsorbed gas, 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 in the moisture adsorption tower 70A, the pressure inside the carbon dioxide capture device 50 is maintained when the moisture piping section is opened again in 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 supplied to the carbon dioxide capture cycle as a dry mixed gas, so that it is 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. In addition, the dry non-adsorbed gas generated in the carbon dioxide capture cycle can be used in the moisture removal cycle to discharge moisture, so that it is possible to improve the efficiency of the work required for moisture removal, reduce power consumption, and the like, and to remove moisture from the moisture-containing mixed gas with high efficiency.

[0068] When 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, when the moisture adsorption step and the dry mixed gas delivery step are being performed in the moisture adsorption tower 70A shown in Figure 5(a), the moisture adsorption tower 70B performs a moisture washing step for desorbing moisture from the moisture adsorbent and a moisture discharge step for discharging the moisture-containing non-adsorbed gas. Although not shown, the moisture adsorption tower 70B may also perform a pressurization step.

[0069] 5(b) to 6, while the moisture washing step, moisture discharge step, and pressure increase step are being performed in the moisture adsorption tower 70A, for example, the moisture adsorption tower 70B performs a moisture adsorption step for removing moisture from a moisture-containing mixed gas, and a dry mixed gas delivery step for 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 of the moisture adsorption towers 20A, 20B is not limited to the example shown in the figure, and can be implemented within a range that does not interfere with each moisture removal cycle. EXAMPLES

[0070] [Carbon dioxide capture and 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 apparatus (10) having each of the piping sections (11 to 15) connected thereto was used to perform a carbon dioxide recovery cycle (adsorption step, non-adsorbed gas delivery step, depressurization step, residual non-adsorbed gas purging step, desorption step) based on processing conditions 1 to 3 described below, and carbon dioxide was recovered from the mixed gas. In this carbon dioxide recovery apparatus, the volume of each of the three carbon dioxide adsorption towers was set to 174 ml, and each was 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 (manufactured by Resonac Universal Co., Ltd., "Li-LSX") 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 of 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 process was 0.2 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption process was atmospheric pressure or less.

[0073] [Processing condition 2] For process condition 2, a simulated gas containing 5 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 process was 0.2 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption process was atmospheric pressure or less.

[0074] [Processing condition 3] For process 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 process was 0.2 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption process was atmospheric pressure or less.

[0075] [Prototype 1] Prototype example 1 is a carbon dioxide recovery process carried out under process condition 1, with adsorbent 1 packed in each carbon dioxide adsorption tower.

[0076] [Prototype 2] Prototype example 2 is a carbon dioxide recovery process carried out under process condition 1, with adsorbent 2 packed in each carbon dioxide adsorption tower.

[0077] [Prototype 3] Prototype example 3 is a carbon dioxide recovery process carried out under process condition 1 with each carbon dioxide adsorption tower packed with adsorbent 3.

[0078] [Prototype 4] Prototype example 4 is a carbon dioxide recovery process carried out under process condition 1 with each carbon dioxide adsorption tower packed with adsorbent 4.

[0079] [Prototype 5] Prototype example 5 is a carbon dioxide capture process carried out under process condition 2, with each carbon dioxide adsorption tower packed with adsorbent 1.

[0080] [Prototype 6] Prototype example 6 is a carbon dioxide capture process carried out under process condition 2, with each carbon dioxide adsorption tower packed with adsorbent 2.

[0081] [Prototype 7] Prototype example 7 is a carbon dioxide capture process carried out under process condition 2 with each carbon dioxide adsorption tower packed with adsorbent 3.

[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 the adsorbent 1 packed in each carbon dioxide adsorption tower.

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

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

[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 capture rate] In the carbon dioxide recovery process of prototypes 1 to 12, a device for measuring the concentration of the recovered carbon dioxide gas and a device for measuring the amount of gas 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. In addition, a mass flow meter (manufactured by Shinagawa Corporation) was used as the device for measuring the amount of carbon dioxide gas.

[0088] In the carbon dioxide recovery process of prototypes 1 to 12, a predetermined adsorption time was set, and the carbon dioxide recovery cycle was repeatedly performed during a certain processing 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 process was performed again, and the adsorption time was sequentially increased until the carbon dioxide gas concentration reached a value close to 90 vol%. From the carbon dioxide concentration and gas amount obtained in each process performed, the CO2 recovery rate (%) of prototypes 1 to 12 was calculated based on the following formula (i). The recovered CO2 concentration and CO2 recovery rate of each prototype 1 to 12 are shown in Tables 1 to 3 described later. In addition, 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 prototype examples 1 to 4 shown in Table 1 are comparisons of carbon dioxide recovery efficiencies when a mixed gas with a lower carbon dioxide concentration (3 vol%) among mixed gases (low carbon dioxide concentration gases) containing low concentrations (10 vol% or less) of carbon dioxide is used as treatment condition 1 in carbon dioxide recovery devices filled with adsorbents 1 to 4, respectively. The carbon dioxide recovery processes of prototype examples 5 to 8 shown in Table 2 are comparisons of carbon dioxide recovery efficiencies when a mixed gas with a higher carbon dioxide concentration (5 vol%) than treatment condition 1 is used. The carbon dioxide recovery processes of prototype examples 9 to 12 shown in Table 3 are comparisons of carbon dioxide recovery efficiencies when a mixed gas with an even higher carbon dioxide concentration (10 vol%) than treatment condition 2 is used.

[0094] In the prototypes 4, 8, and 12 using the adsorbent 4 (activated carbon), the concentration of the captured carbon dioxide gas did not reach 90 vol% even when the adsorption time was increased, so the capture process was discontinued. This shows that activated carbon is not suitable as an adsorbent for capturing carbon dioxide from low carbon dioxide concentration gas.

[0095] In the prototypes 1 to 3, 5 to 7, and 9 to 11 using the adsorbents 1 to 3 (zeolite), all of them were able to recover carbon dioxide gas at a high concentration (around 90 vol%). From this, it was found that A-type zeolite, X-type zeolite, and Y-type zeolite can all be suitably used as adsorbents for recovering carbon dioxide from low carbon dioxide concentration gas. In addition, when comparing the prototypes 1 to 3, 5 to 7, and 9 to 11, the prototypes 2, 6, and 10 using the adsorbent 2 (X-type zeolite) had a better carbon dioxide recovery rate than the prototypes using the other adsorbents 1 and 3. Furthermore, when comparing the prototypes 1 to 3 under the treatment condition 1 (3 vol%), the prototype 2 using the adsorbent 2 was able to recover carbon dioxide more efficiently than the prototypes 1 and 3. Therefore, it is considered that the X-type zeolite is optimal as an adsorbent for recovering carbon dioxide from low carbon dioxide concentration gas.

[0096] [Low adsorption pressure carbon dioxide capture process] Next, as a process for recovering carbon dioxide from a mixed gas by low adsorption pressure, a carbon dioxide recovery process of prototype 13 was carried out based on process condition 4 described below. The carbon dioxide recovery process of prototype 13 was carried out by gradually increasing the adsorption time until the measured carbon dioxide gas concentration reached a value close to 90 vol%, similar to prototypes 1 to 12. The results are shown in Table 4.

[0097] [Processing condition 4] For process condition 4, 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 process was 0.1 MPa, and the internal pressure of the carbon dioxide adsorption tower in the desorption process was atmospheric pressure or less.

[0098] Prototype example 13 is a carbon dioxide recovery process carried out under process 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 about 50%. Therefore, it was found that the carbon dioxide recovery method of the present invention can efficiently recover carbon dioxide from a low carbon dioxide concentration gas even at a low adsorption pressure.

[0101] [Carbon dioxide capture processing of water-containing mixed gas] As a process for recovering carbon dioxide from a moisture-containing mixed gas, a carbon dioxide recovery apparatus (50) having a carbon dioxide recovery means (10A) and a moisture removal means (60) as shown in FIG. 4 was used, and a carbon dioxide recovery process of prototype 14 was performed based on process condition 5 described below. In the carbon dioxide recovery process of prototype 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 cycle was performed in the carbon dioxide recovery means to recover carbon dioxide from the dry mixed gas, and the concentration and gas flow rate were measured. In prototype 14, the adsorption time was gradually increased until the measured carbon dioxide gas concentration reached a value close to 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 process and the internal pressure of the carbon dioxide adsorption tower in the adsorption process were 0.2 MPa, the internal pressure of the moisture adsorption tower in the pressurization process was atmospheric pressure or higher, and the internal pressure of the carbon dioxide adsorption tower in the desorption process was atmospheric pressure or lower.

[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, high-concentration carbon dioxide was able to be captured extremely efficiently. This is thought to be because carbon dioxide was captured by the carbon dioxide capture cycle from the dry mixed gas that was dried after the moisture removal process, suppressing the effect of moisture during carbon dioxide adsorption and improving the carbon dioxide capture efficiency.

[0106] In addition, although the treatment conditions of prototype 14 were the same as those of prototype 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 10. This is considered 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, so that some of the carbon dioxide in the moisture-containing mixed gas is discharged without being supplied to the carbon dioxide capture means. Therefore, the gas containing carbon dioxide 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 a gas with a low carbon dioxide concentration, such as combustion exhaust gas, which has been conventionally discarded, and can contribute to reducing the environmental load. [Explanation of symbols]

[0108] 10,50 Carbon dioxide capture device 10A Carbon dioxide capture methods 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 method for recovering carbon dioxide, comprising the steps of: concentrating and recovering carbon dioxide from a mixed gas containing carbon dioxide at 10 vol% or less, a plurality of carbon dioxide adsorption towers are provided, each of which is filled with one or more of A-type zeolite, X-type zeolite, or Y-type zeolite as an adsorbent for carbon dioxide; 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 to allow the adsorbent to adsorb the carbon dioxide in the mixed gas; a non-adsorbed gas delivery step for delivering a non-adsorbed gas that has not been adsorbed in the adsorption step; a depressurization step of discharging 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 remaining non-adsorbed gas purging step of introducing concentrated carbon dioxide gas into the carbon dioxide adsorption tower after the depressurization step, and pushing out the remaining non-adsorbed gas remaining inside the carbon dioxide adsorption tower even after the depressurization step; a desorption step of aspirating 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 by the desorption step in another carbon dioxide adsorption tower. A method for recovering carbon dioxide.

2. 2. The method for recovering carbon dioxide 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 method for recovering carbon dioxide 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 comprises: A plurality of moisture adsorption towers filled with moisture adsorbent are arranged, a moisture adsorption step of sending the moisture-containing mixed gas to one of the moisture adsorption towers at a pressure of atmospheric pressure or more and 0.2 MPa or less 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 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 to wash the moisture adsorbed by the moisture adsorbent in the moisture adsorption tower; a moisture discharge step of discharging the 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 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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