Carbon dioxide immobilization system and carbon dioxide immobilization method

Abstract

The invention provides a carbon dioxide immobilization system and a carbon dioxide immobilization method. This carbon dioxide immobilization system is provided with: a carbon dioxide recovery device for separating and extracting a second gas containing carbon dioxide at a higher concentration than that of the first gas from the first gas by means of a separation membrane module that selectively permeates carbon dioxide; a carbonate generation device that generates carbonate by reacting the carbon dioxide in the second gas extracted from the carbon dioxide recovery device with an alkaline earth compound; and a sensor for detecting the concentration of carbon dioxide in the second gas. In a carbon dioxide recovery device, a plurality of separation membrane modules are provided so as to be able to be connected in multiple stages, and the number of stages of connection of the separation membrane modules is switched so that the carbon dioxide concentration detected by a sensor is maintained within a predetermined target concentration range.

Description

Technical Field

[0001] The present disclosure relates to a carbon dioxide immobilization system and a carbon dioxide immobilization method. Background Art

[0002] As a technology for reducing carbon dioxide (hereinafter, also referred to as "CO2"), a direct air capture (DAC) technology for directly recovering CO2 in the atmosphere is known. In Patent Document 1, a direct air capture technology using a chemical absorption method in which an absorption liquid absorbs CO2 in the atmosphere for recovery is disclosed.

[0003] The recovered CO2 is immobilized by reacting with, for example, an alkaline earth compound to form a carbonate.

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2023-131882 Summary of the Invention

[0005] In the chemical absorption method disclosed in Patent Document 1 and the like, it is known that a large amount of energy is required to extract CO2 from the absorption liquid that has absorbed CO2.

[0006] Therefore, the inventors are studying a membrane separation method that is more energy-efficient than the chemical absorption method. In the membrane separation method, a separation membrane that selectively allows CO2 in the gas to pass through is used to extract a gas containing CO2 at a higher concentration.

[0007] Here, if the CO2 concentration in the gas extracted by the membrane separation method is too low, the reaction time will be prolonged when forming a carbonate to immobilize CO2. On the other hand, if the CO2 concentration in the extracted gas is too high, the remaining CO2 that does not react with the alkaline earth compound may be released into the atmosphere again when forming a carbonate to immobilize CO2.

[0008] In view of such circumstances, the present disclosure has been completed, and it provides a carbon dioxide immobilization system that can suppress the reaction time and suppress the remaining carbon dioxide when forming a carbonate to immobilize carbon dioxide.

[0009] The carbon dioxide immobilization system according to the present disclosure includes: a carbon dioxide recovery device that separates and extracts a second gas from a first gas by using a separation membrane module that selectively allows carbon dioxide to pass through, and the second gas contains carbon dioxide at a higher concentration than the first gas; a carbonate generation device that reacts carbon dioxide in the second gas extracted from the carbon dioxide recovery device with an alkaline earth compound to generate a carbonate; and a sensor that detects the carbon dioxide concentration in the second gas. In the carbon dioxide recovery device, a plurality of the separation membrane modules are provided in a manner that allows for multi-stage connection, and the connection stage number of the separation membrane modules is switched so as to maintain the carbon dioxide concentration detected by the sensor within a predetermined target concentration range.

[0010] The carbon dioxide immobilization method according to the present disclosure includes: a step of separating and extracting a second gas from a first gas by using a separation membrane module that selectively allows carbon dioxide to pass through, wherein the second gas contains carbon dioxide at a higher concentration than the first gas; and a step of reacting carbon dioxide in the extracted second gas with an alkaline earth compound to generate a carbonate. In the step of separating and extracting the second gas, the carbon dioxide concentration in the extracted second gas is detected, and the connection stage number of the plurality of separation membrane modules provided in a manner that allows for multi-stage connection is switched so as to maintain the detected carbon dioxide concentration within a predetermined target concentration range.

[0011] In one aspect of the present disclosure, the carbon dioxide concentration in the extracted second gas is detected, and the connection stage number of the plurality of separation membrane modules provided in a manner that allows for multi-stage connection is switched so as to maintain the detected carbon dioxide concentration within a predetermined target concentration range. Therefore, when generating a carbonate to immobilize carbon dioxide, the carbon dioxide concentration in the second gas can be maintained within a predetermined target concentration range, thereby suppressing the reaction time and the remaining carbon dioxide.

[0012] It may also be set that when the detected carbon dioxide concentration is lower than the predetermined target concentration range, the connection stage number of the separation membrane modules is increased, and when the carbon dioxide concentration is higher than the predetermined target concentration range, the connection stage number of the separation membrane modules is decreased.

[0013] In addition, it may also be set that the alkaline earth compound is contained in incineration ash, slag, or seawater.

[0014] According to the present disclosure, it is possible to provide a carbon dioxide immobilization system that can suppress the remaining carbon dioxide while suppressing the reaction time when generating carbonate to immobilize carbon dioxide.

[0015] The above content and other objects, features, and advantages of the present disclosure will be more fully understood from the following detailed description and the accompanying drawings given by way of illustration only. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a block diagram showing the structure of the carbon dioxide immobilization system according to the first embodiment.

[0017] Figure 2 It is a block diagram showing a detailed structure of an example of the CO2 recovery device 100.

[0018] Figure 3 It is a flowchart showing the carbon dioxide immobilization method according to the first embodiment.

[0019] Figure 4 It is for showing Figure 3 the flowchart of the CO2 concentration control method in the second gas in step ST1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] Hereinafter, specific embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the present disclosure is not limited to the following embodiments. In addition, for clarity of explanation, the following description and the accompanying drawings have been appropriately simplified.

[0021] (First Embodiment)

[0022] <Carbon Dioxide Immobilization System Structure>

[0023] First, with reference to Figure 1 the structure of the carbon dioxide immobilization system according to the first embodiment will be described. Figure 1 It is a block diagram showing the structure of the carbon dioxide immobilization system according to the first embodiment. In Figure 1 the thicker arrow marks indicate the flow of gas, and the thinner arrow marks indicate the flow of signals.

[0024] As Figure 1 shown, the carbon dioxide immobilization system according to the present embodiment includes a CO2 recovery device 100, a carbonate generation device 200, and a sensor S. Here, the CO2 recovery device 100 includes a CO2 separation unit 101 and a controller 102.

[0025] The CO2 recovery device 100 is, for example, a direct air capture device that uses a separation membrane that selectively allows CO2 to pass through. In the CO2 recovery device 100, the CO2 separation unit 101 using a separation membrane module that selectively allows CO2 to pass through separates and extracts a second gas from a first gas, where the second gas contains carbon dioxide at a higher concentration than the first gas. Here, the first gas is not limited to the atmosphere and also includes exhaust gases from factories, automobiles, etc. The gas other than CO2 in the first gas passes through the CO2 separation unit 101 and is discharged as a permeate gas.

[0026] Here, Figure 2 is a block diagram showing a detailed structure of an example of the CO2 recovery device 100.

[0027] As Figure 2 shown, the CO2 separation unit 101 in the CO2 recovery device 100 includes separation membrane modules SM1 to SM3, suction pumps P1 to P3, and three-way valves V1, V2. The suction pumps P1 to P3 and the three-way valves V1, V2 are controlled by a controller 102, for example. In Figure 2 it, the thicker arrow marks indicate the flow of gas, and the thinner arrow marks indicate the flow of signals.

[0028] The separation membrane modules SM1 to SM3 selectively allow CO2 to pass through the separation membrane. In the separation membrane modules SM1 to SM3, for example, a plurality of hollow filamentous separation membranes extending across both ends are bundled and filled in a cylindrical container.

[0029] As Figure 2 shown, the first gas is introduced into one end of the separation membrane module SM1 and passes through the inside of the separation membrane module SM1. A suction pump P1 is connected to the outer peripheral surface at the other end of the separation membrane module SM1. By the suction pump P1, the CO2 in the first gas passing through the inside of the separation membrane module SM1 passes through the hollow filamentous separation membrane and is extracted to the outside of the separation membrane module SM1. The gas extracted from the separation membrane module SM1 contains CO2 at a higher concentration than the first gas. On the other hand, the gas from which CO2 has been removed is discharged as a permeate gas from the other end of the separation membrane module SM1.

[0030] As Figure 2 shown, the gas extracted from the separation membrane module SM1 can be directly supplied as the second gas to the carbonate production device 200 via the three-way valve V1. On the other hand, the gas extracted from the separation membrane module SM1 can be introduced into one end of the separation membrane module SM2 via the three-way valve V1. That is, by the three-way valve V1, the supply destination of the gas extracted from the separation membrane module SM1 is switched to either the carbonate production device 200 or the separation membrane module SM2.

[0031] A suction pump P2 is connected to the outer peripheral surface at the other end of the separation membrane module SM2. By means of the suction pump P2, CO2 in the gas passing through the inside of the separation membrane module SM2 passes through the hollow filamentous separation membrane and is extracted to the outside of the separation membrane module SM2. The gas extracted from the separation membrane module SM2 contains CO2 at a higher concentration compared to the gas extracted from the separation membrane module SM1. On the other hand, the gas from which CO2 has been removed is discharged as the passing gas from the other end of the separation membrane module SM2.

[0032] As Figure 2 shown, the gas extracted from the separation membrane module SM2 can be directly supplied as the second gas to the carbonate generation device 200 via the three-way valve V2. On the other hand, the gas extracted from the separation membrane module SM2 can be introduced into one end of the separation membrane module SM3 via the three-way valve V2. That is, by means of the three-way valve V2, the supply destination of the gas extracted from the separation membrane module SM2 is switched to either the carbonate generation device 200 or the separation membrane module SM3.

[0033] A suction pump P3 is connected to the outer peripheral surface at the other end of the separation membrane module SM3. By means of the suction pump P3, CO2 in the gas passing through the inside of the separation membrane module SM3 passes through the hollow filamentous separation membrane and is extracted to the outside of the separation membrane module SM3. The gas extracted from the separation membrane module SM3 is supplied to the carbonate generation device 200 and contains CO2 at a higher concentration compared to the gas extracted from the separation membrane module SM2. On the other hand, the gas from which CO2 has been removed is discharged as the passing gas from the other end of the separation membrane module SM3.

[0034] Thus, in the CO2 recovery device 100, the plurality of separation membrane modules SM1 to SM3 are arranged in a manner that enables multi-stage connection. Moreover, by switching the number of connection stages of the separation membrane modules SM1 to SM3, the CO2 concentration in the second gas can be changed. As described above, the more the number of connection stages of the separation membrane modules SM1 to SM3, the higher the CO2 concentration in the second gas, and the fewer the number of connection stages of the separation membrane modules SM1 to SM3, the lower the CO2 concentration in the second gas.

[0035] In addition, of course, the number of separation membrane modules that can be multi-stage connected is not limited to Figure 2 the three shown, and as long as there are a plurality of them. The more the number of separation membrane modules that can be multi-stage connected, the more the CO2 concentration in the second gas can be controlled in multiple stages. Here, as Figure 2As shown, a suction pump is provided for each separation membrane module, and a three-way valve is provided between adjacent separation membrane modules. In addition, the switching unit for the supply destination of the gas extracted from the separation membrane module is not limited to Figure 2 the three-way valve shown. For example, it may also be constituted by two on-off valves.

[0036] As Figure 1 and Figure 2 shown, the controller 102 controls the CO2 separation unit 101 based on the CO2 concentration in the second gas detected by the sensor S. More specifically, the controller 102 switches the connection stages of the separation membrane modules SM1 to SM3 in such a way that the CO2 concentration in the second gas detected by the sensor S is maintained within a predetermined target concentration range.

[0037] Here, when the CO2 concentration detected by the sensor S is lower than the predetermined target concentration range, the reaction time for generating carbonate in the carbonate generation device 200 may become longer. Therefore, the controller 102 increases the connection stages of the separation membrane modules SM1 to SM3 to increase the CO2 concentration in the second gas.

[0038] On the other hand, when the CO2 concentration detected by the sensor S is higher than the predetermined target concentration range, the remaining CO2 that does not react with the alkaline earth compound in the carbonate generation device 200 may be released into the atmosphere again. Therefore, the controller 102 reduces the connection stages of the separation membrane modules SM1 to SM3 to reduce the CO2 concentration in the second gas.

[0039] In Figure 2 the CO2 recovery device 100 shown, the controller 102 controls the three-way valves V1 and V2 to switch the connection stages of the separation membrane modules SM1 to SM3.

[0040] For example, when the controller 102 switches the three-way valve V1 to connect the separation membrane module SM2 to the separation membrane module SM1, in addition to the suction pump P1, the suction pump P2 is also driven.

[0041] In addition, when the controller 102 switches the three-way valve V2 to further connect the separation membrane module SM3 to the separation membrane module SM2 connected to the separation membrane module SM1, in addition to the suction pumps P1 and P2, the suction pump P3 is also driven.

[0042] With such a structure, in Figure 2 the CO2 recovery device 100 shown, the connection stages of the separation membrane modules SM1 to SM3 are switched to 1 to 3 stages.

[0043] Here, although not shown in Figure 1 , the controller 102 includes, for example, an arithmetic unit such as a CPU (Central Processing Unit), and memories such as a RAM (Random Access Memory) and a ROM (Read Only Memory) that store various programs, data, etc. That is, the controller 102 has the function of a computer and performs various processes based on the above-mentioned various programs, etc.

[0044] The carbonate generation device 200 is introduced with the second gas extracted from the CO2 recovery device 100, and causes the CO2 in the second gas to react with an alkaline earth compound to generate a carbonate. Here, the carbonate is a carbonate of an alkaline earth metal and includes bicarbonate or hydrate.

[0045] Although the alkaline earth compound itself can also be added, from the viewpoint of reducing the environmental load, it is preferable to use incineration ash, slag, seawater, etc. Incineration ash, etc. can be used directly, or incineration ash, etc. from which compounds that hinder CO2 immobilization have been removed in advance can be used. That is, for incineration ash, etc., as long as CO2 immobilization can be carried out, it is okay to contain components other than alkaline earth compounds.

[0046] The alkaline earth compound is a compound containing an alkaline earth metal element, and is, for example, a water-soluble alkaline earth compound. Examples of the water-soluble alkaline earth compound include alkaline earth metal oxides, alkaline earth metal nitrates, alkaline earth metal hydroxides, and mixtures of these substances.

[0047] Preferred examples of the alkaline earth metal include Be, Ca, Mg, Sr, Ba, Ra, or a combination thereof. Preferred examples of the alkaline earth metal oxide include CaO, MgO, SrO, BaO, or a combination thereof. As the alkaline earth metal nitrate, examples include Ca(NO3)2, Mg(NO3)2, Sr(NO3)2, Ba(NO3)2, or a combination thereof. As the alkaline earth metal hydroxide, examples include Ca(OH)2, Mg(OH)2, Sr(OH)2, Ba(OH)2, or a combination thereof. Specific examples of the carbonate include CaCO3, MgCO3, SrCO3, BaCO3, or a combination thereof.

[0048] When water is used as the solvent and the incineration ash contains calcium oxide, for example, carbonate ions are consumed through the following reaction to generate a carbonate.

[0049] CaO + H2O → Ca2+ +2OH -

[0050] CO2 + H2O → 2H + + CO3 2-

[0051] Ca 2+ + CO3 2- → CaCO3

[0052] As Figure 1 shown, the sensor S detects the CO2 concentration in the second gas. Although there are no restrictions on the sensor S as long as it can detect the CO2 concentration in the gas, for example, it can be a CO2 concentration meter, a CO2 concentration analyzer, etc. The sensor S is not limited to a CO2 concentration meter, a CO2 concentration analyzer, etc., and can also be a sensor that can indirectly detect the CO2 concentration in the second gas.

[0053] The target concentration range of the CO2 concentration is a concentration range that can suppress the reaction time with the alkaline earth compound while suppressing the remaining CO2 that does not react with the alkaline earth compound. The target concentration range of the CO2 concentration is appropriately determined according to the concentration of the alkaline earth compound in the carbonate generation device 200, etc., and can be appropriately changed according to the progress of the reaction with the alkaline earth compound, etc.

[0054] As described above, in the carbon dioxide immobilization system according to the present embodiment, the connection stages of the separation membrane modules SM1 to SM3 are switched so as to maintain the CO2 concentration in the second gas extracted from the CO2 recovery device 100 within a predetermined target concentration range. Therefore, when generating carbonate to immobilize CO2, the CO2 in the second gas can be maintained within a predetermined target concentration range, so that the remaining CO2 can be suppressed while suppressing the reaction time.

[0055] <Carbon Dioxide Immobilization Method>

[0056] Next, with reference to Figure 3 the carbon dioxide immobilization method according to the first embodiment will be described. Figure 3 is a flowchart showing the carbon dioxide immobilization method according to the first embodiment. When explaining Figure 3 reference will be appropriately made to Figure 1 and Figure 2 .

[0057] First, as Figure 3As shown, by using separation membrane modules SM1 to SM3 that selectively allow CO2 to pass through, a second gas is separated and extracted from a first gas, where the second gas contains CO2 at a higher concentration than the first gas (step ST1).

[0058] Then, as Figure 3 shown, in Figure 1 the carbonate generation device 200 shown, CO2 in the second gas reacts with an alkaline earth compound to generate a carbonate (step ST2).

[0059] In the carbon dioxide immobilization method according to the present embodiment, in step ST1, the CO2 separation unit 101 is controlled based on the CO2 concentration in the second gas detected by the sensor S. More specifically, the controller 102 switches the connection stages of the separation membrane modules SM1 to SM3 in such a way that the CO2 concentration in the second gas detected by the sensor S is maintained within a predetermined target concentration range.

[0060] Here, Figure 4 is a flowchart showing the method for controlling the CO2 concentration in the second gas in Figure 3 step ST1.

[0061] First, as Figure 4 shown, when step ST1 starts, the CO2 concentration in the second gas is detected by the sensor S (step ST11).

[0062] Next, the controller 102 determines whether the detected CO2 concentration is equal to or higher than the lower limit of the predetermined target concentration range (step ST12). If the detected CO2 concentration is lower than the lower limit of the target concentration range (in step ST12, "no"), the reaction time for generating the carbonate in the carbonate generation device 200 may become longer. Therefore, the controller 102 increases the connection stages of the separation membrane modules SM1 to SM3 to increase the CO2 concentration in the second gas (step ST13). After that, if step ST1 has not ended, it returns to step ST11.

[0063] On the other hand, when the detected CO2 concentration is equal to or higher than the lower limit of the target concentration range (in step ST12, "yes"), the controller 102 determines whether the detected CO2 concentration is equal to or lower than the upper limit of the predetermined target concentration range (step ST14).

[0064] When the detected CO2 concentration is relatively high compared to the upper limit of the predetermined target concentration range (No in step ST14), the remaining CO2 that does not react with the alkaline earth compound in the carbonate generation device 200 may be released into the atmosphere again. Therefore, the controller 102 reduces the number of connected stages of the separation membrane modules SM1 to SM3 to lower the CO2 concentration in the second gas (step ST15). After that, if step ST1 has not ended, it returns to step ST11.

[0065] When the detected CO2 concentration is below the upper limit of the predetermined target concentration range (Yes in step ST14), if step ST1 has not ended, it directly returns to step ST11.

[0066] As Figure 4 shown, from the start to the end of step ST1, the controller 102 repeatedly executes the processes of steps ST11 to ST15 described above.

[0067] In addition, the determination in step ST12 and the step ST13 of increasing the number of connected stages of the separation membrane module are a group. Furthermore, the determination in step ST14 and the step ST15 of reducing the number of connected stages of the separation membrane module are a group. Although in Figure 4 for convenience, the determination in step ST12 is implemented first, but the determination in step ST14 can also be implemented first, or the determinations in steps ST12 and ST14 can be implemented simultaneously.

[0068] As described above, in the carbon dioxide immobilization method according to the present embodiment, the number of connected stages of the separation membrane modules SM1 to SM3 is switched in such a way that the CO2 concentration in the second gas extracted in step ST1 is maintained within the predetermined target concentration range. Therefore, when generating carbonate to immobilize CO2, the CO2 in the second gas can be maintained within the predetermined target concentration range, thereby suppressing the reaction time and the remaining CO2 at the same time.

[0069] This disclosure contributes to carbon neutrality, decarbonization, and the Sustainable Development Goals (SDGs).

[0070] It is clearly understood from the disclosure described in this way that the disclosed embodiments can be changed in various ways. Obviously, such changes should not be regarded as departing from the spirit and scope of the present invention, and for those skilled in the art, all such changes should be included in the appended claims.

Claims

1. A carbon dioxide immobilization system, comprising: A carbon dioxide recovery device that separates and extracts a second gas from a first gas using a separation membrane module that selectively allows carbon dioxide to pass through, and the second gas contains carbon dioxide at a higher concentration than the first gas; A carbonate generation device that reacts carbon dioxide in the second gas extracted from the carbon dioxide recovery device with an alkaline earth compound to generate a carbonate; A sensor that detects the carbon dioxide concentration in the second gas, In the carbon dioxide recovery device, a plurality of the separation membrane modules are provided in a manner that allows for multi-stage connection, The connection stage number of the separation membrane module is switched in such a way that the carbon dioxide concentration detected by the sensor is maintained within a predetermined target concentration range.

2. The carbon dioxide immobilization system according to claim 1, wherein, When the carbon dioxide concentration detected by the sensor is lower than the predetermined target concentration range, the connection stage number of the separation membrane module is increased, and when the carbon dioxide concentration is higher than the predetermined target concentration range, the connection stage number of the separation membrane module is decreased.

3. The carbon dioxide immobilization system according to claim 1 or 2, wherein, The alkaline earth compound is contained in incineration ash or slag or seawater.

4. A carbon dioxide immobilization method, comprising: A step of separating and extracting a second gas from a first gas using a separation membrane module that selectively permeates carbon dioxide, wherein, The second gas contains carbon dioxide at a higher concentration than the first gas; A step of reacting carbon dioxide in the extracted second gas with an alkaline earth compound to generate a carbonate, In the step of separating and extracting the second gas, The carbon dioxide concentration in the extracted second gas is detected, The connection stage number of the plurality of separation membrane modules provided in a manner that allows for multi-stage connection is switched in such a way that the detected carbon dioxide concentration is maintained within a predetermined target concentration range.

5. The carbon dioxide immobilization method according to claim 4, wherein, When the detected carbon dioxide concentration is lower than the predetermined target concentration range, the connection stage number of the separation membrane module is increased, and when the carbon dioxide concentration is higher than the predetermined target concentration range, the connection stage number of the separation membrane module is decreased.

6. The carbon dioxide immobilization method according to claim 4 or 5, wherein, The alkaline earth compound is contained in incineration ash or slag or seawater.

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