Carbon dioxide immobilization system and carbon dioxide immobilization method

Abstract

To provide a carbon dioxide immobilization system capable of suppressing excess carbon dioxide while reducing the reaction time during the formation of carbonate for carbon dioxide immobilization.SOLUTION: A carbon dioxide immobilization system includes: a carbon dioxide capture apparatus configured to separate, using a separation membrane module that selectively allows carbon dioxide, from a first gas a second gas containing a higher concentration of carbon dioxide than the first gas does and extract the separated second gas; a carbonate generation apparatus configured to cause carbon dioxide in the second gas extracted from the carbon dioxide capture apparatus to be reacted with an alkaline earth compound to generate carbonate; and a sensor configured to detect a concentration of carbon dioxide in the second gas. In the carbon dioxide capture apparatus, a plurality of the separation membrane modules are provided so as to be connected to each other in multiple stages, and the number of connection stages of the separation membrane modules is switched in such a way that the concentration of carbon dioxide detected by the sensor is maintained within a predetermined target concentration range.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Direct air capture (DAC) technology, which directly captures CO2 from the atmosphere, is known as a technology for reducing carbon dioxide (hereinafter also referred to as CO2). Patent Document 1 discloses a direct air capture technology that uses a chemical absorption method, in which CO2 from the atmosphere is absorbed in an absorption liquid and captured. The captured CO2 is immobilized, for example, by reacting it with alkaline earth compounds to form carbonates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-131882 Summary of the Invention [Problem to be solved by the invention]

[0004] It is known that the chemical absorption method disclosed in Patent Document 1 and the like requires a large amount of energy to extract CO2 from the absorbing solution that has absorbed CO2. Therefore, the inventors are investigating membrane separation, which is more energy efficient than chemical absorption.Membrane separation uses a separation membrane that selectively allows CO2 in the gas to permeate, extracting gas with a higher concentration of CO2.

[0005] If the CO2 concentration in the gas extracted by membrane separation is too low, the reaction time when carbonates are generated and CO2 is fixed increases.On the other hand, if the CO2 concentration in the extracted gas is too high, there is a risk that excess CO2 that does not react with alkaline earth compounds will be released back into the atmosphere.

[0006] The present disclosure has been made in consideration of the above circumstances, and provides a carbon dioxide fixation system that can suppress excess carbon dioxide while reducing the reaction time when producing carbonates and fixing carbon dioxide. [Means for solving the problem]

[0007] The carbon dioxide fixation system according to the present disclosure comprises: a carbon dioxide recovery device that separates and extracts a second gas from a first gas, the second gas containing carbon dioxide at a higher concentration than the first gas, using a separation membrane module that selectively allows carbon dioxide to permeate; a carbonate generator that generates carbonate by reacting carbon dioxide in the second gas extracted from the carbon dioxide recovery unit with an alkaline earth compound; a sensor for detecting a carbon dioxide concentration in the second gas; In the carbon dioxide recovery apparatus, a plurality of the separation membrane modules are provided so as to be connectable in multiple stages, The number of connected stages 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.

[0008] The carbon dioxide fixation method according to the present disclosure includes: a step of separating and extracting a second gas containing carbon dioxide at a higher concentration than the first gas from the first gas using a separation membrane module that selectively allows carbon dioxide to permeate; and a step of reacting the carbon dioxide in the extracted second gas with an alkaline earth compound to produce a carbonate, In the step of separating and extracting the second gas, Detecting the carbon dioxide concentration in the extracted second gas; The number of connected stages of the separation membrane modules, which are provided in a multi-stage connectable manner, is switched so as to maintain the detected carbon dioxide concentration within a predetermined target concentration range.

[0009] In one aspect of the present disclosure, the carbon dioxide concentration in the extracted second gas is detected, and the number of connected stages of a plurality of separation membrane modules that can be connected in multiple stages is switched so as to maintain the detected carbon dioxide concentration within a predetermined target concentration range. Therefore, when producing carbonate to fix carbon dioxide, the carbon dioxide concentration in the second gas can be maintained within the predetermined target concentration range, and excess carbon dioxide can be suppressed while shortening the reaction time.

[0010] If the detected carbon dioxide concentration is lower than the predetermined target concentration range, the number of connected stages of separation membrane modules may be increased, and if the detected carbon dioxide concentration is higher than the predetermined target concentration range, the number of connected stages of separation membrane modules may be decreased. The alkaline earth compound may also be one contained in incineration ash, slag, or seawater. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a carbon dioxide fixation system that can reduce the reaction time and suppress excess carbon dioxide when producing carbonates and fixing carbon dioxide. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram showing the configuration of a carbon dioxide fixation system according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing a detailed configuration of an example of a CO2 recovery device 100. [Figure 3] 1 is a flowchart showing a carbon dioxide fixation method according to a first embodiment. [Figure 4] 4 is a flowchart showing a method for controlling the CO2 concentration in the second gas in step ST1 of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, specific embodiments of the present disclosure will be described in detail with reference to the drawings. However, the present disclosure is not limited to the following embodiments. In addition, the following description and drawings have been simplified as appropriate for clarity of explanation.

[0014] (First embodiment) <Configuration of carbon dioxide fixation system> First, the configuration of a carbon dioxide fixation system according to a first embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of a carbon dioxide fixation system according to a first embodiment. In Fig. 1, thick arrows indicate gas flows, and thin arrows indicate signal flows.

[0015] 1, the carbon dioxide fixation system according to this embodiment includes a CO2 capture device 100, a carbonate generation device 200, and a sensor S. Here, the CO2 capture device 100 includes a CO2 separation unit 101 and a controller 102.

[0016] The CO2 capture device 100 is, for example, a direct air capture device that uses a separation membrane that selectively allows CO2 to permeate. In the CO2 capture device 100, a CO2 separation unit 101 that uses a separation membrane module that selectively allows CO2 to permeate separates and extracts a second gas that contains a higher concentration of carbon dioxide than the first gas from the first gas. Here, the first gas is not limited to the atmosphere but also includes exhaust gases from factories, cars, etc. Gases in the first gas other than CO2 pass through the CO2 separation unit 101 and are discharged as passed gas.

[0017] FIG. 2 is a block diagram showing a detailed configuration of an example of the CO2 recovery device 100. As shown in FIG. As shown in Fig. 2, the CO2 separation unit 101 in the CO2 recovery apparatus 100 includes separation membrane modules SM1 to SM3, suction pumps P1 to P3, and three-way valves V1 and V2. The suction pumps P1 to P3 and the three-way valves V1 and V2 are controlled by, for example, a controller 102. In Fig. 2, thick arrows indicate the flow of gas, and thin arrows indicate the flow of signals.

[0018] The separation membrane modules SM1 to SM3 selectively allow CO2 to permeate through separation membranes. In the separation membrane modules SM1 to SM3, for example, a cylindrical container is filled with a large number of bundled hollow fiber separation membranes that extend to both ends.

[0019] As shown in FIG. 2, a first gas is introduced into one end of the separation membrane module SM1 and passes through the interior 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. The suction pump P1 causes CO2 in the first gas passing through the interior of the separation membrane module SM1 to pass through the hollow fiber separation membranes and be extracted to the outside of the separation membrane module SM1. The gas extracted from the separation membrane module SM1 contains a higher concentration of CO2 than the first gas. On the other hand, the gas from which CO2 has been removed is discharged from the other end of the separation membrane module SM1 as a passing gas.

[0020] 2, the gas extracted from separation membrane module SM1 can be supplied as a second gas directly to the carbonate production apparatus 200 via the three-way valve V1. On the other hand, the gas extracted from separation membrane module SM1 can be introduced into one end of separation membrane module SM2 via the three-way valve V1. That is, the three-way valve V1 can switch the supply destination of the gas extracted from separation membrane module SM1 between the carbonate production apparatus 200 and the separation membrane module SM2.

[0021] A suction pump P2 is connected to the outer peripheral surface at the other end of the separation membrane module SM2. The suction pump P2 causes CO2 in the gas passing through the interior of the separation membrane module SM2 to pass through the hollow fiber separation membranes and be extracted to the outside of the separation membrane module SM2. The gas extracted from the separation membrane module SM2 contains a higher concentration of CO2 than the gas extracted from the separation membrane module SM1. On the other hand, the gas from which CO2 has been removed is discharged from the other end of the separation membrane module SM2 as a passing gas.

[0022] 2, the gas extracted from separation membrane module SM2 can be supplied as a second gas directly to the carbonate production apparatus 200 via the three-way valve V2. On the other hand, the gas extracted from separation membrane module SM2 can be introduced into one end of separation membrane module SM3 via the three-way valve V2. That is, the three-way valve V2 can switch the supply destination of the gas extracted from separation membrane module SM2 between the carbonate production apparatus 200 and the separation membrane module SM3.

[0023] A suction pump P3 is connected to the outer peripheral surface at the other end of the separation membrane module SM3. The suction pump P3 causes CO2 in the gas passing through the interior of the separation membrane module SM3 to pass through the hollow fiber separation membranes and be extracted to the outside of the separation membrane module SM3. The gas extracted from the final separation membrane module SM3 is supplied to the carbonate production device 200 and contains a higher concentration of CO2 than the gas extracted from the separation membrane module SM2. On the other hand, the gas from which CO2 has been removed is discharged from the other end of the separation membrane module SM3 as a passing gas.

[0024] In this way, the CO2 recovery system 100 is provided with a plurality of separation membrane modules SM1-SM3 that can be connected in multiple stages. The CO2 concentration in the second gas can be changed by switching the number of connected separation membrane modules SM1-SM3. As described above, the more connected separation membrane modules SM1-SM3, the higher the CO2 concentration in the second gas, and the fewer connected separation membrane modules SM1-SM3, the lower the CO2 concentration in the second gas.

[0025] Naturally, the number of separation membrane modules that can be connected in multiple stages is not limited to three as shown in FIG. 2, and may be any number. The more separation membrane modules that can be connected in multiple stages, the more stages the CO2 concentration in the second gas can be controlled. Here, as shown in FIG. 2, a suction pump is provided for each separation membrane module, and a three-way valve is provided between adjacent separation membrane modules. Furthermore, the means for switching the supply destination of the gas extracted from the separation membrane module is not limited to the three-way valve shown in FIG. 2, and may be composed of, for example, two on-off valves.

[0026] 1 and 2, 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 number of connected stages of separation membrane modules SM1 to SM3 so as to maintain the CO2 concentration in the second gas detected by the sensor S within a predetermined target concentration range.

[0027] Here, if the CO2 concentration detected by the sensor S is lower than a predetermined target concentration range, there is a risk that the reaction time for producing carbonate will be longer in the carbonate production device 200. Therefore, the controller 102 increases the number of connected stages of the separation membrane modules SM1 to SM3 so as to increase the CO2 concentration in the second gas.

[0028] On the other hand, if the CO2 concentration detected by the sensor S is higher than the predetermined target concentration range, there is a risk that excess CO2 that does not react with the alkaline earth compound in the carbonate production device 200 will be released back into the atmosphere. Therefore, the controller 102 reduces the number of connected stages of the separation membrane modules SM1 to SM3 so as to lower the CO2 concentration in the second gas.

[0029] In the CO2 recovery system 100 shown in FIG. 2, the controller 102 controls the three-way valves V1 and V2 to switch the number of connected stages of the separation membrane modules SM1 to SM3. For example, when the three-way valve V1 is switched so that the separation membrane module SM2 is connected to the separation membrane module SM1, the controller 102 drives the suction pump P2 in addition to the suction pump P1.

[0030] Furthermore, when the three-way valve V2 is switched so that a separation membrane module SM3 is further connected to the separation membrane module SM2 connected to the separation membrane module SM1, the controller 102 drives the suction pump P3 in addition to the suction pumps P1 and P2. With this configuration, in the CO2 recovery apparatus 100 shown in FIG. 2, the number of connected separation membrane modules SM1 to SM3 can be switched between one and three stages.

[0031] 1, the controller 102 includes a calculation 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, various data including the above maps, etc. In other words, the controller 102 functions as a computer and executes various processes based on the above various programs, etc.

[0032] The carbonate generation device 200 receives the second gas extracted from the CO2 recovery device 100 and reacts CO2 in the second gas with alkaline earth compounds to generate carbonates. Here, the carbonates are carbonates of alkaline earth metals, including bicarbonates and hydrates.

[0033] The alkaline earth compound may be added as it is, but it is preferable to use incineration ash, slag, seawater, or the like from the viewpoint of reducing the environmental load. Incineration ash may be used as is, or incineration ash from which compounds that interfere with CO2 fixation have been removed in advance may be used. In other words, as long as the incineration ash can fix CO2, it does not matter if it contains components other than alkaline earth compounds.

[0034] The alkaline earth compound is a compound containing an alkaline earth metal element, such as a water-soluble alkaline earth compound, including alkaline earth metal oxides, alkaline earth metal nitrates, alkaline earth metal hydroxides, and mixtures thereof.

[0035] Suitable examples of alkaline earth metals include Be, Ca, Mg, Sr, Ba, Ra, or a combination thereof. Suitable examples of alkaline earth metal oxides include CaO, MgO, SrO, BaO, or a combination thereof. Suitable examples of alkaline earth metal nitrates include Ca(NO3)2, Mg(NO3)2, Sr(NO3)2, Ba(NO3)2, or a combination thereof. Suitable examples of alkaline earth metal hydroxides include Ca(OH)2, Mg(OH)2, Sr(OH)2, Ba(OH)2, or a combination thereof. Specific examples of carbonates include CaCO3, MgCO3, SrCO3, BaCO3, or a combination thereof.

[0036] When water is used as a solvent and the incineration ash contains calcium oxide, for example, carbonate ions are consumed by the following reaction to produce carbonates. CaO+H2O→Ca 2+ +2OH - CO2+H2O→2H + +CO3 2- Ca 2+ +CO3 2- →CaCO3

[0037] 1, the sensor S detects the CO2 concentration in the second gas. The sensor S is not limited in any way as long as it can detect the CO2 concentration in the gas, and may be, for example, 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 may also be a sensor that can indirectly detect the CO2 concentration in the second gas.

[0038] The target CO2 concentration range is a concentration range that can reduce the reaction time with the alkaline earth compound while suppressing excess CO2 that does not react with the alkaline earth compound. The target CO2 concentration range is determined appropriately depending on the concentration of the alkaline earth compound in the carbonate production device 200, and can be changed appropriately depending on the progress of the reaction with the alkaline earth compound, etc.

[0039] As described above, in the carbon dioxide fixation system according to this embodiment, the number of connected stages of separation membrane modules SM1 to SM3 is 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 carbonates are produced to fix CO2, the CO2 in the second gas can be maintained within a predetermined target concentration range, and excess CO2 can be suppressed while reducing the reaction time.

[0040] <Carbon dioxide fixation method> Next, the carbon dioxide fixation method according to the first embodiment will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the carbon dioxide fixation method according to the first embodiment. In describing Fig. 3, Fig. 1 and Fig. 2 will be referred to as appropriate.

[0041] First, as shown in FIG. 3, separation membrane modules SM1 to SM3 that selectively allow CO2 to permeate are used to separate and extract a second gas that contains CO2 at a higher concentration than the first gas (step ST1). Then, as shown in FIG. 3, in the carbonate producing device 200 shown in FIG. 1, CO2 in the second gas is reacted with the alkaline earth compound to produce carbonate (step ST2).

[0042] In the carbon dioxide fixation method according to this 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 number of connected stages of the separation membrane modules SM1 to SM3 so as to maintain the CO2 concentration in the second gas detected by the sensor S within a predetermined target concentration range.

[0043] FIG. 4 is a flowchart showing a method for controlling the CO2 concentration in the second gas in step ST1 of FIG. First, as shown in FIG. 4, when step ST1 is started, the CO2 concentration in the second gas is detected by the sensor S (step ST11).

[0044] Next, the controller 102 determines whether the CO2 concentration detected by the sensor S is equal to or higher than the lower limit of a predetermined target concentration range (step ST12). If the detected CO2 concentration is lower than the lower limit of the target concentration range (NO in step ST12), the reaction time for producing carbonate in the carbonate production device 200 may become longer. Therefore, the controller 102 increases the number of connected stages of the separation membrane modules SM1 to SM3 so as to increase the CO2 concentration in the second gas (step ST13). Thereafter, if step ST1 is not completed, the process returns to step ST11.

[0045] On the other hand, if the detected CO2 concentration is equal to or higher than the lower limit of the target concentration range (YES in step ST12), 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).

[0046] If the detected CO2 concentration is higher than the upper limit of the predetermined target concentration range (NO in step ST14), there is a risk that excess CO2 that does not react with the alkaline earth compound in the carbonate production device 200 will be released back into the atmosphere. Therefore, the controller 102 reduces the number of connected stages of separation membrane modules SM1 to SM3 so as to lower the CO2 concentration in the second gas (step ST15). Thereafter, if step ST1 is not completed, the process returns to step ST11.

[0047] If the detected CO2 concentration is equal to or lower than the upper limit of the predetermined target concentration range (YES in step ST14), and step ST1 has not ended, the process returns to step ST11. As shown in FIG. 4, the controller 102 repeatedly executes the processes of steps ST11 to ST15 described above from the start to the end of step ST1.

[0048] The determination in step ST12 and step ST13 for increasing the number of connected stages of separation membrane modules are performed as a set. The determination in step ST14 and step ST15 for decreasing the number of connected stages of separation membrane modules are performed as a set. In Fig. 4, the determination in step ST12 is performed first for convenience, but the determination in step ST14 may be performed first, or the determinations in steps ST12 and ST14 may be performed simultaneously.

[0049] As described above, in the carbon dioxide fixation method according to this embodiment, the number of connected separation membrane modules SM1 to SM3 is switched so as to maintain the CO2 concentration in the second gas extracted in step ST1 within a predetermined target concentration range. Therefore, when producing carbonates to fix CO2, the CO2 in the second gas can be maintained within a predetermined target concentration range, and excess CO2 can be suppressed while reducing the reaction time.

[0050] The present disclosure is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the present disclosure. This disclosure also contributes to carbon neutrality, decarbonization, and the Sustainable Development Goals (SDGs). [Explanation of symbols]

[0051] 100 CO2 capture device 101 CO2 Separation Unit 102 Controller 200 Carbonate Generator P1~P3 suction pump S sensor SM1~SM3 Separation membrane modules V1, V2 three-way valve

Claims

1. a carbon dioxide recovery device that separates and extracts a second gas from a first gas, the second gas containing carbon dioxide at a higher concentration than the first gas, using a separation membrane module that selectively allows carbon dioxide to permeate; a carbonate generator that generates carbonate by reacting carbon dioxide in the second gas extracted from the carbon dioxide recovery unit with an alkaline earth compound; a sensor for detecting a carbon dioxide concentration in the second gas; In the carbon dioxide recovery apparatus, a plurality of the separation membrane modules are provided so as to be connectable in multiple stages, switching the number of connected stages of the separation membrane modules so as to maintain the carbon dioxide concentration detected by the sensor within a predetermined target concentration range; Carbon dioxide fixation system.

2. When the carbon dioxide concentration detected by the sensor is lower than the predetermined target concentration range, the number of connected stages of the separation membrane modules is increased, and when the carbon dioxide concentration detected by the sensor is higher than the predetermined target concentration range, the number of connected stages of the separation membrane modules is decreased. The carbon dioxide fixation system according to claim 1 .

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

4. a step of separating and extracting a second gas containing carbon dioxide at a higher concentration than the first gas from the first gas using a separation membrane module that selectively allows carbon dioxide to permeate; and a step of reacting the carbon dioxide in the extracted second gas with an alkaline earth compound to produce a carbonate, In the step of separating and extracting the second gas, Detecting the carbon dioxide concentration in the extracted second gas; switching the number of connected stages of the separation membrane modules, which are provided so as to be connectable in multiple stages, so as to maintain the detected carbon dioxide concentration within a predetermined target concentration range; Carbon dioxide fixation method.

5. When the detected carbon dioxide concentration is lower than the predetermined target concentration range, the number of connected stages of the separation membrane modules is increased, and when the detected carbon dioxide concentration is higher than the predetermined target concentration range, the number of connected stages of the separation membrane modules is decreased. The carbon dioxide fixation method according to claim 4.

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

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