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.SOLUTION: A carbon dioxide immobilization system includes: a carbon dioxide capture apparatus in which a solid adsorbent is caused to adsorb carbon dioxide in a first gas, then the solid adsorbent is heated and depressurized, and a second gas containing a higher concentration of carbon dioxide than the first gas does is extracted; 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. A degree of depressurization in the carbon dioxide capture apparatus is controlled by feedback in such a way that the concentration of carbon dioxide detected by the concentration 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 a chemical adsorption method, which is more energy efficient than chemical absorption. In chemical adsorption, CO2 is extracted by heating and depressurizing a solid adsorbent that has adsorbed CO2.

[0005] Here, when generating carbonates and fixing CO2, if the CO2 concentration is too high, there is a risk that excess CO2 that does not react with the alkaline earth compounds will be released back into the atmosphere, and if the CO2 concentration is too low, there is a risk that the reaction time will be long.

[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. [Means for solving the problem]

[0007] The carbon dioxide fixation system according to the present disclosure comprises: a carbon dioxide recovery device that adsorbs carbon dioxide in a first gas onto a solid adsorbent, and then heats and depressurizes the solid adsorbent to extract a second gas containing carbon dioxide at a higher concentration than the first gas; 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; The degree of pressure reduction in the carbon dioxide capture device is feedback controlled so as to maintain the carbon dioxide concentration detected by the concentration sensor within a predetermined target concentration range.

[0008] The carbon dioxide fixation method according to the present disclosure includes: adsorbing carbon dioxide in the first gas onto a solid adsorbent; heating the solid adsorbent and reducing the pressure to extract a second gas containing carbon dioxide at a higher concentration than the first gas; 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 extracting the second gas, Detecting the carbon dioxide concentration in the extracted second gas; The degree of pressure reduction when carbon dioxide is extracted from the solid adsorbent is feedback controlled so as to maintain the detected carbon dioxide concentration within a predetermined target concentration range.

[0009] In one aspect of the present disclosure, the degree of pressure reduction when extracting carbon dioxide is feedback-controlled so as to maintain the carbon dioxide concentration in the second gas extracted from the solid adsorbent 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] When the carbon dioxide concentration detected by the concentration sensor is lower than the predetermined target concentration range, the degree of pressure reduction may be increased, and when the carbon dioxide concentration detected by the concentration sensor is higher than the predetermined target concentration range, the degree of pressure reduction 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 suppress excess carbon dioxide while reducing the reaction time. [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] 1 is a graph showing the relationship between pressure and CO2 concentration when CO2 is extracted. [Figure 3] 1 is a flowchart showing a carbon dioxide fixation method according to a first embodiment. 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.

[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. The CO2 capture device 100 includes a CO2 adsorption unit 101, a heater 102, a decompression pump 103, and a controller 104.

[0016] The CO2 recovery device 100 is a direct air recovery device that uses, for example, a chemical adsorption method using a solid adsorbent. As shown in Fig. 1, in a CO2 recovery system 100, CO2 in a first gas is adsorbed by a solid adsorbent provided in a CO2 adsorption unit 101. 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 adsorption unit 101 and are discharged as they are.

[0017] Thereafter, in the CO2 recovery device 100, the CO2 adsorption unit 101 (i.e., the solid adsorbent) that has adsorbed the CO2 is heated by a heater 102, and the pressure is reduced by a decompression pump 103. With this configuration, a second gas containing a higher concentration of CO2 than the first gas is extracted from the CO2 recovery device 100.

[0018] That is, the CO2 recovery device 100 repeats a process of passing a first gas through the CO2 adsorption unit 101 at room temperature to recover CO2, and a process of heating the CO2 adsorption unit 101 to, for example, about 100°C and reducing the pressure to extract CO2.

[0019] In the CO2 adsorption unit 101, the first gas is brought into contact with a porous carrier carrying, for example, a solid adsorbent, and the CO2 in the first gas is adsorbed by the carbon dioxide absorbent and recovered. Here, the porous carrier carrying the solid adsorbent is not particularly limited, but may be, for example, coated on a substrate having a honeycomb structure.

[0020] The solid adsorbent is not particularly limited, but is, for example, a hydrophilic polymer, more specifically, an amine-based polymer such as polyethyleneimine, primary amine, secondary amine, or secondary alkanolamine.

[0021] The heater 102 is a heating device for heating the CO2 adsorption unit 101 when CO2 is extracted from the solid adsorbent that has adsorbed CO2. The heater 102 is controlled by a controller 104, for example.

[0022] The decompression pump 103 is a decompression device for decompressing the CO2 adsorption unit 101 when CO2 is extracted from the solid adsorbent that has adsorbed CO2. The decompression pump 103 is controlled by a controller 104, for example. The decompression pump 103 is merely an example of a decompression device, and includes a vacuum pump.

[0023] 1, the controller 104 performs feedback control of the decompression pump 103 based on the CO2 concentration in the second gas detected by the sensor S. More specifically, the controller 104 performs feedback control of the degree of decompression in the CO2 adsorption unit 101 by the decompression pump 103 so as to maintain the CO2 concentration detected by the sensor S within a predetermined target concentration range.

[0024] More specifically, 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 when generating carbonates in the carbonate generating device 200 will be longer. Therefore, the degree of decompression by the decompression pump 103 is increased. 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 generating device 200 will be released back into the atmosphere. Therefore, the degree of decompression by the decompression pump 103 is reduced. Here, when the rotation speed of the decompression pump 103 is increased, the degree of decompression increases, and when the rotation speed of the decompression pump 103 is decreased, the degree of decompression decreases.

[0025] 1, the controller 104 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 maps, etc. In other words, the controller 104 functions as a computer and executes various processes based on the various programs, etc.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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

[0031] 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.

[0032] FIG. 2 is a graph showing the relationship between the pressure and CO2 concentration when CO2 is extracted. As shown in FIG. 2, the lower the gas pressure and the greater the degree of decompression, the higher the CO2 concentration. Here, atmospheric pressure is 101.3 kPa. As shown in FIG. 2, if the relationship between the pressure and CO2 concentration when CO2 is extracted is obtained in advance, the CO2 concentration can be detected from the pressure of the second gas. In other words, the sensor S may be a pressure sensor that detects the pressure of the second gas.

[0033] 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.

[0034] As described above, in the carbon dioxide fixation system according to this embodiment, the degree of pressure reduction in the CO2 capture device 100 is feedback controlled so as to maintain the CO2 concentration in the second gas extracted from the CO2 capture 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.

[0035] <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 will be referred to as appropriate. First, as shown in FIG. 3, CO2 in the first gas is adsorbed onto the solid adsorbent of the CO2 adsorption unit 101 shown in FIG. 1 (step ST1).

[0036] 3, the CO2 adsorption unit 101 (i.e., the solid adsorbent) that has adsorbed CO2 is heated by a heater 102 and depressurized by a decompression pump 103. With this configuration, a second gas containing CO2 at a higher concentration than the first gas is extracted from the CO2 recovery device 100 (step ST2).

[0037] In step ST2, the controller 104 feedback-controls the decompression pump 103 based on the CO2 concentration in the second gas detected by the sensor S. More specifically, the controller 104 feedback-controls the degree of decompression in the CO2 adsorption unit 101 by the decompression pump 103 so as to maintain the CO2 concentration detected by the sensor S within a predetermined target concentration range.

[0038] Finally, 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 ST3).

[0039] As described above, in the carbon dioxide fixation method according to this embodiment, the degree of pressure reduction when extracting CO2 is feedback-controlled so as to maintain the CO2 in the second gas extracted from the solid adsorbent 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 carbon dioxide can be suppressed while reducing the reaction time.

[0040] 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]

[0041] 100 CO2 capture device 101 CO2 adsorption unit 102 Heater 103 Pressure reducing pump 104 Controller 200 Carbonate Generator S sensor

Claims

1. a carbon dioxide recovery device that adsorbs carbon dioxide in a first gas onto a solid adsorbent, and then heats the solid adsorbent and reduces the pressure of the solid adsorbent to extract a second gas containing carbon dioxide at a higher concentration than the first gas; 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; feedback-controlling the degree of pressure reduction in the carbon dioxide capture device 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 degree of pressure reduction is increased, and when the carbon dioxide concentration detected by the sensor is higher than the predetermined target concentration range, the degree of pressure reduction 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. adsorbing carbon dioxide in the first gas onto a solid adsorbent; heating the solid adsorbent and reducing the pressure to extract a second gas containing carbon dioxide at a higher concentration than the first gas; 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 extracting the second gas, Detecting the carbon dioxide concentration in the extracted second gas; feedback-controlling the degree of pressure reduction when extracting carbon dioxide from the solid adsorbent 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 degree of pressure reduction is increased, and when the detected carbon dioxide concentration is higher than the predetermined target concentration range, the degree of pressure reduction 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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