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 that adsorbs carbon dioxide in a first gas on a solid adsorbent, and then decompresses the solid adsorbent while heating the solid adsorbent to extract a second gas that contains carbon dioxide at a higher concentration than the first gas; 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. The degree of pressure reduction in the carbon dioxide recovery device is feedback-controlled so that the carbon dioxide concentration detected by the 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 researching a chemical adsorption method that is superior in energy efficiency compared to the chemical absorption method. In the chemical adsorption method, CO2 is extracted by heating a solid adsorbent that adsorbs CO2 while reducing the pressure.

[0007] Here, when CO2 is immobilized by forming a carbonate, if the concentration of CO2 is too high, the remaining CO2 that does not react with the alkaline earth compound may be released into the atmosphere again, and if the concentration of CO2 is too low, the reaction time may become longer.

[0008] The present disclosure has been completed in view of such circumstances, and provides a carbon dioxide immobilization system that can suppress the remaining carbon dioxide while suppressing the reaction time.

[0009] The carbon dioxide immobilization system according to the present disclosure includes: a carbon dioxide recovery device that adsorbs carbon dioxide in a first gas onto a solid adsorbent and then extracts a second gas while heating the solid adsorbent and reducing the pressure, the second gas containing 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 and feedback-controls the degree of pressure reduction in the carbon dioxide recovery device 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 adsorbing carbon dioxide in a first gas onto a solid adsorbent; a step of extracting a second gas while heating the solid adsorbent and reducing the pressure, 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 extracting the second gas, the carbon dioxide concentration in the extracted second gas is detected, and the degree of pressure reduction when extracting carbon dioxide from the solid adsorbent is feedback-controlled so as to maintain the detected carbon dioxide concentration within a predetermined target concentration range.

[0011] In one aspect of the present disclosure, the degree of pressure reduction when extracting carbon dioxide from the solid adsorbent is feedback-controlled 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 remaining carbon dioxide while suppressing the reaction time.

[0012] It may also be set that 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 is higher than the predetermined target concentration range, the degree of pressure reduction is decreased.

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

[0014] According to the present disclosure, a carbon dioxide immobilization system capable of suppressing the remaining carbon dioxide while suppressing the reaction time can be provided.

[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 which are 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 graph showing the relationship between the pressure and the CO2 concentration when extracting CO2.

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

[0019] 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.

[0020] (First Embodiment)

[0021] <Structure of Carbon Dioxide Immobilization System>

[0022] 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.

[0023] 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 adsorption unit 101, a heater 102, a decompression pump 103, and a controller 104.

[0024] The CO2 recovery device 100 is, for example, a direct air capture device using a chemical adsorption method implemented by a solid adsorbent.

[0025] As Figure 1 shown, the CO2 recovery device 100 adsorbs CO2 in the first gas on the solid adsorbent included in the CO2 adsorption unit 101. Here, the first gas is not limited to the atmosphere and also includes exhaust gas from factories, automobiles, etc. The gas other than CO2 in the first gas passes through the CO2 adsorption unit 101 and is directly discharged.

[0026] Thereafter, in the CO2 recovery device 100, while heating the CO2 adsorption unit 101 (i.e., the solid adsorbent) that has adsorbed CO2 by the heater 102, decompression is performed by the decompression pump 103. With such a structure, a second gas is extracted from the CO2 recovery device 100, where the second gas contains CO2 at a higher concentration compared to the first gas.

[0027] That is, in the CO2 recovery device 100, the process of recovering CO2 by allowing the first gas to pass through the CO2 adsorption unit 101 at normal temperature and the process of extracting CO2 by heating the CO2 adsorption unit 101 to around 100 °C, for example, while performing decompression are repeatedly implemented.

[0028] In the CO2 adsorption unit 101, for example, the first gas is brought into contact with the porous carrier loaded with the solid adsorbent, and CO2 in the first gas is adsorbed on the carbon dioxide absorbent for recovery. Here, although the porous carrier loaded with the solid adsorbent is not particularly limited, it is, for example, coated on a substrate having a honeycomb structure.

[0029] Although the solid adsorbent is not particularly limited, it is, for example, a hydrophilic polymer, and more specifically, an amine polymer such as polyethyleneimine, primary amine, secondary amine, secondary alkanolamine, etc.

[0030] The heater 102 is a heating device for heating the CO2 adsorption unit 101 when extracting CO2 from the solid adsorbent that has adsorbed CO2. The heater 102 is controlled by the controller 104, for example.

[0031] The decompression pump 103 is a decompression device for decompressing the CO2 adsorption unit 101 when extracting CO2 from the solid adsorbent that has adsorbed CO2. The decompression pump 103 is controlled by the controller 104, for example.

[0032] In addition, the decompression pump 103 is merely an example of the decompression device, and it includes a vacuum pump.

[0033] As Figure 1 shown, the controller 104 performs feedback control on 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 on the degree of decompression in the CO2 adsorption unit 101 achieved by the decompression pump 103 in such a way that the CO2 concentration detected by the sensor S is maintained within a predetermined target concentration range.

[0034] More specifically, when the CO2 concentration detected by the sensor S is lower than a predetermined target concentration range, the reaction time for generating carbonate in the carbonate generation device 200 may become longer. Therefore, the degree of decompression achieved by the decompression pump 103 is increased.

[0035] On the other hand, when the CO2 concentration detected by the sensor S is higher than a 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 degree of decompression achieved by the decompression pump 103 is decreased.

[0036] Here, if the rotation speed of the decompression pump 103 is increased, the degree of decompression will increase, and if the rotation speed of the decompression pump 103 is decreased, the degree of decompression will decrease.

[0037] Here, although not shown in Figure 1 the controller 104 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 or data. That is, the controller 104 has the function of a computer and performs various processes based on the above various programs and the like.

[0038] The carbonate generation device 200 receives the second gas extracted from the CO2 recovery device 100 and causes the CO2 in the second gas to react with the alkaline earth compound to generate carbonate. Here, the carbonate is a carbonate of an alkaline earth metal and includes bicarbonate or hydrate.

[0039] Although the alkaline earth compound itself can also be added, from the perspective 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 it can perform CO2 immobilization, it is okay to contain components other than the alkaline earth compound.

[0040] The alkaline earth compound is a compound containing an alkaline earth metal element, 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 the above substances.

[0041] As preferred examples of alkaline earth metals, Be, Ca, Mg, Sr, Ba, Ra, or combinations thereof can be cited. As preferred examples of alkaline earth metal oxides, CaO, MgO, SrO, BaO, or combinations thereof can be cited. As alkaline earth metal nitrates, Ca(NO3)2, Mg(NO3)2, Sr(NO3)2, Ba(NO3)2, or combinations thereof can be cited. As alkaline earth metal hydroxides, Ca(OH)2, Mg(OH)2, Sr(OH)2, Ba(OH)2, or combinations thereof can be cited. As specific examples of carbonates, CaCO3, MgCO3, SrCO3, BaCO3, or combinations thereof can be cited.

[0042] In the case where water is used as the solvent and the incineration ash contains calcium oxide, for example, carbonate ions are consumed by the following reaction to form a carbonate.

[0043] CaO + H2O → Ca 2+ + 2OH -

[0044] CO2 + H2O → 2H + + CO3 2-

[0045] Ca 2+ + CO3 2- → CaCO3

[0046] As Figure 1 shown, the sensor S detects the CO2 concentration in the second gas. Although the sensor S is not particularly limited as long as it can detect the CO2 concentration in the gas, for example, it is 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.

[0047] Here, Figure 2 is a graph showing the relationship between the pressure at the time of extracting CO2 and the CO2 concentration. As Figure 2 shown, the smaller the pressure of the gas and the greater the degree of decompression, the higher the CO2 concentration. Here, the atmospheric pressure is 101.3 kPa. As Figure 2 shown, if the relationship between the pressure at the time of extracting CO2 and the CO2 concentration is obtained in advance, the CO2 concentration can be detected based on the pressure of the second gas. That is, the sensor S may also be a pressure sensor that detects the pressure of the second gas.

[0048] 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 and the like, and can be appropriately changed according to the progress of the reaction with the alkaline earth compound and the like.

[0049] As described above, in the carbon dioxide immobilization system according to the present embodiment, the degree of decompression in the CO2 recovery device 100 is feedback-controlled so that the CO2 concentration in the second gas extracted from the CO2 recovery device 100 is maintained 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, thereby suppressing the remaining CO2 while suppressing the reaction time.

[0050] <Carbon Dioxide Immobilization Method>

[0051] Next, with reference to Figure 3 the carbon dioxide immobilization method according to the first embodiment will be described. Figure 3 FIG. is a flowchart showing the carbon dioxide immobilization method according to the first embodiment. When Figure 3 is described, reference will be appropriately made to Figure 1 .

[0052] First, as Figure 3 shown, the CO2 in the first gas is adsorbed on the solid adsorbent of the CO2 adsorption unit 101 shown in Figure 1 (step ST1).

[0053] Next, as Figure 3 shown, while heating the CO2 adsorption unit 101 (i.e., the solid adsorbent) adsorbed with CO2 by the heater 102, decompression is performed by the decompression pump 103. With such a structure, a second gas is extracted from the CO2 recovery device 100, and the second gas contains CO2 at a higher concentration than the first gas (step ST2).

[0054] In this step ST2, the controller 104 performs feedback control on 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 on the degree of decompression in the CO2 adsorption unit 101 achieved by the decompression pump 103 so that the CO2 concentration detected by the sensor S is maintained within a predetermined target concentration range.

[0055] Finally, as Figure 3 shown, inFigure 1 In the carbonate generation device 200 shown, CO2 in the second gas reacts with an alkaline earth compound to generate carbonate (step ST3).

[0056] As described above, in the carbon dioxide immobilization method according to the present embodiment, the degree of decompression during CO2 extraction is feedback-controlled so as to maintain CO2 in the second gas extracted from the solid adsorbent within a predetermined target concentration range. Therefore, when generating carbonate to immobilize CO2, it is possible to maintain CO2 in the second gas within a predetermined target concentration range, thereby suppressing the remaining carbon dioxide while suppressing the reaction time.

[0057] The present disclosure contributes to carbon neutrality, decarbonization, and the Sustainable Development Goals (SDGs).

[0058] It is clear from the disclosure thus described 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 all such changes should be included in the appended claims for those skilled in the art.

Claims

1. A carbon dioxide immobilization system, comprising: A carbon dioxide recovery device that, after adsorbing carbon dioxide in a first gas onto a solid adsorbent, extracts a second gas while heating the solid adsorbent and reducing the pressure, the second gas containing carbon dioxide at a higher concentration than the first gas; A carbonate generation device that causes carbon dioxide in the second gas extracted from the carbon dioxide recovery device to react with an alkaline earth compound to generate a carbonate; A sensor that detects the carbon dioxide concentration in the second gas, And feedback-controls the degree of pressure reduction in the carbon dioxide recovery device so as to maintain the carbon dioxide concentration detected by the sensor 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 degree of pressure reduction is increased, and when the carbon dioxide concentration is higher than the predetermined target concentration range, the degree of pressure reduction is decreased.

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

4. A carbon dioxide immobilization method, comprising: A step of adsorbing carbon dioxide in a first gas onto a solid adsorbent; A step of reducing the pressure while heating the solid adsorbent to extract a second gas, wherein, The second gas contains carbon dioxide at a higher concentration than the first gas; A step of causing carbon dioxide in the extracted second gas to react with an alkaline earth compound to generate a carbonate, In the step of extracting the second gas, Detecting the carbon dioxide concentration in the extracted second gas, And 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.

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 degree of pressure reduction is increased, and when the carbon dioxide concentration is higher than the predetermined target concentration range, the degree of pressure reduction is decreased.

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

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