Carbon dioxide recovery system, and carbon dioxide recovery method

Abstract

Provided are a carbon dioxide recovery system and carbon dioxide recovery method that make it possible to increase the efficiency of electrochemically generating an acidic aqueous solution and a basic aqueous solution and to reduce power consumption by appropriately controlling the concentration of sodium chloride in circulating salt water. A carbon dioxide recovery system (1) is characterized by comprising: an electrochemical treatment unit (10) that electrochemically decomposes target salt water into an acidic aqueous solution and a basic aqueous solution; a CO2 treatment unit (20) that mixes a gas containing CO2 into the basic aqueous solution to produce a first aqueous solution; a neutralization treatment unit (30) that mixes a basic substance into the acidic aqueous solution to produce a second aqueous solution; a carbonate generation unit (40) that mixes the first aqueous solution and the second aqueous solution to produce a sodium chloride-containing third aqueous solution and a carbonate; and a salt water generation unit (50) that mixes at least one from among salt water, sodium chloride, and water into the third aqueous solution to generate the target salt water to be used by the electrochemical treatment unit.

Description

Carbon dioxide capture system and carbon dioxide capture method

[0001] The present invention relates to a carbon dioxide capture system and a carbon dioxide capture method.

[0002] To achieve carbon neutrality, negative emission technologies (NETs), which remove carbon dioxide by capturing, absorbing, storing, and fixing carbon dioxide from the atmosphere, are attracting attention. Regarding these negative emission technologies, for example, Patent Document 1 proposes a method for fixing carbon dioxide, characterized by "electrolyzing seawater, separating the anode electrolyzed water and cathode electrolyzed water produced by seawater electrolysis, blowing carbon dioxide gas into the cathode electrolyzed water to fix the carbon dioxide gas as a carbonate, and then combining the anode electrolyzed water after pH adjustment with the cathode electrolyzed water after carbonate fixation and discharging it at a pH equivalent to that of seawater."

[0003] Furthermore, regarding the technology for producing a basic aqueous solution in which carbon dioxide is dissolved by electrolyzing seawater, etc., a technology has also been proposed that can reduce the voltage during electrolysis. For example, Patent Document 2 proposes "a carbon dioxide gas neutralization treatment system comprising an electrolytic device, a carbon dioxide treatment device, an acidic liquid neutralization device, and an exhaust device, characterized in that the energy intensity of carbon dioxide absorption is greater than the energy intensity of carbon dioxide emissions from the power generation equipment used in the electrolytic device."

[0004] Japanese Patent No. 5609439, International Publication No. 2022 / 191095

[0005] As described in Patent Documents 1 and 2, when electrolyzing saltwater such as seawater, one possible method to increase the efficiency of electrolysis is to increase the concentration of sodium chloride in the saltwater. However, preparing saltwater with a high concentration of sodium chloride requires pretreatment such as concentration. In addition, since a large amount of saltwater is naturally required to recover a large amount of carbon dioxide, the power consumption for the pretreatment of the saltwater increases significantly. Therefore, in view of these points, the inventors wanted to create a new technology that can appropriately control the concentration of sodium chloride in saltwater. The inventors then considered a technology that circulates saltwater to control the concentration of sodium chloride in saltwater. However, when saltwater is circulated in order to reduce the amount of saltwater newly introduced from an external source, its concentration fluctuates depending on the situation and becomes unstable.

[0006] Therefore, the object of the present invention is to provide a carbon dioxide capture system and a carbon dioxide capture method that can reduce power consumption by increasing the efficiency of electrochemically generating acidic and basic aqueous solutions by appropriately controlling the concentration of sodium chloride in circulating brine.

[0007] To solve the aforementioned problems, the carbon dioxide recovery system according to the present invention includes an electrochemical processing unit that electrochemically decomposes the target saline solution into an acidic aqueous solution and a basic aqueous solution, and a unit that converts CO into the basic aqueous solution. ２ CO2 is mixed with a gas containing CO2 to produce a first aqueous solution. ２ The apparatus comprises a processing unit, a neutralization processing unit that mixes a basic substance with the acidic aqueous solution to produce a second aqueous solution, a carbonate generating unit that mixes the first aqueous solution and the second aqueous solution to produce a third aqueous solution containing sodium chloride and a carbonate, and a brine generating unit that mixes at least one of brine, sodium chloride, and water as a mixture with the third aqueous solution to produce the target brine used in the electrochemical processing unit.

[0008] According to the present invention, a carbon dioxide capture system and carbon dioxide capture method can be provided that can reduce power consumption by increasing the efficiency of electrochemically generating acidic and basic aqueous solutions by appropriately controlling the concentration of sodium chloride in circulating brine.

[0009] This is a diagram showing the configuration of a carbon dioxide capture system according to the first embodiment. This is a diagram showing the flow of the carbon dioxide capture method configuration of a carbon dioxide capture system according to the second embodiment. This is a diagram showing the configuration of a carbon dioxide capture system according to the third embodiment. This is a diagram showing the configuration of a carbon dioxide capture system according to the fourth embodiment. This is a diagram showing the configuration of a carbon dioxide capture system according to the fifth embodiment. This is a diagram showing the configuration of a carbon dioxide capture system according to the sixth embodiment. This is a diagram showing the flow of the carbon dioxide capture method according to the sixth embodiment. This is a diagram showing the configuration of a carbon dioxide capture system according to the seventh embodiment.

[0010] The carbon dioxide capture system and carbon dioxide capture method according to the present invention will be described below with reference to the first to seven embodiments. When describing the second to seventh embodiments, the descriptions of components common to the embodiments already described will be omitted, and the descriptions will focus on the differing components.

[0011] [Carbon dioxide capture system according to the first embodiment] Figure 1 is an overall configuration diagram of the carbon dioxide capture system 1 according to the first embodiment. The carbon dioxide capture system 1 shown in Figure 1 includes an electrochemical processing unit 10 and CO ２ The system comprises a processing unit 20, a neutralization processing unit 30, a carbonate generation unit 40, a brine generation unit 50, a salinity meter 60, and a control unit 70. The components of the carbon dioxide recovery system 1 according to the first embodiment are as follows.

[0012] (Electrochemical Processing Unit) The electrochemical processing unit 10 electrochemically decomposes the target brine into an acidic aqueous solution and a basic aqueous solution. Here, "target brine" refers to the brine that is to be processed by the electrochemical processing unit 10, and is the brine produced by the brine generation unit 50 described later. "Acidic aqueous solution" refers to an aqueous solution containing HCl or hypochlorous acid, and "basic aqueous solution" refers to an aqueous solution containing NaOH. The "electrochemical" decomposition process is a process in which compounds are decomposed by applying voltage to the anode and cathode and passing an electric current through them, and examples include electrolysis and electrodialysis, which will be described in the seventh embodiment described later.

[0013] The electrochemical treatment unit 10 specifically includes a decomposition tank, an anode connected to the + electrode, a cathode connected to the - electrode, and a diaphragm that divides the decomposition tank into an anode side and a cathode side. The diaphragm only needs to allow sodium ions to move from the anode side to the cathode side, and examples include a cation exchange membrane and a selective permeation membrane for monovalent cations. Also, the materials of the anode and cathode are not particularly limited as long as they can cause the chemical reactions described later. The decomposition tank is configured such that target brine is supplied from the brine generation unit 50 to the anode side and water is supplied to the cathode side. Further, the decomposition tank is configured such that an acidic aqueous solution is sent out from the anode side and a basic aqueous solution is sent out from the cathode side. Additionally, the decomposition tank is configured such that a gas containing Cl ２ etc. is discharged from the anode side and a gas containing H ２ etc. is discharged from the cathode side. In addition, the electrochemical treatment unit 10 may be configured to supply metal ions such as iron ions to the anode side in order to reduce the electrolysis voltage. The electrochemical treatment unit 10 is not particularly limited as long as it can decompose target brine into an acidic aqueous solution and a basic aqueous solution, and various conventionally known electrolysis devices and the electrodialysis device described in the seventh embodiment below can be applied.

[0014] (Electrochemical treatment unit: Chemical reaction) Among the chemical reactions occurring in the electrochemical treatment unit 10, the main chemical reactions are shown below. <Anode side> 2Cl － → Cl ２ + 2e － Cl ２ + H ２ O → HCl + HClO HClO → HCl + 1 / 2O ２ <Anode side: Additional chemical reactions that occur when iron ions are supplied to the anode side> 2FeO + 3Cl ２ → 2FeCl ３ + O ２ FeCl ３ + 3H ２ O → Fe(OH) ３ + 3HCl <Cathode side> 2H ２ O + 2e － → H２ +2OH － 2Na ＋ +2OH － →2NaOH

[0015] (CO ２ Processing Unit) CO ２ Processing unit 20 adds CO to a basic aqueous solution. ２ This method involves mixing gases containing CO to produce a first aqueous solution. ２ The term "gas containing carbon dioxide" is not particularly limited to any gas containing carbon dioxide, which is the target of recovery, and includes air and exhaust gases. Furthermore, the term "first aqueous solution" refers to an aqueous solution containing carbonate ions, such as NaHCO3. ３ Na ２ CO ３ It is an aqueous solution containing the following:

[0016] CO ２ Processing unit 20 is, in detail, CO ２ It is equipped with a reaction vessel. And, CO ２ The reaction vessel is supplied with a basic aqueous solution from the cathode side of the electrochemical processing unit 10, and CO ２ The system is configured to supply a gas containing CO. ２ The reaction vessel is configured to discharge the first aqueous solution that has been produced.

[0017] (CO ２ Processing: Chemical reaction) CO ２ The main chemical reactions that occur in the processing unit 20 are shown below: NaOH + CO ２ →NaHCO ３ 2NaOH + CO ２ →Na ２ CO ３ +H ２ O

[0018] (Neutralization Unit) The neutralization unit 30 mixes a basic substance with the acidic aqueous solution sent from the electrochemical unit 10 to produce a second aqueous solution. Here, the "basic substance" is not particularly limited as long as it is a substance that can neutralize the acidic aqueous solution, but examples include basic minerals with a large acid neutralization capacity (mol H+ / kg) such as peridotite and basalt. In the first embodiment, the case in which basic minerals containing calcium oxide and magnesium oxide are used will be described. The "second aqueous solution" is an aqueous solution containing chlorides such as calcium and magnesium contained in the basic substance.

[0019] The neutralization unit 30, in detail, comprises a neutralization tank. The neutralization tank is supplied with an acidic aqueous solution from the electrochemical unit 10, as well as a basic substance. The neutralization tank is also configured to discharge the generated second aqueous solution.

[0020] (Neutralization Treatment Section: Chemical Reactions) The main chemical reactions that occur in the neutralization treatment section 30 are shown below. CaO + 2HCl → CaCl ２ +H ２ O MgO+2HCl→MgCl ２ +H ２ O

[0021] (Carbonate Generation Unit) The carbonate generation unit 40 mixes the first aqueous solution and the second aqueous solution to produce a third aqueous solution containing sodium chloride and a carbonate. Here, the "third aqueous solution" is an aqueous solution containing sodium chloride and is the base aqueous solution for the target saline solution. The "carbonate" is a compound containing carbonate ions, mainly CaCO3 ３ , MgCO ３ It is composed of these elements, and also includes water, among other things.

[0022] The carbonate generation unit 40 is more specifically equipped with a carbonate generation tank. The carbonate generation tank is equipped with CO ２The system is configured such that a first aqueous solution is supplied from the processing unit 20, and a second aqueous solution is supplied from the neutralization processing unit 30. Furthermore, the carbonate generation tank is configured such that the generated third aqueous solution is sent to the brine generation unit 50, and the carbonate generation unit 40 is equipped with a pipe at its bottom for discharging the precipitate of the generated carbonate, thereby ensuring that the generated carbonate is discharged from the system.

[0023] (Carbonate generation section: Chemical reactions) The main chemical reactions that occur in the carbonate generation section 40 are shown below. CaCl ２ +Na ２ CO ３ →CCO ３ +2NaCl MgCl ２ +Na ２ CO ３ →MgCO ３ +2NaCl CaCl ２ +2NaHCO ３ →CO ２ +CaCO ３ +H ２ O+2NaCl MgCl2+2NaHCO3→CO2+MgCO3+H2O+2NaCl

[0024] (Brine Generation Unit) The brine generation unit 50 mixes at least one of brine, sodium chloride, and water with the third aqueous solution to produce the target brine used in the electrochemical processing unit 10. Here, "brine" is not particularly limited as long as it is an aqueous solution containing sodium chloride, but examples include seawater, concentrated seawater, and brine (seawater with a high salt concentration that is a byproduct of seawater desalination). "Sodium chloride" is used to increase the concentration of sodium chloride in the target brine and may be in solid or liquid form when supplied. "Water" is used to decrease the concentration of sodium chloride in the target brine and examples include pure water, distilled water, and deionized water.

[0025] The brine generation unit 50 is further comprised of a brine generation tank. The brine generation tank is supplied with a third aqueous solution from the carbonate generation unit 40, as well as brine, sodium chloride, and water. The brine generation tank is configured to send the generated target brine to the anode side of the electrochemical processing unit 10.

[0026] (Salinity Meter) The salinity meter 60 measures the salinity of the target brine produced in the brine generation unit 50. The salinity meter 60 is not particularly limited as long as it can measure the salinity of the target brine, and any known concentration meter may be used.

[0027] (Control Unit) The control unit 70 controls the amount of brine, sodium chloride, and water mixed in the brine generation unit 50 based on the measurement value of the salinity meter 60. The processing of the control unit 70 is realized by the execution of a program by the CPU (Central Processing Unit) or by a dedicated circuit. It may also be equipped with a memory unit (not shown) for storing the measurement value of the salinity meter 60, and the memory unit can be made up of a general storage device such as RAM (Random Access Memory), ROM (Read Only Memory), HDD (Hard Disk Drive), or flash memory. The control method by the control unit 70 will be described in detail later.

[0028] (Other configurations) The system may also include a heating mechanism 80 that heats the target brine supplied from the brine generation unit 50 to the anode side of the electrochemical processing unit 10, and the water supplied to the cathode side of the electrochemical processing unit 10. The heating mechanism 80 is not particularly limited in its configuration as long as it can heat the target, and examples include a heat exchanger. The parts are connected by piping, and pumps and valves that can adjust the flow rate of the fluid (liquid and gas) may be installed as appropriate.

[0029] [Carbon dioxide recovery method according to the first embodiment] Next, a carbon dioxide recovery method according to the first embodiment will be described. As shown in Figure 2A, the carbon dioxide recovery method according to the first embodiment includes an electrochemical treatment step S1 and CO ２The process includes a processing step S2, a neutralization process S3, a carbonate generation step S4, and a brine generation step S5. In the brine generation step S5, the measurement step S51 and the control step S52 shown in Figure 2B are performed. Steps S2 and S3 are performed in parallel. Each step will be described below.

[0030] (Electrochemical Treatment Process) The electrochemical treatment process S1 is a process in which the target brine is electrochemically decomposed into an acidic aqueous solution and a basic aqueous solution. Referring to Figure 1, in the electrochemical treatment process S1, the target brine is supplied to the anode side of the electrochemical treatment unit 10 and water is supplied to the cathode side, and an electrochemical decomposition process is performed by applying a voltage between the anode and the cathode to conduct electricity. Through this decomposition process, HCl, HClO, etc. are generated on the anode side, and an acidic aqueous solution containing these is sent from the electrochemical treatment unit 10 to the neutralization treatment unit 30. On the other hand, NaOH, etc. is generated on the cathode side, and a basic solution containing this is sent from the electrochemical treatment unit 10 to the CO2 neutralization treatment unit 30. ２ It is sent to the processing unit 20.

[0031] Furthermore, in the electrochemical processing step S1, supplying metal ions such as iron ions to the anode side of the electrochemical processing unit 10 promotes the generation of hydrochloric acid at the anode side, thereby lowering the electrolysis voltage. As a result, the efficiency of electrolysis can be further increased. Note that when the carbon dioxide recovery system 1 is started, the target brine to be supplied to the anode side of the electrochemical processing unit 10 has not yet been generated, so seawater, concentrated seawater, brine, or other brine can be supplied instead.

[0032] (CO ２ Processing process) CO ２ Processing step S2 involves adding CO to a basic aqueous solution. ２ This is a step in which a gas containing CO is mixed to produce a first aqueous solution. Referring to Figure 1, CO ２ In processing step S2, CO ２ CO2 is added to the basic solution supplied to the processing unit 20. ２ A gas containing CO is mixed in. This adds CO to the basic solution. ２ It is absorbed, NaHCO ３ Na ２ CO３ A first aqueous solution containing the above is formed. Then, the first aqueous solution is CO ２ The carbonate is sent from the processing unit 20 to the carbonate generation unit 40.

[0033] (Neutralization Process) The neutralization process S3 is a process in which a basic substance is mixed with an acidic aqueous solution to produce a second aqueous solution. Referring to Figure 1, in the neutralization process S3, a basic substance (basic minerals including calcium oxide and magnesium oxide) is mixed with the acidic aqueous solution supplied to the neutralization processing unit 30. As a result, a neutralization reaction occurs within the neutralization processing unit 30, and CaCl ２ , MgCl ２ A second aqueous solution containing the above is generated. Then, the second aqueous solution is sent from the neutralization section 30 to the carbonate generation section 40.

[0034] (Carbonate Production Process) The carbonate production process S4 is a process in which the first aqueous solution and the second aqueous solution are mixed to produce a third aqueous solution containing sodium chloride and a carbonate. Referring to Figure 1, in the carbonate production process S4, CO ２ The first aqueous solution is supplied from the processing unit 20 to the carbonate generation unit 40, and the second aqueous solution is supplied from the neutralization processing unit 30 to the carbonate generation unit 40, and the two are mixed. As a result, in the carbonate generation unit 40, a third aqueous solution containing sodium chloride and CaCO3 are mixed. ３ or MgCO ３ Carbonates containing these substances are produced. Then, the third aqueous solution is sent from the carbonate production unit 40 to the brine production unit 50. In the carbonate production unit 40, carbon dioxide is fixed by the production of carbonates.

[0035] (Brine Production Process) The brine production process S5 is a process in which at least one of brine, sodium chloride, and water is mixed with the third aqueous solution as a mixture to produce the target brine used in the electrochemical treatment process S1. Referring to Figure 1, in the brine production process S5, the third aqueous solution is supplied from the carbonate production unit 40 to the brine production unit 50, and at least one of brine, sodium chloride, and water is mixed with this third aqueous solution. By mixing sodium chloride with the third aqueous solution, the concentration of sodium chloride in the target brine can be increased, and by mixing with water, the concentration of sodium chloride in the target brine can be decreased. On the other hand, the type of brine used varies, and if concentrated seawater or brine with a higher concentration of sodium chloride than the target brine is used, the concentration of sodium chloride in the target brine can be increased, and if seawater with a lower concentration of sodium chloride than the target brine is used, the concentration of sodium chloride in the target brine can be decreased. In addition, the brine production process S5 is carried out by the following measurement process S51 and control process S52.

[0036] (Measurement Process) Measurement process S51 is a process for measuring the salinity (sodium chloride concentration) of the target saline solution produced in the saline solution production process S5. In measurement process S51, the acquired data of the salinity of the target saline solution is transmitted to the control unit 70, but the data may be stored in a storage unit (not shown) as appropriate for subsequent verification.

[0037] (Control Process) The control process S52 is a process of controlling the amount of brine, sodium chloride, and water mixed in the brine production process S5 based on the salt concentration obtained in the measurement process S51. The control process in the control process S52 is not particularly limited as long as the salt concentration of the target brine can be controlled to a desired value, but an example is given below.

[0038] First, determine the desired upper limit (C) for the salinity of the target saline solution beforehand. ＭＡＸ ) and lower limit (C ＭＩＮ ) is set. Then, in the control step S52, the control unit 70 sets the "salinity (C) of the target saline solution" and the "upper limit (C)" obtained in the measurement step S51. ＭＡＸ ) and "Lower limit (CＭＩＮ Compare this with ). As a result, C ＭＩＮ > If the result is C, perform a treatment to increase the salinity of the target saltwater (mixing with sodium chloride, mixing with concentrated seawater or brine, etc.) and C > C ＭＡＸ If this occurs, a process to reduce the salinity of the target saltwater (mixing with water, mixing with seawater or other saltwater) is carried out. Finally, C ＭＩＮ ≤C ≤C ＭＡＸ Control it so that it satisfies the following conditions.

[0039] (Other steps) After the brine generation step S5, a heating step (not shown) may be performed in which the target brine and water supplied to the electrochemical processing unit 10 are heated by a heating mechanism 80. In the heating step, heating the target brine and water promotes the chemical reaction of the target brine in the electrochemical processing unit 10, thereby increasing the efficiency of electrolysis.

[0040] (First Embodiment: Effects) According to the carbon dioxide recovery system 1 and carbon dioxide recovery method of the first embodiment, the target brine is generated by mixing at least one of salt water, sodium chloride, and water with the third aqueous solution. Therefore, the concentration of sodium chloride in the target brine can be controlled without performing pretreatment that consumes a lot of power.

[0041] During operation of the carbon dioxide recovery system 1, (1) water is consumed by electrolysis on the cathode side of the electrochemical processing unit 10, and (2) water is discharged together with carbonate in the carbonate generation unit 40, causing the concentration of sodium chloride in the third aqueous solution supplied to the brine generation unit 50 to fluctuate. According to the carbon dioxide recovery system 1 and carbon dioxide recovery method of the first embodiment, the salinity of the target brine is measured and the amount of mixture mixed is controlled based on the salinity, so even if the concentration of sodium chloride in the third aqueous solution fluctuates, the concentration of sodium chloride in the target brine can be set to a desired value.

[0042] [Carbon dioxide recovery system according to the second embodiment] Next, a carbon dioxide recovery system according to the second embodiment will be described. As shown in Figure 3, the carbon dioxide recovery system 2 according to the second embodiment differs from the first embodiment shown in Figure 1 in that it includes an emission preparation unit 90.

[0043] (Discharge preparation section) The discharge preparation section 90 adjusts the pH of the third aqueous solution produced in the carbonate generation section 40 to neutral. Here, "neutral" means that the pH of the third aqueous solution is at a level that allows it to be discharged into public waters, for example, pH 5.8 to 8.6.

[0044] The discharge preparation unit 90, in detail, includes a wastewater storage tank. The wastewater storage tank is supplied with the third aqueous solution from the carbonate generation unit 40, as well as a pH adjusting agent to adjust the pH of the third aqueous solution. The wastewater storage tank is also configured to discharge some or all of the pH-adjusted third aqueous solution as wastewater, and to discharge some or all of the third aqueous solution to the brine generation unit 50. The wastewater storage tank is also equipped with a pH meter for measuring the pH of the third aqueous solution. The discharge preparation unit 90 may also include a removal filter to remove impurities contained in the third aqueous solution.

[0045] [Carbon dioxide recovery method according to the second embodiment] Next, a carbon dioxide recovery method according to the second embodiment will be described. The carbon dioxide recovery method according to the second embodiment differs from the first embodiment shown in Figure 2A in that it includes a discharge preparation step between the carbon dioxide generation step S4 and the brine generation step S5.

[0046] (Discharge preparation process) The discharge preparation process is a process of adjusting the pH of the third aqueous solution produced in the carbonate generation unit 40 to neutral. In the discharge preparation process, the pH of the third aqueous solution supplied to the discharge preparation unit 90 is measured. Then, it is determined whether or not the pH is neutral, and if it is not neutral, a pH adjusting agent is added to make the third aqueous solution ready for discharge as wastewater.

[0047] (Second Embodiment: Effect) When the carbon dioxide recovery system 2 is operated for a long time, there is a risk that organic components and the like may remain in each part of the system 2. Therefore, it may be necessary to replace part or all of the aqueous solution circulating in the system 2. According to the carbon dioxide recovery system 2 and the carbon dioxide recovery method according to the second embodiment, since the pH of the third aqueous solution is adjusted to neutral, the third aqueous solution is in a state considering the environment, and part or all of the third aqueous solution can be discharged at a desired timing.

[0048] [Carbon Dioxide Recovery System and Carbon Dioxide Recovery Method According to the Third Embodiment] Next, the carbon dioxide recovery system and the carbon dioxide recovery method according to the third embodiment will be described. As shown in FIG. 4, the carbon dioxide recovery system 3 according to the third embodiment is different from the first embodiment shown in FIG. 1 in that water (liquid) is not supplied to the cathode side of the electrochemical treatment unit 10A. That is, the electrochemical treatment unit 10A of the carbon dioxide recovery system 3 according to the third embodiment is partitioned by a diaphragm into an anode side that generates an acidic aqueous solution and a cathode side that generates a basic aqueous solution. The target brine generated in the brine generation unit 50 is supplied to the anode side, and no liquid is supplied to the cathode side.

[0049] (Third Embodiment: Effect) According to the carbon dioxide recovery system 3 and the carbon dioxide recovery method according to the third embodiment, when sufficient accompanying water is supplied when the protons generated by the reaction of the electrochemical treatment unit 10A move to the cathode, it is only necessary to supply the target brine to the anode side of the electrochemical treatment unit 10A. A basic aqueous solution with a high concentration of NaOH can be generated on the cathode side, and the effect of water conservation is also exhibited by reducing the water usage.

[0050] [Carbon Dioxide Recovery System and Carbon Dioxide Recovery Method According to the Fourth Embodiment] Next, the carbon dioxide recovery system and the carbon dioxide recovery method according to the fourth embodiment will be described. As shown in FIG. 5, the carbon dioxide recovery system 4 according to the fourth embodiment is different from the first embodiment shown in FIG. 1 in that O ２ and CO２ It is different in that it is configured to supply to the cathode side. That is, in the electrochemical treatment unit 10B of the carbon dioxide recovery system 4 according to the fourth embodiment, O generated on the anode side ２ and CO ２ are recovered, and a mechanism for supplying the recovered O ２ and CO ２ to the cathode side is provided.

[0051] (Fourth Embodiment: Effect) According to the carbon dioxide recovery system 4 and the carbon dioxide recovery method according to the fourth embodiment, O generated on the anode side of the electrochemical treatment unit 10 ２ and CO ２ are supplied to the cathode side, so that the electrolysis voltage in the electrochemical treatment unit 10 can be reduced, and further energy saving becomes possible.

[0052] [Carbon Dioxide Recovery System According to the Fifth Embodiment] Next, the carbon dioxide recovery system according to the fifth embodiment will be described. As shown in FIG. 6, the carbon dioxide recovery system 5 according to the fifth embodiment is different from the first embodiment shown in FIG. 1 in that it includes a gas-liquid separation unit 100, a gas dissolution unit 110, and a pH adjustment unit 120. In the fifth embodiment, a gas containing chlorine and dilute hydrochloric acid are sent from the anode side of the electrochemical treatment unit 10.

[0053] (Gas-Liquid Separation Unit) The gas-liquid separation unit 100 separates a gas containing chlorine and dilute brine into gas and liquid. Here, "dilute brine" is brine in which the concentration of sodium chloride has decreased by gas-liquid separation. The gas-liquid separation unit 100 is not particularly limited as long as it is a device capable of performing gas-liquid separation, and a known gas-liquid separation device may be used.

[0054] (Gas Dissolution Unit) The gas dissolution unit 110 dissolves the gas containing chlorine separated by the gas-liquid separation unit 100 to generate an aqueous solution. Specifically, the gas dissolution unit 110 includes a gas dissolution tank in which an aqueous solution capable of dissolving the gas containing chlorine is stored. The gas dissolution tank is configured such that gas is supplied from the gas-liquid separation unit 100, and the generated aqueous solution is sent to the neutralization treatment unit 30.

[0055] (pH adjustment unit) The pH adjustment unit 120 adjusts the pH of the dilute saline solution separated in the gas-liquid separation unit 100. More specifically, the pH adjustment unit 120 includes a pH adjustment tank. The pH adjustment tank is supplied with dilute saline solution from the gas-liquid separation unit 100, as well as a pH adjusting agent to adjust the pH of the dilute saline solution. The pH adjustment tank is also configured to send the dilute saline solution, after pH adjustment, to the saline solution generation unit 50. The pH adjustment tank is equipped with a pH meter for measuring the pH of the dilute saline solution.

[0056] [Carbon dioxide recovery method according to the fifth embodiment] Next, a carbon dioxide recovery method according to the fifth embodiment will be described. The carbon dioxide recovery method according to the fifth embodiment differs from the first embodiment shown in Figure 2A in that it includes a gas-liquid separation step, a gas dissolution step, and a pH adjustment step between the electrochemical treatment step S1 and the neutralization treatment step S3.

[0057] (Gas-Liquid Separation Process) The gas-liquid separation process is a process of separating the chlorine-containing gas and dilute saline water generated from the anode side of the electrochemical processing unit 10 into gas and liquid. In the gas-liquid separation process, the chlorine-containing gas is sent to the gas dissolution unit 110 and the dilute saline water is sent to the pH adjustment unit 120.

[0058] (Gas dissolution process) The gas dissolution process is a process in which the chlorine-containing gas separated in the gas-liquid separation unit 100 is dissolved to produce an aqueous solution. In the gas dissolution process, the produced aqueous solution is sent to the neutralization unit 30 as an acidic aqueous solution.

[0059] (pH adjustment process) The pH adjustment process is a process of adjusting the pH of the dilute saline solution separated in the gas-liquid separation unit 100. In the pH adjustment process, the pH of the dilute saline solution supplied to the pH adjustment unit 120 is measured. Then, it is determined whether or not the pH falls within the desired numerical range, and if it falls outside the numerical range, a pH adjusting agent is added to adjust the pH before it is sent to the saline solution generation unit 50.

[0060] (Fifth Embodiment: Effects) According to the carbon dioxide recovery system 5 and carbon dioxide recovery method of the fifth embodiment, since dilute saline water is separated by gas-liquid separation of the gas generated in the electrochemical processing unit 10, the precipitation of NaCl inside the system 5 can be suppressed, thereby reducing the frequency of maintenance and running costs.

[0061] [Carbon dioxide recovery system according to the sixth embodiment] Next, a carbon dioxide recovery system according to the sixth embodiment will be described. As shown in Figure 7, the carbon dioxide recovery system 6 according to the sixth embodiment differs from the first embodiment shown in Figure 1 in that it does not have a neutralization processing unit 30 and has a carbon dioxide concentration unit 130 instead of a carbonate generation unit 40.

[0062] (Carbon dioxide concentration section) The carbon dioxide concentration section 130 mixes the first aqueous solution and the acidic aqueous solution to CO ２ This process produces a concentrated gas and a fourth aqueous solution containing sodium chloride. Here, the "fourth aqueous solution" is an aqueous solution containing sodium chloride, which is the base aqueous solution for the target saline solution. ２ "A concentrated gas" refers to CO ２ CO supplied to processing unit 20 ２ It is a gas with a higher concentration of carbon dioxide than gases containing [another substance].

[0063] The carbon dioxide concentration unit 130 is, in detail, equipped with a carbon dioxide concentration tank. The carbon dioxide concentration tank is equipped with CO ２ The first aqueous solution is supplied from the processing unit 20, and an acidic aqueous solution is supplied from the anode side of the electrochemical processing unit 10. In addition, the carbon dioxide concentrator is configured such that the generated fourth aqueous solution is sent to the brine generation unit 50, and CO ２ The system is configured to release the concentrated gas out of the system.

[0064] (Carbon dioxide concentration section: Chemical reactions) The main chemical reactions that occur in the carbon dioxide concentration section 130 are shown below. 2HCl + Na ２ CO ３ → 2NaCl + CO ２ +H ２O

[0065] [Carbon Dioxide Recovery Method According to the Sixth Embodiment] Next, a carbon dioxide recovery method according to the sixth embodiment will be described. As shown in Figure 8, the carbon dioxide recovery method according to the sixth embodiment differs from the first embodiment shown in Figure 2A in that it does not include the neutralization treatment step S3 and includes a carbon dioxide concentration step S6 instead of the carbonate production step S4.

[0066] (Carbon dioxide concentration process) The carbon dioxide concentration process S6 is CO ２ The first aqueous solution discharged from the processing unit 20 and the acidic aqueous solution discharged from the electrochemical processing unit 10 are mixed, CO ２ This is a process that produces a concentrated gas and a fourth aqueous solution containing sodium chloride. Referring to Figure 7, in the carbon dioxide concentration process S6, CO ２ The first aqueous solution is supplied from the processing unit 20 to the carbon dioxide concentration unit 130, and the acidic aqueous solution is supplied from the anode side of the electrochemical processing unit 10 to the carbon dioxide concentration unit 130, and the two are mixed. As a result, in the carbon dioxide concentration unit 130, the fourth aqueous solution containing sodium chloride and CO2 are mixed. ２ A concentrated gas is generated. Then, the fourth aqueous solution is sent from the carbon dioxide concentration unit 130 to the brine generation unit 50.

[0067] (Sixth Embodiment: Effects) According to the carbon dioxide recovery system 6 and carbon dioxide recovery method of the sixth embodiment, a gas is generated by mixing the first aqueous solution and the acidic aqueous solution, thus enabling the recovery of highly valuable high-concentration CO ２ It can generate [this].

[0068] [Carbon dioxide recovery system and carbon dioxide recovery method according to the seventh embodiment] Next, a carbon dioxide recovery system and a carbon dioxide recovery method according to the seventh embodiment will be described. As shown in Figure 9, the carbon dioxide recovery system 7 according to the seventh embodiment differs from the first embodiment shown in Figure 1 in that it uses an electrodialysis machine as the electrochemical processing unit 10.

[0069] (Configuration of the electrochemical processing unit) The electrodialysis machine, which is the electrochemical processing unit 10, can be divided into a three-chamber type and a two-chamber type depending on the combination of a bipolar membrane, which is an ion exchange membrane with a structure in which an anion exchange membrane and a cation exchange membrane are bonded together, and a cation exchange membrane and / or anion exchange membrane. However, it is not particularly limited as long as the supplied saline solution can be separated into acid and base. Electrolyte is circulated between the anode and cathode, and acidic aqueous solution, saline solution, and basic aqueous solution are transported and circulated by pumps across the ion exchange membrane. The acidic aqueous solution and basic aqueous solution do not necessarily need to be circulated, and when the desired concentration is reached, they are circulated to the neutralization processing unit 30 and CO2, respectively. ２ It is transported to the processing unit 20.

[0070] (Seventh Embodiment: Effects) When the carbon dioxide recovery system 1 is operated by electrolysis, chlorine, oxygen, and hydrogen gases are generated in the electrochemical processing unit 10. In addition, an increase in overvoltage may occur due to the generation of these gases. As a result, running costs may increase. According to the carbon dioxide recovery system 7 of the seventh embodiment, brine can be separated into acid and base at a lower voltage than electrolysis. Furthermore, since there is no electrode reaction, oxidation-reduction reactions do not occur and no by-products are generated, making it possible to suppress running costs.

[0071] [Modified Version] (Modified Version: Electrochemical Processing Unit) In the first embodiment and others, a method of supplying water to the cathode side of the electrochemical processing unit 10 was described, but it is not limited to water as long as the above-mentioned chemical reaction occurs. In the fourth embodiment, the O generated on the anode side of the electrochemical processing unit 10 ２ and CO ２ The method of supplying O to the cathode side has been described, but it is not generated on the anode side, but is supplied separately. ２ and CO ２ Alternatively, the power may be supplied to the cathode side.

[0072] (Modification: Electrochemical Processing Unit and Neutralization Processing Unit) In the first embodiment, a configuration in which metal ions are supplied to the anode side of the electrochemical processing unit 10 was described, but these metal ions may be extracted from metal ions dissolved in a basic substance in the neutralization processing unit 30.

[0073] It should be noted that the present invention is not limited to the embodiments and modifications described above. Furthermore, the embodiments and modifications are described in detail for the purpose of clearly illustrating the present invention, and are not necessarily limited to those having all the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment or modification, or to add the configuration of another embodiment or modification.

[0074] 1 Carbon dioxide recovery system according to the first embodiment 2 Carbon dioxide recovery system according to the second embodiment 3 Carbon dioxide recovery system according to the third embodiment 4 Carbon dioxide recovery system according to the fourth embodiment 5 Carbon dioxide recovery system according to the fifth embodiment 6 Carbon dioxide recovery system according to the sixth embodiment 7 Carbon dioxide recovery system according to the seventh embodiment 10 Electrochemical processing unit 20 CO ２ Processing Unit 30 Neutralization Processing Unit 40 Carbonate Generation Unit 50 Saltwater Generation Unit 60 Salt Concentration Meter 70 Control Unit 80 Heating Mechanism 90 Discharge Preparation Unit 100 Gas-Liquid Separation Unit 110 Gas Dissolution Unit 120 pH Adjustment Unit 130 Carbon Dioxide Concentration Unit S1 Electrochemical Processing Process S2 CO ２ Processing process S3 Neutralization process S4 Carbonate generation process S5 Saltwater generation process S6 Carbon dioxide concentration process S51 Measurement process S52 Control process

Claims

1. An electrochemical processing unit that electrochemically decomposes the target saline solution into an acidic aqueous solution and a basic aqueous solution, and CO2 is added to the basic aqueous solution. ２ CO2 is mixed with a gas containing CO2 to produce a first aqueous solution. ２ A carbon dioxide recovery system comprising: a processing unit; a neutralization processing unit that mixes a basic substance with the acidic aqueous solution to produce a second aqueous solution; a carbonate production unit that mixes the first aqueous solution and the second aqueous solution to produce a third aqueous solution containing sodium chloride and a carbonate; and a brine production unit that mixes at least one of brine, sodium chloride, and water as a mixture with the third aqueous solution to produce the target brine used in the electrochemical processing unit.

2. The carbon dioxide recovery system according to claim 1, characterized in that the target brine contains brine, which is a by-product of seawater desalination.

3. The carbon dioxide recovery system according to claim 1 or 2, further comprising: a salinity meter for measuring the salinity of the target salinity produced in the salinity generation unit; and a control unit for controlling the amount of the mixture mixed in the salinity generation unit based on the salinity measured by the salinity meter.

4. The carbon dioxide recovery system according to claim 1 or 2, wherein the electrochemical processing unit is divided by a diaphragm into an anode side that generates the acidic aqueous solution and a cathode side that generates the basic aqueous solution, and metal ions are supplied to the anode side.

5. The carbon dioxide recovery system according to claim 1 or 2, further comprising: an discharge preparation unit for adjusting the pH of the third aqueous solution produced in the carbonate generation unit to neutral.

6. The carbon dioxide recovery system according to claim 1 or 2, characterized in that the electrochemical processing unit is divided by a diaphragm into an anode side that generates the acidic aqueous solution and a cathode side that generates the basic aqueous solution, the target brine generated in the brine generation unit is supplied to the anode side, and no liquid is supplied to the cathode side.

7. The carbon dioxide recovery system according to claim 1 or 2, characterized in that the electrochemical processing unit is divided by a diaphragm into an anode side that generates the acidic aqueous solution and a cathode side that generates the basic aqueous solution, and oxygen and carbon dioxide discharged from the anode side are supplied to the cathode side.

8. The carbon dioxide recovery system according to claim 1 or 2, comprising: a gas-liquid separation unit for separating the chlorine-containing gas and dilute saline water generated in the electrochemical processing unit into gas and liquid; a pH adjustment unit for adjusting the pH of the dilute saline water separated in the gas-liquid separation unit; and a gas dissolution unit for dissolving the chlorine-containing gas separated in the gas-liquid separation unit to produce an aqueous solution, wherein the dilute saline water whose pH has been adjusted by the pH adjustment unit is mixed with the third aqueous solution in the saline water generation unit, and the aqueous solution produced by the gas dissolution unit is used as the acidic aqueous solution supplied to the neutralization processing unit.

9. An electrochemical processing unit that electrochemically decomposes the target saline solution into an acidic aqueous solution and a basic aqueous solution, and CO2 is added to the basic aqueous solution. ２ CO2 is mixed with a gas containing CO2 to produce a first aqueous solution. ２ The processing unit mixes the first aqueous solution and the acidic aqueous solution, CO ２ A carbon dioxide recovery system characterized by comprising: a carbon dioxide concentration unit that generates a concentrated gas and a fourth aqueous solution containing sodium chloride; and a brine generation unit that mixes at least one of brine, sodium chloride, and water as a mixture with the fourth aqueous solution to generate the target brine used in the electrochemical processing unit.

10. The carbon dioxide recovery system according to claim 9, further comprising: a salinity meter for measuring the salinity of the target salinity produced in the salinity generation unit; and a control unit for controlling the amount of the mixture mixed in the salinity generation unit based on the salinity measured by the salinity meter.

11. An electrochemical treatment step in which the target saline solution is electrochemically decomposed into an acidic aqueous solution and a basic aqueous solution, and CO2 is added to the basic aqueous solution. ２ CO2 is mixed with a gas containing CO2 to produce a first aqueous solution. ２ A method for recovering carbon dioxide, comprising: a processing step; a neutralization processing step of mixing a basic substance with the acidic aqueous solution to produce a second aqueous solution; a carbonate production step of mixing the first aqueous solution and the second aqueous solution to produce a third aqueous solution containing sodium chloride and a carbonate; and a brine production step of mixing at least one of brine, sodium chloride, and water as a mixture with the third aqueous solution to produce the target brine used in the electrochemical processing step.

12. The carbon dioxide recovery method according to claim 11, comprising: a measurement step of measuring the salinity of the target saline solution produced in the saline solution production step; and a control step of controlling the amount of the mixture to be mixed in the saline solution production step based on the salinity of the solution obtained in the measurement step.

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