Method for collecting carbon dioxide

Abstract

Provided is a method for collecting carbon dioxide which includes a step in which air is brought into contact with spray water and thereafter brought into contact with a carbon dioxide absorbent to make the carbon dioxide absorbent absorb the carbon dioxide contained in the air, the method being characterized in that the spray water has an acid consumption (pH 4.8) of 20 mgCaCO3 / L or greater. In cases when the spray water has an acid consumption (pH 4.8) less than 20 mgCaCO3 / L, a basic substance is added to the spray water so that the spray water comes to have an acid consumption (pH 4.8) of 20 mgCaCO3 / L or greater.

Description

Carbon dioxide capture method

[0001] The present invention relates to a method for recovering carbon dioxide from the atmosphere, and in particular to a method for recovering carbon dioxide using a carbon dioxide absorbent. More specifically, the present invention relates to a method for recovering carbon dioxide by bringing the atmosphere into contact with spray water from a cooling tower or the like and then contacting the atmosphere with a carbon dioxide absorbent.

[0002] Patent Documents 1 and 2 describe methods for capturing carbon dioxide in the atmosphere, in which the atmosphere is brought into contact with a carbon dioxide absorbent to absorb the carbon dioxide in the atmosphere. In Patent Documents 1 and 2, an amine capable of absorbing and desorbing carbon dioxide is used as the absorbent. In Patent Document 1, the atmosphere is blown by a blower to bring it into contact with the carbon dioxide absorbent. In Patent Document 2, a carbon dioxide absorption device is installed above a cooling tower, and the atmosphere is passed through the cooling tower to contact with spray water, and then the blowing function of the cooling tower's fan is used to blow air through the carbon dioxide absorption device.

[0003] Japanese Utility Model Application Publication No. 3-98929 Japanese Patent Application Publication No. 2020-131166

[0004] In addition to carbon dioxide, the atmosphere contains small amounts of acidic gases such as sulfur oxides and nitrogen oxides that are generated during fuel combustion. With long-term operation of a carbon dioxide absorption device, these acidic gases react with the carbon dioxide absorbent, gradually reducing the carbon dioxide absorption performance of the carbon dioxide absorbent. When air is passed through a cooling tower and then brought into contact with the carbon dioxide absorbent, some of the acidic gas components in the atmosphere other than carbon dioxide are absorbed by the water sprayed onto the cooling tower. However, the amount of absorption is not large.

[0005] An object of the present invention is to provide a method for recovering carbon dioxide by bringing atmospheric air into contact with spray water and then into contact with a carbon dioxide absorbent, which method prevents or suppresses a decrease in the absorption performance of the carbon dioxide absorbent due to acid gases other than carbon dioxide caused by the spray water, thereby enabling the carbon dioxide absorption performance of the carbon dioxide absorbent to be maintained at a high level.

[0006] The present inventors have found that by setting the acid consumption (pH 4.8) of the spray water that comes into contact with the air before it comes into contact with the carbon dioxide absorbent to a predetermined value or more, the absorption capacity of this spray water for acidic gases other than carbon dioxide is increased, and by reducing the acidic gas concentration in the air before it comes into contact with the carbon dioxide absorbent in advance, it is possible to prevent a decrease in the carbon dioxide absorption performance of the carbon dioxide absorbent due to acidic gases and maintain the carbon dioxide absorption performance of the carbon dioxide absorbent at a high level.

[0007] The present invention provides the following.

[0008] [1] A method for recovering carbon dioxide, comprising a step of contacting atmospheric air with spray water and then contacting the air with a carbon dioxide absorbent to absorb carbon dioxide in the air into the carbon dioxide absorbent, wherein the acid consumption (pH 4.8) in the spray water is 20 mg CaCO ３ / L or more.

[0009] [2] The acid consumption of the spray water (pH 4.8) is 20 mg CaCO ３ / L, the acid consumption of the spray water (pH 4.8) is 20 mg CaCO ３ The carbon dioxide recovery method according to [1], wherein a basic substance is added to the spray water so that the concentration of the spray water becomes 1 / L or more.

[0010] [3] The method for recovering carbon dioxide according to [2], wherein the basic substance is at least one selected from the group consisting of hydrogen carbonates, carbonates, hydroxides, silicates, ammonia, and amine compounds.

[0011] In the carbon dioxide recovery method of the present invention, the acid consumption (pH 4.8) of the spray water that comes into contact with the air before the air comes into contact with the carbon dioxide absorbent is 20 mg CaCO ３ / L or more, the acid gas concentration in the atmosphere is reduced and deterioration of the carbon dioxide absorbent is suppressed, thereby making it possible to maintain the carbon dioxide absorption performance of the carbon dioxide absorbent at a high level for a long period of time.

[0012] The carbon dioxide absorbed in the carbon dioxide absorbent is generally recovered by heating the carbon dioxide absorbent to desorb the carbon dioxide gas, while the absorbent after desorption is reused.

[0013] Acidic gases other than carbon dioxide are difficult to desorb from the carbon dioxide absorbent, or they denature the carbon dioxide absorbent, causing it to deteriorate.

[0014] According to the present invention, by removing acidic gases other than carbon dioxide from the atmosphere before the atmosphere comes into contact with the carbon dioxide absorbent by absorbing them in spray water in advance, it is possible to minimize deterioration of the carbon dioxide absorbent due to the acidic gases, thereby extending the life of the absorbent.

[0015] For these reasons, according to the present invention, costs such as labor costs and raw material costs for replacing the carbon dioxide absorbent with a new one can be reduced. In addition, the frequency of producing a new carbon dioxide absorbent can be reduced. Therefore, the amount of carbon dioxide generated from this production process can also be reduced.

[0016] FIG. 1 is a schematic cross-sectional view showing an example of a cooling tower system to which the present invention is applied.

[0017] Hereinafter, an embodiment of the present invention will be described in detail.

[0018] In the present invention, in a method for recovering carbon dioxide in which carbon dioxide in the atmosphere is absorbed using a carbon dioxide absorbent, the atmosphere is brought into contact with spray water from a cooling tower or the like, and then brought into contact with the carbon dioxide absorbent.

[0019] There is no particular restriction on the type of sprinkler equipment, such as a cooling tower, that sprays spray water into the atmosphere, as long as it includes a sprinkler means for introducing spray water into the sprinkler equipment, such as a cooling tower, a contact area such as a packed bed that serves as a flow path for the sprayed water and where the air comes into contact with the spray water, and a blower for ventilating the air into the sprinkler equipment, such as a cooling tower. If the equipment does not include one or more of these components, the omitted devices may be added to compensate. An example of a sprinkler equipment is a cooling tower.

[0020] The type of cooling tower is not particularly limited, and may be any of a counter-flow type, a counter-flow type, or a natural convection type, and may be either an open type or a closed type.

[0021] FIG. 1 is a schematic cross-sectional view showing a cooling tower system to which a method according to an embodiment of the present invention is applied.

[0022] Cooling water (circulating return water) heated by a heat exchanger 17 such as a refrigerator is sprayed onto the filler 3 from the sprinkler system 2 of the cooling tower 1. Air taken in from an opening on the side of the cooling tower 1 by driving the fan 5 comes into contact with this sprayed water. When the air comes into contact with the sprayed water, part of the water evaporates and is cooled. After coming into contact with the air, the sprayed water collects in the pit, i.e., the lower water tank 4. The cooling water in the lower water tank 4 is circulated from the water collection tank 6 through a circulation pump 15, a circulation outflow pipe 16, a heat exchanger 17, and a circulation return pipe 18. The water collection tank 6 is recessed downward from the bottom of the lower water tank 4.

[0023] New water in an amount corresponding to the amount of evaporation and droplet scattering loss in the cooling tower 1 and the amount of blown water from the blow valve 8 of the blow line 7 is supplied to the lower water tank 4 through a makeup water pipe 9 and a valve device 10 such as a ball tap.

[0024] The air that has come into contact with the spray water in the cooling tower 1 flows out from the top of the cooling tower 1 and is mixed with CO2 having a carbon dioxide absorbent. ２ It is sent to an absorption facility 20 where the carbon dioxide is removed.

[0025] CO ２ Examples of the absorption equipment 20 include equipment provided with a packed bed of solid carbon dioxide absorbent installed downstream of the spray water equipment of the cooling tower or the like, and equipment in which the atmosphere after contact with the spray water, for example, the outflow gas of a cooling tower, is ventilated into a storage tank of a liquid carbon dioxide absorbent.

[0026] In the present invention, the carbon dioxide absorbent used to absorb carbon dioxide in the atmosphere must have the ability to selectively absorb low concentrations of carbon dioxide in the atmosphere. In view of this, it is desirable to use a basic absorbent that undergoes a neutralization reaction with carbon dioxide or an amine compound absorbent that reacts with carbon dioxide to produce carbamic acid.

[0027] Examples of the basic absorbent that can be used include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, and alkali metal carbonates such as sodium carbonate, potassium carbonate, and lithium carbonate.

[0028] Examples of the amine compound absorbent that can be used include amine absorption liquids such as monoethanolamine, diethanolamine, isopropanolamine, N-methyldiethanolamine, piperazine, and 2-methylpiperazine; solid adsorbents in which an amine compound is supported on a porous material such as zeolite or silica gel; and polymer compounds having an amino group as a functional group.

[0029] These carbon dioxide absorbents may be used alone or in combination of two or more.

[0030] In FIG. 1, a cooling tower is shown as the sprinkler equipment that forms the spray water, but other equipment than a cooling tower, such as a scrubber, an exhaust fan for indoor air conditioning, an air-cooled chiller with a fan, or a heat pump with a fan, may also be used.

[0031] In cooling towers, etc., the air is converted into CO ２ If pressure loss occurs when supplying the gas to the absorption equipment and the minimum air volume that was originally required cannot be secured, an air blower may be added.

[0032] If you want to increase or decrease the amount of water sprayed, you can change, add, or install a new pump, or install an inverter in the power supply.

[0033] In the present invention, in a carbon dioxide recovery method including a step of contacting atmospheric air with sparged water and then contacting the air with a carbon dioxide absorbent to absorb carbon dioxide in the atmospheric air into the carbon dioxide absorbent, the acid consumption amount (pH 4.8) in the sparged water is 20 mg CaCO ３ / L or more.

[0034] The acid consumption in the spray water (pH 4.8) was 20 mg CaCO ３ / L or more, the acid gas concentration in the atmosphere can be effectively reduced. From this point of view, the acid consumption amount of the spray water (pH 4.8) is 30 mg CaCO ３ / L or more, and 50 mg CaCO ３ / L or more is more preferable. On the other hand, if the acid consumption (pH 4.8) of the spray water is excessively high, concerns arise about corrosion and scaling, and the cost of the chemicals for the basic substances described below for increasing the acid consumption (pH 4.8) becomes too high, resulting in excessively high treatment costs. For this reason, the acid consumption (pH 4.8) of the spray water is set to 10,000 mg CaCO ３ / L or less, especially 1,000 mg CaCO ３ It is preferable that the value is 1 / L or less.

[0035] In order to maintain the acid consumption (pH 4.8) of the spray water at or above the lower limit, the acid consumption (pH 4.8) of the spray water is measured, and if the measured value is below the lower limit, a basic substance is added to increase the acid consumption (pH 4.8). The acid consumption (pH 4.8) of the spray water can be analyzed, for example, by the method described in JIS K0101.

[0036] The analysis point for acid consumption (pH 4.8) can be determined by sampling the spray water from upstream of the spray equipment such as a cooling tower if the spray water is used in a pass-through system. If the spray water is used in a circulating system, the sample can be taken from any point within the same water system where the spray water is flowing.

[0037] The acid consumption (pH 4.8) in the spray water may be the acid consumption (pH 4.8) contained in the water supplied to a spraying facility such as a cooling tower, or a basic substance may be added separately to the system to set the acid consumption (pH 4.8) above the lower limit, or both of these may be used.

[0038] When the required acid consumption (pH 4.8) cannot be maintained by the acid consumption (pH 4.8) contained in the water supplied to a sprinkler system such as a cooling tower, a basic substance will be added to the sprinkler system separately. In this case, the basic substance may be added by any method, for example, by using a chemical injection pump or the like to add the basic substance to the sprinkler system continuously or intermittently.

[0039] The basic substance may be added at any location within the spray system, such as the makeup water pipe of a cooling tower, the spray water circulation pipe, etc. In the cooling tower system shown in Figure 1, the basic substance can be added at point A of the cooling water circulation outflow pipe 16, point B of the circulation return pipe 18, or point C of the makeup water pipe 9.

[0040] Examples of the basic substance that can be added include hydrogen carbonates, carbonates, hydroxides, silicates, ammonia, and amine compounds, but other basic substances may also be used.

[0041] As the hydrogen carbonate, hydrogen carbonate of an alkali metal such as sodium hydrogen carbonate, potassium hydrogen carbonate, or lithium hydrogen carbonate, or ammonium hydrogen carbonate can be used.

[0042] As the carbonate, alkali metal carbonates such as sodium carbonate, potassium carbonate, and lithium carbonate, alkaline earth metal carbonates such as calcium carbonate and magnesium carbonate, and ammonium carbonate can be used.

[0043] As the hydroxide, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, and alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide can be used.

[0044] As the silicate, sodium metasilicate, potassium metasilicate, water glass solution, etc. can be used.

[0045] As the ammonia, an ammonia solution can be used.

[0046] As the amine compound, monoethanolamine, monoisopropanolamine, cyclohexylamine, methoxypropylamine, morpholine, aminoethoxyethanol, diethylethanolamine, diethanolamine, etc. can be used.

[0047] These basic substances may be used alone or in combination of two or more. A mixture of a basic substance and a non-basic substance may also be used as long as basicity is maintained.

[0048] When the water system of the spray water contains dissolved salts, the addition of a basic substance may cause scale components such as calcium carbonate, calcium phosphate, magnesium hydroxide, and magnesium silicate to adhere to piping in the water system, which may result in increased pressure loss in the piping, reduced heat transfer efficiency in heat exchangers, reduced cooling efficiency in cooling towers, etc. In this case, a scale inhibitor may be added to suppress the formation of scale.

[0049] As the scale inhibitor, water-soluble polycarboxylic acid or its salt, water-soluble phosphonic acid or its salt, polyphosphoric acid or its salt, phosphate ester compound or its salt, phosphoric acid or its salt, etc. can be used alone or in combination.

[0050] If the structures constituting the water system for spray water contain metal and the metal and spray water are in contact within the system, the metal may corrode at the points where the spray water and the metal come into contact, which may cause an increase in pressure loss in piping, etc., a decrease in heat transfer efficiency in heat exchangers, etc., damage to the structures containing metal, etc. In this case, an anticorrosive may be added to suppress the progress of corrosion.

[0051] As the corrosion inhibitor, hydroxy acids or salts thereof, water-soluble polycarboxylic acids or salts thereof, water-soluble phosphonic acids or salts thereof, polyphosphoric acids or salts thereof, phosphate ester compounds or salts thereof, phosphoric acids or salts thereof, zinc salts, tin salts, molybdic acid or salts thereof, tungstic acid or salts thereof, nitrous acid or salts thereof, surfactants, and the like can be used alone or in combination.

[0052] When spray water comes into contact with the air or when microorganisms are contained in the water supply to a water system, the microorganisms are taken into the water system and multiply within the water system, causing microorganism-containing dirt known as slime to adhere to the piping within the water system, which can cause increased pressure loss in the piping, reduced heat transfer efficiency in heat exchangers, reduced cooling efficiency in cooling towers, etc. In this case, slime control agents can be added to suppress the generation of slime.

[0053] Examples of slime control agents that can be used include hypochlorous acid and its salts, chlorine gas, hypobromous acid and its salts, stabilized chlorine, stabilized bromine, organic disinfectants, ozone, chlorine dioxide, surfactants, and quaternary ammonium salts.

[0054] According to the present invention, the acid consumption (pH 4.8) of the spray water is measured continuously or intermittently, for example, once every 0.1 to 24 hours, and the controller to which the measurement results are input notifies the user that the acid consumption (pH 4.8) of the spray water is 20 mg CaCO ３ / L, the acid consumption of the spray water (pH 4.8) can be adjusted automatically by outputting a chemical injection signal to add the above-mentioned basic substance to the water system of the spray water.

[0055] Since there is a positive correlation between the acid consumption (pH 4.8) and pH, the required acid consumption may be adjusted based on the measured pH value. For example, based on the results of a previous analysis of the acid consumption (pH 4.8) and pH, if the acid consumption (pH 4.8) is 20 mg CaCO ３ / L or more, and by adjusting the pH so that it does not fall below this set value, the acid consumption in the aqueous system (pH 4.8) is reduced to 20 mg CaCO ３ / L or more.

[0056] In the present invention, the carbon dioxide absorbed in the carbon dioxide absorbent is generally recovered by heating the absorbent to desorb the carbon dioxide gas, and the carbon dioxide absorbent after carbon dioxide desorption is reused.

[0057] As described above, acidic gases other than carbon dioxide are difficult to desorb from a carbon dioxide absorbent or denature the carbon dioxide absorbent, thereby deteriorating the carbon dioxide absorbent. According to the present invention, by removing acidic gases other than carbon dioxide from the atmosphere before the atmosphere comes into contact with the carbon dioxide absorbent by absorbing them in spray water in advance, it is possible to minimize the deterioration of the carbon dioxide absorbent due to the acidic gases. As a result, the life of the carbon dioxide absorbent can be extended.

[0058] Furthermore, extending the life of the carbon dioxide absorbent reduces the frequency with which the carbon dioxide absorbent needs to be replaced, thereby reducing costs such as labor and raw material costs for replacement, and reducing the frequency with which new carbon dioxide absorbents are produced also reduces the amount of carbon dioxide generated from the carbon dioxide absorbent production process.

[0059] The present invention will be explained more specifically below by way of experimental examples which serve as substitutes for working examples.

[0060] [Experimental Example I] <Experimental Conditions> It was confirmed whether there was a difference in carbon dioxide absorption performance between an aqueous absorbent solution neutralized with an acidic substance (neutralizing agent) and an aqueous absorbent solution that was not neutralized, and whether there was a difference in absorption performance depending on the type of acidic substance.

[0061] A carbon dioxide concentration monitor and a rotor were placed in a 4 L airtight container, and with the lid of the airtight container open, the rotor was rotated with a stirrer and left to stand until the carbon dioxide concentration in the airtight container stabilized.

[0062] Thereafter, 100 mL of the absorbent aqueous solution shown in Table 1 and a rotor were placed in a beaker, and the beaker was placed in a sealed container. The rotor in the beaker was stirred with a stirrer, and the lid of the sealed container was immediately closed. The carbon dioxide concentration in the sealed container was measured immediately after the start and 10 minutes after the lid was closed, starting from the time when the lid was closed. The results are shown in Table 2.

[0063]

[0064] <Results / Discussion>

[0065] In both Experimental Examples I-1 and 2, the carbon dioxide concentration decreased after 10 minutes, indicating that the absorbent had absorbed carbon dioxide. On the other hand, in Comparative Experimental Examples I-1 to I-4, the carbon dioxide concentration did not decrease, indicating that the absorbent cannot absorb carbon dioxide once it has been neutralized by an acidic substance.

[0066] [Experimental Example II] <Experimental Conditions> It was confirmed whether there was a difference in carbon dioxide absorption performance between an absorbent alone that had been neutralized with an acidic substance and an absorbent alone that had not been neutralized.

[0067] A carbon dioxide concentration monitor and a rotor were placed in a 4 L airtight container, and with the lid of the airtight container open, the rotor was rotated with a stirrer and left to stand until the carbon dioxide concentration in the airtight container stabilized. Then, 10 mmol of the absorbent alone shown in Table 3 was placed in a petri dish and placed in the airtight container, and the lid of the airtight container was immediately closed. Starting from the time when the lid was closed, the carbon dioxide concentration in the airtight container was measured immediately after the start and 10 minutes later. The results are shown in Table 4.

[0068]

[0069] <Results / Discussion>

[0070] In Experimental Example II-1, the carbon dioxide concentration decreased after 10 minutes, indicating that the absorbent had absorbed carbon dioxide. On the other hand, in Comparative Experimental Example II-1, the carbon dioxide concentration did not decrease, indicating that an absorbent that had been neutralized by an acidic substance to become a hydrochloride salt could no longer absorb carbon dioxide.

[0071] [Experimental Example III] <Experimental Conditions> An evaluation was made to see whether or not spray water in a cooling tower can absorb acidic gas. Acetic acid gas was used as the acidic gas.

[0072] In a water system with a capacity of 100 L, which has a cooling tower (Nihon Spindle, CTA-3FNE) and a pump for circulating spray water, the acid consumption (pH 4.8) was 30 mg CaCO3 when pure water was used as spray water. ３The difference in acetic acid gas absorption efficiency was determined between the case where a 1000 ml / L aqueous sodium bicarbonate solution was used and the case where a 1000 ml / L aqueous sodium bicarbonate solution was used. Glacial acetic acid (molecular weight 60) was used as the source of acetic acid gas, and glacial acetic acid exposed to the atmosphere was placed in the intake section of the cooling tower. The amount of gas absorbed was calculated using the following formula (1) by measuring the TOC concentration of the circulating spray water before and after the test. The amount of gas volatilized was calculated from the change in weight of glacial acetic acid before and after the test. The acetic acid gas absorption efficiency was calculated using the following formula (2). The test time was 1 hour. Table 6 shows the acetic acid gas absorption efficiency, and Table 7 shows the acid consumption (pH 4.8) of the spray water before and after the test.

[0073] (Formula 1) Gas absorption amount (g) = (TOC concentration after test (mg / L) - TOC concentration before test (mg / L)) × 60 / 12 × 100 (L) / 1000 (Formula 2) Absorption efficiency (%) = Gas absorption amount (g) / Gas volatilization amount (g) × 100

[0074]

[0075] <Results / Discussion>

[0076]

[0077] In Experimental Example III-1, nearly 100% of the evaporated acidic gas, acetic acid, was absorbed, whereas in Comparative Experimental Example III-1, approximately 10% of the evaporated acetic acid gas passed through the cooling tower without being absorbed. Acetic acid is a compound that is highly soluble in water, and in the spray water of Comparative Experimental Example III-1, where no acid consumption occurred, the absorption of acetic acid caused a decrease in pH, which is thought to be the cause of this, as well as a decrease in the dissolution rate of acetic acid. On the other hand, in Experimental Example III-1, although a decrease in acid consumption was observed, acid consumption continued even after the test, and the spray water remained at a pH of 7.4 after the test without becoming acidic, which is thought to be why the absorption performance of acetic acid gas was maintained.

[0078] From the above experimental results, the acid consumption of the spray water (pH 4.8) was 20 mg CaCO ３ / L or more, acidic gases other than carbon dioxide are absorbed into the spray water before the atmosphere comes into contact with the carbon dioxide absorbent, thereby minimizing the deterioration of the carbon dioxide absorption performance of the carbon dioxide absorbent due to acidic gases other than carbon dioxide, and prolonging the life of the carbon dioxide absorbent.

[0079] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of the effects of the invention. This application is based on Japanese Patent Application No. 2023-097108 filed on June 13, 2023, and is incorporated by reference in its entirety.

[0080] 1 Cooling tower 4 Lower water tank (pit) 6 Water collection tank 10 Valve device 17 Heat exchanger 20 CO ２ Absorption facility

Claims

1. A method for recovering carbon dioxide, comprising a step of contacting air with spray water and then contacting the air with a carbon dioxide absorbent to absorb carbon dioxide in the air, comprising the steps of: reducing the acid consumption (pH 4.8) in the spray water to 20 mg CaCO ３ / L or more.

2. The acid consumption of the spray water (pH 4.8) is 20 mg CaCO ３ / L, the acid consumption of the spray water (pH 4.8) is 20 mg CaCO ３ 2. The method for recovering carbon dioxide according to claim 1, wherein a basic substance is added to the spray water so that the concentration of the basic substance in the spray water is equal to or more than 1 L.

3. The method for recovering carbon dioxide according to claim 2, wherein the basic substance is at least one selected from the group consisting of hydrogen carbonates, carbonates, hydroxides, silicates, ammonia, and amine compounds.

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