Carbon dioxide recovery method and recovery apparatus

Abstract

Provided is a carbon dioxide recovery method having a step for bringing a carbon-dioxide-containing gas into contact with a carbon dioxide absorbent to cause the carbon dioxide absorbent to absorb the carbon dioxide in the carbon-dioxide-containing gas, wherein the carbon dioxide absorbent contains a gel-form or solid first absorbent, and the ratio of the carbon dioxide absorption amount in an environment having a humidity of 80% or higher to the carbon dioxide absorption amount in an environment having a humidity of 40±10% for the carbon dioxide absorbent is 80% or higher. The carbon dioxide absorbent furthermore includes a second absorbent supported by the first absorbent. The second absorbent is preferably at least one of a basic absorbent and an amine compound absorbent.

Description

Carbon dioxide recovery method and recovery device

[0001] The present invention relates to a method and apparatus for recovering carbon dioxide from carbon dioxide-containing gases such as the atmosphere, and in particular to a method and apparatus for recovering carbon dioxide using a carbon dioxide absorbent. The carbon dioxide recovery method and apparatus of the present invention are useful as a method and apparatus for absorbing and recovering carbon dioxide from exhaust gases from cooling towers installed in factories, buildings, etc.

[0002] In recent years, in order to curb global warming, methods for reducing fuel and electricity consumption as well as methods for directly capturing carbon dioxide from the atmosphere have been considered. For example, Patent Document 1 describes an equipment for removing carbon dioxide from the atmosphere using an absorbent capable of adsorbing carbon dioxide. When using this equipment to absorb carbon dioxide from the atmosphere, it is necessary to actively send air into the adsorption equipment using a blower or the like. However, this requires electricity to operate the blower, which can become a new source of carbon dioxide. If a blower is not used, the efficiency of carbon dioxide absorption by the absorbent decreases. To compensate for this, the surface area of ​​the absorbent needs to be increased, which is not economical.

[0003] Patent Document 2 proposes a method that solves the above-mentioned problems by utilizing the power of a blower installed in the existing facility, while allowing for operation in the same manner as the existing facility. Here, the existing facility refers to a cooling tower or the like, and the facility of Patent Document 2 utilizes the power of the blower of the cooling tower used to cool the cooling water, and removes carbon dioxide from the atmosphere by efficiently bringing the atmosphere into contact with a carbon dioxide absorbent. However, Patent Document 2 does not particularly mention the selection of an absorbent that is optimal for this facility.

[0004] Conventionally, methods for absorbing carbon dioxide have been developed, such as a method of absorbing carbon dioxide with an alkaline absorption solution such as an amine or an alkali metal hydroxide, a method of adsorbing carbon dioxide into the pores of a porous body such as silica gel, zeolite, or activated carbon, and a method of absorbing carbon dioxide using a solid absorbent in which an amine is supported on the surface of silica gel, zeolite, or the like (Non-Patent Document 1).

[0005] US Patent Application Publication No. 2017 / 0106330 Patent No. 6738920

[0006] Ahmed Sodiq et al., A review on progress made in direct air capture of CO2, Environmental Technology & Innovation 29 (2023) 102991, https: / / doi.org / 10.1016 / j.eti.2022.102991

[0007] When absorbing carbon dioxide from exhaust gases such as cooling towers, moisture can be a hindrance. For example, it is known that the absorption capacity of zeolites decreases under high humidity conditions when absorbing carbon dioxide. On the other hand, alkaline absorbents such as potassium carbonate and tertiary amines require the presence of water vapor in the air because they react with carbon dioxide by generating hydroxide ions through the hydrolysis of water. Thus, the performance of the absorbent is affected by moisture.

[0008] On the other hand, since the humidity of the exhaust gas from the cooling tower is basically 100%, it is necessary to select a carbon dioxide absorbent that can absorb carbon dioxide under high humidity conditions.

[0009] An object of the present invention is to provide a carbon dioxide recovery method and recovery device that efficiently absorbs and recovers carbon dioxide using an absorbent that fully exhibits carbon dioxide absorption performance under high humidity conditions, in a carbon dioxide absorption technology that utilizes the power of a blower such as a cooling tower to absorb carbon dioxide using a carbon dioxide absorbent.

[0010] The present inventors have found that the above problems can be solved by using a specific carbon dioxide absorbent that shows little deterioration in carbon dioxide absorption performance even under high humidity conditions and does not flow during, before, or after carbon dioxide absorption.

[0011] The present invention provides the following.

[0012] [1] A method for recovering carbon dioxide, comprising a step of contacting a carbon dioxide-containing gas with a carbon dioxide absorbent to absorb carbon dioxide in the carbon dioxide-containing gas into the carbon dioxide absorbent, wherein the carbon dioxide absorbent comprises a first absorbent in a gel or solid state, and the ratio of the amount of carbon dioxide absorbed by the carbon dioxide absorbent in an environment with a humidity of 80% or more to the amount of carbon dioxide absorbed in an environment with a humidity of 40%±10% is 80% or more.

[0013] [2] The method for recovering carbon dioxide according to [1], wherein the carbon dioxide absorbent further includes a second absorbent supported on the first absorbent.

[0014] [3] The carbon dioxide recovery method according to [2], wherein the second absorbent is at least one of a basic absorbent and an amine compound absorbent.

[0015] [4] The method for recovering carbon dioxide according to any one of [1] to [3], wherein the carbon dioxide-containing gas is a gas obtained by contacting atmospheric air with spray water.

[0016] [5] The carbon dioxide recovery method according to [4], wherein the carbon dioxide-containing gas is exhaust gas from a cooling tower.

[0017] [6] A carbon dioxide recovery device that has a water sprinkling means and an air introduction fan, and that uses a carbon dioxide absorbent to absorb carbon dioxide in gas discharged from a cooling tower in which air introduced by the introduction fan comes into contact with sprayed water sprayed by the water sprinkling means to cool the sprayed water, wherein the carbon dioxide absorbent includes a first absorbent in a gel or solid state, and the ratio of the carbon dioxide absorption amount of the carbon dioxide absorbent in an environment with a humidity of 80% or more to the carbon dioxide absorption amount in an environment with a humidity of 40%±10% is 80% or more.

[0018] [7] The carbon dioxide recovery device according to [6], wherein the carbon dioxide absorbent further includes a second absorbent supported on the first absorbent.

[0019] [8] The carbon dioxide recovery device according to [7], wherein the second absorbent is at least one of a basic absorbent and an amine compound absorbent.

[0020] According to the present invention, when using a carbon dioxide absorbent to absorb and capture carbon dioxide in a highly humid carbon dioxide-containing gas such as the atmosphere after contact with spray water from a cooling tower, by utilizing the power of a blower such as a cooling tower, the carbon dioxide absorption capacity is reduced even under high humidity conditions, and by using a carbon dioxide absorbent that does not have any fluidity problems during, before, and after carbon dioxide absorption, high carbon dioxide absorption capacity can be maintained even for a highly humid carbon dioxide-containing gas, and efficient absorption and capture of carbon dioxide can be achieved over a long period of time. This makes it possible to achieve efficient carbon dioxide absorption while utilizing the power of existing equipment such as a cooling tower blower.

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

[0022] Hereinafter, an embodiment of the present invention will be described in detail.

[0023] The carbon dioxide recovery method of the present invention is a carbon dioxide recovery method comprising a step of contacting a carbon dioxide-containing gas with a carbon dioxide absorbent to absorb carbon dioxide in the carbon dioxide-containing gas into the carbon dioxide absorbent, wherein the carbon dioxide absorbent contains a gel-like or solid first absorbent, and is capable of absorbing carbon dioxide (CO ) in an environment of 40%±10% humidity. ２ ) absorption amount and the ratio of carbon dioxide absorption amount in an environment with humidity of 80% or more (hereinafter referred to as "wet / dry CO ２ The carbon dioxide absorbent (hereinafter referred to as the "CO absorbent of the present invention") has a carbon dioxide absorption ratio of 80% or more. ２ It is characterized by the use of a water-repellent material (sometimes referred to as an "absorbent").

[0024] In particular, the present invention is directed to a method for treating a carbon dioxide-containing gas in a high humidity condition after the atmosphere has come into contact with spray water from a cooling tower or the like, by using the CO ２ In contact with the absorbent ２As an example of such application, the carbon dioxide recovery device of the present invention has a water sprinkling means and an air introduction fan, and uses a carbon dioxide absorbent to absorb carbon dioxide in gas discharged from a cooling tower in which air introduced by the introduction fan comes into contact with sprayed water sprayed by the water sprinkling means to cool the sprayed water. ２ It uses an absorbent.

[0025] The present invention will be described in detail below by taking an example of application of the present invention to a cooling tower system. However, the present invention is not limited to cooling tower systems and can be effectively applied to existing facilities such as scrubbers, exhaust fans for indoor air conditioning, air-cooled chillers with fans, and heat pumps with fans. Furthermore, the present invention is not limited to those with fans, but can also be effectively applied to CO2 generators under high humidity conditions. ２ The present invention can be effectively applied to the treatment of contained gases.

[0026] There is no particular limitation on the type of cooling tower etc. to which the present invention is applied, as long as it is equipped with a sprinkler means for taking in spray water into the cooling tower etc. and sprinkling it, a packed bed which is a flow path for the sprayed spray water and a place where the air comes into contact with the spray water, and a blower (intake fan) for passing the air through the inside of the cooling tower etc. If the facility is missing one or more of these, the missing devices may be added to make up for it.

[0027] 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.

[0028] The sprinkling means for sprinkling water, the packed bed which is the flow path for the sprinkled water and where the air comes into contact with the sprinkled water, and the blower (intake fan) for passing the air into the cooling tower or the like may be any general mechanism for efficient contact between air and water. Therefore, other devices such as an aeration tank can be considered to be essentially the same as a cooling tower or the like as long as they have a mechanism for efficient contact between air and water and can create an air flow, and the present invention can be applied to them. In addition, atmospheric CO ２ In addition, CO generated in factories, etc.２ It can also be mixed with air and then pumped into a cooling tower or similar.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 emits CO ２ CO with absorbent ２ Absorption equipment (CO ２ The CO ２ is absorbed and removed.

[0033] CO ２ The absorption equipment is a CO absorbing equipment of the present invention installed in the downstream of the spray water sprinkler equipment such as the cooling tower. ２ Examples of those provided with a packed bed of absorbent include those that ventilate the atmosphere after contact with spray water, for example, the outflow gas of a cooling tower.

[0034] Cooling towers and other equipment are used as sprinklers to remove CO from the atmosphere. ２ If pressure loss occurs when supplying the refrigerant to the absorption facility and the minimum air volume originally required in the cooling tower or the like cannot be ensured, a blower may be added.

[0035] 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 to the power supply, etc. The water sprayed is not limited to a circulating type, but can also be a passing type.

[0036] Hereinafter, the CO ２ The absorbent will now be described.

[0037] General CO ２ The absorbent absorbs low concentrations of CO ２ They have the ability to absorb substances such as ammonium nitrate, ammonium nitrate, and ammonium nitrate. Some absorb substances through chemical mechanisms such as acid-base reactions and carbamic acid production reactions, while others absorb substances through physical mechanisms such as adsorption and dissolution, and some use a combination of these.

[0038] The CO of the present invention ２ The absorbent includes a first absorbent in a gel or solid form, and the wet / dry CO ２ The absorption ratio is 80% or more. ２ CO absorption in a high humidity environment of 80% or more ２ The absorption amount is 80% or more, and the first absorbent is in a gel or solid state with low fluidity, so that CO ２ When filled into an absorption facility, it produces high CO without being affected by humidity. ２ Absorption capacity ensures stable and efficient CO ２ The relative humidity of exhaust gas from cooling towers, etc. is 100%, which is extremely high, so an absorbent that does not lose its absorption capacity even at high humidity and does not undergo state changes due to deliquescence, etc., is suitable.

[0039] The CO of the present invention ２ Wet / Dry CO Absorbent ２ The absorption ratio is measured, for example, by the method described in the Examples section below. ２ Wet / Dry CO Absorbent ２ If the absorption ratio is less than 80%, CO ２ The absorption capacity is reduced, and CO2 is efficiently absorbed in applications such as cooling tower systems. ２ The CO absorption and recovery of the present invention cannot be achieved. ２ Wet / Dry CO Absorbent２ The absorption ratio may be 80% or more, preferably 90% or more, and more preferably 100% or more, i.e., the CO absorption amount in a high humidity environment is equal to or greater than that in a low humidity environment. ２ It may be one that can obtain an absorption amount.

[0040] In the present invention, "humidity 40%±10%" refers to dry conditions with a relative humidity of 30 to 50%. Also, "humidity 80% or higher" refers to a relative humidity of 80% or higher. In the examples described later, the humidity was 40%±10% at a temperature of 25°C. ２ The absorption ratio is measured, and the temperature condition for this measurement is usually within the range of 10 to 50°C.

[0041] Such wet / dry CO ２ The CO absorption ratio of the present invention satisfies ２ The first absorbent is a material that absorbs CO by a physical mechanism (adsorption). ２ These include gel absorbents or solid absorbents that absorb CO by a physical mechanism (adsorption). ２ Examples of gel absorbents or solid absorbents that absorb fluorine include activated carbon, zeolite, silica gel, organometallic structures, gel polymer compounds, etc. These may be used alone or in combination of two or more.

[0042] The CO of the present invention ２ The absorbent preferably further includes a second absorbent supported on the first absorbent. ２ The absorption rate is likely to be improved.

[0043] The second absorbent is a substance that absorbs CO by chemical mechanisms such as acid-base reactions and carbamic acid formation reactions. ２ absorbent, which absorbs CO by physical mechanism (dissolution) ２ These may be used alone or in combination of two or more.

[0044] CO due to acid-base reaction ２Examples of basic absorbents that absorb CO include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, and tertiary amine compounds. ２ Examples of amine compound absorbents that absorb methyl methacrylate include primary or secondary amine absorbents such as monoethanolamine, diethanolamine, isopropanolamine, N-methyldiethanolamine, piperazine, and 2-methylpiperazine. Examples of dissolving agents include a solution of polyethylene glycol in dimethyl ether and methanol.

[0045] The CO of the present invention ２ The absorbent may be, for example, a water-absorbing gel substance that has absorbed a basic absorbent aqueous solution, an amine absorbing solution, or the like; a solid absorbent in which an amine compound or the like is supported on a porous substance such as activated carbon, zeolite, or silica gel; or a gel-like polymer compound that has an amine group as a functional group.

[0046] Wet / Dry CO ２ CO absorption ratio of 80% or more can be achieved ２ The absorbent can be produced using the above-described first absorbent and preferably also a second absorbent, for example, by the following procedure: (1) The first absorbent and the second absorbent, such as an amine absorbing solution or a basic absorbent aqueous solution, are mixed together in order to allow the first absorbent, such as a dry water-absorbing gel substance or porous substance, to absorb the second absorbent. (2) The mixture of the first absorbent and the second absorbent is filtered to remove excess water, and then the water is removed using a rotary evaporator or the like, or in a dry oven or the like at a temperature at which the absorbent components do not volatilize. (3) If there is a concern about carbon dioxide adsorption during drying, the carbon dioxide attached during production is removed by maintaining the mixture at a temperature at which carbon dioxide desorbs in a dry oven or the like.

[0047] In the present invention, the CO ２ CO absorbed in the absorbent ２ is generally CO ２ By heating the absorbent, CO ２ It is recovered by desorption as a gas, and CO２ CO after desorption ２ The absorbent is reused.

[0048] The present invention will be described in more detail below with reference to experimental examples including working examples and comparative examples.

[0049] [Experimental Example: CO ２ CO absorption experiment in different humidity environments ２ The effectiveness of the gas absorbent was confirmed. All of the following experiments were carried out at 25°C. ２ A concentration monitor, a hygrometer, and a rotor were placed in the sealed container, and the rotor was rotated with a stirrer while the lid of the sealed container was left open. ２ The container was left standing until the concentration stabilized. After that, for high humidity conditions (humid environment), a beaker containing a separate stirrer was filled with about 100 mL of water and placed in the sealed container. The water in the beaker and the sealed container were stirred with a starter while being left standing until the relative humidity reached 80% or more (measured value by a hygrometer), and the humidity was adjusted. On the other hand, for low humidity conditions (dry environment), the lid was closed as it was, and the sealed container was left standing for the same amount of time while being stirred, and the humidity was adjusted to 30 to 40%. Then, the CO ２ The absorbent was placed in a petri dish and placed in a sealed container, and the lid of the sealed container was immediately closed. The time when the lid was closed was taken as the starting point, and the CO in the sealed container was measured immediately after the start and 10 minutes later. ２ The results are shown in Table 2. ２ The state of the absorbent was visually observed to check for any change in state due to deliquescence. The results are shown in Table 3.

[0050]

[0051]

[0052]

[0053] <Discussion> The above results reveal the following: In both Examples 1 and 2, CO ２ The decrease in absorption capacity was slight and there was no change in state, so it is not easily degraded under high humidity conditions and is effective in absorbing CO from the exhaust gas of the cooling tower. ２It can be said that the material is suitable for absorbing CO under high humidity conditions. ２ Although the absorption amount was maintained at a high level, a change in state due to deliquescence occurred. ２ In Comparative Example 4, the CO absorption amount was reduced due to the alkaline agent contained in the absorbent. ２ occurs, and after 10 minutes, CO ２ It is believed that the concentration of the alkaline agent has increased. The type of alkaline agent is unknown, but it is likely to be bicarbonate.

[0054] 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. 2023-140204 filed on August 30, 2023, and is incorporated by reference in its entirety.

[0055] 1 Cooling tower 2 Sprinkler system 3 Filler 4 Lower water tank (pit) 5 Fan 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 a carbon dioxide-containing gas with a carbon dioxide absorbent and causing the carbon dioxide in the carbon dioxide-containing gas to be absorbed by the carbon dioxide absorbent, wherein the carbon dioxide absorbent comprises a first absorbent in a gel or solid state, and the ratio of the amount of carbon dioxide absorbed by the carbon dioxide absorbent in an environment with a humidity of 80% or more to the amount of carbon dioxide absorbed in an environment with a humidity of 40%±10% is 80% or more.

2. The method for recovering carbon dioxide according to claim 1, wherein the carbon dioxide absorbent further comprises a second absorbent supported on the first absorbent.

3. The method for recovering carbon dioxide according to claim 2, wherein the second absorbent is at least one of a basic absorbent and an amine compound absorbent.

4. A method for recovering carbon dioxide according to any one of claims 1 to 3, wherein the carbon dioxide-containing gas is a gas obtained after contacting atmospheric air with spray water.

5. The method for recovering carbon dioxide according to claim 4, wherein the carbon dioxide-containing gas is exhaust gas from a cooling tower.

6. A carbon dioxide recovery device that has a water sprinkling means and an air introduction fan, and uses a carbon dioxide absorbent to absorb carbon dioxide in gas discharged from a cooling tower in which the air introduced by the introduction fan comes into contact with the water sprinkled by the water sprinkling means to cool the water, wherein the carbon dioxide absorbent includes a first absorbent in a gel or solid state, and the ratio of the amount of carbon dioxide absorbed by the carbon dioxide absorbent in an environment with a humidity of 80% or more to the amount of carbon dioxide absorbed in an environment with a humidity of 40% ± 10% is 80% or more.

7. The carbon dioxide recovery apparatus according to claim 6, wherein the carbon dioxide absorbent further comprises a second absorbent supported on the first absorbent.

8. The carbon dioxide recovery apparatus according to claim 7, wherein the second absorbent is at least one of a basic absorbent and an amine compound absorbent.

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