Carbon dioxide recovery method and recovery apparatus

Abstract

To provide a method and an apparatus for efficiently absorbing and recovering carbon dioxide by using an absorbent that sufficiently exhibits a carbon dioxide absorption performance under high humidity conditions in a carbon dioxide absorption technique that absorbs carbon dioxide by using the carbon dioxide absorbent by utilizing blower power of a cooling tower or the like.SOLUTION: In a carbon dioxide recovery method including a step of bringing a carbon dioxide-containing gas into contact with a carbon dioxide absorbent to make the carbon dioxide absorbent absorb carbon dioxide in the carbon dioxide-containing gas, the carbon dioxide absorbent includes a first absorbent in a gel or a solid form, and a ratio of a carbon dioxide absorption amount under an environment with 80% or higher of humidity to a carbon dioxide absorption amount under an environment with 40%±10% of humidity of the carbon dioxide absorbent is equal to or greater than 80%. The carbon dioxide absorbent further includes a second absorbent carried on the first absorbent, and the second absorbent is preferably at least one type of a basic absorbent and an amine compound absorbent.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for recovering carbon dioxide from a carbon dioxide-containing gas such as the atmosphere, and in particular to a method and an apparatus for recovering carbon dioxide using a carbon dioxide absorbent. The method and apparatus for recovering carbon dioxide of the present invention are useful as a method and an apparatus for absorbing and recovering carbon dioxide from exhaust gas from a cooling tower installed in a factory, a building, etc. [Background technology]

[0002] In recent years, in order to suppress global warming, methods for directly recovering carbon dioxide from the atmosphere, in addition to methods for reducing the amount of fuel and electricity used, 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 this equipment is used 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, in this case, electricity is required to operate the blower, which may become a new source of carbon dioxide. If a blower is not used, the efficiency of carbon dioxide absorption by the absorbent decreases, so it is necessary to increase the surface area of ​​the absorbent to compensate for this, which is not economical.

[0003] Patent Document 2 proposes a method that can be operated in the same way as existing equipment and solves the above problems by utilizing the power of a blower installed in the existing equipment. Here, the existing equipment refers to a cooling tower or the like, and the equipment of Patent Document 2 utilizes the power of a blower of a cooling tower used to cool cooling water, and efficiently brings the air into contact with a carbon dioxide absorbent, thereby removing carbon dioxide from the air. However, this document does not particularly mention the selection of an absorbent that is optimal for this equipment.

[0004] Conventionally, methods for absorbing carbon dioxide have been developed, such as a method of absorbing carbon dioxide with an alkaline absorbing 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). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2017 / 0106330 [Patent Document 2] Patent No. 6738920 [Non-patent literature]

[0006] [Non-Patent Document 1] 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 Summary of the Invention [Problem to be solved by the invention]

[0007] When absorbing carbon dioxide from exhaust gases such as cooling towers, moisture can be an obstacle. For example, it is known that the amount of carbon dioxide absorbed by zeolite decreases under high humidity conditions. On the other hand, alkaline absorbents such as potassium carbonate and tertiary amines require the presence of water vapor in the air because hydroxide ions are generated by hydrolysis of water and can react with carbon dioxide. In this way, the performance of the absorbent is affected by moisture. On the other hand, since the humidity of the exhaust gas from a cooling tower is basically 100%, it is necessary to select a carbon dioxide absorbent that can absorb carbon dioxide under high humidity conditions.

[0008] The present invention aims 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. [Means for solving the problem]

[0009] As a result of extensive investigations aimed at solving the above problems, the present inventors have found that the above problems can be solved by using a specific carbon dioxide absorbent that exhibits little deterioration in carbon dioxide absorption performance even under high humidity conditions and does not flow during, before, or after carbon dioxide absorption.

[0010] That is, the present invention relates to the following.

[0011] [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, The carbon dioxide absorbent comprises a first absorbent in a gel or solid state; A method for recovering carbon dioxide, wherein 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.

[0012] [2] The method for recovering carbon dioxide described in [1], wherein the carbon dioxide absorbent further includes a second absorbent supported on the first absorbent.

[0013] [3] The method for recovering carbon dioxide according to [2], wherein the second absorbent is at least one of a basic absorbent and an amine compound absorbent.

[0014] [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 after contacting atmospheric air with spray water.

[0015] [5] The method for recovering carbon dioxide described in [4], wherein the carbon dioxide-containing gas is exhaust gas from a cooling tower.

[0016] [6] A carbon dioxide recovery device having a water sprinkling means and an air introduction fan, 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 sprinkled, and which absorbs carbon dioxide in gas discharged from a cooling tower with a carbon dioxide absorbent, The carbon dioxide absorbent comprises a first absorbent in a gel or solid state; A carbon dioxide recovery device in which 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.

[0017] [7] The carbon dioxide recovery apparatus described in [6], wherein the carbon dioxide absorbent further includes a second absorbent supported on the first absorbent.

[0018] [8] The carbon dioxide recovery apparatus according to [7], wherein the second absorbent is at least one of a basic absorbent and an amine compound absorbent. Effect of the Invention

[0019] According to the present invention, when carbon dioxide is absorbed and captured using a carbon dioxide absorbent in a highly humid carbon dioxide-containing gas, such as the atmosphere after contact with water sprayed from a cooling tower, by utilizing the power of a blower such as a cooling tower, a carbon dioxide absorbent that exhibits little decrease in carbon dioxide absorption capacity even under high humidity conditions and has no fluidity problems before, during and after carbon dioxide absorption is used, thereby maintaining high carbon dioxide absorption capacity even for a highly humid carbon dioxide-containing gas, and enabling efficient absorption and capture of carbon dioxide over a long period of time. This makes it possible to realize efficient carbon dioxide absorption while utilizing the power of existing equipment such as cooling tower fans. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a cooling tower system to which the present invention is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments.

[0022] 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 and causing the carbon dioxide in the carbon dioxide-containing gas to be absorbed by the carbon dioxide absorbent, characterized in that the carbon dioxide absorbent comprises a gel or solid first absorbent and uses a carbon dioxide absorbent (hereinafter sometimes referred to as the "CO2 absorbent of the present invention") having a carbon dioxide (CO2) absorption amount in an environment with a humidity of 40%±10% and a ratio of the carbon dioxide absorption amount in an environment with a humidity of 80% or more (hereinafter sometimes referred to as the "wet / dry CO2 absorption amount ratio") of 80% or more.

[0023] The present invention is particularly preferably applied to the case where a carbon dioxide-containing gas in a high humidity condition after the atmosphere has come into contact with water sprayed in a cooling tower or the like is brought into contact with the CO2 absorbent of the present invention to absorb CO2. As an example of such an application, the carbon dioxide recovery device of the present invention has a sprinkling means and an air introduction fan, and the air introduced by the introduction fan comes into contact with the sprayed water sprayed by the sprinkling means to cool the sprayed water, and the carbon dioxide in the gas discharged from the cooling tower is absorbed by a carbon dioxide absorbent, and the above-mentioned CO2 absorbent of the present invention is used as the carbon dioxide absorbent.

[0024] The present invention will be described in detail below with reference to an example of application of the present invention to a cooling tower system, but the present invention is not limited to cooling tower systems and can be effectively applied to existing equipment such as scrubbers, exhaust fans for indoor air conditioning, air-cooled chillers with fans, and heat pumps with fans. The present invention can also be effectively applied to equipment that is not limited to those with fans and is used to treat CO2-containing gas under high humidity conditions.

[0025] There is no particular limit to the type of cooling tower or the like to which the present invention can be applied, as long as it is equipped with a sprinkling means for taking in spray water into the cooling tower or the like and spraying it, a packed bed which is a flow path for the sprayed spray water and where the air comes into contact with the sprayed water, and a blower (intake fan) for passing the air through the interior of the cooling tower or the like. Furthermore, if the equipment is missing one or more of these components, the missing devices may be added to make up for it. There is no particular limitation on the type of cooling tower, and it may be of any of the counter-flow type, counter-current type, and natural convection type, and may be of either the open type or the closed type. The sprinkling means for spraying water, the packed bed which is the flow path for the sprayed water and where the air comes into contact with the sprayed water, and the blower (inlet fan) for passing the air into the interior of a cooling tower or the like may be general mechanisms for efficiently bringing air and water into contact, and other devices, such as an aeration tank, can also be regarded as being essentially the same as a cooling tower or the like as long as they have a mechanism for efficiently bringing air and water into contact and are capable of creating an air flow, and the present invention can be applied to such devices. In addition to atmospheric CO2, which is the source of carbon dioxide, CO2 generated in factories, etc. can also be mixed with air and then sent to a cooling tower, etc.

[0026] 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.

[0027] 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, and accumulates 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 the circulation pump 15, the circulation supply pipe 16, the heat exchanger 17, and the circulation return pipe 18. The water collection tank 6 is recessed downward from the bottom of the lower water tank 4.

[0028] New water in an amount corresponding to the amount of evaporation and splash 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 piping 9 and a valve device 10 such as a ball tap.

[0029] The air that comes into contact with the spray water inside the cooling tower 1 flows out from the top of the cooling tower 1 and is sent to a CO2 absorption equipment (corresponding to the CO2 recovery device of the present invention) 20 containing a CO2 absorbent, where the CO2 is absorbed and removed.

[0030] Examples of CO2 absorption equipment include equipment that is provided with a packed bed of the CO2 absorbent of the present invention, which is installed downstream of a water spraying equipment such as the above-mentioned cooling tower, and that ventilates the air that has come into contact with the sprayed water, for example, the outflow gas from the cooling tower.

[0031] If pressure loss occurs when using a cooling tower or other device as a sprinkler system to supply atmospheric air to the CO2 absorption system, and the minimum amount of air originally required in the cooling tower or other device cannot be secured, a 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 to the power source. The spray water is not limited to a circulating type, but may be a passing type.

[0033] The CO2 absorbent of the present invention will be described below. Typical CO2 absorbents have the ability to absorb low concentrations of CO2 in the atmosphere, and include those that absorb through chemical mechanisms such as acid-base reactions and carbamic acid production reactions, those that absorb through physical mechanisms such as adsorption and dissolution, and those that use a combination of these.

[0034] The CO2 absorbent of the present invention is characterized in that it contains a gel or solid first absorbent and has the above-mentioned wet / dry CO2 absorption ratio of 80% or more. The amount of CO2 absorbed in a high humidity environment of 80% or more is 80% compared to the amount of CO2 absorbed in a low humidity environment of around 40% (humidity 40% ± 10%), and the first absorbent is in a gel or solid state with low fluidity.When filled into a CO2 absorption equipment, it is not affected by humidity and can absorb CO2 stably and efficiently with high CO2 absorption capacity. The relative humidity of exhaust 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.

[0035] The wet / dry CO2 absorption ratio of the CO2 absorbent of the present invention is measured, for example, by the method described in the Examples section below. If the wet / dry CO2 absorption ratio of the CO2 absorbent is less than 80%, the CO2 absorption capacity under high humidity conditions decreases, and efficient CO2 absorption and capture cannot be achieved when applied to cooling tower systems, etc. The wet / dry CO2 absorption ratio of the CO2 absorbent of the present invention may be 80% or more, preferably 90% or more, and may be 100% or more, i.e., a CO2 absorption amount equal to or greater than the absorption amount in a low humidity environment can be obtained even in a high humidity environment.

[0036] In the present invention, "humidity 40%±10%" refers to a dry condition with a relative humidity of 30 to 50%, and "humidity 80% or higher" refers to a relative humidity of 80% or higher. In the examples given later, the measurement for determining the wet / dry CO2 absorption ratio is carried out at a temperature of 25°C, but the measurement temperature condition may usually be within the range of 10 to 50°C.

[0037] The first absorbent of the CO2 absorbent of the present invention that satisfies such a wet / dry CO2 absorption ratio may be a gel absorbent or a solid absorbent that absorbs CO2 by a physical mechanism (adsorption). Gel absorbents or solid absorbents that absorb CO2 by a physical mechanism (adsorption) include absorbents such as activated carbon, zeolite, silica gel, organometallic frameworks, gel polymer compounds, etc. These may be used alone or in combination of two or more.

[0038] The CO2 absorbent of the present invention preferably further comprises a second absorbent supported on the first absorbent, which makes it easier to improve the CO2 absorption amount.

[0039] The second absorbent may be an absorbent that absorbs CO2 by a chemical mechanism such as an acid-base reaction or a carbamic acid production reaction, or a dissolving agent that absorbs CO2 by a physical mechanism (dissolution). These may be used alone or in combination of two or more.

[0040] Basic absorbents that absorb CO2 through an acid-base reaction include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, and tertiary amine compounds. Examples of amine compound absorbents that absorb CO2 through a carbamic acid production reaction include primary or secondary amine absorbents such as monoethanolamine, diethanolamine, isopropanolamine, N-methyldiethanolamine, piperazine, and 2-methylpiperazine. The dissolving agent may be a solution of polyethylene glycol in dimethyl ether, or methanol.

[0041] The CO2 absorbent of the present invention may be, for example, a water-absorbing gel substance having 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 having an amine group as a functional group.

[0042] A CO2 absorbent capable of achieving a wet / dry CO2 absorption ratio of 80% or more can be produced by using the first absorbent as described above and preferably also a second absorbent, for example, by taking the following measures. (1) A first absorbent, such as a dry water-absorbing gel material or porous material, is mixed with a second absorbent, such as an amine absorbing solution or an aqueous basic absorbent solution, so that the first absorbent is absorbed into the second absorbent. (2) The mixture of the first absorbent and the second absorbent is filtered and excess water is removed, and then the water is removed using a rotary evaporator or a dry oven at a temperature that does not cause the absorbent components to volatilize. (3) If there is concern about the adsorption of carbon dioxide during drying, the carbon dioxide that adhered during production can be removed by maintaining the temperature at which carbon dioxide desorbs in a dry oven or similar device.

[0043] In the present invention, the CO2 absorbed by the CO2 absorbent of the present invention is generally recovered by desorbing it as CO2 gas by heating the CO2 absorbent, and the CO2 absorbent after CO2 desorption is reused. EXAMPLES

[0044] The present invention will be described more specifically below with reference to experimental examples including working examples and comparative examples.

[0045] [Experimental example: CO2 absorption experiment] The effectiveness of the CO2 gas absorbent in different humidity environments was confirmed. All of the following experiments were carried out at 25°C. A CO2 concentration monitor, a hygrometer, and a rotor were placed in a 4 L sealed container, and with the lid of the container open, the rotor was rotated with a stirrer and the container was left to stand until the CO2 concentration in the container stabilized. Then, for high humidity conditions (humid environment), a beaker containing approximately 100 mL of water and a stirrer was placed inside the sealed container, and the water in the beaker and the sealed container were stirred with a starter while being left alone until the relative humidity reached 80% or higher (measured value by a hygrometer) to adjust the humidity. On the other hand, for low humidity conditions (dry environment), the lid was closed and the container was left for the same period while stirring to adjust the relative humidity to 30 to 40%. After that, the CO2 absorbent shown in Table 1 was placed in a petri dish, which was then placed in a sealed container, and the lid of the sealed container was immediately closed. The time when the lid was closed was set as the starting point, and the CO2 concentration in the sealed container was measured immediately after the start and 10 minutes later. The results are shown in Table 2. In addition, the state of the CO2 absorbent after the test was visually observed to see whether there was any change in state due to deliquescence. The results are shown in Table 3.

[0046] [Table 1]

[0047] [Table 2]

[0048] [Table 3]

[0049] <Consideration> The above results reveal the following: In both Examples 1 and 2, the decrease in the amount of CO2 absorbed under high humidity conditions was slight, and there was no change in state. Therefore, it can be said that these materials are less susceptible to deterioration under high humidity conditions and are suitable for absorbing CO2 from exhaust gas from cooling towers. In Comparative Examples 1 and 2, the amount of CO2 absorption was maintained high under high humidity conditions, but a change in state occurred due to deliquescence. In Comparative Examples 3 and 4, the amount of CO2 absorption decreased under high humidity conditions. In Comparative Example 4, it is believed that CO2 was generated due to the alkaline agent contained in the absorbent, resulting in a high CO2 concentration after 10 minutes. The alkaline agent is unknown, but is probably bicarbonate. [Explanation of symbols]

[0050] 1 cooling tower 2. Watering system 3 Filling material 4 Lower water tank (pit) 5 Fan 6 Water collection tank 10 Valve gear 17 Heat exchanger 20 CO2 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 to absorb carbon dioxide in the carbon dioxide-containing gas into the carbon dioxide absorbent, The carbon dioxide absorbent includes a first absorbent in a gel or solid state; A method for recovering carbon dioxide, wherein 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. 4. The method for recovering carbon dioxide according to claim 1, wherein the carbon dioxide-containing gas is a gas obtained after contacting atmospheric air with spray water.

5. 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, 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 sprinkled, and that absorbs carbon dioxide in gas discharged from a cooling tower with a carbon dioxide absorbent, The carbon dioxide absorbent includes a first absorbent in a gel or solid state; A carbon dioxide recovery device in which 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 device 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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