Carbon dioxide adsorption / desorption method and device

Abstract

A method and device by which carbon dioxide can be separated from a discharge gas containing carbon dioxide and the sorbing liquid can be easily regenerated. In a sorption tank 2, a discharge gas containing carbon dioxide is brought into contact with a sorbing liquid to obtain an aqueous metal carbonate solution. The aqueous metal carbonate solution is transferred to a desorption tank 3. While the inside of the desorption tank 3 is being depressurized, ultrasonic waves are applied to the aqueous metal carbonate solution to desorb the carbon dioxide from the aqueous metal carbonate solution and regenerate the sorbing liquid. The regenerated sorbing liquid is transferred to the sorption tank.

Description

[Technical field]

[0001] The present invention relates to a carbon dioxide adsorption / desorption method and device. [Background technology]

[0002] In recent years, there has been a demand to reduce emissions of carbon dioxide, a greenhouse gas, in order to curb global warming. In particular, thermal power plants and steelworks generate large amounts of exhaust gas, so various methods are being considered.

[0003] In order to reduce the amount of carbon dioxide emissions, for example, a carbon dioxide adsorption / desorption method has been proposed that includes a step of contacting exhaust gas containing carbon dioxide with an adsorption liquid consisting of an aqueous sodium hydroxide solution in an adsorption tank to obtain an aqueous sodium carbonate solution, a step of transferring the aqueous sodium carbonate solution from the adsorption tank to a desorption tank, a step of desorbing carbon dioxide from the aqueous sodium carbonate solution in the desorption tank to regenerate the adsorption liquid, and a step of transferring the regenerated adsorption liquid from the desorption tank to the adsorption tank (see, for example, Patent Document 1).

[0004] According to the invention described in Patent Document 1, carbon dioxide is adsorbed into the adsorption liquid in the adsorption tank to obtain an aqueous sodium carbonate solution, and then carbon dioxide is desorbed from the aqueous sodium carbonate solution in the desorption tank, thereby making it possible to efficiently separate only carbon dioxide from the exhaust gas containing carbon dioxide, and further, it is claimed that the adsorption liquid regenerated by desorption of carbon dioxide can be reused for adsorbing carbon dioxide in the adsorption tank. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2005-262051 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the method described in Patent Document 1, hydrogen chloride is used when desorbing carbon dioxide from the aqueous solution of sodium carbonate in the desorption tank, and therefore, after the carbon dioxide is desorbed, an aqueous solution of sodium chloride is produced as shown in the following formula: Na2CO3+ 2HCl → CO2+ 2NaCl + H2O

[0007] In order to regenerate the aqueous sodium hydroxide solution from the aqueous sodium chloride solution, the aqueous sodium chloride solution must be treated with a bipolar electrodialysis apparatus, and further, a process for regenerating hydrogen chloride from hydrogen and chlorine produced as by-products in the treatment with the bipolar electrodialysis apparatus is required, which is inconvenient in that the operation becomes complicated.

[0008] The present invention aims to provide a method for eliminating such inconveniences, capable of efficiently separating only carbon dioxide from exhaust gas containing carbon dioxide, and further capable of easily regenerating the adsorption liquid after desorption of carbon dioxide, and an apparatus used for said method. [Means for solving the problem]

[0009] In order to achieve this object, the carbon dioxide adsorption / desorption method of the present invention is a carbon dioxide adsorption / desorption method comprising the steps of: bringing exhaust gas containing carbon dioxide into contact with an adsorption liquid consisting of an aqueous solution of a hydroxide of a metal capable of producing carbonate in an adsorption tank to obtain an aqueous metal carbonate solution; transferring the aqueous metal carbonate solution from the adsorption tank to a desorption tank; desorbing carbon dioxide from the aqueous metal carbonate solution in the desorption tank to regenerate the adsorption liquid; and transferring the regenerated adsorption liquid from the desorption tank to the adsorption tank, wherein the step of desorbing carbon dioxide from the aqueous metal carbonate solution to regenerate the adsorption liquid is carried out by reducing the pressure inside the desorption tank and irradiating the aqueous metal carbonate solution contained in the reduced pressure desorption tank with ultrasound.

[0010] In the carbon dioxide adsorption / desorption method of the present invention, in the adsorption tank, exhaust gas containing carbon dioxide is brought into contact with an adsorption liquid consisting of an aqueous solution of a hydroxide of a metal capable of producing the carbonate, thereby causing the carbon dioxide to be adsorbed into the adsorption liquid and producing an aqueous solution of a metal carbonate.

[0011] In the present invention, the term "metal carbonate" includes metal carbonates and metal hydrogen carbonates.

[0012] Next, the metal carbonate aqueous solution is transferred from the adsorption tank to the desorption tank. The desorption tank is then depressurized, and the metal carbonate aqueous solution contained in the depressurized desorption tank is irradiated with ultrasonic waves to desorb carbon dioxide from the metal carbonate aqueous solution, thereby regenerating the adsorption liquid. The regenerated adsorption liquid is transferred to the adsorption tank and used again to adsorb carbon dioxide.

[0013] According to the carbon dioxide adsorption / desorption method of the present invention, carbon dioxide can be desorbed from the aqueous metal carbonate solution and the adsorption liquid can be regenerated simply by reducing the pressure in the desorption tank and irradiating the aqueous metal carbonate solution contained in the reduced pressure desorption tank with ultrasound. Therefore, it is possible to efficiently separate only carbon dioxide from exhaust gas containing carbon dioxide, and further, after desorption of carbon dioxide, the adsorption liquid can be easily regenerated.

[0014] The carbon dioxide adsorption / desorption method of the present invention can be carried out by a carbon dioxide adsorption / desorption apparatus comprising: an adsorption tank which is equipped with an adsorption liquid supplying means for supplying an adsorption liquid consisting of an aqueous solution of a hydroxide of a metal capable of producing carbonate; an exhaust gas supplying means for supplying exhaust gas containing carbon dioxide, and which obtains an aqueous metal carbonate solution by bringing the exhaust gas into contact with the adsorption liquid; an aqueous metal carbonate solution transferring means for transferring the aqueous metal carbonate solution from the adsorption tank to a desorption tank; a desorption tank which is equipped with an ultrasonic irradiation means and a pressure reducing means, and which desorbs carbon dioxide from the aqueous metal carbonate solution to regenerate the adsorption liquid; a carbon dioxide removal means for removing carbon dioxide from the desorption tank; and an adsorption liquid transfer means for transferring the regenerated adsorption liquid from the desorption tank to the adsorption tank.

[0015] In the carbon dioxide adsorption / desorption apparatus of the present invention, the adsorption tank is preferably part of a conduit for transporting exhaust gas from a source of exhaust gas containing carbon dioxide to the exhaust gas treatment device.

[0016] In the carbon dioxide adsorption / desorption device of the present invention, the conduit is preferably a pipeline connecting a source of exhaust gas containing carbon dioxide and the exhaust gas treatment device. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a system configuration diagram showing an example of an apparatus configuration used in the carbon dioxide adsorption / desorption method of the present invention. [Diagram 2] 1 is a flowchart showing a carbon dioxide adsorption / desorption method of the present invention. [Diagram 3] FIG. 1 is a system configuration diagram showing an example of an apparatus configuration used in the carbon dioxide adsorption / desorption method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0019] The carbon dioxide adsorption / desorption method of this embodiment can be carried out by, for example, a carbon dioxide adsorption / desorption device 1 shown in FIG.

[0020] As shown in Fig. 1, the carbon dioxide adsorption / desorption device 1 of this embodiment includes an adsorption tank 2 and a desorption tank 3. The adsorption tank 2 includes an adsorption liquid conduit 4 that supplies an aqueous solution of a hydroxide of a metal capable of generating carbonate as an adsorption liquid, and an exhaust gas supply conduit 5 that supplies exhaust gas containing carbon dioxide, and stores an aqueous metal carbonate solution 6 generated when the adsorption liquid adsorbs carbon dioxide. The adsorption tank 2 also includes an aqueous metal carbonate solution transfer conduit 7 that transfers the aqueous metal carbonate solution 6 to the desorption tank 3, and the aqueous metal carbonate solution transfer conduit 7 is connected to the desorption tank 3 via a first transfer pump 8.

[0021] The desorption tank 3 is provided with an ultrasonic transducer device 9 on the outside of the bottom surface for irradiating ultrasonic waves to the contained metal carbonate aqueous solution 6, as well as a vacuum pump 10 for reducing the pressure in the space above the metal carbonate aqueous solution 6, and a carbon dioxide transfer conduit 11 for sucking in carbon dioxide desorbed from the metal carbonate aqueous solution 6 and transferring it to the outside. The carbon dioxide transfer conduit 11 is provided with a suction pump 12 in the middle. The desorption tank 3 is also provided with an adsorption liquid transfer conduit 13 for transferring the adsorption liquid 6a regenerated by desorbing carbon dioxide from the metal carbonate aqueous solution 6 to the adsorption tank 2, and the adsorption liquid transfer conduit 13 is connected to the adsorption tank 2 via a second transfer pump 14.

[0022] Next, with reference to FIG. 2, a carbon dioxide adsorption / desorption method of this embodiment using the carbon dioxide adsorption / desorption device 1 shown in FIG. 1 will be described.

[0023] In the carbon dioxide adsorption / desorption method of this embodiment, first, an aqueous hydroxide solution of a metal capable of generating carbonate is supplied as an adsorption liquid to the adsorption tank 2 through the adsorption liquid conduit 4 (STEP 1). At the same time, exhaust gas containing carbon dioxide is supplied to the adsorption tank 2 through the exhaust gas supply pipe 5 (STEP 2), and the adsorption liquid and the exhaust gas are brought into gas-liquid contact in the adsorption tank 2 (STEP 3).

[0024] The aqueous hydroxide solution of a metal capable of generating a carbonate may be any aqueous hydroxide solution of a metal capable of generating a carbonate by reacting with carbon dioxide, and may be, for example, an aqueous hydroxide solution of a metal such as sodium, potassium, calcium, or magnesium, but it is preferable to use an aqueous sodium hydroxide solution. In the following, in this embodiment, a case in which an aqueous sodium hydroxide solution is used as the adsorption liquid will be described as an example.

[0025] The aqueous sodium hydroxide solution may be prepared from commercially available sodium hydroxide crystals or may be produced by electrolysis of an aqueous sodium chloride solution.

[0026] The gas-liquid contact between the adsorption liquid and the exhaust gas may be carried out by bringing the exhaust gas into contact with an aqueous sodium hydroxide solution in the adsorption tank 2 as shown in FIG. 1, or by bubbling the exhaust gas into the aqueous sodium hydroxide solution stored in the adsorption tank 2.

[0027] When the exhaust gas is contacted with the aqueous sodium hydroxide solution in the adsorption tank 2, the contact area between the exhaust gas and the aqueous sodium hydroxide solution may be increased by providing a shelf in the adsorption tank 2 and arranging packing used in a distillation column on the shelf. The gas-liquid contact between the adsorption liquid and the exhaust gas may be performed by combining two or more of the above-mentioned methods.

[0028] As a result of the gas-liquid contact, the aqueous sodium hydroxide solution as the adsorbent reacts with carbon dioxide, so that carbon dioxide is adsorbed into the aqueous sodium hydroxide solution, thereby obtaining an aqueous solution 6 containing sodium carbonate or sodium bicarbonate (STEP 4). In this embodiment, the aqueous solution 6 containing sodium carbonate or sodium bicarbonate is collectively referred to as an aqueous sodium carbonate solution 6 for convenience.

[0029] The end point of the reaction in which the aqueous sodium carbonate solution 6 is produced can be detected by a change in the property of the liquid stored in the adsorption tank 2 from strong alkali to acid. The change in the property of the liquid can be detected by a pH meter (not shown) that is provided in the adsorption tank 2.

[0030] Next, the aqueous sodium carbonate solution 6 produced in the adsorption tank 2 is transferred to the desorption tank 3 via the aqueous metal carbonate solution transfer pipe 7 by operating the first transfer pump 8. The first transfer pump 8 is stopped when a predetermined amount of the aqueous sodium carbonate solution 6 in the adsorption tank 2 has been transferred to the desorption tank 3.

[0031] Next, the upper space of the desorption tank 3 is depressurized to 5 to 50 kPa by the vacuum pump 10, and in the state where the inside of the desorption tank 3 is depressurized to the above-mentioned range, the metal carbonate aqueous solution 6 contained in the desorption tank 3 is subjected to 70 to 120 W / m by the ultrasonic transducer device 9. 2 , preferably 75 to 114 m 2By irradiating the solution with ultrasonic waves having a frequency of 100 to 300 kHz (STEP 5) at an output of 100 to 300 kHz, carbon dioxide is desorbed from the metal carbonate aqueous solution 6 (STEP 6).

[0032] The vacuum pump 10 starts operating after the first transfer pump 8 has stopped, and stops when the pressure in the upper space of the desorption tank 3 reaches the above-mentioned range. The suction pump 12 starts operating after the metal carbonate aqueous solution 6 is irradiated with ultrasonic waves by the ultrasonic transducer device 9, and stops when the reaction of desorbing carbon dioxide reaches its end point.

[0033] The vacuum pump 10 and the suction pump 12 may be any pump capable of reducing the pressure in the desorption tank 3, and may be a vacuum generating device such as an ejector or an aspirator.

[0034] As a modified example of the carbon dioxide adsorption / desorption method, the depressurization of the desorption tank 3 by the vacuum pump 10 in STEP 5 and the desorption of carbon dioxide by the suction pump 12 in STEP 6 may be performed by a single pump.

[0035] The end point of the reaction in which carbon dioxide is desorbed from the aqueous sodium carbonate solution 6 can be detected by a change in the property of the liquid stored in the desorption tank 3 from acidic to alkaline. The change in the property of the liquid can be detected by a pH meter (not shown) disposed in the desorption tank 3.

[0036] Next, the carbon dioxide is removed from the desorption tank 3 via the carbon dioxide transfer pipe 11 by operating the suction pump 12, and is stored separately (STEP 7).

[0037] The aqueous sodium carbonate solution 6 in the desorption tank 3 becomes an aqueous sodium hydroxide solution as carbon dioxide is desorbed, and is regenerated as an adsorbent solution 6a (STEP 8).

[0038] Next, by operating the second transfer pump 14, the regenerated adsorption liquid 6a is transferred to the adsorption tank 2 via the adsorption liquid transfer conduit 13, and can be used again for gas-liquid contact between the adsorption liquid 6a and the exhaust gas containing carbon dioxide. The second transfer pump 14 is stopped when a predetermined amount of the adsorption liquid 6a in the desorption tank 3 has been transferred to the adsorption tank 2.

[0039] Next, another embodiment of the carbon dioxide adsorption / desorption device 1 shown in Fig. 1 will be described with reference to Fig. 3. As shown in Fig. 3, the adsorption tank 2 in the carbon dioxide adsorption / desorption device 1 shown in Fig. 1 can be part of a conduit for transporting exhaust gas from a source 15 of exhaust gas containing carbon dioxide to an exhaust gas treatment device 17, and further, the conduit can be a pipeline 16 connecting the source of exhaust gas containing carbon dioxide and the exhaust gas treatment device.

[0040] Examples of the source 15 of the exhaust gas containing carbon dioxide include a thermal power plant, a steel mill, etc. Examples of the exhaust gas treatment device 17 include a device equipped with a neutralizing means for neutralizing nitrogen oxides, sulfur oxides, etc. contained in the exhaust gas, and a bag filter or the like for removing fly ash contained in the exhaust gas.

[0041] By using a part of a conduit, such as a pipeline 16, which transports exhaust gas from a source 15 of exhaust gas containing carbon dioxide to an exhaust gas treatment device 17 as the adsorption tank 2, the gas-liquid contact can be performed without providing an adsorption tank 2, and the device configuration can be simplified.

[0042] The gas-liquid contact between the adsorbing liquid and the exhaust gas in the pipeline 16 can be achieved by connecting the adsorbing liquid supply means 4 to the downstream side of the pipeline 16 and connecting the metal carbonate aqueous solution transfer means 7 to the upstream side of the pipeline 16, thereby enabling countercurrent contact between the adsorbing liquid and the exhaust gas, and therefore the metal carbonate aqueous solution 6 after adsorbing carbon dioxide can be efficiently transferred to the desorption tank 3. [Explanation of symbols]

[0043] Reference Signs List 1: carbon dioxide adsorption / desorption device, 2: adsorption tank, 3: desorption tank, 4: adsorption liquid supply means, 5: exhaust gas supply means, 6: metal carbonate aqueous solution, 6a: adsorption liquid, 7, 8: metal carbonate aqueous solution transfer means, 9: ultrasonic irradiation means, 10: pressure reduction means, 11, 12: carbon dioxide extraction means, 13, 14: adsorption liquid transfer means.

Claims

1. a step of contacting exhaust gas containing carbon dioxide with an adsorption liquid comprising an aqueous solution of a hydroxide of a metal capable of generating a carbonate in an adsorption tank to obtain an aqueous solution of a metal carbonate; transferring the metal carbonate aqueous solution from the adsorption tank to a desorption tank; desorbing carbon dioxide from the aqueous metal carbonate solution in the desorption tank to regenerate the adsorption solution; and transferring the regenerated adsorption liquid from the desorption tank to the adsorption tank, the step of desorbing carbon dioxide from the aqueous metal carbonate solution and regenerating the adsorption solution is carried out by reducing the pressure inside the desorption tank and irradiating the aqueous metal carbonate solution contained in the reduced-pressure desorption tank with ultrasonic waves.

2. an adsorption tank including an adsorption liquid supplying means for supplying an adsorption liquid consisting of an aqueous solution of a hydroxide of a metal capable of generating a carbonate, and an exhaust gas supplying means for supplying an exhaust gas containing carbon dioxide, and in which the exhaust gas is adsorbed by the adsorption liquid to obtain an aqueous solution of a metal carbonate; a metal carbonate aqueous solution transfer means for transferring the metal carbonate aqueous solution from the adsorption tank to a desorption tank; a desorption tank including an ultrasonic irradiation means and a pressure reducing means, and configured to desorb carbon dioxide from the aqueous metal carbonate solution to regenerate the adsorption solution; a carbon dioxide removal means for removing carbon dioxide from the desorption tank; and an adsorption liquid transfer means for transferring the regenerated adsorption liquid from the desorption tank to the adsorption tank.

3. 3. The carbon dioxide adsorption / desorption apparatus according to claim 2, wherein the adsorption tank is a part of a conduit for transporting exhaust gas containing carbon dioxide from a source of exhaust gas containing carbon dioxide to an exhaust gas treatment device.

4. 4. The carbon dioxide adsorption / desorption device according to claim 3, wherein the conduit is a pipeline connecting a source of the exhaust gas containing the carbon dioxide and the exhaust gas treatment device.

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