Carbon dioxide recovery method and carbon dioxide recovery system

Abstract

To provide a carbon dioxide recovery method in which energy cost can be reduced.SOLUTION: A carbon dioxide recovery method includes: an adsorption step of adsorbing carbon dioxide contained in air to an adsorbent in an adsorption device 2; a depressurization step of reducing pressure in the adsorption device 2 to below atmospheric pressure; a desorption step of heating the adsorbent A to desorb the carbon dioxide; and a cooling step of cooling the adsorbent. In the desorption step, while depressurizing the inside of the adsorption device 2 so that a saturated vapor pressure lower than a temperature of an inner surface of a wall portion of the adsorption device 2 that contacts outside air is obtained, saturated steam having a temperature higher than the temperature of the inner surface of the wall portion of the adsorption device 2 is introduced into the adsorption device 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide recovery method and a carbon dioxide recovery system for recovering carbon dioxide contained in air. [Background technology]

[0002] Global warming caused by carbon dioxide released during the combustion of fossil fuels has become a problem, and there is an urgent need to curb the release of carbon dioxide into the atmosphere as a result of fossil fuel combustion. On the other hand, there are applications where the use of fossil fuels is technically or economically unavoidable, and so there are growing expectations for technology called Direct Air Capture, which directly captures carbon dioxide from the atmosphere.

[0003] Carbon dioxide can be converted into hydrocarbons such as methane by reacting it with hydrogen. If the hydrogen is produced using electricity derived from renewable energy sources such as solar or wind power, and the carbon dioxide is collected from the atmosphere, the resulting hydrocarbons, even when burned, will not increase the atmospheric carbon dioxide concentration throughout the entire process from fuel production to use, making them carbon-neutral hydrocarbons.

[0004] Conventional carbon dioxide capture methods generally involve sequentially repeating the following steps: an adsorption step in which carbon dioxide contained in air is adsorbed onto an adsorbent in an adsorption device, a depressurization step in which the pressure in the adsorption device is reduced to below atmospheric pressure, a desorption step in which the adsorbent is heated to desorb carbon dioxide, and a cooling step in which the adsorbent is cooled. According to this carbon dioxide capture method, after carbon dioxide is adsorbed onto the adsorbent in the adsorption step, a depressurization step and a desorption step in which the adsorbent with adsorbed carbon dioxide is heated under reduced pressure to desorb the carbon dioxide from the adsorbent, thereby making it possible to capture high-concentration carbon dioxide.

[0005] As such a conventional carbon dioxide recovery method, for example, as shown in Patent Document 1 below, a method using water vapor in the desorption step is known. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6622302 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional carbon dioxide capture methods, when steam is used in the desorption process, although there is information on the vessel pressure and temperature, there is no information on how to prevent the input steam from condensing. If operation is not appropriate, the generated steam will lose heat in the vessel, etc., and condense, requiring extra energy in the desorption process, leaving room for improvement in terms of reducing energy costs.

[0008] An object of the present invention is to provide a carbon dioxide recovery method that reduces energy costs. [Means for solving the problem]

[0009] The carbon dioxide recovery method according to the present invention includes an adsorption step of adsorbing carbon dioxide contained in air onto an adsorbent in an adsorption device; a depressurization step of reducing the pressure in the adsorption device to less than atmospheric pressure; a desorption step of heating the adsorbent to desorb carbon dioxide; a cooling step of cooling the adsorbent, In the desorption process, the pressure inside the adsorption device is reduced so that the saturated vapor pressure is lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with the outside air, while saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device is introduced into the adsorption device.

[0010] According to this configuration, in the desorption process, the pressure inside the adsorption device is reduced so that the saturated vapor pressure is at a temperature lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with the outside air, while saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device is introduced into the adsorption device.This means that even if heat is removed inside the adsorption device, the introduced water vapor will not condense, and extra energy is not required in the desorption process, thereby reducing energy costs.

[0011] In the carbon dioxide recovery method according to the present invention, it is preferable that in the depressurization step, the pressure is reduced to a saturated vapor pressure at a temperature lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with outside air, saturated water vapor at a temperature at which carbon dioxide is difficult to desorb is introduced into the adsorption device to purge the air remaining in the adsorption device, and then in the desorption step, saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device is introduced into the adsorption device.

[0012] According to this configuration, the desorption step is carried out after purging the air remaining in the adsorption device, and therefore the purity of the recovered carbon dioxide is improved.

[0013] In the carbon dioxide recovery method according to the present invention, it is preferable that the adsorbent comprises a porous material containing an amine compound.

[0014] According to this configuration, the adsorbent is made of a porous material containing an amine compound, so that carbon dioxide can be adsorbed more efficiently.

[0015] The carbon dioxide capture system according to the present invention is configured to include an adsorption device that adsorbs carbon dioxide contained in air onto an adsorbent, an air supply path that supplies air to the adsorption device, an air discharge path that discharges air from the adsorption device, a heating device that heats the adsorbent, a recovery path that recovers carbon dioxide adsorbed by the adsorbent of the adsorption device, and a decompression device that decompresses the inside of the adsorption device, The pressure reducing device reduces the pressure inside the adsorption device to a saturated vapor pressure at a temperature lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with the outside air, while the heating device introduces saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device into the adsorption device to desorb carbon dioxide from the adsorbent.

[0016] According to this configuration, in the desorption process, the pressure inside the adsorption device is reduced so that the saturated vapor pressure is at a temperature lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with the outside air, while saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device is introduced into the adsorption device.This means that even if heat is removed inside the adsorption device, the introduced water vapor will not condense, and extra energy is not required in the desorption process, thereby reducing energy costs.

[0017] In the carbon dioxide capture system according to the present invention, it is preferable that the pressure reduction device is used to reduce the pressure to a saturated vapor pressure at a temperature lower than the temperature of the inner surface of the wall of the adsorption device, saturated water vapor at a temperature at which carbon dioxide is difficult to desorb is introduced into the adsorption device to purge any air remaining in the adsorption device, and then the heating device is used to introduce saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device into the adsorption device.

[0018] According to this configuration, the desorption step is carried out after purging the air remaining in the adsorption device, and therefore the purity of the recovered carbon dioxide is improved.

[0019] In the carbon dioxide recovery system according to the present invention, it is preferable that the adsorbent comprises a porous material containing an amine compound.

[0020] According to this configuration, the adsorbent is made of a porous material containing an amine compound, so that carbon dioxide can be adsorbed more efficiently. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing the configuration of a carbon dioxide capture system. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described. (Carbon dioxide capture system) As shown in Figure 1, the carbon dioxide capture system 1 includes an adsorption device 2 that adsorbs carbon dioxide contained in the air onto adsorbent material A, an air supply path 3 that supplies air to the adsorption device 2, an air discharge path 4 that discharges air from the adsorption device 2, a heating device 5 that heats the adsorbent material A, a recovery path 6 that recovers the carbon dioxide adsorbed by the adsorbent material A of the adsorption device 2, and a cooling means (not shown) that cools the adsorbent material A.

[0023] In this embodiment, the air supply path 3 includes a blower 30 (such as a blower) and a first switching valve V1. The air discharge path 4 includes a second switching valve V2. The recovery path 6 includes a third switching valve V3, a condenser 60, and a pressure reducing device 61 (such as a vacuum pump).

[0024] The heating device 5 is connected to the adsorption device 2 via a pipe P that can supply a heating medium to the adsorption device 2. Examples of the heating device include an electric heater and a heat exchanger. The heating device is preferably configured to generate the heating medium by utilizing waste heat, geothermal heat, or solar heat.

[0025] The heating medium may be, for example, water vapor such as saturated water vapor or superheated water vapor at a predetermined temperature.

[0026] The adsorption device 2 contains an adsorbent A therein. A heating medium is supplied from a heating device 5 to the adsorption device 2, whereby the adsorbent A is heated.

[0027] The adsorbent A is a component capable of adsorbing and desorbing carbon dioxide contained in air, and is preferably made of a porous material containing an amine compound. By combining the amine compound with an appropriate carrier, carbon dioxide can be desorbed at a relatively low temperature. Examples of applicable amine compounds include tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and polyethyleneimine (PEI). Examples of porous materials include metal-organic frameworks (MOFs), zeolites, and activated carbon.

[0028] (Carbon dioxide capture method) Next, a carbon dioxide recovery method using the carbon dioxide recovery system 1 will be described.

[0029] The carbon dioxide recovery method includes an adsorption process in which carbon dioxide contained in the air is adsorbed onto adsorbent A in adsorption device 2, a depressurization process in which the pressure in adsorption device 2 is reduced to below atmospheric pressure, a desorption process in which adsorbent A is heated to desorb carbon dioxide, and a cooling process in which adsorbent A is cooled, and these processes are carried out repeatedly in sequence.

[0030] In the adsorption step, the first switching valve V1 and the second switching valve V2 are opened, and the third switching valve V3 is closed. At this time, the temperature inside the adsorption device 2 is approximately room temperature, and the pressure is approximately atmospheric pressure. By operating the blower 30, air flows into the adsorption device 2 through the air supply path 3, and at least a portion of the carbon dioxide is adsorbed by the adsorbent A. The air with a reduced carbon dioxide concentration is discharged from the adsorption device 2 through the air discharge path 4.

[0031] In the depressurization step, the first selector valve V1 and the second selector valve V2 are closed, and the third selector valve V3 is opened. Then, by operating the depressurization device 61, the air inside the adsorption device 2 is removed, and the pressure inside the adsorption device 2 is reduced to a saturated vapor pressure at a temperature lower than the temperature T of the inner surface of the wall of the adsorption device 2 that comes into contact with the outside air. As an operation, for example, while monitoring the temperature of the inner surface of the wall of the adsorption device 2 at multiple points, the lowest temperature is set as temperature T, and the pressure is reduced to a saturated vapor pressure at a temperature lower than temperature T. At this time, it is preferable to introduce saturated water vapor at a temperature at which carbon dioxide is difficult to desorb into the adsorption device 2 to purge the air remaining in the adsorption device 2.

[0032] The saturated vapor pressure at a temperature lower than the temperature T of the inner wall of the adsorption device 2 that comes into contact with the outside air means a pressure at which the water vapor that is the heating medium to be input does not condense even when heat is removed, and is preferably a saturated vapor pressure at a temperature about 5°C lower than the temperature T of the inner wall of the adsorption device 2 that comes into contact with the outside air. For example, when the temperature T is about 25°C, the pressure is about 2.3 kPaA (equivalent to a temperature of 20°C).

[0033] Furthermore, the saturated water vapor at a temperature at which carbon dioxide is difficult to desorb during purging, i.e., a temperature at least lower than that during the desorption step, is saturated water vapor at, for example, 25° C. to 35° C. When the saturated water vapor is introduced into the adsorption device 2 for purging, the pressure inside the adsorption device 2 is adjusted by the pressure reducing device 61 to a pressure (for example, about 2.3 kPaA) at which the water vapor does not condense even when heat is removed.

[0034] The processing time of the depressurization step and the output of the depressurization device 61 may be set appropriately depending on the purity required for the carbon dioxide obtained in the subsequent desorption step. In addition, in the depressurization step, the condenser 60 may be operated as necessary to liquefy water vapor contained in the sucked air and discharge it as drain water.

[0035] In the desorption step, following the depressurization step, the first selector valve V1 and the second selector valve V2 are closed, and the third selector valve V3 is opened. Then, by operating the heating / cooling device 5 with the depressurization device 61 in operation, a heating medium (saturated steam or superheated steam) is supplied to the adsorption device 2 via the pipe P to heat the adsorbent A, and carbon dioxide is desorbed from the adsorbent A.

[0036] The heating medium is saturated steam or superheated steam having a temperature at which carbon dioxide is easily desorbed from the adsorbent A, for example, saturated steam or superheated steam at 35°C to 60°C. Also in the desorption step, the pressure inside the adsorption device 2 is adjusted by the pressure reducing device 61 to a pressure at which the steam does not condense even when heat is removed.

[0037] In the desorption step, high-concentration carbon dioxide is recovered via the recovery line 6. The recovered carbon dioxide is, for example, filled into a cylinder or the like while being pressurized by a compressor as necessary. Note that, also in the desorption step, the condenser 60 may be operated as necessary to liquefy water vapor contained in the sucked air and discharge the liquefied water as drain water.

[0038] In the cooling step, the first selector valve V1, the second selector valve V2, and the third selector valve V3 are all closed. Then, the cooling means is operated to cool the adsorbent A. As a result, the adsorbent A is cooled under conditions of low oxygen partial pressure. [Industrial Applicability]

[0039] The present invention can be suitably used in the technical field relating to an apparatus and method for recovering low-concentration carbon dioxide contained in the atmosphere to obtain high-purity carbon dioxide, for example. [Explanation of symbols]

[0040] 1. Carbon dioxide capture system 2 Adsorption device 3 Air supply path 30 Blower 4 Air exhaust route 5 Heating device 6. Recovery route 60 Condenser 61 Pressure reducing device V1 First switching valve V2 Second switching valve V3 Third switching valve A. Adsorbent P piping

Claims

1. an adsorption step of adsorbing carbon dioxide contained in the air onto an adsorbent in an adsorption device; a depressurization step of reducing the pressure in the adsorption device to less than atmospheric pressure; a desorption step of heating the adsorbent to desorb carbon dioxide; a cooling step of cooling the adsorbent, In the desorption step, the pressure inside the adsorption device is reduced so that the saturated vapor pressure is at a temperature lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with outside air, while saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device is introduced into the adsorption device.

2. 2. The carbon dioxide recovery method according to claim 1, wherein, in the depressurization step, the pressure is reduced to a saturated vapor pressure at a temperature lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with outside air, while saturated water vapor at a temperature at which carbon dioxide is difficult to desorb is introduced into the adsorption device to purge air remaining in the adsorption device, and then, in the desorption step, saturated water vapor at a temperature higher than the temperature of the inner surface of the wall of the adsorption device is introduced into the adsorption device.

3. 3. The carbon dioxide recovery method according to claim 1, wherein the adsorbent comprises a porous material containing an amine compound.

4. A carbon dioxide capture system comprising: an adsorption device that adsorbs carbon dioxide contained in air onto an adsorbent; an air supply path that supplies air to the adsorption device; an air discharge path that discharges air from the adsorption device; a heating device that heats the adsorbent; a capture path that captures carbon dioxide adsorbed by the adsorbent of the adsorption device; and a decompression device that decompresses the inside of the adsorption device, a pressure reducing device that reduces the pressure inside the adsorption device to a saturated vapor pressure that is lower than the temperature of the inner surface of the wall of the adsorption device that comes into contact with outside air, while the heating device injects saturated water vapor that is higher in temperature than the temperature of the inner surface of the wall of the adsorption device into the adsorption device, causing carbon dioxide to desorb from the adsorbent.

5. 5. The carbon dioxide capture system according to claim 4, wherein the pressure reduction device reduces the pressure to a saturated vapor pressure at a temperature lower than a temperature of the inner surface of a wall portion of the adsorption device, while saturated water vapor at a temperature at which carbon dioxide is difficult to desorb is introduced into the adsorption device to purge any air remaining in the adsorption device, and then the heating device introduces saturated water vapor at a temperature higher than a temperature of the inner surface of the wall portion of the adsorption device into the adsorption device.

6. The carbon dioxide recovery system according to claim 4 or 5, wherein the adsorbent comprises a porous material containing an amine compound.

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