Carbon dioxide recovery method and carbon dioxide recovery system

Abstract

To provide a carbon dioxide recovery method in which a carbon dioxide adsorbent is unlikely to peel off and cost can be reduced.SOLUTION: A carbon dioxide recovery method includes: an adsorption step of adsorbing carbon dioxide contained in air to an adsorbent A in an adsorption device 2; a depressurization step of reducing a pressure inside the adsorption device 2 to less than atmospheric pressure; a desorption step of heating the adsorbent A to desorb the carbon dioxide; and a cooling step of cooling the adsorbent A. A circulation path 70, through which a fluid can circulate between an inside and an outside of the adsorption device 2, is provided in the adsorption device 2. After the desorption step is performed by heating the adsorbent A using steam, the cooling step is performed by circulating the steam through the circulation path 70.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 air 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 is known in which the adsorbent, which has become hot in the desorption step, is cooled using an indirect heat exchanger or the like to prevent it from being exposed to oxygen and deteriorating. [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 cooling with an indirect heat exchanger, it is necessary to apply an adsorbent to the indirect heat exchanger. However, depending on the length of use, the adsorbent may peel off, resulting in a decrease in carbon dioxide adsorption performance. In such a case, if the adsorbent is replaced to restore the carbon dioxide adsorption performance, this will be expensive and will increase costs.

[0008] An object of the present invention is to provide a carbon dioxide recovery method in which the carbon dioxide adsorbent is less likely to peel off and which can reduce 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 inside 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, a circulation path that allows a fluid to circulate between the inside and the outside of the adsorption device is provided in the adsorption device, After the desorption step is performed by heating the adsorbent using steam, the cooling step is performed by circulating the steam through the circulation path.

[0010] According to this configuration, the adsorbent is heated using steam to perform the desorption step, and then the steam is circulated through the circulation path to perform the cooling step, thereby cooling the adsorbent to a predetermined temperature or lower, which eliminates the need for an indirect heat exchanger coated with an adsorbent and reduces costs.

[0011] 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 inside 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 cooling step, the pressure inside the adsorption device is reduced to a saturated water vapor pressure corresponding to a temperature equal to or lower than a predetermined cooling temperature, while liquid water is introduced into the adsorption device, and the adsorbent is cooled by the heat of evaporation of the water.

[0012] According to this configuration, in the cooling step, the pressure inside the adsorption device is reduced to a saturated water vapor pressure corresponding to a temperature equal to or lower than a predetermined cooling temperature, and liquid water is introduced into the adsorption device, allowing the adsorbent to be cooled by the heat of evaporation of the water. This eliminates the need for an indirect heat exchanger coated with an adsorbent, thereby reducing costs.

[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 cooling device that cools the adsorbent, and a capture path that captures the carbon dioxide adsorbed by the adsorbent of the adsorption device, The cooling device includes a circulation path through which a fluid can circulate between the inside and outside of the adsorption device.

[0016] According to this configuration, the adsorbent is heated using steam to perform the desorption step, and then the steam is circulated through the circulation path to perform the cooling step, thereby cooling the adsorbent to a predetermined temperature or lower, which eliminates the need for an indirect heat exchanger coated with an adsorbent and reduces costs.

[0017] 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 cooling device that cools the adsorbent, and a capture path that captures the carbon dioxide adsorbed by the adsorbent of the adsorption device, the cooling device includes a water supply path for introducing liquid water into the adsorption device; The recovery path includes a pressure reducing device that reduces the pressure inside the adsorption device to below atmospheric pressure.

[0018] According to this configuration, in the cooling step, the pressure inside the adsorption device is reduced to a saturated water vapor pressure corresponding to a temperature equal to or lower than a predetermined cooling temperature, and liquid water is introduced into the adsorption device, allowing the adsorbent to be cooled by the heat of evaporation of the water. This eliminates the need for an indirect heat exchanger coated with an adsorbent, thereby reducing costs.

[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 (first embodiment). [Figure 2] FIG. 1 is a diagram showing the configuration of a carbon dioxide capture system (second embodiment). DETAILED DESCRIPTION OF THE INVENTION

[0022] First Embodiment Hereinafter, an embodiment of the present invention will be described. (Carbon dioxide capture system) 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 cooling device 7 that cools the adsorbent material A, and a recovery path 6 that recovers the carbon dioxide adsorbed by the adsorbent material A of the adsorption device 2.

[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.

[0025] Examples of the heating device 5 include an electric heater and a heat exchanger. The heating device 5 is preferably configured to generate a heating medium using waste heat, geothermal heat, or solar heat. Examples of the heating medium include water vapor such as saturated water vapor or superheated water vapor at a predetermined temperature.

[0026] The cooling device 7 in this embodiment includes a circulation path 70 that allows a fluid to circulate between the inside and outside of the adsorption device 2. The circulation path 70 in this embodiment includes a fourth selector valve V4, a fifth selector valve V5, a blower 71 such as a blower, and a cooling device 72 such as a heat exchanger. The cooling device 7 cools the adsorbent A in the adsorption device 2 by introducing a fluid, such as water vapor present in the adsorption device 2 after the desorption step, into the cooling device 72 via the circulation path 70 and circulating the fluid while cooling it with outside air or the like. By continuing circulation for a predetermined period of time, the temperature of the adsorbent A gradually approaches the outside air temperature (e.g., around 25°C), and when the temperature of the adsorbent A reaches a temperature at which exposure to oxygen is not a problem (e.g., 40°C or below), circulation is stopped. Note that cooling with outside air is merely an example and is not limited thereto; a separate cooling source may also be used.

[0027] The adsorption device 2 contains an adsorbent A. The adsorbent A is heated by supplying a heating medium from the heating device 5 to the adsorption device 2, and the adsorbent A is cooled by supplying a cooling medium from the cooling device 7 to the adsorption device 2.

[0028] 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.

[0029] (Carbon dioxide capture method) Next, a carbon dioxide recovery method using the carbon dioxide recovery system 1 will be described.

[0030] 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 air 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.

[0031] In the adsorption step, the first and second switching valves V1 and V2 are opened, and the third, fourth, and fifth switching valves V3, V4, and V5 are 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 its carbon dioxide concentration reduced is discharged from the adsorption device 2 through the air discharge path 4.

[0032] In the depressurization step, the first selector valve V1, the second selector valve V2, the fourth selector valve V4, and the fifth selector valve V5 are closed, and the third selector valve V3 is open. The depressurization device 61 is then operated to remove air from the adsorption device 2. At this time, the temperature inside the adsorption device 2 is approximately room temperature, but the pressure is below atmospheric pressure. The processing time for the depressurization step and the output of the depressurization device 61 may be appropriately set 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 needed to liquefy water vapor contained in the sucked air and discharge the liquefied water as drain water.

[0033] In the desorption step, following the depressurization step, the first selector valve V1, the second selector valve V2, the fourth selector valve V4, and the fifth selector valve V5 are closed, and the third selector valve V3 is opened. Then, by operating the heating 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.

[0034] 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 25°C to 60°C. Also during the desorption step, the pressure inside the adsorption device 2 is maintained by the pressure reducing device 61 at a pressure (for example, about 2.3 kPaA) at which the steam does not condense even when heat is removed.

[0035] 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.

[0036] In the cooling step, the first selector valve V1, the second selector valve V2, and the third selector valve V3 are closed, and the fourth selector valve V4 and the fifth selector valve V5 are opened. Then, the blower 71 of the cooling device 7 is operated to cause water vapor present in the adsorption device 2 to flow into the cooling section 72 via the circulation path 70 and circulate while being cooled with outside air or the like, thereby cooling the adsorbent A in the adsorption device 2. By continuing the circulation for a predetermined time, the temperature of the adsorbent A gradually approaches the outside air temperature (for example, around 25°C), and when the temperature of the adsorbent A reaches a temperature at which exposure to oxygen is not a problem (for example, 40°C or below), the circulation is stopped and the process returns to the adsorption step.

[0037] Second Embodiment The second embodiment of the present invention will be described below with reference to the drawings. Here, only the configurations that differ from the first embodiment described above will be described, and the same symbols will be used for the configurations that are similar to those in the first embodiment, and the description will be omitted.

[0038] (Carbon dioxide capture system) As shown in Fig. 2, the cooling device 7 in this embodiment includes a water supply path 73 for introducing liquid water into the adsorption device 2. The water supply path 73 includes a liquid delivery unit 74 (such as a liquid delivery pump) capable of supplying a predetermined amount of water, and an injection unit 75 (such as a spray nozzle). It is desirable to atomize the liquid water using a spray nozzle or the like to promote evaporation. In this case, the water may be pressurized appropriately using a liquid delivery pump depending on the characteristics of the injection nozzle used.

[0039] 2, in this embodiment, taking into consideration the falling direction of the introduced water, it is desirable to configure the air supplied to the adsorption device 2 to flow vertically, for example, from bottom to top, and to introduce water from above the adsorption device 2. Furthermore, a drainage path 8 may be provided below the adsorption device 2, if necessary.

[0040] (Carbon dioxide capture method) The adsorption process in which the carbon dioxide contained in the air is adsorbed onto the adsorbent A in the adsorption device 2, the decompression process in which the air pressure in the adsorption device 2 is reduced to below atmospheric pressure, and the desorption process in which the adsorbent A is heated to desorb the carbon dioxide are the same as those in the first embodiment described above.

[0041] In the cooling step of this embodiment, the first and second selector valves V1 and V2 are closed, and the third selector valve V3 is opened. Then, the pressure reducing device 61 is operated to reduce the pressure inside the adsorption device 2 to a saturated water vapor pressure corresponding to a temperature equal to or lower than a predetermined cooling temperature (e.g., 20°C to 30°C), while the liquid delivery section 74 of the cooling device 7 is operated to introduce a predetermined amount of liquid-phase water into the adsorption device 2, thereby cooling the adsorbent A by the heat of evaporation of the water.

[0042] After the pressure is reduced, the water introduced into the adsorption device 2 reaches a state with a dryness fraction of approximately 0 and evaporates by receiving heat from the high-temperature adsorbent A. For example, if 1 g of liquid water is introduced at a saturated vapor pressure of 2.3 kPa and the water evaporates to saturated vapor (dryness fraction = 1), approximately 2.4 kJ of cooling heat is generated. If the water evaporates in one minute, approximately 41 W of cooling capacity is achieved. Note that the introduced water does not necessarily have to evaporate completely; it may also be heated to superheated vapor. By continuing to introduce water for a predetermined period of time, the temperature of the adsorbent A gradually approaches the outside air temperature (e.g., around 25°C). When the temperature of the adsorbent A reaches a temperature at which it is safe to expose it to oxygen (e.g., below 40°C), the introduction of water is stopped and the process resumes. [Industrial Applicability]

[0043] 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]

[0044] 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 7 Cooling device 70 Circulation Route 71 Blower 72 Cooling section 73 Water Supply Route 74 Liquid delivery unit 75 Injection part 8 Drainage route V1 First switching valve V2 Second switching valve V3 Third switching valve V4 Fourth switching valve V5 Fifth 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 inside 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, a circulation path that allows a fluid to circulate between the inside and the outside of the adsorption device is provided in the adsorption device, A carbon dioxide recovery method in which the desorption step is performed by heating the adsorbent using steam, and then the cooling step is performed by circulating the steam through the circulation path.

2. 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 inside 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, a carbon dioxide recovery method in which, in the cooling step, the pressure inside the adsorption device is reduced to a saturated water vapor pressure corresponding to a temperature equal to or lower than a predetermined cooling temperature, while liquid phase water is introduced into the adsorption device, and the adsorbent is cooled by the heat of evaporation of the water.

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 cooling device that cools the adsorbent; and a capture path that captures carbon dioxide adsorbed by the adsorbent of the adsorption device, A carbon dioxide capture system, wherein the cooling device is provided with a circulation path that allows a fluid to circulate between the inside and outside of the adsorption device.

5. 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 cooling device that cools the adsorbent; and a capture path that captures carbon dioxide adsorbed by the adsorbent of the adsorption device, the cooling device includes a water supply path for introducing liquid water into the adsorption device; The carbon dioxide capture system, wherein the capture path includes a pressure reducing device that reduces the air pressure inside the adsorption device to below atmospheric pressure.

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

Images