AIR CONDITIONER, AIR CONDITIONING SYSTEM, METHOD FOR REMOVING CARBON DIOXIDE, ADSORBENT, AND CARBON DIOXIDE REMOVER

Abstract

Provided is an air conditioner 100 used in a space R containing a gas having a concentration of carbon dioxide of 5000 ppm or less, the air conditioner 100 including a flow path 10 connected to the space R, in which a removal section 10c for removing carbon dioxide contained in the gas is disposed in the flow path 10, an adsorbent 80 containing cerium oxide is disposed in the removal section 10c, and the carbon dioxide adsorbs on the adsorbent 80 as the adsorbent 80 comes into contact with the gas.

Claims

1. An air conditioner used in a space comprising a gas having a concentration of carbon dioxide of 5000 ppm or less, the air conditioner comprising: a flow path connected to the space, wherein a removal section for removing carbon dioxide contained in the gas is disposed in the flow path, an adsorbent comprising cerium oxide is disposed in the removal section, and the carbon dioxide adsorbs on the adsorbent as the adsorbent comes into contact with the gas.

2. The air conditioner according to claim 1, wherein a concentration of carbon dioxide in the gas is 1000 ppm or less.

3. The air conditioner according to claim 1, wherein a concentration of carbon dioxide in the gas is 400 ppm to 1000 ppm.

4. The air conditioner according to claim 1, further comprising: a concentration measuring section for measuring a concentration of carbon dioxide in the space; and a control section for controlling presence or absence of inflow of the gas in the removal section based on the concentration of carbon dioxide measured by the concentration measuring section.

5. An air conditioning system comprising a plurality of the air conditioners according to claim 1.

6. A method for removing carbon dioxide, the method comprising: an adsorption step of bringing a gas comprising carbon dioxide into contact with an adsorbent to adsorb carbon dioxide on the adsorbent, wherein the adsorbent contains cerium oxide, and a concentration of carbon dioxide in the gas is 5000 ppm or less.

7. The method for removing carbon dioxide according to claim 6, wherein a concentration of carbon dioxide in the gas is 1000 ppm or less.

8. The method for removing carbon dioxide according to claim 6, wherein a concentration of carbon dioxide in the gas is 400 ppm to 1000 ppm.

9. The method for removing carbon dioxide according to claim 6, further comprising a step of desorbing carbon dioxide from the adsorbent after the adsorption step.

10. An adsorbent used in the method for removing carbon dioxide according to claim 6, the adsorbent comprising cerium oxide.

11. A device for removing carbon dioxide used for removing carbon dioxide from a gas comprising carbon dioxide, the device comprising: an adsorbent comprising cerium oxide, wherein a concentration of carbon dioxide in the gas is 5000 ppm or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a schematic diagram illustrating an air conditioner according to an embodiment of the present invention.

[0027] FIG. 2 is a schematic diagram illustrating an air conditioning system according to an embodiment of the present invention.

[0028] FIG. 3 is a diagram illustrating the results of a CO.sub.2 adsorption breakthrough test.

[0029] FIG. 4 is a diagram illustrating the results of a CO.sub.2 and H.sub.2O desorption test.

[0030] FIG. 5 is a diagram illustrating the measurement results of an adsorption isotherm.

DESCRIPTION OF EMBODIMENTS

[0031] In the present specification, the numerical range expressed by using to indicates the range including the numerical values stated before and after to as the minimum value and the maximum value, respectively. In a numerical range stated in a stepwise manner in the present specification, the upper limit value or lower limit value in the numerical range at a certain stage may be replaced with the upper limit value or lower limit value in the numerical range at another stage. In addition, in a numerical range stated in the present specification, the upper limit value or lower limit value in the numerical range may be replaced with the values stated in Examples.

[0032] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[0033] <Method for Removing Carbon Dioxide and Adsorbent>

[0034] The method for removing carbon dioxide according to the present embodiment includes an adsorption step of bringing a gas containing carbon dioxide into contact with an adsorbent (carbon dioxide trapping agent) to adsorb carbon dioxide on the adsorbent, in which the adsorbent contains cerium oxide and the concentration of carbon dioxide (content of carbon dioxide) in the gas is 5000 ppm or less.

[0035] According to the method for removing carbon dioxide of the present embodiment, carbon dioxide can be efficiently removed in a case in which the CO.sub.2 concentration is 5000 ppm or less. The reason why such an effect is exerted is not clear, but the inventors of the present invention presume as follows. It is considered that carbon dioxide adsorbs on the adsorbent as carbon dioxide does not physically adsorb on the surface of cerium oxide but chemically bonds to the surface of cerium oxide in the adsorption step. In this case, in the method for removing carbon dioxide according to the present embodiment, it is presumed that the partial pressure dependency of carbon dioxide at the time of adsorption on the adsorbent is minor and thus carbon dioxide can be efficiently removed even when the CO2 concentration in the gas is 5000 ppm or less.

[0036] The adsorbent according to the present embodiment is an adsorbent used in the method for removing carbon dioxide according to the present embodiment, which contains cerium oxide. Examples of cerium oxide may include CeOx (x=1.5 to 2.0), and specific examples thereof may include CeO.sub.2 and Ce.sub.2O.sub.3. Cerium oxide can be fabricated by a known method.

[0037] The content of cerium oxide in the adsorbent may be 30% by mass or more, 70% by mass or more, or 90% by mass or more based on the total mass of the adsorbent. The adsorbent may consist of cerium oxide (the content of cerium oxide may be substantially 100% by mass based on the total mass of the adsorbent). The CO.sub.2 adsorptivity is likely to be improved as the content of cerium oxide increases.

[0038] The specific surface area of the adsorbent may be 100 m.sup.2/g or more, 120 m.sup.2/g or more, 130 m.sup.2/g or more, 150 m.sup.2/g or more, or 200 m.sup.2/g or more from the viewpoint of further improving the CO.sub.2 adsorptivity. The specific surface area of the adsorbent may be 500 m.sup.2/g or less or 400 m.sup.2/g or less from the viewpoint that the volume of the pores is not too great and the density of the adsorbent is not too low. The specific surface area of the adsorbent can be measured, for example, by measuring the adsorption isotherm of nitrogen at 196 C. and using the Brunauer-Emmett-Teller (BET) method. The adsorbent may be chemically treated. For example, the specific surface area of the adsorbent may be increased by being mixed with a filler (alumina, silica, or the like) as a binder.

[0039] Examples of the shape of the adsorbent may include a powdery shape, a pellet shape, a granular shape, and a honeycomb shape. The adsorbent may be supported on a honeycomb-shaped substrate or filled in a vessel. The shape and method of use of the adsorbent may be determined in consideration of the required reaction rate, pressure loss, amount adsorbed on the adsorbent, purity (CO.sub.2 purity) of the gas (adsorbed gas) to adsorb on the adsorbent, and the like.

[0040] In the case of using the adsorbent by being filled in a vessel, it is more preferable as the void fraction is smaller in the case of increasing the purity of carbon dioxide in the adsorbed gas. In this case, the amount of gas remaining in the voids other than carbon dioxide decreases and thus the purity of carbon dioxide in the adsorbed gas can be increased. On the other hand, it is more preferable as the void fraction is greater in the case of diminishing the pressure loss.

[0041] The CO.sub.2 concentration in the gas is 5000 ppm or less (0.5% by volume or less) based on the total volume of the gas. From the viewpoint that the effect of efficiently removing carbon dioxide is likely to be confirmed even in a case in which the CO.sub.2 concentration is low, the CO.sub.2 concentration may be 2000 ppm or less, 1500 ppm or less, 1000 ppm or less, 750 ppm or less, or 500 ppm or less based on the total volume of the gas. From the viewpoint that the amount of carbon dioxide removed is likely to increase, the CO.sub.2 concentration may be 100 ppm or more, 200 ppm or more, or 400 ppm or more based on the total volume of the gas. From these viewpoints, the CO.sub.2 concentration may be 100 ppm to 5000 ppm, 100 ppm to 2000 ppm, 100 ppm to 1500 ppm, 100 ppm to 1000 ppm, 200 ppm to 1000 ppm, 400 ppm to 1000 ppm, 400 ppm to 750 ppm, or 400 ppm to 500 ppm based on the total volume of the gas. It is stipulated in the Management Standard of Environmental Sanitation for Buildings that the concentration of carbon dioxide should be adjusted to 1000 ppm or less. The CO.sub.2 concentration in the gas is not limited to the above range, and it may be 500 ppm to 5000 ppm or 750 ppm to 5000 ppm.

[0042] The gas is not particularly limited as long as it is a gas containing carbon dioxide, and it may contain a gas component other than carbon dioxide. Examples of the gas component other than carbon dioxide may include water (water vapor, H.sub.2O), oxygen (O.sub.2), nitrogen (N.sub.2), carbon monoxide (CO), SOx, NOx, and volatile organic compounds (VOC). Specific examples of the gas may include air in the room of a building, a vehicle, and the like. In the adsorption step, in a case in which the gas contains water, carbon monoxide, SOx, NOx, volatile organic compounds, and the like, these gas components adsorb on the adsorbent in some cases.

[0043] Meanwhile, the CO.sub.2 adsorptivity of an adsorbent such as zeolite tends to significantly decrease in a case in which the gas contains water. Hence, in order to improve the CO.sub.2 adsorptivity of the adsorbent in the method using an adsorbent such as zeolite, it is required to perform a dehumidifying step of removing moisture from the gas before bringing the gas into contact with the adsorbent. The dehumidifying step is performed by using, for example, a dehumidifying device, and this thus leads to an increase in facility and an increase in energy consumption. On the other hand, the adsorbent according to the present embodiment exhibits superior CO.sub.2 adsorptivity even in a case in which the gas contains water. Hence, in the method for removing carbon dioxide according to the present embodiment, the dehumidifying step is not required and carbon dioxide can be efficiently removed even in a case in which the gas contains water.

[0044] The dew point of the gas may be 0 C. or more. From the viewpoint of increasing the hydroxyl groups on the surface of cerium oxide and enhancing the reactivity with CO.sub.2, the dew point of the gas may be 40 C. or more and 50 C. or less, 0 C. or more and 40 C. or less, or 10 C. or more and 30 C. or less.

[0045] The relative humidity of the gas may be 0% or more, 30% or more, 50% or more, or 80% or more. The relative humidity of the gas is preferably 100% or less (that is, dew does not condense on the adsorbent), more preferably 0.1% or more and 90% or less, and still more preferably 10% or more and 80% or less from the viewpoint of decreasing the energy consumption due to dehumidification. The relative humidity of the gas may be 0% or more. The above relative humidity is a relative humidity at 30 C., for example.

[0046] The adsorption amount of carbon dioxide can be adjusted by adjusting the temperature T.sub.1 of the adsorbent when bringing the gas into contact with the adsorbent in the adsorption step. The amount of CO.sub.2 adsorbed on the adsorbent tends to decrease as the temperature T.sub.1 is higher. The temperature T.sub.1 may be 20 C. to 100 C. or 10 C. to 40 C.

[0047] The temperature T.sub.1 of the adsorbent may be adjusted by heating or cooling the adsorbent, and heating and cooling may be used in combination. In addition, the temperature T.sub.1 of the adsorbent may be indirectly adjusted by heating or cooling the gas. Examples of a method for heating the adsorbent may include: a method in which a heat medium (for example, a heated gas or liquid) is brought into direct contact with the adsorbent; a method in which a heat medium (for example, a heated gas or liquid) is circulated through a heat transfer pipe or the like and the adsorbent is heated by heat conduction from the heat transfer surface; and a method in which the adsorbent is heated by using an electric furnace which has been electrically heated or the like. Examples of a method for cooling the adsorbent may include: a method in which a refrigerant (for example, a cooled gas or liquid) is brought into direct contact with the adsorbent; and a method in which a refrigerant (for example, a cooled gas or liquid) is circulated through a heat transfer pipe or the like and the adsorbent is cooled by heat conduction from the heat transfer surface.

[0048] In the adsorption step, the adsorption amount of carbon dioxide can be adjusted by adjusting the total pressure (for example, the total pressure in the vessel containing the adsorbent) of the atmosphere in which the adsorbent is present. The amount of CO.sub.2 adsorbed on the adsorbent tends to increase as the total pressure is higher. The total pressure is preferably 0.1 atm or more and more preferably 1 atm or more from the viewpoint of further improving the removal efficiency of carbon dioxide. The total pressure may be 10 atm or less, 2 atm or less, or 1.3 atm or less from the viewpoint of energy saving. The total pressure may be 5 atm or more.

[0049] The total pressure of the atmosphere in which the adsorbent is present may be adjusted by pressurization or depressurization, and pressurization and depressurization may be used in combination. Examples of a method for adjusting the total pressure may include: a method in which the pressure is mechanically adjusted by using a pump, a compressor or the like; and a method in which of a gas having a pressure different from the pressure of the atmosphere surrounding the adsorbent is introduced.

[0050] The method for removing carbon dioxide according to the present embodiment may further include a desorption step of desorbing (detaching) carbon dioxide from the adsorbent after the adsorption step.

[0051] Examples of a method for desorbing carbon dioxide from the adsorbent may include: a method utilizing the temperature dependency of the adsorption amount (temperature swing method. A method utilizing a difference in the amount adsorbed on the adsorbent associated with a change in temperature); a method utilizing the pressure dependency of the adsorption amount (pressure swing method. A method utilizing a difference in the amount adsorbed on the adsorbent associated with a change in pressure), and these methods may be used in combination (temperature and pressure swing method).

[0052] In the method utilizing the temperature dependency of the adsorption amount, for example, the temperature of the adsorbent in the desorption step is set to be higher than that in the adsorption step. Examples of a method for heating the adsorbent may include: the same methods as the methods for heating the adsorbent in the adsorption step described above; and a method utilizing surrounding waste heat. It is preferable to utilize surrounding waste heat from the viewpoint of diminishing energy required for heating.

[0053] The temperature difference (T.sub.2T.sub.1) between the temperature T.sub.1 of the adsorbent in the adsorption step and the temperature T.sub.2 of the adsorbent in the desorption step may be 200 C. or less, 100 C. or less, or 50 C. or less from the viewpoint of energy saving. The temperature difference (T.sub.2T.sub.1) may be 10 C. or more, 20 C. or more, or 30 C. or more from the viewpoint that the carbon dioxide which has adsorbed on the adsorbent is likely to desorb. The temperature T.sub.2 of the adsorbent in the desorption step may be, for example, 40 C. to 300 C., 50 C. to 200 C., or 80 C. to 120 C.

[0054] In the method utilizing the pressure dependency of the adsorption amount, it is preferable to change total pressure so that the total pressure in the desorption step is lower than the total pressure in the adsorption step since the CO.sub.2 adsorption amount is greater as the total pressure of the atmosphere in which the adsorbent is present (for example, the total pressure in the vessel containing the adsorbent) is higher. The total pressure may be adjusted by pressurization or depressurization, and pressurization and depressurization may be used in combination. Examples of a method for adjusting the total pressure may include the same methods as those in the adsorption step described above. The total pressure in the desorption step may be the pressure of the surrounding air (for example, 1 atm) or less than 1 atm from the viewpoint of increasing the CO.sub.2 desorption amount.

[0055] The carbon dioxide desorbed and recovered through the desorption step may be discharged to the outdoor air as it is, but it may be reused in the field using carbon dioxide. For example, in greenhouse cultivation houses and the like, there is a case in which the CO.sub.2 concentration is increased to a 1000 ppm level since the growth of plants is promoted by increasing the CO.sub.2 concentration, and thus the recovered carbon dioxide may be reused for increasing the CO.sub.2 concentration.

[0056] It is preferable that the gas does not contain SOx, NOx, dust and the like since there is a possibility that the CO.sub.2 adsorptivity of the adsorbent in the adsorption step decreases in a case in which SOx, NOx, dust and the like are adsorbed on the adsorbent. In a case in which the gas contains SOx, NOx, dust and the like (for example, a case in which the gas is exhaust gas discharged from a coal fired power plant or the like), it is preferable that the method for removing carbon dioxide according to the present embodiment further includes an impurity removing step of removing impurities such as SOx, NOx, and dust from the gas before the adsorption step from the viewpoint that the CO.sub.2 adsorptivity of the adsorbent is likely to be maintained. The impurity removing step can be performed by using a removal apparatus such as a denitrification apparatus, a desulfurization apparatus, or a dust removing apparatus, and the gas can be brought into contact with the adsorbent on the downstream side of these apparatuses. In addition, in a case in which impurities such as SOx, NOx, dust and the like are adsorbed on the adsorbent, impurities adsorbed on the adsorbent can be removed by heating the adsorbent in addition to exchange of the adsorbent.

[0057] The adsorbent after being subjected to the desorption step can be used again in the adsorption step. In the method for removing carbon dioxide according to the present embodiment, the adsorption step and the desorption step may be repeatedly performed after the desorption step. The adsorbent may be cooled by the method described above and used in the adsorption step in a case in which the adsorbent is heated in the desorption step. The adsorbent may be cooled by bringing a gas containing carbon dioxide (for example, a gas containing carbon dioxide) into contact with the adsorbent.

[0058] The method for removing carbon dioxide according to the present embodiment can be suitably implemented in a sealed space which requires management of CO.sub.2 concentration. Examples of the space which requires management of CO.sub.2 concentration may include a building; a vehicle; an automobile; a space station; a submarine; a manufacturing plant for a food or a chemical product. The method for removing carbon dioxide according to the present embodiment can be suitably implemented particularly in a space (for example, a space with a high density of people such as a building and a vehicle) in which the CO.sub.2 concentration is limited to 5000 ppm or less. In addition, the method for removing carbon dioxide according to the present embodiment can be suitably implemented in a manufacturing plant for a food or a chemical product and the like since there is a possibility that carbon dioxide adversely affects at the time of manufacture of a food or a chemical product.

[0059] <Device for Removing Carbon Dioxide, Apparatus for Removing Carbon Dioxide and System for Removing Carbon Dioxide>

[0060] The device for removing carbon dioxide according to the present embodiment is a device for removing carbon dioxide used for removing carbon dioxide from a gas containing carbon dioxide, the device containing an adsorbent containing cerium oxide and in which the concentration of carbon dioxide in the gas is 5000 ppm or less.

[0061] The apparatus for removing carbon dioxide according to the present embodiment is equipped with the device (reaction vessel) for removing carbon dioxide according to the present embodiment. The apparatus for removing carbon dioxide according to the present embodiment is, for example, an air conditioner used in a space containing a gas having a concentration of carbon dioxide of 5000 ppm or less. The air conditioner according to the present embodiment is equipped with a flow path connected to the space, and a removal section (a device for removing carbon dioxide, a carbon dioxide removing section) for removing carbon dioxide contained in the gas is disposed in the flow path. In the air conditioner according to the present embodiment, the adsorbent containing cerium oxide is disposed in the removal section, and carbon dioxide adsorbs on the adsorbent as the adsorbent comes into contact with the gas. According to the present embodiment, there is provided an air conditioning method including an adsorption step of bringing a gas in a space to be air-conditioned into contact with an adsorbent to adsorb carbon dioxide on the adsorbent. Incidentally, the details of the gas containing carbon dioxide are the same as those of the gas in the method for removing carbon dioxide described above. Hereinafter, an air conditioner will be described as an example of an apparatus for removing carbon dioxide with reference to FIG. 1.

[0062] As illustrated in FIG. 1, an air conditioner 100 according to the present embodiment is equipped with a flow path 10, an exhaust fan (exhaust means) 20, a device for measuring concentration (concentration measuring section) 30, an electric furnace (temperature control means) 40, a compressor (pressure control means) 50, and a control apparatus (control section) 60.

[0063] The flow path 10 is connected to a space R to be air-conditioned containing a gas (indoor gas) containing carbon dioxide. The flow path 10 includes a flow path section 10a, a flow path section 10b, a removal section (a flow path section, a carbon dioxide removing section) 10c, a flow path section 10d, a flow path section (circulation flow path) 10e, and a flow path section (exhaust flow path) 10f, and the removal section 10c is disposed in the flow path 10. The air conditioner 100 is equipped with the removal section 10c as a device for removing carbon dioxide. In the flow path 10, a valve 70a for adjusting the presence or absence of inflow of the gas in the removal section 10c and a valve 70b for adjusting the flow direction of the gas are disposed.

[0064] The upstream end of the flow path section 10a is connected to the space R and the downstream end of the flow path section 10a is connected to the upstream end of the flow path section 10b via the valve 70a. The upstream end of the removal section 10c is connected to the downstream end of the flow path section 10b. The downstream end of the removal section 10c is connected to the upstream end of the flow path section 10d. The downstream side of the flow path section 10d in the flow path 10 is branched into the flow path section 10e and the flow path section 10f. The downstream end of the flow path section 10d is connected to the upstream end of the flow path section 10e and the upstream end of the flow path section 10f via the valve 70b. The downstream end of the flow path section 10e is connected to the space R. The downstream end of the flow path section 10f is connected to the outdoor air.

[0065] An adsorbent 80 containing cerium oxide is disposed in the removal section 10c. The adsorbent 80 is filled in the central portion of the removal section 10c. Two spaces are formed in the removal section 10c via the adsorbent 80, and the removal section 10c includes a space S1 on the upstream side, a central portion S2 filled with the adsorbent 80, and a space S3 on the downstream side. The space S1 is connected to the space R via the flow path sections 10a and 10b and the valve 70a, and the gas containing carbon dioxide is supplied from the space R to the space S1 of the removal section 10c. The gas which has been supplied to the removal section 10c moves from the space S1 to the space S3 through the central portion S2 and then is discharged from the removal section 10c.

[0066] At least a part of carbon dioxide in the gas which has been discharged from the space R is removed in the removal section 10c. The gas from which carbon dioxide has been removed may be returned to the space R by adjusting the valve 70b or discharged to the outdoor air present outside the air conditioner 100. For example, the gas which has been discharged from the space R can flow into the space R from the upstream to the downstream through the flow path section 10a, the flow path section 10b, the removal section 10c, the flow path section 10d, and the flow path section 10e. In addition, the gas which has been discharged from the space R may be discharged to the outdoor air from the upstream to the downstream through the flow path section 10a, the flow path section 10b, the removal section 10c, the flow path section 10d, and the flow path section 10f.

[0067] The exhaust fan 20 is disposed at the discharge position of the gas in the space R. The exhaust fan 20 discharges the gas from the space R and supplies the gas to the removal section 10c.

[0068] The device for measuring concentration 30 measures the concentration of carbon dioxide in the space R. The device for measuring concentration 30 is disposed in the space R.

[0069] The electric furnace 40 is disposed outside the removal section 10c of the air conditioner 100 and can raise the temperature of the adsorbent 80. The compressor 50 is connected to the removal section 10c of the air conditioner 100 and can adjust the pressure inside the removal section 10c.

[0070] The control apparatus 60 can control the operation of the air conditioner 100, and for example, it can control the presence or absence of inflow of the gas in the removal section 10c based on the concentration of carbon dioxide measured by the device for measuring concentration 30. More specifically, the concentration information is transmitted from the device for measuring concentration 30 to the control apparatus 60 in a case in which the device for measuring concentration 30 detects that the concentration of carbon dioxide in the space R has increased by exhalation or the like and reached a predetermined concentration. The control apparatus 60, which has received the concentration information, opens the valve 70a and also adjusts so that the gas discharged from the removal section 10c flows into the space R via the flow path section 10d and the flow path section 10e. Thereafter, the control apparatus 60 operates the exhaust fan 20 to supply the gas from the space R to the removal section 10c. Furthermore, the control apparatus 60 operates the electric furnace 40 and/or the compressor 50 if necessary to adjust the temperature of the adsorbent 80, the pressure in the removal section 10c, and the like.

[0071] The gas comes into contact with the adsorbent 80 and carbon dioxide in the gas adsorbs on the adsorbent 80 as the gas supplied to the removal section 10c moves from the space S1 to the space S3 via the central portion S2. By this, carbon dioxide is removed from the gas. In this case, the gas from which carbon dioxide has been removed is supplied to the space R via the flow path section 10d and the flow path section 10e.

[0072] Carbon dioxide adsorbed on the adsorbent 80 may be recovered in a state of being adsorbed on the adsorbent 80 without being desorbed from the adsorbent 80 or may be desorbed from the adsorbent 80 and recovered. In the desorption step, carbon dioxide can be desorbed from the adsorbent 80 by the temperature swing method, pressure swing method and the like described above as the temperature of the adsorbent 80, the pressure inside the removal section 10c, and the like are adjusted by operating the electric furnace 40 and/or the compressor 50. In this case, for example, the valve 70b is adjusted so that the gas (gas containing the desorbed carbon dioxide) discharged from the removal section 10c is discharged to the outdoor air via the flow path section 10f, and discharged carbon dioxide can be recovered if necessary.

[0073] The system for removing carbon dioxide according to the present embodiment is equipped with a plurality of apparatuses for removing carbon dioxide according to the present embodiment. The system for removing carbon dioxide according to the present embodiment is, for example, an air conditioning system equipped with a plurality of air conditioners according to the present embodiment. The system for removing carbon dioxide according to the present embodiment may be equipped with a control section for controlling the operation of a plurality of apparatuses for removing carbon dioxide (for example, air conditioning operation of the air conditioner). For example, the system for removing carbon dioxide according to the present embodiment comprehensively controls the operation of a plurality of apparatuses for removing carbon dioxide (for example, the air conditioning operation of the air conditioner). Hereinafter, an air conditioning system will be described as an example of the system for removing carbon dioxide with reference to FIG. 2.

[0074] As illustrated in FIG. 2, an air conditioning system 1 according to the present embodiment is equipped with a first air conditioner 100a, a second air conditioner 100b, and a control apparatus (control section) 62. The control apparatus 62 controls the air conditioning operation of the first air conditioner 100a and the second air conditioner 100b by controlling the control apparatus 60 described above in the first air conditioner 100a and the second air conditioner 100b. For example, the control apparatus 62 may be adjusted so that the air conditioning operation of the first air conditioner 100a and the second air conditioner 100b is performed under the same conditions or the air conditioning operation of the first air conditioner 100a and the second air conditioner 100b is performed under different conditions. The control apparatus 62 can transmit the information on the presence or absence of inflow of the gas in the removal section 10c to the control apparatus 60.

[0075] The device for removing carbon dioxide, the apparatus for removing carbon dioxide (air conditioner or the like), and the system for removing carbon dioxide (air conditioning system or the like) are not limited to the above embodiment and may be appropriately changed without departing from the gist thereof. For example, the device for removing carbon dioxide, the apparatus for removing carbon dioxide, and the system for removing carbon dioxide are not limited to being used for air conditioning but can be used in all applications for removing carbon dioxide from a gas containing carbon dioxide.

[0076] In the air conditioner, the adsorbent may be disposed in the removal section, and the adsorbent may be disposed in a part of the inner wall surface without being filled in the central portion of the removal section. The contents of control by the control section of the air conditioner are not limited to control of the presence or absence of inflow of the gas in the removal section, and the control section may adjust the inflow amount of the gas in the removal section.

[0077] In the air conditioner, a gas may be supplied to the carbon dioxide removing section by using a blower instead of the exhaust fan, and the exhaust means may not be used in a case in which the gas is supplied to the carbon dioxide removing section by natural convection. In addition, the temperature control means and the pressure control means are not limited to the electric furnace and the compressor, and various means described in the adsorption step and the desorption step can be used. The temperature control means is not limited to the heating means, and it may be a cooling means.

[0078] In the air conditioner, each of the space to be air-conditioned, the carbon dioxide removing section, the exhaust means, the temperature control means, the pressure control means, the concentration measuring section, the control apparatus, and the like is not limited to one, and a plurality of these may be disposed. The air conditioner may be equipped with a humidity adjuster for adjusting the dew point and relative humidity of the gas; a humidity measuring device for measuring the humidity of the space to be air-conditioned; a removal apparatus such as a denitrification apparatus, a desulfurization apparatus, or a dust removing apparatus.

EXAMPLES

[0079] Hereinafter, the contents of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0080] <Preparation of Adsorbent>

Example 1

[0081] CeOx (x=1.5 to 2.0) was pelletized at 200 kgf by using a pressing machine and a mold having a diameter of 40 mm.

[0082] Subsequently, the pellet thus obtained was pulverized and then adjusted into a granular shape (particle size: 0.5 mm to 1.0 mm) by using a sieve, thereby obtaining an adsorbent of Example 1.

Comparative Example 1

[0083] Zeolite (manufactured by Wako Pure Chemical Industries, Ltd., product name: Molecular Sieves 13X) was prepared as an adsorbent. Incidentally, the zeolite was adjusted into a granular shape (particle size: 0.5 mm to 1.0 mm) by using a sieve.

[0084] <CO.sub.2 Adsorption Breakthrough Test>

[0085] The amount of CO.sub.2 adsorbed on the adsorbent in each of the absence of moisture (in a case in which the gas did not contain water) and the presence of moisture (in a case in which the gas contains water) was calculated by the CO.sub.2 adsorption breakthrough test to be described below.

[0086] [In Absence of Moisture]

[0087] First, the adsorbent was weighed by 1.0 mL by using a measuring cylinder and fixed in a reaction tube made of quartz glass. Subsequently, as a pretreatment, the temperature of the adsorbent was raised to 200 C. by using an electric furnace while circulating He gas (first circulating gas) through the reaction tube at 60 mL/min and then maintained at this temperature for 1 hour. By this, the impurities and the gases adsorbed on the adsorbent were removed. Subsequently, the adsorbent was cooled to room temperature (25 C.), and then the circulating gas was switched from He gas to a mixed gas of CO.sub.2 and He (second circulating gas, CO.sub.2 concentration: 400 ppm). Thereafter, the CO.sub.2 concentration at the outlet of the reaction tube was measured by gas chromatography. The temperature of the adsorbent was adjusted to 25 C. and the total pressure inside the reaction tube was adjusted to 1 atm. The CO.sub.2 adsorption amount until adsorption breakthrough was calculated by regarding the time point at which the CO.sub.2 concentration at the outlet of the reaction tube exceeded 100 ppm as adsorption breakthrough. The CO.sub.2 adsorption amount in Example 1 was 19.448 g/L and the CO.sub.2 adsorption amount in Comparative Example 1 was 3.256 g/L. The results are illustrated in FIG. 3.

[0088] [In Presence of Moisture]

[0089] The CO.sub.2 adsorption breakthrough test in the presence of moisture was performed by the same operation as the CO.sub.2 adsorption breakthrough test in the absence of moisture described above except that a gas into which moisture was introduced into He at about 3.1% by volume (based on the total volume of the first circulating gas) was used as the first circulating gas and a gas into which moisture was introduced into a mixed gas of CO.sub.2 and He (CO.sub.2 concentration: 400 ppm) at about 3% by volume (based on the total volume of the second circulating gas) was used as the second circulating gas. The introduction of moisture was performed by allowing He or a mixed gas of CO.sub.2 and He (CO.sub.2 concentration: 400 ppm) to bubble in water maintained at 25 C. The CO.sub.2 adsorption amount in Example 1 was 9.02 g/L, and the CO.sub.2 adsorption amount in Comparative Example 1 was 0.088 g/L. The results are illustrated in FIG. 3.

[0090] <CO.sub.2 and H.sub.2O Desorption Test>

[0091] The adsorbent after being subjected to the CO.sub.2 adsorption breakthrough test performed in the presence of moisture was taken out and heated to 200 C. at 5 C./min and the desorption amounts of molecules of carbon dioxide and moisture (H.sub.2O) were measured by mass spectrometry. The results are illustrated in FIG. 4.

[0092] <Evaluation on CO.sub.2 Concentration Dependency of CO.sub.2 Adsorption Amount>

[0093] An adsorbent (granular CeOx, x=1.5 to 2.0, particle size: 0.5 mm to 1.0 mm) was pretreated at 200 C. for 1 hour or more in a vacuum. Thereafter, the CO.sub.2 adsorption isotherm (see FIG. 5) was obtained by measuring the CO.sub.2 adsorption amount at each CO.sub.2 partial pressure while maintaining the temperature of the adsorbent at 50 C. Incidentally, the horizontal axis of the adsorption isotherm illustrated in FIG. 5 represents a value obtained by converting the CO.sub.2 partial pressure into the CO.sub.2 concentration at atmospheric pressure (1.0 atm) using the following equation.

CO.sub.2 concentration (ppm)=CO.sub.2 partial pressure (atm)/1.0(atm)10.sup.6

[0094] <Measurement Results>

[0095] The amount of CO.sub.2 adsorbed on the adsorbent of Example 1 was about 6 times that on the zeolite of Comparative Example 1 in the absence of moisture (see FIG. 3). Furthermore, in the presence of moisture, the zeolite of Comparative Example 1 hardly adsorbed CO.sub.2 but the amount of CO.sub.2 adsorbed on the adsorbent of Example 1 was about 50% of the CO.sub.2 adsorption amount in the absence of moisture. From these results, it can be seen that the adsorbent of Example 1 containing cerium oxide is a material capable of adsorbing a sufficient amount of carbon dioxide at a low CO.sub.2 concentration regardless of the presence or absence of moisture.

[0096] In addition, the temperatures at which the desorption amounts of CO.sub.2 and H.sub.2O reached the peaks (desorption peak temperatures) were greatly different from each other in the zeolite of Comparative Example 1, and thus the desorption peak temperature of CO.sub.2 was about 80 C. but the peak of H.sub.2O desorption amount did not appear until the temperature reached 200 C. (see FIG. 4). On the other hand, the desorption peak temperature of CO.sub.2 and the desorption peak temperature of H.sub.2O in the adsorbent of Example 1 were all about 120 C. and the desorption of CO.sub.2 and H.sub.2O was almost completed until the temperature reached 200 C. From the present result, it is presumed that the zeolite of Comparative Example 1 has a stronger adsorptive power for H.sub.2O than CO.sub.2 and preferentially adsorbs H.sub.2O in the presence of H.sub.2O and thus a sufficient CO.sub.2 adsorption amount is not obtained in the presence of moisture but the adsorbent of Example 1 has almost no difference between the adsorptive power for CO.sub.2 and the adsorptive power for H.sub.2O and thus it exhibits excellent CO.sub.2 adsorptivity. In addition, it can be seen that it is difficult to desorb H.sub.2O from the zeolite of Comparative Example 1 once H.sub.2O adsorbs thereon, but H.sub.2O can be more easily desorbed from the adsorbent of Example 1 than from the zeolite of Comparative Example 1 and thus the adsorbent of Example 1 exhibits superior regeneration ability.

REFERENCE SIGNS LIST

[0097] 1: air conditioning system, 10: flow path, 10a, 10b, 10d, 10e, 10f: flow path section, 10c: removal section (device for removing carbon dioxide), 20: exhaust fan, 30: device for measuring concentration (concentration measuring section), 40: electric furnace, 50: compressor, 60, 62: control apparatus (control section), 70a, 70b: valve, 80: adsorbent, 100, 100a, 100b: air conditioner, R: space to be air-conditioned, S1, S3: space, S2: central portion.