Recovery method and recovery device

Abstract

A recovery method according to one embodiment of the present invention comprises: a first concentration step in which a starting material gas is introduced into a first pressure swing adsorption device and a first gas in which carbon dioxide has been concentrated is recovered; and a second concentration step in which the first gas is introduced into a first pressure swing adsorption device and a second gas in which carbon dioxide has been concentrated is recovered. The first pressure swing adsorption device has a first adsorption tower in which activated carbon is housed, and the second pressure swing adsorption device has a second adsorption tower in which zeolite is housed. In the first concentration step, carbon dioxide contained in the starting material gas introduced into the first adsorption tower is adsorbed onto the activated carbon and subsequently desorbed so as to recover the first gas, and in the second concentration step, carbon dioxide contained in the first gas introduced into the second adsorption tower is adsorbed onto the zeolite and subsequently desorbed so as to recover the second gas.

Description

Recovery method and recovery device

[0001] The present invention relates to a method and apparatus for recovering carbon dioxide.

[0002] Nitrogen and carbon dioxide are used in a wide range of fields, and combustion exhaust gas from boilers at chemical plants and other facilities contains high concentrations of nitrogen and low concentrations of carbon dioxide. Carbon dioxide is considered a major cause of global warming, and efforts to curb emissions are gaining momentum worldwide. Various research efforts have been vigorously pursued to enable the capture and storage of carbon dioxide from exhaust gases without releasing it into the atmosphere. Known carbon dioxide capture methods include pressure swing adsorption, membrane separation and concentration, and chemical absorption, which utilizes reactive absorption by basic compounds. However, the current cost of carbon dioxide capture is high, and it has not yet reached the stage of widespread adoption.

[0003] The pressure swing adsorption method involves repeatedly carrying out an adsorption process in which a mixed gas is introduced at a predetermined pressure into an adsorption tower filled with an adsorbent to adsorb specific gas components, and a desorption process in which the adsorption tower to which the specific gas components have been adsorbed is depressurized to a predetermined pressure and the gas components are recovered or discharged.

[0004] For example, Patent Document 1 discloses a method for recovering a gas containing a high concentration of carbon dioxide from a raw material gas containing a low concentration of carbon dioxide using a pressure swing adsorption apparatus having two adsorption towers.

[0005] Japanese Patent Application Publication No. 5-228326

[0006] However, with the current pressure swing adsorption method for separating and recovering carbon dioxide from gases containing low-concentration carbon dioxide as a raw material, it has been difficult to efficiently recover highly pure carbon dioxide.

[0007] Therefore, an object of the present invention is to provide a recovery method and recovery apparatus that can efficiently recover carbon dioxide with high purity from a raw material gas containing low concentrations of carbon dioxide.

[0008] [1] A recovery method according to one aspect of the present invention includes a first concentration step of introducing a feed gas containing carbon dioxide into a first pressure swing adsorption apparatus and recovering a first gas in which the carbon dioxide is concentrated, and a second concentration step of introducing the first gas into a second pressure swing adsorption apparatus and recovering a second gas in which the carbon dioxide is concentrated, wherein the first pressure swing adsorption apparatus has a first adsorption tower into which the feed gas is introduced and which contains activated carbon, and the second pressure swing adsorption apparatus has a second adsorption tower into which the first gas is introduced and which contains zeolite, and in the first concentration step, the carbon dioxide contained in the feed gas introduced into the first adsorption tower is adsorbed by the activated carbon and then desorbed, thereby recovering the first gas, and in the second concentration step, the carbon dioxide contained in the first gas introduced into the second adsorption tower is adsorbed by the zeolite and then desorbed, thereby recovering the second gas.

[0009] In the recovery method described in [1] above, carbon dioxide contained in a raw material gas is concentrated in a first concentration step. Thereafter, the carbon dioxide contained in the first gas recovered in the first concentration step is further concentrated in a second concentration step. In the first concentration step, the carbon dioxide contained in the raw material gas is concentrated by adsorbing the carbon dioxide onto activated carbon and then desorbing it, and in the second concentration step, the carbon dioxide contained in the first gas is concentrated by adsorbing the carbon dioxide onto zeolite and then desorbing it. In this way, by using activated carbon in the first concentration step and zeolite in the second concentration step, high-purity carbon dioxide can be efficiently recovered even from a raw material gas containing a low concentration of carbon dioxide.

[0010] [2] In the recovery method according to [1] above, the carbon dioxide concentration of the feed gas introduced into the first adsorption tower may be 20 vol % or less. In this way, even when the carbon dioxide concentration contained in the feed gas is 20 vol % or less, the carbon dioxide recovery rate can be improved by using activated carbon in the first concentration step and zeolite in the second concentration step.

[0011] [3] In the recovery method according to the above [1] or [2], the zeolite may be a zeolite having a three-dimensional framework. In this case, carbon dioxide can be easily adsorbed, and therefore carbon dioxide of higher purity can be recovered.

[0012] [4] In the recovery method described in [3] above, the zeolite may be an FAU-type zeolite.

[0013] [5] In the recovery method according to any one of [1] to [4] above, in the first concentration step, the first gas obtained in an initial stage of the step of desorbing the carbon dioxide from the activated carbon may be returned to the first pressure swing adsorption device. In this case, the first gas returned to the first pressure swing adsorption device can be used, for example, as a wash gas for washing the first adsorption tower.

[0014] [6] In the recovery method according to any one of [1] to [5] above, in the second concentration step, the second gas obtained in an initial stage of the step of desorbing the carbon dioxide from the zeolite may be returned to the second pressure swing adsorption unit. In this case, the second gas returned to the second pressure swing adsorption unit can be used, for example, as a wash gas for washing the second adsorption tower.

[0015] [7] In the recovery method according to any one of [1] to [6] above, the first pressure swing adsorption unit may include a plurality of the first adsorption towers, and the second pressure swing adsorption unit may include a plurality of the second adsorption towers. In this case, by staggering the timing of recovery of the first gas in the plurality of first adsorption towers, the first gas can be recovered intermittently at short intervals from the first pressure swing adsorption unit. Similarly, by staggering the timing of recovery of the second gas in the plurality of second adsorption towers, the second gas can be recovered intermittently at short intervals from the second pressure swing adsorption unit.

[0016] [8] A recovery system according to another aspect of the present invention includes: a first pressure swing adsorption system having a first adsorption tower containing activated carbon, the first pressure swing adsorption system concentrating carbon dioxide contained in a feed gas introduced into the first adsorption tower by using the activated carbon and recovering a first gas containing the concentrated carbon dioxide; a first line for introducing the feed gas containing carbon dioxide into the first adsorption tower; a second pressure swing adsorption system having a second adsorption tower containing zeolite, the second pressure swing adsorption system concentrating carbon dioxide contained in the first gas introduced into the second adsorption tower by using the zeolite and recovering a second gas containing the concentrated carbon dioxide; and a second line for introducing the first gas recovered in the first pressure swing adsorption system into the second adsorption tower.

[0017] In the recovery system described in [8] above, carbon dioxide contained in the feed gas is concentrated in a first pressure swing adsorption unit. Thereafter, the carbon dioxide contained in the first gas recovered in the first pressure swing adsorption unit can be further concentrated in a second pressure swing adsorption unit. In the first pressure swing adsorption unit, the carbon dioxide contained in the feed gas can be concentrated by adsorbing carbon dioxide onto activated carbon and then desorbing it. In the second pressure swing adsorption unit, the carbon dioxide contained in the first gas can be concentrated by adsorbing carbon dioxide onto zeolite and then desorbing it. In this way, by using activated carbon in the first pressure swing adsorption unit and zeolite in the second pressure swing adsorption unit, high-purity carbon dioxide can be efficiently recovered even from a feed gas containing a low concentration of carbon dioxide.

[0018] [9] The recovery system described in [8] above may have a first return line that returns the first gas recovered from the first pressure swing adsorption system to the first pressure swing adsorption system. In this case, the first gas returned to the first pressure swing adsorption system can be used, for example, as a cleaning gas for cleaning the first adsorption column.

[0019]

[10] The recovery system according to [8] or [9] may have a second return line for returning the second gas recovered from the second pressure swing adsorption system to the second pressure swing adsorption system. In this case, the second gas returned to the second pressure swing adsorption system can be used, for example, as a wash gas for washing the second adsorption column.

[0020]

[11] In the recovery system described in any one of [8] to

[10] above, the first pressure swing adsorption unit may include a plurality of the first adsorption towers, and the second pressure swing adsorption unit may include a plurality of the second adsorption towers. In this case, by staggering the timing of recovery of the first gas in the plurality of first adsorption towers, the first gas can be recovered intermittently at short intervals from the first pressure swing adsorption unit. Similarly, by staggering the timing of recovery of the second gas in the plurality of second adsorption towers, the second gas can be recovered intermittently at short intervals from the second pressure swing adsorption unit.

[0021] According to the present invention, it is possible to provide a recovery method and recovery apparatus that can efficiently recover carbon dioxide with high purity from a raw material gas containing low concentrations of carbon dioxide.

[0022] Fig. 1 is a schematic diagram showing the configuration of an example of a recovery device according to a first embodiment. Fig. 2 is a schematic diagram showing the configuration of an example of a recovery device according to a second embodiment.

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same elements are given the same reference numerals, and duplicated explanations will be omitted. The dimensional ratios in the drawings do not necessarily match those in the description.

[0024] (First embodiment) Fig. 1 is a schematic diagram showing the configuration of an example of a carbon dioxide recovery apparatus according to one embodiment. The recovery apparatus 1 shown in Fig. 1 is an apparatus used to separate and recover carbon dioxide from a raw material gas G1 containing low concentration carbon dioxide.

[0025] The raw material gas G1 is supplied from a raw material gas supply source such as combustion exhaust gas from a boiler in a chemical plant or the like, and is a mixed gas of carbon dioxide and impurity gases such as nitrogen and oxygen. An example of the carbon dioxide concentration (an example of a low concentration) contained in the raw material gas G1 supplied from the raw material gas supply source is 20 vol% or less, and preferably 5.0 vol% or more and 15.0 vol% or less. The raw material gas G1 supplied from the raw material gas supply source may be a compressed gas having a pressure equal to or higher than atmospheric pressure. If the raw material gas G1 supplied from the raw material gas supply source is not a compressed gas, it may be compressed by a blower or the like.

[0026] Recovery system 1 includes a first pressure swing adsorption system 2 (hereinafter simply referred to as "first adsorption system 2") and a second pressure swing adsorption system 3 (hereinafter simply referred to as "second adsorption system 3"). As described above, recovery system 1 is a pressure swing adsorption system (or a pressure swing adsorption system) that includes two pressure swing adsorption systems.

[0027] [First Adsorption Device] The first adsorption device 2 has one or more adsorption towers (first adsorption towers). In the first embodiment, a configuration will be described in which the first adsorption device 2 has two adsorption towers 11 a, 11 b. Activated carbon is stored in the adsorption towers 11 a, 11 b.

[0028] The adsorption towers 11a and 11b are towers for concentrating the carbon dioxide contained in the raw material gas G1 by adsorbing the carbon dioxide contained in the raw material gas G1 onto activated carbon, which is an adsorbent, using the pressure swing adsorption (PSA) method, and then desorbing the carbon dioxide.

[0029] In the first embodiment, the gas extracted from each adsorption tower and containing concentrated carbon dioxide is referred to as a “recovered gas.” The gas discharged from the adsorption tower and containing gas components of the raw material gas G1 other than the carbon dioxide adsorbed by the adsorbent is referred to as an “off-gas” (exhaust gas).

[0030] The activated carbon stored in each of the adsorption towers 11a and 11b is not particularly limited as long as it can roughly concentrate carbon dioxide with a high recovery rate, and may be, for example, activated carbon made from coconut shells. An example of such a high recovery rate is 75% or more. The specific surface area of ​​the activated carbon stored in each of the adsorption towers 11a and 11b is, for example, 500 m２ / g or more 2500m ２ / g or less, and the pore size is, for example, 0.1 nm or more and 20 nm or less. From the viewpoint of pressure loss in the adsorption towers 11a and 11b in the pressure swing adsorption method, activated carbon having a particle size of 1.0 mm or more and 2.5 mm or less is preferred, and the packing density of the activated carbon in each of the adsorption towers 11a and 11b is preferably 0.5 kg / L or more and 1.0 kg / L or less. Such activated carbon may be commercially available, and for example, activated carbon "ZK-420" (specific surface area 1000 m) manufactured by Osaka Gas Chemicals Co., Ltd. ２ / g or more 2000m ２ / g or less, pore diameter 0.3 nm, particle diameter 1.8±0.2 mm).

[0031] Each of the adsorption towers 11a and 11b is connected to an inlet flow path (first line) 12, an off-gas flow path 13, a depressurized gas flow path 14, and a recovered gas flow path 15. Each flow path is constructed using a gas pipe.

[0032] The inlet flow path 12 is a gas flow path for introducing the raw material gas G1 from a raw material gas supply source into the adsorption towers 11a and 11b. The inlet flow path 12 may be provided with a buffer tank 16 for storing the raw material gas G1 from the raw material gas supply source. The downstream end of the inlet flow path 12 (the portion closer to the adsorption towers 11a and 11b) branches toward the adsorption towers 11a and 11b and is connected to gas passages at the upstream ends of the adsorption towers 11a and 11b. The upstream ends of the adsorption towers 11a and 11b are upstream ends in the flow direction of the raw material gas G1 introduced from the inlet flow path 12 into the adsorption towers 11a and 11b.

[0033] On-off valves 17a and 17b corresponding to the adsorption towers 11a and 11b are provided at the downstream end (the portion closer to the adsorption towers 11a and 11b) of the inlet flow path 12. By individually opening and closing the on-off valves 17a and 17b, the source gas G1 can be introduced into each of the adsorption towers 11a and 11b.

[0034] A blower 18 may be provided in the inlet flow path 12. The blower 18 is arranged upstream of the on-off valves 17a and 17b. As shown in Fig. 1, in a configuration in which the buffer tank 16 is provided in the inlet flow path 12, the blower 18 is arranged between the buffer tank 16 and the on-off valves 17a and 17b. The blower 18 may be used to compress the source gas G1 when the source gas G1 is not a compressed gas.

[0035] The off-gas flow path 13 is a gas flow path for discharging gas (off-gas) to be discharged from the adsorption towers 11a and 11b to the outside (normal pressure space) of the first adsorption device 2. The upstream end of the off-gas flow path 13 (the portion closer to the adsorption towers 11a and 11b) branches toward the adsorption towers 11a and 11b and is connected to the adsorption towers 11a and 11b. Specifically, the off-gas flow path 13 is connected to gas passages at the downstream ends of the adsorption towers 11a and 11b. The downstream ends of the adsorption towers 11a and 11b are downstream ends in the flow direction of the raw material gas G1 introduced into the adsorption towers 11a and 11b from the introduction flow path 12.

[0036] On-off valves 19a and 19b corresponding to the adsorption towers 11a and 11b are provided at the upstream end of the off-gas passage 13. The on-off valves 19a and 19b individually open and close the passage between the adsorption towers 11a and 11b and the off-gas passage 13, respectively, so that the off-gas G2 can be discharged from each of the adsorption towers 11a and 11b.

[0037] The downstream end of the off-gas passage 13 (the end opposite the adsorption towers 11a and 11b) is an outlet for the off-gas G2 and communicates with a normal pressure space under atmospheric pressure. The off-gas G2 discharged through the off-gas passage 13 is discharged to the outside of the first adsorption device 2. A pressure control valve 20 for adjusting the back pressure is provided on the downstream end side of the off-gas passage 13.

[0038] The pressure release gas flow path 14 is a gas flow path for discharging gas (hereinafter referred to as "pressure release gas G3") discharged from the adsorption towers 11a, 11b to the outside of the first adsorption device 2 when the pressure in the adsorption towers 11a, 11b is released in a pressure release step described below. The pressure release gas G3 is also an off-gas because it is a gas discharged from the adsorption towers 11a, 11b. The upstream end of the pressure release gas flow path 14 (the portion closer to the adsorption towers 11a, 11b) branches toward the adsorption towers 11a, 11b and is connected to the gas passages at the downstream ends of the adsorption towers 11a, 11b. The downstream end of the pressure release gas flow path 14 is an outlet for the pressure release gas G3 and communicates with a normal pressure space under atmospheric pressure.

[0039] The pressure release gas flow path 14 is provided with on-off valves 21a, 21b corresponding to the adsorption towers 11a, 11b. The on-off valves 21a, 21b individually open and close the communication between each of the adsorption towers 11a, 11b and the pressure release gas flow path 14, thereby allowing the pressure release gas G3 to be discharged from each of the adsorption towers 11a, 11b. A pressure control valve 22 for adjusting back pressure is provided at the downstream end of the pressure release gas flow path 14.

[0040] The recovered gas flow path 15 is a gas flow path for flowing the recovered gas (hereinafter referred to as "first recovered gas") extracted from the adsorption towers 11a and 11b into a buffer tank 25 via a vacuum pump 24. The upstream end of the recovered gas flow path 15 (the portion closer to the adsorption towers 11a and 11b) branches off toward the adsorption towers 11a and 11b and is connected to the adsorption towers 11a and 11b. Specifically, the recovered gas flow path 15 is connected to gas passage ports at the upstream ends of the adsorption towers 11a and 11b. The downstream end of the recovered gas flow path 15 is connected to the buffer tank 25 via the vacuum pump 24.

[0041] On-off valves 23a and 23b corresponding to the adsorption towers 11a and 11b are provided at the upstream end of the recovered gas flow path 15. The on-off valves 23a and 23b individually open and close the connection between each of the adsorption towers 11a and 11b and the recovered gas flow path 15, allowing the first recovered gas (first gas) to flow from each of the adsorption towers 11a and 11b into the recovered gas flow path 15.

[0042] In the configuration of the first adsorption device 2, the first recovered gas recovered from the first adsorption device 2 flows into the buffer tank 25. The buffer tank 25 is a tank for temporarily storing the first recovered gas recovered from the first adsorption device 2.

[0043] The first recovered gas stored in the buffer tank 25 is the gas recovered in the first adsorption device 2 and is a mixed gas containing carbon dioxide, nitrogen, and oxygen. In the first embodiment, the carbon dioxide concentration of the first recovered gas is, for example, 5.0 vol% to 80.0 vol%, 10.0 vol% to 70.0 vol%, or 10.0 vol% to 60.0 vol%. From the viewpoint of reducing the load on the adsorption towers 11a and 11b, the carbon dioxide concentration is preferably 20.0 vol% to 50.0 vol%, more preferably 25.0 vol% to 45.0 vol%, and even more preferably 30.0 vol% to 40.0 vol%. The pressure of the first recovered gas is preferably atmospheric pressure or higher, but if it is not a compressed gas, it may be compressed using a blower or the like.

[0044] [Second Adsorption Device] The second adsorption device 3 has one or more adsorption towers (second adsorption towers). In the first embodiment, the second adsorption device 3 has three adsorption towers 31 a, 31 b, and 31 c. Zeolite is stored in each of the adsorption towers 31 a, 31 b, and 31 c.

[0045] The zeolite contained in each of the adsorption towers 31 a, 31 b, and 31 c is not particularly limited as long as it can concentrate carbon dioxide to a high purity, and may be, for example, zeolite in which at least a portion of the cation species has been exchanged with Na ions. An example of the high purity is 98% or more.

[0046] From the viewpoint of the specific surface area of ​​the adsorbent, the zeolite stored in each of the adsorption towers 31 a, 31 b, and 31 c is preferably a zeolite having a three-dimensional skeleton structure. Examples of zeolites having a three-dimensional skeleton structure include FAU, LTA, MFI, AEI, CHA, EMT, ERI, GIS, MEL, MSE, and RHO zeolites, with FAU zeolite being more preferred.

[0047] The specific surface area of ​​the zeolite stored in each of the adsorption towers 31a, 31b, and 31c is, for example, 500 m ２ / g or more 1000m ２ / g or less. From the viewpoint of pressure loss in the adsorption tower in the pressure swing adsorption method, zeolite having a particle size of 1.0 mm or more and 2.0 mm or less is preferred. The packing density of the zeolite in each of the adsorption towers 31a, 31b, and 31c is preferably 0.5 kg / L or more and 1.0 kg / L or less. As such zeolite, a commercially available product may be used, for example, zeolite "F-9HA" (specific surface area 700 m) manufactured by Tosoh Corporation. ２ / g or more 800m ２ / g or less, particle size of 1.4 mm or more and 1.7 mm or less).

[0048] An inlet flow path 32, an off-gas flow path 33, a depressurized gas flow path 34, a recovered gas flow path 35, and a cleaning gas flow path 36 are connected to each of the adsorption towers 31a, 31b, and 31c.

[0049] The inlet flow path 32 is a gas flow path for introducing the first recovered gas stored in the buffer tank 25 into the adsorption towers 31a, 31b, and 31c. The downstream end of the inlet flow path 32 (the portion closer to the adsorption towers 31a, 31b, and 31c) branches toward the adsorption towers 31a, 31b, and 31c and is connected to gas passage ports at the upstream ends of the adsorption towers 31a, 31b, and 31c. The upstream ends of the adsorption towers 31a, 31b, and 31c are upstream ends with respect to the flow direction of the first recovered gas introduced from the inlet flow path 32. The inlet flow path 32, together with the recovered gas flow path 15, functions as a second line for introducing the first recovered gas from the first adsorption device 2 to the second adsorption device 3.

[0050] On-off valves 37a, 37b, and 37c corresponding to the adsorption towers 31a, 31b, and 31c are provided at the downstream end (the portion closer to the adsorption towers 31a, 31b, and 31c) of the inlet flow path 32. The on-off valves 37a, 37b, and 37c individually open and close the connection between each of the adsorption towers 31a, 31b, and 31c and the inlet flow path 32, thereby allowing the first recovered gas to be introduced into each of the adsorption towers 31a, 31b, and 31c via the inlet flow path 32.

[0051] A blower 38 may be provided in the inlet flow path 32 between the buffer tank 25 and the on-off valves 37 a, 37 b, and 37 c. The blower 38 may be used to compress the first recovered gas when the first recovered gas is not a compressed gas.

[0052] The off-gas flow path 33 is a gas flow path for discharging gas (hereinafter referred to as "off-gas G4") discharged from the adsorption towers 31a, 31b, and 31c to the outside of the second adsorption device 3 in an adsorption process described below. The upstream end of the off-gas flow path 33 (the portion closer to the adsorption towers 31a, 31b, and 31c) branches toward the adsorption towers 31a, 31b, and 31c and is connected to gas passages at the downstream ends of the adsorption towers 31a, 31b, and 31c. The downstream ends of the adsorption towers 31a, 31b, and 31c are downstream ends with respect to the flow direction of the first recovery gas introduced from the introduction flow path 32.

[0053] The downstream end of the off-gas passage 33 (the end opposite the adsorption towers 31 a, 31 b, 31 c) is an outlet for the off-gas G4, and is connected to a normal pressure space under atmospheric pressure. The off-gas G4 discharged through the off-gas passage 33 is discharged to the outside of the second adsorption device 3. A pressure control valve 40 for adjusting the back pressure is provided on the downstream end side of the off-gas passage 33.

[0054] On-off valves 39a, 39b, and 39c corresponding to the adsorption towers 31a, 31b, and 31c are provided at the upstream end of the off-gas passage 33. The on-off valves 39a, 39b, and 39c individually open and close the off-gas passage 33 and each of the adsorption towers 31a, 31b, and 31c, respectively, so that the off-gas G4 can be discharged from each of the adsorption towers 31a, 31b, and 31c.

[0055] The pressure release gas flow path 34 is a gas flow path for discharging gas (hereinafter referred to as "pressure release gas G5") discharged from the adsorption towers 31a, 31b, and 31c to the outside of the second adsorption device 3 when the pressure in the adsorption towers 31a, 31b, and 31c is released in a pressure release step described below. The pressure release gas G5 is an off-gas because it is a gas discharged from the adsorption towers 31a, 31b, and 31c. The upstream end of the pressure release gas flow path 34 (the portion closer to the adsorption towers 31a, 31b, and 31c) branches toward the adsorption towers 31a, 31b, and 31c and is connected to the gas passages at the downstream ends of the adsorption towers 31a, 31b, and 31c. The downstream end of the pressure release gas flow path 34 is an outlet for the pressure release gas G5 and communicates with a normal pressure space under atmospheric pressure.

[0056] The pressure release gas flow path 34 is provided with on-off valves 41a, 41b, and 41c corresponding to the adsorption towers 31a, 31b, and 31c. The on-off valves 41a, 41b, and 41c individually open and close the pressure release gas flow path 34 from each of the adsorption towers 31a, 31b, and 31c, thereby allowing the pressure release gas G5 to be discharged from each of the adsorption towers 31a, 31b, and 31c. A pressure control valve 42 for adjusting back pressure is provided at the downstream end of the pressure release gas flow path 34.

[0057] The recovered gas flow path 35 is a gas flow path for flowing the recovered gas (hereinafter referred to as "second recovered gas") recovered from the adsorption towers 31a, 31b, and 31c toward the buffer tank 44 via the vacuum pump 43. The upstream end of the recovered gas flow path 35 (the portion closer to the adsorption towers 31a, 31b, and 31c) branches toward the adsorption towers 31a, 31b, and 31c and is connected to the adsorption towers 31a, 31b, and 31c. Specifically, the recovered gas flow path 35 is connected to gas passage ports at the upstream ends of the adsorption towers 31a, 31b, and 31c. The downstream end of the recovered gas flow path 35 is connected to the buffer tank 44 via the vacuum pump 43.

[0058] On-off valves 45a, 45b, and 45c corresponding to the adsorption towers 31a, 31b, and 31c are provided at the upstream end of the recovered gas flow path 35. The on-off valves 45a, 45b, and 45c individually open and close the connection between each of the adsorption towers 31a, 31b, and 31c and the recovered gas flow path 35, allowing the second recovered gas (second gas) to flow from each of the adsorption towers 31a, 31b, and 31c to the recovered gas flow path 35.

[0059] An on-off valve 46a is provided in the recovered gas flow path 35 between the vacuum pump 43 and the buffer tank 44. The on-off valve 46a can control the inflow of the second recovered gas into the buffer tank 44.

[0060] The cleaning gas flow path 36 is a gas flow path for flowing cleaning gas into the adsorption towers 31a, 31b, and 31c in a cleaning step described below. The downstream end of the cleaning gas flow path 36 branches off toward the adsorption towers 31a, 31b, and 31c and is connected to gas passage ports at the upstream ends of the adsorption towers 31a, 31b, and 31c. The upstream end of the cleaning gas flow path 36 is connected to the recovered gas flow path 35 via a blower 47. Specifically, the upstream end of the cleaning gas flow path 36 is connected to the recovered gas flow path 35 between the vacuum pump 43 and the on-off valve 46a.

[0061] On-off valves 48a, 48b, and 48c corresponding to the adsorption towers 31a, 31b, and 31c are provided at the downstream end of the cleaning gas flow path 36. The on-off valves 48a, 48b, and 48c individually open and close the communication between each of the adsorption towers 31a, 31b, and 31c and the cleaning gas flow path 36, thereby enabling cleaning gas to be supplied to each of the adsorption towers 31a, 31b, and 31c.

[0062] An on-off valve 46b is provided at the upstream end of the cleaning gas flow path 36. As shown in Fig. 1, the on-off valve 46b is provided between the connection between the cleaning gas flow path 36 and the recovered gas flow path 35 and the blower 47. The on-off valve 46b can control the flow of the second recovered gas flowing in the recovered gas flow path 35 to the cleaning gas flow path 36. By opening the on-off valve 46b, the second recovered gas flowing in the cleaning gas flow path 36 functions as a cleaning gas.

[0063] We will now describe an example of a carbon dioxide recovery method using the recovery apparatus 1. The carbon dioxide recovery method includes a first concentration step of concentrating carbon dioxide contained in the raw material gas G1 and recovering the concentrated carbon dioxide (recovered gas), and a second concentration step of re-concentrating carbon dioxide contained in the recovered gas recovered in the first adsorption apparatus 2 and recovering the concentrated carbon dioxide (recovered gas). We will now describe an example of each step.

[0064] [First Concentration Step] In the first concentration step, the carbon dioxide contained in the raw material gas G1 is adsorbed onto activated carbon in the adsorption towers 11a and 11b, and then desorbed, thereby concentrating the carbon dioxide.

[0065] Specifically, an adsorption step and a desorption step are performed in the adsorption towers 11a and 11b. The adsorption towers 11a and 11b may have a pressure release step between the adsorption step and the desorption step. Below, a configuration including the pressure release step will be described. Because the carbon dioxide concentration method is the same in the adsorption towers 11a and 11b, the adsorption step and desorption step performed in the adsorption tower 11a will be described.

[0066] [Adsorption Process] In the adsorption process, the on-off valves 17a and 19a are opened to allow the raw material gas G1 to flow into the adsorption tower 11a, while the activated carbon stored in the adsorption tower 11a adsorbs carbon dioxide contained in the raw material gas G1. During this process, the on-off valves 21a and 23a are closed, and the pressure in the adsorption tower 11a is adjusted by the pressure control valve 20 to an adsorption pressure that appropriately exceeds atmospheric pressure and is suitable for adsorption of carbon dioxide into the activated carbon. The adsorption pressure is, for example, 0 kPaG or higher and 100 kPaG or lower. In the adsorption process, the portion of the raw material gas G1 that is not adsorbed by the activated carbon is discharged as off-gas G2 from the off-gas flow path 13 to the outside of the first adsorption device 2.

[0067] [Pressure Release Step] The pressure release step is performed after the adsorption step. In the pressure release step, the on-off valves 17a and 19a are closed, and the on-off valve 21a is opened to release the pressure inside the adsorption tower 11a. At this time, the pressure inside the adsorption tower 11a is adjusted by the pressure control valve 22 to a pressure suitable for pressure release that is lower than the pressure in the adsorption step. An example of the pressure inside the adsorption tower 11a in the pressure release step is −9.9 kPaG or higher and 30 kPaG or lower. In the pressure release step, too, the portion of the raw material gas G1 that is not adsorbed by the activated carbon is discharged as pressure release gas G3 from the pressure release gas flow path 14 to the outside of the first adsorption device 2.

[0068] [Desorption Process] The desorption process is performed after the pressure release process. In the desorption process, the on-off valve 21a is closed, while the on-off valve 23a is opened. In the desorption process, the vacuum pump 24 is operated to further reduce the pressure in the adsorption tower 11a, while the carbon dioxide adsorbed on the activated carbon is desorbed. The gas in the adsorption tower 11a containing the desorbed carbon dioxide (first recovered gas) flows into the buffer tank 25 through the recovered gas flow path 15. The first recovered gas that has flowed into the buffer tank 25 is stored in the buffer tank 25. In the desorption process, the first recovered gas that flows from the adsorption tower 11a into the buffer tank 25 is a concentrated gas in which carbon dioxide is concentrated compared to the raw material gas G1.

[0069] In the adsorption tower 11a, the first basic cycle is repeated, with the adsorption step, pressure release step, and desorption step being the first basic cycle.

[0070] In the adsorption tower 11b, the on-off valves 17b, 19b, 21b, and 23b are operated in the same manner as the corresponding on-off valves 17a, 19a, 21a, and 23a, thereby performing the adsorption step, the pressure release step, and the desorption step. The first basic cycle is also repeated in the adsorption tower 11b.

[0071] In the first adsorption device 2, the first basic cycle in the adsorption tower 11a and the first basic cycle in the adsorption tower 11b are performed with a time lag. Specifically, as shown in Table 1, while the pressure release step and the desorption step are performed in sequence in the adsorption tower 11a, the adsorption step is performed in the adsorption tower 11b, and after the adsorption step in the adsorption tower 11b is completed, the adsorption step is performed in the adsorption tower 11a while the pressure release step and the desorption step are performed in sequence.

[0072] By staggering the first basic cycles in the adsorption towers 11a and 11b in this manner, the first recovered gas (gas in which carbon dioxide is concentrated) can be made to flow intermittently into the buffer tank 25 at short intervals.

[0073] [Second concentration step] In the second concentration step, in the adsorption towers 31a, 31b, and 31c, the carbon dioxide contained in the first recovered gas recovered from the first adsorption device 2 is adsorbed onto zeolite and then desorbed, thereby re-concentrating the carbon dioxide.

[0074] Specifically, an adsorption step and a desorption step are carried out in the adsorption towers 31a, 31b, and 31c. In the adsorption towers 31a, 31b, and 31c, at least one of a pressure release step and a cleaning step may be carried out between the adsorption step and the desorption step. In the second concentration step, a first desorption step and a second desorption step may be carried out as the desorption step to obtain high-purity carbon dioxide. Below, an embodiment will be described in which the pressure release step and the cleaning step are included and the desorption step includes a first desorption step and a second desorption step. Because the carbon dioxide concentration method is the same in the adsorption towers 31a, 31b, and 31c, the case of the adsorption tower 31a will be described.

[0075] [Adsorption Process] In the adsorption process, the on-off valves 37a and 39a are opened to allow the first recovery gas stored in the buffer tank 25 to flow into the adsorption tower 31a, while the carbon dioxide contained in the first recovery gas is adsorbed by the zeolite stored in the adsorption tower 31a. During this process, the on-off valves 41a, 45a, and 48a are closed, and the pressure inside the adsorption tower 31a is adjusted by the pressure control valve 40 to an adsorption pressure suitable for the adsorption of carbon dioxide by the zeolite. An example of the adsorption pressure is 0 kPaG or higher and 100 kPaG or lower. In the adsorption process, the portion of the first recovery gas that is not adsorbed by the zeolite is discharged as off-gas G4 from the off-gas flow path 33 to the outside of the second adsorption device 3.

[0076] [Pressure Release Step] The pressure release step is performed after the adsorption step. In the pressure release step, the on-off valves 37a and 39a are closed, and the on-off valve 41a is opened to release the pressure inside the adsorption tower 31a. At this time, the pressure inside the adsorption tower 31a is adjusted by the pressure control valve 42 to a pressure suitable for pressure release that is lower than the pressure in the adsorption step. An example of the pressure inside the adsorption tower 31a in the pressure release step is -9.9 kPaG or higher and 30 kPaG or lower. In the pressure release step, the portion of the first recovery gas that is not adsorbed by the zeolite is discharged as pressure release gas G5 from the pressure release gas flow path 34 to the outside of the second adsorption device 3.

[0077] [Cleaning Step] The cleaning step is performed after the pressure release step. In the cleaning step, the on-off valve 48a is opened and the blower 47 is operated to cause the cleaning gas to flow into the adsorption tower 31a through the cleaning gas flow path 36. The cleaning gas that has flowed into the adsorption tower 31a is discharged to the outside of the second adsorption device 3 through the pressure release gas flow path 34.

[0078] In the cleaning step, the cleaning gas flows through the adsorption tower 31a, and gas components other than carbon dioxide that have adhered to the wall surfaces of the adsorption tower 31a are carried along with the cleaning gas and discharged to the outside of the second adsorption device 3. That is, the cleaning gas discharges the gas components other than carbon dioxide that remain in the adsorption tower 31a from the adsorption tower 31a.

[0079] In the first embodiment, the cleaning gas is a second recovered gas obtained by performing the first desorption process in one of the adsorption towers 31 a, 31 b, and 31 c other than the adsorption tower in which the cleaning process is being performed, and is a gas containing concentrated carbon dioxide. For example, when the cleaning process is being performed in the adsorption tower 31 a, the second recovered gas from the adsorption tower 31 b or the adsorption tower 31 c functions as the cleaning gas.

[0080] In order to use the second recovered gas as a cleaning gas in this way, the on-off valve 46a is closed and the on-off valve 46b is open during the cleaning step. As a result, the second recovered gas obtained by carrying out the first desorption step flows from the recovered gas flow path 35 to the cleaning gas flow path 36 and into the adsorption tower 31a. When the second recovered gas is used as a cleaning gas as described above, the carbon dioxide contained in the second recovered gas is re-adsorbed by the zeolite.

[0081] Even after the adsorption tower undergoing the first desorption step has transitioned to the second desorption step, the adsorption tower that had been undergoing the cleaning step may continue the cleaning step. In this case, however, the on-off valve 46a is opened and the on-off valve 46b is closed, and the cleaning gas remaining in the cleaning gas flow path 36 is allowed to flow into the adsorption tower that continues the cleaning step.

[0082] [First Desorption Step] The first desorption step is performed after the cleaning step. The first desorption step is the initial part of the desorption step. In the first desorption step, the on-off valve 48a and the on-off valve 41a are closed, while the on-off valve 45a is opened. In this state, the vacuum pump 43 is operated to reduce the pressure in the adsorption tower 31a, and the gas in the adsorption tower 31a is caused to flow into the recovered gas flow path 35. In the first desorption step, the pressure in the adsorption tower 31a is reduced as described above, and carbon dioxide is desorbed from the zeolite. As a result, the gas flowing into the recovered gas flow path 35 (second recovered gas) contains carbon dioxide.

[0083] In the first desorption step, the on-off valve 46a is closed, while the on-off valve 46b is open. As a result, the second recovery gas (initial recovery gas) that flows into the recovery gas flow path 35 in the first desorption step flows into the cleaning gas flow path 36, as described in the cleaning step, and functions as a cleaning gas in the cleaning step performed in the adsorption towers 31a, 31b, and 31c other than the adsorption tower performing the first desorption step. For example, when the first desorption step is performed in the adsorption tower 31a, the second recovery gas, which is the initial recovery gas, is flowed as a cleaning gas to the adsorption tower 31b or 31c performing the cleaning step.

[0084] The time for which the first desorption step is performed may be any time long enough to sufficiently discharge gas components other than carbon dioxide that have adhered to the wall surfaces of the adsorption tower 31a and the like, and to prevent the carbon dioxide adsorbed on the zeolite from being desorbed more than necessary. An example of the time for which the first desorption step is performed is from 0 seconds to 150 seconds.

[0085] [Second Desorption Step] The second desorption step is a step that occurs a certain time after the start of the first desorption step. In the second desorption step, the on-off valve 46b is closed, while the on-off valve 46a is opened. As a result, the second recovered gas that has flowed from the adsorption tower 31a to the recovered gas flow path 35 flows into the buffer tank 44 and is stored therein. The second recovered gas stored in the buffer tank 44 is extracted as product gas G6 as appropriate.

[0086] In the second desorption step, since the time during which the first desorption step was performed has elapsed and the pressure inside the adsorption tower 31a has decreased since the start of the first desorption step, more carbon dioxide is desorbed from the zeolite after the transition to the second desorption step. Therefore, in the second desorption step, the gas flowing from the adsorption tower 31a to the recovered gas flow path 35 is a recovered gas containing more concentrated carbon dioxide than the recovered gas recovered in the first adsorption device 2. Furthermore, since impurities remaining in the adsorption tower 31a in the first desorption step have also been discharged, a highly pure recovered gas can be obtained in the second desorption step.

[0087] In the adsorption tower 31a, the second basic cycle is repeated, with the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step being the second basic cycle.

[0088] In the adsorption tower 31b, the on-off valves 37b, 45b, 48b, 39b, and 41b are operated in the same manner as the corresponding on-off valves 37a, 45a, 48a, 39a, and 41a, thereby performing the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step. In the adsorption tower 31b, the second basic cycle is repeated, with the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step as the second basic cycle.

[0089] In the adsorption tower 31c, the on-off valves 37c, 45c, 48c, 39c, and 41c are operated in the same manner as the corresponding on-off valves 37a, 45a, 48a, 39a, and 41a, thereby performing the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step. In the adsorption tower 31c, the second basic cycle is repeated, with the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step as the second basic cycle.

[0090] In the second adsorption device 3, the second basic cycle is performed in the adsorption towers 31a, 31b, and 31c at different times. Specifically, as shown in Table 2, while the adsorption step is being performed in the adsorption tower 31a, the depressurization step and the cleaning step are performed in that order in the adsorption tower 31b, and the first desorption step and the second desorption step are performed in that order in the adsorption tower 31c.

[0091] Specifically, the processes in the adsorption towers 31b and 31c while the adsorption tower 31a is performing the adsorption process will be described. When the pressure release process is started in the adsorption tower 31b, the first desorption process is performed in the adsorption tower 31c. When the adsorption tower 31b transitions from the pressure release process to the cleaning process, the first desorption process is still being performed in the adsorption tower 31c. When the adsorption tower 31c transitions from the first desorption process to the second desorption process, the cleaning process is still being performed in the adsorption tower 31b.

[0092] Although the case where the adsorption process is performed in the adsorption tower 31a has been specifically described, the same applies to the case where the adsorption process is performed in the adsorption towers 31b and 31c.

[0093] As described above, the second basic cycles in the adsorption towers 31a, 31b, and 31c are staggered in time, so that the second recovered gas (gas enriched in carbon dioxide) can be obtained intermittently at short intervals.

[0094] The second recovered gas that flows into and is stored in the buffer tank 44 in the second desorption step is used as product gas G6. For example, the product gas G6 is supplied to a downstream process such as a liquefaction device. The use of the product gas G6 is not limited. In the example shown in FIG. 1 , the second recovered gas is temporarily stored in the buffer tank 44, but, for example, the buffer tank 44 does not have to be provided. In this case, the second recovered gas flowing through the recovered gas flow path 35 can be directly supplied to a downstream process as product gas G6.

[0095] As described above, when the second recovery gas is used as the cleaning gas in the cleaning process, the cleaning gas flow path 36 functions as a return line (second return line) that returns the second recovery gas obtained in the second adsorption device 3 to the second adsorption device 3 for a predetermined period of time while the cleaning process is being carried out.

[0096] In the recovery apparatus 1 and the recovery method using the same, the carbon dioxide in the raw material gas G1 is concentrated once in the first adsorption device 2, and then further concentrated in the second adsorption device 3. That is, the carbon dioxide contained in the raw material gas G1 is concentrated in two stages.

[0097] In the recovery device 1 and the recovery method using the same, it is important to use activated carbon as the adsorbent used for concentration in the first stage (first adsorption device 2).

[0098] As an adsorbent for adsorbing carbon dioxide, zeolite is known to adsorb a larger amount of carbon dioxide than activated carbon, and zeolite is usually used when attempting to recover carbon dioxide from large amounts of combustion exhaust gas from chemical plants, etc. Therefore, when concentrating carbon dioxide in two stages as described above, it is conceivable to use zeolite as an adsorbent in both the first and second stages.

[0099] However, the present inventors have found that when zeolite is used as the first-stage adsorbent for a raw material gas G1 having a low carbon dioxide concentration (for example, 20 vol % or less), the recovery rate decreases, whereas when activated carbon is used, crude concentration can be performed efficiently and the recovery rate is improved compared to when zeolite is used.

[0100] In the embodiment in which the second concentration step includes a cleaning step, impurities (gas components other than carbon dioxide) adhering to the walls of the adsorption towers 31 a, 31 b, and 31 c can be removed in the cleaning step, thereby improving the purity of carbon dioxide.

[0101] In an embodiment in which the desorption process includes a first desorption process and a second desorption process, the first desorption process corresponds to the initial stage of the desorption process. In this case, the second recovery gas may contain a small amount of impurities adhering to the walls of the adsorption towers 31a, 31b, and 31c. In this example of the embodiment, the second recovery gas containing a small amount of impurities in the initial stage of the desorption process is used as a cleaning gas. This allows for effective use of the second recovery gas in the initial stage. By using the second recovery gas in the initial stage as a cleaning gas, there is no need to prepare a separate cleaning gas. This reduces the production cost of the product gas G6. The second recovery gas in the initial stage also contains carbon dioxide. Therefore, when the second recovery gas in the initial stage is returned to the adsorption towers 31a, 31b, and 31c in the cleaning process, the carbon dioxide contained in the second recovery gas is re-adsorbed onto the zeolite. This re-adsorbed carbon dioxide is also recovered in the desorption process. This improves the carbon dioxide recovery rate.

[0102] When the zeolite stored in the adsorption towers 31 a, 31 b, and 31 c in the second adsorption device 3 has a three-dimensional framework, it is possible to adsorb a larger amount of carbon dioxide. Therefore, carbon dioxide can be easily concentrated in the second adsorption device 3, and as a result, high-purity carbon dioxide can be efficiently recovered. FAU-type zeolite is more effective for efficiently recovering high-purity carbon dioxide.

[0103] By using activated carbon as the adsorbent in the first adsorption device 2, when concentrating carbon dioxide in two stages, it is possible to reduce the manufacturing costs and operating costs of the recovery device 1 compared to when zeolite is used as the adsorbent in both the first and second stages.

[0104] Second Embodiment Fig. 2 is a schematic diagram of a recovery apparatus according to a second embodiment. The recovery apparatus 1A is a pressure swing adsorption apparatus (or a pressure swing adsorption system) including a first pressure swing adsorption apparatus 2A and a second adsorption apparatus 3. Hereinafter, the first pressure swing adsorption apparatus 2A will be referred to as the first adsorption apparatus 2A.

[0105] The first adsorption device 2A differs from the first adsorption device 2 of the first embodiment mainly in that it further includes an adsorption tower 11c and a cleaning gas flow path 26.

[0106] Specifically, the first adsorption device 2A includes an adsorption tower 11c containing activated carbon, similar to the adsorption towers 11a and 11b. The example of the activated carbon contained in the adsorption tower 11c is the same as that in the first embodiment.

[0107] The first adsorption device 2A has an inlet flow path (first line) 12, an off-gas flow path 13, a pressure release gas flow path 14, and a recovered gas flow path 15, similar to the first adsorption device 2. The inlet flow path (first line) 12, the off-gas flow path 13, the pressure release gas flow path 14, and the recovered gas flow path 15 in the second embodiment are similar to those in the first embodiment, except that they are also connected to the adsorption tower 11c.

[0108] In the first adsorption device 2A, the downstream end of the inlet flow path 12 branches toward the adsorption towers 11a, 11b, and 11c and is connected to gas passages at the upstream ends of the adsorption towers 11a, 11b, and 11c. The inlet flow path 12 is provided with on-off valves 17a, 17b, and 17c corresponding to the adsorption towers 11a, 11b, and 11c. The source gas G1 can be introduced into each of the adsorption towers 11a, 11b, and 11c by individually opening and closing the on-off valves 17a, 17b, and 17c. As in the first embodiment, the inlet flow path 12 may be provided with a buffer tank 16 that stores the source gas G1 from a source gas supply source and a blower 18.

[0109] In the first adsorption device 2A, the upstream end of the off-gas flow path 13 branches toward the adsorption towers 11a, 11b, and 11c and is connected to gas passages at the downstream ends of the adsorption towers 11a, 11b, and 11c. The off-gas flow path 13 is provided with on-off valves 19a, 19b, and 19c corresponding to the adsorption towers 11a, 11b, and 11c. The on-off valves 19a, 19b, and 19c individually open and close the off-gas flow path 13 from each of the adsorption towers 11a, 11b, and 11c, thereby allowing the off-gas G2 to be discharged from each of the adsorption towers 11a, 11b, and 11c. As in the first embodiment, a pressure control valve 20 for adjusting back pressure is provided at the downstream end of the off-gas flow path 13.

[0110] In the first adsorption device 2A, the upstream end of the pressure release gas flow path 14 branches toward the adsorption towers 11a, 11b, and 11c and is connected to the gas passages at the downstream ends of the adsorption towers 11a, 11b, and 11c. The pressure release gas flow path 14 is provided with on-off valves 21a, 21b, and 21c corresponding to the adsorption towers 11a, 11b, and 11c. The on-off valves 21a, 21b, and 21c individually open and close the pressure release gas flow path 14 from each of the adsorption towers 11a, 11b, and 11c, allowing the pressure release gas G3 to be discharged from each of the adsorption towers 11a, 11b, and 11c. As in the first embodiment, the pressure release gas flow path 14 is provided with a pressure control valve 22 for adjusting back pressure.

[0111] In the first adsorption device 2A, the upstream end of the recovered gas flow path 15 branches toward the adsorption towers 11a, 11b, and 11c and is connected to gas passage ports at the upstream ends of the adsorption towers 11a, 11b, and 11c. The recovered gas flow path 15 is provided with on-off valves 23a, 23b, and 23c corresponding to the adsorption towers 11a, 11b, and 11c. The on-off valves 23a, 23b, and 23c allow the first recovered gas (first gas) to flow from each of the adsorption towers 11a, 11b, and 11c into the recovered gas flow path 15. An on-off valve 27a is provided in the recovered gas flow path 15 between the vacuum pump 24 and the buffer tank 25. The on-off valve 27a controls the inflow of the first recovered gas into the buffer tank 25.

[0112] The first adsorption device 2A further includes a cleaning gas flow path 26. The cleaning gas flow path 26 is a gas flow path for flowing cleaning gas into the adsorption towers 11a, 11b, and 11c in a cleaning process described below. The downstream end of the cleaning gas flow path 26 branches toward the adsorption towers 11a, 11b, and 11c and is connected to gas passages at the upstream ends of the adsorption towers 11a, 11b, and 11c. The upstream end of the cleaning gas flow path 26 is connected to the recovered gas flow path 15 via a blower 28. Specifically, the upstream end of the cleaning gas flow path 26 is connected to the recovered gas flow path 15 between the vacuum pump 24 and the on-off valve 27a.

[0113] On-off valves 29a, 29b, and 29c corresponding to the adsorption towers 11a, 11b, and 11c are provided at the downstream end of the cleaning gas flow path 26. The on-off valves 29a, 29b, and 29c individually open and close the communication between each of the adsorption towers 11a, 11b, and 11c and the cleaning gas flow path 26, thereby enabling cleaning gas to be supplied to each of the adsorption towers 11a, 11b, and 11c.

[0114] An on-off valve 27b is provided on the upstream end side of the cleaning gas flow path 26. As shown in Fig. 2, the on-off valve 27b is provided between the connection portion of the cleaning gas flow path 26 and the recovered gas flow path 15 and the blower 28. The on-off valve 27b can control the flow of the first recovered gas flowing in the recovered gas flow path 15 into the cleaning gas flow path 26. By opening the on-off valve 27b, the first recovered gas flowing in the cleaning gas flow path 26 functions as a cleaning gas.

[0115] The second suction device 3 in the second embodiment is the same as that in the first embodiment, and therefore a description thereof will be omitted.

[0116] In the second embodiment, an example of a method for recovering carbon dioxide using the recovery apparatus 1A includes a first concentration step of concentrating the carbon dioxide contained in the raw material gas G1 and recovering the concentrated carbon dioxide (first recovered gas), and a second concentration step of re-concentrating the carbon dioxide contained in the first recovered gas and recovering the concentrated carbon dioxide (second recovered gas).

[0117] Specifically, an adsorption step and a desorption step are carried out in the adsorption towers 11a, 11b, and 11c. In the adsorption towers 11a, 11b, and 11c, at least one of a pressure release step and a cleaning step may be carried out between the adsorption step and the desorption step. In the first concentration step, a first desorption step and a second desorption step may be carried out as the desorption step to obtain carbon dioxide of higher purity. Below, an embodiment will be described in which the pressure release step and the cleaning step are included and the desorption step includes a first desorption step and a second desorption step. Because the carbon dioxide concentration method is the same in the adsorption towers 11a, 11b, and 11c, the case of the adsorption tower 11a will be described.

[0118] [Adsorption Step] In the adsorption step, except that the on-off valve 23a is closed, carbon dioxide is adsorbed onto the activated carbon in the same manner as in the adsorption step in the first adsorption device 2. In the adsorption step, the portion of the raw material gas that is not adsorbed onto the activated carbon is discharged as off-gas G2 from the off-gas flow path 13 to the outside of the first adsorption device 2A.

[0119] [Pressure Release Step] The pressure release step is performed after the adsorption step. The pressure in the adsorption tower 11a is released in the same manner as the pressure release step in the first adsorption device 2, except that the on-off valve 23a is kept closed. In the pressure release step, the portion of the raw material gas G1 that is not adsorbed by the activated carbon is discharged as pressure release gas G3 from the pressure release gas flow path 14 to the outside of the first adsorption device 2A.

[0120] [Cleaning Step] The cleaning step is performed after the pressure release step. In the cleaning step, the on-off valve 29a is opened and the blower 28 is operated to cause the cleaning gas to flow into the adsorption tower 11a through the cleaning gas flow path 26. The cleaning gas that has flowed into the adsorption tower 11a is discharged to the outside of the first adsorption device 2A through the pressure release gas flow path 14.

[0121] In the cleaning step, the cleaning gas flows through the adsorption tower 11a, and gas components other than carbon dioxide that have adhered to the walls of the adsorption tower 11a are carried along with the cleaning gas and discharged to the outside of the first adsorption device 2A. That is, the cleaning gas discharges the gas components other than carbon dioxide that remain in the adsorption tower 11a from the adsorption tower 11a.

[0122] In the second embodiment, the cleaning gas is a first recovered gas obtained by performing a first desorption process in one of the adsorption towers 11 a, 11 b, and 11 c other than the adsorption tower in which the cleaning process is being performed. For example, when the cleaning process is being performed in the adsorption tower 11 a, the first recovered gas from the adsorption tower 11 b or 11 c functions as the cleaning gas.

[0123] In order to use the first recovered gas as a cleaning gas in this way, on-off valve 27a is closed and on-off valve 27b is open during the cleaning step. As a result, the first recovered gas obtained by carrying out the first desorption step flows from recovered gas flow path 15 to cleaning gas flow path 26 and into adsorption tower 11a. When the first recovered gas is used as a cleaning gas as described above, the carbon dioxide contained in the first recovered gas is re-adsorbed by the activated carbon.

[0124] Even after the adsorption tower undergoing the first desorption step has transitioned to the second desorption step, the adsorption tower that had been undergoing the cleaning step may continue the cleaning step as is. In this case, however, the on-off valve 27a is opened and the on-off valve 27b is closed, and the cleaning gas remaining in the cleaning gas flow path 26 is allowed to flow into the adsorption tower that continues the cleaning step.

[0125] [First Desorption Step] The first desorption step is performed after the cleaning step. The first desorption step is the initial part of the desorption step. In the first desorption step, the on-off valve 29a and the on-off valve 21a are closed, while the on-off valve 23a is opened. In this state, the vacuum pump 24 is operated to reduce the pressure in the adsorption tower 11a, and the gas in the adsorption tower 11a is caused to flow into the recovered gas flow path 15. In the first desorption step, the pressure in the adsorption tower 11a is reduced as described above, causing carbon dioxide to desorb from the activated carbon. As a result, the gas flowing into the recovered gas flow path 15 (first recovered gas) contains carbon dioxide.

[0126] In the first desorption step, the on-off valve 27a is closed, while the on-off valve 27b is open. As a result, the first recovery gas (initial recovery gas) that flows into the recovery gas flow path 15 in the first desorption step flows into the cleaning gas flow path 26, as described in the cleaning step, and functions as a cleaning gas in the cleaning step that is performed in the adsorption towers 11a, 11b, and 11c other than the adsorption tower that is performing the first desorption step. For example, when the first desorption step is performed in the adsorption tower 11a, the initial recovery gas is flowed as a cleaning gas into the adsorption tower 11b or 11c that is performing the cleaning step.

[0127] The time for performing the first desorption step may be any time long enough to sufficiently discharge gas components other than carbon dioxide that have adhered to the wall surfaces of the adsorption tower 11a and the like, and not to desorb more carbon dioxide than necessary. An example of the time for performing the first desorption step is from 0 seconds to 150 seconds.

[0128] [Second Desorption Step] The second desorption step is a step that occurs a certain time after the start of the first desorption step. In the second desorption step, the on-off valve 27b is closed and the on-off valve 27a is opened. As a result, the first recovered gas that has flowed from the adsorption tower 11a to the recovered gas flow path 15 flows into the buffer tank 25 and is stored therein.

[0129] In the second desorption step, since the time since the first desorption step has elapsed and the pressure in the adsorption tower 11a has decreased since the start of the first desorption step, more carbon dioxide is desorbed from the activated carbon after the second desorption step begins. Furthermore, since the impurities remaining in the adsorption tower 11a in the first desorption step have also been discharged, the second desorption step provides a recovered gas with a higher purity than the recovered gas obtained in the first desorption step.

[0130] In the adsorption tower 11a, the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step constitute a 1A basic cycle, which is repeated.

[0131] In adsorption tower 11b, on-off valves 17b, 19b, 21b, 23b, and 29b are operated in the same manner as on-off valves 17a, 19a, 21a, 23a, and 29a, respectively, to perform the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step. In adsorption tower 11b, the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step form the 1A basic cycle, and the 1A basic cycle is repeated.

[0132] In the adsorption tower 11c, the adsorption step, the pressure release step, the cleaning step, the first desorption step, and the second desorption step are performed by operating the on-off valves 17c, 19c, 21c, 23c, and 29c in the same manner as the corresponding on-off valves 17a, 19a, 21a, 23a, and 29a. In the adsorption tower 11c, the adsorption step, the pressure release step, the cleaning step, the first desorption step, and the second desorption step are defined as the 1A basic cycle, and the 1A basic cycle is repeated.

[0133] In the first adsorption device 2A, the adsorption towers 11a, 11b, and 11c perform the 1A basic cycle with a time lag. Specifically, as shown in Table 3, while the adsorption tower 11a performs the adsorption process, the adsorption tower 11b performs the depressurization process and the cleaning process in sequence, and the adsorption tower 11c performs the first desorption process and the second desorption process in sequence.

[0134] Specifically, the processes in the adsorption towers 11b and 11c while the adsorption tower 11a is performing the adsorption process will be described. When the pressure release process is started in the adsorption tower 11b, the first desorption process is performed in the adsorption tower 11c. When the adsorption tower 11b transitions from the pressure release process to the cleaning process, the first desorption process is still being performed in the adsorption tower 11c. When the adsorption tower 11c transitions from the first desorption process to the second desorption process, the cleaning process is still being performed in the adsorption tower 11b.

[0135] When the first recovery gas is used as a cleaning gas in the cleaning process carried out in the first adsorption device 2A, the cleaning gas flow path 26 in the first adsorption device 2A functions as a return line (first return line) that returns the first recovery gas obtained in the first adsorption device 2A to the first adsorption device 2A for a predetermined period of time while the cleaning process is being carried out.

[0136] The second adsorption device 3 in the second embodiment is the same as that in the first embodiment, and therefore the second concentration step is the same as that in the first embodiment.

[0137] By using activated carbon as the adsorbent in the first adsorption device 2A, when concentrating carbon dioxide in two stages, it is possible to reduce the manufacturing costs and operating costs of the recovery device 1A compared to using zeolite as the adsorbent in both the first and second stages.

[0138] The effects of the first adsorption device 2A having the cleaning gas flow path 26 as shown in Fig. 2 (in other words, the first concentration step having a cleaning step) are similar to those described in relation to the second adsorption device 3 of the first embodiment. That is, when the first adsorption device 2A has the cleaning gas flow path 26 as shown in Fig. 2, the carbon dioxide recovery rate in the first adsorption device 2A can be improved.

[0139] The present invention will be specifically described below using examples, but the present invention is not limited to the following examples. In the description of Examples 1 to 4, the elements described in the first and second embodiments are given the same reference numerals, and duplicated descriptions will be omitted.

[0140] Example 1 In Example 1, carbon dioxide was recovered from a raw material gas G1 using the recovery apparatus 1 shown in FIG.

[0141] The raw material gas G1 contained 9.9 vol % carbon dioxide, 83.4 vol % nitrogen, and 6.7 vol % oxygen. The flow rate of the raw material gas G1 supplied to the recovery device 1 was 2.42 NL / min.

[0142] The adsorption towers 11a and 11b of the first adsorption device 2 and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0143] Each of the adsorption towers 11a and 11b was filled with 500 milliliters of activated carbon. Activated carbon "ZK-420" manufactured by Osaka Gas Chemicals Co., Ltd. was used as the activated carbon. The packing density of each of the adsorption towers 11a and 11b was 0.7 g / ml. Each of the adsorption towers 31a, 31b, and 31c was filled with 500 milliliters of zeolite. Zeolite "F-9HA" manufactured by Tosoh Corporation was used as the zeolite. The packing density of each of the adsorption towers 31a, 31b, and 31c was 0.68 g / ml.

[0144] In Example 1, the first concentration step and the second concentration step described in the first embodiment were carried out.

[0145] In the first concentration step (first adsorption device 2), the adsorption step was performed for 200 seconds, the pressure release step for 3 seconds, and the desorption step for 197 seconds, in that order. In the first concentration step, a cycle consisting of the adsorption step, pressure release step, and desorption step was defined as a first basic cycle, and the first concentration step was performed so that the first basic cycles in the adsorption towers 11a and 11b were time-shifted, as described in the first embodiment.

[0146] In the second concentration step (second adsorption device 3), the adsorption step was performed for 400 seconds, the pressure release step for 3 seconds, the cleaning step for 397 seconds, the first desorption step for 85 seconds, and the second desorption step for 315 seconds, in that order. In the second concentration step, a cycle consisting of the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step was defined as a second basic cycle, and the second concentration step was performed so that the second basic cycles in the adsorption towers 31a, 31b, and 31c were shifted in time, as described in the second embodiment.

[0147] In the first adsorption device 2, the internal pressure (adsorption pressure) of each adsorption tower 11a, 11b performing the adsorption process was 20.6 kPaG, the internal pressure (depressurization pressure) of each adsorption tower 11a, 11b performing the depressurization process was -3.3 kPaG, and the internal pressure (desorption pressure) of each adsorption tower 11a, 11b performing the desorption process was -95.1 kPaG.

[0148] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 21.1 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 10.7 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the desorption process was −95.1 kPaG.

[0149] The results of Example 1 are shown in Table 4. In Example 1, the carbon dioxide concentration of the first recovered gas recovered from the first adsorption device 2 was 31.1 vol %, and the carbon dioxide recovery rate was 88.8%. In Example 1, the carbon dioxide concentration of the second recovered gas (product gas) finally recovered from the second adsorption device 3 was 98.6 vol %, and the carbon dioxide recovery rate was 64.5%.

[0150] Example 2 In Example 2, carbon dioxide was recovered from the raw material gas G1 using the recovery apparatus 1A shown in FIG. 2 in accordance with the second embodiment.

[0151] The raw material gas G1 contained 10.5 vol % carbon dioxide, 84.3 vol % nitrogen, and 5.2 vol % oxygen. The supply flow rate of the raw material gas G1 to the recovery apparatus 1A was 3.12 NL / min.

[0152] The adsorption towers 11a, 11b, and 11c of the first adsorption device 2A and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0153] Each of the adsorption towers 11a, 11b, and 11c was filled with 500 milliliters of activated carbon. The activated carbon used was "ZK-420" manufactured by Osaka Gas Chemicals Co., Ltd. The packing density of each of the adsorption towers 11a, 11b, and 11c was 0.7 g / ml. Each of the adsorption towers 31a, 31b, and 31c was filled with 500 milliliters of zeolite. The zeolite used was "F-9HA" manufactured by Tosoh Corporation. The packing density of each of the adsorption towers 31a, 31b, and 31c was 0.68 g / ml.

[0154] In Example 2, the first concentration step and the second concentration step described in the second embodiment were carried out.

[0155] In the first concentration step (first adsorption device 2A), the adsorption step was performed for 100 seconds, the pressure release step for 3 seconds, the cleaning step for 97 seconds, the first desorption step for 10 seconds, and the second desorption step for 90 seconds, in that order. The cycle consisting of the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step was designated the 1A basic cycle, and the first concentration step was performed so that the 1A basic cycles in the adsorption towers 11a, 11b, and 11c were shifted in time, as shown in Table 3 above.

[0156] In the second concentration step (second adsorption device 3), the adsorption step was performed for 400 seconds, the pressure release step for 3 seconds, the cleaning step for 397 seconds, the first desorption step for 50 seconds, and the second desorption step for 350 seconds, in that order. In the second concentration step, a cycle consisting of the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step was defined as a second basic cycle, and the second concentration step was performed so that the second basic cycles in the adsorption towers 31a, 31b, and 31c were shifted in time, as shown in Table 2 above.

[0157] In the first adsorption device 2A, the internal pressure (adsorption pressure) of the adsorption towers 11a, 11b, and 11c performing the adsorption process was 20.4 kPaG, the internal pressure (release pressure) of the adsorption towers 11a, 11b, and 11c performing the depressurization process was 12.5 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 11a, 11b, and 11c performing the second desorption process was −94.0 kPaG.

[0158] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 19.4 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 7.0 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the second desorption process was −95.3 kPaG.

[0159] Other conditions in Example 2 were the same as those in Example 1.

[0160] The results of Example 2 are shown in Table 4. That is, the carbon dioxide concentration in the first recovered gas recovered in the first adsorption device 2A was 40.0 vol%, and the carbon dioxide recovery rate was 91.3%. In Example 2, the carbon dioxide concentration in the second recovered gas (product gas) finally recovered in the second adsorption device 3 was 98.8 vol%, and the carbon dioxide recovery rate was 77.5%.

[0161] Example 3 In Example 3, carbon dioxide was recovered from the raw material gas G1 using the recovery apparatus 1A shown in FIG. 2 in accordance with the second embodiment.

[0162] The raw material gas G1 in Example 3 contained 5.0 vol % carbon dioxide, 85.0 vol % nitrogen, and 10.0 vol % oxygen. The supply flow rate of the raw material gas G1 to the recovery apparatus 1A was 2.60 NL / min.

[0163] The adsorption towers 11a, 11b, and 11c of the first adsorption device 2A and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0164] Each of the adsorption towers 11a, 11b, and 11c was filled with 500 milliliters of activated carbon. The activated carbon used was "ZK-420" manufactured by Osaka Gas Chemicals Co., Ltd. The packing density of each of the adsorption towers 11a, 11b, and 11c was 0.7 g / ml. Each of the adsorption towers 31a, 31b, and 31c was filled with 500 milliliters of zeolite. The zeolite used was "F-9HA" manufactured by Tosoh Corporation. The packing density of each of the adsorption towers 31a, 31b, and 31c was 0.68 g / ml.

[0165] In Example 3, the first concentration step and the second concentration step described in the second embodiment were carried out.

[0166] In the first concentration step (first adsorption device 2A), the adsorption step was carried out for 100 seconds, the pressure release step for 3 seconds, the cleaning step for 97 seconds, the first desorption step for 60 seconds, and the second desorption step for 40 seconds, in that order.

[0167] In the second concentration step (second adsorption device 3), the adsorption step was carried out for 400 seconds, the pressure release step for 3 seconds, the cleaning step for 397 seconds, the first desorption step for 85 seconds, and the second desorption step for 315 seconds, in that order.

[0168] In the first adsorption device 2A, the internal pressure (adsorption pressure) of the adsorption towers 11a, 11b, and 11c performing the adsorption process was 20.0 kPaG, the internal pressure (depressurization pressure) of the adsorption towers 11a, 11b, and 11c performing the depressurization process was 0 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 11a, 11b, and 11c performing the second desorption process was −95.0 kPaG.

[0169] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 21.1 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 10.7 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the second desorption process was −95.1 kPaG.

[0170] Other conditions in Example 3 were the same as those in Example 2.

[0171] The results of Example 3 are shown in Table 4. That is, the carbon dioxide concentration in the first recovered gas recovered in the first adsorption device 2A was 30.0 vol%, and the carbon dioxide recovery rate was 78.2%. In Example 3, the carbon dioxide concentration in the second recovered gas (product gas) finally recovered in the second adsorption device 3 was 98.6 vol%, and the carbon dioxide recovery rate was 56.8%.

[0172] Example 4 In Example 4, carbon dioxide was recovered from the raw material gas G1 using the recovery apparatus 1 shown in FIG.

[0173] The raw material gas G1 in Example 4 contained 14.8 vol % carbon dioxide, 79.0 vol % nitrogen, and 6.2 vol % oxygen. The supply flow rate of the raw material gas G1 to the recovery device 1 was 2.54 NL / min.

[0174] The adsorption towers 11a and 11b of the first adsorption device 2 and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0175] Each of the adsorption towers 11a and 11b was filled with 500 milliliters of activated carbon. Activated carbon "ZK-420" manufactured by Osaka Gas Chemicals Co., Ltd. was used as the activated carbon. The packing density of each of the adsorption towers 11a and 11b was 0.7 g / ml. Each of the adsorption towers 31a, 31b, and 31c was filled with 500 milliliters of zeolite. Zeolite "F-9HA" manufactured by Tosoh Corporation was used as the zeolite. The packing density of each of the adsorption towers 31a, 31b, and 31c was 0.68 g / ml.

[0176] In Example 4, the first concentration step and the second concentration step described in the first embodiment were carried out.

[0177] In the first concentration step (first adsorption device 2), the adsorption step was carried out for 200 seconds, the pressure release step for 3 seconds, and the desorption step for 197 seconds, in that order.

[0178] In the second concentration step (second adsorption device 3), the adsorption step was carried out for 400 seconds, the pressure release step for 3 seconds, the cleaning step for 397 seconds, the first desorption step for 50 seconds, and the second desorption step for 350 seconds, in that order.

[0179] In the first adsorption device 2, the internal pressure (adsorption pressure) of the adsorption towers 11a and 11b performing the adsorption process was 20.2 kPaG, the internal pressure (depressurization pressure) of the adsorption towers 11a and 11b performing the depressurization process was −2.3 kPaG, and the internal pressure (desorption pressure) of each adsorption tower 11a and 11b performing the desorption process was −95.2 kPaG.

[0180] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 19.4 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 7.0 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the desorption process was −95.3 kPaG.

[0181] Other conditions in Example 4 were the same as those in Example 1.

[0182] The results of Example 4 are shown in Table 4. That is, the carbon dioxide concentration contained in the first recovered gas recovered in the first adsorption device 2 was 43.3 vol %, and the carbon dioxide recovery rate was 92.5%. In Example 4, the carbon dioxide concentration contained in the second recovered gas (product gas) finally recovered in the second adsorption device 3 was 98.8 vol %, and the carbon dioxide recovery rate was 78.5%.

[0183] Below, comparative examples 1 to 4 will be described. For ease of explanation, in comparative examples 1 to 4, the same reference numerals are used to designate elements corresponding to those described in the first and second embodiments, and redundant explanations will be omitted.

[0184] Comparative Example 1 In Comparative Example 1, carbon dioxide was recovered from the raw material gas G1 using the recovery apparatus 1A shown in FIG.

[0185] The raw material gas G1 in Comparative Example 1 contained 9.8 vol % carbon dioxide, 81.7 vol % nitrogen, and 8.5 vol % oxygen. The supply flow rate of the raw material gas G1 to the recovery apparatus 1A was 3.10 NL / min.

[0186] The adsorption towers 11a, 11b, and 11c of the first adsorption device 2A and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0187] In Comparative Example 1, each of the adsorption towers 11a, 11b, and 11c of the first adsorption device 2A was filled with 500 milliliters of zeolite. The zeolite used was "F-9HA" manufactured by Tosoh Corporation. The filling density of each of the adsorption towers 11a, 11b, and 11c was 0.68 g / ml.

[0188] In Comparative Example 1, 500 milliliters of activated carbon was packed as an adsorbent into each of the adsorption towers 31a, 31b, and 31c of the second adsorption device 3. The activated carbon used was "ZK-420" activated carbon manufactured by Osaka Gas Chemicals Co., Ltd. The packing density in each of the adsorption towers 31a, 31b, and 31c was 0.7 g / ml.

[0189] In Comparative Example 1, the first concentration step and the second concentration step described in the second embodiment were carried out using a first adsorption device 2A having zeolite as an adsorbent and a second adsorption device 3 having activated carbon as an adsorbent.

[0190] In the first concentration step (first adsorption device 2A), the adsorption step was performed for 200 seconds, the pressure release step for 3 seconds, the cleaning step for 197 seconds, the first desorption step for 20 seconds, and the second desorption step for 180 seconds, in that order. The cycle consisting of the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step was designated the 1A basic cycle, and the first concentration step was performed so that the 1A basic cycles in the adsorption towers 11a, 11b, and 11c were shifted in time, as shown in Table 3 above.

[0191] In the second concentration step (second adsorption device 3), the adsorption step was performed for 200 seconds, the pressure release step for 3 seconds, the cleaning step for 197 seconds, the first desorption step for 40 seconds, and the second desorption step for 160 seconds, in that order. In the second concentration step, a cycle consisting of the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step was defined as a second basic cycle, and the second concentration step was performed so that the second basic cycles in the adsorption towers 31a, 31b, and 31c were shifted in time, as shown in Table 2 above.

[0192] In the first adsorption device 2A, the internal pressure (adsorption pressure) of the adsorption towers 11a, 11b, and 11c performing the adsorption process was 19.5 kPaG, the internal pressure (release pressure) of the adsorption towers 11a, 11b, and 11c performing the depressurization process was 12.1 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 11a, 11b, and 11c performing the second desorption process was −94.8 kPaG.

[0193] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 25.1 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 19.4 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the desorption process was -94.8 kPaG.

[0194] The results of Comparative Example 1 are shown in Table 5. That is, the carbon dioxide concentration contained in the first recovered gas recovered in the first adsorption device 2A was 40.2 vol%, and the carbon dioxide recovery rate was 59.2%. In Comparative Example 1, the carbon dioxide concentration contained in the second recovered gas (product gas) finally recovered in the second adsorption device 3 was 93.8 vol%, and the carbon dioxide recovery rate was 46.8%.

[0195] Comparative Example 2 In Comparative Example 2, carbon dioxide was recovered from the raw material gas G1 using the recovery apparatus 1A shown in FIG.

[0196] The raw material gas G1 in Comparative Example 2 contained 5.1 vol % carbon dioxide, 88.6 vol % nitrogen, and 6.4 vol % oxygen. The supply flow rate of the raw material gas G1 to the recovery apparatus 1A was 3.08 NL / min.

[0197] The adsorption towers 11a, 11b, and 11c of the first adsorption device 2A and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0198] In Comparative Example 2, 500 milliliters of zeolite was packed into each of the adsorption towers 11a, 11b, and 11c of the first adsorption device 2A. The zeolite used was "F-9HA" zeolite manufactured by Tosoh Corporation. The packing density of each of the adsorption towers 11a, 11b, and 11c was 0.68 g / ml.

[0199] In Comparative Example 2, 500 milliliters of activated carbon was packed as an adsorbent into each of the adsorption towers 31a, 31b, and 31c of the second adsorption device 3. The activated carbon used was "ZK-420" activated carbon manufactured by Osaka Gas Chemicals Co., Ltd. The packing density in each of the adsorption towers 31a, 31b, and 31c was 0.7 g / ml.

[0200] In Comparative Example 2, the first concentration step and the second concentration step described in the second embodiment were also carried out using a first adsorption device 2A having zeolite as an adsorbent and a second adsorption device 3 having activated carbon as an adsorbent.

[0201] In the first concentration step (first adsorption device 2A), the adsorption step was carried out for 200 seconds, the pressure release step for 3 seconds, the cleaning step for 197 seconds, the first desorption step for 50 seconds, and the second desorption step for 150 seconds, in that order.

[0202] In the second concentration step (second adsorption device 3), the adsorption step was carried out for 200 seconds, the pressure release step for 3 seconds, the cleaning step for 197 seconds, the first desorption step for 30 seconds, and the second desorption step for 170 seconds, in that order.

[0203] In the first adsorption device 2A, the internal pressure (adsorption pressure) of the adsorption towers 11a, 11b, and 11c performing the adsorption process was 19.9 kPaG, the internal pressure (release pressure) of the adsorption towers 11a, 11b, and 11c performing the depressurization process was 9.3 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 11a, 11b, and 11c performing the second desorption process was −94.6 kPaG.

[0204] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 19.4 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 6.4 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the desorption process was −94.8 kPaG.

[0205] Other conditions in Comparative Example 2 were the same as those in Comparative Example 1.

[0206] The results of Comparative Example 2 are shown in Table 5. The carbon dioxide concentration in the first recovered gas recovered in the first adsorption device 2A was 29.7 vol%, and the carbon dioxide recovery rate was 34.5%. In Comparative Example 2, the carbon dioxide concentration in the second recovered gas (product gas) finally recovered in the second adsorption device 3 was 83.0 vol%, and the carbon dioxide recovery rate was 29.5%.

[0207] Comparative Example 3 In Comparative Example 3, carbon dioxide was recovered from the raw material gas G1 using the recovery apparatus 1A shown in FIG.

[0208] The raw material gas G1 contained 15.2 vol % carbon dioxide, 65.5 vol % nitrogen, and 19.3 vol % oxygen. The supply flow rate of the raw material gas G1 to the recovery unit 1A was 4.11 NL / min.

[0209] The adsorption towers 11a, 11b, and 11c of the first adsorption device 2A and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0210] In Comparative Example 3, each of the adsorption towers 11a, 11b, and 11c of the first adsorption device 2A was filled with 500 milliliters of zeolite. The zeolite used was "F-9HA" manufactured by Tosoh Corporation. The filling density of each of the adsorption towers 11a, 11b, and 11c was 0.68 g / ml.

[0211] In Comparative Example 3, 500 milliliters of activated carbon was packed as an adsorbent into each of the adsorption towers 31a, 31b, and 31c of the second adsorption device 3. The activated carbon used was "ZK-420" activated carbon manufactured by Osaka Gas Chemicals Co., Ltd. The packing density in each of the adsorption towers 31a, 31b, and 31c was 0.7 g / ml.

[0212] In Comparative Example 3, the first concentration step and the second concentration step described in the second embodiment were also carried out using a first adsorption device 2A having zeolite as an adsorbent and a second adsorption device 3 having activated carbon as an adsorbent.

[0213] In the first concentration step (first adsorption device 2A), the adsorption step was carried out for 100 seconds, the pressure release step for 3 seconds, the cleaning step for 97 seconds, the first desorption step for 3 seconds, and the second desorption step for 97 seconds, in that order.

[0214] In the second concentration step (second adsorption device 3), the adsorption step was carried out for 200 seconds, the pressure release step for 3 seconds, the cleaning step for 197 seconds, the first desorption step for 40 seconds, and the second desorption step for 160 seconds, in that order.

[0215] In the first adsorption device 2A, the internal pressure (adsorption pressure) of the adsorption towers 11a, 11b, and 11c performing the adsorption process was 20.0 kPaG, the internal pressure (release pressure) of the adsorption towers 11a, 11b, and 11c performing the depressurization process was 15.7 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 11a, 11b, and 11c performing the second desorption process was −95.2 kPaG.

[0216] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 25.1 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 19.4 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the desorption process was -94.8 kPaG.

[0217] Other conditions in Comparative Example 3 were the same as those in Comparative Example 1.

[0218] The results of Comparative Example 3 are shown in Table 5. That is, the carbon dioxide concentration contained in the first recovered gas recovered in the first adsorption device 2A was 48.1 vol%, and the carbon dioxide recovery rate was 85.6%. In Comparative Example 3, the carbon dioxide concentration contained in the second recovered gas (product gas) finally recovered in the second adsorption device 3 was 93.8 vol%, and the carbon dioxide recovery rate was 67.7%.

[0219] Comparative Example 4 In Comparative Example 4, carbon dioxide was recovered from the raw material gas G1 using the recovery apparatus 1A shown in FIG.

[0220] The raw material gas G1 contained 9.8 vol % carbon dioxide, 81.7 vol % nitrogen, and 8.5 vol % oxygen. The supply flow rate of the raw material gas G1 to the recovery apparatus 1A was 3.10 NL / min.

[0221] The adsorption towers 11a, 11b, and 11c of the first adsorption device 2A and the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 each had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0222] Each of the adsorption towers 11a, 11b, and 11c of the first adsorption device 2A and each of the adsorption towers 31a, 31b, and 31c of the second adsorption device 3 was filled with 500 milliliters of zeolite. Zeolite "F-9HA" manufactured by Tosoh Corporation was used as the zeolite. The filling density in each of the adsorption towers 11a, 11b, 11c, 31a, 31b, and 31c was 0.68 g / ml.

[0223] In Comparative Example 4, the first concentration step and the second concentration step described in the second embodiment were carried out using a first adsorption device 2A having zeolite as an adsorbent and a second adsorption device 3 having zeolite as an adsorbent.

[0224] In the first concentration step (first adsorption device 2A), the adsorption step was carried out for 200 seconds, the pressure release step for 3 seconds, the cleaning step for 197 seconds, the first desorption step for 20 seconds, and the second desorption step for 180 seconds, in that order.

[0225] In the second concentration step (second adsorption device 3), the adsorption step was carried out for 400 seconds, the pressure release step for 3 seconds, the cleaning step for 397 seconds, the first desorption step for 50 seconds, and the second desorption step for 350 seconds, in that order.

[0226] In the first adsorption device 2A, the internal pressure (adsorption pressure) of the adsorption towers 11a, 11b, and 11c performing the adsorption process was 19.5 kPaG, the internal pressure (depressurization pressure) of the adsorption towers 11a, 11b, and 11c performing the depressurization process was 7.0 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 11a, 11b, and 11c performing the second desorption process was −94.8 kPaG.

[0227] In the second adsorption device 3, the internal pressure (adsorption pressure) of the adsorption towers 31a, 31b, and 31c performing the adsorption process was 19.4 kPaG, the internal pressure (release pressure) of the adsorption towers 31a, 31b, and 31c performing the depressurization process was 7.0 kPaG, and the internal pressure (desorption pressure) of the adsorption towers 31a, 31b, and 31c performing the second desorption process was −95.3 kPaG.

[0228] Other conditions in Comparative Example 4 were the same as those in Comparative Example 1.

[0229] The results of Comparative Example 4 are shown in Table 5. That is, the carbon dioxide concentration in the first recovered gas recovered in the first adsorption device 2A was 40.2 vol%, and the carbon dioxide recovery rate was 59.2%. In Comparative Example 4, the carbon dioxide concentration in the second recovered gas (product gas) finally recovered in the second adsorption device 3 was 98.8 vol%, and the carbon dioxide recovery rate was 50.2%.

[0230]

[0231] As shown in Tables 4 and 5, when concentrating carbon dioxide in two stages, it can be confirmed that in Examples 1 to 4, in which activated carbon was used as the adsorbent in the first stage and zeolite was used in the second stage, high-purity carbon dioxide was obtained at a higher recovery rate than in Comparative Examples 1 to 4.

[0232] For example, it can be confirmed that in Examples 1 to 4, in which activated carbon was used as the adsorbent in the first stage, a higher carbon dioxide recovery rate was achieved in the first stage than in Comparative Examples 1 to 4. In particular, in Example 1 and Comparative Examples 1 and 4, the carbon dioxide concentration (CO ２Although the adsorption towers (concentration) were almost the same, Example 1 achieved a higher carbon dioxide recovery rate in the first stage than Comparative Examples 1 and 3. In Comparative Examples 1 and 3, the second-stage adsorption device had three adsorption towers, as described in the second embodiment. On the other hand, in Example 1, the first-stage adsorption device had two adsorption towers, as described in the first embodiment. Despite the smaller number of adsorption towers in the first stage, Comparative Examples 1 and 4 achieved a higher carbon dioxide recovery rate in the first stage than Comparative Examples 1 and 3. Therefore, it can be seen that using activated carbon as the adsorbent in the first stage is effective in improving the carbon dioxide recovery rate in the first stage.

[0233] Although various embodiments and examples of the present invention have been described above, the present invention is not limited to the illustrated embodiments and examples, and is intended to include all modifications within the scope of the claims, as well as the meaning and scope equivalent to the claims.

[0234] For example, just as the second recovery gas is returned to the adsorption tower during the cleaning step in the second pressure swing adsorption apparatus, the second recovery gas recovered in the second pressure swing adsorption apparatus may be returned to the first pressure swing adsorption apparatus.

[0235] The cleaning gas in the cleaning step is not limited to the first recovery gas or the second recovery gas. The number of first adsorption towers included in the first pressure swing adsorption unit may be four or more. The number of second adsorption towers included in the second pressure swing adsorption unit may be two, four or more.

[0236] 1, 1A... recovery device, 2, 2A... first adsorption device (first pressure swing adsorption device), 3... second adsorption device (second pressure swing adsorption device), 11a, 11b, 11c... adsorption tower (first adsorption tower), 12... introduction flow path (first line), 15... recovered gas flow path (second line), 26... cleaning gas flow path (first return line), 31a, 31b, 31c... adsorption tower (second adsorption tower), 32... introduction flow path (second line), 36... cleaning gas flow path (second return line).

Claims

1. A recovery method comprising: a first concentration step of introducing a feed gas containing carbon dioxide into a first pressure swing adsorption device and recovering a first gas in which the carbon dioxide is concentrated; and a second concentration step of introducing the first gas into a second pressure swing adsorption device and recovering a second gas in which the carbon dioxide is concentrated, wherein the first pressure swing adsorption device has a first adsorption tower into which the feed gas is introduced and which contains activated carbon, and the second pressure swing adsorption device has a second adsorption tower into which the first gas is introduced and which contains zeolite, wherein in the first concentration step, the carbon dioxide contained in the feed gas introduced into the first adsorption tower is adsorbed by the activated carbon and then desorbed to recover the first gas, and wherein in the second concentration step, the carbon dioxide contained in the first gas introduced into the second adsorption tower is adsorbed by the zeolite and then desorbed to recover the second gas.

2. The method according to claim 1, wherein the carbon dioxide concentration of the feed gas introduced into the first adsorption tower is 20 vol % or less.

3. The method according to claim 1, wherein the zeolite is a zeolite having a three-dimensional framework.

4. The method according to claim 3, wherein the zeolite is a FAU type zeolite.

5. The method according to any one of claims 1 to 4, wherein in the first concentration step, the first gas obtained at an initial stage in the step of desorbing the carbon dioxide from the activated carbon is returned to the first pressure swing adsorption device.

6. The method according to any one of claims 1 to 4, wherein in the second concentration step, the second gas obtained at an initial stage in the step of desorbing the carbon dioxide from the zeolite is returned to the second pressure swing adsorption device.

7. The recovery method according to any one of claims 1 to 4, wherein the first pressure swing adsorption apparatus has a plurality of the first adsorption towers, and the second pressure swing adsorption apparatus has a plurality of the second adsorption towers.

8. A recovery system comprising: a first pressure swing adsorption apparatus having a first adsorption tower containing activated carbon, the first pressure swing adsorption apparatus concentrating carbon dioxide contained in a raw gas introduced into the first adsorption tower by the activated carbon and recovering a first gas containing concentrated carbon dioxide; a first line for introducing a raw gas containing carbon dioxide into the first adsorption tower; a second pressure swing adsorption apparatus having a second adsorption tower containing zeolite, the second pressure swing adsorption apparatus concentrating carbon dioxide contained in the first gas introduced into the second adsorption tower by the zeolite and recovering a second gas containing concentrated carbon dioxide; and a second line for introducing the first gas recovered in the first pressure swing adsorption apparatus into the second adsorption tower.

9. The recovery system of claim 8, further comprising a first return line for returning said first gas recovered from said first pressure swing adsorption system to said first pressure swing adsorption system.

10. The recovery system according to claim 8 or 9, further comprising a second return line for returning the second gas recovered from the second pressure swing adsorption system to the second pressure swing adsorption system.

11. The recovery system according to claim 8 or 9, wherein the first pressure swing adsorption system has a plurality of the first adsorption towers, and the second pressure swing adsorption system has a plurality of the second adsorption towers.

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