Carbon dioxide recovery method and recovery device

Abstract

To provide a recovery method and a recovery device capable of recovering carbon dioxide at high purity and improving recovery efficiency.SOLUTION: A recovery method according to one embodiment includes: a concentration step of introducing a raw gas to at least one adsorption tower in which an adsorbent that adsorbs carbon dioxide is accommodated, and recovering a concentrated gas in which carbon dioxide contained in the raw gas is concentrated by a pressure swing adsorption method, the concentration step including an adsorption step of making the adsorbent adsorb carbon dioxide contained in the raw gas and a desorption step of desorbing carbon dioxide from the adsorbent and recovering the concentrated gas; a storage step of storing a portion of the concentrated gas recovered in the concentration step in a gas storage section; and a cleaning step of returning the concentrated gas stored in the gas storage section to an adsorption tower that has undergone the adsorption step in the at least one adsorption tower, and cleaning the adsorption tower to which the concentrated gas has been returned. The cleaning step is performed between the adsorption step and the desorption step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Carbon dioxide is seen as a major cause of global warming, and there has been a growing movement worldwide to curb emissions. Various research efforts are being actively pursued to enable the capture and storage of carbon dioxide from exhaust gases without releasing it into the atmosphere. For example, 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 these methods have 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] A specific method for recovering carbon dioxide by pressure swing adsorption is known in which carbon dioxide is physically adsorbed onto an adsorbent, and the pressure is reduced using a vacuum pump to desorb the carbon dioxide adsorbed onto the adsorbent, thereby concentrating and recovering the carbon dioxide (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Unexamined Patent Publication No. 1-172204 Summary of the Invention [Problem to be solved by the invention]

[0006] In the recovery of carbon dioxide by pressure swing adsorption, there is still room for improvement in terms of the carbon dioxide concentration in the recovered gas and the recovery rate.

[0007] Therefore, an object of the present disclosure is to provide a recovery method and recovery device that can recover carbon dioxide with high purity and achieve an improved recovery rate. [Means for solving the problem]

[0008] One aspect of the present disclosure provides the recovery methods described in the following paragraphs. [1] A concentration process for introducing a raw material gas into at least one adsorption tower containing an adsorbent that adsorbs carbon dioxide, and recovering a concentrated gas in which the carbon dioxide contained in the raw material gas is concentrated by a pressure swing adsorption method, the concentration process including an adsorption process for adsorbing the carbon dioxide contained in the raw material gas onto the adsorbent, and a desorption process for desorbing the carbon dioxide from the adsorbent and recovering the concentrated gas; a storage process for storing a portion of the concentrated gas recovered in the concentration process in a gas storage section; and a cleaning process for returning the concentrated gas stored in the gas storage section to one of the at least one adsorption towers that has undergone the adsorption process, and cleaning the adsorption tower to which the concentrated gas has been returned, wherein the cleaning process is carried out between the adsorption process and the desorption process.

[0009] [2] The recovery method according to [1], wherein V1 / V2, which is the ratio of the spatial volume V1 of the gas storage section to the total volume V2 of carbon dioxide in the raw gas introduced into the adsorption tower to concentrate carbon dioxide once in the concentration step, is 0.1 or more.

[0010] [3] The recovery method according to [1] or [2], wherein the carbon dioxide concentration of the raw material gas is 20 vol% or less.

[0011] Another aspect of the present disclosure provides a recovery device as described in the following paragraphs.

[0012] [4] A recovery system having at least one adsorption tower containing an adsorbent that adsorbs carbon dioxide, the recovery system comprising: a concentration section for obtaining a concentrated gas in which carbon dioxide in a raw gas introduced into the at least one adsorption tower is concentrated; a first line for introducing the raw gas into the at least one adsorption tower; a gas storage section for storing the concentrated gas obtained in the concentration section; and a second line for returning the concentrated gas in the gas storage section to the concentration section as a cleaning gas for cleaning the at least one adsorption tower of the concentration section.

[0013] [5] The recovery device described in [4], wherein V1 / V2, which is the ratio of the spatial volume V1 of the gas storage section to the total volume V2 of carbon dioxide in the raw gas introduced into the adsorption tower to perform a single concentration of carbon dioxide in the adsorption tower, is 0.1 or more.

[0014] [6] The recovery device described in [4] or [5], wherein the gas storage section is cylindrical in shape.

[0015] [7] A recovery device described in any of [4] to [6], comprising: a recovery line through which the concentrated gas recovered from the concentration section flows and to which the second line is connected; and a control mechanism for controlling the flow of the concentrated gas flowing in the recovery line into the second line, wherein the gas storage section is located on the second line.

[0016] [8] The recovery apparatus according to any one of [4] to [7], wherein the enrichment section has a plurality of the adsorption towers. [Effects of the Invention]

[0017] According to the recovery method and recovery device of the present disclosure, it is possible to recover carbon dioxide with high purity and to achieve an improved recovery rate. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an example of a recovery device according to the first embodiment. [Figure 2]FIG. 2 is a schematic diagram showing an example of the configuration of a recovery device according to the second embodiment. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of a comparative recovery device. [Figure 4] FIG. 4 is a table showing the results of Examples 1 and 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The same elements are designated by the same reference numerals, and duplicate explanations will be omitted. The dimensional proportions in the drawings do not necessarily correspond to those in the description.

[0020] (First embodiment) Fig. 1 is a schematic diagram showing the configuration of an example of a carbon dioxide recovery apparatus according to a first embodiment. The pressure swing adsorption apparatus 1 shown in Fig. 1 is an apparatus used to separate and recover carbon dioxide (CO2) from a feed gas G101 containing carbon dioxide. Therefore, the pressure swing adsorption apparatus 1 is also a recovery apparatus that recovers carbon dioxide. Hereinafter, the pressure swing adsorption apparatus 1 will be referred to as the "adsorption apparatus 1."

[0021] The raw material gas G101 is a mixed gas of carbon dioxide and impurity gases such as nitrogen and oxygen. Examples of the raw material gas G101 include combustion exhaust gas. The raw material gas G101 is supplied from a raw material gas supply source (not shown) such as a boiler in a chemical plant or the like. An example of the carbon dioxide concentration (an example of a low concentration) contained in the raw material gas G101 supplied from the raw material gas supply source is 20 vol% or less, preferably 5.0 vol% or more and 15.0 vol% or less, and more preferably 7 vol% or more and 12 vol% or less. The raw material gas G101 supplied from the raw material gas supply source may be a compressed gas at atmospheric pressure or higher. If the raw material gas G101 supplied from the raw material gas supply source is not a compressed gas, it may be compressed using a blower or the like.

[0022] [Adsorption device] The adsorption apparatus 1 has an enrichment section 106 having at least one adsorption tower. In this embodiment, an embodiment will be described in which the enrichment section 106 has three adsorption towers 106a, 106b, and 106c.

[0023] The adsorption towers 106a, 106b, and 106c are towers for concentrating the carbon dioxide in the raw material gas G101 by adsorbing the carbon dioxide contained in the raw material gas G101 onto an adsorbent using a pressure swing adsorption (PSA) method and then desorbing the carbon dioxide.

[0024] In this embodiment, the gas extracted from the adsorption tower and containing concentrated carbon dioxide is referred to as the “recovered gas.” The gas discharged from the adsorption tower and containing gas components of the raw material gas G101 other than the carbon dioxide adsorbed by the adsorbent is referred to as the “off-gas” (exhaust gas).

[0025] The adsorbent stored in the adsorption towers 106a, 106b, and 106c is not particularly limited as long as it can concentrate carbon dioxide to a high purity. Examples of the adsorbent include zeolite and activated carbon. From the viewpoint of adsorption capacity, the adsorbent is preferably zeolite.

[0026] The zeolite is, for example, a zeolite in which at least a portion of the cation species has been exchanged with Na ions, and from the viewpoint of the specific surface area of ​​the adsorbent, a zeolite having a three-dimensional skeleton is preferred. Examples of zeolites having a three-dimensional skeleton include FAU-type, LTA-type, MFI-type, AEI-type, CHA-type, EMT-type, ERI-type, GIS-type, MEL-type, MSE-type, and RHO-type zeolites, with FAU-type zeolites being more preferred.

[0027] From the viewpoint of pressure loss in the adsorption towers during pressure swing adsorption, the zeolite stored in the adsorption towers 106a, 106b, and 106c preferably has a particle diameter of 1.0 mm or more and 2.0 mm or less, and the packing density of the zeolite in each adsorption tower is preferably 0.5 kg / L or more and 1.0 kg / L or less.

[0028] Each of the adsorption towers 106a, 106b, and 106c is connected to an introduction flow path (first line) 101, an off-gas flow path 108, a recovered gas flow path (recovery line) 117, and a cleaning gas flow path (second line) 124. A depressurization gas flow path 113 may be connected to each of the adsorption towers 106a, 106b, and 106c. Each flow path is configured using gas piping. In this embodiment, a configuration in which the depressurization gas flow path 113 is also connected to each of the adsorption towers 106a, 106b, and 106c will be described.

[0029] The inlet flow path 101 is a gas flow path for introducing the raw material gas G101 from a raw material gas supply source into the adsorption towers 106a, 106b, and 106c. The inlet flow path 101 may be provided with a buffer tank 102 for storing the raw material gas G101 from the raw material gas supply source. The downstream end of the inlet flow path 101 (the portion closer to the adsorption towers 106a, 106b, and 106c) branches toward the adsorption towers 106a, 106b, and 106c and is connected to gas passages at the upstream ends of the adsorption towers 106a, 106b, and 106c. The upstream ends of the adsorption towers 106a, 106b, and 106c are upstream ends in the flow direction of the raw material gas G101 introduced from the inlet flow path 101 into the adsorption towers 106a, 106b, and 106c.

[0030] On-off valves 105a, 105b, and 105c corresponding to the adsorption towers 106a, 106b, and 106c are provided at the downstream end (near the adsorption towers 106a, 106b, and 106c) of the introduction flow path 101. By individually opening and closing the on-off valves 105a, 105b, and 105c, the source gas G101 can be introduced into each of the adsorption towers 106a, 106b, and 106c.

[0031] A blower 103 may be provided in the inlet flow path 101. The blower 103 is disposed upstream of the on-off valves 105a, 105b, and 105c. In a configuration in which the buffer tank 102 is provided in the inlet flow path 101 as shown in FIG. 1, the blower 103 is disposed between the buffer tank 102 and the on-off valves 105a, 105b, and 105c. The blower 103 may be used to compress the source gas G101 when the source gas G101 is not a compressed gas.

[0032] The off-gas flow path 108 is a gas flow path for discharging gas (off-gas) to be discharged from the adsorption towers 106a, 106b, and 106c to the outside (normal pressure space) of the adsorption apparatus 1. The upstream side of the off-gas flow path 108 (the portion closer to the adsorption towers 106a, 106b, and 106c) branches toward the adsorption towers 106a, 106b, and 106c and is connected to the adsorption towers 106a, 106b, and 106c. Specifically, the off-gas flow path 108 is connected to gas passage ports at the downstream ends of the adsorption towers 106a, 106b, and 106c. The downstream ends of the adsorption towers 106a, 106b, and 106c are downstream ends in the flow direction of the source gas G101 introduced into the adsorption towers 106a, 106b, and 106c from the introduction flow path 101.

[0033] On-off valves 107a, 107b, and 107c corresponding to the adsorption towers 106a, 106b, and 106c are provided on the upstream end side of the off-gas passage 108. The on-off valves 107a, 107b, and 107c individually open and close the connections between the adsorption towers 106a, 106b, and 106c and the off-gas passage 108, respectively, so that the off-gas G102 can be discharged from each of the adsorption towers 106a, 106b, and 106c.

[0034] The downstream end of the off-gas passage 108 (the end opposite the adsorption towers 106a, 106b, and 106c) is an outlet for the off-gas G102 and communicates with a normal pressure space under atmospheric pressure. The off-gas G102 discharged through the off-gas passage 108 is discharged to the outside of the adsorption apparatus 1. A pressure control valve 109 for adjusting the back pressure is provided on the downstream end side of the off-gas passage 108.

[0035] The pressure release gas flow path 113 is a gas flow path for discharging gas (hereinafter referred to as "pressure release gas G103") discharged from the adsorption towers 106a, 106b, and 106c to the outside of the adsorption apparatus 1 when the pressure in the adsorption towers 106a, 106b, and 106c is released in a pressure release step described below. The pressure release gas G103 is also an off-gas because it is a gas discharged from the adsorption towers 106a, 106b, and 106c. The upstream end of the pressure release gas flow path 113 (the portion closer to the adsorption towers 106a, 106b, and 106c) branches toward the adsorption towers 106a, 106b, and 106c and is connected to the gas passages at the downstream ends of the adsorption towers 106a, 106b, and 106c. The downstream end of the pressure release gas flow path 113 is an outlet for the pressure release gas G103 and communicates with a normal-pressure space under atmospheric pressure.

[0036] The pressure release gas flow path 113 is provided with on-off valves 112a, 112b, and 112c corresponding to the adsorption towers 106a, 106b, and 106c. The on-off valves 112a, 112b, and 112c individually open and close the pressure release gas flow path 113 and each of the adsorption towers 106a, 106b, and 106c, allowing the pressure release gas G103 to be discharged from each of the adsorption towers 106a, 106b, and 106c. A pressure regulation valve 114 for regulating back pressure is provided at the downstream end of the pressure release gas flow path 113.

[0037] The recovered gas flow path 117 is a gas flow path for flowing the recovered gas extracted from the adsorption towers 106a, 106b, and 106c to a buffer tank 125 via a vacuum pump 118. The upstream end of the recovered gas flow path 117 (the portion closer to the adsorption towers 106a, 106b, and 106c) branches toward the adsorption towers 106a, 106b, and 106c and is connected to the adsorption towers 106a, 106b, and 106c. Specifically, the recovered gas flow path 117 is connected to gas passages at the upstream ends of the adsorption towers 106a, 106b, and 106c. The downstream end of the recovered gas flow path 117 is connected to a buffer tank 125 via a vacuum pump 118. The recovered gas that flows into and is stored in the buffer tank 125 is extracted from the buffer tank 125 through a gas transport flow path 119 and used as the product gas G104.

[0038] For example, the product gas G104 is supplied to a downstream process such as a liquefaction device. The use of the product gas G104 is not limited. In the example shown in FIG. 1, the recovered gas is temporarily stored in the buffer tank 125, but, for example, the buffer tank 125 does not have to be provided. In this case, the recovered gas flowing through the recovered gas flow path 117 can be directly supplied to the downstream process as the product gas G104.

[0039] On-off valves 116a, 116b, and 116c corresponding to the adsorption towers 106a, 106b, and 106c are provided at the upstream end of the recovered gas flow path 117. The on-off valves 116a, 116b, and 116c individually open and close the connection between each of the adsorption towers 106a, 106b, and 106c and the recovered gas flow path 117, allowing the recovered gas to flow from each of the adsorption towers 106a, 106b, and 106c to the recovered gas flow path 117.

[0040] An on-off valve 120b is provided in the collected gas flow path 117 between the vacuum pump 118 and the buffer tank 125. The inflow of the collected gas into the buffer tank 125 can be controlled by the on-off valve 120b.

[0041] The cleaning gas flow path 124 is a gas flow path for flowing cleaning gas into the adsorption towers 106a, 106b, and 106c in the cleaning step described below. The downstream end of the cleaning gas flow path 124 (the portion closer to the adsorption towers 106a, 106b, and 106c) branches toward the adsorption towers 106a, 106b, and 106c and is connected to gas passages at the upstream ends of the adsorption towers 106a, 106b, and 106c. The upstream end of the cleaning gas flow path 124 is connected to the recovered gas flow path 117. Specifically, in the configuration illustrated in FIG. 1, the connection point X between the upstream end of the cleaning gas flow path 124 and the recovered gas flow path 117 is located between the vacuum pump 118 and the on-off valve 120b in the recovered gas flow path 117.

[0042] An on-off valve 120a is provided in the cleaning gas flow path 124 near the connection part X. As shown in FIG. 1, the on-off valve 120a is provided between the connection part X of the cleaning gas flow path 124 and the recovered gas flow path 117 and on-off valves 110a, 110b, and 110c, which will be described later. The on-off valve 120a controls the flow of the recovered gas flowing in the recovered gas flow path 117 into the cleaning gas flow path 124. The on-off valve 120a is at least a part of a control mechanism (first control mechanism) 120 that controls the inflow of the recovered gas flowing in the recovered gas flow path 117 into the cleaning gas flow path 124. By opening the on-off valve 120a, the recovered gas flowing in the cleaning gas flow path 124 functions as a cleaning gas.

[0043] On-off valves 110a, 110b, and 110c corresponding to the adsorption towers 106a, 106b, and 106c are provided on the downstream end side of the cleaning gas flow path 124. The on-off valves 110a, 110b, and 110c individually open and close the communication between each of the adsorption towers 106a, 106b, and 106c and the cleaning gas flow path 124, thereby enabling the cleaning gas to be supplied to each of the adsorption towers 106a, 106b, and 106c.

[0044] A gas storage section 127 for temporarily storing the cleaning gas is provided between the on-off valves 110a, 110b, 110c and the on-off valve 120a in the cleaning gas flow path 124. A blower 126 for causing the cleaning gas to flow toward the on-off valves 110a, 110b, 110c may be provided in the cleaning gas flow path 124 between the gas storage section 127 and the on-off valves 110a, 110b, 110c.

[0045] In this embodiment, the on-off valve 120b is closed when the collecting gas is flowed through the cleaning gas flow path 124, and is open when the collecting gas is flowed to the buffer tank 125 without flowing through the cleaning gas flow path 124. Therefore, the on-off valve 120b may also be a part of the control mechanism 120.

[0046] The recovered gas that has flowed into the recovered gas flow path 117 is stored as a cleaning gas in the gas storage section 127. The cleaning gas stored in the gas storage section 127 flows into each of the adsorption towers 106a, 106b, and 106c via the cleaning gas flow path 124. At this time, the cleaning gas may be sent by a blower 126 toward the adsorption towers 106a, 106b, and 106c.

[0047] The ratio (V1 / V2) of the spatial volume V1 of the gas storage section 127 to the total volume V2 of carbon dioxide introduced into any one of the adsorption towers 106a, 106b, and 106c at one time in the adsorption step described below is preferably 0.1 or more, more preferably 0.1 or more and 10 or less, and even more preferably 0.2 or more and 9 or less. The total volume V2 is the total volume of carbon dioxide introduced into the adsorption tower among the adsorption towers 106a, 106b, and 106c in which the adsorption step is performed, during one cycle of the adsorption step.

[0048] Here, the spatial volume V1 [L] of the gas storage portion 127 can be considered as a volume capable of storing an ideal gas at atmospheric pressure, and can be simply calculated by the following formula (1). V1=V×(273 / T) (1) In formula (1), V is the volume (L) of gas storage section 127, and T is the absolute temperature (K) of the gas. "273" in formula (1) represents 0°C as an absolute temperature, and the unit is K (Kelvin).

[0049] The total volume V2 of carbon dioxide introduced into any one of the adsorption towers 106a, 106b, and 106c at one time can be simply calculated using the following formula (2). V2=L×t×C (2) In equation (2), L is the flow rate of the raw gas G101 (NL / min), t is the cycle time of the adsorption step (min), and C is the carbon dioxide ratio of the raw gas G101. The "NL" in the flow rate unit stands for normal liters.

[0050] There are no limitations on the gas storage section 127 as long as it can store the collected gas. Examples of the gas storage section 127 include a pipe with a diameter at least twice that of the collected gas flow path 117, a buffer tank, etc. The shape of the gas storage section 127 may be, for example, cylindrical or spherical. From the viewpoint of ease of processing, the shape of the gas storage section 127 is preferably cylindrical.

[0051] An example of a method for recovering carbon dioxide using the adsorption apparatus 1 will be described. The carbon dioxide recovery method is a method for recovering carbon dioxide from a raw material gas G101 by pressure swing adsorption. In this example of the carbon dioxide recovery method, the carbon dioxide contained in the raw material gas G101 is concentrated, and the concentrated carbon dioxide (recovered gas) is recovered.

[0052] The carbon dioxide recovery method includes an adsorption step and a desorption step. In the carbon dioxide recovery method, the carbon dioxide contained in the raw material gas G101 is adsorbed onto an adsorbent in the adsorption step, and then the carbon dioxide is desorbed from the adsorbent. This results in concentrated carbon dioxide. Therefore, the adsorption step and the desorption step correspond to a carbon dioxide concentration step.

[0053] The carbon dioxide recovery method of this embodiment further includes a washing step between the adsorption step and the desorption step. A pressure release step may be carried out between the adsorption step and the washing step. In order to obtain high-purity carbon dioxide, a first desorption step and a second desorption step may be carried out as the desorption step.

[0054] In the following, a description will be given of an embodiment in which the pressure release step is performed and the first and second desorption steps are performed in the desorption step. Since the steps performed in the adsorption towers 106a, 106b, and 106c are the same, only the steps performed in the adsorption tower 106a will be described.

[0055] [Adsorption process] In the adsorption step, the on-off valves 105a and 107a are opened to allow the raw material gas G101 to flow into the adsorption tower 106a, while the carbon dioxide contained in the raw material gas G101 is adsorbed by the adsorbent stored in the adsorption tower 106a. During this process, the on-off valves 112a, 110a, and 116a are closed, and the pressure in the adsorption tower 106a is adjusted by the pressure control valve 109 to an adsorption pressure that appropriately exceeds atmospheric pressure and is suitable for adsorption of carbon dioxide into the adsorbent. The adsorption pressure is, for example, 0 kPaG or more and 100 kPaG or less. In the adsorption step, the portion of the raw material gas G101 that is not adsorbed by the adsorbent is discharged as off-gas G102 from the off-gas flow path 108 to the outside of the adsorption device 1. The "G" in the pressure unit "kPaG" indicates that the pressure is a gauge pressure.

[0056] [Pressure release process] The pressure release step is performed after the adsorption step. In the pressure release step, the on-off valves 105a and 107a are closed, and the on-off valve 112a is opened to release the pressure in the adsorption tower 106a. At this time, the pressure in the adsorption tower 106a is adjusted by the pressure control valve 114 to a pressure suitable for pressure release that is lower than the pressure in the adsorption step. An example of the pressure in the adsorption tower 106a 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 source gas G101 that is not adsorbed by the adsorbent is discharged as pressure release gas G103 from the pressure release gas flow path 113 to the outside of the adsorption apparatus 1.

[0057] [Cleaning process] The cleaning step is performed after the pressure release step. In the cleaning step, the on-off valve 110a is opened and the blower 126 is operated to cause the cleaning gas to flow into the adsorption tower 106a through the cleaning gas flow path 124. The cleaning gas that has flowed into the adsorption tower 106a is discharged to the outside of the adsorption apparatus 1 through the pressure release gas flow path 113.

[0058] In the cleaning step, the cleaning gas flows through the adsorption tower 106a, and gas components other than carbon dioxide that have adhered to the walls of the adsorption tower 106a are carried along with the cleaning gas and discharged to the outside of the adsorption apparatus 1. That is, the cleaning gas causes the gas components other than carbon dioxide that remained in the adsorption tower 106a to be discharged from the adsorption tower 106a.

[0059] The cleaning gas in the first embodiment is the recovered gas obtained by performing the first desorption process in one of the adsorption towers 106a, 106b, and 106c other than the adsorption tower undergoing the cleaning process, and is also the recovered gas returned via the cleaning gas flow path 124 to the adsorption tower undergoing the cleaning process. For example, when the cleaning process is performed in the adsorption tower 106a, the recovered gas from the adsorption tower 106b or 106c is returned to the adsorption tower 106a and used as the cleaning gas for cleaning the adsorption tower 106a. In this way, in the cleaning process, the recovered gas is returned to the adsorption tower undergoing the cleaning process, and therefore the cleaning process corresponds to the recovered gas return process.

[0060] The cleaning gas is the recovered gas obtained by carrying out the first desorption step, and therefore is a gas containing concentrated carbon dioxide.

[0061] In the cleaning step, the on-off valve 120b is closed and the on-off valve 120a is open. As a result, the recovered gas obtained by carrying out the first desorption step flows from the recovered gas flow path 117 to the cleaning gas flow path 124. In this embodiment, the cleaning gas flow path 124 is provided with a gas storage section 127, so the recovered gas is stored in the gas storage section 127 and then returned to the adsorption tower where the cleaning step is carried out. That is, in this embodiment, the recovered gas stored in the gas storage section 127 is used as the cleaning gas.

[0062] Note that even after the adsorption tower performing the first desorption step has transitioned to the second desorption step, the adsorption tower that had been performing the cleaning step may continue the cleaning step. As will be described later, in the second desorption step, the on-off valve 120a is closed while the on-off valve 120b is open, and in this case, the cleaning gas remaining in the gas storage section 127 flows into the cleaning step.

[0063] As described above, when the recovered gas is used as a cleaning gas, the carbon dioxide contained in the recovered gas is re-adsorbed by the adsorbent.

[0064] [First desorption process] The first desorption step is performed after the cleaning step. The first desorption step is an initial step in the desorption step. In the first desorption step, the on-off valves 110a and 112a are closed, while the on-off valve 116a is opened. In this state, the vacuum pump 118 is operated to reduce the pressure in the adsorption tower 106a, and the gas in the adsorption tower 106a is caused to flow into the recovered gas flow path 117. In the first desorption step, the pressure in the adsorption tower 106a is reduced as described above, causing carbon dioxide to be desorbed from the adsorbent. As a result, the gas (recovered gas) flowing into the recovered gas flow path 117 contains carbon dioxide.

[0065] In the first desorption step, the on-off valve 120b is closed, while the on-off valve 120a is open. As a result, the recovered gas (initial recovered gas) that flowed into the recovered gas flow path 117 in the first desorption step flows into the cleaning gas flow path 124, as described in the cleaning step. The recovered gas that flows from the recovered gas flow path 117 to the cleaning gas flow path 124 is stored in the gas storage section 127. The recovered gas stored in this manner in the gas storage section 127 is used as the cleaning gas, as described above. Since the recovered gas is stored in the gas storage section 127 in the first desorption step, at least a part of the first desorption step is a storage step in which the recovered gas is stored in the gas storage section 127.

[0066] The time for performing the first desorption step may be any time that allows gas components other than carbon dioxide adhering to the wall surfaces of the adsorption tower 106a to be sufficiently discharged, and that the carbon dioxide adsorbed on the adsorbent is not desorbed more than necessary. The time for performing the first desorption step is, for example, 1% to 75% of the time for performing the desorption step (a step including the first desorption step and the second desorption step). The time for performing the first desorption step may be, for example, 4 seconds to 300 seconds, assuming that the desorption time is 400 seconds.

[0067] [Second desorption process] The second desorption step is a step in the desorption step that occurs a certain time after the start of the first desorption step. In the second desorption step, the on-off valve 120a is closed, while the on-off valve 120b is opened. As a result, the recovered gas that flows from the adsorption tower 106a to the recovered gas flow path 117 flows into the buffer tank 125 and is stored there. The recovered gas stored in the buffer tank 125 is appropriately extracted as the product gas G104. The time for which the second desorption step is performed is, for example, 25% or more and 99% or less of the time for which the desorption step is performed. For example, if the desorption time is 400 seconds, the time for which the second desorption step is performed may be 100 seconds or more and 396 seconds or less.

[0068] The second desorption step is a step that occurs after the first desorption step has been performed for a certain period of time, and therefore the pressure inside the adsorption tower 106a is lower than when the first desorption step was started. Therefore, after the transition from the first desorption step to the second desorption step, more carbon dioxide is desorbed from the adsorbent. Therefore, in the second desorption step, the gas flowing from the adsorption tower 106a to the recovered gas flow path 117 is a recovered gas containing concentrated carbon dioxide. Furthermore, since the impurities remaining in the adsorption tower 106a in the first desorption step are also discharged, a highly pure recovered gas can be obtained in the second desorption step.

[0069] The recovered gas recovered in the second desorption step is the product gas G104. In other words, in the second desorption step, carbon dioxide is desorbed from the adsorbent so as to obtain the product gas G104. Therefore, in this embodiment, the term "desorption pressure" in the following description refers to the pressure for desorbing carbon dioxide from the adsorbent in the second desorption step.

[0070] In the adsorption tower 106a, a basic cycle is repeated, with the basic cycle consisting of the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step.

[0071] In the adsorption tower 106b, the on-off valves 105b, 116b, 110b, 107b, and 112b are operated in the same manner as the corresponding on-off valves 105a, 116a, 110a, 107a, and 112a, thereby performing the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step. In the adsorption tower 106b, a basic cycle is repeated, with the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step as the basic cycle. In the adsorption tower 106b, the on-off states of the on-off valves 120a and 120b when performing the cleaning step, first desorption step, and second desorption step are the same as in the adsorption tower 106a.

[0072] In the adsorption tower 106c, the on-off valves 105c, 116c, 110c, 107c, and 112c are operated in the same manner as the corresponding on-off valves 105a, 116a, 110a, 107a, and 112a, thereby performing the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step. In the adsorption tower 106c, a basic cycle is repeated, with the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step as the basic cycle. In the adsorption tower 106c, the on-off states of the on-off valves 120a and 120b during the cleaning step, first desorption step, and second desorption step are the same as in the adsorption tower 106a.

[0073] At the start of operation of the adsorption apparatus 1, the adsorption process, pressure release process, first desorption process, and second desorption process may be performed in at least one of the adsorption towers 106a, 106b, and 106c to store the recovered gas in the gas storage section 127. At this stage, the first desorption process and the second desorption process do not need to be distinguished. Alternatively, a gas corresponding to the recovered gas may be stored in the gas storage section 127 before the start of operation of the adsorption apparatus 1.

[0074] In the adsorption apparatus 1, the basic cycles in the adsorption towers 106a, 106b, and 106c are performed with a time lag. For example, as shown in Table 1, while the adsorption step is performed in the adsorption tower 106a, the depressurization step and the cleaning step are performed in the adsorption tower 106b, and the first desorption step and the second desorption step are performed in sequence in the adsorption tower 106c.

[0075] The processes in the adsorption towers 106b and 106c while the adsorption tower 106a is performing the adsorption process will be described. When the pressure release process is started in the adsorption tower 106b, the first desorption process is performed in the adsorption tower 106c. When the adsorption tower 106b transitions from the pressure release process to the cleaning process, the first desorption process is still being performed in the adsorption tower 106c. When the adsorption tower 106c transitions from the first desorption process to the second desorption process, the cleaning process is still being performed in the adsorption tower 106b. [Table 1]

[0076] The basic cycles in the adsorption towers 106a, 106b, and 106c are time-shifted, so that recovered gas (gas enriched with carbon dioxide) can be obtained intermittently at short intervals.

[0077] In the recovery method and adsorption apparatus 1 described in this embodiment, the recovered gas (concentrated gas) that has been stored in the gas storage section 127 is used as the cleaning gas used in the cleaning step. This makes it possible to achieve a high purity of carbon dioxide in the product gas G104 (in other words, a high concentration of carbon dioxide), and also to improve the recovery rate. One reason for this is thought to be that the recovered gas stored in the gas storage section 127 ensures that the composition of the recovered gas used as the cleaning gas is uniform.

[0078] (Second embodiment) The carbon dioxide pressure swing adsorption apparatus 3 shown in Figure 2 differs from the adsorption apparatus 1 according to the first embodiment mainly in that a cleaning gas flow path 124 is connected to the recovered gas flow path 117 on the concentrating section 106 side of the vacuum pump 118. The adsorption apparatus 3 and carbon dioxide recovery method according to the second embodiment will be described focusing on this difference. In the second embodiment, the adsorption apparatus 3 is a recovery apparatus that recovers carbon dioxide from a raw material gas G101.

[0079] The source gas G101 in the second embodiment is the same as the source gas G101 described in the first embodiment, and therefore a description of the source gas G101 will be omitted. In the second embodiment, the source gas G101 supplied from the source gas supply source may be a compressed gas at atmospheric pressure or higher. If the source gas G101 supplied from the source gas supply source is not a compressed gas, it may be compressed by a blower or the like.

[0080] [Adsorption device] The adsorption device 3 has an enrichment section 106 having at least one adsorption tower. In the second embodiment, an embodiment in which the enrichment section 106 has three adsorption towers 106a, 106b, and 106c will also be described.

[0081] The adsorption towers 106a, 106b, and 106c are towers for concentrating the carbon dioxide in the source gas G101 by adsorbing the carbon dioxide contained in the source gas G101 onto an adsorbent and then desorbing the carbon dioxide by the PSA method.

[0082] The adsorption towers 106a, 106b, and 106c and the adsorbents stored in the adsorption towers 106a, 106b, and 106c are the same as those in the first embodiment, so a description of the adsorption towers 106a, 106b, and 106c and the adsorbents will be omitted.

[0083] In the second embodiment, the gas extracted from the adsorption tower and containing concentrated carbon dioxide is also referred to as the “recovered gas.” The gas discharged from the adsorption tower and containing gas components other than the carbon dioxide adsorbed to the adsorbent in the raw material gas G101 is also referred to as the “off-gas” (exhaust gas).

[0084] Each of the adsorption towers 106a, 106b, and 106c is connected to an introduction flow path (first line) 101, an off-gas flow path 108, a recovered gas flow path (recovery line) 117, and a cleaning gas flow path (second line) 124. A pressure release gas flow path 113 may be connected to each of the adsorption towers 106a, 106b, and 106c. Each flow path is configured using gas piping. In the second embodiment, a configuration in which the pressure release gas flow path 113 is also connected to each of the adsorption towers 106a, 106b, and 106c will be described.

[0085] The explanations regarding the inlet passage 101, the off-gas passage 108, and the pressure release gas passage 113 are the same as those in the first embodiment. Therefore, the inlet passage 101, the off-gas passage 108, and the pressure release gas passage 113 will be explained briefly.

[0086] The inlet flow path 101 is a gas flow path for introducing the raw material gas G101 from a raw material gas supply source into the adsorption towers 106a, 106b, and 106c. The inlet flow path 101 may be provided with a buffer tank 102 for storing the raw material gas G101. The downstream end of the inlet flow path 101 branches toward the adsorption towers 106a, 106b, and 106c and is connected to gas passage ports at the upstream ends of the adsorption towers 106a, 106b, and 106c. The upstream ends of the adsorption towers 106a, 106b, and 106c have the same meaning as in the first embodiment.

[0087] On-off valves 105a, 105b, and 105c corresponding to the adsorption towers 106a, 106b, and 106c are provided on the downstream end side of the introduction flow path 101. By individually opening and closing the on-off valves 105a, 105b, and 105c, the source gas G101 can be introduced into each of the adsorption towers 106a, 106b, and 106c.

[0088] The inlet flow path 101 may be provided with a blower 103. The blower 103 is disposed upstream of the on-off valves 105a, 105b, and 105c. As described in the first embodiment, the blower 103 may be disposed between the buffer tank 102 and the on-off valves 105a, 105b, and 105c. The blower 103 may be used to compress the source gas G101 when the source gas G101 is not a compressed gas.

[0089] The off-gas flow path 108 is a gas flow path for discharging the off-gas from the adsorption towers 106a, 106b, and 106c to the outside (normal pressure space) of the adsorption apparatus 1. The upstream side of the off-gas flow path 108 branches toward the adsorption towers 106a, 106b, and 106c and is connected to the adsorption towers 106a, 106b, and 106c. Specifically, the off-gas flow path 108 is connected to the gas passage ports at the downstream ends of the adsorption towers 106a, 106b, and 106c. The downstream ends of the adsorption towers 106a, 106b, and 106c have the same meaning as in the first embodiment.

[0090] On-off valves 107a, 107b, and 107c corresponding to the adsorption towers 106a, 106b, and 106c are provided on the upstream end side of the off-gas passage 108. The on-off valves 107a, 107b, and 107c individually open and close the connections between the adsorption towers 106a, 106b, and 106c and the off-gas passage 108, respectively, so that the off-gas G102 can be discharged from each of the adsorption towers 106a, 106b, and 106c.

[0091] The downstream end of the off-gas passage 108 is an outlet for the off-gas G102, and is connected to a normal pressure space under atmospheric pressure. The off-gas G102 discharged through the off-gas passage 108 is discharged to the outside of the adsorption device 3. A pressure control valve 109 for adjusting the back pressure is provided on the downstream end side of the off-gas passage 108.

[0092] The pressure release gas flow path 113 is a gas flow path for discharging the pressure release gas G103 discharged from the adsorption towers 106a, 106b, and 106c to the outside of the adsorption device 3 when the pressure in the adsorption towers 106a, 106b, and 106c is released in the pressure release step. The pressure release gas G103 is also off-gas. As in the first embodiment, the upstream end of the pressure release gas flow path 113 is connected to the gas passage ports at the downstream ends of the adsorption towers 106a, 106b, and 106c. The downstream end of the pressure release gas flow path 113 is an outlet for the pressure release gas G103 and communicates with a normal pressure space under atmospheric pressure.

[0093] The pressure release gas flow path 113 is provided with on-off valves 112a, 112b, and 112c corresponding to the adsorption towers 106a, 106b, and 106c. The on-off valves 112a, 112b, and 112c individually open and close the pressure release gas flow path 113 and each of the adsorption towers 106a, 106b, and 106c, allowing the pressure release gas G103 to be discharged from each of the adsorption towers 106a, 106b, and 106c. A pressure regulation valve 114 for regulating back pressure is provided at the downstream end of the pressure release gas flow path 113.

[0094] The recovered gas flow path 117 is a gas flow path for flowing the recovered gas extracted from the adsorption towers 106a, 106b, and 106c to a buffer tank 125 via a vacuum pump 118. The upstream end of the recovered gas flow path 117 (the portion closer to the adsorption towers 106a, 106b, and 106c) branches toward the adsorption towers 106a, 106b, and 106c and is connected to the adsorption towers 106a, 106b, and 106c. Specifically, the recovered gas flow path 117 is connected to gas passages at the upstream ends of the adsorption towers 106a, 106b, and 106c. The downstream end of the recovered gas flow path 117 is connected to a buffer tank 125 via a vacuum pump 118. The recovered gas that flows into and is stored in the buffer tank 125 is extracted from the buffer tank 125 through a gas transport flow path 119 and used as the product gas G104.

[0095] For example, the product gas G104 is supplied to a downstream process such as a liquefaction apparatus. The use of the product gas G104 is not limited. In the second embodiment, the adsorption apparatus 3 does not need to have the buffer tank 125. In this case, the recovered gas flowing through the recovered gas flow path 117 can be directly supplied to the downstream process as the product gas G104.

[0096] On-off valves 116a, 116b, and 116c corresponding to the adsorption towers 106a, 106b, and 106c are provided at the upstream end of the recovered gas flow path 117. The on-off valves 116a, 116b, and 116c individually open and close the connection between each of the adsorption towers 106a, 106b, and 106c and the recovered gas flow path 117, allowing the recovered gas to flow from each of the adsorption towers 106a, 106b, and 106c to the recovered gas flow path 117.

[0097] An on-off valve 140a is provided in the recovered gas flow path 117 between the vacuum pump 118 and the concentration section 106. The on-off valve 140a can control the inflow of the recovered gas into the buffer tank 125.

[0098] The cleaning gas flow path 124 is a gas flow path for flowing cleaning gas into the adsorption towers 106a, 106b, and 106c in the cleaning step. The downstream end of the cleaning gas flow path 124 branches toward the adsorption towers 106a, 106b, and 106c and is connected to gas passages at the upstream ends of the adsorption towers 106a, 106b, and 106c. The upstream end of the cleaning gas flow path 124 is connected to the recovered gas flow path 117. Specifically, in the configuration illustrated in FIG. 2, the upstream end of the cleaning gas flow path 124 is connected to the recovered gas flow path 117 between the on-off valve 140a and the enrichment section 106. That is, the connection point X between the cleaning gas flow path 124 and the recovered gas flow path 117 is located between the on-off valve 140a and the enrichment section 106 in the recovered gas flow path 117.

[0099] A gas storage section 127 for temporarily storing the cleaning gas is provided in the cleaning gas flow path 124. A blower 126 for causing the cleaning gas to flow toward the on-off valves 110a, 110b, and 110c may be provided in the cleaning gas flow path 124 between the gas storage section 127 and the on-off valves 110a, 110b, and 110c.

[0100] An on-off valve 140b is provided in the cleaning gas flow path 124 between the connection part X with the collected gas flow path 117 and the gas storage part 127. The on-off valve 140b can control the flow of the collected gas flowing in the collected gas flow path 117 into the cleaning gas flow path 124. By opening the on-off valve 140b, the collected gas flowing in the cleaning gas flow path 124 functions as a cleaning gas. The on-off valve 140b is at least a part of a control mechanism (second control mechanism) 140 that controls the inflow of the collected gas flowing in the collected gas flow path 117 into the cleaning gas flow path 124. The amount of collected gas flowing in the cleaning gas flow path 124 is also controlled by opening and closing the on-off valve 140a, so the control mechanism 140 may include the on-off valve 140a.

[0101] On-off valves 110a, 110b, and 110c corresponding to the adsorption towers 106a, 106b, and 106c are provided on the downstream end side of the cleaning gas flow path 124. The on-off valves 110a, 110b, and 110c individually open and close the communication between each of the adsorption towers 106a, 106b, and 106c and the cleaning gas flow path 124, thereby enabling the cleaning gas to be supplied to each of the adsorption towers 106a, 106b, and 106c.

[0102] In the second embodiment, too, the ratio (V1 / V2) of the spatial volume V1 of the gas storage section 127 to the total volume V2 of carbon dioxide introduced at one time into any of the adsorption towers 106a, 106b, and 106c in the concentration step is preferably 0.1 or more, more preferably 0.1 or more and 10 or less, and even more preferably 0.2 or more and 9 or less.

[0103] The spatial volume V1 of the gas storage section 127 can be considered as the volume capable of storing an ideal gas at atmospheric pressure, and can be easily calculated using equation (1) described in the first embodiment, just like in the first embodiment. The total volume V2 of carbon dioxide introduced into any one of the adsorption towers 106a, 106b, and 106c at one time can be simply calculated using equation (2) described in the first embodiment, as in the first embodiment.

[0104] An example of a method for recovering carbon dioxide using the adsorption apparatus 3 will be described. The carbon dioxide recovery method is a method for recovering carbon dioxide from a raw material gas G101 by pressure swing adsorption. In this example of the carbon dioxide recovery method, the carbon dioxide contained in the raw material gas G101 is concentrated, and the concentrated carbon dioxide (recovered gas) is recovered.

[0105] The carbon dioxide recovery method includes an adsorption step and a desorption step. In the carbon dioxide recovery method, the carbon dioxide contained in the source gas G101 is adsorbed onto an adsorbent in the adsorption step, and then the carbon dioxide is desorbed from the adsorbent. This results in concentrated carbon dioxide. Therefore, in the second embodiment, the adsorption step and the desorption step also correspond to the carbon dioxide concentration step.

[0106] The carbon dioxide recovery method of this embodiment further includes a washing step between the adsorption step and the desorption step. A pressure release step may be carried out between the adsorption step and the washing step. In order to obtain high-purity carbon dioxide, a first desorption step and a second desorption step may be carried out as the desorption step.

[0107] In the following, a description will be given of an embodiment in which the pressure release step is performed and the first and second desorption steps are performed in the desorption step. Since the steps performed in the adsorption towers 106a, 106b, and 106c are the same, only the steps performed in the adsorption tower 106a will be described.

[0108] [Adsorption process] In the adsorption step, the on-off valves 105a and 107a are opened to allow the raw material gas G101 to flow into the adsorption tower 106a, and carbon dioxide contained in the raw material gas G101 is adsorbed by the adsorbent stored in the adsorption tower 106a. During this process, the on-off valves 112a, 110a, and 116a are closed, and the pressure in the adsorption tower 106a is adjusted by the pressure control valve 109 to an adsorption pressure that appropriately exceeds atmospheric pressure and is suitable for adsorption of carbon dioxide into the adsorbent. The adsorption pressure is, for example, 0 kPaG or higher and 100 kPaG or lower. In the adsorption step, the portion of the raw material gas G101 that is not adsorbed by the adsorbent is discharged as off-gas G102 from the off-gas flow path 108 to the outside of the adsorption device 3.

[0109] [Pressure release process] The pressure release step is performed after the adsorption step. In the pressure release step, the on-off valves 105a and 107a are closed, and the on-off valve 112a is opened to release the pressure in the adsorption tower 106a. At this time, the pressure in the adsorption tower 106a is adjusted by the pressure control valve 114 to a pressure suitable for pressure release that is lower than the pressure in the adsorption step. An example of the pressure in the adsorption tower 106a 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 source gas G101 that is not adsorbed by the adsorbent is discharged as pressure release gas G103 from the pressure release gas flow path 113 to the outside of the adsorption device 3.

[0110] [Cleaning process] The cleaning process is performed after the pressure release process. In the cleaning process, the on-off valve 110a is opened and the blower 126 is operated to cause the cleaning gas to flow into the adsorption tower 106a through the cleaning gas flow path 124. The cleaning gas that has flowed into the adsorption tower 106a is discharged to the outside of the adsorption device 3 through the pressure release gas flow path 113.

[0111] In the cleaning step, the cleaning gas flows through the adsorption tower 106a, and gas components other than carbon dioxide that have adhered to the wall surfaces of the adsorption tower 106a are carried along with the cleaning gas and discharged to the outside of the adsorption device 3. That is, the cleaning gas causes the gas components other than carbon dioxide that remained in the adsorption tower 106a to be discharged from the adsorption tower 106a.

[0112] In the second embodiment, as in the first embodiment, the cleaning gas is the recovered gas obtained by performing the first desorption step in one of the adsorption towers 106a, 106b, and 106c other than the adsorption tower in which the cleaning step is being performed, and is the recovered gas returned to the adsorption tower in which the cleaning step is being performed via the cleaning gas flow path 124. As described above, in the cleaning step, the recovered gas is returned to the adsorption tower in which the cleaning step is being performed, and therefore the cleaning step corresponds to the recovered gas return step.

[0113] The cleaning gas is the recovered gas obtained by carrying out the first desorption step, and therefore is a gas containing concentrated carbon dioxide.

[0114] In the cleaning step, the on-off valve 140a is closed and the on-off valve 140b is open. As a result, the recovered gas obtained by carrying out the first desorption step flows from the recovered gas flow path 117 to the cleaning gas flow path 124. In this embodiment, the cleaning gas flow path 124 is provided with a gas storage section 127, so the recovered gas is stored in the gas storage section 127 and then returned to the adsorption tower where the cleaning step is carried out. That is, in this embodiment, the recovered gas stored in the gas storage section 127 is used as the cleaning gas.

[0115] Note that even after the adsorption tower performing the first desorption step has transitioned to the second desorption step, the adsorption tower that had been performing the cleaning step may continue the cleaning step. As will be described later, in the second desorption step, the on-off valve 140b is closed while the on-off valve 140a is open, and in this case, the cleaning gas remaining in the gas storage section 127 flows into the cleaning step.

[0116] As described above, when the recovered gas is used as a cleaning gas, the carbon dioxide contained in the recovered gas is re-adsorbed by the adsorbent.

[0117] [First desorption process] The first desorption step is performed after the cleaning step. The first desorption step is an initial step in the desorption step. In the first desorption step, the on-off valves 110a and 112a are closed, while the on-off valve 116a is opened. In this state, the blower 126 is operated to reduce the pressure in the adsorption tower 106a, and the gas in the adsorption tower 106a is caused to flow into the recovered gas flow path 117. In the first desorption step, the pressure in the adsorption tower 106a is reduced as described above, causing carbon dioxide to be desorbed from the adsorbent. As a result, the gas (recovered gas) flowing into the recovered gas flow path 117 contains carbon dioxide.

[0118] In the first desorption step, the on-off valve 140a is closed, while the on-off valve 140b is open. As a result, the recovered gas (initial recovered gas) that flowed into the recovered gas flow path 117 in the first desorption step flows into the cleaning gas flow path 124, as described in the cleaning step. The recovered gas that flows from the recovered gas flow path 117 to the cleaning gas flow path 124 is stored in the gas storage section 127. The recovered gas stored in the gas storage section 127 in this manner is used as the cleaning gas, as described above. Since the recovered gas is stored in the gas storage section 127 in the first desorption step, at least a part of the first desorption step is a storage step in which the recovered gas is stored in the gas storage section 127.

[0119] The time for performing the first desorption step may be any time that allows gas components other than carbon dioxide adhering to the wall surfaces of the adsorption tower 106a to be sufficiently discharged, and that the carbon dioxide adsorbed on the adsorbent is not desorbed more than necessary. The time for performing the first desorption step is, for example, 1% to 75% of the time for performing the desorption step (a step including the first desorption step and the second desorption step). The time for performing the first desorption step may be, for example, 4 seconds to 300 seconds, assuming that the desorption time is 400 seconds.

[0120] [Second desorption process] The second desorption step is a step in the desorption step that occurs a certain time after the start of the first desorption step. In the second desorption step, the on-off valve 140b is closed, while the on-off valve 140a is opened. As a result, the recovered gas that flows from the adsorption tower 106a to the recovered gas flow path 117 flows into the buffer tank 125 and is stored there. The recovered gas stored in the buffer tank 125 is appropriately extracted as the product gas G104. The time for which the second desorption step is performed is, for example, 25% or more and 99% or less of the time for which the desorption step is performed. For example, if the desorption time is 400 seconds, the time for which the second desorption step is performed may be 100 seconds or more and 396 seconds or less.

[0121] The second desorption step is a step that occurs after the first desorption step has been performed for a certain period of time, and therefore the pressure inside the adsorption tower 106a is lower than when the first desorption step was started. Therefore, after the transition from the first desorption step to the second desorption step, more carbon dioxide is desorbed from the adsorbent. Therefore, in the second desorption step, the gas flowing from the adsorption tower 106a to the recovered gas flow path 117 is a recovered gas containing concentrated carbon dioxide. Furthermore, since the impurities remaining in the adsorption tower 106a in the first desorption step are also discharged, a highly pure recovered gas can be obtained in the second desorption step.

[0122] The recovered gas recovered in the second desorption step is the product gas G104. In other words, in the second desorption step, carbon dioxide is desorbed from the adsorbent so as to obtain the product gas G104. Therefore, in the following description, the term "desorption pressure" also refers to the pressure for desorbing carbon dioxide from the adsorbent in the second desorption step in the second embodiment.

[0123] In the adsorption tower 106a, a basic cycle is repeated, with the basic cycle consisting of the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step.

[0124] In the adsorption tower 106b, the on-off valves 105b, 116b, 110b, 107b, and 112b are operated in the same manner as the corresponding on-off valves 105a, 116a, 110a, 107a, and 112a, thereby performing the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step. In the adsorption tower 106b, a basic cycle is repeated, with the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step as the basic cycle. In the adsorption tower 106b, the on-off states of the on-off valves 140a and 140b when performing the cleaning step, first desorption step, and second desorption step are the same as in the adsorption tower 106a.

[0125] In the adsorption tower 106c, the on-off valves 105c, 116c, 110c, 107c, and 112c are operated in the same manner as the corresponding on-off valves 105a, 116a, 110a, 107a, and 112a, thereby performing the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step. In the adsorption tower 106c, a basic cycle is repeated, with the adsorption step, pressure release step, cleaning step, first desorption step, and second desorption step as the basic cycle. In the adsorption tower 106c, the on-off states of the on-off valves 140a and 140b during the cleaning step, first desorption step, and second desorption step are the same as in the adsorption tower 106a.

[0126] In the adsorption apparatus 3, the basic cycles are also performed in the adsorption towers 106a, 106b, and 106c with a time lag. Specifically, as shown in Table 2, while the adsorption step is being performed in the adsorption tower 106a, the depressurization step and cleaning step are being performed in the adsorption tower 106b, and the first desorption step and second desorption step are being performed in that order in the adsorption tower 106c.

[0127] The processes in the adsorption towers 106b and 106c while the adsorption tower 106a is performing the adsorption process will be described. When the pressure release process is started in the adsorption tower 106b, the first desorption process is performed in the adsorption tower 106c. When the adsorption tower 106b transitions from the pressure release process to the cleaning process, the first desorption process is still being performed in the adsorption tower 106c. When the adsorption tower 106c transitions from the first desorption process to the second desorption process, the cleaning process is still being performed in the adsorption tower 106b. [Table 2]

[0128] The basic cycles in the adsorption towers 106a, 106b, and 106c are time-shifted, so that recovered gas (gas enriched with carbon dioxide) can be obtained intermittently in a short period of time.

[0129] In the recovery method and adsorption apparatus 3 described in the second embodiment, the recovery gas (concentrated gas) that has been stored once in the gas storage section 127 is also used as the cleaning gas used in the cleaning step. Therefore, similar to the first embodiment, it is possible to achieve high purity of carbon dioxide in the product gas G104 (in other words, high concentration of carbon dioxide), and also to improve the recovery rate.

[0130] Although the embodiments of the present invention have been described above, the present invention is not limited to the illustrated embodiments, and is intended to include all modifications within the scope of the claims, as well as the meaning and scope equivalent to the claims.

[0131] For example, since the gas reservoir 127 is intended to store the recovered gas (concentrated gas) obtained by the adsorption towers 106a, 106b, and 106c as a cleaning gas, it may be provided at any location on the line returning the recovered gas from the downstream of the on-off valves 116a, 116b, and 116c to the concentration section 106. For example, in the apparatus shown in FIGS. 1 and 2, the gas reservoir 127 may be provided between one of the on-off valves 110a, 110b, and 110c and the vacuum pump 118. From the viewpoint of ease of operation of various valves, it is preferable to provide the gas reservoir 127 between the blower 126 and an on-off valve (e.g., on-off valve 120a in FIG. 1) for controlling the flow of the recovered gas from the recovered gas flow path to the cleaning gas flow path.

[0132] Although the embodiment in which the enrichment section has three adsorption towers has been exemplified, the number of adsorption towers provided in the enrichment section is not limited. For example, the number of adsorption towers provided in the enrichment section may be four or more. The number of adsorption towers provided in the enrichment section may also be one.

[0133] In an embodiment in which the number of adsorption towers is one, for example, the above basic cycle may be repeated after the adsorption step and the desorption step are performed in the adsorption tower so that the concentrated gas is stored in the gas storage section. In the cleaning step included in the second or subsequent basic cycles performed in the adsorption tower, the concentrated gas recovered in the desorption step of the previous basic cycle and stored in the gas storage section may be used as the cleaning gas. [Example]

[0134] Next, the present invention will be specifically described using examples, but the present invention is not limited to the following examples. In the description of Examples 1 and 2, the elements described in the embodiment are given the same reference numerals, and duplicated description will be omitted.

[0135] [Example 1] Carbon dioxide was recovered from a raw material gas G101 using the adsorption apparatus (recovery apparatus) 1 shown in Fig. 1 according to the recovery method described in the first embodiment. The adsorption apparatus 1 used in Example 1 was provided with a blower 126 on a cleaning gas flow path 124, as shown in Fig. 1.

[0136] The raw material gas G101 contained 10.2 vol% carbon dioxide, 83.7 vol% nitrogen, and 6.1 vol% oxygen. The supply flow rate of the raw material gas G101 to the adsorption apparatus 1 was 3.16 NL / min. The gas temperature was 25°C. The total volume V2 of carbon dioxide introduced into each of the adsorption towers 106a, 106b, and 106c at one time, calculated by equation (2) described in the first embodiment, was 2.15 L.

[0137] Each of the adsorption towers 106a, 106b, and 106c had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0138] 500 mL of zeolite was packed as an adsorbent into each of the adsorption towers 106a, 106b, and 106c of the adsorption device 1. The zeolite used was commercially available zeolite F-9HA manufactured by Tosoh Corporation.

[0139] A cylindrical tank having an inner diameter of 37.1 mm and an internal volume of 0.5 L was installed as the gas storage section 127. The spatial volume V1 of the gas storage section 127 calculated by the formula (1) described in the first embodiment was 0.46 L.

[0140] In the adsorption apparatus 1, the adsorption step was performed for 400 seconds, the pressure release step for 3 seconds, the cleaning step for 397 seconds, and the desorption step for 400 seconds, in that order. Of the desorption steps, the first desorption step was performed for 202 seconds, and the second desorption step was performed for 198 seconds. Since the adsorption apparatus 1 includes the gas storage section 127, the first desorption step included a storage step of storing the recovered gas in the gas storage section 127, as described in the first embodiment.

[0141] The internal pressure (adsorption pressure) of the adsorption towers 106a, 106b, and 106c in the adsorption step was 22 kPaG, and the internal pressure (desorption pressure) in the second desorption step was −95 kPaG.

[0142] As shown in Fig. 4, the carbon dioxide concentration of the product gas G104 recovered by the adsorption apparatus 1 was 98.3 vol%, and the carbon dioxide recovery rate was 51.8%. V1 / V2 in Example 1 was 0.21. Fig. 4 is a chart showing the results of Examples 1 and 2 and Comparative Examples 1 and 2.

[0143] [Example 2] Carbon dioxide was recovered from a raw material gas G101 using the adsorption apparatus 1 shown in Fig. 1 according to the recovery method described in the first embodiment. The adsorption apparatus 1 used in Example 1 was provided with a blower 126 on the cleaning gas flow path 124, as shown in Fig. 1.

[0144] The raw material gas G101 contained 10.2 vol% carbon dioxide, 83.5 vol% nitrogen, and 6.3 vol% oxygen. The supply flow rate of the raw material gas G101 to the adsorption apparatus 1 was 3.24 NL / min. The gas temperature was 25°C. The total volume V2 of carbon dioxide introduced into each of the adsorption towers 106a, 106b, and 106c at one time, calculated by equation (2) described in the first embodiment, was 2.2 L.

[0145] Each of the adsorption towers 106a, 106b, and 106c had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0146] 500 mL of zeolite was packed as an adsorbent into each of the adsorption towers 106a, 106b, and 106c of the adsorption device 1. The zeolite used was commercially available zeolite F-9HA manufactured by Tosoh Corporation.

[0147] A cylindrical tank having an outer diameter of 165 mm and an internal volume of 20 L was installed as the gas storage section 127. The spatial volume V1 of the gas storage section 127 calculated by the formula (1) described in the first embodiment was 18.32 L.

[0148] The adsorption device 1 sequentially performed an adsorption process for 400 seconds, a pressure release process for 3 seconds, a cleaning process for 397 seconds, and a desorption process for 400 seconds. Of the desorption processes, a first desorption process was performed for 55 seconds, and a second desorption process was performed for 345 seconds. Since the adsorption device 1 includes the gas storage section 127, the first desorption process included a storage process of storing the recovered gas in the gas storage section 127, as described in the first embodiment.

[0149] The internal pressure (adsorption pressure) of the adsorption towers 106a, 106b, and 106c in the adsorption step was 22 kPaG, and the internal pressure (desorption pressure) in the second desorption step was −96 kPaG.

[0150] 4, the carbon dioxide concentration of the product gas G104 recovered by the adsorption apparatus 1 was 98.4 vol %, and the carbon dioxide recovery rate was 55.6%. V1 / V2 in Example 2 was 8.32.

[0151] [Comparative Example 1] Carbon dioxide was recovered from the raw material gas G101 using the adsorption apparatus 4 shown in Figure 3. The adsorption apparatus 4 had the same configuration as the adsorption apparatus 1 shown in Figure 1, except that it did not have the gas storage section 127.

[0152] The raw material gas G101 contained 10.0 vol % carbon dioxide, 83.7 vol % nitrogen, and 6.2 vol % oxygen. The flow rate of the raw material gas G101 supplied to the adsorption apparatus 4 was 3.16 NL / min. The gas temperature was 25°C.

[0153] Each of the adsorption towers 106a, 106b, and 106c had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0154] 500 mL of zeolite was packed as an adsorbent into each of the adsorption towers 106a, 106b, and 106c of the adsorption device 4. The zeolite used was commercially available zeolite F-9HA manufactured by Tosoh Corporation.

[0155] Carbon dioxide was recovered using the adsorption device 4 in the same manner as the recovery method described in the first embodiment, except that the recovered gas was not stored in the gas storage section 127. Specifically, the adsorption process was performed for 400 seconds, the pressure release process for 3 seconds, the cleaning process for 397 seconds, and the desorption process for 400 seconds, in that order. Of the desorption processes, the first desorption process was performed for 202 seconds, and the second desorption process was performed for 198 seconds. The internal pressure (adsorption pressure) of the adsorption towers 106a, 106b, and 106c during the adsorption process was 22 kPaG, and the internal pressure (desorption pressure) during the second desorption process was -95 kPaG.

[0156] As shown in FIG. 4, in the adsorption device 4, the carbon dioxide concentration of the recovered product gas G204 was 95.0 vol %, and the recovery rate of carbon dioxide was 54.0%.

[0157] Comparative Example 2 Carbon dioxide was recovered from the raw material gas G101 using the adsorption apparatus 4 shown in Figure 3. The adsorption apparatus 4 had the same configuration as the adsorption apparatus 1 shown in Figure 1, except that it did not have the gas storage section 127.

[0158] The raw material gas G101 contained 10.0 vol % carbon dioxide, 83.7 vol % nitrogen, and 6.2 vol % oxygen. The flow rate of the raw material gas G101 supplied to the adsorption apparatus 4 was 3.16 NL / min. The gas temperature was 25°C.

[0159] Each of the adsorption towers 106a, 106b, and 106c had a cylindrical shape with an inner diameter of 37.1 mm and an inner height of 500 mm.

[0160] 500 mL of zeolite was packed as an adsorbent into each of the adsorption towers 106a, 106b, and 106c of the adsorption device 4. The zeolite used was commercially available zeolite F-9HA manufactured by Tosoh Corporation.

[0161] In the adsorption device 4, carbon dioxide was recovered using the same recovery method as described in the first embodiment, except that the recovered gas was not stored in the gas storage section 127. Specifically, the adsorption process was performed for 400 seconds, the pressure release process for 3 seconds, the cleaning process for 397 seconds, and the desorption process for 400 seconds, in that order. Of the desorption processes, the first desorption process was performed for 336 seconds, and the second desorption process was performed for 64 seconds. The internal pressure (adsorption pressure) of the adsorption towers 106a, 106b, and 106c during the adsorption process was 22 kPaG, and the internal pressure (desorption pressure) during the second desorption process was -95 kPaG.

[0162] As shown in FIG. 4, in the adsorption device 4, the carbon dioxide concentration of the recovered product gas G104 was 98.0 vol %, and the recovery rate of carbon dioxide was 39.0%.

[0163] [evaluation] As mentioned above, Figure 4 is a chart showing the results of Examples 1 and 2 and Comparative Examples 1 and 2. In Figure 4, "V1 / V2" indicates the ratio of spatial volume V1 to total volume V2, and "carbon dioxide concentration" is the carbon dioxide concentration in product gas G104 obtained in Examples 1 and 2 and Comparative Examples 1 and 2.

[0164] As shown in Fig. 4, in Comparative Example 1, in which the gas storage unit 127 was not used, a recovery rate of over 50% was obtained, but the carbon dioxide concentration was less than 98%. Furthermore, in Comparative Example 2, in which the gas storage unit 127 was not used, a carbon dioxide concentration of 98% was obtained, but the recovery rate was less than 50%. In contrast, in Examples 1 and 2, in which the gas storage unit 127 was used, a carbon dioxide concentration of 98% or more was obtained, and a recovery rate of 50% or more (more specifically, exceeding 50%) was obtained. Therefore, it can be seen that by using the gas storage unit 127, high-concentration (or high-purity) carbon dioxide can be recovered from the raw material gas G101 at a high recovery rate.

[0165] 4, it can be seen that when V1 / V2 is 0.1 or more, high-concentration (or high-purity) carbon dioxide can be recovered from the feed gas G101 at a high recovery rate, and that when V1 / V2 is larger, such as 5 or more, 7 or more, 8 or more, or 11 or more, the carbon dioxide concentration in the product gas G104 and the recovery rate can be improved. V1 / V2 is usually 30 or less. [Industrial Applicability]

[0166] The recovery method and recovery device disclosed herein can recover carbon dioxide at a high recovery rate, which can reduce greenhouse gas emissions and contribute to the preservation of the global environment. [Explanation of symbols]

[0167] 1...adsorption device (recovery device), 101...inlet flow path (first line), 106...concentration section, 106a, 106b, 106c...adsorption towers, 117...recovered gas flow path (recovery line), 120...control mechanism, 124...cleaning gas flow path (second line), 127...gas storage section.

Claims

1. a concentration step of introducing a raw material gas into at least one adsorption tower containing an adsorbent that adsorbs carbon dioxide, and recovering a concentrated gas in which carbon dioxide contained in the raw material gas is concentrated by a pressure swing adsorption method, the concentration step including an adsorption step of adsorbing carbon dioxide contained in the raw material gas onto the adsorbent, and a desorption step of desorbing carbon dioxide from the adsorbent and recovering the concentrated gas; a storing step of storing a portion of the concentrated gas recovered in the concentrating step in a gas storage section; a cleaning step of returning the concentrated gas stored in the gas storage section to one of the at least one adsorption towers that has undergone the adsorption step, and cleaning the adsorption tower to which the concentrated gas has been returned; Equipped with The washing step is carried out between the adsorption step and the desorption step. Recovery method.

2. a ratio V1 / V2 of a spatial volume V1 of the gas storage section to a total volume V2 of carbon dioxide in the raw material gas introduced into the adsorption tower for one-time concentration of carbon dioxide in the concentration step is 0.1 or more; The recovery method according to claim 1.

3. The carbon dioxide concentration of the raw material gas is 20 vol% or less. The recovery method according to claim 1 or 2.

4. a concentrating section having at least one adsorption tower containing an adsorbent that adsorbs carbon dioxide, for obtaining a concentrated gas in which carbon dioxide in the raw gas introduced into the at least one adsorption tower is concentrated; a first line for introducing the raw material gas into the at least one adsorption tower; a gas storage section for storing the concentrated gas obtained in the concentration section; a second line for returning the concentrated gas in the gas storage section to the enrichment section as a cleaning gas for cleaning the at least one adsorption column of the enrichment section; Equipped with Recovery device.

5. a ratio V1 / V2 of a spatial volume V1 of the gas storage section to a total volume V2 of carbon dioxide in the raw material gas introduced into the adsorption tower for one time concentration of carbon dioxide in the adsorption tower is 0.1 or more; The recovery device according to claim 4.

6. The gas storage portion has a cylindrical shape. The recovery device according to claim 4.

7. a recovery line through which the concentrated gas recovered from the concentration section flows and to which the second line is connected; a control mechanism for controlling the flow of the concentrated gas flowing through the recovery line into the second line; Equipped with The gas storage section is disposed on the second line. The recovery device according to claim 4.

8. The enrichment section has a plurality of the adsorption towers. The recovery device according to any one of claims 4 to 7.

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