Carbon dioxide recovery device and carbon dioxide recovery method

Abstract

The purpose of the present invention is to provide a technology which relates to the recovery of carbon dioxide and with which it becomes possible to improve a carbon dioxide recovery rate without reducing desorption efficiency. This carbon dioxide recovery device 1 comprises: a plurality of reactors 11 in each of which an adsorption step for adsorbing carbon dioxide and a desorption step for desorbing carbon dioxide are performed; a carbon dioxide line 103 which is branched and connected to each of the reactors 11 and through which carbon dioxide desorbed in the desorption step flows; a carbon dioxide recovery pump 63 which is disposed in a part where the branched parts of the carbon dioxide line 103 are concentrated and which applies a sucking force to the inside of each of the reactors 11 through the carbon dioxide line 103; and a control device 90 which performs such a control procedure that includes, with respect to a first reactor 11a in which the desorption step has been performed firstly and to which the sucking force by the carbon dioxide recovery pump 63 has been applied and a second reactor 11b in which the desorption step is to be performed secondarily among the plurality of reactors 11, applying the sucking force by the carbon dioxide recovery pump 63 to the second reactor 11b when the internal pressure in the first reactor 11a decreases to a predetermined threshold value.

Description

Carbon dioxide capture device and carbon dioxide capture method

[0001] The present invention relates to a carbon dioxide capture device and a carbon dioxide capture method.

[0002] Conventionally, there has been known a technique for recovering carbon dioxide by performing an adsorption step in which carbon dioxide is adsorbed onto an adsorbent from a gas such as the atmosphere containing carbon dioxide, and then performing a desorption step in which the carbon dioxide is desorbed from the adsorbent after the adsorption step. This type of technique is described, for example, in Patent Document 1. Patent Document 1 describes recovering carbon dioxide using a plurality of reactors each including an adsorption structure for adsorbing carbon dioxide.

[0003] Special table 2017-528318 publication

[0004] In the desorption process, carbon dioxide and water are desorbed from the adsorbent by heating the adsorbent to a high temperature and creating a negative pressure. However, because water desorbs before carbon dioxide, the partial pressure of carbon dioxide decreases, increasing the desorption rate of carbon dioxide. However, in the latter half of the desorption process, there is no water to desorb, and the partial pressure of carbon dioxide increases, causing the desorption rate of carbon dioxide to decrease. It is possible to adopt a method in which the carbon dioxide desorption process is terminated after the desorption rate has decreased and the process moves on to the next adsorption process. However, this method ends the desorption process too early, which reduces the amount of carbon dioxide recovered per cycle when the adsorption process and desorption process are considered to be one cycle. Conventional technology has room for improvement in terms of improving carbon dioxide recovery efficiency.

[0005] An object of the present invention is to provide a carbon dioxide recovery apparatus and a carbon dioxide recovery method that can improve the carbon dioxide recovery rate without reducing desorption efficiency.

[0006] (1) The present invention relates to a plurality of reactors (for example, reactor 11 described later) that have an adsorbent (for example, adsorbent 12 described later) therein and perform an adsorption step of sucking a gas containing carbon dioxide into the adsorbent to adsorb the carbon dioxide, and a desorption step of heating the adsorbent under reduced pressure around the adsorbent to desorb the carbon dioxide from the adsorbent; carbon dioxide lines (for example, carbon dioxide line 103 described later) that are branched and connected to each of the reactors and through which the carbon dioxide desorbed in the desorption step flows; and a carbon dioxide line (for example, carbon dioxide line 103 described later) that is arranged at a portion where the branched portions of the carbon dioxide lines converge and that distributes the carbon dioxide to the reactors through the carbon dioxide line. and a control device (for example, a control device 90 described later) that controls the suction force of the carbon dioxide capture pump to also be applied to a second reactor (for example, a second reactor 11b described later) that performs the desorption step secondly when the internal pressure of a first reactor (for example, a first reactor 11a described later) on which the desorption step is first performed and on which the suction force of the carbon dioxide capture pump is acting drops to a predetermined threshold value.

[0007] (2) The carbon dioxide capture device described in (1) above may further include a vacuum pump (e.g., vacuum pump 62 described later) that reduces the pressure inside the reactor, and the control device may apply the suction force of the carbon dioxide capture pump to the first reactor during the desorption process, while driving the vacuum pump during the desorption process of the second reactor to reduce the pressure inside the second reactor and, after raising the temperature of the adsorbent, may also control the suction force of the carbon dioxide capture pump to also apply to the second reactor.

[0008] (3) In the carbon dioxide recovery device described in (2) above, the control device may perform control so that the suction force of the carbon dioxide recovery pump is also applied to the second reactor at the timing when the internal pressure of the second reactor rises to a predetermined suction start pressure value (e.g., a desorption valve opening threshold value described later) after the adsorbent temperature is raised in the desorption step of the second reactor.

[0009] (4) The present invention relates to a plurality of reactors (for example, reactor 11 described later) that have an adsorbent (for example, adsorbent 12 described later) therein and perform an adsorption step of sucking a gas containing carbon dioxide into the adsorbent to adsorb the carbon dioxide, and a desorption step of heating the adsorbent under reduced pressure around the adsorbent to desorb the carbon dioxide from the adsorbent; carbon dioxide lines (for example, carbon dioxide line 103 described later) that are branched and connected to each of the reactors and through which the carbon dioxide desorbed in the desorption step flows; and a carbon dioxide line that is arranged at a portion where the branched portions of the carbon dioxide line are gathered and that creates a suction force inside the reactor through the carbon dioxide line. and a carbon dioxide capture pump (for example, a carbon dioxide capture pump 63 described later) that is used to capture carbon dioxide. When the internal pressure of a first reactor (for example, a first reactor 11a described later), in which the desorption step is first performed and on which the suction force of the carbon dioxide capture pump is acting, drops to a predetermined threshold value (for example, a scavenging start pressure threshold described later), the suction force of the carbon dioxide capture pump is also applied to a second reactor (for example, a second reactor 11b described later) that is second to perform the desorption step.

[0010] According to the present invention, it is possible to provide a carbon dioxide recovery apparatus and a carbon dioxide recovery method that can improve the carbon dioxide recovery rate without reducing the desorption efficiency.

[0011] FIG. 1 is a schematic diagram showing the configuration related to gas flow in a carbon dioxide capture device according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration related to liquid flow in a carbon dioxide capture device of this embodiment. FIG. 3 is a schematic diagram showing the configuration related to gas flow in a reactor of the carbon dioxide capture device of this embodiment. FIG. 4 is a schematic diagram showing the configuration related to liquid flow in a reactor of the carbon dioxide capture device of this embodiment. FIG. 5 is a graph showing the time change in the internal pressure and the amount of desorbed carbon dioxide in each reactor when desorption process control is executed in the carbon dioxide capture device of this embodiment. FIG. 6 is a diagram showing the schematic diagram of gas flow in a first reactor transitioning from a scavenging process to an adsorbent temperature increase process and in a second reactor during an adsorption process. FIG. 7 is a diagram showing the schematic diagram of gas flow in a first reactor during high-temperature desorption and in a second reactor transitioning from an adsorption process to a scavenging process. FIG. 8 is a diagram showing the schematic diagram of gas flow in a first reactor during a desorption process and in a second reactor transitioning from an adsorption process to a scavenging process.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] <Overall configuration> Fig. 1 is a schematic diagram showing the configuration related to gas flow in a carbon dioxide capture device 1 according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing the configuration related to liquid flow in the carbon dioxide capture device 1 of this embodiment. Note that the configuration related to liquid flow in the carbon dioxide capture device 1 is omitted from Fig. 1, and the configuration related to gas flow in the carbon dioxide capture device 1 is omitted from Fig. 2.

[0014] The carbon dioxide capture device 1 of this embodiment is applied to, for example, direct air capture (DAC) technology that captures carbon dioxide from the atmosphere in order to reduce the carbon dioxide concentration in the atmosphere. The carbon dioxide captured by the carbon dioxide capture device 1 is stored underground or reused as fuel or material.

[0015] As shown in Figures 1 and 2, the carbon dioxide capture device 1 of this embodiment includes a reactor 10, a fan 61, a vacuum pump 62, a carbon dioxide capture pump 63, a heat exchanger 64, a separator 65, a carbon dioxide tank 66, an inert gas tank 69, a heat exchanger 70, and a control device 90.

[0016] As shown in FIG. 1, the carbon dioxide capture device 1 includes an adsorption line 101, a vacuum line 102, a carbon dioxide line 103, a circulation line 104, and an inert gas supply line 107 as gas flow paths.

[0017] The reactor 10 is configured by arranging a plurality of reactors 11 in parallel, each of which adsorbs carbon dioxide. In this embodiment, a total of 16 reactors 11 are arranged, each consisting of a pair of reactors 10 on the left and right.

[0018] 3 is a schematic diagram showing a configuration related to the gas flow in the reactor 11 of the carbon dioxide capture device 1 of this embodiment. The reactor 11 is a carbon dioxide capture reactor including an adsorbent 12, a first valve 21, a second valve 22, a third valve 23, a fourth valve 24, a pressure sensor 25, a carbon dioxide sensor 26, and a temperature sensor 27.

[0019] The adsorbent 12 is disposed inside the reactor 11 to adsorb carbon dioxide. The adsorbent 12 is a particulate material that has the property of adsorbing carbon dioxide at low temperatures (for example, in the range of −30° C. to 50° C.) and desorbing (releasing) carbon dioxide at high temperatures (for example, in the range of 50° C. to 110° C.) when the ambient carbon dioxide concentration is low. Examples of such adsorbent 12 include a solid amine carbon dioxide adsorbent formed by supporting an amine on a porous material such as silica.

[0020] The first valve 21 is an on-off valve arranged at the connection between the carbon dioxide line 103 that captures carbon dioxide and the reactor 11. A carbon dioxide capture pump 63 is arranged in the carbon dioxide line 103. The second valve 22 is an on-off valve arranged at the connection between the vacuum line 102, in which the vacuum pump 62 is arranged, and the reactor 11. The third valve 23 is an on-off valve arranged at the inlet that takes in air and the like into the reactor 11. The fourth valve 24 is an on-off valve arranged at the connection between the adsorption line 101 and the reactor 11.

[0021] The first valve 21, the second valve 22, the third valve 23, and the fourth valve 24 are all controlled to open and close by the control device 90. The first valve 21, the second valve 22, the third valve 23, and the fourth valve 24 are each configured by, for example, a normally open butterfly valve.

[0022] The pressure sensor 25 measures the internal pressure of the reactor 11. The carbon dioxide sensor 26 measures the carbon dioxide concentration inside the reactor 11. The temperature sensor 27 measures the temperature of the adsorbent 12. Measurement information from the pressure sensor 25, the carbon dioxide sensor 26, and the temperature sensor 27 is sent to the control device 90.

[0023] Returning to FIG. 1 , the adsorption line 101 and the fan 61 will be described. The adsorption line 101 is branched and connected to each of the reactors 11. The fan 61 is disposed at the point where the branched portions of the adsorption line 101 converge. When driven, the fan 61 generates a gas flow from "intake" to "exhaust" through the adsorption line 101 to the reactor 11. This supplies atmospheric air into the reactor 11. A carbon dioxide concentration sensor 611, a humidity sensor 612, and a temperature sensor 613 are disposed at the gas exhaust portion of the adsorption line 101, and measure the carbon dioxide, humidity, and temperature exhausted from the adsorption line 101. Measurement information from the carbon dioxide concentration sensor 611, the humidity sensor 612, and the temperature sensor 613 is transmitted to the control device 90.

[0024] The vacuum line 102 is branched and connected to each of the reactors 11. The vacuum pump 62 is disposed at the point where the branched portions of the vacuum line 102 converge. When the vacuum pump 62 is driven, it sucks gas from the inside of the reactor 11 through the vacuum line 102, bringing the inside of the reactor 11 into a vacuum state or a state close to a vacuum state.

[0025] The carbon dioxide line 103 is branched and connected to each of the reactors 11. At the point where the branched portions of the carbon dioxide line 103 converge, a carbon dioxide recovery pump 63, a heat exchanger 64, a separator 65, and a carbon dioxide tank 66 are arranged.

[0026] The carbon dioxide capture pump 63 applies suction force to send the carbon dioxide flowing through the carbon dioxide line 103 to the carbon dioxide tank 66. A one-way valve 631 is arranged upstream of the carbon dioxide capture pump 63 in the carbon dioxide line 103. This prevents gas from flowing back from the heat exchanger 64 side to the reactor 11 side.

[0027] The heat exchanger 64 is an intercooler that cools the high-temperature gas containing carbon dioxide recovered from the reactor 11 and separates it into gas and liquid.

[0028] The water separated into gas and liquid in the heat exchanger 64 is recovered in a separator 65. A first valve 651 and a second valve 652 are disposed in the separator 65. The first valve 651 opens and closes a path communicating with the gas phase part of the separator 65. The second valve 652 opens and closes a path communicating with the liquid phase part of the separator 65.

[0029] The carbon dioxide tank 66 stores the carbon dioxide recovered through the carbon dioxide line 103. A tank valve 661 is arranged upstream of the carbon dioxide tank 66 in the carbon dioxide line 103. The tank valve 661 is controlled to open and close by the control device 90. In addition, various sensors such as a pressure sensor 662, a flow rate sensor 663, a humidity sensor 664, a temperature sensor 665, and a carbon dioxide concentration sensor 666 are arranged between the tank valve 661 and the carbon dioxide tank 66 in the carbon dioxide line 103.

[0030] In addition to the carbon dioxide line 103, a circulation line 104 that returns ballast to the carbon dioxide capture pump 63 is connected to the carbon dioxide tank 66. A flow rate sensor 667 is disposed in the circulation line 104. In addition, the carbon dioxide tank 66 is provided with a pressure release valve 668 that releases pressure when the pressure reaches or exceeds a predetermined value.

[0031] Next, the inert gas tank 69 will be described. ２ N as an inert gas supplied from a gas cylinder 691 ２ is stored at a certain pressure or higher (for example, 980 kPa). ２ A gas cylinder valve 692 is disposed between the gas cylinders 691. The inert gas tank 69 is also provided with a pressure release valve 693 that releases pressure when the pressure reaches or exceeds a predetermined pressure. A pressure sensor 694 is disposed inside the inert gas tank 69. Pressure information measured by the pressure sensor 694 is transmitted to the control device 90.

[0032] The inert gas tank 69 is connected to the carbon dioxide line 103 via an inert gas supply line 107. An inert gas valve 695 is disposed on the inert gas supply line 107. The opening and closing of the inert gas valve 695 is controlled by the control device 90.

[0033] The heat exchanger 70 will be described with reference to Fig. 2. The heat exchanger 70 supplies thermal energy for heating the interior of each reactor 11 of the reactor 10 to a predetermined temperature when the reactor 11 performs the desorption step. The heat exchanger 70 also recovers unnecessary thermal energy when the reactor 11 performs the adsorption step.

[0034] The heat exchange device 70 of this embodiment includes a heat source circuit 80 , a cold water line 111 , a hot water line 112 , a three-way valve 30 , a bypass path 31 , and a bypass valve 32 .

[0035] The heat source circuit 80 primarily comprises a heat pump-type heat source device 81, a cold water tank 82, a hot water tank 83, a cold water-side heat source circulation pump 821, and a hot water-side heat source circulation pump 831, and performs heat exchange between a cooling heat medium flowing through the cold water line 111 and a heating heat medium flowing through the hot water line 112. The heat transfer occurring in the heat source circuit 80 cools the heat medium flowing through the cold water line 111 and heats the heat medium flowing through the hot water line 112. The heat medium is a liquid such as water. The cold water-side heat source circulation pump 821 is disposed in a cold water circulation path connecting the heat source device 81 and the cold water tank 82, and the hot water-side heat source circulation pump 831 is disposed in a hot water circulation path connecting the heat source device 81 and the hot water tank 83.

[0036] The cold water line 111 is a pipe through which cold water flows as a cooling heat medium. The cold water line 111 is branched and connected to the upstream and downstream sides of each reactor 11, connecting the cold water tank 82 to each reactor 11. Of the cold water lines 111, the line connected to the upstream side of each reactor 11 is referred to as a cold water supply line 111a, and the line connected to the downstream side of each reactor 11 is referred to as a cold water return line 111b.

[0037] The cold water supply line 111a is connected in parallel to the multiple reactors 11, and cold water can be supplied in parallel to each reactor 11. A first cold water circulation water pump 822 and a second cold water circulation water pump 823 are arranged in the cold water supply line 111a. The first cold water circulation water pump 822 and the second cold water circulation water pump 823 are, for example, cascade pumps.

[0038] Additionally, a circulation line 824 that returns from the downstream side of the second chilled water circulation water pump 823 to the upstream side is disposed in the chilled water supply line 111a. A safety valve 825 is disposed in this circulation line 824. The safety valve 825 relieves pressure when the pressure in the system between the second chilled water circulation water pump 823 and the chilled water line 111 exceeds a certain level, thereby suppressing a pressure increase. By arranging the safety valve 825, which relieves pressure in the event of a pressure abnormality in the chilled water line 111, in parallel with the second chilled water circulation water pump 823, it is possible to achieve both a high flow rate circulation by the second chilled water circulation water pump 823 and safe operation.

[0039] The cold water recovery line 111b is also connected in parallel to the plurality of reactors 11, and the recovery of cold water after cooling can also be carried out in parallel for each reactor 11.

[0040] The hot water line 112 is a pipe through which hot water as a heat medium for heating flows. The hot water line 112 is branched and connected to the upstream and downstream sides of each reactor 11, connecting the hot water tank 83 to each reactor 11. Of the hot water lines 112, the line connected to the upstream side of each reactor 11 is referred to as a hot water supply line 112a, and the line connected to the downstream side of each reactor 11 is referred to as a hot water return line 112b.

[0041] The hot water supply line 112a is connected in parallel to the multiple reactors 11, and hot water can be supplied to each reactor 11 in parallel. A first hot water circulation water pump 832 and a second hot water circulation water pump 833 are arranged in the hot water supply line 112a. The first hot water circulation water pump 832 and the second hot water circulation water pump 833 are, for example, cascade pumps. By using a cascade pump that generates a large amount of heat when driven, it is possible to further heat the heat medium passing through the first hot water circulation water pump 832 and the second hot water circulation water pump 833.

[0042] In addition, a circulation line 834 is arranged in the hot water supply line 112a, returning from the downstream side of the second hot water circulation water pump 833 to the upstream side. A safety valve 835 is arranged in this circulation line 834. The safety valve 835 relieves pressure when the pressure in the system between the second hot water circulation water pump 833 and the hot water line 112 exceeds a certain level, thereby suppressing a pressure increase. By arranging the safety valve 835, which relieves pressure in the event of an abnormality in the hot water line 112, in parallel with the second hot water circulation water pump 833, it is possible to achieve both a high flow rate circulation by the second hot water circulation water pump 833 and safe operation.

[0043] The hot water return line 112b is also connected in parallel to the plurality of reactors 11, and the hot water after heating can also be recovered in parallel for each reactor 11.

[0044] The three-way valve 30 is connected to the cold water line 111, the hot water line 112, and the reactor 11. The three-way valve 30 is disposed on each of the upstream and downstream sides of the reactor 11. The three-way valve 30 is configured to be able to select, by flow path switching, a cold water connection state in which the cold water line 111 is connected to the reactor 11, a hot water connection state in which the hot water line 112 is connected to the reactor 11, and a cut-off state in which the cold water line 111 and the hot water line 112 are cut off from the reactor 11.

[0045] The flow path switching of the three-way valve 30 is controlled by the control device 90. The heat medium is introduced into the reactor 11 through the three-way valve 30 arranged on the upstream side, and the heat medium is returned to the heat source device 81 side through the three-way valve 30 arranged on the downstream side.

[0046] The bypass path 31 is a flow path that allows the heat transfer medium to move between the reactors 11. The bypass path 31 connects two reactors 11. The reactors 11 connected by the bypass path 31 may be adjacent reactors 11 or may be reactors 11 that are not adjacent but located apart.

[0047] The bypass valve 32 is disposed in the bypass path 31. The bypass valve 32 is disposed in each of the plurality of bypass paths 31. The bypass valve 32 is controlled to open and close by the control device 90.

[0048] 4 is a schematic diagram showing a configuration related to the flow of liquid in the reactor 11 of the carbon dioxide capture device 1 of this embodiment. In the following description, the three-way valve 30 arranged upstream of the reactor 11 is referred to as the three-way valve 30a, and the three-way valve 30 arranged downstream of the reactor 11 is referred to as the three-way valve 30b.

[0049] 4, the reactor 11 includes an inlet-side flow path 33 connected to an inlet through which the heat transfer medium flows in, and an outlet-side flow path 34 connected to an outlet through which the heat transfer medium flows out. The bypass path 31 is connected to the outlet-side flow path 34 of the reactor 11 and is also connected to the inlet-side flow path 33 of another reactor 11.

[0050] A three-way valve 30a is disposed at the upstream end of the inlet flow path 33, and a three-way valve 30b is disposed at the downstream end of the outlet flow path 34. In the hot water connection state, the three-way valve 30a is connected to the hot water supply line 112a, and the three-way valve 30b is connected to the hot water return line 112b. In the cold water connection state, the three-way valve 30a is connected to the cold water supply line 111a, and the three-way valve 30b is connected to the cold water return line 111b.

[0051] The three-way valves 30a and 30b are configured to be able to adjust the flow rate. This flow rate adjustment function allows the flow rate of hot water to be adjusted when the hot water supply is connected, and the flow rate of cold water to be adjusted when the cold water supply is connected.

[0052] A temperature sensor 35 is disposed in the inlet-side flow path 33. A temperature sensor 36 and a flow rate sensor 37 are disposed in the outlet-side flow path 34. Measurement information from the temperature sensor 35, the temperature sensor 36, and the flow rate sensor 37 is transmitted to the control device 90.

[0053] Next, the control device 90 will be described. The control device 90 controls the operation of each part of the carbon dioxide capture device 1. The control device 90 controls the operation of devices used for adsorption and desorption of carbon dioxide, such as driving and stopping. The control device 90 selectively controls the timing of supplying a heat medium to each reactor 11 to heat or cool the reactors 11, so that the multiple reactors 11 repeatedly adsorb and desorb in time series.

[0054] The control device 90 controls the opening and closing of the first valve 21, the second valve 22, the third valve 23, and the fourth valve 24 provided in each reactor 11, and the opening and closing of each bypass valve 32. The control device 90 also controls the drive of the fan 61, the vacuum pump 62, the carbon dioxide capture pump 63, the first cold water circulation water pump 822, the second cold water circulation water pump 823, the first hot water circulation water pump 832, the second hot water circulation water pump 833, etc., controls the opening and closing of the safety valve 825 and the safety valve 835, and controls the heat exchange of the heat exchange device 70.

[0055] The control device 90 is a computer having, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The control device 90 may be configured as a single device or as a plurality of devices. The control device 90 may also be configured using an electric circuit such as a relay.

[0056] <Recovery of Carbon Dioxide> Next, a description will be given of the control for recovering carbon dioxide by the control device 90. The carbon dioxide recovery device 1 alternately performs an adsorption process in which the adsorbent 12 in the reactor 11 adsorbs carbon dioxide in a gas such as the air that has been taken in, and a desorption process in which the carbon dioxide adsorbed by the adsorbent 12 is desorbed, and stores the desorbed carbon dioxide in the carbon dioxide tank 66, thereby removing and recovering carbon dioxide from the air.

[0057] The adsorption process is a process in which carbon dioxide is adsorbed by the adsorbent 12 in the reactor 11. During the adsorption process, the third valve 23 and the fourth valve 24 of the reactor 11 are opened, and the first valve 21 and the second valve 22 are closed. In addition to controlling the opening and closing of the valves, the heat exchanger 70 controls the three-way valves 30a and 30b to a cold water connection state, allowing cold water to flow through the reactor 11 and cool the adsorbent 12 in the reactor 11. The fan 61 is driven, generating a gas flow from upstream to downstream, and gas containing carbon dioxide (e.g., atmospheric air) is drawn in through the third valve 23. The drawn gas passes through the adsorbent 12 in the reactor 11. At this time, the inside of the reactor 11 is cooled to room temperature (25°C) by the cold water, and the carbon dioxide in the gas is adsorbed by the adsorbent 12. Gases other than carbon dioxide, such as nitrogen and oxygen, are exhausted to the outside of the carbon dioxide recovery system 1 through the fourth valve 24 and the adsorption line 101.

[0058] The desorption process is a process of desorbing carbon dioxide from the adsorbent 12 in the reactor 11. In the desorption process, the first valve 21, the third valve 23, and the fourth valve 24 of the reactor 11 are closed, and the second valve 22 is opened. The vacuum pump 62 is operated to draw air into the reactor 11 and reduce the pressure to a vacuum or near-vacuum state (scavenging process). In addition to controlling the opening and closing of the valves, the heat exchanger 70 controls the three-way valves 30a and 30b to a hot water connection state, allowing hot water to flow through the reactor 11 to supply thermal energy and raise the temperature of the adsorbent 12 in the reactor 11 (adsorbent temperature rise). By controlling the temperature rise of the adsorbent 12, the adsorbent 12 is also heated to a predetermined temperature (e.g., 80°C) sufficient for the desorption process, and the carbon dioxide adsorbed in the adsorbent 12 is desorbed (high-temperature desorption). The second valve 22, the third valve 23 and the fourth valve 24 are closed, the first valve 21 is opened and the carbon dioxide recovery pump 63 is driven, and the carbon dioxide desorbed through the carbon dioxide line 103 is stored in the carbon dioxide tank 66.

[0059] <Desorption Process Control> The control device 90 of this embodiment controls the desorption processes by staggering the timing of the start of desorption for each reactor 11 while using a common carbon dioxide capture pump 63 for the multiple reactors 11 so that the desorption processes do not start at the same timing. In the following description, the upstream reactor 11 refers to the reactor 11 in which the desorption process is carried out first, and the downstream reactor 11 refers to the reactor 11 in which the desorption process is carried out next after the upstream reactor 11.

[0060] Desorption process control with different timing for each reactor 11 will be described with reference to Fig. 5. Fig. 5 is a graph showing the time variation of the internal pressure and the amount of desorbed carbon dioxide of each reactor 11 when desorption process control is executed in the carbon dioxide recovery device 1 of this embodiment.

[0061] 5 shows pressure changes in three of the multiple reactors 11: the first reactor 11a, the second reactor 11b, and the third reactor 11c. The first reactor 11a is the reactor 11 in which the desorption step is first performed. The second reactor 11b is the reactor 11 in which the desorption step is performed next to the first reactor 11a, and is the reactor 11 in the subsequent stage relative to the first reactor 11a, which serves as the preceding stage. The third reactor 11c is the reactor 11 in which the desorption step is performed next to the second reactor 11b, and is the reactor 11 in the subsequent stage relative to the second reactor 11b, which serves as the preceding stage.

[0062] In order to perform the desorption process with staggered timing, a desorption valve opening threshold and a scavenging start pressure threshold are set in the control device 90 .

[0063] The scavenging start pressure threshold is a suction start pressure value set for the internal pressure (inner cylinder pressure) of the reactor 11 in the preceding stage. The scavenging start pressure threshold serves as a reference for determining the timing to start the scavenging process of the desorption process in the reactor 11 in the following stage. When the internal pressure of the reactor 11 in the preceding stage falls below the scavenging start pressure threshold, the control device 90 starts the scavenging process of the reactor 11 in the following stage. If the reactor 11 in the desorption order is the nth, the scavenging process of the nth reactor 11 starts when the in-cylinder pressure of the (n-1)th reactor 11 drops to a certain scavenging start pressure threshold.

[0064] The desorption valve opening threshold is a predetermined threshold set for the internal pressure (inner cylinder pressure) of the downstream reactor 11. The desorption valve opening threshold serves as a reference for determining the timing to apply suction force by the carbon dioxide capture pump 63 to the downstream reactor 11. When water desorption begins after the start of the scavenging process and the internal pressure of the downstream reactor 11 exceeds the desorption valve opening threshold, the control device 90 controls the first valve 21, which is the desorption valve, to an open state and drives the carbon dioxide capture pump 63, so that suction force is applied to the upstream reactor 11 while also applying suction force to the downstream reactor 11.

[0065] The gas flow in each step will be described with reference to Figures 6 to 8. Figure 6 is a diagram schematically illustrating the gas flow in the first reactor 11a transitioning from the scavenging step to the adsorbent heating step and the second reactor 11b during the adsorption step. Figure 7 is a diagram schematically illustrating the gas flow in the first reactor 11a during high-temperature desorption and the second reactor 11b transitioning from the adsorption step to the scavenging step. Figure 8 is a diagram schematically illustrating the gas flow in the first reactor 11a during the desorption step and the second reactor 11b transitioning from the adsorbent heating step to high-temperature desorption. Note that in Figures 6 to 8, some components such as the third valve 23 and the fourth valve 24 are omitted from the illustration.

[0066] As shown in Fig. 6(a), the control device 90 causes the first reactor 11a, which is the upstream stage, to perform a scavenging process, and the second reactor 11b, which is the downstream stage, to perform an adsorption process. As shown in Fig. 6(b), after performing the scavenging process, the control device 90 controls the second valve 22 to a closed state, and causes the first reactor 11a to perform a heating process in which the adsorbent 12 is heated to a predetermined temperature by the heat exchanger 70. Meanwhile, the control device 90 causes the second reactor 11b to continue the adsorption process.

[0067] 7(a), when the internal pressure of the first reactor 11a exceeds the desorption valve opening threshold, the control device 90 controls the first valve 21 of the first reactor 11a to an open state and drives the carbon dioxide capture pump 63. This causes a suction force to act on the first reactor 11a, and carbon dioxide is captured in the carbon dioxide tank 66 through the carbon dioxide line 103. At this stage, the first valve 21 of the second reactor 11b is controlled to a closed state, so the first reactor 11a and the second reactor 11b are not in communication with each other.

[0068] 7(b), the control device 90 maintains the first valve 21 of the first reactor 11a in an open state and continues high-temperature desorption. On the other hand, when the internal pressure of the first reactor 11a (the upstream reactor) drops to the scavenging start pressure threshold, the control device 90 controls the second valve 22 of the second reactor 11b (the downstream reactor) to an open state and drives the vacuum pump 62. This causes the second reactor 11b to transition to the scavenging process.

[0069] 8(a), the control device 90 maintains the first valve 21 of the first reactor 11a in an open state to continue high-temperature desorption. Meanwhile, the control device 90 controls the second reactor 11b, which has already undergone the scavenging step, to perform a heating step in which the heat exchanger 70 heats the adsorbent 12 to a predetermined temperature.

[0070] At the stage shown in FIG. 8( b), the control device 90 maintains the first valve 21 of the first reactor 11a in an open state and continues high-temperature desorption. Meanwhile, when the internal pressure of the second reactor 11b, which is the latter stage, exceeds the desorption valve opening threshold, the control device 90 controls the first valve 21 of the second reactor 11b to an open state. At this stage, the first valve 21 of the first reactor 11a is also controlled to an open state, so the interiors of the first reactor 11a and the second reactor 11b are in communication with each other through the carbon dioxide line 103. As shown in FIG. 5, the internal pressure of the first reactor 11a and the internal pressure of the second reactor 11b become equal. As a result, the moisture-containing gas generated in the second reactor 11b by the desorption process moves to the first reactor 11a. In the first reactor 11a to which the moisture-containing gas has moved, the partial pressure of carbon dioxide decreases, improving desorption efficiency.

[0071] In the case of the second reactor 11b as the upstream stage and the third reactor 11c as the downstream stage, the control device 90 executes the same control as that described with reference to FIGS. 6 to 8. As shown in FIG. 5, the internal pressure of the second reactor 11b and the internal pressure of the third reactor 11c become equal, and water generated first in the third reactor 11c moves to the second reactor 11b, improving the desorption efficiency of the second reactor 11b. In this example, the internal pressure of the first reactor 11a also becomes equal to the internal pressures of the second reactor 11b and the third reactor 11c, and water is also supplied from the third reactor 11c to the first reactor 11a. In this way, carbon dioxide is captured by staggering the start timing of the desorption process of each of the multiple reactors 11. In the initial stage, the amount of carbon dioxide desorbed from the first reactor 11a gradually increases, and in the next stage, carbon dioxide is recovered not only from the first reactor 11a but also from the second reactor 11b, thereby increasing the amount of carbon dioxide desorbed, and in the next stage, carbon dioxide is recovered not only from the first reactor 11a and the second reactor 11b, but also from the third reactor 11c, thereby increasing the amount of carbon dioxide desorbed.

[0072] As described above, the carbon dioxide capture device 1 of this embodiment includes a plurality of reactors 11 each having an adsorbent 12 therein, which perform an adsorption process in which a gas containing carbon dioxide is drawn into the adsorbent 12 to adsorb the carbon dioxide, and a desorption process in which the adsorbent 12 is heated under reduced pressure to desorb carbon dioxide from the adsorbent 12; a carbon dioxide line 103 that is branched and connected to each of the reactors 11, and through which the carbon dioxide desorbed in the desorption process flows; a carbon dioxide capture pump 63 that is arranged at a portion where the branched portions of the carbon dioxide line 103 gather, and which applies a suction force to the inside of the reactor 11 through the carbon dioxide line 103; and a control device 90 that, when the internal pressure of a first reactor 11a, of the plurality of reactors 11, in which the desorption process is first performed and on which the suction force of the carbon dioxide capture pump 63 is acting, drops to a predetermined threshold value (predetermined threshold value), controls so that the suction force of the carbon dioxide capture pump 63 also applies to a second reactor 11b that is second performing the desorption process. Furthermore, in the carbon dioxide capture method of this embodiment, when the internal pressure of the first reactor 11a, in which the desorption step is performed first among the multiple reactors 11 and to which the suction force of the carbon dioxide capture pump 63 is acting, drops to a predetermined threshold (predetermined threshold), the suction force of the carbon dioxide capture pump 63 is also applied to the second reactor 11b, which is performing the desorption step second.

[0073] By configuring the carbon dioxide capture device 1 and the carbon dioxide capture method in this manner, where n is a natural number, the nth reactor 11 in the desorption order (the first reactor 11a as the preceding stage) starts the desorption process when the in-cylinder pressure of the (n-1)th reactor 11 (the second reactor 11b as the following stage) drops below a certain value. The carbon dioxide capture pump 63 shared by multiple reactors 11 prevents desorption from starting at different times. As a result, even if the (n-1)th reactor 11 is no longer desorbing water in the latter half of the desorption process, water that is generated in advance in the nth reactor 11 where the desorption process has started moves to the (n-1)th reactor 11 in the same system. The moving water reduces the carbon dioxide partial pressure inside the (n-1)th reactor 11 in the latter half of the desorption process, and the desorption rate increases. Furthermore, by maintaining the inlet pressure of the carbon dioxide capture pump 63 at a certain level or higher, it is possible to reduce the time for which the inside of the reactor 11 is maintained at a vacuum, even though no carbon dioxide is captured, and to improve the carbon dioxide capture efficiency relative to the power of the carbon dioxide capture pump 63. Thus, according to the configuration of this embodiment, it is possible to realize a carbon dioxide capture device 1 and a carbon dioxide capture method that can improve the carbon dioxide capture rate without reducing the separation efficiency.

[0074] In addition, the carbon dioxide capture device 1 of this embodiment further includes a vacuum pump 62 that reduces the pressure inside the reactor 11, and the control device 90 applies the suction force of the carbon dioxide capture pump 63 to the first reactor 11a during the desorption process, while during the desorption process of the second reactor 11b, the vacuum pump 62 is driven to reduce the pressure inside the second reactor 11b and, after the temperature of the adsorbent 12 is raised, the control device 90 also applies the suction force of the carbon dioxide capture pump 63 to the second reactor 11b.

[0075] This ensures that the inside of the first reactor 11a and the inside of the second reactor 11b are in a state of communication with each other after the desorption of water starts following the pressure reduction and temperature increase.

[0076] In addition, in this embodiment, the control device 90 controls the suction force of the carbon dioxide capture pump 63 to be applied to the second reactor 11b at the timing when the internal pressure of the second reactor 11b rises to a predetermined desorption valve opening threshold (suction start pressure value) after the adsorbent 12 has been heated during the desorption process of the second reactor 11b.

[0077] As a result, the suction force of the carbon dioxide capture pump 63 acts on the second reactor 11b at the time when water desorption begins, thereby accelerating the timing of water movement to the first reactor 11a and further improving desorption efficiency.

[0078] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and modifications. Furthermore, the effects described in the above embodiments are merely preferred effects, and the present invention is not limited to those described in the above embodiments.

[0079] REFERENCE SIGNS LIST 1 Carbon dioxide recovery device 11 Reactor 12 Adsorbent 62 Vacuum pump 63 Carbon dioxide recovery pump 64 Heat exchanger 65 Separator 70 Heat exchange device 90 Control device 102 Vacuum line 103 Carbon dioxide line

Claims

1. A carbon dioxide capture device comprising: a plurality of reactors each having an adsorbent therein, which perform an adsorption process in which a gas containing carbon dioxide is drawn into the adsorbent to adsorb the carbon dioxide, and a desorption process in which the adsorbent is heated under reduced pressure to desorb the carbon dioxide from the adsorbent; a carbon dioxide line branching off and connected to each of the reactors, through which the carbon dioxide desorbed in the desorption process flows; a carbon dioxide capture pump located where the branched portions of the carbon dioxide line converge, which applies suction force to the inside of the reactor through the carbon dioxide line; and a control device which, when the internal pressure of a first reactor, of the plurality of reactors, in which the desorption process is first performed and to which the suction force of the carbon dioxide capture pump is acting, drops to a predetermined threshold, controls the suction force of the carbon dioxide capture pump to also be applied to a second reactor performing the desorption process.

2. A carbon dioxide capture device as described in claim 1, further comprising a vacuum pump that reduces the pressure inside the reactor, wherein the control device applies the suction force of the carbon dioxide capture pump to the first reactor during the desorption process, and, during the desorption process of the second reactor, drives the vacuum pump to reduce the pressure inside the second reactor and, after raising the temperature of the adsorbent, controls the suction force of the carbon dioxide capture pump to also apply to the second reactor.

3. The carbon dioxide capture device according to claim 2, wherein the control device controls the suction force of the carbon dioxide capture pump to also act on the second reactor at the timing when the internal pressure of the second reactor rises to a predetermined suction start pressure value after the adsorbent has been heated in the desorption step of the second reactor.

4. A carbon dioxide capture method using a carbon dioxide capture device comprising: a plurality of reactors each having an adsorbent therein, which perform an adsorption step in which a gas containing carbon dioxide is drawn into the adsorbent to adsorb the carbon dioxide, and a desorption step in which the adsorbent is heated under reduced pressure to desorb the carbon dioxide from the adsorbent; a carbon dioxide line branching off and connected to each of the reactors, through which the carbon dioxide desorbed in the desorption step flows; and a carbon dioxide capture pump, which is positioned where the branched portions of the carbon dioxide line converge, and which applies suction force to the inside of the reactor through the carbon dioxide line, wherein when the internal pressure of a first reactor, of the plurality of reactors, in which the desorption step is first performed and to which the suction force of the carbon dioxide capture pump is acting, drops to a predetermined threshold, the suction force of the carbon dioxide capture pump is also applied to a second reactor, which performs the desorption step,

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