Device for Controlling the Amount of Introduced Air in a Carbon Dioxide Adsorber

Abstract

To provide an introduction air amount controller for carbon dioxide adsorber that can increase an amount of adsorption of carbon dioxide to a carbon dioxide adsorber.SOLUTION: In an introduction air amount controller for a carbon dioxide adsorber 100, the carbon dioxide adsorber 100 into which the atmosphere is introduced to let an adsorbent adsorb carbon dioxide in the atmosphere comprises: an adsorption state estimation part 252b which estimates a state of adsorption of carbon dioxide to the adsorbent; and an introduced air amount control part which decreases an amount of air introduced into the carbon dioxide adsorber 100 once it is estimated that the state of adsorption of carbon dioxide to the adsorbent reaches a balanced state.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a device for controlling the intake air volume of a carbon dioxide adsorber.

Background Art

[0002] Conventionally, a technique for separating and recovering high-concentration carbon dioxide (CO 2 ) using a solid adsorbent has been known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The technique described in Patent Document 1 above generates a CO 2 rich gas in which the carbon dioxide concentration is higher than that in the atmosphere (25 to 60 vol%), and adsorbs CO 2 onto a zeolite-based adsorbent that is not effective unless the CO 2 concentration is 30% or more. As described in Patent Document 1, when the carbon dioxide concentration is higher than that in the atmosphere, a sufficient amount of carbon dioxide is adsorbed onto the adsorbent even if the gas flow rate is low.

[0005] On the other hand, the carbon dioxide concentration in the atmosphere is very low, about 400 ppm. When trying to recover such low-concentration carbon dioxide from the atmosphere, the adsorption rate of carbon dioxide decreases if the amount of air introduced into the adsorbent is small. Therefore, in order to increase the adsorption rate, it is necessary to increase the amount of air (gas flow rate) introduced into the adsorbent.

[0006] However, when the amount of air introduced into the adsorbent is increased, there is a problem that the contact time between the adsorbent and the air decreases, particularly in the downstream region in the air flow direction, and the adsorption of carbon dioxide onto the adsorbent becomes insufficient in that region.

[0007] In view of the above problems, an object of the present disclosure is to provide an intake air amount control device for a carbon dioxide adsorber that can increase the amount of carbon dioxide adsorbed by the carbon dioxide adsorber.

Means for Solving the Problems

[0008] The gist of the present disclosure is as follows.

[0009] (1) In a carbon dioxide adsorber in which air is introduced to adsorb carbon dioxide in the atmosphere onto an adsorbent, an adsorption state estimation unit that estimates the adsorption state of carbon dioxide onto the adsorbent, and an intake air amount control unit that reduces the amount of intake air into the carbon dioxide adsorber when it is estimated that the adsorption state of carbon dioxide in the adsorbent has reached an equilibrium state. An intake air amount control device for a carbon dioxide adsorber, comprising:

Effects of the Invention

[0010] According to the present disclosure, there is provided an intake air amount control device for a carbon dioxide adsorber that can increase the amount of carbon dioxide adsorbed by the carbon dioxide adsorber.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments will be described in detail with reference to the drawings. In the following description, the same reference numerals are assigned to the same components.

[0013] FIG. 1 is a schematic diagram showing a configuration example of a carbon dioxide adsorber 100 according to one embodiment. The carbon dioxide adsorber 100 is used for recovering carbon dioxide in the atmosphere and adsorbs carbon dioxide in the atmosphere. As a technique for recovering carbon dioxide in the atmosphere, for example, that by Direct Air Capture can be mentioned. The carbon dioxide adsorber 100 is configured by filling the inside of a circular tube 102 with a pellet-shaped solid adsorbent. As the solid adsorbent, for example, those in which amines such as polyethyleneimine (PEI), polyallylamine (PAA), and tetraethylenepentamine (TEPA) are supported on silica are used.

[0014] Air (atmospheric air) is introduced into the circular pipe 102 filled with a solid adsorbent through the inlet-side opening 104. When air is introduced into the carbon dioxide adsorber 100, carbon dioxide in the air is adsorbed by the solid adsorbent inside the carbon dioxide adsorber 100. The air is discharged from the outlet-side opening 106 of the circular pipe 102.

[0015] After the carbon dioxide adsorber 100 adsorbs carbon dioxide, the adsorbed carbon dioxide is desorbed. The desorbed carbon dioxide is concentrated and buried underground. Alternatively, the desorbed carbon dioxide is used for fuel synthesis or the like.

[0016] The carbon dioxide adsorbed by the carbon dioxide adsorber 100 is desorbed by heating the carbon dioxide adsorber 100. Fig. 2 is a characteristic diagram showing the relationship between the amount of the adsorbent filled in the carbon dioxide adsorber 100 (horizontal axis) and the input energy for heating the carbon dioxide adsorber 100 (vertical axis).

[0017] At the time of desorption, in order to increase the kinetic energy of the adsorbed carbon dioxide molecules, it is necessary to heat the entire solid adsorbent filled in the carbon dioxide adsorber 100 and raise the temperature of the entire amount of the solid adsorbent to a high temperature. For this reason, as shown in Fig. 2, the greater the amount of the solid adsorbent filled in the carbon dioxide adsorber 100, the greater the input energy required for desorption. Thus, since the input energy required for desorption is determined by the amount of the solid adsorbent, if a sufficient amount of carbon dioxide is not adsorbed by the solid adsorbent, unnecessary energy will be consumed. Also, when the carbon dioxide adsorber 100 is enlarged in order to recover more carbon dioxide from the atmosphere, the input energy required for desorption also increases. Therefore, in order to effectively utilize the input energy for desorption, it is preferable to adsorb as much carbon dioxide as possible onto the solid adsorbent. Although a liquid adsorbent can be used instead of the solid adsorbent, using the solid adsorbent reduces the latent heat and sensible heat during desorption, so the input energy during desorption is further reduced.

[0018] In addition, when attempting to recover low-concentration carbon dioxide in the atmosphere, if the amount of air introduced into the adsorbent is small, the adsorption rate of carbon dioxide will be low, and it will take a long time to adsorb carbon dioxide onto the solid adsorbent, resulting in a decrease in efficiency. Therefore, it is necessary to increase the amount of air introduced into the adsorbent in order to increase the adsorption rate.

[0019] However, when air is introduced into the carbon dioxide adsorber 100 in one direction, a region where the adsorption of carbon dioxide onto the solid adsorbent becomes insufficient occurs. In particular, on the downstream side in the air flow direction, there is a tendency for the adsorption of carbon dioxide onto the solid adsorbent to be insufficient.

[0020] FIG. 3 is a characteristic diagram showing the distribution characteristics of the carbon dioxide adsorption amount according to the distance from the introduction-side opening 104 of the carbon dioxide adsorber 100, and shows the relationship between the distance (horizontal axis) along the axial direction of the circular tube 102 from the introduction-side opening 104 and the carbon dioxide adsorption amount (vertical axis) onto the solid adsorbent. The adsorption amount on the vertical axis is expressed as the adsorption amount per unit volume onto the solid adsorbent. When air is introduced into the carbon dioxide adsorber 100, the adsorption and desorption of carbon dioxide onto the solid adsorbent are repeated, and finally the adsorption state of carbon dioxide onto the solid adsorbent reaches an equilibrium state. FIG. 3 shows the adsorption amount distribution when a certain amount of time has elapsed since the introduction of air with a constant amount of air introduced into the carbon dioxide adsorber 100 per unit time (hereinafter referred to as the introduced air amount) and the adsorption state of carbon dioxide onto the solid adsorbent has reached an equilibrium state, and can be obtained experimentally, for example, according to the specifications (size, introduced air amount (flow rate), type of solid adsorbent, etc.) of the carbon dioxide adsorber 100. After reaching the equilibrium state, the adsorption amount does not increase or decrease even if air is continuously introduced with the same introduced air amount. As shown in FIG. 1, the distance along the axial direction of the circular tube 102 between the introduction-side opening 104 and the discharge-side opening 106 is D.

[0021] When air is introduced into the carbon dioxide adsorber 100, carbon dioxide is gradually adsorbed onto the solid adsorbent along the air flow direction from the side close to the introduction-side opening 104, and the adsorption amount onto the solid adsorbent increases from the side close to the introduction-side opening 104.

[0022] As shown in FIG. 3, when in an equilibrium state, in the region within a distance d from the introduction-side opening 104, a sufficient amount of carbon dioxide is adsorbed onto the solid adsorbent, and the adsorption amount is almost saturated. Further, in the region beyond the distance d from the introduction-side opening 104, the adsorption amount decreases as the distance from the introduction-side opening 104 increases, and the adsorption amount becomes 0 at the discharge-side opening 206 at a distance D from the introduction-side opening 104.

[0023] On the side closer to the introduction-side opening 104, since there is sufficient time for the introduced air to contact the solid adsorbent when flowing through the circular pipe 102, the adsorption onto the solid adsorbent is promoted. Therefore, when the equilibrium state is reached, in the region within a distance d from the introduction-side opening 104, a sufficient amount of carbon dioxide is adsorbed onto the solid adsorbent. On the other hand, in the region beyond the distance d from the introduction-side opening 104, that is, in the region closer to the discharge-side opening 106, the closer to the discharge-side opening 106, the less time the air contacts the solid adsorbent. For this reason, carbon dioxide is discharged from the discharge-side opening 206 before being adsorbed onto the solid adsorbent, so the adsorption amount decreases as it gets closer to the discharge-side opening 106.

[0024] As described above, according to the distribution characteristics of the carbon dioxide adsorption amount corresponding to the distance from the introduction-side opening 104, the carbon dioxide adsorption amount onto the solid adsorbent is not uniform along the axial direction of the circular pipe 102, and an inflection point occurs at the position of the distance d from the introduction-side opening 104. Downstream of the position of the distance d from the introduction-side opening 104, the carbon dioxide adsorption onto the solid adsorbent becomes insufficient. Thus, when the equilibrium state is reached, if there is a region where the carbon dioxide adsorption amount onto the solid adsorbent is small, as a result, the amount of carbon dioxide that can be recovered from the atmosphere decreases. Also, if there is a region where the carbon dioxide adsorption amount onto the solid adsorbent is small, as described above, unnecessary energy is consumed during desorption.

[0025] FIG. 4 is a characteristic diagram showing the relationship between the flow rate of the atmosphere introduced into the carbon dioxide adsorber 100 (horizontal axis) and the amount of carbon dioxide adsorbed on the solid adsorbent (vertical axis). The adsorbed amount on the vertical axis is expressed as the adsorbed amount per unit volume on the solid adsorbent at a position at a predetermined distance from the introduction-side opening 104, for example. As shown in FIG. 4, the adsorbed amount decreases as the flow rate increases. This is because the time for the air to contact the solid adsorbent decreases as the flow rate increases. Therefore, when the flow rate is lowered and the introduced air amount is reduced, the contact time between the air and the solid adsorbent increases, and the adsorbed amount increases.

[0026] In the present embodiment, in order to increase the amount of carbon dioxide adsorbed on the solid adsorbent on the downstream side in the air flow direction in the carbon dioxide adsorber 100, the amount of the atmosphere introduced into the carbon dioxide adsorber 100 (introduced air amount) is changed according to the adsorption state of carbon dioxide on the solid adsorbent. Specifically, after starting the introduction of the atmosphere into the carbon dioxide adsorber 100, when the equilibrium state shown in FIG. 3 is reached, the introduced air amount (flow rate) into the carbon dioxide adsorber 100 is decreased. As a result, in the region beyond the distance d from the introduction-side opening 104, the time for the introduced air to contact the solid adsorbent increases, so that the amount of carbon dioxide adsorbed on the solid adsorbent increases. Therefore, even in the region beyond the distance d from the introduction-side opening 104, carbon dioxide is sufficiently adsorbed on the solid adsorbent, and the amount of carbon dioxide adsorbed on the solid adsorbent is almost saturated throughout the carbon dioxide adsorber 100.

[0027] FIG. 5 is a timing chart showing the control of the introduced air amount according to the adsorption state of carbon dioxide on the solid adsorbent according to the present embodiment. In FIG. 5, the states of change over time of the amount of carbon dioxide adsorbed on the carbon dioxide adsorber 100, the amount of the introduced air into the carbon dioxide adsorber 100, and the differential pressure of the pressures at the introduction-side opening 104 and the discharge-side opening 106 are shown in order from the top.

[0028] As shown in FIG. 5, when the introduction of air into the carbon dioxide adsorber 100 is started at time t0, the amount of carbon dioxide adsorbed by the carbon dioxide adsorber 100 increases in proportion to the passage of time. At the beginning of the start of air introduction, the introduced air volume is set to a constant value.

[0029] Thereafter, when the equilibrium state shown in FIG. 3 is reached at time t1, control is performed to reduce the introduced air volume into the carbon dioxide adsorber 100. More specifically, the introduced air volume is decreased as time elapses from time t1. As a result, after reaching the equilibrium state at time t1, the adsorption of carbon dioxide is promoted in a region beyond the distance d from the introduction-side opening 104. Therefore, the amount of carbon dioxide adsorbed shown in FIG. 5 also increases after time t1.

[0030] Thereafter, at time t2, carbon dioxide is adsorbed up to the discharge-side opening 106 in a region beyond the distance d from the introduction-side opening 104, and the amount of carbon dioxide adsorbed by the solid adsorbent is almost saturated throughout the carbon dioxide adsorber 100. As a result, the introduction of air into the carbon dioxide adsorber 100 is stopped, and the recovery of carbon dioxide in the atmosphere by the carbon dioxide adsorber 100 is completed.

[0031] Whether or not the equilibrium state shown in FIG. 3 is reached at time t1 is estimated by whether or not the differential pressure between the introduction-side opening 104 and the discharge-side opening 106 has reached the threshold value TH. Since carbon dioxide is trapped and adsorbed in the micropores of the solid adsorbent, the greater the adsorption amount, the lower the fluidity when air passes through the carbon dioxide adsorber 100, and a pressure increase occurs inside the carbon dioxide adsorber 100. For this reason, as the adsorption amount increases and carbon dioxide accumulates inside the carbon dioxide adsorber 100, the differential pressure between the introduction-side opening 104 and the discharge-side opening 106 increases. Therefore, the adsorption state of carbon dioxide in the carbon dioxide adsorber 100 is represented by the differential pressure between the introduction-side opening 104 and the discharge-side opening 106, and the greater the adsorption amount of carbon dioxide, the higher the differential pressure. As the value of the threshold TH, the differential pressure between the introduction-side opening 104 and the discharge-side opening 106 when the equilibrium state shown in FIG. 3 is reached is obtained in advance by experiments or the like. Since the characteristics shown in FIG. 3 vary depending on the specifications of the carbon dioxide adsorber 100 (size, introduced air volume (flow rate), type of solid adsorbent, etc.), it is preferable to obtain the value of the threshold TH in advance according to the specifications of the carbon dioxide adsorber 100. When obtaining the value of the threshold TH experimentally, whether or not the equilibrium state shown in FIG. 3 is reached can be determined by whether or not the adsorption amount of carbon dioxide stops increasing with the introduction amount of air into the carbon dioxide adsorber 100 kept constant.

[0032] Also, since the greater the integrated value of the introduced air volume into the carbon dioxide adsorber 100, the greater the adsorption amount of carbon dioxide on the solid adsorbent, whether or not the equilibrium state at time t1 is reached may be estimated by whether or not the integrated value of the introduced air volume has reached a predetermined threshold value. Also in this case, as the predetermined threshold value, the integrated value of the introduced air volume when the equilibrium state shown in FIG. 3 is reached is obtained in advance by experiments or the like.

[0033] As described above, when attempting to recover low-concentration carbon dioxide in the atmosphere, it is necessary to increase the amount of introduced air to the adsorbent in order to increase the adsorption rate. For this reason, until reaching the equilibrium state shown in FIG. 3, by making the amount of introduced air relatively large, the adsorption rate increases, and carbon dioxide is adsorbed in the region within a distance d or less from the introduction-side opening 104 in a relatively short time. Then, when the equilibrium state is reached, since the adsorption amount is insufficient in the region exceeding the distance d from the introduction-side opening 104, by reducing the amount of introduced air, the adsorption of carbon dioxide in the region exceeding the distance d from the introduction-side opening 104 is promoted. As a result, carbon dioxide is sufficiently adsorbed throughout the solid adsorbent, and no region with a reduced adsorption amount occurs, so the recovery amount of carbon dioxide increases. Also, since the input energy during desorption is optimized to a value corresponding to the adsorption amount, wasteful consumption of energy when desorbing the adsorbed carbon dioxide is suppressed.

[0034] FIG. 6 is a schematic diagram showing a configuration example of a carbon dioxide recovery system 200 that performs the above-described control. The carbon dioxide recovery system 200 includes an inlet-side pressure sensor 210 that detects the pressure of air introduced into the inside of the circular pipe 102 from the introduction-side opening 104, an outlet-side pressure sensor 220 that detects the pressure of air discharged from the inside of the circular pipe 102 to the outside through the discharge-side opening 106, a flow rate sensor 230 that detects the flow rate of air introduced into the carbon dioxide adsorber 100, and a flow rate control device 240 that controls the amount of introduced air to the carbon dioxide adsorber 100, and a control device 250.

[0035] The flow rate control device 240 is provided in the vicinity of the introduction-side opening 104 (for example, on the upstream side of the introduction-side opening 104), and is composed of a fan that controls the flow rate of air introduced into the inside of the circular pipe 102, a flow rate control valve (electromagnetic valve), or the like.

[0036] The control device 250 is an aspect of the intake air amount control device of the carbon dioxide adsorber, and includes a processor 252, a memory 254, and a communication interface 256. The processor 252 includes one or more CPUs (Central Processing Unit) and its peripheral circuits. The processor 252 may further include other arithmetic circuits such as a logic arithmetic unit, a numerical arithmetic unit, or a graphic processing unit. The memory 254 includes, for example, a volatile semiconductor memory and a non-volatile semiconductor memory. The memory 254 stores various information such as the above-mentioned threshold value TH. The communication interface 256 has an interface circuit for connecting the control device 250 to the inlet side pressure sensor 210, the outlet side pressure sensor 220, the flow rate sensor 230, and the flow rate control device 240.

[0037] FIG. 7 is a schematic diagram showing a functional block of the processor 252 of the control device 250 for realizing the above control. The processor 252 includes an acquisition unit 252a, an adsorption state estimation unit 252b, and an intake air amount control unit 252c. Each of these units included in the processor 252 is a functional module realized by, for example, a computer program operating on the processor 252. That is, the functional block of the processor 252 is composed of the processor 252 and a program (software) for operating it. Further, the program may be recorded in the memory 254 provided in the control device 250 or a recording medium connected externally. Alternatively, each of these units included in the control device 250 may be a dedicated arithmetic circuit provided in the processor 252.

[0038] The acquisition unit 252a of the processor 252 acquires the pressure of the air introduced into the inside of the circular pipe 102 from the introduction side opening 104 detected by the inlet side pressure sensor 210, the pressure of the air discharged to the outside of the circular pipe 102 from the discharge side opening 106 detected by the outlet side pressure sensor 220, and the flow rate of the air introduced into the carbon dioxide adsorber 100 detected by the flow rate sensor 230.

[0039] The adsorption state estimation unit 252b of the processor 252 estimates the adsorption state of carbon dioxide on the adsorbent in the carbon dioxide adsorber 100 that introduces air and adsorbs carbon dioxide in the air to the adsorbent. Specifically, when the differential pressure between the pressure detected by the inlet side pressure sensor 210 and the pressure detected by the outlet side pressure sensor 220 reaches the threshold value TH, the adsorption state estimation unit 252b estimates that the adsorption state of carbon dioxide in the solid adsorbent has reached an equilibrium state. Further, the adsorption state estimation unit 252b may estimate that the adsorption state of carbon dioxide in the solid adsorbent has reached an equilibrium state when the integrated value of the introduced air amount reaches a predetermined threshold value based on the flow rate of the air introduced into the carbon dioxide adsorber 100 detected by the flow rate sensor 230.

[0040] When it is estimated that the adsorption state of carbon dioxide in the adsorbent has reached an equilibrium state, the introduced air amount control unit 252c of the processor 252 reduces the amount of air introduced into the carbon dioxide adsorber 100. Specifically, when the adsorption state of carbon dioxide in the adsorbent reaches an equilibrium state, the introduced air amount control unit 252c controls the flow rate control device 240 so as to reduce the amount of air introduced into the carbon dioxide adsorber 100. Thereby, the rotation speed of the fan constituting the flow rate control device 240 is decreased, and the amount of air introduced into the carbon dioxide adsorber 100 is reduced. Further, when the flow rate control device 240 is composed of a flow rate control valve, the opening degree of the valve is decreased, and the amount of air introduced into the carbon dioxide adsorber 100 is reduced.

[0041] (Modification example) FIG. 8 is a schematic diagram showing the configuration of the carbon dioxide adsorber 100 according to the modification example. The carbon dioxide adsorber 100 according to the modification example is configured by filling solid adsorbents with different diameters as pellet-shaped ones.

[0042] As shown in FIG. 8, in the region at a distance D1 from the introduction side opening 104, solid adsorbents with a diameter of A [mm] are filled. Also, in the region at a distance D2 from the discharge side opening 106, solid adsorbents with a diameter of B [mm] are filled. Note that there is a relationship of D (the distance along the axial direction of the circular tube 102 between the introduction side opening 104 and the discharge side opening 106) = D1 + D2.

[0043] The diameter of the solid adsorbent is made larger in the region of the upstream distance D1 in the air flow direction than in the region of the downstream distance D2. That is, there is a relationship of diameter A > diameter B. The smaller the diameter of the solid adsorbent, the easier it is for carbon dioxide to be adsorbed onto the solid adsorbent, and the adsorption amount of carbon dioxide increases. Therefore, by arranging a solid adsorbent with a small diameter in the region where the adsorption amount decreases on the downstream side in the flow direction, the decrease in the adsorption amount is suppressed, and the adsorption amount of carbon dioxide to the carbon dioxide adsorber 100 increases.

[0044] As described above, according to the present embodiment, when the adsorption state of carbon dioxide in the solid adsorbent reaches an equilibrium state according to the adsorption state of carbon dioxide in the carbon dioxide adsorber 100, the amount of introduced air into the carbon dioxide adsorber 100 is decreased. Therefore, particularly on the downstream side in the air flow direction in the carbon dioxide adsorber 100, the adsorption amount of carbon dioxide can be increased. As a result, the amount of carbon dioxide that can be recovered from the atmosphere increases, and the wasteful consumption of energy when desorbing the adsorbed carbon dioxide is suppressed.

Explanation of Reference Numerals

[0045] 100 Carbon dioxide adsorber 102 Circular tube 104 Introduction side opening 106 Discharge side opening 200 Carbon dioxide recovery system 210 Inlet side pressure sensor 220 Outlet side pressure sensor 230 Flow rate sensor 240 Flow rate control device 250 Control device 252 Processor 252a Acquisition unit 252b Adsorption state estimation unit 252c Introduced air amount control unit 254 Memory 256 Communication interface

Claims

【Claim 1】 In a carbon dioxide adsorber that introduces air and adsorbs carbon dioxide in the air to an adsorbent, an adsorption state estimation unit that estimates the adsorption state of carbon dioxide to the adsorbent, and Before the adsorption state of carbon dioxide in the adsorbent reaches an equilibrium state, the amount of introduced air to the carbon dioxide adsorber is set to a constant value, and when it is estimated that the adsorption state of carbon dioxide in the adsorbent has reached an equilibrium state, the amount of introduced air to the carbon dioxide adsorber is decreased as time elapses from the time when it is estimated that the equilibrium state has been reached. An introduced air amount control unit; An apparatus for controlling the introduced air amount of a carbon dioxide adsorber, comprising the same.

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