Carbon dioxide recovery device

Abstract

To provide a carbon dioxide recovery device capable of preventing or suppressing absorption efficiency for carbon dioxide from decreasing.SOLUTION: A control device 27 of a carbon dioxide recovery device 10 comprises a first map of absorption efficiency for carbon dioxide to combinations of a flow rate of carbon dioxide included in an object gas flowing in a carbon dioxide absorption tower 11, flow rates of carbon dioxide absorption solutions supplied to gas-liquid contact parts 53, 56 of respective stages, and the rotational frequencies of the gas-liquid contact parts 53, 56 of the respective stages, searches the first map for a combination such that the absorption efficiency for carbon dioxide reaches a target value or larger when the absorption efficiency for carbon dioxide corresponding to a current combination is less than the target value, and then changes at least one of the flow rates of the carbon dioxide absorption solutions and the rotational frequencies of the gas-liquid contact parts 53, 56 of the respective stages so as to set to the combination having been searched for.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a carbon dioxide recovery device.

Background Art

[0002] The carbon dioxide recovery device disclosed in Patent Document 1 includes a substantially cylindrical gas-liquid contact part (described as a rotating drum in Patent Document 1) configured to allow fluid to pass therethrough in the radial direction, and a nozzle configured to be able to inject a carbon dioxide absorption solution toward the inner peripheral surface of the gas-liquid contact part. And this carbon dioxide recovery device is configured such that the carbon dioxide absorption solution injected from the nozzle toward the inner peripheral surface of the gas-liquid contact part moves from the inner peripheral side to the outer peripheral side of the gas-liquid contact part by the centrifugal force of the rotation of the gas-liquid contact part. For this reason, when gas (engine exhaust gas in Patent Document 1) flows from the outer side to the inner side in the radial direction of the gas-liquid contact part, the gas and the carbon dioxide absorption solution undergo countercurrent contact in the gas-liquid contact part, and the carbon dioxide contained in the gas is absorbed by the carbon dioxide absorption solution.

[0003] By the way, in order to increase the absorption efficiency of carbon dioxide (the ratio of the amount of carbon dioxide absorbed by the carbon dioxide absorption solution to the amount of carbon dioxide contained in the inflowing gas) in such a carbon dioxide recovery device, it is important to control the gas-liquid contact area of the gas-liquid contact part (gas and carbon dioxide absorption liquid) and the ratio (L / G ratio) of the carbon dioxide absorption liquid flow rate to the gas flow rate. For this reason, in order to increase the absorption efficiency of carbon dioxide, it is required to operate at an optimal L / G ratio and to maintain a state in which the carbon dioxide absorption solution is held in the gas-liquid contact part (specifically, a state in which a film of the carbon dioxide absorption solution is formed over a wide range of the surface of the gas-liquid contact part). However, Patent Document 1 does not disclose a configuration for holding the carbon dioxide absorption solution in the gas-liquid contact part (rotating drum) (in other words, a configuration for forming a film of the carbon dioxide absorption liquid on the surface of the gas-liquid contact part), and the efficiency of carbon dioxide absorption in the gas-liquid contact part cannot be improved, and there is no description about the control of the optimal L / G ratio and the rotation speed.

[0004] Most of the carbon dioxide absorption devices currently in practical use employ the chemical absorption method. These devices are equipped with an absorption tower for absorbing carbon dioxide and a desorption tower for desorbing carbon dioxide. The carbon dioxide absorption liquid is supplied while being allowed to fall by gravity into the absorption tower, and the gas is supplied in a countercurrent flow to bring about gas-liquid contact, thereby absorbing the carbon dioxide contained in the gas.

[0005] However, for these absorption devices as well, the configuration for holding the carbon dioxide absorption solution (in other words, the configuration for forming a film of the carbon dioxide absorption liquid on the surface of the gas-liquid contact portion) has a film thickness determined by the material properties of the absorption solution, gravity, and gas pressure, and it is difficult to control the liquid film thickness and the gas-liquid contact area. Therefore, it is necessary to optimize the gas-liquid contact area using tower packings. That is, it leads to an increase in the size of the device. Also, if an attempt is made to downsize the device, the absorption efficiency of carbon dioxide will decrease and the desorption energy (heat) will increase.

[0006] In a rotary carbon dioxide absorption device, when assuming the actual operation from the start of operation to the steady state, it is difficult to judge whether the steady state has been reached. Also, it is difficult to judge the behavior of the absorption efficiency decreasing even in the steady state.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

[0008] (Problems to be Solved by the Invention) In view of the above circumstances, one of the objects of the present invention is to provide a carbon dioxide recovery device that can maintain a state in which a carbon dioxide absorption solution is held in the gas-liquid contact portion (specifically, a state in which a film of the carbon dioxide absorption solution is formed over a wide range of the surface of the gas-liquid contact portion). It can maintain a good steady state from the start of operation, can maintain the absorption efficiency of carbon dioxide, and leads to suppression of desorption energy.

[0009] (Means for Solving the Problem) To achieve the above object, the carbon dioxide recovery apparatus according to the present invention is a carbon dioxide recovery apparatus including a carbon dioxide absorption tower configured to absorb carbon dioxide contained in a target gas into a carbon dioxide absorption solution, a gas-liquid contact part disposed inside the carbon dioxide absorption tower, configured such that the carbon dioxide absorption solution can penetrate therein and the target gas can pass therethrough, and configured to rotate by the driving force of a driving force source; a solution supply part configured to supply the carbon dioxide absorption solution to the gas-liquid contact part; a control device configured to control the driving force source and the solution supply part; a map defining the absorption efficiency of carbon dioxide according to a combination of the flow rate per unit time of the target gas fed to the carbon dioxide absorption tower, the flow rate per unit time of the carbon dioxide absorption solution supplied to the gas-liquid contact part, and the rotation speed of the gas-liquid contact part; and includes. The map also includes a logical formula based on the above-described variables.

[0010] And the control device identifies the absorption efficiency of carbon dioxide by applying at least the flow rate of carbon dioxide contained in the target gas flowing inside the carbon dioxide absorption tower, the flow rate of the carbon dioxide absorption solution supplied to the gas-liquid contact part, and the rotation speed of the gas-liquid contact part to the map. When the identified absorption efficiency of carbon dioxide is less than a preset target value, the control device searches for a combination of the flow rate per unit time of the target gas fed to the carbon dioxide absorption tower, the flow rate per unit time of the carbon dioxide absorption solution supplied to the gas-liquid contact part, and the rotation speed of the gas-liquid contact part such that the absorption efficiency of carbon dioxide becomes equal to or higher than the target value from the map, and controls at least one of the driving force source and the solution supply part so as to achieve the searched combination.

[0011] According to the carbon dioxide recovery device of the present invention, it is possible to prevent or suppress the carbon dioxide absorption efficiency (the ratio indicating the amount of absorbed carbon dioxide to the amount of carbon dioxide contained in the target gas) from falling below a preset target value.

[0012] According to the carbon dioxide recovery device of the present invention, since it can be supplied with the minimum required liquid flow rate described in the map in order to reach the target carbon dioxide absorption efficiency, it is possible to prevent an increase in the heat dissipation energy (heat) generated when carbon dioxide is released from the carbon dioxide absorption liquid.

[0013] By supplying the carbon dioxide absorption solution to the gas-liquid contact part at the minimum required liquid flow rate, the pump power can be minimized.

[0014] When the performance deteriorates compared to the target value set from the map, the control device can detect that there is an abnormality in any of the sensing of the flow rate of carbon dioxide contained in the target gas flowing inside the carbon dioxide absorption tower, the flow rate of the carbon dioxide absorption solution supplied to the gas-liquid contact part, and the rotation speed of the gas-liquid contact part.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described. In the following description, the carbon dioxide recovery device will be abbreviated as "recovery device", the carbon dioxide absorption tower will be abbreviated as "absorption tower", the carbon dioxide stripping tower (sometimes referred to as "carbon dioxide regeneration tower") will be abbreviated as "stripping tower", and the carbon dioxide absorption solution may be abbreviated as "solution". Further, the gas that is the target of carbon dioxide recovery by the recovery device (that is, the gas containing carbon dioxide) may be referred to as "target gas". Further, in the following description, the "flow rate" of the target gas, carbon dioxide, and solution means the flow rate per unit time unless otherwise specified.

[0017] A device or facility that generates a gas containing carbon dioxide is applied to the target gas source 90. For example, as the target gas source 90, a metal melting furnace and a carburizing furnace that utilize the combustion heat of fossil fuels (that is, use fossil fuels as fuel) can be applied. In this case, the combustion exhaust gas of fossil fuels is the target gas. Further, an aqueous amine solution is applied to the solution.

[0018] <Configuration of the Recovery Device> FIG. 1 is a schematic diagram showing the configuration of the recovery device 10. The recovery device 10 includes an absorption tower 11, a stripping tower 12, a target gas introduction path 13, a target gas flow meter 14, a carbon dioxide concentration meter 15, a target gas pump 16, a target gas discharge path 17, a first solution path 18, a second solution path 19, a first solution pump 20, a second solution pump 21, a solution heat exchanger 22, a reboiler 23, a carbon dioxide recovery path 24, a solution cooler 25, an inlet solution flow meter 26, and a control device 27.

[0019] The absorption tower 11 is configured such that, by bringing the solution into gas-liquid contact with the target gas, the solution absorbs carbon dioxide (in other words, carbon dioxide is removed from the target gas). Inside the absorption tower 11, an upper target gas chamber 31, an upper absorption chamber 32, an intermediate solution chamber 33, an intermediate target gas chamber 34, and a lower absorption chamber 35 are provided in this order from the top. Further, inside the absorption tower 11, a rotating body 36 that rotates by the driving force of a driving force source 41 is arranged. The rotating body 36 includes an upper gas-liquid contact part 53 arranged in the upper absorption chamber 32 and a lower gas-liquid contact part 56 arranged in the lower absorption chamber 35. Each stage of the gas-liquid contact parts 53, 56 is a part for promoting the gas-liquid contact between the solution and the target gas. The detailed configurations of the absorption tower 11 and the rotating body 36 will be described later.

[0020] The target gas introduction path 13 is a path for feeding the target gas generated in the target gas source 90 to the absorption tower 11. One end of the target gas introduction path 13 is connected to the absorption tower 11, and the other end is connected to the target gas source 90. A target gas pump 16, a target gas flow meter 14, and a carbon dioxide concentration meter 15 are provided on the target gas introduction path 13. The target gas pump 16 is configured to feed (pressure-feed) the target gas on the other end side of the target gas introduction path 13 (the target gas generated in the target gas source 90) to the one end side (the absorption tower 11) of the target gas introduction path 13 when it operates. A known electric air supply pump can be applied to the target gas pump 16. The target gas flow meter 14 is configured to measure the flow rate of the target gas flowing through the target gas introduction path 13 (that is, the flow rate of the target gas fed to the absorption tower 11). The carbon dioxide concentration meter 15 is configured to measure the carbon dioxide concentration of the target gas flowing through the target gas introduction path 13.

[0021] The target gas discharge path 17 is a path for discharging the target gas (sometimes referred to as off-gas) after carbon dioxide has been absorbed in the absorption tower 11 to the outside of the absorption tower 11. One end of the target gas discharge path 17 is connected to the upper end portion of the absorption tower 11, and the other end is, for example, open to the atmosphere.

[0022] The first solution path 18 is a path for feeding the solution from the absorption tower 11 to the stripping tower 12. One end of the first solution path 18 is connected to the absorption tower 11, and the other end is connected to the stripping tower 12. The first solution pump 20 and the solution heat exchanger 22 are arranged on the first solution path 18. The first solution pump 20 is configured to feed the solution from the absorption tower 11 toward the stripping tower 12 by operating. The configuration of the first solution pump 20 is not particularly limited, and various conventionally known electric liquid feeding pumps can be applied. The solution heat exchanger 22 is configured to perform heat exchange between the solution flowing through the first solution path 18 and the solution flowing through the second solution path 19. By performing heat exchange between the solution flowing through the first solution path 18 and the solution flowing through the second solution path 19 in the solution heat exchanger 22, the solution flowing through the first solution path 18 is heated, and the solution flowing through the second solution path 19 is cooled. Note that the configuration of the solution heat exchanger 22 is not limited, and various conventionally known heat exchangers can be applied.

[0023] The stripping tower 12 is configured such that carbon dioxide is stripped from the solution (a reaction in which the solution strips carbon dioxide occurs) by heating the solution. Inside the stripping tower 12, an upper packing 121 and a lower packing 122 are arranged. Both the upper packing 121 and the lower packing 122 are members through which the solution can penetrate and gas (vapor and carbon dioxide) can pass, and for example, porous metals or mesh-like members with a large specific surface area are applicable. The lower packing 122 is a member for promoting gas-liquid contact between the solution and the vapor generated by heating the solution. The upper packing 121 is arranged near the top of the stripping tower 12, and the lower packing 122 is arranged below it. The other end of the first solution path 18 is connected between the upper packing 121 and the lower packing 122 at the upper part of the stripping tower 12, and the other end of the second solution path 19 is connected below the lower packing 122 at the bottom (or in the vicinity thereof) of the stripping tower 12. Note that the configuration of the stripping tower 12 is not particularly limited, and a conventionally known configuration can be applied.

[0024] The reboiler 23 is configured to generate steam at a predetermined temperature (specifically, a temperature capable of heating the solution fed to the stripping tower 12 to a temperature at which a reaction for stripping carbon dioxide occurs) by heating the solution accumulated inside (bottom) of the stripping tower 12. The reboiler 23 is connected to the bottom of the stripping tower 12 via a first reboiler path 231 and a second reboiler path 232. Then, the reboiler 23 heats the solution flowing in through the first reboiler path 231 to generate steam. The steam generated in the reboiler 23 flows into the inside of the stripping tower 12 via the second reboiler path 232.

[0025] One end of the carbon dioxide recovery path 24 is connected above the upper packing 121 at or near the top of the stripping tower 12. On the carbon dioxide recovery path 24, a demister 45, a mixed gas cooler 46, and a gas-liquid separator 47 are arranged in order from the side closer to the stripping tower 12. The demister 45 is configured to remove the mist of the solution vapor from the mixed gas of the solution vapor and carbon dioxide, and return the condensed water generated by the removed mist to the stripping tower 12. The mixed gas cooler 46 is configured to liquefy the solution vapor by cooling the mixed gas of the solution vapor and carbon dioxide. The gas-liquid separator 47 is configured to separate the solution and carbon dioxide generated by the liquefaction of the vapor. According to such a configuration, gaseous carbon dioxide can be separated from the mixed gas of the solution vapor and carbon dioxide flowing into the carbon dioxide recovery path 24. The separated carbon dioxide is discharged (recovered) to the outside of the recovery device 10. The gas-liquid separator 47 and the stripping tower 12 are connected by a solution reflux path 43. This solution reflux path 43 is configured such that the solution separated from carbon dioxide in the gas-liquid separator 47 returns to the stripping tower 12.

[0026] The second solution path 19 is a path for feeding the solution from the stripping tower 12 to the absorption tower 11. One end of the second solution path 19 is connected to the absorption tower 11, and the other end of the second solution path 19 is connected to the bottom of the stripping tower 12. A second solution pump 21, the above-described solution heat exchanger 22, a solution cooler 25, and an inlet solution flow meter 26 are provided on the second solution path 19.

[0027] The second solution pump 21 is an example of the solution supply section of the present invention. By operating, the second solution pump 21 is configured to feed the solution accumulated inside (specifically, at the bottom) of the stripping tower 12 to the absorption tower 11 through the second solution path 19. A known electric liquid feed pump can be applied to the second solution pump 21. The solution cooler 25 is configured to adjust the temperature (cool) of the solution fed to the absorption tower 11 to the temperature at which the reaction of absorbing carbon dioxide occurs. Various known coolers are applied to the solution cooler 25. The inlet solution flowmeter 26 is configured to measure the flow rate of the solution flowing through the second solution path 19, in other words, the flow rate of the solution supplied to the gas-liquid contact section 53 in the upper stage of the stripping tower 12.

[0028] The control device 27 is connected to the driving power sources 41 of the target gas pump 16, the first solution pump 20, the second solution pump 21, the reboiler 23, the intermediate solution pump 39 (described later), and the rotating body 36, and can control these. Further, the control device 27 is connected to the target gas flowmeter 14, the carbon dioxide concentration meter 15, the inlet solution flowmeter 26, and the intermediate solution flowmeter 40 (described later), and can acquire the measurement results by these. The control device 27 is a device including a computer equipped with a CPU, a RAM, a ROM, a storage device (memory device), and an I / F. A computer program for controlling each part of the recovery device 10 is stored in advance in the ROM. Then, the CPU reads out the computer program stored in the ROM, expands it in the RAM (uses the RAM as a work area), and executes it. Thereby, each part of the recovery device 10 is controlled.

[0029] <Basic operation of the recovery device> Next, the basic operation of the recovery device 10 will be described. The target gas generated at the target gas source 90 is fed (pumped) into the inside of the absorption chamber 35 at the lower stage of the absorption tower 11 by the operation of the target gas pump 16. The target gas flowing into the inside of the absorption chamber 35 at the lower stage sequentially passes through the absorption chamber 35 at the lower stage, the intermediate target gas chamber 34, the intermediate target gas path 38, the absorption chamber 32 at the upper stage, and the upper target gas chamber 31, and is discharged to the outside of the absorption tower 11 through the target gas discharge path 17. Further, the solution temperature-controlled (cooled) to a temperature suitable for carbon dioxide absorption in the solution heat exchanger 22 and the solution cooler 25 flows into the absorption chamber 32 at the upper stage of the absorption tower 11 through the second solution path 19 by the operation of the second solution pump 21. The solution flowing into the inside of the absorption chamber 32 at the upper stage sequentially passes through the absorption chamber 32 at the upper stage, the intermediate solution path 37, and the intermediate solution chamber 33, and then flows into the absorption chamber 35 at the lower stage and accumulates at the bottom of the absorption chamber 35 at the lower stage. Then, in the gas-liquid contact portions 53 and 56 at each stage arranged in the absorption chambers 32 and 35 at each stage, the target gas and the solution are in gas-liquid contact, and carbon dioxide contained in the target gas is absorbed by the solution.

[0030] The solution accumulated at the bottom of the absorption chamber 35 at the lower stage is fed from the absorption tower 11 toward the stripping tower 12 through the first solution path 18 by the operation of the first solution pump 20. The solution flowing through the first solution path 18 is heated by exchanging heat with the solution flowing through the second solution path 19 in the solution heat exchanger 22, and then flows into the inside of the stripping tower 12.

[0031] The solution flowing into the inside of the stripping tower 12 passes through the lower packing 122 and accumulates at the bottom of the stripping tower 12. A part of the solution accumulated at the bottom of the stripping tower 12 flows into the reboiler 23 through the first reboiler path 231 and is heated by the reboiler 23. The vapor generated in the reboiler 23 flows into the inside of the stripping tower 12 through the second reboiler path 232, and then passes through the lower packing 122 while rising from the bottom of the stripping tower 12. At this time, the vapor is in gas-liquid contact (countercurrent contact) with the solution flowing down from the top in the lower packing 122. As a result, the solution flowing down through the lower packing 122 is heated, and carbon dioxide is stripped from the solution.

[0032] The mixture of carbon dioxide emitted from the solution and the vapor remaining without liquefaction passes through the upper packing material 121 and flows into the carbon dioxide recovery path 24 from the top of the emission tower 12. Note that the upper packing material 121 is a porous or mesh-like member. Therefore, when the mixture passes through the upper packing material 121, the mist contained in the mixture is removed to a certain extent.

[0033] In the demister 45 provided in the carbon dioxide recovery path 24, the vapor mist is removed from the mixture that has flowed into the carbon dioxide recovery path 24. Further, the mixture is cooled in the mixture cooler 46, so that the vapor condenses (liquefies). Then, in the gas-liquid separator 47, it is separated into carbon dioxide as a gas and a solution as a liquid. The carbon dioxide separated in the gas-liquid separator 47 is discharged to the outside through the carbon dioxide recovery path 24. That is, carbon dioxide is recovered through the carbon dioxide recovery path 24. On the other hand, the solution separated in the gas-liquid separator 47 returns to the emission tower 12 through the solution return path 43 and flows down through the upper packing material 121. As a result, the upper packing material 121 is cooled, so that the condensation of the vapor contained in the mixture passing through the upper packing material 121 is promoted.

[0034] The solution accumulated at the bottom of the emission tower 12 is fed from the emission tower 12 toward the absorption tower 11 through the second solution path 19 by the operation of the second solution pump 21. Then, the solution flowing through the second solution path 19 is cooled by exchanging heat with the solution flowing through the first solution path 18 in the solution heat exchanger 22, and is further cooled by releasing heat in the solution cooler 25. As a result, the solution reaches a temperature suitable for the absorption of carbon dioxide. Then, the solution flows into the upper absorption chamber 32 of the absorption tower 11 through the rotating body 36 described later.

[0035] In this way, due to the operations of the first solution pump 20 and the second solution pump 21, the solution circulates in the order of the absorption tower 11, the first solution path 18, the stripping tower 12, and the second solution path 19. And while the solution is circulating, it repeats the reaction of absorbing carbon dioxide contained in the target gas in the absorption tower 11 and stripping the absorbed carbon dioxide in the stripping tower 12. The carbon dioxide stripped from the solution in the stripping tower 12 is discharged from the recovery device 10 via the carbon dioxide recovery path 24.

[0036] <Configuration and Operation of Absorption Tower and Rotating Body> Next, the configuration and operation of the absorption tower 11 and the rotating body 36 will be described. FIG. 2 is a cross-sectional view showing the configuration of the absorption tower 11 and the rotating body 36. In FIG. 2, the upper part of the absorption tower 11 and the rotating body 36 is indicated by an arrow Up, and the lower part is indicated by an arrow Dw. As shown in FIG. 2, inside the absorption tower 11, an upper target gas chamber 31, an upper-stage absorption chamber 32, an intermediate solution chamber 33, an intermediate target gas chamber 34, and a lower-stage absorption chamber 35 are provided in order from the upper side. Also, a rotating body 36 is rotatably arranged inside the absorption tower 11. The rotating body 36 rotates by the driving force of a driving power source 41 arranged outside the absorption tower 11 (the lower side in FIG. 2). The driving power source 41 is controlled by the control device 27. Also, the absorption tower 11 is provided with a tachometer 42 for measuring the rotation speed of the rotating body 36 (omitted in FIG. 2; see FIG. 1). And the control device 27 can acquire the measurement result of the rotation speed of the rotating body 36 by the tachometer 42. Note that the driving power source 41 only needs to be able to output rotational power, and the configuration of the driving power source 41 is not particularly limited. Various known motors can be applied to the driving power source 41.

[0037] The absorption chambers 32 and 35 of each stage are both spaces through which the target gas and the solution can pass. Also, the absorption chambers 32 and 35 of each stage are both configured to be able to store the solution at the bottom. One end of the target gas introduction path 13 is connected to the lower absorption chamber 35, and it is configured such that the target gas fed from the target gas source 90 through the target gas introduction path 13 flows in. Also, one end of the first solution path 18 is connected to the lower absorption chamber 35, and the solution accumulated at the bottom of the lower absorption chamber 35 is configured to be fed to the stripping tower 12 through the first solution path 18. And inside the absorption chambers 32 and 35 of each stage, the gas-liquid contact parts 53 and 56 of each stage provided on the rotating body 36 and the gas-liquid separation parts 52 and 55 of each stage are rotatably arranged.

[0038] The intermediate solution chamber 33 is a space provided adjacent to the lower side of the upper absorption chamber 32. The intermediate solution chamber 33 is configured to be able to store the solution. The upper absorption chamber 32 and the intermediate solution chamber 33 are connected by an intermediate solution path 37. An intermediate solution pump 39 and an intermediate solution flow meter 40 are provided on the intermediate solution path 37 (omitted in FIG. 2; see FIG. 1). The intermediate solution pump 39 is an example of the solution supply part of the present invention. The solution accumulated in the lower part of the upper absorption chamber 32 is fed to the intermediate solution chamber 33 through the intermediate solution path 37 by the operation of the intermediate solution pump 39. The intermediate solution pump 39 is controlled by the control device 27. Note that the configuration of the intermediate solution pump 39 is not particularly limited, and various known electric liquid feed pumps are applicable. The intermediate solution flow meter 40 is configured to measure the flow rate of the solution flowing through the intermediate solution path 37, in other words, the flow rate of the solution supplied to the gas-liquid contact part 56 of the lower stage.

[0039] The intermediate target gas chamber 34 is provided so as to be adjacent to the upper side of the lower absorption chamber 35 (in other words, between the lower absorption chamber 35 and the intermediate solution chamber 33). The lower absorption chamber 35 and the intermediate target gas chamber 34 communicate with each other such that the target gas can flow through the intermediate shaft portion 54 (described later) of the rotating body 36. Also, the intermediate target gas chamber 34 and the upper absorption chamber 32 communicate with each other such that the target gas can flow through the intermediate target gas path 38. Therefore, the target gas that has flowed into the intermediate target gas chamber 34 from the lower absorption chamber 35 through the intermediate shaft portion 54 of the rotating body 36 passes through the intermediate target gas chamber 34 and flows into the upper absorption chamber 32 through the intermediate target gas path 38.

[0040] The upper target gas chamber 31 is provided so as to be adjacent to the upper side of the upper absorption chamber 32. One end of the target gas discharge path 17 is connected to the upper target gas chamber 31. Also, the upper target gas chamber 31 communicates with the upper absorption chamber 32 such that the target gas can flow through the upper shaft portion 51 (described later) provided on the rotating body 36 (described later). Therefore, the target gas that has flowed into the upper target gas chamber 31 from the upper absorption chamber 32 through the upper shaft portion 51 of the rotating body 36 passes through the inside of the upper target gas chamber 31 and flows out from the upper target gas chamber 31 (that is, from the absorption tower 11) through the target gas discharge path 17.

[0041] In this way, the upper absorption chamber 32 and the lower absorption chamber 35 are connected in series through the intermediate target gas chamber 34 and the intermediate target gas path 38 such that the target gas fed from the outside passes in a predetermined one direction (specifically, the direction from the lower absorption chamber 35 toward the upper absorption chamber 32). Also, the upper absorption chamber 32 and the lower absorption chamber 35 are connected in series through the intermediate solution chamber 33 and the intermediate solution path 37 such that the solution fed from the outside passes in the direction opposite to the predetermined one direction (specifically, the direction from the upper absorption chamber 32 toward the lower absorption chamber 35).

[0042] The rotating body 36 includes, in order from the upper side, an upper shaft portion 51, an upper gas-liquid separation portion 52, an upper gas-liquid contact portion 53, an intermediate shaft portion 54, a lower gas-liquid separation portion 55, a lower gas-liquid contact portion 56, and a lower shaft portion 57. The respective portions of the rotating body 36 are arranged coaxially and rotate integrally.

[0043] The gas-liquid contact portions 53, 56 of each stage are portions for promoting the absorption of carbon dioxide by the solution. It can also be said that the gas-liquid contact portions 53, 56 of each stage are portions for increasing the contact area between the solution and the target gas. The gas-liquid contact portions 53, 56 of each stage are configured such that the solution can penetrate and diffuse therein, and the target gas can pass through the inside. Specifically, the gas-liquid contact portions 53, 56 of each stage include a substantially cylindrical container and a packing material filled inside the container. The container is formed of a member through which the solution and the target gas can flow. For example, the container is formed of a punching metal (a metal plate with a large number of through holes). As the packing material, a member having a predetermined shape and a large specific surface area is applied. For example, as the packing material, a molded body formed by shaping a metal mesh into a predetermined shape (e.g., a round bar shape) is applied. Then, a plurality (a large number) of molded bodies (packing materials) are filled inside the container. Note that the shape and dimensions of the packing material are not particularly limited.

[0044] Note that the gas-liquid contact portions 53, 56 of each stage are configured such that the solution can penetrate into the inside from the central portion of the upper surface (the upper end portion of the substantially rotation center), and the penetrated solution can flow down (fall) from the outer peripheral surface (the surface on the outer side in the radial direction of rotation) and the lower surface. Also, the gas-liquid contact portions 53, 56 of each stage are configured such that the target gas can flow into the inside from the outer peripheral surface and the lower surface, and the target gas that has passed through the inside can flow out upward from substantially the entire upper surface.

[0045] The gas-liquid separation portions 52, 55 of each stage are portions configured to separate the solution from the target gas after passing through the gas-liquid contact portions 53, 56 of each stage (in other words, the target gas about to flow out from the absorption chambers 32, 35 of each stage). The gas-liquid separation portions 52, 55 of each stage are disposed above the gas-liquid contact portions 53, 56 of each stage. The gas-liquid separation portions 52, 55 of each stage have a reverse bottomed cylindrical configuration (dome-shaped configuration) in which the lower side is open and the outer peripheral side and the upper side are closed, and an internal space through which the target gas can pass is formed.

[0046] The upper shaft portion 51 is a portion located at the upper end of the rotating body 36. The upper shaft portion 51 is rotatably supported with respect to the absorption tower 11 via a bearing. The upper shaft portion 51 has a double-tube structure. Specifically, the upper shaft portion 51 includes a substantially cylindrical outer shaft portion 511 and an inner shaft portion 512, and the inner shaft portion 512 is disposed in the internal space of the outer shaft portion 511.

[0047] The inner shaft portion 512 is a portion configured in a cylindrical shape with both the upper end and the lower end open, and forms a path for the solution. The upper end of the inner shaft portion 512 of the upper shaft portion 51 protrudes upward from the upper end of the outer shaft portion 511 of the upper shaft portion 51 and is located outside the upper target gas chamber 31. And one end of the second solution path 19 is connected to the upper end of the inner shaft portion 512 of the upper shaft portion 51. Thus, the solution is supplied (flows in) to the inner shaft portion 512 of the upper shaft portion 51 by the operation of the second solution pump 21.

[0048] The lower end portion of the upper shaft portion 51 and its vicinity are located inside the upper absorption chamber 32. And the upper gas-liquid contact portion 53 is disposed below the lower end of the inner shaft portion 512 of the upper shaft portion 51. Therefore, the solution flowing out from the lower end portion of the inner shaft portion 512 of the upper shaft portion 51 flows into the upper gas-liquid contact portion 53 from the substantially center of rotation on the upper surface of the upper gas-liquid contact portion 53 (the upper end portion of the rotation center of the upper gas-liquid contact portion 53). And the solution flowing into (penetrating) the upper gas-liquid contact portion 53 diffuses and penetrates radially outward and downward from the substantially center of rotation of the upper surface by the centrifugal force and gravity of the rotation of the upper gas-liquid contact portion 53. For this reason, the solution diffuses over substantially the entire upper gas-liquid contact portion 53. Thereby, a film (liquid film) of the solution is formed on the surface of the upper gas-liquid contact portion 53 (specifically, the surface of the packing material accommodated in the container).

[0049] The solution that has passed through the inside of the upper gas-liquid contact portion 53 flows down (falls) from the outer peripheral surface and the lower surface of the upper gas-liquid contact portion 53. And the solution flowing down from the upper gas-liquid contact portion 53 accumulates at the bottom of the upper absorption chamber 32. The solution accumulated at the bottom of the upper absorption chamber 32 is fed to the intermediate solution chamber 33 through the intermediate solution path 37 by the operation of the intermediate solution pump 39.

[0050] Note that the lower end of the inner shaft portion 512 of the upper shaft portion 51 is a "cylinder with an open bottom". Therefore, if there is no upper-stage gas-liquid contact portion 53 below the lower end portion of the inner shaft portion 512 of the upper shaft portion 51, the solution flowing out from the lower end portion of the inner shaft portion 512 of the upper shaft portion 51 will flow (drop) straight down due to gravity. The same applies to the lower end of the inner shaft portion 542 of the intermediate shaft portion 54 described later.

[0051] The intermediate shaft portion 54 is a hollow shaft-shaped portion provided between the upper-stage gas-liquid contact portion 53 and the lower-stage gas-liquid contact portion 56. The intermediate shaft portion 54 is rotatably supported with respect to the absorption tower 11 via a bearing. The upper part of the intermediate shaft portion 54 is located inside the upper-stage absorption chamber 32. And the upper end portion of the intermediate shaft portion 54 is joined to the lower part of the upper-stage gas-liquid contact portion 53. The lower end portion of the intermediate shaft portion 54 and its vicinity are located inside the lower-stage absorption chamber 35. And a lower-stage gas-liquid contact portion 56 is arranged below the intermediate shaft portion 54. Also, the lower end portion of the intermediate shaft portion 54 and its vicinity are located inside the lower-stage gas-liquid separation portion 55. The vertical intermediate portion of the intermediate shaft portion 54 is located inside the intermediate solution chamber 33 and the intermediate target gas chamber 34.

[0052] The lower part of the intermediate shaft portion 54 (the part located inside the intermediate target gas chamber 34 and inside the lower absorption chamber 35) has a double-pipe structure. Specifically, the intermediate shaft portion 54 includes a substantially cylindrical outer shaft portion 541 and an inner shaft portion 542, and the inner shaft portion 542 is disposed in the lower part of the internal space of the outer shaft portion 541. Note that the upper and lower ends of the inner shaft portion 542 are open, and the internal space of the outer shaft portion 541 in the upper part of the intermediate shaft portion 54 communicates with the internal space of the inner shaft portion 542 in the lower part. A solution passage hole 543 is provided at a position located inside the intermediate solution chamber 33 of the outer shaft portion 541 of the intermediate shaft portion 54 and above the upper end of the inner shaft portion 542. The solution passage hole 543 is a through hole that allows the solution to pass through and communicate the outside and the internal space of the outer shaft portion 541 of the intermediate shaft portion 54. Therefore, the solution accumulated in the intermediate solution chamber 33 flows into the internal space of the outer shaft portion 541 of the intermediate shaft portion 54 through the solution passage hole 543 provided in the intermediate shaft portion 54, further flows down through the internal space of the inner shaft portion 542, and flows out from the lower end of the inner shaft portion 542. In this way, in the part of the intermediate shaft portion 54 located inside the intermediate solution chamber 33, the outer shaft portion 541 forms a path for the solution, and in the middle and lower parts in the vertical direction of the intermediate shaft portion 54, the inner shaft portion 542 (specifically, the internal space of the inner shaft portion 542) forms a path for the solution.

[0053] Below the intermediate shaft portion 54, a lower gas-liquid contact portion 56 is disposed. Further, the vicinity of the lower end portion of the intermediate shaft portion 54 is located in the internal space of the lower gas-liquid separation portion 55. For this reason, the solution flowing out from the lower end of the inner shaft portion 542 of the intermediate shaft portion 54 is supplied to the lower gas-liquid contact portion 56 from the substantially rotation center of the upper surface of the lower gas-liquid contact portion 56 (the upper end portion of the substantially rotation center of the lower gas-liquid contact portion 56). The solution supplied to the lower gas-liquid contact portion 56 diffuses and penetrates radially outward and downward from the substantially rotation center of the upper surface by the centrifugal force and gravity of the rotation of the lower gas-liquid contact portion 56. For this reason, similarly to the upper gas-liquid contact portion 53, the solution diffuses over substantially the entire lower gas-liquid contact portion 56. Then, a film (liquid film) of the solution is formed on the surface of the lower gas-liquid contact portion 56 (specifically, the surface of the packing material accommodated in the container). The solution that has diffused and penetrated into the lower gas-liquid contact portion 56 flows down (falls) from the outer peripheral surface and the lower surface of the lower gas-liquid contact portion 56. The solution that has flowed down from the outer peripheral surface and the lower surface of the lower gas-liquid contact portion 56 accumulates at the bottom of the lower absorption chamber 35. The solution accumulated at the bottom of the lower absorption chamber 35 is discharged from the lower absorption chamber 35 by the operation of the first solution pump 20 and fed toward the stripping tower 12.

[0054] One end of the target gas introduction path 13 is connected to the lower absorption chamber 35. For this reason, the target gas fed from the target gas source 90 by the operation of the target gas pump 16 flows into the interior of the lower absorption chamber 35. The target gas that has flowed into the interior of the lower absorption chamber 35 flows into the interior thereof from the lower surface and the outer peripheral surface of the lower gas-liquid contact portion 56, and flows into the internal space of the lower gas-liquid separation portion 55 from the upper surface of the lower gas-liquid contact portion 56.

[0055] In a portion of the intermediate shaft portion 54 located inside the lower absorption chamber 35, an upstream target gas passage hole 544 is provided, and in a portion located inside the intermediate target gas chamber 34, a downstream target gas passage hole 545 is provided. Both the upstream target gas passage hole 544 and the downstream target gas passage hole 545 are through holes that allow the target gas to communicate between the outside of the outer shaft portion 541 and the internal space of the outer shaft portion 541 (the space between the outer shaft portion 541 and the inner shaft portion 542) so that the target gas can pass through. Therefore, the target gas that has passed through the internal space of the lower gas-liquid separation portion 55 flows into the internal space of the outer shaft portion 541 of the intermediate shaft portion 54 (more specifically, the space between the inner peripheral surface of the outer shaft portion 541 and the outer peripheral surface of the inner shaft portion 542) through the upstream target gas passage hole 544, passes through this internal space, and flows into the inside of the intermediate target gas chamber 34 through the downstream target gas passage hole 545. Note that the upper and lower ends of the space between the outer shaft portion 541 and the inner shaft portion 542 are closed. In the lower portion of the intermediate shaft portion 54 (the portion located inside the intermediate target gas chamber 34 and the lower absorption chamber 35), the outer shaft portion 541 (specifically, the space between the inner peripheral surface of the outer shaft portion 541 and the outer peripheral surface of the inner shaft portion 542) forms a path for the target gas.

[0056] The target gas that has flowed into the intermediate target gas chamber 34 flows into the upper absorption chamber 32 through the intermediate target gas path 38. Then, the target gas that has flowed into the inside of the upper absorption chamber 32 flows into the inside of the upper gas-liquid contact portion 53 from the outer peripheral surface and the lower surface of the upper gas-liquid contact portion 53, passes through the inside of the upper gas-liquid contact portion 53, and flows into the internal space of the upper gas-liquid separation portion 52 from the upper surface of the upper gas-liquid contact portion 53.

[0057] Near the lower end of the upper shaft portion 51, it is located inside the upper gas-liquid separation portion 52. And, in the portion of the outer shaft portion 511 of the upper shaft portion 51 that is located inside the upper gas-liquid separation portion 52, a target gas path hole 513 is provided. The target gas path hole 513 is a through hole (opening) that allows gas to pass through and communicates the internal space of the outer shaft portion 511 (that is, the space between the inner peripheral surface of the outer shaft portion 511 and the outer peripheral surface of the inner shaft portion 512) and the outside (that is, the inside of the upper gas-liquid separation portion 52). The upper end of the outer shaft portion 511 of the upper shaft portion 51 is located inside the upper target gas chamber 31, and the inside of the outer shaft portion 511 (the space between the inner peripheral surface of the outer shaft portion 511 and the outer peripheral surface of the inner shaft portion 512) communicates with the inside of the upper target gas chamber 31.

[0058] Therefore, the target gas that has flowed into the internal space of the upper gas-liquid separation portion 52 flows into the internal space of the outer shaft portion 511 (the space between the inner peripheral surface of the outer shaft portion 511 and the outer peripheral surface of the inner shaft portion 512) through the target gas path hole 513, passes through the internal space of the outer shaft portion 511, and flows into the inside of the upper target gas chamber 31 from the upper end of the outer shaft portion 511. In this way, the outer shaft portion 511 of the upper shaft portion 51 (more specifically, the space between the inner peripheral surface of the outer shaft portion 511 and the outer peripheral surface of the inner shaft portion 512) forms a path for the target gas (off-gas). And, the target gas flows out (is discharged) to the outside of the absorption tower 11 through the target gas discharge path 17.

[0059] The lower shaft portion 57 is a substantially cylindrical or substantially round bar-shaped portion. The lower end portion of the lower shaft portion 57 protrudes outside the absorption tower 11 and is connected to the driving force source 41 so that rotational power is transmitted from the driving force source 41. Also, the lower shaft portion 57 is rotatably supported with respect to the absorption tower 11 via a bearing.

[0060] In this way, the solution that has flowed into the upper absorption chamber 32 through the inner shaft portion 512 of the upper shaft portion 51 passes through the upper gas-liquid contact portion 53 and temporarily accumulates at the bottom of the upper absorption chamber 32. And, the solution that has accumulated at the bottom of the upper absorption chamber 32 is fed to the intermediate solution chamber 33 by the operation of the intermediate solution pump 39 and flows into the lower absorption chamber 35 through the intermediate shaft portion 54. The absorption liquid that has flowed into the lower absorption chamber 35 passes through the lower gas-liquid contact portion 56 and accumulates at the bottom of the lower absorption chamber 35.

[0061] On the one hand, the target gas flowing into the lower absorption chamber 35 through the target gas introduction path 13 sequentially passes through the inside of the lower gas-liquid contact part 56 and the internal space of the lower gas-liquid separation part 55. Thereafter, the target gas flows into the upper absorption chamber 32 through the intermediate shaft part 54, the intermediate target gas chamber 34, and the intermediate target gas path 38. The target gas flowing into the upper absorption chamber 32 sequentially passes through the upper gas-liquid contact part 53 and the upper gas-liquid separation part 52, and flows out (is discharged) to the outside of the absorption tower 11 through the upper shaft part 51, the upper target gas chamber 31, and the target gas discharge path 17.

[0062] And in the gas-liquid contact parts 53 and 56 of each stage arranged in the absorption chambers 32 and 35 of each stage, the solution and the target gas are in gas-liquid contact, whereby carbon dioxide contained in the target gas is absorbed by the solution. For this reason, the carbon dioxide concentration contained in the target gas gradually decreases each time it passes through the lower absorption chamber 35 and the upper absorption chamber 32. On the other hand, while the solution flows through the upper absorption chamber 32 and the lower absorption chamber 35, the absorption rate of carbon dioxide in the solution gradually increases (the loading value of carbon dioxide increases). That is, the solution changes from a carbon dioxide-lean state to a carbon dioxide-rich state.

[0063] As described above, the absorption tower 11 is configured such that the solution fed from the stripping tower 12 via the second solution path 19 passes in one direction through the upper absorption chamber 32, the intermediate target gas chamber 34, and the lower absorption chamber 35 in this order, and is discharged from the lower absorption chamber 35 to the outside of the absorption tower 11 (specifically, fed to the stripping tower 12). Further, the absorption tower 11 is configured such that the target gas fed from the target gas source 90 through the target gas introduction path 13 passes in the direction opposite to the one direction through the lower absorption chamber 35, the intermediate target gas chamber 34, the upper absorption chamber 32, and the upper target gas chamber 31 in this order, and is discharged from the upper target gas chamber 31 to the outside of the absorption tower 11.

[0064] <Control of the flow rate of the solution and the rotational speed of the rotating body> Next, the control of the flow rate of the solution supplied to each stage of the gas-liquid contact parts 53 and 56 and the rotation speed of the rotating body 36 when the target gas source 90 is in operation will be described. During the operation of the target gas source 90, the control device 27 controls at least one of the flow rate of the solution supplied to each stage of the gas-liquid contact parts 53 and 56 and the rotation speed of the rotating body 36 so that the carbon dioxide absorption efficiency is maintained at or above the target value. Note that the carbon dioxide absorption efficiency is a ratio indicating the amount of carbon dioxide absorbed by the solution with respect to the amount of carbon dioxide contained in the target gas. In the present embodiment, the carbon dioxide absorption efficiency indicates a value for the entire absorption tower 11. In this case, the carbon dioxide absorption efficiency is a ratio indicating the "total amount of carbon dioxide absorbed in the lower-stage gas-liquid contact part 56 and the upper-stage gas-liquid contact part 56 per unit time" with respect to the "flow rate of carbon dioxide fed from the target gas source 90 to the absorption tower 11". The target value of the carbon dioxide absorption efficiency is a predefined value. The specific value of the target value of the carbon dioxide absorption efficiency is not particularly limited, but for example, 90% for the entire absorption tower 11 is applicable. Hereinafter, the carbon dioxide absorption efficiency may be simply abbreviated as "absorption efficiency".

[0065] Note that the configuration for the control device 27 to determine whether the target gas source 90 is in operation is not particularly limited. For example, a configuration for determining based on the production plan of the target gas source 90 can be applied. In this case, the production plan of the target gas source 90 may be stored in advance in the ROM or storage device of the computer of the control device 27, or the control device 27 may acquire it from the control device of the target gas source 90 or the control device that oversees the facility including the target gas source 90 and the recovery device 10. Further, the control device 27 determines that the target gas source 90 is in operation when the flow rate of carbon dioxide calculated from the target gas flow rate and the carbon dioxide concentration is equal to or higher than a predefined threshold, rather than whether the target gas source 90 is actually in operation or not, and determines that the target gas source 90 is not in operation when it is less than the threshold.

[0066] The amount of carbon dioxide that can be absorbed by the solution per unit volume is determined according to the type (properties) of the solute and the concentration of the solution, etc. Therefore, if the flow rate of the target gas and the carbon dioxide concentration of the target gas can be measured (are known), the flow rate of the solution required to absorb the total amount of carbon dioxide contained in the target gas can be specified. However, the actual absorption efficiency of the recovery device 10 varies according to the state of the gas-liquid contact parts 53 and 56 of each stage (specifically, whether a solution film exists on the surface of the gas-liquid contact parts 53 and 56 of each stage (the surface of the material of the packing)). Specifically, when a solution film is formed over a wide range (preferably the whole) of the surface of the gas-liquid contact parts 53 and 56 of each stage, the absorption efficiency increases. When the absorption efficiency increases, the dissipation energy (heat) can be reduced.

[0067] Furthermore, the absorption efficiency varies not only according to the state of the gas-liquid contact parts 53 and 56 of each stage, but also according to the flow rate of carbon dioxide, the flow rate of the solution, and the rotation speed of the rotating body 36. Specifically, when the flow rate of carbon dioxide increases, the absorption efficiency tends to decrease. Also, when the rotation speed of the rotating body 36 increases, the absorption efficiency improves, and the absorption efficiency decreases after a certain optimum rotation speed. For this reason, for each flow rate of carbon dioxide, there exists a combination of the flow rate of the solution and the rotation speed of the rotating body 36 such that the absorption efficiency is equal to or higher than the target value.

[0068] Therefore, the control device 27 uses a first map (table) showing the relationship between the flow rate of carbon dioxide, the flow rate of the solution supplied to the gas-liquid contact parts 53 and 56 of each stage, the rotational speed of the rotating body 36, and the absorption efficiency, and controls at least one of the flow rate of the solution supplied to the gas-liquid contact parts 53 and 56 of each stage and the rotational speed of the rotating body 36 according to the flow rate of carbon dioxide so that the absorption efficiency becomes a value equal to or higher than the target value. FIG. 3 is a conceptual diagram of the first map used by the control device 27. As shown in FIG. 3, the first map has a configuration in which two-dimensional maps storing the absorption efficiency corresponding to the combination of the flow rate of carbon dioxide and the flow rate of the solution supplied to the gas-liquid contact parts 53 and 56 of each stage for each rotational speed of the rotating body 36 are stacked. The measured values previously measured by variously changing the flow rate of carbon dioxide, the flow rate of the solution supplied to the gas-liquid contact parts 53 and 56 of each stage, and the rotational speed of the rotating body 36 are applied to the absorption efficiency defined in this first map. When the carbon dioxide concentration of the target gas supplied from the target gas source 90 is substantially constant, the absorption efficiency corresponding to the flow rate of the target gas, the flow rate of the solution supplied to the gas-liquid contact parts 53 and 56 of each stage, and the rotational speed of the rotating body 36 may be defined in the first map.

[0069] In this embodiment, the control device 27 includes one first map for the entire absorption tower 11. In this case, the absorption efficiency defined in the first map is the absorption efficiency of the entire absorption tower 11, that is, the ratio showing "the total amount of carbon dioxide absorbed in the lower gas-liquid contact part 56 and the upper gas-liquid contact part 53 (that is, in all the gas-liquid contact parts 53 and 56) per unit time" with respect to "the total amount of carbon dioxide flowing into the lower absorption chamber 35 and the upper absorption chamber 32 per unit time".

[0070] During the operation of the target gas source 90, the control device 27 continuously and in real-time acquires the measurement result of the flow rate of the target gas by the target gas flow meter 14, the measurement result of the carbon dioxide concentration of the target gas by the carbon dioxide concentration meter 15, the measurement results of the flow rates of the solutions supplied to the gas-liquid contact parts 53 and 56 of each stage by the inlet solution flow meter 26 and the intermediate solution flow meter 40, and the measurement result of the rotation speed of the rotating body 36 by the tachometer 42. Then, the control device 27 calculates the flow rate of carbon dioxide from the acquired measurement result of the flow rate of the target gas and the measurement result of the carbon dioxide concentration, and by applying the calculated flow rate of carbon dioxide, the acquired measurement result of the flow rate of the solution, and the acquired measurement result of the rotation speed of the rotating body 36 to the first map, specifies (or can be said to estimate) the current absorption efficiency in real-time.

[0071] When the current absorption efficiency specified using the first map by the control device 27 is less than the target value, the control device 27 searches the first map for "combinations of the flow rate of the solution and the rotation speed of the rotating body 36 at which the absorption efficiency becomes equal to or higher than the target value". For example, the control device 27 fixes the target gas flow rate and the flow rate of the solution at the current flow rates and searches for "the rotation speed at which the absorption efficiency becomes equal to or higher than the target value". Then, while maintaining the flow rate of the solution at the current flow rate, the control device 27 controls the rotation speed of the rotating body 36 (i.e., the rotation speed of the driving power source 41) to be the rotation speed of the rotating body 36 detected by the search (the rotation speed at which the absorption efficiency becomes equal to or higher than the target value).

[0072] Note that the control device 27 may fix the target gas flow rate and the rotation speed of the rotating body 36 to the current values and search for "the flow rate of the solution at which the absorption efficiency is equal to or higher than the target value". In this case, while maintaining the rotation speed of the rotating body 36 at the current rotation speed, the control device 27 controls the outputs (flow rates) of the second solution pump 21 and the intermediate solution pump 39 so that the flow rate of the solution detected by the search (the flow rate of the solution at which the absorption efficiency is equal to or higher than the target value) is achieved. Further, by fixing the target gas flow rate to the current value and changing both the rotation speed of the rotating body 36 and the flow rate of the solution, "the combination of the rotation speed of the rotating body 36 and the flow rate of the solution at which the absorption efficiency is equal to or higher than the target value" may be searched. In this case, the control device 27 controls both the rotation speed of the rotating body 36 and the flow rate of the solution so that the combination detected by the search (the combination of the rotation speed of the rotating body 36 and the flow rate of the solution at which the absorption efficiency is equal to or higher than the target value) is achieved. That is, the control device controls either the rotation speed of the driving power source 41 or the outputs of the second solution pump 21 and the intermediate solution pump 39.

[0073] In this way, the control device 27 controls at least one of the rotation speed of the rotating body 36 and the flow rate of the solution so that the rotation speed of the rotating body 36 and the flow rate of the solution become "the combination of the rotation speed of the rotating body 36 and the flow rate of the solution at which the absorption efficiency is equal to or higher than the target value" defined in the first map.

[0074] Note that at the first startup of the recovery device 10 (or at the startup after a long-term operation stop), the control device 27 controls the driving power source 41, the second solution pump 21, and the intermediate solution pump 39 so that the rotation speed of the rotating body 36 and the flow rate of the solution become the initial values defined in advance according to the flow rate of the target gas. Then, thereafter, as described above, the control device 27 uses the first map to control (change) at least one of the rotation speed of the rotating body 36 and the flow rate of the solution so that the absorption efficiency becomes equal to or higher than the target value.

[0075] Note that, compared with the control of fixing the flow rate of the solution to the current flow rate and changing the rotational speed of the rotating body 36, the control of fixing the rotational speed of the rotating body 36 to the current value and changing the flow rate of the solution, and the control of changing the rotational speed of the rotating body 36 and the flow rate of the solution, less energy is required for the change. That is, when changing the rotational speed of the rotating body 36, it is only necessary to change the output (rotational speed) of the driving force source 41, but when changing the flow rate of the solution, the output of the reboiler 23 must be changed according to the change in the flow rate. In addition, the pump operation can be minimized by supplying the minimum required flow rate of the solution. Therefore, it is preferable that the control device 27 executes control of fixing the target gas flow rate and the flow rate of the solution to the current flow rate and changing the rotational speed of the rotating body 36.

[0076] And the control device 27 continuously executes such control at a predetermined cycle during the operation of the target gas source 90. Thus, according to the present embodiment, it is possible to prevent or suppress the absorption efficiency from decreasing below the target value during the operation of the target gas source 90. In addition, the control device 27 continuously stores in the storage device the calculation result of the carbon dioxide flow rate (or the measurement result of the target gas flow rate and the measurement result of the carbon dioxide concentration of the target gas) and the measurement result of the rotational speed of the rotating body 36 during the operation of the target gas source 90 for the wetting operation described later. Furthermore, according to the present embodiment, the target absorption efficiency is set from the map of the absorption solution flow rate, gas flow rate, and rotational speed. When the performance deteriorates compared to the target absorption efficiency, it is possible to detect that an abnormality has occurred in the sensing of any of the absorption solution flow rate, gas flow rate, and rotational speed.

[0077] Also, as shown in FIG. 3, the first map does not have to be a map in which the rotational speed of the rotating body 36, the flow rate of carbon dioxide, the solution flow rate, and the value of the carbon dioxide flow rate are directly defined. For example, as the first map, a logical formula that can calculate the absorption efficiency using the rotational speed of the rotating body 36, the flow rate of carbon dioxide, the solution flow rate, and the value of the carbon dioxide flow rate as variables may be applied.

[0078] <Wetting operation> Next, the wetting operation will be described. The wetting operation is control for maintaining the states of the gas-liquid contact parts 53 and 56 of each stage in a state where carbon dioxide can be absorbed with an absorption efficiency equal to or higher than a target value during the non-operation of the target gas source 90. During the non-operation of the target gas source 90, the control device 27 stops the circulation of the solution and the rotation of the rotating body 36. Specifically, the control device 27 stops the operations of the first solution pump 20, the second solution pump 21, the intermediate solution pump 39, and the drive power source 41.

[0079] When the circulation of the solution stops, the solution that has penetrated into the gas-liquid contact parts 53 and 56 of each stage of the absorption tower 11 decreases by falling or vaporizing from the gas-liquid contact parts 53 and 56 of each stage due to gravity. In other words, the liquid film existing on the surfaces of the gas-liquid separation parts 52 and 55 of each stage decreases. When the operation of the target gas source 90 is started (resumed) in a state where the liquid film on the surfaces of the gas-liquid separation parts 52 and 55 of each stage has decreased, if the circulation of the solution and the rotation of the rotating body 36 are started in accordance with the start of the operation of the target gas source 90, until the solution penetrates into the gas-liquid contact parts 53 and 56 of each stage (until a liquid film is formed over a wide range of the surfaces of the gas-liquid contact parts 53 and 56 of each stage), the absorption efficiency decreases, and there is a possibility that the absorption efficiency becomes less than the target value.

[0080] Therefore, in order to prevent or suppress a decrease in the absorption efficiency after the start of the operation of the target gas source 90 (in other words, in order to immediately make the absorption efficiency equal to or higher than the target value after the start of the operation of the target gas source 90), when a predetermined condition is satisfied during the non-operation of the target gas source 90, the control device 27 executes the wetting operation.

[0081] Specifically, when the operation of the target gas source 90 stops, the control device 27 promptly stops the circulation of the solution and the rotation of the rotating body 36. After that, the control device 27 determines whether or not a condition that "it can be considered that the absorption efficiency is less than the target value because the amount of the solution held in the gas-liquid contact parts 53, 56 of each stage is too small (because the liquid film existing on the surfaces of the gas-liquid contact parts 53, 56 of each stage is too small)" is satisfied. Hereinafter, this condition may be referred to as a specific condition. And when the control device 27 determines that the specific condition is satisfied, it executes a wetting operation. Specifically, as the wetting operation, the control device 27 operates the second solution pump 21 and the intermediate solution pump 39 to supply a predetermined amount of the solution to the gas-liquid contact parts 53, 56 of each stage. Further, when the target gas source 90 is in a non-operating state, the control device 27 continuously determines whether or not the specific condition is satisfied, and continues the control of "executing the wetting operation when it is determined that the specific condition is satisfied after one execution of the wetting operation".

[0082] Here, the details of the specific condition and the wetting operation will be described. When the supply of the solution to the gas-liquid separation parts 52, 55 of each stage stops and the rotation of the rotating body 36 stops, as described above, the solution held in the gas-liquid contact parts 53, 56 of each stage flows down from the gas-liquid contact parts 53, 56 of each stage by gravity. Also, as the solution held in the gas-liquid contact parts 53, 56 of each stage vaporizes, the solution held in the gas-liquid contact parts 53, 56 of each stage decreases. Therefore, in advance, the change over time of the liquid holding amount of the gas-liquid contact parts 53, 56 of each stage after the supply of the solution stops is measured.

[0083] Specifically, first, a solution is supplied to each of the gas-liquid contact parts 53 and 56 of each stage that is completely dry at a constant flow rate, and the total amount of the solution supplied to the gas-liquid contact parts 53 and 56 of each stage and the flow rate and total amount of the solution flowing out from the gas-liquid contact parts 53 and 56 of each stage are measured in time series. Then, the difference between the total amount of the solution supplied to the gas-liquid contact parts 53 and 56 of each stage and the total amount of the solution flowing out from the gas-liquid contact parts 53 and 56 of each stage is calculated. This difference is the liquid retention amount of the gas-liquid contact parts 53 and 56 of each stage. Further, when the flow rate of the solution flowing out from the gas-liquid contact parts 53 and 56 of each stage becomes constant, the supply of the solution to the gas-liquid contact parts 53 and 56 of each stage is stopped, and the total amount of the solution flowing out from the gas-liquid contact parts 53 and 56 of each stage from the time when the supply of the solution is stopped is measured in time series. Based on this measurement result, the "change over time of the liquid retention amount after the supply of the solution is stopped" for each flow rate of carbon dioxide and each rotation speed of the rotating body 36 in the gas-liquid contact parts 53 and 56 of each stage can be specified.

[0084] Also, the relationship between the liquid retention amount and the absorption efficiency of the gas-liquid contact parts 53 and 56 of each stage is measured in advance. As described above, since the absorption efficiency changes according to the flow rate of carbon dioxide and the rotation speed of the rotating body 36, the relationship between the liquid retention amount and the absorption efficiency of the gas-liquid contact parts 53 and 56 of each stage is measured for each combination of various flow rates of carbon dioxide and rotation speeds of the rotating body 36.

[0085] And when the relationship between the elapsed time and the liquid retention amount of the gas-liquid contact parts 53 and 56 of each stage becomes clear, and the relationship between the liquid retention amount and the absorption efficiency of the gas-liquid contact parts 53 and 56 of each stage becomes clear, the relationship between the elapsed time and the absorption efficiency becomes clear. For example, a graph as shown in FIG. 4 is created. Specifically, a graph is created in which the horizontal axis represents the elapsed time and the vertical axis represents the liquid retention amount. Then, the carbon dioxide absorption rate corresponding to the liquid retention amount at each time is plotted on this graph. That is, the liquid retention amount Q shown in FIG. 4 L is the liquid retention amount at the elapsed time T L And the carbon dioxide absorption rate R T is the carbon dioxide absorption rate at the liquid retention amount Q L According to such a graph, the relationship between the elapsed time and the absorption efficiency can be defined.

[0086] Then, a "second map defining the relationship between the elapsed time and the absorption efficiency" is created from such a graph and stored in advance in the ROM or storage device of the control device 27 in a computer-readable format. These operations are executed by the user operating the control device 27. Further, the relationship between the elapsed time and the absorption efficiency (i.e., the specific shape of the plot of the graph shown in FIG. 4) varies depending on, in addition to the flow rate of carbon dioxide and the rotational speed of the rotating body 36 as described above, the liquid retention amount of each stage of the gas-liquid contact portions 53, 56 immediately before the supply of the solution is stopped (in other words, the flow rate of the solution immediately before the supply of the solution is stopped). For this reason, this second map is created and stored for each combination of various flow rates of carbon dioxide, the rotational speed of the rotating body 36, and the flow rate of the solution immediately before the supply of the solution is stopped.

[0087] When the operation of the target gas source 90 stops, the control device 27 starts measuring the elapsed time since the stop. Also, when the wetting operation is executed, the control device 27 starts measuring the elapsed time since the execution. Additionally, the control device 27 selects a second map corresponding to the flow rate of carbon dioxide, the rotational speed of the rotating body 36, and the flow rate of the solution acquired before the operation of the target gas source 90 stops (immediately before the stop). Then, the control device 27 identifies the time at which the "liquid retention amount such that the absorption efficiency becomes less than the target value when the operation of the recovery device 10 is started" from the selected second map, and determines that the specific condition is satisfied when the elapsed time since the operation of the target gas source 90 stopped, or the elapsed time since a single wetting operation was executed reaches the identified time.

[0088] When the control device 27 determines that the specific conditions are satisfied, it supplies the solution to the gas-liquid contact parts 53 and 56 of each stage. The supply amount of the solution at this time is at least an amount such that "the liquid retention amount of the gas-liquid contact parts 53 and 56 of each stage results in an absorption efficiency equal to or higher than the target value". The maximum liquid retention amount of the gas-liquid contact parts 53 and 56 of each stage is measured in advance and stored in the ROM or storage device of the computer of the control device 27. However, the specific supply amount of the solution in the wetting operation is not limited. Further, when the control device 27 executes the wetting operation, it measures the elapsed time since the execution. Then, when the control device 27 determines that the specific conditions are satisfied again after executing the wetting operation, it executes the wetting operation.

[0089] As described above, when the target gas source 90 is in a non-operating state or during non-operation, the control device 27 continuously and repeatedly determines whether or not the specific conditions are satisfied, and executes the wetting operation each time it determines that the specific conditions are satisfied. According to such a configuration, during the non-operation of the target gas source 90, the gas-liquid contact parts 53 and 56 of each stage are maintained in a state where "the absorption efficiency becomes equal to or higher than the target value when the operation of the recovery device 10 is started". Therefore, when the target gas source 90 starts (restarts) operation, it is possible to prevent or suppress the absorption efficiency from becoming less than the target value immediately after the start.

[0090] In the present embodiment, a configuration is shown in which the second map used for determining the success or failure of the specific conditions is changed according to the combination of the flow rate of carbon dioxide, the rotation speed of the rotating body 36, and the flow rate of the solution immediately before stopping. However, the configuration is not limited to this. For example, the control device 27 may determine that the specific conditions are satisfied when a predetermined time elapses regardless of the flow rate of carbon dioxide, the rotation speed of the rotating body 36, and the flow rate of the solution immediately before stopping before the operation of the target gas source 90 stops. Also, the supply amount of the solution to the gas-liquid contact parts 53 and 56 in the wetting operation is not limited. For example, the supply amount of the solution to the gas-liquid contact parts 53 and 56 of each stage may be an amount equal to or greater than "the maximum liquid retention amount of the gas-liquid contact parts 53 and 56 of each stage". Further, the supply amount of the solution to the gas-liquid contact parts 53 and 56 of each stage may be a predetermined amount (constant amount) defined in advance.

[0091] Further, the control device 27 may rotate the rotating body 36 during the wetting operation. By rotating the rotating body 36 during the wetting operation, the carbon dioxide absorption solution can be diffused radially outward of the gas-liquid contact portions 53 and 56 of each stage by the centrifugal force generated by the rotation of the rotating body 36. Therefore, it is possible to maintain a state in which a liquid film of the carbon dioxide absorption solution is formed over a wide range of the surfaces of the gas-liquid contact portions 53 and 56 of each stage. Therefore, since the gas-liquid contact area immediately after the start of operation of the target gas source 90 can be increased, the effect of preventing or suppressing a decrease in absorption efficiency can be enhanced. However, the control device 27 does not necessarily have to rotate the rotating body 36 during the wetting operation.

[0092] Further, according to the recovery device 10 according to the present embodiment, since it is possible to supply at the minimum required liquid flow rate described in the first map in order to reach the target carbon dioxide absorption efficiency, an increase in heat dissipation energy (heat) generated when carbon dioxide is dissipated from the carbon dioxide absorption liquid can be prevented.

[0093] Further, by supplying the minimum required liquid flow rate as the flow rate of the solution supplied to the gas-liquid contact portions 53 and 56, the second solution pump 21 and the intermediate solution pump 39 can be minimized.

[0094] Further, when the performance deteriorates from the target value set from the first map, the control device 27 can detect that an abnormality has occurred in the sensing of any one of the flow rate of carbon dioxide contained in the target gas flowing inside the absorption tower 11, the flow rate of the solution supplied to the gas-liquid contact portions 53 and 56, and the rotation speed of the gas-liquid contact portions 53 and 56.

[0095] Further, the second map does not necessarily have to be a map in which specific values of the elapsed time and the absorption efficiency are defined. For example, the second map may be a logical formula that can calculate the absorption efficiency using the elapsed time as a variable, or a logical formula that can calculate the elapsed time using the absorption efficiency as a variable.

[0096] <Processing executed by the control device> Next, the process executed by the control device 27 will be described. FIG. 5 is a flowchart showing the process executed by the CPU of the computer of the control device 27 (hereinafter, may be simply referred to as "CPU"). The computer program for executing this process is stored in advance in the ROM of the computer of the control device 27. Similarly, the first map and the second map used for executing this process are stored in advance in the ROM or the storage device of the computer of the control device 27. The CPU reads this computer program from the ROM, expands it in the RAM (using the RAM as a work area), and executes it. At that time, the CPU reads and refers to the first map and the second map as necessary. Then, the CPU repeatedly executes the process shown in FIG. 5 at a predetermined short cycle. Thereby, the above operation is realized.

[0097] In step S101, the CPU determines whether the target gas source 90 is in operation. If the CPU determines that the target gas source 90 is in operation, the process proceeds to step S102.

[0098] In step S102, if the CPU is in the process of timing started in step S109 or step S110 described later, the CPU ends this timing and resets the result of the timing. Then, the CPU proceeds with the process to step S103.

[0099] In step S103, the CPU acquires the detection result of the flow rate of the target gas by the target gas flow meter 14, the measurement result of the carbon dioxide concentration by the carbon dioxide concentration meter 15, the measurement result of the flow rate of the solution by the inlet solution flow meter 26 (or the intermediate solution flow meter 40), and the measurement result of the rotation speed of the rotating body 36 by the rotation meter 42. Then, the CPU proceeds with the process to step S104.

[0100] In step S104, the CPU calculates the flow rate of carbon dioxide from the measurement results of the flow rate of the target gas and the measurement result of the carbon dioxide concentration that have been obtained. Then, the CPU specifies (estimates) the current absorption efficiency by applying the calculated flow rate of carbon dioxide, the obtained flow rate of the solution, and the obtained rotation speed of the rotating body 36 to the first map. Further, the CPU temporarily stores the calculation result of the flow rate of carbon dioxide, the measurement result of the flow rate of the solution, and the measurement result of the rotation speed of the rotating body 36 in a storage device. Then, the CPU proceeds with the process to step S105.

[0101] In step S105, the CPU determines whether the specified current absorption efficiency is equal to or higher than the target value or less than the target value. If the specified current absorption efficiency is equal to or higher than the target value, the CPU temporarily ends this series of processes. On the other hand, if the specified current absorption efficiency is less than the target value, the CPU proceeds with the process to step S106.

[0102] In step S106, the CPU refers to the first map and searches for a combination of the flow rate of the solution and the rotation speed of the rotating body 36 at which the absorption efficiency becomes equal to or higher than the target value. Then, the CPU changes at least one of the first solution pump 20, the intermediate solution pump 39, and the driving power source 41 so that the actual flow rate of the solution and the rotation speed of the rotating body 36 become the "combination of the flow rate of the solution and the rotation speed of the rotating body 36 at which the absorption efficiency becomes equal to or higher than the target value" detected by the search. For example, the CPU changes the rotation speed (output of the driving power source 41) of the rotating body 36 without changing the flow rate of the solution (outputs of the second solution pump 21 and the intermediate solution pump 39) and the flow rate of the target gas (output of the target gas pump 16). Then, the CPU temporarily ends this series of processes.

[0103] If the CPU determines in step S101 that the target gas source 90 is not in operation, the CPU proceeds with the process to step S107. In step S107, the CPU acquires the calculation result of the flow rate of carbon dioxide, the measurement result of the flow rate of the solution, and the measurement result of the rotation speed of the rotating body 36 that were stored in the storage device before the operation of the target gas source 90 was stopped (for example, immediately before the stop). Then, the CPU proceeds with the process to step S108.

[0104] In step S108, the CPU determines whether a wetting operation has been executed during the stop of the operation of the target gas source 90. If the CPU determines that the wetting operation has not been executed during the stop of the operation of the target gas, the process proceeds to step S109. If it determines that the wetting operation has been executed, the process proceeds to step S110.

[0105] In step S109, the CPU starts measuring (timing) the elapsed time since it was determined that the operation of the target gas source 90 has stopped. Also, in step S110, the CPU starts measuring (timing) the elapsed time since the previous wetting operation was executed. Note that when the CPU is executing the timing, it continues the timing. Then, the CPU proceeds with the process to step S111.

[0106] In step S111, the CPU determines whether a specific condition is satisfied. Specifically, the CPU selects a second map according to the flow rate of carbon dioxide, the rotation speed of the rotating body 36, and the flow rate of the solution obtained in step S107, and applies the elapsed time since the start of the timing in step S109 or step S110 to the selected second map to determine whether the specific condition is satisfied. If the CPU determines that the specific condition is not satisfied, this series of processes is temporarily terminated. However, the timing started in step S109 or step S110 continues. If the CPU determines that the specific condition is satisfied, the process proceeds to step S112.

[0107] In step S112, the CPU executes a wetting operation. Then, the CPU proceeds with the process to step S113.

[0108] In step S113, the CPU stops the timing started in step S108 or step S109 and resets the timing result. Then, the CPU temporarily terminates this series of processes.

[0109] According to such a process, control of the flow rate of the above-described solution and the rotation speed of the rotating body 36 and the wetting operation can be realized.

[0110] <Summary of Embodiment> The carbon dioxide recovery apparatus 10 according to the present embodiment includes a carbon dioxide absorption tower 11 that absorbs carbon dioxide contained in the target gas into a carbon dioxide absorption solution, a gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage) that is disposed inside the carbon dioxide absorption tower 11, into which the carbon dioxide absorption solution can penetrate and through which the target gas can pass, and that is configured to rotate by the driving force of a driving force source 41, a solution supply part (second solution pump 21, intermediate solution pump 39) that is configured to supply the carbon dioxide absorption solution to the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage), a control device 27 that controls the driving force source 41 and the solution supply part (second solution pump 21, intermediate solution pump 39), a map (first map) that defines the absorption efficiency of carbon dioxide according to a combination of the flow rate per unit time of carbon dioxide contained in the target gas fed to the carbon dioxide absorption tower 11, the flow rate per unit time of the carbon dioxide absorption solution supplied to the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage), and the rotation speed of the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage).

[0111] Then, the control device 27 applies the flow rate of carbon dioxide contained in the target gas flowing inside the carbon dioxide absorption tower 11, the flow rate of the carbon dioxide absorption solution supplied to the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage), and the rotation speed of the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage) to the map (first map) to specify the absorption efficiency of carbon dioxide. When the specified absorption efficiency of carbon dioxide is less than a preset target value, the control device 27 searches for a combination of the flow rate of carbon dioxide per unit time contained in the target gas fed to the carbon dioxide absorption tower 11 at which the absorption efficiency of carbon dioxide becomes equal to or higher than the target value, the flow rate of the carbon dioxide absorption solution per unit time supplied to the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage), and the rotation speed of the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage) from the map, and controls at least one of the driving power source 41 and the solution supply part (second solution pump 21, intermediate solution pump 39) so as to achieve the searched combination.

[0112] According to the present embodiment, it is possible to prevent or suppress a decrease in the absorption efficiency of carbon dioxide below the target value.

[0113] When the target gas source 90 that emits the target gas is not in operation, the control device 27 stops the rotation of the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage) and the operation of the solution supply part (second solution pump 21, intermediate solution pump 39), determines whether a specific condition indicating that carbon dioxide contained in the target gas cannot be absorbed at an absorption efficiency of carbon dioxide equal to or higher than the target value is satisfied, and when it is determined that the specific condition is satisfied, executes a wetting operation of supplying a predetermined amount of the carbon dioxide absorption solution to the gas-liquid contact part (gas-liquid contact parts 53, 56 of each stage).

[0114] According to this embodiment, during the stoppage of the operation of the target gas source 90, the wetting operation is executed every time a specific condition is satisfied. Therefore, even during the stoppage of the operation of the target gas source 90, each stage of the gas-liquid contact parts 53, 56 is maintained in a state where "when the recovery device 10 operates, the carbon dioxide absorption efficiency becomes equal to or higher than the target value". Therefore, when the target gas source 90 restarts operation, it is possible to immediately achieve a carbon dioxide absorption efficiency equal to or higher than the target value. In other words, it is possible to prevent or suppress a decrease in the carbon dioxide absorption efficiency after the restart of operation.

[0115] The control device 27 determines that the specific condition is satisfied when a predetermined time has elapsed after the operation of the target gas source 90 has stopped or after a certain wetting operation has been executed.

[0116] According to this embodiment, since the wetting operation is repeatedly executed during the stoppage of the operation of the target gas source 90, each stage of the gas-liquid contact parts 53, 56 is maintained in a state where "when the recovery device 10 operates, the carbon dioxide absorption efficiency becomes equal to or higher than the target value".

[0117] The wetting operation is control for supplying the predetermined amount of the carbon dioxide absorption solution to the gas-liquid contact part (the gas-liquid contact parts 53, 56 of each stage) and rotating the rotating body 36.

[0118] With such a configuration, the carbon dioxide absorption solution can be diffused toward the outer side in the radial direction of the gas-liquid contact parts 53, 56 of each stage by the centrifugal force generated by the rotation of the rotating body 36. Therefore, a liquid film of the carbon dioxide absorption solution can be formed over a wide range of the surfaces of the gas-liquid contact parts 53, 56 of each stage. Therefore, since the gas-liquid contact area immediately after restart can be increased, the effect of improving the carbon dioxide absorption efficiency can be enhanced.

[0119] As described above, the embodiments of the present invention have been described, but the technical scope of the present invention is not limited to the above embodiments. The present invention can be variously modified without departing from its gist, and these are also included in the technical scope of the present invention.

[0120] For example, in the above embodiment, an example where the absorption tower 11 is of a two-stage type is shown, but the number of stages of the absorption tower 11 (the number of absorption chambers 32 and 35) is not limited to two. For example, the absorption tower 11 may be of a single-stage type, or may be of a three-stage type or more.

[0121] Also, in the above embodiment, a configuration in which the control device includes one first map is shown, but the configuration is not limited thereto. For example, the control device 27 may include one first map for each of the gas-liquid contact parts 53 and 56 of each stage. In this case, the control device 27 searches for a combination of the flow rate of the solution and the rotational speed of the rotating body 36 such that the absorption efficiency of the entire absorption tower 11 becomes equal to or higher than a preset target value. In this case, the absorption efficiency of each of the gas-liquid contact parts 53 and 56 of each stage (the target value of the absorption efficiency of the gas-liquid contact parts 53 and 56 of each stage according to the searched combination) may be less than the target value of the absorption efficiency of the entire absorption tower 11. However, the control device 27 may search for a "combination of the flow rate of the solution and the rotational speed of the rotating body 36" such that the absorption efficiency of each of the gas-liquid contact parts 53 and 56 of each stage becomes equal to or higher than the target value of the absorption efficiency of the entire absorption tower 11.

Explanation of Reference Numerals

[0122] 10... Carbon dioxide recovery device, 11... Carbon dioxide absorption tower, 12... Carbon dioxide emission tower, 15... Carbon dioxide concentration meter, 16... Target gas pump, 20... First solution pump, 21... Second solution pump, 26... Inlet solution flow meter, 27... Control device, 32... Upper absorption chamber, 35... Lower absorption chamber, 36... Rotating body, 40... Intermediate solution flow meter, 41... Driving power source, 42... Tachometer, 53... Upper gas-liquid contact part, 56... Lower gas-liquid contact part, 90... Target gas source

Claims

1. A carbon dioxide absorption tower for absorbing carbon dioxide contained in a target gas into a carbon dioxide absorption solution, a gas-liquid contact part disposed inside the carbon dioxide absorption tower, through which the carbon dioxide absorption solution can penetrate and the target gas can pass, and which is configured to rotate by the driving force of a driving force source, a solution supply part configured to supply the carbon dioxide absorption solution to the gas-liquid contact part, a control device for controlling the driving force source and the solution supply part, a map in which the absorption efficiency of carbon dioxide is defined according to a combination of the flow rate per unit time of carbon dioxide contained in the target gas fed to the carbon dioxide absorption tower, the flow rate per unit time of the carbon dioxide absorption solution supplied to the gas-liquid contact part, and the rotational speed of the gas-liquid contact part, comprising, the control device identifies the absorption efficiency of carbon dioxide by applying at least the flow rate of carbon dioxide contained in the target gas flowing inside the carbon dioxide absorption tower, the flow rate of the carbon dioxide absorption solution supplied to the gas-liquid contact part, and the rotational speed of the gas-liquid contact part to the map, and if the identified absorption efficiency of carbon dioxide is less than a preset target value, searches the map for a combination of the flow rate per unit time of carbon dioxide contained in the target gas fed to the carbon dioxide absorption tower, the flow rate per unit time of the carbon dioxide absorption solution supplied to the gas-liquid contact part, and the rotational speed of the gas-liquid contact part such that the absorption efficiency of carbon dioxide is equal to or greater than the target value, and controls at least one of the driving force source and the solution supply part so as to achieve the searched combination. A carbon dioxide recovery device.

2. The carbon dioxide recovery device according to claim 1, wherein when the target gas source emitting the target gas is not operating, the control device stops the rotation of the gas-liquid contact part and the operation of the solution supply part, determines whether a specific condition indicating that carbon dioxide contained in the target gas cannot be absorbed with an absorption efficiency of carbon dioxide equal to or greater than the target value is satisfied, and if it is determined that the specific condition is satisfied, executes a wetting operation of supplying a predetermined amount of the carbon dioxide absorption solution to the gas-liquid contact part. A carbon dioxide recovery device.

3. The carbon dioxide recovery device according to claim 2, The carbon dioxide recovery device determines that the specific condition is satisfied when a predetermined time has elapsed after the operation of the target gas source has stopped or after a certain wetting operation has been performed once.

4. The carbon dioxide recovery device according to claim 2 or claim 3, wherein the wetting operation is control for supplying the predetermined amount of the carbon dioxide absorption solution to the gas-liquid contact part and rotating the gas-liquid contact part.

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