Carbon dioxide recovery system and carbon dioxide recovery method

Abstract

To provide a carbon dioxide recovery system which can suppress enlargement and complication of a facility for recovering carbon dioxide contained in exhaust gas.SOLUTION: A carbon dioxide recovery system includes: a compressor which is configured to compress exhaust gas; an absorption tower which is configured to make an absorption liquid absorb carbon dioxide contained in the exhaust gas compressed by the compressor; a regeneration tower which is configured to separate carbon dioxide gas from the absorption liquid discharged from the absorption tower; an expander which is configured to expand gas containing nitrogen contained in exhaust gas compressed by the compressor; and a liquefier which is configured to liquefy the carbon dioxide gas separated from the absorption liquid by the regeneration tower, using cold heat energy of the gas which is expanded by the expander and contains nitrogen.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a carbon dioxide recovery system and a carbon dioxide recovery method for recovering carbon dioxide contained in exhaust gas discharged from a combustion device.

Background Art

[0002] Carbon dioxide contained in the exhaust gas discharged from a combustion device is introduced into an absorption tower and absorbed by a liquid absorbent such as amine in the absorption tower, thereby separating carbon dioxide gas from the exhaust gas (see, for example, Patent Document 1). Since the recovered carbon dioxide is in a gaseous state, liquefaction and densification of carbon dioxide are required in order to efficiently transport carbon dioxide to a remote storage site.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When carbon dioxide contained in exhaust gas is absorbed and separated by an absorbent in an absorption tower, the absorption tower tends to increase in size as the flow rate of the exhaust gas to be treated increases. In addition, equipment for supplying cold heat is required to liquefy the carbon dioxide recovered from the exhaust gas. For this reason, it is desired to suppress the enlargement and complexity of the equipment for recovering carbon dioxide contained in the exhaust gas.

[0005] In view of the above circumstances, at least one embodiment of the present invention aims to provide a carbon dioxide recovery system and a carbon dioxide recovery method capable of suppressing the enlargement and complexity of equipment for recovering carbon dioxide contained in exhaust gas.

Means for Solving the Problems

[0006] To achieve the above object, a carbon dioxide recovery system according to at least one embodiment of the present disclosure is a carbon dioxide recovery system configured to recover carbon dioxide contained in the exhaust gas discharged from a combustion device, a compressor configured to compress the exhaust gas, an absorption tower configured to absorb carbon dioxide contained in the exhaust gas compressed by the compressor into an absorption liquid, a regeneration tower configured to separate carbon dioxide gas from the absorption liquid discharged from the absorption tower, an expander configured to expand a gas containing nitrogen contained in the exhaust gas compressed by the compressor, a liquefier configured to liquefy the carbon dioxide gas separated from the absorption liquid in the regeneration tower by using the cold and heat energy of the gas containing nitrogen expanded by the expander, and includes.

[0007] To achieve the above object, a carbon dioxide recovery method according to at least one embodiment of the present disclosure is a carbon dioxide recovery method for recovering carbon dioxide contained in the exhaust gas discharged from a combustion device, a compression step of compressing the exhaust gas, an absorption step of absorbing carbon dioxide contained in the exhaust gas compressed in the compression step into an absorption liquid, a separation step of separating carbon dioxide gas from the absorption liquid that has absorbed the carbon dioxide in the absorption step, an expansion step of expanding a gas containing nitrogen contained in the exhaust gas compressed in the compression step, a liquefaction step of liquefying the carbon dioxide gas separated from the absorption liquid by using the cold and heat energy of the gas containing nitrogen expanded in the expansion step, and includes.

Advantages of the Invention

[0008] According to at least one embodiment of the present disclosure, there is provided a carbon dioxide recovery system and a carbon dioxide recovery method capable of suppressing the enlargement and complication of equipment for recovering carbon dioxide contained in exhaust gas.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0010] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the invention thereto, but are merely illustrative examples. For example, expressions indicating relative or absolute arrangements such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric", or "coaxial" not only strictly represent such arrangements, but also represent a state of relative displacement with tolerances or at an angle or distance that can obtain the same function. For example, expressions indicating that things such as "identical", "equal", and "homogeneous" are in an equal state not only strictly represent an equal state, but also represent a state in which there are tolerances or differences that can obtain the same function. For example, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent the geometrically precise rectangular shape or cylindrical shape, etc., but also represent shapes including concave and convex portions, chamfered portions, etc. within the range where the same effect can be obtained. On the other hand, expressions such as "comprising", "having", "including", or "possessing" a certain component are not exclusive expressions that exclude the existence of other components.

[0011] FIG. 1 is a diagram schematically showing a carbon dioxide recovery system 2 according to an embodiment of the present disclosure. The illustrated exemplary carbon dioxide recovery system 2 includes a combustion device 4, a cooling tower 6, an electric turbocharger 8, an absorption tower 10, a regeneration tower 12, a liquefier 14, a storage tank 16, and the like.

[0012] The combustion device 4 is, for example, an engine or the like, which burns fuel to generate exhaust gas. The exhaust gas discharged from the combustion device 4 is supplied to the cooling tower 6 through the cooling tower exhaust gas supply line 7. Hereinafter, "exhaust gas" shall mean the exhaust gas discharged from the combustion device 4 unless otherwise specified.

[0013] The combustion device 4 and the absorption tower 10 are connected via an exhaust gas line 5, and the exhaust gas of the combustion device 4 is supplied to the absorption tower 10 through the exhaust gas line 5. The exhaust gas line 5 includes a cooling tower exhaust gas supply line 7 connecting the combustion device 4 and the cooling tower 6, a compressor exhaust gas supply line 22 connecting the cooling tower 6 and the compressor 24 of the electric turbocharger 8, and an absorption tower exhaust gas supply line 28 connecting the compressor 24 and the absorption tower 10.

[0014] In the cooling tower 6, there are provided a cooling water circulation line 18 for extracting the cooling water stored inside the cooling tower 6 from the cooling tower 6 and spraying it inside the cooling tower 6, a pump 19 provided in the cooling water circulation line 18 for pumping the cooling water, and a cooler 20 for cooling the cooling water flowing through the cooling water circulation line 18 with a heat transfer medium. The cooling tower 6 is configured to cool the exhaust gas to about normal temperature by bringing the exhaust gas introduced into the cooling tower 6 from the cooling tower exhaust gas supply line 7 into gas-liquid contact with the cooling water sprayed inside the cooling tower 6 via the cooling water circulation line 18. The exhaust gas cooled by the cooling tower 6 is supplied to the compressor 24 of the electric turbocharger 8 through the compressor exhaust gas supply line 22. The compressor exhaust gas supply line 22 connects the exhaust gas outlet in the cooling tower 6 and the exhaust gas inlet in the compressor 24.

[0015] The electric turbocharger 8 includes a compressor 24, a turbine 25, and a motor 26. The compressor 24 is driven by the motor 26 to compress the exhaust gas. The compressor 24, the turbine 25, and the motor 26 are connected via a rotating shaft 23, and the turbine 25 is rotationally driven by a nitrogen-rich gas described later to assist in driving the compressor 24.

[0016] The exhaust gas compressed by the compressor 24 is supplied to the absorption tower 10 through the absorption tower exhaust gas supply line 28. The absorption tower exhaust gas supply line 28 connects the exhaust gas outlet in the compressor 24 and the exhaust gas inlet in the absorption tower 10. Heat exchangers 30 and 31 described later are provided in the absorption tower exhaust gas supply line 28. In FIG. 1, the letters A to E described in the rhombus represent the heat transfer destination and the heat transfer source in the heat transfer path.

[0017] The absorption tower 10 is configured to absorb carbon dioxide contained in the exhaust gas compressed by the compressor 24 into the absorption liquid. The absorption liquid contains, for example, an amine compound (hereinafter simply referred to as "amine") which is a compound containing an amino group, and is a liquid in which the amine is dissolved in water or another solvent. The absorption tower 10 includes a spray 29 for spraying the absorption liquid inside the absorption tower 10. When the absorption liquid sprayed from the spray 29 comes into gas-liquid contact with the exhaust gas, carbon dioxide contained in the exhaust gas is absorbed by the absorption liquid. The absorption liquid that has absorbed carbon dioxide is stored at the bottom of the absorption tower 10, and the absorption liquid that has absorbed carbon dioxide is withdrawn from the bottom of the absorption tower 10 and supplied to the regeneration tower 12 through the absorption liquid supply line 32. The absorption liquid supply line 32 is provided with a pump 33 for pumping the absorption liquid from the absorption tower 10 to the regeneration tower 12, and heat exchangers 34 and 35 described later.

[0018] At the upper part of the absorption tower 10, above the spray 29, a spray 36 for spraying cooling water and a receiving plate 37 for receiving the cooling water sprayed from the spray 36 are provided. The cooling water received by the receiving plate 37 is returned to the spray 36 through the cooling water circulation line 38 and sprayed again into the interior of the absorption tower 10 from the spray 36. The cooling water circulation line 38 is provided with a pump 39 for pumping the cooling water to the spray 36 and a heat exchanger 40 described later.

[0019] A nitrogen gas line 41 is connected to the top of the absorption tower 10. Carbon dioxide contained in the exhaust gas supplied to the absorption tower 10 is absorbed by the absorption liquid sprayed from the spray 29 as the exhaust gas rises in the absorption tower 10, and gases such as nitrogen contained in the exhaust gas (gases not absorbed by the absorption liquid in the absorption tower 10) are discharged from the top of the absorption tower 10 to the nitrogen gas line 41. The nitrogen gas line 41 is configured to supply nitrogen-rich gas (nitrogen gas with a higher nitrogen concentration than the exhaust gas at the exhaust gas inlet of the absorption tower 10) discharged from the absorption tower 10 to the turbine 25. The nitrogen gas line 41 is provided with a heat exchanger 42 described later.

[0020] The nitrogen-rich gas supplied from the nitrogen gas line 41 to the turbine 25 expands in the turbine 25 to rotationally drive the turbine 25, whereby the turbine 25 assists in driving the compressor 24. The nitrogen-rich gas expanded in the turbine 25 is supplied to the liquefier 14 through the expansion gas line 27.

[0021] The regeneration tower 12 is configured to separate carbon dioxide gas from the absorption liquid (the absorption liquid discharged from the absorption tower 10) supplied from the absorption liquid supply line 32. The regeneration tower 12 is provided with an absorption liquid circulation line 44 for extracting the absorption liquid that has absorbed carbon dioxide and stored inside the regeneration tower 12 from the regeneration tower 12 and returning it to the regeneration tower 12, and a heat exchanger 45 configured to heat the absorption liquid flowing through the absorption liquid circulation line 44 using the thermal energy of the exhaust gas flowing through the absorption tower exhaust gas supply line 28. A pump 46 for extracting the absorption liquid from inside the regeneration tower 12 and supplying it to the heat exchanger 45 is provided in the absorption liquid circulation line 44. The absorption liquid heated by the heat exchanger 45 is returned to the regeneration tower 12 through the absorption liquid circulation line 44, whereby the absorption liquid inside the regeneration tower 12 is heated and the carbon dioxide gas absorbed by the absorption liquid is separated.

[0022] The gas (high-purity carbon dioxide gas) containing the carbon dioxide gas separated from the absorption liquid is supplied to the liquefier 14 through the carbon dioxide gas supply line 48 connected to the upper part of the regeneration tower 12. An absorption liquid return line 56 for returning a part of the absorption liquid from the regeneration tower 12 to the absorption tower 10 is connected to the lower part of the regeneration tower 12. The absorption product return line 56 is provided with a heat exchanger 35 (to be described later) and a pump 58 for pumping the absorption liquid from the regeneration tower 12 to the absorption tower 10.

[0023] In the illustrated exemplary form, a heat exchanger 49, a moisture separator 50, and a compressor 51 are provided in the carbon dioxide gas supply line 48 in order from the upstream side.

[0024] The heat exchanger 49 is configured to cool the gas (high-purity carbon dioxide gas) flowing through the carbon dioxide gas supply line 48 by heat exchange with the cooling water. The moisture separation device 50 is configured to separate moisture from the gas that has passed through the heat exchanger 49, and the moisture separated from the gas by the moisture separation device 50 is returned to the regeneration tower 12 by the pump 53.

[0025] The gas (high-purity carbon dioxide gas) that has exited the moisture separation device 50 is compressed by the compressor 51 driven by the motor 52 and then supplied to the liquefier 14.

[0026] The liquefier 14 is a heat exchanger. The liquefier 14 is configured to cool and liquefy the carbon dioxide gas supplied from the carbon dioxide gas supply line 48 by heat exchange between the gas (high-purity carbon dioxide gas) supplied from the carbon dioxide gas supply line 48 and the nitrogen-rich gas supplied from the expansion gas line 27. Thus, the liquefier 14 is configured to utilize the cold thermal energy of the nitrogen-rich gas expanded in the turbine 25 to liquefy the carbon dioxide gas separated from the absorbent liquid in the regeneration tower 12. For example, regarding the temperature of various heat media in the liquefier 14, the temperature of the nitrogen-rich gas supplied from the expansion gas line 27 to the liquefier 14 may be about -80°C, the temperature of the gas supplied from the carbon dioxide gas supply line 48 to the liquefier 14 may be about 20°C, the temperature of the liquid carbon dioxide discharged from the liquefier 14 may be -45°C, and the temperature of the nitrogen-rich gas discharged from the liquefier 14 may be about -50°C.

[0027] The carbon dioxide liquefied in the liquefier 14 is introduced through the liquid carbon dioxide discharge line 54 into the storage tank 16 configured to store liquid carbon dioxide and is stored in the storage tank 16.

[0028] Here, the effects of the carbon dioxide recovery system 2 will be described. The absorption efficiency of carbon dioxide in the absorbent containing amine improves as the partial pressure of carbon dioxide in the absorption tower 10 increases. Therefore, according to the carbon dioxide recovery system 2, by supplying the exhaust gas compressed by the compressor 24 to the absorption tower 10, the partial pressure of carbon dioxide in the absorption tower 10 increases and the absorption efficiency of carbon dioxide in the absorbent improves. Thus, a large amount of carbon dioxide can be absorbed by the absorbent in the absorption tower 10 without increasing the size of the absorption tower 10. Also, the gas containing nitrogen (nitrogen-rich gas flowing through the nitrogen gas line 41) contained in the exhaust gas compressed by the compressor 24 is expanded by the turbine 25, and the cold thermal energy of the gas containing nitrogen expanded by the turbine 25 is used to liquefy the carbon dioxide gas in the liquefier 14. Therefore, there is no need to separately provide equipment for supplying the cold heat for liquefying the carbon dioxide gas. Accordingly, it is possible to suppress the increase in size and complexity of the equipment for recovering carbon dioxide contained in the exhaust gas, reduce the cost, and reduce the area of the site for installing the equipment. Further, the power recovered by the turbine 25 can assist in driving the compressor 24.

[0029] In some embodiments, as shown in FIG. 1, the carbon dioxide recovery system 2 includes a heat exchanger 35 (heat exchange device) configured to heat the absorbent flowing through the absorbent supply line 32 using the thermal energy of the absorbent flowing through the absorbent return line 56. By performing heat exchange between the absorbent flowing through the absorbent supply line 32 and the absorbent flowing through the absorbent return line 56 in the heat exchanger 35, the absorbent flowing through the absorbent supply line 32 is heated and the absorbent flowing through the absorbent return line 56 is cooled.

[0030] Since the absorbent containing amine is likely to release carbon dioxide gas as the temperature of the absorbent increases, by providing the heat exchanger 35, it is possible to promote the absorption of carbon dioxide into the absorbent in the absorption tower 10 and the separation of carbon dioxide gas from the absorbent in the regeneration tower 12.

[0031] In some embodiments, as shown in FIG. 1, the carbon dioxide recovery system 2 includes a heat exchanger 60 configured to heat the absorbent flowing through the absorbent circulation line 44 by utilizing the thermal energy of the exhaust gas flowing through the absorption tower exhaust gas supply line 28.

[0032] In the illustrated exemplary embodiment, the heat exchanger 60 includes a heat exchanger 30 provided in the absorption tower exhaust gas supply line 28, a heat exchanger 45 provided in the absorbent circulation line 44, and a heat medium circulation line 62 through which the heat medium circulates. The heat exchanger 30 is configured to heat the heat medium flowing through the heat medium circulation line 62 by utilizing the thermal energy of the exhaust gas flowing through the absorption tower exhaust gas supply line 28. That is, the exhaust gas flowing through the absorption tower exhaust gas supply line 28 and the heat medium flowing through the heat medium circulation line 62 exchange heat in the heat exchanger 30, whereby the exhaust gas flowing through the absorption tower exhaust gas supply line 28 is cooled and the heat medium flowing through the heat medium circulation line 62 is heated. The heat exchanger 45 is configured to heat the absorbent flowing through the absorbent circulation line 44 by utilizing the thermal energy of the heat medium flowing through the heat medium circulation line 62. That is, the heat medium flowing through the heat medium circulation line 62 and the absorbent flowing through the absorbent circulation line 44 exchange heat in the heat exchanger 45, whereby the heat medium flowing through the heat medium circulation line 62 is cooled and the absorbent flowing through the absorbent circulation line 44 is heated. When the outlet temperature of the compressor 24 is about 200°C, the temperature at the outlet of the heat exchanger 30 in the absorption tower exhaust gas supply line 28 may be, for example, about 100°C.

[0033] Thus, the heat exchanger 60 is configured to heat the absorbent flowing through the absorbent circulation line 44 by transferring the thermal energy of the exhaust gas flowing through the absorption tower exhaust gas supply line 28 to the absorbent flowing through the absorbent circulation line 44 via the heat medium flowing through the heat medium circulation line 62.

[0034] In this way, by providing the heat exchanger 60, the heat energy of the exhaust gas compressed by the compressor 24 and having an increased temperature can be utilized to heat the absorbent flowing through the absorbent circulation line 44 and separate carbon dioxide gas from the absorbent. For this reason, a boiler for heating the absorbent flowing through the absorbent circulation line 44 can be made unnecessary, or the equipment capacity of the boiler (not shown) can be reduced.

[0035] In some embodiments, as shown in FIG. 1, the carbon dioxide recovery system 2 includes a heat exchanger 64 configured to heat the absorbent flowing through the absorbent supply line 32 by utilizing the heat energy of the exhaust gas flowing through the downstream side (downstream side of the heat exchanger 60) of the heat exchanger 30 in the absorbent tower exhaust gas supply line 28.

[0036] In the illustrated exemplary embodiment, the heat exchanger 64 includes a heat exchanger 31 provided in the absorbent tower exhaust gas supply line 28, a heat exchanger 34 provided in the absorbent supply line 32, and a heat medium circulation line 66 through which the heat medium circulates. The heat exchanger 31 is configured to heat the heat medium flowing through the heat medium circulation line 66 by utilizing the heat energy of the exhaust gas flowing through the downstream side of the heat exchanger 30 in the absorbent tower exhaust gas supply line 28. That is, the exhaust gas flowing through the downstream side of the heat exchanger 30 in the absorbent tower exhaust gas supply line 28 and the heat medium flowing through the heat medium circulation line 66 exchange heat in the heat exchanger 31, whereby the exhaust gas flowing through the downstream side of the heat exchanger 30 in the absorbent tower exhaust gas supply line 28 is cooled and the heat medium flowing through the heat medium circulation line 66 is heated. The heat exchanger 34 is configured to heat the absorbent flowing through the absorbent supply line 32 by utilizing the heat energy of the heat medium flowing through the heat medium circulation line 66. That is, the heat medium flowing through the heat medium circulation line 66 and the absorbent flowing through the absorbent supply line 32 exchange heat in the heat exchanger 34, whereby the heat medium flowing through the heat medium circulation line 66 is cooled and the absorbent flowing through the absorbent supply line 32 is heated. Incidentally, when the temperature at the outlet of the heat exchanger 30 in the absorbent tower exhaust gas supply line 28 is about 100°C, the temperature at the outlet of the heat exchanger 31 in the absorbent tower exhaust gas supply line 28 may be, for example, about 30°C.

[0037] Thus, the heat exchanger 64 is configured to heat the absorption liquid flowing through the absorption liquid supply line 32 by transferring the thermal energy of the exhaust gas flowing on the downstream side of the heat exchanger 30 in the absorption tower exhaust gas supply line 28 to the absorption liquid flowing through the absorption liquid supply line 32 via the heat medium flowing through the heat medium circulation line 66.

[0038] The absorption liquid containing amine is likely to release carbon dioxide gas as the temperature of the absorption liquid increases. Therefore, by heating the absorption liquid flowing through the absorption liquid supply line 32 using the thermal energy of the exhaust gas flowing on the downstream side (downstream side of the heat exchanger 30) of the heat exchanger 60 in the absorption tower exhaust gas supply line 28, while effectively utilizing the thermal energy of the exhaust gas compressed by the compressor 24, the separation of carbon dioxide gas from the absorption liquid in the regeneration tower 12 can be promoted.

[0039] In some embodiments, as shown in FIG. 1, the carbon dioxide recovery system 2 includes a heat exchanger 42 (heat exchange device) provided in the nitrogen gas line 41. The heat exchanger 42 is configured to cool the nitrogen-rich gas flowing through the nitrogen gas line 41 by utilizing the cold thermal energy of the nitrogen-rich gas flowing on the downstream side of the liquefier 14 in the expansion gas line 27 (surplus cold thermal energy after liquefying carbon dioxide in the liquefier 14). That is, the nitrogen-rich gas flowing on the downstream side of the liquefier 14 in the expansion gas line 27 and the nitrogen-rich gas flowing through the nitrogen gas line 41 exchange heat in the heat exchanger 42, so that the nitrogen-rich gas flowing on the downstream side of the liquefier 14 in the expansion gas line 27 is heated and the nitrogen-rich gas flowing through the nitrogen gas line 41 is cooled. When the temperature of the nitrogen-rich gas at the inlet of the heat exchanger 42 in the expansion gas line 27 is, for example, about -50°C, the temperature of the nitrogen-rich gas at the outlet of the heat exchanger 42 in the expansion gas line 27 may be, for example, about -10°C.

[0040] The gas containing nitrogen discharged from the absorption tower 10 to the nitrogen gas line 41 contains moisture, and if this moisture is supplied to the turbine 25, there is a risk that the blades (not shown) of the turbine 25 will be damaged by the collision of droplets. For this reason, as described above, by using the cold and heat energy of the nitrogen-rich gas flowing on the downstream side of the liquefier 14 in the expansion gas line 27 to cool the nitrogen-rich gas flowing through the nitrogen gas line 41, while effectively utilizing the surplus cold heat after liquefying carbon dioxide, the nitrogen-rich gas flowing through the nitrogen gas line 41 can be dehumidified, and the risk of damage to the blades of the turbine 25 caused by the collision of droplets can be reduced.

[0041] In some embodiments, as shown in FIG. 1, the carbon dioxide recovery system 2 includes a heat exchange device 70 configured to heat the exhaust gas flowing through the compressor exhaust gas supply line 22 by using the heat energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line 48.

[0042] In the illustrated exemplary embodiment, the heat exchange device 70 includes a heat exchanger 49 provided in the carbon dioxide gas supply line 48, a heat exchanger 71 provided in the compressor exhaust gas supply line 22, and a cooling water circulation line 72 through which cooling water circulates. The heat exchanger 49 is configured to cool the exhaust gas flowing on the upstream side of the moisture separation device 50 in the carbon dioxide gas supply line 48 by heat exchange with the cooling water flowing through the cooling water circulation line 72. The heat exchanger 71 is configured to heat the exhaust gas flowing through the compressor exhaust gas supply line 22 by using the heat energy of the cooling water (the cooling water heated by the heat exchanger 49) flowing through the cooling water circulation line 72. That is, by performing heat exchange between the heat medium flowing through the cooling water circulation line 72 and the exhaust gas flowing through the compressor exhaust gas supply line 22 in the heat exchanger 71, the cooling water flowing through the cooling water circulation line 72 is cooled and the exhaust gas flowing through the compressor exhaust gas supply line 22 is heated.

[0043] In this way, the heat exchanger 70 is configured to heat the exhaust gas flowing through the compressor exhaust gas supply line 22 by transferring the thermal energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line 48 to the exhaust gas flowing through the compressor exhaust gas supply line 22 via the cooling water flowing through the cooling water circulation line 72.

[0044] In the regeneration tower 12, the absorbent is heated to separate carbon dioxide gas from the absorbent. Therefore, the carbon dioxide gas flowing through the carbon dioxide gas supply line that supplies the carbon dioxide gas from the regeneration tower 12 to the liquefier 14 is relatively hot. For this reason, as described above, by heating the exhaust gas flowing through the compressor exhaust gas supply line 22 using the thermal energy (surplus heat at the outlet of the regeneration tower 12) of the carbon dioxide gas flowing through the carbon dioxide gas supply line 48, the outlet temperature of the compressor 24 can be increased to promote the absorption of carbon dioxide by the absorbent in the absorption tower 10, and at the same time, the temperature of the carbon dioxide gas flowing through the carbon dioxide gas supply line 48 can be decreased to promote the liquefaction of carbon dioxide in the liquefier 14.

[0045] In some embodiments, as shown in FIG. 1, the carbon dioxide recovery system 2 includes a heat exchanger 74 configured to heat the exhaust gas flowing through the compressor exhaust gas supply line 22 using the thermal energy of the cooling water flowing through the cooling water circulation line 38.

[0046] In the illustrated exemplary embodiment, the heat exchange device 74 includes a heat exchanger 40 provided in the cooling water circulation line 38, a heat exchanger 76 provided in the compressor exhaust gas supply line 22, and a cooling water circulation line 75 through which cooling water circulates. The heat exchanger 40 is configured to cool the cooling water flowing through the cooling water circulation line 38 by heat exchange with the cooling water flowing through the cooling water circulation line 75. The heat exchanger 76 is configured to utilize the thermal energy of the cooling water (cooling water heated by the heat exchanger 40) flowing through the cooling water circulation line 75 to heat the exhaust gas flowing through the compressor exhaust gas supply line 22. That is, by performing heat exchange between the cooling water flowing through the cooling water circulation line 75 and the exhaust gas flowing through the compressor exhaust gas supply line 22 in the heat exchanger 76, the cooling water flowing through the cooling water circulation line 75 is cooled and the exhaust gas flowing through the compressor exhaust gas supply line 22 is heated.

[0047] Thus, the heat exchange device 74 is configured to heat the exhaust gas flowing through the compressor exhaust gas supply line 22 by transferring the thermal energy of the cooling water (cooling water heated by gas-liquid contact with the exhaust gas in the absorption tower 10) flowing through the cooling water circulation line 38 to the exhaust gas flowing through the compressor exhaust gas supply line 22 via the cooling water flowing through the cooling water circulation line 75.

[0048] Since the temperature of the cooling water sprayed in the absorption tower 10 rises due to gas-liquid contact with the exhaust gas in the absorption tower 10, it becomes higher than the temperature of the compressor exhaust gas supply line 22. Therefore, as described above, by heating the exhaust gas flowing through the compressor exhaust gas supply line 22 using the thermal energy of the cooling water flowing through the cooling water circulation line 38, the outlet temperature of the compressor 24 can be increased to promote the absorption of carbon dioxide by the absorption liquid in the absorption tower 10, and the temperature of the cooling water flowing through the cooling water circulation line 38 can be decreased.

[0049] FIG. 2 is a diagram schematically showing a carbon dioxide recovery system 2 according to another embodiment in the present disclosure. In the carbon dioxide recovery system 2 shown in FIG. 2, components having the same reference numerals as those of the carbon dioxide recovery system 2 shown in FIG. 1 represent components having the same configurations as those of the carbon dioxide recovery system 2 shown in FIG. 1 unless otherwise specified, and the description thereof will be omitted.

[0050] In some embodiments, as shown in FIG. 2, the carbon dioxide recovery system 2 further includes a heat exchanger 80 (heat exchange device) configured to cool the absorbent flowing through the absorbent return line 56 by utilizing the cold thermal energy of the nitrogen-containing gas flowing downstream of the liquefier 14 in the expansion gas line 27. In the example shown in FIG. 2, the nitrogen-containing gas flowing downstream of the heat exchanger 42 in the expansion gas line 27 and the absorbent flowing through the absorbent return line 56 exchange heat in the heat exchanger 80, so that the nitrogen-containing gas flowing downstream of the liquefier 14 in the expansion gas line 27 is heated and the absorbent flowing through the absorbent return line 56 is cooled.

[0051] The absorbent containing amine is more likely to absorb carbon dioxide as the temperature of the absorbent decreases. Therefore, as described above, by cooling the absorbent flowing through the absorbent return line 56 by utilizing the cold thermal energy of the nitrogen-containing gas flowing downstream of the liquefier 14 in the expansion gas line 27, it is possible to promote the absorption of carbon dioxide by the absorbent in the absorption tower 10 while effectively utilizing the surplus cold thermal energy after liquefying carbon dioxide.

[0052] FIG. 3 is a diagram schematically showing a carbon dioxide recovery system 2 according to still another embodiment in the present disclosure. In the carbon dioxide recovery system 2 shown in FIG. 3, components having the same reference numerals as those of the carbon dioxide recovery system 2 shown in FIG. 1 represent components having the same configurations as those of the carbon dioxide recovery system 2 shown in FIG. 1 unless otherwise specified, and the description thereof will be omitted.

[0053] In some embodiments, as shown in FIG. 3, the carbon dioxide recovery system 2 may further include a turbocharger 82 into which a part of the exhaust gas of the combustion device 4 flows. The turbocharger 82 includes a turbine 83 into which a part of the exhaust gas of the combustion device 4 flows, and a compressor 85 connected to the turbine 83 via a rotating shaft 84.

[0054] A branch line 86 branched from the cooling tower exhaust gas supply line 7 is connected to the inlet of the turbine 83, and a branch line 88 branched from the compressor exhaust gas supply line 22 is connected to the inlet of the compressor 85.

[0055] A part of the exhaust gas of the combustion device 4 is supplied to the turbine 83 via the branch line 86 to rotationally drive the turbine 83, so that the compressor 85 compresses the exhaust gas supplied via the branch line 88. The exhaust gas compressed by the compressor 85 is supplied to a position between the compressor 24 and the heat exchanger 30 in the absorption tower exhaust gas supply line 28. The exhaust gas discharged from the turbine 83 is supplied to the cooling tower 6.

[0056] According to such a configuration, the surplus exhaust gas of the combustion device 4 can be supplied to the turbine 83 of the turbocharger 82 to recover power, and the exhaust gas can be compressed by the compressor 85. Thereby, the absorption efficiency of carbon dioxide by the absorption liquid in the absorption tower 10 can be improved, and the absorption tower 10 can be miniaturized.

[0057] FIG. 4 is a diagram schematically showing a modified example of the absorption tower 10. In some embodiments, the absorption tower 10 shown in FIGS. 1 to 3 includes a first absorption tower 10A and a second absorption tower 10B, and the carbon dioxide recovery system 2 includes a connection line 90 connecting the first absorption tower 10A and the second absorption tower 10B, and a compressor 91 provided in the connection line 90. The compressor 91 is driven by a motor 92.

[0058] The first absorption tower 10A is configured to absorb carbon dioxide contained in the exhaust gas compressed by the compressor 24 (see FIGS. 1 to 3) into the absorption liquid. The first absorption tower 10A includes a spray 29A that sprays the absorption liquid inside the absorption tower 10. When the absorption liquid sprayed from the spray 29A comes into gas-liquid contact with the exhaust gas, the carbon dioxide contained in the exhaust gas is absorbed by the absorption liquid. The absorption liquid that has absorbed carbon dioxide is stored at the bottom of the absorption tower 10A, and the absorption liquid that has absorbed carbon dioxide is withdrawn from the bottom of the absorption tower 10A and supplied to the regeneration tower 12 through the absorption liquid supply line 32 (see FIGS. 1 to 3).

[0059] The CO2-lean gas (a gas containing carbon dioxide, nitrogen, etc. and having a lower carbon dioxide concentration than the exhaust gas inlet of the first absorption tower 10A) discharged from the first absorption tower 10A to the connection line 90 is compressed by the compressor 91 and supplied to the second absorption tower 10B. The second absorption tower 10B is configured to absorb carbon dioxide contained in the gas supplied from the first absorption tower 10A via the connection line 90 into the absorption liquid. The second absorption tower 10B includes a spray 29B that sprays the absorption liquid inside the absorption tower 10B. When the absorption liquid sprayed from the spray 29B comes into gas-liquid contact with the gas supplied from the connection line 90, the carbon dioxide contained in the gas supplied from the connection line 90 is absorbed by the absorption liquid. The absorption liquid that has absorbed carbon dioxide is stored at the bottom of the absorption tower 10B, and the absorption liquid that has absorbed carbon dioxide is withdrawn from the bottom of the absorption tower 10B and supplied to the regeneration tower 12 through the absorption liquid supply line 32 (see FIGS. 1 to 3).

[0060] According to such a configuration, the gas containing carbon dioxide discharged from the first absorption tower 10A is compressed by the compressor 91 provided in the connection line 90 and then supplied to the second absorption tower 10B. Therefore, the second absorption tower 10B can be downsized as compared with the case where there is no compressor between the first absorption tower 10A and the second absorption tower 10B.

[0061] In the example shown in FIG. 4, a configuration in which two absorption towers (the first absorption tower 10A and the second absorption tower 10B) are connected in series is illustrated. However, in other embodiments, three or more absorption towers may be connected in series, and by individually controlling the driving states of the compressors provided between the absorption towers in the plurality of absorption towers connected in series, the state of the gas supplied to each of the plurality of absorption towers can be freely changed between a pressurized state and a non-pressurized state for each absorption tower.

[0062] FIG. 5 is a diagram schematically showing a carbon dioxide recovery system 2 according to still another embodiment of the present disclosure. In the carbon dioxide recovery system 2 shown in FIG. 5, the same reference numerals as those of the components of the carbon dioxide recovery system 2 shown in FIG. 1 indicate the same components as those of the carbon dioxide recovery system 2 shown in FIG. 1 unless otherwise specified, and the description thereof is omitted.

[0063] In the embodiment shown in FIG. 5, the carbon dioxide recovery system 2 includes an intake line 93, an engine-driven turbocharger 96, an excess exhaust gas line 97, an exhaust heat recovery steam boiler 98, an excess exhaust gas turbocharger 131, a dehumidifying and regenerating heat exchanger 133, a cooler 134, a membrane separation device 135, a cooler 139, a cooler 145, and the like.

[0064] In the embodiment shown in FIG. 5, the combustion device 4 is an engine, and the intake line 93 is configured to supply the air compressed by the compressor 99 of the engine-driven turbocharger 96 to the combustion device 4. The exhaust gas line 95 is configured to supply the exhaust gas of the combustion device 4 to the membrane separation device 135 through the turbine 100 of the engine-driven turbocharger 96, the exhaust heat recovery steam boiler 98, the compressor 24, the cooler 145, the dehumidifying and regenerating heat exchanger 133, and the cooler 134 in this order.

[0065] The surplus exhaust gas line 97 branches from upstream of the turbine 100 in the exhaust gas line 95, bypasses the turbine 100, and is configured to be connected to the downstream side of the turbine 100 in the exhaust gas line 95. A bypass valve 101 is provided in the surplus exhaust gas line 97. A turbine 140 of the surplus exhaust gas turbocharger 131 is provided on the downstream side of the bypass valve 101 in the surplus exhaust gas line 97, and the exhaust gas of the combustion device 4 passing through the surplus exhaust gas line 97 is supplied to the exhaust heat recovery steam boiler 98 after driving the turbine 140. The exhaust gas passing through the turbine 100 or the surplus exhaust gas line 97 is supplied to the exhaust heat recovery steam boiler 98, and the exhaust heat recovery steam boiler 98 heats water to generate steam.

[0066] The carbon dioxide recovery system 2 shown in FIG. 5 includes a bypass line 143. One end of the bypass line 143 is connected to a position between the exhaust heat recovery steam boiler 98 and the compressor 24 in the exhaust gas line 95, and the other end of the bypass line 143 is connected to a position between the compressor 24 and the cooler 145 in the exhaust gas line 95. A compressor 141 of the surplus exhaust gas turbocharger 131 is provided in the bypass line 143, and the exhaust gas of the combustion device 4 exiting the exhaust heat recovery steam boiler 98 is supplied to the dehumidification regeneration heat exchanger 133 through the compressor 24 in the exhaust gas line 95 or the compressor 141 in the bypass line 143.

[0067] The exhaust gas (heat medium containing nitrogen gas) pressurized by the compressor 24 or the compressor 141 is cooled by the cooler 134 (for example, a water-cooled heat exchanger), and then cooled by heat exchange with the nitrogen-rich gas flowing through the expansion gas line 27 in the dehumidification regeneration heat exchanger 133, and further cooled by the cooler 134 (for example, a water-cooled heat exchanger) before being supplied to the membrane separation device 135.

[0068] The membrane separation device 135 includes a separation membrane 135a that preferentially permeates carbon dioxide gas over nitrogen gas, and is configured to separate the exhaust gas compressed by the compressor 24 (the exhaust gas supplied from the exhaust gas line 95) into a nitrogen-rich gas and a carbon dioxide-rich gas by the separation membrane 135a. The membrane separation device 135 is configured to allow carbon dioxide gas to permeate through the separation membrane 135a by utilizing the differential pressure across the separation membrane 135a. From the non-permeating side (the high-pressure side of the separation membrane 135a) of the separation membrane 135a in the membrane separation device 135, a high-pressure nitrogen-rich gas containing nitrogen gas is discharged as the non-permeating side gas, and from the permeating side (the low-pressure side of the separation membrane 135a) of the separation membrane 135a in the membrane separation device 135, a low-pressure carbon dioxide-rich gas containing carbon dioxide gas as the main component is discharged as the permeating side gas.

[0069] Regarding the membrane separation device 135, the "rich gas" with respect to a specific component contained in the gas means a gas having a higher concentration of the specific component compared to the exhaust gas supplied from the exhaust gas line 95 to the membrane separation device 135. For example, the nitrogen-rich gas means a gas having a higher concentration of nitrogen gas compared to the exhaust gas supplied from the exhaust gas line 95 to the membrane separation device 135 (a gas containing nitrogen gas at a concentration higher than the concentration of nitrogen gas in the exhaust gas), and the carbon dioxide-rich gas means a gas having a higher concentration of carbon dioxide gas compared to the exhaust gas supplied from the exhaust gas line 95 to the membrane separation device 135 (a gas containing carbon dioxide gas at a concentration higher than the concentration of carbon dioxide gas in the exhaust gas). Further, hereinafter, the non-permeating side of the separation membrane 135a in the membrane separation device 135 (the side of the exhaust gas inlet closer to the separation membrane 135a in the membrane separation device 135) will be simply referred to as the "non-permeating side of the membrane separation device 135", and the permeating side of the separation membrane 135a in the membrane separation device 135 (the side of the outlet of the carbon dioxide-rich gas closer to the separation membrane 135a in the membrane separation device 135) will be simply referred to as the "permeating side of the membrane separation device 135".

[0070] The non-permeating side of the membrane separation device 135 and the inlet of the turbine 25 are connected by a nitrogen gas line 160 through which the nitrogen-rich gas flows, and a regenerative heat exchanger 162 (a heat exchange device) is provided at a position between the membrane separation device 135 and the turbine 25 in the nitrogen gas line 160.

[0071] The regenerative heat exchanger 162 is configured to perform heat exchange between the nitrogen-rich gas flowing through the nitrogen gas line 160 and the nitrogen-rich gas flowing through the downstream side of the liquefier 14 in the expansion gas line 27. The nitrogen-rich gas flowing through the nitrogen gas line 160 is cooled by heat exchange with the nitrogen-rich gas flowing through the downstream side of the liquefier 14 in the expansion gas line 27 and then supplied to the turbine 25.

[0072] The permeate side of the membrane separation device 135 and the inlet of the absorption tower 10 are connected by a carbon dioxide gas line 166 through which the carbon dioxide-rich gas flows. The carbon dioxide-rich gas discharged from the permeate side of the membrane separation device 135 is cooled in the cooling tower 6 and then supplied to the absorption tower 10.

[0073] Note that the basic configurations of the absorption tower 10, the regeneration tower 12, etc. are as described with reference to FIGS. 1 to 3. In the embodiment shown in FIG. 5, the carbon dioxide recovery system 2 includes a boiler 168, a heat exchanger 45 that performs heat exchange between the steam generated by the boiler 168 and the absorbent flowing through the absorbent circulation line 44, a condenser 170 that cools and condenses the steam exiting the heat exchanger 45, and a feed water pump 172 that supplies water from the condenser 170 to the boiler 168. Further, in the embodiment shown in FIG. 5, the carbon dioxide recovery system 2 includes a cooler 139 (e.g., a water-cooled heat exchanger) provided downstream of the compressor 51. The gas (gas containing high-purity carbon dioxide) exiting the moisture separation device 50 is compressed by the compressor 51 driven by the motor 52, then cooled by the cooler 139, and then supplied to the liquefier 14.

[0074] According to the embodiment shown in FIG. 5, by separating the exhaust gas into a nitrogen-rich gas and a carbon dioxide-rich gas by a relatively compact membrane separation device 135 and then supplying the carbon dioxide-rich gas to the absorption tower 10, the absorption tower 10 can be downsized, and the overall equipment size of the carbon dioxide recovery system 2 can be reduced. Further, since the nitrogen-rich gas discharged from the membrane separation device 135 can be expanded by the turbine 25 and used as a cold heat source for liquefying the carbon dioxide gas, there is no need to separately provide equipment for supplying the cold heat for liquefying the carbon dioxide gas. Therefore, it is possible to suppress the enlargement and complication of the equipment for recovering carbon dioxide contained in the exhaust gas, and it is possible to reduce the cost and the area of the site for installing the equipment. Also, the power recovered by the turbine 25 can assist the driving of the compressor 24.

[0075] The present disclosure is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.

[0076] In the embodiment described with reference to FIG. 1 and the like, the heat exchange device 60 is configured to heat the absorption liquid flowing through the absorption liquid circulation line 44 by transferring the thermal energy of the exhaust gas flowing through the absorption tower exhaust gas supply line 28 to the absorption liquid flowing through the absorption liquid circulation line 44 via the heat medium flowing through the heat medium circulation line 62. However, the heat exchange device 60 may not include the heat medium circulation line 62. That is, the heat exchange device 60 may be configured to transfer the thermal energy of the exhaust gas flowing through the absorption tower exhaust gas supply line 28 to the absorption liquid flowing through the absorption liquid circulation line 44 without passing through another heat medium. In this case, the heat exchange device 60 may be configured to transfer the thermal energy of the exhaust gas flowing through the absorption tower exhaust gas supply line 28 to the absorption liquid flowing through the absorption liquid circulation line 44 by one heat exchanger.

[0077] Also, in the embodiment described with reference to FIG. 1 and the like, the heat exchanger 64 is configured to heat the absorption liquid flowing through the absorption liquid supply line 32 by transferring the thermal energy of the exhaust gas flowing downstream of the heat exchanger 30 in the absorption tower exhaust gas supply line 28 to the absorption liquid flowing through the absorption liquid supply line 32 via the heat medium flowing through the heat medium circulation line 66. However, the heat exchanger 64 may not be provided with the heat medium circulation line 66. That is, the heat exchanger 64 may be configured to transfer the thermal energy of the exhaust gas flowing downstream of the heat exchanger 30 in the absorption tower exhaust gas supply line 28 to the absorption liquid flowing through the absorption liquid supply line 32 without using another heat medium. In this case, the heat exchanger 64 may be configured to transfer the thermal energy of the exhaust gas flowing downstream of the heat exchanger 30 in the absorption tower exhaust gas supply line 28 to the absorption liquid flowing through the absorption liquid supply line 32 by means of a single heat exchanger.

[0078] Also, in the embodiment described with reference to FIG. 1 and the like, the heat exchanger 70 is configured to heat the exhaust gas flowing through the compressor exhaust gas supply line 22 by transferring the thermal energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line 48 to the exhaust gas flowing through the compressor exhaust gas supply line 22 via the cooling water flowing through the cooling water circulation line 72. However, the heat exchanger 70 may be configured to transfer the thermal energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line 48 to the exhaust gas flowing through the compressor exhaust gas supply line 22 without using another heat medium. In this case, the heat exchanger 70 may be configured to transfer the thermal energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line 48 to the exhaust gas flowing through the compressor exhaust gas supply line 22 by means of a single heat exchanger.

[0079] In the embodiment described with reference to FIG. 1 and the like, the heat exchanger 74 is configured to heat the exhaust gas flowing through the compressor exhaust gas supply line 22 by transferring the thermal energy of the cooling water flowing through the cooling water circulation line 38 (the cooling water heated by gas-liquid contact with the exhaust gas in the absorption tower 10) to the exhaust gas flowing through the compressor exhaust gas supply line 22 via the cooling water flowing through the cooling water circulation line 75. However, the heat exchanger 74 may be configured to transfer the thermal energy of the cooling water flowing through the cooling water circulation line 38 to the exhaust gas flowing through the compressor exhaust gas supply line 22 without using another heat medium. In this case, the heat exchanger 74 may be configured to transfer the thermal energy of the cooling water flowing through the cooling water circulation line 38 to the exhaust gas flowing through the compressor exhaust gas supply line 22 by one heat exchanger.

[0080] The content described in each of the above embodiments can be understood as follows, for example.

[0081] [1] The carbon dioxide recovery system according to at least one embodiment of the present disclosure (for example, the carbon dioxide recovery system 2 described above) is a carbon dioxide recovery system configured to recover carbon dioxide contained in the exhaust gas discharged from a combustion device (for example, the combustion device 4 described above), a compressor (for example, the compressor 24 described above) configured to compress the exhaust gas, an absorption tower (for example, the absorption tower 10 described above) configured to absorb carbon dioxide contained in the exhaust gas compressed by the compressor into an absorption liquid, a regeneration tower (for example, the regeneration tower 12 described above) configured to separate carbon dioxide gas from the absorption liquid discharged from the absorption tower, an expander (for example, the turbine 25 described above) configured to expand the gas containing nitrogen contained in the exhaust gas compressed by the compressor, a liquefier (for example, the liquefier 14 described above) configured to liquefy the carbon dioxide gas separated from the absorption liquid in the regeneration tower by using the cold and thermal energy of the gas containing nitrogen expanded by the expander, and includes.

[0082] For example, an absorption liquid containing an amine can absorb more carbon dioxide as the partial pressure of carbon dioxide is higher. According to the carbon dioxide recovery system described in the above [1], by supplying the exhaust gas compressed by the compressor to the absorption tower, the partial pressure of carbon dioxide at the inlet of the absorption tower can be increased. Therefore, a large amount of carbon dioxide can be absorbed by the absorption liquid without increasing the size of the absorption tower. In addition, the gas containing nitrogen in the exhaust gas compressed by the compressor is expanded by an expander, and the cold and heat energy of the gas containing nitrogen expanded by the expander is used to liquefy the carbon dioxide gas. Therefore, there is no need to separately provide equipment for supplying the cold and heat for liquefying the carbon dioxide gas. Therefore, it is possible to suppress the enlargement and complexity of the equipment for recovering carbon dioxide contained in the exhaust gas.

[0083] [2] In some embodiments, in the carbon dioxide recovery system described in the above [1], The expander is a turbine (for example, the above-mentioned turbine 25) connected to the compressor via a rotating shaft (for example, the above-mentioned rotating shaft 23), The carbon dioxide recovery system further includes a nitrogen gas line (for example, the above-mentioned nitrogen gas lines 41 and 160) configured to supply the gas containing nitrogen in the exhaust gas compressed by the compressor from the absorption tower to the turbine.

[0084] According to the carbon dioxide recovery system described in the above [2], by supplying the exhaust gas compressed by the compressor to the absorption tower, carbon dioxide can be efficiently absorbed by the absorption liquid in the absorption tower. The turbine is driven by using the pressure energy of the gas containing nitrogen discharged from the absorption tower, and the energy recovered by the turbine can be used to compress the exhaust gas by the compressor. Therefore, while suppressing the enlargement of the absorption tower, the exhaust gas can be compressed by the compressor using the power recovered by the turbine.

[0085] [3] In some embodiments, in the carbon dioxide recovery system described in the above [2], Further comprising an expansion gas line (e.g., the above-described expansion gas line 27) through which the gas containing nitrogen expanded by the turbine flows. The liquefier is provided in the expansion gas line. The carbon dioxide recovery system further comprises a heat exchange device (e.g., the above-described heat exchanger 42, regenerative heat exchanger 162) configured to cool the gas containing nitrogen flowing through the nitrogen gas line by utilizing the cold thermal energy of the gas containing nitrogen flowing downstream of the liquefier in the expansion gas line.

[0086] The gas containing nitrogen discharged from the absorption tower to the nitrogen gas line contains moisture. If this moisture is supplied to the turbine, there is a risk of damage to the turbine blades due to droplet collision. Therefore, as described in [3] above, by cooling the gas containing nitrogen flowing through the nitrogen gas line by utilizing the cold thermal energy (surplus cold thermal energy after liquefying carbon dioxide) of the gas containing nitrogen flowing downstream of the liquefier in the expansion gas line, while effectively utilizing the surplus cold thermal energy after liquefying carbon dioxide, the gas containing nitrogen flowing through the nitrogen gas line can be dehumidified, and the risk of damage to the turbine blades caused by droplet collision can be reduced.

[0087] [4] In some embodiments, in the carbon dioxide recovery system described in [2] above, An absorption liquid return line (e.g., the above-described absorption liquid return line 56) for returning the absorption liquid from the regeneration tower to the absorption tower, and An expansion gas line (e.g., the above-described expansion gas line 27) through which the gas containing nitrogen expanded by the turbine flows, and Further comprising, The liquefier is provided in the expansion gas line. The carbon dioxide recovery system further comprises a heat exchange device (e.g., the above-described heat exchanger 80) configured to cool the absorption liquid flowing through the absorption liquid return line by utilizing the cold thermal energy of the gas containing nitrogen flowing downstream of the liquefier in the expansion gas line.

[0088] For example, an absorption liquid containing an amine is more likely to absorb carbon dioxide as the temperature of the absorption liquid decreases. Therefore, as described in [4] above, by cooling the absorption liquid flowing through the absorption liquid return line using the cold heat energy of the nitrogen-containing gas flowing on the downstream side of the liquefier in the expansion gas line, while effectively utilizing the surplus cold heat after liquefying carbon dioxide, it is possible to promote the absorption of carbon dioxide by the absorption liquid in the absorption tower.

[0089] [5] In some embodiments, in the carbon dioxide recovery system described in any of [1] to [4] above, the regeneration tower is provided with an absorption tower exhaust gas supply line (for example, the absorption tower exhaust gas supply line 28 above) for supplying the exhaust gas compressed by the compressor to the absorption tower, and an absorption liquid circulation line (for example, the absorption liquid circulation line 44 above) configured to extract the absorption liquid that has absorbed the carbon dioxide from the regeneration tower and return it to the regeneration tower. The carbon dioxide recovery system further includes a first heat exchanger (for example, the heat exchanger 60 above) configured to heat the absorption liquid flowing through the absorption liquid circulation line using the heat energy of the exhaust gas flowing through the absorption tower exhaust gas supply line.

[0090] According to the carbon dioxide recovery system described in [5] above, it is possible to heat the absorption liquid flowing through the absorption liquid circulation line using the heat energy of the exhaust gas compressed by the compressor and having an increased temperature, and separate carbon dioxide gas from the absorption liquid. Therefore, it is possible to reduce the equipment capacity of the boiler for heating the absorption liquid flowing through the absorption liquid circulation line or eliminate the need for the boiler.

[0091] [6] In some embodiments, in the carbon dioxide recovery system described in [5] above, an absorption liquid supply line (for example, the absorption liquid supply line 32 above) for supplying the absorption liquid that has absorbed the carbon dioxide from the absorption tower to the regeneration tower, A second heat exchanger (for example, the heat exchanger 64 described above) configured to heat the absorbent flowing through the absorbent supply line by using the thermal energy of the exhaust gas flowing through the downstream side of the first heat exchanger in the absorption tower exhaust gas supply line; further comprises.

[0092] For example, an absorbent containing an amine is more likely to release carbon dioxide gas as the temperature of the absorbent increases. Therefore, as described in [6] above, by heating the absorbent flowing through the absorbent supply line by using the thermal energy of the exhaust gas flowing through the downstream side of the first heat exchanger in the absorption tower exhaust gas supply line, while effectively utilizing the thermal energy of the exhaust gas compressed by the compressor, the separation of carbon dioxide gas from the absorbent in the regeneration tower can be promoted.

[0093] [7] In some embodiments, in the carbon dioxide recovery system according to any one of [1] to [6] above, a compressor exhaust gas supply line (for example, the compressor exhaust gas supply line 22 described above) for supplying the exhaust gas to the compressor; a carbon dioxide gas supply line (for example, the carbon dioxide gas supply line 48 described above) for supplying the carbon dioxide gas separated from the absorbent from the regeneration tower to the liquefier; a heat exchanger (for example, the heat exchanger 70 described above) configured to heat the exhaust gas flowing through the compressor exhaust gas supply line by using the thermal energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line; further comprises.

[0094] In the regeneration tower, the absorption liquid is heated to separate carbon dioxide gas from the absorption liquid. Therefore, the carbon dioxide gas flowing through the carbon dioxide gas supply line that supplies the carbon dioxide gas from the regeneration tower to the liquefier is at a relatively high temperature. For this reason, as described in [7] above, by heating the exhaust gas flowing through the compressor exhaust gas supply line using the thermal energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line (the surplus heat at the outlet of the regeneration tower), the outlet temperature of the compressor can be increased to promote the absorption of carbon dioxide by the absorption liquid in the absorption tower, and at the same time, the temperature of the carbon dioxide gas flowing through the carbon dioxide gas supply line can be decreased to promote the liquefaction of carbon dioxide in the liquefier.

[0095] [8] In some embodiments, in the carbon dioxide recovery system described in any one of [1] to [7] above, a compressor exhaust gas supply line (for example, the compressor exhaust gas supply line 22 described above) that supplies the exhaust gas to the compressor, and a cooling water circulation line (for example, the cooling water circulation line 38 described above) configured to extract the cooling water discharged to the absorption tower from the absorption tower and return it to the absorption tower, and a heat exchange device (for example, the heat exchange device 74 described above) configured to heat the exhaust gas flowing through the compressor exhaust gas supply line using the thermal energy of the cooling water flowing through the cooling water circulation line, and are further provided.

[0096] The temperature of the cooling water supplied to the absorption tower rises due to heat exchange with the gas in the absorption tower, so it becomes higher than the temperature of the compressor exhaust gas supply line. For this reason, as described in [8] above, by heating the exhaust gas flowing through the compressor exhaust gas supply line using the thermal energy of the cooling water flowing through the cooling water circulation line, the outlet temperature of the compressor can be increased to promote the absorption of carbon dioxide by the absorption liquid in the absorption tower, and at the same time, the temperature of the cooling water flowing through the cooling water circulation line can be decreased.

[0097] [9] In some embodiments, in the carbon dioxide recovery system described in any one of [1] to [8] above, The absorption tower includes a first absorption tower (e.g., the first absorption tower 10A described above) and a second absorption tower (e.g., the second absorption tower 10B described above). The carbon dioxide recovery system further includes a connection line (e.g., the connection line 90 described above) for supplying a gas containing carbon dioxide discharged from the first absorption tower to the second absorption tower, and a compressor (e.g., the compressor 91 described above) provided in the connection line.

[0098] According to the carbon dioxide recovery system described in [9] above, a gas containing carbon dioxide discharged from the first absorption tower is compressed by a compressor provided in the connection line and then supplied to the second absorption tower. Therefore, the second absorption tower can be miniaturized as compared with the case where there is no compressor between the first absorption tower and the second absorption tower.

[0099]

[10] In some embodiments, in the carbon dioxide recovery system described in [1] above, a membrane separation device (e.g., the membrane separation device 135 described above) is provided between the compressor and the absorption tower in the flow direction of the exhaust gas, and is configured to separate the exhaust gas compressed by the compressor into a nitrogen-rich gas and a carbon dioxide-rich gas by a separation membrane (e.g., the separation membrane 135a described above); a carbon dioxide gas line (e.g., the carbon dioxide gas line 166 described above) for supplying the carbon dioxide-rich gas discharged from the membrane separation device to the absorption tower; a nitrogen gas line (e.g., the nitrogen gas line 160 described above) for supplying the nitrogen-rich gas discharged from the membrane separation device to the expander; and further includes.

[0100] According to the carbon dioxide recovery system described in

[10] above, the exhaust gas is separated into a nitrogen-rich gas and a carbon dioxide-rich gas by a relatively compact membrane separation device, and then the carbon dioxide-rich gas is supplied to the absorption tower, so that the absorption tower can be miniaturized and the overall device size of the carbon dioxide recovery system can be reduced. In addition, the nitrogen-rich gas discharged from the membrane separation device can be expanded by the expander and used as a cold heat source for liquefying carbon dioxide gas.

[0101]

[11] In some embodiments, in the carbon dioxide recovery system described in

[10] above, the expander is a turbine (such as the above-described turbine 25) connected to the compressor via a rotating shaft (such as the above-described rotating shaft 23).

[0102] According to the carbon dioxide recovery system described in

[11] above, the exhaust gas compressed by the compressor is supplied to the membrane separation device, the turbine is driven by utilizing the pressure energy of the nitrogen-rich gas discharged from the membrane separation device, and the exhaust gas is compressed by the compressor by utilizing the energy recovered by the turbine. Therefore, while suppressing the enlargement of the absorption tower, the exhaust gas can be compressed by the compressor by utilizing the power recovered by the turbine.

[0103]

[12] The carbon dioxide recovery method according to at least one embodiment of the present disclosure is a carbon dioxide recovery method for recovering carbon dioxide contained in the exhaust gas discharged from a combustion device (such as the above-described combustion device 4), comprising a compression step of compressing the exhaust gas, an absorption step of absorbing carbon dioxide contained in the exhaust gas compressed in the compression step into an absorption liquid, a separation step of separating carbon dioxide gas from the absorption liquid that has absorbed the carbon dioxide in the absorption step, an expansion step of expanding the gas containing nitrogen contained in the exhaust gas compressed in the compression step, a liquefaction step of liquefying the carbon dioxide gas separated from the absorption liquid by utilizing the cold and heat energy of the gas containing nitrogen expanded in the expansion step, and is provided with.

[0104] For example, an absorption liquid containing an amine can absorb more carbon dioxide as the partial pressure of carbon dioxide is higher. Therefore, according to the carbon dioxide recovery system described in the above

[12] , by supplying the compressed exhaust gas to the absorption tower, the partial pressure of carbon dioxide at the inlet of the absorption tower can be increased. Thus, even without increasing the size of the absorption tower, a large amount of carbon dioxide can be absorbed by the absorption liquid. Also, since the gas containing nitrogen in the compressed exhaust gas is expanded and the cold and heat energy of the expanded gas containing nitrogen is used to liquefy the carbon dioxide gas, there is no need to separately provide equipment for supplying the cold and heat for liquefying the carbon dioxide gas. Therefore, it is possible to suppress the enlargement and complication of the equipment for recovering carbon dioxide contained in the exhaust gas.

Explanation of Signs

[0105] 2 Carbon dioxide recovery system 4 Combustion device 5,95 Exhaust gas line 6 Cooling tower 7 Cooling tower exhaust gas supply line 8 Electric turbocharger 10 Absorption tower 10A First absorption tower 10B Second absorption tower 12 Regeneration tower 14 Liquefier 16 Storage tank 18,38,72,75 Cooling water circulation line 19,33,39,46,53,58 Pump 20,134,139,145 Cooler 22 Compressor exhaust gas supply line 23,84 Rotating shaft 24,51,85,91,99,141 Compressor 25,83,100,140 Turbine 26,52,92 Motor 27 Expansion gas line 28 Absorption tower exhaust gas supply line 29,29A,29B,36 Spray 30, 31, 34, 35, 40, 42, 45, 49, 71, 76, 80 Heat exchanger 32 Absorbent supply line 37 Receiving plate 41, 160 Nitrogen gas line 44 Absorbent circulation line 48 Carbon dioxide gas supply line 50 Moisture separator 54 Liquid carbon dioxide discharge line 56 Absorbent return line 60, 64, 70, 74 Heat exchange device 62, 66 Heat medium circulation line 82 Turbocharger 86, 88 Branch line 90 Connection line 93 Intake line 96 Engine - attached turbocharger 97 Excess exhaust gas line 98 Exhaust heat recovery steam boiler 101 Bypass valve 131 Excess exhaust gas turbocharger 133, 162 Regenerative heat exchanger 135 Membrane separation device 135a Separation membrane 143 Bypass line 166 Carbon dioxide gas line 168 Boiler 170 Condenser 172 Feed water pump

Claims

1. A carbon dioxide recovery system configured to recover carbon dioxide contained in the exhaust gas discharged from a combustion device, comprising: a compressor configured to compress the exhaust gas; an absorption tower configured to absorb carbon dioxide contained in the exhaust gas compressed by the compressor into an absorption liquid; a regeneration tower configured to separate carbon dioxide gas from the absorption liquid discharged from the absorption tower; an expander configured to expand the gas containing nitrogen contained in the exhaust gas compressed by the compressor; a liquefier configured to liquefy the carbon dioxide gas separated from the absorption liquid in the regeneration tower by using the cold and heat energy of the gas containing nitrogen expanded by the expander; A carbon dioxide recovery system comprising the above components.

2. The expander is a turbine connected to the compressor via a rotating shaft, The carbon dioxide recovery system further comprises a nitrogen gas line configured to supply the gas containing nitrogen contained in the exhaust gas compressed by the compressor from the absorption tower to the turbine. The carbon dioxide recovery system according to claim 1.

3. The carbon dioxide recovery system further comprises an expansion gas line through which the gas containing nitrogen expanded by the turbine flows, The liquefier is provided in the expansion gas line, The carbon dioxide recovery system further comprises a heat exchange device configured to cool the gas containing nitrogen flowing through the nitrogen gas line by using the cold and heat energy of the gas containing nitrogen flowing downstream of the liquefier in the expansion gas line. The carbon dioxide recovery system according to claim 2.

4. an absorption liquid return line for returning the absorption liquid from the regeneration tower to the absorption tower; an expansion gas line through which the gas containing nitrogen expanded by the turbine flows; The carbon dioxide recovery system further comprises the above components, The liquefier is provided in the expansion gas line, The carbon dioxide recovery system further comprises a heat exchange device configured to cool the absorption liquid flowing through the absorption liquid return line by using the cold and heat energy of the gas containing nitrogen flowing downstream of the liquefier in the expansion gas line. The carbon dioxide recovery system according to claim 2.

5. The regeneration tower is provided with an absorption tower exhaust gas supply line for supplying the exhaust gas compressed by the compressor to the absorption tower, and an absorption liquid circulation line configured to extract the absorption liquid that has absorbed carbon dioxide from the regeneration tower and return it to the regeneration tower. The carbon dioxide recovery system according to claim 1 further comprises a first heat exchanger configured to heat the absorbent flowing through the absorbent circulation line using the thermal energy of the exhaust gas flowing through the absorbent tower exhaust gas supply line.

6. An absorbent supply line for supplying the absorbent that has absorbed the carbon dioxide from the absorption tower to the regeneration tower, a second heat exchanger configured to heat the absorbent flowing through the absorbent supply line using the thermal energy of the exhaust gas flowing downstream of the first heat exchanger in the absorbent tower exhaust gas supply line, The carbon dioxide recovery system according to claim 5, further comprising:

7. A compressor exhaust gas supply line for supplying the exhaust gas to the compressor, a carbon dioxide gas supply line for supplying the carbon dioxide gas separated from the absorbent from the regeneration tower to the liquefier, a heat exchanger configured to heat the exhaust gas flowing through the compressor exhaust gas supply line using the thermal energy of the carbon dioxide gas flowing through the carbon dioxide gas supply line, The carbon dioxide recovery system according to claim 1, further comprising:

8. An exhaust gas supply line for supplying the exhaust gas to the compressor, a cooling water circulation line configured to extract the cooling water discharged to the absorption tower from the absorption tower and return it to the absorption tower, a heat exchanger configured to heat the exhaust gas flowing through the exhaust gas supply line using the thermal energy of the cooling water flowing through the cooling water circulation line, The carbon dioxide recovery system according to claim 1, further comprising:

9. The absorption tower includes a first absorption tower and a second absorption tower, The carbon dioxide recovery system according to claim 1, further comprising a connection line for supplying the gas containing carbon dioxide discharged from the first absorption tower to the second absorption tower, and a compressor provided in the connection line.

10. A membrane separation device provided between the compressor and the absorption tower in the flow direction of the exhaust gas and configured to separate the exhaust gas compressed by the compressor into a nitrogen-rich gas and a carbon dioxide-rich gas by a separation membrane, a carbon dioxide gas line for supplying the carbon dioxide-rich gas discharged from the membrane separation device to the absorption tower, a nitrogen gas line for supplying the nitrogen-rich gas discharged from the membrane separation device to the expander, The carbon dioxide recovery system according to claim 1, further comprising

11. The carbon dioxide recovery system according to claim 10, wherein the expander is a turbine connected to the compressor via a rotating shaft.

12. A carbon dioxide recovery method for recovering carbon dioxide contained in exhaust gas discharged from a combustion device, comprising: a compression step of compressing the exhaust gas; an absorption step of absorbing carbon dioxide contained in the exhaust gas compressed in the compression step with an absorption liquid; a separation step of separating carbon dioxide gas from the absorption liquid that has absorbed the carbon dioxide in the absorption step; an expansion step of expanding a gas containing nitrogen contained in the exhaust gas compressed in the compression step; a liquefaction step of liquefying the carbon dioxide gas separated from the absorption liquid by using the cold and heat energy of the gas containing nitrogen expanded in the expansion step; A carbon dioxide recovery method comprising

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