Carbon dioxide recovery system and carbon dioxide recovery method

Abstract

According to the present invention, a carbon dioxide recovery system for recovering carbon dioxide from a target gas that includes carbon dioxide and nitrogen comprises a first compressor that is configured to compress the target gas, a first membrane separation device that includes a separation membrane that preferentially transmits carbon dioxide gas over nitrogen gas and is configured to separate the target gas compressed at the compressor into a nitrogen-rich gas and a carbon dioxide–rich gas by means of the separation membrane, a first expander that is configured to expand the nitrogen-rich gas discharged from the first membrane separation device, and a liquefier that is configured to liquefy at least a portion of the carbon dioxide gas discharged from the first membrane separation device by means of the cold energy of the nitrogen-rich gas expanded at the first expander.

Description

Carbon dioxide capture system and carbon dioxide capture method

[0001] This application claims priority to Japanese Patent Application No. 2023-196440, filed on November 20, 2023, with the Japan Patent Office, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 describes a method for recovering high-concentration methane by separating biomethane into carbon dioxide and methane using a two-stage membrane separator and recirculating the carbon dioxide-rich gas that permeates the second-stage membrane separator to the upstream side of the first-stage membrane separator. In this method, the carbon dioxide gas separated from the methane separated by the first-stage membrane separator is compressed by a compressor, liquefied in a cooler, and recovered.

[0003] JP 2013-95727 A

[0004] The method described in Patent Document 1 requires equipment to supply a cold heat source for liquefying carbon dioxide gas, which tends to lead to an increase in size and complexity of the equipment for recovering carbon dioxide contained in the target gas.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a carbon dioxide capture system and a carbon dioxide capture method that can prevent the equipment for capturing carbon dioxide contained in a target gas from becoming larger and more complex.

[0006] In order to achieve the above object, a carbon dioxide capture system according to at least one embodiment of the present disclosure is a carbon dioxide capture system for capturing carbon dioxide from a target gas containing carbon dioxide and nitrogen, and includes: a first compressor configured to compress the target gas; a first membrane separation device including a separation membrane that preferentially permeates carbon dioxide gas over nitrogen gas, and configured to separate the target gas compressed by the first compressor into a nitrogen-rich gas and a carbon dioxide-rich gas by the separation membrane; a first expander configured to expand the nitrogen-rich gas discharged from the first membrane separation device; and a liquefier configured to liquefy at least a portion of the carbon dioxide gas discharged from the first membrane separation device using the cold energy of the nitrogen-rich gas expanded by the first expander.

[0007] In order to achieve the above object, a carbon dioxide capture method according to at least one embodiment of the present disclosure is a carbon dioxide capture method for capturing carbon dioxide from a target gas containing carbon dioxide and nitrogen, comprising: a compression step of compressing the target gas; a membrane separation step of separating the target gas compressed in the compression step into a carbon dioxide-rich gas and a nitrogen-rich gas using a separation membrane; an expansion step of expanding the nitrogen-rich gas produced in the membrane separation step; and a liquefaction step of liquefying the carbon dioxide-rich gas produced in the membrane separation step using the cold energy of the nitrogen-rich gas expanded in the expansion step.

[0008] According to at least one embodiment of the present disclosure, a carbon dioxide capture system and a carbon dioxide capture method are provided that can prevent the equipment for capturing carbon dioxide contained in a target gas from becoming larger and more complicated.

[0009] FIG. 1 is a diagram schematically showing a carbon dioxide capture system 1A according to an embodiment of the present disclosure. FIG. 2 is a diagram schematically showing a carbon dioxide capture system 1B according to an embodiment of the present disclosure. FIG. 3 is a diagram schematically showing a carbon dioxide capture system 1C according to an embodiment of the present disclosure. FIG. 4 is a diagram schematically showing a carbon dioxide capture system 1D according to an embodiment of the present disclosure. FIG. 5 is a diagram schematically showing a carbon dioxide capture system 1E according to an embodiment of the present disclosure.

[0010] Several embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the invention. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0011] 1 is a diagram schematically illustrating a carbon dioxide capture system 1A according to one embodiment of the present disclosure. The carbon dioxide capture system 1A is a system that captures carbon dioxide contained in flue gas emitted from a carbon dioxide emission source 2. Hereinafter, when simply referred to as "flue gas," it means the flue gas emitted from the carbon dioxide emission source 2.

[0012] In the exemplary embodiment shown in FIG. 1 , the carbon dioxide capture system 1A includes a carbon dioxide emission source 2, a compressor 4, a cooler 6, a membrane separation device 8, a regenerative heat exchanger 10, an expander 12, a liquefier 14, a compressor 16, a cooler 18, a membrane separation device 20, an expander 22, a compressor 24, a cooler 26, and a storage tank 28.

[0013] The carbon dioxide emission source 2 may be, for example, a combustion device such as an engine, and emits exhaust gas containing carbon dioxide (a target gas from which carbon dioxide is to be captured). The carbon dioxide emission source 2 and the membrane separation device 8 are connected by an exhaust gas line 30, which is a flow path for the exhaust gas.

[0014] The compressor 4 is provided in the exhaust gas line 30 between the carbon dioxide emission source 2 and the membrane separation device 8 , and compresses the exhaust gas emitted from the carbon dioxide emission source 2 .

[0015] The cooler 6 is provided between the compressor 4 and the membrane separation device 8 in the exhaust gas line 30, and is configured to cool the exhaust gas compressed by the compressor 4. The cooler 6 may be, for example, a water-cooled heat exchanger that exchanges heat between the exhaust gas compressed by the compressor 4 and cooling water.

[0016] The membrane separation device 8 includes a separation membrane 13 that preferentially allows carbon dioxide gas to permeate over nitrogen gas, and is configured to separate exhaust gas compressed by the compressor 4 (exhaust gas supplied from the exhaust gas line 30) into a nitrogen-rich gas and a carbon dioxide-rich gas using the separation membrane 13. The membrane separation device 8 includes a separation membrane 13 that preferentially allows carbon dioxide gas to permeate over nitrogen gas. The membrane separation device 8 is configured to allow carbon dioxide gas to permeate through the separation membrane 13 by utilizing a pressure difference between the front and rear of the separation membrane 13, and high-pressure nitrogen-rich gas containing nitrogen gas is discharged as a non-permeate side gas from the non-permeate side of the separation membrane 13 (the high-pressure side of the separation membrane 13) in the membrane separation device 8, and low-pressure carbon dioxide-rich gas containing carbon dioxide gas as a main component is discharged as a permeate side gas from the permeate side of the separation membrane 13 (the low-pressure side of the separation membrane 13) in the membrane separation device 8. In this specification, the term "rich gas" used herein with respect to a specific component contained in a gas refers to a gas having a higher concentration of the specific component compared to the exhaust gas supplied from the exhaust gas line 30 to the membrane separation device 8. For example, a nitrogen-rich gas refers to a gas having a higher concentration of nitrogen gas compared to the exhaust gas supplied from the exhaust gas line 30 to the membrane separation device 8 (a gas containing nitrogen gas at a concentration higher than the nitrogen gas concentration in the exhaust gas). A carbon dioxide-rich gas refers to a gas having a higher concentration of carbon dioxide gas compared to the exhaust gas supplied from the exhaust gas line 30 to the membrane separation device 8 (a gas containing carbon dioxide gas at a concentration higher than the carbon dioxide gas concentration in the exhaust gas). In the following description, the non-permeation side of the separation membrane 13 in the membrane separation device 8 (the side closer to the exhaust gas inlet than the separation membrane 13 in the membrane separation device 8) will be referred to simply as the "non-permeation side of the membrane separation device 8," and the permeation side of the separation membrane 13 in the membrane separation device 8 (the side closer to the carbon dioxide-rich gas outlet than the separation membrane 13 in the membrane separation device 8) will be referred to simply as the "permeation side of the membrane separation device 8."

[0017] The non-permeation side of the membrane separation device 8 and the inlet of the expander 12 are connected by a first nitrogen line 32 (first gas line) through which nitrogen-rich gas flows, and the regenerative heat exchanger 10 is provided at a position on the first nitrogen line 32 between the membrane separation device 8 and the expander 12.

[0018] The regenerative heat exchanger 10 is configured to perform heat exchange between the nitrogen-rich gas flowing through the first nitrogen line 32 and the nitrogen-rich gas flowing through the liquefier downstream line 34 described below, and the nitrogen-rich gas flowing through the first nitrogen line 32 is cooled by heat exchange with the nitrogen-rich gas flowing through the liquefier downstream line 34 before being supplied to the expander 12.

[0019] The expander 12 is configured to expand the nitrogen-rich gas supplied from the first nitrogen line 32. In the illustrated configuration, the expander 12 is a turbine (power recovery expander), and the expander 12 and the compressor 4 are connected by a rotating shaft 9. The compressor 4, the rotating shaft 9, and the expander 12 (turbine) constitute a power recovery turbocharger 15 (first turbocharger). The carbon dioxide capture system 1A also includes an electric motor 11 that drives the rotating shaft 9. The electric motor 11 is supplied with current from a power source (such as a generator) (not shown), and is driven by the current supplied from the power source to drive the rotating shaft 9, the compressor 4, and the expander 12. The expander 12 recovers a portion of the expansion energy generated when the nitrogen-rich gas expands, and the recovered expansion energy assists in driving the compressor 4.

[0020] The nitrogen-rich gas expanded in the expander 12 is supplied to the liquefier 14 through an expander downstream line 36 (expander downstream first line) that connects the outlet of the expander 12 and the liquefier 14 .

[0021] The permeation side of the membrane separation device 8 and the inlet of the membrane separation device 20 are connected by a first carbon dioxide line 38 through which the carbon dioxide-rich gas flows. The first carbon dioxide line 38 is provided with a compressor 16 and a cooler 18, in this order from the upstream side in the flow direction of the carbon dioxide-rich gas, and the carbon dioxide-rich gas discharged from the permeation side of the membrane separation device 8 is compressed by the compressor 16 and cooled by the cooler 18 before being supplied to the membrane separation device 20. The cooler 18 may be a water-cooled heat exchanger that exchanges heat between the carbon dioxide-rich gas compressed by the compressor 16 and cooling water.

[0022] The membrane separation device 20 includes a separation membrane 40 that preferentially allows carbon dioxide gas to permeate over nitrogen gas, and is configured to separate the carbon dioxide-rich gas compressed by the compressor 16 into a nitrogen-rich gas and a carbon dioxide-rich gas using the separation membrane 40. That is, the membrane separation device 20 is configured to discharge a carbon dioxide-rich gas having a higher purity than the carbon dioxide-rich gas supplied to the membrane separation device 20 from the permeation side of the separation membrane 40. The membrane separation device 20 is configured to use a pressure difference across the separation membrane 40 to allow carbon dioxide gas to permeate through the separation membrane 40, and high-pressure nitrogen-rich gas containing nitrogen gas is discharged as a non-permeation side gas from the non-permeation side of the separation membrane 40 (the high-pressure side of the separation membrane 40) in the membrane separation device 20, and low-pressure carbon dioxide-rich gas containing carbon dioxide gas as a main component is discharged as a permeation side gas from the permeation side of the separation membrane 40 (the low-pressure side of the separation membrane 40) in the membrane separation device 20. In the following, the non-permeation side of the separation membrane 40 in the membrane separation device 20 (the exhaust gas inlet side of the separation membrane 40 in the membrane separation device 20) will be simply referred to as the "non-permeation side of the membrane separation device 20," and the permeation side of the separation membrane 40 in the membrane separation device 20 (the carbon dioxide-rich gas outlet side of the separation membrane 40 in the membrane separation device 20) will be simply referred to as the "permeation side of the membrane separation device 20."

[0023] The non-permeation side of the membrane separation device 20 and the inlet of the expander 22 are connected by a second nitrogen line 42 (second gas line) through which nitrogen-rich gas flows, and the regenerative heat exchanger 10 is located between the membrane separation device 20 and the expander 22 in the second nitrogen line 42.

[0024] The regenerative heat exchanger 10 is configured to perform heat exchange between the nitrogen-rich gas flowing through the second nitrogen line 42 and the nitrogen-rich gas flowing through the liquefier downstream line 34, and the nitrogen-rich gas flowing through the second nitrogen line 42 is cooled by heat exchange with the non-permeation side gas flowing through the liquefier downstream line 34 and then supplied to the expander 22.

[0025] The expander 22 is configured to expand the nitrogen-rich gas supplied from the second nitrogen line 42. In the configuration shown, the expander 22 is a turbine (power recovery expander), and the expander 22 and the compressor 16 are connected by a rotating shaft 19. The carbon dioxide capture system 1A also includes an electric motor 21 that drives the rotating shaft 19. The electric motor 21 is supplied with current from a power source (such as a generator) (not shown), and is driven by the current supplied from the power source to drive the rotating shaft 19, the compressor 16, and the expander 22. The expander 22 recovers a portion of the expansion energy generated when the nitrogen-rich gas expands, and the recovered expansion energy assists in driving the compressor 16.

[0026] One end of an expander downstream line 46 (expander downstream second line) is connected to the outlet of the expander 22, and the other end of the expander downstream line 46 is connected to the expander downstream line 36 at a position between the expander 12 and the liquefier 14. A valve 48 is provided on the expander downstream line 46 upstream of the connection position with the expander downstream line 36.

[0027] The nitrogen-rich gas expanded in the expander 22 flows through the expander downstream line 46 into the expander downstream line 36 and is supplied to the liquefier 14 through the expander downstream line 36 .

[0028] The permeation side of the membrane separation device 20 and the inlet (carbon dioxide gas inlet) of the liquefier 14 are connected by a second carbon dioxide line 50 through which the carbon dioxide-rich gas flows. A compressor 24 and a cooler 26 are provided in the second carbon dioxide line 50, in this order from the upstream side in the flow direction of the carbon dioxide-rich gas, and the carbon dioxide-rich gas discharged from the permeation side of the membrane separation device 20 is compressed by the compressor 24 driven by an electric motor 25, cooled by the cooler 26, and then supplied to the liquefier 14. The cooler 26 may be a water-cooled heat exchanger that exchanges heat between the carbon dioxide-rich gas compressed by the compressor 24 and cooling water.

[0029] The liquefier 14 is configured to liquefy at least a portion of the carbon dioxide gas discharged from the permeation side of the membrane separation device 8 by using the cold energy of the nitrogen-rich gas expanded in the expander 12. In the illustrated exemplary embodiment, the liquefier 14 is configured as a heat exchanger that liquefies the carbon dioxide gas flowing through the second carbon dioxide line 50 by heat exchange between the nitrogen-rich gas flowing through the expander downstream line 36 and the carbon dioxide-rich gas flowing through the second carbon dioxide line 50. The carbon dioxide liquefied in the liquefier 14 is supplied to the storage tank 28 through a liquid line 59 and stored in the storage tank 28.

[0030] According to the carbon dioxide recovery system 1B, at least a portion of the carbon dioxide gas discharged from the membrane separation device 8 can be liquefied in the liquefier 14 using the cold energy of the nitrogen-rich gas expanded in the expander 12. This eliminates the need to provide a separate facility for supplying a cold source for liquefying the carbon dioxide gas, and prevents the facility for recovering the carbon dioxide contained in the exhaust gas from the carbon dioxide emission source 2 from becoming larger and more complex.

[0031] Fig. 2 is a diagram schematically illustrating a carbon dioxide capture system 1B according to an embodiment of the present disclosure. In the components of the carbon dioxide capture system 1B shown in Fig. 2, the same reference numerals as those in the carbon dioxide capture system 1A described above indicate the same components as those in the carbon dioxide capture system 1A shown in Fig. 1 unless otherwise specified, and descriptions thereof will be omitted.

[0032] 2, the carbon dioxide capture system 1B differs from the carbon dioxide capture system 1A in that it includes an adsorption tower 60 (adsorption device) instead of the membrane separation device 20. The carbon dioxide capture system 1B also differs from the carbon dioxide capture system 1A in that it does not include the compressor 16, the electric motor 21, and the expander 22, but includes a dehumidifying tower 62 (dehumidifying device) and a regenerative heat exchanger 92.

[0033] 2, in the carbon dioxide recovery system 1B, the permeation side of the membrane separation device 8 and the liquefier 14 are connected by a carbon dioxide line 66 through which the carbon dioxide-rich gas flows. The carbon dioxide line 66 is provided with a dehumidifying tower 62, an adsorption tower 60, a vacuum pump 68, a cooler 70, a compressor 72, and a cooler 84, in this order from the upstream side in the flow direction of the carbon dioxide-rich gas.

[0034] The dehumidifying tower 62 contains a desiccant 86 (for example, alumina, silica gel, zeolite, or MOF) that adsorbs moisture inside the dehumidifying tower 62. The dehumidifying tower 62 is configured to remove moisture contained in the carbon dioxide-rich gas discharged from the permeation side of the membrane separation device 8 by having the desiccant 86 adsorb it. The carbon dioxide-rich gas from which moisture has been removed in the dehumidifying tower 62 is supplied to the adsorption tower 60.

[0035] The adsorption tower 60 includes an adsorbent 88 therein for adsorbing carbon dioxide gas. The adsorption tower 60 is configured to adsorb carbon dioxide contained in the carbon dioxide-rich gas (carbon dioxide-rich gas from which moisture has been removed in the dehumidification tower 62) discharged from the permeation side of the membrane separation device 8 onto the adsorbent 88. The adsorbent 88 adsorbs carbon dioxide contained in the carbon dioxide-rich gas flowing through the carbon dioxide line 66 and separates the adsorbed carbon dioxide by at least one of pressure swing adsorption (PSA) and temperature swing adsorption (TSA). Pressure swing adsorption utilizes a pressure difference as a means for separating carbon dioxide from exhaust gas. That is, pressure swing adsorption separates carbon dioxide gas from the adsorbent 88 by reducing the pressure of the atmosphere around the adsorbent 88 to a second predetermined pressure that is lower than a first predetermined pressure at which carbon dioxide is adsorbed by the adsorbent 88. Temperature swing adsorption (TSA) utilizes a temperature difference as a means for separating carbon dioxide from exhaust gas. That is, in temperature swing adsorption (TSA), the adsorbent 88 that has adsorbed carbon dioxide is heated to a second predetermined temperature that is higher than the first predetermined temperature at which the carbon dioxide is adsorbed into the adsorbent 88, thereby separating the carbon dioxide gas from the adsorbent.

[0036] The adsorbent 88 may be, for example, a solid adsorbent such as zeolite. Note that the adsorbent is not limited to zeolite as long as it is a solid that can adsorb carbon dioxide. The adsorbent may also be, for example, a metal-organic framework (MOF).

[0037] The vacuum pump 68 is configured to reduce the pressure of the atmosphere around the adsorbent 88 in the adsorption tower 60 and discharge the carbon dioxide-rich gas containing carbon dioxide separated from the adsorbent 88 from the adsorption tower 60. The carbon dioxide-rich gas discharged from the adsorption tower 60 is supplied to the cooler 70 through the vacuum pump 68, cooled in the cooler 70, compressed in the compressor 72, and further cooled in the cooler 84 before being supplied to the liquefier 14. Note that each of the coolers 70 and 84 may be a water-cooled heat exchanger that exchanges heat between the carbon dioxide-rich gas flowing through the carbon dioxide line 66 and cooling water. In the illustrated exemplary embodiment, an electric motor 69 is connected to the vacuum pump 68 and drives the vacuum pump 68. An electric motor 73 is connected to the compressor 72 and drives the compressor 72.

[0038] The liquefier 14 is configured to liquefy at least a portion of the carbon dioxide gas discharged from the permeation side of the membrane separation device 8 by using the cold energy of the nitrogen-rich gas expanded in the expander 12. In the illustrated exemplary embodiment, the liquefier 14 is configured as a heat exchanger that liquefies the carbon dioxide gas flowing in the carbon dioxide line 66 by heat exchange between the nitrogen-rich gas flowing in the expander downstream line 36 and the carbon dioxide-rich gas flowing in the carbon dioxide line 66 on the downstream side of the cooler 84. The carbon dioxide liquefied in the liquefier 14 is supplied to the storage tank 28 through a liquid line 59 and stored in the storage tank 28.

[0039] The carbon dioxide recovery system 1B also includes a regenerative heat exchanger 92 and a post-heating line 95. The regenerative heat exchanger 92 is provided downstream of the regenerative heat exchanger 10 in the liquefier downstream line 34, and is configured to heat the nitrogen-rich gas flowing in the liquefier downstream line 34 with thermal energy of the exhaust gas compressed by the compressor 4. The regenerative heat exchanger 92 is configured to exchange heat between the nitrogen-rich gas flowing downstream of the regenerative heat exchanger 10 in the liquefier downstream line 34 and the exhaust gas flowing between the compressor 4 and the cooler 6 in the exhaust gas line 30.

[0040] The post-heating line 95 connects the nitrogen-rich gas outlet of the regenerative heat exchanger 92 to the dehumidifying tower 62. The post-heating line 95 is configured to supply the nitrogen-rich gas heated in the regenerative heat exchanger 92 to the dehumidifying tower 62, thereby drying the dehumidifying material 86 in the dehumidifying tower 62 with the nitrogen-rich gas.

[0041] 2 , moisture contained in the nitrogen-rich gas expanded by the expander 12 is removed by passing through the liquefier 14, the regenerative heat exchanger 10, and the regenerative heat exchanger 92, so that dry nitrogen-rich gas can be supplied to the dehumidifying tower 62 from the post-heating line 95. As a result, the dry nitrogen-rich gas supplied from the post-heating line 95 can be used to dry (regenerate) the desiccant 86, so there is no need to separately prepare dry gas for drying the desiccant, and the energy required to dry the desiccant 86 can be reduced.

[0042] Fig. 3 is a diagram schematically illustrating a carbon dioxide capture system 1C according to an embodiment of the present disclosure. In the components of the carbon dioxide capture system 1C shown in Fig. 3, the same reference numerals as those in the carbon dioxide capture system 1B described above indicate the same components as those in the carbon dioxide capture system 1B unless otherwise specified, and description thereof will be omitted.

[0043] 3, the carbon dioxide capture system 1C differs from the carbon dioxide capture system 1B in that it includes a heater 90. The heater 90 is provided in the adsorption tower 60 and functions as a separator that heats the adsorbent 88 and separates carbon dioxide gas from the adsorbent 88. The adsorbent 88 adsorbs carbon dioxide contained in the carbon dioxide-rich gas flowing through the carbon dioxide line 66 by the above-described temperature swing adsorption and pressure swing adsorption, and separates the adsorbed carbon dioxide.

[0044] The heater 90 may be configured to separate the carbon dioxide adsorbed in the adsorbent 88 by heating the adsorbent 88 using exhaust heat (for example, a heat medium at about 50°C to 90°C) from the carbon dioxide emission source 2 or equipment associated with the carbon dioxide emission source 2. Since the adsorbent has the property of separating carbon dioxide more easily as the temperature increases, the degree of vacuum of the suction pressure of the vacuum pump 68 required to separate a sufficient amount of carbon dioxide from the adsorbent 88 can be lowered compared to when the heater 90 is not used, thereby reducing the power of the vacuum pump 68 and enabling the running costs of the carbon dioxide capture system to be reduced.

[0045] Fig. 4 is a diagram schematically illustrating a carbon dioxide capture system 1D according to an embodiment of the present disclosure. In the components of the carbon dioxide capture system 1D shown in Fig. 4, the same reference numerals as those in the carbon dioxide capture system 1C described above indicate the same components as those in the carbon dioxide capture system 1C unless otherwise specified, and description thereof will be omitted.

[0046] As shown in FIG. 4 , the carbon dioxide recovery system 1D includes an engine 91, an intake line 93, an air cooler 94, an exhaust gas line 30, an engine-attached turbocharger 96, an excess exhaust gas line 97, a waste heat recovery steam boiler 98, and an excess exhaust gas power recovery turbocharger 131.

[0047] In the embodiment shown in Fig. 4, an engine 91 constitutes the carbon dioxide emission source 2. An intake line 93 is configured to supply air compressed by a compressor 99 of an engine-attached turbocharger 96 to the engine 91. An air cooler 94 is provided in the intake line 93 and configured to cool the air supplied to the engine 91. The exhaust gas line 30 is provided with, in order from the upstream side in the flow direction of the exhaust gas, a turbine 100 of the engine-attached turbocharger 96, a heat recovery steam boiler 98, a compressor 4 of the power recovery turbocharger 15, a regenerative heat exchanger 92, a cooler 6, and a membrane separation device 8. That is, the exhaust gas line 30 is configured to supply exhaust gas from the engine 91 to the membrane separation device 8 via the turbine 100 of the engine-attached turbocharger 96, the heat recovery steam boiler 98, the compressor 4, the regenerative heat exchanger 92, and the cooler 6.

[0048] The surplus exhaust gas line 97 is configured to branch off from the exhaust gas line 30 upstream of the turbine 100, bypass the turbine 100, and connect to the exhaust gas line 30 downstream of the turbine 100. That is, the surplus exhaust gas line 97 supplies exhaust gas from the engine 91 downstream of the turbine 100 of the engine-attached turbocharger 96. A bypass valve 101 is provided in the surplus exhaust gas line 97. A turbine 140 of the surplus exhaust gas power recovery turbocharger 131 is provided downstream of the bypass valve 101 in the surplus exhaust gas line 97. The exhaust gas from the engine 91 that has passed through the surplus exhaust gas line 97 drives the turbine 140 and is then supplied to the heat recovery steam boiler 98. The exhaust gas from the engine 91 that has passed through the turbine 100 or the surplus exhaust gas line 97 is supplied to the heat recovery steam boiler 98, where water is heated to generate steam.

[0049] The carbon dioxide recovery system 1 shown in Fig. 4 includes a bypass line 143. One end of the bypass line 143 is connected to a position in the exhaust gas line 30 between the heat recovery steam boiler 98 and the compressor 4, and the other end of the bypass line 143 is connected to a position in the exhaust gas line 30 between the compressor 4 and the regenerative heat exchanger 92. The bypass line 143 is provided with a compressor 141 of the surplus exhaust gas power recovery turbocharger 131, and the exhaust gas from the engine 91 that has left the heat recovery steam boiler 98 is supplied to the regenerative heat exchanger 92 through the compressor 4 in the exhaust gas line 30 or the compressor 141 in the bypass line 143.

[0050] 4 , the power required to pressurize the exhaust gas to ensure a pressure difference across the separation membrane 13 in the membrane separation device 8 can be compensated for by the power recovered by the excess exhaust gas power recovery turbocharger 131, thereby reducing the running costs of the carbon dioxide capture system 1D. Furthermore, for example, if the excess exhaust gas power recovery turbocharger 131 is connected to the vacuum pump 68, the power for driving the vacuum pump 68 can be compensated for by the power recovered from the excess exhaust gas power recovery turbocharger 131, thereby reducing the running costs of the carbon dioxide capture system 1D. Furthermore, for example, if the excess exhaust gas power recovery turbocharger 131 is connected to the compressor 72, the power for driving the compressor 72 can be compensated for by the power recovered from the excess exhaust gas power recovery turbocharger 131, thereby reducing the running costs of the carbon dioxide capture system 1D.

[0051] Fig. 5 is a diagram schematically illustrating a carbon dioxide capture system 1E according to an embodiment of the present disclosure. In the components of the carbon dioxide capture system 1E shown in Fig. 4, the same reference numerals as those in the carbon dioxide capture system 1D described above indicate the same components as those in the carbon dioxide capture system 1D unless otherwise specified, and description thereof will be omitted.

[0052] 5 , the carbon dioxide capture system 1E further includes a bypass line 110 configured to supply a portion of the carbon dioxide-rich gas discharged from the permeate side of the separation membrane 13 in the membrane separation device 8 to the inlet 4a of the compressor 4 of the power recovery turbocharger 15. In the exemplary embodiment shown, one end of the bypass line 110 is connected to a position in the exhaust gas line 30 between the heat recovery steam boiler 98 and the compressor 4, and the other end of the bypass line 110 is connected to a position in the first carbon dioxide line 38 between the membrane separation device 8 and the dehumidification tower 62. The bypass line 110 is provided with a valve 112 that can adjust the flow rate of the carbon dioxide-rich gas flowing through the bypass line 110.

[0053] In a configuration including the engine 91 and the engine-attached turbocharger 96, due to seasonal variations in air density (air density of the intake air of the engine 91), a large amount of excess exhaust gas (exhaust gas flowing through the excess exhaust gas line 97) that bypasses the turbine 100 of the engine-attached turbocharger 96 is likely to be generated, particularly in winter. For this reason, the flow rate of exhaust gas passing through the compressor 4 downstream of the exhaust heat recovery steam boiler 98 is likely to be smaller in winter than in summer.

[0054] Since the compressor 4 is designed to accommodate the maximum flow rate in summer, the compressor 4 operates at a partial load in winter, and there is a risk that the operating point will deviate from the design point, resulting in a decrease in efficiency.

[0055] Therefore, by providing the bypass line 110, it becomes possible to supply a portion of the carbon dioxide-rich gas discharged from the permeation side of the membrane separation device 8 to the inlet 4a of the compressor 4 of the power recovery turbocharger 15 during periods such as winter when the flow rate of the compressor 4 is likely to be low, thereby stabilizing the flow rate of the compressor 4 and suppressing a decrease in the efficiency of the compressor 4.

[0056] Furthermore, by returning the carbon dioxide-rich gas with a high carbon dioxide concentration to the upstream side of the membrane separation device 8 via the bypass line 110, the carbon dioxide concentration of the carbon dioxide-rich gas discharged from the permeation side of the membrane separation device 8 can be further increased, reducing the load on the adsorption tower 60 and reducing the running costs of the carbon dioxide recovery system 1E.

[0057] In some embodiments, for example, in the carbon dioxide capture system 1E shown in FIG. 5 , each of the coolers 6, 70, 84, and 94 may be a water-cooled heat exchanger configured to cool the heat medium by heat exchange with cooling water. Here, the heat medium is exhaust gas from the engine 91 in the case of the cooler 6, carbon dioxide-rich gas in the case of the cooler 70, carbon dioxide-rich gas in the case of the cooler 84, and intake air from the engine 91 in the case of the cooler 94. The carbon dioxide capture system 1E may also include a used cooling water line 114 configured to supply the cooling water used to cool the heat medium in any of the coolers 6, 70, 84, and 94 serving as a water-cooled heat exchanger to the heater 90. In this case, the heater 90 may be configured to heat the adsorbent 88 using the used cooling water (cooling water used to heat the heat medium in any of the coolers 6, 70, 84, and 94) supplied from the used cooling water line 114. For example, if the adsorbent 88 is zeolite, the outlet temperature of the cooling water from one of the coolers 6, 70, 84, and 94 that is connected to the used cooling water line 114 may be about 80°C (e.g., 50°C to 90°C). This allows the equipment of the carbon dioxide capture system 1E to be simplified and prevents increases in equipment costs compared to when a separate heat source (e.g., a boiler) is provided to heat the adsorbent.

[0058] The present disclosure is not limited to the above-described embodiments, and includes modifications of the above-described embodiments and appropriate combinations of these embodiments. For example, in the above-described embodiments, the expander 12 and the expander 22 are each a turbine, but one or both of the expander 12 and the expander 22 may be an expansion valve or the like.

[0059] The contents described in each of the above embodiments can be understood, for example, as follows.

[0060] 1) A carbon dioxide capture system according to at least one embodiment of the present disclosure is a carbon dioxide capture system (1A-1E) for capturing carbon dioxide from a target gas containing carbon dioxide and nitrogen, comprising: a first compressor (4, 16) configured to compress the target gas; a first membrane separation device (8, 20) including a separation membrane (13, 40) that preferentially permeates carbon dioxide gas over nitrogen gas, and configured to separate the target gas compressed by the first compressor into a nitrogen-rich gas and a carbon dioxide-rich gas by the separation membrane; a first expander (12, 22) configured to expand the nitrogen-rich gas discharged from the first membrane separation device; and a liquefier (14) configured to liquefy at least a portion of the carbon dioxide gas discharged from the first membrane separation device by using cold energy of the nitrogen-rich gas expanded by the first expander.

[0061] According to the carbon dioxide recovery system described in 1) above, at least a portion of the carbon dioxide gas discharged from the first membrane separation device can be liquefied using the cold energy of the nitrogen-rich gas expanded in the first expander, so there is no need to install separate equipment to supply a cold source for liquefying the carbon dioxide gas, and it is possible to prevent the equipment for recovering the carbon dioxide contained in the target gas from becoming larger and more complex.

[0062] 2) In some embodiments, in the carbon dioxide capture system described in 1) above, the first expander is a turbine (12, 22), and the carbon dioxide capture system further includes a rotating shaft (9, 19) connecting the first compressor and the turbine, and a motor (11, 21) configured to drive the rotating shaft.

[0063] According to the carbon dioxide capture system described in 2) above, at least a portion of the carbon dioxide gas discharged from the first membrane separation device can be liquefied using the cold energy of the nitrogen-rich gas expanded by the turbine. This eliminates the need for a separate facility to supply a cold source for liquefying the carbon dioxide gas, thereby minimizing the size and complexity of the facility for capturing carbon dioxide contained in the target gas. Furthermore, the energy recovered by the turbine can be used to increase the discharge pressure of the target gas in the first compressor, ensuring a sufficient pressure differential across the separation membrane in the first membrane separation device. This effectively minimizes the size and complexity of the facility for capturing carbon dioxide contained in the target gas. Furthermore, the discharge pressure of the first compressor can be adjusted by adjusting the motor output, allowing the amount of carbon dioxide captured to be adjusted according to the flow rate of the target gas.

[0064] 3) In some embodiments, the carbon dioxide capture system described in 1) or 2) above further includes: a first gas line (32, 42) configured to supply the nitrogen-rich gas discharged from the first membrane separation device to the first expander; a liquefier downstream line (34) through which the nitrogen-rich gas leaving the liquefier flows; and a heat exchanger (10) configured to exchange heat between the nitrogen-rich gas flowing in the first gas line between the first membrane separation device and the first expander and the nitrogen-rich gas flowing in the liquefier downstream line.

[0065] According to the carbon dioxide capture system described in 3) above, by performing heat exchange between the nitrogen-rich gas flowing in the first gas line between the first membrane separation device and the first expander and the nitrogen-rich gas flowing in the line downstream of the liquefier, the nitrogen-rich gas flowing in the first gas line can be cooled by the cold energy of the nitrogen-rich gas flowing in the line downstream of the liquefier before expansion in the first expander. This makes it possible to effectively prevent the equipment for capturing carbon dioxide contained in the target gas from becoming larger and more complicated.

[0066] 4) In some embodiments, the carbon dioxide capture system described in any of 1) to 3) above includes: a second compressor (16) configured to compress the carbon dioxide-rich gas discharged from the first membrane separation device (8); a second membrane separation device (20) including a separation membrane (40) that preferentially permeates carbon dioxide gas over nitrogen gas and configured to separate the carbon dioxide-rich gas compressed by the second compressor into nitrogen-rich gas and carbon dioxide gas by the separation membrane; and a second expander (22) configured to expand the nitrogen-rich gas discharged from the second membrane separation device, wherein the liquefier is configured to liquefy at least a portion of the carbon dioxide gas discharged from the second membrane separation device using cold energy of the nitrogen-rich gas expanded by the first expander and cold energy of the nitrogen-rich gas expanded by the second expander.

[0067] According to the carbon dioxide capture system described in 4) above, the carbon dioxide gas separated (extracted) from the target gas in the first membrane separation device is adsorbed onto the adsorbent of the adsorption device and separated from the adsorbent, thereby obtaining high-purity carbon dioxide gas from the adsorption device. Furthermore, the carbon dioxide gas separated from the adsorbent can be liquefied using the cold energy of the nitrogen-rich gas expanded in the first expander, thereby preventing the equipment for capturing carbon dioxide contained in the target gas from becoming larger and more complicated.

[0068] 5) In some embodiments, the carbon dioxide capture system described in any of 1) to 4) above includes an adsorption device (60) configured to adsorb the carbon dioxide contained in the carbon dioxide-rich gas discharged from the first membrane separation device onto an adsorbent (88), and the liquefier is configured to liquefy the carbon dioxide gas separated from the adsorbent by using the cold energy of the nitrogen-rich gas expanded by the first expander.

[0069] According to the carbon dioxide capture system described in 5) above, the carbon dioxide gas separated and extracted from the target gas in the first membrane separation device is adsorbed onto the adsorbent of the adsorption device and separated from the adsorbent, thereby obtaining high-purity carbon dioxide gas from the adsorption device. Furthermore, the carbon dioxide gas separated from the adsorbent can be liquefied using the cold energy of the nitrogen-rich gas expanded in the first expander, thereby preventing the equipment for capturing carbon dioxide contained in the target gas from becoming larger and more complicated.

[0070] 6) In some embodiments, the carbon dioxide capture system described in 3) above further comprises: a dehumidifier (62) configured to adsorb moisture contained in the carbon dioxide-rich gas discharged from the first membrane separation device onto a desiccant (86); a heater (92) provided downstream of the heat exchanger in the liquefier downstream line and configured to heat the nitrogen-rich gas flowing through the liquefier downstream line with thermal energy of the target gas compressed by the first compressor; and a heated gas line (95) configured to supply the nitrogen-rich gas heated by the heater to the dehumidifier to dry the desiccant of the dehumidifier.

[0071] According to the carbon dioxide capture system described in 6) above, moisture contained in the nitrogen-rich gas expanded by the first expander is removed by passing through the heat exchanger, so that dry nitrogen-rich gas can be supplied to the dehumidifying device from the post-heating line. As a result, the dry nitrogen-rich gas supplied from the post-heating line can be used to dry (regenerate) the desiccant, eliminating the need to separately prepare dry gas for drying the desiccant and reducing the energy required to dry the desiccant.

[0072] 7) In some embodiments, the carbon dioxide capture system described in 5) above comprises: a carbon dioxide gas line (66) that supplies the carbon dioxide gas separated from the adsorbent of the adsorption device to the liquefier; a vacuum pump (68) provided in the carbon dioxide gas line; and a heater configured to heat the adsorbent using exhaust heat from an emission source (2, 91) that discharges the target gas or equipment (96, 98, 131, 15) associated with the emission source.

[0073] According to the carbon dioxide capture system described in 7) above, the carbon dioxide adsorbed in the adsorbent can be separated from the adsorbent by heating the adsorbent with a heater using exhaust heat from the carbon dioxide emission source or equipment associated with the carbon dioxide emission source. Because the adsorbent has the property of separating carbon dioxide more easily as its temperature increases, the degree of vacuum of the suction pressure of the vacuum pump required to separate a sufficient amount of carbon dioxide from the adsorbent can be lowered compared to when a heater is not used, thereby reducing the power required for the vacuum pump and enabling the running costs of the carbon dioxide capture system to be reduced.

[0074] 8) In some embodiments, the carbon dioxide capture system according to any one of 1) to 7) above includes an engine (91); and an engine-attached turbocharger (96) configured to be driven by exhaust gas from the engine and compress intake air of the engine, wherein the carbon dioxide capture system comprises: a first turbocharger (15) that compresses the exhaust gas discharged from a turbine (100) of the engine-attached turbocharger; an excess exhaust gas line (97) that supplies the engine exhaust gas to a downstream side of the turbine of the engine-attached turbocharger, and a second turbocharger (131) including a turbine (140) provided in the excess exhaust gas line and a compressor (4) that compresses the exhaust gas discharged from the turbine (100) of the engine-attached turbocharger, wherein the first compressor is the compressor (4) of the first turbocharger, and the first expander is the turbine (12) of the first turbocharger.

[0075] According to the carbon dioxide capture system described in 8) above, the power required to pressurize the exhaust gas to ensure the differential pressure across the separation membrane in the first membrane separation device can be compensated for by the power recovered by the second turbocharger, thereby reducing the running costs of the carbon dioxide capture system.Furthermore, for example, if an excess exhaust gas power recovery turbocharger is connected to the vacuum pump described in 7) above, the power required to drive the vacuum pump can be compensated for by the power recovered from the excess exhaust gas power recovery turbocharger, thereby reducing the running costs of the carbon dioxide capture system.

[0076] 9) In some embodiments, the carbon dioxide recovery system described in 8) above further comprises a bypass line (110) configured to supply the carbon dioxide-rich gas discharged from the first membrane separation device to the inlet portion (4a) of the compressor of the first turbocharger.

[0077] In a carbon dioxide capture system including the engine and the engine-attached turbocharger described in 8) above, due to seasonal changes in air density, a large amount of excess exhaust gas (exhaust gas flowing through the excess exhaust gas line) bypassing the turbine of the engine-attached turbocharger is likely to be generated, particularly in winter. As a result, the flow rate of exhaust gas passing through the compressor (first compressor) of the first turbocharger is likely to be lower in winter than in summer. Because the first compressor is designed to accommodate the maximum flow rate in summer, unless special measures are taken, the first compressor will operate at partial load in winter, which could cause the operating point to shift from the design point and reduce efficiency. Therefore, by providing the bypass line described in 9) above, during periods such as winter when the flow rate of the first compressor is likely to be low, a portion of the carbon dioxide-rich gas discharged from the permeate side of the separation membrane in the first membrane separation device can be supplied to the inlet of the first compressor. This stabilizes the flow rate of the first compressor and suppresses a decrease in the efficiency of the first compressor.

[0078] Furthermore, by returning the carbon dioxide-rich gas with a high carbon dioxide concentration to the upstream side of the first membrane separation device via a bypass line, the carbon dioxide concentration of the carbon dioxide-rich gas discharged from the permeation side of the separation membrane in the first membrane separation device can be further increased, reducing the load on the adsorption device and reducing the running costs of the carbon dioxide recovery system.

[0079] 10) In some embodiments, the carbon dioxide recovery system described in any of 1) to 9) above comprises: an adsorption device (60) configured to adsorb carbon dioxide contained in the carbon dioxide-rich gas discharged from the first membrane separation device onto an adsorbent (88); a water-cooled heat exchanger (6, 70, 84, 94) configured to cool a heat medium by heat exchange with cooling water; a used cooling water line (114) configured to supply the cooling water after it has been used to cool at least a portion of the target gas in the water-cooled heat exchanger to the adsorption device; and a heater (90) configured to heat the adsorbent using the used cooling water supplied from the used cooling water line.

[0080] According to the carbon dioxide capture system described in 10) above, the adsorbent can be heated using used cooling water supplied from the used cooling water line. Therefore, compared to a case in which a separate heating source (e.g., a boiler) is provided for heating the adsorbent, the carbon dioxide capture system equipment can be simplified and increases in equipment costs can be suppressed.

[0081] 11) A carbon dioxide capture system method according to at least one embodiment of the present disclosure is a carbon dioxide capture method for capturing carbon dioxide contained in a target gas, comprising: a compression step for compressing the target gas; a membrane separation step for separating the target gas compressed in the compression step into a carbon dioxide-rich gas and a nitrogen-rich gas using a separation membrane (13, 40); an expansion step for expanding the nitrogen-rich gas produced in the membrane separation step; and a liquefaction step for liquefying the carbon dioxide-rich gas produced in the membrane separation step using the cold energy of the nitrogen-rich gas expanded in the expansion step.

[0082] According to the carbon dioxide recovery method described in 11) above, at least a portion of the carbon dioxide gas separated in the membrane separation step can be liquefied using the cold energy of the nitrogen-rich gas expanded in the expansion step, so there is no need to install separate equipment for supplying a cold source for liquefying the carbon dioxide gas, and it is possible to prevent the equipment for recovering carbon dioxide contained in the target gas from becoming larger and more complex.

[0083] DESCRIPTION OF SYMBOLS 1A, 1B, 1C, 1D, 1E Carbon dioxide recovery system 2 Carbon dioxide emission source 4, 16, 24, 72, 99, 141 Compressor 4a Inlet 6, 18, 26, 70, 84 Cooler 8, 20 Membrane separation device 9, 19 Rotating shaft 10, 92 Regenerative heat exchanger 11, 21, 25, 69, 73 Electric motor 12, 22 Expander 13, 40 Separation membrane 14 Liquefaction device 15 Power recovery turbocharger 28 Storage tank 30 Exhaust gas line 32 Nitrogen first line 38 Carbon dioxide first line 34 Liquefaction device downstream line 36, 46 Expander downstream line 42 Nitrogen second line 50 Carbon dioxide second line 48, 112 Valve 59 Liquid line 60 Adsorption tower 62 Dehumidification tower 64 Heat exchanger 66 Carbon dioxide line 68 Vacuum pump 86 Desiccant 88 Adsorbent 90 Heater 91 Engine 93 Intake line 94 Air cooler 95 Post-heating line 96 Engine-attached turbocharger 97 Excess exhaust gas line 98 Exhaust heat recovery steam boiler 100, 140 Turbine 101 Bypass valve 110, 143 Bypass line 131 Excess exhaust gas power recovery turbocharger

Claims

1. A carbon dioxide capture system for capturing carbon dioxide from a target gas containing carbon dioxide and nitrogen, comprising: a first compressor configured to compress the target gas; a first membrane separation device including a separation membrane that preferentially permeates carbon dioxide gas over nitrogen gas, and configured to separate the target gas compressed by the first compressor into a nitrogen-rich gas and a carbon dioxide-rich gas by the separation membrane; a first expander configured to expand the nitrogen-rich gas discharged from the first membrane separation device; and a liquefier configured to liquefy at least a portion of the carbon dioxide gas discharged from the first membrane separation device by using the cold energy of the nitrogen-rich gas expanded by the first expander.

2. The carbon dioxide capture system of claim 1, wherein the first expander is a turbine, and the carbon dioxide capture system further comprises a rotating shaft connecting the first compressor and the turbine, and a motor configured to drive the rotating shaft.

3. The carbon dioxide capture system described in claim 1, further comprising: a first gas line configured to supply the nitrogen-rich gas discharged from the first membrane separation device to the first expander; a liquefier downstream line through which the nitrogen-rich gas leaving the liquefier flows; and a heat exchanger configured to exchange heat between the nitrogen-rich gas flowing between the first membrane separation device and the first expander in the first gas line and the nitrogen-rich gas flowing in the liquefier downstream line.

4. A carbon dioxide capture system as described in claim 1, comprising: a second compressor configured to compress the carbon dioxide-rich gas discharged from the first membrane separation device; a second membrane separation device including a separation membrane that preferentially permeates carbon dioxide gas over nitrogen gas, and configured to separate the carbon dioxide-rich gas compressed by the second compressor into nitrogen-rich gas and carbon dioxide gas by the separation membrane; and a second expander configured to expand the nitrogen-rich gas discharged from the second membrane separation device, wherein the liquefier is configured to liquefy at least a portion of the carbon dioxide gas discharged from the second membrane separation device using the cold energy of the nitrogen-rich gas expanded by the first expander and the cold energy of the nitrogen-rich gas expanded by the second expander.

5. A carbon dioxide capture system as described in claim 1, comprising an adsorption device configured to adsorb the carbon dioxide contained in the carbon dioxide-rich gas discharged from the first membrane separation device into an adsorbent, and the liquefier configured to liquefy the carbon dioxide gas separated from the adsorbent by using the cold energy of the nitrogen-rich gas expanded in the first expander.

6. The carbon dioxide capture system described in claim 3, further comprising: a dehumidifier configured to adsorb moisture contained in the carbon dioxide-rich gas discharged from the first membrane separation device onto a desiccant; a heater provided downstream of the heat exchanger in the liquefier downstream line and configured to heat the nitrogen-rich gas flowing through the liquefier downstream line with thermal energy of the target gas compressed by the first compressor; and a heated gas line configured to supply the nitrogen-rich gas heated by the heater to the dehumidifier to dry the desiccant of the dehumidifier.

7. The carbon dioxide capture system described in claim 5, comprising: a carbon dioxide gas line that supplies the carbon dioxide gas separated from the adsorbent of the adsorption device to the liquefier; a vacuum pump provided in the carbon dioxide gas line; and a heater configured to heat the adsorbent using exhaust heat from an emission source that discharges the target gas or equipment associated with the emission source.

8. The carbon dioxide capture system of claim 1, comprising: an engine; and an engine-attached turbocharger configured to be driven by exhaust gas from the engine and compress an intake air of the engine, wherein the carbon dioxide capture system comprises: a first turbocharger that compresses the exhaust gas discharged from a turbine of the engine-attached turbocharger; an excess exhaust gas line that bypasses the turbine of the engine-attached turbocharger and supplies the exhaust gas from the engine to a downstream side of the turbine; and a second turbocharger including a turbine provided in the excess exhaust gas line and a compressor that compresses the exhaust gas discharged from the turbine of the engine-attached turbocharger, wherein the first compressor is the compressor of the first turbocharger and the first expander is the turbine of the first turbocharger.

9. The carbon dioxide capture system of claim 8, further comprising a bypass line configured to supply the carbon dioxide rich gas discharged from the first membrane separation device to an inlet of the compressor of the first turbocharger.

10. The carbon dioxide capture system described in claim 1, comprising: an adsorption device configured to adsorb carbon dioxide contained in the carbon dioxide-rich gas discharged from the first membrane separation device into an adsorbent; a water-cooled heat exchanger configured to cool a heat medium flowing within the carbon dioxide capture system by heat exchange with cooling water; a used cooling water line configured to supply the cooling water after it has been used to cool at least a portion of the target gas in the water-cooled heat exchanger to the adsorption device; and a heater configured to heat the adsorbent using the used cooling water supplied from the used cooling water line.

11. A carbon dioxide capture method for capturing carbon dioxide from a target gas containing carbon dioxide and nitrogen, comprising: a compression step for compressing the target gas; a membrane separation step for separating the target gas compressed in the compression step into a carbon dioxide-rich gas and a nitrogen-rich gas using a separation membrane; an expansion step for expanding the nitrogen-rich gas produced in the membrane separation step; and a liquefaction step for liquefying the carbon dioxide-rich gas produced in the membrane separation step using the cold energy of the nitrogen-rich gas expanded in the expansion step.

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