Gas Processing Systems

Abstract

To separate carbon dioxide from gas to be treated containing the carbon dioxide with less energy than conventional energy.SOLUTION: A gas treatment system 1A includes gas treatment units 10 and 20, and an expander 40. The gas treatment unit 10 includes: compressors 100A and 100B for sequentially pressurizing gas GA to be treated; and a separator 110 for separating the compressed gas GA for treated into first permeation gas G1 having high concentration of carbon dioxide and first non-permeation gas G2 having low concentration of carbon dioxide. The gas treatment unit 20 includes: compressors 200A and 200B for sequentially pressurizing the first permeation gas G1; and a separator 210 for separating the compressed first permeation gas G1 into second permeation gas G3 having high concentration of carbon dioxide and second non-permeation gas G4 having low concentration of carbon dioxide. The expander 40 recovers power from the first non-permeation gas G2 and the second non-permeation gas G4, and transmits the recovered power to the compressor 100A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to gas processing systems. [Background technology]

[0002] Carbon dioxide is contained in exhaust gas or natural gas generated by burning objects such as fossil fuels. Various technologies have been proposed for separating carbon dioxide from exhaust gas or natural gas, which is the gas to be treated. Patent Document 1 discloses an invention of a membrane system that separates carbon dioxide from natural gas that mainly contains methane and carbon dioxide using a carbon dioxide separating membrane. Patent Document 2 discloses an invention of an adsorption system that separates carbon dioxide contained in exhaust gas using an adsorbent such as polyamine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-155987 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-170379 Summary of the Invention [Problem to be solved by the invention]

[0004] In the membrane method, the gas to be treated is supplied across a membrane, and the pressure difference between the inlet and outlet sides is the driving force for separating carbon dioxide. Therefore, when separating carbon dioxide using the membrane method, the gas to be treated is generally pressurized to increase its pressure, and energy is required to compress the gas. Methods other than the membrane method, such as the adsorption method, also require the gas to be compressed or heated, which also requires energy.

[0005] The present disclosure has been made in consideration of the above circumstances, and aims to provide a technology that makes it possible to separate carbon dioxide from a gas to be treated that contains carbon dioxide using less energy than conventional methods. [Means for solving the problem]

[0006] A gas processing system according to one embodiment of the present disclosure is a gas processing system that separates carbon dioxide from a gas to be processed that contains carbon dioxide, and comprises: a first unit including one or more first compressors that pressurize the gas to be processed and a first separator that separates the gas to be processed pressurized by the one or more first compressors into a first gas having a higher carbon dioxide concentration than the gas to be processed and a second gas having a lower carbon dioxide concentration than the gas to be processed; a second unit including one or more second compressors that pressurize the first gas and a second separator that separates the first gas pressurized by the one or more second compressors into a third gas having a higher carbon dioxide concentration than the first gas and a fourth gas having a lower carbon dioxide concentration than the first gas; and an expander that recovers power from the second gas and the fourth gas and transmits the recovered power to one of the one or more first compressors and the one or more second compressors. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating an example of the configuration of a gas processing system 1A according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a separator 110. [Figure 3] FIG. 10 is a diagram showing an example of the configuration of a gas processing system 1B according to a modified example (2). [Figure 4] FIG. 10 is a diagram showing an example of the configuration of a gas processing system 1C according to a modified example (3). DETAILED DESCRIPTION OF THE INVENTION

[0008] 1. Embodiment FIG. 1 is a diagram illustrating an example configuration of a gas processing system 1A according to an embodiment of the present disclosure. The gas processing system 1A is a gas processing system that separates carbon dioxide from a gas to be processed GA containing carbon dioxide. In this embodiment, the gas to be processed GA is exhaust gas generated by burning a fossil fuel such as coal, oil, or natural gas. More specifically, the gas to be processed GA in this embodiment is exhaust gas obtained by removing soot, nitrogen oxides, and sulfur oxides from gas generated by thermal power generation in a thermal power plant. As shown in FIG. 1, the gas processing system 1A includes a gas processing unit 10, a gas processing unit 20, and an expander 40. As shown in FIG. 1, the gas processing unit 20 is connected in series to the gas processing unit 10.

[0009] A gas GA to be treated is supplied to the gas processing unit 10. As shown in FIG. 1, the gas processing unit 10 includes a compressor 100A, a compressor 100B, and a separator 110. As shown in FIG. 1, in the gas processing unit 10, the compressor 100A, the compressor 100B, and the separator 110 are connected in series in this order. Each of the compressor 100A and the compressor 100B is an example of a first compressor in the present disclosure. The separator 110 is an example of a first separator in the present disclosure. The gas processing unit 10 is an example of a first unit in the present disclosure.

[0010] The compressor 100A is a fluid machine that pressurizes the gas supplied thereto by the rotational motion of an impeller or rotor or the reciprocating motion of a piston. A gas GA to be treated is supplied to the compressor 100A. The pressurization by the compressor 100A reduces the volume of the gas GA to be treated and increases the pressure of the gas GA to be treated. Power to drive the impeller, rotor, or piston in the compressor 100A is provided from an electric motor or the like connected to the compressor 100A. In addition, although details will be described later, in this embodiment, power to drive the impeller, rotor, or piston in the compressor 100A is also provided from the expander 40.

[0011] The compressor 100B is supplied with the target gas GA that has been compressed by the compressor 100A. Like the compressor 100A, the compressor 100B is a fluid machine that pressurizes the supplied gas by the rotational motion of an impeller or rotor or the reciprocating motion of a piston. Hereinafter, when there is no need to distinguish between the compressor 100B and the compressor 100A, the compressors 100A and 100B may be referred to as compressors 100. Because the target gas GA that has been compressed by the compressor 100A is supplied to the compressor 100B, the volume of the compressor 100B may be smaller than the volume of the compressor 100A. Compression by the compressor 100B further reduces the volume of the target gas GA and further increases the pressure of the target gas GA. The power required to compress the target gas GA in the compressor 100B is provided by an electric motor or the like connected to the compressor 100B.

[0012] The separator 110 is supplied with the gas GA to be treated that has been compressed by the compressor 100B. FIG. 2 is a diagram showing an example of the configuration of the separator 110. As shown in FIG. 2, the separator 110 is provided with a membrane 110a for separating carbon dioxide from the gas GA to be treated that has been compressed by the compressor 100B. The membrane 110a has the property of selectively allowing carbon dioxide to pass through. In other words, the separator 110 is a membrane-type device that separates carbon dioxide using the membrane 110a that has the property of selectively allowing carbon dioxide to pass through. The reason why a membrane-type device is used as the separator 110 is that, in the adsorption method, post-treatment such as thermal treatment or chemical treatment is required to recover carbon dioxide from the adsorbent that has adsorbed the carbon dioxide, whereas the membrane method does not require such post-treatment.

[0013] Specific examples of the membrane 110a include a polyethylene glycol cross-linked membrane, a rubber-based membrane such as an elastomer, a membrane formed from porous carbon fiber, or a membrane formed from an inorganic material such as ceramic. In the separator 110, the greater the pressure difference between the partial pressure of carbon dioxide at the inlet side, i.e., the partial pressure of carbon dioxide contained in the gas to be treated GA compressed by the compressor 100B, and the partial pressure of carbon dioxide at the outlet side, the more efficiently the carbon dioxide can be separated. In this embodiment, two compressors 100 are provided on the inlet side of the separator 110, and the gas to be treated GA is compressed by these two-stage compressors 100. The partial pressure of carbon dioxide contained in the gas to be treated GA supplied to the first-stage compressor 100A is generally normal pressure of about 0.3 atmospheres. In this embodiment, the pressure of the gas to be treated GA supplied to the separator 110 is increased to 3 to 10 atmospheres by pressurization by the two-stage compressor 100, allowing for efficient carbon dioxide separation.

[0014] In this embodiment, the target gas GA compressed by the compressor 100B is separated by the separator 110 into a first permeable gas G1 that permeates the membrane 110a and a first non-permeable gas G2 that does not permeate the membrane 110a. The first permeable gas G1 is a gas with a higher carbon dioxide concentration than the target gas GA. The size and type of the membrane 110a can be selected, for example, so that the carbon dioxide concentration in the first permeable gas G1 is about 50% higher than the carbon dioxide concentration in the target gas GA. The first permeable gas G1 is an example of the first gas in the present disclosure. The first non-permeable gas G2 is a gas with a lower carbon dioxide concentration than the target gas GA. The first non-permeable gas G2 is an example of the second gas in the present disclosure. As shown in FIG. 1, the first permeable gas G1 is supplied to the gas processing unit 20, and the first non-permeable gas G2 is supplied to the expander 40.

[0015] As shown in FIG. 1, gas processing unit 20 includes compressors 200A and 200B, and separator 210. As shown in FIG. 2, compressors 200A, 200B, and separator 210 are connected in series in this order. Like compressor 100, compressors 200A and 200B are each a fluid machine that compresses supplied gas by the rotational motion of an impeller or rotor or the reciprocating motion of a piston. Hereinafter, when there is no need to distinguish between compressors 200A and 200B, compressors 200A and 200B may be referred to as compressors 200. Like separator 110, separator 210 is a membrane-type device that separates carbon dioxide using a membrane that has the property of selectively allowing carbon dioxide to pass through.

[0016] The compressor 200A is supplied with a first permeable gas G1. As described above, the gas GA to be treated, pressurized by the compressor 100B, is separated into a first permeable gas G1 and a first non-permeable gas G2 by the separator 110. Because only the first permeable gas G1 is supplied to the compressor 200A, the volume of the compressor 200A may be smaller than the volume of the compressor 100B. Compression by the compressor 200A reduces the volume of the first permeable gas G1 and increases the pressure of the first permeable gas G1. The power required to compress the first permeable gas G1 in the compressor 200A is provided by an electric motor or the like connected to the compressor 200A.

[0017] The compressor 200B is supplied with the first permeable gas G1 compressed by the compressor 200A. Because the compressor 200B is supplied with the first permeable gas G1 compressed by the compressor 200A, the volume of the compressor 200B may be smaller than the volume of the compressor 200A. Due to the compression by the compressor 200B, the volume of the first permeable gas G1 is further reduced and the pressure of the first permeable gas G1 is further increased. The power required to compress the first permeable gas G1 in the compressor 200B is provided by an electric motor or the like connected to the compressor 200B.

[0018] The separator 210 is supplied with the first permeable gas G1 compressed by the compressor 100B. In the separator 210, too, separation of carbon dioxide is performed due to the pressure difference between the partial pressure of carbon dioxide on the inlet side, i.e., the partial pressure of carbon dioxide contained in the first permeable gas G1 compressed by the compressor 200B, and the partial pressure of carbon dioxide on the outlet side. In this embodiment, the partial pressure of carbon dioxide on the outlet side of the separator 210 is approximately normal pressure, i.e., the partial pressure of carbon dioxide in the atmosphere. In this embodiment, two compressors 200 are provided on the inlet side of the separator 210, and the first permeable gas G1 is compressed by these two compressors 100, so the partial pressure of carbon dioxide contained in the first permeable gas G1 can be further increased and carbon dioxide can be separated efficiently.

[0019] The first permeable gas G1 compressed by the compressor 200B is separated by the separator 210 into a second permeable gas G3 that permeates the membrane included in the separator 210 and a second non-permeable gas G4 that does not permeate the membrane. The second permeable gas G3 is a gas with a higher carbon dioxide concentration than the first permeable gas G1. The second permeable gas G3 is an example of a third gas in the present disclosure. The second non-permeable gas G4 is a gas with a lower carbon dioxide concentration than the first permeable gas G1. The second non-permeable gas G4 is an example of a fourth gas in the present disclosure.

[0020] The second permeable gas G3 discharged from the separator 210 is stored in a tank or the like (not shown), and the carbon dioxide contained in the second permeable gas G3 may be discharged to an underground reservoir or used for enhanced oil recovery. Enhanced oil recovery is a method of recovering non-self-flowing crude oil from an oil field, etc., by injecting carbon dioxide underground in the oil field and using the pressure of this carbon dioxide to force the crude oil out. Furthermore, the second non-permeable gas G4 discharged from the separator 210 is combined with the first non-permeable gas G2 and then supplied to the expander 40, as shown in FIG. 1 .

[0021] The expander 40 is a device that converts fluid pressure energy into kinetic energy, such as rotational motion. The expander 40 of this embodiment includes a turbine as a mechanism for converting fluid pressure energy into kinetic energy, but may include a piston instead of the turbine. A high-pressure first non-permeable gas G2 and an even higher-pressure second non-permeable gas G4 are supplied to the expander 40. The expander 40 expands the supplied first non-permeable gas G2 and second non-permeable gas G4 to rotate the turbine, thereby generating torque. Converting the pressures of the first non-permeable gas G2 and second non-permeable gas G4 into kinetic energy in this manner is referred to as recovering power from the first non-permeable gas G2 and second non-permeable gas G4. The rotating shaft that generates the torque in the expander 40, such as the rotating shaft of a turbine, is coaxially connected to the rotating shaft of the impeller or rotor of the compressor 100A or the crankshaft that reciprocates the piston. Therefore, the power recovered from the first non-permeable gas G2 and the second non-permeable gas G4 by the expander 40 is transmitted to the compressor 100A.

[0022] The reason why the power recovered by the expander 40 is transmitted to the first-stage compressor 100A in the gas processing system 1A is as follows. As described above, among compressors 100A, 100B, 200A, and 200B, compressor 100A has the largest volume. Generally, the larger the volume of a compressor, the higher the efficiency of the compressor. Therefore, using the power recovered by the expander 40 in compressor 100A, which has the largest volume among compressors 100A, 100B, 200A, and 200B, leads to an improvement in overall efficiency. Furthermore, among compressors 100A, 100B, 200A, and 200B, compressor 100A has the largest gas flow rate and therefore the largest compression work load. Therefore, among compressors 100A, 100B, 200A, and 200B, compressor 100A has the highest compression load, i.e., the power required for compression is also the largest. If the power recovered by expander 40 were transmitted to compressor 100B, 200A, or 200B, it is conceivable that the power recovered by expander 40 would exceed the compression load. If the power recovered by expander 40 exceeds the compression load, the difference between the recovered power and the compression load would be wasted. By transmitting the power recovered by expander 40 to compressor 100A, which has the highest compression load, it is possible to utilize the power recovered by expander 40 without waste.

[0023] In the gas processing system 1A of the present embodiment, the power recovered from the first non-permeable gas G2 and the second non-permeable gas G4 by the expander 40 is used to compress the gas GA to be treated in the gas processing unit 10, making it possible to separate carbon dioxide from the gas GA to be treated with less energy than in conventional techniques that do not use this power. Furthermore, in the gas processing system 1A of the present embodiment, power is recovered collectively from the first non-permeable gas G2 and the second non-permeable gas G4 by the expander 40, making it possible to reduce the manufacturing cost of the gas processing system 1A compared to an embodiment that provides an expander that recovers power from the first non-permeable gas G2 and an expander that recovers power from the second non-permeable gas G4. In other words, the gas processing system 1A of the present embodiment makes it possible to efficiently separate carbon dioxide from the gas GA to be treated at lower cost and with less energy than conventional techniques.

[0024] 2. Transformation The above-described embodiment may be modified as follows. (1) In the above embodiment, the gas to be treated GA is exhaust gas emitted from a thermal power plant. However, the gas to be treated GA may be exhaust gas from a vehicle powered by an internal combustion engine such as a gasoline engine or a diesel engine, or exhaust gas from a ship powered by an internal combustion engine or an external combustion engine. A specific example of an external combustion engine is a combination of a turbine and a boiler that drives the turbine. The gas to be treated GA may also be gas generated by incinerating substances other than fossil fuels, such as exhaust gas from a waste incinerator, or natural gas.

[0025] (2) When the compression workload of compressor 200A is the largest among compressors 100A, 100B, 200A, and 200B, i.e., when the compression load of compressor 200A is the largest, gas processing system 1A shown in FIG. 1 may be modified to gas processing system 1B shown in FIG. 3. As is clear from a comparison of FIGS. 1 and 3, gas processing system 1B differs from gas processing system 1A in that power recovered by expander 40 is transmitted to compressor 200A. As shown in FIG. 3, in gas processing system 1B as well, second non-permeate gas G4 is merged with first non-permeate gas G2 and supplied to expander 40. Therefore, in gas processing system 1B, the power recovered collectively by expander 40 from first non-permeate gas G2 and second non-permeate gas G4 is used to compress first permeate gas G1 in gas processing unit 20. Therefore, the gas processing system 1B also makes it possible to efficiently separate carbon dioxide from the gas GA to be processed at lower cost and with less energy than conventional methods. Furthermore, when the compression work load in the compressor 100B is the largest, the gas processing system 1A may be modified so that the power recovered by the expander 40 is transmitted to the compressor 100B. Similarly, when the compression work load in the compressor 200B is the largest, the gas processing system 1A may be modified so that the power recovered by the expander 40 is transmitted to the compressor 200B. Note that when the compression loads in each of the compressors 100A, 100B, 200A, and 200B all exceed the power recovered by the expander 40, the power recovered by the expander 40 may be transmitted to any of the compressors 100A, 100B, 200A, and 200B.

[0026] (3) Gas processing system 1A shown in Fig. 1 may be modified into gas processing system 1C shown in Fig. 4. As is clear from a comparison between Fig. 1 and Fig. 4, gas processing system 1C differs from gas processing system 1A in the following three points.

[0027] The first difference is that compressor 100C is provided in gas processing unit 10 before separator 110 and after compressor 100B. Compressor 100C is supplied with gas GA to be treated that has been compressed by compressor 100B. Like compressors 100A and 100B, compressor 100C is a fluid machine that pressurizes the supplied gas by the rotational motion of an impeller or rotor or the reciprocating motion of a piston. In gas processing system 1C, gas GA to be treated that has been pressurized sequentially by compressors 100A, 100B, and 100C is provided to separator 110. Note that gas processing unit 10 in gas processing system 1A shown in FIG. 1 may include three or more compressors 100, and gas processing unit 20 in gas processing system 1A may include three or more compressors 200. Similarly, gas processing unit 10 in gas processing system 1B shown in FIG. 3 may include three or more compressors 100, and gas processing unit 20 in gas processing system 1B may include three or more compressors 200.

[0028] The second difference is that compressor 200B is omitted in gas processing unit 20. In gas processing system 1B, first permeable gas G1 pressurized by compressor 200A is provided to separator 210. Similarly, in gas processing system 1A shown in FIG. 1 or gas processing system 1B shown in FIG. 3, gas processing unit 10 may include one compressor 100, and gas processing unit 20 may include one compressor 200. In other words, the number of compressors 100 included in gas processing unit 10 may be one or more, and the number of compressors 200 included in gas processing unit 20 may also be one or more.

[0029] The third difference is that gas processing unit 30 is provided after gas processing unit 20. Gas processing unit 30 includes compressor 300A, compressor 300B, and separator 310. As shown in FIG. 3 , compressor 300A, compressor 300B, and separator 310 are connected in series in this order. Like compressors 100 and 200, compressors 300A and 300B are fluid machines that compress supplied gas by the rotational motion of an impeller or rotor or the reciprocating motion of a piston. Hereinafter, when there is no need to distinguish between compressors 300A and 300B, compressors 300A and 300B may be referred to as compressors 300. Like gas processing unit 10 and gas processing unit 20, gas processing unit 30 may include one or more compressors 300. Similar to separator 110 and separator 210, separator 310 is a device that separates carbon dioxide using a membrane that has the property of selectively allowing carbon dioxide to permeate.

[0030] In the gas processing system 1C, the second permeable gas G3 discharged from the separator 210 is compressed sequentially by the compressors 300A and 300B, and the second permeable gas G3 compressed by the compressor 300B is supplied to the separator 310. The separator 310 separates the second permeable gas G3 compressed by the compressor 300B into a third permeable gas G5 that permeates a membrane having properties that selectively allow carbon dioxide to permeate, and a third non-permeable gas G6 that does not permeate the membrane. In the gas processing system 1C, the third permeable gas G5 is temporarily stored in a tank or the like (not shown), and then discharged to an underground tidal layer, for example. The third non-permeable gas G6 is combined with the first non-permeable gas G2 and the second non-permeable gas G4 and supplied to the expander 40.

[0031] In the gas processing system 1C, the power recovered collectively from the first non-permeable gas G2, the second non-permeable gas G4, and the third non-permeable gas G6 by the expander 40 is used to compress the gas GA to be treated in the gas processing unit 10. Therefore, the gas processing system 1C also makes it possible to efficiently separate carbon dioxide from the gas to be treated GA at lower cost and with less energy than conventional systems. The gas processing unit 10 in the gas processing system 1C is an example of a first unit in the present disclosure, and the gas processing unit 20 in the gas processing system 1C is an example of a second unit in the present disclosure.

[0032] 3, the power recovered in bulk by the expander 40 is used to compress the gas GA to be treated in the gas processing unit 10, but may also be used to compress the first permeable gas G1 in the gas processing unit 20 or the second permeable gas G3 in the gas processing unit 30. In an embodiment in which the power recovered in bulk by the expander 40 in the gas processing system 1C is transmitted to the gas processing unit 20 or the gas processing unit 30, the gas processing unit 20 of the gas processing system 1C is an example of the first unit of the present disclosure, and the gas processing unit 30 of the gas processing system 1C is an example of the second unit of the present disclosure. In other words, of any two consecutive gas processing units in the gas processing system 1C, the gas processing unit in the first stage is an example of the first unit of the present disclosure, and the gas processing unit in the second stage is an example of the second unit.

[0033] (4) In the above embodiment, the separators 110, 210, and 310 were all membrane separators. However, the separators 110, 210, and 310 may be separators that use a separation method in which the temperature of the target gas GA is a control parameter and carbon dioxide is separated from the target gas GA by increasing the temperature of the target gas GA. Because the target gas GA is a gas, under conditions in which the number of moles is constant, i.e., the number of molecules constituting the target gas GA is constant, and the volume of the target gas GA is constant, the temperature increases approximately in proportion to the increase in pressure. In other words, controlling the pressure of the target gas GA is approximately equivalent to controlling the temperature of the target gas GA. Therefore, even if the separation method of carbon dioxide in each of the separators 110, 210, and 310 is a separation method in which carbon dioxide is separated by increasing the temperature, according to the present disclosure, it is possible to efficiently separate carbon dioxide with less energy and at lower cost than conventional methods. Furthermore, the carbon dioxide separation method does not need to be the same in each of separator 110, separator 210, and separator 310. For example, in gas processing system 1A, the separation method in separator 110 may be a membrane method and the separation method in separator 210 may be a separation method that separates carbon dioxide by increasing the temperature, or the separation method in separator 110 may be a separation method that separates carbon dioxide by increasing the temperature and the separation method in separator 210 may be a membrane method.

[0034] 3. Aspects understood from each embodiment and modification The present disclosure is not limited to the above-described embodiments and modifications, and can be realized in various forms without departing from the spirit thereof. For example, the present disclosure can also be realized in the following forms. The technical features in the above embodiments corresponding to the technical features in each form described below can be replaced or combined as appropriate to solve some or all of the problems of the present disclosure or to achieve some or all of the effects of the present disclosure. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

[0035] One aspect of the present disclosure is a gas processing system that separates carbon dioxide from a gas to be treated that contains carbon dioxide, and includes a first unit, a second unit, and an expander. The first unit includes one or more first compressors and a first separator. The one or more first compressors pressurize the gas to be treated. The first separator separates the gas to be treated pressurized by the one or more first compressors into a first gas having a higher carbon dioxide concentration than the gas to be treated and a second gas having a lower carbon dioxide concentration than the gas to be treated. The second unit includes one or more second compressors and a second separator. The one or more second compressors pressurize the first gas. The second separator separates the first gas pressurized by the one or more second compressors into a third gas having a higher carbon dioxide concentration than the first gas and a fourth gas having a lower carbon dioxide concentration than the first gas. The expander recovers power from the second gas and the fourth gas and transmits the recovered power to one of the one or more first compressors and the one or more second compressors. In the gas processing system of this aspect, the power recovered collectively from the second gas and the fourth gas by the expander is used for compression in the first unit or the second unit, making it possible to separate carbon dioxide from the gas to be processed with less energy than conventional methods. Note that the carbon dioxide separation method in the first separator and the second separator may be a membrane method or an adsorption method.

[0036] In a more preferred embodiment of the gas processing system, the power recovered by the expander may be transmitted to any one of the one or more first compressors. According to the gas processing system of this embodiment, the power recovered by the expander is transmitted to any one of the one or more first compressors, making it possible to utilize the power recovered by the expander without waste.

[0037] In a further preferred embodiment of the gas processing system, the one or more first compressors may be a plurality of first compressors connected in series. When the one or more first compressors are a plurality of first compressors connected in series, the expander may be coaxially connected to the first compressor having the largest compression work load among the plurality of first compressors. According to the gas processing system of this embodiment, it is possible to utilize the power recovered by the expander without waste.

[0038] In a more preferred embodiment of the gas processing system, the first separator may include a membrane that separates the first gas by allowing the first gas to permeate from the gas pressurized by the one or more first compressors. The gas processing system of this embodiment enables separation of carbon dioxide by a membrane method regardless of the partial pressure of carbon dioxide contained in the gas to be processed.

[0039] In a more preferred embodiment of the gas processing system, the second separator may include a membrane that separates the third gas by allowing the third gas to permeate from the first gas. The gas processing system of this embodiment also enables separation of carbon dioxide by a membrane method regardless of the partial pressure of carbon dioxide contained in the gas to be processed. [Explanation of symbols]

[0040] 1A, 1B, 1C...gas treatment system, 10, 20, 30...gas treatment unit, 100, 100A, 100B, 100C, 200A, 200B, 300A, 300B...compressor, 110, 210, 310...separator, 110a...membrane, 40...expander, GA...gas to be treated, G1...first permeable gas, G2...first non-permeable gas, G3...second permeable gas, G4...second non-permeable gas, G5...third permeable gas, G6...third non-permeable gas.

Claims

1. A gas treatment system that separates carbon dioxide from a gas to be treated that contains carbon dioxide, a first unit including a plurality of first compressors connected in series to pressurize the gas to be treated, and a first separator that separates the gas to be treated pressurized by the plurality of first compressors into a first gas having a higher concentration of carbon dioxide than the gas to be treated and a second gas having a lower concentration of carbon dioxide than the gas to be treated; a second unit including one or more second compressors that compress the first gas, and a second separator that separates the first gas compressed by the one or more second compressors into a third gas having a higher carbon dioxide concentration than the first gas and a fourth gas having a lower carbon dioxide concentration than the first gas; an expander that recovers power from the second gas and the fourth gas and transmits the recovered power to any one of the plurality of first compressors; Equipped with The expander is coaxially connected to the first compressor having the largest compression work among the plurality of first compressors. Gas treatment system.

2. 2. The gas processing system of claim 1, wherein the first separator includes a membrane that separates the first gas from the gas to be processed compressed by the plurality of first compressors by allowing the first gas to permeate therethrough.

3. 3. The gas processing system of claim 1, wherein the second separator comprises a membrane that separates the third gas from the first gas by allowing the third gas to permeate therethrough.

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