Gas separation system and method for producing CO2-enriched gas and N2-enriched gas

Abstract

CO 2 and N 2 from the combustion exhaust gas containing CO 2 enriched gas and N 2 To provide a method for separating enriched gas at low cost and with space savings. 【Solution means】CO 2 and N 2 from the combustion exhaust gas containing CO 2 enriched gas and N 2 A gas separation system for producing enriched gas, having a unit structure that is a single gas separation membrane unit or a connection body formed by connecting two or more gas separation membrane units. The unit structure includes a gas inlet, a permeate gas outlet, and a non-permeate gas outlet. A combustion exhaust gas supply line connected to the gas inlet for supplying combustion exhaust gas to the unit structure, compression means interposed in the combustion exhaust gas supply line, and cooling means disposed upstream of the compression means in the combustion exhaust gas flow direction for cooling the combustion exhaust gas supplied to the compression means. The non-permeate gas outlet is connected to an N 2 enriched gas utilization device with an N 2 enriched gas supply line, a gas separation system.

Description

Technical Field

[0001] The present invention relates to a gas separation membrane system and a method for producing CO 2 -enriched gas and N 2 -enriched gas.

Background Art

[0002] As a method for separating a mixed gas containing two or more different types of gases into each gas, a membrane separation method using the difference in the permeation rate of gases through a membrane is known. In this method, high-purity highly permeable gas and / or high-purity low-permeable gas, which are target gases, can be obtained by recovering the permeated gas and / or non-permeated gas. For example, Patent Document 1 describes that in ships and offshore facilities, air is separated to produce and utilize N 2 -enriched gas.

[0003] On the other hand, various methods for separating exhaust gas into components are known. Patent Document 2 describes producing CO 2 -enriched gas from exhaust gas using a gas separation membrane. Patent Documents 3 and 4 describe methods for separating N 2 and CO 2 from combustion exhaust gas by a system using an adsorbent or cryogenic separation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, a method for separating CO 2 and N 2 enriched gas and N 2 enriched gas from combustion exhaust gas containing them at low cost, in a space-saving manner, and with a high N 2 recovery rate has not been obtained conventionally. 2

Means for Solving the Problems

[0006] The present invention provides the following configuration. 〔1〕 A gas separation system for producing CO 2 enriched gas and N 2 enriched gas from combustion exhaust gas containing them, 2 wherein the gas separation system has a unit structure that is one gas separation membrane unit or a connection body formed by connecting two or more gas separation membrane units, 2 the unit structure includes a gas inlet, a permeated gas outlet, and a non-permeated gas outlet, the gas separation system further includes a combustion exhaust gas supply line connected to the gas inlet for supplying combustion exhaust gas to the unit structure, compression means interposed in the combustion exhaust gas supply line, and cooling means disposed upstream of the compression means in the combustion exhaust gas flow direction for cooling the combustion exhaust gas supplied to the compression means, and the non-permeated gas outlet is provided with an N enriched gas supply line connected to an N enriched gas utilization device. 2 2 〔2〕 The permeated gas outlet of the gas separation system according to 〔1〕 is provided with a CO 2 enriched gas supply line connected to a CO 2 recovery device. 〔3〕 The gas separation system according to 〔1〕 or 〔2〕, wherein the unit structure is composed of a first gas separation membrane unit. [4] The unit structure includes a first gas separation membrane unit and a second gas separation membrane unit, the first gas separation membrane unit includes a first gas inlet, a first permeated gas outlet, and a first non-permeated gas outlet, the second gas separation membrane unit includes a second gas inlet, a second permeated gas outlet, and a second non-permeated gas outlet, the first non-permeated gas outlet is connected to the second gas inlet of the second gas separation membrane unit, a second permeated gas reflux line is provided to connect the second permeated gas outlet to the suction side of the compression means in the combustion exhaust gas supply line, and a nitrogen-rich gas supply line is connected to the second non-permeated gas outlet. The gas separation system according to any one of [1] to [2]. 2 [5] The separation membrane module used in the unit structure has a CO 2 permeation rate P'CO 2 , a nitrogen permeation rate P'N 2 , and an oxygen permeation rate P'O 2 that satisfy the following relationship. The gas separation system according to any one of [1] to [4]. P'CO 2 > P'O 2 and P'O 2 > P'N 2 [6] The flow rate (Nm 3 / h) of the permeated gas at the permeated gas outlet is 65% or less of the flow rate (Nm 3 / h) of the fuel exhaust gas introduced into the unit structure. The gas separation system according to any one of [1] to [5]. [7] The CO 2 concentration in the combustion exhaust gas is 3 mol% or more. The gas separation system according to any one of [1] to [6]. [8] The CO 2 concentration in the permeated gas at the permeated gas outlet is 30 mol% or more. The gas separation system according to any one of [1] to [7]. [9]​ N in the non-permeating gas discharged from the non-permeating gas outlet 2 The gas separation system according to any one of [1] to [8], wherein the concentration is 90 mol% or more.

[10] The gas separation system according to any one of [1] to [9], wherein the gas separation membrane in the unit structure has a polyimide hollow fiber membrane.

[11] The gas separation system according to any one of [1] to

[10] , wherein pretreatment equipment consisting of one or more selected from a second cooling means, a drain discharge device, a dust removal device, and a temperature raising device is installed on the downstream side of the combustion exhaust gas flow direction in the compression means.

[12] CO of the separation membrane in the first separation membrane unit 2 and N 2 The gas separation selectivity (P'CO 2 / P'N 2 ) is larger than that of the separation membrane used in the second separation membrane unit. The gas separation system according to any one of [4] to

[11] .[[]END]]

[13] The gas separation system according to any one of [1] to

[12] , wherein a branch line connecting the upstream side of the combustion exhaust gas flow direction with respect to the cooling means in the combustion exhaust gas supply line and the temperature raising device is provided, and the combustion exhaust gas supplied through the branch line is used as a heat source for the temperature raising device.

[14] The gas separation system according to any one of [1] to

[13] , wherein the pressurized dew point of the non-permeating gas outlet is -20°C or lower.

[15] The gas separation system according to any one of [1] to

[14] , wherein the refrigerant in the cooling means is seawater.

[16] N 2 The gas separation system according to any one of [1] to

[15] , wherein the N-rich gas utilization device is explosion-proof.

[17] The gas separation system according to any one of [1] to

[16] , which is for ships or offshore facilities.

[18] A method for producing a CO 2 and N 2 enriched gas and an N 2 enriched gas from combustion exhaust gas containing CO 2 using a gas separation system, comprising: The gas separation system has a unit structure that is either a single gas separation membrane unit or a connection body formed by connecting two or more gas separation membrane units. The unit structure includes a gas inlet, a permeate gas outlet, and a non-permeate gas outlet. A combustion exhaust gas supply line connected to the gas inlet for supplying combustion exhaust gas to the unit structure, compression means interposed in the combustion exhaust gas supply line, and cooling means disposed upstream of the compression means in the combustion exhaust gas flow direction for cooling the combustion exhaust gas supplied to the compression means. An N 2 enriched gas supply line is provided that connects the non-permeate gas outlet to an N 2 enriched gas utilization device, for producing a CO 2 enriched gas and an N 2 enriched gas.

Advantages of the Invention

[0007] According to the present invention, there is provided a method for separating a CO 2 enriched gas and an N 2 enriched gas from combustion exhaust gas containing CO 2 at low cost, in a space-saving manner, and with a high N 2 recovery rate. 2

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the present invention will be described with reference to the drawings based on its preferred embodiments. Note that the upper and lower limits of the numerical values in this specification can be combined without any limitation.

[0010] Hereinafter, in each of the gas separation systems shown in FIGS. 1, 4, 5, and 8, one gas separation membrane unit 11 constitutes the unit structure 10. On the other hand, in FIGS. 3 and 6, a connection body of two gas separation membrane units 11 and 12 constitutes the unit structure 10. Further, in FIG. 7, a connection body of three gas separation membrane units 11 to 13 constitutes the unit structure 10.

[0011] As the gas separation membrane units 11 to 13, for example, as shown in Fig. 2, a module 40 can be used which is formed by housing a gas separation membrane 30 made of a hollow fiber membrane or the like and having gas selective permeability in a casing 31. Each gas separation membrane unit can use, for example, the gas separation membrane module 40 shown in Fig. 2 as it is, or a plurality of modules 40 arranged in parallel. The casing 31 in the module 40 has two opposing surfaces opened to form an opening 32. When the gas separation membrane 30 is composed of a hollow fiber membrane bundle, the gas separation membrane 30 is housed in the casing 31 such that each end of the hollow fiber membrane opens near each opening 32 of the casing 31 in its housed state.

[0012] A hollow fiber gas separation membrane module such as the module 40 is obtained, for example, by bundling hollow fiber membranes of an appropriate length, preferably about 100 to 1,000,000 (more preferably about 100 to 500,000), fixing both ends of the hollow fiber membrane bundle with a tube sheet made of a thermosetting resin or the like so that at least one end of the hollow fiber remains in an open state, and housing and attaching the obtained hollow fiber membrane element composed of the hollow fiber membrane bundle and the tube sheet or the like in a container provided with at least a mixed gas inlet, a permeated gas outlet, and a non-permeated gas outlet such that a space communicating with the inside of the hollow fiber membrane and a space communicating with the outside of the hollow fiber membrane are isolated.

[0013] When the gas separation membrane 30 is accommodated in the casing 31, the gas separation membrane 30 is fixed to the inner wall of the casing 31 by the tube sheets 33 and 34 at the positions of both ends in the Y direction, which is the extending direction of the hollow fiber membrane. Each opening 32 of the casing 31 is closed by the lid bodies 35 and 36. A gas inlet 37 is provided in the lid body 35. On the other hand, a non-permeating gas discharge port 38 is provided in the lid body 36. The mixed gas to be separated is introduced into the module from the gas inlet 37 of the lid body 35. Among the introduced gases, the gas that has permeated through the gas separation membrane 30 is discharged out of the module from the permeating gas discharge port 39 provided in the casing 31. On the other hand, the non-permeating gas that has not permeated through the gas separation membrane 30 is discharged out of the module from the non-permeating gas discharge port 38 of the lid body 36. As described above, the separation membrane module of FIG. 2 has been taken as an example for explanation. Of course, the present invention is also applicable to separation membrane modules having other configurations. For example, it can also be applied to a shell-feed type module.

[0014] The gas separation membrane unit and the gas separation membrane module used in the unit structure 10 are for CO 2 permeation rate P'CO 2 , N 2 permeation rate P'N 2 , oxygen permeation rate P'O 2 It is preferably in the following relationship (1), and more preferably in the following relationship (2). In the following embodiments, the gas separation membrane unit and the gas separation membrane module have the relationship (2). P'CO 2 > P'N 2 (1) P'CO 2 > P'O 2 and P'O 2 > P'N 2 (2) P' is the permeation rate (the permeation volume per unit membrane area, per unit time, and per unit partial pressure difference with respect to the membrane), and the unit is ×10 -5 cm 3 (STP) / cm 2 ·sec·cmHg.

[0015] ​​As used hereinafter, "upstream" and "downstream" are based on the flow direction of combustion exhaust gas. As shown in FIG. 1, the unit structure 10 consists of a first gas separation membrane unit 11. The first gas inlet 11a, the first non-permeable gas outlet 11b, and the first permeable gas outlet 11c of the first gas separation membrane unit 11 respectively constitute the gas inlet 10a, the non-permeable gas outlet 10b, and the permeable gas outlet 10c. Also as shown in FIG. 1, the gas separation system 1 includes a combustion exhaust gas supply line 26 that is connected to the gas inlet 10a and supplies combustion exhaust gas to the unit structure 10, a compression means 21 interposed in the combustion exhaust gas supply line 26, and a cooling means 23 disposed upstream of the compression means 21 in the flow direction of the combustion exhaust gas and cooling the combustion exhaust gas supplied to the compression means 21. Further, the non-permeable gas outlet 10b and N 2 are connected to a N 2 rich gas utilization device 50 through a N

[0016] N 2 Examples of the rich gas utilization device 50 include devices for sealing and filling inert gas N 2 into storage containers (tanks, cylinders, etc.) of liquids and powders such as petroleum products, ultra-pure water, pure water, chemical reagents, drugs, and foods; devices for filling N 2 gas into cylinders containing fuels, etc.; devices for filling N 2 gas into tanks containing fuels, etc.; devices for filling N 2 gas into cylinders, etc.); devices for manufacturing liquefied N 2 in containers; devices for purging N 2 in processes that require inert gas in experimental equipment and industrial equipment such as photocuring and chemical synthesis. The rich gas utilization device 50 connected to the non-permeable gas outlet 10b N 2 may be one or a plurality.

[0017] The permeable gas outlet 10c is connected to a CO 2 recovery device 51 through a CO 2 rich gas supply line 18. The CO 2 recovery device 51 includes a CO2 Liquefaction equipment, CO 2 Solidification equipment, CO 2 Absorption equipment, CO 2 Adsorption equipment, etc. can be mentioned. CO 2 The CO recovered by the recovery device 51 2 may be used for artificial photosynthesis. Also, it may be converted to methane by reacting with hydrogen and used as part of the fuel. Here, as the hydrogen, that generated by the electrolysis of water may be used. Also, CO 2 In the recovery device 51, CO 2 The CO recovered through the enriched gas supply line 18 2 The enriched gas may be further concentrated as necessary and then liquefied by a liquefaction device or the like. CO 2 Known methods can be mentioned as methods for concentrating the enriched gas before liquefaction. For example, a method using a gas separation membrane, a method using an absorbent solution such as potassium carbonate or an amine compound, or a method using zeolite or the like can be mentioned. CO connected to the permeated gas discharge port 10c 2 The recovery device 51 may be one or a plurality.

[0018] As the cooling means 23, a heat exchanger can be used. Since the combustion exhaust gas is basically at a high temperature, by using the cooling means 23, it can be cooled to a temperature suitable for the operation of the gas separation membrane. When the refrigerant in the cooling means 23 is seawater, it is preferable in terms of reducing the refrigerant use cost when the system 1 is used in a ship or an offshore facility.

[0019] Also, the compression means 21 is installed for the purpose of pressurizing the combustion exhaust gas supplied from the combustion exhaust gas source. As the compression means 21, a compressor can be used.

[0020] The combustion exhaust gas supply line 26 connects the combustion exhaust gas source 20 that generates the combustion exhaust gas and the gas inlet 10a. The combustion exhaust gas is N 2 and CO 2It contains. As the combustion exhaust gas source 20, there are diesel engines, gasoline engines, gas turbines, boilers such as oil-fired boilers, incinerators for incinerating waste such as garbage, etc. Among them, from the viewpoint of taking advantage of the space-saving of the gas separation membrane, the combustion exhaust gas source in a ship or an offshore facility is preferable. As the combustion exhaust gas source in a ship or an offshore facility, there are ship engines, boilers on ships, boilers for offshore power generation, industrial boilers offshore, etc. The combustion exhaust gas contains N 2 and CO 2 as the main components. In addition, there may be included moisture, nitrogen oxides (NOx), sulfur oxides (SOx), volatile organic compounds (VOC), oxygen, carbon monoxide, PM (fine particles), etc.

[0021] In the system 1, the combustion exhaust gas containing N 2 and CO 2 is supplied from the combustion exhaust gas source 20 to the unit structure 10 (gas separation membrane unit 11) through the combustion exhaust gas supply line 26. The combustion exhaust gas is pressurized by the compression means 21, and its pressure rises. In the unit structure 10 (gas separation membrane unit 11), due to the difference in the permeation rate with respect to the gas separation membrane, it is separated into a permeated gas that is the gas permeated through the gas separation membrane and a non-permeated gas that is the gas not permeated through the gas separation membrane. The non-permeated gas is enriched in N 2 compared to the combustion exhaust gas. The non-permeated gas is discharged from the non-permeated gas discharge port 10b and is supplied to the N 2 enriched gas utilization device 50 through the N 2 enriched gas supply line 15. The permeated gas discharged from the permeated gas discharge port 10c of the unit structure 10 is enriched in CO 2 compared to the combustion exhaust gas. The permeated gas is supplied to the CO 2 recovery device 51 through the CO 2 enriched gas supply line 18. By introducing the CO 2 enriched gas with an increased CO 2 concentration into the CO 2 recovery device 51, the CO 2 recovery efficiency can be increased.

[0022] In the example of FIG. 1, the gas separation system 1 has a branch line 29. The branch line 29 branches from the combustion exhaust gas supply line 26 upstream of the compression means 21 in the combustion exhaust gas flow direction in the combustion exhaust gas supply line 26, and is connected to the combustion exhaust gas supply line 26 and the CO 2 recovery device 51 without passing through the gas separation membrane. With this configuration, among the exhaust gas discharged from the combustion exhaust gas source 20, a part is supplied to the CO 2 recovery device 51 without passing through membrane separation. When separating N 2 from the combustion exhaust gas, usually, the amount of N 2 gas required as an inert gas or the like is less than the discharge amount of the combustion exhaust gas discharged from the combustion exhaust gas source. On the other hand, in order to increase the concentration of N 2 in the non-permeating gas, it is required to install a gas separation membrane with a suitable area with respect to the amount of combustion exhaust gas flowing into the unit structure 10. For these reasons, in the combustion exhaust gas supply line 26, a branch line 29 for adjusting the combustion exhaust gas introduced into the unit structure 10 is provided, and a flow rate adjustment valve (not shown) is provided at the branch point of the branch line 29 or the like, and the combustion exhaust gas with a flow rate suitable for the gas separation membrane of the unit structure 10 is introduced into the unit structure 10, which is preferable from the viewpoint of reducing the equipment cost and operation cost of the system 1. The branch line 29 and the CO 2 enriched gas supply line 18 supply the CO 2 containing gas to the CO 2 recovery device 51, which is preferable in terms of CO 2 recovery efficiency. In FIG. 1, the combustion exhaust gas not introduced into the unit structure 10 is directly introduced into the CO 2 recovery device 51 by the branch line 29. However, another CO 2 concentration device may be provided in the branch line 29, and the combustion exhaust gas in which CO 2 is concentrated by the device may be introduced into the CO 2 recovery device 51. At this time, the CO 2 enriched gas supply line 18 is connected upstream of the other CO 2 concentration device, and the CO 2CO flowing through the enriched gas supply line 18 2 The enriched gas may be further concentrated by the other CO 2 concentrating device.

[0023] In FIG. 1, the cooling means 23 is arranged downstream of the branch point of the branch line 29 in the combustion exhaust gas supply line 26, but it may be arranged upstream of the branch point. CO 2 In the recovery device 51, CO 2 liquefaction, CO 2 solidification, CO 2 absorption, CO 2 The efficiency of adsorption, etc. is often the CO introduced 2 The lower the temperature of the enriched gas, the higher the efficiency. For this reason, installing the cooling means 23 upstream of the branch point of the branch line 29 in the combustion exhaust gas flow direction and cooling the entire combustion exhaust gas is CO in the system 1 2 preferred in terms of increasing the processing capacity.

[0024] N discharged from the unit structure 10 2 Regarding the enriched gas, it is preferable that moisture has been removed because N 2 it can be used in a wide range of applications for the use of enriched gas. The moisture removal level is class 3 or higher as defined in ISO8573-1, that is, the pressure dew point discharged from the non-permeable gas outlet 10b of the unit structure 10 is preferably -20°C or lower, more preferably class 2 or higher, that is, the dew point is more preferably -40°C or lower. When the humidity of the combustion exhaust gas is high, a drain discharge device 28 or the like described later may be used to achieve the above configuration.

[0025] Next, based on FIG. 3, a second embodiment of the present invention will be described. Hereinafter, in the description of the second embodiment and subsequent embodiments, the description will focus on the parts not described in the previous embodiments, and the same reference numerals will be given to the other configurations and the description will be omitted. In the system 2 of this embodiment, the unit structure 10 includes a first gas separation membrane unit 11 and a second gas separation membrane unit 12. The first gas separation membrane unit 11 and the second gas separation membrane unit 12 are connected in series. Hereinafter, when explaining the gas inlets, outlets, supplied gas, permeated gas to be discharged, and non-permeated gas of the first gas separation membrane unit 11 and the second gas separation membrane unit 12, the terms "first" and "second" may be attached respectively. The same applies to the configuration regarding the third gas separation membrane unit 13 described later.

[0026] The first gas separation membrane unit 11 includes a first gas inlet 11a, a first permeated gas outlet 11c, and a first non-permeated gas outlet 11b, and the second gas separation membrane unit 12 includes a second gas inlet 12a, a second permeated gas outlet 12c, and a second non-permeated gas outlet 12b. In the system 2, the first gas inlet 11a and the first permeated gas outlet 11c respectively become the gas inlet 10a and the permeated gas outlet 10c of the unit structure 10, and the second non-permeated gas outlet 12b becomes the non-permeated gas outlet 10b of the unit structure 10. Also, the first permeated gas becomes the permeated gas of the unit structure 10, and the second non-permeated gas becomes the non-permeated gas of the unit structure 10.

[0027] In the system 2, the first non-permeated gas outlet 11b and the second gas inlet 12a of the second gas separation membrane unit 12 are connected by a first non-permeated gas discharge line 14. Also, in the system 2, a second permeated gas reflux line 17 is provided that connects the second permeated gas outlet 12c to the suction side of the compression means 21 in the combustion exhaust gas supply line 26. Furthermore, in the system 2, N 2 The enriched gas supply line 15 is connected to the second non-permeated gas outlet 12b.

[0028] When the compression means 21 returns the second permeated gas discharged from the second gas separation membrane unit 12 to the first gas separation membrane unit 11 through the second permeated gas reflux line 17, the compression means 21 pressurizes the permeated gas.

[0029] Also in system 2, when the combustion exhaust gas pressurized by the compression means 21 is supplied to the first gas separation membrane unit 11, it is separated into a first permeated gas and a first non-permeated gas. The first non-permeated gas discharged from the first non-permeated gas outlet 11b is enriched in N compared to the combustion exhaust gas 2 and is supplied to the second gas separation membrane unit 12 through the first non-permeated gas discharge line 14. On the other hand, the first permeated gas discharged from the first permeated gas outlet 11c (10c) is CO 2 and is supplied to the CO 2 recovery device 51 through the enriched gas supply line 18.

[0030] The first non-permeated gas is separated into a second permeated gas and a second non-permeated gas by the gas separation membrane of the second gas separation membrane unit 12. The second non-permeated gas is further enriched in N and is discharged from the second non-permeated gas outlet 12b and then N 2 is supplied to the N 2 enriched gas utilization device 50 through the enriched gas supply line 15. 2 On the other hand, the second permeated gas is discharged from the second permeated gas outlet 12c, and after being refluxed to the suction side of the compression means 21 in the combustion exhaust gas supply line 26 via the second permeated gas reflux line 17 and mixed with the combustion exhaust gas, it is pressurized by the compression means 21. According to this system 2, by refluxing the permeated gas of the second-stage gas separation membrane unit to the upstream of the first-stage gas separation membrane unit, compared with the system 1 composed of a single-stage gas separation membrane unit, the CO

[0031] concentration in the combustion exhaust gas supplied to the first-stage gas separation membrane unit can be increased. As a result, the CO 2 concentration in the permeated gas supplied to the CO 2 recovery device can be increased, and at the same time, the N 2 recovery rate can also be increased. 2 In a connection body in which two or more gas separation membrane units are connected, the CO

[0032] of the separation membrane in the first separation membrane unit 11 and N 2 and N 2Gas separation selectivity with (P’CO 2 / P’N 2 ) being greater than that of the separation membrane used in the second gas separation membrane unit 12 is preferable in that it can increase the CO 2 concentration in the permeated gas without reducing the N 2 concentration and N 2 recovery rate in the non-permeated gas.

[0033] In the example of FIG. 3, the second permeated gas reflux line 17 is connected to the downstream side of the cooling means 23 in the combustion exhaust gas supply line 26. However, the second permeated gas reflux line 17 may be connected to the upstream side of the cooling means 23 to reflux the second permeated gas to the upstream side of the cooling means 23.

[0034] Also, unlike the system 1 of FIG. 1, as shown in FIG. 4, a branch line 29 may not be provided, and all of the combustion exhaust gas from the combustion exhaust gas source 20 may be subjected to membrane separation by the unit structure 10.

[0035] Furthermore, as shown in FIGS. 5 and 6, compression means 22 (booster) for boosting the non-permeated gas discharged from the non-permeated gas outlet 10b to the pressure required by the N 2 enriched gas utilization device 50 may be provided in the N 2 enriched gas supply line 15. A compressor can be used as the compression means 22. Note that when a plurality of N 2 enriched gas utilization devices 50 are connected to the non-permeated gas outlet 10b and the N 2 enriched gas pressures required by the respective devices are different, after compressing all of the non-permeated gas of the unit structure 10, a part thereof may be decompressed and sent to the N 2 enriched gas utilization device that uses low-pressure N 2 enriched gas. Alternatively, a part of the non-permeated gas of the unit structure 10 may be boosted and sent to the N 2 enriched gas utilization device 50 for use, and the remainder may be used in the N 2 enriched gas utilization device 50 without being boosted.

[0036] Next, the system 3 in FIG. 7 will be described. In the following description, the differences from the form in FIG. 3 will mainly be described. In the form of FIG. 7, the unit structure 10 has a third gas separation membrane unit 13 in addition to the first gas separation membrane unit 11 and the second gas separation membrane unit 12. In the form of FIG. 7, the first gas separation membrane unit 11 and the third gas separation membrane unit 13 are connected in series. Specifically, the first gas separation membrane unit 11 and the third gas separation membrane unit 13 are connected by connecting the first permeate gas discharge port 11c and the third gas inlet 13a with the first permeate gas discharge line 19.

[0037] The third non-permeate gas discharge port 13b is connected to the combustion exhaust gas supply line 26 by the third non-permeate gas reflux line 16. In the form of FIG. 7, the third non-permeate gas reflux line 16 is connected to the suction side position of the compression means 21 in the combustion exhaust gas supply line 26. The third non-permeate gas reflux line 16 is connected to the downstream side of the cooling means 23 in the combustion exhaust gas supply line 26, but it may be connected to the upstream side of the cooling means 23. In the example of FIG. 7, the permeate gas discharge port 13c of the third gas separation membrane unit 13 corresponds to the permeate gas discharge port 10c of the unit structure 10, and the CO 2 enriched gas supply line 18 is connected.

[0038] The compression means 21 is installed for the purpose of pressurizing the combustion exhaust gas supplied from the gas source, the second permeate gas returned from the second gas separation membrane unit 12, and the third non-permeate gas returned from the third gas separation membrane unit 13.

[0039] During the operation for gas separation in the gas separation system 3 of the present embodiment having the above configuration, the first permeate gas discharged from the first gas separation membrane unit 11 is supplied to the third gas separation membrane unit 13 through the first permeate gas discharge line 19. The first permeate gas introduced into the third gas separation membrane unit 13 is separated by the unit 13 into a third permeate gas and a third non-permeate gas. The third permeate gas has a higher CO content than the first permeate gas introduced into the third gas separation membrane unit 13. 2is further concentrated and enriched, and CO is discharged from the permeate gas outlet 13c of the unit 13 2 is supplied to the CO recovery device 51 through the enriched gas supply line 18 2 On the other hand, the third non-permeate gas is discharged from the third non-permeate gas outlet 13b and returned to the suction side of the compression means 21 in the combustion exhaust gas supply line 26 via the third non-permeate gas reflux line 16 connected to the outlet 13b. The third non-permeate gas returned through the third non-permeate gas reflux line 16 is mixed with the combustion exhaust gas and then pressurized by the compression means 21.

[0040] According to the present system 3, the third gas separation membrane unit 13 concentrates CO and refluxes the third non-permeate gas to the first gas separation membrane unit 11, so that the N concentration in the non-permeate gas discharged from the non-permeate gas outlet 10b and the CO concentration in the permeate gas discharged from the permeate gas outlet 10c, the N recovery rate can be further increased. 2 In the present system 3, when the gas separation selectivity (P'CO / P'N) of the separation membrane in the first gas separation membrane unit 11 for CO and N is larger than that of the separation membrane used in the second gas separation membrane unit 12, the gas separation selectivity (P'CO / P'N) of the separation membrane in the third gas separation membrane unit 13 for CO and N is equal to or larger than that of the separation membrane used in the second gas separation membrane unit 12, which is preferable in terms of further increasing the CO concentration and N recovery rate in the permeate gas discharged from the permeate gas outlet 10c, and more preferably larger than that of the separation membrane used in the second gas separation membrane unit 12. 2 concentration and the CO concentration in the permeate gas discharged from the permeate gas outlet 10c 2 concentration, N 2 recovery rate can be further increased.

[0041] In the present system 3, the gas separation selectivity (P'CO 2 / P'N 2 ) of the separation membrane in the first gas separation membrane unit 11 for CO and N 2 / P'N 2 is larger than that of the separation membrane used in the second gas separation membrane unit 12. When the gas separation selectivity (P'CO 2 / P'N 2 ) of the separation membrane in the third gas separation membrane unit 13 for CO and N 2 / P'N 2 ) is equal to or larger than that of the separation membrane used in the second gas separation membrane unit 12, it is preferable in terms of further increasing the CO concentration and N recovery rate in the permeate gas discharged from the permeate gas outlet 10c, and more preferably larger than that of the separation membrane used in the second gas separation membrane unit 12. 2 concentration and N 2 recovery rate, and more preferably larger than that of the separation membrane used in the second gas separation membrane unit 12.

[0042] Another compression means for pressurizing the first permeate gas and sending it to the third gas separation membrane unit may or may not be interposed in the first permeate gas discharge line 19.

[0043] In each of the above gas separation systems, further modifications may be made. For example, pretreatment equipment may be provided on the downstream side of the compression means 21 in the combustion exhaust gas supply line 26. The above pretreatment equipment is provided upstream of the unit structure 10 in the combustion exhaust gas supply line 26. The pretreatment equipment separates N from the combustion exhaust gas 2 Enriched gas or CO 2 It is provided to remove impurities from the enriched gas to make it easier to reuse, and to prevent components in the combustion exhaust gas, etc. from adhering to the gas separation membrane of the unit structure 10 and reducing the separation performance. Examples of the above pretreatment equipment include a second cooling device, a dust removal device, a drain discharge device, a temperature raising device, a desulfurization device, a denitration device, etc., and these can be used alone or in combination of two or more.

[0044] A heat exchanger can be used as the second cooling means or the temperature raising device.

[0045] Examples of the dust removal device include a centrifuge, a water absorption shower, an electrostatic precipitator (ESP), a diesel particulate filter (DPF), a gasoline particulate filter (GPF), an activated carbon filter, etc.

[0046] The drain discharge device is a device that removes the moisture flowing to the bottom of the pipe while maintaining the airtight state of the pipe, and a conventionally known device can be used.

[0047] The desulfurization device only needs to have a function of removing sulfur oxides (SOx) contained in the combustion exhaust gas. For example, it may be a scrubber. The denitration device removes nitrogen oxides (NOx) contained in the combustion exhaust gas. For example, a selective catalytic reduction denitration (SCR (Selective Catalytic Reduction)) device can be mentioned.

[0048] Preferable examples of the pretreatment equipment include, for example, the pretreatment equipment 200 shown in FIG. 8, which is arranged downstream of the compression means 21 and upstream of the unit structure 10 in the combustion exhaust gas supply line 26. The pretreatment equipment 200 includes a second cooling means 24, a drain discharge device 28 arranged downstream of the second cooling means 24, a temperature raising device 46 arranged downstream of the drain discharge device 28, and a dust removal device 25. The dust removal device 25 is arranged downstream of the temperature raising device 46 in the example of FIG. 8. However, as long as the dust removal device 25 is located upstream of the unit structure 10, it may be arranged between any of the devices from upstream of the second cooling means 24 to the temperature raising device 46 from the second cooling means 24. The dust removal device 25 is preferably arranged downstream of the compression means 21 in order to be able to remove particles and the like discharged from the compression means 21. According to the system of FIG. 8, moisture and high-boiling substances contained in the combustion exhaust gas or derived from the compression means 21 are liquefied by the second cooling means 24, and the condensed liquefied substances and particles are removed by a dust removal device 25 such as a filter. Since the liquefied substances stay in the pipe, they are discharged to the outside of the system by the drain discharge device 28. The gas from which impurities have been removed by the drain discharge device 28 is heated by the temperature raising device 46 and supplied to the unit structure 10 in order to prevent re-condensation and a decrease in gas separation performance. Here, the high-boiling substances refer to substances that are in a condensed state under the supply gas pressure and temperature conditions introduced into the separation membrane.

[0049] By using the dust removal device as described above, it is possible to prevent the dust and solid particles contained in the combustion exhaust gas from being supplied to the unit structure 10 and reducing the separation membrane performance. As the removal level of particles in the gas supplied to the unit structure 10, Class 2 or higher defined in ISO8573-1 is preferable, and Class 1 is more preferable. Therefore, as the removal level of particles in the gas supplied to the unit structure 10, particles with a size of 0.1 to 0.5 μm ≤ 400,000 particles / m 3 , particles with a size of 0.5 to 1 μm ≤ 6,000 particles / m 3 , and particles with a size of 1 to 5 μm ≤ 100 particles / m 3 is preferable, and particles with a size of 0.1 to 0.5 μm ≤ 20,000 particles / m 3 , particles with a size of 0.5 to 1 μm ≤ 400 particles / m 3 , and particles with a size of 1 to 5 μm ≤ 10 particles / m 3 is more preferable.

[0050] As shown in FIG. 8, in the combustion exhaust gas supply line 26, a branch line 27 connecting the upstream side of the cooling means 23 in the line 26 and the temperature raising device 46 is provided. Using the uncooled combustion exhaust gas supplied through the branch line 27 as the heat source of the temperature raising device 46 is preferable in terms of reducing the cooling cost and the temperature raising cost of the temperature raising device 46.

[0051] N 2 The enriched gas utilization device 51 is preferably a device that uses N 2 enriched gas, which is advantageous for taking advantage of the space-saving gas separation by the gas separation membrane. Examples of explosion-proof applications include those used in fuel tanks, storage of hydraulic system operating grease, and transportation containers such as fuel cylinders in ships, offshore facilities, aircraft, etc. In particular, from the perspective of taking advantage of the high recovery rate and CO 2 recovery rate of the present invention and the advantages of space saving and energy saving, explosion-proof applications such as fuel tanks in ships or offshore facilities are preferable. 2

[0052] In addition, the gas separation system of the present invention can be used for combustion exhaust gases discharged from ships or offshore facilities, combustion exhaust gases from power plants, and combustion exhaust gases generated from boilers, incinerators, etc. in various factories. Using it for treating combustion exhaust gases in ships or offshore facilities is preferable because it saves space, energy, and 2 the recovery rate and the superiority of the present invention with a high CO 2 recovery rate increases. Examples of offshore facilities include floating production, storage and offloading systems (FPSO), floating storage and offloading systems (FSO), other offshore power plants, offshore factories, and the like.

[0053] In the combustion exhaust gas, it is preferable that CO 2 is 3 mol% or more in terms of increasing the concentration of CO 2 in the permeated gas. From this perspective, 5 mol% or more is preferable, 10 mol% or more is more preferable, and 15 mol% or more is even more preferable. The concentration of CO 2 in the combustion exhaust gas used in the present invention is generally, for example, 30 mol% or less, and 2 20 mol% or less is preferable from the viewpoint of the recovery rate. When describing the composition of the combustion exhaust gas in this specification, unless otherwise specified, it is the composition of the combustion exhaust gas when discharged from the combustion exhaust gas source 20. For example, in the system 2, it refers to the composition of the combustion exhaust gas before mixing with the second permeated gas.

[0054] The combustion exhaust gas used in the present invention is a gas containing at least CO 2 and N 2 . In the present invention, it is preferable that the combustion exhaust gas contains N 2 at 40 mol% or more in terms of the high concentration of N 2 in the obtained non-permeated gas and easy reusability. More preferably, it contains 50 mol% or more. The concentration of N 2 in the combustion exhaust gas is, for example, 95 mol% or less in terms of 2Increase the concentration to improve the CO concentration in the permeated gas 2 This is particularly preferable in terms of improving the concentration, and more preferably 90 mol% or less.

[0055] The flow rate Fp (Nm 3 / h) of the permeated gas at the permeated gas outlet 10c is 65% or less of the flow rate Fs (Nm 3 / h) of the combustion exhaust gas flowing into the system, which is preferable in terms of increasing the CO concentration and N 2 recovery rate of the permeated gas at the permeated gas outlet 10c, more preferably 60% or less, still more preferably 55% or less, and particularly preferably 50% or less. There is no limit to the lower limit of the ratio of the flow rate Fp of the permeated gas to the flow rate Fs of the combustion exhaust gas, but it is usually 5% or more, and particularly 10% or more. Here, the flow rate Fs of the combustion exhaust gas is the flow rate of the combustion exhaust gas discharged from the combustion exhaust gas source 20 introduced into the unit structure 10. The flow rate of the combustion exhaust gas introduced into the unit structure 10 as used herein refers to the flow rate of the combustion exhaust gas introduced into the unit structure 10 from the outside, and thus does not include the flow rate of the reflux gas flowing from the gas outlet of the unit structure to the gas inlet side. For example, in the system 2, the flow rate Fs of the combustion exhaust gas refers to the flow rate of the combustion exhaust gas downstream of the cooling means 23 in the combustion exhaust gas supply line 26 and before mixing with the second permeated gas. 2 2

[0056] The flow rate Fn (Nm 3 / h) of the non-permeated gas at the non-permeated gas outlet 10b is 35% or more with respect to the flow rate Fs (Nm 3 / h) of the combustion exhaust gas supplied to the unit structure 10, which is preferable in terms of increasing the CO concentration and N 2 recovery rate of the permeated gas at the permeated gas outlet 10c, more preferably 40% or more, still more preferably 45% or more. There is no limit to the upper limit of the ratio of the flow rate Fn of the non-permeated gas to the flow rate Fs of the combustion exhaust gas, but it is usually 95% or less, and particularly 90% or less. 2 2

[0057] CO in the permeated gas at the permeated gas outlet 10c 2The concentration is 30 mol% or more. 2 If further concentrated in the recovery device 51, CO 2 The high concentration and small total gas volume reduce CO 2 This is preferable because it leads to a reduction in size of the recovery device 51 and a reduction in running costs. 2 The concentration is more preferably 40 mol % or more, further preferably 50 mol % or more, particularly preferably 60 mol % or more, and particularly preferably 80 mol % or more.

[0058] N in the non-permeation gas discharged from the non-permeation gas discharge port 10b 2 The concentration is 90 mol% or more. 2 From the viewpoint of utilization efficiency in the enriched gas utilization device 50, the concentration is preferably 95 mol % or more, and more preferably 97 mol % or more.

[0059] In addition, in the present invention, N 2 The recovery rate is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. N 2 The recovery rate can be calculated using the following formula. The concentration unit is mol%. N 2 Recovery rate = (non-permeation gas flow rate Fn × N in the non-permeation gas discharged from the non-permeation gas discharge port 10b 2 concentration) / (flow rate of combustion exhaust gas Fs × N in combustion exhaust gas 2 concentration)

[0060] In addition, in the present invention, CO 2 The recovery rate is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. CO 2 The recovery rate can be calculated using the following formula. The concentration unit is mol%. CO 2Recovery rate = (Flow rate of permeated gas Fp × Concentration of CO in the permeated gas discharged from the permeated gas outlet 10c) / (Flow rate of combustion exhaust gas Fs × Concentration of CO in the combustion exhaust gas) 2 Concentration) 2

[0061] Furthermore, the ratio of the concentration of CO (mol%) at the permeated gas outlet 10c to the concentration of CO (mol%) in the combustion exhaust gas is preferably 1.5 times or more, more preferably 2 times or more, still more preferably 2.5 times or more, and even more preferably 3 times or more. 2 Concentration) 2

[0062] The pressure of the compression means 21 is preferably 0.2 MPaG or more, more preferably 0.3 MPaG or more, as the pressure of the gas supplied to the unit structure 10. The pressure of the compression means 21 may be 2 MPaG or less, or may be 1.6 MPaG or less.

[0063] In the gas separation membrane module used in the present invention, a hollow fiber membrane made of a polymer and having an asymmetric structure can be preferably used as the gas separation membrane. The hollow fiber membrane having an asymmetric structure has a skin layer and a porous layer. The skin layer refers to a layer thinner than the porous layer that mainly bears the gas separation performance. The skin layer is a very dense layer compared to the porous layer, usually extremely thin, preferably having a thickness of 1 nm or more and 5 μm or less, more preferably 10 nm or more and 200 nm or less. The porous layer refers to a relatively thick porous layer that supports the skin layer, preferably having a thickness of 10 μm or more and 2000 μm or less, more preferably 20 μm or more and 200 μm or less. The diameter of the pores in the porous layer is not particularly limited, but generally, it is often 0.01 to 100 μm, more preferably 0.01 to 50 μm. Such a hollow fiber membrane has a large effective surface area, high pressure resistance, and is excellent as a gas separation membrane.

[0064] ​​The hollow fiber membrane preferably has an inner diameter of about 10 to 3000 μm, and more preferably 30 to 500 μm. Also, the hollow fiber membrane preferably has an outer diameter of about 30 to 7000 μm, and more preferably 35 to 700 μm. The thicknesses of the skin layer and the porous layer, the inner and outer diameters of the hollow fiber membrane, and the pore diameter can be measured using an optical microscope or an electron microscope.

[0065] The material of the gas separation membrane constituting the gas separation membrane module of the present invention is not particularly limited, and examples thereof include polyimide, polyamide, polysulfone, polyethersulfone, polyamideimide, polyetherimide, polycarbonate, and the like. Among these, the gas separation membrane is preferably made of polyimide in terms of separation performance, durability, heat resistance, and the like.

[0066] Also, the preferable temperature range of the operating temperature (the temperature of the gas separation membrane during operation) of the gas separation membrane units 10, 11, 12, and 13 is preferably 0 to 100°C, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The preferable range of the temperature of the combustion exhaust gas supplied to the unit structure 10 (the temperature at the gas inlet 10a) is the same as the preferable range of the operating temperature mentioned above.

[0067] The gas separation selectivity (P’CO 2 / P’N 2 ) of the separation membrane in the gas separation membrane units 10 to 13 for CO 2 and N 2 is preferably 4 or more, more preferably 7 or more, and even more preferably 15 or more. The gas separation selectivity (P’CO 2 / P’N 2 ) of the separation membrane in the gas separation membrane units 10 to 13 for CO 2 and N 2 is usually 100 or less, and more preferably 50 or less. The gas separation selectivity referred to here may be the selectivity at the operating temperature of the gas separation membrane unit. Among them, the separation selectivity at 60°C is preferably 5 to 100, and particularly preferably 6 to 50.

[0068] CO of the separation membrane in the first separation membrane unit 2 and N 2 If the gas separation selectivity of the separation membrane in the first separation membrane unit is greater than that of the separation membrane used in the second separation membrane unit, the separation selectivity P 1 ’CO 2 / P 1 ’N 2 of the gas separation membrane in the first separation membrane unit is preferably at least 1.2 times, more preferably at least 1.5 times, still more preferably at least 2 times, and particularly preferably at least 2.5 times the separation selectivity P 2 ’CO 2 / P 2 ’N 2 of the gas separation membrane in the second separation membrane unit. Also, the separation selectivity P 1 ’CO 2 / P 1 ’N 2 of the gas separation membrane in the first gas separation membrane unit 11 is preferably usually at most 10 times, more preferably at most 5 times the separation selectivity P 2 ’CO 2 / P 2 ’N 2 of the gas separation membrane in the second separation membrane unit. Note that the gas separation selectivity referred to here may be the selectivity at the operating temperature of each of the gas separation membrane units 11 and 12. Among them, it is preferably that the ratio of the selectivities at 60 °C of each unit is 1.5 to 10, and particularly preferably 2 to 5.

[0069] CO of the separation membrane in the third separation membrane unit 2 and N 2 If the gas separation selectivity of the separation membrane in the third separation membrane unit is greater than that of the separation membrane used in the second separation membrane unit, the separation selectivity P 3 ’CO 2 / P 3 ’N 2 of the gas separation membrane in the third separation membrane unit, with respect to the separation selectivity P 2 ’CO 2 / P 2 ’N 2 of the gas separation membrane in the second separation membrane unit, the preferred range of the ratio is the separation selectivity P 1’CO 2 / P 1 ’N 2 of the separation selectivity P of the gas separation membrane in the second separation membrane unit 2 ’CO 2 / P 2 ’N 2 is the same as the preferred ratio range for

[0070] As described above, the present invention has been described based on its preferred embodiments, but the present invention is not limited to the above embodiments. For example, in addition to the compression means in the above embodiments, a decompression means may be provided on the permeation side of any one or two of each gas separation membrane unit to impart power to the mixed gas supplied to each gas separation membrane unit to pass through the separation membrane. As such a decompression means, a known vacuum pump or the like can be used.

Example

[0071] Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited by these examples.

[0072] <Gas separation membrane module> Regarding the gas separation membrane modules A and B used in the examples and comparative examples, the gas separation characteristics are shown in Table 1. These gas separation membrane modules are those in which a gas separation membrane composed of an aromatic polyimide hollow fiber membrane is housed in a case. The membrane area of the hollow fiber membrane of gas separation membrane module A is 14 m 2 and the area of the hollow fiber membrane of gas separation membrane module B is 16.2 m 2 was.

[0073]

Table 1

[0074] [Examples 1 to 44] The system shown in FIG. 1 was used. In the system shown in FIG. 1, as combustion exhaust gas, CO 2 and N 2A mixed model gas was used. The gas separation membrane unit 11 was composed of one gas separation membrane module. The gas separation membrane module used in the examples of Tables 2 and 3 was Gas Separation Membrane Module A. The gas separation membrane unit 10 was operated under the conditions of Tables 2 and 3. Also, in Tables 2 and 3, the temperature of the combustion exhaust gas refers to the temperature of the gas flowing into the gas separation membrane unit 10. The pressure of the combustion exhaust gas refers to the pressure of the gas flowing into the gas separation membrane unit 11. The operating temperature is the temperature of the gas separation membrane in the gas separation membrane unit 10. The CO concentration and N concentration and N recovery rate in the permeated gas and non-permeated gas are shown in Tables 2 and 3. As described above, the temperature of the combustion exhaust gas shown in each table is the temperature at the time of introduction into the gas separation membrane unit 10, and the membrane temperature of the gas separation membrane unit 10 was the same as the temperature of the combustion exhaust gas. 2 concentration and N 2 concentration and N 2 recovery rate are shown in Tables 2 and 3. As described above, the temperature of the combustion exhaust gas shown in each table is the temperature at the time of introduction into the gas separation membrane unit 10, and the membrane temperature of the gas separation membrane unit 10 was the same as the temperature of the combustion exhaust gas.

[0075] Note that including Tables 2 and 3 below, the flow rate of the combustion exhaust gas in each table refers to the flow rate of the combustion exhaust gas introduced into the unit structure 10. In the examples of each table, the combustion exhaust gas was discharged from the combustion exhaust gas source 20 at 100 °C or higher and cooled to the temperature shown in the table by the cooling means. The composition of the raw material gas indicates the composition when discharged from the combustion exhaust gas source.

[0076]

Table 2

[0077]

Table 3

[0078] As shown in Tables 2 and 3, even in a one-stage system, according to the present invention, CO can be concentrated by 1.7 times or more. 2 can be concentrated by 1.7 times or more.

[0079] [Comparative Examples 1 - 20] For Comparative Examples 1 - 20, air was separated under the conditions of Table 4 using the same system as in Figure 1. O in permeate and non-permeate gases 2 Concentration and N 2 Concentration, N 2 The recovery rates are shown in Table 4. The air pressure shown in Table 4 refers to the pressure of the gas flowing into the gas separation membrane unit 11. The air temperature is the temperature at the time the air flows into the gas separation membrane unit 11. The membrane temperature of the gas separation membrane unit 11 was the same as the air temperature. As can be seen from the comparison between Example 1 and Comparative Example 1, by separating the combustion exhaust gas with the system of the present invention, the same amount of N 2 Concentration N 2 High N for enriched gas 2 It can be seen that the recovery rate can be obtained. 2 In terms of concentration, the ratio of product gas volume to supply gas volume is larger when combustion exhaust gas is used as the raw material. This is N 2 This means that the amount of gas required to be supplied per amount of enriched gas is small (i.e., the energy required to increase the pressure is small), which means that the energy consumption per amount of product gas is small.

[0080] [Table 4]

[0081] [Examples 45 to 69] The system shown in Fig. 3 was used. The first gas separation membrane unit 11 and the second gas separation membrane unit 12 used the numbers of gas separation membrane modules shown in Tables 5 and 6, respectively. When there were multiple modules, the multiple modules were combined in parallel to form a unit. The unit structure 10 was operated under the conditions shown in Tables 5 and 6. The first and second permeable gases and the CO in the first and second permeable gases 2 Concentration and N 2 Concentration and N 2 The recovery rate and the like are shown in Tables 5 and 6. The pressure of the combustion exhaust gas shown in Tables 5 and 6 refers to the pressure of the gas flowing into the gas separation membrane unit 11. The temperature of the combustion exhaust gas shown in each table is the temperature at the time it flows into the gas separation membrane unit 11. The membrane temperatures of the gas separation membrane units 11 and 12 were the same as the temperature of the combustion exhaust gas.

[0082]

Table 5

[0083]

Table 6

[0084] As can be seen from the comparison between Tables 2, 3 and Tables 5, 6, by combining two or more gas separation membrane units, compared with the case of a single stage, at the same N concentration in the enriched gas, the CO concentration in the enriched gas and the N recovery rate can be increased. In particular, as can be seen from Examples 46, 63, and 67 in Table 6, in the first stage, by using a gas separation membrane unit with higher CO / N separation performance, it can be seen that the CO concentration and the N recovery rate can be increased. 2 N in the enriched gas 2 while keeping the concentration equal, CO 2 CO in the enriched gas 2 concentration and N 2 recovery rate can be increased. In particular, as can be seen from Examples 46, 63, and 67 in Table 6, in the first stage, CO 2 / N 2 By using a gas separation membrane unit with higher separation performance, in particular, CO 2 concentration and N 2 recovery rate can be increased.

Explanation of Reference Signs

[0085] 1, 2, 3 Gas separation system 10 Unit structure (gas separation membrane unit) 11 First gas separation membrane unit 11a First gas inlet 11b First non-permeating gas outlet 11c First permeating gas outlet 12 Second gas separation membrane unit 12a Second gas inlet 12b Second non-permeating gas outlet 12c Second permeating gas outlet 13 Third gas separation membrane unit 13a Third gas inlet 13b Third non-permeating gas outlet 13c Third permeating gas outlet 15 N2 Enriched gas supply line 26 Combustion exhaust gas supply line 21 Compression means 23 Cooling means 50 N 2 Enriched gas utilization device

Claims

1. CO ２ and N ２ from combustion exhaust gas containing CO ２ Enriched gas and N ２ 1. A gas separation system for producing an enriched gas, comprising: The gas separation system has a unit structure which is a single gas separation membrane unit or a combination of two or more gas separation membrane units, The unit structure includes a gas inlet, a permeate gas outlet, and a non-permeate gas outlet, a combustion exhaust gas supply line connected to the gas inlet and supplying combustion exhaust gas to the unit structure, a compression means interposed in the combustion exhaust gas supply line, and a cooling means arranged upstream of the compression means in a combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, Further, the non-permeation gas outlet and N ２ N connected to enriched gas utilization device ２ Equipped with an enrichment gas supply line, The combustion exhaust gas contains CO 2 in an amount of 3 mol % or more and 30 mol % or less, and N 2 in an amount of 40 mol % or more and 95 mol % or less, a flow rate (Nm 3 / h) of the permeable gas at the permeable gas outlet is 65% or less of a flow rate (Nm 3 / h) of the fuel exhaust gas introduced into the unit structure; The CO 2 concentration in the permeable gas at the permeable gas outlet is 30 mol % or more, A gas separation system, wherein the non-permeate gas discharged from the non-permeate gas outlet has a N 2 concentration of 90 mol % or more.

2. The permeation gas outlet is CO ２ CO connected to recovery equipment ２ 10. The gas separation system of claim 1 comprising an enriched gas supply line.

3. 3. The gas separation system according to claim 1, wherein the unit structure comprises one gas separation membrane unit.

4. the unit structure comprises a first gas separation membrane unit and a second gas separation membrane unit, the first gas separation membrane unit comprises a first gas inlet, a first permeate gas outlet, and a first non-permeate gas outlet; the second gas separation membrane unit comprises a second gas inlet, a second permeate gas outlet, and a second non-permeate gas outlet; The first non-permeate gas outlet is connected to a second gas inlet of the second gas separation membrane unit; a second permeable gas return line is provided to connect the second permeable gas outlet to the intake side of the compression means in the combustion exhaust gas supply line; The second non-permeable gas outlet ２ 3. The gas separation system of claim 1 or 2, further comprising an enriched gas supply line connected thereto.

5. The separation membrane module used in the unit structure is a CO ２ Permeation rate P'CO ２ , nitrogen permeation rate P'N ２ , oxygen permeation rate P′O ２ The gas separation system according to claim 1 or 2, wherein: P'CO ２ > P'O ２ and P'O ２ > P'N ２

6. 3. The gas separation system according to claim 1, wherein the gas separation membrane in the unit structure comprises a polyimide hollow fiber membrane.

7. The gas separation system according to claim 1 or 2, wherein a pretreatment facility consisting of one or more selected from a second cooling means, a drain discharge device, a dust removal device, and a heating device is installed downstream of the compression means in the flow direction of the combustion exhaust gas.

8. CO of the separation membrane in the first separation membrane unit ２ and N ２ Gas separation selectivity with respect to (P'CO ２ / P'N ２ 5. The gas separation system of claim 4, wherein the first separation membrane unit is a first separation membrane unit, and the second separation membrane unit is a second separation membrane unit.

9. A gas separation system for producing a CO2-enriched gas and an N2-enriched gas from a combustion exhaust gas containing CO2 and N2, comprising: The gas separation system has a unit structure which is a single gas separation membrane unit or a combination of two or more gas separation membrane units, The unit structure includes a gas inlet, a permeate gas outlet, and a non-permeate gas outlet, a combustion exhaust gas supply line connected to the gas inlet and supplying combustion exhaust gas to the unit structure, a compression means interposed in the combustion exhaust gas supply line, and a cooling means arranged upstream of the compression means in a combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, a pretreatment facility including at least one selected from a second cooling means, a drain discharge device, a dust removal device, and a heating device, is installed downstream of the compression means in the flow direction of the combustion exhaust gas; Further, a N 2 enriched gas supply line is provided connecting the non-permeation gas outlet and an N 2 enriched gas utilization device, A gas separation system comprising: a branch line that connects the upstream side of the combustion exhaust gas supply line in the combustion exhaust gas flow direction relative to the cooling means to the heating device; and the combustion exhaust gas supplied through the branch line is used as a heat source for the heating device.

10. 3. The gas separation system according to claim 1, wherein the non-permeate gas outlet has a pressurized dew point of −20° C. or lower.

11. 3. The gas separation system according to claim 1, wherein the refrigerant in the cooling means is seawater.

12. N ２ 3. The gas separation system according to claim 1 or 2, wherein the enriched gas utilization device is explosion-proof.

13. 3. The gas separation system of claim 1 or 2 for use on a ship or offshore installation.

14. CO using gas separation system ２ and N ２ from combustion exhaust gas containing CO ２ Enriched gas and N ２ 1. A method for producing an enriched gas, comprising: The gas separation system has a unit structure which is a single gas separation membrane unit or a combination of two or more gas separation membrane units, The unit structure includes a gas inlet, a permeate gas outlet, and a non-permeate gas outlet, a combustion exhaust gas supply line connected to the gas inlet and supplying combustion exhaust gas to the unit structure, a compression means interposed in the combustion exhaust gas supply line, and a cooling means arranged upstream of the compression means in a combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, The non-permeable gas outlet is N ２ N connected to enriched gas utilization device ２ Provide an enrichment gas supply line; The combustion exhaust gas contains CO 2 in an amount of 3 mol % or more and 30 mol % or less, and N 2 in an amount of 40 mol % or more and 95 mol % or less, a flow rate (Nm 3 / h) of the permeable gas at the permeable gas outlet is 65% or less of a flow rate (Nm 3 / h) of the fuel exhaust gas introduced into the unit structure; The CO 2 concentration in the combustion exhaust gas is 3 mol % or more, The CO 2 concentration in the permeable gas at the permeable gas outlet is 30 mol % or more, The non-permeable gas discharged from the non-permeable gas outlet has a N 2 concentration of 90 mol % or more. ２ Enriched gas and N ２ A method for producing enriched gas.

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