Gas separation system and method for producing co2 enriched gas and n2 enriched gas

Abstract

Provided is a gas separation system for producing CO2 enriched gas and N2 enriched gas from a combustion exhaust gas that contains CO2 and N2. The gas separation system comprises a unit structure which is one gas separation membrane unit or a connected body in which two or more gas separation membrane units are connected. The unit structure is provided with a gas inlet, a permeated gas discharge port, and a non-permeated gas discharge port. The gas separation system comprises a combustion exhaust gas supply line that is connected to the gas inlet and that supplies combustion exhaust gas to the unit structure, a compression means that is disposed in an interposed manner on the combustion exhaust gas supply line, and a cooling means that is disposed upstream of the compression means in the direction of flow of the combustion exhaust gas and that cools the combustion exhaust gas which is supplied to the compression means. The non-permeated gas discharge port is provided with an N2 enriched gas supply line that is connected to a N2 enriched gas-utilizing device.

Description

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

[0001] The present invention relates to a gas separation membrane system and a method for producing a CO₂-enriched gas and a N₂-enriched gas using the same.

[0004] , ２ , ２ , ２ , ２ , ２ , ２ ,<00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​A gas separation system for producing enriched gas, wherein the gas separation system has a unit structure which is either one gas separation membrane unit or a connected body of two or more gas separation membrane units, the unit structure comprises a gas inlet, a permeable gas outlet, and an impermeable 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 the combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, the impermeable gas outlet is N ２ N connected to the enriched gas utilization device ２ A gas separation system equipped with an enriched gas supply line. [2] The permeate gas outlet is CO ２ CO2 recovery device connected ２ [1] A gas separation system according to [1], further comprising an enriched gas supply line. [3] A gas separation system according to [1] or [2], wherein the number of gas separation membrane units in the unit structure is one. [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 impermeable gas outlet, the second gas separation membrane unit comprises a second gas inlet, a second permeate gas outlet and a second impermeable gas outlet, the first impermeable gas outlet is connected to the second gas inlet of the second gas separation membrane unit, and a second permeate gas recirculation line is provided that connects the second permeate gas outlet to the suction side of the compression means in the combustion exhaust gas supply line, and the second impermeable gas outlet is connected to the N ２ A gas separation system according to any one of items [1] to [2], which connects to an enriched gas supply line. [5] The separation membrane module used in the unit structure is CO ２ Transmission rate P'CO ２ , nitrogen permeation rate P'N ２ , oxygen permeation rate P'O ２ However, the gas separation system described in any one of items [1] to [4] below has the following relationship: P'CO ２ > P'O ２ And P'O２ > P'N ２ [6] Flow rate of permeate gas at the permeate gas outlet (Nm ３ The flow rate (Nm³ / h) of the combustion exhaust gas introduced into the unit structure is ３ A gas separation system described in any one of items [1] to [5], wherein CO in the combustion exhaust gas is 65% or less of / h. [7] ２ A gas separation system according to any one of items [1] to [6], wherein the concentration is 3 mol% or more. [8] CO in the permeate gas at the permeate gas outlet ２ A gas separation system according to any one of items [1] to [7], wherein the concentration is 30 mol% or more. [9] N in the impermeable gas discharged from the impermeable gas outlet. ２ A gas separation system according to any one of items [1] to [8], wherein the concentration is 90 mol% or more.

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

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

[10] , 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 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 Gas separation selectivity (P'CO ２ / P'N ２ ) is larger than the separation membrane used in the second separation membrane unit, a gas separation system according to any one of [4] to

[11] .

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

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

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

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

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

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

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

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

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

[16] , for use on ships or offshore facilities.

[18] A gas separation system using CO ２ and N ２ CO from combustion exhaust gases containing ２ Enriched gas and N ２ A method for producing enriched gas, wherein the gas separation system has a unit structure which is either one gas separation membrane unit or a connected body of two or more gas separation membrane units, the unit structure comprises a gas inlet, a permeable gas outlet, and an impermeable 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 the combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, the impermeable gas outlet being N ２ N connected to the enriched gas utilization device ２ CO2 enrichment gas supply line installed, ２ Enriched gas and N ２ A method for producing enriched gas.

[0007] Figure 1 is a schematic diagram showing the configuration of a gas separation system in a first embodiment of the present invention. Figure 2 is a schematic diagram showing the configuration of a gas separation membrane module of the present invention. Figure 3 is a schematic diagram showing the configuration of a gas separation system in a second embodiment of the present invention. Figure 4 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. Figure 5 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. Figure 6 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. Figure 7 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. Figure 8 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention.

[0008] The present invention will be described below with reference to the drawings, based on preferred embodiments thereof. The upper and lower limits of numerical values ​​in this specification can be combined in any way without limitation.

[0009] In the gas separation systems shown in Figures 1, 4, 5, and 8, one gas separation membrane unit 11 constitutes the unit structure 10. On the other hand, in Figures 3 and 6, a connected body of two gas separation membrane units 11 and 12 constitutes the unit structure 10. Furthermore, in Figure 7, a connected body of three gas separation membrane units 11 to 13 constitutes the unit structure 10.

[0010] Each gas separation membrane unit 11 to 13 can be, for example, a module 40 in which a gas separation membrane 30 having gas selective permeability, made of a hollow fiber membrane or the like and housed in a casing 31, can be used as each gas separation membrane unit 11 to 13. Each gas separation membrane unit can be, for example, the gas separation membrane module 40 shown in Figure 2 as is, or multiple modules 40 can be arranged in parallel. In the module 40, the casing 31 has openings on two opposing sides to form openings 32. When the gas separation membrane 30 consists of a bundle of hollow fiber membranes, the gas separation membrane 30 is housed in the casing 31 such that, in its housed state, each end of the hollow fiber membrane is open near each opening 32 of the casing 31.

[0011] A hollow fiber gas separation membrane module, such as module 40, is obtained by bundling together, for example, about 100 to 1,000,000 (more preferably about 100 to 500,000) hollow fiber membranes of appropriate length, fixing both ends of the hollow fiber membrane bundle with a tube sheet made of thermosetting resin or the like so that at least one end of the hollow fiber remains open, and then housing and installing the resulting hollow fiber membrane bundle and hollow fiber membrane element made of the tube sheet or the like in a container equipped with at least a mixed gas inlet, a permeable gas outlet, and a non-permeable gas outlet, such that the space leading to the inside of the hollow fiber membrane and the space leading to the outside of the hollow fiber membrane are separated.

[0012] When the gas separation membrane 30 is housed in the casing 31, the gas separation membrane 30 is fixed to the inner wall of the casing 31 by tube sheets 33 and 34 at both ends in the Y direction, which is the direction in which the hollow fiber membrane extends. Each opening 32 of the casing 31 is closed by lids 35 and 36. A gas inlet 37 is provided in lid 35. On the other hand, a non-permeable gas outlet 38 is provided in lid 36. The mixed gas to be separated is introduced into the module from the gas inlet 37 of lid 35. Of the introduced gas, the gas that permeates through the gas separation membrane 30 is discharged outside the module from a permeable gas outlet 39 provided in the casing 31. On the other hand, the non-permeable gas that does not permeate through the gas separation membrane 30 is discharged outside the module from a non-permeable gas outlet 38 of lid 36. The above explanation has been given using the separation membrane module shown in Figure 2 as an example, but of course, the present invention can be applied to separation membrane modules with other configurations, for example, to shell-feed type modules.

[0013] The gas separation membrane unit and gas separation membrane module used in the unit structure 10 are CO ２ Transmission rate P'CO ２ , N ２ Transmission velocity P'N ２ , oxygen permeation rate P'O ２ However, it is preferable that the relationship is as shown in (1) below, and more preferable that the relationship is as shown in (2) below. In the following embodiment, the gas separation membrane unit and the gas separation membrane module have the relationship shown in (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 (permeation volume per unit membrane area, unit time, and unit partial pressure difference relative to the membrane), and its unit is ×10 －５ cm ３ (STP) / cm ２The value is sec・cmHg. The relationship between (1) and (2) above applies only at the operating temperature of the gas separation membrane unit and the gas separation membrane module. In this specification, the permeation rate may be referred to as "permeability".

[0014] In the following, "upstream" and "downstream" refer to the combustion exhaust gas flow direction. As shown in Figure 1, the unit structure 10 consists of a first gas separation membrane unit 11, and 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 constitute the gas inlet 10a, the non-permeable gas outlet 10b, and the permeable gas outlet 10c, respectively. Also as shown in Figure 1, the gas separation system 1 includes a combustion exhaust gas supply line 26 connected to the gas inlet 10a and supplying 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 positioned upstream of the compression means 21 in the combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means 21, and further includes a non-permeable gas outlet 10b and N ２ N connects to the enriched gas utilization device 50. ２ It is equipped with an enriched gas supply line 15.

[0015] N ２ As an enriched gas utilization device 50, N is used as an inert gas in storage containers (tanks, cylinders, etc.) for liquids and powders such as petroleum products, fuels, ultrapure water and pure water, chemicals, pharmaceuticals, and food. ２ A device for sealing and filling (N ２ A device that fills cylinders containing gas, fuel, etc. ２ A device for filling tanks containing fuel or other substances with gas, N ２ (Equipment for filling cylinders with gas, etc.); Liquefied N2 in containers ２ Apparatus for manufacturing; N ２ Examples include a device for purging. N is connected to the non-permeable gas outlet 10b. ２ The enriched gas utilization device 50 may be one or multiple devices.

[0016] The permeate gas outlet 10c is CO２ CO2 in enriched gas supply line 18 ２ It is connected to the recovery device 51. ２ As for the recovery device 51, CO ２ Liquefaction equipment, CO ２ Solidification equipment, CO ２ CO absorption equipment, ２ Adsorption equipment is one example. ２ CO recovered by recovery device 51 ２ It may be used in artificial photosynthesis. It can also be converted to methane by reacting it with hydrogen and used as part of a fuel. Here, hydrogen produced by the electrolysis of water may be used. Also, CO ２ In the recovery device 51, CO ２ CO recovered through enriched gas supply line 18 ２ The enriched gas may be further concentrated as needed and then liquefied using a liquefaction device or similar equipment. ２ Known methods include concentrating the enriched gas before liquefaction. For example, methods using a gas separation membrane, or methods using an absorbent solution of potassium carbonate or amine compounds, or zeolite. CO connected to the permeate gas outlet 10c ２ The recovery device 51 may be one or multiple devices.

[0017] A heat exchanger can be used as the cooling means 23. Since combustion exhaust gas is basically at a high temperature, using the cooling means 23 allows it to be cooled to a temperature suitable for the operation of the gas separation membrane. It is preferable that the refrigerant in the cooling means 23 is seawater, in terms of reducing refrigerant usage costs, such as when the system 1 is used on a ship or in offshore facilities.

[0018] Furthermore, the compression means 21 is installed for the purpose of pressurizing the combustion exhaust gas supplied from the combustion exhaust gas source. A compressor can be used as the compression means 21.

[0019] The combustion exhaust gas supply line 26 connects the combustion exhaust gas source 20, which generates the combustion exhaust gas, to the gas inlet 10a. The combustion exhaust gas is N ２ and CO ２It contains. As the combustion exhaust gas source 20, there are boilers such as diesel engines, gasoline engines, gas turbines, oil-fired boilers, incinerators for burning waste such as garbage, etc. Among them, from the point of making use of the space-saving advantage 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 contained moisture, nitrogen oxides (NOx), sulfur oxides (SOx), volatile organic compounds (VOC), oxygen, carbon monoxide, PM (fine particles), etc.

[0020] 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 which is the gas that has permeated through the gas separation membrane and a non-permeated gas which is the gas that has not permeated through the gas separation membrane. The non-permeated gas is one in which N ２ is concentrated 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 one in which CO ２ is concentrated 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.

[0021] In the example shown in Figure 1, the gas separation system 1 has a branch line 29. The branch line 29 branches off from the combustion exhaust gas supply line 26 upstream of the compression means 21 in the combustion exhaust gas supply line 26 in the combustion exhaust gas flow direction, and separates the combustion exhaust gas supply line 26 from CO ２ The recovery device 51 is connected without passing through a gas separation membrane. With this configuration, a portion of the exhaust gas discharged from the combustion exhaust gas source 20 is CO2 released without going through membrane separation. ２ N is supplied to the recovery device 51. ２ When separating them, N is usually required as an inert gas, etc. ２ The amount of gas is less than the amount of combustion exhaust gas emitted from the combustion exhaust gas source. On the other hand, N in the impermeable gas ２ To increase the concentration, it is necessary to install a gas separation membrane with an area suitable for the amount of combustion exhaust gas flowing into the unit structure 10. For these reasons, it is preferable to provide a branch line 29 in the combustion exhaust gas supply line 26 for adjusting the combustion exhaust gas introduced into the unit structure 10, and to provide a flow control valve (not shown) at the branching point of the branch line 29, etc., to introduce combustion exhaust gas at a flow rate suitable for the gas separation membrane of the unit structure 10 into the unit structure 10, in order to reduce the equipment costs and operating costs of the system 1. Branch line 29 and CO ２ Enrichment gas supply line 18 has the same CO2 ２ CO2 is released into the recovery device 51. ２ Supplying the contained gas is CO ２ This is preferable in terms of recovery efficiency. In Figure 1, the combustion exhaust gas that is not introduced into the unit structure 10 by the branch line 29 is directly CO ２ It is introduced into the recovery device 51, but another CO ２ A concentration device is installed in the branch line 29, and CO2 is concentrated in this device. ２ The concentrated combustion exhaust gas is CO ２ CO may be introduced into the recovery device 51. ２ The enriched gas supply line 18 is connected to the other CO ２ Connect it upstream of the concentration device, CO ２ CO2 flowing through enriched gas supply line 18 ２ enriched gas is used with the other CO ２The device may be configured to further concentrate the contents using a concentration device.

[0022] In Figure 1, the cooling means 23 is located downstream of the branching point of the branch line 29 in the combustion exhaust gas supply line 26, but it may also be located upstream of the branching point. ２ CO in the recovery device 51 ２ liquefaction, CO ２ Solidification, CO ２ Absorption, CO ２ The efficiency of adsorption, etc., is often determined by the amount of CO introduced. ２ Lower enrichment gas temperatures result in higher efficiency. Therefore, by installing the cooling means 23 upstream of the branching point of the branch line 29 in the direction of combustion exhaust gas flow, the entire combustion exhaust gas is cooled, which is beneficial for CO2 in system 1. ２ This is preferable in terms of increasing processing capacity.

[0023] N discharged from the unit structure 10 ２ Regarding enriched gas, the fact that moisture has been removed is N ２ The enriched gas is preferable because it can be used in a wide range of applications. The moisture removal level is preferably Class 3 or higher as defined in ISO 8573-1, meaning that the dew point under pressure (also called "pressurized dew point") of the gas discharged from the impermeable gas outlet 10b of the unit structure 10 is preferably -20°C or lower, and more preferably Class 2 or higher, meaning that the dew point is preferably -40°C or lower. The pressure referred to here is the discharge pressure of the gas from the impermeable gas outlet 10b. If the humidity of the combustion exhaust gas is high, a drain discharge device 28 or the like, which will be described later, may be used to achieve the above configuration.

[0024] Next, a second embodiment of the present invention will be described with reference to Figure 3. In the following description of the second embodiment and subsequent embodiments, the focus will be on parts not described in earlier embodiments, and other components will be denoted by the same reference numerals and their descriptions will be omitted. In system 2 of this embodiment, the unit structure 10 comprises 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. In the following description, the gas inlets, outlets, supplied gases, discharged permeate gases, and non-permeate gases of the first gas separation membrane unit 11 and the second gas separation membrane unit 12 may be described with the terms "first" and "second," respectively. The same applies to the configuration of the third gas separation membrane unit 13, which will be described later.

[0025] The first gas separation membrane unit 11 includes a first gas inlet 11a, a first permeate gas outlet 11c, and a first impermeable gas outlet 11b, while the second gas separation membrane unit 12 includes a second gas inlet 12a, a second permeate gas outlet 12c, and a second impermeable gas outlet 12b. In system 2, the first gas inlet 11a and the first permeate gas outlet 11c become the gas inlet 10a and permeate gas outlet 10c of the unit structure 10, respectively, and the second impermeable gas outlet 12b becomes the impermeable gas outlet 10b of the unit structure 10. Furthermore, the first permeate gas becomes the permeate gas of the unit structure 10, and the second impermeable gas becomes the impermeable gas of the unit structure 10.

[0026] In system 2, the first impermeable gas outlet 11b and the second gas inlet 12a of the second gas separation membrane unit 12 are connected by the first impermeable gas outlet line 14. In system 2, a second permeable gas return line 17 is provided, which connects the second permeable gas outlet 12c to the suction side of the compression means 21 in the combustion exhaust gas supply line 26. Furthermore, in system 2, N is connected to the second impermeable gas outlet 12b. ２ Connect the enriched gas supply line 15.

[0027] The compression means 21 pressurizes the permeate gas when it returns the second permeate gas discharged from the second gas separation membrane unit 12 to the first gas separation membrane unit 11 through the second permeate gas reflux line 17.

[0028] In system 2 as well, 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 permeate gas and a first impermeate gas. The first impermeate gas discharged from the first impermeate gas outlet 11b has a higher N content compared to the combustion exhaust gas. ２ This is a concentrated form of CO, which is supplied to the second gas separation membrane unit 12 through the first non-permeable gas discharge line 14. Meanwhile, the first permeable gas discharged from the first permeable gas outlet 11c (10c) is CO ２ CO2 ２ It is supplied to the recovery device 51.

[0029] The first non-permeable gas is separated into a second permeable gas and a second non-permeable gas by the gas separation membrane of the second gas separation membrane unit 12. The second non-permeable gas is N ２ It is further concentrated and enriched, and N is released from the second non-permeable gas outlet 12b. ２ Through enriched gas supply line 15, N ２ It is supplied to the enriched gas utilization device 50. Meanwhile, the second permeate gas is discharged from the second permeate gas outlet 12c, returned to the suction side of the compression means 21 in the combustion exhaust gas supply line 26 via the second permeate gas recirculation line 17, mixed with the combustion exhaust gas, and then pressurized by the compression means 21.

[0030] According to this system 2, by recirculating the permeate gas from the second-stage gas separation membrane unit upstream of the first-stage gas separation membrane unit, the CO2 in the combustion exhaust gas supplied to the first-stage gas separation membrane unit is improved compared to system 1, which consists of a single-stage gas separation membrane unit. ２ The concentration can be increased, and this allows CO ２ CO in the permeate gas supplied to the recovery device ２ The concentration can be increased, and N ２ The recovery rate can also be increased.

[0031] In a connected body comprising two or more gas separation membrane units, the CO2 in the separation membrane of the first separation membrane unit 11 ２ and N ２ Gas separation selectivity (P'CO ２ / P'N２ ) is larger than that of the separation membrane used in the second gas separation membrane unit 12, which is the case for N in the non-permeable gas. ２ CO in the permeate gas without reducing its concentration ２ Concentration and N ２ This is preferable because it can increase the recovery rate. 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. In particular, regarding the selectivity of each unit at 60°C, the CO2 in the separation membrane of the first separation membrane unit 11 is preferable. ２ and N ２ Gas separation selectivity (P'CO ２ / P'N ２ It is preferable that the ) is larger than the separation membrane used in the second gas separation membrane unit 12.

[0032] In the example shown in Figure 3, the second permeate gas recirculation line 17 is connected to the downstream side of the cooling means 23 in the combustion exhaust gas supply line 26. However, the second permeate gas recirculation line 17 may also be connected to the upstream side of the cooling means 23 to recirculate the second permeate gas to the upstream side of the cooling means 23.

[0033] Unlike system 1 in Figure 1, as shown in Figure 4, the branch line 29 may be omitted, and the entire amount of combustion exhaust gas from the combustion exhaust gas source 20 may be subjected to membrane separation by the unit structure 10.

[0034] Furthermore, as shown in Figures 5 and 6, the non-permeable gas discharged from the non-permeable gas outlet 10b is N ２ The enriched gas utilization device 50 has a compression means 22 (booster) that increases the pressure to the required level, ２ It may be installed in the enriched gas supply line 15. A compressor can be used as the compression means 22. Multiple N ２ The enriched gas utilization device 50 is connected, and the required amount of N is supplied by each device. ２ If the enrichment gas pressure is different, the entire amount of non-permeable gas in the unit structure 10 is compressed, and then a portion is depressurized to low pressure N ２ N2 ２ It may also be sent to an enriched gas utilization device. Alternatively, a portion of the non-permeable gas in the unit structure 10 can be pressurized and converted to N ２The enriched gas is sent to the enriched gas utilization device 50 for use, and the remainder is not pressurized and is N2 ２ It may also be used in the enriched gas utilization device 50.

[0035] Next, we will describe system 3 in Figure 7. The following description will mainly explain the differences from the configuration in Figure 3. In the configuration of Figure 7, the unit structure 10 has a first gas separation membrane unit 11, a second gas separation membrane unit 12, and a third gas separation membrane unit 13. In the configuration of Figure 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 a first permeate gas outlet 11c and a third gas inlet 13a, respectively, via a first permeate gas outlet line 19.

[0036] The third impermeable gas outlet 13b is connected to the combustion exhaust gas supply line 26 by the third impermeable gas recirculation line 16. In the configuration shown in Figure 7, the third impermeable gas recirculation line 16 is connected to the suction side of the compression means 21 in the combustion exhaust gas supply line 26. The third impermeable gas recirculation line 16 is connected to the downstream side of the cooling means 23 in the combustion exhaust gas supply line 26, but it may also be connected to the upstream side of the cooling means 23. In the example shown in Figure 7, the permeable gas outlet 13c of the third gas separation membrane unit 13 corresponds to the permeable gas outlet 10c of the unit structure 10, and CO ２ A gas enrichment supply line 18 is connected to it.

[0037] 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.

[0038] During operation for gas separation in the gas separation system 3 of this 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 compared to the first permeate gas introduced into the third gas separation membrane unit 13. ２ The CO2 is further concentrated and enriched, and CO2 is released from the permeate gas outlet 13c of the unit 13. ２ CO2 ２ It is supplied to the recovery device 51. Meanwhile, the third impermeable gas is discharged from the third impermeable 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 impermeable gas recirculation line 16 connected to the outlet 13b. The third impermeable gas returned through the third impermeable gas recirculation line 16 is mixed with the combustion exhaust gas and then pressurized by the compression means 21.

[0039] According to this system 3, the third gas separation membrane unit 13 separates CO ２ As the N is concentrated, and the third non-permeable gas is returned to the first gas separation membrane unit 11, the N in the non-permeable gas discharged from the non-permeable gas outlet 10b ２ The concentration and the CO in the permeate gas discharged from the permeate gas outlet 10c ２ Concentration, N ２ This can further increase the recovery rate.

[0040] In this system 3, the CO of the separation membrane in the first gas separation membrane unit 11 ２ and N ２ Gas separation selectivity (P'CO ２ / P'N ２ If the CO2 in the separation membrane of the third gas separation membrane unit 13 is larger than that of the separation membrane used in the second gas separation membrane unit 12, ２ and N ２ Gas separation selectivity (P'CO ２ / P'N ２The CO2 in the permeate gas discharged from the permeate gas outlet 10c is equal to or greater than the separation membrane used in the second gas separation membrane unit 12. ２ Everyone and N ２ It is preferable in terms of further increasing the recovery rate, and it is even more preferable that it is larger than the separation membrane used in the second gas separation membrane unit 12. The gas separation selectivity referred to here may be the selectivity at the operating temperature of the gas separation membrane units 13 and 12, respectively. In particular, in terms of the selectivity of each unit at 60°C, the CO2 in the separation membrane of the second separation membrane unit 13 is preferable. ２ and N ２ Gas separation selectivity (P'CO ２ / P'N ２ It is preferable that the ) is larger than the separation membrane used in the second gas separation membrane unit 12.

[0041] The first permeate gas discharge line 19 may or may not include another compression means for pressurizing the first permeate gas and sending it to the third gas separation membrane unit.

[0042] Further modifications may be made to each of the gas separation systems described above. For example, a pretreatment facility may be provided downstream of the compression means 21 in the combustion exhaust gas supply line 26. The pretreatment facility is provided upstream of the unit structure 10 in the combustion exhaust gas supply line 26. The pretreatment facility separates N from the combustion exhaust gas. ２ enriched gases and CO2 ２ These are provided to remove impurities from enriched gas to facilitate reuse, and to prevent components in combustion exhaust gas, etc., from adhering to the gas separation membrane of the unit structure 10 and reducing separation performance. Examples of the aforementioned pretreatment equipment include a second cooling device, a dust removal device, a drain discharge device, a heating device, a desulfurization device, a denitrification device, etc., and these can be used individually or in combination of two or more types.

[0043] A heat exchanger can be used as the second cooling means or heating device.

[0044] Examples of dust removal devices include centrifugal separators, water absorption showers, electrostatic precipitators (ESPs), diesel particulate filters (DPFs), gasoline particulate filters (GPFs), and activated carbon filters.

[0045] A drain discharge device is a device that removes moisture flowing at the bottom of a pipe while maintaining the airtightness of the pipe, and conventionally known devices can be used.

[0046] A desulfurization device should have the function of removing sulfur oxides (SOx) contained in the combustion exhaust gas. For example, it may be a scrubber. A denitrification device removes nitrogen oxides (NOx) contained in the combustion exhaust gas. For example, a selective catalytic reduction (SCR) device can be used.

[0047] A preferred example of pretreatment equipment is the pretreatment equipment 200 shown in Figure 8, which is located 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 located downstream of the second cooling means 24, a heating device 46 located downstream of the drain discharge device 28, and a dust removal device 25. In the example in Figure 8, the dust removal device 25 is located downstream of the heating device 46. However, the dust removal device 25 may be located upstream of the second cooling means 24 or between any of the devices from the second cooling means 24 to the heating device 46, as long as it is located upstream of the unit structure 10. It is preferable that the dust removal device 25 be located downstream of the compression means 21 so that it can remove particles and the like discharged from the compression means 21. According to the system in Figure 8, moisture and high-boiling-point substances contained in the combustion exhaust gas or originating 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 remain in the piping, they are discharged out of the system by a drain discharge device 28. To prevent the gas from being re-condensed and reducing the gas separation performance by the drain discharge device 28, the gas is heated by a heating device 46 and supplied to the unit structure 10. Here, high-boiling-point substances refer to substances that are in a state of condensation under the supply gas pressure and temperature conditions introduced into the separation membrane.

[0048] As described above, using a dust removal device prevents soot and solid particles contained in the combustion exhaust gas from being supplied to the unit structure 10, thereby preventing a decrease in the separation membrane performance. The particle removal level in the gas supplied to the unit structure 10 is preferably Class 2 or higher as defined in ISO 8573-1, and more preferably Class 1. Therefore, the particle removal level in the gas supplied to the unit structure 10 is ≤400,000 particles / m³ of size 0.1 to 0.5 μm. 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 Preferably, the particle size is 0.1 to 0.5 μm, with a particle size of ≤ 20,000 particles / m². 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 It is preferable that it be so.

[0049] As shown in Figure 8, the combustion exhaust gas supply line 26 is provided with a branch line 27 that connects the upstream side of the cooling means 23 in the line 26 to the heating device 46, and it is preferable to use the uncooled combustion exhaust gas supplied through the branch line 27 as the heat source for the heating device 46, in terms of reducing cooling costs and heating costs for the heating device 46.

[0050] N ２ The enriched gas utilization device 51 uses N for explosion protection. ２ The use of enriched gas in the device is preferable because it allows for easier utilization of the space-saving gas separation advantages of gas separation using gas separation membranes. Examples of explosion-proof applications include fuel tanks and hydraulic system fluid storage in ships, offshore facilities, and aircraft, as well as transport containers such as fuel cylinders. In particular, the N of the present invention ２ Recovery rate and CO2 ２ From the perspective of taking advantage of its high recovery rate, as well as its space-saving and energy-saving benefits, explosion-proof applications such as fuel tanks in ships or offshore facilities are preferred.

[0051] Furthermore, 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. It can be used for the treatment of combustion exhaust gases in ships or offshore facilities in a space-saving, energy-saving, and N ２ Recovery rate and CO2 ２ This is preferable because it enhances the advantages of the present invention, which have a high recovery rate. Examples of offshore facilities include floating production, storage, and offloading systems (FPSOs), floating storage and offloading systems (FSOs), and other offshore power plants and factories.

[0052] CO in combustion exhaust gas２ The CO content in the permeate gas must be 3 mol% or more. ２ In terms of increasing the concentration, it is preferable, from this viewpoint, 5 mol% or more is preferable, 10 mol% or more is more preferable, and 15 mol% or more is even preferable. CO in the combustion exhaust gas used in the present invention ２ The concentration is generally 30 mol% or less, N ２ From the viewpoint of recovery rate, 20 mol% or less is preferred. In this specification, when describing the composition of the combustion exhaust gas, unless otherwise specified, it refers to the composition of the combustion exhaust gas when discharged from the combustion exhaust gas source 20, and for example in system 2, it refers to the composition of the combustion exhaust gas before mixing with the second permeate gas.

[0053] The combustion exhaust gas used in this invention is at least CO ２ and N ２ It is a gas containing N. In the present invention, the combustion exhaust gas is N ２ The resulting non-permeable gas contains 40 mol% or more of N ２ It is preferable because it has a high concentration and is easy to reuse, and it is more preferable that it contains 50 mol% or more. N in combustion exhaust gas ２ The concentration should be, for example, 95 mol% or less, CO ２ Increase the concentration and the CO in the permeate gas. ２ It is particularly preferable in terms of improving the concentration, and more preferably 90 mol% or less.

[0054] Flow rate of permeate gas at the permeate gas outlet 10c Fp (Nm ３ The flow rate Fs (Nm³) of combustion exhaust gas entering the system is / h. ３ The CO content of the permeate gas at the permeate gas outlet 10c is 65% or less of / h. ２ Concentration and N ２In terms of increasing the recovery rate, it is preferable that the ratio is 60% or less, more preferably 55% or less, and particularly preferably 50% or less. There is no lower limit to the ratio of the flow rate Fp of the permeate gas to the flow rate Fs of the combustion exhaust gas, but it is usually 5% or more, and particularly preferably 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 that is introduced into the unit structure 10. The flow rate of the combustion exhaust gas introduced into the unit structure 10 here refers to the flow rate of the combustion exhaust gas introduced into the unit structure 10 from the outside, and does not include the flow rate of the recirculated gas flowing from the gas outlet to the gas inlet side of the unit structure. For example, in 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 before mixing with the second permeate gas. In this specification, Nm ３ This is the amount of gas converted to 0°C and 1 atm.

[0055] Flow rate of non-permeable gas at the non-permeable gas outlet 10b Fn(Nm) ３ The flow rate Fs (Nm³) of the combustion exhaust gas supplied to the unit structure 10 is / h. ３ The CO content of the permeate gas at the permeate gas outlet 10c is 35% or more of the CO content permeate gas at / h. ２ Concentration and N ２ In terms of increasing the recovery rate, it is preferable that it be 40% or more, and more preferably 45% or more. There is no upper limit to the ratio of the flow rate Fn of the non-permeable gas to the flow rate Fs of the combustion exhaust gas, but it is usually 95% or less, and particularly 90% or less.

[0056] CO in the permeate gas at the aforementioned permeate gas outlet 10c ２ The concentration must be 30 mol% or higher. ２ When further concentrated in the recovery device 51, CO ２ Due to the high concentration and low total gas volume, CO ２ This is preferable in that it leads to miniaturization of the recovery device 51 and lower running costs. From this perspective, CO in the permeate gas ２A concentration of 40 mol% or more is more preferable, 50 mol% or more is even more preferable, 60 mol% or more is particularly preferable, and 80 mol% or more is especially preferable.

[0057] N in the non-permeable gas discharged from the non-permeable gas outlet 10b ２ The concentration must be 90 mol% or higher. ２ In terms of utilization efficiency in the enriched gas utilization device 50, it is preferable that the concentration be 95 mol% or higher, and more preferably 97 mol% or higher.

[0058] Furthermore, in the present invention, N ２ A recovery rate of 50% or more is preferable, 60% or more is more preferable, 70% or more is even more preferable, 80% or more is even more preferable, and 90% or more is particularly preferable. ２ The recovery rate can be calculated using the following formula. The unit of concentration is mol%. N ２ Recovery rate = (Non-permeable gas flow rate Fn × N in non-permeable gas discharged from non-permeable gas outlet 10b) ２ (Concentration) / (Combustion flue gas flow rate Fs × N in combustion flue gas) ２ concentration)

[0059] Furthermore, in this invention, CO ２ A recovery rate of 50% or more is preferable, 60% or more is more preferable, 70% or more is even more preferable, 80% or more is even more preferable, and 90% or more is particularly preferable. ２ The recovery rate can be calculated using the following formula. The unit of concentration is mol%. CO ２ Recovery rate = (Permeate gas flow rate Fp × CO in the permeate gas discharged from permeate gas outlet 10c) ２ (Concentration) / (Combustion flue gas flow rate Fs × CO in combustion flue gas) ２ concentration)

[0060] Furthermore, CO at the permeate gas outlet 10c ２ CO2 concentration (mol%) in combustion exhaust gas ２The ratio to the concentration (mol%) is preferably 1.5 times or more, more preferably 2 times or more, even more preferably 2.5 times or more, and even more preferably 3 times or more.

[0061] The pressure of the compression means 21 is preferably 0.2 MPaG or higher, and more preferably 0.3 MPaG or higher, as the pressure of the gas supplied to the unit structure 10. The pressure of the compression means 21 may be 2 MPaG or lower, or 1.6 MPaG or lower.

[0062] In the gas separation membrane module used in the present invention, a hollow fiber membrane made of polymer and having an asymmetric structure can be suitably 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 is a thinner layer than the porous layer and is mainly responsible for gas separation performance. The skin layer is a very dense layer compared to the porous layer and is usually very thin, preferably with a thickness of 1 nm to 5 μm, and more preferably with a thickness of 10 nm to 200 nm. The porous layer is a relatively thick porous layer that supports the skin layer, preferably with a thickness of 10 μm to 2000 μm, and more preferably with a thickness of 20 μm to 200 μm. The diameter of the pores in the porous layer is not particularly limited, but is generally 0.01 to 100 μm, and 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.

[0063] The hollow fiber membrane preferably has an inner diameter of approximately 10 to 3000 μm, with 30 to 500 μm being preferred. Furthermore, the outer diameter of the hollow fiber membrane preferably has an outer diameter of approximately 30 to 7000 μm, with 35 to 700 μm being more preferred. The thickness of the skin layer and 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.

[0064] The material for the gas separation membrane constituting the gas separation membrane module of the present invention is not particularly limited, but examples include polyimide, polyamide, polysulfone, polyethersulfone, polyamideimide, polyetherimide, and polycarbonate. Of these, the gas separation membrane is preferably made of polyimide in terms of separation performance, durability, and heat resistance.

[0065] Furthermore, the preferred operating temperature range for the gas separation membrane units 10, 11, 12, and 13 (temperature of the gas separation membrane during operation) is preferably 0 to 100°C, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The preferred temperature range for the combustion exhaust gas supplied to the unit structure 10 (temperature at the gas inlet 10a) is the same as the preferred operating temperature range mentioned above.

[0066] CO in the separation membranes of gas separation membrane units 10-13 ２ and N ２ Gas separation selectivity (P'CO ２ / P'N ２ ) is preferably 4 or more, more preferably 7 or more, and even more preferably 15 or more. CO of the separation membrane in the gas separation membrane units 10 to 13 ２ and N ２ Gas separation selectivity (P'CO ２ / P'N ２ The gas separation selectivity is usually 100 or less, and more preferably 50 or less. The gas separation selectivity referred to here should be the selectivity at the operating temperature of the gas separation membrane unit. In particular, the separation selectivity at 60°C is preferably 5 to 100, and especially preferably 6 to 50.

[0067] CO in the separation membrane of the first separation membrane unit ２ and N ２ If the gas separation selectivity is greater than that of the separation membrane used in the second separation membrane unit, then the separation selectivity P of the gas separation membrane in the first separation membrane unit is... １ 'CO ２ / P １ 'N ２ This relates to the separation selectivity of the gas separation membrane in the second separation membrane unit. ２ 'CO ２ / P ２ 'N ２ The ratio to is preferably 1.2 or higher, more preferably 1.5 or higher, even more preferably 2 or higher, and particularly preferably 2.5 or higher. Also, the separation selectivity P of the gas separation membrane of the first gas separation membrane unit 11. １ 'CO ２ / P １ 'N ２ This relates to the separation selectivity of the gas separation membrane in the second separation membrane unit. ２ 'CO ２ / P ２ 'N ２ The ratio to is usually preferably 10 or less, and more preferably 5 or less. 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. In particular, the ratio of the selectivity of each unit at 60°C is preferably 1.5 to 10, and especially preferably 2 to 5.

[0068] CO in the separation membrane of the third separation membrane unit ２ and N ２ If the gas separation selectivity is greater than that of the separation membrane used in the second separation membrane unit, the separation selectivity P of the gas separation membrane in the third separation membrane unit ３ 'CO ２ / P ３ 'N ２ The separation selectivity of the gas separation membrane in the second separation membrane unit P ２ 'CO ２ / P ２ 'N ２ The preferred range of the ratio to the separation selectivity P of the gas separation membrane in the first separation membrane unit is １ 'CO ２ / P １ 'N ２ The separation selectivity of the gas separation membrane in the second separation membrane unit P ２ 'CO ２ / P ２ 'N ２ This is similar to the range of preferred ratios for .

[0069] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in addition to the compression means in the above embodiments, a depressurization means may be provided on any one or two permeation sides of each gas separation membrane unit to provide power to the mixed gas supplied to each gas separation membrane unit to pass through the separation membrane. Known vacuum pumps and the like can be used as such depressurization means.

[0070] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited by these examples.

[0071] <Gas Separation Membrane Modules> Table 1 shows the gas separation characteristics of gas separation membrane modules A and B used in the examples and comparative examples. These gas separation membrane modules house a gas separation membrane made of aromatic polyimide hollow fiber membranes within a case. The membrane area of ​​the hollow fiber membrane of gas separation membrane module A is 14 m². ２ The area of ​​the hollow fiber membrane in gas separation membrane module B is 16.2 m². ２ That was the case.

[0072]

[0073] [Examples 1-44] The system shown in Figure 1 was used. In the system shown in Figure 1, CO was used as the combustion exhaust gas. ２ and N ２ A model gas mixture was used. The gas separation membrane unit 11 consisted of one gas separation membrane module. The gas separation membrane module used in the examples in Tables 2 and 3 is gas separation membrane module A. The gas separation membrane unit 10 was operated under the conditions in Tables 2 and 3. In Tables 2 and 3, the combustion exhaust gas temperature refers to the temperature of the gas flowing into the gas separation membrane unit 10. The combustion exhaust gas supply pressure 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. CO in the permeate gas and impermeate gas. ２ Concentration and N ２ Everyone and N ２The recovery rates are shown in Tables 2 and 3. As described above, the combustion exhaust gas temperatures shown in each table are the temperatures at the time they are introduced 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.

[0074] In addition to Tables 2 and 3 below, the combustion exhaust gas flow rate in each table refers to the flow rate of combustion exhaust gas introduced into the unit structure 10. In the examples in each table, the combustion exhaust gas is discharged from the combustion exhaust gas source 20 at a temperature of 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.

[0075]

[0076]

[0077] As shown in Tables 2 and 3, even with a single-stage system, the present invention allows CO ２ It can be concentrated to more than 1.7 times its original concentration.

[0078] [Comparative Examples 1-20] For Comparative Examples 1-20, the same system as in Figure 1 was used, and air was separated under the conditions shown in Table 4. O in the permeate gas and non-permeate gas. ２ Concentration and N ２ Concentration, N ２ The recovery rates are shown in Table 4. The air supply 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 it flows into the gas separation membrane unit 11. The membrane temperature of the gas separation membrane unit 11 was the same as the temperature of the air. 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 level of N is recovered compared to when air is separated. ２ N concentration ２ When obtaining enriched gas, high N ２ It can be seen that a recovery rate can be obtained. ２ In terms of concentration, the ratio of product gas volume to supplied gas volume is larger when combustion exhaust gas is used as the raw material. This is because N ２ This means that the required supply of gas per unit of enriched gas is small (i.e., the energy required for pressurization is small), which in turn means that the energy consumed per unit of product gas is small.

[0079]

[0080] [Examples 45-69] The system shown in Figure 3 was used. The first gas separation membrane unit 11 and the second gas separation membrane unit 12 each used the number of gas separation membrane modules shown in Tables 5 and 6. When there were multiple modules, they were combined in parallel to form a unit. The unit structure 10 was operated under the conditions shown in Tables 5 and 6. CO in the first and second permeates and the first and second permeates was detected. ２ Everyone and N ２ Concentration and N ２ The recovery rates and other data are shown in Tables 5 and 6. The supply 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.

[0081]

[0082]

[0083] As can be seen from the comparison between Tables 2 and 3 and Tables 5 and 6, by combining two or more gas separation membrane units, N is increased compared to the case of a single unit. ２ N in enriched gas ２ While keeping the concentration the same, CO ２ CO in enriched gas ２ Concentration and N ２ It can be seen that the recovery rate can be increased. In particular, as can be seen from Examples 46, 63, and 67 in Table 6, the first stage recovers more CO than the second stage. ２ / N ２ By using a gas separation membrane unit with high separation performance, in particular, CO ２ Concentration and N ２ It can be seen that the recovery rate can be increased.

[0084] According to the present invention, CO ２ and N ２ CO from combustion exhaust gases containing ２ Enriched gas and N ２ Enriched gases are produced at low cost, in a space-saving manner, and with high N2 levels. ２ A method for separating based on recovery rate is provided.

Claims

1. CO ２ and N ２ CO from combustion exhaust gases containing ２ Enriched gas and N ２ A gas separation system for producing enriched gas, wherein the gas separation system has a unit structure which is either one gas separation membrane unit or a connected body of two or more gas separation membrane units, the unit structure comprises a gas inlet, a permeable gas outlet, and an impermeable 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 the combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, further comprising the impermeable gas outlet and N ２ N connects to the enriched gas utilization device. ２ A gas separation system equipped with an enriched gas supply line.

2. The aforementioned permeate gas outlet is CO ２ CO2 recovery device connected ２ The gas separation system according to claim 1, further comprising an enriched gas supply line.

3. The gas separation system according to claim 1 or 2, wherein the number of gas separation membrane units in the unit structure is one.

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 discharge port, and a first non-permeated gas discharge port. The second gas separation membrane unit includes a second gas inlet, a second permeated gas discharge port, and a second non-permeated gas discharge port. The first non-permeated gas discharge port 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 discharge port to the suction side of the compression means in the combustion exhaust gas supply line. The enriched gas supply line is connected to the second non-permeated gas discharge port. The gas separation system according to claim 1 or 2. ２ A gas separation system according to claim 1 or 2, wherein an enriched gas supply line is connected to the second non-permeated gas discharge port.

5. The separation membrane module used in the unit structure is CO ２ Transmission 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 the following relationship exists: P'CO ２ > P'O ２ And P'O ２ > P'N ２ 6. Flow rate of permeate gas at the permeate gas outlet (Nm ３ The flow rate (Nm³ / h) of the combustion exhaust gas introduced into the unit structure is ３ The gas separation system according to claim 1 or 2, wherein the value is 65% or less of / h.

7. CO in combustion exhaust gas ２ The gas separation system according to claim 1 or 2, wherein the concentration is 3 mol% or more.

8. CO in the permeate gas at the permeate gas outlet ２ The gas separation system according to claim 1 or 2, wherein the concentration is 30 mol% or more.

9. N in the impermeable gas discharged from the impermeable gas outlet. ２ The gas separation system according to claim 1 or 2, wherein the concentration is 90 mol% or more.

10. The gas separation system according to claim 1 or 2, wherein the gas separation membrane in the unit structure has a polyimide hollow fiber membrane.

11. 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 combustion exhaust gas flow direction in the compression means.

12. CO2 in the separation membrane of the first separation membrane unit ２ and N ２ Gas separation selectivity (P'CO ２ / P'N ２ The gas separation system according to claim 4, wherein the second separation membrane is larger than the separation membrane used in the second separation membrane unit.

13. The gas separation system according to claim 11, wherein a branch line is provided connecting the upstream side of the combustion exhaust gas flow direction to the cooling means in the combustion exhaust gas supply line to the heating device, and the combustion exhaust gas supplied through the branch line is used as the heat source for the heating device.

14. The gas separation system according to claim 1 or 2, wherein the pressurized dew point of the gas discharged from the impermeable gas outlet is -20°C or lower.

15. The gas separation system according to claim 1 or 2, wherein the refrigerant in the cooling means is seawater.

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

17. The gas separation system according to claim 1 or 2, for use on a ship or offshore facility.

18. Using a gas separation system to CO ２ and N ２ CO from combustion exhaust gases containing ２ Enriched gas and N ２ A method for producing enriched gas, wherein the gas separation system has a unit structure which is either one gas separation membrane unit or a connected body of two or more gas separation membrane units, the unit structure comprises a gas inlet, a permeable gas outlet, and an impermeable 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 the combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, the impermeable gas outlet is N ２ N connected to the enriched gas utilization device ２ CO2 enrichment gas supply line installed, ２ Enriched gas and N ２ A method for producing enriched gas.

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