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

Abstract

This invention provides a low-cost and space-saving method for separating CO2-enriched gas and N2-enriched gas from combustion exhaust gas containing CO2 and N2. [Solution] A gas separation system for producing CO2-enriched gas and N2-enriched gas from combustion exhaust gas containing CO2 and N2, comprising a unit structure which is either a single gas separation membrane unit or a connected body of two or more gas separation membrane units, the unit structure comprising a gas inlet, a permeable gas outlet, and a non-permeable gas outlet, A gas separation system comprising: 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 positioned upstream of the compression means in the combustion exhaust gas flow direction and cooling the combustion exhaust gas supplied to the compression means, wherein the non-permeable gas outlet is connected to an N2-enriched gas supply line connected to an N2-enriched gas utilization device.

Description

[Technical Field]

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

[0002] A known method for separating a mixed gas containing two or more different gases into individual gases is membrane separation, which utilizes the difference in the gas permeation rates through a membrane. In this method, by recovering the permeated gas and / or non-permeated gas, it is possible to obtain the target gas, which is a high-purity, high-permeability gas and / or a high-purity, low-permeability gas. For example, Patent Document 1 describes the production and use of N2-enriched gas by separating air in ships and offshore facilities.

[0003] On the other hand, various methods for separating the components of exhaust gas are known. Patent document 2 describes the production of CO2-enriched gas from exhaust gas using a gas separation membrane. Patent documents 3 and 4 describe methods for separating N2 and CO2 from combustion exhaust gas using systems employing adsorbents and cryogenic separation. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-001902 [Patent Document 2] Japanese Patent Publication No. 2023-122497 [Patent Document 3] Japanese Patent Application Publication No. 4-227017 [Patent Document 4] Japanese Patent Publication No. 2023-515919 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, a method for separating CO2-enriched gas and N2-enriched gas from combustion exhaust gas containing CO2 and N2 at low cost, in a space-saving manner, and with a high N2 recovery rate has not been obtained to date. [Means for solving the problem]

[0006] The present invention provides the following configuration. [1] A gas separation system that produces CO2-enriched gas and N2-enriched gas from combustion exhaust gas containing CO2 and N2, The gas separation system has a unit structure which is either a single gas separation membrane unit or a connected body formed by linking two or more gas separation membrane units. The aforementioned unit structure includes a gas inlet, a permeable gas outlet, and an impermeable gas outlet. The system comprises 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 positioned upstream of the compression means in the combustion exhaust gas flow direction and for cooling the combustion exhaust gas supplied to the compression means. The aforementioned non-permeable gas outlet is a gas separation system equipped with an N2-enriched gas supply line connected to an N2-enriched gas utilization device. [2] The gas separation system according to [1], wherein the permeate gas outlet is equipped with a CO2 enriched gas supply line connected to a CO2 recovery device. [3] The gas separation system according to [1] or [2], wherein the unit structure comprises a first 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 permeable gas outlet, and a first non-permeable gas outlet. The second gas separation membrane unit includes a second gas inlet, a second permeable gas outlet, and a second non-permeable gas outlet. The first non-permeable gas outlet is connected to the second gas inlet of the second gas separation membrane unit, A second permeate gas reflux line is provided to connect the second permeate gas discharge port to the suction side of the compression means in the combustion exhaust gas supply line. The gas separation system according to any one of [1] to [2], wherein the N2-enriched gas supply line is connected to the second non-permeate gas discharge port. [5] The separation membrane module used in the unit structure has a permeation rate P’CO2 of CO2, a permeation rate P’N2 of nitrogen, and a permeation rate P’O2 of oxygen that satisfy the following relationship. The gas separation system according to any one of [1] to [4]. P’CO2 > P’O2 and P’O2 > P’N2 [6] The flow rate (Nm 3 / h) of the permeate gas at the permeate gas discharge port 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 CO2 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 CO2 concentration in the permeate gas at the permeate gas discharge port is 30 mol% or more. The gas separation system according to any one of [1] to [7]. [9] The N2 concentration in the non-permeate gas discharged from the non-permeate gas discharge port is 90 mol% or more. The gas separation system according to any one of [1] to [8].

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

[11] On the downstream side in the flow direction of the combustion exhaust gas in the compression means, 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. The gas separation system according to any one of [1] to

[10] .

[12] The gas separation selectivity (P’CO2 / P’N2) of the separation membrane in the first separation membrane unit for CO2 and N2 is greater than that of the separation membrane used in the second separation membrane unit, and the gas separation system according to any one of [4] to

[11] . 〔13〕 A branch line is provided that connects the upstream side in the combustion exhaust gas flow direction with respect to the cooling means in the combustion exhaust gas supply line and the temperature raising device, and the combustion exhaust gas supplied through the branch line is used as the heat source of the temperature raising device. The gas separation system according to any one of [1] to

[12] . 〔14〕 The pressurized dew point of the non-permeating gas discharge port is -20°C or lower, and the gas separation system according to any one of [1] to

[13] . 〔15〕 The refrigerant in the cooling means is seawater, and the gas separation system according to any one of [1] to

[14] . 〔16〕 The N2-enriched gas utilization device is explosion-proof, and the gas separation system according to any one of [1] to

[15] . 〔17〕 It is for ships or offshore facilities, and the gas separation system according to any one of [1] to

[16] . 〔18〕 A method for producing a CO2-enriched gas and an N2-enriched gas from a combustion exhaust gas containing CO2 and N2 using a gas separation system, The gas separation system has a unit structure that is either one gas separation membrane unit or a combination of two or more connected gas separation membrane units, The unit structure includes a gas inlet, a permeating gas discharge port, and a non-permeating gas discharge port, A combustion exhaust gas supply line connected to the gas inlet for supplying combustion exhaust gas to the unit structure, a compression means disposed in the combustion exhaust gas supply line, and a 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. A method for producing CO2-enriched gas and N2-enriched gas, comprising providing an N2-enriched gas supply line that connects the aforementioned non-permeable gas outlet to an N2-enriched gas utilization device. [Effects of the Invention]

[0007] According to the present invention, a method is provided for separating CO2-enriched gas and N2-enriched gas from combustion exhaust gas containing CO2 and N2 at low cost, in a space-saving manner, and with a high N2 recovery rate. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the configuration of a gas separation system in a first embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing the configuration of the gas separation membrane module of the present invention. [Figure 3] Figure 3 is a schematic diagram showing the configuration of a gas separation system in a second embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. [Figure 5] Figure 5 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. [Figure 6] Figure 6 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. [Figure 7] Figure 7 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. [Figure 8] Figure 8 is a schematic diagram showing the configuration of a gas separation system in yet another embodiment of the present invention. [Modes for carrying out the invention]

[0009] The present invention will be described below with reference to the drawings, based on preferred embodiments thereof. Furthermore, the upper and lower limits of numerical values ​​in this specification can be combined in any way without any limitations.

[0010] 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.

[0011] 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 hollow fiber membrane or the like and housed in a casing 31, as shown in Figure 2, can be used. 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.

[0012] 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 lengths, 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.

[0013] When the gas separation membrane 30 is housed within 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 naturally, the present invention can be applied to separation membrane modules with other configurations, for example, to shell-feed type modules.

[0014] In the gas separation membrane unit and gas separation membrane module used in the unit structure 10, it is preferable that the CO2 permeation rate P'CO2, the N2 permeation rate P'N2, and the oxygen permeation rate P'O2 are in the relationship shown in (1) below, and more preferably in the relationship shown in (2) below. In the following embodiments, the gas separation membrane unit and gas separation membrane module have the relationship shown in (2). P'CO2>P'N2(1) P'CO2 > P'O2 and P'O2 > P'N2(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 ×10⁻⁶. -5 cm 3 (STP) / cm 2 It is ·sec·cmHg.

[0015] In the following, "upstream" and "downstream" refer to the direction of combustion exhaust gas flow. 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 impermeable gas outlet 11b, and the first permeable gas outlet 11c of the first gas separation membrane unit 11 constitute the gas inlet 10a, the impermeable gas outlet 10b, and the permeable gas outlet 10c, respectively. 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. Furthermore, it includes an N2 enriched gas supply line 15 connecting the impermeable gas outlet 10b and the N2 enriched gas utilization device 50.

[0016] Examples of N2 enriched gas utilization equipment 50 include devices that seal and fill N2 as an inert gas into storage containers (tanks, cylinders, etc.) for liquids and powders such as petroleum products, fuels, ultrapure water and pure water, chemicals, pharmaceuticals, and food products (devices that fill cylinders containing fuel with N2 gas, devices that fill tanks containing fuel with N2 gas, devices that fill cylinders with N2 gas, etc.); devices that produce liquefied N2 in containers; and devices that purge N2 in processes requiring inert gas in experimental and industrial facilities such as photocuring and chemical synthesis. There may be one or more N2 enriched gas utilization devices 50 connected to the non-permeable gas outlet 10b.

[0017] The permeate gas outlet 10c is connected to the CO2 recovery device 51 by the CO2 enriched gas supply line 18. Examples of the CO2 recovery device 51 include CO2 liquefaction equipment, CO2 solidification equipment, CO2 absorption equipment, and CO2 adsorption equipment. The CO2 recovered by the CO2 recovery device 51 may be used for artificial photosynthesis. Alternatively, it may be converted into methane by reacting with hydrogen and used as part of a fuel. Here, hydrogen produced by the electrolysis of water may be used. In addition, the CO2 recovery device 51 may further concentrate the CO2 enriched gas recovered through the CO2 enriched gas supply line 18 as needed, and then liquefy it using a liquefaction device or the like. Known methods can be used to concentrate the CO2 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 can be used. There may be one or more CO2 recovery devices 51 connected to the permeate gas outlet 10c.

[0018] 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 System 1 is used on a ship or in offshore facilities.

[0019] 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.

[0020] 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 contains N2 and CO2. Examples of the combustion exhaust gas source 20 include diesel engines, gasoline engines, gas turbines, boilers such as oil-fired boilers, and incinerators for burning waste such as garbage. Among these, combustion exhaust gas sources on ships or offshore facilities are preferred because they can take advantage of the space-saving benefits of gas separation membranes. Examples of combustion exhaust gas sources on ships or offshore facilities include ship engines, boilers on ships, boilers for offshore power generation, and offshore industrial boilers. The combustion exhaust gas mainly consists of N2 and CO2. Other components may include water, nitrogen oxides (NOx), sulfur oxides (SOx), volatile organic compounds (VOCs), oxygen, carbon monoxide, PM (particulate matter), etc.

[0021] In System 1, the combustion exhaust gas containing N2 and CO2 to be separated 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 increases. In the unit structure 10 (gas separation membrane unit 11), due to the difference in permeation rates through the gas separation membrane, the gas is separated into permeate gas, which is the gas that has permeated the gas separation membrane, and impermeable gas, which is the gas that has not permeated the gas separation membrane. The impermeable gas is concentrated with N2 compared to the combustion exhaust gas. The impermeable gas is discharged from the impermeable gas outlet 10b and supplied to the N2 enriched gas utilization device 50 through the N2 enriched gas supply line 15. The permeate gas discharged from the permeate gas outlet 10c of the unit structure 10 is concentrated with CO2 compared to the combustion exhaust gas. The permeate gas is supplied to the CO2 recovery device 51 through the CO2 enriched gas supply line 18. By introducing the CO2 enriched gas, whose CO2 concentration has been increased by membrane separation, into the CO2 recovery device 51, the CO2 recovery efficiency can be improved.

[0022] 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 direction of combustion exhaust gas flow, and connects the combustion exhaust gas supply line 26 and the CO2 recovery device 51 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 supplied to the CO2 recovery device 51 without undergoing membrane separation. When separating N2 from combustion exhaust gas, the amount of N2 gas required as an inert gas is usually less than the amount of combustion exhaust gas discharged from the combustion exhaust gas source. On the other hand, in order to increase the N2 concentration in the impermeable gas, 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 to adjust 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 system 1. It is preferable in terms of CO2 recovery efficiency for the branch line 29 and the CO2 enrichment gas supply line 18 to supply CO2-containing gas to the same CO2 recovery device 51. In Figure 1, combustion exhaust gas that is not introduced into the unit structure 10 is directly introduced into the CO2 recovery device 51 via the branch line 29. However, another CO2 concentration device may be installed in the branch line 29, and the combustion exhaust gas, in which CO2 has been concentrated, may be introduced into the CO2 recovery device 51. In this case, the CO2 enriched gas supply line 18 may be connected upstream of the other CO2 concentration device, and the CO2 enriched gas flowing through the CO2 enriched gas supply line 18 may be further concentrated in the other CO2 concentration device.

[0023] In Figure 1, the cooling means 23 is located downstream of the branching point of the branching line 29 in the combustion exhaust gas supply line 26, but it may also be located upstream of the branching point. In the CO2 recovery device 51, the efficiency of CO2 liquefaction, CO2 solidification, CO2 absorption, and CO2 adsorption is often higher when the temperature of the introduced CO2-enriched gas is lower. For this reason, it is preferable to install the cooling means 23 upstream of the branching point of the branching line 29 in the direction of combustion exhaust gas flow to cool the entire combustion exhaust gas, in order to increase the CO2 processing capacity of system 1.

[0024] Regarding the N2-enriched gas discharged from the unit structure 10, it is preferable that moisture is removed so that the N2-enriched gas can be used in a wide range of applications. The moisture removal level should preferably be Class 3 or higher as defined in ISO 8573-1, meaning that the dew point under pressure of the gas discharged from the impermeable gas outlet 10b of the unit structure 10 should be -20°C or lower, and more preferably Class 2 or higher, meaning that the dew point should be -40°C or lower. 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.

[0025] 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 the 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, 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 using 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.

[0026] 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. Also, 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.

[0027] 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 addition, system 2 is provided with a second permeate gas return line 17 that connects the second permeate gas outlet 12c to the suction side of the compression means 21 in the combustion exhaust gas supply line 26. Furthermore, in system 2, an N2 enriched gas supply line 15 is connected to the second impermeable gas outlet 12b.

[0028] The compression means 21 pressurizes the second permeate gas discharged from the second gas separation membrane unit 12 when it is returned to the first gas separation membrane unit 11 through the second permeate gas reflux line 17.

[0029] 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 permeate gas and a first impermeate gas. The first impermeate gas discharged from the first impermeate gas outlet 11b is concentrated with N2 compared to the combustion exhaust gas and is supplied to the second gas separation membrane unit 12 through the first impermeate gas discharge line 14. On the other hand, the first permeate gas discharged from the first permeate gas outlet 11c (10c) is supplied to the CO2 recovery device 51 through the CO2 enrichment gas supply line 18.

[0030] 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 further enriched with N2 and is supplied from the second non-permeable gas outlet 12b to the N2-enriched gas utilization device 50 through the N2-enriched gas supply line 15. 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 return line 17, mixed with the combustion exhaust gas, and then pressurized by the compression means 21.

[0031] 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 concentration in the combustion exhaust gas supplied to the first-stage gas separation membrane unit can be increased compared to system 1, which consists of a single-stage gas separation membrane unit. This increases the CO2 concentration in the permeate gas supplied to the CO2 recovery device and also increases the N2 recovery rate.

[0032] In a connected body comprising two or more gas separation membrane units, it is preferable that the gas separation selectivity (P'CO2 / P'N2) of the separation membrane in the first separation membrane unit 11 is greater than that of the separation membrane used in the second gas separation membrane unit 12, as this allows for an increase in the CO2 concentration and N2 recovery rate in the permeate gas without decreasing the N2 concentration in the non-permeate gas.

[0033] In the example shown in Figure 3, the second permeate gas recirculation line 17 is connected downstream 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 upstream of the cooling means 23 to recirculate the second permeate gas to the upstream side of the cooling means 23.

[0034] Unlike system 1 in Figure 1, as shown in Figure 4, the branch line 29 may be omitted, and the entire 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 Figures 5 and 6, a compression means 22 (booster) may be provided in the N2-enriched gas supply line 15 to increase the pressure of the impermeable gas discharged from the impermeable gas outlet 10b to the required pressure in the N2-enriched gas utilization device 50. A compressor can be used as the compression means 22. Furthermore, if multiple N2 enriched gas utilization devices 50 are connected to the impermeable gas outlet 10b, and the pressure of the N2 enriched gas required by each device differs, the entire amount of impermeable gas in the unit structure 10 may be compressed, and then a portion of it may be depressurized and sent to an N2 enriched gas utilization device that uses low-pressure N2 enriched gas. Alternatively, a portion of the impermeable gas in the unit structure 10 may be pressurized and sent to the N2 enriched gas utilization device 50 for use, while the remainder may be used by the N2 enriched gas utilization device 50 without pressurizing.

[0036] Next, we will explain System 3 in Figure 7. The following explanation will mainly describe the differences from the configuration in Figure 3. In the configuration shown in Figure 7, the unit structure 10 includes 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 shown in 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.

[0037] The third impermeable gas outlet 13b is connected to the combustion exhaust gas supply line 26 by a 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 permeate gas outlet 13c of the third gas separation membrane unit 13 corresponds to the permeate gas outlet 10c of the unit structure 10, and the CO2 enriched gas supply line 18 is connected to it.

[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 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 impermeate gas. The third permeate gas is more concentrated and enriched with CO2 than the first permeate gas introduced into the third gas separation membrane unit 13, and is supplied to the CO2 recovery device 51 from the permeate gas outlet 13c of the unit 13 through the CO2 enriched gas supply line 18. On the other hand, the third impermeate gas is discharged from the third impermeate 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 impermeate gas recirculation line 16 connected to the outlet 13b. The third impermeable gas, returned through the third impermeable gas reflux line 16, is mixed with the combustion exhaust gas and then pressurized by the compression means 21.

[0040] According to this system 3, CO2 is concentrated by the third gas separation membrane unit 13, and the third non-permeable gas is recirculated to the first gas separation membrane unit 11. As a result, the N2 concentration in the non-permeable gas discharged from the non-permeable gas outlet 10b, the CO2 concentration in the permeable gas discharged from the permeable gas outlet 10c, and the N2 recovery rate can be further increased.

[0041] In this system 3, if the gas separation selectivity (P'CO2 / P'N2) of the separation membrane in the first gas separation membrane unit 11 is greater than that of the separation membrane used in the second gas separation membrane unit 12, it is preferable that the gas separation selectivity (P'CO2 / P'N2) of the separation membrane in the third gas separation membrane unit 13 is equal to or greater than that of the separation membrane used in the second gas separation membrane unit 12, in order to further increase the CO2 concentration and N2 recovery rate in the permeate gas discharged from the permeate gas outlet 10c, and it is even more preferable that it is greater than that of the separation membrane used in the second gas separation membrane unit 12.

[0042] 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.

[0043] Further modifications may be made to each of the aforementioned gas separation systems. For example, a pretreatment facility may be provided downstream of the compression means 21 in the combustion exhaust gas supply line 26. The aforementioned pretreatment equipment is installed upstream of the unit structure 10 in the combustion exhaust gas supply line 26. This pretreatment equipment is installed to remove impurities from the N2-enriched gas and CO2-enriched gas separated from the combustion exhaust gas to make them 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 aforementioned pretreatment equipment include a second cooling device, a dust removal device, a drain discharge device, a heating device, a desulfurization device, and a denitrification device, and these can be used individually or in combination of two or more types.

[0044] A heat exchanger can be used as a second cooling means or heating device.

[0045] 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.

[0046] 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.

[0047] A desulfurization device only needs to have the function of removing sulfur oxides (SOx) contained in the combustion exhaust gas. For example, a scrubber may suffice. Denitrification systems remove nitrogen oxides (NOx) contained in combustion exhaust gas. An example of such a system is a selective catalytic reduction (SCR) system.

[0048] 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 of FIG. 8, moisture and high-boiling point 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 a drain discharge device 28. The gas from which impurities have been removed by the drain discharge device 28 is heated by a temperature raising device 46 to prevent re-condensation and reduction of gas separation performance, and then supplied to the unit structure 10. Here, the high-boiling point 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 soot 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 the 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 the particles in the gas supplied to the unit structure 10, particles with a size of 0.1 - 0.5 μm ≤ 400,000 particles / m 3 , particles with a size of 0.5 - 1 μm ≤ 6,000 particles / m 3 , and particles with a size of 1 - 5 μm ≤ 100 particles / m 3 are preferable, and particles with a size of 0.1 - 0.5 μm ≤ 20,000 particles / m 3 , particles with a size of 0.5 - 1 μm ≤ 400 particles / m 3 , and particles with a size of 1 - 5 μm ≤ 10 particles / m 3 are more preferable.

[0050] As shown in FIG. 8, 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 in the combustion exhaust gas supply line 26. Utilizing 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] The N2-enriched gas utilization device 51 is preferable because it uses N2-enriched gas for explosion protection, as this allows for easier utilization of the space-saving gas separation advantages of gas separation using a gas separation membrane. 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, from the viewpoint of taking advantage of the high N2 and CO2 recovery rates, as well as the advantages of space saving and energy saving, explosion-proof applications such as fuel tanks in ships or offshore facilities are preferred.

[0052] 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. Using it for the treatment of combustion exhaust gases in ships or offshore facilities is preferable because it enhances the advantages of the present invention, which is space-saving, energy-saving, and has high N2 and CO2 recovery rates. 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.

[0053] In the combustion exhaust gas, a CO2 content of 3 mol% or more is preferable in terms of increasing the CO2 concentration in the permeate gas. From this viewpoint, 5 mol% or more is preferable, 10 mol% or more is more preferable, and 15 mol% or more is even preferable. The CO2 concentration in the combustion exhaust gas used in the present invention is generally 30 mol% or less, and from the viewpoint of N2 recovery rate, 20 mol% or less is preferable. When describing the composition of the combustion exhaust gas in this specification, unless otherwise specified, it refers to the composition of the combustion exhaust gas when discharged from the combustion exhaust gas source 20. For example, in system 2, it refers to the composition of the combustion exhaust gas before mixing with the second permeate gas.

[0054] The combustion exhaust gas used in this invention is a gas containing at least CO2 and N2. In the present invention, the combustion exhaust gas preferably contains 40 mol% or more of N2, as this results in a high N2 concentration in the resulting non-permeable gas, making it easy to reuse; more preferably contains 50 mol% or more. The N2 concentration of the combustion exhaust gas is particularly preferably 95 mol% or less, as this increases the CO2 concentration and improves the CO2 concentration in the permeable gas; more preferably 90 mol% or less.

[0055] Flow rate of permeate gas at the permeate gas outlet 10c Fp(Nm 3 The flow rate of combustion exhaust gas Fs(Nm³ / h) into the system is Fs(Nm³ / h). 3 It is preferable that the ratio of the flow rate of the permeate gas to the flow rate of the permeate gas at the permeate gas outlet 10c be 65% or less, more preferably 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 of the permeate gas to the flow rate of the combustion exhaust gas Fs, but it is usually 5% or more, and particularly preferably 10% or more. Here, the flow rate of the combustion exhaust gas Fs 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 recirculating gas flowing from the gas outlet of the unit structure to the gas inlet side. For example, in system 2, the flow rate of the combustion exhaust gas Fs 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.

[0056] Flow rate of non-permeable gas at the non-permeable gas outlet 10b Fn(Nm 3 The flow rate of combustion exhaust gas Fs(Nm³ / h) supplied to the unit structure 10 is Fs(Nm³ / h). 3 A ratio of 35% or more to the flow rate of combustion exhaust gas ( / h) is preferable in terms of increasing the CO2 concentration and N2 recovery rate of the permeate gas at the permeate gas outlet 10c, preferably 40% or more, and more preferably 45% or more. There is no upper limit to the ratio of the flow rate of non-permeate gas Fn to the flow rate of combustion exhaust gas Fs, but it is usually 95% or less, and particularly 90% or less.

[0057] It is preferable that the CO2 concentration in the permeate gas at the permeate gas outlet 10c is 30 mol% or higher, as this results in a higher CO2 concentration and a smaller overall gas volume when the CO2 is further concentrated in the CO2 recovery device 51, leading to miniaturization of the CO2 recovery device 51 and lower running costs. From this viewpoint, it is more preferable that the CO2 concentration in the permeate gas is 40 mol% or higher, even more preferable that it is 50 mol% or higher, particularly preferable that it is 60 mol% or higher, and especially preferable that it is 80 mol% or higher.

[0058] In terms of utilization efficiency in the N2 enrichment gas utilization device 50, it is preferable that the N2 concentration in the impermeable gas discharged from the impermeable gas outlet 10b is 90 mol% or more, preferably 95 mol% or more, and more preferably 97 mol% or more.

[0059] Furthermore, in the present invention, the N2 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. The N2 recovery rate can be calculated using the following formula. The unit of concentration is mol%. N2 recovery rate = (Impermeable gas flow rate Fn × N2 concentration in impermeable gas discharged from impermeable gas outlet 10b) / (Combustion flue gas flow rate Fs × N2 concentration in combustion flue gas)

[0060] Furthermore, in the present invention, the CO2 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. The CO2 recovery rate can be calculated using the following formula. The unit of concentration is mol%. CO2 recovery rate = (Permeate gas flow rate Fp × CO2 concentration in permeate gas discharged from permeate gas outlet 10c) / (Combustion exhaust gas flow rate Fs × CO2 concentration in combustion exhaust gas)

[0061] Furthermore, it is preferable that the ratio of the CO2 concentration (mol%) at the permeate gas outlet 10c to the CO2 concentration (mol%) in the combustion exhaust gas is 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] The gas separation selectivity (P'CO2 / P'N2) of the separation membranes in gas separation membrane units 10 to 13 for CO2 and N2 is preferably 4 or higher, more preferably 7 or higher, and even more preferably 15 or higher. The gas separation selectivity (P'CO2 / P'N2) of the separation membranes in gas separation membrane units 10 to 13 for CO2 and N2 is usually 100 or lower, and more preferably 50 or lower. The gas separation selectivity referred to here may 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.

[0068] When the gas separation selectivity of the separation membrane in the first separation membrane unit for CO2 and N2 is greater than that of the separation membrane used in the second separation membrane unit, the ratio of the separation selectivity P1'CO2 / P1'N2 of the gas separation membrane in the first separation membrane unit to the separation selectivity P2'CO2 / P2'N2 of the gas separation membrane in the second separation membrane unit 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. Furthermore, the ratio of the separation selectivity P1'CO2 / P1'N2 of the gas separation membrane in the first gas separation membrane unit 11 to the separation selectivity P2'CO2 / P2'N2 of the gas separation membrane in the second separation membrane unit is usually 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.

[0069] If the gas separation selectivity of the separation membrane in the third separation membrane unit for CO2 and N2 is greater than that of the separation membrane used in the second separation membrane unit, the preferred range for the ratio of the separation selectivity P3'CO2 / P3'N2 of the gas separation membrane in the third separation membrane unit to the separation selectivity P2'CO2 / P2'N2 of the gas separation membrane in the second separation membrane unit is the same as the preferred range for the ratio of the separation selectivity P1'CO2 / P1'N2 of the gas separation membrane in the first separation membrane unit to the separation selectivity P2'CO2 / P2'N2 of the gas separation membrane in the second separation membrane unit.

[0070] 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. [Examples]

[0071] 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.

[0072] <Gas separation membrane module> 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.

[0073] [Table 1]

[0074] [Examples 1-44] The system shown in Figure 1 was used. In the system shown in Figure 1, a model gas mixture of CO2 and N2 was used as the combustion exhaust gas. 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 shown in Tables 2 and 3. Furthermore, 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 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. The CO2 concentration, N2 concentration, and N2 recovery rate in the permeate gas and non-permeate gas 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 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] 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 was 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.

[0076] [Table 2]

[0077] [Table 3]

[0078] As shown in Tables 2 and 3, even with a single-stage system, the present invention makes it possible to concentrate CO2 by 1.7 times or more.

[0079] [Comparative Examples 1-20] For Comparative Examples 1 to 20, the same system as in Figure 1 was used, and air was separated under the conditions shown in Table 4. Table 4 shows the O2 and N2 concentrations and N2 recovery rates in the permeate and non-permeate gases. 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 of inflow 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 combustion exhaust gas with the system of the present invention, a higher N2 recovery rate can be obtained when obtaining N2-enriched gas of the same N2 concentration compared to when separating air. At all N2 concentrations, the ratio of product gas amount to supply gas amount is larger when combustion exhaust gas is used as the raw material. This means that the required supply of gas per N2-enriched gas is small (i.e., the energy required for pressurization is small), and therefore the energy consumption per unit of product gas is small.

[0080] [Table 4]

[0081] [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. The CO2 and N2 concentrations in the first and second permeates, as well as the N2 recovery rate, are shown in Tables 5 and 6. The combustion exhaust gas pressure shown in Tables 5 and 6 refers to the pressure of the gas flowing into the gas separation membrane unit 11. The combustion exhaust gas temperature 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 and 3 and Tables 5 and 6, by combining two or more gas separation membrane units, it is possible to increase the CO2 concentration in the CO2-enriched gas and the N2 recovery rate compared to the case of a single unit, while maintaining the same N2 concentration in the same N2-enriched gas. In particular, as can be seen from Examples 46, 63, and 67 in Table 6, by using a gas separation membrane unit with higher CO2 / N2 separation performance in the first stage than in the second stage, it is possible to increase the CO2 concentration and N2 recovery rate in particular. [Explanation of Symbols]

[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 impermeable gas outlet 11c First permeable gas outlet 12. Second Gas Separation Membrane Unit 12a Second gas inlet 12b Second impermeable gas outlet 12c Second permeable gas outlet 13. Third Gas Separation Membrane Unit 13a Third gas inlet 13b Third impermeable gas outlet 13c Third permeable gas outlet 15 N2 enriched gas supply line 26 Combustion exhaust gas supply line 21 Compression means 23 Cooling means 50 N2 enriched gas utilization device

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, The gas separation system has a unit structure which is either a single gas separation membrane unit or a connected body formed by linking two or more gas separation membrane units. The aforementioned unit structure includes a gas inlet, a permeable gas outlet, and an impermeable gas outlet. The system comprises 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 positioned upstream of the compression means in the combustion exhaust gas flow direction and for cooling the combustion exhaust gas supplied to the compression means. Furthermore, the non-permeable 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 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 includes a first gas inlet, a first permeable gas outlet, and a first non-permeable gas outlet. The second gas separation membrane unit includes a second gas inlet, a second permeable gas outlet, and a second non-permeable gas outlet. The first non-permeable gas outlet is connected to the second gas inlet of the second gas separation membrane unit. A second permeate gas return line is provided, which connects the second permeate gas outlet to the suction side of the compression means in the combustion exhaust gas supply line. Connecting the enriched gas supply line to the second non-permeable gas discharge port, the gas separation system according to claim 1 or 2. ２ The gas separation system according to claim 1 or 2, wherein an enriched gas supply line is connected to the second non-permeable gas discharge port.

5. The separation membrane module used in the aforementioned 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 aforementioned permeate gas outlet (Nm ３ The flow rate (Nm³ / h) of the fuel 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 aforementioned 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 aforementioned 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. CO 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 non-permeable 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. A gas separation system according to claim 1 or 2, for use on a ship or offshore facility.

18. CO using a gas separation system ２ and N ２ CO from combustion exhaust gases containing ２ Enriched gas and N ２ A method for producing enriched gas, The gas separation system has a unit structure which is either a single gas separation membrane unit or a connected body formed by linking two or more gas separation membrane units. The aforementioned unit structure includes a gas inlet, a permeable gas outlet, and an impermeable gas outlet. The system comprises 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 positioned upstream of the compression means in the combustion exhaust gas flow direction and for cooling the combustion exhaust gas supplied to the compression means. The non-permeable 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.

Images