Gas separation device

Abstract

To perform air separation in which processing capability and separation efficiency are improved while consumption power is suppressed.SOLUTION: A gas separation device 10 comprises a first compressor 21, a first separation membrane unit 11, and a second separation membrane unit 12. The oxygen permeability of a gas separation membrane in the first separation membrane unit 11 is higher than that of a gas separation membrane in the second separation membrane unit 12. The permeation ratio of oxygen to nitrogen of the gas separation membrane in the second separation membrane unit 12 is higher than that of the gas separation membrane in the first separation membrane unit 11. It is preferable that a second compressor 22 that increases the pressure of a first non-permeating gas to form a second supply gas be provided between the first separation membrane unit 11 and the second separation membrane unit 12.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas separation apparatus and a gas separation method used for separating oxygen and nitrogen from air.

Background Art

[0002] As a method for separating a raw material gas containing two or more different types of gases into each gas, a membrane separation method using the difference in the permeation rate of gases with respect to a membrane is known. In this method, a raw material gas containing two or more types of gases is supplied to a gas separation membrane, and is separated into a permeated gas in which a highly permeable gas is enriched and a non-permeated gas in which a low-permeable gas is enriched. Generally, a gas separation membrane is housed in a container provided with a gas inlet, a permeated gas discharge port, and a non-permeated gas discharge port, and is used in the form of a separation membrane module. In the container, the gas separation membrane is mounted so that the spaces on the gas supply side and the gas permeation side are isolated. In a gas separation apparatus, in order to obtain a required membrane area, generally, a plurality of separation membrane modules are used in combination in parallel.

[0003] For the purpose of recovering a target gas with high purity and high recovery rate, various gas separation apparatuses having a gas separation membrane unit in multiple stages are known. For example, in Patent Document 1, as a method for separating nitrogen from air, two gas separation membrane units are connected in series, and a nitrogen-enriched gas, which is a non-permeated gas of the first gas separation membrane unit, is supplied to the second gas separation membrane unit to obtain a non-permeated gas in which nitrogen is further enriched. As the gas separation membrane used in the first gas separation membrane unit and the gas separation membrane used in the second gas separation membrane unit, the same type is used.

[0004] Patent Document 2 describes a gas separation method in which two gas separation membrane units are connected in series, a part of the raw material gas is supplied to the gas separation membrane unit, a low-permeable gas is discharged out of the system, and the permeated gas is mixed with the raw material gas and recovered as a product gas. In Patent Document 3, in a nitrogen gas separation method in which a plurality of gas separation devices for separating nitrogen gas from compressed air are arranged in series and compressed air is sequentially supplied to the plurality of gas separation devices, deterioration due to high humidity of the compressed air is caused to occur in the first gas separation device, so that stable nitrogen gas can be obtained in other gas separation devices. That is, in this method, the first gas separation device is used instead of a moisture filter. Patent Document 4 describes a method for separating nitrogen from air, which uses two or more gas separation membrane units and recycles the permeated gas after the second stage to the supply gas of the gas separation membrane unit immediately preceding it.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] In conventional gas separation methods including the methods described in the above-mentioned documents, when a membrane with a high permeation rate is used, the gas separation selectivity is low, so the gas processing capacity of the entire system increases, and thus the power for gas compression increases. On the other hand, when a membrane with high gas separation selectivity is used, the power for gas compression can be small, but since the permeation rate is low, it is necessary to increase the membrane area. Thus, improving the processing capacity and separation performance while suppressing the power consumption is in an antinomic relationship. Therefore, an object of the present invention is to provide a gas separation device and a gas separation method capable of eliminating the drawbacks of the conventional technologies described above.

Means for Solving the Problems

[0007] The present invention relates to a compressor capable of sucking in raw material air and compressing the raw material air to a predetermined pressure, a first separation membrane unit that takes in the raw material air compressed by the compressor as a first supply gas and separates it into a first permeate gas in which oxygen is concentrated and a first non-permeate gas in which nitrogen is concentrated, a second separation membrane unit that takes in the entire amount of the first non-permeate gas as a second supply gas and separates it into a second permeate gas in which oxygen is concentrated and a second non-permeate gas in which nitrogen is concentrated, and is configured as the oxygen permeability of the gas separation membrane in the first separation membrane unit is higher than the oxygen permeability of the gas separation membrane in the second separation membrane unit, and the oxygen-to-nitrogen permeation ratio of the gas separation membrane in the second separation membrane unit is higher than the oxygen-to-nitrogen permeation ratio of the gas separation membrane in the first separation membrane unit, A gas separation device is provided.

[0008] The present invention takes in compressed raw material air as a first supply gas into a first separation membrane unit and separates it into a first permeate gas in which oxygen is concentrated and a first non-permeate gas in which nitrogen is concentrated, and takes in the entire amount of the first non-permeate gas as a second supply gas into a second separation membrane unit and separates it into a second permeate gas in which oxygen is concentrated and a second non-permeate gas in which nitrogen is concentrated. A gas separation method is provided, wherein, as the first separation membrane unit, one in which the oxygen permeability of the gas separation membrane in the first separation membrane unit is higher than the oxygen permeability of the gas separation membrane in the second separation membrane unit is used, and as the second separation membrane unit, one in which the oxygen-to-nitrogen permeation ratio of the gas separation membrane in the second separation membrane unit is higher than the oxygen-to-nitrogen permeation ratio of the gas separation membrane in the first separation membrane unit is used.

Effects of the Invention

[0009] According to the present invention, it is possible to perform air separation with improved processing capacity and separation efficiency while suppressing power consumption.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described with reference to the drawings based on its preferred embodiments. The gas separation device 10 of the embodiment shown in FIG. 1 includes a first separation membrane unit 11 and a second separation membrane unit 12, which are two gas separation membrane units.

[0012] As each separation membrane unit 11, 12, for example, as shown in FIG. 2, a module can be used in which a gas separation membrane 30 made of a hollow fiber membrane or the like and having gas selective permeability is housed in a casing 31. The casing 31 in the module has two opposing surfaces open to form an opening 32. It should be noted that this opening 32 is for inserting the gas separation membrane 30 into the casing 31 and is not the opening of the gas separation membrane 30. The gas separation membrane 30 is housed in the casing 31 through this opening 32. When the gas separation membrane 30 is composed of a hollow fiber membrane bundle, the gas separation membrane 30 is housed in the casing 31 such that each end of the hollow fiber membrane opens near each opening 32 of the casing 31 in its housed state.

[0013] When the gas separation membrane 30 is accommodated in the casing 31, at the positions of both ends in the Y direction, which is the direction in which the hollow fiber membrane extends, the gas separation membrane 30 is fixed to the inner wall of the casing 31 by the tube sheets 33 and 34. Each opening 32 of the casing 31 is closed by the lid bodies 35 and 36. The lid body 35 is provided with a gas inlet 37. On the other hand, the lid body 36 is provided with a non-permeating gas discharge port 38. The raw material gas to be separated is introduced into the module from the gas inlet 37 of the lid body 35. Among the introduced gases, the gas that has permeated through the gas separation membrane 30 is discharged outside the unit from the permeating gas discharge port 39 provided in the casing 31. On the other hand, the non-permeating gas that has not permeated through the gas separation membrane 30 is discharged outside the module from the non-permeating gas discharge port 38 of the lid body 36. Further, in some cases, a purge gas supply port (not shown) may be provided in the casing 31.

[0014] In addition, as each separation membrane unit 11, 12, in addition to those shown in FIG. 2, those having a cross-array, a woven fabric-like, a spiral-like, etc. of the arrangement form of the hollow fiber membrane bundle can be used. Further, the form of the hollow fiber membrane bundle may be a cylindrical form, a flat plate form, a prismatic form, etc. These forms of hollow fiber membrane bundles may be stored in the casing as they are, or bent into a U shape, or wound in a spiral shape.

[0015] Returning to FIG. 1, as shown in the figure, the first separation membrane unit 11 and the second separation membrane unit 12 are connected in series. Specifically, the first separation membrane unit 11 and the second separation membrane unit 12 are connected by connecting the non-permeating gas discharge port 11b of the first separation membrane unit 11 and the gas inlet 12a of the second separation membrane unit 12 by a non-permeating gas discharge line 14.

[0016] A raw material gas supply line 16 for supplying air, which is the raw material gas, to the first separation membrane unit 11 is connected to the gas inlet 11a of the first separation membrane unit 11. A first compressor 21 is interposed in the middle of the raw material gas supply line 16. The first compressor 21 is installed for the purpose of pressurizing the raw material gas.

[0017] In the second separation membrane unit 12, the non-permeating gas discharged from the first separation membrane unit 11 is supplied through the gas inlet 12a. This non-permeating gas is separated by the second separation membrane unit 12 so that the permeating gas is discharged from the permeating gas discharge port 12c. On the other hand, the non-permeating gas is discharged from the non-permeating gas discharge port 12b.

[0018] The operation of the gas separation apparatus 10 of the present embodiment having the above configuration will be described. The raw material gas to be separated (hereinafter also referred to as "first supply gas"), that is, air, is supplied to the first separation membrane unit 11 through the raw material gas supply line 16. Prior to the supply, the first supply gas is pressurized by the first compressor 21, and its pressure increases. Therefore, the first separation membrane unit 11 takes in compressed air as the first supply gas. As the first compressor 21, the same type as those conventionally used in the relevant technical field can be used. The type of the first compressor 21 is not particularly limited as long as it can suck in the raw material gas and compress it to a predetermined pressure.

[0019] From the viewpoint of improving the processing capacity in the first separation membrane unit 11 and the second separation membrane unit 12, it is preferable to set the pressure of the first supply gas supplied to the first separation membrane unit 11 to 0.1 MPaG or more and 3.0 MPaG or less. From the viewpoint of making this advantage more prominent, it is more preferable to set the pressure of the first supply gas supplied to the first separation membrane unit 11 to 0.3 MPaG or more and 2.5 MPaG or less.

[0020] The first supply gas contains nitrogen and oxygen, which are two different types of gases to be separated. The gas to be recovered by the separation apparatus and separation method of the present invention is nitrogen-enriched gas. The nitrogen-enriched gas is used, for example, in combination with a laser cutting machine or a dryer, used for injection into an oil well, used in combination during soldering or resin molding, used for filling nitrogen in a tire, or used for explosion prevention purposes.

[0021] When the first supply gas pressurized by the first compressor 21 is supplied to the first separation membrane unit 11, due to the difference in permeation rates with respect to the gas separation membrane, it is separated into a permeated gas that has permeated through the gas separation membrane and a non-permeated gas that has not permeated through the gas separation membrane. The gas separation membrane used in the first separation membrane unit 11 of the present embodiment has an oxygen permeation rate P' O2 that is higher than the nitrogen permeation rate P' N2 . Therefore, oxygen is the permeated gas and nitrogen is the non-permeated gas. Thus, the first non-permeated gas discharged from the first separation membrane unit 11 is enriched in nitrogen compared to the first supply gas.

[0022] The first non-permeated gas is discharged from the non-permeated gas discharge port 11b of the first separation membrane unit 11 and supplied to the second separation membrane unit 12 through the non-permeated gas discharge line 14. Therefore, in the following description, the first non-permeated gas is also referred to as the "second supply gas". On the other hand, the first permeated gas that has permeated through the gas separation membrane of the first separation membrane unit 11 is enriched in oxygen compared to the raw material gas. The first permeated gas is discharged from the permeated gas discharge port 11c of the first separation membrane unit 11 and discharged through the permeated gas discharge line 15.

[0023] The first non-permeated gas discharged from the non-permeated gas discharge port 11b of the first separation membrane unit 11, that is, the second supply gas, may take in all of its amount into the second separation membrane unit 12, but a part of it can also be extracted for other uses.

[0024] The second supply gas introduced into the second separation membrane unit 12 is separated by the same unit 12 into a second permeated gas and a second non-permeated gas. The gas separation membrane used in the second separation membrane unit 12 has an oxygen permeation rate P' that is higher than the nitrogen permeation rate P' O2 than that of the gas separation membrane used in the first separation membrane unit 11, and the nitrogen permeation rate P' N2Since it is higher than [the relevant value], the second non-permeating gas will have nitrogen further concentrated and enriched compared to the first non-permeating gas introduced into the second separation membrane unit 12. The second non-permeating gas is taken out from the non-permeating gas discharge port 12b of the second separation membrane unit 12. On the other hand, the second permeating gas is discharged from the permeating gas discharge port 12c of the second separation membrane unit 12. The second permeating gas has oxygen further concentrated and enriched compared to the first non-permeating gas introduced into the second separation membrane unit 12. Part or all of the second permeating gas may be supplied to the raw material gas supply line 16.

[0025] In this embodiment, the gas separation membrane in the first separation membrane unit 11 and the gas separation membrane in the second separation membrane unit 12 have (i) a difference in oxygen permeability and (ii) a difference in the permeation ratio of oxygen and nitrogen. Hereinafter, these (i) and (ii) will be described in detail. In the following description, for simplicity, the gas separation membrane in the first separation membrane unit 11 will be referred to as the "first separation membrane", and the gas separation membrane in the second separation membrane unit 12 will be referred to as the "second separation membrane".

[0026] There is a difference in oxygen permeability between the first separation membrane and the second separation membrane. Specifically, the oxygen permeability of the first gas separation membrane is higher than the oxygen permeability of the second separation membrane. The level of oxygen permeability can be evaluated using the gas permeation rate for oxygen as a measure. The gas permeation rate P' is the permeation volume of gas per unit membrane area, per unit time, and per unit partial pressure difference, and the unit is [×10 -5 cm 3 (STP) / (cm 2 ·sec·cmHg)]. That is, the permeation rate of oxygen in the first separation membrane is greater than the permeation rate of oxygen in the second separation membrane.

[0027] If the magnitude relationship between the permeation rates of oxygen in the first separation membrane and the second separation membrane is as described above, the value of the permeation rate of oxygen itself is not particularly limited.

[0028] There are differences in the oxygen and nitrogen permeation ratios between the first separation membrane and the second separation membrane. Specifically, the oxygen-nitrogen permeation ratio of the second gas separation membrane is higher than that of the first gas separation membrane. The high or low of this permeation ratio can be evaluated using the gas separation selectivity of the membrane as a measure. The gas separation selectivity of the membrane can be expressed as the ratio of [permeation rate of the highly permeable gas / permeation rate of the low-permeable gas], that is, the ratio of [permeation rate of oxygen / permeation rate of nitrogen].

[0029] The magnitude relationship of the gas separation selectivities between the first separation membrane and the second separation membrane is as described above. At the temperature during operation, the gas separation selectivity S 1 of the first separation membrane itself is preferably 3.5 or more from the perspective of energy saving. From the perspective of making this advantage more prominent, the gas separation selectivity S 1 of the first separation membrane is more preferably 4.5 or more, and even more preferably 5.5 or more.

[0030] On the other hand, at the temperature during operation, the gas separation selectivity S 2 of the second separation membrane itself is preferably 4.5 or more from the perspective of energy saving on the condition that it is larger than the value of the gas separation selectivity S 1 of the first separation membrane. From the perspective of making this advantage more prominent, the gas separation selectivity S 2 of the second separation membrane is more preferably 5.5 or more, and even more preferably 6.5 or more.

[0031] As is clear from the comparison between the examples and comparative examples described later, when separating nitrogen and oxygen from air using only a gas separation membrane with high oxygen permeability, the processing capacity is high, but the separation efficiency is inferior, and it is not suitable when a reduction in compression power is desired. On the other hand, when separating nitrogen and oxygen from air using a gas separation membrane with high separation performance for nitrogen and oxygen, the separation efficiency is improved and the compression power is reduced, but it is not suitable when an improvement in processing capacity is desired. In contrast to this, according to the present embodiment, as the gas separation membrane used in the first-stage separation membrane unit, a gas separation membrane having higher oxygen permeability than the gas separation membrane used in the second-stage separation membrane unit is used, and as the gas separation membrane used in the second-stage separation membrane unit, a gas separation membrane having higher gas separation selectivity than the gas separation membrane used in the first-stage separation membrane unit is used, so that air separation with improved processing capacity and separation efficiency can be achieved while suppressing the compression power.

[0032] The gas permeation rate and gas separation selectivity of the gas separation membrane only need to satisfy the above conditions under the temperature conditions in each separation membrane unit 11, 12 during operation.

[0033] As a method of making the gas permeation rate and / or gas separation selectivity different between the separation membrane units 11 and 12 during operation, a method of making the types of gas separation membranes used different between the first separation membrane unit 11 and the second separation membrane unit 12 can be mentioned. In order to make the types of gas separation membranes different between the separation membrane units 11 and 12, for example, between the separation membrane units 11 and 12, (1) a gas separation membrane having different chemical compositions is used, (2) a gas separation membrane having the same chemical composition, but a gas separation membrane having different manufacturing conditions such as film formation conditions and heat treatment temperature is used, and (3) a gas separation membrane having the same chemical composition and manufacturing conditions, but a gas separation membrane having different coating or other surface treatment conditions can be used, and other means can be adopted.

[0034] It should be noted that even when the same gas separation membrane is used, it is generally known that when the operating temperature is set relatively low, the gas permeation rate becomes lower than when the operating temperature is set relatively high. Based on this, the operating temperatures of the respective separation membrane units 11 and 12 may be made different to adjust the gas permeation rate between the two separation membrane units 11 and 12 so as to satisfy the above-mentioned relationship.

[0035] In order to adjust the gas permeation rate and gas separation selectivity of the separation membrane unit 12, the gas separation apparatus 10 may include a cooling device (not shown) for the second supply gas between the first separation membrane unit 11 and the second separation membrane unit 12.

[0036] FIG. 3 shows another embodiment of the present invention. The gas separation apparatus 10 of the embodiment shown in the figure includes a second compressor 22 between the first separation membrane unit 11 and the second separation membrane unit 12. The second compressor 22 is used to boost the pressure of the first non-permeating gas discharged from the first separation membrane unit 11 to obtain the second supply gas. By boosting the pressure of the second supply gas by the second compressor 22, the degree of boosting of the first supply gas by the first compressor 21 can be reduced. As a result, there is an advantage that the compression power per unit volume of the second non-permeating gas can be made lower than in the case where the second compressor 22 is not used.

[0037] From the viewpoint of making the above advantages more prominent, the pressure of the second supply gas supplied to the second separation membrane unit 12 is preferably set to 0.5 MPaG or more and 5.0 MPaG or less, and more preferably set to 0.7 MPaG or more and 3.0 MPaG or less.

[0038] In the present embodiment, in addition to the first compressor 21, the second compressor 22 is used, the oxygen permeability of the gas separation membrane in the first separation membrane unit 11 is high, and the oxygen-nitrogen permeation ratio of the gas separation membrane in the two separation membrane unit 12 is higher than the oxygen-nitrogen permeation ratio of the gas separation membrane in the first separation membrane unit 11. Therefore, it is preferable not to set the pressure of the first supply gas supplied to the first separation membrane unit 11 too high. For example, it is preferable to set the pressure of the first supply gas supplied to the first separation membrane unit 11 lower than the pressure of the second supply gas supplied to the second separation membrane unit 12. Thereby, it becomes possible to suppress the overall power consumption of the gas separation apparatus 10. From the above viewpoints, the pressure of the first supply gas supplied to the first separation membrane unit 11 is preferably set to be 0.1 MPaG or more and 3 MPaG or less, more preferably 0.3 MPaG or more and 2.5 MPaG or less, on the condition that it is lower than the pressure of the second supply gas supplied to the second separation membrane unit 12.

[0039] When the gas separation device 10 of the present embodiment includes a cooling device, the cooling device may be installed upstream of the second compressor 22 or may be installed downstream of the second compressor 22. Since it becomes easier to adjust the operating temperature of the second separation membrane unit 12, it is preferable to install the cooling device downstream of the second compressor 22.

[0040] Regarding the points not particularly described in the embodiment shown in FIG. 3, the description of the embodiment shown in FIG. 1 described above is appropriately applied. Also, in FIG. 3, the same members as those in FIG. 1 are given the same reference numerals.

[0041] In the gas separation device 10 of each of the above embodiments, it is preferable that oxygen and nitrogen are separated so that the oxygen concentration of the first non-permeating gas discharged from the first separation membrane unit 11 is 5 mol% or more and 18 mol% or less, from the viewpoint of efficiently obtaining the first non-permeating gas in which nitrogen is enriched. From the viewpoint of making this advantage more prominent, it is more preferable that oxygen and nitrogen are separated so that the oxygen concentration of the first non-permeating gas discharged from the first separation membrane unit 11 is 10 mol% or more and 15 mol% or less.

[0042] On the other hand, it is preferable that oxygen and nitrogen are separated so that the oxygen concentration of the second non-permeating gas discharged from the second separation membrane unit 12 is 0.1 mol% or more and 5 mol% or less, from the viewpoint of efficiently obtaining the second non-permeating gas in which nitrogen is further enriched. From the viewpoint of making this advantage more prominent, it is more preferable that oxygen and nitrogen are separated so that the oxygen concentration of the second non-permeating gas discharged from the second separation membrane unit 12 is 0.5 mol% or more and 5 mol% or less.

[0043] As the gas separation membrane used in the gas separation apparatus 10 of each of the above embodiments, those similar to those conventionally used in the art can be mentioned. For example, polymer materials such as polyimide, polyetherimide, polyamide, polyamideimide, polysulfone, polycarbonate, silicone resin, and cellulose-based polymers, materials obtained by carbonizing or partially carbonizing the polymer material, and gas separation membranes formed of ceramic materials such as zeolite can be preferably mentioned. In particular, a gas separation membrane made of a polymer material, especially an asymmetric polyimide gas separation membrane, is preferable because it not only has high gas separation performance but also excellent properties such as heat resistance, durability, and solvent resistance.

[0044] The number of modules provided in one gas separation membrane unit may be one or a plurality. When two or more modules are provided in one gas separation membrane unit, it is preferable that the plurality of modules are connected in parallel within the unit. When each of the separation membrane units 11 and 12 has a plurality of modules, the membrane area within the unit can be easily adjusted by changing the number of the modules.

[0045] As described above, the present invention has been described based on its preferred embodiments, but the present invention is not limited to the above embodiments. For example, in the embodiment shown in FIG. 3, the second compressor 22 is interposed in the non-permeate gas discharge line 14, but instead of or in addition to this, the permeate side space of the second separation membrane unit 12 may be depressurized to below atmospheric pressure by a vacuum pump or the like to further reduce the compression power.

Example

[0046] Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[0047] 〔Example 1A and Example 2A〕 Using the gas separation device 10 shown in FIG. 1, nitrogen and oxygen were separated from air. As the modules constituting the first and second separation membrane units 11 and 12, at the operating temperature, P' O2 is 9.7×10 -5 cm 3 (STP) / (cm 2 ·sec·cmHg), and a gas separation membrane with a gas separation selectivity P' O2 / P' N2 of 5.8 was used for module A (the first separation membrane unit 11), and P' O2 is 2.7×10 -5 cm 3 (STP) / (cm 2 ·sec·cmHg), and a gas separation membrane with a gas separation selectivity P' O2 / P' N2 of 6.9 was used for module B (the second separation membrane unit 12). These two types of modules were used. These modules contain a gas separation membrane composed of a polyimide hollow fiber membrane in a case, and when using compressed air as the raw material gas to obtain nitrogen-enriched air, they showed the responses as described in Table 1 below. The values shown in the table are for one module of the same size.

[0048]

Table 1

[0049] The number of modules constituting the first separation membrane unit 11 (the first stage) and the number of modules constituting the second separation membrane unit 12 (the second stage) were set as shown in Table 2 below. When using multiple modules, they were connected in parallel. Also, the gas separation device 10 was operated under the conditions shown in the table so that the oxygen concentration in the second non-permeating gas was 5 mol%.

[0050] 〔Comparative Example 1A〕 Only the first separation membrane unit 11 was used, and the gas separation device 10 was operated under the conditions shown in Table 2 so that the oxygen concentration in the non-permeating gas was 5 mol%. Otherwise, gas separation was performed in the same manner as in Example 1A.

[0051] [Comparative Example 2A] Using only the second separation membrane unit 12, the gas separation apparatus 10 was operated under the conditions shown in Table 2 such that the concentration of oxygen contained in the non-permeating gas was 5 mol%. Gas separation was performed in the same manner as in Example 1A otherwise.

[0052] [Table 2]

[0053] [Example 1B and Example 2B] The number of modules constituting the first separation membrane unit 11 and the number of modules constituting the second separation membrane unit 12 were set as shown in Table 3 below. Also, the gas separation apparatus 10 was operated under the conditions shown in the same table such that the concentration of oxygen contained in the second non-permeating gas was 1 mol%. Gas separation was performed in the same manner as in Example 1A otherwise.

[0054] [Comparative Example 1B] Using only the first separation membrane unit 11, the gas separation apparatus 10 was operated under the conditions shown in Table 3 such that the concentration of oxygen contained in the non-permeating gas was 1 mol%. Gas separation was performed in the same manner as in Example 1A otherwise.

[0055] [Comparative Example 2B] Using only the second separation membrane unit 12, the gas separation apparatus 10 was operated under the conditions shown in Table 3 such that the concentration of oxygen contained in the non-permeating gas was 1 mol%. Gas separation was performed in the same manner as in Example 1A otherwise.

[0056] [Table 3]

[0057] [Example 3A and Example 4A] Using the gas separation device 10 shown in Fig. 3, nitrogen and oxygen were separated from air. The number of modules constituting the first separation membrane unit 11 and the number of modules constituting the second separation membrane unit 12 were set as shown in Table 4 below. Also, the gas separation device 10 was operated under the conditions shown in the same table so that the concentration of oxygen contained in the second non-permeating gas would be 5 mol%. For the purpose of facilitating comparison, the results of Comparative Example 1A and Comparative Example 2A described above are also shown in Table 4.

[0058]

Table 4

[0059] 〔Examples 3B and 4B〕 Using the gas separation device 10 shown in Fig. 3, nitrogen and oxygen were separated from air. The number of modules constituting the first separation membrane unit 11 and the number of modules constituting the second separation membrane unit 12 were set as shown in Table 5 below. Also, the gas separation device 10 was operated under the conditions shown in the same table so that the concentration of oxygen contained in the second non-permeating gas would be 1 mol%. For the purpose of facilitating comparison, the results of Comparative Example 1B and Comparative Example 2B described above are also shown in Table 5.

[0060]

Table 5

[0061] 〔Evaluation〕 The relationships between the amount of the second non-permeating gas and the number of modules, and between the amount of the second non-permeating gas and the compression power in the examples and comparative examples are summarized in Table 6 shown below.

[0062]

Table 6

[0063] From the results shown in the above tables, the following can be understood. From the comparison between Example 1A and Example 2A using the gas separation device shown in FIG. 1 and Comparative Example 1A and Comparative Example 2A, it can be seen that the number of modules per gas volume in Example 1A and Example 2A is the intermediate value between Comparative Example 1A and Comparative Example 2A. Also, it can be seen that the power per gas volume in Example 1A and Example 2A is also the intermediate value between Comparative Example 1A and Comparative Example 2A. Therefore, according to the gas separation device shown in FIG. 1, it can be seen that the options for gas separation conditions increase by a simple method such as selecting the modules to be used. Similar conclusions can also be drawn from the comparison between Example 1B and Example 2B and Comparative Example 1B and Comparative Example 2B.

[0064] From the comparison between Example 3A and Example 4A using the gas separation device shown in FIG. 3 and Comparative Example 1A and Comparative Example 2A, it can be seen that the number of modules per gas volume in Example 3A and Example 4A is improved compared to Comparative Example 2A. Also, it can be seen that the power per gas volume in Example 3A and Example 4A is also improved compared to Comparative Example 2A. Similar conclusions can also be drawn from the comparison between Example 3B and Example 4B and Comparative Example 2B.

Explanation of Reference Numerals

[0065] 10 Gas separation device 11 First separation membrane unit 11a Gas inlet 11b Non-permeating gas discharge port 11c Permeating gas discharge port 12 Second separation membrane unit 12a Gas inlet 12b Non-permeating gas discharge port 12c Permeating gas discharge port 14 Non-permeating gas discharge line 15 Permeating gas discharge line 16 Raw material gas supply line 21 First compressor 22 Second compressor

Claims

1. A compressor capable of sucking in raw material air and compressing the raw material air to a predetermined pressure; A first separation membrane unit that takes in the raw material air compressed by the compressor as a first supply gas and separates it into a first permeated gas with concentrated oxygen and a first non-permeated gas with concentrated nitrogen; A second separation membrane unit that takes in the entire amount of the first non-permeated gas as a second supply gas and separates it into a second permeated gas with concentrated oxygen and a second non-permeated gas with concentrated nitrogen; Comprising The oxygen permeability of the gas separation membrane in the first separation membrane unit is higher than the oxygen permeability of the gas separation membrane in the second separation membrane unit; And The permeation ratio of oxygen to nitrogen of the gas separation membrane in the second separation membrane unit is higher than the permeation ratio of oxygen to nitrogen of the gas separation membrane in the first separation membrane unit; A gas separation device, wherein the oxygen concentration of the first non-permeated gas is 10 to 18 mol%, and the oxygen concentration of the second non-permeated gas is 0.1 to 5 mol%.

2. The gas separation device according to claim 1, further comprising a compressor for boosting the pressure of the first non-permeated gas to the second supply gas between the first separation membrane unit and the second separation membrane unit.

3. The gas separation device according to claim 2, wherein the pressure of the first supply gas is 0.1 to 3 MPaG, and the pressure of the second supply gas is 0.5 to 5 MPaG.

4. The permeated gas that has passed through the second separation membrane unit is either discharged or all or part of it is supplied to the raw material supply line. The gas separation device according to any one of claims 1 to 3.

5. The gas separation device according to any one of claims 1 to 4, further comprising a cooling device for the second supply gas between the first separation membrane unit and the second separation membrane unit.

6. Compressed raw material air is taken into the first separation membrane unit as the first supply gas and separated into a first permeated gas with concentrated oxygen and a first non-permeated gas with concentrated nitrogen, The entire amount of the first non-permeated gas is taken into the second separation membrane unit as the second supply gas and separated into a second permeated gas with concentrated oxygen and a second non-permeated gas with concentrated nitrogen. A gas separation method, As the first separation membrane unit, one having a higher oxygen permeability of the gas separation membrane in the first separation membrane unit than the oxygen permeability of the gas separation membrane in the second separation membrane unit is used. As the second separation membrane unit, a unit in which the oxygen-nitrogen permeation ratio of the gas separation membrane in the second separation membrane unit is higher than the oxygen-nitrogen permeation ratio of the gas separation membrane in the first separation membrane unit is used, the oxygen concentration of the first non-permeating gas is 10 to 18 mol%, and the oxygen concentration of the second non-permeating gas is 0.1 to 5 mol%. A gas separation method.

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