Gas separation system

Abstract

A gas separation system (1) separates NH3 from a mixed gas containing NH3, CO2, and N2. The gas separation system (1) includes: a first separation membrane (10); and a second separation membrane (20) disposed on a downstream side of the first separation membrane (10). The first separation membrane (10) generates a first enriched gas in which NH3 is enriched and a first depleted gas in which NH3 is depleted by selectively allowing NH3 to permeate. The second separation membrane (20) generates a second enriched gas in which CO2 is enriched and a second depleted gas in which CO2 is depleted by separating CO2.

Description

Technical Field

[0001] This invention relates to gas separation systems. Background Technology

[0002] Conventionally, methods for separating specified components contained in a gas mixture include methods that combine pressure variation adsorption (PSA), temperature variation adsorption (TSA), or absorption methods with a separator that employs membrane separation (e.g., Patent Document 1).

[0003] Regarding the method described in Patent Document 1, after separating the mixed gas into waste gas (hydrogen sulfide, water vapor, and heavy hydrocarbons) and concentrated gas (carbon dioxide and light hydrocarbons) in an adsorption tower, the concentrated gas is then separated into carbon dioxide and light hydrocarbons in a separation membrane.

[0004] According to the method described in Patent Document 1, water vapor and heavy hydrocarbons can be separated as waste gas (impurities). Water vapor and heavy hydrocarbons are both condensable gases. Condensable gases refer to gases that, if the partial pressure is high, will condense in the downstream separation membrane when supplied with concentrated gas, which may reduce the separation performance of the membrane.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: U.S. Patent Application Publication No. 2009 / 0151562 Summary of the Invention

[0008] However, the concentrated gas flowing out of the adsorption tower or absorption tower is prone to pressure or temperature fluctuations. Therefore, it is necessary to constantly monitor and control the pressure and temperature of the concentrated gas supplied to the separation membrane or other separators, which is quite complicated.

[0009] The purpose of this invention is to provide a gas separation system that can easily separate condensable gases.

[0010] The first aspect of the present invention relates to a gas separation system that separates a second non-condensable gas from a mixture of a first condensable gas, a first non-condensable gas, and a second non-condensable gas. The gas separation system includes: a first separation membrane; and a first separator disposed downstream of the first separation membrane. The first separation membrane selectively permeates through the first condensable gas to generate a first enriched gas enriched with the first condensable gas and a first depleted gas depleted from the first condensable gas. The first separator separates the first non-condensable gas to generate a second enriched gas enriched with the first non-condensable gas and a second depleted gas depleted from the first non-condensable gas.

[0011] The gas separation system of the second aspect of the present invention is based on the first aspect described above, wherein the first separator is a second separation membrane that allows the second condensable gas to selectively permeate.

[0012] The gas separation system involved in the third aspect of the present invention is based on the second aspect described above, but the composition of the second separation membrane is different from that of the first separation membrane.

[0013] The fourth aspect of the present invention relates to a gas separation system that, based on any of the first to third aspects described above, includes a second separator disposed upstream of the first separation membrane. The mixed gas further includes a second condensable gas. At the operating temperature of the first separator, the saturated vapor pressure of the second condensable gas is lower than the saturated vapor pressure of the first condensable gas.

[0014] The gas separation system of the fifth aspect of the present invention is based on the fourth aspect described above, wherein the second separator is a third separation membrane that selectively allows the first non-condensable gas to pass through.

[0015] The gas separation system involved in the sixth aspect of the present invention is based on the fifth aspect described above, but the composition of the third separation membrane is different from that of the first separation membrane.

[0016] The gas separation system according to the seventh aspect of the present invention is based on any of the first to sixth aspects described above, wherein the concentration of the first condensable gas in the gas supplied to the first separator is lower than the concentration of the first condensable gas in the gas supplied to the first separation membrane.

[0017] The gas separation system involved in the eighth aspect of the present invention is based on any one of the first to seventh aspects described above, wherein the first condensable gas is NH3.

[0018] The gas separation system involved in the ninth aspect of the present invention is based on any one of the first to seventh aspects described above, wherein the first condensable gas is H2O, the first non-condensable gas is N2, and the second non-condensable gas is CH4.

[0019] The gas separation system involved in the tenth aspect of the present invention is based on any one of the first to seventh aspects described above, wherein the first condensable gas is H2O, the first non-condensable gas is H2, and the second non-condensable gas is any one of N2, CO2, and CH4.

[0020] The gas separation system involved in the eleventh aspect of the present invention is based on any one of the first to seventh aspects described above, wherein the first condensable gas is H2O, the first non-condensable gas is CO2, and the second non-condensable gas is any one of CH4 and H2.

[0021] The gas separation system involved in the twelfth aspect of the present invention is based on any one of the first to seventh aspects described above, wherein the first condensable gas is H2O, the first non-condensable gas is CO2, the second non-condensable gas is N2, and the first separation membrane and the first separation body are zeolite membranes.

[0022] Invention Effects

[0023] According to the present invention, a gas separation system capable of easily separating condensable gases can be provided. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the configuration of the gas separation system according to the embodiment.

[0025] Figure 2 This is a schematic diagram showing the configuration of the gas separation system involved in Modification Example 2. Detailed Implementation

[0026] (Gas separation system 1)

[0027] Figure 1 This is a schematic diagram showing the configuration of gas separation system 1.

[0028] The gas separation system 1 includes a first separation membrane 10 and a second separation membrane 20.

[0029] The first separation membrane 10 is an example of the "first separation membrane" involved in this invention. The second separation membrane 20 is an example of the "first separation body" involved in this invention.

[0030] [First separation membrane 10]

[0031] The first separation membrane 10 is disposed upstream of the second separation membrane 20. The first separation membrane 10 is supplied with a mixed gas containing NH3, CO2, and N2. The mixed gas supplied to the first separation membrane 10 is preferably pressurized.

[0032] NH3 is an example of the "first condensable gas" involved in this invention. The dynamic molecular diameter of NH3 is 0.265 nm. CO2 is an example of the "first non-condensable gas" involved in this invention. The dynamic molecular diameter of CO2 is 0.33 nm. N2 is an example of the "second non-condensable gas" involved in this invention. The dynamic molecular diameter of N2 is 0.364 nm. H2 is an example of the "third non-condensable gas" involved in this invention. The dynamic molecular diameter of H2 is 0.289 nm.

[0033] Thus, the mixed gas involved in this embodiment includes one condensable gas (NH3) and three non-condensable gases (H2, CO2 and N2).

[0034] Condensable gases refer to gases whose saturated vapor pressure is below 2 MPaG at the operating temperature of the separator (second separation membrane 20 in this embodiment) used to separate non-condensable gases in the downstream section. Non-condensable gases refer to gases other than condensable gases.

[0035] Preferably, the saturated vapor pressure of the condensable gas at the operating temperature of the separator (in this embodiment, the second separation membrane 20) configured in the downstream section for separating non-condensable gases is less than 1 MPaG. This makes the effect of easily separating the condensable gas and suppressing performance degradation of the "separator," a feature of the present invention, more significant when the condensable gas is more prone to condensation.

[0036] It should be noted that the mixed gas involved in this embodiment includes one condensable gas and three non-condensable gases, but is not limited thereto. It is sufficient for the mixed gas to include at least one condensable gas and at least two non-condensable gases. The mixing ratio of each gas in the mixed gas can be appropriately set.

[0037] In this embodiment, the first separation membrane 10 separates NH3, which is one of the condensable gases, and H2, which is one of the non-condensable gases, from the mixed gas. However, the first separation membrane 10 only needs to be able to separate the condensable gases, and may not be able to separate the non-condensable gases.

[0038] The first separation membrane 10 is a separation membrane capable of selectively permeating NH3 and H2 in the mixed gas. As long as the first separation membrane 10 is a membrane capable of selectively permeating NH3 and H2, the constituent material of the first separation membrane 10 is not particularly limited. For example, zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes can be used as the first separation membrane 10. In particular, zeolite membranes exhibit high separation performance even under high temperature conditions, and are therefore preferred.

[0039] It should be noted that, in this specification, selective permeation means that the desired component is enriched in the permeation space of the separation membrane.

[0040] The first separation membrane 10 selectively permeates NH3 and H2 contained in the mixed gas to generate a first enriched gas enriched with NH3 and H2, and a first depleted gas depleted with NH3 and H2 and enriched with CO2 and N2.

[0041] The first enriched gas is discharged to the outside through the permeate side space of the first separation membrane 10. The individual concentrations of NH3 and H2 in the first enriched gas are not particularly limited; however, the first enriched gas preferably mainly contains NH3 and H2. "Mainly contains NH3 and H2" means that the combined concentration of NH3 and H2 in the first enriched gas exhibits the highest possible concentration. The mixing ratio of NH3 and H2 in the first enriched gas is not particularly limited.

[0042] A first lean gas flows out from the non-permeable side space of the first separation membrane 10 and is supplied to the second separation membrane 20. The first lean gas contains CO2 and N2. Preferably, the first lean gas is substantially free of NH3 and H2, however, it may contain one or both of NH3 and H2.

[0043] [Second separation membrane 20]

[0044] The second separation membrane 20 is disposed downstream of the first separation membrane 10. A first lean gas containing CO2 and N2 is supplied from the first separation membrane 10 to the second separation membrane 20.

[0045] The concentration of NH3 in the first depleted gas supplied to the second separation membrane 20 is lower than the concentration of NH3 in the mixed gas supplied to the first separation membrane 20.

[0046] The second separation membrane 20 separates CO2, which is a first non-condensable gas, from the first lean gas. The second separation membrane 20 is a CO2 separation membrane capable of selectively permeating CO2 from the first lean gas. The constituent material of the second separation membrane 20 is not particularly limited, as long as it is a membrane capable of selectively permeating CO2. Examples of materials that can be used for the second separation membrane 20 include zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes.

[0047] The second separation membrane 20 is preferably composed differently from the first separation membrane 10. The second separation membrane 20 is preferably composed of a structure suitable for CO2 separation. For example, it is preferable that the pore size of the second separation membrane 20 is larger than the dynamic molecular diameter of CO2 and smaller than the dynamic molecular diameter of N2.

[0048] The second separation membrane 20 generates a second enriched gas enriched with CO2 and a second depleted gas enriched with N2 by selectively permeating CO2 contained in the first depleted gas.

[0049] The second enriched gas is discharged to the outside through the permeate side space of the second separation membrane 20. The concentration of CO2 in the second enriched gas is not particularly limited; however, it is preferable that the second enriched gas mainly contains CO2. "Mainly contains CO2" means that the highest concentration of CO2 in the second enriched gas is CO2.

[0050] The second lean gas is discharged to the outside from the non-permeable side space of the second separation membrane 20. The second lean gas mainly contains N2. Preferably, the second lean gas is substantially free of NH3; however, if the first lean gas contains NH3, the second lean gas may also contain NH3.

[0051] (feature)

[0052] (1) Gas separation system 1 separates NH3 from a mixture of NH3 (a first condensable gas), CO2 (a first non-condensable gas), and N2 (a second non-condensable gas). Gas separation system 1 includes: a first separation membrane 10 (first separation membrane); and a second separation membrane 20 (first separator), which is disposed downstream of the first separation membrane 10. The first separation membrane 10 generates a first enriched gas enriched with NH3 and a first depleted gas enriched with CO2 and N2 by selectively permeating NH3. The second separation membrane 20 generates a second enriched gas enriched with CO2 and a second depleted gas by separating CO2.

[0053] Thus, according to gas separation system 1, CO2 and N2 can be separated after NH3 has been pre-separated by passing it through the separation membrane. Therefore, since condensable gases can be pre-separated before non-condensable gases are separated, the reduction in the separation performance of the second separation membrane 20 due to NH3 condensation and liquefaction in the second separation membrane 20 can be suppressed. Furthermore, compared to the case where an adsorption tower is used to separate NH3 via PSA, pressure fluctuations in the first lean gas supplied to the second separation membrane 20 can be suppressed. Accordingly, complex pressure control of the first lean gas is unnecessary. Additionally, the energy required to pressurize the first lean gas after its pressure is reduced can be reduced. Moreover, compared to the case where NH3 is separated via temperature variation adsorption (TSA) or absorption, gas separation system 1 does not require complex temperature control of the first lean gas. Furthermore, in the case of TSA or absorption, the gas temperature is sometimes reduced due to more efficient adsorption or absorption. Therefore, the energy required to heat the first lean gas can be reduced.

[0054] (2) The gas separation system 1 includes a second separation membrane 20 that selectively allows CO2 to pass through, serving as the "first separator". Therefore, compared to cases where adsorption towers or absorption towers are used as separators to separate CO2 by adsorption or absorption methods, the gas separation system 1 can separate CO2 with good accuracy with a simple configuration. In addition, membrane separation is a continuous process, and therefore, compared to adsorption or absorption methods, which are batch processes, it is more susceptible to pressure or temperature fluctuations. Therefore, when a separation membrane is used as the "separator", the effect of the present invention, which can suppress pressure or temperature fluctuations of the first depleted gas, is more significant.

[0055] (3) The composition of the second separation membrane 20 is preferably different from that of the first separation membrane 10. Accordingly, a separation membrane suitable for separating CO2, which is a first non-condensable gas, can be used as the second separation membrane 20.

[0056] (4) The concentration of NH3 in the first lean gas (an example of "gas supplied to the first separator") is lower than the concentration of NH3 in the mixed gas (an example of "gas supplied to the first separation membrane"). This means that NH3, which is a condensable gas, is removed before CO2 and N2, which are non-condensable gases contained in the first lean gas, are separated. Accordingly, CO2 can be separated from the first lean gas with good precision.

[0057] (Modifications of the implementation method)

[0058] The above describes one embodiment of the present invention. However, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention.

[0059] [Variation Example 1]

[0060] In the above embodiments, the gas separation system 1 includes a second separation membrane 20 as an example of a first separator; however, the first separator is not limited to a separation membrane. It is acceptable as long as the first separator is a structure capable of separating the first non-condensable gas. For example, a structure that separates the first non-condensable gas by PSA, TSA, or absorption methods can be used as the first separator.

[0061] [Variation Example 2]

[0062] In the above embodiments, NH3 is cited as an example of the first condensing gas, but it is not limited to this. For example, NH3, H2O, etc. can be used as condensing gases.

[0063] Furthermore, in the above embodiments, CO2 is cited as an example of the first non-condensable gas, N2 is cited as an example of the second non-condensable gas, and H2 is cited as an example of the third non-condensable gas, but the embodiments are not limited thereto. For example, CO2, N2, H2, CH4, etc., can be used as the first to third non-condensable gases.

[0064] Here, representative examples of combinations of a first condensable gas, a first non-condensable gas, and a second non-condensable gas contained in a gas mixture are summarized in Table 1.

[0065] [Table 1]

[0066]

[0067] The combination of gases is determined by the composition of the mixed gases to be treated; however, the gas separation system of the present invention can be used particularly effectively in the following situations.

[0068] First, the mixed gas preferably contains NH3 as the first condensing gas. In this case, the concentration of corrosive NH3 can be preferentially reduced, thus suppressing the deterioration of the separation membrane or the device.

[0069] Furthermore, H2O is preferably included in the gas mixture as the first condensable gas. In this case, by separating H2O, which has a low vapor pressure and is easily condensable, it is possible to suppress the condensation of H2O in the subsequent separation membrane, which would otherwise lead to a decrease in membrane performance.

[0070] In the case where the mixed gas contains H2O as the first condensable gas, it is more preferable to contain N2 as the first non-condensable gas and CH4 as the second non-condensable gas. Therefore, by removing H2O first, the performance of the first separator in the subsequent stage can be prevented from decreasing due to swelling or blockage caused by H2O. By removing N2, which is an inactive gas, immediately after H2O, the purity of CH4, which is a non-permeable gas, gradually increases, thus reducing the risk of CH4 explosion in an emergency.

[0071] Furthermore, if the mixed gas contains H2O as the first condensable gas, it is more preferable to contain H2 as the first non-condensable gas and any one of N2, CO2, and CH4 as the second non-condensable gas. Thus, by removing molecules sequentially starting with those having smaller dynamic molecular diameters, it is possible to suppress the mixing of these molecules into the gases separated in the subsequent stages, thereby obtaining a gas of high purity.

[0072] Furthermore, when the mixed gas contains H2O as the first condensable gas, it is more preferable to contain CO2 as the first non-condensable gas and either CH4 or H2 as the second non-condensable gas. Thus, by removing H2O first, the performance of the first separator in the subsequent stage can be prevented from decreasing due to swelling or blockage caused by H2O. By removing CO2, which is an inactive gas, immediately after H2O, the purity of CH4 and H2, which are non-permeable gases, gradually increases, thereby reducing the risk of CH4 and H2 explosion in an emergency.

[0073] Furthermore, when the mixed gas contains H2O as the first condensable gas, it is particularly preferable to contain CO2 as the first non-condensable gas and N2 as the second non-condensable gas, and the first and second separation membranes 10 and 20 are zeolite membranes. Thus, by first removing H2O, which has a particularly high affinity for zeolite, and then separating CO2 immediately after H2O, the affinity between CO2 and zeolite can be effectively utilized, thereby enabling highly efficient separation.

[0074] [Variation Example 3]

[0075] In the above embodiments, the mixed gas contains one condensable gas and three non-condensable gases, but is not limited thereto. It is sufficient that the mixed gas contains at least one condensable gas and at least two non-condensable gases.

[0076] When the mixed gas contains two or more condensable gases, in the gas separation system of the present invention, it is sufficient to separate at least one second non-condensable gas. This means that the two or more condensable gases can be separated individually, or they can be combined and separated separately. For example, the two or more condensable gases can each permeate through at least one of the first separation membrane and the first separator.

[0077] For example, in the case where the mixed gas contains NH3 (first condensable gas), H2O (second condensable gas), CO2 (first non-condensable gas), N2 (second non-condensable gas), and H2 (third non-condensable gas), such as Figure 2 As shown, the gas separation system 1 only needs to have a third separation membrane 30 disposed in front of the first separation membrane 10.

[0078] The third separation membrane 30 is disposed upstream of the first separation membrane 10. The third separation membrane 30 is supplied with a mixed gas containing H2O, NH3, H2, CO2 and N2.

[0079] The third separation membrane 30 separates H2O, which is one of the condensable gases, from the mixed gas. The third separation membrane 30 is an H2O separation membrane capable of selectively permeating H2O from the mixed gas. As long as the third separation membrane 30 is a membrane capable of selectively permeating H2O, the constituent material of the third separation membrane 30 is not particularly limited. For example, zeolite membranes, carbon membranes, silica membranes, and synthetic resin membranes can be used as the third separation membrane 30.

[0080] The third separation membrane 30 is preferably composed differently from the first and second separation membranes 10 and 20. Specifically, the third separation membrane 30 is preferably a membrane capable of adsorbing H2O.

[0081] The third separation membrane 30 is an example of the "second separator" according to the present invention. By using the third separation membrane 30, which selectively allows H2O to permeate, as the "second separator" in the gas separation system 1, compared to using an adsorption tower that separates H2O via pressure variation adsorption (PSA) as the second separator, pressure fluctuations in the third lean gas supplied to the first separation membrane 10 can be suppressed. Accordingly, complex pressure control of the third lean gas is unnecessary. Furthermore, the energy required to pressurize the third lean gas can be reduced.

[0082] The third separation membrane 30 selectively permeates H2O contained in the mixed gas to generate a third enriched gas enriched with H2O and a third depleted gas depleted with H2O.

[0083] The third enriched gas flows out from the permeate side space of the third separation membrane 30. The third enriched gas mainly contains H2O. The third lean gas flows out from the non-permeate side space of the third separation membrane 30 and is supplied to the first separation membrane 10. The third lean gas contains NH3, H2, CO2, and N2. Preferably, the third lean gas is substantially free of H2O, however, it may contain H2O.

[0084] In this modified example, the structure and function of the first separation membrane 10 and the second separation membrane 20 are as described in the above embodiments. The concentration of H2O in the first depleted gas supplied to the second separation membrane 20 is lower than the concentration of H2O in the mixed gas supplied to the third separation membrane 30.

[0085] Here, at the operating temperature of the second separation membrane 20, the saturated vapor pressure of H2O is lower than that of NH3. That is, when in contact with the operating second separation membrane 20, H2O condenses more easily than NH3.

[0086] Furthermore, in this modified example, H2O, which has a greater impact on the separation performance of the second separation membrane 20, is removed before NH3. Accordingly, the condensation of condensable gases in the second separation membrane 20 can be more reliably suppressed.

[0087] It should be noted that in this modified example, the gas separation system 1, as an example of the second separator, includes a third separation membrane 30; however, the second separator is not limited to a separation membrane. It is acceptable as long as the second separator is a structure capable of separating the second condensable gas. For example, an adsorption tower that separates the second condensable gas using the PSA method can be used as the second separator.

[0088] [Variation Example 4]

[0089] In the above embodiments, after the condensable gas is separated from the mixed gas, the non-condensable gas is separated. However, a portion of the non-condensable gas can be separated before the condensable gas is separated from the mixed gas.

[0090] For example, a portion of the CO2 can be pre-separated by a CO2 separation membrane configured on the upstream side of the first separation membrane 10.

[0091] Explanation of reference numerals in the attached figures

[0092] 1 Gas separation system

[0093] 10 First separation membrane

[0094] 20 Second separation membrane

[0095] 30 Third Separation Membrane

Claims

1. A gas separation system for separating a second non-condensable gas from a mixture of a first condensable gas, a first non-condensable gas, and a second non-condensable gas, characterized in that, The gas separation system comprises: First separation membrane; as well as A first separator is disposed downstream of the first separation membrane. The first separation membrane selectively permeates the first condensable gas to generate a first enriched gas in which the first condensable gas is enriched, and a first depleted gas in which the first condensable gas is depleted and the first non-condensable gas and the second non-condensable gas are enriched. The first separator generates a second enriched gas enriched by the first non-condensable gas and a second depleted gas depleted by the first non-condensable gas by separating the first non-condensable gas.

2. The gas separation system according to claim 1, characterized in that, The first separator is a second separation membrane that allows the second non-condensable gas to selectively permeate.

3. The gas separation system according to claim 2, characterized in that, The second separation membrane has a different structure than the first separation membrane.

4. The gas separation system according to any one of claims 1 to 3, characterized in that, It includes a second separator disposed upstream of the first separation membrane. The mixed gas also contains a second condensable gas. At the operating temperature of the first separator, the saturated vapor pressure of the second condensable gas is lower than that of the first condensable gas.

5. The gas separation system according to claim 4, characterized in that, The second separator is a third separation membrane that allows the second condensable gas to selectively permeate.

6. The gas separation system according to claim 5, characterized in that, The third separation membrane has a different composition than the first separation membrane.

7. The gas separation system according to claim 1, characterized in that, The concentration of the first condensable gas in the gas supplied to the first separator is lower than the concentration of the first condensable gas in the gas supplied to the first separator membrane.

8. The gas separation system according to any one of claims 1 to 3, characterized in that, The first condensable gas is NH3.

9. The gas separation system according to any one of claims 1 to 3, characterized in that, The first condensable gas is H2O. The first non-condensable gas is N2. The second non-condensable gas is CH4.

10. The gas separation system according to any one of claims 1 to 3, characterized in that, The first condensable gas is H2O. The first non-condensable gas is H2. The second non-condensable gas is any one of N2, CO2, and CH4.

11. The gas separation system according to any one of claims 1 to 3, characterized in that, The first condensable gas is H2O. The first non-condensable gas is CO2. The second non-condensable gas is either CH4 or H2.

12. The gas separation system according to any one of claims 1 to 3, characterized in that, The first condensable gas is H2O. The first non-condensable gas is CO2. The second non-condensable gas is N2. The first separation membrane and the first separation body are both zeolite membranes.

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