Gas separation device

Abstract

The present application provides a kind of gas separation device (10), with: separation module (1), it has the separation membrane (M) of selectively allowing specific component in mixed gas to pass, internal space is divided into first space and second space by separation membrane (M);Supply line (L1), it supplies the mixed gas of first specified pressure to first space;Vacuum pump (3);And recovery line (L2), one end is connected with second space, and the other end is connected with vacuum pump (3), so that recovery line (L2) is reduced to second specified pressure, and recovery permeated gas that has passed separation membrane (M).Second specified pressure is determined in the form that the product of the concentration of specific component in permeated gas and the pump efficiency of vacuum pump (3) is maximum.

Description

TECHNICAL FIELD

[0001] The present application relates to a gas separation device that separates a specific component from a mixed gas. BACKGROUND

[0002] As such a device, a device that uses a separation membrane that selectively allows carbon dioxide (CO2) in air to permeate to recover high-concentration CO2 is known (see, for example, Patent Literature 1). In the device of Patent Literature 1, air at atmospheric pressure is supplied to a membrane separation module, and the permeation side of the membrane separation module is depressurized using a vacuum pump, whereby CO2 that has permeated the separation membrane is recovered.

[0003] In the device of Patent Literature 1, the more the permeation side is depressurized, the more the amount of permeation of CO2 increases, and the higher the concentration of CO2 in the recovered gas becomes. However, since the amount of energy use due to depressurization and the amount of permeation of CO2 are in a trade-off relationship, if the depressurization is excessively performed, the efficiency of the entire device decreases.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2020-195968 (JP 2020-195968 A). SUMMARY

[0007] The gas separation device of one aspect of the present application includes: a separation module having a separation membrane that selectively allows a specific component in a mixed gas to permeate, an internal space being divided by the separation membrane into a first space and a second space; a supply line that supplies the mixed gas at a first prescribed pressure to the first space; a vacuum pump; and a recovery line that is connected at one end to the second space and at the other end to the vacuum pump, whereby the recovery line is depressurized to a second prescribed pressure, and a permeation gas that has permeated the separation membrane is recovered. The second prescribed pressure is determined in such a way that the product of the concentration of the specific component in the permeation gas and the pump efficiency of the vacuum pump is maximized. BRIEF DESCRIPTION OF DRAWINGS

[0008] The objects, features, and advantages of the present application will be further clarified by the following description of embodiments with reference to the accompanying drawings.

[0009] Figure 1 is a diagram for explaining a separation membrane used for a gas separation device of an embodiment of the present application.

[0010] Figure 2 is a diagram for explaining the relationship between the difference between the supply side pressure and the permeation side pressure and the permeation side CO2 concentration.

[0011] Figure 3is a graph for illustrating the relationship between the permeation-side pressure and the product of the permeation-side CO2 concentration and the pump efficiency.

[0012] Figure 4 is a graph for illustrating the relationship between the permeation-side pressure and the product of the permeation-side CO2 concentration and the pump efficiency.

[0013] Figure 5 is a graph for illustrating the relationship between the permeation-side pressure and the permeation-side flow rate.

[0014] Figure 6 is a graph for illustrating the membrane performance of the separation membrane of Figure 1

[0015] Figure 7 is a block diagram schematically showing an example of the main part configuration of a gas separation apparatus according to an embodiment of the present application. DETAILED DESCRIPTION

[0016] Hereinafter, an embodiment of the present application will be described with reference to Figures 1 to 7 An embodiment of the present application is a gas separation apparatus that separates a specific component from a mixed gas using a separation membrane that selectively allows the specific component in the mixed gas to permeate. Hereinafter, an example of separating CO2 in the atmosphere will be described.

[0017] Figure 1 is a graph for illustrating a separation membrane M used in the gas separation apparatus according to an embodiment of the present application. As shown in Figure 1 , the separation membrane M is configured as, for example, a thin film of polydimethylsiloxane (PDMS) that selectively allows CO2 in air containing nitrogen (N2), oxygen (O2), CO2, and the like to permeate.

[0018] The permeation of CO2 is driven by the difference in partial pressure of CO2 between the supply side and the permeation side. The difference in the partial pressure of CO2 is represented by the following equation (i) using the supply side pressure Pi that corresponds to the atmospheric pressure (about 101 kPa), the supply side CO2 concentration xi that corresponds to the CO2 concentration in the atmosphere (about 0.04% or so), the permeation side pressure Po, and the permeation side CO2 concentration xo.

[0019] Difference in partial pressure of CO2 = Pixi - Poxo (i)

[0020] The permeation of CO2 is performed until the difference in the partial pressure disappears.

[0021] Pixi = Poxo (ii)

[0022] Therefore, the permeation side CO2 concentration xo (maximum value) is represented by the following equation (iii).

[0023] xo = Pixi / Po (iii) ​

[0024] Figure 2 is a graph for illustrating the relationship between the difference (Pi - Po) of the supply side pressure Pi and the permeation side pressure Po and the permeation side CO2 concentration xo. In Figure 2 , the change in the permeation side CO2 concentration xo when the supply side is pressurized by the compressor is shown by a broken line on the right side, and the change in the permeation side CO2 concentration xo when the permeation side is depressurized by the vacuum pump is shown by a solid line on the left side.

[0025] As shown in Figure 2 , in the case of separating CO2 in the atmosphere or the like, in the case of separating a specific component at a low concentration from a mixed gas at a low pressure, the object gas (CO2) can be obtained at a higher concentration by depressurizing the permeation side than by pressurizing the supply side. That is, in comparison with pressurizing the supply side pressure Pi from atmospheric pressure by 100 kPa to make the numerator side of the formula (iii) about 2 times, depressurizing the permeation side pressure Po from atmospheric pressure by 100 kPa to make the permeation side close to a vacuum state, to make the denominator side of the formula (iii) close to "0", makes it possible to further increase the permeation side CO2 concentration xo.

[0026] Figure 3 is a graph for illustrating the relationship between the permeation side pressure Po and the permeation side CO2 concentration xo and the pump efficiency η, and shows an example of the pump efficiency η of the vacuum pump when the permeation side is depressurized. The pump efficiency η indicates the work amount of the vacuum pump with respect to the work amount of the power source such as a motor. Figure 2 and Figure 3 As shown in Figure 3 , the closer the permeation side is to a vacuum state, the higher the permeation side CO2 concentration xo is, on the other hand, the closer the permeation side is to a vacuum state, the lower the pump efficiency η is. Thus, the permeation side CO2 concentration xo and the pump efficiency η have so-called trade-off relations. By setting the operating conditions in such a manner that the energy usage amount corresponding to the CO2 recovery amount per unit of membrane separation is minimized, it is possible to efficiently perform the membrane separation.

[0027] Figure 4 is a graph for illustrating the relationship between the permeation side pressure Po and the product xoη of the permeation side CO2 concentration xo and the pump efficiency η. By setting the permeation side pressure Po to a prescribed pressure a, the product xoη of the permeation side CO2 concentration xo and the pump efficiency η reaches a maximum. In this case, it is possible to minimize the energy usage amount corresponding to the CO2 recovery amount per unit of membrane separation.

[0028] Figure 5is a graph for explaining the relationship between the permeation side pressure Po and the permeation side flow rate uo, showing an example of the pump performance (exhaust speed curve) of the vacuum pump. Based on such pump performance, the permeation side flow rate uo at which the permeation side pressure Po reaches the prescribed pressure a (prescribed permeation flow rate b), that is, the exhaust speed (prescribed exhaust speed b) of the vacuum pump can be determined.

[0029] Figure 6 is a graph for explaining the membrane performance of the separation membrane M( Figure 1 ), showing an example of the relationship between the membrane area S and the permeation side flow rate uo of the separation membranes M1 to M4 whose membrane performances are different. The membrane performance of each separation membrane M is indicated by the gas permeation rate (permeation rate) and the selectivity ratio.

[0030] The permeation rate is the permeation amount V per unit membrane area S, time t, and pressure difference (partial pressure difference) ΔP. The permeation rate is expressed, for example, using a unit such as GPU (Gas Permeation Unit) indicating the permeation amount V [cm 2 ] per unit membrane area S [cm 3 ] per unit time t [sec] per unit partial pressure difference ΔP [cmHg (stp)].

[0031] The selectivity ratio is the permeation ratio of each component, and is calculated as the ratio of the permeation rate of each component by the following equations (iv), (v).

[0032] CO2 / N2 selectivity ratio = CO2 permeation rate [GPU] / N2 permeation rate [GPU] (iv)

[0033] CO2 / O2 selectivity ratio = CO2 permeation rate [GPU] / O2 permeation rate [GPU] (v)

[0034] Generally, the higher the permeation rate, the lower the selectivity ratio. With respect to the separation membranes M1 to M4, Figure 6 the permeation rate of the separation membrane M4 is the highest, and the permeation rate of the separation membrane M1 is the lowest. With respect to the selectivity ratio of the separation membranes M1 to M4, the selectivity ratio of the separation membrane M1 is the highest, and the selectivity ratio of the separation membrane M4 is the lowest.

[0035] As shown in Figure 6 , among the separation membranes M2 to M4 that can ensure the prescribed permeation flow rate b, for example, the separation membrane M2 having the highest selectivity ratio is selected, and the necessary membrane area S (prescribed membrane area c) is determined. In the case where the size of the entire device is limited, or in the case where the membrane area S is limited, the separation membrane M that can ensure the prescribed permeation flow rate b can be selected within the range of the available membrane area S, and the necessary membrane area S is determined. In the case where a plurality of vacuum pumps are used, the separation membrane M that can ensure an integral multiple (2b, 3b,...) of the prescribed permeation flow rate b can be selected according to the number of vacuum pumps used, and the necessary membrane area S is determined.

[0036] Figure 7 is a block diagram schematically showing an example of a main part structure of a gas separation apparatus 10 of an embodiment of the present application. As shown in the drawing, the gas separation apparatus 10 is provided with a plurality of separation modules 1 (three separation modules la to lc in this example) arranged side by side, a supply line Ll, recovery lines L2 (L2a to L2c), an exhaust line L3, a pressure sensor 2, and a vacuum pump 3. The gas separation apparatus 10 can be configured from a single separation module 1, or can be configured by connecting a single or a plurality of separation modules 1 arranged side by side in series. Figure 7 Figure 7

[0037] The separation module 1 is configured as a hollow type membrane module or a spiral type module using a separation membrane M of a prescribed membrane area c. The inside space of the separation module 1 is divided into a first space on the supply side and a second space on the permeation side by the separation membrane M as a partition. Figure 1

[0038] One end of the supply line Ll is open to the atmosphere, and the other end is connected to the first space of each separation module 1, and supplies air at atmospheric pressure (supply side pressure Pi) to each separation module 1. A compressor can be provided in the supply line Ll.

[0039] One end of the recovery line L2 is connected to the second space of each separation module 1, and the other end is connected to the vacuum pump 3, whereby the recovery line L2 is reduced in pressure to a prescribed pressure a (permeation side pressure Po), and the permeated gas is recovered from each separation module 1. In the example shown in the drawing, a plurality of recovery lines L2a to L2c are provided which recover the permeated gas from the plurality of separation modules la to lc, respectively. Figure 7

[0040] One end of the exhaust line L3 is connected to the supply side of the separation membrane M in each separation module 1, and the other end is open to the atmosphere, and exhausts the air from which CO2 has been separated from each separation module 1. A vacuum pump can be provided in the exhaust line L3. Figure 1 A pressure sensor 2 which detects the pressure (permeation side pressure) Po of the recovery line L2 is provided in the recovery line L2. In addition, an on-off valve 4 is provided in the recovery line L2c of the separation module lc which is arranged side by side with the separation modules la to lb. In other words, an on-off valve 4 is provided in one recovery line L2n of n separation modules 1 which are connected in series. The on-off valve 4 is opened and closed on the basis of the permeation side pressure Po detected by the pressure sensor 2.

[0041] That is, when the supply side pressure Pi which corresponds to atmospheric pressure changes, the pressure difference between the supply side pressure Pi and the permeation side pressure Po changes, and the permeation of the separation membrane M changes.

[0042] Figure 1 ​​​​​The change in the amount of gas passing through makes it impossible to maintain the permeable side pressure Po at the specified pressure a. Figure 4 Therefore, during the operation of the gas separation device 10 with the on / off valve 4 open, the actual permeable side pressure Po detected by the pressure sensor 2 is monitored. If the permeable side pressure Po cannot be maintained at the specified pressure a, the on / off valve 4 is closed.

[0043] By closing the on / off valve 4, it is possible to switch from a parallel 3-stage (parallel n-stage) configuration consisting of separation modules 1a to 1c to a parallel 2-stage (parallel (n-1)-stage) configuration consisting of separation modules 1a to 1b. In this case, the exhaust velocity (permeable flow rate) uo of the vacuum pump 3 required to maintain the permeable side pressure Po at the specified pressure a increases from... Figure 6 The pressure is reduced from "3b" to "2b" (from "nb" to "(n-1)b"), making it easier to maintain the permeate side pressure Po at the specified pressure a. Therefore, by maintaining the permeate side pressure Po at the specified pressure a, the optimal operating conditions are achieved, minimizing the energy consumption per unit of CO2 recovered from membrane separation.

[0044] The following effects can be achieved by adopting this implementation method.

[0045] (1) The gas separation device 10 comprises: a separation module 1 having a separation membrane M that selectively allows CO2 in the air to pass through, the internal space of which is divided by the separation membrane M into a first space on the supply side and a second space on the permeation side; a supply line L1 that supplies air at atmospheric pressure to the first space; a vacuum pump 3; and a recovery line L2, one end of which is connected to the second space and the other end of which is connected to the vacuum pump 3, wherein the recovery line L2 is depressurized to a predetermined pressure a, and the permeated gas that has passed through the separation membrane M is recovered. Figure 1 , Figure 7 The specified pressure 'a' is determined by maximizing the product of the CO2 concentration xo on the permeable side and the pump efficiency η of vacuum pump 3. Figure 4 By determining the permeate-side pressure Po in this way, the energy consumption corresponding to each unit of CO2 recovery generated by membrane separation can be minimized, thereby achieving efficient membrane separation.

[0046] (2) The exhaust velocity (permeable flow rate) uo of vacuum pump 3 is determined as the specified exhaust velocity b according to the specified pressure a. Figure 5 The gas permeability and membrane area S of the separation membrane M are determined according to the specified exhaust velocity b. Figure 6 That is, based on the pump performance, a specified exhaust velocity b that minimizes the energy consumption per unit of CO2 recovery can be determined, and an appropriate separation membrane M with membrane performance that ensures such a specified exhaust velocity b can be selected, thereby determining the necessary membrane area S.

[0047] (3) The gas separation device 10 also has a pressure sensor 2 for detecting the pressure (through-side pressure) Po of the recovery pipeline L2. Figure 7 The separation module 1 includes separation modules 1a-1b and separation module 1c arranged side by side. Figure 7 The recovery pipeline L2 includes recovery pipelines L2a-L2b for recovering permeated gas from separation modules 1a-1b and recovery pipeline L2c for recovering permeated gas from separation module 1c. Figure 7 Install on / off valve 4 on the recovery pipeline L2c. Figure 7 The opening and closing valve 4 opens and closes based on a specified pressure a and the permeate-side pressure Po detected by pressure sensor 2. This maintains the permeate-side pressure Po at the specified pressure a, thereby minimizing the energy consumption per unit of CO2 recovered from membrane separation and ensuring optimal operating conditions.

[0048] In the above embodiments, utilizing Figure 1 Examples of separating CO2 from the atmosphere have been described, but the mixed gas and specific components to be separated by the gas separation device are not limited to these. The gas separation device is preferably suitable for separating low-concentration specific components from low-pressure mixed gases, such as separating CO2 from the atmosphere.

[0049] It is possible to combine one or more of the above-described embodiments and variations, and to combine the variations with each other.

[0050] Using this invention, gases can be separated efficiently.

[0051] The present invention has been described above in conjunction with preferred embodiments, but those skilled in the art should understand that various modifications and alterations can be made without departing from the scope of the following claims.

Claims

1. A gas separation device (10) characterized by, Possessing: a separation module (1) having a separation membrane (M) that selectively allows a specific component in a mixed gas to pass through, an internal space being divided into a first space and a second space by the separation membrane (M); a supply line (L1) that supplies the mixed gas at a first prescribed pressure to the first space; a vacuum pump (3); and a recovery line (L2) that is connected at one end to the second space and at the other end to the vacuum pump (3), whereby the recovery line (L2) is reduced in pressure to a second prescribed pressure, recovering a permeated gas that has passed through the separation membrane (M), the second prescribed pressure being determined in a manner that the product of the concentration of the specific component in the permeated gas and the pumping efficiency of the vacuum pump (3) is maximized.

2. The gas separation device (10) according to claim 1, characterized in that the exhaust speed of the vacuum pump (3) is determined as a prescribed exhaust speed in accordance with the second prescribed pressure, the gas permeability and the membrane area of the separation membrane (M) are determined in accordance with the prescribed exhaust speed.

3. The gas separation device (10) according to claim 1 or 2, characterized in that a detection section (2) that detects the pressure of the recovery line (L2) is further possessed, the separation module (1) includes a first separation module (1a to 1b) and a second separation module (1c) that are arranged side by side, the recovery line (L2) includes a first recovery line (L2a to L2b) that recovers a permeated gas from the first separation module (1a to 1b) and a second recovery line (L2c) that recovers a permeated gas from the second separation module (1c), an on-off valve (4) is provided in the second recovery line (L2c), the on-off valve (4) is opened and closed based on the second prescribed pressure and the pressure of the recovery line (L2) detected by the detection section (2).

4. The gas separation device (10) according to claim 1 or 2, characterized in that the mixed gas is air containing nitrogen, oxygen, and carbon dioxide, the specific component is carbon dioxide.

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