JP7031214B2 - Helium-enriched gas production method and gas separation system - Google Patents

Description

The present invention relates to a method for producing a helium-enriched gas and a gas separation system for producing a helium-enriched gas.

As a method for separating the raw material gas containing helium into each gas, a membrane separation method using the difference in the permeation rate of the gas with respect to the membrane is known. In this method, usually, by recovering the permeated gas, a high-purity helium-enriched gas, which is a target gas, can be obtained. The permeation rate, which is the permeation volume per unit membrane area, unit time, and unit pressure difference with respect to the helium membrane contained in the raw material gas, is _P'He (unit is × ^10-5 cm ³ (STP) / cm ² · sec. -Can be expressed in cmHg).

Generally, the gas separation membrane is used as a gas separation membrane module in which a gas separation membrane having gas selective permeability is housed in a container provided with at least a gas inlet, a permeation gas discharge port, and a non-permeation gas discharge port. Has been done. The gas separation membrane is installed in the container so that the space on the gas supply side and the gas permeation side is separated. In a gas separation system, it is generally used as a gas separation membrane unit in which a plurality of gas separation membrane modules are combined in parallel in order to obtain a required membrane area. Since the plurality of gas separation membrane modules constituting the gas separation membrane unit share the gas inlet, the impermeable gas discharge port, and the permeation gas discharge port, the gas separation membrane unit is a gas separation membrane module having a substantially large membrane area. Acts as.

Conventionally, a method using a gas separation membrane for helium purification has been adopted. Examples of the helium purification by the gas separation membrane include a method of supplying a raw material gas to a one-stage gas separation membrane unit and taking out a permeated gas as a helium-enriched gas, as shown in FIG. Further, a method in which a gas separation membrane unit is provided by connecting two stages, the permeated gas of the first stage is supplied to the second stage, and the permeated gas of the second stage is taken out as a helium-enriched gas (FIG. 4 of Patent Document 1). , A method of taking out the permeated gas while returning the non-permeated gas of the first stage to the first stage by using the gas separation membrane unit of the first stage (FIG. 5 of Patent Document 1) and the like can be mentioned.
Further, as described in Patent Document 2, helium gas containing at least oxygen as an impurity is continuously extracted from the closed container and permeated through a gas separation membrane to purify the helium gas and circulated and recovered in the closed container. In the gas recovery and purification method, a helium gas recovery and purification method in which the flow rate of the non-permeated gas is controlled so that the oxygen concentration contained in the non-permeated gas in the gas separation membrane is constant has also been proposed.

Japanese Patent Publication No. 2004-518522 Japanese Unexamined Patent Publication No. 2003-212523

In the gas separation system 100 of FIG. 3, when trying to increase the purity of helium in the product gas, the flow rate of the non-permeated gas has to be increased with respect to the flow rate of the permeated gas, which sacrifices the recovery rate. On the other hand, there is a problem that there is a limit to the improvement of helium purity when trying to increase the recovery rate.
Further, the two-step gas separation of FIG. 4 of Patent Document 1 has a problem that the equipment cost is higher than that of the one-step gas separation. Further, as shown in FIG. 5 of Patent Document 1, in order to increase the recovery rate and purity of helium, it is necessary to remove the impure component by low temperature treatment, and there is a problem that the equipment cost is high.
Further, as described in Patent Document 2, the method of circulating and collecting using a closed container has a problem that the processing cost is high in that it takes a long time to collect and a special closed container is required.

Therefore, an object of the present invention is to provide a gas separation system that can eliminate the drawbacks of the above-mentioned prior art.

The present invention is a method for producing a helium-enriched gas that supplies a raw material gas containing helium to one gas separation membrane unit.
The gas separation membrane unit includes at least a gas inlet to which the raw material gas is supplied, a permeated gas discharge port, and a non-permeated gas discharge port.
Provided is a method for producing a helium-enriched gas, in which a part of the permeated gas discharged from the permeated gas discharge port is returned and merged with the raw material gas, and the residue of the permeated gas is taken out as a helium-enriched gas. Is.

Further, the present invention is a gas separation system including one gas separation membrane unit.
The gas separation membrane unit includes at least a gas inlet, a permeated gas discharge port, and a non-permeated gas discharge port.
A supply line for a raw material gas containing helium is connected to the gas inlet of the gas separation membrane unit.
A permeated gas discharge line and a non-permeated gas discharge line are connected to the permeated gas discharge port and the non-permeated gas discharge port of the gas separation membrane unit, respectively.
It has a feedback line that connects the permeated gas exhaust line and the raw material gas supply line to join a part of the permeated gas exhaust gas to the raw material supply gas, and takes out the rest of the permeated gas exhaust gas as helium-enriched gas. It provides a gas separation system.

According to the present invention, the cost of equipment and the like can be reduced as compared with the conventional gas separation system and the method for producing a helium-enriched gas, and a high recovery rate and a high purity of the helium-enriched gas can be easily achieved. Manufacturing method and gas separation system are provided.

FIG. 1 is a schematic view showing the configuration of a gas separation system for helium separation according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the structure of an example of a module constituting the gas separation membrane unit used in the gas separation system of the present invention. FIG. 3 is a schematic view showing the configuration of a conventional gas separation system for helium separation.

Hereinafter, the present invention will be described based on the preferred embodiment thereof with reference to the drawings. First, based on FIGS. 1 and 2, a preferred embodiment of the present invention will be described with respect to a gas separation system 10 which is a preferred embodiment of the present invention and a method for producing a helium-enriched gas using the gas separation system 10. As shown in FIG. 1, the gas separation system 10 of the present embodiment includes one gas separation membrane unit 11. As the gas separation membrane unit 11, for example, as shown in FIG. 2, a module 40 made of a hollow fiber membrane or the like and having a gas separation membrane 30 having gas selective permeability is housed in a casing 31 can be used. In the gas separation membrane unit 11 of the present embodiment, the permeation rate of helium P'He (cm ³ (STP) / cm ² · sec · cmHg) is O ₂ and the permeation rate P'O ₂ (cm ³ (cm 3). It is higher than the permeation rate P'N ₂ (cm ³ (STP) / cm ² · sec · cmHg) of STP) / cm ² · sec · cmHg) and N ₂ . Further, in the gas separation membrane of the gas separation membrane unit 11 in the present embodiment, the permeation rate of helium P'He (cm ³ (STP) / cm ² · sec · cmHg) is CO ₂ permeation rate P'CO ₂ (cm). It is preferably higher than ³ (STP) / ^cm2 · sec · cmHg) and the permeation rate of argon P'Ar (cm ³ (STP) / ^cm2 · sec · cmHg).

The gas separation membrane unit 11 of the present embodiment uses, for example, one gas separation membrane module 40 shown in FIG. 2, or a plurality of these modules 40 are arranged in parallel. The casing 31 in the module 40 has two facing surfaces open to form an opening 32. It should be noted that the opening 32 is for inserting the gas separation membrane 30 into the casing 31, not the opening of the gas separation membrane 30. The gas separation membrane 30 is housed in the casing 31 through the opening 32. When the gas separation membrane 30 is composed of a hollow fiber membrane bundle in which a large number of hollow fiber membranes are bundled so as to coincide in the longitudinal direction, the gas separation membrane 30 is in the accommodation state, and each opening 32 of the casing 31 is provided. It is housed in the casing 31 so that each end of the hollow fiber membrane opens in the vicinity of.

When the gas separation membrane 30 is housed in the casing 31, the gas separation membrane 30 is fixed to the inner wall of the casing 31 by the tube plates 33 and 34 at the positions of both ends in the Y direction, which is the extending direction of the hollow fiber membrane. Has been done. Each opening 32 of the casing 31 is closed by the lids 35 and 36. The lid 35 is provided with a gas inlet 37. On the other hand, the lid 36 is provided with a non-permeable gas discharge port 38. The raw material gas, which is the mixed gas to be separated, is introduced into the module (that is, the unit) from the gas inlet 37 of the lid 35. Of the introduced gas, the gas that has permeated through the gas separation membrane 30 is discharged to the outside of the module (that is, outside the unit) from the permeation gas discharge port 39 provided in the casing 31. On the other hand, the impermeable gas that has not permeated through the gas separation membrane 30 is discharged to the outside of the module (that is, outside the unit) from the impermeable gas discharge port 38 of the lid 36. Further, in some cases, the casing 31 may be provided with a purge gas supply port (not shown). Although the separation membrane module of FIG. 2 has been described above as an example, the present invention can be applied to a separation membrane module having other configurations, for example, a shell feed type module or a spiral type module. It can be applied.

Returning to FIG. 1, at the gas inlet 11a of the gas separation membrane unit 11, a raw material gas supply line 16 for supplying a raw material gas from a mixed gas source (not shown) as a raw material to the gas separation membrane unit 11 is provided. It is connected. On the other hand, the impermeable gas discharge line 18 for discharging the impermeable gas of the gas separation membrane unit 11 to the outside of the system 10 is connected to the impermeable gas discharge port 11c of the gas separation membrane unit 11. Further, a permeation gas discharge line 19 is connected to the permeation gas discharge port 11b of the gas separation membrane unit 11. The impermeable gas discharge line 18 has a valve 22 which is a back pressure regulator for adjusting the pressure on the supply side with respect to the gas separation membrane 12 of the gas separation membrane unit.

The permeated gas discharge line 19 is branched into a feedback line 14 connected to the raw material gas supply line 16 and a take-out line 15 for taking out the permeated gas to the outside of the system 10. A valve 13 is provided at this branching point. The valve 13 is configured to be able to adjust the flow rate of the permeated gas flowing out from the permeated gas discharge line 19 to the return line 14 and the take-out line 15, respectively. By configuring the system 10 in this embodiment, a part of the permeated gas discharged from the permeated gas discharge port is merged with the raw material gas supply line 16, and the rest is used as a helium-enriched gas which is a product gas. It is configured to be removable. The valve 13 may be controlled either automatically or manually. For example, a detection device (not shown) for detecting the helium concentration in the helium-enriched gas taken out as a product gas is provided, and the flow rate in the feedback line 14 and the flow rate in the take-out line 15 are increased or decreased based on the detection result of this detection device. It may be configured to cause.

In the present embodiment, the raw material gas supply line 16 and the permeation gas discharge line 19 are directly connected by the feedback line 14. For example, a closed container for storing gas as described in Patent Document 2 is not provided on the return line 14.

The compression means 21 is interposed and arranged in the middle of the raw material gas supply line 16. The compression means 21 is installed for the purpose of pressurizing the raw material gas and supplying it to the gas separation membrane unit 11. The feedback line 14 is connected to the suction side of the compression means 21 in the raw material gas supply line 16.

Examples of the raw material gas include those containing air in addition to helium. More specifically, examples of the raw material gas include those containing at least one selected from oxygen dioxide, oxygen, nitrogen and argon in addition to helium, and containing oxygen dioxide, oxygen and nitrogen in addition to helium. Those containing oxygen dioxide, oxygen, nitrogen and argon in addition to helium are generally used, and those containing oxygen dioxide, oxygen, nitrogen and argon are preferable. The helium concentration in the raw material gas before mixing with the merging gas from the feedback line is preferably 80 mol% or more, for example, in terms of increasing the purity of the helium-enriched gas taken out by the system of the present embodiment, and 85 mol. It is more preferably% or more, and particularly preferably 89 mol% or more.

According to the system 10 of the present embodiment described above, the raw material gas is enriched with helium by merging with the permeated gas through the return line 14 in the raw material gas supply line 16. Further, the helium-enriched raw material gas (hereinafter, the raw material gas after merging with the returned permeated gas is also referred to as “mixed gas after merging”) is supplied to the gas separation membrane unit 11 to discharge the permeated gas. Helium is further enriched by being discharged as a permeated gas from the outlet 11b. In this way, the helium-enriched gas extracted in the present embodiment has high purity as a product gas. The present inventor has found that in the case of helium purification, the system of the present embodiment can easily achieve high recovery rate and high purity of helium. Preferably, the present embodiment easily has a high recovery rate and high purity of helium without increasing the feedback amount of the permeated gas so much, that is, without increasing the compression power so much, even when a certain membrane area is used. Can be achieved.

One of the features of this embodiment is that a part of the permeated gas discharged from the permeated gas discharge port 11b is taken out of the system 10 as it is as a helium-enriched gas as a product. The helium-enriched gas taken out from the take-out line 15 can be used as a product gas as it is. Of course, the helium-enriched gas taken out from the take-out line 15 may be further refined. Examples of the purification means in that case include an adsorption method and deep cold separation. Further purification of the helium-enriched gas is preferably excluded from the viewpoint of cost.

The helium concentration of the helium-enriched gas taken out from the take-out line 15 is, for example, preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 99 mol% or more.

Further, in the present embodiment, the helium recovery rate is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The helium recovery rate is the ratio of the amount of helium in the helium-enriched gas taken out from the take-out line 15 per hour to the amount of helium in the raw material gas supplied per hour.

Further, in the flow rate of the permeated gas discharged from the permeated gas discharge port 11b, the ratio (recirculation rate) of joining the raw material gas supply line 16 by the return line 14 is 60% or more, that is, the high purity and high recovery rate of helium. It is preferable from the viewpoint of ease of achievement, and more preferably 70% or more.

Further, the flow rate of the raw material gas supplied to the raw material gas supply line 16 and the permeated gas merging with the raw material gas is the flow rate of the permeated gas merging with respect to the flow rate of the mixed gas after merging supplied to the raw material gas supply line 16. Is preferably 50% or more and 80% or less in terms of achieving high purity and high recovery rate and being able to reduce compression power in a certain film area, and more preferably 30% or more and 70% or less. preferable.

The gas separation selectivity P'He / P'N ₂ of the gas separation membrane unit should be 30 or more and 300 or less from the viewpoint that the above purity and recovery rate can be easily realized with a constant film area and low compression power. It is preferably 100 or more and 200 or less, more preferably. From the same viewpoint, the gas separation selectivity P'He / P'O ₂ of the gas separation membrane unit is preferably 3 or more and 30 or less, and more preferably 5 or more and 20 or less. From the same viewpoint, the gas separation selectivity P'He / P'CO ₂ of the gas separation membrane unit is preferably 2 or more and 20 or less, and more preferably 3 or more and 10 or less. From the same viewpoint, the gas separation selectivity P'He / P'Ar of the gas separation membrane unit is preferably 20 or more and 150 or less, and more preferably 30 or more and 100 or less. The gas separation selectivity referred to here is a value at 25 ° C.

The gas separation membrane in the gas separation membrane unit 11 can be appropriately selected according to the type of the supplied raw material gas and the target product gas. As the gas separation membrane, the same ones used so far in the art can be used without particular limitation. For example, examples of the polymer material include rubber-like polymer materials such as silicone resin and polybutadiene resin, and glass-like polymer materials such as polyimide, polyetherimide, polyamide, polyamideimide, polysulfone, polycarbonate and cellulose, as well as zeolite and the like. Examples include ceramics materials. The gas separation membrane is preferably a polymer membrane. The gas separation membrane may be a homogeneous membrane, an asymmetric membrane composed of a homogeneous layer and a porous layer, a microporous membrane, or the like. The form of storing the gas separation membrane in the casing may be any of a plate and frame type, a spiral type, a hollow fiber type and the like. Particularly preferably, the gas separation membrane has an asymmetric structure in which the thickness of the homogeneous layer is 10 nm or more and 200 nm or less, the thickness of the porous layer is 20 μm or more and 200 μm or less, and the inner diameter is 30 μm or more and 500 μm or less. It is a hollow fiber gas separation membrane of group polyimide.

The raw material gas supply line 16 may have a further purification means for helium as a preliminary step for supplying the raw material gas to the gas separation membrane unit 11. For example, such means include water condensation by a cooler or the like, a filter for removing impurities such as organic substances, and the like. Such purification means may be upstream or downstream of the connection point of the return gas 14 in the raw material gas supply line 16, but it is preferable to place it upstream. It is preferable that the system 10 does not have a gas separation membrane unit other than the gas separation membrane unit 11 upstream of the gas separation membrane unit 11 in order to reduce the cost of the system.

Further, from the viewpoint of energy efficiency and the like, generally, the pressure of the gas sent to the gas separation membrane unit 11 made of a hollow fiber membrane is preferably 0.3 MPaG to 1.4 MPaG, and is 0.7 MPaG to 1.0 MPaG. Is more preferable.
Further, the temperature of the gas separation membrane module during operation is preferably in the range of 0 to 150 ° C. and 5 to 80 ° C. for operation efficiency and stable operation.

Although the present invention has been described above based on the preferred embodiment thereof, the present invention is not limited to the above embodiment. For example, in the above embodiment, the permeated gas is branched into a feedback line and a take-out line by a valve, but an arbitrary branching means, for example, an orifice may be used instead of the valve.

Further, in each of the above embodiments, a gas separation membrane unit having a hollow fiber membrane is used as an example of each gas separation membrane unit, but a gas separation membrane unit of another form may be used instead.

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the invention is not limited to such examples.

[Example 1]
Using the gas separation system 10 shown in FIG. 1, the raw material gas, which is a mixed gas containing helium, was separated. A compressor was used as the first compression means 21 in the system 10. As the raw material gas, the one having the composition shown in Table 1 was used. As a module constituting the gas separation membrane unit 11, it is composed of a polyimide hollow fiber membrane having the above-mentioned asymmetric structure and an inner diameter in the above range, and has a P'He of 23 × 10.^-5(Cm³(STP) / cm²・ Sec ・ cmHg), P'CO₂Is 6.6 × 10^-5(Cm³(STP) / cm²・ Sc ・ cmHg), P'O₂Is 2.5 x 10^-5(Cm³(STP) / cm²・ Se · cmHg), P' N₂Is 0.33 × 10^-5(Cm³(STP) / cm²・ Se · cmHg), P' Ar is 0.64 × 10^-5(Cm³(STP) / cm²A gas separation membrane module containing a gas separation membrane of sec · cmHg) in a case was used. Each of these permeation rates is a numerical value at an operating temperature of 25 ° C. (same below).

The number of gas separation membrane modules constituting the gas separation membrane unit 11 was set to one, and the operating temperature of the gas separation membrane unit 11 was set to 25 ° C. The raw material gas is merged with the feedback gas at a flow rate of 20 Nm ³ / h, a temperature of 25 ° C., and a pressure of 0 MPaG. When the gas separation system 10 was operated under the conditions shown in Table 1 and the residue that did not merge with the raw material gas was taken out as the product gas in the permeated gas, the helium purity of the product gas was as shown in Table 1. The helium recovery rate was 99.6% and 99.35 mol%.

[Comparative Example 1]
The gas separation system 100 shown in FIG. 3 was used. As the module constituting the gas separation membrane unit 111, the same gas separation membrane module as that used in Example 1 was used. The number of gas separation membrane modules constituting the gas separation membrane unit 111 was set to one. The operating temperature of the gas separation membrane unit 111 was set to 25 ° C. As the raw material gas, the same one as in Example 1 (the composition is shown in Table 2) was used. The raw material gas is supplied to the gas separation membrane unit 111 at a flow rate of 20 Nm ³ / h, a temperature of 25 ° C., and a pressure of 0.8 MPaG, and the gas separation system 100 is operated under the conditions shown in Table 2, and the permeated gas is used as the product gas. When taken out, as shown in Table 2, the helium purity of the product gas was 94.24 mol%, and the helium recovery rate was 99.99%.

[Comparative Example 2]
The gas separation membrane unit 111 has the same structure, inner diameter, and gas selectivity as the gas separation membrane module used in Comparative Example 1, and has a membrane area of 43% of that of the gas separation membrane module used in Comparative Example 1. A gas separation membrane module made of a certain polyimide hollow fiber membrane was used. Except for this point, the same as in Comparative Example 1. The raw material gas is supplied to the gas separation membrane unit 111 at a flow rate of 20 Nm ³ / h, a temperature of 25 ° C., and a pressure of 0.8 MPaG, and the gas separation system 100 is operated under the conditions shown in Table 3, and the permeated gas is used as the product gas. When taken out, as shown in Table 3, the helium purity of the product gas was 99.12 mol%, and the helium recovery rate was 78.2%.

As described above, according to the present invention, it can be seen that high helium purity and recovery rate can be realized by a one-stage gas separation system. On the other hand, when the permeated gas is not returned to the raw material gas, high helium purity cannot be obtained in order to obtain a high recovery rate, and when an attempt is made to increase the amount of non-permeated gas in order to obtain high purity, As shown in Comparative Example 2, it can be seen that the recovery rate is significantly reduced.

10,100 Gas Separation System 11,111 Gas Separation Membrane Unit 12,112 Gas Separation Membrane 11a, 111a Gas Inlet 11b, 111b Permeation Gas Discharge Port 11c, 111c Non-Permeation Gas Discharge Port 14 Return Line 16,116 Raw Material Gas Supply Line 18 , 118 Non-permeated gas discharge line 19,119 Permeated gas discharge line 40 Gas separation membrane module 21,121 Compression means 22, 122 Back pressure regulator

Claims (7)

A method for producing a helium-enriched gas that supplies a raw material gas containing helium to one gas separation membrane unit.
The gas separation membrane unit includes at least a gas inlet to which the raw material gas is supplied, a permeated gas discharge port, and a non-permeated gas discharge port.
A part of the permeated gas discharged from the permeated gas discharge port is returned and merged with the raw material gas, and the residue of the permeated gas is taken out as a helium-enriched gas.
The gas separation membrane of the gas separation membrane unit is made of polyimide.
The raw material gas contains carbon dioxide or argon in addition to helium gas.
A method for producing a helium-enriched gas, wherein the flow rate of the permeated gas merging with the raw material gas is 50% or more and 80% or less with respect to the flow rate of the mixed gas after merging with the raw material gas. .. The method for producing a helium-enriched gas according to claim 1 , wherein the components other than the helium gas contained in the raw material gas include carbon dioxide and argon . The method for producing a helium-enriched gas according to claim 1 or 2, wherein the components other than the helium gas contained in the raw material gas contain oxygen and nitrogen. The method for producing a helium-enriched gas according to any one of claims 1 to 3 , wherein the helium concentration in the raw material gas is 85 mol% or more. The method for producing a helium-enriched gas according to any one of claims 1 to 4 , wherein the ratio of merging with the raw material gas in the flow rate of the permeated gas discharged from the permeated gas discharge port is 60% or more . The gas separation selectivity of the gas separation membrane of the gas separation membrane unit P'He / P'N ₂ is 30 or more and 200 or less, P'He / P'O2 is 3 or more and 30 or less, and P'He / The method for producing a helium-enriched gas according to any one of claims 1 to 5, wherein P'CO2 is 2 or more and 20 or less, and P'He / P'Ar is 20 or more and 150 or less . A gas separation system consisting of one gas separation membrane unit,
The gas separation membrane unit includes at least a gas inlet, a permeated gas discharge port, and a non-permeated gas discharge port.
A supply line for a raw material gas containing helium is connected to the gas inlet of the gas separation membrane unit.
A permeated gas discharge line and a non-permeated gas discharge line are connected to the permeated gas discharge port and the non-permeated gas discharge port of the gas separation membrane unit, respectively.
It has a feedback line that connects the permeated gas exhaust line and the raw material gas supply line to join a part of the permeated gas exhaust gas to the raw material supply gas, and takes out the rest of the permeated gas exhaust gas as helium-enriched gas. It is done like this
The gas separation membrane of the gas separation membrane unit is made of polyimide.
The raw material gas contains carbon dioxide or argon in addition to helium gas.
The flow rate of the permeated gas merging with the raw material gas is such that the flow rate of the permeated gas merging with the raw material gas is 50% or more and 80% or less with respect to the flow rate of the mixed gas after merging. Separation system.

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