JP4044339B2 - Helium gas recovery and purification method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for removing impurities from helium containing an impure gas such as air and recovering and purifying the helium gas.
[0002]
[Prior art]
Helium is conventionally used as a coolant. For example, gaseous helium is used as a coolant for manufacturing an optical fiber, and liquid helium is used for cooling a superconducting magnet.
[0003]
On the other hand, recently, taking advantage of an inert gas having a light specific gravity after hydrogen, it has been used for filling balloons, balloons for communication / broadcasting, and airships for earth observation. Air balloons are usually filled with high-concentration helium gas of 99% or more, but the helium concentration decreases by several percent due to air leakage into the balloon with the passage of time, and the performance of the airship deteriorates. There is a fear. Therefore, when the helium concentration in the balloon is reduced to, for example, about 95%, it is necessary to collect helium gas, purify it to high purity, and refill it.
[0004]
As an operation method for recovering helium gas containing impure gas such as air and purifying it to high purity helium gas, Japanese Patent Laid-Open No. 2-157101 discloses a separation membrane module incorporating a selectively permeable polymer separation membrane and a deoxo reaction. A method of combining an apparatus and an adsorber is disclosed. On the other hand, JP-A-4-280806, JP-A-4-293512, JP-B-5-80242, and JP-B-6-24604 disclose a method using a combination of a separation membrane method and a PSA method. However, these methods require a large facility such as a PSA apparatus, and the operation method is complicated. For example, it is difficult to say that these methods are suitable as a method for recovering and purifying the helium gas of the airship.
[0005]
[Problems to be solved by the invention]
The present invention does not require a large-sized devices, such as a PSA, the operation method is an object to provide a f helium gas recovery and purification method capable of obtaining a simple and high helium gas recovery.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention takes the following technical means. That is, in the method for recovering and purifying helium gas according to the present invention, helium gas containing at least oxygen as an impurity is continuously extracted from the sealed container, and the helium gas is purified by permeating through the gas separation membrane, and circulated and collected in the sealed container. In the method for recovering and purifying helium gas, helium gas containing at least oxygen as an impurity is extracted from the initial stage to the last stage of the recovery and purification at a constant flow rate and pressurized to a constant pressure and introduced into the gas separation membrane, In addition , the non-permeate gas flow rate is controlled so that the concentration of oxygen contained in the non-permeate gas in the gas separation membrane is constant, so that the non-permeate gas flow rate is gradually reduced from the initial stage of recovery and purification to the end stage. It is said.
[0007]
In the present invention, in order to make the helium gas recovery and purification apparatus compact, one compressor is used, tanks are eliminated, and only the gas separation membrane is used to simplify the apparatus. Then, by measuring the oxygen concentration in the non-permeating gas and controlling the amount of gas, the non-permeating gas becomes the minimum amount of gas so that a high helium gas recovery rate can be continuously obtained. In addition, the product helium gas after helium gas recovery and purification is circulated to the user as it is, and in order to increase the replacement speed of helium gas, tanks are eliminated so that helium gas does not stay in the recovery and purification system. ing.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described specifically by taking, for example, a method for recovering and purifying helium gas in a balloon of an airship having a capacity of about 5000 m ³ as an example. The balloon of an airship is filled with helium gas with a purity of 99% or more. When this airship is suspended as a stratosphere platform, air and moisture in the atmosphere leak into the balloon and the purity of the helium gas in the balloon is 95. % Or less. FIG. 1 is a flowchart showing an outline of a process according to the present invention for recovering and purifying helium gas in a balloon containing air as an impure gas.
[0009]
First, helium gas in a balloon containing 5% air as an impure gas and having a purity reduced from 99% to 95% is continuously extracted from the balloon 1 at 100 m ³ / h as a recovered gas. This recovered gas is used as a raw material gas and pressurized by the compressor 2 to a pressure of less than 1.1 MPa, for example, 1.05 MPa. The pressurized helium gas is cooled by the cooler 3 at the outlet of the compressor, moisture in the gas is condensed by the drain separator 4, drained, and discharged out of the system. At this time, the pressure at the outlet of the compressor is detected by the pressure gauge 6, and the pressure is controlled so that the pressure is always less than 1.1 MPa at a constant pressure, and excess gas is returned to the inlet side of the compressor through the recycle valve 5. The water pressure-cooled by the compressor can be condensed and drained, but no more water can be removed, so a separate refrigeration dryer or heat regeneration dryer can be installed at the cooler outlet if necessary. It may be installed to further remove moisture.
[0010]
The dehumidified raw material gas is then introduced into the gas separation membrane module 7, where only helium gas and a small amount of moisture that easily permeate preferentially permeate through the hollow fiber-like separation membrane and are recovered to the permeation side. The gas separation membrane used here is made of a polymer material such as polyimide, polysulfone, or cellulose acetate. In this gas separation membrane module, separation membranes molded into hollow fibers having an inner diameter of 0.1 to 0.5 mm are bundled and incorporated in the module. Since helium molecules are much easier to diffuse in the separation membrane than nitrogen and oxygen molecules, they penetrate to the inside when pressurized from the outside of the hollow fiber and to the outside when pressurized from the inside. The permeated helium gas becomes a high-purity gas of 99.5% or more, is discharged from the module, and is sent to the balloon as it is.
[0011]
In the present invention, when the gas separation membrane module 7 separates helium gas, the flow rate of the non-permeable gas is controlled so that the oxygen concentration contained in the non-permeable gas in the gas separation membrane is constant. It is said. That is, when the helium gas is separated by the gas separation membrane module 7, the oxygen concentration in the non-permeate gas is measured by the oxygen concentration meter 8, and the pressure is reduced by the pressure reducing valve 9 so that the concentration becomes constant at, for example, 10%. The flow rate is controlled by the control valve 10 after the pressure is reduced.
[0012]
Here, for example, when helium gas containing 5% air at the initial stage of recovery and purification is introduced into the gas separation membrane module 7 at 100 m ³ / h, if the purity of helium that permeates to the permeate side is 99.5%, In order to make the concentration of oxygen contained in the permeated gas 10%, the flow rate of the non-permeated gas may be controlled to 9.6 m ³ / h. On the other hand, helium gas having a purity of 99.5% that has permeated to the permeate side becomes a purified gas (permeate gas) and is circulated to the balloon 1 at 90.4 m ³ / h. The balloon is separately supplemented with high-purity helium gas corresponding to 9.6 m ³ / h discarded as a non-permeating gas from the gas separation membrane module.
[0013]
In this way, the inside of the balloon is replaced with the purified gas and the newly supplied helium gas, and the helium concentration in the balloon increases. Therefore, for example, when helium gas containing 3% air is introduced into the gas separation membrane module 7 at 100 m ³ / h in the middle of recovery and purification, if the purity of helium that permeates to the permeate side is 99.5%, the non-permeate gas If the flow rate of the gas is controlled to 5.3 m ³ / h, the oxygen concentration contained in the non-permeating gas is kept constant at 10%.
[0014]
In this way, when the balloon is finally completely replaced with the purified high-purity helium gas having a concentration of 99.5% or more, the amount of non-permeate gas of the gas separation membrane becomes infinitely zero. The instantaneous helium gas recovery rate is 100%. Therefore, when the concentration of helium gas in the source gas extracted from the balloon at the initial stage of recovery is 95%, the instantaneous helium gas recovery rate in the gas separation membrane module is about 95%, and helium gas is used as a piston flow in the balloon. Assuming that it was replaced, the replacement was completed after 5000/100 = 50 hours, and the total recovery of helium gas was 97.5%.
[0015]
Fig. 2 shows the amount of raw material gas at the gas separation membrane inlet, the concentration of helium gas in the raw material gas, the amount of purified gas (permeated gas amount) according to the recovery and purification elapsed time when the piston flow is ideally replaced with new gas. The time change of the amount of non-permeating gas and the recovery rate of helium gas is shown. From this result, it is possible to obtain an almost intermediate value between the recovery rate of helium gas obtained at the initial stage of recovery and the recovery rate of 100% regardless of the amount of recovery and purification gas and the recovery and purification time as the total recovery rate of helium gas. I understand.
[0016]
【The invention's effect】
In the present invention, when the concentration of high-purity helium gas filled in a balloon of an airship is reduced by, for example, 4% from 99% to 95% due to atmospheric leakage, the air is removed. This method is preferably used. That is, the gas separation membrane used in the present invention exhibits a high separation ability when purifying a gas having a relatively high purity compared to an adsorbent such as zeolite, particularly a highly permeable gas such as helium gas. The operation method does not require switching of the gas flow as in the PSA operation using zeolite, and therefore requires no moving parts and has a long mechanical life.
[0017]
Also, when helium gas is continuously collected and purified from the point of use, such as a balloon, if the flow rate is controlled while measuring the concentration of impure gas in the non-permeate gas, for example, the oxygen concentration, the helium gas flows between the balloon and the collection and purification device. Circulation increases the purity of the raw material gas, so the amount of waste gas gradually decreases. Therefore, if the amount of gas is controlled so that the concentration of impure gas in the non-permeating gas becomes constant, the recovery rate of helium gas can be kept high.
[0018]
According to the present invention, it is possible to recover and purify helium gas having a purity of 99.5% or more from helium gas containing air as an impure gas with a high recovery rate regardless of operation time by a compact apparatus and simple operation. it can.
[Brief description of the drawings]
FIG. 1 is a schematic flow chart showing an example of a method for recovering and purifying helium gas according to the present invention.
FIG. 2 is a graph showing the time course of helium gas recovery and purification according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Balloon 2 Compressor 3 Cooler 4 Drain separator 5 Recycle valve 6 Pressure gauge 7 Gas separation membrane module 8 Oxygen concentration meter 9 Pressure reducing valve 10 Control valve

Claims (1)

Continuously extracted helium gas from the sealed container containing at least oxygen as an impurity, was purified helium gas by transmitting gas separation membrane, in the recovery method for purifying helium gas circulating recovered in the sealed container, at least as an impurity Helium gas containing oxygen is withdrawn from the closed vessel at a constant flow rate from the beginning to the end of recovery and purification, pressurized to a constant pressure, introduced into the gas separation membrane, and contained in the non-permeating gas in the gas separation membrane. A method for recovering and purifying helium gas, characterized by controlling the flow rate of the non-permeate gas so that the oxygen concentration is constant, and gradually decreasing the flow rate of the non-permeate gas from the initial stage of recovery and purification to the end stage .

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