Helium gas recovery and purification device

Abstract

To provide a helium gas recovery and purification device capable of achieving more complete circulation utilization of helium.SOLUTION: A helium gas recovery and purification device for purifying impure helium gas in which helium and air are mixed and discharged from a facility includes: an introduction passage 21 for introducing impure helium gas; a cooling separation tank 3 connected to the introduction passage and configured for cooling the impure helium gas and separating the liquefied air in the gas as liquid air at a first pressure higher than atmospheric pressure; a collection passage 25 connected to the cooling separation tank and configured for recovering helium which holds the gas in the cooling separation tank; and a discharge passage 26 connected to the cooling separation tank for discharging the liquid air. The helium gas recovery and purification device further includes a secondary separation tank 4 connected to the discharge passage and configured for storing liquid air while keeping the liquid air at a second pressure lower than the first pressure and a reflux passage 42 for refluxing the impure helium gas vaporized in the secondary separation tank to the introduction passage.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a helium recovery and purification apparatus using cryogenic separation. [Background technology]

[0002] Helium gas is used in applications such as semiconductor manufacturing and gas chromatography, but because production is limited, it is recovered.

[0003] Conventionally, once helium gas has been vaporized and mixed with other gases, it has been difficult to directly separate it from the mixture. Therefore, a cryogenic separation method has been used in which the entire gas is first cooled and then the two substances are separated using the difference in boiling points of each substance.

[0004] That is, while the boiling point of helium gas is -268.93°C, nitrogen is -195.79°C and oxygen is -183.0°C, both of which are higher than the boiling point of helium gas. For this reason, when a gas containing helium gas is cooled, gases other than helium gas (hereinafter referred to as air in this application), i.e., nitrogen and oxygen, are liquefied before the helium is liquefied and liquefied as liquid air, and the helium gas, which is still in gas form, can be separated. The following documents are prior art documents for such helium recovery devices: [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-311674 [Patent Document 2] Patent Publication No. 2021-80966 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even when separation was performed using this conventional separation device, a component analysis of the liquid air being discarded revealed that some helium gas had been absorbed, revealing that a certain amount of helium gas had been discarded together with the liquid air.

[0007] Conventional cryogenic helium recovery and purification systems had the problem that helium remained in the gas components that were discarded, making it impossible to recycle helium gas with a sufficient helium recovery rate.

[0008] Therefore, an object of the present invention is to provide a helium recovery and purification system that can achieve more complete circulation of helium by recovering additional helium from the liquid air discharged from the helium recovery and purification system and returning this to a circulation path for helium recovery. [Means for solving the problem]

[0009] The present invention, which solves the above-mentioned problems, provides a helium gas recovery and purification device that introduces impure helium gas, which is a mixture of helium and air, a gas other than helium, discharged from a facility that uses helium, and performs helium gas purification, the device comprising: an inlet passage for introducing the impure helium gas; a cooling and separation tank connected to the inlet passage for cooling the impure helium gas and separating the liquefied air in the gas as liquid air at a first pressure higher than atmospheric pressure; a recovery passage connected to the cooling tank for recovering helium maintained as a gas in the cooling and separation tank; and a discharge passage connected to the cooling and separation tank for discharging the liquid air, the helium gas recovery and purification device further comprising: a secondary separation tank connected to the discharge passage for storing the liquid air under a state where the liquid air is maintained at a second pressure lower than the first pressure; and a return passage for returning the impure helium gas vaporized in the secondary separation tank to the inlet passage, thereby re-recovering helium gas from the liquid air. Effect of the Invention

[0010] In the helium gas recovery and purification system of the present invention, the secondary separation tank can be used to recover helium contained in the liquid air in the cooling and separation tank together with the air, and this helium-containing gas can be returned to the helium gas recovery and purification system, thereby improving the recovery rate of helium gas. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing the overall configuration of a helium gas recovery device according to a first embodiment. FIG. [Diagram 2] FIG. 2 is a piping explanatory diagram of the helium gas separator according to the embodiment. [Diagram 3] FIG. 2 is a perspective view showing the actual devices of the cooling separation tank and the secondary separation tank which constitute the helium gas separator. [Figure 4] FIG. 2 is a functional explanatory diagram showing the functions of the helium separator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of a helium gas recovery and purification apparatus according to the present invention will be described with reference to the drawings. The helium gas recovery and purification apparatus is an apparatus for purifying impure helium gas that contains helium gas and gases other than helium gas, such as oxygen and nitrogen (hereinafter referred to as air), which is recovered from a factory that uses helium, such as a semiconductor manufacturing factory, and recovering high-purity purified helium gas from which the air has been removed.

[0013] As shown in FIG. 1, the helium gas recovery and purification device A of this embodiment recovers impure helium gas using a pipeline 10 laid from a helium-using factory F, and stores it in a gas bag 11, which is a storage tank for the impure helium gas.

[0014] Then, when the impure helium gas stored in the gas bag 11 at atmospheric pressure (0.1 MPa) reaches a predetermined amount, this impure helium gas is sent to the compression device 12, where the pressure is increased to 14.7 MPa (first pressure), and sent to the helium gas separator 1 via the introduction line 21.

[0015] A liquid nitrogen supply machine 5 that supplies liquid nitrogen (LN2) from the outside is connected to the helium gas separator 1, and a cooling separation process using liquid nitrogen (LN2) is used to purify the impure helium gas by removing air, and the pure helium gas is recovered through a recovery line 25.

[0016] In this embodiment, the helium gas that is entrained in the liquid air and cannot be recovered by the recovery path 25, as described below, is further returned to the gas bag 11 using the return path 42, and the above purification is repeated, thereby improving the recovery rate of the helium gas.

[0017] Hereinafter, the helium gas separator 1 will be described in detail with reference to Figures 2 to 4. The helium gas separator 1 of this embodiment has a cooling and separation tank 3 that performs primary cooling and separation of helium gas using liquid nitrogen, and a secondary separator 4 that secondarily separates and recovers helium gas that has been entrapped in the liquid air.

[0018] The configuration of the helium gas separator 1 will be described in detail with reference to Figure 2. As shown in the figure, the helium gas separator 1 has a liquid nitrogen storage tank 2 that stores liquid nitrogen LN2 supplied from a liquid nitrogen supply unit 5. This liquid nitrogen storage tank 2 has a cooling separation tank 3 and a plurality of adsorption cylinders 24, 24, etc., which are arranged in a state of being immersed in the liquid nitrogen LN2.

[0019] An inlet line 21 for introducing impure helium gas whose pressure has been increased to 14.7 MPa via the above-mentioned compressor 12 is connected to the cooling and separation tank 3. A first heat exchanger (HXA) 22 arranged on the liquid surface of the liquid nitrogen LN2 and a second heat exchanger 23 arranged in the liquid nitrogen LN2 are arranged on this inlet line 21, and the impure helium gas traveling along this path is cooled to an extremely low temperature (-195.79°C).

[0020] Of the impure helium gas introduced into the cooling and separating tank 3, air, which is mainly composed of oxygen and nitrogen and has a boiling point higher than the temperature of liquid nitrogen, is liquefied. On the other hand, helium gas has a boiling point (-268.93°C) lower than that of liquid nitrogen, so it remains in a gaseous state and is separated in a gaseous state from the liquefied air.

[0021] A plurality of adsorption cylinders 24, 24 are arranged on path 25a of recovery line 25, which recovers the helium gas separated in the cooling separation tank 3. These adsorption cylinders 24, 24 absorb the small amount of air that remains and cannot be liquefied and separated using activated carbon or the like, and the purified helium gas is conducted to the outside of the liquid nitrogen storage tank 2 via recovery line 25, where it is recovered and reused as pure helium gas.

[0022] At this time, in the recovery path 25, the helium gas passes through the first heat exchanger 22 described above, and the cooled helium gas exchanges heat with the impure helium gas flowing through the introduction path 21, so that the impure helium gas can be cooled more efficiently.

[0023] Here, the liquid nitrogen (LN2) stored in the liquid nitrogen storage tank 2 is supplied by a liquid nitrogen supplying machine 5. That is, the liquid nitrogen supplying machine 5 has a liquid nitrogen tank 51 and a supply path 52 connected to the liquid nitrogen storage tank 2, and the amount of liquid nitrogen supplied is controlled by a supply valve 55. Meanwhile, excess liquid nitrogen is discharged to a waste liquid tank 54 through a discharge path 53 controlled by a discharge valve 56.

[0024] Next, the liquid air cooled and liquefied in the cooling and separation tank 3 is discharged to the outside of the liquid nitrogen storage tank 2 through the discharge line 26. This discharge line 26 is connected to the secondary separation tank 4 via a discharge valve 27.

[0025] Liquid air is discharged from cooling and separation tank 3 every time the amount of liquid air accumulated in cooling and separation tank 3 reaches a certain amount. The amount of accumulated liquid air is measured using a purity meter 33 that monitors the purity of helium in cooling and separation tank 3, and the opening and closing of discharge valve 27 is controlled using this measurement result.

[0026] The secondary separation tank 4 is a metal container with a vacuum between its double walls, and unlike the cooling and separation tank 3 which actively cools with liquid nitrogen, it simply has a heat retention function. The liquid air introduced into the secondary separation tank 4 was kept at a pressure of 14.7 MPa inside the cooling and separation tank 3, but the pressure (second pressure) has dropped to atmospheric pressure (0.1 MPa) downstream of the discharge valve 27, and the inside of this secondary separation tank 4 is also kept at atmospheric pressure.

[0027] Then, in secondary separation tank 4, which is now at atmospheric pressure, a part of the liquid air introduced from discharge line 26 vaporizes. At this time, the helium gas that was not completely recovered in cooling and separation tank 3 and was entrapped in the liquid air is also released as a gas to the outside of the liquid air, and accumulates above secondary separation tank 4 together with the vaporized air.

[0028] The evaporated air containing helium gas is returned to the gas bag 11 via the return line 42. Then, it is sent again to the cooling and separating tank 3, where the above-mentioned separation process is repeated.

[0029] Any liquid air remaining in the secondary separation tank 4 is discharged to the atmosphere via a waste line 44 by a waste valve 45. The waste valve 45 is attached to the middle of the waste line 44 and is linked to a sensor 46 that monitors the amount of liquid air in the secondary cooling tank 4. Each time a predetermined amount of liquid air accumulates in the secondary separation tank 4, the waste valve 45 opens to perform this disposal operation.

[0030] Fig. 3 is a perspective view of the actual cooling and separation tank 3 and secondary separation tank 4, and Fig. 4 is a diagram illustrating their functions. Using Fig. 3 and Fig. 4, the effects of the cooling and separation tank 3 and secondary separation tank 4 will be described in detail below. Note that the helium gas separator 1 can be designed to have any number of cooling and separation tanks 3 and secondary separation tanks 4, but for simplicity, the following description will be given assuming that the apparatus has one of each.

[0031] The cooling and separating tank 3 is a cylindrical metal bottle 31, which is entirely immersed in liquid nitrogen. An inlet path 21 for impure helium gas (He+Air) and a recovery path 25 for helium gas (He) are connected to the ceiling of the bottle 31. An inlet pipe 32 for the inlet path 21 and a recovery pipe 34 for the recovery path 25 protrude into the bottle 31.

[0032] Here, the gaseous state is maintained within bottle 31, and the separated helium gas (He) is led to and recovered outside bottle 31 through recovery line 25. Although not shown in Figures 3 and 4, a plurality of adsorption cylinders 24, 24 are arranged on recovery line 25, and refined pure helium is recovered outside liquid nitrogen storage tank 2 through recovery line 25 (see Figure 2).

[0033] Meanwhile, among the impure helium gas discharged from the lower end 32 of the introduction pipe 32, air having a boiling point higher than the temperature of liquid nitrogen (-195.79°C) is liquefied and accumulates as liquid air at the bottom 31B of the bottle 31. Meanwhile, helium gas having a boiling point lower than the temperature of liquid nitrogen (-268.93°C) remains in a gaseous state and accumulates in the space 31A above the liquid surface of the bottle 31 and is recovered from the recovery pipe 34 located at the upper part inside the bottle 31.

[0034] During this cooling and separation process, a phenomenon occurs in which some of the unliquefied helium gas is trapped within the liquid air (see Figure 4). As mentioned above, this helium gas exists in a gaseous state, but it is speculated that when the air is liquefied, a phenomenon occurs in which fine gas particles are trapped within the liquid air.

[0035] It is difficult to completely recover the helium gas contained in the impure helium gas only by the separation operation in the cooling and separating tank 3. For this reason, as shown in this embodiment, a secondary separating tank 4 is used to recover the helium gas again from the liquid air.

[0036] Within bottle 31, exhaust pipe 35 connected to exhaust path 26 for liquid air hangs down from the ceiling, and the lower end 35 is located near bottom 31B of bottle 31 and is exhausted to the outside of bottle 31. As described above, the liquid air exhausted by exhaust path 26 contains some helium gas trapped therein.

[0037] A sensor tube 36 connected to a helium gas purity meter 33 is provided inside the bottle 31, and the timing of discharging the liquid air is determined based on the detection results of this purity meter 33, which is also used to measure the amount of stored liquid air.

[0038] Inside bottle 31, a high pressure (14.7 MPa) is maintained by the impure helium gas itself flowing in under high pressure, and by opening exhaust valve 27 (see Figures 2 and 4) linked to purity meter 33, this pressure presses against the liquid air surface, and the liquid air is discharged from bottle 31 through exhaust pipe 35 by this pressure.

[0039] The discharged liquid air is sent via discharge path 26 to secondary separator 4 arranged outside liquid nitrogen storage tank 2 (see FIG. 2). Secondary separator 4 is a cylindrical heat-retaining container 41 with a vacuum layer 41c between outer shell 41a and inner shell 41b, and has the function of maintaining to some degree the temperature of the liquid air sent from cooling separation tank 3. A liquid air pouring pipe 47 connected to discharge path 26 protrudes from the top surface inside heat-retaining container 41.

[0040] On the other hand, since the discharge path 26 does not have a compressor that provides the liquid air with the pressure (14.7 MPa) in the cooling and separation tank 3, the pressure of the liquid air decreases and becomes approximately atmospheric pressure (0.1 MPa) inside the thermal insulation container 41 of the secondary separator 4.

[0041] As a result, most of the liquid air introduced into the insulated container 41 from the pouring pipe 47 drips down in a liquid state and accumulates at the bottom 41B of the insulated container 41, but at the same time, some of it evaporates due to the increase in pressure, and the helium gas that was trapped in the liquid air mentioned above escapes to the outside, and impure helium gas (He+Air), a mixture of air and helium gas, accumulates in a gaseous state in the space 41A above the liquid surface of the insulated container 41.

[0042] The extracted impure helium gas is then recovered in the return path 42 through a return port 48 that opens in the ceiling of the thermal insulation container 41 above the liquid air pouring pipe 47. The recovered impure helium gas is returned to room temperature using a heat exchanger 43 (see FIG. 2) and then sent to the gas bag 11, where it is sent again to the helium gas separator 1 and treated in the cooling and separation tank 3 described above.

[0043] Liquid air remaining in bottom 41B of thermal insulation container 41 is discharged outside thermal insulation container 41 via exhaust path 44 having exhaust valve 45 when a predetermined amount accumulates, and is released into the atmosphere by raising the temperature.

[0044] As described above, according to the helium separation apparatus A of the present embodiment, the secondary separation tank 4 can be used to recover helium gas contained in the liquid air separated and discharged from the cooling and separation tank 3 together with air, and the helium gas-containing gas can be returned to the cooling and separation tank 3 via the gas bag 11, thereby improving the recovery rate of the helium gas.

[0045] In this embodiment, the pressure in the cooling separation tank 3 is 14.7 MPa, and the pressure in the secondary separation tank 4 is 0.1 MPa (atmospheric pressure), but these are not limited to these values, and each pressure can be set arbitrarily as long as the latter pressure is lower than the former pressure.

[0046] In addition, in this embodiment, the secondary separation tank 4 is a heat-insulating container, and is not a container that actively cools, but it may be a container that is equipped with a cooling device and that performs temperature control.

[0047] Furthermore, in this embodiment, the impure helium gas recovered in the secondary separation tank 4 is configured to be returned to the gas bag 11, but it may be configured to be returned directly to the cooling and separation tank 3. [Explanation of symbols]

[0048] A Helium gas recovery and purification equipment F Factory (Facilities using helium) 1 Helium gas separator 2 Liquid nitrogen storage tank 3 Cooling separation tank 4 Secondary separation tank 5 Liquid nitrogen supply machine 6 Linear drive motor 11 Gas Bag 21 (Impurity helium gas) introduction path 25 (Refined helium gas) recovery line 26 Exhaust passage (for liquid air containing helium gas) 42 (Impurity Helium Gas) Circulation Path 44 (Helium-free liquid air) waste passage

Claims

1. In a helium gas recovery and purification device, impure helium gas, which is a mixture of helium and air other than helium and is discharged from a facility that uses helium, is introduced and helium gas is purified. the cooling and separation tank connected to the inlet passage for cooling the impure helium gas and separating the liquefied air in the gas as liquid air at a first pressure higher than atmospheric pressure; a recovery passage connected to the cooling tank for recovering the helium gas held in the cooling and separation tank; and a discharge passage connected to the cooling and separation tank for discharging the liquid air, The helium gas recovery and purification apparatus further comprises a secondary separation tank connected to the discharge line, the secondary separation tank storing the liquid air under a second pressure lower than the first pressure, and a return line for returning the impure helium gas vaporized in the secondary separation tank to the inlet line, wherein the helium gas recovery and purification apparatus re-recovers helium gas from the liquid air.

2. 2. The helium gas recovery and purification system according to claim 1, wherein the secondary separation tank is a thermal insulation container.

3. 2. The helium gas recovery and purification system according to claim 1, wherein the second pressure in the secondary separation tank is atmospheric pressure.

4. 4. The helium gas recovery and purification system according to claim 1, further comprising a gas bag disposed in the middle of the inlet path for temporarily storing the impure helium gas from the facility, and a return path from the separation tank of the secondary separator is connected to the gas bag.

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