System for enriching and purifying helium-3 in liquid helium

Abstract

The utility model relates to the technical field of isotope separation, in particular to a system for enriching and purifying helium-3 in liquid helium. The system comprises a refrigeration unit and an enrichment unit, the refrigeration unit is of a nested structure and sequentially comprises an external Dewar (1), a cold shield (2) and an internal Dewar (3) from outside to inside; the enrichment unit comprises a heater (4) and a shell (5); the shell (5) comprises a linear section and an arc-shaped section which are connected from top to bottom; and the heater (4) is arranged in the cavity of the shell (5) and corresponds to the linear section. The system for enriching helium-3 from liquid helium below the helium-4 superfluid transformation temperature is designed by enriching firstly and then rectifying based on the superfluid characteristic of helium-4 and applying the thermomechanical effect of superfluid helium, it is predicted that the helium-3 concentration is increased from 10 <-7 > magnitude order to 10 <-3 > magnitude order, and subsequent helium-3 purification is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of isotope separation, and in particular to a system for enriching and purifying helium-3 in liquid helium. Background Art

[0002] Helium-3 is a rare isotope of helium. Its boiling point is 3.19K at normal pressure and its superfluid transition temperature is 2.6mK. It is the core working fluid of mK-class dilution refrigerators, clean nuclear fusion and other devices. It is an indispensable strategic material for the development of quantum computers in my country and the long-term safe acquisition of fusion energy. Helium-3 in nature is formed by the β decay of tritium nuclei. Its natural abundance is very small. The content of helium-3 in the atmosphere is about 10 -12 In some helium-containing natural gases, the content of helium-3 is about 10 -10 ~10 -9 At present, my country's helium-3 is completely dependent on imports, but after 2015, the United States no longer officially sells helium-3, which has a great impact on my country's helium-3 supply. Therefore, it is very important to study domestic industrial helium-3 enrichment equipment.

[0003] However, the isotope separation methods currently in common use all require a large amount of raw materials, have a complex operating process, and have low separation efficiency, making them unsuitable for industrial separation of helium-3. Currently, there is no industrial application of helium-3 extraction at home or abroad.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] Aiming at the problem that helium-3 is difficult to purify due to its low concentration, the present invention provides a system for enriching and purifying helium-3 from liquid helium. By first enriching and then rectifying, based on the superfluidity of helium-4 and utilizing the thermomechanical effect of superfluid helium, a system for enriching helium-3 from liquid helium below the superfluid transition temperature of helium-4 is designed. It is expected that the helium-3 concentration will be reduced from 10 -7 The level is increased to 10 -3 This is beneficial for the subsequent purification of helium-3.

[0006] Based on this, the present invention has the following technical solutions:

[0007] In a first aspect, the present invention first provides a system for enriching and purifying helium-3 in liquid helium, comprising: a refrigeration unit and an enrichment unit; the refrigeration unit is a nested structure, and comprises, from the outside to the inside, an external dewar (1), a cold shield (2) and an internal dewar (3);

[0008] The enrichment unit comprises a heater (4) and a shell (5); the shell (5) comprises a straight segment and an arc segment connected from top to bottom; the heater (4) is placed in the cavity of the shell (5) and corresponds to the straight segment.

[0009] Preferably, the material of the shell (5) in the arc section has a thermal conductivity of 8 W / m·K or more at 1.0 K-1.5 K.

[0010] The present invention finds that by controlling the thermal conductivity of the material of the arc segment, the temperature difference between the arc segment and the straight segment in the shell (5) can be more effectively controlled. When the liquid helium in the shell (5) is below the superfluid transition temperature, helium-3 and helium-4 will flow in opposite directions according to the thermomechanical effect of the superfluid helium, thereby achieving the effect of enriching helium-3 at the lower end of the shell (5).

[0011] Further preferably, the material of the shell (5) in the arc section includes copper or aluminum alloy.

[0012] Preferably, the enrichment unit further comprises a first pipeline (7), a second pipeline (9), a third pipeline (10) and a fourth pipeline (12), wherein the first pipeline (7) is used to introduce liquid helium, and the second pipeline (9) is used to discharge the superfluid helium-4 in the shell (5) into the internal dewar (3) after the enrichment and purification is completed; the third pipeline (10) is used to discharge helium vapor, and the fourth pipeline (12) is used to discharge a mixture of helium-3 and helium-4;

[0013] In the present invention, the first pipeline (7), the second pipeline (9), the third pipeline (10) and the fourth pipeline (12) are all connected to the shell (5).

[0014] And / or, the refrigeration unit further comprises a fifth pipeline (8), a sixth pipeline (11), a seventh pipeline (13) and an eighth pipeline (14), wherein the fifth pipeline (8) is used for introducing liquid helium, the sixth pipeline (11) is used for discharging helium vapor, the seventh pipeline (13) is used for introducing liquid nitrogen, and the eighth pipeline (14) is used for discharging nitrogen vapor.

[0015] In the present invention, the fifth pipeline (8) and the sixth pipeline (11) are both connected to the internal Dewar (3); and the seventh pipeline (13) and the eighth pipeline (14) are both connected to the upper external Dewar (1).

[0016] More preferably, a valve V1 is installed on the first pipeline (7), a valve V3 is installed on the second pipeline (9), a valve V4 is installed on the third pipeline (10), a valve V6 is installed on the fourth pipeline (12), a valve V2 is installed on the fifth pipeline (8), a valve V5 is installed on the sixth pipeline (11), a valve V7 is installed on the seventh pipeline (13), and a valve V8 is installed on the eighth pipeline (14).

[0017] Preferably, the shell (5) is also connected to a ninth pipeline (6), and the ninth pipeline (6) is used for measuring temperature and pressure.

[0018] Preferably, the internal Dewar (3) is also connected to a tenth pipeline (15), and the tenth pipeline (15) is used for measuring temperature and pressure.

[0019] Preferably, the system further comprises a separation unit, which is connected to the fourth pipeline (12), and is used for separating helium-3 and helium-4.

[0020] Preferably, the system further comprises a recovery and liquefaction unit, which is connected to the third pipeline (10) and the sixth pipeline (11), and is used for reducing the pressure and evaporating the helium discharged from the third pipeline (10) and the sixth pipeline (11) and then liquefying it again.

[0021] In the present invention, the outlets of the sixth pipeline (11) and the eighth pipeline (14) are both connected to a vacuum pump, the former being used to extract a mixture of helium-4 and helium-3; and the latter being used to decompress and evaporate the liquid helium or helium-4 in the internal Dewar (3).

[0022] In a second aspect, the present invention provides a method for enriching and purifying helium-3 in liquid helium using the above system, comprising:

[0023] S1: Liquid nitrogen is charged into the external Dewar (1) through the seventh pipe (13) for pre-cooling. When liquid accumulates in the external Dewar (1), the temperature of the external Dewar (1) is lowered to a liquid nitrogen temperature range, and nitrogen vapor is discharged through the eighth pipe (14);

[0024] S2: evacuating the interior of the cold shield (2);

[0025] S3: filling the shell (5) with liquid helium through the first pipe (7), and discharging helium vapor through the third pipe (10); when liquid helium accumulates in the shell (5), the shell (5) is cooled to a liquid helium temperature zone, and after the shell (5) is filled with liquid helium, the liquid helium stops flowing into the first pipe and stops being discharged from the third pipe (10);

[0026] At the same time, liquid helium is filled into the internal dewar (3) through the fifth pipe (8), and helium vapor is discharged through the sixth pipe (11); when liquid helium is accumulated in the internal dewar (3), the internal dewar (3) is cooled to a liquid helium temperature zone; when the volume of the liquid helium accumulated in the internal dewar (3) accounts for 2 / 5 to 4 / 5 of the total volume of the internal dewar (3), the liquid helium in the internal dewar (3) is decompressed and evaporated, so that the internal dewar (3) is cooled to 1.0 to 1.5 K and the temperature is maintained, at which time the liquid helium in the shell (5) is cooled to the same temperature as the internal dewar (3);

[0027] S4: Turn on the heater (4) to start enrichment;

[0028] S5: after the enrichment is completed, the mixture of helium-4 and helium-3 is discharged through the fourth pipeline (12), and the mixture of helium-4 and helium-3 in a normal fluid state is separated from the helium-4 in a superfluid state;

[0029] S6: After the separation is completed, the discharge of the normal fluid helium-4 and helium-3 mixture is stopped, and the remaining superfluid helium-4 in the shell (5) is discharged into the internal dewar (3), thus completing a separation cycle.

[0030] Preferably, in S4, the heater (4) controls the temperature of the straight section in the shell (5) to be no higher than 2.17K during heating.

[0031] Preferably, the method for enriching and purifying helium-3 in liquid helium comprises:

[0032] S1: first open valves V7 and V8, and fill the external Dewar (1) with liquid nitrogen for pre-cooling through the seventh pipe (13). When liquid accumulates in the external Dewar (1), the temperature of the external Dewar (1) is reduced to the liquid nitrogen temperature range, and nitrogen vapor is discharged through the eighth pipe (14);

[0033] S2: Using a vacuum pump to evacuate the inside of the cold shield (2);

[0034] S3: opening valves V1 and V4, and filling liquid helium into the shell (5) through the first pipe (7), and discharging helium vapor through the third pipe (10); when liquid helium accumulates in the shell (5), the shell (5) is cooled to a liquid helium temperature zone, and after the shell (5) is filled with liquid helium, V1 and V4 are closed;

[0035] At the same time, valves V2 and V5 are opened, and liquid helium is filled into the internal dewar (3) through the fifth pipe (8), and helium vapor is discharged through the sixth pipe (11); when liquid helium is accumulated in the internal dewar (3), the internal dewar (3) is cooled to the liquid helium temperature zone; when the volume of the liquid helium accumulated in the internal dewar (3) accounts for 2 / 5 to 4 / 5 of the total volume of the internal dewar (3), the liquid helium in the internal dewar (3) is decompressed and evaporated, so that the internal dewar (3) is cooled to 1.0 to 1.5 K, and the temperature is maintained. At this time, the liquid helium in the shell (5) is cooled to the same temperature as the internal dewar (3);

[0036] S4: Turn on the heater (4) to start enrichment;

[0037] S5: After the enrichment is completed, the valve V6 is opened to discharge the mixture of helium-4 and helium-3 through the fourth pipeline (12), and the mixture of helium-4 and helium-3 in a normal fluid state is separated from the superfluid helium-4;

[0038] S6: After the separation is completed, V6 is closed to stop discharging the normal fluid helium-4 and helium-3 mixture; V3 is opened, V2 is reduced, and the remaining superfluid helium-4 in the shell (5) is discharged into the internal dewar (3), thus completing a separation cycle.

[0039] S7: Close V3, open V1 and V4, allow liquid helium to enter the shell (5), and after the shell is filled with liquid, close V1 and V4, so that the liquid helium in the shell (5) is cooled to the same temperature as the internal Dewar (3) through heat conduction of the arc segment structure, and repeat steps S4 to S6.

[0040] In the present invention, those skilled in the art can use existing well-known technologies to separate helium-4 and helium-3 in a normal flow state.

[0041] Preferably, the mixture of helium-4 and helium-3 in the normal flow state in S5 enters the packed cryogenic distillation tower through the fourth pipeline (12), and finally obtains gaseous helium-3 at the top of the distillation tower; and obtains liquid helium-4 at the bottom of the distillation tower.

[0042] In the present invention, the separated helium-4 can be recovered and stored and transported after being reliquefied using the recovery and liquefaction unit.

[0043] Based on the above technical solution, the beneficial effects of the present invention are:

[0044] The present invention provides a system and method for enriching and purifying helium-3 from liquid helium. The method of enriching first and then distilling is adopted. Based on the superfluid characteristics of helium-4 and the thermomechanical effect of superfluid helium, a system for enriching helium-3 from liquid helium below the superfluid transition temperature of helium-4 is designed. It is expected that the concentration of helium-3 can be increased from 10 -7 The level is increased to 10 -3 This is beneficial for the subsequent purification of helium-3. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 It is a schematic diagram of the system layout for enriching and purifying helium-3 in Example 1 provided by the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Unless otherwise specified, all raw materials used in the examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0049] Example 1

[0050] This embodiment provides a system for enriching and purifying helium-3 in liquid helium (see the schematic diagram of the system layout for details) Figure 1 ), which includes: a refrigeration unit, an enrichment unit, a separation unit and a recovery liquefaction unit;

[0051] The refrigeration unit is a nested structure, and comprises, from the outside to the inside, an external dewar (1), a cold shield (2), an internal dewar (3), a fifth pipeline (8), a sixth pipeline (11), a seventh pipeline (13), an eighth pipeline (14) and a tenth pipeline (15); the fifth pipeline (8), the sixth pipeline (11) and the tenth pipeline (15) are all connected to the internal dewar (3); the seventh pipeline (13) and the eighth pipeline (14) are both connected to the upper external dewar (1);

[0052] The fifth pipe (8) is used for introducing liquid helium, the sixth pipe (11) is used for discharging helium vapor, the seventh pipe (13) is used for introducing liquid nitrogen, the eighth pipe (14) is used for discharging nitrogen vapor, and the tenth pipe (15) is used for measuring temperature and pressure;

[0053] The enrichment unit comprises a heater (4), a shell (5), a first pipeline (7), a second pipeline (9), a third pipeline (10), a fourth pipeline (12) and a ninth pipeline (6); the first pipeline (7), the second pipeline (9), the third pipeline (10), the fourth pipeline (12) and the ninth pipeline (6) are all connected to the shell (5); the shell (5) comprises a straight segment and an arc segment connected from top to bottom; the heater (4) is placed in the cavity of the shell (5) and corresponds to the straight segment; wherein the material of the arc segment of the shell (5) is copper, and its thermal conductivity at 1.0-1.5K is above 100 W / m·K.

[0054] The first pipe (7) is used to introduce liquid helium, the second pipe (9) is used to discharge the superfluid helium-4 in the shell (5) into the internal dewar (3) after enrichment and purification; the third pipe (10) is used to discharge helium vapor, the fourth pipe (12) is used to discharge a mixture of helium-3 and helium-4, and the ninth pipe (6) is used to measure temperature and pressure;

[0055] In this embodiment, the outlets of the sixth pipeline (11) and the eighth pipeline (14) are both connected to a vacuum pump, the former being used to extract a mixture of helium-4 and helium-3; and the latter being used to decompress and evaporate the liquid helium or helium-4 in the internal Dewar (3).

[0056] In this embodiment, a valve V1 is installed on the first pipeline (7), a valve V3 is installed on the second pipeline (9), a valve V4 is installed on the third pipeline (10), a valve V6 is installed on the fourth pipeline (12), a valve V2 is installed on the fifth pipeline (8), a valve V5 is installed on the sixth pipeline (11), a valve V7 is installed on the seventh pipeline (13), and a valve V8 is installed on the eighth pipeline (14).

[0057] In the separation unit, helium-3 and helium-4 are separated by a packed cryogenic distillation tower according to their different volatilities: a gaseous helium-3 product is obtained at the top of the distillation tower, and a liquid helium-4 is obtained at the bottom of the distillation tower, which are then stored and transported.

[0058] The recovery and liquefaction unit is connected to the third pipeline (10) and the sixth pipeline (11), and is used to reduce the pressure and evaporate the helium discharged from the third pipeline (10) and the sixth pipeline (11) and then liquefy it again.

[0059] This embodiment further provides a method for enriching and purifying helium-3 in liquid helium using the above system, comprising the following steps:

[0060] S1: First, open valves V7 and V8, and fill the external Dewar (1) with liquid nitrogen for pre-cooling through the seventh pipe (13). When liquid accumulates in the external Dewar (1), the temperature of the external Dewar (1) is reduced to 77K, and nitrogen vapor is discharged through the eighth pipe (14);

[0061] S2: Using a vacuum pump to evacuate the inside of the cold shield (2);

[0062] S3: Open valves V1 and V4, fill liquid helium into the shell (5) through the first pipe (7), and discharge helium vapor through the third pipe (10); when liquid helium accumulates in the shell (5), the shell (5) is cooled to 4.2K, and after the shell (5) is filled with liquid helium, V1 and V4 are closed;

[0063] At the same time, valves V2 and V5 are opened, and liquid helium is filled into the internal dewar (3) through the fifth pipe (8), and helium vapor is discharged through the sixth pipe (11); when liquid helium is accumulated in the internal dewar (3), the temperature of the internal dewar (3) is reduced to 4.2K; when the volume of the liquid helium accumulated in the internal dewar (3) accounts for 1 / 2 of the total volume of the internal dewar (3), the liquid helium in the internal dewar (3) is reduced in pressure and evaporated, so that the temperature of the internal dewar (3) is reduced to 1.0-1.5K, and the temperature is maintained. At this time, the liquid helium in the shell (5) is cooled to the same temperature as the internal dewar (3);

[0064] S4: Turn on the heater (4) to start enrichment;

[0065] S5: After the enrichment is completed, the valve V6 is opened to discharge the mixture of helium-4 and helium-3 through the fourth pipeline (12), and the mixture of helium-4 and helium-3 in a normal fluid state is separated from the superfluid helium-4;

[0066] S6: After the separation is completed, V6 is closed to stop discharging the normal fluid helium-4 and helium-3 mixture; V3 is opened, V2 is reduced, and the remaining superfluid helium-4 in the shell (5) is discharged into the internal dewar (3), thus completing a separation cycle.

[0067] S7: Close V3, open V1 and V4, allow liquid helium to enter the shell (5), and after the shell is filled with liquid, close V1 and V4, so that the liquid helium in the shell (5) is cooled to the same temperature as the internal Dewar (3) through heat conduction of the arc segment structure, and repeat steps S4 to S6.

[0068] Detection by the Noblesse SFT rare gas mass spectrometer showed that the content of helium-3 in the mixture of helium-4 and helium-3 in S5 can be increased by 10,000 times compared to the original liquid helium.

[0069] The basic principle of the Noblesse SFT rare gas mass spectrometer is to freeze all impurities, leaving only helium-3 and helium-4, use a deflection magnetic field to obtain spectral peaks, and obtain data by comparing them with atmospheric standards.

[0070] Example 2

[0071] This embodiment provides a system and method for enriching and purifying helium-3 in liquid helium, which differs from the embodiment 1 only in that the arc-shaped section of the shell (5) is made of aluminum alloy, and its thermal conductivity is above 8W / m·K. According to the detection of the Noblesse SFT rare gas mass spectrometer, in S5, the enrichment effect of the aluminum alloy material is relatively poor compared with that of the copper material.

[0072] Example 3

[0073] This embodiment provides a system and method for enriching and purifying helium-3 in liquid helium, which differs from the embodiment 1 only in that the arc-shaped section of the shell (5) is made of stainless steel with a thermal conductivity of 0.08 W / m·K. According to the detection of the Noblesse SFT rare gas mass spectrometer, there is basically no enrichment effect in S5.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for enriching and purifying helium-3 in liquid helium, characterized in that: include: A refrigeration unit and an enrichment unit; the refrigeration unit is a nested structure, and includes, from the outside to the inside, an external dewar (1), a cold shield (2) and an internal dewar (3); The enrichment unit comprises a heater (4) and a shell (5); the shell (5) comprises a straight segment and an arc segment connected from top to bottom; the heater (4) is placed in the cavity of the shell (5) and corresponds to the straight segment.

2. The system for enriching and purifying helium-3 in liquid helium according to claim 1, characterized in that: The material of the shell (5) in the arc section has a thermal conductivity of more than 8 W / m·K when the temperature is 1.0 K-1.5 K.

3. The system for enriching and purifying helium-3 in liquid helium according to claim 1 or 2, characterized in that: The material of the shell (5) in the arc section includes copper or aluminum alloy.

4. The system for enriching and purifying helium-3 in liquid helium according to claim 1 or 2, characterized in that: The enrichment unit further comprises a first pipeline (7), a second pipeline (9), a third pipeline (10) and a fourth pipeline (12), wherein the first pipeline (7) is used to introduce liquid helium, and the second pipeline (9) is used to discharge the superfluid helium-4 in the shell (5) into the internal dewar (3) after the enrichment and purification is completed; the third pipeline (10) is used to discharge helium vapor, and the fourth pipeline (12) is used to discharge a mixture of helium-3 and helium-4; And / or, the refrigeration unit further comprises a fifth pipeline (8), a sixth pipeline (11), a seventh pipeline (13) and an eighth pipeline (14), wherein the fifth pipeline (8) is used for introducing liquid helium, the sixth pipeline (11) is used for discharging helium vapor, the seventh pipeline (13) is used for introducing liquid nitrogen, and the eighth pipeline (14) is used for discharging nitrogen vapor.

5. The system for enriching and purifying helium-3 in liquid helium according to claim 4, characterized in that: The first pipeline (7) is installed with a valve V1, the second pipeline (9) is installed with a valve V3, the third pipeline (10) is installed with a valve V4, the fourth pipeline (12) is installed with a valve V6, the fifth pipeline (8) is installed with a valve V2, the sixth pipeline (11) is installed with a valve V5, the seventh pipeline (13) is installed with a valve V7, and the eighth pipeline (14) is installed with a valve V8.

6. The system for enriching and purifying helium-3 in liquid helium according to claim 4, characterized in that: It also includes a separation unit, which is connected to the fourth pipeline (12) and is used to separate helium-3 and helium-4.

7. The system for enriching and purifying helium-3 in liquid helium according to claim 4, characterized in that: It also comprises a recovery and liquefaction unit, which is connected to the third pipeline (10) and the sixth pipeline (11), and is used to reduce the pressure and evaporate the helium discharged from the third pipeline (10) and the sixth pipeline (11) and then liquefy it again.

8. The system for enriching and purifying helium-3 in liquid helium according to claim 4, characterized in that: The enrichment unit further comprises a ninth pipeline (6), the ninth pipeline (6) being connected to the shell (5), and the ninth pipeline (6) being used for measuring temperature and pressure.

9. The system for enriching and purifying helium-3 in liquid helium according to claim 4, characterized in that: The refrigeration unit further comprises a tenth pipeline (15), the tenth pipeline (15) being connected to the internal Dewar (3), and the tenth pipeline (15) being used for measuring temperature and pressure.

10. The system for enriching and purifying helium-3 in liquid helium according to claim 4, characterized in that: The outlets of the sixth pipeline (11) and the eighth pipeline (14) are both connected to a vacuum pump, the former being used to extract a mixture of helium-4 and helium-3; and the latter being used to decompress and evaporate the liquid helium or helium-4 in the internal Dewar (3).

11. The system for enriching and purifying helium-3 in liquid helium according to claim 4, characterized in that: The first pipeline (7), the second pipeline (9), the third pipeline (10) and the fourth pipeline (12) are all connected to the shell (5); And / or, the fifth pipeline (8) and the sixth pipeline (11) are both connected to the internal Dewar (3); and the seventh pipeline (13) and the eighth pipeline (14) are both connected to the external Dewar (1).

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