A multi-membrane coupling process for extracting helium-3 from headspace mixed gas of high tritium heavy water tank

Abstract

The application provides a multi-membrane coupling process for extracting helium-3 from headspace mixed gas of a high-tritium heavy water tank, and belongs to the fields of chemistry and chemical engineering. The multi-membrane coupling process takes gas membrane separation technology as a core, and is coupled with catalytic oxidation and low-temperature condensation technology, so that the helium-3 is concentrated efficiently, and the heavy water, deuterium gas and argon gas are fully reused; simulation results show that the concentration of the helium-3 special gas can be increased from 1.0 mol% to more than 95.0 mol%, the single-pass recovery rate is more than 17.5%, the cyclic recovery rate is more than 99.8%, at the same time, the reuse rate of the argon gas is more than 99.8%, and the total reuse rate of the heavy water and the deuterium element is more than 99.95%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemistry and chemical engineering, and relates to a multi-membrane coupling process for extracting helium-3 from the headspace mixed gas of a high-tritium heavy water tank. In view of the helium-3 generated by tritium decay in the long-term storage of high-tritium heavy water, catalytic oxidation, freeze dehydration and gas membrane separation technologies are coupled and integrated to realize efficient extraction and concentration of special gas helium-3. BACKGROUND

[0002] Helium-3 is an isotope gas of helium, which contains 2 protons and one neutron in the atomic nucleus. Compared with the dominant isotope helium-4 in nature, the liquefaction temperature of helium-3 is lower, which is 4.55K for helium-4 and 3.15K for helium-3, and it has unique advantages in ultra-low temperature refrigeration. In nuclear fusion, one helium-3 and one deuterium generate one helium-4 and one proton; two helium-3 generate one helium-4 and two protons, which do not produce neutrons and do not cause radiation and environmental pollution, and it is a world-recognized efficient, clean and safe nuclear power fuel. In addition, helium-3 is also widely used as an absorption medium for neutron detection and lung medical imaging. In summary, efficient extraction and concentration of helium-3 is of great significance to the development of modern society.

[0003] The helium isotopes on earth are mainly helium-3 and helium-4, of which the proportion of helium-3 is only 0.1%, mainly from tritium decay, lithium spallation and the influence of cosmic rays on the upper atmosphere. Due to the extremely similar physical and chemical properties of helium-3 and helium-4, there are key problems such as low resource abundance and great separation difficulty in extracting helium-3 from natural helium gas resources, resulting in complex process flow and extremely high production cost. High-tritium heavy water decay is an important way to produce artificial helium-3. Nuclear power plants can use heavy water, which is composed of two deuterium atoms and one standard oxygen atom, as a moderator in the process of nuclear fission reaction. In this process, part of the deuterium atoms are converted into tritium atoms after being bombarded by high-energy neutrons, and the atomic nucleus contains one proton and two neutrons. Separation of heavy water after participating in nuclear fission reaction can obtain the aforementioned high-tritium heavy water. During the long-term storage of high-tritium heavy water, tritium atoms will gradually transform into helium-3 through beta decay. In order to ensure stable storage pressure and reduce the diffusion and leakage of high-tritium heavy water to the environment, argon gas is usually used as the sealing and isolation atmosphere of the high-tritium heavy water tank, so the main components of the headspace mixed gas of the high-tritium heavy water tank include gaseous heavy water component, helium-3, deuterium, oxygen and argon. Under typical working conditions, the composition of the headspace mixed gas of the high-tritium heavy water tank is as follows: heavy water component content 3.0mol%, helium-3 content 1.0mol%, deuterium content 4.0mol%, oxygen content 2.0mol%, and argon content about 90.0mol%. The temperature of the headspace mixed gas of the high-tritium heavy water tank is slightly higher than the ambient temperature, and the production pressure is about 0.01MPaG. Under normal circumstances, the production flow rate of the headspace mixed gas of the high-tritium heavy water tank is not more than 100 liters per hour.

[0004] For the headspace mixed gas of high tritium heavy water tank, the helium-3 extraction process needs to solve the following problems: 1. The production rate of helium-3 is continuously changing due to the influence of high tritium heavy water reserves and storage period, and the extraction process must meet the requirements of high efficiency enrichment and wide range adaptation; 2. Realize the centralized recovery and recycling of heavy water components; 3. Reduce the frequency of liquid heavy water in the helium-3 extraction process as much as possible; 4. Reduce the loss of deuterium gas as much as possible; 5. Improve the recycling rate of argon gas as much as possible. The molecular size and liquefaction temperature of helium-3 and deuterium gas are very similar, and it is difficult to separate by rectification, absorption, adsorption, membrane separation and other technologies, but deuterium gas has very high reducing activity and can be deeply converted and removed by catalytic oxidation technology. Helium-3, argon and oxygen are all permanent gases, if cryogenic rectification is used, due to the very small scale and very low refrigeration temperature, the equipment investment and operation cost per unit capacity are very high; if pressure swing adsorption is used, due to the small difference between helium-3 and argon in adsorption properties and the very low adsorption capacity of argon, the same problem of very high equipment investment and operation cost per unit capacity exists. Gas membrane separation is a new type of separation technology based on the difference in permeation rate. The molecular size of helium-3 and argon is very different, the molecular diameter of helium-3 is 0.26nm, and the molecular diameter of argon is 0.34nm, so a gas separation membrane with a specific size can be selected, such as a glassy polymer membrane, a molecular sieve membrane and a mixed matrix membrane doped with a microporous material. The headspace mixed gas of high tritium heavy water tank also contains saturated heavy water vapor, which can be separated by cooling and condensation. In summary, the coupling process of catalytic oxidation and low temperature condensation is expected to efficiently extract and concentrate helium-3 special gas from the headspace mixed gas of high tritium heavy water tank, taking gas membrane separation technology as the core. SUMMARY

[0005] The purpose of the present application is to provide a multi-membrane coupling separation process for efficiently extracting helium-3 from the headspace mixed gas of a high tritium heavy water tank. The process converts deuterium and oxygen into heavy water through a catalytic oxidation unit, liquefies and separates most of the heavy water vapor through a low-temperature condensation unit, and finally separates helium-3 from argon through a multi-stage membrane separation unit, ultimately obtaining concentrated helium-3 with an effective concentration of more than 95.0mol%. At the same time, heavy water and argon are returned to the high tritium heavy water tank, realizing recycling.

[0006] The technical solution of the present application is:

[0007] The headspace mixed gas S-1 collected from the upper space of the high tritium heavy water tank 1 first enters the cold dryer 2, and the temperature is reduced to 10℃, then enters the buffer separation tank 3, the heavy water S-2 discharged from the bottom is returned to the high tritium heavy water tank 1, and the gas phase stream collected from the top enters the first compressor 4, and is pressurized to be called high-pressure headspace mixed gas S-3;

[0008] The high-pressure headspace mixed gas S-3 first enters the precision filter 5 to intercept the entrained solid particles, then is combined with the high-purity oxygen gas S-4, and then enters the catalytic oxidation reactor 6. The deuterium gas and excess oxygen gas are converted into heavy water vapor through catalytic oxidation reaction. The stream taken from the catalytic oxidation reactor 6 is referred to as deuterium-depleted mixed gas S-5;

[0009] The deuterium-depleted mixed gas S-5 is first cooled to room temperature in the constant-temperature water tank 7, and then enters the liquid-liquid separator 8. The heavy water discharged from the bottom is returned to the high-tritium heavy water tank 1. The gas phase stream taken from the top enters the refrigerated dehydrator 9, and the temperature is reduced to below -30°C. The heavy water vapor is frozen and separated in the refrigerated dehydrator 9, and after being melted into heavy water, is taken from the bottom and returned to the high-tritium heavy water tank 1. The gas phase stream taken from the top enters the constant-temperature water tank 7 and is heated to room temperature, which is referred to as the first membrane separation unit feed gas S-6, and enters the first membrane separation unit 10.

[0010] The retentate side of the first membrane separation unit 10 obtains the first retentate gas S-7, which is returned to the high-tritium heavy water tank 1 and enters the bottom of the high-tritium heavy water tank through the gas flow distributor 11 at the bottom of the heavy water tank to accelerate the desorption of helium-3 from the high-tritium heavy water. The permeate side of the first membrane separation unit 10 obtains the first permeate gas S-8 preliminarily enriched in helium-3. The first permeate gas S-8 enters the second compressor 13 after balancing the pressure in the first buffer tank 12, is pressurized, and then cooled to room temperature in the constant-temperature water tank 7, which is referred to as the second membrane separation unit feed gas S-9, and enters the second membrane separation unit 14.

[0011] The retentate side of the second membrane separation unit 14 obtains the second retentate gas S-10, which is returned to the buffer liquid-liquid separator 3 for cyclic separation. The permeate side of the second membrane separation unit 14 obtains the second permeate gas S-11, which is again enriched in helium-3. The second permeate gas S-11 enters the third compressor 16 after balancing the pressure in the second buffer tank 15, is pressurized, and then cooled to room temperature in the constant-temperature water tank 7, which is referred to as the third membrane separation unit feed gas S-12, and enters the third membrane separation unit 17.

[0012] The retentate side of the third membrane separation unit 17 obtains the third retentate gas S-13, which is returned to the buffer liquid-liquid separator 3 for cyclic separation. The permeate side of the third membrane separation unit 17 obtains the third permeate gas S-14, which is highly concentrated in helium-3, and the effective concentration of helium-3 in the third permeate gas S-14 exceeds 95.0 mol%. The third permeate gas S-14 enters the fourth compressor 19 after balancing the pressure in the third buffer tank 18, is pressurized, and then cooled to room temperature in the constant-temperature water tank 7, which is referred to as the crude helium-3 product S-15, and then enters the high-pressure helium-3 storage tank 20.

[0013] The beneficial effects of the present application: through the coupling and integration process of gas membrane separation, catalytic oxidation and low-temperature condensation, the efficient extraction and concentration of special gas helium-3 in the headspace mixed gas of high tritium heavy water tank are realized, and the full recycling of heavy water, deuterium gas and argon gas is ensured; the concentration of helium-3 is carried out by taking gas membrane separation technology as the core, and the unique modular adjustment mode is conducive to dealing with the influence of the continuous change of the production rate of helium-3; high-purity oxygen is supplemented before the catalytic oxidation reaction, so that the molar ratio of oxygen and deuterium exceeds the stoichiometric ratio of chemical reaction, and it is ensured that the deuterium gas can be fully oxidized and converted into heavy water, thereby effectively reducing the loss of deuterium resources; before the multi-stage membrane separation process, a refrigerated dewatering machine with a temperature lower than-30℃ is used to deeply remove heavy water vapor from the process stream, so as to prevent the condensation of heavy water in the subsequent compression process, thereby avoiding the adverse effects of condensed heavy water on the compression process and avoiding the pollution of heavy water in the compression process. The process simulation optimization results show that the single-pass yield of special gas helium-3 is more than 17.5%, the cycle yield is more than 99.8%, the concentration of helium-3 can be increased from 1.0mol% to more than 95.0mol%, at the same time, the total recycling rate of heavy water and deuterium element is more than 99.95%, and the recycling rate of argon gas is more than 99.8%. In summary, the coupling separation process integrating catalytic oxidation and low-temperature condensation with gas membrane separation as the core can efficiently extract and concentrate helium-3 special gas from the headspace mixed gas of high tritium heavy water tank, while ensuring the full recovery and utilization of deuterium gas, heavy water and argon gas. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a multi-membrane coupling process flow diagram for extracting helium-3 from the headspace mixed gas of high tritium heavy water tank.

[0015] In the figure: S-1 headspace mixed gas; S-2 heavy water; S-3 high-pressure headspace mixed gas; S-4 high-purity oxygen; S-5 deuterium-removed mixed gas; S-6 first membrane separation unit feed gas; S-7 first retentate gas; S-8 first permeate gas; S-9 second membrane separation unit feed gas; S-10 second retentate gas; S-11 second permeate gas; S-12 third membrane separation unit feed gas; S-13 third retentate gas; S-14 third permeate gas; S-15 helium-3 crude product; 1 high tritium heavy water tank; 2 cold dryer; 3 buffer separation tank; 4 first compressor; 5 precision filter; 6 catalytic oxidation reactor; 7 constant-temperature water tank; 8 separation tank; 9 refrigerated dewatering machine; 10 first membrane separation unit; 11 gas flow distributor; 12 first buffer tank, 13 second compressor; 14 second membrane separation unit; 15 second buffer tank; 16 third compressor; 17 third membrane separation unit; 18 third buffer tank; 19 fourth compressor; 20 high-pressure helium-3 storage tank. DETAILED DESCRIPTION

[0016] The specific embodiments of the present application will be further described below in combination with the drawings and technical solutions.

[0017] Example 1

[0018] The multi-membrane coupling process specially proposed in the application is used to extract and concentrate the special gas helium-3 from the headspace mixed gas of a 100-ton high-tritium heavy water tank in a nuclear power plant. The composition of the headspace mixed gas is as follows: heavy water content 3.0 mol%, helium-3 content 1.0 mol%, deuterium content 4.0 mol%, oxygen content 2.0 mol%, and argon content 90.0 mol%. The temperature of the headspace mixed gas of the high-tritium heavy water tank is about 25℃, and the production pressure is 0.01 MPaG. In the early stage of operation of the high-tritium heavy water tank, the annual production of helium-3 is about 300 standard liters; in the late stage of operation of the high-tritium heavy water tank, the annual production of helium-3 is about 1140 standard liters.

[0019] The headspace mixed gas S-1 collected from the upper space of the high-tritium heavy water tank 1 is first introduced into a cold dryer 2 to reduce the temperature to 10℃, and then introduced into a buffer separation tank 3. The heavy water S-2 discharged from the bottom is returned to the high-tritium heavy water tank 1, and the gas phase stream collected from the top is introduced into a first compressor 4 to increase the pressure to 1.00 MPaG. After the pressure increase, the headspace mixed gas is referred to as high-pressure headspace mixed gas S-3.

[0020] The high-pressure headspace mixed gas S-3 is first introduced into a precision filter 5 to trap the solid particles entrained, and then combined with high-purity oxygen S-4 and introduced into a catalytic oxidation reactor 6. The supplemental amount of high-purity oxygen per hour is 0.04 standard liters. Deuterium and excess oxygen are converted into heavy water vapor through catalytic oxidation reaction, and the concentration of residual deuterium is less than 5 ppmv. The stream collected from the catalytic oxidation reactor 6 is referred to as deuterium-depleted mixed gas S-5.

[0021] The deuterium-depleted mixed gas S-5 is first introduced into a constant-temperature water tank 7 to cool to room temperature, and then introduced into a separation tank 8. The heavy water discharged from the bottom is returned to the high-tritium heavy water tank 1, and the gas phase stream collected from the top is introduced into a refrigerated dewatering machine 9 to reduce the temperature to -40℃. The heavy water vapor is frozen and separated in the refrigerated dewatering machine 9, and the concentration of the gas phase heavy water is not more than 20 ppmv. The frozen heavy water is melted and collected from the bottom to return to the high-tritium heavy water tank 1, and the gas phase stream collected from the top is heated to room temperature in the constant-temperature water tank 7, which is referred to as first membrane separation unit feed gas S-6, and introduced into a first membrane separation unit 10.

[0022] The retentate side of the first membrane separation unit 10 obtains first retentate gas S-7, which is returned to the high tritium heavy water tank 1 and enters the bottom of the heavy water tank through the gas flow distributor 11 at the bottom of the heavy water tank to accelerate the desorption of helium-3 from the high tritium heavy water; the permeate side of the first membrane separation unit 10 obtains first permeate gas S-8 preliminarily enriched in helium-3, and the concentration of helium-3 is increased to 8.44 mol%; the first permeate gas S-8 enters the second compressor 13 after balancing the pressure in the first buffer tank 12, is pressurized to 1.00 MPaG, and then enters the constant-temperature water tank 7 to be cooled to normal temperature, which is referred to as second membrane separation unit feed gas S-9, and enters the second membrane separation unit 14;

[0023] The retentate side of the second membrane separation unit 14 obtains second retentate gas S-10, which is returned to the buffer separation tank 3 for cyclic separation; the permeate side of the second membrane separation unit 14 obtains second permeate gas S-11, which is again enriched in helium-3, and the concentration of helium-3 is increased to 48.21 mol%; the second permeate gas S-11 enters the third compressor 16 after balancing the pressure in the second buffer tank 15, is pressurized to 1.00 MPaG, and then enters the constant-temperature water tank 7 to be cooled to normal temperature, which is referred to as third membrane separation unit feed gas S-12, and enters the third membrane separation unit 17;

[0024] The retentate side of the third membrane separation unit 17 obtains third retentate gas S-13, which is returned to the buffer separation tank 3 for cyclic separation; the permeate side of the third membrane separation unit 17 obtains third permeate gas S-14, which is highly enriched in helium-3, and the effective concentration of helium-3 is more than 95.0 mol%; the third permeate gas S-14 enters the fourth compressor 19 after balancing the pressure in the third buffer tank 18, is pressurized to 1.00 MPaG, and then enters the constant-temperature water tank 7 to be cooled to normal temperature, which is referred to as crude helium-3 product S-15, and then enters the high-pressure helium-3 storage tank 20.

[0025] According to simulation calculation, in the early stage of operation of the high tritium heavy water tank, the annual output of crude helium-3 product of the multi-membrane coupled separation process system is about 309 standard liters, and the concentration of helium-3 can reach more than 97.0 mol%; in the late stage of operation of the high tritium heavy water tank, the annual output of crude helium-3 product of the multi-membrane coupled separation process system is about 1198 standard liters, and the concentration of helium-3 can reach more than 95.0 mol%.

Claims

1. A multi-membrane coupling process for extracting helium-3 from the headspace mixed gas of a high tritium heavy water tank, characterized in that: the headspace mixed gas (S-1) taken from the upper space of the high tritium heavy water tank (1) first enters a cold dryer (2) to reduce the temperature to 10℃, and then enters a buffer decanter (3), the heavy water (S-2) discharged from the bottom of the buffer decanter (3) returns to the high tritium heavy water tank (1), and the gas phase stream taken from the top of the buffer decanter (3) enters a first compressor (4) to become high pressure headspace mixed gas (S-3) after being pressurized; the high pressure headspace mixed gas (S-3) first enters a precision filter (5) to intercept the entrained solid particles, and then enters a catalytic oxidation reactor (6) after being combined with high purity oxygen (S-4), deuterium gas and excess oxygen are converted into heavy water vapor through catalytic oxidation reaction, and the stream taken from the catalytic oxidation reactor (6) is called deuterium removal mixed gas (S-5); the deuterium removal mixed gas (S-5) first enters a constant temperature water tank (7) to be cooled to room temperature, and then enters a decanter (8), the heavy water discharged from the bottom of the decanter (8) returns to the high tritium heavy water tank (1), and the gas phase stream taken from the top of the decanter (8) enters a refrigerated dehydrator (9) to reduce the temperature to below -30℃, the heavy water vapor is frozen and separated in the refrigerated dehydrator (9), and after being melted into heavy water, it is taken from the bottom of the refrigerated dehydrator (9) and returned to the high tritium heavy water tank (1), the gas phase stream taken from the top of the refrigerated dehydrator (9) enters the constant temperature water tank (7) to be heated to room temperature, called first membrane separation unit feed gas (S-6), and enters a first membrane separation unit (10); the retentate side of the first membrane separation unit (10) obtains first retentate gas (S-7) which returns to the high tritium heavy water tank (1) and enters the bottom of the high tritium heavy water through a gas flow distributor (11) at the bottom of the high tritium heavy water tank (1) to accelerate the desorption of helium-3 from the high tritium heavy water; the permeate side of the first membrane separation unit (10) obtains first permeate gas (S-8) preliminarily enriched in helium-3; the first permeate gas (S-8) enters a second compressor (13) after balancing the pressure in a first buffer tank (12), is pressurized, is cooled to room temperature in the constant temperature water tank (7), is called second membrane separation unit feed gas (S-9), and enters a second membrane separation unit (14); the retentate side of the second membrane separation unit (14) obtains second retentate gas (S-10) which returns to the buffer decanter (3) for cyclic separation; the permeate side of the second membrane separation unit (14) obtains second permeate gas (S-11) which is further enriched in helium-3; the second permeate gas (S-11) enters a third compressor (16) after balancing the pressure in a second buffer tank (15), is pressurized, is cooled to room temperature in the constant temperature water tank (7), is called third membrane separation unit feed gas (S-12), and enters a third membrane separation unit (17); The retentate side of the third membrane separation unit (17) obtains the third retentate gas (S-13), which returns to the buffer separation tank (3) for cyclic separation. The permeate side of the third membrane separation unit (17) obtains the third permeate gas (S-14) highly concentrated with helium-3, wherein the effective concentration of helium-3 exceeds 95.0 mol%. The third permeate gas (S-14) enters the fourth compressor (19) after balancing the pressure by the third buffer tank (18), is pressurized, and then enters the constant-temperature water tank (7) to be cooled to room temperature, which is called the helium-3 crude product (S-15), and then enters the high-pressure helium-3 storage tank (20).

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