A low temperature plasma enhanced water detritiation device and detritiation method

Abstract

The present invention discloses a low-temperature plasma enhanced water detritiation device and detritiation method. The device introduces a dual-medium discharge structure and a plasma power supply to realize plasma discharge, and for the first time applies plasma technology to a traditional detritiation device and detritiation method, solving the "water poisoning" phenomenon of hydrophobic catalysts in traditional liquid-phase catalytic exchange columns. The device and method can not only be used alone, but also synergize with traditional fillers to achieve the integration of catalytic and mass transfer performance and realize dual catalysis of hydrogen and water in hydrogen-water isotope exchange reactions, further improving the detritiation performance of liquid-phase catalytic exchange water.

Description

Technical Field

[0001] The invention belongs to the field of tritium water treatment, and in particular relates to a low-temperature plasma enhanced water detritiation device, and also relates to a detritiation method based on the device. Background Art

[0002] Water detritiation technology is widely used in the fields of tritium extraction and upgrading of tritium-containing heavy water, treatment of tritium-containing wastewater and heavy water production. It has great application prospects in the fields of detritium-containing wastewater of inland nuclear power plants, detritium-containing wastewater of spent fuel reprocessing plants and recovery of tritium in fusion reactor blanket cooling water. The core of this technology is the hydrogen-water isotope exchange reaction, which is essentially an exchange reaction between hydrogen and water in a gas (vapor) phase environment. Taking H2 and HTO as an example, the exchange reaction can be expressed as:

[0003]

[0004] The hydrogen-water isotope exchange reaction usually has a slow reaction rate and must be carried out under catalyst conditions to achieve rapid exchange and reaction equilibrium. Different catalysts can be used according to the use environment, and a variety of devices that can achieve hydrogen-water isotope exchange reactions have been developed accordingly. Vapor phase catalytic exchange (VPCE), liquid phase catalytic exchange (LPCE) and combined electrolytic catalytic exchange (CECE) and other technologies have gradually developed.

[0005] Among them, the hydrogen-water isotope exchange reaction in the LPCE column of the LPCE and CECE devices is the key to affecting the detritiation of water. The conversion efficiency of water detritiation is mainly determined by the catalytic performance of the hydrophobic catalyst and the mass transfer performance of the filler. Among them, due to the high water vapor content in the LPCE reaction column, the active components in the hydrophobic catalyst are easily coated by the water film or water droplets, causing "water poisoning", thereby losing the catalytic ability and reducing the performance of water detritiation. Based on the above reasons, in order to ensure the mass transfer function of the reaction, highly hydrophilic fillers must be added, which will cause two materials with different functions to be filled in the LPCE column, affecting the space utilization. In addition, because the reaction temperature in the LPCE and CECE devices is less than 100°C, based on the hydrogen-water isotope exchange reaction Hydrophobic catalysts can only dissociate H2, and conventional catalysts are difficult to achieve the dissociation of HTO molecules in the vapor phase at this temperature, resulting in low isotope exchange efficiency in the LPCE column.

[0006] Therefore, how to solve the "water poisoning" phenomenon of the hydrophobic catalyst in the LPCE column, realize the integration of catalyst catalysis and mass transfer performance, and realize dual catalysis of hydrogen and water in the hydrogen-water isotope exchange reaction is the key to further improve the water detritiation performance of LPCE and CECE devices. Summary of the invention

[0007] To achieve this purpose, a low-temperature plasma enhanced water detritiation device and a detritiation method are proposed.

[0008] A low-temperature plasma enhanced water detritiation device, the low-temperature plasma enhanced water detritiation device is a columnar structure as a whole, an inner electrode, a reaction tube and an outer electrode are coaxially arranged from the center of the columnar structure to the outside, and the three constitute a double dielectric barrier discharge structure;

[0009] The inner electrode includes a tubular dielectric layer and a metal electrode located in the tubular dielectric layer, wherein the tubular dielectric layer is made of inorganic matter; the metal electrode is connected to a low-temperature plasma power source;

[0010] The reaction tube is the place for hydrogen-water exchange reaction, and its material is inorganic material; the two ends of the reaction tube and the inner electrode are connected with flanges, and the flanges are made of inorganic material; the top flange is provided with a water inlet channel and an exhaust channel, which are respectively used for the injection of raw water and the discharge of product gas; the bottom flange is provided with an air inlet channel and a drainage channel, which are respectively used for the injection of raw gas and the discharge of product water;

[0011] The outer electrode is coated on the outer surface of the reaction tube and is grounded.

[0012] Optionally, the reaction tube is also filled with filler, and the shape of the filler is one or more of a triangular spiral, a Dixon ring, and a glass spring; the size requirement of the filler is: less than half of the single-sided discharge gap; the material of the filler is required to be a non-conductive inorganic substance with a dielectric constant ≥3.

[0013] Optionally, the reaction tube material, the top flange and the bottom flange material are quartz glass, alumina, or ceramic.

[0014] Optionally, the outer electrode is a metal foil or a metal mesh.

[0015] Optionally, the outer electrode is a columnar sandwich structure coaxial with the reaction tube, and the sandwich structure includes a shell and a conductive liquid inside the shell;

[0016] Optionally, the conductive liquid is circulated and temperature controlled by a heating-refrigeration cycler, thereby indirectly regulating the temperature in the reaction tube;

[0017] Optionally, a condenser is provided on the top flange to condense H2O in the product gas.

[0018] Optionally, the low-temperature plasma power supply connection has a power supply type of DC high frequency, AC high frequency, modulated pulse or pulse power supply, an output voltage ≥ 3kV, and an adjustable frequency of 1kHz to 30kHz; wherein the modulated pulse or pulse duty cycle is adjustable from 1% to 99%.

[0019] A low-temperature plasma enhanced water detritium method, the steps of which include:

[0020] S10 Raw water purification

[0021] Purify the raw water to remove particles, ions and organic matter. Purity requirements after purification: resistance value must be ≥1MΩ;

[0022] S20 Hydrogen discharge

[0023] High-purity raw gas H2 is introduced into the low-temperature plasma enhanced water detritiation device through the gas inlet channel at the bottom of the low-temperature plasma enhanced water detritiation device to replace the original gas in the device, and the concentration of the high-purity raw gas H2 is required to be ≥99.99%;

[0024] S30 Plasma Reaction

[0025] Adjust the low-temperature plasma power supply, and the maximum output voltage reaches 20kV to ensure the normal operation of the dual dielectric barrier discharge structure;

[0026] S40 Gas-Liquid Countercurrent Reaction

[0027] Purified raw water is continuously introduced from the water inlet channel at the top of the low-temperature plasma enhanced water detritiation device, and high-purity raw gas is continuously introduced from the bottom of the low-temperature plasma enhanced water detritiation device, so that the raw water and the raw gas undergo a gas-liquid countercurrent reaction in the reaction tube;

[0028] S50 Collection Products

[0029] Liquid scintillation is used to detect the tritium concentration in the product water, and an ionization chamber is used to monitor the tritium concentration in the product gas.

[0030] Optionally, the gas-liquid ratio in the gas-liquid countercurrent reaction in step S40 is 1:(0.5-5);

[0031] Beneficial effects of the present invention: (1) The introduction of low-temperature plasma technology can achieve the dissociation of hydrogen and some water vapor molecules, and enhance the efficiency of hydrogen-water isotope exchange reaction. Due to the addition of low-temperature plasma technology, high-energy electrons will be generated in the reaction chamber of the LPCE column. High-energy electrons can activate hydrogen and water vapor. High-energy electrons and hydrogen ions have certain penetrability, so they can contact the filler under the water film, so that the filler can also play a certain catalytic role, realizing the dual catalysis of hydrogen and water vapor to improve the isotope exchange efficiency, solving the problem of "water poisoning" of catalysts in the usual sense. (2) Hydrophilic fillers can be used in the LPCE column to simultaneously serve as fillers and catalysts. Under the action of low-temperature plasma technology, the fillers can also play a role in efficient mass transfer, which can realize the integration of catalysis and mass transfer, which will greatly improve the space utilization rate in the reaction tube and further improve the efficiency of hydrogen-water isotope exchange. (3) Using low-temperature plasma to increase catalytic reactions can change the original reaction model that requires a hydrophobic catalyst plus a hydrophilic filler. In traditional reactions, the filler is responsible for mass transfer and the hydrophobic catalyst is responsible for catalytic reaction. The efficiency of the two is low when they are carried out on different substances. Using low-temperature plasma technology can not only make fillers that have no catalytic activity have a certain catalytic activity, but also make mass transfer and reaction take place on the same substance, greatly improving efficiency. (4) The synergistic combination of low-temperature plasma technology and fillers can eliminate the need for the use of precious metals (Pd, Pt), greatly reducing reaction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the structure of a P-LPCE type low-temperature plasma enhanced water detritiation device with metal foil;

[0033] Figure 2 It is a schematic diagram of the structure of a P-LPCE type low-temperature plasma enhanced water detritiation device with a conductive liquid sandwich structure;

[0034] Figure 3 Schematic diagram of the low-temperature plasma enhanced hydrogen-water isotope exchange process;

[0035] Figure 4 is the hydrogen-water isotope exchange efficiency of TiO2 catalyst without low-temperature plasma;

[0036] Figure 5 is the hydrogen-water isotope exchange efficiency of TiO2 catalyst under low-temperature plasma;

[0037] In the figure:

[0038] 1. Inner electrode; 2. Reaction tube; 3. Outer electrode; 4. Top flange; 5. Bottom flange; 6. Condenser; 7. Low-temperature plasma power supply; 8. Packing; 9. Heating-refrigeration cycle machine; 10. High-voltage wire;

[0039] 11. Metal electrode; 12. Tubular dielectric layer; 31. Shell; 32. Conductive liquid; 33. Conduit. DETAILED DESCRIPTION

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without any creative labor.

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific implementation methods and drawings.

[0042] Figure 1-Figure 2 Two different structural forms of low-temperature plasma enhanced water detritiation devices are demonstrated.

[0043] Example 1

[0044] Figure 1 A P-LPCE type low-temperature plasma enhanced water detritiation device with metal foil was demonstrated. The overall appearance of the device is a columnar structure, and the discharge structure adopts a double dielectric barrier discharge structure. Its specific structure is as follows: the columnar structure coaxially arranges an inner electrode 1, a reaction tube 2, and an outer electrode 3 from the center to the outermost side, and the three constitute a double dielectric barrier discharge structure.

[0045] The inner electrode is divided into two parts: a tubular dielectric layer 12 and a metal electrode 11 located in the tubular dielectric layer. The tubular dielectric layer 12 is made of inorganic material, and a heat-resistant glass tube is used in this embodiment; the metal electrode 11 located in the tubular dielectric layer 12 can be made of powdered metal powder filled in the tubular dielectric layer, and aluminum powder is used in this embodiment. The reaction tube 2 on the outer layer of the inner electrode 1 is the place for the hydrogen-water exchange reaction, and its material is inorganic material, and a heat-resistant glass tube is used in this embodiment.

[0046] The top and bottom ends of the reaction tube 2 and the inner electrode 1 are connected to flanges. The hydrogen-water reactant between the reaction tube 2 and the inner electrode 1 does not contact the metal electrode 11 and the outer electrode 3. The flange material is an inorganic material; wherein the top flange 4 is provided with a water inlet channel and an exhaust channel, which are respectively used for the injection of raw water (tritium-containing water) and the discharge of product gas (tritium-containing hydrogen); the bottom flange 5 is provided with an air inlet channel and a drainage channel, which are respectively used for the injection of raw gas (high-purity hydrogen) and the discharge of product water (tritium-free water). A channel for connecting the metal electrode 11 to the external low-temperature plasma power supply 7 is also provided inside the top flange 4. The metal electrode 11 is connected to the low-temperature plasma power supply 7 through a high-voltage wire 10. The power supply generally selects DC high frequency, AC high frequency, modulated pulse and pulse power supply, and the maximum output voltage can reach 20kV, wherein the input voltage, frequency, duty cycle, etc. of the low-temperature plasma power supply 7 are required to be able to be regulated.

[0047] The outer surface of the reaction tube 2 is coated with an outer electrode 3 in the form of a cylindrical metal foil. Of course, the metal foil can also be replaced with a metal mesh or a segmented metal foil connected to each other. The inner electrode 1, the reaction tube 2, and the outer electrode 3 constitute a double dielectric barrier discharge structure, which cooperates with the low-temperature plasma power supply 7 to generate low-temperature plasma. To ensure the safety of the discharge, the outer electrode 3 must be well grounded.

[0048] There is also a condenser 6 on the top flange 4, which can condense the water vapor in the atmosphere after the reaction, and the condensed liquid will flow back into the reaction tube 2 to continue to participate in the reaction. The liquid after the reaction will flow out from the bottom of the reaction tube 2, and according to different process requirements, this part of the liquid can enter the electrolytic cell or enter the storage.

[0049] In order to further improve the efficiency of detritium removal, a hydrophilic filler 8 can be filled in the reaction tube. The structure of the filler 8 is a triangular spiral, a Dickson ring, a glass spring, etc. It can be one or a mixture of multiple structures. The material of the filler 8 must be a non-conductive material, such as TiO2, Al2O3, SiO2 and other inorganic materials, and the dielectric constant is generally required to be ≥3. The size requirement of the filler 8: less than half of the discharge gap between the inner and outer electrodes.

[0050] Example 2

[0051] Figure 2A P-LPCE type low-temperature plasma enhanced water detritiation device with a conductive liquid sandwich structure is shown. Compared with Example 1, its outer electrode 3 is a sandwich structure with a conductive liquid. The sandwich structure can be made into an integral body with the reaction tube, or it can be tightly sleeved outside the reaction tube 2. A conductive liquid 32 with conductive ability such as tap water and NaCl is introduced into the sandwich structure to cooperate with the inner electrode 1 and the low-temperature plasma power supply 7 to achieve discharge and generate low-temperature plasma. To ensure the safety of the discharge, the liquid outer electrode still needs to be well grounded. A conduit 33 can also be provided on the upper and lower sides of the sandwich structure, which is connected to the heating-refrigeration cycle machine 9. The temperature of the outer electrode can be regulated by circulating the conductive liquid 32 with a certain temperature in the heating-refrigeration cycle machine 9, thereby indirectly regulating the temperature in the reaction tube 2 to achieve the reaction temperature regulation in the P-LPCE column.

[0052] Example 3

[0053] Based on the low-temperature plasma enhanced water detritiation device described in Examples 1 and 2, a low-temperature plasma enhanced detritiation experiment of tritium-containing water was carried out.

[0054] After assembling the experimental device, proceed as follows:

[0055] S10 Raw water purification

[0056] Purify the particles, ions and organic matter in the tritium-containing water, and require the purity of the tritium-containing water after purification to be ≥1MΩ;

[0057] S20 Hydrogen discharge

[0058] High-purity raw gas H2 is introduced into the low-temperature plasma enhanced water detritiation device through the air inlet channel at the bottom of the low-temperature plasma enhanced water detritiation device to replace the original gas in the device to prevent subsequent explosions. The concentration of high-purity raw gas H2 is required to be ≥99.99%;

[0059] S30 Plasma Reaction

[0060] Adjust the low-temperature plasma power supply, the output voltage is ≥3kV, and the maximum does not exceed 20kV to ensure the normal operation of the dual dielectric barrier discharge structure;

[0061] S40 Gas-Liquid Countercurrent Reaction

[0062] Purified raw water is continuously introduced from the water inlet channel at the top of the low-temperature plasma enhanced water detritiation device, and high-purity raw gas is continuously introduced from the bottom of the low-temperature plasma enhanced water detritiation device, so that the raw water and the raw gas are subjected to gas-liquid countercurrent reaction in the reaction tube; the gas-liquid ratio in the gas-liquid countercurrent reaction is 1: (0.5-5);

[0063] S50 Collection Products

[0064] Liquid scintillation is used to detect the tritium concentration in the product water, and an ionization chamber is used to monitor the tritium concentration in the product gas.

[0065] In this embodiment, plasma technology is introduced to generate high-energy electrons (1-2 eV) in the reaction tube. The high-energy electrons react with H2 and HTO in the reaction tube to activate them and cause isotope exchange reaction. The specific action process is as follows: Figure 3 As shown. Under this reaction mode, not only can the hydrogen molecules in the gas phase undergo isotope exchange reactions with water molecules, but some electrons and hydrogen ions can also penetrate the liquid film to react on the surface of the filler. Here, the dissociation ability of hydrogen molecules and water vapor molecules comes from the electrons generated by the low-temperature plasma reactor, which has nothing to do with the catalytic performance of the filler. Therefore, it also effectively solves the problem of "water poisoning" of the catalyst. Based on this, the catalyst filled in the LPCE column can be a hydrophilic catalyst, thereby realizing the integration of catalytic and mass transfer performance, and effectively improving the space utilization rate in the LPCE column. In addition, since the energy of the electrons in the LPCE column can be regulated by the low-temperature plasma power supply, through the synergistic effect with the catalyst, the dual catalytic reaction of hydrogen and water can be achieved at a temperature below 100°C, thereby significantly improving the efficiency of the hydrogen-water isotope exchange reaction, and therefore can effectively solve some difficulties and problems existing in traditional LPCE and CECE.

[0066] Figure 4 The hydrogen-water isotope exchange efficiency of TiO2 catalyst without low-temperature plasma was demonstrated. Figure 4 It can be seen that the hydrogen-water isotope exchange capacity of conventional titanium oxide or modified titanium oxide is very low without the action of low-temperature plasma. Figure 5 is the exchange efficiency under the combined action of low-temperature plasma + TiO2 catalyst, Figure 5 It can be seen that the combined action of low-temperature plasma + TiO2 catalyst significantly improves the efficiency of hydrogen-water isotope exchange reaction. If plasma is not used, the catalyst will be poisoned by water over time, and the reaction rate will be greatly reduced, or even no longer have a catalytic effect, and the reaction rate will be low or not proceed. Figure 5 In the process, the efficiency of the isotope exchange reaction will continue to increase with the increase of input power.

Claims

1. A low-temperature plasma enhanced water detritiation device, characterized in that: The low-temperature plasma enhanced water detritium device is a columnar structure as a whole, and an inner electrode, a reaction tube and an outer electrode are coaxially arranged from the center of the columnar structure to the outside, and the three constitute a double dielectric barrier discharge structure; The inner electrode includes a tubular dielectric layer and a metal electrode located in the tubular dielectric layer, wherein the tubular dielectric layer is made of inorganic matter; the metal electrode is connected to a low-temperature plasma power source; The reaction tube is the place for hydrogen-water exchange reaction, and its material is inorganic material; the two ends of the reaction tube and the inner electrode are connected with flanges, and the flanges are made of inorganic material; the top flange is provided with a water inlet channel and an exhaust channel, which are respectively used for the injection of raw water and the discharge of product gas; the bottom flange is provided with an air inlet channel and a drainage channel, which are respectively used for the injection of raw gas and the discharge of product water; The outer electrode is coated on the outer surface of the reaction tube and is grounded.

2. The low-temperature plasma enhanced water detritiation device according to claim 1, characterized in that: The reaction tube is also filled with fillers, and the filler shape is one or more of a triangular spiral, a Dixon ring, and a glass spring; the filler size requirement is: less than half of a single-sided discharge gap; the filler material requirement is a non-conductive inorganic substance with a dielectric constant ≥3.

3. The low-temperature plasma enhanced water detritiation device according to claim 1, characterized in that: The reaction tube material, the top flange and the bottom flange material are quartz glass, alumina and ceramic.

4. The low-temperature plasma enhanced water detritiation device according to claim 1, characterized in that: The outer electrode is a metal foil or a metal mesh.

5. The low-temperature plasma enhanced water detritiation device according to claim 1, characterized in that: The outer electrode is a columnar sandwich structure coaxial with the reaction tube, and the sandwich structure includes a shell and a conductive liquid inside the shell.

6. The low-temperature plasma enhanced water detritiation device according to claim 1, characterized in that: The conductive liquid is circulated and temperature controlled by a heating-refrigeration cycler, thereby indirectly regulating the temperature in the reaction tube.

7. The low-temperature plasma enhanced water detritiation device according to claim 1, characterized in that: A condenser is arranged on the top of the top flange to condense H2O in the product gas.

8. The low-temperature plasma enhanced water detritiation device according to claim 1, characterized in that: The low-temperature plasma power supply connection is a power supply type of DC high frequency, AC high frequency, modulated pulse or pulse power supply, with an output voltage of ≥3kV and an adjustable frequency of 1kHz to 30kHz; wherein the modulated pulse or pulse duty cycle is adjustable from 1% to 99%.

9. A detritiation method based on the low temperature plasma enhanced water detritiation device according to any one of claims 1 to 8, comprising the steps of: S10 Raw water purification Purify the raw water to remove particles, ions and organic matter. Purity requirements after purification: resistance value must be ≥1MΩ; S20 Hydrogen discharge High-purity raw gas H2 is introduced into the low-temperature plasma enhanced water detritiation device through the gas inlet channel at the bottom of the low-temperature plasma enhanced water detritiation device to replace the original gas in the device, and the concentration of the high-purity raw gas H2 is required to be ≥99.99%; S30 Plasma Reaction Adjust the low-temperature plasma power supply, the maximum output voltage reaches 20kV, to ensure the normal operation of the double dielectric barrier discharge structure; S40 gas-liquid countercurrent reaction Purified raw water is continuously introduced from the water inlet channel at the top of the low-temperature plasma enhanced water detritiation device, and high-purity raw gas is continuously introduced from the bottom of the low-temperature plasma enhanced water detritiation device, so that the raw water and the raw gas undergo a gas-liquid countercurrent reaction in the reaction tube; S50 Collection Products Liquid scintillation is used to detect the tritium concentration in the product water, and an ionization chamber is used to monitor the tritium concentration in the product gas.

10. The detritiation method according to claim 9, characterized in that: The gas-liquid ratio in the gas-liquid countercurrent reaction in step S40 is 1:(0.5-5).

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