A process, system and application for treating carbon-14 in radioactive waste gas from nuclear power plants.

Abstract

This invention belongs to the field of radioactive waste treatment technology, specifically disclosing a process, system, and application for treating carbon-14 in radioactive waste gas from nuclear power plants. The process includes: catalytic oxidation of decay-treated radioactive waste gas from nuclear power plants to convert organic carbon-14 into inorganic carbon-14. 14 CO2; gaseous 14 CO2 turns into liquid. 14 CO2 is separated and then heated to vaporize, yielding a third gaseous effluent; this effluent is then washed with countercurrent water to obtain gaseous substances that have dissolved and absorbed the third gaseous effluent. 14 The second liquid effluent of CO2 is then treated with ion exchange resin to obtain C14-containing waste resin. The system includes a C14 separation unit and a C14 fixation unit. This invention can reduce the amount of gaseous C14 emitted from nuclear power plants into the environment and achieve emission standards, improve treatment efficiency, prevent the generation of other secondary waste, reduce equipment investment and costs, and enable industrial application.

Description

Technical Field

[0001] This invention relates to the field of radioactive waste treatment technology, and in particular to a process, system and application for treating carbon-14 in radioactive waste gas from nuclear power plants. Background Technology

[0002] Carbon-14 exhibits weak beta radioactivity, with a maximum radiation energy of 156 keV, and a relatively long half-life of up to 5730 years. 14 Carbon-14 in CO2 form can react with non-radioactive substances in the air. 12 CO2 mixes with and participates in plant photosynthesis, thus entering the biosphere. It can be absorbed by the human body, potentially posing a risk of long-term internal exposure. Among the airborne radionuclides from nuclear power plants, carbon-14 contributes the largest collective dose to the public. With the increasing number of operating and under-construction nuclear power units, and the growing public awareness and demand for environmental safety, research into the treatment and removal technologies for airborne carbon-14 from nuclear power plants is urgently needed.

[0003] Carbon-14 in nuclear power plants exists in both solid and gaseous forms. Solid carbon-14 is mainly found in radioactive solid waste and decommissioning waste from nuclear power plants. This waste undergoes disposal, storage, and decommissioning within the plant and will not enter the environment. Gaseous carbon-14, however, is mainly found in reactor exhaust gases and coolants. This portion of carbon-14 can enter the environment through emissions and leaks, and then enter the biosphere through diffusion, sedimentation, and absorption by plant photosynthesis. Because carbon-14 can remain in animals and plants for a long time, it can have a significant impact on them. Therefore, gaseous carbon-14 from nuclear power plants should be a key focus of attention and treatment. If appropriate treatment measures are taken before gaseous carbon-14 is released into the environment to fix it, its environmental impact can be reduced.

[0004] The radioactive waste gas emitted by nuclear power plant exhaust gas treatment systems contains nuclides including iodine (I), strontium (Sr), cesium (Cs), krypton (Kr), xenon (Xe), carbon-14, and tritium. Iodine (I), strontium (Sr), and cesium (Cs) exist as aerosols or particles, krypton (Kr) and xenon (Xe) exist as inert gases, and carbon-14 and tritium mainly exist as gaseous compounds. With the current configuration of nuclear power plant radioactive waste gas treatment systems, primary filters, high-efficiency particulate filters, and activated carbon iodine adsorbers can effectively intercept and filter radioactive nuclide aerosols or particles such as iodine (I), strontium (Sr), and cesium (Cs). Due to their short half-lives, rare gases such as krypton (Kr) and xenon (Xe) can effectively attenuate their radioactivity through temporary decay. 133For example, after 60 days of decay, the radioactivity intensity can be reduced to one-thousandth of the original. However, due to the long half-life of carbon-14 nuclides and the stable properties of its compounds, filters cannot effectively retain it. With the existing configuration of nuclear power plants, it is impossible to achieve the reduction of the radioactivity intensity of carbon-14 or to achieve the retention and treatment of radioactive nuclides.

[0005] Research institutions around the world have never stopped testing carbon-14. Numerous studies have shown that carbon-14 in the gaseous effluents of pressurized water reactor nuclear power plants mainly exists in the form of alkanes and is emitted into the environment through the plant's chimney system.

[0006] C14 in gaseous effluents from nuclear power plants mainly originates from exhaust and purging of the primary loop system, existing in the form of compounds, primarily hydrocarbons and carbon dioxide (CO2). In pressurized water reactor (PWR) nuclear power plants, the main components of C14 in gaseous effluents are hydrocarbons, such as CH4 and C2H6, reaching 75-95%.

[0007] Because methane is a nonpolar molecule, it is difficult to separate it from hydrogen-containing waste gas through physical adsorption. Furthermore, methane is chemically stable, and apart from redox reactions with strong oxidants, there are currently no other mature industrial methods for its removal. Current methane conversion processes mainly include direct combustion, low-temperature plasma oxidation, and catalytic combustion oxidation. The advantages and disadvantages of these technologies are as follows:

[0008] Direct combustion of methane: In the field of C14 treatment in nuclear power plants, due to the extremely low organic content in the exhaust gas, a large amount of combustion aid needs to be added, resulting in high energy consumption and large investment. Furthermore, the end exhaust gas contains nitrogen oxides. Therefore, the direct combustion method is not suitable for the removal of trace C14 methane in nuclear power plants.

[0009] Methane low-temperature plasma oxidation technology: This technology has many advantages, such as low energy consumption, suitability for treating low-concentration, high-flow-rate gases, and high decomposition efficiency, theoretically achieving complete decomposition. However, despite these advantages, the high energy of plasma converts nitrogen in the treated gas into NO, NO2, NH3, and other gases, necessitating complex denitrification devices for C14 processing units. Furthermore, the plasma torch equipment used to generate plasma is expensive, there is insufficient experience in its engineering applications, and the risks are significant.

[0010] Methane catalytic combustion oxidation technology: The key to this technology lies in the catalyst. Catalysts can be classified into noble metal catalysts and non-noble metal catalysts according to their active components. The reaction mechanism of noble metal catalysts in the catalytic combustion of methane is as follows: Under the action of the noble metal catalyst, methane dissociates and adsorbs into methyl (CH3) or methylene (CH2). These methyl groups react with oxygen adsorbed on the surface of the noble metal to directly generate CO2 and H2O, or to generate formaldehyde (HCHO). The formaldehyde then further reacts with oxygen adsorbed on the noble metal to generate CO2 and H2O. Compared with direct combustion and plasma treatment technologies, catalytic oxidation technology has advantages such as low energy consumption, no flame, high safety, low waste volume, and mature application, making it more suitable for the treatment of C14 in nuclear power plants.

[0011] Converting organic carbon-14 into inorganic carbon-14 (i.e.) 14 After CO2 is produced, carbon-14 must be converted into a solid state for long-term storage without entering the environment.

[0012] CO2 has active physicochemical properties and is easy to absorb and process. Therefore, the common method used both domestically and internationally is to convert carbon-14 into carbon-14. 14 CO2 is then processed. However, due to 14 CO2 exists in trace amounts, making both detection and collection quite challenging. Research indicates that existing CO2 treatment technologies mainly include the following:

[0013] (1) Alkaline bubbling precipitation method: The principle of alkaline bubbling absorption precipitation method is simple. Ca(OH)2 or Ba(OH)2 is used to make alkaline solution to absorb CO2. After Ca(OH)2 or Ba(OH)2 absorbs CO2, it generates stable carbonates that can meet the requirements of long-term disposal, but it produces a lot of waste.

[0014] (2) Two-step chemical reaction method using sodium hydroxide absorption and lime water precipitation (referred to as wet absorption method). The basic principle is a two-step chemical reaction: sodium hydroxide absorbs CO2 to obtain a Na2CO3 solution, and lime water is added to the solution to precipitate the CO32-. 2- It turns into CaCO3 precipitate, and the precipitate is filtered out and disposed of as low- and intermediate-level radioactive solid waste, which generates a large amount of waste.

[0015] (3) Alkaline bed absorption method (referred to as dry absorption method): The basic principle of alkaline absorption bed is to make a dry absorption bed with a solid absorbent (such as alkali metal hydroxide). When CO2-containing gas passes through the solid absorbent, CO2 reacts with the alkali metal hydroxide in it to achieve the purpose of removing CO2. However, the alkaline bed that is saturated with adsorption still needs to be packaged and treated as waste solids.

[0016] (4) Ethanolamine Absorption Method: Washing the gas in ethanolamine (HOCH2CH2NH2) is a method for removing CO2. The basic principle is that ethanolamine has a high adsorption efficiency for CO2 within a certain temperature range. As the temperature increases, CO2 is released, thus enriching the CO2. A challenge in practical operation using ethanolamine is that it is oxidized into oxalic acid and aminoacetic acid. These oxides can corrode the equipment and affect the absorption efficiency, greatly increasing the difficulty of engineering applications.

[0017] (5) Molecular sieve adsorption method:

[0018] Molecular sieves are synthetic aluminosilicates with a microporous cubic lattice. They can be used to create adsorption beds, where CO2 gas containing C14 is trapped after passing through the molecular sieve. The advantages are: the principle of molecular sieve adsorption devices is simple. The disadvantages are: the adsorption efficiency of molecular sieves is temperature-dependent, requiring a low-temperature operating environment; and since CO2 adsorption is a physical adsorption process, CO2 will still be released if conditions change, making subsequent solidification processes complex.

[0019] (6) Isotope separation method: Isotope separation technology can be used to concentrate CO2 gas containing carbon-14. There are many methods of isotope separation, such as the displacement method, which uses some compounds to replace CO2 containing carbon-14. The principle of the method is relatively simple, but the single separation efficiency is very low, the equipment is large, the single separation efficiency is low, and the required investment is relatively high.

[0020] As mentioned above, existing methane conversion processes and CO2 treatment technologies all have different shortcomings. Therefore, in order to reduce the amount of gaseous carbon-14 emitted from nuclear power plants and achieve emission standards, improve treatment efficiency, prevent the generation of other secondary wastes, reduce equipment investment and costs, and realize industrial application, further research and development of new carbon-14 treatment technologies for radioactive waste gas from nuclear power plants is still needed. This will provide more possibilities for the country to further improve the emission standards for gaseous carbon-14 from nuclear facilities and strengthen the control of gaseous carbon-14 emissions from nuclear facilities. Summary of the Invention

[0021] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a process, system and application for treating C14 in radioactive waste gas from nuclear power plants, which can reduce the amount of gaseous C14 emitted into the environment from nuclear power plants and achieve emission standards, improve treatment efficiency, prevent the generation of other secondary waste, reduce equipment investment and investment costs, and realize industrial application.

[0022] To achieve the above and other related objectives, the present invention provides a process for treating carbon-14 in radioactive waste gas from nuclear power plants, comprising:

[0023] Separation of carbon-14:

[0024] Catalytic oxidation is used to convert organic carbon-14 into inorganic carbon-14 by treating radioactive waste gas from decayed nuclear power plants. 14 CO2 was produced, resulting in the first gaseous effluent.

[0025] The gaseous state in the first gaseous effluent 14 CO2 is converted into liquid. 14 CO2 is separated to obtain the first liquid effluent and the second gaseous effluent that meets the normal emission standards;

[0026] Fixation of carbon-14:

[0027] The first liquid effluent is heated to vaporize it, resulting in a third gaseous effluent;

[0028] The third gaseous effluent is subjected to countercurrent water washing to obtain gaseous substances that have dissolved and absorbed the third gaseous effluent. 14 The second liquid effluent of CO2, and the fourth gaseous effluent with a carbon-14 content reaching a predetermined value;

[0029] The second liquid effluent is treated with ion exchange resin to fix carbon-14 onto the resin, resulting in waste resin containing carbon-14.

[0030] Furthermore, during the catalytic oxidation process, organic carbon-14 undergoes a catalytic oxidation reaction with oxygen to generate inorganic carbon-14. 14 CO2.

[0031] Furthermore, the catalyst used in the catalytic oxidation process is a noble metal catalyst.

[0032] Furthermore, the reaction temperature of the catalytic oxidation process is 350–450°C.

[0033] Furthermore, the gaseous state in the first gaseous effluent... 14 CO2 is converted into liquid. 14 Methods for processing CO2 include:

[0034] Based on the differences in boiling points of the various gases in the first gaseous effluent, the first gaseous effluent is subjected to deep cryogenic pressure to remove the gaseous components. 14 CO2 is converted into liquid. 14 CO2.

[0035] Furthermore, the pressurized cryogenic conditions include: pressurizing to 5 to 6 atmospheres, and / or, cooling temperature of -31 to -39°C.

[0036] Furthermore, the second gaseous effluent can be discharged normally after being heated to room temperature.

[0037] Furthermore, the first liquid effluent is heated to room temperature to vaporize it, resulting in a third gaseous effluent.

[0038] Furthermore, countercurrent water washing is performed using waste liquid from nuclear power plants that has been treated to meet emission standards.

[0039] Furthermore, during the countercurrent washing process, the pH is controlled to be between 7.5 and 8.5.

[0040] Furthermore, during the countercurrent water washing, 14 CO2 and OH - A reaction occurs, producing 14 CO3 2- and / or H 14 CO3 - To dissolve and absorb the gaseous substances in the third gaseous effluent. 14 CO2.

[0041] Furthermore, during the countercurrent water washing, the gas and liquid phases come into countercurrent contact through a packing layer containing particulate packing material, thereby increasing the gas-liquid contact area and making... 14 CO2 is fully dissolved in water.

[0042] Furthermore, during the countercurrent water washing, the gas phase is circulated and countercurrent water washing is performed until the carbon-14 content in the gas phase reaches a predetermined value, thus obtaining gaseous substances that have been fully dissolved and absorbed from the third gaseous effluent. 14 The second liquid effluent of CO2, and the fourth gaseous effluent with a carbon-14 content reaching a predetermined value.

[0043] Furthermore, the fourth gaseous effluent can be discharged normally after being heated to room temperature.

[0044] Furthermore, a weak acid cation exchange resin is used for ion exchange resin treatment, and the functional groups on the weak acid cation exchange resin can... 14 CO3 2- and / or H 14 CO3 - It is fixed to the resin.

[0045] Furthermore, the second liquid effluent is treated with ion exchange resin to fix carbon-14 onto the resin, resulting in a third liquid effluent, which is a waste liquid that meets emission standards.

[0046] Furthermore, the gaseous state in the first gaseous effluent 14 CO2 is converted into liquid. 14 Before CO2, the process also includes: cooling the first gaseous effluent to room temperature.

[0047] Furthermore, the process also includes treating the carbon-14-containing waste resin using a nuclear power plant solid waste treatment method.

[0048] This invention also provides a carbon-14 treatment system for radioactive waste gas from nuclear power plants, comprising a carbon-14 separation unit and a carbon-14 fixation unit, wherein the carbon-14 separation unit includes a catalytic oxidation unit and... 14 The CO2 liquefaction unit, the carbon-14 fixation unit includes a first heating unit, a counter-current water washing unit and an ion exchange resin treatment unit;

[0049] The catalytic oxidation unit is used to catalytically oxidize the decay-treated radioactive waste gas from nuclear power plants, converting organic carbon-14 into inorganic carbon-14. 14 CO2 was produced, resulting in the first gaseous effluent.

[0050] The 14 The CO2 liquefaction unit is used to liquefy the gaseous substances in the first gaseous effluent. 14 CO2 is converted into liquid. 14 CO2 is separated to obtain the first liquid effluent and the second gaseous effluent that meets the normal emission standards;

[0051] The first heating unit is used to heat the first liquid effluent to vaporize it, thereby obtaining a third gaseous effluent;

[0052] The countercurrent washing unit is used to perform countercurrent washing on the third gaseous effluent to obtain gaseous substances that have dissolved and absorbed the third gaseous effluent. 14 The second liquid effluent of CO2, and the fourth gaseous effluent with a carbon-14 content reaching a predetermined value;

[0053] The ion exchange resin treatment unit is used to treat the second liquid effluent with ion exchange resin to fix carbon-14 onto the resin, thereby obtaining waste resin containing carbon-14.

[0054] Furthermore, the catalytic oxidation unit includes a catalytic oxidation reactor, in which organic carbon-14 reacts with oxygen to produce inorganic carbon-14. 14 The location of CO2; the catalytic oxidation reactor is filled with a catalyst, preferably a noble metal catalyst.

[0055] Furthermore, the catalytic oxidation unit also includes an oxygen supply device for providing oxygen for the catalytic oxidation process.

[0056] Furthermore, the aforementioned 14The CO2 liquefaction unit includes a pressurization device and a cryogenic device. The pressurization device is used to pressurize the first gaseous effluent, and the cryogenic device is used to cryogenically process the pressurized first gaseous effluent, thereby removing the gaseous components from the effluent. 14 CO2 is converted into liquid. 14 CO2.

[0057] Furthermore, the countercurrent washing unit includes a packed bed reactor, in which a washing bed is provided, and the washing bed is provided with a packing layer containing particulate packing.

[0058] Furthermore, the countercurrent water washing unit also includes a water supply device, which is used to provide washing liquid for the countercurrent water washing process. The washing liquid is waste liquid from the nuclear power plant that has been treated to meet emission standards.

[0059] Furthermore, the ion exchange resin treatment unit includes an ion exchanger filled with ion exchange resin, preferably a weak acid cation exchange resin.

[0060] Furthermore, the C14 separation unit also includes components disposed in the catalytic oxidation unit and 14 A pre-cooling unit between CO2 liquefaction units, the pre-cooling unit being used to cool the first gaseous effluent to room temperature.

[0061] Furthermore, the carbon-14 fixation unit also includes a waste resin treatment unit, which uses nuclear power plant solid waste treatment methods to treat the carbon-14-containing waste resin.

[0062] Furthermore, the aforementioned 14 The CO2 liquefaction unit is connected to the nuclear power plant's gas emission system to discharge the second gaseous effluent.

[0063] Furthermore, the countercurrent water washing unit is connected to the nuclear power plant's gas emission system to discharge the fourth gaseous effluent.

[0064] Furthermore, the system also includes a second heating unit, which is disposed in the... 14 The CO2 liquefaction unit is located between the nuclear power plant gas emission system and the gas effluent system, and is used to heat the second gaseous effluent. Alternatively, the second heating unit is located between the countercurrent water washing unit and the nuclear power plant gas emission system, and is used to heat the fourth gaseous effluent.

[0065] Furthermore, the first heating unit and the second heating unit include heating devices, which may be, for example, heat exchangers.

[0066] The present invention also provides the application of the carbon-14 treatment process and / or system described above in nuclear power plant radioactive waste gas in radioactive waste treatment.

[0067] As described above, the carbon-14 treatment process, system, and application in nuclear power plant radioactive waste gas of the present invention have the following beneficial effects:

[0068] 1) Using catalytic oxidation to convert organic carbon-14 into inorganic carbon-14. 14 CO2 is then pressurized and cryogenic technology is used to convert the carbon-14 in the first gaseous effluent into liquid and separate it completely, thereby obtaining the second gaseous effluent that meets the normal emission standards and achieving emission compliance.

[0069] 2) Countercurrent water washing is used to transfer C14 from the gas phase to the liquid phase, converting it into... 14 CO3 2- and / or H 14 CO3 - The carbon-14 in the radioactive gas is converted into solid carbon-14 fixed on the waste resin through adsorption using ion exchange resin. This allows the carbon-14 to be treated and disposed of without entering the environment.

[0070] 3) In the countercurrent water washing process, using packing material with a large specific surface area can increase the gas-liquid contact area and improve the reaction efficiency; using waste liquid to be discharged from nuclear power plants to wash carbon-14 can avoid increasing the amount of radioactive wastewater.

[0071] 4) When treating radioactive waste liquid containing C14 after countercurrent water washing, weak acid cation exchange resin is used, which has a higher removal efficiency than weak acid anion exchange resin.

[0072] 5) Nuclear power plants are usually equipped with waste resin treatment facilities. The waste resin generated can be cured and treated together with other waste resins in the nuclear power plant without adding treatment equipment or generating other secondary waste.

[0073] In summary, this invention employs a two-step process to separate and fix carbon-14 in radioactive waste gas from nuclear power plants, reducing the amount of gaseous carbon-14 emitted into the environment and achieving emission standards. Furthermore, the technology used is highly efficient, generates no secondary waste, does not increase the volume of radioactive wastewater, and reduces equipment investment and costs. This makes it highly suitable for industrial application, addresses the urgent needs currently faced by nuclear power plants, and enhances public confidence in the safe operation of nuclear power plants. Therefore, it has extremely high application prospects and significant social importance. Attached Figure Description

[0074] Figure 1The diagram shows a flow chart of the carbon-14 treatment process in radioactive waste gas from nuclear power plants in some embodiments of the present invention.

[0075] Figure 2 The diagram shown is a flow chart of a process for treating carbon-14 in radioactive waste gas from nuclear power plants, as illustrated in some other embodiments of the present invention.

[0076] Figure 3 The diagram shows the layout of a carbon-14 treatment system for radioactive waste gas from a nuclear power plant in some embodiments of the present invention.

[0077] Figure 4 The diagram shows the layout of a carbon-14 treatment system for radioactive waste gas from a nuclear power plant, as shown in some other embodiments of the present invention.

[0078] Explanation of reference numerals in the attached figures:

[0079] C14 separation unit 100,

[0080] Catalytic oxidation unit 110, catalytic oxidation reactor 111, oxygen supply equipment 112,

[0081] Pre-cooling unit 120,

[0082] 14 CO2 liquefaction unit 130, pressurization equipment 131, cryogenic equipment 132;

[0083] Carbon-14 fixed unit 200;

[0084] First heating unit 210,

[0085] Countercurrent washing unit 220, packed bed reactor 221, water supply equipment 222

[0086] Ion exchange resin treatment unit 230,

[0087] Waste resin treatment unit 300,

[0088] Second heating unit 400. Detailed Implementation

[0089] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0090] In this invention, unless otherwise stated, the term "multiple" means two or more.

[0091] The character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0092] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0093] like Figure 1 As shown, one embodiment of the present invention provides a process for treating carbon-14 in radioactive waste gas from nuclear power plants, comprising:

[0094] Separation of carbon-14:

[0095] Catalytic oxidation is used to convert organic carbon-14 into inorganic carbon-14 by treating radioactive waste gas from decayed nuclear power plants. 14 CO2 was produced, resulting in the first gaseous effluent.

[0096] The gaseous state in the first gaseous effluent 14 CO2 is converted into liquid. 14 CO2 is separated to obtain the first liquid effluent and the second gaseous effluent that meets the normal emission standards;

[0097] Fixation of carbon-14:

[0098] The first liquid effluent is heated to vaporize it, resulting in the third gaseous effluent;

[0099] The third gaseous effluent is countercurrently washed with water to obtain gaseous substances that have dissolved and absorbed the third gaseous effluent. 14 The second liquid effluent of CO2, and the fourth gaseous effluent with a carbon-14 content reaching a predetermined value;

[0100] The second liquid effluent was treated with ion exchange resin to fix carbon-14 onto the resin, resulting in waste resin containing carbon-14.

[0101] As described above, the process provided by this invention uses a two-step process to achieve the separation and fixation of carbon-14 in radioactive waste gas from nuclear power plants:

[0102] The first step is the separation of carbon-14: First, the radioactive waste gas from the nuclear power plant, after decay treatment, undergoes catalytic oxidation to convert the organic carbon-14 into inorganic carbon-14. 14 CO2, then at 5-6 atmospheres of pressure, will be in a gaseous state. 14 CO2 is converted into liquid. 14 CO2 is used to separate all the carbon-14 in the first gaseous effluent.

[0103] The second step is the fixation of carbon-14: the separated liquid... 14CO2 (i.e., the first liquid effluent) is heated and vaporized into a gas. This gas is then subjected to counter-current water washing, which completely dissolves the carbon-14 in the water, transforming it into... 14 CO3 2- and / or H 14 CO3 - Then, it is removed by ion exchange resin treatment. 14 CO3 2- and / or H 14 CO3 - Once the resin is saturated, it becomes waste resin containing C14, which can be sent to the nuclear power plant's waste resin treatment system for solidification and other treatments along with other waste resins.

[0104] Because the carbon-14 content in the radioactive gaseous effluents of nuclear power plants is extremely low, typically only a few grams to tens of grams per year, the energy consumption of the aforementioned carbon-14 separation process is also relatively small. However, the separated carbon-14... 14 CO2 is still a radioactive substance and cannot be released into the environment or stored for a long time. Therefore, this invention also performs carbon-14 fixation treatment. Through the above two-step process, carbon-14 in the radioactive waste gas of nuclear power plants is separated and transformed into solid carbon-14 fixed on waste resin, which can be treated and disposed of without entering the environment. At the same time, a second gaseous effluent that meets the normal emission standards and a fourth gaseous effluent with a carbon-14 content reaching a predetermined value are also obtained. Both the second and fourth gaseous effluents can be discharged in compliance with standards, thus achieving the standard emission of gaseous effluents.

[0105] In some embodiments, during the catalytic oxidation process, organic carbon-14 reacts with oxygen in a catalytic oxidation reaction to generate inorganic carbon-14. 14 CO2. It is important to note that the catalytic oxidation process requires the introduction of an appropriate amount of oxygen, meaning the amount of oxygen added needs to be strictly controlled.

[0106] Furthermore, in some embodiments, the catalyst used in the catalytic oxidation process is a noble metal catalyst. The noble metal catalyst of this invention can be any common noble metal catalyst used in the catalytic oxidation of organic hydrocarbons such as methane, without any other special limitations.

[0107] Furthermore, in some embodiments, the reaction temperature of the catalytic oxidation process is 350–450°C, such as 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450°C, etc.

[0108] In some embodiments, the gaseous state in the first gaseous effluent 14 CO2 is converted into liquid. 14 Methods for processing CO2 include:

[0109] Based on the differences in boiling points of the various gases in the first gaseous effluent, the first gaseous effluent is subjected to deep cryogenic pressure to remove the gaseous components. 14 CO2 is converted into liquid. 14 CO2.

[0110] Furthermore, in some embodiments, the first gaseous effluent is pressurized to 5 to 6 atmospheres and then subjected to deep cooling.

[0111] Furthermore, in some embodiments, when the first gaseous effluent is cryogenically cooled, the cooling temperature is -31 to -39°C, for example -31, -32, -33, -34, -35, -36, -37, -38, -39°C, etc.

[0112] Because radioactive waste gas mainly contains nitrogen, hydrogen, and trace amounts of radioactive nuclides, the boiling points of nitrogen (-196℃), hydrogen (-252.87℃), methane (-161.5℃), ethane (-88.6℃), and carbon dioxide (-78.5℃) are all significant. Furthermore, the boiling points of these gases increase with increasing pressure. To conserve energy, this invention employs pressurized cryogenic separation of C14. For example, at 5 atmospheres, carbon dioxide becomes liquid at -31.1℃, while other gases remain gaseous. Therefore, controlling the temperature at approximately -35℃ during cryogenic separation effectively separates the gaseous carbon. 14 CO2 turns into liquid 14 CO2 is used to separate the radioactive waste gas. Of course, the specific pressure and cooling temperature can be adjusted within the above range according to the properties of carbon dioxide and the actual situation.

[0113] In some embodiments, the second gaseous effluent is heated to room temperature before being discharged in accordance with normal standards.

[0114] In some embodiments, heating the first liquid effluent to room temperature can vaporize it, yielding a third gaseous effluent.

[0115] In some embodiments, countercurrent water washing is performed using treated wastewater from a nuclear power plant that meets emission standards. The water used for countercurrent water washing is treated wastewater from a nuclear power plant that meets emission standards and is ready for discharge, thus avoiding the generation of additional radioactive wastewater.

[0116] In some embodiments, during countercurrent washing, the pH is controlled to be 7.5–8.5. Further, in some embodiments, an alkaline adjuster is added to control the pH to 7.5–8.5; the alkaline adjuster includes, but is not limited to, sodium hydroxide, potassium hydroxide, sodium acetate, etc.

[0117] In some embodiments, during counter-current washing... 14 CO2 and OH -A reaction occurs, producing 14 CO3 2- and / or H 14 CO3 - To dissolve and absorb the gaseous substances in the third gaseous effluent. 14 CO2.

[0118] In some embodiments, during countercurrent washing, the gas and liquid phases come into countercurrent contact through a packing layer containing particulate packing material to increase the gas-liquid contact area, thereby... 14 CO2 is fully dissolved in water.

[0119] In some embodiments, during countercurrent water washing, the gas phase is circulated for countercurrent water washing until the carbon-14 content in the gas phase reaches a predetermined value, resulting in a gaseous effluent that has fully dissolved and absorbed the third gaseous effluent. 14 The second liquid effluent of CO2 and the fourth gaseous effluent with a carbon-14 content reaching a predetermined value. In other words, the countercurrent water washing process can be repeated until the carbon-14 content in the gas phase reaches the predetermined value, after which it can be sent to the chimney for normal emission in compliance with standards.

[0120] In some embodiments, the fourth gaseous effluent is heated to room temperature before being discharged in accordance with standards. In some embodiments, a weak acid cation exchange resin is used for ion exchange resin treatment, and the functional groups on the weak acid cation exchange resin can... 14 CO3 2- and / or H 14 CO3 - It is fixed on the resin and has a higher removal efficiency than the anions of weak acid salts.

[0121] In some embodiments, the second liquid effluent is treated with an ion exchange resin to fix carbon-14 onto the resin, yielding a third liquid effluent, which is waste liquid that meets emission standards. Because no other nuclides are introduced during the carbon-14 treatment process of this invention, the emission standards are still met, and the effluent can be sent for compliant discharge.

[0122] like Figure 2 As shown, in some embodiments, the gaseous state in the first gaseous effluent 14 CO2 is converted into liquid. 14 Before CO2, the process includes cooling the first gaseous effluent to room temperature. After catalytic oxidation, the organic carbon-14 has been fully converted into the inorganic form. 14 CO2 is in gaseous form, but the gas temperature is relatively high at this point. Therefore, it needs to be cooled to room temperature first to facilitate subsequent liquefaction and separation.

[0123] In some embodiments, the process further includes treating the C14-containing waste resin using nuclear power plant solid waste treatment methods, which include, but are not limited to, solidification treatment and shallow surface disposal. Nuclear power plants are typically equipped with waste resin treatment facilities, eliminating the need for additional equipment. The generated waste resin can be treated together with other waste resins from the nuclear power plant, thus avoiding the addition of treatment equipment and the generation of other secondary waste.

[0124] Furthermore, it should be noted that meeting the normal emission standards and achieving the predetermined carbon-14 content in this invention both refer to meeting the national standards related to the emission of radionuclides (including carbon-14) from gaseous effluents of nuclear power plants.

[0125] like Figure 3 As shown, another embodiment of the present invention provides a carbon-14 treatment system for radioactive waste gas from a nuclear power plant, comprising a carbon-14 separation unit and a carbon-14 fixation unit arranged sequentially according to the above-described process steps. The carbon-14 separation unit includes a catalytic oxidation unit 110 and a carbon-14 fixation unit arranged sequentially according to the above-described process steps. 14 The CO2 liquefaction unit 130 and the carbon 14 fixation unit include a first heating unit 210, a countercurrent water washing unit 220 and an ion exchange resin treatment unit 230 arranged sequentially according to the above process steps.

[0126] The catalytic oxidation unit 110 is used to catalytically oxidize radioactive waste gas from nuclear power plants that has undergone decay treatment, converting organic carbon-14 into inorganic carbon-14. 14 CO2 was produced, resulting in the first gaseous effluent.

[0127] 14 CO2 liquefaction unit 130 is used to liquefy the gaseous phase in the first gaseous effluent. 14 CO2 is converted into liquid. 14 CO2 is separated to obtain the first liquid effluent and the second gaseous effluent that meets the normal emission standards;

[0128] The first heating unit 210 is used to heat the first liquid effluent to vaporize it, thereby obtaining the third gaseous effluent;

[0129] The countercurrent washing unit 220 is used to perform countercurrent washing on the third gaseous effluent to obtain gaseous substances that have dissolved and absorbed the third gaseous effluent. 14 The second liquid effluent of CO2, and the fourth gaseous effluent with a carbon-14 content reaching a predetermined value;

[0130] The ion exchange resin treatment unit 230 is used to treat the second liquid effluent with ion exchange resin to fix carbon 14 onto the resin, thereby obtaining waste resin containing carbon 14.

[0131] Please refer to the following examples. Figure 4 The image shows a carbon-14 treatment system for radioactive waste gas from a nuclear power plant.

[0132] In some embodiments, the catalytic oxidation unit 110 includes a catalytic oxidation reactor 111, in which organic carbon 14 undergoes a catalytic oxidation reaction with oxygen to generate inorganic carbon 14. 14 The CO2 is located in the catalytic oxidation reactor 111, which is filled with a catalyst, preferably a noble metal catalyst.

[0133] In some embodiments, the catalytic oxidation unit 110 further includes an oxygen supply device 112 for providing oxygen for the catalytic oxidation process.

[0134] In some embodiments, 14 The CO2 liquefaction unit 130 includes a pressurizing device 131 and a cryogenic device 132; the pressurizing device 131 is used to pressurize the first gaseous effluent, for example, it can be a compressor; the cryogenic device 132 is used to cryogenically process the pressurized first gaseous effluent, thereby reducing the gaseous state of the effluent. 14 CO2 is converted into liquid. 14 CO2.

[0135] In some embodiments, the countercurrent washing unit 220 includes a packed bed reactor 221, in which a washing bed is disposed, and a packing layer containing particulate packing is disposed in the washing bed. To achieve countercurrent washing, the gas and liquid phases are fed into the packed bed reactor 221 from the bottom and top, respectively, and pass through the washing bed in countercurrent contact, causing... 14 CO2 is fully dissolved in water.

[0136] In some embodiments, the countercurrent washing unit 220 further includes a water supply device 222, which provides washing liquid for the countercurrent washing process. The washing liquid is waste liquid from a nuclear power plant that has been treated to meet emission standards.

[0137] In some embodiments, the ion exchange resin treatment unit 230 includes an ion exchanger filled with ion exchange resin, preferably a weakly acidic cation exchange resin. The ion exchanger can be a common type, such as an ion exchange adsorption bed.

[0138] In some embodiments, the carbon-14 separation unit further includes components disposed in the catalytic oxidation unit 110 and... 14 The pre-cooling unit 120 between the CO2 liquefaction units 130 is used to cool the first gaseous effluent to room temperature.

[0139] In some embodiments, the carbon-14 fixation unit further includes a waste resin treatment unit 300, which treats the carbon-14-containing waste resin using nuclear power plant solid waste treatment methods.

[0140] In some embodiments, 14 CO2 liquefaction unit 130 is connected to the nuclear power plant's gas emission system (e.g., a chimney) to emit a second gaseous effluent.

[0141] In some embodiments, the countercurrent washing unit 220 is connected to the nuclear power plant gas emission system to discharge a fourth gaseous effluent.

[0142] In some embodiments, the system further includes a second heating unit 400, the second heating unit 400 being disposed in 14 The CO2 liquefaction unit 130 is located between the nuclear power plant gas emission system and is used to heat the second gaseous effluent, and / or the second heating unit 400 is located between the countercurrent water washing unit 220 and the nuclear power plant gas emission system and is used to heat the fourth gaseous effluent.

[0143] In some embodiments, the first heating unit 210 and the second heating unit 400 include heating devices, such as heat exchangers.

[0144] It should be noted that the carbon-14 treatment system for radioactive waste gas from nuclear power plants provided in the above embodiments and the carbon-14 treatment process for radioactive waste gas from nuclear power plants provided in the above embodiments belong to the same concept. The specific operation methods of each unit have been described in detail in the process embodiments and will not be repeated here. In practical applications, the carbon-14 treatment system for radioactive waste gas from nuclear power plants provided in the above embodiments can be assigned to different functional units as needed, that is, the system can be divided into different functional units to complete all or part of the functions described above, and this is not a limitation.

[0145] Another embodiment of the present invention also provides the application of the carbon-14 treatment process and / or system in radioactive waste gas from nuclear power plants as described in the embodiments / exemplaries above in radioactive waste treatment.

[0146] The emissions of airborne carbon-14 from some operating nuclear power plants in China are already approaching the emission limits stipulated by national standards. The technology provided by this invention can address the urgent needs of nuclear power plants on-site, laying the foundation for subsequent research on carbon-14 treatment and reuse technologies in the field of nuclear power plant waste. Simultaneously, it also provides the possibility for the country to further improve airborne carbon-14 emission targets for nuclear facilities and strengthen emission control. Furthermore, if industrial applications are realized, it can reduce the amount of airborne carbon-14 emitted into the environment from nuclear power plants, enhancing public confidence in the safe operation of nuclear power, thus possessing significant social implications.

[0147] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A process for the treatment of carbon 14 in radioactive exhaust gases from a nuclear power plant, characterized in that, The process comprises: Separation of carbon 14: Catalytic oxidation of decayed nuclear power plant radioactive exhaust gas converts organic carbon 14 into inorganic carbon 14 CO2, resulting in a first gaseous effluent 14 CO2, resulting in a first gaseous effluent converting the CO2 in the first gaseous effluent to a liquid 14 CO2 into a liquid 14 CO2 and separating it to obtain a first liquid effluent and a second gaseous effluent that meets normal emission standards. Fixing of carbon 14: Heating the first liquid effluent to vaporize it to obtain a third gaseous effluent; countercurrently washing the third gaseous effluent with a waste liquid from a nuclear power plant that has been treated to meet discharge standards, to obtain a fourth gaseous effluent that has dissolved and absorbed gaseous contaminants from the third gaseous effluent 14 a second liquid effluent of CO2, and a fourth gaseous effluent having a predetermined level of carbon 14 Treating the second liquid effluent with ion exchange resin to fix carbon 14 on the resin to obtain waste resin containing carbon 14.

2. The process of claim 1, wherein: In the catalytic oxidation process, the organic state carbon 14 reacts with oxygen to generate the inorganic state carbon 14 14 CO2; And / or, the catalyst used in the catalytic oxidation process is a noble metal catalyst; And / or, the reaction temperature of the catalytic oxidation process is 350-450℃.

3. The process of claim 1, wherein: converting the gaseous CO2 in the first gaseous effluent into a liquid CO2 14 CO2 into a liquid CO2 14 The method of converting CO2 into a liquid CO2 comprises: based on the difference in boiling points of the various gases in the first gaseous effluent, subjecting the first gaseous effluent to pressurized cryogenic cooling to separate gaseous CO2 from the other gaseous components in the first gaseous effluent 14 CO2 into a liquid state 14 CO2.

4. The process of claim 3, wherein: The pressurized deep cooling condition comprises: pressurizing to 5-6 atmospheres, and / or, the cooling temperature is -31--39℃.

5. The process of claim 1, wherein: The second gaseous effluent and / or the fourth gaseous effluent can be normally discharged after being heated to normal temperature. And / or, heating the first liquid effluent to normal temperature to vaporize it to obtain a third gaseous effluent.

6. The process according to claim 1, wherein: The pH is controlled to be 7.5-8.5 during the countercurrent water washing; and / or, said counter-current water wash is at a temperature of 30°C to 100°C, 14 CO2 and OH - react to form 14 CO3 2- and / or H 14 CO3 - to solubly absorb gaseous 14 CO2 from said third gaseous effluent; And / or, during the countercurrent water washing, the gas phase and the liquid phase are countercurrently contacted through a filler layer filled with particulate filler; and / or, said counter-current water washing, the gas phase is circulated for counter-current water washing until the carbon 14 content in the gas phase reaches a predetermined value, obtaining a fourth gaseous effluent substantially dissolved and absorbed in said third gaseous effluent 14 a second liquid effluent of CO2, and a fourth gaseous effluent with a carbon 14 content reaching a predetermined value.

7. The process of claim 1, wherein: The ion exchange resin treatment is performed by using a weak acid type cation exchange resin.

8. The process of claim 1, wherein: Treating the second liquid effluent with ion exchange resin to fix carbon 14 on the resin also obtains a third liquid effluent, which is waste liquid meeting the discharge standard.

9. The process according to any one of claims 1 to 8, characterized in that: gaseous in said first gaseous effluent 14 CO2 into a liquid state 14 prior to the CO2, further comprising: cooling said first gaseous effluent to ambient temperature; And / or, the process further comprises: treating the waste resin containing carbon 14 by using a nuclear power plant waste solid treatment method.

10. A system for processing carbon 14 in radioactive exhaust gas from a nuclear power plant, characterized by: including a carbon 14 separation unit including a catalytic oxidation unit and 14 a CO2 liquefaction unit, the carbon 14 fixation unit including a first heating unit, a countercurrent water wash unit, and an ion exchange resin treatment unit; The catalytic oxidation unit is used for catalytic oxidation of the decay-treated radioactive exhaust gas of a nuclear power plant, converting carbon 14 in organic state into carbon 14 in inorganic state 14 CO2, obtaining a first gaseous effluent; The 14 The CO2 liquefaction unit is used to convert gaseous CO2 in the first gaseous effluent into liquid CO2 14 CO2 into liquid CO2 14 CO2 and separate it out, obtaining a first liquid effluent, and a second gaseous effluent that meets normal compliance emission conditions; The first heating unit is used for heating the first liquid effluent to vaporize it to obtain a third gaseous effluent; the countercurrent water washing unit is used for countercurrent water washing of the third gaseous effluent, to obtain a second liquid effluent of CO2 and a fourth gaseous effluent with a carbon 14 content reaching a predetermined value 14 CO2, and a fourth gaseous effluent with a carbon 14 content reaching a predetermined value; the countercurrent water washing unit comprises a water supply device used for providing a water washing liquid for the countercurrent water washing process, the water washing liquid being a waste liquid in the nuclear power plant after treatment and meeting discharge standards; The ion exchange resin treatment unit is used for treating the second liquid effluent with ion exchange resin to fix carbon 14 on the resin to obtain waste resin containing carbon 14.

11. The system of claim 10, wherein: The catalytic oxidation unit comprises a catalytic oxidation reactor, which catalytically oxidizes organic-state carbon 14 with oxygen to generate inorganic-state carbon 14 14 CO2; the catalytic oxidation reactor is filled with a catalyst; And / or, the catalytic oxidation unit further comprises an oxygen supply device for providing oxygen for the catalytic oxidation process; and / or, the 14 The CO2 liquefaction unit comprises a pressurization device for pressurizing the first gaseous effluent and a cryogenic device for cryogenically treating the pressurized first gaseous effluent to liquefy the CO2 contained therein. 14 The CO2 is converted into liquid 14 CO2.

12. The system of claim 10, wherein: The countercurrent water washing unit comprises a packed bed reactor, and a water washing bed is arranged in the packed bed reactor, and a filler layer filled with particulate filler is arranged in the water washing bed; And / or, the ion exchange resin treatment unit comprises an ion exchanger filled with ion exchange resin.

13. The system of any of claims 10-12, wherein: The carbon 14 separation unit further comprises a pre-cooling unit disposed between the catalytic oxidation unit and 14 the CO2 liquefaction unit, the pre-cooling unit for cooling the first gaseous effluent to ambient temperature; And / or, the carbon 14 fixing unit further comprises a waste resin treatment unit for treating the waste resin containing carbon 14 by using a nuclear power plant waste solid treatment method; and / or, the 14 The CO2 liquefaction unit is connected to a nuclear power plant gas exhaust system to exhaust the second gaseous effluent. And / or, the countercurrent water washing unit is connected to a nuclear power plant gas discharge system to discharge the fourth gaseous effluent.

14. The system of claim 13, wherein: The system also comprises a second heating unit, which is arranged between the 14 a CO2 liquefaction unit between the nuclear power plant gas exhaust system and for heating the second gaseous effluent, and / or the second heating unit is arranged between the countercurrent water scrubbing unit and the nuclear power plant gas exhaust system and for heating the fourth gaseous effluent.

15. Application of the process for treating carbon 14 in radioactive waste gas of a nuclear power plant according to any one of claims 1-9 and / or the system for treating carbon 14 in radioactive waste gas of a nuclear power plant according to any one of claims 10-14 in radioactive waste treatment.

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