Treatment process and system for carbon-14 in radioactive waste gas of nuclear power plant, and application thereof

Abstract

A treatment process and system for carbon-14 in radioactive waste gas of a nuclear power plant, and an application thereof. The treatment process for carbon-14 in radioactive waste gas of a nuclear power plant comprises: performing catalytic oxidation on decay-treated radioactive waste gas of a nuclear power plant to convert organic carbon-14 into inorganic 14CO2; converting gaseous 14CO2 into liquid 14CO2 and separating same, and then vaporizing the liquid 14CO2 by heating to obtain a third gaseous effluent; obtaining, by means of counter-current washing, a second liquid effluent that has dissolved and absorbed gaseous 14CO2 in the third gaseous effluent; and treating the second liquid effluent by means of an ion exchange resin to obtain a waste resin containing carbon-14. The present invention reduces the emission of airborne carbon-14 from a nuclear power plant to the environment, achieves up-to-standard emission, improves treatment efficiency without producing other secondary waste, reduces equipment and investment costs, and achieves industrial application.

Description

Carbon 14 treatment process and system for radioactive waste gas of nuclear power plant and application thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of radioactive waste treatment, in particular to a carbon 14 treatment process and system for radioactive waste gas of a nuclear power plant and application thereof. BACKGROUND

[0002] Carbon 14 has weak beta radioactivity, the maximum ray energy is 156 keV, and has a long half-life of 5730 years, 14 Carbon 14 in the form of CO2 can be mixed with non-radioactive 12 CO2 in the air, participate in photosynthesis of plants, and thus enter the biosphere. When absorbed by the human body, there is a risk of long-term internal irradiation. Among the airborne radionuclides in the nuclear power plant, carbon 14 has the largest contribution to the collective dose of the public. With the increase in the number of nuclear power units in service and under construction, the public's awareness of environmental safety and the demand for environmental safety have increased, and it is urgent to carry out research on the treatment and removal technology of airborne carbon 14 in nuclear power plants.

[0003] Carbon 14 in the nuclear power plant is divided into solid and gaseous forms. Solid carbon 14 mainly exists in radioactive solid waste and decommissioning waste in the nuclear power plant, and these wastes will be disposed of, stored and decommissioned in the nuclear power plant and will not enter the environment. Airborne carbon 14 mainly exists in reactor exhaust gas and coolant, and this part of carbon 14 will enter the environment through emission, leakage and other ways, and then enter the biosphere through diffusion, sedimentation and photosynthesis of plants. Because carbon 14 can be long-term retained in animals and plants, it has a great impact on animals and plants, so airborne carbon 14 in the nuclear power plant should be the focus of attention and treatment. If appropriate treatment measures are taken to fix carbon 14 before it is discharged into the environment, the impact of carbon 14 on the environment can be reduced.

[0004] The radioactive waste gas discharged by the waste gas treatment system of the nuclear power plant contains nuclides including iodine I, strontium Sr, cesium Cs, krypton Kr, xenon Xe, carbon 14 and tritium, among which iodine I, strontium Sr and cesium Cs exist in the form of aerosol or particles, krypton Kr and xenon Xe exist in the form of inert gas, and carbon 14 and tritium mainly exist in the form of gaseous compounds. With the current configuration of the radioactive waste gas treatment system of the nuclear power plant, the initial filter, the high-efficiency particle filter and the activated carbon iodine adsorber can effectively intercept and filter the radioactive nuclide aerosol or particles of iodine I, strontium Sr and cesium Cs; krypton Kr and xenon Xe are short-lived and can be effectively attenuated by temporary storage and decay; and carbon 14 and tritium mainly exist in the form of gaseous compounds and can be effectively removed by the activated carbon iodine adsorber and the activated carbon tritium adsorber. 133For example, after 60 days of decay, the radioactivity intensity can be attenuated to one thousandth of the original; while carbon 14 has a longer half-life of the nuclide, and the compound is stable, it is difficult to intercept it by the filter. With the existing configuration of nuclear power plants, it is impossible to achieve the attenuation of the radioactivity intensity of carbon 14 or the interception of the radionuclide.

[0005] Research institutions around the world have never stopped detecting carbon 14. A large number of studies have shown that carbon 14 in gaseous effluent of pressurized water reactor nuclear power plants mainly exists in the form of alkanes and is discharged to the environment through the chimney system of the nuclear power plant.

[0006] Carbon 14 in gaseous effluent in nuclear power plants: mainly from exhaust and purge of primary loop system, in the form of compounds, the main components are hydrocarbons and carbon dioxide (CO2). The main components of carbon 14 in gaseous effluent of pressurized water reactor (PWR) are hydrocarbons, such as CH4 and C2H6, which account for 75-95%.

[0007] Because methane is a nonpolar molecule, it is difficult to separate methane from hydrogen-containing waste gas by physical adsorption method. In addition, methane is chemically stable, and except for redox reaction with strong oxidizing agents, there is no other mature method to remove methane in industry at present. The conversion processes of methane at present mainly include methane direct combustion method, methane low temperature plasma oxidation technology, methane catalytic combustion oxidation technology, etc. The advantages and disadvantages of the above technologies are as follows:

[0008] Methane direct combustion method: in the field of carbon 14 treatment in nuclear power plants, due to the extremely low content of organic matter in waste gas, a large amount of combustion-supporting agent needs to be added, which consumes a lot of energy and has high investment, and the end tail gas contains nitrogen oxides, so the direct combustion method is not suitable for the removal of trace carbon 14 methane in nuclear power plants.

[0009] Methane low temperature plasma oxidation technology: this technology has many advantages, such as low energy consumption, suitable for processing low concentration and large flow gas, high decomposition efficiency, and theoretically can achieve complete decomposition. However, although plasma oxidation has many advantages, because plasma has high energy, it can convert nitrogen in the treatment gas into NO, NO2, NH3 and other gases, so the carbon 14 treatment device needs to be equipped with a complex denitration device. In addition, the plasma torch equipment for generating plasma is expensive, and the engineering application experience is insufficient, which has high risk.

[0010] Methane catalytic combustion oxidation technology: the key to the reaction of the catalyst, the catalyst according to the active component can be divided into noble metal catalyst and non-noble metal catalyst, wherein the reaction mechanism of noble metal catalyst in the process of methane catalytic combustion is: under the action of noble metal catalyst, methane is dissociated and adsorbed as methyl (CH3) or methylene (CH2), which reacts with the oxygen adsorbed on the surface of noble metal to directly generate CO2 and H2O or generate formaldehyde (HCHO), and the formaldehyde further reacts with the oxygen adsorbed on the noble metal to generate CO2 and H2O. Compared with direct combustion method and plasma treatment technology, catalytic oxidation technology has the advantages of low energy consumption, no flame, high safety, less waste, mature application, etc., and is more suitable for the treatment of carbon 14 in nuclear power plants.

[0011] After converting organic state carbon 14 into inorganic state carbon 14 (i.e. 14 CO2), the carbon 14 needs to be converted into solid state for treatment before long-term storage and entering the environment.

[0012] CO2 has active physical and chemical properties and is easy to absorb and treat, so the usual way at home and abroad is to convert carbon 14 into 14 CO2 for treatment. However, due to the trace amount of 14 CO2, it is difficult to detect and collect. After investigation, the existing CO2 treatment technologies mainly include the following:

[0013] (1) Alkaline liquid bubbling precipitation method: the principle of alkaline liquid bubbling absorption precipitation method is simple, and Ca(OH)2 or Ba(OH)2 is used to prepare alkaline liquid to absorb CO2. After Ca(OH)2 or Ba(OH)2 absorbs CO2, stable carbonate salt is generated, which can meet the long-term disposal requirements, but a large amount of waste is generated.

[0014] (2) Two-step chemical reaction method of sodium hydroxide absorption and lime water precipitation (referred to as wet absorption method). The basic principle is two-step chemical reaction, sodium hydroxide is used to absorb CO2 to obtain Na2CO3 solution, lime water is added to the solution for precipitation, CO3 2- in the solution is changed into CaCO3 precipitate, and the precipitate is filtered out as medium-low level solid waste for disposal, and a large amount of waste is generated.

[0015] (3) Alkaline bed absorption method (referred to as dry absorption method): the basic principle of alkaline absorption bed is to use solid absorbent (such as alkali metal hydroxide) to prepare dry absorption bed. When the gas containing CO2 passes through the solid absorbent, CO2 reacts with the alkali metal hydroxide in the solid absorbent to remove CO2. However, the saturated alkaline bed still needs to be packaged and treated as waste solid.

[0016] (4) Ethanolamine absorption method: gas is washed in ethanolamine (HOCH2CH2NH2), which is a method for removing CO2, the basic principle of which is that ethanolamine has a high adsorption efficiency for CO2 within a certain temperature range, and when the temperature rises, CO2 is released, and this removal method can enrich CO2. A problem encountered in the actual operation of the ethanolamine method is that ethanolamine can be oxidized into oxalic acid and aminoacetic acid, and the oxidized product can cause a certain degree of corrosion to the equipment and also affect the absorption efficiency, which greatly increases the difficulty of engineering application.

[0017] (5) Molecular sieve adsorption method:

[0018] Molecular sieve is a kind of synthetic silicate with microporous cubic lattice. After the carbon-14-containing CO2 gas passes through the molecular sieve, the CO2 is trapped. The advantages are that the principle of the molecular sieve adsorption device is simple. The disadvantages are that the molecular sieve adsorption efficiency is related to the temperature, and a low-temperature working environment needs to be maintained, and after the molecular sieve adsorbs CO2, it is a physical adsorption process, and after the conditions change, CO2 will still be released, so the subsequent solidification treatment process is complex.

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

[0020] As described above, the existing methane conversion process and CO2 treatment technology all have different defects. Therefore, in order to reduce the emission of nuclear power plant gas-borne carbon-14 to the environment and achieve standard emission, improve the treatment efficiency, not produce other secondary waste, reduce equipment investment and investment cost, realize industrialized application, further research and development of new carbon-14 treatment technology in nuclear power plant radioactive waste gas is still needed, which provides more possibilities for the country to further improve the emission index of nuclear facility gas-borne carbon-14 and strengthen the emission control of nuclear facility gas-borne carbon-14. SUMMARY

[0021] In view of the above-mentioned defects of the prior art, the purpose of the present application is to provide a nuclear power plant radioactive waste gas carbon-14 treatment process, system and application, which can reduce the emission of nuclear power plant gas-borne carbon-14 to the environment and achieve standard emission, improve the treatment efficiency, not produce other secondary waste, reduce equipment investment and investment cost, and realize industrialized application.

[0022] To achieve the above-mentioned purposes and other related purposes, the present application provides a nuclear power plant radioactive waste gas carbon-14 treatment process, comprising:

[0023] Separation of carbon 14:

[0024] Catalytic oxidation of the decayed nuclear power plant radioactive exhaust gas converts organic state carbon 14 into inorganic state 14 CO2, to obtain a first gaseous effluent;

[0025] Conversion of gaseous 14 CO2 in the first gaseous effluent into liquid 14 CO2 and separation thereof to obtain a first liquid effluent, and a second gaseous effluent meeting normal emission standards;

[0026] Fixation of carbon 14:

[0027] Heating the first liquid effluent to vaporize it to obtain a third gaseous effluent;

[0028] Countercurrent water washing of the third gaseous effluent to obtain a second liquid effluent in which gaseous 14 CO2 in the third gaseous effluent is dissolved and absorbed, and a fourth gaseous effluent with a carbon 14 content reaching a predetermined value;

[0029] Treatment of the second liquid effluent with ion exchange resin to fix carbon 14 on the resin to obtain waste resin containing carbon 14.

[0030] Further, in the catalytic oxidation process, organic state carbon 14 reacts with oxygen to generate inorganic state 14 CO2.

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

[0032] Further, the reaction temperature in the catalytic oxidation process is 350-450℃.

[0033] Further, the method for converting gaseous 14 CO2 in the first gaseous effluent into liquid 14 CO2 comprises:

[0034] Based on the boiling point difference of various gases in the first gaseous effluent, the first gaseous effluent is pressurized and deep-cooled to convert gaseous 14 CO2 in the first gaseous effluent into liquid 14 CO2.

[0035] Further, the pressurized and deep-cooled conditions comprise: pressurization to 5-6 atmospheres, and / or cooling temperature of -31 to -39℃.

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

[0037] Further, the first liquid effluent is heated to normal temperature to vaporize and obtain a third gaseous effluent.

[0038] Further, the waste liquid treated in the nuclear power plant to meet the discharge standard is used for countercurrent water washing.

[0039] Further, the pH is controlled to be 7.5-8.5 during the countercurrent water washing.

[0040] Further, during the countercurrent water washing, 14 CO2 reacts with OH - to generate 14 CO3 2- and / or H 14 CO3 - to dissolve and absorb gaseous 14 CO2 in the third gaseous effluent.

[0041] Further, during the countercurrent water washing, the gas phase and the liquid phase are countercurrently contacted through a filler layer filled with particulate fillers to increase the gas-liquid contact area and make 14 CO2 sufficiently dissolved in water.

[0042] Further, during the countercurrent water washing, the gas phase is circulated to perform the countercurrent water washing until the carbon 14 content in the gas phase reaches a predetermined value, to obtain a second liquid effluent in which gaseous 14 CO2 in the third gaseous effluent is sufficiently dissolved and absorbed, and a fourth gaseous effluent with the carbon 14 content reaching the predetermined value.

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

[0044] Further, the ion exchange resin treatment is performed by using a weak acid type cation exchange resin, and the functional groups on the weak acid type cation exchange resin can fix 14 CO3 2- and / or H 14 CO3 - on the resin.

[0045] Further, the second liquid effluent is subjected to the ion exchange resin treatment to fix the carbon 14 on the resin, and a third liquid effluent is further obtained, wherein the third liquid effluent is the waste liquid meeting the discharge standard.

[0046] Further, before gaseous 14 CO2 in the first gaseous effluent is converted into liquid 14 CO2, the first gaseous effluent is further cooled to normal 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 application also provides application of the carbon-14 treatment process and / or system for radioactive waste gas in a nuclear power plant as described above in radioactive waste treatment.

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

[0068] 1) The organic-state carbon-14 is converted into inorganic-state carbon-14 by catalytic oxidation, and then the carbon-14 in the first gaseous effluent is converted into liquid state and separated out completely by pressurization and cryogenic technology, so that the second gaseous effluent meeting the normal emission standard is obtained, and the emission standard is achieved; 14

[0069] 2) The carbon-14 in gas phase is transferred into liquid phase by countercurrent water washing, and is converted into 14 CO3 2- and / or H 14 CO3 - ion state, and then the carbon-14 is fixed on the ion exchange resin by ion exchange resin adsorption, so that the carbon-14 in radioactive gas is converted into solid-state carbon-14 fixed on the waste resin, which can be treated and disposed and will not enter the environment.

[0070] 3) In the countercurrent water washing process, the packing with a large specific surface area is used to increase the gas-liquid contact area and improve the reaction efficiency; and the carbon-14 is washed by the waste liquid to be discharged in the nuclear power plant, so that the amount of radioactive waste water is not increased;

[0071] 4) In the ion exchange resin treatment, the weak acid cation exchange resin is used to treat the radioactive waste liquid containing carbon-14 after countercurrent water washing, and has higher removal efficiency than the weak acid anion;

[0072] 5) The nuclear power plant is usually equipped with a waste resin treatment device, and the generated waste resin can be solidified and treated together with other waste resins in the nuclear power plant, without increasing the treatment equipment and generating other secondary waste.

[0073] In summary, the two-step treatment is adopted to realize the separation and fixation treatment of carbon-14 in radioactive waste gas in a nuclear power plant, reduce the emission amount of carbon-14 in the nuclear power plant to the environment and achieve the emission standard, the treatment efficiency is high, no other secondary waste is generated, the amount of radioactive waste water is not increased, the equipment investment and investment cost are reduced, it is very beneficial to realize industrial application, solves the urgent needs of the nuclear power plant at present, can improve the public's confidence in the safe operation of the nuclear power plant, and therefore has a very high application prospect and important social significance. BRIEF DESCRIPTION OF DRAWINGS

[0074] ​Figure 1 shows a flow chart of a process for treating carbon-14 in radioactive exhaust gas from a nuclear power plant according to some embodiments of the present application.

[0075] Figure 2 shows a flow chart of a process for treating carbon-14 in radioactive exhaust gas from a nuclear power plant according to some other embodiments of the present application.

[0076] Figure 3 shows a schematic diagram of an arrangement of a system for treating carbon-14 in radioactive exhaust gas from a nuclear power plant according to some embodiments of the present application.

[0077] Figure 4 shows a schematic diagram of an arrangement of a system for treating carbon-14 in radioactive exhaust gas from a nuclear power plant according to some other embodiments of the present application.

[0078] Reference signs: carbon-14 separation unit 100, catalytic oxidation unit 110, catalytic oxidation reactor 111, oxygen supply device 112, pre-cooling unit 120, 14 CO2 liquefaction unit 130, pressurizing device 131, cryogenic device 132; carbon-14 fixation unit 200; first heating unit 210, countercurrent water washing unit 220, packed bed reactor 221, water supply device 222, ion exchange resin treatment unit 230, waste resin treatment unit 300, second heating unit 400. DETAILED DESCRIPTION

[0079] The present application is described in greater detail by the following specific examples. Other advantages and effects of the present application will be readily understood from this description by those skilled in the art. The present application can be implemented or applied in other different specific embodiments, and the details in the description can be modified or changed in various ways without departing from the spirit of the present application.

[0080] In the present application, the term "plurality" means two or more, unless otherwise specified.

[0081] The character " / " means that the objects before and after are in an "or" relationship. For example, A / B means: A or B.

[0082] The term "and / or" is a description of the association relationship of the objects, which means that there can be three relationships. For example, A and / or B means: A or B, or, A and B, the three relationships.

[0083] As shown in Figure 1, an embodiment of the present application provides a process for treating carbon-14 in radioactive exhaust gas from a nuclear power plant, comprising:

[0084] Separation of carbon-14:

[0085] Catalytic oxidation of the decay-treated radioactive exhaust gas from a nuclear power plant to convert organic-state carbon-14 into inorganic-state carbon-14 14CO2 was produced, resulting in the first gaseous effluent.

[0086] 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;

[0087] Fixation of carbon-14:

[0088] The first liquid effluent is heated to vaporize it, resulting in the third gaseous effluent;

[0089] 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;

[0090] The second liquid effluent was treated with ion exchange resin to fix carbon-14 onto the resin, resulting in waste resin containing carbon-14.

[0091] 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:

[0092] 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.

[0093] The second step is the fixation of carbon-14: the separated liquid... 14 CO2 (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 waste resin treatment system of a nuclear power plant for solidification and other treatments along with other waste resins.

[0094] Because the carbon 14 content in the radioactive gaseous effluent of the nuclear power plant is very small, generally only several grams to tens of grams per year, the energy consumption of the above carbon 14 separation process is also relatively small. But the separated 14 CO2 is still radioactive and cannot be released to the environment or stored for a long time. Therefore, the carbon 14 is also fixed in the present application. In this way, through the above two-step processing, the carbon 14 in the radioactive waste gas of the nuclear power plant is separated out and converted into solid carbon 14 fixed on the waste resin, which can be treated and disposed of and will not enter the environment; at the same time, the second gaseous effluent meeting the normal emission standard and the fourth gaseous effluent with a carbon 14 content reaching a predetermined value are obtained, and both the second gaseous effluent and the fourth gaseous effluent can be normally emitted to meet the emission standard, realizing the emission of the gaseous effluent to meet the standard.

[0095] In some embodiments, in the catalytic oxidation process, the carbon 14 in the organic state reacts with oxygen to generate carbon 14 in the inorganic state. 14 CO2. It should be noted that the catalytic oxidation process needs to be supplied with an appropriate amount of oxygen, that is, the amount of oxygen added needs to be strictly controlled.

[0096] Further, in some embodiments, the catalyst used in the catalytic oxidation process is a noble metal catalyst. The noble metal catalyst of the present application can use common noble metal catalysts used for catalytic oxidation of organic carbon hydrides such as methane, without other special restrictions.

[0097] Further, in some embodiments, the reaction temperature of the catalytic oxidation process is 350-450℃, such as 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450℃, etc.

[0098] In some embodiments, the method for converting the gaseous 14 CO2 in the first gaseous effluent into liquid 14 CO2 includes:

[0099] Based on the boiling point difference of various gases in the first gaseous effluent, the first gaseous effluent is pressurized and deep-cooled to convert the gaseous 14 CO2 in the first gaseous effluent into liquid 14 CO2.

[0100] Further, in some embodiments, the first gaseous effluent is pressurized to 5-6 atmospheres and then deep-cooled.

[0101] Further, in some embodiments, when the first gaseous effluent is deep-cooled, the cooling temperature is -31 to -39℃, such as -31, -32, -33, -34, -35, -36, -37, -38, -39℃, etc.

[0102] Because the radioactive waste gas mainly contains nitrogen, hydrogen, and a small amount of radionuclides, the boiling point of nitrogen is -196°C, the boiling point of hydrogen is -252.87°C, the boiling point of methane is -161.5°C, the boiling point of ethane is -88.6°C, the boiling point of carbon dioxide is -78.5°C, and the boiling point of each gas will increase as the pressure increases. In order to save energy, the present application uses pressurized cryogenic to separate carbon 14. For example, at 5 atmospheres, carbon dioxide will become liquid at -31.1°C, while other gases are still gaseous. Therefore, when deep cooling, the temperature is controlled at about -35°C, which can effectively separate the gaseous 14 CO2 into liquid 14 CO2 from the radioactive waste gas. Of course, the specific and pressurized pressure and cooling temperature can be adjusted within the above-mentioned numerical range according to the properties of carbon dioxide and actual conditions.

[0103] In some embodiments, the second gaseous effluent is heated to normal temperature and then normally discharged according to standards.

[0104] In some embodiments, the first liquid effluent is heated to normal temperature to vaporize and obtain a third gaseous effluent.

[0105] In some embodiments, the backwashing water is the waste liquid treated in the nuclear power plant and meeting the discharge standards. The water used for backwashing is the waste liquid treated in the nuclear power plant and meeting the discharge standards and to be discharged, so that no additional radioactive waste water is generated.

[0106] In some embodiments, the pH is controlled to be 7.5-8.5 during backwashing. Further, in some embodiments, an alkaline adjusting agent is added to control the pH to be 7.5-8.5, and the alkaline adjusting agent includes but is not limited to sodium hydroxide, potassium hydroxide, sodium acetate, etc.

[0107] In some embodiments, during backwashing, 14 CO2 and OH - react to generate 14 CO3 2- and / or H 14 CO3- to dissolve and absorb gaseous 14 CO2 in the third gaseous effluent.

[0108] In some embodiments, during backwashing, the gas phase and the liquid phase are countercurrently contacted through a packing layer filled with particulate packing to increase the gas-liquid contact area and make 14 CO2 fully dissolved in water.

[0109] In some embodiments, the gas phase is circulated for countercurrent water washing until the carbon 14 content in the gas phase reaches a predetermined value, and the gas phase is sufficiently dissolved and absorbed into the third gaseous effluent 14 The second liquid effluent of CO2, and the fourth gaseous effluent with the carbon 14 content reaching a predetermined value. That is, the countercurrent water washing process can be circulated until the carbon 14 content in the gas phase reaches a predetermined value, and the gas phase can be sent to a chimney for normal standard emission.

[0110] In some embodiments, the fourth gaseous effluent is heated to normal temperature before being normally emitted to meet the standard. In some embodiments, the ion exchange resin treatment is performed by using a weak acid type cation exchange resin. The functional groups on the weak acid type cation exchange resin can fix 14 CO3 2- and / or H 14 CO3 - on the resin, and have a higher removal efficiency with respect to the anion of the weak acid salt.

[0111] In some embodiments, the second liquid effluent is treated by ion exchange resin to fix the carbon 14 on the resin, and a third liquid effluent is obtained, which is a waste liquid meeting the emission standard. Because no other nuclides are introduced in the carbon 14 treatment process of the present application, the emission standard is still met, and the waste liquid can be sent for standard emission.

[0112] As shown in FIG. 2, in some embodiments, before the gaseous 14 CO2 in the first gaseous effluent is converted into liquid 14 CO2, the first gaseous effluent is cooled to normal temperature. After the catalytic oxidation treatment, the organic carbon 14 has been sufficiently converted into inorganic gaseous 14 CO2, but the gas temperature is high at this time, so the gas is cooled to normal temperature first, which is more convenient for subsequent liquefaction separation.

[0113] In some embodiments, the process further comprises: treating the waste resin containing carbon 14 by using a nuclear power plant waste solid treatment method, which includes solidification treatment, shallow surface disposal, but is not limited thereto. The nuclear power plant is usually equipped with a waste resin treatment device, and no other equipment needs to be added. The generated waste resin can be treated together with other waste resins of the nuclear power plant, so that no additional treatment equipment is needed, and no other secondary waste is generated.

[0114] In addition, it should be noted that the normal standard emission condition and the carbon 14 content reaching a predetermined value in the present application both refer to meeting the national standard related to the emission amount of gaseous effluent radionuclides (including carbon 14) of the nuclear power plant.

[0115] As shown in Figure 3, 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.

[0116] 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.

[0117] 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;

[0118] The first heating unit 210 is used to heat the first liquid effluent to vaporize it, thereby obtaining the third gaseous effluent;

[0119] 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;

[0120] 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.

[0121] The following examples are illustrated in Figure 4, which shows a carbon-14 treatment system for radioactive waste gas from a nuclear power plant.

[0122] 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.

[0123] In some embodiments, the catalytic oxidation unit 110 further includes an oxygen supply device 112 for providing oxygen for the catalytic oxidation process.

[0124] In some embodiments, 14The CO2 liquefaction unit 130 comprises a pressurization device 131 and a cryogenic device 132; the pressurization device 131 is used to pressurize the first gaseous effluent, for example, a compressor; the cryogenic device 132 is used to cryogenically treat the pressurized first gaseous effluent, so as to dissolve the gaseous CO2 in the first gaseous effluent into liquid CO2. 14 The CO2 is converted into liquid 14 CO2.

[0125] In some embodiments, the countercurrent water washing unit 220 comprises a packed bed reactor 221, in which a water washing bed is arranged, and the water washing bed is provided with a packing layer filled with granular packing. In order to realize countercurrent water washing, the gas and liquid phases are respectively fed from the bottom and top of the packed bed reactor 221, and pass through the water washing bed to realize countercurrent contact, so that 14 The CO2 is fully dissolved in water.

[0126] In some embodiments, the countercurrent water washing unit 220 further comprises a water supply device 222, which is used to provide a water washing liquid for the countercurrent water washing process, and the water washing liquid is a treated waste liquid in a nuclear power plant meeting the discharge standard.

[0127] In some embodiments, the ion exchange resin treatment unit 230 comprises an ion exchanger filled with ion exchange resin, preferably weak acid cation exchange resin. The ion exchanger can be a common ion exchanger, for example, an ion exchange adsorption bed.

[0128] In some embodiments, the carbon 14 separation unit further comprises a pre-cooling unit 120 arranged between the catalytic oxidation unit 110 and the CO2 liquefaction unit 130, which is used to cool the first gaseous effluent to normal temperature. 14 The CO2 liquefaction unit 130 comprises a pressurization device 131 and a cryogenic device 132; the pressurization device 131 is used to pressurize the first gaseous effluent, for example, a compressor; the cryogenic device 132 is used to cryogenically treat the pressurized first gaseous effluent, so as to dissolve the gaseous CO2 in the first gaseous effluent into liquid CO2.

[0129] In some embodiments, the carbon 14 fixation unit further comprises a waste resin treatment unit 300, which is used to treat the waste resin containing carbon 14 by using a nuclear power plant waste solid treatment method.

[0130] In some embodiments, 14 The CO2 liquefaction unit 130 is connected to a nuclear power plant gas discharge system (for example, a chimney) to discharge the second gaseous effluent.

[0131] In some embodiments, the countercurrent water washing unit 220 is connected to a nuclear power plant gas discharge system to discharge the fourth gaseous effluent.

[0132] In some embodiments, the system further comprises a second heating unit 400 arranged between the catalytic oxidation unit 110 and the CO2 liquefaction unit 130. 14The CO2 liquefaction unit 130 is arranged between the nuclear power plant gas discharge system and is used for heating the second gaseous effluent, and / or the second heating unit 400 is arranged between the countercurrent water washing unit 220 and the nuclear power plant gas discharge system and is used for heating the fourth gaseous effluent.

[0133] In some embodiments, the first heating unit 210 and the second heating unit 400 comprise a heating device, which can be a heat exchanger, for example.

[0134] It should be noted that the nuclear power plant radioactive waste gas carbon 14 treatment system provided in the above embodiments and the nuclear power plant radioactive waste gas carbon 14 treatment process provided in the above embodiments belong to the same concept, wherein the specific manner in which each unit performs the operation has been described in detail in the process embodiments, which will not be repeated here. The nuclear power plant radioactive waste gas carbon 14 treatment system provided in the above embodiments can complete the above-described functions by different functional units according to the actual application, that is, the system is divided into different functional units to complete all or part of the above-described functions, and this is not limited herein.

[0135] Another embodiment of the present application also provides the use of the nuclear power plant radioactive waste gas carbon 14 treatment process and / or system of the above-described embodiments in radioactive waste treatment.

[0136] The emission amount of airborne carbon 14 in some domestic in-service nuclear power plants has approached the emission limit value specified in the national standard. The technology provided by the present application can solve the urgent needs of the nuclear power plant site, lay a foundation for subsequent research on carbon 14 treatment and recycling technology in the field of three wastes of nuclear power plants, and also provide the possibility for the country to further improve the emission index of airborne carbon 14 of nuclear facilities and strengthen the emission control of airborne carbon 14 of nuclear facilities. In addition, if industrial application is realized, the emission amount of airborne carbon 14 of nuclear power plants to the environment can be reduced, and the public's confidence in the safe operation of nuclear power plants can be improved, so it has important social significance.

[0137] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

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 water washing the third gaseous effluent to obtain a gaseous effluent dissolvedly absorbed in water 14 a second liquid effluent of CO2, and a fourth gaseous effluent having a carbon 14 content reaching a predetermined value; 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 conversion to liquid 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 of claim 1, wherein: Countercurrent water washing is performed on the treated waste liquid in the nuclear power plant which meets the discharge standard; And / or, 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 30-90°C, 14 CO2reacts with OH- to form 14 CO3 2- and / or H 14 CO3 - to solubly absorb gaseous 14 CO2; 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: Weak acid type cation exchange resin is used for ion exchange resin treatment.

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 a waste liquid meeting the discharge standard.

9. 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 CO2, further comprising: cooling said first gaseous effluent to ambient temperature prior to 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 decayed nuclear power plant radioactive exhaust gas, converting the organic state carbon 14 into the 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 emission standards The first heating unit is used for heating the first liquid effluent to vaporize it to obtain a third gaseous effluent; the counter-current water scrubbing unit is configured to counter-currently water scrub the third gaseous effluent to obtain a second liquid effluent and a fourth gaseous effluent, the fourth gaseous effluent having a carbon 14 content reaching a predetermined value 14 CO2, and the fourth gaseous effluent having a carbon 14 content reaching a predetermined value. 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 gaseous CO2therein. 14 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 countercurrent water washing unit further comprises a water supply device for providing water washing liquid for the countercurrent water washing process. And / or, the ion exchange resin treatment unit comprises an ion exchanger filled with ion exchange resin.

13. The system according to any one of claims 10 to 12, characterized in that: 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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