A radioactive carbon dioxide recovery system and recovery method

Abstract

The present application relates to a kind of radioactive carbon dioxide recovery system and method, belong to radioactive waste treatment technical field.The system includes conical dryer, nitrogen device can be filled with nitrogen to system and chemical mixing tank, the outlet of conical dryer passes through primary condenser, vacuum pump and secondary condenser, then, by gas buffer tank, first flow regulating valve, first flow meter, by inlet to conical dryer, constitute drying circulation loop;The bottom of gas buffer tank passes through carbon dioxide absorption tank after carbon removal fan, then, by third flow regulating valve, third flow meter, into conical dryer, constitute absorption circulation loop.The present application combines drying circulation loop and absorption circulation loop together, appropriately set and control corresponding pipe valve and driving device, can drive absorption circulation by drying circulation, and can also recover all required radioactive carbon dioxide.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of radioactive carbon dioxide recovery system, also simultaneously relates to corresponding recovery method, belong to radioactive waste treatment technical field. BACKGROUND

[0002] Nuclear power plant in the process of drying waste resin will produce radioactive nuclide-carbon 14 in the form of carbon dioxide, on the one hand, if it is directly discharged into the atmosphere without control, it will mix with non-radioactive carbon dioxide in the air, so as to enter the carbon cycle in nature, so that the entire biosphere faces the risk of internal irradiation. On the other hand, carbon 14 has wide utilization value in many fields. Therefore, it is very necessary to provide a recovery system for absorbing carbon dioxide produced in the drying process of waste resin, and the adsorption efficiency should be close to 100%, so as to reduce the emission of radioactive carbon dioxide in nuclear power plant, and lay a foundation for its secondary utilization.

[0003] According to the search, the Chinese patent document with the application number CN00214581.2 discloses a radioactive carbon dioxide absorption device, which is composed of a sealed shell and a closed absorption tank. The device is characterized in that multiple closed absorption tanks are fixed in the sealed shell, and the upper part of the closed absorption tank is provided with an air inlet pipe and an air outlet pipe. The air inlet pipe is arranged in the carbon dioxide absorption liquid in the tank. Compared with the prior art, the radioactive carbon dioxide absorption device has the characteristics of reasonable design, simple structure, easy processing, small size, convenient use, safety and reliability, accurate detection, rapidity and convenient preservation. However, the technical solution cannot prevent air carbon dioxide from entering the absorption liquid, which affects the recovery effect and is not conducive to the utilization of the recovered product.

[0004] In addition, the Chinese patent document with the application number 201821009637.7 discloses a system for capturing carbon dioxide in flue gas by using sodium hydroxide and sodium carbonate. The system includes the following steps: (1) flue gas purification; (2) first absorption of flue gas and sodium carbonate solution in a primary absorption tower; (3) second absorption of carbon dioxide and sodium hydroxide solution in a secondary absorption tower; (4) transportation of the solution in the secondary absorption tower to the primary absorption tower; (5) heating and decomposition of sodium bicarbonate to release carbon dioxide; (6) collection of carbon dioxide; (7) conversion of sodium carbonate solution into sodium hydroxide solution; and (8) circulation of sodium hydroxide solution to the secondary absorption tower. The process is simple and easy to implement, and the use cost is low. However, in the technical solution, the carbon dioxide is directly discharged after passing through two-stage absorption towers, and part of the carbon dioxide remains in the discharged flue gas.

[0005] Also, the Chinese patent document with the application number CN201910872606 discloses a method for sealing carbon dioxide and cooperatively disposing radioactive waste, comprising: placing waste concrete and active waste residue in a sealed reaction kettle, adding grinding aid and water, and grinding and then standing; adding radioactive waste and waste fiber in the sealed reaction kettle, and passing CO2 gas into it at a constant rate under stirring conditions to obtain slurry; and after the obtained slurry is transported by a conveying pipeline or a ship to a suitable place, injecting it into a stratum with specific geological conditions and a specific depth for hydration hardening. The technical solution has the problem that CO2 is permanently solidified and cannot be reused.

[0006] In summary, the prior art has no system and corresponding recovery method that can recover radioactive carbon dioxide very completely and create conditions for its effective utilization. SUMMARY

[0007] The purpose of the present application is to provide a system and corresponding recovery method for recovering radioactive carbon dioxide almost completely, which is used for treating carbon dioxide generated in the drying process of waste resin, not only ensuring environmental safety, but also laying a foundation for the reuse of recovered carbon dioxide.

[0008] To achieve the above purpose, the basic technical solution of the radioactive carbon dioxide recovery system of the present application is as follows: a conical dryer for storing carbon dioxide to be treated, a nitrogen device that can charge nitrogen into the system, and a chemical mixing tank are provided, the outlet of the conical dryer is connected to a first condenser, a vacuum pump and a second condenser, and then connected to a gas buffer tank, a first flow regulating valve and a first flow meter, and finally returned to the conical dryer through the inlet, forming a drying circulation loop;

[0009] The bottom of the gas buffer tank is connected to a carbon dioxide absorption tank through a decarburization fan, and then connected to a third flow regulating valve and a third flow meter, and finally connected to the conical dryer, forming an absorption circulation loop;

[0010] The gas buffer tank is also connected to a gas discharge port through a second flow regulating valve; and the chemical mixing tank is connected to a carbon dioxide absorption tank through a metering pump.

[0011] The drying circulation loop and the absorption circulation loop are organically combined together in the present application, and appropriate pipe valves and driving devices are set and controlled, so that the drying circulation can drive the absorption circulation, and all the required radioactive carbon dioxide can be recovered.

[0012] The method for recovering radioactive carbon dioxide by using the present application comprises the following basic steps:

[0013] The first step, opening the second flow regulating valve and the third flow regulating valve, starting the vacuum pump, and absorbing the gas in the carbon dioxide absorption tank to negative pressure; opening the nitrogen device to replace the air in the system; when the oxygen content in the system reaches the predetermined value and remains stable, closing the second flow regulating valve and the third flow regulating valve and the vacuum pump, and continuing to supplement nitrogen to the pressure in the system to 0, and closing the nitrogen device;

[0014] The second step, opening the chemical mixing tank to add sodium hydroxide, and adding a predetermined amount of desalted water through the flow meter to prepare a sodium hydroxide solution with a predetermined concentration, and pumping the prepared sodium hydroxide solution into the carbon dioxide absorption tank through the metering pump;

[0015] The third step, opening the second flow regulating valve, starting the vacuum pump to absorb the pressure in the conical dryer to negative pressure again, closing the second flow regulating valve and opening the first flow regulating valve; adjusting the opening of the first flow regulating valve to maintain the vacuum degree in the conical dryer; starting the drying circulation loop;

[0016] The fourth step, opening the inlet and outlet valves of the carbon dioxide absorption tank in the absorption circulation loop and the front and rear stop valves of the third flow regulating valve, starting the decarburization fan, and adjusting the opening of the first flow regulating valve and the third flow regulating valve to maintain the exhaust volume of the decarburization fan at a predetermined flow rate and the absorption circulation loop at a predetermined pressure, and starting the absorption circulation loop;

[0017] The fifth step, when the carbon dioxide gas content is less than the target absorption value, stopping the heating of the conical dryer, continuing to maintain the drying circulation loop and the absorption circulation loop for 2-3 hours, and then stopping.

[0018] After the present application is adopted, the drying circulation loop brings out the water vapor in the conical dryer during the resin drying process by using the circulating gas flow and condenses it, and then the absorption circulation loop takes gas from the gas buffer tank of the drying circulation loop, absorbs the extracted gas, and returns it to the drying circulation loop, so that the gas in the system can reach the absorption standard (the carbon dioxide absorption efficiency is improved to about 99.8%, and is almost completely absorbed), and then is discharged as needed.

[0019] A further improvement of the present application is that the bottom of the carbon dioxide absorption tank is connected to the storage container through a liquid discharge pump. In this way, not only is complete absorption ensured, but also after absorption is completed, the liquid discharge pump is opened to return the carbon dioxide absorption liquid to the storage container for secondary use.

[0020] A further improvement of the present invention is that the nitrogen device is connected to the drying circulation loop, the absorption circulation loop, the chemical mixing tank, and the storage components, especially directly connected to the carbon dioxide absorption tank and the storage container for the recovered absorbent. This not only allows the nitrogen to purge the air in the entire recovery system, but also prevents carbon dioxide in the air from entering the absorbent, thus preventing interference with the absorption efficiency and providing a safety protection for the entire system. Attached Figure Description

[0021] The attached figure shows a schematic diagram of the system structure of the present invention.

[0022] Figure 1 This is a schematic diagram of the system configuration according to an embodiment of the present invention. Detailed Implementation

[0023] Example 1

[0024] The radioactive carbon dioxide recovery system generated during the waste resin drying process in this embodiment is as follows: Figure 1 As shown, the outlet N9 of the conical dryer 1.1 (in this embodiment, the CGCD-20 from Aerospace Morninglight Company is used, but other commercially available similar products can also be used) which stores carbon dioxide to be treated passes through the first-stage condenser 1.2, vacuum pump 1.3 and second-stage condenser 1.4, and then through the gas buffer tank 1-1, the first flow regulating valve 1-3, the first flow meter 1-2 and the gate valve, and returns to the conical dryer 1.1 through the inlet N23, forming a drying cycle loop.

[0025] The upper end of the conical dryer 1.1 is also equipped with a liquid replenishment port N42 for water supply points 1 and 2; the upper end of the gas buffer tank 1-1 is equipped with a pressure sensor, a temperature sensor, a CO2 detector, and an O2 detector to monitor various parameters in real time.

[0026] The bottoms of the primary condenser 1.2, the secondary condenser 1.4, and the gas buffer tank 1-1 are connected to the condensate tank 1.3 via corresponding pipes and valves, so that condensate can be discharged or replenished as needed.

[0027] The bottom of the gas buffer tank 1-1 enters the two parallel carbon dioxide absorption tanks 2-6 containing the absorption liquid through the decarbonization fan 2-2, the fourth flow regulating valve 2-4, and the fourth flow meter 2-5. Then, it enters the inlet N23 of the conical dryer 1.1 (or can be selected before the first-stage condenser 1.2) through the third flow regulating valve 2-3, the third flow meter 2-1, and the gate valve, thus forming an absorption circulation loop.

[0028] The upper parts of the two carbon dioxide absorption tanks 2-6 are respectively equipped with spray devices connected to water sources 3 and 4, which is more conducive to the absorption of carbon dioxide. The outlet of the gas buffer tank 1-1 is also connected to the gas discharge port through a gate valve and a second flow regulating valve 1-4, so that the gas in the circuit can be discharged after reaching the absorption standard.

[0029] The nitrogen device 5 of the embodiment is composed of a nitrogen cylinder, the exhaust port of which is connected to the conical dryer 1.1, the storage container 4-2 and the chemical mixing tank 3-2 through pipelines, and further can be used to fill nitrogen into other parts of the system and clean the air in the whole recovery system to avoid the outside carbon dioxide from entering the absorption liquid.

[0030] The chemical mixing tank 3-2 is connected to the two carbon dioxide absorption tanks 2-6 through the metering pump 3-3, which is used to supplement the absorption liquid as needed, and the top of the chemical mixing tank 3-2 is connected to a desalted water source through a pipeline with a flowmeter 3-1. The bottom of the carbon dioxide absorption tank 2-6 is connected to the storage container 4-2 through the liquid discharge pump 4-1, so that the carbon dioxide absorption liquid can be recovered to the storage container for secondary use after the absorption is completed.

[0031] When working, the following steps are taken to operate the recovery of the carbon dioxide with radioactivity:

[0032] The first step is to open the second flow regulating valve 1-4 and the third flow regulating valve 2-3, start the vacuum pump, and draw the gas pressure in the carbon dioxide absorption tank 2-6 to -0.09 MPa; open the nitrogen device to fill nitrogen into the system until the vacuum degree is reduced to -0.01 to -0.02 MPa; when the oxygen detector shows that the oxygen content in the system reaches 1% and remains stable at 1±0.5%, close the second flow regulating valve 1-4 and the third flow regulating valve 2-3 and the vacuum pump, continue to supplement nitrogen to the pressure in the system to 0, and close the nitrogen device.

[0033] The second step is to open the chemical mixing tank 3-2 to add sodium hydroxide, and introduce a certain amount of desalted water to prepare a 20±1% sodium hydroxide solution, and pump the prepared sodium hydroxide solution into the carbon dioxide absorption tank 2-6 through the metering pump 3-3.

[0034] The third step is to open the second flow regulating valve 1-4, start the vacuum pump to draw the pressure in the conical dryer again to -0.09 MPa, close the second flow regulating valve 1-4 and open the first flow regulating valve 1-3; adjust the opening of the first flow regulating valve 1-3 to keep the vacuum degree in the conical dryer at -0.07 to -0.09 MPa; start the drying circulation loop.

[0035] The fourth step is to open the inlet and outlet valves of the carbon dioxide absorption tank in the absorption circulation loop and the stop valves before and after the third flow regulating valve, start the decarburization fan 2-2, adjust the openings of the first flow regulating valve 1-3 and the third flow regulating valve 2-3 respectively to maintain the exhaust volume of the decarburization fan 2-2 at 10 to 20 Nm3 / h, and the pressure in the absorption circulation loop at 6 to 10 KPa, and start the absorption circulation loop.

[0036] Fifth step, when the carbon dioxide gas content is less than 0.2%, stop the conical dryer heating, continue to keep the drying circulation loop and the absorption circulation loop circulating for about 2-3h, stop.

[0037] In this process, in order to ensure that the system runs in the process of pressure super high, the system is provided with an emergency exhaust port connected with the plant ventilation system, if the dryer pressure exceeds 40kPa, open the flow regulating valve 1-4 to discharge a certain amount of gas to maintain the safety of the system, the discharged gas is the filtered gas after absorption.

[0038] The test proves that the radioactive carbon dioxide generated by drying the waste resin can be recycled and absorbed in the recycling system by using the embodiment, so that the absorption efficiency of carbon dioxide is increased to about 99.8%, and the existing technology cannot achieve this absorption efficiency by directly discharging the carbon dioxide after absorption.

[0039] In addition to the above embodiments, the present application can have other implementation manners, and the technical solutions formed by equivalent transformation all fall within the protection scope required by the present application.

Claims

1. A recovery method with a radioactive carbon dioxide recovery system, the system comprising a conical dryer storing carbon dioxide to be treated, a nitrogen device (5) capable of charging nitrogen to the system, and a chemical mixing tank (3-2), characterized in that: the outlet of the conical dryer is connected to the conical dryer through a primary condenser, a vacuum pump, and a secondary condenser, and then through a gas buffer tank (1-1), a first flow regulating valve (1-3), and a first flow meter (1-2) to form a drying circulation loop; the bottom of the gas buffer tank is connected to a carbon dioxide absorption tank (2-6) storing absorption liquid through a decarburization fan (2-2), a fourth flow regulating valve (2-4), and a fourth flow meter (2-5), and then through a third flow regulating valve (2-3) and a third flow meter (2-1) to the conical dryer to form an absorption circulation loop; the gas buffer tank is also connected to a gas discharge port through a second flow regulating valve (1-4); the chemical mixing tank is connected to the carbon dioxide absorption tank (2-6) through a metering pump (3-3); the method comprises the following steps: first, opening the second flow regulating valve (1-4) and the third flow regulating valve (2-3), starting the vacuum pump, and pumping the gas in the carbon dioxide absorption tank (2-6) to negative pressure; opening the nitrogen device to charge nitrogen into the system to replace the air in the system; when the oxygen content in the system reaches a predetermined value and remains stable, closing the second flow regulating valve (1-4) and the third flow regulating valve (2-3) and the vacuum pump, and continuing to supplement nitrogen to the system until the pressure in the system is 0, and then closing the nitrogen device; second, opening the chemical mixing tank (3-2) to add sodium hydroxide, and then adding a predetermined amount of desalted water through the flow meter (3-1) to prepare a sodium hydroxide solution with a predetermined concentration, and then pumping the prepared sodium hydroxide solution into the carbon dioxide absorption tank (2-6) through the metering pump (3-3); third, opening the second flow regulating valve (1-4), starting the vacuum pump to pump the conical dryer to negative pressure again, closing the second flow regulating valve (1-4), and opening the first flow regulating valve (1-3); adjusting the opening of the first flow regulating valve (1-3) to maintain the vacuum degree in the conical dryer; starting the drying circulation loop; fourth, opening the inlet and outlet valves of the carbon dioxide absorption tank in the absorption circulation loop and the stop valves before and after the third flow regulating valve, starting the decarburization fan (2-2), and adjusting the openings of the first flow regulating valve (1-3) and the third flow regulating valve (2-3) to maintain the exhaust flow of the decarburization fan (2-2) at a predetermined flow rate and the absorption circulation loop at a predetermined pressure, and starting the absorption circulation loop; fifth, when the carbon dioxide content is less than the target absorption value, stopping heating of the conical dryer, continuing to maintain the drying circulation loop and the absorption circulation loop for 2-3 hours, and then stopping the system. The bottom of the carbon dioxide absorption tank is connected to a storage container (4-2) through a liquid discharge pump (4-1). The nitrogen device is directly connected to the carbon dioxide absorption tank and the storage container. The upper end of the gas buffer tank is provided with a pressure sensor, a temperature sensor, a CO2 detector, and an O2 detector. ​ ​ ​ ​ ​ ​ 2. The recovery method of the radioactive carbon dioxide recovery system according to claim 1, characterized by: ​ 3. The recovery method of the radioactive carbon dioxide recovery system according to claim 2, characterized by: ​ 4. The recovery method of the radioactive carbon dioxide recovery system according to claim 3, characterized by: ​ 5. The recovery method of the radioactive carbon dioxide recovery system according to claim 4, characterized by: The bottom of the primary condenser, the secondary condenser and the gas buffer tank is connected to the condensate tank through a corresponding pipe valve.

6. The method of claim 1 to 5, wherein the system is characterized in that: In the first step, the gas pressure in the carbon dioxide absorption tank is drawn to -0.09 MPa; the nitrogen device is opened to charge nitrogen into the system until the vacuum degree is reduced to -0.01 to -0.02 MPa; when the oxygen detector shows that the oxygen content in the system reaches 1% and remains stable at 1±0.5%, the second flow regulating valve, the third flow regulating valve and the vacuum pump are closed; In the second step, a 20±1% sodium hydroxide solution is prepared; In the third step, the vacuum pump is started to draw the pressure in the conical dryer to -0.09 MPa again; the opening degree of the first flow regulating valve is adjusted to maintain the vacuum degree in the conical dryer at -0.07 to -0.09 MPa; In the fourth step, the exhaust volume of the decarburization fan 2-2 is maintained at 10 to 20 Nm3 / h, and the absorption circulation loop pressure is maintained at 6 to 10 KPa; In the fifth step, when the carbon dioxide gas content is less than 0.2%, the heating of the conical dryer is stopped.

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