CN111508631A - External circulation type high-level radioactive waste liquid continuous evaporation concentration denitrator - Google Patents

Abstract

The invention discloses an external circulation type high-level radioactive waste liquid evaporation concentration denitrator, which comprises: concentrated denitration cauldron of evaporation, external circulating pipe, heater, backpressure overheat district and defoaming purifying column, wherein, the concentrated denitration cauldron of evaporation one side bottom opening links to each other with the external circulating pipe, and the external circulating pipe links to each other with the heater, and heater upper portion links to each other with the backpressure overheat district, and the backpressure overheat district links to each other with the another side opening of the concentrated denitration cauldron of evaporation, and the concentrated denitration cauldron top of evaporation links to each other with defoaming purifying column. The evaporation concentration denitrator can not generate a large amount of sediment, effectively separates small liquid drops and breaks foam, prevents bumping, and is suitable for evaporation concentration denitration treatment of high-level radioactive waste liquid generating sediment and/or bumping.

Description

External circulation type high-level waste liquid continuous evaporation concentration and denitrification device

technical field

The invention relates to the technical field of post-processing of nuclear energy spent fuel, in particular to an external circulation type high-level waste liquid continuous evaporation, concentration and denitrification equipment.

Background technique

After a nuclear reactor runs for a certain period of time, the internal fuel burnup reaches a certain level and becomes spent fuel, which needs to be unloaded and reprocessed to recover uranium, plutonium and other precious nuclides. At present, the PUREX process is widely used for spent fuel reprocessing. In the PUREX process and other similar processes, spent fuel is dissolved by nitric acid to form a feed liquid, and then the extraction and separation of uranium and plutonium in the nitric acid solution is achieved by liquid-liquid extraction. After the uranium and plutonium are extracted from the above-mentioned nitric acid solution, it still contains other nuclides with high radioactivity and long life cycle, which is called high-level radioactive waste liquid. High-level waste liquid usually needs to be reduced by evaporation-concentration-denitrification treatment for subsequent temporary storage and continued vitrification or further separation and volume reduction. Therefore, between the main process of spent fuel reprocessing and the auxiliary process of high-level waste liquid, the evaporation, concentration and denitrification of high-level waste liquid is the key link.

For the evaporative concentration and denitration of high-level waste liquid, its three basic operation processes are: heating solution, boiling evaporation of superheated solution, and formaldehyde (or formic acid) denitration reaction. At present, the typical equipment used in the above steps is an externally heated evaporator with the heating chamber and the vapor-liquid separation chamber set separately. A notable feature of this equipment is that the above three basic operation processes are concentrated in the heating chamber, and the operation method generally adopts the staged evaporation concentration-denitrification (first heating the evaporation solution to concentrate the nitric acid to a certain concentration, and then stop heating , add formaldehyde or formic acid for denitration to reduce the concentration of nitric acid to a certain value, then heat the solution again for evaporation and concentration and repeat the above process until the volume of the solution and the concentration of nitric acid meet the requirements) or steam (one-time heating, evaporation and concentration of the solution to the required level) Volume, then stop heating, and then gradually add formaldehyde or formic acid to denitrify to the desired acidity at one time) to process the feed liquid. Analysis of the structural characteristics of the externally heated evaporator shows that, for the feed liquid produced by the evaporation, concentration and denitration process, the three basic operation processes are concentrated in the heating chamber. Therefore, if precipitation occurs, the precipitation will inevitably be deposited in the heating chamber. , in severe cases, the pipeline will be blocked and the operation cannot be carried out normally. For the spent fuel of the power reactor with deep burnup, the content of zirconium in the high-level waste liquid is relatively high. It is deposited in the form of a zirconium molybdate precipitate, so the commonly used externally heated evaporators and other similar ones, such as jacketed kettle evaporators, are not suitable. In addition, the existing types of high-level waste liquid evaporation, concentration and denitrification equipment all have the problem of easy bumping, that is, the high-level waste liquid produces a large amount of foam and overflows the equipment into the subsequent pipeline, which will lead to equipment instability and radioactivity. serious problems such as leakage. To sum up the above, there is currently no high-level waste liquid evaporation concentration and denitrification equipment that can solve the problems of precipitation and bumping.

SUMMARY OF THE INVENTION

The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

Therefore, the purpose of the present invention is to propose an external circulation type high-level waste liquid evaporation concentration denitrifier.

In order to achieve the above purpose, the embodiment of the present invention proposes an external circulation type high-level waste liquid evaporative concentration and denitrification device, including: an evaporation concentration denitrification kettle, an external circulation pipe, a heater, a back pressure superheating zone and a defoaming purification tower. The bottom opening on one side of the evaporation concentration and denitration kettle is connected with the outer circulation pipe, the outer circulation pipe is connected with the heater, the upper part of the heater is connected with the back pressure overheating zone, and the back pressure overheating zone is connected with the heater. The other side opening of the evaporation concentration and denitration kettle is connected with the opening, and the top of the evaporation concentration and denitration kettle is connected with the defoaming purification tower; the evaporation concentration and denitration kettle includes a denitration agent distributor, a partition, an overflow area and a cyclone separation wherein, the denitration agent distributor is arranged at the bottom of the evaporative concentration and denitration kettle, the cyclone separator is arranged on the top of the evaporative concentration and denitration kettle, and the side of the evaporative concentration and denitration kettle passes through the side close to the bottom opening. The separator forms an overflow area isolated from the evaporative concentration and denitration area.

The external circulation type high-level waste liquid evaporative concentration and denitrification device in the embodiment of the present invention adopts the strategy of phase separation between the heating zone and the evaporative concentration and denitrification zone, separation of the evaporative concentration and denitrification zone from the inlet of the external circulation pipe, and a sufficiently large flow rate in the external circulation pipe. , so that the precipitation generated in the evaporation concentration and denitrification zone will not enter and deposit in the heating chamber in large quantities. At the same time, the steam before entering the defoaming purification tower is treated with a cyclone separator, which can effectively separate the small droplets and break the foam. It can effectively prevent the occurrence of bumping, especially suitable for the evaporative concentration and denitration treatment of high-level radioactive waste liquid that produces precipitation and/or bumping, and can be widely used in the field of radionuclear chemical industry.

In addition, the external circulation type high-level waste liquid evaporation concentration denitrifier according to the above-mentioned embodiment of the present invention may also have the following additional technical features:

Further, in an embodiment of the present invention, the liquid in the evaporative concentration and denitration tank is higher than the separator, so that the liquid overflows into the overflow area.

Further, in an embodiment of the present invention, the precipitate generated in the process of evaporative concentration and denitrification will not enter the overflow area under the action of gravity.

Further, in an embodiment of the present invention, the heater is separated from the evaporative concentration and denitrification kettle through the back pressure superheating zone, and the evaporative concentration and denitration kettle is separated from the external circulation pipe through the overflow zone. Separation, the evaporation concentration denitration kettle and the defoaming purification tower are separated by a cyclone.

Further, in an embodiment of the present invention, the height of the back pressure superheating zone is greater than the theoretical value, so as to ensure that the high-level waste liquid passing through the heater starts to boil and evaporate after entering the evaporative concentration and denitration kettle.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

1 is a schematic diagram of the overall structure of an external circulation type high-level waste liquid evaporative concentration denitrifier according to an embodiment of the present invention;

2 is a schematic diagram of the internal structure and principle of an evaporative concentration denitrifier according to an embodiment of the present invention;

FIG. 3 is a flow chart of high-level waste liquid evaporation concentration and denitration according to a specific embodiment of the present invention.

Description of reference numbers:

1- Evaporation concentration and denitrification kettle, 2- External circulation pipe; 3- Heater; 4- Back pressure superheat zone; 5- Defoaming purification tower; 6- Cyclone separator; 7- Evaporation concentration and denitrification zone; 8- Clapboard; 9- Overflow area; 10- Denitration agent distributor; 11- Outlet of back pressure superheating area; 12- Inlet of external circulation pipe; 13- Evaporation concentration and denitrification kettle discharge port; 14- Inlet of cyclone separator; 15- Cyclone separator Liquid seal; 16-water phase discharge port of cyclone separator; A-liquid level of evaporation concentration and denitrification zone; B-denitration reaction zone; C-precipitation produced by denitration reaction.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

The external circulation type high-level waste liquid evaporative concentration and denitrifier proposed according to the embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic structural diagram of an external circulation type high-level waste liquid evaporation concentration denitrator according to an embodiment of the present invention.

As shown in FIG. 1 , the evaporative concentration denitrification device includes: an evaporative concentration denitrification kettle 1 , an external circulation pipe 2 , a heater 3 , a back pressure superheating zone 4 and a defoaming purification tower 5 .

Among them, as shown in FIG. 2 , the bottom opening 12 of the evaporation concentration denitration kettle 1 is connected to the external circulation pipe 2, and the external circulation pipe 2 is connected to the heater 3 after U-shaped bending, and the upper part of the heater 3 has a preset height. The back pressure superheating zone 4 is connected with the back pressure superheating zone 4, which is connected with the side opening 11 of the evaporation concentration denitration kettle, and the top of the evaporation concentration denitration kettle 1 is connected with the defoaming purification tower 5.

Further, the evaporative concentration and denitration kettle 1 includes a cyclone 6, an evaporative concentration and denitration zone 7, a baffle 8, an overflow zone 9 and a denitration agent distributor 10. Inside the top, the side of the evaporation concentration denitration kettle 1 forms an overflow area 9 isolated from the evaporation concentration denitration area 7 through the partition plate 8, and the bottom of the overflow area 9 is provided with an opening 12 to be connected with the outer circulation pipe 2, and the denitration agent distributor 10 is provided. At the bottom of the evaporative concentration denitration kettle 1.

Further, the heating zone 3 is separated from the evaporation concentration and denitrification zone 7 by the back pressure superheat zone 4, the evaporation concentration denitration zone 7 and the external circulation pipe 2 are separated by the overflow zone 9, and the evaporation concentration denitration zone 7 is separated from the cyclone separator 6 and The top defoaming purification tower 5 is separated.

It should be noted that the liquid level A of the evaporation concentration and denitrification zone 7 exceeds the height of the partition plate 8 and can overflow into the overflow zone 9; the precipitate C generated during the evaporation concentration and denitration process will not enter the overflow zone 9 due to the action of gravity; The flow velocity in the circulation pipe 2 is fast enough to prevent the sediment from depositing in it; the height of the back pressure superheating zone 4 must be high enough, which is greater than the theoretical value, so as to ensure that the high-level waste liquid passing through the heater 3 enters the evaporation concentration and denitrification zone 7. Just started to boil and evaporate.

It can be understood that the working process of the external circulation type high-level waste liquid evaporative concentration and denitrification device in the embodiment of the present invention is: put the high-level waste liquid into the evaporation concentration and denitration kettle 1, and use the heater 3 to carry out the high-level waste liquid. After heating, the heated high-level waste liquid passes through the back pressure overheating zone, and boils and evaporates in the evaporative concentration and denitration kettle 1. The denitration agent distributor 10 releases the denitration agent, and a denitration reaction occurs. The nitrogen oxide gas will entrain some small droplets and foam into the cyclone separator 6, and the small droplets with high density will return to the kettle after separation, and the water vapor, nitrogen oxide gas and a small amount of foam will enter the top defoaming purification tower 5. The defoaming purification tower 5 performs thorough defoaming and recovery of volatile nuclides, and the process of evaporative concentration and denitrification continues, but the concentration of metal elements continues to increase and the acidity is low, and some metal elements will form precipitation and deposition. At the bottom of the evaporative concentration and denitration kettle 1 , the flow rate of the external circulation pipe 2 is controlled to be fast enough to prevent sediment from depositing in the external circulation pipe 2 .

The following is a further description of the external circulation type high-level waste liquid evaporative concentration denitrifier in accordance with an embodiment of the present invention with reference to a specific embodiment.

The inner diameter of the evaporative concentration and denitrification kettle 1 in the external circulation type high-level waste liquid evaporative concentration and denitrification device is 410mm, the height of the middle straight section is 1770mm, the height of the lower tapered section is 370mm, the inner diameter of the external circulation pipe is 60mm, and the heater 3 adopts a column tube. type steam heater, the heat exchange area is 3.2m ² , and the height of the back pressure superheating zone 4 is 2.5m. Evaporation, concentration and denitrification zone 7 is provided with a denitration agent formaldehyde distributor 10 at the bottom, an overflow zone 9 is provided on the side close to the inlet 12 of the outer circulation pipe 2 through a partition 8 with a height of 610 mm, and a cyclone separator 6 is provided at the top. The top of the evaporative concentration and denitration kettle 1 is connected with a defoaming purification tower 5, the inner diameter is 60mm, the height is 990mm, and 5 sieve plates are arranged inside.

As shown in Figure 3, taking the above-mentioned external circulation type high-level waste liquid evaporation concentration and denitrification device as an example, specifically the high-level waste liquid evaporation concentration and denitrification process is:

Using 37-40% formaldehyde solution as denitrification agent, under the condition of feeding amount of 10L/h and 105℃, continuously containing 16.5g-NaNO ₃ /L, 0.45g-Cs/L, 0.44g-Ce The nitric acid concentration in the 2.5mol/L nitric acid solution of /L was evaporated, concentrated and denitrified to 1.0mol/L. The following denitration reaction occurs in the denitration reaction zone B:

Evaporation causes a large amount of water to evaporate into water vapor, resulting in the concentration of the feed liquid. At the same time, the above denitration reaction continuously reduces the concentration of nitric acid to ensure that the acidity will not be too high and prevent serious corrosion of equipment. The generated water vapor and the generated nitrogen oxide gas will entrain some small droplets and foam into the cyclone separator 6 . In the cyclone separator 6, the denser droplets are thrown to the outer wall and go down through the liquid seal 15 and the discharge port 16 to return to the kettle, where the foam is destroyed due to the liquid film wrapped around it and eliminates the The effect of foam, and steam, gas and a small amount of foam enter the top of the defoaming purification tower 5. The top of the defoaming purification tower is connected with a steam condenser, and the upward vapor in the tower contacts the condensate refluxing at the top of the tower to achieve complete defoaming and recovery of volatile nuclides. The non-condensable gas discharged from the steam condensate will further enter the tail gas absorption link to absorb the nitrogen oxides therein, and the discharged condensate will enter the storage tank for recovery. With the continuous progress of evaporative concentration and denitrification, although the acidity of the solution in the evaporative concentration and denitrification kettle 1 is always maintained at about 1.0mol/L, the concentration of metal elements continues to increase, and due to the low acidity, some metal elements may form The precipitation is deposited in the tapered section in the lower part of the denitrification zone B. When the total concentration of metal oxides in the solution reaches 200g/L, the feeding and evaporative concentration and denitration operations are stopped, and the feed liquid (including the precipitate) is discharged through the bottom discharge port 13. After the discharge is completed, the evaporative concentration and denitrification operation is performed again. According to the above conditions and operation steps, the acidity of the feed liquid that finally completes the evaporative concentration and denitrification is 0.9-1.1 mol-HNO ₃ /L, and the resulting precipitate is not found to be deposited in the outer circulation pipe 2 and the heater 3 and can be obtained by the evaporative concentration and denitrification kettle. 1. The bottom discharge port 13 is discharged smoothly, and there is no obvious foam overflow accident.

The experimental results of the above embodiments show that the embodiments of the present invention can effectively solve the problems of precipitation formation and bumping in the process of high-level waste liquid evaporation, concentration and denitration.

The external circulation type high-level waste liquid evaporative concentration and denitrification device proposed according to the embodiment of the present invention adopts the phase separation between the heating zone and the evaporative concentration and denitrification zone, the separation between the evaporative concentration and denitrification zone and the entrance of the external circulation pipe, and the flow velocity in the external circulation pipe is large enough. The strategy of the evaporative concentration and denitrification zone prevents a large amount of precipitates from entering and depositing in the heating chamber. At the same time, a cyclone separator is used to treat the steam before entering the defoaming purification tower to effectively separate the small droplets and break the foam. , can effectively prevent the occurrence of bumping, especially suitable for the evaporative concentration and denitration treatment of high-level radioactive waste liquids that produce precipitation and/or bumping, and can be widely used in the field of radionuclear chemical industry.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise expressly and specifically defined.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Claims (5)

1. an external circulation type high-level waste liquid evaporation concentration denitrification device is characterized in that, comprising: evaporation concentration denitration still, external circulation pipe, heater, back pressure superheat zone and defoaming purification tower, wherein, The bottom opening on one side of the evaporation, concentration and denitration kettle is connected with the outer circulation pipe, the outer circulation pipe is connected with the heater, the upper part of the heater is connected with the back pressure superheating zone, and the back pressure superheating zone is connected The area is connected with the other side opening of the evaporation concentration and denitration still, and the top of the evaporation concentration and denitration still is connected with the defoaming purification tower; The evaporative concentration and denitration kettle includes a denitration agent distributor, a baffle, an overflow area, an evaporative concentration and denitration zone and a cyclone separator, wherein the denitration agent distributor is arranged at the bottom of the evaporative concentration and denitration kettle, and the cyclone The separator is arranged on the top of the evaporative concentration and denitration kettle, and the side of the evaporative concentration and denitration kettle is close to the bottom opening to form an overflow area isolated from the evaporative concentration and denitration zone through the separator. 2. The external circulation type high-level waste liquid evaporative concentration and denitrification device according to claim 1 is characterized in that, the liquid in the evaporative concentration and denitrification still needs to be higher than the partition plate, so that the liquid overflows into the overflow Area. 3 . The external circulation type high-level waste liquid evaporative concentration and denitrification device according to claim 1 , wherein the sediment produced in the evaporative concentration and denitrification process will not enter the overflow area under the action of gravity. 4 . 4. The external circulation type high-level waste liquid evaporation concentration denitrification device according to claim 1, is characterized in that, the heater and the evaporation concentration denitration still are separated by the back pressure superheat zone, and the evaporation concentration The denitration kettle and the external circulation pipe are separated by an overflow area, and the evaporation concentration denitration kettle and the defoaming purification tower are separated by a cyclone separator. 5. The external circulation type high-level waste liquid evaporative concentration denitrifier according to claim 1, characterized in that, the height of the back pressure superheat zone is greater than the theoretical value, to ensure that the high-level waste liquid passing through the heater is at Boiling evaporation starts only after entering the evaporation concentration denitration kettle.

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