An evaporator, method for evaporation concentration and oxalic acid destruction of a plutonium containing feed solution

Abstract

The application discloses an evaporator and method for plutonium-containing feed liquid evaporation concentration and oxalic acid destruction, comprising a heating chamber and a separation chamber, wherein: the number of the heating chamber is multiple, multiple heating chambers are symmetrically distributed around the separation chamber, the upper part of each heating chamber is communicated with the separation chamber through an upper circulation pipe, the lower part of each heating chamber is communicated with the separation chamber through a lower circulation pipe, and a communication pipe is arranged between each heating chamber; a feed liquid inlet is arranged on the lower circulation pipe, and a feed liquid outlet is arranged at the bottom of the lower circulation pipe; the separation chamber is provided with a secondary steam outlet and a leaching liquid inlet, a purification tower plate is arranged in the separation chamber, and a demister is arranged on the purification tower plate. The application can perform plutonium-containing feed liquid evaporation concentration, synchronously complete oxalic acid destruction, purify secondary steam, meet the critical safety requirement, and improve the working flux.

Description

Technical Field

[0001] This invention relates to the field of nuclear industry technology, specifically to an evaporator and method for evaporating and concentrating plutonium-containing liquid and destroying it with oxalic acid. Background Technology

[0002] Some nuclear fuels adopt a closed-cycle technology, and nuclear fuel reprocessing is a key step in realizing the nuclear fuel cycle. In the plutonium tail-end process of nuclear fuel reprocessing, the Pu(NO3)3 solution from the plutonium purification cycle is adjusted in valence and acidity, and then oxalic acid solution is added to precipitate it into plutonium(IV) oxalate. The precipitate slurry is filtered to obtain plutonium oxalate filter cake and mother liquor. The plutonium concentration in the plutonium oxalate precipitate mother liquor from the plutonium tail end is approximately tens to 100 mg / L, the nitric acid concentration is approximately 2.5 mol / L, and the oxalic acid content is approximately 0.05–0.1 mol / L. This plutonium-containing liquid needs to be returned to the plutonium purification cycle after the oxalic acid is destroyed. If this liquid is not concentrated, it will lead to an increase in the throughput of the plutonium purification cycle equipment and an increase in waste liquid, which will adversely affect the design and subsequent operation of the plutonium purification cycle.

[0003] Currently, the post-treatment plant has not adopted the mother liquor evaporation and concentration process, but it has proposed an evaporator with a single heating chamber and a single separation chamber. Due to the size of the critical safety limiting device, the heating chamber size is small, resulting in a low operating throughput. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the existing technology by providing an evaporator and method for evaporating and concentrating plutonium-containing liquid and destroying oxalic acid. This method can evaporate and concentrate plutonium-containing liquid and simultaneously destroy oxalic acid, and can also purify secondary steam while meeting critical safety requirements and improving working throughput.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is:

[0006] According to a first aspect of the present invention, an evaporator for evaporating and concentrating plutonium-containing liquid and destroying it with oxalic acid is provided, comprising a heating chamber and a separation chamber, wherein:

[0007] The number of heating chambers is multiple, and the multiple heating chambers are symmetrically distributed around the separation chamber. The upper part of each heating chamber is connected to the separation chamber through an upper circulation pipe, and the lower part is connected to the separation chamber through a lower circulation pipe.

[0008] The lower circulation pipe is provided with a liquid inlet and a liquid outlet at its bottom;

[0009] The separation chamber is equipped with a secondary steam outlet and a scrubbing liquid inlet. The separation chamber is equipped with a purification tower plate, and the purification tower plate is equipped with a demister.

[0010] Optionally, the number of heating chambers is two, and the two heating chambers are symmetrically distributed on both sides of the separation chamber.

[0011] Optionally, the heating chamber includes a shell and tubular heating tubes, wherein: the upper part of the shell is provided with an upper tube plate, and the lower part of the shell is provided with a lower tube plate, dividing the interior of the shell into an upper tube box, a middle heating section, and a lower tube box; the upper tube box is connected to the separation chamber through an upper circulation pipe, and the lower tube box is connected to the separation chamber through a lower circulation pipe; the middle heating section is provided with a steam inlet, a steam condensate outlet, and a non-condensable gas outlet for introducing heating steam; the tubular heating tubes are located in the middle heating section of the shell to circulate the liquid; wherein the top end of each heating tube in the tubular heating tubes is connected to the upper tube box after being distributed and fixed by the upper tube plate, and its bottom end is connected to the lower tube box after being distributed and fixed by the lower tube plate.

[0012] Optionally, the lower circulation pipe includes a lower circulation pipe main pipe and multiple lower circulation pipe branches. The top end of the lower circulation pipe main pipe is connected to the separation chamber, and each lower circulation pipe branch pipe is connected to the lower part of the lower circulation pipe main pipe. The liquid inlet is located on the lower circulation pipe main pipe, and the liquid outlet is located at the bottom end of the lower circulation pipe main pipe.

[0013] Optionally, the cross-sectional area of ​​the upper circulation pipe is 80% to 125% of the total cross-sectional area of ​​the tubular heating tubes; the cross-sectional area of ​​the lower circulation pipe branch is 80% to 100% of the total cross-sectional area of ​​the tubular heating tubes, and the cross-sectional area of ​​the lower circulation pipe main is greater than the sum of the total cross-sectional areas of the lower circulation pipe branch.

[0014] Optionally, a connecting pipe is provided between the heating chambers.

[0015] Optionally, the evaporator adopts a large aspect ratio structure design, wherein the aspect ratio of the separation chamber is 25-15, and the aspect ratio of the heating chamber is 25-15.

[0016] Optionally, the purification tower plate is a bubble cap tower plate or a packed tower plate, and the demister is a wire mesh demister or a baffle plate demister.

[0017] Optionally, the evaporator may be made entirely of zirconium alloy or titanium alloy, and the filler material may be made of ceramic material.

[0018] According to a second aspect of the present invention, a method for evaporating and concentrating plutonium-containing liquid and destroying oxalic acid using the evaporator described above is provided. The steps include: mixing plutonium-containing liquid and manganese solution, introducing the mixture through a liquid inlet, and introducing heating steam through a steam inlet. The liquid is allowed to circulate naturally in the evaporator by utilizing density and temperature differences, thereby completing the evaporation, concentration, and destruction of oxalic acid. The generated secondary steam is discharged from the secondary steam outlet after being treated by a scrubbing liquid, a purification tray, and a demister. The concentrated liquid is discharged from the liquid outlet when the concentration reaches the expected concentration factor and the destruction of oxalic acid meets the requirements.

[0019] The evaporator for evaporating and concentrating plutonium-containing liquid and destroying it with oxalic acid, as described in this invention, is the first of its kind in the industry and has the following advantages compared to existing technologies:

[0020] (1) It can complete the evaporation and concentration of plutonium-containing liquid and the destruction of oxalic acid;

[0021] (2) Because it has multiple heating chambers, it can effectively increase the working throughput of the equipment while meeting the critical safety requirements;

[0022] (3) It can effectively complete secondary steam purification;

[0023] (4) It operates stably and can be applied to spent fuel reprocessing plants. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the evaporator for evaporation and concentration of plutonium-containing liquid and destruction by oxalic acid in an embodiment of the present invention;

[0025] Figure 2 This is a cross-sectional view of the heating chamber in an embodiment of the present invention.

[0026] In the diagram: 10-Heating chamber; 11-Shell-tube heating tube; 12-Lower tube box; 13-Upper tube box; 14-Upper tube sheet; 15-Lower tube sheet; 16-Non-condensable gas outlet; 17-Steam inlet; 18-Steam condensate outlet; 19-Shell; 20-Separation chamber; 21-Purification tray; 22-Demister; 23-Scrubber inlet; 24-Secondary steam outlet; 30-Connecting pipe; 31-Upper circulation pipe; 32-Lower circulation pipe main pipe; 33-Lower circulation pipe branch pipe; 34-Feed inlet; 35-Feed outlet. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0028] To address the problems of small heating chamber size and low operating throughput in existing evaporators due to the size of critical safety limiting devices, this invention provides an evaporator for the evaporation and concentration of plutonium-containing liquid and the destruction by oxalic acid, comprising a heating chamber and a separation chamber, wherein:

[0029] The number of heating chambers is multiple, and the multiple heating chambers are symmetrically distributed around the separation chamber. The upper part of each heating chamber is connected to the separation chamber through an upper circulation pipe, and the lower part is connected to the separation chamber through a lower circulation pipe.

[0030] The lower circulation pipe is provided with a liquid inlet and a liquid outlet at its bottom;

[0031] The separation chamber is equipped with a secondary steam outlet and a scrubbing liquid inlet. The separation chamber is equipped with a purification tower plate, and the purification tower plate is equipped with a demister.

[0032] Furthermore, the present invention also provides a method for evaporating and concentrating plutonium-containing liquid and destroying oxalic acid using the evaporator described above, the steps of which include:

[0033] After mixing plutonium-containing liquid and manganese solution, the mixture is introduced through the liquid inlet and heating steam is introduced through the steam inlet. Utilizing the density and temperature differences, the liquid is allowed to circulate naturally in the evaporator, completing the evaporation, concentration, and oxalic acid destruction. The generated secondary steam is treated by the scrubbing liquid, purification tray, and demister before being discharged from the secondary steam outlet. When the concentrate reaches the expected concentration ratio and the oxalic acid destruction meets the requirements, it is discharged from the liquid outlet.

[0034] Example 1

[0035] like Figure 1 As shown, this embodiment discloses an evaporator for the evaporation and concentration of plutonium-containing liquid and the destruction by oxalic acid, comprising a heating chamber 10 and a separation chamber 20, wherein:

[0036] The number of heating chambers 10 is two, but not limited to this. The two heating chambers 10 are symmetrically distributed on both sides of the separation chamber 20. The upper part of each heating chamber is connected to the separation chamber through an upper circulation pipe, and the lower part is connected to the separation chamber 20 through a lower circulation pipe.

[0037] The lower circulation pipe is provided with a liquid inlet 34 and a liquid outlet 35 at its lowest point. Plutonium-containing liquid (such as plutonium oxalate precipitate mother liquor produced by the plutonium tail process of nuclear fuel reprocessing) is introduced from the liquid inlet. After being heated and concentrated in the heating chamber 10, the generated secondary steam enters the separation chamber 20. At the same time, oxalic acid reacts with nitric acid in the liquid, causing the oxalic acid to be destroyed. When the concentrate reaches the expected concentration factor and the oxalic acid is destroyed as required, it is discharged from the liquid outlet 35.

[0038] The separation chamber 20 is provided with a secondary steam outlet 24 and a scrubbing liquid inlet 23. A purification tower plate 21 is provided inside the separation chamber 20 to purify the secondary steam. The secondary steam outlet 24 is located at the top of the separation chamber 20, and the scrubbing liquid inlet 23 is located above the top purification tower plate 21. A demister 22 is provided on the purification tower plate 21 to remove mist entrainment. The purified and demisted secondary steam is discharged from the secondary steam outlet 24.

[0039] Specifically, the evaporator adopts a slender structural design, with both the heating chamber 10 and the separation chamber 20 having a large length-to-diameter ratio to meet critical safety requirements. The length-to-diameter ratio of the heating chamber 10 is 25 to 15, and the length-to-diameter ratio of the separation chamber 20 is 25 to 15.

[0040] Compared to existing technologies, the evaporator in this embodiment, by employing multiple heating chambers, can effectively increase the working throughput of the equipment while meeting critical safety requirements, thereby solving the problems of small heating chamber size and low working throughput caused by the size of critical safety limiting devices in existing technologies.

[0041] In some implementations, such as Figure 1 , Figure 2 As shown, the heating chamber 10 includes a shell 19 and tubular heating tubes 11. Steam flows through the shell side of the heating chamber, and the liquid flows through the tube side of the heating tubes, wherein:

[0042] The upper part of the shell 19 is provided with an upper tube plate 14, and the lower part of the shell 19 is provided with a lower tube plate 15, so that the interior of the shell 19 is divided into an upper tube box 13, a middle heating section and a lower tube box 12. The upper tube box 13 is connected to the separation chamber 20 through an upper circulation pipe 31, and the lower tube box 12 is connected to the separation chamber 20 through a lower circulation pipe. The middle heating section is provided with a steam inlet 17, a steam condensate outlet 18 and a non-condensable gas outlet 16 to introduce heating steam. The steam inlet 17 is located at the upper part of the middle heating section, the steam condensate outlet 18 is located at the lower part of the middle heating section, and the non-condensable gas outlet 16 is located above the steam inlet 17.

[0043] The tubular heating tubes 11 are located in the middle heating section of the shell 19 to circulate the liquid. The top ends of each heating tube in the tubular heating tubes 11 are distributed and fixed by the upper tube plate 14 and connected to the upper tube box 13. The bottom ends are distributed and fixed by the lower tube plate 15 and connected to the lower tube box 12.

[0044] In this embodiment, the specifications of each heating tube in the shell-and-tube heating tube 11 are φ19 or φ25.

[0045] In some embodiments, the lower circulation pipe includes a lower circulation pipe main pipe 32 and lower circulation pipe branch pipes 33, wherein: the top end of the lower circulation pipe main pipe 32 is connected to the separation chamber 20; the number of lower circulation pipes 33 is the same as the number of heating chambers 10, which is two in this embodiment; each lower circulation pipe branch pipe 33 is connected to the lower part of the lower circulation pipe main pipe 32, that is, the lower part of the lower circulation pipe consists of two lower circulation pipe branch pipes 33 leading to two heating chambers 10; the liquid inlet 34 is provided on the lower circulation pipe main pipe 32, for example, at the lower part of the lower circulation pipe main pipe 32; the liquid outlet 35 is provided at the bottom end of the lower circulation pipe main pipe 32.

[0046] In some embodiments, the cross-sectional area of ​​the upper circulation pipe 31 is 80% to 125% of the total cross-sectional area of ​​the tubular heating pipe 11, so as to ensure that the gas-liquid mixture reaches the separation chamber through the upper circulation pipe for gas-liquid separation; the cross-sectional area of ​​the lower circulation pipe branch pipe 33 is 80% to 100% of the total cross-sectional area of ​​the tubular heating pipe 11, so as to ensure circulation, and the cross-sectional area of ​​the lower circulation pipe main pipe 32 is greater than the sum of the total cross-sectional areas of the lower circulation pipe branch pipes 33.

[0047] In some embodiments, a connecting pipe 30 is provided between the heating chambers 10 to balance the pressure in each heating chamber.

[0048] In some embodiments, the purification tray 21 is a bubble cap tray or a packed tray, but it is not limited to these and can also be other tray forms that can achieve gas purification.

[0049] In some embodiments, the demister 22 is a wire mesh demister or a baffle plate demister, but is not limited thereto.

[0050] In some embodiments, the evaporator is made entirely of zirconium alloy or titanium alloy, and when the purification tray 21 is a packed tray, the packing material therein is made of ceramic material.

[0051] The evaporator for evaporation and concentration of plutonium-containing liquid and destruction by oxalic acid in this embodiment is the first of its kind in the industry and has the following advantages compared with the prior art:

[0052] (1) It can complete the evaporation and concentration of plutonium-containing liquid and the destruction of oxalic acid;

[0053] (2) Because it has multiple heating chambers, it can effectively increase the working throughput of the equipment while meeting the critical safety requirements;

[0054] (3) It can effectively complete secondary steam purification;

[0055] (4) It operates stably and can be applied to spent fuel reprocessing plants.

[0056] Example 2

[0057] This embodiment discloses a method for evaporating and concentrating plutonium-containing liquid and destroying oxalic acid using the evaporator described above, the steps of which include:

[0058] The plutonium-containing liquid and manganese solution (which can be potassium permanganate solution, manganese nitrate solution, etc.) are mixed and introduced into the liquid inlet 34, and heating steam is introduced into the steam inlet 17. Utilizing the density and temperature differences, the liquid is allowed to circulate naturally in the evaporator, completing the evaporation, concentration, and oxalic acid destruction. The generated secondary steam is treated by the scrubbing liquid (e.g., the condensate of the secondary steam), the purification tray 21, and the demister 22 before being discharged from the secondary steam outlet 24. When the concentrate reaches the expected concentration ratio and the oxalic acid destruction meets the requirements, it is discharged from the liquid outlet 35.

[0059] The method for evaporating and concentrating plutonium-containing liquid and destroying oxalic acid in this embodiment can evaporate and concentrate plutonium-containing liquid and destroy oxalic acid simultaneously. It can also purify secondary steam, meet critical safety requirements, has a large working throughput, and the equipment operates stably. It can be applied to spent fuel reprocessing plants.

[0060] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. An evaporator for evaporating and concentrating plutonium-containing liquid and destroying it with oxalic acid, characterized in that, It includes a heating chamber (10) and a separation chamber (20), wherein: The number of heating chambers is multiple, and the multiple heating chambers are symmetrically distributed around the separation chamber. The upper part of each heating chamber is connected to the separation chamber through an upper circulation pipe, and the lower part is connected to the separation chamber through a lower circulation pipe. The lower circulation pipe is provided with a liquid inlet (34) and a liquid outlet (35) at its bottom. The separation chamber is provided with a secondary steam outlet (24) and a scrubbing liquid inlet (23), and a purification tower plate (21) is provided in the separation chamber, with a demister (22) provided on the purification tower plate. The evaporator adopts a slender structural design that meets critical safety requirements. Both the heating chamber and the separation chamber have a large length-to-diameter ratio, with the heating chamber having a length-to-diameter ratio of 25 to 15 and the separation chamber having a length-to-diameter ratio of 25 to 15. The evaporator as a whole is made of zirconium alloy or titanium alloy. The lower circulation pipe includes a lower circulation pipe main pipe (32) and multiple lower circulation pipe branches (33). The top end of the lower circulation pipe main pipe is connected to the separation chamber, and each lower circulation pipe branch is connected to the lower part of the lower circulation pipe main pipe. The number of lower circulation pipe branches is the same as the number of heating chambers. The lower part of the lower circulation pipe consists of multiple lower circulation pipe branches leading to each heating chamber. The liquid inlet is located on the lower circulation pipe main pipe, and the liquid outlet is located at the bottom end of the lower circulation pipe main pipe. A connecting pipe (30) is provided between the heating chambers.

2. The evaporator for evaporation and concentration of plutonium-containing liquid and oxalic acid degradation according to claim 1, characterized in that, There are two heating chambers, which are symmetrically distributed on both sides of the separation chamber.

3. The evaporator for evaporation and concentration of plutonium-containing liquid and oxalic acid degradation according to claim 1, characterized in that, The heating chamber includes a shell (19) and tubular heating tubes (11), wherein: The upper part of the shell is provided with an upper tube plate (13) and the lower part of the shell is provided with a lower tube plate (12), so that the interior of the shell is divided into an upper tube box (14), a middle heating section and a lower tube box (15). The upper tube box is connected to the separation chamber through an upper circulation pipe, and the lower tube box is connected to the separation chamber through a lower circulation pipe. The middle heating section is provided with a steam inlet (17), a steam condensate outlet (18) and a non-condensable gas outlet (16) to introduce heating steam. The tubular heating tubes are located in the middle heating section of the shell to facilitate the flow of liquid. The top ends of each heating tube in the tubular heating tubes are connected to the upper tube box after being distributed and fixed by the upper tube plate, and the bottom ends are connected to the lower tube box after being distributed and fixed by the lower tube plate.

4. The evaporator for evaporation and concentration of plutonium-containing liquid and oxalic acid degradation according to claim 3, characterized in that, The cross-sectional area of ​​the upper circulation pipe is 80% to 125% of the total cross-sectional area of ​​the tubular heating pipe; The cross-sectional area of ​​the lower circulation pipe branch is 80% to 100% of the total cross-sectional area of ​​the tubular heating pipe, and the cross-sectional area of ​​the lower circulation pipe main (32) is greater than the sum of the total cross-sectional areas of the lower circulation pipe branch (33).

5. The evaporator for evaporation and concentration of plutonium-containing liquid and destruction by oxalic acid according to any one of claims 1-4, characterized in that, The purification tower plate is a bubble cap tower plate or a packed tower plate, and the demister is a wire mesh demister or a baffle plate demister.

6. The evaporator for evaporating and concentrating plutonium-containing liquid and destroying it with oxalic acid according to any one of claims 1-4, characterized in that, The packing material in the evaporator is made of ceramic material.

7. A method for evaporating and concentrating plutonium-containing liquid and destroying oxalic acid using the evaporator described above according to any one of claims 1-6, characterized in that the steps include... include: After mixing the plutonium-containing liquid and the manganese solution, the mixture is introduced through the liquid inlet (34) and heating steam is introduced through the steam inlet (17). The liquid is naturally circulated in the evaporator by utilizing the density difference and temperature difference, and the evaporation, concentration and oxalic acid destruction are completed. The generated secondary steam is discharged from the secondary steam outlet (24) after being treated by the scrubbing liquid, the purification tower plate (21) and the demister (22). When the concentrate reaches the expected concentration ratio and the oxalic acid destruction meets the requirements, it is discharged from the liquid outlet (35).

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