Evaporator and purex process system

Abstract

The application discloses an evaporator and a PUREX process system, which comprises a heating chamber and a separation chamber, the heating chamber is an annular gap heating chamber, a feed liquid inlet and a concentrated liquid outlet are arranged on the annular gap heating chamber, a heating piece is arranged outside the heating chamber, and a hollow part is filled with a neutron poison; the bottom of the separation chamber is communicated with the top of the heating chamber, the top of the separation chamber is provided with a secondary steam outlet, and a leaching liquid inlet is further arranged on the separation chamber. The evaporator has the advantages of simple structure, large capacity, long discharge interval, low operation frequency, high purification efficiency, satisfaction of critical safety, very stable operation, realization of evaporation and concentration of plutonium-containing liquid, recovery of plutonium in a reprocessing plant and reduction of plutonium loss.

Description

Technical Field

[0001] This invention relates to the field of spent fuel reprocessing technology, specifically to an evaporator and the PUREX process system. Background Technology

[0002] Currently, the spent fuel reprocessing process mainly adopts the PUREX process, which mainly includes the headend process, chemical separation process, and tailend process (including uranium tailend and plutonium tailend). In the chemical separation process, the plutonium purification system purifies and concentrates the plutonium-containing feed solution (1BP) from the co-decontamination cycle to prepare a qualified high-concentration plutonium feed solution (2BP) for plutonium conversion at the plutonium tailend. In the plutonium tailend process, the high-concentration plutonium feed solution (2BP) from the plutonium purification system is adjusted in oxidation state and acidity, and then oxalic acid is added for precipitation. The precipitate slurry is filtered to obtain plutonium oxalate filter cake and mother liquor. The mother liquor contains a certain amount of plutonium and needs to be returned to the plutonium purification system for plutonium purification recycling. However, the presence of oxalic acid in the mother liquor reduces the partition coefficient of Pu(Ⅳ) during the extraction process, affecting the plutonium yield.

[0003] Therefore, the oxalic acid in the mother liquor needs to be destroyed before it is returned to the plutonium purification system for plutonium purification cycle.

[0004] Currently, some plutonium purification and recycling systems employ reflux extraction, resulting in a large amount of plutonium residue and significant waste. Furthermore, directly returning the mother liquor from the plutonium tail-end process to the plutonium purification system for recycling dilutes the plutonium concentration of the plutonium-containing solution by 1 basis point (BP). Adding an evaporator to these two processes to evaporate and concentrate the plutonium-containing solution would not only simplify the process, significantly reduce waste, and increase plutonium yield, but also allow for the simultaneous oxalic acid destruction of the mother liquor during evaporation and concentration.

[0005] For the evaporation of plutonium-containing liquids, due to critical safety limitations, elongated natural circulation evaporators are currently the most commonly used type. While this type of evaporator can meet critical safety requirements, it is relatively difficult to manufacture, has a small capacity, and requires frequent operation. Stir-pan evaporators are frequently used in post-treatment plants for evaporating waste liquids. They are simple to manufacture and have a large capacity; however, large throughput makes it difficult for ordinary stir-pan evaporators to meet critical safety requirements, making them unsuitable for evaporating liquids containing significant amounts of plutonium. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the above-mentioned shortcomings of the existing technology by providing an evaporator and a PUREX process system. The evaporator has a simple structure, large capacity, long discharge interval time, low operating frequency, high purification efficiency, and can meet critical safety requirements. It is also very stable in operation and can realize the evaporation and concentration of plutonium-containing liquid, recover plutonium from the post-processing plant, and reduce plutonium loss.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is:

[0008] According to a first aspect of the present invention, an evaporator is provided, comprising a heating chamber and a separation chamber, wherein:

[0009] The heating chamber is an annular gap heating chamber, which is provided with a feed liquid inlet and a concentrate outlet. A heating element is provided outside the heating chamber, and the hollow part is filled with neutron poison. The bottom of the separation chamber is connected to the top of the heating chamber. The top of the separation chamber is provided with a secondary steam outlet, and the separation chamber is also provided with a rinsing liquid inlet.

[0010] Optionally, the width of the annular heating chamber is 100-200 mm.

[0011] Optionally, the diameter of the separation chamber is greater than 150 mm.

[0012] Optionally, the neutron poison is one or more of boron-containing cement, boron-containing polyethylene, and boron-containing resin.

[0013] Optionally, the heating element is a heating ring tube or a heating jacket.

[0014] Optionally, the separation chamber is equipped with a purification component, which is a bubble cap tray.

[0015] Optionally, the separation chamber is also equipped with a demister.

[0016] Optionally, the rinsing fluid is a vapor condensate.

[0017] Optionally, a condenser is connected to the secondary steam outlet, and the condensate outlet of the condenser is connected to the scrubbing liquid inlet through a return pipe, which is used to condense the steam discharged from the separation chamber in the condenser to obtain steam condensate, which is then returned to the separation chamber as scrubbing liquid.

[0018] According to a second aspect of the present invention, a PUREX process system is provided, comprising a first-end process, a chemical separation process, a last-end process, and the aforementioned evaporator, wherein:

[0019] The feed inlet of the evaporator is connected to the tail end process, and is used to introduce the mother liquor generated in the tail end process and evaporate and concentrate it to obtain a concentrated liquid; the concentrated liquid outlet of the evaporator is connected to the plutonium purification system in the chemical separation process, and is used to return the concentrated liquid to the plutonium purification system for plutonium purification cycle.

[0020] The evaporator and PUREX process system of the present invention, compared with the prior art, have the following advantages:

[0021] It has the following benefits:

[0022] (1) The evaporator has a large capacity, which can be 3 to 6 times that of a natural circulation evaporator. It has a long discharge interval, low operating frequency, and a concentration ratio of 5 to 15 times.

[0023] (2) The heating chamber of the evaporator is an annular heating chamber, which is filled with neutron poison. Compared with the commonly used autoclave evaporator, it can meet the critical safety requirements through geometric control and poison control.

[0024] (3) The overall structure of the evaporator adopts the form of a kettle, which is a kettle evaporator with a simple structure and is easy to process and manufacture;

[0025] (4) Compared with the slender structure of the natural circulation evaporator, the large diameter separation chamber is easier to manufacture and can improve the steam purification efficiency.

[0026] (5) This system can evaporate and concentrate plutonium-containing liquid, simplify the process, greatly reduce the amount of waste liquid generated, and improve the plutonium yield. The mother liquor can also be destroyed by oxalic acid while being evaporated and concentrated. Attached Figure Description

[0027] Figure 1 This is an elevation view of the evaporator in an embodiment of the present invention;

[0028] Figure 2 This is a top view of the evaporator in an embodiment of the present invention.

[0029] In the diagram: 1-Heating chamber; 2-Feed inlet; 3-Concentrate outlet; 4-Separation chamber;

[0030] 5-Scrubber inlet; 6-Secondary steam outlet; 7-Bubble cap; 8-Weir plate; 9-Downcomer;

[0031] 10-Tear hole; 11-Demister; 12-Steam heating ring; 13-Steam inlet; 14-Non-condensable gas outlet; 15-Condensate outlet; 16-Neutron poison. Detailed Implementation

[0032] 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.

[0033] In the existing PUREX process system, the mother liquor generated at the end of the plutonium tail-end process is recycled back to the plutonium purification system. However, the reflux extraction method has problems such as large plutonium residue retention, excessive waste liquid generation, and dilution of the plutonium concentration of 1 bp of plutonium-containing solution. On the other hand, the evaporation and concentration method has the relatively high difficulty in manufacturing the evaporator.

[0034] Problems include small capacity, frequent operation, or difficulty in meeting critical safety requirements. This invention provides an evaporator that meets critical safety requirements, comprising a lower heating chamber and an upper separation chamber. The heating chamber is an annular heating chamber with a feed inlet and a concentrate outlet. A heating element for heating the heating chamber is located outside the heating chamber. The hollow portion is filled with neutron poison to meet critical safety requirements. The bottom of the separation chamber communicates with the top of the heating chamber. The top of the separation chamber has a secondary steam outlet, and the separation chamber also has a scrubbing liquid inlet.

[0035] Furthermore, the present invention also discloses a PUREX process system, including a first-end process, a chemical separation process, and a last-end process, and also includes the aforementioned evaporator, wherein the feed inlet of the evaporator is connected to the last-end process for introducing the mother liquor generated in the last-end process and concentrating it to obtain a concentrated liquid; the concentrated liquid outlet of the evaporator is connected to the plutonium purification system in the chemical separation process for returning the concentrated liquid to the plutonium purification system for plutonium purification cycle.

[0036] Example 1

[0037] like Figure 1 , Figure 2 As shown, this embodiment discloses an evaporator that meets critical safety requirements, including a lower heating chamber 1 and an upper separation chamber 4, wherein:

[0038] Heating chamber 1 is a well-shaped (e.g., annular, tubular) annular heating chamber. The annular heating chamber is provided with a liquid inlet 2 and a concentrate outlet 3. Heating elements are provided outside heating chamber 1. The heating elements heat the heating chamber, causing the liquid in the heating chamber to evaporate and concentrate, resulting in concentrate and steam. The hollow part of the annular heating chamber is filled with neutron poison 16 to meet critical safety requirements.

[0039] The bottom of the separation chamber 4 is connected to the top of the heating chamber 1. The top of the separation chamber 4 is provided with a secondary steam outlet 6, and the separation chamber 4 is also provided with a washing liquid inlet 5, which is used to introduce washing liquid to purify the steam entering the separation chamber and remove the target product (such as plutonium) entrained therein, so as to improve the yield of the target product.

[0040] In some implementations, the overall structure of the evaporator adopts a kettle-type form, which is a kettle-type evaporator. This structure is simple and easy to process and manufacture.

[0041] In some embodiments, the width of the annular heating chamber is 100–200 mm, but is not limited thereto.

[0042] In some embodiments, the diameter of the separation chamber 4 is greater than 150 mm, but it is not limited to this. Specifically, the steam and eluent in the separation chamber 4 contain very little plutonium, and a larger size can still meet the critical safety requirements. Therefore, the size of the separation chamber 4 can be appropriately increased as needed to reduce the empty tower gas velocity of the steam, increase the residence time, reduce mist entrainment, and improve the purification efficiency.

[0043] In some embodiments, the neutron poison 16 is one or more of boron-containing cement, boron-containing polyethylene, and boron-containing resin, but is not limited thereto.

[0044] In some embodiments, the scrubbing liquid is steam condensate, but it is not limited to this. Specifically, a condenser (not shown in the figure) may be connected to the secondary steam outlet 6 at the top of the separation chamber 4. The condensate outlet on the condenser is connected to the scrubbing liquid inlet 5 through a return pipe. The steam discharged from the separation chamber 4 is condensed in the condenser to obtain steam condensate, which is then returned to the separation chamber 4 as scrubbing liquid through the return pipe.

[0045] In some embodiments, the heating element is a steam heating ring pipe 12, which has a steam inlet 13 at its inlet end and a condensate outlet 15 at its outlet end. Preferably, the steam inlet 13 is located at the upper part of the steam heating ring pipe 12, and the condensate outlet 15 is located at the lower part of the steam heating ring pipe 12. Furthermore, the steam heating ring pipe 12 also has a non-condensable gas outlet 14, which is preferably located at the upper part of the steam heating ring pipe 12 and as far away as possible from the steam inlet 13, for example, on the opposite side of the steam inlet 13.

[0046] In some embodiments, the heating element may also be a heating jacket, with a heating medium inlet at the upper part and a heating medium outlet at the lower part, and the heating medium flows inside the heating jacket.

[0047] In some embodiments, a purification component is provided in the separation chamber 4, located below the eluent inlet 5. Specifically, the purification component can be a bubble cap tray, but is not limited to this. After the eluent enters the separation chamber from the eluent inlet, it undergoes mass transfer with the steam in the separation chamber through the purification component, absorbing plutonium and other radioactive elements from the steam. Simultaneously, the small amount of plutonium contained in the eluent can be returned to the evaporator for further evaporation and concentration to improve the plutonium recovery rate.

[0048] The bubble cap tray in this embodiment has the same or similar structure as commonly available bubble cap trays, including a bubble cap 7, a weir plate 8, a downcomer 9, and teardrop holes 10, which will not be described in detail here. Furthermore, to reduce processing difficulty, the bubble cap 7 can be a standard bubble cap.

[0049] In some embodiments, a demister 11 is also provided in the separation chamber 4, and the demister 11 is located above the washing liquid inlet 5, for example, at the top of the separation chamber 4. Specifically, the demister 11 can be a cyclone separator or a baffle plate demister, but is not limited to these. By providing a demister, the mist entrained in the steam can be removed, effectively preventing product loss.

[0050] The working process of the evaporator in this embodiment is described in detail below, taking a plutonium-containing liquid as an example:

[0051] Plutonium-containing liquid enters the heating chamber of the evaporator through liquid inlet 2. Steam enters the steam heating ring pipe 12 through steam inlet 13 to heat the plutonium-containing liquid in the annular heating chamber (the hollow part is filled with boron-containing cement). After condensation, the steam is discharged through condensate outlet 15, and non-condensable gas is periodically discharged through non-condensable gas outlet 14. During the heating process, after the plutonium-containing liquid is heated to boiling, the boiling gas-liquid mixture enters the bottom of the separation chamber 4, where the gas-liquid mixture is separated. The separated liquid returns to the heating chamber 1 for re-evaporation and concentration. Steam enters the bubble cap tray above the separation chamber 4, and the eluent enters the separation chamber 4 through eluent inlet 5. After filling the bubble cap tray, it overflows from the weir plate 8 in the bubble cap tray and flows to the next stage bubble cap tray through downcomer 9. The steam contacts the eluent through the bubble cap tray for mass transfer, recovering plutonium from the steam and purifying the radioactivity contained therein. After mass transfer, the steam passes through demister 11 to remove entrained droplets and is discharged through secondary steam outlet 6. The discharged steam is condensed to obtain a steam condensate containing a small amount of plutonium. The steam condensate is returned to the separation chamber through the feed inlet as a scrubbing liquid. After mass transfer upon contact with the steam, the scrubbing liquid absorbs the plutonium from the steam. It is then returned to the heating chamber through the downcomer 9 and the teardrop orifice 10 for re-evaporation and concentration, thereby improving the plutonium recovery rate. The plutonium solution after evaporation and concentration (i.e., the concentrate) is discharged from the concentrate outlet 3.

[0052] The evaporator of this embodiment has the following advantages compared with the prior art:

[0053] (1) Large capacity, which can be 3 to 6 times that of a natural circulation evaporator; long discharge interval; low operating frequency; concentration ratio can reach 5 to 15 times.

[0054] (2) The heating chamber of the evaporator is an annular heating chamber, which is filled with neutron poison. Compared with the commonly used autoclave evaporator, it can meet the critical safety requirements through geometric control and poison control.

[0055] (3) The overall structure of the evaporator adopts the form of a kettle, which is a kettle evaporator with a simple structure and is easy to process and manufacture;

[0056] (4) Compared with the slender structure of the natural circulation evaporator, the large diameter separation chamber is easier to manufacture and can improve the steam purification efficiency.

[0057] Example 2

[0058] This embodiment discloses a PUREX process system, including a pre-process, a chemical separation process, and a post-process, and also includes the evaporator described in Embodiment 1, wherein:

[0059] The feed inlet of the evaporator is connected to the tail end process, which is used to introduce the mother liquor generated in the tail end process and evaporate and concentrate it to obtain concentrated liquid;

[0060] The evaporator's concentrate outlet is connected to the plutonium purification system in the chemical separation process, used to return the concentrate to the plutonium purification system for plutonium purification cycle.

[0061] Compared with the prior art, the PUREX process system of this embodiment can evaporate and concentrate plutonium-containing liquid, simplify the process flow, greatly reduce the amount of waste liquid generated, and improve the plutonium yield. The mother liquor can also be destroyed by oxalic acid while being evaporated and concentrated. Furthermore, since it includes the evaporator described in Example 1, it has all the advantages of the evaporator described in Example 1.

[0062] 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, characterized in that, It includes a heating chamber (1) and a separation chamber (4). The heating chamber is an annular gap heating chamber. The annular gap heating chamber is provided with a liquid inlet (2) and a concentrate outlet (3). A heating element is provided outside the heating chamber. The hollow part is filled with neutron poison (16). The heating element heats the heating chamber, causing the liquid inside the heating chamber to evaporate and concentrate. The bottom of the separation chamber is connected to the top of the heating chamber. The top of the separation chamber is provided with a secondary steam outlet (6) and a washing liquid inlet (5). The evaporator has an overall structure in the form of a kettle, and is a kettle-type evaporator.

2. The evaporator according to claim 1, characterized in that, The width of the annular heating chamber is 100~200mm.

3. The evaporator according to claim 1, characterized in that, The diameter of the separation chamber is greater than 150 mm.

4. The evaporator according to claim 1, characterized in that, The neutron poison is one or more of boron-containing cement, boron-containing polyethylene, and boron-containing resin.

5. The evaporator according to claim 1, characterized in that, The heating element is a heating ring tube (12) or a heating jacket.

6. The evaporator according to any one of claims 1-5, characterized in that, The separation chamber is equipped with a purification component, which is a bubble cap tray.

7. The evaporator according to claim 6, characterized in that, The separation chamber is also equipped with a demister (11).

8. The evaporator according to claim 7, characterized in that, The rinsing solution is a vapor condensate.

9. The evaporator according to claim 8, characterized in that, A condenser is connected to the secondary steam outlet. The condensate outlet of the condenser is connected to the scrubbing liquid inlet via a return pipe, which is used to condense the steam discharged from the separation chamber in the condenser to obtain steam condensate, which is then returned to the separation chamber as scrubbing liquid.

10. A PUREX process system, comprising an initial process, a chemical separation process, and an output process, characterized in that, It also includes the evaporator according to any one of claims 1-9, The feed inlet (2) of the evaporator is connected to the tail end process and is used to introduce the mother liquor generated in the tail end process and evaporate and concentrate it to obtain concentrated liquid; The concentrated liquid outlet (3) of the evaporator is connected to the plutonium purification system in the chemical separation process, and is used to return the concentrated liquid to the plutonium purification system for plutonium purification cycle.

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