Method and system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing feed liquid

Abstract

The invention discloses a plutonium-containing feed liquid continuous evaporation concentration and oxalic acid destruction method and system.The method comprises the steps that a manganese solution and nitric acid are added into the plutonium-containing feed liquid for seasoning, and mixed feed liquid is obtained; continuously adding the mixed material liquid into an evaporator, heating and maintaining a preset temperature, so that the mixed material liquid is evaporated and concentrated in the evaporator, and oxalic acid destruction is completed; when the concentration of the feed liquid in the evaporator reaches the required multiple and the damage of oxalic acid meets the requirement, the concentrated feed liquid starts to be continuously discharged to a concentrated liquid receiving tank, continuous feeding and discharging are achieved, the discharging speed is equal to the feeding speed / the concentration multiple, the feeding speed of the mixed feed liquid and the discharging speed of the concentrated liquid are adjusted, and the feeding speed of the mixed feed liquid and the discharging speed of the concentrated liquid are adjusted; and the liquid level is constant at the preset liquid level value. The method has the advantages of large concentration multiple, high oxalic acid damage rate, large working flux, small equipment fatigue damage, stable equipment, continuous operation and simple operation, can meet the operation requirements of a post-treatment plant, greatly reduces the treatment amount of a plutonium purification cycle flow, and reduces the wastewater amount.

Description

Technical Field

[0001] The invention relates to the technical field of spent fuel post-processing, and in particular to a method and system for continuous evaporation and concentration of plutonium-containing liquid and its destruction with oxalic acid. Background Art

[0002] Some nuclear fuels adopt a closed cycle technology route, and nuclear fuel reprocessing is a key link in realizing the nuclear fuel cycle. In the plutonium tail process of nuclear fuel reprocessing, the Pu(NO3)3 solution from the plutonium purification cycle is priced and acidified, and then precipitated by adding oxalic acid solution to convert it into plutonium oxalate (IV) precipitate. The precipitate slurry is filtered to obtain plutonium oxalate filter cake and mother liquor. The plutonium concentration in the plutonium tail oxalate precipitate mother liquor is about tens to 100 mg / L, the nitric acid concentration is about 2.5 mol / L, and the oxalic acid content is about 0.05 to 0.1 mol / L. These plutonium-containing feed liquids need to destroy the oxalic acid and return to the plutonium purification cycle. If the feed liquid is not concentrated, it will have an adverse effect on the design and subsequent operation of the plutonium purification cycle.

[0003] In order to digest the plutonium oxalate precipitation mother liquor, the spent fuel reprocessing plant usually destroys the oxalic acid in the plutonium oxalate precipitation mother liquor and then returns it to the 1BP plutonium-containing feed liquid, but this will dilute the 1BP plutonium-containing feed liquid. In addition, if the mother liquor is not concentrated by evaporation concentration process before returning, it will increase the amount of waste liquid and increase the working flux of the equipment.

[0004] At present, some studies have proposed the use of a batch mother liquor evaporation concentration and oxalic acid destruction process. This process requires cooling the feed liquid in the evaporator, which reduces the working flux and causes the evaporator to alternate between hot and cold, increasing its fatigue. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid in view of the above-mentioned deficiencies in the prior art. The method and system have the advantages of large concentration multiple, high oxalic acid destruction rate, large working flux, small equipment fatigue damage, stable equipment, continuous operation, simple operation, and can meet the operation requirements of the post-processing plant, greatly reducing the processing volume of the plutonium purification cycle process and reducing the amount of wastewater.

[0006] The technical solution of the present invention to solve the above technical problems is:

[0007] According to a first aspect of the present invention, there is provided a method for continuous evaporation concentration and oxalic acid destruction of a plutonium-containing liquid, comprising:

[0008] adding manganese solution and nitric acid into plutonium-containing feed liquid for seasoning to obtain a mixed feed liquid;

[0009] The mixed liquid is continuously added to the evaporator, heated and maintained at a preset temperature, so that the mixed liquid evaporates and concentrates in the evaporator, and the oxalic acid is destroyed under the action of a manganese catalyst;

[0010] When the liquid in the evaporator is concentrated to the required multiple and the oxalic acid destruction meets the requirements, the concentrated liquid begins to be continuously discharged to the concentrated liquid receiving tank to achieve continuous feeding and discharging, wherein the discharging speed = feeding speed / concentration multiple, and the feeding speed of the mixed liquid and the discharging speed of the concentrated liquid are adjusted to keep the liquid level in the evaporator constant at the preset liquid level value.

[0011] Optionally, the manganese content in the mixed liquid is 0.01 mol / L to 0.05 mol / L, and the nitric acid content is 2 mol / L to 3 mol / L.

[0012] Optionally, the pressure in the evaporator is -30 kPa to -0.5 kPa.

[0013] Optionally, the heating and maintaining the preset temperature is performed by using 0.3-0.6Mpa saturated steam.

[0014] Optionally, the mixed liquid is continuously added to the evaporator by air lift, and the concentrated liquid is continuously discharged to the concentrated liquid receiving tank by air lift.

[0015] Optionally, the method further comprises: cooling the concentrated liquid through a heat exchanger before continuously discharging the concentrated liquid into the concentrated liquid receiving tank.

[0016] Optionally, the method further includes: purifying the secondary steam generated in the evaporator and discharging it to the condenser for condensation, returning a portion of the condensate to the evaporator as a rinse liquid for the purification process, discharging another portion of the condensate to a condensate receiving tank, and passing the non-condensable gas into the exhaust system.

[0017] According to a second aspect of the present invention, there is provided a system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid, comprising a feed tank, a first conveying device, an evaporator, a second conveying device and a concentrated liquid receiving tank, wherein:

[0018] The feed tank is used to add manganese solution and nitric acid into the plutonium-containing feed liquid for conditioning to obtain a mixed feed liquid;

[0019] The first conveying device is connected to the feed tank and the evaporator respectively, and is used to continuously add the mixed liquid in the feed tank to the evaporator;

[0020] The evaporator is used to receive the mixed liquid and heat it and maintain it at a preset temperature, so that the mixed liquid evaporates and concentrates in the evaporator, and the oxalic acid is destroyed under the action of the manganese catalyst;

[0021] The second conveying device is connected to the evaporator and the concentrated liquid receiving tank respectively, and is used to discharge the concentrated liquid to the concentrated liquid receiving tank continuously after the liquid in the evaporator is concentrated to a desired multiple and the oxalic acid destruction reaches the requirement, so as to realize continuous feeding and discharging, wherein the discharging speed = feeding speed / concentration multiple;

[0022] In addition, the first conveying device is also used to adjust the feeding speed of the mixed liquid, and the second conveying device is also used to adjust the discharging speed of the concentrated liquid so that the liquid level in the evaporator is constant at a preset liquid level value.

[0023] Optionally, the first conveying device includes a first air lifting mechanism, a second air lifting mechanism, a constant liquid level front tank and a first gas-liquid separation tank, wherein:

[0024] The first air lifting mechanism is connected to the feed tank and the constant liquid level pre-tank respectively, and is used to first add the mixed liquid in the feed tank to the constant liquid level pre-tank for temporary storage;

[0025] The second air lifting mechanism is connected to the constant liquid level pre-tank and the first gas-liquid separation tank respectively, and is used to continuously add the mixed liquid in the constant liquid level pre-tank to the first gas-liquid separation tank for gas-liquid separation and remove the gas therein;

[0026] The first gas-liquid separation tank is connected to the evaporator and is used to continuously add the feed liquid in the first gas-liquid separator to the evaporator.

[0027] Optionally, the evaporator is a natural circulation evaporator, which includes a heating chamber and a separation chamber. The heating chamber is heated by steam and includes a shell side and a tube side. The tube side of the heating chamber is connected to the feed tank to pass the mixed liquid. The heating chamber is also connected to the separation chamber. The secondary steam generated during the evaporation and concentration process is purified in the separation chamber and then discharged through the secondary steam outlet at the top of the separation chamber. A steam inlet, a condensate outlet and a non-condensable gas outlet are provided on the shell side of the heating chamber. The steam inlet is used to pass saturated steam to heat the tube side, so that the mixed liquid in the tube side of the heating chamber is heated and maintained at a preset temperature. The condensate outlet is used to discharge condensed water of the saturated steam, and the non-condensable gas outlet is used to discharge non-condensable gases in the saturated steam.

[0028] Optionally, the evaporator further comprises a temperature controller, the steam inlet is provided with a saturated steam flow controller, and the evaporator is provided with a temperature detector, wherein:

[0029] The temperature detector is electrically connected to the temperature controller and is used to detect the temperature of the mixed liquid in the evaporator and transmit the detected temperature value to the temperature controller;

[0030] The temperature controller is electrically connected to the saturated steam flow controller, and a preset temperature is set in the temperature controller, which is used to receive the temperature value transmitted by the temperature detector and compare it with the preset temperature, and send a steam flow adjustment instruction to the saturated steam flow controller according to the comparison result;

[0031] The saturated steam flow controller is used to receive a steam flow regulation instruction and automatically regulate the saturated steam flow entering the steam inlet according to the steam flow regulation instruction, so that the mixed liquid in the evaporator is heated and maintained at a preset temperature.

[0032] Optionally, the second conveying device includes a third air lifting mechanism and a second gas-liquid separation tank, wherein:

[0033] The third air lifting mechanism is connected to the evaporator and the second gas-liquid separation tank respectively, and is used to continuously discharge the concentrated liquid in the evaporator into the second gas-liquid separation tank for gas-liquid separation to remove the gas therein;

[0034] The second gas-liquid separation tank is connected to the concentrated liquid receiving tank and is used to discharge the feed liquid in the second gas-liquid separator to the evaporator.

[0035] Optionally, the evaporator includes a liquid level controller, the second air lifting mechanism is provided with a feed flow controller, the third air lifting mechanism is provided with a discharge flow controller, and the evaporator is provided with a liquid level detector, wherein:

[0036] The liquid level detector is electrically connected to the liquid level controller, and is used to detect the liquid level of the feed liquid in the evaporator, and transmit the detected liquid level value to the liquid level controller;

[0037] The liquid level controller is electrically connected to the feed flow controller and the discharge flow controller respectively. A preset liquid level value is provided in the liquid level controller, which is used to receive the liquid level value detected by the liquid level detector and compare it with the preset liquid level value, and send a feed flow adjustment instruction to the feed flow controller and send a discharge flow adjustment instruction to the discharge flow controller according to the comparison result;

[0038] The feed flow controller is used to receive a feed flow adjustment instruction and automatically adjust the flow rate of the mixed liquid added to the evaporator according to the feed flow adjustment instruction. At the same time, the feed flow controller is used to receive a discharge flow adjustment instruction and automatically adjust the flow rate of the concentrated liquid discharged from the evaporator according to the discharge flow adjustment instruction, so that the liquid in the evaporator is constant at a preset liquid level value.

[0039] Optionally, the system further comprises a heat exchanger, which is respectively connected to the evaporator and the third air lifting mechanism, and is used for cooling the concentrated liquid through the heat exchanger before the concentrated liquid is continuously discharged into the concentrated liquid receiving tank.

[0040] Optionally, the system also includes a condenser, a condensate cooler and a condensate receiving tank. The condenser is connected to the secondary steam outlet of the evaporator and is used to condense the secondary steam discharged from the evaporator. The condenser is provided with a condensate outlet and a non-condensable gas outlet. The condensate outlet is connected to the condensate cooler. The condensate cooler is further connected to the eluent inlet of the evaporator and the condensate receiving tank, respectively, for returning a portion of the condensate to the evaporator as the eluent for the purification process and discharging the other portion of the condensate to the condensate receiving tank. The non-condensable gas outlet is connected to the exhaust gas system and is used to pass the non-condensable gas into the exhaust gas system.

[0041] Optionally, the system further comprises a plutonium-containing liquid pipeline, a manganese solution storage tank, and a nitric acid storage tank, wherein the plutonium-containing liquid pipeline, the manganese solution storage tank, and the nitric acid storage tank are all connected to a feed tank, the plutonium-containing liquid pipeline is used to introduce plutonium-containing liquid that needs to be evaporated, concentrated, and destroyed with oxalic acid into the feed tank, the manganese solution storage tank is used to add manganese solution into the feed tank, and the nitric acid storage tank is used to add nitric acid into the feed tank.

[0042] The method of continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid of the present invention has the following beneficial effects:

[0043] (1) Compared with the non-evaporation concentration process, the concentration multiple is large, which can effectively reduce the volume of plutonium-containing liquid, increase the plutonium content, greatly reduce the processing volume of the plutonium purification cycle process, reduce the amount of waste liquid, and have a higher oxalic acid destruction rate, which can meet the operation requirements of the reprocessing plant;

[0044] (2) Compared with the batch evaporation concentration process, the working flux is larger and the equipment fatigue damage is smaller;

[0045] (3) Compared with the batch evaporation concentration process, it can realize continuous process, simple operation, convenient automatic control, high degree of self-control and stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the method and system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid in an embodiment of the present invention.

[0047] In the figure: 1-feeding tank; 2-constant liquid level pre-tank; 3-first gas-liquid separation tank; 4-evaporator; 5-second gas-liquid separation tank; 6-concentrate receiving tank; 7-manganese solution storage tank;

[0048] 8-nitric acid storage tank, 9-first metering pump; 10-second metering pump; 11-heat exchanger; 12-feed flow controller; 13-saturated steam flow controller; 14-discharge flow controller;

[0049] 15-condenser, 16-condensate cooler, 17-fan, 18-condensate receiving tank; 19-first air lifting mechanism; 20-second air lifting mechanism; 21-third air lifting mechanism. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0051] In view of the fact that the mother liquor evaporation concentration and oxalic acid destruction process in the prior art requires cooling of the feed liquid in the evaporator, which reduces the working flux and causes the evaporator to alternate between hot and cold, increasing its fatigue, etc. The present invention provides a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing feed liquid, comprising:

[0052] adding manganese solution and nitric acid into plutonium-containing feed liquid for seasoning to obtain a mixed feed liquid;

[0053] The mixed liquid is continuously added to the evaporator, heated and maintained at a preset temperature, so that the mixed liquid evaporates and concentrates in the evaporator, and the oxalic acid is destroyed under the action of a manganese catalyst;

[0054] When the liquid in the evaporator is concentrated to the required multiple and the oxalic acid destruction meets the requirements, the concentrated liquid begins to be continuously discharged to the concentrated liquid receiving tank to achieve continuous feeding and discharging, wherein the discharging speed = feeding speed / concentration multiple, and the feeding speed of the mixed liquid and the discharging speed of the concentrated liquid are adjusted to keep the liquid level in the evaporator constant at the preset liquid level value.

[0055] Accordingly, the present invention also provides a system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid, comprising a feed tank, a first conveying device, an evaporator, a second conveying device and a concentrated liquid receiving tank, wherein:

[0056] The feed tank is used to add manganese solution and nitric acid into the plutonium-containing feed liquid for conditioning to obtain a mixed feed liquid;

[0057] The first conveying device is connected to the feed tank and the evaporator respectively, and is used to continuously add the mixed liquid in the feed tank to the evaporator;

[0058] The evaporator is used to receive the mixed liquid and heat it and maintain it at a preset temperature, so that the mixed liquid evaporates and concentrates in the evaporator, and the oxalic acid is destroyed under the action of the manganese catalyst;

[0059] The second conveying device is connected to the evaporator and the concentrated liquid receiving tank respectively, and is used to continuously discharge the concentrated liquid to the concentrated liquid receiving tank, and control the liquid discharge speed according to the feed flow rate of the mixed liquid and the liquid level in the evaporator, so that the liquid in the evaporator is constant at a preset liquid level value.

[0060] Example 1

[0061] This embodiment discloses a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid, comprising:

[0062] adding manganese solution and nitric acid into plutonium-containing feed liquid for seasoning to obtain a mixed feed liquid;

[0063] The mixed liquid is continuously added to the evaporator, heated and maintained at a preset temperature (e.g., 95-10° C.), so that the mixed liquid is evaporated and concentrated in the evaporator, and the oxalic acid is destroyed under the action of a manganese catalyst, that is, the evaporation concentration and oxalic acid destruction processes are carried out together in the evaporator;

[0064] When the liquid in the evaporator is concentrated to the required multiple and the oxalic acid destruction meets the requirements, the concentrated liquid begins to be continuously discharged to the concentrated liquid receiving tank to achieve continuous feeding and discharging, wherein the discharge rate = feed rate / concentration multiple to ensure that the concentration reaches the selected multiple, and the feed rate of the mixed liquid (i.e. the flow rate of the mixed liquid added to the evaporator) and the discharge rate of the concentrated liquid (i.e. the flow rate of the concentrated liquid discharged from the evaporator) are adjusted to keep the liquid level in the evaporator constant at the preset liquid level value.

[0065] In some embodiments, the manganese content in the mixed liquid is 0.01 mol / L to 0.05 mol / L, and the nitric acid content is 2 mol / L to 3 mol / L. By adding an appropriate amount of manganese solution to the plutonium-containing liquid, oxalic acid is oxidized and reduced by nitric acid under the condition of manganese as a catalyst, thereby achieving oxalic acid destruction, with a fast oxalic acid destruction speed and a high destruction rate.

[0066] Specifically, if Figure 1 As shown, the plutonium-containing liquid is introduced into the feed tank 1, and at the same time, the manganese solution is added to the feed tank 1 from the manganese solution storage tank 7 through the first metering pump 9, and the nitric acid is added to the feed tank 1 from the nitric acid storage tank 8 through the second metering pump 10, and mixed evenly to complete the seasoning to obtain the above-mentioned mixed liquid. Among them, the added form of manganese can be potassium permanganate solution, manganese nitrate solution, etc., which will not be repeated here.

[0067] In some embodiments, the pressure in the evaporator is controlled to be -30 kPa to -0.5 kPa (gauge pressure) to lower the boiling point, which is more conducive to evaporation and concentration of the feed liquid. At the same time, it can avoid excessive process pressure that affects equipment stability.

[0068] Specifically, if Figure 1 As shown, the pressure inside the evaporator can be controlled by the exhaust gas system: a fan is set at the secondary steam outlet end of the evaporator, and the gas in the evaporator is pumped to the exhaust gas system through the fan, so as to maintain the pressure inside the evaporator at -30kpa ~ -0.5kpa (gauge pressure).

[0069] In some embodiments, the heating and maintaining the preset temperature is performed by using saturated steam, and the pressure of the saturated steam is 0.3-0.6 MPa to ensure the heating heat source.

[0070] In some embodiments, Figure 1 As shown, the mixed liquid is continuously added to the evaporator by air lifting, and the concentrated liquid is continuously discharged to the concentrated liquid receiving tank by air lifting.

[0071] In some embodiments, Figure 1 As shown, the method further includes: arranging a heat exchanger at the concentrated liquid outlet of the evaporator, and cooling the concentrated liquid through the heat exchanger before continuously discharging the concentrated liquid into the concentrated liquid receiving tank.

[0072] Specifically, the heat exchanger can be a pipe heat exchanger or a tube sheet heat exchanger, but is not limited thereto. It can also be other forms of heat exchangers that can achieve liquid cooling, which are not described here one by one; the cooling medium is cooling water.

[0073] In some embodiments, Figure 1 As shown, the method also includes: purifying the secondary steam generated in the evaporator and discharging it to the condenser for condensation, returning a portion of the condensate to the evaporator as a rinse liquid in the purification process, discharging another portion of the condensate to the condensate receiving tank, and passing the non-condensable gas into the exhaust system.

[0074] The method of continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid in this embodiment has the following effects:

[0075] (1) Compared with the non-evaporation concentration process, the concentration multiple is large, which can effectively reduce the volume of plutonium-containing liquid, increase the plutonium content, greatly reduce the processing volume of the plutonium purification cycle process, reduce the amount of waste liquid, and have a higher oxalic acid destruction rate, which can meet the operation requirements of the reprocessing plant;

[0076] (2) Compared with the batch evaporation concentration process, the working flux is larger and the equipment fatigue damage is smaller;

[0077] (3) Compared with the batch evaporation concentration process, it can realize continuous process, simple operation, convenient automatic control, high degree of self-control and stable operation.

[0078] Example 2

[0079] This embodiment discloses a system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid, comprising a feed tank 1, a first conveying device, an evaporator 4, a second conveying device and a concentrated liquid receiving tank 6, wherein:

[0080] A feed tank 1 is used to add manganese solution and nitric acid into the plutonium-containing feed liquid for seasoning to obtain a mixed feed liquid;

[0081] The first conveying device is connected to the feed tank 1 and the evaporator 4 respectively, and is used to continuously add the mixed liquid in the feed tank to the evaporator;

[0082] The evaporator 4 is used to receive the mixed liquid and heat it and maintain it at a preset temperature, so that the mixed liquid evaporates and concentrates in the evaporator, and the oxalic acid is destroyed under the action of the manganese catalyst;

[0083] The second conveying device is connected to the evaporator 4 and the concentrated liquid receiving tank 6 respectively, and is used to discharge the concentrated liquid to the concentrated liquid receiving tank continuously after the liquid in the evaporator is concentrated to a desired multiple and the oxalic acid destruction reaches the requirement, so as to realize continuous feeding and discharging, wherein the discharging speed = feeding speed / concentration multiple;

[0084] In addition, the first conveying device is also used to adjust the feed rate of the mixed liquid (i.e. the flow rate of the mixed liquid added to the evaporator), and the second conveying device is also used to adjust the discharge rate of the concentrated liquid (i.e. the flow rate of the concentrated liquid discharged from the evaporator), so that the liquid level in the evaporator is constant at a preset liquid level value.

[0085] Among them, the feed tank 1 and the concentrate receiving tank 6 are both critical safety storage tanks to meet the nuclear critical safety requirements.

[0086] In some embodiments, the system further comprises a plutonium-containing liquid pipeline, a manganese solution storage tank 7, and a nitric acid storage tank 8. The plutonium-containing liquid pipeline, the manganese solution storage tank 7, and the nitric acid storage tank 8 are all connected to the feed tank 1. The plutonium-containing liquid pipeline is used to introduce the plutonium-containing liquid that needs to be evaporated, concentrated, and destroyed with oxalic acid into the feed tank 1. The manganese solution storage tank 7 is used to add manganese solution to the feed tank. The nitric acid storage tank 8 is used to add nitric acid to the feed tank.

[0087] In some embodiments, the first conveying device continuously adds the mixed liquid to the evaporator 4 by air lifting, and the air used is 0.3Mpa compressed air. The device includes a first air lifting mechanism 19, a second air lifting mechanism 20, a constant liquid level pre-tank 2 and a first gas-liquid separation tank 3, wherein:

[0088] The first air lifting mechanism 19 is connected to the feed tank 1 and the constant liquid level pre-tank 2 respectively, and is used to first add the mixed liquid in the feed tank 1 to the constant liquid level pre-tank 2; the second air lifting mechanism 20 is connected to the constant liquid level pre-tank 2 and the first gas-liquid separation tank 3 respectively, and is used to continuously add the mixed liquid in the constant liquid level pre-tank to the first gas-liquid separation tank for gas-liquid separation and removal of the gas therein; the first gas-liquid separation tank 3 is connected to the evaporator 4, and is used to continuously add the liquid in the first gas-liquid separator to the evaporator.

[0089] In some embodiments, the evaporator 4 is a natural circulation evaporator, specifically including but not limited to a single heating chamber and a single separation chamber, a double heating chamber and a single separation chamber, and other evaporators that can realize natural circulation, and the evaporator meets the nuclear criticality safety requirements. The evaporator includes a heating chamber and a separation chamber, and the heating chamber is heated by steam, and includes a shell side and a tube side, the shell side passes steam, and the tube side passes liquid.

[0090] Specifically, the tube side of the heating chamber is connected to the feed tank 1 to pass the mixed liquid, and the tube side of the heating chamber is also connected to the separation chamber. More specifically, the upper part of the heating chamber is connected to the separation chamber through an upper circulation pipe, and the lower part of the heating chamber is connected to the separation chamber through a lower circulation pipe. A purification device is provided in the separation chamber, such as a purification tower plate, a demister, etc. The secondary steam generated during the evaporation and concentration process is purified by the purification device in the separation chamber and then discharged through the secondary steam outlet at the top of the separation chamber; a steam inlet, a condensate outlet and a non-condensable gas outlet are provided on the shell side of the heating chamber, and the steam inlet is used to pass saturated steam (0.3Mpa~0.6Mpa (absolute pressure)) into the shell side to heat the tube side, so that the mixed liquid in the tube side of the heating chamber is heated and maintained at a preset temperature, the condensate outlet is used to discharge condensed water of the saturated steam, and the non-condensable gas outlet is used to discharge non-condensable gas in the saturated steam.

[0091] In some embodiments, the saturated steam flow rate and the temperature of the liquid in the evaporator 4 are interlocked and controlled, and the intake amount of saturated steam is automatically controlled according to the temperature of the liquid in the evaporator 4. At this time, the evaporator 4 also includes a temperature controller (not shown in the figure), and the steam inlet is provided with a saturated steam flow controller 13. The evaporator 4 is provided with a temperature detector (not shown in the figure), wherein: the temperature detector is electrically connected to the temperature controller, and is used to detect the temperature of the mixed liquid in the evaporator, and transmit the detected temperature value to the temperature controller; the temperature controller is electrically connected to the saturated steam flow controller 13, and a preset temperature is set in the temperature controller, and is used to receive the temperature value transmitted by the temperature detector and compare it with the preset temperature, and send a steam flow adjustment instruction to the saturated steam flow controller 13 according to the comparison result. Specifically, when the detected temperature is lower than the preset temperature, an increase flow instruction is sent to the saturated steam flow controller 13, and when the detected temperature is higher than the preset temperature, a decrease flow instruction is sent to the saturated steam flow controller 13; the saturated steam flow controller 13 is used to receive the steam flow adjustment instruction and automatically adjust the saturated steam flow entering the steam inlet according to the steam flow adjustment instruction, so that the mixed liquid in the evaporator is heated and maintained at the preset temperature.

[0092] In some embodiments, the second conveying device continuously discharges the concentrated liquid to the concentrated liquid receiving tank 6 by air lifting, and the air used is 0.3Mpa compressed air. The device includes a third air lifting mechanism 21 and a second gas-liquid separation tank 5, wherein:

[0093] The third air lifting mechanism 21 is connected to the evaporator 4 and the second gas-liquid separation tank 5 respectively, and is used to continuously discharge the concentrated liquid in the evaporator into the second gas-liquid separation tank for gas-liquid separation to remove the gas therein; the second gas-liquid separation tank 5 is connected to the concentrated liquid receiving tank 6, and is used to discharge the liquid in the second gas-liquid separator to the evaporator.

[0094] In some embodiments, the liquid level in the evaporator 4 and the flow rates of the second air lifting mechanism 20 and the third air lifting mechanism 21 are interlocked and controlled. In this case, the evaporator 4 includes a liquid level controller (not shown in the figure), the second air lifting mechanism 20 is provided with a feed flow controller 12, the third air lifting mechanism 21 is provided with a discharge flow controller 14, and the evaporator 4 is provided with a liquid level detector (not shown in the figure), wherein:

[0095] The liquid level detector is electrically connected to the liquid level controller, and is used to detect the liquid level of the feed liquid in the evaporator, and transmit the detected liquid level value to the liquid level controller; the liquid level controller is electrically connected to the feed flow controller 12 and the discharge flow controller 14 respectively, and a preset liquid level value is set in the liquid level controller, which is used to receive the liquid level value detected by the liquid level detector and compare it with the preset liquid level value, and send a feed flow adjustment instruction to the feed flow controller 12 and a discharge flow adjustment instruction to the discharge flow controller 14 according to the comparison result; the feed flow controller 12 is used to receive the feed flow adjustment instruction and automatically adjust the flow rate of the mixed liquid added to the evaporator according to the feed flow adjustment instruction, and at the same time, the discharge flow controller 14 is used to receive the discharge flow adjustment instruction and automatically adjust the flow rate of the concentrated liquid discharged from the evaporator according to the discharge flow adjustment instruction, so that the feed liquid in the evaporator is constant at the preset liquid level value.

[0096] In some embodiments, the preset liquid level value is -200 mm to +50 mm from the center line of the upper circulation tube of the natural circulation evaporator.

[0097] In some embodiments, the system further includes a heat exchanger 11, which is connected to the evaporator 4 and the third air lifting mechanism 21, respectively, and is used to cool the concentrated liquid through the heat exchanger before continuously discharging the concentrated liquid into the concentrated liquid receiving tank.

[0098] In some embodiments, the system also includes a condenser 15, a condensate cooler 16 and a condensate receiving tank 18. The condenser 15 is connected to the secondary steam outlet of the separation chamber in the evaporator 4, and is used to condense the secondary steam discharged from the evaporator. The condenser 15 is provided with a condensate outlet and a non-condensable gas outlet. The condensate outlet is connected to the condensate cooler 16. The condensate cooler 16 is further connected to the eluent inlet of the separation chamber in the evaporator 4 and the condensate receiving tank 18, respectively, for returning a portion of the condensate to the separation chamber in the evaporator as the eluent for the purification process, and discharging another portion of the condensate to the condensate receiving tank. The non-condensable gas outlet is connected to the exhaust gas system through a fan, and is used to pass the non-condensable gas into the exhaust gas system.

[0099] The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid in this embodiment is used in the above-mentioned method and has the following effects:

[0100] (1) Compared with the non-evaporation concentration process, the concentration multiple is large, which can effectively reduce the volume of plutonium-containing liquid, increase the plutonium content, greatly reduce the processing volume of the plutonium purification cycle process, reduce the amount of waste liquid, and have a higher oxalic acid destruction rate, which can meet the operation requirements of the reprocessing plant;

[0101] (2) Compared with the batch evaporation concentration process, the working flux is larger and the equipment fatigue damage is smaller;

[0102] (3) Compared with the batch evaporation concentration process, it can realize a continuous process with simple operation, high degree of automatic control and stable operation.

[0103] Example 3

[0104] like Figure 1 As shown, this embodiment discloses a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid using the above-mentioned system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid, the steps comprising:

[0105] First, 850 L of plutonium-containing liquid with an acidity of 1.9 mol / L is introduced into the feed tank 1, and then 10 L of 1 mol / L manganese nitrate solution and 148 L of 6 mol / L nitric acid solution are added into the feed tank, and mixed evenly to obtain a mixed liquid with an acidity of 2.5 mol / L and a manganese concentration of 0.01 mol / L;

[0106] The mixed liquid in the feed tank 1 is added to the constant liquid level pre-tank 2 through the first air lifting mechanism 19, and the mixed liquid in the constant liquid level pre-tank 2 is continuously added to the first gas-liquid separator 3 for gas-liquid separation through the second air lifting mechanism 20, and the separated liquid is continuously added to the evaporator 4. At the same time, 0.3Mpa (absolute pressure) saturated steam is introduced into the evaporator 4 through the steam inlet for heating, and the flow rate of the saturated steam is controlled to be 200kg / h. The interlocking liquid level is set to the center line position of the upper circulation pipe of the evaporator 4, and the feed self-adjusts the flow rate. The negative pressure in the evaporator 4 is maintained at -25kpa by the fan 17, so that the mixed liquid is evaporated and concentrated in the evaporator, and the oxalic acid is destroyed under the action of the manganese catalyst. The secondary steam generated is introduced into the condenser 15 for condensation, and 10% of the condensate is refluxed to the evaporator 4, and the rest flows to the condensate receiving tank 18;

[0107] After 10 hours, the concentration multiple of the liquid in the evaporator 4 reaches 11 times, and the oxalic acid destruction rate reaches 99.9%. At this time, the evaporator 4 continues to feed, and the saturated steam flow rate is increased to 300kg / h, the third air lifting mechanism 21 and the cooling water of the heat exchanger 11 are turned on, and the discharge flow rate of the concentrated liquid is set to 10% of the feed flow rate of the mixed liquid of the evaporator 4. The concentrated liquid in the evaporator 4 is continuously discharged to the concentrated liquid receiving tank 6, and the feed flow and liquid level interlock are set to maintain a constant liquid level.

[0108] In this embodiment, the oxalic acid destruction rate of the concentrated solution in the concentrated solution receiving tank 6 reaches 99%, the concentration multiple is 10.5 times, and the temperature is 40 degrees Celsius.

[0109] Example 4

[0110] This embodiment discloses a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid using the above-mentioned system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid. Compared with Embodiment 3, the difference is that:

[0111] 1 mol / L potassium permanganate solution was used instead of 1 mol / L manganese nitrate solution, and the concentration and destruction effects were almost the same as those in Example 3.

[0112] Example 5

[0113] This embodiment discloses a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid using the above-mentioned system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid. Compared with Embodiment 3, the difference is that:

[0114] Without adding any manganese ion solution to the feed tank 1, after 10 hours, the concentration multiple of the feed solution in the evaporator reaches 11 times, and the oxalic acid destruction rate is 15%.

[0115] Example 6

[0116] This embodiment discloses a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid using the above-mentioned system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid. Compared with Embodiment 3, the difference is that:

[0117] The flow rate of saturated steam is controlled at 150kg / h, and it takes 15 hours for evaporation concentration to reach 11 times, at which time the oxalic acid destruction rate reaches 99.9%.

[0118] Example 7

[0119] This embodiment discloses a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid using the above-mentioned system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid. Compared with Embodiment 3, the difference is that:

[0120] The negative pressure in the evaporator is maintained at -1 kPa by the fan 17. It takes 11 hours for the evaporation concentration to reach 11 times, at which time the oxalic acid destruction rate reaches 99.9%.

[0121] Example 8

[0122] This embodiment discloses a method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid using the above-mentioned system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid. Compared with Embodiment 3, the difference is that:

[0123] Without adding nitric acid solution for acid adjustment (the plutonium-containing feed liquid itself contains 1.9 mol / L nitric acid), the feed liquid in the evaporator is concentrated 11 times after 10 hours, and the oxalic acid destruction rate is 99.9%. Since the acidity of nitric acid can reach 8-10 mol / L after concentration during evaporation and concentration, the initial nitric acid concentration has little effect on the oxalic acid destruction rate.

[0124] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill 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. A method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid, characterized in that: include: adding manganese solution and nitric acid into plutonium-containing feed liquid for seasoning to obtain a mixed feed liquid; The mixed liquid is continuously added to the evaporator, heated and maintained at a preset temperature, so that the mixed liquid evaporates and concentrates in the evaporator, and the oxalic acid is destroyed under the action of a manganese catalyst; When the liquid in the evaporator is concentrated to the required multiple and the oxalic acid destruction meets the requirements, the concentrated liquid begins to be continuously discharged to the concentrated liquid receiving tank to achieve continuous feeding and discharging, wherein the discharging speed = feeding speed / concentration multiple, and the feeding speed of the mixed liquid and the discharging speed of the concentrated liquid are adjusted to keep the liquid level in the evaporator constant at the preset liquid level value.

2. The method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 1, characterized in that: The manganese content in the mixed liquid is 0.01 mol / L to 0.05 mol / L, and the nitric acid content is 2 mol / L to 3 mol / L.

3. The method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 1, characterized in that: The pressure in the evaporator is -30 kpa to -0.5 kpa.

4. The method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 1, characterized in that: The heating and maintaining the preset temperature is performed by using 0.3-0.6Mpa saturated steam for heating.

5. The method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 1, characterized in that: The mixed liquid is continuously added to the evaporator by air lifting, and the concentrated liquid is continuously discharged to the concentrated liquid receiving tank by air lifting.

6. The method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to any one of claims 1 to 5, characterized in that: Also includes: Before the concentrated liquid is continuously discharged into the concentrated liquid receiving tank, the liquid is first cooled by a heat exchanger.

7. The method for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 6, characterized in that: Also includes: The secondary steam generated in the evaporator is purified and discharged to the condenser for condensation, and a part of the condensate is returned to the evaporator as the eluent for the purification process, and the other part of the condensate is discharged to the condensate receiving tank, and the non-condensable gas is passed into the exhaust system.

8. A system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid, characterized in that: The invention comprises a feed tank (1), a first conveying device, an evaporator (4), a second conveying device and a concentrated liquid receiving tank (6), wherein: The feed tank is used to add manganese solution and nitric acid into the plutonium-containing feed liquid for conditioning to obtain a mixed feed liquid; The first conveying device is connected to the feed tank and the evaporator respectively, and is used to continuously add the mixed liquid in the feed tank to the evaporator; The evaporator is used to receive the mixed liquid and heat it and maintain it at a preset temperature, so that the mixed liquid evaporates and concentrates in the evaporator, and the oxalic acid is destroyed under the action of the manganese catalyst; The second conveying device is connected to the evaporator and the concentrated liquid receiving tank respectively, and is used to discharge the concentrated liquid to the concentrated liquid receiving tank continuously after the liquid in the evaporator is concentrated to a desired multiple and the oxalic acid destruction reaches the requirement, so as to realize continuous feeding and discharging, wherein the discharging speed = feeding speed / concentration multiple; In addition, the first conveying device is also used to adjust the feeding speed of the mixed liquid, and the second conveying device is also used to adjust the discharging speed of the concentrated liquid, so that the liquid level in the evaporator is constant at a preset liquid level value.

9. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 8, characterized in that: The first conveying device comprises a first air lifting mechanism (19), a second air lifting mechanism (20), a constant liquid level pre-tank (2) and a first gas-liquid separation tank (3), wherein: The first air lifting mechanism is connected to the feed tank and the constant liquid level pre-tank respectively, and is used to first add the mixed liquid in the feed tank to the constant liquid level pre-tank; The second air lifting mechanism is connected to the constant liquid level pre-tank and the first gas-liquid separation tank respectively, and is used to continuously add the mixed liquid in the constant liquid level pre-tank to the first gas-liquid separation tank for gas-liquid separation and remove the gas therein; The first gas-liquid separation tank is connected to the evaporator and is used to continuously add the feed liquid in the first gas-liquid separator to the evaporator.

10. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 9, characterized in that: The evaporator is a natural circulation evaporator, which includes a heating chamber and a separation chamber. The heating chamber is heated by steam and is divided into a shell side and a tube side. The tube side of the heating chamber is connected to the feed tank to pass the mixed liquid, and the tube side of the heating chamber is also connected to the separation chamber. The secondary steam generated during the evaporation and concentration process is purified in the separation chamber and then discharged through the secondary steam outlet at the top of the separation chamber. The shell side of the heating chamber is provided with a steam inlet, a condensate outlet and a non-condensable gas outlet. The steam inlet is used to introduce saturated steam to heat the tube side, so that the mixed liquid in the tube side of the heating chamber is heated and maintained at a preset temperature. The condensate outlet is used to discharge condensed water of the saturated steam, and the non-condensable gas outlet is used to discharge non-condensable gas in the saturated steam.

11. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 10, characterized in that: The evaporator further comprises a temperature controller, the steam inlet is provided with a saturated steam flow controller (13), and the evaporator is provided with a temperature detector. The temperature detector is electrically connected to the temperature controller and is used to detect the temperature of the mixed liquid in the evaporator and transmit the detected temperature value to the temperature controller; The temperature controller is electrically connected to the saturated steam flow controller, and a preset temperature is set in the temperature controller, which is used to receive the temperature value transmitted by the temperature detector and compare it with the preset temperature, and send a steam flow adjustment instruction to the saturated steam flow controller according to the comparison result; The saturated steam flow controller is used to receive a steam flow regulation instruction and automatically regulate the saturated steam flow entering the steam inlet according to the steam flow regulation instruction, so that the mixed liquid in the evaporator is heated and maintained at a preset temperature.

12. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 11, characterized in that: The second conveying device comprises a third air lifting mechanism (21) and a second gas-liquid separation tank (5), wherein: The third air lifting mechanism is connected to the evaporator and the second gas-liquid separation tank respectively, and is used to continuously discharge the concentrated liquid in the evaporator into the second gas-liquid separation tank for gas-liquid separation to remove the gas therein; The second gas-liquid separation tank is connected to the concentrated liquid receiving tank and is used to discharge the feed liquid in the second gas-liquid separator to the evaporator.

13. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 12, characterized in that: The evaporator comprises a liquid level controller, the second air lifting mechanism is provided with a feed flow controller (12), the third air lifting mechanism is provided with a discharge flow controller (14), and the evaporator is provided with a liquid level detector. The liquid level detector is electrically connected to the liquid level controller, and is used to detect the liquid level of the feed liquid in the evaporator, and transmit the detected liquid level value to the liquid level controller; The liquid level controller is electrically connected to the feed flow controller and the discharge flow controller respectively. A preset liquid level value is provided in the liquid level controller, which is used to receive the liquid level value detected by the liquid level detector and compare it with the preset liquid level value, and send a feed flow adjustment instruction to the feed flow controller and send a discharge flow adjustment instruction to the discharge flow controller according to the comparison result; The feed flow controller is used to receive a feed flow adjustment instruction and automatically adjust the flow rate of the mixed liquid added to the evaporator according to the feed flow adjustment instruction. At the same time, the feed flow controller is used to receive a discharge flow adjustment instruction and automatically adjust the flow rate of the concentrated liquid discharged from the evaporator according to the discharge flow adjustment instruction, so that the liquid in the evaporator is constant at a preset liquid level value.

14. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 13, characterized in that: The system further comprises a heat exchanger (5), The heat exchanger is connected to the evaporator and the third air lifting mechanism respectively, and is used to cool the concentrated liquid through the heat exchanger before the concentrated liquid is continuously discharged into the concentrated liquid receiving tank.

15. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to claim 14, characterized in that: The system further comprises a condenser (15), a condensate cooler (16) and a condensate receiving tank (18). The condenser is connected to the secondary steam outlet of the evaporator and is used to condense the secondary steam discharged from the evaporator. The condenser is provided with a condensate outlet and a non-condensable gas outlet. The condensate outlet is connected to the condensate cooler, and the condensate cooler is connected to the eluent inlet of the evaporator and the condensate receiving tank respectively, so as to return a part of the condensate to the evaporator as the eluent for the purification process and discharge the other part of the condensate to the condensate receiving tank. The non-condensable gas outlet is connected to the exhaust gas system, so as to pass the non-condensable gas into the exhaust gas system.

16. The system for continuous evaporation concentration and oxalic acid destruction of plutonium-containing liquid according to any one of claims 8 to 15, characterized in that: The system also includes a plutonium-containing liquid pipeline, a manganese solution storage tank (7), and a nitric acid storage tank (8). The plutonium-containing liquid pipeline, the manganese solution storage tank, and the nitric acid storage tank are all connected to the feed tank. The plutonium-containing liquid pipeline is used to introduce the plutonium-containing liquid that needs to be evaporated, concentrated and destroyed with oxalic acid into the feed tank, the manganese solution storage tank is used to add manganese solution to the feed tank, and the nitric acid storage tank is used to add nitric acid to the feed tank.

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