A vacuum membrane distillation apparatus for separating and concentrating a solution containing radioactive elements and a multi-effect vacuum membrane distillation process comprising the same

Abstract

The application discloses a decompression membrane distillation device for separating and concentrating a solution containing radioactive elements and a multi-effect decompression membrane distillation process comprising the same. The application provides a new solution for efficient separation and concentration of tritium-containing nuclide wastewater, can realize efficient separation of a low-vapor-pressure differential substance, ensure that produced water can be discharged up to the standard, and realize efficient recovery of strategic nuclides. In addition, the application designs and develops a device which can realize multi-stage membrane distillation in a single component, and sets an auxiliary heat partition plate to stabilize the temperature of the hot side, ensure a low-vapor-pressure differential separation driving force, and improve the separation efficiency of membrane distillation.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, specifically relating to a vacuum membrane distillation device for separating and concentrating solutions containing radioactive elements, and a multi-effect vacuum membrane distillation process including the same. Background Technology

[0002] The treatment of radioactive nuclear waste generated during nuclear reactions has always been a weak point in the development of the nuclear industry. Modern nuclear fuel element cladding mostly uses welded zirconium alloys instead of stainless steel tubes. Tritium gas emanating from the fuel elements is absorbed by the zirconium, and at reactor operating temperatures, only about 0.1% of the tritium permeates through the zirconium alloy tube walls into the cooling water system. This results in a large amount of tritium-containing radioactive wastewater, whose physicochemical properties are essentially the same as ordinary water, making it one of the most challenging problems in radioactive nuclear waste treatment. Commonly used tritium-containing solution concentration and separation technologies include electrolysis, water distillation, gas-phase catalytic exchange, liquid-phase catalytic exchange, and combined electrolysis-catalytic exchange. Electrolysis involves repeatedly electrolyzing the tritium-containing solution to increase the concentration of deuterium and tritium; however, it is no longer used due to its high energy consumption. Water distillation, due to the small temperature differences among components in the distillation column, requires a large number of trays, resulting in bulky equipment and high energy consumption. Achieving strict temperature control and reducing investment costs have become bottlenecks in the development of cryogenic distillation methods. Moreover, the high operating pressure of existing distillation processes reduces the safety of the distillation system and increases the risk of radioactive material leakage. Combined electrolytic catalytic exchange technology combines liquid-phase catalytic exchange with electrolysis. Compared with gas-phase catalytic exchange, it operates at lower temperatures and is easier to control, making it a current research hotspot. However, this method is highly dependent on catalysts. Large-scale application requires the design and development of structured packing materials and catalysts, as well as large-diameter catalytic exchange columns, resulting in high investment and operating costs and immature technology.

[0003] Membrane separation technology utilizes separation membrane materials and leverages concentration, pressure, or voltage differences for effective separation. Due to its advantages such as energy saving, small footprint, ease of operation, high efficiency, low cost, no chemical additives, minimal secondary pollution, and the ability to recycle treated substances, it has experienced rapid development in recent years. The most representative example is the widespread research and industrial application of membrane distillation (MD) technology in seawater desalination, brine desalination and concentration, and pure water production, which provides a new approach for treating tritium-containing solutions.

[0004] Membrane distillation is a membrane process that uses the vapor pressure difference generated by the temperature difference across a hydrophobic microporous membrane as the driving force to separate the solute and solvent. As a novel membrane technology combining traditional evaporation and membrane technology, membrane distillation offers significant advantages over processes such as electrolysis, adsorption, and traditional evaporation in the concentration and separation of tritium-containing solutions: ① Membrane distillation relies on vapor pressure difference as the driving force to separate the solute and solvent, resulting in significantly lower energy consumption and lower requirements for equipment safety compared to other processes; ② Because membranes allow only gas to permeate while retaining liquid even in the absence of a hydrostatic pressure difference, they offer high concentration efficiency and can achieve high-grade concentration; ③ Compared to traditional evaporation, membrane distillation equipment is simpler, requires less space, can utilize low-grade heat sources (solar energy, geothermal energy, waste heat, residual heat, etc.), and is more economical. Therefore, membrane distillation technology provides a new approach for the concentration and separation of tritium-containing solutions.

[0005] Existing technologies for concentrating tritium-containing solutions in nuclear wastewater involve traditional distillation and electrolysis equipment that requires a large footprint and incurs high costs. A known technology (Japanese Patent 2015073968) uses a multi-stage centrifugal separation method to separate tritium-containing solutions, reducing the footprint of the equipment and achieving a separation efficiency of 90%. However, the use of operating conditions at 3 MPa and 250°C increases energy consumption and operating costs.

[0006] Because tritium-containing solutions have low tritium content and are radioactive, and their physicochemical properties are similar to ordinary water, achieving effective separation, improving separation efficiency, and ensuring operational safety are current technical challenges for membrane distillation technology. Furthermore, the latent heat of vaporization in existing membrane distillation processes reduces thermal energy utilization, thus incurring energy costs.

[0007] Known technology (US Patent 3,562,116) uses hydrophobic microporous membranes with corrugated surfaces to separate volatile substances such as heavy water, reducing the footprint of the device, but the separation efficiency and thermal energy utilization are low. Mechanical seals pose a risk of leakage when used in radioactive environments.

[0008] In the known technology (Chinese patent application 201510441216.6), a multi-stage membrane distillation method was invented, which utilizes the secondary steam generated by the high-temperature feed liquid to heat the second-stage feed liquid in order to make full use of the latent heat of vaporization and improve thermal efficiency. However, the component form of hollow fiber inside the metal tube increases the replacement and maintenance cost.

[0009] In the known technology (Chinese patent application 201410458960.2), the hot liquid in the membrane module is connected in series by setting different positions of the openings in the partition to increase the mass transfer flux. However, the hot liquid chamber and the cold liquid chamber are in contact with each other for heat transfer, which reduces the thermal efficiency.

[0010] In known technologies (International Patent 2019233610), a multi-stage membrane distillation equipment containing evaporation and condensation is prepared using similar modules to achieve multi-stage concentration of the feed liquid to be separated, making full use of the heat of evaporation of the feed liquid and achieving high thermal efficiency. However, the permeate is collected uniformly, which is not suitable for separating materials with low saturated vapor pressure difference (e.g., ethanol aqueous solution, heavy water, etc.), and its separation effect is low.

[0011] Therefore, it is desirable to use membrane distillation technology to achieve multi-stage, multi-effect separation and concentration of solutions containing radioactive elements, so as to obtain product water that meets emission standards and concentrated solutions containing radioactive elements.

[0012] To address the above problems, this invention is proposed. Summary of the Invention

[0013] This invention employs a pioneering multi-stage, multi-effect vacuum membrane distillation process to treat tritium-containing nuclide solutions produced by nuclear reactions, thereby achieving efficient concentration and separation of the strategic nuclide tritium and ensuring that nuclear wastewater is discharged in compliance with standards.

[0014] The first aspect of the present invention provides a vacuum membrane distillation apparatus for separating and concentrating solutions containing radioactive elements, characterized in that the vacuum membrane distillation apparatus includes end plates 1 on both sides and a first partition 2 and a second partition 3 between the end plates 1.

[0015] The first partition 2 has separation membranes 21 on both sides, and a permeate flow chamber 22 is formed between the two separation membranes 21; the second partition 3 has separation membranes 31 on both sides, and an auxiliary heating feed liquid flow chamber 32 is formed between the two separation membranes 31; a feed liquid to be concentrated flow chamber 33 is formed between the separation membranes 31 and the separation membranes 21; the feed liquid to be concentrated in the feed liquid to be concentrated flow chamber 33 is generated by passing through the separation membranes 21 to produce permeate in the permeate flow chamber 22; the auxiliary heating feed liquid in the auxiliary heating feed liquid flow chamber 32 preheats the feed liquid to be concentrated in the feed liquid to be concentrated flow chamber 33.

[0016] The first partition 2 has a permeate outlet 23, which is connected to the permeate flow chamber 22 to draw out the generated permeate from the permeate flow chamber 22.

[0017] The second partition 3 has an auxiliary heating liquid inlet 34 and an auxiliary heating liquid outlet 35. Both the auxiliary heating liquid inlet 34 and the auxiliary heating liquid outlet 35 are connected to the auxiliary heating liquid flow chamber 32 so that the auxiliary heating liquid is introduced from the auxiliary heating liquid inlet 34 into the auxiliary heating liquid flow chamber 32, and the auxiliary heating liquid in the auxiliary heating liquid flow chamber 32 is led out through the auxiliary heating liquid outlet 35.

[0018] The first partition 2 and the second partition 3 have a flow port 24 for the concentrated liquid to be flowed into the flow chamber 33 through the flow port 24.

[0019] One end plate 1 has an auxiliary heating liquid inlet 11, a permeate outlet 12, and a concentrate outlet 13; the other end plate 1 has a concentrate inlet 14 and an auxiliary heating liquid outlet 15.

[0020] The end plates 1 on both sides, as well as the first partition 2 and the second partition 3, are sealed to each other to ensure the separation and concentration of the radioactive element-containing solution from the outside environment. Partitions with different functions are assembled into components using different stacking methods such as adhesive bonding, mechanical sealing, or welding to ensure no leakage of internal materials.

[0021] Preferably, the auxiliary heating liquid inlet 34 and the auxiliary heating liquid outlet 35 are staggered on the second partition 3, with the auxiliary heating liquid inlet 34 at the bottom and the auxiliary heating liquid outlet 35 at the top. That is, the auxiliary heating liquid in the multiple second partitions 3 all enter from the bottom and exit from the top, so that the auxiliary heating liquid can fill the auxiliary heating liquid flow cavity 32 longitudinally. More specifically, the auxiliary heating liquid inflow and the auxiliary heating liquid outflow are two parallel flow channels.

[0022] Preferably, the first partition 2 also has an auxiliary heating liquid passage 25, which is opposite to the auxiliary heating liquid inlet 34 or the auxiliary heating liquid outlet 35, so that the auxiliary heating liquid passes through the first partition 2 and enters the next stage auxiliary heating liquid inlet 34.

[0023] The second partition 3 also has a permeate passage 36, so that the permeate passes through the second partition 3 and merges with the permeate of the next stage.

[0024] Preferably, the auxiliary heating liquid inlet 11 is connected to the auxiliary heating liquid inlet 34, and the auxiliary heating liquid outlet 35 is connected to the auxiliary heating liquid outlet 15;

[0025] The permeate outlet 23 is connected to the permeate outlet 12;

[0026] Both the inlet 14 and the outlet 13 of the liquid to be concentrated are connected to the flow port 24 of the liquid to be concentrated.

[0027] Preferably, there are multiple first partitions 2 and multiple second partitions 3, and the number of both is equal; that is, the vacuum membrane distillation device itself is a multi-stage vacuum membrane distillation process. Multiple first partitions 2 and multiple second partitions 3 are arranged alternately in sequence. That is, one first partition 2 is followed by one second partition 3, then another first partition 2, a second partition 3, and so on.

[0028] Preferably, the separation membrane 21 has a front and a back side, with the side facing the liquid to be concentrated being the front side. The separation membrane 21 only allows the liquid to be concentrated to pass through the separation membrane 21 to generate permeate that enters the permeate flow chamber 22, and does not allow the permeate in the permeate flow chamber 22 to enter the liquid to be concentrated flow chamber 33.

[0029] Preferably, the flow ports 24 of the concentrated liquid on the first partition 2 and the second partition 3 are staggered vertically, so that after the concentrated liquid flows out from the flow port 24 on the first partition 2, it passes through the entire longitudinal direction of the concentrated liquid flow cavity 33 and then flows into the next stage through the flow port 24 on the second partition 3. That is, the flow ports 24 of the concentrated liquid on adjacent first partitions 2 and second partitions 3 are staggered vertically. For example, if the flow port 24 of the concentrated liquid on the first partition 2 is located at the upper position in the longitudinal direction, then the flow port 24 of the concentrated liquid on the second partition 3 is located at the lower position in the longitudinal direction, and the flow port 24 of the first partition 2 of the next stage is located at the upper position in the longitudinal direction. This makes the concentrated liquid flow in the concentrated liquid flow cavity 33 in a "U" shape.

[0030] Preferably, the first partition 2 and / or the second partition 3 also have a mesh 26. The internal supporting mesh provides support for the separator membrane and the separation membrane, and also serves to fully distribute the permeate liquid and the auxiliary heating liquid inside the component.

[0031] Preferably, the radioactive element-containing solution refers to tritium-containing radioactive wastewater.

[0032] Preferably, the end plate 1, the first partition 2, and the second partition 3 are radiation-resistant engineering plastics, selected from, but not limited to, polypropylene; the partition material in this invention is preferably a radiation-resistant engineering plastic such as polypropylene, which reduces manufacturing costs while ensuring radiation resistance. The separation membrane 21 is a hydrophobic microporous membrane, selected from, but not limited to, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polypropylene (PP). The separator 31 is a membrane that is neither water-permeable nor air-permeable, and has good heat transfer performance, selected from, but not limited to, polypropylene (PP), polyethylene (PE), or metal sheets. In this invention, inexpensive and easy-to-assemble engineering plastics are preferred.

[0033] A second aspect of the present invention provides a multi-effect vacuum membrane distillation process comprising the vacuum membrane distillation apparatus described in the first aspect of the present invention, characterized in that the multi-effect vacuum membrane distillation process comprises a plurality of the aforementioned vacuum membrane distillation components;

[0034] The vacuum membrane distillation assembly includes: the vacuum membrane distillation device M1, the first heat exchange module M2, the intermediate storage tank M3, the pump M4, and the second heat exchange module M5;

[0035] The first-effect vacuum membrane distillation device M1 separates and concentrates the liquid to be concentrated, generating first-effect permeate vapor and first-effect concentrated liquid.

[0036] The first-effect permeate vapor transfers heat to the concentrate to be concentrated in the first-effect vacuum membrane distillation device M1 through the first-effect first heat exchange module M2, so as to preheat the concentrate and cool itself into the first-effect permeate liquid by the first-effect permeate vapor.

[0037] The liquid from the first effect enters the intermediate storage tank M3 of the first effect for storage. When the amount reaches the amount required for the second effect, it enters the second heat exchange module M5 of the first effect via the pump M4 of the first effect.

[0038] After the first effect concentration, the feed liquid transfers heat to the first effect permeate liquid through the second heat exchange module M5 of the first effect, thereby preheating the first effect permeate liquid. The preheated first effect permeate liquid enters the vacuum membrane distillation device M1 of the second effect for separation and concentration.

[0039] The above process is repeated for each effect until the permeate liquid of the Nth effect reaches the discharge standard. The permeate liquid of the Nth effect is collected and sent to the product water storage tank. The concentrated liquid after each effect is collected into the concentrated liquid storage tank, thus completing the multi-effect separation and concentration of the solution containing radioactive elements.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. This invention is the first to apply a vacuum membrane distillation device to the separation and concentration of solutions containing radioactive elements. Because the vacuum membrane distillation device of this invention has multiple first partitions 2 and second partitions 3, a single set of vacuum membrane distillation devices constitutes a multi-stage separation process. The separation membrane of this invention can separate the feed solution containing radioactive elements into permeate and concentrate. Through staged separation, the concentrate can be recovered, and the treated water can be safely discharged. This invention provides a new solution for the efficient separation and concentration of wastewater containing tritium nuclides, enabling efficient separation of substances with low vapor pressure differentials, ensuring that the treated water meets discharge standards while achieving efficient recovery of strategic nuclides.

[0042] 2. The end plates 1 on both sides of the present invention, as well as the first partition plate 2 and the second partition plate 3, are sealed to each other to ensure the separation and concentration of the radioactive element-containing solution from the outside environment. This achieves the separation and concentration of the radioactive element-containing solution. The sealing method can be any conventional sealing method in the art. The vacuum membrane distillation device of the present invention is safe and feasible.

[0043] 3. This invention designs and develops a device that can realize multi-stage membrane distillation within a single component, and sets up a second partition for receiving auxiliary heating feed liquid. The separating membrane on the second partition ensures the independent flow of the auxiliary feed liquid. The auxiliary heating feed liquid stabilizes the temperature on the hot side, ensuring low vapor pressure difference separation driving force and improving the separation efficiency of membrane distillation.

[0044] 4. The present invention also provides a multi-stage, multi-effect vacuum membrane distillation process including the above-mentioned vacuum membrane distillation device. The process includes multiple vacuum membrane distillation components, and on the basis of the independent vacuum membrane distillation device having multiple stages, multiple vacuum membrane distillation devices are further used to achieve multi-effect. The process realizes efficient energy recovery and utilization, and saves operation and maintenance costs.

[0045] 5. This invention features a highly integrated plate-and-frame structure, which greatly reduces the equipment footprint and improves resource utilization efficiency compared to traditional separation methods. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the first partition structure;

[0047] Figure 2 This is a schematic diagram of the second partition structure;

[0048] Figure 3 A schematic diagram showing the arrangement of multiple first and second partitions;

[0049] Figure 4 This is a schematic diagram of material flow in a multi-stage vacuum membrane distillation assembly.

[0050] Figure 5 This is a schematic diagram of material flow in the heat exchange module;

[0051] Figure 6 This is a schematic diagram of the multi-effect vacuum membrane distillation process.

[0052] The names of the reference numerals in the attached figures are as follows: 1-End plate, 2-First partition plate, 3-Second partition plate, 21-Separation membrane, 22-Permeate flow chamber, 23-Permeate outlet, 24-Concentrated feed liquid flow port, 25-Auxiliary heating feed liquid passage port, 26-Separator, 31-Separation membrane, 32-Auxiliary heating feed liquid flow chamber, 33-Concentrated feed liquid flow chamber, 34-Auxiliary heating feed liquid inlet, 35-Auxiliary heating feed liquid outlet, 36-Permeate outlet.

[0053] M1 - vacuum membrane distillation unit, M2 - first heat exchange module, M3 - intermediate storage tank, M4 - pump, M5 - second heat exchange module. Detailed Implementation

[0054] The present invention will now be described in further detail with reference to the embodiments.

[0055] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the field or according to the product instructions. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0056] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” to another element, it can be directly connected to the other element, or there may be an intermediate element. Furthermore, the term “connected” as used herein can include wireless connections.

[0057] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. The terms "inner," "upper," "lower," etc., indicate the orientation or state relationship based on the orientation or state relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0058] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "equipped with" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0060] like Figure 1-2 As shown, the partition consists of a permeate channel, a concentrate channel, and an auxiliary heating channel. The permeate partition has side holes in the permeate channel for collecting and transporting the permeate. The auxiliary heating partition has side holes in the auxiliary heating channel for the inflow and outflow of auxiliary heating liquid. The gaps in the sealed areas form the concentrate channel, with different flow directions achieved through different stacking methods, thus forming a multi-stage arrangement of the concentrate within the module. Multiple separator membranes and multiple separation membranes are bonded to the partition on both sides using adhesive or welding. The spaces between the separator membranes form an auxiliary heating area, the spaces between the separation membranes form a permeate area, and the spaces between the separator membranes form a concentrate area. Different functional partitions are stacked using adhesive, mechanical sealing, or welding to create the module, ensuring no leakage of internal materials. An internal support mesh provides support for the separator membranes and separation membranes and also helps to fully distribute the permeate and auxiliary heating liquid within the module. The multi-stage module arrangement is as follows... Figure 3 As shown, the flow direction of different types of feed liquids is controlled by the location and absence of openings in the partitions within the module. The region for the feed liquid to be concentrated can be determined by whether or not openings are made in adjacent partitions, allowing the feed liquid to enter the module in series to form a multi-stage high-efficiency concentration process or in parallel to achieve a single-stage concentration process with a larger membrane area. This module design is as follows... Figure 4-5 As shown, heat exchange between two liquids can be achieved by replacing the separation membrane with a separator membrane, thereby converting it into a heat exchange module. Similarly, the liquid to be heat exchanged can be set in single or multiple stages to meet process requirements.

[0061] The multi-stage, multi-effect vacuum membrane distillation process of this invention is as follows: Figure 6The tritium-containing nuclide solution is stored in a feed tank and then transported via pipeline to the feed inlet of the membrane distillation unit in the first-effect (a single-effect membrane distillation process consisting of multiple vacuum membrane distillation units, two heat exchange modules, an intermediate storage tank, and a pump). The permeate vapor generated in each effect heats the tritium-containing nuclide solution to 70-85°C to meet the temperature requirements for membrane distillation separation. Simultaneously, the permeate vapor generated in each effect is condensed to form condensate, which is stored in the intermediate storage tank. In the multi-stage membrane distillation unit, the feed solution flows through the gaps between the partitions, contacting both the separating membrane and the separating membrane. On the other side of the separating membrane is an auxiliary heating partition, through which the auxiliary heating feed solution provides heat to the tritium-containing nuclide solution to compensate for the energy consumed by the latent heat of vaporization during distillation, thereby achieving greater mass transfer flux and higher energy utilization efficiency. The tritium-containing nuclide solution directly contacts the separation membrane. Easily evaporable light water vapor in the feed solution permeates through the membrane and enters the permeate separator due to the vapor pressure difference across the membrane and the negative pressure generated on the back of the membrane, thus concentrating the tritium content in the solution. The permeate, under negative pressure, enters the heat exchange module to preheat the tritium-containing nuclide solution while simultaneously condensing and entering the intermediate storage tank. When the permeate reaches a certain volume (enough to fill the feed solution area for the next effect), it is pumped to the heat exchange module. In the heat exchange module, the permeate exchanges heat with the concentrated tritium-containing nuclide solution to fully utilize the heat contained in the concentrated solution and to heat the permeate to the temperature required for membrane distillation. It then enters the next effect vacuum membrane distillation process.

[0062] In this invention, each effect of vacuum membrane distillation uses the condensate from the previous effect as raw material. The permeate produced in this process enters the next effect, until the permeate meets the discharge standards and then enters the product water storage tank. The concentrated tritium-containing nuclide solution enters the concentrated feed liquid storage tank.

[0063] In this invention, the auxiliary heating system is self-contained. The auxiliary heating system can use solar energy, geothermal energy, waste heat, etc. to heat the auxiliary heating liquid, thereby maximizing the use of energy and improving energy utilization efficiency, and thus reducing operating costs.

[0064] Because tritium water is radioactive, for experimental safety, this embodiment uses deuterium water, which has similar properties, as the test subject.

[0065] Example 1

[0066] This membrane distillation unit is fed with a mixed solution containing 5 wt.% deuterium and water. The permeate pressure of the module is maintained at 0.85-0.9 bar, the concentration chamber temperature is maintained at 71-75℃, the cold side temperature at 15-20℃, and the auxiliary heating side temperature at 80-85℃. Using a single-stage, four-effect membrane distillation unit, an average permeate flux of 10 L / (m³) can be achieved in 24-26 hours. 2*h), the cumulative deuterium removal rate is 97.6%. Here, the removal rate refers to the proportion of deuterium in the permeate to the amount of deuterium in the feedstock.

[0067] Example 2

[0068] This membrane distillation unit is fed with a mixed solution containing 0.1 wt.% deuterium and water. The permeate pressure of the module is maintained at 0.85-0.9 bar, the concentration chamber temperature is maintained at 71-75℃, the cold side temperature at 15-20℃, and the auxiliary heating side temperature at 80-85℃. Using a single-stage, five-effect membrane distillation unit, an average permeate flux of 11 L / (m³) can be achieved in 24-26 hours. 2 *h), the cumulative deuterium removal rate is 82.9%. Here, the removal rate refers to the proportion of deuterium in the permeate to the amount of deuterium in the feedstock.

Claims

1. A vacuum membrane distillation apparatus for separating and concentrating solutions containing radioactive elements, characterized in that, The vacuum membrane distillation device includes end plates (1) on both sides and a first partition (2) and a second partition (3) between the end plates (1). The first partition (2) has separation membranes (21) on both sides, and the space between the two separation membranes (21) is a permeate flow chamber (22); the second partition (3) has separation membranes (31) on both sides, and the space between the two separation membranes (31) is an auxiliary heating liquid flow chamber (32); the space between the separation membrane (31) and the separation membrane (21) is a liquid to be concentrated flow chamber (33); the liquid to be concentrated in the liquid to be concentrated flow chamber (33) is generated by the separation membrane (21) to produce permeate in the permeate flow chamber (22); the auxiliary heating liquid in the auxiliary heating liquid flow chamber (32) preheats the liquid to be concentrated in the liquid to be concentrated flow chamber (33); The first partition (2) has a permeate outlet (23), which is connected to the permeate flow chamber (22) to draw out the generated permeate from the permeate flow chamber (22); The second partition (3) has an auxiliary heating liquid inlet (34) and an auxiliary heating liquid outlet (35). The auxiliary heating liquid inlet (34) and the auxiliary heating liquid outlet (35) are both connected to the auxiliary heating liquid flow chamber (32) so that the auxiliary heating liquid is introduced from the auxiliary heating liquid inlet (34) into the auxiliary heating liquid flow chamber (32), and the auxiliary heating liquid in the auxiliary heating liquid flow chamber (32) is led out through the auxiliary heating liquid outlet (35). The first partition (2) and the second partition (3) have a flow port (24) for the concentrated liquid to be flowed into the flow chamber (33) through the flow port (24). One end plate (1) has an auxiliary heating liquid inlet (11), a permeate liquid outlet (12), and a concentrate outlet (13); the other end plate (1) has a concentrate inlet (14) and an auxiliary heating liquid outlet (15). The end plates (1) on both sides, as well as the first partition (2) and the second partition (3), are sealed to each other to ensure the separation and concentration of the radioactive element solution from the outside world. There are multiple first partitions (2) and multiple second partitions (3), and the number of both is equal; the multiple first partitions (2) and multiple second partitions (3) are arranged alternately in sequence; The flow ports (24) of the concentrated liquid on the first partition (2) and the second partition (3) are staggered vertically so that after the concentrated liquid flows out from the flow port (24) of the concentrated liquid on the first partition (2), it flows through the longitudinal section of the flow cavity (33) of the concentrated liquid and then flows into the next stage through the flow port (24) of the concentrated liquid on the second partition (3).

2. The vacuum membrane distillation apparatus according to claim 1, characterized in that, The auxiliary heating liquid inlet (34) and the auxiliary heating liquid outlet (35) are staggered on the second partition (3) so that the auxiliary heating liquid passes through the auxiliary heating liquid flow chamber (32) in the longitudinal direction.

3. The vacuum membrane distillation apparatus according to claim 1, characterized in that, The first partition (2) also has an auxiliary heating liquid passage (25), which is opposite to the auxiliary heating liquid inlet (34) or the auxiliary heating liquid outlet (35), so that the auxiliary heating liquid passes through the first partition (2) and enters the next stage auxiliary heating liquid inlet (34). The second partition (3) also has a permeate passage (36) so that the permeate passes through the second partition (3) and merges with the permeate of the next stage.

4. The vacuum membrane distillation apparatus according to claim 1, characterized in that, The auxiliary heating liquid inlet (11) is connected to the auxiliary heating liquid inlet (34), and the auxiliary heating liquid outlet (35) is connected to the auxiliary heating liquid outlet (15). The permeate outlet (23) is connected to the permeate outlet (12); The inlet (14) and outlet (13) of the liquid to be concentrated are both connected to the flow port (24) of the liquid to be concentrated.

5. The vacuum membrane distillation apparatus according to claim 1, characterized in that, The separation membrane (21) has a front and a back side, and the side facing the liquid to be concentrated is the front side. The separation membrane (21) only allows the liquid to be concentrated to pass through the separation membrane (21) to generate permeate and enter the permeate flow chamber (22), and does not allow the permeate in the permeate flow chamber (22) to enter the liquid to be concentrated flow chamber (33).

6. The vacuum membrane distillation apparatus according to claim 1, characterized in that, The first partition (2) and / or the second partition (3) also have a mesh (26); A solution containing radioactive elements refers to wastewater containing tritium.

7. The vacuum membrane distillation apparatus according to claim 1, characterized in that, The end plate (1), the first partition (2), and the second partition (3) are radiation-resistant engineering plastics selected from polypropylene; the separation membrane (21) is a hydrophobic microporous membrane selected from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polypropylene (PP); the separator membrane (31) is a membrane that is neither water-permeable nor air-permeable and has good heat transfer performance, selected from polypropylene (PP), polyethylene (PE), or metal sheet.

8. A multi-effect vacuum membrane distillation process comprising the vacuum membrane distillation apparatus according to any one of claims 1-7, characterized in that, The multi-effect vacuum membrane distillation process includes multiple vacuum membrane distillation components described above. The vacuum membrane distillation assembly includes: the vacuum membrane distillation device (M1), the first heat exchange module (M2), the intermediate storage tank (M3), the pump (M4), and the second heat exchange module (M5); The first-effect vacuum membrane distillation device (M1) separates and concentrates the liquid to be concentrated, producing first-effect permeate vapor and first-effect concentrated liquid; The first-effect permeate vapor transfers heat to the concentrate to be concentrated in the first-effect vacuum membrane distillation device (M1) through the first-effect first heat exchange module (M2) to preheat the concentrate, and is cooled by the first-effect permeate vapor to become the first-effect permeate liquid. The liquid from the first effect enters the intermediate storage tank (M3) of the first effect for storage. When the amount reaches the amount required for the second effect, it enters the second heat exchange module (M5) of the first effect via the pump (M4) of the first effect. After the first effect concentration, the feed liquid transfers heat to the first effect permeate liquid through the second heat exchange module (M5) of the first effect, thereby preheating the first effect permeate liquid. The preheated first effect permeate liquid enters the vacuum membrane distillation device (M1) of the second effect for separation and concentration. The above process is repeated for each effect until the permeate liquid of the Nth effect reaches the discharge standard. The permeate liquid of the Nth effect is collected and sent to the product water storage tank. The concentrated liquid after each effect is collected into the concentrated liquid storage tank, thus completing the multi-effect separation and concentration of the solution containing radioactive elements.

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