A modular multi-stage membrane distillation simultaneous concentration device and method

Abstract

The application belongs to the technical field of water treatment, and particularly relates to a modular multi-stage membrane distillation synchronous concentration device and method. The device comprises one or both of a concentration module and a desalination module; the concentration module and the desalination module comprise the following devices stacked in sequence: a concentration device, a porous membrane, and a vacuum device; each group of the above-mentioned devices stacked in sequence forms a membrane separation unit, and the number of the membrane separation units is one or more. The system adopts an innovative multi-stage modular expansion architecture, the core of which is a stage isolation structure based on gradient pressure balance. The whole process integration of 'front-end desalination and impurity removal-middle-end gradient concentration-end pure water output' is realized in the same plate frame assembly. The structure forms concentration chambers and desalination chambers by alternately stacking hydrophobic microporous membranes and plate frame assemblies, supports flexible expansion from a single stage to multiple stages, and perfectly adapts to different scales and processing requirements of high concentration and desalination application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a modular multi-stage membrane distillation simultaneous concentration device and method. Background Technology

[0002] Membrane distillation (MD), as a heat-driven membrane separation technology, has shown broad application prospects in recent years in fields such as seawater desalination (total dissolved solids (TDS) > 35 g / L), high-salinity wastewater treatment (TDS > 100 g / L), and food concentration, thanks to its ability to achieve high separation rates using low-grade heat sources (30-80℃).

[0003] However, existing single-stage membrane distillation systems still face the following technical bottlenecks in industrial applications:

[0004] Mass transfer driving force attenuation and treatment capacity limitations mean that the permeate flux of single-stage membrane distillation is primarily driven by the vapor pressure difference across the membrane. When treating high-concentration feed solutions (such as industrial wastewater with TDS > 100 g / L), the vapor pressure on the feed side decreases significantly, leading to a decline in the mass transfer driving force. Studies have shown that when the feed TDS exceeds 150 g / L, the permeate flux attenuation rate can reach over 60%. Traditional methods of increasing treatment capacity by increasing membrane area can exacerbate concentration polarization due to uneven channel distribution, resulting in a 30-50% increase in solute concentration at the membrane surface, further reducing mass transfer efficiency.

[0005] The thermal energy utilization efficiency is low. Even with a multi-stage series structure (US20170349447A1), the interstage heat recovery rate is still less than 55%, which is insufficient to meet the energy cost requirements for large-scale industrial applications. Research shows that (Ultra-high freshwater production in multistage solar membrane distillation via waste heat injection to condenser) combines solar energy (top heating) and waste heat (final stage heating) to achieve a "high-temperature-low-temperature" gradient synergy, reducing dependence on a single heat source. Research also shows that (Multistage osmotically assisted reverse osmosis process for concentrating solutions using hollow fiber membrane modules) using 10 HF membrane modules in series, with the concentrate from the first stage used as feed for the next stage, and the same pressure (10–15 bar) applied to each stage, can achieve a gradual increase in concentration.

[0006] Complex structure and difficult maintenance: Multi-stage membrane modules rely on external series equipment (such as CN201110428029.6) to achieve multi-stage operation and meet most non-high temperature and high pressure operating conditions. Research shows that (Optimal design of multi-stage vacuum membrane distillation and integration with supercritical water desalination for improved zero liquid discharge desalination) achieves heat recovery by designing temperature gradients between multi-stage VMD stages and using the latent heat of condensation of the previous stage to preheat the feed of the next stage.

[0007] Insufficient membrane fouling control and system scalability are significant drawbacks. Traditional flat-plate membrane modules are prone to forming localized stagnant zones within the flow channels when processing high-concentration solutions, leading to accelerated solute crystallization. Experimental data shows that when the TDS of the feed solution exceeds 80 g / L, the membrane pore wetting rate increases by 2-3 times. Existing patents (such as CN113354013B) often limit the number of stages (e.g., 40 stages), failing to dynamically adjust flow channel parameters or stage configurations based on feed solution characteristics (salt concentration, viscosity). For example, processing high-viscosity food solutions (viscosity ≥ 300 mPa·s) requires customized equipment modifications, resulting in a module reuse rate of less than 20%. Research indicates that (Application of Vacuum Membrane Distillation for Concentration) simulates a multi-stage effect through cyclic concentration (multiple reflux of the feed solution through a single-stage module), gradually increasing the concentration.

[0008] In contrast, the optimized multi-stage component S-shaped flow channel coupled with a diamond-shaped flow divider array design can increase the salt content at the concentration endpoint by 1.6 times while reducing downstream processing energy consumption by 38-50%. Furthermore, existing multi-stage systems mostly employ a fixed series structure, which cannot flexibly adjust the number of stages or flow channel parameters according to feed characteristics (such as salt concentration and viscosity), limiting process adaptability. Existing membrane distillation technology in heavy water treatment suffers from core problems such as: limited functionality, low thermal efficiency, complex components, insufficient adaptability, and poor system scalability and process adaptability.

[0009] Furthermore, membrane distillation technology faces numerous challenges in industrial applications of concentration and desalination. For example:

[0010] Membrane modules have limited functionality: Traditional systems only support unidirectional operation (such as patent CN113354013B, which only focuses on concentration), and cannot flexibly switch between concentration and desalination modes according to needs, resulting in low equipment utilization and limited application scenarios.

[0011] Poor system scalability and process adaptability: Existing multi-stage membrane modules mostly adopt a fixed series structure (such as patent KR102020012258A), which cannot dynamically adjust channel parameters (such as width and tilt angle) or stage configuration according to feed characteristics (salt concentration, viscosity). Facing diverse application scenarios (such as high-viscosity food solutions and high-salt wastewater), customized equipment modifications are required, leading to a development cycle extension of more than 50%, and a module reuse rate of less than 20%. Research shows (Chemical Engineering Research and Design doi:10.1016 / j.cherd.2020.07.029) that due to the stage limitation exceeding 10 stages, the concentrate viscosity increases significantly, causing a sharp increase in mass transfer resistance and a decrease in flux to 50% of the initial value.

[0012] Low thermal energy utilization efficiency: The latent heat recovery efficiency of steam is low, the multi-stage condensation process does not achieve cascaded utilization of thermal energy (e.g., solar membrane distillation systems rely on single-stage condensation), the energy consumption of auxiliary heating equipment is high, and the overall energy efficiency is insufficient. Existing research (published by the ITEWA team at Shanghai Jiao Tong University in Nature Communications (doi:10.1038 / s41467-024-51880-y)) shows that multi-stage solar membrane distillation systems heavily rely on external heat sources (requiring 250 W·m³). -2 (Continuous power input). The thermal boosting mechanism increases system maintenance costs by more than 30%. Studies show that while air gaps reduce heat loss, they increase water vapor diffusion resistance, which may require higher flow velocities to offset.

[0013] Complex structure and difficult maintenance: Multi-stage membrane modules rely on external series equipment (such as CN201110428029.6), resulting in a large system size, low integration, and difficulty in adapting to high-temperature and high-pressure conditions. Existing research (10.1016 / j.jclepro.2022.132189.) indicates that multi-stage SCWD requires a high-temperature heat source (>450℃), limiting the direct application of renewable energy sources (such as solar energy). The integration of multi-stage VMD with SCWD requires precise thermal matching and pressure control, leading to high equipment investment costs.

[0014] Severe membrane fouling and high maintenance costs: Traditional flat-plate flow channels have dead zones (stagnant zones accounting for >15%), which accelerate solute crystallization and membrane pore wetting (the risk of membrane wetting increases by 2-3 times when TDS>80g / L), requiring frequent shutdowns for cleaning (cycles of 50-80 hours). This results in a membrane lifespan shortened to less than 1 year, equipment maintenance costs increased by 30%-40%, and frequent start-ups and shutdowns reduce the stability of continuous system operation.

[0015] The complexity of the structure and the high manufacturing cost are significant drawbacks. Existing patents (such as CN113354013B) often limit the number of stages (e.g., 40 stages), making it impossible to dynamically adjust the flow channel parameters or stage configuration based on the characteristics of the liquid (salt concentration, viscosity). This limits the flexibility in increasing or decreasing the processing scale and reduces scalability. For example, processing high-viscosity food solutions (viscosity ≥ 300 mPa·s) requires customized equipment modifications, resulting in a module reuse rate of less than 20%. The equipment occupies a large area, making it difficult to adapt to space-constrained industrial sites, and the initial investment cost hinders the promotion of the technology.

[0016] Poor adaptability and insufficient stability: The lack of intelligent control means makes it impossible to dynamically adjust the temperature, vacuum and flow rate according to the concentration of the liquid (e.g., low-concentration heavy water requires high pressure differential drive, and high-concentration requires anti-pollution strategy), resulting in unstable treatment efficiency.

[0017] Lack of technology integration: Existing research focuses on single improvements (such as uniform fabric to prevent pollution) and lacks system integration of multi-stage membrane modules, heat recovery and intelligent control, which makes it difficult to meet the comprehensive requirements of high efficiency, flexibility and low energy consumption.

[0018] This application is made in order to address at least some of the above-mentioned problems. Summary of the Invention

[0019] This application provides a modular multi-stage membrane distillation simultaneous concentration device, the device comprising one or both of a concentration module and a desalination module;

[0020] The concentration module comprises the following components stacked in sequence: a concentration element, a porous membrane, and a vacuum element;

[0021] Each group of the devices stacked in sequence forms a membrane separation unit, and the concentration module contains one or more membrane separation units.

[0022] In each membrane separation unit of the concentration module, the connections between the devices are as follows:

[0023] The concentrate has a concentration channel on at least one surface in the stacking direction, and the concentrate has a concentrate liquid inlet and a concentrate liquid outlet communicating with the concentration channel.

[0024] The porous membrane is stacked onto the surface of the concentration channel of the concentrator;

[0025] The vacuum component has a vacuum chamber facing the porous membrane, which allows a portion of the liquid in the concentration channel of the condenser to vaporize, pass through the porous membrane, enter the vacuum chamber, and condense.

[0026] The liquid outlet of the concentration module is connected to the liquid inlet of the concentration module of the next membrane separation unit to achieve continuous concentration of the liquid.

[0027] The condensate outlet of the vacuum chamber of the membrane separation unit of the concentration module is used to discharge the desalinated liquid, or the liquid inlet of the concentration element connected to the corresponding stage membrane separation unit of the desalination module is used to further desalinate the desalinated liquid.

[0028] The desalination module comprises the following components stacked in sequence: a concentration element, a porous membrane, and a vacuum element;

[0029] Each group of the devices stacked in sequence forms a membrane separation unit, and the concentration module and the desalination module each have one or more membrane separation units;

[0030] In each membrane separation unit of the desalination module, the connections between the devices are as follows:

[0031] The concentrate has a concentration channel on at least one surface in the stacking direction, and the concentrate has a concentrate liquid inlet and a concentrate liquid outlet communicating with the concentration channel;

[0032] The porous membrane is stacked onto the surface of the concentration channel of the concentrator;

[0033] The vacuum component has a vacuum chamber facing the porous membrane, which allows a portion of the liquid in the concentration channel of the condenser to vaporize, pass through the porous membrane, enter the vacuum chamber, and condense.

[0034] The condensate outlet of the vacuum chamber is connected to the liquid inlet of the concentrate of the next membrane separation unit of the desalination module to achieve continuous desalination of the liquid.

[0035] The liquid outlet of the concentrate unit of the desalination module (excluding the first membrane separation unit) is used to discharge the concentrate, or the liquid inlet of the concentrate unit of the corresponding stage of the concentration module is connected to further concentrate the liquid.

[0036] The liquid inlet of the concentrator in the first membrane separation unit of the desalination module is used to receive the liquid to be treated.

[0037] When the device includes both a concentration module and a desalination module:

[0038] The stacking order of the components in the concentration module and the desalination module is reversed;

[0039] The liquid outlet of the concentrate of the first membrane separation unit of the desalination module is connected to the liquid inlet of the concentrate of the first membrane separation unit of the concentration module; or, the concentrate of the first membrane separation unit of the desalination module has concentration channels on both surfaces in the stacking direction, and the liquid outlet of the concentrate of the first membrane separation unit of the desalination module is connected to the inlet of the concentration channel on the back side of the concentrate. In this case, the concentration module and the desalination module share the same concentrate at the junction of the two modules.

[0040] Preferably, the concentration module further includes: a desalination auxiliary heating element stacked on the back of the vacuum chamber of the vacuum component;

[0041] The desalination module further includes: a desalination auxiliary heating element stacked on the back of the vacuum chamber of the vacuum component;

[0042] The desalination auxiliary heating component has a condensate flow channel and a heat source for heating the liquid in the condensate flow channel.

[0043] The condensate outlet of the vacuum chamber is connected to the condensate flow channel inlet of the desalination auxiliary heating element, and the flow channel outlet of the desalination auxiliary heating element is connected to the concentrate liquid inlet of the concentrate element of the next membrane separation unit of the desalination module or the concentration module.

[0044] Preferably, a flow divider is provided between the condenser and the porous membrane;

[0045] The diversion plate includes: a porous base plate and protrusions located on the porous base plate;

[0046] Furthermore, the flow divider is configured such that the protrusion is embedded in the concentration channel of the concentrate. The porous base plate is attached to the surface of the concentration channel of the concentrate.

[0047] Preferably, the concentration channel of the concentration component is provided with protrusions. This eliminates the need for a porous bottom plate.

[0048] Preferably, the porous membrane is a hydrophobic microporous membrane with a pore size in the micrometer or nanometer range.

[0049] Preferably, a sealing ring is provided between the devices.

[0050] Preferably, the vacuum chamber of the vacuum component is connected to a vacuum pumping system;

[0051] The vacuum chamber of the vacuum component is also equipped with a slanted plate;

[0052] One side of the beveled plate is higher than the other side, and the beveled plate has a channel so that the condensate in the vacuum chamber flows through the channel into the collection tank located at the bottom of the vacuum chamber.

[0053] Preferably, in the device, from a certain position forward, the devices in the membrane separation unit are stacked sequentially in the reverse order described above to form the concentration module, and from the certain position backward, the devices in the membrane separation unit are stacked sequentially in the order described above to form the desalination module.

[0054] The second aspect of this application provides a modular multi-stage membrane distillation simultaneous concentration method, wherein the method uses the modular multi-stage membrane distillation simultaneous concentration apparatus described in any one of the first aspects;

[0055] The operation method of the fade-out module includes the following steps:

[0056] The liquid to be treated enters from the liquid inlet of the concentrator of the first membrane separation unit of the desalination module and flows into the concentrator channel;

[0057] In the concentration channel, a portion of the liquid to be treated vaporizes under the negative pressure transmitted from the vacuum chamber and passes through the porous membrane into the vacuum chamber where it condenses.

[0058] The condensed liquid flows out from the condensate outlet of the vacuum chamber and enters the concentrate liquid inlet of the concentrate unit of the next membrane separation unit of the desalination module to flow into the concentration channel, and repeats the above steps to perform multi-stage desalination.

[0059] The unvaporized liquid in the concentration channel of the concentration element is discharged from the concentration element liquid inlet of the concentration element to the desalination module, or discharged into the concentration element liquid inlet of the corresponding stage membrane separation unit of the concentration module for further concentration of the liquid;

[0060] The operation of the concentration module includes the following steps:

[0061] The liquid to be treated enters the concentration channel of the concentration element of the first membrane separation unit of the concentration module. In the concentration channel, part of the liquid to be treated vaporizes under the negative pressure transmitted from the vacuum chamber and passes through the porous membrane into the vacuum chamber and condenses.

[0062] The liquid obtained after condensation flows out of the concentration module from the condensate outlet of the vacuum chamber, or is discharged into the liquid inlet of the concentration element of the corresponding membrane separation unit of the desalination module for further desalination of the desalinated liquid.

[0063] The liquid that has not vaporized flows from the liquid inlet of the condenser to the liquid inlet of the condenser of the next membrane separation unit of the condensation module to enter the condensation channel, and the above steps are repeated to perform multi-stage concentration.

[0064] When the device includes both a concentration module and a desalination module:

[0065] In the concentration channel of the concentration element of the first membrane separation unit of the desalination module, the liquid that has not vaporized flows out from the liquid inlet of the concentration element and then enters the concentration channel on the back of the concentration element or the concentration channel of the concentration element of the first membrane separation unit of the concentration module.

[0066] The liquid to be processed is 30-80 degrees Celsius.

[0067] Preferably, the liquid obtained after condensation flows out from the condensate outlet of the vacuum chamber before entering the concentrate liquid inlet of the concentrate unit of the next membrane separation unit of the desalination module:

[0068] The condensed liquid flows out from the condensate outlet of the vacuum chamber, enters the condensate channel through the condensate inlet of the desalination auxiliary heating element, is heated by the heat source in the condensate channel, and then enters the concentrate liquid inlet of the concentrate of the next membrane separation unit of the desalination module from the condensate channel outlet of the desalination auxiliary heating element.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] 1. Multi-level Modular Expansion: This system adopts an innovative multi-level modular expansion architecture, the core of which lies in the inter-stage isolation structure based on gradient pressure balance. It achieves full-process integration of "front-end desalination and impurity removal - mid-stage gradient concentration - end-stage pure water production" within the same set of plate-and-frame components. This structure forms concentration and desalination chambers by alternately stacking high-performance hydrophobic microporous membranes such as PTFE / PVDF / PP with plate-and-frame components, supporting flexible expansion from single-stage to multi-stage, perfectly adapting to high-concentration and desalination applications of different scales and treatment requirements (such as zero discharge of industrial wastewater, drug extraction and purification, seawater desalination concentrate treatment, high-salt material concentration, azeotropic separation, radioactive wastewater treatment, fruit juice concentration, dairy processing, etc.).

[0071] 2. Integrated Multi-Stage Membrane Module Process: Utilizing a plate-and-frame membrane module design with full-process coupling, the concentration and desalination modules are isolated and connected in series via inter-stage sealing structures. This eliminates the need for external switching valves and pipeline reconfiguration, enabling simultaneous gradient concentration of the feed solution and pure water production, thus constructing a highly integrated multi-stage treatment system. Equipment utilization is increased to over 95%, pipeline connection points are reduced by 40%, lowering the risk of leaks and control complexity.

[0072] 3. High-efficiency condensation recovery: The vacuum chamber integrates a beveled baffle and a cold-wall condensation module, achieving a three-stage treatment path of condensation, liquid accumulation, and waste heat recovery. The vacuum chamber's beveled baffle angle and cold-wall heat exchange area can be optimized through three-dimensional flow field simulation, achieving a steam phase change efficiency of over 98%. The condensate is directly discharged into the bottom collection tank of the vacuum chamber through 4-5 sets of guide holes on the beveled baffle, shortening the transmission path by 30% and improving latent heat recovery efficiency by 25%.

[0073] 4. Multi-functional S-shaped flow channel integrated design—compact flow channel design: Preferably, the condensate flow channel on the surface of the desalination auxiliary heating component is an S-shaped flow channel, and the other surface of the desalination auxiliary heating component has an S-shaped auxiliary heating liquid flow channel. A heat source is located within the S-shaped auxiliary heating liquid flow channel to heat the liquid within the condensate flow channel. By integrating the front S-shaped condensate flow channel and the back S-shaped auxiliary heating liquid flow channel into the double-sided composite flow channel plate of the desalination auxiliary heating component, direct heat exchange is achieved, reducing energy consumption. The above can be optimized through CFD simulation to achieve reverse thermal energy coupling of hot and cold fluids. This design simplifies the piping system by 60%, reduces the device volume by 40%, lowers manufacturing costs by 35%, and achieves a thermal energy utilization rate of 85%. Furthermore, both the concentration component and the desalination auxiliary heating component are equipped with S-shaped flow channels with different functions, which can be further refined using CFD simulation optimization to reduce heat loss.

[0074] 5. Membrane fouling control and elimination of dead zones: Preferably, the protrusions on the flow divider are rhomboid blocks. By optimizing the flow field and creating a regular array of rhomboid blocks, with the blocks connected at an angle of 60°-120°, dead zones (stagnant zone ratio < 5%) are eliminated, the membrane shear rate is increased by 30%, and concentration polarization is suppressed (ΔC / C0 ≤ 15%). This structural design guides the fluid to flow along a preset trajectory, solving the problems of concentration polarization and turbulence.

[0075] Preferably, the protrusions on the diverter plate can be coated with a hydrophilic coating. After hydrophilic coating treatment (contact angle < 60°), the contaminant adhesion rate is reduced by 65%, and the membrane cleaning cycle is extended to 2.5 times that of conventional devices. Attached Figure Description

[0076] Figure 1 This is an exploded view of the multi-stage membrane distillation simultaneous concentration and desalination device of this application.

[0077] Figure 2 This is a schematic diagram of the condenser component.

[0078] Figure 3 A schematic diagram of the front structure of the auxiliary heating element to minimize its appearance.

[0079] Figure 4 A schematic diagram of the back structure of the auxiliary heating element to minimize its appearance.

[0080] Figure 5 This is a schematic diagram of the vacuum component structure.

[0081] Figure 6 This is a structural diagram of a rhomboid flow divider.

[0082] Figure 7 Schematic diagram of the location of the diamond-shaped flow divider and the concentration channel of the concentration component.

[0083] Figure 8 This is a velocity contour map of the flow field without rhomboid manifolds in the concentrated flow channel.

[0084] Figure 9 Velocity contour plot of the flow field with a diamond-shaped manifold added inside the concentration channel.

[0085] List of reference numerals in the attached diagram:

[0086] 1. Concentrator, 1-1. Liquid inlet of concentrator, 1-2. Sealing ring groove of concentrator, 1-3. Concentrator flow channel, 1-4. Liquid outlet of concentrator, 1-5. Outlet of concentrator flow channel;

[0087] 2. Porous membrane;

[0088] 3. Vacuum components; 3-1. Vacuuming channel; 3-2. Vacuuming through hole; 3-3. Condensation wall; 3-4. Beveled plate through hole; 3-5. Beveled plate; 3-6. Condensate outlet; 3-7. Vacuum component sealing ring groove.

[0089] 4. Desalination auxiliary heating components: 4-1. Condensate flow channel outlet; 4-2. Desalination side sealing ring groove; 4-3. Condensate flow channel inlet; 4-4. Condensate flow channel; 4-5. Auxiliary heat inlet; 4-6. Auxiliary heat side sealing ring groove; 4-7. Auxiliary heat outlet; 4-8. Auxiliary heat liquid flow channel.

[0090] 5. Rhomboid flow divider plate; 5-1. Rhomboid block; 5-2. Turbulent zone of rhomboid flow divider plate channel;

[0091] 6. Sealing ring. Detailed Implementation

[0092] The present application will now be described in further detail with reference to the embodiments.

[0093] 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 this application. 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 manual. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0094] 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. In the description of this application, unless otherwise stated, “a plurality” means two or more. It should be further understood that the term “comprising” as used in the specification of this application means the presence of the stated feature, integer, step, operation, element, and / or component, 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.

[0095] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application 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. Therefore, they should not be construed as limitations on this application.

[0096] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0097] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0098] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0099] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0100] 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 application 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.

[0101] This application provides a modular multi-stage membrane distillation and concentration apparatus and method.

[0102] The device includes one or both of a concentration module and a desalination module.

[0103] The concentration module includes the following components stacked in sequence: concentration element 1, porous membrane 2, and vacuum element 3;

[0104] Each group of the devices stacked in sequence forms a membrane separation unit, and the concentration module contains one or more membrane separation units.

[0105] In each membrane separation unit of the concentration module, the connections between the devices are as follows:

[0106] The condenser 1 has a condensation channel 1-3 on at least one surface in the stacking direction, and the condenser 1 has a condenser liquid inlet 1-1 and a condenser liquid outlet 1-4 communicating with the condensation channel 1-3.

[0107] Concentration channel 1-3, concentration channel outlet 1-5, and concentration component liquid outlet 1-4 are connected in sequence;

[0108] The porous membrane 2 is stacked on the surface of the concentration channels 1-3 of the concentration component 1;

[0109] The vacuum component 3 has a vacuum chamber facing the porous membrane 2, which allows a portion of the liquid in the concentration channels 1-3 of the condenser 1 to vaporize, pass through the porous membrane 2, enter the vacuum chamber, and condense.

[0110] The liquid outlet 1-4 of the concentration module 1 is connected to the liquid inlet 1-1 of the concentration module 1 of the next membrane separation unit to achieve continuous concentration of the liquid.

[0111] The condensate outlet 3-6 of the vacuum chamber of the membrane separation unit of the concentration module is used to discharge the desalinated liquid, or it is connected to the liquid inlet 1-1 of the concentration element 1 of the corresponding stage membrane separation unit of the desalination module for further desalination of the desalinated liquid.

[0112] The desalination module comprises the following components stacked sequentially: a concentrator 1, a porous membrane 2, and a vacuum unit 3; the connection method of each component in each membrane separation unit of the desalination module is as follows:

[0113] Each group of the devices stacked in sequence forms a membrane separation unit, and the concentration module and the desalination module each have one or more membrane separation units;

[0114] The condenser 1 has a condensation channel on at least one surface in the stacking direction, and the condenser 1 has a condenser liquid inlet 1-1 and a condenser liquid outlet 1-4 communicating with the condensation channel 1-3;

[0115] The porous membrane 2 is stacked on the surface of the concentration channels 1-3 of the concentration component 1;

[0116] The vacuum component 3 has a vacuum chamber facing the porous membrane 2, which allows a portion of the liquid in the concentration channels 1-3 of the condenser 1 to vaporize, pass through the porous membrane 2, enter the vacuum chamber, and condense.

[0117] The condensate outlet 3-6 of the vacuum chamber is connected to the liquid inlet 1-1 of the concentrate 1 of the next membrane separation unit of the desalination module to achieve continuous desalination of the liquid.

[0118] The liquid outlet 1-4 of the concentration element 1 of the desalination module (excluding the first membrane separation unit) is used to discharge the concentrated liquid, or it is connected to the liquid inlet 1-1 of the concentration element 1 of the corresponding stage membrane separation unit of the concentration module for further concentration of the liquid.

[0119] The liquid inlet 1-1 of the concentration element of the first membrane separation unit of the desalination module is used to receive the liquid to be treated.

[0120] When the device includes both a concentration module and a desalination module:

[0121] The stacking order of the components in the concentration module and the desalination module is reversed;

[0122] The liquid inlet 1-1 of the concentrate 1 of the first membrane separation unit of the desalination module is connected to the liquid inlet 1-1 of the concentrate 1 of the first membrane separation unit of the concentration module; or, the concentrate 1 of the first membrane separation unit of the desalination module has a concentration channel 1-3 on both surfaces in the stacking direction, and the liquid inlet 1-1 of the concentrate 1 of the first membrane separation unit of the desalination module is connected to the inlet of the concentration channel 1-3 on the back side of the concentrate 1. In this case, the concentration module and the desalination module share the same concentrate at the junction of the two modules.

[0123] Preferably, the concentration module further includes: a desalination auxiliary heating element 4 stacked in reverse order on the surface of the vacuum element 3;

[0124] The desalination module also includes: a desalination auxiliary heating element 4 that is sequentially stacked on the surface of the vacuum element 3;

[0125] The desalination auxiliary heating element 4 has a condensate flow channel 4-4 and a heat source for heating the liquid in the condensate flow channel 4-4.

[0126] The condensate outlet 3-6 of the vacuum chamber is connected to the condensate inlet 4-3 of the desalination auxiliary heating element 4, and the condensate inlet 4-1 of the desalination auxiliary heating element 4 is connected to the concentrate liquid inlet 1-1 of the concentrate 1 of the next membrane separation unit of the desalination module or the concentration module.

[0127] The porous membrane 2 is preferably a hydrophobic microporous membrane.

[0128] In the preferred embodiment:

[0129] Details of the concentrator 1 are as follows: The concentrator 1 has a concentration chamber. The concentration chamber of the first membrane separation unit of the desalination module serves as the first-stage feed chamber, and is equipped with an S-shaped concentration channel 1-3. Diamond-shaped flow dividers 5 are stacked within the S-shaped concentration channel. Enhanced turbulence reduces concentration polarization at the membrane surface. The feed liquid enters the S-shaped concentration channel 1-3 through the liquid inlet 1-1 of the concentrator. Within the S-shaped concentration channel 1-3, the flow is agitated by the diamond-shaped flow dividers 5, reducing dead zones. The diamond-shaped flow dividers 5 have diamond-shaped blocks 5-1. The spaces between different diamond-shaped blocks 5-1 form the turbulence zone 5-2 of the diamond-shaped flow divider channel. The stacked diamond-shaped flow dividers 5 and the S-shaped concentration channels 1-3 enhance the fluid dynamics within the assembly. Under the action of the porous membrane 2 and the vacuum component 3, a vacuum membrane distillation process is facilitated, with some gas permeating through the hydrophobic microporous membrane into the vacuum chamber and condensing into first-stage desalinated water.

[0130] Figure 6 This is a structural diagram of a rhomboid flow divider. The holes on the porous base plate are not shown.

[0131] The remaining feed liquid that has not vaporized flows through S-shaped concentration channels 1-3 and eventually exits through them. It then flows into the primary concentration chamber of the concentration module through the liquid inlet 1-2 of the first membrane separation unit. Under the action of the porous membrane 2 and vacuum element 3, the membrane distillation process described above occurs, completing one concentration cycle. The unvaporized liquid becomes primary concentrated water. This primary concentrated water enters the second stage of the concentration module. Through the stacking of porous membrane 2 and vacuum element 3, the vacuum membrane distillation process is repeated. Part of the liquid vaporizes and permeates through the hydrophobic microporous membrane into the vacuum chamber, becoming secondary desalinated water. The remaining feed liquid that has not vaporized flows through S-shaped channel 2-2 and enters the secondary concentration chamber of the second membrane separation unit of the concentration module. Through the stacking of porous membrane 2 and vacuum element 3, the vacuum membrane distillation process is repeated, achieving secondary concentration. This process can be extended to achieve a multi-stage membrane distillation concentration process.

[0132] The S-shaped concentration channel 1-3 of the concentration element is provided with a sealing ring groove 1-2 on its outer periphery, and a sealing ring 6 is installed inside it to seal the S-shaped concentration channel 1-3 of the concentration element. Each membrane separation unit is composed of stacked components such as the concentration element 1, the sealing ring 6, the diamond-shaped flow divider 5, the porous membrane 2, and the vacuum element 3.

[0133] The pore size of the hydrophobic microporous separation membrane can be in the micrometer or nanometer range. For example, the pore size is 0.1–0.5 μm. The hydrophobic microporous separation membrane is made of PTFE, PP, or PVDF. The surface of the hydrophobic microporous membrane is bonded to the rhomboid flow divider 5, and this process realizes the stepwise concentration or desalination process.

[0134] The structure of vacuum component 3 is as follows: Vacuum component 3 contains a vacuum chamber. Only the side of the vacuum chamber facing the porous membrane 2 is open. The vacuum chamber contains a beveled plate 3-5 with beveled plate through-holes 3-4. Vacuum component 3 has a vacuum extraction channel 3-1 communicating with the outside. The top wall of the vacuum chamber has three vacuum extraction through-holes 3-2 connecting the vacuum chamber cavity and the vacuum extraction channel 3-1, used for vacuuming the vacuum chamber. After entering the vacuum chamber, steam liquefies upon contact with the vacuum chamber wall (condensation wall surface 3-3), flows along the condensation wall surface 3-3 through the beveled plate through-holes 3-4 on the beveled plate 3-5 to the bottom of the vacuum chamber, and finally collects and flows through the condensate outlet 3-6 of the vacuum chamber into the primary desalination chamber, completing one desalination process. The first-stage desalinated water enters the second stage, where it passes through a stack of single-stage vacuum membrane distillation modules. The vacuum membrane distillation process is repeated, and some of the liquid passes through the hydrophobic microporous membrane into the vacuum chamber to become second-stage desalinated water. The remaining feed liquid flows out through the S-shaped flow channel into the second-stage concentration chamber to achieve second-stage desalination. This process can be extended to achieve a multi-stage membrane distillation desalination process.

[0135] Vacuum component 3 also has a vacuum component sealing ring groove 3-7 on the outer periphery of the vacuum chamber, which is used to set the sealing ring 6 to seal the vacuum chamber.

[0136] The working process of the desalination auxiliary heating element 4 is as follows: The primary desalination condensate collected by the vacuum element 3 flows from the condensate inlet 4-3 into the condensate channel 4-4 of the desalination auxiliary heating element 4. Simultaneously, the back of the desalination auxiliary heating element 4 has an S-shaped auxiliary heating channel 4-8. The liquid in the condensate channel 4-4 is heated by the S-shaped auxiliary heating channel 4-8 of the auxiliary heating chamber 4, bringing the primary desalination condensate to the feed temperature. It then enters the concentration channel 1-3 of the concentration element 1 in the next stage membrane separation unit of the desalination module from the condensate channel outlet 4-1, where a membrane distillation process occurs. Part of the vapor permeates through the hydrophobic microporous membrane into the vacuum chamber and condenses into secondary desalinated water, thus achieving secondary desalination. This process is repeated to complete the multi-stage desalination process.

[0137] The heating medium in the auxiliary heating fluid flow channel 4-8 enters from the auxiliary heating inlet 4-5 and then exits through the auxiliary heating outlet 4-7. The condensate flow channel 4-4 of the desalination auxiliary heating component 4 is surrounded by auxiliary heating side sealing ring grooves 4-6 for setting the sealing ring 6.

[0138] The condensate flow channel 4-4 is surrounded by a desalination side sealing ring groove 4-2, which is used to install the sealing ring 6.

[0139] The technical effects of the technical solution provided in this application are:

[0140] 1. Highly efficient concentration effect, enhanced turbulence and suppressed concentration polarization. The S-shaped flow channels and stacked manifolds within the concentrator work synergistically to improve fluid dynamics, breaking away from the traditional method of simply supporting the membrane surface with a mesh. By extending the flow path and generating secondary eddies, the Reynolds number is increased by 3-5 times, and the boundary layer shear rate reaches >100s. -1 This effectively disrupts the concentration polarization layer on the membrane surface. Combined with the salt-blocking properties of the hydrophobic microporous membrane (0.1-0.5μm pore size), the risk of salt precipitation and crystallization on the membrane surface is reduced by more than 70%, significantly extending membrane life. A single-stage concentration chamber achieves a feed concentration ratio of 1.5-2 times through vacuum membrane distillation; unevaporated high-concentration liquid flows into the next stage. After multi-stage membrane separation units are connected in series, the total concentration ratio can reach more than 10 times (with 6 stages in series, the concentrate TDS > 200g / L). The modular design allows for the addition or removal of stages as needed, flexibly adapting to different concentration targets.

[0141] 2. Advantages of Multi-Stage Membrane Modules: Utilizing a modular, stacked architecture, the concentrator, porous membrane, vacuum unit, and desalination auxiliary heating unit are arranged in alternating, multi-stage configurations to simultaneously achieve concentration and desalination functions. Through the selective permeation characteristics of the hydrophobic microporous membrane material, a directional steam transport channel is constructed while effectively isolating the liquid phase. This multi-stage collaborative operation mode can simultaneously complete the efficient concentration of solute and the directional recovery of solvent within the same system. Relying on the gradient separation efficiency of the multi-stage membrane modules, the overall system recovery rate exceeds 60%, forming a highly efficient membrane treatment system integrating separation, concentration, and recovery, significantly improving resource recycling efficiency.

[0142] 3. Optimized Vacuum Condensation Efficiency. The vacuum chamber employs a beveled plate and a distributed vacuum system (3 Φ6mm vacuum ports), stabilizing the working pressure at 5-15kPa (abs), reducing steam transmission resistance by 35%, and increasing condensation efficiency by 40%. The chamber wall forms a gradient cooling wall (top 40℃ → bottom 25℃) combined with a guide port design, achieving rapid steam liquefaction and a single-stage freshwater recovery rate >20%.

[0143] 4. Energy efficiency and stability advantages: The final-stage condensation heat is used to preheat the feed liquid. The auxiliary heating liquid flow channel and S-shaped flow channel are coupled to achieve cascade utilization of interstage heat energy, reducing energy consumption by 30-40% compared to traditional membrane distillation. The structure of fluororubber / EPDM sealing rings 6 and stainless steel diamond-shaped flow divider plates 5 ensures no leakage risk during long-term operation (pressure resistance > 0.3MPa). Multi-stage membrane distillation processes can be realized by utilizing modular stacking of single-stage membrane distillation.

[0144] 5. Wide applicability: Capable of treating high-salinity wastewater (TDS>100g / L), seawater desalination, and low-temperature concentration of high-value substances (such as lithium salts and antibiotics). Operating temperature range is 40-80℃, adapting to complex working conditions. CFD simulation optimization of the flow channel geometry (such as S-shaped flow channels and diamond-shaped manifold layout) enhances near-membrane interface turbulence intensity. Experiments show that arranging a 45° diamond-shaped manifold in the flow channel can increase the flux of vacuum membrane distillation (VMD membrane) by 20%, with only an 8% increase in pressure drop along the flow path.

[0145] 6. The modular multi-stage membrane distillation unit of this invention, through structural innovation and process optimization, simultaneously achieves high-efficiency concentration and high-quality desalination, while also possessing low energy consumption, high recovery rate, and strong anti-fouling characteristics. Application areas include: In the field of zero-discharge industrial wastewater, for high-salt, high-COD wastewater from industries such as petrochemicals, coal chemicals, and electroplating, it can achieve a deep reduction in the solid-liquid content of the concentrate by ≥20%, and when paired with an MVR evaporation system, the total energy consumption is reduced by 30%; In the field of water purification, it is suitable for seawater (35000ppm) and brackish water (below 10000ppm) desalination, with the produced water quality meeting the GB / T19923-2005 industrial boiler water standard, particularly suitable for island, marine, and emergency water supply scenarios; In the field of azeotropic system separation, for… For azeotropic systems such as ethanol-water and methanol-acetone, membrane distillation leverages the difference in gas-liquid phase equilibrium to overcome the azeotropic limitations of traditional distillation, achieving highly efficient separation of systems with boiling point differences <5℃ and purity exceeding 99.9%. In specialized separation scenarios, such as biopharmaceuticals (antibiotic concentration, vaccine purification), food and beverages (juice concentration, plant extract refining), and new energy fields (lithium battery electrolyte recovery, rare earth element enrichment), gradient membrane configurations with pore sizes of 0.1-10μm enable precise molecular-level sieving and directional solute migration. These technologies have significant application value in these fields.

[0146] This application utilizes an innovative design to create an integrated endplate structure that combines a concentrator (1), a rhomboid flow divider (5), a porous membrane (2), a vacuum component (3), and a desalination auxiliary heating component (4) in a stacked and coupled configuration. This integrated S-shaped flow channel and multi-stage stacking technology achieves high efficiency and compactness in the membrane module. The detachable concentration / desalination membrane frame incorporates the rhomboid flow divider (5), with an S-shaped flow channel separating the concentration and desalination chambers, supporting rapid switching between application modes as needed (concentration mode TDS>300g / L, desalination mode TDS<10mg / L). The system features high recovery rate, low energy consumption, and strong anti-fouling characteristics, flexibly adapting to various scenarios such as zero discharge of industrial wastewater, high-salinity seawater desalination, and low-temperature concentration of high-value substances. This overcomes the technical bottlenecks of traditional membrane distillation modules, which are characterized by complex maintenance and limited functionality.

[0147] This application features a synergistic innovation in transmembrane separation processes. In practical applications, its applicable processes not only cover membrane distillation (including direct contact membrane distillation, purge membrane distillation, vacuum membrane distillation, and air-gap membrane distillation), but can be extended to forward osmosis (FO), reverse osmosis (RO), ultrafiltration (UF), nanofiltration (NF), and other processes, forming a multi-stage system. For example, a three-stage system of "nanofiltration-reverse osmosis-membrane distillation" can be used. The porous membrane materials used in the experiments include, but are not limited to, polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyethylene (PE), or modified materials thereof, with pore sizes ranging from 0.1 μm to 10 μm.

[0148] Vacuum component 3, concentration component 1, desalination auxiliary heating component 4, etc. can be made of a variety of materials such as PP, PET, PE, PVC, PS, PP, metal, etc.

[0149] The diamond-shaped manifold 5 can be made of various materials such as PTFE, PVC, FRP, alumina ceramic, and metal. Furthermore, the manifold used is not limited to a diamond shape; it can also be rectangular, square, polygonal, etc. The flow channels in the condenser and desalination auxiliary heating components are not limited to S-shaped; serpentine, rectangular, multi-channel coupling, and geometrically optimized forms are also applicable.

[0150] In the design of vacuum components, the style, angle, and opening position of the beveled plate can vary. The connection structure between the vacuum component, the concentration component, the desalination auxiliary heating component, the porous membrane 2, and the flow divider 5 includes: mechanical seal structure, using any one or combination of O-rings, rectangular rings, PTFE gaskets, and asbestos gaskets; non-contact sealing structure, including setting labyrinth-type bosses and stepped mating surfaces on the sealing surface, achieving medium barrier through micro-gap of 0.1mm to 0.5mm and multi-stage baffle paths; liquid film / gas film sealing structure, forming a pressure barrier by opening an annular flow channel on the sealing surface and introducing sealing liquid (water, oil) or sealing gas (nitrogen); rigid connection structure, including any one or combination of welding, riveting, flange connection, and press-fit fastenerless connection.

[0151] For those skilled in the art, any simple deductions, structural imitations, or module substitutions made without departing from the core concept of this invention should be considered to fall within the protection scope of this invention.

[0152] The following specific embodiments further illustrate this application.

[0153] Example 1: (Simultaneous Concentration and Depreciation Mode)

[0154] The concentration module of this device is used to treat nuclear wastewater containing 0.015 wt% heavy water. The concentration module contains 5 membrane separation units, forming a 5-stage treatment process.

[0155] The porous membrane is specifically a PP horizontal plate membrane with a thickness of 0.2-0.3 mm and a pore size of 0.1-0.3 μm.

[0156] The parameters of the processing are as follows: liquid flow rate 25L / h, feed temperature 80℃, vacuum degree of vacuum chamber 0.07Mpa, cooling bath temperature 10℃.

[0157] After 5 stages of concentration, the concentration of the heavy water concentrate is 0.0183 wt% (an increase of 0.0033 wt%), the deuterium content of the permeate is 0.00675 wt%, the deuterium removal rate reaches 55% (deuterium removal rate = 1 - (deuterium content after treatment / initial deuterium content) × 100%), the energy consumption is reduced by 35% compared to the traditional system (calculated compared to the power consumption of 800 kWh for evaporating 1 ton of water), and the concentration rate is 22% (concentration rate = concentrate concentration / feed concentration - 1).

[0158] Example 2 (High-salinity wastewater resource utilization treatment mode)

[0159] The desalination module of this device is used to treat high-salt chemical wastewater containing 15wt% sodium chloride, 0.5wt% sodium sulfate and trace heavy metal ions, with a COD (chemical oxygen demand) concentration of 800mg / L and a temperature of 35℃.

[0160] Module configuration and process parameters:

[0161] The desalination module contains three membrane separation units, forming a three-stage treatment process.

[0162] In the primary membrane separation unit: the porous membrane is a nanofiltration (NF) membrane. The operating pressure of the nanofiltration (NF) membrane is 1.8 MPa. The feed temperature is 40°C. The porous membrane retains sodium sulfate, with a divalent ion rejection rate >99%. Vacuum component function: pressure-bearing seal (vacuum degree 0 bar).

[0163] In the secondary membrane separation unit: polyamide reverse osmosis membrane (RO), concentrated sodium chloride, pressure 4.0 MPa, feed temperature 50℃, NaCl rejection rate >99.5%. Vacuum component function: pressure-bearing seal (vacuum degree 0 bar).

[0164] In the three-stage membrane separation unit: PTFE hydrophobic microporous membrane (VMD), deep desalination / pure water production, feed temperature 65℃, vacuum degree 0.08MPa, membrane flux 12L / (m²). 2 ·h).

[0165] After three stages of treatment, the liquid from the condensate outlet of the vacuum chamber of the third-stage membrane separation unit is taken for testing:

[0166] The salinity of the tertiary freshwater effluent is reduced to <100mg / L, meeting the industrial reuse water standard, and the COD removal rate is >95% (COD removal rate = (COD concentration of wastewater before treatment - COD concentration of wastewater after treatment) / COD concentration of wastewater before treatment × 100%).

[0167] Primary concentrate: Na2SO4 purity >98%, which can be recovered by evaporation and crystallization to prepare sodium sulfate.

[0168] Secondary concentrate: NaCl concentration >18wt%, which can be recycled by evaporation and crystallization to prepare industrial salt (purity >96%).

[0169] Tertiary concentrate: a heavy metal liquid containing trace amounts of NaCl (total <5wt%), which can be used for hazardous waste solidification treatment.

[0170] Mass fraction (wt%) = mass concentration (mg / L) ÷ 10,000 (when solution density ≈ 1 g / mL).

[0171] Example 3 (Organic Matter-Water Separation Mode) Desalination Module

[0172] The desalination module of this device is used to treat pharmaceutical wastewater containing 5% methanol (methanol / water azeotropic system).

[0173] Module configuration and process parameters:

[0174] Feed flow rate: 30 L / h; Vacuum chamber vacuum level: 0.65 bar; Membrane distillation module temperature: 65℃ (feed side) / 25℃ (permeate side). Membrane material: Sintered polypropylene (PP) microporous membrane, pore size 0.8 μm.

[0175] Module configuration and process parameters:

[0176] In the primary membrane separation unit: a PP hydrophobic microporous membrane (VMD) is used for azeotropic pre-separation: feed temperature 65℃, vacuum degree 0.065MPa, pore size 0.8μm. This achieves a methanol rejection rate >99.8% (previously >99.6%), with effluent methanol <0.02%. Rejection rate = [1 - (200 / 50,000)] × 100% = 99.6%.

[0177] In the secondary membrane separation unit: PP hydrophobic microporous membrane (VMD) is used for deep methanol retention: feed temperature 60℃, vacuum degree 0.07MPa (gradient pressurization), water recovery rate reaches 78%. Distillation: 8.2kWh / t. VMD: 3.7kWh / t, reducing energy consumption by 55% compared to distillation.

[0178] In the three-stage membrane separation unit: PP hydrophobic microporous membrane (VMD), high-purity water production: feed temperature 55℃, vacuum degree 0.075MPa, condensation 25℃.

[0179] The module occupies only 20% of the area of ​​a distillation column, achieving an 80% improvement in compactness.

[0180] Example 4 (Lithium-Magnesium Separation Mode in Salt Lake Brine) Concentration Module

[0181] The concentration module of this device is used to process materials containing 1.2% wt Li + 8% wt Mg 2+ High magnesium-to-lithium ratio salt lake brine.

[0182] Module configuration and process parameters:

[0183] Feed flow rate: 18 L / h, feed temperature: 25℃. Nanofiltration membrane module pressure: 1.5 MPa, porous membrane selective block copolymer nanofiltration membrane, this membrane is suitable for Li + / Mg 2+ Separation coefficient = C > 50. α Li / Mg =24.035 / 0.15=160.23>50.

[0184] Primary membrane separation unit: Li + Selective nanofiltration membrane (NF), Mg 2+ Pre-retention, pressure 1.5MPa, 25℃, Li / Mg separation coefficient >50, vacuum component function: pressure sealing (vacuum degree 0bar).

[0185] Secondary membrane separation unit: PTFE hydrophobic membrane (VMD), Li + Deep concentration, feed temperature 40℃, vacuum degree 0.08MPa, membrane flux 8L / (m²) 2 ·h).

[0186] After nanofiltration in the first-stage membrane separation unit: Li + Concentration: 11.4 g / L, Mg 2+ Concentration: 0.474 g / L, α Li / Mg =11.4 / 0.474=24.05, achieving efficient magnesium separation and increasing the Li / Mg ratio by 160 times.

[0187] After VMD in the secondary membrane separation unit: Li + Concentration: 16.29 g / L, Mg 2+ Concentration: 0.677 g / L, lithium concentration is further concentrated in preparation for lithium extraction.

Claims

1. A modular multi-stage membrane distillation and simultaneous concentration device, characterized in that, The device includes: a concentration module and a desalination module; The concentration module comprises the following components stacked in sequence: a concentration element, a porous membrane, and a vacuum element; Each group of the devices stacked in sequence forms a membrane separation unit, and the concentration module may contain one or more membrane separation units. In each membrane separation unit of the concentration module, the connections between the devices are as follows: The concentrate has a concentration channel on at least one surface in the stacking direction, and the concentrate has a concentrate liquid inlet and a concentrate liquid outlet communicating with the concentration channel. The porous membrane is stacked onto the surface of the concentration channel of the concentrator; The vacuum component has a vacuum chamber facing the porous membrane, which allows a portion of the liquid in the concentration channel of the condenser to vaporize, pass through the porous membrane, enter the vacuum chamber, and condense. The liquid outlet of the concentration module is connected to the liquid inlet of the concentration module of the next membrane separation unit to achieve continuous concentration of the liquid. The condensate outlet of the vacuum chamber of the membrane separation unit of the concentration module is used to discharge the desalinated liquid, or the liquid inlet of the concentration element connected to the corresponding stage membrane separation unit of the desalination module is used to further desalinate the desalinated liquid. The desalination module comprises the following components stacked in sequence: a concentration element, a porous membrane, and a vacuum element; Each group of the devices stacked in sequence forms a membrane separation unit, and the desalination module has one or more membrane separation units; In each membrane separation unit of the desalination module, the connections between the devices are as follows: The concentrate has a concentration channel on at least one surface in the stacking direction, and the concentrate has a concentrate liquid inlet and a concentrate liquid outlet communicating with the concentration channel. The porous membrane is stacked onto the surface of the concentration channel of the concentrator; The vacuum component has a vacuum chamber facing the porous membrane, which allows a portion of the liquid in the concentration channel of the condenser to vaporize, pass through the porous membrane, enter the vacuum chamber, and condense. The condensate outlet of the vacuum chamber is connected to the liquid inlet of the concentrate of the next membrane separation unit of the desalination module to achieve continuous desalination of the liquid. The liquid outlet of the concentrate unit of the desalination module (excluding the first membrane separation unit) is used to discharge the concentrate, or the liquid inlet of the concentrate unit of the corresponding stage of the concentration module is connected to further concentrate the liquid. The liquid inlet of the concentrator in the first membrane separation unit of the desalination module is used to receive the liquid to be treated. The stacking order of the components in the concentration module and the desalination module is reversed; The liquid outlet of the concentrate of the first membrane separation unit of the desalination module is connected to the liquid inlet of the concentrate of the first membrane separation unit of the concentration module; or, the concentrate of the first membrane separation unit of the desalination module has concentration channels on both surfaces in the stacking direction, and the liquid outlet of the concentrate of the first membrane separation unit of the desalination module is connected to the inlet of the concentration channel on the back side of the concentrate. In this case, the concentration module and the desalination module share the same concentrate at the junction of the two modules.

2. The modular multi-stage membrane distillation and simultaneous concentration device according to claim 1, characterized in that, The concentration module further includes: a desalination auxiliary heating element stacked on the back of the vacuum chamber of the vacuum component; The desalination module further includes: a desalination auxiliary heating element stacked on the back of the vacuum chamber of the vacuum component; The desalination auxiliary heating component has a condensate flow channel and a heat source for heating the liquid in the condensate flow channel. The condensate outlet of the vacuum chamber is connected to the condensate flow channel inlet of the desalination auxiliary heating element, and the condensate flow channel outlet of the desalination auxiliary heating element is connected to the concentrate liquid inlet of the concentrate element of the next membrane separation unit of the desalination module or the concentration module.

3. The modular multi-stage membrane distillation and simultaneous concentration device according to claim 1, characterized in that, A flow divider is provided between the condenser and the porous membrane; The diversion plate includes: a porous base plate and protrusions located on the porous base plate; Furthermore, the flow divider is configured such that the protrusion is embedded into the concentration channel of the condenser; Alternatively, the concentration channel of the concentration component may be provided with protrusions.

4. The modular multi-stage membrane distillation and simultaneous concentration device according to claim 1, characterized in that, The porous membrane is a hydrophobic microporous membrane with a pore size in the micrometer or nanometer range.

5. The modular multi-stage membrane distillation and simultaneous concentration device according to claim 1, characterized in that, A sealing ring is provided between the components.

6. The modular multi-stage membrane distillation and simultaneous concentration device according to claim 1, characterized in that, The vacuum chamber of the vacuum component is connected to the vacuum pumping system; The vacuum chamber of the vacuum component is also equipped with a slanted plate; One side of the beveled plate is higher than the other side, and the beveled plate has a channel so that the condensate in the vacuum chamber flows through the channel into the collection tank located at the bottom of the vacuum chamber.

7. The modular multi-stage membrane distillation and simultaneous concentration device according to claim 1, characterized in that, In the device, starting from a certain position, the components in the membrane separation unit are stacked in reverse order to form the concentration module, and starting from the same position, the components in the membrane separation unit are stacked in sequence to form the desalination module.

8. A modular multi-stage membrane distillation simultaneous concentration method, characterized in that, The method uses the modular multi-stage membrane distillation simultaneous concentration apparatus as described in any one of claims 1 and 3-7; The operation method of the fade-out module includes the following steps: The liquid to be treated enters from the liquid inlet of the concentrator of the first membrane separation unit of the desalination module and flows into the concentrator channel; In the concentration channel, a portion of the liquid to be treated vaporizes under the negative pressure transmitted from the vacuum chamber and passes through the porous membrane into the vacuum chamber where it condenses. The condensed liquid flows out from the condensate outlet of the vacuum chamber and enters the concentrate liquid inlet of the concentrate unit of the next membrane separation unit of the desalination module to flow into the concentration channel, and repeats the above steps to perform multi-stage desalination. The unvaporized liquid in the concentration channel of the concentration unit is discharged from the concentration liquid outlet of the concentration unit to the desalination module, or discharged into the concentration liquid inlet of the concentration unit of the corresponding stage of the concentration module for further concentration of the liquid. The operation of the concentration module includes the following steps: The liquid to be treated enters the concentration channel of the concentration element of the first membrane separation unit of the concentration module. In the concentration channel, part of the liquid to be treated vaporizes under the negative pressure transmitted from the vacuum chamber and passes through the porous membrane into the vacuum chamber and condenses. The liquid obtained after condensation flows out of the concentration module from the condensate outlet of the vacuum chamber, or is discharged into the liquid inlet of the concentration element of the corresponding membrane separation unit of the desalination module for further desalination of the desalinated liquid. The unvaporized liquid flows from the liquid outlet of the condenser to the liquid inlet of the condenser of the next membrane separation unit of the condensation module to enter the condensation channel, and the above steps are repeated to perform multi-stage concentration. In the concentration channel of the concentration element of the first membrane separation unit of the desalination module, the liquid that has not vaporized flows out from the liquid outlet of the concentration element and then enters the concentration channel on the back of the concentration element or enters the concentration channel of the concentration element of the first membrane separation unit of the concentration module. The liquid to be processed is 30-80 degrees Celsius.

9. The modular multi-stage membrane distillation and simultaneous concentration method according to claim 8, characterized in that, The method uses the modular multi-stage membrane distillation and simultaneous concentration apparatus as described in claim 2; The condensed liquid flows out from the condensate outlet of the vacuum chamber before entering the concentrate liquid inlet of the concentrate unit of the next membrane separation unit of the desalination module: The condensed liquid flows out from the condensate outlet of the vacuum chamber, enters the condensate channel through the condensate inlet of the desalination auxiliary heating element, is heated by the heat source in the condensate channel, and then enters the concentrate liquid inlet of the concentrate of the next membrane separation unit of the desalination module from the condensate channel outlet of the desalination auxiliary heating element.

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