A graded electric field driven flow electrode capacitive deionization seawater desalination device

Abstract

A graded electric field-driven flowing electrode capacitive deionization seawater desalination device comprises a first FCDI unit, a second FCDI unit, and a third FCDI unit, wherein the three FCDI units are assembled in series and subjected to three levels of electric field strength from low to high. Each FCDI unit is assembled symmetrically and has the same structure. The electric field strength is within the maximum allowable voltage or current in the ohmic region of the FCDI unit. The present invention utilizes convection between seawater and flowing electrode liquid, repeated flow channels in a single graphite plate, and multi-level stacking of single FCDI units in combination with a graded electric field to enhance the desalination effect of FCDI in the limiting current region and the over-limit current region, while simultaneously optimizing the operating efficiency, water production rate, and energy consumption of FCDI.

Description

Technical Field

[0001] The present invention relates to the technical field of seawater desalination, and in particular to a graded electric field driven mobile electrode capacitor deionization seawater desalination device. Background Art

[0002] The allocation of freshwater resources is limited by factors such as climate, geographic location, population density, and the level of local industrial and agricultural development. However, seawater reserves are abundant and unconstrained by geopolitical constraints. Developing and utilizing seawater resources is a crucial approach to addressing the impact of extreme natural disasters, resolving global and regional freshwater shortages, and providing a stable source of freshwater for industry and agriculture. Currently, widely used desalination technologies include thermally driven methods (such as multi-effect distillation and low-temperature flash evaporation), pressure-driven membrane methods (such as nanofiltration and reverse osmosis), and electric field-driven methods (such as electrodialysis). Although these methods are widely used, they still suffer from drawbacks such as high energy consumption, high membrane costs, the generation of secondary pollutants, or slow desalination rates. Many scholars and engineers are still committed to research to address these issues.

[0003] The electric field-driven membrane capacitive deionization process has been proven to be effective in desalinating seawater, but it suffers from intermittent operation, high energy consumption, and low water production rate. In order to improve the water production rate and further reduce energy consumption, scholars have developed a mobile electrode capacitive deionization seawater desalination technology. By using only highly conductive mobile electrodes and ion exchange membranes, it can delay the electrolysis reaction, inhibit common ion rejection, increase the desalination rate, and achieve continuous seawater desalination. However, although the conventional three-channel mobile electrode capacitive deionization device can directly desalinate seawater, it is limited by the high resistance of the brine in the solution channel and the high salt concentration difference between the mobile electrode and the feed seawater. There is still a problem of the inability to balance energy consumption and desalination rate, making it impossible to achieve an efficient, low-consumption, and low-cost mobile electrode capacitive deionization seawater desalination process. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a graded electric field driven flow electrode capacitor deionization seawater desalination device, which can significantly improve the efficiency of flow electrode capacitor deionization seawater desalination and reduce process energy consumption and operating costs.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A graded electric field driven mobile electrode capacitive deionization seawater desalination device comprises a first FCDI unit, a second FCDI unit, and a third FCDI unit. The three FCDI units are assembled in series and three levels of electric field strength are applied sequentially from low to high. Each FCDI unit is assembled symmetrically and has the same structure.

[0007] The electric field strength is within the maximum voltage or current allowed in the ohmic region of the FCDI unit;

[0008] Each FCDI unit includes a first support plate, a salt separation assembly, a current collecting plate, and a second support plate. The current collecting plate is located between the first support plate and the second support plate, and the salt separation assembly is located between two adjacent current collecting plates.

[0009] Preferably, the electric field strength of the first FCDI unit does not exceed 1.6V, the electric field strength of the second FCDI unit does not exceed 2.4V, and the electric field strength of the third FCDI unit does not exceed 3.2V.

[0010] Preferably, there is at least one salt separation component.

[0011] More preferably, there are three salt separation components.

[0012] Preferably, the salt separation component includes an anion exchange membrane, a solution chamber and a cation exchange membrane, the solution chamber is located between the anion exchange membrane and the cation exchange membrane, and the ends of the anion exchange membrane and the cation exchange membrane away from the solution chamber are respectively connected to the collecting plate.

[0013] Preferably, the current collecting plate includes a graphite plate and a flow electrode channel, and the flow electrode channel is distributed as multiple repeating units on the graphite plate; the graphite plate includes a cathode graphite plate and an anode graphite plate, and the anode graphite plate is connected to the solution chamber through an anion exchange membrane, and the cathode graphite plate is connected to the solution chamber through a cation exchange membrane.

[0014] More preferably, the flow electrode channels are distributed as 4 repeating units on the graphite plate.

[0015] Preferably, the shape of the flow electrode channel includes one of a serpentine shape, a rotating square shape or a rotating circle shape.

[0016] Preferably, each FCDI unit further includes a waterproof buffer layer, which is symmetrically arranged and includes a sealing gasket and a buffer gasket, one end of the sealing gasket is connected to the cathode graphite plate or the anode graphite plate, the other end of the sealing gasket is connected to the buffer gasket, and one end of the buffer gasket is connected to the first support plate or the second support plate.

[0017] Preferably, the first support plate, the second support plate, the cathode graphite plate, the anode graphite plate, the sealing gasket, the buffer gasket, the anion exchange membrane and the cation exchange membrane are respectively provided with a flow electrode inlet and a seawater inlet; the cathode graphite plate, the anode graphite plate, the sealing gasket, the buffer gasket and the solution chamber are respectively provided with electrode ears.

[0018] More preferably, eight flow electrode inlets and four seawater inlets are respectively provided on the first support plate and the second support plate; symmetrical flow electrode inlets are provided in the middle of each anode graphite plate and cathode graphite plate, and a seawater inlet is provided in the middle of each of the four sides;

[0019] Preferably, each FCDI unit further comprises a position control plate, one end of the position control plate is connected to the sealing gasket, and the other end of the position control plate is connected to the second support plate via the buffer gasket.

[0020] The present invention has the following advantages and beneficial effects compared to the prior art:

[0021] (1) The present invention is based on the different voltage-current characteristics of a flowing electrode capacitive deionization device (FCDI) under different influent salt concentrations and electrolyte salt concentrations. It utilizes the convection between seawater and flowing electrode liquid, repeated flow channels of a single graphite plate, and a combination of multi-stage stacking of a single FCDI unit and a graded electric field to enhance the desalination effect of FCDI in the limiting current region and the over-limit current region, and simultaneously optimize the operating efficiency, water production rate and energy consumption of FCDI.

[0022] (2) The seawater and the mobile electrode flow relative to each other, effectively reducing the reverse diffusion of salt ions caused by the concentration difference between the seawater and the mobile electrode electrolyte. Specifically, the seawater flows from bottom to top, passing through the third, second and first FCDI units in sequence, and the salt concentration of the seawater gradually decreases; while the mobile electrode flows from top to bottom, passing through the first, second and third FCDI units in sequence, and the electrolyte concentration of the mobile electrode gradually increases, ultimately making the salt concentration of the seawater and the mobile electrode electrolyte in the third FCDI unit the highest, the second FCDI unit the second, and the first FCDI unit the lowest; not only that, the present invention divides the flow channel on the single-sheet graphite plate current collector into four repeated areas to avoid clogging of the mobile electrode due to device enlargement and excessive length of the flow channel; the present invention performs multi-level stacking in a single FCDI unit to increase the contact area between the seawater and the mobile electrode, extend the effective residence time of the seawater and the mobile electrode in the single FCDI unit, and thus enhance the desalination effect of the single FCDI unit. According to the voltage-current characteristics of the first FCDI unit, the second FCDI unit and the third FCDI unit, three levels of electric field strength are applied to the third FCDI unit, the second FCDI unit and the first FCDI unit in sequence from high to low, so that the electric field strengths are all within the maximum voltage or current allowed in the ohmic region of the FCDI unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a working diagram of a flow electrode capacitive deionization seawater desalination device driven by a graded electric field;

[0024] Figure 2This is a front view of a flow electrode capacitive deionization seawater desalination device driven by a graded electric field;

[0025] Figure 3 It is the main view of the third FCDI unit;

[0026] Figure 4 is a top view of the cathode graphite plate;

[0027] Figure 5 is a top view of the anode graphite plate;

[0028] Figure 6 is a side view of the first support plate;

[0029] Figure 7 is a side view of the salt separation component;

[0030] Figure 8 is a top view of the solution chamber;

[0031] The markings of the components in the accompanying drawings are:

[0032] 1-first support plate, 2-salt separation assembly, 21-anion exchange membrane, 22-solution chamber, 23-cation exchange membrane, 3-current collecting plate, 31-graphite plate, 311-cathode graphite plate, 312-anode graphite plate, 32-flow electrode channel, 4-second support plate, 5-waterproof buffer layer, 51-sealing gasket, 52-buffer gasket, 6-position control plate, 7-electrode ear, 8-flow electrode inlet and outlet, 9-seawater inlet and outlet, 10-first FCDI unit, 11-second FCDI unit, 12-third FCDI unit DETAILED DESCRIPTION

[0033] The purpose of the present invention is described in further detail below with reference to the accompanying drawings and specific examples. The examples cannot be described one by one here, but the implementation methods of the present invention are not limited to the following examples.

[0034] Example 1

[0035] A graded electric field driven mobile electrode capacitive deionization seawater desalination device and system includes a first FCDI unit 10, a second FCDI unit 11 and a third FCDI unit 12. The three FCDI units are assembled in series and three levels of electric field strength are applied sequentially from low to high.

[0036] The third FCDI unit 10 includes a first support plate 1, three salt separation assemblies 2, a current collecting plate 3, a second support plate 4, two waterproof cushion layers 5, a position control plate 6, 16 electrode tabs 7, 88 flow electrode inlets and outlets 8, and 44 seawater inlets and outlets 9. The salt separation assembly 2 includes an anion exchange membrane 21, a solution chamber 22, and a cation exchange membrane 23. The current collecting plate 3 includes 16 flow electrode channels 32 and a graphite plate 31. The graphite plate 31 includes two cathode graphite plates 311 and two anode graphite plates 312. The waterproof cushion layer 5 includes a sealing gasket 51 and a buffer washer 52.

[0037] Each FCDI unit comprises, from bottom to top, a first support plate 1, a buffer gasket 52, a sealing gasket 51, an anode graphite plate 312, anion exchange membrane 21, a solution chamber 22, a cation exchange membrane 23, a cathode graphite plate 311, a cation exchange membrane 23, a solution chamber 22, anion exchange membrane 21, an anode graphite plate 312, anion exchange membrane 21, a solution chamber 22, a cation exchange membrane 23, a cathode graphite plate 311, a sealing gasket 51, a position control plate 6, a buffer gasket 52, and a second support plate 4. All components between the first support plate 1 and the second support plate 4 constitute the third FCDI unit 12. The components of the second FCDI unit 11 and the first FCDI unit 10 are identical to those of the third FCDI unit 12. Each FCDI unit is symmetrically assembled and has the same structure. The electric field strength is within the maximum allowable voltage or current in the ohmic region of the FCDI unit. The electric field strength of the first FCDI unit 10 does not exceed 1.6V, the electric field strength of the second FCDI unit 11 does not exceed 2.4V, and the electric field strength of the third FCDI unit 12 does not exceed 3.2V. The symmetrical assembly of the FCDI units allows the flowing electrodes to converge in the external container, which helps optimize charge balance. This design helps reduce electrode oxidation and corrosion, extending the life of the device. By reducing electrode loss, the device can operate stably for longer, reducing the frequency of maintenance and component replacement, and improving the reliability and durability of the device.

[0038] The cathode graphite plate 311 and the anode graphite plate 312 are respectively engraved with a 2 mm deep and 3 mm wide serpentine flow electrode channel 32 at the center of the outer surface away from the support plate. The flow electrode channel 32 is distributed as 4 repeating units on each cathode graphite plate 311 and anode graphite plate 312; a pole ear 7 is set directly below the anode graphite plate 312, and a pole ear 7 is set directly above the cathode graphite plate 311. The carbon-based flow electrode is embedded in the graphite plate 31 and circulated, which can effectively promote transmembrane charge / ion penetration. The positive and negative poles of the DC power supply are respectively clamped to the pole ears 7 on both sides with metal to apply an electric field.

[0039] The first support plate 1 and the second support plate 4 are each provided with eight flow electrode inlets and four seawater inlets. Four symmetrical flow electrode inlets and outlets 8 are positioned between each anode graphite plate 312 and cathode graphite plate 311, and a seawater inlet and outlet 9 is positioned in the middle of each of the four sides. The flow electrode inlets and outlets 8 and seawater inlets and outlets 9 are also positioned within the solution chamber 22, sealing gasket 51, buffer gasket 52, anion exchange membrane 21, and cation exchange membrane 23.

[0040] The solution chamber 22 is a rubber cushion measuring 220 mm x 220 mm x 3 mm. The center of the chamber 22 includes four solution passageways measuring 78 mm x 73 mm x 3 mm. Each of these small sections is symmetrically configured with a water inlet and outlet. The flow electrodes are fed in from the top and discharged from the bottom, while the seawater is fed in from the bottom and discharged from the top. This ensures sufficient contact between the solutions, improves desalination efficiency, and reduces the possibility of leakage.

[0041] The solution chamber 22, the sealing gasket 51 and the buffer gasket 52 are provided with tabs in the middle of the four sides. The two sides in contact with the tabs of the graphite plate are meshed with pure copper rods, and the two sides of the graphite plate without tabs are meshed with organic glass rods.

[0042] Four circular grooves are provided on the upper side of the first support plate for fixing the positions of the copper rod and the organic glass rod. The second support plate is provided with four through holes for fixing the positions of the copper rod and the organic glass rod. Grooves are provided in the first support plate 1 and the second support plate 4 for placing the control plate 6, the waterproof buffer layer 5, the graphite plate 31, and the salt separation component 2. A circle of threaded holes is provided around the first support plate 1 and the second support plate 4, respectively. The number of threaded holes on the surface of each component is 24. Threaded rods are engaged and installed in the threaded holes. The threaded rods pass through the threaded holes and extend into the device to connect with the second support plate 4, so that the above components are fixedly connected. Four insulating bases are also provided at the bottom of the first support plate to support the entire device and provide installation space for the bottom support plate joint pipe connection.

[0043] Four insulating rubber buffer columns are installed between the second support plate of the third FCDI unit 12 and the first support plate of the second FCDI unit 11, and between the second support plate of the second FCDI unit 11 and the first support plate of the first FCDI unit 12, respectively. These provide space for connecting the joint pipes between the FCDI units. The first and second support plates 1 and 4 are surrounded by through-holes for mounting bolts. The threaded rods of the bolts extend through the through-holes of the first support plate 1 to connect to the second support plate 4 inside the FCDI unit, where they are fastened with nuts to prevent leakage.

[0044] Before assembling the device, the anion exchange membrane 21 and the cation exchange membrane 23 were soaked in 0.5 M NaCl solution for at least 24 h. The flow electrodes and feed solution flowed through the assembled FCDI unit in a bottom-in and top-out manner at the same flow rate, such as 30 ml min -1 Loop through its corresponding receiving collector.

[0045] The key equipment required for the system operation is as follows: DC power supply, pH / conductivity multi-parameter tabletop meter, four-channel peristaltic pump and magnetic stirrer. Taking the actual seawater collected from Shenzhen Dapeng Bay, Zhuhai Qi'ao Island and Guishan Island as an example, the concentration of seawater is about 35g L -1 , the solution volume is not less than 5L.

[0046] The flow electrodes and seawater flow through the assembled FCDI unit in the upper inlet and lower outlet and lower inlet and upper outlet modes, respectively, at the same flow rate of 30 ml min -1 After the system was stable for 10 minutes, voltages of 1.6 V, 2.4 V, and 3.0 V were applied to the three FCDI units for 30 minutes, respectively.

[0047] In the same FCDI unit, the flow electrodes have two flow patterns. The first is flowing in from the cathode graphite plate 311 at the bottom of the device, then passing through the first solution chamber 22, the anode graphite plate 312, the second solution chamber 22 from bottom to top, entering the cathode graphite plate 311, and finally passing through the third solution chamber 22 and the anode graphite plate 312 to exit the unit. The other is flowing downward from the second salt separation component 2, passing through the cathode graphite plate 311 in the middle of the device, the second solution chamber 22, the anode graphite plate 312, the first solution chamber 22, entering the cathode graphite plate 311, and finally exiting the unit through the support plate 1. The flow electrodes with two different flow patterns are mixed in a pre-placed energy recovery device to achieve energy recovery. The mixed flow electrodes flow into the solution buffer tank, and then into the next level of flow electrodes, repeating the above flow pattern.

[0048] The seawater solution flows from the support plate into the solution chamber 22, where it is desalinated by the flow electrodes, voltage, and ion exchange membranes. This process repeats through the three solution chambers 22 before exiting the unit and entering a pre-placed seawater buffer tank, where it enters the next unit. During the experiment, the FCDI unit's current response, along with the seawater's pH and conductivity, was recorded at one-minute intervals using the accompanying software. The NaCl concentration in the seawater was then determined using the conductivity-concentration relationship.

[0049] The multi-stage seawater desalination device using flow electrode capacitive deionization (FCDI) disclosed in the present invention has a desalination rate of 95%. The salt removal rate can still be improved by optimizing the seawater treatment capacity per unit membrane area.

[0050] Example 2

[0051] The mobile electrode capacitive deionization seawater desalination device of the present invention can also be combined with a seawater pretreatment device, a pretreated seawater storage tank, a mobile electrode and a seawater pumping device, a mobile electrode and a seawater property monitoring device, a multi-channel power supply device, an energy recovery device, a mobile electrode storage tank, a mobile electrode buffer tank, a mobile electrode regeneration tank, a graded treatment seawater buffer tank, and a desalinated water storage tank to form a graded electric field driven mobile electrode seawater desalination system.

[0052] The energy recovery device includes a support plate, a waterproof cushioning layer, a current collecting plate, and an ion exchange membrane. Its structure and materials are consistent with those of the mobile electrode capacitive deionization desalination device. The energy recovery device is used to compensate for the high voltage applied by the first FCDI unit 10, thereby reducing the high energy consumption caused by the application of higher voltage. A buffer tank is installed between the FCDI units to monitor the treatment process online and prevent excessive hydrostatic pressure accumulation within the device due to the long flow path of seawater and the mobile electrode, thereby preventing leakage. Finally, a mobile electrode regeneration tank is installed to maintain the mobile electrode's salt component acceptance capacity, allowing the device to operate continuously.

[0053] The above specific implementation manner is a preferred embodiment of the present invention and does not limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A graded electric field driven flow electrode capacitive deionization (FCDI) seawater desalination method, characterized in that: The invention comprises a first FCDI unit (10), a second FCDI unit (11) and a third FCDI unit (12), wherein the three FCDI units are assembled in series and three levels of electric field strength are sequentially applied from low to high; each FCDI unit is assembled in a combined symmetrical manner and the three units have the same structure; The electric field strength is within the maximum voltage or current allowed in the ohmic region of the FCDI unit; Each FCDI unit comprises a first support plate (1), a salt separation assembly (2), a current collecting plate (3) and a second support plate (4), wherein the current collecting plate (3) is located between the first support plate (1) and the second support plate (4), and the salt separation assembly (2) is located between two adjacent current collecting plates (3); The electric field strength of the first FCDI unit (10) does not exceed 1.6 V, the electric field strength of the second FCDI unit (11) does not exceed 2.4 V, and the electric field strength of the third FCDI unit (12) does not exceed 3.2 V; The salt separation component (2) comprises an anion exchange membrane (21), a solution chamber (22) and a cation exchange membrane (23), wherein the solution chamber (22) is located between the anion exchange membrane (21) and the cation exchange membrane (23), and the ends of the anion exchange membrane (21) and the cation exchange membrane (23) away from the solution chamber (22) are respectively connected to the current collecting plate (3); The current collecting plate (3) comprises a graphite plate (31) and a flow electrode channel (32), wherein the flow electrode channel (32) is distributed as a plurality of repeating units on the graphite plate (31); the graphite plate (31) comprises a cathode graphite plate (311) and an anode graphite plate (312), wherein the anode graphite plate (312) is connected to the solution chamber (22) via the anion exchange membrane (21), and the cathode graphite plate (311) is connected to the solution chamber (22) via the cation exchange membrane (23).

2. The hierarchical electric field driven flow electrode capacitive deionization (FCDI) seawater desalination method according to claim 1, characterized in that: The salt separation component (2) is at least one.

3. The hierarchical electric field driven flow electrode capacitive deionization (FCDI) seawater desalination method according to claim 1, characterized in that: The shape of the flow electrode channel (32) includes one of a serpentine shape, a rotating square shape or a rotating circle shape.

4. The hierarchical electric field driven flow electrode capacitive deionization (FCDI) seawater desalination method according to claim 1, characterized in that: Each FCDI unit further comprises a waterproof buffer layer (5), wherein the waterproof buffer layer (5) is symmetrically arranged, and comprises a sealing gasket (51) and a buffer gasket (52), wherein one end of the sealing gasket (51) is connected to the cathode graphite plate (311) or the anode graphite plate (312), and the other end of the sealing gasket (51) is connected to the buffer gasket (52), and one end of the buffer gasket (52) is connected to the first support plate (1) or the second support plate (4).

5. The hierarchical electric field driven flow electrode capacitive deionization (FCDI) seawater desalination method according to claim 4, characterized in that: The first support plate (1), the second support plate (4), the cathode graphite plate (311), the anode graphite plate (312), the sealing gasket (51), the buffer gasket (52), the anion exchange membrane (21), and the cation exchange membrane (23) are respectively provided with a flow electrode inlet and outlet (8) and a seawater inlet and outlet (9); and the cathode graphite plate (311), the anode graphite plate (312), the sealing gasket (51), the buffer gasket (52), and the solution chamber (22) are respectively provided with a pole lug (7).

6. The hierarchical electric field driven flow electrode capacitive deionization (FCDI) seawater desalination method according to claim 4, characterized in that: Each FCDI unit further comprises a position control plate (6), one end of the position control plate (6) is connected to the sealing gasket (51), and the other end of the position control plate (6) is connected to the second support plate (4) via the buffer gasket (52).

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