CN110510712B - Electrodialysis system and method for desalting brackish water - Google Patents

Abstract

The invention provides an electrodialysis system and method for desalting bitter water, which comprises an electrodialysis membrane stack system, a raw water pump, a raw water tank, an electrode liquid pump, an electrode liquid tank and a direct-current stabilized power supply, wherein the electrodialysis membrane stack system comprisesThe device comprises a plurality of sectional type electrodialysis membrane stacks, a cathode chamber and an anode chamber, wherein the electrodialysis membrane stacks are sequentially connected, a cathode and a cation exchange membrane are arranged between the anode chamber and the cathode chamber, the anode chamber is provided with a concentrated water inlet, a fresh water inlet, an anolyte water inlet and an anolyte water outlet, and the cathode chamber is provided with a first water outlet, a second water outlet, a catholyte water inlet and a catholyte water outlet; the electrodialysis membrane stack is provided with a direct current stabilized voltage power supply. Aiming at typical brackish water, the system and the method provided by the invention can be not higher than 0.8kWh/m³The method provided by the invention optimizes the brackish water desalination process, and achieves the purposes of energy reduction and consumption reduction by adjusting voltage and current.

Description

An electrodialysis system and method for desalination of brackish water

technical field

The invention belongs to the field of water treatment, in particular to a high-efficiency and energy-saving electrodialysis system and method for desalination of brackish water.

Background technique

Electrodialysis is a technology that combines electrochemical process and dialysis diffusion process, rather than a differential pressure filtration process. Therefore, electrodialysis technology has relatively strong anti-pollution ability and relatively low requirements on raw water quality. Concentrated, high salinity water. Electrodialysis technology is widely used in concentrated salt production due to its advantages of small footprint, low investment and easy automation. It has also achieved good results in the fields of water production, industrial wastewater treatment and chemical industry.

Electrodialysis is often used for desalination of low-concentration brackish water. In China, a multi-stage continuous desalination process is often used, and constant voltage operation is used. Requirements, continuous effluent, high desalination rate, stable operation, but small operation flexibility, poor adaptability when the salt content of feed water changes.

In the existing electrodialysis desalination technology, there are the following common defects: (1) The middle electrode of the multi-stage electrodialysis system is mostly a common electrode, and the voltage and current of each stage cannot be adjusted independently. On the other hand, its concentration decreases step by step. When the voltages at all levels are equal, the voltage of the latter part of the electrodialysis stage is too large, resulting in unnecessary energy consumption; The linear flow velocity in the single compartment of the pre- and post-stage, pre- and post-electrodialysis stages is made equal, but the concentration of desalinated water in the latter stage or the latter stage is lower than that of the previous stage or the former stage, so the limiting current density of the next stage is Compared with the former, polarization is easy to occur in the fresh water chamber, and the current efficiency decreases; (3) In the process of conventional brackish water electrodialysis, the solution resistance of the electrode chamber still occupies a certain proportion, so a considerable amount of energy consumption of the electrode chamber will be generated.

Therefore, it is urgent to develop a new energy-saving electrodialysis desalination system and method, which can adjust the voltage and current at all levels, and minimize the energy consumption of the body on the premise of achieving the target water quality.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the existing electrodialysis desalination technology, provide an energy-saving multistage and multistage electrodialysis continuous desalination system, and solve the low desalination efficiency that reverse osmosis and conventional electrodialysis technologies exist in the process of desalination of brackish water. , high energy consumption, long-term operation stability still needs to be improved and other issues, to promote energy reduction and consumption reduction in the application of brackish water electrodialysis desalination.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is: including an electrodialysis membrane stack system, a raw water pump, a raw water tank, an electrode pump, an electrode tank and a DC voltage stabilized power supply, and the electrodialysis membrane stack system is a plurality of The segmented electrodialysis membrane stacks are sequentially connected to form, an anode chamber and a cathode chamber are arranged on the electrodialysis membrane stack, anion and cation exchange membranes are arranged between the anode chamber and the cathode chamber, and the anode chamber is arranged with a concentrated Water inlet, fresh water inlet, anolyte water inlet and anolyte water outlet, the cathode chamber is provided with a first water outlet, a second water outlet, a catholyte water inlet and a catholyte water outlet; the outlet of the original water tank The water is divided into two water flows, namely the first effluent and the second effluent. The first effluent and the second effluent are respectively connected to the concentrated water inlet and the fresh water inlet in the electrodialysis membrane stack system. The water outlet is connected to the external discharge pipeline, and the second water outlet is connected to the water user pipeline; the water outlet of the eletrolyte tank is divided into two pole liquid flows, which are respectively anolyte and catholyte, and the anolyte and catholyte pass through the pole liquid. The pipes are respectively connected to the anolyte water inlet and the catholyte water inlet, and the catholyte water outlet and the anolyte water outlet are connected to the anolyte tank through the pipes; the electrodialysis membrane stack is equipped with a DC stabilized power supply.

Further, the electrode chamber of the electrodialysis membrane stack is made of a resin-packed bed type ultra-thin electrode plate frame; the resin-packed bed type ultra-thin electrode plate frame includes a resin-packed bed ultra-thin anode plate frame and a resin-packed bed ultra-thin electrode plate frame. Thin cathode plate frame, the anode chamber and cathode chamber are respectively made of resin packed bed ultra-thin anode plate frame and resin packed bed ultra-thin cathode plate frame; the resin packed bed ultra-thin anode plate frame and resin packed bed ultra-thin plate frame The cathode plate frame includes an electrode plate and a pole frame, the resin packed bed type ultra-thin electrode plate frame has a thickness of 1-3mm, and the electrode plate and the pole frame are filled with a strong acid and strong alkali mixture with a volume ratio of 1:1. Bed anion and cation exchange resin.

Further, the electrodialysis membrane stack system is formed by sequentially connecting three segmented electrodialysis membrane stacks, which are the first-stage electrodialysis membrane stack, the second-stage electrodialysis membrane stack, and the third-stage electrodialysis membrane stack; Wherein, the thickness of the electrode plate frame in the first-stage electrodialysis membrane stack is 1-3mm; the thickness of the electrode plate frame in the second-stage electrodialysis membrane stack is 1-3mm; the third-stage electrodialysis membrane The electrode plate frame thickness in the stack is 1-3mm.

Further, the electrodialysis membrane stack is designed by using the asymmetric membrane logarithm between stages, and the asymmetric membrane logarithm between the stages includes the asymmetric membrane logarithm between the stages and the asymmetric membrane logarithm between each stage. Logarithm: the membrane stacks of each stage are designed with the asymmetric membrane logarithm between the stages, wherein each stage of the membrane stack unit adopts different membrane pairs, and the total membrane logarithm is calculated as 360 pairs.

Further, the number of membrane pairs in the first-stage electrodialysis membrane stack is 120-160 pairs; the number of membrane pairs in the second-stage electrodialysis membrane stack is 100-140 pairs; the third-stage electrodialysis membrane stack The number of membrane pairs in the membrane stack is 80-120 pairs.

Further, in the electrodialysis membrane stacks of all levels designed with asymmetric membrane logarithms among the sections, each level of electrodialysis membrane stacks is provided with a reversing separator, and the membrane before the reversing separator is The logarithm is more than the film logarithm after the commutation separator; and the ratio of the film logarithm on both sides of the commutation separator is between 1-1.3.

Further, the membrane stacks at all levels are connected by non-common electrodes, and each level of the electrodialysis membrane stack is equipped with a DC voltage stabilized power supply; the first-stage electrodialysis membrane stack, the second-stage electrodialysis membrane stack and the The third-stage electrodialysis membrane stack is respectively connected to the first-stage DC regulated power supply, the second-stage DC regulated power supply and the third-stage DC regulated power supply; the cathode plate of the first-stage electrodialysis membrane stack is connected to the second-stage power supply. An insulating plate with a thickness of 3, 5, 7, 9 or 10 mm is arranged between the anode plates of the dialysis membrane stack; between the cathode plate of the second-stage electrodialysis membrane stack and the anode plate of the third-stage electrodialysis membrane stack An insulating plate with a thickness of 3, 5, 7, 9 or 10 mm is provided.

A high-efficiency and energy-saving electrodialysis method for desalination of brackish water, the method adopts the means of co-current flow of yin and yang electrode liquids and counter-current of concentrated fresh water, and is integrated and optimized through a multi-stage and multi-stage system that is independently adjustable at all levels, forming a solution for brackish and brackish water. Continuous energy-saving electrodialysis technology for water desalination; the cathode and anode electrode liquids flow in parallel and the cathode and anode liquids of each stage are transported to the cathode and anode chambers respectively, so as not to flow in series with each other; The water inlets are located on both sides of the respective membrane stacks, so that the liquid flow in the concentrated chamber and the liquid flow in the thin chamber of the membrane stacks flow in opposite directions. The specific implementation steps are as follows:

Step 1: Turn on the electrolyte pump, then the electrode solution in the electrolyte tank is transported to the cathode chamber and the anode chamber of the electrodialysis membrane stack of each stage respectively through the electrolyte pump, and the electrode solution is stored in each stage. After the confluence at the exit of the pole chamber, it is circulated to the pole liquid tank;

Step 2: Turn on the raw water pump, then the raw water in the raw water tank is two water outflow water, and is transported to the concentrated water inlet and the fresh water inlet through the raw water pump respectively, and then enters the first-stage electrodialysis membrane stack to flow; During the flow process, the concentrated water enters the concentrated water inlet of the next-stage electrodialysis membrane stack from the first water outlet of the previous-stage electrodialysis membrane stack and continues to flow in the next-stage electrodialysis membrane stack. The fresh water enters the fresh water inlet of the next-stage electrodialysis membrane stack from the second water outlet of the upper-stage electrodialysis membrane stack and continues to flow in the next-stage electrodialysis membrane stack. Flow from top to bottom, fresh water flows from bottom to top, through the action of reversing baffles, the second stage of concentrated water flows from bottom to top, and fresh water flows from top to bottom; the last stage of electrodialysis The concentrated water of the membrane stack, that is, the third-stage electrodialysis membrane stack, is discharged from the equipment through the first water outlet, and the fresh water is connected to the water users through the pipeline through the second water outlet;

Step 3: During the operation of Step 2, adjust the voltage and current of the DC voltage stabilized power supply connected to each stage of the electrodialysis membrane stack to achieve independent adjustment of the voltage and current of the electrodialysis membrane stack at each stage, thereby further reducing the operating time. Body energy consumption.

The advantages and positive effects that the present invention has are:

1. The present invention adopts non-common electrode connection, the electrodialysis membrane stack of each stage is controlled by a DC voltage stabilized power supply, and its voltage and current can be adjusted at any time according to the concentration change of the raw material solution of each stage. Under the condition of ensuring a certain range of desalination rate, the energy consumption of the desalination system can be further reduced.

2. For the electrodialysis membrane stacks at all levels provided by the present invention, the thickness of the electrode chamber is not more than 3mm, the difficulty of moulding is small, and it is easy for large-scale industrial production; the asymmetric membrane logarithm design between each section can improve the membrane surface of the concentration chamber of the next section. The flow rate can be reduced, thereby reducing the concentration diffusion and concentration polarization in the latter stage, thereby reducing the operating energy consumption of the entire membrane stack; the water quality of the entire energy-saving electrodialysis desalination system can be adjusted flexibly, the operation is simple and convenient, and the operation stability is high.

3. The electrodialysis system for desalination of brackish water proposed by the present invention can continuously produce desalinated water with an energy consumption of not more than 0.8kWh/ ^m3 , and the quality of desalinated water can be adjusted dynamically (TDS is between 132-241mg/L). ).

Description of drawings

1 is a schematic structural diagram of an electrodialysis membrane stack system in an electrodialysis system and method for desalination of brackish water according to the present invention;

Fig. 2 is a kind of method experiment flow chart of the present invention for the electrodialysis system and method for desalination of brackish water;

In the picture: 1- Resin packed bed ultra-thin anode plate frame, 2- Anion and cation exchange membrane, 3- Reversing separator, 4- Resin packed bed ultra-thin cathode plate frame, 5- Insulation plate, 6- First stage Electrodialysis membrane stack, 7-second-stage electrodialysis membrane stack, 8-third-pole electrodialysis membrane stack, 9-raw water tank, 10-concentrated water inlet, 11-fresh water inlet, 13-first-stage DC stabilizer Piezoelectric power supply, 14-second-stage DC stabilized power supply, 15-third-stage DC stabilized power supply, 16-anolyte water inlet, 17-catholyte water inlet, 18-anolyte water outlet, 19-catholyte water outlet , 20- the first water outlet, 21- the second water outlet, 22- pole liquid tank, 23- pole liquid pump, 24- original water pump.

Detailed ways

The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in Figure 1 and Figure 2, an electrodialysis system for desalination of brackish water includes an electrodialysis membrane stack system, a raw water pump 24, a raw water tank 9, an electrode pump 23, an electrode tank 22 and a DC voltage stabilizer The power supply is characterized in that the electrodialysis membrane stack system is formed by connecting a plurality of segmented electrodialysis membrane stacks in sequence, an anode chamber and a cathode chamber are arranged on the electrodialysis membrane stack, and the anode chamber and the cathode chamber are connected to each other. Anion and cation exchange membranes 2 are arranged between them, the anode chamber is provided with a concentrated water inlet 10, a fresh water inlet 11, an anolyte water inlet 16 and an anolyte water outlet 18, and the cathode chamber is provided with a first water outlet 20 , the second water outlet 21, the catholyte water inlet 17 and the catholyte water outlet 19; the water outlet of the original water tank 9 is two water streams, respectively the first water outlet and the second water outlet, the first water outlet and the second water outlet The effluent is respectively connected to the concentrated water inlet 10 and the fresh water inlet 11 in the electrodialysis membrane stack system, the first water outlet 20 is connected to the external drainage pipeline, and the second water outlet 21 is connected to the water user pipeline; the The effluent of the electrode tank 22 is divided into two polar streams, which are anolyte and catholyte respectively, and the anolyte and catholyte are respectively connected to the anolyte water inlet 16 and the catholyte water inlet 17 through the polar liquid pipeline. The liquid water outlet 19 and the anolyte water outlet 18 are connected to the electrode tank 22 through pipes; the electrodialysis membrane stack is equipped with a DC stabilized power supply. The cathode and anolyte in the electrode tank 22 are respectively transported to the cathode and anode chambers through the pipeline under the action of the electrode pump 23 . It is transported into the anode chamber through the concentrated water inlet 10 and the fresh water inlet 11 respectively.

Further, the electrode chamber of the electrodialysis membrane stack is made of a resin-packed bed type ultra-thin electrode plate frame; the resin-packed bed type ultra-thin electrode plate frame includes a resin-packed bed ultra-thin anode plate frame 1 and a resin-packed bed type ultra-thin electrode plate frame. Ultra-thin cathode plate frame 4, the anode chamber and cathode chamber are respectively made of resin-packed bed ultra-thin anode plate frame 1 and resin-packed bed ultra-thin cathode plate frame 4; the resin-packed bed ultra-thin anode plate frame 1 and The resin-packed bed ultra-thin cathode plate frame 4 includes an electrode plate and a pole frame, the resin-packed bed type ultra-thin electrode plate frame has a thickness of 1-3 mm, and is filled with a volume ratio of 1:1 between the electrode plate and the pole frame. Strong acid and strong base mixed bed anion and cation exchange resin. The anolyte water inlet 16, the anolyte water outlet 18, the catholyte water inlet 17 and the catholyte water outlet 19 are all provided with water replenishment grooves with a water replenishment gap width of 0.1/0.2/0.3/0.4 or 0.5mm, and adjacent to the water replenishment tank. The pitch of the gap is 2.0/2.2/2.4/2.6/2.8 or 3.0mm, and the electrode plate is 1.0/2.0 or 3.0mm lower than the pole frame to facilitate resin filling.

Further, the electrodialysis membrane stack system is formed by connecting three segmented electrodialysis membrane stacks in sequence, which are the first-stage electrodialysis membrane stack 6, the second-stage electrodialysis membrane stack 7 and the third-stage electrodialysis membrane stack respectively. Stack 8; wherein, the thickness of the electrode plate frame in the first-stage electrodialysis membrane stack 6 is 1-3 mm; the thickness of the electrode plate frame in the second-stage electrodialysis membrane stack 7 is 1-3 mm; The thickness of the electrode plate frame in the three-stage electrodialysis membrane stack 8 is 1-3 mm.

Further, the electrodialysis membrane stack is designed by using the asymmetric membrane logarithm between stages, and the asymmetric membrane logarithm between the stages includes the asymmetric membrane logarithm between the stages and the asymmetric membrane logarithm between each stage. logarithm; the membrane stacks at all levels of the inter-stage asymmetric membrane logarithm design, wherein each stage membrane stack unit adopts a different membrane logarithm, and the total membrane logarithm is counted as 360 pairs; the first-stage electrodialysis The number of membrane pairs in the membrane stack 6 is 120-160 pairs; the number of membrane pairs in the second-stage electrodialysis membrane stack 7 is 100-140 pairs; the number of membrane pairs in the third-stage electrodialysis membrane stack 8 For 80-120 pairs.

Further, in the electrodialysis membrane stacks at all levels of the asymmetric membrane logarithm design between the sections, each level of the electrodialysis membrane stacks is provided with a reversing separator 3 , before the reversing separator 3 . The number of film pairs of 3 is more than the number of film pairs after the reversing separator; and the ratio of the film pairs on both sides of the reversing separator 3 is between 1-1.3.

Further, the membrane stacks at all levels are connected by non-common electrodes, and each stage of the electrodialysis membrane stack is equipped with a DC voltage stabilized power supply; the first-stage electrodialysis membrane stack 6 and the second-stage electrodialysis membrane The stack 7 and the third-stage electrodialysis membrane stack 8 are respectively connected to the first-stage DC power supply 13, the second-stage DC power supply 14 and the third-stage DC power supply 15; the first-stage electrodialysis membrane stack 6 An insulating plate 5 with a thickness of 3, 5, 7, 9 or 10 mm is arranged between the cathode plate of the second-stage electrodialysis membrane stack 7 and the anode plate of the second-stage electrodialysis membrane stack 7; An insulating plate 5 with a thickness of 3, 5, 7, 9 or 10 mm is arranged between the anode plates of the three-stage electrodialysis membrane stack 8 .

A high-efficiency and energy-saving electrodialysis method for desalination of brackish water, the method adopts the means of co-current flow of yin and yang electrode liquids and counter-current of concentrated fresh water, and is integrated and optimized through a multi-stage and multi-stage system that is independently adjustable at all levels, forming a solution for brackish and brackish water. Continuous energy-saving electrodialysis technology for water desalination; the cathode and anode electrode liquids flow in parallel and the cathode and anode liquids of each stage are transported to the cathode and anode chambers respectively, so as not to flow in series with each other; The water inlets are located on both sides of the respective membrane stacks, so that the liquid flow in the concentrated chamber and the liquid flow in the thin chamber of the membrane stacks flow in opposite directions. The specific implementation steps are as follows:

Step 1: Turn on the electrolyte pump 23, then the electrode solution in the electrolyte tank 22 is transported to the cathode chamber and the anode chamber of each stage of the electrodialysis membrane stack respectively through the electrolyte pump 23, and the electrode solution is stored in the anolyte chamber. The outlet of each pole chamber is confluent and circulated to the pole liquid tank 22;

Step 2: Turn on the raw water pump 24, then the raw water in the raw water tank 9 is divided into two outflow waters, which are respectively transported to the concentrated water inlet 10 and the fresh water inlet 11 through the raw water pump 24, and then enter the first-stage electrodialysis membrane stack. 6 to flow; during the flow, the concentrated water enters the concentrated water inlet 10 of the next-stage electrodialysis membrane stack from the first water outlet 20 of the electrodialysis membrane stack of the previous stage and continues to flow in the electrodialysis membrane of the next stage. The fresh water flows in the stack, and the fresh water enters the fresh water inlet 11 of the next-stage electrodialysis membrane stack from the second water outlet 21 of the upper-stage electrodialysis membrane stack and continues to flow in the next-stage electrodialysis membrane stack. The concentrated water of the first section of the membrane stack flows from top to bottom, and the fresh water flows from the bottom to the top. Through the action of the reversing diaphragm, the concentrated water of the second section of the membrane stack of each level flows from the bottom to the top, and the fresh water flows from the top to the bottom. ; The concentrated water of the electrodialysis membrane stack described in the last stage, namely the third-stage electrodialysis membrane stack 8, is discharged from the equipment through the first water outlet 20, and the fresh water is connected to the water users through the pipeline through the second water outlet 21;

Step 3: During the operation of Step 2, adjust the voltage and current of the DC voltage stabilized power supply connected to each stage of the electrodialysis membrane stack to achieve independent adjustment of the voltage and current of the electrodialysis membrane stack at each stage, thereby further reducing the operating time. Body energy consumption.

The following is an experiment of desalination of seawater nanofiltration water with typical brackish water quality using the electrodialysis system described above:

Example 1:

Among them, the thickness of the reversing separator 3 in the electrodialysis membrane stack is 0.9mm, the electrode plate is 3mm lower than the pole frame, the width of the water distribution tank is 6mm, the width of the water replenishment gap is 0.3mm, and the spacing between adjacent water replenishment gaps is 2.6 mm. mm; fully mix the anion and cation exchange resins according to the volume ratio of 1:1, and fill them into the electrode chamber in a wet state, and the thickness of the electrode chamber is 3mm; the membrane area of the ion exchange membrane is 400*800mm, and the effective membrane area is 340*620mm; The number of membrane pairs of the electrodialysis system is 360 pairs in total, and the number of membrane pairs of the three-stage electrodialysis membrane stack is set to 140 pairs, 120 pairs and 100 pairs in turn. The specific operating parameters and the water quality of the incoming and outgoing water are shown in Table 1 below:

Table 1 Operational parameters of embodiment 1 and water quality of inlet and outlet water 1

Specifically, in this embodiment, the water produced by electrodialysis is 18L/min, that is, 1.08t/h, the electrical conductivity of the produced water is as low as 187 μS/cm, the TDS is as low as 132.6 mg/L, and the desalination rate is above 95%. The electricity consumption per ton of water is 0.759KWh/m ³ .

On the basis of Example 1, by adjusting the voltages or currents at all levels, Example 2 can be obtained, and its specific operating parameters and the water quality of the incoming and outgoing water are shown in Table 2 below:

Example 2

The operating parameters of table 2 embodiment 2 and inlet and outlet water quality 2

In this test, by appropriately reducing the working voltage and current of the electrodialysis desalination system at all levels, the freshwater conductivity is 410 μS/cm, the TDS is 241 mg/L, the desalination rate can still reach more than 90%, and the power consumption per ton of water is reduced to 0.52 KWh/m ³ ; compared with Example 1, the water flow rate and pressure of Example 2 are the same, and the conductivity of the influent water is the same. Only by properly adjusting the voltage and current of the electrodialysis membrane stacks at all levels, the salt rejection rate can still reach 90 % or more, and compared with the power consumption per ton of water in Example 1, it saves 0.25KWh/m ³ .

Obviously, by reasonably adjusting the voltage and current of the electrodialysis membrane stacks at all levels, the energy consumption of the desalination system can be further reduced under the condition of ensuring a certain range of desalination rates.

The electrodialysis membrane stack at all levels provided by the present invention has the thickness of the electrode chamber not more than 3 mm, the difficulty of moulding is small, and the large-scale industrial production is easy; High stability.

Through the operation and comparison of the above embodiments, the present invention can achieve the following beneficial effects:

1. The present invention adopts non-common electrode connection, the electrodialysis membrane stack of each stage is controlled by a DC voltage stabilized power supply, and its voltage and current can be adjusted at any time according to the concentration change of the raw material solution of each stage. Under the condition of ensuring a certain range of desalination rate, the energy consumption of the desalination system can be further reduced.

2. For the electrodialysis membrane stacks at all levels provided by the present invention, the thickness of the electrode chamber is not more than 3mm, the difficulty of moulding is small, and it is easy for large-scale industrial production; the asymmetric membrane logarithm design between each section can improve the membrane surface of the concentration chamber of the next section. The flow rate can be reduced, thereby reducing the concentration diffusion and concentration polarization in the latter stage, thereby reducing the operating energy consumption of the entire membrane stack; the water quality of the entire energy-saving electrodialysis desalination system can be adjusted flexibly, the operation is simple and convenient, and the operation stability is high.

3. The electrodialysis system for desalination of brackish water proposed by the present invention can continuously produce desalinated water with an energy consumption of not more than 0.8kWh/ ^m3 , and the quality of desalinated water can be adjusted dynamically (TDS is between 132-241mg/L). ).

The two embodiments of the present invention have been described in detail above, but the above contents are only preferred embodiments of the present invention and cannot be considered as limiting the scope of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still belong to the scope of the patent of the present invention.

Claims (7)

1. An electrodialysis system for desalting brackish water comprises an electrodialysis membrane stack system, a raw water pump (24), a raw water tank (9), an electrode liquid pump (23), an electrode liquid tank (22) and a direct-current stabilized voltage power supply, and is characterized in that the electrodialysis membrane stack system is formed by sequentially connecting a plurality of sectional type electrodialysis membrane stacks, an anode chamber and a cathode chamber are arranged on the electrodialysis membrane stack, anion and cation exchange membranes (2) are arranged between the anode chamber and the cathode chamber, the anode chamber is provided with a concentrated water inlet (10), a fresh water inlet (11), an anolyte water inlet (16) and an anolyte water outlet (18), and the cathode chamber is provided with a first water outlet (20), a second water outlet (21), a catholyte water inlet (17) and a catholyte water outlet (19); the water outlet of the raw water tank (9) is divided into two water flows, namely a first water outlet and a second water outlet, wherein the first water outlet and the second water outlet are respectively connected to a concentrated water inlet (10) and a fresh water inlet (11) in the electrodialysis membrane stack system, the first water outlet (20) is connected with an external discharge pipeline, and the second water outlet (21) is connected with a water user pipeline; the water outlet of the anolyte tank (22) is divided into two anolyte flows, namely anolyte and catholyte, the anolyte and the catholyte are respectively connected to an anolyte water inlet (16) and a catholyte water inlet (17) through anolyte pipelines, and a catholyte water outlet (19) and an anolyte water outlet (18) are connected with the anolyte tank (22) through pipelines;

the electrodialysis membrane stack is designed by adopting inter-stage asymmetric membrane pairs, wherein the inter-stage asymmetric membrane pairs comprise inter-stage asymmetric membrane pairs and inter-stage asymmetric membrane pairs; each level of film stack of the interstage asymmetric film logarithm design, wherein each level of film stack unit adopts different film logarithms, and the total film logarithms are counted in 360 pairs;

and the membrane stacks are connected by a non-common electrode, and each electrodialysis membrane stack is provided with a direct current stabilized voltage supply.

2. Electrodialysis system for desalinating brackish water according to claim 1, characterized in that the polar compartments of the electrodialysis membrane stack are made of resin-packed bed type ultra thin electrode plate frames; the resin packed bed type ultrathin electrode plate frame comprises a resin packed bed ultrathin anode plate frame (1) and a resin packed bed ultrathin cathode plate frame (4), and the anode chamber and the cathode chamber are respectively made of the resin packed bed ultrathin anode plate frame (1) and the resin packed bed ultrathin cathode plate frame (4); the resin packed bed ultrathin anode plate frame (1) and the resin packed bed ultrathin cathode plate frame (4) both comprise an electrode plate and an electrode frame, the thickness of the resin packed bed type ultrathin electrode plate frame is 1-3mm, and strong-base strong-acid mixed bed anion-cation exchange resin with the volume ratio of 1:1 is filled between the electrode plate and the electrode frame.

3. Electrodialysis system for desalinating brackish water according to claim 2, characterized in that the electrodialysis membrane stack system is formed by three segmented electrodialysis membrane stacks connected in series, respectively a first electrodialysis membrane stack (6), a second electrodialysis membrane stack (7) and a third electrodialysis membrane stack (8); wherein the thickness of an electrode plate frame in the first-stage electrodialysis membrane stack (6) is 1-3 mm; the thickness of an electrode plate frame in the second-stage electrodialysis membrane stack (7) is 1-3 mm; the thickness of an electrode plate frame in the third-stage electrodialysis membrane stack (8) is 1-3 mm.

4. Electrodialysis system for desalinating brackish water according to claim 3, wherein the number of membrane pairs in the first electrodialysis membrane stack (6) is 120-160 pairs;

the number of membrane pairs in the second-stage electrodialysis membrane stack (7) is 100-140 pairs;

the number of membrane pairs in the third electrodialysis membrane stack (8) is 80-120.

5. Electrodialysis system for desalinating brackish water according to claim 3, wherein each electrodialysis membrane stack of the interstage asymmetric membrane pair design is provided with a reversing partition (3), and the number of membrane pairs before the reversing partition (3) is greater than the number of membrane pairs after the reversing partition; and the film log ratio of the two sides of the reversing partition plate (3) is between 1 and 1.3.

6. Electrodialysis system for desalinating brackish water according to claim 3, wherein the first (6), second (7) and third (8) electrodialysis membrane stacks are connected to a first (13), second (14) and third (15) regulated DC supply, respectively;

an insulating plate (5) with the thickness of 3, 5, 7, 9 or 10mm is arranged between the cathode plate of the first-stage electrodialysis membrane stack (6) and the anode plate of the second-stage electrodialysis membrane stack (7);

an insulating plate (5) with the thickness of 3, 5, 7, 9 or 10mm is arranged between the cathode plate of the second-stage electrodialysis membrane stack (7) and the anode plate of the third-stage electrodialysis membrane stack (8).

7. An efficient and energy-saving electrodialysis method for brackish water desalination, which uses the electrodialysis system for brackish water desalination as claimed in any one of claims 1 to 6, and is characterized in that the method adopts a co-current and counter-current method of cathode and anode liquid and a counter-current method of dense and fresh water, and forms a continuous type energy-saving electrodialysis technology facing brackish water desalination through integration and optimization of a multi-stage system with independently adjustable voltage of electrodialysis membrane stacks; the cathode and anode electrode solutions are in parallel flow and are respectively conveyed to the cathode and anode chambers of each stage, so that the cathode and anode solutions are not mutually connected in series; the concentrated fresh water flows reversely, concentrated fresh water inlets of the membrane stacks are positioned on two sides of the respective membrane stacks, so that the membrane stack concentrated chamber liquid flow and the membrane stack dilute chamber liquid flow in opposite directions, and the method comprises the following specific implementation steps:

step 1: when the polar liquid pump (23) is started, the electrode liquid in the polar liquid tank (22) is respectively conveyed to the cathode chamber and the anode chamber of each electrodialysis membrane stack through the polar liquid pump (23), and the electrode liquid is merged at the outlet of each polar chamber and then circulated to the polar liquid tank (22);

step 2: starting a raw water pump (24), dividing raw water in a raw water tank (9) into two branches of effluent, and respectively conveying the effluent to a concentrated water inlet (10) and a fresh water inlet (11) through the raw water pump (24) so as to enter a first-stage electrodialysis membrane stack (6) for flowing; in the flowing process, the concentrated water enters a concentrated water inlet (10) of a next-stage electrodialysis membrane stack from a first water outlet (20) of the previous-stage electrodialysis membrane stack and continuously flows in the next-stage electrodialysis membrane stack, the fresh water enters a fresh water inlet (11) of the next-stage electrodialysis membrane stack from a second water outlet (21) of the previous-stage electrodialysis membrane stack and continuously flows in the next-stage electrodialysis membrane stack, wherein the concentrated water at the front section of each-stage membrane stack flows from top to bottom, the fresh water flows from bottom to top, and the concentrated water at the second section of each-stage membrane stack flows from bottom to top and the fresh water flows from top to bottom under the action of a reversing partition plate; concentrated water of the last electrodialysis membrane stack, namely a third electrodialysis membrane stack (8), is discharged out of the equipment through a first water outlet (20), and fresh water is connected with a water user through a second water outlet (21) through a pipeline;

and step 3: in the operation process of the step 2, the voltage and the current of the direct-current stabilized voltage power supply connected with each stage of electrodialysis membrane stack are adjusted, so that the voltage and the current of each stage of electrodialysis membrane stack are independently adjusted, and the energy consumption of the operation body is further reduced.

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