First, the working principle

The basic principle of desalination in electrodialysis is to use the selective permeability of ion exchange membranes. The cation exchange membrane only allows the passage of anion, and under the action of an external DC electric field, the mat migrates in a directed manner. Most of the ions in the water migrated to the other ionized water. As shown in the figure: In the dilute chambers (2, 4 and 6), the anions and cations are transferred to the adjacent concentric chambers (rooms 1, 3 and 5). So as to achieve the purpose of desalination with salt water. month

Second, the scope of application

Electrodialysis device has the advantages of simple process, high salt removal rate, low water production cost, convenient operation, and no pollution to the environment. It is widely used in desalination of water, and its specific application is as follows:

Seawater and brackish water desalination, according to the experimental data of my unit, can dilute brackish water with a salt content of up to 60g/l to drinking water and solve the drinking water source in desert areas.

The preparation of soft water, (water resistivity of 105 ohm centimeters) can be used for low-pressure boiler feed water, without the need for salt regeneration can save about 20%.

The pretreatment of deep demineralized water and high-purity water adopts electrodialysis-ion exchange method to expand the scope of application of raw water, and is widely used in power, electronics, chemical industry, pharmaceuticals, scientific research and other occasions, reducing the cost of water production by more than 50%, and saving ion exchange. About 80% of acid and alkali is used for regeneration, and the regeneration cycle is extended by more than five times. The purification used in the beverage and food industry has improved the quality of beer and soft drinks and created conditions for creating high-quality brand products.

Electrodialysis can also be used for chemical separation, concentration and industrial wastewater treatment and recovery.

Third, the structure and assembly methods

1. Structure: Electrodialysis device consists of three parts: membrane stack, polar region and pressing device.

(1) Membrane Heap: It is a combination of a considerable number of membrane pairs.

Membrane pair: It consists of a cation exchange membrane, a partition A (or B) and a partition B (or A).

Ion Exchange Membrane: It is a key component of the electrodialysis machine. Our factory adopts a heterogeneous membrane produced by Shanghai Chemical Plant.

Separator: Concentrated, fresh water separator, alternately protected between the yin and yang membranes, maintain a certain gap between the anterior membrane and the osmium membrane, pass the flow of water along the plane of the separator, and pass current through the plane of the vertical separator. Partition thickness 0.9 mm

(2) The polar region includes the electrode, the pole frame, and the deflector.

Electrode: Used for connecting power supply, our factory adopts titanium coating.

Pole box: placed between the electrode and the membrane to prevent the membrane from sticking to the electrode and acting as a support.

(3) Compression device: It is used to compress the electrodialyzer so that the membrane stack, electrode and other components form a whole without leakage.

2. Assembly method: The assembly of the electrodialyzer is represented by “levels” and “segments”, and the membrane stack between a pair of electrodes is called “level 1”. Each film that flows in the same direction is called a "segment." Increasing the number of stages is equivalent to increasing the desalination process, that is, the assembly method can be adjusted according to the different requirements of freshwater production and effluent quality. There are generally the following types: one stage, one stage, multiple stages, multiple stages, and multiple stages.

Fourth, auxiliary equipment

Electrodialysis apparatus must be equipped with rectifiers, filters, pickling facilities, and water pump meters in addition to the body. For the convenience of users, our factory can provide a complete set of auxiliary equipment and instruments, and now we will list auxiliary equipment supporting with electrodialysis (Table 2).

Table 2 shows some points:

(1) This table applies to the salt content of raw water ≤ 800 mg/L. If the raw water salt content is 10,000 mg/L, the model of the rectifier shall be adjusted according to the salt content.

(2) DDS-IIA conductance meter is used for calculation of salt removal in electrodialyzer, and it is supplied with matching.

(3) When the concentrated water circulation system is used, a thick water tank and a water pump are required. The thick water tank may use a plastic water tank, and the volume thereof is equivalent to approximately 40% of the fresh water amount.

V. Precautions

1. The pretreatment of water is one of the factors that ensure the normal operation of the electrodialyzer. Therefore, the necessary pretreatment must be performed before the water enters the electrodialyzer to ensure that the quality of the raw water entering the electrodialyzer meets the following criteria.

A: Turbidity:> 3 mg/1 b: Total iron content: <0.3 mg/1; c: Total manganese content: <0.1 mg/1; d: Color <15 degrees; * Oxygen content : <3mg/1 (KMn04): f: water temperature: 5-40°C; g: pollution index: <7

2. Pay attention to the start-up, you must first pass the water, after the power, stop when the first power, after the water, non-stop water is not blackouts.

3. The ratio of fresh water flow to rich and polar water flow should be adjusted properly. To prevent the leakage of concentrated water, the pressure of concentrated water and polar water can be appropriately reduced, generally smaller than 0.2×9.38×104Pa.

4, depending on the water quality, the electrodialysis device should replace the electrode after working for 28 hours.

5. It is forbidden to place gold objects on the membrane stack to prevent short circuits.

6. The electrodialyzer is used in operation. Refer to the device manual for details.

Six, orders need to add

1. The order form must specify the specifications and specifications. If special specifications or other requirements are required, additional instructions must be provided.

2. If you need auxiliary equipment, please specify the requirements.

3. If the user needs the design of the factory, water pretreatment is one of the factors that ensure the normal operation of the electrodialyzer. Therefore, necessary pretreatment must be performed before the water enters the electrodialyzer to ensure that the quality of the raw water entering the electrodialyzer meets the following requirements. index.