First, multi-media filtering
The main task of this stage is to carry out coarse filtration of tap water to prepare for entering the reverse osmosis membrane to ensure a certain water quality before entering the reverse osmosis membrane to protect the use effect and service life of the reverse osmosis membrane. The process is to remove the tap water of the raw water tank through the fine sand, activated carbon and precision filter to remove impurities, organic matter, colloids, suspended matter, etc. in the water, and prevent the large particle impurities from entering the reverse osmosis membrane and blocking the reverse osmosis membrane. After coarse filtration, the water quality has been improved. And allow access to the next link.
Second, the first stage reverse osmosis
After the crude filtered water passes through the reverse osmosis membrane, it is a first-stage reverse osmosis, and the reverse osmosis membrane is a semi-permeable membrane, which can prevent large ions such as Ga2+, Mg2+, Fe-2, SO4-2, Cl-1, Na+ from passing through. To ensure the effect of reverse osmosis and to protect the reverse osmosis membrane, it is necessary to continuously add the scale inhibitor to the reverse osmosis vessel, and at the same time, the water temperature must be above 25 °C (the steam heat exchanger is used in winter) and a certain water pressure is guaranteed. Pump) Under a certain pressure, the ionized water is squeezed through the reverse osmosis membrane to form two kinds of water. The water that passes through the reverse osmosis membrane, that is, the finished water enters the next step, and the water that has not passed through the reverse osmosis membrane is discharged. After the first-stage reverse osmosis treatment, the water enters the next step--secondary reverse osmosis.
Third, two-stage reverse osmosis
The principle of two-stage reverse osmosis is the same as that of first-order reverse osmosis. Its function is to further remove salt in water, (Ga2+, Mg2+, Fe-2, SO4-2, Cl-1, Na+ plasma) to further improve water quality. After reverse osmosis, the water conductivity can be close to 1 MΩ.CM. After the first and second stage reverse osmosis pretreatment, the retained water becomes the feed water of EDI, and the water (concentrated water) that has not passed through the reverse osmosis membrane is discharged in time, and the ratio is generally 1:3, that is, one ton per production. For qualified water, drain about 3 tons of concentrated water (medium water).
Fourth, EDI (Electro deionization) processing
After the secondary reverse osmosis water is stored in the intermediate tank, more than 99% of the ions have been removed, but in order to further improve the water quality, ultrapure water is produced, and trace elements and CO2 dissolved in water must be removed. Dialysis, ie, EDI treatment, the principle is as follows, EDI is continuous electric desalting, which uses mixed ion exchange resin to adsorb anion and cation in water, and these adsorbed ions are exchanged by anion and cation under the action of DC voltage. The process of removing the film. In this process, the ion exchange resin is continuously regenerated by electricity, so that it is not required to be regenerated by using an acid or a base. This technology can replace the traditional ion exchange device to produce ultrapure water with a resistivity of up to 18MΩ.CM. This process technology is known as the revolution in the water treatment industry. Compared with traditional ion exchange, EDI has the following advantages: EDI does not require chemical regeneration; EDI does not require downtime during regeneration; provides stable water quality; low energy consumption; easy operation, low labor intensity;
(1) EDI water treatment
Feedwater pretreatment is important for EDI. The life, performance and maintenance of components depend on the amount of impurities in the feed water. If the pretreated water is supplied to EDI, the cleaning rate of the components will be reduced. The EDI concentrated water is partially recycled (when the water supply is low in hardness and conductivity, it may not circulate), and the other part may be returned to the reverse osmosis feed water, or it may be recycled for other purposes or discharged directly to the sewer.
(II) EDI component structure
1. Fresh water chamber: The ion exchange resin is filled between the anion and cation exchange membranes to form a fresh water unit.
2. Concentrated water chamber: Each EDI unit is separated by a mesh to form a concentrated water chamber.
3. Polar water room.
4. Insulation board and compression plate.
5. Power and water connections.
The EDI can be operated in parallel for greater flow.
(3) EDI process
Generally, there are dissolved substances such as sodium, calcium, magnesium, chloride, nitrate, and bicarbonate in the city water source. These compounds consist of a negatively charged anion and a positively charged cation. More than 99% of the ions can be removed by reverse osmosis pretreatment. In addition, raw water may also include other trace elements, dissolved gases (such as CO2) and some weak electrolytes (such as boron, silica). These impurities must be removed in industrial desalinated water. However, the reverse osmosis process has a poor effect on the removal of these impurities.
Ion exchange membranes and ion exchange resins work in a similar way to allow specific ions to migrate. The anion exchange membrane only allows the passage of anions and does not allow passage of cations; the cation exchange membranes are just the opposite. An EDI unit is formed by filling a mixed ion exchange resin between a pair of anion-cation exchange membranes. The space occupied by the mixed ion exchange resin between the anion-cation exchange membrane is referred to as a fresh water chamber. A number of EDI units are listed together, the anion exchange membrane and the cation exchange membrane are alternately arranged, and each EDI unit is separated by a mesh to form a concentrated water chamber. Under the impetus of a given DC voltage, in the fresh water chamber, the anions and cations in the ion exchange resin migrate to the positive and negative electrodes under the action of the electric field, respectively, and enter the concentrated water chamber through the anion-cation exchange resin, and at the same time, in the feed water. The ions are adsorbed by the ion exchange resin to occupy vacancies that flow down by ion electromigration. In fact, the migration and adsorption of ions occur simultaneously and continuously. Through such a process, ions in the feed water pass through the ion exchange membrane and enter the concentrated water chamber to be removed to become demineralized water.
Negatively charged anions (eg, 0H-, Cl-) are attracted by the positive (+) and passed through the anion exchange membrane into the adjacent concentrated water chamber. Thereafter, these ions encounter adjacent cation exchange membranes while continuing to migrate toward the positive electrode, while the cation exchange membrane does not allow it to pass, and these ions are blocked in concentrated water, and the ions passing through the cation membrane remain electrically neutral in concentrated water.
The amount of EDI component current is proportional to the amount of ion migration. The electrical current consists of two parts, one from the migration of the removed ions and the other from the H+ and 0H- produced by the ionization of the water itself. These in situ H+ and 0H- are continuously regenerated from the ion exchange resin.
The ion exchange resin in the EDI module can be divided into two parts, one part called working resin and the other part called polishing resin, and the boundary between them is called the working front. The working resin mainly acts as a conductor, and the polishing resin is continuously exchanged and continuously regenerated. The working resin is responsible for the removal of most of the ions, while the polishing resin is responsible for removing ions that are difficult to remove, such as weak electrolytes.
(4) EDI power supply
The DC power source used should be air conditioned within the operating voltage range and provide the voltage required for regeneration. The power of the DC power supply should meet the requirements of the EDI zui high current (6A). The ripple rate of the DC power supply cannot exceed 30%. Excessive ripple rates can cause the EDI component to withstand higher than apparent effective current/voltage in an instant, causing damage to the component. When multiple EDI components share a DC power supply, each EDI voltage/current should be independently adjustable. Equipped with voltmeter and ammeter. At the same time, a current limiting device should be provided. To protect the EDI components, the power should be turned off when the flow of water through the EDI assembly is below a certain point.
(5) Instruments used in EDI
1. Pressure gauge: Determination of EDI pure water, concentrated water, polar water feed water pressure and effluent pressure.
Secondary reverse osmosis + EDI water treatment
2. Flowmeter: measure the flow rate of pure water effluent, concentrated water, water, and concentrated water.
3. Conductivity meter: Measure the electrical conductivity of EDI feed water and concentrated water.
4. Resistivity meter: Measure the pure water resistivity of EDI.
5. Flow switch: If the flow of pure water, concentrated water, or polar water flowing into the EDI component is too low, the flow switch will cause the system to shut down.
5. Preservation and water supply of pure water
The water after the EDI treatment can be the finished water and stored in the pure water tank. To ensure the water quality, the nitrogen seal is generally adopted, that is, the nitrogen tank is filled from the top of the pure water tank. After the water is supplied, the liquid level solenoid valve cooperates with the PLC. When the water level of the pure water tank is lower than the low water level, the PLC starts the water production process, and the whole system starts to produce water until the water level of the pure water tank reaches a high water level, and the system stops the water production. Cycle back and forth, always have a certain water level in the pure water tank.
The deionized water equipment for electroplating is characterized by stable water quality and relatively low cost. The deionized water equipment is a water treatment device that removes anions and cations in water by means of reverse osmosis, ion exchanger, EDI, and the like. Deionized water equipment has stable performance and is widely used in medicine, electronics, chemical, glass, paint, boiler, laboratory and other industries.
Process flow for deionized water equipment for electroplating
1, using ion exchange, the process is as follows
Raw water → raw water pressure pump → sand filter → activated carbon filter → precision filter → cation resin filter bed → anion resin filter bed → yin and yang resin mixed bed → microporous filter → water point
2, using reverse osmosis, the process is as follows
Raw water → raw water pressure pump → sand filter → activated carbon filter → precision filter → reverse osmosis → pure water tank
3, using reverse osmosis mixed bed method, the process is as follows
Raw water → raw water pressure pump → sand filter → activated carbon filter → precision filter → reverse osmosis → pure water tank → pressure pump → anion-cation mixed bed → precision filter → water point
Industrial application and market demand for EDI deionized water equipment
In recent years, EDI deionization has been paid more and more attention in various industrial fields. Many industrial systems have begun to use electrodeionization as a replacement technology for their water treatment systems, such as power industry, pharmaceutical industry, microelectronics industry, electroplating and metal surface. Processing and so on.
(1) Power industry
It is estimated that the operating cost of the water treatment unit in the power industry accounts for about 10% of the cost of electricity, and the replacement of ion exchange resin by deionization can reduce the cost per 1000 gallons of water from $11 to $1.75.
(2) Pharmaceutical industry
Although the characteristics of medicinal water are not required to require a high degree of deionization, the electrodeionization system has the characteristics of simultaneous salt removal and microbial control. Therefore, many companies have adopted the RO/EDI integrated system. It is said that the performance of this type of system is stable, the whole process computer is continuously monitored, and the fully automatic operation is unattended.
(3) Electronics industry
The electronics industry has extremely high water quality requirements. The water resistivity should be more than 18MΩ, and the EDI water is generally about 15-17MΩ. Therefore, the EDI+ polishing resin system is used in the production of electronic water, that is, the ion exchange is carried out after EDI. Although this project still requires ion exchange, since the EDI has removed most of the ions, the polishing resin hardly needs to be regenerated, so the water treatment cost is still low.
(4) Electroplating and metal surface treatment
Electrodeionized water equipment can be used for electroplating wastewater treatment to reuse water and recover heavy metal ions. There are experimental devices for this type of system in the United States.
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