Industrial application and market demand of secondary ro + EDI water treatment and EDI deionized water equipment

1、 The main task of multi-media filtration in this stage is to carry out the coarse filtration of tap water to prepare for entering the reverse osmosis membrane, to ensure that the water quality reaches a certain level before entering the reverse osmosis membrane, so as to protect the service effect and service life of the reverse osmosis membrane The process is to filter the tap water of the raw water tank through fine sand, active carbon and precision filter, remove the impurities, organics, colloids, suspensions, etc in the water, so as to prevent these large particles 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 of reverse osmosis is the first stage of reverse osmosis after the rough filtered water passes through the reverse osmosis membrane The reverse osmosis membrane is a semi permeable membrane, which can prevent Ga2 +, Mg2 +, FE-2 , SO4-2, CL-1, Na + and other large ions pass through In order to ensure the reverse osmosis effect and protect the reverse osmosis membrane, scale inhibitor must be added to the reverse osmosis vessel continuously, and the water temperature must be above 25 ℃ (steam heat exchanger is used in winter) and a certain water pressure must be ensured (vertical pump is used) under a certain pressure, the water containing ions is squeezed through the reverse osmosis membrane, thus forming two Seed water, usually through the reverse osmosis membrane water that is the finished water into the next link, but not through the reverse osmosis membrane water is discharged, after the first stage of reverse osmosis treatment water into the next link - the second stage of reverse osmosis Third, the principle of the second-stage reverse osmosis is the same as that of the first-stage reverse osmosis Its function is to further remove the salt in the water, (Ga2 +, Mg2 +, FE-2, SO4-2, CL-1, Na + plasma) to further improve the water quality After the second-stage reverse osmosis, the water conductivity can be close to 1m Ω Cm After the primary and secondary ro pretreatment, the remaining water becomes EDI feed water, while the water (concentrated water) without RO membrane is discharged in time The proportion is generally 1:3, i.e about 3 tons of concentrated water (reclaimed water) will be discharged for each ton of qualified water produced IV EDI (electronic deionization) processing The water after secondary reverse osmosis is stored in the intermediate water tank, and more than 99% of its ions have been removed However, in order to further improve the water quality, produce ultra pure water, remove the trace elements and CO2 dissolved in the water, it must also undergo electrodialysis, i.e EDI treatment The principle is as follows: EDI, i.e continuous electrodialysis, is to use the mixed ion exchange resin to absorb the anions and anions in the water supply Under the action of DC voltage, these adsorbed ions are removed through the anion exchange membrane In this process, the ion exchange resin is regenerated continuously by electricity, so it does not need to be regenerated by acid and alkali This technology can replace the traditional ion exchange device to produce ultra pure water with resistivity up to 18m Ω Cm This technology is called the revolution of water treatment industry Compared with the traditional ion exchange, EDI has the following advantages: EDI does not need chemical regeneration; EDI does not need shutdown during regeneration; provides stable water quality; low energy consumption; convenient operation, low labor intensity; low operating cost (I) EDI feed water treatment feed water pretreatment is very important for EDI The service life, performance and maintenance amount of components depend on the content of impurities in feed water If better pretreatment water is provided to EDI, the cleaning rate of components will be reduced Part of EDI concentrated water can be recycled (when the hardness and conductivity of feed water are low, it can not be recycled) The other part can be returned to ro feed water, or recycled for other use or directly discharged to sewer (II) component structure of EDI 1 Fresh water chamber: filling ion exchange resin between anion exchange membrane and cation exchange membrane to form fresh water unit 2 Concentrated water chamber: separate each EDI unit with a mesh to form a concentrated water chamber 3 Extreme water chamber 4 Insulating plate and pressing plate 5 Power supply and water connection EDI can be operated in parallel to achieve greater flow (3) dissolved substances such as sodium, calcium, magnesium, chloride, nitrate, bicarbonate, etc exist in the general urban water source of EDI process These compounds are composed of negatively charged anions and positively charged cations More than 99% ions can be removed by RO pretreatment In addition, impurities such as other trace elements, dissolved gases (such as CO2) and some weak electrolytes (such as boron and silica) in raw water must be removed in industrial demineralised water However, the removal effect of these impurities in RO process is poor The working principle of ion exchange membrane is similar to that of ion exchange resin, which can transfer specific ions Anion exchange membrane only allows anions to pass through, not cations; while cation exchange membrane is the opposite An EDI unit is formed by filling a mixed ion exchange resin between a pair of anion exchange membranes The space occupied by mixed ion exchange resin between cation and anion exchange membrane is called fresh water chamber A certain number of EDI units are listed together, so that the anion exchange membrane and cation exchange membrane are alternately arranged, and each EDI unit is separated by a network to form a concentrated water chamber Driven by a given DC voltage, in the fresh water chamber, the anion and cation in the ion exchange resin migrate to the positive and negative poles respectively under the action of electric field, and enter the concentrated water chamber through the anion and cation exchange resin At the same time, the ions in the water supply are absorbed by the ion exchange resin and occupy the vacancy under the current caused by the ion electromigration In fact, the migration and adsorption of ions occur simultaneously and continuously Through this process, the ions in the feed water pass through the ion exchange membrane and enter the concentrated water chamber to be removed and become demineralised water The negatively charged anions (such as 0h -, Cl -) are attracted by the positive electrode and enter the adjacent concentrated water chamber through the anion exchange membrane After that, these ions encounter the adjacent cation exchange membrane when they continue to migrate to the positive pole, and the cation exchange membrane does not allow them to pass through These ions are blocked in the concentrated water, and in the concentrated water, the ions passing through the anion and cation membrane maintain the electric neutrality The current of EDI module is directly proportional to the ion migration The current is composed of two parts, one is from the migration of the removed ions, the other is from the H + and 0h - produced by the ionization of water itself These H + and 0h - produced in situ regenerate the ion exchange resin continuously The ion exchange resin in EDI components can be divided into two parts, one is called working resin, the other is called polishing resin, and the boundary between them is called working front Working resin is mainly conductive, while polishing resin is continuously exchanged and regenerated Working resin is responsible for the removal of most ions, while polishing resin is responsible for the removal of ions such as weak electrolyte (IV) the DC power used for EDI power supply shall be air-conditioned within the operating voltage range and can provide the voltage required for regeneration The power of DC power supply shall meet the requirements of EDI high current (6a) The ripple rate of DC power supply shall not exceed 30% Too high ripple rate will make EDI components withstand higher than apparent effective current / voltage in an instant, causing damage to components When multiple EDI components share a DC power supply, each EDI voltage / current shall be independently adjustable Equipped with voltmeter and ammeter At the same time, current limiting devices shall be provided In order to protect EDI components, when the water flow through EDI components is lower than a certain point, the power should be turned off (V) instruments for EDI 1 Pressure gauge: measure the pressure of EDI pure water, concentrated water, extreme water supply and outlet Secondary ro + EDI water treatment 2 Flowmeter: measure the flow of pure water outlet, concentrated water inlet, extreme water inlet and concentrated water make-up water 3 Conductivity meter: measure the conductivity of EDI feed water and concentrated water 4 Resistivity meter: measure EDI pure water resistivity 5 Flow switch: if the flow of pure water, concentrated water and extreme water into EDI components is too low, the flow switch will make the system shut down V the water after EDI treatment for pure water storage and feed water can be finished water, which will enter the pure water tank for storage In order to ensure the water quality, nitrogen sealing method is generally adopted, i.e filling nitrogen from the top of the pure water tank After water supply, the liquid level solenoid valve cooperates with PLC When the water level of the pure water tank is lower than the low water level, PLC starts the water making program, and the whole system starts to make water until the water level of the pure water tank reaches the high water level, and the system stops making water In this way, the water level in the pure water tank is kept at a certain level Deionized water equipment for electroplating is characterized by stable water quality and relatively low cost Deionized water equipment is a water treatment device which can remove the anions and cations in water by means of reverse osmosis, ion exchanger, EDI, etc Deionized water equipment with stable performance is widely used in medicine, electronics, chemical industry, glass, coating, boiler, laboratory and other industries The process flow of deionized water equipment for electroplating is as follows: 1 The method of ion exchange is adopted The process flow is as follows: raw water → raw water pressure pump → sand filter → activated carbon filter → precision filter → cation resin filter bed → anion resin filter bed → anion and cation resin mixed bed → microporous filter → water point 2 Reverse osmosis is adopted The process flow is as follows Raw water → raw water booster pump → sand filter → activated carbon filter → precision filter → reverse osmosis → pure water tank 3 Reverse osmosis plus mixed bed method is adopted, the process is as follows: raw water → raw water booster pump → sand filter → activated carbon filter → precision filter → reverse osmosis → pure water tank → booster pump → anion and cation mixed bed → precision filter → water point In recent years, EDI deionization has been paid more and more attention in various industrial fields Many industrial systems have begun to use electric deionization as the renewal technology of their water treatment systems, such as power industry, pharmaceutical industry, microelectronics industry, electroplating and metal surface treatment (1) It is estimated that the operating cost of water treatment unit in the power industry accounts for about 10% of the power cost, while the cost of treating 1000 gallons of water can be reduced from $11 to $1.75 by using deionization instead of ion exchange resin (2) Although the pharmaceutical industry does not require a high degree of deionization, the electrodeionization system has the characteristics of simultaneous desalination and microbial control, so many enterprises have adopted Ro / EDI integrated system It is said that the performance of this kind of system is stable, the whole process is continuously monitored by computer, and the full-automatic operation is unattended (3) Electronic industry The requirement of electronic industry for water quality is very high The resistance of water and electricity should be more than 18m Ω, while EDI effluent is generally about 15-17m Ω Therefore, EDI + polishing resin system is often used in the production process of electronic grade water, i.e adding ion exchange after EDI Although ion exchange is still needed in this project, most of the ions have been removed from EDI, and the polishing resin hardly needs regeneration, so the water The cost of management is still very low (4) Electrodeionized water equipment for electroplating and metal surface treatment can be used for electroplating wastewater treatment, which can reuse water and recover heavy metal ions There are some experimental devices for this type of system in the United States.