Electrode Ionisation Plants
Electrode ionisation (EDI) is a combination of two highly trusted water purification techniques: Electro-dialysis and deionisation via ion exchange. The objective of this method lies in removing released substances completely at low cost in a continuous process. Under the assumption of electrolytic conductivity, the water purity levels achieved through this method is below 0.06 µS/cm.
The EDI process uses a combination of ion-selective membrane and mixed bed ion exchanger resins that are inserted between the two electrodes (anode (+) and cathode (-)). The electrodes are located at the ends of the EDI module. As against electro-dialysis, electrode ionisation works with ion exchanger resins. These form a fixed bed in the rain water flow of the cleaning chambers. The cations and anions released in the water are replaced with oxygen or rather hydroxide ions. Compounds with poor dissociation such as boric acid, silicic acid and carbonic acid are separated very effectively. By creating an electrical direct current field between the electrodes, the ions are simultaneously led into the concentrate flow along the resin surfaces and through the membranes. Thus, the ion exchanger resins are continuously freed from charged ions and a balance is maintained between charging and regeneration. Regeneration with chemicals is not necessary in electrode ionisation systems; hence it is not necessary to undertake any infrastructural measures for handling hazardous, caustic substances and for storing water-polluting materials according to the safety laws for water management.
The feed water for the electrode ionisation plants can either be reverse osmosis (RO) permeate or desalinated water from cation and anion exchanger plants. The feed water should meet the following minimum specifications:
- Maximum conductivity of 20 µS/cm,
- Maximum silicate content of 300 µg/l,
- Maximum carbon dioxide concentration of 5 mg/l.
When combined with reverse osmosis plants, the desalinated feed water is in the range of 18.2 MOhm and the silicic acid content is below 20 µg/l. Further, the growth of bacteria, algae and mushrooms is completely suppressed if the plant is operated regularly with less idling time, In combination with WAT RO plants, it is possible to achieve water purity levels up to 99% with reference to the feed water quantity.
The plant is controlled via a programmable logic control that enables simple operations and optionally allows incorporation of customer-specific requirements. Consistent quality control takes place via precise temperature-compensated measurement of electrolytic conductivity. Optionally, it is also possible to add a silicic acid analyzer to the quality control system.Due to the modular structure of the implemented EDI modules, EDI systems can be expanded as and when required and can therefore cover a wide range of services. The plants are ready-to-plug-in, compact and user-friendly; they are mounted on a powder-coated steel frame.
Areas of application
Feed water preparation for steam generators
Boiler feed water must conform to certain quality requirements to ensure that the boilers are operated in a safe and damage-free environment. The requirements depend on the model, operating pressure and the operating conditions. Increased optimisation of boiler models with respect to economic operations leads to increased quality requirements of the feed water. Once-through boilers, spray coolers for regulating the steam temperature and circulation boilers > 68 bar need desalinated feed water that meets the TRD 611 requirements. The electrolytic conductivity in such cases is 0.2 µS/cm and the silicic acid content is restricted to 20 µg/l. The feed water quantity required for industrial production is quite high and can be in the range of 10 to 100 m3/h. These requirements can be easily met using a combination of RO / EDI.
Spray-water for industrial production
The enormous growth in the semi-conductor industry in the last few decades has increased the need for ultrapure water and the quality requirements for rinsing water in production have also increased dramatically. The demand for ultrapure water in solar cell production will continue to increase with the growing market for photo-voltaic systems.
Processes in the range of production of a varied range of systems and accessories such as optical devices and devices for medical diagnostics also need ultrapure water qualities. The requirements for rinsing water are in the range of 18.2 MOhm with a silicate content of less than 20 µg/l. Ultrapure water produced with a process combination of RO / EDI meet the important high quality requirements according to ASTM D5127-99.
Ultrapure water in the production of pharmaceuticals
Electrode ionisation is a cost-effective process for water desalination that has to meet high quality standards. By subsequently installing membrane barriers (ultra-filtration or reverse osmosis) or destillation, the generated purest quality water can be used for producing medicines or injection water (WFI). This ensures compliance with the stipulation of international standards (such as USP24).
Ultrapure water in Laboratories
Chemical and biological laboratories in industrial and government research institutions and hospitals normally need ultrapure water that meets high quality requirements. The ultrapure water requirements for highly sensitive devices in forensic laboratories (AAS, ICP, MS, HPLC) and in biomedical application are normally in the range of 18 MOhm. All the three quality standards can be met by DIN ISO 3696. The required quality standards can be met in a cost-effective manner through a combination of RO/ EDI with subsequent need-based micro-filtration or destillation.
