Electrodeionization, EDI systems for the production of ultrapure water

Electrodeionization ultrapure water is an application for the production of ultrapure water for industrial purposes (e.g. semiconductors, optics, hydrogen production). In contrast to a reverse osmosis system or a demineralization system this is not a single system, but a downstream system for the further purification of VE water with a conductance of 3-5 µS/cm to a so-called diluate with a conductance of up to 0.056 µS/cm or 18.18 MΩ-cm.

Some industrial processes (e.g. semiconductors, optics, hydrogen production) require an even purer water than demineralized water, so-called ultrapure water. This is a further purified demineralized water with the lowest possible conductance of up to 0.056 µS/cm or 18.18 MΩ-cm. The process essentially consists of a mixed bed exchanger that is surrounded by cationic and anionic ion exchanger membranes and where a continuous ion outflow is generated under current. The residual substances still contained in the demineralized water are captured by the mixed bed resin in the electrodeionization process and immediately discharged due to the current flow. Chemical regeneration of the mixed bed resin does not take place. Diluate, i.e. ultrapure water, is produced at the end of the electrodeionization process. However, as electrodeionization is only functional under stable process conditions, it is a component that is not installed individually as a system, but requires additional system components. In particular, the flow rate and inflow loads must remain constant.

A common application for electrodeionization is the production of ultrapure water for semiconductor manufacturers, where a conductance value of 0.08 µS/cm is regularly required. A conductance value of 0.25 µS/cm is regularly required for the production of hydrogen in water electrolysis. Electrodeionization systems in the full process engineering stage can safely achieve this value with the average city water.

Electrodeionization is usually installed in combination with an upstream, possibly double, permeate-staged reverse osmosis system. This also requires pre-softening, e.g. via a strongly acidic cation exchanger with common salt regeneration or temporary hardness stabilization including the additionally required preliminary stages, such as system separators and pre-filters. In addition, either CO2 capture is required upstream of the system or it is carried out via a compressed air or vacuum membrane degasser directly before electrodeionization. Since electrodeionization is a process that requires a constant flow rate, a tank is regularly required downstream, which in turn requires special installations to prevent the purified ultrapure water in the tank from becoming too salty. Finally, the tank is regularly integrated into an extraction circuit with an externally regenerated polisher mixed bed ion exchanger with UPW mixed bed resins, e.g. Ambertec UP6040, and subsequent closed-pool regeneration, which then supplies the individual suppliers in the loop. The separate closed-pool regeneration prevents cross-contamination with other customers and ensures consistent resin quality. This creates defined changeover times for the pool in the later life cycle of the UPW resins.

The diluate from electrodeionization with a pretreatment from a reverse osmosis system combines the quality advantages of a reverse osmosis system via the separation due to the size of the molecule and the advantages of a demineralization system via the charge. Final fine purification via an externally regenerated mixed-bed polisher ion exchanger (demineralization cartridge) also compensates for any unavoidable fluctuations (e.g. in the temperature of the city water) and ensures constant quality of the ultrapure water at the transfer point.

Products

Reverse osmosis system EDI system with mixed bed polisher circuit.
Electrodeionization with 0.056 µS/cm
Mixed bed polisher circuit according to EDI with 18.18 MegaOhms

An electrodeionization ultrapure water production system consists of various components: If a softening system is installed upstream of a reverse osmosis system, this is always equipped with its own regeneration station with common salt (NaCl).

The separator modules installed in the reverse osmosis systems, so-called RO membranes, have a typical service life of ~5-7 years, depending on the load from the input water. Please note that the system is at least acc. Annex 31 of the Wastewater Ordinance (AbwV) subject to notification, if more than 10 m³/week of wastewater is produced. The wastewater is made up of the pre-filter backwash, the regenerate from the softening system, the concentrate from the reverse osmosis system and (in some cases, if not recycled) the concentrate from the electrodeionization system. The local drainage regulations also apply to every discharge.

Customized design for the process (city water or well water ingredients) and desired safety requirements for consistent quality.

  • Adaptation to any existing control technology and connection to a process control system and the existing structural conditions at the site or the entry to the site
  • Fulfillment of customer requirements for industrial processes
  • Siemens PLC circuit with/without touch display and with the option of external access or microprocessor control
  • Duplex version on the softener for uninterrupted 24/7 operation optional
  • Duplex design on the reverse osmosis system, permeate-staged
  • Concentrate treatment of wastewater streams from the reverse osmosis system optional
  • “Plug-and-play” design for the user. Only connection to electricity, city water, permeate (ultrapure water for further use) and concentrate/regenerate pipes (waste water) required.
  • Stainless steel frame
  • Pipes and fittings in PVC or PP or stainless steel
  • Internal rinsing/cleaning processes to preserve the membranes
  • Possibility of pre-acceptance and trial operation in our own workshop
  • Modular, maintenance-friendly design according to customer requirements with various optional expansion options, e.g. UV-irradiated storage tanks with sterile filtration, chemical storage tanks as dosing stations or as AwSV LAU systems, collecting trays, simple feeding to redundant FU duplex pressure boosting stations, membrane degassing systems.
  • Externally regenerated demineralization cartridge as a mixed-bed polisher with UPW resins and closed-pool external regeneration directly at the system manufacturer to prevent cross-contamination and ensure a defined service life cycle of the resins used to maintain consistent quality.

We will be happy to help you.