Demineralization plant, VE-system

A demineralization system, VE-system, is used to produce so-calledVE-water (demineralized water). In this process, all ionogenic substances (usually salts and dissolved gases such as carbon dioxide) are removed from the incoming water, usually city water, via an ion exchanger and replaced with H2O. This produces highly pure demineralized water (also known as DM water or “forklift water” or “battery water”) for industrial purposes.

High-purity water is often required in industrial processes, e.g. in industrial rinsing and cleaning processes or when filling forklift truck batteries. The typical parameters of the existing water, city water “from the tap” or well water, are generally not sufficient, as particularly limescale deposits of the hardness formers calcium and magnesium are disturbing in the processes. The demineralization system, VE-system, removes cationic ions such as sodium, calcium, magnesium and also copper (drinking water regulations allow up to 2.0 mg/L) via the cation exchanger and anionic ions such as corrosive chlorides or sulphate via the anion exchanger. Within the scope of their available capacities, the strongly acidic cation exchanger releases H+ ions in exchange and the strongly basic anion exchanger releases OH- ions in exchange. A weakly basic anion exchanger, on the other hand, binds the proton and an equivalent amount of anions. Together, H20 is produced in the outlet of the system instead of the input ion loads. By removing the ionic substances, this ensures a low conductivity value of typically < 3-5 µS/cm at the outlet of the demineralization system resp. VE-system so that the demineralized water can be used for most industrial processes. Additional filter stages are required for the separation of any organic matter or other apolar substances present in well water, or for a further reduction of the conductance value.

A common application for a demineralization system is the production of demineralized water, e.g. in an electroplating plant with a conductance of < 20 µS/cm salt load from city water. Depending on the requirements, the VE-system consists of one or two lines, each with a strongly acidic cation exchanger, so-called SAC (sulphonic acid exchanger on styrene-divinylbenzene copolymer) and a strongly basic anion exchanger, so-called SBA (quaternary amine exchanger on styrene-divinylbenzene copolymer). In applications that require an even lower conductivity value, a mixture of a strongly acidic and a strongly alkaline exchanger is additionally connected downstream for external regeneration, so-called mixed bed resin or mixed bed exchanger (and/or a electrodeionization)which can achieve a conductance of up to 0.1 µS/cm (so-called pure water) up to, under optimum technical conditions, the lowest achievable conductance of 0.056 µS/cm or 18.18 MΩ-cm at 25°C (based on the salt content of the demineralized water), so-called ultra-pure water.

The system can also be optimized for lower regeneration chemical consumption by adding further ion exchanger stages, e.g. weakly acidic cation exchangers and weakly basic anion exchangers.

Furthermore, depending on the application, physical pre-filtration is carried out using gravel filters or multi-layer filters or filter cartridges, as well as denaturation of any interfering biology by UV light and/or removal of apolar or non-ionic substances using activated carbon or a scavenger resin as an exchange unit.

Mixed bed polishing resins, possibly also so-called UPW mixed bed resins, can be connected downstream for the external ion exchanger regeneration service in the central regeneration station in order to reduce the achievable conductance even further. Additional silicate monitoring may be necessary.

Fully demineralized water(VE-water)or demineralized resp. deionized water (DM water, Di water or DeMi water) is not defined separately as such, but its parameters are derived from the customer-specific process. The main aim is to avoid stains during subsequent use. Higher purity levels than demineralized water are pure water with 1-0.1 µS/cm and ultra-pure water with 0.1 – 0.056 µS/cm, both at 25°C.

Typically, however, the following conductance values are required at the outlet of the system: Semiconductor < 0.1 µS/cm (0.06 µS/cm), hard chrome plating < 3 µS/cm, electroplating < 20 µS/cm, anodized < 30 µS/cm, hot-dip galvanizing < 50 µS/cm, forklift water or battery water during filling: < 30 µS/cm.

Consideration of the conductance alone is often not sufficient for a reliable process design, as the slip phase of the ion exchanger begins as soon as the conductance rises for the first time. The anion exchanger in a demineralization process in particular starts early with the release of weakly bound substances, e.g. silicic acid, which hardly affects the conductance and (corrosive) chlorides. Both substances are generally undesirable in the process and may require additional technical measures in the ion exchanger system.

As a rule, the demineralized water produced by the demineralization system or VE-system is monitored using the conductance in [µS/cm] at the outlet of the ion exchanger system. Typical conductance values at the outlet of the ion exchanger system are between 30 µS/cm – 3 µS/cm, depending on the system and expansion stage.

In special cases, requirements are not only placed on the sum parameter conductance in [µS/cm], but other parameters in the treated effluent water are also important: e.g. pH value, residual concentrations of substances that only have a minor effect on the conductance, e.g. substances with a low degree of dissociation such as silicic acid, silicates, cyanides or salts of organic acids. Demineralized water produced with the help of an ion exchanger system therefore contains different residual substances than the permeate from a reverse osmosis system.

A typical question for system operators with a desired conductance of around 20 µS/cm is whether to purchase an industrial reverse osmosis system or a VE-ystem or demineralization system (or just a demineralization cartridge or VE-cartridge that can be recycled via the external ion exchanger regeneration service for small quantities of < 4 m³/week). Both typically achieve this conductivity value, but differ in the process and the composition of the demineralized water produced. If only the conductivity is required as a sum parameter, the main differences can be summarized as follows: A chemical-physical wastewater treatment system is required for demineralized water systems, but not usually for reverse osmosis systems. Both systems do not require a WHG (Water Resources Act) permit on their own up to 10m³/week of wastewater production (the municipal monitoring values nevertheless apply; copper in particular can be problematic here due to the limit values in the Drinking Water Ordinance of 2.0 mg/L compared to the monitoring values in the Wastewater Ordinance of 0.5 mg/L (or 1.0 mg/L in most drainage statutes for discharges < 10 m³/week). The reverse osmosis system constantly produces waste water via the concentrate discharge, whereas the ion exchanger system only produces waste water during regeneration. Cost considerations can be made over the entire period of use, in which the generally higher acquisition costs for the VE system can be weighed up against the lower operating costs, see here as an example.

Products

A demineralization system or VE-system has an automatic regeneration station on site. For smaller quantities, a demineralization cartridge is available, for example, which does not require wastewater to be produced on site, as it is treated centrally in the regeneration station in 92348 Berg via the ion exchanger regeneration service.

The resins used in the system in the various columns are regenerated with acid and alkali, usually with hydrochloric acid and caustic soda. The regenerates from the plant are then treated in the company’s own chemical and physical wastewater treatment system. Please note that the system is subject to approval under water legislation in accordance with Annex 31 of the Wastewater Ordinance if more than 10 m³/week of wastewater is produced.

Customer-specific adaptation of demineralization system / VE-system:

  • Customer-specific design to suit the process (city water/well water ingredients) and the budget, starting from a semi-automated, functional simplex basic design through to an automated and remotely monitored duplex design.
  • 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
  • Duplex version for uninterrupted 24/7 operation optional
  • Stainless steel or plastic frame construction for corrosive environments
  • Pressure tanks in PE/GfK or coated steel
  • Ion exchange resin from LANXESS Lewatit or Purolite or according to customer requirements
  • Piping and fittings in PVC or PP from the manufacturers GF, GEMÜ (pneumatic or electrical) or according to customer requirements; otherwise design with standard industrial components without special elements where possible.
  • Single valve control, combination head control optionally possible
  • Internal recirculation to avoid counterion re-dissolution effects
  • System design for operation in compliance with occupational safety requirements, even in the event of typical misuse
  • Disinfection option for the resin bed
  • 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. with storage tanks, chemical storage tanks as dosing stations or as AwSV LAU systems, drip pans, simple feeding to redundant FU duplex pressure booster stations, pressure difference display, actual consumption and production data recording, separate resin changeover connections, system access control, valve position feedback, separate silica cleaning.

We will be happy to help you.