Applications of continuous electrodeionization

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The demand by industry for high-purity water in the electronic industry but also in analytical laboratories and power stations is rapidly increasing. Generally, well or surface water is purified in a series of processes that include water softening, microfiltration, reverse osmosis, ultrafiltration, UV sterilization, and mixed-bed ion-exchange, which is used as a final polishing process, producing water with a conductivity of less than 0.06 mS cm~ . While processes such as reverse osmosis, micro- and ultrafiltration, or UV sterilization can be operated in a continuous mode, the mixed-bed

Continuous Electrodeionization Unit

Figure 22 Schematic diagram illustrating the recovery of acids from a pickling solution containing an acids/salt mixture.

V

Feed

solution

-4*

Figure 22 Schematic diagram illustrating the recovery of acids from a pickling solution containing an acids/salt mixture.

De-gasing

Storage tank EDI-concentrate

Point-of-use filter

Feed water rM

Microfiltration

Sterilization

Reverse osmosis EDI-unit

Ultra pure water

Figure 23 Ultrapure water production line used for the boiler feedwater preparation.

ion-exchanger, which is necessary to reach the required low conductivity, must be regenerated at certain time intervals. This regeneration is not only labor-intensive and costly but it requires extremely long rinse down times to remove traces of regeneration chemicals. By replacing the mixed-bed ion-exchanger by a continuous deionization using separate ion-exchange beds and bipolar membranes, the ultrapure water production can be substantially simplified, yielding consistently high-quality water in a completely continuous process as illustrated in Fig. 23.

The advantages of the ultrapure water production with an integrated electrodeionization unit compared to the use of a mixed-bed ion-exchanger are a simpler process, no necessity of regeneration chemicals, less raw water consumption, and a substantial reduction in costs.

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