Continuous ion exchange systems

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Continuous ion exchange processes are one of the many techniques that can be used in water treatment for the salination and / or removal of dissolved salts from liquids (also known as ion exchange ).

With the development of modern ion exchange resins (in the following text only briefly referred to as resins ) after 1945, the technical processes for the application of ion exchange were also further developed in practice. While only set plants with approximately 1,960 direct current regeneration were used advancements middle led from the 1960s to the early 1970s to set plants with Schichtbettaustauschern or Gegenstromaustauschern as well as to investments that are fully or almost continuously. For example, from the late 1960s to the early 1970s, patents were filed for 39 such continuous processes in 11 countries.

Basis of the procedure

The basis of all continuous processes are the following criteria:

  • Loading (operation) and regeneration including purging take place simultaneously in separate areas of the system
  • the entire resin volume in the system is minimized as far as is reasonable
  • Loading and regeneration are carried out according to the countercurrent principle
  • Resins that are as abrasion-resistant as possible are used, as the mechanical stress on the resins is higher than with typesetting systems

By taking these criteria into account, a reduction in the number and dimensions of the exchange containers, including the required amounts of resin, is achieved in comparison with batch systems. The aim of the development of a continuously operating system was a better economy for the treatment of water.

List of procedures

Below are some of these systems, of which at least one or more large-scale systems have been implemented in practice:

  • ASAHI process developed in Japan
  • CHEM-SEP process, developed by the American company Permutit
  • Higgins loop, developed in USA
  • CCS process, a further development of the Higgins process from the former German company Hoechst AG
  • Fluicon process, developed by the former German company Permutit
  • CIX process, developed by the English company Permutit
  • Kontimat process, developed by the German company Hager & Elsässer
  • Mannesmann Konti process, developed by the former German company Mannesmann Rohrbau

All systems consist of 2 mutually lockable areas. In the first area the desalination or salination takes place and in the second the rinsing and regeneration of the resins takes place. Almost all processes work in a pulsating manner. The resins to be regenerated and the freshly regenerated resins are removed from or fed into the operating column in batches with only brief interruptions. This short interruption is followed by a longer operating phase in which the liquid to be treated reacts with the resins and these are loaded. Rinsing and regeneration of the separated loaded resins are carried out during this phase in the separated regeneration area of ​​the system.

Operating values

A continuous system for desalination consists of at least 1 cation and 1 anion unit. As an example of the pure water quality that can be achieved with these systems, the data from a CSS system. With full demineralization, for example, the conductivity achieved is 1–3 µS / cm and the silica content ( SiO 2 content ) <10 µg / l. The specified operating values ​​for a Kontimat system are in the same range. These values ​​are only slightly higher than the values ​​after a batch system equipped with counterflow exchangers . On the other hand, the chemical consumption with an average of 130-160% of theory is noticeably higher than with a countercurrent system. This higher chemical expenditure is due to the fact that a complete, optimal countercurrent effect is partially canceled out by the inevitably necessary resin movements between the loading and regeneration areas. Furthermore, a combined use of weakly and strongly acidic cation resins - the same applies analogously to the anion resins - in one cation unit is not possible. However, an optimally low chemical expenditure can be achieved with these resin combinations in compounding systems.

As in the case of the batching systems for desalination, mainly dilute solutions of hydrochloric acid and sodium hydroxide are used as regeneration chemicals .

economics

Due to the development of particularly economical processes for the desalination of water with resins such as short cycle systems and countercurrent systems with multi-chamber filters as well as with reverse osmosis , the continuous resin processes mentioned were not economical and therefore not competitive. These systems were rarely used for new systems from around the late 1980s.

Individual evidence

  1. ↑ Erhart Schmidt, about: Documentation Water Ref.No. DW 12-80-2479 / A 810114, from book:?, P. 181
  2. ↑ G. Greiner + P. Knosala, VGB Kraftwerkstechnik, vol. 64, issue 10, p. 953
  3. ↑ G. Greiner + P. Knosala, VGB Kraftwerkstechnik, vol. 64, issue 10, p. 955
  4. ↑ KH Walter, H. Böse and K. Marquardt, Energie, Vol. 27, No. 10, Oct. 1975, p. 250

literature

  • ME Gilwood, Saving Capital and Chemicals, Chemical Engineering, Dec. 1967
  • DC Holliday, Chemistry and Industrie, 1972, pp. 717-723
  • KH Walter, H. Böse + K. Marquard, Continuously working full desalination plant, Energie, 27th year 1975, issue 10, pp. 245-251
  • Patent DAS 1,767,623 , Method and Apparatus for Desalinating Liquids, 1976
  • Erhart Schmidt, on: Documentation Water, Ref.No. DW 12-80-2479 / A 810114, from book:?, Pp. 179-183
  • G. Greiner + P. Knosala, quasi-continuous ion exchange according to the CCS process, VGB Kraftwerkstechnik, vol. 1984, issue 10, pp. 952-956