Can anyone explain to me how mixed bed vessels work in demineralised water plants, with both cation and anion resins mixed in the same bed, perhaps detailed internal drawing as well
The same way as the cation and anion beds work. There is no difference, per se, except that cation and anion exchange resins are separated by difference in their densities. Purging air inside the vessel, after regeneration, complements the separation process.
The primary differences between those resin operating in two vessels instead of one are:
1. The water quality produced is much better than a 2 vessel system. That because the cation/anion exchanges take place throughout the resin bed rather that all cation exchanges in the cation bed and all anion exchanges in the anion bed.
2. With a 2 vessel system you regenerate each vessel separately. With a Mixed Bed system you regenerate the 2 resins separately in the same vessel. First you separate the two beds by backwashing. Then regenerate each bed with the appropriate regenerant which can be done simultaneously. Then you remix the two resins with air.
3. A Mixed Bed system is best operated by feeding soft water during the service run. Soft water feed prevents hardness fouling of the anion resin. A 2 vessel system can be operated by feeding hard water during the service run since the anion resin never see's hard water.
