How to Design an Ion Exchange System

Step 1: Regeneration System Selection

Steps:

Step 1: Regeneration System Selection
Step 2: Selection of Layout and Resin Types (Configuration)
Step 3: Chemical Efficiencies for Different Resin Configurations
Step 4: Atmospheric Degassifier
Step 5: Resin Operating Capacities and Regenerant Levels
Step 6: Vessel Sizing
Step 7: Number of Lines
Step 8: Mixed Bed Design Considerations

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There are a number of different ion exchange regeneration technologies that can be used, from the basic co-current regenerated systems to counter-flow block systems and through to packed bed technology, including the Dow UPCORE™ System.

Selection of regeneration system:
Counter-Current Regeneration Systems (Blocked Systems or Packed Bed Systems)
Co-Current Regeneration Systems

Counter-Current Regeneration Systems: in these systems, the regenerant is applied in the opposite direction to the service flow, resulting in reduced chemical consumption, improved water quality and less waste volumes compared to traditional co-current regenerated systems. Counter-current regeneration systems should provide a water quality of better than 2 µS/cm (0.5 MW.cm) and residual silica of 0.020 to 0.050 mg/l as SiO₂. Depending upon water composition and regeneration conditions, the specific conductivity could be as low as 0.2 µS/cm (5 MW.cm). The normal counter-current endpoint is 4 µS/cm conductivity. A maximum endpoint value of 0.3 mg/l SiO₂ above the average leakage should not be exceeded in order to avoid a high contamination of the polishing resin layer and unacceptably high silica leakage during subsequent cycles. Silica leakage can be minimized by operating the plant at silica break rather than conductivity end point. This secures the lowest silica leakage, but at the expense of a 5 -10 % throughput reduction.

There are two main types of counter-current systems:

• Blocked Systems, including air hold down, water hold down and inert mass blocked. The service flow is downwards and regeneration upflow. To avoid disturbance of the resin polishing zone at the bottom of the vessel, the resin bed is held down (blocked) during regeneration by air pressure, water flow or an inert mass in the top part of the vessel. The regenerant passes up through the resin and out of a collector system in the middle part of the vessel. Such systems have similar high cylindrical height as co-current systems to allow resin backwash within the vessel.
• Packed Bed Systems, these may be up-flow service with down-flow regeneration or down-flow service with up-flow regeneration, such as the Dow UPCORE system.

Co-Current Regeneration Systems: these are the simplest systems, where the resin is regenerated in the same direction as the service flow (downwards). The vessel has a large freeboard to allow expansion of the resin bed when backwashing is carried out to remove suspended solids and resin fines. Co-current regeneration single bed systems will generally produce water of much lower quality than counter-current systems, with typical leakage values ~10 times higher. Such quality will also be even more affected by the water composition, the type of regenerant chemical and dosage being used.

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