How to Design an Ion Exchange System

Step 8: Mixed Bed Design Considerations

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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A polishing mixed-bed will be required if the product water specification is below that achievable from the demineralization plant alone or if a higher degree of safety is required to ensure water quality. The mixed bed outlet water should be about 0.10 µS/cm at 25°C and 0.010 to 0.020 mg/l as SiO₂ (10 to 20 ppb).

Below are some general guidelines for designing a working mixed bed downstream of a demineralization plant:

• Resin volume ratio of cation to anion should be in the range 40:60 to 60:40.
• Flow rate 20-40 bed volumes per hour.
• Regenerant levels of 80-100 g HCl/L or 120-160 g H₂SO₄/L cation and 80-100 g NaOH /L anion.
• Maximum service run length < 4 weeks.
• Maximum silica loading lower than 1.0 g SiO₂ /L anion resin at end-of-cycle.
• Minimum cation resin bed depth of 450 mm (1.5 feet).

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