How to Design an Ion Exchange System

Step 6: Vessel Sizing

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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The vessels should be made from typical, well-known materials of construction such as rubber-lined carbon steel or fiberglass. The vessel should have distribution / collector systems that give a good distribution of fluids during all phases of the operation. For this reason, a maximum vessel diameter of 3.5m (11.5 feet) is recommended. It is advisable to install sight-glasses in order to check resin levels and separation in the case of layered beds and mixed beds.

The design of the vessels should give a maximum resin bed depth, while limiting the pressure drop across the resin bed to ~1 bar. The optimum column diameter must be a balance between the resin bed height, the ratio of resin height to diameter (H/D) and the linear velocity. H/D should be in the range 2/3 to 3/2.

Vessel sizing should be adjusted to allow for resin expansion if backwashing is performed (80-100% of the settled resin bed height), resin swelling during service, the minimum bed height requirements and the guidelines given for service and regenerant flow rates in the Design Guidelines table below. These values are for orientation and should not be regarded as exclusive. Some applications may function outside of the guidelines. Typical resin bed depth is 1.2 m (4 ft) for co-current and block regeneration systems and 2 m (6.5 ft) for counter-current packed bed systems.

Design Guidelines for Operating DOWEX™ Resins

Swelling:
Strong Acid Cation Na+ H+	5-8%
Weak Acid Cation H+ Ca+	15-20%
Strong Base Anion Cl- OH-	15-25%
Weak Base Anion FB HCl	15-25%
Bed depth, min.
Co-current single resin	800 mm (2.6 ft)
Counter-current single resin	1200 mm (4 ft)
Layered bed strong base anion	800 mm (2.6 ft)
Layered bed weak base anion	600 mm (2 ft)
Backwash flow rate:
Strong Acid Cation	10-25 m/h (4-10 gpm/ft2)
Weak Acid Cation	10-20 m/h (4-8 gpm/ft2)
Strong Base Anion	5-15 m/h (2-6 gpm/ft2)
Weak Base Anion	3-10 m/h (1.2-4 gpm/ft2)
Flow rates:
Service/fast rinse	5-60 m/h (2-24 gpm/ft2)
Service/condensate polishing	75-150 m/h (30-60 gpm/ft2)
Co-current regeneration/displacement rinse	1-10 m/h (0.4-4 gpm/ft2)
Counter-current regeneration/displacement rinse	5-20 m/h (2-8 gpm/ft2)
Total Rinse requirements:
Strong Acid Cation	2-6 Bed volumes
Weak Acid Cation	3-6 Bed volumes
Strong Base Anion	3-6 Bed volumes
Weak Base Anion	2-4 Bed volumes

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