WaterSolutions How to Design an Ion Exchange System

Step 2: Selection of Layout and Resin Types (Configuration)

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

The plant configuration will depend on the feed water composition, the water quality required and the economics of operation. The following general guidelines are given to help in configuration and resin selection. Due to their improved performance, the uniform DOWEX™ MARATHON™ resins are recommended over standard (polydispersed) resins. The uniform DOWEX UPCORE™ Mono resins are designed for UPCORE systems.

Selection of Resin Types:
Strong Acid Cation Resin
Weak Acid Cation Resin
Strong Base Anion Resin Type I
Strong Base Anion Resin Type II
Weak Base Anion Resin

Strong Acid Cation Resin

Strong Acid Cation Resin is used for water softening in the Na cycle and for demineralization when the temporary hardness in the feed is < 40%. For small plants and with HCl as regenerant, a strong acid cation also offers a simple effective solution on waters with > 40% temporary hardness. DOWEX MARATHON C is the resin of choice for most applications and DOWEX UPCORE Mono C-600 resin for UPCORE systems.

Weak Acid Cation Resin

Weak Acid Cation Resin is used as a single resin for dealkalization in the H cycle and for brackish water softening in Na cycle. In demineralization, the use of a weak acid cation in front of a strong cation is preferred with feed waters containing a high proportion of temporary hardness (>40%) and low FMA. This configuration has advantages in terms of regeneration efficiency and operating capacity.

With sulfuric acid regeneration, two separate cation columns should be used in order to allow acid dilution at the weak acid resin inlet. For counter-flow regeneration, a double compartment layered bed cation including a facility for acid dilution at the weak acid cation inlet can be used, but is more complex to operate. Selected resins are DOWEX MAC-3 or DOWEX UPCORE MAC-3 for UPCORE systems.

Strong Base Anion Resin Type I

Strong Base Anion Resin Type I as a single resin is particularly recommended for treating low FMA (Free Mineral Acid) water with high silica and where low silica leakage is required (~20 ppb in counter-current operation). The resin can be regenerated up to 50°C (122°F) for more effective silica removal. DOWEX MARATHON A resin is designed for general demineralization and for UPCORE plants, the resins are DOWEX UPCORE Mono A-500 or DOWEX UPCORE Mono A-625 resin.

Strong Base Anion Resin Type II

Strong Base Anion Resin Type II is well suited for small plants, owing to its excellent regeneration efficiencies for water compositions where CO₂ and SiO₂ are < 30% of the total feed anions. Type II anions have a much better operating capacity and regeneration efficiency compared to Type I, but are limited to lower temperature operation (<35°C/95°F caustic treatment) and have a higher SiO₂ leakage (~50 ppb in counter-current operation). DOWEX MARATHON A2 resin is the resin of choice for general demineralization and DOWEX UPCORE Mono A2-500 for the UPCORE system.

Weak Base Anion Resin

Weak Base Anion Resin is used as a single resin to obtain partially deionized water without removal of CO₂ and SiO₂. For complete demineralization, the combination of weak base and strong base anion is an excellent choice for larger plants, as it provides optimum operation costs. The weak base has very high regeneration efficiency and provides additional capacity to the system. The weak and strong anion combination is well suited to treat waters with low alkalinity or degassed feed, when the FMA (Cl + NO₃ + SO₄) is typically > 60% of the total anions. DOWEX MARATHON WBA resin is the resin of choice for general demineralization.

Weak base anions are particularly effective in handling natural organics, which are usually high molecular weight weakly acidic compounds that affect both weak base and strong base anion resins. In a weak base - strong base anion configuration, some of the organics will pass through the weak to the strong base. The design should therefore account for SBA organic loading at the end of the cycle, as the resin will require additional NaOH to desorb the organics. There are important differences in loading capacity or reversibility to organics between different anion types.

For treating resins contaminated with silica or organics, see silica removal (20KB PDF) and brine cleaning of anion resins for organic contamination (26KB PDF).

The weak and strong anion resins can either be designed in two separate vessels or for counter-flow regeneration in one vessel with or without a separation nozzle plate. For separated anions, DOWEX MARATHON WBA and DOWEX MARATHON A resins are recommended. DOWEX MARATHON WBA and DOWEX MARATHON A LB are designed to be used together as a layered bed in a single column without a nozzle plate. For UPCORE plants, the resins are DOWEX UPCORE Mono WB-500 and DOWEX UPCORE Mono A-500 or DOWEX UPCORE Mono A-625.

Previous Step     Next Step