How to Design an Ion Exchange System

Step 5: Resin Operating Capacities and Regenerant Levels

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

In co-current operation, the product water quality requirements will define the minimum levels of acid and caustic regenerant to be used. The regenerant levels and the feed water composition will then define the resin operating capacity. Although high regenerant levels result in increased capacity and lower ionic leakages, the chemical efficiency of the system becomes worse.

More precise determinations of resin operating capacities and ionic leakages can be calculated using the CADIX design program or from the engineering curves given in the DOWEX™ Resin Engineering Brochures. These Brochures provide complete engineering information for individual DOWEX resins, including operating capacity and leakage curves as well as backwash and pressure drop data.

Guidelines for Typical Regeneration Level and Corresponding Resin Operating Capacity:

Regeneration System
Regenerant Level
Typical Operating Capacity
(g/l)
(lbs/ft3)
(eq/l)
 (kgr/ft3)
Co-Current Regeneration:

HCl
80 - 120
5 - 7.5
0.8 - 1.2
17.5 - 26

H2SO4
150 - 200
9.5 - 12.5
0.5 - 0.8
11 - 17.5

NaOH
80 - 120
5 - 7.5
0.4 - 0.6
8.5 - 13
Counter-Current Regeneration:

HCl
40 - 55
2.5 - 3.5
0.8 - 1.2
17.5 - 26

H2SO4
60 - 80
3.75 - 5
0.5 - 0.8
11 - 17.5

NaOH
30 - 45
2 - 2.8
0.4 - 0.6
8.5 - 13

The choice between hydrochloric acid and sulfuric acid is principally economic. HCl is a trouble-free regenerant with high efficiency. H2SO4 is less efficient and has lower operating capacity, particularly if stepwise regeneration is required in high hardness waters to avoid calcium sulfate precipitation.

Guidelines for amounts and concentrations of H2SO4 in stepwise regeneration:

Calcium in feed water (%) Amount and concentration of H2SO4
Ca < 15 3 %
15 < Ca < 50 1/3 at 1.5 % and 2/3 at 3 %
50 < Ca < 70 1/2 at 1.5 % and 1/2 at 3 %
Ca > 70 1 % or use HCl

The specifications on the purity of the regeneration chemicals have to assure a trouble-free operation of the ion exchange resins after regeneration. Recommendations on the quality of regeneration chemicals (12KB PDF) are given.

In order to compensate for non-ideal operating conditions and resin aging on a working plant, it is recommended to apply a safety factor to operating capacity figures. Typical safety margins are 5% for cations and 10% for anions. Once the operating capacity has been determined, the required resin volume can be calculated from the throughput (volume treated per cycle) as follows:

Resin volume (litres) =
(Feed salinity (eq/m3)) x (Throughput (m3))
Resin operating capacity (eq/l)

DOWEX Resin Engineering Brochures

Engineering Information for Strong Acid Cation Resins for Water Softening
DOWEX Resins for Softening

Engineering Information for Resins for Water Demineralization

Strong Acid Cation Resins
DOWEX MARATHON™ C (131KB PDF)
DOWEX MARATHON MSC (74KB PDF)

Weak Acid Cation Resins
DOWEX MAC-3 (79K PDF)

Strong Base Anion Resins
DOWEX MARATHON A (170KB PDF)
DOWEX MARATHON 11 (120KB PDF)
DOWEX MARATHON MSA (230KB PDF)
DOWEX MARATHON A2 (238KB PDF)

Weak Base Anion Resins
DOWEX MARATHON WBA (67KB PDF)

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