DOWEX Ion Exchange Resins WATER CONDITIONING MANUAL

Brackish Water Softening
Using H2SO4 requires very careful control of the concentration of acid and flow rates to keep precipitation
of CaSO4 from occurring in the resin bed or unit piping. Table 3 offers guidelines for concentrations and
flow rates to minimize this potential problem.
Table 3. Recommended concentrations and flow rates for H2SO4 regeneration.
4.3 Equipment Required
H2SO4
Flow Rate
(%) (gpm/ft 3 ) (m 3 /h)/m 3
0.3 1.0 8.0
0.8–1.0 4.5 36.1
A vessel is required that will accommodate DOWEX MAC-3 resin, with piping, valves, chemical tank, and
accessories properly engineered for economical balance of resin capacity and chemical efficiency and
proper regeneration. Because the regeneration uses two steps, it may be necessary to supply two
regeneration systems.
In this service, DOWEX MAC-3 resin undergoes significant volume change when converted from the
hydrogen to the calcium form. Typically, swelling will be in the range of 15% and will be as much as 50%
when going to the sodium form. Sufficient freeboard should be allowed in the tank to accommodate this
volume change. The tank height-to-diameter ratio should also be maintained close to 1 to allow relief of
swelling pressures that develop.
Figure 12 is a general flow diagram for this operation. In this scheme the sodium-form weak acid cation
(WAC) resin is a polishing bed that reduces the hardness that leaks from the strong acid cation (SAC)
bed. Regeneration of the weak acid cation resin is a three-step process: first with acid, secondly a rinse,
and then treatment with caustic.
Figure 12. Weak acid resin polisher on strong acid system or weak acid series system.
Limit: 20,000 ppm TDS
Raw Water HCl, Rinse, NaOH
Ca
RNa RNa
RCa
SAC WAC WAC
Soft Water
DOWEX Ion Exchange Resins 27 Water Conditioning Manual
H + H +
LOADING REGENERATION
2NaR + CaCl 2 CaR 2 + 2NaCl
CaR 2 + 2HCl 2HR + CaCl 2
HR + NaOH NaR + HOH