MIL-HDBK-1003/6
f) With supporting gravel and rinsing space for backwash, the
height will be 6 ft 3 inch (1.91 m). This based on a 1 ft (0.305 m) support
bed and a rinse space height equal to 3/4 of the resin bed depth. Rinse space
or freeboard should be not less than 18 inches.
g) Regeneration for the selected resin requires 10 pounds of salt
per cubic foot (160.2 kg/cubic meter) of resin times 28.8 cubic feet (0.811
cubic meters) or 288 pounds (130.6 kg).
h) The amount of salt per 1,000 gallons (3.79 cubic meters) of
softened water is 288 divided by 72 or 3.96 pounds.
Sodium Hydrogen Ion Exchange Split Stream Softening. This system
7.5.3
reduces both hardness and alkalinity when arranged as in Figure 32. It blends
water from the hydrogen and sodium units for 4.4 to 13.1 grains per cubic foot
alkalinity. A degasifier after the cation exchangers will reduce the carbon
dioxide from the hydrogen cation exchanger. The proportion of flow through
the hydrogen cation exchanger about equals the alkalinity reduction divided by
the total cations, as calcium carbonate. Since both the regenerant and
effluent water of the hydrogen cation unit are acid, the tank is usually
fiberglass reinforced plastic (FRP) and the piping polyvinyl chloride (PVC).
Sodium Cation Chloride Anion Conditioning. This system, as
7.5.4
arranged in series (see Figure 33), reduces hardness and alkalinity but
increases the chloride content. Cations are exchanged in the sodium-cation
system and anions in the chloride-anion system. The latter reduces alkalinity
80 to 90 percent, using salt and caustic. Since no acid is required, this
system is favored for low pressure boilers, even though other methods are
often more economical and efficient. Caustic will increase capacity only if
total alkalinity is less than 50 percent of total anions; otherwise caustic
provides no benefit.
Demineralizer. A demineralization unit is a combination of a
7.5.5
hydrogen cation exchanger with an anion exchanger. See Figure 34. After the
hydrogen cation process, the effluent contains dilute hydrochloric and
sulfuric acid, plus carbon dioxide. Hydrogen ions have also converted the
dissolved silica to hydrogen silicon trioxide. The effluent then passes
through the anion exchanger. Refer to Table 18, for recommended applications.
Weakly Basic Material. If a weakly basic material is used in the
7.5.5.1
anion exchanger, the acids are neutralized but both carbon dioxide and silica
pass through the exchanger. Utilize a degasifier to remove the carbon dioxide
mechanically to a residual carbon dioxide content of 2 to 5 milligrams per
liter. Weak base materials are used when the raw water is high in sulfate and
chlorides, and when silica is not objectionable.
135
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