UFC 3-240-13FN
25 May 2005
between regeneration cycles is determined by the softener capacity and the hardness in
the water. See the example calculations below.
English Units
The maximum capacity of the ion exchange softener is 2,000,000 grains.
The water being treated has 257 ppm total hardness. If the softener
regenerations cycle is set for maximum capacity, how many gallons of
water can be softened before the softener must be regenerated?
Removal
=
Capacity, grains x 17.12
Total hardness, ppm, in raw water
=
2,000,000 grains x 17.12 ppm/1 grain per gallon
257 ppm
=
133,230 gallons
Metric Units
2,000,000 grains x (1 pound/7,000 grains) x (453.6 grams/1 pound)
= 129,600 grams
Removal
=
Capacity, grams x 1000 mg/gram
Total hardness, ppm (mg/liter), in raw water
=
129,600 grams x 1000 mg/gram
257 ppm (mg/liter)
=
504,280 liters
Thus, for a softener with a rated capacity of 2,000,000 grains (129,600
grams), 133,230 gallons (504,280 liters) of water, with 257 ppm total
hardness, can be softened between regeneration cycles.
2-2.5.1.2
Regeneration Cycle. Regeneration of the ion exchange resin refers to
replacement of the calcium/magnesium hardness that has accumulated on the ion
exchange resin as a result of the exchange with sodium ions. The regeneration cycle is
a process involving a number of steps during which the softener is taken off-line and
backwashed. The resin is regenerated by treatment with a strong solution of salt
(sodium chloride) and then rinsed.
When the exhausted ion exchange resin material is washed with a strong
sodium chloride salt solution (brine), the resin is regenerated by the hardness (calcium
and magnesium ions) being exchanged for sodium ions.
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