UFC 3-240-13FN
25 May 2005
Volume, m3 = (Radius, m)2 x (Depth, m) x 3.14
Check the bed depth at 10 points and use the average value. If there is much
difference (15% or more) in the thickness of different points, channeling may be
occurring. Channeling can be caused by too low a backwash rate.
If the calculated bed volume is less than the volume given by the
manufacturer, material has been lost during the backwash step. The lost material
should be replaced and the backwash rate carefully controlled to ensure material is not
being washed out. If the cause of the unit's performance problem or deficiency cannot
be determined, the manufacturer's service representative should be consulted.
2-2.5.1.4.4 Resin Replacement. The resin in the ion exchanger should be replaced
when either the resin capacity or the softening efficiency has decreased by 25% and
cannot be restored by cleaning and by following the specific procedures recommended
by the manufacturer. Based on a normal decrease of 1 to 5% per year, the typical ion
exchange resin should last from 5 to 25 years. With good operation, the average service
life is 8 to 10 years.
2-2.5.2
Hydrogen Ion Exchange. The hydrogen ion exchange process is
essentially the same as the sodium ion exchange process except that the regenerant
chemical is an acid (sulfuric or hydrochloric) rather than a salt. The hydrogen ion
exchange process will reduce both the amount of the total dissolved solids and the
alkalinity of the treated water. During operation of the hydrogen cycle softener, it is
necessary to check the outlet (softened) water at regular intervals. The hardness of the
outlet water should always be less than 1 ppm. The ion exchange resin must be
regenerated if the hardness exceeds 1 ppm. This check can be performed daily, once
per shift, or as required depending on unit capacity.
2-2.5.2.1
Exchange Process. Resins exchange calcium, magnesium, sodium and
all cations with hydrogen ions.
→
+
Hydrogen
+
Hydrogen
Calcium/
Calcium/
Salts in
Zeolite
Magnesium/
Magnesium/
Water
Sodium
Sodium Salts
Zeolite
The hydrogen salts are acidic and will react with alkalinity to produce carbon
dioxide and water. To provide for effective operation, the carbon dioxide must be
removed after leaving the vessel by other means.
2-2.5.2.2
Regeneration Method. The spent ion exchange material is regenerated
by contact with dilute acid, such as sulfuric acid or hydrochloric acid.
→
+
Sulfuric Acid
Hydrogen Zeolite
+
Hardness
Hardness
and
and
Sodium Salt
Sodium Salts
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