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Dayton
Water Systems’ Dual Bed DI tanks are identified by model
and batch numbers beginning with the number 6. These tanks are
readily identifiable by green tops or the green tape at the top
of the tank.
Dual Bed deionizers have 60% strong acid cation
resin in the hydrogen form and 40% weak base anion resin in the
hydroxyl form. This resin system produces a large quantity of
deionized water suitable for spot-free rinse or low solids water.
In the Dual Bed deionizers, the resins are not mixed, but placed
in separate vessels.
The cation resin initially removes positively
charged ions from the influent water supply. These ions are
replaced with hydrogen ions and the water becomes acidic and is
transferred to the anion tank. The weak base anion resin removes
only “strong acids” from the water supply. Weak acids, make up primarily of bicarbonate and
carbonate alkalinity, are not removed. Because these contaminants
are not removed, water quality is not high. However, bicarbonate
and carbonate contaminats are not part of the “dissolved
solids” which so often cause problems in industrial
applications.
Dual Bed resin can produce deionized water, up
to 200,000ohm, depending upon certain conditions. These
conditions include flow rate, feed water quality, the system set
up, condition of the resin, and the amount of time the system
sets idle. We guarantee Dual Bed resins will initially produce at
least 50,000 ohm before exhaustion of the resin bed begins.
To understand the capacity of Dual Bed resin,
it is necessary to understand in this system there is not equal amounts of resin and capacities.
Cation resin has an exchange capacity of 30,000 grains per Cu.
Ft. and anion resin has an exchange capacity of 20,000 grains per
Cu. Ft. In the 6244 Dual Bed system, there is 1.5 Cu Ft. of
cation resin or 45,000 grains of removal and 1 Cu. Ft. of anion
resin or 20,000 grains of removal.
While the mix is 45 to 20, keep in mind that
the weak base anion resin will not be “used up” with
the negative ions bicarbonate and carbonate alkalinity. By
measuring the alkalinity in the water supply and subtracting the
alkalinity from the total grains, the amount of “strong
acid” anions can be determined. In order to accurately
calculate capacity of Dual Bed tanks, the following formula
should be used. The lower capacity is what can be expected of the
Dual Bed deionizer.
45,000 ÷ Feed Water Quality (grains) = Cation
Capacity (gals.)
20,000 ÷ [Feed Water Quality –
Alkalinity] = Anion Capacity (gals.)
Typically, we use the grains capacity of 45,000
grains for the 6244 because most water supplies have high levels
of alkalinity. Because water quality indicate
devices should be used.
any other water
treatment vendors utilized Dual Beds as pre-treatment to mixed
bed exchange tanks. With Dayton Water Systems’ unique use of
weak base anion resin, it is not advantageous to use Mixed Bed
tanks to polish Dual Bed tanks or to install Dual Beds I a
worker/polisher format. To explain in further detail, the weak
base anion resin will remove approximately 25% of the alkalinity
from the water. The remaining 75% will be allowed to feed the
polishing tank. The anion resin in the polishing tank will begin
to immediately exhaust and the polishing tank will begin to
immediately exhaust and the polishing tank will exhaust before
the Dual Bed.
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