Page 270 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological
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Coagulation 225
Mass flux of polymer as neat emulsion mass amount required for 6 month’s polymer
storage is
¼ 400 mg polymer=s
¼ Q(neat) C(neat) Mass polymer (6 months storage)
¼ Q(neat) 1,064,000 mg polymer=L ¼ 1000 L=s 0:4mg=L 3600 s=h 24 h=day 180 day
Q(neat) ¼ 0:000376 L=s ¼ 6221 kg polymer
¼ 0:376 mL=s V(barrel) ¼ 55:0 gal ¼ 208:2L
¼ 22:5mL= min Mass(barrel) ¼ 208:2L 1:064 kg=L ¼ 222 kg=barrel
N(barrels) ¼ Mass polymer(6 month storage)=Mass(barrel)
Discussion
The example is given to illustrate how the polymer con- ¼ 6221 kg polymer=222 kg polymer=barrel
centration is calculated on the ‘‘as supplied’’ mass of ¼ 28 barrels
polymer as it comes from the barrel. A second point is
that the flow of polymer from the barrel, Q(neat), is very For delivery in 275 gal ‘‘tote’’ tanks with V ¼ 275
low, for example, 0.000376 L=s, which must be mixed gal ¼ 1041 L,
6
with a flow of 1000 L=s, that is, a factor of 10 . The
problem is to adequately mix the polymer with the raw
water flow so that particle-polymer contacts are made Mass(tote tank) ¼ 1041 L 1:064 kg=L
(mixing is the topic of Chapter 10). ¼ 1108 kg=tote tank
N(tote tank) ¼ Mass polymer
Example 9.9 Design for Emulsion Polymer Storage, (6month storage)=Mass(tote tank)
Dilution=Mixing
¼ 6221 kg polymer=1108 kg polymer=barrel
¼ 5:6 tote tanks per 6 month period
Given
The polymer Clarifloc A-210P, an emulsion polymer (see
3. Initial dilution=mixing. Dilute to the recommended
Example 9.8), has been selected for water treatment with a
concentration, that is, 0.5% by weight. The initial
flow, Q ¼ 1000 L=s.
high-energy mixing tank should have a detention time
Required of 30 s. Since Q (neat) ¼ 0.376 mL=s (Example 9.8),
Apply the manufacturer’s recommendation for feeding the
polymer into the raw water flow and translate this into a M(mass flux neat) ¼ 0:376 mL=s L=1000 mL 1:064 kg=L
design.
¼ 0:00040 kg=s
Solution
Concentration(diluted polymer)
1. Excerpts from Clarifloc A-210P Data Sheet
. Polymer density (as supplied) ¼ 1.064 kg=L. ¼ 0:005 kg polymer=kg water
. Suggested in-plant storage life is 6 months in
unopened drums. ¼ 5000 mg polymer=L water
. Bulk tanks should be mixed by periodically recir- Since mass flux polymer ¼ 400 mg=s
culating the contents bottom to top. Bulk tanks
can also be fitted with an agitator type mixer that and
reaches the bottom 2 ft of the tank. Drums should
be mixed very well before first use.
. In most cases, the product should not be applied Mass flux polymer ¼ Q(first dilution)
neat. C(diluted polymer)
. One method for dilution is adding the neat poly-
400 mg polymer=s ¼ Q(first dilution)
mer into the vortex of a mixing tank at a concen-
5000 mg polymer=L water
tration between 0.25% and 1.0% polymer (0.5%
is recommended) by weight. Q(first dilution) ¼ 0:08 L=s ¼ 80 mL=s
. The best-feed systems use initial high energy
mixing (>1000 rpm) for <30 s to achieve V(tank, first dilution) ¼ Q(first dilution) t(tank)
good dispersion followed by low energy ¼ 0:080 L=s 30 s
mixing (<400 rpm) for a longer time, that is,
10 < t < 30 min. ¼ 2:4L
. Polymer solution should be aged for 15–60 min.
Solution shelf life is 8–16 h. The tank requires mixing at about 1000 rpm, which
2. Storage. Based on a uniform raw water flow of can be done using a small mixer set-up; probably a
1000 L=s and polymer concentration 0.4 mg=L, the 100 W motor would work.