COUNTERFLOW
(CASCADE) RINSING
Another advantage of using counterflow rinsing to reduce water
usage is that the efficiency of an existing waste water treatment
system is enhanced and the requirements for any new system are
reduced. The graph on the reverse side of this page show a single
(top line), double counterflow (center), and triple counterflow
(bottom) rinse configuration. To maintain a 100 ppm residual in
a final rinse chamber would require less than 1 ppm for a triple
counterflow rinse, (Follow the 100 ppm line on the vertical scale
( residual concentration is 100 ppm in the clean rinse chamber)
across the graph to where it intersects the curves), a double
counterflow rinse intersects at 8 l/min, or about 10 times the
flow rate for the same concentration. A single rinse tank can't
even get to down to 100 ppm at the dragout and flow rates graphed!
Formula and assumptions for the attached graph.
Calculating the required flow into a rinse tank to maintain a
required dilution level in the last work cell. For a single rinse
tank, without counterflow:
The required flow Q = K (dragout) x Cp (salt concentration
in dragout solution)
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Cn (salt consentration allowed in rinse)
1. Q = KCp/Cn
For example:
A. Copper bath having 250 grams/liter copper.
B. Dragout = 20 ml/sq.ft
C. Production of 100 panels /hour @ six sq.ft. each panel.
The attached graph and following formulas show how much water
reduction is possible by changing from one type of rinsing program
to another. An advantage of this approach is amount of water required
for rinsing is easily calculated.
Then: 6 sq.ft./panel x 100 panels/hr x 20 ml/sq.ft x .25 grams/ml
= KCp
KCp = 3000 grams/hour of copper.
For Cn = 200 mg/l
Converting to miligrams/minute Q=50 g/min
For
Cn = Q=
50 mg/l 1000 l/m (264 gpm)
100 mg/l 500 l/m (132 gpm)
200 mg/l 250 l/m (66 gpm)
For a counterflow rinse station, the equation changes to:
2. Q = [(Cp/Cn)1/n+1/n]K
For a two stage counterflow rinse, n = 2:
3. Q = [(Cp/Cn)1/2+1/2]K
Using the same example as above, we find the following relationship
exists as graphed below.
Where: K = 6 sq.ft./panel x 100 panels/hr x 20 ml/sq.ft = 12,000
ml/hr or 200 ml/minute.
Cp = .25 grams/ml as above.
Example: Flow rate required to maintain 100 ppm in a single, double
or triple final rinse tank.Find the 100 ppm line on the vertical
scale. Move to the right until it intersects each line. Triple
rinse requires 2.8 liters per minute(not shown on graph).
Double rinse requires 10 liters per minute.
Single rinse can't get below 1000 ppm, even at 44 liters/minute.
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