          
Furrow Pump, Inc.
P.O.
Box 1849
8525 SW
St. Helens Dr.
Wilsonville,
OR 97070
Phone:
(800) 937-3666
FAX:
(800) 377-9960
www.furrowpump.com
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| Example 2: The
Rest of the Story |
| A local tool
manufacturer uses acid to clean and prepare the surfaces of its components, and caustic
cleaner for its tanks and other maintenance purposes. Along with their process and
cooling water, their water flows can vary from zero to 500 gallons per minute. As
much as possible, acid and caustic dumps are planned and done at the same time so that
they neutralize each other, minimizing the amount of pH treatment chemical needed to keep
the plant discharge pH within the allowed window of 5 to 10. Still, it is difficult
to always do this, so the wastewater pH can vary from as low as 3 to as high as 11, so a
treatment system was called for to insure that the plant effluent always complies with
environmental standards. |
| There is of course no
need to treat water within the acceptable discharge range, but when sudden surges of acid
or caustic are detected by the pH probe, the system must respond instantly, and it must
respond in proportion to that moment's flow to get the treatment right. This is
possible due to the plant's effluent flowmeter, which has a 4 to 20 mA output signal.
With the chemical pumps connected directly to this control signal, they are ready
to respond immediately at the appropriate level whenever the pH goes beyond its programmed
set points. For this application, having those set points at 6 and 9 should prevent
the discharge from going below 5 or above 10. This does depend on adequate mixing and
reaction time, of course, which need to be engineered into the system. |
| The system described
here works by controlling power to the pumps in relation to the measured pH load.
Essentially, the pumps are "asleep" inside the 5 to 10 discharge window, because
they have no 120 VAC power to operate with. The flow signal might be telling one of
the pumps to go like mad, but with a neutral pH there is no need to treat the water, and
they can't work without power. But as soon as the pH wanders, a relay turns on the
power and the pump responds in proportion to the demand. All in all, this is a
pretty efficient way to operate. The only time water that could use treatment
doesn't get treated, is when it is below the minimum measurable flow (which is neutralized
by the bulk of the water already in the system). The tool manufacturer gets an
efficient and economical package to solve his discharge problem. |
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