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News
CROWN
Solutions, Inc. Technical Resource
 Foaming
Cooling Tower
By James McDonald, PE, CWT
You
walk into work one day and see white tufts of foam shooting
out the top of your cooling tower and floating down
onto the nearby cars and equipment. The Plant Manager
calls you into his office and says, “Make it stop before
I get complaints and bills for car washes and new paint
jobs!” Your mind races for a solution, and then you
remember reading about cooling tower foaming in the
March 2006 issue of the CROWN Solutions, Inc. Technical
Resource.
Foaming
Causes
There are multiple reasons for a cooling tower to have
foaming. Your cooling tower may have one or a combination
of these causes at work. Causes for cooling tower foaming
can include:
- Chemical
overfeed,
- Over
cycling,
- Excessive
suspended solids,
- Protein
byproducts from microbiological growth,
- High
alkalinity,
- Process
contamination, and
- Surfactants.
Chemical
Overfeed
An overfeed of biocide or treatment chemical can cause
foaming. Reduce the chemical feed, blow down the cooling
tower, and add an antifoam if necessary. It usually
does not take much antifoam to work, so be careful not
to add too much antifoam because this can cause foaming
too. (If you do not have an antifoam onhand, WD-40 has
antifoam properties and will work in a pinch. Be aware
that this adds oil to the system though.)
Over
Cycled
An over cycled cooling tower can foam. Blowdown the
system to within control parameters.
Excessive
Suspended Solids
Excessive suspended solids in a cooling tower due to
nearby construction, a nearby dirt road, grain unloading,
a dry summer, etc. can cause foaming in the cooling
tower. Remember that cooling towers act as air scrubbers
too. Any dirt in the air will eventually end up in the
cooling tower water. Eliminate the source of the suspended
solids, blow the system down, or use an antifoam.
Protein
Byproducts from Microbiological Growth
If your tower has excessive microbiological growth,
their waste and decomposition byproducts can cause "protein
foam" in your cooling tower. Also, if your tower uses
an intermittent biocidal feed instead of a continuous
feed, the decomposition products during these biocidal
events  can
cause "protein foam" in the cooling tower. Re-evaluate
your biocide program and use an antifoam if necessary.
High
Alkalinity
High alkalinity in a cooling tower can cause foaming.
This can be especially true when softened, nondegasified
reverse osmosis concentrate is used as makeup to the
cooling tower. Because the RO concentrate is soft water,
you may be able to run at higher alkalinity levels;
however, higher alkalinity can cause foaming. Re-evaluate
your control parameters and increase blowdown if necessary
to reduce foaming.
Process
Contamination
Process contaminants such as oil can cause foaming in
the cooling tower. Eliminate the contamination, blowdown
the cooling tower to remove the contaminant, and use
an antifoam if necessary.
Surfactants
Often times cooling tower sumps are located in the floor
of a facility. If the floors are washed down with detergents,
these detergents can end up in the sump and cause foaming.
Also, never rule out the possibility that someone has
simply poured a bottle of soap into your system. In
an  industrial
setting this is probably not a possibility, but in a
commercial or college setting you never know. Remove
the surfactant if possible, blowdown the cooling tower,
and use an antifoam if necessary.
Conclusions
As you can see, cooling tower foaming can have many
causes and is the end result of other problems that
need to be addressed. Cooling tower foaming can damage
nearby equipment, ruin paint on cars, and may even be
an inhalation source for Legionella bacteria. The “big
picture” when dealing with a foaming cooling tower is
as follows, but will be unique for each system.
- Return
the cooling tower to normal operating parameters.
- Eliminate
the source of the foam.
- Blowdown
the system to remove foamcausing contaminants.
- Apply
antifoams/defoamers as required.
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