By Colter Marcks
Prevent Moist Air Contamination
Every food and beverage manufacturing process uses air, which commonly has direct contact
with the product or surfaces the product
touches. Compressed air is used to
texturize food, dry sterilized equipment,
form bottles, move ingredients through
lines and protect liquids in storage tanks.
However, compressed air can introduce
moisture into a finished product.
It’s critical then, to keep process
air clean and sterile. If not removed,
organisms within air can quickly multiply
downstream, altering the taste — and
potentially the safety — of your product.
The contaminant most prevalent in
compressed air systems is not rust or dirt.
It’s liquid, with water and oil both common
moisture threats. All intake air has
humidity, and most compressors operate
with lubricants. Water and oil make an
ideal organic diet for microorganisms, and
the dark warm crevices in compressed air
lines can provide a breeding space. Any
oil/water biofilm that seeps downstream
can also clog and degrade process piping
Keeping air dry and oil-free, then, is a
very important part of keeping it sterile.
A series of filters after air is generated
and cooled will help minimize the risk
of water, oil and bacteria migrating
downstream into your product. Here are
Filtration Steps for
All compressed air systems will have a
water problem starting in the compressor
room, whether the inlet is plumbed to the
outside or draws from a plant’s indoor air.
The volume of humidity will simply vary
with ambient air conditions, depending on
seasonal weather or climate.
As ike air gets squeezed in the
compressor, it heats up and needs to be
cooled to a subtle temperature useful for
processing. Compressor systems have an
after-cooler for this purpose. The after-
cooler also functions as a refrigerated dryer,
chilling the air and removing bulk moisture
produced during condensation — similar to
air condensing on a cold glass of beer.
However, there is still significant liquid
content in compressed air after it leaves
a refrigerated dryer. It’s important to send
the air — and any residual oil — through
a sequence of treatments that will remove
progressively smaller liquid particles.
These filters are:
• A cyclone separator to remove bulk
water in high volumes
• A coalescing filter to extract more
difficult aerosol liquid
• An air dryer to eliminate remaining
Each component should be carefully
selected and sized for your source air
humidity and processing requirements.
A cyclone separator is a housing
without a filter element inside. It operates
on principles of inertia, taking advantage
of the density differences between air
and water. Spinning at high velocity, liquid
particles (heavier than air) fall out of the
rotating path and hit a receptacle, where
they’re drained away.
In choosing a cyclone separator, be
aware that higher velocities produce
higher separation efficiencies. It’s also
important for optimal device functioning
not to over-size the separator. Match the
device’s design flow rate with the system
flow rate, so it operates efficiently.
As important as the cyclone is in
removing bulk water and courser
contaminants, it’s only the first step. A
coalescing filter afterwards is necessary
to capture aerosols.
Air flowing through the heat exchanger
in a refrigerated dryer encounters pipes,
fittings and elbows that will aerosolize
any liquid in that air. Like fog, aerosols are
hard to catch — and that’s the purpose of
a coalescing filter.
A coalescing filter is designed to
capture very tiny droplets of liquid and
combine (coalesce) them into larger
droplets that can be drained away. When
choosing a coalescing filter, it’s important
to know the removal efficiency you
require, as well as filter media that will
readily shed water. This shedding factor
is important, because wet filters restrict
airflow. You want your filter to remove
water while still operating in as close to a
dry state as possible.
The best coalescing filters will have
a pleated media, a high flow rate and
low pressure drop. Look for filters with
hydrophobic and oleo-phobic pleated
media that have been proven to perform
according to ISO 12500 testing. These
test results ensure that different
manufacturers’ products can be compared
directly. Pleated filters with a free fiber
structure are typically better-performing
than wrapped or resin-bonded medias,
which have glues (resins) that take up
space and block airflow. Filters with
high flow rates and low pressure drop
provide improved cost-savings, since less
pressure and energy are needed to move
air through the system.
A coalescing filter operates “inside
out” compared with traditional particle
Water and Oil in Compressed Air Pose High Risk to Food and Beverages
A facility supervisor inspects a
cyclone separator on a compressed
air system, followed by coalescing