Types of Compressed Air Dryers
In the world of manufacturing,
there are three utilities that are considered essential to most
processes: water, electricity and natural gas. That said, there is one
more utility considered nearly as important as these. Compressed air, is
considered the fourth utility in manufacturing
A compressed air dryer is a
machine that sucks in and significantly reduces the moisture content of
ambient air. In manufacturing, air dryers serve the vital role of
rendering air more sanitary and conducive for workers and products
alike. Depending on the moisture levels of a given environment, the use
of a compressed air system can make all the difference between whether
or not a production is even achievable.
Compressed air dryers can be
split into the following categories:
- Refrigerated drying units:
- Desiccant drying units:
- Heatless
- Heated — internal or external
The main difference between each dryer type is the agent placed inside the machine to dry the incoming air.
Out of all the compressed air dryers,
the refrigerated dryer is the most popular and widespread type. True to
its name, the
refrigerated air dryer functions in a similar manner to
home refrigerators in that a cooling process is employed that prevents
moisture. The main difference is the objects or elements being cooled,
because whereas a kitchen refrigerator cools and preserves perishable
foods and beverages, a refrigerated air dryer maintains the quality of
air in manufacturing plants.
In a
refrigerated dryer, compressed air is cooled to around 35 degrees Fahrenheit.
After the air has passed through the inlet valve, the moisture is
extracted and drained, and the newly dried air is reheated by incoming
air. At the end of each cycle, the outgoing compressed air has a dew
point in the range of 35 to 40 degrees Fahrenheit.
Overall, the process of the
refrigerated dryer creates a more sanitary
working environment that is also far more conducive for manufacturing.
In a non-cycling refrigerated dryer, the refrigerant perpetually
circulates within the machine. This allows for quick responses to
changes in the load, be it low or high densities of moisture within the
incoming air. As such, factory environments with steamy engines can be
de-moisturized in much the same way as low-moisture environments. The
flow of the refrigerant is regulated with a bypass or unloader valve. In
most units, the refrigerant is condensed by a heat exchanger after the
compression process has completed a cycle.
CFC refrigerants like
R12 and R22 were used in vintage refrigerant
air dryers, though times
have changed regarding the acceptability of such gases due to concerns
over their impact on the environment. Therefore, in newer
refrigerant dryers, a different range of chlorine-free refrigerants are used, such
as the eco-friendlier R134A and R410A. The change was brought about by
the Montreal Protocol, an international, anti-ozone-depletion treaty
that was implemented in 1989.
Refrigerant dryers of the cycling variety use refrigerant to cool
down a glycol or aluminum mass, which surrounds the air passage. The
compressed air is then cooled by a thermostat-controlled heat sink. The
advantages of a
refrigerant air dryer break down as follows:
- Advantages of refrigerant dryers in general:
- Inexpensive to set up
- Inexpensive to operate
- Low maintenance costs
- Resistant to airborne oil particles
- Disadvantages of refrigerant dryers in general:
- Minimal dew point capacity
- Advantages of non-cycling units:
- Consistent dew point
- Continual operation
- Disadvantages of non-cycling units:
- Don’t conserve energy during low airflow
- Advantagesof cycling units:
- Conserve energy during low airflow
- Disadvantagesof cycling units:
- Variable dew point
- Larger and heavier due to heat sink
- Higher overhead cost
