Page 184 - Fluid mechanics, heat transfer, and mass transfer
P. 184
162 PUMPS, EJECTORS, BLOWERS, AND COMPRESSORS
. What are the possible causes of reciprocating compres- & Water separators are installed at different points in
sors problems? the air header system to remove condensate as the air
& Table 5.13 presents a summary of possible recipro- continuously cools on its movement through the air
cating compressor problems. distribution system.
. What are the differences between the utility and the & Instrument grade compressed air is used for both
instrument grades of compressed air used in process task-specific functions and some times, as a part of
industry? the manufacturing process.
& Utility grade compressed air is typically used as a & These applications require air free from particulate
source to power air tools, air motors, hoists, and for contamination, oil aerosols, and water vapor.
othertaskswithinafacilitythatrequiretheairtosimply & Examples of instrument quality air being used as a
be of sufficient pressure to do the intended work. component of the process include oil-free air that is
& The quality of this air stream is not normally mon- injected into a blending process as a means of
itored for the presence of water, oil aerosols or introducing oxygen into the process and use of
particulate matter, as it is not used in or consumed instrument air in injection molding process for
by the actual manufacturing process itself. plastics.
& A typical utility grade compressed air system con- & In order to achieve instrument grade air, the com-
sists of a compressor, aftercooler, receiver, and water pressed air system should be equipped with an oil-
separator. The compressor is usually of an oil-flooded free compressor, such as a dry rotary screw or a
design, equipped with an air–oil separator that is centrifugal compressor along with a refrigerated or
intended to prevent the passage of oil downstream. regenerative desiccant dryer.
This is done primarily to maintain the volume of oil & The items in an instrument air system that are often
required in the lubrication of internal components common to both utility grade and instrument grade
and to ensure proper levels for introduction into the systems include the aftercooler and the receiver
compression cycle. vessel.
& The aftercooler is also normally integrated into the & The compressed air cycle in both utility grade and
compressor package and may utilize a heat exchang- instrument grade air are equipped with removal
er as a means of removing the heat of compression system for the heat of compression, particulate con-
from the compressed air stream. tamination and water vapor.
& The receiver vessel (if used) will be sized according & The major difference between the two systems en-
to consumption trends and as a surgevessel to control sures the oil-free compressor module and the use of
pressure fluctuations in the header. an air dryer.