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Using Accessories on
Air Compressors 2
The purpose of separators is to separate
liquids contained in the gas or air. In order to remove the
condensation, a separator is usually installed after each intercooler or
after-cooler. Direction and velocity changes occur and it may include
impingement baffles.
On lubricant-injected rotary compressors the injected lubricant must be
separated before it is cooled and re-circulated to the compressor. To
achieve this process, an air/lubricant coalescing separator is installed
directly after the compressor discharge in order to separate the
injected lubricant. It is important that the separation occurs before
cooling to prohibit condensed moisture from being entrained in the
lubricant.
With the correct use of compressed air dryers, corrosion and
contamination of the point of use processes can be avoided. This problem
can occur when air exits an after-cooler and moisture separator, which
may cause saturation. Further condensation can occur as radiant cooling
goes through the distribution piping which is exposed to cold
temperatures. The condensation can then cause corrosion and
contamination at the point of use processes.
The air in the atmosphere may contain moisture. The air is able to
contain more moisture when the air temperature is high. Relative vapor
pressure is the proper term for the moisture content in the air because
the air and water vapor are considered as gases. (The more commonly used
term is relative humidity.) Under current conditions, when the air has
all of the possible moisture, it is considered saturated. For example,
air at 80% relative humidity contains 80% of the maximum. As the air is
cooled, it reaches a temperature wherein the amount of moisture cannot
be contained and some of the moisture will then condense and fall out.
Dew point is the term for the temperature at which the moisture
condenses. The moisture content can be reduced by about 50% if the
temperature of saturated compressed air is reduced by 20 degrees F. When
the air is constricted and inhabits a smaller volume, the air cannot
contain all of the possible moisture for the atmospheric conditions.
However, some of the moisture will drop out as the liquid condensates. A
difference between the dew point at the atmospheric condition and the
dew point at higher pressures is the result of the above conditions.
Unnecessary energy and expenses will result when drying compressed air
reaches beyond the required pressure dew point. Compressed air dryers of
different types have diverse functional features, as well as differing
degrees of dew point containment. Standard dryer inlet conditions are
the basis for the dryer ratings. These ratings are normally referred to
as the three 100s, which means 100 psig, 100 degrees F (inlet compressed
air temperature), and 100 degrees F for the encompassing temperature.
The capacity of a dryer is affected if these conditions differentiate.
The dryer's rated competence can be affected by either an increase in
inlet temperature or a reduction in inlet pressure. Correction factors
are usually indicated by the manufacturer.
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