Advanced Heat Exchanger Design Improves Compressed Air Dryer Systems

Moisture, oils, vapors, and other contaminants in industrial compressed air systems have long been a costly problem that negatively affect the efficiency of pneumatically operated appliances, controls, instruments, machinery, and tools, and reduces the service life of motors, air tools and cylinders. If not corrected, wet, contaminated compressed air causes equipment problems that increase maintenance costs and downtime. In many applications, liquid water in compressed air directly impacts the quality of finished products, resulting in rejects and reduced productivity.

Temperature and pressure are the variables that affect the water-carrying capacity of saturated air. Air at lower temperature and higher pressure carries less moisture. Compressed air at the inlet to a dryer is saturated, at a temperature higher than ambient. Any drop in temperature throughout the compressed air lines will cause the unwanted moisture to condense into water droplets.

Refrigerated industrial air dryers use this principle to remove water from compressed air before it is fed through the compressed air lines to the systems that use it. This removal is accomplished by cooling the air with a refrigeration unit to a low temperature at which moisture in the air is condensed and separated from the air stream. The temperature (typically between 35°F and 39°F) becomes the pressure dew point of the air. The condensate is then separated from the air and drained. After reheating (typically), the air is discharged to the compressed-air system. No further moisture will condense in the air lines assuming the temperature is kept above the pressure dew point temperature.

Of course, there is a price to pay for the operation of the compressed air dryer. Energy costs consumed by the dryer are proportional to the dryer's refrigeration system efficiency and the effectiveness of its transfer of heat away from the compressed air passing through the dryer. In a True-Cycling dryer design from Zeks Compressed Air Solutions, West Chester, PA, a heat sink reservoir is used as an intermediary between the refrigeration and the air flow systems. This intermediary enables the refrigeration system to cycle, or turn off, when it is not needed, reducing energy consumption and saving costs. True-Cycling operation also reduces the wear-and-tear on the dryer's refrigeration system under most operating conditions, decreasing operating costs, improving compressed air quality, boosting productivity, and increasing plant equipment life. Cycling operation creates the added benefit of allowing the dryer to make use of the greater refrigeration system capacity and efficiency at lower ambient temperatures.

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