Monday 27 May 2019

What is the function of an air dryer?

Functioning of air dryer


A compressed air dryer is used for removing water vapor from compressed air. Compressed air dryers are commonly found in a wide range of industrial and commercial facilities. The process of air compression concentrates atmospheric contaminants, including water vapor.

This raises the dew point of the compressed air relative to free atmospheric air and leads to condensation within pipes as the compressed air cools downstream of the compressor.

Excessive water in compressed air, in either the liquid or vapor phase, can cause a variety of operational problems for users of compressed air. These include freezing of outdoor air lines, corrosion in piping and equipment, malfunctioning of pneumatic process control instruments, fouling of processes and products, and more.

There are various types of compressed air dryers. Their performance characteristics are typically defined by the dew point.
  •     Regenerative desiccant dryers, often called "regens" or "twin tower" dryers
  •     Refrigerated dryers
  •     Deliquescent dryers
  •     Membrane dryers

Refrigerated dryer

Refrigeration dryers employ two heat exchangers, one for air-to-air and one for air-to-refrigeration. However, there is also a single TRISAB heat exchanger that combines both functions. The compressors used in this type of dryer are usually of the hermetic type and the most common gas used is R-134a and R-410a for smaller air dryers up to 100 cfm. Older and larger dryers still use R-22 and R-404a refrigerants. The goal of having two heat exchangers is that the cold outgoing air cools down the hot incoming air and reduces the size of compressor required. At the same time the increase in the temperature of outgoing air prevents re-condensation.

Some manufacturers produce "cycling dryers". These store a cold mass that cools the air when the compressor is OFF. When the refrigeration compressor runs, the large mass takes much longer to cool, so the compressor runs longer, and stays OFF longer. These units operate at lower dew points, typically in the 35–40 °F range. When selected with the optional "cold coalescing filter", these units can deliver compressed air with lower dew points. Non-cycling dryers use a hot gas by pass valve to prevent the dryer from icing up.

Some manufacturers produce "cold coalescing filters" that are positioned inside of the air dryer at the point of the lowest air temperature (the point at which maximum condensation has occurred).

Some manufacturers are marketing compressors with built-in refrigeration dryers, but these have had a mixed acceptance in the market. 

Useful Links:-




No comments:

Post a Comment