A compressed-air dryer and filter installation supplies clean, dry compressed air to equipment that uses the air as motive power. Filtering and drying the air protects the equipment from damage from contaminants in the air such as liquid water, water vapor, dust from the atmosphere, scale from the inside of the pipes, and breakdown products from the lubricants in the air compressor.
The compressed-air dryer and its associated filter are selected based on several considerations. These begin with the volume and pressure of the air to be cleaned and dried. Then look at the environment the dryer and filter will be in: What are the surrounding temperatures; will they be subject to vibration? Another consideration is how dry, that is, how low the dew point, of the compressed air supply must be. The availability of maintenance and reliability of operation are other considerations. Another question is whether continuous operation of the compressed-air system is required.
There are three common types of compressed-air dryers: the single-tower dryer, the regenerative dryer and the refrigerated dryer.
The single-tower dryer is filled with a deliquescent desiccant that dissolves as it absorbs water vapor. The liquefied desiccant must be drained periodically and replaced by fresh desiccant. This is usually done only a few times a year. The single-tower dryer does not require any external power supply.
The regenerative, or twin-tower dryer, uses one tower to dry the compressed-air flow while the other tower is having the moisture in its desiccant removed. The desiccant is dried (regenerated) by heat or by air bled off from the active tower. The regenerative dryer is used when the flow of compressed air is continuous.
The refrigerated compressed-air dryer uses a refrigeration unit to condense the water vapor in the compressed air and a water separator to remove the liquid water. A refrigerated dryer can provide a supply of compressed air with a dew point between 35 and 38 degrees Fahrenheit. Refrigerated air dryers are used to supply air to pneumatic temperature control systems. They do well in an indoor, clean, temperature-controlled environment.
The selection of a type of compressed-air dryer is based on an examination of its use, location, the power available and the pneumatic equipment served. If more than one type will do the job, then initial cost, reliability and maintenance costs are additional considerations.
Compressed-air filters protect the dryer and the equipment using compressed air from damage. There are two types of filter elements, particulate and coalescing.
Particulate filters remove particles not removed by the air compressor pre-filter and other particulate matter. Coalescing filters bring contaminants together so they can be captured by the filter element. The selection of the type of filter used is based on an evaluation of various contaminants likely to be present.