compressed air system in several ways:
1.Erosion: Water mist erodes piping, valves, and other systemcomponents.
2.Corrosion: Mist condenses and combines with salts and acids within the system forming highly corrosive solutions.
3.Microbial Contamination: Moisture supplies a growth medium for bacteria and mold, which produce acidic waste and can be a health
threat.
4.Freezing: Water can freeze in compressed air lines shutting down the
system.
The result is lower productivity, increased maintenance, and higher
operating costs. Compressed air is dried to protect the system’s piping and
process equipment. Dry air also protects against lost product. Most
pneumatic equipment has a recommended operating pressure, dryness level,
and a maximum operating temperature.
Types of Compressed Air Dryers
The most common types of air dryers are:
1. Refrigerated Air Dryer
2. Desiccant Air Dryer
3. Deliquescent Air Dryer
1. Refrigerated Air Dryers
1. Refrigerated Air Dryers
Refrigerated air dryers are the most economical types of dryer that cool air to 35-50°F, condense, mechanically separate, and discharge the water, and then reheat the air. These utilize a mechanical refrigeration system to cool the compressed air and condense water and hydrocarbon vapor. The
saturated, moist air entering is precooled by the exiting cooled air in the precooler/reheater. Further cooling is provided by refrigerant in the air-torefrigerant heat exchanger. The separator removes condensed water droplets, oil, and solid particles from the air stream. Condensate is automatically discharged by a condensate drain trap. The compressed air, now free of liquid moisture, is reheated in the air-to-air precooler/reheater and discharged
into the compressed air system.
2. Desiccant Air Dryers
Desiccant dryers utilize chemicals beads, called desiccant, to absorb water vapor from compressed air (Refer to Figure 5.3). Silica gel, activated alumina, and molecular sieve are the most common desiccants used. (Silica
gel or activated aluminas are the preferred desiccants for compressed air dryers.) A desiccant dries air by absorbing moisture on its surface and holding the water as a mono or bimolecular film. The method of regeneration, the process of removing absorbed water from the desiccant, is the primary distinguishing feature among the various types of desiccant
dryers. Most regenerative desiccant dryers are dual-chamber systems with one chamber on-stream drying the compressed air while the other is offstream being regenerated. There are three ways to regenerate a desiccant:
with air, internal or external heaters, or a heat pump.
3. Deliquescent Air Dryer
Deliquescent dryers are simply large pressure vessels filled with a chemical having an affinity for water (Refer to Figure 5.4). Salt, urea, and
calcium chloride are the common chemicals used. As the compressed air passes through the vessel, the salt dissolves in the water vapor and drips to the bottom of the tank where it is drained. The dried air is then discharged through the outlet port at the same temperature at which it entered.
