As those who work in industries that require the use of compressed air know, it is very important not to get excessive water trapped in the air, whether in the vapour or liquid phase.
Compressed air contains not just water droplets and vapour but also debris, oil, and other foreign matter. If there is too much water vapour in the compressed air, this could cause a number of operational problems that range from corrosion and rust in pipelines to fouling of processes and frozen external airlines.
Compressed air dryers are mechanisms that remove water vapour from compressed air. There are three common types of compressed air dryers: refrigerated compressed air dryers, membrane compressed air dryers and desiccant compressed air dryers.
Refrigerated Compressed Air Dryers
These dryers operate via the use of air-to-air and air-to-refrigerator heat exchanges. Incoming compressed air is cooled by the air-to-air exchange, as the outgoing cool and dry air reduce the temperature of the warmer incoming air.
This incoming air then goes into the air-to-refrigerator exchanger, where the temperature is reduced through the use of liquid refrigerant to 3 degrees Celsius. This condenses any moisture that is present in liquid water, which subsequently drains off, and the cool outgoing air starts off the process all over again.
Membrane Compressed Air Dryers
Membrane dryers remove both contaminants and water vapour, as they are a filtration system that works with existing compressed air systems. Humid compressed air passes through a bundle of hollow fibres made of a membrane designed specifically to attract water vapour.
Moisture is diffused through to the outside of the thin membrane where it is removed, and the higher the pressure in the compressed air system, then the better the membrane dryer will perform. This is a space-saving system and does not use refrigerating agents in its operation.
Desiccant Compressed Air Dryers
As the name suggests, this type of compressed air dryer works by moving compressed air through a compartment that is filled with desiccants. Desiccants are materials with natural moisture-absorbing properties.
A desiccant compressed air dryer or regenerative dryer as it is also known usually has two identical desiccant chambers. The unit will automatically use one compartment to dry out compressed air while the other compartment, which is also filled with desiccant, is being regenerated.
The use of the two compartments alternate automatically, ensuring a constant supply of dry compressed air, and because it self-regenerates, it also allows for easy maintenance of the unit. The regeneration can be done utilising heat, compressed air, vacuum or a combination of these technologies.
