How it Works: Heat of Compression Dryer

Air naturally contains some moisture. Depending on where you are, there could be a high amount of moisture in the air (think Orlando, Florida or Houston, Texas) or very little moisture (think Death Valley, California). This moisture, also called humidity, can have drastic implications on your manufacturing processes when not properly regulated. It is important to make sure your compressed air is properly dried to achieve optimal results.

How it Works

A heat of compression dryer is a type of regenerative desiccant dryer. These machines dry air through adsorption, a chemical process in which a highly porous material attracts and holds on to surrounding water molecules, effectively removing moisture from the air.

A compressor’s direct output stream is directed through the desiccant bed or into the drum. As the air passes through, the desiccant attracts and removes moisture through adsorption. The final pressure dew point (PDP) of the surrounding air can drop to as low as -50 degrees F. The desiccant is then regenerated (heated and dried) with hot air from the compressor for continuous use.

There are two models of compression dryers: single vessel and twin tower models. Both use the same basic process to achieve dry air, but differ in structure.

Single Vessel

Single vessel dryers have two airstreams moving simultaneously through the desiccant bed: one with moist air moving from the air compressor to the desiccant to be dried and the other with hot air (sometimes with temperatures higher than 300 degrees F) to regenerate the saturated desiccant. Approximately three-quarters of the desiccant bed is devoted to drying the moist air while the remaining one-quarter is undergoing regeneration. The drum of the dryer rotates slowly (about 7 rotations per hour) to ensure that the desiccant is fully regenerated.

Twin Tower

A twin tower model uses two desiccant beds to produce dry air. One tower captures moisture from the air using adsorption, while the other regenerates desiccant through a stream of hot air directly from the compressor. The towers periodically switch functions. Once a tower is regenerated, it begins capturing moisture from the air until the desiccant becomes saturated again. Many types of twin tower dryers require an extra amount of purge air to regenerate the desiccant, sometimes equaling 15-20 percent of the compressor’s rated capacity. However, heat of compression dryers use recovered heat from the compression process, saving energy and money.

With low installation and power costs and no purge air loss on most models, compression dryers are an economical buy for most users. Determining which heat of compression dryer is best for your compressed air system starts with understanding your compressed air needs. Whether you’re looking for energy savings and recovery, low PDP, or low lifecycle maintenance costs, compression dryers can provide the solution.