Compressed Air Dryer Types
Moisture can be extremely harmful to a compressed air system, causing damage through corrosion, erosion, freezing and microbial contamination. Compressed air dryers were created to reduce the amount of water, hydrocarbon and water vapor within the system, thereby increasing overall productivity and decreasing maintenance over an extended period of time. There are four main types of compressed air dryers, and you will have to decide which one is best for you based on your particular needs. Does this Spark an idea?
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Refrigerated
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Refrigerated air dryers are the most popular on the market since they are easy to operate, reasonably priced and require little maintenance. This type condenses some moisture through an air-to-air heat exchanger, where hot incoming air is cooled by colder, drier outgoing air. The incoming air then goes through another heat exchanger that uses a refrigerant to cool any remaining moisture, condensing it into a liquid and draining it out of the system. Most refrigerated air dryers provide a stable pressure dew point of around 35 to 38 degrees Fahrenheit, which is the temperature that water vapor condenses into liquid water for easy removal. The two main types of refrigerated air dryers are cycling and non-cycling. The former runs automatically only when cooling is needed and shuts off when it is not; the latter starts working as soon as it is turned on and doesn't stop until someone shuts it off.
Membrane
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Membrane air dryers push the compressed air through a porous membrane large enough to allow air molecules through, but small enough to trap water molecules. Dry air is then blown over the membrane, picking up and carrying the trapped water vapor out of the system. Water will not form in the air system as long as the dried air is not exposed to temperatures below the dew point. Additionally, water is removed as a vapor, with no liquid to dispose of. These dryers can be designed to produce dew points that are anywhere from 50 degrees to negative 40 degrees F. Membrane air dryers come in a very limited number of sizes and are typically reserved for use in smaller, portable applications.
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Desiccant
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Desiccant air dryers (also referred to as regenerative air dryers) force the compressed air through a chamber filled with a moisture-absorbing substance called a desiccant. The most popular desiccants are activated alumina and silica gel since both attract water naturally, absorb it through millions of pores and hold it extremely well. Desiccant air dryers have two chambers, switching the air from one to the other when the desiccant in the first chamber reaches its dew point. Then, while the second chamber takes over, hot air dries the desiccant in the first chamber so that it is ready to take over when the desiccant in the second chamber reaches its dew point. This cycle continues over and over. Some use a smart controller to automatically switch chambers while others are on a set timer. Dew points in this type of dryer can be set as low as negative 100 degrees F.
Deliquescent
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Deliquescent air dryers are very similar to desiccant ones, using a substance -- in this case, salt tablets -- to absorb moisture from the compressed air being passed through the tank. However, the difference is that desiccants do not dissolve as they absorb water, but rather must be dried. Salt tablets, on the other hand, deliquesce into brine that is simply drained from the system. Deliquescent dryers are the cheapest to buy and maintain because they require no power and have no moving parts. Costs are limited to buying and shipping the salt tablets. The dew point of the compressed air leaving the dryer is hard to control, however, varying based on the temperature as it enters the dryer. This dryer type is most effective during the winter at preventing freezing within the system.
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