4 Compressed Air Dryer Types
In industrial settings, sometimes dry compressed air is a necessity for the end product. This is where compressed air dryers come in, but how many types are there?
There are four different types of compressed air dryers on the market, they are refrigerated, desiccant, membrane, and chemical air dryers. Understanding how each one works and how much moisture can be removed will help determine which is needed for certain applications.
Explaining Compressed Air Dryers
Compressed air is used for many operations, but air compressors can cause moisture to condense inside tanks or pass along the collected moisture to the end product. This can cause rust in machines, malfunctioning parts, or contaminate the finished products.
Compressed air dryers significantly reduce the moisture in the air. In humid environments where compressed air is essential for production, these machines can mean the difference between quality products and profits, or inferior products, and/or delayed manufacturing.
A compressed air dryer’s performance is measured by the dew point of the air. The dew point is the temperature at which cold air can no longer hold ambient moisture, and it condenses into liquid, often forming droplets, i.e., dew.
Four Types Of Compressed Air Dryers
It’s important to understand the different types of compressed air dryers, the advantages and disadvantages of each, and how they work. Depending on how dry the air needs to be may determine which air dryer will be best.
Refrigerated Air Dryers
Refrigerated air dryers work on the same principle as air conditioners. They use a chemical known as freon that is passed through aluminum or copper coils. When the freon is compressed it gets very cold and causes the coils to drop into subzero temperatures.
Outside air is then passed over these coils which condense the moisture, leading to dryer air. Using this process, refrigerated air dryers can reduce the dew point of compressed air to 36°F (2°C).
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Cycling Refrigerant Air Dryers
These compressed air dryers work to conserve energy. When the compressed air isn’t being used, the machine cycles down or turns off until it is needed again. They still use refrigerants to cool and condense the air, but they are more energy efficient.
The savings in energy comes at a cost though, the moisture removed from the air is not constant because of the cycling. They also have a high, initial set-up cost because of their size and weight. In areas where extremely dry air isn’t as important, these machines work well.
Non-Cycling Refrigerant Compressed Air Dryers
Refrigerant is continually cycled through the compressors and coils in non-cycling air dryers. This helps to keep a more constantly low dew point regardless if the air compressor is constantly running or not.
Advantages of Refrigerant Compressed Air Dryers
This type of compressed air dryer can be relatively inexpensive compared to other options. Though the refrigerant may need to be replaced or refilled on occasion, this and other maintenance costs are often lower. In areas where oil particles can become airborne, refrigerant compressed air dryers are not sensitive to these particles.
Disadvantages of Refrigerant Compressed Air Dryers
Though these types of compressed air dryers can remove a lot of moisture from humid air, they are somewhat limited in how much moisture they can remove. Applications, where end products will be subjected to sub-freezing temperatures, are not recommended for refrigerant air dryers. The moisture still in the air could freeze and cause major damage.
While refrigerant compressed air dryers can remove a lot of moisture from the air, these dryers shouldn’t be used where applications are very sensitive to water.
Desiccant Compressed Air Dryers
Desiccant air dryers use drying agents such as silica gel or activated alumina to remove moisture from the air. These dryers typically have a pair of containers filled with the desiccant agent. When one container becomes saturated with moisture, the other container is then used to dry the air as the saturated container is dried.
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The saturated container can be dried using a heat source or dry air. This process cycles back and forth and produces much drier air than refrigerant units.
Most desiccant compressed air dryers deliver air at dew points down to -40°F/-40°C, though some can even deliver dew points as low as -100°F/-73°C. When compressed air will be constantly subjected to extremely low temperatures, desiccant compressed air dryers are the best choice.
Advantages of Desiccant Compressed Air Dryers
From the start, desiccant air dryers can produce dramatically lower humidity compressed air and dew points into sub-zero temperatures. They can work in cooler temperatures than refrigerant compressed air dryers which work best in warmer climates.
Operating costs for desiccant air dryers can be minimal. Though desiccant air dryers that use a heating system to dry the saturated containers will have a higher energy cost compared to units that use compressed air to dry them.
Disadvantages of Desiccant Compressed Air Dryers
These compressed air dryers can be quite expensive first off compared to refrigerant dryers, plus the desiccant material will need to be replaced about every three to five years.
Desiccant compressed air dryers need filtration in place to capture any oil particulates in the air. When oil settles on desiccant materials it can degrade them and reduce the ability to dry the air.
Chemical Compressed Air Dryers
Chemical air dryers use beds of deliquescent materials such as calcium chloride, sodium, or lithium chloride to extract moisture from the air that passes over. As moisture combines with these chemicals, they eventually turn to liquid themselves and have to be replaced.
A good filtration system is needed on these compressed air dryers to prevent the chemicals from ending up in the final product. Without this filter, the chemicals could cause buildup and equipment failure as well as contaminated air.
Chemical compressed air dryers can achieve dew points in compressed air as low as 27°F (15°C). While desiccant dryers consistently achieve lower dew points, chemical air dryers still outperform refrigerant compressed air dryers.
Advantages of Chemical Compressed Air Dryers
Set-up and operation of chemical compressed air dryers is relatively easy and inexpensive as there are no moving parts to maintain. The only costs incurred with these air dryers are the replacement and disposal of chemicals and filters.
Disadvantages of Chemical Compressed Air Dryers
Depending on the chemicals used to dry the air and how frequently compressors are used, changing chemicals can become expensive. Disposal of these drying chemicals can become expensive as well. These spent chemicals have certain protocols in place for disposal and may be difficult to maintain.
Membrane Compressed Air Dryers
Membrane compressed air dryers use special masses of semi-permeable microtubes that let air pass through but can be made to capture moisture or other materials like certain gasses.
As air is pushed through the fibrous microtubes, water vapor is absorbed leaving behind dry air. To dry out the membrane filter, a small amount of air is recirculated back along the outer surface area of the microtubes.
These compressed air dryers can produce dry air with a dew point as low as -40°F/-40°C. Some of the great things about membrane compressed air dryers is they have no moving parts, they create almost no noise, and they have no need for electricity. They require very little maintenance because of the above benefits.
There are no parts to service aside from replacing the membrane filter yearly on average. Membrane compressed air dryers don’t have costly chemicals or need fluids like oil or refrigerant added constantly.
Membrane dryers are ideal for food production, areas such as explosive environments because they are basically explosion-proof, and sub-freezing environments because of the extremely low dew point they produce.
Advantages of Membrane Compressed Air Dryers
Membrane compressed air dryers are easy to operate and maintain. There is no need for specialized service people to work on them. The only thing that needs to be done on membrane compressed air filters is to replace filters as needed.
These air dryers can be used in remote locations that don’t have much access to electricity because they have no moving parts and don’t use any power. Membrane air dryers are also nearly noiseless.
Disadvantages of Membrane Compressed Air Dryers
Because of the delicate, fibrous microtubes, membrane-compressed air dryers need a quality pre-filter to effectively clean the air before passing through. The membranes have to be free of dust, particulates, and oil. Because of this, the pre-filter will need to be replaced frequently.
Conclusion
Depending on how dry the compressed air needs to be, and the working environment, there are four different types of compressed air dryers that can be employed. Desiccant, refrigerant, chemical, and membrane air dryers.
Desiccant compressed air dryers can remove the most humidity from the air, but they can be expensive in the beginning and need the drying medium changed periodically.
Refrigerant air dryers can work in steamy, or dirty environments because these particulates don’t affect drying. They are relatively inexpensive to set up and maintain, but they reduce the moisture in the air the least.
Chemical compressed air dryers are easy and inexpensive to set up, and there are no moving parts. The chemicals used to dry the air can get costly as they need to be replaced frequently and may have disposal issues.
Membrane air dryers also have no moving parts, and can be used in remote and hazardous locations, but need a good quality pre-filtration to keep the membranes clean as possible.
