Instrument Air Dryer Types – How Industrial Air Dryers Work
Compressed air is a vital utility in industrial and petrochemical processes. It is used to operate critical machinery such as jackhammers, pneumatic drills, and wrenches as well as process equipment like air cylinders and pumps.
What Are Industrial Air Dryers Used For?
An industrial air dryer is a piece of equipment or machinery used to dehumidify compressed (process) air to significantly lessen or eliminate moisture present in the air stream. Industrial air dryers can be used to reduce the dew point of compressed air to below the lowest temperature obtained on the site (typically up to 18°F lower than the coolest point). Compressed air testing can determine if your equipment is at risk.
The Importance of Air Dehumidification in Industrial Processes
Atmospheric air typically contains a percentage of water vapor which can create several problems in pneumatic equipment and adversely affect the quality of the final products.
- Vapors present in the air stream can condense into the compressed air system and cause corrosion, scaling, or clogged apertures and valves. For this reason, dry air is used for pipeline decommissioning, pipeline drying after hydrotesting,
- The presence of moisture in process systems reduces the lubrication, leading to wear of mechanical moving parts.
- Condensed vapors can cause freezing of control lines, which interferes with the operation of controls.
- Moisture in compressed air systems can cause industrial metering equipment to give inaccurate readings which could lead to unnecessary shutdowns.
Instrument Air Dryer Types
Now that you understand the importance of utilizing an air dryer for your industrial equipment, learn about the common types of air dryers for air compressors to help you select the best option for your needs.
Refrigerated Air Dryer
Refrigerated air dryers are a popular option for eliminating water vapors, aerosols, and mist present in compressed air systems. They can achieve dew points suitable for most applications and are relatively simple to design, install, and maintain.
Refrigerated Air Dryer Working Principle
The working principle of a refrigerated air dryer is the same as a domestic refrigerator or air conditioning unit. Compressed air entering the unit is first cooled in an air-to-air heat exchanger.
The outgoing cooled air pre-cools the hot incoming air, condensing the moisture present into liquid water which is drained out of the system. The pre-cooled air then enters an air-to-refrigerant heat exchanger which cools it using a liquid refrigerant. The moisture condenses into liquid form and is drained out of the system.
There are two types of refrigerated air dryers, cycling and non-cycling:
Cycling type dryers use a refrigerant (such as R314A or R407C) to cool a liquid or solid mass surrounding the air inlet of the heat exchanger. The mass may be glycol or metal block which acts as a heat sink which cools the compressed air. A thermostat is used to regulate the temperature by shutting off the compressor during times of partial or zero loads, thus providing energy savings.
In the non-cycling type air dryer, the refrigerant circulates continuously through the system and there is no intermittent shut off. The flow of the refrigerant is regulated using a bypass or unloader valve to match the volume of compressed air entering the system and maintain a stable operating temperature.
Cycling vs. Non-Cycling Air Dryer
The main advantage of using a cycling type air dryer is that it achieves energy savings at partial and no air flow. On the downside, it has a higher initial capital cost than the non-cycling type, takes up more space (due to the heat sink mass) and is prone to dew point swings.
The key benefits of non-cycling air dryers are continuous compressor operation and a consistent dew point. However, there are no energy savings at partial and no air flow.
Regenerative Desiccant Air Dryers
This type of air dryer utilizes two towers – one containing a desiccant that removes moisture from the air stream coming from the compressor, while the other regenerates the used desiccant after the pressure has dropped to atmospheric conditions. Similarly, regenerative desiccant dryers are either heatless, externally heated or heat of compression type.
Heatless Air Dryer Working Principle
Heatless desiccant air dryers use a desiccant in twin towers – one for drying, and the other for regeneration. Wet compressed air enters the drying tower and passes over the desiccant which adsorbs it and exits as dry air (dew point between –40 and –100° F). The regenerating tower recovers the desiccant in its pure form. Heatless air dryers do not require internal or external heaters.
Heated Instrument Air Dryer Working Principle
The heatless dryer operation uses internal/external heaters to generate heat and uses a twin-tower arrangement. Like in the heatless type, humid air flows into the drying tower and is dried by the desiccant. The second tower regenerates the desiccant.
Some of the dry air exiting the tower passes through the heater and desiccant which removes the adsorbed moisture. Moist air is drained out of the system through a muffler. Heated type air dryers can achieve dew points of –40 to –100° F.
Membrane Air Dryer
Membrane dryer systems utilize semi-permeable membrane fibers to separate moisture from compressed air. Membrane systems are low-cost and eco-friendly alternatives to other air dryer types with additional space saving and reduced maintenance benefits.
Membrane Dryer Working Principle
A membrane air dryer consists of a bundle of hollow fiber membranes of a specific porosity housed in a hollow cylindrical vessel. Wet compressed air introduced via an inlet flows through the cylinder and a pressure differential inside the tube allows water molecules to pass through the membrane pores while dry air flows through the outlet. The efficiency of membrane air dryers depends on the selectivity of the membrane which is dependent on the pore size.
Trust NiGen For Reliable Air Dryer Technology
NiGen offers instrument air dryer packages to suit a broad range of industrial operations. Available services include on-site nitrogen generation units, rotary-screw air compressors, desiccant air dryers, and more on a rental basis.