How Does an Air Dryer Work?
July 03, 2018
Compressed air dryers are necessary utilities in most manufacturing production plants. Moisture in the air can damage pneumatic systems, cause pipes to freeze, allow rust to form and damage moving parts — the list can go on.
Having a reliable air dryer in your factory is an absolute must, but which design is the right fit for your business? By understanding the differences between the various instrument air dryer types, you can make the right decision for your company.
Types of Air Dryer
There are multiple methods for removing moisture and other unwanted products from compressed air systems. Based on these methods there are four main types of air dryers for air compressors:
1. Refrigerant Types
How does a refrigerated air dryer work? Refrigerant types work on the principle of reducing moisture by cooling the air and condensing the moisture. The condensed moisture is then drained off. The cooled, dry air is then blown out while the warmer, moist air is pre-cooled and taken into the system. In this case, the air is cooled by coolants that run continuously to keep the system at a regular temperature.
Refrigerant types comes in two varieties: cycling and non-cycling.
Cycling types run continuously and maintain their dew point at a consistent temperature; however, this means that they must be kept on constantly. This can drive up maintenance costs.
Non-cycling types work by turning on and off to maintain a set temperature. Although this method saves energy and reduces costs, it is less stable in maintaining the dew point as compared to the cycling types.
Refrigerant designs are, all in all, very popular and cost-effective dryers but are limited in the dew points that can be maintained when compared to other types.
2. Regenerative Desiccant Types
A regenerative air dryer works by using two towers. One tower contains a desiccant that absorbs moisture from incoming air. The other tower regenerates the desiccant after the pressure returns to normal. This process allows you to time the cycle and run it as needed. There are three different types of these systems: heatless , heated systems and heat-of-compression type systems.
- Heatless regenerative air dryers operate on the principle of using “purge” air to push out the moisture and regenerate the tower.
- Internally heated dryer systems use a heat source placed within the tower to heat the desiccant and reduce the need for purge air significantly.
- Heat-of-compression type systems use both towers at once by keeping them at the same temperature. This allows you to operate at a lower cost but with a relatively inconsistent dew point.
Regenerative desiccant type dryers operate at moderate cost and, if you use the heatless type, can be designed to work pneumatically as well. In exchange, this system requires a high initial capital cost and will require constant maintenance.
3. Single Tower Types
Single tower type dryers contain a single tower of desiccant, which absorbs the moisture from outside. This type of dryer is efficient and self-contained, requires no electricity and has no moving parts. This type of air dryer is even well-suited to work in corrosive and harsh environments.
The down side is that these towers need to have their desiccant replaced regularly. The particles within the tower can get dislodged and cause problems downstream.
4. Membrane Types
Membrane type dryers are basic and have a very simple method of functioning. Nitrogen separation membranes contain specialized semi-permeable material that separates gases. Since water vapor (moisture) is a gas, it is separated from the remaining air and is thus dried. This is the same method used in CO2 separation membranes, and are frequently carried by separation vessel suppliers.
These simplified systems are efficient but better suited for lower capacity systems. However, they contain no moving parts and cost much less than competing types of air dryers.