Atmospheric air contains more water vapor at high temperatures and less at lower temperatures. In the summer, the weather in Middle East especially the coastal areas like UAE is very hot and humid, with temperatures exceeding 43 °C (109 °F) and humidity averaging over 90%. This has a significant effect on the water concentration when the air is compressed. Problems and disturbances, such as pipe corrosion, can occur due to water precipitation in the pipes and connected equipment. To avoid this, the compressed air must be dried.
Selecting the proper dryer to treat wet compressed air is largely dependent on the specific requirements and moisture tolerance levels of the machines that utilize compressed air. While there are several types of air dryers available, one of the most common used for critical applications in the Middle East region is a desiccant air dryer.
What is a desiccant air dryer?
A desiccant air dryer for compressed air uses special drying agent beads like silica gel and activated alumina to absorb water vapor from an air stream. These air dryer units are often regenerative so that the drying agent doesn’t need replacing in order to provide vapor-free compressed air consistently.
Which applications do you need desiccant air dryer?
Most industrial and manufacturing facilities can achieve such requirements with a refrigerated air dryer, while critical applications requiring critically dry air as below, a desiccant air dryer is a must.
- Plastic mold blowing. Drying of pellets prior to processing.
- Electronics production. Printed Circuit Boards (PCB) and other electronic components. To avoid any moisture during production process as it could cause short circuit or oxidation.
- Power plant. Compressed air is used to control actuators of different valves. If an actuator does not function this might lead to power plant shutdown. The better the air quality is, the more secure is the actuator operation.
- Food & beverage manufacturing. In packing machines where air contacts direct the goods need to have a dewpoint at min -40°C to combat the growth of micro-organisms.
- Marine: Offshore or Onshore rigs. Production of N2 (-70°C PDP) especially for ships who run with LNG. Outdoor piping should only carry dry air as otherwise humidity in the pipe will start freezing. Dry air is also required for aeration of cargo and fuel tanks prior to inspection and for critical control or instrument air applications.
- Laser cutting. Dry air keeps the lenses clean and dry in order to have an optimized cutting result.
How do desiccant air dryers work?
Wet air passes directly through the desiccant medium which adsorbs the moisture. The desiccant medium has a finite capacity for adsorbing moisture before it must be dried out, or regenerated. To do this, the tower containing saturated desiccant medium is depressurized and the accumulated water is driven off. How this happens depends on the type of desiccant air dryer:
- Heatless dryers use only compressed air as a purge
- Blower purge dryers use a combination of air from an external blower, heat and minimal compressed air
- Heat of compression dryers use the heat of the compression
- Zero purge desiccant dryers use the residual heat generated by air compressors to re-generate desiccant
Two types of desiccant drying technologies
The desiccant in air dryers has always consisted of loose beads made of activated alumina, molecular sieves or silica gel. However, new technologies are emerging to provide more efficient alternatives. Let’s explore the two types of desiccant drying technologies.
1. Drying with desiccant beads
2. Drying with structured desiccant
