Desiccant Dryers
Desiccant dryers are used when a low dew point is required. This type can produce a pressure dew point down to -100° F or most commonly to -40° F.
Continuous duty dryers use a regeneration cycle to dry the "wet" off-line desiccant tower while an on-line tower dries the system air. Regeneration is available in a number of the following ways:
- Heatless
- Externally Heated
- Internally Heated
- Blower Purge Heated
- Heat of Compression
- Steam Reactivated
Heatless
Heatless dryers are the least expensive to purchase, however sometimes the most expensive to operate. The regeneration purge air is approximately 15% of rated flow. This air is swept through the off line tower to remove the moisture. Sizing is available from 5 scfm to 5400 scfm in wall mountable to stand alone floor models. The entire plant load can be dried or a small branch line to prevent outdoor freezing such as a dust collector. Energy saving controls are available to reduce the purge flow at partial loads which reduces energy costs.
Heated
External and internally heated dryers use a heater located either inside or outside of the desiccant bed. The heat regenerates the desiccant with a small percentage of purge air required. While more expensive to purchase, heated dryers can be more efficient to operate than the non-heated desiccant dryers.
Blower Purge
Blower purge dryers operate with an external heater or heat source such as steam and a blower to force the hot air through the desiccant bed. The switching from one tower to the other is controlled by a PLC on either a fixed time or a demand basis. A 1% flow of compressed air may or may not be used as a cool down period to minimize dew point spikes.
Heat of Compression
Heat of compression dryers use the heat from an air compressor discharge to regenerate the desiccant beds. This type can be one of the most efficient way to save energy. Compressor type and loading must be considered when looking into this dryer.