Labotek Desiccant Flex Dryer Manual page 6

Rev. 01 Desiccant Flex Dryer DFD Side 5 af 40
After the drying air has heated the raw material and transformed the moisture to water vapour, it is
fed back through the return air cartridge filter (8). The humid air may then be cooled by the return
air cooler (9) (optional) just before it reaches the blower (10).
R1862
2.5.2 Regeneration (Fig. R1862)
The DFD dryer has 2 desiccant beds (2) and (3) with molecular sieves for dehumidifying of the
drying air. One of the beds is always operative in the drying cycle whereas the other is either
regenerating in the regeneration cycle or, when fully regenerated, is in stand-by mode.
Regeneration occurs when hot air passes through the desiccant bed (2) or (3).
The regeneration blower (13) takes in ambient air through the fresh air filter (11) and the fresh air
valve (12) and sends it to the heating element for regeneration (4) where the air temperature is
increased to approx. 180°C. The moisture adsorbed in the desiccant bed is evaporated and is forced
into the ambient air in the form of water vapour.
In the last phase of the regeneration cycle, the heating element for regeneration (4) is disengaged
and as the position of the fresh air valve (12) changes, the air is recirculated in a closed system
where the air is cooled down through the regeneration air cooler (15).
The desiccant beds (2) and (3) are placed between 2 automatic, double-acting valve units (5) and (6)
ensuring that one of the desiccant beds is always operative in the drying cycle and the other in the
regeneration cycle. The desiccant beds switch every 90 to 180 minutes depending on the load on the
desiccant beds.
The time required for regeneration of a desiccant bed, depending on the amount of moisture
adsorbed, is controlled by the regeneration sensor (14) which is mounted on the discharge pipe of
the regeneration cycle.