4.1 Description of operation
Figure 3. Schematic of Dryspell Plus dryer
Compressed air containing moisture and oil droplets enters the pre-filter. Bulk liquids are removed from the air by the pre-
filter. The air then flows through the inlet shuttle valve, which diverts it to tower 1. The desiccant in tower 1 dries the
compressed air to -40°F PDP as it flows through. The dried air leaves tower 1 via the after-filter. A small part (15%) of
the compressed air is passed through the purge orifice by means of opening a two-way purge valve and thereby expanded
till its pressure is near-atmospheric. This expansion of the already-dry gas (purge air) to near-atmospheric pressure increases
its capacity to strip adsorbed water vapour from the desiccant bed in tower 2. The purge-air stream passes through tower
2, removing water vapour from the desiccant. This purge operation is carried out for 1 minute and 30 seconds. Then the
purge valve is closed, and the pressure in tower 2 begins to rise again. The repressurisation is carried out for 30 seconds.
The purge valve is opened, and purge air passes through tower 1.
During the first 2 minutes of each 4-minute cycle of operation, the following processes take place:
l The online tower (tower 1) dries compressed air for 2 minutes.
l The offline tower (tower 2) regenerates (adsorbed moisture is removed from the desiccant in it) for 1 minute and 30
seconds.
l The offline tower is re-pressurised for 30 seconds.
During the next half of the cycle, these processes are repeated with tower 2 being the online tower and tower 1 the offline
tower.
INSTRUCTION MANUAL - Dryspell Plus
Reference : Manual Version
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