INSTALLATION, START-UP & MAINTENANCE MANUAL
MODEL NO.: SD-220 TO SD-600- DDS OPTION
REV 0 – May 24,,.2001
13
SECTION 3
3.2 DESCRIPTION OF THE OPERATION
The
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adsorption dryer of the series SD-220 / SD-600 functions according to
the pressure change principle, using dry air regeneration. Two adsorption vessels
filled with desiccant are installed parallel to each other for this purpose. While the
medium is being dried in one vessel, regeneration takes place in the other vessel.
The changeover from one vessel to the other is performed in a fixed rhythm by
means of a time-dependent control system. The adsorption dryer operates
continuously and fully automatically.
3.2.1 Description of the operation
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The
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SD dryer has a NEMA cycle time of 10 minutes. In a 10 minute
cycle, 5 minutes is dedicated to drying for each chamber (5 minutes half cycle).
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Through the inlet switching valve wet air enters either desiccant chamber at the
inlet (bottom) and is dried as it flows upward through the desiccant bed. Dry air
exits the dryer through the outlet check valve.
•
At the outlet of each chamber, a portion of the dry air (purge air) is diverted to
the regenerating chamber. The dry air, at near atmospheric pressure, will
remove previously adsorbed moisture as it flows downward through the
desiccant bed exiting through the purge exhaust mufflers.
•
The purge air is controlled by a purge adjusting valve and purge orifices located
in the purge line. Purge pressure can be monitored on the purge pressure
gauge. Refer to section on purge adjustment for instructions on setting the
purge rate.
•
Near the end of each half cycle, the chamber being regenerated will be re-
pressurized. For this to occur, the exhaust valve of the chamber being
regenerated closes while purge air continues to flow. Re-pressurizing the
regenerated chamber to operating pressure before placing it into service
minimizes fluidization of the desiccant and helps prevent desiccant abrasion
which causes desiccant dust to prematurely block pilot and after-filter elements.
•
Dryers operating at pressures greater than 120-125 PSIG or in an accelerated
NEMA cycle could be fitted with a re-pressurizing valve. This valve assists the
regenerated chamber to reach dryer operating pressure before chamber
switchover.
•
Chamber switchover takes place when both towers are fully pressurized to
minimize desiccant movement.
When switchover is complete, the regenerated tower will be placed into service and
the exhausted tower will begin a depressurization/regeneration cycle.
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