Sullair DEX Series, User & Service Manual

Page: 19 / 48

Section 5
19
DEX HEATED REGENERATIVE DRYER
OPERATION
5.1 ADSORPTION
Compressed air flows through the system prefilter
and into the bottom of the online desiccant chamber
via the inlet switching valve and desiccant support
screen. The air flow passes upwards through the
desiccant bed where it is dried. At the top of the
vessel the dried air exits the adsober through the
flow distributor (desiccant retaining screen) and
passes through the system afterfilter into the
downstream system.
5.2 REGENERATION
Regeneration is carried out at with the off stream
desiccant chamber isolated from the system and
depressurized to atmosphere for regeneration. To
achieve this, the inlet valve closes automatically and
the depressurization valve is opened. When a low
chamber pressure is sensed with a pressure switch,
the regeneration outlet valve is opened. Now
regeneration (Heating and Cooling) may take place.
The regeneration air passes over the regeneration
heater, where the correct regeneration temperature
is obtained, and into the desiccant chambers via the
regeneration inlet check valves. The air flow is evenly
distributed over the area of the desiccant chamber by
the upper flow distributors of vessels “1” or “2” and
downwards through the desiccant beds to liberate
previously adsorbed moisture.
The regeneration air leaves the desiccant chambers
via the regeneration outlet valves and passes to
atmosphere. Under these conditions all of the
previously adsorbed moisture is liberated from the
desiccant and removed to atmosphere in the
regeneration flow. The process described above
continues for the duration of the heating period or
until a suitable exhaust temperature is obtained.
The regeneration air heater outlet temperature is
monitored and controlled by a thermocouple and
PLC Heater sheath over temperature control is
provided by PLC temperature controller )Type K
thermocouple)
5.3 COOLING
The cooling process takes place in the same flow
pattern as regeneration except the regeneration
heater is turned off.
The cooling cycle will operate until the cooling period
time is complete. At this point purge exhaust valves
will close and the regenerated chamber will re-
pressurize prior to returning to service in the
adsorption mode.
The amount of air used for cooling is manually
adjustable by a service valve in the cooling/repress
manifold located at the bottom right hand side of the
dryer. This valve is pre-adjusted at start-up to provide
sufficient air for cooling. If the valve is partially closed
or closed from the start up position then satisfactory
cooling will not take place. This will result in hot air
passing downstream and an accompanying dewpoint
bump. If the valve is opened up more than the start
up position then more air than necessary will be used
in the cooling period.
5.4 TIME CONTROLLED VESSEL
CHANGE OVER
The vessel change over procedure will be initiated by
the PLC control system when the timed adsorption
phase for the in process vessel has been completed.
Also, it is required that the regenerated vessel has
fully repressurized, the vessel pressure is sensed by
the vessel pressure switch and the repressurization
time has elapsed prior to changeover occurring.
During “Time controlled” operation, “Dewpoint
controlled” operation may be selected at any time.
5.5 DEWPOINT CONTROLLED
VESSEL CHANGE OVER
(OPTION)
The vessel change over will be initiated by the PLC
control system when the timed adsorption phase for
the in process vessel has been completed and when
the dew point control senses the required moisture
level at the dryer outlet.
During “Dewpoint controlled” operation, “Time
controlled” operation may be selected at any time.