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Large Dehumidifying Dryers Functional Description 14
Regeneration
Filter
Regeneration
Blower
Process
Blower
Regeneration
Exhaust
Process
Heater
Process
Filter
Insulated
Drying
Hopper
Right Desiccant
Regeneration
Heaters
Dryer Valve
Left Desiccant
AD600-AD1500
Dryer Flow Schematic
Left Desiccant in
Regeneration
Sequence of Operation
When the dryer is started, the main air valve rotates 360º and then moves to place the last
successfully regenerated desiccant bed online. If the dryer was powered off using the main
power disconnect or E-stopped, then the regenerating bed is placed back into regeneration,
and the regeneration cycle is started over. The main air valve is allowed a period of time to
move from one position to the other. If the main air valve does not complete positioning
within the allotted time, then a “Main Air Valve Fail” alarm is generated and the dryer stops
the process air blower and disables the drying hoppers and regeneration circuit.
If the closed loop regeneration option is enabled, the regeneration closed loop valve moves to
the open loop position. The system always begins the cooling phase for a regeneration cycle
using ambient (open loop) air. The closed loop regeneration valve is allowed a period of time
to move from the closed to the open loop position and a “Closed Loop Valve” alarm is
generated if the valve fails to reach the commanded position within this time. This alarm will
disable the regeneration circuit but does not stop the process air system or drying hoppers.
Once the main air valve and closed loop regeneration valve are in place, the process air
blower starts. The system monitors the process air blower’s overload, starter auxiliary contact
feedback and air pressure. Loss of any of these items when the process air blower is running
will cause the process air blower and the drying hopper’s process heaters to shut down.
The process air heaters will turn on after a delay to allow the process air blower to accelerate
the operating speed.
During normal operation, one set of desiccant beds is connected to the process air circuit
while the other set is being regenerated. When the offline beds are done regenerating, they
will be switched into the process air circuit and the other beds will be regenerated. The
default bed switch setting is based on time. If the Dewpoint Switch option is enabled, the
beds will switch when the process air dewpoint reaches the dewpoint switch point. The
dewpoint option will automatically disable itself and an alarm will be generated if the
dewpoint sensor or related electronics fail.