HL Series Desiccant Dryer Models 90-5000
http://www.ingersollrandproducts.com
4
7.0 PRINCIPLES OF OPERATION
7.1 INTRODUCTION
As described in Section 2, water vapor is removed from compressed air
by diverting air flow alternately between two towers filled with desiccant.
While one tower processes the compressed air stream, adsorbing water
vapor, the opposite tower is regenerated by desorbing the water vapor
and venting it to atmosphere. Refer to the Flow Diagram for a visual
representation of the drying and regenerating cycles.
7.2 DRYING CYCLE
Saturated compressed air enters the dryer and is diverted to the
appropriate tower by the Inlet Flow Valves. Referring to the Flow
Diagram (Section 16.0), the Left Inlet Flow Valve is actuated to a closed
position to prevent air flow from entering the regenerating tower.
Simultaneously, the Right Inlet Flow Valve is actuated to an open
position, allowing air flow to the right hand tower. During this time, the
Right Tower Purge Valve is actuated to a closed position, preventing the
compressed air from venting to atmosphere. As the compressed air
flows through the desiccant material at pressure, removal of water vapor
from the air stream begins to occur through adsorption. In the
adsorption process, the desiccant material draws water vapor out of the
compressed air and "holds" it until the right tower drying cycle is
complete. Compressed air flows out of the tower for delivery to the
process use. The Outlet Flow Check Valves provide air flow diversion
to the outlet air connection of the dryer. The Right Outlet Flow Check
Valve allows air flow through to the outlet connection of the dryer while
The Left Outlet Flow Check Valve checks off to prevent flow back to the
regenerating tower.
7.3 REGENERATION CYCLE
Previously adsorbed moisture, removed from the process stream, gets
stripped or desorbed from the desiccant material in the regeneration
process. The first stage of regeneration is tower depressurization. After
the Inlet Flow Valves are switched to divert air flow away from the
regenerating tower, the appropriate Purge Valve will be opened and the
tower will be depressurized. Through rapid depressurization, a
significant portion of the previously adsorbed water vapor is stripped off
of the desiccant material and exhausted to atmosphere.
The second stage of regeneration uses a portion of the dry, compressed
air, expanded to atmospheric pressure to complete the desorption
process. As shown on the FLow Diagram, the compressed air exits the
drying tower and a portion of the air flows through the Purge Adjustment
Valve and the Purge Orifice. Once the air has passed through Purge
Orifice, it expands to atmospheric pressure and continues the
regeneration process. Desorption occurs as the desiccant releases
water vapor into the regeneration air and is exhausted through the
Purge Muffler.
Heatless dryers are equipped with the ability to use air from a
downstream source to purge the regenerating towers. This feature is
useful for applications with downstream (dry) storage tanks, as pulling
air from a downstream source can minimize cycling of the air
compressor.
7.4 SETTING THE REGENERATION AIR FLOW
Proper setting of the purge is necessary to achieve proper dryer
performance. Setting the purge flow too high will waste compressed air
and if set too low, the dryer will not achieve proper dew point
performance.
The purge adjustment manifold consists of the Purge Adjustment Valve,
the Purge Pressure Gauge and the Purge Orifice. Manually adjust the
Purge Adjustment Valve until the gauge reading on the purge pressure
gauge matches the Purge Pressure Gauge setting listed on the
laminated tag affixed to the Orifice Plate Assembly.
NOTICE
On dryers equipped with the optional EMS feature, the purge valve
MUST be set to the factory set point to ensure proper operation of this
feature.
7.5 TOWER REPRESSURIZATION
Upon completion of tower regeneration, and prior to the Inlet Flow
Valves changing position to switch towers, the regenerated tower must
be repressurized.
NOTICE
Failure to re-pressurize prior to tower switchover will result in shocking
the desiccant material and cause premature desiccant dusting.
Repressurization is accomplished by closing the appropriate Purge
Valve. Closing the Purge Valve allows the regeneration air to begin to
pressurize the tower. In addition to the regeneration air, the
Repressurization Valve, (standard on -100°F dew point and high
pressure dryers) opens allowing some additional air from the outlet of
the dryer to ensure adequate pressurization. During normal tower
regeneration, the Repressurization Valve is held closed so that the only
source of air for regeneration passes through the purge adjustment
assembly.
7.6 VALVES
Solenoid control valves are used to actuate the Flow Valves, Purge
Valves and the optional Repressurization Valve on Heatless Dryers. The
Inlet Flow Valves and optional Repressurization Valve are normally open
valves, while the Purge Valves are connected as normally closed valves.
This arrangement permits air to flow through the dryer during periods of
loss of power.
Outlet Check Valves are single direction check valves that will allow flow
in the direction shown on the Flow Diagram, but not allow flow in the
opposite direction.
7.7 TIMING SEQUENCE
All timing functions are controlled by the Microprocessor Controller.
Timing for HL Series dryers is as follows:
7.7.1 TIMING CYCLE FOR -40°F DEW POINT DRYERS
The standard timing cycle for -40°F operation switches the
Inlet Flow Valve position every five minutes which alternates
the drying tower. At the same time as a tower Inlet Valve
opens, the appropriate tower Purge Valve opens to
depressurize the regenerating tower. Tower regeneration
occurs for 4 minutes and 15 seconds, at which time the Purge
Valve closes to initiate repressurization.
