Van Air Systems FR-800 - Manual (Page 7)

PAGE 7
6.1 DESCRIPTION OF OPERATION
The Prep-40 is a portable skid mounted system consisting of a strainer,
pre-cooler, separator, prefilter, heatless regenerative dryer and an
afterfilter. Wet warm air enters the pre-cooler where it is cooled to a
temperature approcahing ambient. Water is condensed out during
this cooling process. The saturated air and the liquid water proceed to
the inlet of the separator where the liquid water is removed. Then the
saturated air enters the coalescing filter where additional oil and liquid
water is removed. Then the air enters the heatless twin tower dryer where
it moves upward through the desiccant bed. The moisture is adsorbed
onto the surface of the desiccant. Dry air exits the heatless dryer and
passes through the general purpose particulate after-filter where residual
particulate is removed.
This package dryer will take saturated air at 100 psig @ 150°F and reduce
the mositure content to -40°F pressure dew point.
START UP SECTION 5
OPERATION SECTION 6
Operate the until NO desiccant dust is visible at the purge valves.
Then the mufflers can be installed.
IMPORTANT
The dryer system must be operated for several hours without
the mufflers after the towers have been filled with desiccant.
This will prevent the mufflers from becoming clogged.
FIGURE 5A PURGE MUFFLER INSTALLATION
5.6 INSTALLING THE PURGE MUFFLERS
To reduce the sound level during purge and tower depressurization,
this dryer system was supplied with mufflers for installation on the
purge exhaust valves.
Mufflers were shipped separately. They should NOT be installed until
the dryer system has been operated for several hours. From
desiccant installation, some dust may be present in the desiccant
towers. Operating the dryer system with the mufflers installed
immediately after the towers have been filled with the desiccant or
during initial start up may cause the mufflers to clog.
The dryer operation consists of four stages; REPRESSURIZATION,
CHANGEOVER/DEPRESSURIZATION, DRYING and
REGENERATION.
6.2-1 REPRESSURIZATION STAGE
Repessurization occurs in the off-stream (regenerating) tower.
Repessurization must occur before tower changover to reduce shock
to the desiccant and the possibility of downstream pressure spikes.
Pilot valve SV1 or SV2 de-energizes causing the purge valve on the
off-stream (regenerated) tower to close. The purge air, which was
vented to atomosphere earlier in the cycle, is now used to
repressurize the off-stream tower.
6.2 HEATLESS DRYER PRINCIPLE OF OPERATION
The Heatless Regenerative Air Dryer utilizes the pressure swing principle
of operation. The desiccant bed in one tower dries the air stream while
the desiccant bed in the other tower is regenerated.
A purge of dry air is used for tower regeneration. It is taken from the
outlet of the dryer.
The dryer is equipped with a purge metering valve to allow the correct
amount of dry air to flow into the regenerating tower. The heat created
during adsorption of moisture in the drying tower is retained in the desiccant
bed and increases the moisture removal capacity of the purge air.
The timing cycle of the dryer is controlled by two 3-way pilot valves.
A patented shuttle valve system is used to repressurize, changeover,
and depressurize the towers. The inlet transfer valve is controlled by
the pilot valves.
To achieve maximum performance from this dryer, it should be operated
continuously. Operating this dryer for single shift periods may result in
varied outlet dew point performance.
6.2-2 CHANGEOVER/DEPRESSURIZATION STAGE
Tower changeover occurs after the off-stream (regenerated) tower is
pressurized. The SmartRelay signals SV1 or SV2 to open causing pilot
air to be supplied to the opposite side of the inlet transfer valve and
cause exhaust valve to open on regenerative tower. The inlet transfer
valve shuttle will move to the side that has pilot pressure placing the
regenerated tower on-stream. The tower that was on line and drying
the process air is now off-stream.
When the inlet transfer valve changes position, the position indicator
will move.
6.2-3 DRYING AND REGENERATION STAGE
One tower is on-stream (pressurized) drying process air. The process
air passes through the desiccant bed, which adsorbs moisture from
the air.
The regeneration stage of the off-stream tower occurs at the same time
as the drying stage in the on-stream tower. During the regeneration
stage, a percentage of dry air is directed through the desiccant bed
of the offstream tower. The purge air is vented through the purge
valve to the atmosphere.
If pilot valve SV2 is energized, the LEFT tower is drying and if pilot
valve SV1 is energized, the RIGHT tower is drying.