Manual
9
the dust on the outside surface of the individual filter bags. The
cleaned air leaves the filter bags and discharges into the plenum at
the top of the collector, where it is then exhausted through the outlet.
The filter bags are periodically cleaned by bursts of compressed air
that are directed down the inside of the bags. A venturi located in the
top of the bag cage induces additional air to the inside of the bags
being cleaned. This reverses the flow of air through the bags and
dislodges the dust cake from the surface of the bag, allowing it to
settle into the hopper. Since only a small percentage of the bags are
cleaned at one time, the unit remains in continuous operation.
Hoppers are designed to receive the dust and are not for
storage. The recommended practice is to continuously empty the
hopper by means of a rotary lock and/or screw conveyor, or by some
other discharge device.
6.0 Maintenance
6.1 Daily
Record the collector pressure drop daily for at least the first 30 days
of operation. Adverse operating conditions can be detected by a
change in pressure drop. An optional pressure gauge is available from
AAF to provide the pressure drop reading across the dust cake and
fabric. After startup, the pressure drop will gradually rise to its normal
operating level of approximately 2" to 5" w.g.
6.2 Monthly
A regular inspection of the filter bags should be made within 30 days
of start up. Any faulty or worn bags/tubes must be replaced to prevent
damage to the collector. The compressed air line regulator, dryer, and
filter should be checked for proper operation. Also inspect the dust
discharge device on the hopper outlet for proper operation.
6.3 Six Months
Ducts leading to and from the collector should be inspected for dust
accumulation at a minimum of every six months. In addition, the
following inspections should be made:
1. Examine the bags for wear with special attention to seams
and stitching.
2. Examine the internal components for wear.
3. Inspect all joints for evidence of air or dust leakage.
4. Check for evidence of moisture or dust accumulation within
the collector.
5. Check all electrical apparatus for proper operation.
6. Ensure the diaphragm and solenoid valves are pulsing when
energized by the timer.
7. Check discharge gas condition for signs of dust.
8. Check explosion vents.
7.0 Troubleshooting
7.1 High Pressure Drop Reading
1. Improper Timer Operation
Check the wiring, fuses, and setting of pulse duration and interval.
CAUTION: Do not adjust the pulse duration without consulting an
AAF representative.
2. Insufficient Compressed Air
Check the air supply to ensure the compressor is providing 80 to
100 psig. Check for a plugged filter in the compressed air line.
3. Solenoid Pilot Valve Malfunction
Listen to verify the solenoid valves are firing. Check for momentary
air venting each time they fire. Clean or replace, if necessary.
4. Pulse Valve Malfunction
Pulse pipe jets should be checked to verify operation of the
pulse valves. Pulse valves can be easily disassembled and
rebuilt in place.
5. Leaking Dust Discharge Device
A leaking rotary lock, screw conveyor, slide gate, etc. can overload
the Millennium by preventing dust discharge after pulsing. This
causes high pressure drop, excessive bag wear, and reduced air
volume. Seal any such leaks.
6. Condensation
High humidity may cause blinding of bags, which results in
excessive pressure drop. Run the cleaning mechanism with the
fan off and the program timer on, or with the pressure switch set to
zero, to release the dust cake. If condensation is a recurring
problem, pre-processing warm-up and post-processing purge
periods of 15 to 30 minutes each may help. Exterior insulation may
also be necessary. Sources of moisture may come from leaking
process ductwork, moisture in the process gas stream, or moisture
in the compressed air system.
7. Static Electricity
Static buildup can cause a high pressure drop. If possible,
increase the humidity using discretion to avoid creating
condensation. Grounded bags may also be required in situations
where a spark may result in ignition of an explosive dust.
8. Collector Overloads
Too much air or dust will create high pressure drops across the
collector. Check the fan speed, system design, pre-cleaners, and
the damper position. Also ensure the dust load and air volume is
within the system design parameters.