APV Dryer Handbook - Umbc

70
HIGH FAT PRODUCTS
If the powder contains fat, however, the higher pressure drop has an overall
dis-advantage. The higher velocity causes the fatty powder to smear around
the lower part of the conical cyclone body. This smearing results in a firm layer
building up on the inside surface, which can ultimately cause the cyclone to block
and cease to discharge any powder. With this type of powder, it is necessary
to reduce the cyclone pressure drop to also reduce the swirl velocity as well
as the chance of bridging the cyclone.
If two inner cone inserts are available, install the larger diameter cone insert for
high fat powders. It may also be necessary to adjust the main airflow to trim
the cyclone pressure drop, understanding that this will reduce the instantaneous
production rate. The actual pressure drop that will allow the system to operate
successfully may depend on the fat content, but could be as low as 4 inches (100
mm) w.c. This low pressure drop is not really detrimental to collection efficiency,
since higher fat products tend to be easier to collect than low fat powders.
LEAKING SEALS
One frequent cause of reduced airflow is leaking seals around access doors and
clean-out ports. These seals should be checked visually when the plant is being
washed, but they can also be checked by ear while the plant is in operation.
If a whistling noise can be heard coming from a flange or door seal, it probably
indicates a leak. The source of the noise should be found and the area marked
for checking at the next opportunity.
Powder deposits can be another indication of a leak, which should be corrected.
Leaking seals in the chamber or powder carrying ducts usually cause a localized
deposit to occur. These deposits are due to condensation on the cold surfaces
adjacent to the leak and can be seen immediately prior to cleaning the plant after
a production run.
DETECTION AND CORRECTION
The simplest method of accurately locating the leaking part of a door seal is to