Maintenance; Maintenance Procedures For Pvc Etc - Techne IFB-121 Operator's Manual

1) The aluminium oxide fluidising medium, not being degradable, will only require replacement when
losses occur due to attrition and spillage, or contamination with inert pigments, fillers or acidic by
products from the cleaning process. Fluidising medium lost through entrainment in the exhaust may
be collected in a cyclone trap.
Should the fluidised bath be stored for long periods of time under damp or humid conditions,
moisture may be absorbed by the alumina which is hydroscopic. To avoid violent fluidisation which
occurs when damp alumina is heated above 100°C, operate the bath for a period of approximately
8 hours at 90°C prior to operation at elevated temperatures.
NEVER ADD COLD OR DAMP ALUMINA TO A HOT BATH AS THIS WILL ALSO CAUSE VIOLENT
FLUIDISATION WHICH CAN BE DANGEROUS.
Allow the bath to cool then add the fresh alumina. If this fresh alumina is a large proportion of the
charge then dry the whole charge as above.
The fluidised bath may be emptied via the drain chute. The blanking cap should be removed whilst
the bed is unfluidised, a suitable container positioned under the chute and the bed fluidised, causing
a flow of medium from the chute. This flow may be interrupted at any time by turning off the
fluidising air.
2) On a daily basis at least, the bed should be cleaned of floating residues by means of a wire mesh
hand scoop. This procedure removes carbon char which impairs fluidisation and acts as an
absorbent.
3) The air line filter supplied with the fluidised bath is self draining. However, it should be kept in good
condition by inspection at two weekly intervals and by cleaning the bowls and washing or replacing
the filter elements as necessary. With exceptionally dirty or wet air supplies this frequency may have
to be increased. Free water or water vapour in the air supply is a notorious source for the production
of hydrochloric acid in the bed when PVC is being processed.
In addition, oil vapours in the air supply which reach the porous plate are carbonised within the pores
of the plate, quickly causing blockage and consequent poor fluidisation, local overheating,
premature heater failure and possible distortion of the inner container.
4) The fume extraction system (if used) should be regularly maintained. The cyclone trap collection bin
should be emptied at the end of each days use; the collected fluidising medium being returned to
the fluidised bath. It is important to ensure that the air tight seal between the cyclone and collector
bin is remade.
For maintenance of other fume treatment equipment see the associated maintenance manuals.
SPECIAL MAINTENANCE PROCEDURES TO BE ADOPTED WHEN BURNING OFF PVC OR OTHER
HALOGENATED POLYMERS
Burning off PVC (polyvinyl chloride) in a fluidised bath offers one of the most severe conditions of
operation. Hydrogen chloride (HCL), liberated on the breakdown of PVC, is absorbed by the bed
medium, creating an acidic environment within the bed, especially when the bed also absorbs water
from the atmosphere or fluidising air when cold. HCL is extremely corrosive, especially when aerated
and wet. In addition, in water it produces water ions which,even in neutral or alkaline solutions,
promote corrosion and rusting in steel; witness for example, the corrosive nature of sea water and
calcium chloride road de-icer.
Consequently, fluidised beds used for burning off PVC require strict supervision to minimise

MAINTENANCE

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