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the dilution tee may be used to ensure that the oxygen content of the exhaust is high enough to
maintain the burner flame during the smoke cycle. the dilution tee also enables the velocity in the
cyclone to be maintained at a suitable value to ensure efficient separation of any fluidising medium, while
the velocity in the fluidised bath exhaust duct may be limited to reduce the amount of fluidising medium
entrained.
a correctly adjusted system should result in a minimal loss of fluidising medium from the fluidised bath.
the majority of the entrained medium should be retained by the cyclone, from where it may be returned
to the bath. the fume concentration within the ducting should be below the LeL (lower explosion limit)
for the various products generated during the cleaning process. the exhaust emission from the
afterburner outlet should be within locally acceptable limits. the environment adjacent to the fluidised
bath should have gas concentrations within locally accepted tLV (threshold limit values).
setting the extrAction system
1.
Switch on the extraction system setting the dampers initially as follows:
dilution tee 50%
damper 50%
2.
heat up the bath to the working temperature, adjusting the air flow for correct fluidisation.
3.
When at the working temperature, adjusting the damper so that any fine dust particles omitted
from the surface of the bath are just entrained by the extraction system.
4.
operate as above for 30 minutes.
5.
Switch off the extraction system and check:
a.
the amount of sand in the collector bin (cyclone)
b.
the amount of sand in the duct
6.
If there is more than 2" of sand in the bin ensure that fluidisation is not excessive and that the bath
was not overfilled. tip the sand back into the bath.
7.
If 6 is satisfactory check that the extraction rate is not excessive.
note: if A lid is used on the BAth, ensure thAt it is not Airtight
8.
If there is sand in the afterburner the velocity through the cyclone is incorrect. therefore open the
dilution tee and increase damper so that system still just entrains fines. re-check the system from 4.
9.
check the operation of the afterburner. Set the flame to maximum (gate valve fully open).
10.
With the afterburner running immerse slightly contaminated component.
11.
check fume extraction above the bath visibly ensuring all fumes are extracted
ie: drager to check concentration. check the Lower explosive Limit.
12.
check the visible smoke from the stack, check the fume concentration is acceptable.
13.
If the visible smoke is present or the fume concentration is too high decrease the smoke generation
rate, ie: reduce the temperature of the bath.
14.
When 11 is satisfactory, immerse a maximum contamination item and re-check as 11.
15.
repeat 14 and decrease the flame size until conditions are just acceptable to minimise gas
consumption.
8
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