Techne IFB-131, Operator'S Manual

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I F B - 1 3 1 O P E R A T O R ’ S M A N U A L
PAGE 14
Fume Ignition
Spontaneous ignition may occur above the surface of the fluidised bath or within the
exhaust ductwork if the concentration exceeds the lower explosive limit.
The fume concentration is dependent upon the rate of fume production in the
fluidised bath and the level of dilution achieved by entraining air from above the bath or through
the dilution tee.
The rate of fume production is dependent upon the type and amount of material
being treated and the temperature of the bath.
To ensure that the concentration of inflammable fumes is below the lower explosive
limit, ensure that the amount of combustible material immersed in the bath at any one time is
within the design capacity of the extraction system.
Ensure that the temperature of the bath is at minimum level to which satisfactory
results can be achieved. Increased working temperatures result in increased fume
concentration. By way of example, an extraction rate of 2m
3
/min is required to ensure that the
fume concentration is below 25% of the lower explosive limit when thermally decomposing
1kg/hr of polythene at 450°C.
To safeguard the fluidised bath from damage, two safety features are included in the
control console: an adjustable over temperature cut-out which guards against controller failure,
and an air pressure switch which inhibits operation if the compressed air supply to the fluidised
bath fails. Both of these devices isolate the electrical supply to the heater elements and
illuminate the cut-out indicator in a fault condition. The over temperature cut-out is factory
preset at 630°C. Under no circumstances should this setting be increased, but lower limits may
be set to safeguard particular processes in the fluidised bath.