Fume Extraction And Cleaning - Cole Parmer FSB-200 Series Instruction Manual

rate of 2m /min is required to ensure that the fume concentration is below 25% of the lower explosive
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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 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 pre-set 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.

FUME EXTRACTION AND CLEANING

When used for processing items which may emit toxic or inflammable fumes, it is essential that an adequate
fume extraction system be installed. A typical schematic diagram of a full fume extraction system is shown
in Figure 4. The system consists of the following components: -
Ductwork to connect the fluidised bath extract duct via the various fume treatment equipment to the input
of the fume extraction fan. The ductwork should include an air dilution tee, positioned as close as possible
to the fluidised bath. The dilution tee enables the fumes within the system to be diluted with air. The
ductwork should also include a damper valve which is normally positioned adjacent to the extraction fan.
This valve allows the extraction velocity to be reduced. In general, the ductwork may be manufactured out
of galvanised mild steel; however, in installations where PVC or other halogenated polymers are being
processed, it is recommended that stainless steel ducting is used. The ductwork should be as short as
possible and contain the minimum number of bends and horizontal runs to reduce the possibility of a
blockage.
A cyclone separator should be mounted directly after the dilution tee. The cyclone removes any fluidised
medium that may be present in the extracted fumes. The fluidised medium is collected in the cyclone
collection bin from where it may be returned to the fluidised bath. In applications where the components
being cleaned are contaminated by polymers which contain inorganic pigments or fillers such as titanium
oxide, of a particle size less than 0.005mm diameter which will not be retained by the cyclone, it is
recommended that a filtration system be fitted after the cyclone.
In applications where the materials being treated produce acidic vapours during thermal decomposition, it
is recommended that a fume scrubber be utilised to ensure that the final fume emission from the plant
conforms with local regulations. A caustic dosing system may also be required to ensure that the scrubbing
liquid is maintained at an acceptable pH level.
An extraction fan is required in all applications to provide the motive force for the exhaust.
In applications where it is not permissible to emit visible smoke from the plant or where local regulations
specify the maximum fume concentrations that may be emitted from an exhaust stack, an afterburner may
be required. The afterburner heats the fumes to a point where thermal incineration eliminates the visible
content of the fumes while reducing the fume concentration.
Finally, an exhaust stack is required to direct the treated fumes away from the working environment. The
exhaust stack will generally be manufactured out of the same materials as the ductwork system. However,
in installations where an afterburner is fitted, the exhaust stack should be manufactured out of insulated
stainless steel.
The exact combination of fume treatment components required depends upon the application and local
conditions.
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