Techne IFB-201 Operator's Manual page 18

The most commonly used fluidising gas is ordinary compressed air obtained from a blower or
compressor. For situations where a non oxidising atmosphere is required, cracked gas can be
employed with a silicon carbide bed.
The unique characteristic of gas fluidised particles is the relatively high rate of heat transfer which
yields highly isothermal conditions, as well as excellent heat transfer to solid surfaces. This
characteristic is due to the turbulent motion and rapid circulation rate of the solid particles in
conjunction with the extremely high solid gas interface area. Therefore, despite the fact that gas
solid interfaces normally yield low heat transfer coefficients and the solids normally used have low
thermal conductivities, the overall heat transfer characteristics of fluidized particles approach
those of a liquid.
The combination of excellent heat transfer characteristics and high heat capacity are ideal for
attaining rapid stabilisation at an isothermal condition. Techne industrial fluidised baths use
aluminium oxide as the fluidising medium. They have been designed to remove plastic residue
from extruder and moulding machine tools, paint build up from paint fixtures, and carry out
various heat treatment processes.
The fluidised bed is housed in a stainless steel container. The container is surrounded by a
radiant furnace which is enclosed within thermal insulation. The inner assembly is housed in a
rectangular outer case. There is also an electrical and pneumatic control console.
The following control options are available:
•
A manual control system which consists of a temperature controller, and a manually
adjustable fluidising air control valves. Supplied as standard with this, and all other
options, is an air pressure regulator and filter assembly. During operation the correct
fluidising air flow rate must be determined by visually inspecting the surface of the
fluidised bath. When the fluidised bath is heated the air within the bath expands; it is
therefore necessary to decrease the amount of air supplied to the bath during the heat up
period to ensure that the bath is correctly fluidised at all times.
•
A modified manual control system is available which is fitted with air flowmeters. In this
case, the correct level of fluidisation may be set by adjusting the air flow rate in
accordance with the valves recommended within this manual or those gained by
experience with individual installations. The air flow rate must still be manually adjusted
during the heat up period. A non standard version of this industrial fluidised bath is
available for applications where continued treatment of components contaminated by
PVC and other halogenated polymers is envisaged. This version is manufactured from
materials that resist the effects of corrosion which are experienced when processing the
above polymers.
The compressed air supply to the fluidised bath must be kept clean, dry, and free from oil. When
used for processing items which may emit toxic or inflammable fumes it is essential that an
adequate fume extraction system be installed. The extraction system must be correctly sized to
ensure that any toxic fumes are removed from the working environment. To eliminate the risk of
spontaneous ignition the concentration of inflammable fumes above the bath and within the
exhaust ductwork must be kept below the lower explosive limit. A later section of this manual
details the various fume treatment equipment that is available, and how it should be installed and
adjusted.
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