Thermascrew® / BLANCHER
| The Thermascrew®
Dryer exchanges heat indirectly through a hollow screw and a
jacketed body trough. Product is conveyed by the rotation of
a single or double screws. Residence time is controlled by the
rotor speed and ranges from several minutes to one hour. The
gentle screw action handles friable products with minimal particle
size reduction. The twin-screw design handles dough-like materials
for cooking and reaction processes. |
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TYPICAL APPLICATIONS OF THERMASCREW®
INDIRECT HEATING SYSTEM
- Blanching
- Chilling
- Cooking
- Cooling
- Crystallizing
- Drying
- Heating
- Mixing
- Evaporating
- Desolventizing
- Reacting
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TYPICAL PRODUCTS
- Chemicals
- Crystals
- Fats
- Feeds
- Fish
- Fruits and Vegetables
- Glutinous Materials
- Granular Materials
- Liquids
- Meals
- Meat By-Products
- Pastes
- Pharmaceuticals
- Powders
- Pulpy Materials
- Salt
- Slurries
- Solids
- Starch
- Sugar
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The product usually enters one end and moves by screw rotation
to the discharge point at the other end. Heat is transferred
when it comes into contact with the hollow screw, shaft and
jacket surfaces.
The heat exchange medium enters at the rotary joint, moves through
the hollow screw, and moves back out again. The medium also enters
the jacket near the product outlet point, discharging at the
opposite end of the trough. A baffle arrangement in the jacket
ensures positive flow.
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Screw rotation speed controls retention time and discharge
temperature of the product. The tumbling action of the short
pitch screw makes the heat exchange uniform and efficient. |
TYPES OF DESIGN
There are two basic Thermascrew® designs:
- Conveyor - Type
consists of one or more slowly rotating hollow screws mounted
in a jacketed pipe or trough.
- Agitated Vessel-
Type consists of hollow screw rotors mounted in a jacketed vessel.
Material circulates within the unit, agitated by the rotating
screws and overflows with residence time determined by feed rate
and hold up.
The Thermascrew® indirect drying system is made of carbon or stainless
steel as well as other alloys. Body styles include a non-jacketed
trough, a jacketed trough, a pipe trough with jacket and a trough
with multiple screws.
Optional steam orifices along the trough permit direct as well as
conductive heating, making the unit useful in live steam heating,
sterilizing, cooking or blanching. Purge gas or air may be injected
as well.
Enclosed models isolate the product from airborne contaminants (dust,
fumes, water vapor or reactant gases) and eliminate toxic or expensive
product dust losses.
Thermascrews® may operate in either a pressure or vacuum environment
and can serve as reactors for mixing liquid or gas reactants with
the product. Any gases produced during the process can be recovered.
Rotor styles include a hollow screw the same diameter as the trough
and a hollow screw with a smaller diameter than the trough. With the
first type, optional lifter bars - mounted between screw flights -
improve agitation by tumbling the product. With the second style,
continuous ribbons or lifter bars - mounted between the outer edge
of the screw and flush with the inner surface of the trough - mix
the product even more and require higher rotational rates, improving
heat-transfer coefficients.
The Thermascrew® indirect drying systems are available in seven trough diameters from 8"
to 29" and eight trough lengths from 4' to 30'.
Chart below shows overall heat transfer factor
(U)
in BTU/HR/SQ. FT./°F in typical applications:
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