Thoreson-McCosh Inc
EDITION 05/07/10
5
IB201001.doc
SECTION 2.2 TRIPLE BED METHOD OF OPERATION
The operation of the triple bed dryer is based on each of the three beds being indexed to
one of three separate stations within the unit.
The first position is the regeneration station. Here, super-heated ambient air is blown
through the bed to remove adsorbed moisture from the desiccant material. This moisture is
exhausted to the atmosphere near the bottom of the dryer.
The second position is the cool down station. Here, a small percentage of return air from
the hopper passes through the bed to gradually cool down the hot desiccant material. The
heat captured by this air is used to heat the process air, thus minimizing process heater
energy requirements. As the bed cools, it begins to contribute to the material drying
process.
The third position is the process station. Here, the rest of the return air from the hopper
passes through this desiccant bed. The dried, cooled, desiccant material is now permitted
to adsorb any moisture removed from the plastic resin that is carried in with the return air,
before it is heated and sent back to the drying hopper in a completely closed loop cycle.
Automatic indexing of the beds is performed by separating the manifolds upper and lower
airflow from the desiccant beds with an electric lineal actuator motor. The beds are then
rotated with a gear motor/chain drive assembly. A limit switch stops the beds at the next
sequential station. The lineal actuator motor then clamps the manifold seals located on the
upper and lower air flow manifolds against the beds for an airtight operation.
On standard units, the automatic bed indexing time cycle is controlled by the
microprocessor, which is maximized to guarantee very dry process air, even while
operating under extremely severe drying conditions.
In the optional dewpoint control mode, the dewpoint of the process air is continuously
monitored. Automatic bed indexing will occur only when the dewpoint is approaching an
unacceptable level.
The process air heating elements are located in the heater box which is nearest the control
box mounted on the upper deck. An indicating light is provided to indicate when the
process heater elements are activated.
The regeneration air heating elements are located in the heater box, on the upper deck,
furthest from the control box. On standard units the regeneration heater and blower are
timed to be on during the first portion of the bed index cycle, and off during the remainder of
the cycle. Only units with the optional
regeneration power saver
, the heaters and blower
will shut off early if the regeneration of the bed is sensed as being completed (regeneration
exhaust temperature reaches a minimum of 325°F/ 163°C). An indicating light is provided
to indicate when the regeneration heater elements are on.
