Thoreson-McCosh Inc
EDITION 05/07/10
18
IB201001.doc
SECTION 8.2 FORCING A BED INDEX
If the Air Flow Rate indication option is installed, a second press of the Optional Setpoints
key (single press if not installed) will display the following:
I n d e x b e d s ? ( Y E S / N O )
FIGURE 8.2 BED INDEX DISPLAY
Pr
essing the “NO” key returns to the First Screen (figure 3.2) and does not affect the dryer.
Pressing the “YES” key causes the dryer to shift immediately.
NOTE: SHIFTING THE BEDS SHOULD NOT BE DONE UNLESS IT IS NECESSARY AS
IT WILL CAUSE IMPROPER DRYING, AND MAY CAUSE A SEVERE TEMPERATURE
SPIKE
.
Any time a shift is required, make sure two additional shifts are complete so that the dryers
desiccant beds are put into their original position.
SECTION 8.3 REGEN BLOWER OFF-DELAY TIMER
The Regen Blower Off-Delay Timer allows additional cooling of the regenerated desiccant
bed.
Regeneration of the desiccant beds is accomplished by blowing extremely hot (550°F/
288°C) ambient air through the desiccant for a predetermined length of time. The blower
and heaters then shut off until the process cycle is complete. Normal cooling is
accomplished through static (conduction) heat transfer during the remainder of the process
cycle, then through convection while the bed is in the cool down position during the next
process cycle. This is accomplished by bleeding off a small portion of the process air
through the lower air flow manifold, thru the desiccant bed, and back into the process
heater box. This cools down the bed and allows reuse of the energy used to regenerate
the bed.
However, because desiccant, as it captures moisture gives off heat, this energy and the
heat from the bed that is cooling down can make it very difficult to attain low process
temperatures (<150°F/ 66°C). Therefore, we have made it possible to ex
tend the regen
blower running time with the regen heaters off. This allows the convective cooling to be
achieved before the bed rotates to the cool down position. The danger is that the ambient
air will introduce some moisture as the bed cools down, thereby reducing the effectiveness
of the desiccant to dry the process air. This is less of a danger than letting the process air
stream go open loop, because desiccant will not adsorb moisture until its temperature is
below approximately 200°F/ 93°C. Thores
on-McCosh would not recommend using the off-
delay unless necessary, and recommends that the dryer be monitored closely to determine
