Thoreson-McCosh Inc
EDITION 05/07/10
12
IB201001.doc
SECTION 5 DELTA-T OPTION
SECTION 5.1 INTRODUCTION TO DELTA-TEMPERATURE
The Delta T function determines the material has achieved an acceptable dry level based
on the idea that when the hopper air return temperature approaches the hopper air inlet
temperature, the material is dry. Obviously, due to losses of energy in a drying
environment, the air inlet and outlet will never be the same, but at some point, the
difference is small enough to indicate that the material can be considered dry. At this point,
the process air flow heaters will turn off. The process blower will continue to cycle keeping
positive dry air pressure in the drying hopper. This will prevent the material from being over
dried and also keep it from being saturated with moisture. This also saves energy.
The
Process Setpt
should be set to the drying temperature recommended by the material
manufacturer or supplier. The
Hop
Exh Setpt
is determined by drying the material for the
manufactures suggested residence time. (typically 3 to 4 hours). Note the
Hop Exh
Temp
at the end of the residence time and set the
Hop Exh Setpt
at this temperature. If the
Hop
Exh
Temp
falls below the Low Temp Return Setpoint, the Process heaters will come back
on.
SECTION 5.2 READING THE DELTA-T FIRST SCREENS
The first screen is special for the Delta T dryer. The first screen is actually made of 2
screens that will scroll from one to the other. To freeze the screens, Press the ENTER key,
to make the screens resume scrolling, press the RETURN key.
P r o c e s s S e t p t = 2 2 5 ° F
P r o c e s s T e m p = 2 2 4 ° F
H o p E x h S e t p t = 1 8 5 ° F
H o p E x h T e m p = 1 8 0 ° F
R e g e n T e m p = 2 2 5 ° F
D e w p o i n t = -
4 0 ° F
( D r y e r A l a r m )
D r y e r i s O N
FIGURE 5.2 The Delta-T First Screens Display
