5. Control system goal
The industrial dryer had only two temperature sensors,
one in the furnace and another at the collecting
box, and was worker experience based operated. Workers
tried to process the maximum of fresh solid, maintaining
the operation conditions as constant as
possible, avoiding the plugs and sharp discharges (they
observed the dryer output at the conveyor belt), and
the dryer overload, that can stop the dryer with a high
fire risk. The outlet moisture of the first dryer is not a
critical variable because the second dryer has enough
drying capacity to reach the desired outlet moisture.
The first dryer behaviour is the key to improve the plant
reliability.
The main objective of the automatic control system is
basically the same, i.e. to maximise the dryer production
maintaining a safe operation. In order to reach this goal
Fig. 2. Schematic view of dryer. and avoid the fire risk it is necessary to achieve at least
242 R. Arjona et al. / Journal of Food Engineering 68 (2005) 239–247
quasi-stationary conditions. As a secondary target, the
energetic yield is also considered