ABSTRACT
The energy consumption in a drum dryer may range
between 1.1 kg steam per kg of evaporated water and
1.6 kg steam per kg of evaporated water, corresponding
to energy efficiencies of about 60-90%.[2-4] Under ideal
conditions, the maximum evaporation capacity of a drum
dryer can be as high as 80 kg H2O/hr m 2.[4] A drum dryer
can produce products at a rate between 5 and50 kg hr-1 m-2,
depending upon type of foods, initial and final moisture
content, and other operation conditions.[2]
Drum dryers are classified into single drum dryer
(Fig. 1a), double drum dryer (Fig. 1b), and twin drum
dryer.[3] A double drum dryer has two drums that revolve
toward each other at the top. The spacing between the two
drums controls the thickness of the feed layer applied to the
drum surfaces. A twin drum dryer also has two drums, but
they rotate away from each other at the top. Among the
three types, single and double drum dryers are most com-
monly used for fruits and vegetables. For example, large
quantities of mashed potato flakes are produced using
single drum dryers with specially designed roll feeding
system. Double drum dryers are used in California to dry
tomato paste. Twin drum dryers are used only for drying
materials yielding dusty products.
