2. PRINCIPLE
• A heated hollow metal drum rotates on its
longitudinal axis is partially dipped in the
solution to be dried
• Conduction is the heat transfer mechanism
• The solution is carried as a film on the surface
of the dryer
• The dried film scraped with the help of a knife
while the drum is rotating
4. CONSTRUCTION
• Horizontally mounted hollow steel drum
• Diameter- 0.6-3 m
• Length -0.6-4m
• External surface –smoothly polished
• Feed pan placed below the drum
• Spreader at one side
• Doctor’s knife on other side
• Storage bin or conveyor connected to the knife-
to collect the dried material
5. WORKING
1.Steam is passed inside the drum
2.Simultaneously drum is rotated at a rate of 1-10
rpm ,drum dips partially in to the feed
3.The liquid material present in the feed pan
adheres as a thin layer to the external surface of
the drum during rotation
4.The material is completely dried in one rotation
itself
5.The dried material scrapped by the doctors knife
6.Materials collected in to storage bin
6. USES
• Used for drying solutions, slurries,
suspensions etc.
The products dried are
milk products
starch products
ferrous salts
Suspensions of zno
7. ADVANTAGE
• Drying time is less(6-15 seconds) so heat
sensitive materials can be dried
• Compact, less space
• Product obtained is completely dried
8. DISADVANTAGE
• Maintenance cost is higher than spray dryer
• Skilled operators required to control feed rate
,film thickness, speed of rotation and
temperature
