The sizing and design of a rotary dryer is a complex process involving a number of factors and considerations. This presentation looks at the importance of custom rotary drum dryer design over a one-size-fits-all solution, and the many material characteristics and environmental factors that should be considered during the design process.

1. Sizing & Design
Experts in process design and material
processing for over 60 years.
Rotary Dryer

2. Rotary dryers are a critical component in
many industrial processes, capable of
processing all sorts of materials, from
chemicals and fertilizers, to minerals and
ores, and nearly everything in between.

3. The process of sizing and designing a rotary
dryer around a material’s unique processing
needs is one of precise engineering, requiring
careful consideration of a variety of factors.

4. The process of sizing and designing a rotary
dryer around a material’s unique processing
needs is one of precise engineering, requiring
careful consideration of a variety of factors.
A one-size-fits-all approach to an industrial
drying system may seem tempting, but as you
will soon see, a custom solution will produce
the best results.

5. Many of the material’s characteristics will play
an integral role in not only determining how
material will behave in the dryer, but also in
how the design of the dryer and other
operational mechanics will need to
accommodate the material in order to
produce desired results.

6. The following material characteristics all
play a role in dryer sizing and design:

7. The following material characteristics all
play a role in dryer sizing and design:
- Moisture Content

8. The following material characteristics all
play a role in dryer sizing and design:
- Moisture Content
- Bulk Density

9. The following material characteristics all
play a role in dryer sizing and design:
- Moisture Content
- Bulk Density
- Specific Heat

10. The following material characteristics all
play a role in dryer sizing and design:
- Moisture Content
- Bulk Density
- Specific Heat
- Heat Transfer Properties

11. The following material characteristics all
play a role in dryer sizing and design:
- Moisture Content
- Bulk Density
- Specific Heat
- Heat Transfer Properties
- Material Limitations

12. Moisture Content

13. Both inlet (raw) and outlet moisture will
need to be considered.

14. Both inlet (raw) and outlet moisture will
need to be considered.
The difference between actual and
desired moisture will in part determine
what the dryer will need to accomplish, as
well as how hard it will have to work to
achieve this goal.

15. Bulk Density

16. The bulk density of a material refers to the
weight of the material, per a specific
volume. This is an indicator on the
operational load the dryer must be able
to accommodate.

17. The bulk density of a material refers to the
weight of the material, per a specific
volume. This is an indicator on the
operational load the dryer must be able
to accommodate.
A material’s bulk density is critical to
determining sizing of components such as
bearings, gear train, trunnion wheels, and
the motor.

18. Specific Heat

19. Specific heat refers to how much energy it
takes to raise 1 gram of material by 1
degree Celcius.

20. Specific heat refers to how much energy it
takes to raise 1 gram of material by 1
degree Celcius.
In other words, the specific heat of a
material will help to determine how much
energy will be needed to cause the
desired change in temperature for that
specific material.

21. Heat Transfer
Properties

22. The heat transfer properties of a material
refer to how well a material will transfer heat.

23. The heat transfer properties of a material
refer to how well a material will transfer heat.
This is another factor that will help in
determining how hard a dryer will have to
work to remove the specified amount of
moisture.

24. Material Limitations

25. The limitations of a material also play a
critical role in dryer design. Factors such as
fragility, material consistency, end use,
and other characteristics, will steer the
design process in one direction or
another.

26. The limitations of a material also play a
critical role in dryer design. Factors such as
fragility, material consistency, end use,
and other characteristics, will steer the
design process in one direction or
another.
For example, some materials may require
a sterile processing environment. Others
may be too fragile to handle the dropping
action of flights and would require a
“bald” section at the inlet of the dryer.

27. Other factors to be considered include:

28. Other factors to be considered include:
- Processing Environment

29. Other factors to be considered include:
- Processing Environment
- Flight Design

30. Other factors to be considered include:
- Processing Environment
- Flight Design
- Air-Flow

31. Other factors to be considered include:
- Processing Environment
- Flight Design
- Air-Flow
- Retention Time

32. Processing
Environment

33. The environment in which the dryer will
work will also need to be considered.
Factors such as humidity, elevation, and
climate can all influence how a dryer will
perform, and how much energy will be
required to reach desired results.

34. Flight Design

35. Both flight design and pattern can be
customized to work with the material’s
unique characteristics in order to reach
optimal processing efficiency.

36. Both flight design and pattern can be
customized to work with the material’s
unique characteristics in order to reach
optimal processing efficiency.
A material’s angle of repose, flowability,
and more, will all have an influence on
flight design.

37. Air-Flow

38. Air-flow refers to the direction in which the
drying air flows in relation to the material.

39. Air-flow refers to the direction in which the
drying air flows in relation to the material.
Rotary dryers are available in two types of
air-flow configurations: co-current and
counter current.

40. Air-flow refers to the direction in which the
drying air flows in relation to the material.
Rotary dryers are available in two types of
air-flow configurations: co-current and
counter current.
Which air-flow will best suit the process is
based on the material’s characteristics.

41. For materials that cannot come into
contact with drying air, indirect dryers are
also an option.

42. For materials that cannot come into
contact with drying air, indirect dryers are
also an option.
Indirect dryers are externally heated to
avoid contact between the drying air and
the material being processed. This could
be because the processing environment
must be inert, or the material is composed
of fines that could otherwise become
entrained in the air stream.

43. Retention Time

44. Retention time is another factor that will
need to be considered during the sizing
and design process.

45. Retention time is another factor that will
need to be considered during the sizing
and design process.
Retention time is the duration of time that
a material will need to remain in the dryer
in order to achieve the desired
characteristics.

46. Retention time is determined by looking at
the material’s specific heat, heat transfer
properties, and moisture content.

47. Retention time is determined by looking at
the material’s specific heat, heat transfer
properties, and moisture content.
Retention time can be controlled through
a combination of factors, including the
dryer length, slope, dam plates, and
more.

48. Many material characteristics will influence the
drying process, and how the dryer should be
designed to achieve desired results.

49. Many material characteristics will influence the
drying process, and how the dryer should be
designed to achieve desired results.
For this reason, feasibility testing is often
recommended in order to work out process
variables and other valuable processing data.

50. Conclusion
The process of sizing and designing a rotary
dryer to meet your material’s exact processing
needs is one of precise engineering.

51. Conclusion
The process of sizing and designing a rotary
dryer to meet your material’s exact processing
needs is one of precise engineering.
While a one-size-fits-all approach may be
tempting, as can be seen, a custom solution
will produce the best results, as many factors
will need to be accommodated for.

52. has been a leader in the thermal processing
industry since the 1950s, providing process &
product development, feasibility testing,
maintenance services, and high-quality,
custom rotary dryers.
FEECO

53. Want to learn more?
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Rotary Dryer Handbook
The Rotary Dryer Handbook
Rotary Dryer Sizing & Design
Processing Challenges
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