Rotary kiln design is a complex process, with a variety of factors and material characteristics influencing the sizing and design. This presentation gives an overview of the sizing and design process, including the many factors that will need to be considered during the design stage.

1. Sizing & Design
Experts in process design and material
processing for over 65 years.
Rotary Kiln

2. Rotary kilns are an advanced thermal
processing tool used to cause a chemical
reaction or physical change in a solid
material through the application of
high temperatures.

3. Rotary kilns are engineered around the unique
characteristics of the material to be processed.

4. Rotary kilns are engineered around the unique
characteristics of the material to be processed.
And while the process of sizing and designing a
custom rotary kiln is not one easily explained in
brief, this presentation offers an introduction to
the basics of the sizing and design process.

5. Material Characteristics
that Influence Design

6. Every material behaves differently in a rotary
kiln. Many characteristics will influence how the
material will respond, requiring a thorough
thermal and chemical analysis before
processing can begin.

7. Every material behaves differently in a rotary
kiln. Many characteristics will influence how the
material will respond, requiring a thorough
thermal and chemical analysis before
processing can begin.
This will aid in determining how the kiln will
need to be engineered around those
characteristics in order to produce the
desired results.

8. Particle Size Distribution & Bulk Density
The particle size distribution and bulk
density of a material can influence some
of the physical and mechanical aspects
of a kiln.

9. Particle Size Distribution & Bulk Density
The particle size distribution and bulk
density of a material can influence some
of the physical and mechanical aspects
of a kiln.
A material with a high bulk density, for
example, will likely require more
horsepower, and subsequently a more
robust drive system.

10. If the material to be processed is in the
form of pellets, or has a larger particle size
distribution (as opposed to fines), the kiln
diameter can be smaller, because a
higher air velocity can be utilized.

11. Abrasiveness & Corrosiveness
A material that is corrosive or abrasive
may not have a direct effect on the sizing
of the kiln, but it will influence the materials
of construction.

12. Abrasiveness & Corrosiveness
A material that is corrosive or abrasive
may not have a direct effect on the sizing
of the kiln, but it will influence the materials
of construction.
Corrosive or abrasive materials will often
require that parts, or all of the kiln be lined
or constructed of a corrosion/abrasion-
resistant material.

13. Specific Heat
Specific heat is the amount of energy it
takes to raise the temperature of 1 gram
of material by 1 degree Celsius.

14. Specific Heat
Specific heat is the amount of energy it
takes to raise the temperature of 1 gram
of material by 1 degree Celsius.
The specific heat of a material determines
how much energy the kiln will require to
cause the desired reaction.

15. Specific heat varies considerably among
materials, with metals having a low
specific heat, and water having a high
specific heat.

16. Thermal Conductivity
Similar to specific heat, how a material
transfers heat will also influence how the
kiln will need to be designed around the
material.

17. Thermal Conductivity
Similar to specific heat, how a material
transfers heat will also influence how the
kiln will need to be designed around the
material.
Will the material transfer its heat easily,
allowing for even distribution and low
retention time, or will it hold onto its heat,
causing cold pockets and increasing
retention time, or even requiring the need
for additional accessories such as dams or
bed disturbers?

18. Heat of Reaction
In many kiln applications, heat (in addition
to energy) is required in order for a
reaction to occur.

19. Heat of Reaction
In many kiln applications, heat (in addition
to energy) is required in order for a
reaction to occur.
For example, when performing
calcination on limestone to convert it to
lime, energy is required to perform the
dissociation of CaCO3 into CaO and CO2.

20. Heat of Reaction
In many kiln applications, heat (in addition
to energy) is required in order for a
reaction to occur.
For example, when performing
calcination on limestone to convert it to
lime, energy is required to perform the
dissociation of CaCO3 into CaO and CO2.
However, the dissociation will not happen
at a temperature lower than 900ºC.

21. The temperature and energy required for
a reaction to occur can be found in
published data, or by performing a
Differential Thermal Analysis (DTA), also
known as a Differential Scanning
Calorimeter (DSC).

22. Temperature Profiles
Temperature profiles are gathered by
performing a Thermal Gravimetric
Analysis, or TGA, which describes the
temperature ranges at which mass loss
occurs.

23. Temperature Profiles
Temperature profiles are gathered by
performing a Thermal Gravimetric
Analysis, or TGA, which describes the
temperature ranges at which mass loss
occurs.
This helps to show where (in terms of
temperature) a reaction begins and ends.

24. A TGA will also reveal reactions that might
occur between the start and end point of
the intended reaction.

25. Chemical Composition
The chemical composition of a material is
also critical in the kiln design process for
many reasons.

26. Chemical Composition
The chemical composition of a material is
also critical in the kiln design process for
many reasons.
One reason is that many materials will
combust during processing, requiring the
kiln to be designed to accommodate this
excess heat.

27. Furthermore, knowing the chemical
composition of a material can help to
predict what exhaust gases will result from
the process, and ultimately, what type of
exhaust gas treatment system will be
needed.

28. Sizing
A Rotary Kiln

29. Once the material has been thermally and
chemically analyzed, the actual sizing process
can begin.

30. Once the material has been thermally and
chemically analyzed, the actual sizing process
can begin.
The sizing of a rotary kiln is a highly complex
process that combines engineering principles
with the thermal and chemical analyses.

31. The size of a rotary kiln is not just a function
of capacity, but also of the amount of
heat that can be generated during
processing due to combustible and/or
volatizing material.

32. The size of a rotary kiln is not just a function
of capacity, but also of the amount of
heat that can be generated during
processing due to combustible and/or
volatizing material.
Kiln length and diameter are calculated
based on the maximum feed rate, the
required retention time, and what the bed
profile will need to be (how full of material
the kiln will be).

33. Once a rough design of the kiln is achieved,
various computer programs can be used to
help predict how the design will work with the
material.

34. Once a rough design of the kiln is achieved,
various computer programs can be used to
help predict how the design will work with the
material.
With the preliminary design configured, kiln
internals can be considered, such as what
type of refractory will work best.

35. Because kiln sizing and design is such a
complex process, it is often recommended
that testing be conducted.

36. Because kiln sizing and design is such a
complex process, it is often recommended
that testing be conducted.
Testing helps to work out process variables,
define time and temperature profiles, and
provide data for process scale-up, ensuring the
most efficient processing solution is achieved.

37. Conclusion
Rotary kiln design is a complex process that
must take many factors into account. Material
characteristics such as specific heat, bulk
density, and more, will all influence how
material will behave in the kiln, and
subsequently, how the kiln will need to be
designed in order to produce desired results.

38. 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 kilns.

39. Want to learn more?
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