Indirect-fired Rotary Kiln Design

Indirect-fired kilns are unusually important where direct-fired operation cannot be employed due to controlled heating, product contamination, etc. These challenges respond to niche applications of unusually high value.

Typical Gas-fired Indirect Rotary Kiln
Electrically-heated Indirect Rotary Kiln (Harper International, Buffalo, NY)

In the forefront of the indirect-fired kiln offering is Harper International, a reliable AlphaThermal collaborator. We have been privileged in having a cordial working relationship with Harper in the area of indirect kiln design for several applications including Ni-Co processing in China, design of a nickel briquette in South Africa, reduction of copper oxide to elemental copper in Germany, molybdenum ore reduction kilns, and metal-alloy kilns in the US. A typical design approach for a recent job may be summarized as including the following:

  • Flue Design and Combustion Chamber Emissions
  • Refractory Selection
  • Heat Balance
  • Miscellaneous Design Review or Questions
  • Kiln direction of rotation
  • Evaluation of bed fill fraction, fill angle, bed depth, and residence time using an in-house model

Addressing these via the use of an OpenFOAM computer modeling provided the optimum layout of burners, heating patterns, etc.

Velocity distribution rescaled to 0-20 m/s to highlight flue velocity magnitude
Outer Tube Temp. Profile. Note: Temperatures are in °C. Scale is 1100 to 1200°C.
Temp. Sections through burners 2, 4, 6, and 7