How the Indirect Heat Dryer Works

Materials are fed into a rotary drum that is encased in a stationary refractory lined furnace. This furnace casing has a series of burners mounted down the length of one side firing into the furnace chamber. As the material progresses down the length of the unit, it is subjected to different temperatures in different “zones” based on the firing rate setting of the mounted burners.

Because the heat source is separated from the processed material, air velocities within the rotating drum are kept to a minimum or are non-existent. Heat transfer is accomplished through conduction of the heat from the shell to the product and radiation of heat off the shell. The internal flighting inside the rotating drum is specially designed to gently roll the material being processed, constantly exposing new material to the heated shell to maximize the heat transfer process. Flights are designed to avoiding showering the product as that actually decreases heat transfer due to the minimum airflow inside the shell.

The process side of the drum can be blanketed with inert gasses such as nitrogen, argon, or others allowing for specific chemical reactions that would be uniquely designed to meet the customers needs. In addition, due to the lack of air movement within the rotating drum, very fine particles can be handled without entraining particulate into the exhaust gas stream. This stream is minimal as its only purpose is to remove moisture vapor from the unit. Louisville high temperature indirect heat units can operate at temperatures upwards of 1800 degrees F. Whether your process demands moisture removal, calcination, crystalline structure modification, or other unique requirements, Louisville Dryer Company has the experience to solve your processing needs.

Components in an indirect fired rotary dryer (kiln) include:

  • Burners to provide the heat source
  • Rotating drum to provide continuous contact between the shell and product
  • Stationary firebox
  • Combustion gas evacuation system

Combustion Systems:

Typically involve multiple burners, varying from 3-9 units (application-specific)


  • Diesel fuel oil
  • Propane
  • Natural Gas

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