Two shafts are typical in regenerative kilns and these are operated alternately.

  • When shaft A is the "primary" and B is "secondary", combustion air is added from the top of shaft A, while fuel is added below that via burner lances
  • Hot gases pass downward, cross to shaft B via the so-called "channel" and pass upward to the exhaust of shaft B
  • In both shafts cooling air is added from the bottom to cool the lime
  • The combustion air and cooling air leave the kiln jointly via an exhaust on top of shaft B, which also serves to preheat the limestone

The direction of flow is reversed every 12 – 15 minutes, shaft A and B changing roles as "primary" and "secondary" shaft. Heat loss in the regenerative kiln is minimal and fuel consumption is low. Regenerative kilns are today mainstream technology as fuel costs are high. Regenerative kilns are built with 150 to 800 t/day output, 300 to 450 being typical.