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