Abstract: A mechanism and method for calcining cement including a precalciner and a rotary tubular kiln receiving material therefrom and discharging through a vertical conduit to a cooler, means for delivering air through the cooler to flow up through the conduit to the kiln with a laterally movable plate type valve controllably positioned in the shaft to increase the resistance to gas flow from the cooler to the kiln and a branch conduit for receiving excess air from the cooler as tertiary air and delivering the air to the precalciner with means for separating a dust from the tertiary air.