Installations for the calcination of alumina and similar products

The method of improving the thermal efficiency of a calcining installation comprising a long rotary kiln having an inlet for raw material to be calcined at an upstream end thereof and an outlet for the calcined material at a downstream end thereof, a burner generating heat in the kiln for calcining the raw material, an air inlet at the downstream end, a flue gas outlet at the upstream end, and a cyclone separator means for separating dust from the flue gas exhausted through the flue gas outlet, the cyclone separator means having an inlet connected to the flue gas outlet and a dust outlet, which comprises the steps of

• (a) cycling the raw material through an additional cyclone separator having an inlet for the raw material, a gas outlet and an outlet for the raw material, and from the raw material outlet into the upstream end of the kiln,
• (1) the raw material inlet of the additional cyclone separator being connected to the upstream end of the kiln and the gas outlet of the additional cyclone separator being connected to the inlet of the cyclone separator means through a pipe having a vertical portion,
• (b) introducing the raw material in a lower part of the vertical pipe portion for preheating the raw material by the flue gas before the raw material passes through the raw material inlet of the additional cyclone separator,
• (c) subjecting the raw material cycled into the upstream end of the kiln to the heat generated by the burner in a half of the kiln adjacent the upstream end for calcining the preheated raw material, and
• (d) cooling the calcined material in the other half of the kiln adjacent the downstream end thereof.