Abstract: A calcining installation of improved thermal efficiency comprises a long rotary tubular kiln having an upstream inlet, a downstream outlet and an air inlet at the downstream end. A burner is positioned in the upstream half of the kiln, the upstream part of the kiln constituting a calcining zone and the downstream kiln part constituting a cooling zone for the calcined material. A cyclone separator for separating dust from the kiln flue gases has an inlet and a dust outlet, and an additional cyclone separator has an inlet, a gas outlet and a material outlet connected to the upstream end of the kiln. A pipe connects the gas outlet of the additional cyclone separator to the inlet of the cyclone separator, the pipe having a vertical portion and an inlet for the raw material in the lower part of the vertical portion.

Abstract: The invention relates to a process for continuously circulating a fluidized powder in a heat exchanger between a heat-carrying gas and a fluidized powder, and to heat exchangers using this process. In the process according to the invention, the circuit through which the fluidized material circulates is in the form of two series of tubes, merely one series of ascending tubes and another series of descending tubes, and the material is fluidized in these tubes with a density that is higher in the descending tubes than in the ascending tubes. The invention applies to any heat exchanger between a gas and a powder and, more particularly, to installations, for calcining hydrated alumina.