Abstract: A process for the thermal treatment of carbon-containing substances, in particular of sludges which, after mechanical indirect pre-drying, are subjected to direct drying by means of drying gas is disclosed. Object of the invention is to simplify the elimination of the noxious matter contained in the sewage sludge, to allow for energy recovery, and to improve the efficiency of the entire process. The problem is solved by the fact that the drying gas used for direct sludge drying is recovered by partial oxidation of the sludge subjected to direct drying.

Abstract: Referring to process and equipment for the indirect drying of sludge, especially for the drying of wastewater sludge, which may undergo previous mechanical dehydration and/or preheating, it is intended to provide a method that permits utilizing low-value energy for drying purposes while avoiding environmental nuisance. With reference to the process, the problem is solved by drying the sludge under vacuum which is produced by withdrawing the water vapor by means of an injection condenser, the equipment provided for solving the problem comprising a barometric condensor associated with a mechanical sludge dehydrator and at least one sludge drier for indirect drying with an hermetically closed sludge space, the gas dome of the sludge space being connected to the injection condenser through a line for withdrawal of the water vapor.