In the case of mono sewage sludge incineration, a solution may be created that enables sewage sludge ash, which may still have a low proportion of unburned carbon, to be discharged from a mono sewage sludge incineration plant. This is achieved by a method for the post-combustion of sewage sludge ash obtained in a mono sewage sludge incineration in a rotary kiln by means of a hot and a low oxygen content, such as an oxygen content of 5-10 vol. % oxygen. The gas stream from the rotary kiln may escape the sewage sludge ash and is fed to the gas flow. This sufficiently hot gas flow may cause oxidation or afterburning of unburned carbon contained in the sewage sludge ash.

A method for cooling solid residues of a combustion process, which are deposited onto the conveying surface of a conveyor belt of a conveying device and are conveyed in the direction of a solid residue outlet, wherein during conveying heat is transferred from the solid residues to a gaseous coolant. The method is characterized in that the conveyor belt is acted upon by coolant only on its side oriented away from the conveying surface, the conveyor belt is essentially impermeable to the coolant and at least part of the coolant heated by contact with the conveyor belt is extracted on that side oriented away from the conveying surface.