Recovering energy from a stream of wet oxidn. prods. directs the filtered stream to oriented nozzles forming part of a rotatable cylinder. The cylinder is mounted inside a cooled partial vacuum chamber, and is used to drive an electrical generator. Condensate in the chamber provides a source of heat recovery.    Pref. the method uses a prod. stream from a conventional wet combustion-process carried out using a gravity pressure reactor vessel (11). This stream, e.g. a mixture of steam, carbon dioxide, oxygen, nitrogen, liquids and solids, passes along updraught column (20), and pref. is then directed through filter (21) for solids removal. Thereafter, it is passed via control valve (22) into the hollow axle of a rotor mounted in a stationary housing (10). The rotor carries a number of rings, each of which has several internal passageways communicating with the rotor bore and leading to approximately tangential outlet nozzles. In the interests of smooth running, the rings are pref. displaced circumferentially with respect to one another, i.e. so that the outlet nozzles do not lie on axial lines. The rotor is pref. coupled to an electrical generator (43), and is driven by discharge of the filtered prod. stream, the effects of which are augmented by maintaining housing (10) at reduced internal pressure using vacuum pump (80). Efficiency is further increased by cooling the housing, pref, using water cooled by heat exchange with the liq. oxygen to be utilised in reactor vessel (11). Condensate forming in housing (10) is withdrawn by pump (99), and recirculated to tank (12) in which the waste material (13) is mixed with water prior to combustion in vessel (11).    USE/ADVANTAGE -   Applied during the combustion of wet organic material. e.g. municipal sludge, waste or coal, by the gravity pressure reaction technique. Generation of electricity is more efficient than in the prior method of steam separation followed by expansion in a turbine, and heat available from the condensate contributes towards the combustion process.