Abstract: An apparatus for generating electrical and/or mechanical energy from at least a low-grade fuel comprises a closed circuit in which steam is formed in a steam boiler fired with low-grade fuel, the steam formed in superheated in a superheater with the aid of heat originating from a heat source in which high-grade fuel is burned, the superheated steam is fed to a steam turbine in which the steam is expanded, thereby delivering work, the expanded steam is condensed in a condensor and the condensed steam is fed back to the steam boiler via a condensate degasser. The combination of forming steam with the aid of heat originating from low-grade fuel and superheating said steam with the aid of heat originating from high-grade fuel provides a process for converting fuel into electrical and/or mechanical energy with a relatively high overall efficiency.