Abstract: During combustion of a water-vapor generating sulfur-containing fuel, the pressurized flue gases are cooled, while extracting the main part of the latent heat of evaporation of the water vapor included and while removing sulfur impurities, using a coolant liquid in drop form in a scrubber. After having passed through the scrubber, the flue gases are mixed with a proportion of heated flue gases, which have previously passed through the scrubber, so that the temperature of the flue gases after said mixing exceeds the dew point for sulfuric acid in the flue gases. The flue gases are then heated in a heat exchanger and are thereafter expanded in an expansion machine to atmospheric pressure while reducing their temperature again without falling below the dew point for sulfuric acid.