Method for operating a power generating plant which has at least one compressor, at least one turbine and at least one burner arrangement, - in which an oxidator gas containing an oxygen gas is compressed in the compressor, - in which the compressed oxidator gas is lean burned with a fuel gas in at least one pre-burner of the burner arrangement, - in which a combustion exhaust gas from the pre-burner is supplied to an oxygen extraction device which extracts from the combustion exhaust gas part of the oxygen gas contained therein, - in which the combustion exhaust gas with reduced oxygen content is burned with a fuel gas downstream of the oxygen extraction device in at least one after-burner of the burner arrangement, - in which a combustion exhaust gas from the after-burner is supplied to the turbine and expanded therein, - in which the oxygen extracted from the combustion exhaust gas of the pre-burner is removed from the oxygen extraction device by means of a flushing gas, - wherein a synthetic gas generator is provided which generates a synthetic gas containing hydrogen gas from a fuel, from water vapour and from oxygen gas, - wherein the oxygen gas extracted from the combustion exhaust gas of the preburner by means of the oxygen extraction device is used to supply the synthetic gas generator with oxygen gas, - wherein the synthetic gas generated by the synthetic gas generator is supplied to the pre-burner and/or to the after-burner as a fuel gas, - wherein a steam generating device is provided which is incorporated in an exhaust gas path of the turbine and which evaporates a fluid, in particular water, by means of a turbine exhaust gas, wherein at the same time the turbine exhaust gas is cooled, characterised in that - as a flushing gas, an inert gas or at least a gas free from fuel is used, - the steam generating device subjects the steam to a high pressure, - the high-pressure steam is expanded in a steam turbine, and - a partially expanded steam is extracted from the steam turbine as a medium-pressure steam and mixed in with the synthetic gas upstream of the pre-burner and/or the after-burner. - in which an oxidator gas containing an oxygen gas is compressed in the compressor, - in which the compressed oxidator gas is lean burned with a fuel gas in at least one pre-burner of the burner arrangement, - in which a combustion exhaust gas from the pre-burner is supplied to an oxygen extraction device which extracts from the combustion exhaust gas part of the oxygen gas contained therein, - in which the combustion exhaust gas with reduced oxygen content is burned with a fuel gas downstream of the oxygen extraction device in at least one after-burner of the burner arrangement, - in which a combustion exhaust gas from the after-burner is supplied to the turbine and expanded therein, - in which the oxygen extracted from the combustion exhaust gas of the pre-burner is removed from the oxygen extraction device by means of a flushing gas, - wherein a synthetic gas generator is provided which generates a synthetic gas containing hydrogen gas from a fuel, from water vapour and from oxygen gas, - wherein the oxygen gas extracted from the combustion exhaust gas of the preburner by means of the oxygen extraction device is used to supply the synthetic gas generator with oxygen gas, - wherein the synthetic gas generated by the synthetic gas generator is supplied to the pre-burner and/or to the after-burner as a fuel gas, - wherein a steam generating device is provided which is incorporated in an exhaust gas path of the turbine and which evaporates a fluid, in particular water, by means of a turbine exhaust gas, wherein at the same time the turbine exhaust gas is cooled, - as a flushing gas, an inert gas or at least a gas free from fuel is used, - the steam generating device subjects the steam to a high pressure, - the high-pressure steam is expanded in a steam turbine, and - a partially expanded steam is extracted from the steam turbine as a medium-pressure steam and mixed in with the synthetic gas upstream of the pre-burner and/or the after-burner.