A method of generating electrical power comprising: generating a synthesis gas stream in a gasifier; partially oxidizing the synthesis gas stream in at least one partial oxidation stage (160; 180, 186) to oxidize a volatile content of the synthesis gas stream and to heat the synthesis gas stream, the at least one partial oxidation stage (160; 180, 186) being formed by an oxygen transport membrane reactor generating oxygen to support the partial oxidation of the synthesis gas stream; expanding the synthesis gas stream in an expander (168; 182, 188) of at least one expansion stage after having been heated in the at least one partial oxidation stage (160; 180, 186) and generating electrical power from a generator (170; 184, 190) coupled to the expander (168; 182, 188); combusting the synthesis gas stream, after having been expanded, within an oxygen transport membrane boiler to generate heat and a flue gas, the synthesis gas stream being combusted while at an elevated temperature; the flue gas containing carbon dioxide; the combusting of the synthesis gas stream supported by separating additional oxygen from an oxygen containing stream within an oxygen transport membrane system provided in the oxygen transport membrane boiler; producing steam within the boiler by indirectly transferring the heat to boiler feed water; extracting energy from the steam by a steam turbine system of a steam cycle operatively associated with the oxygen transport membrane boiler and converting the energy to additional electrical power by an additional electrical generator coupled to the steam turbine system; and purifying the flue gas stream to produce a carbon dioxide-rich stream. generating a synthesis gas stream in a gasifier; partially oxidizing the synthesis gas stream in at least one partial oxidation stage (160; 180, 186) to oxidize a volatile content of the synthesis gas stream and to heat the synthesis gas stream, the at least one partial oxidation stage (160; 180, 186) being formed by an oxygen transport membrane reactor generating oxygen to support the partial oxidation of the synthesis gas stream; expanding the synthesis gas stream in an expander (168; 182, 188) of at least one expansion stage after having been heated in the at least one partial oxidation stage (160; 180, 186) and generating electrical power from a generator (170; 184, 190) coupled to the expander (168; 182, 188); combusting the synthesis gas stream, after having been expanded, within an oxygen transport membrane boiler to generate heat and a flue gas, the synthesis gas stream being combusted while at an elevated temperature; the flue gas containing carbon dioxide; the combusting of the synthesis gas stream supported by separating additional oxygen from an oxygen containing stream within an oxygen transport membrane system provided in the oxygen transport membrane boiler; producing steam within the boiler by indirectly transferring the heat to boiler feed water; extracting energy from the steam by a steam turbine system of a steam cycle operatively associated with the oxygen transport membrane boiler and converting the energy to additional electrical power by an additional electrical generator coupled to the steam turbine system; and purifying the flue gas stream to produce a carbon dioxide-rich stream.