A combined thermodynamic system is described, for the production of mechanical power. The system comprises a gas turbine (1) and a turbomachinery (2) driven by the gas turbine (1). The system further comprises a thermodynamic organic Rankine cycle (5) with a turboexpander (13). A heat transfer arrangement (9a, 9, 11) transfers heat from exhaust combustion gases of the gas turbine to the thermodynamic organic Rankine cycle, wherein heat is converted into mechanical power used for driving a driven a turbomachine.