Geared axial multistage expander system and assembly method

A geared axial multistage expander system and assembly method including a casing (42) and a plurality of stages (R1 to R6). A stage includes a stator part (44) connected to the casing and having plural statoric airfoils (55) and a rotor part (50) configured to rotate relative to the stator part and having plural rotoric airfoils (54). The axial multistage expander (40) also includes a support mechanism (48) connected to the casing and configured to rotatably support the rotor part. Rotoric airfoils of at least one stage of the plurality of stages are configured to rotate with a speed different from rotoric airfoils of the other stages. An epicyclic gearbox (52) is connected between the at least one stage and the turbine shaft (50). The stator part, the rotor part and the support mechanism of the plurality of stages are provided inside the casing. The axial multistage expander may be used within a thermal energy storage (120) and gas storage (122) cycle (110).