Mechanical Energy Recovery from Low Grade Thermal Energy Sources

An ORC based power plant for waste heat recovery in stationary applications has been developed and experimentally characterized. The aim of the study was to investigate the performance of a sliding vane rotary expander as the device to convert the enthalpy of the working fluid, namely R236fa, into mechanical and electric energy. A theoretical model of the expander supported the design and allowed to assess the thermodynamic transformations that take place in it. Furthermore, a deep experimental campaign explored the behavior of the expander and the one of the recovery system also at off design conditions. The experimental activity on the expander included the reconstruction of the indicated diagram using a set of high frequency piezoelectric pressure transducers that provided an accurate prediction of the pressure evolution inside the cell. The overall cycle efficiency achieved was close to 8% and further improvements concerned to the expander design have been addressed. The temperature of the upper thermal source at around 120 °C and the mechanical output power close to 2 kW make the expander and the whole system suitable for plenty of potential recovery applications.