The ORC turbogenerator uses medium-to-high-temperature thermal oil to preheat and vaporize a suitable organic working fluid in the evaporator (4>5). The organic fluid vapor rotates the turbine (5>6), which is directly coupled to the electric generator, resulting in clean, reliable electric power.

2.7. An organic Rankine cycle (ORC), is fundamentally the same as a steam Rankine cycle; however, it uses a lower boiling point organic fluid to better match its operation to lower temperature heat sources. ORC systems can achieve better efficiencies than steam turbines for smaller systems (less than a few MW_e).

Exergy analysis is an advantageous method in examining the causes and locations of losses in thermodynamic systems and determining optimum conditions [22]. Sun et al. [23] performed exergy analysis for ORC and ORC combined systems using lowtemperature industrial waste heat as a heat source.

η=WnetQin=1−QoutQin. The basic Rankine cycle is presented in terms of temperature and entropy change in Figure 10.2. The ideal state of this cycle is reflected in the vertical lines 1-2 and 3-4, when the fluid compressed and expanded. Those processes are shown to proceed isentropically, i.e., without entropy change.