Organic Rankine Cycles (ORC) are systems that can effectively recover low-grade heat for electric power generation. For ORC to be a viable technology, it should operate safely and efficiently under variable operating conditions due to exogenous and operating specifications changes.

thermal power plant works on principle of the Rankine Cycle shown in Fig. 2[5]The cycle consists of four processes: (1-2) Isentropic compression on pump; (2-3) Constant pressure heat addition in a boiler; (3-4) Isentropic expansion in a turbine; (4-1) Constant pressure heat rejection in a condenser.

The Rankine cycle operates in the following steps: 1-2-3 Isobaric Heat Transfer. High pressure liquid enters the boiler from the feed pump (1) and is heated to the saturation temperature (2). Further addition of energy causes evaporation of the liquid until it is fully converted to saturated steam (3).

Real Rankine cycle (non-ideal) In a real power-plant cycle (the name "Rankine" cycle is used only for the ideal cycle), the compression by the pump and the expansion in the turbine are not isentropic. In other words, these processes are non-reversible, and entropy is increased during the two processes.