The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into mechanical work while undergoing phase change. The thermal efficiency equals 1 minus the ratio of the low-to-high pressures to the power of 1 minus the reciprocal of the heat capacity ratio.

The low speed ORC process has an electricity output of 400–1100 kW and electricity to heat ratio of 0.18–0.22. The ORC-concept has two circuits, one for thermal oil and another for organic fluid.

ORC: How it works In a typical ORC design, a thermal energy source feeds an evaporator to drive an expander or “reverse compressor”, which in turn generates the electricity. The provider of the heat can be natural, such as in the case of geothermal energy, or waste heat from any number of industrial waste heat sources.

Water is the working fluid for a Rankine cycle process where the turbine and the pump have isentropic efficiencies of 85% and 70%, respectively. Superheated vapor enters the turbine at 8 MPa and 500 ◦C. The condenser pressure is 7.5 kP a. The net power output of the cycle is 100 MW.