The rankine cycle is a conventional and proven technology that has been around for many years. The cycle, traditional powered by coal or gas, uses water as a working fluid. The name of the case goes back to William John Macquorn Rankine, a Scottish-British physicist and engineer.
If the temperature of the heat source is too low, the classic steam cycle becomes inefficient. By exchanging the working medium for a fluid with a lower boiling point, a thermodynamic cycle can be established analogously. By choosing a suitable fluid so additional heat sources can be developed to generate electricity. These cycles are referred to as Organic Rankine Cycle (ORC).
Therefor an ORC, with an organic compound is used as a working fluid due to their unique properties such as low evaporation temperatures, they are more suitable for lower heat sources of 100-280°C.
The feed pump compress the working fluid (WF) to a higher pressure level. The evaporator heat up and evaporate the WF in a plate heat exchanger. The turbine expand the highly compressed and hot vapor and released it to the condenser where it is cooled and liquefied. The expander convert at first the extracted heat into mechanical energy and then with the connected generator to electrical energy.
Today, the process is mainly used for electricity generation in the field of geothermal energy, combined heat and power production and the use of waste heat. The expansion machines (turbine, screw expander, steam engine / reciprocating expander) are typically operate with silicone oil, refrigerant or combustible gas e.g. propane.