Waste heat recovery


Commercially available ORC systems can generate electricity from waste heat with temperatures as low as 55°C (131°F).

Working principle

An ORC system works according to the same principles as a normal steam turbine. The main difference is that the working medium is an organic fluid instead of water, and that waste heat is used to vaporize the fluid instead of a boiler.

The organic fluid has a boiling point lower than that of water, making it possible to use low-temperature waste heat to generate electricity.
The basic working principle is as follows:

  1. The waste heat causes the working media to evaporate at high pressure.
  2. The vapour is expanded to low pressure in a turbine, generating electricity or mechanical work.
  3. The low-pressure vapour is condensed using cooling water and is pumped back to the high-pressure side.

The driving force and what determines the potential for electricity generation is the difference between the outgoing waste heat temperature and outgoing cooling water temperature.

Efficiency is typically 5-10% conversion of waste heat to electricity.

ORC systems are profitable where:

  • Electricity prices are above 60 EUR/MWh
  • >7 MW (23.9 MMBtu/h) waste heat is available
  • Cooling water is available
  • Delta T between outgoing cooling water and waste heat >60°C

Operating principle of an ORC system



The graph shows a profitability analysis based on information from a supplier of organic Rankine cycle systems.

The cycle converts waste heat to electricity with an efficiency of approximately 10%. In this case the ORC system converts approximately 7 MW (23.9 MMBtu/h) of waste heat into 0.7 MW of electricity, i.e. an annual production of 5,880 MWh.