Electricity

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
  (140°F)

Operating principle of an ORC system