Principle

The waste energy produced by under-floor traction equipment in MU stock may be used for comfort functions. While the use of waste heat by means of heat exchangers is limited to heating, advanced technology based on the Organic Rankine Cycle (ORC) allows for the production of electric power from waste heat and thus for the use of waste energy for cooling or lighting purposes.

The Rankine Cycle

In the Rankine cycle superheated steam produced by a boiler is expanded in a steam turbine which drives a generator converting the work into electricity. The remaining steam is condensed and fed back to the boiler. This thermodynamic cycle is used to generate electricity in many power stations.

The Organic Rankine Cycle (ORC)

In the Rankine cycle overheating of the steam water mixture is required. The efficiency of the cycle can be improved by using organic substances instead, that can be used below 400°C and do not need overheating. This is called an Organic Rankine Cycle (ORC). By means of the ORC, waste heat can be exploited to produce electricity at low temperatures where a steam cycle would be inefficient. Organic compounds eligible for the use in ORC include CFCs, freon, iso-pentane and ammonia. The substance used should match the temperature of the available waste heat (waste heat temperatures can be as low as 70-80°C). ORC reach an efficiency 10 to 20% depending on temperature levels.

Fields of application

Possible applications of ORC technology range from low temperature waste heat recovery in industry and efficiency improvement in power stations to the recovery of geothermal and solar heat.