Fachinformationszentrum Karlsruhe

Transforming waste heat into electricity

Steam expansion engine with ORC technology increases electricity yield

Much waste heat is generated in industrial production and power generation. It is estimated that a quarter of energy production in Germany is lost this way. Waste heat is currently often emitted into the atmosphere unused because there are no suitable technical procedures that allow it to be used efficiently. In order to utilise these untapped energy resources and turn them into electricity, a technology company from Saarland, Germany, has combined a steam expansion engine with ORC technology. The BINE Projektinfo brochure “Transforming waste heat into electricity” (13/2011) introduces the system and some initial results from a field test.

ORC processes work like a conventional steam power plant. The only difference is that they use an organic working fluid, which evaporates at lower temperatures than water. This process allows the utilisation of heat at temperatures between 200 and 500 °C to produce electricity. Until now, the ORC process has usually been used in combination with turbines, which, however, has lower part-load efficiency. Combining it with a steam expansion engine proves to be more flexible. Here, it is possible to adapt it to different levels of temperature and pressure. Given the same level of heat, an ORC process together with the steam expansion engine can generate significantly more electricity than in combination with turbines. Any waste heat still remaining after the generation of electricity can then be used for heating purposes.

The new system is currently being tested in several branches as part of a field test and is expected to be ready for market in 2013. Around 500 industrial firms in Germany, especially in the areas of metal processing, glass production, the chemical and paper industry as well as around 1,000 larger CHP plants are potential areas of application.