Direct Generation of Compressed Air from Low-Temperature Waste Heat

Abstract

Low-temperature waste heat is quite abundant in industrial processes. However, only a few processes allow for the sensible use of waste heat with a temperature level significantly below 100 °C. A plant concept is therefore currently being validated under realistic laboratory conditions, which allows gases to be compressed to an industrially relevant pressure level using low-temperature waste heat. The principle exploits the volume increase that occurs during the melting of a phase change material (PCM) such as paraffin and, thus, converts heat directly into mechanical energy. In suitable industrial environments, this might replace electric compressor stations and save considerable amounts of electricity. This paper explains the working principle, the experimental setup and gives lab test results on a functional prototype that has been tested under application-oriented conditions in the thermal engineering laboratory of Fraunhofer IFAM Dresden. First results demonstrate that it is possible to generate compressed air with an absolute pressure of 7 bar in one step from ambient air. In theory, pressure levels of several hundred bar are possible.