Review of supercritical carbon dioxide (sCO2) technologies for high-grade waste heat to power conversion

In the European Industry, 275 TWh of thermal energy is rejected into the environment at temperatures beyond 300 °C. To recover some of this wasted energy, bottoming thermodynamic cycles using supercritical carbon dioxide (sCO2) as working fluid are a promising technology for the conversion of the waste heat into power. CO2 is a non-flammable and thermally stable compound, and due to its favourable thermo-physical properties in the supercritical state, can lead to high cycle efficiencies and a substantial reduction in size compared to alternative heat to power conversion technologies. In this work, a brief overview of the sCO2 power cycle technology is presented. The main concepts behind this technology are highlighted, including key technological challenges with the major components such as turbomachinery and heat exchangers. The discussion focuses on heat to power conversion applications and benefits of the experience gained from the design and construction of a 50 kWe sCO2 test facility at Brunel University London. A comparison between sCO2 power cycles and conventional heat to power conversion systems is also provided. In particular, the operating ranges of sCO2 and other heat to power systems are reported as a function of the waste heat source temperature and available thermal power. The resulting map provides insights for the preliminary selection of the most suitable heat to power conversion technology for a given industrial waste heat stream.