Feasibility study on the use of supercritical CO2 for waste heat recovery

Internal combustion engines and many industrial applications produce a large amount of process heat, which is often emitted into the immediate surroundings. Thermal engines generally allow to recover waste heat and generate electrical energy, but conventional processes, for example based on steam, are not feasible or efficient for most heat sources. For mobile and stationary applications, the heat quantity lost is below 500 kW and the process temperature is in the range of 250 – 500°C. In these ranges, Organic Rankine Cycles (ORCs) are suitable. Within this project, we investigated an ORC based on supercritical CO2 to verify economic feasibility.

Supercritical CO2 has several advantages over alternative organic substances and refrigerants. Compared with steam processes, supercritical CO2 processes can achieve higher thermal efficiency. Due to a high density, a compact design can be realized, from which mobile applications in particular benefit. In addition, CO2 has a Global Warming Potential (GWP) of 1 and an Ozone Depletion Potential (ODP) of 0, making it climate-neutral and environmentally friendly.

The study we conducted is designed to clarify which steps are necessary to realize the high process pressures and which components qualify for the core task of the process. The thermodynamic process is analyzed, optimized and adapted to restrictions caused by component availability. A cost report can then be produced, which enables assessment of the technology.