With the decentralisation of electricity and heat generation, small-scale CHP solutions are also gaining in importance. So far, however, this segment lacks a system that can also efficiently utilise biogenic residues. Due to the high temperatures required for combustion, contamination of the heat exchangers has been an issue with current approaches.

It may be possible to overcome this using a micro-CHP with fluidised bed firing and a Stirling engine: while fluidised bed firing permits the use of different biogenic fuels, the Stirling engine increases the overall efficiency of the plant through higher combustion efficiency. The efficient cooling of the combustion chamber also prevents contamination of the heat exchangers.

The “BioWasteStirling” project aims to develop and commercialise such a system: long-term testing of the pilot plant developed by scientists at Friedrich–Alexander University Erlangen–Nürnberg together with project partners SWW Wunsiedel and Frauscher Thermal Motors was already successfully completed in February 2019. In the laboratory, a maximum electrical efficiency of approximately 15% and an overall combustion efficiency of over 90% were achieved. The 5kWel rated power of the engine was already reached with the first commissioning. No slagging, caking or erosion was recorded, and emissions of CO and particulate matter remained below the applicable limits.

The findings from the long-term testing have since then been used for constructive and control-technological improvements of the plant. Modifications were also made to enable weekly operation and the use of other fuels. The field testing, which started at the end of June 2019, is supposed to provide further insights.

The “BioWasteSterling” project is funded within the framework of the German Federal Ministry Economic Affairs and Energy (BMWi) “Energetic Biomass Use” funding area and will be supported until 2020.