In order to limit the global temperature increase to 1.5 degrees, the Intergovernmental Panel on Climate Change (IPCC) expects a share of more than 20 percent bioenergy in 2050. The use of biomass for energy releases CO₂, which can then be used industrially. In technical jargon, this is called BECCU, »Bioenergy Carbon Capture and Utilisation«. However, before the CO₂ is available, it must be separated from the gases of the combustion process.

This is where Fraunhofer research comes in. Felix Lehner, a doctoral student at Fraunhofer UMSICHT, says: »We combine an innovative combustion process of biogas - the so-called oxyfuel combustion - with the BECCU approach. Our goal is to produce CO₂ with a purity of 99.5 percent.« In this process, the high-purity carbon dioxide is not blown out into the atmosphere as a waste product, but is used as a product for industrial processes, e.g. for the production of fuels, fertilisers or for direct application in the beverage industry. Since CO2 from bioenergy applications is climate-neutral by definition, the technology would provide a sustainable, alternative carbon source.  

Oxyfuel combustion + BECCU = BO₂CCU

In oxyfuel combustion, biogenic gases are burnt with pure oxygen (O₂) instead of air in this project. As a result, only CO₂ and H₂O are contained in the exhaust gas as combustion products. The water vapour (H₂O) condenses, the released heat can be used and what remains is an exhaust gas with a CO₂ concentration of over approx. 95%. The process is flexible as far as the quality of the gaseous fuels is concerned. In addition to biogas, sewage gas, pyrolysis gas or synthesis gas can be used. 

At the Fraunhofer UMSICHT site in Sulzbach-Rosenberg, a burner system with a thermal output of 50 kW is being built on a demonstration scale. The decentralised scale of such a plant can enable small and medium-sized enterprises (SMEs) in the bioenergy sector to implement CO₂-neutral plants. 

Use of oxygen from the hydrogen economy

Oxyfuel combustion processes could continue to gain in importance, as an expansion of the hydrogen economy would also produce considerable amounts of oxygen (O2) in the future. In the electrolysis process, eight times the amount of O2 is produced per unit of hydrogen. According to the Federal Ministry of Economics and Climate Protection (BMWK), electrolysis capacities are to be gradually expanded by 2050. As a result, around 1.8 million tonnes of oxygen would be produced in 2030 and up to 18 million tonnes of oxygen in 2050 as a hitherto unused by-product. The Fraunhofer technology could supplement electrolysis sites and create an economic recycling option for the O₂.

The project has a duration of 3 years and is financed by the Fraunhofer-Gesellschaft as in-house research.