Experimental Investigation of Circulating Fluidized Bed Combustion with Solid Recovered Fuel and Integrated CO₂ Capture at Megawatt Scale

The integration of refuse derived fuels such as processed waste fractions in the form of solid recovered fuel (SRF) into combustion processes offers considerable potential for decarbonizing existing fossil-based energy systems attributable to their abundancy and high biogenic content. Circulating fluidized bed (CFB) plants are, due to their high fuel flexibility, particularly suitable for substituting fossil fuels with SRF. Although the co-combustion of SRF and coal is already established in specially designed industrial CFB plants, there is still a lack of detailed scientific knowledge about the thermodynamic and hydrodynamic effects of up to 100% fuel substitution in fluidized bed plants designed for the use of fossil fuels (for example coal). In addition, changes in the energy market, with a rising share of fluctuating renewable energy production, are enhancing the demand for dynamic operation of existing plant systems. The simultaneous integration of CO₂ capture technologies is an additional important aspect of the future energy market. The aforementioned aspects were investigated in two experimental campaigns in a 1 MW_{th} CFB system to evaluate the potential of existing CFB systems as retrofit options. The gradual substitution of coal with 100% SRF and its influence on the hydrodynamic and thermodynamic conditions in the CFB were analyzed as first step, showing a shift of combustion to higher reactor areas as the share of volatile components in the fuel mixture increases. The positive influence of implementing the active bed material ilmenite on both, the homogenization of combustion within the CFB and the reduction of CO (up to 69%) and CH₄ (up to 95%) was confirmed in the second step. This measure provides the possibility to counteract the combustion shift identified in the first investigation step. The third step involved the investigation of oxyfuel-combustion for assessing CO₂ capture technology in CFBs. By combining an active bed material (ilmenite) with oxyfuel combustion on the 1 MW_{th} scale for the first time, while simultaneously utilizing 100% SRF as feedstock, it was not only possible to successfully demonstrate the implementation of a CO₂ capture technology in existing CFB systems, but also to confirm the positive influence of ilmenite on the combustion process as well as the positive influence of oxyfuel combustion on hydrodynamic and thermodynamic conditions in the CFB. The four-stage research process was completed by integrating a new concept of partial flue gas recirculation, enabling repetitive load changes without hydrodynamic or thermodynamic disturbances of the CFB system. Thus, this work demonstrates the possibility of integrating existing CFB plants into the energy market of the future.