The effect of biomass co-combustion with coal on ash quality and utilization aspects was investigated. Co-combustion tests were performed in lab, semi-industrial and industrial scale plants, using several coal-biomass blends. Two different sets of co-combustion residues were analyzed according to their production process and analysis method. Samples collected from lab and semi-industrial scale tests were analysed for major elements and heavy metals content, loss on ignition (LOI), free CaO content and their grain size distribution. Natural Radioactivity and radon exhalation rate were also measured in samples collected From tests performed at large-scale power plants.
The effect of biomass co-combustion on the radioactivity content of fly ash was dependent on the fuel mixture used as well as the ash sampling location along the flue gas pathway.

The results showed that properties of co-combustion residues are directly connected to the combustion conditions and individual blend components. Biomass utilisation as secondary fuel in co combustion processes is technically and economicaIIy feasible up to 20% wIw and the produced ash could be further utilised without any major treatment.