Two series of experiments were carried out in the lab-scale fluidized bed combustor of the NTUA’s Steam Boilers and Thermal Plants Laboratory (NTUA-LSB), using the fossil fuels of Greek pre-dried lignite or Göttelborn hard coal with either biomass materials or various waste wood species. The aim of the co-combustion trials was to determine the applicability limits of the coal partial substitution by biomass or waste wood. Therefore, the effects on combustion behaviour, flue gases emissions, residual matter and the ash tendency for agglomerates formation were thoroughly examined. Furthermore, a qualitative assessment for the ash deposition propensity, including the measurement of the characteristic ash-fusibility temperatures of various fuel blends was accomplished. The obtained results, both experimentally and theoretically, showed that biomass or waste wood addition in the fuel blend, up to a certain percentage, is technically feasible and could be extended in large-scale firing installations, provided that difficulties arising mainly from the ash melting in high temperatures can be industrially confronted.

Keywords: co-combustion, fossil fuels, biomass, waste wood, fluidised bed, emissions, ash agglomerates.