The role of limestone during fluidized bed oxy-combustion of coal and biomass

•Indirect sulfation of limestone yields high desulphurization efficiency but increases NO emissions.•Bed agglomeration is not found, even for the highest temperature (925°C).•Limestone fragmentation largely influences the desulphurization efficiency.•Sulfation ratios of the alkali chlorides are consistent with HCl and SO2 concentrations in the gas‐phase.•In comparison to air‐firing, oxy‐firing reduces the corrosion risk and does not affect deposition.