Deposits and emissions during the co-combustion of biodiesel residue with coal and biomass in a CFB pilot

The emissions, bed material behaviour and the formation of deposits in the co-combustion of granular rapeseed expeller - a residue from biodiesel production - both with bituminous coal and wood chips was studied at VTT’s 50kW CFB pilot reactor. The NO and SO2 emissions increased while the ratio of granular rapeseed expeller was increased in the fuel mixture. The deposition rate with fuel mixtures containing coal was lower than with wood chips-expeller mixtures. Potassium and phosphorous content in deposit increased consistently with the ratio of expeller in the biomass co-firing cases. A large ratio of expeller in the mixture with wood created slag on the riser over the secondary air feed. The expeller was found to have a clear agglomeration effect over the bed material when fired alone or co-fired with wood. On the contrary, co-combustion with coal resulted in no problems to the pilot furnace or its operation.