Benefits of biomass and coal co-combustion in fluidised bed boilers

Composition of deposits, formation of gaseous emissions and distribution of toxic elements in fly ash were studied during the co-combustion of biomass with coal and lignite in electrically stabilised 20 kW bubbling fluidised bed (BFB) and 100 kW circulating fluidised bed (CFB) reactors. Several benefits were detected favouring the extensive use of biomass in energy production together with coal. Combustion of bark and logging residue alone produced Cl-containing deposits, which tend to be corrosive. Sulphur and aluminium silicates inhibited Cl-deposition. Lignite contained less Al and Si and more sulphur and calcium than coal. Even a small addition of coal to the feedstock hindered Cl-deposition. Wood-derived biomass strengthened SO2 capture from the flue gases of coal combustion. The benefit was stronger in CFB than in BFB combustion. Addition of coal improved the quality of fly ash by decreasing the sum concentration of the nine toxic elements included in the new EU co-incineration directive.