The Occurrence of Inorganic Elements in Various Biofuels and Its Effect on the Formation of Melt Phases During Combustion

The Pennsylvania State University is performing a feasibility analysis on installing a circulating fluidized bed (CFB) boiler at Penn State’s University Park campus for cofiring multiple biofuels and other wastes with coal. Twenty feedstocks are being considered. Chemical fractionation analysis was performed on eleven of the fuels. It is the objective of this paper to present the results of characterizing selected biomass fuels via chemical fractionation. The chemical analysis of the fuels is then used to determine the net ash composition of possible fuel blends and their propensity to form liquid phases during combustion based on thermodynamic modeling. The FactSage equilibrium calculations suggest that a cofire of biofuels with an appropriate non-fouling coal should not pose any problems in a CFB system given that the coal makes up a majority of the thermal input. FactSage consistently predicted K₂Si₄O₉(l) to be present at 1171K with biofuels having low aluminum levels and significant concentration of alkali earth elements. Only 10% of K₂O present in a system was enough to result in the formation of K₂Si₄O₉(l) at equilibrium that could compromise a CFB system.