FUEL QUALITY OF WOOD CHIPS - CHEMICAL ELEMENTS AND FUEL INDEXES

Critical chemical elements such as nitrogen (N), sulphur (S), chloride (Cl), potassium (K) or heavy metals might determine high temperature corrosion, emission behavior and slagging of solid biofuels during combustion. Recently developed biomass fuel indexes may help to pre-evaluate fuel behavior during combustion. In total, 92 samples of wood chips (n = 75), of unchipped material (n = 11) and of twigs and needles (n = 6) were collected and analyzed for elemental composition (As, Ca, Cd, Cl, Cr, Cu, Hg, K, Mg, N, Na, Ni, Pb, S, Si, Zn). Biomass fuel indexes were calculated from the results to pre-evaluate NOX and particle emissions, high temperature corrosion, K release and slagging behavior. Wood chips from natural wood showed low concentrations of critical chemical elements. With increasing shares of mineral soil, critical elements also increased. Biomass fuel indexes such as the sum of aerosol forming elements (K, Na, Pb, Zn) or the molar Si/(Ca+Mg) ratio for ash-melting behavior indicated that biomass fuels without contamination with mineral soil, road salt or other anthropogenic waste can be considered uncritical for combustion.