Cyclone fly ash from a grate-fired biomass combustion plant: dependence of the concentration of various components on the particle size

In this study cyclone fly ash from a grate-fired combustion plant using forest residues as fuel was split into particle size classes with mass median diameters of 2.0 μm, 4.3 μm, 9.1 μm, 18 μm and 43 μm by use of an air classifier. The particle classes were analysed for total carbon, Na, K, Mg, Ca, Sr, Ba, Ti, V, Cr, Mo, Mn, Fe, Si, Co, Ni, Cu, Zn, Cd, Hg, B, Al, Pb, As, Sb, Bi, Cl^-, NO₃^-, PO₄^3- and SO₄^2- and the size dependence of the concentrations c was modelled using the relation c ~ 1/d^N. For several components a considerable dependence of the concentration on the particle size was observed. Increasing concentration with decreasing particle size was found for K, Bi, Cd, Cu, Hg, Pb, Zn and for Cl^-, NO₃^- and SO₄^2-. The metals Al, As, Ba, Fe, Si, Ti and V showed the opposite behaviour. Other components, including TC, Ca, Mg, PO₄^3-, Na and Mn showed no size-dependence. Investigation of single particles by scanning electron microscope in combination with energy-dispersive X-ray spectroscopy revealed that the analysed concentrations are representative for the particle classes only, the composition of single particles in a particle class can deviate considerably.