Vaporization of trace elements and their emission with submicrometer aerosols in biomass combustion

The concentration of a number of trace elements (Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, and Pb) in submicrometer aerosols generated in the combustion of a biomass in an entrained flow reactor has been determined in a wide range of realistic combustion conditions (which included variations in temperature and concentration of O 2 and SO 2 in combustion gases). Fine particles were enriched in most of these elements with respect to the bulk fly ash; the fraction of each one found in fines is ascribed to vaporization and subsequent condensation. Their concentrations increased with the combustion temperature, were little affected by the SO 2 concentration (except for Fe) or the major composition of fine particles, and displayed element-dependent behaviors when the oxygen concentration was varied. Also, the sequential condensation of trace elements was experimentally studied at moderate temperatures (900-560 °C); Pb was found to condense in this temperature range, whereas Cu remained partly as vapor still at 560 °C.