Occurrence of Zinc and Lead in Aerosols and Deposits in the Fluidized-Bed Combustion of Recovered Waste Wood. Part 1: Samples from Boilers

Combustion of recovered waste wood (RWW) has led to increased fouling and corrosion of furnace walls, superheaters, and economizers. These problems have been associated. mainly with chlorine, zinc, and lead in the deposits but also. with sodium and titanium. The presence of lead and zinc compounds, especially lead and zinc chlorides, has been shown to increase the corrosivity of the deposits even at relatively low metal temperatures (230-450 degrees C). The present work determined experimentally the distribution and speciation of zinc and lead, compounds in aerosol particles and deposits in the fluidized-bed combustion of RWW. Measurements were conducted in both a full-scale (20 MW(th)) plant with as-received RWW and in a pilot-scale (2 MW(th)) setup with as-received RWW and RWW doped with zinc and lead. The results show that the amount and speciation of zinc a ad lead in the deposits vary depending upon the fuel composition, flue gas temperature, and metal temperature. Both lead and Zinc chlorides are found in temperature ranges typical for the primary superheater area. A caracolite-type compound [Na(3)Pb(2)-(SO(4))(3)Cl] was identified in deposits from the economizer Area and K(2)ZnCl(4) in the sub micrometer aerosol particle fraction.