Incineration of doped sludges in fluidized bed. Fate and partitioning of six targeted heavy metals. I. Pilot plant used and results

Incineration of sewage sludge doped with several heavy metals was studied a t small pilot plant scale in a bubbling fluidized bed of 15 cm i.d. and 5.2 m height. Some ceramic and metallic filters were tested at a relatively hig h temperature (600-700 degreesC) to check their usefulness for partitioning of heavy metals in the hue gas. The work was focused on the fate of six se lected heavy metals (Cr, Cd, Ni, Zn, Cu, Pb). In this process, there were f our exit flows or discharges for these metals: bottom ash, coarse fly ash, cake filter or fine fly ash and flue exit gas. The distribution or partitio ning of each heavy metal (HM) among these four exit hows was studied. Only cadmium and sometimes lead showed any difference between the different HMs considered. All other HMs seems to have the same fate, distribution or part itioning. Such distribution is governed or ruled by the fluid dynamics in t he incinerator, cyclone and ceramic filter. Most of the HMs do not have eno ugh residence time in this incinerator type to diffuse out of the ash parti cle and so remain in the particle. The amount of each HM in each exit how i n this process is governed by fluid dynamics and kinetics and not at all by thermodynamics. (C) 2000 Elsevier Science B.V. All rights reserved.