T. Lind et al., Volatilization of the heavy metals during circulating fluidized bed combustion of forest residue, ENV SCI TEC, 33(3), 1999, pp. 496-502
Citations number
20
Categorie Soggetti
Environment/Ecology,"Environmental Engineering & Energy
The environmental impact of the heavy metals contained in the combustion pr
oduct ash depends an the speciation of the heavy metals and the size distri
butions of the heavy metals in the ash. Therefore, the behavior of cadmium,
lead, copper, and zinc was studied experimentally during circulating fluid
ized bed combustion (CFBC) of Swedish forest residue. The size distribution
s and concentrations of the heavy metals in the fly ash particles and in th
e gas phase were determined by low-pressure impactors and filters upstream
of the convective back pass at 830 degrees C. Downstream of the convective
back pass at T= 150 degrees C, the size distributions were determined. The
fly ash from CFBC was found to contain two separate particle classes. Fine
particles (D-p < 0.5 mu m) consisted mainly of KCI, and coarse particles (D
-p > 0.5 mu m) contained as major elements Ca and Si. Major fraction of all
the studied heavy metals were found in the coarse fly ash particles at loc
ation 1 at 830 degrees C; 7-26% of Pb, 24-27% of Cu, 1-8% of Cd, and less t
han 1% of Zn were found in the gas phase. The gas-to-particle conversion ro
ute for Cd, Pb, and Cu was found by chemical surface reaction, probably wit
h silicates. None of the studied heavy metals were enriched in the fine par
ticles at the inlet of the electrostatic precipitator.