PAH EMISSIONS FROM THE FLUIDIZED-BED INCINERATION OF AN INDUSTRIAL SLUDGE

An industrial waste sludge was incinerated in a laboratory-scale fluid ized-bed incinerator and sixteen priority polyaromatic hydrocarbons (P AHs), including the vapor-phase PAHs adsorbed by XAD-2 and the solid-p hase ones intercepted by glass fiber filters, were monitored. The expe rimental parameters were equivalence ratio (phi = 0.83 and 1.25) and i ncinerating temperature (500, 600, 700, and 800 degrees C). The fuel-r ich condition was carried out to resemble ''fault-mode'' operation. Th e nominal gaseous residence times were in the 0.7-1.2 second range. A gas chromatograph/flame ionization detector (GC/FID) was used to ident ify the PAHs qualitatively and quantitatively. Three priority PAHs - p henanthrene (PhA), fluoranthane (FluA), and pyrene (Pyr) - were detect ed in great quantities for all incineration runs. Two other priority P AHs - fluorene (Flu) and anthracene (AnT) - were found only in the sol id phase for the fuel-rich run at 500 degrees C. In general, the PAH l evels detected were lower for the runs at higher incineration temperat ures and lower equivalence ratio. A comparison of the PAH emission pat terns in studies using incinerators of various types and scale showed a difference in PAH concentration in the flue gases of 2 to 3 orders o f magnitude. The reason for the high emission level of PAHs in this st udy might be attributed to the high contents of native PAHs in the inc inerated sludge; the short residence time, which was too short to allo w the native PAHs to be sufficiently destructed; the rapid heating rat e, as in a flash or rapid pyrolysis condition that could accelerate th e fusion of organic matters to form PAHs; and a low-to-medium incinera tion temperature that was not high enough to allow quick destruction o f the PAHs. The correlation between log (PAH(vapor)/PAH(solid)) and (1 /T) derived from the Langmuir adsorption equation was used to examine the emitted PAHs. Each PAH emitted from the fuel-lean incineration of waste sludge was satisfactorily described if the 500 degrees C-run dat a were excluded (at which temperature the organic matter was considere d to be under incomplete combustion or oxygen-deficient pyrolysis). Co ntrarily, the fuel-rich cases gave either poor or no correlation.