PAH emissions from the fluidized-bed incineration of an industrial sludge

An industrial waste sludge was incinerated in a laboratory-scale fluidized-bed incinerator and sixteen priority polyaromatic hydrocarbons (PAHs), including the vapor-phase PAHs adsorbed by XAD-2 and the solid-phase ones intercepted by glass fiber filters, were monitored. The experimental parameters were equivalence ratio (phi = 0.83 and 1.25) and incinerating temperature (500, 600, 700, and 800 degrees C). The fuel-rich condition was carried out to resemble ''fault-mode'' operation. The nominal gaseous residence times were in the 0.7-1.2 second range. A gas chromatograph/flame ionization detector (GC/FID) was used to identify the PAHs qualitatively and quantitatively. Three priority PAHs - phenanthrene (PhA), fluoranthane (FluA), and pyrene (Pyr) - were detected in great quantities for all incineration runs. Two other priority PAHs - fluorene (Flu) and anthracene (AnT) - were found only in the solid phase for the fuel-rich run at 500 degrees C. In general, the PAH levels detected were lower for the runs at higher incineration temperatures and lower equivalence ratio. A comparison of the PAH emission patterns in studies using incinerators of various types and scale showed a difference in PAH concentration in the flue gases of 2 to 3 orders of magnitude. The reason for the high emission level of PAHs in this study might be attributed to the high contents of native PAHs in the incinerated sludge; the short residence time, which was too short to allow the native PAHs to be sufficiently destructed; the rapid heating rate, as in a flash or rapid pyrolysis condition that could accelerate the fusion of organic matters to form PAHs; and a low-to-medium incineration temperature that was not high enough to allow quick destruction of 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 data were excluded (at which temperature the organic matter was considered to be under incomplete combustion or oxygen-deficient pyrolysis). Contrarily, the fuel-rich cases gave either poor or no correlation.