PAH Emissions from the Fluidized-Bed Incineration of an Industrial Sludge

Abstract

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 ( φ = 0.83 and 1.25) and incinerating temperature (500, 600, 700, and 800 °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 °C. In general, the PAH levels detected were lower for the runsat 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 (PAHvapor/PAHsolid) 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 °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.