PAH emission from the incineration of waste oily sludge and PE plastic mixtures

Abstract

A batch-type, controlled-air incinerator was used for the treatment of oily sludge and polyethylene (PE) plastic mixtures. The concentration and composition of 21 individual PAHs (polycyclic aromatic hydrocarbons) in the raw wastes, flue gas (gas and particle phases) and ash were determined. Stack flue-gas samples were collected by a PAH stack-sampling system. Twenty one individual PAHs were analyzed primarily by a gas chromatograph and a gas chromatography/mass spectrometer. Due to incomplete combustion, PAH content in the feeding wastes have a strong influence on PAH emission in both stack flue gas and ash residue. With the oily sludge in the feeding waste mixtures, the input mass of lower molecular weight PAHs — Nap, AcPy, Acp, Flu, PA, Ant and FL — was contributed mainly by liquid diesel, while the input mass of higher molecular weight PAHs — Pyr, CYC, CHR, BbF, BkF, BeP, BaP, PER, IND, DBA, BbC, BghiP and COR — was primarily contributed by the oily sludge. For the distribution of individual PAH mean output mass, lower molecular weight PAHs — Nap, AcPy, Acp and Flu — have > 87% of their mass discharged by the stack flue gas. However, the higher molecular weight PAHs — Ant, FL, CHR, BbF, BeP, BaP, PER, IND, DBA, BbC, BghiP and COR — have significant mass fractions (>18%) discharged by the ash residue. The total-PAH output/input mass ratios were between 0.00103 and 0.00360 and averaged 0.00203. This result indicated that the depletion of PAH mass in the combustion process was very significant. The PAH content in the fuel during the combustion process is the control factor of PAH emission. The co-combustion of oily sludge with plastic is a potential method of reducing the PAH emission and of saving the consumption of auxiliary fuel.