Laboratory investigation of the products of the incomplete combustion of waste plastics and techniques for their minimization

Abstract

This laboratory investigation aimed at reducing the emissions of pollutants from the batch combustion of three major waste plastics, polyethylene (PE), polystyrene (PS), and poly(vinyl chloride) (PVC). Results are reported herein on the emissions of CO, light aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and particulates. Two-stage combustion of the polymers was investigated, with the first stage (primary furnace) operated at either 600 or 900 °C and the second stage (afterburner) at 1000 °C. Before exiting the afterburner, the effluent passed through a high-temperature ceramic filter, which retained and destroyed particulate products of incomplete combustion (PICs). The effect of the polymer quantity burned was examined, as well as the effect of mixing PS with PVC to explore the influence of chlorine on emissions of PICs. The results indicated that PVC produced the lowest amounts of all PICs, whereas PS produced the highest amounts of PAHs and particulates, and PE produced the highest amounts of CO, for the same mass of polymer burned. The combined effects of the afterburner treatment and the high-temperature filtration were consistently effective at minimizing all PICs when the primary furnace was operated at 600 °C. At that temperature, the emission yields at the exit of the filtered afterburner were lower than those at the exit of the primary furnace for the combustion of PS, PE, and PVC, respectively, as follows: CO by 70, 74, and 99%; particulates by 92, 99, and 99%; and PAHs such as fluorene by 96, 93, and 96%; phenanthrene by 73, 79, and 80%; fluoranthene by 86, 93, and 98%; and benzo[a]pyrene by 99, 96, and 99%. Model calculations, performed using a detailed kinetic network, indicated continued depletion of both PAHs and soot in the afterburner if their retention times therein were extended beyond those investigated in the absence of the ceramic filter.