Emissions from Premixed Combustion of Polystyrene

Pyrolysis of polystryrene (PS) followed by combustion was tested in a two-stage drop-tube furnace at steady-state steady-flow conditions. PS particles were pyrolyzed at 1000 °C in nitrogen, and subsequently, the pyrolyzate gases were mixed with oxygen-containing gases and were burned homogeneously at 900, 1000, or 1100 °C. Nominally premixed combustion occurred at different equivalence ratios, depending on the feed rates of the polymer. The effluents of pyrolysis and combustion were analyzed for fixed gases (CO, CO2, O2), light hydrocarbons, PAH, and particulates. It was found that the yields of pyrolysis gas decreased with increasing polymer feed rate. CO2 emissions peaked at an equivalence ratio near unity, while the CO emissions were significantly large only at fuel-rich equivalence ratios, φ > 1. The total light hydrocarbon and the PAH yields from combustion of the PS pyrolyzates increased with increasing equivalence ratio. The generated particulates were mostly in the ranges of 0–0.4 and 0.65–1.10 µm. Overall, PAH and soot emissions from the indirect burning of PS, i.e., the homogeneous combustion of the pyrolyzates, were an order of magnitude lower than corresponding emissions from direct burning of the solid polymer, as previously monitored in this laboratory using identical sampling and analytical techniques. Therefore, pyrolysis/gasification of PS followed by combustion is shown to be a credible method for low-emission waste-to-energy conversion.