Comparison of Products of Incomplete Combustion of Waste Polystyrene and Styrene in Diffusion Flames and Ethyl Benzene in Fuel-Rich Premixed Flames

This study examined the effects of the mode of combustion of waste polystyrene (PS) on the emissions of products of incomplete combustion (PIC). Typically, combustion of PS in furnaces takes place with diffusion flames forming around devolatilizing chunks (pieces, shreds, pellets, etc.) of the solid polymer. In such flames a broad range of local fuel/air equivalence ratios exist, at any given instant of time. The inner side of a diffusion flame is fuel-rich and the outer side is fuel-lean, making it impossible to assess local conditions. Results are typically reported on the basis of a global equivalence ratio, φglobal, which is calculated based on the total amounts of fuel and air consumed in combustion. To examine the effects of local equivalence ratios, φ, on pollutant emissions, premixed flame combustion is necessary. In this investigation emissions from batch combustion of solid PS pellets in fixed beds, placed inside a horizontal furnace, are compared with emissions from steady-state steady-flow combustion of PS particle clouds (aerosols), inside a vertical furnace. Sampling was conducted at the exits of the furnaces. In addition, effluents from both diffusion and premixed flames of PS precursors are also compared. Liquid styrene is the monomer precursor of polystyrene; it is also the most abundant pyrolyzate. It was burned in batches inside the horizontal furnace. However, because of its unstable, often explosive combustion ethyl-benzene was chosen for the premixed combustion experiments. This choice was based on work conducted elsewhere, which showed that in flames the conversion of ethyl-benzene to styrene is extensive and extremely fast. Ethyl-benzene was pre-vaporized in nitrogen, mixed with oxygen and nitrogen, and burned in a flat flame burner. Fuel-rich conditions (φ = 2.5) were implemented to enhance the product yield. Product sampling was conducted in the luminous region of the premixed flame.