Comparative study on destruction of polycyclic aromatic hydrocarbons from combustion of waste polystyrene

Abstract

This work examines the emissions of polycyclic aromatic hydrocarbon (PAH) and soot from two-stagebatch combustion of polystyrene, in air, in a muffle furnace, kept at Tgas=1000°C. The gaseous combustion products of the ensuing diffusion flame were mixed with additional gas in a venturi mixing unit. Therefrom, they were channeled to a secondary furnace (afterburner), kept at Tgas=900–1100°C, where they experienced residence times of ≈1 s. The additional gas was either nitrogen, air, or oxygen resulting in baseline oxygen partial pressures of 0.14, 0.21, or 0.47 atm, respectively, in the afterburner. A hightemperature barrier filter was placed just before the exit of the primary furnace to prevent flame-generated particulates from entering the afterburner. Concentrations of major product species (CO, CO2, O2), semivolatile hydrocarbons, such as PAH, as well as particulates were simultaneously monitored at the exits of both furnaces. Results showed that the presence of the afterburner was beneficial in reducing the concentrations of CO and PAH pollutants, as well as particulates in most cases. As a result, additional CO2 was generated in the afterburner. Augmenting the oxygen partial pressure in the venturi drastically decreased the PAH and particulate emissions, while it increased CO2 yields: the CO yields first increased and then decreased. Increasing the temperature in the afterburner reduced the PAH yields, increased the CO2, had little effect on CO; and it increased the particulate emissions. Under the high-oxygen partial pressure (0.47 atm) in the afterburner, when soot was absent, global oxidation rate constants for most PAH species ranged from ≈1×104 to 1×106 cm3 mol−1 s−1, at Tgas=900–1100°C. Based on these oxidation rates, rate constants describing soot formation were calculated from the cases of 0.14 and 0.21 atm of oxygen, where soot was detected, to be in the range of ≈1×108 to 3×1010 cm3 mol−1s−1.