Polynuclear Aromatic Hydrocarbon and Particulate Emissions from Two-Stage Combustion of Polystyrene:  The Effects of the Secondary Furnace (Afterburner) Temperature and Soot Filtration

Abstract

Laboratory experiments were conducted in a two-stage horizontal muffle furnace in order to monitor emissions from batch combustion of polystyrene (PS) and identify conditions that minimize them. PS is a dominant component of municipal and hospital waste streams. Bench-scale combustion of small samples (0.5 g) of shredded styrofoam cups was conducted in air, using an electrically heated horizontal muffle furnace, kept at Tgas = 1000 degrees C. Upon devolatilization, combustion of the polymer took place in a diffusion flame over the sample. The gaseous combustion products were mixed with additional air in a venturi and were channeled to a secondary muffle furnace (afterburner) kept at Tgas = 900-1100 degrees C; residence time therein varied between 0.6 and 0.8 s. At the exits of the primary and the secondary furnace the emissions of CO, CO2, O2, NOx, particulates as well as volatile and semivolatile hydrocarbons, such as polycyclic aromatic hydrocarbons (PAH), were monitored. Online analyzers, gravimetric techniques, and gas chromatography coupled to mass spectrometry (GC-MS) were used. Experiments were also conducted with a high-temperature barrier filter, placed just before the exit of the primary furnace to prevent the particulates from entering into the secondary furnace. Results demonstrated the beneficial effect of the afterburner in reducing PAH concentrations, including those of mutagenic species such as benzo[a]pyrene. Concentrations of individual PAH exhibited a pronounced after burner temperature dependence, typically ranging from a small decrease at 900 degrees C to a larger degree of consumption at 1100 degrees C. Consumption of PAH was observed to be the dominant feature at 900 degrees C, while significant quantities of benzene and some of its derivatives, captured by means of carbosieve/Carbotrap adsorbents, were formed in the afterburner at a temperature of 1000 degrees C. In the primary furnace, about 30% of the mass of the initial polystyrene was converted into soot, while the total mass of PAH represented about 3% of the initial mass of combustible. The afterburner reduced the particulate (soot) emissions by only 20-30%, which indicates that once soot is formed its destruction is rather difficult because its oxidation kinetics are slow undertypical furnace conditions. Moreover, increasing the afterburnertemperature resulted in an increasing trend of soot emissions therefrom, which might indicate competition between soot oxidation and formation, with some additional formation occurring at the higher temperatures. Contrary to the limited effect of the afterburner, high-temperature filtration of the combustion effluent prior to the exit of the primary furnace allowed for effective soot oxidation inside of the ceramic filter. Filtration drastically reduced soot emissions, by more than 90%. Limited soot formation in the afterburner was again observed with increasing temperatures. The yields of both CO and CO2 were largely unaffected by the temperature of the afterburner but increased at the presence o...

The effect of equivalence ratio on the soot onset chemistry in one-dimensional, atmospheric-pressure, premixed ethylbenzene flames

“…Since polystyrene ((C 8 H 8 ) n ) also converts primarily to styrene (∼75%) [12], it may be considered as a surrogate for polystyrene combustion as well. Thus, this investigation also relates to past work in this laboratory on the combustion and emissions of waste polystyrene (PS), styrene, and ethylbenzene [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Combustion of polystyrene (PS), which amounts to 22 wt% of all high-volume waste plastics [29], generates larger amounts of polycyclic aromatic hydrocarbons (PAH) and soot than other plastics.…”

Toxic Environmental Releases from Medical Waste Incineration: A Review

“…The effect of the afterburner in reducing PAH concentrations from batch combustion of polystyrene was observed by Wang et al (2002). Lower molecular weight PAHs were having a higher fraction in liquid phase than that in the solid phase.…”

“…Lee et al (2002Lee et al ( , 2003 investigated emission of PAHs from two batch-type MWIs, one MG-MWI and the other FG-MWI for the disposal of general MW and special MW, respectively. Wang et al (2002) conducted Laboratory experiments in a two-stage horizontal muffle furnace to monitor emissions from batch combustion of polystyrene, a dominant component of MW and MSW streams and identified conditions to minimize them. Levendis et al (2001) explored PAH and soot emissions from burning components of surgical gloves and cotton pads in a laboratory scale horizontal muffle furnace.…”

The effect of temperature on PAHs emission from incineration of acrylic waste

“…PAHs emissions have been reported from various laboratory scale studies from the incineration of polyvinyl chloride, polyethylene, polystyrene, latex gloves and cotton pads (HawleyFedder et al, 1984;Panagiotou et al, 1996;Levendis et al, 2001;Wang et al, 2002Wang et al, , 2003Kim et al, 2004;Aracil et al, 2005). However, there seems to be no report regarding study of PAHs emissions from incineration of acrylic waste solution (AWS) in laboratory or industrial scale.…”