Polycyclic Aromatic Hydrocarbon and Particulate Emissions from Two-Stage Combustion of Polystyrene:  The Effect of the Primary Furnace Temperature

Abstract

A study is presented on laboratory-scale combustion of polystyrene (PS) to identify staged-combustion conditions that minimize emissions. Batch combustion of shredded PS was conducted in fixed beds placed in a bench-scale electrically heated horizontal muffle furnace. In most cases, combustion of the samples occurred by forming gaseous diffusion flames in atmospheric pressure air. The combustion effluent was mixed with additional air, and it was channeled to a second muffle furnace (afterburner) placed in series. Further reactions took place in the secondary furnace at a residence time of 0.7 s. The gas temperature of the primary furnace was varied in the range of 500-1,000 degrees C, while that of the secondary furnace was kept fixed at 1,000 degrees C. Sampling for CO, CO2, O2, soot, and unburned hydrocarbon emissions (volatile and semivolatile, by GC-MS) was performed at the exits of the two furnaces. Results showed that the temperature of the primary furnace, where PS gasifies, is of paramount importance to the formation and subsequent emissions of organic species and soot. Atthe lowesttemperatures explored, mostly styrene oligomers were identified at the outlet of the primary furnace, but they did not survive the treatment in the secondary furnace. The formation and emission of polycyclic aromatic hydrocarbons (PAH) and soot were suppressed. As the temperature in the first furnace was raised, increasing amounts of a wide range of both unsubstituted and substituted PAH containing up to at least seven condensed aromatic rings were detected. A similar trend was observed for total particulate yields. The secondary furnace treatment reduced the yields of total PAH, but it had an ambiguous effect on individual species. While most low molecular mass PAH were reduced in the secondary furnace, concentrations of some larger PAH increased under certain conditions. Thus, care in the selection of operating conditions of both the primary furnace (gasifier/ burner) and the secondary furnace (afterburner) must be exercised to minimize the emission of hazardous pollutants. The emissions of soot were also reduced in the afterburner but not drastically. This indicates that soot is indeed resistant to oxidation; thus, it would be best to avoid its formation in the first place. An oxidative pyrolysis temperature of PS in the vicinity of 600 degrees C appears to accomplish exactly that. An additional afterburner treatment at a sufficiently high temperature (1,000 degrees C) may be a suitable setting for minimization of most pollutants. To obtain deeper understanding of chemical processes, the experimental results were qualitatively compared with preliminary predictions of a detailed kinetic model that describes formation and destruction pathways of chemical species including most PAH observed in the present work. The modeling was performed forthe secondary furnace assuming plug-flow conditions therein. The experimentally determined chemical composition at the outlet of the primary furnace was part of the input parameters of the m...

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.…”

Effect of MSW Source-Classified Collection on Polycyclic Aromatic Hydrocarbons in Residues from Full-Scale Incineration in China

“…Previous studies have demonstrated that PAHs could be generated from incineration of combustible materials in MSW such as plastics including HDPE, PP, PVC (Li et al 2001;Wheatley et al 1993;Müller et al 1997), PE (polyethylene) (Li et al 1995) and PS (polystyrene) (Wang et al 2001;Durlak et al 1998;Westblad et al 2002), rubber (Arion et al 2001), and biomass material (McGrath et al 2001) containing kitchen waste, bamboo, wood, straw, etc. In the classified MSW, significant decreases of plastics, metal and glass content were observed, while an increase of kitchen waste and biomass was also noted (Table 1).…”

Particle and volatile organic emissions from the combustion of a range of building and furnishing materials using a cone calorimeter

“…Additionally studies were conducted to assess emissions from a range of burning materials under well-controlled conditions during small bench-scale experiments [26][27][28][29][30][31][32][33][34][35][36][37][38], emissions from largescale simulated room fires which were set up with a variety of furnishing materials [39][40][41][42] and emissions from vehicle fires [43]. These studies provide essential information on air pollutants released during combustion of materials.…”

“…The most extensively studied class of combustion products was inorganic gases. A small number of studies also investigated other pollutants including VOCs [27,31,32,35,39,44], PAHs [27][28][29]31,33,37,38,[45][46][47][48], dioxins and/or other persistent organic pollutants [33,40,47,[49][50][51][52] and particle size distribution [45,53]. Organic compounds were considered to be a potential hazard, but in most studies individual compounds have not been identified or quantified.…”