Joel B. Carlson

On the survivability and pyrosynthesis of PAH during combustion of pulverized coal and tire crumb

Abstract Results are presented on the emissions of semivolatile polycyclic aromatic hydrocarbons (PAH) from the combustion of a pulverized bituminous coal and ground waste automobile tires. Streams of fuel particles were injected at steady-state steady-flow conditions, and burned inside an isothermal drop-tube furnace, in air, at a gas temperature and gas residence time of 1150°C and 0.75 s, respectively. Combustion occurred under either very fuel-lean conditions (bulk equivalence ratio, φ 1.6 and, especially, under pyrolytic conditions in N 2 . These PAHs were mostly attributed to pyrosynthesis since none of the deuterated PAHs, adsorbed on the fuels, survived the combustion process. Small amounts of the labeled compounds, however, survived under purely pyrolytic conditions. These results were confirmed with separate experiments, where deuterium-labeled PAH standards were adsorbed on highly porous calcium/magnesium oxide or mullite particles. Again, small amounts of some PAHs survived in high-temperature pyrolytic conditions, but none in oxidative environments. These observations suggest that pyrosynthesis is the major contributing mechanism to the PAH emissions from the combustion of these fuels. Survivability of parent PAHs may be a minor mechanism at very high equivalence ratios. Finally, both fuels were mixed with powders of calcium magnesium acetate (CMA), calcium carbonate (CaCO 3 ), and calcium oxide (CaO), all of which are known sulfur reduction agents, at a molar Ca/S ratio of 1. Combustion of the fuels mixed with CMA or CaCO 3 generated enhanced amounts of PAHs, while combustion with CaO had no effect on the PAH emissions.

Aromatic Hydrocarbon Emissions from Burning Poly(styrene), Poly(ethylene) and PVC Particles at High Temperatures

A study on the semi-volatile aromatic hydrocarbon emissions from the pyrolysis/combustion of poly(styrene) (PS), poly(ethylene) (PE) and PVC particles was conducted. Dispersions (aerosols) or batches (fixed beds) of the above types of polymer particles, 90-300 μm in diameter, were burned in bench-scale, drop-tube or muffle-type electrically-heated furnaces, respectively. In the drop-tube furnace, pyrolysisis/combustion took place at gas temperatures ranging from 900 to 1200°C and particle heating rates were in the order of 10 3 -10 4 °C/s. The total residence times of the gases in the furnaces were 1 or 2 s ; envelope flames surrounding the particles lasted for 6-130 ms, while residence times in the post-flame region were 0.3-1.8 s depending on the polymer. Semi-volatile organic emissions were captured from the gas and solid phases using XAD-4 adsorbers and glass fiber filters, respectively, and analysis was conducted with gas chromatography coupled with mass spectrometry (GC-MS). The combustion characteristics of single particles of the three plastics were studied in earlier experiments using optical pyrometry and high-speed cinematography. Gaseous diffusion, chemical kinetics and pyrolysis kinetics were inferred, therein, to govern combustion of PS, PVC and PE particles, respectively. The types of the aromatic hydrocarbon emissions were found to depend on the polymer burned, while their relative amounts were influenced by combustion parameters such as temperature, residence time, etc. Substituted poly-aromatic hydrocarbons (PAHs), oxygenated compounds and chlorinated aromatics were detected in the combustion products of PVC. PAHs with fused rings were emitted from the combustion of PE. PAHs, either substituted or with fused rings were emitted from the combustion of PS. As the gas temperatures and residence times increased, the amount of PAH emissions from all polymers decreased. The results indicated that as the size of PVC sample decreased, in the presence of oxygen, the amount of PAHs decreased. However, as the size of PE sample decreased, or when oxygen was present, the amount of PAHs did not necessarily decrease. The behavior of PS was found to be between that of PVC and PS.

The effect of the bulk equivalence ratio on the pah emissions from the combustion of PVC, poly(styrene), and poly(ethylene)

This is an investigation on the effects of the bulk equivalence ratio on the polynuclear aromatic hydrocarbon (PAH) emissions from the combustion of poly(vinyl-chloride) (PVC), poly(ethylene) (PE), and poly(styrene) (PS) particles. Steady-flow dispersions (clouds) of the above types of polymer particles, 150–212 μm in diameter, were burned in a drop-tube, electrically heated furnance at different bulk equivalence ratios ( ϕ bulk =0.1–7.3) or were pyrolyzed in N 2 . The gas temperature and residence time in the furnance were 1100°C and 1 s, respectively. (a) The total (specific) amounts of condensed and gaseous-phase PAH emissions increased with the equivalence ratio. In the present experiments, the recorded maxima in the total amounts of PAHs were obtained under pyrolysis in N 2 and accounted for 0.7, 4, and 4% of the input masses of PVC, PE, and PS, respectively. (b) PVC particles were found to oxidize effectively in air, since only minimal amounts of PAHs were produced at ϕ bulk ϕ bulk . or in N 2 . Combustion of PE and PS particles produced substantial amounts of PAHs at, or near, stoichiometric conditions. PE particles were prone to flash pyrolysis and readily formed group flames (“puffs”), even at mildly fuel-rich or near-stoichiometric conditions. (c) PAH emissions from pyrolysis of PE and PS were sensitive to the particle mass loading (mass of polymer per mass of N 2 ) in the furnance. This was not the case for PVC. (d) For all polymers, the percentage of naphthalene in the total amount of PAHs was influenced by the combustion conditions and experienced a minimum close to stoichiometry. (e) Finally, the experimentally measured molar fractions of pairs of selected PAH isomers were compared with those obtained from chemical equilibrium calculations. For all polymers, the pairs fluoranthene (F)—acephenanthrylene (AP) and cyclopenta[cd]pyrene (CP[ed]P)-benzo[ghi]fluoranthene (B[ghi]F) were at equilibrium, while the pairs fluoranthene (F)—pyrene (P) and benzo[k]fluoranthene (B[k]F)—benzo[a]pyrene (B[a]P) were not at equilibrium. PS produced much higher soot emissions than PE or PVC.

Burning Characteristics and Gaseous/Solid Emissions of Blends of Pulverized Coal with WasteTire-Derived Fuel

Abstract This work examined the combustion behavior (flame characteristics and temperatures) and the emissions (SO2, NO, NO2, CO, CO2, polynuclear aromatic hydrocarbons (PAH), soot and ash) from blends of a pulverized bituminous coal and ground waste automobile tires. The following fuel feed compositions were examined: 100% coal, 75–25% and 50–50% coal and tire blends, as well as 100% tire. Coal and tire particles were in the size ranges of 63–75 and 180–212 μm, respectively. Combustion of cylindrical streams of particles look place under steady flow conditions, in an electrically-heated drop-tube furnace in air, at a gas temperature of 1150°C and a particle heating rate of ≈105°C/s, The bulk equivalence ratio, φ, in the furnace was varied in the range of 0.5 to 2, by varying the particle mass loading. Combustion observations on burning clouds of particles were conducted with simultaneous pyrometry and cinematography. Interparticle flame interactions were visually observed mostly in the near-stoichiometri...

A study on toxic organic emissions from batch combustion of styrene

Results from a laboratory-scale investigation on batch combustion of styrene are reported herein. Limited quantities of waste styrene monomer are incinerated, however this monomer is, also, the primary pyrolyzate during combustion of waste polystyrene, the second most abundant polymer produced worldwide. Thus, its combustion-generated emissions are of importance to the operation of hazardous waste incinerators and municipal waste-to-energy powerplants. This work focuses on emissions of polycyclic aromatic hydrocarbons (PAHs), particulates, as well as carbon monoxide. To investigate methods for minimizing such emissions, batch combustion of the monomer was conducted in a two-stage muffle furnace. An additional air mixing chamber was installed between the two stages. Small quantities of the liquid monomer were inserted in the primary furnace which served as a gasifier/burner. The furnace temperature was in the range of 300-1000 degrees C and diffusion flames were formed under most conditions. Upon mixing with additional air, combustion of unburned gaseous fuel and primary reaction products continued in the secondary furnace (afterburner), which was kept at a constant temperature of either 1000 or 800 degrees C. Using this technique, conditions that minimize emissions were explored and theoretical investigations on the fate of pollutants in the secondary furnace were undertaken. Results revealed that combustion of styrene, which is a highly volatile fuel, occurred with the formation of flames that were often non-anchored, unsteady and unstable. Emissions of organic pollutants, soot and CO were more intense than in the case of the polystyrene combustion, studied previously under identical conditions, due to the additional depolymerization/pyrolysis steps therein. The emissions from the secondary furnace exceeded those of the primary furnace, consistent with the fact that a very significant fraction of the fuel conversion occurred in the secondary chamber. Clear trends in the emissions of PAHs and soot, products of incomplete combustion, with the temperature of the primary furnace (gasifier) were observed. Emissions were drastically reduced with lowering the gasifier temperature. While final cumulative emissions of PAHs and soot accounted for more than one third of the mass of the fuel at high temperatures, their concentrations at the exit of the afterburner were negligible when the primary furnace was operated at 300 degrees C under pyrolytic conditions. In the latter case air was added to the afterburner. Numerical modeling based on a complex reaction network was used for the description of the primary furnace as well as of the afterburner. Kinetic analysis showed acetylene and benzene to be key species in the growth of PAHs. Formation of PAHs in the afterburner, found experimentally, was reproduced by the model using a plug-flow assumption.

PAH and Soot Emissions from Combustion of Coal and Waste Tire-derived-fuel in Fixed Beds

This is a laboratory investigation on the emissions from batch combustion of waste tire-derived-fuel (TDF) and coal in fixed beds. The goal was to compare the magnitude of the emissions of this mode of combustion to that of continuous combustion of streams of particles of the same fuels in pulverized form, conducted previously (Levendis et al., 1996; Levendis et al., 1998). In the experiments herein waste tire chunks (in the range of 3-9 mm), tire crumb (180 212 μm) and bituminous coal (63-75 μm) were burned in a horizontal muffle furnace, at a gas temperature of 1000°C. The fuel mass loading in the furnace was varied; the residence time of the post-combustion gases was 1 s. At the exit of the furnace CO, CO 2 , NO,, polynuclear aromatic hydrocarbon (PAH) and particulate emissions were measured. Results showed that the PAH emissions from batch combustion of tire chunks were higher than those from tire crumb, which in turn were an order of magnitude higher than those from coal, under similar combustion conditions. Increasing the mass loading for both tire crumb and pulverized coal, increased the specific emissions of PAHs. Increasing the segmentation of the tire, at a fixed mass loading also increased the specific PAH emissions. Emissions of particulates closely followed the trend of PAH emissions. Batch combustion of tire chunks resulted in higher particulate yields than tire crumb, with pulverized coal a distant third. Specific CO emissions from batch combustion of TDF were an order of magnitude higher than those from coal combustion. For both fuels, CO emissions were detected during the release and combustion of the volatiles only. On the other hand, specific CO 2 , and, especially, NO x emissions from batch combustion oftire crumb were lower than those from coal. The comparison of the emissions of batch combustion of pulverized fuels in fixed beds with those of continuous combustion of streams of particles was conducted under laminar flow conditions, similar gas temperatures and similar post combustion residence times. Results showed that (i) the PAH and CO emissions of tire crumb were much lower in the latter mode of combustion, even at bulk equivalence ratios as high as 1.4; (ii) to the contrary, for coal the mode of combustion had little influence on the PAH and CO emissions.

EMISSIONS OF BATCH COMBUSTION OF WASTE TIRE CHIPS: THE PYROLYSIS EFFECT

ABSTRACT Staged pyrolysis and combustion of waste tire chips was investigated as a technique to minimize emissions of pollutants. Fixed quantities of chips were introduced to a furnace under pyrolytic conditions (in nitrogen) and devolatilized at furnace temperatures in the range 500–1000°C. The pyrolyzate gases were then mixed with additional streams of either nitrogen or oxygen in a venturi mixer, placed in-side the furnace. In the oxygen case, a nominally premixed flame occurred at the exit of the venturi, still inside the furnace. The effluent of either case was channeled to a secondary furnace for further treatment at 1000°C for a duration of 0.6 s. Sampling for combustion emissions, including products of incomplete combustion (PIC), took place at the exits of both furnaces. Sampled species included CO2, CO, polynuclear aromatic hydrocarbons (PAHs), particulates, as well as nitrogen and sulfur oxides. Results showed that under inert conditions in both furnaces (pyrolysis–pyrolysis case) the emissions of PAHs and particulates from the primary furnace were high and drastically increased by the secondary furnace treatment. To the contrary, in the pyrolysis-oxidation case, when the pyrolyzates ignited and formed a flame at the exit of the venturi, the particulate and PAH emissions were low at the exit of the primary furnace. PIC were further reduced in the secondary furnace as oxidative conditions prevailed therein. As these experiments measured the PAH and soot amounts in the tire pyrolyzates before and after the flame, they illustrated the effectiveness of a nominally premixed flame for oxidizing such species. They also illustrated that a sequential pyrolysis–oxidation approach has the potential for low emissions in waste tire-to-energy plants.

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

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 T gas =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 T gas =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, CO 2 , O 2 ), 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 CO 2 was generated in the afterburner. Augmenting the oxygen partial pressure in the venturi drastically decreased the PAH and particulate emissions, while it increased CO 2 yields: the CO yields first increased and then decreased. Increasing the temperature in the afterburner reduced the PAH yields, increased the CO 2 , 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 ≈1×10 4 to 1×10 6 cm 3 mol −1 s −1 , at T gas =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 ≈1×10 8 to 3×10 10 cm 3 mol −1 s −1 .

Structural Considerations of Meso-Substituted Zinc Tetrabenzporphyrins by Liquid Secondary Ionization Mass Spectroscopy

Metallotetrabenzporphyrins are being extensively investigated because of their large and rapid non-linear optical response. This non-linear optical response, which has potential applications in the fields of optical communications and optical data processing, varies relative to the structural characteristics of the meso-substituted metallotetrabenzporphyrin. A group of meso-substituted zinc tetrabenzporphyrins (ZnTBP) were evaluated by liquid secondary ion mass spectrometry (LSIMS). The ionization of these highly symmetrical, charged/neutral complexes produces a stable odd-electron molecular ion (M + ) and fragments representing the loss of up to three ruesa-subsfituents. The number of fragments and their ratio relative to that of the molecular ion is related to the electron-withdrawing or electron-donating characteristics of the meso-substituent. The observed isotope ratios of the molecular ion as well as the fragments are consistent with calculated isotope ratios. No LSIMS-induced reduction of the zinc ion was observed with the tetrabenzporphyrins.

EXPERIMENTAL AND NUMERICAL STUDY OF EMISSIONS FROM FUEL-RICH COMBUSTION OF PULVERIZED POLYSTYRENE

This is an investigation on the formation of products of incomplete combustion (PIC) of waste poly(styrene) (PS). Pulverized PS was steadily injected into an externally-heated drop-tube laboratory furnace and burned therein in fuel-rich conditions, corresponding to a bulk equivalence ratio of approximately 2.5. Iso-kinetic and iso-axial sampling with a probe was performed at five different heights along the centerline of the furnace. The goal has been to investigate the evolution of fixed product gases, unburned light volatile organic compounds (VOC) and semi-volatile organic compounds (SVOC), with emphasis to polycyclic aromatic hydrocarbons (PAH), along the reaction zone of the furnace. The magnitude of species therein and their respective trends were assessed. The centerline gas temperature was measured by suction thermometry. Moreover, the flow field and gas temperature distribution in the furnace were computed with a 3-dimensional model using the CFD code Fluent. Results showed that of the measured light VOC, acetylene exhibited the highest yields in the combustion effluent, followed by methane, ethylene and benzene. These yields were comparable to those of the most prevalent PAH species. PAH profiles varied somewhat in the sampling zone, with yields spanning the range between 13.8 mg (naphthalene) and 0.058 mg (perylene) per each gram of polystyrene burned. The results for fixed exhaust gases showed an increase in CO values with distance traveled, from 85 to 175 mg whereas CO2 stayed close to 1000 mg, per gram of PS burned. Oxygen remained somewhat steady near 85 mg/g PS burned. Copious amounts of soot were generated and collected through the probe, 0.25–0.42 g for each gram of PS burned. Computations were conducted using a detailed chemical kinetic model, allowing for the prediction of formation and depletion of major PAH and soot particles of different sizes. In this computation styrene was input as the fuel. In comparing experimental hydrocarbon species concentrations to theoretical predictions, a large number of species were found to be within a factor of 7 or less.