Thomai Panagiotou

Measurements of particle flame temperatures using three-color optical pyrometry

Abstract A three-color near-infrared optical pyrometer, with wavelengths centered at 998, 810, and 640 nm, was used to monitor the combustion of polymer particles. Individual spherical poly(styrene) particles, 47–355 μm in diameter, burned in air at 1050–1400 K gas temperatures, surrounded by sooting, diffusion envelope flames. The pyrometric results were interpreted in view of two models for soot radiation: (a) A conventional model, which assumes that the flame is optically thin and isothermal and thus, the spectral emissivity is inversely proportional to the wavelength. With this method the calculated flame temperatures are averages, biased to areas with high temperature and/or soot concentration. (b) An alternative model, in which the envelope flames are assumed to be again optically thin but nonisothermal in the radial direction. The theoretical development of the latter model is included herein. For nonisothermal flames the spectral emissivity was shown to be nearly independent of the wavelength. This model in conjunction with three-color pyrometry may provide a way of estimating the highest temperature of soot in the flame, as well as the temperature gradient across the flame. Temperatures calculated this way were higher by 200–230 K than those calculated using the conventional model. Experimental results suggest that the agreement among the three individual temperatures obtained from three-color pyrometry depends on which of the above models for soot radiation is used. Based on the agreement between temperatures, the degree of isothermality of the flame may be determined and thus, indications about the controlling processes during combustion (oxygen diffusion or volatile combustion) may be obtained. However, additional work is needed, involving simpler, one-dimensional flame configurations to confirm this model.

A study on the combustion characteristics of PVC, poly(styrene), poly(ethylene), and poly(propylene) particles under high heating rates

Abstract The combustion characteristics of four commonly encountered plastics: poly(styrene), PVC, poly(ethylene) and poly(propylene) were studied under conditions pertinent to incinerators, that is, high heating rates (in the order of 10,000 K/s) and elevated gas temperatures (1200–1500 K). Batches of spherical and monodisperse particles of these plastics were generated in the size range of 53–300 μm. Combustion of single particles, of known size and mass, was conducted in a laminar-flow drop-tube furnace, at controlled atmospheres. The radiation emitted from burning particles was monitored, along their flight path, by simultaneous three-color optical pyrometry and high-speed cinematography. With these techniques the total particle/flame combustion duration, as well as the flame temperature and diameter were measured. Results indicate that polymer particles (plastics) burned expediently with burntimes similar to those of light oil drops such as kerosene, hexadecane, etc. Both PVC and poly(styrene) burned with very luminous yellow flames, which were attributed to high soot loadings. The flame combustion of PVC was the brightest and fastest with steadily decreasing temperature and flame diameter, while that of poly(styrene) occurred mostly at constant flame diameter and mildly decreasing temperature. Combustion of both poly(ethylene) and poly(propylene) was dimmer and somewhat lengthier. Furthermore, in this temperature region, it is argued herein that the combustion of poly(styrene), poly(ethylene), and poly(propylene) occurred concurrently with, and was partially controlled by, pyrolysis reactions. PVC seemed to undergo significant pyrolysis prior to ignition; thereafter, combustion occurred in a premixed-like flame mode and, finally, dimly glowing combustion of the remaining char was observed. An energy balance during the flame combustion period enabled the calculation of the instantaneous burning rate and the average soot loading of the flame. PVC exhibited the highest soot volume fraction in its flame (3 × 10 −5 ), followed by poly(styrene) (3 × 10 −6 ), poly(propylene) (2.5 × 10 −6 ), and poly(ethylene) (1 × 10 −6 ). Moreover, it was observed that the rate of burning was the highest for PVC particles and the lowest for poly(ethylene).

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.

Observations on the Combustion of Pulverized PVC and Poly(ethylene)

Abstract The combustion characteristics of PVC (a chlorinated polymer) and poly (ethylene) (PE) (the non-chlorinated counterpart of PVC) were studied at conditions pertinent to municipal waste incinerators i.e., ambient temperatures in the range of 1050–1400 K and heating rates in the order of 10,000 K/s, in air. Spherical or quasi-spherical particles in the range of 90–250 μm in diameter were used. A three-color near infrared-pyrometer and a high speed cinematographic camera were used to simultaneously monitor the complete combustion of single particles, during their free flight in an electrically-heated drop-tube furnace. In contrast to PVC particles, which burned with large, yellow and very bright envelope flames, PE particles experienced longer ignition delays and burned with faint and bluish flames. Despite their shorter ignition delays, PVC particles experienced higher mass loss prior to ignition (at least 55%) as attested by their lower terminal velocities. Upon extinction of the volatile flames a ...

Observations on the Combustion of Polymers (Plastics): From Single Particles to Groups of Particles

Abstract This investigation aimed at examining the combustion behavior of polymer particles in groups and at comparing it to that of single particles. Combustion observations were subsequently related to measurements on emissions of organic pollutants, such as PAHs and soot, which were previously measured in this laboratory under similar conditions. The following plastics (polymers), commonly found in municipal waste streams, were burned in powder form: poly(styrene) (PS), poly(ethylene) (PE), polyvinyl chloride) PVC, and poly(methyl methacry-late) (PMMA). Particles, 125-212um, were introduced to a drop-tube furnace, at steady-flow conditions, and burned in cylindrical streams (clouds), in 1250 K air. The particle mass loading in the furnace was varied to achieve either dilute clouds, where isolated (single) particle combustion occurred, or dense clouds where interactive particle combustion look place. Information on the combustion characteristics and flame temperatures of the particles was obtained by ci...