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).