OBSERVATIONS ON THE COMBUSTION OF PULVERIZED PVC AND POLY(ETHYLENE)

The combustion characteristics of PVC (a chlorinated polymer) and poly (ethylene) (PE) (the nonchlorinated 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 orde r of 10,000 K/s, in air. Spherical or quasi-spherical particles in the range of 90-250 mu m in diameter were used. A three-color near infrar ed-pyrometer and a high speed cinematographic camera were used to simu ltaneously monitor the complete combustion of single particles, during their free flight in an electrically-heated drop-tube furnace. In con trast to PVC particles, which burned with large, yellow and very brigh t envelope flames, PE particles experienced longer ignition delays and burned with faint and bluish flames. Despite their shorter ignition d elays, PVC particles experienced higher mass loss prior to ignition (a t least 55%) as attested by their lower terminal velocities. Upon exti nction of the volatile flames a lengthy char combustion period was obs erved in the case of PVC only. Flame/char temperatures were measured t o range between 1800-2500 K. At any given ambient temperature, the bur ning times of both PVC and PE particles were found to increase almost linearly with the particle size. While higher ambient temperatures res ulted in shorter combustion times for the PE particles as expected, th e opposite was true for PVC particles. The irregular behavior of PVC w as thought to be due to the high concentration of chlorine in the Vola tiles that escaped initially. Time integrated spatially-average soot v olume fractions during burnout of PVC particles were found to be 30-60 ppm and 15-30 ppm for particles that burned at 1250 K and 1400 K, res pectively, while for PE were an order of magnitude lower. Fluctuations in the calculated instantaneous spatially-average soot volume fractio n profiles in the flame of PVC suggested temporal evolution of species of different sooting tendencies.. This was supported qualitatively by TGA experiments where three distinctive pyrolysis steps were detected during gasification of PVC, but only one for PE.