COMBUSTION BEHAVIOR OF POLY(STYRENE) PARTICLES OF VARIOUS DEGREES OF CROSS-LINKING AND STYRENE MONOMER DROPLETS

This is a study on the combustion characteristics of poly (styrene) (P S) particles either plain, or with various degrees of crosslinking in the range of 5-25%. Effects of crosslinking were examined by producing and burning individual particles in the size range of 47-63 mu m, whi le effects of particle size were examined by burning particles of the same degree of crosslinking (8%) in the size range of 47-350 mu m. Mea surements during combustion of styrene monomer droplets were also cond ucted. Combustion took place in a laminar, drop tube furnace at thermo chemical conditions pertinent to municipal waste incinerators, i.e., i n air at high heating rates and gas temperatures ranging from 1050 to 1400 K. Combustion of single particles/drops was monitored by three-co lor pyrometry and high-speed cinematography, to obtain temporal inform ation on the radiant intensity, size, temperature and soot content of the flame, as well as the total burnout time of the particles. Plain ( uncrosslinked) PS particles, in the size range of 47-63 mu m, formed c onstant diameter envelope dames, somewhat larger than the maximum fame diameter of similar size crosslinked particles. As the degree of cros slinking increased, the total burnout time also increased and the inst antaneous flame diameter decreased throughout the combustion period of these particles. Heterogeneous (char) combustion was observed in cros slinked particles only, upon extinction of the volatile flames. At hig h degrees of crosslinking, indications of a second wave of pyrolysis, pronounced in the plain PS, ceased to be present. Comparisons between low heating rate TGA experiments and high heating rate combustion expe riments for plain PS indicated that the pyrolysis (decomposition) mech anisms depend on the heating rate. The maximum flame diameters were 10 to 25 times larger than the initial particle diameters and the flame/ char temperatures ranged from 1800 to 2200 K. Average burning rates we re estimated to be in the range of 0.01 to 0.14 mg/s. For particles in the range of 150-340 mu m the average mass burning rate as well as th e maximum flame diameter were found to be proportional to the initial particle diameter, which suggests that the combustion was diffusion co ntrolled. Smaller particles (47-63 mu m) were found to burn faster tha n what the above trend would predict, probably due to enhanced diffusi on of oxygen to the flame. The monomer droplets burned with elongated and, overall, larger and hotter flames than those of similar size poly mer particles. The furnace wall temperature was found to affect the bu rnout time and the ignition delay of the particles, but not the flame temperature, which was, instead, influenced by the particle size. Inst antaneous soot volume fractions in the flame were found to change thro ughout combustion, averaging in the range of 4 x 10(-6) to 4 x 10(-5).