Combustion dynamics of polymer wastes in a bubbling fluidized bed

Abstract

This paper compares the combustion of selected artificial polymers and biomasses in a fluidized bed reactor. Two types of the artificial polymers were tested. The first one was used in packaging: polyethylene, polypropylene, polyethylene terephthalate, and polystyrene. The second one included construction polymers: polyamide, polycarbonate, copolymer acrylonitrile-butadiene-styrene and polyvinyl chloride. For comparison the combustion of the biomasses in the form of processed briquettes and pellets as well as beech and pine wood samples was also presented. The tests were carried out in a bubble fluidized bed built of quartz sand (granulation 0.385–0.43 mm). In the first part of the research, the samples of polymers and biomasses were burned in the presence of gaseous fuel at a bed temperature of approximately 850°C. In the second part, after heating the bed to a temperature of approximately 900°C, the supply of gaseous fuel was closed. The samples were dosed when the bed was fluidized only with air. It has been found that the combustion times for packaging and construction materials (samples: 0.1–1.8 g) were similar (T = 10.8 s), except for the polyvinyl chloride and polyamide samples whose combustion time was twice as long. The time of combustion of the biomass particles depended strongly on the sample mass rather than its type, which was of less importance. The presence of radicals resulting from liquefied petroleum gas combustion influenced the process of carbon chain fragmentation, thus shortening the time of combustion of polymers in comparison to the tests carried out without a gaseous supporting fuel. The combustion of polymers and biomasses was accompanied by the release of pyrolytic gases which, after mixing with oxidiser, ignited in regular time intervals, with frequencies 2 and 1.1 Hz. The general scheme of sequence of events making up the dynamics of the process was presented.