Key thermal events during pyrolysis and CO2-gasification of selected combustible solid wastes in a thermogravimetric analyser

Key characteristic thermal events during the pyrolysis and CO2-gasification of six representative combustible solid wastes (CSWs), namely, poplar, paper, polyethylene (PE), rubber, dacron and rice, were investigated using a thermogravimetric analyser (TGA) in order to observe and contrast the thermal behaviour of these materials during pyrolysis and gasification and as a means to reveal their thermal conversion mechanisms. The TGA experiments were carried out in N-2 and CO2 atmospheres, respectively, and from room temperature to 1193 K at various heating rates ranging from 5 to 30 K min(-1). Three generic characteristic thermal events, namely, pyrolysis of the raw CSW (stage I), gasification of the char of incomplete carbonisation (stage II), and gasification of the fixed carbon (stage III), were identified during the CO2 gasification processes. It was observed that the poplar and paper samples went through all the three key events, however, the PE and rice samples only incurred stage I, while the rubber and dacron samples only showed the stages I and III events. In addition, the pyrolysis process (stage I) of all six CSW samples during the CO2-gasification was similar to that in N-2 but, as expected, the reaction was shifted to occur at slightly higher temperatures in CO2. The activation energy of the CO2-gasification reactions in the different stages of conversion was estimated from the TGA data using the Friedman iso-conversional method. The activation energy for the pyrolysis of poplar, PE and dacron remained relatively constant while that for paper, rice and rubber increased with increasing the degree of conversion in stage I. (C) 2014 Elsevier Ltd. All rights reserved.