Thermal analysis of energy crops: Part I: The applicability of a macro-thermobalance for biomass studies

In this work young shoots of poplar (Populus euramericana), tree of heaven (Ailanthus altissima) and pellets of a type of energy grass (Agropyron) were studied in order to get information about the applicability of these biomass materials for energy production by direct combustion. During the combustion of plant materials three main processes take place: (i) formation of volatiles, (ii) burning of volatiles and (iii) burn-off of the produced char. The thermal behavior of the samples was studied with the help of a macro-thermobalance built at the Norwegian University of Science and Technology. Pyrolysis experiments have been performed in inert atmosphere to get a deeper insight into the formation of volatile products, whereas measurements in oxidative atmosphere have provided information about the burn-off of the samples, as well. In addition to monitoring the weight loss of the samples, the analysis of the evolved gases was carried out with gas chromatography (GC). and DTG curves and the profiles of the evolved gases obtained in the pyrolysis experiments are similar in the case of the poplar and the tree of heaven samples implying that the thermal behavior of these crops is alike, whereas those of the energy grass sample show significant differences. The decomposition of poplar occurs at a lower temperature in the presence of oxygen than that of energy grass. The evolution curves of the monitored products also exhibit differences. The results will be interpreted in terms of the chemical composition of the samples determined by proximate and ultimate analysis.