Experimental and modeling study of the heat of biomass pyrolysis

The present study investigated the thermal effects in the pyrolysis conversion process of four energy crops, focusing on the influence of the experimental conditions on the heat of pyrolysis. The heat of pyrolysis and the residual char yield were measured by the integrated use of thermogravimetric analysis and differential scanning calorimetry, also taking advantage of a pressurized DSC cell. The explored parameters evidenced a significant influence on the heat of pyrolysis and on char yields. An increase of the operative pressure, as well as an increase in the initial weight of the sample, as well as the presence of a lid on the crucible, all resulted in higher char yields and in lower heat demands. These results confirm the presence of a competitive mechanism between the endothermic reactions of the primary decomposition process, leading to volatile formation, and the exothermic vapour-solid interactions, leading to secondary char formation. These findings can be interpreted considering that experimental conditions limiting mass transfer provide a higher residence time of the volatiles products from primary thermal degradation reactions. These primary volatiles react with the pyrolysis products, resulting in exothermic reactions with the formation of secondary char. The heterogeneous secondary reactions lead to carbon enrichment of the final residue.