Effects of temperature and aspect ratio on heterogeneity of the biochar from pyrolysis of biomass pellet

In pyrolysis of biomass pellet, heterogeneity in char is almost inevitable, due to the intra-particle mass/heat transfer limitation. In this study, the effects of temperature (350-600 degrees C) and aspect ratio of a cylindrical sawdust pellet (Diameter = 6, 8, 12, or 16 mm) on the heterogeneity of char structure at radial and axial directions were investigated with a micro-Raman spectroscopy. Based on the spatial distribution of Raman band area ratios, heterogeneity index was proposed to quantify the degree of heterogeneity in char structures. Results show that the heterogeneity exists in both radial and axial directions and could be weakened by the increase of temperature or enlarging the variance between radius and height of the pellet through enhancing the average heat and mass transfer inside the pellet. The heterogeneity index of different biochar decreased with increasing surface-area-to-volume ratio. The char structures was the most heterogeneous (HI(A(D)/A(G)) = 5.399 x 10(-5), HI(A(D)/A((Gr+Vr+Vl))) = 2.359 x 10(-5)) for the pellet with a diameter of 8 mm.

Automated summary

Heterogeneity in char is almost inevitable in the pyrolysis of biomass pellet due to intra-particle mass/heat transfer limitation. This study investigated the effects of temperature and aspect ratio of cylindrical sawdust pellet on the heterogeneity of char structure. A heterogeneity index was proposed to quantify the degree of heterogeneity. Results showed that heterogeneity exists in both radial and axial directions and can be weakened by increasing temperature or enlarging the variance between radius and height of the pellet. The heterogeneity index decreased with increasing surface-area-to-volume ratio.