Flame combustion of single wet-torrefied wood particle: Effects of pretreatment temperature and residence time

Abstract

In this work, combustion behaviors of single wet-torrefied wood particle in a high temperature flame reactor (1226 °C, 4.2 vol% O2) simulating suspension biomass fired combustion were studied. 4 mm schima wood spheres were pretreated at various wet torrefaction (WT) conditions (at 175, 200, 225, 250 °C, for 5, 30, 60 min). For the WT pretreated particle has less mass than the raw feedstock, linear regressions were performed to fit ignition, devolatilization and char burnout time with R2 higher than 0.961, 0.995 and 0.988 respectively. The slopes of the fitting lines, indicating the conversion rates, were then used to assess the combustion time on the basis of per sample mass. All three combustion stages, i.e., ignition, devolatilization and char combustion, are prolonged after WT, which is related to the severity of the torrefaction conditions and the diminished AAEMs content. The largest variation lies in the char combustion behavior: the wet-torrefied wood particle produces significantly less char (accumulated char yield reduced from 8.2% to as low as 2.8% after WT), but the char combustion rate decreases up to a factor of 2.4–4.6. The reduced char reactivity is also confirmed by the TGA analysis.