Influence of pellet size on product yields and syngas composition during solar-driven high temperature fast pyrolysis of biomass

The growing interest in syngas production from biomass has extended research towards solar-driven pyrolysis taking place at high temperature and heating rate, due to its high efficiency and environmental advantages. The aim of this work is to experimentally study and compare the effect of pellet size (5, 10 and 15 mm height) on product yields (liquid, char and gas), gas composition (H-2, CO, CO2, CH4) and tar secondary reactions during fast solar pyrolysis of sawdust pellets (800, 1200 and 1600 degrees C and heating rates of 10 and 50 degrees C/s). Additionally, the influence of pellet height on syngas quality is analyzed by parameters such as H-2/CO, CH4/H-2 ratios, mechanical gas efficiency and carbon conversion efficiency, focused on methanol production. An analysis based on characteristic times and dimensionless numbers is also performed to estimate the rate-controlling phenomena. Experimental results showed that, for temperatures below 1200 degrees C, there were no significant differences in the gas yield for the three pellet heights. However, the gas product distribution was influenced by the pellet size even at 800 degrees C. A further increase in temperature emphasized the influence of the pellet height on both gas yield and gas composition. Therefore, it can be argued that, in order to improve the gas yield and the quality of the syngas, the fast pyrogasification of large particles is advisable.