CFD analysis and characterization of biochar produced via fixed-bed gasification of fallen leaf pellets.

Biochar (BC) is a solid byproduct of gasification and could be valorized looking for contributing to the feasibility of gasification projects. In this study, the effect of airflow during fixed-bed gasification of pelletized fallen leaves to BC was evaluated at 0.075 and 0.150 kg/s/m2. The influence of glycerol in the leaf feedstock was also studied, and the gasification products were characterized. BC formation under gasification conditions was simulated using a two-dimensional (2D) unsteady computational fluid dynamics (CFD) model. When airflow was increased, convective heat transfer from the gas to the solid phase increased by 250%, and absorption of radiative heat transfer in the solid phase increased by 59%. This was ascribed to the increase in the process temperature, which also promoted the release of volatile matter. The H:C and O:C ratios in the feedstocks were reduced by 80% and 92%, respectively. The surface areas and pore volumes of the samples increased by up to 50%. The BC with the largest surface area (68.63 m2/g) also had the highest total organic carbon content (21.3%) and the highest water retention capacity (408.13%). The pH of the BCs obtained in the study ranged from 8.7 to 10, making them suitable for acid soils. • Gasification's cold gas efficiency of fallen leaves pellets (FLP) is up to 60%. • Convective and radiative heat transfer affect physicochemical properties of biochar. • If glycerol increases, biochar (BC) density decreases and BC temperature increases. • FLP's BC as a byproduct of fixed-bed gasification is suitable for acid soils. • FLP's BC is not suitable as a solid fuel due to its high ash content (∼58 wt%). [ABSTRACT FROM AUTHOR]