CFD modeling of sawdust gasification in a lab-scale entrained flow reactor based on char intrinsic kinetics. Part 1: Model development

Abstract

The heterogeneous reactions between char and gases are crucial for the whole biomass gasification process due to their slow reaction rates. In this study, the intrinsic kinetics of birch wood chars react with CO2 and O2were investigated through thermogravimetric analysis (TGA) experiments. For char-CO2 reaction, the pre-exponential factor, activation energy and reaction order were 2.130 × 102 1/s Pam, 160.01 kJ/mol, and 0.525, respectively. For char-O2 reaction, the intrinsic kinetic parameters were 0.570 1/s Pam (pre-exponential factor), 134.15 kJ/mol (activation energy), and 1.796 (reaction order). Biomass gasification model was then built based on the Euler-Lagrange approach, and the intrinsic kinetic parameters were adopted in the char-gas reaction submodel to calculate the heterogeneous reaction rates with consideration of mass diffusion limitation and chemical reaction. Sawdust-air gasification in an entrained flow reactor under different equivalence ratios (ERs) and temperatures were simulated. The relative errors for produced gas compositions were mainly less than 20%, and the relative errors for gasification performances were 9.65–23.33% (gas heating value), 1.17–5.95% (gas production), and 9.76–16.57% (carbon conversion efficiency), respectively. The model based on intrinsic kinetics can therefore be employed to predict the biomass gasification performances.