Integrated kinetic and reactor-scale evaluation of pinewood gasification in a downdraft reactor: mechanistic insights and performance assessment

Biomass gasification offers a sustainable pathway to convert renewable carbonaceous feedstocks into clean energy carriers. While kinetic and reactor studies are usually performed in isolation, this work provides a novel integrated assessment that directly links the thermal decomposition kinetics of pinewood to its overall performance in a downdraft reactor. Pinewood, selected for its high volatile matter content (80.88%) and low ash content (0.83%), exhibited two major thermogravimetric analysis (TGA) decomposition zones with mass losses of 52.4% and 28.6%. Model-free KAS analysis and Criado master plots revealed a mechanistic transition: the low-temperature zone is characterized by an m3 diffusion-controlled mechanism with an average activation energy of 128 kJ/mol, whereas the higher-temperature zone shifts to an m12 first-order reaction-controlled model with an average activation energy of 200 kJ/mol. Bench-scale downdraft gasification experiments conducted at equivalence ratios (ERs) of 0.25, 0.29, 0.35, and 0.37 validated the kinetic findings. The optimum ER was 0.29, yielding 2.48 Nm3/kg gas, 33% carbon conversion, 6.5 MJ/Nm3 LHV, and syngas containing 18.42% CO, 15.31% H2, 6.12% CH4, and 11.58% CO2. By establishing a predictive link between thermal decomposition mechanisms and gasifier performance, this study provides a framework for optimizing pinewood and other lignocellulosic biomass conversion systems.