CFD ANALYSIS OF STEAM AND CO₂ GASIFICATION OF BIOCHAR IN A DOWNDRAFT REACTOR

To mitigate greenhouse gas emissions, carbon capture is typically recommended to be implemented in various applications. CO₂ gasification of biomass can be an alternative to fossil fuels in minimizing CO₂ emissions. In this study, biochar was used for the CO₂ gasification process due to its low volatile content, which could reduce the tar generation. A 3D downdraft gasifier was modeled using the commercial Ansys Fluent software. A species transport model was used for chemical kinetics. The k-epsilon model and p-1 model were used to model turbulence and radiation, respectively. To feed the biochar into the gasifier reactor, a discrete phase model (DPM) was implemented. To further investigate the gasification behavior, the developed model was applied to simulate the steam gasification of biochar. The model predictions were validated against the experimental data, with an error margin ranging from 3% to 10%. In the CO₂ gasification simulations, the CO₂ concentration varied between 15 to 60%, and the temperature range considered was 700°C to 900°C. Among these conditions, a CO₂ concentration of 60% at 900°C resulted in the highest CO yield. Maximum hydrogen concentration of 59.73% in syngas was obtained at 800ºC for the steam flow rates of 5 ml/min.