Modeling of Biomass Gasification in a Downdraft Gasifier with Integrated Tar Adsorption

Thermal gasification of biomass is known for its capabilities in flexible and decentral power station applications for cogeneration. However, the product gas contains tar compounds adversely for a stable operation. Integrated tar adsorption in a subsequent cooled section is therefore an option to reduce the tar pollution. The char coal, used here as adsorption agent, is formed by biomass pyrolysis in the gasifier. A kinetic model is proposed, considering the kinetics of all main reactions as well as heat and mass transport phenomena. Results are presented for axial temperature profiles, gas compositions, and the gas purity at different air-to-fuel ratios. The resulting output mass flows could indicate a requirement on the adsorption capacity of at least 0.3 g g(-1) for the activated char coal.