A MATHEMATICAL-MODEL OF FLUIDIZED-BED BIOMASS GASIFICATION

A mathematical model of biomass gasification in a fluidized bed has be en developed. It considers axial variations of concentrations and temp erature in the bubble and emulsion phases. The mass balance involves i nstantaneous oxidation and equilibrium devolatilization of the biomass , kinetics of solid-gas gasification reactions as well as of gaseous p hase reactions and interphase mass transfer and gas convection. The en ergy balance is solved locally for each vertical volume element, and g lobally on the reactor by iteration on the temperature at the bottom o f the bed. Three parameters have been adjusted based on the experiment al results: the heat transfer coefficient at the wall, the weighting o f the kinetics of the water-gas shift reaction and the fraction of bio mass carbon remaining as char after devolatilization. The model is use d to simulate a pilot scale (50 kg/h) biomass gasifier, and its predic tions compared to experimental measurements. The temperature and gaseo us concentrations are estimated with good accuracy for the experiments using a wood feedstock, except for the concentration of hydrogen whic h is overestimated.