Numerical Study on the Steam Gasification of Biomass in a 100 kW Dual Fluidized Bed Gasifier

The dual fluidized bed (DFB) shows great potential for the steam gasification of biomass to produce hydrogen. Understanding the hydrodynamics and thermochemical characteristics in a pilot-scale DFB system is crucial for optimizing the operating conditions and devising the reactor design. In this study, a three-dimensional model, based on the multiphase particle-in-cell (MP-PIC) method, is developed for a 100 kW biomass DFB system featuring a staged gasification reactor. The entire DFB system is simulated, with a focus on the gasification reaction in the gasifier reactor and ignoring the reactions in the combustion reactor. The basic simulation settings are optimized based on the pressure distribution observed in the cold experiment results. The optimized model correctly predicts the reactor temperature, pressure distribution, and gas production characteristics of the gasification process. Then, the effects of temperature, steam-to-biomass ratio (S/B), and gasification atmosphere on gasification performance are explored based on the verified model. It shows that the H2 production and CO2 production are increased together with an increasing H2/CO ratio with the increase of gasification temperature. With the increase of S/B, the yields of H2 and CO2 and the ratio of H2/CO first increase and then decrease. The optimal S/B for this DFB is 0.5, as excessive steam can lower the reaction temperature, which is unfavorable for gasification conversion. Changing the gasification agent from pure steam to a CO2/H2O mixture results in increased CO yield and a lower H2 content because of the competition of CO/H2O gasification and water gas shift reactions. This study provides meaningful insights on biomass gasification with steam in a large-scale fluidized bed gasifier, and the findings are beneficial for designing and optimizing DFB, particularly in the context of staged gasification processes.