A computational fluid dynamic (CFD) model has been developed for the fuel reactor of a chemical looping gasification (CLG) system with biomass as fuel and natural hematite as oxygen carrier (OC). By coupling the fluid dynamics and the chemical kinetics, the multiphase continuum model is able to describe the motion of gas and solid phases and the heterogeneous reactions between them, which take place in a bubbling fluidized bed reactor. The simulated average concentrations of five gas species fit the experimental data provided in the literature quite well, with a deviation for each gas component lower than 2%. This verified model is then applied to investigate the effects of various gasifying agents on the compositions of syngas. The results show that the biomass CLG performance is significantly improved in the presence of CO2/H2O and their mixture. Furthermore, synergistic effect of CO2/H2O mixture can be observed based on the evolution of char mass within the reactor.
Keywords biomass gasification, chemical looping, synergistic effect, gasification atmosphere