(451d) Computational Fluid Dynamic Simulations for Woodchips Chemical Looping Gasification in a Bubbling Fluidized Bed Fuel Reactor

Using the gasification process, in a fluidized bed reactor, in conjunction with chemical looping technology has been found to be one of the most promising ways for biomass conversion called chemical looping gasification (CLG). In this study, a two-dimensional transient computational fluid dynamic (CFD) model is developed to simulate hydrodynamics, the homogeneous and heterogeneous reaction rates taking place in chemical looping gasification of woodchips as fuel and iron oxide (Fe₂O₃) as oxygen carrier (OC) in a bubbling fluidized bed fuel reactor. All three phases including two solid phases and one gas phase are treated using a two-fluid model (TFM) scheme based on the Eulerian-Eulerian multiphase approach. First, the predicted results by CFD are compared with experimental data where a good agreement is achieved. Then, the impact of operating conditions; temperature, steam to biomass, and oxygen content of OC to biomass; on the outlet gas composition distribution and chemical looping gasification (CLG) performance are analyzed. The simulation results demonstrate that these operating conditions have a considerable effect on the gas yield and CLG efficiency. It is found that higher temperature increases the syngas yield, gasification, and carbon conversion efficiency due to favoring endothermic reactions at escalated temperature while the H₂/CO concentration ratio decreases because of higher reactivity of H₂ with OC. Also, higher steam to biomass ratio promotes the H₂ concentration as it enhances carbon-steam gasification reaction and water-gas shift reaction. Raising the feeding rate of OC leads to a marked drop in H2 and CO relative concentrations but a higher carbon efficiency due to a relatively higher OC-Fuel ratio.