Continuous Operation of a 10 kWth Chemical Looping Integrated Fluidized Bed Reactor for Gasifying Biomass Using an Iron-Based Oxygen Carrier

Chemical looping gasification (CLG) was investigated in a 10 kW(th) interconnected fluidized bed reactor with Fe2O3/Al2O3 as oxygen carriers (OC) and pine sawdust as fuel. The effects of the operation temperatures and sawdust feeding rate on the gas composition, cold gas efficiency, and carbon conversion rate of biomass were investigated. The fresh and used oxygen carrier particles were characterized by means of XRD, SEM, and BET. The results indicated that the sawdust was partially oxidized to syngas by lattice oxygen from the oxygen carrier. The syngas yield, cold gas efficiency, and carbon conversion increased with increasing operating temperature. Also, the concentrations of CO, H-2, and CH4 in the syngas increased at the elevated temperature, while the CO2 fraction decreased. The feeding rate of biomass has a significant impact on the syngas composition and cold gas efficiency. There was an optimal value of feeding rate at 2.24 kg/h corresponding to the maximum cold gas efficiency in the tested reactor system. XRD analysis showed that the oxygen carrier particles were reduced to Fe3O4 from Fe2O3 in the course of the CLG reactions. BET results indicated the surface area, total pore volume, and average pore size of the oxygen carrier particles increased initially and then slightly decreased with the reaction proceeding, due to the interstice and thermal sintering. However, the OC samples were well regenerated and maintained a good crystalline state after 60 h of operation, which illustrated that the synthesized oxygen carrier had a stable reactivity and good resistance to agglomeration.