Biomass Direct Chemical Looping Conversion in a Fluidized Bed Reactor with Natural Hematite as an Oxygen Carrier

Biomass direct chemical looping (BDCL) process has the potential to thermochemically convert biomass to hydrogen/synthesis gas and/or electricity with high efficiency and CO₂ capture. BDCL gasification involves the use of an oxygen carrier which transfers oxygen from air to biomass to convert the biomass into synthesis gas, and the traditional gasifying agents, such as oxygen enriched air or high temperature steam, are avoided. BDCL gasification with natural hematite (Fe₂O₃) as an oxygen carrier was experimentally investigated in a bubbling fluidized bed reactor using argon as fluidizing gas. The effect of reaction temperature, reaction time, and the presence of oxygen carriers on the gas product distribution, gas yield, carbon conversion ratio, and gasification efficiency were examined. The experimental results show that the natural hematite could be used as oxygen carrier in CLG of biomass. It was observed that the CO and H₂ concentrations increased slightly, while CO₂ and CH₄ concentration declined slightly with increasing temperature during biomass gasification. In addition, H₂, CO, CH₄ concentration in the syngas slowly increased with the reaction time increases and the CO₂ concentration showed an opposite trend. The presence of oxygen carriers can significantly increase gas production rate and carbon conversion rate. Scanning electron microscopy- Energy Disperse Spectroscopy (SEM-EDS) shows that the hematite particles exhibited obvious agglomeration when the reaction temperature was above 850°C. However, the composition and the element content on the particle surface did not change remarkably before and after reaction.