Agglomeration mechanism of Fe2O3/Al2O3 oxygen carrier in chemical looping gasification

Abstract

In chemical looping gasification (CLG), as one of the most commonly used oxygen carrier (OC), agglomeration is one of the most crucial triggers of Fe2O3/Al2O3 OC deactivation. However, the formation mechanism of agglomeration is not clear due to the complexity of the interaction between biomass and OC. In this study, we investigated agglomeration process of Fe2O3/Al2O3 OC in CLG from two dimensions of time and space. The results showed that in the time dimension, after ten cycles, the DT (deformation temperature) of the spent OC decreased by 5.39%, showing melting point was lower after cycles. Meanwhile, it caused the significant increase of the average particle size (59.73%) and the agglomeration degree (120.13%), indicating more severe agglomeration. Further, it led an obvious decrease in the CLG performance of efficiencies and gas yield. In the space dimension, when agglomeration occurred, low melting point K and Na compounds would first melt on the OC surface to form the K–Na inner layer (KAlSi2O6 and NaAlSiO4). As the reaction continued, high melting point Ca and Mg compounds would also be adhered to the surface of inner layer to form the Ca–Mg outer layer (CaAl2Si2O8 and Mg4Al10Si2O23), resulting in the continuous increase of OC particle size. In addition, more molten substances of KAlSi2O6 and NaAlSiO4 would lead to more adhesion between the OC particles.