Numerical investigation of flow, heat transfer, and kinetic reaction in a large-difference bidisperse, circulating fluidized-bed reactor

To study particle bidispersity effect on the comprehensive performance of a gas–solid fluidized system, multi-field coupling numerical research of large-difference bidisperse circulating fluidized bed was performed. First, numerical simulation was conducted on the dynamic characteristic of a bidisperse gas–solid system that contained both Geldart A and B particles; heat transfer and reaction performances were then studied with the introduction of a propane dehydrogenation (PDH) kinetic reaction model; and finally, the concept of coupling fluid catalytic cracking (FCC) and PDH processes was proposed, and the feasibility was preliminarily discussed. The results showed that the two particle phases were hierarchically distributed with a pronounced segregation layer due to their large-difference bidispersity characteristic, the Geldart B-type particle was in a bubbling fluidizing state, while the Geldart A-type particle was in a turbulent fluidizing state. With the initialized bed and regeneration temperature set to 973 K, the regenerated catalyst's final, balanced temperature could decrease to 942 K, which demonstrated that a significant decline in contact temperature between the feedstock and catalyst could be achieved in the following FCC risers. Additionally, this coupling process also achieved a nearly complete conversion of propane into propene, with a conversion efficiency of above 95%. The results showed the feasibility of this coupling process, which could optimize FCC riser reaction conditions and further achieve a higher-valued light gas yield. This research can provide a reference for the study of the bidispersity effect on a gas–solid system, and the introduced coupling process can provide a new model for the FCC process's optimization.