In-situ gas flow separation between biochar and the heat carrier in a circulating fluidized bed reactor for biomass pyrolysis

Abstract

The circulating fluidized bed (CFB) reactor is extensively utilized in biomass fast pyrolysis, which typically employs a heat carrier as a heat transfer medium. The regeneration of the heat carrier relies on carbon combustion. However, direct combustion of carbon for heating purposes results in ash accumulation, leading to decreased yields of bio-oil and biochar. To overcome the limitations of conventional techniques and address the challenges associated with separating biochar from the heat carrier, a novel in-situ gas flow bed separator was designed. This separator enables continuous, rapid, and highly efficient separation of biochar and the heat carrier. The impact of various operational conditions on separation efficiency was investigated, and the operational range that yields effective and efficient separation was obtained. The entrainment effect of bubble wakes on particles and the mechanism of binary particles distribution in the bubble hole in the gas flow bed were investigated by numerical simulation and a high-speed digital camera. The results show that bubble activity, as well as the density and size disparities of binary particles, significantly influence the separation process. When the mass ratio of binary particles and U/Umf (the ratio of fluidization velocity to the minimum fluidization velocity) were 30/1 and 1.67, the separation efficiency of carbon and the heat carrier could reach 99%. This innovative technology holds tremendous potential for substantially enhancing product yields in CFB systems, thereby significantly increasing their competitiveness in fast pyrolysis applications.