Standpipes,or downcomers,are commonly used in fluidized beds to transport particles.The outlet structure of the downcomer greatly affects the performance of flow from it and even overall reactor performance.In this study,the hydrodynamics in commercial-scale intally circulating fluidized beds (ICFBs) with central downcomers having different outlet structures was investigated using computational fluid dynamics simulations with an energy minimization multi-scale drag model.The predicted results closely agreed with experimental data.Results showed that in an ICFB with a downcomer outlet directly open to the bed (model A),nearly 12.7％ to 5.4％ of the gas in the draft tube bypasses into the downcomer.In the ICFB models B and C with a conic baffle below the downcomer,the gas bypass is significantly weakened or even eliminated when the diameter of the conic baffle is 1.1 times that of the downcomer (model C).In addition,the solids circulation mass flux in ICFBs increased by about 62.5％,from 126.8 kg/(m2 s) in model A to 206 kg/(m2 s) in model C.