The multi-regime CFB riser equipped with a bottom diameter-enlarged section has been demonstrated to be efficient in increasing the overall solids holdup and enhancing the gas-solid contact previously. In this work, the swirling gas nozzles have been incorporated into the diameter-enlarged section to further improve the gas-solid mixing behavior, and the effect of the nozzle directions on the gas-solid flow patterns has been systematically studied. The results indicated that, with the sacrifice of small amount of solids circulation rate, the solids concentration in the diameter-enlarged section using swirling gas nozzles was further increased, and the height of the dense phase was elevated, providing more available catalyst for gas-solid contact reactions. In addition, the gas phase injected through the swirling nozzles exhibited a rotational rising flow behavior and effectively penetrated into the solid phase near the wall region, consequently intensifying the gas-solid fluctuation and contact. (C) 2020 Elsevier B.V. All rights reserved.