Abstract: An improved air distribution device for distributing fluidizing gas to a bed of fluidized solids. The distribution device is arranged to maintain a bed of fluidized particles above a planar region of air injection and allow withdrawal of solids from below the region of air injection. The fluidizing gas is distributed to a bed of fluidized particles by a central dome and a series of horizontally extending branch pipes arranged about the periphery of the dome. In order to improve the structural integrity of the apparatus and the operation of the device, the horizontal branch pipes are attached to a knuckle region of the central dome by a series of extruded outlets that minimize stress concentrations in the branch pipe connection and locate outlet holes in the branch pipes at an elevation close to the outlet holes in the dome.