A quench zone mixing apparatus is supported within a vessel of a reactor by a support structure that includes a concentric hub, which may be formed to act as a torsion tube, and at least a first set of radial beams extending radially outward from the hub and terminating at a support ring that is attached to the reactor vessel wall. In particular, the radial beams comprise a flange that supports the redistribution tray and a web of the beams preferably includes a plurality of openings to allow the passage of fluids across the vessel. In addition, the webs also carry the channels. The radial beams also support the mixing chamber and, in the area between the wall of the mixing chamber and the vessel wall, the radial beams may have a vertical height that slopes downward from the vessel wall to the mixing chamber wall.