A radial flow reactor is described. It includes a vertically extending vessel, an outer conduit, and a central conduit. At least a portion of the outer conduit and the central conduit comprises a screen. A particle retaining space is defined by at least one of the vessel, the central conduit, and the outer conduit, and it communicates with the screen of the outer conduit and the central conduit. An inlet distribution ring is positioned on the outer conduit. The inlet distribution ring comprises a ring having at least one opening and at least one vertically extending riser tube. One end of the riser tube is sealed to the ring, and the other end is positioned inside the outer conduit.