Scallop assembly and reactor

A radial flow reactor comprising:

• a vertically extending vessel having a fluid inlet and a fluid outlet;
• at least one vertically extending outer conduit in the vessel, at least a portion of the outer conduit comprising a screen defining a plurality of perforations and communicating with the fluid inlet;
• a central conduit communicating with the fluid outlet, at least a portion of the central conduit comprising a screen defining a plurality of perforations;
• a particle retaining space in the vessel defined by at least one of the vessel, the central conduit, and the outer conduit, the particle retaining space communicating with the plurality of perforations and the central conduit;
• an inlet distribution ring positioned on the outer conduit and communicating with the fluid inlet, the inlet distribution ring comprising a ring having at least one opening and at least one vertically extending riser tube, one end of the riser tube sealed to the ring, the other end of the riser tube positioned inside the outer conduit;
• a seal plate in contact with the outer conduit;
• wherein there is a first gap between the riser tube and the outer conduit, and a second gap between the riser tube and the seal plate, and wherein the second gap is smaller than the first gap.