The invention relates to a process and an apparatus of the type wherein a fluid such as a gas or vapor is used to react with or treat a particulate type of contact material such as a catalyst, which is in a fixed bed or which is in a bed which is passing by gravity from one reaction or treating zone to another. Examples of processes carried out in such an apparatus include various hydroprocessing techniques such as catalytic reforming, catalyst regeneration, hydrotreating, dehydrogenation of butane and dehydrocyclodimerization, to name a few. A specific example of a catalyst regeneration appararus in which a catalyst whose surface has been covered with coke during a catalytic reforming operation, moves downward through a carbon burn-off section, through a halogenation section and into a drying section is shown and described in Greenwood et al., U.S. Pat. No. 3,652,231, the subject matter of which is herein incorporated by reference. In the embodiment of FIG. 3 of the referenced patent, the catalyst moves downwardly in the annular space between a pair of spaced concentric perforated screens and is subjected initially to a first radially flowing recycle flue gas having a relatively low oxygen content and secondly, to a radially flowing second gas containing air, a halogen and steam. The catalyst continues to move from the aforesaid annular space as a descending bed into a generally cylindrical drying section wherein it is contacted by a hot and dry air stream, or other suitable drying medium before it exits the bottom of the apparatus. The drying medium is typically distributed by an arrangement of perforated distributor members including a central trunk with a plurality of laterally extending branches positioned generally uniformly in a horizontal plane near the bottom of the drying section. In order to minimize plugging of the distributor members by the catalyst particles, the distributor members usually have their flow openings located only in their downwardly facing portions. However, even when the distributor members are intricately fabricated so as to include spaced apart wedge wire screen portions which form slots in their bottom surfaces and internal baffles to help distribute the flow uniformly through all of the slots, it appears that plugging of the distributors is still possible. Also, since plugging of a few slots produces higher velocities at the other slots, the plugging becomes progressively greater since the higher velocities can produce unwanted fluidization and consequent catalyst attrition which can cause additional plugging. The placing of a large number of branch pipes or laterals on a distributor pipe can permit lower flow velocities, and thus less chance of damaging fluidization, than where fewer branches are present. However, the mere presence of any pipes in the catalyst bed produces an obstruction in the downward flow path of the catalyst bed which can accelerate attrition and, of course, a greater number of pipes would increase the problem. In addition to the attrition caused to the catalyst when gas velocities become too large due to screen plugging, the use of perforated distributor members is also very costly, especially when such members must be fabricated from sections of slotted screens.