Collector assembly for a gaseous fluid for a radial reactor

A collector assembly (8) for a gaseous fluid suitable for being disposed in a reaction section with a moving bed of catalyst of a radial reactor, said collector assembly comprising a vertical cylindrical screen (9) which is permeable to gaseous fluid and impermeable to particles of catalyst, and a vertical cylindrical tube (10) which is supported by said screen (9) and disposed in a concentric manner with respect to said screen, said tube being permeable to gaseous fluid and impermeable to particles of catalyst, in which the tube (10) comprises one or more zones (17a, 17b) which are permeable to gaseous fluid comprising a plurality of through holes and a plurality of zones (18a, 18b, 18c, 18d) with a “reduced permeability” to gaseous fluid compared with the permeable zone, each zone with reduced permeability having a lower porosity than that of a zone which is said to be permeable, the porosity of the zones being defined as the ratio between the total permeable surface area of said zone and the total developed surface area of said zone, and in which the porosity of a zone with reduced permeability is in the range 0 to 0.005, it being understood that a zone with reduced permeability excludes any space comprised between the through holes of the permeable zone or zones.