Axial flow reactors feature top-to-bottom downward flow of process fluids, enabling chemical reactions to occur as feed streams contact solid catalysts. In the common two-stage downflow reactor layout, incoming feed is first spread across the lower distributor tray via an inlet diffuser. This tray uniformly partitions liquid onto the underlying catalyst bed, which rests on a catalyst support grid.

Beneath the first catalyst bed lies the quench section: feed fluid is cooled by quenching gas injection before flowing into a mixing chamber. Liquid exiting the chamber is redistributed onto the next catalyst bed via another distributor tray. An outlet collector fitted at the reactor base bears the weight of the bottom catalyst bed and routes fully reacted effluent out of the vessel.