The invention concerns a device for supplying and dispensing a powdery material in an ascending gas stream (F), in a substantially vertical reactor contacting said powdery material, in particular a chemical and/or physical neutralizing agent of at least one effluent of the gas stream to be purified, with said gas stream, comprising means for distributing said powdery material in said gas stream which are fed by gravity feeding means and means conveying said powdery material in fluidized bed (10). Said conveying means comprise at least one airslide (3) outside the reactor and directly adjacent the reactor side wall (4), and said gravity feeding means are gravity distributors (13) each of which has one end (14), wherein emerges a feeding orifice (12) into the reactor side wall (4), and through which the powdery material from the fluidized bed (10) flows.