Certain embodiments of the invention relate to a method and facility for purifying a high-flow gas stream by absorption, the purification facility comprising at least one absorber having a parallelepipedal enclosure arranged horizontally and comprising: a gas stream inlet and outlet, two fixed-bed absorbent masses each having a likewise parallelepipedal shape, the surfaces of which are parallel to the surfaces of the enclosure, and a set of volumes allowing the traversing of the two absorbent masses by the gas streams, in parallel but opposite directions, the traversing occurring horizontally over the entire cross-section of each of the absorbent masses and over their entire thicknesses.