A reactor for reactivating solids, comprising: - an elongate trough, which defines a reactivation chamber extending in a longitudinal direction from a first end of the trough to a second end of the trough, this reactivation chamber having: an inlet, which is situated at the first end of the trough and by which solids to be reactivated enter the reactivation chamber, and an outlet, which is situated at the second end of the trough and by which the reactivated solids leave the reactivation chamber; - two shafts, which are arranged in the reactivation chamber and which extend therein parallel to one another in the longitudinal direction, each of the two shafts successively comprising: a first part, which extends from the first end of the trough toward the second end of the trough and which is provided with a coil for conveying solids, and a second part, which extends from the second end of the trough toward the first end of the trough and which is provided with blades for mixing solids, the length of the first part representing between 10% and 33% of the sum of the respective lengths (L1, L2) of the first and second parts; and - a duct for distributing a gaseous reactivation fluid, which is arranged in the reactivation chamber at bottom of the trough, which extends in the longitudinal direction while running below at least the second part of the two shafts, and which is provided with one or several intake orifices for entering the gaseous reactivation fluid into the reactivation chamber. - an elongate trough, which defines a reactivation chamber extending in a longitudinal direction from a first end of the trough to a second end of the trough, this reactivation chamber having: an inlet, which is situated at the first end of the trough and by which solids to be reactivated enter the reactivation chamber, and an outlet, which is situated at the second end of the trough and by which the reactivated solids leave the reactivation chamber; an inlet, which is situated at the first end of the trough and by which solids to be reactivated enter the reactivation chamber, and an outlet, which is situated at the second end of the trough and by which the reactivated solids leave the reactivation chamber; - two shafts, which are arranged in the reactivation chamber and which extend therein parallel to one another in the longitudinal direction, each of the two shafts successively comprising: a first part, which extends from the first end of the trough toward the second end of the trough and which is provided with a coil for conveying solids, and a second part, which extends from the second end of the trough toward the first end of the trough and which is provided with blades for mixing solids, the length of the first part representing between 10% and 33% of the sum of the respective lengths (L1, L2) of the first and second parts; and a first part, which extends from the first end of the trough toward the second end of the trough and which is provided with a coil for conveying solids, and a second part, which extends from the second end of the trough toward the first end of the trough and which is provided with blades for mixing solids, the length of the first part representing between 10% and 33% of the sum of the respective lengths (L1, L2) of the first and second parts; and - a duct for distributing a gaseous reactivation fluid, which is arranged in the reactivation chamber at bottom of the trough, which extends in the longitudinal direction while running below at least the second part of the two shafts, and which is provided with one or several intake orifices for entering the gaseous reactivation fluid into the reactivation chamber.