A mixed flow grain dryer according to the present disclosure includes a plenum, a blower operable to force outside air into the plenum, a heater operable to heat air flowing from the blower to the plenum, at least one column, and a conveyor. The at least one column is configured to receive heated air from the plenum such that the heated air dries grain flowing through the at least one column. The at least one column is configured to change a flow direction of the heated air. The conveyor is configured to meter a discharge of grain from the at least one column.

A hopper for the heat treatment of a material contained therein includes a casing with an upper portion, into which the material to be treated is introduced, and a bottom part or lower portion, from which the material is discharged; a diffuser of a process fluid located inside the hopper; a system for introducing the process fluid inside the diffuser; a mixing chamber arranged to enclose at least the lower portion of the hopper externally; a system for introducing the process fluid inside the mixing chamber; and a system that fluidically connects the interior of the mixing chamber with the interior of the diffuser.