A drying tower for bulk materials, in particular agricultural grains, includes a drying zone through which bulk material to be dried must pass from top to bottom, and an air guide for passing air through the drying zone. An air inlet is provided for introducing fresh air from the surroundings of the drying tower as supply air into the drying zone. An air outlet is provided for discharging exhaust air from the drying zone. A heat exchanger is provided for discharging heat from the exhaust air to the fresh air and an air return line for exhaust air is connected to the air outlet and the heat exchanger. An air supply line for fresh air is connected to the heat exchanger and the air inlet.

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.