PURPOSE: To execute a perfect drying with a low energy consumption by perfectly mixing a wet material in a circulating fluidized bed and partially evaporating the liquid contained in the wet material under reduced pressure, passing a heating gas and partially saturating the heating gas with extracted vapor.

CONSTITUTION: The wet material is mixed completely over the entire part thereof in the circulating fluidized bed mechanically formed by a mixing or stirring machine 1. The liquid contained in the wet material is at least partially evaporated under the reduced pressure by a vacuum pump 16 by utilizing the heat potential of the wet material. In a next treatment step, the heating gas is passed through the inside of the fluidized bed from a heat exchange section 7. This heating gas is at least partly saturated by the vapor of the liquid extracted from the wet material, by which the drying stage is perfectly executed. Consequently, the perfect execution of the drying stage in the min. energy consumption and the shortest drying time is made possible.