the invention relates to a device for continuous heat treatment of granulated materials , especially to the crystallization of polymer granulate , such as polyethyleneterephthalate for example . the device comprises several adjacent fluidization chambers respectively provided with a sieve plate through which a fluidization gas used to fluidize the granulate can be insufflated into the respective chamber from below via a gas inlet , the gas being able to escape via a gas outlet in the top area of the device . the first chamber takes up the greater part of the overall volume of all chambers and neighboring chambers are , respectively , fluidically connected by product throughflow openings in the separating walls arranged therebetween . the granulated material can be guided through several adjacent fluidization chambers , the absolute filling level of the fluidized granulating material in the first chamber being at least as high as the absolute filling level of the other adjacent chambers disposed downstream therefrom .