This installation comprises an enclosure (1) in the form of a tunnel and means (2, 3, 4) for generating therein a current of hot air; the materials to be dehydrated are transported in the form of a layer by an endless conveyor belt (6) which exposes them to the current of hot air, this belt (6) having a sinuous trajectory consisting of a set of superposed horizontal sections (60, 60') and transfer means (7) arranged at the downstream end of each of the belt sections are adapted to scrape the materials and to pour them onto the subjacent section. <IMAGE>
