Thin Film Dryers
Thin Film Dryers are characterized by a mechanically agitated thin product layer inside the dryer The Horizontal Thin Film Dryer consists of a cylindrical, horizontal shell with heating jacket and a rotor in the shell which is equipped with rows of fixed blades. The fixed blades spread the wet feed in a thin layer over the heated wall. The thickness of the layer is defined by the clearance between the blade and the heated wall. A highly agitated bow wave is formed in front of the rotating blade. The turbulence increases as the product passes through the clearance. The volatile component evaporates continuously. The product layer is a few millimeters in thickness. The blades of the rotor are designed to give a minimum clearance with the dryer wall to prevent fouling of the heat transfer surface by product, but do not themselves contact the heated wall. Pumps, screws or other feeding devices feed the product into the dryer. The wet feed can be a thick liquid, a paste or a powder. The product is conveyed in a thin layer through the dryer. The necessary residence time which is product or process specific is controlled by adjusting the blade configuration along the length of the rotor between mixing, conveying and cleaning blades. The vapour produced passes counter-current to the product flow through the dryer towards the vapour exit nozzle. Entrained fine particles are reagglomerated in contact with the wet feed. The free flowing powder leaves the dryer via a suitable air lock system. Other final product forms are possible like pastes, melts etc.