Drying Desk: Tray drying basics
Tray drying is one of the oldest batch drying methods. In simplest terms, you place material on a tray, expose it to a heat source, and provide a way to remove the evaporated moisture. You can dry from a few grams to tons of feed material per charge. This article looks at some basic design approaches relating to the heat transfer method and operating pressure conditions.
In direct-contact drying, heated circulating air (or inert gas) flows over the surface of the material contained on the tray(s). If several trays are used, they're typically stacked in a vertical rack, and the circulating air flows in parallel paths above the trays. The circulating air also removes the evaporated moisture from the enclosure housing the trays and rack. Adiabatic evaporation proceeds with the material temperature reaching the heated air's wet bulb temperature during the constant-rate drying zone. If drying were to continue into the diffusion-rate limited zone, the material temperature would approach the heated air’s dry bulb temperature.