Advance SG-400 Industrial Hopper Dryer Capacity 400 kg/h, Hopper dryers, also called hot air dryers, are the ideal choice for removing moisture from the surface of pellets of non-hygroscopic resin prior to melting.Hot-air dryers pull ambient air from the surrounding environment, heat it with a heating element, and then pass it through a hopper filled with plastic resin. The hot air picks up the moisture from the resin pellets and carries the moisture out of the hopper.