you should know how to choose a good fluid bed dryer

The invention pertains to the field of direct dryers for industrial and commercial use, and in particular to a continuous flow fluid bed dryer. Such dryers are typically used for the drying of delicate free flowing products such as certain grains. Such grains tend to suffer degradation in dryers having rapidly moving mechanical parts that interact with the product. The fluid bed dryer typically has a drum or housing with a plenum region beneath a product drying region and separated from it by a porous screen. Heated air is introduced into the plenum. Particulate matter to be dried is "fluidized", that is it is suspended above the screen on the heated air rising through the screen. This produces a turbulent mixing action between the target product and the air resulting in the drying of the product without damage to it. The screen openings can be canopied to direct air flow and deter clogging of the screen openings. In such dryers the heated air flow is used both to dry the product and move it along the dryer to a discharge. The amount of air needed to fluidize the product is often greater that the amount of heated air needed to dry it. This results is wasted heat since the amount of heated air supplied is a function of the amount of air needed to fluidize the product.
A continuous flow fluid bed dryer for drying of particulate product, comprising: a dryer housing having housing walls defining a drying chamber and a plenum chamber located beneath the drying chamber; a product inlet to the drying chamber and a product outlet from the drying chamber; a porous screen separating the drying chamber from the plenum chamber between the product inlet and the product outlet; an heated air inlet to the plenum chamber for introduction of heated air for movement through the plenum chamber to the drying chamber; a rotor shaft mounted for axial rotation in the drying chamber, and means for rotation of the shaft; a plurality of paddles connected to the rotor shaft for movement about a path whereby the paddle ends sequentially sweep over the surface of the screen to move product away from the screen permitting a rush of heated air into the drying chamber from the plenum chamber;
There is a momentary fluidizing of the product at that locale resulting in mixing and drying of the material. The advantages of a fluid bed dryer are realized without fluidizing the entire bed at once. Paddle movement is slow and gentle. Product moves forward to the discharge opening. Since the entire bed is not fluidized, the particles are not classified by weight or size. Varying size particles remain mixed together. The high sidewalls of the drying chamber leave a large upper area where air flow is considerably lessened. This avoids separation of the lighter and smaller particles from the bed.

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