Material handling drying beds

The beam-breaker technique is useful for detecting large and abrasive materials such as coal, minerals, wood chips, and vegetable pulp. It is also useful for detecting very light materials such as dry sawdust and powdered materials in fluidized beds. This technique can also be considered for use on difficult-to-handle liquids that are viscous, toxic, or hazardous because the detector is isolated from the vessel contents. 

For direct drying of liquids, slurries, and pastes, drum dryers are the only competition for spray dryers, although fluidized bed dryers sometimes can be adapted to the purpose. Spray dryers are capable of large evaporation rates, 12,000-15,000 lb/hr or so, whereas a 300sqft drum dryer for instance may have a capacity of only 3000 lb/hr. The spherelike sprayed particles often are preferable to drum dryer flakes. Dust control is intrinsic to spray dryer construction but will be an extra for drum dryers. The completely enclosed operation of spray dryers also is an advantage when toxic or noxious materials are handled. 

The moisture content of the 15 tray-dried batches following final mix remained essentially unchanged from the drying step. The batches from the fluid bed process gained moisture. This is probably attributable to handling very dry material in a relatively humid environment. Both groups are still below the target for this step of 1.5 %, however. 

The maltodextrin solids are amorphous, white, or off-white powders or granules, which are non-sweet and odorless. The materials are processed by spray drying, fluidized bed agglomeration, and roller compaction to improve their handling properties. Maltodextrins are hygroscopic above 50% RH and need to be stored below... 

Agitated batch driers consist of a jacketed cylindrical vessel with agitator blades designed to scrape the bottom and walls. They may operate at atmospheric pressure or under vacuum. Pasty materials that could not be handled in tumbling or fluidized-bed driers, may be successfully dried at rates higher than can be achieved in an oven. 

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