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Heated-air fixed-bed batch dryers

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1. In heated-air fixed-bed batch dryers, the hot drying air enters the grain bulk at the inlet, moves through the grain while absorbing water and exits the grain bulk at the outlet. 

2. The grain at the inlet dries faster because of the drying air has the highest water absorbing capacity. Because of the shallow bed and relatively high airflow rates, drying occurs fastest in all layers of the grain bulk at the inlet and slowest at the outlet. As a result a moisture gradient develops, which is still present at the end of drying.

3. The drying process is stopped when the average moisture content of the grain is equal with the desired final moisture content. 

4. When the grain is unloaded and filled in bags the individual grains equilibrates, meaning that wetter grains release water which the dryer grains adsorb so that after some time all grains have the same moisture content. 

5.The re-wetting of the dryer grains, however, leads to fissuring causing the grains to break in the milling process. 

File Courtesy: 
http://www.knowledgebank.irri.org/rkb/index.php/drying-basics/heated-air-and-low-temperature-drying
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