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Low-temperature drying

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1.In low-temperature drying the objective of the dryer management is to keep the RH of the drying air at the equilibrium relative humidity (ERH) corresponding to the desired final moisture content of the grain, or the equilibrium moisture content (EMC). 

2. The effect of the temperature is minimal compared to the RH. For example a final MC of 14% is desired one should target an RH of the drying air of around 75%. 

3. In practice the ambient air can be used at daytime in the dry season. At night and during the rainy season slightly pre-heating of the ambient air by 3-6ºK is sufficient to drop the RH to appropriate levels

4.The drying air enters the grain bulk at the inlet and while moving through the grain bulk it dries the wet grains until the air is saturated. 

5. While absorbing the water the air cools down by a few degrees. On its further way through the grain bulk the air cannot absorb more water, since it is already saturated, but it picks up the heat created by respiration, insects and fungal growth and thus, prevents heating up of the wet grain section. 

6. A drying front of several centimetres depth develops and slowly moves towards the outlet leaving dried grain behind.

7. After the drying front, leaves the grain bulk, the drying process is finished. Depending on initial moisture content, airflow rate, grain bulk depth and drying air properties this can take from 5 days to several weeks.

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