How do farmers use grain bins

Store grain safely - cleaning, drying and cooling

4. Storage ventilation drying in flat storage

Storage ventilation drying uses the principle of equilibrium humidity. For example, there is an equilibrium between 14% moisture content in wheat and 65% relative humidity at an air temperature of 20 ° C. According to this, the drying air is conditioned in such a way that it corresponds to the moisture equilibrium. About 1 g of water is absorbed per cubic meter of air. The goods to be dried can be brought into the flat storage area with a humidity of up to 19% and are dried by the air flowing through them. Due to the low water absorption, a high air rate is necessary. Air rates of 60–80 cubic meters of air per cubic meter of grain per hour are usually passed through the stored goods. This leads to high air velocities in the grain pile and high flow resistance. The latter ensure an additional increase in temperature and thus a further decrease in the relative humidity in the drying air. In order to avoid major fluctuations in the drying success, a partial air circulation process is usually carried out in the storage ventilation drying. Moist air is sucked in from the hall and mixed with fresh air before it is pushed into the main air duct by the radial fan. In this way, humidity fluctuations in the ambient air are leveled out and the drying process is stabilized.

If the preconditioned drying air flows into the items to be dried, a drying horizon of 70 cm is built up and moisture is removed until the moisture equilibrium is reached. From this point on, the drying horizon moves up the pile of grain. The drying target is achieved when a relative humidity of 65% is reached above the grain.

Usually the air regime is operated with 70% circulating air and 30% fresh air. Today's control technology uses appropriate combination sensors for the relative humidity and temperature to regulate the air flaps or their opening width and thus the mixing ratio between fresh and circulating air.

The layer-by-layer storage of the items to be dried is inherent in the system. This is usually realized by a fully automatic stationary conveyor system in the hall. Conveyor belts with swiveling devices have established themselves as a mobile solution. Storage ventilation drying places high demands on air flow and storage height. The channel spacing depends on the removal of moisture, the ventilation system and the dump height. If corrugated iron ducts are used for air routing, the duct spacing is 1.25 - 1.5 m. Underfloor ducts require a duct spacing of 1 - 1.25 m. The storage height is quite variable. The standard is 3 to a maximum of 6 m. Higher bearings are advantageous due to the temperature increase through compression and do not require additional thermal heating. However, these require special care, since encrustation can occur on the stack surface. This must be broken up every 2 days with a 20 cm deep rake.

Storage ventilation drying is the low energy drying method. These have a specific energy requirement of 0.4–0.7 kWh per kg of withdrawn water. Storage ventilation drying is limited, however. Good moisture levels above 19% cannot be processed.