November 20, 2009
Grain Drying 101 — Guidelines and Tips
If you're one of the many producers still trying to dry down their corn and soybeans, you'll want to check these tips and reminders to ensure quality grain storage.
Which Bins Should be Unloaded First?
- High moisture grain
- Grain that’s peaked — unload enough to level
- Grain that was dried in a high speed dryer
- Older grain
- Dirty grain — grain with a lot of fines
If feeding grain, unload some grain from all bins first, removing fines and peaked grain before leveled, clean grain.
The airflow achieved by a given fan depends on the static pressure it must overcome. Deeper grain depths or higher airflow rates require higher static pressures.
Rule of Thumb
• Doubling the grain depth requires about 10 times the horsepower in the fan to maintain constant airflow.
• Doubling airflow at a constant depth requires over 5 times the horsepower.
Actions: Keep grain depth shallow. Build larger diameter rather than taller bins. Only partially fill bins during drying when you need higher airflow rates.
Push the temperature front all the way through the grain before discontinuing aeration. If you discontinue aeration before the front is pushed all the way through the grain mass, you can have horizontal zones of spoiled grain due to moisture condensation where the two zones meet.
With a Given Airflow, How Long Will it Take to Pass a Cooling Front?
Rule of Thumb
- The time it takes to push a temperature front through a grain bin is 15 divided by the cfm/bu.
If the airflow is 1 cfm/bu, it will take 15 hours.
If the airflow is 0.5 cfm/bu, it will take 30 hours.
If the airflow is 0.2 cfm/bu, it will take 75 hours.
Actions: Provide one square foot of vent opening for each 1,000 cfm of airflow.
Cover fan opening after fan operation is stopped for the winter. This prevents moisture in the grain from condensing on the cold steel mesh bottom of the bin when the cold air fills the empty, plenum space. Wet grain on the bottom of the bin can spoil when warmer air temperatures return.
Which Is Better — Airflow From The Bottom Up Or Top Down?
Both work, the advantage of pushing from the bottom is it is easier to monitor the drying and temperature fronts. The advantage of top down is you won’t get condensation on a bin roof on a cold day.
Which Type Of Fan Should I Buy?
Axial flow fans deliver more cfm per horsepower when static pressure is below 4 inches.
Centrifugal fans deliver more cfm per horsepower when static pressure is higher than 4 inches.
Where is the breaking point between axial flow and centrifugal? This depends on both the grain depth and the airflow (cfm/bu). Four inches of static pressure is required for the following:
1.0 cfm/bu and 20 feet deep
1.25 cfm and about 17 feet
1.5 cfm and about 15.5 feet
2.0 cfm and about 13 feet
Axial flow fans generally cost less per unit of horsepower.
Centrifugal fans are quieter.
Stirring System Management — How Much is Too Much?
Don’t turn on the stirring system too soon. Running it when grain depth is less than about 5 feet can result in erratic behavior of the down augers and may damage bin walls.
When Using Natural Air
If you have a stirring system installed in a bin dried by natural air,
• Run it while filling to loosen the pack factor from grain dropping long distances from the loading auger or if a mechanical spreader is used to level the grain and distribute fines. Then shut the stirring system off and allow a drying front to form and move through the grain mass.
• Natural air drying takes a long time. Running the stirring system the whole time results in mechanical grain damage and shortens the life of the motors and down augers.
• Research has shown that continuous stirring can actually lengthen drying time in natural air systems because stirring destroys the drying front and the air leaves the grain mass less saturated.
• Run the stirring system a couple of rounds just before discontinuing fan operation for the winter to mix the drier grain on the bottom of the bin with the higher moisture grain on top.
When Using Heated Air
When drying grain with heated air, especially when the added heat is more than 20 degrees, run the stirring system throughout the drying process to keep the grain mass mixed and reduce the amount of over dried grain on the bottom of the bin.
Extension Educator, Lancaster County