THREE MINUTE AGPublished Sep 5, 2019
More Than Just Cane
With a considerable amount of last year’s grain crop still in storage, and a bumper crop and low prices this year, the demand for grain storage is high.
“Grain can be stored in many types of facilities,” North Dakota State University Extension Service agricultural engineer Ken Hellevang says. “But all storage options should keep the grain dry and provide adequate aeration to control grain temperature.”
Grain must be dry and cool (near the average outdoor temperature) when placed in alternative storage facilities because providing adequate, uniform airflow to dry grain or cool grain coming from a dryer is not feasible, according to Hellevang.
Grain pushing against the walls can damage buildings not built for grain storage. To estimate the amount of force that grain exerts on a wall, multiply the grain depth by the grain’s equivalent fluid density (EFD). For example, the force pushing against the base of a 5-foot wall of a structure containing corn would be about 115 pounds per linear foot of the wall (5 feet x 23 pounds per cubic foot = 115 pounds per linear foot).
The wall must be anchored securely, and its structural members must be strong enough to transfer the force to the building poles or support structure without breaking or excessive bending. The total force per linear foot on the wall is the force at the base multiplied by the grain depth divided by two.
For this example, the total force is 288 pounds per linear foot (115 x 5 / 2). In a pole building with poles spaced 8 feet apart, the force against each pole is 2,304 pounds (288 x 8). Typically, you’ll need additional poles and a grain wall to support the grain force in a pole building.
Before placing grain in a building previously used for grain storage, look for anything out of alignment, such as the wall bowing. Also check the roofline. Bowing or bending indicates the load on the building exceeds the load for which it was designed and built.
Examine connections for separation or movement. A connector failure can lead to a building failure. You may need to reinforce the connection by adding a gusset or splice.
Storing in Bags
Storing grain in poly bags is a good option, but it does not prevent mold growth in damp grain or insect infestations, Hellevang says. Grain should be placed in the bag at recommended storage moisture contents based on grain and outdoor temperatures. Heating will occur if the grain exceeds a safe storage moisture content. Because the grain cannot be aerated to control heating, do not bag damp grain. The average temperature of dry grain will follow the average outdoor temperature.
Select an elevated, well-drained site for the storage bags, and run the bags north and south so solar heating is similar on both sides of the bags. Sunshine on just one side heats that side, which can lead to moisture accumulation in the grain on the cool side. Wildlife can puncture the bags, creating an entrance for moisture and releasing the grain smell, which attracts more wildlife. Monitor the grain temperature at several places in the bags.
Grain frequently is stored short term in outdoor piles. However, precipitation is a severe problem for uncovered grain because grain is very porous. A 1-inch rain will increase the moisture content of a 1-foot layer of corn by 9 percentage points. This typically leads to the loss of at least a couple of feet of grain on the pile surface, which is a huge loss.
For example, a cone-shaped pile 25 feet high is approximately 59,000 bushels of grain. Losing just 1 foot of grain on the surface is a loss of about 13 percent of the grain, which is $39,000 if the grain value is $4 per bushel.
Hellevang strongly recommends using a cover to prevent water infiltration. Aeration and wind blowing on the pile generally will not dry wet grain adequately to prevent spoilage.
Drainage is critically important to the success of any grain storage. About 25,000 gallons of water will run off an area about 100 by 400 feet during a 1-inch rain. This water must flow away from the grain and the area next to it. Examine the entire area to assure that flooding will not occur during major rain events.
The outdoor ground surface where grain will be piled needs to be prepared with lime, fly ash, cement or asphalt to prevent soil moisture from reaching the grain. The storage floor also should be higher than the surrounding ground to minimize moisture transfer from the soil into the grain. Make sure the ground surface is crowned so moisture that does get into the pile drains out rather than creating a wet pocket that leads to grain deterioration.
Look for anything out of alignment in a bunker or bulkhead wall. Any twisting, flexing or bending of a structural member may lead to a failure. Also examine connections for any separation or movement, and reinforce them if necessary. Look for any material deterioration as well, and repair rotted, rusted or corroded members.
A combination of restraining straps and suction from the aeration system holds grain covers in place. However, you must provide adequate airflow through the grain to control grain temperature. Place perforated ducts on the grain under the cover to provide a controlled air intake for the aeration system and airflow near the cover to minimize condensation problems under the cover. Properly sized and spaced ducts are placed under the pile to pull air through the grain. If you use a perforated wall, it should permit airflow through the grain but minimize the amount of open area so the air does not “short-circuit” to the fan.
Wind velocity will determine the amount of suction you need to hold the cover in place. Some control systems measure wind velocity and start fans based on the wind speed. Backup power may be used to assure that the cover is held down during power outages. Check the backup power to make sure it starts when needed.
Cooling Stored Grain
Cool grain with aeration to reduce the insect infestation potential. Insect reproduction is reduced at temperatures below about 60 F, insects are dormant below about 50 F, and insects can be killed by extended exposure to temperatures below about 30 F.
Cooling grain as outdoor temperatures cool will reduce moisture migration and the condensation potential near the top of the grain pile. Grain moisture content and temperature affect the rate of mold growth and grain deterioration. The allowable storage time approximately doubles with each 10-degree reduction in grain temperature.
For example, the allowable storage time for 17 percent moisture corn is about 130 days at 50 F and about 280 days at 40 F. The grain should be cooled whenever the average outdoor temperature is 10 to 15 degrees cooler than the grain. It should be cooled to near or below 30 degrees for winter storage, depending on available air temperature.
Aeration ducts need to have perforations sized and spaced correctly for air to enter and exit the ducts uniformly and obtain the desired airflow through the grain. Space aeration ducts equal to the grain depth to achieve acceptable airflow uniformity.
Source: North Dakota State University
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