Using Existing Buildings for Temporary Grain Storage
David P. Shelton, Extension Agricultural Engineer
Gerald R. Bodman, P.E., Extension Agricultural Engineer
David D. Jones, Associate Professor, Biological Systems Engineering
Existing structures such as machinery storage buildings, warehouses, or even livestock buildings are sometimes considered for temporary grain storage, particularly in years when grain yields are high and prices are low. These buildings are generally referred to as flat storage. Flat storage can be used for short term (harvest to mid-June) storage of cool, dry grain if the grain is in good condition when placed in storage and if good management is provided and the challenges of grain handling, aeration, and pest control can be met. Things to consider when deciding whether a given building would be suitable for temporary grain storage include the following.
Can you get the building clean enough for grain storage? If the building previously contained manure, agricultural chemicals, or petroleum products, can you completely remove these materials and their odors so that grain will not be physically contaminated or pick up odors that would result in down grading?
Bird and rodent exclusion
Inspect how the building is constructed to determine whether you can keep birds and rodents out of the building and away from the grain. Expect grain losses and contamination if these pests are not excluded from the building.
Check the roof for leaks and estimate how difficult and expensive it would be to repair. Be sure the grade around the building slopes so water will readily drain away from the building, rather than onto or under the floor. Look at the floor. A vapor barrier (6-mil plastic) is needed beneath the grain to prevent moisture from moving from the soil into the grain. One option is to install a new concrete floor with a vapor barrier under it. Keep in mind, though, that new concrete floors should be allowed to cure for several weeks before grain is placed on them. If the building has an earthen floor or an older concrete floor without a vapor barrier, put down plastic (6-mil) over the floor as the building is filled with grain.
When deciding whether it is worth using an existing building for grain storage, estimate how much grain the building can hold. It is disappointing to find how few bushels can actually be stored in some flat buildings, especially those with low ceilings or when grain cannot be piled against the sidewalls.
Dry grain exerts high pressure on walls and unless the building was specifically designed to withstand the pressure of grain or some other granular product, it will need to be reinforced. Some possible options are: a) If the building was designed and erected by an agricultural building company, you may be able to purchase a retro-fit "grain package" from the company. b) Strengthen the walls by adding cables and/or braces to the posts, trusses, and post-to-truss connections. [Note: these modifications must be designed by a licensed engineer.] c) Set free-standing bulk heads inside the building to keep grain away from the walls. (Refer to North Dakota State University publication AE-84 "Temporary Grain Storage" for bulk head details.) d) Set free-standing metal grain bin rings (without floors or roofs) inside the building. e) Limit grain depth along the walls to no more than 2 feet, as most buildings are able to withstand this amount of pressure.
Filling and unloading the building
Grain handling is not as convenient in flat storage as it is in conventional round metal bins, and it can be a challenge to move grain in and out of the building. There is specialized equipment such as pneumatic grain conveyors for this purpose that you may be able to buy, rent, or custom-hire. Portable grain augers can often be used to fill flat storage. However, this sometimes requires making openings in the roof or frequently moving the auger around inside the building. Unloading can be accomplished by using a portable auger or a bucket loader, although this becomes more difficult when there is plastic on the floor and cables or other bracing are in the way .
Grain moisture content is critical in temporary flat storage buildings. Maximum recommended moisture contents are given in Table 1. Remember, these are maximums for high quality grain - reduce by at least one percentage point for lower quality and/or damaged grain.
|Table 1. Maximum recommended moisture contents for properly managed, high quality, aerated grain in existing buildings used for temporary storage.|
|Storage Period||Corn and Sorghum||Soybeans|
|Removed by mid-April||15%||12%|
|Removed by mid-June||14%||12%|
|Beyond mid-June||not recommended||not recommended|
Even though the grain is dry when moved into flat storage, a well-designed aeration system consisting of fans, supply tubes, and perforated ducts is imperative to control grain temperature and moisture migration. Perforated ducts (metal or plastic) that are made for grain aeration work best. Ordinary plastic drainage tile doesn't work very well because it doesn't have enough perforated area for good air movement. Provide a minimum of 0.1 cubic feet of airflow per minute per bushel (cfm/bu) of grain. Proper fan sizing and system design are critical - refer to MWPS-29 "Dry Grain Aeration Systems Design Handbook" or consult with an experienced aeration system designer to help assure satisfactory operation.
Positive pressure aeration system designs (air blowing into ducts and out the top of the pile) tend to work best for flat storage, but be aware of potential condensation problems under the roof. You can minimize condensation problems by providing adequate air exhaust area out of the building (at least 1 ft2 of open area per 1000 cfm of fan capacity) and plenty of air movement over the pile while the fans are running. As with grain stored in conventional bins, there are two primary aeration objectives: 1) maintaining the temperature of the grain mass within 10 to 15 F of the average outside air temperature; and 2) maintaining no more than a 10 F difference in temperature within the grain mass. Refer to NebGuide G84-692-A "Aeration of Stored Grain" for specific aeration management recommendations.
Checking grain condition
With peaked grain, low ceilings, etc., checking the grain in flat storages is more difficult than in conventional bins. However, because of less than ideal storage and aeration conditions, it is imperative that the grain be monitored at least every two weeks to be sure that the grain remains in good condition. Some areas and conditions to check include:
Outside the building for open doors, damaged components, proper drainage, etc.
Inside the building roof for condensation and leaks.
Grain surface for condensation, crusting, wet areas, molds, and rodent and insect activity.
Grain mass for non-uniform temperatures, high moisture pockets or layers, molds, and insects.
Exhaust air for any off-odors.
If problems are detected, they need to be evaluated and corrected as soon as possible. This may include cooling with aeration, rodent control, fumigation for insect control, or moving the grain.
In summary, conventional round metal grain bins are hard to beat for convenient grain handling and storage, but flat storage can work satisfactorily for temporary grain storage with good management, and if grain handling, aeration, pest control, and monitoring challenges are met.
Adapted from the article "Using Flat Buildings For Dry Grain Storage" by Bill Wilke, Extension Agricultural Engineer, University of Minnesota.