For many grain managers, it may have been several years since they dried corn, let alone beans. Here are some general reminders to jog the memory and hopefully avoid some costly mistakes this fall.
Natural air bin drying: Equilibrium moisture content tables will tell you the moisture content to which grain will dry based on the temperature and humidity of the drying air.
http://www.ag.ndsu.nodak.edu/abeng/pdffiles/GrainEquilibriumMoistureContentCharts.pdf
For successful natural air drying in Iowa, plan for at least 1.25 cubic feet per minute of airflow through the grain. Fan horsepower required to get 1.25 cfm per bushel depends on grain depth. For grain up to 15 feet deep, 1 horsepower of fan per 1000 bushels of grain will usually meet the goal. For grain 16 to 20 feet deep, 1.3 hp per 1000 bushels will be needed. For corn above 20 percent moisture, Charlie Hurburgh recommends 2 hp per 1000 bushels. To get precise estimates of airflow for your bin/fan combination, see the fans computer program at http://www.bbe.umn.edu/Post-Harvest_Handling_of_Crops
Grain drying time for 10 points of moisture removal at 15 to 20 feet deep will be 3 to 6 weeks. For more precise drying time estimates, Joel DeJong recommends this article for corn
http://cropwatch.unl.edu/web/cropwatch/archive?articleID=1990301
or this article for beans
http://cropwatch.unl.edu/web/cropwatch/archive?articleID=1971361
Natural air bin drying summary:
- 1.25 cfm per bushel minimum airflow
- 15 feet maximum grain depth with 1 fan hp per 1000 bushels
- 20 feet maximum grain depth with 1.3 fan hp per 1000 bushels
Typically only one bin batch can be dried per season
Heated air bin drying: Heated air bin drying for soybeans is best done with no more than 20 degrees of added heat. Heated air bin drying for corn is best done with air temperatures of 120 to 180 degrees. Lower temperatures produce slow drying and loss of allowable storage time for the corn. Keep in mind that heated air bin drying must be done either in shallow layers or with stirring equipment. Airflow rates of 5 to 10 cfm per bushel are required.
Non-stirred heated air bin drying: To avoid severely over-drying the grain near the floor, shallow layers are restricted to 2.5 to 4 feet deep. High airflow rates of 5 to 10 cfm per bushel are required to get the top grain dried before the bottom grain is severely over-dried. Maximum moisture difference between the wettest grain and driest grain should be no more than 5 points. Fan horsepower needed to create 5 cfm per bushel at 3-4 feet deep is about one horsepower per 1000 bushels. Drying rates for 10 points of moisture removal from corn are about 5 bushels per hour per 1000 cfm at 120 degrees, and 8 bushels per hour per 1000 cfm at 160 degrees. At 2.5 to 4 feet deep, you may be able to dry 1 to 2 batches per day.
Stirred heated air bin drying: Stirring devices remove dry grain from the bin floor and blend it back into the wet grain above, allowing drying of deeper grain layers without over-drying. Drying batches work best at 6 to 9 feet deep. Deeper grain greatly increases fan horsepower requirement and reduces drying rate. Fan horsepower needed to create 5 cfm per bushel with 8 feet grain depth is about 4 hp per 1000 bushels. Drying rates are similar to non-stirred heated air bin drying. More precise bin/fan airflow calculation is available with the computer program mentioned in the natural air drying section. At 6 to 9 feet deep, expect 2 to 3 days drying time per batch.
Heated air drying summary:
- Beans – 20 degrees maximum added heat.
- Corn – 120 to 180 degrees allowable temperature range
- Non-stirred drying limited to 4 feet maximum depth with 1 fan hp per 1000 bushels
- Stirred drying limited to 8 feet maximum depth with 4 fan hp per 1000 bushels
- 5 points maximum difference between driest and wettest kernels
For quick bin capacity estimates, bin diameter squared times 0.63 equals bushels per foot of depth.
Charlie Hurburgh has written some good news articles on this topic recently. Review them at
/CropNews/2009/1030hurburgh.htm
/CropNews/2009/1019hurburgh.htm
/CropNews/2009/1015hurburghelmore02.htm