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Drying High-moisture Corn Can Be Tricky

Drying high-moisture corn requires extra care.

Moisture content, airflow rates, drying temperatures and the drying method used all affect the quality of the dried corn, according to North Dakota State University grain-drying expert Ken Hellevang.

For example, corn above 21 percent moisture should not be dried using natural-air and low-temperature drying to minimize spoilage during drying. Because the drying capacity is extremely poor at temperatures below 35 to 40 degrees, little drying may be possible during late fall using a natural-air or low-temperature system.

Hellevang recommends cooling the corn to 20 to 25 degrees for winter storage and starting to dry it in early April.

“Adding heat does not permit drying wetter corn and only slightly increases drying speed,” he says. “The primary effect of adding heat is to reduce the corn moisture content. Natural-air drying in the spring is the most energy- and cost-effective method of drying.”

Corn depth in storage should be limited to about 20 to 22 feet to obtain the desired airflow rate for drying.

Turn fans off during extended rain, fog or snow to minimize the amount of moisture moved into the bin by the fan.

When drying with a high-temperature dryer, using the maximum drying temperature that will not damage the corn increases the dryer capacity and reduces energy consumption, Hellevang says. The amount of energy required to remove a pound of water is about 20 percent less using a drying air temperature of 200 F than 150 F. The typical recommended drying temperature is about 210 F.

“Be aware that high drying temperatures may result in a lower final test weight and increased breakage susceptibility,” Hellevang cautions. “In addition, as the drying time increases with high-moisture corn, the corn becomes more susceptible to browning.”

In 2008, dryer temperatures needed to be reduced below 200 F to minimize corn kernel damage. Housekeeping during drying also was critical during 2008 due to condensation occurring on the dryer, creating a wet surface for debris to accumulate. The debris sometimes reduced airflow through the dryer, reducing drying capacity and creating a fire hazard.

Hellevang suggests using in-storage cooling instead of in-dryer cooling to boost the capacity of high-temperature dryers. Cooling corn slowly in a bin rather than in the high-temperature dryer also will reduce the potential for stress cracks in the kernels.

In-storage cooling requires a positive-pressure airflow rate of about 0.20 cubic feet per minute per bushel (cfm/bu) or 12 cfm/bu per hour of fill rate. Cooling should be started immediately after corn is placed in the bin from the dryer. Dryer capacity is increased 20 percent to 40 percent, and about 1 percentage point of moisture is removed during corn cooling.

Condensation problems can be reduced by cooling the corn in the dryer to about 90 degrees before placing it in storage. More condensation occurs at cold outdoor temperatures than when outdoor temperatures are warmer.

Dryeration will increase the dryer capacity about 50 percent to 75 percent, reduce energy used by about 25 percent and remove about 2 to 2.5 points of moisture (0.25 percent for each 10 degrees the corn is cooled.) With dryeration, hot corn from the dryer is placed in a dryeration bin with a perforated floor, allowed to steep for four to six hours without airflow, cooled and then moved to a storage bin.

A tremendous amount of condensation will form during the steeping and cooling process, so the corn must be moved to a different bin for storage or spoilage will occur along the bin wall and on the top grain surface.

Costs are another big part of the drying process. A dryer that captures the heat from cooling the dry corn and a portion of the air from the final drying portion of the dryer can reduce the energy used to dry the corn by about 20 percent or more, depending on outdoor temperature, Hellevang says. Newer dryers typically have incorporated features to make them more energy efficient than older models.

Use the following formula to estimate the cost of propane for high-temperature drying: cost/bu-pt (cost per bushel per percentage point of moisture removed) = 0.022 x propane price/gal. For example, the drying cost is $0.022/bu-pt if the cost of propane is $1 per gallon (0.022 x $1). Removing 10 percentage points of moisture from 120 bushels of corn using $1 propane will cost about $26 (120 x .022 x 10).

The estimated quantity of propane needed for drying is 0.02 gallon per bushel per point of moisture removed. For example, 24 gallons of propane is needed to dry 120 bushels of corn from 25 percent to 15 percent (0.02 x 120 bushels x 10 points). This is based on 0.72 pound of water being removed per point of moisture per bushel, 2,500 British thermal units (Btu) of heat required to remove a pound of water in a high-temperature dryer and a propane heat content of 91,500 Btu/gallon.

For more information, do an Internet search for NDSU corn drying or visit http://www.ag.ndsu.nodak.edu/abeng/postharvest.htm.


NDSU Agriculture Communication

Source:Ken Hellevang, (701) 231-7243, kenneth.hellevang@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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