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Weather Could Drive Busy Fall for High-Temp Dryers

Tuesday, August 30, 2011
filed under: Harvest/Storage

It’s been a weather-crazy year around much of the Great Plains. But unlike the Southern Plains, where the issue has been insufficient rain, much of the Dakotas and Minnesota started out wet and has stayed wet. If that trend continues into the fall, one predictable result would be a lot of sunflower fields stuck with higher seed moistures at harvest.

“The forecast now (early August) is for continued moisture, which will limit field drying,” notes Ken Hellevang, extension agricultural engineer with North Dakota State University. “This is a particular concern with sunflower, because the tipped head creates a water catch basin.”

Frequent rain will limit the ability for the sunflower to dry in the field, Hellevang points out, thus requiring more high-temperature drying prior to storage.

The rate of in-field drying slows, of course, as outdoor temperatures cool down. Given typical fall temperatures in North Dakota, Hellevang says the state’s corn producers should be looking at mechanical — rather than field — drying after mid-October. “This also is typically true with sunflower,” he notes. “Outdoor temperatures drop during October and relative humidity increases — which limits both field drying and air drying in the bin.”

Move into November and the limitations of natural-air drying become even more pronounced. “The average [North Dakota] temperature for October is 50 degrees; for November, it is 30 degrees,” Hellevang points out. That temperature drop makes a huge difference in drying efficiency. Given an airflow rate of 1.0 cubic foot/minute/bushel, the estimated natural-air drying time for 17% moisture oil sunflower with October-like conditions of 47 degrees and 65% relative humidity is about 27 days. A similar air flow rate in November, at an ambient temperature of 27 degrees, would require 47 days of drying, the NDSU ag engineer explains — simply due to the cooler air’s reduced moisture-carrying capacity.

Energy efficiency of one’s high-temp dryer obviously becomes even more important as temperatures dip and humidity rises. As Hellevang has reported previously in The Sunflower, the use of heat reclaim systems in some of the new generations of dryers has provided significant savings in energy costs — 20-25% or higher.

The NDSU drying/storage specialist has developed a simple formula for growers to use to calculate the cost of energy required for drying sunflower seeds: multiply the per-gallon cost of propane by 0.037. That will equate to dollars per hundredweight of seed per point of moisture removed. (For drying corn and wheat, Hellevang uses a factor of 0.022.)

Hellevang reminds growers that lowering the drying temperature will not result in improved energy efficiency; in fact, the opposite will occur. As shown in the accompanying figure, the amount of energy required to dry corn in a conventional crossflow dryer declines as temperature increases. It’s a similar scenario with sunflower. Run the dryer, he advises, at the manufacturer’s maximum recommended temperature. But it’s equally important to not overdry beyond what’s needed for safe seed storage. That’s just going to cost more money — and heighten the chance of fires.

Hellevang has been emphasizing the importance of cleanliness, both inside and around the dryer, for many years. It’s a message that he believes bears repeating every drying season. The main danger when drying sunflower seeds, he stresses, comes in the form of fire threat from “fines” and other trash. “Any dryer that uses an open flame to heat the air poses a constant fire hazard,” he notes. “Clean the dryer, air ducts and area around the dryer at least daily. Frequently remove the collection of sunflower lint on the dryer column and in the plenum chamber, since that material can become extremely dry and be ignited during dryer operation.”

In reviewing sunflower dryer fires through the years, the same message keeps coming through, Hellevang concludes: “It’s not so much temperature related as it is housekeeping — and making sure the seeds continue flowing through the dryer.”

The big increase in corn acreage across North Dakota in recent years has driven the installation of more and more high-temperature dryers — dryers that are naturally used for sunflower and other crops as well. But the cost/benefit advantage for natural-air drying still exists — if the timing of harvest and environment allow it, Hellevang adds. “If we’re looking at sunflower seed moistures of 17% or lower, and we have good air flow on them and can get started early, natural air will work well. But if it’s a late harvest with high moistures, it’s a different story.”

Safe Storage Rules

In an article in the August/September 1979 issue of The Sunflower, then-NDSU drying/storage specialist Harvey Hirning used an intriguing analogy to underscore the importance of checking one’s bins on a regular basis:

“ ‘Once a week, go check the storage and find out what’s going on in there. It’s most important in the fall cool-down and spring warm-up, but it should be checked even in the middle of winter,’ ” Hirning stated. The article goes on: “To emphasize his point, Hirning remarks that about 135,000 pounds of sunflower are stored in a 4,500-bushel bin. Allowing for fluctuating prices, that amount of sunflower is worth roughly $13,000. ‘If you put that in cash in a tin bucket hanging in the middle of the bin, most people would spend a fair amount of time going out and checking it,’ he illustrates.”

Today, average bin size is a lot larger than 4,500 bushels; and current sunflower seed prices are much higher than what they were in the fall of 1979. But Hirning’s point remains a valid one: If an equivalent amount of cash was sitting inside that bin, you can bet we’d be checking it on a regular basis.

Here’s a recap of proper sunflower storage basics, supplied by current NDSU crop drying/storage specialist Ken Hellevang in the most recent edition of NDSU’s Sunflower Production handbook.

• Seed should be cleaned for storage. Fines tend to concentrate in the center of the bin if a distributor is not used. Since this material tends to be wetter, this area is more prone to storage problems. Also, airflow will be restricted by the fines, limiting cooling by aeration in the center of the bin.

• Oil sunflower should not be stored above 10% moisture during the winter and 8% during the summer. Nonoilseed sunflower should not be stored above 11% moisture during the winter and 10% during the summer. Sunflower can be stored for short periods in the fall at 12% with adequate airflow to keep the seeds cool.

• Aeration to control seed temperature is essential. Aeration fans normally are sized to provide 0.05 to 0.2 cfm/bu (0.15 to 0.6 cfm/cwt) of sunflower. Sunflower should be rotated between bins during the storage period when aeration is not available.

• Cooling sunflower reduces the potential for sunflower deterioration from insects and mold. Sunflower should be cooled to 40 degrees or below before or soon after it is put in the bin, and to 25 degrees for winter storage.

• Moisture and heat accumulate in the peak due to moisture migration, which results in crusting, spoilage and increased possibility of insect infestations. This can be prevented by cooling the sunflower using aeration.

• Bins should be checked initially every two weeks for moisture condensation on the roof, crusting and changes in temperature within the pile. Any of these conditions could indicate the presence of mold or insects. The sunflower should be checked at least monthly after the seeds have been cooled to about 25 degrees F for winter storage and a history of temperature and moisture content has been developed.

— Don Lilleboe
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