Dry Is Good (But Not Too Dry)
Monday, September 1, 2008
filed under: Harvest/Storage
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With North Dakota’s corn acreage having doubled since 2002, it’s not surprising Ken Hellevang has been getting considerably more phone calls on corn drying and storage — and fewer on sunflower. But a lot of Northern Plains sunflower seed still goes into on-farm storage after harvest, and the North Dakota State University extension ag engineer says it remains a good idea for ‘flower producers to regularly review their drying and storage strategies. That’s especially true, he adds, given the current levels of energy costs and commodity prices.
Some years ago, Hellevang published a table estimating the energy costs for drying sunflower in a high-temperature dryer. The highest propane price listed in that table was 90 cents per gallon; the highest fan electric rate was 7.71 cents per kilowatt hour; the highest electric heat rate, 3.86 cents per kWh. Today, the average gallon of propane ranges between $1.80-$2.80. “Electric rates probably average around $0.07 per kWh, with a range of 0.06 to 0.09,” Hellevang notes. The average electric heat rate in North Dakota (off-peak basis) is around 0.03 per kWh. He equates a $0.03 electric rate to $0.70 propane, while $0.08 would rank with a $2.00 propane price.
Rather than printing more tables to keep up with ever- changing propane costs, Hellevang developed a formula that growers can use to easily calculate the cost of energy required for drying sunflower seeds: Simply multiply the per-gallon cost by 0.037. That will equal the dollars per hundredweight of seed per point of moisture removed. (For corn and wheat drying, he uses a factor of 0.022.)
With the ever-increasing size of farms, the days of the standard free-standing batch dryer are long gone. The capacity of many of today’s on-farm drying/storage systems is equitable to that of some commercial elevators of a couple decades ago. “There are a lot of farmers buying [high-temperature] grain dryers that will dry 500 to 1,000 bushels of corn per hour,” Hellevang points out. “And for many North Dakota farmers, a ‘small’ bin today is one 36 feet in diameter; a lot of 42- and 48-ft diameter bins have gone up.”
Energy Efficiency & Dryer CleanlinessRegardless of dryer size, operating the unit for optimum energy efficiency is more important than ever. And that does not imply you’ll save money by lowering the drying temperature.
“A lot of people have the idea that if we turn down the heat, it’s going to be more energy efficient — for example, going from 200 degrees down to 150,” Hellevang says. “Actually, it’s the opposite.” The amount of energy required to dry corn in a conventional cross-flow dryer goes down as temperature increases. It’s a similar story with sunflower. “So one thing that’s going to make the most efficient use of energy is to run the dryer at the maximum recommended temperature,” the North Dakota ag engineer advises.
One concern with sunflower is its high oil content. Growers obviously don’t want to dry at a temperature that could impact the seeds’ oil quality. NDSU’s maximum recommended temperature for sunflower is 200 degrees in a continuous flow dryer. “You’d have to get well above 200 before oil quality is affected,” Hellevang says. “But again, if we’re running at just 150 or 160 degrees in a continuous flow dryer, we’re sacrificing energy efficiency.”
Back in the 1980s, many sunflower producers tended to lower drying temperature as a way to reduce the risk of fires. Hellevang examined a number of insurance records for units that had caught on fire while drying sunflower. The records documented how the dryer was operated, where the fire occurred and other relevant items. “I found there was no correlation between drying temperature and fires,” he recounts. “But there was a very definite correlation between fires and dryer cleanliness.”
That brings the North Dakota ag engineer to a point he has been emphasizing for a long time: the critical importance of good housekeeping with a high-temperature dryer — particularly when drying sunflower. As in a combine, the accumulation of ‘fines’ coming off sunflower hulls and sticking to a dryer poses a real fire threat. “We need to keep that dryer clean,” Hellevang stresses. “Pay attention to spots where seeds may get hung up. Make sure you get a complete unload so we’re not leaving in seeds that then become overdried.”
The downsides of overdrying are well known: First, there’s the increased risk of fire; second, shrink loss if the moisture falls below 10%; and third, the extra — and unnecessary — energy costs incurred. “I tell farmers ‘you lose two ways’ by overdrying,” Hellevang remarks. “You spent the money to dry, and then you end up with less to haul to market” than what the market pays for.
Natural Air / Low-Temp DryingNatural air/low-temperature drying is, of course, utilized successfully by many sunflower producers in lieu of a high-temperature system. It’s an especially good fit for High Plains growers with their warmer and typically drier fall conditions. But Northern Plains producers who tend to harvest their sunflower a little earlier also reap the benefits of a natural air system.
It doesn’t work well, however, for northern growers who end up harvesting in late October or early November. “I’ve frequently watched the pattern in North Dakota where the sunflower is drying down and everything is looking great in early October; then we get some rain or snow — and all of a sudden sunflower that was at 12 or 13% moisture is now sitting at 20,” Hellevang observes.
“With a natural air system, sunflower at 15% is a ‘comfortable’ moisture level,” he adds. “When you get to 17% or higher, you need a lot of air flow.” With oil-type sunflower at 17% moisture, “we really need an air flow rate of 1.0 cfm per bushel,” Hellevang advises. “Then you’re looking at about 27 days of fan time (under ‘typical’ North Dakota October conditions) to get it dried down. If you go at 15%, I encourage growers to look at about 0.75 cfm per bushel — and we’re still looking at about 30 days.”
It takes roughly double the fan horsepower to go from 0.75 cfm up to 1.0 — which is why Hellevang is not very keen on natural air drying for sunflower that’s above 15% moisture, especially later in the fall. “What works very well in October doesn’t in November,” he states. “The earlier we can harvest and get that drying process started, the more efficient we’ll be.”
Moisture TestersStill waiting for that “magic bullet” when it comes to eliminating the moisture rebound complication with sunflower seeds? So is everyone else.
“Even the expensive farm meters are still working off an electrical measurement, and that measurement is very much affected by where the moisture is within the seed,” Hellevang explains. “It’s much more influenced by the moisture near the surface; so the hull can indicate that the seed is actually dry, whereas the true moisture is higher.
“That’s where the rebound is coming from: it tends to measure the hull and not the kernel.”
The near-infrared (NIR) testers found at commercial elevators minimize the difference; but the cost of such units means the average farmer is not going to own one. So Hellevang’s advice is quite similar to what it was 10 or 15 years ago:
1) Check the seed moisture with your meter, place the sample in a sealed container, and then recheck it at least 12 hours later. By then the moisture will have equalized throughout the seeds, and you’ll get an accurate reading.
2) Review your meter operator’s manual. “Understand the degree of accuracy, understand the recommended testing procedures — and to get an accurate reading, I still recommend that the sample be at the same temperature as the meter.” If you have a cold sample and the meter is at room temperature, “there will be some variability.” All meters have a minimum temperature at which they’re accurate, Hellevang adds. That information should be in the operator’s manual.
3) When it comes to discounts, of course, the elevator’s moisture reading is the one that really counts. “The easiest way for the farmer to calibrate his own meter is to take a sample, check it, take the same sample to the elevator, check it there — and then compare the readings.”