Grain drying turned upside down


Use fans only at night | Throw what you thought you knew about drying grain out the window

MELVILLE, Sask. — Farmers can dry their binned grain more quickly by running aeration fans only at night, new research has found.

That contradicts decades-old wisdom that suggested fans should run continuously until grain is dry.

In fact, that practice can actually damage grain by heating it and adding water to the kernels, said Ron Palmer, a retired University of Regina professor, who is best known for developing auto steering.

About 18 months ago, Palmer began looking at data gathered in 2007 in Saskatchewan at the Indian Head Agricultural Research Foundation. The information recorded bin temperature and relative humidity hourly, but it had never been analyzed.

“It shocked the hell out of me,” Palmer told farmers gathered at an IHARF seminar. “This is too weird to make up.”

The combination of temperature, relative humidity and grain moisture are all at play, but Palmer said it comes down to the basic idea that drying is occurring if more moisture is leaving the bin than entering.

“By using a black box approach, we don’t really care about all the complications that are going on inside that bin,” he said. “The only thing we’re concerned about overall is are we taking water out of that bin or not.”

The temperature determines how much water the air can hold; relative humidity is how much moisture is in the air.

For example, at 27 C the air can hold 4.3 kilograms of water; at 50 percent relative humidity it is holding 2.15 kg of water.

Palmer said these numbers are well established in psychrometric charts.

But cold air has less capacity to hold water. So a higher relative humidity, say on a cool night, actually can mean less water in the air than during the hot day.

Farmers are not doing themselves any favours by turning on the dryer during a hot day, thinking they are taking advantage of the heat, Palmer said.

“Turns out it’s backwards,” he said.

The moisture carried in that hot air collides with the cold grain and is released into the grain.

At night, the air is both cooler and drier so more grain drying takes place.

Even on a hot, humid summer night, the amount of water in the air is actually small, Palmer said.

When he plotted temperature and grain moisture on a chart, he found the first day of continuous drying removes the most water. But after that, drying during the day is only delaying the process.

In one example, a fan was turned on in the afternoon and began taking out about 77 kg of water per hour, according to the psychrometric charts.

The rate declined to 23 kg and then, after 20 hours of continuous drying, water started going back into the grain.

His charts show a curve flowing up and down over days of drying.

“We’re putting water back in by continuous drying. Pounds and pounds of it,” Palmer said.

Eventually, the grain does dry, but it takes a long time.

In another example, a fan turned on at 1:30 p.m. removed 446 kg of water by 9 a.m. the next day. Over the next five days, net removal was 386 kg.

“We actually removed more water in the first cycle than we did running it four or five days,” Palmer said.

He advised farmers to run their fans only at night and said supplemental heating is not good.

Chad Skinner, who farms north of Indian Head and is on the IHARF board, volunteered to try the new method.

He measured average moisture in his bins, left one bin on continuous drying and used the night-only method on several others.

He tried the system with wheat and lentils at about 18 percent moisture. He dried the wheat down to 13.6 percent and the lentils to 14 percent.

“On average, on a 5,000 bushel bin, we probably dried the wheat three days faster than running continuously,” Skinner said.

He figured he saved 100 hours of time on his 7.5 horsepower fan, at about 50 cents an hour, for per bin cost savings of about $50.

“If you take that over, say, 20 bins, it adds up ,and over a number of years it will add up, not to mention the wear and tear on your equipment,” he said.

Skinner also said that only about half of his on-farm storage is aerated. A three-day time saving could allow him to rotate other grain in and out of those bins for drying.

He said the biggest challenge was psychological.

“When you take 20 percent moisture grain and put it in a bin at harvest time and it’s 35 degrees outside and you’re not turning that fan on, it’s pretty hard to get over that first initial shock,” he said. “But we didn’t have any issues in any of the grain we pulled out.”

Skinner said he turned the fan off in the morning when he checked the bins and turned it back on at night when he brought the last load in from the field.

“I don’t think it’s going to be very hard to convince people to switch to this way,” he said.

Palmer is fine-tuning a scientific paper on his research for peer review, but he urged farmers to jump on this research now.

“I was really surprised at how much water we were putting back into the bin,” he said. “We were not only wasting electricity. We were actually doing damage putting water back into the bin and heating the grain back up. That’s not a good situation.”

5 Responses

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  1. Scott Renze on

    Is the above article referring to air dried grain and or with the assistance of LP heated air. I have air and low temp air dry bins. Is your concept similar for all drying types?

    • Excuse me if I am wrong, but I did not see any where in your article that adressed the settling affect that grains have when your dry grain with areation. I think that you will find that when you put grain into a bin with a high teen moisture content and bring it down to dry you will find that the affect of settling will cut down on the air flow considerbly. Slowing the removal of moisture. We have found that flipping your bin, or removing the grain and putting it back in the bin, after the first 48 hrs will enhance the flow back to the point where you will remove the moisture faster.

  2. Dave Taylor on

    One thing one must not forget, is that the fan must be turned on every night or a moisture front will form and a hot spot will be created as the wind will find the easiest way to get to the top, by passing some of the grain in the middle of the bin , which will cause part of the bin of grain to be spoiled when it is removed .

  3. Elmer Holm on

    This is the best article on the subject that I have ever read and makes the most sense.
    Thanks for the information.

    Elmer

  4. farmingsk on

    The situation is a more complicated than this article makes it out. It really comes down to relative humidity (RH) of the air flowing through the grain. For each type of grain, there is an “equilibrium moisture content” for each air relative humidity. If the air is below that RH then the seed will dry otherwise it will absorb moisture.

    The point raised by Ron Palmer is very interesting. If the air coming into the fan is colder than the grain then it will warm and end up with a lower RH. If that RH is below the equilibrium level for the seed then it will dry. However, if the cold air doesn’t warm enough to get below the needed RH, the grain will not dry.

    The situation is even more complicated when you consider that grain temperatures and moisture levels are not even throughout the bin. The lower part of the bin will be cooler and thus warm the air less. However, the air picks up moisture as it moves upwards.

    I’d be interested to see the paper. I think a simple fan control system using grain temperature, air temperature, and relative humidity could do quite a bit better job than manual control.

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