Drying and storing tough grain will likely be commonplace on prairie farms this winter in the aftermath of snow and rain that swept across large swaths of the region in early October.
Batch and continuous grain dryers are the most effective way to dry tough grain, especially when it’s cold out, but they are the most energy intensive method and can be cost prohibitive as well as labour intensive.
Natural air drying uses fans to pull moisture out of aeration bins and is a popular and cost effective method of drying grain. Unfortunately, natural air drying requires weather conditions that may already be behind us this fall.
“You could have dry air passing through your grain, but if the air and the grain is below 5 C, you’re unlikely to get significant drying,” said Joy Agnew, a grain storage expert at PAMI.
“At this point, supplemental heat is your friend.”
Using supplemental heat with natural air drying systems drastically enhances the air’s capacity to dry because the air’s capacity to hold the moisture depends on its temperature: the warmer air is, the more water it can hold before it becomes saturated.
Intuitively, -5 C air with 90 percent relative humidity is too wet with which to dry grain.
However, relative humidity is just a measure of how much water is in the air versus how much water the air can hold. Air that is -5 C can’t hold very much water before it becomes saturated, Agnew said.
“Now, if you take that air and you heat it up to 15 C, you’re drastically increasing its capacity to hold moisture, and it’s not holding that much to begin with. So now you have this huge amount of space to take up more moisture,” Agnew said.
With supplemental heating, it doesn’t matter what the humidity is outside because once the air is heated up by 10 or 15 C, it becomes the equivalent of a warm fall day for drying.
Agnew said a rule of thumb when using supplemental heat to dry grain in a bin is that growers shouldn’t increase the temperature of the incoming air by more than 10 to 15 C. Nor should the air going into the bin be heated to any hotter than 15 C.
The Canola Council of Canada recommends not increasing the air temperature by more than 10 C when drying canola with supplemental heat.
Late in the fall, a 10 degree in-crease of intake air temperature may not be enough for significant drying and may instead just cause higher temperature in the bin and a greater potential for spoilage.
“The other rule of thumb is for every 10 degree increase (of air temperature), you’re effectively cutting the relative humidity in half,” Agnew said.
Producers also have to make sure they have at least .75 cubic feet per minute per bushel of airflow for drying with supplemental heat.
“A much lower airflow rate, like .1 or .2 CFM per bushel, is perfect for aeration and cooling only.”
But with a lower airflow rate “you don’t have enough air movement to actually pull the moisture out of the grain. So now you have tough grain that you’re heating, and that is recipe for disaster.”
Supplemental heating for grain drying is a tried and true method of drying grain that has been around for decades.
Growers have purchased or built biomass boilers to heat the intake air with radiators on their bin fans, which are fueled by biofuel such as wood, corn, screenings and bales.
Other growers have simply run water lines from their existing biomass boiler on their farm to a radiator installed on the air intake of their bin fans.
“If it’s properly designed and controlled, any sort of heat source is going to work. Whatever fuel that you have access to that is the most economical and easiest for you to work with, go with it,” Agnew said.
The trouble with using biomass for supplemental heat when drying grain is that it takes a large capacity heater to properly heat the intake air on a bin fan, and it may prove to be labour intensive to keep the boiler stoked.
“You’re looking at a pretty large capacity heater, like 100,000 BTU per hour,” Agnew said.
“Luckily, it is possible to rent dry air units. There are rental companies like Handy Rental Centre. They have these huge diesel or natural gas heaters for the construction industry that aren’t being used this time of year, and they are ideal. They have the exact capacity required for supplemental heating in these bins.”
Growers can also purchase supplemental heating solutions from companies such as DryAir Manufacturing Corp, which has been selling grain-drying systems for 20 years.
“What we tell guys is what we’re doing is creating a perfect aeration day 24 hours a day, no matter if it’s raining or snowing or what it is,” said Myrlen Kleiboer of DryAir, which is based in St. Brieux, Sask.
“The system runs 24 hours, and typically you’ll remove a point a day with the right type of air flow.”
The DryAir heaters are powered by natural gas, propane or diesel, and a glycol water solution is used to transfer the heat through water pipes to a radiator mounted on the intake side of an aeration fan.
“The one we primarily sell for grain drying is 1.2 million BTUs. If you take wheat, for instance, it will dry about 160,000 bushels in about 30 days,” Kleiboer said. “You’ll typically dry grain anywhere from four to 10 cents per bushel.”
The DryAir system is meant to supply heat for up to six bins at a time.
“The size of the bin doesn’t matter,” Kleiboer said.
‘It’s more important the size of your fan to the size of the bin that you have because it’s the airflow that is the determining factor on how long or how well it works.”
Some operators of the DryAir heating system mount the boiler on a trailer so they can move it to different yards, while others run water lines to their bins from a permanent placement of the heater.
Producers have also run water lines to farm buildings from their DryAir for heat.
“You’re not going to just buy it for heating, but if you have it there already for drying grain, why not use it for other things too, when it’s needed,” Kleiboer said.
If warmer temperatures do return this fall, growers using natural air drying should use caution if their grain is already cool because the air’s capacity to dry also depends on the grain’s temperature.
Grain that is colder than the air temperature will take a few days of running the fans to warm up the grain, during which time moisture may be added to the grain.
“If you already have it (grain) down to minus one or two, you’re likely not going to be able to dry it using natural air. You’re going to need either heated air or a really long stretch of nice weather.”
She said she urges growers to use bin-monitoring technology, especially when dealing with tough grain.
“The temperature cables are an almost must, and I would argue they need more than what the manufacturers are saying.”
Manufacturers claim one cable down the centre in an 18-foot diameter bin is sufficient, but localized hot spots can form and they have to grow considerably before the sensor actually detects it.
“We did a study here to see how close a hot spot has to be to a sensor before it actually picks up a temperature change, and it has to be within a foot,” Agnew said.
“You can have sensors down the centre of the bin, but you are only monitoring less than one percent of that bin.”
She said it is possible but dangerous to temporarily store tough grain in bins by running fans to cool grain to prevent spoilage.
“I’ve heard producers say they also turn it (tough grain) frequently throughout the winter, even if they do get it cold, and they will run the fan for a day or two after they turn it to chill it down again,” Agnew said.
“I’ve heard it has been done, but I’ve heard the other side of that also where bins are lost.”
Research shows it’s possible to store wet grain in grain bags, as long as the bags are properly sealed.
“The microbial activity that causes spoilage is aerobic activity, so it needs oxygen. So if the bag can be sealed, you can starve those microbials of oxygen, they won’t spoil the grain,” Agnew said.
However, she also said storing wet grain in bags isn’t really a realistic option because it is difficult to get and keep an airtight seal in real- world conditions.
It is important to remember that natural air drying and aeration is not the same thing, Agnew said.
Aeration uses a low airflow rate and results in cooling or conditioning of the grain. In other words, aeration evens out the temperature distribution within the bin and can equalize the internal bin temperature with the outside temperature.
For natural air drying, you need enough energy to pull the moisture out of the grain and take it out the top of the bin. PAMI recommends .5 to one cubic foot per minute per bushel for natural air drying, and .75 to one cubic foot per minute per bushel for natural air drying with supplemental heat.