Posted on October, 24, 2024 at 02:32 pm
With short seasons and what seems like increasingly unpredictable weather patterns these days, many growers now routinely using grain drying systems to add a little time to the harvest window. But for those considering an investment in a grain drying system, how do you choose which one is right for your farm?
Producers can opt for aeration systems, in-bin drying or dedicated grain drying systems. Each of those options has its own capital costs, advantages and disadvantages.
“It comes down to understanding what you’re trying to accomplish and using the right tool for the job,” says Lorne Grieger, director of technical sales at the Prairie Agricultural Machinery Institute (PAMI).
When grain needs only a small reduction in moisture, aeration bins used without additional heat could do the job. But there is a difference between just keeping grain cool and actually drying it down. A key difference is in the airflow rates.
“Aeration we would define as cooling only,” he explains, “but it doesn’t have the airflow rates that would be effective for drying grain inside a bin.”
When using aeration only for cooling, current airflow recommendations are 0.1 cubic foot per minute (c.f.m.) per bushel. But that jumps to a minimum of 1.0 c.f.m. per bushel for natural air drying systems.
“They are two different ways of doing things, and how you set up equipment is different,” he adds.
To ensure airflow rates are adequate, Grieger cautions that producers need to understand what their fan systems are capable of and how the contents of the bin could affect airflow rates.
“Grain like canola has a lot more back pressure on the fan,” he says. “You may not get the airflow you expect. You may potentially have to limit the amount of grain you have in the bin.”
A pressure gauge on the fan plenum can help in determining actual flow rates.
Ambient air conditions need to be warm and dry to accomplish natural drying without additional heat.
“It depends on what the weather is at the time to what you can accomplish in the grain bin,” Grieger says. “Adding heat allows you to turn a cool damp day into a warm summer day.”
Grieger points to a three-year Alberta study he was associated with that took a look at what was possible with adding heat to in-bin systems.
The study’s intent, he says, was to understand the details of the drying rate for in-bin systems that aren’t dedicated dryers and that apply lower heat to the grain — as well as the capacity of an in-bin system compared to a dedicated dryer. “They are two different ways of doing it and two different options.”
The study looked at the efficiency of adding indirect and direct heat to a bin. Direct heat uses a heater venting burned exhaust gases directly into the bin and out through the grain mass on top. An indirect heater uses a heat exchanger, and exhaust gases don’t go directly into the bin.
The published results of the study found an advantage to the indirect system.
“Although the indirect fired systems have a slightly lower combustion efficiency,” it reads, “the supply air has a lower relative humidity (combustion gases are exhausted) resulting in an overall lower specific energy when compared to direct fired systems. Therefore, the indirect fired systems condition grain more efficiently with shorter run times and have on average 65 per cent of the fuel consumption of direct fired systems.”
Grieger cautions that when using in-bin systems, heating temperatures that are too high can damage grain.
“Because of how they’re configured you want to manage your inlet air temperatures well. And recommendations are 15 to 20 C above ambient temperature before the risk of damage occurs. There are limitations of how much additional heat you want to put into the grain bin mass as a whole as part of that process.”
While in-bin systems provide a relatively low-risk way to dry down tough grain, the risk of spoilage goes up with the increased moisture content of the grain. Anything in the “damp” category would need to go through a dedicated drying system to avoid that problem.
“If your grain is damp you want to use a dedicated dryer system,” he says. “It’s a lower-risk approach to making sure you get the grain dried down before spoilage compared to putting it in a bin. There are limitations on the in-bin systems.”
Dedicated drying systems, with increased control and the ability to monitor results, provide options for speeding up the drying process, allowing for drying at higher rates.
“The advantage of a dedicated drying system is to minimize risk and allow drying to happen on a timely basis, compared to the in-bin system,” Grieger says.
So when growers consider which type of drying system to invest in, it really depends on their anticipated needs. How wet will the grain be when it comes off the combine? That will be a prime consideration.
“It depends on your growing conditions and management strategy,” Grieger says. “If you’re in the damp range, you definitely want to use a dryer system. If you’re tough then you can dry down in bin.”
The effectiveness of using natural air to dry grain is very dependent on the environmental conditions at the time. Knowing the relative humidity and temperature of the ambient air is key in determining if unheated airflow can help reduce the moisture content in stored grain.
PAMI has published a guide on its website to help growers determine when they would see a benefit from using natural in-bin air drying.
In this example, if the goal is to dry wheat down to 14.4 per cent moisture content, then all the environmental conditions in the red shaded area seen above would help achieve that.
If the relative humidity remains at 60 per cent and the temperature at 10 C, then grain would eventually dry to 13.6 per cent, as shown in the red circle.
PAMI’s website contains several information pages with expanded details on grain drying. They are listed under the “Resource Library” tab.
Source: Grain News