“When looking at grain drying — and I'm going to focus on corn, mostly — there are several things to consider,” says Arkansas Extension agricultural engineer Dennis Gardisser.
The first thing to consider is air quality. “How are we drying? What causes the grain to dry? The answer is the quality of the air, how dry it is, and how much we can push through the grain.”
To measure this Gardisser uses a ‘sling psychrometer,’ which contains a wet bulb/dry bulb and gives readings of the temperature and relative humidity. That tells the quality of air and how much moisture the air can absorb when it is pushed through grain.
Which is best?
A typical on-farm situation, particularly if rice is involved, is just a bin with a dryer on it. “There's a centrifugal fan and a dryer or some type of heating mechanism. That allows the air to be conditioned and is fine for corn that you're not worried about moving too quickly,” says Gardisser, who spoke at the Arkansas Agricultural Expo in Forrest City on Feb. 7.
But if a farmer needs to move corn through when it's really moist, he needs to do some different things, says Gardisser.
“When looking at fans, what's important? We want to move a lot of air. We've got vane axials and centrifugals. Which is best to move air? If you're moving very much and have deep grain, the vane axial isn't the way to go.
“If I was buying a fan, I'd purchase one with larger diameter blades. That's the most efficient. What about a vane axial? — A vane axial can't work against very much head, so if your grain is very deep, you won't be moving very much air through it.”
In looking at 10-horsepower systems and comparing the vane axial and centrifugal systems, they cost the same amount of money to run, says Gardisser. But even with very light pressure, the vane axial will move only about half of what a 36-inch centrifugal fan will.
“When we're moving grain, we need to get the corn in and out fairly quickly. You need to be able to get the bins unloaded fast. If you want to unload a typical bin system, if the center auger is running, all you need to do is flip on motor A, B, or C. Or you can run all three if you want.”
The grain pump system is a newer setup that allows quick grain movement. It takes a center leg out and the pump runs through and over the tops of bins. That allows a farmer to go into any bin quickly.
If a farmer is cutting 150- to 200-bushel corn, he can fill up a bin per day pretty fast, says Gardisser. If that's the case, he won't have the fan capacity to handle the load if it's all pushed into one bin.
“You'd be a lot better off putting a third in bin A, a third in bin B and a third in bin C. That might allow quick drying because there's three times the air running through it. Tripling the amount of air, triples the quickness of drying.”
Gardisser says a drying system in use at a state prison uses a leg. “The leg isn't really tall. What they do is use lateral augers on bins that are in line. That way they can go into any bin or come out of one by simply flipping a switch.”
Another type of system, a circular setup, is very unmanageable in terms of getting grain in and out. Farmers usually need a pit in the middle and workers on site to move the auger around and position it over the bins.
“What will you do if you're cutting and everyone is busy? Usually, that means the auger stays at one bin until it's full and then it gets moved. That isn't efficient.”
With corn, farmers normally use some sort of stationary dryer, says Gardisser. Typically, workers feed grain into the backend and it comes out the bottom.
“What does the switch at the top do? It just keeps the system full. What you do is set the moisture level at the bottom. As grain comes out the bottom, more is fed into the top.”
In regards to holding bins which are dumped into as harvesting machines come out of the field, Gardisser says farmers need about a day's worth of holding capacity. That way when the combines shut down at night, the system keeps going. About every 30 minutes a load can go into it.
Spread the grain
One of the things you must do with any grain system, is when using a bin, keep the grain spread out. You can't pump air through grain with a lot of chaff, dirt and small particles in it, says Gardisser.
If you allow the grain to cone-up in a bin, the whole kernels roll down the side and situate along the outside edge. The trash and smaller bits stay in the middle. When you start drying, the avenue for air travel will be on the outside, The middle will be too clogged up for air to get through. “You'll pump and pump and not dry the middle down.”
If a farmer is drying in a bin and wants to hurry the process along, should he use a stir-all? Gardisser says the answer is yes. Say a farmer is wanting to sell corn at 15.5 percent moisture. The air he's shooting through it is 12 percent moisture. The cost of that is almost 6 cents of energy per bushel. It costs him another 10 cents per bushel in extra shrinkage because he can't sell that amount of water — that's 3.5 percent loss. Added all up, the farmer is losing about 15 cents per bushel in over-drying.
“If you use a stir-all and mix and blend the grain, things work better. You have to be a bit careful with rice, but corn works well. Just on one 10,000-bushel bin-load, you'll save over $2,000. That stir-all pays for itself pretty quickly.”
It takes energy to dry grain and farmers must run the motor. But if dry air hits the area like it did last year, pay close attention, says Gardisser.
“I went out in the field last year during corn harvest and measured moisture at 9 percent. That was before any heat was applied at the bin. In that case, don't turn the heater on, just the fan.”