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Sizing up grain dryers

Some farmers are shifting from in-bin drying to continuous flow dryers to get more capacity. The trade-off may be grain quality. Manufacturers are striving to give you both. Dryer manufacturers are reporting a renaissance in sales of high-speed, continuous flow dryers. Beard, Delux, Farm Fans, GSI, Mathews and QED all report increases over previous years. In most cases, the increases are significant.

At Beard Industries, sales are up 50% from 1994. "Last year was a peak," says president Bill Beard. "And (sales of continuous flow dryers) will continue to increase as a percentage of new dryers."

Dryer buyers are either switching from drying in a bin or upgrading from a smaller continuous flow dryer. Both types of buyers are looking for the same thing: more capacity. The last surge of dryer sales was in the mid-1970s, and many existing drying systems are 25 years old or older. Since that time, farms have gotten bigger. So has harvesting equipment. Farmers need bigger dryers to keep up.

"It's not uncommon to be taking 16,000 bu./day out of the field," says Dr. Marvin Paulsen, professor of agricultural engineering at the University of Illinois. "You have to do something with that wet grain. So if you are harvesting at those kinds of rates, you steadily move into a higher-temperature, higher-capacity dryer."

As an added push, farmers are entering fields earlier to finish on time. As a result, some grain is being harvested wetter than ever before. Continuous flow dryers can handle moisture levels as high as 25 and 30%. In-bin systems can't handle those moisture levels as easily.

It's in the heat. Two things dry grain: air and heat. The higher the heat, the faster corn dries. Obviously, you can dry grain faster in a dryer than you can in a bin because you are using higher temperatures. How high depends on the dryer and the crop, but 180 degrees to 220 degreesF is typical for corn. Grain is dried in sections or columns to expose all kernels to about the same level of heat. That distribution allows for higher air flows and temperatures.

Compare that to bin drying, where grain is dried in mass anywhere from 6 to 12 ft. deep in a bin, and heat moves in a front from the bottom up. Temperatures range from no heat (natural air-drying) to around 160 degrees depending on the system. Higher temperatures would scorch the bottom layer of grain closest to the heat source.

Continuous flow dryers are categorized according to the direction in which air flows in relation to grain, according to Dr. Bill Wilcke, extension engineer, University of Minnesota. There are four types: crossflow - air blows at a right angle across perforated columns of grain; concurrent flow - air and grain move in the same direction down the columns; counterflow - air blows up the columns opposite the grain; and mixed flow, which incorporates a combination of these air flows.

The vast majority of continuous flow dryers sold in the Midwest are the crossflow type. It also is the kind most grain elevators use. Now it's time to clear up a little confusion. Descriptively, continuous flow dryers that fall under this category have many names. They are called column-type, box, upright, self-contained, free-standing, portable or stationary dryers. Their common denominator is that they dry grain in a column that is completely separate from the grain bin or storage unit. Everyone agrees the proper term to use, in most cases, is high-capacity, continuous flow dryers.

Beard, Delux, Farm Fans, GSI, Mathews, and QED, among others, make a crossflow design. All work on basically the same principle. Gas-fired burners heat the air within the dryer's plenum chamber. High-speed fans force the air at a right angle across columns of grain about a foot thick. The columns reduce airflow resistance and allow for more uniform distribution of heat within the grain as the grain moves through the dryer. "That's one of the reasons you limit column thickness to 12 or 14 inches," Wilcke says. "If the column gets too wide, the moisture and temperature variations across the column get too big. The narrower the column, the smaller those differences are."

The point to keep in mind when buying a continuous flow dryer is that they aren't all the same. You need to know what you are getting because each type has a different minimum and maximum drying temperature range. Run it too hot and you'll damage the grain. The kernel itself should never get much hotter than 140 degrees for milling. Any hotter and it will lose starch extraction value or suffer stress cracks, which could result in a higher number of broken corn and foreign materials (BCFM) at the elevator. "With a concurrent flow dryer, you can turn the drying air temperature up to 300 degrees and the corn never gets that hot," Wilcke says. "But if you tried that with a counterflow dryer, the kernel would reach about 300 degrees. So if 140 degrees is your magic kernel temperature, that helps you figure out how high you can set the temperature on that dryer."

The temperature you choose within that range will depend on your goals. For maximum capacity, set it for the recommended maximum, Wilcke says. For maximum grain quality, set it for the minimum within that range.

Manufacturers of continuous flow dryers have made major improvements to boost grain quality while maintaining capacity in the past five to 10 years. These include: Automated controls. With modern continuous flow dryers, loading and unloading are fully automated. Once you set the drying temperature and target moisture level of the grain, you can basically walk away. With older models, you had to periodically check moisture content as grain was being dried and manually adjust the speed of the metering rolls that control the flow rate through the dryer, according to Dr. Charles Hurburgh, extension agricultural engineer, Iowa State University. "Now, moisture sensors automatically estimate the moisture content, and a computer makes those adjustments on the fly." The wetter the grain, the slower it moves through the dryer. The end result is less baby-sitting and pinpoint accuracy of final moisture. Many modern dryers feature this level of automation. For example, GSI's new software called Watchdog lets you monitor moisture, temperature and dryer status from your office computer. Data are transferred through your telephone line. If the dryer shuts down, an alert appears on your computer screen.

Better airflows. Improved air flows allow for lower drying temperatures. Today's crossflow dryers have bigger fans, larger drying chambers and "grain turners," which turn grain as it moves down the column to distribute heat more uniformly. Before, when grain fell straight down the column, the side closest to the heat source would get hotter than the opposite side because the air comes from one direction across the column. "A grain turner takes grain on the inside of the column closest to the flame and inverts it, or puts it on the outside, and mixes it around," Hurburgh says. "That way you don't have some grain on the inside getting very dry and some grain on the outside not so dry."

Better energy efficiency. Much of the heat generated by earlier-model dryers was lost to the atmosphere. Modern designs recapture and recycle that exhaust to improve energy efficiency and lower fuel costs.

Should you switch? The decision to switch from in-bin drying to a high-temperature self-contained dryer basically comes down to capacity. How many bushels per year do you need to dry?

"As far as a magic crossover number, there isn't any," says University of Illinois' Paulsen. But he says on average, when farmers produce more than 100,000 bu./year, they start to consider continuous flow dryers.

Where you farm can also dictate drying method. For instance, Paulsen says in his state of Illinois, natural air and low-temperature in-bin drying is common. In Michigan, almost all systems are continuous flow because of higher moisture and shorter growing season. "Farmers in Iowa often are done harvesting before Michigan farmers have even started," says Dr. Fred Bakker-Arkema, professor of agricultural engineering at Michigan State University. "So we must turn it around much faster and at a higher moisture content." As a rule, the further north you are, the more you rely on heated air drying.

Another consideration is cost. Continuous flow dryers cost more than a drying bin. The dryer itself may run as high as $100,000. To know whether you can justify it, divide the total annual cost by the number of bushels per year you plan to dry, advises Minnesota's Wilcke. That will give you a cost per bushel. Do the same for your current system for comparison.

When buying a continuous flow dryer, you'll need to specify whether you want a heat-and-cool or an all-heat model. The former not only dries the grain but cools it once it is dried in a second chamber within the dryer. An all-heat unit dries only and requires that you dump the grain hot into a grain bin with a perforated floor and a fan for cooling. Heat-and-cool units cost more but are less hassle. All-heat units, although more work, give you almost double the capacity because you are tying up less dryer time by transferring the grain out of the dryer sooner to make room for more wet grain.

Alan Brutlag, a farmer near Wendell, MN, converted an old heat-and-cool Butler-Kan-Sun dryer to an all-heat unit to increase drying capacity. He stopped the dryer from cooling by tinning the inside of the cooling chamber. By adding a full dryer floor, a 12-hp axial flow fan and power sweep, he converted a standard 12,000-bu. bin into a wet holding bin. He now uses the dryer to dry corn down to 18 to 20% moisture, after which he dumps it hot into a lineup of six 10,000-bu. bins with full floors and 10-hp axial flow fans. There, he lets it steep at 125 degreesF for six to 12 hrs. Afterward, he turns on the fans to cool it to outside air temperature. For every 10 degrees of cooling, he removes .25 pints of moisture for a total of 21/2 pints. Any moisture beyond that is removed by natural air drying. "Because of combination drying, I am able to unload grain from the dryer at 18% moisture instead of 15% and increase my capacity from 400 bu./hr. up to 1,000 bu./hr.," Brutlag says.

He had to add an oil cooling system to the gearbox to keep it from overheating. "At the end of the season the corn is drier, and I finish off by using the wet holding bin to natural air dry the last bushels of corn."

Depending on your current system, a continuous flow dryer might require additional storage and handling equipment than what you're using now. Basically what you'll need are a wet holding bin to hold grain awaiting drying, bins with false floors for cooling or storage, and conveyors to transfer the grain to and away from the dryer. Bins previously used for drying can be converted to storage or wet holding bins. Wilcke knows of farmers who are converting 10,000-bu. storage bins for wet holding. "A few years ago, people would have thought that size was ridiculous. But these days, I don't think that's out of line."

Size to fit. To know what size continuous flow dryer you need, estimate how many bushels per day you will harvest and how many hours you want to run the dryer in a given day, says Richard Zinke, general sales manager with Mathews. For example, if you are going to harvest 15,000 bu./day and you run the dryer 24 hrs./day, then divide the 15,000 by 24 which gives you a capacity of 625 bu./hr.

Most continuous flow dryers used on farms have capacities anywhere from 100 bu./hr. up to 1,000 bu./hr., depending on initial moisture content. Some continuous flow dryers can be stacked one on top of another to double or triple capacity.

The highest-capacity continuous flow dryers are called tower dryers. These dryers have grain columns more than 30 ft. high to achieve the capacities required by commercial elevators. As farms get bigger, farmers may need the same capacity. "A lot of farmers in certain areas have crossed into that small commercial level on their farm," says Don Nicol, vice president of drying systems, GSI. "So now we are seeing tower dryers sold on farms."

Most manufacturers of continuous flow dryers make a tower dryer. GSI claims to make the largest in the industry at 10,000 bu./hr. Some market them under different names. For example, Farm Fans markets its tower dryers under the Zimmerman name, and Mathews markets its tower dryers under the Kan-Sun name, formerly owned by Butler.

Tower manufacturers that before sold only to commercial elevators are now finding a niche with large farms. Examples include Delux Manufacturing out of Kearney, NE, which makes both stacked and tower continuous flow dryers, and QED Dryer Sales out of Rockford, IL, maker of modular tower dryers (circle 224). "We fit well with the young farmer who is operating a few thousand acres," says Steve Morreim, president of QED. "Our dryers are modular so we can expand them in hours."

Steve Schultz, sales manager with Delux, says that farmers start to look at tower dryers when the farm size approaches 10,000 acres and need drying capacities of 2,000 bu./hr. and up. The size of your farmstead may also dictate need. "If you are filling with a leg system and have limited ground space, a tower may be your only option," he says. "You need to build up versus out."

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