Air SupplyPosted in: Technology By John Dietz September 30 2014
Shooting air horizontally through grain in storage appears to be faster — and cheaper — than standard vertical aeration for cooling and drying.
A new trend in grain drying known as cross-flow aeration appears to be picking up steam across the Prairies. If the outcome of a handful of farm trials is any indication, this novel Canadian technology may make aeration floors look very dated, very fast.
Gavin Green, who farms near Portreeve, Saskatchewan, installed a horizontal flow drying system called CrossFlow into two new 50,000-bushel bins that stand 65 feet tall. Each bin has one 15-HP fan.
Green filled the first bin with durum wheat during hot, muggy late summer weather. It was a bit cooler when he filled the second bin with chickpeas.
Both products needed to be cooled and kept dry. It was an impossible job for a traditional aeration floor and natural air drying (NAD). Moisture would gather at the top and eventually block the air flow — that is, if the fan had enough power to overcome static pressure.
But during his cross-flow experiment, Green was pleased to see that the air was running cool and dry after just three or four days, in both bins.
“I’m pretty happy with it,” he asserts.
The two tall bins have six roof vents. Green checked the vents after he turned on each fan. “The air was just whipping through them,” he recalls. “We were happy to feel the amount of air coming through.”
The air flowing out of the chickpeas was completely saturated at first. Later, without fan power, air continued flowing from the vents as a gentle cold breeze.
When he unloaded both bins this past spring, he was pleased to see the durum and chickpeas were in good dry condition, top to bottom.
Other producers have been running similar tests on their farms, with the same glowing reports.
Lee Randall, who farms in southeast Montana, used four older bins to run a similar experiment with corn.
After retrofitting the conventional 6,000-bushel bins a month before harvest with two systems, Randall — who describes himself as a rookie when it comes to drying corn — gave it a try.
He’s glad he did.
“CrossFlow had the grain cooled a day or two faster, and maintained a colder temperature throughout the cycle than the Keho system,” he says.
Randall paid about $3,000 each for CrossFlow systems and added two 3-hp, $1,500 fans. Shortline Ag Inc. of Scobey, Montana supplied the systems.
He put an $1,800 standard Keho Cross Duct system in the other bins, each with a $2,000, 5-hp fan.
All four bins were monitored with OPI-1 temperature and moisture cables.
The temperature was around 50 degrees F when Randall loaded the bins on Oct 31, 2013. He powered up the fans for all of November and monitored air flow.
On all four bins the temperature dropped “pretty quickly,” said Randall, but it went down faster in the CrossFlow bins. Moisture content dropped to 15 or 16 percent.
“It seemed like the CrossFlow system moved quite a bit more air, more efficiently,” he notes. “It also was superior when we cleaned out the bins. Our bins use floor sweeps and this worked slick [for CrossFlow]. You move a little foot for the centre air tube and then there’s nothing on the floor.”
Shortline Ag manager, Allen Juel says further study is needed. It appears that energy savings will be substantial, but many variables will need to be tested.
Randall says if he could do it over, he would install the new Canadian system in all four bins.
“I think that system is going to be vastly superior when you have a little heat and dry air, because it’s got the better air flow.”
Gary Schreiner, the president of Gatco Manufacturing Inc. who invented CrossFlow, has his own farm near Swift Current, Saskatchewan. Schreiner came up with the idea for flowing air across a bin — outside to centre, then out the top — about five years ago.
“We were having a bad fall with aeration,” he says. “My neighbour would fill his own aeration bins only half way because he could only dry the bottom half. That’s the problem with aeration,” says Schreiner.
“I started thinking, I’ve already got my bins split in half with a vertical air tube, so why not push air the other way, horizontally? That got the idea rolling.”
He built a prototype, called it CrossFlow, and tried out the idea in 2012. His early results suggested CrossFlow could cool grain safely and faster than traditional aeration while using smaller fans.
In 2013, Gatco sent CrossFlow systems to six farms for early trials. By January 2014, Schreiner had assembled patents for his new technology in both Canada and the U.S.
Since then, he’s had a tremendous level of interest at farm shows.
CrossFlow utilizes another Gatco product, the GrainAir Tube. These 7-inch, 18-gauge perforated tubes are boosters for aeration floor bins. CrossFlow, including the air tube, is an easy retrofit for flat-bottom or hopper-bottom bins.
CrossFlow works on a simple concept - Air takes the easiest path to a release point. The taller the bin, the better CrossFlow compares to conventional full floor aeration.
Normally, air released under a perforated floor must flow straight to the top of the grain to be released. As height increases, more power is needed.
CrossFlow uses a gentle horizontal flow on a typical path that is only one-third to one-sixth the length of the path for vertical aeration.
The inside wall of the storage is equipped with four to eight vertical ducts, similar to furnace ducts. The ducts are installed in four-foot or eight-foot sections with louvers and a damper. The dampers manually operate from outside if the bin is less than full.
At the base of the bin, a duct is wrapped to the outside wall and connected to a fan. Inlet ports are cut into the bin wall, connecting the main duct to each inner vertical duct. This allows air to flow from the fan through the ducts and louvers and outward across the grain to the open-air column in the centre.
Air encounters very little static pressure in the grain and, at the air column it flows freely upward without resistance to exit above the stored grain.
The open-air column is like a magnet for air coming from the fan outside. It has a very easy, and very short, path. Released from any pressure at the open column, it shoots upward, taking along the excess heat and moisture.
Schreiner’s first CrossFlow systems have ducts reaching 60% of the bin wall height.“Air moving horizontally has less static friction and provides a more even drying environment,” says Schreiner. “This approach also avoids over-drying the bottom and soaking the peak.”
He adds, “My system favors the top half of the grain. It’s opposite to traditional aeration, but I’m drying the top half of the bin faster than the bottom half. The top of the grain in storage gets a real good air current, and the air gains momentum as it funnels into the centre tube.”
He suspends the GrainAir Tube from the reinforcement ring that runs around the cap of most bins. The tube nearly reaches the floor of the bin and has a cap that keeps it from plugging with grain.
For flat bottom bins, the tube is tethered at the bottom to allow movement when the bin is being unloaded. Loosening a screw allows it to move out of the way for cleaning. For hoppers, a horizontal cross-brace across the hopper bottom supports the GrainAir Tube. A magnetic base centered on the cross-brace keeps the tall tube in place while grain flows past. Industry Goes with the Flow An industry expert who has made a career of measuring and developing grain aeration, agrees that cross-flow air movement in stored grain is much more efficient than upward vertical movement.
Ronald Noyes, retired Oklahoma State University engineer and designer, patented a cross-flow in-bin grain dryer in 2010, and measured the efficiency improvements.
Noyes found horizontal air flow:
- encounters about half of the resistance per foot of air-path (for elongated kernels like corn, wheat, oats, barley, rice, sunflowers, etc) because the air is moving with – not against – the orientation of the grain. For relatively round grain, like beans or peas, over the same distance, resistance to airflow is about the same regardless of direction.
- fan power that produces vertical airflow at 0.2 cfm/bu for natural air drying will produce 10 times as much airflow when moving horizontally.
- requires only 8-15 percent of the power needed for the same rate of vertical airflow.
- costs only 15 to 30 percent as much as drying and cooling with vertical drying and aeration.
In the late 1980s through 1990s, Noyes developed a series of advanced grain storage, automatic aeration controls and recirculation fumigation systems for grain elevators. He is currently developing an in-bin cross-flow grain dryer, with air moving outward from a centre column.
Future of Natural Air Drying
Prairie Agricultural Machinery Institute project manager Joy Agnew confirms that using fans and aeration floors to cool dry grain in tall storage bins has limits.
Agnew writes, “The greater the depth, the higher the static pressure. Typically, for Natural Air Drying (NAD) a grain depth of 15 ft would require a 5 hp fan to provide enough airflow and would generate about 7.5 inches of static pressure.
“There is not a lot of information available on the expected static pressure or required fan size for large grain bins and grain depths. Based on the old rule of thumb for full-floor aeration, 1 hp/1000 bushels, Green’s 50,000 bushel bins would need 50 hp fans.
“But, static pressure also depends on grain type, airflow rate and the type of ducting. GATCO’s arrangement might reduce the static pressure and allow a smaller fan to do the job. “Green was conditioning (cooling) the grain, not drying it. Effective NAD requires more airflow than aeration.
It is unlikely that a 15 hp fan with the CrossFlow aeration system would provide the 50,000 cfm that is recommended for NAD. Simple cooling reduces moisture content by maybe half a percent, but removing more than 1% of moisture would require higher airflow rates. “So yes, I would agree that a 15 hp fan on a 50,000 bu bin with a fully perforated floor would definitely cause issues and would not effectively aerate the grain (and possibly generate a moisture front).”
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