Corn+Soybean Digest [1]

PowerPoints | Save energy in grain drying and field operations.

Looking for ways to cut your energy bill this fall? Start with grain-drying systems, which are huge fuel guzzlers on most corn [3] and soybean [4] operations.

That’s exactly what John Meylink, (left) Burnett, WI, did and he slashed his fuel use nearly 40%. He replaced his 12-year-old batch cross-flow dryer in 2008 with a continuous-cross-flow dryer that has heat recycling and electronic controls.

Meylink typically dries about 54,000 bu. of corn on the farm using natural gas. His old dryer, which had a manually controlled thermostat, was hard to manage, he says, and the moisture content of the grain coming out of the dryer was inconsistent.

After a grain-dryer audit from GDS Associates, Madison, WI, Meylink upgraded to a Brock Superb continuous-cross-flow dryer with suction cooling and heat recovery. Outside air is pulled past warm grain in the cooling section of the column, reclaiming the heat, which is then recycled to wet grain in the upper part of the column. Heat recovery cost savings can be huge for northern growers, says Extension Ag Engineer Kenneth Hellevang at North Dakota State University [5] (NDSU).

Continuous grain-moisture sensors have improved drying consistency, Meylink says, and variable-speed augers match grain flow rates to drying time, yielding additional energy savings.

In 2007,his old dryer used over 3,000 Btus/lb. of water removed. In 2008, the new system used 1,841 Btus/lb. of water removed, according to an audit by GDS Associates – a 39% gain in efficiency. Meylink’s savings: $2,600. The expected payback from energy savings on the new dryer is just over 10 years, he says. A USDA [6]REAP [7] grant, which covered 25% of the dryer cost, pushed the payback down to 5.7 years.

Upgrading grain-drying equipment is one of the best ways to conserve fuel on row-crop farms, says Steve Faust, founder and president of Vermont-based EnSave, a farm energy auditing company with more than 2,000 audits under its belt. Older grain-drying equipment “is very inefficient compared to equipment available now,” Faust says. For perspective, last year in Illinois average drying costs topped $22/acre.

Many farmers’ drying equipment dates from the 1980s or earlier, says Hellevang. Although grain dryers vary a lot in energy efficiency, a typical older system requires 2,200-3,000 Btus/lb. of water removed, he says. Many new systems need only “1,800-2,000 Btus to take out a pound of water.”

For example, continuous-mixed-flow dryers are 20-40% more fuel-efficient than typical cross-flow column dryers, consuming about 2,000 Btus/lb. of water removed, says Scott Sanford, a University of Wisconsin energy specialist. Heated air moves through the grain in both concurrent and counter-flow paths. “Due to intermittent exposure to heat, multiple airflow paths and multiple heat zones, mixed-flow dryers can be adjusted to optimize crop drying,” Sanford says.

Chad Brandt of Oakes, ND, dries about 225,000 bu./season, using propane. Two years ago, he replaced his 1979 cross-flow screen dryer with a 10-tier Neco mixed-flow dryer. An NDSU dryer audit predicted that the new system would be 20% more efficient than his old system, he says. Corn moisture of 26-29% the last two years has highlighted the need for energy efficiency, Brandt says.

If you have grain bins with perforated floors and drying fans, combination drying can cut your energy use in half, compared to high-temperature cross-flow dryers, says Hellevang. In this two-stage method, grain is dried to about 20% moisture in the high-temperature dryer, then transferred hot to a low-temperature or natural-air bin dryer for finishing.

Combination drying can boost your system’s fuel efficiency to about 1,500 Btus/lb. of moisture removed, Sanford says, and double or triple the capacity of your high-temperature dryer. If you add supplemental heat, a stirring device also bumps up energy efficiency, he says, and prevents over-drying in the bottom corn layers.

Heat recovery increases the en-ergy efficiency of continuous-flow heating and cooling dryers by about one-third, Hellevang says.

But not everybody can expect a 40% boost in energy efficiency from a new dryer, Sanford cautions. And meaningful energy-efficiency comparisons are tricky, he adds, because of “the numerous things that affect energy use from year to year.”

Two Energy Strategies
Two other energy-saving strategies are in-bin cooling and dryeration. They can be used with either continuous-flow or batch dryers that don’t have heat recovery.

In-bin cooling cuts fuel use by about 15%, while boosting dryer capacity by about a third, says Scott Sanford, University of Wisconsin energy specialist. Hot grain is removed from the dryer when it’s 1-1.5% above the desired moisture level and transferred to a storage bin. The fans are started as soon as the grain is delivered to the bin and operated continuously. “The remaining moisture evaporates during the slow cooling process in the storage bin,” Sanford says.

A similar method, called dryeration, can cut fuel use by up to 25% while increasing dryer capacity about 30%, North Dakota State University Ag Engineer Kenneth Hellevang says. Hot grain leaves the high-temperature dryer when it’s 2-3% above the desired moisture level, and then “steeps” in an intermediate bin for four to 12 hours without airflow. Then the fans are turned on and the grain is cooled. The cooled grain must be moved from the dryeration bin to a storage bin because water will condense on the bin walls during steeping and cause spoilage if the grain is not moved. The dryeration bin can be used to store the last batch of grain, substituting in-bin cooling for dryeration.

Dryeration saves fuel, Hellevang says, but the downside is the need for a dedicated steeping bin and a lot of extra handling at harvest time, when many growers are already stretched thin.

In-bin cooling is more popular among smaller producers, Hellevang says, but that, too, requires careful management to avoid swapping fuel savings for storage problems. Moisture can condense on the roof or bin walls, especially when it’s cold outside. “The last few years, there have been a lot of reports of spoiled grain from condensation along the bin walls with slow cooling.

“Many things affect dryer energy efficiency,” Hellevang says, including the operator’s management skill, outside temperatures, field grain moisture, starch content, even the hybrid.

Tips for saving dryer fuel

  • Tune up your drying system. Inspect and clean drying floors, says Scott Sanford, University of Wisconsin. Clean fan housing and blades, check belt drives, clean the burner, have the gas company check gas pressure regulators and adjust air inlet. Calibrate temperature and grain-moisture sensors annually.
  • Clean grain before it enters the dryer. Fines restrict airflow, Sanford says.
  • Level grain in a bin-drying system creates more uniform, economical drying.
  • Assure unrestricted airflow. Transitions from the fan to the bin should have a cross-sectional area larger than the fan, says NDSU’s Hellevang.
  • Monitor drying temperature. “The most energy-efficient high-temperature drying uses the maximum drying temperature that will not damage grain,” Drying temps of 210-230° F are the most fuel-efficient, he says.
  • Invest in a grain-dryer energy audit.

August 2010