August 22, 2008

With energy prices up dramatically in recent years, grain producers are asking how to reduce the cost of drying grain on the farm. This article will discuss high capacity grain drying and a couple of variations that can save energy costs.

High speed batch or continuous-flow dryers have the highest bushel capacity per hour of any of the on-farm systems. Temperature, grain bed depth and airflow rates are vastly different in high speed, high-capacity dryers compared to deep-bed, in-bin drying systems. Air temperatures of 120°F to 140°F are typical in high capacity dryers. Column widths of grain being dried are measured in inches (10 to 20 inches) in batch or continuous flow dryers as opposed to feet (4 to 20 feet) for in-bin drying systems. Airflow rates of 50 to 100 cfm/bu are common in high speed dryers as opposed to 1.0 to 2.5 cfm/bu for deep bed in-bin systems.

There are two limiting factors that affect the efficiency of high capacity systems. The first limiting factor is the rate moisture can migrate from the interior of the kernels to the surface where it can evaporate into the air stream. The second limiting factor is the short contact time the air stream has with the grain. High volumes of very hot, dry air moving through shallow beds of grain dry the grain quickly, but the air leaving the grain mass is much less saturated with moisture compared to deep-bed, in-bin drying systems. This is reflected in higher energy costs per point of moisture removed per bushel as compared to in-bin systems. Some high capacity dryers recover some energy by channeling the air used to cool the grain back into the drying chamber air stream or by re-circulating a high percentage of the previously heated air back through the grain mass.

High temperatures and uneven moisture content within the kernel result in a much higher incidence of stress cracks as compared to in-bin drying. Stress cracks created in the dryer result in a much higher percentage of broken kernels upon subsequent grain handling.

Dryeration

If you have bins equipped with mesh floors and high capacity aeration fans, you might want to try a variation known as dryeration. Dryeration is a system where hot grain is removed from the high-speed dryer one or two points of moisture above desired storage moisture, then transferred to a bin where it is allowed to temper for four to six hours before starting the aeration fan for final cooling. The final one or two points of moisture are easily removed in the process of cooling the grain because the moisture deep inside the kernels has had time to redistribute during the tempering period. This method of grain drying increases the throughput capacity of the high-speed dryer and results in higher quality grain with fewer stress cracks than drying followed by rapid cooling in the high-speed dryer.

Combination Drying

Another intermediate system using both the high temperature dryer and in-bin aeration is called combination drying. With combination drying, you "take the edge off" high moisture corn by drying the grain to 20%-22% moisture with the high temperature, high speed dryer. The grain is then moved while still hot to a bin equipped with an aeration fan able to push at least two cfm/bu of unheated air through the grain mass to complete the drying and cooling process. This cuts some of the reliance on heat compared to completely drying the grain in the high speed dryer and increases the throughput volume of the high temperature dryer even more than dryeration. It also cuts the energy cost provided the heating fuel is a higher cost energy source than the energy for fan operation.

If you have been completely drying and initially cooling your corn in the high-speed dryer but have bins equipped with mesh floors and high capacity aeration fans, either dryeration or combination drying can result in faster throughput, higher quality grain and lower energy costs.

Tom Dorn
Extension Educator, Lancaster County